Principles of the hydrolysis assisted solidification (HAS) process for forming ceramic bodies from aqueous suspension

Hydrolysis-assisted solidification (HAS) is a new method for net-shaping ceramic green parts from aqueous suspensions in non-porous molds. The process exploits the thermally activated and/or accelerated hydrolysis of aluminium-nitride powder, which has been added to ceramic suspensions. Several simultaneously occurring effects accompany the hydrolysis of AlN: an increased solids content in the suspension due to internal water consumption, a decreased ζ-potential due to the pH change caused by ammonia formation, and the formation of Al-hydroxides. The overall result is a dramatic increase in the suspension's viscosity, which ultimately leads to the formation of a solid body. The contributions of individual mechanisms were studied and are discussed in this paper. At very high solids loading, each of these mechanisms can lead to a significant increase in the viscosity of the suspension. At lower solids loadings, the precipitation of aluminium hydroxide seems to play the major role in the suspension's solidification.