JP2838129B2 - Manufacturing method of superconducting ceramics - Google Patents

Description

The present invention relates to a method for producing a superconducting ceramic exhibiting zero resistance and Meissner effect, and relates to a method for producing a Ba-Y-Cu superconducting ceramic having a high critical current density. It relates to a manufacturing method. The superconducting ceramics obtained by the present invention are widely used in connection with superconducting applied technology, but are mainly used as a conductive member for superconducting power transmission, a member for magnetic levitation, or an electromagnetic shielding member.

[Prior Art] As a method for producing superconducting ceramics, there has been a solid phase sintering method. Ba-Y-Cu-based, for example BaO-Y ₂ O ₃ -CuO
In superconducting ceramics, the raw material powder is molded,
This is a method of baking at 900 ° C to 950 ° C for several hours and then performing heat treatment in oxygen at around 500 ° C.

Superconducting ceramics produced by this method are polycrystalline and have crystal grain boundaries. In particular, cracks and second phases are present at the grain boundaries, so good-quality superconductors have weak joints. It is in a state where it is connected by a part. Therefore, characteristics such as critical current density, which are important in practical use, are strongly controlled by the properties of the joint.

As a method of improving the critical current density by improving the bonding at the crystal grain boundaries, (1) using a fine and uniform raw material powder and sintering at a relatively low temperature to obtain a clean and well-matched grain boundary. (2) A method of improving grain boundaries by aligning crystal orientations during processing, (3) A method of growing a superconducting phase from a molten state to produce oriented ceramics and improving bonding at grain boundaries Etc. have been reported.

Of these methods, the method (1) has difficulty in obtaining a grain boundary with good consistency over the entire bulk ceramics. The methods (2) and (3) inevitably complicate the manufacturing process and make the method difficult. This is not always a preferred method because of the increased production cost.

[Problems to be Solved by the Invention] As described above, the conventional technique has a problem that the manufacturing process becomes complicated in order to manufacture a superconducting ceramic having a high critical current density.

The present inventors have earnestly studied a method of manufacturing a superconducting ceramic having a high critical current density relatively easily without requiring such a complicated manufacturing process, and have completed the present invention.

An object of the present invention is to provide a superconducting ceramic having a high critical current density by a relatively easy manufacturing method.

[Means for Solving the Problems] That is, the present invention preliminarily sinters a molded body of a raw material powder comprising a component containing yttrium, barium, and copper, and applies a pressure of 200 k
g / cm ^{2 to} 1000 kg / cm ² , at a temperature of 700 ° C to 950 ° C and in an oxidizing atmosphere.However, the temperature rise and fall during heating is performed in an inert atmosphere or a reducing atmosphere. The present invention relates to a method for producing a superconducting ceramic, which comprises heat-treating a sintered product in an oxygen atmosphere.

 Next, the present invention will be described in more detail.

Raw material powder used in the present invention, yttrium, barium, uses a component containing copper, e.g., high purity Y ₂ O ₃ as starting _{material, BaC 2 O 4 · H 2} O, CuC 2 O 4 · 1 / When 2H ₂ O is used, it is obtained by preliminarily sintering (for example, 900 ° C. for 3 hours) in a stream of oxygen a mixture obtained by sufficiently mixing these using a wet ball mill. However, the present invention is not limited to the raw material powder obtained by such a method, and any fine powder having the above components and having a uniform composition can be used in the present invention. Further, the composition ratio of the raw material powder to be used is a stoichiometric amount so as to be a constituent ratio of the final product.

In the present invention, the raw material powder is molded under pressure, and the molded body is pre-fired. Although the conditions at this time are not particularly limited, it is usually, for example, 700 to 1000 ° C., preferably 800 to 900 ° C. for 2 to 5 hours under an oxygen atmosphere. Any conditions may be used as long as a sintered body free from problems such as cracking during sintering can be obtained. By performing the preliminary firing in this manner, carbon and the like remaining in the raw material molded body can be removed.

In the present invention, it is essential that the pre-baked product is heated and held under pressure and sintered. The conditions for this pressurization and heating are as follows: pressure 200 kg / cm ^{2 to} 1000 kg / cm ² , temperature 700 ° C to 950 ° C
Range. In the present invention, at least the pressurizing and heating are performed under an oxidizing atmosphere in order to prevent melting during sintering, but the pressurizing and heating time at this time is 0.5 to 2 hours,
Usually, about one hour is sufficient. Further, in the present invention, this is performed in an oxidizing atmosphere during the heating and pressurizing and holding as described above, but the temperature rise to a predetermined heating temperature, and the cooling after the heating and pressurizing and holding are performed in an inert atmosphere or It is preferred to do this in a reducing atmosphere. If the temperature increase and decrease during heating and pressurization are performed, for example, in an oxidizing atmosphere, the resulting ceramics will absorb a little oxygen, making it difficult to obtain dense ceramics.

