JP3709999B2

JP3709999B2 - Manufacturing method of high-temperature superconducting joints

Info

Publication number: JP3709999B2
Application number: JP32485894A
Authority: JP
Inventors: 孝夫中田; 修一郎下田; 寅之助芦沢
Original assignee: Japan Science and Technology Agency; National Institute for Materials Science; National Institute of Japan Science and Technology Agency
Current assignee: Japan Science and Technology Agency; National Institute for Materials Science; National Institute of Japan Science and Technology Agency
Priority date: 1994-11-24
Filing date: 1994-12-27
Publication date: 2005-10-26
Anticipated expiration: 2020-10-26
Also published as: JPH08203652A

Description

【０００１】
【産業上の利用分野】
本発明は、製造が比較的容易な小型の高温超電導体から大型の高温超電導体を製造するのに有効な高温超電導接合体の製造法に関する。
【０００２】
【従来の技術】
高温超電導体は、焼成が可能な温度幅が狭く、また機械的強度が低いため機械加工が困難であるなどの理由で大型又は複雑な形状のものを一体で製造できないという問題点がある。この問題点に対して、あらかじめ適当な大きさ又は形状の金属、セラミックス等の基材を作製し、この基材の表面に高温超電導体を焼き付け、基材及び高温超電導体同士を接合して一体化する方法が考えられている。基材及び高温超電導体同士を接合する方法としては、例えば特開平５−１４５２６７号公報に示されるように、基材上に形成した高温超電導体同士を接触させてその接合部分を局所的に加熱して接合したり、基材と高温超電導体との複合基材の各層それぞれを接合する方法が提案されている。
【０００３】
【発明が解決しようとする課題】
しかしながら、高温超電導体結晶は緻密に焼結しにくい性質のため、高温超電導体を単に加熱焼成する方法では多孔質のままになり、高温超電導体結晶間に残存する隙間によって良好な超電導接合（超電導特性が途中で遮断されずに接続されるようにした接合）が困難であり、良好な超電導接合を得ようとして加熱温度を上昇させると高温超電導体結晶が分解又は溶融したり、基材と反応するなどの問題点が生じる。
【０００４】
即ち高温超電導体は、焼結しにくく、また極めて狭い温度条件で結晶生成及び成長するものであり、接合部分に超電導体結晶粉を塗布し、これを加熱して接合部分を緻密化させて超電導接合をしようとすると、高温の処理温度が必要になるため、周囲の高温超電導体がその温度により相変化して超電導体でなくなったり、高温超電導体以外の結晶が生成するなどにより特性を低下させてしまうという問題点が生じる。
【０００５】
例えば、良好な超電導特性が得られる方法として知られている部分溶融法は、高温超電導体結晶がある結晶と融液とに分解して緻密化し、次に冷却して再度高温超電導体結晶に結晶化させる方法であるが、これを加熱接合の条件に適用しようとすると、その部分溶融で生じた融液で周囲の高温超電導体も分解してしまう。従って部分的な加熱焼成で接合部分だけは超電導体化して良好な接合が得られても、周囲の高温超電導体は特性の低下又は非超電導化するため結局良好な超電導接合とはならない。
特性の低下を避けるには、全体を焼成するのと同じような精密な焼成技術が必要であるが、全体を焼成するのでは接合する意義が無くなる。
【０００６】
本発明は、上記のような問題点が生じないよう、接合する高温超電導体を分解及び／又は溶融する温度に加熱しないで、しかも望ましい板状の高温超電導体結晶が基材表面に並行に配向した状態になる良好な超電導体接合が得られる高温超電導接合体の製造法を提供するものである。
【０００７】
【課題を解決するための手段】
本発明者らは、基材上に形成された高温超電導体同士を接合するため、高温超電導体結晶が分解する温度より低い温度で、各種の高温超電導体前駆体が示す挙動を詳細に調査した結果、高温超電導体前駆体は加熱すると高温超電導体結晶を析出するが、その作製法によっては結晶化する前に溶融して緻密な組織が得られることを見出した。溶融する例をさらに検討した結果、溶融するのは高温超電導体の組成からはずれた組成物であり、溶融しながら近傍の組織を徐々に溶かし込むことで高温超電導体の組成になり、高温超電導体結晶を析出する。即ち溶融などの方法で粉体の粒子単位で均一な組成にすると加熱工程で溶融しにくくなり、高温超電導体の組成になり、高温超電導体結晶が析出することを見出し本発明を完成するに至った。
【０００８】
本発明は、基材上に形成された高温超電導体同士を接合する方法において、貴金属板上に高温超電導体前駆体の膜を形成して複合材料を得、次いで該複合材料の高温超電導体前駆体の膜の部分を下側にして接合する高温超電導体間の上部に載置した後、基材上に形成された高温超電導体結晶が分解及び／又は溶融せず、かつ載置した高温超電導体前駆体の一部が溶融し、その後高温超電導体前駆体全体が結晶化する温度で加熱して高温超電導体同士を接合することを特徴とする高温超電導接合体の製造法に関する。
【０００９】
本発明において、基材の種類、組成については特に制限はないが、高温超電導体の加熱温度に耐えられ、かつ機械的強度を有する材料、例えばインコネル、ステンレス、ハステロイ等の金属基材、セラミックスなどを用いることが好ましく、このうち加工の容易さ、熱膨張率等の点からインコネルを用いることが好ましい。なお加熱工程で高温超電導体が基材と望ましくない反応を起こすおそれがある場合は、基材の表面に銀、金等の貴金属の膜や酸化マグネシウムの膜を形成して用いられる。
