Novel cordierite cementless refractory castable based on silica sol. Its properties and comparison with classical CAC cordierite castable

Novel cordierite cementless refractory castable based on silica sol. Its properties and comparison with classical CAC cordierite castable | 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 Novel cordierite cementless refractory castable based on silica sol. Its properties and comparison with classical CAC cordierite castable Oleksii Lapenko, Ivan Priesol, Gabriel Sučik, Beatrice Plešingerová, and 1 more This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-7399699/v1 This work is licensed under a CC BY 4.0 License Status: Posted Version 1 posted You are reading this latest preprint version Abstract The aim of this study is to investigate the properties of refractory cordierite based cement-free castable utilizing silica sol as a binder. An additional objective is to compare the performance of this novel material with that of conventional cordierite refractory castable based on calcium aluminate cement. The findings are intended to evaluate the feasibility of applying the proposed material in the production of various monolithic components of thermal units operating under relatively low-temperature conditions (up to 1200°C), but subject to frequent and intense thermal cycling—such as coke oven doors or household waste incineration chambers. A significant advantage of silica sol–based concrete is the absence of chemically bound water, enabling complete drying at 110°C within 10 hours. In contrast, conventional concrete requires drying at 350–550°C for 20–80 hours, depending on the size of the component. This property significantly reduces both time and energy consumption during the manufacturing process. cordierite cementless refractory castable sol-gel thermal shock resistance Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Highlights • Cordierite is the basis for refractory linings with high thermal shock resistance. • Sol-gel bonding reduces preparation time and saves energy resources. • New material properties are comparable or superior to conventional ones. 1. Introduction The thermal expansion behaviour of cordierite Mg 2 Al 4 Si 5 O 18 arises from a combination of general Grüneisen strain parameters of both positive and negative signs, along with the unique form of the elastic compliance tensor, which also exhibits components of opposite sign. This interplay reflects the coexistence of the tension effect and the hinge-like structural mechanism, which together result in anisotropic thermal expansion—manifesting as both positive and near-zero (or “fuzzy”) thermal expansion along different crystallographic axes. The overall thermal response is governed by a delicate balance between these competing contributions, ultimately accounting for the characteristically low mean thermal expansion coefficient of cordierite. This property has made cordierite a key material for applications requiring high thermal stability, particularly in advanced ceramic and high-performance composite systems [ 1 – 3 ] Cordierite-based products can be manufactured using a range of ceramic processing techniques, including semi-dry pressing, plastic forming, isostatic pressing, as well as slip and tape casting. For the fabrication of large monolithic blocks and stationary linings of certain thermal units, conventional refractory castables are typically employed [ 4 , 5 ]. The latter is usually made of a material consisting of cordierite filler and a refractory calcium aluminate cement binder [ 6 ]. Such refractory concretes are usually relatively inexpensive and easy to use [ 7 ]. On the other hand, a significant drawback of conventional calcium aluminate cement is the presence of chemically bound water in its hydration products [ 8 ]. This water necessitates a specific drying regime, typically involving exposure to temperatures of 350–550°C [ 9 – 11 ] for 20–80 hours, depending on the size of the product [ 12 ]. Furthermore, it contributes to the formation of a low-strength zone in the material [ 13 ] between the point of complete dehydration at approximately 550°C and the onset of ceramic bond formation at temperatures of 1300°C and above [ 14 ]. To address these shortcomings, calcium aluminate cement in the formulation can be replaced with a binder based on silica sol, which does not contain chemically bound water in its structure [ 15 , 16 ]. This substitution enables a reduction in drying time and energy consumption. Additionally, the reactive alumina used in the cement-free formulation transforms into corundum at approximately 1040°C [ 17 ], which exhibits high mechanical strength at typical service temperatures of around 1200°C. In turn, replacing the binder component in the formulation necessitates conducting standard tests for refractory materials, including porosity, compressive strength, and permanent linear change. In addition, a comparison of thermal expansion coefficients between conventional and modified refractory castables is required. These evaluations are essential for assessing the feasibility and practical applicability of the new castable formulation under high-temperature operating conditions. 