JP2018055975A - Mixed anion compound iron-based superconducting wire material and manufacturing method therefor - Google Patents
Mixed anion compound iron-based superconducting wire material and manufacturing method therefor Download PDFInfo
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Classifications
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- 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
Abstract
Description
本発明は、混合アニオン化合物鉄系超電導線材とその製造方法に関する。 The present invention relates to a mixed anion compound iron-based superconducting wire and a method for producing the same.
液体ヘリウムによる冷却を要しない高温超電導線材として、銅酸化物超電導線材が開発されており、中でもＢｉ系超電導線材とＹ系超電導線材が実用化されている。
Ｂｉ系超電導線材は超電導体の結晶自体が配向し易い特徴を有するため、金属シースに多結晶試料を充填して縮径し、熱処理を行うというパウダーインチューブ法（Powder-in-tube法）により線材化が可能となる。
一方で２０Ｋ程度の伝導冷却条件において磁場下での臨界電流特性はＢｉ系超電導線材に比べ、Ｙ系超電導線材が勝っている。ところが、Ｙ系超電導線材は超電導体の結晶方位を厳密に揃えないと、臨界電流特性が低下する特徴があるため、成膜法などによる２軸配向化プロセスが必要となる。ところが、成膜法による２軸配向化プロセスは製造プロセスの肥大化、高コスト化につながる問題がある。２０Ｋ程度の伝導冷却とは冷凍機を用いて到達できる冷却温度である。
このため、実用超電導線材を用いた超電導コイルの分野では２０Ｋ以上の運転温度の高磁場下において、より高い臨界電流密度を示す超電導材料を用いた超電導線材が求められている。
Copper oxide superconducting wires have been developed as high-temperature superconducting wires that do not require cooling with liquid helium, and Bi-based superconducting wires and Y-based superconducting wires have been put into practical use.
Bi-based superconducting wire has the characteristic that the superconductor crystal itself is easily oriented. Therefore, the powder-in-tube method (Powder-in-tube method) in which a polycrystalline sheath is filled with a polycrystalline sample, the diameter is reduced, and heat treatment is performed. Wire materialization is possible.
On the other hand, the Y-based superconducting wire is superior in the critical current characteristics under a magnetic field under the conduction cooling condition of about 20K compared to the Bi-based superconducting wire. However, the Y-based superconducting wire has a characteristic that the critical current characteristic is deteriorated unless the crystal orientation of the superconductor is strictly aligned, and therefore a biaxial orientation process such as a film forming method is required. However, the biaxial orientation process by the film forming method has problems that lead to enlargement of the manufacturing process and high cost. Conductive cooling of about 20K is a cooling temperature that can be reached using a refrigerator.
For this reason, in the field of superconducting coils using a practical superconducting wire, a superconducting wire using a superconducting material exhibiting a higher critical current density under a high magnetic field at an operating temperature of 20 K or more is required.
近年、銅酸化物超電導体とは異なる高温超電導体として、鉄を中心とした鉄系混合アニオン化合物が発見された。
この種の鉄系超電導体として、５６Ｋ程度の臨界温度（Ｔｃ）を示すＺｒＣｕＳｉＡｓ型の結晶構造をもつ１１１１系化合物、３８Ｋ程度のＴｃを示すＴｈＣｒ２Ｓｉ２型結晶構造をもつ１２２系化合物、１５Ｋ程度のＴｃを示すα‐ＰｂＯ型結晶構造をもつ１１系化合物など、異なる結晶構造を有する多くの超電導体が見つかっている。
このうち、Ｔｃの高い１１１１系化合物や１２２系化合物については、銅酸化物超電導体に匹敵する高い上部臨界磁場（Ｈｃ２）を示すため、線材への応用を目指しＰＩＴ法によるシース線材作製や、ＰＬＤ法等の成膜法により超電導膜を積層したテープ線材の作製が試みられている（特許文献１参照）。
In recent years, iron-based mixed anion compounds centered on iron have been discovered as high-temperature superconductors different from copper oxide superconductors.
As this type of iron-based superconductor, a 1111 series compound having a ZrCuSiAs type crystal structure exhibiting a critical temperature (Tc) of about 56K, a 122 series compound having a ThCr 2 Si 2 type crystal structure exhibiting a Tc of about 38K, 15K Many superconductors having different crystal structures have been found, such as 11-based compounds having an α-PbO type crystal structure exhibiting a degree of Tc.
Among these, 1111 series compounds and 122 series compounds with high Tc show a high upper critical magnetic field (Hc 2 ) comparable to copper oxide superconductors, so that sheath wire preparation by PIT method aiming at application to wire, An attempt has been made to produce a tape wire in which superconducting films are laminated by a film forming method such as a PLD method (see Patent Document 1).
また、Ｎｂ−ＴｉやＮｂ３Ｓｎなどの液体ヘリウム冷却が必要な低温超電導体では、永久電流モードを実現可能な超電導コイルが市販されている。しかしながら、銅酸化物超電導線材あるいは鉄系高温超電導線材を長尺化した超電導コイルにあっては、未だ永久電流モードが実現されていないのが現状である。
従来の高温超電導線材において永久電流モードを実現できない原因は、超電導体の結晶粒同士の粒間において生じる超電導電流を阻害する弱結合（ウィークリンク）を生じることが原因とされている。
この問題を解決できる１つの技術として、ＰＩＴ法と称される線材作製プロセスにより製造可能な超電導材料による超電導線材の長尺化とその接合方法が重要であると考えられている。
For low-temperature superconductors that require liquid helium cooling such as Nb—Ti and Nb 3 Sn, superconducting coils that can realize a permanent current mode are commercially available. However, in a superconducting coil obtained by lengthening a copper oxide superconducting wire or an iron-based high-temperature superconducting wire, a permanent current mode has not yet been realized.
The reason why the permanent current mode cannot be realized in the conventional high-temperature superconducting wire is that weak coupling (weak link) that inhibits the superconducting current generated between the crystal grains of the superconductor is caused.
As one technique that can solve this problem, it is considered that the superconducting wire is made long by a superconducting material that can be manufactured by a wire manufacturing process called a PIT method and the joining method thereof is important.
特許文献１に記載の従来の混合アニオン化合物鉄系超電導体の線材化では、線材加工と線材の熱処理時に生じる超電導体の化学組成変化により超電導転移温度の著しい低下が避けられなかった。
そこで本発明者らは、ＰＩＴ法を適用して超電導線材を製造する場合に有望な鉄系超電導体の候補として、３０Ｋ程度の超電導転移温度を有し、臨界磁場が２００Ｔを超えると報告されているＳｒ２ＶＦｅＡｓＯ３-δなる組成の混合アニオン化合物鉄系超電導体を選択し、線材化の研究を行った。現状では本発明者の知る限り、このような組成の混合アニオン化合物鉄系超電導体を用いて超電導線材の製造に成功したという報告はなされていない。
In the conventional mixed anion compound iron-based superconductor described in Patent Document 1, the superconducting transition temperature is inevitably lowered due to a change in the chemical composition of the superconductor generated during wire processing and heat treatment of the wire.
Therefore, the present inventors have reported that a superconducting transition temperature of about 30K and a critical magnetic field exceeds 200T as a promising iron-based superconductor candidate in the case of manufacturing a superconducting wire by applying the PIT method. A mixed anion compound iron-based superconductor having a composition of Sr 2 VFeAsO 3 -δ was selected, and research into wire was conducted. As far as the present inventors know, there has been no report that the superconducting wire has been successfully produced using the mixed anion compound iron-based superconductor having such a composition.
そこで、本発明者が上述の混合アニオン化合物鉄系超電導体を用い、ＰＩＴ法に従って超電導線材の製造について試験したところ以下の知見を得ることができた。
混合アニオン化合物鉄系超電導体の原料粉末からなる超電導コアをＡｇの内部シースとＦｅの外部シースで覆う構造を採用し、この超電導コアを熱処理した。その結果、熱処理時にＡｓがシース側に拡散してしまい、超電導コアに含まれるべきＡｓが不足し、超電導コアに生成するべき超電導体の化学組成が崩れることを確認できた。また、ＰＩＴ法による製造条件を種々検討したところ、混合アニオン化合物鉄系超電導体の一部のものは、熱処理による化学変化に対し臨界温度の変化を鈍感にすることが可能なことを確認できた。
Then, when this inventor tested about manufacture of a superconducting wire according to PIT method using the above-mentioned mixed anion compound iron system superconductor, the following knowledge was able to be acquired.
A structure in which a superconducting core made of a raw material powder of a mixed anion compound iron-based superconductor was covered with an Ag inner sheath and an Fe outer sheath was employed, and the superconducting core was heat-treated. As a result, it was confirmed that As diffused to the sheath side during the heat treatment, As to be contained in the superconducting core was insufficient, and the chemical composition of the superconductor to be generated in the superconducting core was destroyed. Moreover, when various manufacturing conditions by the PIT method were examined, it was confirmed that some of the mixed anion compound iron-based superconductors can be insensitive to changes in critical temperature with respect to chemical changes due to heat treatment. .
本発明は、前記の課題に鑑みなされたものであって、線材熱処理による化学変化に対し臨界温度の変化を鈍感にすることが可能な混合アニオン化合物鉄系超電導体を用いた超電導線材とその製造方法を提供することを目的とする。 The present invention has been made in view of the above problems, and a superconducting wire using a mixed anion compound iron-based superconductor capable of desensitizing a change in critical temperature with respect to a chemical change caused by a wire heat treatment, and its manufacture It aims to provide a method.
本発明は、上記課題を解決する手段として、以下の構成を有する。
（１）本発明の超電導線材は、Ａ２ＤＦｅＡｓＯ３-δ（Ａはアルカリ土類金属Ｍｇ、Ｃａ、Ｓｒ、Ｂａの中から選択される１種または２種以上の元素を示し、Ｄは遷移金属Ｓｃ、Ｔｉ、Ｖ、Ｃｒ、Ｍｎ、Ｃｏ、Ｎｉ、Ｃｕ、Ｙ、Ｚｒ、Ｎｂ、Ｍｏ、Ｒｕ、Ｒｈ、Ｐｄ、Ａｇ、Ｈｆ、Ｔａ、Ｗ、Ｒｅ、Ｏｓ、Ｉｒ、Ｐｔ、Ａｕ、希土類Ｌａ、Ｃｅ、Ｐｒ、Ｎｄ、Ｐｍ、Ｓｍ、Ｅｕ、Ｇｄ、Ｔｂ、Ｄｙ、Ｈｏ、Ｅｒ、Ｔｍ、Ｙｂ、Ｌｕ、アルカリ土類金属Ｍｇ、典型金属元素Ａｌの中から選択される１種または２種以上の元素を示す。）なる組成式で示される混合アニオン型鉄系超電導体を含むコア部が金属シースの内部に充填されたことを特徴とする。
Ａ２ＤＦｅＡｓＯ３-δなる組成式で示される鉄系超電導体を含むコア部を金属シースの内部に充填した構造の超電導線材であるならば、２０Ｋ程度の臨界温度を示すとともに、優れた臨界電流密度を示す超電導線材を提供できる。
The present invention has the following configuration as means for solving the above problems.
