Yi. Aristov et al., Selective water sorbents for multiple applications. 11. CaCl2 confined to expanded vermiculite, REACT KIN C, 71(2), 2000, pp. 377-384
This paper presents the water sorption properties of a new selective water
sorbent based on expanded vermiculite as a host matrix and calcium chloride
as a hygroscopic salt. Sorption isobars, isosters and isotherms at T = 30-
150 degreesC and vapor partial pressure 8.2-42.0 mbar clearly show that at
low water contents crystalline hydrates with 0.33, 1 and 2 molecules of wat
er per 1 molecule of CaCl2 are formed in the pores. These hydrates are stab
le over a temperature change of 20-30 degreesC and exhibit kinetically slow
transformations. At higher water uptake, the vapor absorption leads to the
formation of a CaCl2 aqueous solution inside the pores, which properties a
re close to those in the bulk. Isosteric sorption heat was found to depend
on water sorption and change from 76.3 kJ/mol for solid hydrates to 39.1-46
.6 kJ/mol.