Calcium aluminate cement in castable alumina: From hydrate bonding to the in situ formation of calcium hexaluminate

authors	Salomao, R; Kawamura, MA; Emilio, ABV; Sakihama, J; Segadaes, AM
nationality	International
journal	CERAMICS INTERNATIONAL
author keywords	Calcium hexaluminate; Alumina; Calcium aluminate cement; Porous ceramics
keywords	MICROSTRUCTURE DEVELOPMENT; MECHANICAL-PROPERTIES; THERMAL-CONDUCTIVITY; SETTING BEHAVIOR; TEMPERATURE; DEHYDRATION; FABRICATION; STABILITY; KINETICS
abstract	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.
publisher	ELSEVIER SCI LTD
issn	0272-8842
isbn	1873-3956
year published	2021
volume	47
issue	11
beginning page	15082
ending page	15093
digital object identifier (doi)	10.1016/j.ceramint.2021.02.066
web of science category	12
subject category	Materials Science, Ceramics
unique article identifier	WOS:000640984300007