Superconductor, manufacturing method of superconductor, liquid hydrogen level sensor, and liquid hydrogen level gauge

Abstract

To provide a superconducting material that can be used for a liquid hydrogen level meter and that offers a simple manufacturing process and has reproducibility.SOLUTION: The superconductor comprises a metal compound having a molar ratio of magnesium (Mg) and boron (B) of 1:2, does not contain SiC, and has a critical temperature (Tc) of about 32 K to about 34 K at which electrical resistance becomes substantially zero. Thus, a liquid hydrogen level meter that offers a simple manufacturing process and has reproducibility can be realized.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a superconductor, a method for manufacturing a superconductor, a liquid hydrogen level sensor, and a liquid hydrogen level gauge. [Background technology]

[0002] There is a growing global awareness that global warming is a common issue that we must address now and in the future, but a major challenge is the movement toward decarbonization to reduce fossil fuel consumption. One option is the use and utilization of hydrogen. In Japan, the "Basic Policy for the Realization of Green Transformation (GX)" was approved by the Cabinet in February 2023, and the promotion of hydrogen introduction is being touted. However, accurate measurement of the amount of liquid hydrogen is required during its transportation, storage, and consumption.

[0003] Liquid hydrogen is an extremely low-temperature substance with a boiling point of approximately 20 K under normal pressure, and there has been a demand for a material that exhibits superconductivity at temperatures higher than the temperature of liquid hydrogen as a sensor material for a liquid hydrogen level gauge that utilizes changes in electrical resistance. At the beginning of the 21st century, the relatively high-temperature superconductivity of MgB2 (magnesium diboride) was reported as an intermetallic compound, and efforts are underway to develop a liquid hydrogen level gauge using MgB2.

[0004] Patent Document 1 describes an intermetallic compound made of magnesium (Mg) and boron (B) that has a critical temperature (Tc) of 39K at which the electrical resistance becomes substantially zero. Patent Document 2 describes a liquid hydrogen level gauge that is constructed using a long superconductor in which some of the B atoms in MgB2 are replaced with C atoms. Patent Document 3 describes the process of filling one end of a metal sheath with a first powder made of a mixture of Mg and B with an average particle size of less than 2 μm, filling the other end of the metal sheath with a second powder made of a mixture of Mg and B with an average particle size of 2 μm or more and less than 15 μm, and then performing wire drawing and thermal processing to produce a superconducting wire. [Prior art documents] [Patent documents]

[0005] Patent Document 1: Japanese Patent Application Laid-Open No. 2002-211916 Patent Document 2: Japanese Patent Application Laid-Open No. 2000-175034 Patent document 3: Re-table 2014 / 162379 publication Summary of the Invention [Problem to be solved by the invention]

[0006] However, the intermetallic compound described in Patent Document 1 has a high critical temperature (Tc) of 39 K, which is too high for a superconductor to be used in a level gauge for liquid hydrogen, whose boiling point at normal pressure is approximately 20 K.

[0007] In addition, the superconductor in which some of the B atoms of MgB2 are replaced with C atoms, as described in Patent Document 2, has the problem that some of the B atoms must be replaced with C atoms, making the manufacturing method complicated and difficult to achieve reproducibility.

[0008] Furthermore, the superconducting wire described in Patent Document 3 also has a problem in that the manufacturing method is complicated because two types of B having different average particle sizes are used.

[0009] An object of the present invention is to solve the above problems and to realize a superconducting material that can be used in a liquid hydrogen level gauge and that can be manufactured simply and reproducibly. [Means for solving the problem]

[0010] In order to solve the above problems, the present invention provides a superconductor having a critical temperature (Tc) that can be used in a liquid hydrogen level gauge, Magnesium (Mg) And Ho It is composed of a metal compound with uranium (B) in a molar ratio of 1:2, and does not contain SiC. figure, The critical temperature (Tc) at which the electrical resistance becomes essentially zero is 32.4K. The present invention provides a superconductor characterized by the above.

