WO2015146993A1 - バルク酸化物超電導体、およびバルク酸化物超電導体の製造方法 - Google Patents
バルク酸化物超電導体、およびバルク酸化物超電導体の製造方法 Download PDFInfo
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- WO2015146993A1 WO2015146993A1 PCT/JP2015/058947 JP2015058947W WO2015146993A1 WO 2015146993 A1 WO2015146993 A1 WO 2015146993A1 JP 2015058947 W JP2015058947 W JP 2015058947W WO 2015146993 A1 WO2015146993 A1 WO 2015146993A1
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- 238000004519 manufacturing process Methods 0.000 title claims description 11
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Definitions
- the present invention relates to a bulk oxide superconductor having high workability and high critical current density, and a method for producing the bulk oxide superconductor.
- RE-based bulk oxide superconductor manufactured by a so-called melting method that is, RE 2 BaCuO 5 (211) phase is a single crystal REBa 2 Cu 3 O 7 -x (where RE is one of rare earth elements including Y)
- the rare earth oxide superconductor finely dispersed in the type or combination thereof has a higher magnetic flux pinning force than other oxide superconductors, and particularly has a high critical current density even at a high temperature close to the liquid nitrogen temperature (77 K). Therefore, it is expected to be used in various application fields such as bulk magnets, magnetic levitation devices, and current leads.
- a small amount of Pt, Rh, Ce or the like is added to such a bulk material, and the RE 2 BaCuO 5 phase is refined to about 1 ⁇ m.
- the melting method represented by the QMG (Quench and Melt Growth) method disclosed in Patent Documents 1, 2, and 3 is based on the RE 2 BaCuO 5 phase or the RE 4 Ba 2 Cu 2 O 10 phase and the Ba—Cu once.
- the temperature is raised to a temperature range where a liquid phase mainly composed of -O coexists, and this is cooled to just above the peritectic temperature where REBa 2 Cu 3 O 7 -x (123) is formed, and then gradually cooled from that temperature.
- This is a method for obtaining a large bulk material composed of a single crystal grain by performing crystal growth and controlling nucleation and crystal orientation.
- a bulk material in which Ag particles of several ⁇ m to several hundred ⁇ m are dispersed can be obtained by adding Ag to a molded body containing raw materials such as REBa 2 Cu 3 O 7 -x and RE 2 BaCuO 5 .
- the material added with Ag is superior in machinability compared to the additive-free material with less chipping by machining. In the vicinity of the boiling point of liquid nitrogen (77 K), the critical current tends to increase in the Y-based material or Gd-based material.
- Patent Document 2 that uses a seed crystal with a high peritectic temperature to grow the seed crystal has a melting point higher than that of the RE1Ba 2 Cu 3 O 7 -x oxide superconductor to be produced.
- a RE2Ba 2 Cu 3 O 7 -x single crystal sample having a high (peritectic temperature) is used.
- RE1Ba 2 Cu 3 O 7 the -x-based oxide superconductor material precursor, RE1Ba 2 Cu 3 O 7 -x peritectic temperature and RE2Ba 2 Cu 3 O 7 -x Co-existence of RE1Ba 2 Cu 3 O 7 -x and RE12BaCuO 5 phase or RE14Ba 2 Cu 2 O 10 phase and liquid phase mainly composed of Ba-Cu-O
- one surface of the RE2Ba 2 Cu 3 O 7 -x crystal is brought into contact with the precursor.
- RE1Ba 2 Cu 3 O 7 -x RE1Ba 2 Cu 3 O 7 was cooled to peritectic temperature of -x, by performing slow cooling at a peritectic temperature near, RE2Ba 2 Cu 3 O 7 -
- the crystal is grown in the same orientation as the crystal orientation of the contact surface of x.
- Non-Patent Document 1 discloses the presence / absence of crystal growth, the structure, etc. at each temperature under the Ag addition conditions of 3, 5, 7, 10, 15, and 20 mass% in the Y-based material. It is known that when the added amount of Ag2O is less than 5% by mass, a structure in which Ag particles are not precipitated at 970 ° C. or less is obtained and the shape of Ag particles changes to a disk shape or a spherical shape depending on conditions. .
- the performance (critical current density characteristics) of the bulk superconductor is based on the external conditions of temperature and magnetic field, as well as the material itself such as the addition amount of 211 phase, particle size distribution, oxygen annealing conditions, presence / absence of Ag addition, Ag addition amount, etc. Varies depending on manufacturing conditions. These material design elements are used by optimizing appropriately according to the use conditions.
- the 123 phase of the superconductor bulk material originally has a two-dimensional crystal structure, and is a material that easily causes wall cracking. Therefore, if Ag particles are dispersed in the superconductor bulk material, it is important in terms of suppressing the introduction of defects such as chipping during precision machining and not creating a crack starting point.
