CN108975936B - Graphite ceramic composite type and preparation method thereof - Google Patents
Graphite ceramic composite type and preparation method thereof Download PDFInfo
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- CN108975936B CN108975936B CN201811011951.3A CN201811011951A CN108975936B CN 108975936 B CN108975936 B CN 108975936B CN 201811011951 A CN201811011951 A CN 201811011951A CN 108975936 B CN108975936 B CN 108975936B
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Abstract
The invention provides a graphite ceramic composite type and a preparation method thereof. The graphite ceramic composite type is formed by compounding a porous graphite framework and ceramic, wherein the graphite ceramic is alternately and relatively uniformly distributed, the volume fraction of the porous graphite framework is 30-70%, and the balance is ceramic. The preparation method comprises the following steps: firstly, a porous graphite skeleton is quickly prepared by using a selective laser sintering molding technology, and is carbonized and coated with ceramic paint, then ceramic slurry is poured into the porous graphite skeleton by using a gel injection molding technology, and the graphite-ceramic composite type is obtained after vacuum freeze drying, binder removal and high-temperature sintering. The graphite ceramic composite prepared by the method has the characteristics of low heat conduction and high strength, has good chemical stability, low thermal expansion coefficient and excellent thermal shock resistance, can bear the impact of high-temperature molten metal for a long time, is subjected to secondary mechanical cutting processing and can be repeatedly used for multiple times, replaces the traditional sodium silicate sand mould, is matched with a graphite casting mould for use, and is used in the production of steel castings.
Description
Technical Field
The invention relates to a graphite ceramic composite type and a preparation method thereof, belonging to the technical field of non-metallic material forming and manufacturing.
Background
Graphite molds are typically machined from high strength, high density synthetic graphite. The graphite casting mold has high heat conductivity coefficient (generally between 60 and 150W/m.k), strong chilling capability, good mechanical property, low thermal expansion coefficient, good chemical stability and thermal shock resistance, and can be subjected to secondary cutting processing and repeatedly used for many times. The casting produced by the graphite casting mold has the advantages of good surface quality, stable dimensional precision, good mechanical property of the casting, high production efficiency and low production cost. As a mold for continuous casting or semi-continuous casting, the graphite mold is widely applied to the production of castings of zinc alloy, copper alloy, aluminum alloy, medium and low carbon steel and the like.
In the industrial actual production, the casting structure is relatively complex, and if some parts, particularly thin-wall parts, on the casting are cooled and crystallized and solidified before a riser or a pouring gate, the flowing channel of high-temperature molten metal is adversely affected, so that defects such as insufficient pouring, cold shut, shrinkage porosity and the like are generated. Therefore, the most common technical measure is to perform secondary molding on a graphite casting mold, and form a graphite-sodium silicate sand composite type by building a sodium silicate sand mold, which increases the technical links and the operation difficulty, but because the sodium silicate sand mold has a small heat conductivity coefficient (only 0.6-1.2W/m.k), strong heat storage capacity and good heat insulation performance, the graphite-sodium silicate composite type can control the distribution of the temperature field of the casting, thereby achieving the purpose of adjusting the cooling and solidification sequence of each part of the casting.
However, the sodium silicate sand mold, as an auxiliary sand mold in the graphite mold, has the following disadvantages: firstly, the sodium silicate sand mould can not bear the impact of high-temperature molten steel above 1550 ℃ for a long time, namely, the sand cleaning, core making or modeling are required to be carried out once the mould is cast, and the process route is complex and long; secondly, due to the restriction of the current technological level, the recovery and reutilization rate of the sodium silicate sand is low (about 25 percent), the waste sand needs to be stacked in a special field and is used as solid waste, and the harmfulness to the surrounding environment is large; and thirdly, the sodium silicate sand mold is a loose porous material and has poor mechanical properties (when the residual water content is 0.5%, the compressive strength is about 0.8MPa, and the tensile strength is only 0.01 MPa), so that the low-strength sand mold is extremely easy to damage, and cannot be synchronized with the graphite mold through technological measures such as secondary cutting processing recovery and shaping, and the purpose of repeated use is achieved. Therefore, there is a need to develop a mold material that is high temperature resistant, low thermal conductivity, high strength, and reusable, and matches with the traditional synthetic graphite mold, so as to replace the traditional sodium silicate sand mold.
