High-purity, high-hardness and high-density oxygen-free boron block and preparation method thereof

Abstract

The application relates to the field of non-oxide structural ceramics, and particularly relates to a high-purity, high-hardness and high-density oxygen-free boron block and a preparation method thereof. Commercial boron powder and boron carbide powder or a boron-carbon mixture are used as raw materials, the powder is proportioned, the raw material powder is mixed, dried and sieved, and then sintering is carried out on the powder in a pressureless sintering, hot-pressing sintering or discharge plasma sintering environment to obtain the required oxygen-free boron block. The B6O is removed by changing the content of the additive added to the boron powder, and then the high-purity, high-hardness and high-density oxygen-free boron block is obtained, and the microstructure and mechanical properties of the oxygen-free boron block are in-situ regulated.

Description

Technical Field

[0001] This invention relates to the field of non-oxide structural ceramics, specifically to a high-purity, high-hardness, and high-density oxygen-free boron bulk and its preparation method. Background Technology

[0002] Boron (B) is widely used in various fields such as cutting tools, thermoelectric conversion materials, semiconductor targets, propulsion devices, and nuclear energy applications due to its lightweight, high strength, high hardness, and high melting point. Elemental boron is also a highly efficient neutron absorber (~3840 barns) in the nuclear energy industry. There are two main types of commercially available boron powder. One type is micron-sized amorphous boron powder obtained through a metal reduction method using boron oxide and magnesium as reducing agents. Using this method, the purity of crude boron is 80%, which increases to over 95% after purification, but it has a high oxygen content. The other type is crystalline boron powder obtained by zone melting boron powder to obtain boron crystal blocks, which are then crushed. This type has the advantages of high purity and low oxygen content, but the grain size is large, making sintering difficult.

[0003] High-purity boron powder is difficult to obtain and expensive. Boron has a melting point of only 2076℃, and its sintering window is very narrow, which makes sintering difficult and the bulk boron is prone to cracking. Another process for preparing high-purity boron is the reduction of haloboranes with hydrogen. The gas-to-gas reaction has low yield, complex synthesis equipment, and high manufacturing cost. (DRStern; Lynds, Lahmer. High-Purity Crystalline Boron. Journal of the Electrochemical Society. 1958, 105(11): 676.). Recently, Zhang et al. used commercial boron powder as raw material to densify polycrystalline rhombic boron bulks by spark plasma sintering (SPS) (Journal of Materials Science & Technology, 2022, 99: 148-160). The hardness and fracture toughness of the prepared β-B were approximately 31 GPa and 2.2 MPa m1 / 2, respectively. The results show that the in-situ grown nano-boron-rich oxides enhanced the densification and mechanical properties of β-B. However, the presence of oxides is detrimental to some applications requiring high-purity boron, such as semiconductor pure boron sputtering targets. Therefore, with the increasing demand for high-precision applications, the preparation of high-purity oxygen-free boron bulk materials is of great significance.

[0004] For commercial boron powder, some low-melting-point metal oxides are inevitably present in the starting boron powder. The oxygen remaining in the boron powder is difficult to completely remove through post-processing, and these oxygen impurities can also make subsequent sintering difficult and prone to cracking.

[0005] Therefore, by adding a small amount of additives to boron powder, the present invention can not only achieve sintering densification of boron powder, but also remove impurities such as B6O from boron blocks in situ, thereby obtaining pure oxygen-free elemental boron blocks with excellent mechanical properties. Summary of the Invention

[0006] To address the shortcomings of existing technologies, the present invention aims to provide a high-purity, high-hardness, and high-density oxygen-free boron bulk and its preparation method. This invention uses commercially available boron powder as the starting material. Residual oxygen impurities in the powder react in situ with elemental boron to form submicron-scale boron-rich oxides (e.g., B6O grains). These oxygen impurities are difficult to completely remove through post-processing. To address this, the present invention utilizes additional additives such as boron carbide or a mixture of boron and carbon to not only remove oxygen from the boron bulk but also form additional boron during the reaction, thus improving the yield of pure boron. The pure boron bulk obtained using this method exhibits characteristics such as uniform structure, refined grains, and excellent mechanical properties.

