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Zinc Anodizing


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Q. Is it true that you can anodize zinc?—L.J.

A. The answer is yes and no. If you were a purist, you would say no, but if you are a pragmatist the answer is yes. A purist will tell you that a true anodized coating consists of essentially 100 percent oxides of the metals. Aluminum is by far the most common example of this. The so-called zinc anodized surface really consists of a mixture of oxides, phosphates and chromates. The zinc anodizing process uses alternating current as opposed to direct current, and again, most but not all aluminum anodizing processes use direct current.

A few details of the zinc anodizing process: The process was introduced commercially approximately 50 years ago under the trade name Iridize. It has not been a screaming success in the marketplace. The process gives coatings that have excellent corrosion resistance, but due to the cost involved and the required equipment, it is not widely used.

The commercial process requires a three-phase power supply with a variable output of 50-250 volts AC. The baths are run at a temperature of 150°–180°F and at a current density of 35-45 ASF. Besides aluminum, magnesium, titanium and zinc, other metals have been “anodized.” These include beryllium, tin, copper, germanium and cadmium. In most cases, the methods used are strictly experimental/laboratory.

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