US2919186A

US2919186A - Uranium alloys

Info

Publication number: US2919186A
Application number: US681120A
Authority: US
Inventors: Colbeck Eric Winearls
Original assignee: Individual
Current assignee: Individual
Priority date: 1946-07-02
Filing date: 1946-07-02
Publication date: 1959-12-29
Anticipated expiration: 1976-12-29

Description

Unie

as represented by the United States Atomic Energy Commission No Drawing. pplication July 2, 1946 Serial No. 681,120

7 Claims. or. 75-13:!

This invention relates to new ternary alloys of uranium.

An object of the invention is to provide a composition predominantly of uranium metal having a resistance to corrosion substantially greater than uranium metal.

Another object is to provide a corrosion-resistant uranium alloy.

Another object is to provide a metallic composition containing uranium having a resistance to corrosion substantially greater than uranium metal and a neutron-capture cross section predominantly determined by the uranium content.

Another object is to improve the resistance to corrosion of uranium metal by admixture of one or more other elements of small competitive neutron absorption.

When uranium is to be subject to irradiation by thermal neutrons for purposes involving atomic disintegration the extent to which any impurity in the uranium metal can be tolerated is determined by the competitive neutron absorption (referred to as C.A.) of that impurity. The CA. of an element contained in uranium depends on the capture cross-section (for thermal neutrons) of its atom compared to that of a uranium atom and upon the proportion or actualconcentration of atoms present. Thus the CA. due to an amount of impurity or adulterant expressed as a proportion by weight can be calculated.

In co-pending application Serial No. 678,887, filed June 24, 1946, and now abandoned, I have described new alloys containing uranium and molybdenum, such alloys primarily having greater corrosion resistance than uranium itself.

According to the present invention I provide a new ternary alloy of which the major proportion consists of uranium, and the minor proportion of molybdenum and silicon. I have found it possible to achieve a marked improvement in corrosion resistance by employing only a small proportion of molybdenum and of silicon, e.g. of the order of 1 percent of each. I have not observed any marked further improvement in corrosion resistance by increasing the proportions of molybdenum and silicon to higher values, but it is to be understood that the present invention does not exclude such higher proportions, although in the case of alloy compositions containing considerably greater proportions of molybdenum and silicon, e.g. more'than percent ofeach, difiiculty may be experienced in the manufacture of the alloys and the competitive absorption becomes inconveniently large. Accordingly the preferred alloys contain between 0.1% and 5% molybdenum and between 0.1% and 5% silicon, the balance being substantially uranium. I believe that any impurities conventionally present in uranium, molybdenum or silicon do not militate against the corrosionresistance which is characteristic of the preferred alloys of the present invention, and it is to be understood that the terms uranium, molybdenum and silicon as used herein denote those metals in the degree of purity customarily available.

Molybdenum has a neutron capture cross-section, such States atent that its competitive absorption is about 1% when it is uniformly admixed with uranium in the proportion of 1% Similarly silicon has a competitive absorption of about 1% when it is present in the proportion of 3.6%. Thus molybdenum and silicon each present in the proportion of 1% in a uranium alloy introduce a total competitive absorption of about 2.7%. Ina specific alloy referred to hereinafter containing 0.34% molybdenum and 0.57% silicon the competitive absorption due to these two elements is about 0.5%.

The alloy compositions of the present invention may be manufactured by'melting suitable proportions of uranium, molybdenum and silicon together, e.g. in a thoria crucible at 1150-l400 C., out of contact with air, for example under a flux covering or in vacuo.

If desired, these compositions may be annealed in order to relieve stresses in the alloy. The annealing conditions depend primarily on the proportions of molybdenum and silicon in the alloy. With for example 0.2-1 percent of each of molybdenum and silicon the annealing may be carried out at 600-500 C. for 8 hours followed by quenching or slow cooling, or at 700-800 C., for 4 hours.

The following is an example of the improvement in the corrosion-resistant properties of uranium which can be effected by alloying with small amounts of both molybdenum and silicon. An alloy containing 0.34 percent molybdenum, 0.57 percent silicon and the remainder uranium, obtained by fusion under vacuum in a thoria crucible at 1300 C., and subsequently annealed at 800 C. for 2 hours and allowed to cool slowly, had a corrosion rate in boiling water of between 0.03 and 0.3 mm. per annum and a Brinell hardness of 290-360. For comparison, metals of the same degree of purity being employed, the corrosion rates of uranium itself, an alloy containing 0.42 percent molybdenum, and an annealed alloy containing 0.77 percent silicon, are respectively 7-16, 6-12 and 2.5 mms. per annum. The Brinell hardness was 180-210. Thus, the improvement in corrosion-resistant properties for the ternary alloys is greater than would be expected from a knowledge of the two binary alloys involved.

In addition, the tensile strength of these alloys is higher in general than that of uranium itself, especially when the alloys are annealed. For example, an alloy containing 0.5% silicon, 0.5 molybdenum, the balance being uranium except principally for 0.07% iron, 0.015% copper, and made by melting suitable proportions of silicon, molybdenum and uranium under an absolute pressure of 10- mms. of mercury, had an ultimate stress of 35 tons per square inch, elongation 1%, and reduction in area nil. The same alloy was also annealed at 600 C. for 8 hours under an absolute pressure of 10- mms. of mercury and cooled in the furnace at a rate such that the alloy took 8 hours to cool to C. and 14 hours to cool to room temperature. The annealed alloy had an ultimate stress of 44 tons per square inch, elongation 1-2% and reduction in area 1-2%. For comparison, the original uranium used for making up these alloys, either in the form of extruded bar which normally has a higher tensile strength than similar material in the ascast condition, or in the annealed condition after heat treatment at 600 C. for 8 hours and cooling in the furnace, had an ultimate stress of only 25-30 tons per square inch. The analysis of this uranium was as follows: uranium 99.69%, magnesium 0.001%, silicon 0.049%, tin less than 0.001%, iron 0.055%, copper 0.060%, calcium less than 0.001%. More highly purified uranium generally has a higher tensile strength and improved ductility, but even with such material the tensile strength is increased by the addition of small amounts such as 0.2% to 5% of silicon and molybdenum.

I claim: l. Ternary alloy comprising uranium predominating amount and minor proportions not more than five percent. by weight each of silicon and molybdenum, the,

5. An annealed uranium alloy containing from 0.2 percent to 1 percent of molybdenum and from 0.2 percent to 1 percent of silicon, the balance uranium.

6. Alloy comprising at least 98 percent by weight of uranium and silicon and molybdenum each in amount from 0.1 percent up to one percent by weight.

7. Uranium alloy comprising 0.34 percent molybdenum and 0.57 percent silicon, the balance uranium.

References Cited in the file of this patent UNITED STATES PATENTS 969,064 Kuzel Aug. 30, 1910 1,551,333 Schriiter et al. Aug. 25, 1925 1,994,805 Kluger Feb. 19, 1935 Hensel et a1 Apr. 16, 1940

Claims

1. TENARY ALLOY COMPRISING ARANIUM PREDOMINATING AMOUNT AND MINOR PROPORTIONS NOT MORE THAN FIVE PERCENT BY WEIGHT EACH OF SILICON AND MOLYBDENUM, THE ALLOY HAVING A CVORROSION RESISTANCE GREATER THAN THAT OF URANIUM AND A NEUTRON-CAPTURE CROSS-SECTION PREDOMINANTLY DETERMINED BY THE URENIUM CONTENT.