(1) The superconducting wire of the present invention is A 2 DFeAsO 3 -δ (A represents one or more elements selected from the alkaline earth metals Mg, Ca, Sr and Ba, and D represents a transition. Metals Sc, Ti, V, Cr, Mn, Co, Ni, Cu, Y, Zr, Nb, Mo, Ru, Rh, Pd, Ag, Hf, Ta, W, Re, Os, Ir, Pt, Au, rare earth One or two selected from La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, alkaline earth metal Mg, and typical metal element Al The core portion containing the mixed anion type iron superconductor represented by the composition formula is filled in the metal sheath.
A superconducting wire having a structure in which a core containing an iron-based superconductor represented by the composition formula of A 2 DFeAsO 3 -δ is filled in a metal sheath has a critical temperature of about 20 K and an excellent critical current. A superconducting wire exhibiting a density can be provided.
（２）本発明において、前記組成式における酸素欠損量を示すδの値を０＜δ＜０.２の範囲で選択できる。
超電導線材のコア部に適用する鉄系超電導体としてＡ２ＤＦｅＡｓＯ３-δなる組成式で示されるものを適用することができ、酸素欠損量を示すδの値を０＜δ＜０.２の範囲とすることで、臨界温度の高い、臨界電流密度の高い超電導線材を得ることができる。
(2) In the present invention, the value of δ indicating the amount of oxygen vacancies in the composition formula can be selected within the range of 0 <δ <0.2.
As the iron-based superconductor applied to the core portion of the superconducting wire, one represented by the composition formula of A 2 DFeAsO 3 -δ can be applied, and the value of δ indicating the oxygen deficiency is 0 <δ <0.2. By setting the range, a superconducting wire having a high critical temperature and a high critical current density can be obtained.
（３）本発明において、前記金属シースがＣｕシース、Ｆｅシース、ＣｕとＦｅの複合材シース、Ａｇシース、ＡｇとＦｅの複合材シースのうち、いずれかからなるものを選択できる。
超電導コアを取り囲む金属シースとしてこれらの金属からなるシースを適用することができ、金属シースで超電導コアを覆った安定性の良好な臨界温度の高い、臨界電流密度の高い超電導線材を得ることができる。
(3) In the present invention, the metal sheath can be selected from any one of a Cu sheath, an Fe sheath, a composite sheath of Cu and Fe, an Ag sheath, and a composite sheath of Ag and Fe.
A sheath made of these metals can be applied as a metal sheath surrounding the superconducting core, and a superconducting wire with high critical temperature and high critical current density can be obtained by covering the superconducting core with the metal sheath. .
（４）本発明において、臨界温度（Ｔｃ）の測定値と、１０Ｋ〜２０Ｋにおける臨界電流密度の測定値（Ｊｃ）との関係において、Ｊｃ（０）｛１−（Ｔ／Ｔｃ）２｝…（１）式の関係から求められる０Ｋにおける臨界電流密度が２５Ａ／ｃｍ２以上の超電導線材を得ることができる。 (4) In the present invention, in the relationship between the measured value of the critical temperature (Tc) and the measured value (Jc) of the critical current density at 10K to 20K, Jc (0) {1- (T / Tc) 2 } It is possible to obtain a superconducting wire having a critical current density at 0 K of 25 A / cm 2 or more obtained from the relationship of the formula (1).
（５）本発明の製造方法は、Ａ２ＤＦｅＡｓＯ３-δ（Ａはアルカリ土類金属Ｍｇ、Ｃａ、Ｓｒ、Ｂａの中から選択される１種または２種以上の元素を示し、Ｄは遷移金属Ｓｃ、Ｔｉ、Ｖ、Ｃｒ、Ｍｎ、Ｃｏ、Ｎｉ、Ｃｕ、Ｙ、Ｚｒ、Ｎｂ、Ｍｏ、Ｒｕ、Ｒｈ、Ｐｄ、Ａｇ、Ｈｆ、Ｔａ、Ｗ、Ｒｅ、Ｏｓ、Ｉｒ、Ｐｔ、Ａｕ、希土類Ｌａ、Ｃｅ、Ｐｒ、Ｎｄ、Ｐｍ、Ｓｍ、Ｅｕ、Ｇｄ、Ｔｂ、Ｄｙ、Ｈｏ、Ｅｒ、Ｔｍ、Ｙｂ、Ｌｕ、アルカリ土類金属Ｍｇ、典型金属元素Ａｌの中から選択される１種または２種以上の元素を示す。）なる組成式で示される混合アニオン型鉄系超電導体を金属シースの内部に設けた超電導線材を製造するに際し、
元素Ａの単体粉末あるいは酸化物粉末と元素Ｄの単体粉末あるいは酸化物粉末とＦｅの単体粉末あるいは酸化物粉末とＡｓの単体粉末あるいは酸化物粉末を各元素が前記組成式で示される割合あるいは前記組成式に近似した割合になるように混合して原料混合粉末を得、この原料混合粉末を仮焼きして仮焼き粉末を得、この仮焼き粉末を金属チューブの内部に充填した後、前記金属チューブを圧縮して金属シースとその内部に圧縮充填されたコア部を有する圧縮体を得るとともに、前記圧縮体を本焼成して前記コア部内にＡ２ＤＦｅＡｓＯ３-δなる組成式で示される超電導体を生成することを特徴とする。
Ａ２ＤＦｅＡｓＯ３-δで示される組成比となるように原料粉末を配合した原料混合粉末を仮焼きして仮焼き粉末を得、この仮焼き粉末を金属シースに充填して圧縮した圧縮体を本焼成することにより、原料粉末に含まれて近接配置された成分どうしが反応してＡ２ＤＦｅＡｓＯ３-δで示される超電導体を生成することができ、目的の超電導コアを備えた超電導線材が得られる。
(5) The production method of the present invention comprises A 2 DFeAsO 3 -δ (A represents one or more elements selected from the alkaline earth metals Mg, Ca, Sr and Ba, and D represents a transition. Metals Sc, Ti, V, Cr, Mn, Co, Ni, Cu, Y, Zr, Nb, Mo, Ru, Rh, Pd, Ag, Hf, Ta, W, Re, Os, Ir, Pt, Au, rare earth One or two selected from La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, alkaline earth metal Mg, and typical metal element Al When producing a superconducting wire having a mixed anion type iron-based superconductor represented by a composition formula:
Element A single powder or oxide powder and element D single powder or oxide powder and Fe single powder or oxide powder and As single powder or oxide powder, the ratio of each element represented by the above composition formula or the above The raw material mixed powder is obtained by mixing so that the ratio is close to the composition formula, and the raw material mixed powder is calcined to obtain a calcined powder. After the calcined powder is filled inside the metal tube, the metal The tube is compressed to obtain a compressed body having a metal sheath and a core portion that is compressed and filled therein, and the compressed body is subjected to main firing and superconductivity represented by a composition formula of A 2 DFeAsO 3 -δ in the core portion. It is characterized by generating a body.
A raw material mixed powder in which raw material powders were blended so as to have a composition ratio represented by A 2 DFeAsO 3-δ was calcined to obtain a calcined powder, and a compressed body obtained by filling the calcined powder in a metal sheath and compressing the calcined powder By performing the main firing, the components placed in close proximity in the raw material powder can react to generate a superconductor represented by A 2 DFeAsO 3 -δ , and a superconducting wire having a target superconducting core is obtained. can get.
（６）本発明において、前記本焼成温度を８００〜１０３０℃、前記本焼成時間を１６時間以内とすることが好ましい。
８００〜１０３０℃の焼成温度で本焼成し、本焼成時間を１６時間以内とすることで超電導コアに含まれている元素の金属シース側への拡散を低く抑制できる。このため、超電導コアにおける特定元素の不足を抑制しつつ組成の整った超電導体を含む超電導コアを有する超電導線材を製造できる。
(6) In this invention, it is preferable that the said baking temperature shall be 800-1030 degreeC and the said baking time shall be less than 16 hours.
The main baking is performed at a baking temperature of 800 to 1030 ° C., and the main baking time is set to 16 hours or less, so that diffusion of elements contained in the superconducting core to the metal sheath side can be suppressed to a low level. For this reason, it is possible to manufacture a superconducting wire having a superconducting core including a superconductor having a well-structured composition while suppressing a shortage of a specific element in the superconducting core.
（７）本発明において、前記Ａ２ＤＦｅＡｓＯ３-δなる組成式で示される超電導体が、Ｓｒ２ＶＦｅＡｓＯ３-δなる組成式で示されるペロブスカイト関連混合アニオン型鉄系超電導体であることが好ましい。
Ｓｒ２ＶＦｅＡｓＯ３-δなる組成式で示されるペロブスカイト関連混合アニオン型鉄系超電導体であるならば、２０Ｋ程度以上の臨界温度を示し、臨界電流密度の高い超電導線材を提供できる。
(7) In the present invention, the superconductor represented by the composition formula of A 2 DFeAsO 3 -δ is preferably a perovskite-related mixed anionic iron-based superconductor represented by a composition formula of Sr 2 VFeAsO 3 -δ. .
If it is a perovskite-related mixed anionic iron-based superconductor represented by the composition formula Sr 2 VFeAsO 3 -δ , a superconducting wire having a critical temperature of about 20 K or higher and a high critical current density can be provided.
（８）本発明において、前記Ａ２ＤＦｅＡｓＯ３-δなる組成式で示される超電導体が、Ｓｒ２ＶＦｅＡｓＯ３-δなる組成式で示されるペロブスカイト関連混合アニオン型鉄系超電導体であり、前記一次混合粉末を得る場合、Ｓｒの酸化物粉末と、ＦｅＡｓ粉末と、Ｖの単体粉末またはＶの酸化物粉末を混合して焼成することが好ましい。 (8) In the present invention, the superconductor represented by the composition formula A 2 DFeAsO 3 -δ is a perovskite-related mixed anionic iron-based superconductor represented by the composition formula Sr 2 VFeAsO 3 -δ , When obtaining a mixed powder, it is preferable to mix Sr oxide powder, FeAs powder, V single powder or V oxide powder, and to fire.
本発明によれば、Ａ２ＤＦｅＡｓＯ３-δなる組成式で示される鉄系超電導体を含むコア部を金属シースの内部に充填した構造の超電導線材であるので、２０Ｋ程度以上の臨界温度を示すとともに、優れた臨界電流密度を示すペロブスカイト関連混合アニオン型鉄系超電導線材を提供できる。 According to the present invention, since it is a superconducting wire having a structure in which a core containing an iron-based superconductor represented by the composition formula of A 2 DFeAsO 3 -δ is filled inside a metal sheath, it exhibits a critical temperature of about 20K or more. In addition, a perovskite-related mixed anionic iron-based superconducting wire exhibiting an excellent critical current density can be provided.
以下、本発明の実施形態を挙げて本発明の詳細について説明する。
図１は本発明に係るペロブスカイト関連混合アニオン型鉄系超電導線材の横断面構造の一例を示すもので、この実施形態の超電導線材Ａは、超電導体の結晶を内部に含む円形断面の超電導コア１と、この超電導コア１の外周を取り囲むチューブ状の金属製の内部シース２と、この内部シース２の外周を取り囲むチューブ状の金属製の外部シース３とからなる。
超電導線材Ａの全体形状は長尺の線材であることが好ましいが、用途に応じた必要な長さの線材あるいは短尺の線材であっても良い。長尺の線材であれば超電導コイル用の巻線や送電線用途に使用することができ、短尺のものでも超電導線接続用の端子などの用途に適用することができるので、長さは問わない。
また、超電導線材Ａの断面形状は図１に示すような断面円形状に限らず、矩形断面形状や十字型や四葉型などの異形断面形状であっても良い。更に、超電導コア１を内部シース２の内に１つのみ有する図１の単芯構造に限らず、内部シース２の内部に複数の超電導コアを有する多芯構造であっても良い。
Hereinafter, details of the present invention will be described with reference to embodiments of the present invention.
