WO2015107636A1 - Matériau supraconducteur, son précurseur et son procédé de production - Google Patents

Matériau supraconducteur, son précurseur et son procédé de production Download PDF

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Publication number
WO2015107636A1
WO2015107636A1 PCT/JP2014/050587 JP2014050587W WO2015107636A1 WO 2015107636 A1 WO2015107636 A1 WO 2015107636A1 JP 2014050587 W JP2014050587 W JP 2014050587W WO 2015107636 A1 WO2015107636 A1 WO 2015107636A1
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carbon
boron
superconducting material
magnesium diboride
containing phase
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PCT/JP2014/050587
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English (en)
Japanese (ja)
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水上　貴彰
菅野　周一
楠　敏明
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株式会社日立製作所
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Priority to PCT/JP2014/050587 priority Critical patent/WO2015107636A1/fr
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    • H—ELECTRICITY
    • H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
    • H10N—ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
    • H10N60/00—Superconducting devices
    • H10N60/80—Constructional details
    • H10N60/85—Superconducting active materials
    • H10N60/855—Ceramic superconductors
    • H—ELECTRICITY
    • H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
    • H10N—ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
    • H10N60/00—Superconducting devices
    • H10N60/01—Manufacture or treatment
    • H10N60/0856—Manufacture or treatment of devices comprising metal borides, e.g. MgB2

