M.Ing. / This work is an investigation into the production of nanosized vanadium-tungsten-carbide [V,W)C] powder by mechanical alloying (MA) starting from vanadium (V), tungsten (W) and amorphous carbon (C) powders. The milling conditions were optimized first for the production of tungsten carbide (WC) due to the high cost of V powder with variations of W/C ratios to determine the minimum time required (at a selected energy) to obtain a full synthesis, i.e. to obtain only carbide without primary powders left. Ball to powder ratio (BPR) of 11:1 at 300 revolutions per minute (rpm) was used with stoichiometric carbon for WC, and using the equilibrium formula (Vo.7,Wo.3)Ci_x ) for (V,W)C. The powder phase composition was monitored by X-ray diffraction (XRD), shape and morphology was monitored by scanning electron microscopy (SEM). The production of synthesized nanocrystallite (V,W)C and WC without residual elemental powders required different times. WC powder required 8 hours of MA, while (V,W)C required 40 hours. On account of the difficult choice of stoichiometry, in general WC was also formed together with (V,W)C but the WC formation will be useful in final WC-(V,W)C-Co alloy for toughness. Crystallite sizes of about 8 to 11 nm were obtained from synthesized (V,W)C, and WC powders respectively. The amount of free carbon was measured on both synthesized WC and (V,W)C by a Leco carbon analyzer. Free carbon was found to be 2.05 wt % for WC, and 5.83 wt % for (V,W)C. Oxygen content was also measured on both the synthesized powders, to check if oxidation had occurred. The amount of oxygen in (V,W)C was measured to be 9.2 wt % higher than that of WC which was measured to be 2.7 wt %.
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:uj/uj:3216 |
| Date | 27 August 2012 |
| Creators | Bolokang, Sylvester Amogelang |
| Source Sets | South African National ETD Portal |
| Detected Language | English |
| Type | Thesis |
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