The dehydration kinetics and microtexture of analcime from two parageneses

The dehydration behavior of an analcime formed by ion exchange from leucite (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 analcime). 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 fit 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 H-type analcime. Washed and ultrasonically cleaned samples of the same grain size have very different BET (N adsorption) surface areas, being 20 m²/g for X-type analcime and 2 m²/g for H-type analcime, consistent with the high porosity of the surface of X-type analcime, as observed by SEM. Further analysis of the N adsorption data shows the pore size distribution for the X-type analcime to have a maximum at 100 Å. The rate of Na drift under electron microprobe is more than 15 times higher for X-type analcime than for H-type analcime and could be a convenient means of distinguishing the two parageneses.