JPH0311044B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to a method for producing a PbMo ₆ S ₈ compound superconducting wire.

[Prior art] In recent years, there has been an increasing demand for magnets with higher magnetic fields in fields such as nuclear fusion, high-energy physics research, and condensed matter research, and the development of superconducting magnets that generate even higher magnetic fields is desired. . The wire rods of superconducting magnets currently in practical use are Nb-Ti based alloys, Nb 3 Sn based compounds, or Nb ₃ Sn based wires.
Although it is a V ₃ Ga system, its critical magnetic field is said to be about 11 T (Tesla) and about 22 T, respectively, at 4.2 K, so the maximum magnetic field obtained is the current capacity,
Considering efficiency, it was about 14T. Therefore, if higher fields are to be achieved, materials with higher critical fields are required.

Therefore, Mo ternary chalcogenides called Siebrel phase compounds are attracting attention, and among them, PbMo ₆ S ₈ (Siebrel phase lead molybdenum sulfide) based compounds have a high critical magnetic field of more than 50T at 4.2K. It is said that if a magnet using this compound is put into practical use, it will become possible to create an ultra-high field magnet that can generate a critical magnetic field of 20 to 30 T.

Conventionally, the method for producing PbMo ₆ S ₈ compounds is as follows:
Powder consisting of each component of PbMo ₆ S ₈ , e.g.
Mixed powder of Mo, Pb, MoS ₂ , etc. is mixed with Ta or
After being placed in a Nb tube and processed, it is heat-treated to internally generate PbMo ₆ S ₈ compounds. However, because this method does not produce a dense compound layer, the critical current density (Jc) under the application of a magnetic field is only extremely low. Therefore, a method was considered in which the mixed powder was sintered using a hot press in order to achieve densification, and the Jc characteristics were improved. However, this method could only produce bulk-shaped samples, and it could not be used as a winding material for superconducting magnets. It was not possible to produce a useful long wire.

[Summary of the Invention] In view of the above points, an object of the present invention is to provide a method for producing a PbMo ₆ S ₈ compound superconducting wire having excellent electrical properties.

That is, this invention can be applied to Mo material, Mo sulfide material, Pb material,
A composite material is obtained by mixing raw materials selected from Pb sulfide material and sulfur in a ratio such that a PbMo ₆ S ₈ compound is generated during subsequent heat treatment, or by filling a barrier material with PbMo ₆ S ₈ material. process, reducing the cross-section of the obtained composite, and heating the composite after cross-section reduction at 800-1080°C under a pressure of 100-2000 Kg/ ^cm2 .
The process consists of heat treatment at a temperature range of
This is a method for manufacturing _{PbMo6S8 -} based compound superconducting wire.

The heat treatment temperature shows its effect from 800°C, and the higher the temperature, the more desirable it is, but if it exceeds 1080°C, Cu, which is a stabilizing material, will melt, which is not desirable. Furthermore, the characteristics improve from a (static) pressure of 100 Kg/cm ^{2 ,} and the higher the pressure, the better, but the best is 2000 Kg/cm ² .

In addition, in this invention, as a _{PbMo6S8 type} compound, for example, Mo such as _{PbMo5.1S6 , PbMo6S7} , _etc.
Although there are compounds with varying S values, these will be collectively referred to as PbMo ₆ S ₈ compounds. moreover,
As M′, for example, Ga, Bi, Ba, Sn, La, Ho,
Added small amounts of Eu, Gd, Lu, Y, Nd, etc.
PbM′xMo ₆ S ₈ compounds are also included in PbMo ₆ S ₈ -based compounds.

[Embodiments of the invention] The present invention will be explained below with reference to Examples.

Example 1 Mo, Pb, and the constituent components of PbMo ₆ S ₈ compounds
MoS ₂ powder (particle size and purity are 3 μm and
99.9%, 40 μm and 99.9%, 2 μm and 99%) in a ratio of 5:2:7 as uniformly as possible and molded using a press to form Mixed Body 1 (see figure). This mixture 1 was combined with a Ta tube 2 as a barrier material and a Cu tube 3 as a stabilizing material, and the cross section was reduced by cold drawing, and the wire was drawn to a diameter of 1.0 mm to a length of 30 mm.
A wire rod of m was obtained. The figure is a cross-sectional view of this wire. The process showed extremely good workability with no wire breakage.

Next, this wire was wound into a ring shape with a diameter of 300 mm, and this was placed in a hot isostatic pressure device, and heat treated at 800 to 1080° C. for 0.5 hour under hydrostatic pressure of 100 to 2000 Kg/cm ² . Inert argon gas was chosen as the pressure medium. A portion of the obtained wire was sampled and its critical current (Ic) characteristics were measured at liquid helium temperature (4.2K) and under an applied magnetic field (maximum 12T). As a result, a very high Ic of 143A was obtained at 12T, which is about 10 times higher than that of a wire with the same structure that was heat-treated without applying conventional pressure. Furthermore, when compared with a bulk sample subjected to the same heat treatment conditions using a conventional hot press, the critical current density was improved by about 50%.

