The use of isothermal TGA with Knudsen-like cells allows determination ofthe thermodynamic activity of water, aW. The typical experiment implies aslow dehydration of the aqueous solution atconstant temperature in dynamic vacuum conditions.The method is alternative to the classical isopiestic approach and offers the advantage of a continuous record on increasing the solute concentration. These data can be directly treated according to the classical thermodynamic relationships drawn from the Gibbs-Duhem expression to evaluate the activity and osmotic coefficient of the aqueous solutions of electrolytes and non-electrolytes, and, in the case of electrolytes, allow determination of solubility of the solute. Discrepancies with respect to the literature data are observed when the viscosity of the systems becomes too high, as in the case of sugars with a very large solubility. Such a mismatch may however be accounted for either slowing the dehydration rate with use of a narrower Knudsen orifice, or correcting the experimental aW with a calibration curve. The same approach can be applied to non-aqueous solutions.
Compounds
#
Formula
Name
1
ClNa
sodium chloride
2
ClK
potassium chloride
3
KNO3
potassium nitrate
4
H2O
water
Datasets
The table above is generated from the ThermoML associated json file (link above).
POMD and RXND refer to PureOrMixture and Reaction Datasets. The compound numbers are included in properties, variables, and phases, if specificied;
the numbers refer to the table of compounds on the left.