Alok Awasthi

Vanadium is prepared by aluminothermic reduction of oxides. As the reaction with V ₂ O ₅ is highly vigorous, the reduction is carried out with V ₂ O ₅ /V ₂ O ₃ mixture for controlled reaction. Reduction of V ₂ O ₅ alone to vanadium with the addition of Al ₂ O ₃ as heat-sink is proposed in this work. While keeping the heat of process constant at 3680 kJ/kg in laboratory thermite reactors, the slag fluidiser CaO was partially and then fully replaced with Al ₂ O ₃ . Use of Al ₂ O ₃ resulted in controlled reaction (with recovery as metal reaching from 50% to 83%), lesser loss in slag (from 10% to 1% vanadium) and lower nitrogen (from 1000 ppm to 130 pm) in metal. MgO of the reactor sometimes participates in the reaction. The loss of vanadium in slag is related to MgAl ₂ O ₄ content of the slag. Molten Al ₂ O3 appears to scavenge the dissolved nitrogen from molten vanadium. Results have been explained from available thermodynamic data.

The reduction of yttrium fluoride (YF₃) by calcium in a molybdenum crucible was investigated. A visual observation technique was used to monitor the reduction process. It was observed that the reaction initiated immediately after the melting of calcium. Based on the results, a two-step reduction sequence was attempted. First, the charge was heated to 950°C to minimise the calcium loss by vaporisation and to ensure completion of reaction. The products were then fast heated to 1600°C for slag/metal separation. Molybdenum content of yttrium was found to be in a range of 3.5–4.75 wt-%, which is much lower than the equilibrium content predicted by Mo–Y phase diagram. The yttrium/molybdenum interface was studied using an electron probe microanalyser, which confirmed that the overall equilibrium was not reached, indicating the possibility of lowering the molybdenum contamination further by process optimisation.