Jimmie G. Edwards

High‐Temperature Mass Spectrometry, Vaporization, and Thermodynamics of Titanium Monosulfide

A high temperature mass spectrometric investigation of the congruent vaporization of vanadium monosulfide, VS(s), from 1700 to 2000°K has shown that the two principal vaporization reactions produce VS(g) and V(g) + S(g) with a minor contribution from the reaction to produce VS2(g) + V(g). Thermodynamic results were obtained from three investigations of the congruent vaporization of the stoichiometric monosulfide. The second law enthalpy changes for the vaporization reactions at absolute zero were calculated from the experimental data and by use of a measured low temperature heat capacity for VS(s), estimated heat capacities for the solid above room temperature and for the vapor molecules, and literature values for the heat capacities of the atomic species. The Δ H0° values obtained and the estimated uncertainties are: 143±3 kcal for the reaction to form VS(g), 259±5 kcal for the reaction to form V(g) + S(g), and 144±5 kcal for the reaction to form ½ VS2(g) + ½ V(g). Ionic fragmentation of VS+ is considere...

Vaporization chemistry and thermodynamics of the lead–indium–sulfur system by computer‐automated Knudsen and torsion effusion methods

Vaporization of PbIn2S4(s) was studied by computer‐automated simultaneous Knudsen and dynamic torsion effusion. Vapor pressures and the apparent molecular weight of the effusing vapor were displayed in real time. The vaporization reaction was PbIn2S4(s)=In2S3(s)+PbS(g). The vapor pressure was measured 108 times in the temperature range 948–1086 K. For the vaporization reaction, third‐law analyses gave ΔH°(298 K)=253.0±0.1 kJ/mol. The enthalpy of PbIn2S4(s) with respect to its constituents PbS(s) and In2S3(s) was −23±4 kJ/mol. The apparent molecular weight showed stoichiometry changes in indium sulfide during the experiment. Residual indium sulfide, remaining after loss of all PbS, vaporized with some nonstoichiometry by In2S3(s)= In2S(g)+S2(g). The vapor pressure of the residual indium sulfide was measured 57 times in the temperature range 1035–1121 K;third‐law analyses yielded ΔH°(298 K)=613.4±0.4 kJ/mol for the dissociative vaporization reaction. The compound Pb2In6S11(s), found at lower temperatures, h...

Effusion from Spherical Orifices. I. Transmission by Molecular Flow

Molecular flow through orifices which are spherical segments is treated by a method analogous to that which previously has been applied to cylindrical and conical orifices. The integral equation which expresses the rate at which molecules impinge on a unit area is shown to possess a simple, closed‐form solution for spherical orifices, and the transmission probability for such orifices is derived in closed form. Transmission probabilities are presented for several spherical orifices and are shown to be always larger than those for conical or cylindrical orifices of the same dimensions. For very short and very long divergent spherical orifices the transmission probability approaches unity, and at intermediate lengths it passes through a minimum. For very short spherical orifices with equal and parallel plane entrance and exit, the transmission probability approaches unity, and it decreases to a limiting value of one‐half for very great length.