Preparation method of a highly dense MgB2 bulk material

Abstract

The present invention discloses a method for preparing a highly dense MgB2 bulk material. The method includes: First, grinding B powder and Mg powder respectively to obtain ground B powder and ground Mg powder; Second, pressing the ground B powder into a B block; Third, laying the ground Mg powder around the B block and pressing to obtain a mixed block; Fourth, performing a heat sintering treatment on the mixed block to obtain a highly dense MgB2 bulk material. In the present invention, after pressing the B powder into a dense B block, Mg powder is laid around it for heat sintering treatment, so that the Mg powder diffuses towards the B block located in the center and rapidly generates the MgB2 bulk material, and the voids generated during the formation of MgB2 are concentrated on the outside, thereby obtaining a highly dense MgB2 bulk material, and it is not easy to have residues of Mg and B. The prepared MgB2 bulk material has high density, high purity and strong crystallinity, and is suitable for large-scale industrial production.

Description

Technical Field

[0001] The present invention belongs to the technical field of superconducting materials, and particularly relates to a method for preparing highly dense MgB2 bulk materials. Background Art

[0002] In 2001, MgB2 was found to have superconducting properties at T c = 39 K, which has received extensive attention from researchers. Due to its simple composition elements, low raw material cost, weak intrinsic anisotropy of the material, and relatively high T c and other advantages, MgB2 is generally considered by domestic and foreign researchers to be the most likely superconducting material to be the first to achieve large-scale application, and has relatively broad commercial prospects. In the field of magnetic resonance imaging (MRI), researchers believe that in the future, MgB2 may replace NbTi and Nb3Sn, which have extremely high costs and poor thermal stability, and further reduce the manufacturing and use costs of MRI systems. In addition, MgB2 bulk materials also have the potential to be used as hydrogen storage materials in solid oxide fuel cells, propellants in the aviation field, cathode solutions in Li-S batteries, and even in the field of photocatalysis (Green Chemistry Letters and Reviews, 2022, 15(3): 646-657.).

[0003] Currently, the methods for preparing MgB2 bulk materials mainly include hot isostatic pressing (such as the literature Applied Physics Letters. 2003, 82(23): 4104-4106) and solid-phase sintering (such as the Chinese authorized invention patent with application number 201010561460.3, the Chinese authorized invention patent with application number 201910452039.X). The hot isostatic pressing method can prepare high-performance MgB2 bulk materials with almost 100% density. However, its equipment cost is high and the process is complex, which is not suitable for large-scale commercial production. The solid-phase sintering method is to uniformly mix Mg powder and B powder in an oxygen-free environment, press them into blocks in a mold, and through the heat treatment and cooling process, the formed MgB2 bulk materials can be obtained. Although the solid-phase sintering method has a simple process and is easy to operate, the MgB2 bulk materials prepared by the solid-phase sintering method often have disadvantages such as poor grain connectivity, many pores, and low density, resulting in a low critical current density J C of the MgB2 bulk materials, which severely limits its commercial application process. Some researchers have also used a two-step heat treatment method after blending Mg powder and B powder to prepare highly dense MgB2 bulk materials (the Chinese authorized invention patent with application number 200510111916.5).

[0004] Although the preparation methods disclosed above can produce MgB2 bulk materials, in summary, the hot isostatic pressing method is costly and difficult to meet industrial needs; the MgB2 produced by the solid phase sintering method is a loose, porous, low-density bulk material; and the problem with the two-step method is that the reaction is insufficient and Mg or B may remain; in addition, long-term high-temperature insulation treatment is prone to produce non-superconducting phases such as MgB4, which affects grain connectivity. Summary of the invention

[0005] The technical problem to be solved by the present invention is to provide a method for preparing a high-density MgB2 block in view of the deficiencies of the above-mentioned prior art. The method first presses B powder into a dense B block and then lays Mg powder around it for thermal sintering treatment, so that the Mg powder diffuses to the B block located in the center and quickly generates a MgB2 block, and the voids generated when generating MgB2 are concentrated on the outside, thereby obtaining a high-density MgB2 block, and it is not easy to have Mg and B residues, reducing the preparation cost, and solving the problem that the existing preparation method has high cost and MgB2 is a loose, porous, low-density block.

[0006] In order to solve the above technical problems, the technical solution adopted by the present invention is: a method for preparing a high-density MgB2 block, characterized in that the method comprises the following steps:

[0007] Step 1: Grind the B powder into an agate mortar and grind it thoroughly, and grind the Mg powder into another agate mortar and grind it thoroughly to obtain uniform and non-agglomerated ground B powder and ground Mg powder respectively;

[0008] Step 2: Put the ground B powder obtained in step 1 into a briquetting mold, and then load it onto a hydraulic press for pressing to obtain a B block;

[0009] Step 3: placing the block B obtained in step 2 in a block pressing mold, laying the ground Mg powder obtained in step 1 around the block B, and then loading it into a hydraulic press for pressing to obtain a mixed block;

[0010] Step 4: Place the mixed block obtained in step 3 into a quartz boat, seal the quartz boat with iron wire, and then place it in a tubular vacuum furnace, heat it up under the protection of an argon atmosphere for thermal sintering, and then cool it with the furnace to obtain a high-density MgB2 block.

