CN109485430B - Method for preparing bionic porous ceramic with complex three-dimensional structure - Google Patents

Method for preparing bionic porous ceramic with complex three-dimensional structure Download PDF

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CN109485430B
CN109485430B CN201811454986.4A CN201811454986A CN109485430B CN 109485430 B CN109485430 B CN 109485430B CN 201811454986 A CN201811454986 A CN 201811454986A CN 109485430 B CN109485430 B CN 109485430B
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dimensional structure
needle cylinder
ceramic
temperature
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CN109485430A (en
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张斗
陈何昊
廖晶晶
周科朝
熊慧文
黄玉娟
赵连仲
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Central South University
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Abstract

The invention belongs to the three-dimensional structure forming range, and particularly relates to a preparation method of a complex three-dimensional structure ceramic with bionic porous structure. The ceramic precursor is dissolved in a solvent, and a direct-writing slurry is obtained through partial cross-linking reaction, the obtained direct-writing slurry is subjected to degassing treatment, and then is subjected to direct-writing forming in an oriented cold field environment, and then the ceramic with the bionic porous three-dimensional structure is obtained through processes of freeze drying, cross-linking-cracking and the like. The invention realizes the high-efficiency combination of direct-writing molding and freezing casting technology for the first time; the method overcomes the limitation of the traditional preparation technology in the aspect of realizing a multi-scale hole structure and a complex three-dimensional structure.

Description

Method for preparing bionic porous ceramic with complex three-dimensional structure
Technical Field
The invention belongs to the three-dimensional structure forming range, and particularly relates to a preparation method of a complex three-dimensional structure ceramic with bionic porous structure.
Background
In 2006, the journal of Science publishes Deville et al, Deville S, Saiz E, Nalla R K, Tomsia AP. Freezing as a path to build complex J Science,2006,311(5760) from the perspective of a pearl lamellar structure of a bionic shell structure, a lamellar oriented HA porous structure similar to the structure of a pearl layer is prepared by Freeze Casting (Freeze Casting), the mechanical properties of the lamellar oriented HA porous structure can be equivalent to those of a biological compact bone, the huge advantage of the method in preparing a porous material of an oriented lamellar assembly structure is shown, and the research heat tide of the oriented porous material is raised. Freeze Casting (Freeze Casting), also known as Ice-templating method (Ice-templating method), freezes and solidifies slurry under a directed temperature field, causes powder particles to aggregate and rearrange under the pushing and pushing repulsion of directionally growing and solidifying Ice crystals, Freeze-dries the resulting Ice embryo, and finally leaves a porous structure with directional arrangement using Ice as a template. By utilizing the directional growth characteristic of ice crystals, the growth speed of the ice crystals in the direction vertical to a certain crystal direction is higher than that in other directions under the condition of a certain temperature gradient, and after the ice crystals are sublimated and removed, the obtained structure takes the ice as a template and has directional, lamellar and porous characteristics. Compared with other methods for preparing the directional porous material (such as a metal/gas eutectic directional solidification method, a fiber winding method, a wood pyrolysis framework method and the like), the method has the characteristics of wide application range of freeze casting, simple process parameters, convenience in regulation and control, convenience in controlling the pore structure of the material, environmental friendliness and the like when the slurry solvent is water.
However, the freeze casting can realize the construction of the micro-pore structure in the blank. But still relies on the die to achieve the shaping of the blank. Not only limits the preparation of complex three-dimensional blanks, but also increases the preparation cost.
Meanwhile, Joseph Cesarano III et al [ Lewis, J.A., J.E.Smay, et al.. Direct Ink Writing of Three-Dimensional Ceramic structures. journal of the American Ceramic Society,2006,89(12):3599-3609 ], of the American national laboratory, propose a Direct-write molding technique. The technology firstly designs a required three-dimensional structure pattern by means of Computer Aided Design (CAD), and then extrudes the suspension in the needle cylinder from the needle nozzle to be precise by automatically controlling a suspension conveying device which is arranged on a Z axis and consists of the needle cylinder and the needle nozzle through a computerAnd (3) the linear fluid with certain size moves along the track set by a program in the X-Y axis, and the linear fluid is deposited on the motion platform to obtain a first layer structure. After the first layer of formation is completed, the suspension conveyor is driven by the Z-axis motor to move up precisely to the height determined by the structural scheme, and the second layer of formation is carried out on the first layer of structure. Subsequently, a complex three-dimensional periodic structure which cannot be prepared by the traditional forming process is obtained in a layer-by-layer stacking mode. This structure has a large aspect ratio and a range of dimensional control (from 10)-6To 100m), and the like, and can form complex three-dimensional structures containing span (unsupported portion) features, the method is receiving more extensive attention. Additive manufacturing of ceramics with complex three-dimensional structures has begun to be achieved by this technique.
However, the linear shaping technique can achieve the preparation of complex three-dimensional structures of the green body. But for the realization of a micro-porous structure, the realization still relies on a pore former. The addition of the pore-forming agent not only increases the difficulty and cost for slurry preparation, but also leads to single and disordered shape characteristics of the microscopic porous of the green body.
Aiming at the characteristics of the two technologies, the preparation of the bionic porous complex three-dimensional structure ceramic is realized by organically combining the two technologies. Meanwhile, so far, no relevant technical report combining the directional temperature field in the freeze casting and the 3D printing is available.
