A Cu2Se-doped MgB2 bulk material and preparation method thereof

Abstract

The present invention relates to a Cu2Se-doped MgB2 bulk material. This superconducting material is prepared by solid-phase sintering a mixture of boron powder, magnesium powder, and a Cu2Se dopant. The present invention also relates to a method for preparing the Cu2Se-doped MgB2 bulk material, comprising the following steps: preparing raw materials: magnesium powder with a purity of 99.9% and a particle size of 40 μm; amorphous boron powder with a purity of 99% and a particle size of 0-20 μm; and cuprous selenide powder with a purity of 99.5%, wherein the molar ratio of the boron powder to the magnesium powder is 2:1, and the weight of the cuprous selenide dopant powder accounts for 5% to 30% of the total powder weight; weighing the raw materials in proportion, and thoroughly grinding the powder in an agate mortar for 1 hour to form a uniform mixed powder; placing the resulting uniform mixed powder into a mold and pressing it into a bulk material at a pressure of 6-10 MPa; and placing the bulk material into a ceramic ark and sintering it at high temperature in a vacuum tube furnace with an inert gas Ar flowing. The Cu2Se-doped MgB2 bulk material and the preparation method thereof of the present invention effectively improve the current-carrying performance of the MgB2 superconductor.

Description

Technical Field

[0001] The present invention belongs to the field of superconducting material preparation, and in particular relates to a Cu2Se-doped MgB2 bulk material for improving the performance of MgB2 superconductors and a preparation method thereof. Background Art

[0002] New high-temperature superconducting materials, superconducting physics and applications have been hot research directions for the past two decades. Today, superconducting materials have been applied to medical imaging, nuclear fusion reactors, transportation and other fields. Among them, the critical temperature of MgB2 is 39K (located in the liquid hydrogen temperature range), which is the simplest and most stable metal compound superconducting material with the highest critical temperature discovered so far. After more than 20 years of research on the application of various synthesis methods and preparation technologies to MgB2, it has achieved gratifying results in both theoretical and experimental research. MgB2 has now been used in magnetic resonance imaging (MRI) devices. However, the current critical current density (J c ) experimental value is only 4% of the value predicted by Gingzburg-Landau theory. Only by significantly increasing the critical current density of MgB2 bulk and wire can we improve MRI testing accuracy while reducing application costs. The critical current density of MgB2 decreases sharply with increasing magnetic field strength. As a Type II superconductor, the current-carrying performance of MgB2 in the low-field superconducting state is primarily related to the grain connectivity of the sample. The lack of effective flux pinning centers within the sample in the mixed state is the main reason for the reduction in the critical current of MgB2 superconductors at high magnetic fields.

[0003] Researchers have used spark plasma sintering, irradiation, chemical doping, high-pressure densification and other methods to improve its superconducting properties in order to increase the current carrying capacity of MgB2 materials under high fields. Chemical doping is a simple and effective method. When the mechanism of metal doping of MgB2 was first explored, people focused on the hope of introducing vacancy doping to change the electronic structure of MgB2, so as to obtain a material with higher T c In previous studies, researchers have introduced metal elements such as La, Na, Ca and Ti to change the electronic structure of MgB2 in order to increase T c But it failed. However, people found that some metal elements can effectively improve the current carrying performance of MgB2 under high field and increase the irreversible field H irr Wang et al. synthesized in situ the molar ratio of Mg 0.5 Cd 0.5 For the B2 sample, it was found that the addition of Cd can react with Mg to form MgCd3 phase, which can act as an effective pinning center, making the J of the sample at 5K and 0T c The value reached 5.0×10 5 A.cm-2 Muralidhar et al. studied the effect of Ag addition on the superconducting properties of MgB2. The results showed that when the Ag content was 4 wt.%, the J c The value reached 430KA / cm 2 This is because the generated nanoscale AgMg₃ phase can serve as effective flux pinning centers, thereby increasing the critical current density of the sample. Most of the above-mentioned preparations of high-performance MgB₂ bulk materials are based on traditional solid-phase sintering methods. Using a simple powder metallurgy sintering process, MgB₂ bulk and wire strips can be produced, significantly reducing production costs. However, due to the melting point of Mg being only 650°C, some Mg volatilizes before fully reacting to form MgB₂, leaving a large amount of pores within the sample. This results in poor density in the MgB₂ bulk and wire strips. When the material is loaded, the stress concentration caused by the internal pores makes the material prone to fracture. Therefore, metal doping has not fundamentally solved the problems of Mg volatilization and poor density during powder metallurgy sintering of MgB₂. These defects are detrimental to the current-carrying performance of MgB₂ under low magnetic fields. In recent years, a new liquid-phase-assisted sintering method has attracted widespread attention. Currently, liquid-phase sintering is mainly achieved by adding a single metal that forms a low-temperature eutectic liquid phase with Mg. The presence of liquid phase will accelerate the diffusion between Mg and B atoms, thereby promoting the low-temperature synthesis of MgB2 phase; this method can reduce the volatilization of Mg and effectively improve the connectivity between grains, while also greatly shortening the time of low-temperature reaction sintering and improving the sintering efficiency. There are limited metals that form eutectic liquid phase with Mg at low temperatures, such as Cu, Ni and Ga. Chen et al. added Ga with an atomic fraction of less than 5% to MgB2. When the sintering temperature was 422°C, a Mg-Ga eutectic liquid phase could be formed. This liquid phase can effectively improve the connectivity of MgB2 grains, and the J at 20K c The value is 10 times higher than that of the pure sample. Ma et al. reported the effect of Cu on the sintering and superconducting properties of MgB2. The addition of Cu can first form a Mg-Cu eutectic liquid phase with Mg at a sintering temperature of 485°C. This liquid phase provides a fast channel for the diffusion of Mg to B at low temperatures, thereby improving the sintering rate of MgB2. However, only certain research has been conducted on the doping of elemental copper, and effective research on copper compounds has not yet been carried out. Based on the above analysis, this paper selects Cu2Se as a dopant to systematically study its effect on the sintering phase formation process, microstructure and superconducting properties of MgB2. Summary of the Invention

