Preparation Of Nano-TiN/NiFe₂O₄ Ceramic-based Inert Anodes

The graphite anodes widely used in electrolytic aluminum industry has many disadvantages,such as large consumption,environmental pollution,frequent replacement,complicated operation,and large heat loss.Inert anode materials are one of the key technologies for aluminum electrolysis because of their advantages of low consumption,no CO₂ generation,and long service life.In this paper,inert anodes were prepared by introducing TiN to NiFe₂O₄ spinel-based ceramics.Based on the requirements of its performance indicators,the technological conditions for the preparation of NiFe₂O₄/Nano-TiN ceramic inert anodes with high-temperature solid-phase synthesis method were determined,and the sintering mechanism and sitering dynamics during the preparation process were studied.?1?Based on the thermodynamic calculation of Fe₂O₃-NiO-TiN system,the TG-DSC tests were carried out under atmospheres of air,argon and nitrogen,respectively.The results showed that NiFe₂O₄ will be produced for Fe₂O₃-NiO system sintered at 1100?.The main product of Fe₂O₃-NiO-TiN sintering system with air atmosphere is NiFe₂O₄ and Ni₃TiO₅,and the Ni appears in the ceramic matrix under argon and nitrogen atmospheres.?2?The micro-structure and properties of the NiFe₂O₄ spinel ceramic substrate were tested under the atmospheres of air,argon and nitrogen,respectively.The results showed that Ni₃TiO₅ phase formation all have been observed in the samples with 4wt%TiN,which were sintered at 1300°C for 4h under three atmospheres.The argon atmosphere is more beneficial for promoting the sintering process of the samples,and the sintered samples have better shrinkage,bending strength,thermal shock resistance,and electrical conductivity.?3?The effects of sintering time and sintering temperature on the structure and properties of the samples synthesized under argon atmosphere were investigated.The results show that the extension of sintering time and increasing the sintering temperature have no significant effect on the densities of the samples.With increasing sintering temperature and expanding holding time,the bending strength increases,and then a downward trend was observed.A maximum bending strength of 80.2 MPa for the samples with 1wt%TiN sintered at 1300°C for 4 h was observed.And the thermal shock resistance was>40 times under this condition.Conductivity increases with increasing sintering temperature and expanding holding time.?4?The influence of TiN amount on the structure and properties of the specimens under argon atmosphere was investigated.The results showed that after adding1.0 wt%TiN,the shrinkage increased from 11.5%to 16.60%,and the porosity decreased from26.67%to 6.10%for the specimens sintered at 1300?for 2h.The TiN could promote the compactness of the samples,the maximum thermal shock resistance of>40 times,the maximum bending strength of 75.3 MPa,and the maximum electrical conductivity of 8.12 S·cm^-1 all occurred at the TiN content of 1.0 wt%.?5?The effect of heating rate and TiN on the sintering mechanism during the initial sintering stage was studied by the constant heating rate method.The results show that the heating rate can affect the densification of the system,and the lower heating rate can promote the densification of sintering process.At a heating rate of 5 K/min,denser samples can be obtained.At a heating rate of 5 K/min,after adding 1.0 wt%TiN,the sintering neck temperature of the samples reduced from the initial 1093°C to 1033°C,and the maximum value of linear shrinkage,¹3.81%can be obtained.After adding TiN,the sintering mechanism of Fe₂O₃-NiO system can be changed from grain boundary diffusion to volume diffusion.And the sintering activation energy of the system reduced from 446.3kJ/mol to 217.4kJ/mol.