- Patent Document 3 in order to control the Ag concentration in the bulk superconductor, a compact with different addition amounts of AgO powder is prepared, and these are laminated and melted and solidified to control the Ag concentration. It has been proposed to get
- a superconductor bulk material in which Ag particles are dispersed at least around the bulk superconductor magnet and there is no Ag particle in the center is required. Further, in order to obtain a current lead member with low contact resistance and low heat conduction, a superconducting bulk material in which Ag particles are precipitated only at both ends and Ag particles are not present at the center is necessary.
- an object of the present invention is to provide a structure in which a portion where Ag particles are present and a portion where Ag particles are not present are adjacent to each other in a bulk superconductor.
- the portion where Ag particles are present is a bulk superconductor having a structure sandwiching the portion where Ag particles are not present.
- the present inventors have obtained the following knowledge.
- the amount of Ag added to the precursor of the bulk oxide superconductor is 5.0% by mass or less, and if produced by the QMG method, the RE-based bulk near the seed crystal It has been found that there are no Ag particles having a particle size of 1 to 10 ⁇ m in the structure of the oxide superconductor, and a region in which the Ag particles having a particle size of 1 to 10 ⁇ m are dispersed and precipitated can be formed in the periphery thereof.
- the structure is such that the portion where Ag particles are present is the surface and the portion where Ag particles are not present is the central portion. That is, the present inventors have found that a portion where Ag particles are not present has a structure surrounded by a portion where Ag particles are present.
- the bulk superconductor obtained so that the part where Ag particles are present is placed in the part where more workability is required, the bulk having the necessary workability while ensuring high current density. It has been found that a superconductor can be obtained. In particular, it has also been found that a portion where Ag particles are present can have a structure sandwiching a portion where Ag particles are not present.
- the present invention has been made on the basis of these findings, and the gist thereof is as follows.
- the bulk oxide superconductor is rod-shaped, the portions where the Ag particles are present are arranged at both ends, and the regions other than the both ends are portions where no Ag particles are present ( The bulk oxide superconductor according to any one of 1) to (4).
- the bulk oxide superconductor precursor is heated to a semi-molten state, the seed crystal is brought into contact with it, and the RE 2 BaCuO 5 phase is finely dispersed in the single-crystal REBa 2 Cu 3 O 7 -x phase.
- a bulk oxide superconductor is manufactured by adding 0.5 to 5.0% by mass of Ag to the bulk oxide superconductor precursor and heating it so as to be in a semi-molten state.
- a method for producing a bulk oxide superconductor comprising: bringing a precursor into contact with the semi-molten precursor, gradually cooling it, and solidifying the precursor into a single crystal. (7) The bulk oxide superconductor according to (6), wherein the portion where Ag is present is processed into a rod shape from the bulk oxide superconductor so that the portion where Ag is not present is sandwiched between the portions. Method.
- the present invention high-accuracy outer periphery reinforcing processing is possible, and a bulk oxide superconducting magnet that generates a high magnetic field can be realized more easily. From this, it is possible to generate a high magnetic field that cannot be obtained by a normal permanent magnet, and it is possible to obtain a bulk oxide superconductor and a superconducting current lead having low contact resistance and excellent heat insulation properties. The effect is enormous.
- FIG. 1A is a conceptual diagram showing a bulk oxide superconductor grown from a seed crystal.
- FIG.1 (b) is a figure which shows the mode of the cross section in the dotted-line position of Fig.1 (a).
- FIG. 2A is a conceptual diagram showing a bulk oxide superconductor grown from a seed crystal.
- FIG. 2B is a diagram showing a state of a cross section at a position indicated by a dotted line A in FIG.
- FIG. 2C is a diagram showing a cross section at the position of the dotted line B in FIG.
- FIG. 3A is a diagram showing an example of a bulk oxide superconductor grown from a seed crystal (Ag: 3 mass% added. Diameter: about 37 mm).
- FIG.3 (b) is a figure which shows the mode of the cross section in the position of 5 mm and 10 mm from the top of Fig.3 (a).
- FIG.3 (c) is a figure which shows the rod-shaped sample processed so that both ends might become the area
- FIG. 4A is a diagram showing an example of a bulk oxide superconductor grown from a seed crystal (Ag: 4 mass% added. Diameter: about 45 mm).
- FIG. 4B is a diagram showing a state of a cross section at positions of 5 mm and 10 mm from the top of FIG.
- FIG.4 (c) is a figure which shows the rod-shaped sample processed so that both ends might become the area
- the bulk oxide superconductor used in the present invention has a structure in which a non-superconducting phase typified by a RE 2 BaCuO 5 phase (211 phase) is finely dispersed in a single crystal REBa 2 Cu 3 O 7 -x (So-called QMG material) is desirable.
