JP4171253B2 - Low resistance composite conductor and method of manufacturing the same - Google Patents
Low resistance composite conductor and method of manufacturing the same Download PDFInfo
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- JP4171253B2 JP4171253B2 JP2002199957A JP2002199957A JP4171253B2 JP 4171253 B2 JP4171253 B2 JP 4171253B2 JP 2002199957 A JP2002199957 A JP 2002199957A JP 2002199957 A JP2002199957 A JP 2002199957A JP 4171253 B2 JP4171253 B2 JP 4171253B2
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- 239000004020 conductor Substances 0.000 title claims description 205
- 239000002131 composite material Substances 0.000 title claims description 106
- 238000004519 manufacturing process Methods 0.000 title claims description 19
- 239000002887 superconductor Substances 0.000 claims description 99
- 239000010949 copper Substances 0.000 claims description 79
- RYGMFSIKBFXOCR-UHFFFAOYSA-N Copper Chemical compound [Cu] RYGMFSIKBFXOCR-UHFFFAOYSA-N 0.000 claims description 50
- 229910052802 copper Inorganic materials 0.000 claims description 50
- BQCADISMDOOEFD-UHFFFAOYSA-N Silver Chemical compound [Ag] BQCADISMDOOEFD-UHFFFAOYSA-N 0.000 claims description 47
- 229910052709 silver Inorganic materials 0.000 claims description 47
- 239000004332 silver Substances 0.000 claims description 47
- 229910052782 aluminium Inorganic materials 0.000 claims description 21
- XAGFODPZIPBFFR-UHFFFAOYSA-N aluminium Chemical compound [Al] XAGFODPZIPBFFR-UHFFFAOYSA-N 0.000 claims description 21
- 229910001316 Ag alloy Inorganic materials 0.000 claims description 20
- 229910000838 Al alloy Inorganic materials 0.000 claims description 19
- 229910001020 Au alloy Inorganic materials 0.000 claims description 19
- 229910000881 Cu alloy Inorganic materials 0.000 claims description 19
- PCHJSUWPFVWCPO-UHFFFAOYSA-N gold Chemical compound [Au] PCHJSUWPFVWCPO-UHFFFAOYSA-N 0.000 claims description 19
- 229910052737 gold Inorganic materials 0.000 claims description 19
- 239000010931 gold Substances 0.000 claims description 19
- 239000003353 gold alloy Substances 0.000 claims description 19
- PXHVJJICTQNCMI-UHFFFAOYSA-N Nickel Chemical compound [Ni] PXHVJJICTQNCMI-UHFFFAOYSA-N 0.000 claims description 18
- 241000954177 Bangana ariza Species 0.000 claims description 17
- XEEYBQQBJWHFJM-UHFFFAOYSA-N Iron Chemical compound [Fe] XEEYBQQBJWHFJM-UHFFFAOYSA-N 0.000 claims description 16
- 229910052751 metal Inorganic materials 0.000 claims description 16
- 239000002184 metal Substances 0.000 claims description 16
- 229910000679 solder Inorganic materials 0.000 claims description 16
- 229910052761 rare earth metal Inorganic materials 0.000 claims description 14
- 238000000034 method Methods 0.000 claims description 12
- 229910000640 Fe alloy Inorganic materials 0.000 claims description 8
- 229910000990 Ni alloy Inorganic materials 0.000 claims description 8
- 229910001069 Ti alloy Inorganic materials 0.000 claims description 8
- 229910052742 iron Inorganic materials 0.000 claims description 8
- 229910052759 nickel Inorganic materials 0.000 claims description 8
- 230000007704 transition Effects 0.000 claims description 8
- 239000012298 atmosphere Substances 0.000 claims description 4
- 238000000576 coating method Methods 0.000 claims description 4
- 229910001000 nickel titanium Inorganic materials 0.000 claims description 4
- 239000011888 foil Substances 0.000 claims description 3
- 239000000463 material Substances 0.000 description 29
- IJGRMHOSHXDMSA-UHFFFAOYSA-N Atomic nitrogen Chemical compound N#N IJGRMHOSHXDMSA-UHFFFAOYSA-N 0.000 description 22
- 239000013078 crystal Substances 0.000 description 16
- 238000001816 cooling Methods 0.000 description 12
- 239000007788 liquid Substances 0.000 description 11
- 229910052757 nitrogen Inorganic materials 0.000 description 11
- 239000013590 bulk material Substances 0.000 description 8
- 239000000843 powder Substances 0.000 description 6
- 238000004544 sputter deposition Methods 0.000 description 6
- 229910000831 Steel Inorganic materials 0.000 description 5
- QVGXLLKOCUKJST-UHFFFAOYSA-N atomic oxygen Chemical compound [O] QVGXLLKOCUKJST-UHFFFAOYSA-N 0.000 description 5
- 239000001301 oxygen Substances 0.000 description 5
- 229910052760 oxygen Inorganic materials 0.000 description 5
- 239000010959 steel Substances 0.000 description 5
- 238000010438 heat treatment Methods 0.000 description 4
- 239000002994 raw material Substances 0.000 description 4
- 238000005476 soldering Methods 0.000 description 4
- 238000000151 deposition Methods 0.000 description 3
- 239000010408 film Substances 0.000 description 3
- 238000002844 melting Methods 0.000 description 3
- 230000008018 melting Effects 0.000 description 3
