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Could the inside or outside of Zinc-plated A/C ducts be a source of Zinc Whiskers?



(-----) 2006

I am an installer of high-end projection equipment and related signal switching and processing equipment. In working closely with large companies' IT (Information Technology)departments, the "zinc whisker" phenomenon was recently brought to my attention.

During the renovation of one company's raised-floor computer room, they experienced a rash of power supply failures among critical computer equipment. Tests in the computer room confirmed the presence of high concentrations of the whiskers which were causing the failures.

Most articles site the zinc-plated raised-floor computer room tiles as a primary culprit, but I was also wondering about the several miles and thousands of square feet of A/C ducting running through the buildings. Aren't they zinc-plated also? And aren't they in the ideal environment (carrying cold air after sitting dormant all night while off and filling with moist, warm air from the rooms, causing a film of condensation within them)for the growth of these whiskers?

Stephen H. Lemoine
Lion Multimedia Services - Slidell, Louisiana
^


2006

Sorry, I'm not up to date with all of the studies on this subject and can't point you to one, but your supposition certainly sounds reasonable to me.

Ted Mooney, finishing.com
Ted Mooney, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
^


2006

It depends on whether the ductwork is hot-dip galvanized (not susceptible) or electroplated. Whiskers have been known to occur on zinc electroplating since the 1940s, but never on galvanized. The driving force for whisker growth is probably compressive residual plating stress. Moisture isn't necessary -- whiskers can grow in vacuum. Suitable alloying may prevent zinc whiskers, so likely will be required for electronic gear (as already true for some tin electroplating).

Nearly all existing HVAC ductwork is galvanized (usually spangled appearance on sheetmetal, dull gray on fittings), but some electroplated sheetmetal is being used for interior applications where a thinner zinc coating is acceptable corrosion-wise. The electroplated material is more expensive but sometimes used where exposed portions are to be painted. So, maybe a future problem, as whiskers are (likely) an inhalation hazard as well as a source of electrical shorts.

Information on all types of whiskers (tin, zinc, silver, gold, cadmium) is available from NASA at http://nepp.nasa.gov/whisker/

Ken Vlach [dec]
- Goleta, California

contributor of the year Finishing.com honored Ken for his countless carefully researched responses. He passed away May 14, 2015.
Rest in peace, Ken. Thank you for your hard work which the finishing world, and we at finishing.com, continue to benefit from.

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