Development of Long-Life-Span Coating Films

为了验证半导体涂层在光照下对金属阴极保护的适用性，在实验室研究了用溶胶-凝胶法在铜、碳钢和不锈钢表面镀上TiO_2薄膜后的光电化学行为。然而，对于采用这种方法作为“太阳光下金属的阴极保护”的方式，仍然必须克服一个严重的问题：非常频繁地，电极电位在停止照射后不久就达到活性区。然而，有些涂有TiO_2的样品表现出一种有趣的现象，我们称之为“记忆效应”，即即使在停止光照后，光电压下降也很缓慢，阴极电位保持数小时。本研究的主要目的是解释“记忆效应”，并表明这种现象使金属在一整天的阳光下都能得到阴极保护，发现304不锈钢上TiO_2溶胶-凝胶涂层中存在缓慢下降的光电压是由于Fe从基体扩散到涂层中。在溶胶溶液中加入Fe掺杂剂，表明TiO_2涂层对金属的阴极保护作用是可能的，即使在夜间也是如此。

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.