Abstract
This study presents an original, effective, and environmentally friendly method for synthesizing pure molybdenum carbide (Mo(2)C) from ammonium molybdate tetrahydrate (AMT) without generating carbon dioxide, a greenhouse gas. The process involves the sequential transformation of AMT to Mo(2)C, which follows the reaction pathway of (NH(4))(6)Mo(7)O(24)→MoO(3)→MoO(2)→Mo→Mo(2)C. This transformation is achieved by strategically altering the gas atmosphere, switching from Ar to H(2) at 800 K and then from H(2) to CH(4) at 1000 K. Thermal analysis, X-ray diffraction (XRD), and scanning electron microscopy (SEM) techniques were used to characterize AMT and the products. Mass measurements were used to follow the conversion of AMT to intermediate products and to the final product (Mo(2)C). It was found that 57.67% of AMT was converted to Mo(2)C, in agreement with the theoretical value (57.74%). Differential scanning calorimetry/thermogravimetry curves revealed four steps at 401 K, 495 K, 507 K, and 595 K during AMT decomposition to MoO(3). XRD patterns revealed the formation of phase-pure Mo(2)C, with characteristic diffraction peaks 2θ = 34.176°, 2θ = 37.712°, and 2θ = 39.197° assigned to the (100), (002), and (101) crystal planes, respectively. SEM images showed that fine Mo(2)C particles with a thickness of 0.1 μm was obtained from very coarse AMT particles (>50 μm). In order to determine the solid and gaseous phases likely to form during the reaction, thermodynamic analysis using Gibbs' free energy minimization method was also carried out prior to synthesis. The reduction reactions and the resulting morphologies of the synthesized materials were discussed in terms of thermodynamic results and density changes associated with the conversions. This study demonstrates a novel reaction pathway that sequentially converts the molybdenum species from Ammonium Molybdate Tetrahydrate (AMT) to the final Mo(2)C phase without the release of CO(2).