CN114478054B

CN114478054B - Porous ceramic and preparation method thereof

Info

Publication number: CN114478054B
Application number: CN202210177242.2A
Authority: CN
Inventors: 裴亚星; 曹剑锋; 张昕; 孙正斌; 宋运运; 刘勋
Original assignee: Zhengzhou Research Institute for Abrasives and Grinding Co Ltd
Current assignee: Zhengzhou Research Institute for Abrasives and Grinding Co Ltd
Priority date: 2022-02-25
Filing date: 2022-02-25
Publication date: 2022-10-18
Anticipated expiration: 2042-02-25
Also published as: CN114478054A

Abstract

The invention discloses a porous ceramic and a preparation method thereof, belonging to the technical field of functional ceramic materials. The invention adopts the film with a ventilating structure as the inner pad of the upper and lower pressure heads of the porous ceramic forming die; and (2) putting the mixed and granulated powder into a die cavity of a forming die, uniformly spreading, jolting and leveling, wrapping and clamping the two sides of the granulated powder by using a film, pressing into a formed ceramic wet blank with a certain shape and thickness, then placing the formed ceramic wet blank on an air-permeable tray with the flatness of less than 0.1mm, drying by using microwave and hot air circulation, and sintering at high temperature to obtain the large-size thin-wall porous ceramic. The film prepared by the invention effectively solves the problems of sticking, microcracks and the like of the porous ceramic forming blank in the pressing process, and the tray and the drying process are assisted, so that the risks of deformation and cracking in the drying process of the blank are reduced, and the yield of the product is improved.

Description

Porous ceramic and preparation method thereof

Technical Field

The invention belongs to the technical field of functional ceramic materials, and relates to porous ceramic and a preparation method thereof.

Background

The porous ceramic has the characteristics of high hardness, high strength, good air permeability, high grinding precision, acid and alkali corrosion resistance and the like, so that the porous ceramic is widely applied to the semiconductor industry. Such as QFN (quad flat non-leaded package), PCB (printed circuit board) and other package substrates, and 6-12 inch silicon chips. With the gradual development of wafers in the semiconductor industry to a larger size direction, the manufacturing cost of large-scale packaging test factories is higher and higher, and higher requirements are correspondingly put forward on high strength, high hardness, ventilation uniformity, high precision stability, blockage prevention and the like of porous ceramic plates with large sizes and thin walls.

At present, the preparation process of the sheet and plate porous ceramics adopts a mould pressing forming method, and has the advantages of simple mould, high dimensional precision, convenient operation, high production efficiency and the like. The molding method is to fill a molding material containing about 3% of water into a mold, form a blank with a certain shape and strength under the action of pressure, and then prepare the porous ceramic through the processes of drying and high-temperature sintering. The key of the method is that the wet blank is required to reach the specified size, the ceramic density is ensured to be uniform, and the defects of die sticking, cracks and the like are avoided. However, the press molding method has great limitation in the formation of large-size and thin-walled ceramics, which is mainly due to the fact that the pressed wet blank is very easy to have the defects of sticking, microcrack and the like in the demolding process, and finally the ceramic fracture rate is extremely high. At present, the traditional method adopts a die smooth surface method, a release agent method and other methods to solve the problems of die sticking and microcrack, and has certain effect, but the application of the method is limited due to the defects of high grinding times of the die, easy pollution of the release agent to a blank body and the like.

Therefore, aiming at the problems of die sticking, cracks and the like which are easy to occur in the compression molding of large-size and thin-wall porous ceramic plates, the research of technical personnel in the field is always important on how to provide a preparation method which has simple process steps, low raw material cost, no die sticking, microcrack and other defects of a pressed green body and good sintering quality stability.

Disclosure of Invention

The invention provides a porous ceramic and a preparation method thereof, which solve the technical problem that the wet blank of large-size and thin-wall porous ceramic is easy to have the defects of sticking and microcracks during compression molding in the prior art, thereby greatly improving the sintering yield of the porous ceramic.

