Abstract:Crystal structure, pressure-composition isotherms and electrochemical properties of the Zr 0.6−x Ti 0.4 Nb x Ni (x = 0.01, 0.02, and 0.05) alloys were investigated. Their X-ray diffraction profiles demonstrated that all the Zr 0.6−x Ti 0.4 Nb x Ni alloys consisted of the primary phase with the B33-type orthorhombic structure and the secondary phase with the B2-type Ti 0.6 Zr 0.4 Ni cubic structure. Rietveld refinement demonstrated that the atomic fraction of the secondary phase increased with the Nb content. The Zr 0.6−x Ti 0.4 Nb x Ni alloys were lower in hydrogen storage capacity than the Nb-free Zr 0.6 Ti 0.4 Ni alloy due to an increase in the abundance of the secondary phase. In the charge-discharge tests with the Zr 0.6−x Ti 0.4 Nb x Ni alloy negative electrodes, all the initial discharge curves had two potential plateaus due to the electrochemical hydrogen desorption of trihydride to monohydride and monohydride to alloy of the primary phase. The total discharge capacities at 333 and 303 K for the Zr 0.58 Ti 0.4 Nb 0.02 Ni alloy negative electrode were 384 and 335 mAh g −1 , respectively, which were higher than those of the other Zr 0.6−x Ti 0.4 Nb x Ni and Zr 0.6 Ti 0.4 Ni alloy negative electrodes.
Ti electrolysis by using a DC-ESR unit was performed in a CaF2-CaO-TiO2 bath, and the influence of the bath composition was discussed. Ti metal in liquid was electrodeposited though some impurity elements were contained. The cathodic current efficiency strongly depended on the bath composition, and reached about 25% in the bath where the molar ratio of CaO to TiO2 was 1.5. The consumed electric power was also affected by the bath composition so that the close relationship between the cathodic current efficiency and the electric power was seen. The influence of the bath composition was considered due to the change in the species in the bath, and Ca3Ti2O7 seemed suitable for Ti deposition.
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