All You Need to Know About Phosphate Coatings
Phosphate Coating or Phosphating is a process of coating metals like iron and steel are coated using other metals like manganese phosphate coating or zinc phosphate coating. The process is done to protect the metals from corrosion and to have strong adhesion of the metal and paint. This is the initial stage of coating which is done before applying the final paint solution on to a metallic surface. Phosphate’s property of low solubility is taken into consideration for making the phosphate coating stay for a longer time.
The coating doesn’t lie on the metal, but it chemically changes the surface of the metal. So, it is called conversion coating. This prevents the coating from scratching off or chipping off from the surface. Manganese Phosphate coating can be a standalone coating for purposes such as lubrication.
Process of Phosphating
Phosphoric Acid is used in the procedure of phosphate coating. Whether it is zinc or iron or manganese phosphate coating, the metals are dissolved in phosphoric acid solution. When metals like iron come in contact with phosphoric acid, metal and acid reaction takes place which raised the pH level and causes the dissolved salts to precipitate on the surface.
Coatings are formed by various metal precipitates
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| Manganese Phosphate Coating |
Various metal precipitates form various types of coatings. Sodium Nitrate must be frequently added to prevent the generation of hydrogen gas. The coating can be carried out in three or five stage process.
The three-stage process is
- Clean/ Phosphate
- Rinse
- Seal/ Rinse
The five-stage process can be carried out in two ways:
- Clean
- Rinse
- Phosphate
- Rinse
- Seal
Another way of phosphating is
- Clean
- Rinse
- Activated Rinse
- Phosphate
- Seal
Metals used for Phosphate Coating
- Phosphate
- Manganese Phosphate
- Zinc Phosphate
- Iron Phosphate
- Palaforizing (non- traditional chemical method)
Manganese Phosphate Coating
The Phosphate coating is done in two ways. They are black phosphate coating and dark gray manganese phosphate coating. There are different kinds of phosphate coatings and out of the manganese phosphate coating is hardest and provides best abrasion and corrosion protection. They offer continuous wear and tear protection. They are applied through a high-quality immersion method. This manganese phosphate coating process is used where the sliding mechanism is required i.e., automotive field and transmission systems.
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| Manganese Phosphate Coating |
Zinc Phosphate Coating
Zinc Phosphate coating is used as rustproofing for metals. They can be applied in two methods, spraying and immersion. Zinc Phosphate coating can be gray or black as they are deepened with oil application. It reduces the reflectivity in defense applications. It can be considered as a lighter alternative of manganese phosphate coating.
Iron Phosphate Coating
Iron Phosphate coating is most commonly used in interior equipment. It is cost effective. It is not a thick coating. They come in light yellow and blue red. Iron phosphate coating increases paint adherence and improves flexibility. It is used in etching, cleaning of aluminum and galvanized metals.
Phosphate is also used directly as part of coating techniques. Phosphating is a method of applying phosphate to metals. This doesn’t include any metal combination and the phosphate coating is done with pure phosphate only.
Benefits of Phosphate Coating
The application of phosphate coating for metals has numerous benefits.
- Increased lubricant and oil adhesion.
- Property of anti-galling.
- No distortion of the coating is applied as thin layers.
- Cost efficient.
- Anti-corrosion and rust properties.
- Great appeal to the overall finished look of a coating or structure on metallic surfaces.
These are some of the benefits of phosphate coating. The best way to protect any metal from rust or corrosion is by using phosphate coating only. They serve for many purposes in both metal and paint industries.
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