JP4013409B2

JP4013409B2 - Superconducting connection method of oxide superconducting material and superconducting connection structure

Info

Publication number: JP4013409B2
Application number: JP20905299A
Authority: JP
Inventors: 岳海室賀
Original assignee: Hitachi Cable Ltd
Current assignee: Hitachi Cable Ltd
Priority date: 1999-07-23
Filing date: 1999-07-23
Publication date: 2007-11-28
Anticipated expiration: 2019-07-23
Also published as: JP2001035282A

Description

【０００１】
【発明の属する技術分野】
本発明は、酸化物超電導材どうしを超電導接続する酸化物超電導材の超電導接続方法及び酸化物超電導材の超電導接続構造体に関する。
【０００２】
【従来の技術】
ＭＲＩ（核磁気共鳴イメージング）医療診断装置やＮＭＲ（核磁気共鳴装置）などのように、高精度安定磁場が要求されるものにあっては、これらの装置に装備される超電導マグネットが酸化物超電導材を用いて構成されるものがある。この酸化物超電導材は、希土類元素−アルカリ土類元素−銅酸化物系セラミックスを酸化物超電導体として有するものである。
【０００３】
このような酸化物超電導材を線材として用いて超電導マグネットの超電導コイルを形成する場合には、上記酸化物超電導材どうしを超電導接続することが必要となる。
【０００４】
酸化物超電導材どうしの超電導接続においては、超電導化熱処理の前に、酸化物超電導前駆体が金属被覆体にて被覆されて構成された少なくとも２本の仮酸化物超電導材において、（ａ）上記金属被覆体の一部を除去して酸化物超電導前駆体の露出部分を重ね合わせた後、（ｂ）もしくは少なくとも２本の仮酸化物超電導材における酸化物超電導前駆体の露出部分を、第３の仮酸化物超電導材の酸化物超電導前駆体を介して接触させた後、（ｃ）または少なくとも２本の仮酸化物超電導材の端面の酸化物超電導前駆体どうしを突き合わせた後、これら（ａ）、（ｂ）、（ｃ）のいずれの場合も、接続部に金属テープを巻き付け、その後超電導化熱処理を実施して、酸化物超電導前駆体を酸化物超電導体とし、仮酸化物超電導材を酸化物超電導材として、これらの酸化物超電導材を超電導接続することが知られている。
【０００５】
上記（ｂ）に示す酸化物超電導材の超電導接続方法は、例えば低温工学誌（１９９５）、Ｖｏｌ．３０、Ｎｏ．５、第２２４〜２３０頁に記載されている。
【０００６】
また、上記（ｃ）に示す酸化物超電導材の超電導接続方法を、図３を用いて以下に詳説する。
【０００７】
まず、酸化物超電導体としてのＢｉ系２２１２型酸化物超電導前駆体５０が、金属被覆体としてのＡｇパイプ５１中に充填されて構成された仮酸化物超電導材としてのシーステープ材５２及び５３の端面を接合する。（図３（Ａ）及び（Ｂ））。次に、シーステープ材５２及び５３の接続部５４の周囲に金属テープとしてのＡｇテープ５５を巻き付けて接続部５４を補強する（図３（Ｃ）及び（Ｄ））。その後、シーステープ材５２及び５３の超電導化熱処理を実施して（図３（Ｅ））、図３（Ｆ）に示すように、シーステープ材５２、５３のそれぞれのＢｉ系２２１２型酸化物超電導前駆体５０をＢｉ系２２１２型酸化物超電導体５６とする。この結果、シーステープ材５２、５３のそれぞれがＢｉ系２２１２型酸化物超電導材５７、５８となって、両者５７、５８間に超電導接続が形成され、Ｂｉ系２２１２型酸化物超電導接続構造体６０を形成する。
【０００８】
【発明が解決しようとする課題】
ところが、この図３に示すＢｉ系２２１２型酸化物超電導材５７及び５８の超電導接続方法では、超電導化熱処理がシーステープ材５２及び５３のＢｉ系２２１２型酸化物超電導前駆体５０を一度融解させた後凝固させるものであるため、シーステープ材５２及び５３の接続部５４にＡｇテープ５５を巻き付けていても、これらシーステープ材５２、５３のＡｇパイプ５１とＡｇテープ５５との間からＢｉ系２２１２型酸化物超電導前駆体５０の融液が流出し、または染み出てしまう場合がある。
【０００９】
図３（Ｆ）の符号５９が、Ｂｉ系２２１２型酸化物超電導前駆体５０の融液が流出した流出跡５９を示す。この流出跡５９は、図３に示す超電導接続方法を実施して構成されたＢｉ系２２１２型酸化物超電導接続構造体６０における１０個のサンプル１１〜２０の全てについて図４に示すように認められた。
【００１０】
このように、超電導化熱処理時にＢｉ系２２１２型酸化物超電導前駆体５０の融液が流出し、この流出量が多い場合には、超電導熱処理後、Ｂｉ系２２１２型酸化物超電導材５７及び５８の両Ｂｉ系２２１２型酸化物超電導体５６の超電導接続部に隙間が発生して接続不良となってしまう。
【００１１】
しかも、この接続不良は、超電導接続が終了するまで判定できないので、超電導接続工程中に接続不良に対する対策を施すことができず、超電導接続に関する歩留まりが低下してしまうおそれがある。
【００１２】
本発明の目的は、上述の事情を考慮してなされたものであり、超電導接続部に隙間の発生を防止して、超電導接続を良好に実施できる酸化物超電導材の超電導接続方法及び超電導接続構造体を提供することにある。
【００１３】
【課題を解決するための手段】
