阅读说明：本技术 一种均质化大尺寸氮化硅陶瓷平板的制备方法 (Preparation method of homogenized large-size silicon nitride ceramic flat plate ) 是由 董衡 李淑琴 韩耀 余娟丽 张剑 吕毅 张昊 于 2021-08-17 设计创作，主要内容包括：本发明公开一种均质化大尺寸氮化硅基陶瓷平板的制备方法,属于功能陶瓷制备技术领域,通过将硅溶胶、水溶性大分子有机物、烧结助剂与酸洗氮化硅陶瓷粉体混合均匀,其中酸洗氮化硅陶瓷粉体包含0.5～0.8μm的颗粒和1～2μm的颗粒,进行球磨后获得浆料；将所述浆料真空脱气注入模具后,使其悬浮在液氮中进行充分固化成型,然后脱模得到坯体,坯体经干燥、烧结,得到均质化氮化硅基陶瓷平板材料。(The invention discloses a preparation method of a homogenized large-size silicon nitride-based ceramic panel, which belongs to the technical field of functional ceramic preparation, wherein silica sol, a water-soluble macromolecular organic substance, a sintering aid and acid-washing silicon nitride ceramic powder are uniformly mixed, the acid-washing silicon nitride ceramic powder comprises 0.5-0.8 mu m particles and 1-2 mu m particles, and slurry is obtained after ball milling; and after the slurry is subjected to vacuum degassing and injected into a mold, suspending the slurry in liquid nitrogen for full solidification and molding, then demolding to obtain a blank, and drying and sintering the blank to obtain the homogenized silicon nitride-based ceramic flat plate material.)

1. A preparation method of a homogenized large-size silicon nitride-based ceramic flat plate is characterized by comprising the following steps:

uniformly mixing silica sol, a water-soluble macromolecular organic matter, a sintering aid and acid-washed silicon nitride ceramic powder, wherein the acid-washed silicon nitride ceramic powder comprises 0.5-0.8 mu m particles and 1-2 mu m particles, and performing ball milling to obtain slurry; the slurry comprises the following components in percentage by weight: 20-30 wt% of silica sol, 2.1-4.0 wt% of water-soluble macromolecular organic matter, 3.5-6.4 wt% of sintering aid and 70-80 wt% of acid-washing silicon nitride ceramic powder;

and after the slurry is subjected to vacuum degassing and injected into a mold, suspending the slurry in liquid nitrogen for full solidification and molding, then demolding to obtain a blank, and drying and sintering the blank to obtain the homogenized silicon nitride-based ceramic flat plate material.

2. The method of claim 1, wherein the silica sol has a pH of 5.0 to 6.0 and a concentration of 15 to 25 wt%.

3. The method according to claim 1, wherein the water-soluble macromolecular organic substance is one or more of polyethylene glycol, polyvinyl alcohol and polyglycerol, and the addition amount of the water-soluble macromolecular organic substance is 3.0-5.0 wt% of the mass of the acid-washed silicon nitride ceramic powder.

4. The method according to claim 1, wherein the sintering aid is one or more of alumina, yttria, silica and ytterbia, and the addition amount is 5-8 wt% of the mass of the acid-washed silicon nitride ceramic powder.

5. The method according to claim 1, wherein the ratio of the particles of 0.5 to 0.8 μm to the particles of 1 to 2 μm is 15 to 20 wt% and 80 to 85 wt%, respectively.

6. The method of claim 1, wherein the ball milling time is 48 to 96 hours.

7. The method of claim 1, wherein the degassing time is 10 to 40 min.

8. The method of claim 1, wherein the mold material is aluminum or copper, the thickness of the mold is 2-4 mm, the casting time in the mold is 3-8 min, and the curing time is 1-2 h.

9. The method according to claim 1, wherein the drying temperature is 35-45 ℃, the drying humidity is 65-75%, and the drying time is 48-96 h.

10. The method according to claim 1, wherein the sintering temperature is 1600-1800 ℃ and the sintering holding time is 3-6 h.

Technical Field

The invention belongs to the technical field of functional ceramic preparation, and particularly relates to a preparation method of a homogenized large-size silicon nitride ceramic flat plate.

