NiFe ₂ O ₄ Inert Anode Preparation And Metal / NiFe ₂ O ₄ Wettability Studies

Inert anode is becoming a hot topic and has great applied value in electrolytic production of aluminium. Energy-saving, environmentally friendly, reducing emissions and increase of efficiency are the main developing trend in electrolytic production of aluminium. Inert anode preparation and performance investigation have made great progress after many years of research. Even so, the good performance of NiFe2O4based cermet still could not meet the requirement of the inert anode for aluminum electrolysis industry due to their non-wetting of metal/NiFe2O4, electrical conductivity, corrosion resistance and mechanical strength, etc. These problems have seriously hindered the development of industrialization of inert anode.In the thesis, the NiFe2O4-NiO-Cu-Ni inert anode was synthesized by manufacturing route of planetary mill grinding, calcination, secondary planetary mill grinding, cold isostatic compaction (CIP) and sintering technology. The research aimed at resistances to thermal shock, corrosion resistances and wettability of metal/NiFe2O4in NiFe2O4-NiO-Cu-Ni Inert anode systems. The experimental operating parameters of mill grinding, experimental operating parameters of CIP, the wettability of metal/NiFe2O4in NiFe2O4-NiO-Cu-Ni Inert anode systems and sintering technology were studied systematically. Main contents and conclusions of this thesis are as follows:(1) The relations of grinding efficiency and noisy-power dissipation in NiO/Fe2O3wet grinding process have been studied. The experimental results show that the best grinding parameters are as follows:water-tilling ratio64.1%～85.47%, balls number ratio18, rotation-to-revolution speed300.9rpm, powder-filling ratio about10.88%, ball-filling ratio20.53%～23.88%, grinding time about6h. By the XRD, SEM and BET characterization, the results show that the particle size is about200nm, the appearance of particle is plate-shaped. The degree of mixedness of powder is>95%by mathematical analysis. Furthermore, the discrete element method (DEM) is employed to investigate and analyze the relations of noisy-power dissipation and efficiency. The empirical equation between noisy-power dissipation and ball-filling ratio was obtaind by fitting. It is interesting to find that the mean particle size of powder increase, the efficiency of planetary ball mill grinding and utilization of specific impact energy decrease with the noisy-power dissipation increases. (2) The lifting pressure rate, briquetting pressure, dwell time, pressure release rate and length diameter ratio are investigated on the CIP. The experimental results show that the best CIP parameters are as follows:lifting pressure rate1.0MPa·s-1, briquetting pressure～240MPa, dwell time has less influence on small-diameter pressed green compact, pressure release rate≤0.5MPa·s-1, length diameter ratio8.00. Based on the model analysis on the briquetting pressure and length diameter ratio, the results show that the bulk density of pressed compact is positively correlated with briquetting pressure. The empirical Equation between bulk density of pressed compac and briquetting pressure is as follows:ph=bpα, a=0.127and6=1.70. The empirical Equation between mean bulk density of pressed compac and length diameter ratio is as follows: ph=q(1+x)n, the p=-0.052and q=3.722.(3) The CH3CH2OH+PVP as novel grinding aid, dispersant agent, filmogen and binders is investigated. The results show that the disperstiveness of Cu in the NiFe2O4powder is improved and powder particle size is much smaller with increasing PVP and grinding time based on XRD, SEM and EDS characterization. The the disperstiveness of Cu in the NiFe2O4powder is great and grinded powder particle size is the smallest when the PVP=2%and grinding time=24h, and the NiFe2O4-NiO-Cu-Ni powder particle size is43.7nm. The high disperstiveness NiFe2O4-NiO-Cu-Ni nano-powder are prepared by mill grinding at first time.(4) The wetting angles of Cu-Ni/NiFe2O4-NiO are measured about NiFe2O4-NiO-Cu-Ni inert anodes by different preparation methods at first time. The wetting mechanism is discussed. The results show that the wetting angles of Cu-Ni/NiFe2O4-NiO is116.7°about NiFe2O4-NiO-Cu-Ni inert anodes by common preparation methods, and the dihedral angle of Cu-Ni/NiFe2O4-NiO is124.6°. The wetting angles of Cu-Ni/NiFe2O4-NiO is44.3°about NiFe2O4-NiO-Cu-Ni inert anodes by the novel preparation methods which NiFe2O4-NiO-Cu-Ni nano-powder is raw material and CH3CH2OH+PVP as novel grinding aid, dispersant agent, filmogen and binders. And the dihedral angle of Cu-Ni/NiFe2O4-NiO is32.7～72.9°. The wetting angles of Cu-Ni/NiFe2O4-NiO is0°when the Ti-doped in NiFe2O4-NiO-Cu-Ni inert anodes by the annovel preparation methods which NiFe2O4-NiO-Cu-Ni nano-powder is raw material and CH3CH2OH+PVP as novel grinding aid, dispersant agent, filmogen and binders. And the dihedral angle of Cu-Ni/NiFe2O4-NiO is0°.The problem of Cu-Ni/NiFe2O4-NiO wetting is fixed at first time.(5) The research results show that NiFe2O4-NiO-Cu-Ni inert anode can be obtained by sintering with Ar atmospheres. Six preparation methods for NiFe2O4-NiO-Cu-Ni inert anode preparation are studied. By analysis and comparison, it is the best manufacturing route that CH3CH2OH+PVP is novel grinding aid, dispersant agent, filmogen and binders planetary mill grinding, Ti-doped, cold CIP and sintering technology.(6) The research results show that the best sintering temperature is900℃. The small amount of Cu(Ti) solid solution and Cu4Ti alloy is formed by Ti-doped in NiFe2O4-NiO-Cu-Ni inert anode. And the nterfacial reaction wetting may be formed on the grain boundary due to reactive metal Ti-doped. And this makes the sprawl of Cu-Ni/NiFe2O4-NiO, acceleration of sintering, refine the grain and second phase particles, improvement of cermet inert anode density. The resistances to thermal shock is improved to185.71%and static corrosion is smaller than2.046mm·y-1by Ti-doped in NiFe2O4-NiO-Cu-Ni inert anode. Research result shows that the static corrosion decreases with the Ti-doped increases in NiFe2O4-NiO-Cu-Ni inert anode. The best Ti-doped amount is about1%in NiFe2O4-NiO-Cu-Ni inert anode.