請求項１に記載の発明は、酸化物超電導前駆体（Ａ）が被覆体にて被覆されて構成された少なくとも２本の仮酸化物超電導材どうしを、介在物を介して接触させ、その後、超電導化熱処理を実施して、上記酸化物超電導前駆体（Ａ）を酸化物超電導体とし、上記仮酸化物超電導材を酸化物超電導材として、これらの酸化物超電導材どうしを超電導接続する酸化物超電導材の超電導接続方法において、上記介在物が、上記酸化物超電導前駆体（Ａ）よりも融点が高く、且つこの酸化物超電導前駆体（Ａ）と同一組成から成るが各組成成分の組成比が異なる酸化物超電導前駆体（Ｂ）を備えて成り、上記超電導化熱処理が、上記酸化物超電導前駆体（Ａ）の融点よりも高く、且つ上記酸化物超電導前駆体（Ｂ）の融点よりも低い温度で、上記酸化物超電導前駆体（Ａ）を超電導化させるものであることを特徴とするものである。
【００１４】
請求項２に記載の発明は、請求項１に記載の発明において、上記酸化物超電導前駆体（Ａ）、（Ｂ）がＢｉ系酸化物超電導前駆体であることを特徴とするものである。
【００１５】
請求項３に記載の発明は、請求項１に記載の発明において、上記酸化物超電導前駆体（Ａ）、（Ｂ）がＢｉ系２２１２型酸化物超電導前駆体であることを特徴とするものである。
【００１６】
請求項４に記載の発明は、酸化物超電導前駆体（Ａ）が被覆体にて被覆されて構成された少なくとも２本の仮酸化物超電導材どうしを、介在物を介して接触させ、超電導化熱処理により上記酸化物超電導前駆体（Ａ）を酸化物超電導体とし、上記仮酸化物超電導材を酸化物超電導材として、これらの酸化物超電導材どうしが超電導接続される酸化物超電導材の超電導接続構造体において、上記介在物が、上記酸化物超電導前駆体（Ａ）よりも融点が高く、且つこの酸化物超電導前駆体（Ａ）と同一組成から成るが各組成成分の組成比が異なる酸化物超電導前駆体（Ｂ）を備えて成り、上記超電導化熱処理が、上記酸化物超電導前駆体（Ａ）の融点よりも高く、且つ上記酸化物超電導前駆体（Ｂ）の融点よりも低い温度で、上記酸化物超電導前駆体（Ａ）を超電導化させるものであることを特徴とするものである。
【００１７】
請求項５に記載の発明は、請求項４に記載の発明において、上記酸化物超電導材どうしの超電導接続により、酸化物超電導コイルが構成されたことを特徴とするものである。
【００１８】
請求項６に記載の発明は、請求項４または５に記載の発明において、上記酸化物超電導前駆体（Ａ）、（Ｂ）がＢｉ系酸化物超電導前駆体であることを特徴とするものである。
【００１９】
請求項７に記載の発明は、請求項４または５に記載の発明において、上記酸化物超電導前駆体（Ａ）、（Ｂ）がＢｉ系２２１２型酸化物超電導前駆体であることを特徴とするものである。
【００２０】
請求項１乃至７に記載の発明には、次の作用がある。
【００２１】
仮酸化物超電導材どうしを接触させる介在物が、酸化物超電導前駆体（Ａ）よりも融点が高く、且つこの酸化物超電導前駆体（Ａ）と同一組成から成るが各組成成分の組成比が異なる酸化物超電導前駆体（Ｂ）を備えて成り、また、超電導化熱処理が、酸化物超電導前駆体（Ａ）の融点よりも高く、且つ酸化物超電導前駆体（Ｂ）の融点よりも低い温度で、酸化物超電導前駆体（Ａ）を超電導化させることから、この超電導化熱処理により、酸化物超電導前駆体（Ａ）が融解し、この融液が酸化物超電導前駆体（Ｂ）と接触してこれを溶融させようとするが、酸化物超電導前駆体（Ｂ）は完全には溶融しないため、酸化物超電導前駆体（Ａ）の融液の流れが止まる。この結果、酸化物超電導前駆体（Ａ）の融液の流出が抑制されて、酸化物超電導材どうしにおける酸化物超電導体の超電導接続部に隙間の発生を防止できるので超電導接続を良好に実施でき、超電導接続に関する歩留まりを向上させることができる。
【００２２】
また、仮酸化物超電導材の酸化物超電導前駆体（Ａ）の融液に接触した介在物の酸化物超電導前駆体（Ｂ）は、固相焼結して緻密化されるとともに、仮酸化物超電導材の被覆体との密着性も良好となる。このため、この介在物によって、酸化物超電導材の超電導接続部の強度を十分に確保できる。
【００２３】
【発明の実施の形態】
以下、本発明の実施の形態を、図面に基づき説明する。
【００２４】
図１は、本発明に係る酸化物超電導材の超電導接続方法の一実施の形態である、Ｂｉ系２２１２型酸化物超電導材の超電導接続構造体を製造する工程を示す工程図である。
【００２５】
ＭＲＩ（核磁気共鳴イメージング）医療診断装置やＮＭＲ（核磁気共鳴装置）などの超電導マグネットを構成する超電導コイル（ともに図示せず）は、図１に示す少なくとも２本の酸化物超電導材としてのＢｉ系２２１２型酸化物超電導材１１及び１２が互いに超電導接続されることによって構成される。これらの超電導接続は、図１に示すように、仮酸化物超電導材としてのシーステープ材１３及び１４の接続部１５に、介在物としてのコートテープ１６を巻き付け、その後超電導化熱処理を施すことによって実施される。
【００２６】
以下、この図１に示す超電導接続方法を詳説する。
【００２７】
（１）まず、シーステープ材１３及び１４をパウダーインチューブ法を用いて作成する。つまり、Ｂｉ₂Ｏ₃、ＳｒＣＯ₃、ＣａＣＯ₃、ＣｕＯの各粉末をＢｉ：Ｓｒ：Ｃａ：Ｃｕ＝２：２：１：２の組成比となるように混合し、約８２０℃で仮焼した後粉砕し、この仮焼・粉砕を２回繰り返してＢｉ系２２１２型酸化物超電導前駆体（Ａ）１７の粉末を形成する。次に、例えば外径１０ｍｍ内径９ｍｍのＡｇパイプからなる被覆体としての基材１８内に、上記Ｂｉ系２２１２型酸化物超電導前駆体（Ａ）１７の粉末を充填して、このＢｉ系２２１２型酸化物超電導前駆体（Ａ）１７を基材１８により被覆する。その後、この基材１８内にＢｉ系２２１２型酸化物超電導前駆体（Ａ）１７の粉末が充填されたものを、外径２ｍｍまでドローベンチで線引き加工した後ロール圧延して、厚さ０．２〜１ｍｍ、幅３〜６ｍｍのシーステープ材１３、１４を作成する。ここで、これらのシーステープ材１３、１４におけるＢｉ系２２１２型酸化物超電導前駆体（Ａ）１７の融点は８８０℃である。
