Interference of Solution Constituents on Corrosion Inhibition of Phosphate Species on Grade 202 Stainless Steel

Interference of Solution Constituents on Corrosion Inhibition of Phosphate Species on Grade 202 Stainless Steel | 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 Research Article Interference of Solution Constituents on Corrosion Inhibition of Phosphate Species on Grade 202 Stainless Steel M.H.N. Revon, Namal Priyantha This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-5077929/v1 This work is licensed under a CC BY 4.0 License Status: Under Review Version 1 posted 17 You are reading this latest preprint version Abstract Strong corrosion resistance of Grade 202 Stainless Steel (SS) in mild acidic conditions is attributed to the presence of chromium which is responsible for the formation of a passive surface film of chromium oxide which inhibits corrosion. Additionally, the deposition of polymer coatings, polymer composites with nanomaterials as well as organic compounds containing hetero atoms such as N, O, S, and P on SS, or other metallic objects leads to high corrosion inhibition efficiency. Nevertheless, the corrosion stability of SS in certain environments, especially under aggressive conditions, is questionable. Investigation of the impact of different chemical constituents under moderate and aggressive acidic conditions on the corrosion of SS, however, has not received sufficient attention despite the widespread use of SS-based machinery in industrial applications. Although the corrosion-inhibitory action of phosphate species on SS has been documented, detailed investigation, especially in the presence of interferents, has not been given due consideration. As such, variation of corrosion inhibition efficiency of HNO 3 and H 3 PO 4 on SS at different concentrations, and the impact of HNO 3 and H 3 PO 4 in the presence of chloride ions along with the effect of various phosphate species were investigated in this study. Despite the pitting corrosion promotion action of chloride species, mass loss measurements of rectangular stainless-steel specimens immersed separately in HNO 3 and H 3 PO 4 acid solutions at different concentrations in the presence of HCl, under ambient conditions, conclusively demonstrate the superior corrosion inhibitory behavior of H 3 PO 4 over HNO 3 on SS, even in chloride-rich environments under low acidic conditions. Polarization resistance determined by electrochemical impedance spectroscopy further supports the corrosion inhibitory action of H 3 PO 4 on SS, while open circuit measurements indicate the strong correlation between H 3 O + and surface characteristics. The order of corrosion inhibition ability of phosphate species on SS, as determined by mass loss measurements, electrochemical impedance spectroscopy, and Tafel slope analysis follows the order, Na 3 PO 4 > Na 2 HPO 4 ~ NaH 2 PO 4 > H 3 PO 4 . Corrosion Impedance Inhibition Stainless steel Tafel slope Mass loss measurements Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 Figure 7 Figure 8 Highlights Orthophosphates impact on corrosion inhibitory action on Grade 202 stainless steel. Analyzing mass loss measurements, EIS, OCP, and Tafel slope to probe inhibition. Corrosion inhibitory action in an order of HCl < H 3 PO 4 < Na 2 HPO 4 ~ NaH 2 PO 4 < Na 3 PO 4. Introduction Corrosion is a natural phenomenon that can damage metallic objects in dry or wet medium causing high economic losses. Deterioration of structural and engineering material caused by corrosion has become a serious issue. The annual cost attributed to corrosion is estimated to be more than $500 billion in the United States alone [1]. Considerable efforts are thus being deployed to search for suitable reagents as corrosion inhibitors of metallic objects. Effective corrosion inhibitors would interact with the interface of the target object, thereby hindering its corrosion reactions through passivating film formation, precipitation, or adsorption [2]. Corrosion inhibition has been deployed by the use of organic compounds and synthetic heterocyclic compounds [3]. Different types of corrosion inhibitors are needed depending on the type of the object and its intended use whether in normal environments or under aggressive conditions [4]. Inexpensive, sustainable, and eco-friendly reagents are important attributes of corrosion inhibitors. The corrosion rate of metal alloys, such as steel, can be slowed down by inhibitors at low dosages which are already in use in cooling systems, and oil and gas pipelines. Organic composite layer coatings have also been used to enhance inhibition efficiency. Stainless steel (SS) is an iron-based alloy with Cr, while mild steel is an alloy with C. Mild steel is a vital metal due to its great mechanical properties. It is broadly utilized beneath distinctive conditions in chemical and petrochemical processes dealing with acidic, alkaline, and salt arrangements [5]. Nevertheless, mild steel undergoes corrosion in the H 3 PO 4 medium [6, 7]. On the other hand, SS, broadly utilized in different mechanical applications, is famous for its remarkable erosion resistance credited to the arrangement of chromium-rich passive films. Other than being a Fe-based alloy with Cr, SS also consists of Ni, N, and other elements which lead to a high level of resistance to corrosion. Nitrogen addition boosts mechanical strength and enhances resistance to pitting corrosion. Consequently, several grades of SS are manufactured with different amounts of alloying elements to accommodate the conditions the alloy must withstand [8]. Based on the environment that SS is exposed to, it tends to create a very thin passive film that is rich in chromium oxide and/or hydrogen thereby inhibiting corrosion [9]. SS-based machinery is heavily used in many industries, including food/drug production, pharmaceutical industries, cookware, and cutlery. Apart from the above-mentioned industrial usage of SS, it is also used in outdoor site furnishing. Even though SS is corrosion resistant, it is prone to Galvanic, pitting, and crevice corrosions in some environments, for instance in chloride environments, leading to damaging effects [10]. Moreover, corrosion products of Cr and Ni could be poisonous/toxic. Hence, corrosion inhibition attempts for SS are required. Various types of composite layers have been implemented to the inhibition of SS. Apart from consideration of polymerization, corrosion inhibition of SS can be carried out with low concentrations of organic acids due to their conjugated bases [11]. Due to biological reasons, it is necessary to supplant the nitrite-based inhibitors with eco-friendly and less harmful ones [12]. As an alternative, phosphate-based inhibitors have been utilized as transient inhibitors to decrease the erosion and corrosion of metals and alloys [13]. Phosphate ions are capable of promoting ferrous phosphate precipitation on SS. Such inhibitors have picked up noteworthy considerations in various sectors [14]. Although phosphate has been well-known to have corrosion-inhibitive properties on SS, the effect of other solution constituents as well as the effect of different phosphate species on the corrosion stability of SS has not been given due attention. This study is thus implemented to distinguish the corrosion behavior of SS in various acid and salt exposures at different concentrations with special emphasis on investigating the effect of phosphate species as corrosion inhibitors. Focusing on the exposure of SS to various concentrations of different phosphate species in the presence and absence of Cl ̄ environment was investigated using a multi-technique approach of mass loss measurements, electrochemical impedance spectroscopy [15], Tafel slope analysis, and open circuit potential measurements [16], to identify the effect Cl - interferent on inhibition action of phosphate toward corrosion stability of SS. Materials and Methods Grade 202 SS specimens (Table 1) obtained from a local transformer company were cut into rectangular-shaped specimens of dimensions 2.0 cm × 0.5 cm × 0.2 cm for mass loss and electrochemical measurements. All specimens were rinsed thoroughly with distilled water followed by acetone and dried, and all experiments were performed under ambient conditions. Table 1 : Composition of Grade 202 stainless steel as a percentage (%) Stainless-Steel C Mn P S Si Cr Ni Fe N 202 ≤ 0.15 7.50-10.00 ≤ 0.06 ≤ 0.03 ≤ 1.00 17.0-19.0 4.0-6.0 ≤ 68.0 ≤ 0.25 For mass loss measurements, the initial mass of each cleaned SS specimen was recorded. Thereafter, the specimens were immersed in various solutions at ambient temperature, and they were taken out every 24 h period, cleaned, dried, weighed, and immersed in the solution again [17]. Mass measurements were continued for at least one week. Mass loss was determined from the difference between pre-and post-immersion masses. The percentage mass loss and the corrosion inhibition efficiency were then determined using Equations (1) and (2), respectively. where m 0 and m masses of the specimen in the blank and test solutions, respectively. The impact of solution constituents on mass loss was investigated using HCl, H 3 PO 4, and HNO 3 solutions each of which having concentrations of 0.10 M, 0.25 M, 0.50 M, 1.00 M, 2.00 M, and 4.00 M. The mass loss of SS specimens was also determined for mixed acid solutions of different concentrations, and for Na 3 PO 4 , Na 2 HPO 4, and NaH 2 PO 4 salt solutions, to investigate the correlation between corrosion inhibition action and chemical constituents present in the solution. Electrochemical impedance spectroscopy (EIS) was performed using a PGSTAT-204 electrochemical analyzer using a three-electrode cell consisting of SS working, platinum wire counter, and Ag(s)/AgCl(s)/KCl(aq) reference electrodes within a frequency range between 1.0´10 6 Hz and 0.1 Hz [18, 19]. The linear polarization technique was carried out to produce Tafel plots under the potential range from -0.1 V to 0.1 V at a 10 mV s -1 scan rate [20]. Further, open circuit potentials (OCP) of SS specimens were recorded with respect to Ag(s)/AgCl(s)/KCl(aq) reference electrode. Results 3.1 Effect of chloride ions on mass loss of SS in H 3 PO 4 and HNO 3 acid solutions Low percentage mass loss measurements of SS specimens recorded separately in HNO 3 and H 3 PO 4 acid solutions at different concentrations of 0.10 M, 0.25 M, 0.50 M, 1.00 M, 2.00 M, and 4.00 M, over a one-week period clearly indicate that these two acids act as corrosion inhibitors of SS. The maximum mass loss recorded under the above experimental conditions is 1%, and moreover, negative mass losses were obtained in some H 3 PO 4 solutions due to the deposition of insoluble metal phosphate species. At low concentrations of H 3 PO 4 , the inhibitory action of SS shows an inclined trend more strongly than that of the same concentrations of HNO 3 , and an increase in the concentration of HNO 3 slightly promotes the corrosion of SS. It is thus clear that H 3 PO 4 acts as a superior corrosion inhibitor for SS to HNO 3 [21]. The fact that H 3 PO 4 is a stronger corrosion inhibitor than HNO 3 based on mass loss measurements can be further supported by determining the percentage inhibition efficiency (%IE) of SS in two acids. The inhibition efficiency is almost 100% within the one-week period although a slight decrease in inhibition efficiency is observed in the HNO 3 acid solution at higher concentrations. Moreover, the superior corrosion inhibitory action of phosphate, as compared to that of nitrate, is further evidenced by observing the decrease in inhibition efficiency with time (Figure 1). The superior corrosion inhibition ability of H 3 PO 4 to HNO 3 is further supported through mass loss measurements of SS specimens in mixed solutions of HCl and either H 3 PO 4 or HNO 3 , each at a series of concentrations (Figure 2). Although the chloride ion is a pitting corrosion promoter, the presence of phosphate in the solution is able to overpower the effect of chloride. Higher mass loss percentages are illustrated in HNO 3 solutions than in H 3 PO 4 according to Figure 2 where SS specimens are dissolved even at the beginning when the concentration of HNO 3 is above 2.00 M in the presence of 0.25 M HCl, confirming that chloride ions overcome the corrosion inhibition barrier of HNO 3 beyond a certain concentration limit. An increase in the concentration of H 3 PO 4 at a fixed concentration of Cl ̄ (0.25 M) leads to an increase in the mass loss of SS specimens, stressing the fact that Cl ̄ together with H 3 O + mitigates the corrosion inhibitory action of phosphate at higher concentrations. Based on the above observations, it is concluded that mixed solutions of HNO 3 and HCl would not function as strong corrosion inhibitors at higher concentrations of HNO 3 ; yet H 3 PO 4 solutions together with HCl demonstrate stronger corrosion inhibition activity. 