WO2019061484A1 - 一种浸渍法制备SiCN/Si3N4复合陶瓷的方法 - Google Patents

一种浸渍法制备SiCN/Si3N4复合陶瓷的方法 Download PDF

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WO2019061484A1
WO2019061484A1 PCT/CN2017/104957 CN2017104957W WO2019061484A1 WO 2019061484 A1 WO2019061484 A1 WO 2019061484A1 CN 2017104957 W CN2017104957 W CN 2017104957W WO 2019061484 A1 WO2019061484 A1 WO 2019061484A1
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sicn
preparing
composite ceramic
impregnation
silicon nitride
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龚红宇
冯玉润
张玉军
郭学
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山东大学
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    • C04—CEMENTS; CONCRETE; ARTIFICIAL STONE; CERAMICS; REFRACTORIES
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    • C04B35/00—Shaped ceramic products characterised by their composition; Ceramics compositions; Processing powders of inorganic compounds preparatory to the manufacturing of ceramic products
    • C04B35/515—Shaped ceramic products characterised by their composition; Ceramics compositions; Processing powders of inorganic compounds preparatory to the manufacturing of ceramic products based on non-oxide ceramics
    • C04B35/58—Shaped ceramic products characterised by their composition; Ceramics compositions; Processing powders of inorganic compounds preparatory to the manufacturing of ceramic products based on non-oxide ceramics based on borides, nitrides, i.e. nitrides, oxynitrides, carbonitrides or oxycarbonitrides or silicides
    • C04B35/584—Shaped ceramic products characterised by their composition; Ceramics compositions; Processing powders of inorganic compounds preparatory to the manufacturing of ceramic products based on non-oxide ceramics based on borides, nitrides, i.e. nitrides, oxynitrides, carbonitrides or oxycarbonitrides or silicides based on silicon nitride
    • C—CHEMISTRY; METALLURGY
    • C04—CEMENTS; CONCRETE; ARTIFICIAL STONE; CERAMICS; REFRACTORIES
    • C04B—LIME, MAGNESIA; SLAG; CEMENTS; COMPOSITIONS THEREOF, e.g. MORTARS, CONCRETE OR LIKE BUILDING MATERIALS; ARTIFICIAL STONE; CERAMICS; REFRACTORIES; TREATMENT OF NATURAL STONE
    • C04B35/00—Shaped ceramic products characterised by their composition; Ceramics compositions; Processing powders of inorganic compounds preparatory to the manufacturing of ceramic products
    • C04B35/622—Forming processes; Processing powders of inorganic compounds preparatory to the manufacturing of ceramic products
    • C—CHEMISTRY; METALLURGY
    • C04—CEMENTS; CONCRETE; ARTIFICIAL STONE; CERAMICS; REFRACTORIES
    • C04B—LIME, MAGNESIA; SLAG; CEMENTS; COMPOSITIONS THEREOF, e.g. MORTARS, CONCRETE OR LIKE BUILDING MATERIALS; ARTIFICIAL STONE; CERAMICS; REFRACTORIES; TREATMENT OF NATURAL STONE
    • C04B38/00—Porous mortars, concrete, artificial stone or ceramic ware; Preparation thereof
    • C04B38/06—Porous mortars, concrete, artificial stone or ceramic ware; Preparation thereof by burning-out added substances by burning natural expanding materials or by sublimating or melting out added substances
    • C—CHEMISTRY; METALLURGY
    • C04—CEMENTS; CONCRETE; ARTIFICIAL STONE; CERAMICS; REFRACTORIES
    • C04B—LIME, MAGNESIA; SLAG; CEMENTS; COMPOSITIONS THEREOF, e.g. MORTARS, CONCRETE OR LIKE BUILDING MATERIALS; ARTIFICIAL STONE; CERAMICS; REFRACTORIES; TREATMENT OF NATURAL STONE
    • C04B41/00—After-treatment of mortars, concrete, artificial stone or ceramics; Treatment of natural stone
    • C04B41/80—After-treatment of mortars, concrete, artificial stone or ceramics; Treatment of natural stone of only ceramics
    • C04B41/81—Coating or impregnation
    • C04B41/85—Coating or impregnation with inorganic materials
    • C04B41/87—Ceramics

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  • the invention relates to a preparation method of a SiCN/Si 3 N 4 composite ceramic, in particular to a method for synthesizing a silicon carbon nitrogen composite porous silicon nitride ceramic by an impregnation method, belonging to the field of inorganic nonmetal materials.
  • Electromagnetic wave absorption and shielding materials involve electromagnetic field and electromagnetic wave theory, many branches of materials science, and reflection and refraction phenomena and related material structures and combinations derived from electromagnetic wave and material interaction. In combination with the above-mentioned electromagnetic radiation pollution problem, electromagnetic wave absorbing materials with thin thickness, light weight, absorption frequency bandwidth and high absorption intensity have gradually attracted wide interest.
  • the Si 3 N 4 material has excellent comprehensive performance, good mechanical properties and thermodynamic properties, low dielectric constant and dielectric loss, and low density, which has become a hot spot in the research field of radome. At present, domestic research on Si 3 N 4 ceramic radome is relatively late, and the application level is low.
  • the simple Si 3 N 4 ceramic material has high brittleness and poor toughness. Introducing the reinforcing phase is an effective way to improve the toughness of the ceramic.
  • the SiCN precursor ceramic material has excellent electrical conductivity and electromagnetic properties, and is impregnated with SiCN precursor ceramics with excellent electromagnetic properties. It has a certain absorbing property, broadens its application field, and can improve its strength and toughness to some extent.
  • the Si 3 N 4 radome developed by Israel is a composite material consisting of two layers of silicon nitride with different densities.
  • the literature indicates that the wave-transparent material can withstand temperatures up to 1600 ° C, so the only available binder is phosphate (melting point of aluminum phosphate > 1500 ° C).
  • the high-density sealing layer is uniformly mixed with the binder after the Si 3 N 4 powder and compacted, and when sintered at a high temperature (greater than 1600 ° C), the binder becomes a liquid phase and wets with Si 3 N 4 to form a ceramic material.
  • a high temperature greater than 1600 ° C
  • the porous low-density wave-transporting layer is difficult to control the size and distribution of pores. Once individual macropores appear, the transmission characteristics of electromagnetic waves will be significantly affected.
