To determine the optimal conditions for the synthesis of the solid phase 2MgO.2B2O3.MgCl2.14H2O, its crystallization kinetics from solns. containing 0.65 MgO, 1.14 B2O3, and 24, 28, and 32% MgCl2 was studied. The experiments were carried out without stirring. At different time intervals, solution samples were taken for anal., and their d. and pH were determine until the solution d. remained basically constant Then the solid phase was separated and identified by chem. anal., IR spectra, x-ray powder diffraction, and thermal anal. The crystallization kinetic curves were all in reverse S shape. At <40? the crystal growth rate increased with rising temperature, but at >40?it decreased. At constant 30? the crystallization rate decreased with increasing MgCl2 concentration At the experimental temps. and concns., only 2MgO.2B2O3.MgCl2.14H2O crystd. from the solution An appropriate math. modification of Nielsen's mononuclear-layer and polynuclear-layer controlled-growth mechanism was made. The experimental data were fitted using a simple optimum method and a Runge-Kutta solution of a differential-equation system. The kinetic equation of the crystallization reactions is given, and a mechanism of crystallization reactions is proposed.

Key words: REACTION MECHANISM, CAMSELLITE, BORATES, MAGNESIUM OXIDE, HYDRATE, MAGNESIUM CHLORIDE, BORON OXIDE, CRYSTALLIZATION KINETICS, DIFFERENTIAL EQUATION, KINETIC STUDY