EFFECT OF Cu-Ni CONTENT ON THE CORROSION RESISTANCE OF(Cu-Ni)/(10NiO-90NiFe204)CERMET INERT ANODE FOR ALUMINUM ELECTROLYSIS

（Cu-Ni）/（10NiO-90NiFe204） cermet inert anodes containing metal Cu-Ni0, 5, 10, 15 and 20 wt pct were prepared and their corrosion resistance to Na3AlF6-Al2O3 melts was investigated. The results indicate that the content of metal Cu-Ni has little effect on the steady-state concentration of Ni in the electrolyte and the values could not be used to effectively differentiate their corrosion resistance. The steady-state concentration of Fe decreases from 304×10^-6 to 168×10^-6 and that of Cu increases from 21×10^-6 to 71×10^-6 with the content of metal Cu-Ni increasing from 0 to 20 wt pct. Post-examination shows that metallic phase Cu-Ni is corroded preferentially during electrolysis and many pores are left at the anode surface. Considering the corrosion resistance and electrical conductivity, the cermet containing metal Cu-Ni 5 wt pct should be selected and studied further.

EFFECT OF STRUCTURAL PARAMETERS ON THE THERMAL STRESS OF A NiFe_(2)O_(4)-BASED CERMET INERT ANODE IN ALUMINUM ELECTROLYSIS

Inert anode has been a hot issue in the aluminum industry for many decades. With the help of FEA （finite element analysis） software ANSYS, a model was developed to simulate the thermal stress distribution working condition of an inert anode. To reduce its thermal stress, the effect of some parameters on the thermal stress distribution was investigated, including the anode height, the anode radius, the hole depth, the hole radius, and the radius of inner chamfer and outer chamfer. The results showed that in the actual working condition of an inert anode, there existed a large axial tensile stress near the tangent interface between the anode and bath, which was the major cause of anode breaking. Increasing the anode height and reducing the hole depth properly seemed to be beneficial for the stress distribution. With the increase of anode radius, the stress distribution became better first and then deteriorated, the reasonable value was between 0.045 to 0.06m. The hole radius had a significant effect on the stress and a smaller radius would reduce the thermal stress. The effect of the radius of the inner chamfer and the outer chamfer was less than other parameters.

Microstructure and electrolysis behavior of self-healing Cu-Ni-Fe composite inert anodes for aluminum electrowinning

The microstructure evolution and electrolysis behavior of(Cu_(52)Ni_(30)Fe_(18))–x Ni Fe_2O_4(x=40wt%,50wt%,60wt%,and 70wt%)composite inert anodes for aluminum electrowinning were studied.Ni Fe_2O_4 was synthesized by solid-state reaction at 950°C.The dense anode blocks were prepared by ball-milling followed by sintering under a N_2 atmosphere.The phase evolution of the anodes after sintering was determined by scanning electron microscopy and energy-dispersive X-ray spectroscopy.The results indicate that a substitution reaction between Fe in the alloy phase and Ni in the oxide phase occurs during the sintering process.The samples were also examined as inert anodes for aluminum electrowinning in the low-temperature KF–NaF–AlF_3 molten electrolyte for 24 h.The cell voltage during electrolysis and the corrosion scale on the anodes were analyzed.The results confirm that the scale has a self-repairing function because of the synergistic reaction between the alloy phase with Fe added and the oxide phase.The estimated wear rate of the(Cu_(52)Ni_(30)Fe_(18))–50Ni Fe_2O_4 composite anode is 2.02 cm·a^(-1).

Electrical Conductivity and Corrosion Resistanceof ZnFe _(2)O _(4) Based Materials Used as Inert Anodefor Aluminum Electrolysis

ZnFe 2O 4 and ZnFe 2O 4 based materials were tested to obtain the electrical conductivity and corrosion resistance in melting bath for aluminum electrolysis. The results proved that adequate additives, such as Ni 2O 3 CuO, Cu, ZnO and CeO 2 would increase the electrical conductivity, and the ZnFe 2O 4 based anodes with these additives were of good corrosion resistance. The current density on anode, the mole ratio of NaF/AlF 3 (MR) and the content of alumina in the bath effect the anode corrosion rate in different way.