2. Experimental procedure 2.1. Materials and sample preparations The formulation of the new sol-gel cordierite refractory castable (hereinafter referred to as KOR sol ) was based on the Tecast BPV CS cement-free bauxite castable developed by IPC Refractories a.s., Slovakia, which has demonstrated excellent performance as a safety lining for tundishes in metallurgical applications. In the modified KOR sol composition, the bauxite aggregates in the original Tecast BPV CS formulation were substituted with equivalent cordierite fractions supplied by České lupkové závody a.s. (Czechia). Cordierite fractions of 0–0.1 mm, 0–1 mm, 1–3 mm, and 2–6 mm, of the C65 grade, were used. The material had an Al₂O₃ content ranging from 32.17–32.80% and an MgO content between 11.14% and 11.50%. The binder system responsible for the development of mechanical strength remained unchanged and consisted of reactive alumina with an Al₂O₃ content of 99.4% and a particle size distribution (X₅₀) of 1.8 µm, along with colloidal silica (silicon oxide sol) containing 30% solid content and a pH of 10.5. For comparison, a reference refractory castable (hereinafter referred to as KOR CAC ) was used. It contained the same cordierite fractions as KOR sol . The binder in this composition was refractory calcium aluminate cement with an Al₂O₃ content of 68.5% or higher. Water was used for the preparation of the castable specimens. Taking into account the water present in the colloidal silica, the KOR CAC formulation required approximately 2% more added water than KOR sol to achieve comparable workability. 2.2. Experimental methods and equipment Test specimens of shapes C (230x64x64 mm) and D (160x40x40 mm) were prepared from both types of castables in accordance with the ISO 1927-6 standard. The samples were subsequently dried at 110°C and fired to 1200°C with a holding time of five hours. The heating rate was constant at 5°C/min. Given the relatively small size of the specimens compared to monolithic linings, this rate can be considered sufficient to ensure that the decomposition of hydrates in the cement phase does not significantly influence the mechanical strength or other performance parameters of the materials. Permanent linear changes, bulk density, apparent porosity, and cold compressive strength of the fired samples were evaluated in accordance with the previously mentioned ISO 1927-6 standard. Thermal shock resistance was assessed following the ISO 1927-8 procedure. In this test, the samples were heated to 1200°C and subsequently quenched in water at 20°C. The thermal-physical characterization of the samples was performed on a thermal analyser NETZSCH STA 449 F3 Jupiter, with Netzsch Proteus TA version 6.1 software at a heating rate of 10°C/min in air atmosphere. The coefficient of linear thermal expansion, which is one of the key parameters affecting the thermal shock resistance of the material, was measured using a NETZSCH T-ZP-0032 dilatometer, the heating rate was 5°C/min. The crystalline phase composition was determined using a Rigaku MiniFlex 600 X-ray diffractometer, CuKa with PDXL2 software and ICCD database. 3. Results and discussion 3.1. Identification of the key physicochemical processes occurring in the studied materials during heating Primarily, to confirm the above-mentioned hypotheses regarding the presence or absence of chemically bound water, differential thermal analysis (DTA) and thermogravimetric analysis (TG) were conducted (Fig. 1 , 2 ) . For the KOR sol sample, a weight loss of approximately 0.2% is observed in the temperature range of 350–450°C, which is associated with the decomposition of a small amount of boehmite. In the case of the KOR CAC sample, the weight loss is more significant, amounting to 3.3% in the range of 200–400°C. According to the DTA curve, the decomposition occurs in two stages: dehydration of aluminium hydroxide to boehmite, followed by the decomposition of boehmite itself. For both samples, a minor endothermic effect accompanied by weight loss is observed in the range of 680–720°C, most likely associated with the decomposition of magnesium carbonate present in the cordierite filler. Notably, the exothermic effect related to the phase transition of γ-Al₂O₃ to α-Al₂O₃ (corundum) at around 1040°C is more pronounced in the sample containing calcium aluminate cement than in the sample with reactive alumina (0,3 µV/mg for KOR CAC against 0,1 µV/mg for KOR sol ). 3.2. XRD-based characterization of phase composition The phase composition analysis of each tested castable fired sample confirmed the presence of cordierite originating from the aggregate. In the KOR CAC sample (Fig. 3 ), three distinct calcium aluminate phases were identified. In the KOR sol sample (Fig. 4 ), the presence of the corundum phase was clearly detected. The mullite phase, which was identified in both samples along with cordierite, is primarily attributed to the cordierite-based raw material. However, in the case of KOR sol , the formation of secondary mullite is also possible as a result of the reaction between reactive alumina and silica derived from the colloidal silica binder during firing. 