TY - JOUR
T1 - Calcium aluminate cement in castable alumina
T2 - From hydrate bonding to the in situ formation of calcium hexaluminate
AU - Salomão, Rafael
AU - Kawamura, Mirian A.
AU - Emilio, Ana B.V.
AU - Sakihama, José
AU - Segadães, Ana M.
N1 - Publisher Copyright:
© 2021 Elsevier Ltd and Techna Group S.r.l.
PY - 2021/6/1
Y1 - 2021/6/1
N2 - Calcium hexaluminate (CA6) is an intrinsically densification-resistant material, therefore, its porous structures are key materials for applications as high-temperature thermal insulators. This article reports on the combination of calcined alumina and calcium aluminate cement (CAC) in castable aqueous suspensions for the in situ production of porous CA6. The CAC content (10–34 vol%) and the curing conditions ensure structural integrity prior to sintering and maximize the development of hydrated phases. Changes in physical properties, crystalline phases, and microstructure were investigated after isothermal treatments (120–1500 °C), and three sequential porogenic events were observed. The hydration of CAC preserved the water-derived pores (up to 120 °C), and the dehydroxylation of CAC hydrates (250–700 °C) generated inter-particles pores. Moreover, the in situ expansive formation of CA2 and CA6 (900–1500 °C) hindered densification and generated intra-particle pores. Such events differed from those observed with other CaO sources, and resulted in significantly higher pores content and lower thermal conductivity.
AB - Calcium hexaluminate (CA6) is an intrinsically densification-resistant material, therefore, its porous structures are key materials for applications as high-temperature thermal insulators. This article reports on the combination of calcined alumina and calcium aluminate cement (CAC) in castable aqueous suspensions for the in situ production of porous CA6. The CAC content (10–34 vol%) and the curing conditions ensure structural integrity prior to sintering and maximize the development of hydrated phases. Changes in physical properties, crystalline phases, and microstructure were investigated after isothermal treatments (120–1500 °C), and three sequential porogenic events were observed. The hydration of CAC preserved the water-derived pores (up to 120 °C), and the dehydroxylation of CAC hydrates (250–700 °C) generated inter-particles pores. Moreover, the in situ expansive formation of CA2 and CA6 (900–1500 °C) hindered densification and generated intra-particle pores. Such events differed from those observed with other CaO sources, and resulted in significantly higher pores content and lower thermal conductivity.
KW - Alumina
KW - Calcium aluminate cement
KW - Calcium hexaluminate
KW - Porous ceramics
UR - http://www.scopus.com/inward/record.url?scp=85101293131&partnerID=8YFLogxK
U2 - 10.1016/j.ceramint.2021.02.066
DO - 10.1016/j.ceramint.2021.02.066
M3 - Article
AN - SCOPUS:85101293131
SN - 0272-8842
VL - 47
SP - 15082
EP - 15093
JO - Ceramics International
JF - Ceramics International
IS - 11
ER -