Development of Long-Life-Span Coating Films

为了证明半导体涂层在照明条件下对金属进行阴极保护的适用性，采用溶胶-凝胶法研究了镀有TiO_2薄膜的Cu、碳钢和不锈钢的光电化学行为。然而，采用这种方法作为“金属在阳光下的阴极保护”的一种方式，仍然有一个严重的问题需要克服：非常频繁地，在停止照明后不久，电极电位到达有源区域。然而，一些涂有TiO_2的样品表现出一种有趣的现象，我们称之为“记忆效应”，即即使在停止照明后，光电压下降非常缓慢，阴极电位保持几个小时。本研究的主要目的是解释“记忆效应”，并表明这种现象使得金属在一整天的阳光下的阴极保护成为可能。结果表明，304不锈钢表面TiO_2溶胶-凝胶涂层的光电压缓慢下降是由于Fe从基体扩散到涂层中造成的。在溶胶溶液中加入Fe作为掺杂剂，表明了TiO_2涂层对金属进行夜间阴极保护的可能性。

To demonstrate the applicability of cathodic protection of metals by a semiconductor coating under illumination, the photoelectrochemical behaviors of Cu, carbon steel and stainless steel coated with thin TiO_2 film by a sol-gel method have been studied in our laboratory. However, for the adoption of this method as a way of "cathodic protection of metals under sun light", there was a serious problem that still had to be overcome : very frequently, the electrode potential reaches the active region soon after stopping illumination. Nevertheless, some specimens coated with TiO_2 exhibited an interesting phenomenon, which we call "Memory-Effect", where even after stopping illumination, the photovoltage decreases very slowly, and the cathodic potential is kept for several hours. The main objective of this research is to explain the "Memory-Effect", and show that this phenomenon makes possible the cathodic protection of metals by sun light during a whole day.It was found that the existence of a slow decline of photovoltage in TiO_2 sol-gel coating on type 304 stainless steel was due to the diffusion of Fe from the substrate into the coating. The use of Fe as dopant in the sol solution showed the possibility of the cathodic protection of metals by TiO_2 coating even for night-time.