Application: Pre-painting treatment for automobiles, home appliances, hardware, etc.
Author: Robby
(1) Zinc phosphating (most commonly used)
Application: Pre-painting treatment for automobiles, home appliances, hardware, etc.
Composition of the potion:
Ingredient Function
Zinc dihydrogen phosphate (Zn(H₂PO₄)₂) Provides Zn²⁺ and PO₄³- to form a zinc phosphate (Zn₃(PO₄)₂-4H₂O) film.
Nitrates (NaNO₃, Zn(NO₃)₂) Oxidising agents, accelerating the phosphating reaction and refining the crystals.
Nickel salts (Ni²⁺) or manganese salts (Mn²⁺) Improve the corrosion resistance of the film and improve the crystalline structure.
Fluoride (NaF, Na₃AlF₆) Promotes the reaction of hard-to-phosphatise metals such as aluminium and galvanised sheet metal.
Surfactant Wets the metal surface and improves film uniformity.
Typical formulation (example)
Zinc dihydrogen phosphate (30~50 g/L)
Zinc nitrate (80~120 g/L)
Sodium fluoride (1~3 g/L)
Nickel salt (0.5~2 g/L)
pH 2.5~3.5, temperature 35~50°C
(2) Manganese phosphating
Application: Wear-resistant parts (e.g. bearings, gears).
Composition of the potion:
Ingredient Function
Manganese dihydrogen phosphate (Mn(H₂PO₄)₂) Forms manganese phosphate (Mn₃(PO₄)₂-3H₂O) film with high hardness.
Manganese nitrate (Mn(NO₃)₂) Promotes film formation and improves wear resistance.
Phosphoric acid (H₃PO₄) Regulates free acidity and controls reaction rate.
Typical formula (example):
Manganese dihydrogen phosphate (30~50 g/L)
Manganese nitrate (10~20 g/L)
Phosphoric acid (adjust free acidity)
pH 2.0~3.0, temperature 80~95℃ (heating required)
(3) Iron phosphating (light phosphating)
Application: low-cost rust prevention, painting substrates (e.g., electrical appliance shells).
Composition of the potion:
Ingredient Function
Sodium dihydrogen phosphate (NaH₂PO₄) Formation of iron phosphate (FePO₄) film, film thin and porous.
Oxidising agent (sodium chlorate NaClO₃) Accelerates the reaction and improves the densification of the film.
Typical formulation (example):
Sodium dihydrogen phosphate (10~30 g/L)
Sodium chlorate (1~5 g/L)
pH 3.5~5.0, temperature 40~60°C