Silicon nitride conductive ceramic added with carbon fibers and method for manufacturing the same

Abstract

The application belongs to the technical field of ceramic materials, and particularly relates to a silicon nitride conductive ceramic and a preparation method thereof. The silicon nitride conductive ceramic provided by the application comprises a silicon nitride sintered body and carbon fibers embedded in the silicon nitride sintered body; the carbon fibers comprise carbon fibers in a three-dimensional network structure and free carbon fibers, and the mass of the carbon fibers in the three-dimensional network structure accounts for more than 97% of the total mass of the carbon fibers. Most of the carbon fibers are in a state of mutual connection, forming a conductive network, and the integrity of the conductive network does not suddenly break due to the gradual reduction of the fiber content, resulting in a sudden increase in resistance, but presents a slow increase in resistance effect; the conductivity of the overall material can be effectively controlled by the content of the carbon fibers. In the application, the content of the carbon fibers in the silicon nitride conductive ceramic is low, the sintering activity of the material is good, and the density is high, so that the material has good mechanical properties.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of ceramic materials, and particularly relates to a silicon nitride conductive ceramic and a preparation method thereof. BACKGROUND

[0002] Silicon nitride ceramic has high strength, high temperature resistance, thermal shock resistance, oxidation resistance and other characteristics, and is suitable for preparing electric heating elements. However, the silicon nitride has poor conductivity, and it is necessary to introduce some conductive components to realize the conductivity. The traditional method mainly improves the conductivity of silicon nitride by embedding one-dimensional continuous conductive phases such as long tungsten wires in the silicon nitride ceramic. However, the conductivity is greatly affected by the shape of the tungsten wire, and has certain directionality, which limits the conductivity. In order to further ensure the conductivity of the silicon nitride ceramic, researchers introduce carbon fibers, titanium nitride, molybdenum silicide and other conductive phases into the silicon nitride to prepare a silicon nitride conductive ceramic. However, a large amount of conductive phases need to be added in the silicon nitride conductive ceramic, and the content needs to reach the percolation threshold to ensure the formation of a conductive path. However, a high content of conductive phases will lead to poor sintering activity, and it is difficult to realize the densification of the silicon nitride ceramic, thereby affecting the mechanical properties of the silicon nitride conductive ceramic. It is a technical problem to be solved to provide a silicon nitride conductive ceramic with good conductivity and mechanical properties. SUMMARY

[0003] Therefore, the application provides a silicon nitride conductive ceramic and a preparation method thereof. The silicon nitride conductive ceramic provided by the application has good conductivity and mechanical properties, and the application range is expanded.

[0004] In order to solve the above technical problems, the application provides a silicon nitride conductive ceramic, which comprises a silicon nitride sintered body and carbon fibers embedded in the silicon nitride sintered body. The carbon fibers comprise carbon fibers forming a three-dimensional network structure and carbon fibers in a free state, and the mass of the carbon fibers forming the three-dimensional network structure accounts for more than 97% of the total mass of the carbon fibers.

[0005] Preferably, the volume content of the carbon fibers in the silicon nitride conductive ceramic is 5-40 vol%.

[0006] The average diameter of the carbon fibers is 0.1-120 μm, and the average length is 10-30000 μm.

[0007] Preferably, the silicon nitride sintered body comprises a silicon nitride crystal phase and a glass phase formed by a sintering aid.

[0008] The mass ratio of the silicon nitride crystal phase to the glass phase formed by the sintering aid is 4-20:1.

[0009] The application also provides a preparation method of the silicon nitride conductive ceramic.

[0010] mixing silicon nitride, sintering aids, solvent and dispersant to obtain ceramic slurry;

[0011] drying after the ceramic slurry penetrates into the carbon fiber preform to obtain conductive ceramic blank;

[0012] sintering the conductive ceramic blank to obtain the silicon nitride conductive ceramic.

[0013] Preferably, the carbon fiber preform includes carbon felt, graphite felt or carbon fiber felt;

[0014] The porosity of the carbon fiber preform is 80-96%.

[0015] Preferably, the penetration is performed under the condition of vibration in vacuum;

[0016] The temperature of the drying is 40-80℃, and the time is 4-24h.

