Preparation And Study Of Al₃Ti-based Alloy As Inert Anode

Nowadays, In Aluminum industry, inert anodes attract more and more attention for saving high-quality carbon, a high degree of automation and being friendly to the environment without releasing carbon dioxide. There are increasingly scholars seeking appropriate inert anode materials, which can be used in aluminum electrolysis. In the thesis the possibility of using Al3Ti alloy and Al3Ti-Cu alloy as dynamic anode were studied.Al3Ti intermetallic compounds had been prepared by vacuum induction melting. The XRD and SEM of ingots show that the major phase is Al3Ti and chemical composition is homogeneous. In addition, Al3Ti-Cu had been prepared by vacuum carbon tube melting. The XRD of ingots show that the major phase is Al3Ti, Al and TiCu.Oxidation tests were taken in air and oxygen atmosphere at different temperature, obtaining the oxidation kinetics, investigating the influence of the temperature, oxygen concentration and oxidation time on the Al3Ti alloy. The XRD and SEM of samples showed that there were Al2O3films, the thickness was5～8μm. The oxidation kinetics curves of Al3Ti alloy follow cubic law, the alloy has excellent oxidation resistance.Oxidation kinetic constants were calculated at different temperature; It is discovered that oxidation kinetic constants increases with the temperature increases in air atmosphere, which indicates that the increasing in temperature could accelerate the oxidation of the anode. At900℃, the oxidation rate of Al3Ti in oxygen atmosphere is greater than that in air atmosphere.In addition, at1000℃, extending the oxidation time has little influence on oxide film, which has the same composition, and the thickness of the layer slightly increased. Therefore, extending the oxidation time has no significant contribution on the oxide film of Al3Ti.In this paper, the organization and morphology of Al3Ti inert anodes before and after oxidation were studied. The SEM of samples show that the pre-oxidation Al3Ti grains distribute uniform, the gap between the grains is small, and Al exist in the gap. After oxidation, Al3Ti grains become larger and orderly, the gap between Al3Ti grains become the channels of aluminum proliferation, the channels directly to the outer surface of the anode. Aluminum is oxidized into alumina at the surface of the anode, the formation of oxide layer protect the anode from corrosion.Oxidation test of Al3Ti-Cu was taken in air atmosphere for12hours at900℃, The XRD of sample shows that Al2O3and CuO films were formed. The SEM of sample showed that the oxide layer was about10～15μm.The non-polarization corrosion experiment of Al3Ti sample was taken. The corrosion rate is0.656mg/cm·h.; Electrolysis experiments had been done in Aluminum Reduction Cell, analysis of the process of electrolysis shows that the electrolysis process of "inert" anode occurred. There is no remarkable difference in the size of anode before and after electrolysis. There is one corrosion layer on the surface of anode because of the invasion of electrolyte, which indicates that the oxide film dissolution rate is greater than the formation rate.Electrochemical corrosion experiments of Al3Ti and Al3Ti-Cu anode were taken, polarization curves in different Al2O3concentrations were obtained by potentiodynamic scanning method. It is discovered that the passivating film of Al3Ti is unstable in the unsaturated Al2O3concentration, the oxide film dissolution rate is greater than the formation rate, while in saturated Al2O3concentration, passivation is occurred on the anode, passivating film is formed and can be used to protect the anode substrate, oxygen is evolved on the anode, it indicates that Al3Ti anode is "inert", the critical passivation current density of Al3Ti is8.6A/cm2, and the the critical passivation potential is2.5V.Polarization curves of Al3Ti-Cu anode in saturated Al2O3concentration was obtained, the critical passivation current density is5.2A/cm2, which is apparently less than Al3Ti, it indicates that the corrosion rate of Al3Ti-Cu anode is less than Al3Ti, and has better corrosion resistance than Al3Ti, it means that Al3Ti-based alloy anode can be used as inert anode material in aluminum electrolysis, and we should do more further research about it.