Method for producing conductive diamagnetic material and conductive diamagnetic material

Abstract

To provide a method for producing a conductive diamagnetic material more suitable for industrial application or the like than conventional materials.SOLUTION: A method for producing a conductive diamagnetic material includes a low-pressure heating step of heating samarium under a low-pressure environment. According to each viewpoint of the present invention, it becomes possible to provide a conductive diamagnetic material that can realize superconducting transition temperature exceeding 120[K] of a bismuth-based copper oxide superconductor known as a conventional superconductive cable or 130[K] of a mercury-based copper oxide.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a method for producing an electrically conductive diamagnetic material and to an electrically conductive diamagnetic material. [Background technology]

[0002] Although conductive materials, including superconducting materials, have been developed in various material systems, industrial applications of superconducting materials have remained limited. The reasons for this include: (1) the superconducting transition temperature (Tc) at atmospheric pressure is low, at most 130 K (see Non-Patent Document 1), so superconducting properties can only be exhibited in cryogenic environments; (2) the difficulty of fabricating wire rods has prevented their widespread use in power transmission lines and coils, which are considered important application fields; and (3) the heterogeneity of the material structure and organization makes it difficult to fabricate thin films, requiring advanced processing techniques for fabricating devices.

[0003] Bismuth-based copper oxide superconductors with a superconducting transition temperature of approximately 120 K have been known as superconducting cables (Non-Patent Document 2). Figure 4 shows an example of the structure of a conventional superconducting cable. Figure 4(a) is a diagram illustrating a cross-section of a superconducting cable. Figure 4(b) is a diagram illustrating a perspective view of a cable core. Figure 4(c) is a diagram illustrating a cross-section of the conductor layer of a cable core. A cable with the structure shown in Figure 4 is known as a three-core superconducting cable, and is expected to be used in situations requiring low voltage and high current.

[0004] Referring to Figure 4(a), a conventional superconducting cable 101 has a multi-layer structure. From the outside, these layers are a corrosion protection layer 103, a corrugated outer pipe 105, a heat insulating layer 107, and a corrugated inner pipe 109. A three-core cable core 111 is housed inside the corrugated inner pipe 109, and liquid nitrogen 113 is filled between the corrugated inner pipe 109 and the cable core 111. The cable core is further comprised of, from the outside, a protective layer, a shield layer (superconducting layer), an insulating layer (PPLP), a conductor layer (superconducting layer), and a former. The conductor layer is made of a wire material, a superconducting filament Bi2223, which is a bismuth-based copper oxide superconductor, housed in silver.

[0005] The structure of the cable core 111 will be described with reference to FIG. 4(b). The cable core 111 includes, concentrically from the outside, a protective layer 121, a shielding layer 123, an insulating layer 125, a conductor layer 127, and a former 129. The shielding layer 123 is in a superconducting state. The insulating layer 125 is made of PPLP (registered trademark, Polypropylene Laminated Paper) impregnated with liquid nitrogen. The conductor layer 127 is formed by winding a Bi2223 wire 131 around a former 129. The former 129 is made of twisted copper wire.

[0006] 4(c), the structure of the Bi2223 wire 131 will be described. The Bi2223 wire 131 has a structure in which a plurality of superconducting filaments 135 are housed inside a silver wire 133.

[0007] FIG. 5 illustrates a production process for the Bi2223 wire 131, which is part of the cable core 111. This process mainly consists of a powdering process ST101 in which the material is powdered and a processing process ST103 in which the powder is processed into a wire. First, in the powdering process ST101, the material is repeatedly sintered (ST105) and crushed (ST107). Next, in the processing process ST103, the precursor powder is first filled into a silver pipe for segments (ST109) and subjected to single-filament wire drawing (ST111). Multiple such wires are fitted into holes in a silver pipe for sheathing (ST113). Next, multi-filament wire drawing is performed (ST115), followed by rolling and incineration (primary rolling ST117 and primary incineration ST119). The wire is further rolled and incinerated (secondary rolling ST121 and secondary incineration ST123) to produce the Bi2223 wire 131 that forms the conductor layer of the cable core. [Prior art documents] [Non-patent literature]

[0008] [Non-Patent Document 1] A. Schilling et al., Nature (London) 363, 56 (1993). [Non-patent document 2] H. Maeda et al.,Jpn. J. Appl. Phys. 27, L209 (1988). Summary of the Invention [Problem to be solved by the invention]

[0009] However, the superconducting cable described in Patent Document 1 has a complicated structure that is fabricated through the above-mentioned process, which means that it is very costly to produce a wire and its range of application is limited.

