A boron nitride-based ceramic composite and a method for producing the same

Abstract

The application belongs to the technical field of ceramic composite materials, and provides a boron nitride-based ceramic composite material and a preparation method thereof.The preparation method comprises the following steps: ball-milling hexagonal boron nitride, silicon dioxide, a metal oxide and a solvent, and then removing the solvent to obtain a ball-milled powder; sequentially drying and refining the ball-milled powder to obtain a mixed powder; and sequentially pre-pressing and sintering the mixed powder to obtain the boron nitride-based ceramic composite material.The boron nitride-based ceramic composite material prepared by the application has high compactness, excellent mechanical properties, thermal properties and dielectric properties, the relative density of the boron nitride-based ceramic composite material is 94.5-96%, the bending strength is 225-235 MPa, the dielectric constant is 4.10-4.12 F / m, and the tangent value of dielectric loss is 0.01; and the preparation method is simple, fast in preparation speed, and suitable for industrial application.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of ceramic composite materials, and particularly relates to a boron nitride-based ceramic composite material and a preparation method thereof. BACKGROUND

[0002] Hexagonal boron nitride (h-BN) ceramic is an advanced structural ceramic formed by sintering hexagonal boron nitride powder, and has excellent physical properties, such as high insulation, low dielectric coefficient, high thermal conductivity, and excellent thermal shock resistance. The hexagonal boron nitride ceramic is widely used as a wall material of a plasma engine nozzle. However, due to the special layered structure of the hexagonal boron nitride ceramic, the binding force in the c-axis direction is much smaller than the binding force perpendicular to the c-axis direction, and the van der Waals force between the layers is very weak, which results in poor mechanical properties and low strength of the prepared hexagonal boron nitride ceramic, thereby limiting the further development and application thereof.

[0003] When the silicon dioxide is combined with the hexagonal boron nitride, a very good synergistic strengthening phenomenon is exhibited, the sintering temperature can be reduced, and the mechanical properties of the composite material can be improved. However, when the composite material is used as a wall material of a plasma engine nozzle, the high-temperature mechanical strength is still insufficient, the thermal shock resistance is insufficient, and the plasma sputtering resistance is poor. Therefore, it has a good application prospect to research and develop a preparation method of a boron nitride-based ceramic composite material with high mechanical strength and good dielectric properties. SUMMARY

[0004] The present application aims at providing a boron nitride-based ceramic composite material and a preparation method thereof to overcome the defects in the prior art.

[0005] In order to achieve the above-mentioned application purposes, the present application provides the following technical solutions.

[0006] The present application provides a preparation method of a boron nitride-based ceramic composite material, comprising the following steps:

[0007] 1) Ball-milling hexagonal boron nitride, silicon dioxide, metal oxide and solvent, and removing the solvent to obtain a ball-milled powder;

[0008] 2) sequentially drying and refining the ball-milled powder to obtain a mixed powder;

[0009] 3) sequentially pre-pressing and sintering the mixed powder to obtain a boron nitride-based ceramic composite material;

[0010] In step 3), the sintering temperature is 1800-2000 DEG C, the sintering pressure is 30-50 MPa, and the sintering time is 10-20 min.

[0011] Preferably, the particle size of the hexagonal boron nitride in step 1) is 1-3 μm, and the purity of the hexagonal boron nitride is ≥99%; the particle size of the silicon dioxide is 3-5 μm, and the purity of the silicon dioxide is ≥99%.

[0012] Preferably, the metal oxide in step 1) is one or more of aluminum oxide, yttrium oxide and zirconium oxide, the particle size of the metal oxide is 1-3 μm, and the purity of the metal oxide is ≥99%.

[0013] Preferably, the solvent in step 1) is anhydrous ethanol; and the mass ratio of the hexagonal boron nitride, the silicon dioxide and the metal oxide is 70-75:15-20:5-10.

[0014] Preferably, the ball-to-material ratio of the ball milling in step 1) is 2-4:1, the speed of the ball milling is 200-300 r / min, and the time of the ball milling is 12-24 h.

