Interactions of Ta2O5 with water vapor at elevated temperatures

Tantalum pentoxide (Ta2O5) and its solid solution phases are candidate coatings for components to be used in combustion environments. Thus, it is important to understand the response of Ta2O5 to high-temperature water vapor, a product of combustion. Thermogravimetric methods are used to examine the oxide in reactant streams of controlled water vapor contents at 1250 degrees C-1450 degrees C. The observed weight loss indicates a reaction of the general form 1/2 Ta2O5(s) + x H2O(g)=TaOy(OH)(x)(g). Methodical variation in the water vapor pressure suggests the products are a mix of TaO(OH)(3)(g) and Ta(OH)(5)(g). Evidence of TaO(OH)(3)(g) was observed with a sampling mass spectrometer. The measured hydroxide and oxyhyroxide vapor fluxes from Ta2O5 are compared with calculated vapor fluxes from SiO2 and Al2O3. Ta2O5 exhibits fluxes similar to those from SiO2 due to gaseous metal hydroxide formation.