The technical scheme of the invention is as follows:

a process for preparing porous ceramic includes such steps as putting the powdered granulating material on the lower press head with lower film, spreading an upper film on the surface of said powdered granulating material, putting the upper press head on the upper film, assembling the mould, pressing, drying and high-temp sintering.

The invention provides a preparation method of porous ceramic, which comprises the following steps:

(1) Designing and manufacturing a porous ceramic forming die, wherein the porous ceramic forming die comprises an upper pressing head, a die ring and a lower pressing head;

(2) Manufacturing an upper film and a lower film according to the sizes of the upper pressure head and the lower pressure head of the porous ceramic forming die in the step (1);

(3) Putting the main material, yttrium oxide, a pore-forming agent and water into a mixing machine for mixing, and removing impurities from the mixed wet material to obtain a mixed material;

(4) Placing the mixture obtained in the step (3) in a spray drying tower for spray granulation to obtain granulated powder;

(5) Assembling the lower pressing head and the die ring of the porous ceramic forming die in the step (1), paving a layer of the lower film in the step (2) on the surface of the lower pressing head, placing the granulating powder in the step (4) on the lower film, jolting and scraping, paving a layer of upper film on the upper surface of the granulating powder, installing the pressing head, moving the pressing head into a pressing machine for prepressing, and pressing again after the prepressing is finished to obtain a formed ceramic wet blank;

(6) Placing the formed ceramic wet blank in the step (5) on an air-permeable tray, and circularly drying by microwave and hot air to obtain a dried blank body;

(7) And (5) burying and sintering the dried green body obtained in the step (6) to obtain the porous ceramic.

Furthermore, the fit clearance between the upper and lower pressing heads and the die ring of the porous ceramic forming die in the step (1) is required to be within the range of 0.1-0.4 mm.

Further, the preparation steps of the film in the step (2) are as follows: uniformly coating a layer of water-based acrylic glue on a plastic bottom film with the thickness of 80-100 mu m, bonding the plastic bottom film with a metal substrate with the surface roughness Ra of 0.3-1 mu m to prepare a double-layer composite film with the thickness of 100-200 mu m, and rolling micro-airway lines with the width of 10-50 mu m and the depth of 40-100 mu m on the metal substrate to prepare a film; wherein the plastic basement membrane is a polyester basement membrane, a polyvinyl chloride basement membrane or a polyimide basement membrane, and the metal substrate is a copper substrate, an aluminum substrate or a silver-based calendered sheet.

Further, in the step (3), the main materials comprise alumina powder and clay; the particle size range of the alumina powder is 5-500 mu m, and the particle size range of the clay is 5-20 mu m; the mass ratio of the alumina powder to the clay is 1 (0.15-0.3).

Further, in the step (3), yttrium oxide accounts for 0.2-0.5% of the total mass of the main materials, a pore-forming agent accounts for 0.2-2% of the total mass of the main materials, and water accounts for 2-8% of the total mass of the main materials; the pore-forming agent is coke, wood powder or walnut shell.

Wherein the yttrium oxide acts with the main phase Al ₂ O ₃ The ceramic is sintered in a liquid phase at a high temperature to form a solid solution, so that the sintering strength of the ceramic is improved; the deionized water is used for increasing the integral plasticity of the main material and improving the strength of the formed blank body; the pore former serves to increase the porosity of the porous ceramic.

Further, the parameters of the spray drying tower in the step (4) are that the rotating speed of a rotary table is 7000-14000rpm, the negative pressure is 100-150Pa, the inlet temperature is 140-190 ℃, and the outlet temperature is 50-70 ℃; the prepressing pressure in the step (5) is 5-15MPa, and the pressure maintaining time is 5-20s; the secondary pressing pressure is 10-30MPa, and the dwell time is 120-300s.

Further, in the step (6), the microwave power is 10-30kW, the drying temperature is 40-80 ℃, and the drying time is 1-3 hours; the water content of the dried green body is not higher than 1%, and the flatness of the tray is lower than 0.1mm.