- the term “single crystal” means that it is not a complete single crystal, but also includes those having defects that may be practically used such as a low-angle grain boundary.
- RE in REBa 2 Cu 3 O 7 -x phase (123 phase) and RE 2 BaCuO 5 phase (211 phase) is Y, La, Nd, Sm, Eu, Gd, Dy, Ho, Er, Tm, Yb, Lu Rare earth elements consisting of and combinations thereof.
- the 123 phase containing La, Nd, Sm, Eu, and Gd may deviate from the stoichiometric composition of 1: 2: 3 and may be in a state where Ba is partially substituted at the RE site.
- the 211 phase which is a non-superconducting phase La and Nd are somewhat different from Y, Sm, Eu, Gd, Dy, Ho, Er, Tm, Yb and Lu, and the ratio of metal elements is non-stoichiometric. It has a theoretical composition and is known to have a different crystal structure.
- substitution of the Ba element described above tends to lower the critical temperature. Further, in an environment having a lower oxygen partial pressure, substitution of Ba element tends to be suppressed.
- the 123 phase is a peritectic reaction between the 211 phase and a liquid phase composed of a complex oxide of Ba and Cu, that is, This can be achieved by a reaction of 211 phase + liquid phase (complex oxide of Ba and Cu) ⁇ 123 phase.
- the temperature at which the 123 phase is formed by this peritectic reaction (Tf: 123 phase formation temperature) is substantially related to the ionic radius of the RE element, and Tf also decreases as the ionic radius decreases. Further, Tf tends to decrease with the addition of a low oxygen atmosphere and Ag.
- a material in which the 211 phase is finely dispersed in the single-crystal 123 phase can be formed because 211 unreacted grains are left in the 123 phase when the 123 phase is crystal-grown. That is, the QMG material is 211 phase + liquid phase (complex oxide of Ba and Cu) ⁇ 123 phase + 211 phase.
- the fine dispersion of the 211 phase in the QMG material is extremely important from the viewpoint of improving the critical current density (Jc).
- the grain growth of the 211 phase in the semi-molten state (a state consisting of the 211 phase and the liquid phase) is suppressed, and as a result, the 211 phase in the material is reduced to about Refine to about 1 ⁇ m.
- the addition amount is 0.2 to 2.0 mass% for Pt, 0.01 to 0.5 mass% for Rh, and 0.5 to 2.0 mass for Ce from the viewpoint of the amount of the effect of miniaturization and the material cost. The mass% is desirable.
- the added Pt, Rh, and Ce partially dissolve in the 123 phase.
- elements that could not be dissolved form a composite oxide with Ba and Cu, and are scattered in the QMG material.
- the bulk oxide superconductor constituting the magnet needs to have a high critical current density even in a magnetic field.
- the phase is a single-crystal 123 phase that does not include large-angle grain boundaries that are superconductively weakly coupled.
- a pinning center for stopping the movement of magnetic flux is required. What functions as the pinning center is a finely dispersed 211 phase, and it is desirable that many finely dispersed.
- Pt, Rh, and Ce have a function of promoting the refinement of the 211 phase.
- the non-superconducting phase such as the 211 phase has an important function of mechanically strengthening the superconductor by being finely dispersed in the 123 phase that is easy to cleave, and as a bulk material.
- the ratio of the 211 phase in the 123 phase is preferably 5 to 35% by volume from the viewpoint of Jc characteristics and mechanical strength.
- the QMG material generally contains 5 to 20% by volume of voids (bubbles) of about 50 to 500 ⁇ m.
- voids bubbles
- when Ag is added it includes the case where the amount of Ag or Ag compound of about 1 to 500 ⁇ m is more than 0% by volume and 25% by volume or less depending on the amount added.
- the oxygen deficiency (x) of the material after crystal growth is about 0.5, indicating a temperature change in semiconductor resistivity.
- the present inventor has arrived at the present invention by examining in detail the addition amount of Ag, heat treatment conditions, and crystal growth process, and intensively searching and clarifying the precipitation behavior of Ag in the material.
- the addition amount of Ag in the 123 and 211 phases, Ag or Ag2O powder mixed powder, or bulk oxide superconductor precursor as a compact is less than 5% by mass
- Ag dissolves in the liquid phase.
- seed crystal was made to contact this liquid phase and crystal growth was carried out, it discovered that Ag particle did not precipitate in the seed crystal vicinity.
- the concentration of Ag in the liquid phase increases as the crystal grows. For example, in the case of Gd-based materials, it is found that Ag particles precipitate when the concentration of Ag in the liquid phase exceeds about 5% by mass. It was.
