Parkerizing

Parkerizing, bonderizing, phosphating, or phosphatizing is a method of protecting a steel surface from corrosion and increasing its resistance to wear through the application of a chemical phosphate conversion coating. Parkerizing is usually considered to be an improved zinc or manganese phosphating process, and not to be an improved iron phosphating process, although some use the term parkerizing as a generic term for applying phosphating (or phosphatizing) coatings that does include the iron phosphating process.

Parkerizing is commonly used on firearms as a more effective alternative to bluing, which is an earlier-developed chemical conversion coating. It is also used extensively on automobiles to protect unfinished metal parts from corrosion.

The Parkerizing process cannot be used on non-ferrous metals such as aluminium, brass, or copper. It similarly cannot be applied to steels containing a large amount of nickel, or on stainless steel. Passivation can be used for protecting other metals.

The process involves submerging the metal part into a phosphoric acid solution whose key ingredient is often zinc or manganese, with varying additional amounts of nitrates, chlorates, and copper. In one of the many processes that have been developed, the solution is heated to a temperature of 88–99 °C (190–210 °F) for a period ranging between 5 and 45 minutes. A stream of small bubbles is emitted from the metal part as the process takes place; when the bubbling stops, the process is complete. In addition to this particular processing temperature, there have also been various similar Parkerizing processes developed and patented that permit using either lower temperatures (for energy efficiency) or higher temperatures (for faster processing).

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