THERMODYNAMICS OF TERNARY NITRIDE FORMATION BY AMMONOLYSIS - APPLICATION TO LIMON2, NA3WN3, AND NA3WO3N

An approximate method for predicting the feasibility of synthesis of t ernary nitrides from appropriate oxides and ammonia gas is outlined. T he known thermodynamic data for binary oxides and nitrides may be a he lpful guide in predicting the formation of ternary nitrides by ammonol ysis of ternary oxides. When the difference between the free energy of formation of the ternaries from the binary oxides (DELTAG(f)b(0)) and binary nitrides (DELTAG(f)b(N)) is small, the predictions are expecte d to be reliable. Such considerations suggest that ternary oxides cont aining the most electropositive 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/hydr oxide and binary transition-metal nitride. When the metals in the tern ary oxide are from group V or greater, ternary nitride formation by re action with ammonia is likely. We have developed a new high-temperatur e calorimetric procedure for determining the standard enthalpies of fo rmation of ternary nitrides and applied it to: LiMoN2, Na3WN3, and Na3 WO3N. The standard enthalpies of formation: DELTAH(f)-degrees(LiMoN2) = -386.0 +/- 6.4 kJ/mol, DELTAH(f)-degrees(Na3WN3) -358.7 +/- 53.3 kJ/ mol and DELTAH(f)-degrees(Na3WO3N) = -1358.8 +/- 18.2 kJ/mol were obta ined.