JPH0453805B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Technical Field) The present invention relates to a method for producing superconducting ceramic powder. More specifically, the present invention relates to a method for producing ceramic powder that has a high oxygen content, excellent superconducting properties, and high density.

(Background Art) Conventionally, superconducting materials have been limited to metals such as Nb ₃ Ge and Nb-Al-Ge alloys. These have high density and extensibility, but the critical temperature (T _C )
Liquid helium, which has a low temperature of less than 23K and is expensive, had to be used as a coolant, and superconducting machines and sensors using these were large and expensive, posing economic problems. Recently, superconducting ceramics with a T _C higher than the liquid wall elementary temperature have been discovered, and there are signs that cheaper superconducting machines, devices, sensors, etc. will be developed.

High-temperature superconducting materials are actively being developed for energy-saving and highly sensitive sensors. Because of the former, power storage coils, magnetic levitation objects, etc. are important in the field of strong electricity.
On the other hand, in the field of light electrical devices, devices for ultra-high-speed computers, infrared/millimeter wave detection devices, and low heat loss wiring for electronic circuits are attracting attention.

However, these superconducting ceramic materials proposed so far have poor stretchability and
It is difficult to increase density and has drawbacks such as low current density.

Furthermore, in recent superconducting ceramics, those produced by solid phase reaction have a porosity of 20-30%.
However, high-density sintered bodies have not been obtained and it is difficult to obtain high critical current.

The inventor of the present invention has carried out intensive studies to overcome the above-mentioned problems, and has completed a new method for forming superconducting ceramic powder. In other words, first of all, when looking at superconducting ceramic materials, the requirements for such materials are (1) high critical temperature, (2)
Higher critical current, (3) Higher critical magnetic field, (4) Higher density, (5)
This is uniformization or smoothing of thick/thin films. especially,
In the field of strong electric current, lamination is necessary to allow large currents to flow, and in the field of weak electric current, it is important to reduce heat capacity and increase sensitivity. This requires dense materials with high critical temperatures, high critical currents, and high critical magnetic fields. If developed, it could also be used as an element for high-speed computers and highly sensitive sensors.

The inventors of the present invention believe that the superconducting function of such superconducting ceramic materials, especially in high-temperature superconducting ceramics containing steel, is enhanced as the content of oxygen increases, and that the c-axis of the orthorhombic system and The method of the present invention was completed based on the knowledge that superconducting current flows in the vertical direction, and that it is therefore important to produce fine, highly oriented powder that facilitates the oxidation process.

(Purpose of the Invention) This invention was made based on the above circumstances, and it overcomes the drawbacks of conventional superconducting ceramic materials, has a high oxygen content, has excellent superconducting properties, and has a fine structure. The purpose of the present invention is to provide a new powder manufacturing method capable of forming highly oriented superconducting ceramic powder.

(Disclosure of the Invention) In order to achieve the above object, the present invention involves heating and melting ceramic powder having a conductive composition above its melting point, compressing and rapidly cooling the melt to produce a thick film, and then manufacturing a thick film. The present invention provides a method for producing superconducting ceramic powder, which comprises performing thermal oxidation treatment in an oxygen-containing atmosphere or oxygen plasma, and then pulverizing it into powder.

To explain the manufacturing method of the present invention in more detail, for example, oxides, hydroxides, carbonates, nitrates, or oxalates of elements such as Y, Ba, and Cu constituting the high-temperature oxide superconductor are mixed in a predetermined ratio. Grind and heat at 500-950℃ for 1-12 hours to volatilize water, carbonate, nitrate, and oxalate. Then,
As shown in Figure 1 of the attached drawings, for example, the powder or agglomerate 1 obtained in this process is placed in a platinum nozzle 2 and heated for 1-5 minutes at a temperature of 1250-1450°C.
After melting for several minutes, a gas 3 such as air is injected from above the nozzle 2, and the molten mass is blown out from the hole 4 below the nozzle. 5-15mm, thickness 5-3000μm)
to form. The phase of the substance at this point is an amorphous metastable phase or several phase-separated crystalline phases. This thick film is heat-treated in air, in an oxygen stream, or in an oxygen plasma at 850-950℃ for 2-60 hours to form a perovskite phase, and then in the same atmosphere for 200-200 hours.
It is sufficiently oxidized to form a superconducting phase at 700°C for 5-24 hours.

