苛刻腐蚀环境下钛合金钝化膜的稳定性研究

Study on Stability of Titanium Alloy Passivation Film under Severe Corrosion Environment

在高含CO_2、H_2S苛刻环境腐蚀试验分析的基础上,通过钛合金钝化膜的原位电化学测试分析,结合钝化膜/溶液界面第一性原理计算及分子动力学模拟,探讨了钛合金管材钝化膜的热力学稳定性。结果表明:在180℃的高温CO_2和H_2S环境中,钛合金的阳极极化曲线均有明显钝化区,腐蚀反应为阳极反应过程控制,钛合金的腐蚀速率仅分别为0.4μm/a、0.9μm/a,具有良好的抗均匀腐蚀和点蚀性能。相比于CO2腐蚀环境,TC4钛合金在H_2S环境中的腐蚀电流密度相对较高,施主浓度较高,钛合金钝化膜在H_2S环境抗腐蚀性能较差。当吸附达到稳定态后,Cl^-、HCO_3^-和HS-3种腐蚀性离子与TiO_2界面成键主要是由Cl-3p5、O-2p4、S-3p4和Ti-3d2产生电子轨道杂化。随着温度升高、Cl-浓度增大,腐蚀性离子与Ti O2的界面结合能减小,钝化膜的稳定性降低。HS^-与TiO_2的界面结合能相对较负,TC4钛合金钝化膜在H_2S环境中的热力学稳定性相对较差。

The thermodynamic stability of the passivation film of titanium alloy pipe material was discussed by the analysis of corrosion test results under the severe environment of high CO2 and H2S content,the in-situ electrochemical test of the passivation film of titanium alloy pipe material and the first-principle calculation and molecular dynamics simulation of the passivation film/solution interface. The result show that,under the CO2 and H2S environment separately and the high temperature of 180°C,the anodic polarization curves of titanium alloy have obvious passivation area,the corrosion reactions were controlled by the anode reaction process,and the corrosion rate of titanium alloy is only 0. 4 μm/a and 0. 9 μm/a respectively in CO2 and H2S environment,which shows that the titanium alloy has good resistance to uniform corrosion and pitting corrosion. Compared with CO2 corrosion environment,TC4 titanium alloy displays higher corrosion current density and higher donor concentration in H2S corrosion environment,which shows that the corrosion resistance of titanium alloy passivation film in H2S environment is worse. When the adsorption reaches a steady state,the interaction between three corrosive ions of Cl^-,HCO3^-and HS-and Ti O2 is mainly due to electron orbital hybridization of Cl-3 p5,O-2 p4,S-3 p4 and Ti-3 d2.With the increase of temperature and Cl-concentration,both the interfacial binding energy between three corrosive ions of Cl-,HCO3-and HS-and TiO2 and the stability of the passivation film of TC4 titanium alloy decrease. Compared with Cl-and HCO3-,the interface binding energy between HS-ion and TiO2 is more negative,and therefore the thermodynamic stability of the passivation film of TC4 titanium alloy in H2S environment is worse.