[0007] To achieve the above objectives, the present invention is implemented through the following technical solution:

[0008] This invention provides a high-purity, high-hardness, and high-density oxygen-free boron bulk material, using commercially available boron powder and boron carbide powder or a mixture of boron and carbon as raw materials, and proportioning the raw materials according to any one of the following chemical reaction equations (1) to (3):

[0009] (100-y) B + y B₂O₃ + 3y B x C=(100+13y) B + 3y CO (1)

[0010] (100-y) B + y B2O3 + 3y B4C=(100+13y) B + 3y CO (2)

[0011] (100-y) B + y B2O3 + 3y C=(100+y) B + 3y CO (3)

[0012] The parameter x has a range of 4 ≤ x ≤ 10.5, and the parameter y has a range of 0 ≤ y ≤ 100. The value of x depends on the solid solubility of boron carbide, i.e., the boron-to-carbon ratio; the value of y depends on the oxygen content in the actual boron powder. The oxygen content in commercially available boron powder varies. According to reaction formula (4), powder with a higher oxygen content will also form boron blocks with a higher content of boron oxides after sintering. According to chemical reaction formula (5), adding boron carbide powder or boron-carbon mixtures and other additives to the boron powder will gradually consume the already formed boron oxides. By removing easily volatile impurities such as Mg in the boron through in-situ vacuum treatment during the sintering process, a high-purity boron block without oxides is finally formed.

[0013] 16 B + B₂O₃ = 3 B₆O (4)

[0014] B6O + B4C = 10B + CO (5)

[0015] As a further optimization of the present invention, the carbon is graphite or carbon black.

[0016] As a further optimization of the present invention, the graphite has a purity greater than 99% and a particle size of 0.5-100μm; the carbon black has a purity greater than 99% and a particle size of 5-500nm.

[0017] As a further optimization of the present invention, the purity of B4C is greater than 99% and the particle size is 0.5-5μm; when x=6, the purity of B6C is greater than 99% and the particle size is 1-5μm.

[0018] This invention also provides a method for preparing the high-purity, high-hardness, and high-density oxygen-free boron bulk material described above, the method comprising:

[0019] Step 1: Weigh the raw material powder according to the proportions of the designed chemical reaction equation, mix the raw material powder, dry it, and sieve it.

[0020] Step 2: Pour the raw material powder obtained in Step 1 into a mold and sinter it under pressureless sintering, hot pressing sintering, or spark plasma sintering conditions to obtain the desired oxygen-free boron block. Densification and performance optimization of the boron block are achieved by changing parameters such as sintering temperature, holding time, loading pressure, and heating rate.

[0021] As a further optimization of the present invention, in step 2, the sintering environment is a vacuum or a flowing argon atmosphere.

[0022] As a further optimization of the present invention, in step 2, the sintering temperature range is 1600℃-2000℃.

[0023] As a further optimization of the present invention, in step 2, the heat preservation time ranges from 5 to 180 minutes.

[0024] As a further optimization of the present invention, in step 2, the loading pressure range is 5-75 MPa.

[0025] As a further optimization of the present invention, in step 2, the heating rate ranges from 10 to 300°C / min.

[0026] The technical solution provided by this invention has the following beneficial effects:

[0027] (1) In the sintering of the initial boron powder, B6O particles inevitably form in the boron block, making it impossible to obtain a pure boron block. This invention removes B6O by adding boron carbide or a mixture of boron and carbon as an additive and by changing the additive content. This effectively removes oxygen impurities from the boron powder and forms additional pure boron during the reaction process, thereby obtaining a high-purity, high-hardness, and high-density oxygen-free boron block. Its microstructure and mechanical properties can be controlled in situ, which is particularly important for applications requiring high-purity boron (such as semiconductor pure boron targets).

[0028] (2) The additives in this invention not only help with deoxygenation but also promote densification during the sintering process, resulting in a higher density in the final boron bulk. High density means fewer pores and defects, which is crucial for improving the mechanical properties of the material. This invention utilizes advanced sintering technologies such as pressureless sintering, hot pressing, or spark plasma sintering (SPS), combined with reasonable sintering parameters (such as sintering temperature, holding time, loading pressure, and heating rate), to achieve densification of the boron bulk, avoid cracking, and improve the overall performance of the bulk.

