Abstract
The hydrothermal synthesis of solid solutions between aluminosilicate and gallosilicate mordenites was performed in the system Na2O-TEA2O-Al2O3-Ga2O3-SiO2-H2O, and the continuous solid solution has been obtained though some doubt exists still as to the phases formed in the vicinity of 0.5 for the Ga2O3/(Al2O3+Ga2O3) molar fraction of gel. The Ga end-member contains alumina which came from impurity alumina present in silica source and hence its Ga2O3 molar fraction was 0.82. Similarly the solid solution formed was contaminated with the impurity alumina. The SiO2/(Al2O3+Ga2O3) molar ratios of solid solution increased with the Ga2O3 fraction of gel and the ratios are 16.9 for Al end-member and 19.8 for Ga end-member.
The solid solutions grew up to 10μm in size and changed morphologically from prismatic to platy shapes with increase of Ga contents of them. The lattice constants a, b and c of Al and Ga end-members are 18.10, 20.46 and 7.51Å, and 18.09, 20.42 and 7.50Å, respectively. Although ionic radius of Ga3+ is larger than that of Al3+, the unit cell volume of the Ga end-member is slightly smaller than that of the Al end-member. The volume contraction in the Ga rich product would be brought about by increasing of the SiO2/(Al2O3+Ga2O3) molar ratio.
A part of TEA base in the structure of the solid solution is present as cations to neutralize negative framework charge, and the remainder is supposed to exist as a neutral form.
