Study Of Sintering Atmosphere And Atmosphere-changing Sintering Process For Fabricating NiFe₂O₄ Based Cermet

The new technology for aluminum smelting based on inert anode, is expected to greatly reduce energy consumption and eliminating green-house gas release. The inert anode is the key and prerequisite for successfully empoldering the new aluminum electrolysis technology.This thesis is founded by the National High Technology Research and Development Program (863 program) and the National Basic Research Program of China (973 program), aiming at improving the corrosion resistance and mechanical properties of NiFe2O4 based cermet inert anode. Based on the research of our institute, the NiFe2O4 materials are used as the inert anode, the atmosphere employed in the fabricating process of NiFe2O4 based inert anode was changed to investigate its effects on the phase composition, microstructure, corrosion resistance, mechanical properties as well as the electrical conductivity of acquired inert anode samples. Besides, further optimization of atmosphere changing sintering process for making NiFe2O4 based inert anode and investigation of their microstructure, properties are also carried out in this thesis. The major results are summarized as follows:(1) The corrosion resistance, bending strength, and electrical conductivity varied with the variation of phase composition, grainsize, and prorsity caused by altering the atmosphere. Within the range of our study, the (Ar+O2) atmosphere with about 10ppm oxygen was considered the most favorable sintering atmosphere. NiFe2O4,10NiO-NiFe2O4,5Cu/(10NiO-NiFe2O4),5Ni/(10NiO-NiFe2O4),17Ni/(10NiO-NiFe2O4), obtanined sintering in (Ar+O2) atmosphere with about lOppm oxygen, respectively have an annual corrosion rate of 2.54 cm·y-1,1.87 cm·y-1, 3.02 cm·y-1,2.32 cm·y-1,2.30 cm·y-1, a bending strength of 73.83MPa. 75.81Mpa,80.05MPa,115.70MPa,100.21MPa, and a electrical conductivity of 2.43 S·cm-1,2.09 S·cm-1,2.38 S·cm-1,4.53 S·cm-1,4.56 S·cm-1。(2) Decrease of presintering temperature and extension of oxidizing time can increase the thickness of oxidized layer formed in the outer zone of acquired inert anode samples made by atmosphere-changing sintering method. Presintering at 1125℃and oxidizing for 1h is considered the most favorable parameter for atmosphere-changing sintering process. The 17Ni/(10NiO-NiFe2O4) and 30Ni/(10NiO-NiFe2O4) fabricated under that condition got an 1504μm,506μm oxidized layer respectively. The annual corrosion rate of them amout to 0.66cm·y-1 and 1.52 cm·y-1 respectively, decreased by 71% and 72%, comparing with anodes made by traditional sintering method.