3.3. Comparison of linear thermal expansion Figure 5 shows the results of measuring the thermal linear expansion of the compared fired samples (1200°C, 5°C/min). Based on the obtained data, it can be concluded that the castable with the sol-gel ( KOR sol ) binder exhibits slightly higher thermal expansion across the entire measured temperature range. This is likely due to the higher coefficient of thermal expansion of corundum compared to that of calcium aluminates. The graph also clearly demonstrates that both materials undergo irreversible shrinkage upon reaching a temperature of 1250°C, which may be attributed to the sintering of cordierite present in the filler. Consequently, the recommended maximum service temperature for both materials should be limited to 1200°C. 3.4. Comparison of the main properties of the novel and standard castables Table 1 presents a comparison of the key parameters used to evaluate the quality of refractory materials. Table 1 Main properties of the novel and standard castables. Parameter KOR sol KOR CAC Permanent linear changes, to 1200°C [%] 0.0 0.0 Bulk density [kg/m 3 ] 1 753 1 710 Apparent porosity [%] 24.9 23.9 Cold compressive strength after drying 110°C [MPa] 11.9 12.6 Cold compressive strength after firing 1200°C [MPa] 42.3 8.9 Coefficient of thermal expansion at 900°C [%] 0.36 0.33 Coefficient of thermal expansion at 1200°C [%] 0.51 0.47 The differences in the measured parameters can be attributed to the processes occurring during the firing of each castable. Given that the quantity and quality of the cordierite filler are identical in both formulations, primary attention must be paid to the reactions and phase transformations involving the binder component. In the case of the castable based on calcium aluminate cement ( KOR CAC ), the predominant transformation is the decomposition of chemically bound water in the temperature range of 350–550°C. In contrast, for the sol-gel castable ( KOR sol ), a key transformation is the conversion of reactive alumina (γ-Al 2 O 3 ) into corundum (α-Al 2 O 3 ) at approximately 1040°C. This explains why the KOR sol castable exhibits a little bit higher bulk density despite having greater apparent porosity. These transformations in both materials occur without substantial volumetric changes, as evidenced by the negligible permanent linear changes after firing. The compressive strength after drying is slightly higher in the CAC-based castable but decreases following firing at 1200°C. The sol-gel castable, on the other hand, shows a significant increase in strength after firing, which correlates with the aforementioned phase changes. It should be noted, however, that the compressive strength of the sol-gel castable in the undried state is significantly lower than that of the CAC castable, typically ranging from 2 to 4 MPa. Precise values are not provided in this work due to methodological challenges in measuring the compressive strength of the sol-gel material prior to drying. Thermal shock resistance testing revealed no visible damage or cracking in either material after 20 heating–cooling cycles. As a result, additional testing was deemed redundant. 4. Conclusions The results of the study demonstrated the feasibility of using cordierite in sol-gel bonded, cement-free refractory castables to produce durable materials suitable for industrial applications involving frequent thermal cycling. The next stage should involve validating the compliance of the developed castable with production standards through pilot-scale testing. Successful confirmation of quality at this level would enable the launch of block production, with significantly reduced costs due to the replacement of the energy- and time-intensive drying process at 550–600°C (required for conventional cement-based castables) with accelerated drying at 120–180°C. Declarations Funding This study was financially supported by the Grant Agencies of the Slovak Republic through the VEGA– MŠVVaŠ SR and SAV project No.1/0219/25. The authors gratefully acknowledge ČLUZ (Czech Republic) company for providing the materials used in this research. Appreciation is also extended to IPC Refractories a.s. (Slovakia) for supplying valuable information that contributed to this study. Author Contribution Oleksii Lapenko - Project administration, Investigation, Formal analysis, Writing – original draftIvan Priesol – Conceptualization, ResourcesGabriel Sučik – SupervisionBeatrice Plešingerová – MethodologyĽuboš Popovič - Data curation Acknowledgement The authors gratefully acknowledge ČLUZ (Czech Republic) company for providing the materials used in this research. Data Availability The authors declare that the data supporting the findings of this study are available within the paper and its Supplementary Information files. Should any raw data files be needed in another format they are available from the corresponding author upon reasonable request. References M.T. Dove, L. Li, Anomalous thermal expansion of cordierite, Mg₂Al₄Si₅O₁₈, understood through lattice simulations. Matter , 8(3), (2025) 101943. https://doi.org/10.1016/j.matt.2024.101943 M. Elmaghraby, A. Ismail, Z. Belal, Thermal expansion, physico-mechanical properties and microstructure of cordierite synthesized from different starting materials. Interceram - International Ceramic Review , 64, (2015) 209–213. https://doi.org/10.1007/BF03401125 R.N. Das, C. Madhusoodana, P. Panda, K. Okada, Evaluation of thermal shock resistance of cordierite honeycombs. Bulletin of Materials Science , 25, (2002) 127–132. https://doi.org/10.1007/BF02706232 D.W. Richerson, W.E. Lee, Modern Ceramic Engineering: Properties, Processing, and Use in Design . CRC Press, London, (2018). ISBN: 9781498716918 M.N. Rahaman, Ceramic Processing and Sintering , 2nd ed. CRC Press, Boca Raton, (2017). ISBN: 9780824709884 L. Frolova, V. Primachenko, E. Degtyareva, Refractories for coke oven doors. Refractories and Industrial Ceramics , 25, (1984) 474–485. S. Banerjee, Monolithic Refractories . Answer Technology Inc., USA, (1998). ISBN–13: 9789810231200 C. Fentiman, R. Mangabhai, K. Scrivener, Calcium Aluminate Cements — Proceedings of the Centenary Conference . BRE Press, Cheltenham, (2008). ISBN-13: 978-1-84806-045-6 F.A. Cardoso, M.D. Innocentini, M.F. Miranda, F.A. Valenzuela, V.C. Pandolfelli, Drying behavior of hydratable alumina-bonded refractory castables. Journal of the European Ceramic Society , 24(5), (2004) 797–802. T.