The thermal transformation of Na LiA zeolites. A new polymorph in the system Li<inf>2</inf>OAl<inf>2</inf>O<inf>3</inf>SiO<inf>2</inf>

Abstract

High-temperature phase transformations of A zeolite with various degrees of exchange of Na+ with Li+ ions were investigated. An increase in the number of Li+ ions per unit cell accelerates the thermal transformation of the zeolite framework to the amorphous state. Above 730°C, four phases (carnegieite, nepheline, β-eucryptite, and a new phase-γ-eucryptite) were identified. Only γ- and β-eucryptite phases were obtained from pure LiA zeolite. γ-eucryptite is a new metastable polymorph in the system Li2OAl2O3SiO2. γ-eucryptite a0 = 7.231(3)Å, b0 = 10.270(6) Å, c0 = 12.054(7) Å) is transformed to β-eucryptite (a0 = 10.533(5) Å, c0 = 11.148(5) Å) above 840°C. © 1986.