[0029] (3) The chemical reaction equation in this invention provides a variety of raw material ratios to choose from, and the y-value can be flexibly adjusted according to the oxygen content in commercially available boron powder, thereby optimizing the reaction process and product performance. At the same time, the flexible adjustment of sintering parameters also provides more possibilities for performance optimization.

[0030] (4) Compared with the traditional high-purity boron preparation process, the method of the present invention not only simplifies the preparation process and reduces the complexity of equipment, but also improves the yield and purity, thus having lower manufacturing costs and higher economic benefits.

[0031] (5) The raw materials of the present invention are readily available, the preparation process is mature and the cycle is short. The sintering and densification of boron bulk can be achieved at 1600℃-2000℃, which is conducive to reducing the energy consumption required for the material preparation process and obtaining boron bulk with high density. Attached Figure Description

[0032] Figure 1 The microstructure of the sample was obtained for Comparative Example 2;

[0033] Figure 2 XRD patterns of the sample were obtained for Comparative Example 2;

[0034] Figure 3 The microstructure of the sample was obtained for Comparative Example 3;

[0035] Figure 4 XRD patterns of the sample were obtained for Comparative Example 3;

[0036] Figure 5 The microstructure of the sample obtained in Example 1;

[0037] Figure 6 The microstructure of the sample obtained in Example 2 is shown. Detailed Implementation

[0038] To enable those skilled in the art to better understand the technical solutions of the present invention, the preferred embodiments of the present invention are described below in conjunction with specific examples. However, these should not be construed as limiting the present invention and are merely examples.

[0039] Unless otherwise specified, the test methods or experimental methods described in the following examples are conventional methods; unless otherwise specified, the reagents and materials are obtained from conventional commercial sources or prepared by conventional methods.

[0040] Comparative Example 1

[0041] Using boron powder (purity 95%, particle size 0.1-5μm) as raw material, the obtained boron sample contained 16% (volume content) of B6O as a second phase.

[0042] The weighed powder is soaked in ethanol (purity >99%) for 1-6 hours, and the resulting slurry is dried at 60-85℃ by vacuum rotary evaporation. After drying, the powder is crushed and sieved, then poured into a graphite mold and pressure sintered using a discharge plasma sintering device. The entire process is carried out under vacuum.

[0043] The sintering process includes the following steps: From room temperature to 450°C, the temperature is increased at a rate of 100°C / min, and a pressure of 5 MPa is applied to the sample. The pressure is then increased to 60 MPa over 2 minutes. From 450°C to 2000°C, the temperature is increased at a rate of 100°C / min, and the pressure is 60 MPa. After holding at 2000°C for 5 minutes, the pressure is reduced to 5 MPa and heating is stopped. The sample is then cooled to room temperature with the furnace.

[0044] Compared to samples with added additives, the resulting samples contained 16% (by volume) of B6O as a second phase. The relative density of the boron bulk was 99.8%, the Vickers hardness was 30-38 GPa, the three-point bending strength was 140-300 MPa, and the fracture toughness was 2.5-3.5 MPa. 0.5 The thermal conductivity at room temperature is 15-20 W / mK.

[0045] Comparative Example 2

[0046] Using boron powder (purity 95%, particle size 0.1-5μm) as raw material, the obtained boron sample contained 16% (volume content) of B6O as a second phase.

[0047] The weighed powder is soaked in ethanol (purity >99%) for 1-6 hours, and the resulting slurry is dried at 60-85℃ by vacuum rotary evaporation. After drying, the powder is crushed and sieved, then poured into a graphite mold and pressure sintered using a discharge plasma sintering device. The entire process is carried out under vacuum.

[0048] The sintering process included the following steps: From room temperature to 450℃, the heating rate was 300℃ / min, and the pressure applied to the sample was 5 MPa. The pressure was then increased to 60 MPa over 2 minutes. From 450℃ to 1800℃, the heating rate was 300℃ / min, and the pressure was 60 MPa. After holding at 1800℃ for 5 minutes, the pressure was reduced to 5 MPa and heating was stopped. The sample was then cooled to room temperature with the furnace. The morphology and XRD pattern of the sintered sample are shown below. Figure 1 and Figure 2 As shown.