Background

With the development of novel missiles towards supersonic velocity, hypersonic velocity and long-term flight, stricter requirements are provided for the selection of antenna window materials. The research on a material system discovers that the silicon nitride-based ceramic material has excellent mechanical, thermal and electrical properties, and meanwhile, the decomposition temperature is above 1850 ℃, so that the silicon nitride-based ceramic material is very suitable for being used as a hypersonic tactic missile antenna window material, and therefore, the ceramic material is the focus of research in recent years.

The antenna window of the hypersonic aircraft is of a special-shaped structure and complex in shape, and is mostly prepared by adopting a finish machining mode of a large-size silicon nitride ceramic flat plate. Among them, isostatic compaction and dry compaction are necessary to modify the powder and have high cost; ceramics prepared by tape casting have anisotropy and can be used only under specific conditions; the grouting forming preparation period is longer; the gel injection molding method has the defects of difficult drying condition and glue discharging process and the like; the ceramic green body prepared by freezing and forming has low strength, and the drying process needs to be carried out under the conditions of vacuum and freezing. The freeze-gelation technology is a ceramic forming technology which is near net size, low in shrinkage rate, high in efficiency and low in cost in the true sense, and the in-situ solidification forming of ceramic particles is realized by utilizing the characteristic of silica sol freeze-gelation.

The published patent CN107759240A adopts freezing gelation to prepare silicon nitride multiphase ceramics (the mold is kept in liquid nitrogen for a certain time), and the uniformity of the final product is greatly influenced because the silicon nitride multiphase ceramics adopt micromolecule organic matters and the temperature gradient is difficult to inhibit the growth of ice crystals during freezing. In addition, patent CN110698186A has been published for preparing homogenized alumina ceramic by using freeze-gel forming, but no process optimization method for preparing large-size flat plates is mentioned. The material prepared by the patent CN104496521A has gradient structure phenomenon, is uneven, has compact surface and loose inner layer, which is because the freezing forming process is heated unevenly, so that the slurry close to the mould is solidified first and is more compact, while the slurry far away from the mould is cooled slowly, so that the ice crystal grows, and in addition, the prepared porous material has low solid content originally, and the ice crystal grows more easily. The published patent CN105198475A only discloses a preparation method of porous material, and compact material can not be prepared.

Disclosure of Invention

In view of the defects of the prior art, the invention provides a preparation method of a homogenized silicon nitride ceramic flat plate. And optimizing and preparing the homogenized large-size silicon nitride ceramic flat plate one by one from green body forming, drying and sintering. In the aspect of green body forming, the growth structure of the ice crystal is controlled by regulating and controlling the rheological property of the slurry, the addition amount of organic matters and a temperature field, so that the mechanical property and reliability of a final product cannot be adversely affected by removing the micropores left by moisture in the drying process. In the drying and sintering aspects, the large-size silicon nitride ceramic flat plate with uniform mechanical properties is prepared by regulating and controlling the drying temperature and humidity of the green body and the sintering system.

The technical scheme of the invention is as follows:

a preparation method of a homogenized large-size silicon nitride-based ceramic flat plate comprises the following steps:

preparing slurry: uniformly mixing silica sol, a water-soluble macromolecular organic matter, a sintering aid and acid-washed silicon nitride ceramic powder in sequence, wherein the acid-washed silicon nitride ceramic powder comprises 0.5-0.8 mu m particles and 1-2 mu m particles, and performing ball milling to obtain slurry; the slurry comprises the following components in percentage by weight: 20-30 wt% of silica sol, 2.1-4.0 wt% of water-soluble macromolecular organic matter, 3.5-6.4 wt% of sintering aid and 70-80 wt% of acid-washing silicon nitride ceramic powder;

preparing homogenized silicon nitride ceramics: and after the slurry is subjected to vacuum degassing and injected into a mold, suspending the slurry in liquid nitrogen for full solidification and molding, then demolding to obtain a blank, and drying and sintering the blank to obtain the homogenized silicon nitride-based ceramic flat plate material.

Further, the silica sol has a pH of 5.0 to 6.0 and a concentration of 15 to 25 wt%.