Disclosure of Invention
The invention aims to provide a graphite ceramic composite type and a preparation method thereof. The graphite ceramic composite type ceramic is formed by compounding a porous graphite framework and ceramic, wherein the graphite ceramic is alternately and relatively uniformly distributed, the volume fraction of the porous graphite framework is 30-70%, the balance is ceramic, the graphite ceramic composite type ceramic comprises ceramic paint and ceramic slurry, and the volume fraction of the ceramic paint is not more than 3%.
The preparation method of the graphite ceramic composite material comprises the following steps: firstly, a porous graphite skeleton rapidly prepared by using a selective laser sintering molding technology is subjected to post-treatment such as carbonization, ceramic coating and the like, then ceramic slurry is poured into the porous graphite skeleton by using a gel injection molding technology, and the graphite-ceramic composite type is obtained after vacuum freeze drying, binder removal and high-temperature sintering. The method has the characteristics of short process flow, high material utilization rate, no pollution, low energy consumption, low production cost and the like, and the graphite ceramic composite type has low heat conduction and high strength, good chemical stability, low thermal expansion coefficient and excellent thermal shock resistance, can bear the impact of high-temperature molten metal for a long time, can be subjected to secondary mechanical cutting processing and can be repeatedly used for many times, and can replace the traditional sodium silicate sand mold.
The present invention thus achieves the above objects: firstly, the comprehensive performance of the graphite ceramic composite type is regulated and controlled by changing the composition of phenolic resin/graphite mixed powder and the composition of a ceramic slurry formula; secondly, the comprehensive performance of the porous graphite is regulated and controlled by optimizing the size of a skeleton structure or basic characteristic units of the porous graphite, and then the comprehensive performance is regulated and controlled by improving the interface bonding state between the graphite and the ceramic in the composite mode. Specifically, the following can be taken:
(1) under the action of laser, thermosetting phenolic resin in the mixed powder in the selected area is melted and solidified to bond the graphite powder together to obtain a porous graphite skeleton with loose and porous interior, the porous graphite skeleton has low heat conductivity coefficient and belongs to a heat storage and insulation material, after carbonization, the phenolic resin is pyrolyzed, gasified and converted into glassy carbon to bond the graphite powder together, and CO and H are released simultaneously2And H2Small molecules such as O, etc., producing many micro-molecules thereinAnd (4) a hole. The carbonization temperature rise speed directly influences the number and the size of micropores, and further influences the heat conduction performance and the strength of the porous graphite skeleton; in addition, similar effects can be achieved by changing the formula composition of the mixed powder, for example, high-purity silicon powder is added into the mixed powder, and when the high-purity silicon powder and glassy carbon react in situ at high temperature to generate silicon carbide ceramic particles, the silicon carbide ceramic is used as a high-thermal-conductivity reinforcing phase along with 30% or more of volume expansion, and the generation of the silicon carbide ceramic is beneficial to improving the thermal conductivity of the porous graphite skeleton, and in addition, the volume expansion is beneficial to densification and improving the strength of the porous graphite skeleton.
(2) Compounding the porous graphite skeleton and the ceramic slurry by using a gel injection molding technology to obtain a graphite ceramic composite biscuit, and performing vacuum freeze drying, binder removal, high-temperature sintering and other treatments to obtain the graphite ceramic composite biscuit.
The size and the number of the internal pores of the graphite ceramic composite type can be regulated and controlled by changing the solid phase volume fraction of the ceramic slurry, the size of ceramic particles, the content of organic matters (tiny pores can be left by ablation in the glue discharging process) and the like; the ceramic sintering degree and the size and the number of the internal pores of the graphite-ceramic composite type can also be regulated and controlled by changing the vacuum freeze-drying process parameters (such as the pre-freezing temperature, the lower the pre-freezing temperature, the finer the crystal grains of the deionized water under the same volume fraction, the more the number of the ice crystals) and the high-temperature sintering process parameters (such as the sintering temperature, the heating rate, the heat preservation time and the like), and the process measures can influence the heat-conducting property and the strength of the graphite-ceramic composite type.
(3) The existence of the porous graphite skeleton not only ensures that graphite and ceramic are alternately and relatively uniformly distributed, but also directly influences the volume ratio of the graphite and ceramic phases in the composite type by changing the structure type of the three-dimensional porous graphite or the size of a basic characteristic unit, thereby influencing the heat-conducting property and the strength of the composite type.
(4) In order to avoid the defects of microcracks, micropores and the like at the joint of the interfaces of the graphite ceramics after high-temperature sintering, ceramic paint is coated on the surface of the porous graphite framework in advance so as to improve the joint condition of the interfaces of the graphite ceramics and regulate and control the composite heat-conducting property and strength of the graphite ceramics.
