Article ID: M2009313
Compositional heterogeneity along the thickness of compacted disc specimens of graphite/tungsten powder mixtures with sub-stoichiometric carbon atom ratios (0.35, 0.50 and 1.00) heated by concentrated solar beam to 1600°C was characterised by X-ray diffraction. Top surface of any examined test piece was consisted purely of mono-carbide WC while the bottom surface showed different constitution depending on the net initial C/W ratio of the test piece; almost pure metallic W for the C/W=0.35 specimen, dominant metallic W associated with small proportion of W2C for the C/W=0.50 and dominant W2C with trivial proportion of WC for the C/W=1.0. In the intermediate zone between the top and the bottom layers, the constitution held virtually constant depending on the nominal C/W ratio of the starting material: co-existing metallic W and W2C for the C/W=0.35, pure W2C for the C/W=0.50 and predominant WC with trace W2C for the C/W=1.00. Unlike for the top surface of the C/W=0.35 test piece heated in a solar furnace to 1900°C reported earlier, no evidence of formation of nano-meter scale WC whisker was detected for the top surface in any sample heated to 1600°C in the present work.