【００２８】
（２）一方、コートテープ１６を製作する。つまり、Ｂｉ₂Ｏ₃、ＳｒＣＯ₃、ＣａＣＯ₃、ＣｕＯの粉末をＢｉ：Ｓｒ：Ｃａ：Ｃｕ＝１．９５：２：１：２．０５の組成比となるように混合し、この混合物を約８２０℃で仮焼して粉砕し、これを２回繰り返すことによってＢｉ系２２１２型酸化物超電導前駆体（Ｂ）１９の粉末を形成する。次に、このＢｉ系２２１２型酸化物超電導前駆体（Ｂ）１９の粉末に有機溶剤（例えばエタノール）を加えて攪拌する。その後、この攪拌により形成された懸濁液を、例えば幅１０ｍｍ、長さ１００ｍｍ、厚さ５０μｍの寸法のＡｇ板からなる基材２０上にコーティングしてコートテープ１６を作成する。ここで、このコートテープ１６におけるＢｉ系２２１２型酸化物超電導前駆体（Ｂ）１９の粉末の融点は８８７℃であり、Ｂｉ系２２１２型酸化物超電導前駆体（Ａ）１７の融点よりも高い。
【００２９】
上述の如く、Ｂｉ系２２１２型酸化物超電導前駆体（Ａ）１７とＢｉ系２２１２型酸化物超電導前駆体（Ｂ）１９とは同一組成からなるが、各組成成分の組成比が異なる。このＢｉ系２２１２型酸化物超電導前駆体（Ａ）１７とＢｉ系２２１２型酸化物超電導前駆体（Ｂ）１９の組成比の相違は、各成分とも０％を除き±１０％以内に設定されることが最も望ましい。例えば、組成比のＢｉ分は、Ｂｉ系２２１２型酸化物超電導前駆体（Ａ）１７が「２」、Ｂｉ系２２１２型酸化物超電導前駆体（Ｂ）１９が「１．９５」であり、両者には±０．５％の差異がある。
【００３０】
Ｂｉ系２２１２型酸化物超電導前駆体（Ａ）１７とＢｉ系２２１２型酸化物超電導前駆体（Ｂ）１９の各組成成分の差を０％を除き±１０％以内に設定した理由は、０％とすると、Ｂｉ系２２１２型酸化物超電導前駆体（Ａ）１７とＢｉ系２２１２型酸化物超電導前駆体（Ｂ）１９の組成が完全に同一となって、これらの融点も完全に一致してしまう可能性があり、また、上記±１０％以上になると、後述するＢｉ系２２１２型酸化物超電導前駆体（Ａ）１７の融液の流出防止に関しては支障ないが、Ｂｉ系２２１２型酸化物超電導前駆体（Ａ）１７の融液に接触して少量溶融したＢｉ系２２１２型酸化物超電導前駆体（Ｂ）１９の影響で、後述するＢｉ系２２１２型酸化物超電導体（Ａ）２１とＢｉ系２２１２型酸化物超電導体（Ｂ）２２の接続部分に異相が生成してしまうことがあるからである。
【００３１】
（３）上述のようにしてシーステープ材１３、１４及びコートテープ１６を製作した後、図１（Ａ）及び（Ｂ）に示すように、シーステープ材１３と１４の端面を突き合わせて接合する。
【００３２】
（４）次に、コートテープ１６を所定長に切り出し、図１（Ｃ）及び（Ｄ）に示すように、コートテープ１６のＢｉ系２２１２型酸化物超電導前駆体（Ｂ）１９をシーステープ材１３及び１４の基材１８に接触させて、コートテープ１６をシーステープ材１３と１４の接続部１５周囲に巻き付ける。シーステープ材１３及び１４は、互いの端面どうしの接合により、更にコートテープ１６のＢｉ系２２１２型酸化物超電導前駆体（Ｂ）１９を介して接触される。
【００３３】
（５）その後、Ｂｉ系２２１２型酸化物超電導前駆体（Ａ）１７の融点（８８０℃）よりも高く、Ｂｉ系２２１２型酸化物超電導前駆体（Ｂ）１９の融点（８８７℃）よりも低い温度を最高温度として、例えば最高温度を８８３℃として、図１（Ｄ）に示すシーステープ材１３、１４及びコートテープ１６に超電導化熱処理を施す。（図１（Ｅ））。
【００３４】
この超電導化熱処理によって、Ｂｉ系２２１２型酸化物超電導前駆体（Ａ）１７がＢｉ系２２１２型酸化物超電導体（Ａ）２１となり、Ｂｉ系２２１２型酸化物超電導前駆体（Ｂ）１９がＢｉ系２２１２型酸化物超電導体（Ｂ）２２となり、シーステープ材１３、１４のそれぞれがＢｉ系２２１２型酸化物超電導材１１、１２となって、これらＢｉ系２２１２型酸化物超電導材１１及び１２どうしの超電導接続により、Ｂｉ系２２１２型酸化物超電導接続構造体１０が形成される。
【００３５】
超電導化熱処理の最高温度とＢｉ系２２１２型酸化物超電導前駆体（Ｂ）１９の融点との温度差は１０℃以内が望ましい。これら両者の差を１０℃以上とすると、超電導化熱処理により融解されたＢｉ系２２１２型酸化物超電導前駆体（Ａ）１７の融液に接しても、Ｂｉ系２２１２型酸化物超電導前駆体（Ｂ）１９が全く溶融しなくなる場合があり、従来のＡｇテープ５５の場合と同様に、Ｂｉ系２２１２型酸化物超電導前駆体（Ａ）１７の融液が流出または染み出る恐れがあるからである。
【００３６】
このようにして形成されたＢｉ系２２１２型酸化物超電導接続構造体１０の１０個のサンプル（試料）を観察したところ、図２に示すように全てのサンプルについて、Ｂｉ系２２１２型酸化物超電導接続構造体１０の超電導接続部２３にＢｉ系２２１２型酸化物超電導前駆体（Ａ）１７の融液の流出跡が全くまたはほとんど観察できなかった。
【００３７】
従って、上記実施の形態によれば、次の効果▲１▼及び▲２▼を奏する。
【００３８】
