Construction of a Scanning Electrochemical Microscope for Evaluation of the Heterogeneity of Passive Films

扫描电化学显微镜（SECM）的成功构建，以评估钝化膜的不均匀性。使用密封到玻璃管中的直径为10 μ m的Pt线的横截面作为扫描探针电极。将一种商用型恒电位仪改进为双恒电位仪，它能独立控制探针电极和试样电极的电位。在pH8.4的硼酸盐溶液中，将两块嵌在环氧树脂中的铁片在不同电位下阳极极化，形成不同厚度的钝化膜。然后，在pH 8.4的含Fe（CN）_6 ~（2+）硼酸盐溶液中<4->，将探针电极在Fe（CN）_6 ~（2+<4->）氧化为Fe（CN）_6 ~（2+<3->）的电位下极化，而将两块铁板在Fe（CN）_6 ~（2+<3->）还原为Fe（CN）_6 ~（2+）的电位下极化<4->。的厚度差 关于我们 从探针电流图像可以区分两块铁板上钝化膜之间的差异。用同样的方法研究了在晶粒明显的多晶铁电极上形成的钝化膜的不均匀性。探针电流图像依赖于晶粒取向，并且探针电流按晶粒取向的顺序增加，{100}，{111}和{110}。在pH8.4的硼酸盐溶液中阳极氧化电抛光的钛试样形成钝化膜。用扫描电子显微镜（SECM）对钝化膜的不均匀性进行了评价，从探针电流图像可以看出，当阳极成膜电位大于4V时，钝化膜的不均匀性随阳极成膜电位的增加而增加<SHE>。这种不均匀性对应于每个衬底颗粒的形状，表明每个衬底颗粒上的钝化膜的厚度和缺陷结构不同。少

A scanning electrochemical microscope (SECM) was successfully constructed to evaluate the heterogeneity of passive films. A cross section of Pt wire with a diameter of 10mum sealed into glass tube was used as a scanning probe electrode. A commercial type of potentiostat was improved to a bipotentiostat which is capable of controlling independently the potentials of probe and specimen electrodes. The constructed SECM has a lateral resolution of 20mum, wich is two times as much as a diameter of probe electrode.Two iron plates embedded in epoxy resin were anodically polarized at different potentials in pH8.4 borate solution to form passive films with different thickness. Afterward, in pH8.4 borate solution containing Fe (CN) _6^<4->, the probe electrode was polarized at the potentioal at which Fe (CN) _6^<4-> can be oxidized to Fe (CN) _6^<3->, whereas the two iron plates were polarized at the potetial at which Fe (CN) _6^<3-> can be reduced to Fe (CN) _6^<4->. The difference in thickness … More between passive films on two iron plates could be distinguished from the probe current image. The heterogeneity of passive film formed on polycrystalline iron electrode with distinct grains was also examined in the same manner. The probe current image depended on the grain orientation and the probe current increased in the order of grain orientation, {100}, {111}, and {110}. This difference in probe current results from the difference in thickness of passive films.An electropolished titanium specimen was anodically oxidized in pH 8.4 borate solution to form the passive film. The heterogeneity of the passive film was evaluated using the SECM.It is found from the probe current image that the heterogeneity of the passive film increases with increasing anodic potential for film formation above 4 V_<SHE>. This heterogeneity corresponds to the shape of each substrate grain, suggesting that the passive film on each substrate grain differs in thickness and defective structure.A scanning photoelectrochemical microscope (SPECM) is being developed by attaching an optical fiber to the probe electrode of SECM.SPECM would be useful to evaluate the difference in defective structures of the passive films. Less