Preliminary testing of NiFe_2O_4-NiO as ceramic matrix of cermet inert anode in aluminum electrolysis

摘要

Sintered samples of nickel ferrite-nickel oxide ceramic, usually used as the ceramic phase of cermet inert anode in aluminum electrolysis, were prepared and characterized. The solubilities of NiFe_2O_4-NiO ceramics were measured using an equilibration technique in the Na_3AlF_6-10%AlF_3-5%CaF_2-5%Al_2O_3 melts at 960℃. Electrical resistivity was also measured for NiFe_2O_4-NiO ceramic samples prepared using the usual ceramic technique as function of temperature and content of NiO with an improved pyroconductivity test device, consisting of a specially constructed closed furnace and a Potentiostat/Galvanostat, based on the conventional direct current four-probe technique. Results show that, under the experimental conditions, the solubility of Fe from NiFe_2O_4 is 0.06% and Ni from NiFe_2O_4 is 0.008%. The solubility of Fe and Ni from NiFe_2O_4-NiO ceramic is inversely related to each other. The solubility of Ni increases but overall solubility of NiFe_2O_4-NiO ceramics decreases with increasing NiO content. The studied ceramic samples have a semiconductor behavior where electrical resistivity ρ decreases with increasing temperature and the resistivity ρ increases with increasing porosity. The resistivity ρ of NiFe_2O_4-NiO ceramic shows a minimum with increasing the content of NiO at various temperatures.