Disclosure of Invention
The invention firstly tries a scheme of preparing the bionic porous complex three-dimensional structure ceramic by combining the directional temperature field in the freeze casting with the 3D printing.
The invention relates to a method for preparing bionic porous ceramic with a complex three-dimensional structure; dissolving a ceramic precursor serving as a solute in a solvent, uniformly mixing, and performing a crosslinking reaction; obtaining slurry; printing the slurry in an oriented temperature field through printing equipment, and curing and forming to obtain a ceramic precursor blank with a three-dimensional structure; freezing, drying and cracking the obtained blank to obtain the bionic porous complex three-dimensional structure ceramic; the highest temperature of the orientation temperature field is less than the melting point of the used solvent; the boiling point of the organic solvent is less than the crosslinking reaction temperature.
The invention relates to a method for preparing bionic porous ceramic with a complex three-dimensional structure; the solvent is preferably a high melting point organic substance; the melting point of the high-melting-point organic matter is more than or equal to 0 ℃. Preferably from 0 to 50 ℃. In industrial use, the high-melting organic substance is at least one selected from the group consisting of camphene (melting point: 35 ℃ C., boiling point: 159 ℃ C.), dimethyl carbonate (melting point: 2-4 ℃ C., boiling point: 90 ℃ C.), cyclooctane (melting point: 14.3 ℃ C., boiling point: 149 ℃ C.), cyclohexane (melting point: 5 ℃ C., boiling point: 81 ℃ C.), tert-butanol (melting point: 25.7 ℃ C., boiling point: 82 ℃ C.), dioxane (melting point: 12 ℃ C., boiling point: 101 ℃ C.), and p-xylene (melting point: 13 ℃ C., boiling point: 139 ℃ C.).
The invention relates to a method for preparing bionic porous ceramic with a complex three-dimensional structure; partial cross-linking of the ceramic precursor is achieved by a cross-linking agent; the cross-linking agent is at least one of a cross-linking agent containing vinyl, dibutyltin dilaurate, trimethoxy silane and trichlorosilane. Preferably, the vinyl-containing crosslinking agent is at least one selected from divinylbenzene, diallylamine, vinyltrichlorosilane, and methylvinyldichlorosilane.
The invention relates to a method for preparing bionic porous ceramic with a complex three-dimensional structure; the ceramic precursor is selected from at least one of polycarbosilane, polyoxosilane, polyazetasilane and polyborosilane.
The invention relates to a preparation method of 3D printing bionic porous ceramic; the cross-linking agent is a vinyl-containing cross-linking agent; the amount of the cross-linking agent added is 10-100%, preferably 10-40% of the mass of the ceramic precursor used.
The invention adopts high-melting-point organic matter as a solvent of the slurry and adopts a ceramic precursor as a solute of the slurry. At a certain temperature, the organic matter is melted and fully dissolved with the ceramic precursor. Meanwhile, under the action of a cross-linking agent, the ceramic precursor is subjected to partial cross-linking reaction. And then, injecting the slurry into a needle cylinder of printing equipment (the printing equipment comprises a needle cylinder), and controlling the rheological property of the slurry by controlling the temperature of the material output end (such as the needle cylinder and a needle nozzle) of the printing equipment. By adopting the slurry sent by the invention to carry out direct writing forming, the slurry can smoothly pass through a needle nozzle at the material output end of the printing equipment, and can be solidified and formed on a substrate with lower temperature, and finally the three-dimensional structure of the ceramic precursor is printed. And then, carrying out freeze drying and cracking treatment on the blank to obtain the bionic porous complex three-dimensional structure ceramic.
The invention relates to a method for preparing bionic porous ceramic with a complex three-dimensional structure; the method comprises the following steps:
step one
Selecting a specific organic matter with a proper melting point as a solvent according to the difference of the crystallization morphology of the organic solvent; heating the organic matter to a temperature higher than the melting point to completely melt the organic matter; then adding the ceramic precursor powder and the cross-linking agent into the completely melted organic matter, and uniformly mixing the mixture by stirring; then heating to a certain temperature to make the ceramic precursor generate partial cross-linking reaction; obtaining slurry;
step two
Placing the slurry obtained in the step one in a printing needle cylinder, heating the slurry to a temperature higher than the melting point of the organic solvent, standing for 1-2 hours, and removing air bubbles; then reducing the temperature of the needle cylinder to be lower than the melting point of the organic solvent, and realizing the regulation and control of the rheological property of the slurry by changing the temperature of the slurry; to thereby obtain a composition having a suitable viscosity (1 s)-1Viscosity under shearing rate is 500 Pa.s-1000 Pa.s) and has rheological property caused by shearing so as to meet the requirement of printing;
on the other hand, the optimal temperature is adjusted to be below the melting point of the organic solvent by adjusting the temperature of the heat-conducting substrate to be proper, and finally, the curing of the slurry can be realized;
printing a complex three-dimensional structure on the heat-conducting substrate through a designed printing program to obtain a semi-finished product;
step three
Fully freezing and solidifying the semi-finished product obtained in the step two in a temperature field; placing the mixture into a freeze dryer, and drying the mixture for 24 to 48 hours in an environment with the temperature of the melting point of the used solvent to minus 80 ℃, preferably 0 to minus 60 ℃ and the air pressure of 1 to 10Pa until the organic solvent is completely sublimated; and then placing the blank in a protective atmosphere, and cracking at 1000-1400 ℃ for at least 1h to obtain the 3D ceramic with the multi-scale hole structure.