- 239000000853 adhesive Substances 0.000 description 2
- 230000001070 adhesive effect Effects 0.000 description 2
- 229910045601 alloy Inorganic materials 0.000 description 2
- 239000000956 alloy Substances 0.000 description 2
- 238000000137 annealing Methods 0.000 description 2
- 239000011248 coating agent Substances 0.000 description 2
- 238000009826 distribution Methods 0.000 description 2
- 230000000694 effects Effects 0.000 description 2
- 230000020169 heat generation Effects 0.000 description 2
- 229910001120 nichrome Inorganic materials 0.000 description 2
- 238000005245 sintering Methods 0.000 description 2
- 239000010935 stainless steel Substances 0.000 description 2
- 229910001220 stainless steel Inorganic materials 0.000 description 2
- 229910000883 Ti6Al4V Inorganic materials 0.000 description 1
- ATJFFYVFTNAWJD-UHFFFAOYSA-N Tin Chemical compound [Sn] ATJFFYVFTNAWJD-UHFFFAOYSA-N 0.000 description 1
- 238000010586 diagram Methods 0.000 description 1
- 230000005611 electricity Effects 0.000 description 1
- LQBJWKCYZGMFEV-UHFFFAOYSA-N lead tin Chemical compound [Sn].[Pb] LQBJWKCYZGMFEV-UHFFFAOYSA-N 0.000 description 1
- 239000011812 mixed powder Substances 0.000 description 1
- 239000012299 nitrogen atmosphere Substances 0.000 description 1
- 230000003647 oxidation Effects 0.000 description 1
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- 238000003825 pressing Methods 0.000 description 1
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- 238000011282 treatment Methods 0.000 description 1
- 239000011800 void material Substances 0.000 description 1
- 239000013585 weight reducing agent Substances 0.000 description 1
Images
Classifications
-
- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
- Y02E40/00—Technologies for an efficient electrical power generation, transmission or distribution
- Y02E40/60—Superconducting electric elements or equipment; Power systems integrating superconducting elements or equipment
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- Containers, Films, And Cooling For Superconductive Devices (AREA)
- Non-Insulated Conductors (AREA)
- Superconductors And Manufacturing Methods Therefor (AREA)
Description
【０００１】
【発明の属する技術分野】
本発明は、実質的に低抵抗の複合導体およびその製造方法、さらに、このような複合導体を用いた機器に関する。
【０００２】
【従来の技術】
電気を通す導体として、現在、銅が最も多く使用されている。これは、室温での比抵抗が銀とほぼ同程度で他の物質に比べ最も低く、かつ比較的安価であることによる。導体の比抵抗を下げる方法には、導体を冷却する方法がある。銅の場合、液体窒素温度(77K)に冷却すると、比抵抗は約1/7の約2.5×10-9Ωｍとなる 。
【０００３】
超伝導線材は、超伝導転移温度以下に冷却する必要はあるものの、電気抵抗がほぼゼロであり、理想の導体である。金属系超伝導線材は、線材としての完成度も高く、ＭＲＩ等のマグネットとして実用化されているが、極低温への冷却の必要性から広く普及するに至っていない。一方、液体窒素温度で超伝導になる酸化物系の超伝導材料には、大別してBi系と Y系の２種類がある。Bi系は主に銀シース付きのテープ線材として、また、 Y系は金属テープ表面にバッファ層を形成し、その上に超伝導薄膜を形成したテープ線材の開発が進められている。これらの線材は、高特性が得られた場合、取り扱いの容易な液体窒素で冷却できるため、実用化の期待が高まっている。そして、これらの線材を用いた電気機器の開発及び普及が期待されている。
【０００４】
液体窒素温度で十分な臨界電流密度を有するバルク材料として、単結晶状のREBa2Cu3O7-x(REは、Yを含む希土類元素)中にRE2BaCuO5が微細分散した材料が知られている。このような材料は、単結晶状であるため、大型の材料の製造には、技術的な限界があり、現在、直径 100mm程度のものが得られるに過ぎない。
【０００５】
【発明が解決しようとする課題】
実質的に抵抗が十分低く、かつ安価で取り扱いの容易な導体が製造可能であれば、必ずしも電気抵抗が完全にゼロである超伝導材料である必要はない。そこで、本発明は、常伝導導体と超伝導材料を組み合わせることによって、簡便に超伝導転移温度以下で、常伝導導体の抵抗を減らし、さらに通電時の通電損失等を低減する、低抵抗複合導体およびその製造方法、並びにこの複合導体を用いた機器を提供することを目的とする。
【０００６】
【課題を解決するための手段】
一例として、主にY系の酸化物超伝導バルク材料では、既に77Kにおいて高い臨界電流密度が得られている。このような材料に代表される超伝導体を常伝導導体に電気的に接続又は貼り付けることにより、容易にかつ高い信頼度で低抵抗の複合導体が得られる。すなわち、本発明は下記の通りである。
（１） 銅、銅合金、アルミニウム、アルミニウム合金、銀、銀合金、金又は金合金の１種又は２種以上からなる常伝導導体表面の一部又は全体に、一部又は全部がREBa2Cu3O7-x系超伝導体（ここで、REはYを含む希土類元素の１種類又はその組合せ）からなる複数のバルク超伝導体を接続してなる複合導体であって、前記バルク超伝導体の超伝導転移温度以下における前記複合導体の見かけ上の比抵抗が、前記温度における銅の比抵抗より低いことを特徴とする低抵抗複合導体。
（２） 鉄、鉄合金、ニッケル、ニッケル合金、チタン合金の１種又は２種以上からなる常伝導導体表面の一部又は全体に、一部又は全部がREBa2Cu3O7-x系超伝導体（ここで、REはYを含む希土類元素の１種類又はその組合せ）からなる複数のバルク超伝導体を接続してなる複合導体であって、前記バルク超伝導体の超伝導転移温度以下における前記複合導体の見かけ上の比抵抗が、前記温度における銅の比抵抗より低いことを特徴とする低抵抗複合導体。
【０００７】
（３） 銅、銅合金、アルミニウム、アルミニウム合金、銀、銀合金、金又は金合金の１種又は２種以上からなる常伝導導体表面の一部又は全体に、一部又は全部がREBa2Cu3O7-x系超伝導体（ここで、REはYを含む希土類元素の１種類又はその組合せ）からなる複数のバルク超伝導体を接続してなる複合導体であって、７７Ｋにおける前記複合導体の見かけ上の比抵抗が、７７Ｋにおける銅の比抵抗より低いことを特徴とする低抵抗複合導体。
（４） 鉄、鉄合金、ニッケル、ニッケル合金、チタン合金の１種又は２種以上からなる常伝導導体表面の一部又は全体に、一部又は全部がREBa2Cu3O7-x系超伝導体（ここで、REはYを含む希土類元素の１種類又はその組合せ）からなる複数のバルク超伝導体を接続してなる複合導体であって、７７Ｋにおける前記複合導体の見かけ上の比抵抗が、７７Ｋにおける銅の比抵抗より低いことを特徴とする低抵抗複合導体。
（５） 前記バルク超伝導体は、前記常伝導導体内の電流経路に対して並列の関係にある電流経路を形成していることを特徴とする（１）〜（４）の何れかに記載の低抵抗複合導体。
（６） 前記常伝導導体の両端部に銅、銅合金、アルミニウム、アルミニウム合金、銀、銀合金、金又は金合金の１種又は２種以上の電極部を有することを特徴とする（２）又は（４）に記載の低抵抗複合導体。
【０００８】
（７） 前記バルク超伝導体の一部又は全部の長手方向が、該バルク超伝導体の結晶学的方位においてｃ軸と垂直方向であることを特徴とする（１）〜（５）の何れかに記載の低抵抗複合導体。
（８） 前記常伝導導体又は前記バルク超伝導体の少なくとも一方が、棒状又は板状の形状を有してなることを特徴とする（１）〜（７）の何れかに記載の低抵抗複合導体。
（９） 前記バルク超伝導体を前記常伝導導体で挟んで接続してなる複合導体あることを特徴とする（１）〜（８）の何れかに記載の低抵抗複合導体。
【０００９】
（１０） 前記接続の一部又は全部が、銅、銅合金、アルミニウム、アルミニウム合金、銀、銀合金、金又は金合金の１種又は２種以上である金属を介する常伝導接続であることを特徴とする（１）〜（９）の何れかに記載の低抵抗複合導体。