▲１▼シーステープ材１３及び１４どうしを接触させるコートテープ１６が、シーステープ材１３、１４のＢｉ系２２１２型酸化物超電導前駆体（Ａ）１７よりも融点が高く、且つこのＢｉ系２２１２型酸化物超電導前駆体（Ａ）１７と同一組成のＢｉ系２２１２型酸化物超電導前駆体（Ｂ）１９を備えて構成され、また、超電導化熱処理が、シーステープ材１３、１４のＢｉ系２２１２型酸化物超電導前駆体（Ａ）１７の融点よりも高く、且つコートテープ１６のＢｉ系２２１２型酸化物超電導前駆体（Ｂ）１９の融点よりも低い温度で、Ｂｉ系２２１２型酸化物超電導前駆体（Ａ）１７を超電導化させることから、この超電導化熱処理により、シーステープ材１３、１４のＢｉ系２２１２型酸化物超電導前駆体（Ａ）１７が融解し、この融液がコートテープ１６のＢｉ系２２１２型酸化物超電導前駆体（Ｂ）１９と接触してこれを溶融させようとするが、酸化物超電導前駆体（Ｂ）１９は完全には溶融しないため、シーステープ材１３、１４のＢｉ系２２１２型酸化物超電導前駆体（Ａ）１７の融液の流れが止まる。この結果、シーステープ材１３、１４のＢｉ系２２１２型酸化物超電導前駆体（Ａ）１７の融液の流出が抑制されて、Ｂｉ系２２１２型酸化物超電導材１１のＢｉ系２２１２型酸化物超電導体（Ａ）２１とＢｉ系２２１２型酸化物超電導材１２のＢｉ系２２１２型酸化物超電導体（Ｂ）２２との超電導接続部２３に隙間の発生を防止して超電導接続を良好に実施でき、超電導接続に関する歩留まりを向上させることができる。
【００３９】
▲２▼シーステープ材１３、１４のＢｉ系２２１２型酸化物超電導前駆体（Ａ）１７の融液に接触したコートテープ１６のＢｉ系２２１２型酸化物超電導前駆体（Ｂ）１９は、固相焼結して緻密化されるとともに、シーステープ材１３及び１４の基材１８との密着性も良好となる。このため、このコートテープ１６によってＢｉ系２２１２型酸化物超電導材１１及び１２の超電導接続部２３の強度を十分に確保できる。
【００４０】
以上、本発明を上記実施の形態に基づいて説明したが、本発明はこれに限定されるものではない。
【００４１】
たとえば、Ｂｉ系２２１２型酸化物超電導材１１、１２のＢｉ系２２１２型酸化物超電導体（Ｂ）２２が多芯構造または多層構造であっても本発明を適用できる。また、超電導化熱処理前にシーステープ材１３と１４の端面を離して配置し、これらのシーステープ材１３及び１４に巻き付けられたコートテープ１６のみを介してシーステープ材１３と１４が互いに接触しても良い。更に、基材１８または基材２０はＡｇに限らず、Ａｕ、Ｐｔ、ＰｄまたはＣｕを備えて構成されたものでも良い。
【００４２】
また、Ｂｉ系２２１２型酸化物超電導材に限らず、Ｂｉ：Ｓｒ：Ｃａ：Ｃｕ＝２：２：２：３の組成比からなるＢｉ系２２２３型酸化物超電導材に本発明を適用しても良く、更に、Ｙ系酸化物超電導材またはＴｌ系酸化物超電導材に本発明を適用しても良い。また、超電導接続において融解及び凝固を伴う超電導化熱処理であれば、Ｎｂ₃Ａｌ、ＮｂＴｉ、Ｎｂ₃Ｓｎなどの金属系超電導材に本発明を適用しても良い。
【００４３】
また、シーステープ材１３、１４を製造する方法として、パウダーインチューブ法の他、ディップコード法、ドクターブレード法、塗布法、ジェリーロール法、溶射法、スクリーン印刷法、蒸着法、ＣＶＤ（ＣｈｅｍｉｃａｌＶａｐｏｒＤｅｐｏｓｉｔｉｏｎ：化学気相成長）法、スパッタリング法、レーザーアブレーション法等で製造したテープ材や線材を用いても良い。
【００４４】
更に、本発明の超電導接続方法及び接続構造体を超電導マグネットの他、伝送ケーブル、電流リード、磁気シールド、限流器または永久電流スイッチなどに適用しても良い。
【００４５】
【発明の効果】
請求項１に記載の発明に係る酸化物超電導材の超電導接続方法、及び請求項４に記載の発明に係る酸化物超電導材の超電導接続構造体によれば、酸化物超電導前駆体（Ａ）を備えた少なくとも２本の仮酸化物超電導材どうしを接触させる介在物が、酸化物超電導前駆体（Ａ）よりも融点が高く、且つこの酸化物超電導前駆体（Ａ）と同一組成から成るが各組成成分の組成比が異なる酸化物超電導前駆体（Ｂ）を備えて成り、酸化物超電導材どうしを超電導接続するための超電導化熱処理が、酸化物超電導前駆体（Ａ）の融点よりも高く、且つ酸化物超電導前駆体（Ｂ）の融点よりも低い温度で、酸化物超電導前駆体（Ａ）を超伝導させることから、超電導接続部に隙間の発生を防止して超電導接続を良好に実施できる。
【図面の簡単な説明】
【図１】本発明に係る酸化物超電導材の超電導接続方法における一実施の形態である、Ｂｉ系２２１２型酸化物超電導材の酸化物超電導接続構造体を製造する工程を示す工程図である。
【図２】図１（Ｆ）に示すＢｉ系２２１２型酸化物超電導接続構造体におけるサンプル１〜１０の検査結果を示す図表である。
【図３】従来のＢｉ系２２１２型酸化物超電導材の酸化物超電導接続構造体を製造する工程を示す工程図である。
【図４】図３（Ｆ）に示すＢｉ系２２１２型酸化物超電導接続構造体におけるサンプル１１〜２０の検査結果を示す図表である。
【符号の説明】
１０Ｂｉ系２２１２型酸化物超電導接続構造体
１１Ｂｉ系２２１２型酸化物超電導材
１２Ｂｉ系２２１２型酸化物超電導材
１３シーステープ材（仮酸化物超電導材）
１４シーステープ材（仮酸化物超電導材）
１６コートテープ（介在物）
１７Ｂｉ系２２１２型酸化物超電導前駆体（Ａ）
１８基材（被覆体）
１９Ｂｉ系２２１２系酸化物超電導前駆体（Ｂ）
２１Ｂｉ系２２１２型酸化物超電導体（Ａ）
２２Ｂｉ系２２１２型酸化物超電導体（Ｂ）[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a superconducting connection method for an oxide superconducting material for superconductingly connecting oxide superconducting materials and a superconducting connection structure for an oxide superconducting material.
