A Study On Trivalent Chromium Passivation And The Process Of Electrogalvanized Sheets

Through surface passivating treatment with chromate, Zinc electrodeposited sheet can get passivation film with good external appearance and corrosion resistance. But being toxic, Cr6* has great poisonousness to human body and environment. To avoid the disadvantageous influence of Cr6+, it' s needed to find alternatives to chromate passivation.This paper studys the effect of SiO Ce1+ CTand Fe2+ to Cr3+ passivation film by means of SEM. XPS. measurement in polarization resistance rate and salt spray test.Existing in the passivation liquid as colloid granule, SiO2 s content must be in proportion to trivalent chromium, so as to retain the passivation liquid' s stabilization and get transparent trivalent chromating film with bright color and better corrosion-resistance.OF is the accelerant of metal deliquescence. It quickens the formation of passivation film, shortens passivation time by accelerating anode' s deliquescence. In addition, by "anion effect" , CT makes the reaction of colloid precipitation go along at even speed so as to get even fine granule. The granules fill in the holes of passivation film richly and advance the film' s corrosion-resistance.Ce'1+ has very strong oxidbillity in the acidity liquor and can accelerate electrochemistry reaction by reducing polarization of cathode reaction to increase the thickness of film. Ce'4+ and its deoxidization productions together with all kinds of anions in liquid form complicated infusibility compounds. The compounds settle into the holes of passivation film to make the film more compact. These two aspects improve the film' s corrosion resistance obviously.Fe2+ chiefly polishes up the film's color in coordination with Ce4+, doesn' t function much to corrosion resistance.Through orthogonal experiment , FS-3 passivation composition , the process and parameters are studied and established. FS-3 passivation film ' s external appearance and corrosion-resistance can compare with that of chromating. Moreover, the peformance of heat tolerance is more excellent.Above Discussion about the formation machanism of FS-3 passivation film illustrates that the formation process is a complex process composed of electrochemistry reaction . colloid polymerized . precipitation reaction, etc. Through XPS analysis, FS-3 passivation film contains multiple elements such as Zn. Cr. Si. 0. F. Ce. Cl. Fe. S, etc, composed of many metal compounds and their hydrates.