Method for modifying surface of silicon carbide micro-powder and application thereof in heat insulation plate

Abstract

The application discloses a silicon carbide micro-powder surface modification method and application thereof in heat insulation plates, and belongs to the technical field of silicon carbide heat insulation plates, and is used for solving the technical problem that the compression strength and heat insulation performance of the heat insulation plate material prepared by taking silicon carbide as a main material in the prior art need to be further improved; the application comprises the following steps: using an epoxy-based silane coupling agent to perform surface modification on silicon carbide micro-powder, preparing epoxy-modified silicon carbide, and using polyvinyl alcohol to perform surface coating on the epoxy-modified silicon carbide, thereby preparing PVA-coated silicon carbide; the application is characterized in that the particle size composition of the silicon carbide micro-powder is optimized, and the silicon carbide particles are coated and modified by inorganic powder composed of graphite, boron carbide and aluminum silicate powder loaded with aluminum phosphate; and the microwave sintering condition is optimized; the compression strength and true porosity of the heat insulation plate material are effectively improved; and the heat insulation performance of the heat insulation plate material is also improved.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of silicon carbide heat insulation plate, and particularly relates to a silicon carbide micro-powder surface modification method and application thereof in a heat insulation plate. BACKGROUND

[0002] The heat insulation plate is a material capable of effectively blocking heat conduction, and is widely applied in multiple important industries such as aerospace, energy, electronics and building. With the rapid development of these industries, the performance requirements of the heat insulation material are also higher and higher. Traditional heat insulation materials such as asbestos and glass fiber can meet part of the heat insulation demand in a certain range, but have many limitations. For example, the asbestos heat insulation material may change in structure at high temperature, resulting in a decrease in heat insulation performance and limiting the application scenarios. The silicon carbide material becomes a potential ideal material in the field of heat insulation plate due to its excellent high-temperature resistance, corrosion resistance and high strength.

[0003] In the prior art, an application with the publication number CN103979993B discloses a preparation method of a large-size carbon / silicon carbide composite heat insulation bottom plate, which comprises the following steps: 1, densifying a carbon fiber preform to obtain a carbon / carbon composite material; 2, mechanically processing the carbon / carbon composite material to obtain a carbon / carbon composite heat insulation bottom plate; and 3, uniformly laying a first silicon slurry on the plate, and then placing the carbon / carbon composite heat insulation bottom plate on the first silicon slurry. The service life of the prepared carbon / silicon carbide composite heat insulation bottom plate is improved by more than 50% compared with that of the carbon / carbon composite heat insulation bottom plate, and can reach more than 18 months.

[0004] However, the traditional heat insulation material is mainly prepared in the form of carbon and silicon carbide composite. However, the dispersibility of silicon carbide is poor, and it is difficult to uniformly disperse when mixed with other materials, resulting in that the compression strength and heat insulation performance of the material need to be further improved. In addition, silicon carbide has high thermal conductivity, and when the heat insulation plate is prepared by using silicon carbide as the main material, the silicon carbide is easy to be thermally conducted by mutual lapping, resulting in that the heat insulation performance of the heat insulation plate needs to be further improved. SUMMARY

[0005] The present application provides a silicon carbide micro-powder surface modification method and application thereof in a heat insulation plate, which is used to solve the technical problem that the compression strength and heat insulation performance of the heat insulation plate prepared by using silicon carbide as the main material need to be further improved in the prior art.

[0006] The purpose of the present application can be achieved by the following technical scheme: a silicon carbide micro-powder surface modification method, comprising the following steps:

[0007] S1, performing surface modification on the silicon carbide micro-powder by using an epoxy silane coupling agent to prepare an epoxy modified silicon carbide;

[0008] S2, polyvinyl alcohol is used to coat the surface of the epoxy modified silicon carbide to obtain PVA coated silicon carbide;

[0009] S3, graphite, boron carbide and aluminum silicate powder are mixed to obtain inorganic powder, and polyvinyl alcohol is mixed with the inorganic powder to obtain a modifier.

[0010] S4, the modifier is used to modify the surface of the PVA coated silicon carbide to obtain surface modified silicon carbide powder.

[0011] Further, the preparation method of the epoxy modified silicon carbide is as follows: silicon carbide powder, anhydrous ethanol and KH-560 are mixed, ultrasonic dispersion is performed for 60-80 min, the temperature of the reaction system is increased to 50-60℃, a catalyst is added to the reaction system, and the reaction is maintained for 60-70 min, and then the product is obtained after post-treatment.

[0012] The synthesis reaction mechanism of the epoxy modified silicon carbide is as follows:

[0013] KH-560 is used as an epoxy silane coupling agent, and under the action of an alkali catalyst, the siloxane bond on the KH-560 molecule is hydrolyzed to form a silicon hydroxyl group, which reacts with the active groups on the surface of the silicon carbide powder to form an epoxy group modification on the surface of the silicon carbide powder, thereby obtaining the epoxy modified silicon carbide.