FIG. 1 shows an example of a cross-sectional structure of a perovskite-related mixed anionic iron-based superconducting wire according to the present invention. A superconducting wire A of this embodiment is a superconducting core 1 having a circular cross-section including a superconductor crystal inside. And a tube-shaped metal inner sheath 2 surrounding the outer periphery of the superconducting core 1 and a tube-shaped metal outer sheath 3 surrounding the outer periphery of the inner sheath 2.
The overall shape of the superconducting wire A is preferably a long wire, but may be a wire having a required length or a short wire depending on the application. Long wires can be used for windings for superconducting coils and power transmission lines, and even short ones can be used for applications such as terminals for connecting superconducting wires. .
Further, the cross-sectional shape of the superconducting wire A is not limited to the circular cross-section as shown in FIG. 1, but may be a rectangular cross-sectional shape or a modified cross-sectional shape such as a cross shape or a four-leaf shape. Furthermore, not only the single core structure of FIG. 1 having only one superconducting core 1 in the inner sheath 2, but also a multi-core structure having a plurality of superconducting cores in the inner sheath 2 may be used.
本実施形態の超電導コア１は、後述する製造工程において説明するようにＡ２ＤＦｅＡｓＯ３-δなる組成式で示される超電導体の構成元素を含む複数の原料粉末をシース材とともに圧延し、焼成してなる。原料粉末の圧密時に内部シース２と外部シース３も圧着一体化されるので、焼成後に得られる超電導コア１と内部シース２と外部シース３は相互に密着一体化されている。 The superconducting core 1 of the present embodiment is formed by rolling a plurality of raw material powders containing superconductor constituent elements represented by the composition formula of A 2 DFeAsO 3 -δ together with a sheath material and firing as described in the manufacturing process described later. It becomes. Since the inner sheath 2 and the outer sheath 3 are also pressed and integrated when the raw material powder is consolidated, the superconducting core 1, the inner sheath 2 and the outer sheath 3 obtained after firing are closely integrated with each other.
前記組成式Ａ２ＤＦｅＡｓＯ３-δにおいて、Ａはアルカリ土類金属Ｍｇ、Ｃａ、Ｓｒ、Ｂａの中から選択される１種または２種以上の元素を示し、Ｄは遷移金属Ｓｃ、Ｔｉ、Ｖ、Ｃｒ、Ｍｎ、Ｃｏ、Ｎｉ、Ｃｕ、Ｙ、Ｚｒ、Ｎｂ、Ｍｏ、Ｒｕ、Ｒｈ、Ｐｄ、Ａｇ、Ｈｆ、Ｔａ、Ｗ、Ｒｅ、Ｏｓ、Ｉｒ、Ｐｔ、Ａｕ、希土類Ｌａ、Ｃｅ、Ｐｒ、Ｎｄ、Ｐｍ、Ｓｍ、Ｅｕ、Ｇｄ、Ｔｂ、Ｄｙ、Ｈｏ、Ｅｒ、Ｔｍ、Ｙｂ、Ｌｕ、アルカリ土類金属Ｍｇ、典型金属元素Ａｌの中から選択される１種または２種以上の元素を示す。１つの具体例として、Ｓｒ２ＶＦｅＡｓＯ３-δなる組成式で示されるペロブスカイト関連混合アニオン型鉄系超電導体を例示することができるが、この他にＣａ２（Ａｌ，Ｔｉ）ＦｅＡｓＯ３なる組成、Ｓｒ２（Ｍｇ，Ｔｉ）ＦｅＡｓＯ３なる組成、Ｃａ２ＡｌＦｅＡｓＯ３なる組成の鉄系超電導体を例示できる。 In the composition formula A 2 DFeAsO 3 -δ , A represents one or more elements selected from the alkaline earth metals Mg, Ca, Sr, Ba, and D represents the transition metals Sc, Ti, V , Cr, Mn, Co, Ni, Cu, Y, Zr, Nb, Mo, Ru, Rh, Pd, Ag, Hf, Ta, W, Re, Os, Ir, Pt, Au, rare earth La, Ce, Pr, Indicates one or more elements selected from Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, alkaline earth metal Mg, and typical metal element Al . As one specific example, can be exemplified perovskite related mixed anionic-type iron-based superconductors represented by the composition formula comprising Sr 2 VFeAsO 3-δ, the addition to Ca 2 (Al, Ti) FeAsO 3 having a composition, An iron-based superconductor having a composition of Sr 2 (Mg, Ti) FeAsO 3 and a composition of Ca 2 AlFeAsO 3 can be exemplified.
組成式Ｓｒ２ＶＦｅＡｓＯ３-δで表される超電導体の結晶構造の一例を図２に示す。
図２に示す結晶構造は、層状ペロブスカイト構造のＳｒ２ＶＯ３-δ層をブロック層としてＦｅＡｓ層を上下のブロック層でサンドイッチした結晶構造であり、この結晶構造の結晶格子定数はａ＝０.３９３ｎｍ、ｃ＝１.５７ｎｍであり、空間群Ｐ４／ｎｍｍに分類される結晶構造を有する化合物である。
An example of the crystal structure of the superconductor represented by the composition formula Sr 2 VFeAsO 3 -δ is shown in FIG.
The crystal structure shown in FIG. 2 is a crystal structure in which an Sr 2 VO 3−δ layer having a layered perovskite structure is used as a block layer and an FeAs layer is sandwiched between upper and lower block layers, and the crystal lattice constant of this crystal structure is a = 0. The compound has a crystal structure of 393 nm, c = 1.57 nm, and is classified into the space group P4 / nmm.
図１に示す超電導コア１の周囲を取り囲む内部シース（金属シース）２はＡｇ、Ｃｕ、Ａｕ、Ｆｅなどの良電気伝導性の金属材料あるいはこれら金属材料を主体とする合金からなり、内部シース２の周囲を取り囲む外部シース（金属シース）３はＦｅ、Ａｇ、Ｃｕ、Ａｕなどの金属材料あるいはこれら金属材料を主体とする合金からなることが好ましい。なお、内部シース２は超電導体の結晶と隣接配置されるので、超電導体の安定化材として機能することが好ましく、特に電気伝導性の優れたＡｇやＣｕなどの金属材料からなることが好ましい。 An inner sheath (metal sheath) 2 surrounding the periphery of the superconducting core 1 shown in FIG. 1 is made of a metal material having good electrical conductivity such as Ag, Cu, Au, Fe, or an alloy mainly composed of these metal materials. The outer sheath (metal sheath) 3 surrounding the periphery of the metal is preferably made of a metal material such as Fe, Ag, Cu, Au, or an alloy mainly composed of these metal materials. Since the inner sheath 2 is disposed adjacent to the superconductor crystal, it preferably functions as a superconductor stabilizer, and is particularly preferably made of a metal material such as Ag or Cu having excellent electrical conductivity.
図３は図１に示す超電導線材Ａの製造方法の一例工程を示すもので、まず、出発材料となる原料混合粉末を用意する。原料混合粉末は、例えば、Ａ２ＤＦｅＡｓＯ３-δなる組成式で示される目的の組成比となるように元素Ａと元素ＤとＦｅとＡｓを含む原料の混合粉末である。
原料混合粉末を得る場合、元素Ａの単体粉末あるいは酸化物粉末と、元素Ｄの単体粉末あるいは酸化物粉末と、Ｆｅの単体粉末あるいは酸化物粉末と、Ａｓの単体粉末あるいは酸化物粉末を混合することができる。また、元素Ａの単体粉末あるいは酸化物粉末と、元素Ｄの単体粉末あるいは酸化物粉末と、ＦｅＡｓ粉末を混合して原料混合粉末を得ることもできる。例えば、元素Ａの酸化物粉末と、ＦｅＡｓ粉末と、元素Ｄの粉末または元素Ｄの酸化物粉末を混合して原料混合粉末を得ることができる。
なお、原料混合粉末を調整する場合、後の焼成時に昇華などの理由により消失する成分がある場合は、その成分を多く原料混合粉末に混入しておくことが好ましい。
例えば、酸素（Ｏ）やヒ素（Ａｓ）は８００〜１０００℃焼成時に昇華するおそれがあるので、原料混合粉末中に前述の組成比の割合よりも０〜５原子％程度多く含有させておくことができる。酸素の割合を調整する場合は、例えば、原料のＶとＶ酸化物の割合を調整することで実施できる。原料のＶに対してＶ酸化物を増量すれば酸素の割合を増加できる。このため、本明細書においてＡ２ＤＦｅＡｓＯ３-δなる組成式で示される目的の組成比となるように元素Ａと元素ＤとＦｅとＡｓを含む原料の混合粉末を得る場合、組成式で規定する割合に近似する割合としてこれらの元素を０〜５原子％程度多く配合する場合を含むものとする。なお、Ａ２ＤＦｅＡｓＯ３-δなる組成式において酸素含有量については２．５〜３．１の範囲を採用することが可能である。
FIG. 3 shows an example of a process for producing the superconducting wire A shown in FIG. 1, and first, a raw material mixed powder as a starting material is prepared. The raw material mixed powder is, for example, a mixed powder of raw materials including the element A, the element D, Fe, and As so as to have a target composition ratio represented by a composition formula of A 2 DFeAsO 3 -δ .
When obtaining a raw material mixed powder, a simple powder or oxide powder of element A, a simple powder or oxide powder of element D, a simple powder or oxide powder of Fe, and a simple powder or oxide powder of As are mixed. be able to. Alternatively, a raw material mixed powder can be obtained by mixing element A simple powder or oxide powder, element D simple powder or oxide powder, and FeAs powder. For example, an element A oxide powder, an FeAs powder, and an element D powder or an element D oxide powder can be mixed to obtain a raw material mixed powder.
In addition, when preparing a raw material mixed powder, when there exists a component lose | disappeared for reasons, such as sublimation, at the time of subsequent baking, it is preferable to mix many that component in a raw material mixed powder.
For example, oxygen (O) and arsenic (As) may be sublimated during firing at 800 to 1000 ° C., and therefore, the raw material mixed powder should contain about 0 to 5 atomic% more than the above-described composition ratio. Can do. When adjusting the ratio of oxygen, for example, it can be carried out by adjusting the ratio of V and V oxide of the raw material. If the amount of V oxide is increased with respect to V of the raw material, the proportion of oxygen can be increased. Therefore, when obtaining the mixed powder of raw material containing an element A and the element D and Fe and As so as to have the composition ratio of interest represented by A 2 DFeAsO 3-δ having the composition formula in the present specification, defined by the formula As a ratio that approximates the ratio, the case of adding these elements in an amount of about 0 to 5 atomic% is included. In the composition formula of A 2 DFeAsO 3 -δ, a range of 2.5 to 3.1 can be adopted as the oxygen content.