[0011] This configuration makes it possible to realize a superconductor that can be used in a liquid hydrogen level gauge, and that can be manufactured simply and reproducibly. The temperature of liquid hydrogen is 20K at normal pressure, but rises to 30K at 1MPaG. Therefore, a superconductor for a liquid hydrogen level gauge must have a critical temperature (Tc) of at least 31K or higher in order to handle a liquid hydrogen temperature of 20-30K. The applicant has found that a superconductor with Tc of about 32K to about 34K can be realized by mixing magnesium (Mg) 1 part with boron (B) having an average particle size of 17μm to 7μm in a molar ratio of 2 parts to produce MgB2, as described below.

[0012] In order to solve the above problems, the present invention provides Has a critical temperature (Tc) that can be used for liquid hydrogen level gauges A method for producing a superconductor, comprising the steps of: Magnesium (Mg) and, Boron (B) with an average particle size of 17μm to 7μm And A mixing step of mixing the ingredients; a firing step of firing the mixture of Mg and B mixed in the mixing step; of By executing Let MgB2 The present invention provides a method for producing a superconductor, comprising the steps of:

[0013] This configuration makes it possible to realize a superconducting material that can be used in a liquid hydrogen level gauge and that can be manufactured simply and with high reproducibility.

[0014] In order to solve the above problems, the present invention does not contain SiC and is based on Mg and B and are metal compounds with a molar ratio of 1:2. the law of nature, The critical temperature (Tc) at which electrical resistance becomes essentially zero is 32.4K. The present invention provides a liquid hydrogen level sensor comprising a long superconductor and a metal coating covering the surface of the superconductor.

[0015] This configuration makes it possible to realize a liquid hydrogen level sensor that can be used in liquid hydrogen level gauges and is equipped with a superconducting material body that can be manufactured simply and with high reproducibility.

[0016] In order to solve the above problems, the present invention does not contain SiC and is based on Mg and B and are metal compounds with a molar ratio of 1:2. the law of nature, The critical temperature (Tc) at which electrical resistance becomes essentially zero is 32.4K. a liquid hydrogen level sensor having a long superconductor and a metal coating covering the surface of the superconductor; a heater for heating the liquid hydrogen level sensor; a power source for supplying a current to the liquid hydrogen level sensor; a voltmeter for measuring a voltage at the liquid hydrogen level sensor; The present invention provides a liquid hydrogen level gauge comprising:

[0017] With this configuration, it is possible to realize a liquid hydrogen level gauge that can be manufactured simply and with high reproducibility. Effect of the Invention

[0018] The superconductor and the method for manufacturing a superconductor of the present invention make it possible to realize a superconductor which can be manufactured simply and reproducibly, and therefore it is possible to easily realize a liquid hydrogen level sensor and a liquid hydrogen level gauge. [Brief description of the drawings]

[0019] [Figure 1] 1 shows measurement data of the critical temperature (Tc) of a superconductor in Example 1 of the present invention (including comparative data). [Diagram 2] FIG. 2 is a diagram illustrating a liquid hydrogen level sensor according to the first embodiment of the present invention. [Diagram 3] FIG. 2 is a diagram for explaining a liquid hydrogen level gauge in the first embodiment of the present invention. [Figure 4] 1 is a graph showing the relationship between the average particle size of boron and the critical temperature in Example 1 of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS EXAMPLES

[0020] Example 1 of the present invention will be described with reference to FIGS. 1 to 4. FIG. 1 shows the measurement data of the critical temperature (Tc) of the superconductor in Example 1 of the present invention (including comparative examples). FIG. 2 is a diagram for explaining the liquid hydrogen level sensor in Example 1 of the present invention. FIG. 3 is a diagram for explaining the liquid hydrogen level gauge in Example 1 of the present invention. FIG. 4 is a graph showing the relationship between the average particle size of boron and the critical temperature in Example 1 of the present invention.

[0021] (Superconductor) The superconductor in Example 1 can be used for a liquid hydrogen level gauge. The critical temperature (Tc) at which the electrical resistance of liquid hydrogen becomes substantially zero is 20 K at normal pressure, but it rises to 30 K at 1 MPaG. Therefore, in order to correspond to a superconductor for a liquid hydrogen level gauge with a critical temperature Tc = 20 - 30 K, a superconductor with Tc = 32.4 K - 34.3 K was realized.