The composite phase composition of the graphite ceramic prepared by the invention is graphite, glassy carbon, silicon carbide ceramic particles, mullite ceramic and the like, so that the composite phase composition has good chemical stability, low thermal expansion coefficient and high temperature resistance.
In order to obtain the graphite ceramic composite type, the following steps are adopted:
a. uniformly mixing natural crystalline flake graphite (the carbon content is more than 99.5%), high-purity silicon powder (the chemical purity is 99%) and thermosetting phenolic resin powder according to a certain mass ratio;
b. introducing stl files (triangular patch files) of a porous graphite framework CAD model into a selective laser sintering forming machine, selecting reasonable process parameters, and quickly preparing a porous graphite framework blank;
c. carrying out secondary curing on the porous graphite skeleton blank;
d. under the protection of inert gas, carrying out carbonization treatment on the porous graphite framework blank;
e. coating the ceramic coating on the surface of the porous graphite skeleton preform, and drying to obtain a porous graphite skeleton;
f. injecting the ceramic slurry into a mold with a built-in porous graphite framework, completely curing the ceramic slurry, demolding, and taking out to obtain a graphite ceramic composite biscuit;
g. carrying out vacuum freeze drying treatment on the graphite ceramic composite biscuit;
h. under the protection of inert gas, removing glue, sintering at high temperature, cooling along with the furnace, and taking out to obtain the graphite ceramic composite type.
Preferably, the natural crystalline flake graphite powder in the step a is 200-500 meshes (the carbon content is more than 99%), the thermosetting phenolic resin powder is 500-900 meshes, and the high-purity silicon powder is 200-300 meshes; the mass fraction of the natural crystalline flake graphite is 40-60%, the mass fraction of the thermosetting phenolic resin powder is 30-35%, and the balance is high-purity silicon powder (the purity is more than 99%).
Preferably, the selective laser sintering forming process parameters of the step b are as follows: the filling power is 20-30W, the layering thickness is 0.1-0.15 mm, the filling interval is 0.1-0.15 mm, the filling speed is 1500-3000 mm/s, and the filling is carried out in an outline scanning mode.
Preferably, the step c secondary curing process parameters are as follows: in the first stage, the temperature is kept at 60-90 ℃ for 5-10 min; in the second stage, the temperature is 90-120 ℃, and the heat preservation time is 10-30 min; and in the third stage, the temperature is 150-160 ℃, and the heat preservation time is 5-30 min.
The porous graphite skeleton is a regular and three-dimensional porous structure and is formed by arraying basic characteristic units along the direction X, Y, Z, the basic characteristic units can be spheres, cylinders, cuboids, combinations of the spheres, the cylinders, the cuboids and the like, and preferentially, the maximum size of the basic characteristic units is not more than 5 mm.
Preferably, the inert protective atmosphere in steps d and h is over 99% of high-purity nitrogen or argon.
Preferably, the carbonation process in the step d: putting the porous graphite skeleton blank into a vacuum atmosphere carbonization furnace, embedding with more than 99% of graphite powder, vacuumizing, heating to 400 ℃ at the speed of 60-120 ℃/h, and preserving heat for 0.5-1 h; when the vacuum degree reaches 10-20 pa, introducing nitrogen or argon with the purity of 99%, and heating to 600 ℃ at the speed of 30-60 ℃/h; and finally, heating to 800 ℃ at a speed of 240-300 ℃/h, preserving heat for 0.5-1 h, cooling to room temperature along with the furnace, and taking out to obtain the porous graphite skeleton preform.
Preferably, the coating process in step e: putting the porous graphite skeleton preform into a ceramic coating for 1-3 min, taking out, and drying by using an electrothermal blowing constant-temperature drying oven, preferably, the drying temperature is 100-150 ℃, and the drying time is 10-30 min; preferably, the ceramic coating formulation consists of: d50 is 90-120 parts of fused quartz powder with the particle size of 5-10 mu m, 0.3-0.6 part of sodium carboxymethylcellulose, 3-5 parts of aluminum magnesium silicate and 230-260 parts of water. The thickness of the ceramic coating is not more than 0.2 mm.