原料混合粉末の粒径は微細な方が望ましいが、微細に過ぎると粉末の製造が容易ではなくなり、粉末のハンドリングも容易ではなくなるので、平均粒径１〜３０μｍなどの範囲でできるだけ粒径が整った混合粉末とすることが好ましい。
原料混合粉末を得る場合、図３（Ａ）に示すように必要量秤量した複数の原料粉末１０、１１をめのう乳鉢などの混合鉢１２に収容して乳棒などの混合棒１３で摺り合わせることで複数の粉末を混合粉砕することができる。勿論、工業的に原料混合粉末を大量処理する場合は、ボールミルやアトライタなどの混合装置を用いて大量の原料粉末を混合しても良い。
Although it is desirable that the particle size of the raw material mixed powder is fine, if it is too fine, it will not be easy to manufacture the powder, and handling of the powder will not be easy. It is preferable to use a mixed powder.
When obtaining the raw material mixed powder, as shown in FIG. 3 (A), a plurality of raw material powders 10 and 11 weighed in a necessary amount are housed in a mixing bowl 12 such as an agate mortar and rubbed with a mixing bar 13 such as a pestle. A plurality of powders can be mixed and pulverized. Of course, when a large amount of raw material mixed powder is processed industrially, a large amount of raw material powder may be mixed using a mixing device such as a ball mill or an attritor.
原料混合粉末を得る場合、一例として、図４に示すように、Ｓｒ（ＯＨ）２・８Ｈ２Ｏ粉末を９００℃程度の温度で数時間〜数１０時間程度、例えば１０時間程度加熱してＳｒＯ粉末を得る。続いて、Ｆｅ粉末とＡｓ粉末を混合して６００℃程度の温度で数時間〜数１０時間程度、例えば１０時間程度加熱してＦｅＡｓ粉末を得、先のＳｒＯ粉末とともにこれらの粉末にＶ粉末とＶ２Ｏ５粉末を混合して組成式Ｓｒ２ＶＦｅＡｓＯ３-δで表される組成比になるように各粉末の配合量を調整することができる。 When obtaining the raw material mixed powder, as shown in FIG. 4, for example, as shown in FIG. 4, the Sr (OH) 2 .8H 2 O powder is heated at a temperature of about 900 ° C. for several hours to several tens of hours, for example, about 10 hours. Obtain a powder. Subsequently, the Fe powder and the As powder are mixed and heated at a temperature of about 600 ° C. for about several hours to several tens of hours, for example, about 10 hours to obtain FeAs powder, and together with the previous SrO powder, these powders and V powder V 2 O 5 powder can be adjusted amount of each powder so that the composition ratio expressed by the admixture composition formula Sr 2 VFeAsO 3-δ.
なお、Ｓｒの単体金属は粘度が高いので微細粉末とすることが容易ではない。このため、Ｓｒを含む原材料としては、純度の高いものが入手容易なＳｒ（ＯＨ）２・８Ｈ２Ｏ粉末を利用し、この粉末を加熱脱水してＳｒＯ粉末とすることで微細粉末化を容易とすることができる。また、Ｓｒ（ＯＨ）２・８Ｈ２Ｏ粉末を焼成してＳｒＯ粉末とする場合、酸素以外の他の不要元素の混入が生じ難いのでＳｒＯ粉末の状態で原料粉末混合の配合に適用することが有利となる。また、ＦｅＡｓ粉末は脆いので微細粉末化が容易にできる。Ｖ粉末については高純度のものは高価であるので酸化物として広く入手可能なＶ２Ｏ５粉末を用いることができるが、Ｖ２Ｏ３粉末やＶＯ２粉末などの他の酸化物粉末を用いても良い。Ｖ２Ｏ５粉末を多く用いると酸素の割合が多くなり過ぎるので、Ｖ粉末とＶ２Ｏ５粉末の混合粉末を用いることが好ましい。
以上説明のように原料混合粉末を得る場合の各粉末配合の具体例を説明したが、原料混合粉末を得る場合の配合例はこの例に限らず、目的の組成比になるように各粉末を配合する方法を適宜選択すればよい。
In addition, since the single metal of Sr has a high viscosity, it is not easy to make it a fine powder. Therefore, as the raw material containing Sr, utilizing easy Sr (OH) 2 · 8H 2 O powder obtained is high purity, ease of fine powdered With SrO powder by heating and dehydrating the powder It can be. In addition, when Sr (OH) 2 .8H 2 O powder is baked to form SrO powder, it is difficult to mix other unnecessary elements other than oxygen, so that it can be applied to the mixing of raw material powder in the state of SrO powder. It will be advantageous. Further, since FeAs powder is brittle, it can be easily made into a fine powder. As for the V powder, high-purity ones are expensive, and thus V 2 O 5 powder that is widely available as an oxide can be used, but other oxide powders such as V 2 O 3 powder and VO 2 powder are used. May be. If a large amount of V 2 O 5 powder is used, the proportion of oxygen becomes too high, so it is preferable to use a mixed powder of V powder and V 2 O 5 powder.
As described above, specific examples of powder blending in the case of obtaining a raw material mixed powder have been described. However, the blending example in the case of obtaining a raw material mixed powder is not limited to this example. What is necessary is just to select the method of mix | blending suitably.
原料混合粉末を得たならば、この原料混合粉末をプレス装置などで加圧して例えば図３（Ｂ）に示すペレット状（円盤状）の圧縮体１５を得る。この圧縮体１５を必要個数揃えて図３（Ｃ）に示すオーブンなどの加熱炉１６に収容して真空雰囲気中あるいはアルゴン等の不活性雰囲気中において５００〜１１５０℃程度の高温に加熱して仮焼きする。
一例として、組成式Ｓｒ２ＶＦｅＡｓＯ３-δで表される超電導体を製造する場合に前述の原料混合粉末を用いると１０５０℃を超える温度で成分の一部が溶融するおそれがあるので、１０５０℃の仮焼き温度を上限とすることが好ましい。また、５００℃未満の焼成温度では成分元素の反応が進まないので５００℃以上とする必要がある。なお、仮焼き温度を低く設定し過ぎると反応に要する焼成時間が長くなり、仮焼き時間が長くなるので、実質的には８００〜１０５０℃程度の温度範囲で仮焼きすることが好ましい。
When the raw material mixed powder is obtained, the raw material mixed powder is pressurized with a press device or the like to obtain, for example, a pellet-shaped (disk-shaped) compact 15 shown in FIG. The necessary number of the compressed bodies 15 are prepared and accommodated in a heating furnace 16 such as an oven shown in FIG. 3C and heated to a high temperature of about 500 to 1150 ° C. in a vacuum atmosphere or an inert atmosphere such as argon. Bake.
As an example, in the case of producing a superconductor represented by the composition formula Sr 2 VFeAsO 3 -δ , if the above raw material mixed powder is used, a part of the components may be melted at a temperature exceeding 1050 ° C. It is preferable to make the calcining temperature of the upper limit. Further, since the reaction of the component elements does not proceed at a firing temperature of less than 500 ° C., it is necessary to set it to 500 ° C. or more. If the calcining temperature is set too low, the firing time required for the reaction becomes long and the calcining time becomes long. Therefore, it is preferable that the calcining is substantially performed in a temperature range of about 800 to 1050 ° C.
仮焼き後のペレット状の圧縮体１７を図３（Ｅ）に示すめのう乳鉢などの混合鉢１８に収容して乳棒などの混合棒１９で摺り合わせて再度混合粉砕することで図３（Ｆ）に示すような最終混合粉末２０を得ることができる。なお、ここで得た最終混合粉末２０から再度ペレットを形成して粉砕混合し、仮焼きする処理を必要回数繰り返し施しても良い。
前記最終混合粉末２０を図３（Ｆ）に示すように内部シースを構成する金属からなるチューブ２１の内部に充填する。内部シース２をＡｇから構成する場合はＡｇのチューブ２１を用いる。チューブ２１に最終混合粉末２０を充填したならば、外部シースを構成する金属からなる外チューブに全体を収容する。外部シース３をＦｅから構成する場合はＦｅの外チューブに収容する。あるいは、予めＡｇのチューブ２１の外部にＦｅの外チューブを被せておいた複合管を用意し、この複合管に最終混合粉末２０を充填しても良い。
The pellet-like compressed body 17 after calcination is accommodated in a mixing bowl 18 such as an agate mortar shown in FIG. 3 (E), rubbed with a mixing stick 19 such as a pestle, and mixed and pulverized again. The final mixed powder 20 as shown in FIG. Note that the final mixed powder 20 obtained here may be re-formed, pulverized and mixed, and pre-baked repeatedly.
As shown in FIG. 3F, the final mixed powder 20 is filled into a tube 21 made of metal constituting an inner sheath. When the inner sheath 2 is made of Ag, an Ag tube 21 is used. When the final mixed powder 20 is filled in the tube 21, the whole is accommodated in the outer tube made of metal constituting the outer sheath. When the outer sheath 3 is made of Fe, it is accommodated in an Fe outer tube. Alternatively, a composite tube in which an outer tube of Fe is covered in advance on the outside of the Ag tube 21 may be prepared, and the final mixed powder 20 may be filled in the composite tube.
次に、最終混合粉末２０を充填したチューブ２１を内部に収容した図３（Ｇ）に示す外チューブ２２を圧延装置２３にて圧延する。ここで用いる圧延装置２３は、上下に配置された圧延ロール２３Ａ、２３Ａを有し、圧延ロール２３Ａ、２３Ａの長さ方向中央部外周に周溝２３ａが形成された装置である。本実施形態で図１に示す断面円形状の超電導線材Ａを製造する場合に、圧延ロール２３Ａに設ける周溝２３ａは丸溝型の周溝で良い。なお、図３（Ｇ）では後述する実施例において矩形断面形状の超電導線材を得るための凹型の周溝２３ａが描かれている。
なお、断面矩形型の超電導線材を製造する場合は角溝型の周溝２３ａとすれば良く、周溝の幅を大きくして浅い周溝とすればシート状の超電導線材を製造することもできる。本願の明細書で記載する超電導線材とは断面丸型の線材や矩形断面形状の線材に限らず、シート状の線材も含む概念とするので、圧延ロール２３Ａ、２３Ａに形成する周溝２３ａの断面形状を工夫することで任意の断面形状の超電導線材を製造できる。
Next, the outer tube 22 shown in FIG. 3G in which the tube 21 filled with the final mixed powder 20 is accommodated is rolled by the rolling device 23. The rolling device 23 used here is a device that has rolling rolls 23A and 23A arranged above and below, and a circumferential groove 23a formed on the outer periphery of the center portion in the length direction of the rolling rolls 23A and 23A. When the superconducting wire A having a circular cross section shown in FIG. 1 is manufactured in this embodiment, the circumferential groove 23a provided in the rolling roll 23A may be a round groove type circumferential groove. In FIG. 3G, a concave circumferential groove 23a for obtaining a superconducting wire having a rectangular cross section is illustrated in an example described later.
In addition, when manufacturing a superconducting wire having a rectangular cross section, it is only necessary to use a square groove type peripheral groove 23a, and a sheet-like superconducting wire can be manufactured by increasing the width of the peripheral groove to a shallow peripheral groove. . The superconducting wire described in the specification of the present application is not limited to a wire having a round cross-section or a wire having a rectangular cross-section, but also includes a sheet-like wire, so the cross-section of the circumferential groove 23a formed in the rolling rolls 23A and 23A By devising the shape, a superconducting wire having an arbitrary cross-sectional shape can be manufactured.