Further, the sand burying and sintering process in the step (7) comprises the steps of heating to 400-600 ℃ at the speed of 17-25 ℃/h, preserving heat for 1-3h, heating to 1250-1550 ℃ at the speed of 27-48 ℃/h, and preserving heat for 1-2h; when the sand is buried and sintered, the flatness of the sand cushion on the bottom surface of the dry blank is lower than 0.1mm, and the granularity number of the sand is 10-30 meshes.

The purpose of sand burying is to improve the heating uniformity of the ceramic, reduce the shrinkage deformation of the ceramic and improve the sintering yield.

The invention also discloses a porous ceramic, which is sheet-shaped or block-shaped, the length or diameter of the porous ceramic is more than 350mm, the thickness of the porous ceramic is less than 5mm, the diameter of the pores of the porous ceramic is 10-300 mu m, and the porosity of the porous ceramic is 25-40%.

The invention has the following beneficial effects:

(1) The invention adopts the vacuum breaking adsorption principle for the first time, and the upper surface and the lower surface of the wet blank are directly contacted with the film with the micro-air channel structure during compression molding by adopting the film with the micro-air channel structure, and gas is directly released from the air channel of the film during compression molding, so that vacuum negative pressure is not easy to form, thereby thoroughly solving the defects that the wet blank is easy to stick and microcrack during compression molding of large-size and thin-wall porous ceramics, greatly improving the yield of the porous ceramics and breaking through the technical barrier that the shape and the size of the compression molding of ceramic products are limited.

(2) The film air flue has the functions of being beneficial to gas emission in the compression molding process, not easy to generate vacuum adsorption, and preventing powder from blocking the air flue in the molding process, wherein the width of the air flue is smaller than the particle size of the ceramic powder; the surface of the film is smooth and has low roughness, so that the surface of the pressed ceramic wet blank is smooth; meanwhile, the film is not easy to deform, so that the size of the film cannot be increased during pressing, and the ceramic wet blank is prevented from being damaged by demoulding.

(3) According to the invention, the formed ceramic wet blank is dried by a drying method combining microwave and hot air circulation for the first time, and the deformation of the wet blank is reduced by using the tray with low flatness and air permeability, so that the problems of extreme difficulty in drying and easy deformation and cracking caused by uneven heating in the traditional method are avoided, the water content of the wet blank can be easily reduced to the process requirement, the water content of the ceramic wet blank can be controlled to be not higher than 1%, and the drying time is shortened; meanwhile, the yield of the porous ceramic prepared by the preparation method is at least 90%, and compared with the yield of the product prepared by the traditional preparation method, the yield of the porous ceramic prepared by the preparation method is at least 28%.

(4) The invention provides a preparation method of porous ceramic, the size of the porous ceramic prepared by the preparation method is larger than 350mm, and the thickness is lower than 5mm; meanwhile, the porous ceramic prepared by the preparation method has higher bending strength and stable comprehensive performance. The preparation method disclosed by the invention has the advantages of simple steps, convenience in adjusting the shape and the size of the porous ceramic, low manufacturing cost of the film material and high production efficiency. The method can be popularized to other molded ceramic products and other industries, such as superhard material products and the like.

Drawings

FIG. 1 is a schematic view of a film with a square airway structure according to the present invention.

FIG. 2 is a schematic view of a circular airway structure membrane of the present invention.

FIG. 3 is a schematic view of a forming mold according to the present invention.

FIG. 4 is an SEM photograph of the porous ceramic obtained in example 1.

FIG. 5 is an SEM photograph of the porous ceramic obtained in example 2.

FIG. 6 is an SEM photograph of the porous ceramic obtained in example 3.

FIG. 7 is an SEM photograph of the porous ceramic obtained in example 4.

FIG. 8 is an SEM photograph of the porous ceramic obtained in comparative example 1.

