CA2249790A1 - Method of alloying a noble-metal bypass layer of a high-temperature superconductor - Google Patents
Method of alloying a noble-metal bypass layer of a high-temperature superconductor Download PDFInfo
- Publication number
- CA2249790A1 CA2249790A1 CA002249790A CA2249790A CA2249790A1 CA 2249790 A1 CA2249790 A1 CA 2249790A1 CA 002249790 A CA002249790 A CA 002249790A CA 2249790 A CA2249790 A CA 2249790A CA 2249790 A1 CA2249790 A1 CA 2249790A1
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- Canada
- Prior art keywords
- layer
- metal
- noble
- alloy
- bypass
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- H—ELECTRICITY
- H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
- H10N—ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
- H10N60/00—Superconducting devices
- H10N60/30—Devices switchable between superconducting and normal states
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- Superconductors And Manufacturing Methods Therefor (AREA)
- Other Surface Treatments For Metallic Materials (AREA)
- Emergency Protection Circuit Devices (AREA)
- Superconductor Devices And Manufacturing Methods Thereof (AREA)
Abstract
Ceramic high-temperature superconductors (1) which are used as current limiters in alternating-current lines should have a bypass layer (2) whose electrical resistivity is increased by more than 10 times with respect to that of a noble metal. In order to achieve this, the noble-metal bypass layer (2) of the high-temperature superconductor (1), preferably of silver is alloyed with a base metal, preferably Pb or Bi or Ga or Al, by a thermal treatment. A plurality of methods are specified for the application of an alloy-metal layer (3) to the noble-metal bypass layer (2) of the high-temperature superconductor (1) before the thermal treatment. The high-temperature superconductor (1) is adjusted to a superconductor layer thickness (dl) of < 500 µm. The ratio of the bypass layer thickness (d2) of the noble-metal bypass layer (2) to the superconductor layer thickness (dl) is adjusted to <
1/5.
1/5.
Description
TITLE OF THE INVENTION
Method of alloying a noble-metal bypass layer of a high-temperature superconductor BACKGROUND OF THE INVENTION
Field of the Invention The invention proceeds from a method of alloying a noble-metal bypass layer of a high-temperature superconductor in accordance with the preamble of patent claim 1.
Discussion of Background In the preamble of patent claim 1, the invention makes reference to a prior art, such as is disclosed in US-A-5,079,223. The latter specifies a method of produc-ing a composite in which a high-temperature superconductor is provided with a 30 nm - 100 nm thick noble-metal layer of silver or gold or their alloys by means of ion-beam evaporation or sputtering. Said composite is joined to a metal substrate of copper or aluminum or lead or zinc or their alloys by means of a binder of In, Ga, Sn, Bi, Zn, Cd, Pb, Tl or their alloys, which may form intermediate phases or solid solutions with the noble metal, by pressing together at a temperature of < 400~C (below the melting point of said metals). No data are to be inferred from this patent relating to the electrical resistivity of the bypass layer obtained in this way to the high-temperature superconductor.
It is known from JP 06-309955 A (in Patent Abstracts of Japan) to impregnate silver-coated high-temperature superconductors with a Pb-Sn solder.
It is known from US-A 4,914,081 to apply a metal layer of silver or copper or tin or lead or zinc or cadmium or indium or nickel or their alloys to a high-temperature superconductor by electrolytic deposition.
Method of alloying a noble-metal bypass layer of a high-temperature superconductor BACKGROUND OF THE INVENTION
Field of the Invention The invention proceeds from a method of alloying a noble-metal bypass layer of a high-temperature superconductor in accordance with the preamble of patent claim 1.
Discussion of Background In the preamble of patent claim 1, the invention makes reference to a prior art, such as is disclosed in US-A-5,079,223. The latter specifies a method of produc-ing a composite in which a high-temperature superconductor is provided with a 30 nm - 100 nm thick noble-metal layer of silver or gold or their alloys by means of ion-beam evaporation or sputtering. Said composite is joined to a metal substrate of copper or aluminum or lead or zinc or their alloys by means of a binder of In, Ga, Sn, Bi, Zn, Cd, Pb, Tl or their alloys, which may form intermediate phases or solid solutions with the noble metal, by pressing together at a temperature of < 400~C (below the melting point of said metals). No data are to be inferred from this patent relating to the electrical resistivity of the bypass layer obtained in this way to the high-temperature superconductor.
