A method for preparing fine-grained alumina ceramics

Abstract

This invention discloses a method for preparing fine-grained alumina ceramics, comprising the following steps: preparing a first grinding ball with attached material, wherein the first grinding ball is attached with alumina powder; a second grinding ball with attached material is attached with alumina powder and a second phase mixed powder; detaching the material attached to the second grinding ball from the grinding ball to obtain a first mixed material; grinding the first mixed material to obtain a second mixed material; preparing a primary slurry using the second mixed material and polyvinyl butyral; degassing the primary slurry to obtain a casting slurry; casting the casting slurry to obtain a sheet green body; stacking the sheet green bodies and then isostatically pressing them to obtain a block green body; debinding and sintering the block green body to obtain fine-grained alumina ceramics; thereby achieving a uniform internal structure, small grain size, and uniform grain size distribution in the prepared fine-grained alumina ceramics.

Description

Technical Field

[0001] This invention relates to the field of alumina ceramic preparation technology, and in particular to a method for preparing fine-grained alumina ceramic. Background Technology

[0002] Fine-grained alumina ceramics possess excellent physical properties and chemical stability, such as high strength, high hardness, high wear resistance, good thermal stability, and electrical properties, making them ideal materials for key components such as electrostatic chucks.

[0003] Current methods for preparing fine-grained alumina ceramics using extrusion molding or isostatic pressing suffer from problems such as wide grain distribution and inhomogeneous structure within the alumina ceramic. The main reasons are twofold: First, there is a conflict between powder particle size and agglomeration. When the particle size is too fine, the surface energy is high, and electrostatic and capillary action promotes the formation of soft agglomerates, leaving abnormally large grains after sintering. Conversely, slightly coarser particle sizes result in insufficient sintering driving force, leading to rapid grain coarsening and the loss of the fine-grained advantage. Second, the non-uniformity of the forming stress field further amplifies these defects. The extrusion shear gradient or isostatic pressing pressure decay causes spatial differences in the density of the green body. Differential shrinkage during sintering induces micropores and microcracks, making it difficult to achieve a uniform microstructure. Powder dispersion, forming density, and grain boundary migration are mutually constraining; any mismatch in any of these stages will leave structural defects spanning a wide range of dimensions in the final ceramic.

[0004] Therefore, how to simultaneously achieve fine, narrowly distributed, and uniform internal grains in the prepared fine-grained alumina ceramics has become a core challenge in the development of fine-grained alumina ceramic processes. Summary of the Invention

[0005] To address the aforementioned technical problems, this invention provides a method for preparing fine-grained alumina ceramics, which achieves a uniform internal structure, small grain size, and uniform grain size distribution in the prepared fine-grained alumina ceramics.

[0006] This invention provides a method for preparing fine-grained alumina ceramics, comprising the following steps:

[0007] Nano-alumina powder and polyvinylpyrrolidone are mixed in a ball mill to prepare a first-attached material grinding ball, which is coated with alumina powder.

[0008] Preparation of a second-phase mixed powder containing inorganic powder;

[0009] The second phase mixed powder and the first attached material grinding balls are mixed in a ball mill to prepare the second attached material grinding balls, which are coated with alumina powder and the second phase mixed powder.

[0010] The material attached to the second grinding ball is detached from the grinding ball to obtain the first mixture.

[0011] The first mixture is ground to obtain the second mixture;

[0012] A primary slurry is prepared by using a second mixture of materials and polyvinyl butyral.

[0013] The primary slurry is degassed to obtain a casting slurry;

[0014] The casting slurry is cast to obtain a sheet preform;

[0015] The sheet blanks are stacked and then warm isostatically pressed to obtain a block blank;

[0016] Fine-grained alumina ceramics are obtained by debinding and sintering the bulk blanks.

[0017] The volume resistivity of the prepared fine-grained alumina ceramics is 2.0-5.7 × 10⁻⁶. 14 Ω·cm; The density of fine-grained alumina ceramics is 3.88-3.9 g / cm³. 3 The flexural strength of fine-grained alumina ceramics is 380-390 MPa.

[0018] Preferably, when stacking the sheet blanks, the number of blanks is 6-10; more preferably, each stacked sheet blank is pressurized in a mold.

[0019] Compared with the prior art, the present invention has the following beneficial effects: by attaching alumina powder to the first attachment material grinding ball, and then mixing the second phase mixed powder and the first attachment material grinding ball in a ball mill, a second attachment material grinding ball is prepared. The second attachment material grinding ball is attached with alumina powder and the second phase mixed powder, so as to achieve uniform mixing of the nano alumina powder and inorganic powder, and avoid the problem of agglomeration.

[0020] By separating the material attached to the second attached material grinding ball from the grinding ball, a first mixture is obtained, thereby separating the uniformly mixed nano alumina powder and inorganic powder from the grinding ball;

[0021] By grinding the first mixture to obtain the second mixture, the nano alumina powder and inorganic powder are mixed evenly, and the powder particles after mixing are of moderate size, thus avoiding the problem of agglomeration when the mixed powder is used to prepare the primary slurry.

