US1734560A - Inhibitor - Google Patents

Description

Patented Nov. 5, 1929 UNITED STATES PATENT OFFICE LUDWIG J. CHRISTMANN, .OF JERSEY CITY, NEW JERSEY, ASSIGNOR TO AMERICAN CYANAMIID COMPANY, OF NEW YORE, N. Y., A CORPORATION OF MAINE INHIBITOR No Drawing.

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

In the me'tal industries, particularly in the manufacture of iron or steel sheets or the like, which are to be coated with protective metals such as zinc, tin or cadmium, it is a common expedient to first clean the metal surface in order that the subsequent coating materialmay 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 acidmaterial, such as sulphuric acid,

called a pickling bath, and immersing the metal articles 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 undes rable 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 off 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.

1 have discovered that thiobenzamide is highly effective as an inhibitor in a pickling bath. This material may be obtained in any suitable and well known manner.

The inhibitor constituting the subject mat- Application filed September 18, 1929. Serial No. 303,589.

ter of my invention was tested in a pickling bath in the following manner:

A pickling solution Was prepared consisting of 250 cc. of dilute sulphuric acid containing 6% by weight of 66 B. acid. The solution was placed in a suitable vessel, maintained at a temperature of l83185 F. and 0.100 grams of thiobenzamide was added to the solution. a This is equivalent to about 4 one-hundredths of one percent of inhibitor in the bath.

Strips 3 long and wide of30 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 subjectedto another20 minute test. Throughout the tests, check runs were made with similar pickling baths but without-using any inhibitor. The table given belowshows the results obtained with and without thiobenzamide in the pickling bath:

- Im- Immersed Per Per $2 mersed v20 min. cent cent ,5 20 min. more loss in loss in P loss total 20min. 40min.

loss

Grams Grams Grams No inhibltorin bath"--- 4.060 100.0 Thl0beu1amide1nbath-. 4.014 0. 014 0.033 0.35 0.83

From the above it is clear that thiobenzamide is a good inhibitor and eflectively'curtails the action of the acid upon the meta-1.

This is particularly true in view of the fact .1 that the-sample pickled in the bath containing no inhibitor was so rapidly dissolved I A,

the acid that before the end of forty ni in-"9'5" utes it was completely in solution. There- I fore, no effort was made to weigh the checksamples during the tests. In similar tests carried out at higher and lower temperatures, it was found that the thiobenaaf mide was equally effective as at temperatures originally described.

a non-oxidizing mineral acid Although I have described my invention in some detail, it is not l'imitedto the specific matters set forth. The amounts of inhibitor used in pickling baths may, of course, be varied wldely 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 for most purposes less than 0.1% is sufficient. 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 thiobenzamide.

2. A method of cleaning or pickling metals which comprises subjecting the same to a pickling bath'containing less than 1% of thiobenzamide.

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 thiobenzamide.

4. A method of cleaning or pickling als which comprises subjecting the same to a pickling or cleaning bath containing about 0.01% of thiobenzamide.

' 5. A bath for pickling metals comprising a non-oxidizing mineral acid and a small amount of thiobenzamide. k

6. A bath for pickling metals comprising a non-oxidizingmineral acid and less than 1% of thiobenzamide. I

7 A bath for pickling metals comprising and less than 0.1% of thiobenzamide.

8. A bath for pickling metals coin rising sulphuric acid and about-0.01% of t 'obenzamide.

- I In testimony whereof, I have hereunto subscribed my name this 16th day of September,

LUDWIG J. CHRISTMANN.

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