CRITICAL-EXAMINATION OF A CRYOCHEMICAL METHOD FOR THE PREPARATION OF HIGH SURFACE-AREA SEMICONDUCTING POWDERS .2. NON-AQUEOUS SOLVENTS - BEHAVIOR OF SOLID-SOLUTIONS IN FREEZE-DRYING

A solid solution which is sublimed under vacuum during the preparation of a high surface area powder will melt if the temperature of the surface is greater than the eutectic temperature, irrespective of the initial concentration of the solution. Three criteria may be used in selecting a suitable solvent for freeze drying: (1) For solvents whose surface temperatures are considerably below the eutectic temperature a small value of the latent heat of sublimation is desirable; or for those whose melting points limit the heat input, a high equilibrium vapour pressure at the melting point is required. (2) A low freezing point depression. (3) A high solubility of the solute. Acetic acid was shown to be a useful solvent for preparing Co2 NiO4 spinel. A computer model of the drying process was modified to take account of added solutes and solvents other than water. © 1979 Chapman and Hall Ltd.