US3294529A

US3294529A - Superconductive alloys

Info

Publication number: US3294529A
Application number: US312309A
Authority: US
Inventors: Robert C Haverstraw; Malcolm J Fraser
Original assignee: Westinghouse Electric Corp
Current assignee: CBS Corp
Priority date: 1963-09-30
Filing date: 1963-09-30
Publication date: 1966-12-27
Anticipated expiration: 1983-12-27
Also published as: JPS5116756B1; GB1034546A; DE1279331B; BE653466A; ES303961A1; CH413019A

Description

United States Patent M 3,294,529 SUPERCONDUCTIVE ALLOYS Robert C. Haverstraw, Willoughby, Ohio, and Malcolm J.

Fraser, Penn Hills, Pittsburgh, Pa., assignors to Westinghouse Electric Corporation, East Pittsburgh, Pa., a corporation of Pennsylvania No Drawing. Filed Sept. 30, 1963, Ser. No. 312,309 5 Claims. (Cl. 75-134) This invention relates to the preparation of superconductive alloys and in particular comprises a method to improve cryogenic properties of superconductive alloys as well as to provide novel superconductive alloys.

A major goal in research in superconductive alloys is the improvement of the critical current density at high magnetic fields. Changes in alloy content as Well as the use of different alloying constituents are ways in which improved critical current densities have been obtained. However, upon making such changes, production problems are changed and may create insurmountable obstacles to the use of an otherwise promising material. Accordingly, it is highly desirable to find ways of improving cryogenic properties in superconductive alloys that are known to be fabricable or to provide improved cryogenic properties in ways such that fabrication problems are not encountered.

It is therefore a primary object of the present invention to provide a method whereby the cryogenic properties of superconductive alloys can be improved by an easily practiced procedure that does not deleteriously affect the mechanical properties of the materials.

A further object of the invention is to provide a method in accordance with the foregoing object in which fabrication problems are not complicated and there result superconductive materials having improved cryogenic properties.

Another object of the invention is to provide new superconductive materials.

Other objects and advantages of the invention will appear from the following detaileddescription and discusmen.

It has now been discovered, and it is on this discovery that the invention is in large part predicated, that upon introducing hydrogen into superconductive materials, as described more particularly hereinafter, there results a superconductive material comprising the metal constituents and hydrogen having an increased volume. Upon determining, for example, the critical current density of the superconductive material before and after the hydrogen addition, it is found that a surprising increase therein results. Moreover, since the introduction of hydrogen can be practiced on the superconductive material after it has been worked to the desired state, it is evident that loss, if any, in mechanical properties need not prevent use of the improved superconductive material.

The invention can be practiced with superconductive alloys and compounds generally. This includes alloys and compounds of superconducting, exothermic, hydrogen occluding elements. These elements are in two groups. The first group includes titanium, vanadium, niobium, zirconium, lanthanum, tantalum, thorium and uranium, while the second group includes aluminum, zinc, gallium, cadmium, indium, tin, mercury, thallium and lead. The compounds and alloys can be composed of 1) any two or more elements of the first group, or (2) one or more elements of the first group with any one or more elements of the second group. The preferred superconductive materials with which the invention can be practiced are the zirconium-niobium alloys in which zirconium may range from about to 65, and preferably to 50, weight percent, and the bimetallic compound of niobium and tin,

3,294,529 Patented Dec. 27, 1966 Nb Sn, since the former of these can be fabricated to fine Wire or other shape readily and the latter has the highest known critical current density attained prior to the present invention. These materials may be used in the invention in the conventional forms now used in superconducing applications, with thin wires on the order of 0.015 inch and smaller down to about 0.001 inch in diameter being preferred. The shapes can be formed in the usual manner of alloying the metals, preferably in a purity of at least 99 weight percent, and then working the resulting material to final size and shape by practices presently known, for example, hot and cold working at light passes, the latter suitably using intermediate annealing steps.

In the invention hydrogen is added to superconductive material by electrolytically liberating it on the superconductor while the latter is a cathode in an electrolytic system. Accordingly, an electrolyte that liberates hydrogen upon electrolysis is required. Any hydrogen liberating electrolyte is operative in the invention, but it is preferred to use aqueous mineral acid solutions of, for example, hydrofluoric acid, hydrochloric acid, nitric acid, sulfuric acid and mixtures thereof. Preferably, an aqueous electrolyte having an acid concentration within the range of about 5 to 25 weight percent is used. The usual parameters in electrolysis, such as the electrolyte constitution and concentration, current density and the like, vary the effectiveness of the hydrogen charging process and are not independently critical. Generally a current density on the order of 0.1 to 5 amperes per square centimeter of cathode is used. As will be apparent to the artisan, the best conditions of operation as well as electrolyte constitution will be largely dictated by the specific application and materials involved in any given process. Platinum and stainless steel are the preferred materials for the anode in these cells, but other materials can be used as well.

The amount of cathodic charging that can be practiced in thi sinvention is limited by embrittlement of the superconductive cathode from hydrogen occlusion. That, of course, is a practical limitation rather than a limitation affecting operability. Generally cathodic charging is conducted sufficiently to cause a volume increase in the superconductor being treated of about 5 to 15 percent or more, based on the original volume. It is to be noted that the volume change adds considerably to the plastic deformation of the matrix. While reference 'has been made above to the hydrogen addition as being an occlusion phenomenon, it should be understood that this has been done for purposes of discussion and our invention is not to be limited by any theory regarding the, nature of the hydrogen retention. Whatever the manner by which the hydrogen is held, there result new superconductive materials composed of hydrogen and the two metals. These materials are stable at ordinary conditions and it is expected that stability will be retained for a number of years.