[0017] Preferably, the temperature of the sintering is 1500-1800℃, and the time is 8-60min.

[0018] Preferably, the sintering is normal pressure sintering, hot pressing sintering, gas pressure sintering, discharge plasma sintering or hot isostatic pressing sintering.

[0019] Preferably, the silicon nitride is alpha silicon nitride or beta silicon nitride, and the average particle size of the silicon nitride is 0.2-10μm;

[0020] The sintering aids include one or more of alumina, magnesia, silica and rare earth oxides; the average particle size of the sintering aids is 0.2-10μm;

[0021] The mass ratio of the sintering aids and silicon nitride is 4-20:80-100.

[0022] Preferably, the solvent includes one or more of anhydrous ethanol, water, methanol and acetone;

[0023] The dispersant includes one or more of triethyl phosphate, polyethyleneimine, castor oil, castor oil glyceride, polyvinylpyrrolidone, sodium hexametaphosphate and sodium tripolyphosphate;

[0024] The mass ratio of the dispersant and solvent is 1-10:100.

[0025] The present application provides a silicon nitride conductive ceramic, comprising a silicon nitride sintered body and carbon fibers embedded in the silicon nitride sintered body, the carbon fibers comprising carbon fibers with a three-dimensional network structure and carbon fibers in a free state, the mass of the carbon fibers with a three-dimensional network structure accounting for more than 97% of the total mass of the carbon fibers. In the present application, the carbon fibers with a three-dimensional network structure remain in a state of mutual communication; after sintering, a three-dimensional conductive network is formed between the carbon fibers with a three-dimensional network structure, and the integrity of the conductive network does not suddenly break due to gradual reduction of the fiber content, resulting in a sudden increase in resistance, but shows a slow increase in resistance; the conductivity of the overall material can be effectively controlled by the content of the carbon fibers. At the same time, the carbon fibers also have a certain improvement on the fracture toughness of the ceramic. In the present application, the content of the carbon fibers in the silicon nitride conductive ceramic is relatively low, the sintering activity of the material is maintained, and the density is high, thereby having good mechanical properties. BRIEF DESCRIPTION OF DRAWINGS

[0026] Figure 1 XRD spectrum of the silicon nitride conductive ceramic prepared for Example 1;

[0027] Figure 2 SEM image of the cross section of the silicon nitride conductive ceramic prepared for Example 1. DETAILED DESCRIPTION

[0028] The present application provides a silicon nitride conductive ceramic, comprising a silicon nitride sintered body and carbon fibers embedded in the silicon nitride sintered body, the carbon fibers comprising carbon fibers with a three-dimensional network structure and carbon fibers in a free state, the mass of the carbon fibers with a three-dimensional network structure accounting for more than 97% of the total mass of the carbon fibers.

[0029] In the present application, the silicon nitride sintered body preferably comprises a silicon nitride crystalline phase and a glass phase formed by a sintering aid; the mass ratio of the silicon nitride crystalline phase and the glass phase formed by the sintering aid is preferably 4-20:1, more preferably 5-18:1.

[0030] In the present application, the average diameter of the carbon fibers is preferably 0.1-120 μm, more preferably 1-20 μm; the average length of the carbon fibers is preferably 10-30000 μm, more preferably 100-20000 μm, and more preferably 1000-10000 μm. In the present application, the volume content of the carbon fibers in the silicon nitride conductive ceramic is preferably 5-40 vol%, more preferably 7-20 vol%. In the present application, the mass of the carbon fibers with a three-dimensional network structure accounts for more than 97% of the total mass of the carbon fibers, preferably 98-99%.

[0031] The application further provides a preparation method of the silicon nitride conductive ceramic, comprising the following steps:

[0032] The silicon nitride, a sintering aid, a solvent and a dispersant are mixed to obtain a ceramic slurry;

[0033] The ceramic slurry is infiltrated into a carbon fiber preform and dried to obtain a conductive ceramic blank;

[0034] The conductive ceramic blank is sintered to obtain the silicon nitride conductive ceramic.

