US1830566A

US1830566A - Method of cleaning and pickling metals

Info

Publication number: US1830566A
Application number: US324066A
Authority: US
Inventors: Waldo L Semon
Original assignee: BF Goodrich Corp
Current assignee: Goodrich Corp
Priority date: 1928-12-05
Filing date: 1928-12-05
Publication date: 1931-11-03
Anticipated expiration: 1948-11-03

Description

Patented Nov. 3, 1931 UNITED STATES Examines PATENT OFFICE WALDO L. SEMON, OF CUYAHOGA FALLS, OHIO, ASSIGNOR TO THE B. F. GOOIDRICH COM- rm, NEW YORK, N. Y, A CORPORATION OF NEW YORK METHOD OI CLEANING No Drawing. Application filed December This invention relates to the art of pickling metals such as iron or steel, that is, to the art of removing scale or rust from the surface of such metals by a process of solution.

It is the common practice to remove scale and rust from the surface of iron or steel by immersion in a dilute solution of sulphuric or muriatic acid, which is frequently heated to a temperature of about 70 C. to accelerate the solution of the iron oxides.

However, the pickling acid, in addition to its dissolving action on the oxides, rapidly attacks the metal itself, dissolving it and liberating hydrogen gas. The hydrogen gas escaping from the liquid carries with it some of the acid in the form of a fine mist which is very disagreeable to workmen in the vicinity and which rapidly corrodes all metal in the room or building. The attack and solution of the metal is also undesirable because of the consequent loss of metal and of acid. which cannot economically be recovered, and because of the fact that the process of solution is not uniform, but localized, causing pitting of the surface.

Heretofore the addition of so-called picklinginhibitors to the acid has been proposed, such inhibitors possessing the property of retarding the solution of iron in acid,

while not appreciably affecting the solution of its oxides. Among the inhibitors which have been proposed, sugars, proteins, and the salts of certain nitrogenous bases, such as quinoline ethiodide have found considerable commercial use.

This invention consists in adding a small proportion of a member of a new class of extremely effective pickling inhibitors to an acid pickling bath. This class of inhibitors comprises alkylated thioureas, such as may AND PICKLHVG METALS 5, 1928. Serial No. 824,066.

lkyl halides og polyhalides. For example, suBsfitfitEdthioureas sucli as diphenylthiourea k rea,-plienikethylthicai a difig'p yltliioiirfea, etc. may be reactedwith ylahlafid ethyl b ql il b1 7 5 li .lfgpt 1 ,C -hl ridc methylene dibromidgjthyl- ,liloride. A

dibron ide methylene d15r"oinide," etc. The halogen of the alky l halide apparently reacts with the sulphur atom of the thiourea with the formation of the hydrohalide of an amino-thioether, as follows:

In the above equations R and R may be aryl or alkyl groups, while R is an alkyl group and X a halogen. The substituted thiourea (1) probably undergoes a molecular rearrangement to the imino or pseudo form (2), which reacts with the alkyl halide to form the alkylated thiourea (3), which may be considered a thioether. These compounds are also known as alkyl substituted pseudothioureas because they have the same empirical formulae as the substituted thioureas, but have a different chemical constitution and hence also different properties.

If an alkylene dihalide be employed in place of the simple alkyl halide the second alogen atom reacts further with the hydrogen on the nitrogen atom, producing an aliphatic heterocylic nucleus containing a sulphur atom between two carbon atoms, and which may therefore also be considered be obtained by the react on of'thioureas with as a thioether type compound.

B: R R: BI n. ilk-I l nr-r z x-z'm Bx-N x-tn Brew-tn =s- -s-n+x- 11,- --sm .nx- --s-- a, .231: Br-N Brr- @113513156 dibroihidfbutylene In this equation again, R and R may be aryl or alkyl groups, while R is hydrogen or an alkyl group and X a halogen. The substituted thiourea (1) may again be considered as undergoing rearrangement to the form (2), which reacts with the alkylene halide with the possible formation of an intermediate compound (3) and a final compound (4). Since the unsaturated five-membered cyclic nucleus containing non-adjacent sulphur and nitrogen atoms is termed a thiazole, the saturated compounds of the type of (4) may be considered as derivatives of tetrahydrothiazole. This is, if diphenylthiourea is reacted with ethylene chloride, R and R are phenyl groups and R is hydrogen, and the compound (4) in equation II above is 2-phenyl-imino-3-phenyl-tetrahydrothiazole.

