What are Zinc Whiskers ?
Metal whiskers can be a regular and ultimately very disruptive phenomenon within Tin, Cadmium and Zinc electroplated, both alkaline and acid based products. The whiskers are relatively long, but very thin, single-crystals of Zinc that form sometime after the plating process. The whiskers can take several weeks or even several months to appear, typically reaching sizes of around 2mm by 2 microns and can migrate into electronic components where they can distort signals and cause short circuits within equipment, ultimately leading to product failure. This was first observed by NASA during their space programme research and was obviously deemed a risk to the operation of any components within the space vehicle environment.
How are they formed ?
Zinc whiskers originate from stress in the coating deposit, generated from either internal or external forces. External stress can originate from such locations as the post manipulation, repeat flexing or thermal expansion of the product. Internal stress comes from within the crystal structure of the coating. In both situations, the stress induces energy release that causes diffusion of the Zinc atoms. This leads to tiny nodules forming on the surface of the coating that grow continuously from the base as more zinc atoms diffuse. The process continues until all the stress is released and no further energy exists to diffuse the atoms. Some coatings have a high misaligned structure and naturally self-alleviate the stress via the expulsion of the misaligned zinc atoms to the surface. Alkaline Zinc is one of these coatings and as such has one of the highest tendencies to form Zinc whiskers.
Will this affect my Raised Floor ?
Components of raised flooring are quite likely to have a zinc passivation coating in particular the pedestals. Most panels are manufactured from steel which has been Hot dipped galvanised and this process does not put the molecular structure under stress and does not allow the “whiskers” to form. So depending on the coating the metal components receive in manufacture will determine if the “whiskers” have potential to form.
What is the risk ?
Zinc passivation is an every day process that you will find on millions of components within a modern building, most commonly on screws and fixings. The risk within an ordinary office is minimal, although within a data centre depending on how mission critical the centre is, it can be perceived as a higher risk, also there is a tendency for hardware manufactures of electronic components to blame electronic failures without substantiation on “zinc whiskers”. The has led to some of the Data Centre providers taking a zero risk approach and insisting on “zinc whisker free” metal coatings within the environment.
What can be done ?
Several standard coatings can be applied to the metal components of raised flooring components during manufacture which are deemed “Zinc Whisker free” the most common ones are listed below, these will all come at an extra cost to the installation of a raised floor. The specifier should specify “all metal components to have corrosion resistant coatings that eliminate the possibility of the formation of zinc whiskers”
Hot Dipped Galvanised
Zinc Nickel Plated
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