GROWTH OF BETA-LINASO4 AND LI2SO4-CENTER-DOT-H2O - EPITAXY AND INTERGROWTH PHENOMENA

Isothermal crystallization in the system Na2SO4-Li2SO4-H2O was carried out at 50 degrees C by ''salting out'' in a tetrametoxysilane (TMS) gel medium. Under these conditions the solid phases that can crystallize are Na,SO,, Li2SO4.H2O and beta-LiNaSO4, depending on the initial composition of the gel interstitial solution. When the initial [Na2SO4]/[Li2SO4] molar ratio in the interstitial solution is smaller than 1, first beta-LiNaSO4 crystallizes and, subsequently, Li2SO4.H2O. The nucleation of Li2SO4.H2O is always heterogeneous and occurs epitaxially on the surface of beta-LiNaSO4 crystals. Occasionally, successive heterogenous nucleation events promote the development of intergrowth phenomena. In this paper a detailed study of both epitactic growth and crystal morphology is worked out. Finally, the observed epitaxial relationships are interpreted on the ground of structural considerations.