貴金属の膜を形成する場合、下地金属として銅又は銅合金の膜を形成しておけば、貴金属の膜が剥離するのを防止できるので好ましい。
【００１０】
高温超電導体前駆体は、高温超電導体の組成になるように酸化物又は炭酸塩などの原料を秤量、混合、仮焼したもの若しくは前記原料を秤量、混合、仮焼及び／又は溶融後粉砕した２種類以上の粉体をさらに混合したものを用いることが好ましい。該高温超電導体前駆体は、高温超電導体の分解温度以下で溶融し、次いで高温超電導体結晶を生成させるために、各組成からなる粒子が均一に分散された微粉を用いることが好ましく、その平均粒径は溶融し易く、取り扱いの容易さから１〜１５μｍであることが好ましく、３〜１０μｍであればさらに好ましい。
【００１１】
接合する高温超電導体は介在させる高温超電導体前駆体とは異なり、各原料を混合した後、溶融などの方法で粉体の粒子単位まで均一な組成にすれば、高温超電導体の結晶含有率が高く、加熱工程で異相の生成等の異常な挙動が低減できるため好ましい。また銀を添加すれば結晶の生成を促進するなどの効果があり好ましい。
【００１２】
高温超電導体前駆体に、接合する高温超電導体と同じ結晶構造を有する高温超電導体結晶粉を５０重量％含有させれば、結晶が成長し易く、成長の方向も制御でき、また安価に製造できるので好ましい。
【００１３】
高温超電導体前駆体を高温超電導体間に介在させる方法については特に制限はなく、例えば高温超電導体前駆体の粉末をスプレーで吹き付けたり、スラリー状又はペースト化した液状の高温超電導体前駆体を塗布したり、シート状に成形した高温超電導体前駆体を張り合わせたりする等の方法で介在させることができる。高温超電導体同士は重ねてもよく、また横に並べて高温超電導体前駆体を高温超電導体間に介在させてもよい。
【００１４】
高温超電導体前駆体の膜を形成する貴金属板としては、銀または銀を主成分とする合金板を用いることが好ましい。高温超電導体前駆体の膜の形成方法についても特に制限はないが、シート状に成形した高温超電導体前駆体を貴金属板上に加圧して成形したものを接合部に張り合わせれば高温超電導体結晶が配向し、かつ高温超電導体結晶の成長方向が制御できるので好ましい。
【００１５】
高温超電導体前駆体及び接合する高温超電導体に用いられる超電導体の種類については特に制限はなく、例えばＢｉ系高温超電導体、Ｙ系高温超電導体、Ｔｌ系高温超電導体等が適用できるが本発明においてはＢｉ系高温超電導体を用いれば良好な超電導接合が得られ易いので好ましい。なおＢｉ系高温超電導体には２２１２相、２２２３相等があるが、このうちＢｉ系２２１２相が操作し易いうえ、結晶成長速度が比較的大きいので好ましい。
【００１６】
高温超電導体同士を接合するための加熱条件は、基材上に形成された超電導体結晶が分解及び／又は溶融せず、かつ介在する高温超電導体前駆体の一部が溶融し、その後高温超電導体前駆体全体が結晶化する温度で加熱することが必要とされ、これ以外の条件では超電導接合が困難であったり、超電導特性が低下するなどの問題点が生じる。なお、加熱に最適の温度は、高温超電導体前駆体の結晶粒径や周囲の酸素分圧、昇温速度等の焼成条件により変化するため適宜選定する。焼成雰囲気は大気中、酸素分圧を制御した雰囲気中で行うことが好ましい。
【００１７】
【実施例】
以下本発明の実施例を説明する。なお本発明はこれらに制限されない。
参考例
純度９９．９重量％以上の酸化ビスマス（高純度化学研究所製、３Ｎ）４６６ｇ、炭酸ストロンチウム（高純度化学研究所製、３Ｎ）２９５．２ｇ、炭酸カルシウム（高純度化学研究所製、３Ｎ）１００．１ｇ及び酸化第二銅（高純度化学研究所製、３Ｎ）１５９．１ｇを秤量し、合成樹脂製ボールミルに直径１０mmの合成樹脂製ボール２kg及び蒸留水１kgと共に入れ７２時間湿式混合した。混合液は１００℃で２４時間乾燥し、乾燥粉を銀製容器に移し替えて８２０℃で５時間仮焼した。仮焼後らいかい機で平均粒径が７μｍに乾式粉砕して高温超電導体前駆体（Ａ）を得た。この高温超電導体前駆体（Ａ）は２２１２相が約６重量％及び少量の同定できない結晶を含む非晶質体であった。
【００１８】
次に、上記で得た高温超電導体前駆体（Ａ）をジルコニア容器に入れて、１０５０℃で２時間加熱後、内容物を銀板上に流し出して急冷し、さらにらいかい機で平均粒径８μｍに乾式粉砕して溶融粉（Ａ）を得た。
【００１９】
次いで溶融粉（Ａ）１００重量部にポリビニールブチラール樹脂（積水化学製、商品名ＢＬ−２）５重量部、ジブチルフタレート（和光純薬製、試薬一級）２重量部及びエチルアルコール（和光純薬製、試薬一級）１５重量部を添加して混合した後、真空脱気して得られたスラリーを厚さが１００μｍのポリエステル製フィルム（東レ製）上に供給し、ドクターブレード法でシート成形して厚さ１５０μｍのグリーンシート（Ａ）を得た。
【００２０】
この後厚さ０．１mmの銀板上に上記で得たグリーンシート（Ａ）を６０℃で１０MPaの条件で熱圧着し、断面流速５cm/分で空気を流しながら焼成し、結晶が十分に成長して配向し、かつ平滑な表面になる条件及び高温超電導体結晶が得られる温度条件を調べた。その結果、最高温度は８７２〜８８６℃の範囲で、保持時間は２時間以内、降温速度は８５０℃以上では５℃／時間以下が良好であることを確認した。そこで断面流速５cm/分で空気を流しながら、８８３℃に加熱し、３０分間保持した後２℃／時間の速度で８５０℃まで降温し、以後１００℃／時間の速度で室温まで冷却して銀板上に高温超電導体を形成した超電導複合体を得た。次いで得られた超電導複合体の超電導体結晶が溶融する温度を調べるため、超電導複合体を８６０〜８９０℃まで１℃ずつ温度を変えて２０分保持した後に炉外に取り出して、Ｘ線回折法で結晶状態を調べた。その結果、８７３℃を越えると含まれていたＢｉ系２２１２相結晶は消失し、２２０１結晶が大量に検出されたことから加熱温度の限界を８７３℃とした。
【００２１】
一方高温超電導体前駆体（Ａ）１００重量部にグリーンシート（Ａ）を得る工程と同様の工程を経て厚さ１７０μｍのグリーンシート（Ｂ）（高温超電導体前駆体(Ｂ)）を得た。この後、上記と同様に厚さ０．１mmの銀板上に上記で得た高温超電導体前駆体（Ｂ）を６０℃で１０MPaの条件で熱圧着し、断面流速５cm/分で空気を流しながら焼成し、高温超電導体前駆体（Ｂ）の一部が溶融し、かつ高温超電導体結晶が得られる温度条件を調べた。その結果、最高温度は８６５〜８７５℃の範囲で、保持時間は２時間以内、降温速度は８５０℃以上では５℃／時間以下の降温速度が良好であることを確認した。