（１１） 前記バルク超伝導体又は前記常伝導導体の少なくとも一方の一部又は全部に平面を有し、該平面内において前記バルク超伝導体と前記常伝導導体が常伝導接続されてなることを特徴とする（１０）に記載の低抵抗複合導体。
（１２） 前記常伝導接続の一部又は全部が、前記常伝導導体と同種又は異種の常伝導体を用いてなることを特徴とする（１０）又は（１１）に記載の低抵抗複合導体。
（１３） 前記接続部の厚みが100μm以下であることを特徴とする（１０）〜（１２）の何れかに記載の低抵抗複合導体。
（１４） 前記バルク超伝導体の長手方向の一部又は全部が、通電方向であることを特徴とする（１）〜（１３）の何れかに記載の低抵抗複合導体。
【００１０】
（１５） 銅、銅合金、アルミニウム、アルミニウム合金、鉄、鉄合金、ニッケル、ニッケル合金、チタン合金、銀、銀合金、金又は金合金の１種又は２種以上からなる常伝導導体表面の一部又は全部に、常伝導体を介して、一部又は全部がREBa2Cu3O7-x系超伝導体（ここで、REはYを含む希土類元素の１種類又はその組合せ）からなる複数の超伝導体を配置し、必要に応じて加圧して接続処理する複合導体の製造方法であって、７７Ｋにおける前記複合導体の見かけ上の比抵抗が、前記温度における銅の比抵抗より低いことを特徴とする低抵抗複合導体の製造方法。
（１６） 前記常伝導体が半田であることを特徴とする（１５）に記載の低抵抗複合導体の製造方法。
（１７） 銅、銅合金、アルミニウム、アルミニウム合金、鉄、鉄合金、ニッケル、ニッケル合金、チタン合金、銀、銀合金、金又は金合金の１種又は２種以上からなる常伝導導体表面の一部又は全部に、常伝導体を介して、一部又は全部がREBa2Cu3O7-x系超伝導体（ここで、REはYを含む希土類元素の１種類又はその組合せ）からなる超伝導体を配置し、必要に応じて加圧した後、減圧雰囲気又は真空中で熱処理する複合導体の製造方法であって、７７Ｋにおける前記複合導体の見かけ上の比抵抗が、前記温度における銅の比抵抗より低いことを特徴とする低抵抗複合導体の製造方法。
（１８） 前記超伝導体が、前記常伝導導体内の電流経路に対して並列の関係にある電流経路を形成するように配置することを特徴とする（１５）〜（１７）の何れかに記載の低抵抗複合導体の製造方法。
（１９） 前記常伝導体が、銅、銅合金、アルミニウム、アルミニウム合金、銀、銀合金、金又は金合金のペースト又は箔であることを特徴とする（１５）又は（１７）に記載の低抵抗複合導体の製造方法。
（２０） 前記超伝導体の表面に銅、銅合金、アルミニウム、アルミニウム合金、銀、銀合金、金又は金合金の１種又は２種以上の被覆を有することを特徴とする（１５）〜（１９）の何れかに記載の低抵抗複合導体の製造方法。
【００１１】
（２１） （１）〜（１４）の何れかに記載の低抵抗複合導体を少なくとも一部に配してなることを特徴とする通電用部材。
（２２） （１）〜（１４）の何れかに記載の低抵抗複合導体を少なくとも一部に配してなることを特徴とする電流リード。
（２３） （２１）に記載の通電用部材又は（２２）に記載の電流リードを有してなることを特徴とする超伝導トランス。
（２４） （２１）に記載の通電用部材又は（２２）に記載の電流リードを有してなることを特徴とする磁場発生装置。
【００１２】
【発明の実施の形態】
図１ (a)に示すように、銅、銅合金、アルミニウム、アルミニウム合金、銀、銀合金、金又は金合金の良導体に代表される常伝導導体に通電した場合、通電流は、抵抗値が最小になるように、導体内をほぼ均一に流れる。図１ (b)のように前記常伝導導体の表面内に超伝導体の一部又は全部を電気的に接続し、超伝導体の超伝導転移温度以下に冷却した場合、通電電流は、導体全体を均一に流れるのではなく、導体全体の抵抗値が最小になるように、抵抗がゼロの超伝導体により高い電流密度で流れようとする。超伝導体への分流の割合は、超伝導体と常伝導導体との接触抵抗、超伝導体の臨界電流や常伝導導体の比抵抗等によって変化し、超伝導体の臨界電流以下の通電においては、接触抵抗が小さいほど、また、常伝導導体の比抵抗が大きいほど、超伝導体への分流割合は大きくなる。電気抵抗がゼロである超伝導体への分流が大きいほど、複合導体全体としての抵抗は減少し、それに応じて複合導体内での発熱も減少する。
【００１３】
超伝導体と常伝導導体との接触抵抗を減らすには、接触面積を大きく取るようにすれば良く、超伝導体および常伝導導体の少なくとも一方が、平面を有し、この平面内において接続されていることが望ましい。さらに、体積当たりの表面積を大きくするために、超伝導体および常伝導導体の少なくとも一方が、棒状又は板状の形状を有し、かつ超伝導体の少なくとも片面の全面が常伝導導体と接合していることが望ましい。
【００１４】
超伝導体の材質は、REBa2Cu3O7-x系超伝導体（ここで、REはYを含む希土類元素の１種類又はその組合せ）であり、単結晶状のREBa2Cu3O7-x系にRE2BaCuO5が微細分散した組織を有するバルク材料が望ましい。また、a−b面内にマイクロクラックが入りやすいことから、単結晶状のREBa2Cu3O7-x超伝導相のｃ軸がバルク超伝導体の長手方向に対し垂直であることが望ましい。
【００１５】
複数の超伝導体を常伝導導体表面に配置する本願発明では、図２（ａ）に示すように直列に配置することが望ましい。さらに、望ましくは図２（ｂ）のように複数の超伝導体の列を千鳥状に配置し、超伝導体同士の隙間（図中のdおよびg）を小さくし、極力超伝導体に電流が多く流れるようにすることが望ましい。
【００１６】
常伝導導体の材質は、安価で抵抗率の低い銅、銅合金、アルミニウム、アルミニウム合金、銀、銀合金、金又は金合金である。さらに、耐酸化性の観点では銀が、また、軽量化の観点ではアルミが優れている。常伝導導体の熱膨張率と超伝導体の熱膨張率は一般に異なり、また、超伝導体と常伝導導体とを接続した時点での温度と接続された導体を冷却した時点での温度が一般に異なるため、超伝導体および常伝導導体中には応力が働く。この応力が大きい場合、導体が反ったり、超伝導体が破損する可能性がある。したがって、常伝導導体の表面に超伝導体を接続する等の応力が対称的にバランスするような対称的な配置が望ましい。また、高剛性の材料により低抵抗複合導体そのものを補強することは、さらに望ましい。
【００１７】
常伝導体の長さが比較的長い場合は、上記理由から常伝導金属の選定は、電気伝導度の大きい材料よりは、むしろ超伝導材料の熱膨張挙動に近い熱膨張挙動を示す材料が優先される。酸化物超伝導体は、一般に圧縮応力には比較的強いが、引っ張り応力には比較的弱い。単結晶状のREBa2Cu3O7-x系に RE2BaCuO5が微細分散した組織を有するバルク材料の場合、接続後の冷却時に比較的小さな圧縮応力がかかるため、Ｎｉ鋼、ニクロム、Ｔｉ合金等が適している。また冷却温度における圧縮応力を低減するには超伝導体と常伝導体が固定される温度がより低い温度にすればよく、低温半田等による接続が望ましい。また、Ｎｉ鋼、ニクロム、Ｔｉ合金等は、比抵抗が比較的高いため、端部の電極には、抵抗率の低い銅、銅合金、アルミニウム、アルミニウム合金、銀、銀合金、金又は金合金が特に望ましい。
また、超伝導体に均一に適度な圧縮応力をかけるには、板状の超伝導材料を常伝導体を挟み込む形で接続することが望ましい。さらにこの時、同種でかつ同形状の常伝導導体を板状超伝導体の両面に対称的に接続することが望ましい。
【００１８】
超伝導体と銀又は銀合金との接触抵抗は、比較的容易に小さくすることができる。そのため、予め超伝導体の表面上に銀被膜を設けておき、被膜を有する面を常伝導体表面に接続することが望ましい。このような超伝導体を常伝導導体に半田等を用いて接続する場合、半田は一般に銅、銀、アルミニウム等の良導体に比べ比抵抗が大きいため、極力半田等の超伝導体と常伝導導体の間に存在する金属層の厚さは、薄いことが望ましい。具体的には、加圧状態での接続によって得られる100μm以下である。
【００１９】
超伝導体と常伝導導体との接続方法には、大別して、錫および鉛等を主成分とする半田による方法と銀ペースト等の金属ペースト又は箔による方法とがある。半田は、室温での局所的な加熱により容易に接合処理できるなど、簡便な作業で処理できる点が優れている。半田接続の場合、接続部の金属層の厚さは、通常100〜50m程度となる。また、銀ペースト等の接着剤も次の点で優れている。銀ペーストを接着剤として用い、加熱処理により焼結させた場合は、銀そのものの比抵抗が小さいことや、焼結による接合部の金属層が収縮することにより、25μm 以下の薄い金属層が得られるため接続抵抗を半田接続に比べ低減できる。この焼結工程においては、ボイド除去の観点から、減圧雰囲気中又は真空中での加熱処理が望ましい。
【００２０】
前述の低抵抗複合導体は、抵抗が小さく、発熱が小さいため、超伝導体又は超伝導コイルに通電するための通電用部材又は電流リードとして、応用が可能である。
また、このような電流リードは、超伝導転移温度以下での冷却を必要とする超伝導トランスや、直冷式又は伝導冷却式超伝導マグネット等の磁場発生装置のリードとして優れている。
【００２１】
【実施例】
（実施例１）
Y2O3、BaO2、CuOの各原料粉末を、各金属元素のモル比(Y:Ba:Cu)が(13:17:24)になるように混合し、さらに、この混合粉に0.5質量%のPtを添加し、混合した原料粉末を作製した。この原料粉末を 900℃、酸素気流中で仮焼した。ラバープレス機を用いて、この仮焼粉を2ton/cm2の圧力で直径55mm、厚さ20mmの円盤状成形体に成形した。
【００２２】
これを大気中で1150℃まで8時間で昇温し、1時間保持した。その後、Sm系の種結晶を用い、1040℃で、盤面の法線が c軸にほぼ一致するように種結晶を配置した。しかる後、1005℃に30分で降温し、さらに、970℃まで220時間かけて徐冷し、結晶成長を行った。続いて、20時間で室温まで冷却した。得られた材料を厚さ 1.0mmにスライス加工し、さらに30mm×2mm×1mmの棒状バルク超伝導材料および25mm×8mm×1mmの板状バルク超伝導材料を作製した。このようにして得られた材料は、単結晶状のYBa2Cu3O7-x相中に1μm 程度のY2BaCuO5相が微細分散した組織を有していた。また、YBa2Cu3O7-x相のc軸は、棒表面の最も広い平面の法線方向および板面の法線方向に対応していた。
【００２３】
これらの板状試料表面に銀を約2μmスパッタにより成膜した後、酸素気流中でアニール処理した。アニール処理の熱処理パターンは、室温から600℃まで6時間で昇温し、1時間保持した後、450℃まで2時間で降温し、さらに380℃まで60時間で降温、室温まで12時間で冷却した。
【００２４】
