US2574627A - Uranium-cobalt alloy - Google Patents

Description

Nov. 13, 1951 A. H. DAANE Er Al. 2,574,627

URANIUM-COBALT ALLOY Filed Aug. 26, 1947 Patented Nov. 13, 1951 VRANIIW-COBALT ALLOY Adrian H. Daane, Ames, Iowa, and William K.

Noyce, Fayetteville, Ark.,

assignors to the United States of Americal as represented by the United States Atomic Energy Commission Application August 26, 1947, Serial No. 770,624

The present invention is concerned with binary uranium-base alloys and more particularly relates to binary uranium-base alloys containing cobalt. I

Uranium metal is extremely corrodible, oxidizes readily andmay even ignite spontaneously when exposed/to air at room temperature.

4An object of the present invention is to improve the physical-metallurgical properties of uranium metal soas to enhance the corrosion re-m sistance o`f uranium and to render the same useful for various purposes for which uranium metal heretofore has not been satisfactory.

Another object of this invention is to produce binary uranium-cobalt alloys which are useful in the construction of neutronic reactors.

A further object of the invention is directed toward the formation of new and novel compositions of binary uranium-cobalt alloys to be used as additives in the formation of more complex alloys containing uranium and cobalt.

Other objects of the present invention will be apparent from the following description taken with the accompanying drawing in which the single figure is a phase equilibrium diagram defining the uranium-cobalt system.

In accordance with the present invention the enhancement of chemical inertness of uranium metal is accomplished by the alloying eifects of cobalt which tends toward decreasing corrosive attack by chemical reagents. In addition, by such alloying, uranium compositions are obtained in a form having al much lower melting point than uranium metal.

The present invention is particularly concerned with new and novel compounds of binary uranium-cobalt alloy compositions wherein the cobalt atomic per cent content is less than 50 atomic per cent of the combined uranium-cobalt composition. It was found when preparing low cobalt content alloys of uranium that the uranium liquidus temperature was lowered rather rapidly, as appears in the uranium-cobalt equilibrium diagram of the drawing, by the addition of cobalt until a eutectic composition of 34 atomic per cent cobalt was reached, the eutectic having a melting point of 734 C. The eutectic composition of 34 atomic per cent cobalt with uranium shows a lowering of the melting point of uranium by approximately 400 C.

Referring to the equilibrium diagram, the compound, UsCo (14.3 atomic per cent cobalt), which separates as a primary phase in alloys containing less than 34 atomic per cent cobalt is a highly crystalline metal which is formed by a peritectic i reaction at 826 C. In the alloys in which UsCo is present, the primary phase of the peritectic reaction appears to go to completion. Thermal and X-ray data indicate that there is no dedectable solubility of cobalt in uranium in the primary phase.

The alloy compound UeCo is an extremely crystalline phase which can be separated from lower cobalt content alloys of uranium either mechanically or chemically since this compound is not attacked Very rapidly by nitric acid. Single crystal diagrams were taken of this phase and the unit cell dimensions of this phase were determined from photomicrographs of isolated needles rotated about the needle (four-fold) axis. It was found that the compound UeCo was body centered, tetragonal with the following constants:

The density is about 17.7 grams per cubic centimeter, and the Volume of a unit cell equal to 550 .3 containing 24 uranium atoms and 4 cobalt atoms.

Thermal and microscopic data gave very definite evidence when extending the cobalt atomic per cent content beyond the 34 atomic per cent cobalt eutectic and approaching atomic per cent cobalt that a compound having the formula, UCo, existed. The compound, UCo, 50 atomic per cent cobalt composition decomposed peritectically at 805 C. This compound has a unit ceu volume of about 255.4 A3 which contains 8 molecules per unit cell to give a density of about 15.4 grams per cubic centimeter.

The alloys of the present invention were prepared from uranium metal having a purity greater than 99.9 per cent and of cobalt metal of 99.9 per cent purity. These metals were melted together in beryllia crucibles in vacuo by means of induction heating. Each alloy mass, weighing about 250-450 grams, was held at about 1500 C. for 20 minutes to allow the melt to come to equilibrium. Thermal data were taken by remelting the alloys and cooling at rates of about 6 to7 C. per minute in the range of about l000 C. with correspondingly lower rates at lower temperatures.

The alloys were prepared for microscopic examination by mechanical polishing techniques and electrolytic polishing using a phosphoric acid-ethylene glycol-ethyl alcohol solution.

The 34 atomic per cent eutectic alloy of uranium and cobalt affords a low melting uranium nium is an essential component in the construction of neutronic reactors, it is extremely imporalloy, exhibits high resistance to oxidation, and possesses a high density which makes this alloy a very suitable alloying additive for the preparatant to substantially decrease the corrodibility tion of more complex alloys containing uranium. of uranium metal Without introducing a large When the 34 atomic per cent cobalt eutectic of 5 quantity of neutron absorbers other than the uranium is added to a ladle of molten steel, nickel essential alloyng agent, cbalt, Which has a rele- 01 copper; it-JapidlygSi-nks and: alloys' Withft'bhe tively 10W neutron absorption IBIOSSeSeCtQn. molten bathcwitli'out excessive oxidation and losse It`wil1 b'efzunderstoodthattl'e particular alloy of expensive uranium. Furthermore, the chemcomposition described above should not be ical resistance to acid, such as nitric acid, indier 101; deemed to constitute the limits of the invention. categ that uranium-cobalt alloys, with or without The Seepe 0f the invention iS defined in the the addition of other elements, constituteanew appended'claim. series of corrosion-resistingmaterialstwhich offen` Whatristclaimedcist unique advantages over uranium; 1t-sh0u1d be.- A-ompositionloftmatter consisting of an internoted that the preferred; corrosirn resistant;15ametal1ic compoundof uranium and cobalt dened uranium-cobalt binary compositions.: aref: 0nabytheefrmlilaato having a density of about tained in a range from about 44 atomicl per cent. 1.7.7 gramspelxeubic centimeter. cobalt to about 40 atomic per cent`cob'a1t."

It should be noted that the addition of 'atomic per cent of cobalt to uranium gives a reduction 20 f Y' in the meltingfpoint ofairam'umfof approximately: REFERENCES; GITE,l 50 C. The decreaseof melting pontefis1praci- Y l n* tioally .-linearto approximately 20 .atom-ic per-'centr Thefouwmg-"rerens 'are 0f recom 1n the* cobalt vvand then the-rate vof `decrease'in- -theme1t fue 0f this patent. ing 1 point of uranium-1 becomes somewhat LlessiA 25` All of the alloys above described'. addition. to: the physical-metallurgical advantages, exhibit resistance. to corrosion-.fan superorto that-of. uranium metal.A

It should vbeA noted that the. invention is pri-v marilyconcerned .with binary alloyV compositions, consisting, of:- uranium andv cobalt Since'fura- Friend; Teigmock' o-ff Inorganic chemistry:

CharlesfGriir 8zf4Cof,V Ltd.; L'ondn:

Hansen, Aufbau der' Zwerstofflegierungen" 1936;" Photo'-T.'Iitl'iopriifitv Reproduction --by Edwardsi 30 Brothers,'1nc., AnnArborpMiohr, 1943pages--5-5" and '9595

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