Influence of Colour Filter on Reaction Products from Mo and W Heated to 2000&deg;C by Concentrated Solar Beam in N<SUB>2</SUB> Gas Environment in a Solar Furnace at PROMES-CNRS

Abstract

In a preceding work, we reported attempts of synthesizing nitride of d-group transition metals including Ti, V, Nb and Ta using a solar furnace at PROMES-CNRS. In standard solar furnace experimental setup, graphite crucible is used as the sample holder on account of its resistance against high temperature and thermal shock. Plume of C 2 radical with high chemical activity a(C) of C was reported to yield from graphite crucible under irradiation of concentrated solar beam. Thus, synthesis of pure metal nitride MN was not successful in the preceding work done in N 2 gas environment heated by solar beam irradiation under standard experimental setup. To overcome this problem of undesired carburization in solar furnace, insertion of colour filter in the path of solar beam was tried and it was found that the C 2 radical yield from the graphite crucible was effectively suppressed by insertion of Sky blue filter and carbo-nitride M(C,N) with comparatively low C-content was synthesized for Ti, V, Nb and Ta at 2000 C in N 2 gas environment while, without the Sky blue filter, M(C,N) with high C-content and low Ncontent was synthesized under the otherwise comparable conditions of temperature and nitrogen partial pressure. These evidences appeared to suggest that nitride synthesis might be realized in standard solar furnace experimental setup using standard sample holder made of graphite by insertion of Sky blue filter. In the present work, reaction products from Mo and W in N 2 gas environment under solar heating to 2000 C were characterized and effectiveness of the Sky blue filter for suppression of C 2 radical yield from the graphite crucible was ascertained.

Effects of Colour-filtering Solar Beam on Reaction Product Fromd-group Transition Metals in N<SUB>2</SUB>Gas Environment under Heating with Concentrated Solar Beam

“…The evidences so far acquired through colour-filtering experiments in our recent solar nitride synthesis [3][4][5] were still very scarce and thence further systematic investigation is definitely desirable. Anyway, as well as for PVC energy conversion efficiency enhancement, selective filtering of solar beam must be of pragmatic merit on usage of concentrated solar beam as the heat source for synthesis of refractory materials including nitride and carbide.…”

“…The consequence was significant suggesting satisfactory extent of suppression of carburizing fo r M C 1-x N x type carbo-nitrides for IVa-group element (Ti) and Va-group elements (V, Nb and Ta) [3]. For VIa-g roup elements (Mo and W) [4], starting material M remained in metallic state after 30 min heating at 2000ºC in N 2 gas environment without showing no evidence of carburization. Mo and W are known to be very difficult to be converted to nitride with N 2 [8,9] but relatively easy to be carburized.…”

“…However, we detected unmistakable evidences of surface morphological modification for carbo-nitrides of Ti, V, Nb and Ta by insertion of the Mediu m yello w filter. In this report, the results so-far-acquired during the course of colour-filtering experiments [3][4][5] are interpreted under new light of recently reported evidence by Noda and co-workers [1,2]. Detailed contents of the published work by de Zoysa et al [1] were quite physical and not at all easy to understand straightforwardly the pragmatic significance by readers like myself who are not familiar with proper physics but digested newspaper introduction of this article [2] concisely demonstrated the essence of the reported work.…”

“…During the course of recent attempts of nitride synthesis using a solar furnace at PROM ES-CNRS (Laboratoire Procédés Materiaux et Energie Solaire) in Odeillo (France) undertaken in July 2010, the authors [3][4][5] detected also some intriguing effects of colour filtering of solar beam on reaction products.…”

“…[3], N content x in the synthesized carbo-nitride MC 1-x N x under concentrated solar beam colour-filtered through the Sky blue filter was appreciably higher than the counterpart synthesized under heating with concentrated solar beam with no insertion of the Sky blue filter for M = Ti, V, Nb and Ta. For the VIa-group elements, Mo and W which are known to be extremely difficu lt to be converted to nitride in N 2 gas environment [8,9], reaction product remained in metallic M without being converted to neither carbide nor n itride by 30 min heating to 2000ºC using the Sky blue co lour-filtered concentrated solar beam [4] imply ing that C 2 plu me yield was well suppressed to inhibit carburizing reaction while chemical activ ity a(N) of N 2 gas mo lecules were too low to pro mote nitrid ing reaction.…”