[0002]
[Prior art]
For devices that require a high-precision stable magnetic field, such as MRI (nuclear magnetic resonance imaging) medical diagnostic equipment and NMR (nuclear magnetic resonance equipment), superconducting magnets equipped with these equipment are oxide superconductors. Some are composed of materials. This oxide superconducting material has a rare earth element-alkaline earth element-copper oxide-based ceramic as an oxide superconductor.
[0003]
In the case where a superconducting coil of a superconducting magnet is formed using such an oxide superconducting material as a wire, it is necessary to superconductingly connect the oxide superconducting materials.
[0004]
In superconducting connection between oxide superconducting materials, before superconducting heat treatment, at least two provisional oxide superconducting materials constituted by covering the oxide superconducting precursor with a metal coating, (a) the above After removing a part of the metal covering and superposing the exposed portions of the oxide superconducting precursor, the exposed portion of the oxide superconducting precursor in (b) or at least two provisional oxide superconducting materials is replaced with the third portion. (C) or after matching the oxide superconducting precursors on the end faces of at least two provisional oxide superconducting materials with each other (a) ), (B), and (c), a metal tape is wound around the connecting portion, and then a superconducting heat treatment is performed to make the oxide superconductor precursor an oxide superconductor, and a temporary oxide superconductor is formed. Oxide superconductivity As is known to the superconductive connecting these oxide superconducting materials.
[0005]
The superconducting connection method of the oxide superconducting material shown in the above (b) is described in, for example, the Journal of Low Temperature Engineering (1995), Vol. 30, no. 5, pages 224-230.
[0006]
Moreover, the superconducting connection method of the oxide superconducting material shown in the above (c) will be described in detail below with reference to FIG.
[0007]
First, sheath tape materials 52 and 53 as temporary oxide superconducting materials constituted by filling a Bi-based 2212 type oxide superconducting precursor 50 as an oxide superconductor into an Ag pipe 51 as a metal coating. Join the end faces. (FIGS. 3A and 3B). Next, an Ag tape 55 as a metal tape is wound around the connection portion 54 of the sheath tape materials 52 and 53 to reinforce the connection portion 54 (FIGS. 3C and 3D). Thereafter, the superconducting heat treatment of the sheath tape materials 52 and 53 was performed (FIG. 3E), and as shown in FIG. 3F, the Bi-based oxide superconductivity of each of the sheath tape materials 52 and 53 was obtained. The precursor 50 is a Bi-based 2212 type oxide superconductor 56. As a result, the sheath tape materials 52 and 53 become Bi-based 2212 type oxide superconducting materials 57 and 58, respectively, and a superconducting connection is formed between the two 57 and 58, and the Bi-based 2212 type oxide superconducting connection structure 60. Form.
[0008]
[Problems to be solved by the invention]
However, in the superconducting connection method of the Bi-based 2212 type oxide superconducting materials 57 and 58 shown in FIG. 3, the superconducting heat treatment once melted the Bi-based 2212 type oxide superconducting precursor 50 of the sheath tape materials 52 and 53. Since it is to be post-solidified, even if the Ag tape 55 is wound around the connecting portion 54 of the sheath tape materials 52 and 53, the Bi system 2212 is inserted between the Ag pipe 51 and the Ag tape 55 of the sheath tape materials 52 and 53. The melt of the type oxide superconducting precursor 50 may flow out or ooze out.
[0009]
A reference numeral 59 in FIG. 3F indicates an outflow trace 59 from which the melt of the Bi-based 2212 type oxide superconducting precursor 50 has flowed out. The outflow trace 59 is recognized as shown in FIG. 4 for all ten samples 11 to 20 in the Bi-based 2212 type oxide superconducting connection structure 60 configured by performing the superconducting connection method shown in FIG. It was.
[0010]
As described above, the melt of the Bi-based 2212 type oxide superconducting precursor 50 flows out during the superconducting heat treatment. A gap is generated in the superconducting connection part of both Bi-based 2212 type oxide superconductors 56, resulting in poor connection.
[0011]
In addition, since this connection failure cannot be determined until the superconducting connection is completed, it is not possible to take measures against the connection failure during the superconducting connection process, and there is a concern that the yield related to the superconducting connection may be reduced.
[0012]
The object of the present invention has been made in view of the above circumstances, and a superconducting connection method and a superconducting connection structure of an oxide superconducting material capable of satisfactorily performing superconducting connection by preventing generation of a gap in the superconducting connection portion. To provide a body.
[0013]
[Means for Solving the Problems]
In the invention according to claim 1, at least two provisional oxide superconducting materials constituted by covering the oxide superconducting precursor (A) with a covering are brought into contact with each other through an inclusion, Oxide that conducts superconducting heat treatment and uses the oxide superconducting precursor (A) as an oxide superconductor, the temporary oxide superconducting material as an oxide superconducting material, and a superconducting connection between these oxide superconducting materials In the superconducting connection method of a superconducting material, the inclusion has a higher melting point than the oxide superconducting precursor (A) and has the same composition as the oxide superconducting precursor (A), but the composition ratio of each composition component Comprising a different oxide superconducting precursor (B), and the superconducting heat treatment is higher than the melting point of the oxide superconducting precursor (A) and higher than the melting point of the oxide superconducting precursor (B). The above oxidation at low temperature It is characterized in that the superconductor precursor (A) is intended to be superconductive.
[0014]
The invention according to claim 2 is characterized in that, in the invention according to claim 1, the oxide superconducting precursors (A) and (B) are Bi-based oxide superconducting precursors.
[0015]
The invention according to claim 3 is the invention according to claim 1, wherein the oxide superconducting precursors (A) and (B) are Bi-based 2212 type oxide superconducting precursors. is there.
