Preparation structural and thermal properties of MAlSiO4 (M = Li, Na, K, Rb, Cs, Tl, Ag) of ABW-type
1992; Elsevier BV; Volume: 12; Issue: 8 Linguagem: Inglês
10.1016/0144-2449(92)90153-g
ISSN1873-3115
Autores Tópico(s)Zeolite Catalysis and Synthesis
ResumoThe preparation of new, hydrated and anhydrous members of the ABW class of aluminosilicates using hydrothermal methods or ion exchange in molten salts are described. Of these, NaAlSiO4·0.8 H2O, AgAlSiO4·0.8 H2O, and AgAlSiO4·0.68 H2O contain zeolitic water. Dehydration occurs, within rather narrow temperature intervals, at 450, 330 (partially), and 380 K, respectively. Upon complete dehydration, new, probably ABW type, modifications of AgAlSiO4 and NaAlSiO4 are obtained. Thermal expansion behavior and temperature-induced phase transitions are described for MAlSiO4·x H2O (M = Li, Na, Ag) and MAlSiO4 (M = Li, Na, Rb, Tl, and Ag). The different-sized unit cells, and, accordingly, the axial ratios, of the ABW-type compounds, are discussed in relation to the turning of tetrahedra, which are the essential building units of the crystal structure. Minimum and maximum unit cells, with respect to volume, are described. The differences in thermal expansion behavior found for different MAlSiO4 are discussed in terms of the same concept. At high temperatures, MAlSiO4, M = Li, Na, K, and Ag, transforms into other polymorphs, being, respectively, γ-eucryptite, nephelin, kalsilite, and a cubic F-centered phase related to the cristobalite type. On cooling, cubic AgAlSiO4 transforms reversibly into a triclinic modification of the carnegeite type.
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