[0022] A primary slurry is prepared by mixing the second mixture and polyvinyl butyral to achieve uniform mixing of the second mixture and polyvinyl butyral. The thermoplasticity of polyvinyl butyral enables the subsequent casting slurry to be cast into a film.

[0023] By degassing the primary slurry to obtain the casting slurry, the absence of air bubbles in the casting slurry helps to avoid the problem of voids in the subsequent sheet preform; at the same time, it enables control of the viscosity of the casting slurry, which not only helps to achieve good flowability of the casting slurry, but also reduces the time required for the casting slurry to remove excess solvent in the casting equipment, effectively reducing the requirements on the casting equipment.

[0024] By casting the casting slurry, a sheet-like green body is obtained, achieving a uniform internal structure and uniform particle size distribution of the ceramic powder.

[0025] By stacking the sheet blanks and then warm isostatically pressing them to obtain a block blank, the resulting block blank has a uniform internal structure and uniform internal powder particle size; thus, the resulting fine-grained alumina ceramic has a uniform internal structure, small grain size, and uniform grain size distribution.

[0026] Furthermore, the process of preparing the first coated material grinding ball includes the following steps:

[0027] The polyvinylpyrrolidone is added to a ball mill for ball milling, and the material temperature is raised to 130-150°C during ball milling.

[0028] Then, while ball grinding, the temperature is lowered to room temperature, and polyvinylpyrrolidone is applied to the surface of the grinding ball;

[0029] Then add nano-alumina powder and ball mill at room temperature for 10-50 minutes;

[0030] Then, while ball milling, heat the material to 130-135℃ at a rate of 2-5℃ / min, and ball mill at 130-135℃ for 10-20 minutes.

[0031] Then, the ball is milled while being cooled down until the first grinding ball with the attached material is obtained after cooling to room temperature.

[0032] The mass ratio of nano-alumina powder to polyvinylpyrrolidone is (85-98):(1-5);

[0033] Preferably, the diameter of the grinding ball is 1.0-2.0 mm, and the volume ratio of the grinding ball to nano-alumina is (2-4):1.

[0034] The beneficial effect of the previous step is that by adding the polyvinylpyrrolidone to the ball milling equipment for ball milling, and raising the material temperature to 130-150℃ during ball milling, the polyvinylpyrrolidone is liquefied and comes into uniform contact with the grinding balls.

[0035] Then, by adding nano-alumina powder and ball milling at room temperature for 10-50 minutes, uniform contact between the nano-alumina powder and the grinding balls with attached polyvinylpyrrolidone is achieved.

[0036] By simultaneously ball milling and heating, the material temperature is raised to 130-135℃ at a rate of 2-5℃ / min. The material is then ball-milled at 130-135℃ for 10-20 minutes, which slowly melts the polyvinylpyrrolidone on the surface of the grinding balls and evenly adheres the nano-alumina powder to the surface of the grinding balls, thus obtaining grinding balls with nano-alumina powder attached.

[0037] Furthermore, the process for preparing the second-phase mixed powder includes the following steps:

[0038] Inorganic powder is added to a ball mill and mixed, then polyethylene glycol is added and ball milled at room temperature to obtain a second-phase mixed powder.

[0039] The inorganic powder includes one or more of Y2O3, CeO2, MgO, and ZrO2;

[0040] The mass ratio of nano-alumina powder, inorganic powder, and polyethylene glycol is (85-98):(1-10):(0.1-0.5).

[0041] The beneficial effect of the previous step is that by adding inorganic powder into the ball mill and mixing it, and then adding polyethylene glycol and ball milling it at room temperature, the polyethylene glycol and inorganic powder are mixed evenly, thereby enabling the inorganic powder to be attached to the surface of the second attachment material grinding ball through polyethylene glycol in the subsequent preparation process of the second attachment material grinding ball.

[0042] By using one or more inorganic powders, including Y2O3, CeO2, MgO, and ZrO2, it is possible to suppress abnormal grain growth at high temperatures during sintering, refine the grains, and improve the density and strength of ceramics.

[0043] Furthermore, the preparation process of the second attached material grinding ball includes the following steps:

[0044] The second phase mixed powder and the first attached material are ground into grinding balls in a ball mill, and the temperature is increased while grinding, so that the material is heated to 64-68℃.

[0045] After ball milling at 64-68℃ for 10-20 minutes, the material is cooled to room temperature to obtain the second type of coated grinding balls.

[0046] The beneficial effect of the previous step is that the second phase mixed powder and the first attached material grinding balls are milled in a ball mill while the temperature is raised to 64-68℃, so that the polyethylene glycol in the second phase mixed powder melts, while the polyvinylpyrrolidone on the surface of the grinding balls does not melt.