Similar cyclic arylated thioureas containing 4, 5, 6 or even more atoms in the saturated ring may be obtained by reacting a substituted thiourea with a dihalogenated aliphatic hydrocarbon with 1, 2, 3 or more carbon atoms between the halogen atoms.

The alkylated thioureas are, in general, basic in their reaction and are fairly soluble in acid solutions, readily forming salts such as the hydrochlorides, sulphates, etc. They probably owe their peculiar efiicacy to the presence of the basic nitrogen atom together; with a sulphur atom in a thioether type molecule. However, it is to be understood that it is not intended to limit the scope of this invention by any theories which have been or may be herein advanced, such theories being merely illustrative and explanatory in nature.

The particular substance or substances selected from this class of pickling inhibitors should preferably be soluble in acid solutions, stable at normal or slightly elevated temperatures, and substantially non-volatile. These conditions are particularly well satisfied by the reaction products of the diaryl substituted thiroureas with ethylene chloride. The raw materials are inexpensive, the reaction is practically quantitative, and the products are crystalline. For example, to obtain the 2- phenyl imino 3 phenyl tetrahydrothiazole mentioned above, 228 parts by weight of diphenylthiourea, commonly known as thiocarbanilide, are mixed with 99 parts of ethylene dichloride and the mixture is heated on a steam bath for 24 hours.

The reaction takes place according to the following equation, the hydrogen chloride probably adding on the nitrogen atoms to form the hydrochloride of the base:

um carbonate, and the insoluble base filtered OE and dried. The product is usually uite pure and is ready to use. The residue om the water extraction, consisting chiefly of unreacted material, is added to the next batch. The 2-phenylimino-3-phenyl-tetrohydrothiazole thus obtained is only slightly soluble in water, but dissolves readily in acid solutions, since its hydrochloride, sulphate, etc. are soluble.

EwampZe J.The following tests illustrate clearly the remarkable efiiciency of the products of this invention. Pickling solutions were prepared containing respectively, 5% by weight of hydrochloric (muriatic) acid, 19% hydrochloric acid, 4% and 10% sulphuric acid. Each of these was divided into several port-ions, one of which was used as a control. To the other portions were added various porportions of the 2-phenylimino-3- phenyl-tetrahydrothiazole prepared as hereinabove described, or of quinoline ethiodide, a substance which has heretofore been proposed as a very effective pickling inhibitor.

Test pieces of sheet steel, about 2 cm. x 5 cm. in size were cut from a single sheet of metal. The metal strips were all given a preliminary treatment in an acid solution to remove the scale, were washed, bent at right angles, and placed on edge, each in the bottom of a widemouthed bottle. Each bottle was completely filled with one of the acid solutions previously prepared, and closed with a rubber stopper pierced by a bent glass tube so arranged that tbe hydrogen gas evolved by the reaction of the acid with the metal displaced an equal volume of the liquid, which flowed through the tube into a measuring device. The bottles were then placed in water baths maintained at constant temperatures, and the volume of hydrogen evolved in a period of one hour was carefully measured. The results are tabulated below.

Volume of hydrogen evolved, in cubic centimeters Pickling solution Inhibitor 35,

5% H01 19% HCl 4% H2804 10%H1SO4 at60 C. at 40 C. at 60 C. at 60 G.

Control 0 56. 0 153. 0 l4. 5 62.0

quinoline 0.03% 21.2 2.6

ethiodide- Z-Phenylimino- 0. 03% 5. 4 1. 9 3 p h e n y l tetrahyd ro- 0. 05% 9. 2 3 0 thlazole It is evident that the preferred products of this invention are extremely valuable in preventing the corrosion of iron and steel in acid pickling baths after the scale has been dis- 252. COMPOSITIONS,

assumes solved, the negligible volume of hydrogen evolved indicating that the reaction of the acid with the iron is almost com letely checked, and that they are far more e ective than even such previously proposed substances as quinoline ethiodide. However, the addition of such inhibitors has practically no effect on the rate of solution of the scale or other oxide of the metal.

