A method and system for preparing a multi-scale heterogeneous structure ceramic

Abstract

The application provides a preparation method and system of a multi-scale heterogeneous structure ceramic, and belongs to the field of ceramic manufacturing.The preparation method of the multi-scale heterogeneous structure ceramic comprises the following steps: preparing a green body from ceramic powder; removing the organic component from the green body to obtain a degummed body; placing the degummed body in conductive powder, and electrically sintering to obtain the multi-scale heterogeneous structure ceramic.The method can realize ultrafast heating sintering, the temperature of the sintering area is controllable and adjustable, and multi-scale heterogeneous structure ceramics with different shapes can be prepared, so the method has a wide application prospect.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of ceramic manufacturing, and relates to a preparation method and system of a heterogeneous structure ceramic, in particular to a preparation method and system of a multi-scale heterogeneous structure ceramic. BACKGROUND

[0002] Heterogeneous structure ceramic refers to a ceramic material with special macroscopic or microscopic organizational structure or phase distribution. The traditional preparation process of ceramic materials is mainly kiln sintering method, which makes the green body re-crystallize by high temperature generated by the kiln to form a dense ceramic structure. The traditional sintering method has the following five disadvantages: first, it takes a long time to sinter, which takes several hours or even several days, and the slow heating speed is one of the key factors leading to long sintering time, resulting in low efficiency of ceramic manufacturing; second, the temperature is low, and it is difficult to reach a temperature higher than 2000℃ by kiln sintering method, which is lower than the melting temperature of some high melting point powders, and it is impossible to melt high melting point powders; third, it is difficult to control the temperature, and the repeatability is poor, and it is difficult to accurately control the temperature; fourth, it is impossible to apply different temperatures to different regions of the green body, and it is more difficult to prepare heterogeneous structure ceramics containing multiple different grain sizes; fifth, the applicability is poor, and it is difficult to realize the heterogeneous structure preparation of ceramic products with different shapes and macroscopic configurations due to the heating structure.

[0003] The article "Ultrafast High-temperature Sintering of Asymmetrically Graded YSZ Ceramics" (China Ceramics 58.10 (2022): 14-23) discloses a preparation method of ultrafast high-temperature sintering of asymmetrically graded yttrium-stabilized zirconia (YSZ) ceramics. The method places the sample on a single carbon strip, and the joule heat generated by the single carbon strip is conducted from the lower to the upper surface of the sample and the carbon strip, and the preparation of the gradient material is completed through the temperature gradient formed in the green body during the conduction process. However, this method cannot prepare ceramic materials with macroscopic three-dimensional structures.

[0004] Chinese patent application 202210024459.X discloses a preparation method of a ceramic material with gradient distribution of grain size. The method places the YSZ ceramic green body on the heating table and directly applies electricity to the green body, and the temperature is raised to 300-1200℃ at a rate of 1-50℃, and the holding time is 1-10h. This method can realize the gradient change of the grain size of the ceramic, and also reduces the sintering temperature of the ceramic material through the joint action of the electric field, magnetic field and thermal field, but the heating speed is slow and the whole preparation time is still long.

[0005] Chinese patent application 202211362701.0 discloses a preparation method of a heterogeneous stacked co-fired ferrite ceramic. This method uses different powders to construct a heterogeneous ceramic structure by layering, and the sintering temperature of the entire structure is the same, which cannot obtain a heterogeneous structure with different grain sizes of the same chemical composition ceramic by controlling the different sintering temperatures of different regions.

[0006] Chinese patent application 202110705871.3 discloses a multi-gradient yttrium oxide type shell and a preparation method thereof. This method uses yttrium oxide particles of different sizes to construct a green body using 3D printing technology, and claims to obtain a gradient structure ceramic material with gradually increasing grain size and pore size. However, the grain size and pore size obtained by this method are limited by the size of the yttrium oxide used, and the grain size at different positions cannot be arbitrarily adjusted during the experiment, and the sintering time needs 20-100h, which is still relatively long.

[0007] In summary, for the preparation of multi-scale heterogeneous structure ceramics, the existing technology has the problems of long sintering time, poor controllability of thermal process, poor universality of sample shape and macroscopic configuration, and difficulty in controlling different microstructures at different positions of the ceramic green body, which need to be solved. SUMMARY

[0008] Therefore, in view of the problems of long sintering time, poor controllability of reaction conditions, and difficulty in controlling different grain sizes of microstructure at different positions of the ceramic green body in the prior art for preparing multi-scale heterogeneous structure ceramics, the purpose of the present application is to provide a preparation method and system for multi-scale heterogeneous structure ceramics.