[0014] Further, the amount ratio of the silicon carbide powder, anhydrous ethanol, KH-560 and catalyst is 4g:15mL:2g:5mL, the silicon carbide powder is composed of coarse powder with a particle size of 10-30mm, medium powder with a particle size of 3-10mm and fine powder with a particle size of 50-500μm in a weight ratio of 4:1:3, the catalyst is a 0.2-0.5mol / L sodium hydroxide aqueous solution, and the post-treatment includes: after the reaction is completed, the temperature of the reaction system is reduced to room temperature, the filter cake is washed with purified water until it is neutral, then it is dried, the filter cake is transferred to a drying box with a temperature of 60-70℃, and vacuum drying is performed until the weight is constant, thereby obtaining the epoxy modified silicon carbide.

[0015] Further, the preparation method of the PVA coated silicon carbide is as follows: polyvinyl alcohol and purified water are mixed, the temperature of the reaction system is increased to 70-80℃, stirring is performed until the system is clear, epoxy modified silicon carbide and tetrabutylammonium hydroxide are added to the reaction system, and the reaction is maintained for 3-5h, and then the product is obtained after post-treatment.

[0016] The synthesis reaction mechanism of the PVA coated silicon carbide is as follows:

[0017] Polyvinyl alcohol is a water-soluble polymer, which, as a coating agent, interacts with the surface of the epoxy-modified silicon carbide through the hydroxyl group, and tetrabutylammonium hydroxide is used as a strong organic alkali catalyst to promote the ring-opening condensation of the epoxy group and the hydroxyl group, so that the PVA and the silicon carbide particles are more closely combined, the dispersion liquid is added to reduce the polarity of water, promote the PVA chain to shrink, and tightly coat the silicon carbide, and sodium dodecylbenzenesulfonate and tetrabutylammonium hydroxide are used in combination to stabilize the uniform dispersion of silicon carbide and prevent particle agglomeration, thereby preparing PVA-coated silicon carbide.

[0018] Further, the amount ratio of the polyvinyl alcohol, purified water, epoxy-modified silicon carbide and tetrabutylammonium hydroxide is 1g:15mL:3g:0.1g, and the post-treatment includes: after the reaction is completed, a dispersion liquid is added to the reaction system under rapid stirring, the reaction system is naturally lowered to room temperature, and then filtered, the filter cake is washed with 50%vol ethanol aqueous solution for 2 times and then dried, the filter cake is transferred to a drying box with a temperature of 50-60℃, and vacuum dried to constant weight to obtain PVA-coated silicon carbide, wherein the dispersion liquid is composed of anhydrous ethanol, purified water and sodium dodecylbenzenesulfonate in a ratio of 100mL:10mL:3g.

[0019] Further, the weight ratio of the loaded graphite, boron carbide and aluminum silicate powder is 2:3:1.

[0020] Further, the preparation method of the loaded graphite is: mixing expanded graphite, aluminum nitrate and purified water, ultrasonic dispersion for 60-80min, increasing the temperature of the reaction system to 60-70℃, adding phosphoric acid to the reaction system, and keeping the reaction for 30-50min, adding sodium hydroxide aqueous solution to the reaction system to adjust the pH of the system to 7, and then post-treating to obtain the loaded graphite.

[0021] The synthesis reaction mechanism of the loaded graphite is:

[0022] In the reaction process, ultrasonic dispersion is used to promote the uniform dispersion of aluminum nitrate and expanded graphite, the porous structure of the expanded graphite provides a loading site for the aluminum nitrate, the addition of phosphoric acid causes the reaction of phosphate ions and aluminum ions to form amorphous aluminum phosphate, and the increase in temperature promotes the completion of the reaction, the aluminum phosphate is deposited on the surface / pores of the graphite, the excess phosphoric acid is neutralized by sodium hydroxide to adjust the pH to neutral, and the strong acidity is avoided to destroy the structure of the graphite, so that the aluminum phosphate is uniformly dispersed and loaded between the layers or on the surface of the graphite to prepare the loaded graphite.

[0023] Further, the amount ratio of the expanded graphite, aluminum nitrate and purified water is 3g:1g:15mL, the molar ratio of the aluminum nitrate and the phosphoric acid is 1:1.1, and the post-treatment includes: after the reaction is completed, the temperature of the reaction system is lowered to room temperature, and then filtered, the filter cake is washed with purified water for 3 times and then dried, the filter cake is transferred to a drying box with a temperature of 70-80℃, and vacuum dried to constant weight to obtain the loaded graphite.

[0024] Further, the preparation method of the surface modified silicon carbide powder comprises the following steps: mixing the PVA coated silicon carbide and the modifier, increasing the temperature of the reaction system to 70-80 DEG C, keeping stirring for 30-50 min, reducing the temperature of the reaction system to room temperature, adding anhydrous ethanol into the reaction system, and performing post-treatment to obtain the surface modified silicon carbide powder.

