Characterization of aluminum hydroxide (Al(OH)3) for use as a porogenic agent in castable ceramics

Porous structures based on aluminum oxide-hydroxide (Al2O3-Al(OH)3) show high refractoriness. Regarding their use as thermal insulators, the preparation of aqueous castable suspensions requires suitable conditions to produce stable co-dispersions and a deeper knowledge on their porogenic-sintering behaviors. This study reports on the characterization of a commercial grade of Al(OH)3 and several transition phases of Al2O3 (attained through the calcination of Al(OH)3) aiming at their use as porogenic agents for castable porous ceramics. X-ray diffraction, thermogravimetry, Helium picnometer method, specific surface area and electron microscopy were used. The dispersion and rheology of Al(OH)3 and Al2O3 were investigated with pH variations and dispersants. Aluminum oxide and hydroxide particles showed high compatibility in aqueous medium and favored the preparation of suspensions. As porogenic agents, the transition phases showed a large quantity of meso-macro pores and a huge variation in the specific surface area, which highlight their potential to produce high refractoriness porous structures.