LOW TEMPERATURE ALUMINUM FLOATING ELECTROLYSIS IN HEAVY ELECTROLYTE Na_3AlF_6-AlF_3-BaC1_2-NaCl BATH SYSTEM

Multiple regression equations of liquidus temperature, electrical conductivity and bath density of the Na_3AlF_6-AlF_3-BaC1_2-NaCl system were obtained from experiments by using orthogonal regression method. The experiments were carried out in 100A cell with low melting point electrolyte, the influences of cathodic current density, electrolytic temperature, density differences of bath and liquid aluminum on current efficiency (CE) were studied; when the electrolyte cryolite ratio was 2.5, w(BaC1_2) and w(NaCl) were 48% and 10%, respectively, CE reached 90% and specific energy consumption was 10.97k Wb/kg/kg. Because of the fact that aluminum metal obtained floated on the surface of molten electrolyte, this electrolysis method was then defined as low temperature aluminum floating electrolysis. The results showed that the new low temperature aluminum electrolysis process in the Na_3AlF_6-AlF_3-BaC1_2-NaCl bath system was practical and promising.

MATHEMATICAL MODELLING OF BUBBLE DRIVENFLOWS IN A NOVEL ALUMINUM ELECTROLYSIS CELL

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Laboratory study of property-modified prebaked carbon anode and application in large aluminum electrolysis cells

A kind of complex additive mainly containing Al, Mg, F, and O was prepared. The synthetical performances of the property-modified prebaked anodes containing additives were tested in laboratory. On the basis of ideal testing results obtained, a large number of industrial prebaked property-modified anodes are prepared in a large-scale aluminum company. Further more, they are all used in 160 kA prebaked anode aluminum electrolysis cells. The statistic result show that, compared with common anodes, the property-modified ones enhance current by 11.6 kg per ton aluminum averagely.

Digital characterization and mathematic model of sodium penetration into cathode material for aluminum electrolysis

The sodium expansion curves of semi-graphitic cathode and TiB2/C composite cathode with different TiB2 contents were measured with the improved Rapoport-Samoilenko apparatus. The mathematic model of the sodium expansion was deduced on the basis of the experimental results. The sodium expansion parameter (a) and penetration rate factor (Q), were introduced into the model. The model was validated with the experimental sodium expansion curves self-measured and reported. The results show that the variation tendency of the sodium expansion parameter (a) and penetration rate factor (Q) is consistent with that of the experimental curves. The model is capable of not only conveniently judging the cathode quality, but also favorably establishing a unified standard of the resistance to sodium penetration of cathode.

Preparation and preliminary testing of cermet inert anode for aluminum electrolysis

Recent development of inert anodes for the primary aluminium industry was reviewed. The preparation method of functionally gradient material was introduced into inert anode research area, and a research flow sheet of functionally gradient cermet inert anode was set down. In order to carry out the preparation and optimization of composite oxides as the ceramic matrix of cermet inert anode, the following problems: solid state reaction synthesis of complex oxides, corrosion mechanism of complex oxides in Na 3AlF 6 Al 2O 3 melts, effects of NiO content on the corrosion rate and resistivity at high temperature of NiFe 2O 4 NiO ceramics were studied. The preparation and sintering mechanism of NiFe 2O 4 based cermets were deeply studied to properly control the sintering atmosphere and temperature system. By efficaciously controlling the sintering atmosphere, the oxidization of metallic phase and the decomposition or deoxidization of ceramic phase are avoided effectively during the sintering process of cermets at various temperatures. By optimizing the composition recipe and sintering temperature system, cermets of relatively high density are prepared without the spillage or asymmetric distribution of metallic phase.

Electrical resistivity of TiB_2/C composite cathode coating for aluminum electrolysis

The electrical resistivity of TiB2/C cathode composite coating at different temperatures was measured with the electrical conductivity test device; the effects of TiB2 content and kinds of carbonaceous fillers as well as their mean particle size on their electrical resistivities were investigated. The results show that electrical resistivity of the coating decreases with the increase of TiB2 content and the decrease of its mean particle size. When the mass fraction of TiB2 increases from 30% to 60%, the electrical resistivity of the coating at room temperature decreases from 31.2μΩ·m to 23.8μΩ·m. The electrical resistivity of the coating at 960℃ lowers from 76.1μΩ· m to 38.4μΩ·m with the decrease of TiB2 mean particle size from 12μm to 1μm. The kinds of carbonaceous fillers have great influence on the electrical resistivity of TiB2/C composite coating at 960℃, when the graphite, petroleum coke and anthracite are used as fillers, the electrical resistivities of the coating are 20.3μΩ·m, 53.7μΩ·m and 87.2μΩ·m, respectively. For the coating with petroleum coke filler, its electrical resistivity decreases with the increase of the mean particle size of petroleum coke filler. The electrical resistivity at 960℃ decreases from 56.2μΩ·m to 48.2μΩ·m with the mean particle size of petroleum coke increasing from 44μm to 1200μm. However, too big carbonaceous particle size has adverse influence on the abrasion resistance of coating. Its proper mean particle size is 420μm.

