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A revised equation for estimating the vapour pressure of low-volatility substances from isothermal TG data

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Abstract

Previous investigators have used the Langmuir vaporisation relation to estimate the vapour pressures of low-volatility compounds from thermogravimetric data. However, this equation is strictly valid for evaporation into a vacuum only. For measurements conducted at finite pressures, molecular diffusion must be taken into account. A revised equation is proposed: dm A/dt8M A P A D A B/T. It is also shown that the proportionality between vapour pressure and vaporisation rate is very general. It arises from the assumptions of ideal gas behaviour, Raoult's law and a negligible concentration of the sample compound far from the sample surface.

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Authors and Affiliations

  1. Institute of Applied Materials, Department of Chemical Engineering, University of Pretoria, Lynnwood Road, Pretoria, South Africa

    W. W. Focke

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  1. W. W. Focke
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Focke, W.W. A revised equation for estimating the vapour pressure of low-volatility substances from isothermal TG data. Journal of Thermal Analysis and Calorimetry 74, 97–107 (2003). https://doi.org/10.1023/A:1026325719190

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