  • Liu Hongli of Jiamusi University used precursor conversion method and organic foam impregnation method to prepare SiCN foam ceramics with vinyl polysilazane.
  • the temperature of the pyrolysis temperature range of 1000-1400 °C increased with temperature.
  • the compressive strength first increases and then decreases, reaching a maximum at 1300 ° C, but the mechanical strength is still lower at 11.5 MPa.
  • Chinese patent document CN 101265106A (Application No.: 200810086327.X) discloses a novel method for preparing nano/nano type SI 3 N 4 /SIC nanocomposite ceramics.
  • the method comprises the following specific steps: (1) low-temperature cross-linking curing: the organic precursor is subjected to low-temperature cross-linking curing under a protective atmosphere to obtain an amorphous solid; (2) ball-milling pulverization: ball-milling the amorphous solid in a ball mill (3) High temperature pyrolysis: The mixture after ball milling is subjected to high temperature pyrolysis under a protective atmosphere to obtain SICN powder.
  • the present invention provides an immersion method for preparing SiCN/Si.
  • the method of 3 N 4 composite ceramics has the advantages of simple process, low production cost, short preparation period, uniform distribution of pores of Si 3 N 4 ceramics, and preparation of SiCN/Si 3 N 4 composite ceramics by impregnation method.
  • the electromagnetic wave attenuation coefficient of the product is high and the microwave absorption performance is good.
  • a method for preparing a SiCN/Si 3 N 4 composite ceramic by an impregnation method comprising:
  • the sintered material is impregnated with SiCN and subjected to a heat treatment step.
  • the mass ratio of the silicon nitride powder, Y 2 O 3 , and PVP in the granulation step is 8 to 9.5: 0.5 to 2: 0.008 to 0.01; further preferably 8.5 to 9.5: 0.5 to 1.5: 0.008 ⁇ 0.01;
  • the pore former is stearic acid, benzoic acid, graphite or/and PMMA (polymethyl methacrylate).
  • the granulation step is carried out by subjecting the raw material and the pore forming agent to wet ball milling, drying, and then grinding and sieving;
  • the ball milling medium of the wet ball milling is anhydrous ethanol, the ball milling time is 10-30 min, and the wet ball milling body is silicon nitride. ball;
  • the raw material wet ball mill: the ball mill medium has a mass ratio of 1: (2-5): (1-3), further preferably 1: 3: 2;
  • the drying temperature after wet ball milling is 45 ° C -75 ° C, the drying time is 20-24 h, and the meshing number is 40-80 mesh;
  • the drying temperature is 60 ° C, and the alcohol volatilization speed is suitable, which is favorable for obtaining a raw material with good humidity.
  • the pore former is added in an amount of from 1% to 20%, more preferably from 10% to 15%, based on the total amount of the raw materials.
  • the molding step is to subject the granulated raw material to uniaxial pressing, cold isostatic pressing to obtain a green body, vacuum-packaging the green body, and isostatic pressing;
  • the pressure of the uniaxial press molding is 20 to 40 MPa, more preferably 30 MPa; preferably, after vacuum packaging the green body, the isostatic pressure is 150 to 300 MPa, more preferably 200 MPa, and the dwell time is 150 to 300 s.
  • the sintering step is to sinter the isostatically pressed green body at 1600 ° C to 1650 ° C under a nitrogen atmosphere, and keep it for 1 to 4 hours, and then reduce it to 1000 ° C for 2-5 hours.
  • the sintered material is impregnated with SiCN, the mass ratio of the sintered material to the SiCN is 1: (1 ⁇ 3), more preferably 1: 2, the immersion time is 5 ⁇ 20min;
  • the heat treatment after the SiCN is impregnated is heat-treated to a heat treatment temperature under the protection of a N 2 atmosphere, the heat treatment temperature is 1000 ° C to 1400 ° C, the heating rate is 3 to 5 ° C / min, and the temperature is raised to the heat treatment temperature and then the heat is maintained 2 - 5h.
  • the method for preparing a SiCN/Si 3 N 4 composite ceramic by the impregnation method a preferred embodiment is as follows:
  • the silicon nitride powder, Y 2 O 3 , PVP (polyvinylpyrrolidone) is used as a raw material, and a pore former is added, which comprises the following steps:
  • the mass ratio of the silicon nitride powder: Y 2 O 3 :PVP is 8.5:1.5:0.01, and the mass ratio of the raw material, the silicon nitride ball, and the grinding medium is 1:3:2;
  • Impregnation The sintered porous silicon nitride ceramic is placed in SiCN for 5-20 min, and then placed in a tube furnace, and heat-treated at a temperature of 1000 ° C to 1300 ° C under the protection of N 2 atmosphere. 3 ⁇ 5 ° C / min, heat preservation 4h.
  • the present invention utilizes a pressureless sintering method to prepare a porous Si 3 N 4 ceramic, and by impregnating a SiCN precursor, a composite ceramic material having excellent magnetic wave absorption performance is obtained.
  • SiCN/Si 3 N 4 composite ceramics not only can promote the development of military materials such as radar, but also can be applied to absorb electromagnetic radiation and protect human health. It has a very broad application prospect.
  • the present invention prepares SiCN/Si 3 N 4 composite ceramic by impregnation method, and uses porous silicon nitride as a matrix, and the lower dielectric constant enables electromagnetic waves to effectively enter the interior of the absorbing material and occurs with the absorbing absorbing material of SiCN.
  • the porous design can effectively reduce the density of the composite material and obtain a composite ceramic with excellent microwave absorption performance.
  • the invention adopts the dipping method, the experimental equipment is simple, and the operation is convenient.
  • the present invention adds suitable pore-forming agents such as stearic acid, benzoic acid, graphite and PMMA, and controls the addition ratio of the pore-forming agent and the sintering temperature to obtain a material having a porous structure, and has good mechanical strength, which is more advantageous. Impregnation of SiCN gives the impregnated product excellent absorbing properties.
  • FIG. 1 is an SEM image of the silicon nitride ceramic obtained in the step (3) of Example 4 and Comparative Examples 1-3.
  • a, b, c, and d correspond to Comparative Example 1, Comparative Example 2, Example 4, and Comparative Example 3, respectively.
  • FIG. 2 is a graph showing the dielectric properties of the SiCN/Si 3 N 4 composite ceramics obtained in Comparative Example 4 and Example 4-7.
