US2884364A - Method of electroplating on uranium - Google Patents

Description

2,884,364 METHOD 'OF ELECTROPLATING ON URANIUM I Elmer W. Rebol, Richland, Wash., and Ralph F. Wehrmann, Dayton, Ohio, assignors to the United States of America as represented by the United States Atomic Energy Commission No Drawing. Application May 14, 1946 Serial No. 669,585

7 Claims. (Cl. 204-15) This invention relates to methods of electroplating metals. It more particularly concerns the preparation of metallic uranium surfaces for receiving coatings particularly in order to secure firmly adherent electroplated coatings upon uranium metal. The problem of securing such coatings has been complicated by the fact'that electroplated coatings deposited upon uranium frequently have poor adherence, are porous and are otherwise unsuitable for the prevention of corrosion.

In accordance with the present invention it has been found that satisfactory coatings may be deposited upon uranium which has been pretreated by pickling in trichloroacetic acid. This treatment is best accomplished by making the uranium the anode in an aqueous solution of trichloroacetic acid until work-distorted crystals or oxide present on the metal surface have been removed and the basic crystalline structure of the base metal has been exposed. Adherent firmly bonded coatings of electroplated metal can then be deposited upon the cleaned or pickled uranium.

The process may be conducted very effectively in conjunction with other cleaning or pickling processes. In accordance with one suitable embodiment the uranium may be subjected to a series of treatments as follows: First, the surface of the uranium may be cleaned and degreased in any suitable manner, for example, in trichloroethylene or by anodic treatment in strong alkaline solutions such as those used on steel. Degreasing cleaners containing soluble chlorides should not be used. Next the metallic uranium surface may be shot-blasted or sandblasted. The shotor sand-blasting treatment is not absolutely essential and may be omitted if desired; 'however, we have found that this treatment aids rapid and uniform attack by the trichloroacetic acid used in a subsequent step. Following these initial steps the metallic uranium is immersed in nitric acid. For best results a 25 percent to 50 percent by weight of nitric acid solution may be used. At room temperature (25-35 C.) the immersion is continued for from 1 to minutes. This nitric acid treatment removes loose oxide from the surface of the uranium. After the nitric acid treatment has been completed the metallic uranium is given a runningwater rinse for a period of about one minute. It has been discovered that it is essential that no nitric acid be carried over to the subsequent steps of the surface treatment if optimum results are to be obtained.

After the running-water rinse described above has been completed the metallic uranium is given an anodic pickling in an aqueous solution of trichloroacetic acid. Numerous experiments have shown that best results are obtained using a solution containing about 15 percent to 50 percent by weight of trichloroacetic acid, although more dilute solutions, for example, 3 percent to 5 percent solutions of trichloroacetic acid may also be used particularly when hydrochloric acid, for example, about 0.1 percent to 1 percent by weight of concentrated (37 percent) hydrochloric acid is introduced into the solution. Similar amounts of hydrochloric acid may also be 2,884,364 Patented Apr. 28, 19 59 2 used, if desired, with the stronger trichloroacetic acid solutions and good results will be obtained.

The addition of small amounts of hydrochloric acid to the trichloroacetic acid pretreatment bath apparently helps to eliminate irregularities in the microcrystalline etch.

Freshly prepared solutions of trichloroacetic acid frequently do not properly etch metallic uranium surfaces probably due to the absence of chloride ion. Heat and/or electrolysis liberate the necessary concentrations of chloride ion, or the necessary chloride ions may be added in h the form of hydrochloric acid; continued use of the solutionultimately ensures the required etching. The length of time required for the natural production of chloride 1011 varies inversely with the concentration of trichloroacetic acid, and, since the uniformity of etch increases with increasing concentration, it is generally desirable to use the more concentrated trichloroacetic acid solutions 'as stated above or to establish an initial concentration (0.2% or 0.3%) of HCl in the solution.

The metallic uranium is treated until the basic struc-' ture of the metal is exposed, usually for about 3 to 10 minutes, in the trichloroacetic acid solution at an elevated temperature, for example, about 50 to 60 C. The current density may be about 40 to 60 amperes per square foot; carbon cathodes are used. The metal is also attacked by simple immersion. However, the application of an e.m.f. between the metal and electrolyte affords greater speed and uniformity. The rate of attack is accelerated with increased temperatureand concentration of the trichloroacetic acid. The treament tanks may be made from any suitable material such as glass or earthenware.

After the trichloroacetic acid treatment the metallic! uranium is again rinsed to remove the acid. This may be accomplished by rinsing in running bath for a period of 3 to 6 minutes at room temperature. We have found that from 25 percent to 50 percent by weight nitric acid makes a very satisfactory solution for rinsing. More dilute solutions dissolves the black deposite on the surface of the metal rather slowly. The use of very concentrated solutions is not recommended, because such treatment tends to cause blistering in subsequent electro' plates. Hot nitric acid solutions are to be avoided for the reaction reaches quite violent proportions at about 50 C. After this second nitric acid treatment the metal-' lic uranium is rinsed in running water for a short time, for example for about one minute, after which time the uranium is introduced into the selected metal plating bath as quickly as possible.

The following example is presented for the purpose of illustrating a specific application of the invention and is not to be construed as limiting the invention thereto.