[0049] Compared to samples with added additives, the resulting samples contained 16% (by volume) of B6O as a second phase. The relative density of the boron bulk was 99.2%, the Vickers hardness was 30-38 GPa, the three-point bending strength was 140-300 MPa, and the fracture toughness was 2-3 MPa. 0.5 The thermal conductivity at room temperature is 12-18 W / mK.

[0050] Figure 1 The microstructure of the sample was obtained for Comparative Example 2. As can be seen from the figure, the gray part represents the boron matrix, and the white part represents boron-rich oxide grains.

[0051] Figure 2 The XRD of the sample was obtained for Comparative Example 2; it can be seen from the figure that the two typical phases corresponding to the microstructure are shown.

[0052] Comparative Example 3

[0053] Using boron powder (purity 95%, particle size 0.1-5μm) as raw material, the obtained boron sample contained 7% (volume content) of B6O as a second phase.

[0054] The weighed powder is soaked in ethanol (purity >99%) for 1-6 hours, and the resulting slurry is dried at 60-85℃ by vacuum rotary evaporation. After drying, the powder is crushed and sieved, then poured into a graphite mold and pressure sintered using a discharge plasma sintering device. The entire process is carried out under vacuum.

[0055] The sintering process included the following steps: From room temperature to 450℃, the heating rate was 50℃ / min, and a pressure of 5 MPa was applied to the sample. The pressure was then increased to 60 MPa over 2 minutes. From 450℃ to 1600℃, the heating rate was 50℃ / min, and the pressure was 60 MPa. After holding at 1600℃ for 5 minutes, the pressure was reduced to 5 MPa and heating was stopped. The sample was then cooled to room temperature with the furnace. The morphology and XRD pattern of the sintered sample are shown below. Figure 3 and Figure 4 As shown.

[0056] Compared to samples with added additives, the resulting samples contained 16% (by volume) of B6O as a second phase. The relative density of the boron bulk was 84.8%, the Vickers hardness was 15-25 GPa, the three-point bending strength was 140-250 MPa, and the fracture toughness was 2.5-3.5 MPa. 0.5 The thermal conductivity at room temperature is 8-12 W / mK.

[0057] Figure 3 The image shows the microstructure of the sample obtained for Comparative Example 3. As can be seen from the image, the gray area represents the boron matrix, the white area represents boron-rich oxide grains, and there are also a large number of pores.

[0058] Figure 4 The XRD pattern of the sample was obtained for Comparative Example 3. The figure shows the two typical phases corresponding to the microstructure.

[0059] Example 1

[0060] Boron powder (purity 95%, particle size 0.1-5μm) and B4C (particle size 0.5-5μm) were used as raw materials and the mixture was prepared according to equation (6):

[0061] 98 B + 2 B2O3+ 6 B4C=126 B + 6 CO (6)

[0062] A pure boron sample without the B6O phase was obtained.

[0063] Using ethanol (purity >99%) as the solvent and zirconia spheres as the mixing medium, the weighed powder is mixed using a mixer at a speed of 30-100 rpm. After mixing for 12-36 hours, the resulting slurry is dried at 60-85℃ via vacuum rotary evaporation. The dried powder is then crushed, sieved, and poured into a graphite mold. Pressure sintering is then performed using a discharge plasma sintering device, with the entire process conducted under vacuum.

[0064] The sintering process includes the following steps: From room temperature to 450℃, the temperature is increased at a rate of 300℃ / min, and a pressure of 5 MPa is applied to the sample. The pressure is then increased to 60 MPa over 2 minutes. From 450℃ to 1800℃, the temperature is increased at a rate of 300℃ / min, and the pressure is 60 MPa. After holding at 1800℃ for 5 minutes, the pressure is reduced to 5 MPa and heating is stopped. The sample is then cooled to room temperature with the furnace. The morphology of the sintered sample is as follows: Figure 5 As shown.

[0065] Compared to samples without additives, the obtained samples were pure boron samples without the B6O phase. The relative density of the pure boron bulk was 98.2%, the Vickers hardness was 30-35 GPa, the three-point bending strength was 140-300 MPa, and the fracture toughness was 3-3.5 MPa m. 0.5 The room temperature thermal conductivity is 20-30 W / mK.

