A lamellar oriented boron nitride ceramic and its preparation method and application

Abstract

The present invention discloses a lamellar boron nitride ceramic with oriented alignment, as well as its preparation method and application. This relates to the technical field of boron nitride ceramic preparation. The method comprises the following steps: using a template method, using graphite as a substrate, alternately scraping an inorganic glue and boron nitride powder onto the surface, and heating to produce the lamellar boron nitride ceramic with oriented alignment. The lamellar boron nitride ceramic produced by this method can be used in aerospace applications such as fighter aircraft tip radomes. It exhibits excellent high-temperature oxidation resistance and minimal temperature-dependent mechanical property changes.

Description

Technical Field

[0001] The present invention belongs to the technical field of boron nitride ceramic preparation, and in particular relates to a lamellar oriented boron nitride ceramic and a preparation method and application thereof. Background Art

[0002] The rapid development of contemporary aviation has sparked considerable interest in materials for various applications, such as fighter aircraft radomes. These materials must possess low dielectric constants, excellent oxidation resistance, and minimal temperature-dependent mechanical property variations. However, due to the mismatch in thermal expansion coefficients between materials, the mechanical properties of many ceramic materials are significantly affected by temperature due to the clamping effect of internal thermal stresses. Consequently, the preparation and research of these materials has been difficult, costly, and poorly designed.

[0003] Therefore, there is an urgent need to provide a method for preparing lamellar oriented boron nitride ceramics. Summary of the Invention

[0004] In response to the above technical problems, the present invention proposes a lamellar oriented boron nitride ceramic and its preparation method and application. The present invention innovatively proposes a template method using graphite as the matrix of lamellar oriented boron nitride ceramics, and uses high-temperature heating to fully oxidize the graphite matrix to obtain undamaged lamellar oriented boron nitride ceramics, whose mechanical properties change little with temperature. The preparation method is simple, the raw materials are cheap, and it is conducive to large-scale production. Therefore, the present invention discloses a method for preparing lamellar oriented boron nitride ceramics using a template method, and explores the mechanism of the evolution of microstructure and mechanical properties with temperature, as well as the intrinsic relationship between thermal stress and crystal orientation, and designs the microscopic crystal arrangement of the material to improve the mechanical properties of the material.

[0005] To achieve the above object, the present invention provides the following technical solutions:

[0006] One of the technical solutions:

[0007] A method for preparing lamellar oriented boron nitride ceramics using a template method comprises the following steps:

[0008] By using the template method, a carbonaceous material graphite with a smooth surface is used as the matrix, inorganic glue and boron nitride powder are alternately scraped on its surface, and then heated to prepare lamellar oriented boron nitride ceramics.

[0009] Beneficial effects: The present invention uses graphite as a matrix and adopts a scraping method to synthesize lamellar oriented boron nitride ceramics on the surface of the matrix material. The prepared lamellar oriented boron nitride ceramics have the advantages of low dielectric constant, good oxidation resistance, and small variation of mechanical properties with temperature.

[0010] In addition, according to the template method design concept proposed in the present invention, after the inorganic glue and boron nitride powder are scraped and dried on the graphite substrate multiple times, the graphite substrate can be oxidized by high-temperature heating treatment, thereby achieving the purpose of removing the substrate and obtaining a directionally arranged boron nitride ceramic.

[0011] Preferably, the inorganic colloidal solvent includes aluminum phosphate and / or sodium silicate.

[0012] Beneficial Effects: The inorganic glue (sodium silicate or aluminum phosphate colloid) defined in this invention can achieve low-temperature adhesion and high-temperature curing. Specifically, its high viscosity and strong wettability at low temperatures facilitate the rotation of boron nitride powder (h-BN powder) sheets by doctor blade coating, thereby facilitating their unidirectional alignment. Upon heating, the inorganic glue can connect the BN sheets through dehydration polymerization, enhancing the stability of the ceramic matrix sheets.

[0013] Preferably, the mass fraction of the solute is 30-80%.

[0014] Preferably, the type of boron nitride in the boron nitride powder is h-BN.

