Preparation Of Scandium Oxide And Aluminum Magnesium Scandium Master Alloy Experiments

In this paper, preparation of aluminium-magnesium- scandium master alloy from scandium oxide(purity is 98.89% ) was studied, the method is: scandium oxide was chlorinated to prepare anhydrous scandium chloride molten salt, then the anhydrous scandium chloride molten salt was reduced by aluminium and magnesium to prepare aluminium-magnesium- scandium master alloy .Through the thermodynamic calculation of the reaction that aluminum and magnesium reduce anhydrous scandium chloride molten salt to prepare aluminium-magnesium-scandium master alloy, we got that the standard equilibrium constant of the reaction is 1.074 ×10¹⁹, and the experimental equilibrium constant of it is approximately 6.874 × 10¹⁴under around 1200 K and 1 standard pressure, which demonstrate that the reaction can take place and proceed thoroughly.Therefore, refering to the chemical thermodynamics, the method of the preparation of the aluminium-magnesium-scandium master alloy through aluminium-magnesium thermoreducing anhydrous scandium chloride molten salt is feasible.In the experiments of the preparation of anhydrous scandiumchloride molten salt, we experimented on the key step--sublimingammonium chloride and dehydrating remanent crystal water,and adopted a new way to sublime ammonium chloride and dehydrate remanent crystal water, that is directly raising temperature to 400℃ fast in the inert gas current .Through the experiments , we got the optimum condition: temperature was 400℃ , weight ratio of scandium oxide to ammonium chloride was 1 : 1. 5 , time was 120 minutes, temperature raising speed was 10℃/min,volume of inert gas flow was 5L/min.Under the optimum technology condition,we can get the anhydrous scandium chloride molten salt whose hydrolysis rate is2.3%.In the experiments of aluminium-magnesium-scandium master alloy preparation,through the small experiments and extent experiments,we gained the optimum technology condition: reduction temperature was 900℃ , content of scandium in molten salt was 8.0%, molten salt was divide into 3 portions and pressed into the molten aluminium-magnesium alloy with clock cover, molten alloy was stirred with argon gas for 4 times and every time lasted for about 30 seconds, reduction time was 20 minutes.Under the optimum technology condition,we conducted the middle experiment which filled with 10kg(metal weighet)material. In the master alloy prepared,the average content of scandium was 2.18%, the average content of magnesium was 5. 64%,the recovery of scandium was 90. 8%, the content of Cu was below 0.0066%, the content of Si was below 0.33%, the content of Ti was below 0.032%, the content of Fe was below 0.19%, the content of Zn was below 0.094%, the content of Na was below 0.031%,all the impurity elements' content was low relatively,but scandium segregated badly in ingot casting.In the experiments reducing scandium segregation in the ingot casting, we have investigated the scandium segregation case of the ingot casting and found that scandium segregation was small in transverse ingot casting and was big in longitudinal ingot casting .Through the experiments of reducing scandium segregation in the ingot casting, the problem that scandium segregates badly in the ingot casting was resolved to some extent ,scandium segregation in the ingot casting prepared was below ±0.3%.Then we discussed the reason of scandium segregation in the ingot casting, and thought that region segregation and weight segregation existed at the same time.