pH值对X70钢在海泥模拟溶液中微生物腐蚀行为的影响

Effect of pH Value on Microbial Corrosion Behavior of X70 Steel in a Sea Mud Extract Simulated Solution

采用动电位极化、电化学阻抗技术研究了不同pH值对X70钢在含硫酸盐还原菌(SRB)的南海海泥模拟溶液中电化学行为的影响,分析了X70钢表面发生的电化学反应。结果表明,溶液的pH值能影响SRB的生长,进而影响X70钢在南海海泥模拟溶液中的腐蚀行为。SRB在pH值为8条件下生长情况最好,在pH值为6条件下次之,在pH值为10条件下最差。pH值为8时,SRB生长期分为3个阶段:对数增长期、稳定生长期和衰亡期;pH值为6和10时,SRB生长期分为两个阶段:对数增长期和衰亡期。在对数增长期,SRB数量较少,微生物腐蚀作用较弱,X70钢的Ecorr较高,但当SRB数量增多后,微生物腐蚀作用增强,生物膜疏松且易脱落,导致局部腐蚀现象严重,Ecorr逐渐降低,金属腐蚀热力学倾向增大。在pH值为8条件下,微生物腐蚀作用最强,金属腐蚀速率最快;在pH值为10条件下,金属表面易形成钝化膜,且微生物腐蚀作用较弱,腐蚀速率最慢。

The effect of pH value on the corrosion behavior of X70 steel in an artificial liquid containing sulfate-reducing bacteria(SRB) was investigated by means of potentiondynamic polarization, electrochemical impedance spectroscopy(EIS). The artificial liquid aims to simulate a sea mud extract, while the very sea mud was collected from the shallow seabed from off shore at Sanya of Hainan Island. The results show that the p H value of the simulated solution can affect the growth of SRB, and thus further affect the corrosion behavior of X70 steel. The solution with pH=8 is the best environment for SRB growth,pH=6 is the next and pH=10 is the worst. The SRB growth phase by pH=8 can be divided into three phases: logarithmic growth-, stable growth-and decay-phase. SRB growth phase by pH=6 and pH=10 can be divided into two phases: logarithmic growth-and decay-phase. In the logarithmic growth phase, the number of SRB is less and the effect of microbial corrosion is weak, therefore the Ecorrof X70 is higher. However, when the number of SRB increases, the effect of microbial corrosion becomes serious, while the formed biofilm is loose and easy to fall off, which result in serious local corrosion, thereby the Ecorrgradually decreases. In the simulated solution with pH=8 the effect of microbial corrosion is highest, which results further in the fastest corrosion rate of the steel. In the simulated solution with pH=10, the effect of microbial corrosion is weak, thus the passivation film can form easily on the steel surface, therefore, results in the slowest corrosion rate of the steel.