-H. Kim, B. Ye, B. Jeong, M.-J. Lee, Influence of CaCO₃ on density and compressive strength of calcium aluminate cement-based cementitious materials in binder jetting. Materials , 17(14), (2024). https://doi.org/10.3390/ma17143463 Ö.S. Bideci, H. Yılmaz, O. Gencel, A. Bideci, Fiber-reinforced lightweight calcium aluminate cement-based concrete: Effect of exposure to elevated temperatures. Sustainability , 15(6), (2023). https://doi.org/10.3390/su15064722 A. Piippo, K. Ruotanen, V.-V. Visuri, N. Poutiainen, E.-P. Heikkinen, Experimental study on the effect of calcium aluminate cement addition on the drying and physical properties of refractory castables containing colloidal silica. Materials , 17(21), (2024). https://doi.org/10.3390/ma17215308 A. Abolhasani, B. Samali, F. Aslani, Physicochemical, mineralogical, and mechanical properties of calcium aluminate cement concrete exposed to elevated temperatures. Materials , 14, (2021) 3855. https://doi.org/10.3390/ma14143855 S. Martinović, M. Vlahović, T. Boljanac, J. Majstorović, T. Volkov-Husović, Influence of sintering temperature on thermal shock behavior of low cement high alumina refractory concrete. Composites Part B: Engineering , 60, (2014) 400–412. R.K. Iler, The Chemistry of Silica . Wiley, New York, (1979). ISBN: 9780471024040 B. Buľko, P. Demeter, I. Priesol, The benefits of using an advanced material for production of spherical impact pad for tundish. Engineering Proceedings , 64(1), (2024). https://doi.org/10.3390/engproc2024064017 A. Blažek, Termická analýza . 1st ed. SNTL, Praha, (1972), p. 295. Additional Declarations No competing interests reported. Supplementary Files GraphicalAbstract.jpg Cite Share Download PDF Status: Posted Version 1 posted 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-7399699","acceptedTermsAndConditions":true,"allowDirectSubmit":true,"archivedVersions":[],"articleType":"Research Article","associatedPublications":[],"authors":[{"id":505338812,"identity":"054da253-e61a-4aaa-a739-c4df857c0ce2","order_by":0,"name":"Oleksii Lapenko","email":"data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAZAAAAAyAQMAAABI0h/eAAAABlBMVEX///8AAABVwtN+AAAACXBIWXMAAA7EAAAOxAGVKw4bAAAA/ElEQVRIie3QsWrDMBCA4QsCeTmq9UIgfQUbQdohD2MjkBcnZOxUCgFn8QP0bVojyOTuGQOBTKUYshjqIbKbZKqSjh30o0EaPrgTgM/3HwuAAYQEd/3rHcYAvLvFbsJOhJ+IxL8RgAtJiltEMGaiZvEIPPgod4tqmr6RTrbQaicZLrlS2A2GcyVfN3pWkDbhIM+cJDQozc8u2WSEtbEkzWnw8nSFiEPZdER8PnxbkiKlqwbaawRZ3A9G2YThxsRIem1/wz2Y3UVKS5DTlxphpaOi2itKcvf6Iljuhk37PBZiVh5wPb0PVjqq61Y5yTnsz6X4Jjgrn8/n8/3WEX2VRyWbT95dAAAAAElFTkSuQmCC","orcid":"","institution":"Technical University of Kosice","correspondingAuthor":true,"prefix":"","firstName":"Oleksii","middleName":"","lastName":"Lapenko","suffix":""},{"id":505338813,"identity":"72ff0010-7ed1-4f7b-98eb-a956da03b04d","order_by":1,"name":"Ivan Priesol","email":"","orcid":"","institution":"I.P.C. 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Its properties and comparison with classical CAC cordierite castable","fulltext":[{"header":"Highlights","content":"\u003cp\u003e\u0026bull; Cordierite is the basis for refractory linings with high thermal shock resistance.\u003c/p\u003e\u003cp\u003e\u0026bull; Sol-gel bonding reduces preparation time and saves energy resources.\u003c/p\u003e\u003cp\u003e\u0026bull; New material properties are comparable or superior to conventional ones.\u003c/p\u003e"},{"header":"1. Introduction","content":"\u003cp\u003eThe thermal expansion behaviour of cordierite Mg\u003csub\u003e2\u003c/sub\u003eAl\u003csub\u003e4\u003c/sub\u003eSi\u003csub\u003e5\u003c/sub\u003eO\u003csub\u003e18\u003c/sub\u003e arises from a combination of general Gr\u0026uuml;neisen strain parameters of both positive and negative signs, along with the unique form of the elastic compliance tensor, which also exhibits components of opposite sign. This interplay reflects the coexistence of the tension effect and the hinge-like structural mechanism, which together result in anisotropic thermal expansion\u0026mdash;manifesting as both positive and near-zero (or \u0026ldquo;fuzzy\u0026rdquo;) thermal expansion along different crystallographic axes. The overall thermal response is governed by a delicate balance between these competing contributions, ultimately accounting for the characteristically low mean thermal expansion coefficient of cordierite. This property has made cordierite a key material for applications requiring high thermal stability, particularly in advanced ceramic and high-performance composite systems [\u003cspan additionalcitationids=\"CR2\" citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e3\u003c/span\u003e] Cordierite-based products can be manufactured using a range of ceramic processing techniques, including semi-dry pressing, plastic forming, isostatic pressing, as well as slip and tape casting. For the fabrication