[0015] Preferably, the specific operation of the alternating scraping is:

[0016] A layer of inorganic glue is first scraped on the graphite surface, and then a layer of boron nitride powder is applied. The obtained sample is solidified, and this is a complete cycle.

[0017] Preferably, the usage ratio of the graphite, inorganic glue and boron nitride powder is 20:1:10.

[0018] Preferably, the temperature during the curing process is 80-200°C.

[0019] Preferably, the number of cycles is 50-100 times.

[0020] Preferably, the heating process is:

[0021] Raise the temperature to 500-900℃ and then keep at this temperature for 10 hours.

[0022] Technical solution 2:

[0023] The above preparation method prepares a lamellar oriented boron nitride ceramic.

[0024] Technical solution three:

[0025] The application of the above-mentioned lamellar oriented boron nitride ceramics in the aerospace field.

[0026] Compared with the prior art, the present invention has the following advantages and technical effects:

[0027] The template method for preparing lamellar oriented boron nitride ceramics provided by the present invention has high stability, strong controllability, simple preparation steps, and cheap and readily available raw materials, which is conducive to large-scale production.

[0028] The lamellar oriented boron nitride ceramics prepared by the preparation method of the present invention can be used in aerospace fields such as fighter jet tip antenna covers, and have excellent high-temperature oxidation resistance and small changes in mechanical properties with temperature. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] The accompanying drawings, which constitute part of this application, are intended to provide a further understanding of this application. The exemplary embodiments and descriptions of this application are intended to explain this application and do not constitute an improper limitation on this application. In the accompanying drawings:

[0030] Figure 1 Scanning images of the surface and cross section of the boron nitride ceramic prepared in Example 1 of the present invention;

[0031] Among them, (a) and (b) are surface scans; (c) and (d) are cross-sectional scans. DETAILED DESCRIPTION

[0032] Various exemplary embodiments of the present invention will now be described in detail. This detailed description should not be considered as limiting the present invention, but rather as a more detailed description of certain aspects, features, and embodiments of the present invention.

[0033] It should be understood that the terms described herein are intended only to describe particular embodiments and are not intended to limit the present invention. In addition, for numerical ranges herein, it should be understood that each intermediate value between the upper and lower limits of the range is also specifically disclosed. Each smaller range between any intermediate value within a stated value or stated range and any other stated value or intermediate value within the stated range is also encompassed by the present invention. The upper and lower limits of these smaller ranges may be independently included or excluded within the scope.

[0034] Unless otherwise indicated, all technical and scientific terms used herein have the same meaning as commonly understood by those skilled in the art. Although only preferred methods and materials are described herein, any methods and materials similar or equivalent to those described herein may also be used in the practice or testing of the present invention. All documents mentioned in this specification are incorporated by reference to disclose and describe the methods and / or materials associated with the documents. In the event of any conflict with any incorporated document, the contents of this specification shall prevail.

[0035] It will be apparent to those skilled in the art that various modifications and variations may be made to the specific embodiments described herein without departing from the scope or spirit of the invention. Other embodiments will be apparent to those skilled in the art from the description of the invention. The description and examples are intended to be illustrative only.

[0036] The words “include,” “including,” “have,” “contain,” etc. used in this document are open-ended terms, meaning including but not limited to.

[0037] The present invention discloses a method for preparing lamellar oriented boron nitride ceramics using graphite as a matrix template, comprising the following steps:

[0038] 1) Alternately apply inorganic glue and boron nitride powder on the surface of the graphite block;

[0039] 2) drying and curing the inorganic glue and boron nitride;

[0040] 3) Repeated scraping and drying and curing, and then subjecting the obtained sample to high-temperature heating and heat preservation treatment to obtain lamellar oriented boron nitride ceramics.

[0041] In some preferred embodiments of the present invention, the mass fraction of the solute in the inorganic glue in step 1) is 30-80%, preferably 50%.

[0042] Inorganic colloidal solvents include aluminum phosphate and sodium silicate; aluminum phosphate is preferred.

[0043] In some preferred embodiments of the present invention, the drying temperature after each alternating scraping of the inorganic glue and the BN powder in step 3) is in the range of 80-200°C, preferably 200°C.