- the amount of Ag dissolved in the liquid phase component is about 5% by mass of the mixed powder.
- This amount varies depending on the amount and composition of the liquid phase in the semi-molten state, and the more the liquid phase component, the larger the amount of Ag that can be dissolved. In addition, it depends somewhat on the crystal growth temperature, and the higher the crystal growth temperature, the more the amount of dissolved Ag tends to increase.
- the Ag concentration in the liquid phase increases with crystal growth.
- the Ag concentration in the precursor exceeds about 5% by mass, fine Ag particles of about 1 to 10 ⁇ m are precipitated from the liquid phase and taken into the crystal phase.
- the upper limit of the Ag concentration (addition amount) in the precursor is set to 5% by mass.
- the lower limit of the Ag concentration is 0.1% by mass.
- the upper limit is preferably 4.8% by mass, and more preferably 4.6% by mass.
- the lower limit is preferably 0.5% by mass, and more preferably 1% by mass.
- the dispersion means a state in which the precipitated Ag particles are present at a certain distance from each other without aggregating.
- the initial stage of crystal growth that is, bulk
- the central part of the surface of the body does not contain Ag particles, but a material containing fine Ag particles of about 1 to 10 ⁇ m is obtained in the peripheral part.
- fine Ag particles are formed around rectangular region 3 that does not contain Ag particles as shown in FIG. A region 4 including is formed.
- the particle size of Ag particles is relatively fine, about 1 to 3 ⁇ m, in the vicinity of the boundary between the region containing Ag particles and the region not containing Ag particles, but the particle size of Ag particles tends to increase with distance from this boundary. is there. This is because in the region far from the boundary, the saturation state of Ag in the liquid phase is maintained for a long time, and as a result, nuclei from which Ag particles precipitate are likely to be generated. It is thought that the diameter becomes larger. In a region far from the boundary, many Ag particles have a particle size of about 10 ⁇ m. From such a phenomenon, a situation occurs in which Ag particles of about 1 to 10 ⁇ m surround a region not containing Ag particles.
- the crystal growth start temperature of the bulk oxide superconductor containing Ag varies depending on the amount of Ag added.
- the addition amount of Ag is 0 mass%: about 1040 ° C., 1 mass%: about 1034 ° C., 2 mass%: about 1025 ° C.
- Crystal growth temperature decreases. Further, the decrease in crystal growth temperature tends to saturate when the added amount of Ag is around 7% by mass, such as 5% by mass: about 1010 ° C., 7% by mass: about 1004 ° C., 10% by mass: about 1004 ° C. .
- the crystal growth when the difference between the crystal growth start temperature and the actual growth temperature, that is, when the degree of supercooling is 10 ° C. or less, the crystal grows while maintaining a relatively stable facet. An oxide superconductor is obtained. Therefore, for example, in the case where the crystal growth is performed to the entire compact with respect to the material to which 2% by mass of Ag is added, if the furnace temperature at the initial stage of the crystal growth is lowered from 1025 ° C. to several ° C., the Ag at the peripheral portion of the bulk material Is concentrated. In order to obtain a structure in which Ag particles are dispersed, it is necessary to gradually cool to a temperature lower by at least 1010 ° C.
- the heat treatment is different from a material in which the crystal growth start temperature does not change with crystal growth, for example, a material to which 10% by mass of Ag is added.
- the amount of Ag added is 5% by mass or more and less than 10% by mass in the Gd-based material
- a part of the added Ag dissolves in the liquid phase, but a part thereof is semi-molten. It is trapped as liquid Ag particles in the green compact.
- the size of the Ag particles at this time is determined by the size of the Ag particles added to the mixed powder of the 123 powder and the 211 phase powder, the size of the Ag2O powder, or the secondary particle diameter in which these particles are aggregated. In the case of continuous sieving, etc., it is often about 30 to 300 ⁇ m.
- fine Ag particles of about 1 to 10 ⁇ m are present in the corners of the crystal phase, that is, in the vicinity region (width 0.2 to 1.0 mm) grown in the [110], [101] and [111] directions.
- a region that does not include is formed.
- the region 4 and the Ag particles containing fine Ag particles as shown in FIGS. 2 (b) and (c) are included.
- a tissue having a linear region 5 that is not formed is formed. In the linear region 5 that does not contain Ag particles, either the precipitated Ag with the crystal growth is dissolved again in the liquid phase, or the precipitated liquid Ag particles are pushed away by the facets of the corners. It seems to have been.
- the crystal phase is black
- Ag particles have a metallic luster.