[0022] The superconductor in Example 1 is composed of magnesium (Mg) and boron (B) without using SiC. A mixture of boron (B) with a molar ratio of 2 to magnesium (Mg) 1 was filled into a hollow metal tube, drawn, and then heat-treated in an argon atmosphere at about 600 °C to produce an intermetallic compound. The critical temperature (Tc) of the superconductor is 32.4 K in (d) and 34.3 K in (c) as shown in the experimental data of FIG. 1. The horizontal axis in FIG. 1 indicates temperature (K), and the vertical axis indicates output voltage (mV). When the output voltage becomes substantially zero, the resistance becomes zero, and the temperature at that time is the critical temperature (Tc). In FIG. 1, the graph in (d) is the result of measuring the critical temperature (Tc) = 32.4 K when boron with an average particle size of 14 μm was mixed with magnesium, and the graph in (c) is the result of measuring the critical temperature (Tc) = 34.3 K when boron with an average particle size of 2 μm was mixed with magnesium. The magnesium used at this time was 325 mesh (manufactured by Alfa Aesar, particle size about 44 μm).

[0023] With reference to FIG. 1, the results of an experiment in which the critical temperature (Tc) was measured comparatively while changing the average particle size of boron will be described. Graphs (a), (b), (e), (f), and (g) in FIG. 1 are all experimental data (comparison data) in which the critical temperature (Tc) was not within the range of 32K to 34K. That is, graph (a) shows the result of mixing 1 part magnesium and 2 parts boron with an average particle size of 0.7μm, and the critical temperature (Tc) is 35.6K. Graph (b) shows the result of mixing 1 part magnesium and 2 parts boron with an average particle size of 1μm, and the critical temperature (Tc) is 35.5K. That is, the data in (a) and (b) have critical temperatures (Tc) higher than 35K and cannot be used as superconductors for liquid hydrogen level gauges.

[0024] Graph (e) in Figure 1 shows the results when magnesium is mixed with boron having an average particle size of 36 μm in a ratio of 1 part to 2 parts, with a critical temperature (Tc) of 27.3 K. Graph (f) shows the results when magnesium is mixed with boron having an average particle size of 38 μm in a ratio of 2 parts to 1 part, with a critical temperature (Tc) of 29.2 K. Graph (g) shows the results when magnesium is mixed with boron having an average particle size of 39 μm in a ratio of 2 parts to 1 part, with a critical temperature (Tc) of 26.9 K. In other words, the data in (e), (f), and (g) have critical temperatures (Tc) lower than 32 K and cannot be used as superconductors for liquid hydrogen level gauges.

[0025] The graph in Figure 1 (d) shows the results when magnesium is mixed with two parts boron with an average particle size of 14 μm to one part magnesium, with a critical temperature (Tc) of 32.4 K. The graph in (c) shows the results when magnesium is mixed with two parts boron with an average particle size of 2 μm to one part magnesium, with a critical temperature (Tc) of 34.3 K. In other words, the data in (c) and (d) show values ​​close to the target values ​​for a superconductor for use in a liquid hydrogen level gauge.

[0026] Here, we will explain how to determine the average particle size and critical temperature (Tc) shown in the experimental data. The average particle size was measured using Shimadzu's SALD-2300 (laser diffraction particle size distribution analyzer). The critical temperature (Tc) was not measured according to JISH7309, but was determined by approximating the measurement data (25K to 45K data) of a short sample using a cryostat device with a sigmoid curve (transition curve) using the least squares method, and the value at 50% of the height was taken as Tc.

[0027] From the above experimental data, it was discovered that the smaller the average particle size of boron, the higher the critical temperature (Tc), and the larger the average particle size, the lower the critical temperature (Tc). Next, we investigated what the average particle size of boron should be to achieve a critical temperature (Tc) of approximately 32K to approximately 34K. The graph shown in Figure 4 shows the average particle size of boron (μm) on the horizontal axis and the critical temperature (Tc) on the vertical axis, with seven pieces of data from the above experimental results plotted on this graph. As can be seen from Figure 4, these data have a very strong linear approximation relationship as shown in Equation 1. Equation 1: Tc temperature = -0.2 x average particle size (μm) + 35.35

[0028] The average particle size of boron required to obtain a critical temperature (Tc) of approximately 32 K to approximately 34 K obtained from this approximation line is 7 to 17 μm. In other words, by mixing 1 part magnesium with 2 parts boron having an average particle size of 7 to 17 μm, a superconductor with a critical temperature (Tc) of 32 K to 34 K can be obtained.

