The adsorption characteristics of corrosive anions (Cl−, HS−, S2−, HCO3− and CO32−) on TiO2 of TC4 titanium alloy in a NaCl solution containing H2S and CO2 were studied by density functional theory (DFT). The stable adsorption configuration of each corrosive species on the TiO2 (110) surface was obtained by geometric optimization, and the electronic structure and interface binding energy were calculated and analyzed. The results showed that the optimal adsorption positions of Cl−, HS−, S2−, HCO3−and CO32− on TiO2 (110) were all bridge positions. There was a strong charge interaction between the negatively charged Cl, S and O atoms in Cl−, HS−, S2−, HCO3− and CO32− and the positively charged Ti atoms of TiO2. The interface bonding was mainly caused by charge movement from around Ti atoms to around Cl, O, S atoms. The energy levels were mainly caused by the electron orbital hybridization of Cl-3p5, S-3p4, O-2p4 and Ti-3d2. All adsorption configurations were chemical adsorption. The order of influence of the five ions on the stability of TiO2 was S2− > CO32− > Cl− > HS− > HCO3−. Finally, a novel corrosion mechanism was proposed to illustrate the dynamic evolution processes of pits.
The service environment of OCTG (Oil Country Tubular Goods) in oil and gas fields is becoming more and more severe due to the strong affinity between ions or atoms of corrosive species coming from solutions and metal ions or atoms on metals. While it is difficult for traditional technologies to accurately analyze the corrosion characteristics of OCTG in CO2-H2S-Cl− systems, it is necessary to study the corrosion-resistant behavior of TC4 (Ti-6Al-4V) alloys based on an atomic or molecular scale. In this paper, the thermodynamic characteristics of the TiO2(100) surface of TC4 alloys in the CO2-H2S-Cl− system were simulated and analyzed by first principles, and the corrosion electrochemical technologies were used to verify the simulation results. The results indicated that all of the best adsorption positions of corrosive ions (Cl−, HS−, S2−, HCO3−, and CO32−) on TiO2(100) surfaces were bridge sites. A forceful charge interaction existed between Cl, S, and O atoms in Cl−, HS−, S2−, HCO3−, CO32−, and Ti atoms in TiO2(100) surfaces after adsorption in a stable state. The charge was transferred from near Ti atoms in TiO2 to near Cl, S, and O atoms in Cl−, HS−, S2−, HCO3−, and CO32−. Electronic orbital hybridization occurred between 3p5 of Cl, 3p4 of S, 2p4 of O, and 3d2 of Ti, which was chemical adsorption. The effect strength of five corrosive ions on the stability of TiO2 passivation film was S2− > CO32− > Cl− > HS− > HCO3−. In addition, the corrosion current density of TC4 alloy in different solutions containing saturated CO2 was as follows: NaCl + Na2S + Na2CO3 > NaCl + Na2S > NaCl + Na2CO3 > NaCl. At the same time, the trends of Rs (solution transfer resistance), Rct (charge transfer resistance), and Rc (ion adsorption double layer resistance) were opposite to the corrosion current density. The corrosion resistance of TiO2 passivation film to corrosive species was weakened owing to the synergistic effect of corrosive species. Severe corrosion resulted, especially pitting corrosion, which further proved the simulation results mentioned above. Thus, this outcome provides the theoretical support to reveal the corrosion resistance mechanism of OCTG and to develop novel corrosion inhibitors in CO2-H2S-Cl− environments.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.