図３（Ｇ）に示すように圧延装置２３で加圧することで内部の最終混合粉末２０は加圧されて棒状の圧密体となり、チューブ２１を圧延した内部シース２で圧密体を覆い、更に外チューブ２２を圧延した外部シース３で内部シース２を覆った構造の複合線材２５が得られる。
この複合線材２５を図３（Ｈ）に示すオーブンなどの加熱炉２６に収容し、真空雰囲気中あるいはアルゴン等の不活性雰囲気中において（５００〜１０００）℃、より好ましくは８００〜９５０℃に加熱する本焼成処理を行う。本焼成の温度は原料成分の溶融を防止するために、前述の仮焼き温度の望ましい上限１０５０℃より低い温度とすることが好ましい。また、銀からなるシースを用いる場合に銀の融点である９６１℃より高くすることができないので本焼成の場合の上限温度を９５０℃としている。
この本焼成処理によって原料混合粉末の圧密体の内部で必要な成分元素どうしの反応が進み、Ａ２ＤＦｅＡｓＯ３-δなる組成式で示される酸化物超電導体、例えば、組成式Ｓｒ２ＶＦｅＡｓＯ３-δなる組成式で表される図２に示す結晶構造の超電導体が生成し、図１に示す超電導コア１を備えた超電導線材Ａが得られる。
As shown in FIG. 3 (G), the final mixed powder 20 inside is pressed into a rod-like compact by pressing with the rolling device 23, and the compact 21 is covered with the inner sheath 2 in which the tube 21 is rolled. A composite wire 25 having a structure in which the inner sheath 2 is covered with the outer sheath 3 obtained by rolling the tube 22 is obtained.
The composite wire 25 is housed in a heating furnace 26 such as an oven shown in FIG. 3 (H) and heated to (500 to 1000) ° C., more preferably 800 to 950 ° C. in a vacuum atmosphere or an inert atmosphere such as argon. The main firing process is performed. In order to prevent melting of the raw material components, it is preferable that the temperature of the main baking is lower than the desirable upper limit of 1050 ° C. of the calcining temperature. In addition, when a sheath made of silver is used, the upper limit temperature in the main firing is set to 950 ° C. because it cannot be higher than 961 ° C. which is the melting point of silver.
By this main calcination treatment, reaction between necessary component elements proceeds inside the compact of the raw material mixed powder, and an oxide superconductor represented by a composition formula of A 2 DFeAsO 3 -δ , for example, a composition formula Sr 2 VFeAsO 3- The superconductor having the crystal structure shown in FIG. 2 represented by the composition formula δ is generated, and the superconducting wire A including the superconducting core 1 shown in FIG. 1 is obtained.
本焼成時間は１分〜２４時間程度の範囲が望ましく、１分〜１６時間程度の範囲がより望ましく、１分〜８時間程度の範囲が最も望ましい。本焼成の時間と本焼成の温度の関係の一例を図５に示す。
図５は目的の本焼成温度を９００℃に設定した場合の温度履歴の一例を示し、目的の温度例えば９００℃に、常温から２時間程度かけて昇温し、上述の範囲の時間保持した後、加熱装置のヒーターへの通電を停止してから空冷する条件を記載している。常温から目的の温度まで昇温する場合、昇温速度は特に制限はない。例えば、９００℃に加熱した加熱炉の外部に試料を保持しておき、加熱炉に試料を挿入して急速加熱する方法を用いても良い。
The main baking time is preferably in the range of about 1 minute to 24 hours, more preferably in the range of about 1 minute to 16 hours, and most preferably in the range of about 1 minute to 8 hours. An example of the relationship between the firing time and the firing temperature is shown in FIG.
FIG. 5 shows an example of a temperature history when the target main firing temperature is set to 900 ° C., after the temperature is raised from the normal temperature to about 900 ° C. over about 2 hours and held for the time in the above range. The conditions for air cooling after stopping energization of the heater of the heating device are described. When the temperature is raised from room temperature to the target temperature, the rate of temperature rise is not particularly limited. For example, a method may be used in which a sample is held outside a heating furnace heated to 900 ° C., and the sample is inserted into the heating furnace and rapidly heated.
本焼成時間が長い場合はＡ２ＤＦｅＡｓＯ３-δなる組成式で示される酸化物超電導体において特にＡｓが内部シース２側に拡散するか、内部シース２を通過して外部シース３側にまで拡散する。Ａｓの拡散が進行すると超電導コア１の内部に含まれるＡｓの量が減少する結果、目的とするＡ２ＤＦｅＡｓＯ３-δなる組成式のＦｅ系超電導体を生成するためのＡｓ量が不足するので、超電導コア１の内部に生成するＦｅ系超電導体の割合が減少するか、目的の組成から外れたＡｓ量の少ない物質が多く生成されてしまうおそれがある。
前述の範囲の熱処理時間とすることで、目的の組成比のペロブスカイト関連混合アニオン型鉄系超電導体の生成割合が高くなり、生成するペロブスカイト関連混合アニオン型鉄系超電導体の量も増加する結果、臨界温度の高い、臨界電流密度の高い超電導線材Ａを得ることができる。
When the main firing time is long, particularly in the oxide superconductor represented by the composition formula of A 2 DFeAsO 3 -δ , As diffuses to the inner sheath 2 side, or passes through the inner sheath 2 and diffuses to the outer sheath 3 side. To do. As the diffusion of As proceeds, the amount of As contained in the superconducting core 1 decreases. As a result, the amount of As for generating the Fe-based superconductor having the composition formula of A 2 DFeAsO 3 -δ is insufficient. The ratio of the Fe-based superconductor generated inside the superconducting core 1 may decrease, or a large amount of a substance with a small amount of As deviating from the target composition may be generated.
By setting the heat treatment time in the above range, the generation ratio of the perovskite-related mixed anionic iron-based superconductor having the target composition ratio is increased, and the amount of the perovskite-related mixed anionic iron-based superconductor to be generated is increased. A superconducting wire A having a high critical temperature and a high critical current density can be obtained.
以上説明の製造方法により得られた、例えば、組成式Ｓｒ２ＶＦｅＡｓＯ３-δで表される図２に示す結晶構造の超電導体を含む超電導コア１を有する超電導線材Ａであるならば、Ｔｃ＝２０Ｋ前後の優れた臨界温度を示し、臨界電流密度の高い超電導線材Ａを提供できる。
特に前述の製造方法ではチューブ２１の内部に最終混合粉末２０を充填してから圧縮し、熱処理するというＰＩＴ法により超電導線材Ａを製造しているので、２軸配向制御を要する成膜法などのコストのかかる特別な方法を採用する必要がない。このため、本実施形態の製造方法によれば、優れた臨界温度を示し、臨界電流密度の高いペロブスカイト関連混合アニオン型鉄系超電導線材Ａを成膜法で製造する場合に比べて低コストで製造できる特徴を有する。
また、上述の製造方法によれば、２０Ｋ以上の高い臨界温度を示す組成式Ｓｒ２ＶＦｅＡｓＯ３-δで表されるペロブスカイト関連混合アニオン型鉄系超電導体の原料である最終混合粉末２０をチューブ２１の内部に充填し、圧縮してから焼成するというＰＩＴ法により製造しているので、臨界電流密度の高い超電導線材を提供できる。
For example, if the superconducting wire A has the superconducting core 1 including the superconductor having the crystal structure shown in FIG. 2 represented by the composition formula Sr 2 VFeAsO 3−δ obtained by the manufacturing method described above, Tc = A superconducting wire A having an excellent critical temperature around 20K and a high critical current density can be provided.
In particular, in the manufacturing method described above, the superconducting wire A is manufactured by the PIT method in which the final mixed powder 20 is filled into the tube 21 and then compressed and heat-treated. There is no need to adopt costly special methods. For this reason, according to the manufacturing method of the present embodiment, the perovskite-related mixed anionic iron-based superconducting wire A exhibiting an excellent critical temperature and having a high critical current density is manufactured at a lower cost compared to the case of manufacturing by a film forming method. It has the characteristics that can.
In addition, according to the above-described manufacturing method, the final mixed powder 20 that is a raw material of the perovskite-related mixed anionic iron-based superconductor represented by the composition formula Sr 2 VFeAsO 3 -δ exhibiting a high critical temperature of 20 K or higher is added to the tube 21. The superconducting wire having a high critical current density can be provided because it is manufactured by the PIT method in which the inside is filled and compressed and then fired.
ペロブスカイト関連混合アニオン型鉄系超電導線材を製造するに際し、初めに前駆体としてＳｒＯ及びＦｅＡｓを合成した。
Ｓｒ（ＯＨ）２８Ｈ２Ｏ（１．３７４ｇ）を９００℃に１０時間加熱して脱水し、ＳｒＯ（０．５３６０ｇ）粉末を得た。次に、Ｆｅ（３Ｎ、０．１４４４ｇ）粉末とＡｓ粉末を（６Ｎ、０．１９３８ｇ）を秤量して混合し、混合粉末を真空雰囲気中において６００℃で焼成し、ＦｅＡｓ（０．３３８２ｇ）粉末を得た。焼成後のＦｅＡｓ粉末をめのう乳鉢と乳棒を用いて粉砕し、ＦｅＡｓ粉砕物の粉末を得た。
ＳｒＯ粉末（０．５３６０ｇ）、ＦｅＡｓ粉末（０．３３８２ｇ）、Ｖ粉末（０．０７９１ｇ）、Ｖ２Ｏ５粉末（０．０９４１ｇ）を秤量して混合し、圧延によりペレット状に成形した後、真空雰囲気中で１０５０℃に加熱する仮焼きを行った。仮焼き時の加熱条件は、常温から３０分間かけて１０５０℃まで昇温し、１０５０℃に４０分間保持し、６００℃になるまで８０分間かけて降温し、６００℃に降温後、大気中で放冷した。
In producing a perovskite-related mixed anionic iron-based superconducting wire, SrO and FeAs were first synthesized as precursors.
Sr (OH) 2 8H 2 O (1.374 g) was heated to 900 ° C. for 10 hours for dehydration to obtain SrO (0.5360 g) powder. Next, Fe (3N, 0.1444 g) powder and As powder (6N, 0.1938 g) are weighed and mixed, and the mixed powder is fired at 600 ° C. in a vacuum atmosphere to obtain FeAs (0.3382 g) powder. Got. The baked FeAs powder was pulverized using an agate mortar and pestle to obtain a pulverized FeAs powder.
SrO powder (0.5360 g), FeAs powder (0.3382 g), V powder (0.0791 g), V 2 O 5 powder (0.0941 g) were weighed and mixed, formed into a pellet by rolling, Calcination was performed by heating to 1050 ° C. in a vacuum atmosphere. The heating conditions at the time of calcining were as follows: normal temperature was raised to 1050 ° C. over 30 minutes, held at 1050 ° C. for 40 minutes, lowered to 600 ° C. over 80 minutes, lowered to 600 ° C., and then in the atmosphere Allowed to cool.
