COMPOSITION FOR CHROMATING METAL SURFACES AND METHOD OF OBTAINING COMPONENTS FOR PREPARING SAID COMPOSITION Russian patent published in 2010 - IPC C01G37/14 C01B33/141 C01B33/146 C23C22/05 C23F15/00 

FIELD: chemistry.

SUBSTANCE: invention can be used to make a protective coating on metal surfaces. The composition for chromating metal surfaces contains an aqueous solution of basic bichromate of trivalent chromium and silica sol. Total content of CrO₃ in the said composition is 135-145 g/l, while content of SiO₂ is 120-130 g/l. The method of preparing an aqueous solution of basic bichromate of trivalent chromium involves addition of activated carbon into the a solution of chromic anhydride until achieving molar ratio CrO₃/Cr₂O₃ = 4-4.15 and subsequent separation of the precipitate. The method of obtaining silica sol through cationisation of liquid glass involves step-by-step autoclaving of freshly prepared sol. To obtain freshly prepared sol, liquid glass containing 3-4 wt % SiO₂ is used. The autoclaving process has at least three steps. The product from the previous step is used as seeding material for the next step. The silica sol obtained at the last step is evaporated until attaining SiO₂ content of not less than 250 g/l.

EFFECT: invention enables to obtain a protective coating which forms a strong, stable, uniform film with high adhesion after deposition of the said composition on a metal surface and subsequent thermal treatment.

5 cl, 1 ex