The transpiration method

The transpiration method is a simple and versatile method for vapor pressure measurement at high temperatures. An inert carrier gas is passed over the condensed substance in a constant temperature furnace zone. The flow rate of the carrier gas is constant and sufficiently small so that the carrier gas is saturated with vapor, which condenses at some point downstream. The mass of vapor transported by a known volume of carrier gas is determined. If the total vapor pressure is known, from the boiling point method, the results from the transpiration method may be used to calculate the average molar mass of the vapor. 

Assumption (iii) is important, which avoids uniform total pressure in the apparatus, assumed in the former works. 

Similarly as in the theoretical treatment of the boiling point method discussed in Section 7.2.1.1., the correct transport equations for a binary gaseous mixture with gradients in both composition and total pressure are also applied to the case of the transpiration 

The relation between the flow rates n of carrier gas and ti2 of vapor, the total pressure Pf at the exit end of the capillary, and the equilibrium vapor pressure Pa can be written in the form 

For the explanation of parameters A, C, and y, look into the theory of the boiling point method. The above equations consider diffusion and flow of vapor only through the exit capillary of the apparatus. The equations become very complex when the diffusion upstream through the entrance capillary is taken into account. Their application is not practical, as they contain too many unknown parameters. 

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During the course of exploratory experimentation involved in the preparation of 8-242pU203, some limited oxygen potential measurements over Pu02-X fluorite phase were made at 1750 and 2050 K. The transpiration method was used for this study because, for a given temperature, the composition of the condensed phase can be fixed by appropriate choice of oxygen potential (via H2/... 

Second, no work has yet been done on the application of the transpiration method to the preparation of samples for chemical analysis. In this area the same strictures on odour sampling apply, even where sub-ambient-temperature trapping techniques are used. Especially where cryogenic trapping is proposed, preparation of the odour sample in the laboratory is a considerable advantage. 

Vasiltsova, T.V. et al.. Thermodynamic properties of mixtures containing ionic liquids. Activity coefficients of ethers and alcohols in l-methyl-3-ethyl-imid-azolium bis(trifluoromethyl-sulfonyl)imide using the transpiration method, /. Chem. Eng. Data, 50,142,2005. 

The molar enthalpy of formation of [C4mim][DCA] was determined to be 206.2 2.5 kJ mol-1 with combustion calorimetry [27], The molar enthalpy of vaporization of [C4mim][DCA] (157.2 1.1 kJ mol"1) was obtained from the temperature dependence of the vapor pressure measured using the transpiration method. The... 

In using the transpiration method for determining the average molar mass of the vapor, one should carry out the following ... 

Cordfunke [484] recently investigated the vaporization of cesium iodide in the vicinity of the melting point by the transpiration method. 

Taking the minimum numbers obtained by v. Wartenberg and me (3) by the transpiration method, which constituted the first accurate determinations of the dissociation of water vapour, and may be still the most reliable, we have... 

Verevkin, S. P. Safarov, J. T- Bich, E. Hassel, E. Heintz, A. Thermodynamic properties of mixtures containing ionic liquids. Vapor pressure and activity coefficients of n-alcohols and benzene in binary mixtures with l-methyl-3-butyl-imidazolium bis(trifluoromethyl-sulfonyl) imide using the transpiration method Fluid Phase Equilib. 2005,236, 222-228... 

The transpiration method is adequately discussed by Thomson, but there has been one recent development the use of a flame-ionization... 

A recent and promising modification of the transpiration method incorporates levitation heating of the specimen as problems associated with specimen + container reactions are thereby avoided. Thus Svyzahineto/. have combined levitation melting with transpiration measurements, using argon as carrier gas, in determinations of the vapour pressure of iron at temperatures around 2275 K, and Mills and Kinoshita have used... 

The decomposition pressures of ZrCl4 have also been measured by the transpiration method.The transported zirconium chloride condensate was dissolved and analyzed spectrographically for the Zr content. 

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