  • Figure 2(a) is the real part of the complex permittivity ( ⁇ ')
  • Figure 2(b) is the imaginary part of the complex permittivity ( ⁇ "). 1, 2, 3, 4, 5 in Figure 2.
  • Comparative Example 4 Example 4, Example 5, Example 6, and Example 7, respectively.
  • Fig. 3 is a graph showing the absorbing properties of the SiCN/Si 3 N 4 composite ceramics obtained in Comparative Example 4 and Example 4-7.
  • Figure 3 (a) is the electromagnetic attenuation coefficient
  • Figure 3 (b) is the electromagnetic wave reflectivity.
  • 1, 2, 3, 4, and 5 in Fig. 3 correspond to Comparative Example 4 (no pore former added), Example 4 (stearing agent is stearic acid), and Example 5 (porosity agent is benzoic acid), Example 6 (Pore forming agent is graphite), and Example 7 (Pore forming agent is PMMA).
  • Example 4 is a graph showing the effect of the number of times of impregnation of SiCN/Si 3 N 4 composite ceramics on the dielectric properties of Example 4 using stearic acid as a pore former.
  • Fig. 5 is a graph showing the effect of the number of times of impregnation of SiCN/Si 3 N 4 composite ceramics obtained by using stearic acid as a pore-forming agent on the absorbing properties of Example 4.
  • Fig. 6 is a graph showing the effect of the number of times of impregnation of SiCN/Si 3 N 4 composite ceramics on the dielectric properties of Example 7 using PMMA as a pore former.
  • Fig. 7 is a graph showing the effect of the number of times of impregnation of the SiCN/Si 3 N 4 composite ceramic obtained by using PMMA as a pore-forming agent on its absorbing property.
  • the raw materials used in the examples are all conventional raw materials, and the equipment used is conventional equipment and commercially available products.
  • Granulation Pour silicon nitride powder, Y 2 O 3 , polyvinylpyrrolidone and pore forming agent into a ball mill tank according to a certain ratio, using silicon nitride balls as the grinding body and anhydrous ethanol as the grinding medium. Wet ball milling for 10-30 min; the slurry obtained by ball milling is placed in a vacuum drying oven and dried at 55 ° C for 24 h; the dried raw material is ground with an agate mortar and sieved through a 60 mesh sieve;
  • the mass ratio of the silicon nitride powder: Y 2 O 3 :PVP is 9:1:0.01, and the mass ratio of the material, the ball and the grinding medium is 1:3:2;
  • the pore former was stearic acid, and the pore former was added in an amount of 15 vol% of the total volume of the raw material.
  • Impregnation The sintered porous silicon nitride ceramic was placed in SiCN for 10 min, and the sample was placed in a tube furnace and heat-treated at a temperature of 1000 ° C under the protection of N 2 atmosphere at a heating rate of 5 ° C/min. , heat preservation 4h.
  • the mass ratio of the silicon nitride powder: Y 2 O 3 :PVP is 9:1:0.008, and the mass ratio of the material, the ball and the grinding medium is 1:3:2;
  • the pore former is stearic acid, and the pore former is added in an amount of 10 vol% of the total volume of the raw material.
  • Impregnation The sintered porous silicon nitride ceramic was placed in SiCN for 10 min, and the sample was placed in a tube furnace and heat-treated at a temperature of 1100 ° C under the protection of N 2 atmosphere at a heating rate of 3 ° C/min. , heat preservation 4h.
  • Granulation Pour silicon nitride powder, Y 2 O 3 , polyvinylpyrrolidone and pore forming agent into a ball mill tank according to a certain ratio, using silicon nitride balls as the grinding body and anhydrous ethanol as the grinding medium. Wet ball milling for 10 to 30 min; the slurry obtained by ball milling is placed in a vacuum drying oven and dried at 60 ° C for 24 hours; the dried raw material is ground with an agate mortar and sieved through a 60 mesh sieve;
  • the mass ratio of the silicon nitride powder: Y 2 O 3 :PVP is 8.5:1.5:0.008, and the mass ratio of the material, the ball and the grinding medium is 1:3:2;
  • the pore former was stearic acid, and the pore former was added in an amount of 15 vol% of the total volume of the raw material.
  • Impregnation The sintered porous silicon nitride ceramic was placed in SiCN for 5-20 min, and the sample was placed in a tube furnace and heat-treated at a temperature of 1200 ° C under the protection of N 2 atmosphere at a heating rate of 3 ° C. /min, keep warm for 4h.
  • the mass ratio of the silicon nitride powder: Y 2 O 3 :PVP is 8.5:1.5:0.01, and the mass ratio of the material, the ball and the grinding medium is 1:3:2;
  • the pore former is stearic acid, and the pore former is added in an amount of 10 vol% of the total volume of the raw material.
  • Impregnation The sintered porous silicon nitride ceramic was placed in SiCN for 10 min, and the sample was placed in a tube furnace and heat-treated at a temperature of 1100 ° C under the protection of N 2 atmosphere at a heating rate of 3 ° C/min. , heat preservation 4h.
  • the SEM image of the silicon nitride ceramic obtained in the step (3) of the present embodiment is as shown in Fig. 1(c).
  • the obtained composite ceramic has a high density, a good crystallinity, and a large number of pores.
  • the pore former in the step (1) is benzoic acid.
  • the pore former in the step (1) is graphite.
  • the pore former in the step (1) is PMMA.
  • the sintering temperature in the step (3) was 1500 °C.
  • Fig. 1(a) The SEM image of the silicon nitride ceramic obtained in the comparative step (3) is shown in Fig. 1(a). It can be clearly seen from Fig. 1(a) that crystal grains are formed in the sample, and the ceramic density is not high.
  • the sintering temperature in the step (3) was 1550 °C.
  • Fig. 1(b) The SEM image of the silicon nitride ceramic obtained in the comparative step (3) is shown in Fig. 1(b). It can be seen from Fig. 1(b) that the density in the sample is improved, but the crystallinity is poor and the pores are small.
  • the sintering temperature in the step (3) was 1700 °C.
  • Fig. 1(d) The SEM image of the silicon nitride ceramic obtained in the comparative step (3) is shown in Fig. 1(d). It can be clearly seen from Fig. 1(d) that the density in the sample is too high and the porosity is low, which ultimately results in poor absorbing properties of the obtained silicon nitride-impregnated porous silicon nitride ceramic.
