Zinc plating - a new perspective of the old technology on application of polymers for shiny non-cyanic zinc plating

A widespread galvanic zinc-plating technology is known as one of the most accessible ways to protect iron and steel constructions against corrosion. This technology is effective for producing shiny surfaces designed to decorate products.

The galvanic technique for producing zinc-plated surfaces was first used at the dawn of the 20th century. It won a fast recognition as an inexpensive method for producing shiny surfaces noted for high corrosion resistance.

Unfortunately, the relatively low cost of shiny zinc-plated products has its price: galvanic zinc plating is known as one of the most harmful industries. It can largely be attributed to a wide application of cyanic electrolytes in galvanic technologies. This problem cannot but evoke public anxiety and dictate a necessity for its scientific solution.

The principal problem of all the branches of galvanic technology is the search for less toxic substitutes for the cyanide solutions. Thus, for instance, pyrophosphate, chloride and ammonium, polyethylene polyamine and other solutions were tested as electrolytes for galvanisation.

The zincate technologies have been found to be most similar to the cyanide know-how in their production capacity and deposited layer quality. Yet, the application of special organic substances and their compositions (additives) proves to be a decisive condition for producing semi-shiny and shiny surfaces. Such additives produce a strong effect on the process of metal electrodeposition and on the quality of the produced coatings.

A number of organic brighteners have been offered recently for alkaline non-cyanic galvanisation. However, such additives can help to make only semi-shiny zinc-plated surfaces. Furthermore, they operate effectively only in highly concentrated alkaline solutions.

Such electrolytes are very aggressive and toxic; this makes electrolyte leakage particularly dangerous. The organic substances recommended as additives for the production of shiny zinc-plated surfaces are highly toxic themselves.

The Institute of Ecotechnologies (IET) offers new environment-friendly techniques for alkaline non-cyanic galvanisation. These methods are based on the application of the polymer materials developed and produced by the IET. The novel technique allows producing top quality shiny surfaces.

Extensive testing has been performed and the technology has been introduced at several local production facilities. Both the field tests and production experience show that the quality of final products is greatly enhanced. The novel technique developed by the IET also allows improving the technical, economic and environmental characteristics of the production process. The new technology makes it possible:

* producing shiny zinc-plated surfaces with a 85-90 % degree of shine (with respect to the silver-plated mirror);

* providing conditions for an even distribution of zinc coating across the surface of a complex configuration;

* increasing the rate of zinc deposition. This together with uniformity of zinc-coating allows galvanising products of intricate configuration on automatic lines equipped with suspenders or drums;

* ensuring the environmental safety of the production process because the applied additives are stable in alkaline media, electrochemically non-active and non-toxic;

* refraining from the neutralisation of the applied polymer additives in sewage.

The technology of shiny zinc plating in alkaline media with GEK-2 polymeric additive developed by the Institute of Ecotechnologies has been successfully tested under various production conditions. Drum, bell, and suspension-type equipment with tub volume of 60-1500 litres was used for testing at the following production sites of the following companies: Elektroapparat and Electroagregat (Kursk, Russia), research and production Company Dolgoprudnenskoe and Severin, Ltd. (Moscow Region, Russia).

Application of alkaline electrolytes with GEK-2 brightener in the industry proved a success. The quality of the zinc coatings (brightness, uniformity, and plasticity) was enhanced. Relatively low consumption of the electrolyte components and their low toxicity significantly enhances the economic efficiency of zinc plating compared with the techniques based on application of zincate electrolytes.

Enhanced technological, economical, and environmental properties of zinc plating using GEK-2 brightener open a wide perspective for the application of the know-how and additives developed by the IET in various industries (machine-building, instrument-making, furniture manufacture, etc.).

Alexander KONAREV,

Ph.D. (technology)

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