【００２２】
次に高温超電導体前駆体（Ｂ）の超電導体結晶が溶融する温度を調べるため、銀板上に載置した高温超電導体前駆体（Ｂ）を８６０〜８９０℃まで１℃ずつ温度を変えて２０分保持した後に炉外に取り出して、Ｘ線回折法で結晶状態を調べた。その結果、８７１℃以上になると含まれていたＢｉ系２２１２相結晶は消失し、２２０１結晶が大量に検出された。なお高温超電導体前駆体（Ｂ）は８７０温度以下から急冷しても２２１２相と共に多量の２２０１相が検出され、また８６８℃以上の温度で再加熱して除冷すると、超電導体ではない柱状結晶が大量に生成した。
【００２３】
上記で得られた超電導複合体を図１の（ａ）及び（ｂ）に示すように突き合わせ、かつ突き合わせた双方の銀板１、１′の先端部を加締めて固定した後、銀板１、１′の上部に形成した高温超電導体２、２′間に、上記で得た高温超電導体前駆体（Ｂ）３をブチルアルコール（和光純薬製、試薬）を塗布して接着し、大気中で最高温度が８６８℃で３０分間保持（加熱処理）し、その後８５０℃まで１５時間かけて降温し、更に２０℃まで５時間かけて冷却して高温超電導接合体を得た。なお冷却工程で６８０℃からは雰囲気を窒素雰囲気に変更した。図１の（ｂ）において４は銀板１、１′の加締め部である。
【００２４】
上記で得た高温超電導接合体の接合部とその周辺を顕微鏡及びＸ線回折法で観察すると共に４端子法で臨界電流密度（以下Ｊｃとする）を測定した。その結果、高温超電導体の液体窒素温度７７．３ＫでのＪｃは、接合前は８６００A/mm²及び接合後は７４００A/mm²であり、また接合部分のＪｃは、接合部分の超電導体膜厚さで算出した値で６２００A/mm²であった。また接合部の接合状態は、高温超電導体の流動による異常な凹凸、発泡、異相等がなく、接合面と並行に良く配向されており、良好な接合が得られていた。
【００２５】
比較例１
超電導複合体を突き合わせ、銀板の上部に形成した高温超電導体間に高温超電導体前駆体（Ｂ）を接着した後の加熱温度を８６４℃とした以外は実施例１と同様の工程を経て高温超電導接合体を得た。得られた高温超電導接合体の接合部とその周辺を顕微鏡及びＸ線回折法で観察すると共に４端子法でＪｃを測定した。その結果、高温超電導体の液体窒素温度７７．３ＫでのＪｃは、接合前は８６００A/mm²及び接合後は８４００A/mm²であり、また接合部分のＪｃは、接合部分の超電導体膜厚さで算出した値で８００A/mm²と低かった。また接合部分は光沢がなく、小さな凹凸を示し、超電導体の２２１２相結晶は生成していたがごく微細であった。
【００２６】
比較例２
超電導複合体を突き合わせ、銀板の上部に形成した高温超電導体間に高温超電導体前駆体（Ｂ）を接着した後の加熱温度を８７５℃とした以外は実施例１と同様の工程を経て高温超電導接合体を得た。得られた高温超電導接合体の接合部とその周辺を顕微鏡及びＸ線回折法で観察すると共に４端子法でＪｃを測定した。その結果、高温超電導体の液体窒素温度７７．３ＫでのＪｃは、接合前は８６００A/mm²及び接合後は４３００A/mm²であり、また接合部分のＪｃは、接合部分の超電導体膜厚さで算出した値で１２００A/mm²と低かった上に、接合部分は高温超電導体が溶けて流出し、高温超電導体の合計膜厚さ１００μｍの設定値に対して約２０μｍに減少した。また、異相（柱状結晶）が接合の境界に異常生成していた。
【００２７】
実施例１
参考例で得た超電導複合体から高温超電導体の部分だけを剥がしとり、乳鉢で軽く粗砕して４０μｍの板状結晶体を得た。次いで参考例で得た高温超電導体前駆体（Ａ）７０重量％に前記板状結晶体を３０重量％添加したもの１００重量部に、参考例のグリーンシート（Ａ）を得る工程と同様の工程を経て厚さ１７０μｍのグリーンシート（高温超電導体前駆体（Ｃ））を得た。
【００２８】
次に参考例で得た超電導複合体を図２の（ａ）及び（ｂ）に示すように突き合わせ、かつ突き合わせた双方の銀板１、１′の先端部を加締めて固定した後、上記とは別の厚さ０．１mmの銀板６上に上記で得たグリーンシート（Ｃ）、即ち高温超電導体前駆体（Ｃ）７を６０℃で１０MPaの条件で熱圧着して複合材料５を得た。次いで該複合材料５の高温超電導体前駆体（Ｃ）の部分を下側にして、超電導複合体の高温超電導体２、２′間の上部に載置し、しかる後大気中で８７０℃で３０分間保持（加熱処理）し、その後８５０℃まで１５時間かけて降温し、更に２０℃まで５時間かけて冷却して高温超電導接合体を得た。なお冷却工程で６８０℃からは雰囲気を窒素雰囲気に変更した。
【００２９】
上記で得た高温超電導接合体の接合部とその周辺を顕微鏡及びＸ線回折法で観察すると共に４端子法でＪｃを測定した。その結果、高温超電導体の液体窒素温度７７．３ＫでのＪｃは、接合前は８６００A/mm²及び接合後は７９００A/mm²であり、また接合部分のＪｃは、接合部分の超電導体膜厚さで算出した値で９８００A/mm²であった。また接合部の接合状態は、高温超電導体の流動による異常な凹凸、発泡、異相等がなく、接合面と並行に良く配向されており、良好な接合が得られていた。
【００３０】
実施例２
純度９９．９重量％以上の酸化ビスマス（高純度化学研究所製、３Ｎ）３００ｇ、炭酸ストロンチウム（高純度化学研究所製、３Ｎ）１４７．６ｇ、炭酸カルシウム（高純度化学研究所製、３Ｎ）５０．１ｇ及び酸化第二銅（高純度化学研究所製、３Ｎ）７９．５ｇを秤量し、合成樹脂製ボールミルに直径１０mmの合成樹脂製ボール１kg及び蒸留水５００ｇと共に入れ７２時間湿式混合した。混合物は１００℃で２４時間乾燥し、乾燥粉をジルコニア容器に移し替えて、１０５０℃で２時間加熱後、内容物を銀板上に流し出して急冷し、さらにらいかい機で平均粒径８μｍに乾式粉砕して溶融粉（Ｂ）を得た。
【００３１】
一方上記とは別に純度９９．９重量％以上の酸化ビスマス（高純度化学研究所製、３Ｎ）１６６ｇ、炭酸ストロンチウム（高純度化学研究所製、３Ｎ）１４７．６ｇ、炭酸カルシウム（高純度化学研究所製、３Ｎ）５０．０ｇ及び酸化第二銅（高純度化学研究所製、３Ｎ）７９．６ｇを秤量し、合成樹脂製ボールミルに直径１０mmの合成樹脂製ボール１kg及び蒸留水５００ｇと共に入れ７２時間湿式混合した。混合物は１００℃で２４時間乾燥し、乾燥粉をジルコニア容器に移し替えて、１０５０℃で２時間加熱後、内容物を銀板上に流し出して急冷し、さらにらいかい機で平均粒径８μｍに乾式粉砕して溶融粉（Ｃ）を得た。
