Nickel and cobalt carcinogen effects
M. Gajo, G. Gajo
Elsy Research s.n.c., V. Mons. Zoppas, 20 - 31020 Scomigo di Conegliano (Treviso).
A. Zingales, G. Quartarone, T.Bellomi
Università di Venezia - Dipartimento di Chimica
Università di Padova - Dipartimento di Ingegneria Meccanica
The problem of Nickel allergy is known and has been already faced by the European Community with Directive 94/27/CE.
Less known it is, instead, the problem of Cobalt allergy. Tests carried out already in the 70s, show as Cobalt is perhaps also more allergenic than Nickel.
Still less known, but very important, it is the problem that Nickel, Cobalt and their compounds, such as carbonates, sulphates and chlorides, are carcinogens.
The European Community and U.S. Government have classified Nickel and Cobalt compounds as carcinogens. In particular, with European directive 98/98/CEE, 25th amendment of 67/548/CEE, Nickel compounds are classified as carcinogens of class 3 (substances to consider with suspicion for the possible cancerogenous effects on humans), but Cobalt compounds in category 2 (sufficient elements exist to believe exposure to such substances to be likely to cause tumours).
The carcinogen nature of Nickel compounds is therefore still in phase of study. It cannot be excluded however that in a near future galvanic plants must be modified to prevent Nickel and Cobalt emissions the same as it is already made against the Chrome emissions. However, a major difference exists. Chrome tends to form a passive layer which reduces significantly the corrosion. Nickel and Cobalt, instead, when not adequately protect, are rapidly corroded by sweat (as proved by the allergy phenomena), with formation on the human skin of such compounds, as chlorides and sulphates, currently classified as carcinogens.
Perhaps modifying galvanic plants to prevent Nickel and Cobalt emissions during operation may be not enough and total elimination of both metals may be required.
Nickel is widely used in the galvanic processes because of its several properties: nickel-plating baths have simple composition, are easy to manage and with a decidedly low costs. The coatings are extremely bright and levelling, so that Nickel is an ideal substrate for decorative galvanic.
Between the more economic solutions for eliminating Nickel, three of them are here discussed, as they currently are of interest for the galvanic processes. All the three systems have been experimented by the R&D team in laboratory and production, with different results.
Silver coatings are bright, discreetly levelling and easy to control. The experimentation have been carried out with Elsy Research silver bath by depositing 5 mof Silver and 2 m of 24K Gold. The results were at the first moment positive, but in the long run remarkable problems became evident. After approx. one month, grey-black spots appeared on the surface, clear index of oxide formation. This was certainly due to silver, which is for its tendency to migrate towards the surface. Silver was found to migrate Gold barrier layers of 20 m. The worse problem was that the oxides were formed in a long time, misleading from the real result that, from the first moment, seemed extremely positive.
Acid tin plating
Acid tin bath exists from a long time and had been recently revived. Already experimented in the 50s, it didn't have a big success. The coatings are extremely soft, to the point that they are scratched by the slightest contact, and they are not so bright. The worse problem is, however, the tendency to migrate, which is even greater than silver. In fact, after depositing 5 m of tin and 2 m of 24K Gold, oxides appeared in a very short time.
Copper and white bronze plating
Copper cost is similar to Nickel, therefore almost negligible if compared to labour cost. However, it has 2 weak points:
it has an excellent levelling action, but not brightening
if it is not adequately blocked, it tends to migrate to surface to create oxidation as silver and tin.
Therefore Copper needs a bright coating, which should also an efficient barrier layer. It had been verified that bronze alloy is an optimal barrier layer. Also the Bronze alloy exists in galvanic from many years. It has been not successful in the past because, being a ternary alloy, almost nobody was able to set up a reliable bronze bath. The experimentation was carried out with a bath produced from Elsy Research and has demonstrated to be reliable and easy to manage. Some characteristics are here following listed:
Identical Aspect to a Palladium coating.
It totally blocks the migration of Copper.
it confers to substrate the typical brightness of the Nickel.
easy to strip in case of mistakes (contrarily to palladium).
It should be kept in mind that this galvanic treatment purpose is to replace Nickel. Even if the final decorative effect is identical to Palladium coatings, it cannot be expected that Copper-Tin-Zinc alloy has characteristics of resistance to wear and corrosion as a noble metal. The treatment needs a protective coating, which, because of the optimal characteristics of the alloy, can be also one simple paint coating.
Regarding the migration problem, objects coated with 5 m of Copper, 2 m of bronze and 2 m of 24K Gold did not show oxide traces even after various months and 180°C heat treatments.
Cobalt has been used in the decorative galvanic much less of Nickel and perhaps for that reason it passed over. In fact, literature does not list as much research as for Nickel. In galvanic, Cobalt is mostly used as alloying element in flash or high thickness gold plating baths to obtain several tonalities of yellow colour.
The solution proposed by the R&D team and adopted already with success also in production is to replace Cobalt with absolutely not carcinogen metals, as Zinc, Iron or Tin, obtaining all the colours normed from 1N to 3N.
All treatments examined to eliminate Nickel from decorative galvanic presents the problem of the migration towards the surface and therefore they demand one barrier layer.
Regarding Silver, the problem has not yet been investigated but, as the cost for coating is high, it is interesting like final treatment, but not in substitution of the Nickel.
There are no cost problem with acid tin plating but, apart from its lack of hardness and brightness, further research is required to set up an optimal barrier layer.
The most attractive solution seems to be the copper-bronze cycle: the cost is reasonable and surface-migration problem has been fully solved, as proven by the long production experience.
Eliminating Cobalt from the decorative galvanic is suitable and seems possible without variations of costs. The gold baths tested appear to be reliable and easy to control and a wide use is expected in the next few years.
J. Foussereau “L'eczéma allergique au Cobalt” Institut National de recherche et de securité Paris, Fiches d'allergologie-dermatologie professionelles N°8 (Ottobre 1976)
Direttiva 67/548/CEE del Consiglio, del 27 giugno 1967, concernente il ravvicinamento delle disposizioni legislative, regolamentari ed amministrative relative alla classificazione, all'imballaggio e all'etichettatura delle sostanze pericolose.
Direttiva 76/769/CEE del Consiglio concernente il ravvicinamento delle disposizioni legislative, regolamentari ed amministrative degli Stati membri relative alle restrizioni in materia di immissione sul mercato e di uso di talune sostanze e preparati pericolosi.
Direttiva 94/27/CEE della commissione del 30 giugno 1994 che adegua per la terza volta al progresso tecnico allegato I della direttiva 76/769/CEE del Consiglio concernente il ravvicinamento delle disposizioni legislative, regolamentari ed amministrative degli Stati membri relative alle restrizioni in materia di immissione sul mercato e di uso di talune sostanze e preparati pericolosi.
Direttiva 88/379/CEE del Consiglio del 7 giugno 1988 per il ravvicinamento delle disposizioni legislative, regolamentari ed amministrative degli Stati Membri relative alla classificazione, all'imballaggio e all'etichettatura dei preparati pericolosi.
Direttiva 98/98/CE del 15 dicembre 1998, venticinquesimo adeguamento al progresso tecnico della direttiva 67/548/CEE del Consiglio concernente il ravvicinamento delle disposizioni legislative, regolamentari ed amministrative relative alla classificazione, all'imballaggio e all'etichettatura delle sostanze pericolose pag. 115-116-442-443
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