Vapor pressure determination by thermogravimetry

A method for measuring the vapor pressures of a wide range of materials usi ng a conventional thermobalance and standard sample holders is described. T he equipment is calibrated using pure reference materials of known vapor pr essure and exploiting the relationship between volatilization rate and vapo r pressure based on the Langmuir equation for free evaporation. Enthalpies of vaporization and sublimation can be determined, in some cases, the melti ng temperature and enthalpy of fusion can be obtained directly from thermog ravimetry. Applications to the study of plasticizers and UV absorbers are d escribed. Poor correlation of experimental results with predicted values ob tained by molecular modeling is found. The application of modulated tempera ture thermogravimetry for the determination of enthalpies of sublimation an d vaporization is also explored. (C) 2001 Elsevier Science B.V. All rights reserved.