Corrosion Performance of Acrylic–Polyurethane and Polyacrylamide Coatings on Quaternary Bronze

Corrosion Performance of Acrylic–Polyurethane and Polyacrylamide Coatings on Quaternary Bronze | Research Square window.SnipcartSettings = { analytics: { enabled: false } }; (function() { var accessVector = localStorage.getItem('access_vector') || ''; window.dataLayer = window.dataLayer || []; if (accessVector) { window.dataLayer.push({ user: { profile: { profileInfo: { snid: accessVector } } } }); } })(); (function(w,d,s,l,i){w[l]=w[l]||[];w[l].push({'gtm.start':new Date().getTime(),event:'gtm.js'});var f=d.getElementsByTagName(s)[0],j=d.createElement(s),dl=l!='dataLayer'?'&l='+l:'';j.async=true;j.src='https://www.googletagmanager.com/gtm.js?id='+i+dl;f.parentNode.insertBefore(j,f);})(window,document,'script','dataLayer','GTM-K279D39R'); Browse Preprints In Review Journals COVID-19 Preprints AJE Video Bytes Research Tools Research Promotion AJE Professional Editing AJE Rubriq About Preprint Platform In Review Editorial Policies Our Team Advisory Board Help Center Sign In Submit a Preprint Cite Share Download PDF Article Corrosion Performance of Acrylic–Polyurethane and Polyacrylamide Coatings on Quaternary Bronze Mostafa I. Eladawy, Mohamed Abdelbar, Mohamed M. Megahed, Nabil Abdel Ghany, and 1 more This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-7502286/v1 This work is licensed under a CC BY 4.0 License Status: Posted Version 1 posted You are reading this latest preprint version Abstract To mitigate outdoor corrosion of cultural bronze, this study compares three transparent polymer coatings—PUR-129 (acrylic–polyurethane), Paraloid B-82 (acrylic), and polyacrylamide (PACM)—applied as monolayer, multilayer, and emulsion films on quaternary bronze coupons replicating the alloy of Sabil al-Ahmadi’s window grilles (Tanta, Egypt). Performance was assessed after 12 months of on-site natural exposure using weight change, gloss retention, and electrochemical testing (OCP, EIS, and potentiodynamic polarization). Post-aging SEM/EDS characterized surface morphology and elemental signatures. Across metrics, multilayer designs outperformed single-layer applications; PUR-129 multilayer was consistently the top performer, maintaining ~ 90.5% gloss, showing the lowest weight change, and exhibiting the highest electrochemical barrier relative to the bare control. The results indicate that transparent multilayer polymer systems—particularly PUR-129—provide durable protection for outdoor bronze while better preserving visual appearance under the Nile-Delta climate. Physical sciences/Chemistry Physical sciences/Materials science Polymeric coatings Quaternary bronze Corrosion behavior Acrylic Polyurethane Polyacrylamide Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 Figure 7 1. Introduction Outdoor bronze—encompassing sculptures, fountains, plaques, gates, and railings—is highly vulnerable to atmospheric deterioration owing to prolonged exposure to weathering, airborne pollutants, and microclimatic fluctuations ‎ 1 -‎ 5 . Upon exposure, bronze surfaces undergo electrochemical reactions that generate corrosion products such as cuprite (Cu₂O), copper sulfates (e.g., CuSO₄·5H₂O), and basic copper chlorides (e.g., Cu₂(OH)₃Cl) ‎ 6 -‎ 8 . Moisture from rain, dew, or high relative humidity functions as an electrolyte, enabling dissolution/transport of copper and alloying elements, while pollutants including SO₂ and Cl⁻ accelerate degradation through acid formation and chloride complexation that destabilize the passive film ‎ 9 -‎ 11 . Thermal and humidity cycling further intensifies these processes by driving repeated wet–dry episodes that favor porous, poorly protective corrosion layers‎ 12 . Over time, a patina develops whose protective role depends on its composition, structure, and adhesion; stable patinas may inhibit further attack, whereas unstable or chloride-rich layers can promote continued deterioration ‎ 2 ,‎ 13 . Mitigation strategies, therefore, rely on protective systems—coatings and inhibitors—to reduce ion transport and pollutant ingress. Conventional single-layer coatings, although widely used, frequently fail to ensure long-term stability under harsh outdoor conditions ‎ 14 -‎ 17 . In contrast, multilayer designs have gained prominence for combining complementary functions (e.g., adhesion, barrier performance, UV/weathering resistance) within a stratified film, thereby delivering enhanced durability and corrosion resistance on outdoor bronze substrates ‎ 18 -‎ 20 . The performance of protective coatings depends on both material chemistry and application design. Polyurethane–acrylic systems (e.g., PUR-129) are noted for strong adhesion to metals and good mechanical/chemical durability, making them effective primers or stand-alone barriers‎ 21 . In addition, UV-curable polyurethane acrylates achieve densely cross-linked networks that improve mechanical, chemical, and optical stability on metallic substrates ‎ 22 . These attributes position polyurethane–acrylic coatings as promising candidates for outdoor bronze conservation. Acrylic coatings (e.g., Paraloid B-82) are valued in heritage contexts for transparency, barrier performance, weathering stability, and reversibility, allowing use either alone or as part of multilayer designs‎ 23 . Polyacrylamide (PAM/PACM), a high–high-molecular-weight, water-soluble polymer, forms clear films that can be formulated to tailor surface energy and flexibility; when combined appropriately within a coating build, it can contribute to environmental resistance in outdoor service. By combining polymers in multilayer designs, complementary functions (adhesion, barrier properties, optical stability) can be integrated to achieve more durable protection than single layers. This study assesses the corrosion resistance and visual stability of coatings on outdoor bronze using quaternary bronze coupons that replicate the alloy used in the window grilles of Sabil al-Ahmadi (Tanta, Egypt) ‎ 24 . Coatings were applied as monolayer, multilayer, and emulsion films and exposed naturally for 12 months at the case-study site. Laboratory analyses—electrochemical impedance spectroscopy (EIS) and potentiodynamic polarization (to derive polarization resistance, Rp), weight change, gloss retention, and post-aging SEM/EDS—were employed to compare protective performance. Together, these methods provide a comprehensive evaluation of barrier behavior and appearance retention relevant to conservation practice. This work provides a site-specific, 12-month natural-exposure comparison of three transparent polymer families—acrylic–polyurethane (PUR-129), acrylic (Paraloid B-82), and polyacrylamide (PACM). Beyond the general expectation that multilayers outperform monolayers, our goal is to quantify how film architecture (monolayer, multilayer, emulsion) governs both corrosion-barrier kinetics and visual stability. We integrate time-resolved electrochemical impedance spectroscopy (EIS) and potentiodynamic measurements with optical ageing metrics (visual examination and gloss retention) and post-ageing SEM/EDS. The novelty lies in this multi-metric, field-based assessment across distinct coating chemistries and layer designs, producing decision-ready guidance for selecting multilayer systems that maximize corrosion protection while minimizing visible alteration under the Nile-Delta urban climate. 2. Material and Methods 2.1 Bronze Coupons and Surface Preparation Commercial quaternary bronze (Cu–Sn–Zn–Pb; composition in Table 1) was machined into coupons (30 × 30 × 11 mm³ for natural exposure; 20 × 11 × 3 mm³ for laboratory tests). Whereas metal analogues are often artificially aged to reproduce the corrosion layers found on historic objects, our coupons were kept as clean metal to reflect the post-cleaning state stipulated for the Sabil al-Ahmadi grille. Surfaces were progressively abraded with 600–1200-grit papers to a smooth finish, degreased in a mild alkaline solution, rinsed with running and then deionized water, swabbed with ethyl alcohol, and dried. Coupons were handled with talc-free gloves and tongs, individually numbered, and stored dry before coating. Table 1 . Chemical composition (wt%) of the quaternary bronze coupons used in this study, values are means ± SD from replicate analyses (totals normalized to 100 wt%). Element Cu Sn Pb Zn Ni Fe Sb Wt. % 84.7 ± 0.3 5.1 ± 0.2 4.3 ± 0.2 5.5 ± 0.3 0.2 ± 0.1 0.08 ± 0.03 0.05 ± 0.02 2.2 Protective Coatings Three transparent polymer coatings were selected for comparison: PUR-129, polyacrylamide and Paraloid B-82. PUR-129 is a clear acrylic–polyurethane coating (CMB-Egypt) applied at the manufacturer’s standard concentration. Film formation proceeds by the reaction of hydroxyl-functional polyols with isocyanates to generate urethane linkages, yielding a densely cross-linked network with good adhesion and mechanical/chemical durability. According to the technical data sheet, the formulation includes light-stabilizing additives, which limit UV-induced yellowing and photodegradation—attributes relevant to outdoor service. Polyacrylamide (PAM) was included as a water-borne, low-VOC candidate to benchmark a hydrophilic matrix against the more hydrophobic acrylic–polyurethane and acrylic systems. It is high-molecular-weight polymer (Mn > 5 × 10⁶; BDH Chemicals) prepared as a 5 wt% aqueous solution ‎ 25 - ‎ 31 . Paraloid B-82 is a thermoplastic acrylic resin applied here as a 5 wt% solution in acetone. It forms transparent, removable films and is widely used in conservation where reversibility and optical clarity are required; in multilayer builds it can serve as either primer or topcoat ‎ 19 , ‎ 32 - ‎ 34 . Coatings (PUR-129, Paraloid B-82, PACM) were applied by brush as monolayers or multilayers (three coats, 12 h between coats) following the parameters in Table 2. Table 2 . Coating configurations and specimen allocation. Triplicate bronze coupons (IDs shown as letters) were coated by brush as monolayers (one coat) or multilayers (three coats, 12 h between coats). Mono or multi-layer Protection system Coupons Blank Blank A, B, C Monolayer B-82 (5% in acetone) D, E, F Multilayer B-82 (5% in acetone) G, H, I Monolayer PUR-129 (Standard) J, K, L Multilayer PUR-129 (Standard) M, N, O Monolayer Polyacrylamide (5% in water) P, Q, R Multilayer Polyacrylamide (5% in water) S, T, U Multilayer One layer of PACM and two layers of B-82 AA, BB, CC Monolayer Emulsion of (PACM+B-82 1:1) DD, EE, FF Multilayer Emulsion of (PACM+B-82 1:1) GG, HH, II 2.3 Corrosion Tests Corrosion testing provides quantitative evidence of coating performance under relevant environmental stresses. Electrochemical methods—notably electrochemical impedance spectroscopy (EIS) and potentiodynamic polarization—are well suited to coated bronzes because they non-destructively track barrier integrity and corrosion kinetics over time. Metrics such as the low-frequency impedance modulus, polarization resistance, and coating capacitance sensitively indicate water uptake, defect growth, and underfilm corrosion, enabling time-dependent comparisons among formulations and layer designs. When paired with controlled natural or accelerated exposures and appropriate statistics (replicates, error bars), these techniques yield robust durability rankings and clarify failure modes, thereby guiding the selection and optimization of protective coatings for long-term service in aggressive atmospheres ‎ 35 - ‎ 38 . 2.3.1 Short-term testing Electrochemical measurements were conducted using an Origaflex-OGF01A system (Origalys, France). The setup consisted of an Ag/AgCl reference electrode, a platinum sheet as the auxiliary electrode, and (coated, uncoated) bronze coupons as the working electrode. Electrochemical impedance spectroscopy (EIS) was performed at open circuit potential (OCP), while Tafel plots were used to determine the corrosion rate (C.R.) and corrosion current density (I corr. ) with a scan rate of 2 mV/s over a potential range of -300 to 300 mV. EIS measurements spanned a frequency range of 0.1 Hz to 100 kHz, with a 10 mV amplitude, following ASTM G106-89 standards. Measurements were performed in aerated 3.5 wt% NaCl at 25 ± 1 °C , a standard chloride electrolyte used to benchmark coatings on copper alloys. This medium imposes a chloride-dominated, high-conductivity challenge that sensitively probes barrier properties by EIS/polarization. In our Nile-Delta setting, outdoor surfaces are periodically wetted by chloride-bearing aerosols and moisture, in addition to urban pollutants , so chloride is an appropriate stressor for accelerated ranking. We emphasize that the NaCl cell does not aim to replicate the entire urban atmosphere (NOx/SOx, soot, organics) ; those stressors were assessed by the 12-month on-site exposure . Together, the NaCl cell provides a controlled, worst-case ionic environment for ranking coatings, while natural exposure demonstrates real-world durability . 2.3.2 Long-term testing A reinforced plastic rack was mounted on two delta-shaped aluminum bases and set at 45° from the horizontal, facing south (Northern Hemisphere). Bronze coupons were hung from 5-cm plastic pins with broad heads, leaving a 3-cm standoff below each coupon to ensure free drainage and full exposure. Coupons were arranged in triplicate (Fig. 1,a-b). The rack was installed on the roof of a building adjacent to Sabil al-Ahmadi in Tanta so that the coupons experienced the same outdoor environment as the historic grille. The 45° equator-facing configuration follows common practice for direct natural weathering of coatings (ASTM G7) and is consistent with ISO guidance (ISO 9223) for selecting exposure geometry; rack construction and placement conformed to ISO 877-2 Method A and ASTM D4141 ‎ 8 , ‎ 19 . Corrosion progression was tracked every two months by visual/microscopic examination, gloss measurements, and mass (weight) change determinations. 