Similar tests of other reaction products of substituted thioureas with alkyl chlorides show that the members of this class in general are excellent picklin inhibitors. The products prepared from itolylthiourea and ethylene dichloride, and from diphenylthiourea and ethyl chloride, for example, are practically as effective as the product obtained from diphenylthiourea and ethylene dichloride as hereinabove described.

Example 2.-A sample of 2 o-tolylimino 3 o-tolyl tetrahydrothiazole was prepared by the reaction of ethylene dichloride with di-otolylthiourea, as described above, and the ethyl ether of diphenylthiourea was similarly prepared by reacting ethyl iodide with diphenylthiourea. These two products were compared with the 2 phenylimino 3 phenyl tetrahydrothiazole in the following experiment.

Strips of sheet steel were prepared as described in Example 1 above and were placed in flasks with 10% sulphuric acid without any inhibitor and with the same solution containing 0.03% of the inhibiting materials.

The extent of the reaction of the acid with the iron was gauged in this case by weighing the metal strips before and after treatment in the 10% acid at C. for 20 minutes. The loss in weight of the iron in the control sample was arbitrarily termed 100 and the losses in thenothersqll iion were calculated in the same proportion;

In the practice of this invention on a commercial scale, an acid solution containing hydrochloric or sulphuric acid is prepared in the usual manner and a small proportion of the inhibitor is dissolved therein, for example one pound of the inhibitor to from one hundred to one thousand pounds of acid being used. The metal, which is preferably first degreased by treatment with an organic solvent or with an alkali, is treated in this bath in the customary manner, except that it may be left in the solution for a longer time, since there is little danger of overpickling. Pittmg of the metal is almost completely eliminated, the consumption of acid and of metal is very greatly reduced, and embrittlement of the metal and formation of acid mist due to the evolution of hydrogen gas is largely prevented.

Metals may be pickled or cleaned in the improved pickling solutions containing the inibitors of the class hereinabove described in many widely different manner. For example, the metal may be completely immersed in the acid, if desired being carried into and out of the solution by automatic devices which also wash and dry the metal; or the solution may be sprayed onto the surface of the metal, and be later washed ofi' by a water spray. The concentration of the acid, and the temperature of the solution may be varied as desired; and the inhibitors may be added in either greater or less proportions than described in the examples above. It is evident that even proportions of less than 0.01% of the inhibitor are quite eifective, whereas comparatively large proportions, up to several per cent. may be necessary to reduce the corrosion of the metal to an absolute minimum. Although either hydrochloric or sulphuric acid is usually employed in pickling iron, because of the low cost of these substances, any of the other non-oxidizing acids may be substituted therefor in whole or in part. For example, pickling solutions containing phosphoric or hydrofluoric acid are useful in many cases. Because of their remarkable stability, the alkylated thioureas may even be employed as inhibitors in pickling solutions containing strong oxidizing acids such as nitric acid.

It will often be found convenient to add the requisite amount of the inhibitor to the concentrated acid at the time of manufacture or at any later time, and simply dilute this s ock pickling acid containing the inhibitor to the desired concentration as it is needed. Such a stock pickling acid may for example be prepared by dissolving 1 part by weight of 2 phenylimino 3 phenyl tetrahydrothiazole in 500 parts of concentrated sulphuric acid.

While I have herein disclosed with considerable fparticularity certain preferred manners o performing my invention, I do not thereby desire or intend to limit myself solely thereto, for, as hitherto stated, the precise proportions of the materials utilized may be varied and other materials having equivalent chemical properties may be employed if desired without departing from the spirit and scope of the invention as defined in the appended claims.

I claim:

1. The method of cleaning metals which comprises treating metals with a solution comprising a strong acid and a small proportion of an alkyl substituted pseudothiourea.

2. The method of cleaning ferrous metals which comprises treating ferrous metals with a solution comprising a mineral acid and a small proportion of an alkyl substituted aryl 5 pseudo-thiourea.