3.2 Mass loss of SS in orthophosphate anion solutions Mass loss measurements of SS specimens recorded in different orthophosphate anion solutions at a fixed initial concentration of 0.25 M over a period of one week clearly show the order of corrosion inhibition as, Na 3 PO 4 > Na 2 HPO 4 ~NaH 2 PO 4 > H 3 PO 4 (Figure 3). This further convinces the strong inhibitory action of phosphate species and the contrary effect of H 3 O + ions. This is supported by the literature report that hydrogen harms the steadiness of the inactive film, and as a result, promotes the anode's actuation of steel, which gradually promotes pitting corrosion [22]. Negative mass losses observed in Na 3 PO 4 solutions beyond the 3 rd day and in Na 2 HPO 4 and NaH 2 PO 4 solutions toward the end of the seven-day period would be due to the deposition of insoluble phosphates with metal ions present in SS, which would make it difficult to quantify corrosion effects [23]. Moreover, negative mass losses were not observed in H 3 PO 4 solutions. Overall, it can be concluded that all the orthophosphate anions and H 3 PO 4 demonstrate corrosion-inhibitory activity under certain circumstances. For example, phosphate is ordinarily dosed at > 3.0 mg/L as orthophosphate to realize passivation of untreated water distribution systems [24] while the ordinary upkeep measurement to guarantee corrosion control is 0.5-1.5 mg/L as orthophosphate [25]. Considering mass loss measurements within a period of one week of all orthophosphate salts at a series of concentrations illustrates the contribution towards superior corrosion inhibitory action from H 3 PO 4 acid. Percentage mass loss of SS specimens recorded in Na 3 PO 4 , Na 2 HPO 4, and NaH 2 PO 4 solutions (Figure 4) each at a series of concentrations lead to the order of corrosion inhibition as Na 3 PO 4 > Na 2 HPO 4 NaH 2 PO 4 > H 3 PO 4 , confirming the strong inhibition action of phosphate species and the opposite effect of H 3 O + ions. The synthesis of insoluble phosphates with metal ions found in SS is most likely the cause of negative mass losses. With the inclusion of each three-phosphate salt at a different concentration, it is possible to form insoluble phosphates. To find out how orthophosphate salts inhibit SS specimens in a Cl - rich environment, more experiments were performed by changing the solution composition. 3.3 Mass loss of SS in orthophosphate anion solution in the presence of Cl ̄ ions There is no significant mass loss of SS specimens in any of the three solutions, NaH 2 PO 4 , Na 2 HPO 4, and Na 3 PO 4 in the presence of 0.25 M HCl (Figure 5). However, the promotion of corrosion due to the presence of H 3 O + and Cl - is evident when compared to the observations in the absence of HCl as shown in Figure 4. The association between the corrosion inhibitory tendency and high quantities of phosphate species can be generalized in SS specimens, as assessed by mass loss studies in the presence and absence of HCl, having the best inhibitory action by Na 3 PO 4 . 3.4 EIS measurements Electrochemical impedance spectroscopy (EIS) is one of the foremost critical electrochemical methods where the impedance in a circuit/solution is measured in ohms as a resistance unit when the experiment is conducted over a wide range of frequencies [26]. The outcome of EIS is a Nyquist plot where the diameter of the semicircular portion is used to determine polarization resistance associated with the working electrode, SS specimens in this study when exposed to the solution in the electrochemical cell with various constituents of that influence on corrosion is to be investigated. Analyzing EIS data typically involves fitting them to an equivalent electrical circuit, consisting of common electrical components, such as resistors, capacitors, and inductors. In addition to polarization resistance which is a valuable parameter in corrosion studies due to its inverse relationship with the extent of corrosion, the electrical circuit can be used to determine other resistances, such as charge transfer resistance and solution resistance [27, 28]. Nyquist plots of SS specimens recorded in different acid and phosphate salt solutions of the same initial concentration of 0.25 M and the proposed equivalent circuit are given in Figure 6. In supporting mass loss measurements, the largest diameter of the semicircle plot is observed for Na 3 PO 4 , while the smallest diameter is for HCl, indicating the strongest corrosion inhibition efficiency is provided by Na 3 PO 4 solutions. Less diametric semi-circled responses for other phosphate solutions also indicate that they also act as good corrosion inhibitors as compared to HCl and H 3 PO 4 . The corrosion inhibitory actions of the solutions are in the order of HCl < H 3 PO 4 < Na 2 HPO 4 ~ NaH 2 PO 4 < Na 3 PO 4 . The polarization resistance values obtained for the proposed equivalence circuit, which also indicate the same trend as given above, are shown in Table 2. Increase in the concentration of phosphate salt ensures less corrosion of SS specimens in the ambient environment (Figure 7). As shown in the figure, a much higher value of R p is obtained in favor of the inhibition of 0.50 M Na 3 PO 4 even in the presence of HCl which promotes corrosion. Table 2 : Polarizations resistance ( R P ) values for SS when immersed in different solutions based on the equivalent circuit. Solution of SS immersed R P (Ω) HCl (0.25 M) 8.66 Mixture of HCl (0.25 M) and Na 3 PO 4 (0.25 M) 4.06´10 1 H 3 PO 4 (0.25 M) 4.07´10 1 Na 2 HPO 4 (0.25 M) 5.90´10 1 NaH 2 PO 4 (0.25 M) 6.95´10 1 Na 3 PO 4 (0.25 M) 6.73´10 2 Na 3 PO 4 (0.50 M) 6.10´10 3 3.5 Tafel Plots Tafel extrapolation is one of the polarization strategies broadly utilized to degree corrosion rates, a quicker method compared with the classical mass loss estimation [29]. Also, various corrosion reactions can be portrayed utilizing the Tafel plots make it doable, anticipating the corrosion rate and potential concurring to the energy and thermodynamics of reactions taking put on a metal surface. When a metallic electrode is submerged in an aqueous corrosive environment, anodic and cathodic reactions naturally occur on the electrode surface, causing corrosion of the electrode [30]. The equilibrium potentials of each reaction occurring on the surface in this scenario will differ from the consequent potential of the electrode [31]. According to the values obtained as listed in Table 3, HCl is confirmed to be a corrosion promoter of SS whilst Na 3 PO 4 contributes to the corrosion inhibition action. Approximately equal values have resulted for both Na 2 HPO 4 and NaH 2 PO 4 based on corrosion rate as well, as already stated in mass loss and EIS results. Furthermore, increase in the concentration of Na 3 PO 4 in a Cl-rich environment decreases the corrosion rate of SS. The relationship of corrosion potential is inversely proportional to corrosion rate and generalizes the corrosion inhibition trend of Na 3 PO 4 > Na 2 HPO 4 ~ NaH 2 PO 4 > H 3 PO 4. which has been implemented in impedance studies as well. Table 3 . Tabulated values for corrosion potentials ( E corr ), corrosion current ( I corr ), and corrosion rate (in mm per year) of SS. Solution SS immersed E corr (V) I c orr (A) Corrosion rate (mpy) HCl (0.25 M) -0.444 1.24´10 -3 1.44´10 1 Mixture of HCl (0.25 M) and Na 3 PO 4 (0.25 M) -0.208 4.15´10 -5 4.82´10 -1 H 3 PO 4 (0.25 M) -0.067 8.54´10 -7 9.93´10 -3 Na 2 HPO 4 (0.25 M) -0.047 4.52´10 -8 5.25´10 -3 NaH 2 PO 4 (0.25 M) -0.042 4.39´10 -7 5.10´10 -3 Na 3 PO 4 (0.25 M) -0.036 9.39´10 -8 1.09´10 -3 Na 3 PO 4 (0.50 M) -0.030 8.19´10 -8 9.52´10 -4 3.6 Open Circuit Potentials (OCP) The OCP of a working electrode is an indication of the tendency of a metallic substrate to be subject to deterioration in a specific environment. The metallic substrate can fend off the aggressive action of the electrolyte and build a protective coating if the OCP continues to rise and remain stable. However, the opposite trend shows that metallic substrates are more prone to corrosion phenomena having lower potentials of SS in HCl solution (Figure 8). Solutions having the highest inhibition efficiency have the highest potential. Accordingly, the strong corrosion inhibition behavior of H 3 PO 4 is further convincing. Conclusion HNO 3 and H 3 PO 4 are both effective corrosion inhibitors of Grade 202 stainless steel (SS) according to mass loss measurement, with the latter being more effective even in situations with high concentrations of chloride under mildly acidic conditions. In settings rich in chlorides, high concentrations of H 3 PO 4 similarly encourage SS corrosion to that of HNO 3 . Among ortho-phosphate species, phosphate contributes a large amount in inhibiting 202 SS, having the order Na 3 PO 4 > Na 2 HPO 4 ~NaH 2 PO 4 > H 3 PO 4 as per mass loss measurements, electrochemical impedance spectroscopy (EIS) and Tafel slope analysis. Specifically, the polarization resistances of 202 SS in 0.25 M solutions of HCl, H 3 PO 4 , Na 2 HPO 4 , NaH 2 PO 4 and Na 3 PO 4 are 8.66, 4.07´10 1 , 5.90´10 1 , 6.95´10 1 and 6.73´10 2 W, respectively. The corrosion rates determined by Tafel slope analysis for the above solutions are 1.44´10 2 , 9.93´10 -3 , 5.10´10 -3 5.25´10 -3, and 1.09´10 -3 mpy, respectively, which are parallel to the polarization resistance values. A strong correlation of corrosion with H 3 O + indicates having a feasible corrosion mechanism of phosphate species. The impact of H 3 O + on corrosion is evidenced by open circuit potential measurements as well. The results of this study can be used to optimize the phosphorizing procedures of SS on an industrial scale. Abbreviations EIS – Electrochemical impedance spectroscopy IE – Inhibition efficiency OCP – Open circuit potentials R P – Polarization resistance SS – Stainless steel Declarations Acknowledgement Special thanks goes to H.B.M.W.Y.T.K. Mahagedara and Department of Chemistry, Faculty of Science, University of Peradeniya. Funding This research did not receive any specific grant from funding agencies in the public, commercial, or not-for-profit sectors. Competing Interests The authors have no relevant financial or non-financial interests to disclose regarding this work. Author Contributions All authors contributed to the conception and design of the study in different aspects. Initial planning of the study, supervision, and final corrections was performed by N. Priyantha * . Sample preparations, sample analysis, bench works and manuscript writing were done by M.H.N. Revon. All authors have read, commented, and approved the final manuscript of the study. Data Availability The data generated during and/or analysed during the current study are available from the corresponding author; N. Priyantha * upon request. Code Availability Not applicable Ethics approval Not applicable – This research did not involve any human or animal subjects or biological material or their data. Consent to participate Not applicable – This research did not involve any human subjects. Consent for publication Not applicable - This research did not involve any human subjects. References Khan, M.A.A., Irfan, O.M., Djavanroodi, F. and Asad, M. (2022b). Development of Sustainable Inhibitors for Corrosion Control. Sustainability , 14(15), p.9502. doi:https://doi.org/10.3390/su14159502. Li, P. and Du, M. (2022) Effect of chloride ion content on pitting