High-strength high-deformation hexagonal boron nitride ceramic and method for preparing the same

Abstract

This invention provides a high-strength, high-deformability hexagonal boron nitride ceramic and its preparation method, comprising the following steps: mixing hexagonal boron nitride and a sintering aid in water to obtain a mixture, wherein the general formula of the sintering aid is M2O(H2O). x (CO2) y The mixture is dehydrated and dried to obtain a mixed powder; the mixed powder is then hot-pressed and sintered under an inert atmosphere to obtain the high-strength, high-deformability hexagonal boron nitride ceramic. The method and equipment of this invention are simple, and it can prepare high-strength, high-deformability hexagonal boron nitride ceramic at a relatively low processing temperature (1500℃). Compared with ordinary hexagonal boron nitride ceramics, it not only has higher density but also significantly improved mechanical properties and superior dielectric properties, making it suitable for use as a material for circuit boards, packaging, and heat dissipation in high-frequency electronic devices.

Description

Technical Field

[0001] This invention relates to the field of functional ceramic materials technology, and in particular to a high-strength, high-deformability hexagonal boron nitride ceramic and its preparation method. Background Technology

[0002] With the continuous development of wireless communication technology, high-frequency electronic devices are evolving towards integration, high power, and miniaturization. While this progress makes electronic devices more portable and efficient, it also places higher demands on the dielectric and heat dissipation properties of the materials used. Fundamental materials used in high-frequency electronic devices, including printed circuit boards and packaging shells, not only need to have low dielectric constants and dielectric losses to reduce interference with high-frequency signals and high thermal conductivity to prevent heat accumulation, but also require high mechanical strength to prevent physical damage.

[0003] Hexagonal boron nitride (BN) is an inorganic non-metallic material with a graphite-like structure composed of a hexagonal network of boron nitride, bonded by alternating groups of Group III boron and Group V nitrogen. Strong BN covalent bonds form within the layers, while weaker van der Waals forces connect the layers. Its theoretical density is 2.27 g / cm³. 3 With a Mohs hardness of 2 and an optical band gap of 6.0 eV, boron nitride (BN) is white in appearance and is therefore also known as "white graphite." It is very stable in air, can withstand temperatures up to 1270 K, and possesses good electrical insulation, thermal conductivity, and lubricity. It also exhibits radiation resistance, chemical corrosion resistance, oxidation resistance, and excellent wave transmission and dielectric properties, making it suitable for many important applications, such as high-temperature ceramics, electronic packaging materials, solid lubricants, aerospace, defense, and the nuclear industry. However, boron nitride ceramics are often brittle and have low mechanical strength. This is because the lamellar stacking of hexagonal boron nitride forms abundant arched structures, reducing density. Furthermore, the chemical inertness of hexagonal boron nitride makes it difficult to react and densify during sintering, resulting in a loose structure and reduced mechanical properties. Traditional pressureless sintering methods, without the addition of sintering aids, even at ultra-high temperatures of 2100 °C, only produce hexagonal boron nitride ceramics with a flexural strength of 30.7 MPa. Commonly used sintering aids, such as B2O3 and MAS, have limited effect on improving the mechanical properties of hexagonal boron nitride ceramics. Significant improvements are only achieved with very high amounts of these aids, while excessive addition inevitably reduces the inherent superior properties of hexagonal boron nitride. Furthermore, the molding and sintering of hexagonal boron nitride ceramics generally requires high temperatures (>1600℃), which increases energy consumption and cost, and is not conducive to energy conservation and emission reduction. Summary of the Invention

[0004] Based on this, the present invention provides a method for preparing high-strength, high-deformability hexagonal boron nitride ceramics under relatively mild conditions.

[0005] A method for preparing a high-strength, high-deformability hexagonal boron nitride ceramic includes the following steps:

[0006] A mixture is obtained by mixing hexagonal boron nitride and a sintering aid in water, wherein the general formula of the sintering aid is M2O(H2O). x (CO2) y M is Na, Li, or K; the values ​​of x and y satisfy x + y = 1;

[0007] The mixture was dehydrated and dried to obtain a mixed powder;

[0008] The mixed powder was hot-pressed and sintered under an inert atmosphere to obtain the high-strength, high-deformability hexagonal boron nitride ceramic.

