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采用电化学阻抗法和阴极极化曲线法研究了X70钢在0.20mol/L Na2SO4薄层液膜下的电化学行为。结果表明,液膜厚度减薄,X70钢的极限扩散电流增大,液膜厚度约为50μm时,阴极极限扩散电流达到最大值。液膜厚度约为40~50μm时,阴极极限扩散电流反而降低。液膜厚度进一步减薄,阴极极限扩散电流又增大。在薄层液膜下,随着液膜厚度的减薄,X70钢的腐蚀过程发生变化。液膜厚度减至45μm以下时,X70钢的腐蚀速率控制步骤转变为物质扩散和电荷传递过程的混合控制,腐蚀速率先增大后降低。随着浸泡时间的延长,液膜厚度为100μm的腐蚀速率先增大后减小再增大,200μm的趋于稳定,400μm的和空白溶液中先减小后增大。
Electrochemical impedance spectroscopy and cathodic polarization curve were used to study the electrochemical behavior of X70 steel under 0.20 mol / L Na2SO4 thin film. The results show that the ultimate diffusion current of X70 steel increases with the decrease of the thickness of the liquid film, and the maximum cathodic diffusion current reaches the maximum when the thickness of the liquid film is about 50μm. When the thickness of the liquid film is about 40 to 50 μm, the cathodic limit diffusion current decreases instead. Further thinning the thickness of the liquid film, cathodic limit diffusion current increases. Under the thin liquid film, the corrosion process of X70 steel changes with the decrease of film thickness. When the thickness of the liquid film is reduced below 45μm, the corrosion rate control procedure of X70 steel is changed to mixed control of material diffusion and charge transfer process. The corrosion rate first increases and then decreases. With the extension of immersion time, the corrosion rate of the liquid film with the thickness of 100μm first increased then decreased then increased, while that of 200μm tended to be stable, and then decreased at 400μm and blank solution and then increased.