corrosion of dispersion-strengthened-high-strength steel. Corrosion Communications, 7:23-34. doi: 10.1016/j.corcom.2022.03.005. Desai, P.D., Pawar, C.B., Avhad, M.S. and More, A.P. (2022). Corrosion inhibitors for carbon steel: A review. Vietnam Journal of Chemistry , 61(1), 15–42. doi:https://doi.org/10.1002/vjch.202200111. Shwetha, K.M., Praveen, P.B.M. and Devendra, B.K. (2024). A review on corrosion inhibitors: types, mechanisms, electrochemical analysis, corrosion rate and efficiency of corrosion inhibitors on mild steel in an acidic environment. Results in Surfaces and Interfaces , 100258. doi:https://doi.org/10.1016/j.rsurfi.2024.100258. Khadom, A.A. (2015) Kinetics and synergistic effect of iodide ion and naphthylamine for the inhibition of corrosion reaction of mild steel in hydrochloric acid. Reaction Kinetics, Mechanisms and Catalysis , 115(2), 463–481. doi:10.1007/s11144-015-0873-9. Noor, E.A. (2005) The inhibition of mild steel corrosion in phosphoric acid solutions by some N-heterocyclic compounds in the salt form. Corrosion Science , 47(1), 33–55. doi:10.1016/j.corsci.2004.05.026. Yaro, A.S., Khadom, A.A. and Wael, R.K. (2013) Apricot Juice as green corrosion inhibitor of mild steel in phosphoric acid. Alexandria Engineering Journal , 52(1), 129–135. doi:10.1016/j.aej.2012.11.001. Di Schino, A. (2020) Manufacturing and applications of Stainless Steels. Metals , 10(3), 327. doi:10.3390/met10030327. Varshney, P., Mishra, R.S. and Kumar, N. (2022). Understanding the nature of passivation film formed during corrosion of Fe 39 Mn 20 Co 20 Cr 15 Si 5 Al 1 high entropy alloy in 3.5 wt% NaCl solution. Journal of Alloys and Compounds , 904, 164100. doi:https://doi.org/10.1016/j.jallcom.2022.164100. Hong, T. and Nagumo, M. (1997) The effect of chloride concentration on early stages of pitting for type 304 stainless steel revealed by the AC impedance method. Corrosion Science , 39(2), 285–293. doi:10.1016/s0010-938x(96)00127-8. Afshari, F., Ghomi, E.R., Dinari, M. and Ramakrishna, S. (2023). Recent advances on the corrosion inhibition behavior of Schiff base compounds on mild steel in acidic media. Chemistry Select , 8(9), 24–30. doi:https://doi.org/10.1002/slct.202203231. Mandal, S., Singh, J.K., Lee, D-E. and Park, T. (2020) Effect of phosphate-based inhibitor on corrosion kinetics and mechanism for formation of passive film onto the steel rebar in chloride-containing pore solution, Materials , 13(16): 3642. doi: 10.3390/ma13163642. Zhang, J., Lu, X., Zhang, J., Zhang, L., Zhu, C., Zhang, Y. and Wu, T. (2019). Corrosion-inhibition effect of different phosphate compounds for carbon steel in chloride-contaminated mortars. International Journal of Electrochemical Science , 14(9), pp.8601–8610. doi:https://doi.org/10.20964/2019.09.29. Kim, H.J., Hong, J.S., Choi, J.H., Han, G.S. and Jung, H.S, (2022). Effect of phosphate ions on the formation of iron oxide/hydroxide as a stabilizer. Journal of Solid State Chemistry , 305, 122688–122688. doi:https://doi.org/10.1016/j.jssc.2021.122688. Priyantha, N., Jayaweera, P., Macdonald, D.D. and Sun, A. (2004b). An electrochemical impedance study of Alloy 22 in NaCl brine at elevated temperature. I. Corrosion behavior. Journal of Electroanalytical Chemistry , 572(2), 409–419. doi:https://doi.org/10.1016/j.jelechem.2004.06.031. Macdonald, D.D., Priyantha, N. Jayaweera, P., Engelhardt, G. and Davydov, A. (2004). The localized corrosion of Alloy 22 in simulated HLNW environments. Corrosion Alaoui, L.M., Kertit, S., Bellaouchou, A., Guenbour, A., Benbachir, A. and Hammouti, B. (2007). Phosphate of aluminum as corrosion inhibitor for steel in H 3 PO 4 . Portugaliae Electrochimica Acta , 26(4) 339–347. doi:https://doi.org/10.4152/pea.200804339. Benabdellah, M., Benkaddour M., Hammouti, B., Bendahhou, B. and Aouniti, A. (2006). Inhibition of steel corrosion in 2M H3PO4 by artemisia oil. Applied Surface Science , 252(18), pp.6212–6217. doi:https://doi.org/10.1016/j.apsusc.2005.08.030. Birla Singh, M., Gabriel, B.I., Venkatraman, M.S., Cole, I.S., Moorthy, G.C. and Emmanuel, B. (2022). Theory of impedance for initial corrosion of metals under a thin electrolyte layer: a coupled charge transfer-diffusion model. Journal of chemical sciences/Proceedings of the Indian Academy of Sciences. Chemical sciences , 134(1), 4–10. Ramón, J., Martínez, I., Gandía-Romero, J. and Soto, J. (2022). Improved Tafel-based potentiostatic approach for corrosion rate monitoring of reinforcing steel. Journal of Nondestructive Evaluation , 41(4). doi:https://doi.org/10.1007/s10921-022-00903-z. Su, G., Xie, D., Wu, F., Feng, D., Meng, Y., Mei, Y. and Xie, Y. (2024b). Corrosion mechanisms of 316L stainless steel in polyphosphoric acid at elevated temperature: behavior and mechanistic insights. Corrosion Science , 236, 112277–112277. doi:https://doi.org/10.1016/j.corsci.2024.112277. Li, W., Cao, R., Xu, L. and Qiao, L. (2021). The role of hydrogen in the corrosion and cracking of steels - a review. Corrosion Communications , 4, 3–32. doi:https://doi.org/10.1016/j.corcom.2021.10.005. Olsson, C.-O.A. and Landolt, D. (2003) Passive films on stainless steels—chemistry, structure and growth. Electrochimica Acta , 48(9), 1093–1104. doi:10.1016/s0013-4686(02)00841-1. Treatment Plant Operator. (2021, October 8). Treatment Plant Operator . Treatment Plant Operator. https://www.tpomag.com/online_exclusives/2021/10/phosphate-corrosion-control-in-drinking-water_sc_00h7h Rosales, E., Del Olmo, G., Calero Preciado, C. and Douterelo, I. (2020b). Phosphate Dosing in Drinking Water Distribution Systems Promotes Changes in Biofilm Structure and Functional Genetic Diversity. Frontiers in Microbiology , 11, 1–5. doi:https://doi.org/10.3389/fmicb.2020.599091. Magar, H.S., Hassan, R.Y. and Mulchandani, A. (2021) Electrochemical impedance spectroscopy (EIS): Principles, construction, and biosensing applications. Sensors , 21(19), 6578. doi:10.3390/s21196578. Mei, B.-A., Munteshari, O., Lau, J., Dunn, B. and Pilon, L. (2017). physical interpretations of Nyquist plots for EDLC electrodes and devices. The Journal of Physical Chemistry C , 122(1), 194–206. doi:https://doi.org/10.1021/acs.jpcc.7b10582. Al-Amiery, A.A., Mohamad, A.B., Kadhum, A.A.H., Shaker, L.M., Isahak, W.N.R.W. and Takriff, M.S. (2022). Experimental and theoretical study on the corrosion inhibition of mild steel by nonanedioic acid derivative in hydrochloric acid solution. Scientific Reports , 12(1), 4705. doi:https://doi.org/10.1038/s41598-022-08146-8. Park, K., Chang, B.-Y. and Hwang, S. (2019) Correlation between Tafel analysis and electrochemical impedance spectroscopy by prediction of amperometric responses. ACS Omega , 4(21), 19307–19313. doi:10.1021/acsomega.9b02672. Mansfeld, F. (1973) Tafel slopes and corrosion rates from polarization resistance measurements. Corrosion , 29(10), 397–402. doi:10.5006/0010-9312-29.10.397. Papavinasam, S. (2008c). Electrochemical polarization techniques for corrosion monitoring. Techniques for Corrosion Monitoring , 49–85. doi:https://doi.org/10.1533/9781845694050.1.49. Additional Declarations No competing interests reported. Cite Share Download PDF Status: Under Review Version 1 posted Editorial decision: Revision requested 15 Oct, 2024 Reviews received at journal 15 Oct, 2024 Reviews received at journal 11 Oct, 2024 Reviews received at journal 08 Oct, 2024 Reviews received at journal 06 Oct, 2024 Reviews received at journal 05 Oct, 2024 Reviewers agreed at journal 04 Oct, 2024 Reviewers agreed at journal 03 Oct, 2024 Reviews received at journal 02 Oct, 2024 Reviewers agreed at journal 01 Oct, 2024 Reviewers agreed at journal 01 Oct, 2024 Reviewers agreed at journal 01 Oct, 2024 Reviewers agreed at journal 01 Oct, 2024 Reviewers invited by journal 01 Oct, 2024 Editor assigned by journal 25 Sep, 2024 Submission checks completed at journal 19 Sep, 2024 First submitted to journal 12 Sep, 2024 You are reading this latest preprint version Research Square lets you share your work early, gain feedback from the community, and start making changes to your manuscript prior to peer review in a journal. As a division of Research Square Company, we’re committed to making research communication faster, fairer, and more useful. We do this by developing innovative software and high quality services for the global research community. Our growing team is made up of researchers and industry professionals working together to solve the most critical problems facing scientific publishing. Also discoverable on Platform About Our Team In Review Editorial Policies Advisory Board Help Center Resources Author Services Accessibility API Access RSS feed Manage Cookie Preferences © Research Square 2026 | ISSN 2693-5015 (online) Privacy Policy Terms of Service Do Not Sell My Personal Information {"props":{"pageProps":{"initialData":{"identity":"rs-5077929","acceptedTermsAndConditions":true,"allowDirectSubmit":false,"archivedVersions":[],"articleType":"Research Article","associatedPublications":[],"authors":[{"id":366379515,"identity":"87fc0db0-eebe-494d-99d2-ff3c81d8a74d","order_by":0,"name":"M.H.N. Revon","email":"","orcid":"","institution":"University of Peradeniya","correspondingAuthor":false,"prefix":"","firstName":"M.H.N.","middleName":"","lastName":"Revon","suffix":""},{"id":366379516,"identity":"88c8b705-9c61-470b-83b2-f8fa7f14bc75","order_by":1,"name":"Namal Priyantha","email":"data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAZAAAAAyAQMAAABI0h/eAAAABlBMVEX///8AAABVwtN+AAAACXBIWXMAAA7EAAAOxAGVKw4bAAABC0lEQVRIiWNgGAWjYLCCB0DMBmIwNjDIMTDwEKElAablYAODMfFaGKBaEhsIaTFnP534IYHhTj6fRPKzxx932KVvOH724IMPDHZyug3YtVj25G6WSGB4ZtkmkWZucPBMcu6GM3nJhjMYko3NDmDXYnAgdwNQy2EDNokEM4mDbcy5Gw7kmEnzMBxI3IZLy/m3m39AtKR/A2qpTzc4/4aAlhu526C25IBsOZxgcIOQLTfebrNIMHhmwMbzpkzibNtxw5k33hgbzjDA45fzuZtvfKi4YyDfnr5NorKtWp7vfI7hgw8VdnK4tMACgYFBIAHCVgCrNMCnHAyAyvihhso3EFQ9CkbBKBgFIwwAABShZAn4fiMkAAAAAElFTkSuQmCC","orcid":"","institution":"University of Peradeniya","correspondingAuthor":true,"prefix":"","firstName":"Namal","middleName":"","lastName":"Priyantha","suffix":""}],"badges":[],"createdAt":"2024-09-12 13:17:10","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-5077929/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-5077929/v1","draftVersion":[],"editorialEvents":[],"editorialNote":"","failedWorkflow":false,"files":[{"id":68930025,"identity":"ec4d903e-549e-4d1d-9f2b-64c9d62fae1f","added_by":"auto","created_at":"2024-11-13 15:16:36","extension":"png","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":102205,"visible":true,"origin":"","legend":"\u003cp\u003eInhibition efficiency of SS specimens in HCl solution in the presence of (1) 0.25 M H\u003csub\u003e3\u003c/sub\u003ePO\u003csub\u003e4\u003c/sub\u003e and (2) 0.25 M HNO\u003csub\u003e3\u003c/sub\u003e.\u003c/p\u003e","description":"","filename":"1.png","url":"https://assets-eu.researchsquare.com/files/rs-5077929/v1/50415b38ea9f480ec6e0a662.png"},{"id":68928864,"identity":"8fbed23c-097a-44e3-84bf-a2ed05f3799f","added_by":"auto","created_at":"2024-11-13 15:08:36","extension":"png","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":278784,"visible":true,"origin":"","legend":"\u003cp\u003ePercentage mass loss of SS specimens in mixtures of 0.25 M HCl with (a) H\u003csub\u003e3\u003c/sub\u003ePO\u003csub\u003e4\u003c/sub\u003e and (b) HNO\u003csub\u003e3\u003c/sub\u003e of different concentrations (1) 0.10 M (2) 0.25 M (3) 0.50 M (4) 1.00 M (5) 2.00 M (6) 4.00 M.\u003c/p\u003e","description":"","filename":"2.png","url":"https://assets-eu.researchsquare.com/files/rs-5077929/v1/a9796c8649a6e846d91694a8.png"},{"id":68928870,"identity":"97b0383f-2c4f-4a7b-a2a0-904e6f1be385","added_by":"auto","created_at":"2024-11-13 15:08:36","extension":"png","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":98663,"visible":true,"origin":"","legend":"\u003cp\u003ePercentage of mass loss of SS specimens in solutions of different phosphate species each at 0.25 M initial concentration: (1) Na\u003csub\u003e3\u003c/sub\u003ePO\u003csub\u003e4 \u003c/sub\u003e(2) Na\u003csub\u003e2\u003c/sub\u003eHPO\u003csub\u003e4\u003c/sub\u003e (3) NaH\u003csub\u003e2\u003c/sub\u003ePO\u003csub\u003e4\u003c/sub\u003e (4) H\u003csub\u003e3\u003c/sub\u003ePO\u003csub\u003e4\u003c/sub\u003e.