[0025] Further, the use amount ratio of the PVA coated silicon carbide, the modifier and the anhydrous ethanol is 10g:30mL:30mL, and the post-treatment comprises the following steps: after the reaction is completed, performing suction filtration, washing the filter cake with anhydrous ethanol for 2 times and then performing suction drying, transferring the filter cake into a drying box with a temperature of 50-60 DEG C, and performing vacuum drying until the weight is constant to obtain the surface modified silicon carbide powder.

[0026] Further, the preparation method of the modifier comprises the following steps: mixing polyvinyl alcohol and purified water, increasing the temperature of the reaction system to 70-80 DEG C, stirring until the system is clear, adding inorganic powder into the reaction system, keeping stirring for 40-60 min to obtain the modifier, wherein the use amount ratio of the polyvinyl alcohol, the purified water and the inorganic powder is 1g:20mL:5g.

[0027] The application further provides an application of the surface modified silicon carbide powder in a heat insulation plate, wherein the surface modified silicon carbide powder is added into a mold, a mold pressing pressure is set to 100-110 KPa, mold pressing is performed for 3-5 min to obtain a heat insulation plate blank, the heat insulation plate blank is placed in a microwave vacuum sintering furnace, heating is performed at a temperature increasing rate of 20 DEG C / min to 600 DEG C, keeping the temperature for 30 min, heating is performed at a temperature increasing rate of 10 DEG C / min to 1200 DEG C, microwave sintering is performed for 40 min, the microwave vacuum sintering furnace is reduced to room temperature, and the heat insulation plate is obtained after discharging.

[0028] The application has the following advantages:

[0029] 1. The surface modified silicon carbide powder is prepared by coating and modifying silicon carbide particles with polyvinyl alcohol as a binder and inorganic powder composed of loaded graphite, boron carbide and aluminum silicate powder as reinforcing powder, and the particle size composition of the silicon carbide powder is optimized.

[0030] 2. The surface-modified silicon carbide micropowder of the present invention optimizes the particle size composition of the silicon carbide micropowder and increases the porosity of the insulation board by using smaller particles. The proportion of fine powder increases, thereby forming a higher porosity in the insulation board. At the same time, the smaller particles increase the interface contact thermal resistance, hindering the formation of heat conduction paths, thereby reducing the thermal conductivity, and increasing the proportion of fine powder, increasing the density of the insulation board material and improving its compressive strength. The surface of the silicon carbide micropowder is modified by an epoxy silane coupling agent to enhance its surface polarity, so that it can be evenly distributed in polyvinyl alcohol. Dispersion, and using the reactivity of the epoxy group, a uniform PVA coating is formed on the silicon carbide micropowder, and then it is used as a bonding layer to bond the inorganic powder to its outside, so that the inorganic powder is evenly dispersed along with the silicon carbide powder, thereby improving the dispersion stability of each material composition. When preparing the insulation board, the stacking mode between the particles is improved, the internal defects are reduced, thereby enhancing the bonding force between the particles and improving the overall strength of the material. The inorganic powder coated on the silicon carbide surface promotes the further bonding and densification of the silicon carbide particles during the microwave sintering process, thereby further improving the compressive strength.

[0031] 3. The surface modified silicon carbide micropowder of the present invention is composed of inorganic powder composed of loaded graphite loaded with aluminum phosphate, boron carbide and aluminum silicate, which is mixed with polyvinyl alcohol to form a modifier, and polyvinyl alcohol is used as a dispersant and binder to promote the uniform dispersion of inorganic powder and PVA coated silicon carbide, and then anhydrous ethanol is used as a poor solvent to promote the crystallization of polyvinyl alcohol, so that the inorganic powder is bonded to the surface of silicon carbide, forming a coating modification on the surface of silicon carbide micropowder, and the aluminum phosphate loaded on the loaded graphite can form a glass phase during the sintering process to react with the SiC surface, thereby enhancing the interface bond between graphite and the substrate. The combined force reduces interface defects. At the same time, aluminum phosphate itself is a ceramic material with low thermal conductivity. It cooperates with the expanded graphite with a porous structure to act as a barrier layer to reduce heat conduction. Boron carbide with high hardness and strength acts as a rigid reinforcement phase, directly bearing the load and inhibiting matrix deformation. Both silicon carbide and boron carbide have good thermal conductivity. Through coating treatment, during microwave roasting, silicon carbide and boron carbide particles are wrapped by aluminum phosphate / aluminum silicate while polyvinyl alcohol decomposes, and the overall heat conduction path is blocked, forming an isolated "heat conduction island", which further improves its thermal insulation performance. DETAILED DESCRIPTION