Of course, the organic solvent can be applied to the present invention when the following 4 conditions are satisfied; (1) the organic solvent is easy to melt, and the optimal melting point is 0-50 ℃. (2) The ceramic precursor and the cross-linking agent can be fully and uniformly dissolved in the organic solvent. (3) The boiling point of the organic solvent should be below the crosslinking reaction temperature. (4) The organic solvent should be selected from low-toxicity organic substances.
The invention relates to a method for preparing bionic porous ceramic with a complex three-dimensional structure; in the second step;
firstly, connecting a needle cylinder with degassed slurry with a needle head, a piston and an air duct, and then integrally mounting the needle cylinder, the piston and the air duct on a clamp on a Z axis; then, by means of a three-dimensional structure pattern required by computer aided design, automatically controlling the pressure of a needle cylinder (the pressure range is 1-1000 PSI, specifically determined according to precursor slurry, preferably 10-100PSI, and further preferably 20-45PSI) arranged on a Z axis through a computer, enabling the slurry to flow out of a needle nozzle and be deposited on an X-Y axis forming platform (the structure is generally directly written on a glass slide on the platform) which moves according to a program (the moving speed is 0.1-500 mm/s, specifically determined according to the precursor slurry, and generally preferably 1-10mm/s, and further preferably 4-7mm/s), thereby obtaining a first layer of structure; thereafter, the Z-axis is moved or rotated precisely upwards to a height determined by the structural solution, and the second layer formation will be carried out on the first layer structure; and then, obtaining the complex three-dimensional structure in a layer-by-layer superposition mode.
The pressure is 1-1000 PSI; the moving speed of the X-Y axis forming platform is 0.1-500 mm/s.
In the second step, a temperature field is provided by a liquid nitrogen system, and the specific operation is to fill liquid nitrogen into the heat-insulating container and place the heat-conducting substrate above the liquid nitrogen, so that heat can be conducted only through the heat-conducting substrate, and further an oriented temperature field perpendicular to the substrate is formed around the printing blank body, as shown in fig. 1. And printing a complex three-dimensional structure on the heat-conducting substrate through a designed printing program to obtain a semi-finished product.
As a preferred scheme, the invention relates to a method for preparing bionic porous complex three-dimensional structure ceramic;
when polycarbosilane is used as a ceramic precursor and camphene is used as an organic solvent; heating camphene to over 35 ℃ to fully melt the camphene; then adding polycarbosilane powder with the total mass of 10-50 wt% of the organic solvent, and fully dissolving the powder in camphene under the action of magnetic stirring; then, divinylbenzene with the mass of 10-100 wt.% of the ceramic precursor is dripped to be used as a cross-linking agent; magnetically stirring for 1-5h, preferably 2.5-4h at 80-160 ℃, preferably 115-135 ℃ and further preferably 120-130 ℃ to promote partial crosslinking of polycarbosilane; obtaining slurry;
then placing the slurry in a needle cylinder, heating the slurry in the needle cylinder to over 35 ℃, standing for 1-2h, and carrying out defoaming treatment; then adjusting the temperature of the needle cylinder to 25-30 ℃, and regulating the slurry to 1s-1The viscosity under the shearing rate is 500 Pa.s-1000 Pa.s, and the standby slurry is obtained; meanwhile, pouring excessive liquid nitrogen into the lower end of the heat-conducting substrate to provide a directional temperature field vertical to the substrate; and (4) performing direct-writing forming on the standby slurry, and printing a set three-dimensional structure to obtain a semi-finished product.
Or
When polycarbosilane is used as a ceramic precursor and cyclooctane is used as an organic solvent; heating cyclooctane to above 14 deg.C to melt completely; then adding polycarbosilane powder with the total mass of 10-50 wt% of the organic solvent, and fully dissolving the powder in cyclooctane under the action of magnetic stirring; then, divinylbenzene with the mass of 10-100 wt.% of the ceramic precursor is dripped to be used as a cross-linking agent; magnetically stirring for 1-5h at 80-120 ℃ to promote partial crosslinking of polycarbosilane; thus obtaining the slurry.
Then placing the slurry in a needle cylinder, heating the slurry in the needle cylinder to above 14 ℃, standing for 1-2h, and carrying out defoaming treatment; then adjusting the temperature of the needle cylinder to 4-14 ℃, and regulating the slurry to 1s-1The viscosity under the shearing rate is 500 Pa.s-1000 Pa.s, and the standby slurry is obtained; meanwhile, pouring excessive liquid nitrogen into the lower end of the heat-conducting substrate to provide a directional temperature field vertical to the substrate; directly writing the standby slurry intoAnd printing a set three-dimensional structure to obtain a semi-finished product.
