US2848796A

US2848796A - Alloy coatings and method of applying

Info

Publication number: US2848796A
Application number: US588060A
Authority: US
Inventors: Lowell D Eubank; Ernest R Boller
Original assignee: Individual
Current assignee: Individual
Priority date: 1945-04-12
Filing date: 1945-04-12
Publication date: 1958-08-26
Anticipated expiration: 1975-08-26

Description

ALLOY COATINGS AND ME'IHQD F APPLYING Lowell D. Eubank, Richland, Wash, and Ernest R. Boiler, Marion, Ind., assignors to the United States of America as represented by the United States Atomic Energy Coission No Drawing. Application April 12, 1945 Serial No. 588,060

14 Claims. (Cl. 2919-l-) This invention relates to the coating of metallic uranium.

An object of the invention is the provision of firmly adherent protective coatings on metallic uranium. A further object is the provision of such coatings suitable for use as bases for the application of other metal coatings.

In accordance with the present invention metallic uranium is provided with a coating of uranium-aluminum alloy. The application of such a coating to uranium by dipping the uranium in a bath of molten aluminum results in the formation of a relatively thick alloy coating characterized by objectionable brittleness. However, coatings highly satisfactory for a variety of purposes may be formed by dipping the metallic uranium in a molten metal bath comprising a major proportion of zinc and a minor proportion of aluminum (by Weight).

The thickness of the uranium-aluminum alloy coating may be varied by varying the proportion of aluminum in the coating bath. Thus extremely thin coatings may be applied by using a zinc coating bath containing an amount of aluminum in the neighborhood of 1% of the bath. For the application of thicker coatings, correspondingly higher proportions of aluminum should be employed.

The invention is capable of a variety of applications.

The uranium just as it comes from the hot dipping bath is suitably coated for many purposes. Such a product comprises a multiple layer coating in which the metallic uranium is coated with a firmly adherent layer of uranium-aluminum alloy containing in the neighborhood of 70% to 75% of uranium, to of aluminum and about 5% of zinc. These proportions of aluminum and uranium correspond approximately to the known alloy, UAI Over this alloy layer firmly adherent to it is a Zinc layer which contains about the same proportion of aluminum as present in the coating bath. The uranium-aluminum layer serves as a blocking layer with the result that very little uranium finds its way into the zinc layer. The amounts of uranium found in this layer have been of the order of one percent.

For the preparation of multiple protective coatings by a single dip process, proportions of aluminum between about 5% and about 15% by weight in the coating bath have been found to be most satisfactory. Coatings applied from such coating baths include a layer of uranium-aluminum alloy adequate to afford excellent protection for the uranium. Proportions of about 1% aluminum have been used in coating baths for the production of Zinc coatings useful for many purposes despite the thinness of the alloy layer.

The invention has been found to be useful in bonding uranium to aluminum sheathing. Such sheathing may be bonded directly to the zinc layer by applying the sheathing while the coating is still molten. Alternatively the coated metal may be soldered to the aluminum by means of ordinary aluminum solder (about 90% tin 2,848,796. Patented Aug. 26, 1958 and 10% zinc). Coatings applied by means of a molten bath of 99 parts by weight of zinc and one part by weight of aluminum have been found highly satisfactory for such applications.

The coatings of the invention are useful as bonding coatings for the application of other metal coatings, such as coatings of aluminum-silicon brazing and casting alloys, lead, and terne.

in cases where zinc coatings are undesirable, the uranium-aluminum alloy coating of the invention may be applied as described above and the zinc layer may be removed by centrifuging the coated article while yet hot or by subsequently treating the surface of the article with an acid, such as nitric, sulfuric or hydrochloric acid, to dissolve the zinc, or by mechanically removing a portion of the solid coating so as to expose the uraniumaluminum alloy layer.

Some commercial grades of zinc, used alone, are not satisfactory for coating uranium; thus Prime Western Spelter has been found to atford only spotty coverage. The present invention makes possible the use of such grades of zinc to provide continuous adherent coatings.