- Ag particles dispersed in the material tend to increase the mechanical strength when Ag is added to the superconductor because it has the effect of suppressing the progress of cracking of the crystal phase. Further, since it has an effect of suppressing the progress of cracks in the crystal phase, the workability of the material is increased during grinding and cutting, and defects such as chipping are less likely to occur. Therefore, in the case of applying to a bulk magnet, in order to reinforce the outer ring, when the outer periphery of the bulk oxide superconductor is precisely processed with an accuracy of about 0.1 mm, it has a structure in which Ag is dispersed. Highly desirable.
- an oxide superconductor current lead member containing fine Ag particles of about 1 to 10 ⁇ m is formed in the peripheral part, although the central part does not contain Ag particles. Can be produced. At this time, Ag particles are finely dispersed in both end portions to which the Ag coating is applied, and Ag particles are not included in the central portion. Thus, at both ends, Ag coating can be applied to the electrode portion of the energization element to efficiently reduce the contact resistance, and heat penetration can be sufficiently suppressed between the electrodes.
- Example 1 Each reagent Gd 2 O 3 , BaO 2 , CuO having a purity of 99.9% has a molar ratio of the metal element of Gd: Ba: Cu of 10:14:20 (that is, the molar ratio of 123 phase: 211 phase of the final structure is 3: 1). Furthermore, a mixed powder was prepared by adding 1.0% by mass of CeO 2 and 3% by mass of Ag2O (about 2.8% by mass in terms of Ag). Each mixed powder was temporarily calcined at 900 ° C. for 8 hours. The calcined powder was filled in a cylindrical mold having an inner diameter of 50 mm, and formed into a disk shape having a thickness of about 30 mm to produce a Gd-based molded body.
- Sm 2 O 3 and Yb 2 O 3 were used to produce Sm-based and Yb-based disk-shaped molded bodies having a thickness of 4 mm by the same method as the molded body. Furthermore, each molded body was compressed at about 100 MPa by an isotropic isostatic press.
- each of the precursors (Sm-based, Yb-based, Gd-based) containing no Ag produced without adding Ag2O in the production of the above-mentioned Sm-based, Yb-based, Gd-based molded body (precursor) as a comparative material A molded body) was produced.
- each precursor of the present invention example was stacked on an alumina support material in the order of Sm-based, Yb-based, and Gd-based molded body (precursor), and placed in a furnace. These precursors were heated in the atmosphere for 15 hours up to 700 ° C. for 160 hours up to 1040 ° C., further heated up to 1120 ° C. over 1 hour, held for 30 minutes, then cooled down to 1030 ° C. over 1 hour and held for 1 hour. did. In the meantime, an Sm-based seed crystal prepared in advance was used, and the seed crystal was placed on the precursor in a semi-molten state.
- the orientation of the seed crystal was such that the cleaved surface was placed on the precursor so that the c-axis was the normal line of the disc-shaped precursor. Thereafter, it was cooled to 1025 to 1000 ° C. in the atmosphere over 120 hours to grow crystals. Furthermore, it cooled to room temperature over about 35 hours, and obtained the Gd type single crystal bulk oxide superconductor with an outer diameter of about 37 mm and a thickness of about 22 mm.
- each precursor not containing Ag as a comparative example is also placed in the furnace in the same manner, and after heat treatment until the same seeding, it is cooled to 1045 to 1025 ° C. over 120 hours to perform crystal growth, Similarly, a Gd-based single crystal bulk oxide superconductor as a comparative material was obtained.
- the obtained sample of the present invention was cut at a position of 5 mm, 10 mm, and 15 mm from the top surface on which the seed crystal 31 was placed, and an oxygen annealing treatment (400 in an oxygen stream) was performed.
- the surface was polished and the structure was observed.
- each has a structure in which the Gd2BaCuO5 phase (211 phase) is finely dispersed in the single-crystal GdBa2Cu3O7-x phase, and at positions of 5 mm and 10 mm from the upper surface, as shown in FIG.
- grains was confirmed in the area
- the area ratio of Ag particles was about 5%.
- the tendency for a particle size to become large was seen, so that it was near a peripheral part. However, at the position of 15 mm, the facet was disturbed and a concave facet was formed in the crystal growth direction, so that precipitation of Ag particles was confirmed in the central part together with the peripheral part.
- a sample cut out from a position of 5 to 10 mm from the upper surface was processed with an accuracy of an outer diameter of 36.0 + 0.0 to ⁇ 0.1 mm and a thickness of 4.5 ⁇ 0.1 mm. Since the outer periphery contains Ag particles, it could be processed without chipping. Then, a SUS ring having an inner diameter of 36.0 + 0.1 to ⁇ 0.0 mm, an outer diameter of 40.0 ⁇ 0.1 mm, and a height of 4.5 ⁇ 0.1 mm was fitted into this sample and fixed with a resin. Next, after cooling in liquid nitrogen (77 K) in a magnetic field of 2.0 T and removing the external magnetic field, the trapped magnetic flux distribution was measured.