It is known from JP 06-309955 A (in Patent Abstracts of Japan) to impregnate silver-coated high-temperature superconductors with a Pb-Sn solder.
It is known from US-A 4,914,081 to apply a metal layer of silver or copper or tin or lead or zinc or cadmium or indium or nickel or their alloys to a high-temperature superconductor by electrolytic deposition.
EP 0592797 B1 discloses a method of producing a rotationally symmetrical molding of a high-temperature superconductor in which the metal, preferably of silver or gold or of an alloy of these metals, introduced into the fusion mold acts as a bypass with good conduction if the high-temperature superconductor is to be used for screening purposes. There are no data therein about a method of alloying, for example, a silver fusion mold.
The use of an electrical bypass of pure noble metal is unsuitable for a use of a high-temperature superconductor as current limiter in alternating-current lines, in particular for electrical powers of 2 1 MW, since it is unsuitable for an economical current limita-tion because of its low electrical resistivity, for example, of 0.35 ~Q x cm at 77 K for silver. An electri-cal bypass whose electrical resistance is less than that of the high-temperature superconductor in the non-super-conducting state would be desirable.
Accordingly, one object of the invention, as it is defined in patent claim 1, is to provide a method of alloying a noble-metal bypass layer of a high-temperature superconductor of the type mentioned at the outset, with which the electrical resistivity of a previously pure noble-metal bypass layer can be increased by more than 10 times at a temperature of 77 K.
30Advantageous refinements of the invention are defined in the dependent patent claims.
An advantage of the invention is that a high-temperature superconductor of this type can be used as current limiter in alternating-current lines.
35According to an advantageous refinement of the invention, an increase in the electrical resistivity of a previously pure silver bypass layer by 20 times can be achieved.
.
.
BRIEF DESCRIPTION OF THE DRA~INGS
A more complete appreciation of the invention and many of the attendant advantages thereof will be readily obtained as the same becomes better understood by reference to the following detailed description when considered in connection with the accompanying drawing, wherein the sole figure shows a layer sequence of high-temperature superconductor, noble-metal bypass layer and alloy-metal layer before alloying.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
Referring now to the drawing, in the sole figure, a layer of a ceramic high-temperature superconductor (1) which has a uniform superconductor layer thickness (dl) is in good electrical and thermally conducting contact with a noble-metal bypass layer (2) which has a uniform bypass layer thickness (d2). Applied to said noble-metal bypass layer (2) is an alloy-metal layer (3) having a uniform alloy-metal layer thickness (d3).
The high-temperature superconductor (1) is preferably of the type: Bi2+xEA3Cu2Oy~ where -0.15 < x <
0.9, 8 < y < 8.3 and EA - an alkaline earth metal or a mixture of alkaline earth metals, in particular a mixture of Sr and Ca in the ratio Sr Ca = (2 + z) : (1 - z), where 0 < z < 0.2.
The noble-metal bypass layer (2) to be alloyed is preferably composed of silver (Ag). The alloy-metal layer (3) contains lead (Pb) and/or bismuth (Bi) and/or tin (Sn) and/or indium (In) and/or gallium (Ga) and/or aluminum (Al) and/or mercury (Hg), preferably lead or bismuth or gallium or aluminum.
The noble-metal bypass layer (2) is preferably alloyed by diffusing the base-metals of the alloy-metal layer (3) by means of a thermal treatment.
It is important that the high-temperature superconductor (1) is adjusted to a superconductor laver thickness (dl) of < 500 ~m. The ratio of a bypass layer thickness (d2) of the noble-metal bypass layer (2) to the superconductor layer thickness (dl) should be ad~usted to < 1/5.
It goes without saying that the desired alloy can also be produced by ion implantation, but this is associated with relatively high cost.
A bismuth layer having an alloy-metal layer thickness (d3) of 0.5 ~m is applied to a noble-metal bypass layer (2) of a silver foil having a bypass layer thickness (d2) of 50 ~m:
a) by direct soldering onto the surface of the silver foil (2) or b) by immersing the silver foil (2) alone or the layer sequence: high-temperature superconductor (1) and noble-metal bypass layer (2) of silver in a Bi or Bi/Ag bath at a temperature of 400~C
or c) by sputtering Bi under vacuum or 20 d) by electrochemical deposition from a commercial Bi-containing solution.
