Stabilization of Hydrogen Peroxide in Acid Baths for Cleaning Metals

The present invention relates to processes for pickling metals with acid solutions containing hydrogen peroxide, and more particularly, it relates to methods for stabilizing hydrogen peroxide in such solutions, as well as to the solutions themselves.

It is known to use sulfuric acid baths containing hydrogen peroxide to pickle or clean metals. In the case of a divalent metal, M, the reaction occurs according to the following equation:

the hydrogen peroxide, however, is a material which is very sensitive to the presence of impurities which catalyse its decomposition. Among these impurities, metallic impurities are among the most active, and it is accordingly necessary to stabilize hydrogen peroxide-containing baths for pickling metals.

Among the additive materials proposed to stabilize the hydrogen peroxide in such baths are ethylene glycol and polyethylene glycols in British Patent 1,157,038 and French Patent 1,539,960; saturated aliphatic alcohols in U.S. Pat. No. 3,957,290; urea and its derivatives in British Patent 1,160,134; phenacetin and sulfathiazole in French Patent 1,427,149; and phenol in U.S. Pat. No. 3,649,194 and French Patent 2,065,380. Such prior art stabilizing agents used even up to the present time suffer a number of disadvantages. Thus, some of them are only slightly soluble in the pickling baths, while others complex the metal to be pickled. Yet others are toxic, while some of these prior art agents also inhibit or retard the pickling action of the baths.

It has now been discovered that certain quinoline derivatives and/or a certain polycondensation surface active agent stabilize the hydrogen peroxide in acid pickling baths and do not suffer the disadvantages of the prior art materials. The quinoline derivatives contemplated for use herein are 8-hydroxyquinolines which are salts of certain acids or nitro or sulfo derivatives. More specifically the present invention embraces hydrogen peroxide-containing metal pickling baths which are stabilized with an effective amount of one or more 8-hydroxy-quinolines such as the neutral sulfate of 8-hydroxyquinoline, (C.sub.9 H.sub.6 NOH).sub.2 H.sub.2 SO.sub.4, (also known as orthohydroxyquinoline), the 8-oxyquinoline derivative of phthalylsulfathiazole, 5-sulfo-6-methyl-8-oxyquinoline, and 8-hydroxy-quinoline salicylate and/or an ethylene oxide polycondensate of fatty alcohol. The use of such baths for cleaning or pickling metals is also contemplated herein.

The oxyquinoline stabilizers of the present invention are used in quantities sufficient to protect the hydrogen peroxide. It is generally desirable to use from about 10 to 500 ppm of the oxyquinoline stabilizers in the pickling baths, and amounts of from 20 to 100 ppm are preferred.

Unless otherwise indicated, all parts percentages, proportions, and ratios herein are by weight.

It has also been found desirable to have the baths according to the present invention contain a surface active agent. In effect, the surface active agent, by modifying the surface tension of the baths, permits a better solid-liquid contact and improves the speed of the pickling. It also permits improving the quality of the film on the workpieces, at the time they are removed from the baths.

It has further been found according to the present invention that surface active agents formed by polycondensation of fatty alcohols with ethylene oxide provide excellent results and permit the same notable improvement in the stability of the pickling baths. Surface active agents prepared from fatty alcohols containing from about eight to about twenty carbon atoms condensed with from about two to about fifty moles of ethylene oxide are preferred, and one particularly effective fatty alcohol polycondensate is sold under the name "UKANIL" by Produits Chimiques Ugine Kuhlmann, Paris, France. This material is prepared by condensing about nine moles of ethylene oxide with fatty alcohols derived from olefin.

Even used alone, without the oxyquinoline derivative stabilizers of this invention, these fatty alcohol-derived surface active agents effectively stabilize such pickling baths. The amohnt of surface active agent added to the pickling baths is desirably sufficient to provide a concentration of from about 0.3 to about 2 g/liter.

The temperatures utilized for the pickling treatment of the present invention can range from ambient to somewhat elevated. Generally, temperatures from 25.degree. to about 65.degree. C. can be used, and temperatures of about 50.degree. C. give very good results.

A typical bath used for pickling metals, and in particular copper, according to the present invention contains from about 100 to 400 g/liter of sulfuric acid, from about 2 to about 80 g/liter of 100% hydrogen peroxide, from about 10 to about 500 mg/liter of the oxyquinoline stabilizer, and from about 0.3 to about 2 g/liter of surface active agent. In practice, the pickling bath contains, except at the beginning of the operation, fairly substantial quantities of the sulfate of the metal to be pickled.

The following examples are given to illustrate embodiments of the invention as it is presently preferred to practice it. It will be understood that these examples are illustrative, and the invention is not to be considered as restricted thereto except as indicated in the appended claims.

This illustration relates to the pickling of copper with a solution which does not contain a stabilizer according to the present invention.

A pickling solution is prepared to contain 100 g/liter of sulfuric acid, expressed as 100% acid, 30 g/liter of copper in the form of copper sulfate tetrahydrate, and 20 g/liter of hydrogen peroxide, expressed as 100% peroxide. The temperature of this solution is maintained at 50.degree. C.

After six hours, the solution does not contain more than 67% of the hydrogen peroxide initially added, and after 24 hours it does not contain more than 20%.

A solution is prepared identically to that described in Example I, but 30 mg/liter of the neutral sulfate of 8-hydroxy-quinoline is added. The temperature of this solution is then maintained at 50.degree. C.

At the end of six hours, this solution contains about 99% of the hydrogen peroxide originally added, and at the end of 24 hours the bath contains about 93% of the original hydrogen peroxide.

The same solution is prepared as in Example I, except that 50 mg/liter of the neutral sulfate of 8-hydroxy-quinoline is added. The solution is then maintained at a temperature of 50.degree. C.

After six hours, all of the hydrogen peroxide originally introduced is still present in the solution, and at the end of 24 hours, it still contains 97% of the peroxide.

To a bath having the composition described in Example I, 100 mg/liter of the sulfate of ortho-oxyquinoline is added. This bath is then maintained at 50.degree. C.

At the end of six hours, there remains 99% of the initial amount of hydrogen peroxide; at the end of 24 hours, 98%; and after 48 hours, 68%.

A bath is prepared as in Example I, and one gram/liter of "UKANIL" fatty alcohol-ethylene oxide condensate is added. The temperature of the bath is thereupon maintained at 50.degree. C..

At the end of six hours, there remains 92% of the original hydrogen peroxide; after 24 hours, 86%; and after 48 hours, 67%.

To a bath having the composition set forth in Example I is added one gram/liter of "UKANIL" and 50 mg/liter of ortho-oxyquinoline sulfate. The temperature of the solution is maintained at 50.degree. C.

After six hours, there remains 99% of the original hydrogen peroxide; at the end of 24 hours, 93%; and after 48 hours, 80%.

It will be understood from the present description that the other 8-oxyquinoline derivatives disclosed herein will provide comparable results in stabilizing hydrogen peroxide in acid baths for pickling metals. Such baths can be used to pickle a wide variety of metals, and it will be understood that the baths according to this invention exhibit longer life and provide very good cleaning action on the metals.