[0035] The silicon nitride, a sintering aid, a solvent and a dispersant are mixed to obtain a ceramic slurry. In the application, the silicon nitride is preferably alpha silicon nitride or beta silicon nitride, and more preferably beta silicon nitride; the average particle size of the silicon nitride is preferably 0.2-10 μm, and more preferably 0.3-5 μm.

[0036] In the application, the sintering aid preferably comprises one or more of aluminum oxide, magnesium oxide, silicon oxide and rare earth oxide, and more preferably two of aluminum oxide, magnesium oxide, silicon oxide and rare earth oxide, and more preferably a mixture of aluminum oxide and rare earth oxide, a mixture of magnesium oxide and rare earth oxide, or a mixture of silicon oxide and rare earth oxide. In the application, the rare earth oxide preferably comprises yttrium oxide or ytterbium oxide, and more preferably yttrium oxide. In the application, when the sintering aid comprises two or more of the above specific substances, the specific substances are not particularly limited in terms of the ratio of the amount used. In the application, the average particle size of the sintering aid is preferably 0.2-10 μm, and more preferably 0.3-5 μm.

[0037] In the application, the mass ratio of the sintering aid to the silicon nitride is preferably 4-20:80-100, and more preferably 6-12:85-96.

[0038] In the application, the solvent preferably comprises one or more of anhydrous ethanol, water, methanol and acetone, and more preferably one of anhydrous ethanol, water, methanol and acetone, and more preferably anhydrous ethanol or water. In the application, the water is preferably deionized water. The application does not have a particular requirement for the amount of the solvent, as long as it can be uniformly mixed.

[0039] In the application, the dispersant preferably comprises one or more of triethyl phosphate, polyethyleneimine, castor oil, castor oil glyceride, polyvinylpyrrolidone, sodium hexametaphosphate and sodium tripolyphosphate, and more preferably one of triethyl phosphate, polyethyleneimine, castor oil, castor oil glyceride, polyvinylpyrrolidone, sodium hexametaphosphate and sodium tripolyphosphate, and more preferably castor oil or sodium tripolyphosphate. In the application, the mass ratio of the dispersant to the solvent is preferably 1-10:100, and more preferably 2-6:100.

[0040] In the present application, the mixing method is preferably ball milling; the ball milling preferably includes planetary ball milling or tumbling, more preferably planetary ball milling. In the present application, the rotation speed of the ball milling is preferably 100-300 rpm, more preferably 200-250 rpm; the ball milling time is preferably 1-24 h, more preferably 4-12 h. In the present application, the ball used in the ball milling preferably includes silicon nitride balls, alumina balls, agate balls or silicon carbide balls, more preferably silicon nitride balls.

[0041] After obtaining the ceramic slurry, the present application penetrates the ceramic slurry into a carbon fiber preform and then dries to obtain a conductive ceramic green body. In the present application, the carbon fiber preform preferably includes carbon felt, graphite felt or carbon fiber felt, more preferably carbon fiber felt. In the present application, the porosity of the carbon fiber preform is preferably 80-96%, more preferably 88-96%. In the present application, too low porosity of the carbon fiber preform can easily lead to too high carbon fiber content, reducing the sintering activity of silicon nitride ceramic material; the present application limits the porosity of the carbon fiber preform in the above range to ensure good electrical conductivity while ensuring the sintering activity of silicon nitride to improve the mechanical properties of silicon nitride conductive ceramic.

[0042] In the present application, the penetration is preferably performed under vacuum conditions with vibration; the vibration time is preferably 0.5-10 h, more preferably 2-5 h. The present application does not have special limitations on the vacuum degree of the vacuum condition and the frequency of the vibration, as long as the ceramic slurry can be fully infiltrated into the carbon fiber preform. In the present application, the ceramic slurry is vibrated under vacuum conditions to fill the entire carbon fiber preform with voids and then dried.

[0043] In the present application, the drying temperature is preferably 40-80℃, more preferably 50-70℃; the drying time is preferably 4-24 h, more preferably 8-20 h. The present application preferably performs drying in a forced air drying oven.

