Study On Synthesis Of V-Al Alloy By Microwave-Assisted Self-Propagating

At present, with the development of economic and the improving of the nationaldefense capabilities, the mount of titanium and Super titanium alloy which were widelyused in military and aviatic and astronautic industries would be increased significantly.V-Al intermediate alloy is an important raw material for the production of Supertitanium alloy and vanadium, so its market potential is very promising. From the currentprocess in domestic, aluminothermic reduction method is the most common processingtechnology of V-Al alloy synthesis. However, the recovery of vanadium in smelting andpurity of alloy made are not high by this method, since there are slower velocity andfewer hour of separation for metal pool and slag pool in aluminothermic reduction, ithas made much waste of vanadium. At the same time the application value of V-Al alloyis limited to a certain extent. Therefore, in order to overcome these shortcoming, moreperfect preparation process and conditions are need explored to produce high purityalloy in a more effective vanadium resource utilization ratio, which were of greatimportant significance for bringing into full play the economic and social efficiency ofsubstantial vanadium resource in the west of china, which is only way for developmentof modern vanadium industry.In this paper, V-Al alloy was fabricated by microwave heating assistedself-propagating high-temperature synthesis （SHS） technology, Al powder was onlyneeded as a reducing agent and microwave heating replace other ways to provide heatfor the melt after reaction with the aims of accelerating the sedimentation rate andprolonging sedimentation time of alloy, which is helpful to separate the metal from slagand decrease the content of nonmetallic inclusions and so on. First of all, adiabaticflame temperatures and the thermal effect value of unit mass of Al-V₂O₅-CaO systemwere calculated, it shows that a SHS reaction can occur in the system. Kinetics ofreaction in the system were studyed by thermoanalysis, apparent activation energy ofaluminothermic reaction was205.2kJ/mol, and the reaction belongs to the liquid-solidreaction, which had some guiding significance for preparation processing improvementof V-Al alloy, also make theoretically preparations for systhesis experiment of V-Alalloy.Next, temperature rising behavior of slag after SHS reaction and oxides underdifferent microwave power were study, the results show that either the microwave power or the molecular structure of materials had different effects on the heating rate.When microwave power were500W and1kW, the average heating rate of slag were34.8℃/min and39.2℃/min respectively. For heating rate of oxides, that the tendency is:V₂O₅>Al₂O₃>CaO. There is a direct connection between the structure difference ofoxide molecular and its heating rate in microwave field, which led to the conclusion thatthe more structure defects in the crystal, the faster the heating rate was. The results ofexperiment provided important theory and experiment foundation for the study aboutmelt temperature distribution in microwave field and microwave heating mechanism.Finally, the effects of amount of CaO, microwave power, holding time and Alcontent on the alloy recovery and composition of V-Al intermediate alloy was studied inthe paper. The phase compositions and the distribution of component of the V-Al alloywere detected by X-ray diffractometer and scanning electron microscopy respectively.The results show that the main phases of the V-Al intermediate alloy produced bymicrowave heat-assisted SHS process are V-Al compounds matrix, a small amounts ofalumina and other non-metal oxide inclusions. The recovery of vanadium increased andthe content of inclusions decreased with the amount of Al appropriately increased andthe holding time extended. Microwave heating assisted SHS process has betterprospects in the preparing V-Al intermediate alloy, since it can increase V recovery aswell as improve the quality of the intermediate alloy. Under1000W of microwavepower,10min of heating time,30%excess Al and CaO:V₂O₅is11:6, more pure alloywere obtained and the recovery rate of vanadium was higher.