US1734561A - Inhibiting compound - Google Patents

Description

252. COMPOSITIONS,

Patented Nov. 5, 1929 UNITED STATES LAIIIHIv PATENT OFFICE LUD'WIG J. GHRISTMANN, OF JERSEY CITY, NEW JERSEY, ASSIGNOR TO AMERICAN CYANAIID COMPANY, OF NEW YORK, N. Y., A CORPORATION OF MAINE INHIBITING COMPOUND No Drawing.

This invention relates to methods of cleaning or pickling metals by subjecting the same to an acid bath.

In the metal industries, particularly in the manufacture of iron or steel sheets or the like, which are to be coated with protective metals such as tin, zinc or cadmium, it is a common expedient to first clean the metal surface in order that the subsequent coating material may adhere firmly thereto, without danger of peeling off of the coating. This cleaning treatment usually consists in providing a dilute solution of a non-oxidizing mineral acid material, such as sulphuric acid, called a ickling bath, and immersing the metal art cles to be cleaned in the bath for a length of time sufiicient to remove scale, oxide and other matter from the surface of the metal. The bath is usually maintained at a predetermined temperature, usually above room temperature, during the pickling operation.

The acid in the pickling bath not only acts to remove the undesirable surface materials but also tends to attack the metal itself and, to protect the metal from attack by the acid, there is usually added to the pickling bath a small amount of a substance called an inhibitor. The inhibitor permits the acid to remove the undesirable surface material from the metal and prevents, either in whole or in part, the action of the acid upon the metal itself. Ordinarily, in the absence of an inhibitor, the acid in attacking the metal gives oil a substantial quantity of hydrogen or other gaseous substances with the production of an acid mist or spray which is injurious to the workmen and, in addition, results in appreciable loss of acid.

The present invention is intended to provide an inhibitor which may be prepared easily, which is low in cost and which is highly effective in a pickling bath even though present in small amounts.

I have discovered that a condensation producppf o-toluidine and sulfur chloride is highly effective as an inhibitdfiii' apickling bath. This material may be obtained in any suitable and well known manner. For in- Application filed September 18, 1929. Serial No. 393,591.

stance, one method of preparing my inhibitor is as follows:

One mol. of dry o-toluidine hydrochloride is made into a slurry with benzol and this mixture is poured into a suitable container fitted with a thermometer, a reflux condenser and an efiicient stirrer. Six mols. of sulfur chloride (S Cl are quickly added and the mixture warmed on a steam bath to 60-7 0 C. with stirring until the reaction is complete. When a sample of the reaction mixture can no longer be di-azotized or coupled it is considered to be complete. The di-azotization test is carried out in the usual manner with sodium nitrite and B-naphthol. The reaction mixture is filtered and the filter cake washed with benzol, reslurrying with additional benzol if necessary to wash out excess sulfur chloride. The material may then be dried.

The inhibitor constituting the subject matter of my invention was tested in a pickling bath in the following manner:

A pickling solution was prepared consisting of 250 cc. of dilute sulfuric acid containing 8% by weight of 66 B. acid. The solution was placed in a suitable vessel, maintained at a temperature of 183-185 F. and 0.100 grams of condensation product of o-toluidine and sulfur chloride was added to the solution. This is equivalent to about 4 one-hundredths of one percent of inhibitor in the bath.

Strips 3 long and 4" wide'of 30 gauge tin plate stock were used for the tests. The specimens were first cleaned with ether to remove any oil or grease on the surface, and, after drying were immersed in the pickling bath for five minutes to remove the oxide scale. The specimens were removed from the bath, dried and weighed. The specimens were immediately returned to the pickling bath, immersed for twenty minutes, washed, dried and weighed again. The loss in weight was determined and the specimens were subjected to another 20 minute test. Throughout the tests, check runs were made with similar pickling baths but without using any inhibitor. The table given below shows the results obtained with and without the condensation product of o-toluidine and sulfur chloride in the pickling bath From the above it is clear that the condensation product of o-toluidine and sulfur chloride is a good inhibitor and effectively curtails the action of the acid upon the metal. This is particularly true in view of the fact that the sample pickled in the bath containing no inhibitor was so rapidly dissolved in the acid that before the end of forty minutes it was completely in solution. Therefore, no effort was made to weigh the check samples during the tests. In similar tests carried out at higher and lower temperatures, it was found that this inhibitor was equally effective as at temperatures originally described.

Although I have described my invention in some detail, it is not limited to the specific matters set forth. The amounts of inhibitor used in pickling baths may, of course, be varied widely and the nature of the bath may also be changed to suit any particular conditions which may prevail. In general, it is not necessary to use more than 1% of inhibitor in the bath and for most purposes less than 0.1% is suflicient. It is to be understood that my invention is not to be limited except as set forth in the claims appended hereto.

I claim 1. A method of cleaning or pickling metals which comprises subjecting the same to a pickling or cleaning bath containing a small amount of a condensation product of o-toluidine and sulfur chloride.

2. A method of cleaning or pickling metals which comprises subjecting the same to a pickling bath containing less than 1% of a condensation product of o-toluidine and sulfur chloride.

3. A method of cleaning or pickling metals which comprises subjecting the same to a pickling or cleaning bath containing less than 0.1% of a condensation product of o-toluidine and sulfur chloride.

4. A method of cleaning or pickling metals which comprises subjecting the same to a. pickling or cleaning bath containing about 0.01% of a condensation product of o-toluidine and sulfur chloride.

5. A bath for pickling metals comprising a non-oxidizing mineral acid and a small amount of a condensation product of o-toluidine and sulfur chloride.

6. A bath for pickling metals comprising a. non-oxidizing mineral acid and less than 1%