[0047] By ball milling at 64-68℃ for 10-20 minutes and then cooling down to room temperature, inorganic powder is attached to the first attachment material grinding ball by molten polyethylene glycol, thus obtaining the second attachment material grinding ball.

[0048] Furthermore, the process of detaching the material adhering to the second adhering material grinding ball from the grinding ball includes the following steps:

[0049] Place the second attached material grinding balls into a ball mill and heat them while grinding to 250-260℃; then ball mill at 250-260℃ for 10-20 minutes.

[0050] Then, while ball milling, the temperature is gradually reduced until it reaches room temperature, and ball milling continues for 10-20 minutes.

[0051] The alumina powder and inorganic powder attached to the grinding balls detach from the grinding balls, resulting in a mixture.

[0052] and / or

[0053] The particle size of the second mixture is D50 = 3.0-5.0 μm.

[0054] The beneficial effect of the previous step is that the second attached material grinding ball is placed in the ball mill equipment and heated while grinding to 250-260℃; grinding at 250-260℃ for 10-20 minutes allows the polyethylene glycol and polyvinylpyrrolidone attached to the second attached material grinding ball to melt and volatilize, thereby achieving the separation of nano alumina powder and inorganic powder from the surface of the grinding ball, and the nano alumina powder and inorganic powder to be mixed evenly;

[0055] By using a particle size of D50 = 3.0-5.0 μm for the second mixture, agglomeration during the preparation of the primary slurry is avoided.

[0056] Furthermore, the process of preparing the primary slurry includes the following steps:

[0057] Mix toluene and isopropanol and stir.

[0058] Then add polyethylene glycol and stir;

[0059] Then add polyvinyl butyral and stir to obtain a mixed solution;

[0060] Then, the second mixture is added to the mixed solution and stirred for 2.5-3.0 hours, then allowed to stand for 5.5-6.0 hours, and then stirred again for 0.5-1.5 hours to obtain the primary slurry.

[0061] The beneficial effect of the previous step is that by mixing and stirring toluene and isopropanol, then adding polyethylene glycol and stirring, and then adding polyvinyl butyral and stirring, the polyethylene glycol and polyvinyl butyral are dissolved in toluene and isopropanol, thereby achieving uniform dispersion of the second mixture in the mixed solution.

[0062] The second mixture is added to the mixing solution and stirred for 2.5-3.0 hours to achieve uniform dispersion of the second mixture in the mixing solution; then, by standing and aging for 5.5-6.0 hours, the particle size of the uniformly mixed nano-alumina powder and inorganic powder is dispersed to be close to that of the raw material nano-alumina powder and inorganic powder.

[0063] Furthermore, the mass ratio of toluene, isopropanol, polyethylene glycol, and polyvinyl butyral is (60-70):(20-30):(20-30):(1-10);

[0064] The mass ratio of the mixed solution to the second mixture is (1.5-2.1):1.

[0065] The beneficial effect of the previous step is that the mass ratio of toluene, isopropanol, polyethylene glycol, and polyvinyl butyral is (60-70):(20-30):(20-30):(1-10), and the mass ratio of the mixed solution to the second mixture is (1.5-2.1):1. This ensures that the materials in the obtained primary slurry are evenly dispersed, and that the second mixture is fully dispersed in the mixed solution. It also facilitates the reduction of the particle size of the nano-alumina powder and inorganic powder in the second mixture during the subsequent aging process. The particle size of the nano-alumina powder and inorganic powder in the second mixture is basically consistent with that of the raw material nano-alumina powder and inorganic powder, and is relatively small.

[0066] Furthermore, the process of degassing the primary slurry to obtain the casting slurry includes the following steps:

[0067] The primary slurry is added to a ball mill and milled for 20-25 hours, then filtered.

[0068] The filter screen has a mesh size of 250-400.

[0069] The filtered primary slurry is fed into a degassing device with nitrogen gas. The primary slurry is heated to 85-95°C while being vacuumed. When the viscosity reaches 2-6 Pa·s, a casting slurry is obtained. Preferably, the casting slurry is cooled and maintained at 85-95°C for later use.

[0070] The beneficial effect of the previous step is that the primary slurry is added to a ball mill and milled for 20-25 hours, then filtered. This further reduces the particle size of the nano-alumina powder and inorganic powder in the second mixture, making them basically consistent with the particle size of the raw material nano-alumina powder and inorganic powder, both relatively small, and the mixture is uniform. The filtered primary slurry is then transported to a degassing device with nitrogen gas, heated to 85-95℃, and simultaneously vacuumed. When the viscosity reaches 2-6 Pa·s, a casting slurry is obtained, removing excess solvent. This ensures good flowability of the casting slurry while reducing the difficulty of solvent removal during casting. Simultaneously, heating the primary slurry to 85-95℃ melts the polyethylene glycol and softens the polyvinyl butyral, thus avoiding excessive viscosity changes in the casting slurry during subsequent casting and preventing uneven thickness of the sheet blanks due to excessive fluidity.