of large monolithic blocks and stationary linings of certain thermal units, conventional refractory castables are typically employed [\u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e4\u003c/span\u003e, \u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e5\u003c/span\u003e]. The latter is usually made of a material consisting of cordierite filler and a refractory calcium aluminate cement binder [\u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e6\u003c/span\u003e]. Such refractory concretes are usually relatively inexpensive and easy to use [\u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e7\u003c/span\u003e]. On the other hand, a significant drawback of conventional calcium aluminate cement is the presence of chemically bound water in its hydration products [\u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e8\u003c/span\u003e]. This water necessitates a specific drying regime, typically involving exposure to temperatures of 350\u0026ndash;550\u0026deg;C [\u003cspan additionalcitationids=\"CR10\" citationid=\"CR9\" class=\"CitationRef\"\u003e9\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e11\u003c/span\u003e] for 20\u0026ndash;80 hours, depending on the size of the product [\u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e12\u003c/span\u003e]. Furthermore, it contributes to the formation of a low-strength zone in the material [\u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e13\u003c/span\u003e] between the point of complete dehydration at approximately 550\u0026deg;C and the onset of ceramic bond formation at temperatures of 1300\u0026deg;C and above [\u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e14\u003c/span\u003e]. To address these shortcomings, calcium aluminate cement in the formulation can be replaced with a binder based on silica sol, which does not contain chemically bound water in its structure [\u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e15\u003c/span\u003e, \u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e16\u003c/span\u003e]. This substitution enables a reduction in drying time and energy consumption. Additionally, the reactive alumina used in the cement-free formulation transforms into corundum at approximately 1040\u0026deg;C [\u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e17\u003c/span\u003e], which exhibits high mechanical strength at typical service temperatures of around 1200\u0026deg;C.\u003c/p\u003e\u003cp\u003eIn turn, replacing the binder component in the formulation necessitates conducting standard tests for refractory materials, including porosity, compressive strength, and permanent linear change. In addition, a comparison of thermal expansion coefficients between conventional and modified refractory castables is required. These evaluations are essential for assessing the feasibility and practical applicability of the new castable formulation under high-temperature operating conditions.\u003c/p\u003e"},{"header":"2. Experimental procedure","content":"\u003cdiv id=\"Sec3\" class=\"Section2\"\u003e\u003ch2\u003e2.1. Materials and sample preparations\u003c/h2\u003e\u003cp\u003eThe formulation of the new sol-gel cordierite refractory castable (hereinafter referred to as \u003cem\u003eKOR sol\u003c/em\u003e) was based on the Tecast BPV CS cement-free bauxite castable developed by IPC Refractories a.s., Slovakia, which has demonstrated excellent performance as a safety lining for tundishes in metallurgical applications. In the modified \u003cem\u003eKOR sol\u003c/em\u003e composition, the bauxite aggregates in the original Tecast BPV CS formulation were substituted with equivalent cordierite fractions supplied by Česk\u0026eacute; lupkov\u0026eacute; z\u0026aacute;vody a.s. (Czechia). Cordierite fractions of 0\u0026ndash;0.1 mm, 0\u0026ndash;1 mm, 1\u0026ndash;3 mm, and 2\u0026ndash;6 mm, of the C65 grade, were used. The material had an Al₂O₃ content ranging from 32.17\u0026ndash;32.80% and an MgO content between 11.14% and 11.50%. The binder system responsible for the development of mechanical strength remained unchanged and consisted of reactive alumina with an Al₂O₃ content of 99.4% and a particle size distribution (X₅₀) of 1.8 \u0026micro;m, along with colloidal silica (silicon oxide sol) containing 30% solid content and a pH of 10.5.\u003c/p\u003e\u003cp\u003eFor comparison, a reference refractory castable (hereinafter referred to as \u003cem\u003eKOR CAC\u003c/em\u003e) was used. It contained the same cordierite fractions as \u003cem\u003eKOR sol\u003c/em\u003e. The binder in this composition was refractory calcium aluminate cement with an Al₂O₃ content of 68.5% or higher. Water was used for the preparation of the castable specimens. Taking into account the water present in the colloidal silica, the \u003cem\u003eKOR CAC\u003c/em\u003e formulation required approximately 2% more added water than \u003cem\u003eKOR sol\u003c/em\u003e to achieve comparable workability.\u003c/p\u003e\u003c/div\u003e\u003cdiv id=\"Sec4\" class=\"Section2\"\u003e\u003ch2\u003e2.2. Experimental methods and equipment\u003c/h2\u003e\u003cp\u003eTest specimens of shapes C (230x64x64 mm) and D (160x40x40 mm) were prepared from both types of castables in accordance with the ISO 1927-6 standard. The samples were subsequently dried at 110\u0026deg;C and fired to 1200\u0026deg;C with a holding time of five hours. The heating rate was constant at 5\u0026deg;C/min. Given the relatively small size of the specimens compared to monolithic linings, this rate can be considered sufficient to ensure that the decomposition of hydrates in the cement phase does not significantly influence the mechanical strength or other performance parameters of the materials.