Preferably, the gel injection molding process in step f comprises: and (2) injecting the ceramic slurry prepared in advance into a mold with a built-in porous graphite skeleton, vibrating while grouting (vibration frequency is 30-60 Hz and vibration amplitude is 1-3 mm) to ensure that the ceramic slurry is filled in the mold, and demolding and taking out after the ceramic slurry is completely cured to obtain the graphite ceramic composite biscuit. Preferably, the ceramic slurry is prepared by uniformly mixing deionized water, organic matters, ceramic particles and a sintering aid, wherein the ceramic particles in the ceramic slurry have a volume fraction of 40-55%, the ceramic particles are mullite powder or fused corundum powder (the purity is more than 99%, and the D50 is not more than 30 μm), the sintering aid has a volume fraction of 1-2% (the sintering aid is one or two of magnesia powder and yttria powder, and the D50 is not more than 2 μm), and the rest is a premixed solution which is a solution obtained by dissolving the organic matters into the deionized water and has a concentration of 10-20%; an organic matter (composed of acrylamide monomer and N, N '-methylene bisacrylamide (component mass ratio of 20-30: 1)) or composed of methyldiallylamide monomer and N, N' -methylene bisacrylamide (component mass ratio of 3-10: 1)). Before grouting, a catalyst (a tetramethylethylenediamine solution with the mass concentration of 33 percent, the addition amount is 0.1-0.2 wt percent of the mass of the premixed liquid) and an initiator (an ammonium persulfate solution with the mass concentration of 25 percent, the addition amount is 1-2 wt percent of the mass of the premixed liquid) are added into the ceramic slurry to cure the organic monomer.
The vacuum freeze drying process in the step g comprises the following steps: comprises two stages of prefreezing and sublimating, preferably, the precooling temperature is-10 ℃ to-70 ℃, and the prefreezing time of the graphite ceramic composite biscuit is not less than 3 hours; during sublimation, the vacuum degree of a freeze dryer needs to be controlled below 200Pa, the freeze-drying temperature is always controlled below 50 ℃, and the freeze-drying time is not less than 12 h;
preferably, the high-temperature hot-pressing sintering process in the step h comprises the following steps: putting the graphite ceramic composite biscuit subjected to vacuum freeze drying into a vacuum atmosphere sintering furnace, embedding graphite powder with the carbon content of more than 99% (in the steps of carbonization, binder removal and high-temperature sintering, the aim of the invention is to uniformly heat and support and prevent deformation), vacuumizing to 10-20 Pa, introducing nitrogen or argon with the purity of more than 99%, heating to 650 ℃ at the speed of 120-240 ℃/h, preserving heat for 0.5-1 h, then quickly heating to 1500-1600 ℃ at the speed of 360-480 ℃/h, preserving heat for 3-6 h, finally cooling to room temperature along with the furnace, and taking out to obtain the graphite ceramic composite biscuit.
By adopting the technical scheme, the invention has the following advantages and positive effects:
injecting the ceramic slurry into the porous graphite framework by utilizing a gel casting technology, so that the distribution range of graphite and ceramic is completely controllable, and a homogeneous interphase composite material is quickly obtained; after the porous graphite framework is carbonized and coated with the coating, the porous graphite framework is combined with the ceramic through high-temperature sintering, which is beneficial to reducing the adverse effect caused by the unmatched physical and chemical properties, thereby ensuring the composite comprehensive performance of the graphite and the ceramic. The method has the advantages of short process flow, high material utilization rate, no pollution, low energy consumption, low production cost and the like.
The graphite ceramic composite type is formed by embedding graphite ceramic, so that the respective excellent characteristics of graphite and ceramic are favorably and fully exerted, the porous graphite framework not only has interconnected macroscopic holes, but also a large number of microscopic holes are formed in the stacking and forming process of graphite powder, in the graphite ceramic composite type, the porous graphite framework mainly plays the roles of low heat conduction and making up the thermal shock resistance of a ceramic material, and the ceramic after high-temperature sintering mainly plays the roles of high strength and making up the insufficiency of the mechanical property of the graphite framework.
The prepared graphite ceramic composite type has the characteristics of low heat conduction and high strength, has good chemical stability, low thermal expansion coefficient and excellent thermal shock resistance, can bear the impact of high-temperature molten metal for a long time, is alternate and uniformly distributed, and is favorable for improving the composite type cutting processing manufacturability, so that the graphite ceramic composite type cutting processing method can be used for secondary mechanical cutting processing and repeated use, can replace the traditional sodium silicate sand mold, and is matched with a graphite casting mold for use.
Drawings
FIG. 1 is a schematic diagram of a composite graphite ceramic in the present invention, wherein 101 is a porous graphite skeleton, and 102 is a filled ceramic material;
FIG. 2 is a front view of a composite graphite-ceramic composite structure of the present invention, in which 201 is a graphite skeleton base sphere, 202 is a connection sphere, and 203 is a filled ceramic material;
FIG. 3 is a basic process flow for preparing graphite ceramic in a composite mode.