[0009] To achieve the above-mentioned purpose of the application, the present application provides a preparation method for multi-scale heterogeneous structure ceramics, comprising the following steps:

[0010] S1, preparing a green body: preparing a ceramic powder into a green body;

[0011] S2, preparing a degreased green body: removing the organic component from the green body prepared in step S1 to obtain a degreased green body;

[0012] S3, sintering: placing the degreased green body prepared in step S2 in a conductive powder, and sintering by electricity to obtain a heterogeneous structure ceramic;

[0013] Among them, the conductive powder is a conductive powder with unequal average particle size or a conductive powder containing a dopant.

[0014] Among them, the source of the ceramic powder in step S1 is not limited, that is, the source of the ceramic powder includes but is not limited to natural ceramic powder, commercial ceramic powder, self-made ceramic powder, self-processed ceramic powder, etc.

[0015] The ceramic powder in step S1 includes but is not limited to silicon carbide powder, alumina powder, silicon nitride powder, boron carbide powder, etc.

[0016] Preferably, the ceramic powder in step S1 includes at least one of silicon carbide powder, alumina powder, silicon nitride powder, and boron carbide powder.

[0017] More preferably, the ceramic powder in step S1 is one of silicon carbide powder, alumina powder, silicon nitride powder, and boron carbide powder.

[0018] Further preferably, the ceramic powder in step S1 is silicon carbide powder or alumina powder.

[0019] As a preferred embodiment of the present application, the ceramic powder in step S1 is silicon carbide powder.

[0020] As a preferred embodiment of the present application, the ceramic powder in step S1 is alumina powder.

[0021] Preferably, the melting point of the ceramic powder in step S1 is ≥1750℃.

[0022] Preferably, the preparation method of the green body in step S1 is selected from at least one of dry pressing, slip casting, tape casting, and 3D printing.

[0023] More preferably, the preparation method of the green body in step S1 is selected from one of dry pressing, slip casting, tape casting, and 3D printing.

[0024] Further preferably, the preparation method of the green body in step S1 is selected from one of dry pressing and 3D printing.

[0025] As a preferred scheme of the present application, the preparation method of the green body in step S1 is dry pressing.

[0026] Preferably, the dry pressing includes the following steps:

[0027] The ceramic powder is bonded with an organic binder and granulated to obtain granulated powder; the granulated powder is placed in a mold and subjected to preliminary dry pressing to obtain a preliminary dry-pressed body; the preliminary dry-pressed body is vacuum sealed and cold isostatic pressed to obtain a green body.

[0028] Preferably, the ceramic powder is silicon carbide powder.

[0029] More preferably, the particle size of the silicon carbide powder is 0.45μm.

[0030] Preferably, the type of the organic binder is selected from at least one of polyethylene glycol, paraffin, and polyethylene.

[0031] Preferably, the mass ratio of the ceramic powder to the organic binder is 60wt%:40wt%.

[0032] Preferably, the average particle size of the granulated powder is 80μm.

[0033] Preferably, the size of the mold is 50mmx50mm.

[0034] Preferably, the mold is a square mold.

[0035] Preferably, the preliminary dry pressing is performed at a uniaxial pressure of 20MPa.

[0036] Preferably, the vacuum sealing is performed by placing the preliminary dry-pressed body in a vacuum sealing bag and sealing the bag with a vacuum sealing machine.

[0037] Preferably, the cold isostatic pressing is performed by using a cold isostatic pressing machine at a pressure of 200-250MPa.

[0038] More preferably, and as a specific embodiment of the present application, the pressure of the cold isostatic pressing is 250MPa.

[0039] Preferably, the cold isostatic pressing is followed by shaping, which is selected from at least one of cutting, grinding and polishing.

[0040] As a preferred scheme of the present application, the method for preparing the ceramic green body in step S1 is a 3D printing method.

[0041] Preferably, the 3D printing method comprises the following steps:

[0042] The surface of the ceramic powder is modified to obtain a modified ceramic powder; the modified ceramic powder, a dispersing agent, a monomer, a photoinitiator and an additive are mixed to obtain a 3D printing raw material; the 3D printing raw material is introduced into a forming device of a 3D printer, the parameters of the 3D printer are set, and 3D printing is performed according to model slices to obtain a body.

[0043] Preferably, the ceramic powder is an alumina powder.

[0044] More preferably, the average particle size of the alumina powder is 100nm.

[0045] Preferably, the surface modification is performed by placing the powder, oleic acid, grinding balls and anhydrous ethanol in a ball mill jar, performing planetary ball milling at a speed of 250r / min for 120min, rotary evaporation, drying and sieving to obtain the modified ceramic powder.

