Gaseous titanium molybdates and tungstates: Thermodynamic properties and structures

Abstract

RATIONALE Titanium is a component of various construction materials, which is often used at high temperature and in an oxidizing atmosphere. Thermally stable even at high temperatures, titanium compounds may appear in the condensed phase. To predict the possibility of existence of gaseous associates formed by titanium oxides it is important to know their thermodynamic characteristics. Until the present investigation no gaseous salts of titanium were known. METHODS Measurements were performed by high‐temperature Knudsen effusion mass spectrometry with a MS‐1301 mass spectrometer. Vaporization was carried out using molybdenum and tungsten effusion cells containing samples of pure Au, Ti 3 O 5 and SiO 2 . A theoretical study of gaseous titanium molybdates and tungstates in different spin states was performed by quantum chemical density functional theory (DFT) B3LYP and M06 methods. RESULTS On the basis of the equilibrium constants of gaseous reactions, the standard formation enthalpies of gaseous TiMoO 3 (−424 ± 28 kJ/mol), TiWO 3 (−400 ± 22 kJ/mol), TiMoO 4 (−795 ± 29 kJ/mol), TiWO 4 (−750 ± 24 kJ/mol), TiMoO 5 (−1146 ± 23 kJ/mol) and TiWO 5 (−1125 ± 22 kJ/mol) at 298 K were determined. Energetically favorable structures were localized and vibrational frequencies were evaluated in the harmonic approximation. Natural atomic charges, bond orders, and valence indices were calculated for all relevant structures. CONCLUSIONS The stability of gaseous species TiMoO n and TiWO n (n = 3, 4, 5) was confirmed by high‐temperature mass spectrometry. A number of gas‐phase reactions involving titanium‐containing gaseous salts were studied. Enthalpies of reactions of gaseous TiXO n (X = Mo, W; n = 3, 4, 5) formation were evaluated theoretically and the obtained values are in agreement with the experimental ones. Copyright © 2014 John Wiley & Sons, Ltd.