2Cr-1Ni-1.2Mo-0.2V钢在NH_(4)H_(2)PO_(4)溶液中的电化学腐蚀行为研究

Electrochemical Corrosion Behavior of 2Cr-1Ni-1.2Mo-0.2V Steel in NH_(4)H_(2)PO_(4) Solution

通过激光共聚焦显微镜、扫描电镜 (SEM)、能谱仪 (EDS)、X 射线衍射仪 (XRD)、X 射线光电子能谱(XPS)、开路电位、极化曲线、电化学阻抗谱等研究了NH_(4)H_(2)PO_(4)溶液浓度对2Cr-1Ni-1.2Mo-0.2V钢电化学腐蚀行为的影响。结果表明,随着NH_(4)H_(2)PO_(4)溶液浓度的增大,2Cr-1Ni-1.2Mo-0.2V钢的腐蚀速率先快速增大后缓慢增大;2Cr-1Ni-1.2Mo-0.2V钢仅在低浓度NH_(4)H_(2)PO_(4)溶液中萌发点蚀,一旦溶液浓度大于或等于30 mmol/L,材料腐蚀形态仅表现为均匀腐蚀;2Cr-1Ni-1.2Mo-0.2V钢表面腐蚀产物膜为双层结构,外层膜主要由Fe_(3)(PO_(4))_(2)、FeO_(4)组成,内层膜主要由Fe_(3)O_(4)构成;随着NH_(4)H_(2)PO_(4)溶液浓度的增大,外层膜覆盖度及致密度均提高,内层膜中Cr、Mo出现富集,一定程度抑制材料腐蚀。

The electrochemical corrosion behavior of 2Cr-1Ni-1.2Mo-0.2V steel in NH_(4)H_(2)PO_(4)solutions was investigated by means of open circuit potential measurement, polarization curve measurement,electrochemical impedance spectroscopy, laser scanning confocal microscopy, scanning electron microscopy (SEM), energy dispersive spectrometer (EDS), X-ray polycrystalline diffractometer (XRD) and X-ray photoelectron spectroscopy (XPS). The results show that with the increase of NH_(4)H_(2)PO_(4)concentration,the corrosion rate of 2Cr-1Ni-1.2Mo-0.2V steel was increased rapidly at first and then slowly. Pitting corrosion occurred when the 2Cr-1Ni-1.2Mo-0.2V steel immersed in solutions of 0-1 mmol/L NH_(4)H_(2)PO_(4)for 20 h.But only uniform corrosion might occur when the steel immersed in solutions of 30-120 mmol/L NH_(4)H_(2)PO_(4)for 20 h. The corrosion product of 2Cr-1Ni-1.2Mo-0.2V steel was a two layered scale, the outer layer composed mainly of Fe_(3)(PO_(4))_(2)and FePO_(4), and the inner layer composed mainly of Fe_(3)O_(4). With the increase of NH_(4)H_(2)PO_(4)concentration, the coverage and compactness of the outer corrosion product layer increased, and Cr, Mo enriched in the inner corrosion product layer, thereby the corrosion resistance of 2Cr-1Ni-1.2Mo-0.2V steel was increased.