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 °C 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 °C 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 °C, 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.