DE1790062A1 - Superconductor with an Nb3Sn layer on the surface and process for its production - Google Patents

Description

SIEMEFS AKTIENGESELLSOHAFT Erlangen, September 3rd, 1968

ELA 68/1443

Superconductor with a Nb, Sn-rail on the surface and method for the "x- ' ^T <3rd division

The invention relates to a superconductor consisting of a Carrier with, one by deposition of niobium and tin from 'gaseous Compounds of these elements produced Nb, Sn layer on the Surface.

Such superconductors, in which, for example, the Nb, Sn layer by reducing the chlorides of niobium and tin using hydrogen is deposited on the heated carrier on the surface of this carrier are known (articles by Hanak, Strater and Cullen

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in "RCA Review", Volume XXV, Sept. 1964, pp. 342 to 365 and British Patent 989,381). You can especially tape or be wire-shaped, and are suitable for the windings, for example of superconducting magnet coils to generate high magnetic fields. as Carriers are used in particular for high-temperature metals or metal alloys, for example that known under the trade name "Hastelloy" Nickel based alloy.

Critical to the technical use of The so-called critical current density j is superconductors. When this current density passes through one in a superconducting state The current flowing through the superconductor is exceeded, the superconductor changes from the superconducting to the electrically normal conducting state, whereby the ohmic resistance of the superconductor increases from zero to a relatively high value. The critical current density 3 depends on the external magnetic field H, in which the superconductor is located and usually decreases as the external magnetic field increases. The connection between the two external magnetic field and critical current density can be represented by what are known as H-j curves, which are known from the different superconductor materials run differently.

Superconductors with Nb, Sn layers are known to be of particular technical importance, since these layers still show high critical current densities even in high magnetic fields. Superconductors with such layers are therefore particularly suitable for magnetic coils for generating very high magnetic fields. Since the HJ _c curve of Nb, Sn

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runs almost hyperbolic in the range of H between 50 and 80 kilooersted, it makes sense to use the product H · j _c as a measure of the current carrying capacity of superconductors with Nb ^ Sn layers. In the case of the known superconductors with FtuSn layers deposited on the surface from the gas phase, this product reaches H * j ■

10-2

maximum values of about 4 * 10 A'Gauss · cm. A superconductor with this one The H j value therefore has, for example, in an external magnet

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field H of 50 kOe a critical current density i _n = 8 · 10 ^ A ^; cm. Although the H * j values of these known superconductors are already relatively high, it is nevertheless desirable, especially for the generation of very high φ magnetic fields, to increase the H'jv values even further, since a higher possible current density is used to generate a specific magnetic field fewer turns are required and thus superconductor material can be saved and the outer diameter of the magnet coil can be reduced. In addition, there is a certain difficulty in the production of these known superconductors in that the H · j values achieved are subject to fluctuations and cannot always be set in a reproducible manner.

The invention is based on the problem of superconductors consisting of ■ from a carrier with one made by the deposition of niobium and tin gaseous compounds of this. Elements produced Nb ^ Sn layer on the surface, on the one hand to further increase the H * i values and on the other hand to make the H * j values reproducible. ■

To achieve this object, the superconductor is formed according to the invention such that the Nb ^ Sn layer is 0.1 to 1, 5 wt. ^Q / o carbon.

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Pie. Invention is based on the surprising finding that by targeted introduction of carbon into the gas phase

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different "Nb-Sn layers the critical current density j of these Layers and thus also the product h * j are adjusted to be reproducible and in particular substantially - can be increased.

In the previously known superconductors with deposited from the gas phase Nb-Sn layers, on the other hand, are carbon, if at all, at most as accidental, unintentional, due to the starting material ™ Very small amounts of contamination caused by the contamination are present in these layers.

In a preferred embodiment of the superconductor according to the invention the Nb, Sn layer contains 0.25 to 1.3% by weight of carbon. Superconductors with these carbon contents in the Nb, Sn layer

10-2

show H * j values of over 5 * 10 A'Gauss'cm.

With carbon contents of 0.4 to 1.1% by weight in the Nb ^ Sn layer

• Even H'j "values between 7 * 10 and about 9 to 10 * 10 A * '■ -2 ■ ·

Gauss'cm can be achieved.