[0004] The purpose of the present invention is to overcome the deficiencies of the prior art and provide a Cu2Se-doped MgB2 bulk material and a preparation method thereof, which can effectively improve the current-carrying performance of the MgB2 superconductor.

[0005] The present invention solves the technical problem by the following technical solutions:

[0006] A Cu2Se-doped MgB2 bulk material is prepared by mixing boron powder, magnesium powder and cuprous selenide powder as dopants and subjecting the mixture to solid-phase sintering, wherein the mass ratio of the components is:

[0007] 0.22 parts by weight of boron powder;

[0008] 0.24 parts by weight of magnesium powder;

[0009] 0.0242 g to 0.1971 parts by weight of cuprous selenide powder.

[0010] A method for preparing a Cu2Se-doped MgB2 bulk material, wherein the specific steps of the preparation method are:

[0011] (1) Raw material preparation: magnesium powder, purity 99.9%, particle size 40 μm; amorphous boron powder, purity 99%, particle size 0-20 μm, cuprous selenide powder, purity 99.5%, wherein the molar ratio of the boron powder to the magnesium powder is 2:1, and the mass of the dopant cuprous selenide powder accounts for 5% to 30% of the total powder weight;

[0012] (2) Weigh the raw materials according to the proportion of step (1), and grind the powder thoroughly in an agate mortar for 1 h to form a uniform mixed powder;

[0013] (3) The uniformly mixed powder obtained in step (2) is placed in a mold and pressed into a block at a pressure of 6 to 10 MPa;

[0014] (4) The block material obtained in step (3) is placed in a ceramic ark and sintered at high temperature in a vacuum tube furnace with inert gas Ar flowing, heating from room temperature to 750°C at a heating rate of 20°C / min and holding time of half an hour, and then cooled to room temperature in the furnace to obtain a Cu2Se-doped MgB2 block material.

[0015] The advantages and beneficial effects of the present invention are:

[0016] 1. The Cu2Se-doped MgB2 block and preparation method thereof of the present invention comprises the following steps: cuprous selenide dopant is uniformly mixed with magnesium powder and boron powder and pressed into a block. After sintering for a certain period of time, the cuprous selenide dopant first reacts with the magnesium powder to generate magnesium selenide and magnesium dicopper. The magnesium dicopper reacts with the boron powder during subsequent sintering at a higher temperature to regenerate magnesium diboride and magnesium dicopper, thereby creating a new pathway for the generation of magnesium diboride. This allows magnesium to solidify in advance to avoid volatilization at high temperatures. Furthermore, since the reaction between cuprous selenide and magnesium is an exothermic reaction, increasing the temperature of the system is beneficial to the diffusion of magnesium, thereby advancing the solid-state reaction of magnesium diboride, thereby improving the connectivity of the MgB2 superconductor grains and presenting a dense state.

[0017] 2. The Cu2Se-doped MgB2 bulk material and preparation method thereof of the present invention introduce second-phase particles into the superconductor as effective magnetic flux pinning centers to increase the critical current density.

