In Situ Production of Microporous Calcium Hexaluminate by Direct Molding
DOI:
https://doi.org/10.19142/rpq.v17i34.706Keywords:
porous ceramic, calcium hexaluminate, direct castingAbstract
The microporous calcium hexaluminate ceramic compound (CaO.6Al2 O3 or CA6 ) excels in applications such as thermal insulation, industrial furnace and boiler coatings, molten metal, and gas filter, among others. CA6 is commercially produced by the α-Al2 O3 -CaCO3 route generating CO2 gas emissions in the environment during the burning process. Therefore, this work evaluated the production of CA6 by alternative routes using different sources of alumina (α-Al2 O3 and ρ-Al2 O3 ) and calcium (CaCO3 , Ca(OH)2 and CaO) by the direct molding technique. The raw materials were characterized as size distribution of their particles, as well as suspensions as to the time of gripping, that is, the workability time until the final hardening (stuck). The products obtained after sintering at 1550 and 1600 °C were characterized for diameter and thickness shrinkage, crystalline phases, and microstructure. This work showed that CA6 can be produced through the direct molding technique, using the proposed alternative sources for both alumina and calcium. α-Al2 O3 presented finer particles when compared to hydraulic alumina, as well as CaCO3. Compared to Ca(OH)2 and especially to CaO. CaO was the calcium source with
the greatest accelerating effect on setting time, being intensified in α-Al2 O3 suspensions. The product produced by the α-Al2 O3 route showed greater packing in its microstructure with grains with a high aspect ratio, thinner and longer when compared to the production by ρ-Al2 O3.
References
1. SOLA, A. V. H.; MOTA, C. M. M. Melhoria da eficiência energética em sistemas motrizes industriais. Production, v. 25, n. 3, pp. 498-509 (2015).
2. NAGAOKA, T. et al. Forming and sintering of porous calciumhexaluminate ceramics with hydraulic alumina. Journal Material Science, v. 41, p. 7401-7405. (2006)
3. DOMINGUEZ, C. et al. Microstruture development in calcium hexaluminate. Journal of the European Ceramic Society, v. 21, p. 381-387. (2001)
4. GARSEL, D. V. et al. New insulating raw material for high temperature applications. International Colloquium On Refractories Aachen, v. 41, p. 122 – 128. (1998)
5. OLIVEIRA, I. R. et al. Production of porous ceramic material using different sources of alumina and calcia. Revista Matéria, v. 20 n. 03, p. 739 – 746. (2015)
6. SALOMÃO, R. et al. Hydrotalcite synthesis via co-precipitation reaction using MgO and Al(OH)3 precursors. International Ceramic, v. 37, n. 8, p. 3063 – 3070. (2011)
7. AMTHAUER, K. et al. New european sinter aggregate with 96% Al2O3. International Colloquium On Refractories Aachen, v. 54, p. 95 – 98. (2011)
8. BRAULIO, M. A. L. et al. Agentes ligantes e seus efeitos em concretos refratários alumina-magnésia. Cerâmica, v. 56, p. 325-330. (2010)
9. SALOMÃO, R.; FERNANDES, L.; SPERA, NATALIA C. M. Combined effects of SiO2 ratio and purity on physical properties and microstructure of in situ alumina-mullite ceramic. International Journal of Applied Ceramic Technology, v. 00, p. 1-8. (2021)
10. SOUZA, A. D. V.; SOUSA, L. L.; FERNANDES, L., et al. Development of densification-resistant castable porous structures from in situ mullite. J. Eur. Ceram. Society, v. 35, p. 1943 (2015).
11. SALOMÃO, R.; FERREIRA, V. L.; COSTA, L. M. M.; OLIVEIRA, I. R. Effects of the initial CaO-Al2 O3 ratio on the microstructure development and mechanical properties of porous calcium hexaluminate. Ceramics International, v. 44, p. 2626-2631. (2017)
12. SALOMÃO, R. et al. Mechanism of pore generation in calcium hexaluminate (CA6) ceramics formed in situ from calcined alumina and calcium carbonate aggregates. Journal of the European Ceramic Society, v. 36, p. 4225 – 4235. (2016)
13. GUZMAN, I. Y. Certain principles of formation of porous ceramic structures, properties and applications (a Review). Glass and Ceramics, v. 60, n. 9 – 10, p. 280 – 283. (2003)
14. SCHNABEL, M. et al., Advantages of calcium hexaluminate in a corrosive environment. Refractories WorldForum, v. 3, n. 4, p. 87-94. (2011)
15. LORENZ, R. K.; BUHR, A.; RACHER, R. P. Industrial application experiences with microporous calcium hexaluminate insulating material SLA-92. International Colloquium On Refractories, v. 48, p. 66 – 70. (2005)
16. AN, L.; CHAN, H. M.; SONI, K. K.; Control of calcium hexaluminate grain morphology in situ toughened ceramic composites. Journal Material Science, v. 31, p. 3223-3229. (1996)
17. SALOMÃO, R. et al. Hydratable Alumina-Bonded Suspensions: Evolution of Microstructure and Physical Properties During First Heating. Interceram Refractories Manual, v. 66, p. 28-37. (2017)
