Direct Electrochemical Preparation of Ni-Cr Alloy from Solid Oxides in Molten CaCl₂

Abstract

Direct electro-reduction of mixed powders of chromium oxide (Cr 2 O 3 ) and nickel oxide (NiO) to the intermetallic compound Cr 1.12 Ni 2.88 was successfully demonstrated in CaCl 2 molten salt at 900 • C. The reduction mechanism was investigated by cyclic voltammetry using a metallic cavity electrode (MCE) as well as the characterizations of some partially electrolyzed products and Ni-Cr alloy prepared from constant voltage electrolysis by terminating the reduction process after different times, which were characterized by means of XRD and SEM et al. It was found that the reduction starts with the formation of Ni metal, accompanied with the formation of an intermediate product CaCr 2 O 4 . Then, the intermediate product CaCr 2 O 4 is further electro-reduced to Cr, which is directly alloyed with the newly-formed Ni to form the Ni-Cr intermetallic compound. At the same time, pure Cr phase could not be detected by the XRD or EDXA when the Cr content is relatively low in the NiO-Cr 2 O 3 mixture. Intermetallic compound with the target stoichiometry containing 6000 ppm oxygen is obtained after 4 h electro-reduction in CaCl 2 molten salt at 900 • C.

Studies on Preparation of Thorium-Based Intermetallics in CaCl2 Melt by Electrochemical De-Oxidation Process

“…Liu et al studied the electroreduction behaviour of NiO in Mo-CE in CaCl 2 melt at 900 °C by cyclic voltammetry and reported the reduction potential of NiO as 1.5 V (vs Ca 2+ |Ca). 59 Qiu et al also probed into the reduction phenomenon of NiO in molten CaCl 2 using Mo cavity electrodes by cyclic voltammetry technique. 60 In the study, the reduction of NiO was found to occur at 0.8 V (vs Ca 2+ |Ca) in Mo-CE with one mechanically drilled hole and at 1.1 V (vs Ca 2+ |Ca) in Mo-CE with two laser-drilled holes.…”