This thick film has a highly oriented C-plane which is a cleavage plane and is easily broken. This is crushed into powder. The powder is a plate-like crystal, and the plate surface is orthorhombic c
parallel to the plane.

In this type of superconducting material, current mainly flows parallel to the c-plane, so when the obtained powders are arranged two-dimensionally, the superconducting current flows parallel to the film surface, which is extremely difficult for practical purposes. It's advantageous. Therefore, by using the powder produced by the method of the present invention as a raw material for printing methods, doctor blade methods, pressureless sintering methods, hot pressing methods, etc., it is possible to achieve oriented film thickness and three-dimensional sintering with good superconducting properties. A concretion can be produced.

Superconducting ceramic powders and thick films include
YBa ₂ Cu ₃ O ₇ − ₈ as the substrate composition (A _x B _y ) _Cup
A compound of M _q ) O _r can be used.

Here, A: Y, Sc, loess Ln (La, Ce, Pr,
Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er,
Tm, Yb, Lu), B: Ba, Sr, Ca, Mg, M:
V, Nb, Zn, Ni, Co, Fe, Mn, Ag, Cu: copper,
O: means oxygen, and the range of x, y, p, q is:
0.5≦x≦1.5, 1.5≦y≦2.5, 2.0≦p≦4.0, 0≦
q≦1.5r is determined by the valences of A, B, Cu, and M. Each element may be a mixture as long as it does not exceed this range.

In the method of the present invention, when forming a thick film, the thick film is provided with chemical durability and extensibility, and the nucleation, growth and orientation of crystals are controlled, or the coefficient of thermal expansion with respect to the substrate is controlled. Glass network forming oxides such as B ₂ O ₃ , SiO ₂ , GeO ₂ , P ₂ O ₅ , Al _{2 O}
−ZnO−B ₂ O ₃ system, PbO−Tl ₂ O−B ₂ O ₃ system, Bi ₂ O ₃
−Tl ₂ O system, etc.) can be added up to 20 mol%. In addition, in order to impart superconductivity to this thick film produced by ultra-quenching, a thermal oxidation process is required, but in order to process it in a short time, it is preferable that the film is thin, especially 5-300 μm. It is optimal for the production of superconducting powder to have a temperature of about 100%.

Note that the compression quenching device used in this invention includes a twin roll melt super quenching device, a twin soft roll melt super quenching device, a single roll type melt super quenching device, and a piston-type melt super quenching device.
There are anvil devices, etc. At this time, as a heating method for producing the melt, an electric furnace, a high frequency furnace, an infrared condensing furnace, a laser beam, etc. can be used.

Further, the produced thick film can be crushed into powder by a conventionally known mechanical crushing method. The size of the particles after pulverization can be appropriately selected depending on the usage and purpose of the powder.

The superconducting ceramic powder that can be produced by the method of the present invention described in detail above is fine, has a high oxygen content, and has high orientation, so it can realize a high critical temperature and cross-critical current. , the composition is uniform due to passing through a molten state during the manufacturing process.

Powders with such excellent properties that can be produced by the method of the invention can be produced by screen printing, for example on ceramic substrates or metal plates,
It can be used to manufacture a large-area superconducting film that is obtained by bringing it into close contact with a substrate by heating. In addition, by repeating this printing and firing process, it becomes three-dimensional.
It can also have a structure that allows a large current to flow.

For example, more specifically, the oriented powder of the present invention is used as a raw material for the doctor blade method, kneaded with an organic binder such as propylene glycol, formed into a film, and then fired to form an oriented thick film. Can be done. It is also possible to form a superconducting object in which the togter blade films are laminated and brought into close contact with each other by heating to create a three-dimensional structure and allow a large current to flow through the object.

