Nucleation and growth of ammonium sulphate crystals from aqueous solution

The refractive index, density and viscosity of aqueous solutions of ammonium sulphate have been measured in the range 20‐30°. The solubility of ammonium sulphate was checked over the range 20‐45° by measuring saturation temperatures in a simple apparatus. The same technique was also used for nucleation studies; the maximum allowable undercoolings with and without seed crystals range from ˜ 3.5° and 5°, respectively, for fast cooling rates, to ˜ 1.5 and 3.5° for slow. Growth rates of two major faces (100) and (001) of ammonium sulphate crystals were measured in a flow cell. The (100) face growth rate is directly proportional to the concentration driving force and independent of solution velocity, whereas that of the (001) face appears to be a second‐order process and slightly velocity‐dependent.