Detailed Description
A composite graphite-ceramic material is prepared through designing porous graphite skeleton with CAD software, introducing stl file (triangular patch file) of CAD model of porous graphite skeleton into selective laser sintering machine to quickly prepare porous graphite skeleton blank, secondary solidifying, carbonizing, coating ceramic slurry, injecting the prepared ceramic slurry, solidifying, freeze drying, removing adhesive and high-temp sintering. The present invention will be further illustrated with reference to the following examples.
Example 1
The porous graphite skeleton structure 101 is designed by taking the combination of two spheres of different sizes as basic characteristic units and through a space array, wherein the diameter of a base sphere 201 is 10mm, and the diameter of a connecting sphere 202 is 5 mm.
Putting 99.5% of carbon content, 270-mesh natural crystalline flake graphite powder, 500-mesh thermosetting phenolic resin and 99% and 200-mesh high-purity silicon powder into a dry-method high-efficiency roller ball mill in batches according to the mass ratio of 55:35:10, and uniformly mixing the materials, wherein the volume fraction of a porous graphite framework is 60%.
And 3D printing and molding the graphite/phenolic resin mixed powder by using a selective laser sintering molding technology to obtain a porous graphite skeleton biscuit. The selective laser sintering forming process parameters are as follows: the filling power is 20W, the layering thickness is 0.1mm, the filling interval is 0.1mm, the filling speed is 2000mm/s, and the filling is carried out in a contour scanning mode.
Putting the porous graphite skeleton biscuit into an electric heating furnace, embedding the porous graphite skeleton biscuit with more than 99 percent of graphite powder with 200 meshes, and then heating and curing. Preferentially, the secondary curing process parameters are as follows: in the first stage, the temperature is 60 ℃, and the heat preservation time is 10 min; in the second stage, the temperature is 100 ℃, and the heat preservation time is 15 min; the third stage is 160 deg.C, and the holding time is 5 min.
Putting the porous graphite skeleton blank into a vacuum atmosphere carbonization furnace, embedding by more than 99% of graphite powder, vacuumizing, heating to 400 ℃ at a speed of 60 ℃/h, and preserving heat for 0.5 h; when the vacuum degree reaches 20pa, introducing nitrogen with the purity of 99 percent, and then heating to 600 ℃ at the speed of 60 ℃/h; and finally, heating to 800 ℃ at the speed of 240 ℃/h, preserving the heat for 0.5h, cooling to room temperature along with the furnace, and taking out to obtain the porous graphite framework preform.
Putting the porous graphite skeleton preform into the ceramic coating for 1min, taking out, and drying by using an electrothermal blowing constant-temperature drying oven, preferably, the drying temperature is 100 ℃ and the drying time is 15 min; the ceramic coating formula comprises the following components: d50 is 100g of fused quartz powder with the thickness of 5 mu m, 0.3g of sodium carboxymethylcellulose, 3g of magnesium aluminum silicate and 230mL of water, and the thickness of the ceramic coating is controlled to be 0.1 mm. The volume fraction of the ceramic coating accounts for 2.2 percent of the total composite volume of the graphite and the ceramic.
And (2) injecting the ceramic slurry prepared in advance into a mold with a built-in porous graphite skeleton, vibrating while grouting (vibration frequency of 30Hz and vibration amplitude of 1 mm) to ensure that the ceramic slurry is filled in the mold, and demolding and taking out after the ceramic slurry is completely cured to obtain the graphite ceramic composite biscuit. The ceramic slurry is formed by mixing deionized water, organic matters, ceramic particles and a sintering aid, and the volume fraction of the ceramic slurry accounts for 37.8 percent of the total composite quantity of the graphite ceramic. When the ceramic slurry is prepared, 120 g of acrylamide monomer and 5g of N, N' -methylene bisacrylamide (the mass ratio of the components is 24: 1) are dissolved in 1000ml of deionized water to obtain a premixed solution with the concentration of 11.1%, then 3160g of mullite powder (the purity is 99.5%, and the D50 is 20 microns) and 35.8g of magnesium oxide powder (the purity is 99%, and the D50 is 2 microns) are added in batches and are fully and uniformly stirred to obtain 50vol% of water-based ceramic slurry, and before grouting, a catalyst (a tetramethylethylenediamine solution with the mass concentration of 33%, an ammonium persulfate solution with the mass concentration of 25%, and a 1.125 g) and an initiator (an ammonium persulfate solution with the mass concentration of 25% and a mass ratio of 1% to 11.25 g) are added into the ceramic slurry.