Definitions

  • the present invention relates to a superconducting material, a precursor thereof, and a method of manufacturing the same.
  • Magnesium diboride (MgB 2 ) is a superconducting material discovered in 2001, and has a high critical temperature (39 K) as a metal system. Therefore, by manufacturing a superconducting wire using magnesium diboride, there is a possibility that the superconducting device can be operated at 10 to 20 K which is higher than the temperature of a device using conventional liquid helium. Therefore, for example, the application of magnesium diboride to medical diagnostic equipment such as nuclear magnetic resonance analyzer (NMR) and medical magnetic resonance imaging (MRI), where the stability of magnetic field is an important technical element It is expected.
  • NMR nuclear magnetic resonance analyzer
  • MRI medical magnetic resonance imaging
  • a superconducting wire using magnesium diboride can be obtained, for example, by filling a metal tube with a raw material powder such as magnesium or boron and subjecting it to surface reduction processing to draw it into a wire and heat treatment.
  • Magnesium diboride is produced in the metal tube.
  • Such a manufacturing method is called a powder-in-tube method (PIT method).
  • PIT method powder-in-tube method
  • Magnesium diboride prepared by PIT method shows the critical current density required for MRI for low magnetic field but does not show the critical current density required for MRI for high magnetic field exceeding about 3 T It is known.
  • M is at least one selected from titanium, zirconium and hafnium
  • M 1
  • Magnesium diboride superconductor obtained by forming and sintering a powder mixture obtained by mixing so as to be 2: 2 x (0.001 ⁇ x 0.1 0.1);
  • M is finely dispersed and present as metal and / or boride, and other unavoidable impurities are finely dispersed and exist, and the diboration with high critical current density and high irreversible magnetic field Magnesium based superconductors are described.
  • U.S. Pat. No. 5,075,015 is a superconducting element containing magnesium diboride, at least one of 5 to 500 microns in size sealed in a metal matrix and also comprising at least one high conductivity ohmic element. It comprises a superconducting filament, wherein the superconducting filament is separated from the matrix and the conductive ohmic element by a protective metal layer, and the superconducting filament comprises boron powder and magnesium powder and boron carbide powder as a first additive. And a superconducting element in which one or more additional carbon-containing powder additives are present in the reaction of the powder mixture comprising magnesium, boron and boron carbide.
  • Patent Document 1 describes that it is preferable to sinter at a relatively high temperature because the reaction of magnesium is accelerated in a temperature range of 600 ° C. or higher.
  • sintering in such a temperature range may reduce the number of grain boundaries acting as a pinning effect (pinning effect) in an applied magnetic field. That is, in the technique described in Patent Document 1, since the sintering temperature is high, the number of grain boundaries may be reduced, which makes it difficult to obtain a superconducting material having a good critical current density. There is.
  • Patent Document 2 describes coexistence of, for example, silicon carbide (SiC) together with magnesium, boron and boron carbide at the time of formation of a superconducting filament. And, it is described that it is expected by this that a good critical current density can be achieved.
  • silicon carbide is contained as in the technique described in Patent Document 2
  • magnesium silicide Mg 2 Si
  • Magnesium silicide does not take part in energization, and as a result of the presence of the impurity silicon carbide, the flow resistance of the resulting superconducting material may increase. As a result, the critical current density may not be improved.
  • the present invention has been made in view of these problems, and the problem to be solved by the present invention is to provide a superconducting material having a good critical current density, a precursor thereof and a method of manufacturing the same.
  • the present inventors earnestly studied to solve the above problems, and as a result, they found out the following findings. That is, it has been found that, in a superconducting material containing magnesium diboride, the above problems can be solved by setting crystal particles of magnesium diboride to a predetermined structure.
  • FIG. 1 is a view showing the structure of the superconducting material 10 of the present embodiment.
  • the superconducting material 10 of the present embodiment is formed by collecting a plurality of crystal particles 3 of magnesium diboride (magnesium diboride crystal particles).
  • FIG. 1 shows how four crystal grains 3 are gathered, and grain boundaries 4 are formed between adjacent crystal grains 4.
  • Crystalline particle 3 has carbon-containing phase 2 including main phase 1 containing magnesium diboride, and magnesium diboride and carbon contained in the crystal lattice of magnesium diboride.
  • the composition of the crystal particle 3 is represented by the following formula (1).
  • x is a number satisfying 0 ⁇ x ⁇ 1
  • y is a number satisfying y ⁇ 2.
  • the boron contained in magnesium diboride is in a state of being substituted by carbon, and in the case of y> 2, the state of an excess of carbon in the crystal lattice of magnesium diboride (Including substituted states).
  • the main phase 1 may be composed of magnesium diboride (comprised of magnesium diboride) from the viewpoint of obtaining the superconducting material 10 exhibiting particularly good critical current density.
  • the carbon-containing phase 2 is formed so as to surround the main phase 1, and specifically, is formed at the crystal grain boundary 4 (that is, on the surface of the crystal particle 3).
  • This form can be said to be a so-called "core-shell structure" in which the main phase 1 is formed as a core.
  • the formation of the carbon-containing phase 2 at the grain boundaries 3 has an advantage (effect) that the pinning effect can be improved.
  • the main phase 1 is composed of crystals of magnesium diboride in the present embodiment. Therefore, when the superconducting material 10 is formed into a wire, a current flows mainly through the main phase 1 to form a magnetic field around the wire.
  • the size of the magnesium diboride crystal contained in the main phase 1 is preferably 0.01 ⁇ m to 10 ⁇ m as an average crystallite diameter. By setting this range, it is possible to secure a sufficient current flow path and sufficient connectivity of magnesium diboride, and to obtain a higher critical current density.
  • the average crystallite size can be measured, for example, by image analysis of an image taken with a scanning transmission electron microscope (STEM) or crystallite size analysis using X-ray diffraction (XRD).
  • the carbon-containing phase 2 contains carbon in the crystal lattice of magnesium diboride as described above.