[0044] After obtaining the conductive ceramic green body, the present application sintering the conductive ceramic green body to obtain the silicon nitride conductive ceramic. In the present application, the sintering temperature is preferably 1500-1800℃, more preferably 1700-1750℃; the sintering time is preferably 8-60 min, more preferably 15-30 min. In the present application, the sintering method preferably includes normal pressure sintering, gas pressure sintering, hot-press sintering, spark plasma sintering (SPS) or hot isostatic pressing sintering, more preferably spark plasma sintering. In the present application, the pressure of the spark plasma sintering is preferably 30-40 MPa.

[0045] In the present application, when the sintering method is gas pressure sintering, before sintering, preferably further comprising: cold isostatic pressing heat treatment is carried out on the conductive ceramic blank; the pressure of the cold isostatic pressing treatment is preferably 50-200 MPa, more preferably 100-150 MPa. The present application is treated by cold isostatic pressing, which is conducive to better densification of silicon nitride ceramic during sintering.

[0046] The present application first prepares a silicon nitride slurry with high solid content and good fluidity, the silicon nitride slurry is fully infiltrated into the carbon fiber preform, then the dried preform is sintered to obtain a silicon nitride sintered body containing three-dimensionally connected carbon fibers. In the carbon fiber preform, no matter the porosity is high or low or the density of carbon fibers, the carbon fibers can be connected together in the form of mutual lapping. This structure makes it have good electrical conductivity. Each carbon fiber in the carbon fiber preform cannot be in a suspended state independent of the preform, and at least two points are connected to other carbon fibers to be in a stable state. The present application directly introduces this carbon fiber preform into the silicon nitride sintered body and maintains the structure of mutual connection between the carbon fibers, thereby achieving the effect of good uniform conductivity of the material. At the same time, the lower content of carbon fibers can also achieve electrical conductivity, and the high sintering activity of silicon nitride ceramic is maintained. Unlike the way of introducing carbon fibers by ball milling dispersion, the slurry is infiltrated into the complete carbon fiber preform and the subsequent sintering process does not destroy the connection state between the carbon fibers. Unlike the way of layering carbon fiber cloth, the three-dimensional carbon fiber preform has more uniform conductivity in three-dimensional direction.

[0047] In order to further illustrate the present application, the technical solutions provided by the present application are described in detail below in conjunction with examples, but they should not be understood as limiting the scope of protection of the present application.

[0048] Example 1

[0049] Put 90g of alpha silicon nitride powder with an average particle size of 0.5μm, 5g of yttria powder with an average particle size of 0.5μm, 5g of alumina powder with an average particle size of 0.5μm, 70g of absolute ethanol, and 3g of castor oil into a nylon ball mill jar, add 100g of silicon nitride ceramic balls, and planetary ball mill at a speed of 200rpm for 4h to obtain a ceramic slurry;

[0050] Pour the ceramic slurry into a carbon felt with a porosity of 92% (the average diameter of carbon fibers is 1μm and the average length is 200μm), fully immerse the carbon felt, and then perform vacuum degassing; after 2h of vibration under vacuum, place it in a drying box at 60℃ and dry for 8h to obtain a conductive ceramic blank;

[0051] Place the conductive ceramic blank in a mold, and sinter it in a spark plasma pressure sintering furnace at 40MPa and 1750℃ for 10min to obtain a silicon nitride conductive ceramic.

[0052] Example 2

[0053] Put 85 g of beta silicon nitride powder with an average particle size of 0.3 μm, 8 g of yttrium oxide powder with an average particle size of 0.3 μm, 7 g of magnesium oxide powder with an average particle size of 0.4 μm, 60 g of deionized water, and 6 g of sodium hexametaphosphate into a nylon ball mill tank, add 100 g of alumina ceramic balls, and perform planetary ball milling at a speed of 100 rpm for 24 h to obtain a ceramic slurry;

[0054] Pour the ceramic slurry into carbon felt (carbon fiber with an average diameter of 20 μm and an average length of 3000 μm) with a porosity of 95%, completely immerse the carbon felt, and perform vacuum degassing; after vibrating the vibrating table for 10 h under vacuum, place it in a drying box at 70 °C and dry for 20 h to obtain a conductive ceramic blank;

[0055] Place the conductive ceramic blank in a mold, and sinter it in a spark plasma pressure sintering furnace at 30 MPa and 1500 °C for 15 min to obtain a silicon nitride conductive ceramic.

