Research Of Preparation Of Cr And CeNi₅ By Electro-deoxidization In Molten Salt

Chromium is an important material for its good rigidity, high molten point and acid-resistance, it is wildly used in metallurgy and fire-resistant industry. CeNi₅ is a kind of excellent hydrogen storage material and an important component in commercial hydrogen storage material. The existing technologies of manufacture are complex, the equipment are expensive, and the technologies are harmful to the environment. New process of direct reduction of metal oxide to metal or intermetallic compounds in molten salt is an interesting and relatively new development which can lower the cost and shorten the crafts. Development of this process has important meaning to expand new technique applying in the metallurgy.The method of electro-deoxidization was used to prepare Cr, Ce, CeNi₅ from Cr₂O₃, CeO₂ and NiO-CeO₂ respectively. Some key parameters were studied. The impact of the sintering temperature, voltage, time of electrolysis, molten salt temperature was studied. The mechanism of reaction was studied by cyclic voltammograms. The capability of hydrogen storage of CeNi₅ was tested.The results showed: Cr₂O₃ can be reduced into Cr step by step from outside to inside. The higher the sintering temperature is, the lower the porosity is, the lower the speed of electro-deoxidization is. The diffusion played an important role on the reduction process, it may be useful to increase porosity of the pellets.CeNi₅ can be prepared by electro-deoxidization in molten salt. The product was examined by XRD and SEM respectively. The results show that sintering temperature has strong impact on the porosity and morphology of the pellet. Pure CeNi₅ was produced from NiO-CeO₂ pellets sintered at 850℃, 1050℃after electrolyzed for 11h under the voltage of 3.1V. The electro-deoxidization can be carried out under the voltage of 2.5～3.1V. There was no CeNi₅ exists in the product if the voltage was lower than 2.2V. The molten salt temperature was also an important parameter, the higher the molten salt temperature is, the purer the product is. The cyclic voltammograms and XRD analyses showed that the deoxidization of NiO-CeO₂ began with reduction of NiO, CeO₂ was reduced and alloys was formed on the surface of newly-formed Ni. The product CeNi₅ has excellent capacity and stability of hydrogen storage.