Further, the water-soluble macromolecular organic matter is one or more of polyethylene glycol, polyvinyl alcohol and polyglycerol, and the addition amount of the water-soluble macromolecular organic matter is 3.0-5.0 wt% of the mass of the acid-washed silicon nitride ceramic powder.

Further, the sintering aid is one or more of aluminum oxide, yttrium oxide, silicon oxide and ytterbium oxide, and the addition amount of the sintering aid is 5-8 wt% of the mass of the acid-washed silicon nitride ceramic powder.

Further, the proportion of the particles with the particle size of 0.5-0.8 mu m to the particles with the particle size of 1-2 mu m is 15-20 wt% and 80-85 wt%, respectively.

Furthermore, the ball milling time is 48-96 h.

Further, the degassing time is 10-40 min.

Further, the material of the mold is aluminum or copper, the thickness of the mold is 2-4 mm, the casting time in the mold is 3-8 min, and the curing time is 1-2 h.

Further, the drying temperature is 35-45 ℃, the drying humidity is 65-75%, and the drying time is 48-96 h.

Further, the sintering temperature is 1600-1800 ℃, and the sintering heat preservation time is 3-6 h.

Compared with the prior art, the invention has the beneficial effects that:

the invention prepares the homogenized large-size silicon nitride ceramic flat plate by optimizing the green body forming, drying and sintering one by one, and in the aspect of green body forming, the freezing gelation process is optimized by utilizing the synergistic effects of temperature field regulation, addition of water-soluble macromolecular organic matters, slurry rheological property and the like. Firstly, selecting proper pouring time at the temperature of liquid nitrogen to carry out suspension rapid freezing solidification on the slurry, weakening the contact between the slurry and air and the instability influenced by gravity, leading the slurry close to the cold surface to rapidly reach a supercooled state, rapidly generating a large amount of micro ice nuclei in water, and inhibiting the growth of ice crystals; in the freezing and gelling process, the advantage that the macromolecular organic matter has branch chain length relative to the micromolecular organic matter has more obvious effect on inhibiting expansion when water is frozen in the freezing process, the prepared ceramic blank is more uniform, in addition, the addition amount of the macromolecular organic matter cannot be too much, otherwise, the compactness and the mechanical property of the final ceramic material are influenced, and if the addition amount is too little, no effect on inhibiting expansion of ice crystals is realized; the pickling silicon nitride ceramic powder can form close packing by selecting proper particle size distribution, smaller gaps exist among particles, the viscosity of slurry is effectively reduced, the dispersity and the solid content are improved, the growth of ice crystals can be inhibited, the homogenization degree and the mechanical property are improved, in addition, the surface oxidation degree of the pickling silicon nitride powder is reduced, the repulsion force among the particles is enhanced, the viscosity is also reduced, and the solid content is improved. Secondly, suspension quick freezing and optimization of the thickness and the material of the mold compared with the Z-axis heat transfer of the existing method can enable a temperature field to be more uniform, improve the heat exchange rate, limit the growth of dendrites and weaken the appearance of a conventional freezing gelation gradient structure; compared with the patent CN110698186A, the mould forming method has the advantages that the mould forming method can reduce heat transferability, improve heat exchange rate in the forming process, refine casting time which is 3-8 min, lead to longer contact time with air and introduce bubbles, lead to too short time, change stability of slurry under the influence of gravity and lead to too high density of the bottom of a green body; meanwhile, the macromolecular organic matters have synergistic effect, so that the growth of ice crystals is better controlled, and the homogenized microstructure of a formed blank body is realized. And finally, acid washing is carried out on the silicon nitride powder, the particle size is optimized, because the proper particle size distribution can form close packing, and smaller gaps exist among particles, so that the viscosity of the slurry is effectively reduced, the dispersity and the solid content are improved, the growth of ice crystals can be inhibited, the homogenization degree and the mechanical property are improved, the surface oxidation degree of the acid-washed silicon nitride powder is reduced, the repulsion force among the particles is enhanced, the viscosity is also reduced, the solid content is improved, and the relative growth of the ice crystals is relatively reduced by water. In the aspects of drying and sintering, the large-size silicon nitride ceramic flat plate with uniform mechanical properties is prepared by regulating and controlling the drying temperature and humidity of the green body (reducing the water loss of the outer surface of the large-size green body so as to prevent the inner diffusion rate from following the evaporation rate to cause cracks) and the sintering system (realizing the uniformity of the temperature of the inner field and the outer field of the large-size sample and reducing the generation of thermal stress).