\u003c/p\u003e\u003cp\u003ePermanent linear changes, bulk density, apparent porosity, and cold compressive strength of the fired samples were evaluated in accordance with the previously mentioned ISO 1927-6 standard. Thermal shock resistance was assessed following the ISO 1927-8 procedure. In this test, the samples were heated to 1200\u0026deg;C and subsequently quenched in water at 20\u0026deg;C. The thermal-physical characterization of the samples was performed on a thermal analyser NETZSCH STA 449 F3 Jupiter, with Netzsch Proteus TA version 6.1 software at a heating rate of 10\u0026deg;C/min in air atmosphere. The coefficient of linear thermal expansion, which is one of the key parameters affecting the thermal shock resistance of the material, was measured using a NETZSCH T-ZP-0032 dilatometer, the heating rate was 5\u0026deg;C/min. The crystalline phase composition was determined using a Rigaku MiniFlex 600 X-ray diffractometer, CuKa with PDXL2 software and ICCD database.\u003c/p\u003e\u003c/div\u003e"},{"header":"3. Results and discussion","content":"\u003cdiv id=\"Sec6\" class=\"Section2\"\u003e\n \u003ch2\u003e3.1. Identification of the key physicochemical processes occurring in the studied materials during heating\u003c/h2\u003e\n \u003cp\u003ePrimarily, to confirm the above-mentioned hypotheses regarding the presence or absence of chemically bound water, differential thermal analysis (DTA) and thermogravimetric analysis (TG) were conducted (Fig. \u003cspan class=\"InternalRef\"\u003e1\u003c/span\u003e,\u003cspan class=\"InternalRef\"\u003e2\u003c/span\u003e) .\u003c/p\u003e\n \u003cp\u003eFor the \u003cem\u003eKOR sol\u003c/em\u003e sample, a weight loss of approximately 0.2% is observed in the temperature range of 350\u0026ndash;450\u0026deg;C, which is associated with the decomposition of a small amount of boehmite. In the case of the \u003cem\u003eKOR CAC\u003c/em\u003e sample, the weight loss is more significant, amounting to 3.3% in the range of 200\u0026ndash;400\u0026deg;C. According to the DTA curve, the decomposition occurs in two stages: dehydration of aluminium hydroxide to boehmite, followed by the decomposition of boehmite itself.\u003c/p\u003e\n \u003cp\u003eFor both samples, a minor endothermic effect accompanied by weight loss is observed in the range of 680\u0026ndash;720\u0026deg;C, most likely associated with the decomposition of magnesium carbonate present in the cordierite filler.\u003c/p\u003e\n \u003cp\u003eNotably, the exothermic effect related to the phase transition of \u0026gamma;-Al₂O₃ to \u0026alpha;-Al₂O₃ (corundum) at around 1040\u0026deg;C is more pronounced in the sample containing calcium aluminate cement than in the sample with reactive alumina (0,3 \u0026micro;V/mg for \u003cem\u003eKOR CAC\u003c/em\u003e against 0,1 \u0026micro;V/mg for \u003cem\u003eKOR sol\u003c/em\u003e).\u003c/p\u003e\n\u003c/div\u003e\n\u003cdiv id=\"Sec7\" class=\"Section2\"\u003e\n \u003ch2\u003e3.2. XRD-based characterization of phase composition\u003c/h2\u003e\n \u003cp\u003eThe phase composition analysis of each tested castable fired sample confirmed the presence of cordierite originating from the aggregate. In the \u003cem\u003eKOR CAC\u003c/em\u003e sample (Fig. \u003cspan class=\"InternalRef\"\u003e3\u003c/span\u003e), three distinct calcium aluminate phases were identified. In the \u003cem\u003eKOR sol\u003c/em\u003e sample (Fig. \u003cspan class=\"InternalRef\"\u003e4\u003c/span\u003e), the presence of the corundum phase was clearly detected. The mullite phase, which was identified in both samples along with cordierite, is primarily attributed to the cordierite-based raw material. However, in the case of \u003cem\u003eKOR sol\u003c/em\u003e, the formation of secondary mullite is also possible as a result of the reaction between reactive alumina and silica derived from the colloidal silica binder during firing.\u003c/p\u003e\n\u003c/div\u003e\n\u003cdiv id=\"Sec8\" class=\"Section2\"\u003e\n \u003ch2\u003e3.3. Comparison of linear thermal expansion\u003c/h2\u003e\n \u003cp\u003eFigure \u003cspan class=\"InternalRef\"\u003e5\u003c/span\u003e shows the results of measuring the thermal linear expansion of the compared fired samples (1200\u0026deg;C, 5\u0026deg;C/min).\u003c/p\u003e\n \u003cp\u003eBased on the obtained data, it can be concluded that the castable with the sol-gel (\u003cem\u003eKOR sol\u003c/em\u003e) binder exhibits slightly higher thermal expansion across the entire measured temperature range. This is likely due to the higher coefficient of thermal expansion of corundum compared to that of calcium aluminates. The graph also clearly demonstrates that both materials undergo irreversible shrinkage upon reaching a temperature of 1250\u0026deg;C, which may be attributed to the sintering of cordierite present in the filler. Consequently, the recommended maximum service temperature for both materials should be limited to 1200\u0026deg;C.