Community hub
Recent from talks
Contribute something to knowledge base
Content stats: 0 posts, 0 articles, 0 media, 0 notes
Members stats: 0 subscribers, 0 contributors, 0 moderators, 0 supporters
Subscribers
Supporters
Contributors
Moderators
Phosphate conversion coating
Phosphate conversion coating is a chemical treatment applied to steel parts that creates a thin adhering layer of iron, zinc, or manganese phosphates to improve corrosion resistance or lubrication or as a foundation for subsequent coatings or painting. It is one of the most common types of conversion coating. The process is also called phosphate coating, phosphatization, phosphatizing, or phosphating. It is also known by the trade name Parkerizing, especially when applied to firearms and other military equipment.
A phosphate coating is usually obtained by applying to the steel part a dilute solution of phosphoric acid, possibly with soluble iron, zinc, and/or manganese salts. The solution may be applied by sponging, spraying, or immersion. Phosphate conversion coatings can also be used on aluminium, zinc, cadmium, silver and tin.
The phosphatizing of firearms was discovered around 1910, when it was found that the surface of steel if changed to a phosphate acquires significant corrosion resistance. Until the 1940s it was very popular in the USA until more modern but similar methods of metal finishes were introduced.
The main types of phosphate coatings are manganese, iron, and zinc.
The process takes advantage of the low solubility of phosphates at medium or high pH. The bath is a solution of phosphoric acid (H3PO4), containing the desired iron, zinc or manganese cations and other additives. The acid reacts with the iron metal producing hydrogen and iron cations:
The reaction consuming protons raises the pH of the solution in the immediate vicinity of the surface, until eventually the phosphates become insoluble and get deposited over it. The acid and metal reaction also creates iron phosphate locally which may also be deposited. When depositing zinc phosphate or manganese phosphate the additional iron phosphate may be an undesired impurity.
The bath often includes an oxidizer, such as sodium nitrite (NaNO2), to consume the hydrogen gas (H
2) — which otherwise would form a layer of tiny bubbles over the surface, slowing down the reaction.
The main phosphating step can be preceded by an "activation" bath that creates tiny particles of titanium compounds on the surface.
Phosphate conversion coating
Phosphate conversion coating is a chemical treatment applied to steel parts that creates a thin adhering layer of iron, zinc, or manganese phosphates to improve corrosion resistance or lubrication or as a foundation for subsequent coatings or painting. It is one of the most common types of conversion coating. The process is also called phosphate coating, phosphatization, phosphatizing, or phosphating. It is also known by the trade name Parkerizing, especially when applied to firearms and other military equipment.
A phosphate coating is usually obtained by applying to the steel part a dilute solution of phosphoric acid, possibly with soluble iron, zinc, and/or manganese salts. The solution may be applied by sponging, spraying, or immersion. Phosphate conversion coatings can also be used on aluminium, zinc, cadmium, silver and tin.
The phosphatizing of firearms was discovered around 1910, when it was found that the surface of steel if changed to a phosphate acquires significant corrosion resistance. Until the 1940s it was very popular in the USA until more modern but similar methods of metal finishes were introduced.
The main types of phosphate coatings are manganese, iron, and zinc.
The process takes advantage of the low solubility of phosphates at medium or high pH. The bath is a solution of phosphoric acid (H3PO4), containing the desired iron, zinc or manganese cations and other additives. The acid reacts with the iron metal producing hydrogen and iron cations:
The reaction consuming protons raises the pH of the solution in the immediate vicinity of the surface, until eventually the phosphates become insoluble and get deposited over it. The acid and metal reaction also creates iron phosphate locally which may also be deposited. When depositing zinc phosphate or manganese phosphate the additional iron phosphate may be an undesired impurity.
The bath often includes an oxidizer, such as sodium nitrite (NaNO2), to consume the hydrogen gas (H
2) — which otherwise would form a layer of tiny bubbles over the surface, slowing down the reaction.
The main phosphating step can be preceded by an "activation" bath that creates tiny particles of titanium compounds on the surface.