2014 年 65 巻 8 号 p. 380-384
In response to recent environmental regulation, e.g., RoHS Directives, chromate-free coatings have been developed and applied to electrical appliances. However, thinner chromate-free coatings are necessary to obtain better electroconductivity, which influences the electromagnetic shielding performance of digital electrical appliances. We investigated the corrosion resistance and film structure of thiol self-assembly ultra-thin layers on zinc coated steel sheets. The thiol layers' corrosion prevention mechanism was discussed to develop a new design concept of thinner chromate-free coatings with high corrosion resistance. The remarkably thin triazinethiol layers with three thiol groups per molecular showed excellent corrosion resistance despite their thickness of a few molecules. Their corrosion resistance derives from their suppression of oxygen reduction reaction. Nevertheless, identifying the layer structure using XPS analysis was difficult because of the high surface roughness of the zinc-coated steel sheets. We investigated the structure of thiol self-assembly ultra-thin layers on zinc single crystals. Results showed that triazinethiol molecules were partially decomposed by dissolution to water and drying. A new molecular assembly was formed by combination to Zn. Thinner chromate-free coatings with better corrosion resistance can be produced by applying compounds that can form a molecular assembly and which can be combined to Zn.