[0015] Preferably, the method for removing the solvent in step 1) is rotary evaporation or suction filtration; the drying in step 2) is vacuum drying, the temperature of the vacuum drying is 60-80 ℃, the time of the vacuum drying is 12-24 h, and the vacuum degree of the vacuum drying is -0.15 to -0.05 MPa.

[0016] Preferably, the particle size of the mixed powder in step 2) is ≤75 μm; and the pressure of the pre-pressing in step 3) is 4-6 MPa, and the time of the pre-pressing is 1-3 min.

[0017] Preferably, in step 3), the temperature is raised to the sintering temperature in three stages, and the pressure is raised to the sintering pressure; the first sintering temperature is 900-1100 ℃, the first sintering pressure is 10-15 MPa; the second sintering temperature is 1500-1600 ℃, the second sintering pressure is 20-25 MPa; and the third sintering temperature is 1800-2000 ℃, and the third sintering pressure is 30-50 MPa.

[0018] Preferably, in step 3), the rate of raising the temperature from room temperature to the first sintering temperature is 80-120 ℃ / min, the rate of raising the temperature from the first sintering temperature to the second sintering temperature is 60-80 ℃ / min, and the rate of raising the temperature from the second sintering temperature to the third sintering temperature is 40-60 ℃ / min.

[0019] The application also provides a boron nitride-based ceramic composite material prepared by the preparation method.

[0020] The application has the following advantages:

[0021] 1) The boron nitride-based ceramic composite material prepared by the application has high density and good mechanical properties, the relative density thereof is 94.5-96%, and the bending strength thereof is 225-235 MPa.

[0022] 2) The dielectric performance of the boron nitride-based ceramic composite prepared by the method is excellent, and the dielectric constant is 4.10-4.12 F / m and the dielectric loss tangent is 0.01 in the frequency range of 2-18 GHz.

[0023] 3) The boron nitride-based ceramic composite can be quickly prepared by using the spark plasma sintering technology, and the comprehensive performance of the boron nitride-based ceramic composite is improved by adding metal oxides as the third phase, and the thermal and dielectric performances of the boron nitride-based ceramic composite can be effectively adjusted by controlling the sintering temperature, sintering time and proportioning of components, so that the boron nitride-based ceramic composite can meet different working requirements.

[0024] 4) The preparation method is simple, fast and suitable for industrial application. BRIEF DESCRIPTION OF DRAWINGS

[0025] Figure 1 SEM image of the planar boron nitride-based ceramic composite of Example 1;

[0026] Figure 2 SEM image of the cross-section of the boron nitride-based ceramic composite of Example 1;

[0027] Figure 3 The dielectric constant and dielectric loss tangent curve of the boron nitride-based ceramic composite of Example 1 in the frequency range of 2-18 GHz;

[0028] Figure 4 The dielectric constant and dielectric loss tangent curve of the boron nitride-based ceramic composite of Example 2 in the frequency range of 2-18 GHz. DETAILED DESCRIPTION

[0029] The application provides a preparation method of a boron nitride-based ceramic composite, which comprises the following steps:

[0030] 1) Ball milling hexagonal boron nitride, silicon dioxide, metal oxides and a solvent, and removing the solvent to obtain a ball-milled powder;

[0031] 2) sequentially drying and refining the ball-milled powder to obtain a mixed powder;

[0032] 3) sequentially pre-pressing and sintering the mixed powder to obtain a boron nitride-based ceramic composite;

[0033] The sintering temperature in step 3) is 1800-2000 DEG C, the sintering pressure is 30-50 MPa, and the sintering time is 10-20 min.

[0034] In the present application, the particle size of the hexagonal boron nitride in step 1) is preferably 1-3 μm, further preferably 1.5-2.5 μm, and more preferably 2 μm, and the purity of the hexagonal boron nitride is preferably ≥ 99%, and further preferably ≥ 99.5%; the particle size of the silicon dioxide is preferably 3-5 μm, further preferably 3.5-4.5 μm, and more preferably 4 μm, and the purity of the silicon dioxide is preferably ≥ 99%, and further preferably ≥ 99.5%.