According to a further invention, the superconductor with a carbon-containing Nb ^ Sn layer can advantageously be produced in such a way that gaseous halides of niobium and tin are mixed and attached to a carrier made of a high-temperature metal or a ^{high-temperature metal alloy, which is heated to about 750 to 1000 ° C.} be reduced by means of hydrogen and that the mixture of halides is a gaseous

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Carbon compound is admixed, which is attached to the heated carrier at least partially decomposed or at least partially decomposed with the elimination of carbon by which hydrogen is reduced.

As gaseous halides of niobium and tin are in particular Niobium tetrachloride (NbCl) or niobium pentachloride (-Nb-CIc) and tin chloride

rid (SnCIp) suitable. However, bromides such as niobium pentabromide (NbBr ₁ -) or niobium tetrabromide (NbBr.) And tin dibromide (SnBr ₀ ),

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as well as iodides of niobium and tin can be used.

Furthermore, as already suggested in the German patent application, file number P 16 21 345.9 (PLA 67/1386), niobium tetrachloride can be used together with tin dibromide ^ which is easier to reduce than tin dichloride / In addition, as in 'the German patent application , file number P 15 21 505.1 (PLA 66/1477) has been proposed for avoiding possibly occurring störenden'Niobtrichlorid (NbCl -) - deposition on the walls of the coating chamber, in which the reductive (tk tion of halides takes place, the gaseous niobium tetrachloride can be converted at least partially into niobium pentachloride by adding chlorine gas.

Carbon tetrachloride (CCl.) And carbon monoxide (CO) are particularly suitable as gaseous carbon compounds. In the presence of hydrogen at temperatures of 750 to 1000 ⁰ C, these compounds split off a sufficient amount of carbon, but hardly decompose at lower temperatures, so that the

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Carbon deposition only on the carrier and not on the lower ones Parts of the loading device located at temperatures, By suitable choice of the amount of the gaseous carbon compounds added to the halides, the particular desired Carbon content in the Nb ^ Sn layer can be set very precisely.

The invention is intended to be even more detailed with the aid of a few figures and examples • be explained.

w Fig. 1 shows schematically an embodiment of a device for the production of a tape-shaped superconductor according to the invention.

Fig. 2 shows schematically in longitudinal section a tape-shaped superconductor according to the invention.

Fig. 3 shows the dependence of the product H * j on the carbon

stop in the Nb, Sn <layer in a superconductor according to Er-A finding.

The device shown in Fig. 1 is suitable for example Manufacture of a tape-shaped superconductor according to the invention, wherein assumed from gaseous niobium tetrachloride and tin dichloride generated by passing chlorine gas over heated niobium or heated tin.

The device essentially consists of a coating

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chamber serving quartz tube 1 and a second quartz tube 2, the is divided by means of a quartz wall 3. The one part 4 of the tube 2, in which there is a niobium supply during operation of the device 5 is used as a niobium chlorinator. The other.-Part 6 of the pipe 2, in which there is a supply of tin during operation of the device? serves as a tin chlorinator. The quartz tube 2 is with at both ends Pipe sockets 8 and 9 are provided for introducing chlorine gas. Through the Quartz wall 3 will cause an inflow of gas from part 4 of tube 2 in part 6 and vice versa. The tube 1 is on both Ends closed with graphite bodies 10 and 11, each marked with " an opening as narrow as possible for the implementation of a band-shaped carrier 12 are provided. The carrier 12 is unwound from the roll 13 and wound onto the motor-driven roller 14 after coating. The carrier 12 stands with the graphite bodies 10 and 11 in electrically conductive connection. These are about the Leads 15 and 16 connected to an electrical power source.

The is used to introduce the hydrogen into the coating chamber Pipe socket 17, which is arranged in a coating chamber J, tube 19 provided with numerous openings opens. Through this tube 19 is a uniform distribution of the hydrogen in the Coating chamber causes. For supplying the gaseous carbon compound the tube 20 is used, for example with a storage vessel 21 for liquid carbon tetrachloride 22 can be connected. The storage vessel 21 is located in a liquid thermostat 23, which is used to set the temperature of the carbon tetrachloride supply 22 serves. The residues arising during the coating reaction

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Gases are released from the coating chamber through the pipe socket 24. 1' discharged. The coating chamber 1 is connected through the quartz tube 25 connected to the quartz tube 2. The quartz tubes 1, 2 and 25 are suitable from shaped, for example, hinged tubular ovens 26, through which the individual parts of the door direction can be heated,

In the following exemplary embodiment, the production of a tape-shaped superconductor with an Nb ₅ Sn layer with 0.4 wt. ^ Carbon content using carbon tetrachloride is described in more detail.