[0046] More preferably, the mass ratio of the powder, oleic acid, grinding ball, anhydrous ethanol is 19.8%:0.2%:40%:40%, and the size of the grinding ball is 5mm diameter alumina grinding ball.

[0047] Preferably, the dispersant is at least one selected from BYK9077, BYK9076.

[0048] Preferably, the monomer is at least one selected from 1,6-ethanediol diacrylate, polyurethane acrylate, pentaerythritol tetraacrylate.

[0049] More preferably, the monomer is a mixture of 1,6-ethanediol diacrylate, polyurethane acrylate, pentaerythritol tetraacrylate.

[0050] Preferably, the photoinitiator is one selected from diphenyl ketone, alpha-diethoxy phenyl ketone, irgacure 819.

[0051] Preferably, the auxiliary agent is a mixture of polyethylene glycol and n-octanol.

[0052] Preferably, the mixing process is specifically: adding the modified ceramic powder and the dispersant into the mixture of the monomer and the auxiliary agent, rotating in the high-speed homogenizer at 2500rpm for 4min, and then adding the photoinitiator.

[0053] Preferably, the 3D printer parameters are specifically: layer thickness 10-30μm, single layer solidification time 1-3s, maximum power density 5-20mW / cm 2 .

[0054] More preferably, and as a specific embodiment of the present application, the 3D printer parameters are specifically: layer thickness 20μm, single layer solidification time 1.2s, maximum power density 12mW / cm 2 .

[0055] Preferably, the method of removing the organic component is at least one selected from preliminary debinding and degreasing.

[0056] Preferably, the preliminary debinding is specifically: placing the green body to rise to 600-1000℃ at a heating rate of 1℃ / min, and keeping the temperature for 100-120min.

[0057] More preferably, and as a specific embodiment of the present application, the preliminary debinding is specifically: placing the green body to rise to 600℃ at a heating rate of 1℃ / min, and keeping the temperature for 120min.

[0058] More preferably, the atmosphere of the preliminary debinding is argon atmosphere.

[0059] Preferably, the debinding is specifically as follows: the green body or the green body after the initial degumming is raised to 600-800℃ at a temperature raising rate of 1-5℃ / min, and is kept for 1-2h.

[0060] More preferably, and as a specific embodiment of the present application, the debinding step is specifically as follows:

[0061] The green body after the initial degumming is placed in a muffle furnace in an air atmosphere, and is raised to 600℃ at a temperature raising rate of 1℃ / min, kept for 120min, and is cooled with the furnace, and then it is placed in a muffle furnace in an air atmosphere, and is raised to 800℃ at a temperature raising rate of 5℃ / min, kept for 120min, so as to remove the organic matter in the green body as much as possible.

[0062] More preferably, and as a specific embodiment of the present application, the debinding step is specifically as follows:

[0063] The green body is placed in a vacuum tube furnace, and is raised to 700℃ at a temperature raising rate of 5℃ / min under an argon atmosphere, kept for 1-2h, and is cooled with the furnace.

[0064] Preferably, the conductive powder is selected from graphite powder.

[0065] More preferably, and as a specific embodiment of the present application, the conductive powder is graphite powder.

[0066] Preferably, the debinding green body in step S3 is placed in the conductive powder specifically as follows: the debinding green body is entirely buried in the conductive powder.

[0067] Preferably, in step S3, the conductive powder is two kinds of conductive powders with different average particle sizes.

[0068] Preferably, the debinding green body is buried in two kinds of conductive powders with different average particle sizes, and the average particle sizes of the two kinds of conductive powders with different average particle sizes are respectively selected from 100-200μm and 30-80μm.

[0069] Further preferably, and as a specific embodiment of the present application, the average particle sizes of the two kinds of conductive powders with different average particle sizes are respectively 44μm and 150μm.

[0070] More further preferably, the debinding green body is buried in two kinds of conductive powders with different average particle sizes specifically as follows: the sample is buried in graphite powder with an average particle size of 150μm at the two end regions, and is buried in graphite powder with a median particle size of 44μm in the middle part.

[0071] Preferably, the conductive powder is a conductive powder containing a dopant.

[0072] Preferably, the mass content of the dopant is 0.1-3%.

[0073] As a specific embodiment of the present application, the conductive powder is uniformly doped with a dopant with a mass content of 0.1%.

[0074] The dopant is a metal element, a metal oxide and / or a solid non-metal oxide.

[0075] Preferably, the dopant is selected from at least one of ferriferrous oxide, yttrium oxide, aluminum oxide, silicon dioxide, aluminum, magnesium and zirconium.

[0076] More preferably, the dopant is selected from one of ferriferrous oxide, yttrium oxide, aluminum oxide, silicon dioxide, aluminum, magnesium and zirconium.

