Epitaxial growth of zeolite X on zeolite A and twinning in zeolite A: structural and topological analysis

Synthesis of large zeolite A and X crystals by a modified Charnell's method led to the formation of twinned zeolite NaA crystals, overgrowth of NaX on to NaA and co-crystallization of another phase analysed by electron micropr obe as a Na aluminosilicate but not yet identified. Single crystals of NaA have a perfect cubic habit with a 100 mu m edge. Twinned crystals of NaA ar e of the same size and correspond to an intergrowth of two cubes like that found in twinned fluorite crystals. NaX single crystals are octahedral, 220 mu m along the [100] direction. Based on the difference in morphology of A and X crystals, epitaxial growth of NaX zeolite on NaA was also clearly id entified by scanning electron micrographs. The object of this contribution is to provide topological and structural information on the twinning and ep itaxy.