Growth of β-LiNaSO4 and Li2SO4 . H20: epitaxy and intergrowth phenomena

Abstract

Isothermal crystallization in the system Na2SO4-Li2SO4-H20 was carried out at 50°C by "salting out" in a tetrametoxysilane (TMS) gel medium. Under these conditions the solid phases that can crystallize are Na2SO4, Li2SO4 . H20 and β-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 β-LiNaSO4 crystallizes and, subsequently, Li2SO4 • H20. The nucleation of Li2SO4 • H20 is always heterogeneous and occurs epitaxially on the surface of β-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.