[0032] The technical solutions of the present invention will be clearly and completely described below in conjunction with the embodiments. Obviously, the embodiments described are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0033] In this application, KH-560 is γ-glycidyloxypropyltrimethoxysilane, CAS number 2530-83-8;

[0034] In the present application, the polyvinyl alcohol is selected from Shandong Mayna New Material Co., Ltd., the brand is Mayna, the CAS is 9002-89-5, the viscosity is 3-70, and the content is ≥99%;

[0035] In the present application, the expanded graphite is expanded flake graphite powder, selected from Shijiazhuang Fenghua Mining Products Co., Ltd., the particle size is 80 mesh, and the expandable multiple is 300 times;

[0036] In the present application, the boron carbide is selected from Hubei Xingyan New Material Technology Co., Ltd., the CAS number is 12069-32-8, and the boron content is 99.4%;

[0037] In the present application, the particle size of the aluminum silicate powder is 80 mesh, and the CAS number is 12141-46-7.

[0038] Example 1

[0039] The present embodiment provides a preparation method of surface modified silicon carbide powder, comprising the following steps:

[0040] S1, preparing epoxy modified silicon carbide

[0041] The silicon carbide coarse powder with a particle size of 10-30 mm, the silicon carbide medium powder with a particle size of 3-10 mm, and the silicon carbide fine powder with a particle size of 50-500 μm are mixed uniformly in a weight ratio of 4:1:3 to obtain silicon carbide powder;

[0042] Weighing: 1 kg of silicon carbide powder, 3.75 L of anhydrous ethanol and 500 g of KH-560 are added to a 5 L reaction bottle, and ultrasonic dispersion is performed for 60 min. The reaction bottle is fixed in a water bath kettle with mechanical stirring, the temperature of the reaction bottle is raised to 50℃, 1.75 L of 0.2 mol / L sodium hydroxide aqueous solution is added to the reaction bottle, and the reaction is carried out for 60 min. The temperature of the reaction bottle is reduced to room temperature, and the filter cake is washed to neutral with purified water and then dried by suction. The filter cake is transferred to a drying box with a temperature of 60℃, and vacuum drying is performed until the weight is constant to obtain epoxy modified silicon carbide.

[0043] S2, preparing PVA coated silicon carbide

[0044] The anhydrous ethanol, purified water and sodium dodecylbenzenesulfonate are mixed uniformly in a ratio of 100 mL:10 mL:3 g to obtain a dispersion liquid, which is prepared;

[0045] Take: polyvinyl alcohol 300 g, purified water 4.5 L into the 10 L reaction bottle stirring, the reaction bottle temperature rises to 70 ℃, stirring to the system solution clear, to the reaction bottle into the epoxy modified silicon carbide 900 g and tetrabutylammonium hydroxide 30 g, incubation reaction 3 h, the reaction bottle temperature decreases to room temperature, set the stirring speed of 800 r / min, to the reaction bottle into the dispersion liquid 4 L, stirring dispersion 25 min, suction filtration, filter cake with 50% vol ethanol aqueous solution washing 2 times after dry, filter cake into the temperature is 50 ℃ drying box, vacuum drying to constant weight, get PVA coated silicon carbide.

[0046] S3, preparation of modifier

[0047] Take: expanded graphite 120 g, aluminum nitrate 40 g and purified water 600 mL into the 2 L reaction bottle, ultrasonic dispersion 60 min, the reaction bottle is fixed in the water bath with mechanical stirring, the reaction bottle temperature rises to 60 ℃, to the reaction bottle into the 5 mol / L phosphoric acid solution 41.3 mL, incubation reaction 30 min, to the reaction bottle into the 1 mol / L sodium hydroxide aqueous solution, adjust the system pH = 7, the reaction bottle temperature decreases to room temperature, suction filtration, filter cake with purified water washing 3 times after dry, filter cake into the temperature is 70 ℃ drying box, vacuum drying to constant weight, get the graphite loaded;

[0048] The graphite loaded, boron carbide, aluminum silicate powder is mixed according to the weight ratio of 2:3:1, get inorganic powder;

[0049] Take: polyvinyl alcohol 24 g, purified water 480 mL into the 2 L reaction bottle stirring, the reaction bottle temperature rises to 70 ℃, stirring to the system solution clear, to the reaction bottle into the inorganic powder 120 g, incubation stirring 40 min, get the modifier.

[0050] S4, preparation of surface modified silicon carbide powder

[0051] Take: PVA coated silicon carbide 900 g and modifier 2.7 L into the 10 L reaction bottle stirring, the reaction bottle temperature rises to 70 ℃, incubation stirring 30 min, the reaction bottle temperature decreases to room temperature, to the reaction bottle into the anhydrous ethanol 2.7 L, stirring 20 min, suction filtration, filter cake with anhydrous ethanol washing 2 times after dry, filter cake into the temperature is 50 ℃ drying box, vacuum drying to constant weight, get the surface modified silicon carbide powder.

