Browsing by Author "Granier, Bernard"
Now showing 1 - 2 of 2
Results Per Page
Sort Options
- Carbide phases synthesised from C/Mo powder compacts at specified sub-stoichiometric ratios by solar radiation heating to temperatures between 1600 C and 2500 CPublication . Granier, Bernard; Shohoji, Nobumitsu; Almeida Costa Oliveira, Fernando; Magalhães, Teresa; Fernandes, Jorge Cruz; Rosa, Luís GuerraThere are a number of distinguishable carbide phases in the binary Mo-C system depending on C/Mo ratio as well as on temperature. In a preceding work published in this journal, carbide formation performance for graphite/molybdenum powder mixtures at specified levels of substoichiometric C/Mo atom ratio (C/Mo = 1/1, 3/4, 2/3 and 1/2) by exposure to concentrated solar radiation in a solar furnace at PROMESCNRS in Odeillo (France) was reported at a target temperature 1900 C. In the present work, the similar carbide synthesis experiments were carried out at 1600 C as well as at temperature exceeding 2500 C. The target temperature setting was adjusted by controlling the downward deviation of the test piece top surface position from the exact focal spot of the parabolic mirror concentrator located above. In this solar furnace at PROMES-CNRS, temperature of the test piece was raised from ambient temperature to the target temperature within fractions of a second. Reaction products detected were hexagonal -MoC1 x and -Mo2C (high temperature sub-carbide phase) depending on the C/Mo ratio in the starting material as well as on the processing temperature. No evidence of formation of cubic -MoC1 x was detected by X-ray diffraction analysis for any test piece examined.
- Nano-meter size WC whiskers grown over a compacted pellet of praphite: tungsten powder mixture heated with an ultra-fast heating rate by a concentrated solar beamPublication . Dias, Susana; Oliveira, Fernando Almeida Costa; Granier, Bernard; Badie, Jean Marie; Fernandes, Jorge Cruz; Rosa, Luís Guerra; Shohoji, NobumitsuIn equilibrium binary W-C system, mono-carbide WC is acknowledged as the stable phase under presence of excess free carbon up to temperature 2700 C whereas sub-carbideW2C would form between 1250 C and 2700 C under the carbon-deficiency condition. In unique setup of solar furnace at PROMES-CNRS in Odeillo (France), temperature of specimen is raised from the ambient temperature to target temperature up to 2000 C within fractions of a second. In the recent experimental attempts of W2C phase synthesis using this unique experimental facility starting from compacted pellet consisted of graphite and tungsten powders at ratios smaller than 0.50, we detected growth of nano-meter size WC whisker at the top surface directly exposed to the concentrated solar beam. The presence of WC was confirmed also by X-ray diffraction (XRD) of the top surface but, when the specimen as a whole was subjected to powder XRD analysis, WC became indiscernible being masked by principal W2C phase. Mechanism of formation of the detected WC nano-whisker over sub-stoichiometric C/W pellet during ultra-fast heating by concentrated solar beam is discussed.