2.3.2.1 Visual Examination and Post-Aging SEM/EDS Surface condition was monitored at two-month intervals by visual inspection under ambient light and documented by digital photography. After 12 months, representative coupons from each coating system were examined by scanning electron microscopy (SEM) coupled with energy-dispersive X-ray spectroscopy (EDS) to assess surface morphology and elemental signatures (JEOL JSM-6510LV, Japan). SEM observations were performed at appropriate accelerating voltages in low-vacuum (LV) mode to minimize charging; images are presented with calibrated scale bars. EDS spectra were acquired from multiple fields per sample to confirm the presence of corrosion products and/or environmental deposits. 2.3.2.2 Weight-change measurements Weight measurement emerges as a common technique for corrosion monitoring, involving the weighing of metal specimens before and after exposure to corrosive agents. An increase in the weight of a bronze object indicates an active corrosion process ‎ 36 - ‎ 39 . Each coupon was weighed after coating and then at two-month intervals for 12 months (six time points) on an analytical balance (readability 0.0001 g). Before weighing, surfaces were gently cleaned with oil-free air and a soft brush; no chemical pickling was performed to avoid altering corrosion products or the coatings. The inhibition Efficiency (%) of the coating systems was calculated employing the formula: Efficiency (η) % = W a – W b / W a × 100 (1) Where W a and W b are the weight gain average of the unprotected and protected coupons after 12 months of exposure, respectively ‎ 40 . 2.3.2.3 Gloss measurements Specular gloss was measured using an Erichsen Picogloss 503 at the standard 60° geometry in accordance with ISO 2813 / ASTM D523. The instrument was calibrated against the supplied black-glass standard before each session. Baseline gloss (G 0 ) was recorded after coating cure; after 12 months of natural exposure, gloss (G t ) was re-measured to quantify weathering-induced change. For each coupon, five readings were taken at the same marked locations and averaged. Results are reported as gloss retention GR (%) =100×(G t /G 0 ) (mean ± SD for replicates); ΔG (%) =100×(G t −G 0 )/G 0 is provided where percent change is discussed. 3. Results and Discussion 3.1 Electrochemical Measurements The corrosion resistance of coated and uncoated bronze coupons was measured using electrochemical impedance spectroscopy (EIS) and Polarization plots. Polarization plots are utilized to evaluate the corrosion behavior of coated and uncoated bronze, as seen in Fig. 2(a) and Table 3. The Tafel polarization results demonstrated that differences in corrosion potential (E corr. ) correspond to the degree of passivation obtained by each coating. According to the data, coatings greatly improve corrosion resistance when compared to uncoated bronze, especially multilayers. Tafel graphs show lower corrosion current densities for coated coupons, indicating that protective layers minimize corrosion rates ‎ 41 . PUR-129 monolayer coupon (2) and three layers of PUR-129 coupon (3) exhibit greater resistance to anodic dissolution than the uncoated coupon (1). Lower I corr. values correlate with lower corrosion rates ‎ 42 , demonstrating high corrosion inhibition efficacy of 99.98% and 99.96%, respectively. The combination of polyurethane and acrylic offers environmental protection, quick drying, and strong corrosion resistance, making PUR-129 an excellent choice for protecting exposed metal surfaces in challenging outdoor environments. PUR-129 offers exceptional resistance to cracking and imperfections, as shown in Fig. 2. Polyurethane's high adherence to metal surfaces provides stability and longevity, making it perfect for outdoor applications ‎ 38 , ‎ 43 . PUR-129 three-layer coupon (3) and monolayer coupon (2) have similar C.R., but coupon 3's polarization resistance R p value is 225.48×10 3 ohm.cm² compared with coupon 2's 40.18 ohm.cm², as shown in the EIS plot in Fig. 3(b). Multi-layer systems, acting as diffusion barriers, restrict electrochemical reactions, reducing ion transit, and thereby increasing corrosion resistance, as shown in Table 3. In addition, the coatings with homogenous multi-layers of PUR-129 showed lower roughness, which decreased the area for electrochemical processes ‎ 44 , potentially increasing R p in coupon (3), as seen in Fig. 3(b). Microscopic investigations in Fig. 6(k, n) show that the multi-layered PUR-129 surface is completely free of corrosion products and dust deposition, whereas the mono-layered PUR-129 coating had only tiny corrosion spots, confirming the R p values. Finally, coatings with multilayers of PUR-129 coupon (3) show better corrosion protection performance in this study. Multi-layer coatings, such as three layers of Paraloid B-82 coupon (5) and three layers of PACM coupon (7), displayed low corrosion rates as well, with 96.23% and 95.53% effectiveness, respectively, as illustrated in Table 3. Confirming the morphology images in Fig. 6(e, h), Paraloid B-82 for mono or multi-layer coatings shows green corrosion spots in some areas. The PACM coating provided the least protection against corrosion; although multiple layers of PACM coupon (7) performed slightly better than a single-layer coupon (6), they still did not offer the desired level of protection. Confirming that multi-layer designs improve coating durability ‎ 15 , ‎ 16 , ‎ 45 . Coating efficacy may vary based on composition and application techniques ‎ 46 , as illustrated in Table 3. Since there were weak areas where corrosion products were gathered for PACM, the surface paleness and defective clarity of Paraloid B-82 Coupon (8) were improved in these coupons. Coupon (8), which consists of one layer of PACM and three layers of B-82, demonstrated a high corrosion inhibition efficacy of 98.65% when compared to multi-layers of B-82 or PACM. Emulsion coatings of Paraloid B-82 and polyacrylamide can considerably improve bronze's corrosion resistance, including coupons (9 and 10). Paraloid B-82, an acrylic copolymer, provides a long-term protective coating, while polyacrylamide helps to increase adhesion and flexibility. They combine to produce a barrier against moisture and corrosive products, effectively preventing oxidation and degradation on bronze surfaces. According to research, such coatings can beat standard approaches in terms of durability and environmental resistance. However, when compared to coupon (1) of bronze without coating, emulsion coatings give a balanced approach with reasonable protection and produce reasonably satisfactory results, as shown in Table 3, with efficiency of 95.84% and 93.10%. The corrosion parameters in Table 3 were determined using the Tafel extrapolation measurements. The C.R. is calculated from equation (2): where M.W. is the molecular weight of the corroded material (g/mol), C.R. is the corrosion rate (mpy), and I corr. is the current density of corrosion (A cm −2 ), n is the number of charge transfers throughout the corrosion process, and d is the density (g cm −3 ) [42]. In general, multi-layer coatings provide better protection than monolayers because the additional layers form a stronger barrier that inhibits corrosion. Reduced pore size, protective film generation, and better chemical stability [45], as seen in Figs. 2(b) contribute to a longer lifetime. We also investigated the impact of the coating thickness layer on corrosion parameters. Table 3 . Electrochemical parameters obtained from potentiodynamic polarization of blank and coated bronze coupons. Coupon No. Protection system R p (ohm.cm²) Beta a (mV) Beta c (mV) E (i =0) (mV) I corr. (µA/cm 2 ) Corrosion rate (C.R.) (µm/y) Efficiency η% 1 Blank 29.39 181.4 -168.5 -19.1 1000.1 12000 2 One layer of PUR-129 40.18 80.4 -88.2 -47.3 0.3145 3.6409 99.96% 3 Three layers of PUR-129 225.48× 10 3 350.7 -507.6 -133.7 0.169 1.9608 99.98% 4 One layer of B-82 610.47 217.6 -218.2 -96.8 34.8871 403.87 96.51% 5 Three layers of B-82 624.44 198.4 -356.0 -92.7 37.6264 435.58 96.23% 6 One layer of PACM 556.86 343.4 -1292.8 -97.9 58.8268 681.02 94.11% 7 Three layers of PACM 985.80 189.5 -856.4 -87.6 46.4950 538.25 95.35% 8 One layer of PACM and two layers of B-82 1.75 189.5 -155.4 -64.4 13.4766 156.01 98.65% 9 One layer of emulsion of (PACM+B-82 1:1) 677.77 345.8 -615.9 -106.9 41.5261 480.73 95.84% 10 Three layers of emulsion of (PACM+B-82 1:1) 445.10 258.5 -636.6 -125.9 69 798.88 93.10% Figure 2(b) OCP curve further illustrates the stability of the bronze electrode under various conditions over time. The uncoated coupon (1) maintained a nearly constant potential, indicating early interactions with the corrosive environment interaction due to the formation of a stable oxide layer that exhibits passive behavior due to a stable layer, providing inherent corrosion resistance ‎ 47 . In contrast, generally coated coupons (2–10) show superior corrosion resistance compared to uncoated ones, enhancing the alloy's ability to resist corrosion by acting as additional barriers against corrosive environments ‎ 48 . Coated coupons (2–10) also show potential shifts, with an initial drop in potential. Despite this negative shift, coated coupons often resist corrosion better than uncoated ones because their initial protective layers reduce overall corrosion rates until they fail ‎ 49 . The nature of the corrosive environment (saline) has a significant impact on how coatings perform ‎ 50 . Different coatings will have varying levels of resistance depending on their chemical composition and durability‎ 51 . Gradual shifts to more positive or stable potentials, as observed in Coupons 4 and 8, suggested improved corrosion resistance, likely due to the formation of protective layers that hindered further oxidation ‎ 52 . EIS of bronze, particularly when coated, can be determined using Nyquist plots, as shown in Fig. 3(a-c). Coatings composed of multi-layer polymers such as polyurethane, acrylic, and polyacrylamide significantly improve corrosion resistance by forming a protective barrier ‎ 45 , ‎ 52 . Nyquist plots of EIS data demonstrate that the resistances and capacitive semi-circles of the coatings vary depending on whether they are monolayer or multilayer systems, as shown in Fig. 3(b, c). Higher impedance values, as illustrated by larger semicircles, are related to increased corrosion resistance due to less charge transfer. Coupon (7) (three layers of polyacrylamide coating) showed the highest impedance of the coupons, indicating superior barrier properties‎ 52 , probably due to its multi-layer structure, as illustrated in Fig. 3 (c). In contrast, monolayer coatings such as PUR-129 and Paraloid B-82 exhibited reduced impedance, as seen in Figs. 3 (b, c), showing that layering increases corrosion resistance ‎ 45 . Emulsion-based coating coupons (9 and 10) comprising Paraloid B-82 and polyacrylamide provided balanced protection due to their combined barrier properties, as seen in Fig. 3.(c). Figure 3(d) shows the equivalent circuit for the most efficient coating system, PUR-129 multi-layer coupon (3), and the reference parameters were extracted from the EIS fitting plots for coupon (3) in Table 4. According to studies, these coatings improve charge transfer resistance and reduce ion penetration, resulting in greater inhibition efficiency over time‎ 53 , as indicated by OCP plots in Fig. 2(b). EIS exhibits capacitive behavior, showing effective insulation against corrosive environments. Bronze coatings can enhance electrochemical properties and boost corrosion resistance‎ 51 . Table 4 . Representative EIS equivalent-circuit fit parameters for the PUR-129 multilayer. Coupon 3 R s CPE-T CPE-P R p C R ct Chi-Squared Three layers of PUR-129 12.82 0.00021523 0.81268 665.3 0.0024102 241.2 0.0010832 Bode plots are useful for discriminating between various corrosion causes by examining the frequency-dependent behavior of impedance in Fig. 4(a, b). The magnitude plot in Fig. 4(a) shows how resistance changes with frequency and the effect of the coated PUR-129 multi-layer coupon (3) and the uncoated coupon (1). Coated bronze PUR-129 multi-layer coupon (3) often exhibits a change to a higher impedance than the uncoated bronze coupon (1), demonstrating differences in resistance of specific corrosion mechanisms under comparable conditions‎ 44 . In Fig. 4(b), the shift in phase angle plot illustrates the time constants associated with distinct electrochemical processes, which can help to determine whether corrosion is controlled by charge transfer or diffusion ‎ 54 . Figure 4 (b) depicts a localized corrosion mechanism that results in a more significant phase change at lower frequencies‎ 55 . 