2012 Volume 53 Issue 3 Pages 537-545
In recent attempts of reacting d-group transition metals with N2 gas under irradiation of concentrated solar beam at temperatures around 2000°C using a standard setup with graphite specimen holder, reaction products obtained were carbo-nitrides rather than targeted nitrides on account of yield of C2 radical plume from the graphite crucible. To suppress the interference of C2 radical possessing high carbon chemical activity a(C) in nitriding d-group transition elements in solar furnace, we investigated effectiveness of inserting colour filters in the solar beam path. Two readily available colour filters, Sky blue and Medium yellow filters, were tested for this purpose. As reported in our earlier publications, XRD (X-ray diffraction) phase identification results indicated that insertion of the Sky blue filter was effective for suppressing C2 radical yield under solar beam radiation to synthesize carbo-nitride with comparatively high N content. On the other hand, insertion of the Medium yellow filter did not result in so remarkable effect for suppressing carburization as the one detected with the Sky blue filter. In the present work, aspects of microstructures developed for Ti, V, Nb and Ta surfaces heated to 2000°C under exposure to colour-filtered solar beam in N2 gas environment are reviewed. The present experimental evidences indicated that, by insertion of the Sky blue filter, appreciable crystallite grain size refinement was realized for the synthesized M(C,N) with high N content while, by insertion of the Medium yellow filter, certain extent of influence on the morphological development, that varied depending on the substrate material, was unmistakably discernible.