US2956956A - Inhibitors for acid solutions employed in the surface treatment of metals - Google Patents

Description

Alan

United States Patent INHIBITORS FOR A'CID SOLUTIONS EMPLOYED IN THE SURFACE TREATMENT OF METALS Wennemar Strauss, Dusseldorf-Benrath, Alfred Kirstahler, Dusseldorf, Wolfgang Giindel, Dusseldorf- Oberkassel, and Wolf-Dieter Willmund, Dusseldorf- Holthausen, Germany, assignors to Dehydag, Deutsche Hydrierwerke G.m.b.H., Dusseldorf, Germany, a corporation of Germany No Drawing. Filed Feb. 9, 1955, Ser. No. 487,224

Claims priority, application Germany Feb. 10, 1954 7 Claims. (Cl. 252-149) i aftentea. Oct. 18, 196d 'ice . hibitors which possess all of theabove characteristics.

This invention relates to inhibitors for acid solutions employed in the surface treatment of metals, and more particularly to organic sulfonic acid compounds and their use as inhibitors in the surface treatment of metals with acid agents.

The treatment of metal surfaces with acid agents is well I known in industry and is frequently referred to as pickling. For example, prior to the application of coatings or electrodeposits to metal surfaces, and sometimes Prior to machining Working metal P it is "".2 lined above. The bivalent hydrocarbon radical R in the necessary to remove dirt, grease, rust or the like which may have accumulated on thesur faces during handling or storage. For this purpose, the metal objects, such as, for example, iron or steel objects, are immersed into acid solutions, particularly into more or less concentrated solutions of mineral acids or their acid salts which are often called pickling liquor. The same or similar processes are used for cleaning other metals, such as zinc or aluminum. The acid solution readily dissolves or removes any extraneous matter adhering to the metal surface and exposes the clean, uncorroded metal. However, if the metal object is not promptly withdrawn from the acid bath after all the dirt, grease, rust and the like have been removed and the bare metal is exposed, the acid agent or pickle liquor will begin to attack the metal itself.

Many methods for preventing the attack of the clean metal by the acid pickling agent have been proposed. The most common method is to modify the acid solution with various additives which form a protective layer on the clean metal surface and thereby prevent the acid agent from attacking the bare metal. Such additives are known in the art as inhibitors.

A great number of compounds have been found to be etfective as inhibitors. However, while the individual inhibitors known to the prior art possess certain desirable characteristics which make them suitable for special purposes, for use in only certain particular acid baths, or for use with only certain types of metal, the prior art fails to disclose inhibitors adapted for substantially universal use.

Modern practice in the art of treating the surfaces of metals with acid solutions requires not only that the inhibitor give a maximum degree of protection against attack by the acid solution on the virgin metal at relatively low concentrations of inhibitor, but also that the inhibitor have a lasting eliect, i.e. that the inhibitor be resistant against decomposition under the operating conditions and l ahigh grade modern inhibitor should not generate gases 5 Another object of the present invention is to provide inhibitors which may be employed universally in all types of acid baths and in conjunction with a wide variety of metals.

Other objects and advantages of the present invention will become apparent as this description proceeds.

We have found that organic sulfonic acids having the general structural formula wherein X represents a halogen atom or an atom group chemically related to halogen, such as a cyanide group or a thiocyanide group, for example, and R representsa bivalent aliphatic,*cycloaliphatic or aromatic radical, or their salts, have excellent?corrosion-preventing properties and may be used as inhibitors in acid solutions for the treatment of metal surfaces. When used as inhibitors in such solutions, these compounds have all of the desirable characteristics which modern practice demands, as outgeneral structural formula may be an unsubstituted radical or it may carry substituents such as alkyl radicals, oxy- "groups, .nitro-groups, additional sulfonic acid radicals and/orhalog'en atoms, cyano-groups or thiocyano-gronps;

Representative examples of sulfonic acids which may advantageously be used, as inhibitors as such min the form of their salts in accordance with our invention are the following:

Chloromethanesulfonic acid Bromomethanesulfonic acid Iodomethanesulfonic acid Dibromomethanesulfonic aci'd 2-chloro-ethanesulfonic acid-1 2-bromo-ethanesulfonic acid-1 2-cyano-ethanesulfonic acid-1 2-thiocyano-ethanesulfonic acid-1 3-bromo-propanesulfonic acid-1 4-bromo-butanesulfonic acid-l 4-bromo-butanesulfonic acid-2 3-iod0-propanesulfonic acid-1 3-cyano-propanesulfonic acid-l 4-thiocyano-butanesulfonie acid-l 2,3-dichloro-propanesulfonic acid-l 6-bromo-hexanesulfonic acid-l 3-bromo-camphor-sulfonic acid-7 2-chloro-benzenesulfonic acid-1 3-chloro-benzenesulfonic acid-1 4-chloro-benzenesulfonic acid-1 2,3-dichloro-benzenesulfonic acid-1 2,4,5-trichloro-benzenesulfonic acid- 1 7 4-bromo-benzenesulfonic acid-1 6-chloro-3bromo-benzenesulfonic acid-1 2,4-dibromo-benzenesulfonic acid-1 2,-5-dibrorno-benzenesulfonic acid-1 3,4,5-tribromo-benzenesulfonic acid-1 2,3,4,S-tetrabromo-benzenesnlfonic acid-l 4-iodo -benzenesulfonic acid-l 4-chloro-3-nitro-benzenesulfonic acid-1 5-bromo-2-nitro-benzenesulfonic acid-1 4-chloro-toluenesulfonic acid-2 4-bromo toluenesulfonic acid-2 4-iodo-toluenesulfonic acid-'2 3,4,5-trichloro-toluenesulfonic acid-2 4 chloro-toluenesulfonic acid-3 1 2-chloro toluenesulfonic acid-4i 6-bromo-toluenesulfonic acid-3 2,4-dichloro-toluenesulfonic acid-4 2-bromo-toluenesulfonic acid-4 4-Chl010-b6I1Zyl-w-SU1fOIliC acid 4-bromo-benzyl-w-sulfonic acid 5-bromo-o-xylenesulfonic acid-4 2,6-dichloro-m-xylenesulfonic acid-4 4-chloro-naphthalenesulfonic acid-l 4-bromo-naphthalenesulfonic acid-1 4,7-dichloro-naphthalenesulfonic acid-l l-chloro-naphthalenesulfonic acid-2 6 bromo-naphthalenesulfonic acid-2 5,8-dibromo-naphthalenesulfonic acid-2 4-brorno-toluene-di-sulfonic acid-2,6 4-bromo-naphthalene-di-sulfonic acid-2,7 4,4-dibromo-diphenyl-disulfonic acid-2,2 2-chloro-phenolsulfonic acid-4 2-bromo-phenolsulfonic acid-4 2,6-dichloro-phenolsulfonic acid-4 2,6-dibromo-phenolsulfonic acid-4 2,6-di-iodo-phenolsulfonic acid-4 6-bromo-phenol-di-sulfonic acid-2,4 6-bromo-naphthol-l-sulfonic acid-3 8-bromo-naphthol-l-di-sulfonic acid-3,5 l-bromo-naphthol2-sulfonic acid-8 The organic sulfonic acid compounds can be used as inhibitors in the manner customary in the art of treating the surface of metals with acid agents. The amounts of inhibitor added to acid baths may vary within wide limits and depend upon the composition of the acid bath, upon the metal to be treated and sometimes also upon the temperature of the acid bath. In general, however, it is sufficient to add between 0.01% and 0.5% by weight of organic sulfonic acid inhibitor, based upon the amount of acid agent used.

Acid solutions modified in this manner may be used for extended periods of time without any loss of effectiveness of the inhibitor. Such modified solutions are also effective over wide temperature ranges and may be used in conjunction with virtually any metal which is customarily subjected to a surface treatment, such as, for example, iron, zinc, aluminum and the like. The organic sulfonic acid inhibitors are non-poisonous, will not escape with the steam or acid vapors generated by such acid solutions, and are virtually free from objectionable odors. In addition, the inhibitors used according to our invention do not generate gases which tend to interfere with the surface treatment of the metal. In other words, the organic sulfonic acid compounds having the above general structural formula represent inhibitors which individually combine all of the desirable characteristics required of high grade inhibitors in modern practice.

Moreover, the inhibitors described above are readily compatible with known inhibitors and may be used either in conjunction therewith or alone.

Acid solutions which may be modified with the organic sulfonic acid inhibitors in accordance with our invention include solutions of mineral acids and mineral acid salts, as well as organic acids.

Solutions modified with such inhibitors can advantageously be employed in a variety of surface treatments of metals, such as, for example, cleaning, pickling, etching, sealing and the like.

The following example will further illustrate our invention and enable others skilled in the art to understand our invention more completely. It is understood, however, that the example is given only for the purpose of illustration and that our invention is not limited thereto.

Example Two sections of sheet iron, each having a surface area of about 18 cm. were placed into a 4 N solution of hydrochloric acid and a 4 N solution of sulfuric acid, respectively. The attack of the acid upon each of the sections was recorded by measuring the amount of hydrogen given oif. The temperature of the acid baths was maintained at 60 C. The rate of corrosion of each metal section thus determined furnished a control value to which the rates of corrosion of acid baths modified with organic sulfonic acid inhibitors in accordance with our invention could be compared to determine the effectiveness of such inhibitors.

Identical sections of sheet iron were then placed into 4 N solutions of hydrochloric acid and 4 N solutions of sulfuric acid which were modified with 1 gm./ liter of various representative organic sulfonic acid inhibitors such as described above. The amount of hydrogen generated by each solution was again recorded. The following table shows the type of organic sulfonic acid compound used and its corrosion-preventing effect in 4 N hydrochloric acid and 4 N sulfuric acid, expressed in percent of complete prevention based upon the control values obtained from unmodified acid baths, as described above.