[0016]
In the invention according to claim 4, at least two provisional oxide superconducting materials constituted by covering the oxide superconducting precursor (A) with a covering are brought into contact with each other through inclusions, thereby superconducting. The oxide superconducting precursor (A) is an oxide superconductor by heat treatment, and the temporary oxide superconducting material is an oxide superconducting material. These oxide superconducting materials are superconductingly connected to each other. In the structure, the inclusion has a higher melting point than the oxide superconducting precursor (A) and has the same composition as that of the oxide superconducting precursor (A), but the composition ratio of each component is different . Comprising the superconducting precursor (B), wherein the superconducting heat treatment is at a temperature higher than the melting point of the oxide superconducting precursor (A) and lower than the melting point of the oxide superconducting precursor (B), Before the oxide superconductivity It is characterized in that the body (A) is one in which is superconductive.
[0017]
The invention described in claim 5 is characterized in that, in the invention described in claim 4, an oxide superconducting coil is formed by superconducting connection between the oxide superconducting materials.
[0018]
The invention according to claim 6 is the invention according to claim 4 or 5, characterized in that the oxide superconducting precursors (A) and (B) are Bi-based oxide superconducting precursors. is there.
[0019]
The invention according to claim 7 is the invention according to claim 4 or 5, characterized in that the oxide superconducting precursors (A) and (B) are Bi-based 2212 type oxide superconducting precursors. Is.
[0020]
The inventions according to claims 1 to 7 have the following effects.
[0021]
Inclusions contacting the provisional oxide superconducting material to each other is an oxide superconductor precursor (A) a higher melting point than, and the oxide superconductor precursor (A) and the composition ratio of but each composition component composed of the same composition It comprises different oxide superconducting precursors (B), and the temperature of the superconducting heat treatment is higher than the melting point of the oxide superconducting precursor (A) and lower than the melting point of the oxide superconducting precursor (B). Since the oxide superconducting precursor (A) is superconducted, the superconducting heat treatment melts the oxide superconducting precursor (A), and the melt comes into contact with the oxide superconducting precursor (B). However, since the oxide superconducting precursor (B) is not completely melted, the flow of the melt of the oxide superconducting precursor (A) is stopped. As a result, the outflow of the melt of the oxide superconducting precursor (A) is suppressed, and it is possible to prevent the formation of gaps in the superconducting connection portions of the oxide superconductors between the oxide superconducting materials. In addition, the yield related to superconducting connection can be improved.
[0022]
The inclusion oxide superconducting precursor (B) in contact with the melt of the oxide superconducting precursor (A) of the temporary oxide superconducting material is solidified and densified, and the temporary oxide Adhesiveness with the superconductor covering is also improved. For this reason, this inclusion can sufficiently secure the strength of the superconducting connection portion of the oxide superconducting material.
[0023]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to the drawings.
[0024]
FIG. 1 is a process diagram showing a process of manufacturing a superconducting connection structure of Bi-based 2212 type oxide superconducting material, which is an embodiment of a superconducting connecting method of an oxide superconducting material according to the present invention.
[0025]
A superconducting coil (both not shown) constituting a superconducting magnet such as an MRI (nuclear magnetic resonance imaging) medical diagnostic apparatus or NMR (nuclear magnetic resonance apparatus) is Bi as at least two oxide superconducting materials shown in FIG. The system 2212 type oxide superconducting materials 11 and 12 are superconductively connected to each other. As shown in FIG. 1, these superconducting connections are obtained by winding a coating tape 16 as an inclusion around the connecting portion 15 of the sheath tape materials 13 and 14 as a temporary oxide superconducting material and then performing superconducting heat treatment. To be implemented.
[0026]
Hereinafter, the superconducting connection method shown in FIG. 1 will be described in detail.
[0027]
(1) First, the sheath tape materials 13 and 14 are prepared using a powder-in-tube method. That is, Bi ₂ O ₃ , SrCO ₃ , CaCO ₃ , and CuO powders were mixed so as to have a composition ratio of Bi: Sr: Ca: Cu = 2: 2: 1: 2, and calcined at about 820 ° C. After pulverization, this calcination and pulverization are repeated twice to form a Bi-based 2212 type oxide superconducting precursor (A) 17 powder. Next, a powder of the Bi-based 2212 type oxide superconducting precursor (A) 17 is filled in a base material 18 as a covering made of an Ag pipe having an outer diameter of 10 mm and an inner diameter of 9 mm, for example, and this Bi-based 2212 type The oxide superconducting precursor (A) 17 is covered with a base material 18. Thereafter, the Bi-type 2212 type oxide superconducting precursor (A) 17 powder filled in the substrate 18 was drawn with a draw bench to an outer diameter of 2 mm, and then roll-rolled. The sheath tape materials 13 and 14 having a width of 2 to 1 mm and a width of 3 to 6 mm are prepared. Here, the melting point of the Bi-based 2212 type oxide superconducting precursor (A) 17 in these sheath tape materials 13 and 14 is 880 ° C.
[0028]
(2) On the other hand, the coated tape 16 is manufactured. That is, Bi ₂ O ₃ , SrCO ₃ , CaCO ₃ , and CuO powders were mixed so as to have a composition ratio of Bi: Sr: Ca: Cu = 1.95: 2: 1: 2.05. It is calcined at 820 ° C. and pulverized, and this is repeated twice to form a Bi-based 2212 type oxide superconducting precursor (B) 19 powder. Next, an organic solvent (for example, ethanol) is added to the Bi-based 2212 type oxide superconducting precursor (B) 19 powder and stirred. Thereafter, the suspension formed by this agitation is coated on a base material 20 made of an Ag plate having a width of 10 mm, a length of 100 mm, and a thickness of 50 μm, for example, to produce a coated tape 16. Here, the melting point of the powder of the Bi-based 2212 type oxide superconducting precursor (B) 19 in the coated tape 16 is 887 ° C., which is higher than the melting point of the Bi-based 2212 type oxide superconducting precursor (A) 17.
[0029]
As described above, the Bi-based 2212 type oxide superconducting precursor (A) 17 and the Bi-based 2212 type oxide superconducting precursor (B) 19 have the same composition, but the composition ratios of the respective composition components are different. The difference in composition ratio between the Bi-based 2212 type oxide superconducting precursor (A) 17 and the Bi-based 2212 type oxide superconducting precursor (B) 19 is set within ± 10% except for 0% for each component. It is most desirable. For example, the Bi component of the Bi-based 2212 type oxide superconducting precursor (A) 17 is “2” and the Bi-based 2212 type oxide superconducting precursor (B) 19 is “1.95”. There is a difference of ± 0.5%.