3.2 Natural Aging Effects of Coating Systems 3.2.1 Visual and Microscopic Examination Macroscopic inspection after 12 months (Fig. 5; a-g) revealed clear differences between the coated and uncoated coupons. The PUR-129 multilayer exhibited a uniform, clean surface with no visible corrosion products or soiling. The PUR-129 monolayer showed only occasional, small discoloration spots (Fig. 5-b,c). In contrast, Paraloid B-82 —in both mono- and multilayer designs—displayed scattered greenish spots/streaks consistent with incipient copper-chloride corrosion; multilayer application reduced but did not eliminate these features (Fig. 5-d,e). PACM provided the least protection: the monolayer showed widespread green corrosion and patchy coverage , and the multilayer, while improved, still exhibited visible defects (Fig. 5-f,g). The uncoated coupon darkened markedly. The superior protection offered by the PUR-129 coatings can be attributed to their complete surface coverage, resulting in a smooth, transparent layer that minimizes dust adherence. This comprehensive isolation effectively shields the surface from various environmental degradation factors, maintaining its protective efficiency over an extended period of natural exposure. In contrast, the moderate efficiency of Paraloid B-82 is due to its partial vulnerability to external factors, leading to surface paleness and incomplete clarity. PACM, on the other hand, failed to provide adequate protection because its layers receded and peeled off in different areas after drying, creating weak points where corrosion products formed. To provide structural and compositional validation of the corrosion behavior observed electrochemically, Scanning Electron Microscopy (SEM) and Energy Dispersive X-ray Spectroscopy (EDS) analyses were performed on selected bronze coupons coated with different protective systems. The purpose was to correlate surface morphology and elemental composition with corrosion resistance as inferred from Tafel polarization and electrochemical impedance spectroscopy (EIS). The SEM micrographs (Fig. 6; a–i) reveal the degradation states of each coating. The best-performing system, three layers of PUR-129 (Fig. 6-b), exhibited a dense, smooth, and defect-free surface with no observable corrosion features. This compact and continuous morphology directly supports its outstanding electrochemical performance (R p = 225.48 × 10³ Ω·cm²; C.R. = 1.96 µm/y; efficiency = 99.98%). The EDS spectrum associated with this sample showed minimal elemental copper (Cu Kα = 6.60 atomic%) and a high oxygen signal (O Kα = 93.40%), consistent with the intact polymeric coating isolating the metal surface. In contrast, the mono-layer PACM coating (Fig. 6-e) presented a rough, fibrous morphology with visible cracks and surface porosity, clearly exposing the substrate. These defects confirm the inadequate protection observed electrochemically (C.R. = 681.02 µm/y, efficiency = 94.11%). The corresponding EDS data revealed elevated copper and oxygen, alongside traces of chlorine, indicating surface oxidation and formation of copper corrosion products (e.g., chlorides and oxides). This aligns with its poor wetting and film-forming behavior. Hybrid systems such as PACM + B-82 ( Fig. 6- g) offered intermediate surface morphology, where the coating appeared more cohesive than PACM alone but still displayed minor defects. Electrochemical measurements for this system (C.R. = 156.01 µm/y, efficiency = 98.65%) were correspondingly moderate. EDS results revealed less exposed copper and a lower oxygen-to-copper ratio, indicating improved but not full surface coverage. The B-82 coatings (Fig. 6-c,d), both mono and multilayer, show unexpectedly smooth SEM surfaces, with minimal apparent porosity. However, electrochemical data for these systems (C.R. = ~403–435 µm/y; efficiency = ~96%) indicate significantly lower protection than what the micrographs alone would suggest. This discrepancy may be attributed to internal porosity or microcracking invisible at 2000× magnification, or to the lower chemical barrier properties of B-82 compared to PUR-129. Furthermore, B-82 is known to undergo plasticization or degradation under UV or moisture exposure, which may compromise its performance despite its visually intact appearance. The uncoated blank sample (Fig. 6–j) exhibited a heavily corroded, pitted, and heterogeneous surface, confirming total exposure to atmospheric degradation. EDS analysis showed high copper signals and prominent corrosion product peaks, further validating the severe electrochemical deterioration (C.R. = 12,000 µm/y; efficiency = 0%). Lastly, the emulsion systems (Fig. 6-h,i) presented irregular and granular surfaces with visible agglomerates. The one-layer emulsion sample revealed intermediate protection (efficiency = 95.84%), while the three-layer variant surprisingly showed worse performance (93.10%), likely due to phase separation or poor cross-linking between PACM and B-82. The EDS results confirmed higher elemental Cu and the presence of Zn and Sn, possibly due to underlying alloy exposure. 3.2.2 Weight measurements The weight gain calculation technique serves as a chemical test to assess the effectiveness of various coating systems, both multi-layered and mono-layered, in protecting bronze coupons exposed to natural elements for 12 months in the outdoor environment adjacent to Al-Sabil Al-Ahmadi in the city of Tanta. A higher weight gain indicates greater damage and thus inefficiency of both the type of coating and the application technique in protecting bronze from corrosion risks. Conversely, a lower weight gain suggests the effectiveness of the coating type and application technique in safeguarding bronze coupons. Coupons were weighed every two months for 12 months, and thus, we have six readings to calculate the results of this test. It was observed that coupons coated with a single layer of protective coatings experienced greater weight gain compared to those coated with multiple layers after 12 months of exposure at the site of Sabil Al-Ahmadi in the city of Tanta. This finding suggests that multiple layers of coating offer superior protection compared to a single layer. The weight gain test results indicated that the PUR-129 multi-layer coating was the most efficient, achieving an efficiency rate of 95.33%. In contrast, the single-layer PUR-129 coating achieved an efficiency rate of 93.64%, as shown in Fig. 7. The average weight gain for each group over 12 months was computed using Formula (1), and the efficiency of each coating was assessed. The data clearly demonstrates that multi-layer coatings significantly enhance the protective capabilities of the coatings, with PUR-129 multi-layer exhibiting the best performance. 3.2.3 Gloss measurement Preserving the visual appearance of outdoor bronze is a core conservation goal. Specular gloss was therefore measured before exposure and after 12 months to quantify appearance retention. Performance is expressed as gloss retention GR (%) =100×(G t /G 0 ), where G 0 is the post-cure gloss and G t is the gloss after exposure. Higher GR indicates better maintenance of surface appearance; large decreases are consistent with darkening from corrosion products and soiling. As summarized in Table 5., PUR-129 (multilayer) showed the highest retention (≈90.5%), followed by PUR-129 (monolayer) (≈85.9%), B-82 (multilayer) (≈83.4%), and B-82 (monolayer) (≈78.5%). PACM retained less gloss (multilayer ≈71.3%; monolayer ≈62.8%), while the uncoated coupons exhibited the lowest retention (≈18.4%). Overall, multilayer designs outperformed monolayers in preserving gloss, with PUR-129 multilayer providing the most effective appearance protection. Table 5 . Gloss (60° geometry) of bronze coupons before and after 12-month natural exposure , and gloss retention (GR) . Values are averages of five readings per coupon; groups are triplicates. Protective coatings Average Gloss Before Exposure After Exposure Gloss Retention (%) Blank 64.2 11.8 18.43 % PUR-129 monolayer 590.8 507.3 85.86 % PUR-129 multi-layer 268 242.8 90.5 % B-82 monolayer 80.8 63.4 78.46 % B-82 multi-layer 83.2 69.4 83.41 % PACM monolayer 84.7 53.2 62.8 % PACM multi-layer 78.4 55.9 71.30 % 4. Conclusions A combined assessment of 12-month natural exposure and laboratory electrochemistry shows that multilayer coating designs provide more durable protection for outdoor bronze than single layers. Among the systems tested, PUR-129 (acrylic–polyurethane) in a multilayer build gave the most consistent performance: it preserved appearance (gloss retention ≈ 90.5%), exhibited the lowest weight change relative to bare bronze, and delivered the strongest electrochemical barrier, findings corroborated by post-aging SEM/EDS. Monolayer applications of PUR-129, B-82, and PACM showed larger gloss losses and higher mass changes, indicating reduced long-term protection. While the B-82 multilayer improved over its monolayer counterpart, it remained less effective than PUR-129. The PACM coatings were the least durable; field observations revealed partial film retraction during drying, leaving areas of incomplete coverage and diminished resistance. Overall, the results support adopting multilayer acrylic–polyurethane systems for bronze exposed to Nile-Delta–type climates, with B-82 multilayer as a secondary option when reversibility is paramount. Reported “efficiency” values derived from mass change should be interpreted as comparative rankings rather than absolute corrosion rates. The study reflects performance on clean (post-cleaning) bronze; future work should extend field duration and examine behavior over retained patinas and under varied orientations/pollutant regimes. Declarations Funding The authors declare that no funds were received during the preparation of this manuscript. Author Contribution Mostafa I. Eladawy: Writing – Original Draft. Mohamed Abdelbar: Methodology, Supervision, Validation, Writing – Review & Editing. Mohamed M. Megahed and Nabil Abdel Ghany: Investigation, Formal Analysis, Visualization. Eman AbdElRhiem: Experimental Work, Software, Data Interpretation, Review & Editing. Data Availability The datasets used and/or analysed during the current study available from the corresponding author on reasonable request. References Mendoza, A. R. & Corvo, F. 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Scale:\u003c/strong\u003ecoupon edge length = \u003cstrong\u003e30.\u003c/strong\u003e\u003c/p\u003e","description":"","filename":"5.png","url":"https://assets-eu.researchsquare.com/files/rs-7502286/v1/b119416ba7c3303063b00379.png"},{"id":92865620,"identity":"5361dd70-01bd-4611-bf14-4c603f4fa1dc","added_by":"auto","created_at":"2025-10-06 13:02:54","extension":"png","order_by":6,"title":"Figure 6","display":"","copyAsset":false,"role":"figure","size":1568326,"visible":true,"origin":"","legend":"\u003cp\u003eSEM/EDS micrographs of coated and uncoated bronze coupons after 12 months of exposure, showing surface morphology and corrosion product development. Images (a–i) correspond to different coating configurations: (a, b) PUR-129 mono/multi-layer, (c, d) B-82 mono/multi-layer, (e, f) PACM mono/multi-layer, (g) PACM+B-82 hybrid, (h, i) PACM+B-82 emulsions, and (j) blank.\u003c/p\u003e","description":"","filename":"6.png","url":"https://assets-eu.researchsquare.com/files/rs-7502286/v1/8e03f5e3d804ab49339d4067.png"},{"id":92864115,"identity":"a8de1169-ced3-4ad0-a62e-22d2a25898e9","added_by":"auto","created_at":"2025-10-06 12:46:54","extension":"png","order_by":7,"title":"Figure 7","display":"","copyAsset":false,"role":"figure","size":98040,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eThe i\u003c/strong\u003enhibition \u003cstrong\u003eefficiency of each coating system after 12 months of natural exposure.\u003c/strong\u003e\u003c/p\u003e","description":"","filename":"7.png","url":"https://assets-eu.researchsquare.com/files/rs-7502286/v1/e129cfdf6e869e67508a92f1.png"},{"id":94598653,"identity":"96826891-4871-4439-97df-c5e24662f4c4","added_by":"auto","created_at":"2025-10-28 18:55:28","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":6047831,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-7502286/v1/3ea15790-e852-443c-a605-7c8880be55d8.pdf"}],"financialInterests":"No competing interests reported.","formattedTitle":"Corrosion Performance of Acrylic–Polyurethane and Polyacrylamide Coatings on Quaternary Bronze","fulltext":[{"header":"1. Introduction","content":"\u003cp\u003eOutdoor bronze\u0026mdash;encompassing sculptures, fountains, plaques, gates, and railings\u0026mdash;is highly vulnerable to atmospheric deterioration owing to prolonged exposure to weathering, airborne pollutants, and microclimatic fluctuations\u003csup\u003e\u0026lrm;\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e-\u0026lrm;\u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e5\u003c/span\u003e\u003c/sup\u003e. Upon exposure, bronze surfaces undergo electrochemical reactions that generate corrosion products such as cuprite (Cu₂O), copper sulfates (e.g., CuSO₄\u0026middot;5H₂O), and basic copper chlorides (e.g., Cu₂(OH)₃Cl)\u003csup\u003e\u0026lrm;\u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e6\u003c/span\u003e-\u0026lrm;\u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e8\u003c/span\u003e\u003c/sup\u003e. Moisture from rain, dew, or high relative humidity functions as an electrolyte, enabling dissolution/transport of copper and alloying elements, while pollutants including SO₂ and Cl⁻ accelerate degradation through acid formation and chloride complexation that destabilize the passive film\u003csup\u003e\u0026lrm;\u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e9\u003c/span\u003e-\u0026lrm;\u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e11\u003c/span\u003e\u003c/sup\u003e. Thermal and humidity cycling further intensifies these processes by driving repeated wet\u0026ndash;dry episodes that favor porous, poorly protective corrosion layers\u0026lrm;\u003csup\u003e\u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e12\u003c/span\u003e\u003c/sup\u003e. Over time, a patina develops whose protective role depends on its composition, structure, and adhesion; stable patinas may inhibit further attack, whereas unstable or chloride-rich layers can promote continued deterioration\u003csup\u003e\u0026lrm;\u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2\u003c/span\u003e,\u0026lrm;\u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e13\u003c/span\u003e\u003c/sup\u003e.