致密、具有保护性的腐蚀产物膜析出动力学机制的研究

Corrosion product scale plays an important role in corrosion process. A protective scale with high density and adhesive strength to substrate will protect the substrate from further damage, while more serious damage, such as pitting and mesa corrosion, will occur when the substrate is covered by a loose and flaky scale. So, it is necessary to investigate the condition under which a protective scale can form..CO2 corrosion is a serious problem in oil and gas industry and the corrosion mechanism is still under investigation. In addition, recently, the development of CO2 capture and storage techniques become more and more urgent as the global temperature increases. The captured CO2 will be transported to the storage area under supercritical condition. However, the mechanism of CO2 corrosion under supercritical condition is still not clear, although previous studies reported that the supercritical CO2 exhibits more corrosive than that under low CO2 partial pressure. .During CO2 corrosion, CO2 corrosion product scale will form and control the subsequent corrosion process. So, in this proposal, the formation mechanism of CO2 corrosion product scale under low CO2 partial pressure and supercritical CO2 conditions will be studied. It will focus on the nucleation and growth of FeCO3 crystal, which is the main composition of CO2 corrosion product scale, in order to make clear how the FeCO3 crystal precipitates. The influence of temperature, CO2 partial pressure, pH value of the aggressive solution, and ions, such as Ca2+ and Cl-, will be determined. A relationship between the nucleation and growth dynamic processes and the formation of a protective scale will be established based on understanding the mechanism of multi-layer scale formation. Comparation between corrosion processes under low CO2 partial pressure and supercritical CO2 condition will be performed, so that the reason why the corrosion rate under the supercritical CO2 condition is higher than that under low CO2 partial pressure will be revealed. The results of these investigations will improve the understanding of CO2 corrosion mechanism and enhance the development of anti-corrosion techniques in oil and gas industry, especially in CO2 capture and storage techniques.

腐蚀产物膜是材料腐蚀过程的重要控制因素。致密、黏附性好的腐蚀产物膜能够保护基体不再发生进一步的腐蚀，而多孔、疏松、黏附性差的腐蚀产物膜不仅对基体不具有保护性，还有可能引起更严重的腐蚀。因此，关于致密、具有保护性腐蚀产物膜形成过程和机制的研究具有重要意义。.本申请将针对CO2捕集、储运以及油气行业中存在的CO2腐蚀现象，研究CO2腐蚀产物膜的形成过程和机制。以跟踪观察CO2腐蚀产物膜的主要成份FeCO3的形核、长大过程为研究重点，弄清CO2腐蚀产物膜的生长过程；考察温度、CO2分压、溶液pH值、钙离子、氯离子浓度等环境因素的作用，阐明多层膜形成的顺序及其控制因素，建立形核、长大动力学过程与形成致密、具有保护性CO2腐蚀产物膜之间的相关性。对比研究低压、超临界CO2条件下FeCO3形核、长大规律，澄清超临界CO2条件下腐蚀速率明显增大的原因，进一步揭示超临界CO2腐蚀的机制。

腐蚀产物膜是材料腐蚀过程的重要控制因素。致密、黏附性好的腐蚀产物膜能够保护基体不再发生进一步的腐蚀，而多孔、疏松、黏附性差的腐蚀产物膜不仅对基体不具有保护性，还有可能引起更严重的腐蚀。因此，关于致密、具有保护性腐蚀产物膜形成过程和机制的研究具有重要意义。.本申请针对CO2捕集、储运以及油气行业中存在的CO2腐蚀现象，研究了腐蚀产物膜的形成过程和机制。采用宏观观测、腐蚀产物形貌和结构分析、电化学测试等分析手段，研究了低合金钢和不锈钢在含CO2环境中的腐蚀产物膜形成机制，考察了温度、CO2分压、溶液中阴离子浓度、钙离子浓度以及试样暴露角度等环境因素的作用。.研究表明：（1）超临界CO2和低压CO2条件下，低合金钢在液相中的阴极电化学反应过程相同，成膜过程相反；（2）在动态液相中低合金钢的局部腐蚀可以在两个不同阶段萌生：腐蚀初期非晶层向FeCO3膜转变过程中，以及腐蚀后期FeCO3膜的破坏过程中，其中前者为主要局部腐蚀诱因；（3）在单一阴离子溶液中，低合金钢的缝隙腐蚀对SO42- 最为敏感，而在多种阴离子共存溶液中，Cl- 对低合金钢的缝隙腐蚀过程起控制作用；（4）相同体积条件下，水在超临界CO2相中的溶解度（g/L）远大于气态CO2相，因此低合金钢在超临界CO2相中腐蚀更加严重；（5）随Cr含量增加，低合金钢在静态和动态液相中耐均匀和局部腐蚀的性能均得到提高；然而，当含有微量H2S时，在动态液相中低合金钢以均匀腐蚀为主，含Cr后均匀和局部腐蚀严重，不锈钢发生明显点蚀；在动态超临界CO2相中，低合金钢以局部腐蚀为主，不锈钢基本不发生腐蚀；（6）在超临界CO2相中，低合金钢向下面均匀和局部腐蚀最严重，随后依次是向上面和竖直放置面；液相中试样的向上面的腐蚀程度高于向下面，氧浓差是导致向上面和向下面腐蚀差异的主要原因，向下面为阴极，有利于致密的CaCO3沉积；向上面为阳极，反应生成的FeOOH会抑制CaCO3沉积。