Furthermore, it is possible to form an oriented sintered body by compacting and molding this oriented powder and firing it in an oxygen-containing atmosphere at normal pressure, or by compacting and molding the oriented powder to form an oriented sintered body. By firing in an atmosphere of oxygen, nitrogen or inert gas, a high-density oriented sintered body is formed.

Next, the method of the present invention will be explained in more detail with reference to Examples. Of course, the invention is not limited to the following examples.

Example 1 An example of manufacturing a superconducting ceramic powder having _a composition of YBa ₂ Cu ₃ O _7-8 is shown below.

Special reagent grade Y ₂ (CO ₃ ) ₃ , BaCO ₃ , and CuO were used as raw materials, and a total of 10 g of predetermined amounts were weighed out to give the desired composition, ground in an agate mortar for 30 minutes, and mixed.

After pressing this powder into a disk shape,
It was calcined in 3 hours. Next, the reaction was completed at 950°C for 10 hours to obtain a perovskite phase. A piece of the sintered body (0.2 g) was placed into a platinum nozzle in a twin-roll melt ultra-quenching device and melted at 1300° C. for 1 minute. After melting, air pressure (1.2
By dropping the melt between twin rolls rotating at ^1000-3000 rpm, a thick film approximately 10 mm wide, 30-50 mm long and 5-1000 μm thick was immediately obtained. This thick film was heated at 950℃ and 54℃ in air.
After the heat treatment for a period of time, the mixture was slowly cooled to room temperature over 6 hours to ensure sufficient oxidation.

The obtained crystalline thick film was pulverized to form a powder. Figure 2 shows the X-ray diffraction pattern of a powder obtained by treating a 50 μm thick film at 950° C. for 54 hours, air oxidation during slow cooling, and then pulverizing. Moreover, FIG. 3 is an X-ray diffraction diagram of a powder obtained by pulverizing a sintered body produced by a normal solid phase reaction.
As is clear from the comparison of FIGS. 2 and 3, the powder produced by the method of the present invention has a high intensity of the (001) and (002) diffraction lines representing the c-plane of the orthorhombic system. , which is about 2.6 times stronger than the non-oriented one produced by normal solid-phase reaction.

In this type of material, current mainly flows parallel to the c-plane, so when this powder is arranged two-dimensionally, superconducting current flows parallel to the membrane surface, which is extremely advantageous in practice.

Example 2 An ultra-quenched membrane with a thickness of 50 μm produced in the same manner as in Example was crushed and then heat treated at a temperature of 950° C. for 14 hours to effect crystallization and sintering. After slow cooling and oxidation in the air, it was powdered again.

FIG. 4 shows an X-ray diffraction diagram of this powder.

As shown in FIG. 4, the peak intensities of (001) and (002) are approximately four times stronger than those resulting from a normal solid phase reaction (FIG. 3).

This shows that it is an oriented powder with a developed c-plane, and when this powder is arranged two-dimensionally,
The superconducting current flows parallel to the membrane surface, which is extremely advantageous in practice.

[Brief explanation of the drawing]

FIG. 1 shows an example of a twin-roll type melt quenching apparatus used in the method of the present invention. FIGS. 2 and 3 are X-ray diffraction diagrams of a powder according to an example of the present invention and a powder produced by a conventional method for comparison, respectively. FIG. 4 is a powder X-ray diffraction diagram of another embodiment of the present invention. 1... Sample powder, sample lump, 2... Platinum nozzle, 3... Gas, 4... Hole, 5... Twin roll ultra-quenching device.

Claims (1)

[Claims] 1. Heat and melt superconducting ceramic powder above its melting point, press and quench the melt to create a thick film, then thermally oxidize this thick film in an oxygen-containing atmosphere or oxygen plasma, and then crush it. A method for producing superconducting ceramic powder, which is characterized by pulverizing it.