PHOSPHATE COAT­ING 101

Knives Illustrated - - Points Of Interest -

An­other ap­proach to in­crease cor­ro­sion re­sis­tance is by pro­duc­ing a pro­tec­tive layer on the sur­face. One of the most com­mon coat­ings con­sists of a phosphate—usu­ally a phosphate of iron, man­ganese, or zinc. The phosphate coat­ing is pro­duced by plac­ing the ob­ject to be coated in phos­phoric acid that con­tains the metal phosphate. As the ob­ject to be coated slowly re­acts with the acid, the so­lu­tion be­comes less acidic and the metal phosphate is de­posited on the sur­face of the ob­ject. Zinc phosphate is used in the coat­ing process on many OKC knives. Cor­ro­sion is a prob­lem with any iron-based al­loy. As a re­sult, knife blades are made from al­loys that are more re­sis­tant to cor­ro­sion than those made of typ­i­cal car­bon steels. In this re­gard, high car­bon steels such as 420HC or stain­less steels are em­ployed.

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