Aluminum Electrolytic Cathode Carbon Block Mechanical Performance Degradation Studies

The aluminum electrolysis industry of China is developing rapidly in recent years, the technical level of which is above the average in the international, but there is still a large gap in the cell life of aluminum compared with the international leading level. China’s aluminum electrolytic cells are often damaged seriously in the early time, and the problem of short cell life is very outstanding, which has been the bottleneck of our aluminum electrolysis industry, restricting the sustainable development. Among the accidents of early damage of aluminum electrolysis cells, cathode carbon blocks, the most important part of the cell, becoming invalid at the beginning is one of the most common triggering factors. Therefore, as the weakest link in the cell, the cathode carbon blocks have become one of the key components of the aluminum electrolysis cell structure, gathering more and more concerns in aluminum electrolysis industry.In this subject, relevant mechanical properties of the cathode carbon blocks are studied under the aluminum electrolysis environment using experiment device developed by ourselves, and evolution rule is described using the mathematical method, which will provide technical parameters and theoretical basis for optimization design of aluminum electrolytic cell and prolonging and forecasting the cell life. The main research contents are as follows:The influencing factors of sodium expansion of the cathode carbon blocks are studied, microscopic structure and chemical composition are compared before and after the aluminum electrolysis, the concentration and stress field distribution rule of sodium in the cathode carbon blocks is simulated by analytical method during the process of aluminum electrolysis. The results show that the higher the graphitization degree of cathode carbon blocks is,the better the sodium expansion performance is; Sodium expansion rate and final sodium expansion rate of cathode carbon blocks will increases when the electrolyte molecular ratio is increased; If the current density increase, sodium expansion rate of the cathode carbon blocks increases, but eventual sodium molecular rates are the same; The concentration and stress field distribution rule with time and space of sodium are well simulated by the analytic method, and the correctness of the simulation method and the reliability of the results are verified by sodium expansion experiment.Creep mechanics characteristic of cathode carbon blocks is studied under uniaxial compression, the creep mechanism is analyzed, and experimental results are simulated and analyzed. The results show that, in the same experimental conditions, the performance of contra variance mechanics of SMH carbon block is the best, second is HC35carbon block, HC100carbon block is the worst; Carbon block creep strains as stress level increases; In the same load stress, the order of the degree of creep deformation from small to large is as follows:30℃,965℃, aluminum electrolytic conditions; The main creep forms of carbon block are dislocation and slippage; The comparisons of simulation and the experimental results show that Burgers model gives a good description of the former two stages of the creep.The mechanical behavior of cathode carbon blocks under uniaxial compression is studied, damage theory is applied to the cathode carbon blocks, uniform damage evolutions and a constitutive model are constructed to the reflect damage and mechanical behavior of cathode carbon blocks. The results show that, in the same electrolytic conditions, mechanical properties of SMH carbon block are the best, second is HC100carbon block, HC35carbon block is the worst; Mechanics properties of Carbon block under the high temperature perform better than the one under normal temperature, and the worst is the one under high temperature melt salt electrolytic conditions; Along with the increase of the loading rate, the peak of the strength and elastic modulus of carbon block are increased; Along with the increase of electrolytic time, corrosion damage of carbon block is intensified, mechanical performance is degradated constantly; the influencing mechanism of the aluminum electrolysis environment on the mechanics properties of carbon block can be attributed to the carbon block damage accumulation; The damage evolution equation and constitutive model well reflect the influence of different aluminum electrolytic time on the mechanical properties of carbon block, and effectively describe damage process of cathode carbon blocks under the aluminum electrolytic environment.