- liquid nitrogen 77 K
- a Gd-based sample not containing Ag as a comparative example was similarly obtained by cutting a sample cut from a position of 5 to 10 mm from the upper surface to an outer diameter of 36.0 + 0.0 to ⁇ 0.1 mm and a thickness of 4.5 ⁇ 0.00 mm. Although it processed similarly with the precision of 1 mm, the chipping was confirmed by three places. Moreover, when the trapped magnetic flux distribution of this sample was measured similarly, the maximum magnetic flux density of 0.95 T was confirmed. This comparative experiment confirmed that the material of the present invention was superior to the comparative material.
- the sample of the present invention cut out from a position of 0 to 5 mm from the upper surface was cut from about 5 mm to 2.0 mm in thickness, and both ends thereof were Ag particles.
- a rod-shaped sample having a width of 8 mm and a length of about 34 mm was cut out so as to be a region where the precipitate was deposited.
- a 2 ⁇ m thick Ag film was formed by sputtering in the region where the Ag particles were deposited at both ends of the rod-shaped sample, and heat treatment was performed to adjust the Ag film to the rod-shaped sample.
- the whole rod-shaped sample was sandwiched between glass fiber reinforced plastics and screwed, and then solidified with resin to produce a current lead. This current lead was able to pass 1500A at 77K, and it was confirmed that it functions sufficiently as a current lead.
- Example 2 Each reagent Y 2 O 3 , BaO 2 , CuO having a purity of 99.9% has a molar ratio of the metal element of Gd: Ba: Cu of 13:17:24 (that is, the molar ratio of 123 phase: 211 phase of the final structure is 7: 3) was mixed. Further, a mixed powder was prepared by adding 1.5% by mass of CeBaO3 and 4% by mass of Ag2O (about 3.7% by mass in terms of Ag). Each mixed powder was temporarily calcined at 900 ° C. for 8 hours.
- the calcined powder was filled in a cylindrical mold having an inner diameter of 60 mm, and formed into a disk shape having a thickness of about 35 mm to produce a Y-based molded body. Further, Sm2O3 and Yb2O3 were used to produce Sm-based and Yb-based disk-shaped molded bodies having a thickness of 4 mm by the same method as the molded body. Furthermore, each molded body was compressed at about 100 MPa by an isotropic isostatic press.
- each of the precursors (Sm-based, Yb-based, Y-based) containing no Ag produced without adding Ag2O in the production of the above-mentioned Sm-based, Yb-based, Y-based molded body (precursor) as a comparative material A molded body) was produced.
- each precursor of the present invention example was stacked on an alumina support in the order of Sm-based, Yb-based, and Y-based molded body (precursor) and placed in a furnace. These precursors were heated in the atmosphere for 15 hours to 700 ° C. for 160 hours, to 1040 ° C. for 1 hour, further to 1100 ° C. for 1 hour, held for 30 minutes, then cooled to 1020 ° C. for 1 hour and held for 1 hour. did. In the meantime, an Sm-based seed crystal prepared in advance was used, and the seed crystal was placed on the precursor in a semi-molten state.
- the orientation of the seed crystal was such that the cleaved surface was placed on the precursor so that the c-axis was the normal line of the disc-shaped precursor. Thereafter, it was cooled to 990-970 ° C. over 140 hours in the air, and crystal growth was performed. Furthermore, it cooled to room temperature over about 35 hours, and obtained the Y type single crystal-shaped bulk oxide superconductor with an outer diameter of about 45 mm and a thickness of about 26 mm.
- each precursor not containing Ag as a comparative example is similarly placed in a furnace, and after heat treatment until the same seeding, it is cooled to 1005 to 990 ° C. over 140 hours to perform crystal growth, Similarly, a Y-based single crystal oxide superconducting material as a comparative material was obtained.
- the obtained sample of the present invention was cut at 5 mm, 10 mm, and 15 mm from the top surface on which the seed crystal 41 was placed, and an oxygen annealing treatment (400 in an oxygen stream) was performed.
- the surface was polished and the structure was observed.
- each has a structure in which the Y2BaCuO5 phase (211 phase) is finely dispersed in the single-crystal YBa2Cu3O7-x phase, and at positions 5 mm and 10 mm from the upper surface, as shown in FIG.