Preferred temperatures for the application of the coatings of the present invention are temperatures between 20 and 200 centigrade degrees above the melting point of the particular coating bath being applied. Thus higher temperatures are most suitable for baths of a composition relatively remote from the eutectic alloy composition (95% zinc, 5% aluminum) and lower temperatures are most suitable for alloys nearer to this composition.

Before coating metallic uranium, it is desirable to prepare the uranium surface by a suitable pickling treatment. Pickling treatments which have'been found to be suitable are treatments in aqueous nitric acid having a concentration of about 50% HNO for a few minutes at a temperature between 60 and C. Other pickling procedures, for example, pickling by means of a sulfuric acid pickling reagent, have been employed with somewhat less satisfactory results. A pickling treatment which has been found to be most satisfactory is the pickling treatment described in U. S. patent application Serial Number 619,265 of E. R. Boiler, Lowell D. Eubank and John W. Robinson filed September 28, 1945, and entitled Nitric Acid Pickling Process.

While treatment of the metal with a flux is not essential to the application of satisfactory coatings, it is sometimes desirable. The application of a flux of the type described in U. S. patent application Serial Number 583,176 of Lowell D. Eubank filed March 16, 1945, and entitled Method of Flux-treating Metal Surfaces been. found be very satisfactory. These fluxes comprise alkali-metal halides, preferably mixtures including lithium and potassium chlorides.

When a flux is employed, the uranium may be dipped first into the flux and then into the coating bath, but it is preferred to employ the flux as a protective layer on top of the coating bath and to dip the uranium article through this flux into the bath. In this way possible exposure of the metal to air after withdrawal from the flux is avoided and the flux serves the dual function of protecting the coating bath and preparing the surface to be coated.

After removing the article from the coating bath it may be cooled slowly in air. Cylindrical bodies may be cooled to solidify the coating by rolling on smooth continuous rollers as described in U. S. patent application Serial Number 577,382 of Harold A. Gage, filed February 12, 1945, and entitled Method of Leveling Metal Coatings.

When the coatings of the invention are used as bases for hot-dipped metallic over-coatings, the latter may be applied while the zinc layer is still molten. Such coatings as well as electroplated coatings and non-metallic coatings may be applied .to the coatings of the invention after they have solidified and either with or without removal of the outer zinc-aluminum alloy layer.

The following examples illustrate specific applications of the invention. In the examples quantities areexpressed in terms of weight unless otherwise indicated.

Example 1 A metallic uranium rod, about 1.1 inch in diameter and 4 inches long, was pickled in aqueous 50% nitric acid solution at 60-65 C. for three minutes. Following this it was rinsed in clean water and air-dried. It was then dipped through a flux consisting of 53% potassium chloride, 42% lithium chloride, and sodium chloride into a molten bath comprising 85 parts of zinc and 15 parts of aluminum, at 560 C., for three minutes. The rod was withdrawn from the bath, shaken to remove excess coating metal, and rolled. on Transite rollers until the coating solidified. The rod was then allowed to cool in air to room temperature. The coating was tested by placing the rod in a current of hot air maintained at 200 C. for 40 days. At the end of this period the coating was perfect. The rod was then placed in a current of air at 250 C. After 122 additional days the coating was still perfect, at which time the specimen was removed from test.

Example 2 A metallic uranium rod about 1.1 inch in diameter by 4 inches long was pickled in aqueous 50% HNO solution at about 65 C. for 2% minutes. It was then dipped through a flux comprising 53% KCl, 42% LiCl, and 5% IaCl into a molten bath comprising 85 parts of zinc (Prime Western Spelter) and 15 parts of aluminum at 530 C. for 4 minutes.

The rod was withdrawn from the bath, shaken to remove excess coating metal and rolled on Transite rollers until the coating solidified. The rod was then placed in an oven at 250 C. for 3 hours to allow the coated rod to cool gradually to this temperature and then was allowed to cool in air to room temperature.

