Crystallization of β"-LiNH4SO4 and (NH4)2SO 4 in gels: growth morphology and epitaxy phenomena

Abstract

The crystallization sequences in the system (NH4)2SO4 Li2SO4-H20 at 50C have been studied for solutions with an initial [(NH4)2SO4]/[LizSO4] molar ratio higher than l. The crystal growth experiments were carried out under isothermal conditions in a gel medium, where supersaturation was achieved by "drowning out". The phases obtained are [The crystallization sequences in the system (NH4)2SO4 Li2SO4-H20 at 50C have been studied for solutions with an initial [(NH4)2SO4]/[LizSO4] molar ratio higher than l. The crystal growth experiments were carried out under isothermal conditions in a gel medium, where supersaturation was achieved by "drowning out". The phases obtained are [β"-LiNH4SO4 (LAS) and (NH4)2SO4 (AS). The similarities exhibited by the structures of both compounds favours the development of orientational overgrowth phenomena. The main epitaxial relationship found is the parallelism between [0 0 1]LAS and [1 0 1]AS- The most common contact planes are (0 1 0)LAS and (1 0 1)As. Although less frequent, other epitaxial relationships have also been observed: (0 1 0)LAS ║(0 1 0)AS and [1 0 0]Las ║ [1 0 0]AS. The development of the overgrowth is interpreted on the grounds of the structural considerations and the characteristics of the crystallization medium.