US2853441A

US2853441A - Surface treatment of uranium

Info

Publication number: US2853441A
Application number: US118630A
Authority: US
Inventors: Flint Oliver
Original assignee: Individual
Current assignee: Individual
Priority date: 1949-09-29
Filing date: 1949-09-29
Publication date: 1958-09-23
Anticipated expiration: 1975-09-23

Description

Sept. 23, 1958 o. FLl 2,853,441

SURFACE TREATMENT or mama Filed Sept. 29, I949 OLIVER FLINT Inventor y M B w assignments, to the United States of America as represented by the United States Atomic Energy Commission Application September 29, 1949, Serial No. 118,630

' 15 Claims. cram-1.5

This invention relates to thesurface treatment of bodies of uranium or uranium-rich alloy.

An object of the invention is to provide a method of treating such bodies whereby to produce a bright lustrous finish which shows little or .no change on exposure to-air for substantially 3 hours and which may serve as a basis for electroplating, coating by dipping, or the like.

A further object of the invention is to provide a method treating bodies of uranium or uranium-rich alloy which have become coated with oxide, in particular black oxide layers, whereby to remove or reduce the oxide, substantially' without loss of the metal carrying the coating.

In accordance with theinvention, the surface of a body of uranium or uranium-rich alloy, which is substantially free from black oxide coating, is given abright lustrous finish by anodic electrolytic treatment in a solution of-a weak organic acid, particularly a hydroxypolycarboxylic acid or a polycarboxylic acid. Examples of acid which may be employed are citric acid, tartaric acid, oxalic acid. Citric acid is the preferred organic acid. Tartaric acid is somewhat slower in operation'than citric acid and with oxalic acid, there is a tendency for basic uranium oxalates to precipitate. The treatment is preferably carried out at ordinary temperature employing a low current density at the anode,vfor example 3 amperes per square foot. Concentrations of 1 to percent by weight or more of the organic acid in water may be employed.

The bright silvery finish which is produced in this manner has been found. to be. stable in air forperiods of 3 hours and to form a satisfactory basis for electroplating on the uranium or uranium alloy, and for coatings produced by dipping into molten metal baths. Objects provided with the finish may also be subjected to controlled oxidation to produce desired oxide coatings.

Uranium or. uranium-rich alloy having black oxide coating, may be rendered suitable for treatment accordingto.

the invention by a preliminary anodic electrolytic treatment in an alkaline solution preferably at elevated temperature. An aqueous sodium carbonate solution constitutes a preferred electrolyte for1use in; this aspect of the invention, and by its use removal of the blackpxide is effected. A further preferred electrolyte is an aqueQus solution of'sodium hydroxide partially neutralis'ed'by citric acid, or alternatively a solution of sodium hydroxide to which has been added sodium citrate, the use of either of which results in conversion of black oxide coatings into brown hydroxide which is removed by anodic electrolytic treatment in solution of citric acid. Preferred anodic current densities for use with these electrolytes are approximately 60 ampere per square foot.

Uranium bars having surface contamination of electrically conducting particles, especially graphite, when treated according to the invention have frequently been found to develop surface pits, presumably owing to local action between the particles and uranium accelerated by the conditions of the treatment. Such pitting has been avoided by suspending bars of uranium having such con- 2,853,441 Patented Sept. 23, 1958 tamination in 10 percent aqueous sodium carbonate solution at 100 C. for fifteen minutes prior to treatment according to the invention, whereby the contaminating particleswere loosened'and weresubsequently washed off in running water. Oxide scale on the uranium-bar was then removed, anda bright finish applied in the manner set out above.

The presence of halides has a disturbing effect on the treatment of the invention, owing it is believed, to halides accelerating accelerating the rate of'oxidation. They should therefore be removed before treatment. A pretreatment in hot water-has been found to be effective-in removing barium chloride. Thus uranium bars-wereimmersed in boiling water for 30 minutes, rinsed in cold water and immersed'ina fresh bath'of boiling water for a further- 30 minutes, after which a final rinsing incold water was given before treatment according to the invention.

The following are examples of preferred ways of-carrying the invention intoefiect.

Example .1

A cylindrical barofuranium-which' had a heavy' black oxide coating formed thereon and carried brazing'scale and inorganic contamination was degreased-in acetone, clipped into a mild steel supporting rack and suspended in an electrolyte consisting of a 10 percent aqueoussodium carbonate solution maintained at C.

The supporting rack employed isillustrated in the accompaniyng drawing. It is formed from a round her of steel 1, one end of which has been-ground or machined to a point 5. The bar is' bent as shownand providedwith a tapped hole 6 receiving the set screw-3=which is also provided with apoint 4. The position'of the hole-6 is such that its axis is in the line of point 5. The handle portion 2 may be provided with a rubber or the like grip. The bar of uranium to be'treated is provided at the center of each end with a depression for engagement by the points 4 ands of the supporting rack, the screw 3 being tightened to hold the rod.

Using mild steel cathodes, the'bar was subjectedto anodic electrolyte treatment for approximately 10 minutes with acurrent density of 60 amperesrpersquarefoot. All oxide, scale andinorganic contamination was removed from the bar by the treatment.

The bar was then removed from the electrolyte, rinsed in cold water and immersed in an electrolyte consistingot 10 percent aqueous citric acid solution at ordinary temperature, in which it was made anode to a, graphite electrode. Ananode current density of 3 amperes per square foot was maintained for one minute, after which' the bar was removed, washed with cold water and'dried'with acetone. Abright silvery finish was obtained.