[0010] Therefore, an object of the present invention is to provide a method for producing a conductive material that is expected to produce superconducting materials that are more suitable for industrial applications than conventional methods. [Means for solving the problem]

[0011] A first aspect of the present invention is a method for producing a conductive material, which includes a low-pressure heating step of heating samarium in a low-pressure environment.

[0012] A second aspect of the present invention is the method for producing an electrically conductive diamagnetic material according to the first aspect, wherein the samarium is heated to 200° C. or higher in the low pressure heating step.

[0013] In a third aspect of the present invention, in the low pressure heating step, samarium is added at a concentration of 2×10 -2 Heat at a low pressure of 1 Torr or more.

[0014] A fourth aspect of the present invention is an electrically conductive diamagnetic material, characterized in that the electrically conductive diamagnetic material is samarium, at least a part of whose laminate structure has a hexagonal close-packed structure.

[0015] In addition to the above, power transmission lines, magnetic shields, electronic devices, or apparatuses utilizing the magnetic levitation phenomenon, which use the conductive material according to the third aspect of the present invention, are also envisioned as aspects of the present invention. [Effects of the Invention]

[0016] According to each aspect of the present invention, it is possible to provide a conductive diamagnetic material that is expected to achieve a maximum superconducting transition temperature of 165 K, exceeding the 120 K of bismuth-based copper oxide superconductors and the 130 K of mercury-based copper oxide superconductors known as conventional superconducting cables. If it becomes possible to provide a material that exhibits superconducting properties more easily than ever before under atmospheric pressure, it will be possible to expand the industrial application fields of superconducting materials.

[0017] Furthermore, according to each aspect of the present invention, it is expected that a metallic material with a simple composition consisting of a single element can be provided as a high-temperature superconducting material. Therefore, it is easy to form wires or thin films without the complicated processes used in the past. Therefore, it is expected that superconducting cables, superconducting coils, superconducting devices, etc. can be provided at low cost.

[0018] The inventors have discovered that samarium, which was previously thought not to be a superconducting substance, exhibits superconductivity under a high-pressure environment of 200,000 atmospheres. However, the present invention is expected to provide an even more revolutionary superconducting material in that it can provide samarium as a superconducting material that can exist under atmospheric pressure. [Brief explanation of the drawings]

[0019] [Figure 1] 10A and 10B are diagrams illustrating the temperature dependence and external magnetic field strength dependence of the magnetization of the sample of this example. [Figure 2] FIG. 2 is a diagram showing measurement results of other characteristics of the sample of FIG. 1. [Figure 3] FIG. 10 is a diagram showing the dependence of magnetization per unit weight of a sample on the annealing temperature during sample preparation. [Figure 4] FIG. 1 is a diagram showing an example of the structure of a conventional superconducting cable. [Figure 5] 1 is a diagram illustrating a part of a conventional superconducting cable production process. DETAILED DESCRIPTION OF THE INVENTION

[0020] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings. However, the present invention is not limited to the following embodiments. [Example]

[0021] In this example, the samples to be measured were prepared by heating samarium in a low-pressure environment (an example of the "low-pressure heating step" in this claim). Specific sample preparation conditions are shown in Table 1. The pressure at which each sample was sealed in a glass tube was 2 × 10 -2 The vacuum level was set to 0 [Torr] or higher. Table 1 also lists the value of the slight remaining magnetic field, M [emu / g] @ H = 1 [Oe], when set to 0 [Oe].

[0022] [Table 1]

[0023] The prepared samples were analyzed to detect superconductivity by magnetic measurement. Specifically, the magnetization M under a DC magnetic field was observed using a Superconducting Quantum Interference Device (SQUID) magnetometer. The analytical results of the prepared samples are described below.

[0024] FIG. 1 illustrates the temperature dependence and external magnetic field dependence of the magnetization M of the sample of this example. FIG. 1(a) shows the measurement results when the external magnetic field strength H was set to 50 to 20 k[Oe], and FIG. 1(b) shows the measurement results when the external magnetic field strength H was set to 1 to 400 [Oe]. The horizontal axis is the measurement temperature [K], and the vertical axis is the magnetization M [emu]. Measurements were performed after zero-field cooling (ZFC) from 250 [K]. The sample used for measurement in FIG. 1 was 2×10 -2 The film was fabricated by heating to 578°C in a low-pressure environment with a vacuum of 1 Torr or more and annealing for 1.5 hours.