[0071] Furthermore, the process of casting the slurry to obtain a sheet preform includes the following steps:

[0072] The temperature of the casting slurry is 165-175℃ when it is cast through the casting equipment.

[0073] The casting speed is 10-300 mm / min, and the height of the scraper from the casting belt conveying the sheet blank during the casting process is 0.3-0.6 mm; the preferred sheet blank thickness is 0.3-0.6 mm.

[0074] The advantage of the previous step is that when the casting slurry is cast through the casting equipment at a temperature of 165-175℃, the polyvinyl butyral is completely melted, resulting in a uniform and fine casting slurry.

[0075] By using a casting speed of 1-300 mm / min and keeping the height of the scraper from the casting belt conveying the sheet blank at 0.3-0.6 mm during the casting process, a sheet blank thickness of 0.3-0.6 mm can be achieved.

[0076] Furthermore, the pressure during the warm isostatic pressing process is 25-35 MPa, the temperature is 60-80℃, and the holding time is 20-40 min;

[0077] The block-shaped green body undergoes debinding and sintering using segmented temperature control, and the specific process includes the following steps:

[0078] The block blank is heated from room temperature to 100-110℃ at a heating rate of 1-2℃ / min.

[0079] The temperature is increased from 100-110℃ to 250-260℃ at a rate of 0.3-0.5℃ / min; the temperature is increased from 250-260℃ to 700-720℃ at a rate of 0.1-0.2℃ / min; and the temperature is held at 700-720℃ for 8-10 hours.

[0080] The temperature is increased from 700-720℃ to 1200-1220℃ at a rate of 1.5-2.0℃ / min; then held at 1200-1220℃ for 120-150 min. The temperature is then increased from 1200-1220℃ to 1560-1580℃ at a rate of 2.5-3.0℃ / min; then held at 1560-1580℃ for 120-150 min.

[0081] Then, cooling is performed, and the cooling process includes:

[0082] The temperature is reduced from 1560-1580℃ to 1380-1400℃ at a rate of -1 to -1.5℃ / min; the temperature is reduced from 1380-1400℃ to 480-500℃ at a rate of -2 to -2.5℃ / min; and the temperature is reduced from 480-500℃ to room temperature along with the furnace.

[0083] The beneficial effect of the previous step is that by using a pressure of 25-35MPa and a temperature of 60-80℃ during the warm isostatic pressing process, and holding the temperature for 20-40 minutes, the viscosity of polyethylene glycol increases and polyvinyl butyral softens without melting. Under this pressure, isostatic pressing further achieves a uniform block structure.

[0084] The debinding and sintering of the block blanks employs segmented temperature control. The specific process includes the following steps: First, the block blanks are heated from room temperature to 100-110℃ at a rate of 1-2℃ / min to achieve a rapid heating rate, quickly evaporating residual small-molecule volatiles and forming small-pore channels. Then, the temperature is increased from 100-110℃ to 250-260℃ at a rate of 0.3-0.5℃ / min to achieve a slower heating rate, allowing for the slow decomposition of larger molecular weight volatiles, such as polyethylene glycol and polyvinyl butyral. Next, the temperature is increased from 250-260℃ to 700-720℃ at a rate of 0.1-0.2℃ / min, and held at 700-720℃ for 8-10 hours. This further slow heating allows the volatiles from the decomposition of large molecules to evaporate through the pores formed by the evaporation of small molecules, preventing cracking of the block blanks.

[0085] The temperature is increased from 700-720℃ to 1200-1220℃ at a rate of 1.5-2.0℃ / min.

[0086] Hold at 1200-1220℃ for 120-150 min, then raise the temperature from 1200-1220℃ to 1560-1580℃ at a rate of 2.5-3.0℃ / min. This increased heating rate helps to avoid the problem of increased ceramic powder particle size after sintering. Detailed Implementation

[0087] To better understand the technical solution of the present invention, the present invention will be further described below with reference to specific embodiments.

[0088] Example 1:

[0089] This embodiment provides a method for preparing fine-grained alumina ceramics, including the following steps:

[0090] Nano-alumina powder and polyvinylpyrrolidone are mixed in a ball mill to prepare a first-attached material grinding ball, which is coated with alumina powder.

[0091] The process of preparing the first coated material grinding ball includes the following steps:

[0092] The polyvinylpyrrolidone was added to a ball mill for ball milling, and the material temperature was raised to 140°C during ball milling.

[0093] Then, while ball grinding, the temperature is lowered to room temperature, and polyvinylpyrrolidone is applied to the surface of the grinding ball;

[0094] Then add nano-alumina powder and ball mill at room temperature for 30 minutes;

[0095] Then, while ball milling, heat the material and raise the temperature to 132℃ at a rate of 3.5℃ / min. Then, ball mill the material at 132℃ for 15 minutes.