Or
When the polyoxosilane is used as a ceramic precursor and the tertiary butanol is used as an organic solvent; heating tert-butyl alcohol to over 28 deg.c to melt completely; then adding polyoxosilane powder with the total mass of 10-50 wt.% of the organic solvent, and fully dissolving the powder in tert-butyl alcohol under the action of magnetic stirring; then dropwise adding dibutyltin dilaurate which accounts for 10-100 wt% of the mass of the ceramic precursor as a cross-linking agent; magnetically stirring for 1-5h at 50-60 deg.C to promote partial cross-linking of polysiloxane; thus obtaining the slurry.
Then placing the slurry in a needle cylinder, heating the slurry in the needle cylinder to above 28 ℃, standing for 1-2h, and carrying out defoaming treatment; then adjusting the temperature of the needle cylinder to 18-28 ℃, and regulating the slurry to 1s-1The viscosity under the shearing rate is 500 Pa.s-1000 Pa.s, and the standby slurry is obtained; meanwhile, pouring excessive liquid nitrogen into the lower end of the heat-conducting substrate to provide a directional temperature field vertical to the substrate; and (4) performing direct-writing forming on the standby slurry, and printing a set three-dimensional structure to obtain a semi-finished product.
Or
When polyborosilane is used as a ceramic precursor and tert-butyl alcohol is used as an organic solvent, heating the tert-butyl alcohol to be more than 28 ℃ so as to fully melt the tert-butyl alcohol; then adding polyborosilane powder with the total mass of 10-50 wt.% of the organic solvent, and fully dissolving the powder in tert-butyl alcohol under the action of magnetic stirring; then dropwise adding dibutyltin dilaurate which accounts for 10-100 wt% of the mass of the ceramic precursor as a cross-linking agent; magnetically stirring for 1-5h at 50-60 ℃ to promote partial cross-linking of polyborosilane; thus obtaining the slurry.
Then placing the slurry in a needle cylinder, heating the slurry in the needle cylinder to above 28 ℃, standing for 1-2h, and carrying out defoaming treatment; then adjusting the temperature of the needle cylinder to 18-28 ℃, and regulating the slurry to 1s-1The viscosity under the shearing rate is 500 Pa.s-1000 Pa.s, and the standby slurry is obtained; meanwhile, pouring excessive liquid nitrogen into the lower end of the heat-conducting substrate to provide a directional temperature field vertical to the substrate; and (4) performing direct-writing forming on the standby slurry, and printing a set three-dimensional structure to obtain a semi-finished product.
Or
Respectively taking polysilane as a ceramic precursor and taking camphene as an organic solvent; heating camphene to over 35 ℃ to fully melt the camphene; then adding polyazetasilane powder with the total mass of 10-50 wt.% of the organic solvent, and fully dissolving the powder in camphene under the action of magnetic stirring; then, divinylbenzene with the mass of 10-100 wt.% of the ceramic precursor is dripped to be used as a cross-linking agent; magnetically stirring for 1-5h at the temperature of 110-120 ℃ to promote partial crosslinking of the polysilazane; obtaining slurry;
then placing the slurry in a needle cylinder, heating the slurry in the needle cylinder to over 35 ℃, standing for 1-2h, and carrying out defoaming treatment; then adjusting the temperature of the needle cylinder to 25-30 ℃, and regulating the slurry to 1s-1The viscosity under the shearing rate is 500 Pa.s-1000 Pa.s, and the standby slurry is obtained; meanwhile, pouring excessive liquid nitrogen into the lower end of the heat-conducting substrate to provide a directional temperature field vertical to the substrate; and (4) performing direct-writing forming on the standby slurry, and printing a set three-dimensional structure to obtain a semi-finished product.
The invention relates to a method for preparing bionic porous ceramic with a complex three-dimensional structure; the protective atmosphere is selected from one of vacuum atmosphere, argon atmosphere and nitrogen atmosphere.
