COMPOSITION FOR CHROMATING METAL SURFACES AND METHOD OF OBTAINING COMPONENTS FOR PREPARING SAID COMPOSITION

摘要

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