METHOD OF PRODUCING BICHROMATE OF TRIVALENT CHROME AND COMPOSITION FOR CHROME TREATMENT OF METAL SURFACES Russian patent published in 2009 - IPC C01G37/00 

FIELD: chemistry.

SUBSTANCE: freshly deposited and washed chromium hydroxide in mass ratio Cr⁶⁺/Cr³⁺=1.9-2.1 is added to a solution of chromic anhydride with concentration CrO₃ 350-450 g/l and temperature ranging from 70 to 90°C. The mixture is boiled for 1.5 to 2 hours until attaining pH of not less than 1.3. The suspension is filtered from the insoluble residue. The obtained solution is boiled for 20 minutes to 1 hour and cooled to room temperature. The obtained basic bichromate of trivalent chrome and silica sol are used in the composition for chrome treatment of metal surfaces. Concentration of Cr⁶⁺ in the mixture ranges from 45 to 55 g/dm³, concentration of Cr³⁺ - 21.8 to 26.8 g/dm³, concentration of silica sol ranges from 16 to 130 g/dm³ in terms of SiO₂, and the size of the particles of the silica sol ranges from 5 to 300 nm.

EFFECT: obtaining a strong and uniform film on metal surfaces, which has polymer properties, not prone to cracking and is suitable for depositing polyethylene coating.

3 cl, 1 ex