- grains was confirmed in the area
- a sample cut out from a position of 5 to 10 mm from the upper surface was processed with an accuracy of an outer diameter of 44.0 + 0.0 to ⁇ 0.1 mm and a thickness of 4.5 ⁇ 0.1 mm. Since the outer periphery contains Ag particles, it could be processed without chipping. Then, a SUS ring having an inner diameter of 44.0 + 0.1 to ⁇ 0.0 mm, an outer diameter of 45.0 ⁇ 0.1 mm, and a height of 4.5 ⁇ 0.1 mm was fitted into this sample and fixed with resin. Next, after cooling in liquid nitrogen (77 K) in a magnetic field of 3.0 T and removing the external magnetic field, the trapped magnetic flux distribution was measured, and the concentric magnetic flux density distribution and 1.25 T magnetic flux density were measured. Checked on the surface. Thereby, it was confirmed that crystals of the superconducting phase (123 phase) were continuous throughout the sample and the c-axis was aligned.
- a Y-based sample containing no Ag which is a comparative example, was obtained by similarly cutting a sample cut from a position of 5 to 10 mm from the top surface with an outer diameter of 44.0 + 0.0 to ⁇ 0.1 mm and a thickness of 4.5 ⁇ 0.00 mm. Although it processed similarly with the precision of 1 mm, the chipping was confirmed by five places. Moreover, when the captured magnetic flux distribution of this sample was measured similarly, the maximum magnetic flux density of 1.10 T was confirmed. This comparative experiment confirmed that the material of the present invention was superior to the comparative material.
- the sample of the present invention cut out from a position of 0 to 5 mm from the upper surface was cut to a thickness of about 5 mm to 2.0 mm, and both ends thereof were Ag particles.
- a rod-shaped sample having a width of 8 mm and a length of about 42 mm was cut out so as to be a region where the precipitate was deposited.
- a 2 ⁇ m thick Ag film is formed by sputtering in the region where the Ag particles are deposited at both ends of the rod-shaped sample, heat treatment is performed, and the Ag film is further adapted to the rod-shaped sample.
- the electrode was soldered, the entire rod-shaped sample was sandwiched between glass fiber reinforced plastics and screwed, and then solidified with resin to produce a current lead.
- This current lead was able to pass 1500A at 77K, and it was confirmed that it functions sufficiently as a current lead.
- the bulk oxide superconductor according to the present invention can be used for a superconducting magnet.
- Superconducting magnets can be used for linear motors and as an alternative to current permanent magnets.
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Abstract
Description
RE系バルク酸化物超電導体を製造する際に、バルク酸化物超電導体の前駆体に添加するAgの量を5.0質量%以下として、QMG法により製造すれば、種結晶近傍のRE系バルク酸化物超電導体の組織中には粒径1~10μmのAg粒子がなく、その周辺部に粒径1~10μmのAg粒子が分散析出した領域を形成することができることを見出した。