[0096] The mass ratio of nano-alumina powder to polyvinylpyrrolidone is 91:3;

[0097] Then, the material was ball-milled and cooled down until it reached room temperature, at which point the first coated grinding ball was obtained. The diameter of the grinding ball was 1.0 mm, and the volume ratio of the grinding ball to nano-alumina was 4:1.

[0098] The process of preparing a second-phase mixed powder containing inorganic powder includes the following steps:

[0099] Inorganic powder is added to a ball mill and mixed, then polyethylene glycol is added and ball milled at room temperature to obtain a second-phase mixed powder.

[0100] The inorganic powder includes Y2O3 and MgO;

[0101] The mass ratio of nano-alumina powder, inorganic powder, and polyethylene glycol is 91:5.7:0.3.

[0102] The second phase mixed powder and the first attached material grinding balls are mixed in a ball mill to prepare the second attached material grinding balls, which are coated with alumina powder and the second phase mixed powder.

[0103] The preparation process of the second-attached material grinding ball includes the following steps:

[0104] The second phase mixed powder and the first attached material are ground into grinding balls in a ball mill, and the temperature is increased while grinding, so that the material is heated to 66°C.

[0105] After ball milling at 66℃ for 15 minutes, the material was cooled to room temperature to obtain the second type of coated grinding balls.

[0106] The material attached to the second grinding ball is detached from the grinding ball to obtain the first mixture.

[0107] The process of removing the material adhering to the second-attached grinding ball from the grinding ball includes the following steps:

[0108] Place the second attached material grinding balls into a ball mill and heat them while grinding until they reach 255°C; then ball mill at 255°C for 15 minutes.

[0109] Then, while ball milling, the temperature is lowered until it reaches room temperature, and ball milling continues for 15 minutes.

[0110] The alumina powder and inorganic powder attached to the grinding balls detach from the grinding balls, resulting in a mixture.

[0111] The first mixture is ground to obtain a second mixture; the particle size of the second mixture is D50 = 3.0-5.0 μm.

[0112] A primary slurry is prepared by mixing a second mixture of materials and polyvinyl butyral. The process of preparing the primary slurry includes the following steps: mixing and stirring toluene and isopropanol; then adding polyethylene glycol and stirring; then adding polyvinyl butyral and stirring to obtain a mixed solution.

[0113] Then the second mixture was added to the mixed solution and stirred for 2.8 hours, then allowed to stand for 5.7 hours, and then stirred again for 1 hour to obtain the primary slurry.

[0114] The mass ratio of toluene, isopropanol, polyethylene glycol, and polyvinyl butyral is 65:25:25:6.

[0115] The mass ratio of the mixed solution to the second mixture is 1.8:1;

[0116] The primary slurry is degassed to obtain a casting slurry; the process of degasing the primary slurry to obtain the casting slurry includes the following steps:

[0117] The primary slurry is added to a ball mill and milled for 23 hours, then filtered. The filter screen is 325 mesh and vacuum degassing is used to prevent the filter screen from clogging.

[0118] The filtered primary slurry is fed to a degassing device with nitrogen gas, and the primary slurry is heated to 90°C while being vacuumed. When the viscosity reaches 4 Pa·s, a casting slurry is obtained. Preferably, the casting slurry is cooled and maintained at 90°C for later use.

[0119] The casting slurry is cast to obtain a sheet preform; the temperature of the casting slurry during casting is 170°C.

[0120] The casting speed is 150 mm / min, and the height of the scraper from the casting belt conveying the sheet blank during the casting process is 0.45 mm; the sheet blank thickness is 0.45 mm.

[0121] The sheet blanks are stacked and then warm isostatically pressed to obtain a block blank;

[0122] When the sheet blanks are stacked, there are 8 blanks. During the isostatic pressing process, the pressure is 30 MPa, the temperature is 70°C, and the holding time is 30 min.

[0123] Fine-grained alumina ceramics are obtained by debinding and sintering the bulk blanks.

[0124] The block blank was heated from room temperature to 105℃ at a heating rate of 1.5℃ / min; from 105℃ to 255℃ at a heating rate of 0.4℃ / min; from 255℃ to 710℃ at a heating rate of 0.15℃ / min; and held at 710℃ for 9 hours.

[0125] The temperature was increased from 710℃ to 1210℃ at a rate of 1.8℃ / min; then held at 1210℃ for 135 min. The temperature was increased from 1210℃ to 1570℃ at a rate of 2.8℃ / min; then held at 1570℃ for 135 min.

[0126] Then, cooling is performed, and the cooling process includes:

[0127] The temperature was reduced from 1570℃ to 1390℃ at a rate of -1.2℃ / min; the temperature was reduced from 1390℃ to 490℃ at a rate of -2.2℃ / min; and the temperature was reduced from 490℃ to room temperature in the furnace.