The coating was tested by placing the rod in a current of hot air maintained at 200 C. for 59 days. At the end of this period the coating was still perfect. The rod was then placed in a current of air at 250 C. After 106 days more at this higher temperature the coating was still free from defects.

Example 3 A small metallic uranium article having a machined surface was dipped in 50% HNO solution at between 60 and 65 C. for 2% minutes. It was then rinsed in water and wiped dry.

The article was next dipped through a top flux comprising 42% LiCl, 53% KCl and 5% NaCl into a molten zinc-aluminum bath containing 85 parts of zinc (Prime Western Spelter) and 15 parts of aluminum, the bath temperature being 600 C.

The article was withdrawn after 2 /2 minutes in the bath and rolled in air on carbon rollers for about 2 minutes to cause the coating to solidify. The article was then dipped into a zinc bath at a temperature of 450 C. for one minute. It was withdrawn from this bath and again placed on carbon rollers where it was rolled until the coating had solidified (1 /2 minutes).

It was then placed in an annealing oven at a temperature of 248 C. and allowed to cool therein to this temperature. After remaining in the oven for about 2 /2 hours, it was inspected and found to be smooth and bright in appearance.

It was then tested by holding it in-contact with hot air at 200 C. After 78 days of exposure, the coating was still in perfect condition.

Example 4 A metallic uranium rod of the same size and type as employed in Example 1 was pickled for 2 /2 minutes at 60 C. in 50% nitric acid solution, rinsed in water and wiped dry.

it was then dipped through a top flux comprising 42% LiCl 53% KCl, and 5% NaCl into a zinc-aluminum bath comprising parts of zinc (P. W. S.) and 15 parts of aluminum at a temperature of 600 C. After 2 /2 minutes the rod was withdrawn from the bath and rolled for 2 minutes in air to cause the coating to solidify.

It was then placed in an annealing oven which Was maintained at a temperature between 250 and 260 C. for 2 /2 hours and finally allowed to cool in air to room temperature. The appearance of the rod was smooth and slightly dull.

The coated rod was placed in air at 200 C. to test the durability of the coating. After 70 days of exposure th coating was still in perfect condition.

Example 5 A small uranium rod about 1.1 inch in diameter and 4 inches in length was pickled in nitric acid as in the preceding example, rinsed and dried.

It was then dipped into a fluxless molten metal bath comprising 85 parts of zinc (P. W. S.) and 15 parts of aluminum at a temperature of 560 C. and held in this bath for 3 minutes. It was removed from the bath and then dipped for one minute in a fluxless molten terne bath comprising 97.5 parts of lead and 2.5 parts of tin at a temperature of about 400 C.

The coated rod was cooled on smooth rotating rollers for 2 minutes and then allowed to cool further in air to room temperature.

It was then placed in a hot air oven maintained at a temperature of 200 C. After 7 days, the coating was still in perfect condition, and the rod was removed from the oven and placed in a second oven at a temperature of 250 C. in contact with air. After 30 days of exposure at 250 C., the coating was still free from defects.

Example 6 A small uranium rod, after pickling as in the preceding example, was dipped through a flux of 42% LiCl, 53% KCl and 5% NaCl into a molten metal bath comprising 85 arts of zinc (Prime Western Spelter) and 15 parts of aluminum at 560 C. for 3 minutes.

It was then removed and dipped through a flux of the same composition into a molten metal bath comprising 88 parts of aluminum and 12 parts of silicon at 600 C. for one minute. It was withdrawn from this second bath and placed in an annealing oven at a temperature of 250 C. and allowed to cool to this temperature in a period of about 3 hours. It was then withdrawn and cooled in air to room temperature.

The durability of this coating was tested by placing the rod in a hot air stream at a temperature of 200 C. After 30 days of exposure, the coating was examined and found to be still in perfect condition. It was then placed in a hot air stream at a temperature of 250 C. for an additional 17 days. At the end of this period the coating was still free from defects.