\u003c/p\u003e","description":"","filename":"3.png","url":"https://assets-eu.researchsquare.com/files/rs-5077929/v1/3bc3adef9ae2c565bf9621c9.png"},{"id":68928245,"identity":"ecb15ea9-dafa-4bb4-aba9-b0145b0439da","added_by":"auto","created_at":"2024-11-13 15:00:36","extension":"png","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":431837,"visible":true,"origin":"","legend":"\u003cp\u003ePercentage mass loss of SS specimens in (a) NaH\u003csub\u003e2\u003c/sub\u003ePO\u003csub\u003e4\u003c/sub\u003e, (b) Na\u003csub\u003e2\u003c/sub\u003eHPO\u003csub\u003e4 \u003c/sub\u003eand (c) Na\u003csub\u003e3\u003c/sub\u003ePO\u003csub\u003e4\u003c/sub\u003e at different concentrations (1) 0.10 M (2) 0.25 M (3) 0.50 M and (4) 1.00 M.\u003c/p\u003e","description":"","filename":"4.png","url":"https://assets-eu.researchsquare.com/files/rs-5077929/v1/357cf2351239c25d762854cf.png"},{"id":68928867,"identity":"e24216dc-d16d-457f-9b35-b3de6845017e","added_by":"auto","created_at":"2024-11-13 15:08:36","extension":"png","order_by":5,"title":"Figure 5","display":"","copyAsset":false,"role":"figure","size":378577,"visible":true,"origin":"","legend":"\u003cp\u003ePercentage mass loss of SS specimens in mix solutions of 0.25 M HCl with (a) NaH\u003csub\u003e2\u003c/sub\u003ePO\u003csub\u003e4\u003c/sub\u003e, (b) Na\u003csub\u003e2\u003c/sub\u003eHPO\u003csub\u003e4 \u003c/sub\u003eand (c) Na\u003csub\u003e3\u003c/sub\u003ePO\u003csub\u003e4\u003c/sub\u003e at different concentrations (1) 0.10 M (2) 0.25 M and (3) 0.50 M.\u003c/p\u003e","description":"","filename":"5.png","url":"https://assets-eu.researchsquare.com/files/rs-5077929/v1/d5948cce1e7893fb65b3d47f.png"},{"id":68928244,"identity":"6a5451aa-214c-44ed-80d8-d8ede050f428","added_by":"auto","created_at":"2024-11-13 15:00:36","extension":"png","order_by":6,"title":"Figure 6","display":"","copyAsset":false,"role":"figure","size":233391,"visible":true,"origin":"","legend":"\u003cp\u003eNyquist plots for each at 0.25 M initial concentration: HCl, H\u003csub\u003e3\u003c/sub\u003ePO\u003csub\u003e4\u003c/sub\u003e, Na\u003csub\u003e3\u003c/sub\u003ePO\u003csub\u003e4\u003c/sub\u003e, Na\u003csub\u003e2\u003c/sub\u003eHPO\u003csub\u003e4\u003c/sub\u003e and NaH\u003csub\u003e2\u003c/sub\u003ePO\u003csub\u003e4\u003c/sub\u003e; Insert indicates the equivalent electrical circuit.\u003c/p\u003e","description":"","filename":"6.png","url":"https://assets-eu.researchsquare.com/files/rs-5077929/v1/4637e6344948184677611109.png"},{"id":68928241,"identity":"9bc034df-cdd5-4c03-94a7-8f1332efd0f5","added_by":"auto","created_at":"2024-11-13 15:00:36","extension":"png","order_by":7,"title":"Figure 7","display":"","copyAsset":false,"role":"figure","size":45772,"visible":true,"origin":"","legend":"\u003cp\u003eNyquist plots for mixed solutions of 0.25 M HCl with Na\u003csub\u003e3\u003c/sub\u003ePO\u003csub\u003e4\u003c/sub\u003e of (1) 0.25 M (2) 0.50 M.\u003c/p\u003e","description":"","filename":"7.png","url":"https://assets-eu.researchsquare.com/files/rs-5077929/v1/85c7b5ae0a3933577a48b66d.png"},{"id":68928246,"identity":"7231e53e-2ac9-4100-b9cc-65ec40bf7036","added_by":"auto","created_at":"2024-11-13 15:00:36","extension":"png","order_by":8,"title":"Figure 8","display":"","copyAsset":false,"role":"figure","size":146950,"visible":true,"origin":"","legend":"\u003cp\u003eOpen circuit potentials of HCl (0.25 M), H\u003csub\u003e3\u003c/sub\u003ePO\u003csub\u003e4\u003c/sub\u003e (0.25 M) and a mixture of HCl (0.25 M) and H\u003csub\u003e3\u003c/sub\u003ePO\u003csub\u003e4\u003c/sub\u003e (0.25 M).\u003c/p\u003e","description":"","filename":"8.png","url":"https://assets-eu.researchsquare.com/files/rs-5077929/v1/2872e5bed94a51ddab0b9cd2.png"},{"id":68930942,"identity":"e6a056b9-8db5-4b2e-b3ce-c73207194a6d","added_by":"auto","created_at":"2024-11-13 15:24:37","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":2371418,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-5077929/v1/4c2a927a-a369-4250-a67e-421f9a6c35b5.pdf"}],"financialInterests":"No competing interests reported.","formattedTitle":"Interference of Solution Constituents on Corrosion Inhibition of Phosphate Species on Grade 202 Stainless Steel","fulltext":[{"header":"Highlights","content":"\u003cul\u003e\n \u003cli\u003eOrthophosphates impact on corrosion inhibitory action on Grade 202 stainless steel.\u003c/li\u003e\n \u003cli\u003e\u0026nbsp;Analyzing mass loss measurements, EIS, OCP, and Tafel slope to probe inhibition.\u0026nbsp;\u003c/li\u003e\n \u003cli\u003eCorrosion inhibitory action in an order of HCl \u0026lt; H\u003csub\u003e3\u003c/sub\u003ePO\u003csub\u003e4\u003c/sub\u003e \u0026lt; Na\u003csub\u003e2\u003c/sub\u003eHPO\u003csub\u003e4\u003c/sub\u003e ~ NaH\u003csub\u003e2\u003c/sub\u003ePO\u003csub\u003e4\u003c/sub\u003e \u0026lt; Na\u003csub\u003e3\u003c/sub\u003ePO\u003csub\u003e4.\u0026nbsp;\u003c/sub\u003e\u003c/li\u003e\n\u003c/ul\u003e"},{"header":"Introduction","content":"\u003cp\u003eCorrosion is a natural phenomenon that can damage metallic objects in dry or wet medium causing high economic losses. Deterioration of structural and engineering material caused by corrosion has become a serious issue. The annual cost attributed to corrosion is estimated to be more than $500 billion in the United States alone [1]. Considerable efforts are thus being deployed to search for suitable reagents as corrosion inhibitors of metallic objects. Effective corrosion inhibitors would interact with the interface of the target object, thereby hindering its corrosion reactions through passivating film formation, precipitation, or adsorption [2]. Corrosion inhibition has been deployed by the use of organic compounds and synthetic\u0026nbsp;heterocyclic compounds\u0026nbsp;[3]. Different types of corrosion inhibitors are needed depending on the type of the object and its intended use whether in normal environments or under aggressive conditions [4].\u0026nbsp;Inexpensive, sustainable, and eco-friendly reagents are important attributes of corrosion inhibitors.\u0026nbsp;The corrosion rate of metal alloys, such as steel, can be slowed down by inhibitors at low dosages which are already in use in cooling systems, and oil and gas pipelines. Organic composite layer coatings have also been used to enhance inhibition efficiency.\u003c/p\u003e\n\u003cp\u003eStainless steel (SS) is an iron-based alloy with Cr, while mild steel is an alloy with C. Mild steel is a vital metal due to its great mechanical properties. It is broadly utilized beneath distinctive conditions in chemical and petrochemical processes dealing with acidic, alkaline, and salt arrangements [5]. Nevertheless, mild steel undergoes corrosion in the\u0026nbsp;H\u003csub\u003e3\u003c/sub\u003ePO\u003csub\u003e4\u003c/sub\u003e medium [6, 7]. On the other hand, SS,\u0026nbsp;broadly\u0026nbsp;utilized\u0026nbsp;in\u0026nbsp;different\u0026nbsp;mechanical\u0026nbsp;applications, is\u0026nbsp;famous\u0026nbsp;for its\u0026nbsp;remarkable\u0026nbsp;erosion\u0026nbsp;resistance\u0026nbsp;credited\u0026nbsp;to the\u0026nbsp;arrangement\u0026nbsp;of chromium-rich\u0026nbsp;passive films.\u0026nbsp;Other than being a Fe-based alloy with Cr, SS also consists of Ni, N, and other elements which lead to a high level of resistance to corrosion. Nitrogen addition boosts mechanical strength and enhances resistance to pitting corrosion. Consequently, several grades of SS are manufactured with different amounts of alloying elements to accommodate the conditions the alloy must withstand [8]. Based on the environment that SS is exposed to, it tends to create a very thin passive film that is rich in chromium oxide and/or hydrogen thereby inhibiting corrosion [9].\u003c/p\u003e\n\u003cp\u003eSS-based machinery is heavily used in many industries, including food/drug production, pharmaceutical industries, cookware, and cutlery. Apart from the above-mentioned industrial usage of SS, it is also used in outdoor site furnishing. Even though SS is corrosion resistant, it is prone to Galvanic, pitting, and crevice corrosions in some environments, for instance in chloride environments, leading to damaging effects [10]. Moreover, corrosion products of Cr and Ni could be poisonous/toxic. Hence, corrosion inhibition attempts for SS are required. Various types of composite layers have been implemented to the inhibition of SS. Apart from consideration of polymerization, corrosion inhibition of SS can be carried out with low concentrations of organic acids due to their conjugated bases [11].\u003c/p\u003e\n\u003cp\u003eDue to biological reasons, it is necessary to supplant the nitrite-based inhibitors with eco-friendly and less harmful ones [12]. As an alternative, phosphate-based inhibitors have been utilized as transient inhibitors to decrease the erosion and corrosion of metals and alloys [13]. Phosphate ions are capable of promoting ferrous phosphate precipitation on SS. Such inhibitors have picked up noteworthy considerations in various sectors [14]. Although phosphate has been well-known to have corrosion-inhibitive properties on SS, the effect of other solution constituents as well as the effect of different phosphate species on the corrosion stability of SS has not been given due attention.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eThis study is thus implemented to distinguish the corrosion behavior of SS in various acid and salt exposures at different concentrations with special emphasis on investigating the effect of phosphate species as corrosion inhibitors. Focusing on the exposure of SS to various concentrations of different phosphate species in the presence and absence of Cl ̄\u0026nbsp;environment was investigated using a multi-technique approach of mass loss measurements, electrochemical impedance spectroscopy [15], Tafel slope analysis, and open circuit potential measurements [16], to identify the effect Cl\u003csup\u003e-\u003c/sup\u003e interferent on inhibition action of phosphate toward corrosion stability of SS.\u0026nbsp;\u003c/p\u003e"},{"header":"Materials and Methods","content":"\u003cp\u003eGrade 202 SS specimens (Table 1) obtained from a local transformer company were cut into rectangular-shaped specimens of dimensions 2.0 cm \u0026times; 0.5 cm \u0026times; 0.2 cm for mass loss and electrochemical measurements. All specimens were rinsed thoroughly with distilled water followed by acetone and dried, and all experiments were performed under ambient conditions.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eTable\u003c/strong\u003e \u003cstrong\u003e1\u003c/strong\u003e: Composition of Grade 202 stainless steel as a percentage (%)\u003c/p\u003e\n\u003ctable border=\"1\" cellspacing=\"0\" cellpadding=\"0\"\u003e\n \u003ctbody\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 12.5198%;\"\u003e\n \u003cp\u003e\u003cstrong\u003eStainless-Steel\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 9.82567%;\"\u003e\n \u003cp\u003e\u003cstrong\u003eC\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 9.98415%;\"\u003e\n \u003cp\u003e\u003cstrong\u003eMn\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 9.82567%;\"\u003e\n \u003cp\u003e\u003cstrong\u003eP\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 9.82567%;\"\u003e\n \u003cp\u003e\u003cstrong\u003eS\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 9.82567%;\"\u003e\n \u003cp\u003e\u003cstrong\u003eSi\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 8.55784%;\"\u003e\n \u003cp\u003e\u003cstrong\u003eCr\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 8.55784%;\"\u003e\n \u003cp\u003e\u003cstrong\u003eNi\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 10.4596%;\"\u003e\n \u003cp\u003e\u003cstrong\u003eFe\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 10.6181%;\"\u003e\n \u003cp\u003e\u003cstrong\u003eN\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 12.5198%;\"\u003e\n \u003cp\u003e202\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 9.82567%;\"\u003e\n \u003cp\u003e\u0026le; 0.15\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 9.98415%;\"\u003e\n \u003cp\u003e7.50-10.00\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 9.82567%;\"\u003e\n \u003cp\u003e\u0026le; 0.06\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 9.82567%;\"\u003e\n \u003cp\u003e\u0026le; 0.03\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 9.82567%;\"\u003e\n \u003cp\u003e\u0026le; 1.00\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 8.55784%;\"\u003e\n \u003cp\u003e17.0-19.0\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 8.55784%;\"\u003e\n \u003cp\u003e4.0-6.0\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 10.4596%;\"\u003e\n \u003cp\u003e\u0026le; 68.0\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 10.6181%;\"\u003e\n \u003cp\u003e\u0026le; 0.25\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003c/tbody\u003e\n\u003c/table\u003e\n\u003cp\u003e\u0026nbsp;For mass loss measurements, the initial mass of each cleaned SS specimen was recorded. Thereafter, the specimens were immersed in various solutions at ambient temperature, and they were taken out every 24 h period, cleaned, dried, weighed, and immersed in the solution again [17]. Mass measurements were continued for at least one week. Mass loss was determined from the difference between pre-and post-immersion masses. The percentage mass loss and the corrosion inhibition efficiency were then determined using Equations (1) and (2), respectively.