DE2226119A1 - Process for the manufacture of superconducting material - Google Patents

Description

ALEXANDER R. HERZFELD 6, -λαν kfurt α. μ. w 13

- LAWYER ^{SO PH} ' ^EN «TRASS ES 2

AT THE LAN DGE, FRAN KFURTAM MAIN JUDGES

Applicant: United States Atomic Energy Commission Washington D. C, USA

Ancestors for making superconducting material

The invention "relates to a method for manufacturing superconducting Material of certain niobium and vanadium compounds or alloys.

It is well known that certain metals or alloys lose when Cooling to very low temperatures the resistance to electrical current and v / ground superconducting. A once generated current flow / S remains in this superconducting state exist in a closed circuit for an indefinite period of time without any further power supply, so that, for example, an electromagnet is caused by the excitation current of a superconductor without an energy supply can be operated except for the required low temperature.

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The manufacture of the required superconducting wire with the desired physical and mechanical properties has been very expensive so far. This also applies to production of superconductors made of the "particularly cheap metals niobium" with tin, titanium or zirconium.

The invention has a method of making a drawable The task of superconducting material is simple, inexpensive and can be carried out in sections or continuously is.

The object of the invention is achieved in that the suitably interconnected pores of a niobium or vanadium material with a metallic material such as tin, aluminum, germanium, antimony, gallium or their Mixtures are impregnated or infiltrated and in the impregnated material by heat diffusion with one another connected fibers of a are formed by reacting the porous metal and the impregnating material.

The superconducting phase consists, for example, of Nb ^ Sn, Nb-A.1, Nb ^ (Al ₁ Ge), Nb ^ Sb or V ^ Ga. The porous niobium or vanadium material can also initially consist of the metal hydrides, which decompose to the porous metal during sintering.

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Further favorable configurations can be found in the description and the subclaims.

In the drawings show:

FIG. 1 schematically shows an apparatus suitable for carrying out a continuous process;

Figures 2-4 as an example of Nb, Sn the structure, des superconducting material in different successive process stages.

The hopper containing finely powdered niobium with particle sizes of, for example -100-400 mesh, is arranged above the press rollers 12 which, when rotated in the direction of the arrow, roll the powder into a green, unfired strip or band 13 of porous niobium. The • interconnected pores Find in the figure? already shown ^ it filled with tin. As an example, two rollers with a diameter of approx. ^ Cm and a roller gap of 0.5 mm are mentioned, which roll out a green strip 13 with a thickness of 0.48 mm. The strip is passed through a sintering furnace 14 with vacuum r), in-n +; τΉτ _Ο τ> A +; mocnhäre b ^ i in ^ o -? ^ ^Π Ο during etwn 3 we.

directed. T) nv svc dnm Ofm tro ^ en ^ ⁰ S ^ n ^^^ ntreifen l? - " ¹ innnder vorbunden ^ Po ^ en bpi in weifen o-" PTi7, en. a

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adjustable porosity. (Example: Density = 6.71 GMS / ccm = 78.3% of the theoretical density, approximately 21.7% porosity). The sintered strip is passed around the pulleys 16, 17 through a tin melt 15 in which the porous niobium is impregnated with tin and the pores are filled. The tin melt has z. B. a temperature of 500 - 1000 and the immersion time is a few seconds to several minutes. The impregnated strip 13-2 is passed over the deflection roller 18 and passed through a cold press roll 19, in which the thickness is further reduced and the interconnected tin threads of the strip 13-3 are given the shape shown in FIG. A reduction in thickness of 75% can easily be achieved here, but this cold rolling is not absolutely necessary depending on the desired thickness and the previous heat treatment. The strip 13-3 is then passed through an oven 20 for thermal diffusion treatment. Here the tin is converted to Nb ₅ JSn (FIG. 4). The strip 13-4 is finally rolled up, e.g. B. on a take-up reel 21 or the like. The diffusion temperature of the strip in the oven is up to about 1100 °, preferably 925-1075 °, for less than 1 minute up to several hours, depending on the desired amount of conversion. By adjusting the deformation as well as the time and temperature of the heat treatment, the tin can be completely or partially y, xi Nb-, Sn umpoR ^ t - ^. T.

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Instead of being in the furnace, the diffusion can also take place by passing through a tin melt.

The diffusion heat treatment can also be carried out as a separate process. Then the strip 13-3 is rolled directly onto the take-up reel 21 and then heated in an inert atmosphere or in a vacuum. This is beneficial, for example, for material that has to be treated for a long time at a low temperature, such as B. V ₇ JIl.

