Effect of Preheating Profiles on Nitrogen Contents of Mono-carbonitrides Synthesized by Heating W, Mo and W-Mo Powders in CH₄NH₃ Mixed Gas of Normal-Pressure

Abstract

Powders of new mono-carbonitride of W, MO and W-70at%Mo alloy, i.e., W(C, N), Mo(C, N) and (W_0.3Mo_0.7) (C, N) have already been found by the authors to be synthesized by heating the metal and alloy powders at 1373-1573 K in CH₄+NH₃ mixed gas of normal-pressure. In this study, the effect of some intermediate phases such as Me₂C and Me₂N (Me: W, Mo and W-70at%Mo), which are generated during the temperature-raising stage, i.e., preheating, on the amount and N content of the mono-carbonitrides, were investigated.
The following were clarified or strongly suggested. (1) W(C, N) is generated from W and W₂N, while not from WC. (2) Mo(C, N) is generated from Mo₂C and Mo₂N, while hardly from Mo. (3) (W_0.3MO_0.7)(C, N) is generated from all of W-70at%Mo, (W_0.3MO_0.7)₂C and (W_0.3MO_0.7)₂N, while not from (W_0.3MO_0.7)C. (4) Me₂N is an appropriate precursor for these three kinds of mono-carbonitrides, compared with Me, Me₂C and MeC. (5) By changing the atmosphere in the temperature-ranging stage from CH₄+NH₃ to NH₃, the nitrogen contents (N/metal) of W(C, N) and Mo(C, N) could be increased from 5 and 17 at% (by the conventional profile) to 9 and 22 at%, respectively, while the nitrogen content of (W_0.3MO_0.7) (C, N) could not be increased (23 at%).