JPH0193403A - Production of ceramic-based superconducting material and apparatus therefor - Google Patents

Abstract

PURPOSE:To readily obtain the title material, having the high critical tempera ture and critical current density and useful in the field of superconductivity technology, by heating and evaporating a raw material for a ceramic-based superconducting substance at a high temperature, cooling and solidifying the substance and recovering fine powder having a specific particle diameter. CONSTITUTION:A raw material for a ceramic-based superconducting substance containing a rare earth element, such as La, is charged from a raw material storing box 1 into a hybrid furnace 9 and continuously fed into a DC plasma joined stream 6 formed by converting Ar gas, etc., into a plasma by a DC plasma gun 4. The raw material is then heated at a high temperature of 4,000-5,000 deg.C, evaporated and annealed to afford solidified fine powder having <=1mum average particle diameter. The above-mentioned fine powder is subsequently collected in a powder recovery device 11, formed and calcined to afford the aimed ceramic-based superconducting material.

Description

Detailed Description of the Invention (Field of Industrial Application) The present invention relates to a method and apparatus for producing oxide-based high-temperature superconducting materials, etc. The present invention facilitates producing superconducting materials with high critical current density. .

(Prior art) Recently, Y, Ba2Cu30. -, l (X is degree of oxygen deficiency)
Various oxide-based ceramics, represented by the composition of ing. When applying this to magnetically levitated trains, nuclear magnetic resonance tomography devices, superconducting propulsion ships, etc., conductors (e.g. wires, tapes) with a large amount of circulating current per unit cross-sectional area, i.e. critical current density (Jc ) is essential, and the establishment of manufacturing technology is required.

However, regarding the superconducting properties of these oxide-based ceramics, although it has been confirmed that Tc can be achieved in the high temperature range of 90 or higher in the basic material, ie, the powder of such ceramics, it is extremely difficult to achieve a large Jc. Partly because there is no accumulation of research and development results for practical application, very few effective and specific proposals for improving Jc have been reported.

(Problems to be Solved by the Invention) Ceramic superconducting materials such as Y1Ba2Cu3O7-H and oxides having a similar form to stiffness can be manufactured using La20.
.

Blending raw material powders such as Y2O, 5rC03, l1aCO, and CuO in a predetermined ratio to form a superconducting material composition,
This is calcined to volatilize and remove unintended components such as carbonic acid, and then pulverized to produce ceramic superconducting material powder as an intermediate material, and this powder is pressure-molded to form the desired material. This is generally done by heat treatment (finish sintering) after shaping.

Incidentally, the smaller the particle size and the higher the dispersibility of the powder of the ceramitsu-based superconducting material, the more dense and compositionally uniform a sintered body, ie, the superconducting material, can be obtained. If the superconducting material is dense, the influence of grain boundaries will be reduced, so the critical temperature Tc,
Critical current density Jc and critical magnetic field Hc become higher. Thereby, it is possible to achieve high performance and miniaturization of electrical equipment. Furthermore, it becomes possible to perform fine and complicated processing, making it possible to apply it to electronic devices. Therefore, the densification of superconducting materials has an extremely large effect on improving the performance of electrical equipment and electronic devices.

However, the ceramic superconducting material powder obtained by the above conventional manufacturing method is La2O5+ Y2O3*Sr
Since a plurality of raw materials in the form of CO3, BaCO3, CuO, etc. are simply ground and dispersed mechanically using a bot mill or the like, the particle size ranges from several μm to several tens of μm. Pressure-molded products of this type have multiple types of composition and a mixture of coarse and fine particles, so partial (semi-macro) non-uniformity of the components is unavoidable. Furthermore, since it is a mixture of a low melting point substance such as (:uO (melting point: 1026°C)) and a high melting point substance such as Y2O3 (melting point: 2410°C), there is semi-macroscopic non-uniformity of the components as described above. In some cases, it is extremely difficult to achieve uniform diffusion of components by final sintering. In other words, with conventional methods, it is difficult to obtain a superconducting material (bulk) formed from a homogeneous and dense sintered body. This is due to the critical temperature Tc, This is a major obstacle in terms of manufacturing technology for improving the critical current density Jc and critical magnetic field tic.In other words, from a different perspective, it is difficult to industrially manufacture extremely fine ceramic superconducting material powder. If it could be obtained, it would greatly contribute to improving and stabilizing the practical characteristics (eg, Tc, Jc) of ceramic superconducting materials, and there was a demand for its realization.

(Means for Solving the Problems) The purpose of the present invention is to provide a ceramic superconducting material with a large critical current density Jc. Once evaporated, it is cooled and solidified to recover a fine powder with an average particle size of 1 micron or less, and the fine powder obtained in this way can be molded as it is or filled into a hollow container to form the desired shape. After processing and/or heat treatment, finish sintering is performed to obtain a ceramic M conductive material.