[0077] Further preferably, and as a specific embodiment of the present application, the dopant is ferriferrous oxide.

[0078] Preferably, the particle size of the dopant is 50 nm-20 μm.

[0079] More preferably, the particle size of the dopant is 5 μm-20 μm.

[0080] Further preferably, and as a specific embodiment of the present application, the particle size of the dopant is 10 μm.

[0081] Preferably, the process of electric current sintering in step S3 is specifically:

[0082] The atmosphere in the reaction chamber is an inert gas, and the conductive powder is subjected to electric current through electrodes, the maximum electric current is 10-100 A, the temperature rising rate is 400-1500 ℃ / min, the sintering temperature is 1500-2000 ℃, and the holding time is 240-600 s.

[0083] More preferably, the inert gas is selected from at least one of helium, neon, argon, krypton and xenon.

[0084] Further preferably, and as a specific embodiment of the present application, the inert gas is argon.

[0085] More preferably, the pressure of the inert gas is 1 atm.

[0086] More preferably, the maximum electric current is 10-100 A.

[0087] Further preferably, the maximum electric current is 10-60 A.

[0088] As a specific embodiment of the present application, the maximum electric current is 30 A.

[0089] As a specific embodiment of the present application, the maximum electric current is 55 A.

[0090] More preferably, the temperature rising rate is 400-1500℃ / min.

[0091] More preferably, the temperature rising rate is 400-1000℃ / min.

[0092] As a specific embodiment of the present application, the temperature rising rate is 485℃ / min.

[0093] As a specific embodiment of the present application, the temperature rising rate is 770℃ / min.

[0094] More preferably, the sintering temperature is 1500-2300℃.

[0095] More preferably, the sintering temperature is 1800-2200℃.

[0096] As a specific embodiment of the present application, the sintering temperature is 2000℃.

[0097] As a specific embodiment of the present application, the sintering temperature is 2140℃.

[0098] More preferably, the holding time is 30-500s.

[0099] More preferably, the holding time is 30-400s.

[0100] As a specific embodiment of the present application, the holding time is 80s.

[0101] As a specific embodiment of the present application, the holding time is 300s.

[0102] More preferably, the power supply is direct current.

[0103] More preferably, the current of the direct current is freely adjustable within a range not exceeding the maximum current.

[0104] In another aspect, the present application provides a heterostructure ceramic prepared by the above method.

[0105] Preferably, the heterostructure ceramic comprises a microstructure of two different types of grains.

[0106] More preferably, the heterostructure ceramic consists of a microstructure of two different types of grains.

[0107] Preferably, the average Vickers hardness of the heterostructure ceramic is 14-25GPa.

[0108] More preferably, the average Vickers hardness of the heterostructure ceramic is 19-23GPa.

[0109] Preferably, the relative density of the heterogeneous structure ceramic is 90%-96%.

[0110] More preferably, the relative density of the heterogeneous structure ceramic is 94%-96%.

[0111] In another aspect, the present application also provides a preparation system of a multi-scale heterogeneous structure ceramic, which comprises a reaction chamber, conductive powder placed inside the reaction chamber, and electrodes inserted into the conductive powder at both ends of the reaction chamber.

[0112] Compared with the prior art, the present application has the following beneficial effects:

[0113] (1) The preparation method of the heterogeneous structure ceramic has a fast heating and cooling speed (up to 1200℃ / min at the fastest), and a high heating temperature (up to 2140℃ at the highest), which greatly shortens the sintering time compared with the traditional furnace sintering method, and is beneficial to the ultra-fast sintering of ceramic powder with an ultra-high melting point.

[0114] (2) The present application realizes the preparation of a heterogeneous structure ceramic containing at least two different types of grain structures by adjusting the particle size and distribution of the conductive powder, the type and content of the dopant in the conductive powder, and the current intensity and waveform, which is simple and adjustable, greatly facilitates the preparation of heterogeneous structure ceramic materials, and is beneficial to the popularization and application of heterogeneous structure ceramics.

[0115] (3) The preparation method of the heterogeneous structure ceramic can be used to prepare ceramic devices with different macroscopic structures, such as ceramic cutters and ceramic heat exchangers, which have strong versatility and are beneficial to the production of heterogeneous structure ceramic devices of various shapes, and have broad application prospects. BRIEF DESCRIPTION OF DRAWINGS

[0116] Figure 1 Figure 1 is a schematic diagram of sintering a degumming blank using conductive powder with different particle sizes in Example 1, wherein the meanings of the respective numbers are as follows: 1 reaction chamber, 2 graphite powder with an average particle size of 150μm, 3 electrode, 4 graphite powder with an average particle size of 44μm, and 5 degumming blank.