  • carbon contained in the carbon-containing phase 2 is one in which a part of boron atoms constituting the crystal lattice of magnesium diboride contained in the carbon-containing phase 2 is substituted.
  • the crystal lattice of magnesium diboride is usually formed in a dense manner, there is an advantage that the carbon-containing phase 2 can be easily formed by substituting a boron atom with a carbon atom.
  • magnesium atoms and boron atoms are usually bonded in a stable arrangement.
  • a carbon atom is inserted into the crystal lattice of magnesium diboride or part of the boron atoms constituting the crystal lattice are substituted by carbon atoms, the boron atom and the carbon atom Because of the difference in size, distortion occurs in the crystal lattice. Then, when distortion occurs in the crystal lattice, when a superconducting material is produced using such a material and current flows, the generated magnetic flux tends to be retained at the distorted portion. Thus, the pinning effect is increased. Therefore, if such a superconducting material is used, the critical current density can be improved.
  • the thickness of the carbon-containing phase 2 is not particularly limited. That is, the carbon-containing phase 2 may be formed, and the thickness thereof is usually 1 nm or more.
  • the preferred thickness of the carbon-containing phase 2 varies depending on the size of the main phase 1 and the size of the crystal particles 3 but can not generally be mentioned, but preferably 25 nm or more, and its upper limit is preferably 150 nm or less Preferably it is 100 nm or less, especially preferably 75 nm or less.
  • the amount of carbon contained in the carbon-containing phase 2 is also not particularly limited. However, in view of the fact that carbon is not contained in main phase 1 as the content of carbon contained in phase 2 containing carbon, or if it is contained in a very small amount, 5 with respect to the entire crystal particle 3 % Or less is preferred. Thereby, the critical current density can be further improved without excessively increasing the flow resistance.
  • the carbon content can be measured by STEM-EDX analysis using a scanning transmission electron microscope (STEM) and an energy dispersive X-ray spectrometer (EDX) in combination.
  • the crystal particles 3 composed of the main phase 1 and the carbon-containing phase 2 are preferably formed by performing heat treatment (baking) at a temperature of 650 ° C. or less. That is, the crystal particle 3 is preferably obtained by heat-treating the raw material at 650 ° C. or less. By heat-treating the raw material at a relatively low temperature of 650 ° C. or less, excessive diffusion of carbon during heat treatment can be suppressed in main phase 1, and main phase 1 and carbon-containing phase 2 coexist more reliably. It can be done. In addition, it can be confirmed by photographing the crystal particle 3 with a scanning electron microscope and observing the form of the crystal particle 3 whether the crystal particle 3 is heat treated at a temperature of 650 ° C. or less. .
  • the superconducting material 10 is obtained by mixing and heat-treating a magnesium material (for example, a single substance of magnesium) and a boron material.
  • the superconducting material 10 contains the carbon-containing phase 2 containing magnesium diboride and carbon contained in the crystal lattice of the magnesium diboride. Therefore, in the present embodiment, the boron raw material includes boron crystal particles (carbon-doped boron) having a main phase containing boron and a carbon-containing phase containing boron and carbon contained in the crystal lattice of the boron.
  • boron material 11 shown in FIG. 2 a boron material (precursor of a superconducting material; boron material 11 shown in FIG. 2) is used.
  • the superconducting material 10 of the present embodiment can be obtained more easily and reliably.
  • carbon doping causes distortion in the crystal lattice of boron and facilitates sintering.
  • the main phase which comprises a boron material is comprised (it consists of boron) similarly to the said main phase 1 by boron.
  • Such a boron material can be obtained, for example, by heat treating a boron powder (a single substance of boron) in a hydrocarbon gas atmosphere containing boron trichloride gas.
  • a boron material can also be produced by performing heat treatment while controlling the pressure in the reactor.
  • the heat treatment temperature can be, for example, about 1000 ° C. to 2000 ° C.
  • hydrocarbon gas which is the atmosphere at the time of heat processing, methane, ethane, propane, butane, ethylene, acetylene etc. are mentioned, for example.
  • carbon is contained in the crystal lattice of boron in the vicinity of the surface of the boron particle.
  • the inside does not contain carbon or contains only a trace amount of carbon. That is, according to such a method, a carbon-containing phase (FIG. 2 (b) shown in FIG. 2 (b) etc.) and a carbon contained in the crystal lattice of the boron and the boron.
  • the carbon-containing phase possessed by the boron crystal particles reacts with magnesium preferentially to the main phase by heat treatment of the boron crystal particles with magnesium. Therefore, a phase containing a large amount of carbon in the crystal lattice of magnesium diboride (that is, the carbon-containing phase in the superconducting material 10 described above) is preferentially formed. Note that when the heat treatment atmosphere is an inert atmosphere, carbon and boron contained in the raw material are not released to the outside. Therefore, it can be said that the carbon-containing phase of the boron crystal particles is directly changed to the carbon-containing phase of the superconducting material 10 by the heat treatment.
  • the thickness of the carbon-containing phase of the boron crystal particles is not particularly limited. That is, the carbon-containing phase may be formed in the boron crystal particles, and the thickness thereof is usually 1 nm or more.
  • the preferred thickness of the carbon-containing phase is not unique because it varies depending on the size of the boron-containing main phase and the size of the boron crystal particles, but preferably 25 nm or more, and the upper limit thereof is preferably 150 nm or less. More preferably, it is 100 nm or less, and particularly preferably 75 nm or less.
  • By setting the thickness of the carbon-containing phase in this range it is possible to obtain the superconducting material 10 exhibiting a particularly good critical current density. Further, by setting the thickness of the carbon-containing phase to 50 nm or less, as in the case of the above-mentioned carbon-containing phase 2, excessive labor by carbon doping can be omitted, and the carbon-containing phase can be particularly easily formed. .
  • the thickness of the carbon-containing phase can be controlled by changing the heat treatment time. That is, the longer the heat treatment time, the thicker the carbon-containing phase. Further, since the crystal lattice of boron is usually densely packed, according to the above-mentioned production method, in the carbon-containing phase, a form in which a boron atom contained in the crystal lattice of boron is substituted by a carbon atom It has become. Therefore, using such a boron material as a raw material has the advantage that it is easier to prepare the raw material.