(Function) The method of the present invention uses high-temperature heating means such as thermal plasma to vaporize all of the raw materials of the ceramic superconducting material,
Since the method is basically to precipitate particles from a gas, it has the following characteristics.

■Ideal uniformity is ensured once the material is vaporized, regardless of the type or form of the raw material.

(2) Since it starts from particles obtained by precipitation from gas in space, the target powder is sufficiently fine.

■In the process of changing from gas to liquid to solid, particles collide and coalesce while in the liquid state, allowing them to grow to an appropriate size. The size of this particle is the raw material supply ffl (g/m1
n) It can be controlled by the amount of power supplied to the plasma, the amount of plasma gas, the cooling rate of the plasma gas (residence time in a liquid state), etc.

■The particles become spherical due to the action of the surface tension of the liquid, and the resulting solid also becomes dense particles that are spherical or nearly spherical. Furthermore, the particles obtained by the powder method have a narrower particle size distribution range and excellent dispersibility than those obtained by the conventional method, which are obtained by pulverization or pulverization and classification.

■The plasma gas flow in direct current plasma, high frequency plasma, hybrid plasma consisting of direct current plasma and high frequency plasma, etc. can be cooled sufficiently rapidly, so that there is little segregation of components between the precipitated particles and they are homogeneous.

■The superconducting material powder obtained does not contain volatile components such as crystal water, carbonates, and nitrates.

The ceramic superconducting material powder obtained by the method of the present invention having the above-mentioned characteristics can be used in the production of superconducting materials without requiring any steps of pulverization after calcination, which are essential in conventional techniques. Can be used for pressure molding. By molding such powder and final sintering, it is possible to obtain a dense sintered body with homogeneous components, that is, a superconducting material with high Jc and Tc.

Now, a dense sintered body with homogeneous ingredients can basically be obtained by uniformly mixing fine particles, forming them into a dense shape, and then final sintering them. This causes the formation of secondary particles, making it impossible to obtain a homogeneous and dense molded body. According to the knowledge obtained by the inventors, a powder having an average particle diameter in the range of 0.1 to 1.0 μm and a narrow particle size distribution can be obtained, and good results can be obtained. That is, when the above-mentioned powder is used, densification can be achieved at a lower sintering temperature and in a shorter sintering time. In this case, the lower the sintering temperature is, the finer the crystal grain size of the sintered body becomes, so the crystal grain size can be controlled by selecting the sintering temperature.

Now, in the present invention, as means for high-temperature heating, an ultra-high temperature of 4000 to 5000°C or more is required to evaporate a rare earth element or its compound with a high melting point, so thermal plasma such as direct current plasma, high frequency plasma, direct current Hybrids consisting of plasma and high-frequency plasma, transitional plasma, carbon electrode mark plasma, etc. are used.

Appropriate raw materials for ceramic superconducting materials are selected depending on the composition of the target material, but LIA2 (:u
In the production of +07-x type oxide-based high temperature superconducting materials, rare earth elements (L), alkaline earth metals (A) and copper are used. Examples of rare earth elements include La
, En, Dy, )lo, Er, Tm, Yb
or Y, and those selected from alkaline earth metals are Ca, Sr, Ra or Ba. These raw materials do not need to be single elements, but may be any material that can generate oxides and be separated from other components in an oxygen atmosphere in a gaseous or molten state. That is, forms other than simple substances include, for example, sulfides, carbides, nitrides, hydroxides, hydrides, nitrates, oxalates, carbonates, sulfates, and, of course, oxides.

Inert gas as plasma gas, 02+N2+H2
+ and N20 gases are available. Usually, Ar gas or (Ar+02) gas is used, but N2 gas is used to adjust the thermal output of the plasma. N2. It is also possible to mix H,0. However, in either case, the plasma gas is sufficiently 00000 from the beginning so that sufficient oxygen can be added to the rare earth elements, alkaline earth metals, and copper elements that solidify and precipitate from the gas flow as the temperature of the plasma gas flow decreases. □, or if the plasma gas itself does not contain 02 at all or has a small amount of 02, add 02 gas to the plasma gas flow from the outside, or create a sufficient 02 atmosphere around it. You need to either leave it or ask for one of these methods.

The fine powder thus solidified and precipitated from the hot plasma gas stream is collected by a cyclone or bag filter. By molding and sintering the ceramic superconducting powder thus obtained, a high-density and homogeneous superconducting material can be produced.

Hereinafter, the present invention will be explained in more detail with reference to Examples.