これらの板状試料および板状試料を、図３(a)〜(c)に示した配置で、150mm ×8mm × 5mmサイズの銅の常伝導導体に、銀を含有する半田を用いて電気的に接続し、低抵抗複合導体を作製した。このとき、通常の半田付けでは金属層の厚さが100μm程度になったが、加圧しながら半田を固化させることにより、銅と超伝導体間の金属層の厚さを、約 50μmまで低減することができた。そして、それぞれの接続方法により作製された低抵抗複合導体に電流導入端子および電圧端子を取り付けた後、液体窒素中に浸し、超伝導体を超伝導状態にした。
【００２５】
完成した各低抵抗複合導体に通電し、液体窒素温度 (77K)での抵抗を測定し、見かけ状の比抵抗を計算したところ、それぞれ、1.2×10-9Ωｍ、1.0×10-9Ωｍ、0.56×10-9Ωｍであった。銅の常伝導導体のみの場合の比抵抗は、2.5×10-9 Ωｍであり、十分に低い比抵抗を示すことがわかった。
【００２６】
（実施例２）
原料粉末をY2O3からDy2O3に変えるだけで、実施例1で述べた同様の方法により、Dy系のバルク材料を作製した。これを厚さ 0.6mmにスライス切断した後、30mm×2.5mm×0.6mmの棒状試料を作製した。このようにして得られた材料は、単結晶状のYBa2Cu3O7-x相中に1μm程度のDy2BaCuO5相が微細分散した組織を有していた。また、 DyBa2Cu3O7-x相のc軸は、棒表面の最も広い平面の法線方向に対応していた。
【００２７】
これらの棒状試料表面にスパッタ法により厚さ2μmの銀を成膜した後、図４に示すように、 150mm×7mm×5mmサイズの銀の常伝導導体の対向する２面に銀ペーストを用いて電気的に接続し、さらに、約1.3×102 Paの減圧下において約900℃で約 1時間加熱し、銀ペーストの銀粒子と棒状材料表面の銀の膜および銀の常伝導導体とを焼結させた。その後、室温から 600℃まで6時間で昇温し、1時間保持した後、450℃まで2時間で降温し、さらに380℃まで60時間で降温、室温まで 12時間で冷却し、さらに、酸素アニール処理を行い、低抵抗複合導体を作製した。
【００２８】
完成した各低抵抗複合導体を液体窒素で冷却し、 77Kでの電気抵抗を測定し、見かけの比抵抗を計算したところ、0.6×10-9Ωｍであった。銀の常伝導導体の みの場合の比抵抗は、2.6×10-9Ωｍであり、十分に低い抵抗値を示すことがわ かった。
【００２９】
（実施例３）
実施例１のY2O3をGd2O3に変えて、さらに銀を15質量%添加し、実施例１で作製したように円盤状成型体を作製した。
【００３０】
これを0.1原子%酸素の窒素雰囲気中で1150℃まで8時間で昇温し、1時間保持した。その後、Sm系の種結晶を用い、1040℃で、盤面の法線が c軸にほぼ一致するように種結晶を配置した。しかる後、1005℃に30分で降温し、さらに 970℃まで220時間かけて徐冷し、結晶成長を行った。続いて、室温まで 20時間で冷却した。得られた銀添加Gd系バルク材を、厚さ1.5mmにスライス加工し、30mm×2.5mm×1.5mmの棒状試料を作製した。このようにして得られた材料は、単結晶状のGdBa2Cu3O7-x相中に1μm程度のGd2BaCuO5相が微細分散した組織を有していた。また、GdBa2Cu3O7-x相の c軸は、棒表面の最も広い平面の法線方向に対応していた。
【００３１】
この棒状材料表面に銀を約 2μmスパッタにより成膜した後、室温から600℃まで6時間で昇温し、1時間保持した後、450℃まで 2時間で降温し、さらに380℃まで60時間で降温、室温まで12時間で冷却し、酸素アニール処理を行った。
【００３２】
次に、図５に示すように、厚さ 2mmのステンレス板２枚で補強された銅の常伝導導体に上記超伝導体を半田で接続し、低抵抗複合導体を作製した。
完成した低抵抗複合導体を液体窒素で冷却し、 77Kでの電気抵抗を測定し、見かけの比抵抗を計算したところ、 0.59×10-9Ωｍであった。銅の常伝導導体の みの場合の比抵抗は、2.5×10-9Ωｍであり、十分に低い抵抗値を示すことがわ かった。
【００３３】
（実施例４）
実施例２で作製した低抵抗複合導体２本を電流リードとして、既存の直冷式超伝導マグネットの電流リードに取り付けた。取り付け箇所は、既存のBi系電流リードの低温端側であり、既存の銅製のリードの一部を切り取った後、取り付けた。
【００３４】
10Tの磁場を発生するために70Aを連続通電し、低抵抗導体の有無による超伝導マグネットの到達冷却温度を比較した。低抵抗複合導体を挿入しない状態では、到達温度は4.5Kであったのに対し、低抵抗導体を挿入した場合は4.1Kにまで到達した。
この結果から、前記の低抵抗複合導体は、電流リードとして機能し、直冷式マグネットの性能を高めることが分かった。
【００３５】
（実施例５）
実施例１で述べた同様の方法により、 Y系のバルク材料を作製した。これを厚さ 0.6mmにスライス切断した後、20mm×7mm×0.6mmの棒状試料を作製した。このようにして得られた材料は、単結晶状のYBa2Cu3O7-x相中に1μm程度の Y2BaCuO5相が微細分散した組織を有していた。また、 YBa2Cu3O7-x相の c軸は、棒表面の平面法線および板面の法線方向に対応していた。
【００３６】
これらの棒状試料表面にスパッタ法により厚さ2μmの銀を成膜した後、図６に示すように80mm×7mm×5mmの２本の銅で超伝導体を挟み込むようにして、約80℃の融点を有する低温半田を用いて電気的に接続し、低抵抗複合導体を作製した。完成した各低抵抗複合導体を液体窒素で冷却し、 77Kでの電気抵抗を測定し、見かけの比抵抗を計算したところ、0.59×10-9Ωｍであった。銅の常伝導導体のみの場合の比抵抗は、2.5×10-9Ωｍであり、十分に低い抵抗値を示すことがわ かった。
【００３７】
（実施例６）
実施例１で述べた同様の方法により、 Y系のバルク材料を作製した。これを厚さ 0.6mmにスライス切断した後、 30mm×10mm×0.6mmの棒状試料を作製した。このようにして得られた材料は、単結晶状のYBa2Cu3O7-x相中に1μm程度のY2BaCuO5相が微細分散した組織を有していた。また、 YBa2Cu3O7-x相のc軸は、棒表面の平面法線および板面の法線方向に対応していた。
【００３８】
これらの棒状試料表面にスパッタ法により厚さ2μmの銀を成膜した後、図７に示すように、両端部に20mmの銅電極を有する200mm×10mm×5mmの２本の９Ｎｉ鋼で超伝導体を挟み込むようにして接続した。銅と９Ｎｉ鋼とは、図７の様にネジ止めおよび半田により接続した。超伝導体と金属との接続は、約 10μmの錫鉛系半田層を形成した後、 120℃の融点を有する低温半田を用いて電気的に接続し、低抵抗複合導体を作製した。
【００３９】
完成した各低抵抗複合導体を液体窒素で冷却し、 77Kでの電気抵抗を測定し、見かけの比抵抗を計算したところ、 1.0×10-9Ωｍであった。銀の常伝導導体のみの場合の比抵抗は、2.6×10-9Ωｍであり、十分に低い抵抗値を示すことがわ かった。
【００４０】
（実施例７）
実施例１で述べた同様の方法により、 Y系のバルク材料を作製した。これを厚さ0.6mmにスライス切断した後、30mm×8mm×0.6mmおよび 15mm×8mm×0.6mmの棒状試料を作製した。このようにして得られた材料は、単結晶状の YBa2Cu3O7-x相中に1μm程度のY2BaCuO5相が微細分散した組織を有していた。また、 YBa2Cu3O7-x相の c軸は、棒表面の平面法線および板面の法線方向に対応していた。
【００４１】
これらの棒状試料表面にスパッタ法により厚さ2μmの銀を成膜し、図８に示すように、継ぎ目を覆うように二層に積層した。また、両端部に20mmの銅電極を有する 200mm×８mm×3mmの２本のＴｉ-６Ａｌ-４Ｖl合金で超伝導体を挟み込むようにして接続した。銅とＴｉ-６Ａｌ-４Ｖ合金とは、図８の様にネジ止めおよび半田により接続した。超伝導体と金属との接続は、Ｔｉ合金の表面を予め１μm の銀層を形成した後、約80℃の融点を有する低温半田を用いて電気的に接続し、低抵抗複合導体を作製した。
【００４２】
完成した各低抵抗複合導体を液体窒素で冷却し、 77Kでの電気抵抗を測定し、見かけの比抵抗を計算したところ、 1.0×10-9Ωｍであった。銀の常伝導導体のみの場合の比抵抗は、 2.6 ×10-9Ωｍであり、十分に低い抵抗値を示すことが わかった。
【００４３】
【発明の効果】
以上述べたように、本願発明は、実質的に銅の比抵抗より小さい低抵抗複合導体を提供するものであり、その工業的効果は甚大である。
【図面の簡単な説明】
【図１】 (a) 均質な良導体に通電したときの電流分布
(b) 均質な常伝導体に超伝導体を接続したときの電流分布
【図２】 (a) 常伝導体に複数の超伝導体を接続した複合導体
(b) 常伝導体に千鳥状に超伝導体を接続した複合導体
【図３】 (a) 常伝導体に３本の棒状超伝導体を直列に接続した複合導体
(b) 常伝導体に千鳥状に複数の棒状超伝導体を接続した複合導体
(c) 常伝導体に３枚の板状超伝導体を接続した複合導体
【図４】常伝導導体（Ａｇ）に超伝導体が対称的に接続した複合導体
【図５】ステンレスで補強した常伝導体（Ｃｕ）に超伝導体を接続した複合導体
【図６】銅で両面から超伝導体を挟み込んだ構造を有する複合導体の組み立て図
【図７】両端に銅電極部を有する９Ｎｉ鋼で超伝導体を挟み込んだ構造を有する複合導体の組み立て図
【図８】両端に銅電極部を有するＴｉ合金で２層の超伝導体を挟み込んだ構造を有する複合導体の組み立て図[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a composite conductor having a substantially low resistance, a method for manufacturing the same, and a device using such a composite conductor.
[0002]
[Prior art]
Currently, copper is most frequently used as a conductor for conducting electricity. This is because the specific resistance at room temperature is almost the same as that of silver, the lowest relative to other materials, and relatively inexpensive. As a method of reducing the specific resistance of the conductor, there is a method of cooling the conductor. In the case of copper, when it is cooled to liquid nitrogen temperature (77K), the specific resistance becomes about 2.5 × 10 −9 Ωm, which is about 1/7.