  • FIG. 2 is a view for explaining the method of manufacturing the superconducting material 10 of the present embodiment, wherein (a) shows a state in which the raw materials are mixed, and (b) shows that magnesium melts in part A of (a).
  • (C) is a diagram showing the crystal growth process of the superconducting material 10 of the present embodiment in (b)
  • (d) is a diagram showing a sufficiently grown crystal of (c) in (b) .
  • (B), (c) and (d) are all figures which expand and show the A section of (a).
  • the superconducting wire 10 shown in FIG. 1 is manufactured through the state shown in FIG. 2 by heat-treating the raw material.
  • FIG. 2A is an enlarged view of a portion A of FIG. 2A.
  • the inside thereof is boron (which may contain a slight amount of carbon or the like), while boron and carbon coexist in the vicinity of the surface. Therefore, as shown in FIG. 2B, the main phase 13 present inside the boron material 11 is difficult to contact with the molten magnesium 12, so the main phase 13 hardly reacts.
  • the carbon-containing phase 14 present in the vicinity of the surface of the boron material 11 is in contact with the molten magnesium 12, the carbon-containing phase 14 preferentially reacts with the magnesium 12 compared to the main phase 13. It will be.
  • Example 1 The boron powder having an average particle size of 5 ⁇ m or less was heat-treated at 1500 ° C. for 2 hours in a methane gas atmosphere containing boron trichloride gas to obtain a boron material (precursor of a superconducting material) containing carbon on the surface of boron particles.
  • the content of carbon atoms in the boron material was 0.02 mass% with respect to the whole of the boron particles.
  • the obtained boron material was grind
  • the obtained boron material powder having an average particle diameter of 5 ⁇ m or less and a magnesium powder having an average particle diameter of 45 ⁇ m (purity: 97 mass% or more) were mixed.
  • the mixing amount was made to be 1: 2 in molar ratio of magnesium and boron.
  • the mixing was carried out for 5 hours in an argon atmosphere while sufficiently pulverizing using a planetary ball mill equipped with zirconium oxide balls.
  • Raw material mixed powder was obtained by the above operation.
  • the obtained raw material mixed powder was filled in a copper-coated iron pipe with an outer diameter of 20 mm, an inner diameter of 16 mm, and a length of 500 mm. After filling, drawing was repeated so that the reduction in area per pass was in the range of 8 to 12%, and drawing was performed until the diameter (outer diameter) of the wire became 1.2 mm. In addition, all the wires were able to be processed with the all-around wire even if annealing etc. were not performed at all during processing.
  • the drawn wire was heat treated at 630 ° C. for 30 hours in an argon atmosphere. Thus, a superconducting wire including a superconducting material containing magnesium diboride was obtained. It was 37 K when the critical temperature of the obtained superconducting wire was measured.
  • the cross section of the obtained superconducting wire was observed using a scanning electron microscope, and the structure (fine structure) of magnesium diboride crystal particles present inside the crystal was confirmed. As a result, it was found that the average crystallite diameter of magnesium diboride crystal particles present inside the crystal was 10 ⁇ m or less.
  • STEM-EDX analysis was performed on the same cross section using a scanning transmission electron microscope with spherical aberration correction. As a result, it was found that in the crystal particles of magnesium diboride, a main phase consisting of magnesium diboride and a phase different from the main phase were formed so as to surround the main phase.
  • the graph obtained by STEM-EDX analysis is shown in FIG.
  • FIG. 3 is a graph showing the results of STEM-EDX analysis.
  • the carbon concentration in the vicinity of the grain boundaries was high. From this, it was found that in the phase formed so as to surround the main phase, carbon is contained together with magnesium diboride. That is, in the obtained superconducting wire, the crystal particles of magnesium diboride contained contain main phase 1 (see FIG. 1) and carbon-containing phase 2 containing carbon in the crystal lattice of magnesium diboride (FIG. 1). It turned out that it is constituted by (refer). Further, the carbon-containing phase 2 is formed on the surface of the crystal particles 3 of magnesium diboride so as to surround the main phase 1, and is formed at the crystal grain boundaries 4 of adjacent magnesium diboride crystal particles 3 (see FIG. 1) I also knew that it was done.
  • Examples 2 to 6 Comparative Example 1 The same as Example 1, except that the heat treatment time during the preparation of the boron material containing carbon on the surface of the boron particles is controlled, and the thickness of the carbon-containing phase 2 possessed by the crystal particles 3 of magnesium diboride is made different. Superconducting wires were produced (Examples 2 to 6).
  • the carbon-containing phase 2 of Example 2 has a thickness of 25 nm
  • the carbon-containing phase 2 of Example 3 has a thickness of 50 nm
  • the carbon-containing phase 2 of Example 4 has a thickness of 75 nm
  • the carbon-containing example of Example 5 The thickness of phase 2 is 100 nm
  • the thickness of carbon-containing phase 2 of example 6 is 150 nm.
  • the critical current density was 200 A / mm 2 .
  • the critical current density was about 600 A / mm 2 .
  • the maximum critical current density was obtained when the thickness of the carbon-containing phase 2 was 50 nm, and the critical current density at that time was 620 A / mm 2 .
  • Comparative Example 1 when heat-treated at a relatively low temperature of 630 ° C., the critical current density is not very high. It is considered that this is because crystal growth of magnesium diboride is not sufficiently performed because the sintering temperature is low, and the connectivity between magnesium diboride is not good.
  • Examples 2 to 6 by forming the carbon-containing phase 2, the crystal grain boundaries 4 can be sufficiently secured even by heat treatment at a relatively low temperature of 630 ° C. A critical current density three times as high as that in the case where the carbon-containing phase 2 is not formed can be obtained.
  • the critical current density has been improved by coexisting silicon carbide or the like with the raw material, but in the present embodiment, even if heat treatment is performed at a low temperature without using a material such as silicon carbide
  • the critical current density can be improved. That is, since all of the components contained in the raw material powder participate in the formation reaction of the superconducting material 10 (main phase 1 and carbon-containing phase 2), an impurity such as magnesium silicide is less likely to be generated. Therefore, the increase in the flow resistance of the obtained superconducting material 10 can be avoided, and the improvement of the critical current density is promoted.