Drawings

FIGS. 1 to 3 are SEM images of the microstructures of the homogeneous silicon nitride ceramics obtained in examples 1 to 3 of the present invention;

FIGS. 4 to 8 are SEM images of microstructures of the silicon nitride ceramics obtained in comparative examples 1 to 5 in this order;

FIG. 9 is a schematic diagram of a large-sized (450 mm. times.630 mm) silicon nitride ceramic plate and its partitions.

Detailed Description

In order to make the technical solution of the present invention more comprehensible, embodiments accompanied with figures are described in detail below.

A preparation method of a homogenized large-size silicon nitride-based ceramic flat plate comprises the following steps:

(1) preparing slurry: uniformly mixing silica sol, a water-soluble macromolecular organic matter, a sintering aid and acid-washed silicon nitride ceramic powder in sequence, and carrying out ball milling to obtain slurry. The slurry comprises the following components in percentage by weight: 20 to 30 wt% of silica sol (can be any value within the range, such as 20 wt%, 21 wt%, 22 wt%, 23 wt%, 24 wt%, 25 wt%, 26 wt%, 27 wt%, 28 wt%, 29 wt%, 30 wt%), 2.1 to 4.0 wt% of water-soluble macromolecular organic substance (can be any value within the range, such as 2.1 wt%, 2.5 wt%, 3.0 wt%, 3.5 wt%, 4.0 wt%), 3.5 to 6.4 wt% of sintering aid (can be any value within the range, such as 3.5 wt%, 3.6 wt%, 3.7 wt%, 3.8 wt%, 3.9 wt%, 4.0 wt%), 70 to 80 wt% of acid-washed silicon nitride ceramic powder (can be any value within the range, such as 70 wt%, 71 wt%, 72 wt%, 73 wt%, 74 wt%, 75 wt%, 76 wt%, 77 wt%, 78 wt%, 79 wt%, 80 wt%).

Wherein the silica sol has a pH of 5.0 to 6.0 (can be any value within this range, e.g., 5.0, 5.5, 6.0) and a concentration of 15 to 25 wt% (can be any value within this range, e.g., 15 wt%, 16 wt%, 17 wt%, 18 wt%, 19 wt%, 20 wt%, 21 wt%, 22 wt%, 23 wt%, 24 wt%, 25 wt%). The water-soluble macromolecular organic substance is one or more of polyethylene glycol, polyvinyl alcohol and polyglycerol, and the addition amount is 3.0-5.0 wt% (any value within the range, such as 3.0 wt%, 3.5 wt%, 4.0 wt%, 4.5 wt%, 5.0 wt%) of the mass of the acid-washed silicon nitride ceramic powder. The sintering aid can be one or more of alumina, yttria, silica and ytterbia, and the addition amount is 5-8 wt% (any value in the range, such as 5 wt%, 6 wt%, 7 wt% and 8 wt%) of the mass of the acid-washed silicon nitride ceramic powder. The acid-washed silicon nitride ceramic powder contains 0.5 to 0.8 μm (any value within the range, such as 0.5 μm, 0.6 μm, 0.7 μm, 0.8 μm) of particles, 15 to 20 wt% (any value within the range, such as 15 wt%, 16 wt%, 17 wt%, 18 wt%, 19 wt%, 20 wt%), and 1 to 2 μm (any value within the range, such as 1 μm, 1.1 μm, 1.2 μm, 1.3 μm, 1.4 μm, 1.5 μm, 1.6 μm, 1.7 μm, 1.8 μm, 1.9 μm, 2 μm) of particles, 80 to 85 wt% (any value within the range, such as 80 wt%, 81 wt%, 82 wt%, 83 wt%, 84 wt%, 85 wt%). The ball milling time is 48-96 h (any value in the range can be used, such as 48h, 50h, 55h, 60h, 65h, 70h, 75h, 80h, 85h, 90h and 96 h).

