Sorption Properties of Calcium Chloride Dispersed in Silica Gel Pores
Russian Journal of Physical Chemistry A
, E-ISSN: 1531-863X
Boreskov Institute of Catalysis SB RAS
Novosibirsk State University
The phase composition of composite sorbents "calcium chloride in mesopores of silica gel" with different contents of the salt was studied by differential dissolution and x-ray powder diffraction analysis. Their sorption equilibria with water vapors were studied by thermogravimetry in a temperature range from 20 to 200degreesC at p = 10 to 50 mbar. It was shown that calcium chloride interacts with silica gel to form two phases in pores, namely, crystalline bulk and x-ray amorphous surface phases. The ratio between these phases depends on the salt content of the composite; the fraction of the crystalline phase grows with an increase in the salt concentration. The sorption equilibrium between composite sorbents and water vapors was found to be sensitive to the ratio between the crystalline and x-ray amorphous phases. It was demonstrated that vapor sorption by high-salt sorbents, in which the salt is predominantly crystalline, is accompanied by the reaction CaCl2 + 2H(2)O reversible arrow CaCl2 . 2H(2)O; the sorbed water amount in pores changes stepwise. In low-salt sorbents with an x-ray amorphous salt phase, the composition of the condensed phase in pores changes continuously, which is typical of solutions of salts or their hydrates with a vacancy structure.