Example 7 A metallic uranium rod inch in diameter and 2 inches in length was dipped in an aqueous 50% HNO solution at about 65 C. for 3 minutes. It was then dipped through a flux of the composition 37% LiCl, 53% KCl and 10% NaCl into a molten bath containing 94 parts of zinc (Prime Western Spelter) and 6 parts of aluminum at 485 C. V

The rod was withdrawn from the coating bath and rolled in air on carbon rollers for 2 minutes to allow the coating to solidify. It was then dipped in cold water to cool the rod to normal temperature.

The rod was then placed in an oven through which air at 200 C. was circulated, to determine its resistance to corrosion. After 135 days of this treatment, the rod was still in perfect condition.

Example 8 A metallic uranium rod about 1.1 inch in diameter by 4 inches long was pickled in aqueous 50% nitric acid solution at 60 C. for five minutes. Following this it was rinsed in clean water and air-dried. It was then dipped through a flux consisting of 53% potassium chloride, 42% lithium chloride, and 5% sodium chloride into a molten bath consisting of 85 parts of zinc and parts of aluminum at 530 C. for four minutes. The rod was withdrawn from the bath, shaken to remove excess coating metal and rolled on Transite rolls until the coating solidified. It was allowed to cool to room temperature in air.

The outer coating of zinc-aluminum alloy was removed by immersing the coated rod in 25% nitric acid at room temperature. This left a substantially continuous uranium-aluminum alloy coating remaining on the specimen. The alloy coating was tested by placing the rod in a current of hot air at 300 C. At the end of 30 days a few pinholes had developed in the coating, the sum total of the areas involved amounting to less than 0.1% of the total coating. This rate of failure was comparable to that normally obtained with specimens carrying the zincaluminum over-coating when tested under similar conditions.

Example 9 A metallic uranium rod about 1.36 inches in diameter by 8 inches long was pickled in aqueous 50% HNO solution for five minutes at 60 to 70 C., rinsed in flow ing water and dried. The rod was then dipped into a bath of 99-1 Zn-Al alloy at 450475 C. for 1 /2 minutes and then inserted into an aluminum can held at 425 C., the aluminum can having been previously coated with the Zn-Al alloy by brushing with the molten alloy. A firm bond between the uranium rod and the aluminum can was thus obtained.

It will be understood that we intend to include variations and modifications of the invention and that the preceding examples are illustrations only and in no wise to be construed as limitations upon the invention, the scope of which is defined in the appended claims, wherein we claim:

1. A solid metallic uranium article having its surface protected by a layer of uranium-aluminum alloy.

2. A solid metallic uranium article having its surface protected by a multiple layer coating comprising a firmly adherent inner layer of uranium-aluminum alloy and a second layer of zinc firmly bonded to the uranium-aluminum alloy.

3. A solid metallic uranium article having its surface protected by a layer of uranium-aluminum alloy of the approximate composition UA l containing about 5% of Z111C.

4. A solid metallic uranium article having its surface protected by a multiple layer coating comprising an inner layer of a uranium-aluminum alloy of the approximate composition UAl containing about 5% of zinc, firmly bonded to the uranium, and a layer of zinc firmly bonded to the alloy layer.

5. A solid metallic uranium article having its surface protected by a multiple layer coating comprising an inner layer of a uranium-aluminum alloy, a second layer of Zinc-aluminum alloy, and a third layer of lead-tin alloy.

6. The method of protectively coating solid metallic uranium, which comprises removing oxide film from the solid metallic uranium and dipping the solid metallic uranium into a molten metal bath comprising about 55 to 99 parts of zinc and 45 to 1 part of aluminum at a temperature between and 200 centigrade degrees above the melting point of the metal bath.

7. The method of applying a multiple layer coating to solid metallic uranium, which comprises removing oxide film from the uranium, dipping the solid metallic uranium in a molten metal bath comprising between 5 and 15 parts of aluminum and between 95 and parts of Zinc at a temperature between 20 and 200 centigrade degrees above the melting point of the metal bath, withdrawing the solid metallic uranium from the metal bath, and cooling the coated metallic uranium to cause the coating to solidify.