A tape made of the high-temperature alloy known under the trade name "Hastelloy Alloy B" (DIN designation NiMo 30), for example, is used as the carrier 12, which contains about 62. $ nickel, 26 to 30 $> molybdenum and the remainder small amounts of the Contains elements cobalt, silicon, manganese, iron, carbon and vanadium. This carrier 12 is. suitably employed in the quartz tube 1 and moved during the coating with konstanteer speed through the tube hindurchge- Mk. Furthermore, the starting materials niobium and tin are introduced into the niobium chlorinator 4 and the tin chlorinator 6 as well as a carbon tetrachloride supply 22 in the storage vessel 2T. Before the beginning of the deposition reaction, the air is displaced from the device, for example by introducing an inert gas such as helium or argon. Electric current is passed through the carrier 12 via the leads 15 and 16, said current being dimensioned such that the carrier is heated to a temperature of approximately 900.degree. With the aid of the wall of the tube furnaces 26 Beschichtungskaramer 1 to about 700 ⁰ C, the Niobchlorinator 4 and are

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Zinnchlorinator 6 heated to about 800 ⁰ G and the connecting pipe 25 to avoid condensation of the chlorides to about 650 ° C. The carbon tetrachloride supply 22 is kept at a temperature of 5 ° C. with the aid of the liquid thermostat 23 gaseous niobium tetrachloride is formed, when the chlorine gas is passed over the molten tin 7 gaseous tin dichloride is formed. The chlorides of the niobium and tin mix in the tube 25 and flow through this tube into the coating chamber 1. At the same time, hydrogen is supplied to the coating chamber 1 through the pipe socket 17, to which, in order to avoid Nb ^ Sn deposits on the wall of the Coating chamber gaseous hydrogen chloride is added-? Furthermore, hydrogen is introduced as a carrier gas into the storage vessel 21, which is loaded there with gaseous carbon tetrachloride and this gaseous carbon tetrachloride is transported through the pipe 20 into the coating chamber 1. The chlorides of niobium and tin and the "carbon tetrachloride are reduced by the hydrogen on the heated carrier 12, which is coated with a carbon-containing Nb ^ Sn layer. The coated carrier is led out of the tube 1 and wound onto the roll 14.

In the present example, the coating chamber in the tube 1 had a length of about 30 cm. The niobium chlorinator 4 ^{and the} tin chlorinator 6 were each about 40 cm and the connecting pipe 25 was about 20 cm

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long. The tubes 1, 2 and 25 also each had the same diameter of about 3 »5 cm. The chlorine gas throughput through the niobium chlorinator 4 was about 4 l / h, the chlorine gas throughput through the tin chlorinator 6 was about 101 / h. Through the port 17 15 l / h of hydrogen were introduced about, which was about 2.5 l / h of hydrogen chloride gas ^# admixed. Over the carbon tetrachloride supply 22, 3 l / h of hydrogen were passed as carrier gas, which were saturated with gaseous carbon tetrachloride at a temperature of 5 ° C. * The band-shaped carrier 12, which is 0.2 cm wide and 50 μ. was thick, was pulled through the tube 1 at a speed of about 20 to 25 cm per minute and was coated with an approximately 8 ll thick Nb ^ Sn coating with 0.4% by weight carbon content. The coated tape exhibited an external magnetic field of 50 kOe

10 - »2 has an H · j value of about 7 * 10 A« Gauss »cm. The critical current density j_ is related to the cross section of the Nb ^ Sn layer.

Nb, Sn layers with different carbon contents can be produced under otherwise constant conditions by changing the temperature of the carbon tetrachloride supply 22 with the aid of the liquid thermostat 23. When the temperature is increased, the hydrogen serving as the carrier gas is charged with more carbon tetrachloride, and when the temperature is lowered, it is charged with less carbon tetrachloride. The carbon tetrachloride is not completely reduced in the coating chamber under the specified conditions, but only reduced to about $ 20.

When using carbon monoxide for the production of super-

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Conductors with carbon-containing Nb ^ Sn layers can be proceeded in practically the same way as in the exemplary embodiment described above. Only through the pipe 20 is hydrogen not loaded with gaseous carbon tetrachloride, but gaseous carbon monoxide directly introduced. 1 -l / h carbon monoxide through the pipe 20 into the coating chamber of a "device of FIG. 1 and in the remaining unchanged Versuchsbedingungeri on the D-shaped bai Träger.12 a Nb, Sn layer with 0.22 wt. $> carbon was deposited. The tape-shaped superconductor produced in this way had an H * J _c -r value of about 5 * 10 A in an external magnetic field of 50 kOe.