\u003c/p\u003e\u003cp\u003eMitigation strategies, therefore, rely on protective systems\u0026mdash;coatings and inhibitors\u0026mdash;to reduce ion transport and pollutant ingress. Conventional single-layer coatings, although widely used, frequently fail to ensure long-term stability under harsh outdoor conditions\u003csup\u003e\u0026lrm;\u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e14\u003c/span\u003e-\u0026lrm;\u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e17\u003c/span\u003e\u003c/sup\u003e. In contrast, multilayer designs have gained prominence for combining complementary functions (e.g., adhesion, barrier performance, UV/weathering resistance) within a stratified film, thereby delivering enhanced durability and corrosion resistance on outdoor bronze substrates\u003csup\u003e\u0026lrm;\u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e18\u003c/span\u003e-\u0026lrm;\u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e20\u003c/span\u003e\u003c/sup\u003e.\u003c/p\u003e\u003cp\u003eThe performance of protective coatings depends on both material chemistry and application design. Polyurethane\u0026ndash;acrylic systems (e.g., PUR-129) are noted for strong adhesion to metals and good mechanical/chemical durability, making them effective primers or stand-alone barriers\u0026lrm;\u003csup\u003e\u003cspan citationid=\"CR21\" class=\"CitationRef\"\u003e21\u003c/span\u003e\u003c/sup\u003e. In addition, UV-curable polyurethane acrylates achieve densely cross-linked networks that improve mechanical, chemical, and optical stability on metallic substrates\u003csup\u003e\u0026lrm;\u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e22\u003c/span\u003e\u003c/sup\u003e. These attributes position polyurethane\u0026ndash;acrylic coatings as promising candidates for outdoor bronze conservation.\u003c/p\u003e\u003cp\u003eAcrylic coatings (e.g., Paraloid B-82) are valued in heritage contexts for transparency, barrier performance, weathering stability, and reversibility, allowing use either alone or as part of multilayer designs\u0026lrm;\u003csup\u003e\u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e23\u003c/span\u003e\u003c/sup\u003e. Polyacrylamide (PAM/PACM), a high\u0026ndash;high-molecular-weight, water-soluble polymer, forms clear films that can be formulated to tailor surface energy and flexibility; when combined appropriately within a coating build, it can contribute to environmental resistance in outdoor service. By combining polymers in multilayer designs, complementary functions (adhesion, barrier properties, optical stability) can be integrated to achieve more durable protection than single layers.\u003c/p\u003e\u003cp\u003eThis study assesses the corrosion resistance and visual stability of coatings on outdoor bronze using quaternary bronze coupons that replicate the alloy used in the window grilles of Sabil al-Ahmadi (Tanta, Egypt)\u003csup\u003e\u0026lrm;\u003cspan citationid=\"CR24\" class=\"CitationRef\"\u003e24\u003c/span\u003e\u003c/sup\u003e. Coatings were applied as monolayer, multilayer, and emulsion films and exposed naturally for 12 months at the case-study site. Laboratory analyses\u0026mdash;electrochemical impedance spectroscopy (EIS) and potentiodynamic polarization (to derive polarization resistance, Rp), weight change, gloss retention, and post-aging SEM/EDS\u0026mdash;were employed to compare protective performance. Together, these methods provide a comprehensive evaluation of barrier behavior and appearance retention relevant to conservation practice.\u003c/p\u003e\u003cp\u003eThis work provides a site-specific, 12-month natural-exposure comparison of three transparent polymer families\u0026mdash;acrylic\u0026ndash;polyurethane (PUR-129), acrylic (Paraloid B-82), and polyacrylamide (PACM). Beyond the general expectation that multilayers outperform monolayers, our goal is to quantify how film architecture (monolayer, multilayer, emulsion) governs both corrosion-barrier kinetics and visual stability. We integrate time-resolved electrochemical impedance spectroscopy (EIS) and potentiodynamic measurements with optical ageing metrics (visual examination and gloss retention) and post-ageing SEM/EDS. The novelty lies in this multi-metric, field-based assessment across distinct coating chemistries and layer designs, producing decision-ready guidance for selecting multilayer systems that maximize corrosion protection while minimizing visible alteration under the Nile-Delta urban climate.\u003c/p\u003e"},{"header":"2. Material and Methods","content":"\u003cp\u003e\u003cstrong\u003e2.1 Bronze Coupons \u003cstrong\u003eand Surface Preparation\u003c/strong\u003e\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eCommercial quaternary bronze (Cu\u0026ndash;Sn\u0026ndash;Zn\u0026ndash;Pb; composition in\u0026nbsp;Table\u0026nbsp;1) was machined into coupons (30 \u0026times; 30 \u0026times; 11 mm\u0026sup3; for natural exposure; 20 \u0026times; 11 \u0026times; 3 mm\u0026sup3; for laboratory tests). Whereas metal analogues are often artificially aged to reproduce the corrosion layers found on historic objects, our coupons were kept as clean metal to reflect the post-cleaning state stipulated for the Sabil al-Ahmadi grille. Surfaces were progressively abraded with 600\u0026ndash;1200-grit papers to a smooth finish, degreased in a mild alkaline solution, rinsed with running and then deionized water, swabbed with ethyl alcohol, and dried. Coupons were handled with talc-free gloves and tongs, individually numbered, and stored dry before coating.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eTable\u0026nbsp;\u003c/strong\u003e\u003cstrong\u003e1\u003c/strong\u003e\u003cstrong\u003e.\u003c/strong\u003e Chemical composition (wt%) of the quaternary bronze coupons used in this study, values are means \u0026plusmn; SD from replicate analyses (totals normalized to 100 wt%).\u003c/p\u003e\n\u003ctable border=\"0\" cellspacing=\"0\" cellpadding=\"0\"\u003e\n \u003ctbody\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 71px;\"\u003e\u003cstrong\u003e\u003cem\u003eElement\u003c/em\u003e\u003c/strong\u003e\u003cbr\u003e\u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 71px;\"\u003e\u003cstrong\u003e\u003cem\u003eCu\u003c/em\u003e\u003c/strong\u003e\u003cbr\u003e\u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 71px;\"\u003e\u003cstrong\u003e\u003cem\u003eSn\u003c/em\u003e\u003c/strong\u003e\u003cbr\u003e\u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 71px;\"\u003e\u003cstrong\u003e\u003cem\u003ePb\u003c/em\u003e\u003c/strong\u003e\u003cbr\u003e\u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 71px;\"\u003e\u003cstrong\u003e\u003cem\u003eZn\u003c/em\u003e\u003c/strong\u003e\u003cbr\u003e\u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 71px;\"\u003e\u003cstrong\u003e\u003cem\u003eNi\u003c/em\u003e\u003c/strong\u003e\u003cbr\u003e\u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 84px;\"\u003e\u003cstrong\u003e\u003cem\u003eFe\u003c/em\u003e\u003c/strong\u003e\u003cbr\u003e\u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 76px;\"\u003e\u003cstrong\u003e\u003cem\u003eSb\u003c/em\u003e\u003c/strong\u003e\u003cbr\u003e\u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 71px;\"\u003e\u003cem\u003eWt. %\u003c/em\u003e\u003cbr\u003e\u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 71px;\"\u003e84.7 \u0026plusmn; 0.3\u003cbr\u003e\u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 71px;\"\u003e5.1 \u0026plusmn; 0.2\u003cbr\u003e\u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 71px;\"\u003e4.3 \u0026plusmn; 0.2\u003cbr\u003e\u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 71px;\"\u003e5.5 \u0026plusmn; 0.3\u003cbr\u003e\u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 71px;\"\u003e0.2 \u0026plusmn; 0.1\u003cbr\u003e\u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 84px;\"\u003e0.08 \u0026plusmn; 0.03\u003cbr\u003e\u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 76px;\"\u003e0.05 \u0026plusmn; 0.02\u003cbr\u003e\u003c/td\u003e\n \u003c/tr\u003e\n \u003c/tbody\u003e\n\u003c/table\u003e\n\u003cp skip=\"true\"\u003e\u003cstrong\u003e2.2 Protective Coatings\u0026nbsp;\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThree transparent polymer coatings were selected for comparison: PUR-129, polyacrylamide and Paraloid B-82. PUR-129 is a clear acrylic\u0026ndash;polyurethane coating (CMB-Egypt) applied at the manufacturer\u0026rsquo;s standard concentration. Film formation proceeds by the reaction of hydroxyl-functional polyols with isocyanates to generate urethane linkages, yielding a densely cross-linked network with good adhesion and mechanical/chemical durability. According to the technical data sheet, the formulation includes light-stabilizing additives, which limit UV-induced yellowing and photodegradation\u0026mdash;attributes relevant to outdoor service. Polyacrylamide (PAM) was included as a water-borne, low-VOC candidate to benchmark a hydrophilic matrix against the more hydrophobic acrylic\u0026ndash;polyurethane and acrylic systems. It is high-molecular-weight polymer (Mn \u0026gt; 5 \u0026times; 10⁶; BDH Chemicals) prepared as a 5 wt% aqueous solution\u003csup\u003e\u0026lrm;\u003c/sup\u003e\u003csup\u003e25\u003c/sup\u003e\u003csup\u003e-\u003c/sup\u003e\u003csup\u003e\u0026lrm;\u003c/sup\u003e\u003csup\u003e31\u003c/sup\u003e. Paraloid B-82 is a thermoplastic acrylic resin applied here as a 5 wt% solution in acetone. It forms transparent, removable films and is widely used in conservation where reversibility and optical clarity are required; in multilayer builds it can serve as either primer or topcoat\u003csup\u003e\u0026lrm;\u003c/sup\u003e\u003csup\u003e19\u003c/sup\u003e\u003csup\u003e,\u003c/sup\u003e\u003csup\u003e\u0026lrm;\u003c/sup\u003e\u003csup\u003e32\u003c/sup\u003e\u003csup\u003e-\u003c/sup\u003e\u003csup\u003e\u0026lrm;\u003c/sup\u003e\u003csup\u003e34\u003c/sup\u003e.\u0026nbsp;Coatings (PUR-129, Paraloid B-82, PACM) were applied by brush as \u003cstrong\u003emonolayers\u003c/strong\u003e or \u003cstrong\u003emultilayers\u003c/strong\u003e (three coats, 12 h between coats) following the parameters in Table\u003cstrong\u003e\u0026nbsp;\u003c/strong\u003e2.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eTable\u0026nbsp;\u003c/strong\u003e\u003cstrong\u003e2\u003c/strong\u003e\u003cstrong\u003e.\u003c/strong\u003e Coating configurations and specimen allocation. Triplicate bronze coupons (IDs shown as letters) were coated by brush as monolayers (one coat) or multilayers (three coats, 12 h between coats).\u0026nbsp;\u003c/p\u003e\n\u003cdiv align=\"\"\u003e\n \u003ctable dir=\"rtl\" border=\"1\" cellspacing=\"0\" cellpadding=\"0\" width=\"552\"\u003e\n \u003ctbody\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 144px;\"\u003e\u003cstrong\u003eMono or multi-layer\u003c/strong\u003e\u003cbr\u003e\u003c/td\u003e\n \u003ctd style=\"width: 276px;\"\u003e\u003cstrong\u003eProtection system\u003c/strong\u003e\u003cbr\u003e\u003c/td\u003e\n \u003ctd style=\"width: 132px;\"\u003e\u003cstrong\u003eCoupons\u0026nbsp;\u003c/strong\u003e\u003cbr\u003e\u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 144px;\"\u003eBlank\u003cbr\u003e\u003c/td\u003e\n \u003ctd style=\"width: 276px;\"\u003eBlank\u003cbr\u003e\u003c/td\u003e\n \u003ctd style=\"width: 132px;\"\u003eA, B, C\u003cbr\u003e\u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 144px;\"\u003eMonolayer\u003cbr\u003e\u003c/td\u003e\n \u003ctd style=\"width: 276px;\"\u003eB-82 (5% in acetone)\u003cbr\u003e\u003c/td\u003e\n \u003ctd style=\"width: 132px;\"\u003eD, E, F\u003cbr\u003e\u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 144px;\"\u003eMultilayer\u003cbr\u003e\u003c/td\u003e\n \u003ctd style=\"width: 276px;\"\u003eB-82 (5% in acetone)\u003cbr\u003e\u003c/td\u003e\n \u003ctd style=\"width: 132px;\"\u003eG, H, I\u003cbr\u003e\u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 144px;\"\u003eMonolayer\u003cbr\u003e\u003c/td\u003e\n \u003ctd style=\"width: 276px;\"\u003ePUR-129 (Standard)\u003cbr\u003e\u003c/td\u003e\n \u003ctd style=\"width: 132px;\"\u003eJ, K, L\u003cbr\u003e\u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 144px;\"\u003eMultilayer\u003cbr\u003e\u003c/td\u003e\n \u003ctd style=\"width: 276px;\"\u003ePUR-129 (Standard)\u003cbr\u003e\u003c/td\u003e\n \u003ctd style=\"width: 132px;\"\u003eM, N, O\u003cbr\u003e\u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 144px;\"\u003eMonolayer\u003cbr\u003e\u003c/td\u003e\n \u003ctd style=\"width: 276px;\"\u003ePolyacrylamide (5% in water)\u003cbr\u003e\u003c/td\u003e\n \u003ctd style=\"width: 132px;\"\u003eP, Q, R\u003cbr\u003e\u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 144px;\"\u003eMultilayer\u003cbr\u003e\u003c/td\u003e\n \u003ctd style=\"width: 276px;\"\u003ePolyacrylamide (5% in water)\u003cbr\u003e\u003c/td\u003e\n \u003ctd style=\"width: 132px;\"\u003eS, T, U\u003cbr\u003e\u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 144px;\"\u003eMultilayer\u003cbr\u003e\u003c/td\u003e\n \u003ctd style=\"width: 276px;\"\u003eOne layer of PACM and two layers of B-82\u003cbr\u003e\u003c/td\u003e\n \u003ctd style=\"width: 132px;\"\u003eAA, BB, CC\u003cbr\u003e\u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 144px;\"\u003eMonolayer\u003cbr\u003e\u003c/td\u003e\n \u003ctd style=\"width: 276px;\"\u003eEmulsion of (PACM+B-82 1:1)\u003cbr\u003e\u003c/td\u003e\n \u003ctd style=\"width: 132px;\"\u003eDD, EE, FF\u003cbr\u003e\u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 144px;\"\u003eMultilayer\u003cbr\u003e\u003c/td\u003e\n \u003ctd style=\"width: 276px;\"\u003eEmulsion of (PACM+B-82 1:1)\u003cbr\u003e\u003c/td\u003e\n \u003ctd style=\"width: 132px;\"\u003eGG, HH, II\u003cbr\u003e\u003c/td\u003e\n \u003c/tr\u003e\n \u003c/tbody\u003e\n \u003c/table\u003e\n\u003c/div\u003e\n\u003cp\u003e\u003cstrong\u003e2.3 Corrosion Tests\u0026nbsp;\u003c/strong\u003e\u003c/p\u003e\n\u003cp skip=\"true\"\u003eCorrosion testing provides quantitative evidence of coating performance under relevant environmental stresses. Electrochemical methods\u0026mdash;notably electrochemical impedance spectroscopy (EIS) and potentiodynamic polarization\u0026mdash;are well suited to coated bronzes because they non-destructively track barrier integrity and corrosion kinetics over time. Metrics such as the low-frequency impedance modulus, polarization resistance, and coating capacitance sensitively indicate water uptake, defect growth, and underfilm corrosion, enabling time-dependent comparisons among formulations and layer designs. When paired with controlled natural or accelerated exposures and appropriate statistics (replicates, error bars), these techniques yield robust durability rankings and clarify failure modes, thereby guiding the selection and optimization of protective coatings for long-term service in aggressive atmospheres\u003csup\u003e\u0026lrm;\u003c/sup\u003e\u003csup\u003e35\u003c/sup\u003e\u003csup\u003e-\u003c/sup\u003e\u003csup\u003e\u0026lrm;\u003c/sup\u003e\u003csup\u003e38\u003c/sup\u003e.