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 med ium involves a reaction process which is controlled by out-of-equilibrium s teps. The reaction product, the yield and the colloidal stability then stro ngly depend on the process. In particular, the rate of addition of the wate r in the reaction medium is of importance. Its influence was investigated b y 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 conv ersion. A progressive addition of water leads to stable suspensions of calc ium 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 di stribution and with lower yields. The transient formation of calcium hydrox ide colloidal particles is proposed as the origin of the formation of large r particles found in the one-shot process. (C) 2000 Elsevier Science B.V. A ll rights reserved.