仮焼き後のペレットをめのう乳鉢と乳棒を用いて粉砕し、この粉砕物を最終混合粉末として、内径３.０ｍｍ、外径４.１ｍｍのＡｇからなるチューブに充填し、このチューブの外方に内径４.１ｍｍ、外径６.０ｍｍのＦｅからなるパイプを被せ、図６の写真に示す概形の複合体を得た。
この複合体を図３に（Ｇ）に示すような圧延ロールで圧延し、横断面略４角形状で対角線に沿う外径約１ｍｍの圧延線材を得た。この圧延線材に対し、大気中において図５に示す温度履歴で本焼成（９００℃加熱）した。昇温時間は常温から９００℃となるまで２時間に設定し、９００℃で所定時間加熱後、加熱炉の加熱ヒーターへの通電を停止し、６００℃になるまで炉冷し、６００℃になってから大気中に取り出して放冷した。
The calcined pellets are pulverized using an agate mortar and pestle, and the pulverized product is filled as a final mixed powder into a tube made of Ag having an inner diameter of 3.0 mm and an outer diameter of 4.1 mm. A pipe made of Fe having an inner diameter of 4.1 mm and an outer diameter of 6.0 mm was covered to obtain a composite having a general shape shown in the photograph of FIG.
This composite was rolled with a rolling roll as shown in FIG. 3 (G) to obtain a rolled wire rod having a substantially quadrangular cross section and an outer diameter of about 1 mm along the diagonal line. This rolled wire was subjected to main firing (heating at 900 ° C.) in the atmosphere with a temperature history shown in FIG. The temperature raising time is set to 2 hours from normal temperature to 900 ° C. After heating for a predetermined time at 900 ° C., the energization to the heater of the heating furnace is stopped, the furnace is cooled to 600 ° C., and becomes 600 ° C. Then, it was taken out into the atmosphere and allowed to cool.
同等の条件で複数の圧延線材を用意し、それぞれについて図５に示す温度履歴に従い、９００℃に保持する時間を１時間、２時間、４時間、８時間、１６時間、３２時間、６４時間、１２８時間のいずれかに設定して焼成し、複数の超電導線材を作成した。
得られた複数の超電導線材のうち、１時間本焼成した試料の断面写真を図７に示す。図７に示す断面構造の超電導線材は、中心部分に四葉型に圧縮加工された超電導コアを有し、その周囲をＡｇからなる薄い内部シース材が覆い、この内部シース材の周囲をＦｅからなる厚い外部シース材が覆った構造となっている。図７に示すようにこの４角柱状の超電導線材の対角部分の長さは約１ｍｍである。
A plurality of rolled wire rods are prepared under the same conditions, and according to the temperature history shown in FIG. 5 for each, the time for holding at 900 ° C. is 1 hour, 2 hours, 4 hours, 8 hours, 16 hours, 32 hours, 64 hours, A plurality of superconducting wires were prepared by firing at any one of 128 hours.
FIG. 7 shows a cross-sectional photograph of a sample fired for one hour among the obtained plurality of superconducting wires. The superconducting wire having the cross-sectional structure shown in FIG. 7 has a superconducting core compressed into a four-leaf type at the center, and a thin inner sheath material made of Ag covers the periphery, and the periphery of the inner sheath material is made of Fe. The structure is covered with a thick outer sheath material. As shown in FIG. 7, the length of the diagonal portion of this quadrangular columnar superconducting wire is about 1 mm.
図８は上述の超電導線材を製造するためにＡｇのチューブに充填した最終混合粉末をペレット状に加圧成形し、そのペレットを９００℃で本焼成して得た超電導バルク体の抵抗の温度依存性を示すグラフである。ここで前記粉砕物の粉末に対する本焼成の際の昇温時と降温時の温度履歴は先の実施例の場合と同等にしている。
図８に示すグラフから、ペレット状の超電導バルク体のＴｃonsetは３６.２７Ｋであり、Ｔｃzeroは３０.６Ｋであることがわかった。即ち、上述の最終混合粉末をペレット状に加工し、焼成して得られた超電導バルク体の臨界温度がこの種のＦｅ系超電導体の臨界温度として知られている値に近似するので、前述の工程において超電導線材の製造に用いた最終混合粉末はＦｅ系超電導体を製造するために望ましい組成比の最終混合粉末であることがわかる。
FIG. 8 shows the temperature dependence of the resistance of a superconducting bulk material obtained by press-molding the final mixed powder filled in an Ag tube into a pellet to produce the above-described superconducting wire and firing the pellet at 900 ° C. It is a graph which shows sex. Here, the temperature history at the time of temperature rise and temperature drop during the main firing of the powder of the pulverized product is set to be the same as in the previous embodiment.
From the graph shown in FIG. 8, Tc onset of pelletized bulk superconductor is 36.27K, it was found that Tc zero is 30.6K. That is, since the critical temperature of the superconducting bulk body obtained by processing the above-mentioned final mixed powder into a pellet and firing it approximates the value known as the critical temperature of this type of Fe-based superconductor. It can be seen that the final mixed powder used for manufacturing the superconducting wire in the process is a final mixed powder having a desirable composition ratio for manufacturing the Fe-based superconductor.
本焼成時間を１時間、２時間、４時間、８時間、１６時間、３２時間、６４時間、１２８時間のいずれかに設定して得た超電導線材について、超電導コアの部分から内部シースの部分まで到達する図９に示す矩形領域(走査型電子顕微鏡：Hitchi, TM3030 Plus Miniscope にて表面観察して特定した領域)に沿ってＥＤＸ（エネルギー分散型蛍光Ｘ線分光装置：Brunker nano GmbH,Quantax 70）によるライン分析を元素毎に行った結果について、図１０〜図１５に示す。
図１０はＳｒに関するＥＤＸライン分析結果を示し、図１１はＶに関するＥＤＸライン分析結果を示し、図１２はＡｇに関するＥＤＸライン分析結果を示し、図１３はＦｅに関するＥＤＸライン分析結果を示し、図１４はＯに関するＥＤＸライン分析結果を示し、図１５はＡｓに関するＥＤＸライン分析結果を示す。
From the superconducting core part to the inner sheath part of the superconducting wire obtained by setting the main firing time to any one of 1, 2, 4, 8, 16, 32, 64, and 128 hours EDX (energy dispersive X-ray fluorescence spectrometer: Brunker nano GmbH, Quantax 70) along the rectangular area shown in FIG. 9 (scanning electron microscope: area specified by surface observation with Hitchi, TM3030 Plus Miniscope) The results of the line analysis performed for each element are shown in FIGS.
10 shows an EDX line analysis result for Sr, FIG. 11 shows an EDX line analysis result for V, FIG. 12 shows an EDX line analysis result for Ag, FIG. 13 shows an EDX line analysis result for Fe, and FIG. Shows the EDX line analysis results for O, and FIG. 15 shows the EDX line analysis results for As.
図１０に示すＳｒの測定結果について、横軸に示す距離０（Distance：μｍ）の位置が超電導コアの部分と内部シースとの界面に相当し、０〜４００μｍの領域にＳｒが多く存在し、０〜−１００μｍの領域に殆どＳｒが存在しない。このため、０〜４００μｍの領域が超電導コアに該当し、０〜−１００μｍの領域が内部シースに対応する。
図１０に示す測定結果から、Ｓｒについて、１〜１２８時間のいずれの焼成時間においても超電導コアの部分と内部シースとの間でＳｒは殆ど拡散していないと思われる。
図１１に示す結果から、Ｖについて、１〜１２８時間のいずれの焼成時間においても超電導コアの部分と内部シースとの間でＶ含有量のバランスを変えるほど大量の拡散が生じたとは思われないことが判る。
In the measurement result of Sr shown in FIG. 10, the position of distance 0 (Distance: μm) shown on the horizontal axis corresponds to the interface between the superconducting core portion and the inner sheath, and there is a lot of Sr in the region of 0 to 400 μm. There is almost no Sr in the region of 0 to -100 μm. For this reason, the region of 0 to 400 μm corresponds to the superconducting core, and the region of 0 to −100 μm corresponds to the inner sheath.
From the measurement results shown in FIG. 10, it is considered that Sr hardly diffuses between the portion of the superconducting core and the inner sheath at any firing time of 1 to 128 hours.
From the results shown in FIG. 11, it is unlikely that a large amount of diffusion of V occurred so as to change the balance of the V content between the superconducting core portion and the inner sheath at any firing time of 1 to 128 hours. I understand that.
図１２に示す結果から、Ａｇについて、１〜１２８時間のいずれの焼成時間においても超電導コアの部分と内部シースとの間でＡｇ含有量のバランスを変えるほど大量の拡散が生じたとは思われないことが判る。
図１３に示す結果から、Ｆｅについて、０〜４００μｍの領域において多く、０〜−１００μｍの領域において少ないが、いずれの焼成時間でも０〜−１００μｍの領域にある程度存在していると推定できる。これは外部シースと超電導コアの両方にＦｅが含まれているので、それぞれの領域から内部シース側に微量のＦｅ拡散がなされているとも推定できる。
図１４に示す結果から、Ｏについては０〜４００μｍの領域において多く、０〜−１００μｍの領域において少ない結果が得られた。
From the results shown in FIG. 12, it is unlikely that Ag diffused so much that the balance of the Ag content was changed between the superconducting core portion and the inner sheath at any firing time of 1 to 128 hours. I understand that.
From the results shown in FIG. 13, it can be estimated that Fe is large in the region of 0 to 400 μm and small in the region of 0 to −100 μm, but is present to some extent in the region of 0 to −100 μm at any firing time. Since Fe is contained in both the outer sheath and the superconducting core, it can be estimated that a small amount of Fe is diffused from each region to the inner sheath side.
From the results shown in FIG. 14, for O, a large result was obtained in the region of 0 to 400 μm, and a small result was obtained in the region of 0 to −100 μm.
図１５に示す結果から、Ａｓについてはかなりの量の拡散がなされていることが想定される。焼成時間が１６時間までの超電導線材はいずれも距離０の境界付近のＡｓ濃度が急激に変化しているが、３２時間以上の超電導線材では距離０付近のＡｓ濃度の変化は緩やかになっている。これはＡｓが超電導コアからシース側に相当量拡散し、超電導コアと内部シースの境界部分にＡｓが拡散したことにより両層の境界部分に拡散層が生成し、この拡散層の幅が焼成時間の増加に応じて徐々に拡がったことを示唆している。
図１５においてＩＡｇはＡｇ（内部シース）の部分の回折強さを示し、Ｉｃｏｒｅは超電導コアの部分の回折強さを示す。焼成時間が長いほど、両層の境界部分の幅が大きくなっていることがわかる。
From the results shown in FIG. 15, it is assumed that a considerable amount of diffusion is performed for As. The superconducting wire with a firing time of up to 16 hours has a rapid change in the As concentration near the boundary of the distance 0, but the change in As concentration near the distance 0 is moderate in the superconducting wire having a firing time of 32 hours or more. . This is because a considerable amount of As diffuses from the superconducting core to the sheath side, and As diffuses into the boundary portion between the superconducting core and the inner sheath, a diffusion layer is formed at the boundary portion between the two layers. It suggests that it gradually expanded with the increase of.
In FIG. 15, I Ag indicates the diffraction intensity of the Ag (inner sheath) portion, and I core indicates the diffraction intensity of the superconducting core portion. It can be seen that the longer the firing time, the greater the width of the boundary between both layers.
