Calculated and experimental mass spectra (at temperatures region of 1100-1500 K) of alkali metals tungstates are presented. Vapor pressures and thermodynamic characteristic of gaseous alkali metal tungstates are determined.

It is shown that the molecular composition of the vapor–gas phase of many chemical compounds and their mixtures, including carbides, nitrides, and oxides, is substantially more complex and diverse than it appeared before. In addition to monomeric molecules, various gaseous molecules of these compounds are detected in the vapors of carbides, nitrides, and oxides. Data on the composition of the vapors of nitrides of almost all the chemical elements from the periodic system as well as thermodynamic properties of gaseous nitrides are presented in this work.

Приведены данные по термодинамике испарения вольфраматов щелочных металлов.

High-temperature mass-spectrometry is used to study the evaporation of Na 2 MoO 4(l) at 1050–1300 K. Na 2 MoO 4(g) molecules are found to be present in the vapor. The partial pressure of Na 2 MoO 4(g) is determined to be log p = 13794/ T + 6.19. The enthalpy of sublimation Δ s H 0 ∘ (Na 2 MoO 4 (s) ) = 352 ± 20 kJ/mol is determined using the third law of thermodynamics. The atomization energy of the Na 2 MoO 4(g) molecules is calculated to be Δ at H 0 ∘ (Na 2 MoO 4(g) ) = 2960 ± 40 kJ/mol.

High-temperature mass-spectrometric analysis is used to study the sublimation of SrMoO4(s) at 1570–1800 K. SrMoO4(g) molecules are found to be present in the vapor. The vapor pressure of the SrMoO4(g) molecule is determined to be log p = −19980/T + 7.99. The heat of sublimation ΔH s, 0 o (SrMoO4(s)) = 480 ± 40 kJ/mol is determined using the third law of thermodynamics. The atomization energy of the SrMoO4(g) molecules is calculated to be ΔH at, 0 o (SrMoO4(g)) = 2860 ± 40 kJ/mol.

High-temperature mass-spectrometric analysis is used to study the evaporation of SrWO 4 (J) at 1805–1890 K. SrWO 4 (g) molecules are found to be present in the vapor. The pressure of the SrWO 4 (g) molecule vapor is determined to be log P = −25052/ T + 7.13. The heat of sublimation (Δ H ° s , 0 (SrWO 4(s) ) = 620 ± 20 kJ/mol) is determined using the third law of thermodynamics. The atomization energy of the SrWO 4 (g) molecules is calculated to be Δ H ° at, 0 (SrWO 4 (g) ) = 3030 ± 40 kJ/mol.

Data are given on the evaporation rates of practically all chemical elements in the periodic table, in units of g/cm(2).sec, at three temperatures (room temperature, the melting point, and the boiling point) and also in the form of tables covering the temperatures corresponding to molecular effusion of vapor in the Knudsen method.

Presented are summary data on vapor pressure and composition, as well as on heat of vaporization and sublimation for the majority of elements of the periodic system. Vapor pressures are given at room temperature and at the melting point. Boiling points, vapor pressures, vaporization and sublimation heat at selected temperatures are presented as well, Published data [1-3] on equilibrium vapor pressure and heat of vaporization of metals are also given.

The sublimation of Cs2MoO4(s) in the range 1026-1148 K is investigated by high-temperature mass spectrometry. The gas phase consists of Cs2MoO4(g) molecules, Their vapor pressure is determined in the form log P = -13723/T + 6.47, and the third law of thermodynamics is employed to find the heat of sublimation Delta H-s,H-298*(Cs2MoO4(s)) = 74.11 +/- 1 kcal/mole.