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Quantum chemical calculations of the thermochemistry of tantalum oxyhydroxide species
Author(s) -
Bauschlicher Charles W.,
Jacobson Nathan S.,
Myers Dwight L.
Publication year - 2019
Publication title -
journal of the american ceramic society
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.9
H-Index - 196
eISSN - 1551-2916
pISSN - 0002-7820
DOI - 10.1111/jace.16410
Subject(s) - thermochemistry , chemistry , vapor pressure , water vapor , tantalum pentoxide , thermodynamics , tantalum , standard enthalpy of formation , kinetic energy , analytical chemistry (journal) , organic chemistry , physics , quantum mechanics
Tantalum pentoxide and water vapor are predicted to react at elevated temperatures to form TaO(OH) 3 (g), TaO 2 (OH)(g), and Ta(OH) 5 (g). The thermochemistry of these species is calculated with quantum chemistry methods. Geometries and vibrational frequencies are determined from B3LYP DFT methods. Energetics are calculated from high levels of theory—CCSD(T) and larger basis sets for Ta, O, and H. We report the enthalpies of formation at 0 K and 298.15 K, entropy at 298.15 K, and heat capacity. These quantities are used to calculate vapor pressures at 1400‐1800 K and 50% water vapor. TaO(OH) 3 (g) is found to be the dominant species. The calculated vapor pressure of TaO(OH) 3 (g) is converted to a vapor flux and compared to previous experimental flux measurements from a flat plate in a slowly flowing H 2 O/Ar gas and also vapor flux from a steam jet experiment. These “open system” experiments result in lower fluxes that are within 1.12‐17X of the calculated equilibrium fluxes. This suggests that the experimental measurements are near equilibrium or have a small kinetic barrier.