The Structure and Composition of Corrosion Product Film and its Relation to Corrosion Rate for Carbon Steels in CO2 Saturated Solutions at Different Temperatures

For carbon steels immersed in CO2 saturated solutions at different temperatures, the structure and the composition of corrosion product film formed on the steel surface were studied by scanning electron microscope (SEM), X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). The corrosion rate of the steel was evaluated by potentiodynamic polarization, and the relation between the corrosion rate and the film property was discussed. The corrosion rate of the steel was very closely associated with the structure and the composition of corrosion product film, which were affected significantly by the solution temperature. From 30 to 60 ºC, the corrosion product film composed of FeCO3 was porous and poorly adherent, and the corrosion rate increased with the rise of temperature. At 70 and 80 ºC, the corrosion product film was also composed of FeCO3 and presented a compact and dense cubic crystal structure, resulting in the decrease on the corrosion rate. The corrosion rate increased once again when the temperature was up to 90 ºC, which was attributed to the negative effect of high temperature water vapor corrosion on the grain coarsening and the part exfoliation for the FeCO3 film.针对浸泡于不同温度二氧化碳饱和溶液中的碳钢，采用扫描电子显微镜（Scanning Electron Microscope, SEM）、X射线衍射（X-ray Diffraction, XRD）及X射线光电子能谱（X-ray Photoelectron Spectroscopy, XPS），对钢表面形成的腐蚀产物膜的结构与组成进行了研究。通过动电位极化法评估了该碳钢的腐蚀速率，并探讨了腐蚀速率与腐蚀产物膜性能之间的关联。碳钢的腐蚀速率与腐蚀产物膜的结构和组成密切相关，而后者又显著受溶液温度的影响。在30~60 ℃范围内，由FeCO₃构成的腐蚀产物膜孔隙率较高且附着性较差，腐蚀速率随温度升高而增大。在70 ℃和80 ℃时，腐蚀产物膜同样由FeCO₃组成，呈现出致密紧实的立方晶体结构，进而使腐蚀速率降低。当温度升至90 ℃时，腐蚀速率再次上升，这归因于高温水蒸气腐蚀对FeCO₃膜的晶粒粗化和部分剥落产生的负面影响。