The invention is characterized in that the preparation of the multi-scale porous ceramic 3D structure is realized by using the idea of freezing and pouring and through the direct-writing forming technical means. In the operation process, the following difficulties are encountered in sequence: timing of crosslinking selection; the manner of crosslinking; controlling the crosslinking degree before direct writing; before direct writing, selecting and controlling the temperature of a slurry output device; selection of a direct-write movement mode and selection of a direct-write movement parameter. For example: 1. polycarbosilane was dissolved in molten camphene to make a 20 wt.% slurry with divinylbenzene as the crosslinking agent. If chemical crosslinking treatment is carried out after printing and drying, the three-dimensional complex structure of the green body can be damaged to a great extent because the crosslinking agent and the ceramic precursor are mutually soluble. For example, after printing and drying, oxidation crosslinking treatment is performed, and a large amount of water vapor and gas are generated due to polycondensation reaction, so that large internal stress is formed in a blank, and the structure is damaged. The timing of the paste cross-linking should be chosen prior to printing. 2. If the oxidative crosslinking reaction is used as a slurry crosslinking method before printing, the precursor powder needs to be subjected to a preliminary oxidative crosslinking treatment. Since air is not in sufficient contact with the powder (the powder on the surface layer is always more susceptible to cross-linking reaction with air), the degree of cross-linking in non-regions of the same batch of powder is significantly different, and even a part of the powder (the powder in the deep layer) is not subjected to cross-linking reaction. This leads to local melting of the green body during the pyrolysis process, which can destroy the structure of the microscopic holes and even the structure of the macroscopic holes. Therefore, by using chemical crosslinking as the crosslinking means of the slurry, the precursor powder can be sufficiently and uniformly crosslinked in a dissolved state to the same extent. 3. The chemical crosslinking degree has a crucial influence on the printing of the paste and the appearance of the cleavage products at a later stage. The degree of crosslinking is closely related to the temperature and time of the crosslinking reaction. 4g of polycarbosilane were dissolved in 16g of molten camphene to make a 20 wt.% slurry and 0.8g of divinylbenzene was added as a crosslinking agent. If the crosslinking reaction is carried out for 2 hours at the temperature of 80 ℃, the obtained cracking product is melted, and the pore structure is seriously damaged. If the crosslinking reaction is carried out for 2 hours at 120 ℃, the morphological structure of the holes of the obtained cracking product is kept very complete. If the paste is crosslinked for 2 hours at 150 ℃, the paste is in a 'jelly-like' state after being subjected to sufficient crosslinking reaction, does not have any fluidity, and therefore does not meet the basic conditions required by printing paste. If the crosslinking reaction is carried out for 0.5h at 120 ℃, the obtained cracking product is locally melted, and the pore structure is seriously damaged. If the crosslinking reaction is carried out at 120 ℃ for 8 hours, the sizing agent is in a 'jelly shape' after the full crosslinking reaction, does not have any fluidity, and therefore does not meet the basic condition required by printing sizing agent. 4. In the direct-write molding process, the selection of the temperature of the syringe and the temperature of the substrate depends on the melting point of the organic solvent. Reasonable temperature setting is a key factor for realizing extrusion and solidification of the slurry. For example, 20 wt.% polycarbosilane/camphene slurry, the organic solvent camphene has a melting point of about 35 ℃. The temperature of the syringe is adjusted to make the slurry have certain viscoelasticity. If the syringe temperature is above 35 degrees celsius or higher, the slurry exhibits significant flow behavior, but the modulus of elasticity is negligible. During extrusion, a large amount of the slurry will be ejected, rather than being extruded in a string-like manner. On the other hand, even if the paste is deposited on a substrate at a lower temperature (-50 ℃ C. or lower), it takes a certain time for the paste to solidify, and thus the printed structure may collapse. If the temperature of the syringe is far lower than 35 ℃ or lower than 25 ℃, the slurry does not have any melting phenomenon, has higher elastic modulus, but does not have proper flowing behavior. During the extrusion process, the phenomenon of nozzle blockage can be caused. If the temperature of the syringe is selected to be between 25 ℃ and 35 ℃, the slurry has proper viscoelasticity, presents higher elastic modulus and also has proper flowing behavior. In the printing process, extrusion and solidification can be easily realized. 5. In the direct-writing forming process, reasonably adjusting the printing speed and the printing pressure is a key factor for constructing a complete three-dimensional complex structure. Using 20 wt.% polycarbosilane/camphene slurry as an example, the syringe was heated to 30 ℃ for direct writing. If the printing speed is too low and the pressure is too high (printing speed: 2mm/s, extrusion pressure: 100PSI), the paste is accumulated in a large amount and does not have a linear structure. If the printing speed is too high and the pressure is too low (printing speed: 100mm/s, extrusion pressure: 10PSI), a large number of breakpoints occur in the extruded linear structure, resulting in poor printing continuity.
The invention has the advantages that:
1. the method overcomes the defects of the conventional preparation of porous complex three-dimensional structure ceramics, and realizes the preparation of a macroscopic porous structure while retaining a microscopic directional porous structure.
2. The method directly regulates and controls the rheological property of the slurry by changing the temperature of the slurry and due to the solid-liquid transition of the organic solvent. The method simplifies the mode of regulating and controlling the rheological property of the slurry by adding the rheological modifier, changing the solid content of the slurry and the like in the traditional process.
3. The method realizes the directional solidification of the organic solvent by reducing the temperature of the substrate, and promotes the solidification of the slurry. The curing process of the traditional direct-writing forming slurry is simplified, and the addition of a curing agent is avoided.
4. The method uses solvent volatilization as a pore-forming mode, avoids adding a pore-forming agent, reduces the preparation cost and improves the product purity.
5. The green body prepared by the method has a larger specific surface area due to the existence of a multi-scale porous three-dimensional structure.
6. After optimization, the yield of the product is high.
Drawings
FIG. 1 is a schematic diagram of a bionic porous ceramic prepared by direct-writing forming.
FIG. 2 is a physical representation of the green bodies obtained in example 6 and comparative example 1;
FIG. 3 is a scanning electron micrograph of a cross section of a green body obtained after example 6 and comparative example 2.
The schematic process of the preparation of the process designed by the invention can be seen from fig. 1.
FIG. 2A is an optical image of a green body prepared from the slurry subjected to the chemical crosslinking treatment in example 6; from graph A, it can be seen that the macro-porous structure of the obtained product is kept very intact; FIG. 2B is an optical image of the product obtained in comparative example 1 after printing and oxidative crosslinking; it can be seen that the body is severely cracked and the integrity of the macro porous structure is destroyed after 2-8h of oxidative crosslinking.