【００３２】
さらにＢｉ系２２１２相の理論組成になるように上記で得た溶融粉（Ｂ）を１０２．２ｇ及び溶融粉（Ｃ）を６５．４ｇを秤量し、この溶融粉（Ｂ）及び（Ｃ）１００重量部にポリビニールブチラール樹脂（積水化学製、商品名ＢＬ−２）５重量部、ジブチルフタレート（和光純薬製、試薬一級）２重量部及びエチルアルコール（和光純薬製、試薬一級）１５重量部を添加して混合した後、真空脱気して得られたスラリーを厚さが１００μｍのポリエステル製フィルム（東レ製）上に供給し、ドクターブレード法でシート成形して厚さ１７０μｍのグリーンシート（Ｄ）（高温超電導体前駆体(Ｄ)）を得た。
【００３３】
この後厚さ０．１mmの銀板上に上記で得た高温超電導体前駆体（Ｄ）を６０℃で１０MPaの条件で熱圧着し、断面流速５cm/分で空気を流しながら焼成し、高温超電導体前駆体（Ｄ）の一部が溶融し、かつ高温超電導体結晶が得られる温度条件を調べた。その結果、最高温度は８６４〜８７０℃の範囲で、保持時間は２時間以内、降温速度は８５０℃以上は５℃／時間以下が良好であることを確認した。
【００３４】
次に参考例で得た超電導複合体を実施例１と同様の方法で突き合わせ、かつ突き合わせた双方の銀板の先端部を加締めて固定した後、上記とは別の厚さ０．１mmの銀板上に上記で得たグリーンシート（Ｄ）、即ち高温超電導体前駆体（Ｄ）を６０℃で１０MPaの条件で熱圧着して複合材料を得た。次いで該複合材料の高温超電導体複合体（Ｄ）の部分を下側にして、超電導複合体の高温超電導体間の上部に載置し、以下加熱処理を８６７℃で行った以外は実施例１と同様の工程を経て高温超電導接合体を得た。
【００３５】
上記で得た高温超電導接合体の接合部とその周辺を顕微鏡及びＸ線回折法で観察すると共に４端子法でＪｃを測定した。その結果、高温超電導体の液体窒素温度７７．３ＫでのＪｃは、接合前は８６００A/mm²及び接合後は８８００A/mm²であり、また接合部分のＪｃは、接合部分の超電導体膜厚さで算出した値で６３００A/mm²であった。また接合部の接合状態は、高温超電導体の流動による異常な凹凸、発泡、異相等がなく、良好な接合が得られていた。
【００３６】
【発明の効果】
本発明の製造法によって得られる高温超電導接合体は、接合する高温超電導体の超電導特性を低下させることもなく、また接合部分の超電導体結晶も高く配向させることができる為、良好な超電導接合が得られる。
さらに本発明によれば、高温超電導体の一部に欠陥が生じ、高温超電導体で補修する必要が生じた場合にも適用できる。
【図面の簡単な説明】
【図１】（ａ）は本発明の参考例になる高温超電導接合体の製造作業状態を示す平面図及び（ｂ）はその断面図である。
【図２】（ａ）は本発明の一実施例になる高温超電導接合体の製造作業状態を示す平面図及び（ｂ）はその断面図である。
【符号の説明】
１、１′ 銀板
２、２′ 高温超電導体
３高温超電導体前駆体（Ｂ）
４加締め部
５複合材料
６銀板
７高温超電導体前駆体（Ｃ）[0001]
[Industrial application fields]
The present invention relates to a method of manufacturing a high temperature superconducting joint effective for manufacturing a large high temperature superconductor from a small high temperature superconductor that is relatively easy to manufacture.
[0002]
[Prior art]
The high temperature superconductor has a problem that a large or complicated shape cannot be manufactured integrally because the temperature range that can be fired is narrow and the mechanical strength is low and the machining is difficult. In response to this problem, a base material of metal, ceramics, etc. of an appropriate size or shape is prepared in advance, a high temperature superconductor is baked on the surface of this base material, and the base material and the high temperature superconductor are joined together. A way to make it possible is considered. As a method for joining the base material and the high-temperature superconductors, for example, as disclosed in Japanese Patent Laid-Open No. 5-145267, the high-temperature superconductors formed on the base material are brought into contact with each other to locally heat the joint portion. In other words, a method of joining each layer of a composite base material composed of a base material and a high-temperature superconductor has been proposed.
