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

利用扫描电化学显微镜（SECM）对钝化膜的非均质性进行了评价。采用直径为10mum的Pt丝横截面密封在玻璃管中作为扫描探针电极。将一种商用的恒电位器改进为能够独立控制探针电极和试样电极电位的双恒电位器。所构建的SECM具有20mum的横向分辨率，是探针电极直径的两倍。在ph . 8.4硼酸盐溶液中，用环氧树脂包埋的两块铁板在不同电势下阳极极化，形成不同厚度的钝化膜。然后，在pH8.4硼酸盐溶液中，探针电极在Fe (CN) _6^<4->氧化成Fe (CN) _6^<4->的电位处发生极化，而两块铁板在Fe (CN) _6^<3->氧化成Fe (CN) _6^<3->的电位处发生极化。利用探针电流图像可以区分两块铁板上钝化膜的厚度差异。用同样的方法考察了不同晶粒的多晶铁电极上钝化膜的非均质性。探针电流图像依赖于晶粒取向，探针电流按晶粒取向{100}、{111}、{110}的顺序增大。探针电流的差异是由钝化膜厚度的差异造成的。电抛光钛试样在pH 8.4硼酸盐溶液中阳极氧化形成钝化膜。采用SECM对钝化膜的非均质性进行了评价。探针电流图像表明，在4 V_<SHE>以上，钝化膜的非均质性随阳极电位的增大而增大。这种非均质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在厚度和结构上存在差异。将光纤连接到扫描光电化学显微镜的探针电极上，研制了扫描光电化学显微镜（SPECM）。SPECM可用于评价钝化膜缺陷结构的差异。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