The synthesis of colloidal particles of calcium thiophosphates in a microemulsion: influence of the parameters of the process

The synthesis of colloidal particles of calcium thiophosphate from calcium oxide and phosphorus pentasulfide catalyzed by water in a microemulsion medium involves a reaction process which is controlled by out-of-equilibrium steps. The reaction product, the yield and the colloidal stability then strongly depend on the process. In particular, the rate of addition of the water in the reaction medium is of importance. Its influence was investigated by means of a kinetic study where both the products of the chemical reaction and the structure of the suspension were studied as a function of the conversion. A progressive addition of water leads to stable suspensions of calcium thiophosphate particles of small size with high yields. On the contrary, a one-shot addition of water leads to a suspension with a bimodal size distribution and with lower yields. The transient formation of calcium hydroxide colloidal particles is proposed as the origin of the formation of larger particles found in the one-shot process.