JPH0738512B2 - Method for manufacturing plate-shaped shield material - Google Patents

Description

The present invention relates to a method for manufacturing a plate-shaped shield material.

[Conventional technology and its problems] In devices using strong electromagnetic fields such as motors, transformers, magnetic levitation trains, MRI-CT devices (nuclear magnetic medical diagnostic devices), and magnetic separators, magnetic flux leaks to the outside. It is feared that this may cause malfunction of the electric and electronic equipment and may have a harmful effect on the human body. Therefore, in order to prevent the magnetic flux from being emitted to the outside in the above equipment, and to shield the magnetic flux from the outside in the precision magnetic measurement equipment, take measures to cover the equipment with a magnetic material such as an iron plate. Has been. However, because of this, the size of the entire device is increased and the weight of the device is increased, which poses a problem in practical use.

Shielding technology using the Meissner effect of superconductors has been put to practical use in some superconducting devices against such problems, but liquid He is required as a refrigerant because a metal superconductor is used as the shielding material, which is economical. There is a drawback that the range of use is restricted.

By the way, in recent years, it becomes superconducting at liquid nitrogen temperature (77K) (Ln
_1-x Sr _x ) CuO ₄ , (Ln _1-x Ba _x ) ₂ CuO ₄ , LnBa ₂ Cu ₃ O ₇ , LnBa _2-x S
_Rx Cu ₃ O ₇ etc. (however, Ln is Y, Sc or a rare earth element) has been found as an oxide superconductor having a layered perovskite structure. As described above, plastic working cannot be performed, and it is difficult to industrially manufacture an effective shield material. Therefore, it has been attempted to process this oxide superconductor by using a PVD method such as a sputtering method, but this involves scattering the constituent elements in a vacuum and forming a film on the support material for a long time. Since it is a method of precipitating in, productivity is poor, and powder is molded,
Alternatively, an attempt has been made to form a paste and print it on a support material by thick film printing and sinter, but there are drawbacks in that the process is not always simple and a sufficient shielding effect cannot be obtained. It is thought that this is because individual particles have different superconductivity, some of them are non-superconducting, and many non-superconducting parts such as grain boundaries and holes are present. There is.

[Means and Actions for Solving Problems]

The present invention has been made in view of such circumstances, and an object of the present invention is to provide a small-sized, lightweight, inexpensive plate-like shield material manufacturing method utilizing the Meissner effect in an oxide superconductor.

That is, the present invention, the oxide superconductor or a precursor thereof is blended in a predetermined amount, and after melting this in an oxygen-containing atmosphere, this melt is desired to be cooled to at least 950 ° C at a rate of 10 ° C / sec or more. It is characterized in that it is molded into the shape of, and then this molded body is heat-treated in an oxygen-containing atmosphere at 500 ° C. or higher for 10 minutes or longer.

In the present invention, an oxide superconductor such as YBa ₂ Cu ₃ O ₇ or a precursor thereof is used as the melting raw material, and the latter precursor is an oxide or carbonate of an element constituting the above superconductor. Inorganic compounds such as nitrates, organic compounds such as alkoxides and complex salts, or metal or alloys of the constituent elements are used.

The above precursor will be specifically described by taking a YBa ₂ Cu ₃ O ₇ superconductor as an example. Y is Y ₂ O ₃ , Y (NO ₃ ) ₃ , Y (CH ₃ CO ₃
O) ₃ , Y alone, Ba is Ba (OH) ₂ , Ba (NO ₃ ), BaCO ₃ , Ba soap, Cu is Cu ₂ O, CuO, Cu (OH) ₂ , CuSO ₄ , Cu (NO ₃ ) ₂ , Acetyl acetate, Cu powder, Cu-Ba and the like.

It is also possible to mix a predetermined amount of the above-mentioned raw materials and calcinate this mixture to obtain a mixture of oxides or a superconductor oxide, which is processed into powder or rod-shaped bodies or blocks for use.

In the present invention, the above raw materials are heated in a crucible or the like to 1200 ° C. or higher to be melted, and the heat source at this time is electricity,
Infrared rays, electron beams, laser light, etc. are applied. The rod-shaped body or the like can be melted by directly applying a beam of infrared rays or the like thereto.

In the present invention, the reason for melting the raw material and forming it into a plate is
This is because the blended components are homogenized in a short time, and a homogeneous dense body close to the theoretical density can be obtained. When the melting is performed in an O ₂ -containing atmosphere, O ₂ deficiency of the superconductor is prevented, and the heat treatment condition of the subsequent process can be performed at a low temperature in a short time. When the partial pressure of O ₂ in the atmosphere is 5 atm or more, particularly 15 to ₂₀₀ atm, the supply of O ₂ is sufficient and the properties such as J _c are further improved.

The reason for cooling the melt to at least 950 ° C. at a cooling rate of 10 ° C./sec or more in the molding process in the present invention is
When the crystal structure of the obtained molded body is made dense and the superconductor of YBa ₂ Cu ₃ O ₇ is taken as an example, the above superconductor has Y ₂ O ₃ , Cu ₂ O and BaCu.
This is because phase separation into O _{2 and the} like is suppressed, and even if phase separation occurs, each phase is finely dispersed and can be easily homogenized in the heat treatment in the subsequent step. The melt is cooled by pouring or contacting the melt with a mold or a cooler, and the cooling rate thereof is particularly preferably 50 ° C./sec or more.