[0003]
Although a superconducting wire needs to be cooled below the superconducting transition temperature, it has an almost zero electrical resistance and is an ideal conductor. Metal-based superconducting wires have a high degree of completeness as wires, and have been put into practical use as magnets such as MRI, but have not yet become widespread due to the necessity of cooling to cryogenic temperatures. On the other hand, there are roughly two types of oxide-based superconducting materials that become superconducting at liquid nitrogen temperature: Bi-based and Y-based. Development of tape wires with a silver sheath as the main material for the Bi series and a superconducting thin film formed on the buffer layer on the metal tape surface is underway for the Y series. Since these wires can be cooled with liquid nitrogen which is easy to handle when high characteristics are obtained, the expectation for practical use is increasing. And development and the spread of electric equipment using these wires are expected.
[0004]
As a bulk material having a sufficient critical current density at liquid nitrogen temperature, a material in which RE 2 BaCuO 5 is finely dispersed in single-crystal REBa 2 Cu 3 O 7-x (RE is a rare earth element including Y) is known. It has been. Since such a material is in the form of a single crystal, there are technical limitations in the production of large materials, and currently only a material with a diameter of about 100 mm can be obtained.
[0005]
[Problems to be solved by the invention]
If a conductor having a sufficiently low resistance, low cost, and easy handling can be manufactured, it is not always necessary to use a superconducting material having a completely zero electric resistance. Therefore, the present invention provides a low-resistance composite conductor that combines a normal conductor and a superconductive material to easily reduce the resistance of the normal conductor at a temperature lower than the superconducting transition temperature and further reduce current loss during energization. Another object of the present invention is to provide an apparatus using the composite conductor, and a manufacturing method thereof.
[0006]
[Means for Solving the Problems]
As an example, a high critical current density has already been obtained at 77K, mainly for Y-based oxide superconducting bulk materials. By electrically connecting or pasting a superconductor represented by such a material to a normal conductor, a composite conductor having a low resistance and a high resistance can be easily obtained. That is, the present invention is as follows.
(1) Part or all of the surface of the normal conductor composed of one or more of copper, copper alloy, aluminum, aluminum alloy, silver, silver alloy, gold or gold alloy, part or all of which is REBa 2 Cu A composite conductor formed by connecting a plurality of bulk superconductors made of 3 O 7-x superconductor (where RE is one or a combination of rare earth elements including Y), A low-resistance composite conductor, wherein an apparent specific resistance of the composite conductor at a temperature lower than a superconducting transition temperature of the body is lower than a specific resistance of copper at the temperature.
(2) Part or all of the surface of the normal conductor composed of one or more of iron, iron alloy, nickel, nickel alloy and titanium alloy, part or all of which exceeds the REBa 2 Cu 3 O 7-x series A composite conductor formed by connecting a plurality of bulk superconductors made of a conductor (here, RE is one or a combination of rare earth elements including Y), which is not higher than the superconducting transition temperature of the bulk superconductor. A low-resistance composite conductor characterized in that an apparent specific resistance of the composite conductor in is lower than a specific resistance of copper at the temperature.
[0007]
(3) Part or all of the surface of the normal conductor composed of one or more of copper, copper alloy, aluminum, aluminum alloy, silver, silver alloy, gold or gold alloy is partially or entirely REBa 2 Cu A composite conductor formed by connecting a plurality of bulk superconductors made of 3 O 7-x superconductor (where RE is one or a combination of rare earth elements including Y), and the composite at 77K A low-resistance composite conductor characterized in that an apparent specific resistance of a conductor is lower than a specific resistance of copper at 77K.
