REVERSIBLE COLOR CHANGES IN ZEOLITE-A TREATED WITH AMMONIUM POLYSULFIDE

A method for synthesis of ultramarine analogues, that consists of gene ration of the radical anion S-3(.-) inside zeolites has been developed , previously. Ammonium polysulfide has been used as the S-3(-) radical precursor for modification of zeolites A, X and hydroxysodalite. It w as found that modification of zeolite NaA results in a thermochromic e ffect; the product being blue at temperatures above 520 degrees C and almost colourless on cooling; the colour change is reversible. The sam ple preserves the LTA structure regardless of the thermal treatment. T he original structure is also preserved in the other modified zeolites studied although hydroxysodalite turns blue whilst zeolite X remains colourless.