V. Piacente

Mass Spectrometric Study of the GaAs System

The vaporization of GaAs has been investigated by means of the mass spectrometric method. The activity values of the components were determined in a composition range of 50–95 at.% Ga at 1283°K. The heteronuclear gaseous species GaAs was detected by the aid of double‐oven experiments. Its dissociation energy D°298 = 50.1 ± 0.3 kcal mole−1 was determined using the third‐law method. The equilibrium reaction As4⇋2As2 was considered in the study of the vapor over GaAs. Second‐law and third‐law values D°298 = 77 ± 5 and 73.5 ± 0.3 kcal mole−1, respectively, for the As2–As2 bond were obtained. The value D°298 = 71.0 ± 3.0 kcal mole−1 is proposed as a result of comparison with previous determinations.

Vaporization of Aluminum Phosphide

The vaporization of aluminium phosphide was investigated over the temperature range of 1270°–1800°K using the Knudsen effusion method in combination with mass spectrometry. Aluminium phosphide decomposes according to the reaction 2AlP(s) → 2Al(g) + P2(g). The enthalpy for Reaction (1), ΔH°298, as calculated by the second‐ and third‐law method is 261.7 ± 5.9 and 254.8 ± 2.1 kcal/mole, respectively. The second‐ and third‐law enthalpies ΔH°298 for the reaction 4Al(g) + Al2O3(s) → 3Al2O(g) have been determined as − 10.7 ± 2.0 and − 10.5 ± 0.5 kcal/mole, respectively. The error terms given represent the standard deviation. On the basis of a selected value of 255.0 ± 6.0 kcal/mole for the enthalpy of Reaction (1) and of pertinent literature data, the standard heat of aluminium phosphide formation, ΔH°f,298 = − 28.2 ± 3.2 kcal/mole is obtained.

Vapor pressures of calcium and strontium by transpiration method

The vapor pressures of calcium and strontium have been determined by transpiration in the temperature range 1126 to 1300 K and 1086 to 1310 K respectively. The temperature dependence of the vapor pressure is given by the equations: Calcium: log10(p/atm)=(4.93±0.13)−(8550±158)K/T Strontium: log10(p/atm)=(4.75±0.14)−(7720±161)K/T Agreement between second-law and third-law values was obtained for the enthalpy of sublimation of both elements; the values ΔHsubo(Ca, 298.15 K) = (43.0 ± 0.5) kcalth mol−1 and ΔHsubo(Sr, 298.15 K) = (39.5 ± 1.0) kcalth mol−1 are proposed.

Dissociation Energy of the Gaseous AlP Molecule

The Knudsen cell‐mass spectrometric technique has been used to identify the heteronuclear molecule TlBi. The thermodynamic treatment of the data led to a value of the dissociation energy D0° (TlBi)=28 ± 3 kcal mole−1. A comparison between bond energies in condensed and gaseous IIIb—Vb binary compounds is reported.

Dissociation Energy of TiO and TiO2 Gaseous Molecules

Using the Kundsen effusion‐mass spectrometric technique, the reactions: TiO2(g)=TiO(g) + O(g) and TiO2(g) + Ti(g)=2TiO(g) were studied in the temperature ranges 2000°–2250°K and 2150°–2500°K. The dissociation energy of TiO(g) and TiO2(g) were derived from all gas reactions involving only titanium‐oxygen species: D0 ° (TiO)=144 ± 5 and D0 ° (TiO2)=286 ± 10 kcal/mole, respectively. A comparison with the results by other authors is also reported.