[0128] The volume resistivity of the prepared fine-grained alumina ceramic is 2.7 × 10⁻⁶. 14Ω·cm; The density of fine-grained alumina ceramic is 3.89 g / cm³. 3 The flexural strength of fine-grained alumina ceramic is 385 MPa.

[0129] Example 2:

[0130] The same content as in Example 1 will not be repeated here; the different aspects of this embodiment compared to Example 1 are as follows:

[0131] The polyvinylpyrrolidone was added to a ball mill for ball milling, and the material temperature was raised to 148°C during ball milling.

[0132] After cooling, add nano-alumina powder and ball mill at room temperature for 40 minutes;

[0133] Then, while ball milling, the material temperature was raised to 134℃ at a rate of 4.8℃ / min, and ball milled at 134℃ for 18 minutes.

[0134] The grinding ball has a diameter of 2 mm, and the volume ratio of the grinding ball to nano-alumina is 2:1.

[0135] The inorganic powder includes CeO2 and ZrO2;

[0136] The mass ratio of nano-alumina powder to polyvinylpyrrolidone is 96:2;

[0137] The mass ratio of nano-alumina powder, inorganic powder, and polyethylene glycol is 96:1.6:0.4.

[0138] After ball milling at 66℃ for 18 minutes, the material was cooled to room temperature to obtain the second type of coated grinding balls.

[0139] Place the second attached material grinding balls into a ball mill and heat them while grinding until they reach 259°C; then ball mill at 259°C for 12 minutes.

[0140] Then, while ball milling, the temperature is lowered until it reaches room temperature, and ball milling continues for 12 minutes.

[0141] Then the second mixture was added to the mixed solution and stirred for 2.9 hours, then allowed to stand for 5.9 hours, and then stirred again for 1.3 hours to obtain the primary slurry.

[0142] The mass ratio of toluene, isopropanol, polyethylene glycol, and polyvinyl butyral is 68:29:29:9;

[0143] The mass ratio of the mixed solution to the second mixture is 1.6:1;

[0144] The filtered primary slurry is fed into a degassing device using nitrogen gas. The primary slurry is heated to 93°C while being vacuumed. When the viscosity reaches 5 Pa·s, a cast slurry is obtained. Preferably, the cast slurry is cooled and maintained at 93°C for later use. The filter screen is 260 mesh to cooperate with vacuum degassing and prevent the filter screen from clogging.

[0145] The casting slurry is cast to obtain a sheet preform; the temperature of the casting slurry during casting is 173°C.

[0146] The casting speed is 280 mm / min, and the height of the scraper from the casting belt conveying the sheet blank during the casting process is 0.55 mm; the sheet blank thickness is 0.55 mm.

[0147] When the sheet blanks are stacked, there are 7 blanks; during the isostatic pressing process, the pressure is 26 MPa, the temperature is 79°C, and the holding time is 39 min; the block blank is heated from room temperature to 109°C at a heating rate of 1.8°C / min; from 109°C to 259°C at a heating rate of 0.49°C / min; from 259°C to 718°C at a heating rate of 0.9°C / min; and held at 718°C for 8.5 h.

[0148] The temperature was increased from 718℃ to 1218℃ at a rate of 1.9℃ / min; the temperature was then held at 1218℃ for 122 min; the temperature was increased from 1218℃ to 1578℃ at a rate of 2.9℃ / min; the temperature was then held at 1578℃ for 122 min.

[0149] Then, the temperature is lowered, and the cooling process includes: cooling from 1578℃ to 1390℃ at a rate of -1.4℃ / min; cooling from 1390℃ to 495℃ at a rate of -2.4℃ / min; and cooling from 495℃ to room temperature in the furnace.

[0150] The volume resistivity of the prepared fine-grained alumina ceramic is 5.7 × 10⁻⁶. 14 Ω·cm; The density of fine-grained alumina ceramic is 3.9 g / cm³. 3 The flexural strength of fine-grained alumina ceramic is 388 MPa.

[0151] Example 3:

[0152] The same content as in Example 1 will not be repeated here; the different aspects of this embodiment compared to Example 1 are as follows:

[0153] The polyvinylpyrrolidone was added to a ball mill for ball milling, and the material temperature was raised to 132°C during ball milling.

[0154] Then add nano-alumina powder and ball mill at room temperature for 48 minutes;

[0155] Then, while ball milling, the material temperature was raised to 132℃ at a rate of 2.2℃ / min, and ball milled at 132℃ for 18 minutes.

[0156] The grinding ball has a diameter of 1.5 mm, and the volume ratio of the grinding ball to nano-alumina is 3:1.

[0157] The inorganic powder includes Y2O3;

[0158] The mass ratio of nano-alumina powder to polyvinylpyrrolidone is 86:4;

[0159] The mass ratio of nano-alumina powder, inorganic powder, and polyethylene glycol is 86:9.8:0.2.