[0035] In the present application, the metal oxide in step 1) is preferably one or more of aluminum oxide, yttrium oxide and zirconium oxide, the particle size of the metal oxide is preferably 1-3 μm, further preferably 1.5-2.5 μm, and more preferably 2 μm, and the purity of the metal oxide is preferably ≥ 99%, and further preferably ≥ 99.5%.

[0036] In the present application, the solvent in step 1) is preferably anhydrous ethanol; and the mass ratio of the hexagonal boron nitride, the silicon dioxide and the metal oxide is preferably 70-75:15-20:5-10, further preferably 71-74:16-19:6-9, and more preferably 72-73:17-18:7-8.

[0037] In the present application, the total volume of the hexagonal boron nitride, the silicon dioxide, the metal oxide, the solvent and the ball milling medium in step 1) is preferably 1 / 3-2 / 3 of the volume of the ball milling tank, and further preferably 1 / 2.

[0038] In the present application, the ball-to-material ratio of the ball milling in step 1) is preferably 2-4:1, further preferably 2.5-3.5:1, and more preferably 3:1; the speed of the ball milling is preferably 200-300 r / min, further preferably 220-280 r / min, and more preferably 240-260 r / min; and the time of the ball milling is preferably 12-24 h, further preferably 16-20 h, and more preferably 18 h.

[0039] In the present application, the method for removing the solvent in step 1) is preferably rotary evaporation or suction filtration; the drying in step 2) is preferably vacuum drying; the temperature of the vacuum drying is preferably 60-80℃, further preferably 65-75℃, and more preferably 70℃; the time of the vacuum drying is preferably 12-24 h, further preferably 16-20 h, and more preferably 18 h; and the vacuum degree of the vacuum drying is preferably -0.15 to -0.05 MPa, further preferably -0.12 to -0.08 MPa, and more preferably -0.1 MPa.

[0040] In the present application, the particle size of the mixed powder in step 2) is preferably ≤75 μm, further preferably ≤70 μm, and more preferably ≤60 μm; the pressure of the pre-pressing in step 3) is preferably 4-6 MPa, further preferably 4.5-5.5 MPa, and more preferably 5 MPa; and the time of the pre-pressing is preferably 1-3 min, further preferably 1.5-2.5 min, and more preferably 2 min.

[0041] In the present application, in step 3), the sintering is preferably performed in three stages, and the temperature is raised to the sintering temperature and the pressure is raised to the sintering pressure; the first sintering temperature is preferably 900-1100 °C, further preferably 950-1050 °C, and more preferably 1000 °C; the first sintering pressure is preferably 10-15 MPa, further preferably 12-14 MPa, and more preferably 13 MPa; the second sintering temperature is preferably 1500-1600 °C, further preferably 1520-1580 °C, and more preferably 1540-1560 °C; the second sintering pressure is preferably 20-25 MPa, further preferably 22-24 MPa, and more preferably 23 MPa; and the third sintering temperature is preferably 1800-2000 °C, further preferably 1850-1950 °C, and more preferably 1900 °C; and the third sintering pressure is preferably 30-50 MPa, further preferably 35-45 MPa, and more preferably 40 MPa.

[0042] In the present application, the sintering in step 3) is preferably performed under vacuum, and the vacuum degree is preferably ≤10 Pa, and further preferably ≤8 Pa.

[0043] In the present application, in step 3), the rate of raising the temperature from room temperature to the first sintering temperature is preferably 80-120 °C / min, further preferably 90-110 °C / min, and more preferably 100 °C / min; the rate of raising the temperature from the first sintering temperature to the second sintering temperature is preferably 60-80 °C / min, further preferably 65-75 °C / min, and more preferably 70 °C / min; and the rate of raising the temperature from the second sintering temperature to the third sintering temperature is preferably 40-60 °C / min, further preferably 45-55 °C / min, and more preferably 50 °C / min.