[0066] Figure 5 The image shows the microstructure of the sample obtained in Example 1. As can be seen from the image, the gray area represents the boron matrix, and there are no white boron-rich oxide particles.

[0067] Example 2

[0068] Boron powder (purity 95%, particle size 0.1-5μm) and B4C (particle size 0.5-5μm) were used as raw materials and the mixture was prepared according to equation (6):

[0069] 98 B + 2 B2O3+ 6 B4C=126 B + 6 CO (6)

[0070] A pure boron sample without the B6O phase was obtained.

[0071] Using ethanol (purity >99%) as the solvent and zirconia spheres as the mixing medium, the weighed powder is mixed using a mixer at a speed of 30-100 rpm. After mixing for 12-36 hours, the resulting slurry is dried at 60-85℃ via vacuum rotary evaporation. The dried powder is then crushed, sieved, and poured into a graphite mold, where it is pressure sintered using a hot-pressing sintering device. The entire process is carried out under vacuum.

[0072] The sintering process includes the following steps: From room temperature to 450℃, the temperature is increased at a rate of 20℃ / min, and a pressure of 5 MPa is applied to the sample. The pressure is then increased to 60 MPa over 2 minutes. From 450℃ to 1800℃, the temperature is increased at a rate of 10℃ / min, and the pressure is 60 MPa. After holding at 1800℃ for 5 minutes, the pressure is reduced to 5 MPa and heating is stopped. The sample is then cooled to room temperature with the furnace. The morphology of the sintered sample is as follows: Figure 6 As shown.

[0073] Compared to samples without additives, the obtained samples were pure boron samples without the B6O phase. The relative density of the pure boron bulk was 98.2%, the Vickers hardness was 30-35 GPa, the three-point bending strength was 140-300 MPa, and the fracture toughness was 3-3.5 MPa m. 0.5 The room temperature thermal conductivity is 20-30 W / mK.

[0074] Figure 6 The image shows the microstructure of the sample obtained in Example 2. As can be seen from the image, the gray matrix is ​​boron, and there are no white boron-rich oxide particles.

[0075] Example 3

[0076] Boron powder (purity 95%, particle size 0.1-5μm) and B4C (particle size 0.5-5μm) were used as raw materials and the mixture was prepared according to equation (6):

[0077] 98 B + 2 B2O3+ 6 B4C=126 B + 6 CO (6)

[0078] The obtained boron sample contained 8% (volume content) of B6O as a second phase.

[0079] Using ethanol (purity >99%) as the solvent and zirconia balls as the mixing medium, the weighed powder is mixed using a mixer at a speed of 30-100 rpm. After mixing for 12-36 hours, the resulting slurry is dried at 60-85℃ via vacuum rotary evaporation. The dried powder is then heat-treated using a pressureless sintering device. After heat treatment, the powder is crushed, sieved, and then sintered again under pressureless conditions. The entire process is carried out under vacuum.

[0080] The pressureless sintering process includes the following steps: heating from room temperature to 1650℃ at a rate of 10℃ / min, holding at 1650℃ for 0.5 hours, then stopping heating, and allowing the sample to cool to room temperature with the furnace. The pressureless sintering process after crushing and sieving the heat-treated powder includes the following steps: heating from room temperature to 2000℃ at a rate of 10℃ / min, holding at 2000℃ for 3 hours, then stopping heating, and allowing the sample to cool to room temperature with the furnace.

[0081] Compared to samples without additives, the obtained samples contained 8% (by volume) of B6O as a second phase. The relative density of the boron bulk was 91.8%, the Vickers hardness was 20-25 GPa, the three-point bending strength was 160-250 MPa, and the fracture toughness was 2-2.5 MPa. 0.5 The thermal conductivity at room temperature is 8-12 W / mK.

[0082] Example 4

[0083] Boron powder (80% purity, particle size 0.1-5μm) and B4C (0.5-5μm particle size) were used as raw materials and formulated according to equation (7):

[0084] 93 B + 7 B2O3+ 21 B4C=191 B + 21 CO (7)

[0085] A pure boron sample without the B6O phase was obtained.

