| 摘要 |
The process consists in subjecting the articles to nitriding, for example in a cyanate/carbonate bath, then to an oxidation, for example a bath containing alkali metal nitrates, alkali metal hydroxides, alkali metal carbonates and a small quantity of oxygen-containing alkali metal salts whose normal oxidation-reduction potential is lower than -1 volt relative to the hydrogen electrode, so as to obtain a nitrided layer comprising a compact deep sublayer with a thickness of more than 4 mu m and a porous superficial sublayer with a thickness of between 2 and 20 mu m, the diameter of the pores being not smaller than 100 nm, then in depositing a fluoroethylene-propylene (FEP) coating with a thickness of between 3 and 20 mu m and preferably lower than 15 mu m. The rubbing properties of the articles thus treated are at least as good as those of articles which have undergone nitriding and oxidising operations, whereas the corrosion resistance is increased remarkably, passing from 200 - 250 hours' standardised exposure to saline mist before appearance of corrosion to at least 500 hours, and commonly to 1,000 hours and more. The results obtained are comparable with coatings made of PTFE, fluorine or silicon-containing polyurethane polymers and copolymers and polyamide-polyimides. |