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003e\u003cimg src=\"https://myfiles.space/user_files/122228_c8a1650c59388082/122228_custom_files/img1731508945.png\"\u003e\u003c/p\u003e\n\u003cp\u003ewhere \u003cem\u003em\u003csub\u003e0\u003c/sub\u003e\u003c/em\u003e and \u003cem\u003em\u003c/em\u003e masses of the specimen in the blank and test solutions, respectively. The impact of solution constituents on mass loss was investigated using HCl, H\u003csub\u003e3\u003c/sub\u003ePO\u003csub\u003e4,\u003c/sub\u003e and HNO\u003csub\u003e3\u003c/sub\u003e solutions each of which having concentrations of 0.10 M, 0.25 M, 0.50 M, 1.00 M, 2.00 M, and 4.00 M. The mass loss of SS specimens was also determined for mixed acid solutions of different concentrations, and for Na\u003csub\u003e3\u003c/sub\u003ePO\u003csub\u003e4\u003c/sub\u003e, Na\u003csub\u003e2\u003c/sub\u003eHPO\u003csub\u003e4,\u0026nbsp;\u003c/sub\u003eand NaH\u003csub\u003e2\u003c/sub\u003ePO\u003csub\u003e4\u003c/sub\u003e salt solutions, to investigate the correlation between corrosion inhibition action and chemical constituents present in the solution.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eElectrochemical impedance spectroscopy (EIS) was performed using a PGSTAT-204 electrochemical analyzer using a three-electrode cell consisting of SS working, platinum wire counter, and Ag(s)/AgCl(s)/KCl(aq) reference electrodes within a frequency range between 1.0\u0026acute;10\u003csup\u003e6\u003c/sup\u003e Hz and 0.1 Hz [18, 19]. The linear polarization technique was carried out to produce Tafel plots under the potential range from -0.1 V to 0.1 V at a 10 mV s\u003csup\u003e-1\u003c/sup\u003e scan rate [20]. Further, open circuit potentials (OCP) of SS specimens were recorded with respect to Ag(s)/AgCl(s)/KCl(aq) reference electrode.\u003c/p\u003e"},{"header":"Results","content":"\u003cp\u003e\u003cstrong\u003e3.1 Effect of chloride ions on mass loss of SS in\u0026nbsp;\u003c/strong\u003e\u003cstrong\u003eH\u003csub\u003e3\u003c/sub\u003ePO\u003csub\u003e4\u0026nbsp;\u003c/sub\u003eand HNO\u003csub\u003e3\u003c/sub\u003e acid solutions\u0026nbsp;\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eLow percentage mass loss measurements of SS specimens recorded separately in HNO\u003csub\u003e3\u0026nbsp;\u003c/sub\u003eand H\u003csub\u003e3\u003c/sub\u003ePO\u003csub\u003e4\u0026nbsp;\u003c/sub\u003eacid solutions at different concentrations of 0.10 M, 0.25 M, 0.50 M, 1.00 M, 2.00 M, and 4.00 M, over a one-week period clearly indicate that these two acids act as corrosion inhibitors of SS. The maximum mass loss recorded under the above experimental conditions is 1%, and moreover, negative mass losses were obtained in some H\u003csub\u003e3\u003c/sub\u003ePO\u003csub\u003e4\u003c/sub\u003e solutions due to the deposition of insoluble metal phosphate species. At low concentrations of H\u003csub\u003e3\u003c/sub\u003ePO\u003csub\u003e4\u003c/sub\u003e, the inhibitory action of SS shows an inclined trend more strongly than that of the same concentrations of HNO\u003csub\u003e3\u003c/sub\u003e, and an increase in the concentration of HNO\u003csub\u003e3\u003c/sub\u003e slightly promotes the corrosion of SS. It is thus clear that H\u003csub\u003e3\u003c/sub\u003ePO\u003csub\u003e4\u003c/sub\u003e acts as a superior corrosion inhibitor for SS to HNO\u003csub\u003e3\u003c/sub\u003e[21].\u003c/p\u003e\n\u003cp\u003eThe fact that H\u003csub\u003e3\u003c/sub\u003ePO\u003csub\u003e4\u0026nbsp;\u003c/sub\u003eis a stronger corrosion inhibitor than HNO\u003csub\u003e3\u003c/sub\u003e based on mass loss measurements can be further supported by determining the percentage inhibition efficiency (%IE) of SS in two acids. The inhibition efficiency is almost 100% within the one-week period although a slight decrease in inhibition efficiency is observed in the HNO\u003csub\u003e3\u003c/sub\u003e acid solution at higher concentrations. Moreover, the superior corrosion inhibitory action of phosphate, as compared to that of nitrate, is further evidenced by observing the decrease in inhibition efficiency with time (Figure 1).\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eThe superior corrosion inhibition ability of H\u003csub\u003e3\u003c/sub\u003ePO\u003csub\u003e4\u0026nbsp;\u003c/sub\u003eto HNO\u003csub\u003e3\u003c/sub\u003e is further supported through mass loss measurements of SS specimens in mixed solutions of HCl and either H\u003csub\u003e3\u003c/sub\u003ePO\u003csub\u003e4\u0026nbsp;\u003c/sub\u003eor HNO\u003csub\u003e3\u003c/sub\u003e, each at a series of concentrations (Figure 2). Although the chloride ion is a pitting corrosion promoter, the presence of phosphate in the solution is able to overpower the effect of chloride. Higher mass loss percentages are illustrated in HNO\u003csub\u003e3\u003c/sub\u003e solutions than in H\u003csub\u003e3\u003c/sub\u003ePO\u003csub\u003e4\u003c/sub\u003e according to Figure 2 where SS specimens are dissolved even at the beginning when the concentration of HNO\u003csub\u003e3\u003c/sub\u003e is above 2.00 M in the presence of 0.25 M HCl, confirming that chloride ions overcome the corrosion inhibition barrier of HNO\u003csub\u003e3\u003c/sub\u003e beyond a certain concentration limit. An increase in the concentration of H\u003csub\u003e3\u003c/sub\u003ePO\u003csub\u003e4\u003c/sub\u003e at a fixed concentration of Cl ̄ (0.25 M) leads to an increase in the mass loss of SS specimens, stressing the fact that Cl ̄ together with H\u003csub\u003e3\u003c/sub\u003eO\u003csup\u003e+\u003c/sup\u003e mitigates the corrosion inhibitory action of phosphate at higher concentrations. Based on the above observations, it is concluded that mixed solutions of HNO\u003csub\u003e3\u003c/sub\u003e and HCl would not function as strong corrosion inhibitors at higher concentrations of HNO\u003csub\u003e3\u003c/sub\u003e; yet H\u003csub\u003e3\u003c/sub\u003ePO\u003csub\u003e4\u003c/sub\u003e solutions together with HCl demonstrate stronger corrosion inhibition activity. \u0026nbsp;\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003e3.2 Mass loss of SS in orthophosphate anion solutions\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eMass loss measurements of SS specimens recorded in different orthophosphate anion solutions at a fixed initial concentration of 0.25 M over a period of one week clearly show the order of corrosion inhibition as, Na\u003csub\u003e3\u003c/sub\u003ePO\u003csub\u003e4\u003c/sub\u003e \u0026gt; Na\u003csub\u003e2\u003c/sub\u003eHPO\u003csub\u003e4\u0026nbsp;\u003c/sub\u003e~NaH\u003csub\u003e2\u003c/sub\u003ePO\u003csub\u003e4\u003c/sub\u003e \u0026gt; H\u003csub\u003e3\u003c/sub\u003ePO\u003csub\u003e4\u003c/sub\u003e (Figure 3). This further convinces the strong inhibitory action of phosphate species and the contrary effect of H\u003csub\u003e3\u003c/sub\u003eO\u003csup\u003e+\u003c/sup\u003e ions. This is supported by the literature report that hydrogen harms the steadiness of the inactive film, and as a result, promotes the anode\u0026apos;s actuation of steel, which gradually promotes pitting corrosion [22]. Negative mass losses observed in Na\u003csub\u003e3\u003c/sub\u003ePO\u003csub\u003e4\u003c/sub\u003e solutions beyond the 3\u003csup\u003erd\u003c/sup\u003e day and in Na\u003csub\u003e2\u003c/sub\u003eHPO\u003csub\u003e4\u0026nbsp;\u003c/sub\u003eand\u003csub\u003e\u0026nbsp;\u003c/sub\u003eNaH\u003csub\u003e2\u003c/sub\u003ePO\u003csub\u003e4\u003c/sub\u003e solutions toward the end of the seven-day period would be due to the deposition of insoluble phosphates with metal ions present in SS, which would make it difficult to quantify corrosion effects [23]. Moreover, negative mass losses were not observed in H\u003csub\u003e3\u003c/sub\u003ePO\u003csub\u003e4\u003c/sub\u003e solutions. Overall, it can be concluded that all the orthophosphate anions and H\u003csub\u003e3\u003c/sub\u003ePO\u003csub\u003e4\u003c/sub\u003e demonstrate corrosion-inhibitory activity under certain circumstances. For example, phosphate is ordinarily dosed at \u0026gt; 3.0 mg/L as orthophosphate to realize passivation of untreated water distribution systems [24] while the ordinary upkeep measurement to guarantee corrosion control is 0.5-1.5 mg/L as orthophosphate [25]. \u0026nbsp;\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eConsidering mass loss measurements within a period of one week of all orthophosphate salts at a series of concentrations illustrates the contribution towards superior corrosion inhibitory action from H\u003csub\u003e3\u003c/sub\u003ePO\u003csub\u003e4\u003c/sub\u003e acid. Percentage mass loss of SS specimens recorded in Na\u003csub\u003e3\u003c/sub\u003ePO\u003csub\u003e4\u003c/sub\u003e, Na\u003csub\u003e2\u003c/sub\u003eHPO\u003csub\u003e4,\u003c/sub\u003e and NaH\u003csub\u003e2\u003c/sub\u003ePO\u003csub\u003e4\u0026nbsp;\u003c/sub\u003esolutions (Figure 4) each at a series of concentrations lead to the order of corrosion inhibition as Na\u003csub\u003e3\u003c/sub\u003ePO\u003csub\u003e4\u003c/sub\u003e \u0026gt; Na\u003csub\u003e2\u003c/sub\u003eHPO\u003csub\u003e4\u003c/sub\u003e NaH\u003csub\u003e2\u003c/sub\u003ePO\u003csub\u003e4\u003c/sub\u003e \u0026gt; H\u003csub\u003e3\u003c/sub\u003ePO\u003csub\u003e4\u003c/sub\u003e, confirming the strong inhibition action of phosphate species and the opposite effect of H\u003csub\u003e3\u003c/sub\u003eO\u003csup\u003e+\u003c/sup\u003e ions. The synthesis of insoluble phosphates with metal ions found in SS is most likely the cause of negative mass losses. With the inclusion of each three-phosphate salt at a different concentration, it is possible to form insoluble phosphates. To find out how orthophosphate salts inhibit SS specimens in a Cl\u003csup\u003e-\u003c/sup\u003erich environment, more experiments were performed by changing the solution composition. \u0026nbsp;\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003e3.3 Mass loss of SS in orthophosphate anion solution in the presence of Cl ̄ ions\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThere is no significant mass loss of SS specimens in any of the three solutions, NaH\u003csub\u003e2\u003c/sub\u003ePO\u003csub\u003e4\u003c/sub\u003e, Na\u003csub\u003e2\u003c/sub\u003eHPO\u003csub\u003e4,\u0026nbsp;\u003c/sub\u003eand Na\u003csub\u003e3\u003c/sub\u003ePO\u003csub\u003e4\u003c/sub\u003e in the presence of 0.25 M HCl (Figure 5). However, the promotion of corrosion due to the presence of H\u003csub\u003e3\u003c/sub\u003eO\u003csup\u003e+\u003c/sup\u003e and Cl\u003csup\u003e-\u003c/sup\u003e is evident when compared to the observations in the absence of HCl as shown in Figure 4. The association between the corrosion inhibitory tendency and high quantities of phosphate species can be generalized in SS specimens, as assessed by mass loss studies in the presence and absence of HCl, having the best inhibitory action by Na\u003csub\u003e3\u003c/sub\u003ePO\u003csub\u003e4\u003c/sub\u003e.