FIG. 3A is a scanning electron micrograph of a cross section of a green body obtained in example 6; it can be seen from the A picture that the micro-pore structure of the cracked product is well preserved after the sufficient chemical crosslinking treatment, and the B picture of FIG. 3 is a scanning electron microscope picture of the cross section of the green body obtained in comparative example 2; it can be seen from the B picture that the micro-pore structure of the cracked product is obviously damaged due to the local melting of the green body during the cracking process after the insufficient crosslinking treatment.
The specific implementation mode is as follows:
the present invention is further illustrated by the following examples, but is not limited thereto.
Example 1
The method is adopted to prepare the multi-scale porous silicon carbide ceramic with the complex three-dimensional structure by respectively taking polycarbosilane as a ceramic precursor and camphene as an organic solvent.
Heating camphene to over 35 ℃ to fully melt the camphene. Then 10 wt.% to 20 wt.% polycarbosilane powder is added, and the powder is fully dissolved in camphene under the action of magnetic stirring. Then 20 wt.% (mass ratio of cross-linker to ceramic precursor, same below) of divinylbenzene was added dropwise as cross-linker. And magnetically stirring for 3 hours at the temperature of 120 ℃ to promote the polycarbosilane to be partially crosslinked.
And then placing the slurry into a needle cylinder, heating the slurry to over 35 ℃ in the needle cylinder, and standing for 1-2h for defoaming treatment. And then adjusting the temperature of the needle cylinder to 25-35 ℃, and regulating the rheological property of the slurry to a proper range. Meanwhile, excess liquid nitrogen is poured into the lower end of the heat-conducting substrate to provide an oriented temperature field perpendicular to the substrate.
Then a needle with 200um aperture is loaded on the top of the syringe. And (4) performing direct-writing molding on the slurry to obtain a criss-cross three-dimensional structure on the heat-conducting substrate. The molding pressure is 30 PSI; the moving speed was 5 mm/s.
And after the blank body is formed, carrying out freeze drying treatment on the blank body to remove the organic solvent in the blank body. The vacuum degree adopted in the freeze drying process is 1Pa, and the freezing conditions are as follows: at-50-30 deg.C, one temperature section is set at 5 deg.C intervals, and each temperature section is kept constant for 3 hr.
And (3) cracking the completely dried blank, heating to 1200 ℃ at the heating rate of 5 ℃/min in a vacuum atmosphere, and cracking for 2 hours at 1200 ℃ to obtain the product.
Example 2
The method is adopted to prepare the multi-scale porous silicon carbide ceramic with the complex three-dimensional structure by respectively taking polycarbosilane as a ceramic precursor and cyclooctane as an organic solvent.
Heating cyclooctane to above 14 deg.C to melt completely. Then 10 wt.% to 20 wt.% of polycarbosilane powder is added, and the powder is fully dissolved in cyclooctane under the action of magnetic stirring. Then 20 wt.% (mass ratio of cross-linker to ceramic precursor, same below) of divinylbenzene was added dropwise as cross-linker. And magnetically stirring for 3 hours at the temperature of 120 ℃ to promote the polycarbosilane to be partially crosslinked.
And then placing the slurry into a needle cylinder, heating the slurry to be more than 14 ℃ in the needle cylinder, and standing for 1-2h for defoaming treatment. And then adjusting the temperature of the needle cylinder to 4-14 ℃, and regulating the rheological property of the slurry to a proper range. Meanwhile, excess liquid nitrogen is poured into the lower end of the heat-conducting substrate to provide an oriented temperature field perpendicular to the substrate.
Then a needle with 200um aperture is loaded on the top of the syringe. And (4) performing direct-writing molding on the slurry to obtain a criss-cross three-dimensional structure on the heat-conducting substrate. Forming pressure is 20 PSI; the moving speed was 10 mm/s.
And after the blank body is formed, carrying out freeze drying treatment on the blank body to remove the organic solvent in the blank body. The vacuum degree adopted in the freeze drying process is 1Pa, and the freezing conditions are as follows: the temperature is kept constant for 3 hours at the temperature of minus 50 ℃ to minus 10 ℃ and at the interval of 5 ℃ for one temperature section.
And (3) cracking the completely dried blank, heating to 1200 ℃ at the heating rate of 5 ℃/min in a vacuum atmosphere, and cracking for 2 hours at 1200 ℃ to obtain the product.
Example 3
The method is adopted to prepare the multi-scale porous carbon-silicon-oxygen ternary ceramic with the complex three-dimensional structure by respectively taking the polyoxosilane as a ceramic precursor and the tert-butyl alcohol as an organic solvent.
T-butanol was heated to 28 ℃ or higher to melt it sufficiently. Then 10 wt.% to 20 wt.% of polysiloxane powder is added, and the powder is fully dissolved in the tertiary butanol under the action of magnetic stirring. 10-20 wt.% (mass ratio of cross-linker to ceramic precursor, same below) of dibutyltin dilaurate was then added dropwise as cross-linker. Magnetically stirring for 3h at 50-60 ℃ to promote the partial crosslinking of the polysiloxane.
And then placing the slurry into a needle cylinder, heating the slurry to be more than 28 ℃ in the needle cylinder, and standing for 1-2h for defoaming treatment. And then adjusting the temperature of the needle cylinder to 18-28 ℃, and regulating the rheological property of the slurry to a proper range. Meanwhile, excess liquid nitrogen is poured into the lower end of the heat-conducting substrate to provide an oriented temperature field perpendicular to the substrate.