[0086] Using ethanol (purity >99%) as the solvent and zirconia spheres as the mixing medium, the weighed powder is mixed using a mixer at a speed of 30-100 rpm. After mixing for 12-36 hours, the resulting slurry is dried at 60-85℃ via vacuum rotary evaporation. The dried powder is then crushed, sieved, and poured into a graphite mold. Pressure sintering is then performed using a discharge plasma sintering device, with the entire process conducted under vacuum.

[0087] The sintering process includes the following steps: From room temperature to 450°C, the temperature is increased at a rate of 300°C / min, and a pressure of 5 MPa is applied to the sample. The pressure is then increased to 60 MPa over 2 minutes. From 450°C to 1800°C, the temperature is increased at a rate of 300°C / min, and the pressure is 60 MPa. After holding at 1800°C for 5 minutes, the pressure is reduced to 5 MPa and heating is stopped. The sample is then cooled to room temperature with the furnace.

[0088] Compared to samples without additives, the obtained samples were pure boron samples without the B6O phase. The relative density of the pure boron bulk was 97.8%, the Vickers hardness was 28-33 GPa, the three-point bending strength was 130-280 MPa, and the fracture toughness was 3-3.5 MPa m. 0.5 The room temperature thermal conductivity is 20-30 W / mK.

[0089] Example 5

[0090] Boron powder (purity 95%, particle size 0.1-5μm) and boron-rich boron carbide (B6C particle size 1-5μm) were used as raw materials and the mixture was prepared according to equation (8):

[0091] 98 B + 2 B2O3+ 6 B6C=138 B + 6 CO (8)

[0092] A pure boron sample without the B6O phase was obtained.

[0093] Using ethanol (purity >99%) as the solvent and zirconia spheres as the mixing medium, the weighed powder is mixed using a mixer at a speed of 30-100 rpm. After mixing for 12-36 hours, the resulting slurry is dried at 60-85℃ via vacuum rotary evaporation. The dried powder is then crushed, sieved, and poured into a graphite mold. Pressure sintering is then performed using a discharge plasma sintering device, with the entire process conducted under vacuum.

[0094] The sintering process includes the following steps: From room temperature to 450°C, the temperature is increased at a rate of 300°C / min, and a pressure of 5 MPa is applied to the sample. The pressure is then increased to 60 MPa over 2 minutes. From 450°C to 1800°C, the temperature is increased at a rate of 300°C / min, and the pressure is 60 MPa. After holding at 1800°C for 5 minutes, the pressure is reduced to 5 MPa and heating is stopped. The sample is then cooled to room temperature with the furnace.

[0095] Compared to samples without additives, the obtained samples were pure boron samples without the B6O phase. The relative density of the pure boron bulk was 98.8%, the Vickers hardness was 30-35 GPa, the three-point bending strength was 140-300 MPa, and the fracture toughness was 3-3.5 MPa m. 0.5 The room temperature thermal conductivity is 20-30 W / mK.

[0096] Example 6

[0097] Boron powder (purity 95%, particle size 0.1-5μm) and carbon black (particle size 5-500nm) are used as raw materials, and the mixture is prepared according to equation (9):

[0098] 98 B + 2 B2O3+ 6 C=102 B + 6 CO (9)

[0099] A pure boron sample without the B6O phase was obtained.

[0100] Using ethanol (purity >99%) as the solvent and zirconia spheres as the mixing medium, the weighed powder is mixed using a mixer at a speed of 30-100 rpm. After mixing for 12-36 hours, the resulting slurry is dried at 60-85℃ via vacuum rotary evaporation. The dried powder is then crushed, sieved, and poured into a graphite mold. Pressure sintering is then performed using a discharge plasma sintering device, with the entire process conducted under vacuum.

[0101] The sintering process includes the following steps: From room temperature to 450°C, the temperature is increased at a rate of 300°C / min, and a pressure of 5 MPa is applied to the sample. The pressure is then increased to 60 MPa over 2 minutes. From 450°C to 1800°C, the temperature is increased at a rate of 300°C / min, and the pressure is 60 MPa. After holding at 1800°C for 5 minutes, the pressure is reduced to 5 MPa and heating is stopped. The sample is then cooled to room temperature with the furnace.