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003e3.4 EIS measurements\u0026nbsp;\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eElectrochemical impedance spectroscopy (EIS) is one of\u0026nbsp;the foremost\u0026nbsp;critical\u0026nbsp;electrochemical\u0026nbsp;methods\u0026nbsp;where the impedance in a circuit/solution is measured in ohms as a resistance unit when the experiment is conducted over\u0026nbsp;a\u0026nbsp;wide\u0026nbsp;range of frequencies [26]. The outcome of EIS is a Nyquist plot where the diameter of the semicircular portion is used to determine polarization resistance associated with the working electrode, SS specimens in this study when exposed to the solution in the electrochemical cell with various constituents of that influence on corrosion is to be investigated. Analyzing EIS data typically involves fitting them to an equivalent electrical circuit, consisting of common electrical components, such as resistors, capacitors, and inductors. In addition to polarization resistance which is a valuable parameter in corrosion studies due to its inverse relationship with the extent of corrosion, the electrical circuit can be used to determine other resistances, such as charge transfer resistance and solution resistance [27, 28]. \u0026nbsp;\u003c/p\u003e\n\u003cp\u003eNyquist plots of SS specimens recorded in different acid and phosphate salt solutions of the same initial concentration of 0.25 M and the proposed equivalent circuit are given in Figure 6. In supporting mass loss measurements, the largest diameter of the semicircle plot is observed for Na\u003csub\u003e3\u003c/sub\u003ePO\u003csub\u003e4\u003c/sub\u003e, while the smallest diameter is for HCl, indicating the strongest corrosion inhibition efficiency is provided by Na\u003csub\u003e3\u003c/sub\u003ePO\u003csub\u003e4\u003c/sub\u003e solutions. Less diametric semi-circled responses for other phosphate solutions also indicate that they also act as good corrosion inhibitors as compared to HCl and H\u003csub\u003e3\u003c/sub\u003ePO\u003csub\u003e4\u003c/sub\u003e. \u0026nbsp;The corrosion inhibitory actions of the solutions are in the order of HCl \u0026lt; H\u003csub\u003e3\u003c/sub\u003ePO\u003csub\u003e4\u003c/sub\u003e \u0026lt; Na\u003csub\u003e2\u003c/sub\u003eHPO\u003csub\u003e4\u003c/sub\u003e ~ NaH\u003csub\u003e2\u003c/sub\u003ePO\u003csub\u003e4\u003c/sub\u003e \u0026lt; Na\u003csub\u003e3\u003c/sub\u003ePO\u003csub\u003e4\u003c/sub\u003e. The polarization resistance values obtained for the proposed equivalence circuit, which also indicate the same trend as given above, are shown in Table 2.\u003c/p\u003e\n\u003cp\u003eIncrease in the concentration of phosphate salt ensures less corrosion of SS specimens in the ambient environment (Figure 7). As shown in the figure, a much higher value of \u003cem\u003eR\u003csub\u003ep\u003c/sub\u003e\u003c/em\u003e is obtained in favor of the inhibition of 0.50 M Na\u003csub\u003e3\u003c/sub\u003ePO\u003csub\u003e4\u003c/sub\u003e even in the presence of HCl which promotes corrosion.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eTable 2\u003c/strong\u003e: Polarizations resistance (\u003cem\u003eR\u003csub\u003eP\u003c/sub\u003e\u003c/em\u003e) values for SS when immersed in different solutions based on the equivalent circuit.\u003c/p\u003e\n\u003ctable border=\"1\" cellspacing=\"0\" cellpadding=\"0\"\u003e\n \u003ctbody\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 75.641%;\"\u003e\n \u003cp\u003e\u003cstrong\u003eSolution of SS immersed\u003c/strong\u003e\u003c/p\u003e\n \u003cp\u003e\u003cstrong\u003e\u0026nbsp;\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 24.359%;\"\u003e\n \u003cp\u003e\u003cstrong\u003e\u003cem\u003eR\u003csub\u003eP\u003c/sub\u003e\u0026nbsp;\u003c/em\u003e\u003c/strong\u003e\u003cstrong\u003e\u0026nbsp;(\u0026Omega;)\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 75.641%;\"\u003e\n \u003cp\u003eHCl (0.25 M)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 24.359%;\"\u003e\n \u003cp\u003e8.66\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 75.641%;\"\u003e\n \u003cp\u003eMixture of HCl (0.25 M) and Na\u003csub\u003e3\u003c/sub\u003ePO\u003csub\u003e4\u003c/sub\u003e (0.25 M)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 24.359%;\"\u003e\n \u003cp\u003e4.06\u0026acute;10\u003csup\u003e1\u0026nbsp;\u003c/sup\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 75.641%;\"\u003e\n \u003cp\u003eH\u003csub\u003e3\u003c/sub\u003ePO\u003csub\u003e4\u003c/sub\u003e (0.25 M)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 24.359%;\"\u003e\n \u003cp\u003e4.07\u0026acute;10\u003csup\u003e1\u003c/sup\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 75.641%;\"\u003e\n \u003cp\u003eNa\u003csub\u003e2\u003c/sub\u003eHPO\u003csub\u003e4\u003c/sub\u003e (0.25 M)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 24.359%;\"\u003e\n \u003cp\u003e5.90\u0026acute;10\u003csup\u003e1\u003c/sup\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 75.641%;\"\u003e\n \u003cp\u003eNaH\u003csub\u003e2\u003c/sub\u003ePO\u003csub\u003e4\u003c/sub\u003e (0.25 M)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 24.359%;\"\u003e\n \u003cp\u003e6.95\u0026acute;10\u003csup\u003e1\u003c/sup\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 75.641%;\"\u003e\n \u003cp\u003eNa\u003csub\u003e3\u003c/sub\u003ePO\u003csub\u003e4\u003c/sub\u003e (0.25 M)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 24.359%;\"\u003e\n \u003cp\u003e6.73\u0026acute;10\u003csup\u003e2\u003c/sup\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 75.641%;\"\u003e\n \u003cp\u003eNa\u003csub\u003e3\u003c/sub\u003ePO\u003csub\u003e4\u003c/sub\u003e (0.50 M)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 24.359%;\"\u003e\n \u003cp\u003e6.10\u0026acute;10\u003csup\u003e3\u003c/sup\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003c/tbody\u003e\n\u003c/table\u003e\n\u003cp\u003e\u003cstrong\u003e3.5 Tafel Plots\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eTafel extrapolation is one of the polarization strategies broadly utilized to degree corrosion rates, a quicker method compared with the classical mass loss estimation [29].\u0026nbsp;Also, various corrosion reactions can be portrayed utilizing the Tafel plots make it doable, anticipating the corrosion rate and potential concurring to the energy and thermodynamics of reactions taking put on a metal surface. When a metallic electrode is submerged in an aqueous corrosive environment, anodic and cathodic reactions naturally occur on the electrode surface, causing corrosion of the electrode [30]. The equilibrium potentials of each reaction occurring on the surface in this scenario will differ from the consequent potential of the electrode [31].\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eAccording to the values obtained as listed in Table 3, HCl is confirmed to be a corrosion promoter of SS whilst Na\u003csub\u003e3\u003c/sub\u003ePO\u003csub\u003e4\u003c/sub\u003e contributes to the corrosion inhibition action. \u0026nbsp;Approximately equal values have resulted for both Na\u003csub\u003e2\u003c/sub\u003eHPO\u003csub\u003e4\u003c/sub\u003e and NaH\u003csub\u003e2\u003c/sub\u003ePO\u003csub\u003e4\u003c/sub\u003e based on corrosion rate as well, as already stated in mass loss and EIS results. Furthermore, increase in the concentration of Na\u003csub\u003e3\u003c/sub\u003ePO\u003csub\u003e4\u003c/sub\u003e in a\u0026nbsp;Cl-rich environment decreases the corrosion rate of SS. The relationship of corrosion potential is inversely proportional to corrosion rate and generalizes the corrosion inhibition trend of\u0026nbsp;Na\u003csub\u003e3\u003c/sub\u003ePO\u003csub\u003e4\u003c/sub\u003e \u0026gt; Na\u003csub\u003e2\u003c/sub\u003eHPO\u003csub\u003e4\u0026nbsp;\u003c/sub\u003e~ NaH\u003csub\u003e2\u003c/sub\u003ePO\u003csub\u003e4\u003c/sub\u003e \u0026gt; H\u003csub\u003e3\u003c/sub\u003ePO\u003csub\u003e4.\u003c/sub\u003e which has been implemented in impedance studies as well.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eTable 3\u003c/strong\u003e. Tabulated values for corrosion potentials (\u003cem\u003eE\u003c/em\u003e\u003csub\u003ecorr\u003c/sub\u003e), corrosion current (\u003cem\u003eI\u003c/em\u003e\u003csub\u003ecorr\u003c/sub\u003e), and corrosion rate (in mm per year) of SS.\u003c/p\u003e\n\u003ctable border=\"0\" cellspacing=\"0\" cellpadding=\"0\" width=\"691\"\u003e\n \u003ctbody\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 47.7569%;\"\u003e\n \u003cp\u003e\u003cstrong\u003eSolution SS immersed\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 14.9059%;\"\u003e\n \u003cp\u003e\u003cstrong\u003e\u003cem\u003eE\u003c/em\u003e\u003c/strong\u003e\u003cstrong\u003e\u003csub\u003ecorr\u003c/sub\u003e\u003c/strong\u003e\u003c/p\u003e\n \u003cp\u003e\u003cstrong\u003e(V)\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 17.3661%;\"\u003e\n \u003cp\u003e\u003cstrong\u003e\u003cem\u003eI\u003c/em\u003e\u003c/strong\u003e\u003cstrong\u003ec\u003csub\u003eorr\u003c/sub\u003e\u003c/strong\u003e\u003c/p\u003e\n \u003cp\u003e\u003cstrong\u003e(A)\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 19.9711%;\"\u003e\n \u003cp\u003e\u003cstrong\u003eCorrosion rate (mpy)\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 47.7569%;\"\u003e\n \u003cp\u003eHCl (0.25 M)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 14.9059%;\"\u003e\n \u003cp\u003e-0.444\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 17.3661%;\"\u003e\n \u003cp\u003e1.24\u0026acute;10\u003csup\u003e-3\u003c/sup\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 19.9711%;\"\u003e\n \u003cp\u003e1.44\u0026acute;10\u003csup\u003e1\u003c/sup\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 47.7569%;\"\u003e\n \u003cp\u003eMixture of HCl (0.25 M) and Na\u003csub\u003e3\u003c/sub\u003ePO\u003csub\u003e4\u003c/sub\u003e (0.25 M)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 14.9059%;\"\u003e\n \u003cp\u003e-0.208\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 17.3661%;\"\u003e\n \u003cp\u003e4.15\u0026acute;10\u003csup\u003e-5\u003c/sup\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 19.9711%;\"\u003e\n \u003cp\u003e4.82\u0026acute;10\u003csup\u003e-1\u003c/sup\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 47.7569%;\"\u003e\n \u003cp\u003eH\u003csub\u003e3\u003c/sub\u003ePO\u003csub\u003e4\u003c/sub\u003e (0.25 M)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 14.9059%;\"\u003e\n \u003cp\u003e-0.067\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 17.3661%;\"\u003e\n \u003cp\u003e8.54\u0026acute;10\u003csup\u003e-7\u003c/sup\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 19.9711%;\"\u003e\n \u003cp\u003e9.93\u0026acute;10\u003csup\u003e-3\u003c/sup\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 47.7569%;\"\u003e\n \u003cp\u003eNa\u003csub\u003e2\u003c/sub\u003eHPO\u003csub\u003e4\u003c/sub\u003e (0.25 M)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 14.9059%;\"\u003e\n \u003cp\u003e-0.047\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 17.3661%;\"\u003e\n \u003cp\u003e4.52\u0026acute;10\u003csup\u003e-8\u003c/sup\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 19.9711%;\"\u003e\n \u003cp\u003e5.25\u0026acute;10\u003csup\u003e-3\u003c/sup\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 47.7569%;\"\u003e\n \u003cp\u003eNaH\u003csub\u003e2\u003c/sub\u003ePO\u003csub\u003e4\u003c/sub\u003e (0.25 M)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 14.9059%;\"\u003e\n \u003cp\u003e-0.042\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 17.3661%;\"\u003e\n \u003cp\u003e4.39\u0026acute;10\u003csup\u003e-7\u003c/sup\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 19.9711%;\"\u003e\n \u003cp\u003e5.10\u0026acute;10\u003csup\u003e-3\u003c/sup\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 47.7569%;\"\u003e\n \u003cp\u003eNa\u003csub\u003e3\u003c/sub\u003ePO\u003csub\u003e4\u003c/sub\u003e (0.25 M)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 14.9059%;\"\u003e\n \u003cp\u003e-0.036\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 17.3661%;\"\u003e\n \u003cp\u003e9.39\u0026acute;10\u003csup\u003e-8\u003c/sup\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 19.9711%;\"\u003e\n \u003cp\u003e1.09\u0026acute;10\u003csup\u003e-3\u003c/sup\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 47.7569%;\"\u003e\n \u003cp\u003eNa\u003csub\u003e3\u003c/sub\u003ePO\u003csub\u003e4\u003c/sub\u003e (0.50 M)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 14.9059%;\"\u003e\n \u003cp\u003e-0.030\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 17.3661%;\"\u003e\n \u003cp\u003e8.19\u0026acute;10\u003csup\u003e-8\u003c/sup\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 19.9711%;\"\u003e\n \u003cp\u003e9.52\u0026acute;10\u003csup\u003e-4\u003c/sup\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003c/tbody\u003e\n\u003c/table\u003e\u003cstrong\u003e\u003c/strong\u003e\n\u003cp\u003e\u003cstrong\u003e3.6 Open Circuit Potentials (OCP)\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe OCP of a working electrode is an indication of the tendency of a metallic substrate to be subject to deterioration in a specific environment.