Formation of molybdenum nitrides by ammonia nitridation of Mo powder and sheet

Overview & Synopsis

The formation of molybdenum nitrides was investigated at temperature up to 1200°C in flowing ammonia with various flow rates and reaction times. The products were charaterized by XRD, chemical analysis, metallography and EPMA. The phases gamma-MoN(1-x) delta-MoN formed at temperature above 600°C only at high flow rates of about 20l/h. If the flow decreases even powders did not show the delta-MoN phase. Beta-Mo2N was observed by XRD in both, powder samples and compact samples. While a distinct and dense gamma-MoN(1-x) layer formed, the layer of delta-MoN was to thin to be detected by metallography of the wedge-type samples and could only be observed by XRD of the surface. Microhardness of a gamma-MoN(1-x) diffusion layer revealed at 1000°C was measured as a function of composition. the homogeneity range of gamma-MoN(1-x) at around 900-1000°C was determined by EPMA. The diffusivity of nitrogen in gamma-MoN(1-x) at 1000°C was calculated.