[0003]
[Problems to be solved by the invention]
However, because high-temperature superconductor crystals are difficult to sinter densely, simply heating and firing high-temperature superconductors remains porous, and good superconducting junctions (superconductivity) due to gaps remaining between high-temperature superconductor crystals. It is difficult to bond the properties without being interrupted in the middle), and when the heating temperature is raised to obtain a good superconducting junction, the high-temperature superconductor crystal decomposes or melts or reacts with the substrate. This causes problems.
[0004]
That is, high-temperature superconductors are difficult to sinter and produce and grow crystals under extremely narrow temperature conditions. Superconducting crystal powder is applied to the joints and heated to make the joints dense and superconducting. When joining, a high processing temperature is required, so the surrounding high-temperature superconductor changes its phase depending on the temperature and becomes a non-superconductor, or crystals other than the high-temperature superconductor are generated. The problem that it will end up occurs.
[0005]
For example, the partial melting method known as a method for obtaining good superconducting properties is a method in which a high-temperature superconductor crystal is decomposed into a crystal and a melt and densified, then cooled and crystallized again in the high-temperature superconductor crystal. However, if this is applied to the conditions of heat bonding, the surrounding high-temperature superconductor is also decomposed by the melt generated by the partial melting. Therefore, even if only a bonded portion is converted into a superconductor by partial heating and baking and a good bond is obtained, the surrounding high temperature superconductor deteriorates in characteristics or becomes non-superconductive, so that it does not become a good superconductive bond after all.
In order to avoid the deterioration of the characteristics, a precise firing technique similar to that for firing the entire body is necessary. However, if the entire body is fired, the significance of joining is lost.
[0006]
The present invention does not heat the high-temperature superconductor to be joined to a temperature at which the high-temperature superconductor to be joined is decomposed and / or melted so that the above-mentioned problems do not occur, and the desired plate-like high-temperature superconductor crystal is oriented in parallel on the substrate surface. The present invention provides a method for producing a high-temperature superconducting joined body in which a good superconducting joint can be obtained.
[0007]
[Means for Solving the Problems]
In order to join the high-temperature superconductors formed on the base material, the present inventors investigated in detail the behavior of various high-temperature superconductor precursors at a temperature lower than the temperature at which the high-temperature superconductor crystal decomposes. As a result, when the high-temperature superconductor precursor is heated, a high-temperature superconductor crystal is precipitated, but depending on the preparation method, it has been found that the high-temperature superconductor precursor melts before crystallization to obtain a dense structure. As a result of further examination of the example of melting, it is a composition that deviates from the composition of the high-temperature superconductor, and the composition of the high-temperature superconductor is obtained by gradually dissolving the nearby structure while melting, resulting in a high-temperature superconductor composition. Crystals are precipitated. That is, when the composition is made uniform in units of powder particles by a method such as melting, it is difficult to melt in the heating process, the composition of the high-temperature superconductor is found, and the high-temperature superconductor crystal is precipitated, leading to the completion of the present invention. It was.
[0008]
The present invention relates to a method for joining high temperature superconductors formed on a base material to form a high temperature superconductor precursor film on a noble metal plate to obtain a composite material, and then to the high temperature superconductor precursor of the composite material. The high-temperature superconducting material is placed on the upper part between the high-temperature superconductors to be bonded with the body film side down, and then the high-temperature superconducting crystal formed on the base material is not decomposed and / or melted. The present invention relates to a method for producing a high-temperature superconducting joint, characterized in that a part of a body precursor is melted and then heated at a temperature at which the entire high-temperature superconductor precursor is crystallized to join the high-temperature superconductors.
[0009]
In the present invention, the type and composition of the substrate are not particularly limited, but a material that can withstand the heating temperature of the high-temperature superconductor and has mechanical strength, for example, a metal substrate such as Inconel, stainless steel, Hastelloy, ceramics, etc. Of these, it is preferable to use Inconel from the viewpoints of ease of processing, thermal expansion coefficient, and the like. In the case where the high-temperature superconductor may cause an undesirable reaction with the base material in the heating step, a film of a noble metal such as silver or gold or a magnesium oxide film is used on the surface of the base material.
In the case of forming a noble metal film, it is preferable to form a copper or copper alloy film as the base metal since it is possible to prevent the noble metal film from peeling off.
[0010]
The high-temperature superconductor precursor is obtained by weighing, mixing, calcining, or pulverizing the raw materials such as oxides or carbonates so that the composition of the high-temperature superconductor is obtained. It is preferable to use a mixture of two or more kinds of powders. The high-temperature superconductor precursor is preferably melted below the decomposition temperature of the high-temperature superconductor, and then a fine powder in which particles of each composition are uniformly dispersed is used in order to produce a high-temperature superconductor crystal, and its average The particle size is easily melted and is preferably 1 to 15 μm, more preferably 3 to 10 μm, from the viewpoint of easy handling.
[0011]
Unlike the high-temperature superconductor precursors that intervene, the high-temperature superconductor to be joined has a uniform composition up to the particle size of the powder by mixing each raw material and then melting, etc., so that the crystal content of the high-temperature superconductor is increased. This is preferable because abnormal behavior such as generation of a heterogeneous phase can be reduced in the heating step. Addition of silver is preferable because of the effect of promoting the formation of crystals.
[0012]
If the high-temperature superconductor precursor contains 50% by weight of high-temperature superconductor crystal powder having the same crystal structure as that of the high-temperature superconductor to be joined, the crystal can be easily grown, the direction of growth can be controlled, and it can be manufactured at low cost. Therefore, it is preferable.
[0013]
There are no particular restrictions on the method of interposing the high-temperature superconductor precursor between the high-temperature superconductors, for example, spraying high-temperature superconductor precursor powder by spraying or applying a liquid high-temperature superconductor precursor in the form of a slurry or paste Or a high temperature superconductor precursor formed into a sheet shape can be bonded together. The high-temperature superconductors may overlap each other, or the high-temperature superconductor precursors may be interposed between the high-temperature superconductors side by side.
[0014]
As the noble metal plate for forming the high-temperature superconductor precursor film, it is preferable to use silver or an alloy plate containing silver as a main component. The method of forming the film of the high-temperature superconductor precursor is not particularly limited, but if the high-temperature superconductor precursor formed into a sheet is pressed on a noble metal plate and bonded to the joint, the high-temperature superconductor crystal Is preferable, and the growth direction of the high-temperature superconductor crystal can be controlled.