[0056] Example 3

[0057] Put 90 g of alpha silicon nitride powder with an average particle size of 0.5 μm, 4 g of yttrium oxide powder with an average particle size of 0.5 μm, 6 g of alumina powder with an average particle size of 0.5 μm, 65 g of absolute ethanol, and 1 g of polyvinylpyrrolidone into a nylon ball mill tank, add 100 g of silicon nitride ceramic balls, and perform planetary ball milling at a speed of 250 rpm for 4 h to obtain a ceramic slurry;

[0058] Pour the ceramic slurry into carbon felt (carbon fiber with an average diameter of 1 μm and an average length of 200 μm) with a porosity of 92%, completely immerse the carbon felt, and perform vacuum degassing; after vibrating the vibrating table for 2 h under vacuum, place it in a drying box at 50 °C and dry for 8 h to obtain a conductive ceramic blank;

[0059] Place the conductive ceramic blank in a mold, and sinter it in a spark plasma pressure sintering furnace at 40 MPa and 1700 °C for 8 min to obtain a silicon nitride conductive ceramic.

[0060] Example 4

[0061] Put 96 g of alpha silicon nitride powder with an average particle size of 0.5 μm, 3 g of silicon oxide powder with an average particle size of 0.2 μm, 1 g of yttrium oxide powder with an average particle size of 0.5 μm, 80 g of acetone, and 2 g of triethyl phosphate into a nylon ball mill tank, add 100 g of agate balls, and perform planetary ball milling at a speed of 300 rpm for 1 h to obtain a ceramic slurry;

[0062] The ceramic slurry was poured into the graphite felt (the average diameter of the carbon fiber was 2 μm and the average length was 5000 μm) with a porosity of 90%, and the graphite felt was completely immersed, and then vacuum degassing was performed; after the vibration table was vibrated for 0.5 h under the vacuum state, the conductive ceramic blank was obtained by placing it in a drying box at 80 °C and drying for 4 h.

[0063] The conductive ceramic blank was placed in a mold, and sintering was performed at 40 MPa and 1800 °C for 15 min in a spark plasma sintering furnace to obtain the silicon nitride conductive ceramic.

[0064] Example 5

[0065] The 80 g of alpha silicon nitride powder with an average particle size of 10 μm, 10 g of yttrium oxide powder with an average particle size of 5 μm, 10 g of silicon oxide powder with an average particle size of 10 μm, 75 g of methanol, and 2 g of castor oil glyceride were placed in a nylon ball mill jar, 100 g of silicon nitride ceramic balls were added, and planetary ball milling was performed at a speed of 300 rpm for 12 h to obtain a ceramic slurry.

[0066] The ceramic slurry was poured into the carbon fiber felt (the average diameter of the carbon fiber was 0.1 μm and the average length was 10 μm) with a porosity of 80%, and the carbon fiber felt was completely immersed, and then vacuum degassing was performed; after the vibration table was vibrated for 5 h under the vacuum state, the conductive ceramic blank was obtained by placing it in a drying box at 50 °C and drying for 8 h.

[0067] The conductive ceramic blank was placed in a mold, and sintering was performed at 40 MPa and 1700 °C for 30 min in a hot-pressing sintering furnace to obtain the silicon nitride conductive ceramic.

[0068] Example 6

[0069] The 88 g of alpha silicon nitride powder with an average particle size of 1 μm, 6 g of ytterbium oxide powder with an average particle size of 1 μm, 6 g of aluminum oxide powder with an average particle size of 1 μm, 70 g of acetone, and 2 g of polyethyleneimine were placed in a nylon ball mill jar, 100 g of silicon carbide ceramic balls were added, and planetary ball milling was performed at a speed of 250 rpm for 4 h to obtain a ceramic slurry.

[0070] The ceramic slurry was poured into the carbon felt (the average diameter of the carbon fiber was 120 μm and the average length was 30000 μm) with a porosity of 92%, and the carbon felt was completely immersed, and then vacuum degassing was performed; after the vibration table was vibrated for 3 h under the vacuum state, the conductive ceramic blank was obtained by placing it in a drying box at 50 °C and drying for 8 h.