In addition, the conventional pressure-free wire rod PbMo ₆ S ₈
The packing density of these compounds is up to 60%, but those heat-treated under hydrostatic pressure reach about 80%, so the Ic
It seems that the characteristics have been improved. Also, this wire has a Jc ratio of 10T and 12T: Jc(10T)/Jc(12T)
is approximately 1.3, compared to 2.1 for typical practical Nb ₃ Sn-based wire materials.
2.4, and in higher magnetic fields (in the case of the wire in this example, magnetic fields of 16T or higher)
It was shown that it has a higher Jc than Hb ₃ Sn-based wire.

Therefore, it is considered to be effective as a winding material for ultra-high magnetic field magnets with a generated magnetic field of 16 T or more.

Example 2 Mo, which is a constituent of the PbMo ₆ S ₈ compound,
PbS, MoS ₂ powder (particle size and purity are Mo, PbS,
As for MoS ₂ , as in Example 1, PbS (40 μm and 99%) was mixed as uniformly as possible in a ratio of 3:1:3, and this was pressed to form pellets. This pellet is vacuum sealed in a quartz tube, and
Heat treatment is performed at 1200℃ to generate PbMo ₆ S ₈ compound. Next, the pellets were crushed to obtain a powder, which was then re-pressed to form a mixture. This mixture was combined with a Ta tube as a barrier material and a Cu tube as a stabilizing material, and the diameter was 1 mm as in Example 1.
The wire was drawn to Furthermore, heat treatment under hydrostatic pressure was performed under the same conditions as in Example 1. The Ic characteristics of this wire were also measured, and the Ic was about 20% higher at 12T than the wire of Example 1.

As described above, this example gave very good results, and therefore the wire according to the present invention is extremely effective as a winding material for high magnetic fields.

In addition, in the above Example 1, the mixture 1 in the figure was
Although it was manufactured from Mo, Pb, and MoS ₂ powders, it is possible to use constituent materials other than these powders regardless of the form of the constituent material, such as using a Pb thin plate instead of Pb powder. Furthermore, the combination of constituent materials of the mixture 1 is not limited to the above. That is, mixture 1
In addition to the above combinations, Mo,
PbS, MoS ₂ ; Mo, Pb, PbS; Mo, Pb, PbS,
MoS ₂ ; Pb, Mo, S, etc. in the subsequent heat treatment process
Any combination that produces a PbMo ₆ S ₈ compound is effective.

Furthermore, as a constituent material of Mixture 1, it was reacted and produced in advance by heat treatment, crushed and re-powdered.
The use of the PbMo ₆ S ₈ compound is used to reduce the sulfur pressure inside the Ta tube, which is the barrier material shown in the figure, to prevent sulfurization of the barrier material, and to improve the superconducting properties of the PbMo ₆ S ₈ compound that is finally produced. It is extremely effective, offering immense advantages as it facilitates achieving the required stoichiometry.

In addition, in the above example, the PbMo ₆ S ₈ compound wire is made into a single-fiber wire, but combining it into a multi-filament wire and twisting it is extremely effective in reducing AC loss and stabilizing the magnet. It is effective and can be easily performed using the same method as conventional Nb ₃ Sn wire.

[Effect of the invention] As explained above, according to this invention, dense
It has become possible to generate PbMo ₂ S ₆ compounds and to obtain superconducting long wire rods of PbMo ₆ S ₈ compounds that have excellent superconducting properties that could not be obtained conventionally, making it possible to produce PbMo ₂ S 6 compounds efficiently. This makes it possible to generate ultra-high magnetic fields of 16 T or more, which were previously impossible to generate, and will help promote nuclear fusion and high-energy physics research.

[Brief explanation of the drawing]

The figure is a cross-sectional view of a composite rod after cross-section reduction processing of a wire rod in an embodiment of the present invention. 1...Mixture, 2...Ta tube, 3...Cu tube.

Claims (1)

[Claims] 1 Raw materials selected from Mo material, Mo sulfide material, Pb material, Pb sulfide material, and sulfur are used in subsequent heat treatment.
The process of obtaining a composite by filling a barrier material with a mixed material or _PbMo6S8 material blended in a proportion such that a PbMo _{6 S 8 compound} is generated, a process of reducing the cross section of the obtained composite, and a process of reducing the cross section. 100 for the reduced composite
A method for producing a PbMo ₆ S ₈ compound superconducting wire comprising a step of heat treatment at a temperature of 800 to 1080°C under a pressure of ~200 Kg/cm ² .