-2
Gauss' cm.

Of course, the gaseous halides of niobium and Tin not necessarily by passing halogen gas over heated Kiob or tin can be produced. Rather, it can also be directly from the gaseous compounds are assumed.

A belt-shaped one produced by the method described above Superconductor is shown in longitudinal section in FIG. Of the ribbon-shaped "Hastelloy Alloy B" carrier is 51 »on this Carefully adhering carbon-containing Nb, Sn layer is designated by 32. Investigations on metallographic sections suggest that the incorporation of carbon into the Nb, Sn base material takes place in the form of finely divided excretions. It can however, it cannot be excluded that some of the carbon with the niobium also forms niobium carbide precipitates.

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In Fig. 3, the dependence of the Ή '- ^ - value on the carbon content in the Nb ^ Sn layer is shown in ribbon-shaped superconductors with Nb ^ Sn layers on the surface. The H · j value is plotted on the ordinate and the carbon content in the Nb, Sn layer in wt. $ Is plotted on the abscissa. The duichgehend drawn part of the curve and dfer measured at 1.5 wt. $> Carbon would by. A large number of measurements were determined on ribbon-shaped superconductors which were produced in accordance with the above exemplary embodiment using carbon tetrachloride or carbon monoxide. The dashed part of the curve was estimated on the basis of the measured values. The external magnetic field H was 50 kOe in each of these measurements. The curve in FIG. 3 clearly shows that the H * j values initially increase rapidly with increasing carbon content in the Nb, 3n layer and then decrease again after passing through a maximum. The highest H, j value measured so far is

10 -2 *

was 9.2 * 10 A'Gauss'cm. A maximum of the H * j value of about 10 · 10 A'Gauss'cm is for carbon contents from about 0.8 to about 1.0 wt. $ Expected. The. Fig. 3 shows very clearly that carbon admixtures increase the H * j values compared to the previously known Values can be increased significantly.

The thickness of the carbonaceous Nb, Sn layers in the inventive Superconductors is advantageously between about 3 and 10 ^ U-. Thinner layers are very difficult to deposit evenly from the gas phase, thicker layers tend to lead to electrical instabilities, i.e. to the sudden transition to the electrically normal conducting state before reaching the critical one that is to be expected Current density.

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In addition to the tape or wire shape, the superconductors according to the invention also have other forms. For example, s-ich are one-sided Hollow cylinders coated with a carbon-containing Nb, Sn-rail for shielding · from magnetic fields. In addition to highly heat-resistant Metals or metal alloys are also suitable as carriers for such superconducting bodies, for example, quartz or ceramic.

7 claims
3 figures

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Claims (7)

PLA 68/1443. Claims. - · 1. Superconductor, consisting of a carrier with a deposition of niobium and tin from gaseous compounds of these elements generated Nb ^ Sn layer on the surface, characterized in that the Nb ^ Sn layer contains 0.1 to 1.5 wt. # Carbon. 2. The superconductor of claim 1, characterized in that the Nb, Sn layer contains $> Carbon 0.25 to 1.3 wt.. 3. Superconductor according to claim 2, characterized in that the Nb, Sn layer contains 0.4 to 1.1 wt. # Carbon. 4. A method for producing a superconductor according to any one of claims 1 to 3, characterized in that gaseous halides of niobium and tin are mixed and reduced on a ^{heated to about 750 to 1000 0} O carrier made of a high temperature metal or a high temperature metal alloy by means of hydrogen and that the mixture of halides is admixed with a gaseous carbon compound which is at least partially decomposed or reduced by the hydrogen on the heated support with the elimination of carbon. 5. The method according to claim 4, characterized in that as gaseous Niobium halides and tin niobium tetrachloride and niobium pentachloride, respectively and tin dichloride can be used. -109849/0380 - 14 - Kb / Kö PLA 68/1443 6. The method according to claim 4 or 5, characterized in that as gaseous carbon compound carbon tetrachloride is used will. 7. The method according to claim 4 or 5 »characterized in that as gaseous carbon compound carbon monoxide is used. 109849/0360 - 15 - Kb / Kü ι Ä -f Blank page