[0029] In Example 1, the particle size of boron was expressed as an average particle size. The average particle size is a representative diameter obtained by averaging the measurements of the SALD-2300 described above, and is obtained by multiplying and adding up the particle size on the horizontal axis of the histogram and the frequency on the vertical axis. However, if the particle size distribution, which represents the distribution of particle sizes of particulate matter, differs, the critical temperature (Tc) may differ. Therefore, in the present application, the critical temperature (Tc) obtained from the approximation line is expressed as about 32K to about 34K, with the word "about" added.

[0030] (Method for manufacturing a superconductor) First, a mixing step is performed in which boron (B) with an average particle size of 14 μm is mixed with magnesium (Mg) of 325 mesh (manufactured by Alfa Aesar, particle size of about 44 μm) 1 at a molar ratio of 2. Next, a firing step is performed in which the mixture of Mg and B mixed in the mixing step is fired at 600 °C for 1 hour in an argon atmosphere to complete the superconductor of MgB2. Incidentally, as will be described later, when making a long liquid hydrogen level sensor, the fired MgB2 may be made into powder, put into a long tube, and drawn, or the mixed Mg and B powders may be drawn and then fired.

[0031] Here, boron (B) was purchased and used as the one sold by Nilaco with a particle size of 40 μm, but when the average particle size was measured with the above-described laser diffraction particle size distribution measuring device, it was 14 μm. Also, magnesium (Mg) was purchased and used as the one sold by Alfa Aesar with 325 mesh (particle size of about 44 μm).

[0032] Boron (B) with an average particle size of 14 μm was mixed with magnesium (Mg) of 325 mesh (manufactured by Alfa Aesar, particle size of about 44 μm) 1 at a molar ratio of 2, drawn, and the critical temperature (Tc) of the fired superconductor was 32.4 K (see Figure 1).

[0033] Also, a mixing step is performed in which boron (B) with an average particle size of 2 μm is mixed with magnesium (Mg) of 325 mesh (manufactured by Alfa Aesar, particle size of about 44 μm) 1 at a molar ratio of 2. Next, a firing step is performed in which the mixture of Mg and B mixed in the mixing step is fired at 600 °C for 1 hour in an argon atmosphere.

[0034] Here, boron (B) was purchased and used as the one sold by nanogaraphi technology with a particle size of 10 μm, but when the average particle size was measured with the above-described laser diffraction particle size distribution measuring device, it was 2 μm. Also, magnesium (Mg) was purchased and used as the one sold by Alfa Aesar with 325 mesh (particle size of about 44 μm).

[0035] A molar ratio of 1 part magnesium (Mg) of 325mesh (manufactured by Alfa Aesar, particle size approximately 44μm) to 2 parts boron (B) of average particle size 2μm was mixed, and the critical temperature (Tc) of the sintered superconductor was 34.3K (see Figure 1).

[0036] In Example 1, the magnet was manufactured without any other substances than MgB2, but this is not necessarily limited to this and can be changed as appropriate. For example, the magnet may contain SiC or other substances that do not affect the critical temperature (Tc).

[0037] After boron (B) and magnesium (Mg) are mixed and before the sintering process, the Mg and B powder particles are in contact at their contact points. If the sintering process is carried out in this state, MgB2 crystal nuclei are generated from the contact points and these nuclei grow. The number of MgB2 crystal nuclei generated is affected by the number of contact points, which varies depending on the particle size ratio of the powders being mixed. When there are many crystal nuclei (many contact points), the overall reaction is fast and adjacent crystals collide at the interface, fuse and grow, resulting in perfect crystals with no unreacted powder that can become impurities.