Results from 100 h electrolysis testing of NiFe_2O_4 based cermet as inert anode in aluminum reduction

A 100 mm diameter cup-shaped inert anode for aluminum electrolysis consisting of cermet 17Ni/83(10NiO-90NiFe2O4) was prepared and the operating performance was evaluated in a laboratory cell with the electrolyte CR2.3 and Al2O3 concentration 7.43% (mass fraction). The results indicate that no major operational difficulties are encountered during the testing which lasts for 101.5 h and the inert anode exhibits good general performances. The steady-state average concentration of impurity Ni in the bath is close to the solubility, however, the Fe concentration is lower than its solubility. The contents of the main contaminants for aluminum produced are Ni 0.128 8%, Fe 1.007 4%. The corrosion rate of inert anode under electrolysis conditions based on the content of impurity Ni in metal aluminum is approximately 8.51 mm/a.

Numerical simulation of busbar configuration in large aluminum electrolysis cell

Various busbar configurations were built and modeled by the custom code based on the commercial package ANSYS for the 500 kA aluminum electrolysis cell.The configuration parameters,such as side riser entry ratio,number of cathode bars connected to each riser,vertical location of side cathode busbar and short side cathode busbar,distance between rows of cells in potline,the number of neighboring cells,ratio of compensation busbar carried passing under cell and its horizontal location under cell along with large magnetohydrodynamic(MHD) computation based on the custom evaluation function were simulated and discussed.The results show that a cell with riser entry ratio of 11:9:8:9:11 and cathode busbar located at the level of aluminum solution,50% upstream cathode current passing under cell for magnetic field compensation,the distance between rows of 50 m is more stable.

Ambient temperature cured TiB_2 cathode coating for aluminum electrolysis

The concept of ambient temperature curable TiB 2 cathode coating was put forward, and the ambient temperature curable TiB 2 cathode coating was prepared successfully. Differing from the previous TiB 2 cathode coating solidified approximately at 200 ℃,the ambient temperature curable TiB 2 cathode coating can be solidified at room temperature, so the heating equipment is not necessary, which simplifies the preparation process and facilitates the industrial application of TiB 2 cathode coating. Many kinds of resin and curing agent were investigated. On the above mentioned basis, the ambient temperature curable TiB 2 cathode coating was prepared with furan resin 5 500 mixed with complex resins B as carbon binder and DXG1 as curing agent in 24 h. The results show that the properties of prepared coating are excellent, the electrical resistivity is 29.8 μΩ·m, the compressive strength is 33.6 MPa, which are all better than the relevant properties of partially graphitized cathode carbon block for aluminum electrolysis prescribed by the GB 8744 88. SEM morphologies show that the section morphology of the TiB 2 coating is unaltered during the electrolysis test, the TiB 2 coating can be used in aluminum electrolysis industry to save energy and prolong the life of aluminum electrolysis cell.

A Cell Condition-Sensitive Frequency Segmentation Method Based on the Sub-Band Instantaneous Energy Spectrum of Aluminum Electrolysis Cell Voltage

Cell voltage is a widely used signal that can be measured online from an industrial aluminum electrolysis cell.A variety of parameters for the analysis and control of industrial cells are calculated using the cell voltage.In this paper,the frequency segmentation of cell voltage is used as the basis for designing filters to obtain these parameters.Based on the qualitative analysis of the cell voltage,the sub-band instantaneous energy spectrum(SIEP)is first proposed,which is then used to quantitatively represent the characteristics of the designated frequency bands of the cell voltage under various cell conditions.Ultimately,a cell condition-sensitive frequency segmentation method is given.The proposed frequency segmentation method divides the effective frequency band into the[0,0.001]Hz band of lowfrequency signals and the[0.001,0.050]Hz band of low-frequency noise,and subdivides the lowfrequency noise into the[0.001,0.010]Hz band of metal pad abnormal rolling and the[0.01,0.05]Hz band of sub-low-frequency noise.Compared with the instantaneous energy spectrum based on empirical mode decomposition,the SIEP more finely represents the law of energy change with time in any designated frequency band within the effective frequency band of the cell voltage.The proposed frequency segmentation method is more sensitive to cell condition changes and can obtain more elaborate details of online cell condition information,thus providing a more reliable and accurate online basis for cell condition monitoring and control decisions.

