Creation of Oxide functional thin film with nano Scale Structure Formed by Modulated Electrolysis Process

在奥氏体不锈钢、Fe-18Cr合金、不锈钢等表面形成超厚、多孔的钝化膜。在50~80ﾟC的5kmol/m~2 H_2SO_4溶液中极化。透射电子显微镜观察表明，膜层由尺寸约为1~4 nm的椭圆形纳米晶组成。膜层有大量相互连接的开路，容易被离子或水分子穿透。根据外加电位的不同，多孔膜的成膜机理可分为两个过程。对多孔膜的电化学阻抗和光电化学性能进行了测试。对于阳极型膜，研究了膜的电化学性质和光电化学性质由于阴极型薄膜的电容与衬底钢的电容几乎相等，且与厚度、结构等性质无关，因此，电容只出现在衬底/溶液界面处，厚膜的多孔结构与衬底没有电化学联系。对阳极型薄膜的光电化学响应进行了测试。结果表明，阴极型薄膜的光电响应为p型半导体响应，光电流谱与在硫酸中形成的普通薄多孔膜的光电流谱相似，光电流效率远大于薄的钝化膜，即光电流随膜厚的增加而增大，在10 nm左右的厚度处出现最大值，然后减小。电化学阻抗和光电化学响应表明，厚多孔膜具有不同的电化学性质，这可能是由电解条件决定的。

Extraordinarily thick and porous passive film can be obtained on austenitic stainless steels, Fe-18Cr alloy, and Ni-18Cr alloys by square wave potential pulse polarisation in hot sulphuric acid.The material was polarised in 5 kmol / m^3 H_2S0_4 solution at 50 - 80 ﾟC with applied potential modulated as square wave.The transmission electron microscopy revealed that the film consists of nano-crystalline oval-shape grains of around 1-4 nm in its size.The film has large amount of open pathways linking with each others to be penetrated easily by ions or water molecule.The film formation mechanism is classified into two processes according to the applied potentials.Electrochemical impedance and photoelectrochemical properties of the porous films were also examined.For the anodic type film, the capacitance is fairly larger than that of the substrate steel, and is nearly proportional to the total thickness of the film.On the other hand, the capacitance for the cathodic type film was almost equivalent to that of the substrate steel, and was independent of thickness, structure, and other properties.Therefore, the capacitance arised only at the substrate / solution interface, and porous structure of the thick film has no electrochemical connection with substrate.Photoelectrochemical response was measured for the anodic type film.The photo current revealed the p-type semiconductor response, and the photo current spectrum is similar to that for ordinary thin passive film formed in sulphuric acid.The photo current efficiency is fairly larger than that for thin passive film.That is, the photo current increased with increasing film thickness, revealed a maximum at the thickness of about 10 nm, then decreased.The electrochemical impedance and the phoelectrochemical response revealed that the thick porous film has various electrochemical properties depending on the structure, which is possible to be ordered by electrolysis conditions.