  • step (1) No pore former is added to step (1).
  • Fig. 2(a) is the real part ( ⁇ ') of the complex permittivity.
  • Figure 2(b) shows the imaginary part of the complex permittivity ( ⁇ ").
  • 1, 2, 3, 4, and 5 correspond to Comparative Example 4 (without adding pore former), and Example 4 (Pore Making)
  • the agent was stearic acid), Example 5 (the pore forming agent was benzoic acid), Example 6 (the pore forming agent was graphite), and Example 7 (the pore forming agent was PMMA).
  • the SiCN/Si 3 N 4 composite ceramic obtained by adding graphite as a pore-forming agent has good dielectric properties, and its dielectric constant can reach 1 near 17 GHz, which is due to the carbon removal process.
  • graphite residue There is a certain amount of graphite residue in the sample, and graphite is a resistive absorbing material, which mainly relies on the electron polarization or interfacial polarization attenuation of the medium to absorb electromagnetic waves, and has a high dielectric constant and a dielectric loss tangent.
  • the addition of pore-forming agent is better than that of the SiCN/Si 3 N 4 composite ceramic without the addition of pore-forming agent. This is because the porosity of the obtained ceramic is increased after the addition of the pore-forming agent, which can provide greater impregnation. space. Therefore, the impregnation amount of SiCN can be remarkably increased, the impregnation effect can be improved, and the carbon content precipitated after the cracking is increased, thereby improving the dielectric properties.
  • Fig. 3(a) shows the electromagnetic attenuation coefficient
  • Fig. 3(b) shows the electromagnetic wave.
  • Reflectivity. 1, 2, 3, 4, and 5 in Fig. 3 correspond to Comparative Example 4 (no pore former added), Example 4 (stearing agent is stearic acid), and Example 5 (porosity agent is benzoic acid), Example 6 (Pore forming agent is graphite), and Example 7 (Pore forming agent is PMMA).
  • the sample obtained by adding graphite as a pore former has a distinct decaying resonance peak at 11 GHz and a more prominent attenuating reflection peak around 15 GHz.
  • the addition of PMMA as a pore former sample also has a distinct decaying resonance peak at 11 GHz, which also has a relatively significant attenuation formant at around 18 GHz with a coefficient of up to 600.
  • the addition of stearic acid as a pore former can achieve a low reflectance of ⁇ 25 dB at 10 GHz
  • the addition of benzoic acid as a pore former can achieve a low reflectance of -15 dB at 16 GHz. .
  • Test Example 3 Effect of the number of immersion on dielectric properties and absorbing properties
  • Fig. 5(a) shows the electromagnetic attenuation coefficient
  • Fig. 5(b) shows the reflectance of the electromagnetic wave
  • 0, 1, and 2 represent the samples obtained by not immersing, immersing once, and immersing twice.
  • Figure 5(b) shows that the reflectance of the sample has a significant decrease around 10 GHz, with a minimum value of ⁇ 43 dB.
  • the sample has low reflectivity and high electromagnetic attenuation coefficient, indicating that the SiCN/Si 3 N 4 composite ceramic has good electromagnetic properties.
  • the dielectric properties of the sample were also significantly higher as the number of times of immersion increased.
  • Fig. 7(a) shows the electromagnetic attenuation coefficient
  • Fig. 7(b) shows the reflectance of the electromagnetic wave
  • 0, 1, and 2 represent the samples obtained by not immersing, immersing once, and immersing twice.
  • the sample has a significant attenuation peak around 10 GHz, and the attenuation coefficient can reach up to 385.
  • the reflection coefficient is the smallest near the band (10 GHz), which is about -13 dB, which also shows that the sample has excellent electromagnetic properties.

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Abstract

一种浸渍法制备SiCN/Si 3N 4复合陶瓷的方法，包括：以氮化硅粉体、Y 2O 3、聚乙烯吡咯烷酮为原料，添加造孔剂进行造粒的步骤；造粒完成后的物料进行成型、烧结的步骤；烧结后的物料浸渍SiCN并进行热处理的步骤。通过控制造孔剂的添加比例和烧结温度，得到具有多孔结构的材料，该材料具有良好的机械强度，更有利于浸渍SiCN，得到的浸渍产物吸波性能优良。

Description

一种浸渍法制备SiCN/Si3N4复合陶瓷的方法 技术领域
本发明涉及SiCN/Si3N4复合陶瓷的制备方法，具体涉及一种浸渍法合成硅碳氮复合多孔氮化硅陶瓷的方法，属无机非金属材料领域。
背景技术
伴随着电子化、信息化的迅猛发展，电磁波作为信息传递的重要载体，已经渗入生活的各个方面。无论是军用还是民用，电磁波都得到了广泛的应用。与此同时，信息时代电子电气产品的广泛应用，形成了复杂的电磁环境，也带来了大量负面效应，诸如电磁干扰、电磁信息安全性和电磁辐射对人体健康带来的危害等。因此，如何有效地屏蔽或吸收电磁波是亟待解决的问题。电磁波吸收与屏蔽材料涉及到电磁场与电磁波理论、材料学科的众多分支以及电磁波与材料相互作用引申出的反射、折射现象及与之相关的材料结构和组合。结合以上出现的电磁波辐射污染问题，厚度薄、轻质、吸收频带宽和吸收强度高的电磁波吸收材料逐渐引起人们广泛的兴趣。
Si3N4材料综合性能优异，拥有良好的机械性能和热力学性能、低介电常数和介电损耗以及低密度，成为当前天线罩研究领域的热点。目前，国内对Si3N4陶瓷天线罩的研究较晚，且应用水平较低。单纯的Si3N4陶瓷材料脆性大，韧性差，引入增强相是改善陶瓷韧性的有效途径，SiCN前驱体陶瓷材料具有优异的导电性和电磁性能，通过浸渍电磁性能优良的SiCN前驱体陶瓷，使其具有一定的吸波性能，拓宽了它的应用领域，并能在一定程度上提高它的强度和韧性。
国外对于Si3N4陶瓷天线罩的研究起始于80年代。以色列研制的Si3N4天线罩是由密度不同的两层氮化硅为主料的复合材料。里层用低密度1000-2200kg/m3多孔氮化硅，外表为2880-3200kg/m3的高密度封闭层，可防止雨水渗透，其介电性能为ε＝2.5-8，tanδ<3×10-3。。文献中指出该透波材料可耐1600℃的高温，因此可用的黏合剂只有磷酸盐最为适宜(磷酸铝熔点>1500℃)。高密度封闭层用Si3N4粉料与黏合剂混合均匀后压实，高温烧结(大于1600℃)时，黏合剂变为液相并与Si3N4润湿形成陶瓷材料。然而多孔低密度的透波层，其孔的大小和分布比较难控制，一旦出现个别大孔，将明显影响电磁波的传输特性。[Medding J A.Nondestructive evaluation of zirconium phosphate bonded silicon nitride radome[R].Virginia  Polytechnic Institute and State University.1996]
佳木斯大学的刘洪丽等采用先驱体转化法和有机泡沫浸渍法，利用含乙烯基聚硅氮烷制备SiCN泡沫陶瓷，在1000-1400℃的热解温度范围内，随温度的上升，该泡沫陶瓷的抗压强度先升高后降低，在1300℃时达到最大，但机械强度仍较低为11.5MPa。(参见：刘洪丽,钟文武,宋春梅,等.采用聚硅氮烷制备SiCN泡沫陶瓷[J].稀有金属材料与工程,2007,36:538-541.)