Putting the graphite ceramic composite biscuit into a vacuum freeze dryer, setting the precooling temperature to be-40 ℃, and pre-freezing for 4 hours; then, vacuumizing to below 200Pa, controlling the freeze-drying temperature to be below 40 ℃, and freeze-drying for 20 h;
putting the graphite ceramic composite biscuit subjected to vacuum freeze drying into a vacuum atmosphere sintering furnace, embedding the graphite ceramic composite biscuit by using graphite powder with the carbon content of more than 99%, vacuumizing to 10Pa, introducing nitrogen with the purity of more than 99%, heating to 650 ℃ at 120 ℃/h, preserving heat for 0.5h, quickly heating to 1550 ℃ at 360 ℃/h, preserving heat for 4h, finally cooling to room temperature along with the furnace, and taking out to obtain the graphite ceramic composite biscuit.
The compression strength of the graphite-based ceramic composite type material is 20.5MPa, the bending strength is 30.3MPa, the thermal conductivity coefficient is 0.72W/(m.k), the thermal expansion coefficient is 4.2 multiplied by 10-6 mm/DEG C, the graphite-based ceramic composite type material can bear the high temperature of 1550 ℃ for a long time, the mechanical cutting processing manufacturability is good, and the graphite-based ceramic composite type material can be repeatedly used for many times.
Example 2
The porous graphite skeleton structure 101 is designed by taking the combination of two spheres of different sizes as basic characteristic units and through a space array, wherein the diameter of the basic sphere 201 is 8mm, and the diameter of the connecting sphere 202 is 3 mm.
Putting 99.5% of carbon content, 300-mesh natural crystalline flake graphite powder, 800-mesh thermosetting phenolic resin and 99% and 200-mesh high-purity silicon powder into a dry-method high-efficiency roller ball mill in batches according to the mass ratio of 50:35:15, and uniformly mixing the materials, wherein the volume fraction of a porous graphite framework is 70%.
And 3D printing and molding the graphite/phenolic resin mixed powder by using a selective laser sintering molding technology to obtain a porous graphite skeleton biscuit. The selective laser sintering forming process parameters are as follows: the filling power is 25W, the layering thickness is 0.1mm, the filling distance is 0.1mm, the filling speed is 2500mm/s, and the filling is carried out in a contour scanning mode.
Putting the porous graphite skeleton biscuit into an electric heating furnace, embedding the porous graphite skeleton biscuit with more than 99 percent of graphite powder with 200 meshes, and then heating and curing. Preferentially, the secondary curing process parameters are as follows: in the first stage, the temperature is 60 ℃, and the heat preservation time is 10 min; in the second stage, the temperature is 100 ℃, and the heat preservation time is 15 min; in the third stage, the temperature is 160 ℃, and the heat preservation time is 10 min.
Putting the porous graphite skeleton blank into a vacuum atmosphere carbonization furnace, embedding by more than 99% of graphite powder, vacuumizing, heating to 400 ℃ at a speed of 60 ℃/h, and preserving heat for 0.5 h; when the vacuum degree reaches 15pa, introducing nitrogen with the purity of 99 percent, and then heating to 600 ℃ at the speed of 30 ℃/h; and finally, heating to 800 ℃ at the speed of 240 ℃/h, preserving the heat for 0.5h, cooling to room temperature along with the furnace, and taking out to obtain the porous graphite framework preform.
Putting the porous graphite skeleton preform into the ceramic coating for 2min, taking out, and drying by using an electrothermal blowing constant-temperature drying oven, preferably, the drying temperature is 120 ℃ and the drying time is 12 min; the ceramic coating formula comprises the following components: d50 is fused quartz powder 100g with the diameter of 5 μm, sodium carboxymethylcellulose 0.4g, magnesium aluminum silicate 3g and water 235 ml. The volume fraction of the ceramic coating accounts for 1.5 percent of the total composite volume of the graphite and the ceramic.
