THE DEHYDRATION KINETICS AND MICROTEXTURE OF ANALCIME FROM 2 PARAGENESES

The dehydration behavior of an analcime formed by ion exchange from le ucite (X-type analcime, or secondary analcime) is contrasted with the behavior of an analcime formed by hydrothermal recrystallization from structurally dissimilar materials (hydrothermal analcime, or H-type an alcime). The kinetics of dehydration of X-type analcime is consistent with a high specific surface area, showing surface equilibration with H2O vapor and fast initial H2O loss. The kinetic data approximately fi t the Austin-Rickett equation, yielding an empirical activation energy for the dehydration of X-type analcime of 33 kJ/mol, compared with 92 kJ/mol for I-I-type analcime. Washed and ultrasonically cleaned sampl es of the same grain size have very different BET (N adsorption) surfa ce areas, being 20 m(2)/g for X-type analcime and 2 m(2)/g for II-type analcime, consistent with the high porosity of the surface of X-type analcime, as observed by SEM. Further analysis of the N adsorption dat a shows the pore size distribution for the X-type analcime to have a m aximum at 100 Angstrom. The rate of Na drift under electron microprobe is more than 15 times higher for X-type analcime than for H-type anal cime and could be a convenient means of distinguishing the two paragen eses.