中国专利文件CN 101265106A(申请号：200810086327.X)公开了一种新的制备纳米/纳米型SI3N4/SIC纳米复相陶瓷的方法。其包括以下具体步骤:(1)低温交联固化:有机前驱体在保护气氛下于进行低温交联固化,得到非晶态固体；(2)球磨粉碎:将非晶态固体在球磨机中进行球磨粉碎；(3)高温热解:球磨后的混合物在保护气氛下进行高温热解得到SICN粉末。(4)球磨粉碎:将SICN粉末进一步球磨粉碎,同时引入烧结助剂；(5)放电等离子体烧结(SPS):高能球磨后的混合物进行SPS快速烧结,得到纳米/纳米型SI3N4/SIC纳米复相陶瓷。但是，该专利文件制得的复相陶瓷的吸波性能欠佳。
因此，开发吸波能力强，工艺简单的复合陶瓷材料的制备工艺，成为本领域亟待解决的问题。
发明内容
针对现有技术的不足，尤其是现有吸波材料，气孔分布不均匀，吸波能力不强的特点，以及制备步骤繁琐，成本较高的缺陷，本发明提供一种浸渍法制备SiCN/Si3N4复合陶瓷的方法，该方法工艺简单、生产成本低、制备周期短，所制得的Si3N4陶瓷气孔分布均匀，通过浸渍法制备出SiCN/Si3N4复合陶瓷后，所得产品电磁波衰减系数高，微波吸收性能好。
本发明技术方案如下：
一种浸渍法制备SiCN/Si3N4复合陶瓷的方法，包括：
以氮化硅粉体、Y2O3、PVP(聚乙烯吡咯烷酮)为原料，添加造孔剂进行造粒的步骤；
造粒完成后的物料进行成型、烧结的步骤；
烧结后的物料浸渍SiCN并进行热处理的步骤。
根据本发明，优选的，造粒步骤中氮化硅粉体、Y2O3、PVP的质量比为8～9.5：0.5～2：0.008～0.01；进一步优选8.5～9.5：0.5～1.5：0.008～0.01；
优选的，所述的造孔剂为硬脂酸、苯甲酸、石墨或/和PMMA(聚甲基丙烯酸甲酯)。
根据本发明，优选的，造粒步骤为将原料和造孔剂进行湿法球磨后干燥，再进行研磨过筛；
优选的，湿法球磨的球磨介质为无水乙醇，球磨时间为10-30min，湿法球磨体为氮化硅 球；
优选的，原料：湿法球磨体：球磨介质为质量比为1：(2-5)：(1-3)，进一步优选1:3:2；
优选的，湿法球磨后的干燥温度为45℃-75℃，干燥时间为20-24h，过筛目数为40～80目；
优选的，干燥温度为60℃，酒精挥发速度适宜，有利于得到湿度良好的原料。
根据本发明，优选的，造孔剂的添加量为原料总体积的1％-20％，进一步优选10％-15％。
根据本发明，优选的，成型步骤为将造粒后的原料进行单轴压制成型，冷等静压，获得生坯，将生坯真空封装后，等静压；
优选的，单轴压制成型的压力为20～40MPa，更优选30MPa；优选的，将生坯真空封装后，等静压的压力为150～300MPa，更优选200MPa，保压时间为150～300s。
根据本发明，优选的，烧结步骤为将等静压后的生坯在氮气氛围下于1600℃-1650℃烧结，并保温1～4h，再经2-5h降到1000℃。
根据本发明，优选的，烧结后的物料浸渍SiCN过程中，烧结后的物料与SiCN的质量比为1：(1～3)，更优选1：2，浸渍时间为5～20min；
优选的，浸渍SiCN后进行热处理的过程为在N2气氛保护下升温至热处理温度进行热处理，热处理温度为1000℃～1400℃，升温速率3～5℃/min，升温至热处理温度后保温2-5h。
根据本发明，所述的浸渍法制备SiCN/Si3N4复合陶瓷的方法，一种优选的实施方案如下：
以氮化硅粉体、Y2O3、PVP(聚乙烯吡咯烷酮)为原料，添加造孔剂，包括以下步骤：
(1)造粒：将氮化硅粉体、Y2O3、聚乙烯吡咯烷酮、造孔剂按比例倒入球磨罐中，以氮化硅球为研磨体，以无水乙醇为研磨介质湿法球磨10～30min；将球磨得到的料浆置于真空干燥箱中，在45℃～75℃下干燥24h；将干燥好的原料用玛瑙研钵研磨，过40～80目筛造粒；
所述氮化硅粉体：Y2O3：PVP的质量比为8.5：1.5：0.01，原料、氮化硅球、研磨介质的质量比为1:3:2；
(2)成型：将造粒后的粉料装入模具中，在20～40MPa的压力下单轴压制成型，冷等静压，获得生坯，将生坯真空封装后，等静压150～300MPa，保压150～300s；
(3)烧结：将等静压后的生坯置于无压烧结炉，在氮气氛围下于1600℃～1650℃烧结，并保温1～4h，再经4h降到1000℃，得多空氮化硅陶瓷；
(4)浸渍：将烧结得到的多孔氮化硅陶瓷置于SiCN中浸渍5～20min，然后装入管式炉中，在N2气氛保护下在1000℃～1300℃的温度进行热处理，升温速率3～5℃/min，保温4h。
(5)二次浸渍：重复步骤(4)，即得。
本发明利用无压烧结法制备多孔Si3N4陶瓷，通过浸渍SiCN前驱体，得到磁波吸收性能优 越的复合陶瓷材料。SiCN/Si3N4复合陶瓷不仅能够促进雷达等军事材料的发展还可应用于吸收电磁辐射、保护人体健康等方面，具有十分广阔的应用前景。
本发明的有益效果：
1、本发明通过浸渍法制备SiCN/Si3N4复合陶瓷，以多孔氮化硅为基体，其较低的介电常数可使电磁波有效进入吸波材料内部，与吸波的SiCN耗损材料发生作用，多孔的设计可有效降低复合材料密度，得到微波吸收性能优异的性能复合陶瓷。