(4) Part or all of the surface of the normal conductor composed of one or more of iron, iron alloy, nickel, nickel alloy and titanium alloy, part or all of which exceeds the REBa 2 Cu 3 O 7-x series A composite conductor formed by connecting a plurality of bulk superconductors made of a conductor (here, RE is one or a combination of rare earth elements including Y), and the apparent specific resistance of the composite conductor at 77K Is a low resistance composite conductor characterized by being lower than the specific resistance of copper at 77K.
(5) The bulk superconductor forms a current path having a parallel relationship with a current path in the normal conductor, according to any one of (1) to (4), Low resistance composite conductor.
(6) One or more electrode parts of copper, copper alloy, aluminum, aluminum alloy, silver, silver alloy, gold or gold alloy are provided at both ends of the normal conductor (2) Or the low resistance composite conductor as described in (4).
[0008]
(7) Any of (1) to (5), wherein the longitudinal direction of a part or all of the bulk superconductor is perpendicular to the c-axis in the crystallographic orientation of the bulk superconductor. A low resistance composite conductor according to any one of the above.
(8) The low-resistance composite according to any one of (1) to (7), wherein at least one of the normal conductor or the bulk superconductor has a rod-like or plate-like shape. conductor.
(9) The low resistance composite conductor according to any one of (1) to (8), wherein the composite conductor is formed by sandwiching and connecting the bulk superconductor with the normal conductor.
[0009]
(10) A part or all of the connection is a normal connection through a metal that is one or more of copper, copper alloy, aluminum, aluminum alloy, silver, silver alloy, gold, or gold alloy. The low resistance composite conductor according to any one of (1) to (9).
(11) A part or all of at least one of the bulk superconductor or the normal conductor has a plane, and the bulk superconductor and the normal conductor are normally connected in the plane. The low-resistance composite conductor according to (10), which is characterized in that
(12) The low resistance composite conductor according to (10) or (11), wherein a part or all of the normal conductive connection is formed using a normal conductor of the same type or different type from the normal conductor.
(13) The low resistance composite conductor according to any one of (10) to (12), wherein a thickness of the connection portion is 100 μm or less.
(14) The low-resistance composite conductor according to any one of (1) to (13), wherein a part or all of the bulk superconductor in the longitudinal direction is a conduction direction.
[0010]
(15) One surface of a normal conductor composed of one or more of copper, copper alloy, aluminum, aluminum alloy, iron, iron alloy, nickel, nickel alloy, titanium alloy, silver, silver alloy, gold or gold alloy A part or all of a plurality of REBa 2 Cu 3 O 7-x- based superconductors (where RE is one or a combination of rare earth elements including Y) via a normal conductor. Is a method of manufacturing a composite conductor in which a superconductor is disposed and pressurized and connected as necessary, and the specific resistivity of the composite conductor at 77K is lower than the specific resistance of copper at the temperature A method for producing a low resistance composite conductor.
(16) The method for producing a low-resistance composite conductor according to (15), wherein the normal conductor is solder.
(17) One surface of a normal conductor composed of one or more of copper, copper alloy, aluminum, aluminum alloy, iron, iron alloy, nickel, nickel alloy, titanium alloy, silver, silver alloy, gold or gold alloy Part or all of a superconductor consisting of a REBa 2 Cu 3 O 7-x- based superconductor (where RE is one or a combination of rare earth elements including Y) via a normal conductor. A method of manufacturing a composite conductor in which a conductor is disposed, pressurized as necessary, and heat-treated in a reduced-pressure atmosphere or in vacuum, wherein the apparent specific resistance of the composite conductor at 77K is the resistance of copper at the temperature A method for producing a low-resistance composite conductor, characterized by being lower than a specific resistance.
(18) The superconductor is disposed so as to form a current path having a parallel relationship with the current path in the normal conductor. The manufacturing method of the low-resistance composite conductor of description.
(19) The low conductivity according to (15) or (17), wherein the normal conductor is a paste or foil of copper, copper alloy, aluminum, aluminum alloy, silver, silver alloy, gold or gold alloy. Manufacturing method of resistance composite conductor.
(20) The surface of the superconductor has one or more coatings of copper, copper alloy, aluminum, aluminum alloy, silver, silver alloy, gold or gold alloy (15) to (15) 19) The method for producing a low-resistance composite conductor according to any one of the above.
[0011]
(21) A current-carrying member comprising at least part of the low-resistance composite conductor according to any one of (1) to (14).
(22) A current lead comprising the low-resistance composite conductor according to any one of (1) to (14) disposed at least in part.
(23) A superconducting transformer comprising the energizing member according to (21) or the current lead according to (22).
(24) A magnetic field generator comprising the energization member according to (21) or the current lead according to (22).
[0012]
DETAILED DESCRIPTION OF THE INVENTION
As shown in Fig. 1 (a), when a normal conductor such as copper, copper alloy, aluminum, aluminum alloy, silver, silver alloy, gold, or gold alloy is energized, the current passed is the resistance value. It flows almost uniformly in the conductor so as to be minimized. When part or all of the superconductor is electrically connected to the surface of the normal conductor as shown in FIG. 1 (b) and cooled below the superconductor transition temperature of the superconductor, Instead of flowing uniformly throughout, the superconductor with zero resistance tends to flow at a higher current density so that the resistance value of the entire conductor is minimized. The ratio of the shunt current to the superconductor varies depending on the contact resistance between the superconductor and the normal conductor, the critical current of the superconductor, the specific resistance of the normal conductor, etc. The smaller the contact resistance and the greater the specific resistance of the normal conductor, the greater the proportion of shunting to the superconductor. The greater the shunt to a superconductor with zero electrical resistance, the lower the overall resistance of the composite conductor, and accordingly the heat generation in the composite conductor.
[0013]
In order to reduce the contact resistance between the superconductor and the normal conductor, it is only necessary to increase the contact area, and at least one of the superconductor and the normal conductor has a plane and is connected within this plane. It is desirable that Further, in order to increase the surface area per volume, at least one of the superconductor and the normal conductor has a rod-like or plate-like shape, and at least one surface of the superconductor is joined to the normal conductor. It is desirable that
[0014]
The material of the superconductor is a REBa 2 Cu 3 O 7-x superconductor (where RE is one or a combination of rare earth elements including Y), and the single crystal REBa 2 Cu 3 O 7 A bulk material having a structure in which RE 2 BaCuO 5 is finely dispersed in the -x system is desirable. Also, since microcracks are likely to occur in the ab plane, it is desirable that the c-axis of the single-crystal REBa 2 Cu 3 O 7-x superconducting phase be perpendicular to the longitudinal direction of the bulk superconductor. .
[0015]
In the present invention in which a plurality of superconductors are arranged on the surface of a normal conductor, it is desirable to arrange them in series as shown in FIG. Further, preferably, as shown in FIG. 2 (b), a plurality of superconductor rows are arranged in a staggered manner, the gaps between the superconductors (d and g in the figure) are reduced, and the current flows in the superconductor as much as possible. It is desirable to make a lot of flow.
[0016]
The material of the normal conductor is copper, copper alloy, aluminum, aluminum alloy, silver, silver alloy, gold or gold alloy which is inexpensive and has low resistivity. Furthermore, silver is superior from the viewpoint of oxidation resistance, and aluminum is superior from the viewpoint of weight reduction. The coefficient of thermal expansion of the normal conductor and the coefficient of thermal expansion of the superconductor are generally different, and the temperature at the time of connecting the superconductor and the normal conductor and the temperature at the time of cooling the connected conductor are generally Due to the difference, stress acts in the superconductor and the normal conductor. When this stress is large, the conductor may be warped or the superconductor may be damaged. Therefore, a symmetrical arrangement is desirable in which stresses such as connecting a superconductor to the surface of the normal conductor are balanced symmetrically. It is further desirable to reinforce the low-resistance composite conductor itself with a highly rigid material.
