A microwave sintering method of BN-ZrO2 composite ceramics

Abstract

The application provides a microwave sintering method of BN-ZrO2 composite ceramic and belongs to the technical field of ceramic microwave sintering preparation. Zirconium oxychloride is used as a zirconium source to prepare zirconia sol; then, boron nitride powder is immersed in the zirconia sol, and ultrasonic treatment, standing and drying are sequentially performed to obtain composite powder; the composite powder is sequentially subjected to dry pressing preforming and cold isostatic pressing preforming to obtain a green body; and the green body is subjected to microwave sintering to obtain the BN-ZrO2 composite ceramic. The application prevents the formation of a laminar structure of boron nitride in the high-temperature sintering process by constructing the composite powder with a BN-ZrO2 coating structure, simultaneously utilizes the electric field driven atomic diffusion mechanism in the microwave sintering process to prepare the dense BN-ZrO2 composite ceramic under pressureless sintering, and improves the performance of the pressureless sintered BN-ZrO2 composite ceramic.

Description

Technical Field

[0001] This invention relates to the field of microwave sintering preparation technology for ceramics, and more particularly to a microwave sintering method for BN-ZrO2 multiphase ceramics. Background Technology

[0002] Thin strip continuous casting is an advanced steel production technology that produces steel plates through continuous casting. Compared to traditional processes, thin strip continuous casting significantly simplifies the production process, reducing emissions of waste gas, wastewater, and solid waste. Furthermore, due to its rapid solidification characteristics, the steel plates produced by thin strip continuous casting have a fine grain structure, resulting in significantly improved mechanical properties such as strength and toughness. With the continuous development and transformation of the steel industry, thin strip continuous casting has become an important direction for achieving green development and intelligent manufacturing in the steel industry. In twin-roll thin strip continuous casting technology, side sealing technology is a crucial technical link. During twin-roll thin strip continuous casting, molten metal flows between two rotating rolls and forms a thin strip. Side sealing technology is used to seal the gap between the rolls and the molten pool to prevent molten metal leakage, ensuring the stable operation of the continuous casting process. It is a key technology determining product quality, production efficiency, and cost.

[0003] Currently, solid-state side-sealing technology has significant advantages in improving product quality and reducing production costs, and is gradually becoming a major research hotspot in the field of side-sealing technology. The core component of solid-state side-sealing technology is the side-sealing plate. Since side-sealing plates are typically used in relatively extreme service environments, the materials selected for them must possess good thermal shock resistance, excellent high-temperature mechanical properties, good corrosion resistance, and thermal insulation performance. This significantly narrows the range of materials that can be used for side-sealing plates. Therefore, developing a ceramic material that combines thermal shock resistance, high-temperature stability, corrosion resistance, and thermal insulation is of great significance for advancing the continuous casting process of thin strip steel.

[0004] BN-ZrO2 multiphase ceramics, with h-BN as the matrix and zirconium oxide as the reinforcing phase, possess numerous advantages such as good thermal shock resistance, corrosion resistance, and thermal insulation properties. Therefore, they have been widely researched and applied in the field of side sealing plates. Currently, the difficulty in sintering BN-ZrO2 multiphase ceramics lies in the fact that BN forms a lamellar structure during pressureless sintering, affecting its density and mechanical properties. Therefore, the current preparation of dense BN-ZrO2 multiphase ceramics mainly relies on hot pressing sintering. However, hot pressing sintering for BN-ZrO2 multiphase ceramics suffers from high energy consumption, high cost, and significant technical difficulties, greatly limiting its practical application in the field of side sealing plates.

[0005] Therefore, it is very important to provide a method for producing BN-ZrO2 multiphase ceramics with good density and mechanical properties that can reduce energy consumption and cost. Summary of the Invention

[0006] The purpose of this invention is to provide a microwave sintering method for BN-ZrO2 multiphase ceramics, in order to solve the technical problems of poor density and mechanical properties of multiphase ceramics, high energy consumption and cost of preparation methods, and high technical difficulty in the prior art.