Through the heating and pressurization holding process under these conditions, the heat treatment in an oxygen atmosphere is followed by high-efficiency phase transformation into orthorhombic, which is a superconducting phase, to obtain high-quality superconducting ceramics. Characteristic of the method.

The heat treatment after the heating / pressurizing step is performed in the presence of oxygen, for example, in an oxygen atmosphere at 400 ° C. to 700 ° C. for 20 to 30 hours. This heat treatment step is also effective for removing residual stress in the obtained ceramics. By this heating / pressing / heat treatment process, the sintered body has a superconducting phase structure, the density is improved and the structure is dense, and a clean and consistent crystal grain boundary is formed. . Therefore, a superconducting ceramic having a high critical temperature and a high critical current density can be obtained.

In the present invention, the above-mentioned sintering method by heating and pressing may be any of a normal hot isostatic pressing method and a hot pressing method. The pressure is less than 200 kg / cm ² in the pressure sintering, the powder is not densified, also not observed effect of pressure sintering, observed the effect of pressure increase exceeds 1000 kg / cm ² Not so desirable. The pressure sintering temperature is 700 ℃
If it is less than 950 ° C., there is no effect of improving the critical current density.

[Effects of the Invention] In the present invention, since the sintered body is manufactured in a pressure sintering-heat treatment step different from the conventional one, the sintered body has a superconducting phase structure, and the density is improved. The organization becomes dense,
In addition, since a clean and well-matched crystal grain boundary is formed, a superconducting material having a high critical temperature and a high critical current density can be obtained.

[Examples] Hereinafter, the present invention will be described in more detail by way of examples, but the present invention is not limited thereto.

Example _{1 3N, Y 2 O 3,} BaC 2 O 4 · H 2 O, the _{CuC 2 O 4 · 1 / 2H} 2 O using,
Each was weighed so as to have a YBa ₂ Cu ₃ O ₇ —Y composition, and crushed and mixed by a wet ball mill for 12 hours. Thereafter, the mixture was temporarily calcined in an oxygen stream at 900 ° C. for 3 hours to obtain a mixed powder.
After molding this powder into a pellet,
Preliminary baking was performed at 3 ° C. for 3 hours. This calcined product is heated to a predetermined temperature under an argon atmosphere, and then heated under an oxygen atmosphere.
The temperature was maintained at 935 ° C. and 550 kg / cm ² by heating and pressurizing for 1 hour, and the temperature was lowered to room temperature under an argon atmosphere. The obtained pellets were subjected to a heat treatment at 935 ° C. for 10 minutes and then at 500 ° C. for 24 hours in an oxygen stream. The obtained sintered body was confirmed to be a superconducting single phase by powder X-ray diffraction measurement. This sintered body has a density
6.05 g / cm ³ , the critical temperature for superconductivity was 93 K, and the critical current density was 510 A / cm ² at a temperature of 77 K.

Example 2 The hot-pressed pellets obtained in the same manner as in Example 1 were subjected to a heat treatment at 500 ° C. for 24 hours in an oxygen stream.
X-ray diffraction measurement confirmed that the obtained sintered body was a single superconducting phase. This sintered body has a density of 6.05 g / cm ³ , a superconducting critical temperature of 95 K, and a critical current density of 77 A at 700 A / cm ^2.
Met.

Comparative Example 1 The powder obtained in the same manner as in Example 1 was formed into a pellet, and then prefired in an oxygen stream at 900 ° C. for 3 hours. This was hot-pressed in an oxygen stream at 935 ° C. and 900 kg / cm ² for 1 hour. The resulting pellets are placed in an oxygen stream for 500
° C, 24 hours, then 935 ° C, 10 minutes, then 500 ° C,
Heat treatment was performed for 24 hours. The obtained sintered body was confirmed to be a superconducting single phase by powder X-ray diffraction measurement. This sintered body had a density of 6.15 g / cm ³ , a critical temperature of superconductivity of 81 K, and a critical current density of 4 A / cm ² .

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-64-76953 (JP, A) JP-A-63-310764 (JP, A) JP-A 64-24066 (JP, A) (58) Field (Int.Cl. ⁶ , DB name) C01G 1/00-57/00 H01L 39/00-39/24 H01B 12/00

Claims (1)

(57) [Claims] 1. A pre-fired molded body of a raw material powder comprising a component containing yttrium, barium and copper, and a pressure of 200 kg / cm ²
Up to 1000 kg / cm ² , temperature 700 ° C to 950 ° C and in an oxidizing atmosphere, but heating and cooling were performed under an inert atmosphere or a reducing atmosphere, and were sintered by heating and holding under pressure. A method for producing a superconducting ceramic, comprising subjecting a material to a heat treatment in an oxygen atmosphere.