SEEDING EFFECTS ON CRYSTALLIZATION OF KALSI3O8, RBALSI3O8, AND CSALSI3O8 GELS AND GLASSES

Crystallization of stoichiometric KAISi(3)O(8), RbAlSi3O8, and CsAlSi3O8 gels (single-phase and multiphasic gels) and glasses with and without seeding has been investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM), and energy dispersive spectrometry (EDS). The pure gels of K-, Rb-, and Cs-feldspar compositions crystallized mainly to leucite (KAISi(2)O(6)), a Rb analogue of leucite (RbAISi(2)O(6)), and pollucite (CsAISi(2)O(6)), respectively. The KAISi(3)O(8) glass also yielded leucite. No feldspar phases crystallized in the temperature region studied, The leucite crystallization temperature was lowered by using multiphasic gels. The crystallization sequence of the KAISi(3)O(8) glasses and single-phase gels did not change upon seeding with isostructural feldspar crystals, No significant crystallization effects mere detected with the use of RbAISi(3)O(8) and CsAISi(3)O(8) multiphasic gels. However, K-feldspar (sanidine) was crystallized by using both compositionally and structurally different gels of KAISi(3)O(8), i.e., multiphasic gels seeded with feldspar crystals. The microstructure of oriented sanidine crystals around the seeds indicated an epitaxial crystallization mechanism.