| NiFe2O4based cermets are one of the most promising industrial inert anode materials, which have been carried out4kA and6kA pilot electrolysis. The electrolysis test shown that the electrical conductivity and thermal shock resistance of the cermet anodes need further improving. In order to increase the electrical conductivity and improve the thermal shock resistance of the cermet anodes, while not reducing the corrosion resistance, the effects of oxygen partial pressure and the addition of Ni on the wettability of Cu and NiFe2O4, and the phase reactions and sintering behavior of copper alloy-nickel ferrite cermets during sintering process were firstly studied. Then a dense copper alloy-nickel ferrite cermet with interpenetrating structure was preparated respectively by conventional ceramic process and infiltration through optimizing the sintering condition. The effects of the material porosity, metal phase content, metal phase composition, oxidation temperature on the oxidation behavior of the prepared cermets were studied. Also the influences of pre-oxidation thermal treatment, current density, electrolytic temperature on the corrosion behavior of the cermet anodes with interpenetrating structure were studied. The main results were shown as follow:(1) A new method to drastically improve the wettability of Cu and NiFe2O4was developed. It was found that increasing the oxygen partial pressure or adding Cu2O into Cu could improve the wettability of Cu and NiFe2O4. The contact angle decreased to0°at1200℃when Cu2O content was upto7wt%. A Cu/NiFe2O4-10NiO cermet with a relative density of99%and interpenetrating structure was firstly prepared by pressureless infiltration.(2) The mechanisms of NiO and the metal phase on the densification of copper alloy-nickel ferrite cermets were clarified. The dissolution precipitation mechanism of NiO was found in copper alloy melt, which was conducive to the sintering densification during liquid sintering process. The oxidation of Ni of Cu-Ni alloy could promote the decomposition and sintering densification of NiFe2O4phase.(3) The cause of the increase of Ni content in the metal phase was clarified. The reduction of NiFe2O4was found when binder burnout process was performed in N2, which produced metal Ni and increased the Fe2+content of NiFe2O4. The merging of new formed Ni with the additive Cu-Ni was the main reason that caused the increase of Ni content in the metal phase. The reduction of NiFe2O4during binder burnout process could promate the sintering densification of NiFe2O4.(4) A copper alloy-nickel ferrite cermet with good mechanical property and electrical conductivity was prepared. The bending strength and fracture toughness of40(Cu-50Ni)/NiFe2O4-10NiO cermets prepared by conventional ceramic process were206MPa and16.1MPa·m1/2, respectively. The bending strength hardly decreased after Δ200℃thermal treatment. The electrical conductivity of the cermets was about513S/cm at960℃. The mechanical property and electrical conductivity of26Cu/NiFe2O4-10NiO cermet prepared by infiltration were comparable with that of the cermets with40wt%metal phase content prepared by conventional ceramic process.26Cu/NiFe2O4-10NiO cermet has the characteristic of metal conductivity, whose electrical conductivity was about1369S/cm at960℃.(5) A technique that could inhibit the fast electrochemical corrosion of metal phase of copper alloy-nickel ferrite cermets with interpenetrating structure was developed. Oxidation of the metal phase before dissolution could be realized by pre-oxidation thermal treatment and controlling the electrolysis temperature, to avoid the fast electrochemical corrosion of the metal phase. The study showed that a dense ceramic layer could be formed on the bottom of40(Cu-50Ni)/NiFe2O4-10NiO cermet anode when electrolysis was carried out at960℃and pre-oxidized at880℃for48h in air, was conducive to impede the penetration of the electrolyte and metal phase electrochemical corrosion, and well corrosion resistance.This research is of great significance on the preparation of cermet inert anode, connection of cermet anode and alloy guide bar, even on the promotion of the industrial application of cermet anode. |
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