THERMAL-ANALYSIS OF CATION-EXCHANGED ZEOLITES BEFORE AND AFTER THEIR AMORPHIZATION BY BALL-MILLING

Zeolite X, synthetic mordenite and zeolite A in which a part of the or iginal sodium ions has been exchanged by other cations (Li+, K+, Cs+) were investigated by means of simultaneous thermal analysis, before an d after mechanochemical amorphization by ball milling. In all the exam ined cases, the initial rate of dehydration of amorphized sample was h igher than the initial rate of dehydration of the original (crystallin e) Samples, and the temperature at which the rate of dehydration is la rgest was lower in the case of the amorphized samples than in the case of the crystalline samples. The influence of cations on the rate of d ehydration and on the critical temperature of dehydration of amorphize d samples was different from the influence of cations on the rate of d ehydration and on the critical temperature of dehydration of the origi nal (crystalline) samples. Analysis of the experimental data led to th e conclusion that the rate of dehydration of crystalline samples is co ntrolled by the diffusion of desorbed water through the channel/void s ystem of the zeolite structure and that the rate of dehydration of the amorphized samples is controlled by the cation-water interactions. Th e observed differences are explained by the difference in the pore sys tem between the original (crystalline) and amorphized samples.