Electrochemical preparation of NiAl intermetallic compound from solid oxides in molten CaCl2 and its corrosion behaviors in NaCl aqueous solution

Nickel aluminide powders were prepared by direct electrochemical reduction of solid mixture of NiO–NiAl2O4 (Ni:Al = 1:1 in mol) precursor in molten CaCl2 at 850 °C. The reduction process of the solid oxide cathode was investigated by analyzing the intermediate products using X-ray diffraction (XRD) and scanning electron microscopy (SEM). It reveals that nickel is preferentially reduced and it benefits to prevent aluminum leaving from the cathode. The products obtained at the constant cell voltage electrolysis of 3.0 V for more than 4 h were stoichiometric NiAl. The energy consumption could be as low as 6.1 kWh (kg-NiAl)−1 based on the applied cell voltage and the consumed electrolysis charge. Furthermore, the NiAl powders were made into a dense rod by spark plasma sintering (SPS) technique. The corrosion behaviors of the NiAl rod in 0.5 mol L−1 NaCl aqueous solution at room temperature were investigated by polarization curve and ac impedance measurements. It was found that the NiAl rod had satisfactory anti-corrosion ability in the solution.

► Stoichiometric NiAl powder was prepared by one-step electrolysis of solid NiO–NiAl2O4 in molten CaCl2.
► The energy consumption was as low as 6.1 kWh (kg-NiAl)−1.
► Uniform distribution and co-reduction of Ni and Al oxide played key role for Al retaining.
► Electrolytic NiAl powder was made into dense NiAl rod by spark plasma sintering (SPS).
► Obtained NiAl rod was self-passivated in NaCl solution and show very high corrosion resistance.