8. The method of protectively coating metallic uranium, which comprises applying to the metallic uranium a coating of zinc containing aluminum, applying to the zinc-coated uranium a layer of molten lead containing tin, and causing the molten tin-containing lead to cool and solidify on the zinc-coated uranium.

9. The method of applying a multiple layer coating to solid metallic uranium, which comprises removing oxide film from the uranium, dipping the solid metallic uranium in a molten metal bath comprising between 5 and 15 parts of aluminum and between and 85 parts of Zinc at a temperature between 20 and 200 centigrade degrees above the melting point of the metal bath, withdrawing the solid metallic uranium from the metal bath, dipping the coated uranium while yet hot into a molten lead bath containing a minor proportion of tin and maintained at a temperature not substantially above the melting point of the Zinc aluminum bath, subsequently withdrawing the coated uranium from the lead bath and cooling it to cause the coating to solidify thereon.

10. The method of protectively coating a metallic uranium rod of cylindrical cross-section, which comprises removing oxide film from the metallic uranium rod, dipping the rod into a molten metal bath comprising about 55 to 99 parts of zinc and 45 to one part of aluminum at a temperature between 20 and 200 centigrade degrees above the melting point of the metal bath, withdrawing the rod and rolling it until the coating solidifies.

11. The method of protectively coating a solid metallic uranium article, which comprises applying a molten metal solution of aluminum in zinc to the solid metallic uranium article, said solution containing sufficient aluminum to react with the uranium under the prevailing conditions to form a protective layer of a aluminum-uranium alloy on the surface of the metallic uranium, withdrawing the coated article and dipping it into a molten metal bath comprising an alloy of aluminum and silicon, withdrawing the coated article from the aluminum silicon alloy bath, and subsequently cooling the article to cause the coating to solidify thereon.

12. The method of forming a protective uraniumaluminum alloy coating on a solid metallic uranium article which comprises removing oxide film from the uranium, dipping the uranium into a molten bath comprising about 55 to 99 parts of zinc and 45 to 1 parts of aluminum at a temperature between 20 and 200 C. above the melting point of the metal bath, whereby a coating of uranium-aluminum alloy is formed upon the surface of the uranium article and an outer coating of zinc is formed about said uranium-aluminum coating, removing the article from the bath and thereafter removing the zinc layer.

13. The method of claim 12 wherein the zinc is removed by centrifuging the coated article at a temperature greater than the melting point of Zinc.

14. The method of forming a protective uraniumaluminum alloy coating on a solid metallic uranium article which comprises removing oxide film from the uranium, dipping the uranium into a molten bath comprising about 55 to 95 parts of zinc and about 45 to 1 parts of aluminum at a temperature between 20 and 200 C. above the melting point of the molten bath whereby a coating of uranium-aluminum alloy is formed upon the surface of the uranium article and an outer coating of zinc is formed about said uranium-aluminum coating, removing the article from the bath, cooling the article to UNITED STATES PATENTS 943,161 Rockey 'Q Dec. 14, 1909 1,378,052 Peacock May 17, 1921 1,764,132 Wehr June 17, 1930 8 Austin Jan. 16, 1934 Liban Jan. 26, 1937 FOREIGN PATENTS Great Britain Oct. 3, 1941 OTHER REFERENCES 1 Metal Cleaning and Finishing, Qctober 1934, pp. 509- 512, 526,"A1uminum Improves Finish in Galvanizing by Wallace G. Imhofl.

Claims

6. THE METHOD OF PROTECTIVELY COATING SOLID METALLIC URANIUM, WHICH COMPRISES REMOVING OXIDE FILM FROM THE SOLID METALLIC URANIUM AND DIPPING THE SOLID METALLIC URANIUM INTO A MOLTEN METAL BATH COMPRISING ABOUT 55 TO 99 PARTS OF ZINC AND 45 TO 1 PART OF ALUMINUM AT A TEMPERATURE BETWEEN 20 AND 200 CENTIGRADE DEGREES ABOVE THE MELTING POINT OF THE METAL BATH.