[0009] In one embodiment, the hot pressing sintering temperature is not lower than 1100°C, for example, it can be 1100°C to 1500°C (1200°C, 1300°C, 1400°C, etc.). Increasing the hot pressing temperature is beneficial to preparing hexagonal boron nitride ceramics with higher mechanical properties.

[0010] In one embodiment, the pressure of the hot pressing sintering is not less than 20 MPa, for example, it can be 20 to 40 MPa (30 MPa, 50 MPa, etc.). Increasing the pressure applied by hot pressing is beneficial to preparing hexagonal boron nitride ceramics with higher mechanical properties.

[0011] In one embodiment, the hot pressing sintering time is not less than 0.3 hours, for example, it can be 0.3 to 3 hours but is not limited thereto. Extending the hot pressing time is beneficial to preparing hexagonal boron nitride ceramics with higher mechanical properties.

[0012] In one embodiment, the sintering aid is selected from one or more of lithium hydroxide, sodium hydroxide, potassium hydroxide, sodium carbonate, lithium carbonate, and potassium carbonate.

[0013] In one embodiment, the mass ratio of the hexagonal boron nitride to the sintering aid is 9 to 19:1.

[0014] In one embodiment, the inert atmosphere is a nitrogen atmosphere, but is not limited thereto.

[0015] In one embodiment, the preparation method further includes the following steps: grinding and cutting the hot-pressed sintered product.

[0016] The present invention also provides a high-strength, high-deformability hexagonal boron nitride ceramic, which is prepared according to the above preparation method.

[0017] The present invention also provides an electronic device comprising the above-mentioned high-strength, high-deformability hexagonal boron nitride ceramic.

[0018] The above-described solution of the present invention has the following beneficial effects:

[0019] The hexagonal boron nitride ceramic prepared by this invention not only has higher density than ordinary hexagonal boron nitride ceramics, but also exhibits significantly improved mechanical properties and superior dielectric properties, making it suitable for use as a material in circuit boards, packaging, and heat dissipation for high-frequency electronic devices. This hexagonal boron nitride ceramic has a dielectric constant of 3.2–4.3 and a dielectric loss of (0.8–4.6) × 10⁻⁶ in the frequency range of 1–12 MHz. -3 It has a thermal conductivity as high as 30.53 W / mK and a density of 1.59–2.19 g / cm³. 3 Its compressive strength can reach 73–421 MPa, and its compressive strain can reach 1.57%–6.67%. Its flexural strength can reach 31–170 MPa, and its flexural strain can reach 0.13%–6.70%.

[0020] The sintering aid used in the preparation of hexagonal boron nitride ceramics in this invention can decompose at high temperatures to form alkali metal oxides, which can chemically react with hexagonal boron nitride at high temperatures to form a dense structure, greatly improving the mechanical properties of the product. While maintaining the excellent dielectric properties and thermal conductivity of hexagonal boron nitride, this invention solves the problems of its difficulty in sintering and the poor mechanical properties of the product, providing technical and product solutions for its application in high-frequency electronics and other fields.

[0021] The preparation method of this invention uses a lower temperature than other hexagonal boron nitride ceramics sintering temperatures, which helps reduce energy consumption and costs. The hexagonal boron nitride used in this invention is a commercially available hexagonal boron nitride powder, and the preparation method is hot pressing sintering, which is easy to scale up for production and helps reduce costs. Attached Figure Description

[0022] Figure 1 The image shows the physical specimen (left) and the SEM image (right) of the cross-sectional morphology of the hexagonal boron nitride ceramic prepared in Example 1 of this invention.

[0023] Figure 2 The graph shows the mechanical properties of the hexagonal boron nitride ceramic prepared in Example 1 of this invention. The upper graph shows the compressive strength, and the lower graph shows the flexural strength.