[0038] Therefore, in the range of particle sizes from several μm to several tens of μm, the smaller the particle size of B is compared to the particle size of Mg, the more contact points there are, and the generated MgB2 becomes a perfect crystal, so the critical temperature (Tc) becomes higher. This supports the relationship between the average particle size of B and the critical temperature (Tc) explained in Figure 4 above.

[0039] The above steps have made it possible to produce superconductors with reproducibility, but to ensure even greater reproducibility, it is necessary to strictly control the heat treatment (rate and time of heating, constant temperature, and cooling), the particle size and particle size ratio of Mg and B, and the particle size distribution, etc., to ensure the same conditions in production.

[0040] (Liquid hydrogen level sensor) The liquid hydrogen level sensor 10 in Example 1 is composed of a superconductor 11 and a metal coating 12, and forms a long core wire with a length of about 1 m and a diameter of about 0.3 mm as shown in Fig. 2. The superconductor 11 is made by mixing magnesium (Mg) of 325 mesh (manufactured by alfa Aesar, particle size about 44 μm) with boron (B) of an average particle size of 14 μm in a molar ratio of 2 (mixing process), drawing the mixture in a wire drawing process, and then baking it to make a MgB2 superconductor. In the wire drawing process, the mixture of Mg and B obtained in the mixing process is powdered and placed in a tube of about 1 m in length, and drawn into a long shape.

[0041] In the first embodiment, the mixing step, the wire drawing step, and the firing step are performed in this order, but this is not necessarily limited to this and can be changed as appropriate. For example, the firing step may be performed after the mixing step, followed by a powdering step for powdering the mixture, and finally the wire drawing step. Also, the heat treatment step may be performed multiple times.

[0042] In the first embodiment, a long core wire having a length of about 1 m and a diameter of about 0.3 mm is formed, but this is not necessarily limited to this and can be changed as appropriate. For example, the length may be about 5 m or 0.5 m, and may be created according to the depth of the liquid hydrogen. In addition, in the first embodiment, the diameter is set to about 0.3 mm, but it is not necessarily limited to this and can be changed appropriately. For example, it may be 0.5 mm or 0.2 mm, and the diameter may be selected in consideration of the critical temperature (Tc).

[0043] Furthermore, the metal coating 12 may be any metal having high conductivity. Although cupronickel was used in the first embodiment, other metals such as stainless steel may also be used.

[0044] In Example 1, boron (B) with an average particle size of 14 μm was mixed with magnesium (Mg) of 325 mesh (manufactured by Alfa Aesar, particle size of about 44 μm) at a molar ratio of 2, but it is not necessarily limited to this and can be appropriately changed. For example, boron (B) with an average particle size of 2 μm may be mixed with magnesium (Mg) of 325 mesh (manufactured by Alfa Aesar, particle size of about 44 μm) at a molar ratio of 2.

[0045] The resistance value of the liquid hydrogen level sensor 10 at room temperature in Example 1 is 1 Ω / m to 6 Ω / m, but it is not limited to this and can be appropriately changed.

[0046] In Example 1, the length of the liquid hydrogen level sensor 10 was about 1 m, but it is not necessarily limited to this and can be appropriately changed. For example, the length may be about 5 m or about 0.5 m. As long as it is at least the length capable of measuring the liquid level of liquid hydrogen.

[0047] (Liquid hydrogen level gauge) The configuration of the liquid hydrogen level gauge 100 in Example 1 is shown in FIG. 3. The tank T is filled with liquid hydrogen M, and the liquid hydrogen level sensor 10 is installed vertically in the tank T. The liquid hydrogen level sensor 10 is arranged deep in the liquid of the liquid hydrogen M.

[0048] The liquid hydrogen level sensor 10 in the normal temperature area above the liquid level can generate resistance heat by passing an electric current from the heater power supply 21 through the heater 20 to heat the liquid hydrogen level sensor 10. Thereby, the influence of the temperature of the liquid hydrogen M can be eliminated and the area above the liquid level can be kept in a normal conductive state.