2、本发明采用浸渍法，实验设备简单，操作方便。
3、本发明加入合适的造孔剂硬脂酸、苯甲酸、石墨以及PMMA等，控制造孔剂的添加比例和烧结温度，得到具有多孔结构的材料，同时具有良好的机械强度，更有利于浸渍SiCN，得到浸渍产物的吸波性能优良。
附图说明
图1为实施例4和对比例1-3步骤(3)所得的氮化硅陶瓷的SEM图。图1中a、b、c、d分别对应对比例1、对比例2、实施例4、对比例3。
图2为对比例4和实施例4‐7所得SiCN/Si3N4复合陶瓷的介电性能测试图。其中：图2(a)为复介电常数的实部(ε′)，图2(b)为复介电常数的虚部(ε″)。图2中1、2、3、4、5分别对应对比例4、实施例4、实施例5、实施例6、实施例7。
图3为对比例4和实施例4‐7所得SiCN/Si3N4复合陶瓷的吸波性能测试图。其中：图3(a)为电磁衰减系数，图3(b)电磁波的反射率。图3中1、2、3、4、5分别对应对比例4(不添加造孔剂)、实施例4(造孔剂为硬脂酸)、实施例5(造孔剂为苯甲酸)、实施例6(造孔剂为石墨)、实施例7(造孔剂为PMMA)。
图4为实施例4以硬脂酸为造孔剂所得SiCN/Si3N4复合陶瓷浸渍次数对其介电性能的影响图。
图5为实施例4以硬脂酸为造孔剂所得SiCN/Si3N4复合陶瓷浸渍次数对其吸波性能的影响图。
图6为实施例7以PMMA为造孔剂所得SiCN/Si3N4复合陶瓷浸渍次数对其介电性能的影响图。
图7为实施例7以PMMA为造孔剂所得SiCN/Si3N4复合陶瓷浸渍次数对其吸波性能的影响图。
具体实施方式
下面结合实施例对本发明的技术方案做进一步说明，但本发明所保护范围不限于此。
实施例中所用原料均为常规原料，所用设备均为常规设备，市购产品。
实施例1：
一种浸渍法制备SiCN/Si3N4复合陶瓷的方法，以氮化硅粉体、Y2O3、PVP(聚乙烯吡咯烷酮)为原料，添加比例不同的造孔剂，该方法包括以下步骤：
(1)造粒：将氮化硅粉体、Y2O3、聚乙烯吡咯烷酮、造孔剂按一定比例倒入球磨罐中，以氮化硅球为研磨体，以无水乙醇为研磨介质湿法球磨10～30min；将球磨得到的料浆置于真空干燥箱中，在55℃下干燥24h；将干燥好的原料用玛瑙研钵研磨，过60目筛造粒；
所述氮化硅粉体：Y2O3：PVP的质量比为9：1：0.01，料、球、研磨介质质量比为1:3:2；
造孔剂为硬脂酸，造孔剂的加入量为原料总体积的15vol％。
(2)成型：将粉料装入模具中，在30MPa的压力下单轴压制成型，冷等静压，获得生坯，将生坯真空封装后，等静压200MPa，保压200s；
(3)烧结：将等静压后的生坯置于无压烧结炉，在氮气氛围下于1600℃烧结，并保温2h，再经4h降到1000℃，得多孔氮化硅陶瓷。
(4)浸渍：将烧结得到的多孔氮化硅陶瓷置于SiCN中浸渍10min，将样品装入管式炉中，在N2气氛保护下在1000℃的温度进行热处理，升温速率5℃/min，保温4h。
(5)二次浸渍：重复步骤(4)，即得。
实施例2：
一种浸渍法制备SiCN/Si3N4复合陶瓷的方法，以氮化硅粉体、Y2O3、PVP(聚乙烯吡咯烷酮)为原料，添加比例不同的造孔剂，该方法包括以下步骤：
(1)造粒：将氮化硅粉体、Y2O3、聚乙烯吡咯烷酮、造孔剂按一定比例倒入球磨罐中，以氮化硅球为研磨体，以无水乙醇为研磨介质湿法球磨20min；将球磨得到的料浆置于真空干燥箱中，在70℃下干燥24h；将干燥好的原料用玛瑙研钵研磨，过40～80目筛造粒；
所述氮化硅粉体：Y2O3：PVP的质量比为9：1：0.008，料、球、研磨介质质量比为1:3:2；
造孔剂为硬脂酸，造孔剂的加入量为原料总体积的10vol％。
(2)成型：将粉料装入模具中，在25MPa的压力下单轴压制成型，冷等静压，获得生坯，将生坯真空封装后，等静压250MPa，保压250s；
(3)烧结：将等静压后的生坯置于无压烧结炉，在氮气氛围下于1600℃烧结，并保温1h，再经3h降到1000℃，得多孔氮化硅陶瓷。
(4)浸渍：将烧结得到的多孔氮化硅陶瓷置于SiCN中浸渍10min，将样品装入管式炉中，在N2气氛保护下在1100℃的温度进行热处理，升温速率3℃/min，保温4h。
(5)二次浸渍：重复步骤(4)，即得。
实施例3：
一种浸渍法制备SiCN/Si3N4复合陶瓷的方法，以氮化硅粉体、Y2O3、PVP(聚乙烯吡咯烷酮)为原料，添加比例不同的造孔剂，该方法包括以下步骤：
(1)造粒：将氮化硅粉体、Y2O3、聚乙烯吡咯烷酮、造孔剂按一定比例倒入球磨罐中，以氮化硅球为研磨体，以无水乙醇为研磨介质湿法球磨10～30min；将球磨得到的料浆置于真空干燥箱中，在60℃下干燥24h；将干燥好的原料用玛瑙研钵研磨，过60目筛造粒；
所述氮化硅粉体：Y2O3：PVP的质量比为8.5：1.5：0.008，料、球、研磨介质质量比为1:3:2；
造孔剂为硬脂酸，造孔剂的加入量为原料总体积的15vol％。
(2)成型：将粉料装入模具中，在40MPa的压力下单轴压制成型，冷等静压，获得生坯，将生坯真空封装后，等静压200MPa，保压300s；