[0044] In the present application, after the sintering in step 3), the product is preferably cooled; and the cooling is preferably performed in two stages; the temperature of the first stage cooling is preferably 900-1100 °C, further preferably 950-1050 °C, and more preferably 1000 °C; the rate of the first stage cooling is preferably 20-30 °C / min, further preferably 22-28 °C / min, and more preferably 24-26 °C / min; and the temperature of the second stage cooling is preferably 20-30 °C, further preferably 22-26 °C, and more preferably 25 °C.

[0045] The application further provides the boron nitride-based ceramic composite material prepared by the preparation method.

[0046] The technical solutions provided by the application are described in detail below in combination with examples, but they should not be understood as limiting the protection scope of the application.

[0047] Example 1

[0048] 75 g of hexagonal boron nitride (the particle size of the hexagonal boron nitride is 3 μm, and the purity is 99%), 20 g of silicon dioxide (the particle size of the silicon dioxide is 5 μm, and the purity is 99.5%), and 5 g of aluminum oxide (the particle size of the aluminum oxide is 2 μm, and the purity is 99.5%) are put into a polyurethane ball mill tank with a volume of 150 mL, then the ball milling is carried out under the conditions that anhydrous ethanol is used as a solvent, agate balls are used as a ball milling medium, the ball-to-material ratio is 3:1, and the ball milling speed is 300 r / min for 24 h (the total volume of the hexagonal boron nitride, the silicon dioxide, the aluminum oxide, the anhydrous ethanol, and the agate balls is 1 / 2 of the volume of the polyurethane ball mill tank), and then the anhydrous ethanol is removed by using a rotary evaporation method under the conditions that the temperature is 55 ℃ and the speed is 40 r / min, to obtain a ball-milled powder.

[0049] The ball-milled powder is dried in a vacuum drying box with a vacuum degree of -0.1 MPa and a temperature of 70 ℃ for 12 h, and then is ground in an agate mortar to obtain a mixed powder with a particle size of 65 μm; the mixed powder is placed in a graphite mold, and is pre-pressed for 2 min under a pressure of 5 MPa, and then is put into a spark plasma sintering furnace, the sintering furnace is vacuumized to a vacuum degree of 10 Pa, then the sintering furnace is heated from room temperature to 1000 ℃ at a rate of 100 ℃ / min, is pressurized to 15 MPa, is heated from 1000 ℃ to 1600 ℃ at a rate of 70 ℃ / min, is pressurized to 25 MPa, is heated from 1600 ℃ to 1900 ℃ at a rate of 50 ℃ / min, is pressurized to 50 MPa, and is sintered at 1900 ℃ and 50 MPa for 15 min; after the sintering is completed, the product is cooled to 1100 ℃ at a rate of 30 ℃ / min, and then is cooled to 25 ℃ with the furnace, to obtain a boron nitride-based ceramic composite material.

[0050] The relative density of the boron nitride-based ceramic composite material prepared in the example is 95.5%, and the bending strength is 232.4631 MPa.

[0051] The SEM image of the boron nitride-based ceramic composite material prepared in the example is shown in Figure 1 It can be known that: Figure 1 The surface of the boron nitride-based ceramic composite material has no obvious pores, and the density is relatively high.

[0052] The SEM image of the cross section of the boron nitride-based ceramic composite material prepared in the example is shown in Figure 2As shown in Figure 2 It can be seen that the combination between the two phases of hexagonal boron nitride and silicon dioxide is good, which is beneficial to improve the mechanical properties of the boron nitride-based ceramic composite material.

[0053] The dielectric constant and dielectric loss tangent curve of the boron nitride-based ceramic composite material prepared in this example in the frequency range of 2-18 GHz is shown in Figure 3 As shown in Figure 3 It can be seen that in the frequency range of 2-18 GHz, the dielectric constant of the boron nitride-based ceramic composite material is 4.10 F / m, and the dielectric loss tangent is 0.01.

