不锈钢电化学着黑色工艺与成膜机理研究

采用电化学着色法对不锈钢着黑色进行了研究,讨论了钝化处理、着色液组成等因素对着色的影响,测定了着色膜的耐磨性和耐蚀性,并根据着色膜的组成、微观结构分析了成膜机理.结果表明:钝化和封闭处理能明显提高着色膜的耐磨性和抗色变性;电化学分析表明在1 mol/L H2SO4溶液、3.5%NaC l溶液和10%NaOH溶液中,着色膜腐蚀电位比不锈钢基体分别正移1130、565和790 mV,且腐蚀电流密度都比相应介质中的小;扫描电镜和能谱结果显示膜层为封闭块状结构,着色膜主要成分是Fe、Cr、Mn等元素,封闭处理能明显减少其裂纹数目.该成膜反应机理为:1)不锈钢基体的溶解形成大量的M e2+;2)金属/溶液界面上的M e2+与Cr3+水解形成合金氧化膜沉积在基体表面上;3)电化学致密过程中4H2MoO4+2SO42-+4H+2(MoO)2SO4+6H2O+6O]和M e+O]=M eO反应是着色膜致密的主要原因.

Process and Formation Mechanism of Electrochemically Blackened Film for Stainless Steel

    The process of black-coloring for stainless steel by electrochemical method was studied.The effect of the bath composition and passivation process on black colored film were discussed.The corrosion resistance and anti wear performance of the blackening film were investigated.The relevant mechanism of the process was discussed in terms of the surface morphology,microstructure and chemical composition of the blackening film.The results show that the passivation is beneficial to the corrosion resistance and the color durability of the film.Electrochemical measurement results show that the corrosion potentials of the blackened steel in solutions of 1 mol/L H₂SO₄, 3.5% NaCl and 10% NaOH were respectively about 1130、565 and 790 mV higher than that of the bare stainless steel substrate,correspondingly less corrosion current densities,which implies that the corrosion resistance of stainless steel is enhanced remarkably.The results of scanning electron microscopy and energy dispersive spectra show that the film shows a morsaic pavement-like morphology with net-like cracks,the amount of which can be decreased after passivation,and the main elements of black colored film are Fe,Cr and Mn.The formation mechanism of the colored film was proposed as follows:1)a large number of Me²⁺ were formed as a result of the dissolving of the atoms of the stainless steel,2)an oxide film deposited on the surface as that the Me²⁺ and Cr³⁺ were hydrated on the interface between metal and solution and,3)the main reason for the compactness of blackening film is due to the following reactions: 4H₂MoO₄+2SO^2-₄+4H⁺  2(MoO)₂SO₄+6H₂O+6［O］,and Me+［O］=MeO in the process of electrochemical passivation.