NEW CRITERION OF QUANTITATIVE ESTIMATE OF THE CORRELATION OF SURFACE AND VOLUME PROCESSES DURING CRYSTAL GROWTH FROM SOLUTION. A.M. Askhabov, Inst. of Geol., RAS, Syktyvkar, Russia

Criterion is based on real concentration conditions, taking place at the time of crystal growth on boundary layer. The criterion is introduced as a relation of surface [[sigma]]S and volume [[sigma]] supersaturation, i.e. [[sigma]]=[[sigma]]S/[[sigma]], (1). If [[sigma]]S=[[sigma]] then [[eta]]=1, and crystal growth is fully controlled by the surface processes. If [[sigma]]S=0 then [[eta]]=0, and growth regime is fully diffusion. Both extreme cases do not take place in real life and always 0<[[eta]]<l. Quantitative character of the criteria [[eta]] makes it comfortable to use it for comparison of growth, regimes of different crystals, growing in different conditions, but in the same supersaturation of solutions. In fact [[eta]] is a dimensionless criterion of similarity, characterising the relative role of surface and volume processes. The unknown supersaturation on the growing surface [[sigma]]S, necessary for calculation of [[eta]], for layer crystal growth is given by the following expression [[sigma]]S=[[sigma]]*[(1+4[[sigma]],/[[sigma]]*)l/2- 1]/2 (2). Substituting (2) into (1) we get that [[eta]]=[[sigma]]*[(1+4[[sigma]],/[[sigma]]*)1/2- l]/2[[sigma]], or transforming [[eta]]=(l+[[eta]][[sigma]]/[[sigma]])- l (3). In the expressions (2) and (3) constant for given conditions of growth parameter [[sigma]]*=Kd[[rho]]/,[[beta]]C0, where Kd- coefficient of mass- transfer, [[rho]]- crystal density, [[beta]]- average kinetic coefficient, C0- equilibrium concentration.

Parameter [[sigma]]* directly defines out of experimental dependencies of growth rates on supersaturation in the volume of solution. From the same dependencies V([[sigma]]) we find Kd, through which hydrodynamic conditions influence on growth regime. This approach was used for establishment of growth regime of crystals, growing from water solutions. Calculation kinetic data for some crystals, growing in different conditions, the role of surface and volume processes is comparable in all the range of reasonable supersaturation.