[0015]
There are no particular restrictions on the type of superconductor used for the high-temperature superconductor precursor and the high-temperature superconductor to be joined. For example, Bi-based high-temperature superconductor, Y-based high-temperature superconductor, Tl-based high-temperature superconductor, etc. can be applied. In Bi, it is preferable to use a Bi-based high-temperature superconductor because a good superconducting junction can be easily obtained. Bi-based high-temperature superconductors include 2212 phase and 2223 phase. Among these, Bi-based 2212 phase is preferable because it is easy to operate and the crystal growth rate is relatively high.
[0016]
The heating conditions for joining the high-temperature superconductors are that the superconductor crystal formed on the substrate does not decompose and / or melt, and a part of the intervening high-temperature superconductor precursor melts, and then the high-temperature superconductivity It is necessary to heat at a temperature at which the entire body precursor is crystallized. Under other conditions, problems such as difficulty in superconducting bonding and deterioration of superconducting properties occur. The optimum temperature for heating varies depending on the firing conditions such as the crystal grain size of the high-temperature superconductor precursor, the surrounding oxygen partial pressure, and the temperature rise rate. The firing atmosphere is preferably performed in the air and in an atmosphere in which the oxygen partial pressure is controlled.
[0017]
【Example】
Examples of the present invention will be described below. The present invention is not limited to these.
Reference example bismuth oxide with a purity of 99.9% by weight (manufactured by High Purity Chemical Laboratory, 3N) 466 g, strontium carbonate (manufactured by High Purity Chemical Laboratory, 3N) 295.2 g, calcium carbonate (manufactured by High Purity Chemical Laboratory, 3N) 100.1 g and cupric oxide (manufactured by High Purity Chemical Laboratory, 3N) 159.1 g were weighed and placed in a synthetic resin ball mill with 2 kg of synthetic resin balls having a diameter of 10 mm and 1 kg of distilled water for 72 hours. did. The mixed solution was dried at 100 ° C. for 24 hours, and the dried powder was transferred to a silver container and calcined at 820 ° C. for 5 hours . After calcination, the high-temperature superconductor precursor (A) was obtained by dry pulverization to a mean particle size of 7 μm using a cracking machine. The high-temperature superconductor precursor (A) was an amorphous body containing about 6% by weight of the 2212 phase and a small amount of unidentifiable crystals.
[0018]
Next, the high-temperature superconductor precursor (A) obtained above is put in a zirconia container and heated at 1050 ° C. for 2 hours, and then the contents are poured onto a silver plate and rapidly cooled. Dry pulverization to a diameter of 8 μm gave a molten powder (A).
[0019]
Next, 100 parts by weight of molten powder (A), 5 parts by weight of polyvinyl butyral resin (product name: BL-2, manufactured by Sekisui Chemical Co., Ltd.), 2 parts by weight of dibutyl phthalate (manufactured by Wako Pure Chemicals, reagent grade 1) and ethyl alcohol (Wako Pure Chemicals) After the addition of 15 parts by weight and mixing, the slurry obtained by vacuum degassing is fed onto a 100 μm thick polyester film (manufactured by Toray) and formed into a sheet by the doctor blade method. Thus, a green sheet (A) having a thickness of 150 μm was obtained.
[0020]
Thereafter, the green sheet (A) obtained above was thermocompression-bonded on a silver plate having a thickness of 0.1 mm under the conditions of 10 MPa at 60 ° C. and fired while flowing air at a cross-sectional flow rate of 5 cm / min. The conditions for growth and orientation and a smooth surface and the temperature conditions for obtaining a high-temperature superconductor crystal were investigated. As a result, it was confirmed that the maximum temperature was in the range of 872 to 886 ° C., the holding time was within 2 hours, and the cooling rate was 5 ° C./hour or less at 850 ° C. or higher. Therefore, while flowing air at a cross-sectional flow rate of 5 cm / min, it was heated to 883 ° C., held for 30 minutes, cooled to 850 ° C. at a rate of 2 ° C./hour, and then cooled to room temperature at a rate of 100 ° C./hour. A superconducting composite having a high-temperature superconductor formed on a plate was obtained. Next, in order to investigate the temperature at which the superconductor crystal of the obtained superconducting composite melts, the superconducting composite is kept at 20 ° C. while changing the temperature from 860 to 890 ° C. by 1 ° C. and then taken out of the furnace. The crystal state was examined. As a result, when the temperature exceeded 873 ° C., the Bi-based 2212 phase crystals contained were lost and a large amount of 2201 crystals were detected, so the limit of the heating temperature was set to 873 ° C.
[0021]
On the other hand, a green sheet (B) (high temperature superconductor precursor (B)) having a thickness of 170 μm was obtained through the same process as the step of obtaining the green sheet (A) in 100 parts by weight of the high temperature superconductor precursor (A). Thereafter, the high-temperature superconductor precursor (B) obtained above was thermocompression bonded at 60 ° C. under the condition of 10 MPa on a silver plate having a thickness of 0.1 mm in the same manner as described above, and air was flowed at a cross-sectional flow rate of 5 cm / min. While firing, the temperature conditions under which a part of the high-temperature superconductor precursor (B) was melted and a high-temperature superconductor crystal was obtained were examined. As a result, it was confirmed that the maximum temperature was in the range of 865 to 875 ° C., the holding time was within 2 hours, and the cooling rate was 5 ° C./hour or less when the cooling rate was 850 ° C. or more.
[0022]
Next, in order to investigate the temperature at which the superconductor crystal of the high-temperature superconductor precursor (B) melts, the temperature of the high-temperature superconductor precursor (B) placed on the silver plate is changed by 1 ° C. from 860 to 890 ° C. After holding for 20 minutes, it was taken out of the furnace and examined for crystal state by X-ray diffraction. As a result, the Bi-based 2212 phase crystals contained at 871 ° C. or higher disappeared, and 2201 crystals were detected in large quantities. Even if the high-temperature superconductor precursor (B) is rapidly cooled from 870 ° C. or less, a large amount of 2201 phase is detected together with the 2212 phase. Produced in large quantities.
