Synthesis and characterization of nanostructured molybdenum & tungsten carbide materials, and study of diffusion model

Abstract

Powders of two molybdenum carbides (Mo 2C and MoC 1-x) and tungsten carbide (WC) were prepared by means of temperature programmed reaction (TPR) method. Mo 2C and MoC 1-x were synthesized by reacting MoO 3 with a preselected molar ratio of methane/hydrogen and carbon monoxide/hydrogen gas mixtures respectively. WC was prepared using tungsten oxide (WO 3) and a methane/hydrogen gas mixture. These carbides were ultrasonically dispersed in de-ionized water. Samples were characterized using room temperature x-ray diffraction and scanning microscopy. A kinetic diffusion model is also studied to determine diffusivities in solids where the diffusing species desorbs or reacts at the external surfaces, and where the diffusivity does not vary appreciably with concentrations. The method involves measuring the flux of the diffusive species into the solid under the influence of a temperature program.