\u003c/p\u003e\n\u003c/div\u003e\n\u003cdiv id=\"Sec9\" class=\"Section2\"\u003e\n \u003ch2\u003e3.4. Comparison of the main properties of the novel and standard castables\u003c/h2\u003e\n \u003cp\u003eTable \u003cspan class=\"InternalRef\"\u003e1\u003c/span\u003e presents a comparison of the key parameters used to evaluate the quality of refractory materials.\u003c/p\u003e\n \u003cdiv class=\"gridtable\"\u003e\n \u003ctable id=\"Tab1\" border=\"1\" class=\"fr-table-selection-hover\"\u003e\n \u003ccaption language=\"En\"\u003e\n \u003cdiv class=\"CaptionNumber\"\u003eTable 1\u003c/div\u003e\n \u003cdiv class=\"CaptionContent\"\u003e\n \u003cp\u003eMain properties of the novel and standard castables.\u003c/p\u003e\n \u003c/div\u003e\n \u003c/caption\u003e\n \u003cthead\u003e\n \u003ctr\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eParameter\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003e\u003cem\u003eKOR sol\u003c/em\u003e\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003e\u003cem\u003eKOR CAC\u003c/em\u003e\u003c/p\u003e\n \u003c/th\u003e\n \u003c/tr\u003e\n \u003c/thead\u003e\n \u003ctbody\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003ePermanent linear changes, to 1200\u0026deg;C [%]\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0.0\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0.0\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eBulk density [kg/m\u003csup\u003e3\u003c/sup\u003e]\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e1 753\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e1 710\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eApparent porosity [%]\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e24.9\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e23.9\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eCold compressive strength after drying 110\u0026deg;C [MPa]\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e11.9\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e12.6\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eCold compressive strength after firing 1200\u0026deg;C [MPa]\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e42.3\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e8.9\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eCoefficient of thermal expansion at 900\u0026deg;C [%]\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0.36\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0.33\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eCoefficient of thermal expansion at 1200\u0026deg;C [%]\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0.51\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0.47\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003c/tbody\u003e\n \u003c/table\u003e\n \u003c/div\u003e\n \u003cp\u003e\u003cbr\u003e\u003c/p\u003e\n \u003cp\u003eThe differences in the measured parameters can be attributed to the processes occurring during the firing of each castable. Given that the quantity and quality of the cordierite filler are identical in both formulations, primary attention must be paid to the reactions and phase transformations involving the binder component.\u003c/p\u003e\n \u003cp\u003eIn the case of the castable based on calcium aluminate cement (\u003cem\u003eKOR CAC\u003c/em\u003e), the predominant transformation is the decomposition of chemically bound water in the temperature range of 350\u0026ndash;550\u0026deg;C. In contrast, for the sol-gel castable (\u003cem\u003eKOR sol\u003c/em\u003e), a key transformation is the conversion of reactive alumina (\u0026gamma;-Al\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e) into corundum (\u0026alpha;-Al\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e) at approximately 1040\u0026deg;C. This explains why the \u003cem\u003eKOR sol\u003c/em\u003e castable exhibits a little bit higher bulk density despite having greater apparent porosity.\u003c/p\u003e\n \u003cp\u003eThese transformations in both materials occur without substantial volumetric changes, as evidenced by the negligible permanent linear changes after firing. The compressive strength after drying is slightly higher in the CAC-based castable but decreases following firing at 1200\u0026deg;C. The sol-gel castable, on the other hand, shows a significant increase in strength after firing, which correlates with the aforementioned phase changes.\u003c/p\u003e\n \u003cp\u003eIt should be noted, however, that the compressive strength of the sol-gel castable in the undried state is significantly lower than that of the CAC castable, typically ranging from 2 to 4 MPa. Precise values are not provided in this work due to methodological challenges in measuring the compressive strength of the sol-gel material prior to drying.\u003c/p\u003e\n \u003cp\u003eThermal shock resistance testing revealed no visible damage or cracking in either material after 20 heating\u0026ndash;cooling cycles. As a result, additional testing was deemed redundant.\u003c/p\u003e\n\u003c/div\u003e"},{"header":"4. Conclusions","content":"\u003cp\u003eThe results of the study demonstrated the feasibility of using cordierite in sol-gel bonded, cement-free refractory castables to produce durable materials suitable for industrial applications involving frequent thermal cycling. The next stage should involve validating the compliance of the developed castable with production standards through pilot-scale testing. Successful confirmation of quality at this level would enable the launch of block production, with significantly reduced costs due to the replacement of the energy- and time-intensive drying process at 550\u0026ndash;600\u0026deg;C (required for conventional cement-based castables) with accelerated drying at 120\u0026ndash;180\u0026deg;C.