(3)烧结：将等静压后的生坯置于无压烧结炉，在氮气氛围下于1600℃烧结，并保温4h，再经4h降到1000℃，得多孔氮化硅陶瓷。
(4)浸渍：将烧结得到的多孔氮化硅陶瓷置于SiCN中浸渍5～20min，将样品装入管式炉中，在N2气氛保护下在1200℃的温度进行热处理，升温速率3℃/min，保温4h。
(5)二次浸渍：重复步骤(4)，即得。
实施例4：
一种浸渍法制备SiCN/Si3N4复合陶瓷的方法，以氮化硅粉体、Y2O3、PVP(聚乙烯吡咯烷酮)为原料，添加比例不同的造孔剂，该方法包括以下步骤：
(1)造粒：将氮化硅粉体、Y2O3、聚乙烯吡咯烷酮、造孔剂按一定比例倒入球磨罐中，以氮化硅球为研磨体，以无水乙醇为研磨介质湿法球磨30min；将球磨得到的料浆置于真空干燥箱中，在65℃下干燥24h；将干燥好的原料用玛瑙研钵研磨，过60目筛造粒；
所述氮化硅粉体：Y2O3：PVP的质量比为8.5：1.5：0.01，料、球、研磨介质质量比为1:3:2；
造孔剂为硬脂酸，造孔剂的加入量为原料总体积的10vol％。
(2)成型：将粉料装入模具中，在30MPa的压力下单轴压制成型，冷等静压，获得生坯，将生坯真空封装后，等静压300MPa，保压200s；
(3)烧结：将等静压后的生坯置于无压烧结炉，在氮气氛围下于1650℃烧结，并保温4h，再经5h降到1000℃，得多孔氮化硅陶瓷。
(4)浸渍：将烧结得到的多孔氮化硅陶瓷置于SiCN中浸渍10min，将样品装入管式炉中，在N2气氛保护下在1100℃的温度进行热处理，升温速率3℃/min，保温4h。
(5)二次浸渍：重复步骤(4)，即得。
本实施例步骤(3)所得的氮化硅陶瓷的SEM图如图1(c)所示。由图1(c)可知，所得复合陶瓷致密度较高、结晶度良好，气孔较多。
实施例5：
如实施例4所述：不同的是：
步骤(1)中造孔剂为苯甲酸。
实施例6：
如实施例4所述：不同的是：
步骤(1)中造孔剂为石墨。
实施例7：
如实施例4所述：不同的是：
步骤(1)中造孔剂为PMMA。
对比例1：
如实施例4所述，不同的是：
步骤(3)中的烧结温度为1500℃。
本对比例步骤(3)所得的氮化硅陶瓷的SEM图如图1(a)所示。由图1(a)可以明显看出样品中晶粒开始形成，陶瓷致密度不高。
对比例2：
如实施例4所述，不同的是：
步骤(3)中的烧结温度为1550℃。
本对比例步骤(3)所得的氮化硅陶瓷的SEM图如图1(b)所示。由图1(b)可以看出样品中致密度有所提高，但结晶度差，气孔少。
对比例3：
如实施例4所述，不同的是：
步骤(3)中的烧结温度为1700℃。
本对比例步骤(3)所得的氮化硅陶瓷的SEM图如图1(d)所示。由图1(d)可以明显看出样品中致密度过高，气孔率低，最终导致得到的浸渍硅碳氮的多孔氮化硅陶瓷吸波性能较差。
对比例4：
如实施例4所述，不同的是：
步骤(1)中不加入造孔剂。
试验例1、介电性能测试
测试对比例4和实施例4‐7所得SiCN/Si3N4复合陶瓷的介电性能，结果如图2所示，其中：图2(a)为复介电常数的实部(ε′)，图2(b)为复介电常数的虚部(ε″)。图2中1、2、3、4、5分别对应对比例4(不添加造孔剂)、实施例4(造孔剂为硬脂酸)、实施例5(造孔剂为苯甲酸)、实施例6(造孔剂为石墨)、实施例7(造孔剂为PMMA)。
从图2中可以看出，添加石墨作为造孔剂所得的SiCN/Si3N4复合陶瓷介电性较好，其介电常数在17GHz附近可以达到1，这是由于在除碳过程中，样品中会有一定量石墨残留，而石墨是一种电阻型吸波材料，其主要依靠介质的电子极化或界面极化衰减来吸收电磁波，具有较高的介电常数和介电损耗角正切。
同时，添加造孔剂比不添加造孔剂所得SiCN/Si3N4复合陶瓷介电性能更好，这是由于添加造孔剂后，所得陶瓷气孔率升高，能够为浸渍提供更大的空间。因此，可显著提高SiCN的浸渍量，提升浸渍效果，使得裂解后析出的碳含量增大，从而提高其介电性能。
试验例2、吸波性能测试
测试对比例4和实施例4‐7所得SiCN/Si3N4复合陶瓷的吸波性能，结果如图3所示，其中：图3(a)为电磁衰减系数，图3(b)电磁波的反射率。图3中1、2、3、4、5分别对应对比例4(不添加造孔剂)、实施例4(造孔剂为硬脂酸)、实施例5(造孔剂为苯甲酸)、实施例6(造孔剂为石墨)、实施例7(造孔剂为PMMA)。
从图3(a)可以看出，添加石墨作为造孔剂所得样品在11GHz处有一个明显的衰减共振峰，在15GHz左右有一个更突出的衰减反射峰。同时，添加PMMA作为造孔剂样品也在11GHz处有一个明显的衰减共振峰，其还在18GHz左右有比较明显的衰减共振峰，其系数可达600。从图3(b)可以看出，添加硬脂酸作为造孔剂样品在10GHz处反射率较低可以达到‐25dB，添加苯甲酸作为造孔剂样品在16GHz处反射率很低可以达到‐35dB。
试验例3、浸渍次数对介电性能和吸波性能的影响
