Thermodynamics of ternary nitride formation by ammonolysis: application to lithium molybdenum nitride (LiMoN2), sodium tungsten nitride (Na3WN3), and sodium tungsten oxide nitride (Na3WO3N)

Abstract

An approximate method for predicting the feasibility of synthesis of ternary nitrides from appropriate oxides and ammonia gas is outlined. The known thermodynamic data for binary oxides and nitrides may be a helpful guide in predicting the formation of ternary nitrides by ammonolysis of ternary oxides. When the difference between the free energy of formation of the ternaries from the binary oxides ([Delta]G[sub f][sup b](O)) and binary nitrides ([Delta]G[sub f][sup b](N)) is small, the predictions are expected to be reliable. Such considerations suggest that ternary oxides containing the most electropositve metals (alkaline, alkaline earth, rare earth) will not form ternary nitrides by ammonolysis but perhaps will form oxynitrides or decompose to the electropositive metal oxide/hydroxide and binary transition-metal nitride. When the metals in the ternary oxide are from group V or greater, ternary nitride formation by reaction with ammonia is likely. The authors have developed a new high-temperature calorimetric procedure for determining the standard enthalpies of formation of ternary nitrides and applied it to: LiMoN[sub 2], Na[sub 3]WN[sub 3], and Na[sub 3]WO[sub 3]N. The standard enthalpies of formation: [Delta]H[sub f][degrees](LiMoN[sub 2]) = 386.0 [+-] 6.4 kJ/mol, [Delta]H[sub f][degrees] (Na[sub 3]WN[sub 3]) = [minus]358.7 [+-] 53.3 kJ/mol and [Delta]H[sub f][degrees] (Na[submore » 3]WO[sub 3]N) = 1358.8 [+-] 18.2 kJ/mol were obtained. 41 refs., 1 fig., 7 tabs.« less