[0052] Example 2

[0053] The present embodiment provides a kind of preparation method of surface modified silicon carbide powder, comprising the following steps:

[0054] S1, preparation of epoxy modified silicon carbide

[0055] Silicon carbide coarse powder with a particle size of 10-30 mm, silicon carbide medium powder with a particle size of 3-10 mm, and silicon carbide fine powder with a particle size of 50-500 μm are mixed uniformly at a weight ratio of 4:1:3 to obtain silicon carbide micro powder;

[0056] Weighing: 1 kg of silicon carbide micro powder, 3.75 L of anhydrous ethanol, and 500 g of KH-560 are added to a 5 L reaction bottle, and ultrasonic dispersion is performed for 70 min. The reaction bottle is fixed in a water bath kettle with mechanical stirring, and the temperature of the reaction bottle is raised to 55℃. 1.75 L of 0.35 mol / L sodium hydroxide aqueous solution is added to the reaction bottle, and the reaction is kept for 65 min. The temperature of the reaction bottle is reduced to room temperature, and then filtration is performed. The filter cake is washed with purified water until it is neutral, and then it is dried. The filter cake is transferred to a drying box with a temperature of 65℃, and vacuum drying is performed until the weight is constant. Thus, epoxy-modified silicon carbide is obtained.

[0057] S2, preparation of PVA-coated silicon carbide

[0058] Anhydrous ethanol, purified water, and sodium dodecylbenzenesulfonate are mixed uniformly at a ratio of 100 mL:10 mL:3 g to obtain a dispersion liquid, which is prepared for use;

[0059] Weighing: 300 g of polyvinyl alcohol and 4.5 L of purified water are added to a 10 L reaction bottle and stirred. The temperature of the reaction bottle is raised to 75℃, and stirring is performed until the system is clear. 900 g of epoxy-modified silicon carbide and 30 g of tetrabutylammonium hydroxide are added to the reaction bottle, and the reaction is kept for 4 h. The temperature of the reaction bottle is reduced to room temperature, and the stirring speed is set to 850 r / min. 4 L of the dispersion liquid is added to the reaction bottle, and stirring and dispersion are performed for 30 min. Filtration is performed, and the filter cake is washed with 50% vol ethanol aqueous solution for 2 times and then dried. The filter cake is transferred to a drying box with a temperature of 55℃, and vacuum drying is performed until the weight is constant. Thus, PVA-coated silicon carbide is obtained.

[0060] S3, preparation of a modifier

[0061] Weighing: 120 g of expanded graphite, 40 g of aluminum nitrate, and 600 mL of purified water are added to a 2 L reaction bottle and ultrasonic dispersion is performed for 70 min. The reaction bottle is fixed in a water bath kettle with mechanical stirring, and the temperature of the reaction bottle is raised to 65℃. 41.3 mL of 5 mol / L phosphoric acid solution is added to the reaction bottle, and the reaction is kept for 40 min. 1 mol / L sodium hydroxide aqueous solution is added to the reaction bottle to adjust the pH of the system to 7. The temperature of the reaction bottle is reduced to room temperature, and then filtration is performed. The filter cake is washed with purified water for 3 times and then dried. The filter cake is transferred to a drying box with a temperature of 75℃, and vacuum drying is performed until the weight is constant. Thus, graphite support is obtained.

[0062] The graphite support, boron carbide, and aluminum silicate powder are mixed at a weight ratio of 2:3:1 to obtain inorganic powder.

[0063] Take: polyvinyl alcohol 24 g, purified water 480 mL into a 2 L reaction bottle stirring, the reaction bottle temperature rises to 75 DEG C, stirring to system solution clear, to the reaction bottle 120 g of inorganic powder, heat stirring 50 min, get modifier.

[0064] S4, preparation of surface modified silicon carbide powder

[0065] Take: PVA coated silicon carbide 900 g and modifier 2.7 L into a 10 L reaction bottle stirring, the reaction bottle temperature rises to 75 DEG C, heat stirring 40 min, the reaction bottle temperature decreases to room temperature, to the reaction bottle 2.7 L of absolute ethanol, stirring 20 min, suction filtration, filter cake with absolute ethanol washing 2 times after suction, filter cake is transferred to the temperature of 55 DEG C drying box, vacuum drying to constant weight, get surface modified silicon carbide powder.