\u003c/p\u003e\n\u003cp skip=\"true\"\u003e\u003cstrong\u003e2.3.1 Short-term testing\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eElectrochemical measurements were conducted using an Origaflex-OGF01A system (Origalys, France). The setup consisted of an Ag/AgCl reference electrode, a platinum sheet as the auxiliary electrode, and (coated, uncoated)\u0026nbsp;bronze coupons as the working electrode. Electrochemical impedance spectroscopy (EIS) was performed at open circuit potential (OCP), while Tafel plots were used to determine the corrosion rate (C.R.) and corrosion current density (I\u003csub\u003ecorr.\u003c/sub\u003e) with a scan rate of 2 mV/s over a potential range of -300 to 300 mV. EIS measurements spanned a frequency range of 0.1 Hz to 100 kHz, with a 10 mV amplitude, following ASTM G106-89 standards.\u0026nbsp;Measurements were performed in aerated \u003cstrong\u003e3.5 wt% NaCl\u003c/strong\u003e\u003cstrong\u003e\u0026nbsp;\u003c/strong\u003eat\u003cstrong\u003e\u0026nbsp;\u003cstrong\u003e25 \u0026plusmn; 1 \u0026deg;C\u003c/strong\u003e\u003c/strong\u003e, a standard chloride electrolyte used to benchmark coatings on copper alloys. This medium imposes a \u003cstrong\u003echloride-dominated, high-conductivity challenge\u003c/strong\u003e that sensitively probes barrier properties by EIS/polarization. \u003cstrong\u003eIn our Nile-Delta setting, outdoor surfaces are periodically wetted by chloride-bearing aerosols and moisture, in addition to urban pollutants\u003c/strong\u003e, so chloride is an appropriate stressor for accelerated ranking. We emphasize that the \u003cstrong\u003eNaCl cell does not aim to replicate the entire urban atmosphere\u003c/strong\u003e \u003cem\u003e(NOx/SOx, soot, organics)\u003c/em\u003e; those stressors were assessed by the \u003cstrong\u003e12-month on-site exposure\u003c/strong\u003e. Together, the NaCl cell provides a \u003cstrong\u003econtrolled, worst-case ionic environment\u003c/strong\u003e for ranking coatings, while natural exposure demonstrates \u003cstrong\u003ereal-world durability\u003c/strong\u003e.\u003c/p\u003e\n\u003cp skip=\"true\"\u003e\u003cstrong\u003e2.3.2 Long-term testing\u003c/strong\u003e\u003c/p\u003e\n\u003cp skip=\"true\"\u003eA reinforced plastic rack was mounted on two delta-shaped aluminum bases and set at 45\u0026deg; from the horizontal, facing south (Northern Hemisphere). Bronze coupons were hung from 5-cm plastic pins with broad heads, leaving a 3-cm standoff below each coupon to ensure free drainage and full exposure. Coupons were arranged in triplicate (Fig. 1,a-b). The rack was installed on the roof of a building adjacent to Sabil al-Ahmadi in Tanta so that the coupons experienced the same outdoor environment as the historic grille. The 45\u0026deg; equator-facing configuration follows common practice for direct natural weathering of coatings (ASTM G7) and is consistent with ISO guidance (ISO 9223) for selecting exposure geometry; rack construction and placement conformed to ISO 877-2 Method A and ASTM D4141\u003csup\u003e\u0026lrm;\u003c/sup\u003e\u003csup\u003e8\u003c/sup\u003e\u003csup\u003e,\u003c/sup\u003e\u003csup\u003e\u0026lrm;\u003c/sup\u003e\u003csup\u003e19\u003c/sup\u003e. Corrosion progression was tracked every two months by visual/microscopic examination, gloss measurements, and mass (weight) change determinations.\u003c/p\u003e\n\u003cp skip=\"true\"\u003e\u003cstrong\u003e2.3.2.1 Visual Examination and Post-Aging SEM/EDS\u003c/strong\u003e\u003c/p\u003e\n\u003cp skip=\"true\"\u003eSurface condition was monitored at two-month intervals by visual inspection under ambient light and documented by digital photography. After 12 months, representative coupons from each coating system were examined by scanning electron microscopy (SEM) coupled with energy-dispersive X-ray spectroscopy (EDS) to assess surface morphology and elemental signatures (JEOL JSM-6510LV, Japan). SEM observations were performed at appropriate accelerating voltages in low-vacuum (LV) mode to minimize charging; images are presented with calibrated scale bars. EDS spectra were acquired from multiple fields per sample to confirm the presence of corrosion products and/or environmental deposits.\u003c/p\u003e\n\u003cp skip=\"true\"\u003e\u003cstrong\u003e2.3.2.2 Weight-change measurements\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eWeight measurement emerges as a common technique for corrosion monitoring, involving the weighing of metal specimens before and after exposure to corrosive agents. An increase in the weight of a bronze object indicates an active corrosion process\u003csup\u003e\u0026lrm;\u003c/sup\u003e\u003csup\u003e36\u003c/sup\u003e\u003csup\u003e-\u003c/sup\u003e\u003csup\u003e\u0026lrm;\u003c/sup\u003e\u003csup\u003e39\u003c/sup\u003e. Each coupon was weighed after coating and then at two-month intervals for 12 months (six time points) on an analytical balance (readability 0.0001 g). Before weighing, surfaces were gently cleaned with oil-free air and a soft brush; no chemical pickling was performed to avoid altering corrosion products or the coatings.\u003c/p\u003e\n\u003cp\u003eThe inhibition Efficiency (%) of the coating systems was calculated employing the formula: \u0026nbsp; \u0026nbsp;\u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp;Efficiency (\u0026eta;) % = W\u003csub\u003ea\u003c/sub\u003e \u0026ndash; W\u003csub\u003eb\u0026nbsp;\u003c/sub\u003e\u003cstrong\u003e/\u003c/strong\u003e\u003csub\u003e\u0026nbsp;\u003c/sub\u003eW\u003csub\u003ea\u0026nbsp;\u003c/sub\u003e\u0026times; 100 \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp;(1)\u003c/p\u003e\n\u003cp\u003eWhere W\u003csub\u003ea\u003c/sub\u003e and W\u003csub\u003eb\u003c/sub\u003e are the weight gain average of the unprotected and protected coupons after 12 months of exposure, respectively\u003csup\u003e\u0026lrm;\u003c/sup\u003e\u003csup\u003e40\u003c/sup\u003e.\u003c/p\u003e\n\u003cp skip=\"true\"\u003e\u003cstrong\u003e2.3.2.3 Gloss measurements\u003c/strong\u003e\u003c/p\u003e\n\u003cp skip=\"true\"\u003eSpecular gloss was measured using an Erichsen Picogloss 503 at the standard 60\u0026deg; geometry in accordance with ISO 2813 / ASTM D523. The instrument was calibrated against the supplied black-glass standard before each session.\u003cspan dir=\"RTL\"\u003e \u003c/span\u003eBaseline gloss (G\u003csub\u003e0\u003c/sub\u003e) was recorded after coating cure; after \u003cstrong\u003e12 months\u003c/strong\u003e of natural exposure, gloss (G\u003csub\u003et\u003c/sub\u003e) was re-measured to quantify weathering-induced change. For each coupon, \u003cstrong\u003efive readings\u003c/strong\u003e were taken at the \u003cstrong\u003esame marked locations\u003c/strong\u003e and averaged. Results are reported as \u003cstrong\u003egloss retention\u003c/strong\u003e GR (%) =100\u0026times;(G\u003csub\u003et\u003c/sub\u003e/G\u003csub\u003e0\u003c/sub\u003e) (mean \u0026plusmn; SD for replicates); \u0026Delta;G (%) =100\u0026times;(G\u003csub\u003et\u003c/sub\u003e\u0026minus;G\u003csub\u003e0\u003c/sub\u003e)/G\u003csub\u003e0\u003c/sub\u003e\u003csub\u003e \u003c/sub\u003eis provided where percent change is discussed.\u003c/p\u003e"},{"header":"3. Results and Discussion","content":"\u003cp\u003e\u003cstrong\u003e3.1 Electrochemical\u0026nbsp;\u003c/strong\u003e\u003cstrong\u003eMeasurements\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe corrosion resistance of coated and uncoated bronze coupons was measured using electrochemical impedance spectroscopy (EIS) and Polarization plots. Polarization plots are utilized to evaluate the corrosion behavior of coated and uncoated bronze, as seen in\u0026nbsp;Fig.\u0026nbsp;2(a)\u0026nbsp;and\u0026nbsp;Table\u0026nbsp;3. The Tafel polarization results demonstrated that differences in corrosion potential (E\u003csub\u003ecorr.\u003c/sub\u003e) correspond to the degree of passivation obtained by each coating. According to the data, coatings greatly improve corrosion resistance when compared to uncoated bronze, especially multilayers. Tafel graphs show lower corrosion current densities for coated coupons, indicating that protective layers minimize corrosion rates\u003csup\u003e\u0026lrm;\u003c/sup\u003e\u003csup\u003e41\u003c/sup\u003e.\u003c/p\u003e\n\u003cp\u003ePUR-129 monolayer coupon (2) and three layers of PUR-129 coupon (3) exhibit greater resistance to anodic dissolution than the uncoated coupon (1). Lower I\u003csub\u003ecorr.\u003c/sub\u003e values correlate with lower corrosion rates\u003csup\u003e\u0026lrm;\u003c/sup\u003e\u003csup\u003e42\u003c/sup\u003e, demonstrating high corrosion inhibition efficacy of 99.98% and 99.96%, respectively. The combination of polyurethane and acrylic offers environmental protection, quick drying, and strong corrosion resistance, making PUR-129 an excellent choice for protecting exposed metal surfaces in challenging outdoor environments. PUR-129 offers exceptional resistance to cracking and imperfections, as shown in\u0026nbsp;Fig.\u0026nbsp;2. Polyurethane\u0026apos;s high adherence to metal surfaces provides stability and longevity, making it perfect for outdoor applications\u003csup\u003e\u0026lrm;\u003c/sup\u003e\u003csup\u003e38\u003c/sup\u003e\u003csup\u003e,\u003c/sup\u003e\u003csup\u003e\u0026lrm;\u003c/sup\u003e\u003csup\u003e43\u003c/sup\u003e.\u003c/p\u003e\n\u003cp\u003ePUR-129 three-layer coupon (3) and monolayer coupon (2) have similar C.R., but coupon 3\u0026apos;s polarization resistance R\u003csub\u003ep\u003c/sub\u003e value is 225.48\u0026times;10\u003csup\u003e\u003cspan dir=\"RTL\"\u003e3\u003c/span\u003e\u003c/sup\u003e ohm.cm\u0026sup2; compared with coupon 2\u0026apos;s 40.18 ohm.cm\u0026sup2;, as shown in the EIS plot in Fig. 3(b).\u003c/p\u003e\n\u003cp\u003eMulti-layer systems, acting as diffusion barriers, restrict electrochemical reactions, reducing ion transit, and thereby increasing corrosion resistance, as shown in Table\u0026nbsp;3. In addition, the coatings with homogenous multi-layers of PUR-129 showed lower roughness, which decreased the area for electrochemical processes\u003csup\u003e\u0026lrm;\u003c/sup\u003e\u003csup\u003e44\u003c/sup\u003e, potentially increasing R\u003csub\u003ep\u003c/sub\u003e in coupon (3), as seen in Fig. 3(b). Microscopic investigations in Fig. 6(k, n) show that the multi-layered PUR-129 surface is completely free of corrosion products and dust deposition, whereas the mono-layered PUR-129 coating had only tiny corrosion spots, confirming the R\u003csub\u003ep\u0026nbsp;\u003c/sub\u003evalues. Finally, coatings with multilayers of PUR-129 coupon (3) show better corrosion protection performance in this study.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eMulti-layer coatings, such as three layers of\u0026nbsp;Paraloid\u0026nbsp;B-82 coupon\u0026nbsp;(5) and three layers of PACM coupon\u0026nbsp;(7), displayed low corrosion rates as well, with 96.23% and 95.53% effectiveness, respectively, as illustrated in\u0026nbsp;Table\u0026nbsp;3. Confirming\u0026nbsp;the morphology images in\u0026nbsp;Fig.\u0026nbsp;6(e, h), Paraloid B-82 for mono or multi-layer coatings shows green corrosion spots in some areas. The PACM coating provided the least protection against corrosion; although multiple layers of PACM\u0026nbsp;coupon\u0026nbsp;(7)\u0026nbsp;performed slightly better than a single-layer\u0026nbsp;coupon\u0026nbsp;(6), they still did not offer the desired level of protection. Confirming that multi-layer designs improve coating durability\u003csup\u003e\u0026lrm;\u003c/sup\u003e\u003csup\u003e15\u003c/sup\u003e\u003csup\u003e,\u003c/sup\u003e\u003csup\u003e\u0026lrm;\u003c/sup\u003e\u003csup\u003e16\u003c/sup\u003e\u003csup\u003e,\u003c/sup\u003e\u003csup\u003e\u0026lrm;\u003c/sup\u003e\u003csup\u003e45\u003c/sup\u003e. Coating efficacy may vary based on composition and application techniques\u003csup\u003e\u0026lrm;\u003c/sup\u003e\u003csup\u003e46\u003c/sup\u003e, as illustrated in\u0026nbsp;Table\u0026nbsp;3.\u003c/p\u003e\n\u003cp\u003eSince there were weak areas where corrosion products were gathered for PACM, the surface paleness and defective clarity of Paraloid B-82 Coupon (8) were improved in these coupons. Coupon (8), which consists of one layer of PACM and three layers of B-82, demonstrated a high corrosion inhibition efficacy of 98.65% when compared to multi-layers of B-82 or PACM.