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.
keywords
MICROSTRUCTURE DEVELOPMENT; MECHANICAL-PROPERTIES; THERMAL-CONDUCTIVITY; SETTING BEHAVIOR; TEMPERATURE; DEHYDRATION; FABRICATION; STABILITY; KINETICS
subject category
Materials Science, Ceramics
authors
Salomao, R; Kawamura, MA; Emilio, ABV; Sakihama, J; Segadaes, AM
our authors
Ana Maria B C Segadães
Retired Professoracknowledgements
This research was supported by Brazilian Research Foundations FAPESP [grant numbers 2010-19274-5; 2017/06738-2; 2018/19773-3], CNPq [grant numbers 305877/2017-8], and CAPES [Financial code 001]. The authors acknowledge Almatis (Brazil) and Elfusa Geral de Eletrofusao (Brazil) for supplying the raw materials used, and the Electron Microscopy Laboratory of Advanced Materials Research Support Center (EESC/IFSC) for the SEM images. They also declare that, to the best of their knowledge, no competing interests (financial or personal) affected the results reported in this paper and that they cited all funding and supporting sources.