[0018] 3. The Cu2Se-doped MgB2 bulk material and its preparation method of the present invention have a simple preparation process, a significant effect of improving the critical superconducting current of superconducting materials, and have broad application prospects. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 This is a simplified diagram of the block material preparation process of the present invention;

[0020] Figure 2 XRD patterns of MgB2 bulk materials prepared by the present invention at different doping levels of cuprous selenide;

[0021] Figure 3 The SEM images of the fracture surfaces of MgB2 bulk materials prepared by the present invention at different doping levels of cuprous selenide are shown;

[0022] Figure 4 TEM diffraction pattern of MgB2 bulk material prepared at the cuprous selenide doping level prepared in Example 3;

[0023] Figure 5 (a) is the normalized curve of the magnetic susceptibility of the MgB2 bulk material prepared by the present invention at different doping amounts of cuprous selenide versus temperature;

[0024] Figure 5 (b) is the superconducting transition temperature of the cuprous selenide prepared by the present invention at different doping levels;

[0025] Figure 6 The critical current density and magnetic field relationship curve of MgB2 bulk material prepared by the present invention at different doping amounts of cuprous selenide;

[0026] Figure 7 The graph is a normalized curve showing the change of the pinning force density of the MgB2 bulk material prepared by the present invention at different doping amounts of cuprous selenide as a function of the magnetic field. DETAILED DESCRIPTION

[0027] The present invention will be further described in detail below through specific examples. The following examples are only illustrative and not restrictive, and the scope of protection of the present invention cannot be limited thereto.

[0028] Example 1: A Cu2Se-doped MgB2 bulk material, which is a superconducting material prepared by mixing boron powder, magnesium powder and cuprous selenide (Cu2Se) dopant and then sintering the mixture through conventional solid phase sintering.

[0029] The mass of each component is:

[0030] Boron powder 0.22g;

[0031] 0.24g magnesium powder;

[0032] 0.0242g of cuprous selenide powder.

[0033] A method for preparing a Cu2Se-doped MgB2 bulk material comprises the following steps:

[0034] (1) First, prepare the required raw materials: magnesium powder (purity 99.9%, 40 μm), amorphous boron powder (purity 99%, 0-20 μm) and cuprous selenide powder (purity 99.5%), wherein the molar ratio of the boron powder to the magnesium powder is 2:1, and the mass of the dopant cuprous selenide powder accounts for 5 wt% of the total powder weight.

[0035] (2) Weigh the raw materials according to the proportions in step (1), and grind the mixed powder thoroughly in an agate mortar for 1 h.

[0036] (3) The uniformly mixed powder obtained in step (2) is placed in a mold and pressed into a block at a pressure of 7 MPa.

[0037] (4) The block material obtained in step (3) is placed in a ceramic ark and sintered at high temperature in a vacuum tube furnace with inert gas (Ar) circulation, heating from room temperature to 750°C at a heating rate of 20°C / min, and holding time of half an hour. The block material is cooled to room temperature in the furnace to obtain a Cu2Se-doped MgB2 block material.

[0038] Example 2: This example is a Cu2Se-doped MgB2 block. The superconducting material is prepared by mixing boron powder, magnesium powder and cuprous selenide (Cu2Se) dopant and then sintering the mixture through conventional solid phase sintering.

[0039] The mass of each component is:

[0040] Boron powder 0.22g;

[0041] 0.24g magnesium powder;

[0042] 0.0511 g of cuprous selenide powder.

[0043] A method for preparing a Cu2Se-doped MgB2 bulk material comprises the following steps:

[0044] (1) First, prepare the required raw materials: magnesium powder (purity 99.9%, 40 μm), amorphous boron powder (purity 99%, 0-20 μm) and cuprous selenide powder (purity 99.5%), wherein the molar ratio of the boron powder to the magnesium powder is 2:1, and the mass of the dopant cuprous selenide powder accounts for 10 wt% of the total powder weight.

[0045] (2) Weigh the raw materials according to the proportions in step (1), and grind the mixed powder thoroughly in an agate mortar for 1 h.

[0046] (3) The uniformly mixed powder obtained in step (2) is placed in a mold and pressed into a block at a pressure of 7 MPa.

[0047] (4) The block material obtained in step (3) is placed in a ceramic ark and sintered at high temperature in a vacuum tube furnace with inert gas (Ar) circulation, heating from room temperature to 750°C at a heating rate of 20°C / min, and holding time of half an hour. The block material is cooled to room temperature in the furnace to obtain a Cu2Se-doped MgB2 block material.