[0071] After the conductive ceramic blank was cold isostatic pressed at 200 MPa, the silicon nitride conductive ceramic was obtained by sintering at 2 MPa and 1700 °C for 60 min in a gas pressure sintering furnace.

[0072] Example 7

[0073] Put 88 g of alpha silicon nitride powder with an average particle size of 1 μm, 6 g of ytterbia powder with an average particle size of 1 μm, 6 g of alumina powder with an average particle size of 1 μm, 70 g of acetone, and 2 g of castor oil into a nylon ball mill tank, add 100 g of silicon nitride ceramic balls, and roll mill at a speed of 300 rpm for 1 h to obtain a ceramic slurry;

[0074] Pour the ceramic slurry into carbon felt with a porosity of 88% (the average diameter of the carbon fibers is 10 μm and the average length is 500 μm), vacuumize and degas after the carbon felt is completely immersed, vibrate the vibrating table under vacuum for 2 h, and then place it in a drying box at 50 ℃ for 8 h to obtain a conductive ceramic blank;

[0075] After the conductive ceramic blank is subjected to cold isostatic pressing at 300 MPa for 10 min, it is sintered at 1750 ℃ for 60 min in a pressureless sintering furnace to obtain a silicon nitride conductive ceramic.

[0076] Example 8

[0077] Put 88 g of alpha silicon nitride powder with an average particle size of 1 μm, 6 g of ytterbia powder with an average particle size of 1 μm, 6 g of alumina powder with an average particle size of 1 μm, 70 g of acetone, and 6 g of castor oil glyceride into a nylon ball mill tank, and planetary ball mill at a speed of 150 rpm for 8 h to obtain a ceramic slurry;

[0078] Pour the ceramic slurry into carbon felt with a porosity of 96% (the average diameter of the carbon fibers is 0.5 μm and the average length is 50 μm), vacuumize and degas after the carbon felt is completely immersed, vibrate the vibrating table under vacuum for 3 h, and then place it in a drying box at 50 ℃ for 8 h to obtain a conductive ceramic blank;

[0079] After the conductive ceramic blank is subjected to cold isostatic pressing at 150 MPa, it is sintered at 1 MPa and 1750 ℃ for 60 min in a gas pressure sintering furnace to obtain a silicon nitride conductive ceramic.

[0080] Comparative Example 1

[0081] Put 90 g of alpha silicon nitride powder with an average particle size of 0.5 μm, 5 g of yttria powder with an average particle size of 0.5 μm, 5 g of alumina powder with an average particle size of 0.5 μm, 70 g of absolute ethanol, and 3 g of castor oil into a nylon ball mill tank, and planetary ball mill at a speed of 200 rpm for 4 h to obtain a ceramic slurry;

[0082] Directly vacuumize and degas the ceramic slurry, vibrate the vibrating table under vacuum for 2 h, and then place it in a drying box at 60 ℃ for 8 h to obtain a ceramic blank;

[0083] The ceramic green body is placed in a mold, sintered in a spark plasma pressure sintering furnace at 40 MPa and 1750 °C for 10 min, and a ceramic sintered body is obtained.

[0084] Comparative Example 2

[0085] 90 g of alpha silicon nitride powder with an average particle size of 0.5 μm, 5 g of yttrium oxide powder with an average particle size of 0.5 μm, 5 g of aluminum oxide powder with an average particle size of 0.5 μm, 5 g of carbon fiber powder (the average diameter of the carbon fiber is 1 μm, and the average length is 200 μm), 70 g of anhydrous ethanol, and 3 g of castor oil are placed in a nylon ball mill tank, 100 g of silicon nitride ceramic balls are added, and planetary ball milling is performed at a speed of 200 rpm for 4 h to obtain a ceramic slurry;

[0086] The ceramic slurry is directly vacuum degassed, vibrated on a vibration table for 2 h in a vacuum state, placed in a drying box at 60 °C, and dried for 8 h to obtain a conductive ceramic green body.

[0087] The conductive ceramic green body is placed in a mold, sintered in a spark plasma pressure sintering furnace at 40 MPa and 1750 °C for 10 min, and a conductive ceramic sintered body is obtained.

