Corrosion Resistance Mechanism of Mica/Epoxy Coatings with Different Mica Contents in a CO2-Cl- System

• Published in: International journal of electrochemical science 2022-04, Vol.17 (4), p.22043, Article 22043
• Main Authors: Zhu, Shidong, Dong, Pan, Zhang, Xiaobo, Li, Chengzheng, Hu, Xiao, Fu, Anqing, Song, Shaohua, Wang, Ziwen
• Format: Article
• Language: English
• Subjects: Coating; Corrosion resistance; Electrochemical characteristics; Epoxy resin; Mica
• ISSN: 1452-3981; 1452-3981
• DOI: 10.20964/2022.04.17

With the development of deeper oil and gas reservoirs, the service environment for tubings applied for oil and gas transport is getting worse, and the requirements for the corrosion protection levels of tubings and casings have become more stringent. As a result, a heavy-duty coating was applied. Mica, often used as a filler in anticorrosive coatings, has good heat resistance, (electro)chemical corrosion resistance and electrical insulating properties, which can increase the corrosion resistance of polymer-based coatings. In this paper, the mica was first modified, and then the thermal stability of the resultant mica/epoxy coating was analysed by a thermogravimetric analyser. The service environment of the coating was simulated by a high-temperature autoclave, the electrochemical characteristics of the coating were studied using an electrochemical workstation assisted by three electrodes, and the coating’s surface characteristics were observed by electron scanning microscopy. The results showed that the modified mica was successfully grafted with the coupling agent KH-550, which enhanced the stability of the mica in the epoxy coating. The thermal stability of the mica/epoxy coating first increased and then decreased with increasing mica content, and the thermal stability was best for the mica/epoxy coating containing 35 wt% mica. The addition of mica effectively slowed the diffusion rate of the corrosive medium through the coating in a CO2-Cl- system (the diffusion coefficient was reduced by an order of magnitude), improved the corrosion resistance of the coating, and prolonged the protective time of the coating towards the metal matrix. The protective performance of the coating also increased first and then decreased with increasing mica content, and the mica/epoxy coating prepared with 35 wt% mica had the best protective performance. Furthermore, combined with information about the contact angle, water absorption characteristics and adhesion properties of the composite coating, it was found that the internal diffusion rate of the medium through the coating decreased, and there was a negative correlation between water absorption kinetics and corrosion kinetics. Finally, a corrosion resistance mechanism for the mica/epoxy coating was proposed to provide theoretical support for the development of new heavy corrosion coatings.