[0044] The number of repeated scraping and drying curing is in the range of 50-100 times, preferably 70 times.

[0045] The temperature range of the high temperature heating treatment is 500-900°C, preferably 800°C.

[0046] This invention uses graphite as a matrix. By leveraging its oxidation reaction at high temperatures, the template can be easily removed to produce aligned boron nitride ceramics. The template method is widely applicable and can be used in a variety of research contexts, providing a new approach to ceramic material preparation. Furthermore, the material preparation method is simple, the raw materials are inexpensive, and it is easy to scale up.

[0047] The principle behind this invention is that after a lamellar structure contracts or expands due to temperature, its mechanical properties change minimally in directions perpendicular to or parallel to the laminae. This effectively addresses the current issues of mismatched thermal expansion coefficients between heated materials, as well as the significant temperature-dependent effects of mechanical properties on many ceramic materials and structures due to the clamping effect of internal thermal stress.

[0048] The preparation method disclosed in the present invention can produce lamellar, oriented boron nitride ceramics. These ceramics have excellent high-temperature oxidation resistance and minimal temperature-dependent mechanical property changes, making them suitable for aerospace applications such as cutting-edge radome materials for fighter aircraft.

[0049] Unless otherwise specified, the "room temperature" in the present invention refers to 20-30°C.

[0050] The raw materials used in the present invention are all purchased from the market.

[0051] The technical solution of the present invention is further illustrated by the following examples.

[0052] Example 1

[0053] A method for preparing lamellar oriented boron nitride ceramics using a template method comprises the following steps:

[0054] 1) Alternately apply a 50% by mass aluminum phosphate solution and h-BN powder to the surface of a graphite block, first applying the aluminum phosphate solution and then applying the h-BN powder. The coating amounts of each layer of aluminum phosphate solution and h-BN powder are 0.1 g and 1 g, respectively.

[0055] 2) Drying and curing the graphite block after the coating at a temperature of 200°C to a constant weight;

[0056] 3) Repeat the above-mentioned scraping and drying steps 70 times, and then heat the obtained sample at 800°C for 10 hours to fully oxidize and remove the graphite blocks, thereby obtaining lamellar oriented boron nitride ceramics.

[0057] Figure 1 These are scans of the surface and cross-section of the boron nitride ceramic prepared in Example 1 of the present invention; wherein, (a) (b) are surface scans, from which it can be seen that the boron nitride is distributed and superimposed along the lamellar shape as a whole, the layered structure can be clearly observed, and the boron nitride distribution is flat; (c) (d) are cross-sectional scans, from which the distribution direction of the boron nitride lamellar layers can be observed.

[0058] Example 2

[0059] Same as Example 1, except that the aluminum phosphate solution in step 1) is replaced by a sodium silicate solution.

[0060] Example 3

[0061] Same as Example 1, except that the mass fraction of the aluminum phosphate solution in step 1) is adjusted to 30%.

[0062] Example 4

[0063] Same as Example 1, except that the drying temperature in step 2) is adjusted from 200°C to 80°C.

[0064] Example 5

[0065] The same as Example 1, except that the number of repeated scraping and drying steps in step 3) is adjusted to 100 times.

[0066] Example 6

[0067] Same as Example 1, except that the temperature of the high-temperature heating treatment in step 3) is adjusted to 900°C.

[0068] Comparative Example 1

[0069] Same as Example 1, except that the h-BN powder in step 1) is replaced by SiO2.

[0070] The results showed that the structure of SiO2 is not a simple lamellar structure, but a three-dimensional network structure formed by silicon-oxygen tetrahedron as the basic structure. During the preparation process, it is impossible to obtain SiO2 ceramics with directional arrangement.

[0071] Comparative Example 2

[0072] Same as Example 1, except that the mass fraction of the aluminum phosphate solution in step 1) is adjusted to 25%.

[0073] The results showed that the aluminum phosphate solution was too dilute, which resulted in poor adhesion of h-BN powder and difficulty in forming a film on the surface of the graphite block.