(2) Preparing homogenized silicon nitride ceramics: and after the slurry is subjected to vacuum degassing and injected into a mold, suspending the slurry in liquid nitrogen for full solidification and molding, then demolding to obtain a blank, and drying and sintering the blank to obtain the homogenized silicon nitride-based ceramic flat plate material.

Wherein the degassing time is 10-40 min (any value in the range, such as 10min, 15min, 20min, 25min, 30min, 35min, 40 min). The material of the mold can be aluminum or copper, the thickness of the mold is 2-4 mm (any value in the range, such as 2mm, 2.5mm, 3mm, 3.5mm, 4mm), the casting time in the mold is 3-8 min (any value in the range, such as 3min, 4min, 5min, 6min, 7min, 8min), and the curing time is 1-2 h (any value in the range, such as 1h, 1.5h, 2 h). The drying temperature is 35-45 ℃ (which can be any value in the range, such as 35 ℃, 36 ℃, 37 ℃, 38 ℃, 39 ℃, 40 ℃, 41 ℃, 42 ℃, 43 ℃, 44 ℃ and 45 ℃), the drying humidity is 65-75% (which can be any value in the range, such as 65%, 66%, 67%, 68%, 69%, 70%, 71%, 72%, 73%, 74% and 75%), and the drying time is 48-96 h (which can be any value in the range, such as 8h, 50h, 55h, 60h, 65h, 70h, 75h, 80h, 85h, 90h and 96 h). The sintering temperature is 1600-1800 ℃ (can be any value in the range, such as 1600 ℃, 1650 ℃, 1700 ℃, 1750 ℃ and 1800 ℃), and the sintering heat preservation time is 3-6 h (can be any value in the range, such as 3h, 4h, 5h and 6 h).

The following are examples of the present invention:

example 1

Step 1: preparing slurry, namely preparing polyvinyl alcohol, 20 wt% of silica sol with the pH value of 5.0, acid-washed silicon nitride ceramic powder, and a sintering aid (aluminum oxide: yttrium oxide ═ 1:3) according to a mass ratio of 4:28:100: 8: uniformly mixing and carrying out ball milling to obtain silicon nitride ceramic slurry; wherein the silicon nitride ceramic powder comprises 20 wt% of particles with the particle size of 0.5-0.8 μm and 80 wt% of particles with the particle size of 1-2 μm, and the ball milling time is 60 hours.

Step 2: preparing homogenized silicon nitride ceramics, wherein the slurry is subjected to vacuum degassing for 20min and then is injected into an aluminum mold with the bottom thickness of 3mm (the casting time is 5min), so that the slurry is quickly suspended in liquid nitrogen (suspended by a support body with a fixed net-shaped structure in a liquid nitrogen tank) and is fully cured for 1h, and then demolding is carried out to obtain a blank; the blank body is dried for 60 hours at the temperature of 40 ℃ and the humidity of 70 percent and sintered for 6 hours at the temperature of 1750 ℃ to prepare the homogenized silicon nitride ceramic material.

Example 2

Step 1: preparing slurry, namely mixing polyvinyl alcohol and polyglycerol, 25 wt% of silica sol with the pH value of 5.5, acid-washed silicon nitride ceramic powder and sintering aid (aluminum oxide) according to the mass ratio of 5:28:100: 6: uniformly mixing and carrying out ball milling to obtain silicon nitride ceramic slurry; wherein the silicon nitride ceramic powder comprises 15 wt% of particles with the particle size of 0.5-0.8 μm and 85 wt% of particles with the particle size of 1-2 μm, and the ball milling time is 96 h.

Step 2: preparing silicon nitride ceramics, wherein the slurry is vacuum degassed for 40min and then poured into an aluminum mold with the bottom thickness of 4mm (the pouring time is 8min), so that the slurry is quickly suspended in liquid nitrogen and fully solidified for 2h, and then demolding is carried out to obtain a blank; the blank is dried for 96 hours at the temperature of 35 ℃ and the humidity of 65 percent and sintered for 5 hours at the temperature of 1800 ℃ to prepare the homogenized silicon nitride ceramic material.