[0088] Comparative Example 3

[0089] 90 g of alpha silicon nitride powder with an average particle size of 0.5 μm, 5 g of yttrium oxide powder with an average particle size of 0.5 μm, 5 g of aluminum oxide powder with an average particle size of 0.5 μm, 10 g of carbon fiber powder (the average diameter of the carbon fiber is 1 μm, and the average length is 200 μm), 70 g of anhydrous ethanol, and 3 g of castor oil are placed in a nylon ball mill tank, 100 g of silicon nitride ceramic balls are added, and planetary ball milling is performed at a speed of 200 rpm for 4 h to obtain a ceramic slurry;

[0090] The ceramic slurry is directly vacuum degassed, vibrated on a vibration table for 2 h in a vacuum state, placed in a drying box at 60 °C, and dried for 8 h to obtain a conductive ceramic green body.

[0091] The conductive ceramic green body is placed in a mold, sintered in a spark plasma pressure sintering furnace at 40 MPa and 1750 °C for 10 min, and a conductive ceramic sintered body is obtained.

[0092] Comparative Example 4

[0093] 90 g of alpha silicon nitride powder with an average particle size of 0.5 μm, 5 g of yttrium oxide powder with an average particle size of 0.5 μm, 5 g of aluminum oxide powder with an average particle size of 0.5 μm, 20 g of carbon fiber powder (the average diameter of the carbon fiber is 1 μm, and the average length is 200 μm), 70 g of anhydrous ethanol, and 3 g of castor oil are placed in a nylon ball mill tank, 100 g of silicon nitride ceramic balls are added, and planetary ball milling is performed at a speed of 200 rpm for 4 h to obtain a ceramic slurry;

[0094] The ceramic slurry was directly vacuumed to remove air, and then the vibrating table was vibrated for 2 hours under vacuum. The ceramic slurry was dried in a drying box at 60°C for 8 hours to obtain a conductive ceramic body;

[0095] The conductive ceramic body was placed in a mold and sintered in a spark plasma pressure sintering furnace at 40 MPa and 1750°C for 10 minutes to obtain a conductive ceramic sintered body.

[0096] The conductive ceramic sintered body was subjected to XRD detection, and the XRD spectrum is shown in Figure 1 As can be seen from the XRD spectrum, the main components of the conductive ceramic sintered body prepared in Example 1 are silicon nitride and carbon, and no other phase is observed, indicating that no obvious chemical reaction occurs during sintering. Figure 1

[0097] The cross section of the conductive ceramic sintered body prepared in Example 1 was observed by scanning electron microscopy, and the SEM image is shown in Figure 2 As can be seen from the SEM image, the conductive ceramic sintered body prepared in Example 1 is mainly composed of a silicon nitride matrix and carbon fibers. The silicon nitride matrix structure is compact, and no other pores are observed except for pores left during the pulling out of the carbon fibers, indicating good sintering activity. The carbon fibers appear to be pulled out during the fracture of the sintered body, which is very beneficial to the improvement of the toughness of the ceramic. Figure 1 Figure 2 The XRD and SEM results of Examples 2-8 are similar to those of Example 1, which are not given here.

[0098] The density of the ceramic materials prepared in Examples 1-8 and Comparative Examples 1-4 was detected according to the Archimedes drainage method, and the results are shown in Table 1.

[0099] The resistivity of the ceramic materials prepared in Examples 1-8 and Comparative Examples 1-4 was detected according to the voltammetric characteristic curve method, and the results are shown in Table 1.

[0100] The mechanical properties of the ceramic materials prepared in Examples 1-8 and Comparative Examples 1-4 were detected according to the three-point bending method, and the results are shown in Table 1.

[0101] The mechanical properties of the ceramic materials prepared in Examples 1-8 and Comparative Examples 1-4 were detected according to the three-point bending method, and the results are shown in Table 1.