[0160] After ball milling at 65℃ for 18 minutes, the material was cooled to room temperature to obtain the second type of coated grinding balls.

[0161] The second attached material grinding balls are placed in a ball mill and heated while grinding to 252°C; the balls are then ground at 252°C for 18 minutes.

[0162] Then, while ball milling, the temperature is gradually reduced until it reaches room temperature, and ball milling continues for 18 minutes.

[0163] The particle size of the second mixture is D50 = 4.8 μm.

[0164] Then the second mixture was added to the mixed solution and stirred for 2.9 hours, then allowed to stand for 5.9 hours, and then stirred again for 1.48 hours to obtain the primary slurry.

[0165] The mass ratio of toluene, isopropanol, polyethylene glycol, and polyvinyl butyral is 62:22:22:2;

[0166] The mass ratio of the mixed solution to the second mixture is 1.6:1;

[0167] The filtered primary slurry is fed into a degassing device with nitrogen gas, and the primary slurry is heated to 86°C while being vacuumed. When the viscosity reaches 2.2 Pa·s, a casting slurry is obtained. Preferably, the casting slurry is cooled and maintained at 86°C for later use.

[0168] The casting slurry is cast to obtain a sheet preform; the temperature of the casting slurry during casting is 166°C.

[0169] The casting speed is 60 mm / min, and the height of the scraper from the casting belt conveying the sheet blank during the casting process is 0.32 mm; the sheet blank thickness is 0.32 mm.

[0170] When the sheet blanks are stacked, there are 9 blanks, and the stacking pressure is 18MPa.

[0171] The temperature during the warm isostatic pressing process is 33 MPa, 62°C, and held for 22 minutes.

[0172] The block blank was heated from room temperature to 102℃ at a rate of 1.2℃ / min; from 102℃ to 252℃ at a rate of 0.35℃ / min; from 252℃ to 702℃ at a rate of 0.12℃ / min; and held at 702℃ for 9.6 hours.

[0173] The temperature was increased from 702℃ to 1205℃ at a rate of 1.6℃ / min; the temperature was held at 1205℃ for 146 min; the temperature was increased from 1205℃ to 1565℃ at a rate of 2.6℃ / min; the temperature was held at 1565℃ for 148 min.

[0174] Then, the temperature is lowered, and the cooling process includes: cooling from 1565℃ to 1385℃ at a rate of -1.1℃ / min; cooling from 1385℃ to 485℃ at a rate of -2.2℃ / min; and cooling from 485℃ to room temperature in the furnace.

[0175] The volume resistivity of the prepared fine-grained alumina ceramic is 2.7 × 10⁻⁶. 14 Ω·cm; The density of fine-grained alumina ceramic is 3.9 g / cm³. 3 The flexural strength of fine-grained alumina ceramic is 383 MPa.

[0176] The above description is merely a preferred embodiment of this application and an explanation of the technical principles employed. Those skilled in the art should understand that the scope of the invention involved in this application is not limited to the technical solutions formed by specific combinations of the above-described technical features, but should also cover other technical solutions formed by arbitrary combinations of the above-described technical features or their equivalent features without departing from the inventive concept, such as those features that have similar functions to (but are not limited to) those disclosed in this application.

Claims

1. A method for producing a fine-crystal alumina ceramic, characterized by, The method comprises the following steps: Mixing nano-alumina powder and polyvinylpyrrolidone in a ball mill device to prepare first material-attached grinding balls, the first material-attached grinding balls being attached with alumina powder; Preparation of second phase mixed powder containing inorganic powder; Mixing the second phase mixed powder and the first material-attached grinding balls in a ball mill device to prepare second material-attached grinding balls, the second material-attached grinding balls being attached with alumina powder and the second phase mixed powder; Separating the material attached to the second material-attached grinding balls from the grinding balls to obtain first mixed material; Grinding the first mixed material to obtain second mixed material; Preparation of primary slurry from the second mixed material and polyvinyl butyral; Defoaming the primary slurry to obtain casting slurry; Casting the casting slurry to obtain sheet-shaped green body; Stacking the sheet-shaped green body and then warm isostatic pressing to obtain block-shaped green body; Degassing and sintering the block-shaped green body to obtain fine-crystal alumina ceramic.

2. The method for preparing fine-grained alumina ceramics according to claim 1, characterized in that, The process for preparing the first material-attached grinding balls comprises the following steps: Adding the polyvinylpyrrolidone into the ball mill device for ball milling, and increasing the temperature of the material during ball milling to 130-150°C; Then decreasing the temperature to room temperature while ball milling, so that the polyvinylpyrrolidone is attached to the surface of the grinding balls; Then adding nano-alumina powder and ball milling at room temperature for 10-50 min; Then heating while ball milling, and then increasing the temperature of the material to 130-135°C at a rate of 2-5°C / min, and ball milling at 130-135°C for 10-20 min; Then decreasing the temperature while ball milling, and obtaining the first material-attached grinding balls after decreasing to room temperature; The mass ratio of the nano-alumina powder to the polyvinylpyrrolidone is (85-98):(1-5).

