A thermo-chemical surface treatment of AlN powder for the aqueous processing of AlN ceramics


Dense aluminum nitride ceramics were prepared by sintering green bodies at 1750 degreesC for 2 h. These green bodies were prepared by aqueous slip-casting from a powder that was surface-treated to prevent hydrolysis. The surface treatment of the aluminum nitride (AlN) powder consisted of dispersing the powder in warm-water solutions of aluminum dihydrogenphosphate Al(H2PO4)(3). Different treatment temperatures in the range 30-80 degreesC were tested. For all the tested temperatures, the surface-treated AlN powder was found to be water-resistant, even after drying and/or redispersion. Various commercial dispersants were tested for their effectiveness, and the amount of dispersant was optimized in terms of a high solids loading of the suspension and an acceptable viscosity for slip casting. Based on these studies, a stable aqueous suspension of AlN powder, treated at 60 degreesC, with a total solids loading of 50 vol%, was prepared using CaF2 as a sintering additive. The well-dispersed powder made it possible to prepare green samples with close particle packing and relatively high sintered densities; that is, more than 96% of the theoretical density.




Materials Science


Olhero, SM; Novak, S; Oliveira, M; Krnel, K; Kosmac, T; Ferreira, JMF

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