Metallic uranium which was to be electroplated was first thoroughly degreased with trichloroethylene. After degreasing, the metallic uranium was blasted using mesh steel grit for a period of about 3 minutes. Next, the'metallic uranium was treated for a period of about 3 minutes at room temperature in a 40 percent by weight nitric acid solution. This nitric acid treatment removed loose oxide remaining in the uranium surface after the blasting. The ntiric acid treatment was followed by rinsing the metallic uranium in hot (50-60 C.) running water after which the uranium was pickled as an anode in a 45 percent by weight solution of trichloroacetic acid. This anodic treatment was continued for a period of about 10 minutes at 50 C. and the current density was 50 amperes/square foot using carbon cathodes. Following the anodic treatment the metallic uranium was again rinsed in cold running water and then placed in a nitric acid bath for a period of 5 minutes. This nitric acid bath also consisted of 40 percent by weight nitric acid solution and the treatment was carried out at room accuses.

temperature. Immediately following the second nitric acid" treatment the metallic uranium was again rinsed thoroughly in cold running water and then immediately tran er d o a n ls l plat ng a h, nd a c a g of nickel was electrodeposited thereon.

Th above detai e desc ptio has een. given 13 n noscs o llust a ion only an it is to e understood tha he pec fi detail t o a no intendedv as l m alcns upon t e pe f the nvention, w ich is. t be imi ed only by th sc p of he oll wing cla m Wha i claimed s:

l- Th pr ce s o Prepa ing an elec t pla ed uranium ar icle. hich omprises pi klin the ranium m tal. with aqu us richlo ace i c d, t ating the pickled uranium w th tr c d and hen e e t opla ng a m t l oating upon th m talli u an m,

Th p c s of p pa g a e ec ropl t uran um art le, which. mpri he ep of Pic ing th ur nium surf c t nit i a d, m ing n tr a id fr m h urani m, nc i l y Pi k i g aid u nium, u ace n que us r c or aceti i n e f er re ting he pickled uranium with nitric acid and electroplating a met l o ting upo h tr e me a 3. The method of preparing a metallic uranium surface for electroplating which comprises subjecting said metallic uranium to the action of a degreasing agent, subjecting said metallic uranium to, the action of a 25 percent to 50 percent by weight nitric acid solution, subjecting said metallic uranium to the action of aqueous trichloroacetic acid and then subjecting said metallic, uranium to the action of a second 25 percent to 50 percent by weight nitric acid solution, rinsing said metallic uranium in water and then immediately electroplating a n tial coating upon said uranium.

4. The method of preparing an electroplated uranium article which comprises subjecting said metallic uranium to the action of a degreasing agent, subjecting said metallie uranium to the action of a 25 percent to 50 percent by weight nitric acid solution, treating said metallic uranium anodically in a 30 percent to 50 percent by weight aqueous trichloroacetic acid solution, and then subjecting said metallic uranium to the action of a second 25 percent to 50 percent by weight nitric acid solution, rinsing to remove nitric acid from the metallic uranium and then immediately electroplating a metal coating upon the uranium.

5. T m ho of p p ing a me llic ra i m urface for electroplating which comprises subjecting said metallic uranium to the action of a degreasing agent, subjecting said metallic uranium to the action of a 25 percent to percent by weight nitric acid solution, treating said metallic uranium anodically in a 30 percent to 50 percent by weight aqueous trichloroacetic acid solution at about 50 C. to C., and then subjecting said metallic uranium to the action of a second 25 percent to 50 percent by weight nitric acid solution, rinsing said metallic uranium in water and then immediately electroplating a. metal coating upon said uranium.

6. The method of preparing a metallic uranium surface for electroplating which comprises subjecting said metallic uranium to the action of a degreasing agent, subjecting said metallic uranium to. the action of a 25 percent to 50 percent by weight nitric acid solution, treating said metallic uranium anodically in a 30 percent to 50 percent by weight aqueous trichloroacetic acid solution at about 50 C. to 60 C. with a current density of about 40 to 60 amperes per square foot, and then subic t ng aid me allic uranium o he action of a second 25 percent to 50 percent by weigh nitric acid. solution, in ing said metalli u anium in water and then immcdh tcly ele tr pl ting, a metal coating upon. said ranium- 7. A process of preparing an electroplated uranium. article,- which comprises subjecting the surface of a. uranium. article to th action of a degreasing agent followed by blasting the surface with an abrasive material, thereafter rinsing said surface with an aqueous solution of nitric acid, rinsing in water, pickling the surface of said uranium article anodically in an aqueous solution of, trichloroacetic acid, rinsing said surface of the uranium article with an aqueous dilute nitric acid solution, and electroplating said treated uranium article.

Referenc,es Cited in the file of this patent UNITED STATES PATENTS 1,787,672 Davenport Jan. 6, 1931 2,080,506 Rinek, et a1. May 18, 1937 2,109,675 Miller Mar. 1, 1938' 2,180,798 Collins Nov. 21, 1939 2,234,189 Murray Mar. 11, 1941 2,851,766. Gray Sept. 16, 1958 OTHER REFERENCES Langes, Handbook of Chemistry (1937), 2nd Ed., publ., by Handbook Publishers, Inc., Sandusky, Ohio, pp. 1156, 1157 (on Ionization Constants of Acids).

The Monthly Review of the American Electroplaters societytfebruary 1945, pp. 119,120.