Carbide Synthesis from Graphite/molybdenum Powder Mixtures at Sub-Stoichiometric Ratios under Solar Radiation Heating to 1900°C

Abstract

A solar furnace at PROMES-CNRS in Odeillo (France) is with very unique capacity of heating the specimen material from ambient temperature to a target temperature exceeding 2000°C within fractions of a second in arbitrary gas environment with pressure no higher than 1 atm. In the preceding work on the Mo-C synthesis using this solar furnace with the set target temperature 1600°C, evidence of formation of η-MoC_1−x besides α-Mo₂C (the low temperature phase of Mo₂C) was confirmed under presence of excess free carbon (graphite). The η-MoC_1−x is known to be stable at temperatures between 1650°C and 2500°C with range of x between 0.25 and 0.35. Thus, in the present work, carbide synthesis experiments were carried out for compacted powder mixtures between graphite and molybdenum at C/Mo mole ratios, 2/3 and 3/4, as well as the ratios, 1/2 and 1/1, as the references in the solar furnace at Odeillo under application of the ultra-fast heating rate to the set target temperature 1900°C in search of favourable processing condition for η-MoC_1−x synthesis. The gained experimental evidences indicated that, at any chosen C/Mo ratio in the starting powder compact, formation of β-Mo₂C (the high temperature phase of Mo₂C) took place preferentially while certain proportion of the η-MoC_1−x formed besides the β-Mo₂C from the powder compacts with C/Mo mole ratios, 2/3 and 3/4.