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  • Chemical & Material Sciences (AREA)
  • Ceramic Engineering (AREA)
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  • Superconductors And Manufacturing Methods Therefor (AREA)
  • Inorganic Compounds Of Heavy Metals (AREA)

Abstract

La présente invention cherche à résoudre le problème consistant à fournir : un matériau supraconducteur possédant une bonne densité de courant critique; un précurseur du matériau supraconducteur; et un procédé de production du matériau supraconducteur. La solution selon l'invention porte sur un matériau supraconducteur (10) conçu en agglomérant une pluralité de grains de cristaux de diborure de magnésium, chacun desdits grains comportant une phase principale (1) contenant du diborure de magnésium et une phase contenant du carbone (2) contenant du diborure de magnésium et du carbone contenu dans le réseau cristallin du diborure de magnésium, de sorte que la phase contenant du carbone (2) est formée à la frontière des grains cristallins (4) entre les grains cristallins de diborure de magnésium adjacents.
PCT/JP2014/050587 2014-01-15 2014-01-15 Matériau supraconducteur, son précurseur et son procédé de production WO2015107636A1 (fr)

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Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP3410445A4 (fr) * 2016-01-28 2019-09-11 Hitachi, Ltd. Matériau de fil supraconducteur, précurseur de matériau de fil supraconducteur, procédé de production de matériau de fil supraconducteur, bobine supraconductrice, mri et nmr

Citations (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JP2012014912A (ja) * 2010-06-30 2012-01-19 Hitachi Ltd ＭｇＢ２超電導線材の製造方法およびＭｇＢ２超電導線材
JP2013152784A (ja) * 2012-01-24 2013-08-08 Hitachi Ltd ＭｇＢ２超電導線材の前駆体及びその製造方法

Patent Citations (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JP2012014912A (ja) * 2010-06-30 2012-01-19 Hitachi Ltd ＭｇＢ２超電導線材の製造方法およびＭｇＢ２超電導線材
JP2013152784A (ja) * 2012-01-24 2013-08-08 Hitachi Ltd ＭｇＢ２超電導線材の前駆体及びその製造方法

Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP3410445A4 (fr) * 2016-01-28 2019-09-11 Hitachi, Ltd. Matériau de fil supraconducteur, précurseur de matériau de fil supraconducteur, procédé de production de matériau de fil supraconducteur, bobine supraconductrice, mri et nmr

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