Category: coatings

Accelerators In Phosphate Coating

Accelerators

 Are the additives which are added at a small amount in a reaction to promote or enhance the reaction without involving in it.

Inhibitors or Decelerators

Are the additives which are added at a small amount in a reaction to stop or decrease the reaction without involving in it.

Application of Accelerators

Accelerator is actually an oxidizer used in various applications are given below.

• Zn phosphating
• Fe phosphating
• Mn phosphating
• Ca modified Zn phosphating
• Tri-cation phosphating
• Zn coating

Oxidizing agent always undergoes reduction process, Reducing agent always undergoes oxidation process before going to this topic we must know some basics of it.

Oxidation

• Addition of oxygen
• Removal of hydrogen
• Removal of electron
• Increase in oxidation number
• Takes place at anode 

Reduction

• Addition of hydrogen
• Removal of oxygen
• Adding of electron
• Decrease in oxidation number
• Take place at cathode

Mnemonics

• LEO- Loss of electron is oxidation
• GER- Gain of electron is reduction
• OIL- Oxidation is Loss of electron
• RIG- Reduction is gain of electron

So oxidation helps to prevent corrosion and further oxidation by forming sacrificial or protecting layer known as rust.

Example: Zinc, Iron oxide, Anodisation of Aluminum in which an oxide layer is formed.

The oxidizing agent helps in oxidizing other metals also. Oxidation is an electron positive behavior, so metal undergoes oxidation due to electropositive nature.

Electro positivity

The electron releasing tendency that is very behavior of metal.

This is also known as rusting (accepted as protecting area)

Example: Iron oxide, Ferric oxide, Ferrous oxide are the Iron oxide pigments.

So we apply Red oxide paint which is nothing but Iron oxide.

Similarly we want to oxidize the virgin surface of the metal into metal oxide but at the same time it should be aberrant.

In case of phosphate it is called as Metal phosphate and with all that we take some efficient metal also they are

• Tri-cation Zn-Mg-Ni phosphate
• Ca modified Zn phosphates
• Nano-ceramic coating
• Zirconium coating

How to Accelerators in Industry

• There must be proper storage facility for storing accelerators.
• There should be two-path systems for applying accelerators.
• Nitride should be supplied separately.

Variety of Accelerators

Compounds	Ratio
Nitrite (NO2–)	0.1 – 0.25 g/L
Nitrate (NO3–)	1 – 10 g/L
Hydrogen peroxide (H2O2 – 100% Conc.)	0.5 – 5 g/L
Meta-nitro benzene sulphonic acid	0.05 – 2 g/L
Meta-nitro benzoate	0.05 – 2 g/L
Para-nitro phenol	0.05 – 2 g/L
Poly ethylene imine (PEI)

Precautions

Kindly follow the Material safety data sheet, Product data sheet.

Phosphate Coating

Phosphate Cation

Cations	Ratios
Zn2+	0.3 – 2 g/L
Ni2+	0.3 – 4 g/L
Mn2+	0.3 – 2 g/L

Phosphate Anion

Anions	Ratios
PO43-	5 – 25 g/L
F-	– 2 g/L
NO3-	4 g/L
NO2-	0.1 – 2 g/L

The above parameters are depend upon by customers and time period of salt spray system (200 h, 440 h, 600 h, 1000 h)

Various Types of Phosphating

• Electro phosphating
• Electrolytic phosphating
• Electrolysis phosphating
• Phosphate conversion coating
• Nano coating etc.