[0024] Figure 3 The X-ray powder diffraction pattern (top) and infrared spectrum (bottom) of the hexagonal boron nitride ceramic prepared in Example 1 of this invention are shown. Detailed Implementation

[0025] To make the technical problems, solutions, and advantages of this invention clearer, a detailed description will be provided below with reference to the accompanying drawings and specific embodiments. Obviously, the described embodiments are only some, not all, of the embodiments of this invention. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without creative effort are within the scope of protection of this invention.

[0026] Furthermore, the technical features involved in the different embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other. Unless otherwise specified, the reagents and instruments used in the embodiments are conventional choices in the art. Experimental methods not specifying specific conditions in the embodiments are implemented according to conventional conditions, such as those described in literature, books, or methods recommended by the manufacturer.

[0027] The following are specific examples.

[0028] Example 1

[0029] Add 4.0 g of sodium hydroxide to 180 mL of deionized water, followed by 36.0 g of hexagonal boron nitride powder, and mix thoroughly. Dry the mixture at 100 °C until all moisture is evaporated, then remove and cool. Grind the dried mixture in an agate mortar and pass it through a 120-mesh sieve to obtain the precursor material.

[0030] Weigh 30g of the prepared white precursor powder and place it into a graphite hot press mold with an inner diameter of 40mm. Use graphite paper to line both ends of the sample to prevent contamination. Then, place the graphite mold into a vacuum atmosphere hot press furnace and sinter it under a nitrogen atmosphere. The heating rate is 10℃ / min, the hot pressing temperature is 1500℃, the applied pressure is 40MPa, and the holding time at the target temperature is 1 hour.

[0031] After sintering, allow the material to cool naturally to room temperature. Remove the graphite mold from the furnace, take out the sample, and clean the graphite paper on both sides with sandpaper to obtain a white hexagonal boron nitride ceramic product. Figure 1 As shown in the left figure.

[0032] The density of the prepared hexagonal boron nitride ceramic was measured to be 2.19 g / cm³. 3 The product was characterized by scanning electron microscopy, such as... Figure 1 As shown in the right figure, the prepared hexagonal boron nitride ceramic has a dense structure.

[0033] The prepared hexagonal boron nitride ceramic was cut into standard specimens for compression and bending tests using a cutting machine. The compressive strength and three-point bending strength tests of the specimens were then conducted according to national standards GB / T 1964-1996 and GB / T 1965-1996, respectively. The results are as follows: Figure 2As shown, the compressive strength and deformation strain of the prepared ceramic sample were measured to be 421 MPa and 5.36%, respectively, and the flexural strength and deformation strain were 170 MPa and 5.86%, respectively.

[0034] The prepared hexagonal boron nitride ceramic was cut into thin slices with a diameter of 40 mm and a thickness of 2 mm for dielectric property testing. The dielectric constant of the ceramic was measured to be 3.619 and the dielectric loss was 0.912 × 10⁻⁶ in the range of 1–12 MHz. -3 .

[0035] The prepared hexagonal boron nitride ceramic was subjected to laser thermal conductivity testing, and the thermal conductivity of the ceramic at 100℃ was measured to be 30.53 W / mK.

[0036] The prepared hexagonal boron nitride ceramic was subjected to X-ray powder diffraction and infrared analysis, and the results are as follows: Figure 3 As shown, the prepared hexagonal boron nitride ceramic has high purity and high crystallinity.

[0037] Example 2

[0038] As a control example, the sintering aid in Example 1 was replaced with boron oxide, and the temperature was changed to 1400℃. The prepared hexagonal boron nitride had a density of 1.89 g / cm³. 3 The compressive strength and deformation strain can reach 152MPa and 2.26% respectively, and the flexural strength and deformation strain can reach 79MPa and 3.98% respectively, which are used as the objects for performance comparison in the examples.

[0039] Example 3

[0040] The temperature in Example 1 was changed to 1400℃, while other conditions remained unchanged. The prepared hexagonal boron nitride had a density of 2.18 g / cm³. 3 The compressive strength and strain can reach 385 MPa and 4.39%, respectively; the flexural strength and strain can reach 161 MPa and 4.42%, respectively; the dielectric constant is 3.710 (10MHz) and the dielectric loss is 0.796 × 10⁻⁶. -3 All performance characteristics are significantly higher than those of Example 2.