[0023]
The superconducting composite obtained above is abutted as shown in FIGS. 1 (a) and 1 (b), and the ends of both abutted silver plates 1, 1 'are swaged and fixed, and then the silver plate 1 The high temperature superconductor precursor (B) 3 obtained as described above is bonded between the high temperature superconductors 2 and 2 'formed above 1' by applying butyl alcohol (made by Wako Pure Chemicals, reagent), Among them, the maximum temperature was maintained at 868 ° C. for 30 minutes (heat treatment), then the temperature was lowered to 850 ° C. over 15 hours, and further cooled to 20 ° C. over 5 hours to obtain a high-temperature superconducting joined body. In the cooling process, the atmosphere was changed from 680 ° C. to a nitrogen atmosphere. In FIG. 1B, reference numeral 4 denotes a caulking portion of the silver plates 1 and 1 ′.
[0024]
The joint portion of the high-temperature superconducting joint obtained above and its periphery were observed with a microscope and an X-ray diffraction method, and the critical current density (hereinafter referred to as Jc) was measured by a four-terminal method. As a result, the Jc at the liquid nitrogen temperature 77.3K of high temperature superconductors, before joining the 8600A / mm ² and after bonding are 7400A / mm ^2, also Jc of the joint portion is, superconductor film thickness of the joint portion The calculated value was 6200 A / mm ² . Further, the bonded state of the bonded portion was free of abnormal irregularities, foaming, heterogeneous phase, and the like due to the flow of the high-temperature superconductor, and was well oriented in parallel with the bonded surface, and good bonding was obtained.
[0025]
Comparative Example 1
The superconducting composite was butted and the high temperature superconductor precursor (B) was bonded between the high temperature superconductors formed on the upper part of the silver plate. A superconducting assembly was obtained. The joint of the obtained high-temperature superconducting joined body and its periphery were observed with a microscope and an X-ray diffraction method, and Jc was measured by a four-terminal method. As a result, the Jc at the liquid nitrogen temperature 77.3K of high temperature superconductors, before joining the 8600A / mm ² and after bonding are 8400A / mm ^2, also Jc of the joint portion is, superconductor film thickness of the joint portion The calculated value was as low as 800 A / mm ² . Further, the bonded portion was not glossy, showed small irregularities, and a superconductor 2212 phase crystal was formed but very fine.
[0026]
Comparative Example 2
The superconducting composite was abutted and the high temperature superconductor formed on the top of the silver plate was bonded to the high temperature superconductor precursor (B). A superconducting assembly was obtained. The joint of the obtained high-temperature superconducting joined body and its periphery were observed with a microscope and an X-ray diffraction method, and Jc was measured by a four-terminal method. As a result, the Jc at the liquid nitrogen temperature 77.3K of high temperature superconductors, before joining the 8600A / mm ² and after bonding are 4300A / mm ^2, also Jc of the joint portion is, superconductor film thickness of the joint portion The calculated value was as low as 1200 A / mm ^2, and the high temperature superconductor melted and flowed out of the joint, and the joint thickness was reduced to about 20 μm with respect to the set value of the total film thickness of 100 μm. Further, a heterogeneous phase (columnar crystal) was abnormally generated at the boundary of the junction.
[0027]
Example 1
Only the portion of the high-temperature superconductor was peeled off from the superconducting composite obtained in the Reference Example , and lightly crushed in a mortar to obtain a 40 μm plate crystal. Next, the same step as the step of obtaining the green sheet (A) of the reference example in 100 parts by weight of the high-temperature superconductor precursor (A) obtained in the reference example added to 70% by weight of the plate crystal 30% by weight. A green sheet (high temperature superconductor precursor (C)) having a thickness of 170 μm was obtained.
[0028]
Next, the superconducting composite obtained in the reference example was butted as shown in (a) and (b) of FIG. 2, and the tips of both silver plates 1, 1 ′ were fastened and fixed, and then the above-mentioned The green sheet (C) obtained above, that is, the high-temperature superconductor precursor (C) 7 is thermocompression bonded at 60 ° C. under the condition of 10 MPa on the silver plate 6 having a thickness of 0.1 mm different from the above. Got. Next, the composite material 5 is placed on the upper part between the high-temperature superconductors 2 and 2 'of the superconducting composite with the high-temperature superconductor precursor (C) portion facing down, and then 30 minutes at 870 ° C. in the atmosphere. This was held for 1 minute (heat treatment), then cooled to 850 ° C. over 15 hours, and further cooled to 20 ° C. over 5 hours to obtain a high-temperature superconducting joined body. In the cooling process, the atmosphere was changed from 680 ° C. to a nitrogen atmosphere.
[0029]
The joint part and its periphery of the high-temperature superconducting joint obtained above were observed with a microscope and an X-ray diffraction method, and Jc was measured by a four-terminal method. As a result, the Jc at the liquid nitrogen temperature 77.3K of high temperature superconductors, before joining the 8600A / mm ² and after bonding are 7900A / mm ^2, also Jc of the joint portion is, superconductor film thickness of the joint portion The calculated value was 9800 A / mm ² . Further, the bonded state of the bonded portion was free of abnormal irregularities, foaming, heterogeneous phase, and the like due to the flow of the high-temperature superconductor, and was well oriented in parallel with the bonded surface, and good bonding was obtained.
[0030]
Example 2
300 g of bismuth oxide with a purity of 99.9% by weight (manufactured by High Purity Chemical Laboratory, 3N), 147.6 g of strontium carbonate (manufactured by High Purity Chemical Laboratory, 3N), calcium carbonate (manufactured by High Purity Chemical Laboratory, 3N) 50.1 g and 79.5 g of cupric oxide (manufactured by High Purity Chemical Laboratory, 3N) were weighed and placed in a synthetic resin ball mill together with 1 kg of synthetic resin balls having a diameter of 10 mm and 500 g of distilled water and wet-mixed for 72 hours. The mixture is dried at 100 ° C. for 24 hours, the dried powder is transferred to a zirconia container, heated at 1050 ° C. for 2 hours, then the contents are poured onto a silver plate and rapidly cooled, and an average particle size of 8 μm is obtained with a coarse machine. To obtain a molten powder (B).