[0117] Figure 2 Figure 2 is a schematic diagram of the microstructure of different regions of silicon carbide ceramic in Example 1, wherein the microstructure photos are SEM photos, the lower left is the microstructure of the middle region of the silicon carbide ceramic, and the lower right is the microstructure of the end region of the silicon carbide ceramic.

[0118] Figure 3 Figure 3 is a schematic diagram of sintering a degumming blank using conductive powder doped with a dopant in Example 2, wherein the meanings of the respective numbers are as follows: 1 reaction chamber, 2 graphite powder doped with 0.1% mass content of magnetite, 3 electrode, and 4 degumming blank.

[0119] Figure 4 is a schematic view of the shape of the alumina ceramic prepared by the method described in Example 2.

[0120] Figure 5 is a SEM image of the microstructure gradient variation of the alumina ceramic prepared in Example 2.

[0121] Figure 6 is a waveform diagram of the current size of the direct current over time in Examples 1 and 2. DETAILED DESCRIPTION

[0122] The following non-limiting examples can make those of ordinary skill in the art more fully understand the present application, but in no way limit the present application. The following content is only an exemplary description of the scope of the present application claimed by the person skilled in the art can make various changes and modifications to the application disclosed in the present application, and it should also belong to the scope of the present application claimed.

[0123] The present application is further described in the following specific examples. The various chemical reagents used in the examples of the present application are obtained by conventional commercial routes unless otherwise specified. If not otherwise specified, the content described below is the mass content. If not otherwise specified, it is understood to be carried out at room temperature.

[0124] In the following examples, the raw materials are as follows:

[0125] Name Manufacturer Alumina Japan Daming Chemical Industry Co., Ltd. Anhydrous ethanol National Pharmaceutical Group Chemical Reagent Co., Ltd. Oleic acid National Pharmaceutical Group Chemical Reagent Co., Ltd. Dispersant BYK9077 Germany BYK Group Co., Ltd. Photoinitiator irgacure819 Germany BASF SE 1,6-ethanediol diacrylate Shanghai Guangyi Chemical Co., Ltd. Polyurethane acrylate Shanghai Guangyi Chemical Co., Ltd. Pentaerythritol tetraacrylate Shanghai Guangyi Chemical Co., Ltd. Polyethylene glycol PEG300 Shanghai Guangyi Chemical Co., Ltd. n-octanol Shanghai Aladdin Biochemical Technology Co., Ltd. Ferrosoferric oxide Hebei Yaha Mineral Products Co., Ltd. Graphite Beijing Jinglong Special Carbon Co., Ltd. Silicon carbide powder Weifang Kaihua Silicon Carbide Powder Co., Ltd. Organic binder Shanghai Aladdin Biochemical Technology Co., Ltd.

[0126] In the following examples, the characterization method of the properties of the heterostructure ceramic is as follows:

[0127]

[0128] Among them, the definition of relative density is that the actual density of the ceramic sample accounts for the percentage of the theoretical density, and the calculation formula is as follows.

[0129] Relative density = actual density ÷ theoretical density x 100%.

[0130] Example 1

[0131] A method for preparing a silicon carbide heterostructure ceramic, the specific process is as follows.

[0132] S1, preparing a green body. 45 g of commercially available silicon carbide powder with an average particle size of 0.45 μm was mixed with 15 g of an organic binder to form a mixture, and the mixture was subjected to adhesion. The mixture was granulated by a spray-drying granulation method. Then, 30 g of the granulated powder was placed in a square mold with a size of 50 mm x 50 mm x 40 mm, and a tablet press was used to perform a preliminary dry pressing under a uniaxial pressure of 20 MPa to obtain a preliminary dry-pressed body. The preliminary dry-pressed body was placed in a vacuum bag, and the vacuum bag was sealed by a vacuum sealing machine. Subsequently, a cold isostatic pressing machine was used to perform cold isostatic pressing under a pressure of 250 MPa to obtain a cold isostatic pressed green body. The cold isostatic pressed green body was ground to obtain a green body with a size of 10 mm x 10 mm x 25 mm in a cuboid shape.

[0133] S2, preparing a degreased body. The green body was placed in a vacuum tube furnace, and the temperature was increased to 700°C at a rate of 5°C / min under an argon atmosphere. The temperature was maintained for 1-2 h, and the furnace was cooled to obtain a silicon carbide degreased body.

