Standard Gibbs Energy of Formation of K3NbO4 and K3TaO4 and Threshold Oxygen Levels for their Formation in Potassium, Niobium and Tantalum
Liquid potassium metal is being considered as a working fluid in heat pipes, heat transfer media in solar energy converters and as a thermodynamic working fluid in advanced Rankine-type power stations . The high temperatures encountered in these systems necessitate the use of special containment materials for the liquid metals. Niobium, tantalum and their alloys have been investigated for this purpose. It has been shown that corrosion of these metals and alloys in liquid potassium is greatly influenced by oxygen present in the alloy or in the liquid metal [2, 3]. Corrosion is believed to be through the formation of the ternary oxides K3NbO4 and K3TaO4 which have been identified as corrosion products [4 – 6] of niobium and tantalum specimens, respectively, exposed to liquid potassium. A knowledge of thermodynamic stabilities of these ternary oxides would be essential to understand the corrosion mechanism of niobium and tantalum in liquid potassium. This investigation was undertaken in order to generate accurate data on Gibbs energy of formation of K3NbO4 and K3TaO4. This data could be utilised to predict threshold oxygen levels in the liquid metal (K) as well as in the solid metals (Nb, Ta) for the formation of these ternary oxides on the solid metals exposed to high temperature liquid potassium.
KeywordsLiquid Metal Corrosion Product Heat Pipe Phase Field Oxygen Potential
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