図１５に示すＡｓのＥＤＸラインスキャンに対して、Ｂｏｌｔｚｍａｎｎ−Ｍａｔａｎｏ解析を行う場合、得られたデータに沿ったなめらかなＡｓ量の増加曲線を決定しなければならない。より正確なＡｓ量の増加曲線を得るためには、拡散に寄与する区間の設定が必要である。この際、ノイズ対策として、Ｆｅ外部シースにおけるＡｓ量のスポット分析の焼成時間に対する変化（図１６）と矛盾のないように区間の設定を行った。則ち、Ｆｅ外部シースにおけるＡｓ含有量と拡散に寄与する区間の長さは正の相関をもつと仮定した。図１６は、鉄からなる外部シースにおけるＡｓ量のスポット分析について焼成時間に対するＡｓ量の変化を示すグラフである。 When the Boltzmann-Matano analysis is performed on the As EDX line scan shown in FIG. 15, a smooth As amount increase curve along the obtained data must be determined. In order to obtain a more accurate As amount increase curve, it is necessary to set a section that contributes to diffusion. At this time, as a noise countermeasure, the interval was set so as not to contradict the change in the amount of As in the Fe outer sheath with respect to the firing time of the spot analysis (FIG. 16). In other words, it was assumed that the As content in the Fe outer sheath and the length of the interval contributing to diffusion had a positive correlation. FIG. 16 is a graph showing a change in As amount with respect to firing time for spot analysis of As amount in an outer sheath made of iron.
Ａｓに対するＥＤＸラインスキャンのプロットに関して、銀シース側から１，２，３， ……．．とプロット番号を付ける。あるプロット番号ｎのときに、ｎからｎ＋４９まで連続する５０プロットに対して最小二乗法による線形近似を行い、このときに求まる近似直線の傾きａに対して、縦軸をａ、横軸をｎ＋４９としてａの位置依存を図１７に示す。このとき、強度変化によるピークをある一つに決定し、そのピークまわりで、傾きａが負から正になるプロット番号を強度変化開始プロット番号ｎｓ、傾きａが正から負になるプロット番号を強度変化終了プロット番号ｎｆとした。また、強度変化開始位置ＸｓをＮｓ＝ｎｓのときの位置、強度変化終了位置ＸｆをＮｆ＝ｎｆ−４９のときの位置とした。 Regarding the plot of EDX line scan against As, 1, 2, 3, ... from the silver sheath side. . And plot number. For a certain plot number n, 50 approximate plots from n to n + 49 are linearly approximated by the least square method, and the vertical axis is a and the horizontal axis is n + 49 with respect to the slope a of the approximate straight line obtained at this time. FIG. 17 shows the position dependency of a. At this time, the peak due to the intensity change is determined to be one, and around that peak, the plot number where the slope a becomes negative to positive is set as the intensity change start plot number n s , and the plot number where the slope a becomes positive from negative is set. was a change in intensity end plot number n f. The position when the intensity change start position Xs Ns = n s, the intensity change end position X f and the position when the N f = n f -49.
図１７において、傾きａの極大は複数観察されるが、これらのうち、最も大きいａ＝ ０．００００６の極大を示すａ＞０の構造をＡｓの濃度変化によるものと帰属する。このＡｓの濃度変化による構造を拡大したものが図１８（ａ）である。このとき、ｎｓ＝１０６、ｎｆ＝１６１である。よって、Ｎｓ＝１０６，Ｎｆ＝１１２であり、Ｘｓ＝−６．１３１、ｘｆ＝−１．０５３である。
図１８（ｂ）〜（ｈ）に、焼成時間２ｈ〜１２８ｈの結果を示す。焼成時間１６ｈ，６４ｈ、１２８ｈの結果では図に示す○印で囲む１の極大付近の構造をＡｓの濃度変化に帰属して結果をまとめたものが以下の表１である。
In FIG. 17, a plurality of local maxima of inclination a are observed. Among these, the structure of a> 0 showing the maximum of a = 0.00006 is attributed to the change in As concentration. FIG. 18A is an enlarged view of the structure due to this As concentration change. At this time, n s = 106 and n f = 161. Therefore, N s = 106, N f = 112, X s = −6.131, and x f = −1.053.
The result of baking time 2h-128h is shown to FIG.18 (b)-(h). Table 1 below summarizes the results of the firing times of 16h, 64h, and 128h by assigning the structure near the maximum of 1 surrounded by circles shown in the figure to the concentration change of As.
強度変化距離ｘｆ−ｘｓ（μｍ）は１ｈから８ｈまで焼成時間とともに大きくなっている。ところが、この方法では１６ｈ以上では焼成時間との正の相関がみられない。これは、図１８（ｆ）で見られるように、Ａｓの濃度変化によるａ＞０の構造内において極小が出現する場合があることに起因する。この極小がａ＜０となる場合、正確なＡｓの濃度分布、則ち、正確なＭａｔａｎｏ面を得ることができない。これは、強度変化の傾きが緩やかになり、ノイズの効果が相対的に大きくなったことに起因する。 The intensity change distance x f −x s (μm) increases with the firing time from 1 h to 8 h. However, in this method, a positive correlation with the firing time is not observed at 16 hours or longer. This is because, as seen in FIG. 18 (f), a minimum may appear in the structure of a> 0 due to the change in As concentration. When this minimum is a <0, an accurate As concentration distribution, that is, an accurate Matano surface cannot be obtained. This is due to the fact that the gradient of the intensity change becomes gentle and the effect of noise becomes relatively large.
よって、以上のような問題点を解決する解析上の手段として、以下のような処理を行った。
強度変化による極大をとるａ＞の構造を一つではなく、図１６の結果と矛盾しないように複数考慮し、拡散係数の算出に寄与する区間として用いる。
焼成時間１６ｈ、６４ｈについて、図１８（ｅ）及び（ｇ）の○印で囲む１に加え、○印で囲む２もそれぞれのＡｓの濃度変化による構造として帰属した。また、１２８ｈに関しては、○印で囲む０、１、２を同様に帰属した。このとき、処理の適用前後のそれぞれのパラメータの変化をまとめたものが表２、３である。この補正を行い、それぞれのｘｓ，ｘｆをＡｓのＥＤＸラインスキャンデータに追加したものが図１９である。これらの結果をまとめたものが以下の表４である。
Therefore, the following processing was performed as an analytical means for solving the above problems.
The structure of a> that takes the maximum due to the intensity change is not one, but is considered as a section that contributes to the calculation of the diffusion coefficient in consideration of a plurality so as not to contradict the result of FIG.
Regarding firing times 16h and 64h, in addition to 1 surrounded by circles in FIGS. 18 (e) and 18 (g), 2 surrounded by circles were also assigned as structures according to respective As concentration changes. For 128h, 0, 1, and 2 enclosed in circles were similarly assigned. At this time, Tables 2 and 3 summarize changes in parameters before and after application of the processing. FIG. 19 shows the result of performing this correction and adding the respective x s and x f to As EDX line scan data. Table 4 below summarizes these results.
図２０はＡｇのチューブに充填する前の最終混合粉末の仮焼き粉末についてペレット状に成形して本焼成したものにおいて、Ｘ線回折パターンを求めた結果（図２０（Ａ）にバルクと表示）と、上述の実施例において本焼成時間を２時間に設定して得られた超電導線材の超電導コアについてＸ線回折パターンを求めた結果（図２０（Ｂ）に２時間焼成線材と表示）を対比して示す。
図２０（Ａ）に示すバルクの試験結果と図２０（Ｂ）に示す超電導コアの試験結果を対比すると、異相が示す回折ピークを除くと両者とも類似した回折ピークを得られたことがわかる。
よって実施例の超電導線材において超電導コアに形成されている物質は、鉄系超電導体であると推定できる。
FIG. 20 shows the result of obtaining the X-ray diffraction pattern of the calcined powder of the final mixed powder before filling into the Ag tube, which was formed into a pellet and subjected to main firing (indicated as bulk in FIG. 20A). And a result of obtaining an X-ray diffraction pattern for the superconducting core of the superconducting wire obtained by setting the main firing time to 2 hours in the above-described embodiment (displayed as a 2-hour fired wire in FIG. 20B). Show.
Comparing the bulk test results shown in FIG. 20A and the superconducting core test results shown in FIG. 20B, it can be seen that similar diffraction peaks were obtained except for the diffraction peaks exhibited by the different phases.
Therefore, it can be estimated that the substance formed in the superconducting core in the superconducting wire of the example is an iron-based superconductor.
図２１は先に１時間焼成により製造した超電導線材と２時間焼成により製造した超電導線材と４時間焼成により製造した超電導線材と８時間焼成により製造した超電導線材と１６時間焼成により製造した超電導線材について個々の線材の電気抵抗率の温度依存性（０−３００Ｋ）を測定した結果を示す。図２２は同等超電導線材の電気抵抗率の温度依存性（０−５０Ｋ）を測定した結果を示す。図２３は同等超電導線材の電気抵抗率の温度依存性（６−１５Ｋ）を測定した結果を示す。これらの図の測定結果は、４端子法に従い、±５０ｍＡ通電した場合の結果を示す。±の両方の電圧を印加することで配線抵抗やゼーベック系数に起因する熱電効果の影響を相殺して除去することができる。 FIG. 21 shows a superconducting wire produced by firing for 1 hour, a superconducting wire produced by firing for 2 hours, a superconducting wire produced by firing for 4 hours, a superconducting wire produced by firing for 8 hours, and a superconducting wire produced by firing for 16 hours. The result of having measured the temperature dependence (0-300K) of the electrical resistivity of each wire is shown. FIG. 22 shows the result of measuring the temperature dependence (0-50K) of the electrical resistivity of the equivalent superconducting wire. FIG. 23 shows the results of measuring the temperature dependence (6-15K) of the electrical resistivity of an equivalent superconducting wire. The measurement results in these figures show the results when ± 50 mA current is applied according to the 4-terminal method. By applying both ± voltages, the influence of the thermoelectric effect due to the wiring resistance and the Seebeck system number can be offset and removed.
図２１、図２２に示す結果から、１〜１６時間のいずれの焼成時間で焼成した超電導線材であっても、電気抵抗がほぼ０となることを確認できた。なお、これらの図に示す電気抵抗値の状態から類推すると、焼成時間１〜８時間の超電導線材の方が焼成時間１６時間の超電導線材よりも電気抵抗率の低下の割合が急峻である。このため、焼成時間によるＡｓの拡散の進行度合いからＰＩＴ法による焼成時間を１〜８時間とすることがより好ましいと考えられる。 From the results shown in FIG. 21 and FIG. 22, it was confirmed that the electrical resistance was almost zero even when the superconducting wire was fired at any firing time of 1 to 16 hours. By analogy with the state of the electrical resistance values shown in these figures, the rate of decrease in electrical resistivity is higher in the superconducting wire having a firing time of 1 to 8 hours than in the superconducting wire having a firing time of 16 hours. For this reason, it is considered that it is more preferable that the firing time by the PIT method is 1 to 8 hours from the degree of progression of As diffusion due to the firing time.