[0025] As shown in Figure 1(a), at an external magnetic field strength H = 50 Oe, M is nearly equal to 0 in the temperature range below Tc, which indicates the superconducting transition temperature, and above approximately 120 K. This indicates that most of the samples exhibit perfect diamagnetism, a characteristic of superconductivity. In contrast, as the magnetic field strength increases, the cubic site anomaly near 15 K becomes larger. The hexagonal site anomaly near 110 K also becomes larger. Furthermore, the temperature range in which diamagnetism is exhibited narrows. Although there is a temperature range in which diamagnetism is exhibited below an external magnetic field strength H = 3 kOe, at an external magnetic field strength H = 4 kOe, the value of M at T < 120 K becomes larger than the value at 120 K, and the temperature range in which diamagnetism is exhibited disappears.

[0026] In addition, Figure 1(b) shows anomalies around T = 5, 14, and 20 K. The sample weighed 155.5 mg. The magnetization M = 7 × 10 at an external magnetic field strength H = 1 Oe. -3[emu]=4.5×10 -2 Furthermore, as shown in Figure 1(c), when the temperature dependence of the magnetization M of the same sample at an external magnetic field strength H = 1 Oe was extensively confirmed, signals suggesting superconducting properties were observed even at T = 135 K and 165 K.

[0027] Figure 2 shows the results of measuring other characteristics of the sample in Figure 1. Figure 2(a) shows the relationship between the external magnetic field strength H and the temperature Tc that is suggested to be the superconducting transition temperature. Figure 2(b) shows the DC magnetic field dependence of the magnetization M of the sample in Figure 1.

[0028] Referring to Figure 2(a), H = 3 × 10 3 [Oe] and H=3×10 3 This H dependence of Tc is characteristic of superconductors, but for H≦3×10 3 The region in [Oe] indicates the region where the diamagnetic region exists.

[0029] Referring to FIG. 2(b), the magnetization M is determined by the DC magnetic field H DC This is a characteristic of type II superconductors, and the sample in this example shows a minimum value at the lower critical magnetic field H c1 These measurements suggest that the material is a type II superconductor with a superconductivity of ~30 Oe.

[0030] Furthermore, based on the measurement results of other samples according to the present invention, we will discuss the relationship between the annealing temperature and the behavior that appears to be superconducting properties. Figure 3 shows the relationship between the magnetization per unit weight ΔM [emu / g] and the annealing temperature T anneal FIG. 1 shows the [K] dependency.

[0031] Referring to Figure 3, the annealing temperature T anneal The sample with T = 578[℃] was the main Tc = 120[K], which was not the highest value among the samples in this study, but the magnitude of the magnetic shielding effect ΔM was the largest. annealThe sample at 500°C exhibited the highest Tc value of 165K among the samples tested.

[0032] As shown in Figure 3 and Table 1, diamagnetism was confirmed at annealing temperatures of 200°C or higher, but the -3 To increase the probability of diamagnetism of [emu / g] or more, it is preferable that the annealing temperature of the sample is 400°C or higher.

[0033] The present invention provides a superconducting material with wide versatility, which can contribute to technological innovation in technological fields where the use of superconductivity is expected, such as power transmission lines, coils, and magnetic levitation.

[0034] If the material of this example is a material in which superconducting layers and magnetic layers are alternately laminated, it can be applied to superconducting device elements that utilize the Josephson effect, in which a tunnel current flows between superconducting layers sandwiching a very thin layer of about a few nm, or as a magnetic shield. Furthermore, by processing to extract only the superconducting layer, it can be applied to superconducting power transmission lines, etc.

Claims

1. 1. A method for producing an electrically conductive diamagnetic material, comprising: Samarium 2×10-2 A low-pressure heating step is performed in which the material is heated at 200°C or higher in a low-pressure environment with a vacuum of [Torr] or higher. Method for producing conductive diamagnetic materials.

2. An electrically conductive diamagnetic material, A conductive diamagnetic material, characterized in that at least a part of the laminated structure is samarium with a hexagonal close-packed structure.

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