\u003c/p\u003e\n\u003cp\u003eEmulsion coatings of Paraloid B-82 and polyacrylamide can considerably improve bronze\u0026apos;s corrosion resistance, including coupons\u0026nbsp;(9 and 10). Paraloid B-82, an acrylic copolymer, provides a long-term protective coating, while polyacrylamide helps to increase adhesion and flexibility. They combine to produce a barrier against moisture and corrosive products, effectively preventing oxidation and degradation on bronze surfaces. According to research, such coatings can beat standard approaches in terms of durability and environmental resistance.\u003c/p\u003e\n\u003cp\u003eHowever, when compared to coupon\u0026nbsp;(1) of bronze without coating, emulsion coatings give a balanced approach with reasonable protection and produce reasonably satisfactory results, as shown in Table\u0026nbsp;3, with efficiency of 95.84% and 93.10%.\u003c/p\u003e\n\u003cp\u003eThe corrosion parameters in Table 3 were determined using the Tafel extrapolation measurements. The C.R. is calculated from equation (2):\u003c/p\u003e\n\u003cp\u003e\u003cimg src=\"https://myfiles.space/user_files/58895_8739fc6c57c1c19a/58895_custom_files/img1759754061.png\" width=\"629\" height=\"78\"\u003e\u003c/p\u003e\n\u003cp\u003ewhere M.W. is the molecular weight of the corroded material (g/mol), C.R. is the corrosion rate (mpy), and I\u003csub\u003ecorr.\u003c/sub\u003e is the current density of corrosion (A cm\u003csup\u003e\u0026minus;2\u003c/sup\u003e), n is the number of charge transfers throughout the corrosion process, and d is the density (g cm\u003csup\u003e\u0026minus;3\u003c/sup\u003e) [42].\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eIn general, multi-layer coatings provide better protection than monolayers because the additional layers form a stronger barrier that inhibits corrosion. Reduced pore size, protective film generation, and better chemical stability [45], as seen in Figs.\u0026nbsp;2(b)\u0026nbsp;contribute to a longer lifetime.\u0026nbsp;We also investigated the impact of the coating thickness layer on corrosion parameters.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eTable\u0026nbsp;\u003c/strong\u003e\u003cstrong\u003e3\u003c/strong\u003e\u003cstrong\u003e.\u0026nbsp;\u003c/strong\u003eElectrochemical parameters obtained from potentiodynamic polarization of blank and coated bronze coupons.\u003c/p\u003e\n\u003cdiv align=\"\"\u003e\n \u003ctable border=\"1\" cellspacing=\"0\" cellpadding=\"0\" width=\"702\"\u003e\n \u003ctbody\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 74px;\"\u003e\u003cstrong\u003eCoupon No.\u003c/strong\u003e\u003cbr\u003e\u003c/td\u003e\n \u003ctd style=\"width: 89px;\"\u003e\u003cstrong\u003eProtection system\u003c/strong\u003e\u003cbr\u003e\u003c/td\u003e\n \u003ctd style=\"width: 101px;\"\u003e\u003cstrong\u003eR\u003csub\u003ep\u003c/sub\u003e\u003c/strong\u003e\u003cbr\u003e\u003cstrong\u003e\u003csub\u003e\u0026nbsp;\u003c/sub\u003e\u003c/strong\u003e\u003cbr\u003e\u003cstrong\u003e(ohm.cm\u0026sup2;)\u003c/strong\u003e\u003cbr\u003e\u003c/td\u003e\n \u003ctd style=\"width: 60px;\"\u003e\u003cstrong\u003eBeta a\u003c/strong\u003e\u003cbr\u003e\u003cstrong\u003e\u0026nbsp;\u003c/strong\u003e\u003cbr\u003e\u003cstrong\u003e(mV)\u003c/strong\u003e\u003cbr\u003e\u003c/td\u003e\n \u003ctd style=\"width: 72px;\"\u003e\u003cstrong\u003eBeta c\u003c/strong\u003e\u003cbr\u003e\u003cstrong\u003e\u0026nbsp;\u003c/strong\u003e\u003cbr\u003e\u003cstrong\u003e(mV)\u003c/strong\u003e\u003cbr\u003e\u003c/td\u003e\n \u003ctd style=\"width: 66px;\"\u003e\u003cstrong\u003eE\u003cspan dir=\"RTL\"\u003e\u0026nbsp;\u003c/span\u003e(i =0)\u003c/strong\u003e\u003cbr\u003e\u003cstrong\u003e\u0026nbsp;\u003c/strong\u003e\u003cbr\u003e\u003cstrong\u003e(mV)\u003c/strong\u003e\u003cbr\u003e\u003c/td\u003e\n \u003ctd style=\"width: 72px;\"\u003e\u003cstrong\u003eI \u003csub\u003ecorr.\u003c/sub\u003e\u003c/strong\u003e\u003cbr\u003e\u003cstrong\u003e\u003csub\u003e\u0026nbsp;\u003c/sub\u003e\u003c/strong\u003e\u003cbr\u003e\u003cstrong\u003e\u003csub\u003e(\u0026micro;A/cm\u003c/sub\u003e\u003c/strong\u003e\u003cstrong\u003e\u003csup\u003e2\u003c/sup\u003e\u003c/strong\u003e\u003cstrong\u003e\u003csub\u003e)\u003c/sub\u003e\u003c/strong\u003e\u003cbr\u003e\u003c/td\u003e\n \u003ctd style=\"width: 84px;\"\u003e\u003cstrong\u003eCorrosion rate (C.R.) (\u0026micro;m/y)\u003c/strong\u003e\u003cbr\u003e\u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 84px;\"\u003e\u003cstrong\u003eEfficiency\u003c/strong\u003e\u003cbr\u003e\u003cstrong\u003e\u0026eta;%\u003c/strong\u003e\u003cbr\u003e\u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 74px;\"\u003e\u003cstrong\u003e1\u003c/strong\u003e\u003cbr\u003e\u003c/td\u003e\n \u003ctd style=\"width: 89px;\"\u003eBlank\u003cbr\u003e\u003c/td\u003e\n \u003ctd style=\"width: 101px;\"\u003e29.39\u003cbr\u003e\u003c/td\u003e\n \u003ctd style=\"width: 60px;\"\u003e181.4\u003cbr\u003e\u003c/td\u003e\n \u003ctd style=\"width: 72px;\"\u003e-168.5\u003cbr\u003e\u003c/td\u003e\n \u003ctd style=\"width: 66px;\"\u003e-19.1\u003cbr\u003e\u003c/td\u003e\n \u003ctd style=\"width: 72px;\"\u003e1000.1\u003cbr\u003e\u003c/td\u003e\n \u003ctd style=\"width: 84px;\"\u003e12000\u003cbr\u003e\u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 84px;\"\u003e\u0026nbsp;\u003cbr\u003e\u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 74px;\"\u003e\u003cstrong\u003e2\u003c/strong\u003e\u003cbr\u003e\u003c/td\u003e\n \u003ctd style=\"width: 89px;\"\u003eOne layer of PUR-129\u003cbr\u003e\u003c/td\u003e\n \u003ctd style=\"width: 101px;\"\u003e40.18\u003cbr\u003e\u003c/td\u003e\n \u003ctd style=\"width: 60px;\"\u003e80.4\u003cbr\u003e\u003c/td\u003e\n \u003ctd style=\"width: 72px;\"\u003e-88.2\u003cbr\u003e\u003c/td\u003e\n \u003ctd style=\"width: 66px;\"\u003e-47.3\u003cbr\u003e\u003c/td\u003e\n \u003ctd style=\"width: 72px;\"\u003e0.3145\u003cbr\u003e\u003c/td\u003e\n \u003ctd style=\"width: 84px;\"\u003e3.6409\u003cbr\u003e\u003c/td\u003e\n \u003ctd style=\"width: 84px;\"\u003e99.96%\u003cbr\u003e\u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 74px;\"\u003e\u003cstrong\u003e3\u003c/strong\u003e\u003cbr\u003e\u003c/td\u003e\n \u003ctd style=\"width: 89px;\"\u003eThree layers of PUR-129\u003cbr\u003e\u003c/td\u003e\n \u003ctd style=\"width: 101px;\"\u003e225.48\u0026times; 10\u003csup\u003e3\u003c/sup\u003e\u003cbr\u003e\u0026nbsp;\u003cbr\u003e\u003c/td\u003e\n \u003ctd style=\"width: 60px;\"\u003e350.7\u003cbr\u003e\u003c/td\u003e\n \u003ctd style=\"width: 72px;\"\u003e-507.6\u003cbr\u003e\u003c/td\u003e\n \u003ctd style=\"width: 66px;\"\u003e-133.7\u003cbr\u003e\u003c/td\u003e\n \u003ctd style=\"width: 72px;\"\u003e0.169\u003cbr\u003e\u003c/td\u003e\n \u003ctd style=\"width: 84px;\"\u003e1.9608\u003cbr\u003e\u003c/td\u003e\n \u003ctd style=\"width: 84px;\"\u003e99.98%\u003cbr\u003e\u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 74px;\"\u003e\u003cstrong\u003e4\u003c/strong\u003e\u003cbr\u003e\u003c/td\u003e\n \u003ctd style=\"width: 89px;\"\u003eOne layer of B-82\u003cbr\u003e\u003c/td\u003e\n \u003ctd style=\"width: 101px;\"\u003e610.47\u003cbr\u003e\u003c/td\u003e\n \u003ctd style=\"width: 60px;\"\u003e217.6\u003cbr\u003e\u003c/td\u003e\n \u003ctd style=\"width: 72px;\"\u003e-218.2\u003cbr\u003e\u003c/td\u003e\n \u003ctd style=\"width: 66px;\"\u003e-96.8\u003cbr\u003e\u003c/td\u003e\n \u003ctd style=\"width: 72px;\"\u003e34.8871\u003cbr\u003e\u003c/td\u003e\n \u003ctd style=\"width: 84px;\"\u003e403.87\u003cbr\u003e\u003c/td\u003e\n \u003ctd style=\"width: 84px;\"\u003e96.51%\u003cbr\u003e\u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 74px;\"\u003e\u003cstrong\u003e5\u003c/strong\u003e\u003cbr\u003e\u003c/td\u003e\n \u003ctd style=\"width: 89px;\"\u003eThree layers of B-82\u003cbr\u003e\u003c/td\u003e\n \u003ctd style=\"width: 101px;\"\u003e624.44\u003cbr\u003e\u003c/td\u003e\n \u003ctd style=\"width: 60px;\"\u003e198.4\u003cbr\u003e\u003c/td\u003e\n \u003ctd style=\"width: 72px;\"\u003e-356.0\u003cbr\u003e\u003c/td\u003e\n \u003ctd style=\"width: 66px;\"\u003e-92.7\u003cbr\u003e\u003c/td\u003e\n \u003ctd style=\"width: 72px;\"\u003e37.6264\u003cbr\u003e\u003c/td\u003e\n \u003ctd style=\"width: 84px;\"\u003e435.58\u003cbr\u003e\u003c/td\u003e\n \u003ctd style=\"width: 84px;\"\u003e96.23%\u003cbr\u003e\u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 74px;\"\u003e\u003cstrong\u003e6\u003c/strong\u003e\u003cbr\u003e\u003c/td\u003e\n \u003ctd style=\"width: 89px;\"\u003eOne layer of PACM\u003cbr\u003e\u003c/td\u003e\n \u003ctd style=\"width: 101px;\"\u003e556.86\u003cbr\u003e\u003c/td\u003e\n \u003ctd style=\"width: 60px;\"\u003e343.4\u003cbr\u003e\u003c/td\u003e\n \u003ctd style=\"width: 72px;\"\u003e-1292.8\u003cbr\u003e\u003c/td\u003e\n \u003ctd style=\"width: 66px;\"\u003e-97.9\u003cbr\u003e\u003c/td\u003e\n \u003ctd style=\"width: 72px;\"\u003e58.8268\u003cbr\u003e\u003c/td\u003e\n \u003ctd style=\"width: 84px;\"\u003e681.02\u003cbr\u003e\u003c/td\u003e\n \u003ctd style=\"width: 84px;\"\u003e94.11%\u003cbr\u003e\u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 74px;\"\u003e\u003cstrong\u003e7\u003c/strong\u003e\u003cbr\u003e\u003c/td\u003e\n \u003ctd style=\"width: 89px;\"\u003eThree layers of PACM\u003cbr\u003e\u003c/td\u003e\n \u003ctd style=\"width: 101px;\"\u003e985.80\u003cbr\u003e\u003c/td\u003e\n \u003ctd style=\"width: 60px;\"\u003e189.5\u0026nbsp;\u003cbr\u003e\u003c/td\u003e\n \u003ctd style=\"width: 72px;\"\u003e-856.4\u003cbr\u003e\u003c/td\u003e\n \u003ctd style=\"width: 66px;\"\u003e-87.6\u003cbr\u003e\u003c/td\u003e\n \u003ctd style=\"width: 72px;\"\u003e46.4950\u003cbr\u003e\u003c/td\u003e\n \u003ctd style=\"width: 84px;\"\u003e538.25\u003cbr\u003e\u003c/td\u003e\n \u003ctd style=\"width: 84px;\"\u003e95.35%\u003cbr\u003e\u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 74px;\"\u003e\u003cstrong\u003e8\u003c/strong\u003e\u003cbr\u003e\u003c/td\u003e\n \u003ctd style=\"width: 89px;\"\u003eOne layer of\u0026nbsp;PACM and two layers of B-82\u003cbr\u003e\u003c/td\u003e\n \u003ctd style=\"width: 101px;\"\u003e1.75\u003cbr\u003e\u003c/td\u003e\n \u003ctd style=\"width: 60px;\"\u003e189.5\u003cbr\u003e\u003c/td\u003e\n \u003ctd style=\"width: 72px;\"\u003e-155.4\u003cbr\u003e\u003c/td\u003e\n \u003ctd style=\"width: 66px;\"\u003e-64.4\u003cbr\u003e\u003c/td\u003e\n \u003ctd style=\"width: 72px;\"\u003e13.4766\u003cbr\u003e\u003c/td\u003e\n \u003ctd style=\"width: 84px;\"\u003e156.01\u003cbr\u003e\u003c/td\u003e\n \u003ctd style=\"width: 84px;\"\u003e98.65%\u003cbr\u003e\u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 74px;\"\u003e\u003cstrong\u003e9\u003c/strong\u003e\u003cbr\u003e\u003c/td\u003e\n \u003ctd style=\"width: 89px;\"\u003eOne layer of\u0026nbsp;emulsion of (PACM+B-82 1:1)\u003cbr\u003e\u003c/td\u003e\n \u003ctd style=\"width: 101px;\"\u003e677.77\u003cbr\u003e\u003c/td\u003e\n \u003ctd style=\"width: 60px;\"\u003e345.8\u003cbr\u003e\u003c/td\u003e\n \u003ctd style=\"width: 72px;\"\u003e-615.9\u003cbr\u003e\u003c/td\u003e\n \u003ctd style=\"width: 66px;\"\u003e-106.9\u003cbr\u003e\u003c/td\u003e\n \u003ctd style=\"width: 72px;\"\u003e41.5261\u003cbr\u003e\u003c/td\u003e\n \u003ctd style=\"width: 84px;\"\u003e480.73\u003cbr\u003e\u003c/td\u003e\n \u003ctd style=\"width: 84px;\"\u003e95.84%\u003cbr\u003e\u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 74px;\"\u003e\u003cstrong\u003e10\u003c/strong\u003e\u003cbr\u003e\u003c/td\u003e\n \u003ctd style=\"width: 89px;\"\u003eThree layers of emulsion of (PACM+B-82 1:1)\u003cbr\u003e\u003c/td\u003e\n \u003ctd style=\"width: 101px;\"\u003e445.10\u003cbr\u003e\u003c/td\u003e\n \u003ctd style=\"width: 60px;\"\u003e258.5\u003cbr\u003e\u003c/td\u003e\n \u003ctd style=\"width: 72px;\"\u003e-636.6\u003cbr\u003e\u003c/td\u003e\n \u003ctd style=\"width: 66px;\"\u003e-125.9\u003cbr\u003e\u003c/td\u003e\n \u003ctd style=\"width: 72px;\"\u003e69\u003cbr\u003e\u003c/td\u003e\n \u003ctd style=\"width: 84px;\"\u003e798.88\u003cbr\u003e\u003c/td\u003e\n \u003ctd style=\"width: 84px;\"\u003e93.10%\u003cbr\u003e\u003c/td\u003e\n \u003c/tr\u003e\n \u003c/tbody\u003e\n \u003c/table\u003e\n\u003c/div\u003e\n\u003cp\u003eFigure 2(b) OCP curve further illustrates the stability of the bronze electrode under various conditions over time. The uncoated coupon (1) maintained a nearly constant potential, indicating early interactions with the corrosive environment interaction due to the formation of a stable oxide layer that exhibits passive behavior due to a stable layer, providing inherent corrosion resistance\u003csup\u003e\u0026lrm;\u003c/sup\u003e\u003csup\u003e47\u003c/sup\u003e. In contrast, generally coated coupons (2\u0026ndash;10) show superior corrosion resistance compared to uncoated ones, enhancing the alloy\u0026apos;s ability to resist corrosion by acting as additional barriers against corrosive environments\u003csup\u003e\u0026lrm;\u003c/sup\u003e\u003csup\u003e48\u003c/sup\u003e.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eCoated coupons (2\u0026ndash;10) also show potential shifts, with an initial drop in potential. Despite this negative shift, coated coupons often resist corrosion better than uncoated ones because their initial protective layers reduce overall corrosion rates until they fail\u003csup\u003e\u0026lrm;\u003c/sup\u003e\u003csup\u003e49\u003c/sup\u003e. The nature of the corrosive environment (saline) has a significant impact on how coatings perform\u003csup\u003e\u0026lrm;\u003c/sup\u003e\u003csup\u003e50\u003c/sup\u003e. Different coatings will have varying levels of resistance depending on their chemical composition and durability\u0026lrm;\u003csup\u003e51\u003c/sup\u003e.