[0007] To achieve the above-mentioned objectives, the present invention provides the following technical solution:

[0008] This invention provides a microwave sintering method for BN-ZrO2 multiphase ceramics, comprising the following steps:

[0009] (1) Zirconia dichloride, ethanol solution and formamide are mixed to obtain zirconium oxide sol;

[0010] (2) BN powder is immersed in zirconium oxide sol, and then subjected to ultrasonic treatment, standing and drying in sequence to obtain composite powder;

[0011] (3) The composite powder is subjected to dry pressing preforming and cold isostatic pressing preforming in sequence to obtain a green body;

[0012] (4) Microwave sintering of the green body yields BN-ZrO2 multiphase ceramic.

[0013] Furthermore, in step (1), the molar ratio of water to anhydrous ethanol in the ethanol solution is 1-2:5-15, the pH value of the ethanol solution is 4-6, and the reagent used to adjust the pH value includes hydrochloric acid.

[0014] The mass ratio of the ethanol solution, zirconium dichloride, and formamide is 47–80:0.5–3:0.1–2.

[0015] Furthermore, in step (2), the ultrasonic treatment time is 10 to 20 minutes, and the ultrasonic treatment power is 0.5 to 1 kW.

[0016] Furthermore, in step (2), the standing time is 8 to 16 hours; the drying method includes atmospheric pressure drying or freeze drying.

[0017] Furthermore, when using atmospheric pressure drying, the temperature for atmospheric pressure drying is 40–60℃, and the drying time is 6–10 hours;

[0018] When freeze drying is used, the freeze drying temperature is -60 to -40℃, and the drying time is 48 to 72 hours.

[0019] Furthermore, in step (3), the pressure of dry pressing preforming is 60-90 MPa, and the time of dry pressing preforming is 2-4 min;

[0020] The pressure of the cold isostatic pressing preforming is 200-350 MPa, and the time of the cold isostatic pressing preforming is 60-90 s.

[0021] Furthermore, in step (4), the microwave sintering frequency is 2.45 to 9.15 GHz, and the microwave sintering output power is 2 to 15 kW.

[0022] Furthermore, in step (4), the microwave sintering procedure is as follows: when the temperature is less than or equal to 500℃, the power increases by 1kW every 5 to 10 minutes; when the temperature is greater than 500℃, the heating rate is 10 to 15℃ / min, the temperature is raised to 1200 to 1700℃, and the temperature is held for 20 to 60 minutes.

[0023] Furthermore, in step (4), the green body is placed in an insulating structure for microwave sintering.

[0024] Furthermore, the insulation structure is composed of multiple layers, which, from the inside out, consist of an alumina hollow sphere layer, a lightweight mullite sheet layer or a lightweight quartz layer, a polycrystalline mullite fiber cotton layer or an alumina fiber layer, a lightweight mullite sheet layer or a lightweight quartz layer, and an alumina crucible layer.

[0025] The beneficial effects of this invention are:

[0026] (1) By coating zirconium oxide onto the surface of boron nitride powder, the present invention avoids interfacial contact of the difficult-to-sinter-bear boron nitride, improves interfacial contact of the easily-sinter-bearable zirconium oxide, and prevents the formation of a lamellar structure of boron nitride during high-temperature sintering, which can significantly reduce the sintering temperature for densification of BN-ZrO2 multiphase ceramics.

[0027] (2) This invention achieves densification of BN-ZrO2 multiphase ceramics under normal pressure by constructing a composite powder with a BN-ZrO2 coating structure and combining it with an interface-driven mechanism of microwave heating. Compared with the existing technology where BN-ZrO2 multiphase ceramics require reheating at 30-100 MPa and above 1800℃ to achieve a density of 90%, this invention utilizes microwave heating, without the need for pressure, and can achieve a density greater than 90% within 3 hours at 1500-1700℃. Detailed Implementation

[0028] This invention provides a microwave sintering method for BN-ZrO2 multiphase ceramics, comprising the following steps:

[0029] (1) Zirconia dichloride, ethanol solution and formamide are mixed to obtain zirconium oxide sol;

[0030] (2) BN powder is immersed in zirconium oxide sol, and then subjected to ultrasonic treatment, standing and drying in sequence to obtain composite powder;

[0031] (3) The composite powder is subjected to dry pressing preforming and cold isostatic pressing preforming in sequence to obtain a green body;

[0032] (4) Microwave sintering of the green body yields BN-ZrO2 multiphase ceramic.

[0033] In this invention, in step (1), the molar ratio of water to anhydrous ethanol in the ethanol solution is 1-2:5-15, preferably 1-2:6-12, and more preferably 1-2:8-10; the pH value of the ethanol solution is 4-6, preferably 4.5-5.5, and more preferably 5; the reagent used to adjust the pH value is preferably hydrochloric acid.

[0034] The mass ratio of the ethanol solution, zirconium dichloride, and formamide is 47–80:0.5–3:0.1–2, preferably 47.3–79.9:0.7–2.85:0.12–1.9, and more preferably 47.8–79.8:0.9–2.75:0.14–1.8.

[0035] In this invention, in step (2), the ultrasonic treatment time is 10-20 min, preferably 12-18 min, and more preferably 14-16 min; the ultrasonic treatment power is 0.5-1 kW, preferably 0.6-0.9 kW, and more preferably 0.7-0.8 kW.

[0036] In this invention, in step (2), the standing time is 8 to 16 hours, preferably 9 to 15 hours, and more preferably 10 to 14 hours; the purpose of standing is to allow the zirconium oxide sol to fully gel on the surface of the boron nitride powder.

[0037] In this invention, the drying method includes atmospheric pressure drying or freeze drying, preferably atmospheric pressure drying.

[0038] In this invention, when atmospheric pressure drying is used, the temperature of atmospheric pressure drying is 40-60°C, preferably 42-58°C, and more preferably 45-55°C; the drying time is 6-10 hours, preferably 7-9 hours, and more preferably 8 hours.

[0039] When freeze drying is used, the freeze drying temperature is -60 to -40°C, preferably -58 to -38°C, and more preferably -55 to -35°C; the drying time is 48 to 72 hours, preferably 50 to 70 hours, and more preferably 52 to 68 hours.

[0040] In this invention, in step (3), the pressure of dry pressing preforming is 60-90 MPa, preferably 65-85 MPa, and more preferably 70-80 MPa; the time of dry pressing preforming is 2-4 min, preferably 2.5-3.5 min, and more preferably 3 min.

[0041] In this invention, in step (3), the pressure of the cold isostatic pressing preforming is 200-350 MPa, preferably 210-330 MPa, and more preferably 250-300 MPa; the time of the cold isostatic pressing preforming is 60-90 s, preferably 65-85 s, and more preferably 70-80 s.

[0042] In this invention, in step (4), the frequency of microwave sintering is 2.45 to 9.15 GHz, preferably 2.45 GHz or 9.15 GHz, and more preferably 9.15 GHz; the output power of microwave sintering is 2 to 15 kW, preferably 3 to 10 kW, and more preferably 5 to 8 kW.

[0043] In this invention, the microwave sintering procedure in step (4) is as follows: when the temperature is less than or equal to 500°C, the power increases by 1kW every 5 to 10 minutes; when the temperature is greater than 500°C, the heating rate is 10 to 15°C / min, the temperature is raised to 1200 to 1700°C, and the temperature is held for 20 to 60 minutes.

[0044] Preferably, when the temperature is less than or equal to 500℃, the power increases by 1kW every 7 to 10 minutes; when the temperature is greater than 500℃, the heating rate is 10 to 13℃ / min, the temperature is raised to 1300 to 1600℃, and the temperature is held for 40 to 60 minutes.

[0045] Further preferably, when the temperature is less than or equal to 500℃, the power increases by 1kW every 10 minutes; when the temperature is greater than 500℃, the heating rate is 10℃ / min, the temperature is raised to 1500℃, and then held for 60 minutes.

[0046] In this invention, in step (4), the green body is placed in a heat-insulating structure for microwave sintering.

[0047] In this invention, the thermal insulation structure is composed of multiple layers, which, from the inside out, consist of an alumina hollow sphere layer, a lightweight mullite sheet layer or a lightweight quartz layer, a polycrystalline mullite fiber cotton layer or an alumina fiber layer, a lightweight mullite sheet layer or a lightweight quartz layer, and an alumina crucible layer; preferably, it consists of an alumina hollow sphere layer, a lightweight mullite sheet layer, a polycrystalline mullite fiber cotton layer, a lightweight mullite sheet layer, and an alumina crucible layer.

[0048] In this invention, the microwave sintering process also includes a step of recording the reflected power and temperature changes. With the same input power, the lower the reflected power, the better the microwave absorption capability of the surface material, and the microwave energy can be efficiently converted into heat energy, resulting in a good heating effect. When the reflected power gradually increases, it indicates that the material has poor microwave absorption capability, and the input power needs to be further increased to ensure the smooth progress of the microwave sintering process.

[0049] The technical solutions provided by the present invention will be described in detail below with reference to the embodiments, but they should not be construed as limiting the scope of protection of the present invention.

[0050] Example 1

[0051] Deionized water and anhydrous ethanol were mixed in a molar ratio of 2:5, and the pH was adjusted to 5 with hydrochloric acid to obtain an ethanol solution. Zirconia dichloride and formamide were then added, with a mass ratio of ethanol solution, zirconium dichloride, and formamide of 79.8:1.82:1.8. The mixture was stirred at 25°C for 60 min to allow for complete hydrolysis, resulting in a zirconium oxide sol. BN powder was impregnated in the zirconium oxide sol and then subjected to ultrasonic treatment for 15 min at a power of 0.8 kW to ensure the zirconium oxide sol fully adhered to the surface of the BN powder. After ultrasonic treatment, the impregnated BN powder was filtered out and allowed to stand at 25°C for 12 h to allow the zirconium oxide sol to fully gel on the surface of the BN powder. Finally, the powder was transferred to a drying oven and dried at 60°C for 6 h to obtain the final product. The composite powder was transferred to a mold for dry pressing preforming at a pressure of 80 MPa for 2 minutes. Then, a cold isostatic press was used for cold isostatic pressing preforming at a pressure of 300 MPa for 80 seconds to obtain a green body. The green body was placed in an insulation structure, and the insulation structure was placed together into a microwave resonant cavity. The microwave source was turned on, and the input power was adjusted from low to high. Below 500℃, the input power was uniformly increased by 1 kW every 10 minutes. After reaching 500℃, the heating rate was controlled at 10℃ / min. When the temperature reached 1500℃, it was held for 40 minutes. During sintering, the reflected power and temperature changes were recorded. The microwave source was then turned off to obtain BN-ZrO2 multiphase ceramic.

[0052] The porosity and bulk density of the multiphase ceramic prepared in Example 1 were tested using the Archimedes' displacement method. The results showed that the porosity of the multiphase ceramic was 6% and the bulk density was 2.76 g / cm³. 3 .

[0053] Example 2

[0054] Deionized water and anhydrous ethanol were mixed in a molar ratio of 1:10, and the pH was adjusted to 4 with hydrochloric acid to obtain an ethanol solution. Zirconia dichloride and formamide were then added, with a mass ratio of ethanol solution, zirconium dichloride, and formamide of 47.8:0.91:1.8. The mixture was stirred at 25°C for 40 min to allow for complete hydrolysis, resulting in a zirconium oxide sol. BN powder was impregnated in the zirconium oxide sol and then subjected to ultrasonic treatment for 20 min at a power of 0.7 kW to ensure the zirconium oxide sol fully adhered to the surface of the BN powder. After ultrasonic treatment, the impregnated BN powder was filtered out and allowed to stand at 25°C for 8 h to allow the zirconium oxide sol to fully gel on the surface of the BN powder. Finally, the powder was transferred to a drying oven and dried at 40°C for 10 h. Composite powder was obtained; the composite powder was transferred to a mold for dry pressing preforming at a pressure of 60 MPa for 4 min; then, cold isostatic pressing was performed at a pressure of 350 MPa for 60 s to obtain a green body; the green body was placed in an insulation structure and then placed together with the insulation structure into a microwave resonant cavity, the microwave source was turned on, and the input power was adjusted from low to high. Below 500℃, the input power was increased uniformly every 5 min, increasing by 1 kW each time. After reaching 500℃, the heating rate was controlled at 15℃ / min. When the temperature reached 1300℃, it was held for 60 min. The reflected power and temperature changes were recorded during sintering. The microwave source was then turned off to obtain BN-ZrO2 multiphase ceramic.

[0055] The porosity and bulk density of the multiphase ceramic prepared in Example 2 were tested using the Archimedes' displacement method. The results showed that the porosity of the multiphase ceramic was 8% and the bulk density was 2.66 g / cm³. 3 .

[0056] Example 3

[0057] Deionized water and anhydrous ethanol were mixed in a molar ratio of 1:10, and the pH was adjusted to 5 with hydrochloric acid to obtain an ethanol solution. Zirconia dichloride and formamide were then added, with a mass ratio of ethanol solution:zirconia dichloride:formamide of 47.8:2.75:0.14. The mixture was stirred at 25°C for 60 min to allow for complete hydrolysis, resulting in a zirconia sol. BN powder was impregnated in the zirconia sol and then subjected to ultrasonic treatment for 10 min at a power of 1 kW to ensure the zirconia sol fully adhered to the surface of the BN powder. After ultrasonic treatment, the impregnated BN powder was filtered out and allowed to stand at 25°C for 16 h to allow the zirconia sol to fully gel on the surface of the BN powder. Finally, the powder was transferred to a freeze dryer and freeze-dried at -40°C for 72 h. The composite powder was obtained; the composite powder was transferred to a mold for dry pressing preforming at a pressure of 70 MPa for 4 min; then, a cold isostatic press was used for cold isostatic pressing preforming at a pressure of 250 MPa for 70 s to obtain a green body; the green body was placed in an insulation structure and then placed together with the insulation structure into a microwave resonant cavity, the microwave source was turned on, and the input power was adjusted from low to high. Below 500℃, the input power was increased uniformly every 10 min, increasing by 1 kW each time. After reaching 500℃, the heating rate was controlled at 15℃ / min. When the temperature reached 1400℃, it was held for 40 min. The reflected power and temperature changes were recorded during sintering. The microwave source was then turned off to obtain BN-ZrO2 multiphase ceramic.

[0058] The porosity and bulk density of the multiphase ceramic prepared in Example 3 were tested using the Archimedes' displacement method. The results showed that the porosity of the multiphase ceramic was 5% and the bulk density was 2.81 g / cm³. 3 .

[0059] Example 4

[0060] Deionized water and anhydrous ethanol were mixed in a molar ratio of 1:10, and the pH was adjusted to 6 with hydrochloric acid to obtain an ethanol solution. Zirconia dichloride and formamide were then added, with a mass ratio of ethanol solution, zirconium dichloride, and formamide of 47.8:3:0.14. The mixture was stirred at 25°C for 60 min to allow for complete hydrolysis, yielding a zirconium oxide sol. BN powder was impregnated in the zirconium oxide sol and then subjected to ultrasonic treatment for 15 min at a power of 0.8 kW to ensure the zirconium oxide sol fully adhered to the surface of the BN powder. After ultrasonic treatment, the impregnated BN powder was filtered out and allowed to stand at 25°C for 10 h to allow the zirconium oxide sol to fully gel on the surface of the BN powder. Finally, the powder was transferred to a freeze dryer and freeze-dried at -60°C for 48 h. The composite powder was obtained; the composite powder was transferred to a mold for dry pressing preforming at a pressure of 80 MPa for 3 min; then, a cold isostatic press was used for cold isostatic pressing preforming at a pressure of 200 MPa for 90 s to obtain a green body; the green body was placed in an insulation structure and then placed together with the insulation structure into a microwave resonant cavity, the microwave source was turned on, and the input power was adjusted from low to high. Below 500℃, the input power was increased uniformly every 5 min, increasing by 1 kW each time. After reaching 500℃, the heating rate was controlled at 10℃ / min. When the temperature reached 1300℃, it was held for 60 min. The reflected power and temperature changes were recorded during sintering. The microwave source was then turned off to obtain BN-ZrO2 multiphase ceramic.

[0061] The porosity and bulk density of the multiphase ceramic prepared in Example 4 were tested using the Archimedes' displacement method. The results showed that the porosity of the multiphase ceramic was 7.5% and the bulk density was 2.56 g / cm³. 3 .

[0062] Comparative Example 1

[0063] Zirconia sol was prepared according to the method in Example 1. The zirconia sol was dried at 100°C for 2 hours and then placed in a high-temperature furnace, where it was heated to 800°C at a rate of 5°C / min and calcined for 2 hours to obtain zirconia powder. Boron nitride and zirconia powder were ball-milled and mixed to obtain a composite powder. The composite powder was transferred to a mold for dry pressing pre-forming at a pressure of 80 MPa for 3 minutes. Cold isostatic pressing pre-forming was then performed using a cold isostatic press at a pressure of 200 MPa. The isostatic pressing preforming time is 90s to obtain a green body. The green body is placed in the insulation structure and then placed in the microwave resonant cavity together with the insulation structure. The microwave source is turned on, and the input power is adjusted from low to high. Below 500℃, the input power is increased uniformly every 5 minutes, increasing by 1kW each time. After reaching 500℃, the heating rate is controlled at 10℃ / min. When the temperature rises to 1300℃, it is held for 60 minutes. The reflected power and temperature changes are recorded during the sintering process. The microwave source is then turned off to obtain BN-ZrO2 multiphase ceramic.

[0064] The porosity and bulk density of the multiphase ceramic prepared in Comparative Example 1 were tested using the Archimedes' displacement method. The results showed that the porosity of the multiphase ceramic was 19% and the bulk density was 2.1 g / cm³. 3 .

[0065] Comparative Example 2

[0066] Deionized water and anhydrous ethanol were mixed in a molar ratio of 2:5, and the pH was adjusted to 5 with hydrochloric acid to obtain an ethanol solution. Zirconia dichloride and formamide were then added, with a mass ratio of ethanol solution, zirconium dichloride, and formamide of 79.8:1.82:1.8. The mixture was stirred at 25°C for 60 min to allow for complete hydrolysis, yielding a zirconium oxide sol. BN powder was then impregnated in the zirconium oxide sol and subjected to ultrasonic treatment for 15 min at a power of 0.8 kW to ensure the zirconium oxide sol fully adhered to the surface of the BN powder. After the treatment, the impregnated BN powder was filtered out and allowed to stand at 25°C for 12 minutes. After the zirconia sol is fully gelled on the surface of BN powder, it is transferred to a drying oven for atmospheric pressure drying at 60℃ for 6 hours to obtain composite powder. The composite powder is then transferred to a mold for dry pressing preforming at a pressure of 80MPa for 2 minutes. Cold isostatic pressing preforming is then performed using a cold isostatic press at a pressure of 300MPa for 80 seconds to obtain green body. The green body is then hot-pressed and sintered at 1900℃ for 8 hours to obtain multiphase ceramic.

[0067] The porosity and bulk density of the multiphase ceramic prepared in Comparative Example 2 were tested using the Archimedes' displacement method. The results showed that the porosity of the multiphase ceramic was 8% and the bulk density was 2.68 g / cm³. 3 .

[0068] As can be seen from the above embodiments, the present invention provides a microwave sintering method for BN-ZrO2 multiphase ceramics. Zirconia dichloride is used as the zirconium source to prepare a zirconium oxide sol; then boron nitride powder is impregnated in the zirconium oxide sol, and sequentially subjected to ultrasonic treatment, settling, and drying to obtain a composite powder; the composite powder is then sequentially subjected to dry pressing preforming, cold isostatic pressing preforming, and microwave sintering to obtain BN-ZrO2 multiphase ceramics. Compared with Comparative Example 1, the method of the present invention constructs a BN-ZrO2 coated structure to prepare a high-density multiphase ceramic; compared with hot pressing sintering, the microwave sintering method used in this application has a shorter sintering time (less than 3 hours), while hot pressing sintering has a longer time, which not only reduces the technical difficulty in the production process but also reduces production costs and energy consumption.

[0069] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle 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 microwave sintering of BN-Zr02 composite ceramics, characterized in that, The method comprises the following steps: (1) mixing zirconium oxychloride, an ethanol solution and formamide to obtain a zirconia sol; (2) immersing BN powder in the zirconia sol, and then sequentially performing ultrasonic treatment, standing and drying to obtain a composite powder; (3) sequentially performing dry pressing preforming and cold isostatic pressing preforming on the composite powder to obtain a green body; (4) microwave sintering the green body to obtain BN-ZrO2 composite ceramic.

2. The microwave sintering method of BN-Zr02 composite ceramics according to claim 1, characterized in that, In the step (1), the molar ratio of water to anhydrous ethanol in the ethanol solution is 1-2:5-15, and the pH value of the ethanol solution is 4-6, and the reagent used for adjusting the pH value comprises hydrochloric acid; The mass ratio of the ethanol solution, zirconium oxychloride and formamide is 47-80:0.5-3:0.1-2.

3. The microwave sintering method of BN-Zr02 composite ceramics according to claim 1 or 2, characterized in that, In the step (2), the ultrasonic treatment time is 10-20 min, and the ultrasonic treatment power is 0.5-1 kW.

4. The microwave sintering method of BN-Zr02 composite ceramics according to claim 3, characterized in that, In the step (2), the standing time is 8-16 h, and the drying mode comprises atmospheric drying or freeze drying.

5. The microwave sintering method of BN-Zr02 composite ceramics according to claim 4, characterized in that, When atmospheric drying is adopted, the atmospheric drying temperature is 40-60℃, and the drying time is 6-10 h; When freeze drying is adopted, the freeze drying temperature is -60--40℃, and the drying time is 48-72 h.

6. The microwave sintering method of BN-Zr02 composite ceramics according to claim 1 or 2 or 5, characterized in that, In the step (3), the dry pressing preforming pressure is 60-90 MPa, and the dry pressing preforming time is 2-4 min; The cold isostatic pressing preforming pressure is 200-350 MPa, and the cold isostatic pressing preforming time is 60-90 s.

7. The microwave sintering method of BN-Zr02 composite ceramics according to claim 6, characterized in that, In the step (4), the microwave sintering frequency is 2.45-9.15 GHz, and the microwave sintering output power is 2-15 kW.

8. The method of microwave sintering of BN-Zr02 composite ceramics according to claim 7, characterized in that, In the step (4), the microwave sintering program is: when the temperature is less than or equal to 500℃, the power is increased by 1 kW every 5-10 min; when the temperature is greater than 500℃, the temperature is increased at a rate of 10-15℃ / min to 1200-1700℃, and the temperature is kept for 20-60 min.

9. The microwave sintering method of BN-Zr02 composite ceramics according to claim 7 or 8, characterized in that, In the step (4), the green body is placed in a heat preservation structure for microwave sintering.

10. The method of microwave sintering of BN-Zr02 composite ceramics according to claim 9, characterized in that, In the step (4), the heat preservation structure is composed of a multi-layer structure, and the multi-layer structure comprises, from the inside to the outside, an alumina hollow sphere layer, a lightweight mullite sheet layer or a lightweight quartz layer, a polycrystalline mullite fiber cotton layer or an alumina fiber layer, a lightweight mullite sheet layer or a lightweight quartz layer and an alumina crucible layer.