CS224406B1 - Method for fly preventing of chromium trioxide from a chromizing bath - Google Patents

Description

BACKGROUND OF THE INVENTION The present invention relates to a method for preventing chromium trioxide from escaping from chromating electrolytic baths.

In electrolytic chrome plating of metal surfaces with evolving and evolving gases, chromium trioxide is drawn off from the bath surface, which heavily contaminates the environment, causing many hygienic problems. The entrained chromium oxide drift increases its losses. Preventing chromium oxide from escaping from electrolytic baths is therefore an essential requirement for operation.

Up to now, chromium trioxide has not been allowed to escape from the chromium plating baths with high fluorine-containing surfactants or mechanically free floating bodies at the bath surface. The disadvantage of fluorinated surfactants is the very high production costs and reaction products resulting from their electrochemical decomposition in the plating bath.

The disadvantage of the floating-proof floating method is that these clog various bath outflow openings, adhere to articles passing through the chromium bath continuously and clog subsequent technological devices when released. The method of preventing chromium trioxide from escaping from a chromium bath according to the invention is to add to the chromium bath a surfactant of the oxyethylated alkylamine or alkylarylamine type having from 5 to 25 moles of bound ethylene oxide, the alkyl having 8 to 20 carbon atoms and the aryl being phenyl and / or an oxyethylated higher fatty acid alkanolamide with 5 to 25 moles of bound ethylene oxide, having 11 to 17 carbon atoms in the fatty acid alkyl chain and 2 to 3 carbon atoms in the amide-linked alkyl, with an effective surfactant concentration in the chromating bath of 10 ¹⁴ to 0.1 wt. As oxyethylated alkylamine, an alkylaminopolyethylene glycol ether having 18 carbon atoms in alkyl and 7 moles of bound ethylene oxide and / or 20 moles of bound ethylene oxide and / or a mixture thereof is added.

The oxyethylated alkanolamide is an oxyethylated stearic acid diethanolamide with 6 moles of bound ethylene oxide.

The above surfactants are cheaper and more affordable than the fluoride-containing surfactants. The effect of preventing chromium oxide from escaping from the chromium bath is at least the same.

The method of preventing drift according to the invention is documented in the following examples:

Example 1

Alkylaminopolyethylene glycol ether having 10 to 20 carbon atoms in alkyl and 7 moles of bound ethylene oxide was added to the bath for 24406: djp * · j β 'β \>' Ϊ j. For example ^{: a} continuous galvanic chrome plating of steel pre-nickel-plated objects with an electrical current of 15A / dm ^{2 of the} surface to be coated. The bath volume was byl 6 7001, its temperature was 42 ° C. The concentration of chromium trioxide in the bath was 50% and the concentration of sulphates did not exceed 0.5% by weight. The above surfactant was added to the chromium bath in an amount of 40 g. It formed a foam on the surface of the bath which prevented the chromium oxide from escaping for 3 hours. After the addition of the above-mentioned surfactant, the galvanic chrome plating continued without interruption of operation.

Example 2

To a 16,700 L bath at 43 ° C containing 400 g / L of chromium trioxide and 0.45 wt% sulfate, each was added. 224406 hour 10% by weight, a solution of alkylaminopolyethylene glycol ether having 18 carbon atoms in alkyl and 20 moles of bound ethylene oxide in an amount of 150 ml. The current density was 15 A / dm ^{2 of the} metallized area. Throughout the period of operation, the constantly forming foam prevented the chromium oxide from escaping fully.

Example 3

To a bath of 16 7001 and a temperature of 43 ° C containing 400 g / l of chromium trioxide and a content of 0.45% by weight of sulphates was added 4000 ml of a 10% by weight aqueous solution of alkylaminopolyethylene glycol ether s. 18 carbon atoms in the alkyl and 20 moles of bound ethylene oxide. The current density was 15 A / dm ^{2 of the} metallized area. The resulting foam for 32 hours prevented the chromium oxide from escaping fully.

Claims (3)

1. A method for preventing chromium trioxide from escaping from a chromium bath, characterized in that an oxyethylated alkylamine or alkylarylamine surfactant of 5 to 25 moles of bound ethylene oxide is added to the chromium bath, wherein the alkyl contains 8 to 8 carbon atoms and the aryl is phenyl and / or oxyethylated alkanolamide. higher fatty acids with 5 to 25 moles of attached ethylene oxide, having 11 to 17 carbon atoms in the alkyl chain of the fatty acid and 2 to 3 carbon atoms in the alkyl linked to the amide group, with an effective surfactant concentration in the chromating bath of ^10-14 % to 0.1 wt. The process according to claim 1, characterized in that the alkylated alkylamine is a C 18 alkyl alkylaminopolyethylene glycol ether and 7 moles of bound ethylene oxide and / or 20 moles of bound ethylene oxide and / or a mixture thereof. 3. The process of claim 1 wherein the oxyethylenated alkanolamide is oxyethylenated diethanolamide of stearic acid with 6 moles of bound ethylene oxide.