\u0026nbsp;Gradual shifts to more positive or stable potentials, as observed in Coupons 4 and 8, suggested improved corrosion resistance, likely due to the formation of protective layers that hindered further oxidation\u003csup\u003e\u0026lrm;\u003c/sup\u003e\u003csup\u003e52\u003c/sup\u003e.\u003c/p\u003e\n\u003cp\u003eEIS of bronze, particularly when coated, can be determined using Nyquist plots, as shown in Fig. 3(a-c). Coatings composed of multi-layer polymers such as polyurethane, acrylic, and polyacrylamide significantly improve corrosion resistance by forming a protective barrier\u003csup\u003e\u0026lrm;\u003c/sup\u003e\u003csup\u003e45\u003c/sup\u003e\u003csup\u003e,\u003c/sup\u003e\u003csup\u003e\u0026lrm;\u003c/sup\u003e\u003csup\u003e52\u003c/sup\u003e. Nyquist plots of EIS data demonstrate that the resistances and capacitive semi-circles of the coatings vary depending on whether they are monolayer or multilayer systems, as shown in\u0026nbsp;Fig. 3(b, c). Higher impedance values, as illustrated by larger semicircles, are related to increased corrosion resistance due to less charge transfer. Coupon (7) (three layers of polyacrylamide coating) showed the highest impedance of the coupons, indicating superior barrier properties\u0026lrm;\u003csup\u003e52\u003c/sup\u003e, probably due to its multi-layer structure, as illustrated in Fig. \u0026nbsp;3 (c). In contrast, monolayer coatings such as PUR-129 and Paraloid B-82 exhibited reduced impedance, as seen in Figs. 3 (b, c), showing that layering increases corrosion resistance\u003csup\u003e\u0026lrm;\u003c/sup\u003e\u003csup\u003e45\u003c/sup\u003e. Emulsion-based coating coupons (9 and 10) comprising Paraloid B-82 and polyacrylamide provided balanced protection due to their combined barrier properties, as seen in\u0026nbsp;Fig.\u0026nbsp;3.(c). Figure\u0026nbsp;3(d)\u0026nbsp;shows the equivalent circuit for\u0026nbsp;the most efficient coating system, PUR-129 multi-layer coupon (3), and\u003cstrong\u003e\u0026nbsp;\u003c/strong\u003ethe reference parameters were extracted from the EIS fitting plots for coupon (3) in\u0026nbsp;Table\u0026nbsp;4.\u0026nbsp;According to studies, these coatings improve charge transfer resistance and reduce ion penetration, resulting in greater inhibition efficiency over time\u0026lrm;\u003csup\u003e53\u003c/sup\u003e, as indicated by OCP plots in\u0026nbsp;Fig.\u0026nbsp;2(b). EIS exhibits capacitive behavior, showing effective insulation against corrosive environments. Bronze coatings can enhance electrochemical properties and boost corrosion resistance\u0026lrm;\u003csup\u003e51\u003c/sup\u003e.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eTable\u0026nbsp;\u003c/strong\u003e\u003cstrong\u003e4\u003c/strong\u003e\u003cstrong\u003e.\u003c/strong\u003e Representative EIS equivalent-circuit fit parameters for the PUR-129 multilayer.\u003c/p\u003e\n\u003ctable border=\"1\" cellspacing=\"0\" cellpadding=\"0\" width=\"660\"\u003e\n \u003ctbody\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 133px;\"\u003e\u003cstrong\u003eCoupon 3\u003c/strong\u003e\u003cbr\u003e\u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 52px;\"\u003e\u003cstrong\u003eR\u003csub\u003es\u003c/sub\u003e\u003c/strong\u003e\u003cbr\u003e\u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 90px;\"\u003e\u003cstrong\u003eCPE-T\u003c/strong\u003e\u003cbr\u003e\u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 77px;\"\u003e\u003cstrong\u003eCPE-P\u003c/strong\u003e\u003cbr\u003e\u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 54px;\"\u003e\u003cstrong\u003eR\u003csub\u003ep\u003c/sub\u003e\u003c/strong\u003e\u003cbr\u003e\u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 82px;\"\u003e\u003cstrong\u003eC\u003c/strong\u003e\u003cbr\u003e\u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 73px;\"\u003e\u003cstrong\u003eR\u003csub\u003ect\u003c/sub\u003e\u003c/strong\u003e\u003cbr\u003e\u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 99px;\"\u003e\u003cstrong\u003eChi-Squared\u003c/strong\u003e\u003cbr\u003e\u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 133px;\"\u003e\u003cstrong\u003eThree layers of PUR-129\u003c/strong\u003e\u003cbr\u003e\u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 52px;\"\u003e12.82\u003cbr\u003e\u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 90px;\"\u003e0.00021523\u003cbr\u003e\u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 77px;\"\u003e0.81268\u003cbr\u003e\u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 54px;\"\u003e665.3\u003cbr\u003e\u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 82px;\"\u003e0.0024102\u003cbr\u003e\u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 73px;\"\u003e241.2\u003cbr\u003e\u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 99px;\"\u003e0.0010832\u003cbr\u003e\u003c/td\u003e\n \u003c/tr\u003e\n \u003c/tbody\u003e\n\u003c/table\u003e\n\u003cp\u003eBode plots are useful for discriminating between various corrosion causes by examining the frequency-dependent behavior of impedance in\u0026nbsp;Fig.\u0026nbsp;4(a, b). The magnitude plot in\u0026nbsp;Fig.\u0026nbsp;4(a)\u0026nbsp;shows how resistance changes with frequency and the effect of the coated PUR-129 multi-layer coupon (3) and the uncoated coupon (1). Coated bronze PUR-129 multi-layer coupon (3) often exhibits a change to a higher impedance than the uncoated bronze coupon (1), demonstrating differences in resistance of specific corrosion mechanisms under comparable conditions\u0026lrm;\u003csup\u003e44\u003c/sup\u003e. In\u0026nbsp;Fig.\u0026nbsp;4(b), the shift in phase angle plot illustrates the time constants associated with distinct electrochemical processes, which can help to determine whether corrosion is controlled by charge transfer or diffusion\u003csup\u003e\u0026lrm;\u003c/sup\u003e\u003csup\u003e54\u003c/sup\u003e. Figure\u0026nbsp;4\u0026nbsp;(b)\u0026nbsp;depicts a localized corrosion mechanism that results in a more significant phase change at lower frequencies\u0026lrm;\u003csup\u003e55\u003c/sup\u003e. \u0026nbsp;\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003e3.2\u003cem\u003e\u0026nbsp;\u003c/em\u003e\u003cstrong\u003eNatural Aging Effects of Coating Systems\u003c/strong\u003e\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003e3.2.1\u003cem\u003e\u0026nbsp;\u003c/em\u003e\u003c/strong\u003e\u003cstrong\u003eVisual and Microscopic Examination\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eMacroscopic inspection after 12 months (Fig.\u0026nbsp;5; a-g)\u003cspan dir=\"RTL\"\u003e\u0026nbsp;\u003c/span\u003erevealed clear differences between the coated and uncoated coupons. The \u003cstrong\u003ePUR-129 multilayer\u003c/strong\u003e exhibited a uniform, clean surface with \u003cstrong\u003eno visible\u003c/strong\u003e corrosion products or soiling. The \u003cstrong\u003ePUR-129 monolayer\u003c/strong\u003e showed only \u003cstrong\u003eoccasional, small\u003c/strong\u003e discoloration spots (Fig.\u0026nbsp;5-b,c). In contrast, \u003cstrong\u003eParaloid B-82\u003c/strong\u003e\u0026mdash;in both mono- and multilayer designs\u0026mdash;displayed \u003cstrong\u003escattered greenish spots/streaks\u003c/strong\u003e consistent with incipient copper-chloride corrosion; multilayer application reduced but did not eliminate these features (Fig.\u0026nbsp;5-d,e). \u003cstrong\u003ePACM\u003c/strong\u003e provided the least protection: the monolayer showed \u003cstrong\u003ewidespread green corrosion and patchy coverage\u003c/strong\u003e, and the multilayer, while improved, still exhibited visible defects (Fig.\u0026nbsp;5-f,g). The uncoated coupon darkened markedly.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eThe superior protection offered by the PUR-129 coatings can be attributed to their complete surface coverage, resulting in a smooth, transparent layer that minimizes dust adherence. This comprehensive isolation effectively shields the surface from various environmental degradation factors, maintaining its protective efficiency over an extended period of natural exposure. In contrast, the moderate efficiency of Paraloid B-82 is due to its partial vulnerability to external factors, leading to surface paleness and incomplete clarity. PACM, on the other hand, failed to provide adequate protection because its layers receded and peeled off in different areas after drying, creating weak points where corrosion products formed.\u003c/p\u003e\n\u003cp\u003eTo provide structural and compositional validation of the corrosion behavior observed electrochemically, Scanning Electron Microscopy (SEM) and Energy Dispersive X-ray Spectroscopy (EDS) analyses were performed on selected bronze coupons coated with different protective systems. The purpose was to correlate surface morphology and elemental composition with corrosion resistance as inferred from Tafel polarization and electrochemical impedance spectroscopy (EIS).\u003c/p\u003e\n\u003cp\u003eThe SEM micrographs (Fig.\u0026nbsp;6; a\u0026ndash;i) reveal the degradation states of each coating. The best-performing system, \u003cstrong\u003ethree layers of PUR-129\u003c/strong\u003e (Fig.\u0026nbsp;6-b), exhibited a dense, smooth, and defect-free surface with no observable corrosion features. This compact and continuous morphology directly supports its outstanding electrochemical performance (R\u003csub\u003ep\u003c/sub\u003e = 225.48 \u0026times; 10\u0026sup3; \u0026Omega;\u0026middot;cm\u0026sup2;; C.R. = 1.96 \u0026micro;m/y; efficiency = 99.98%). The EDS spectrum associated with this sample showed minimal elemental copper (Cu K\u0026alpha; = 6.60 atomic%) and a high oxygen signal (O K\u0026alpha; = 93.40%), consistent with the intact polymeric coating isolating the metal surface.\u003c/p\u003e\n\u003cp\u003eIn contrast, the \u003cstrong\u003emono-layer PACM coating\u003c/strong\u003e (Fig.\u0026nbsp;6-e) presented a rough, fibrous morphology with visible cracks and surface porosity, clearly exposing the substrate. These defects confirm the inadequate protection observed electrochemically (C.R. = 681.02 \u0026micro;m/y, efficiency = 94.11%). The corresponding EDS data revealed elevated copper and oxygen, alongside traces of chlorine, indicating surface oxidation and formation of copper corrosion products (e.g., chlorides and oxides). This aligns with its poor wetting and film-forming behavior.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eHybrid systems\u003c/strong\u003e such as \u003cstrong\u003ePACM + B-82 (\u003c/strong\u003eFig.\u0026nbsp;6-\u003cstrong\u003eg)\u003c/strong\u003e offered intermediate surface morphology, where the coating appeared more cohesive than PACM alone but still displayed minor defects. Electrochemical measurements for this system (C.R. = 156.01 \u0026micro;m/y, efficiency = 98.65%) were correspondingly moderate. EDS results revealed less exposed copper and a lower oxygen-to-copper ratio, indicating improved but not full surface coverage.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eThe B-82 coatings\u003c/strong\u003e (Fig.\u0026nbsp;6-c,d), both mono and multilayer, show unexpectedly smooth SEM surfaces, with minimal apparent porosity. However, electrochemical data for these systems (C.R. = ~403\u0026ndash;435 \u0026micro;m/y; efficiency = ~96%) indicate significantly lower protection than what the micrographs alone would suggest. This discrepancy may be attributed to internal porosity or microcracking invisible at 2000\u0026times; magnification, or to the \u003cstrong\u003elower chemical barrier properties\u003c/strong\u003e of B-82 compared to PUR-129. Furthermore, B-82 is known to undergo plasticization or degradation under UV or moisture exposure, which may compromise its performance despite its visually intact appearance.\u003c/p\u003e\n\u003cp\u003eThe \u003cstrong\u003euncoated blank sample\u003c/strong\u003e (Fig.\u0026nbsp;6\u0026ndash;j) exhibited a heavily corroded, pitted, and heterogeneous surface, confirming total exposure to atmospheric degradation. EDS analysis showed high copper signals and prominent corrosion product peaks, further validating the severe electrochemical deterioration (C.R. = 12,000 \u0026micro;m/y; efficiency = 0%).\u003c/p\u003e\n\u003cp\u003eLastly, the \u003cstrong\u003eemulsion systems\u003c/strong\u003e (Fig. 6-h,i) presented irregular and granular surfaces with visible agglomerates. The one-layer emulsion sample revealed intermediate protection (efficiency = 95.84%), while the three-layer variant surprisingly showed worse performance (93.10%), likely due to phase separation or poor cross-linking between PACM and B-82. The EDS results confirmed higher elemental Cu and the presence of Zn and Sn, possibly due to underlying alloy exposure.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003e3.2.2 \u003cstrong\u003eWeight measurements\u0026nbsp;\u003c/strong\u003e\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe weight gain calculation technique serves as a chemical test to assess the effectiveness of various coating systems, both multi-layered and mono-layered, in protecting bronze coupons exposed to natural elements for 12 months in the outdoor environment adjacent to Al-Sabil Al-Ahmadi in the city of Tanta. A higher weight gain indicates greater damage and thus inefficiency of both the type of coating and the application technique in protecting bronze from corrosion risks. Conversely, a lower weight gain suggests the effectiveness of the coating type and application technique in safeguarding bronze coupons.