Phosphating


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phosphating

[′fäs‚fād·iŋ]
(metallurgy)
Forming a phosphate coating on a metal. Also known as phosphatizing.
McGraw-Hill Dictionary of Scientific & Technical Terms, 6E, Copyright © 2003 by The McGraw-Hill Companies, Inc.
The following article is from The Great Soviet Encyclopedia (1979). It might be outdated or ideologically biased.

Phosphating

 

the creation of a conversion coating of insoluble phosphates (phosphate coating) on metal articles. When covered by paint or varnish, the conversion coating inhibits corrosion. Phosphating is used mainly on low-alloy and carbon steels and on cast iron. The phosphate coating (thickness, 2–5 micrometers) retains lubricant, a feature that acts to lower the coefficient of friction. Owing to their high electrical resistivity, the coatings can withstand potential differences of 300–500 volts, and they are stable at temperatures up to 400°–500°C.

Phosphating is carried out by immersing the article in a solution of iron, manganese, zinc, and cadmium phosphates that has been heated to 90°–100°C. Industry produces manganese ferric phosphate mixture in a form designed expressly for phosphating. The process usually takes approximately one hour. After being dried, the article is passivated in a weak chromate solution. Phosphating can also be carried out electrochemically with alternating or direct current; here, the process takes 15–20 min.

REFERENCES

Lainer, V. I. Zashchitnye pokrytiia metallov. Moscow, 1974.
V. I. LAINER
The Great Soviet Encyclopedia, 3rd Edition (1970-1979). © 2010 The Gale Group, Inc. All rights reserved.
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