Study On Interface Characteristics Of Titanium Alloy Tubes In Severe Corrosion Environments

In this thesis,the interfacial characteristics of the passivation film for titanium alloy pipe were studied by in-situ electrochemical test combined with the first principle and molecular dynamics simulation of passivation film/Solution interface on the basis of severe environmental corrosion test analysis.The corrosion test results show that TC4 titanium alloy presents excellent resistance to uniform corrosion and pitting corrosion in the formation water containing CO₂ and formation water containing H₂S as well as residual acid corrosion environment due to a high thermodynamic stability passivation film has formed on the alloy surface.However,the corrosion rate of TC4 titanium alloy in the corrosive environment with high pH completion fluid is much faster than that of other corrosive environments.The results of in-situ electrochemical test display that all the polarization curves of TC4Ti alloy in the above harsh corrosive environments exist obvious passivation zone,and the electrochemical corrosion is controlled by anodic reaction process;the titanium alloy retains large polarization resistance even decrease was detected with the temperature increases.The passivation film still has good protective effect in high temperature corrosive environment,and the corrosion rate is kept in a low level.The semiconductor type of the passivation film is n-type,which has cationic selectivity.As temperature increases,the donor concentration of the passivation film increases while the corrosion resistance decreases.The first principle of the simulation results show that there is a strong charge effect between the negatively charged Cl,O and S atoms and the positively charged Ti atoms when the adsorption for corrosive ions of Cl^-,HCO₃^-,HS^-on the TiO₂ interface achieve a stable state.The charge is mainly moved from the Ti atoms to Cl,O and S surrounding.Lots of interface bonding form between Cl,O,S and Ti atoms,electronic orbital hybridization is generated by Cl-3p⁵,O-2p⁴,S-3p⁴ and Ti-3d².The results of molecular dynamics calculation of simulated working conditions show that the thermodynamic stability of the TiO2 passivation film in the H₂S environment is weak,but the TiO₂ passivation film containing noble metals,such as Pd and Ru,has great thermodynamic stability.