\u003c/p\u003e\n\u003cp\u003eCoupons were weighed every two months for 12 months, and thus, we have six readings to calculate the results of this test. It was observed that coupons coated with a single layer of protective coatings experienced greater weight gain compared to those coated with multiple layers after 12 months of exposure at the site of Sabil Al-Ahmadi in the city of Tanta. This finding suggests that multiple layers of coating offer superior protection compared to a single layer. The weight gain test results indicated that the PUR-129 multi-layer coating was the most efficient, achieving an efficiency rate of 95.33%. In contrast, the single-layer PUR-129 coating achieved an efficiency rate of 93.64%, as shown in\u0026nbsp;Fig.\u0026nbsp;7.\u003c/p\u003e\n\u003cp\u003eThe average weight gain for each group over 12 months was computed using Formula (1), and the efficiency of each coating was assessed. The data clearly demonstrates that multi-layer coatings significantly enhance the protective capabilities of the coatings, with PUR-129 multi-layer exhibiting the best performance.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003e3.2.3 Gloss measurement\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003ePreserving the visual appearance of outdoor bronze is a core conservation goal. Specular gloss was therefore measured before exposure and after 12 months to quantify appearance retention. Performance is expressed as \u003cstrong\u003egloss retention\u003c/strong\u003e GR (%) =100\u0026times;(G\u003csub\u003et\u003c/sub\u003e/G\u003csub\u003e0\u003c/sub\u003e), where G\u003csub\u003e0\u003c/sub\u003e is the post-cure gloss and G\u003csub\u003et\u003c/sub\u003e is the gloss after exposure. Higher GR indicates better maintenance of surface appearance; large decreases are consistent with darkening from corrosion products and soiling. As summarized in Table 5.,\u003cstrong\u003e\u0026nbsp;\u003cstrong\u003ePUR-129 (multilayer)\u003c/strong\u003e\u003c/strong\u003e showed the highest retention (\u0026asymp;90.5%), followed by \u003cstrong\u003ePUR-129 (monolayer)\u003c/strong\u003e\u003cstrong\u003e\u0026nbsp;\u003c/strong\u003e(\u0026asymp;85.9%), \u003cstrong\u003eB-82 (multilayer)\u003c/strong\u003e (\u0026asymp;83.4%), and \u003cstrong\u003eB-82 (monolayer)\u003c/strong\u003e (\u0026asymp;78.5%). \u003cstrong\u003ePACM\u003c/strong\u003e retained less gloss (multilayer \u0026asymp;71.3%; monolayer \u0026asymp;62.8%), while the \u003cstrong\u003euncoated\u003c/strong\u003e coupons exhibited the lowest retention (\u0026asymp;18.4%). Overall, \u003cstrong\u003emultilayer designs\u003c/strong\u003e outperformed monolayers in preserving gloss, with PUR-129 multilayer providing the most effective appearance protection.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eTable\u0026nbsp;\u003c/strong\u003e\u003cstrong\u003e5\u003c/strong\u003e\u003cstrong\u003e.\u003c/strong\u003e Gloss (60\u0026deg; geometry) of bronze coupons \u003cstrong\u003ebefore\u003c/strong\u003e and \u003cstrong\u003eafter 12-month natural exposure\u003c/strong\u003e, and \u003cstrong\u003egloss retention (GR)\u003c/strong\u003e. Values are averages of five readings per coupon; groups are triplicates.\u003c/p\u003e\n\u003cdiv align=\"\"\u003e\n \u003ctable border=\"1\" cellspacing=\"0\" cellpadding=\"0\" width=\"584\"\u003e\n \u003ctbody\u003e\n \u003ctr\u003e\n \u003ctd rowspan=\"2\" style=\"width: 180px;\"\u003e\u003cstrong\u003eProtective\u003c/strong\u003e\u003cstrong\u003e\u0026nbsp;coatings\u003c/strong\u003e\u003cbr\u003e\u003c/td\u003e\n \u003ctd colspan=\"3\" style=\"width: 252px;\"\u003e\u003cstrong\u003eAverage Gloss\u0026nbsp;\u003c/strong\u003e\u003cbr\u003e\u003c/td\u003e\n \u003ctd colspan=\"2\" style=\"width: 153px;\"\u003e\u003cstrong\u003e\u0026nbsp;\u003c/strong\u003e\u003cbr\u003e\u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 123px;\"\u003eBefore Exposure\u003cbr\u003e\u003c/td\u003e\n \u003ctd style=\"width: 120px;\"\u003eAfter Exposure\u003cbr\u003e\u003c/td\u003e\n \u003ctd colspan=\"2\" style=\"width: 153px;\"\u003eGloss Retention (%)\u003cbr\u003e\u003c/td\u003e\n \u003ctd style=\"width: 9px;\"\u003e\u0026nbsp;\u003cbr\u003e\u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 180px;\"\u003eBlank\u003cbr\u003e\u003c/td\u003e\n \u003ctd style=\"width: 123px;\"\u003e64.2\u003cbr\u003e\u003c/td\u003e\n \u003ctd style=\"width: 120px;\"\u003e11.8\u003cbr\u003e\u003c/td\u003e\n \u003ctd colspan=\"2\" style=\"width: 153px;\"\u003e18.43 %\u003cbr\u003e\u003c/td\u003e\n \u003ctd style=\"width: 9px;\"\u003e\u0026nbsp;\u003cbr\u003e\u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 180px;\"\u003ePUR-129 monolayer\u003cbr\u003e\u003c/td\u003e\n \u003ctd style=\"width: 123px;\"\u003e590.8\u003cbr\u003e\u003c/td\u003e\n \u003ctd style=\"width: 120px;\"\u003e507.3\u003cbr\u003e\u003c/td\u003e\n \u003ctd colspan=\"2\" style=\"width: 153px;\"\u003e85.86 %\u003cbr\u003e\u003c/td\u003e\n \u003ctd style=\"width: 9px;\"\u003e\u0026nbsp;\u003cbr\u003e\u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 180px;\"\u003ePUR-129 multi-layer\u003cbr\u003e\u003c/td\u003e\n \u003ctd style=\"width: 123px;\"\u003e268\u003cbr\u003e\u003c/td\u003e\n \u003ctd style=\"width: 120px;\"\u003e242.8\u003cbr\u003e\u003c/td\u003e\n \u003ctd colspan=\"2\" style=\"width: 153px;\"\u003e90.5 %\u003cbr\u003e\u003c/td\u003e\n \u003ctd style=\"width: 9px;\"\u003e\u0026nbsp;\u003cbr\u003e\u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 180px;\"\u003eB-82 monolayer\u003cbr\u003e\u003c/td\u003e\n \u003ctd style=\"width: 123px;\"\u003e80.8\u003cbr\u003e\u003c/td\u003e\n \u003ctd style=\"width: 120px;\"\u003e63.4\u003cbr\u003e\u003c/td\u003e\n \u003ctd colspan=\"2\" style=\"width: 153px;\"\u003e78.46 %\u003cbr\u003e\u003c/td\u003e\n \u003ctd style=\"width: 9px;\"\u003e\u0026nbsp;\u003cbr\u003e\u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 180px;\"\u003eB-82 multi-layer\u003cbr\u003e\u003c/td\u003e\n \u003ctd style=\"width: 123px;\"\u003e83.2\u003cbr\u003e\u003c/td\u003e\n \u003ctd style=\"width: 120px;\"\u003e69.4\u003cbr\u003e\u003c/td\u003e\n \u003ctd colspan=\"2\" style=\"width: 153px;\"\u003e83.41 %\u003cbr\u003e\u003c/td\u003e\n \u003ctd style=\"width: 9px;\"\u003e\u0026nbsp;\u003cbr\u003e\u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 180px;\"\u003ePACM monolayer\u003cbr\u003e\u003c/td\u003e\n \u003ctd style=\"width: 123px;\"\u003e84.7\u003cbr\u003e\u003c/td\u003e\n \u003ctd style=\"width: 120px;\"\u003e53.2\u003cbr\u003e\u003c/td\u003e\n \u003ctd colspan=\"2\" style=\"width: 153px;\"\u003e62.8 %\u003cbr\u003e\u003c/td\u003e\n \u003ctd style=\"width: 9px;\"\u003e\u0026nbsp;\u003cbr\u003e\u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 180px;\"\u003ePACM multi-layer\u003cbr\u003e\u003c/td\u003e\n \u003ctd style=\"width: 123px;\"\u003e78.4\u003cbr\u003e\u003c/td\u003e\n \u003ctd style=\"width: 120px;\"\u003e55.9\u003cbr\u003e\u003c/td\u003e\n \u003ctd colspan=\"2\" style=\"width: 153px;\"\u003e71.30 %\u003cbr\u003e\u003c/td\u003e\n \u003ctd style=\"width: 9px;\"\u003e\u0026nbsp;\u003cbr\u003e\u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\u003c/tr\u003e\n \u003c/tbody\u003e\n \u003c/table\u003e\n\u003c/div\u003e"},{"header":"4. Conclusions","content":"\u003cp\u003eA combined assessment of 12-month natural exposure and laboratory electrochemistry shows that multilayer coating designs provide more durable protection for outdoor bronze than single layers. Among the systems tested, PUR-129 (acrylic\u0026ndash;polyurethane) in a multilayer build gave the most consistent performance: it preserved appearance (gloss retention\u0026thinsp;\u0026asymp;\u0026thinsp;90.5%), exhibited the lowest weight change relative to bare bronze, and delivered the strongest electrochemical barrier, findings corroborated by post-aging SEM/EDS. Monolayer applications of PUR-129, B-82, and PACM showed larger gloss losses and higher mass changes, indicating reduced long-term protection. While the B-82 multilayer improved over its monolayer counterpart, it remained less effective than PUR-129. The PACM coatings were the least durable; field observations revealed partial film retraction during drying, leaving areas of incomplete coverage and diminished resistance. Overall, the results support adopting multilayer acrylic\u0026ndash;polyurethane systems for bronze exposed to Nile-Delta\u0026ndash;type climates, with B-82 multilayer as a secondary option when reversibility is paramount. Reported \u0026ldquo;efficiency\u0026rdquo; values derived from mass change should be interpreted as comparative rankings rather than absolute corrosion rates. The study reflects performance on clean (post-cleaning) bronze; future work should extend field duration and examine behavior over retained patinas and under varied orientations/pollutant regimes.\u003c/p\u003e"},{"header":"Declarations","content":"\u003ch2\u003eFunding\u003c/h2\u003e\u003cp\u003eThe authors declare that \u003cb\u003eno funds\u003c/b\u003e were received during the preparation of this manuscript.\u003c/p\u003e\u003ch2\u003eAuthor Contribution\u003c/h2\u003e\u003cp\u003eMostafa I. Eladawy: Writing \u0026ndash; Original Draft. Mohamed Abdelbar: Methodology, Supervision, Validation, Writing \u0026ndash; Review \u0026amp; Editing. Mohamed M. Megahed and Nabil Abdel Ghany: Investigation, Formal Analysis, Visualization. Eman AbdElRhiem: Experimental Work, Software, Data Interpretation, Review \u0026amp; Editing.\u003c/p\u003e\u003ch2\u003eData Availability\u003c/h2\u003e\u003cp\u003eThe datasets used and/or analysed during the current study available from the corresponding author on reasonable request.\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\n\u003cli\u003eMendoza, A. R. \u0026amp; Corvo, F. Outdoor and indoor atmospheric corrosion of non-ferrous metals. \u003cstrong\u003eCorros. Sci.\u003c/strong\u003e \u003cstrong\u003e42\u003c/strong\u003e, 1123\u0026ndash;1147. https://doi.org/10.1016/S0010-938X(99)00135-3 (2000).\u003c/li\u003e\n\u003cli\u003eRocca, E. \u0026amp; Mirambet, F. Corrosion inhibitors for metallic artefacts: temporary protection. 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Soc.\u003c/strong\u003e\u003cstrong\u003e 132\u003c/strong\u003e, 1288\u0026ndash;1294. https://doi.org/10.1149/1.2114104 (1985).\u003c/li\u003e\n\u003c/ol\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":false,"hideJournal":true,"highlight":"","institution":"","isAcceptedByJournal":false,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"researchsquare","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":true,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"/submission","title":"Research Square","twitterHandle":"researchsquare","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"","reportingPortfolio":"","inReviewEnabled":false,"inReviewRevisionsEnabled":true},"keywords":"Polymeric coatings, Quaternary bronze, Corrosion behavior, Acrylic, Polyurethane, Polyacrylamide","lastPublishedDoi":"10.21203/rs.3.rs-7502286/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-7502286/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003eTo mitigate outdoor corrosion of cultural bronze, this study compares three transparent polymer coatings\u0026mdash;PUR-129 (acrylic\u0026ndash;polyurethane), Paraloid B-82 (acrylic), and polyacrylamide (PACM)\u0026mdash;applied as monolayer, multilayer, and emulsion films on quaternary bronze coupons replicating the alloy of Sabil al-Ahmadi\u0026rsquo;s window grilles (Tanta, Egypt). Performance was assessed after 12 months of on-site natural exposure using weight change, gloss retention, and electrochemical testing (OCP, EIS, and potentiodynamic polarization). Post-aging SEM/EDS characterized surface morphology and elemental signatures. Across metrics, multilayer designs outperformed single-layer applications; PUR-129 multilayer was consistently the top performer, maintaining\u0026thinsp;~\u0026thinsp;90.5% gloss, showing the lowest weight change, and exhibiting the highest electrochemical barrier relative to the bare control. The results indicate that transparent multilayer polymer systems\u0026mdash;particularly PUR-129\u0026mdash;provide durable protection for outdoor bronze while better preserving visual appearance under the Nile-Delta climate.\u003c/p\u003e","manuscriptTitle":"Corrosion Performance of Acrylic–Polyurethane and Polyacrylamide Coatings on Quaternary Bronze","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2025-10-06 12:46:48","doi":"10.21203/rs.3.rs-7502286/v1","editorialEvents":[{"type":"communityComments","content":0}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"researchsquare","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":true,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"/submission","title":"Research Square","twitterHandle":"researchsquare","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"","reportingPortfolio":"","inReviewEnabled":false,"inReviewRevisionsEnabled":true}}],"origin":"","ownerIdentity":"87e1ea66-2e60-4857-a0f7-026bcb789849","owner":[],"postedDate":"October 6th, 2025","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"posted","subjectAreas":[{"id":55711350,"name":"Physical sciences/Chemistry"},{"id":55711351,"name":"Physical sciences/Materials science"}],"tags":[],"updatedAt":"2025-10-28T18:15:55+00:00","versionOfRecord":[],"versionCreatedAt":"2025-10-06 12:46:48","video":"","vorDoi":"","vorDoiUrl":"","workflowStages":[]},"version":"v1","identity":"rs-7502286","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-7502286","identity":"rs-7502286","version":["v1"]},"buildId":"8U1c8b4HqxoKbykW_rLl7","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}