When the cleaned bar was removed from the first electrolytic bath -a golden oxidefilm formed on the cleaned surface,- but the film was removed by the treatment in th'e citric-acid bath; V

Example 2 A uranium bar similar to that used in Example -1 was degreased in acetone and then suspended in an electrolyte consisting of an aqueous solution containing 20 percent sodium hydroxide and 7.5 percent citric acid. Using a mild steel cathode and an anodic current density of 60 amperes per square foot and an electrolyte temperature of 80 C., the bar was subjected to anodic electrolytic treatment for 30 minutes, by which treatment the black oxide coating was converted to brown hydroxide. The bar was removed from the electrolyte rinsed in cold water and made anode to graphite in a 10 percent aqueous citric acid electrolyte as in Example 1. The brown hydroxide layer was removed by the treatment in the citric acid-containing electrolyte and a bright silvery finish was obtained. The bar was finally washed in water and dried with acetone.

Example 3 A uranium bar which had been treated in a percent aqueous sodium carbonate solution as described in Example 1 to remove oxide and scale was rinsed in cold water and immersed in an electrolyte consisting of a 10 percent aqueous tartaric acid solution at ordinary temperature. It was made anode to a graphite electrode, and current was passed for one minute employing an anode current density of amp. per sq. ft. The bar was then removed, washed with cold water and dried with acetone. A bright clean surface resulted.

By the expression uranium-rich alloy employed in the present specification is meant an alloy containing at least 97 percent by weight of uranium. The term polycarboxylic'acid means an acid containing more than one carboxyl group.

I claim:

;l. A method of producing a bright lustrous finish on surfaces of bodies of uranium and uranium-rich alloy, wherein the surface is caused to undergo anodic electrolytic treatment in a solution of a weak organic acid -of the class consisting of hydroxy-polycarboxylic acids and polycarboxylic acids.

2. A method of producing a bright lustrous finish on surfaces of bodies of uranium and uranium-rich alloy, wherein the surface is caused to undergo anodic electrolytic treatment in a solution of citric acid.

3. A method according to claim 2 wherein an aqueous solution of from 1 to 10 percent citric acid is employed.

4. A method according to claim 2 wherein a low anodic current density of the order of 3 amperes per square foot is employed.

5. A method of producing a bright lustrous finish on surfaces of bodies of uranium and uranium-rich alloy, wherein the surface is caused to undergo anodic electrolytic treatment at ordinary temperature in an aqueous citric acid solution. 7 6. A method of producing a bright lustrous finish on surfaces of bodies of uranium and uranium-rich alloy carrying a black oxide coating, wherein the surface is caused to undergo anodic electrolytic treatment in an aqueous alkaline solution, and is then caused to undergo anodic electrolytic treatment in a solution of a weak organic acid of the class consisting of hydroxy-polycarboxylic acids and polycarboxylic acids.

7. A method of producing a bright lustrous finish on surfaces of bodies of uranium, and uranium-rich alloy carrying a black oxide coating, wherein the surface is made anode in an aqueous sodium carbonate solution substantially to remove the said black oxide coating, and is then made anode in a solution of a weak organic acid of the class consisting of hydroxy-polycarboxylic acids and polycarboxylic acids.

8. A method of producing a bright lustrous finish on made anode in an aqueous sodium carbonate solution substantially to remove the said black oxide coating and is then made anode in a solution of citric acid.

9. A method according to claim 8 wherein the said citric acid solution in an aqueous solution of from 1 to 10 percent concentration.

10. A method according to claim 8 wherein the said citric acid solution is an aqueous solution of from 1 to 10 percent by weight, and a current density at the anode of the order of 3 amperes per square foot is employed.

11. A method of producing a bright lustrous finish on surfaces of bodies of uranium and uranium alloy carrying a black oxide coating, wherein the surface is caused to undergo anodic electrolytic treatment at elevated temperature in an aqueous sodium carbonate solution for approximately ten minutes substantially to remove the said oxide coating and is then caused to undergo anodic electrolytic treatment in an aqueous citric acid solution of approximately 10 percent concentration at ordinary temperature for approximately one minute.

12. A method according to claim 11 wherein the said first anodic treatment is carried out with a current density of approximately 60 amperes per square foot of anode surface.

13. A method of producing a bright lustrous finish on a body of uranium having a black oxide coating thereon, which comprises subjecting the body to anodic electrolytic treatment for about 10 minutes in an aqueous sodium carbonate solution at 80 C. and an anode current density of 60 amperes per square foot, rinsing the body and subjecting it to anodic electrolytic treatment in a 10 percent aqueous citric acid solution for one minute at a current density of 3 amperes per square foot.

14. A method of producing a bright lustrous finish on a body of uranium having a black oxide coating thereon which comprises subjecting the body to anodic electrolytic treatment for about 10 minutes in an aqueous solution containing 20 percent sodium hydroxide and 7.5 percent citric acid employing an anodic current density of 60 amperes per square foot and a temperature of 80 C., rinsing the body and subjecting it to anodic electrolytic treatment in a 10 percent aqueous citric acid solution for one minute at a current density of 3 amperes per square foot of anode.

15. A method of producing a bright lustrous finish on a body of uranium which comprises subjecting the body to anodic electrolytic treatment for about 10 minutes in surfaces of bodies of uranium and uranium-rich alloy carrying a black oxide coating, wherein the surface is an aqueous sodium carbonate solution at C. and an anode current density of 60 amperes per square foot, rinsing the body and subjecting it to anodic electrolytic treatment in a 10 percent aqueous tartaric acid solution for one minute at an anode current density of 15 amperes per square foot.

References Cited in the file of this patent UNITED STATES PATENTS