[0054] Example 2

[0055] Put 74.4g of hexagonal boron nitride (the particle size of the hexagonal boron nitride is 2μm, and the purity is 99.5%), 18.6g of silicon dioxide (the particle size of the silicon dioxide is 3μm, and the purity is 99.6%) and 7g of yttrium oxide (the particle size of the yttrium oxide is 3μm, and the purity is 99.8%) into a polyurethane ball mill tank with a volume of 150mL, then use anhydrous ethanol as the solvent, and use agate balls as the ball milling medium, and ball mill under the conditions of a ball-to-material ratio of 4:1 and a ball milling speed of 250r / min for 12h (the total volume of the hexagonal boron nitride, the silicon dioxide, the yttrium oxide, the anhydrous ethanol and the agate balls is 1 / 2 of the volume of the polyurethane ball mill tank), and then remove the anhydrous ethanol by rotary evaporation under the conditions of a temperature of 55℃ and a speed of 40r / min, to obtain the ball-milled powder.

[0056] After the ball-milled powder is dried in a vacuum drying box at a vacuum degree of-0.05MPa and a temperature of 60℃ for 24h, it is ground in an agate mortar to obtain a mixed powder with a particle size of 75μm; the mixed powder is placed in a graphite mold and pre-formed under a pressure of 6MPa for 3min, and then it is placed in a spark plasma sintering furnace, the sintering furnace is vacuumed to a vacuum degree of 8Pa, then the sintering furnace is heated from room temperature to 900℃ at a rate of 80℃ / min, and the pressure is increased to 12MPa, then the sintering furnace is heated from 900℃ to 1500℃ at a rate of 60℃ / min, and the pressure is increased to 20MPa, then the sintering furnace is heated from 1500℃ to 1800℃ at a rate of 40℃ / min, and the pressure is increased to 40MPa, and sintering is carried out at 1800℃ and 40MPa for 20min; after sintering is completed, the product is cooled to 1000℃ at a rate of 20℃ / min, and then cooled to 20℃ with the furnace, to obtain the boron nitride-based ceramic composite material.

[0057] The relative density of the boron nitride-based ceramic composite material prepared in this example is 95.46%, and the bending strength is 227.9546MPa.

[0058] The dielectric constant and dielectric loss tangent curve of the boron nitride-based ceramic composite prepared in this embodiment in the frequency range of 2-18 GHz is shown in the figure Figure 4 As can be seen from the figure, the dielectric constant of the boron nitride-based ceramic composite is 4.12 F / m and the dielectric loss tangent is 0.01 in the frequency range of 2-18 GHz. Figure 4

[0059] Embodiment 3

[0060] 73 g of hexagonal boron nitride (the particle size of the hexagonal boron nitride is 1 μm and the purity is 99.8%), 17 g of silicon dioxide (the particle size of the silicon dioxide is 4 μm and the purity is 99.6%) and 10 g of zirconium oxide (the particle size of the zirconium oxide is 1 μm and the purity is 99.4%) were put into a polyurethane ball mill tank with a volume of 150 mL, then the ball milling was carried out under the conditions of using anhydrous ethanol as a solvent, agate balls as a ball milling medium, a ball-to-material ratio of 2:1 and a ball milling speed of 200 r / min for 20 h (the total volume of the hexagonal boron nitride, the silicon dioxide, the zirconium oxide, the anhydrous ethanol and the agate balls is 2 / 3 of the volume of the polyurethane ball mill tank), and then the anhydrous ethanol was removed by suction filtration to obtain the ball-milled powder.

[0061] After the ball-milled powder was dried in a vacuum drying box at a vacuum degree of -0.15 MPa and a temperature of 80 ℃ for 16 h, the powder was ground in an agate mortar to obtain a mixed powder with a particle size of 55 μm; the mixed powder was placed in a graphite mold and pre-formed under a pressure of 4 MPa for 1 min, and then was placed in a spark plasma sintering furnace, the sintering furnace was vacuumized to a vacuum degree of 10 Pa, then the sintering furnace was heated from room temperature to 1100 ℃ at a rate of 120 ℃ / min, the pressure was increased to 10 MPa, then the sintering furnace was heated from 1100 ℃ to 1550 ℃ at a rate of 80 ℃ / min, the pressure was increased to 22 MPa, then the sintering furnace was heated from 1550 ℃ to 2000 ℃ at a rate of 60 ℃ / min, the pressure was increased to 30 MPa, and sintering was carried out at 2000 ℃ and 30 MPa for 10 min; after sintering was completed, the product was cooled to 900 ℃ at a rate of 25 ℃ / min, and then was cooled to 30 ℃ in the furnace to obtain the boron nitride-based ceramic composite.