Densification of Ni-NiFe_2O_4 cermets for aluminum electrolysis

The density of cermet inert anodes in aluminum electrolysis is of great importance. Ni-NiFe2O4 cermets were studied with respect to their densification affected by ball milling time, particle size of raw powders, contents of metallic phase, sintering atmosphere and temperature. The results show that, prolonging ball milling time will increase the density with the optimum value of 150min; cermets containing 0-15%Ni（mass fraction） have high relative density ranging from 94% to 96%, but with Ni content increasing, the density slightly decreases; weak reductive atmosphere is favorable to densification; the relative density increases from 80.38% to 96.85% with the sintering temperature increasing from 1100℃ to 1300℃ while it decreases at 1400℃, which may be due to crystal grain coarsening. So the sintering temperature of Ni-NiFe2O4 cermets in current work should be controlled at 1300℃, where the relative density is 96.85%.

Effect of metallic phase content on mechanical properties of (85Cu-15Ni)/(10NiO-NiFe_2O_4) cermet inert anode for aluminum electrolysis

(85Cu-15Ni)/(10NiO-NiFe2O4) cermets were prepared with Cu-Ni mixed powders as toughening metallic phase and 10NiO-NiFe2O4 as ceramic matrix. The phase composition, microstructure of composite and the effect of metallic phase content on bending strength, hardness, fracture toughness and thermal shock resistance were studied. X-ray diffraction analysis indicates the coexistence of (Cu-Ni), NiO and NiFe2O4 phases in the cermets. Within the content range of metallic phase from 0% to 20% (mass fraction), the maximal bending strength (176.4 MPa) and the minimal porosity (3.9%) of composite appear at the metallic phase content of 5%. The fracture toughness increases and Vickers’ hardness decreases with increasing metal content. When the thermal shock temperature difference (△t) is below 200 ℃, the loss rate of residual strength for 10NiO-NiFe2O4 ceramic is only 8%, but about 40% for (85Cu-15Ni)/(10NiO-NiFe2O4) cermets. As △t is above 200 ℃, the residual strength sharply decreases for sample CN0 and falls slowly for samples CN5-CN20.

Industrial testing of property-modified prebaked carbon anode for aluminum electrolysis

Aiming at reducing energy and carbon consumption and enhancing current efficiency of aluminum electrolysis, a batch of property modified prebaked carbon anodes prepared in industrial production were applied to 160 kA prebaked anode aluminum electrolysis cells in a domestic aluminum company. The industrial statistical data show that, the property modified anodes can averagely reduce carbon consumption 11.6 kg per ton aluminum and energy consumption 106.1 kW·h, further more, enhance current efficiency 0.72%. The industrial testing results prove that this kind of new type of prebaked anodes has remarkable effect of saving energy, reducing carbon consumption and enhancing current efficiency of aluminum electrolysis.

Effect of electromagnetic force and anode gas on electrolyte flow in aluminum electrolysis cell

Based on the commercial computational fluid dynamics software CFX-4.3, electrolyte flow fields in a 156 kA pre-baked anode aluminum electrolysis cell were investigated in three different cases where the electrolyte melt was driven by different kinds of force, i.e. electromagnetic force only, the anode gas drag force only and both of the former two forces. The results show that when electromagnetic force was introduced only, most of the electrolyte moves horizontally; when anode gas drag force was introduced only, the electrolyte flows mainly around each anode with small circulation; when electromagnetic force and anode gas drag force were both introduced together, the structure of the electrolyte flow fields and the velocity of electrolyte are similar to that of the case where only anode gas drag force is used. The electrolyte flow fields are mainly determined by the anode gas drag force.

Industrial preparation and performance testing of property-modified prebaked carbon anodes for aluminum electrolysis

On the base of filtering composite additives in laboratory, the industrial property-modified prebaked carbon anodes containing composite additives were prepared in factory. The performance tests show that this kind of anodes not only have the same excellent physical performance as common (contrasting) ones used in aluminum electrolysis production at the present time, but also have better chemical and electrochemical performance than that of the common ones. Furthermore, the industrial preparation of the property-modified prebaked anode lays the foundation of electrolysis test. It can be forecasted that property-modified anodes will have good behavior in aluminum electrolysis production.

Effect of electromagnetic force on turbulent flow of molten metal in aluminum electrolysis cells

The standard k-ε model was adopted to simulate the flow field of molten metal in three aluminum electrolysis cells with different anode risers. The Hartman number, Reynolds number and the turbulent Reynolds number of molten metal were calculated quantitatively. The turbulent Reynolds number is in the order of 103 , and Reynolds number is in the order of 104 if taking the depth of molten metal as the characteristic length. The results show that the molten metal flow is the turbulence of high Reynolds number, the turbulent Reynolds number is more appropriate than Reynolds number to be used to describe the turbulent characteristic of molten metal, and Hartman number displays very well that electromagnetic force inhibits turbulent motion of molten metal.