[0066] Example 3

[0067] The present embodiment provides a kind of preparation method of surface modified silicon carbide powder, comprising the following steps:

[0068] S1, preparation of epoxy modified silicon carbide

[0069] The particle size of 10-30 mm of silicon carbide coarse powder, particle size of 3-10 mm of silicon carbide powder, particle size of 50-500 μm of silicon carbide fine powder is mixed uniformly according to the weight ratio of 4:1:3, to obtain silicon carbide powder;

[0070] Take: silicon carbide powder 1 kg, absolute ethanol 3.75 L and KH-560 500 g into a 5 L reaction bottle, ultrasonic dispersion 80 min, reaction bottle is fixed in water bath with mechanical stirring stirring, the reaction bottle temperature rises to 60 DEG C, to the reaction bottle 1.75 L of 0.5 mol / L sodium hydroxide aqueous solution, heat reaction 70 min, the reaction bottle temperature decreases to room temperature, suction filtration, filter cake is washed to neutral with purified water after suction, filter cake is transferred to the temperature of 70 DEG C drying box, vacuum drying to constant weight, get epoxy modified silicon carbide.

[0071] S2, preparation of PVA coated silicon carbide

[0072] Absolute ethanol, purified water and sodium dodecyl benzene sulfonate are mixed uniformly according to 100 mL:10 mL:3 g, to obtain dispersion, ready for use;

[0073] Take: polyvinyl alcohol 300g, purified water 4.5L into the 10L reaction bottle stirring, the reaction bottle temperature rises to 80℃, stirring to system solution clear, to the reaction bottle into the epoxy modified silicon carbide 900g and tetrabutylammonium hydroxide 30g, heat reaction 5h, the reaction bottle temperature decreases to room temperature, set the stirring speed of 900r / min, to the reaction bottle into the dispersion liquid 4L, stirring dispersion 35min, suction filtration, filter cake with 50%vol ethanol aqueous solution washing 2 times after dry, filter cake into the temperature of 60℃ drying box, vacuum drying to constant weight, get PVA coated silicon carbide.

[0074] S3, preparation of modifier

[0075] Take: expanded graphite 120g, aluminum nitrate 40g and purified water 600mL into the 2L reaction bottle, ultrasonic dispersion 80min, the reaction bottle is fixed in the water bath with mechanical stirring, the reaction bottle temperature rises to 70℃, to the reaction bottle into the 5mol / L phosphoric acid solution 41.3mL, heat reaction 50min, to the reaction bottle into the 1mol / L sodium hydroxide solution, adjust the system pH=7, the reaction bottle temperature decreases to room temperature, suction filtration, filter cake with purified water washing 3 times after dry, filter cake into the temperature of 80℃ drying box, vacuum drying to constant weight, get the graphite loaded;

[0076] The graphite loaded, boron carbide, aluminum silicate powder is mixed according to the weight ratio of 2:3:1, get inorganic powder;

[0077] Take: polyvinyl alcohol 24g, purified water 480mL into the 2L reaction bottle stirring, the reaction bottle temperature rises to 80℃, stirring to system solution clear, to the reaction bottle into the inorganic powder 120g, heat stirring 60min, get modifier.

[0078] S4, preparation of surface modified silicon carbide powder

[0079] Take: PVA coated silicon carbide 900g and modifier 2.7L into the 10L reaction bottle stirring, the reaction bottle temperature rises to 80℃, heat stirring 50min, the reaction bottle temperature decreases to room temperature, to the reaction bottle into the anhydrous ethanol 2.7L, stirring 20min, suction filtration, filter cake with anhydrous ethanol washing 2 times after dry, filter cake into the temperature of 60℃ drying box, vacuum drying to constant weight, get surface modified silicon carbide powder.

[0080] Example 4

[0081] The present embodiment provides a kind of using surface modified silicon carbide powder preparation heat insulation plate method, comprising the following steps:

[0082] Step one, the surface modified silicon carbide powder prepared in example 1 is added to the mold, set the mold pressing pressure to 100 KPa, mold pressing 3 min, get the heat insulation plate blank.

[0083] Step two, the heat insulation plate blank is placed in the microwave vacuum sintering furnace, heated to 600℃ at a heating rate of 20℃ / min, keep warm for 30 min, then heated to 1200℃ at a heating rate of 10℃ / min, microwave sintering for 40 min, the microwave vacuum sintering furnace is reduced to room temperature, discharge, get the heat insulation plate sample.

[0084] Example 5

[0085] The present embodiment provides a method for preparing a heat insulation plate using surface modified silicon carbide powder, comprising the following steps:

[0086] Step one, the surface modified silicon carbide powder prepared in example 2 is added to the mold, set the mold pressing pressure to 105 KPa, mold pressing 4 min, get the heat insulation plate blank.

[0087] Step two, the heat insulation plate blank is placed in the microwave vacuum sintering furnace, heated to 600℃ at a heating rate of 20℃ / min, keep warm for 30 min, then heated to 1200℃ at a heating rate of 10℃ / min, microwave sintering for 40 min, the microwave vacuum sintering furnace is reduced to room temperature, discharge, get the heat insulation plate sample.

[0088] Example 6

[0089] The present embodiment provides a method for preparing a heat insulation plate using surface modified silicon carbide powder, comprising the following steps:

[0090] Step one, the surface modified silicon carbide powder prepared in example 3 is added to the mold, set the mold pressing pressure to 110 KPa, mold pressing 5 min, get the heat insulation plate blank.

