Gibbs energy of formation of Na 2WO 4 and Na 3WO 4 in liquid sodium

Abstract

Oxygen potentials of the equilibrated mixtures of Na+WO 3 and Na+WO 2 at temperatures in the range of 623 to 823 K, measured with electrochemical oxygen meters using ThO 2–Y 2O 3 solid electrolyte, showed two linear oxygen potential ranges corresponding to the two three-phase fields, [Na(l)–W(s)–Na 2WO 4(s)] at 623 to 695 K and [Na(l)–W(s)–Na 3WO 4(s)] between 695 and 823 K. The reaction products of WO 3 and WO 2 with an excess of sodium were identical. Standard molar Gibbs energy of formation data for the two ternary oxides were derived from the oxygen potentials: Δ f G°〈Na 2WO 4〉±11.2/(kJ mol −1)=−1516.78+0.2088( T/K) (623–695 K), Δ f G°〈Na 3WO 4〉±1.7/(kJ mol −1)=−1680.97+0.4465( T/K) (695–823 K)