本発明は、これら知見を基に成されたものであり、その要旨は以下の通りである。
(2)前記Ag粒子が存在する部分が、前記Ag粒子が存在しない部分を挟む構造であることを特徴とする(1)記載のバルク酸化物超電導体。
(3)前記Ag粒子が存在する部分が、前記Ag粒子が存在しない部分を取り囲む構造であることを特徴とする(1)に記載のバルク酸化物超電導体。
(4)前記Ag粒子の粒径が1~10μmであることを特徴とする(1)~(3)のいずれか1項に記載のバルク酸化物超電導体。
(5)前記バルク酸化物超電導体が棒状であって、前記Ag粒子が存在する部分を両端部に配置し、前記両端部以外の領域をAg粒子が存在しない部分としたことを特徴とする(1)~(4)のいずれか1項に記載のバルク酸化物超電導体。
(6)バルク酸化物超電導体の前駆体を加熱して半溶融状態とし、種結晶を接触させて単結晶状のREBa2Cu3O7-x相中に、RE2BaCuO5相が微細分散したバルク酸化物超電導体を製造する方法であって、前記バルク酸化物超電導体の前駆体にAgを0.5~5.0質量%添加して半溶融状態になるように加熱後、種結晶を前記半溶融状態の前駆体に接触させ、徐冷し、前記前駆体を単結晶状に凝固させることを特徴とするバルク酸化物超電導体の製造方法。
(7)Agが存在する部分が、Agが存在しない部分を挟むように、前記バルク酸化物超電導体から棒状に加工することを特徴とする前記(6)に記載のバルク酸化物超電導体の製造方法。
211相+液相(BaとCuの複合酸化物)→123相
という反応によりできる。そして、この包晶反応により、123相ができる温度(Tf:123相生成温度)は、ほぼRE元素のイオン半径に関連し、イオン半径の減少に伴いTfも低くなる。また、低酸素雰囲気及びAg添加に伴い、Tfは低下する傾向にある。
211相+液相(BaとCuの複合酸化物)→123相+211相
で示される反応によりできる。QMG材料中の211相の微細分散は、臨界電流密度(Jc)向上の観点から極めて重要である。Pt、Rh又はCeの少なくとも一つを微量添加することで、半溶融状態(211相と液相からなる状態)での211相の粒成長を抑制し、結果的に材料中の211相を約1μm程度に微細化する。添加量は、微細化効果が現れる量及び材料コストの観点から、Ptで0.2~2.0質量%、Rhで0.01~0.5質量%、Ceで0.5~2.0質量%が望ましい。添加されたPt、Rh、Ceは123相中に一部固溶する。また、固溶できなかった元素は、BaやCuとの複合酸化物を形成し、QMG材料中に点在することになる。
次に、当該QMG材料中へのAg添加効果について述べる。一般に、使用条件に適した良質な超電導体バルク材料を効率よく安価に製造することは重要であり、高価なAgを必要な部分にのみ微細分散させることは経済的に有用な技術と言える。
さらに、結晶成長に伴い液相中のAgの濃度が上昇し、例えばGd系材料の場合には、前記液相中のAgの濃度が約5質量%を超えるとAg粒子が析出することを見出した。
211相+液相(BaとCuの複合酸化物)→123相
純度99.9%の各試薬Gd2O3、BaO2、CuOをGd:Ba:Cuの金属元素のモル比が10:14:20(即ち、最終組織の123相:211相のモル比が3:1)になるように混合した。さらに、CeO2を1.0質量%、Ag2Oを3質量%(Ag換算で約2.8質量%)添加した混合粉を作製した。各混合粉は、一旦900℃で8時間仮焼した。仮焼粉は、内径50mmの円筒状金型中に充填し、厚さ約30mmの円盤状に成形し、Gd系成形体を作製した。
また、Sm2O3及びYb2O3を用いて、上記成形体と同様の方法により、厚さ4mmのSm系及びYb系円盤状成形体を作製した。さらに、各成形体について等方静水圧プレスにより約100MPaで圧縮加工した。
純度99.9%の各試薬Y2O3、BaO2、CuOをGd:Ba:Cuの金属元素のモル比が13:17:24(即ち、最終組織の123相:211相のモル比が7:3)になるように混合した。さらに、CeBaO3を1.5質量%、Ag2Oを4質量%(Ag換算で約3.7質量%)添加した混合粉を作製した。各混合粉は、一旦900℃で8時間仮焼した。仮焼粉は、内径60mmの円筒状金型中に充填し、厚さ約35mmの円盤状に成形し、Y系成形体を作製した。また、Sm2O3及びYb2O3を用いて、上記成形体と同様の方法により、厚さ4mmのSm系及びYb系円盤状成形体を作製した。さらに、各成形体について等方静水圧プレスにより約100MPaで圧縮加工した。
3 Ag粒子を含まない矩形の領域
4 微細なAg粒子を含む領域
5 Ag粒子を含まない線状の領域
Claims (7)
- 単結晶状のREBa2Cu3O7-x相中に、RE2BaCuO5相およびAg粒子を有するバルク酸化物超電導体であって、Ag粒子が存在する部分とAg粒子が存在しない部分が隣接した構造であり、Ag粒子は粒子径が10μm以下であって分散していることを特徴とするバルク酸化物超電導体。
- 前記Ag粒子が存在する部分が、前記Ag粒子が存在しない部分を挟む構造であることを特徴とする請求項1に記載のバルク酸化物超電導体。
- 前記Ag粒子が存在する部分が、前記Ag粒子が存在しない部分を取り囲む構造であることを特徴とする請求項1に記載のバルク酸化物超電導体。
- 前記Ag粒子の粒径が1~10μmであることを特徴とする請求項1~3のいずれか1項に記載のバルク酸化物超電導体。
- 前記バルク酸化物超電導体が棒状であって、前記Ag粒子が存在する部分を両端部に配置し、前記両端部以外の領域をAg粒子が存在しない部分としたことを特徴とする請求項1~4のいずれか1項に記載のバルク酸化物超電導体。
- バルク酸化物超電導体の前駆体を加熱して半溶融状態とし、種結晶を接触させて単結晶状のREBa2Cu3O7-x相中に、RE2BaCuO5相が微細分散したバルク酸化物超電導体を製造する方法であって、前記バルク酸化物超電導体の前駆体にAgを0.5~5.0質量%添加して半溶融状態になるように加熱後、種結晶を前記半溶融状態の前駆体に接触させ、徐冷し、前記前駆体を単結晶状に凝固させることを特徴とするバルク酸化物超電導体の製造方法。
- Agが存在する部分が、Agが存在しない部分を挟むように、前記バルク酸化物超電導体から棒状に加工することを特徴とする請求項6に記載のバルク酸化物超電導体の製造方法。
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