図２４は１時間焼成、２時間焼成、４時間焼成によりそれぞれ得られた超電導線材に対し超電導転移温度以下、すなわち１時間焼成は１６Ｋと１８Ｋ、２時間焼成は１７Ｋと１８Ｋ、４時間焼成は１３Ｋと１５Ｋにおいて臨界電流Ｉｃを測定した場合、超電導コアの単位面積当たりの臨界電流密度ＪｃはＪｃ（Ｔ）＝Ｊｃ（０）｛１−（Ｔ／Ｔｃ）２｝…（１）式で示す外挿式が成立するため、０Ｋにおける臨界電流密度Ｊｃ（０）を計算により算出できることを示す説明図である。
超電導線材の測定により図２４の１時間焼成（１ｈ）の１６ＫにおけるＩｃ（１６Ｋ）＝２９．７ｍＡ、Ｉｃ（１８Ｋ）＝１６．７ｍＡとなる。また、この超電導線材において、Ｊｃ（１７Ｋ）＝１７．２Ａ／ｃｍ２、Ｊｃ（１８Ｋ）＝９．６５Ａ／ｃｍ２と測定できた。この場合の超電導線材のＴｃは２０．３Ｋとなる。上述の１６Ｋ、１８ＫのＪｃの場合、（１）式を用いてＪｃ（０）を算出すると、Ｊｃ（０）＝４５．３Ａ／ｃｍ２と見積もることができる。
FIG. 24 shows a superconducting transition temperature for superconducting wires obtained by firing for 1 hour, 2 hours, and 4 hours, respectively, that is, 16K and 18K for 1 hour firing, 17K and 18K for 2 hour firing, and 13K for 4 hour firing. When the critical current Ic is measured at 15 K and the critical current density Jc per unit area of the superconducting core is Jc (T) = Jc (0) {1- (T / Tc) 2 } (1) It is explanatory drawing which shows that the critical current density Jc (0) in 0K can be calculated by calculation because an insertion type is materialized.
According to the measurement of the superconducting wire, Ic (16K) = 29.7 mA and 16 (1K) = 16.7 mA at 16 K after firing for 1 hour (1 h) in FIG. Moreover, in this superconducting wire, it was measured with Jc (17K) = 17.2 A / cm 2 and Jc (18K) = 9.65 A / cm 2 . The Tc of the superconducting wire in this case is 20.3K. In the case of JC of 16K and 18K described above, Jc (0) = 45.3 A / cm 2 can be estimated by calculating Jc (0) using equation (1).
同じく、 超電導線材の測定により図２３の２時間焼成（２ｈ）の１７ＫにおけるＩｃ（１７Ｋ）＝１９．８ｍＡ、Ｉｃ（１８Ｋ）＝１２．９ｍＡ、Ｊｃ（１７Ｋ）＝１０．６Ａ／ｃｍ２、Ｊｃ（１８Ｋ）＝６．９４Ａ／ｃｍ２と測定できた。この場合の超電導線材のＴｃは１９．７Ｋとなる。１）式を用いてＪｃ（０）を算出すると、Ｊｃ（０）＝４１．２Ａ／ｃｍ２と見積もることができる。
同じく、超電導線材の測定により図２３の４時間焼成（４ｈ）の１３ＫにおけるＩｃ（１３Ｋ）＝２０．１ｍＡ、Ｉｃ（１５Ｋ）＝８．３５ｍＡ、Ｊｃ（１３Ｋ）＝９．６６Ａ／ｃｍ２、Ｊｃ（１５Ｋ）＝４．０１Ａ／ｃｍ２と測定できた。この場合の超電導線材のＴｃは１６．３Ｋとなる。
Similarly, according to the measurement of the superconducting wire, Ic (17K) = 19.8 mA, Ic (18K) = 12.9 mA, Jc (17K) = 10.6 A / cm 2 , Jc at 17 K after firing for 2 hours (2 h) in FIG. (18K) = 6.94 A / cm 2 . The Tc of the superconducting wire in this case is 19.7K. When Jc (0) is calculated using the equation (1), it can be estimated that Jc (0) = 41.2 A / cm 2 .
Similarly, according to the measurement of the superconducting wire, Ic (13K) = 20.1 mA, Ic (15K) = 8.35 mA, Jc (13K) = 9.66 A / cm 2 , Jc at 13 K for 4 hours firing (4 h) in FIG. (15K) = 4.01 A / cm 2 . In this case, the Tc of the superconducting wire is 16.3K.
以上説明のように、図２４を基に説明した如く本実施例の超電導線材は０Ｋにおいて、４５．３Ａ／ｃｍ２、４１．２Ａ／ｃｍ２あるいは２６．７Ａ／ｃｍ２の優れた臨界電流密度を得ることができると見積もることができた。 As described above, as described with reference to FIG. 24, the superconducting wire of this example has an excellent critical current density of 45.3 A / cm 2 , 41.2 A / cm 2 or 26.7 A / cm 2 at 0K. I was able to estimate that
以上説明した組成式Ｓｒ２ＶＦｅＡｓＯ３-δで表されるペロブスカイト関連混合アニオン型鉄系超電導体の原料をＰＩＴ法に従い金属チューブの内部に充填し、金属チューブを圧縮して原料を圧縮体としてから本焼成することで臨界温度の高い、臨界電流密度の高い超電導線材を得ることができることが判明した。このことは、成膜法などのように超電導体の結晶を２軸配向する技術を用いなくとも、ＰＩＴ法によりある程度高い臨界温度と臨界電流密度の超電導線材を製造できたこととなる。このことは、組成式Ｓｒ２ＶＦｅＡｓＯ３-δで表されるペロブスカイト関連混合アニオン型鉄系超電導体は、熱処理（焼成）による元素拡散の影響を受け難く、熱処理（焼成）による化学変化に対し臨界温度の変化を鈍感にできる超電導体であることを確認できた。従って、ペロブスカイト関連混合アニオン型鉄系超電導体は、ＰＩＴ法を更に改良することで更に超電導特性を向上できる可能性を秘めた超電導体であると期待できる。 The raw material of the perovskite-related mixed anionic iron-based superconductor represented by the composition formula Sr 2 VFeAsO 3 -δ described above is filled in the metal tube according to the PIT method, and the metal tube is compressed to form the compressed material. It has been found that a superconducting wire having a high critical temperature and a high critical current density can be obtained by this firing. This means that a superconducting wire having a somewhat high critical temperature and critical current density can be produced by the PIT method without using a technique for biaxially orienting superconductor crystals such as a film forming method. This indicates that the perovskite-related mixed anionic iron-based superconductor represented by the composition formula Sr 2 VFeAsO 3 -δ is not easily affected by element diffusion due to heat treatment (firing) and is critical to chemical changes due to heat treatment (firing). It was confirmed that the superconductor was capable of insensitive to temperature changes. Therefore, the perovskite-related mixed anionic iron-based superconductor can be expected to be a superconductor having the possibility of further improving the superconducting characteristics by further improving the PIT method.
図２４を基に先に説明した０Ｋにおける臨界電流密度Ｊｃ（０）の見積もりについて、０〜２０Ｋにおける臨界電流密度の推定値をまとめて図２５に示す。
先の（１）式が示す臨界電流密度の関係は０〜２０Ｋの温度範囲に展開すると図２４に示す１ｈ（１時間焼成の超電導線材）と２ｈ（２時間焼成の超電導線材）と４ｈ（４時間焼成の超電導線材）の線分で示される。
これらのデータを基に解析すると、先の実施例の如く１〜１６時間の本焼成時間を選択する場合、できるだけ短い時間で本焼成することでより、より高い臨界電流密度の超電導線材を得られることがわかる。図２５に示す結果によれば、本焼成時間を１時間〜２時間にすることが最も望ましい焼成条件であると推定できる。
Regarding the estimation of the critical current density Jc (0) at 0K described above based on FIG. 24, the estimated values of the critical current density at 0 to 20K are collectively shown in FIG.
When the relationship of the critical current density shown by the above equation (1) is developed in a temperature range of 0 to 20 K, 1h (superconducting wire baked for 1 hour), 2h (superconducting wire baked for 2 hours) and 4h (4 It is indicated by the line segment of the superconducting wire with time firing).
Based on these data, when a main firing time of 1 to 16 hours is selected as in the previous example, a superconducting wire having a higher critical current density can be obtained by performing the main firing in as short a time as possible. I understand that. According to the results shown in FIG. 25, it can be estimated that the main firing time is 1 hour to 2 hours, which is the most desirable firing condition.
図２６は先に本出願人が研究した結果により得られたＳｒ２ＶＦｅＡＳＯ３-δの組成式で示されるペロブスカイト関連混合アニオン型鉄系超電導体の相図を示す。
この相図からＳｒ２ＶＦｅＡＳＯ３-δの組成式で示されるペロブスカイト関連混合アニオン型鉄系超電導体において、酸素欠損量を示すδの値は、０＜δ＜０.２の範囲の中でも、０＜δ＜０.１４５の範囲が好ましく、０.０６＜δ＜０.１４５の範囲が最も好ましいことがわかる。
FIG. 26 shows a phase diagram of the perovskite-related mixed anionic iron-based superconductor represented by the composition formula of Sr 2 VFeASO 3-δ obtained by the results of the previous study by the present applicant.
From this phase diagram, in the perovskite-related mixed anionic iron-based superconductor represented by the composition formula of Sr 2 VFeASO 3-δ , the value of δ indicating the amount of oxygen deficiency is 0 in the range of 0 <δ <0.2. It can be seen that the range <δ <0.145 is preferable, and the range 0.06 <δ <0.145 is most preferable.
Ａ…超電導線材、１…超電導コア、２…内部シース（金属シース）、３…外部シース（金属シース）、１０、１１…原料粉末、１５…ペレット、１６…加熱炉、１７…圧縮体、２０…最終混合粉末、２１…チューブ、２２…外チューブ、２３…圧延装置、２３Ａ…圧延ロール、２３ａ…周溝、２５…複合線材、２６…加熱炉。 A ... superconducting wire, 1 ... superconducting core, 2 ... inner sheath (metal sheath), 3 ... outer sheath (metal sheath), 10, 11 ... raw material powder, 15 ... pellet, 16 ... heating furnace, 17 ... compression body, 20 ... final mixed powder, 21 ... tube, 22 ... outer tube, 23 ... rolling device, 23A ... rolling roll, 23a ... circumferential groove, 25 ... composite wire, 26 ... heating furnace.
Claims (8)
元素Ａと元素ＤとＦｅとＡｓを前記組成式の割合または前記組成式に近似した割合で含む原料混合粉末を用意し、この原料混合粉末を予備焼成して仮焼き粉末を得、この仮焼き粉末を金属チューブの内部に充填した後、前記金属チューブを圧縮して金属シースとその内部に充填されたコア部を有する圧縮体を得るとともに、前記圧縮体を本焼成して前記コア部内にＡ２ＤＦｅＡｓＯ３-δなる組成式で示される超電導体を生成することを特徴とする混合アニオン型鉄系超電線材の製造方法。 A 2 DFeAsO 3 -δ (A represents one or more elements selected from the alkaline earth metals Mg, Ca, Sr, Ba, and D represents the transition metals Sc, Ti, V, Cr, Mn , Co, Ni, Cu, Y, Zr, Nb, Mo, Ru, Rh, Pd, Ag, Hf, Ta, W, Re, Os, Ir, Pt, Au, rare earth La, Ce, Pr, Nd, Pm, The composition is one or more elements selected from Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, alkaline earth metal Mg, and typical metal element Al. When manufacturing a superconducting wire in which a mixed anion type iron superconductor represented by the formula is provided inside a metal sheath,
A raw material mixed powder containing element A, element D, Fe, and As in a proportion of the composition formula or a proportion approximate to the composition formula is prepared, and the raw material mixed powder is pre-fired to obtain a calcined powder. After filling the inside of the metal tube with the powder, the metal tube is compressed to obtain a compressed body having a metal sheath and a core portion filled in the metal sheath, and the compressed body is subjected to main firing to obtain A in the core portion. A method for producing a mixed anion type iron-based super-wire material, characterized in that a superconductor represented by a composition formula of 2 DFeAsO 3 -δ is generated.
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