Enhanced Densification and Mechanical Performance of Fused Silica via Gel Casting

Document Type : Research Paper

Authors

Department of Materials Science and Engineering, School of Engineering, Shiraz University, Shiraz, Iran

Abstract

The sintering behavior, phase evolution, and mechanical properties of fused silica ceramics were systematically investigated for samples fabricated by gel casting and dry pressing. Gel-cast samples were prepared using an optimized aqueous formulation containing 58 wt.% solids, whereas dry-pressed compacts were produced at 100 MPa. All specimens were sintered in air between 1100 °C and 1300 °C for 5 h. Dilatometric analysis revealed distinct densification characteristics for the two forming methods. Despite their lower initial green density (~30–33% of theoretical), gel-cast bodies exhibited faster and more complete shrinkage than dry-pressed samples (~57–60% of theoretical), achieving near-full densification above 1150 °C. This enhanced sintering efficiency is attributed to the superior microstructural homogeneity of gel-cast green bodies, whose fine and interconnected pore network provides higher capillary driving forces and more efficient mass transport during viscous sintering. In contrast, heterogeneous particle packing in dry-pressed compacts produced isolated pores that impeded densification. Flexural strength increased with sintering temperature but decreased with higher polymer content due to residual porosity formed during burnout. The maximum strength (~85 MPa) was observed for gel-cast specimens sintered at 1250 °C, while a subsequent drop in 1300 °C corresponded to extensive cristobalite crystallization, as confirmed by XRD and SEM. Crystallization induced microcracking and limited further densification. These results demonstrate that microstructural uniformity is more critical than initial green density for achieving dense, high-strength fused silica. Gel casting thus represents a superior forming technique for producing defect-free amorphous silica ceramics below the cristobalite formation threshold.

Keywords

References

[1] Manivannan, R., Kumar, A., & Subrahmanyam, C. (2013). Aqueous gelcasting of fused silica using colloidal silica binder. Journal of the American Ceramic Society, 96(8), 2432-2436. https://doi.org/10.1111/jace.12448
[2] Zhang, Y., & Cheng, Y. B. (2006). Use of HEMA in gelcasting of ceramics: a case study on fused silica. Journal of the American Ceramic Society, 89(9), 2933-2935. https://doi.org/10.1111/j.1551-2916.2006.01152.x
[3] Reed, J. S. (1995). Principles of ceramic processing, 2nd ed. Wiley.
[4] Shelby, J. E. (2005). Introduction to glass science and technology, 2nd ed. RSC.
[5] Kim, Y. H., Yeo, J. G., & Choi, S. C. (2016). The effect of fused silica crystallization on flexural strength and shrinkage of ceramic cores for investment casting. Journal of the Korean Ceramic Society, 53(2), 246–252. https://doi.org/10.4191/kcers.2016.53.2.246
[6] Pascual, M. J., & Durán, A. (1985). Preparation of glass by sintering. Journal of Materials Science, 20, 4259–4297. https://doi.org/10.1007/BF00559317
[7] Kingery, W. D., Bowen, H. K., & Uhlmann, D. R. (1976). Introduction to ceramics, 2nd ed. Wiley.
[8] Jiajun Liu, Shuang Yin, Chengyun Sun, Yao Zhang, Liqiang Liu, Ruzhong Zuo. (2025). Rheological engineering and sintering control for colloidal shaping of high-performance fused silica ceramics. Ceramics International, 51(26), 51623-51634. https://doi.org/10.1016/j.ceramint.2025.08.383
[9] Gupta, T. K., & Jean, J. H. (1994). Origin of cristobalite formation during sintering of a binary mixture of borosilicate glass and high silica glass. Journal of Materials Research, 9(4), 999-1005. https://doi.org/10.1557/JMR.1994.0999
[10] Wagstaff, F. E. (1969). Crystallization and melting kinetics of cristobalite. Journal of the American Ceramic Society, 52(12), 650-654. https://doi.org/10.1111/j.1151-2916.1969.tb16069.x
[11] Omatete, O. O., Janney, M. A., & Nunn, S. D. (1997). Gelcasting: from laboratory development toward industrial production. Journal of the European Ceramic Society, 17(2-3), 407-413. https://doi.org/10.1016/S0955-2219(96)00147-1
[12] Breneman, R. C., & Halloran, J. W. (2014). Kinetics of cristobalite formation in sintered silica. Journal of the American Ceramic Society, 97(7), 2272-2278. https://doi.org/10.1111/jace.12889
[13] Yang, J., Yu, J. and Huang, Y. (2011). Recent developments in gelcasting of ceramics. Journal of the European Ceramic Society, 31(14), 2569-2591. https://doi.org/10.1016/j.jeurceramsoc.2010.12.035
[14] Tabrizian, P., Golestanifard, F., Alem, A., Ghassemi, E. (2016). The influence of gel-casting parameters on the preparation of Si porous bodies. Materials Letters, 183(15), 19-22. https://doi.org/10.1016/j.matlet.2016.07.068
[15] Prabhakaran K., Ojha P. K., Gokhale N. M., Sharma S. C. (2009). Effect of polymer concentration on porosity and pore size characteristics of alumina membrane substrates prepared by gelcasting. Ceramics International, 35(5), 2083-2085. https://doi.org/10.1016/j.ceramint.2008.10.001
[16] Liang, J. J., Lin, Q. H., Zhang, X., Jin, T., Zhou, Y. Z., Sun, X. F., Choi, B. G., Kim, I. S., Do, J. H., & Jo, C. Y. (2017). Effects of alumina on cristobalite crystallization and properties of silica-based ceramic cores. Journal of Materials Science & Technology, 33(2), 204-209. https://doi.org/10.1016/j.jmst.2016.02.012
[17] Pinckney, L. R., & Beall, G. H. (2008). Microstructural evolution in some silicate glass–ceramics: a review. Journal of the American Ceramic Society, 91(3), 773-779. https://doi.org/10.1111/j.1551-2916.2007.02129.x
[18] Benjira, A., Antou, G., Andre, D., Rochais, D., Piquero, T., Scaringella-Guerritat, Y., & Maitre, A. (2025). In-depth characterization of the early sintering stages of an amorphous silica powder. Journal of the European Ceramic Society, 45(3), 117031. https://doi.org/10.1016/j.jeurceramsoc.2024.117031
[19] B. Wachtman J. B., Cannon W. R., John M. (2009). Mechanical properties of ceramics. 2nd ed., John Wiley & Sons.
[20] Babashov, V. G. and Varrik, N. M. (2023). Gel casting method for producing ceramic materials: A review. Glass Ceram., 80, 9-16. https://doi.org/10.1007/s10717-023-00547-z
[21] Afgarazordeh, M. and Paydar, M. H. (2025). Densification behavior of fused silica: effects of particle size, compaction pressure, sintering temperature/time, and boron oxide addition, Iranian Journal of Materials Forming, 12(4), 44-53. https://doi.org/10.22099/IJMF.2025.53990.1345
[22] Afgarazordeh, M. and Paydar, M. H. (2026). Optimization of gel casting parameters for high-strength fused silica green bodies, Iranian Journal of Materials Forming, 13(2), 4-12. https://doi.org/10.22099/IJMF.2025.54433.1353
[23] Tari, G. (2003). Gelcasting ceramics: A review. American Ceramic Society Bulletin, 82, 43-46.
Iranian Journal of Materials Forming
Volume 13, Issue 3
July 2026
Pages 4-11

Files

Share

How to cite

Statistics