[0102] Table 1 Performance comparison of ceramic materials prepared in Examples 1-8 and Comparative Examples 1-4

[0103]

[0104]

[0105] ​​As can be seen from the results in Table 1, compared with Comparative Example 1, the silicon nitride conductive ceramic prepared in the examples not only realizes conductivity while ensuring high density, but also has improved toughness, and the bending strength does not change significantly, indicating that the introduction of the carbon fiber preform has a significant effect. As can be seen from Comparative Example 2, the direct introduction of carbon fiber powder has little effect on the electrical properties when the content is low, because the carbon fiber content does not reach the percolation threshold and cannot form a connected structure. As can be seen from Comparative Examples 3 and 4, increasing the amount of carbon fiber introduced will lead to a decrease in the sintering density of the sintered body, and thus the mechanical properties are severely affected, which is due to the poor sintering activity caused by excessive carbon content. Simply increasing the carbon content can improve the conductivity, but due to the high porosity, the effect is still not as good as the examples.

[0106] Although the above examples have made a detailed description of the present application, it is only a part of the embodiments of the present application, not all the embodiments, and people can also obtain other embodiments according to the present embodiments without creativity, which all belong to the protection scope of the present application.

Claims

1. A silicon nitride conductive ceramic, characterized by, The silicon nitride sintered body and carbon fibers embedded in the silicon nitride sintered body, the carbon fibers including carbon fibers that are mutually stacked to form a three-dimensional network structure and carbon fibers in a free state, the carbon fibers that are mutually stacked to form a three-dimensional network structure accounting for more than 97% of the total mass of the carbon fibers; the volume content of the carbon fibers in the silicon nitride electrically conductive ceramic being 5-40 vol%; The preparation method of the silicon nitride electrically conductive ceramic includes the following steps: Mixing silicon nitride, a sintering aid, a solvent and a dispersing agent to obtain a ceramic slurry; The sintering aid includes one or more of aluminum oxide, magnesium oxide, silicon oxide and rare earth oxides; the average particle size of the sintering aid is 0.2-10 μm; the mass ratio of the sintering aid to silicon nitride is 4-20:80-100; After the ceramic slurry is infiltrated into a carbon fiber preform and dried, an electrically conductive ceramic blank is obtained; Sintering the electrically conductive ceramic blank to obtain the silicon nitride electrically conductive ceramic; the sintering temperature is 1500-1800 ℃, and the sintering time is 8-60 min.

2. The silicon nitride conductive ceramic according to claim 1, wherein The average diameter of the carbon fibers is 0.1-120 μm, and the average length is 10-30000 μm.

3. The silicon nitride conductive ceramic of claim 1, wherein, The silicon nitride sintered body includes a silicon nitride crystalline phase and a glass phase formed by the sintering aid; The mass ratio of the silicon nitride crystalline phase to the glass phase formed by the sintering aid is 4-20:

1.

4. The preparation method of the silicon nitride electrically conductive ceramic according to any one of claims 1-3, including the following steps: Mixing silicon nitride, a sintering aid, a solvent and a dispersing agent to obtain a ceramic slurry; After the ceramic slurry is infiltrated into a carbon fiber preform and dried, an electrically conductive ceramic blank is obtained; Sintering the electrically conductive ceramic blank to obtain the silicon nitride electrically conductive ceramic; the sintering temperature is 1500-1800 ℃, and the sintering time is 8-60 min.

5. The preparation method according to claim 4, characterized in that, The carbon fiber preform includes carbon felt, graphite felt or carbon fiber felt; The porosity of the carbon fiber preform is 80-96%.

6. The preparation method according to claim 4, characterized in that, The infiltration is performed under vibration in a vacuum; The drying temperature is 40-80 ℃, and the drying time is 4-24 h.

7. The preparation method according to claim 4, characterized in that, The sintering is normal pressure sintering, hot-press sintering, gas pressure sintering, discharge plasma sintering or hot isostatic sintering.

8. The preparation method according to claim 4, characterized in that, The silicon nitride is alpha silicon nitride or beta silicon nitride, and the average particle size of the silicon nitride is 0.2-10 μm.

9. The preparation method according to claim 4, characterized in that, The solvent includes one or more of anhydrous ethanol, water, methanol and acetone; The dispersing agent includes one or more of triethyl phosphate, polyethylene imine, castor oil, castor oil glyceride, polyvinyl pyrrolidone, sodium hexametaphosphate and sodium tripolyphosphate; The mass ratio of the dispersing agent to the solvent is 1-10:100.

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