[0074] Comparative Example 3

[0075] Same as Example 1, except that the mass fraction of the aluminum phosphate solution in step 1) is adjusted to 85%.

[0076] The results showed that because the aluminum phosphate solution was too thick, it was difficult to evenly apply the BN powder on the surface of the graphite block and it was not easy to form a smooth surface.

[0077] Comparative Example 4

[0078] Same as Example 1, except that the temperature of the high-temperature heating treatment in step 3) is adjusted to 1300°C.

[0079] The results showed that excessively high heating temperature caused some BN ceramics to be oxidized, the planar structure to be destroyed, and defects to occur, which affected the subsequent mechanical properties testing.

[0080] Comparative Example 5

[0081] Same as Example 1, except that the temperature of the high-temperature heating treatment in step 3) is adjusted to 300°C.

[0082] The results showed that the heating temperature was too low, resulting in incomplete oxidation of the graphite block, and the graphite block could not be completely eliminated. The prepared lamellar oriented boron nitride ceramics could not be removed from the graphite block.

[0083] Effect verification

[0084] (I) The ceramics prepared in Examples 1-6 and Comparative Examples 1-5 were subjected to three-point bending tests in both the perpendicular and parallel directions. The samples were prepared into 40 × 4 × 3 mm strips with a span of 30 mm and a loading rate of 0.5 mm / min in two stress directions to verify their variable temperature mechanical (thermal stress) performance. The relevant performance data are shown in Tables 1 and 2 below.

[0085] Table 1 Vertical plane direction

[0086]

[0087]

[0088] Table 2 Parallel plane directions

[0089]

[0090] As can be seen from the above table, when external pressure is applied to the silicon nitride ceramics prepared in Examples 1-6 of the present invention in both the perpendicular and parallel plane directions, the mechanical properties change little with temperature during the heating process from room temperature to 800°C, making them suitable for aerospace materials such as antenna covers at the tip of fighter jets.

[0091] (II) The ceramics prepared in Examples 1-6 and Comparative Examples 1-5 were subjected to high-temperature oxidation tests at temperatures of 800, 1000, and 1300° C., respectively, for 10 minutes. Specific data are shown in Table 3.

[0092] Table 3 Weight loss rate before and after oxidation

[0093]

[0094] The above are merely preferred embodiments of the present application, but the scope of protection of the present application is not limited thereto. Any changes or substitutions that can be easily conceived by a person skilled in the art within the technical scope disclosed in this application should be included in the scope of protection of the present application. Therefore, the scope of protection of the present application should be based on the scope of protection of the claims.

Claims

1. A method for preparing lamellar oriented boron nitride ceramics using a template method, characterized in that: The following steps are involved: Using the template method, graphite is used as the substrate, inorganic glue and boron nitride powder are alternately scraped on its surface, and then heated to prepare lamellar oriented boron nitride ceramics. The solute in the inorganic glue includes aluminum phosphate and / or sodium silicate; wherein the mass fraction of the solute in the inorganic glue is 30-80%; The specific operation of the alternating scraping is as follows: First, a layer of inorganic glue is scraped on the graphite surface, and then a layer of boron nitride powder is applied. The resulting sample is cured, and this is considered a complete cycle of scraping. The temperature during the curing process is 80-200°C; The heating process is: heating to 500-900° C. and then keeping the temperature at this temperature for 10 hours.

2. The method for preparing lamellar oriented boron nitride ceramics by using a template method according to claim 1, characterized in that: The boron nitride powder is hexagonal boron nitride.

3. The method for preparing lamellar oriented boron nitride ceramics by using a template method according to claim 1, characterized in that: In each cycle, the mass ratio of the inorganic glue to the boron nitride powder applied is 1:

10.

4. The method for preparing lamellar oriented boron nitride ceramics by using a template method according to claim 1, characterized in that: The number of cycles is 50-100 times.

5. A lamellar oriented boron nitride ceramic, characterized in that: The method is prepared by any one of claims 1 to 4.

6. Application of the lamellar oriented boron nitride ceramic according to claim 5 in the field of aerospace.

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