Corrosion-preventing effect in percent Inhibitor added In each case the pickling, or cleaning, effect of the acid on unclean or rusted metal surfaces was the same but in the baths using our new inhibitors the attack of the acid on the virgin metal surfaces as compared with the attack by the uninhibited acid was reduced by the percentage given. Each of the materials listed earlier as representative examples of materials which may be used as inhibitors according to our invention, and other materials coming under the general structural formula previously set forth, will show similar corrosion-preventing effects in acid pickling bath.

While we have given certain specific embodiments of our invention, we wish it to be understood that the invention is not limited to such embodiments and that various changes and modifications can be made therein without departing from the spirit of the invention or the scope of the following claims.

We claim:

1. The method of preventing acid corrosion of the metal during the pickling with a mineral acid pickling bath wherein the mineral acid is selected from the group consisting of hydrochloric and sulfuric acids, of metal surfaces subject to corrosion by mineral acids, which consists of adding to said mineral acid pickling bath from 0.01% to 0.5% by weight, based on the amount of said mineral acid in said pickling bath, of an inhibitor selected from the group consisting of compounds having the general structural formula and their sodium salts, wherein X is a radical selected from the group consisting of chlorine, bromine, iodine, cyanide and thiocyanide, and R is a lower aliphatic radical containing from 1 to 6 carbon atoms.

2. The method of preventing acid corrosion of the metal during the pickling with a mineral acid pickling bath, wherein the mineral acid is selected from the group consisting of hydrochloric and sulfuric acids, of metal surfaces subject to corrosion by said mineral acids, said metal being selected from the group consisting of zinc, aluminum, iron and its alloys, which consists of adding to said mineral acid pickling bath an inhibitor in the amount of from 0.01% to 0.5%, based on the amount of said mineral acid in said pickling ath, elected from and their sodium salts, wherein X is a radical selected from the group consisting of chlorine, bromine, iodine, cyanide and thiocyanide, and R is a bivalent lower alkyl radical containing from 1 to 6 carbon atoms.

3. The method of preventing acid corrosion of the metal during the pickling with a mineral acid pickling bath, wherein the mineral acid is selected from the group consisting of hydrochloric and sulfuric acids, of metal surfaces subject to corrosion by said mineral acids, said metal being selected from the group consisting of zinc, aluminum, iron or its alloys, which consists of adding to said mineral acid pickling bath an inhibitor in the amount of from 0.01% to 0.5%, based on the amount of said mineral acid in said pickling bath, consisting of the sodium salt of a compound having the general structural formula wherein X is a radical selected from the group consisting of chlorine, bromine, iodine, cyanide and thiocyanide, and R is a bivalent lower aliphatic radical containing from 1 to 6 carbon atoms.

4. The method of preventing acid corrosion of the metal during the pickling with a mineral acid pickling bath, wherein the mineral acid is selected from the group consisting of hydrochloric and sulfuric acids, of metal surfaces subject to corrosion by said mineral acids, said metal being selected from the group consisting of zinc, aluminum, iron and its alloys, which consists of adding to said mineral acid pickling bath an inhibitor in the amount of from 0.01% to 0.5% based on the amount of said mineral acid in said pickling bath, consisting of the sodium salt of a compound having the general structural formula wherein X is a chlorine atom and R is a bivalent lower aliphatic radical containing from 1 to 6 carbon atoms.

5. The method of preventing acid corrosion of the metal during the pickling with a mineral acid pickling bath, wherein the mineral acid is selected from the group consisting of hydrochloric and sulfuric acids, of metal surfaces subject to corrosion by said mineral acids, said metal being selected from the group consisting of zinc, aluminum, iron and its alloys, which consists of adding to said mineral acid pickling bath an inhibitor in the amount of from 0.01% to 0.5%, based on the amount of said mineral acid in said pickling bath, consisting of the sodium salt of a compound having the general formula wherein X is a bromine atom and R is a bivalent lower aliphatic radical containing from 1 to 6 carbon atoms.

6. The method of preventing acid corrosion of the metal during the pickling with a mineral acid pickling bath, wherein the mineral acid is selected from the group consisting of hydrochloric and sulfuric acids, of metal surfaces subject to corrosion by said mineral acids, said metal being selected from the group consisting of zinc, aluminum, iron and its alloys, which consists of adding to said mineral acids an inhibitor in the amount of from 0.01% to 0.5%, based on the amount of said mineral acid in said pickling bath, consisting of the sodium salt of a compound having the general structural formula wherein X is an iodine atom and R is a bivalent lower aliphatic radical, containing from 1 to 6 carbon atoms.

7. A mineral acid pickling bath solution for pickling the surface of metal objects subject to attack by mineral acid, comprising a mineral acid selected from the group consisting of hydrochloric and sulfuric acids and from 0.01% to 0.5% by weight, based on the amount of said mineral acid in said pickling bath of an inhibitor, selected from the group consisting of compounds having the general structural formula XRSO H and their sodium salts, wherein X is a radical selected from the group consisting of chlorine, bromine, iodine, cyanide and thiocyanide, and R is a bivalent lower aliphatic radical containing from 1 to 6 carbon atoms.

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