[0011] In the present invention, after the B block is placed in the briquetting mold, ground Mg powder is laid around the B block, thereby avoiding the problem that the flatness of the bottom of the B block in the mixed block after pressing is difficult to maintain and control due to laying Mg powder on the bottom of the B block, thereby improving the repetitive stability of the preparation method and simplifying the operation process.

[0012] The above-mentioned method for preparing a highly dense MgB2 bulk material is characterized in that, in step one, the mass ratio of the Mg powder to the B powder is 1 to 1.3:1. By controlling the mass ratio of the Mg powder to the B powder, the present invention compensates for the volatilization loss of the Mg powder during the subsequent hot sintering process, ensures the full reaction between the Mg powder and the B powder, and thus obtains a MgB2 phase with high purity.

[0013] The above-mentioned method for preparing a highly dense MgB2 bulk material is characterized in that, in step two, the pressure used for pressing is 4 MPa to 20 MPa, and the pressure holding time is 3 min to 20 min.

[0014] The above-mentioned method for preparing a highly dense MgB2 bulk material is characterized in that, in step three, the pressure used for pressing is 4 MPa to 20 MPa, and the pressure holding time is 3 min to 20 min.

[0015] By controlling the pressure and pressure holding time of the two pressings, the present invention enables the fragile B block to be successfully formed, and then a complete mixed block is obtained.

[0016] The above-mentioned method for preparing a highly dense MgB2 bulk material is characterized in that, in step four, the heating rate used for the hot sintering treatment is 5 °C / min, the sintering temperature is 500 °C to 900 °C, and the heat preservation time is 30 min to 300 min. By controlling the sintering process parameters, especially the sintering temperature, the present invention enables the Mg powder and the B powder to fully react to form the MgB2 phase, and at the same time avoids the problems of grain growth caused by too high temperature, the formation of MgB4 and excessive MgO, which reduce the phase purity of MgB2 and thus affect the performance of the MgB2 bulk material.

[0017] The present invention has the following advantages compared with the prior art:

[0018] 1. Different from the sintering process of the conventional solid-phase method in which Mg melts and diffuses to react with B, leaving voids in situ, resulting in a porous and low-density MgB2 bulk material, the present invention first presses the B powder into a dense B block and then lays the Mg powder around it. Thus, during the hot sintering process, the surrounding Mg powder diffuses towards the B block located in the center and quickly forms a MgB2 bulk material, making the voids left in situ by the diffusion of the Mg powder, that is, the voids generated when MgB2 is formed, concentrated on the outside, and a highly dense MgB2 bulk material is obtained.

[0019] 2. During the preparation process of the present invention, the B block is wrapped by Mg, increasing the diffusion interface between Mg and B and promoting the full reaction between Mg and B. Therefore, the formed MgB2 bulk material has high purity and is not prone to the residue of Mg and B.

[0020] 3. The preparation method of the present invention is simple, does not require complex equipment, and only requires requirements for the pressing die. Therefore, the preparation cost is low and industrial production can be realized.

[0021] The technical solution of the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. Description of the Drawings

[0022] Figure 1 It is the process flow chart for the preparation of the high-density MgB2 bulk material of the present invention.

[0023] Figure 2 It is the X-ray diffraction image of the high-density MgB2 bulk material prepared in Example 1 of the present invention.

[0024] Figure 3 It is the SEM morphology image of the high-density MgB2 bulk material prepared in Example 1 of the present invention. Detailed Embodiments

[0025] Example 1

[0026] As Figure 1 shown, this example includes the following steps:

[0027] Step 1: Put 1.0 g of B powder into an agate mortar and grind it thoroughly. Separately, take 1.1 g of Mg powder and put it into another agate mortar and grind it thoroughly to obtain uniformly dispersed and non-agglomerated ground B powder and ground Mg powder respectively.

[0028] Step 2: Put the ground B powder obtained in Step 1 into a briquetting mold with a diameter of 10 mm, then load it onto a hydraulic press, and press it under a pressure of 6 MPa for 10 minutes to obtain a B block.

[0029] Step 3: Place the B block obtained in Step 2 into a briquetting mold with a diameter of 13 mm, and spread the ground Mg powder obtained in Step 1 around the B block. Then load it onto a hydraulic press and press it under a pressure of 10 MPa for 15 minutes to obtain a mixed block.