[0091] Step two, the heat insulation plate blank is placed in the microwave vacuum sintering furnace, heated to 600℃ at a heating rate of 20℃ / min, keep warm for 30 min, then heated to 1200℃ at a heating rate of 10℃ / min, microwave sintering for 40 min, the microwave vacuum sintering furnace is reduced to room temperature, discharge, get the heat insulation plate sample.

[0092] Comparative example 1

[0093] The difference between the present comparative example and example 1 is that the surface modified silicon carbide powder used in the preparation, in step S1, no silicon carbide powder is added to the silicon carbide powder.

[0094] Comparative example 2

[0095] The difference between the present comparative example and Example 1 is that the surface-modified silicon carbide powder used in the preparation is replaced by the expanded graphite in step S3 instead of the loaded graphite in the inorganic powder.

[0096] Comparative Example 3

[0097] The difference between the present comparative example and Example 1 is that the surface-modified silicon carbide powder used in the preparation is replaced by the expanded graphite in step S3 instead of the loaded graphite in the inorganic powder.

[0098] Comparative Example 4

[0099] The difference between the present comparative example and Example 1 is that the molding pressure in step one is 500 KPa.

[0100] Performance test:

[0101] The compressive strength of the heat insulation plate samples prepared in Examples 4-6 and Comparative Examples 1-4 is tested according to the standard GB / T 8489-2006 “Fine Ceramic Compression Strength Test Method”;

[0102] The true porosity of the heat insulation plate samples prepared in Examples 4-6 and Comparative Examples 1-4 is tested according to the standard GB / T 2998-2015 “Fixed Shape Heat Insulation Refractory Product Volume Density and True Porosity Test Method”;

[0103] The thermal conductivity of the heat insulation plate samples prepared in Examples 4-6 and Comparative Examples 1-4 is tested according to the standard GB / T 10297-2015 “Determination of Thermal Conductivity of Non-metallic Solid Materials Hot-wire Method”, and the specific test results are shown in Table 1 below.

[0104] Table 1-Performance test data table of samples

[0105] Data analysis:

[0106] Comparing and analyzing the data in Table 1 above, the true porosity of the heat insulation plate prepared by the present application with surface-modified silicon carbide powder as raw material reaches 65.42%, the thermal conductivity is reduced to 0.1106 W / (m·K), the compressive strength reaches 7.88 MPa, and the volume density of the heat insulation plate reaches 1.31 g / cm 3 after testing, and the performance test data is better than that of the comparative examples, so the present application optimizes the particle size composition of the silicon carbide powder, and coats and modifies the silicon carbide particles with the inorganic powder composed of loaded aluminum phosphate loaded graphite, boron carbide and aluminum silicate powder, and optimizes the microwave sintering conditions, which not only effectively improves the compressive strength and true porosity of the heat insulation plate material, but also improves the heat insulation performance of the heat insulation plate material.

[0107] The above merely illustrates and describes the structure of the present application, and those skilled in the art can make various modifications or supplements to the described specific embodiments or adopt similar ways to replace, as long as the modifications or supplements do not deviate from the structure of the present application or exceed the scope defined by the present claims, and should belong to the protection scope of the present application.

Claims

1. A method for surface modification of silicon carbide micropowder, characterized by, The method comprises the following steps: S1, surface modification of silicon carbide powder using an epoxy silane coupling agent to prepare epoxy modified silicon carbide, wherein the epoxy silane coupling agent is KH-560; S2, surface coating of the epoxy modified silicon carbide using polyvinyl alcohol to prepare PVA coated silicon carbide; S3, mixing of loaded graphite, boron carbide, aluminum silicate powder and mullite powder to obtain inorganic powder, mixing of polyvinyl alcohol and the inorganic powder to prepare a modifier; S4, surface modification of the PVA coated silicon carbide using the modifier to prepare surface modified silicon carbide powder; The preparation method of the PVA coated silicon carbide is as follows: mixing of polyvinyl alcohol and purified water, temperature of the reaction system is raised to 70-80 DEG C, stirring until the system is clear, epoxy modified silicon carbide and tetrabutylammonium hydroxide are added to the reaction system, heat preservation reaction for 3-5 h, post-treatment, and PVA coated silicon carbide is obtained.

