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Small knowledge of oxide film dyeing

Release time:

2021-10-14 13:05

Dyeing of Aluminum Alloy Oxide Film

1. Definition of aluminum alloy oxide film staining

The dyeing method is that the aluminum alloy just after oxidation is cleaned and immediately immersed in a solution containing dyes, and the pores of the oxide film are dyed in various colors due to adsorption and dyeing. This process is fast in color, bright in color and easy to operate, but it needs to be sealed after dyeing.

2. Dyeing requirements for oxide film

A. aluminum in sulfuric acid solution to get the oxide film colorless and porous, the most suitable for dyeing. Oxalic acid oxide film itself is yellow can only be dyed dark, chromic acid film porosity is low, the film itself is gray, can only be dyed dark.

B. oxide film must have a certain thickness, the minimum requirement is greater than 7um, thin oxide film can only be dyed very light color.

C. oxide film should have a certain porosity and adsorption, so hard oxide film and chromic acid conventional oxide film are not suitable for dyeing.

d. The oxide film shall be complete and uniform without defects such as scratches, blisters and pitting corrosion.

e. The film itself has a suitable color, and there is no difference in the metallographic structure, such as different grain sizes or severe segregation, etc.

3. Dyeing mechanism of oxide film

a.organic dye dyeing mechanism:Based on the theory of substance adsorption, it is divided into physical adsorption and chemical adsorption; physical adsorption refers to the adsorption of molecules or ions by electrostatic force; chemical adsorption is called chemical adsorption by chemical force (covalent bond, hydrogen bond, chelate bond, etc. generated by reaction). Physical adsorption hope low temperature, high temperature easy desorption; chemical adsorption at a certain temperature, it is generally believed that the two kinds of adsorption at the same time to chemical adsorption, so in the middle temperature.

b. inorganic dye dyeing mechanism:Usually carried out at room temperature, the workpiece in a certain order first immersed in an inorganic salt solution, and then immersed in another inorganic salt solution, so that these inorganic chemical reactions in the membrane pores to generate water-insoluble colored compounds, filling the pores of the oxide film and sealing the membrane pores (in some cases, the sealing process can be omitted). Inorganic dyes have a limited range of colors and are not bright enough, but they have good temperature and light resistance.

4. Fading of unqualified dyed film

After dyeing, the defects found before sealing can be removed by 27% nitric acid (mass fraction) or 5ml/l sulfuric acid at 25 degrees.