In the present invention, the molded body obtained by cooling the melt is 500 ° C.
The reason why the heat treatment is performed in the above O ₂ -containing atmosphere is to maximize the formation of the superconductor phase in the molded body and to remove harmful thermal strain during the cold molding.

In the above heat treatment, the temperature may be maintained at a predetermined heat treatment temperature directly from the temperature at which the melt is cooled at a predetermined rate, or may be once again cooled to room temperature and then reheated. When the molded product is finished to a desired size and then heat-treated, additional effects such as removal of processing strain can be obtained.

In the present invention, the heat treatment described above is performed at a temperature of 500 ° C. or higher, preferably 500 to 950 ° C., and 10 minutes or longer, preferably 1 to 24.
It is practical for the time of H to be carried out in an atmosphere in which the O ₂ partial pressure is 0.2 atm or more, particularly preferably 1 to 5 atm. In the above, if the O ₂ partial pressure in the atmosphere is less than 0.2 atm, it is not possible to obtain a sufficient shield effect.

The shield material of the present invention can be molded all at once using a mold having a predetermined shape, but may be cut into a desired shape from a large molded body. In addition, the superconductor as a tile-shaped molded body,
This can be used by being joined to a metal plate, a ceramic plate, a plastic plate or the like. Al other than Fe as a metal plate,
When Cu, Ni or their alloys are used, the electromagnetic shield effect can be simultaneously provided. For joining with a metal plate, it is desirable to use a metal brazing material such as solder to provide electrical and thermal conduction.

The shield material of the present invention is used as a molded body as described above, surrounding a magnet or an electric / electronic device, and in order to have a shielding effect on this, the molded body is cooled to a temperature below its inherent critical temperature (Tc). Therefore, when Tc is equal to or lower than room temperature, the molded body is used by being disposed in the flow path of the cooling medium or the inner and outer surfaces of the cooling pipe body.

〔Example〕

 Next, the present invention will be described in detail with reference to Examples.

Example 1 Er ₂ O ₃ , Y ₂ O ₃ , BaCO ₃ , and CuO are Er + Y: Ba: Cu in an atomic ratio of 1: 2 :.
3 (however, Er: Y = 1: 4) was mixed, put in a platinum crucible and heated and melted at 1,360 ° C in the atmosphere, and then poured into a 100 mm ^□ × 3 mm ^h iron mold. It was shaped into tiles and then heat-treated under various conditions. The cooling rate during melt cooling was adjusted to various rates by using a cooling medium together with the mold.

Conventional Example 1 The same raw material as that used in Example 1 was calcinated at 900 ° C. for 6H in the air, and then the powder obtained by crushing this was press-molded,
This compact was heated and sintered in an O ₂ stream at 950 ° C. for 2 hours and 700 ° C. for 24 hours.

The relative density and the magnetic flux density at 77 K in liquid nitrogen of each of the samples thus obtained were measured, and the shield efficiency was calculated by the following formula.

X: Magnetic flux density when the sample is sandwiched between the electromagnet and the glass meter.

X ₀ : Magnetic flux density without sandwiching the sample (750 gauss).

The obtained results are shown in Table 1 together with the production conditions.

As is clear from Table 1, the method products (1 to 4) of the present invention have higher relative density and shield efficiency than the conventional method product 8.

Among the comparative method products, the one having a slow melt cooling rate (5), the one having a short heat treatment time (6), and the one having a low heat treatment temperature (7) all showed a low shield efficiency.

Example 2 Y ₂ O ₃ , BaCO ₃ , SrCO ₃ and CuO were added to Y: (Ba + Sr): Cu (provided that Ba: S
(r = 4: 1) is mixed in an atomic ratio of 1: 2: 3, then this is calcinated at 920 ° C for 6H in the air, crushed and molded into a rod, then 800 ° C for 6H. Heat and sinter, then suspend this sintered body in a pressure vessel, apply infrared rays to the lower end of this sintered body to gradually melt from the lower end, and melt this melt at 900 ° C.
It was dripped into an iron mold of 100 mm ^□ × 3 mm ^h which was heated.
After the dropping is completed, the mold is cooled to cool the resulting molded body to 500 ° C., and then the solidified body is cooled to 800 ° C. in an O ₂ atmosphere of 2 atm.
H heat treated. The atmosphere in the pressure vessel and the cooling rate of the molded body were variously changed.

The results are shown in Table 2 together with the production conditions.

As is clear from Table 2, the method products (9 to 12) of the present invention are
Both the relative density and the shield efficiency are higher than those of the conventional method (8 in Table 1).

Among the comparative methods, products without heat treatment (13) and products without O ₂ gas in the atmosphere of heat treatment (14)
In both cases, the shield efficiency is significantly reduced.

〔effect〕

As described above, according to the present invention, it is possible to easily manufacture a small-sized, lightweight, plate-shaped shield material that effectively operates at the liquid nitrogen temperature and has a high shield efficiency, and therefore an industrially significant effect is exhibited.

Claims (2)

[Claims] 1. A predetermined amount of an oxide superconductor or a precursor thereof is mixed and melted in an oxygen-containing atmosphere, and then the melt is cooled at a rate of 10 ° C./sec or more to at least 950 ° C. 1. A method for producing a plate-shaped shield material, which is characterized by molding into the shape of, and then heat-treating this molded body in an oxygen-containing atmosphere at 500 ° C. or higher for 10 minutes or longer. 2. The production of a plate-shaped shield material according to claim 1, wherein the oxygen partial pressure in the oxygen-containing atmosphere is 5 atm or more during melt cooling and 0.2 atm or more during heat treatment. Method.