[0134] S3, sintering. Sintering was performed using an ultrafast high-temperature heating device as shown in Figure 1 . The degreased body was buried between two electrodes, and the two end regions of the degreased body were buried in large-particle graphite powder with an average particle size of 150 μm, and the middle part of the degreased body was buried in fine-particle graphite powder with an average particle size of 44 μm. The reaction chamber was evacuated, and the entire sintering process was performed under an argon atmosphere at 1 atm. Direct current was passed through the electrodes located at both ends of the reaction chamber and inserted into the conductive powder. The maximum current of the applied direct current was 55 A, the average temperature rise rate from room temperature was 770°C / min, the sintering temperature was 2140°C, and the holding time was 300 s. During the above-mentioned direct current sintering process, the waveform of the applied current varied with time as shown in Figure 6 .

[0135] During the above-mentioned sintering process, Joule heat was generated by the graphite powder to achieve ultrafast heating. Because the particle sizes of the graphite powder between the electrodes were different, the resistances were different. By controlling the current waveform, different temperature field distribution forms can be formed to jointly promote the formation of a phase composition with a 4H phase-rich structure at both ends and a 6H phase-rich structure in the middle of the silicon carbide ceramic.

[0136] The silicon carbide heterogeneous structure ceramic was successfully prepared by the above-mentioned preparation method. The relative density was 96%, the Vickers hardness was 21.1 ± 1.6 Gpa, and the resistivity was 36 mΩ·cm. The ceramic had a cuboid shape as shown in Figure 2 , and the microstructure of the two ends of the sample was mainly long rod-shaped grains, and the microstructure of the middle part of the sample was mainly equiaxed grains. The average temperature rise rate from room temperature reached 770°C / min, the sintering temperature was 2140°C, and the holding time was 300 s, and the sintering was completed, realizing the preparation of an ultrafast high-melting-point silicon carbide heterogeneous structure ceramic.

[0137] Example 2

[0138] A method for preparing an aluminum oxide heterogeneous structure ceramic, the specific process is as follows.

[0139] S1, preparing a green body. A ceramic green body is prepared by 3D printing. The specific process is as follows:

[0140] Micron-sized alumina powder, oleic acid, grinding balls, and anhydrous ethanol are uniformly mixed in a mass ratio of 19.8%:0.2%:40%:40%, and then placed in a ball mill tank. The rotation speed is 250 rpm, and the planetary ball milling is performed for 120 min. The mixed solution after ball milling is rotary evaporated, dried, and sieved to obtain modified alumina powder. The 3D printing raw material is prepared according to the following table:

[0141] 1,6-hexanediol diacrylate, polyurethane acrylate, pentaerythritol tetraacrylate, polyethylene glycol 4000, and n-octanol are mixed in a mass ratio of 5:4:4:3:4. The above mixture is mixed with dispersant BYK9077 in a mass ratio of 98:2 to obtain a mixed solution. The mixed solution is mixed with the modified alumina powder in a volume ratio of 13:12, and the mixture is rotated in a high-speed homogenizer at 2500 rpm for 4 min to obtain an alumina ceramic slurry. The alumina ceramic slurry is mixed with a photoinitiator irgacure819 in a mass ratio of 99:1 to obtain a 3D printing raw material.

[0142] The 3D printing raw material is introduced into the forming equipment of the 3D printer, and the 3D printing parameters of the 3D printer are set. The 3D printing is performed according to the model slices to obtain a green body. The 3D printing parameters are as follows: layer thickness 20 μm, single layer solidification time 1.2 s, and maximum power density 12 mW / cm 2 . The model is a heat exchanger-shaped structure as shown in Figure 4 .

[0143] S2, preparing a degreasing green body. It includes two parts of initial degreasing and debinding.

[0144] Initial degreasing: the 3D formed green body is placed in a tube furnace, and the temperature is raised to 600℃ at a rate of 1℃ / min in an argon atmosphere. The initial degreasing is completed after 120 min of heat preservation.

[0145] Debinding: after degreasing, the green body is placed in a muffle furnace in an air atmosphere, and the temperature is raised to 600℃ at a rate of 1℃ / min. The debinding is completed after 120 min of heat preservation. Then the green body is placed in a muffle furnace in an air atmosphere, and the temperature is raised to 800℃ at a rate of 5℃ / min. The green body is heat preserved for 120 min to obtain a degreasing green body. The purpose of this step is to remove as much organic matter as possible from the green body.

[0146] S3, sintering. The sintering is performed according to the method as shown in Figure 3The superfast high-temperature heating device shown is used for sintering. The degummed blank is buried in graphite powder containing a uniform doping mass content of 0.1% ferroferric oxide dopant. The reaction chamber is exhausted of air, and the entire sintering process is carried out under an argon atmosphere of 1 atm. Direct current is passed through electrodes located at both ends of the reaction chamber and inserted into the conductive powder, with a maximum current of 30 A, an average temperature rise rate of 485°C / min starting at room temperature, a sintering temperature of 2000°C, and a holding time of 80 s. During the above-mentioned direct current sintering process, the waveform of the current size changing with time is as shown in Figure 6 .