And (2) injecting the ceramic slurry prepared in advance into a mold with a built-in porous graphite skeleton, vibrating while grouting (vibration frequency of 45Hz and vibration amplitude of 2 mm) to ensure that the ceramic slurry is filled in the mold, and demolding and taking out after the ceramic slurry is completely cured to obtain the graphite ceramic composite biscuit. The ceramic slurry is formed by mixing deionized water, organic matters, ceramic particles and a sintering aid, and the volume fraction of the ceramic slurry accounts for 28.5 percent of the total composite quantity of the graphite ceramic. During preparation, firstly 130g of acrylamide monomer and 6.5g of N, N' -methylene bisacrylamide (the mass ratio of the components is 20: 1) are dissolved into an appropriate amount of 1000ml of deionized water to obtain a premixed solution with the concentration of 12.0%, and then 3476g of mullite powder (the purity is 99.5%, the D50 is 20 μm) and 71.6g of magnesium oxide powder (the purity is 99%, the D50 is 2 μm) are added in batches and are fully and uniformly stirred to obtain 52.8vol% water-based ceramic slurry. Before grouting, a catalyst (a 33% tetramethylethylenediamine solution by mass, the addition amount of which is 0.1wt% of the mass of the premix and is 1.137 g) and an initiator (an ammonium persulfate solution by mass, the addition amount of which is 1.5wt% of the mass of the premix and is 17.048 g) are added into the ceramic slurry.
Putting the graphite ceramic composite biscuit into a vacuum freeze dryer, setting the precooling temperature to be 50 ℃ below zero, and pre-freezing for 6 hours; then, vacuumizing to below 200Pa, controlling the freeze-drying temperature to be below 50 ℃, and freeze-drying for 15 h;
putting the graphite ceramic composite biscuit subjected to vacuum freeze drying into a vacuum atmosphere sintering furnace, embedding the graphite ceramic composite biscuit by using graphite powder with the carbon content of more than 99%, vacuumizing to 20Pa, introducing nitrogen with the purity of more than 99%, heating to 650 ℃ at 180 ℃/h, preserving heat for 0.5h, quickly heating to 1600 ℃ at 360 ℃/h, preserving heat for 4h, finally cooling to room temperature along with the furnace, and taking out to obtain the graphite ceramic composite biscuit.
The compression strength of the graphite-based ceramic composite type material is 25.5MPa, the bending strength is 35.6MPa, the thermal conductivity is 1.08W/(m.k), the thermal expansion coefficient is 4.3 multiplied by 10-6 mm/DEG C, the graphite-based ceramic composite type material can bear 1600 ℃ high temperature for a long time, the mechanical cutting processing manufacturability is good, and the graphite-based ceramic composite type material can be repeatedly used for many times.
Claims (7)
1. The preparation method of the graphite ceramic composite type is characterized by comprising the following steps of:
(1) uniformly mixing natural crystalline flake graphite, silicon powder and thermosetting phenolic resin powder, introducing the porous graphite skeleton model into a selective laser sintering forming machine, and preparing a porous graphite skeleton blank according to the mixed material;
(2) carrying out secondary curing on the porous graphite skeleton blank; under the protection of inert gas, carrying out carbonization treatment on the porous graphite framework blank to obtain a porous graphite framework prefabricated body;
(3) coating ceramic paint on the surface of a porous graphite skeleton preform, and drying to obtain the porous graphite skeleton, wherein the coating process comprises the following steps: putting the porous graphite skeleton preform into a ceramic coating for 1-3 min, taking out, and drying by using an electric hot blast constant-temperature drying oven at the drying temperature of 100-150 ℃ for 10-30 min, wherein the thickness of the ceramic coating is not more than 0.2mm, and the formula of the ceramic coating comprises the following components: d50 is 90-120 parts of fused quartz powder with the particle size of 5-10 mu m, 0.3-0.6 part of sodium carboxymethylcellulose, 3-5 parts of aluminum magnesium silicate and 230-260 parts of water;
(4) and (3) gel injection molding process: injecting the ceramic slurry into a mold with a built-in porous graphite skeleton, wherein the vibration frequency is 30-60 Hz, the vibration amplitude is 1-3 mm, and the lower side of the mold is subjected to grouting and vibration simultaneously so as to ensure that the ceramic slurry is filled in the mold, and demolding and taking out after the ceramic slurry is completely cured to obtain a graphite ceramic composite biscuit;
the ceramic slurry is formed by uniformly mixing deionized water, organic matters, ceramic particles and a sintering aid, wherein the volume fraction of the ceramic particles in the ceramic slurry is 40-55%, the volume fraction of the sintering aid is 1-2%, and the balance is a premixed solution; the premixed solution is formed by dissolving an organic matter into deionized water, and the mass concentration of the organic matter in the deionized water is 10-20%; the ceramic particles comprise mullite powder or fused corundum powder, the purity of the mullite powder or the fused corundum powder is more than 99%, and D50 is not more than 30 microns; the sintering aid is magnesium oxide powder and/or yttrium oxide powder, and D50 is not more than 2 mu m; the organic matter comprises acrylamide monomer and N, N' -methylene diacrylamide which are mixed according to the mass ratio of 20-30: 1; or the organic matter comprises methyl diacrylamide monomer and N, N' -methylene diacrylamide which are mixed according to the mass ratio of 3-10: 1;
(5) carrying out vacuum freeze drying treatment on the graphite ceramic composite biscuit; under the protection of inert gas, removing glue, sintering at high temperature, cooling along with the furnace, and taking out to obtain the graphite ceramic composite type.