3. The method for preparing fine-grained alumina ceramics according to claim 1, characterized in that, The process for preparing the second phase mixed powder comprises the following steps: Adding inorganic powder into the ball mill device for mixing, and then adding polyethylene glycol and ball milling at room temperature to obtain the second phase mixed powder; The inorganic powder comprises one or more of Y2O3, CeO2, MgO and ZrO2; The mass ratio of the nano-alumina powder, the inorganic powder and the polyethylene glycol is (85-98):(1-10):(0.1-0.5).

4. The method for preparing fine-grained alumina ceramics according to claim 1, characterized in that, The process for preparing the second material-attached grinding balls comprises the following steps: Mixing the second phase mixed powder and the first material-attached grinding balls in a ball mill device, and increasing the temperature while ball milling to increase the temperature of the material to 64-68°C; After ball milling at 64-68°C for 10-20 min, decreasing the temperature to obtain the second material-attached grinding balls after decreasing to room temperature.

5. The method for preparing fine-grained alumina ceramics according to claim 1, characterized in that, The process for separating the material attached to the second material-attached grinding balls from the grinding balls comprises the following steps: Putting the second material-attached grinding balls into the ball mill device, and heating while ball milling to 250-260°C, and ball milling at 250-260°C for 10-20 min; Then decreasing the temperature while ball milling to room temperature and continuing ball milling for 10-20 min; The alumina powder and the inorganic powder attached to the grinding balls are separated from the grinding balls to obtain the first mixed material; And / or The particle size of the second mixed material is D50=3.0-5.0μm.

6. The method for preparing fine-grained alumina ceramics according to claim 1, characterized in that, The process for preparing the primary slurry comprises the following steps: Mixing toluene and isopropyl alcohol and stirring; Then add polyethylene glycol and stir; Then add polyvinyl butyral and stir to obtain a mixed solution; Then add the second mixture to the mixed solution and stir for 2.5-3.0 h, then stand for 5.5-6.0 h, and then stir again for 0.5-1.5 h to obtain the primary slurry.

7. The method for preparing fine-grained alumina ceramics according to claim 6, characterized in that, The mass ratio of toluene, isopropyl alcohol, polyethylene glycol, and polyvinyl butyral is (60-70):(20-30):(20-30):(1-10). The mass ratio of the mixed solution to the second mixture is (1.5-2.1):

1.

8. The method for preparing fine-grained alumina ceramics according to claim 1, characterized in that, The process of defoaming the primary slurry to obtain the casting slurry includes the following steps: Put the primary slurry into a ball milling device and mill for 20-25 h, and then filter; the mesh size of the filter is 250-400 mesh; Transfer the filtered primary slurry into a defoaming device using nitrogen, heat the primary slurry to 85-95℃, and simultaneously perform vacuum extraction, and when the viscosity reaches 2-6 Pa·s, the casting slurry is obtained.

9. The method for preparing fine-grained alumina ceramics according to claim 1, characterized in that, The process of casting the casting slurry to obtain the sheet-shaped green body includes the following steps: The temperature during casting the casting slurry through a casting device is 165-175℃; The casting speed is 10-300 mm / min, and the height of the doctor blade from the casting belt of the sheet-shaped green body during casting is 0.3-0.6 mm.

10. The method for preparing fine-grained alumina ceramics according to claim 1, characterized in that, The pressure during the warm isostatic pressing process is 25-35 MPa, and the temperature is 60-80℃, and the holding time is 20-40 min; The process of degassing and sintering the block-shaped green body adopts segmented temperature control, and includes the following steps: Increase the temperature of the block-shaped green body from room temperature to 100-110℃ at a rate of 1-2℃ / min; Increase the temperature from 100-110℃ to 250-260℃ at a rate of 0.3-0.5℃ / min; increase the temperature from 250-260℃ to 700-720℃ at a rate of 0.1-0.2℃ / min; and hold the temperature at 700-720℃ for 8-10 h; Increase the temperature from 700-720℃ to 1200-1220℃ at a rate of 1.5-2.0℃ / min; hold the temperature at 1200-1220℃ for 120-150 min; increase the temperature from 1200-1220℃ to 1560-1580℃ at a rate of 2.5-3.0℃ / min; and hold the temperature at 1560-1580℃ for 120-150 min; Then perform cooling, which includes the following steps: Decrease the temperature from 1560-1580℃ to 1380-1400℃ at a rate of -1 to -1.5℃ / min; decrease the temperature from 1380-1400℃ to 480-500℃ at a rate of -2 to -2.5℃ / min; and decrease the temperature from 480-500℃ to room temperature at a rate of -1 to -1.5℃ / min.