[0041] Example 4

[0042] The temperature in Example 1 was changed to 1300℃, while other conditions remained unchanged. The prepared hexagonal boron nitride had a density of 2.05 g / cm³. 3 The compressive strength and strain can reach 284 MPa and 3.35%, respectively; the flexural strength and strain can reach 112 MPa and 4.42%, respectively; the dielectric constant is 3.852 (10MHz) and the dielectric loss is 1.112 × 10⁻⁶. -3 All performance characteristics are significantly higher than those of Example 2.

[0043] Example 5

[0044] The temperature in Example 1 was changed to 1200℃, while other conditions remained unchanged. The prepared hexagonal boron nitride had a density of 1.95 g / cm³. 3 The compressive strength and strain can reach 144 MPa and 1.89%, respectively; the flexural strength and strain can reach 56 MPa and 4.54%, respectively; the dielectric constant is 3.631 (10 MHz), and the dielectric loss is 2.152 × 10⁻⁶. -3 The density and resistance to bending fracture deformation strain are higher than those in Example 2.

[0045] Example 6

[0046] The temperature in Example 1 was changed to 1100℃, while other conditions remained unchanged. The prepared hexagonal boron nitride had a density of 1.59 g / cm³. 3 The compressive strength and strain can reach 73 MPa and 1.57%, respectively; the flexural strength and strain can reach 31 MPa and 4.62%, respectively; the dielectric constant is 3.214 (10 MHz), and the dielectric loss is 4.632 × 10⁻⁶. -3 The bending fracture strength strain is higher than that in Example 2.

[0047] Examples 1, 3-6 show that, while keeping other conditions constant, increasing the hot-pressing temperature is beneficial for preparing hexagonal boron nitride ceramics with high mechanical properties. Hot-pressing temperatures exceeding 1500°C should also be considered within the scope of this invention.

[0048] Example 7

[0049] The pressure in Example 3 was changed to 30 MPa, while other conditions remained unchanged. The prepared hexagonal boron nitride had a density of 2.17 g / cm³. 3 The compressive strength and strain can reach 363 MPa and 4.15%, respectively; the flexural strength and strain can reach 143 MPa and 5.01%, respectively; the dielectric constant is 4.208 (10 MHz), and the dielectric loss is 1.547 × 10⁻⁶. -3 All performance characteristics are significantly higher than those of Example 2.

[0050] Example 8

[0051] The pressure in Example 3 was changed to 20 MPa, while other conditions remained unchanged. The prepared hexagonal boron nitride had a density of 2.08 g / cm³. 3 The compressive strength and strain can reach 236 MPa and 3.41%, respectively; the flexural strength and strain can reach 107 MPa and 3.48%, respectively; the dielectric constant is 4.256 (10 MHz), and the dielectric loss is 2.346 × 10⁻⁶. -3 All performance characteristics are significantly higher than those of Example 2.

[0052] Example 9

[0053] The heat treatment time in Example 8 was changed to 3 hours, while other conditions remained unchanged. The density of the prepared hexagonal boron nitride reached 2.12 g / cm³. 3 The compressive strength and strain can reach 345 MPa and 6.67%, respectively; the flexural strength and strain can reach 146 MPa and 6.70%, respectively; the dielectric constant is 4.080 (10 MHz), and the dielectric loss is 1.209 × 10⁻⁶. -3 All performance characteristics are significantly higher than those of Example 2.

[0054] Example 10

[0055] The pressure in Example 3 was changed to 10 MPa, while other conditions remained unchanged. The density of the prepared hexagonal boron nitride reached 1.70 g / cm³. 3 The compressive strength and strain can reach 131 MPa and 2.17%, respectively, and the flexural strength and strain can reach 38 MPa and 2.18%, respectively; the dielectric constant is 3.092 (10MHz), and the dielectric loss is 3.390 × 10⁻⁶. -3 .

[0056] Examples 3, 7, 8, and 10 show that, while keeping other conditions constant, increasing the pressure applied during hot pressing is beneficial for preparing hexagonal boron nitride ceramics with high mechanical properties. Pressures exceeding 40 MPa applied during hot pressing should also be considered within the scope of this invention.