Said layer structure produced in this way is then tempered at a tempering temperature in the 200~C - 400~C temperature range, preferably at 350~C, in a pure nitrogen atmosphere for a tempering time of 1 h.
It is important that oxidation of the Bi is prevented during this heat treatment.
Exemplary embodiment 1:
A 40 ~m thick silver foil (2) and a high-temperature superconductor (1) with 20 ~m silver were immersed in a hot bismuth bath at 400~C and then tempered in a nitrogen atmosphere at 350~C for 1 h.
Cooling was then carried out slowly to room temperature.
The electrical resistivity of the alloy produced was 6.28 ~Q x cm at 77 K.
Exemplary embodiment 2:
A 1 cm wide and 20 ~m thick aluminum foil was placed on a 2 cm wide and 50 ~m thick silver foil (2).
This was followed by a 1 hour tempering in a nitrogen atmosphere at 650 C. The electrical resistivity of the alloy produced was 8.8 ~Q x cm at 77 K.
Exemplary embodiment 3:
Silver foils (2) having layer thicknesses (d2) of 20 ~m, 30 ~m and 50 ~m were coated with liquid gallium so that they were then covered with an alloy-metal layer thickness (d3) of 10 ~m. These 3 specimens were tempered in air for 4 h at 90~C and then cooled.
The electrical resistivity of the alloy produced was 8.4 ~Q x cm and 5.0 ~Q x cm and 2.6 ~Q x cm, respectively, in each case at 77 Ki it increased with increasing tempering time and increasing tempering temperature. If the 3 specimens were tempered at 450~C
for 4 h, their electrical resistivity was > 10 ~Q x cm.
Preferably, the alloy metal gallium is tempered at a temperature in the 400~C - 500~C range for a time in the 1 h - 5 h range.
Obviously, numerous modifications and variations of the present invention are possible in light of the above teachings. It is therefore to be understood that, within the scope of the appended claims, the invention may be practiced otherwise than as specifically described herein.
The use of an electrical bypass of pure noble metal is unsuitable for a use of a high-temperature superconductor as current limiter in alternating-current lines, in particular for electrical powers of 2 1 MW, since it is unsuitable for an economical current limita-tion because of its low electrical resistivity, for example, of 0.35 ~Q x cm at 77 K for silver. An electri-cal bypass whose electrical resistance is less than that of the high-temperature superconductor in the non-super-conducting state would be desirable.
Accordingly, one object of the invention, as it is defined in patent claim 1, is to provide a method of alloying a noble-metal bypass layer of a high-temperature superconductor of the type mentioned at the outset, with which the electrical resistivity of a previously pure noble-metal bypass layer can be increased by more than 10 times at a temperature of 77 K.
30Advantageous refinements of the invention are defined in the dependent patent claims.
An advantage of the invention is that a high-temperature superconductor of this type can be used as current limiter in alternating-current lines.
35According to an advantageous refinement of the invention, an increase in the electrical resistivity of a previously pure silver bypass layer by 20 times can be achieved.
.
.
BRIEF DESCRIPTION OF THE DRA~INGS
A more complete appreciation of the invention and many of the attendant advantages thereof will be readily obtained as the same becomes better understood by reference to the following detailed description when considered in connection with the accompanying drawing, wherein the sole figure shows a layer sequence of high-temperature superconductor, noble-metal bypass layer and alloy-metal layer before alloying.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
Referring now to the drawing, in the sole figure, a layer of a ceramic high-temperature superconductor (1) which has a uniform superconductor layer thickness (dl) is in good electrical and thermally conducting contact with a noble-metal bypass layer (2) which has a uniform bypass layer thickness (d2). Applied to said noble-metal bypass layer (2) is an alloy-metal layer (3) having a uniform alloy-metal layer thickness (d3).
The high-temperature superconductor (1) is preferably of the type: Bi2+xEA3Cu2Oy~ where -0.15 < x <
0.9, 8 < y < 8.3 and EA - an alkaline earth metal or a mixture of alkaline earth metals, in particular a mixture of Sr and Ca in the ratio Sr Ca = (2 + z) : (1 - z), where 0 < z < 0.2.
