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How to Improve Purity of Oxide Film for Aluminum Mirror Sheets

March 7, 2019

The purity of oxide film plays a crucial role in deciding quality of aluminum mirror sheets. Some manufacturers supplies reflective aluminum sheet metal pieces as bring as mirrors, while others offer shiny aluminum sheet pieces that are not shiny at all. An impure oxide film makes a piece of mirror finish anodized aluminum sheet look like being covered with a layer of fog. How to improve the purity of oxide films, then? The answer includes purity of solution and raw material, film thickness, film pore rate and proper whole sealing.

1. The impurities in oxide films mainly come from aluminum substrates and oxide solutions, therefore, it’s efficient to enhance purity of oxide films by reducing alloy metal contents or adopting aluminium of high purity. The other way is to decrease alien icons of oxide solutions by keeping the solutions fresh.

mirror finish anodized aluminum sheet

2. High pore rate proves to be a root of serious light scattering. Especially when pores are of shapes of horns, the light scattering degree climbs dramatically, which leads to obvious decrease in film purity. The pore rate of an oxide film depends on the formation speed of the solute film. The higher the speed, the higher the rate. The speed rises with that of sulfuric acid concentration, solution temperature and electricity current density, thus appropriate decrease of any the three helps to reduce the pore rate of oxide films for mirror finish anodized aluminum sheets.

3. Although the oxide film is transparent, light scattering still exists with the increase of film thickness which should be controlled between 10 and 12um. If the reflective aluminum sheet metal pieces are used for products requiring little about film thickness, 6 or 8um is also acceptable.

4. The key to good pore sealing lies in perfect control of temperature and time. Standard sealing has no impact on transparency of oxide films, but problems arise if there’s failure in controlling temperature or time. Pore sealing at the common temperature should focus on content control of Ni and Fi. Excessive (time) pore sealing will lead to formation of powders that scatter light. In case of excessive pore sealing, the shiny aluminum sheet pieces should be placed into dilute nitric acid to remove powders.

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