[0017]
When the length of the normal conductor is relatively long, for the above reasons, the selection of the normal metal has priority over materials that exhibit thermal expansion behavior close to that of superconducting materials rather than materials with high electrical conductivity. Is done. An oxide superconductor is generally relatively strong against compressive stress but relatively weak against tensile stress. In the case of a bulk material having a structure in which RE 2 BaCuO 5 is finely dispersed in a single-crystal REBa 2 Cu 3 O 7-x system, a relatively small compressive stress is applied during cooling after connection. Therefore, Ni steel, Nichrome, Ti Alloys are suitable. Further, in order to reduce the compressive stress at the cooling temperature, the temperature at which the superconductor and the normal conductor are fixed may be set to a lower temperature, and connection by low-temperature solder or the like is desirable. In addition, since Ni steel, Nichrome, Ti alloy, etc. have a relatively high specific resistance, copper, copper alloy, aluminum, aluminum alloy, silver, silver alloy, gold or gold alloy with low resistivity are used for the electrode at the end. Is particularly desirable.
Further, in order to uniformly apply an appropriate compressive stress to the superconductor, it is desirable to connect a plate-shaped superconductive material in such a manner as to sandwich the normal conductor. Further, at this time, it is desirable to connect the same type and shape of normal conductors symmetrically on both sides of the plate-like superconductor.
[0018]
The contact resistance between the superconductor and silver or silver alloy can be reduced relatively easily. Therefore, it is desirable to provide a silver coating on the surface of the superconductor in advance and connect the surface having the coating to the normal conductor surface. When such a superconductor is connected to a normal conductor using solder or the like, since the solder generally has a higher specific resistance than a good conductor such as copper, silver, or aluminum, the superconductor such as solder and the normal conductor are used as much as possible. It is desirable that the thickness of the metal layer existing between the two is thin. Specifically, it is 100 μm or less obtained by connection in a pressurized state.
[0019]
The connection method between the superconductor and the normal conductor is roughly classified into a method using solder mainly composed of tin and lead and a method using metal paste such as silver paste or foil. Solder is excellent in that it can be easily processed by local heating at room temperature, such as easy bonding. In the case of solder connection, the thickness of the metal layer in the connection portion is usually about 100 to 50 m. Also, an adhesive such as silver paste is excellent in the following points. When silver paste is used as an adhesive and sintered by heat treatment, a thin metal layer of 25 μm or less is obtained due to the small specific resistance of silver itself and the shrinkage of the metal layer at the joint due to sintering. Therefore, connection resistance can be reduced compared to solder connection. In this sintering step, heat treatment in a reduced pressure atmosphere or vacuum is desirable from the viewpoint of void removal.
[0020]
The low-resistance composite conductor described above has low resistance and low heat generation, so that it can be applied as a current-carrying member or current lead for energizing the superconductor or superconducting coil.
Such a current lead is excellent as a lead for a magnetic field generator such as a superconducting transformer that requires cooling below the superconducting transition temperature or a direct cooling type or a conduction cooling type superconducting magnet.
[0021]
【Example】
(Example 1)
Each raw material powder of Y 2 O 3 , BaO 2 , CuO is mixed so that the molar ratio of each metal element (Y: Ba: Cu) is (13:17:24), and 0.5% is further added to this mixed powder. A mass powder of Pt was added to prepare a mixed raw material powder. This raw material powder was calcined at 900 ° C. in an oxygen stream. Using a rubber press, this calcined powder was molded into a disk-shaped compact having a diameter of 55 mm and a thickness of 20 mm at a pressure of 2 ton / cm 2 .
[0022]
This was heated up to 1150 ° C. in the atmosphere over 8 hours and held for 1 hour. After that, using an Sm-based seed crystal, the seed crystal was arranged at 1040 ° C. so that the normal of the board surface substantially coincided with the c-axis. Thereafter, the temperature was lowered to 1005 ° C. over 30 minutes, and further cooled gradually to 970 ° C. over 220 hours to carry out crystal growth. Subsequently, it was cooled to room temperature in 20 hours. The obtained material was sliced to a thickness of 1.0 mm, and a rod-shaped bulk superconducting material of 30 mm × 2 mm × 1 mm and a plate-shaped bulk superconducting material of 25 mm × 8 mm × 1 mm were produced. The material thus obtained had a structure in which a Y 2 BaCuO 5 phase of about 1 μm was finely dispersed in a single crystal YBa 2 Cu 3 O 7-x phase. The c-axis of the YBa 2 Cu 3 O 7-x phase corresponded to the normal direction of the widest plane of the bar surface and the normal direction of the plate surface.
[0023]
Silver was deposited on the surface of these plate samples by sputtering of about 2 μm, and then annealed in an oxygen stream. The annealing heat treatment pattern was raised from room temperature to 600 ° C in 6 hours, held for 1 hour, then lowered to 450 ° C in 2 hours, further lowered to 380 ° C in 60 hours, and cooled to room temperature in 12 hours .
[0024]
These plate-like samples and plate-like samples are electrically arranged by using silver-containing solder on a 150 mm × 8 mm × 5 mm copper normal conductor in the arrangement shown in FIGS. A low resistance composite conductor was prepared. At this time, the thickness of the metal layer was about 100 μm in normal soldering, but by solidifying the solder while applying pressure, the thickness of the metal layer between the copper and the superconductor was reduced to about 50 μm. I was able to. Then, after the current introduction terminal and the voltage terminal were attached to the low resistance composite conductor produced by each connection method, the superconductor was put into a superconducting state by being immersed in liquid nitrogen.
[0025]
Each completed low-resistance composite conductor was energized, measured for resistance at liquid nitrogen temperature (77K), and the apparent specific resistance was calculated to be 1.2 × 10 -9 Ωm, 1.0 × 10 -9 Ωm, It was 0.56 × 10 −9 Ωm. The specific resistance in the case of only the copper normal conductor was 2.5 × 10 −9 Ωm, and it was found that the specific resistance was sufficiently low.
[0026]
(Example 2)
By simply changing the raw material powder from Y 2 O 3 to Dy 2 O 3 , a Dy-based bulk material was produced by the same method described in Example 1. This was sliced and cut to a thickness of 0.6 mm, and then a rod-shaped sample of 30 mm × 2.5 mm × 0.6 mm was produced. The material thus obtained had a structure in which a Dy 2 BaCuO 5 phase of about 1 μm was finely dispersed in a single crystal YBa 2 Cu 3 O 7-x phase. The c-axis of the DyBa 2 Cu 3 O 7-x phase corresponded to the normal direction of the widest plane of the bar surface.
[0027]
After depositing 2μm thick silver on the surface of these rod-shaped samples by sputtering, as shown in Fig.4, using silver paste on the two opposing surfaces of 150mm × 7mm × 5mm size silver normal conductor Further, electrically connected and further heated at about 900 ° C. for about 1 hour under a reduced pressure of about 1.3 × 10 2 Pa to sinter the silver particles of the silver paste, the silver film on the surface of the rod-like material, and the silver normal conductor I concluded. Then, the temperature was raised from room temperature to 600 ° C in 6 hours, held for 1 hour, then lowered to 450 ° C in 2 hours, further lowered to 380 ° C in 60 hours, cooled to room temperature in 12 hours, and further oxygen annealed Processing was performed to produce a low-resistance composite conductor.
[0028]
Each completed low resistance composite conductor was cooled with liquid nitrogen, the electrical resistance at 77K was measured, and the apparent specific resistance was calculated to be 0.6 × 10 -9 Ωm. The specific resistance of only the silver normal conductor was 2.6 × 10 -9 Ωm, indicating a sufficiently low resistance value.
[0029]
(Example 3)
Y 2 O 3 of Example 1 was changed to Gd 2 O 3 , and 15% by mass of silver was further added to produce a disc-shaped molded body as produced in Example 1.