\u003cem\u003e\u0026nbsp;\u003c/em\u003eThe metallic substrate can fend off the aggressive action of the electrolyte and build a protective coating if the OCP continues to rise and remain stable.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eHowever, the opposite trend shows that metallic substrates are more prone to corrosion phenomena having lower potentials of SS in HCl solution (Figure 8). Solutions having the highest inhibition efficiency have the highest potential. Accordingly, the strong corrosion inhibition behavior of H\u003csub\u003e3\u003c/sub\u003ePO\u003csub\u003e4\u003c/sub\u003e is further convincing.\u0026nbsp;\u003c/p\u003e"},{"header":"Conclusion","content":"\u003cp\u003eHNO\u003csub\u003e3\u003c/sub\u003e and H\u003csub\u003e3\u003c/sub\u003ePO\u003csub\u003e4\u003c/sub\u003e are both effective corrosion inhibitors of Grade 202 stainless steel (SS) according to mass loss measurement, with the latter being more effective even in situations with high concentrations of chloride under mildly acidic conditions. In settings rich in chlorides, high concentrations of H\u003csub\u003e3\u003c/sub\u003ePO\u003csub\u003e4\u003c/sub\u003e similarly encourage SS corrosion to that of HNO\u003csub\u003e3\u003c/sub\u003e. Among ortho-phosphate species, phosphate contributes a large amount in inhibiting 202 SS, having the order Na\u003csub\u003e3\u003c/sub\u003ePO\u003csub\u003e4\u003c/sub\u003e \u0026gt; Na\u003csub\u003e2\u003c/sub\u003eHPO\u003csub\u003e4\u0026nbsp;\u003c/sub\u003e~NaH\u003csub\u003e2\u003c/sub\u003ePO\u003csub\u003e4\u003c/sub\u003e \u0026gt; H\u003csub\u003e3\u003c/sub\u003ePO\u003csub\u003e4\u003c/sub\u003e as per mass loss measurements, electrochemical impedance spectroscopy (EIS) and Tafel slope analysis. Specifically, the polarization resistances of 202 SS in 0.25 M solutions of HCl, H\u003csub\u003e3\u003c/sub\u003ePO\u003csub\u003e4\u003c/sub\u003e, Na\u003csub\u003e2\u003c/sub\u003eHPO\u003csub\u003e4\u003c/sub\u003e, NaH\u003csub\u003e2\u003c/sub\u003ePO\u003csub\u003e4\u003c/sub\u003e and Na\u003csub\u003e3\u003c/sub\u003ePO\u003csub\u003e4\u003c/sub\u003e are 8.66, 4.07\u0026acute;10\u003csup\u003e1\u003c/sup\u003e, 5.90\u0026acute;10\u003csup\u003e1\u003c/sup\u003e, 6.95\u0026acute;10\u003csup\u003e1\u003c/sup\u003e and 6.73\u0026acute;10\u003csup\u003e2\u003c/sup\u003e W, respectively. The corrosion rates determined by Tafel slope analysis for the above solutions are 1.44\u0026acute;10\u003csup\u003e2\u003c/sup\u003e, 9.93\u0026acute;10\u003csup\u003e-3\u003c/sup\u003e, 5.10\u0026acute;10\u003csup\u003e-3\u003c/sup\u003e 5.25\u0026acute;10\u003csup\u003e-3,\u003c/sup\u003e and 1.09\u0026acute;10\u003csup\u003e-3\u003c/sup\u003e mpy, respectively, which are parallel to the polarization resistance values.\u0026nbsp;A strong correlation of corrosion with H\u003csub\u003e3\u003c/sub\u003eO\u003csup\u003e+\u0026nbsp;\u003c/sup\u003eindicates having a feasible corrosion mechanism of phosphate species. The impact of H\u003csub\u003e3\u003c/sub\u003eO\u003csup\u003e+\u003c/sup\u003e on corrosion is evidenced by open circuit potential measurements as well. The results of this study can be used to optimize the phosphorizing procedures of SS on an industrial scale.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003e\u003cbr\u003e\u003c/p\u003e"},{"header":"Abbreviations","content":"\u003cp\u003eEIS \u0026ndash; Electrochemical impedance spectroscopy\u003c/p\u003e\n\u003cp\u003eIE \u0026ndash; Inhibition efficiency\u003c/p\u003e\n\u003cp\u003eOCP \u0026ndash; Open circuit potentials\u003c/p\u003e\n\u003cp\u003eR\u003csub\u003eP\u003c/sub\u003e \u0026ndash; Polarization resistance\u003c/p\u003e\n\u003cp\u003eSS \u0026ndash; Stainless steel\u003c/p\u003e\n\u003cp\u003e\u0026nbsp;\u003c/p\u003e"},{"header":"Declarations","content":"\u003cp\u003e\u003cstrong\u003eAcknowledgement\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eSpecial thanks goes to H.B.M.W.Y.T.K. Mahagedara and Department of Chemistry, Faculty of Science, University of Peradeniya.\u003c/p\u003e\n\n\u003cp\u003e\u003cstrong\u003eFunding\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThis research did not receive any specific grant from funding agencies in the public, commercial, or not-for-profit sectors.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eCompeting Interests\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe authors have no relevant financial or non-financial interests to disclose regarding this work.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eAuthor Contributions\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eAll authors contributed to the conception and design of the study in different aspects. Initial planning of the study, supervision, and final corrections was performed by N. Priyantha\u003csup\u003e*\u003c/sup\u003e. Sample preparations, sample analysis, bench works and manuscript writing were done by\u0026nbsp;M.H.N. Revon.\u003c/p\u003e\n\u003cp\u003eAll authors have read, commented, and approved the final manuscript of the study.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eData Availability\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe data generated during and/or analysed during the current study are available from the corresponding author; N. Priyantha\u003csup\u003e*\u003c/sup\u003e upon request.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eCode Availability\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eNot applicable\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eEthics approval\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eNot applicable \u0026ndash; This research did not involve any human or animal subjects or biological material or their data.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eConsent to participate\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eNot applicable \u0026ndash; This research did not involve any human subjects.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eConsent for publication\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eNot applicable - This research did not involve any human subjects.\u003c/p\u003e\n\u003cp\u003e\u0026nbsp;\u003c/p\u003e\n\u003cp\u003e\u0026nbsp;\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\n\u003cli\u003eKhan, M.A.A., Irfan, O.M., Djavanroodi, F. and Asad, M. (2022b). Development of Sustainable Inhibitors for Corrosion Control. \u003cem\u003eSustainability\u003c/em\u003e, 14(15), p.9502. doi:https://doi.org/10.3390/su14159502.\u003c/li\u003e\n\u003cli\u003eLi, P. and Du, M. (2022) Effect of chloride ion content on pitting corrosion of dispersion-strengthened-high-strength steel. Corrosion Communications, 7:23-34. doi: 10.1016/j.corcom.2022.03.005.\u003c/li\u003e\n\u003cli\u003eDesai, P.D., Pawar, C.B., Avhad, M.S. and More, A.P. (2022). Corrosion inhibitors for carbon steel: A review. \u003cem\u003eVietnam Journal of Chemistry\u003c/em\u003e, 61(1), 15\u0026ndash;42. doi:https://doi.org/10.1002/vjch.202200111.\u003c/li\u003e\n\u003cli\u003eShwetha, K.M., Praveen, P.B.M. and Devendra, B.K. (2024). A review on corrosion inhibitors: types, mechanisms, electrochemical analysis, corrosion rate and efficiency of corrosion inhibitors on mild steel in an acidic environment. \u003cem\u003eResults in Surfaces and Interfaces\u003c/em\u003e, 100258. doi:https://doi.org/10.1016/j.rsurfi.2024.100258.\u003c/li\u003e\n\u003cli\u003eKhadom, A.A. (2015) Kinetics and synergistic effect of iodide ion and naphthylamine for the inhibition of corrosion reaction of mild steel in hydrochloric acid. \u003cem\u003eReaction Kinetics, Mechanisms and Catalysis\u003c/em\u003e, 115(2), 463\u0026ndash;481. doi:10.1007/s11144-015-0873-9.\u003c/li\u003e\n\u003cli\u003eNoor, E.A. (2005) The inhibition of mild steel corrosion in phosphoric acid solutions by some N-heterocyclic compounds in the salt form. \u003cem\u003eCorrosion Science\u003c/em\u003e, 47(1), 33\u0026ndash;55. doi:10.1016/j.corsci.2004.05.026.\u003c/li\u003e\n\u003cli\u003eYaro, A.S., Khadom, A.A. and Wael, R.K. (2013) Apricot Juice as green corrosion inhibitor of mild steel in phosphoric acid. \u003cem\u003eAlexandria Engineering Journal\u003c/em\u003e, 52(1), 129\u0026ndash;135. doi:10.1016/j.aej.2012.11.001. \u003c/li\u003e\n\u003cli\u003eDi Schino, A. (2020) Manufacturing and applications of Stainless Steels. \u003cem\u003eMetals\u003c/em\u003e, 10(3), 327. doi:10.3390/met10030327.\u003c/li\u003e\n\u003cli\u003eVarshney, P., Mishra, R.S. and Kumar, N. (2022). Understanding the nature of passivation film formed during corrosion of Fe\u003csub\u003e39\u003c/sub\u003eMn\u003csub\u003e20\u003c/sub\u003eCo\u003csub\u003e20\u003c/sub\u003eCr\u003csub\u003e15\u003c/sub\u003eSi\u003csub\u003e5\u003c/sub\u003eAl\u003csub\u003e1\u003c/sub\u003e high entropy alloy in 3.5 wt% NaCl solution. \u003cem\u003eJournal of Alloys and Compounds\u003c/em\u003e, 904, 164100. doi:https://doi.org/10.1016/j.jallcom.2022.164100.\u003c/li\u003e\n\u003cli\u003eHong, T. and Nagumo, M. (1997) The effect of chloride concentration on early stages of pitting for type 304 stainless steel revealed by the AC impedance method. \u003cem\u003eCorrosion Science\u003c/em\u003e, 39(2), 285\u0026ndash;293. doi:10.1016/s0010-938x(96)00127-8.\u003c/li\u003e\n\u003cli\u003eAfshari, F., Ghomi, E.R., Dinari, M. and Ramakrishna, S. (2023). Recent advances on the corrosion inhibition behavior of Schiff base compounds on mild steel in acidic media. \u003cem\u003eChemistry Select\u003c/em\u003e, 8(9), 24\u0026ndash;30. doi:https://doi.org/10.1002/slct.202203231.\u003c/li\u003e\n\u003cli\u003eMandal, S., Singh, J.K., Lee, D-E. and Park, T. (2020) Effect of phosphate-based inhibitor on corrosion kinetics and mechanism for formation of passive film onto the steel rebar in chloride-containing pore solution, \u003cem\u003eMaterials\u003c/em\u003e, 13(16): 3642. doi: 10.3390/ma13163642.\u003c/li\u003e\n\u003cli\u003eZhang, J., Lu, X., Zhang, J., Zhang, L., Zhu, C., Zhang, Y. and Wu, T. (2019). Corrosion-inhibition effect of different phosphate compounds for carbon steel in chloride-contaminated mortars. \u003cem\u003eInternational Journal of Electrochemical Science\u003c/em\u003e, 14(9), pp.8601\u0026ndash;8610. doi:https://doi.org/10.20964/2019.09.29.\u003c/li\u003e\n\u003cli\u003eKim, H.J., Hong, J.S., Choi, J.H., Han, G.S. and Jung, H.S, (2022). Effect of phosphate ions on the formation of iron oxide/hydroxide as a stabilizer. \u003cem\u003eJournal of Solid State Chemistry\u003c/em\u003e, 305, 122688\u0026ndash;122688. doi:https://doi.org/10.1016/j.jssc.2021.122688.\u003c/li\u003e\n\u003cli\u003ePriyantha, N., Jayaweera, P., Macdonald, D.D. and Sun, A. (2004b). An electrochemical impedance study of Alloy 22 in NaCl brine at elevated temperature. I. Corrosion behavior. \u003cem\u003eJournal of Electroanalytical Chemistry\u003c/em\u003e, 572(2), 409\u0026ndash;419. doi:https://doi.org/10.1016/j.jelechem.2004.06.031.