Kinetics of nucleation in solutions

Some results of experiments on the kinetics of nucleation from water solution are presented in this paper. The experimental work, carried out in the Research Institute of Inorganic Chemistry inÚstínad Labem is based on measuring the width of the metastable zone of concentrations under varying conditions. When the supersaturation P exceeds a certain limit the nucleation rate increases very rapidly; in a system where the supersaturation is achieved by moderate cooling it is practically impossible for the concentration to exceed the limit of metastable supersaturation under given conditions and, therefore, the nucleation rate at the beginning of nucleation will be identical with the supersaturation rate for a limited period of time, i.e. dmzdτ=kPm=k1b where k1 represents the weight of the substance precipitated by cooling a unit volume of the saturated solution by 1 °C and b is the cooling rate (°C/hr). From the measurements of the metastable zone width P at various cooling rates b the kinetic constant of nucleation k and the order of nucleation m can be calculated. The measurements were carried out by using many different systems of salt solutions. The measuring and evaluation method is described in the paper, the results of the measurements are discussed and some generalized conclusions are presented. Data obtained according to the described method may be used for calculation of crystal product size in a commercial crystallization unit.