Study On Preparation Technique Of High Purity Gadolinium

For optimizing the process condition and finding out removing and introducing of impurities in each process of preparation of high purity gadolinium, this paper studied several processes systematicly, such as preparation of high purity gadolinium fluoride, metallothermic reduction of gadolinium, vacuum remelting, vaccum distillation and purification by Solid state electrotransport of gadolinium. The results showed that:HF fluorination is the more proper method to preparation of high purity GdF3. Following the steps of first fluorination in550℃for4hours, second fluorination in660℃for10hours and third fluorination in660℃in12hours, gadolinium fluoride was prepared with oxygen content below100ppm. Low oxygen content GdF3with purity of99.96%has been prepared from material of99.99%Gd2O3under such conditions; Oxygen content could been decreased by GdF3-LiF melting in750℃under HF atmosphere.Gd reduced by Li and Ca has almost same impurity distribution, major impurities are Fe, Si, Al, Ti and W. Fe was mainly from reductant, Si and Al was from raw material and operation environment, Ti and W was introduced by reaction container. In this study, Li reductant prepared lower impurity content Gd.Vacuum remelting in high temperature can remove Fe, Al and Ti, but could introduce impurities such as Si and W; in vacuum distillation, O, Fe, N, C and W could been removed efficiently, Si, Al and S were hard to remove. Gd was refine from99.79%to99.96%for once distillation.Constant current SSE purification under10-/-Pa showed that:Oxygen concentration in Gd processed in0.88Tm(450A/cm2) constant current SSE was reduced to1651ppm from120ppm, residual rate was7.3%; oxygen residual rate was4.2%after processing in0.95Tm(500A/cm2), which is above the BCC transformation point. Nitrogen was removed more efficiently in0.95Tm, residual rate was47.0%after0.95Tm100h processing compared76.9%in0.88Tm. Carbon was not removed after0.88Tm processing, but removed efficiently after0.95Tm processing. Constant current SSE could purify Cu, Mn, Pb and Ni et al. and for those can be purified, longer time was better.SSE using pulse current could maintain higher current in same temperature. In this paper, pulse current(800A/cm2,1000ms cycle and500ms square-wave pulse) SEE in0.88Tm60h was studied, it showed that pulse current SSE wasn’t more efficient than constant current SSE in same temperature and further study of pulse current SSE was required.Cathode of rods after SSE were researched by metallographic analysis. Results showed grain was growing by time in processing and grain size after0.95Tm constant current SSE was larger than0.88Tm constant current SSE; grain size after pulse current SSE was smaller than after constant current SSE.