Thermodynamic analysis and synthesis of porous Mo2C sponge by vapor-phase condensation and in situ carburization of MoO3

Abstract

Spongy porous MoO3 deposits were grown by vaporization, vapor-phase transportation and condensation of MoO3 in Ar flow. It was observed that increased source temperature (>= 1200 K) and temperature gradient (>= 100 K/cm) favor the formation of spongy deposit owing to high supersaturation of the oxide vapor at similar to 900 K. Spongy Mo2C deposits consisting of intermingled platelet crystals with thin walls were synthesized by in situ carburization of the condensed MoO3 using 0.05-0.1 mol of CH4 and 1 mol of H-2 at 900 K. Thermodynamic analysis in the Mo-O-C-H system was used as a guide to predict the conditions for the formation of Mo2C from the MoO3-CH4-H-2 reactants at 900 K. X-ray diffraction analysis showed that the carburized deposits consisted of single phase Mo2C, in agreement with the thermodynamic prediction. The equilibrium analysis was also used to reveal possible reaction pathways to Mo2C formation from MoO3-CH4-H-2 reactants which yielded gaseous products of H2O, CO2, CO, C2H6 and C2H4. (C) 2009 Elsevier B.V. All rights reserved.