Freezing behaviour and spray freeze granulation drying of silicon nitride slurries prepared from tert-butyl alcohol and cyclohexane solvent mixtures

A spray freeze granulation drying technique is suitable for obtaining soft and homogeneous granules, but the use of an aqueous slurry could degrade raw materials such as nitride. In this study, the freezing behaviour of silicon nitride slurries prepared from tert-butyl alcohol, cyclohexane, and their solvent mixtures was investigated, and granules were obtained from these slurries by the spray freeze granulation drying technique. An in situ optical coherence tomography observation of the freezing behaviour showed that the slurry from a solvent mixture of the eutectic composition froze in a single step in a shorter time than the other solvent mixtures. The solvent mixture of the eutectic composition yielded a homogeneous internal structure with fine pores in the freeze-dried body. The granules of that composition prepared by spray freeze granulation drying had a smaller size and a narrower size distribution, which resulted in a homogeneous internal structure of silicon nitride ceramics.