Example 3

Step 1: preparing slurry, namely mixing polyglycerol, 15 wt% of silica sol with the pH value of 6.0, acid-washed silicon nitride ceramic powder and a sintering aid (yttrium oxide) according to the mass ratio of 3:28:100: 5: uniformly mixing and carrying out ball milling to obtain silicon nitride ceramic slurry; wherein the silicon nitride ceramic powder comprises 17 wt% of particles with the particle size of 0.5-0.8 μm and 83 wt% of particles with the particle size of 1-2 μm, and the ball milling time is 48 h.

Step 2: preparing homogenized silicon nitride ceramics, wherein the slurry is vacuum degassed for 10min and then injected into an aluminum mold with the bottom thickness of 2mm (the casting time is 3min), so that the slurry is quickly suspended in liquid nitrogen and fully solidified for 1.5h, and then demolding is carried out to obtain a blank; the blank is dried for 48 hours at the temperature of 45 ℃ and the humidity of 75 percent and sintered for 3 hours at the temperature of 1600 ℃ to prepare the homogenized silicon nitride ceramic material.

The following are comparative examples:

comparative example 1

Step 1: preparing slurry, namely preparing a silica sol with the concentration of 20 wt% and the pH value of 5.0, acid-washed silicon nitride ceramic powder and a sintering aid (aluminum oxide: yttrium oxide ═ 1:3) according to the mass ratio of 28:100: 8: uniformly mixing and carrying out ball milling to obtain silicon nitride ceramic slurry; wherein the silicon nitride ceramic powder comprises 20 wt% of particles with the particle size of 0.5-0.8 μm and 80 wt% of particles with the particle size of 1-2 μm, and the ball milling time is 60 hours.

Step 2: preparing silicon nitride ceramics, wherein the slurry is vacuum degassed for 20min and then poured into an aluminum mold with the bottom thickness of 3mm (the pouring time is 5min), so that the slurry is quickly suspended in liquid nitrogen and fully solidified for 1h, and then demolding is carried out to obtain a blank; the blank body is dried for 60 hours at the temperature of 40 ℃ and the humidity of 70 percent and sintered for 6 hours at the temperature of 1750 ℃ to prepare the homogenized silicon nitride ceramic material.

Comparative example 2

Step 1: preparing slurry, namely mixing polyvinyl alcohol, 20 wt% of silica sol with the pH value of 5.0, silicon nitride ceramic powder and a sintering aid (aluminum oxide: yttrium oxide ═ 1:3) in a mass ratio of 4:28:100: 8: uniformly mixing and carrying out ball milling to obtain silicon nitride ceramic slurry; wherein the silicon nitride ceramic powder comprises 20 wt% of particles with the particle size of 0.5-0.8 μm and 80 wt% of particles with the particle size of 1-2 μm, and the ball milling time is 60 hours.

Step 2: preparing silicon nitride ceramics, wherein the slurry is vacuum degassed for 20min and then poured into an aluminum mold with the bottom thickness of 3mm (the pouring time is 5min), so that the slurry is quickly suspended in liquid nitrogen and fully solidified for 1h, and then demolding is carried out to obtain a blank; the blank body is dried for 60 hours at the temperature of 40 ℃ and the humidity of 70 percent and sintered for 6 hours at the temperature of 1750 ℃ to prepare the homogenized silicon nitride ceramic material.

Comparative example 3

Step 1: preparing slurry, namely mixing polyvinyl alcohol, 20 wt% of silica sol with the pH value of 5.0, acid-washed silicon nitride ceramic powder and a sintering aid (aluminum oxide: yttrium oxide ═ 1:3) in a mass ratio of 4:28:100: 8: uniformly mixing and carrying out ball milling to obtain silicon nitride ceramic slurry; wherein the particle size of the silicon nitride ceramic powder is 1-2 μm, and the ball milling time is 60 h.

Step 2: preparing silicon nitride ceramics, wherein the slurry is vacuum degassed for 20min and then poured into an aluminum mold with the bottom thickness of 3mm (the pouring time is 5min), so that the slurry is quickly suspended in liquid nitrogen and fully solidified for 1h, and then demolding is carried out to obtain a blank; the blank body is dried for 60 hours at the temperature of 40 ℃ and the humidity of 70 percent and sintered for 6 hours at the temperature of 1750 ℃ to prepare the homogenized silicon nitride ceramic material.

