The articles to zinc are placed on appropriate chases and then dipped in the zincking bath. In the same bath are dipped (respecting some geometric postulate) some deposited metal rails link to the anode and into the bath some soluble sals of the deposited metal. When the current aliment itself, the metal positive ions to deposit go to the negative pole, where they disgorge becoming a continuous metallic strate. To the positive pole we have, instead, the metallic dissolution with ions formation in solution, which they go to add the disgorged ions to the cathode. The total reaction is an oxidation-reduction, like result of the metallic cathodic oxidation that dissolve losting electronsand the ion cathodic reduction that deposit itself like a metal assuming electrons. We can differ two important zincking groups, it depends on zincking bath of chemical composition.
The zinc forms many soluble sals and, under determinate conditions, it can be electric-deposited from acid solutions (to the sulfate, fluo borate, chloride, sulfamate, ecc.) and from alkalin solutions ( to the cyanid, pyrosulfate, zincked, ecc.). Apiece of the production exigence and the kind of zincking, we can realize automatic implants for various workings. The electrolytic zincking cappings can be better into the aspect and into the protective power with a final treatment of "passivation".
It results important to get pure zinc deposit, because the presence the foreign metals in them ( nickel, plumb, pond and copper) can accelerate a lot the atmospheric collision.
Under this point of view the acid solutions to the sulfate are better to the cyanid, because there is less metallic impurities passage tendence from the anodes to the sulfate bath deposits than in those to the cyanid. An example is given by the brassing, in which the zinc and the copper are only deposited from their cyanid solutions, instead it is impossible deposit them from acid situations. The consequence is that is more important in the zincking to use pure zinc anodes during the cyanid baths than in those to the sulfate.
The why the zinc, little noble metal, it well divide from acid solutions and with some many high current capacity, it is because the hydrogen on the zinc has a very high overvoltage. To avoid a contemporary hydrogen separation with the zinc is necessary the absence in the umpurities bath, that could reduce the overvoltage, or the absence carbon parcels or of graphite on cathodic area. If we must zinc baked iron containing these last essences, for the low hydrogen overvoltarage on the graphite, the acid baths ( and also those to the cyanid) work very bad. A strong hydrogen developing always gives place to spongy cappings. Cyanalkalin baths, thanks to their brazen power, are particulary used to zinc outlined artifact. Sometimes we make a prezincking in cyanalkalin bath on these pieces and reinforce them with a zincking in acid bath.
While the limited brazen power can be correct in part with auxiliary anodes with conductor sals addends ( sodium chloride, sodium sulfate, ecc..), the cyanalkalin baths present the inconvenience of a minor current capacity and, above all, it depends on electrodeposition conditions. Also under this aspect, for the iron discs and lines, we prefer the acid baths to those cyanalkalin.
Beyond the current capacity , also the anodes solubility is usually better into the acid solutions than in those alkalin. Moreover acid baths present a higher conductibility, which brings to reduce the electric energy expenditure.
The great evolution of zincked artifacts production (to thinking, in a car the zinc represents about the 70% of electrodeposit metals) has imposed the automatic implants adoption that, in the more dynamic versions, are programmable in relation to the working exigencies. The work cycles are, obviously, in function of the performances to which the pieces have to submit: firstly the corrosion resistence, secondly physical-mechanical qualities and aesthetic aspects. The normal cycle into the alkalin baths, after preparation treatments and the zincking, includes passivation processes, is the case of the couplings with alkalin cadmium-plating. However the polish deposits the cycles can change, above all for the final treatments.
Transformation stratum colour can be nacreous, irised, amber- bronze, olive apiece the kind of chemical conversion.