[0102] Compared to samples without additives, the obtained samples were pure boron samples without the B6O phase. The relative density of the pure boron bulk was 99.1%, the Vickers hardness was 30-35 GPa, the three-point bending strength was 160-300 MPa, and the fracture toughness was 3-3.5 MPa m. 0.5 The room temperature thermal conductivity is 20-30 W / mK.

[0103] Example 7

[0104] Boron powder (purity 95%, particle size 0.1-5μm) and graphite (particle size 0.5-100μm) are used as raw materials, and the ingredients are prepared according to equation (9):

[0105] 98 B + 2 B2O3+ 6 C=102 B + 6 CO (9)

[0106] A pure boron sample without the B6O phase was obtained.

[0107] Using ethanol (purity >99%) as the solvent and zirconia spheres as the mixing medium, the weighed powder is mixed using a mixer at a speed of 30-100 rpm. After mixing for 12-36 hours, the resulting slurry is dried at 60-85℃ via vacuum rotary evaporation. The dried powder is then crushed, sieved, and poured into a graphite mold. Pressure sintering is then performed using a discharge plasma sintering device, with the entire process conducted under vacuum.

[0108] The sintering process includes the following steps: From room temperature to 450°C, the temperature is increased at a rate of 300°C / min, and a pressure of 5 MPa is applied to the sample. The pressure is then increased to 60 MPa over 2 minutes. From 450°C to 1800°C, the temperature is increased at a rate of 300°C / min, and the pressure is 60 MPa. After holding at 1800°C for 5 minutes, the pressure is reduced to 5 MPa and heating is stopped. The sample is then cooled to room temperature with the furnace.

[0109] Compared to samples without additives, the obtained samples were pure boron samples without the B6O phase. The relative density of the pure boron bulk was 97.7%, the Vickers hardness was 25-30 GPa, the three-point bending strength was 130-250 MPa, and the fracture toughness was 3-3.5 MPa m. 0.5 The room temperature thermal conductivity is 20-30 W / mK.

[0110] Example 8

[0111] Boron powder (purity 95%, particle size 0.1-5μm) and B4C (particle size 0.5-5μm) were used as raw materials and the mixture was prepared according to equation (6):

[0112] 98 B + 2 B2O3+ 6 B4C=126 B + 6 CO (6)

[0113] A pure boron sample without the B6O phase was obtained.

[0114] Using ethanol (purity >99%) as the solvent and zirconia spheres as the mixing medium, the weighed powder is mixed using a mixer at a speed of 30-100 rpm. After mixing for 12-36 hours, the resulting slurry is dried at 60-85℃ via vacuum rotary evaporation. The dried powder is then crushed, sieved, and poured into a graphite mold. Pressure sintering is then performed using a discharge plasma sintering device, with the entire process conducted under vacuum.

[0115] The sintering process includes the following steps: From room temperature to 450°C, the temperature is increased at a rate of 300°C / min, and a pressure of 5 MPa is applied to the sample. From 450°C to 2000°C, the temperature is increased at a rate of 300°C / min. After reaching 2000°C, the pressure is increased to 75 MPa within 2 minutes, and then held at 2000°C for 10 minutes. After the holding period, the pressure is reduced to 5 MPa and heating is stopped. The sample is then cooled to room temperature with the furnace.

[0116] Compared to samples without additives, the obtained samples were pure boron samples without the B6O phase. The relative density of the pure boron bulk was 99.1%, the Vickers hardness was 31-35 GPa, the three-point bending strength was 150-300 MPa, and the fracture toughness was 3-3.5 MPa m. 0.5 The room temperature thermal conductivity is 20-30 W / mK.

[0117] Example 9

[0118] Boron powder (purity 95%, particle size 0.1-5μm) and B4C (particle size 0.5-5μm) were used as raw materials and the mixture was prepared according to equation (6):

[0119] 98 B + 2 B2O3+ 6 B4C=126 B + 6 CO (6)

[0120] A pure boron sample without the B6O phase was obtained.

[0121] Using ethanol (purity >99%) as the solvent and zirconia spheres as the mixing medium, the weighed powder is mixed using a mixer at a speed of 30-100 rpm. After mixing for 12-36 hours, the resulting slurry is dried at 60-85℃ via vacuum rotary evaporation. The dried powder is then crushed, sieved, and poured into a graphite mold. Pressure sintering is then performed using a discharge plasma sintering device, with the entire process conducted under vacuum.

