Synthesis and characterization of KAlSiO<inf>4</inf> polymorphs on the SiO<inf>2</inf>-KAlO<inf>2</inf> join

Abstract

High-temperature phase transformations of K-LTA zeolite were investigated in the temperature range 800-1800°C. The nano-structured KAlSiO4 precursor was prepared at 850°C and after annealing at 1000°C, the first polymorph of KAlSiO4, synthetic kaliophilite was formed. With increasing temperature, the following polymorphs were synthesized: kalsilite (1100°C), low KAlSiO4-O1 (1200°C), KAlSiO4-ANA (1300°C), and high KAlSiO4-O2 at (1430°C). Synthetic kaliophilite and KAlSiO4-ANA phases are the new polymorphs in the system studied. Consequently, the KAlSiO4-ANA phase is the ANA-type end member of the zeolite framework having the ratio Si/Al = 1. From XRD powder patterns a distorted leucite unit cell for a KAlSiO4-ANA phase was calculated: a0 = 13.638(6) Å, b0 = 13.811(8) Å, c = 13.817(9) Å, α0 = 99.98(4)°, β0 = 102.28(4)°, and γ0 = 62.80(4)°. 29Si MAS NMR chemical shifts at -89.08 and -98.01 ppm suggest that the KAlSiO4-ANA phase has an ordered framework cation topology. © 1995 Academic Press. All rights reserved.