[0030] Step 4: Put the mixed block obtained in Step 3 into a quartz boat, seal the quartz boat with iron wire, then place it in a tube-type vacuum furnace, heat it to 700 °C at a heating rate of 5 °C / min under the protection of an argon atmosphere and keep it warm for 120 minutes, and then cool it with the furnace to obtain a high-density MgB2 bulk material.

[0031] Figure 2 It is the X-ray diffraction image of the high-density MgB2 bulk material prepared in this example. From Figure 2 it can be seen that the X-ray diffraction characteristic peaks of this MgB2 bulk material (corresponding to the card number PDF#04-010-6) are very sharp, indicating that the generated MgB2 has a very high purity and good crystallinity.

[0032] Figure 3This is the SEM morphology image of the high-density MgB2 block prepared in this example. Figure 3 It can be seen that the MgB2 block has a flaky morphology, and the size and uniformity of the flaky structure are good, indicating that the MgB2 block has good crystallinity; in addition, there is almost no gap between the MgB2 flakes, indicating that the density of the MgB2 block is extremely high, that is, the prepared MgB2 block has the characteristics of high density.

[0033] In summary, the MgB2 bulk material prepared in this embodiment has high crystallinity and high density.

[0034] Example 2

[0035] like Figure 1 As shown, this embodiment includes the following steps:

[0036] Step 1: Put 1.0 g of B powder into an agate mortar and grind them thoroughly, and take 1.0 g of Mg powder into another agate mortar and grind them thoroughly to obtain uniform and non-agglomerated ground B powder and ground Mg powder respectively;

[0037] Step 2: Put the ground B powder obtained in step 1 into a briquetting mold with a diameter of 10 mm, then load it onto a hydraulic press, and press it at a pressure of 8 MPa for 5 minutes to obtain a B block;

[0038] Step 3: Place the block B obtained in step 2 in a briquetting mold with a diameter of 13 mm, and lay the ground Mg powder obtained in step 1 around the block B, then load it into a hydraulic press, and press it at a pressure of 8 MPa for 12 minutes to obtain a mixed block;

[0039] Step 4: Place the mixed block obtained in step 3 into a quartz boat, seal the quartz boat with wire, and then place it in a tubular vacuum furnace. Heat the temperature to 600°C at a heating rate of 5°C / min under argon atmosphere and keep it warm for 50 minutes. Then cool it with the furnace to obtain a high-density MgB2 block.

[0040] The properties of the MgB2 block prepared in this example are basically the same as those in Example 1.

[0041] Example 3

[0042] like Figure 1 As shown, this embodiment includes the following steps:

[0043] Step 1: Grind 1.0 g of B powder into an agate mortar and grind it thoroughly. Grind 1.2 g of Mg powder into another agate mortar and grind it thoroughly to obtain uniform and non-agglomerated ground B powder and ground Mg powder respectively.

[0044] Step 2: Put the ground B powder obtained in step 1 into a briquetting mold with a diameter of 10 mm, then load it onto a hydraulic press, and press it at a pressure of 15 MPa for 15 minutes to obtain a B block;

[0045] Step 3: Place the block B obtained in step 2 in a briquetting mold with a diameter of 13 mm, and lay the ground Mg powder obtained in step 1 around the block B, then load it into a hydraulic press, and press it at a pressure of 12 MPa for 10 minutes to obtain a mixed block;

[0046] Step 4: Place the mixed block obtained in step 3 into a quartz boat, seal the quartz boat with wire, and then place it in a tubular vacuum furnace. Under the protection of argon atmosphere, heat it to 800°C at a heating rate of 5°C / min and keep it warm for 200 minutes. Then cool it with the furnace to obtain a high-density MgB2 block.

[0047] The properties of the MgB2 block prepared in this example are basically the same as those in Example 1.

[0048] Example 4

[0049] like Figure 1 As shown, this embodiment includes the following steps:

[0050] Step 1: Grind 1.0 g of B powder into an agate mortar and grind it thoroughly. Grind 1.3 g of Mg powder into another agate mortar and grind it thoroughly to obtain uniform and non-agglomerated ground B powder and ground Mg powder respectively.

[0051] Step 2: Put the ground B powder obtained in step 1 into a briquetting mold with a diameter of 10 mm, then load it onto a hydraulic press, and press it at a pressure of 20 MPa for 8 minutes to obtain a B block;

[0052] Step 3: Place the block B obtained in step 2 in a briquetting mold with a diameter of 13 mm, and lay the ground Mg powder obtained in step 1 around the block B, then load it into a hydraulic press, and press it at a pressure of 20 MPa for 15 minutes to obtain a mixed block;

[0053] Step 4: Place the mixed block obtained in step 3 into a quartz boat, seal the quartz boat with wire, and then place it in a tubular vacuum furnace. Under the protection of argon atmosphere, heat it to 900°C at a heating rate of 5°C / min and keep it warm for 90 minutes. Then cool it with the furnace to obtain a high-density MgB2 block.