[0147] During the above-mentioned sintering process, Joule heat is generated by the graphite powder to achieve superfast heating. Under the action of superfast heating, the chemical components doped therein are rapidly liquefied or vaporized, and rapid infiltration, diffusion, deposition, and reaction of the ceramic green body are formed, inducing the formation of a microstructure morphology or phase distribution with a heterogeneous structure, and completing the preparation of a sample with a heterogeneous structure.

[0148] An alumina heterogeneous structure ceramic is successfully prepared by the above-mentioned preparation method, with a relative density of 95% and a Vickers hardness of 19.74±1.63 GPa. The ceramic has a honeycomb shape as shown in Figure 4 , and the microstructure of the ceramic is observed to have a gradient distribution of grain size and densification as shown in Figure 5 . The average temperature rise rate starting at room temperature reaches 485°C / min, the sintering temperature is 2000°C, and the holding time is 80 s, which completes the sintering and realizes the preparation of a superfast high-melting-point alumina heterogeneous structure ceramic.

[0149] Example 3

[0150] Compared with Example 1, in step S1, the commercially available silicon carbide powder is replaced by commercially available liquid-phase silicon nitride ceramic powder, and the rest is the same.

[0151] A liquid-phase silicon nitride heterogeneous structure ceramic is successfully prepared by the above-mentioned preparation method, with a relative density of 91.62% and a Vickers hardness of 14.5±1.57 GPa. The ceramic has a cuboid shape as shown in Figure 2 , and the microstructure of the sample at both ends is mainly long rod-shaped grains, and the microstructure of the sample in the middle is mainly equiaxed grains. The average temperature rise rate starting at room temperature reaches 875°C / min, the sintering temperature is 1750°C, and the holding time is 120 s, which completes the sintering and realizes the preparation of a superfast high-melting-point liquid-phase silicon nitride heterogeneous structure ceramic.

[0152] Example 4

[0153] Compared with Example 1, the graphite powder with an average particle size of 150 μm in step S3 is replaced with graphite powder with an average particle size of 80 μm, and the graphite powder with an average particle size of 44 μm is replaced with graphite powder with an average particle size of 30 μm, and the rest is the same.

[0154] The silicon carbide heterostructure ceramic is successfully prepared by the above preparation method, the relative density is 92%, and the Vickers hardness is 19.54±1.18 Gpa. The ceramic is in the shape of a cuboid, and the phase composition at both ends of the sample is mainly rich in 4H phase structure, and the phase composition in the middle of the sample is mainly rich in 6H phase structure. The average temperature rising speed at room temperature reaches 1200 ℃ / min, the sintering temperature is 2140 ℃, and the sintering can be completed by keeping the temperature for 300 s, so that the preparation of the super-fast high-melting-point silicon carbide heterostructure ceramic is realized.

[0155] Example 5

[0156] Compared with Example 1, the graphite powder with an average particle size of 150 μm in step S3 is replaced with graphite powder with an average particle size of 325 μm, and the graphite powder with an average particle size of 44 μm is replaced with graphite powder with an average particle size of 200 μm, and the rest is the same.

[0157] The silicon carbide heterostructure ceramic is successfully prepared by the above preparation method, the relative density is 95%, and the Vickers hardness is 22.77±1.69 Gpa. The ceramic is in the shape of a cuboid, and the phase composition at both ends of the sample is mainly rich in 4H phase structure, and the phase composition in the middle of the sample is mainly rich in 6H phase structure. The average temperature rising speed at room temperature reaches 1000 ℃ / min, the sintering temperature is 2140 ℃, and the sintering can be completed by keeping the temperature for 300 s, so that the preparation of the super-fast high-melting-point silicon carbide heterostructure ceramic is realized.

[0158] Example 6

[0159] Compared with Example 2, in step S1, the micron-sized alumina powder is replaced with commercially available silicon carbide powder with a particle size of 0.45 μm, and in step S3, the dopant is replaced with yttria with a particle size of about 50 nm and a mass content of 0.5% and alumina with a particle size of about 50 nm and a mass content of 0.5%, and the rest is the same.

[0160] The silicon carbide heterostructure ceramic is successfully prepared by the above preparation method, the relative density is 93.7%, and the Vickers hardness is 19.78±1.35 Gpa. The average temperature rising speed at room temperature reaches 800 ℃ / min, the sintering temperature is 2000 ℃, and the sintering can be completed by keeping the temperature for 300 s, so that the preparation of the super-fast high-melting-point silicon carbide heterostructure ceramic is realized.