Then a needle with the aperture of 300um is loaded at the top of the syringe. And (4) performing direct-writing molding on the slurry to obtain a criss-cross three-dimensional structure on the heat-conducting substrate. Forming pressure 40 PSI; the moving speed was 8 mm/s.
And after the blank body is formed, carrying out freeze drying treatment on the blank body to remove the organic solvent in the blank body. The vacuum degree adopted in the freeze drying process is 1Pa, and the freezing conditions are as follows: at the temperature of minus 50 ℃ to minus 5 ℃, 5 ℃ intervals are taken as temperature sections, and each section is kept at the constant temperature for 3 hours.
And (3) cracking the completely dried blank, heating to 1200 ℃ at the heating rate of 5 ℃/min in a vacuum atmosphere, and cracking for 2 hours at 1200 ℃ to obtain the product.
Example 4
The method is adopted to prepare the multi-scale porous carbon-silicon-oxygen ternary ceramic with the complex three-dimensional structure by respectively taking the polyborosilane as a ceramic precursor and the tertiary butanol as an organic solvent.
T-butanol was heated to 28 ℃ or higher to melt it sufficiently. Then 10 wt.% to 20 wt.% of polyborosilane powder is added, and the powder is fully dissolved in tert-butanol under the action of magnetic stirring. 10-20 wt.% (mass ratio of cross-linker to ceramic precursor, same below) of dibutyltin dilaurate was then added dropwise as cross-linker. Magnetically stirring for 3h at 50-60 ℃ to promote the polyborosilane to be partially crosslinked.
And then placing the slurry into a needle cylinder, heating the slurry to be more than 28 ℃ in the needle cylinder, and standing for 1-2h for defoaming treatment. And then adjusting the temperature of the needle cylinder to 18-28 ℃, and regulating the rheological property of the slurry to a proper range. Meanwhile, excess liquid nitrogen is poured into the lower end of the heat-conducting substrate to provide an oriented temperature field perpendicular to the substrate.
Then a needle with the aperture of 300um is loaded at the top of the syringe. And (4) performing direct-writing molding on the slurry to obtain a criss-cross three-dimensional structure on the heat-conducting substrate. Forming pressure 40 PSI; the moving speed was 8 mm/s.
And after the blank body is formed, carrying out freeze drying treatment on the blank body to remove the organic solvent in the blank body. The vacuum degree adopted in the freeze drying process is 1Pa, and the freezing conditions are as follows: at the temperature of minus 50 ℃ to minus 5 ℃, 5 ℃ intervals are taken as temperature sections, and each section is kept at the constant temperature for 3 hours.
And (3) cracking the completely dried blank, heating to 1200 ℃ at the heating rate of 5 ℃/min in a vacuum atmosphere, and cracking for 2 hours at 1200 ℃ to obtain the product.
Example 5
The method is adopted to prepare the multi-scale porous silicon carbide ceramic with the complex three-dimensional structure by respectively taking the polysilane as a ceramic precursor and the camphene as an organic solvent.
Heating camphene to over 35 ℃ to fully melt the camphene. Then adding 10 wt.% to 20 wt.% of polyazetasine powder, and fully dissolving the powder in camphene under the action of magnetic stirring. Then 20 wt.% (mass ratio of cross-linker to ceramic precursor, same below) of divinylbenzene was added dropwise as cross-linker. And magnetically stirring for 3 hours at the temperature of 120 ℃ to promote the partial crosslinking of the polysilazane.
And then placing the slurry into a needle cylinder, heating the slurry to over 35 ℃ in the needle cylinder, and standing for 1-2h for defoaming treatment. And then adjusting the temperature of the needle cylinder to 25-30 ℃, and regulating the rheological property of the slurry to a proper range. Meanwhile, excess liquid nitrogen is poured into the lower end of the heat-conducting substrate to provide an oriented temperature field perpendicular to the substrate.
Then a needle with 200um aperture is loaded on the top of the syringe. And (4) performing direct-writing molding on the slurry to obtain a criss-cross three-dimensional structure on the heat-conducting substrate. The molding pressure is 30 PSI; the moving speed was 5 mm/s.
And after the blank body is formed, carrying out freeze drying treatment on the blank body to remove the organic solvent in the blank body. The vacuum degree adopted in the freeze drying process is 1Pa, and the freezing conditions are as follows: at-50-30 deg.C, one temperature section is set at 5 deg.C intervals, and each temperature section is kept constant for 3 hr.
And (3) cracking the completely dried blank, heating to 1200 ℃ at the heating rate of 5 ℃/min in a vacuum atmosphere, and cracking for 2 hours at 1200 ℃ to obtain the product.
Example 6
5g of polycarbosilane was dissolved in 10g of camphene, and 1g of divinylbenzene was added as a crosslinking agent to prepare a slurry. Then oil bath at 130 ℃ for 2 h. The printed bodies were then freeze-dried using a 400um needle tip, with the macro-porous structure remaining very intact (see a in fig. 2 and a in fig. 3), and other operations were consistent with example 1.
