Large Particle Ammonium Molybdophosphate: Preparation and Crystallization Kinetics

Large particle ammonium molybdophosphate (AMP) was prepared by slowly dropping a nitric acid solution of potassium pyrophosphate into an ammonium molybdate solution. The nucleation rate (G) and crystal growth rate for AMP were studied. Compared with crystal growth, the nucleation has a higher reaction order. Initially, large particle AMP crystallizes in the kinetic region controlled by phase transfer reaction when the growing speed of supersaturation is higher than the removing speed. The crystal linear growth rate (L) and supersaturation degree (AC) of the solution increases first and decreases thereafter. In the medium dropping stage, the increase in removing speed of supersaturation is the same as the growing speed. During the late dropping stage, the nucleation rate rises rapidly when the crystal linear growth rate decreases and the nucleation rate is the only control step for the removing speed of supersaturation. Therefore, the nucleation of AMP almost completes in local solution as soon as meeting the nitric acid solution.