Thermochimica Acta 460 (2007) 15–21 Assessment of systematic errors in measurement of vapor pressures by thermogravimetric analysis Federica Barontini a , Valerio Cozzani b,∗ a Dipartimento di Ingegneria Chimica, Chimica Industriale e Scienza dei Materiali, Universit` a degli Studi di Pisa, via Diotisalvi n.2, 56126 Pisa, Italy b Dipartimento di Ingegneria Chimica, Mineraria e delle Tecnologie Ambientali, Alma Mater Studiorum – Universit` a di Bologna, viale Risorgimento n.2, 40136 Bologna, Italy Received 9 March 2007; received in revised form 19 April 2007; accepted 1 May 2007 Available online 6 May 2007 Abstract The present study explores the application of the diffusion limited evaporation theory to the estimation of vapor pressure from TG experimental data. A simplified method was developed to calculate the apparent values of the vapor pressure of pure substances from TG data, based on isothermal TG runs with crucibles having different surface areas available for evaporation. Antoine parameters are estimated through a numerical procedure based on a non-linear least square algorithm. The procedure also evaluates the substance diffusivity in nitrogen. The methodology developed might be used for a preliminary screening of the vapor pressure of pure compounds, due to the limited amounts of sample that are necessary and to the limited time frame required for the experimental runs. However, the estimation of diffusivity and vapor pressures values by the TG technique is possible with limited accuracy. Possible sources of error were thoroughly investigated and discussed. © 2007 Elsevier B.V. All rights reserved. Keywords: Thermogravimetric analysis; Evaporation rate; Vapor pressure; Diffusive evaporation; Data analysis 1. Introduction Several techniques are currently used for measurement of the vapor pressure of a pure substance [1–3]. The vapor pressure is usually determined by either ebulliometric or static methods [1–6]. In ebulliometric (or dynamic) methods, the vapor pres- sure is determined by measuring the boiling temperature of the substance at various specified pressures or, as in comparative ebulliometry, comparing the vapor pressure to that of a refer- ence substance [7–10]. In static methods, the vapor pressure established in a closed system at thermodynamic equilibrium is determined at a specified temperature [11–15]. These con- ventional techniques for vapor pressure measurement are highly accurate and reliable. However, they require rather large amounts of sample (millilitres) and are time-consuming. Several alter- native experimental methods for vapor pressure determination are described in the literature, and include gas chromatography (GC) [16], effusion [17,18] and gas saturation methods [19–22]. ∗ Corresponding author. Tel.: +39 051 2093141; fax: +39 051 581200. E-mail address: valerio.cozzani@unibo.it (V. Cozzani). Recently, a thermal analyzer was adopted as a transpiration apparatus for vapor pressure measurement [23]. Several attempts have been made to use thermal analysis tech- niques as alternative screening tools for the determination of vapor pressure [24–47]. The use of differential thermal analysis (DTA) and differential scanning calorimetry (DSC) was pro- posed [24–28], and a standard method for the measurement of vapor pressure by DTA or DSC was developed by the American Society for Testing and Materials [48]. Thermogravimetry (TG) was proposed as well for estimating the vapor pressures of pure substances [29–45] and of mixtures [46,47]. Compared with conventional techniques for vapor pressure measurement, ther- mogravimetry presents several advantages: the simplicity of the experimental set-up, the small amounts of sample (microlitres) and short experimental times required. However, the absence of sample mixing, the possible heat transfer and mass transfer limitations as well as the open configuration inherently limit the accuracy of the vapor pressure data that may be obtained by this technique. Moreover, the procedure for the estimation of vapor pressure data from experimental TG weight loss data is still con- troversial. Most of the former studies [31–41,44,45] proposed to derive information on vapor pressure from TG experimen- 0040-6031/$ – see front matter © 2007 Elsevier B.V. All rights reserved. doi:10.1016/j.tca.2007.05.005