[0030]
The reason for setting the difference between the composition components of the Bi-based 2212 type oxide superconducting precursor (A) 17 and the Bi-based 2212 type oxide superconducting precursor (B) 19 within ± 10% excluding 0% is 0% Then, the composition of the Bi-based 2212 type oxide superconducting precursor (A) 17 and the Bi-based 2212 type oxide superconducting precursor (B) 19 are completely the same, and their melting points are also completely matched. There is a possibility, and when it becomes ± 10% or more, there is no problem in preventing the outflow of the melt of the Bi-based 2212 type oxide superconducting precursor (A) 17 described later, but the Bi-based 2212 type oxide superconducting precursor The Bi 2212 type oxide superconductor (A) 21 and Bi 2212 described below are affected by the Bi 2212 type oxide superconducting precursor (B) 19 which is in contact with the melt of the body (A) 17 and melted in a small amount. Type oxide superconductor (B) 22 This is because a different phase may be generated in the connection portion.
[0031]
(3) After manufacturing the sheath tape materials 13 and 14 and the coat tape 16 as described above, the end surfaces of the sheath tape materials 13 and 14 are butted and joined as shown in FIGS. 1 (A) and 1 (B). .
[0032]
(4) Next, the coated tape 16 is cut out to a predetermined length, and as shown in FIGS. 1C and 1D, the Bi-based 2212 type oxide superconducting precursor (B) 19 of the coated tape 16 is sheathed as a sheath tape material. The coated tape 16 is wound around the connecting portion 15 of the sheath tape materials 13 and 14 in contact with the base materials 18 of 13 and 14. The sheath tape members 13 and 14 are further brought into contact with each other via the Bi-based 2212 type oxide superconducting precursor (B) 19 of the coat tape 16 by joining the end faces to each other.
[0033]
(5) After that, it is higher than the melting point (880 ° C.) of the Bi-based 2212 type oxide superconducting precursor (A) 17 and lower than the melting point (887 ° C.) of the Bi-based 2212 type oxide superconducting precursor (B) 19. The sheath tape members 13 and 14 and the coating tape 16 shown in FIG. 1D are subjected to superconducting heat treatment at a maximum temperature, for example, a maximum temperature of 883 ° C. (FIG. 1 (E)).
[0034]
By this superconducting heat treatment, Bi-based 2212 type oxide superconducting precursor (A) 17 becomes Bi-based 2212 type oxide superconducting conductor (A) 21 and Bi-based 2212 type oxide superconducting precursor (B) 19 becomes Bi-based. 2212 type oxide superconductor (B) 22 and sheath tape materials 13 and 14 become Bi type 2212 type oxide superconducting materials 11 and 12, respectively, and Bi type 2212 type oxide superconducting materials 11 and 12 are connected to each other. A Bi-based 2212 type oxide superconducting connection structure 10 is formed by superconducting connection.
[0035]
The temperature difference between the maximum temperature of the superconducting heat treatment and the melting point of the Bi-based 2212 type oxide superconducting precursor (B) 19 is preferably within 10 ° C. If the difference between the two is 10 ° C. or more, even if it is in contact with the melt of Bi-based 2212 type oxide superconducting precursor (A) 17 melted by superconducting heat treatment, Bi-based 2212 type oxide superconducting precursor (B ) 19 may not melt at all, and the melt of Bi-based 2212 type oxide superconducting precursor (A) 17 may flow out or ooze out as in the case of the conventional Ag tape 55.
[0036]
Ten samples (samples) of the Bi-based 2212 type oxide superconducting connection structure 10 thus formed were observed. As shown in FIG. 2, the Bi-based 2212 type oxide superconducting connection was observed for all the samples. No or almost no trace of melt outflow of the Bi-based 2212 type oxide superconducting precursor (A) 17 was observed at the superconducting connection 23 of the structure 10.
[0037]
Therefore, according to the above embodiment, the following effects (1) and (2) are achieved.
[0038]
(1) The coating tape 16 that contacts the sheath tape materials 13 and 14 has a higher melting point than the Bi-based 2212 type oxide superconducting precursor (A) 17 of the sheath tape materials 13 and 14, and this Bi-based 2212 type The Bi-type 2212 type oxide superconducting precursor (B) 19 having the same composition as the oxide superconducting precursor (A) 17 is provided, and the Bi-type 2212 type of the sheath tape materials 13 and 14 is formed by superconducting heat treatment. Bi based 2212 type oxide superconducting precursor at a temperature higher than the melting point of oxide superconducting precursor (A) 17 and lower than the melting point of Bi based 2212 type oxide superconducting precursor (B) 19 of coating tape 16 (A) Since 17 is superconductive, the Bi-type 2212 type oxide superconductive precursor (A) 17 of the sheath tape materials 13 and 14 is melted by this superconductive heat treatment. The liquid comes into contact with the Bi-based 2212 type oxide superconducting precursor (B) 19 of the coating tape 16 and attempts to melt it, but the oxide superconducting precursor (B) 19 does not melt completely, so the sheath The flow of the melt of the Bi-based 2212 type oxide superconducting precursor (A) 17 of the tape materials 13 and 14 stops. As a result, the outflow of the melt of the Bi-based 2212 type oxide superconducting precursor (A) 17 of the sheath tape materials 13 and 14 is suppressed, and the Bi-based 2212 type oxide superconducting material 11 of the Bi-based 2212 type oxide superconducting material 11 is suppressed. The superconducting connection can be satisfactorily performed by preventing the formation of a gap in the superconducting connection portion 23 between the body (A) 21 and the Bi-based 2212-type oxide superconductor (B) 22 of the Bi-based 2212-type oxide superconducting material 12, The yield regarding superconducting connection can be improved.
[0039]
(2) The Bi-based 2212 type oxide superconducting precursor (B) 19 of the coating tape 16 in contact with the melt of the Bi-based 2212 type oxide superconducting precursor (A) 17 of the sheath tape materials 13 and 14 is a solid phase. While being densified by sintering, the adhesion of the sheath tape materials 13 and 14 to the base material 18 is also improved. For this reason, the coating tape 16 can sufficiently secure the strength of the superconducting connection portions 23 of the Bi-based 2212 type oxide superconducting materials 11 and 12.
[0040]
As mentioned above, although this invention was demonstrated based on the said embodiment, this invention is not limited to this.
