Study on aluminothermic reduction of V₂O₅: effect of slag chemistry

Vanadium alloys are promising candidate materials for structural components of fusion reactors because of their superior high temperature thermal and physical properties, low cross section to neutrons, low activation properties and good resistance against neutron irradiation. Increased level of interstitial impurities like O and N in vanadium is known to have several detrimental effects on the workability and weldability of alloys. Activation consideration also place limitation on N content. In the present study, systematic work is done with the use of modern analytical techniques to better understand the science of the thermit process of vanadium so that it can be applied efficiently at bigger scale. In literature, generally CaO is used as a fluxing agent, to minimize excess heat and also for good slag metal separation in aluminothermy. Normally heat sinks are added in order to control the heat of reaction. This study shows that apart from the quantity, it is the nature of heat sink/flux, which plays an important role in controlling the heat of reaction, which subsequently result in better yield and quality of the product. Effect of various parameters like amount of heat sink/flux, nature of heat sink, excess aluminum and particle size of Al has been studied. Heat sink materials/ fluxes were added to control the vigorous nature of the reaction and a corresponding increase in slag volume (resulting in thicker slag layer) was also intended. Increased slag volume was expected to decrease the interaction of air with the molten metal thereby resulting in minimization of nitrogen in the final metal. This aspect is examined in detail in the present work. It will help in better understanding of the process as far as the contribution of nitrogen in thermit from air and starting material. In general, during the aluminothermic reduction, MgO walled reactors is used, but in this study it is shown that substantial amount of MgO also participate in the aluminothermy. The role of MgO of reactor in the reaction has been brought out for the first time in this work. The effect of linings on reactor has also been studied. The nature of vanadium loss to slag has also been assessed for the first time. (author)