[0122] The sintering process includes the following steps: from room temperature to 450°C, the heating rate is 200°C / min, and the pressure applied to the sample is 5 MPa. From 450°C to 1800°C, the heating rate is 200°C / min, and then the sample is held at 1800°C for 5 min. After the holding period, heating is stopped, and the sample is cooled to room temperature with the furnace.

[0123] Compared to samples without additives, the obtained samples were pure boron samples without the B6O phase. The relative density of the pure boron bulk was 97.5%, the Vickers hardness was 28-31 GPa, the three-point bending strength was 150-250 MPa, and the fracture toughness was 3-3.5 MPa m. 0.5 The thermal conductivity at room temperature is 15-25 W / mK.

[0124] In summary, by using commercial boron powder as raw material and adding boron carbide and other additives as oxygen scavengers, oxygen in the starting boron powder can be effectively removed, thereby obtaining oxygen-free boron blocks with high purity, high hardness, and high density.

[0125] The above are merely preferred embodiments of the present invention. It should be noted that the above preferred embodiments should not be considered as limitations on the present invention, and the scope of protection of the present invention should be determined by the scope defined in the claims. For those skilled in the art, several improvements and modifications can be made without departing from the spirit and scope of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A high-purity, high-hardness, and high-density oxygen-free boron bulk material, characterized in that, Commercially available boron powder and boron carbide powder are used as raw materials, or commercially available boron powder and carbon are used as raw materials, or commercially available boron powder and boron-rich boron carbide are used as raw materials; the raw materials are proportioned according to any one of the following chemical reaction equations (1) to (3), and sintered in an environment of pressureless sintering, hot press sintering or spark plasma sintering to obtain the required oxygen-free boron bulk; 98B+2B₂O₃+6B₆C=138B+6CO (1); (100-y)B+yB₂O₃+3yB₄C=(100+13y)B+3yCO (2); (100-y)B+yB₂O₃+3yC=(100+y)B+3yCO (3); Wherein, the value range of the parameter y is 0<y≤100; the purity of said B₄C is greater than 99%, and the particle size is 0.5-5μm; the purity of said B₆C is greater than 99%, and the particle size is 1-5μm.

2. The high-purity, high-hardness, and high-density oxygen-free boron bulk material according to claim 1, characterized in that, Said carbon is graphite or carbon black.

3. The high-purity, high-hardness, and high-density oxygen-free boron bulk material according to claim 2, characterized in that, The purity of said graphite is greater than 99%, and the particle size is 0.5-100μm; the purity of said carbon black is greater than 99%, and the particle size is 5-500nm.

4. A method for preparing a high-purity, high-hardness, and high-density oxygen-free boron bulk material as described in any one of claims 1-3, characterized in that, Said preparation method comprises: Step 1: Weigh the raw material powders according to the proportion of the designed chemical reaction equation, mix, dry and sieve the raw material powders; Step 2: Pour the raw material powder obtained in Step 1 into a mold, and sinter it in an environment of pressureless sintering, hot press sintering or spark plasma sintering to obtain the required oxygen-free boron bulk.

5. The method for preparing a high-purity, high-hardness, and high-density oxygen-free boron bulk material according to claim 4, characterized in that, In Step 2, the sintering atmosphere is vacuum or flowing argon atmosphere.

6. The method for preparing a high-purity, high-hardness, and high-density oxygen-free boron bulk material according to claim 4, characterized in that, In Step 2, the sintering temperature ranges from 1600°C to 2000°C.

7. The method for preparing a high-purity, high-hardness, and high-density oxygen-free boron bulk material according to claim 4, characterized in that, In Step 2, the holding time ranges from 5 to 180min.

8. The method for preparing a high-purity, high-hardness, and high-density oxygen-free boron bulk material according to claim 4, characterized in that, In Step 2, the applied pressure ranges from 5 to 75MPa.

9. The method for preparing a high-purity, high-hardness, and high-density oxygen-free boron bulk material according to claim 4, characterized in that, In Step 2, the heating rate ranges from 10 to 300°C / min.

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