What is the difference between traditional blackening and phosphating blackening process?

1, the process is different:

The blackening is mainly made of sodium hydroxide and sodium nitrite boiled at 135-145 degrees. Its alkalinity is stronger. Phosphate is the main component of phosphoric acid and the main salt, such as: zinc, calcium, manganese and so on. Temperature 5-95 degrees ranging.

2, different corrosion resistance:

Phosphate corrosion resistance is much better than blackening. Such as manganese phosphating (after rust oil) its corrosion resistance is 10-20 times better than blackening.

3, different choice of agents:

Phosphate blackening is the use of manganese-containing phosphating solution, generated by the phosphating film is black. As the phosphate film in the deposition process of the substrate has a gas out, so the phosphate film is actually a microporous structure, in terms of rust prevention, is not very good, it is best to make a closure.

Expanded information:

Phosphate blackened by the factors affecting:

I. Temperature

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1. The higher the temperature, the thicker the phosphating layer, the more coarse crystallization.

2. The lower the temperature, the thinner the phosphide layer, the finer the crystallization.

3. But the temperature should not be too high, otherwise Fe2 + easily oxidized into Fe3 +, increase the amount of precipitate, the solution is not stable.

Two, free acidity

1. Free acidity refers to free phosphoric acid. Its role is to promote the dissolution of iron to form more nuclei, so that the membrane crystallization dense.

2. Free acidity is too high, the role of iron and accelerate the precipitation of hydrogen, so that the interface layer of phosphate is not easily saturated, resulting in the formation of nuclei difficult, loose film structure, porous, corrosion resistance decreased, so that the phosphate time is extended.

3. Free acidity is too low, phosphate film becomes thin, or even no film.

Three, total acidity

1. Total acidity refers to the sum of phosphate, nitrate and acid. Total acidity is generally controlled in the specified range of upper limit for good, is conducive to accelerate the phosphating reaction, so that the film grain fine, phosphating process, the total acidity continues to decline, reflecting slow.

2. Total acidity is too high, the film layer becomes thin, can be diluted with water.

3. Total acidity is too low, the film layer is loose and rough.

Reference:

Baidu Encyclopedia-Blackening

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Reference:

Baidu Encyclopedia-Phosphorization