[0048] Example 3: This example is a Cu2Se-doped MgB2 block. The superconducting material is prepared by mixing boron powder, magnesium powder and cuprous selenide (Cu2Se) dopant and then sintering the mixture through conventional solid phase sintering.

[0049] The mass of each component is:

[0050] Boron powder 0.22g;

[0051] 0.24g magnesium powder;

[0052] 0.511 g of cuprous selenide powder.

[0053] A method for preparing a Cu2Se-doped MgB2 bulk material comprises the following steps:

[0054] (1) First, prepare the required raw materials: magnesium powder (purity 99.9%, 40 μm), amorphous boron powder (purity 99%, 0-20 μm) and cuprous selenide powder (purity 99.5%), wherein the molar ratio of the boron powder to the magnesium powder is 2:1, and the mass of the dopant cuprous selenide powder accounts for 20 wt% of the total powder weight.

[0055] (2) Weigh the raw materials according to the proportions in step (1), and grind the mixed powder thoroughly in an agate mortar for 1 h.

[0056] (3) The uniformly mixed powder obtained in step (2) is placed in a mold and pressed into a block at a pressure of 7 MPa.

[0057] (4) The block material obtained in step (3) is placed in a ceramic ark and sintered at high temperature in a vacuum tube furnace with inert gas (Ar) circulation, heating from room temperature to 750°C at a heating rate of 20°C / min, and holding time of half an hour. The block material is cooled to room temperature in the furnace to obtain a Cu2Se-doped MgB2 block material.

[0058] Example 4: This example is a Cu2Se-doped MgB2 bulk material. The superconducting material is prepared by mixing boron powder, magnesium powder and cuprous selenide (Cu2Se) dopant and then sintering the mixture through conventional solid phase sintering.

[0059] The mass of each component is:

[0060] Boron powder 0.22g;

[0061] 0.24g magnesium powder;

[0062] 0.1971g of cuprous selenide powder.

[0063] A method for preparing a Cu2Se-doped MgB2 bulk material comprises the following steps:

[0064] (1) First, prepare the required raw materials: magnesium powder (purity 99.9%, 40 μm), amorphous boron powder (purity 99%, 0-20 μm) and cuprous selenide powder (purity 99.5%), wherein the molar ratio of the boron powder to the magnesium powder is 2:1, and the mass of the dopant cuprous selenide powder accounts for 30 wt% of the total powder weight.

[0065] (2) Weigh the raw materials according to the proportions in step (1), and grind the mixed powder thoroughly in an agate mortar for 1 h.

[0066] (3) The uniformly mixed powder obtained in step (2) is placed in a mold and pressed into a block at a pressure of 7 MPa.

[0067] (4) The block material obtained in step (3) is placed in a ceramic ark and sintered at high temperature in a vacuum tube furnace with inert gas (Ar) circulation, heating from room temperature to 750°C at a heating rate of 20°C / min, and holding time of half an hour. The block material is cooled to room temperature in the furnace to obtain a Cu2Se-doped MgB2 block material.

[0068] Comparative Example 1: This embodiment provides a method for preparing a Cu2Se-doped MgB2 bulk material. The superconducting material is prepared by mixing boron powder and magnesium powder through traditional solid-phase sintering. The specific process is as follows:

[0069] (1) First, prepare the required raw materials: magnesium powder (purity 99.9%, 40 μm) and amorphous boron powder (purity 99%, 0-20 μm), wherein the molar ratio of the boron powder to the magnesium powder is 2:1.

[0070] (2) Weigh the raw materials according to the proportions in step (1), and grind the mixed powder thoroughly in an agate mortar for 1 h.

[0071] (3) The uniformly mixed powder obtained in step (2) is placed in a mold and pressed into a block at a pressure of 7 MPa.

[0072] (4) The block material obtained in step (3) is placed in a ceramic ark and sintered at high temperature in a vacuum tube furnace with inert gas (Ar) circulation, heating from room temperature to 750°C at a heating rate of 20°C / min, holding time of half an hour, and then cooled to room temperature to obtain a MgB2 block material.

[0073] Figure 2The XRD patterns of the MgB2 bulk material prepared by the present invention with different doping amounts of cuprous selenide show that in addition to the superconducting phase and a small amount of unavoidable magnesium oxide, two new impurity phases, MgSe and MgCu2, are introduced into the sample with cuprous selenide added.