\u003c/li\u003e\n\u003cli\u003eMacdonald, D.D., Priyantha, N. Jayaweera, P., Engelhardt, G. and Davydov, A. (2004). The localized corrosion of Alloy 22 in simulated HLNW environments. \u003cem\u003eCorrosion \u003c/em\u003e\u003c/li\u003e\n\u003cli\u003eAlaoui, L.M., Kertit, S., Bellaouchou, A., Guenbour, A., Benbachir, A. and Hammouti, B. (2007). Phosphate of aluminum as corrosion inhibitor for steel in H\u003csub\u003e3\u003c/sub\u003ePO\u003csub\u003e4\u003c/sub\u003e. \u003cem\u003ePortugaliae Electrochimica Acta\u003c/em\u003e, 26(4) 339\u0026ndash;347. doi:https://doi.org/10.4152/pea.200804339.\u003c/li\u003e\n\u003cli\u003eBenabdellah, M., Benkaddour M., Hammouti, B., Bendahhou, B. and Aouniti, A. (2006). Inhibition of steel corrosion in 2M H3PO4 by artemisia oil. \u003cem\u003eApplied Surface Science\u003c/em\u003e, 252(18), pp.6212\u0026ndash;6217. doi:https://doi.org/10.1016/j.apsusc.2005.08.030.\u003c/li\u003e\n\u003cli\u003eBirla Singh, M., Gabriel, B.I., Venkatraman, M.S., Cole, I.S., Moorthy, G.C. and Emmanuel, B. (2022). Theory of impedance for initial corrosion of metals under a thin electrolyte layer: a coupled charge transfer-diffusion model. \u003cem\u003eJournal of chemical sciences/Proceedings of the Indian Academy of Sciences. Chemical sciences\u003c/em\u003e, 134(1), 4\u0026ndash;10.\u003c/li\u003e\n\u003cli\u003eRam\u0026oacute;n, J., Mart\u0026iacute;nez, I., Gand\u0026iacute;a-Romero, J. and Soto, J. (2022). Improved Tafel-based potentiostatic approach for corrosion rate monitoring of reinforcing steel. \u003cem\u003eJournal of Nondestructive Evaluation\u003c/em\u003e, 41(4). doi:https://doi.org/10.1007/s10921-022-00903-z.\u003c/li\u003e\n\u003cli\u003eSu, G., Xie, D., Wu, F., Feng, D., Meng, Y., Mei, Y. and Xie, Y. (2024b). Corrosion mechanisms of 316L stainless steel in polyphosphoric acid at elevated temperature: behavior and mechanistic insights. \u003cem\u003eCorrosion Science\u003c/em\u003e, 236, 112277\u0026ndash;112277. doi:https://doi.org/10.1016/j.corsci.2024.112277.\u003c/li\u003e\n\u003cli\u003eLi, W., Cao, R., Xu, L. and Qiao, L. (2021). The role of hydrogen in the corrosion and cracking of steels - a review. \u003cem\u003eCorrosion Communications\u003c/em\u003e, 4, 3\u0026ndash;32. doi:https://doi.org/10.1016/j.corcom.2021.10.005.\u003c/li\u003e\n\u003cli\u003eOlsson, C.-O.A. and Landolt, D. (2003) Passive films on stainless steels\u0026mdash;chemistry, structure and growth. \u003cem\u003eElectrochimica Acta\u003c/em\u003e, 48(9), 1093\u0026ndash;1104. doi:10.1016/s0013-4686(02)00841-1. \u003c/li\u003e\n\u003cli\u003eTreatment Plant Operator. (2021, October 8). \u003cem\u003eTreatment Plant Operator\u003c/em\u003e. Treatment Plant Operator. https://www.tpomag.com/online_exclusives/2021/10/phosphate-corrosion-control-in-drinking-water_sc_00h7h \u003c/li\u003e\n\u003cli\u003eRosales, E., Del Olmo, G., Calero Preciado, C. and Douterelo, I. (2020b). Phosphate Dosing in Drinking Water Distribution Systems Promotes Changes in Biofilm Structure and Functional Genetic Diversity. \u003cem\u003eFrontiers in Microbiology\u003c/em\u003e, 11, 1\u0026ndash;5. doi:https://doi.org/10.3389/fmicb.2020.599091.\u003c/li\u003e\n\u003cli\u003eMagar, H.S., Hassan, R.Y. and Mulchandani, A. (2021) Electrochemical impedance spectroscopy (EIS): Principles, construction, and biosensing applications. \u003cem\u003eSensors\u003c/em\u003e, 21(19), 6578. doi:10.3390/s21196578. \u003c/li\u003e\n\u003cli\u003eMei, B.-A., Munteshari, O., Lau, J., Dunn, B. and Pilon, L. (2017). physical interpretations of Nyquist plots for EDLC electrodes and devices. \u003cem\u003eThe Journal of Physical Chemistry C\u003c/em\u003e, 122(1), 194\u0026ndash;206. doi:https://doi.org/10.1021/acs.jpcc.7b10582.\u003c/li\u003e\n\u003cli\u003eAl-Amiery, A.A., Mohamad, A.B., Kadhum, A.A.H., Shaker, L.M., Isahak, W.N.R.W. and Takriff, M.S. (2022). Experimental and theoretical study on the corrosion inhibition of mild steel by nonanedioic acid derivative in hydrochloric acid solution. \u003cem\u003eScientific Reports\u003c/em\u003e, 12(1), 4705. doi:https://doi.org/10.1038/s41598-022-08146-8.\u003c/li\u003e\n\u003cli\u003ePark, K., Chang, B.-Y. and Hwang, S. (2019) Correlation between Tafel analysis and electrochemical impedance spectroscopy by prediction of amperometric responses. \u003cem\u003eACS Omega\u003c/em\u003e, 4(21), 19307\u0026ndash;19313. doi:10.1021/acsomega.9b02672. \u003c/li\u003e\n\u003cli\u003eMansfeld, F. (1973) Tafel slopes and corrosion rates from polarization resistance measurements. \u003cem\u003eCorrosion\u003c/em\u003e, 29(10), 397\u0026ndash;402. doi:10.5006/0010-9312-29.10.397.\u003c/li\u003e\n\u003cli\u003ePapavinasam, S. (2008c). Electrochemical polarization techniques for corrosion monitoring. \u003cem\u003eTechniques for Corrosion Monitoring\u003c/em\u003e, 49\u0026ndash;85. doi:https://doi.org/10.1533/9781845694050.1.49.\u003c/li\u003e\n\u003c/ol\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":false,"hideJournal":false,"highlight":"","institution":"","isAcceptedByJournal":true,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"discover-chemistry","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"","sideBox":"Learn more about [Discover Chemistry](https://link.springer.com/journal/44371)","snPcode":"44371","submissionUrl":"https://submission.nature.com/new-submission/44371/3","title":"Discover Chemistry","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"stoa","reportingPortfolio":"Discover Series","inReviewEnabled":true,"inReviewRevisionsEnabled":true},"keywords":"Corrosion, Impedance, Inhibition, Stainless steel, Tafel slope, Mass loss measurements","lastPublishedDoi":"10.21203/rs.3.rs-5077929/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-5077929/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003eStrong corrosion resistance of Grade 202 Stainless Steel (SS) in mild acidic conditions is attributed to the presence of chromium which is responsible for the formation of a passive surface film of chromium oxide which inhibits corrosion. Additionally, the deposition of polymer coatings, polymer composites with nanomaterials as well as organic compounds containing hetero atoms such as N, O, S, and P on SS, or other metallic objects leads to high corrosion inhibition efficiency. Nevertheless, the corrosion stability of SS in certain environments, especially under aggressive conditions, is questionable. Investigation of the impact of different chemical constituents under moderate and aggressive acidic conditions on the corrosion of SS, however, has not received sufficient attention despite the widespread use of SS-based machinery in industrial applications. Although the corrosion-inhibitory action of phosphate species on SS has been documented, detailed investigation, especially in the presence of interferents, has not been given due consideration. As such, variation of corrosion inhibition efficiency of HNO\u003csub\u003e3\u003c/sub\u003e and H\u003csub\u003e3\u003c/sub\u003ePO\u003csub\u003e4\u003c/sub\u003e on SS at different concentrations, and the impact of HNO\u003csub\u003e3\u003c/sub\u003e and H\u003csub\u003e3\u003c/sub\u003ePO\u003csub\u003e4\u003c/sub\u003e in the presence of chloride ions along with the effect of various phosphate species were investigated in this study. Despite the pitting corrosion promotion action of chloride species, mass loss measurements of rectangular stainless-steel specimens immersed separately in HNO\u003csub\u003e3\u003c/sub\u003e and H\u003csub\u003e3\u003c/sub\u003ePO\u003csub\u003e4\u003c/sub\u003e acid solutions at different concentrations in the presence of HCl, under ambient conditions, conclusively demonstrate the superior corrosion inhibitory behavior of H\u003csub\u003e3\u003c/sub\u003ePO\u003csub\u003e4\u003c/sub\u003e over HNO\u003csub\u003e3\u003c/sub\u003e on SS, even in chloride-rich environments under low acidic conditions. Polarization resistance determined by electrochemical impedance spectroscopy further supports the corrosion inhibitory action of H\u003csub\u003e3\u003c/sub\u003ePO\u003csub\u003e4\u003c/sub\u003e on SS, while open circuit measurements indicate the strong correlation between H\u003csub\u003e3\u003c/sub\u003eO\u003csup\u003e+\u003c/sup\u003e and surface characteristics. The order of corrosion inhibition ability of phosphate species on SS, as determined by mass loss measurements, electrochemical impedance spectroscopy, and Tafel slope analysis follows the order, Na\u003csub\u003e3\u003c/sub\u003ePO\u003csub\u003e4\u003c/sub\u003e \u0026gt; Na\u003csub\u003e2\u003c/sub\u003eHPO\u003csub\u003e4 ~ \u003c/sub\u003eNaH\u003csub\u003e2\u003c/sub\u003ePO\u003csub\u003e4\u003c/sub\u003e \u0026gt; H\u003csub\u003e3\u003c/sub\u003ePO\u003csub\u003e4\u003c/sub\u003e.\u003c/p\u003e","manuscriptTitle":"Interference of Solution Constituents on Corrosion Inhibition of Phosphate Species on Grade 202 Stainless Steel","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2024-11-13 15:00:31","doi":"10.21203/rs.3.rs-5077929/v1","editorialEvents":[{"type":"communityComments","content":0},{"type":"decision","content":"Revision requested","date":"2024-10-15T15:08:15+00:00","index":"","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2024-10-15T15:00:25+00:00","index":"hide","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2024-10-11T10:00:51+00:00","index":"hide","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2024-10-08T10:47:13+00:00","index":"hide","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2024-10-06T22:21:58+00:00","index":"hide","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2024-10-05T21:11:56+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"256150282110591510315747064371682517659","date":"2024-10-04T10:06:04+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"176869899871258282564297386424637388490","date":"2024-10-03T21:04:47+00:00","index":"hide","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2024-10-02T19:37:46+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"214452324300585768261442838491658984580","date":"2024-10-02T03:11:41+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"210766861466111852614351331204940779100","date":"2024-10-02T00:29:03+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"255938104299462917395410038460911896660","date":"2024-10-01T10:43:30+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"125457837955956169011110254544482751012","date":"2024-10-01T10:28:25+00:00","index":"hide","fulltext":""},{"type":"reviewersInvited","content":"","date":"2024-10-01T10:11:09+00:00","index":"","fulltext":""},{"type":"editorAssigned","content":"","date":"2024-09-25T05:13:42+00:00","index":"","fulltext":""},{"type":"checksComplete","content":"","date":"2024-09-19T10:30:55+00:00","index":"","fulltext":""},{"type":"submitted","content":"Discover Chemistry","date":"2024-09-12T13:15:41+00:00","index":"","fulltext":""}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"discover-chemistry","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"","sideBox":"Learn more about [Discover Chemistry](https://link.springer.com/journal/44371)","snPcode":"44371","submissionUrl":"https://submission.nature.com/new-submission/44371/3","title":"Discover Chemistry","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"stoa","reportingPortfolio":"Discover Series","inReviewEnabled":true,"inReviewRevisionsEnabled":true}}],"origin":"","ownerIdentity":"408e2abd-a419-4f2a-b64a-41f4762441c9","owner":[],"postedDate":"November 13th, 2024","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"under-review","subjectAreas":[],"tags":[],"updatedAt":"2025-04-02T11:08:47+00:00","versionOfRecord":[],"versionCreatedAt":"2024-11-13 15:00:31","video":"","vorDoi":"","vorDoiUrl":"","workflowStages":[]},"version":"v1","identity":"rs-5077929","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-5077929","identity":"rs-5077929","version":["v1"]},"buildId":"8U1c8b4HqxoKbykW_rLl7","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}