The noble-metal bypass layer (2) to be alloyed is preferably composed of silver (Ag). The alloy-metal layer (3) contains lead (Pb) and/or bismuth (Bi) and/or tin (Sn) and/or indium (In) and/or gallium (Ga) and/or aluminum (Al) and/or mercury (Hg), preferably lead or bismuth or gallium or aluminum.
The noble-metal bypass layer (2) is preferably alloyed by diffusing the base-metals of the alloy-metal layer (3) by means of a thermal treatment.
It is important that the high-temperature superconductor (1) is adjusted to a superconductor laver thickness (dl) of < 500 ~m. The ratio of a bypass layer thickness (d2) of the noble-metal bypass layer (2) to the superconductor layer thickness (dl) should be ad~usted to < 1/5.
It goes without saying that the desired alloy can also be produced by ion implantation, but this is associated with relatively high cost.
A bismuth layer having an alloy-metal layer thickness (d3) of 0.5 ~m is applied to a noble-metal bypass layer (2) of a silver foil having a bypass layer thickness (d2) of 50 ~m:
a) by direct soldering onto the surface of the silver foil (2) or b) by immersing the silver foil (2) alone or the layer sequence: high-temperature superconductor (1) and noble-metal bypass layer (2) of silver in a Bi or Bi/Ag bath at a temperature of 400~C
or c) by sputtering Bi under vacuum or 20 d) by electrochemical deposition from a commercial Bi-containing solution.
Said layer structure produced in this way is then tempered at a tempering temperature in the 200~C - 400~C temperature range, preferably at 350~C, in a pure nitrogen atmosphere for a tempering time of 1 h.
It is important that oxidation of the Bi is prevented during this heat treatment.
Exemplary embodiment 1:
A 40 ~m thick silver foil (2) and a high-temperature superconductor (1) with 20 ~m silver were immersed in a hot bismuth bath at 400~C and then tempered in a nitrogen atmosphere at 350~C for 1 h.
Cooling was then carried out slowly to room temperature.
The electrical resistivity of the alloy produced was 6.28 ~Q x cm at 77 K.
Exemplary embodiment 2:
A 1 cm wide and 20 ~m thick aluminum foil was placed on a 2 cm wide and 50 ~m thick silver foil (2).
This was followed by a 1 hour tempering in a nitrogen atmosphere at 650 C. The electrical resistivity of the alloy produced was 8.8 ~Q x cm at 77 K.
Exemplary embodiment 3:
Silver foils (2) having layer thicknesses (d2) of 20 ~m, 30 ~m and 50 ~m were coated with liquid gallium so that they were then covered with an alloy-metal layer thickness (d3) of 10 ~m. These 3 specimens were tempered in air for 4 h at 90~C and then cooled.
The electrical resistivity of the alloy produced was 8.4 ~Q x cm and 5.0 ~Q x cm and 2.6 ~Q x cm, respectively, in each case at 77 Ki it increased with increasing tempering time and increasing tempering temperature. If the 3 specimens were tempered at 450~C
for 4 h, their electrical resistivity was > 10 ~Q x cm.
Preferably, the alloy metal gallium is tempered at a temperature in the 400~C - 500~C range for a time in the 1 h - 5 h range.
Obviously, numerous modifications and variations of the present invention are possible in light of the above teachings. It is therefore to be understood that, within the scope of the appended claims, the invention may be practiced otherwise than as specifically described herein.
Claims (7)
1. A method of alloying a noble-metal bypass layer (2) of a ceramic high-temperature superconductor (1), a) in which at least one alloy-metal layer (3) is applied to the layer (2) to be alloyed, b) wherein the high-temperature superconductor (1) is adjusted to a superconductor layer thickness (dl) of < 500 µm, c) wherein the ratio of the noble-metal bypass layer thickness (d2) of the noble-metal bypass layer (2) to the superconductor layer thickness (dl) is adjusted to < 1/5 and d) wherein the thickness (d3) of the alloy-metal layer (3) is adjusted so that the electrical resistivity of the total bypass layer comprising the noble-metal bypass layer (2) and the alloy-metal layer (3) to the high-temperature superconductor (1) is increased by more than 10 times with respect to the electrical resistivity of a previously pure, unalloyed noble-metal bypass layer (2) at a temperature of 77 K.