[0057] Example 11

[0058] The heat treatment time in Example 3 was changed to 0.3 hours, while other conditions remained unchanged. The density of the prepared hexagonal boron nitride reached 2.20 g / cm³. 3 The compressive strength and deformation strain can reach 295MPa and 3.53%, respectively, and the flexural strength and deformation strain can reach 77MPa and 0.13%, respectively; the density, compressive strength and deformation strain are higher than those of Example 2.

[0059] Examples 3 and 11, 8 and 9 show that, while keeping other conditions constant, extending the hot-pressing time is beneficial for preparing hexagonal boron nitride ceramics with high mechanical properties. Hot-pressing times exceeding 3 hours should also be considered within the scope of this invention.

[0060] Example 12

[0061] The sintering aid in Example 2 was replaced with sodium carbonate, while other conditions remained unchanged. The prepared hexagonal boron nitride had a density of 2.12 g / cm³. 3The compressive strength and deformation strain can reach 184MPa and 2.38%, respectively, and the flexural strength and deformation strain can reach 34MPa and 0.99%, respectively; the density and compressive strength are higher than those of Example 2.

[0062] Example 13

[0063] The sintering aid in Example 2 was replaced with lithium hydroxide, while other conditions remained unchanged. The prepared hexagonal boron nitride had a density of 2.13 g / cm³. 3 The compressive strength and deformation strain can reach 278 MPa and 3.04%, respectively, and the flexural strength and deformation strain can reach 69 MPa and 0.16%, respectively; the density, compressive strength and deformation strain are higher than those of Example 2.

[0064] The condition parameters and performance test results for each embodiment are shown in Table 1.

[0065] Table 1

[0066]

[0067]

[0068] The above description represents the preferred embodiments of the present invention. It should be noted that those skilled in the art can make various improvements and modifications without departing from the principles 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 method for preparing high-strength, high-deformability hexagonal boron nitride ceramic, characterized in that, Includes the following steps: A mixture is obtained by mixing hexagonal boron nitride and a sintering aid in water; wherein the mass ratio of the hexagonal boron nitride to the sintering aid is 9~19:1; the sintering aid is selected from one or more of lithium hydroxide, sodium hydroxide, potassium hydroxide, sodium carbonate, lithium carbonate, and potassium carbonate; The mixture was dehydrated and dried to obtain a mixed powder; The mixed powder is placed in a graphite hot pressing mold, and then the graphite hot pressing mold is placed in a hot pressing furnace and hot pressing sintered under an inert atmosphere to obtain the high-strength and high-deformability hexagonal boron nitride ceramic; wherein the hot pressing sintering temperature is not lower than 1100℃, the hot pressing sintering pressure is not lower than 20 MPa, and the hot pressing sintering time is not less than 0.3 hours.

2. A high-strength, high-deformability hexagonal boron nitride ceramic, characterized in that, It is prepared according to the preparation method according to claim 1.

3. The high-strength, high-deformability hexagonal boron nitride ceramic according to claim 2, characterized in that, The high-strength high-deformation hexagonal boron nitride ceramic has a density of 1.59-2.19 g / cm 3 .

4. The high-strength, high-deformability hexagonal boron nitride ceramic according to claim 2, characterized in that, The high-strength, high-deformability hexagonal boron nitride ceramic has a compressive strength of 73~421 MPa and a deformation strain of 1.57%~6.67% before compressive fracture.

5. The high-strength, high-deformability hexagonal boron nitride ceramic according to claim 2, characterized in that, The high-strength, high-deformability hexagonal boron nitride ceramic has a flexural strength of 31~170 MPa and a deformation strain of 0.13%~6.70% before flexural fracture.

6. The high-strength, high-deformability hexagonal boron nitride ceramic according to claim 2, characterized in that, The high-strength high-deformation hexagonal boron nitride ceramic has a dielectric constant of 3.2-4.3 and a dielectric loss of 0.8*10 -3 -4.6*10 -3 -4 in a frequency range of 1-12 MHz.

7. An electronic device, characterized in that, The electronic device contains the high-strength, high-deformation hexagonal boron nitride ceramic as described in claim 2.

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