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Purification of Some Fluorides by Sublimation Ⅱ. Purification of ZrF_4 and HfF_4 by Sublimation

Yu Yaochu; Liu Chuangxin; Hu Hefang(Shanghai Institute of Optics Fine Mechanics Chinese Academy of Sciences Shanghai 201800)  
Even if sublimation method is very effective for removing oxides, one still must take note of dehydrating and hydrolyzing temperatures of ZrF4 and HfF4, and FeF3 etc. inclusions of fluorides cannot effectively be separated out. On the ground of that FeF63-, CoF63- are outer orbital complexes, and instable and easily dissociate into Fe3+ and Co3+, while FeZrF6-6H2O also easily dissociates into Fe2+, so that the extraction of (NH4)3ZrF7 and (NH4)3HfF7 becomes posible by DDTC-CHCl3 with pH 3~3.5. In two-component system of ZrF4 and HfF4, sublimating and solidifying processes will follow the law of the phase equilibrium shown in Fig.2. Sublimated products were examined by XRD to be β-monoclinic anhydrous ZrF4 or HfF4 crystals; By GFAAS, before and after sublimation, Fe contents were 0.8ppm and 0.5ppm respectively. The batch was 250g.
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