2. The method of claim 1, wherein the silicon carbide micropowder is surface-modified by a method comprising the steps of: The preparation method of the epoxy modified silicon carbide is as follows: mixing of silicon carbide powder, anhydrous ethanol and KH-560, ultrasonic dispersion for 60-80 min, temperature of the reaction system is raised to 50-60 DEG C, a catalyst is added to the reaction system, heat preservation reaction for 60-70 min, post-treatment, and epoxy modified silicon carbide is obtained. ​ 3. The method of claim 2, wherein the surface modification is performed by a method selected from the group consisting of a chemical modification method, a physical modification method, and a combination thereof. The dosage ratio of the silicon carbide powder, anhydrous ethanol, KH-560 and the catalyst is 4g:15mL:2g:5mL, the silicon carbide powder is composed of coarse powder with a particle size of 10-30mm, medium powder with a particle size of 3-10mm and fine powder with a particle size of 50-500um at a weight ratio of 4:1:3, the catalyst is 0.2-0.5mol / L sodium hydroxide aqueous solution, and the post-treatment comprises the following steps: after the reaction is completed, the temperature of the reaction system is reduced to room temperature, suction filtration, the filter cake is washed with purified water until it is neutral, then suction drying, the filter cake is transferred to a drying box with a temperature of 60-70 DEG C, vacuum drying until constant weight, and epoxy modified silicon carbide is obtained.

4. The method of claim 1, wherein the silicon carbide micropowder is heated to a temperature of 1,000°C to 1,200°C. The dosage ratio of the polyvinyl alcohol, purified water, epoxy modified silicon carbide and tetrabutylammonium hydroxide is 1g:15mL:3g:0.1g, and the post-treatment comprises the following steps: after the reaction is completed, a dispersion liquid is added to the reaction system under rapid stirring, the temperature of the reaction system is naturally reduced to room temperature, suction filtration, the filter cake is washed with 50%vol ethanol aqueous solution for 2 times, then suction drying, the filter cake is transferred to a drying box with a temperature of 50-60 DEG C, vacuum drying until constant weight, and PVA coated silicon carbide is obtained, wherein the dispersion liquid is composed of anhydrous ethanol, purified water and sodium dodecyl benzene sulfonate at a ratio of 100mL:10mL:3g.

5. The method of claim 1, wherein the silicon carbide micropowder is surface modified by a method comprising: The weight ratio of the loaded graphite, boron carbide, aluminum silicate powder and mullite powder is 2:3:1:1, and the preparation method of the loaded graphite is as follows: mixing of expanded graphite, aluminum nitrate and purified water, ultrasonic dispersion for 60-80 min, temperature of the reaction system is raised to 60-70 DEG C, phosphoric acid is added to the reaction system, heat preservation reaction for 30-50 min, sodium hydroxide aqueous solution is added to the reaction system, the pH of the system is adjusted to 7, post-treatment, and loaded graphite is obtained. ​ 6. The method of claim 5, wherein the surface modification is performed by a method selected from the group consisting of a chemical modification method, a physical modification method, and a combination thereof. The use amount ratio of the expanded graphite, aluminum nitrate and purified water is 3g:1g:15mL, the molar ratio of the aluminum nitrate to the phosphoric acid is 1:1.1, and the post-treatment comprises: after the reaction is completed, the temperature of the reaction system is reduced to room temperature, suction filtration is performed, the filter cake is washed with purified water for three times and then suction dried, the filter cake is transferred to a drying box with a temperature of 70-80℃, and vacuum drying is performed until the constant weight is obtained, so as to obtain the loaded graphite.

7. The method of claim 1, wherein the silicon carbide micropowder is heated to a temperature of 1,000°C to 1,200°C. The preparation method of the surface modified silicon carbide powder comprises: mixing the PVA coated silicon carbide and the modifier, increasing the temperature of the reaction system to 70-80℃, maintaining stirring for 30-50min, reducing the temperature of the reaction system to room temperature, adding anhydrous ethanol into the reaction system, and post-treating, so as to obtain the surface modified silicon carbide powder.

8. The method of claim 7, wherein the surface modification is performed by a method selected from the group consisting of a chemical modification method, a physical modification method, and a combination thereof. The use amount ratio of the PVA coated silicon carbide, the modifier and the anhydrous ethanol is 10g:30mL:30mL, and the post-treatment comprises: after the reaction is completed, suction filtration is performed, the filter cake is washed with anhydrous ethanol for two times and then suction dried, the filter cake is transferred to a drying box with a temperature of 50-60℃, and vacuum drying is performed until the constant weight is obtained, so as to obtain the surface modified silicon carbide powder.

9. Use of surface-modified silicon carbide micropowder in a heat shield, characterized in that The surface modified silicon carbide powder prepared by the surface modification method of the silicon carbide powder according to any one of claims 1-8 is added into a mold, the mold pressing pressure is set to 100-110KPa, mold pressing is performed for 3-5min, so as to obtain a heat insulation plate blank, the heat insulation plate blank is placed in a microwave vacuum sintering furnace, heated to 600℃ at a heating rate of 20℃ / min, maintained for 30min, then heated to 1200℃ at a heating rate of 10℃ / min, microwave sintering is performed for 40min, the microwave vacuum sintering furnace is reduced to room temperature, and the material is discharged, so as to obtain a heat insulation plate.

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