Comparative example 4

Step 1: preparing slurry, namely mixing polyvinyl alcohol, 20 wt% of silica sol with the pH value of 5.0, acid-washed silicon nitride ceramic powder and a sintering aid (aluminum oxide: yttrium oxide ═ 1:3) in a mass ratio of 4:28:100: 8: uniformly mixing and carrying out ball milling to obtain silicon nitride ceramic slurry; wherein the silicon nitride ceramic powder comprises 20 wt% of particles with the particle size of 0.5-0.8 μm and 80 wt% of particles with the particle size of 1-2 μm, and the ball milling time is 60 hours.

Step 2: preparing silicon nitride ceramics, wherein the slurry is vacuum degassed for 20min and then poured into an aluminum mold with the bottom thickness of 6mm (pouring time is 5min), so that the slurry is quickly suspended in liquid nitrogen and fully solidified for 1h, and then demolding is carried out to obtain a blank; the blank body is dried for 60 hours at the temperature of 40 ℃ and the humidity of 70 percent and sintered for 6 hours at the temperature of 1750 ℃ to prepare the homogenized silicon nitride ceramic material.

Comparative example 5

Step 1: preparing slurry, namely mixing polyvinyl alcohol, 20 wt% of silica sol with the pH value of 5.0, acid-washed silicon nitride ceramic powder and a sintering aid (aluminum oxide: yttrium oxide ═ 1:3) in a mass ratio of 4:28:100: 8: uniformly mixing and carrying out ball milling to obtain silicon nitride ceramic slurry; wherein the silicon nitride ceramic powder comprises 20 wt% of particles with the particle size of 0.5-0.8 μm and 80 wt% of particles with the particle size of 1-2 μm, and the ball milling time is 60 hours.

Step 2: preparing silicon nitride ceramics, wherein the slurry is vacuum degassed for 20min and then poured into an aluminum mold with the bottom thickness of 3mm (the pouring time is 2min), so that the slurry is quickly suspended in liquid nitrogen and fully solidified for 1h, and then demolding is carried out to obtain a blank; the blank body is dried for 60 hours at the temperature of 40 ℃ and the humidity of 70 percent and sintered for 6 hours at the temperature of 1750 ℃ to prepare the homogenized silicon nitride ceramic material.

The homogenized silicon nitride ceramic materials prepared in the above examples and comparative examples were subjected to a performance test, the materials were divided into five regions a to E, the five regions were tested for flexural strength as shown in fig. 9, and the test data are shown in table 1.

Table 1 shows the data of the performance tests of the silicon nitride ceramic samples prepared in the examples and comparative examples

From the SEM images, the synergistic effects of temperature field regulation, organic matter addition, slurry rheological property and the like are utilized, the microstructure of the material blank can be changed, and the ice crystal growth control and homogenization are realized, namely, the examples 1-3 are compared with the comparative examples 1-5; by combining optimization of drying and sintering, a large-size silicon nitride ceramic flat plate with uniform mechanical properties is prepared (A-E partition sampling is carried out on the flat plate, the uniformity is achieved when the discreteness is less than 5%, see table 1), and examples 1-3 are superior to comparative examples 1-5.

Features that are described and/or illustrated above with respect to one embodiment may be used in the same way or in a similar way in one or more other embodiments and/or in combination with or instead of the features of the other embodiments.

It should be emphasized that the term "comprises/comprising" when used herein, is taken to specify the presence of stated features, integers, steps or components but does not preclude the presence or addition of one or more other features, integers, steps, components or groups thereof.

The many features and advantages of these embodiments are apparent from the detailed specification, and thus, it is intended by the appended claims to cover all such features and advantages of these embodiments which fall within the true spirit and scope thereof. Further, since numerous modifications and changes will readily occur to those skilled in the art, it is not desired to limit the embodiments of the invention to the exact construction and operation illustrated and described, and accordingly, all suitable modifications and equivalents may be resorted to, falling within the scope thereof.

The invention has not been described in detail and is in part known to those of skill in the art.