2. The preparation method of the graphite ceramic composite type according to claim 1, wherein the porous graphite skeleton in the step (1) is a regular and three-dimensional porous structure, and is formed by arraying basic characteristic units along the direction X, Y, Z, wherein the basic characteristic units can be spheres, cylinders, cuboids or a combination thereof, and the maximum size of the basic characteristic units is not more than 10 mm.
3. The composite graphite ceramic preparation method according to claim 1, wherein the mixed powder in the step (1) comprises 40-60% by mass of natural crystalline flake graphite, 30-35% by mass of thermosetting phenolic resin powder and the balance of silicon powder; the natural crystalline flake graphite powder is 200-500 meshes, the thermosetting phenolic resin powder is 500-900 meshes, and the high-purity silicon powder is 200-300 meshes; the selective laser sintering forming process parameters are as follows: the filling power is 20-30W, the layering thickness is 0.1-0.15 mm, the filling interval is 0.1-0.15 mm, the filling speed is 1500-3000 mm/s, and the filling is carried out in an outline scanning mode.
4. The preparation method of the graphite ceramic composite type according to claim 1, wherein the secondary curing process parameters in the step (2) are as follows: in the first stage, the temperature is kept at 60-90 ℃ for 5-10 min; in the second stage, the temperature is 90-120 ℃, and the heat preservation time is 10-30 min; in the third stage, the temperature is 150-160 ℃, and the heat preservation time is 5-30 min; the carbonization process comprises the following steps: putting the porous graphite skeleton blank into a vacuum atmosphere carbonization furnace, embedding graphite powder with the purity of more than 99%, vacuumizing, heating to 400 ℃ at the speed of 60-120 ℃/h, and keeping the temperature for 0.5-1 h; when the vacuum degree reaches 10-20 Pa, introducing nitrogen or argon with the purity of 99%, and heating to 600 ℃ at the speed of 30-60 ℃/h; and finally, heating to 800 ℃ at a speed of 240-300 ℃/h, preserving heat for 0.5-1 h, cooling to room temperature along with the furnace, and taking out to obtain the porous graphite skeleton preform.
5. The preparation method of the graphite ceramic composite type according to claim 1, wherein the vacuum freeze drying process in the step (5) comprises two stages of pre-freezing and sublimating, the pre-cooling temperature is-10 ℃ to-70 ℃, and the pre-freezing time is not less than 3 hours; during sublimation, the vacuum degree of a freeze dryer needs to be controlled below 200Pa, the freeze-drying temperature is always controlled below 50 ℃, and the freeze-drying time is not less than 12 h; the high-temperature hot-pressing sintering process comprises the following steps: putting the freeze-dried graphite ceramic composite biscuit into a vacuum atmosphere sintering furnace, embedding the graphite powder with the carbon content of more than 99%, vacuumizing to 10-20 Pa, introducing nitrogen or argon with the purity of more than 99%, heating to 650 ℃ at the speed of 120-240 ℃/h, preserving heat for 0.5-1 h, quickly heating to 1500-1600 ℃ at the speed of 360-480 ℃/h, preserving heat for 3-6 h, finally cooling to room temperature along with the furnace, and taking out to obtain the graphite ceramic composite biscuit.
6. The preparation method of the graphite-ceramic composite type according to claim 1, wherein the graphite-ceramic composite type is prepared by compounding a porous graphite skeleton and ceramic, wherein the graphite ceramic is distributed alternately and uniformly, the volume fraction of the porous graphite skeleton is 30-70%, and the balance is ceramic material, and the ceramic material comprises ceramic paint and ceramic slurry; the volume fraction of the ceramic coating accounts for not more than 3% of the total composite graphite ceramic.
7. The preparation method of the graphite ceramic composite type according to claim 1, wherein the ceramic slurry further comprises a catalyst and an initiator, wherein the catalyst is a tetramethylethylenediamine solution with a mass concentration of 30-40%, and the addition amount of the catalyst is 0.1-0.2 wt% of the mass of the premixed liquid; the initiator is an ammonium persulfate solution with the mass concentration of 20-30%, and the addition amount of the initiator is 1-2 wt% of the mass of the premixed liquid.
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