The invention will be described further in conjunction with the following examples in which the details are given by way of illustration and not by way of limitation.

An 0.010 inch diameter cold drawn Wire having a composition, by weight, of 25 percent zirconium and the remainder niobium was used. This Wire was connected as a cathode to a DC. power source and placed in an electrolyte formed from a concentrated acid mixture of, by weight, 1 part of hydrofluoric acid, 3 parts of nitric acid and 5 parts of sulfuric acid, the acid mixture having been diluted with Water to a 10 weight percent solution. A platinum electrode was :used as the anode. The cathode was then hydrogen charged in accordance with this invention by passing current through the cell at a current density, measured at the cathode, of 1 ampereper square centimeter.

The foregoing procedure was carried out on several samples. A first sample was charged for a total of 3 minutes under the above conditions. In another run a sample was charged for a period of 6 minutes. In addition, another sample was changed for two 3-minute cycles. The critical current density (in amperes) at fields of 5 to 20 kilogauss was determined on each sample before and after each charging cycle. The data obtained are:

It should be noted that these tests were of a qualitative rather than of a quantitative nature and no attempts were made to produce the highest possible current density. The above data demonstrate markedly that cathodic charging with hydrogen produce a significant increase in the critical current density at each of the fields tested. At the 20 kilogauss field and with 6 minutes of the cathodic charging, an increase in the critical current density of as high as 30 percent occurred. It is thus apparent that the invention can produce significant improvements in the critical current density of these materials.

To determine whether or not hydrogen charging destroyed the mechanical properties of the material, ductility tests were conducted on the sample charged for the 6-minute cycle. It was found that it could be bent to a radius at least as small as 0.005 inch without breakage. This sample was then cold reduced by rolling it to a ribbon 0.0025 inch thick and 0.025 inch wide. The critical current (in amperes) was again determined at fields of 5 to 20 kilogauss. In addition, a sample of the same 0.010 inch diameter wire that had not been charged was similarly cold reduced and its critical current (amperes) determined. The data obtained are:

Though the cold rolling was conducted to see if the charged material could be further worked, we were surprised to find further marked improvements in the critical current as shown by the above data. The values transverse to the rolled surface should be compared with those under sample 2 in Table I. Thus the invention provides an additional Way by which superconductive materials with improved critical current density can be obtained.

The hydrogen charging of the other superconductive materials is carried out in the same general fashion but with suitable variations of electrolyte composition to avoid unnecessary attack on the superconductive cathode. It is to be noted that even Nb Sn, the material with the highest known critical current density, can be improved in accordance with our discoveries, that is by cathodically charging it with hydrogen in aqueous mineral acid electrolyte.

From the foregoing discussion and description, it is manifest that a markedly simple and effective procedure is provided by which the critical current density of a superconductive material can be improved.

While the invention has been described with regard to detailed specific embodiments, it will be understood that variations, substitutions, changes and the like can be made without departing from its scope.

We claim:

1. A method of improving the cryogenic properties of superconductive materials comprising electrolytically liberating hydrogen on said superconductive material while said material is disposed as a cathode in a hydrogen liberating electrolyte, the said superconductive material being composed of at least one member selected from the group consisting of titanium, vanadium, niobium, zirconium, lanthanum, tantalum, thorium and uranium and one diflerent member of the group consisting of each of the members of the foregoing group and aluminum, zinc, gallium, cadmium, indium, tin, mercury, thallium and lead, and recovering the resulting hydrogen occluding superconductive material.

2. A method of improving the cryogenic properties of superconductive materials comprising electrolytically liberating hydrogen on said superconductive material while said material is disposed as a cathode in a hydrogen liberating electrolyte, said superconductive material comprising an alloy of 10 to weight percent zirconium and the remainder niobium, and recovering the resulting hydrogen occluding superconductive alloy.

3. A method in accordance with claim 2 in which the zirconium-niobium alloy superconductor is in wire form and is hydrogen charged until its volume increases up to about 15 percent.

4. A process in accordance with claim 3 in which the charged zirconium-niobium alloy superconductor is then cold worked to further increase the cryogenic properties.

5. A new superconductor comprising hydrogen and a zirconium-niobium alloy in which the zirconium is present to an amount of 15 to 60 weight percent of the alloy, the hydrogen being present in an amount sutficient to provide a volume in the superconductor of about 5 to 15 percent greater than that of the Zirconium-niobium alloy free from the hydrogen.

References Cited by the Examiner UNITED STATES PATENTS 1/1957 Brown 204- OTHER REFERENCES DAVID L. RECK, Primary Examiner.

W. C. TOWNSEND, Examiner. v C. N. LQVELL, Assistant Examiner.

Claims

5. A NEW SUPERCONDUCTOR COMPRISING HYDROGEN AND A ZIRCONIUM-NIOBIUM ALLOY IN WHICH THE ZIRCONIUM IS PRESENT TO AN AMOUNT OF 15 TO 60 WEIGHT PERCENT OF THE ALLOY, THE HYDROGEN BEING PRESENT IN AN AMOUNT SUFFICIENT TO PROVIDE A VOLUME IN THE SUPERCONDUCTOR OF ABOUT 5 TO 15 PERCENT GREATER THAN THAT OF THE ZIRCONIUM-NIOBIUM ALLOY FREE FROM THE HYDROGEN.