Comparative example 1
5g of polycarbosilane is dissolved in 10g of camphene to prepare slurry. Then, the printed green body is subjected to freeze drying treatment by using a 400-micron needle nozzle, and then under the air atmosphere of 200 ℃, the green body is subjected to oxidation crosslinking for 2-8h, so that the green body is seriously cracked, and the integrity of a macro porous structure is damaged, as shown in figure 2 (B).
Comparative example 2
5g of polycarbosilane was dissolved in 10g of camphene, and 1g of divinylbenzene was added as a crosslinking agent to prepare a slurry. Oil bath was carried out at 100 ℃ for 1 h. And then, a 400-micron needle nozzle is adopted to perform cracking treatment on the printed blank, and the blank is locally melted due to insufficient crosslinking, so that the microstructure appearance of the blank is seriously damaged, as shown in fig. 3 (B).
Comparative example 3
5g of polycarbosilane was dissolved in 10g of camphene, and 1g of divinylbenzene was added as a crosslinking agent to prepare a slurry. Oil bath was carried out at 150 ℃ for 4 h. The slurry is in a 'jelly' shape due to excessive crosslinking, and cannot be smoothly extruded from a needle nozzle. Therefore, when polycarbosilane, camphene or divinylbenzene is used, the chemical crosslinking temperature is preferably 130 ℃ and the crosslinking time is preferably 2 hours.
Other conditions of comparative examples 1, 2 and 3 were the same as those of example 6.

Claims (2)

1. A method for preparing bionic porous ceramic with a complex three-dimensional structure; the method is characterized by comprising the following steps:
when the polyoxosilane is used as a ceramic precursor and the tertiary butanol is used as an organic solvent; heating tert-butyl alcohol to over 28 deg.c to melt completely; then adding polyoxosilane powder with the total mass of 10-50 wt.% of the organic solvent, and fully dissolving the powder in tert-butyl alcohol under the action of magnetic stirring; then dropwise adding dibutyltin dilaurate which accounts for 10-100 wt% of the mass of the ceramic precursor as a cross-linking agent; magnetically stirring for 1-5h at 50-60 deg.C to promote partial cross-linking of polysiloxane; obtaining slurry;
then placing the slurry in a needle cylinder, heating the slurry in the needle cylinder to above 28 ℃, standing for 1-2h, and carrying out defoaming treatment; then adjusting the temperature of the needle cylinder to 18-28 ℃, and regulating the slurry to 1s-1The viscosity under the shearing rate is 500-1000 Pa.s, and the standby slurry is obtained; meanwhile, pouring excessive liquid nitrogen into the lower end of the heat-conducting substrate to provide a directional temperature field vertical to the substrate; performing direct writing molding on the standby slurry, and printing a set three-dimensional structure to obtain a semi-finished product;
or
When polyborosilane is used as a ceramic precursor and tert-butyl alcohol is used as an organic solvent, heating the tert-butyl alcohol to be more than 28 ℃ so as to fully melt the tert-butyl alcohol; then adding polyborosilane powder with the total mass of 10-50 wt.% of the organic solvent, and fully dissolving the polyborosilane powder in tert-butyl alcohol under the action of magnetic stirring; then dropwise adding dibutyltin dilaurate which accounts for 10-100 wt% of the mass of the ceramic precursor as a cross-linking agent; magnetically stirring for 1-5h at 50-60 ℃ to promote partial cross-linking of polyborosilane; obtaining slurry;
then placing the slurry in a needle cylinder, heating the slurry in the needle cylinder to above 28 ℃, standing for 1-2h, and carrying out defoaming treatment; then adjusting the temperature of the needle cylinder to 18-28 ℃, and regulating the slurry to 1s-1The viscosity under the shearing rate is 500-1000 Pa.s, and the standby slurry is obtained; meanwhile, pouring excessive liquid nitrogen into the lower end of the heat-conducting substrate to provide a directional temperature field vertical to the substrate; performing direct writing molding on the standby slurry, and printing a set three-dimensional structure to obtain a semi-finished product;
fully freezing and solidifying the obtained semi-finished product in a temperature field; placing the mixture in a freeze dryer, and drying the mixture for 24 to 48 hours in an environment with the temperature of 0 to 60 ℃ and the air pressure of 1 to 10Pa until the organic solvent is completely sublimated; and then placing the blank in a protective atmosphere, and cracking at 1000-1400 ℃ for at least 1h to obtain the 3D ceramic with the multi-scale hole structure.
2. A method for preparing a complex three-dimensional structure ceramic having biomimetic porosity according to claim 1; the method is characterized in that:
connecting the needle cylinder with the degassed slurry with a needle head, a piston and an air duct, and then mounting the whole on a fixture on a Z axis; then, by means of the pattern of the three-dimensional structure required by computer-aided design, automatically controlling the pressure of a needle cylinder arranged on the Z axis through a computer, enabling the slurry to flow out of a needle nozzle and be deposited on an X-Y axis forming platform moving according to a program, and obtaining a first layer structure; thereafter, the Z-axis is moved or rotated precisely upwards to a height determined by the structural solution, and the second layer formation will be carried out on the first layer structure; then, obtaining a complex three-dimensional structure in a layer-by-layer superposition mode; the pressure range is 1~1000PSI, and the speed of the removal of shaping platform is 0.1~500 mm/s.
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