The heats of combustion of niobium carbides

Abstract

A series of niobium carbides, NbCx, has been burned in an oxygen bomb calorimeter. The carbides covered a range from x = 0.489 to x = 0.984. Extrapolation of the curve, ΔH = 6.60 -70.95x + 30.75x2, obtained for eight compositions (NbC0.686 through NbC0.984) to x = 1 gave -33.6 ± 0.6 kcal./mole as the heat of formation of NbC. The heat of formation of Nb2C was -46.6 ± 1.2 kcal./mole. Combustion of powdered Nb metal gave a heat of formation of -454.4 ± 1.6 kcal./ mole for Nb2O5. A comparison of these values with those of other workers is made.