(Example) (1) Example 1 [Production of ceramic superconducting material powder] Particle size is 10 (1 to 44 utn Y2O3, BaCO3,
The atomic ratio of CuO powder is Y:Ba:Cu = 1:
The mixture was blended at a ratio of 2:3 and placed in a bot mill for 12 hours to mix uniformly. This mixed raw material was continuously supplied at a rate of 4 g/min to the confluence of three DC plasma streams of the hybrid plasma shown in FIG. This hybrid plasma is shielded from the atmosphere. The output of the three DC plasmas is 15 and 3 stomachs, the plasma gas is Ar gas, 1517m1nx 3, the high frequency plasma is 80kw, the high frequency plasma gas is Ar+ 10
02 gas is added from the top of the high-frequency plasma so that the temperature becomes 9602.

The inner diameter of the hybrid plasma reaction vessel is 75 mmφ
02 was blown at 1001/min from the inner wall of the reaction vessel toward the center below the high-frequency plasma. The above-mentioned mixed raw material was instantaneously heated to a high temperature by this plasma and the entire amount evaporated once, but it was subsequently rapidly cooled, precipitated, and solidified into fine powder. These generated powders were captured by a bag filter connected to the reaction vessel.

This powder had a specific surface area of 10 to 20 m + 27 g, and a particle size of 0.1 to 1.0 JJOI. When observed under a transmission electron microscope after boiling, it was found to be approximately spherical. At the same time as the particle shape was observed using an electron microscope, the constituent components of several randomly selected particles were analyzed using an energy dispersive (YBa2Cu
30y-x).

Here, the properties of ceramic powder obtained by the conventional method will be shown and compared with those obtained by the method of the present invention. In this example, the powder obtained by molding (granulating), calcining (950°C x 2 hours) and pulverizing (normal ball milling) the above blended powder raw materials has a particle size of 0.1 μm to 30 μm. Wide distribution and segregation of components within large grains was observed.

(2) Example 2 [Manufacture of superconducting material ■] The powder produced by the method of the present invention in Example 1 was put into a die with a diameter of 25+sm, and 100
7ton/cm” after negative axis pressing of “kg/c+s”
Perform isostatic press ((:IP) of 20 mm in diameter and 5 in thickness.
It was made into a disc-shaped bulk of 1IIfl+. This disk was sintered at 900° C. for 8 hours in an oxygen atmosphere. This sintered body exhibited regular crystal grains of 1.0 to 2.0 μm. When the electrical resistance of this sintered body was measured, it had superconducting properties with good reproducibility (Tc = 93, Jc -120
0A/cm2).

Here, for comparison, a sintered body was manufactured using ceramic superconducting material powder by a conventional method. That is,
The powder produced by the conventional method described in Example 1 (average particle size: approximately 3 μI9 particle size distribution range = 0.1 to 30 μm) was molded under the same conditions as in the case of the powder produced by the present invention method described above in this example. (formed into a disc), and this molded body was heated at 900°C x 8 hr and at 950°C x 8 hr in a 100% oxygen atmosphere.
Sintering was performed for hr. Among these, those treated at 900°C did not lead to sufficient sintering. In addition, in the case of the sample treated at 950°C, the majority of crystal grains had a size of 10 to 20 um, bubbles were found here and there, and segregation of components within the grains was observed. The superconducting properties of the sintered body treated at 950°C are as follows:
Wide variation Tc = 80-90, Jc = 5
0-150 A/cm''), which was poor compared to that produced from the powder according to the invention.

(3) Example 3 [Manufacture of superconducting material] A small amount of AgO fine powder was added as an oxygen supply source to the powder produced by the method of the present invention in Example 1, and mixed uniformly to form a powder with an outer diameter of 20 mm and a thickness of 2 mm. The superconducting material was filled into a 18-8 stainless steel tube and subjected to diameter reduction processing by groove rolling and drawing to obtain a thin round wire-shaped superconducting material with a final dimension of 2+nmφ. 950℃ x 8 on this thin line
Finish sintering for 1 hour and subsequent slow cooling in a furnace were performed. When the critical temperature and critical current density of the thin wire subjected to this treatment were measured, they were 91 K and 8 K, respectively.
00A/cm2.

When a similar experiment was carried out on the comparative material (powder produced by the conventional method) shown in Example 1, the critical temperature and critical current density were 85 K and 100 A/cm2, respectively.

(4) Example 4 Y ions, Ba ions, and Cu ions at an atomic ratio of Y:Ba
Oxalic acid was added to a nitrate aqueous solution containing a ratio of :C:u=1:2:3 to precipitate an oxalate containing a uniform mixture of Y, Ba, and Cu. Dry this precipitate,
Grind with a ball mill and pass through a 325 mesh sieve to 44
A powder of μ below was obtained.

