Obtenção de carbeto de molibdênio (Mo2C) nanoestruturado através de heptamolibdato de amônio por meio da reação gás-sólido a baixas temperaturas

Abstract

Obtaining nanostructured transition metal carbides has shown to be promising due to the various applications that the material can offer, but the conventional technique for preparing carbides, inherited by the metallurgical industry, involves reactions at high temperatures, above 1000°C. Therefore, the search for new methods of obtaining are investigated to optimize the process, aiming to reduce the time and temperature and consequently the operating costs. In view of this, the carborreduction process via gassolid reaction has gained great prominence, as it brings unique combinations of physical, chemical and mechanical properties to the material. This work aimed to synthesize and characterize molybdenum carbide, using the gas-solid reaction method in a fixed bed reactor. Ammonium heptamolybdate was used as a precursor for the formation of molybdenum carbide (Mo2C) at temperatures of 600°C, 650°C and 700°C, using an isotherm of 60 min., 90 min. and 120 min. The samples were characterized by X-ray diffraction (XRD) and Rietveld refinement, scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDS). With the characterization of the synthesized powders, it was possible to prove the formation of the molybdenum carbide (Mo2C) phase for the samples synthesized under the following conditions: 600°C, isotherm of 120 minºC; 700°C, isotherm 60 min and 700°C, isotherm 120 min. Molybdenum carbide synthesized at 600°C with an isotherm of 120 min. showed the smallest crystallite size, 19.70 nm. All samples showed morphology with an undefined format with small agglomerations of varying sizes. The other samples did not form the pure Mo2C phase, presenting intermediate phases, such as Mo and Mo oxides.