[0074] Figure 3 These are SEM images of the fracture of MgB2 bulk materials with different doping amounts of cuprous selenide prepared by the present invention, where (a~e) are doped Cu2Se samples at low magnification and (f~j) are doped Cu2Se samples at high magnification, (a, f) are comparative example 1, (b, g) are example 1, (c, h) are example 2, (d, i) are example 3, and (e, j) are example 4, indicating that the connectivity between the sample grains is good. At high magnification, the grains of comparative example 1, example 1 and example 4 are mostly irregular hexagonal morphology, which is the typical micromorphology of MgB2 grains, which is consistent with the main phase of XRD analysis being MgB2. However, the grain morphology of example 2 and example 3 at high magnification is significantly different from that of other samples. In the SEM image, it can be seen that the MgB2 grains are connected into sheets and are in a dense state. At the same time, no typical six-membered ring (MgB2) grains are found, which indicates that appropriate amount of Cu2Se doping plays a key role in improving the connectivity of MgB2 grains.

[0075] Figure 4 This is the TEM diffraction pattern of the MgB2 bulk material prepared under the cuprous selenide doping amount prepared in Example 3. Figure 4 In (a), it can be observed that there are many small particles with a diameter of about 5-15nm distributed in the matrix. The size of the second phase particles is close to the coherence length of MgB2, which is expected to serve as an effective magnetic flux pinning center. High-resolution lattice phase analysis of this area is performed, such as Figure 4 As shown in (b), the (311) crystal plane of MgCu2 and the (220) crystal plane of MgSe can be observed, and the interplanar spacing is 0.1608nm and 0.1743nm respectively. Figure 4 (c) Electron diffraction patterns were selected and the interatomic distances were calculated using the formula Rd = Lλ. Comparison of the results with the standard PDF card revealed the presence of MgSe and MgCu2 phases in the bulk, further confirming that the black matter distributed in the matrix is ​​a second-phase particle.

[0076] Figure 5 The normalized curve of magnetic susceptibility variation with temperature of MgB2 bulk material prepared by the present invention at different doping amounts of cuprous selenide shows that the critical transition temperature of the sample of the embodiment has little effect, which also indicates that the inhibitory effect of Cu2Se on the superconducting transition temperature is not obvious.

[0077] Figure 6The critical current density and magnetic field relationship curve of the MgB2 bulk material prepared by the present invention at different doping amounts of cuprous selenide is shown. Except for the sample in Example 4, the critical current density of the other samples is improved under the overall magnetic field compared with the control example, especially under low magnetic field.

[0078] Figure 7 This is a normalized curve of the pinning force density of the MgB2 bulk material prepared by the present invention at different doping amounts of cuprous selenide as a function of the magnetic field. The figure shows that the peak position of the embodiment is shifted to the right compared with pure MgB2, introducing an effective flux pinning center, thereby enhancing the flux pinning strength of the sample.

[0079] Although the embodiments and drawings of the present invention are disclosed for illustrative purposes, those skilled in the art will understand that various substitutions, changes and modifications are possible without departing from the spirit and scope of the present invention and the appended claims. Therefore, the scope of the present invention is not limited to the contents disclosed in the embodiments and drawings.

Claims

1. A Cu2Se-doped MgB2 bulk material, characterized by: The block is prepared by mixing boron powder, magnesium powder and cuprous selenide powder as dopants and then solid-phase sintering, wherein the mass ratio of each component is: 0.22 parts by weight of boron powder; 0.24 parts by weight of magnesium powder; 0.0242 to 0.1971 parts by weight of cuprous selenide powder.

2. A method for preparing Cu2Se-doped MgB2 bulk material, characterized by: The specific steps of the preparation method are: (1) Raw material preparation: magnesium powder, purity 99.9%, particle size 40 μm; amorphous boron powder, purity 99%, particle size 0-20 μm, cuprous selenide powder, purity 99.5%, wherein the molar ratio of the boron powder to the magnesium powder is 2:1, and the mass of the dopant cuprous selenide powder accounts for 5% to 30% of the total powder weight; (2) Weigh the raw materials according to the proportion of step (1), and grind the powder thoroughly in an agate mortar for 1 h to form a uniform mixed powder; (3) The uniformly mixed powder obtained in step (2) is placed in a mold and pressed into a block at a pressure of 6 to 10 MPa; (4) The block material obtained in step (3) is placed in a ceramic ark and sintered at high temperature in a vacuum tube furnace with inert gas Ar flowing, heating from room temperature to 750°C at a heating rate of 20°C / min and holding time of half an hour, and then cooled to room temperature in the furnace to obtain a Cu2Se-doped MgB2 block material.

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