Preparation method of chromium-free passivating solution for brass surface

Abstract

The invention discloses a preparation method of a chromium-free passivating solution for the brass surface. The preparation method of the passivating solution comprises the following steps: adding a proper amount of water into a reaction kettle, adding boric acid and tartaric acid, stirring until boric acid and tartaric acid are dissolved, heating to 40-50DEG C, adding benzotriazol and 1-phenyl-5-mercaptotetrazole, stirring for 6-10min to make the obtained solution uniform, cooling to room temperature, sequentially adding sodium citrate, sodium molybdate, sodium tungstate, hydrogen peroxide, sodium silicate and sodium dodecyl sulfonate according to a condition that a later substance is added after a previous substance is dissolved, stirring for 13-17min after all above substances are added, adding water to a constant volume, and adjusting the pH value to 2.5-3.5.

Description

technical field [0001] The invention relates to the technical field of surface treatment, in particular to a preparation method of a chromium-free passivation solution for brass surfaces. Background technique [0002] Copper and brass are easily rusted in the atmosphere. For a long time, people have generally used chromic acid passivation process for surface treatment to improve the surface corrosion resistance of copper and brass. Although the appearance of the product treated by this process is golden yellow and has good corrosion resistance, a large amount of chromate or chromium trioxide is used in this process, and the total amount of hexavalent chromium added is as high as about 250 g / Lift. According to medical data reports, hexavalent chromium is a strong carcinogen, which can also cause respiratory ulcers, perforation of nasal septum, toxic hepatitis, dermatitis, anemia and other diseases, which is very harmful to human health. The allowable discharge of toxic sub...

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Problems solved by technology

Although the appearance of the product treated by this process is golden yellow and has good corrosion resistance, a large amount of chromate or chromium trioxide is used in this process, and the total amount of hexavalent chromium added is as high as about 250 g / Lift

According to medical data reports, hexavalent chromium is a strong carcinogen, which can also cause respiratory ulcers, perforation of nasal septum, toxic hepatitis, dermatitis, anemia and other diseases, which is very harmful to human health. The allowable discharge of toxic substances is <0.5mg / l, but the concentration of toxic substances in the chromic acid waste liquid is more than 500,000 times higher than the national standard, and it is difficult to recycle it even at a huge cost

The fact that these harmful substances cannot be recycled means that the pollution to the environment cannot be fundamentally solved, and thus the fact that it is harmful to human health cannot be avoided.

In order to solve this problem, some people used tannic acid and dilute chromic acid to treat the surface of brass, but the color of the workpiece after treatment was poor, the resistance to atmospheric corrosion was weak, the product could not be stored and used for a long time, and the raw materials were scarce and the cost was high. Therefore, it has not been widely adopted by people

In addition, some people use silicate to treat the surface of copper and brass. Although the film layer treated by this process has good corrosion resistance, because the workpiece is processed at high temperature, it is required that the workpieces cannot contact each other to avoid sticking on the surface of the workpiece. It directly affects the quality of the surface film layer, so it cannot be mass-produced, especially for the mass production of watch parts and bearing parts.

At present, the ideal treatment method is to use benzotriazole (BTA) to passivate the surface of copper and copper alloys. After the treatment, a thin film of tens to hundreds of angstroms is formed on the surface. The film is very thin and easy to wipe. It is easy to be slowly oxidized to Cu(II)BTA in the air, resulting in the gradual darkening of the appearance color, which affects the appearance aesthetics, and the corrosion resistance of salt water or ammonia water is also low, although in weak acidic solutions containing NaCl enables the membrane to However, the corrosion resistance of the thick film is poor, and the color is not as good as that treated with chromic acid.