[0031]
On the other hand, apart from the above, 166 g of bismuth oxide having a purity of 99.9% by weight or more (manufactured by High Purity Chemical Laboratory, 3N), 147.6 g of strontium carbonate (manufactured by High Purity Chemical Laboratory, 3N), calcium carbonate (high purity chemical research) Weigh 50.0 g of 3N) and 79.6 g of cupric oxide (manufactured by High-Purity Chemical Laboratory, 3N) and put them in a synthetic resin ball mill together with 1 kg of synthetic resin balls having a diameter of 10 mm and 500 g of distilled water. Wet mixed for hours. The mixture is dried at 100 ° C. for 24 hours, the dried powder is transferred to a zirconia container, heated at 1050 ° C. for 2 hours, then the contents are poured onto a silver plate and rapidly cooled, and an average particle size of 8 μm is obtained with a coarse machine. To obtain a molten powder (C).
[0032]
Further, 102.2 g of the molten powder (B) obtained above and 65.4 g of the molten powder (C) were weighed so that the theoretical composition of the Bi-based 2212 phase was obtained, and the molten powder (B) and (C) 100 5 parts by weight of polyvinyl butyral resin (product name: BL-2), 2 parts by weight of dibutyl phthalate (manufactured by Wako Pure Chemicals, reagent grade) and 15 parts by weight of ethyl alcohol (made by Wako Pure Chemicals, grade of reagent) The slurry obtained by vacuum degassing is added to a 100 μm thick polyester film (manufactured by Toray) and formed into a sheet by the doctor blade method to form a 170 μm thick green sheet. (D) (High temperature superconductor precursor (D)) was obtained.
[0033]
Thereafter, the high-temperature superconductor precursor (D) obtained above is thermocompression-bonded on a silver plate having a thickness of 0.1 mm at 10 ° C. at 60 ° C., and fired while flowing air at a cross-sectional flow rate of 5 cm / min. A temperature condition under which a part of the superconductor precursor (D) was melted and a high-temperature superconductor crystal was obtained was examined. As a result, it was confirmed that the maximum temperature was in the range of 864 to 870 ° C., the holding time was within 2 hours, and the cooling rate was 850 ° C. or more and 5 ° C./hour or less.
[0034]
Next, the superconducting composite obtained in the reference example was abutted in the same manner as in Example 1 and the tips of both abutted silver plates were fixed by caulking, and then a thickness of 0.1 mm different from the above was used. The green sheet (D) obtained above, that is, the high-temperature superconductor precursor (D) was thermocompression bonded at 60 ° C. under the condition of 10 MPa on a silver plate to obtain a composite material. Then high-temperature superconductors composite of the composite parts of (D) on the lower side, except that then put on between the high-temperature superconductors of the superconducting composite was subjected heat treatment at 867 ° C. The following examples 1 A high-temperature superconducting joined body was obtained through the same steps as above.
[0035]
The joint part and its periphery of the high-temperature superconducting joint obtained above were observed with a microscope and an X-ray diffraction method, and Jc was measured by a four-terminal method. As a result, the Jc at the liquid nitrogen temperature 77.3K of high temperature superconductors, before joining the 8600A / mm ² and after bonding are 8800A / mm ^2, also Jc of the joint portion is, superconductor film thickness of the joint portion The calculated value was 6300 A / mm ² . In addition, the bonded state of the bonded part was free from abnormal irregularities, foaming, heterogeneous phase, and the like due to the flow of the high-temperature superconductor, and good bonding was obtained.
[0036]
【The invention's effect】
The high-temperature superconducting joint obtained by the production method of the present invention does not deteriorate the superconducting properties of the high-temperature superconductor to be joined, and the superconducting crystal of the joint portion can be highly oriented, so that a good superconducting joint can be obtained. can get.
Furthermore, according to the present invention, the present invention can also be applied to a case where a defect occurs in a part of the high-temperature superconductor and it is necessary to repair the high-temperature superconductor.
[Brief description of the drawings]
FIG. 1A is a plan view showing a manufacturing operation state of a high-temperature superconducting joined body according to a reference example of the present invention, and FIG.
FIG. 2A is a plan view showing a manufacturing operation state of a high-temperature superconducting assembly according to an embodiment of the present invention , and FIG. 2B is a cross-sectional view thereof.
[Explanation of symbols]
1, 1 'silver plate 2, 2' high temperature superconductor 3 high temperature superconductor precursor (B)
4 Caulking part 5 Composite material 6 Silver plate 7 High-temperature superconductor precursor (C)

Claims

In a method for joining high temperature superconductors formed on a base material, a high temperature superconductor precursor film is formed on a noble metal plate to obtain a composite material, and then the high temperature superconductor precursor film of the composite material is formed. After placing on the upper part between the high-temperature superconductors to be joined with the part facing down, the high-temperature superconductor crystal formed on the substrate does not decompose and / or melt, and the placed high-temperature superconductor precursor A method for producing a high-temperature superconducting joint, characterized in that a part of the high-temperature superconductor precursor is melted and then heated at a temperature at which the entire high-temperature superconductor precursor is crystallized to join the high-temperature superconductors together.

The method for producing a high-temperature superconducting joint according to claim 1, comprising 50 wt% or less of high-temperature superconductor crystal powder having the same crystal structure as that of the high-temperature superconductor to which the high-temperature superconductor precursor is bonded .

The method for producing a high-temperature superconducting joint according to claim 1 or 2, wherein the high-temperature superconductor and the high-temperature superconductor precursor are Bi-based high-temperature superconductor 2212 phases .

The method for producing a high-temperature superconducting joint according to claim 1, 2 or 3 , wherein the composition of the high-temperature superconductor precursor is a Bi-based high-temperature superconductor 2212 phase composition obtained by mixing and calcining raw materials .

Mixing raw materials composition of the high-temperature superconductor precursor according to claim 1 is calcined and / or high temperature superconductors 2212 phase composition further mixed Bi system of two or more of the powder after the pulverization melted, 3. A method for producing a high-temperature superconducting assembly according to 3 or 4.

6. The method for producing a high-temperature superconducting joined body according to claim 1 , wherein the noble metal plate is silver or an alloy plate containing silver as a main component .