A tin-impregnated niobium strip that has not been cold-treated retains considerable amounts of unreacted tin for 2 hours when heated to 975 ° (no drawability), while if the thickness is reduced by 75%, it lasts only 1 minute Heating to 1000 ° (drawability: malleable around a mandrel with a diameter of 1 cm) the larger part of the tin Hb ^ Sn is implemented.

The advantages of the superconducting material according to the invention can e.g. B. by measuring the current density and the current conduction skapaz it ät certain strips can be detected, the otherwise depends on numerous factors, such as the material, the process conditions such as porosity (and thus strength of the impregnation), the reduction in thickness of the impregnated Strip, the temperature and duration of heat diffusion and

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thus the degree of implementation. According to this, the conversion from the superconducting to the normally conductive state is based required critical temperature.

As an example, niobium powder of grain size -270 mesh was rolled out into a strip, sintered, impregnated with tin, reduced by 75% to a thickness of 0.1-1.4 mm and diffusion heat treated. The resulting Fb ₃ Sn strip was wound around a mandrel and tested for the critical current strength by placing it in a variable magnetic field and passing various amounts of current through the coil. This was repeated for magnetic field strengths of 15 KG, 2OKG and 50 KG. To determine the current flow through the coil required for the transition from the supra-normal conductor, the voltage at the coil ends was tapped, with a measurable voltage value indicating the beginning of the transition; this was the case in the examples of the above magnetic field strengths at 8.7 10 ⁴ , 7 10 ⁴ and 3.1 χ 10 ⁴ Amp./qcm. The cross-section of the strip or strip served as a measurement basis for these measured values. The volume fraction of Nb, Sn was measured to be about 7%. The current-carrying capacity can thus be increased significantly by increasing this volume proportion accordingly.

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After these measurements, the strip was reversed Senses wrapped around the thorn and checked again. There was no significant change in the measurement results. That The superconducting material of the invention is therefore easy to draw.

The Fb-JBn phase is just an example. Further examples are briefly indicated.

For the production of superconducting material with a niobium-aluminum phase, Fb ^ Al, a niobium strip became a niobium strip in less than 1 min. At 800 with an aluminum melt soaked and otherwise treated as before.

To produce material with a niobium-aluminum-germanium phase, Fb _x (Al, Ge), an aluminum-germanium eutectic (approx. 53% by weight Ge) with a melting point of 4-24 ° at 700 ° was used as an infiltrant, in that the niobium strip was immersed for about 30 seconds. This resulted in good pore impregnation. Further treatment was the same as before.

In the example case for vanadium gallium (V ^ Ga) became vanadium powder rolled out into a porous vanadium strip, ge ^ sinters and passed through a gallium bath at 100 ° (gallium melting point 30 °). The impregnated gallium strip was then treated as previously described.

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As mentioned, the conversion of the infiltrant with the porous metal depends quantitatively on the time and temperature Diffusion treatment abj the required time and temperature values vr were each determined by individual tests.

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Claims (9)

Fat according to spriiche 1. A method for producing a drawable superconducting material comprising interconnected fibers of a superconducting phase with a critical field above 100 EG, characterized in that the appropriately among each other connected pores of a niobium or vanadium material with a metallic material such as tin, aluminum, Germanium, antimony, gallium or their mixtures are impregnated or infiltrated and fibers connected to one another by heat diffusion in the impregnated material one formed by reacting the porous metal and the impregnating material. 2. The method according to claim 1, characterized in that powdered niobium or vanadium as metal or hydride rolled into a porous band or strip and then rolled out is sintered. 3. The method according to claim 1 or 2, characterized in that the porous material is passed through a metal melt and thereby the pores are essentially completely filled. - 10 - 209853/0630 4-, method according to claim 3 »characterized in that the impregnated material is reduced in thickness prior to thermal diffusion. 5. The method according to claim 2, characterized in that the material in a vacuum or inert atmosphere at 1850 2250 ° is sintered for 3 minutes. 6. The method according to claim 3 »characterized in that the molten metal of tin with a temperature of 500 1000 ° "and the dwell time of a niobium strip is less than 1 min. to 3 min. 7 «Method according to claims 4 and 6, characterized in that that the impregnated material by cold rolling by 75% in the thickness is reduced. 8. The method according to claim 6, characterized in that the heat diffusion in an oven at 925-1075 for less than 1 minute to several hours. 9. The method according to claims 1-8, characterized in that the impregnated material is first rolled up and then or later treated by thermal diffusion. 20 BB 5 37 m