[0041]
For example, the present invention can be applied even if the Bi 2212 type oxide superconductor (B) 22 of the Bi 2212 type oxide superconductors 11 and 12 has a multi-core structure or a multilayer structure. Further, the end surfaces of the sheath tape materials 13 and 14 are arranged apart from each other before the superconducting heat treatment, and the sheath tape materials 13 and 14 come into contact with each other only through the coat tape 16 wound around the sheath tape materials 13 and 14. May be. Furthermore, the base material 18 or the base material 20 is not limited to Ag, and may be configured to include Au, Pt, Pd, or Cu.
[0042]
Moreover, even if the present invention is applied to a Bi-based 2223 type oxide superconducting material having a composition ratio of Bi: Sr: Ca: Cu = 2: 2: 2: 3, not limited to the Bi-based 2212 type oxide superconducting material. Furthermore, the present invention may be applied to a Y-based oxide superconductor or a Tl- based oxide superconductor. Further, the present invention may be applied to metallic superconducting materials such as Nb ₃ Al, NbTi, and Nb ₃ Sn as long as they are superconducting heat treatment that involves melting and solidification in superconducting connection.
[0043]
In addition to the powder-in-tube method, the sheath tape materials 13 and 14 are manufactured by a dip code method, a doctor blade method, a coating method, a jelly roll method, a thermal spraying method, a screen printing method, a vapor deposition method, a CVD (Chemical Vapor Deposition). : A chemical vapor deposition method, a sputtering method, a laser ablation method or the like, a tape material or a wire material may be used.
[0044]
Furthermore, the superconducting connection method and connection structure of the present invention may be applied to a transmission cable, a current lead, a magnetic shield, a current limiter, a permanent current switch, etc. in addition to a superconducting magnet.
[0045]
【The invention's effect】
According to the superconducting connection method of the oxide superconducting material according to the invention of claim 1 and the superconducting connection structure of the oxide superconducting material according to the invention of claim 4, the oxide superconducting precursor (A) inclusions contacting at least two of the temporary oxide superconducting material to each other with the oxide superconductor precursor (a) a higher melting point than, but of the same composition and the oxide superconductor precursor (a) and the It comprises an oxide superconducting precursor (B) having different composition ratios of the composition components, and the superconducting heat treatment for superconducting connection between the oxide superconducting materials is higher than the melting point of the oxide superconducting precursor (A), In addition, since the oxide superconducting precursor (A) is superconducted at a temperature lower than the melting point of the oxide superconducting precursor (B), the formation of a gap in the superconducting connecting portion can be prevented and superconducting connection can be carried out satisfactorily. .
[Brief description of the drawings]
FIG. 1 is a process diagram showing a process for manufacturing an oxide superconducting connection structure of a Bi-based 2212 type oxide superconducting material, which is an embodiment of a superconducting connection method of an oxide superconducting material according to the present invention.
2 is a chart showing test results of samples 1 to 10 in the Bi-based 2212 type oxide superconducting connection structure shown in FIG.
FIG. 3 is a process diagram showing a process for manufacturing a conventional oxide superconducting connection structure of a Bi-based 2212 type oxide superconducting material.
4 is a chart showing the inspection results of samples 11 to 20 in the Bi-based 2212 type oxide superconducting connection structure shown in FIG. 3 (F).
[Explanation of symbols]
10 Bi-based 2212-type oxide superconducting connection structure 11 Bi-based 2212-type oxide superconducting material 12 Bi-based 2212-type oxide superconducting material 13 Sheath tape material (temporary oxide superconducting material)
14 Sheath tape material (temporary oxide superconducting material)
16 Coated tape (inclusions)
17 Bi-type 2212 oxide superconducting precursor (A)
18 Base material (covered body)
19 Bi-based 2212-based oxide superconducting precursor (B)
21 Bi-type 2212 oxide superconductor (A)
22 Bi-based 2212 oxide superconductor (B)

Claims

The oxide superconducting precursor (A) is covered with a covering, and at least two provisional oxide superconducting materials are brought into contact with each other through inclusions, and thereafter a superconducting heat treatment is performed, In the superconducting connection method of the oxide superconducting material, the oxide superconducting precursor (A) is an oxide superconductor, the temporary oxide superconducting material is the oxide superconducting material, and these oxide superconducting materials are superconductingly connected.
An oxide superconducting precursor having a melting point higher than that of the oxide superconducting precursor (A) and having the same composition as that of the oxide superconducting precursor (A), but having a different composition ratio of each composition component ( B) comprising
Superconducting the oxide superconducting precursor (A) at a temperature higher than the melting point of the oxide superconducting precursor (A) and lower than the melting point of the oxide superconducting precursor (B). A superconducting connection method for an oxide superconducting material, characterized by comprising:

The superconducting connection method for an oxide superconducting material according to claim 1, wherein the oxide superconducting precursors (A) and (B) are Bi-based oxide superconducting precursors.

The superconducting connection method for an oxide superconducting material according to claim 1, wherein the oxide superconducting precursors (A) and (B) are Bi-based 2212 type oxide superconducting precursors.

At least two provisional oxide superconducting materials constituted by covering the oxide superconducting precursor (A) with a covering are brought into contact with each other through inclusions, and the oxide superconducting precursor ( In the superconducting connection structure of an oxide superconductor in which A) is an oxide superconductor, the temporary oxide superconductor is an oxide superconductor, and these oxide superconductors are superconductively connected to each other.
An oxide superconducting precursor having a melting point higher than that of the oxide superconducting precursor (A) and having the same composition as that of the oxide superconducting precursor (A), but having a different composition ratio of each composition component ( B) comprising
Superconducting the oxide superconducting precursor (A) at a temperature higher than the melting point of the oxide superconducting precursor (A) and lower than the melting point of the oxide superconducting precursor (B). A superconducting connection structure of an oxide superconducting material, characterized by comprising:

5. The superconducting connection structure of oxide superconducting material according to claim 4, wherein an oxide superconducting coil is formed by superconducting connection between the oxide superconducting materials.

6. The superconducting connection structure of oxide superconducting material according to claim 4, wherein the oxide superconducting precursors (A) and (B) are Bi-based oxide superconducting precursors.

6. The oxide superconducting superconducting connection structure according to claim 4, wherein the oxide superconducting precursors (A) and (B) are Bi-based 2212 type oxide superconducting precursors.