1、将实施例4以硬脂酸为造孔剂所得SiCN/Si3N4复合陶瓷，测试浸渍次数对介电性能的影响，结果如图4所示。图4(a)为复介电常数的实部(ε′)，图4(b)为其虚部(ε″)，0、1、2分别代表未浸渍、浸渍一次、浸渍两次所得试样。
从图4中可以看出，10GHz附近存在一个明显的振动峰，浸渍两次所得试样的介电常数 峰值达到1。随着浸渍次数的增多，其介电性能不断增强。这是由于第一次浸渍时，试样存在大量气孔，有利于SiCN前驱体浸入试样中，使得试样介电性能增强；二次浸渍后，试样中的SiCN前驱体量增多，裂解后析出的碳增多，其介电性能进一步增强。
2、将实施例4以硬脂酸为造孔剂所得SiCN/Si3N4复合陶瓷，测试浸渍次数对吸波性能的影响，结果如图5所示。图5(a)为电磁衰减系数，图5(b)为电磁波的反射率，0、1、2分别代表未浸渍、浸渍一次、浸渍两次所得试样。
由图5(a)可知，试样电磁衰减系数在10‐16GHz存在几个明显的峰值，尤其浸渍两次所得试样在10GHz附近电磁衰减系数值可以达到500。
图5(b)显示，试样反射率在10GHz附近有一个明显的降低，其最低值可以达到‐43dB。样品反射率低且电磁衰减系数高，说明SiCN/Si3N4复合陶瓷具有良好的电磁性能。
3、将实施例7以PMMA为造孔剂所得SiCN/Si3N4复合陶瓷，测试浸渍次数对介电性能的影响，结果如图6所示。图6(a)为复介电常数的实部(ε′)，图6(b)为其虚部(ε″)，0、1、2分别代表未浸渍、浸渍一次、浸渍两次所得试样。
由图6可知，与添加硬脂酸作为造孔剂类似，试样的介电性能同样随着浸渍次数增加而明显高。
4、将实施例7以PMMA为造孔剂所得SiCN/Si3N4复合陶瓷，测试浸渍次数对吸波性能的影响，结果如图7所示。图7(a)为电磁衰减系数，图7(b)为电磁波的反射率，0、1、2分别代表未浸渍、浸渍一次、浸渍两次所得试样。
由图7(a)可以看出，试样在10GHz附近有明显的衰减峰，其衰减系数值最高可达到385。由图7(b)可以看出，反射系数在该波段附近(10GHz)达到最小，约为‐13dB，同样说明试样电磁性能优异。
需要说明的是，以上列举的仅是本发明的若干个具体实施例，显然本发明不仅仅限于以上实施例，还可以有其他变形。本领域的技术人员从本发明公开内容直接导出或间接引申的所有变形，均应认为是本发明的保护范围。

Claims (10)

  1. 一种浸渍法制备SiCN/Si3N4复合陶瓷的方法，包括：
    以氮化硅粉体、Y2O3、PVP(聚乙烯吡咯烷酮)为原料，添加造孔剂进行造粒的步骤；
    造粒完成后的物料进行成型、烧结的步骤；
    烧结后的物料浸渍SiCN并进行热处理的步骤。
  2. 根据权利要求1所述的浸渍法制备SiCN/Si3N4复合陶瓷的方法，其特征在于，造粒步骤中氮化硅粉体、Y2O3、PVP的质量比为8～9.5：0.5～2：0.008～0.01；优选8.5～9.5：0.5～1.5：0.008～0.01。
  3. 根据权利要求1所述的浸渍法制备SiCN/Si3N4复合陶瓷的方法，其特征在于，所述的造孔剂为硬脂酸、苯甲酸、石墨或/和PMMA。
  4. 根据权利要求1所述的浸渍法制备SiCN/Si3N4复合陶瓷的方法，其特征在于，造粒步骤为将原料和造孔剂进行湿法球磨后干燥，再进行研磨过筛；
    湿法球磨的球磨介质为无水乙醇，球磨时间为10-30min，湿法球磨体为氮化硅球。
  5. 根据权利要求4所述的浸渍法制备SiCN/Si3N4复合陶瓷的方法，其特征在于，原料：湿法球磨体：球磨介质为质量比为1：(2-5)：(1-3)。
  6. 根据权利要求4所述的浸渍法制备SiCN/Si3N4复合陶瓷的方法，其特征在于，湿法球磨后的干燥温度为45℃-75℃，干燥时间为20-24h，过筛目数为40～80目。
  7. 根据权利要求1所述的浸渍法制备SiCN/Si3N4复合陶瓷的方法，其特征在于，造孔剂的添加量为原料总体积的1％-20％，优选10％-15％。
  8. 根据权利要求1所述的浸渍法制备SiCN/Si3N4复合陶瓷的方法，其特征在于，成型步骤为将造粒后的原料进行单轴压制成型，冷等静压，获得生坯，将生坯真空封装后，等静压；
    优选的，单轴压制成型的压力为20～40MPa，将生坯真空封装后，等静压的压力为150～300MPa，保压时间为150～300s。
  9. 根据权利要求8所述的浸渍法制备SiCN/Si3N4复合陶瓷的方法，其特征在于，烧结步骤为将等静压后的生坯在氮气氛围下于1600℃-1650℃烧结，并保温1～4h，再经2-5h降到1000℃。
  10. 根据权利要求1所述的浸渍法制备SiCN/Si3N4复合陶瓷的方法，其特征在于，烧结后的物料浸渍SiCN过程中，烧结后的物料与SiCN的质量比为1：(1～3)，浸渍时间为5～20min；
    优选的，浸渍SiCN后进行热处理的过程为在N2气氛保护下升温至热处理温度进行热处理，热处理温度为1000℃～1400℃，升温速率3～5℃/min，升温至热处理温度后保温2-5h。
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