亜鉛めっき鋼板の耐白錆性に及ぼす化成皮膜成分複合化の影響

抄録

This study investigated synergic effects of phosphoric acid（H₃PO₄）, amino-propyltriethoxysilane（3-APS）and ammonium metavanadate（NH₄VO₃）in a conversion coating on electro-galvanized steel（EG）to clarify EG corrosion suppression by these substances.

Results showed that the ratio of white rust during salt spray testing（SST）was lessened when a coating was formed with 3-APS and H₃PO₄. The phenomenon was explained: adding 3-APS into H₃PO₄ causes the decrease of corrosion resistance by suppressing salt water uptake in the coating because the coating itself became compact. Moreover, a coating formed with NH₄VO₃, 3-APS, and H₃PO₄ exhibited higher corrosion resistance in SST than a coating with 3-APS and H₃PO₄. Results show that NH₄VO₃ changed more into tetravalent or trivalent vanadium by oxidation reaction of zinc when the coating was formed together with 3-APS and H₃PO₄ on EG. These vanadium compounds in the coating were estimated as dissolved easily in the case in which salt water permeated into coating. The compounds were then deposited at the corroded area to reduce EG corrosion. These findings suggest that NH₄VO₃, 3-APS, and H₃PO₄ in the conversion coating contributed both to the high barrier and to self-protective effects of the coating.