Torsion-effusion method

Cubicciotti et al.5 used a torsion-effusion method to determine decomposition pressures in the range 723 to 767 K and found only S02 in the vapor. They surmised that the salt is in metastable equilibrium with respect to disproportionation below 775 K. 

The vaporization of K2S04 was studied by the torsion-effusion method, and by mass spectrometry in the range 1180 to 1280 K.61 Sublimation contributes 63% of the flux, and decomposition... 

The vaporization/decomposition of Rb2S04 has been studied by mass spectrometry and the torsion-effusion method.23 Molecular vaporization accounts for 75% of the total, with the decomposition... 

Both reactions were studied by Brittain, Lau, Knittel, and Hildenbrand102 using a torsion-effusion method in the temperature range 800 to 900 K. They found the S03 pressure over both the sulfate and oxysulfate derived from extrapolation of steady-state pressures to the zero orifice area to be a factor of five lower than those calculated from established thermodynamic data. This indicates that the products are formed in a finely divided metastable state. 

Balson, E.W. (1958) The Measurement of Vapour Pressure by Torsion-Effusion Method Surface Phenomena in Chemistry and Biology. Pergamon Press, Oxford, England. 

H. Wagner and K. Neumann, Z. Phys. Chem. 51 (1961), torsion-effusion method. 

In the present review, the enthalpies of formation at 625 K in Table III of the paper were recalculated to 298.15 K using the selected heat capacities of Se(cr, I), Se2(g), and Se5(g)-Ses(g) to provide for a comparison with other investigations. Similarly, third law enthalpies of formation and second law entropies were evaluated by combining the data of Table 111 in the paper and the total pressure measurements by the Knudsen torsion-effusion method in the same paper with the selected values for the heat capacities and entropies. The results are summarised in the Table A-70. 

The total vapour pressure measured by the torsion-effusion method was given as log, (p/bar) = (6.84 0.12) - (6350 + 70) T . The expression was re-evaluated by matching observed and calculated total pressures considering all species in the series Se(g)-Scg(g) and Hg(g). The selected thermodynamic data of the selenium species and the CODATA [89COX/WAG] values of mercury were used. A stoichiometric composition of the gas phase was assumed. The mole fractions of the most important selenium species are given in Table A-l 13. 

This is a careful study of the vaporisation chemistry of the indium-selenium system using simultaneous Knudsen effusion and torsion effusion methods, by X-ray powder diffraction, and by sealed tube and closed cell methods. It was found that In2Se3(cr) vaporises incongruently according to the simultaneous reactions 41n2Se3(cr) 2104805(1) +... 

The sublimation of ThBr4(cr) was studied in the temperature range 631 to 768 K by the torsion-effusion method. Supplementary mass-spectrometric measurements indicated that only monomeric ThBr4(g) exists in the vapour at these temperatures, in agreement with the molecular weight derived from the torsion-effusion measurements. The entropy of sublimation was considered to be more consistent with a distorted tetrahedral stmc-ture, but later theoretical studies indicate that the ThBr4(g) molecule, in fact has tetrahedral symmetry, as discussed in Section VIII.3.1.4.1. 

Among the most reliable methods for measuring the vapour pressures of solids as a function of temperature are the mass loss [86] or torsion [87] Knudsen effusion techniques. The torsion-effusion method is a complementary method to mass-loss effusion and both have often been measured simultaneously [88,89]. This combination provides additional information useful in assessing the presence of association in the vapour because vapour pressure information is provided that is dependent (mass loss) and independent (torsion) of the molar mass of the effusing vapour. 

As cited previously, one of the most successful methods for the indirect determination of enthalpies of sublimation is based on the Knudsen-cell mass-loss effusion methods. Recently equipment has been described with three [189] and nine [190] Knudsen cells used for simultaneous measurements. The torsion effusion method has been used recently to determine enthalpies of sublimation of uracil derivatives [191] and sublimation enthalpies have also been determined in drop calorimeters [192,193]. 

The only thermodynamic study of the system was performed by [1989Hay] who used torsion effusion method for measuring Mn vapor pressure in alloys with iron to cobalt ratio 1.05 and Mn content 10.8 to 93.7 at.% at 977 to 1177°C. The alloys of the Fe-Mn and Co-Mn edges with the same Mn content range were also studied. 

The Knudsen and torsion-effusion methods have been combined in a single apparatus, for example by Lindscheid and Lange. In this work the torsion cell was suspended from a microbalance, thus enabling simultaneous observations of mass loss and cell rotation to be made. The values of vapour pressure calculated from the two sets of results can be combined through the Knudsen and torsion-effusion equations to obtain the molar mass of the vapour species. Lindscheid and Lange carried out such measurements for Fe, Co, and Ni, and for Ni + Co alloys. 

Brunetti B, Piacente V, Scardala P (2008) Vapor pressures and sublimation cmthalpies of copper difluoiide and silver(I, II) fluorides by the torsion- effusion method. J Chem Eng Data 53 687-693... 

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