用电位-电容测试和Mott-Schottky分析技术研究碳钢/环氧涂层在 5%H2SO4溶液中腐蚀失效过程的极化及半导体行为. 结果表明: 碳钢/环氧涂层在5%H2SO4溶液中浸泡10 min时形成了一个金属-绝缘体-半导体(MIS)结构, 随着浸泡时间的延长, 涂层逐渐表现出半导体的性质. 碳钢/环氧涂层在浸泡1 d时, 涂层表现为n型半导体, Nyquist图在整个频率域内其交流阻抗出现两个半圆弧, 说明此时的金属/涂层电极存在两个时间常数. 碳钢/环氧涂层在浸泡3 h到5 d时, 在电场作用下发生偶极极化, 偶极电场阻碍了涂层中载流子的迁移, 起到减缓腐蚀的作用. 偶极弛豫效应使碳钢/环氧涂层电极的电容随电位绝对值的增大而减小, 并且造成了其频率的依赖性. 碳钢/环氧涂层在浸泡7 d以上时, 碳钢与涂层形成金属-半导体接触, 随着浸泡时间延长, 载流子密度逐渐增加.
In this paper, the corrosion degradation process and semiconducting character of epoxy coating/carbon steel were examined in 5%H2SO4 solution by used of potential-capacitance measurement and Mott-Schottky analysis techniques. A film with MIS structure may formed on the surface of epoxy coating/carbon steel immersed in 5%H2SO4 for 10 min, with the extension of soaking time, the system gradually showed a semiconductor-like nature. When epoxy coating/carbon steel immersed for 1 d, the system exhibited n-type semiconducting, its Nyquist frequency map had two semi-impedance arcs in the whole frequency region, which showed that the epoxy coating/carbon steel electrode had two time constants. The epoxy coating/carbon steel immersed in 5%H2SO4 for 3 h~5 d, the dipole polarization had occurred under the electric field, electric dipole might hinder the migration of carriers, and slowed down the corrosion. Dipole relaxation effect made the capacitor of epoxy coating/carbon steel reduced with the absolute value of potential increased, and resulted in dependence on its frequency. The epoxy coating steel immersed in 5%H2SO4 for more than 7 d, the carbon and coating formed metal-semiconductor contacts, with the extension of soaking time, the carrier density increased gradually.
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