2. The method as claimed in claim 1, wherein the alloy-metal layer (3) is applied to the layer (2, 1) to be alloyed by direct soldering of at least one alloy metal to at least one surface of the layer (2) to be alloyed.
3. The method as claimed in claim 1, wherein the alloy metal layer (3) is applied to the layer (2) to be alloyed by immersion of the layer (2) to be alloyed alone or of the layer sequence: high-temperature superconductor (1) and noble-metal bypass layer (2) in a bath containing at least one alloy metal.
4. The method as claimed in claim 1, wherein the alloy metal layer (3) is applied to the layer (2) to be alloyed by sputtering at least one alloy metal under vacuum.
5. The method as claimed in any of the preceding claims, a) wherein the noble-metal bypass layer (2) contains predominantly silver and b) wherein aluminum is used as alloy metal for the alloy-metal layer (3).
6. The method as claimed in any of the preceding claims, wherein this layer structure is tempered at a tempering temperature of at least 80°C for at least 50 min.
7. The method as claimed in any of claims 1 to 5, a) wherein the noble-metal bypass layer (2) contains predominantly silver, b) is alloyed with gallium and c) is tempered at a tempering temperature in the 400°C - 500°C range for a tempering time in the 1 h - 5 h range.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| DE19746975A DE19746975C1 (en) | 1997-10-24 | 1997-10-24 | Alloying of a precious metal by-pass layer of a high temperature superconductor |
| DE19746975.2 | 1997-10-24 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA2249790A1 true CA2249790A1 (en) | 1999-04-24 |
Family
ID=7846473
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA002249790A Abandoned CA2249790A1 (en) | 1997-10-24 | 1998-10-06 | Method of alloying a noble-metal bypass layer of a high-temperature superconductor |
Country Status (5)
| Country | Link |
|---|---|
| EP (1) | EP0911890A3 (en) |
| JP (1) | JPH11219627A (en) |
| CA (1) | CA2249790A1 (en) |
| DE (1) | DE19746975C1 (en) |
| NO (1) | NO984945L (en) |
Families Citing this family (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US6762673B1 (en) * | 1998-02-10 | 2004-07-13 | American Superconductor Corp. | Current limiting composite material |
Family Cites Families (7)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US4941081A (en) * | 1985-06-03 | 1990-07-10 | Microfast Controls Corp. | Interrupt zone in rung of ladder program in programmable controller |
| US5079223A (en) * | 1988-12-19 | 1992-01-07 | Arch Development Corporation | Method of bonding metals to ceramics |
| US5296456A (en) * | 1989-08-09 | 1994-03-22 | Furukawa Electric Co., Ltd. | Ceramic superconductor wire and method of manufacturing the same |
| CH682358A5 (en) * | 1991-02-22 | 1993-08-31 | Asea Brown Boveri | Ceramic high temp. superconductor prodn. - by pouring starting material into mould, heating, cooling, thermally treating in oxygen@ and cooling, for shield magnetic fields in switching elements |
| JPH05251761A (en) * | 1992-03-04 | 1993-09-28 | Mitsubishi Electric Corp | Current limiting conductor using oxide superconductive film |
| JP3185467B2 (en) * | 1993-04-28 | 2001-07-09 | 日立電線株式会社 | Oxide superconducting conductor |
| JPH0883932A (en) * | 1994-09-09 | 1996-03-26 | Sumitomo Electric Ind Ltd | Current limiting element |
-
1997
- 1997-10-24 DE DE19746975A patent/DE19746975C1/en not_active Expired - Fee Related
-
1998
- 1998-10-01 EP EP98810989A patent/EP0911890A3/en not_active Withdrawn
- 1998-10-06 CA CA002249790A patent/CA2249790A1/en not_active Abandoned
- 1998-10-23 NO NO984945A patent/NO984945L/en not_active Application Discontinuation
- 1998-10-26 JP JP10304207A patent/JPH11219627A/en active Pending
Also Published As
| Publication number | Publication date |
|---|---|
| EP0911890A3 (en) | 1999-05-12 |
| NO984945D0 (en) | 1998-10-23 |
| JPH11219627A (en) | 1999-08-10 |
| DE19746975C1 (en) | 1999-03-11 |
| NO984945L (en) | 1999-04-26 |
| EP0911890A2 (en) | 1999-04-28 |
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Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| FZDE | Discontinued |