[0049] A power supply 30 is connected to both ends of the liquid hydrogen level sensor 10, and a voltmeter 40 is also connected. Then, an electric current is passed from the power supply 10 through the liquid hydrogen level sensor 10, and the voltage at both ends of the liquid hydrogen level sensor 10 is measured by the voltmeter 40 and stored in the processing unit 50. Then, based on a predetermined known relational expression, the liquid level position is calculated from the stored voltage.

[0050] Thus, in Example 1, it is a superconductor composed of a metal compound of magnesium (Mg) and boron (B) with a molar ratio of 1:2 and containing no SiC, characterized by a superconductor having a critical temperature (Tc) at which the electrical resistance becomes substantially zero of about 32K to about 34K, which can be used for a liquid hydrogen level gauge, and a superconductor with a simple manufacturing method and reproducibility can be obtained.

[0051] Also, in Example 1, it is a method for manufacturing a superconductor having a critical temperature (Tc) at which the electrical resistance becomes substantially zero of about 32K to about 34K, a mixing step of mixing boron (B) having an average particle size of 17μm to 7μm in a molar ratio of 2 with respect to 1 of magnesium (Mg), a firing step of firing the mixture of Mg and B mixed in the mixing step, According to the method for manufacturing a superconductor characterized by comprising the above, a superconductor for a liquid hydrogen level gauge with a simple manufacturing method and reproducibility can be realized.

[0052] Also, in Example 1, it is a liquid hydrogen level sensor characterized by comprising a long superconductor made of MgB2 containing no SiC and having a critical temperature (Tc) at which the electrical resistance becomes substantially zero of about 32K to about 34K, and a coating metal covering the surface of the superconductor, and a liquid hydrogen level gauge with a simple manufacturing method and reproducibility can be realized.

[0053] Furthermore, in Example 1, it is a liquid hydrogen level sensor having a long superconductor made of MgB2 containing no SiC and having a critical temperature (Tc) at which the electrical resistance becomes substantially zero of about 32K to about 34K, and a coating metal covering the surface of the superconductor, a heater for heating the liquid hydrogen level sensor, a power source for passing an electric current through the liquid hydrogen level sensor, a voltmeter for measuring the voltage in the liquid hydrogen level sensor, By using the liquid hydrogen level gauge having the above features, it is possible to realize a liquid hydrogen level gauge that can be manufactured simply and reproducibly. [Industrial Applicability]

[0054] The superconductor, the method for manufacturing the superconductor, the liquid hydrogen level sensor, and the liquid hydrogen level gauge of the present invention can be widely applied in the field of liquid hydrogen level gauges. [Explanation of symbols]

[0055] 10: Liquid hydrogen level sensor 11: Superconductor 12: Metal coating 20: Heater section 21: Heater power supply 30: Power supply 40: Voltmeter 50: Processing section 100: Liquid hydrogen level gauge

Claims

1. A superconductor having a critical temperature (Tc) that can be used for a liquid hydrogen level gauge, A metal compound containing magnesium (Mg) and boron (B) in a molar ratio of 1:2, not containing SiC, A superconductor characterized in that the critical temperature (Tc) at which the electrical resistance becomes substantially zero is 32.4K.

2. A method for producing a superconductor having a critical temperature (Tc) usable for a liquid hydrogen level gauge, comprising the steps of: A mixing step of mixing magnesium (Mg) with boron (B) having an average particle size of 17 μm to 7 μm; a firing step of firing the mixture of Mg and B mixed in the mixing step; By executing A method for producing a superconductor, characterized in that MgB2 is used.

3. A metal compound containing no SiC and having Mg and B in a molar ratio of 1:2, A liquid hydrogen level sensor comprising: a long superconductor having a critical temperature (Tc) of 32.4 K at which the electrical resistance becomes substantially zero; and a coating metal covering the surface of the superconductor.

4. A metal compound containing no SiC and having Mg and B in a molar ratio of 1:2, A liquid hydrogen level sensor comprising: a long superconductor having a critical temperature (Tc) of 32.4K at which the electrical resistance becomes substantially zero; and a metal coating covering the surface of the superconductor; a heater for heating the liquid hydrogen level sensor; a power source for supplying a current to the liquid hydrogen level sensor; a voltmeter for measuring a voltage at the liquid hydrogen level sensor; A liquid hydrogen level gauge comprising:

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