\u003c/p\u003e"},{"header":"Declarations","content":"\u003ch2\u003eFunding\u003c/h2\u003e\u003cp\u003eThis study was financially supported by the Grant Agencies of the Slovak Republic through the VEGA\u0026ndash; MŠVVaŠ SR and SAV project No.1/0219/25. The authors gratefully acknowledge ČLUZ (Czech Republic) company for providing the materials used in this research. Appreciation is also extended to IPC Refractories a.s. (Slovakia) for supplying valuable information that contributed to this study.\u003c/p\u003e\u003ch2\u003eAuthor Contribution\u003c/h2\u003e\u003cp\u003eOleksii Lapenko - Project administration, Investigation, Formal analysis, Writing \u0026ndash; original draftIvan Priesol \u0026ndash; Conceptualization, ResourcesGabriel Sučik \u0026ndash; SupervisionBeatrice Plešingerov\u0026aacute; \u0026ndash; MethodologyĽuboš Popovič - Data curation\u003c/p\u003e\u003ch2\u003eAcknowledgement\u003c/h2\u003e\u003cp\u003eThe authors gratefully acknowledge ČLUZ (Czech Republic) company for providing the materials used in this research.\u003c/p\u003e\u003ch2\u003eData Availability\u003c/h2\u003e\u003cp\u003eThe authors declare that the data supporting the findings of this study are available within the paper and its Supplementary Information files. Should any raw data files be needed in another format they are available from the corresponding author upon reasonable request.\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\u003cli\u003e\u003cspan\u003eM.T. Dove, L. Li, Anomalous thermal expansion of cordierite, Mg₂Al₄Si₅O₁₈, understood through lattice simulations. \u003cem\u003eMatter\u003c/em\u003e, 8(3), (2025) 101943. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1016/j.matt.2024.101943\u003c/span\u003e\u003cspan address=\"10.1016/j.matt.2024.101943\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eM. Elmaghraby, A. Ismail, Z. 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SNTL, Praha, (1972), p. 295.\u003c/span\u003e\u003c/li\u003e\u003c/ol\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":false,"hideJournal":true,"highlight":"","institution":"","isAcceptedByJournal":false,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"researchsquare","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":true,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"/submission","title":"Research Square","twitterHandle":"researchsquare","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"","reportingPortfolio":"","inReviewEnabled":false,"inReviewRevisionsEnabled":true},"keywords":"cordierite, cementless refractory castable, sol-gel, thermal shock resistance","lastPublishedDoi":"10.21203/rs.3.rs-7399699/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-7399699/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003eThe aim of this study is to investigate the properties of refractory cordierite based cement-free castable utilizing silica sol as a binder. An additional objective is to compare the performance of this novel material with that of conventional cordierite refractory castable based on calcium aluminate cement. The findings are intended to evaluate the feasibility of applying the proposed material in the production of various monolithic components of thermal units operating under relatively low-temperature conditions (up to 1200\u0026deg;C), but subject to frequent and intense thermal cycling\u0026mdash;such as coke oven doors or household waste incineration chambers.\u003c/p\u003e\u003cp\u003eA significant advantage of silica sol\u0026ndash;based concrete is the absence of chemically bound water, enabling complete drying at 110\u0026deg;C within 10 hours. In contrast, conventional concrete requires drying at 350\u0026ndash;550\u0026deg;C for 20\u0026ndash;80 hours, depending on the size of the component. This property significantly reduces both time and energy consumption during the manufacturing process.\u003c/p\u003e","manuscriptTitle":"Novel cordierite cementless refractory castable based on silica sol. Its properties and comparison with classical CAC cordierite castable","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2025-08-27 15:49:29","doi":"10.21203/rs.3.rs-7399699/v1","editorialEvents":[{"type":"communityComments","content":0}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"researchsquare","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":true,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"/submission","title":"Research Square","twitterHandle":"researchsquare","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"","reportingPortfolio":"","inReviewEnabled":false,"inReviewRevisionsEnabled":true}}],"origin":"","ownerIdentity":"32e80833-a562-4eea-9c82-225a4638b09e","owner":[],"postedDate":"August 27th, 2025","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"posted","subjectAreas":[],"tags":[],"updatedAt":"2025-09-06T08:38:41+00:00","versionOfRecord":[],"versionCreatedAt":"2025-08-27 15:49:29","video":"","vorDoi":"","vorDoiUrl":"","workflowStages":[]},"version":"v1","identity":"rs-7399699","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-7399699","identity":"rs-7399699","version":["v1"]},"buildId":"XKTyCvWXoU3ODBz1xrDgd","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}