3. The method which comprises pickling iron or steel in a solution comprising a nonoxidizing mineral acid and a small proportion of a substance selected from the class comprising alkyl substituted diaryl pseudothiourea.

4. The method which comprises pickling iron or steel in a solution comprising a nonoxidizing mineral acid and a small proportion of a substance selected from the class comprising cyclic alkylated diaryl-thioureas.

5. The method which comprises pickling iron or steel in a solution comprising a nonoxidizing mineral acid and a small proportion of a substance selected from the class comprising cyclic alkylated diaryl-thioureas, the cycle containing 5 atoms.

6. The method which comprises pickling iron or steel in a solution comprising a non- 5 oxidizing mineral acid and a small proportion of 2 phenylimino 3 phenyl tetrahydrothiazole.

7. A bath for cleaning or pickling metals comprising a strong acid and a small proportion of an alkyl substituted pseudo-thiourea.

8. A bath for cleaning or pickling metals comprising a strong mineral acid and a small proportion of an alkyl substituted aryl pseudo-thiourea.

9. A bath for cleaning or pickling metals, which comprises a strong mineral acid and a small proportion of a substance selected from the class comprising alkyl substituted diaryl seudo-thiourea.

10. A bath for cleaning or pickling ferrous metals, which comprises a strong mineral acid and a small proportion of a substance selected from the class comprising cyclic alkylated diaryl thioureas.

11. A bath for cleaning or pickling iron or steel, which comprises a non-oxidizing mineral acid and a small proportion of a substance selected from the class comprising cyclic alkylated diaryl-thioureas, the cycle containing 5 atoms.

12. A bath for cleaning or pickling iron or steel, which comprises a non-oxidizing mineral acid and a small proportion of a 2 arylimino 3 aryl tetrahydrothiazole.

13. A bath for cleaning or pickling iron or steel, which comprises a non-oxidizing mineral acid and a small proportion of 2 phenylimino 3 phenyl tetrahydrothiazole.

14. A bath for cleaning or pickling iron or steel, which comprises sulphuric acid and a small proportion of 2 phenyh'mino 3 phenyl tetrahydrothiazole.

15. The method of cleaning metals which 55 comprises treating metals with a solution comprisin a strong acid and a thioether containing a asic nitrogen atom.

16. The method which comprises pickling iron or steel in a solution comprising a nonoxidizing mineral acid and a small proportion of a thioether containing a basic nitrogen atom.

17. A bath for cleaning or pickling iron or steel, which comprises a strong mineral acid and a small proportion of a thioether containing a basic nitrogen atom.

18. An aqueous solution of a non-oxidizing acid capable of dissolving iron oxides to which has been added an inhibitor comprising an organic pseudo-substitution product of thiourea.

19. An aqueous solution of a non-oxidizing acid capable of dissolving iron oxides to which has been added an inhibitor comprising an organic pseudo-substitution product of NH C(bHyNH in which the hydro en attached to sulphur is replaced by an a yl group.

20. An aqueous solution of a non-oxidizing acid capable of dissolving iron oxides to which has been added an inhibitor comprising a substance having the general formula Nit C(SR).NR in which R represents hydrogen or an alkyl or aryl group, and R represents an alkyl group.

21. The process of pickling iron and steel products which consists in treating said products with an aqueous solution of a nonoxidizing acid capable of dissolving iron oxides to which has been added an inhibitor comprising an organic pseudo-substitution product of thiourea.

22. The process of pickling iron and steel products which consists in treating said products with an aqueous solution of a nonoxidizing acid capable of dissolving iron oxides to which has been added an inhibitor comprising an organic seudo-substitution product of NH:C(SH). H in which the hydrogen attached to sulphur is replaced by an alkyl group.

23. The process of pickling iron and steel products which consists in treating said products with an aqueous solution of a non-- oxidizing acid capable of dissolving iron oxides to which has been added an inhibitor comprisin a substance having the general formula I51: C(SR).NR in which R represents hydrogen or an alkyl or aryl group, and R represents an alkyl group.

In witness whereof I have hereunto set my hand this 4th day of December, 1928.

WALDO L. SEMON.