This powder of 44 μm or less was continuously charged at a rate of 3 g/min into a reactor in which only high-frequency plasma of a hybrid plasma device shown in FIG. 1 was operated. The output of high-frequency plasma is 80kW, and the plasma gas is (^r+to!k
02) Gaste 50 i/min. Below, actual h'6
As in Example 1, 0□ is 10027 m1n from the bottom of the reaction vessel.
The powder produced under such thermal plasma treatment conditions was captured by a bag filter. The particle size of the captured powder was distributed in the range of 1 to 100 μm, and was a mixture of fine particles to agglomerated large particles. This is because the heat output of the high-frequency plasma is insufficient compared to the case of Example 1, and the input raw material does not pass through the high-temperature part of the plasma but passes through a low temperature, so the vaporization of the input raw material is not necessarily complete. This is due to the fact that they were combined in a liquid state.

This captured powder is divided into ■ those with the same particle size distribution, 0
10μm or less (obtained by crushing and classifying), ■5μm
The following three types of powders (obtained by pulverization and classification) were prepared.

These three types of powder were subjected to the same treatment as in Example 2 (sintering and final sintering at 950°C for 8 hours) and the superconducting properties of the bulk (disk) were measured.
Tc=83, Jc=40A/cm2. For ■, Tc=888. Jc = 150A/cm2, ■
For, Tc=928. Jc=400A/c
m2 was shown. In other words, although the results of this example are not as good as the properties of the sintered body made from the powder produced by the method of the present invention in Example 1, they are far superior to the properties of the sintered body made from the powder produced by the conventional method on the same side. There was something there. This shows that powder for producing an excellent sintered body can be obtained even by the method of this example, in other words, by using only high-frequency plasma without using hybrid plasma. The reason for this is that although it is not possible to obtain extremely fine powder using a thermal plasma with a rather low power as in this example, even if it is, the solidification time after being heated to a high temperature is very short, so it is difficult to obtain particles. This is due to the fact that the segregation of components between and within the grains is extremely small, and by selectively extracting the fine powder side using methods such as classification or re-grinding, the sintered body can be made uniform and dense. .

The method of this example requires only a simple plasma device;
It can be fully adopted industrially.

(Effects of the Invention) According to the present invention, (1) There are fewer restrictions on raw materials than in the prior art, and a wide variety of raw materials can be selected, making production itself easier. Furthermore, manufacturing costs can be reduced.

■Since it becomes possible to produce superconducting materials that have both stable and high critical temperatures and high critical current densities, this opens the door to a wide range of practical applications of superconducting technology, and has great industrial benefits.

[Brief explanation of the drawing]

FIG. 1 is an apparatus configuration diagram showing an example of an apparatus for producing fine ceramic superconducting material powder used in the present invention. ! ...raw material storage box, 2...raw material cutting device, 3...
・Raw rice charging device, 4...DC plasma gun, 5...
DC plasma, 6... DC plasma combined flow, 7...
High frequency plasma work coil, 8... High frequency plasma, 9... Hybrid furnace, lO... Cooling or reaction gas blowing hole, 11-... Powder recovery device.

Claims (7)

[Claims] (1) It is characterized by comprising a step of heating the raw material of the ceramic superconducting material to high temperature and evaporating it, and a step of cooling and solidifying the evaporated raw material and recovering it as a fine powder with an average particle size of 1 micron or less. A method for manufacturing a ceramic superconducting material. (2) The method according to claim 1, wherein the step of heating and vaporizing the raw material of the ceramic superconducting material at a high temperature uses thermal plasma. (3) The method according to claim 1, wherein the step of heating and vaporizing the raw material of the ceramic superconducting material at a high temperature uses a hybrid plasma that is a combination of direct current plasma and high frequency plasma. (4) A step of heating the raw material of the ceramic superconducting material to a high temperature and evaporating it; a step of cooling and solidifying the evaporated raw material and recovering it as a fine powder with an average particle size of 1 micron or less; and molding the fine powder as it is. A method for producing a ceramic superconducting material, comprising the steps of: filling the material into a hollow container and subjecting it to necessary processing and/or heat treatment; and finishing sintering. (5) The method according to claim 4, wherein the step of heating and vaporizing the raw material of the ceramic superconducting material at a high temperature uses thermal plasma. (6) The method according to claim 4, wherein the step of heating and vaporizing the raw material of the ceramic superconducting material at a high temperature uses a hybrid plasma that is a combination of direct current plasma and high frequency plasma. (7) A device for storing and cutting raw materials for ceramic superconducting materials, a high-frequency plasma generator, and a central axis of a work coil of the high-frequency plasma generator arranged so that the confluence of the plurality of DC plasma flows coincides with the central axis of the work coil of the high-frequency plasma generator. It is comprised of a plurality of DC plasma generators, a device that feeds the raw material of the ceramic superconducting material to the confluence of the plurality of DC plasmas, and a device that cools, solidifies, and recovers the raw material evaporated by plasma heating. A manufacturing device for ceramic superconducting materials characterized by: