Preparation method of high-temperature-resistant low-dielectric-loss SiBCN composite ceramic

Abstract

The application discloses a preparation method of high-temperature-resistant SiBCN composite ceramic with low dielectric loss, and relates to the preparation method of SiBCN composite ceramic. The application aims at solving the problems that the existing SiBCN ceramic is difficult to prepare dense bulk ceramic, and the dielectric constant and dielectric loss are relatively high. The method comprises the following steps: 1, slurry preparation; 2, precursor slurry solidification; 3, ceramic pyrolysis; and 4, heat treatment. The application is used for the preparation of high-temperature-resistant SiBCN composite ceramic with low dielectric loss.

Description

TECHNICAL FIELD

[0001] The present application relates to a preparation method of SiBCN composite ceramic. BACKGROUND

[0002] With the continuous development of science and technology, the science and technology level in the field of aerospace has become an important symbol of national comprehensive strength. Space engines need precise control of temperature and pressure during operation. Precursor-derived ceramics can be designed from a molecular perspective to have specific structures and functions, and have the advantages of being able to prepare heterogeneous components, low sintering temperature, high thermal stability, etc.

[0003] SiBCN ceramic has more excellent thermal stability than SiC, SiOC and SiCN ceramic, and generally occurs phase separation above 1500℃. However, SiBCN precursor has a large mass loss during pyrolysis due to the release of small molecule gases such as CH4 and NH3, and it is not easy to directly prepare bulk ceramic, and its dielectric constant and dielectric loss are relatively high, which limits its application in high-temperature wireless passive pressure sensors. SUMMARY

[0004] The present application solves the problem that the existing SiBCN ceramic is difficult to prepare dense bulk ceramic, and its dielectric constant and dielectric loss are relatively high, and further provides a preparation method of high-temperature-resistant low-dielectric-loss SiBCN composite ceramic.

[0005] A preparation method of high-temperature-resistant low-dielectric-loss SiBCN composite ceramic, which is carried out according to the following steps:

[0006] I. Preparation of slurry:

[0007] Mixing and defoaming inorganic oxide filler and SiBCN precursor to obtain filler / SiBCN precursor slurry;

[0008] II. Precursor slurry solidification:

[0009] Place the filler / SiBCN precursor slurry in a mold for solidification, then demold and perform surface polishing to obtain a precursor solidification product;

[0010] III. Ceramic pyrolysis:

[0011] The precursor solidified product is heated to 200-300 DEG C at a heating rate of 1-3 DEG C / min, and is kept at the temperature of 200-300 DEG C for 0.5-2 h, then heated to 550-650 DEG C at a heating rate of 0.5-1 DEG C / min, then heated to 1000-1400 DEG C at a heating rate of 1-3 DEG C / min, and kept at the temperature of 1000-1400 DEG C for 1-12 h, finally cooled to room temperature at a cooling rate of 2-5 DEG C / min, to obtain the pyrolyzed ceramic;

[0012] IV. Heat treatment:

[0013] The surface of the pyrolyzed ceramic is polished, cleaned and dried, then heat treated in air atmosphere, and finally cooled with the furnace, to obtain the high-temperature-resistant low-dielectric-loss SiBCN composite ceramic.

[0014] The present application has the following advantages:

[0015] 1. The SiBCN precursor solidified product is composed of amorphous ceramic matrix and free carbon, and the dielectric properties of the material are affected by the polarization loss and electric conduction loss caused by the free carbon, resulting in the increase of dielectric constant and dielectric loss. The introduction of inorganic oxide as the second phase can reduce the dielectric loss of the composite ceramic, for two reasons: on the one hand, during the sintering of the ceramic, the inorganic oxide reacts with the carbon in the precursor solidified product at high temperature through carbothermal reduction, reducing the content of free carbon in the composite ceramic and lowering the dielectric loss of the ceramic; on the other hand, the size of the carbon clusters in the free carbon is reduced, and the degree of carbon disorder is higher, reducing the electric conduction loss and the overall dielectric loss.

[0016] 2. In order to further reduce the dielectric loss of the composite ceramic, the present application uses low-temperature oxidation method to remove the free carbon in the ceramic; in order to prevent the severe oxidation of the composite ceramic, the heat treatment temperature is selected to be 600-1200 DEG C; taking 800 DEG C as an example, the oxidation degree of the composite ceramic is relatively weak, and almost no oxidation product is formed on the surface, and the change of the dielectric properties of the composite ceramic is mainly due to the oxidation of a small amount of free carbon in the ceramic during the oxidation process, which generates CO and CO2 and releases them in the form of gas, thereby reducing the dielectric constant and dielectric loss of the material.

[0017] 3. The heating rate, pyrolysis temperature and pyrolysis time in the present application will affect the preparation and dielectric properties of the composite ceramic. When the sintering temperature is higher than 1500 DEG C, nanocrystals such as SiC and Si3N4 will be precipitated from the composite ceramic, or oxidation products such as SiO2 will be generated, increasing the electric conduction loss and polarization loss of the ceramic, thereby causing the increase of the dielectric constant and dielectric loss of the composite ceramic. When the temperature is between 1000 DEG C and 1400 DEG C, the SiBCN matrix of the composite ceramic remains amorphous, and the dielectric constant and dielectric loss are relatively low.

[0018] 4. By introducing inert fillers with low dielectric constant and dielectric loss as the second phase, serving as the filling skeleton, reducing the volume shrinkage during pyrolysis, and densifying the bulk.

[0019] FIG. 1

[0020] Figure 1 TG curve of the SiBCN precursor prepared in step one of Example 1;

[0021] Figure 2 Photographs of the precursor cured product prepared in step two and the pyrolyzed ceramic prepared in step three of Example 1 and Comparative Experiment 1, (a) precursor cured product prepared in step two of Comparative Experiment 1, (b) pyrolyzed ceramic prepared in step three of Comparative Experiment 1, (c) precursor cured product prepared in step two of Example 1, (d) pyrolyzed ceramic prepared in step three of Example 1;

[0022] Figure 3 SEM and EDS photographs of the pyrolyzed ceramic prepared in step three of Example 1, (a) SEM photograph, (b) EDS photograph, (c-h) element distribution;

[0023] Figure 4 XRD pattern, 1 is the high-temperature-resistant low-dielectric-loss SiBCN composite ceramic prepared in step four of Example 1, 2 is the pyrolyzed ceramic prepared in step three of Example 1, and 3 is the pyrolyzed ceramic prepared in step three of Comparative Experiment 1;

[0024] Figure 5 Raman spectrum, 1 is the pyrolyzed ceramic prepared in step three of Example 1, and 2 is the pyrolyzed ceramic prepared in step three of Comparative Experiment 1;

[0025] Figure 6 Dielectric property graph, 1 is the pyrolyzed ceramic prepared in step three of Comparative Experiment 1, and 2 is the pyrolyzed ceramic prepared in step three of Example 1, (a) dielectric constant, (b) dielectric loss;

[0026] Figure 7 Dielectric property graph, 1 is the pyrolyzed ceramic prepared in step three of Example 1, and 2 is the high-temperature-resistant low-dielectric-loss SiBCN composite ceramic prepared in step four of Example 1, (a) dielectric constant, (b) dielectric loss;

[0027] Figure 8 XRD patterns of the pyrolyzed ceramics prepared in step three of Example 1, Example 3, Example 4, Comparative Experiment 2, and Comparative Experiment 3. DETAILED DESCRIPTION

[0028] Embodiment 1: The embodiment is a preparation method of a high-temperature-resistant low-dielectric-loss SiBCN composite ceramic, which is performed according to the following steps.

[0029] I. Preparation of slurry:

[0030] The inorganic oxide filler is mixed with the SiBCN precursor to remove bubbles, to obtain a filler / SiBCN precursor slurry;

[0031] II. Solidification of precursor slurry:

[0032] The filler / SiBCN precursor slurry is placed in a mold for solidification, then demolded and polished to obtain a precursor solidification product;

[0033] III. Ceramic pyrolysis:

[0034] The precursor solidification product is heated to 200-300℃ at a heating rate of 1-3℃ / min, and then kept at 200-300℃ for 0.5-2h, and then heated to 550-650℃ at a heating rate of 0.5-1℃ / min, and then heated to 1000-1400℃ at a heating rate of 1-3℃ / min, and then kept at 1000-1400℃ for 1-12h, and finally cooled to room temperature at a cooling rate of 2-5℃ / min, to obtain a pyrolyzed ceramic.

[0035] IV. Heat treatment:

[0036] The pyrolyzed ceramic is polished, cleaned and dried, and then subjected to heat treatment in an air atmosphere, and finally cooled in the furnace, to obtain a high-temperature-resistant low-dielectric-loss SiBCN composite ceramic.

[0037] In the step III of the embodiment, the precursor solidification product is accompanied by a large mass loss during pyrolysis, and the heating rate should not be too fast.

[0038] The embodiment has the following beneficial effects:

[0039] 1. The SiBCN precursor solidification product is composed of an amorphous ceramic matrix and free carbon, and the dielectric properties of the material are affected by the polarization loss and the electric conduction loss caused by the free carbon, resulting in an increase in the dielectric constant and the dielectric loss. The introduction of inorganic oxides as a second phase will reduce the dielectric loss of the composite ceramic, for two reasons: on the one hand, during the sintering of the ceramic, the inorganic oxides will undergo a carbothermic reduction reaction with the carbon in the precursor solidification product at high temperatures, reducing the content of free carbon in the composite ceramic and lowering the dielectric loss of the ceramic; on the other hand, the size of the carbon clusters in the free carbon in the composite ceramic is reduced, and the degree of carbon disorder is higher, resulting in a reduction in the electric conduction loss of the material and the overall dielectric loss.

[0040] 2. In order to further reduce the dielectric loss of the composite ceramic, the free carbon in the ceramic is removed by low-temperature oxidation; in order to prevent the composite ceramic from being severely oxidized, the heat treatment temperature is selected to be 600-1200℃; taking 800℃ as an example, the oxidation degree of the composite ceramic is relatively weak, and almost no oxidation product is formed on the surface, and the change of the dielectric properties of the composite ceramic is mainly because a small amount of free carbon in the ceramic is oxidized to generate CO and CO2 in the form of gas during the oxidation process, thereby reducing the dielectric constant and dielectric loss of the material.

[0041] 3. In the present application, the heating rate, pyrolysis temperature and pyrolysis time will affect the preparation and dielectric properties of the composite ceramic. When the sintering temperature is higher than 1500℃, nanocrystals such as SiC and Si3N4 will be precipitated from the composite ceramic, or oxidation products such as SiO2 will be generated, which will increase the electrical conduction loss and polarization loss of the ceramic, thereby causing the dielectric constant and dielectric loss of the composite ceramic to rise. When the temperature is between 1000℃ and 1400℃, the SiBCN matrix of the composite ceramic remains amorphous, and the dielectric constant and dielectric loss are relatively low.

[0042] 4. By introducing inert fillers with low dielectric constant and dielectric loss as the second phase, the fillers act as a filling skeleton, reducing the volume shrinkage during pyrolysis, and the bulk is dense.

[0043] Specific embodiment two: The difference between this embodiment and specific embodiment one is that the inorganic oxide filler in step one is a powder or a whisker. The others are the same as specific embodiment one.

[0044] When the filler is a powder, the added filler will not react with the SiBCN ceramic matrix, the ceramic matrix does not crystallize, and remains amorphous, the particles are uniformly distributed in the ceramic matrix, and there are no cracks or other defects at the joint between the two, and the two are well combined.

[0045] When the filler is a whisker, the added filler will not react with the SiBCN ceramic matrix, the ceramic matrix does not crystallize, and remains amorphous, and the whisker can hinder crack propagation, and selecting a whisker as a filler can improve the strength of the composite ceramic.

[0046] Specific embodiment three: The difference between this embodiment and one of specific embodiments one or two is that the particle size of the powder is 0.01-10μm; the diameter of the whisker is 0.1-1μm, and the length is 10-100μm. The others are the same as specific embodiments one or two.

[0047] Specific embodiment four: the difference between this embodiment and one of the specific embodiments one to three is that when the powder particle size is 10 nm to 100 nm, the mass percentage of the filler in the filler / SiBCN precursor slurry in step one is 1% to 25%; when the powder particle size is 0.1 μm to 10 μm, the mass percentage of the filler in the filler / SiBCN precursor slurry in step one is 1% to 50%; when the whisker diameter is 0.1 μm to 1 μm and the length is 10 μm to 100 μm, the mass percentage of the filler in the filler / SiBCN precursor slurry in step one is 1% to 70%. The others are the same as specific embodiments one to three.

[0048] Specific embodiment five: the difference between this embodiment and one of the specific embodiments one to four is that the inorganic oxide filler in step one is Al2O3 filler, SiO2 filler or ZrO2 filler. The others are the same as specific embodiments one to four.

[0049] Specific embodiment six: the difference between this embodiment and one of the specific embodiments one to five is that the mixing and defoaming in step one is specifically using a vacuum defoaming stirrer, mixing for 10 min to 90 min at a rotation speed of 1000 rpm to 4000 rpm, and then vacuum defoaming for 5 min to 10 min at a rotation speed of 1000 rpm to 2500 rpm. The others are the same as specific embodiments one to five.

[0050] Specific embodiment seven: the difference between this embodiment and one of the specific embodiments one to six is that the solidification in step two is specifically first at a temperature of 50 ℃ to 100 ℃ for 10 min to 30 min, and then at a temperature of 120 ℃ to 160 ℃ for 2 h to 12 h. The others are the same as specific embodiments one to six.

[0051] In this specific embodiment, the solvent and gas dissolved in the precursor are fully discharged at a temperature of 50 ℃ to 100 ℃ for 10 min to 30 min.

[0052] Specific embodiment eight: the difference between this embodiment and one of the specific embodiments one to seven is that the surface polishing in step two is to make the upper and lower surfaces parallel to each other. The others are the same as specific embodiments one to seven.

[0053] Specific embodiment nine: the difference between this embodiment and one of the specific embodiments one to eight is that the pyrolysis in step three is specifically carried out in a nitrogen atmosphere, an argon atmosphere or vacuum. The others are the same as specific embodiments one to eight.

[0054] Specific implementation ten: the difference between this implementation and one of the specific implementations one to nine is that the heat treatment in step four is specifically performed as follows: under an air atmosphere, heating to 600-1200℃ at a heating rate of 3-10℃ / min, and keeping the temperature at 600-1200℃ for 2-48h under the air atmosphere. The rest is the same as specific implementations one to nine.

[0055] The beneficial effects of the present application are verified by the following examples:

[0056] Example one:

[0057] A method for preparing a high-temperature-resistant low-dielectric-loss SiBCN composite ceramic, which is performed as follows:

[0058] I. Preparation of slurry:

[0059] First, using a vacuum defoaming stirrer, mix the inorganic oxide filler and SiBCN precursor at a rotation speed of 1000rpm for 5min, then at a rotation speed of 2500rpm for 30min, and then at a rotation speed of 1500rpm for 5min to defoam under vacuum, to obtain a filler / SiBCN precursor slurry;

[0060] The mass percentage of the filler in the filler / SiBCN precursor slurry is 5%;

[0061] II. Solidification of precursor slurry:

[0062] Place the filler / SiBCN precursor slurry in a mold, first keep the temperature at 80℃ for 20min, then keep the temperature at 140℃ for 4h, finally demold and polish the surface to make the upper and lower surfaces parallel to each other, to obtain a precursor solidification product;

[0063] III. Ceramic pyrolysis:

[0064] Under a nitrogen atmosphere, heat the precursor solidification product to 220℃ at a heating rate of 2℃ / min, and keep the temperature at 220℃ for 2h under the nitrogen atmosphere, then heat to 600℃ at a heating rate of 0.5℃ / min under the nitrogen atmosphere, then heat to 1000℃ at a heating rate of 1℃ / min under the nitrogen atmosphere, and keep the temperature at 1000℃ for 2h under the nitrogen atmosphere, finally cool to room temperature at a cooling rate of 3℃ / min, to obtain a pyrolyzed ceramic;

[0065] IV. Heat treatment:

[0066] The pyrolyzed ceramic surface is polished, cleaned and dried, then heated to 800℃ at a heating rate of 5℃ / min in air atmosphere, and kept at 800℃ for 12h in air atmosphere, and finally cooled down with the furnace to obtain the high-temperature-resistant SiBCN composite ceramic with low dielectric loss.

[0067] The inorganic oxide filler in step one is Al2O3 powder with a particle size of 1-10μm.

[0068] The SiBCN precursor in step one is purchased from the Institute of Chemistry, Chinese Academy of Sciences, model: KH-SiBCN.

[0069] Example two: this example is different from example one in that the mass percentage of the filler in the filler / SiBCN precursor slurry in step one is 15%. The others are the same as example one.

[0070] Example three: this example is different from example one in that 1000℃ in step three is changed to 1200℃. The others are the same as example one.

[0071] Example four: this example is different from example one in that 1000℃ in step three is changed to 1400℃. The others are the same as example one.

[0072] Comparative experiment one: this comparative experiment is different from example one in that the filler is not added in step one. The others are the same as example one.

[0073] Comparative experiment two: this comparative experiment is different from example one in that 1000℃ in step three is changed to 1500℃. The others are the same as example one.

[0074] Comparative experiment three: this comparative experiment is different from example one in that 1000℃ in step three is changed to 1600℃. The others are the same as example one.

[0075] Figure 1 The TG curve of the SiBCN precursor in step one of example one is shown in the figure. It can be seen from the figure that the ceramic yield generated in the process of curve test of SiBCN precursor is about 52.8%, there is a large mass loss, the ceramic shrinks greatly, and defects are easy to produce. Before 300℃, the mass loss is slow, between 300℃ and 600℃, the mass loss is very fast, a reasonable heating rate should be set, after 600℃, the ceramic mass loss slows down again, and the mass is basically stable, the precursor conversion ceramic is basically completed.

[0076] Figure 2Figure (a) is the solidified precursor prepared in step two of the first comparative experiment, (b) is the pyrolyzed ceramic prepared in step three of the first comparative experiment, (c) is the solidified precursor prepared in step two of the first example, (d) is the pyrolyzed ceramic prepared in step three of the first example; it can be seen from the figure that the shrinkage rate of the pyrolyzed ceramic of the first comparative experiment compared to the solidified precursor is 29.36%, the shrinkage rate of the pyrolyzed ceramic of the first example compared to the solidified precursor is 28.17%, and the ceramic shrinkage rate is reduced after the addition of the second phase.

[0077] The post-pyrolysis ceramic shrinkage rate of the second example compared to the solidified precursor is 25.91% after testing.

[0078] Figure 3 Figure (a) is the SEM image of the pyrolyzed ceramic prepared in step three of the first example, (b) is the EDS image, and (c-h) are element distribution images; it can be seen from the figure that in the pyrolyzed ceramic, the interface between the Al2O3 particles and the SiBCN ceramic is clear, and there are no defects such as cracks, indicating that the Al2O3 does not diffuse in the matrix after pyrolysis at 1000°C, and the SiBCN matrix is still amorphous and does not crystallize. At the same time, it can be seen that there are no voids, cracks and other defects in the composite ceramic, and the ceramic is very dense; the density of the pyrolyzed ceramic prepared in step three is 5.9%.

[0079] Figure 4 Figure is an XRD pattern, 1 is the high-temperature resistant low-dielectric loss SiBCN composite ceramic prepared in step four of the first example, 2 is the pyrolyzed ceramic prepared in step three of the first example, and 3 is the pyrolyzed ceramic prepared in step three of the first comparative experiment; it can be seen from the figure that by comparing the XRD patterns of the pyrolyzed ceramics prepared in step three of the first comparative experiment and the first example, since the raw material Al2O3 is crystalline, the addition of Al2O3 can obviously observe the diffraction peak of Al2O3, and no crystallization product (SiC, Si3N4, etc.) of SiBCN and the diffraction peak of the possible reaction product of SiBCN ceramic and Al2O3 ceramic are detected, indicating that the introduction of Al2O3 will not affect the phase composition of the SiBCN ceramic after pyrolysis at 1000°C, and the SiBCN matrix of the pyrolyzed ceramic prepared in step three of the first example is still amorphous, and there is no reaction between them. By comparing the XRD patterns of the ceramic before and after oxidation in step four of the first example, the XRD pattern does not change significantly, and there is no diffraction peak of the oxidation product such as SiO2, indicating that no oxidation product is generated on the surface.

[0080] Figure 5Raman spectra, 1 is the pyrolysis ceramic prepared in step three of the embodiment, 2 is the pyrolysis ceramic prepared in step three of the comparative experiment; as can be seen from the figure, after adding Al2O3, the D peak shifts left and the G peak shifts right, and the half-height width of the D peak and the G peak decreases, indicating that the order degree of free carbon increases, the size decreases, and the dielectric loss of the ceramic decreases.

[0081] Figure 6 Dielectric property figure, 1 is the pyrolysis ceramic prepared in step three of the comparative experiment, 2 is the pyrolysis ceramic prepared in step three of the embodiment, (a) dielectric constant, (b) dielectric loss; as can be seen from the figure, the average value of the real part of the dielectric constant of the pyrolysis ceramic of the comparative experiment one is 3.24, the average value of the real part of the dielectric constant of the pyrolysis ceramic of the embodiment one is 3.15, the average value of the imaginary part of the dielectric constant of the pure SiBCN ceramic of the comparative experiment one is 0.01763, and the average value of the real part of the dielectric constant of the pyrolysis ceramic of the embodiment one is 0.00609, that is, after adding 5% Al2O3, the real part and the imaginary part of the dielectric constant decrease.

[0082] The average value of the real part of the dielectric constant of the pyrolysis ceramic prepared in step three of the embodiment two is 3.30, and the average value of the imaginary part of the dielectric constant is 0.01544.

[0083] Figure 7 Dielectric property figure, 1 is the pyrolysis ceramic prepared in step three of the embodiment, 2 is the high-temperature-resistant low-dielectric-loss SiBCN composite ceramic prepared in step four of the embodiment; (a) dielectric constant, (b) dielectric loss; as can be seen from the figure, the dielectric property figure of the comparative step four before and after heat treatment, the average value of the real part of the dielectric constant of the ceramic before heat treatment is 3.15, the average value of the real part of the dielectric constant of the ceramic after heat treatment is 2.88, the average value of the real part of the dielectric constant of the ceramic before heat treatment is 0.00609, the average value of the imaginary part of the dielectric constant of the ceramic after heat treatment is 0.00419, and the real part and the imaginary part of the dielectric constant after heat treatment decrease.

[0084] Figure 8 Pyrolysis ceramic XRD figure prepared in step three of the embodiment one, the embodiment three, the embodiment four, the comparative experiment two and the comparative experiment three; as can be seen from the figure, at 1000℃-1400℃, only the diffraction peak of the added Al2O3 appears in the XRD figure, and no other diffraction peak appears, the ceramic remains amorphous, at 1500℃, the diffraction peaks of SiC and Si3N4 appear, indicating that the material begins to crystallize at this time, and nano-crystals appear, at 1600℃, the diffraction peaks of SiC and Si3N4 begin to appear, indicating that phase separation occurs inside the Al2O3 / SiBCN composite ceramic.

[0085] According to the three-point bending method (GB / T 6569-2006) fine ceramic bending strength test method, the bending strength of the pyrolyzed ceramic prepared in step 3 of Example 1 to 2 and Comparative Experiment 1 to 3 is tested, and the bending strength of Comparative Experiment 1 is measured to be 20.58 MPa, the bending strength of Example 1 is measured to be 38.32 MPa, and the bending strength of Example 2 is measured to be 45.62 MPa.

[0086] Table 1 Average values of dielectric constant and dielectric loss of the pyrolyzed ceramic prepared in step 3 of Example 1, Example 3, Example 4, Comparative Experiment 2 and Comparative Experiment 3 at 4 GHz to 8 GHz

[0087]

Claims

1. A method for preparing high temperature resistant and low dielectric loss SiBCN composite ceramics, characterized in that It is carried out in the following steps:

1. Slurry preparation: Mixing the inorganic oxide filler with the SiBCN precursor and defoaming the mixture to obtain a filler / SiBCN precursor slurry; The inorganic oxide filler is Al2O3 filler, SiO2 filler or ZrO2 filler; The inorganic oxide filler is powder or whisker; the particle size of the powder is 1 μm to 10 μm; the diameter of the whisker is 0.1 μm to 1 μm, and the length is 10 μm to 100 μm; The mixing and defoaming is specifically performed by using a vacuum defoaming stirrer at a rotation speed of 1000 rpm to 4000 rpm for mixing for 10 min to 90 min, and then at a rotation speed of 1000 rpm to 2500 rpm for vacuum defoaming for 5 min to 10 min; 2. Precursor slurry solidification: The filler / SiBCN precursor slurry is placed in a mold for solidification, and then demoulded and surface polished to obtain a solidified precursor; The curing is specifically carried out by first keeping the temperature at 50°C to 100°C for 10 minutes to 30 minutes, and then keeping the temperature at 120°C to 160°C for 2 hours to 12 hours; 3. Ceramic pyrolysis: The precursor solidified material is heated to 200°C to 300°C at a heating rate of 1°C / min to 3°C / min, and kept at 200°C to 300°C for 0.5h to 2h, then heated to 550°C to 650°C at a heating rate of 0.5°C / min to 1°C / min, then heated to 1000°C at a heating rate of 1°C / min to 3°C / min, and kept at 1000°C for 1h to 12h, and finally cooled to room temperature at a cooling rate of 2°C / min to 5°C / min to obtain a pyrolyzed ceramic; 4. Heat treatment: The ceramic surface after pyrolysis is polished, cleaned and dried, and then heat-treated in an air atmosphere, and finally cooled in the furnace to obtain a high-temperature resistant and low dielectric loss SiBCN composite ceramic.

2. The method for preparing a high temperature resistant and low dielectric loss SiBCN composite ceramic according to claim 1, characterized in that When the powder particle size is 10nm~100nm, the mass percentage of the filler in the filler / SiBCN precursor slurry described in step one is 1%~25%; when the powder particle size is 0.1μm~10μm, the mass percentage of the filler in the filler / SiBCN precursor slurry described in step one is 1%~50%; when the whisker diameter is 0.1μm~1μm and the length is 10μm~100μm, the mass percentage of the filler in the filler / SiBCN precursor slurry described in step one is 1%~70%.

3. The method for preparing a high temperature resistant and low dielectric loss SiBCN composite ceramic according to claim 1, characterized in that In step 2, the surface is polished until the upper and lower surfaces are parallel to each other.

4. The method for preparing a high temperature resistant and low dielectric loss SiBCN composite ceramic according to claim 1, characterized in that The pyrolysis in step 3 is specifically carried out under nitrogen atmosphere, argon atmosphere or vacuum.

5. The method for preparing a high temperature resistant and low dielectric loss SiBCN composite ceramic according to claim 1, characterized in that The heat treatment in air atmosphere in step 4 is specifically carried out according to the following steps: in air atmosphere, heating the temperature to 600℃~1200℃ at a heating rate of 3℃ / min~10℃ / min, and keeping it warm for 2h~48h under the conditions of air atmosphere and temperature of 600℃~1200℃.

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