The dehydration kinetics of BaCl2.H2O powders were examined as a finction of water vapor pressure, sample bed depth, particle diameter and temperature. The conversion behavior were modeled in both kinetic and the combined diffusion and kinetic limited regimes with modified forms of the Avrami-Erofe'ev equation. Kinetic data were obtained by the thermogravimetric techniques and by calorimetry. Structural data for interme diates and products were obtained by X-ray diffraction and optical microscopy. Dehydrations were conducted isothermally between 317 an d 335 K either under vacuum or in controlled pure water vapor atmospheres ranging from 40 to 6.67 X 10^2 Pa.
The dehydration rate decreased as the water vapor pressure, bed
sample
depth and particle diameter increased. The estimated bed diffusivity is
1.0 X 10^ (-6) cm^2 s^-1. After a critical pressure was exceeded, severe
reductions in rate were observed. The dehydration of BaCl2.H2O proceeded
stepwise via the crystalline monohydrate above about 80 Pa at 317 K;
below
this pressure the crystalline monohydrate was not observed. Transient
increases in water vapor pressure in the sample bed caused
crystallization of the monohydrate under conditions where it did not
otherwise form.