[0161] Example 7

[0162] Compared with Example 2, in step S1, the micron-sized alumina powder is replaced by 0.45 μm commercially available silicon carbide powder, and in step S3, the doping body is replaced by 1% by mass of yttrium oxide with a particle size of about 0.1 μm, 1% by mass of alumina with a particle size of about 0.1 μm, and 1% by mass of silicon dioxide with a particle size of about 0.1 μm, and the rest is the same.

[0163] The silicon carbide heterostructure ceramic is successfully prepared by the above preparation method, has a relative density of 94.6%, and a Vickers hardness of 20.78±1.67 Gpa. The average temperature rising speed at room temperature is 800 ℃ / min, the sintering temperature is 1950 ℃, and the sintering is completed after 300 s of holding, so that the preparation of the super-fast high-melting-point silicon carbide heterostructure ceramic is realized.

[0164] Example 8

[0165] Compared with Example 2, in step S1, the micron-sized alumina powder is replaced by 0.45 μm commercially available silicon carbide powder, and in step S3, the doping body is replaced by 1% by mass of aluminum and 1% by mass of magnesium, and the rest is the same.

[0166] The silicon carbide heterostructure ceramic is successfully prepared by the above preparation method, has a relative density of 92.6%, and a Vickers hardness of 20.18±1.37 Gpa. The average temperature rising speed at room temperature is 830 ℃ / min, the sintering temperature is 1950 ℃, and the sintering is completed after 300 s of holding, so that the preparation of the super-fast high-melting-point silicon carbide heterostructure ceramic is realized.

[0167] In the above examples, the experimental conditions and part of the experimental results of each example are as follows.

[0168]

[0169] As can be seen from the above results, the preparation method and system provided by the application can realize the unification of short holding time, high sintering temperature, and high temperature rising speed, and successfully prepare ceramic materials with high relative density and high Vickers hardness.

[0170] Finally, it should be noted that the above content is only used to illustrate the technical solutions of the application, and is not a limitation on the protection scope of the application. Simple modifications or equivalent replacements of the technical solutions of the application made by those skilled in the art do not deviate from the essence and scope of the technical solutions of the application.

Claims

1. A method for preparing a multiscale heterogeneous structure ceramic, characterized by, The method comprises the following steps: S1, preparing a green body from ceramic powder; S2, removing the organic component from the green body prepared in step S1 to obtain a degummed body; S3, completely burying the degummed body prepared in step S2 in conductive powder, and electrically sintering to obtain a heterogeneous structure ceramic; The conductive powder is graphite powder with different average particle sizes or graphite powder containing a dopant; In step S3, the degummed body is completely buried in the conductive powder, specifically as follows: the sample is buried in graphite powder with an average particle size of 100-200 μm at both ends, and is buried in graphite powder with a median particle size of 30-80 μm in the middle part; The dopant is selected from at least one of ferric oxide, yttrium oxide, aluminum oxide, silicon dioxide, aluminum, magnesium, and zirconium; the heating rate of sintering is 400-1000 ℃ / min; The heterogeneous structure ceramic has a microstructure containing two different types of grains.

2. The production method according to claim 1, characterized by, The ceramic powder in step S1 includes at least one of silicon carbide powder, aluminum oxide powder, silicon nitride powder, and boron carbide powder, and is not limited to the above-mentioned ceramic powders; the preparation method of the green body is selected from at least one of dry pressing, slip casting, tape casting, and 3D printing.

3. The preparation method according to claim 1, characterized in that, The melting point of the ceramic powder in step S1 is ≥1750 ℃.

4. The method of claim 1, wherein, The method for removing the organic component in step S2 is selected from at least one of initial glue removal and degreasing; the initial glue removal is specifically as follows: the green body is heated to 600-1000 ℃ at a heating rate of 1 ℃ / min, and is kept at the temperature for 100-120 min; the degreasing is specifically as follows: the green body or the green body after initial glue removal is heated to 600-800 ℃ at a heating rate of 1-5 ℃ / min, and is kept at the temperature for 1-2 h.

5. The preparation method according to claim 1, characterized in that, The conductive powder in step S3 is graphite powder containing a dopant, and the mass content of the dopant is 0.1-3%.

6. The method of claim 1, wherein, The electric current of the direct current is freely adjustable within the maximum current range of not more than 10-100 A.

7. The preparation method according to claim 1, characterized in that, The preparation method is carried out in a preparation system composed of the following parts: a reaction chamber, conductive powder placed in the reaction chamber, and electrodes inserted into the conductive powder at both ends of the reaction chamber.

Images