[0062] The relative density of the boron nitride-based ceramic composite prepared in this embodiment is 94.51% and the bending strength is 225.2368 MPa.

[0063] The present application not only improves the density, mechanical properties, thermal properties and dielectric properties of the boron nitride-based ceramic composite, but also improves the preparation efficiency of the boron nitride-based ceramic composite by adding metal oxides as the third phase, reasonably controlling the sintering temperature, sintering time and the ratio of each component and using the spark plasma sintering technology.

[0064] ​The above merely describes the preferred embodiments of the present application, and it should be pointed out that, for those skilled in the art, several improvements and refinements can be made without departing from the principles of the present application, and these improvements and refinements should also be considered as falling within the protection scope of the present application.

Claims

1. A method for producing a boron nitride-based ceramic composite material, characterized by, The preparation method comprises the following steps: 1) ball-milling hexagonal boron nitride, silicon dioxide, metal oxide and solvent, and removing the solvent to obtain a ball-milled powder; 2) sequentially drying and refining the ball-milled powder to obtain a mixed powder; 3) sequentially pre-pressing and sintering the mixed powder to obtain a boron nitride-based ceramic composite material; The sintering temperature in step 3) is 1800-2000 ℃, the sintering pressure is 30-50 MPa, and the sintering time is 10-20 min; The metal oxide in step 1) is one or more of aluminum oxide, yttrium oxide and zirconium oxide, the particle size of the metal oxide is 1-3 μm, and the purity of the metal oxide is ≥ 99%; The solvent in step 1) is anhydrous ethanol, and the mass ratio of the hexagonal boron nitride, silicon dioxide and metal oxide is 70-75:15-20:5-10; In step 3), the temperature is raised to the sintering temperature in three stages, and the pressure is raised to the sintering pressure; the first sintering temperature is 900-1100 ℃, and the first sintering pressure is 10-15 MPa; The second sintering temperature is 1550-1600 ℃, the second sintering pressure is 20-25 MPa; the third sintering temperature is 1800-2000 ℃, and the third sintering pressure is 30-50 MPa; In step 3), the rate of raising the temperature from room temperature to the first sintering temperature is 80-120 ℃ / min, the rate of raising the temperature from the first sintering temperature to the second sintering temperature is 60-80 ℃ / min, and the rate of raising the temperature from the second sintering temperature to the third sintering temperature is 40-60 ℃ / min.

2. The production method according to claim 1, characterized by, The particle size of the hexagonal boron nitride in step 1) is 1-3 μm, and the purity of the hexagonal boron nitride is ≥ 99%; the particle size of the silicon dioxide is 3-5 μm, and the purity of the silicon dioxide is ≥ 99%.

3. The preparation method according to claim 1, characterized in that, The ball-to-material ratio of the ball-milling in step 1) is 2-4:1, the ball-milling speed is 200-300 r / min, and the ball-milling time is 12-24 h.

4. The production method according to claim 1 or 3, characterized by, The method for removing the solvent in step 1) is rotary evaporation or suction filtration; the drying in step 2) is vacuum drying, the vacuum drying temperature is 60-80 ℃, the vacuum drying time is 12-24 h, and the vacuum degree of the vacuum drying is -0.15 to -0.05 MPa.

5. The preparation method according to claim 4, characterized in that, The particle size of the mixed powder in step 2) is ≤ 75 μm; The pre-pressing pressure in step 3) is 4-6 MPa, and the pre-pressing time is 1-3 min.

6. The boron nitride-based ceramic composite material prepared by the preparation method in any one of claims 1-5.

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