Electrodeposit copper protection on iron has a cathodic kind: the soluble anode is the iron into the iron-copper pile, which goes on through the damp. Copper film has to be relatively deep and compact to achieve the maximum protection. If we consider that copper-nickel-chrome deposit on iron can present a cathodic totally protection, the galvanic operators have to obtain protective galvanic stratum in a maximum compactness. In mat copper or nickel electrodeposits on iron and in necessity of a mechanic cleaning this reduce the porosity and realize a compact and resistant stratum. It also explains the major protective valor of copper-nickel deposits. Many foreign capitulations shall advise copper-nickel connection in their unificated norms to better ferrous material protection, only if the copper density is at 50% of the nickel.
Coppering is largely achieved like nickeling intermediate stratum, silvering, gilding, etc.of aluminium and its alloies, zinc and its alloies, in the alloies with a high percentual of plumb or tin or antimony. On which the other metals electrodeposition is not possible, without impair the adherence. Copper can be electrodeposited by solutions present to the bivalent status ( cupric solutions) and by monovalent solution ( cuprous solutions). In the first case we usually use sulfate, borate, sulfamate baths, etc.; in the second case cyanid baths.
Operating copperings from cuprous solutions (cyanid baths) is supposed a current cathodic capacity of 100%, a A7h could deposit g 2,372 of copper; from cupric solutions (f. ex sulfate baths), instead, with the same current capacity , it coul deposit g 1,186 of copper, that is the half, because the electrochemical analog is different ( Faraday's lows). Instead in the cuprous solutions the capacity goes down to 70 and to 50%; except some cyanid baths, too much concentrated and they can be also utilized to high current density.
Actually cyanide and sulfate baths are the major used. These lasts are more diffused for the minor cost and the major chemical stability. Also fluoborate, pirofosfate and ammine baths are affirmed.but bath choice is determinate by the kind of work and the metal.base nature. In this way the major part of acid cupric solutions can't be utilized to copper the steel and the zinc because on these the copper could already deposit for immersion and an a little adherent form.
Alkalin baths are often used diluted to cyanid, producing a first thin deposit, because these baths have a penetrant good power and give life adherent thin deposits; then it goes on the electrodeposition with acid cupric baths, f. ex,. Sulfate baths, or with concentrated cyanid baths (speed baths) or, better, with pirofosfate baths. When the electrodeposition needs to have a good penetrant power from the bath, it is good choose cyanid or pirofosfate baths.
The most used anodes are those laminated electrolytic and its area must be the same to the cathodic area. They can remain dipped into the alkalin baths also without electrolysis; not in this way for the acid baths in which we have copper dissolution also without electrolysis. Useful to put nylon, propylene or terylene in bags. The basin for the alkalin baths are in adapted iron and resin, with heaters and aspiration; for the other baths in plumb, gumma, polyethylene, and various plastic materials.
COMMON BATHS - they are also named diluited cyanalkalin baths, that is with a low copper content. They are very used and them diffusion is above all due to awesome penetrant and adherent deposit proprieties. They chemically have for fundamental sals a series of complexes cuprocyanid that derive from the addend of cupric sals or cuprous (cuprous cyanid) to potassium cyanid or sodium cyanid solutions; this last composed is the most used for its inferior cost compared to potassium sal.
- Cycle with periodic inversion of the current. The anodic current dissolves the rugosity and lets to obtain smoother deposits, excluding the pores and tending to brilliant; the anode attach is more uniform and we can use density of high current. The most frequently adopted cycle is of 15 seconds of deposit for 5 seconds of inversion.
- Cycle with interrupted current. The current interruption is of 2-3 seconds for 8-10 seconds of deposit. The advanteges of this method are the brightness addiction and the possibility to using
Higher current densities
- Current rendering. Cyanalkalin baths current rendering of coppering to low temperature moves from the 40% and the 70%; usually is 60%. Elevating the concentration in complex copper cyanid and the temperature (speed baths) is possible to achieve a current rendering almost of 100%.