[0054] The properties of the MgB2 block prepared in this example are basically the same as those in Example 1.

[0055] Example 5

[0056] like Figure 1As shown, this embodiment includes the following steps:

[0057] Step 1: Put 1.0 g of B powder into an agate mortar and grind it thoroughly. Take another 1.0 g of Mg powder and put it into another agate mortar and grind it thoroughly to obtain uniformly dispersed and non-agglomerated ground B powder and ground Mg powder respectively.

[0058] Step 2: Put the ground B powder obtained in Step 1 into a briquetting die with a diameter of 10 mm, then load it onto a hydraulic press, and keep it under pressure for 3 min at a pressure of 10 MPa for pressing to obtain a B block.

[0059] Step 3: Place the B block obtained in Step 2 into a briquetting die with a diameter of 13 mm, and spread the ground Mg powder obtained in Step 1 around the B block. Then load it onto a hydraulic press and keep it under pressure for 20 min at a pressure of 4 MPa for pressing to obtain a mixed block.

[0060] Step 4: Put the mixed block obtained in Step 3 into a quartz boat, seal the quartz boat with iron wire, then place it in a tubular vacuum furnace, heat it up to 500 °C at a heating rate of 5 °C / min under the protection of an argon atmosphere and keep it at this temperature for 300 min, and then cool it down with the furnace to obtain a highly dense MgB₂ block.

[0061] The properties of the MgB₂ block prepared in this embodiment are basically the same as those in Example 1.

[0062] Example 6

[0063] As Figure 1 shown, this embodiment includes the following steps:

[0064] Step 1: Put 1.0 g of B powder into an agate mortar and grind it thoroughly. Take another 1.1 g of Mg powder and put it into another agate mortar and grind it thoroughly to obtain uniformly dispersed and non-agglomerated ground B powder and ground Mg powder respectively.

[0065] Step 2: Put the ground B powder obtained in Step 1 into a briquetting die with a diameter of 10 mm, then load it onto a hydraulic press, and keep it under pressure for 20 min at a pressure of 4 MPa for pressing to obtain a B block.

[0066] Step 3: Place the B block obtained in Step 2 into a briquetting die with a diameter of 13 mm, and spread the ground Mg powder obtained in Step 1 around the B block. Then load it onto a hydraulic press and keep it under pressure for 3 min at a pressure of 18 MPa for pressing to obtain a mixed block.

[0067] Step 4: Put the mixed block obtained in Step 3 into a quartz boat, seal the quartz boat with iron wire, then place it in a tubular vacuum furnace, heat it up to 900 °C at a heating rate of 5 °C / min under the protection of an argon atmosphere and keep it at this temperature for 30 min, and then cool it down with the furnace to obtain a highly dense MgB₂ block.

[0068] The properties of the MgB2 bulk material prepared in this example are basically the same as those in Example 1.

[0069] As described above, it is only a preferred embodiment of the present invention and does not impose any limitations on the present invention. Any simple modifications, changes, and equivalent variations made to the above embodiments based on the technical essence of the invention still fall within the protection scope of the technical solution of the present invention.

Claims

1. A method for preparing a high-density MgB2 block, characterized in that: The method comprises the following steps: Step 1: Grind the B powder into an agate mortar and grind it thoroughly, and grind the Mg powder into another agate mortar and grind it thoroughly to obtain uniform and non-agglomerated ground B powder and ground Mg powder respectively; Step 2: Put the ground B powder obtained in step 1 into a briquetting mold, and then load it onto a hydraulic press for pressing to obtain a B block; the pressing pressure is 4MPa to 20MPa, and the holding time is 3min to 20min; Step 3, placing the block B obtained in step 2 in a block pressing mold, laying the ground Mg powder obtained in step 1 around the block B, and then loading it onto a hydraulic press for pressing to obtain a mixed block; the pressing pressure is 4MPa to 20MPa, and the holding time is 3min to 20min; Step 4: Place the mixed block obtained in step 3 into a quartz boat, seal the quartz boat with iron wire, and then place it in a tubular vacuum furnace, heat it up under the protection of an argon atmosphere for thermal sintering, and then cool it with the furnace to obtain a high-density MgB2 block.

2. The method for preparing a high-density MgB2 block according to claim 1, characterized in that: The mass ratio of Mg powder to B powder in step 1 is 1-1.3:

1.

3. The method for preparing a high-density MgB2 block according to claim 1, characterized in that: The heating rate of the thermal sintering treatment in step 4 is 5°C / min, the sintering temperature is 500°C to 900°C, and the holding time is 30min to 300min.

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