[0030]
This was heated up to 1150 ° C. for 8 hours in a nitrogen atmosphere of 0.1 atomic% oxygen and held for 1 hour. After that, using an Sm-based seed crystal, the seed crystal was arranged at 1040 ° C. so that the normal of the board surface substantially coincided with the c-axis. Thereafter, the temperature was lowered to 1005 ° C. over 30 minutes, and further cooled gradually to 970 ° C. over 220 hours for crystal growth. Subsequently, it was cooled to room temperature in 20 hours. The obtained silver-added Gd-based bulk material was sliced to a thickness of 1.5 mm to prepare a rod-shaped sample of 30 mm × 2.5 mm × 1.5 mm. The material thus obtained had a structure in which a Gd 2 BaCuO 5 phase of about 1 μm was finely dispersed in a single crystalline GdBa 2 Cu 3 O 7-x phase. The c-axis of the GdBa 2 Cu 3 O 7-x phase corresponded to the normal direction of the widest plane of the rod surface.
[0031]
After depositing silver on the surface of this rod-shaped material by sputtering of about 2 μm, the temperature was raised from room temperature to 600 ° C. in 6 hours, held for 1 hour, then lowered to 450 ° C. in 2 hours, and further to 380 ° C. in 60 hours. After cooling down to room temperature in 12 hours, oxygen annealing treatment was performed.
[0032]
Next, as shown in FIG. 5, the superconductor was connected to a copper normal conductor reinforced with two stainless steel plates having a thickness of 2 mm by soldering to produce a low resistance composite conductor.
The completed low-resistance composite conductor was cooled with liquid nitrogen, the electrical resistance at 77K was measured, and the apparent specific resistance was calculated to be 0.59 × 10 -9 Ωm. The specific resistance of only the copper normal conductor was 2.5 × 10 -9 Ωm, indicating a sufficiently low resistance value.
[0033]
Example 4
Two low-resistance composite conductors produced in Example 2 were used as current leads and attached to the current leads of an existing direct cooling superconducting magnet. The attachment location is the low temperature end side of the existing Bi-based current lead, and after attaching a part of the existing copper lead, it was attached.
[0034]
In order to generate a magnetic field of 10T, 70A was continuously energized, and the ultimate cooling temperature of the superconducting magnet with and without the low resistance conductor was compared. When the low resistance composite conductor was not inserted, the ultimate temperature was 4.5K, whereas when the low resistance conductor was inserted, it reached 4.1K.
From this result, it was found that the low-resistance composite conductor functions as a current lead and improves the performance of the direct-cooling magnet.
[0035]
(Example 5)
A Y-based bulk material was produced by the same method described in Example 1. This was sliced and cut to a thickness of 0.6 mm, and a 20 mm × 7 mm × 0.6 mm rod-shaped sample was prepared. The material thus obtained had a structure in which a Y 2 BaCuO 5 phase of about 1 μm was finely dispersed in a single crystal YBa 2 Cu 3 O 7-x phase. The c-axis of the YBa 2 Cu 3 O 7-x phase corresponded to the plane normal of the bar surface and the normal direction of the plate surface.
[0036]
After forming a silver film with a thickness of 2μm on the surface of these rod-shaped samples by sputtering, the superconductor is sandwiched between two pieces of copper of 80mm × 7mm × 5mm as shown in FIG. Electrical connection was made using a low-temperature solder having a melting point to produce a low-resistance composite conductor. Each completed low-resistance composite conductor was cooled with liquid nitrogen, the electrical resistance at 77K was measured, and the apparent specific resistance was calculated to be 0.59 × 10 -9 Ωm. The specific resistance in the case of only a copper normal conductor was 2.5 × 10 −9 Ωm, indicating a sufficiently low resistance value.
[0037]
(Example 6)
A Y-based bulk material was produced by the same method described in Example 1. This was sliced and cut to a thickness of 0.6 mm, and then a 30 mm × 10 mm × 0.6 mm rod-shaped sample was prepared. The material thus obtained had a structure in which a Y 2 BaCuO 5 phase of about 1 μm was finely dispersed in a single crystal YBa 2 Cu 3 O 7-x phase. The c-axis of the YBa 2 Cu 3 O 7-x phase corresponded to the plane normal of the bar surface and the normal direction of the plate surface.
[0038]
After depositing 2μm thick silver on the surface of these rod-shaped specimens by sputtering, as shown in Fig.7, superconductivity with two 9Ni steels of 200mm x 10mm x 5mm with 20mm copper electrodes at both ends Connected as if sandwiching the body. Copper and 9Ni steel were connected by screwing and soldering as shown in FIG. The superconductor and metal were connected by forming a tin-lead solder layer of about 10 μm and then using a low-temperature solder having a melting point of 120 ° C. to produce a low-resistance composite conductor.
[0039]
Each completed low-resistance composite conductor was cooled with liquid nitrogen, the electrical resistance at 77K was measured, and the apparent specific resistance was calculated to be 1.0 × 10 -9 Ωm. The specific resistance in the case of only the silver normal conductor was 2.6 × 10 −9 Ωm, indicating a sufficiently low resistance value.
[0040]
(Example 7)
A Y-based bulk material was produced by the same method described in Example 1. This was sliced and cut to a thickness of 0.6 mm, and rod-shaped samples of 30 mm × 8 mm × 0.6 mm and 15 mm × 8 mm × 0.6 mm were prepared. The material thus obtained had a structure in which a Y 2 BaCuO 5 phase of about 1 μm was finely dispersed in a single crystal YBa 2 Cu 3 O 7-x phase. The c-axis of the YBa 2 Cu 3 O 7-x phase corresponded to the plane normal of the bar surface and the normal direction of the plate surface.
[0041]
A silver film having a thickness of 2 μm was formed on the surface of these rod-like samples by sputtering, and was laminated in two layers so as to cover the seam as shown in FIG. In addition, the superconductor was sandwiched between two Ti-6Al-4Vl alloys of 200 mm × 8 mm × 3 mm having 20 mm copper electrodes at both ends. Copper and Ti-6Al-4V alloy were connected by screwing and soldering as shown in FIG. The superconductor and the metal were connected by forming a 1 μm silver layer on the surface of the Ti alloy in advance and then electrically connecting it using a low-temperature solder having a melting point of about 80 ° C. to produce a low-resistance composite conductor. .
[0042]
Each completed low-resistance composite conductor was cooled with liquid nitrogen, the electrical resistance at 77K was measured, and the apparent specific resistance was calculated to be 1.0 × 10 -9 Ωm. The specific resistance in the case of the silver normal conductor alone was 2.6 × 10 -9 Ωm, indicating that the resistance was sufficiently low.
[0043]
【The invention's effect】
As described above, the present invention provides a low-resistance composite conductor that is substantially smaller than the specific resistance of copper, and its industrial effect is enormous.
[Brief description of the drawings]
[Fig.1] (a) Current distribution when a homogeneous good conductor is energized
(b) Current distribution when a superconductor is connected to a homogeneous normal conductor [Fig. 2] (a) A composite conductor in which a plurality of superconductors are connected to a normal conductor
(b) Composite conductor in which superconductors are connected to normal conductors in a staggered pattern [Fig. 3] (a) Composite conductor in which three rod-shaped superconductors are connected in series to normal conductors
(b) A composite conductor in which a plurality of rod-shaped superconductors are connected to a normal conductor in a staggered manner
(c) Composite conductor with three plate-shaped superconductors connected to normal conductor [Fig. 4] Composite conductor with superconductor symmetrically connected to normal conductor (Ag) [Fig. 5] Reinforced with stainless steel Composite conductor in which superconductor is connected to normal conductor (Cu) [Fig. 6] Assembly drawing of composite conductor having a structure in which the superconductor is sandwiched from both sides with copper [Fig. 7] 9Ni steel having copper electrode portions at both ends FIG. 8 is an assembly diagram of a composite conductor having a structure in which a two-layer superconductor is sandwiched between Ti alloys having copper electrode portions at both ends.
Claims (24)
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