Mechanism of Silanization Treatment on Metal Surface

Summary:
Composition of Pottery Liquid

1) Silane treatment agent

The aqueous solution usually exists in the form of hydrolysis: after hydrolysis, the silane is rapidly adsorbed on the metal surface by the shrinkage reaction of its SiOH group with the MeOH group (M represents the metal) on the metal surface; on the one hand, the silane forms a Si-O-Me covalent bond at the metal interface.

Si(OR)3 H2O →Si(OH) 3ROH (1)

Si(OH) MOH →SiOM H2O (2)

In general, the covalent bond force can reach 70010, and the bond between silane and metal is very strong; on the other hand, the remaining silane molecules form a silane film with a Si-O-Si three-dimensional network structure on the metal surface through the polycondensation reaction between SiOH groups. The silane film is bonded together by a cross-linking reaction during the drying process and a subsequent electrocoat or powder, forming a strong chemical bond. In this way, a stable film structure can be formed between the substrate, the silane and the paint by chemical bonding.

Advantages: ① It does not contain heavy metals and phosphates, and the wastewater treatment is simple, which can reduce the cost of wastewater treatment and reduce environmental pollution.

② do not need to adjust the table, do not need nitrite promoter, etc., less dosage of chemicals, can speed up the processing speed, improve production efficiency, but also reduce the environmental pollution of such chemicals. ③ can be carried out at room temperature, without heating, reduce energy consumption. ④

The 1 treatment liquid can treat iron, aluminum and other materials at the same time, does not need to replace the bath liquid, reduce production costs.

1.2 ceramic mechanism

It is based on zirconium salt on the metal surface to generate a layer of nano-scale ceramic film. The ceramic agent does not contain heavy metals, phosphates and any.

What organic volatile components, almost no sediment in the process of film forming reaction, can deal with iron, zinc, aluminum, magnesium and other metals.

pottery principle:

1) Acid erosion reduces the concentration of H on the metal surface: Fe-2e-Fe2 H, 2H2e-2 [H]

2) Nano silicon promotes reaction acceleration:

[Si]:ZrO2 4[H]-[Zr] 2H2O

In the formula, [Si] is nano-silicon,[Zr] is a reduction product, and nano-silicon is a reaction activation body, which accelerates the reaction speed and further leads to a sharp decrease in the concentration of H on the metal surface, and the generated [Zr] becomes a film-forming crystal nucleus.

3) Two-stage dissociation of zirconium acid:

H2ZrF6 H -ZrF62- 2H

Due to the sharp decrease of H concentration on the surface, the dissociation equilibrium of zirconate at all levels shifted to the right, and finally ZrF6-.

4) Zirconate precipitation crystallization film formation: when the surface dissociation of ZrF6-and the dissolved metal ion Fe2 reach the solubility product constant Ksp, zirconate precipitation will be formed.

Fe2 ZrF62-H2O-FeZrF6 2H20

Zirconate precipitation and water molecules together to form a film-forming substance, with [Zr] as the film crystal nucleus continuously accumulating, the crystal nucleus continues to grow into crystal grains, and countless managers accumulate to form a conversion film. Silanization treatment and ceramic treatment can be called phosphorus-free film-forming treatment. At present, there are other methods of phosphorus-free film-forming treatment in the market. These new technologies have many similarities with silanization or ceramic treatment. Generally, they contain trace or even no heavy metals and phosphates, do not need to be modified, and can handle various plates, etc. The treatment time is short, which can improve production efficiency and has considerable advantages in energy saving and emission reduction, phosphorus-free film forming technology will become the main treatment method of chemical conversion film on steel surface in the future.