Detailed Description

The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. All other embodiments, which can be obtained by a person skilled in the art without inventive effort based on the embodiments of the present invention, are within the scope of the present invention.

A process for preparing porous ceramic includes such steps as putting the powdered granular material on the lower press head with lower film, spreading an upper film on the surface of said powdered granular material, putting the upper press head on the upper film, assembling the mould, pressing, drying and high-temp sintering.

A preparation method of porous ceramic comprises the following specific steps:

(1) Designing and manufacturing a porous ceramic forming die, wherein the porous ceramic forming die comprises an upper pressing head, a die ring and a lower pressing head; wherein, the fit clearance between the upper and lower pressure heads and the die ring of the porous ceramic forming die is required to be within the range of 0.1-0.4mm, as shown in figure 3.

(2) And (2) manufacturing an upper film and a lower film according to the sizes of the upper pressure head and the lower pressure head of the porous ceramic forming die in the step (1), wherein the steps are as follows: uniformly coating a layer of water-based acrylic glue on a plastic bottom film with the thickness of 80-100 mu m, bonding the plastic bottom film with a metal substrate with the surface roughness Ra of 0.3-1 mu m to prepare a double-layer composite film with the thickness of 100-200 mu m, and rolling micro-airway lines with the width of 10-50 mu m and the depth of 40-100 mu m on the metal substrate to prepare a film; wherein the plastic basement membrane is a polyester basement membrane, a polyvinyl chloride basement membrane or a polyimide basement membrane, and the metal substrate is a copper substrate, an aluminum substrate or a silver-based calendered sheet.

(3) Alumina powder with the particle size range of 5-500 mu m and clay with the particle size range of 5-20 mu m are mixed, wherein the mass ratio of the alumina powder to the clay is 1 (0.15-0.3), yttrium oxide accounts for 0.2-0.5% of the total mass of the main material, pore-forming agent accounts for 0.2-2% of the total mass of the main material, and water accounts for 2-8% of the total mass of the main material; and putting the mixture into a mixer for mixing, and then removing impurities from the mixed wet material to obtain the mixed material.

(4) And (4) placing the mixture obtained in the step (3) into a spray drying tower for spray granulation, wherein the parameters of the spray drying tower comprise the rotating disc rotating speed of 7000-14000rpm, the negative pressure of 100-150Pa, the inlet temperature of 140-190 ℃ and the outlet temperature of 50-70 ℃, and granulating powder is prepared.

(5) Assembling the lower pressure head and the die ring of the porous ceramic forming die in the step (1), paving a layer of the lower film in the step (2) on the surface of the lower pressure head, placing the granulating powder in the step (4) on the lower film, jolting and scraping, paving a layer of upper film on the upper surface of the granulating powder, installing the pressure head, moving the pressure head into a press for prepressing at the prepressing pressure of 5-15MPa for 5-20s, and after the prepressing is finished, performing secondary pressing at the pressing pressure of 10-30MPa for 120-300s to obtain a formed ceramic wet blank.

(6) And (3) placing the wet formed ceramic blank in the step (5) on an air-permeable tray with the flatness of less than 0.1mm, then sending the wet formed ceramic blank into a drying box with a microwave radio frequency source arranged at the top, wherein the frequency of the microwave radio frequency source is 2350-2450MHz, the microwave power is 10-30kW, drying the wet formed ceramic blank at the temperature of 40-80 ℃ for 1-3h by adopting a microwave and hot air circulation drying method to obtain a dried blank body, and the water content of the dried blank body is not more than 1%.

(7) And (5) burying and sintering the dried green body obtained in the step (6), wherein during burying and sintering, the flatness of sand cushion on the bottom surface of the green body is lower than 0.1mm, the granularity number of the sand is 10-30 meshes, and the burying and sintering process comprises the steps of heating to 400-600 ℃ at the speed of 17-25 ℃/h, preserving heat for 1-3h, heating to 1250-1550 ℃ at the speed of 27-48 ℃/h, and preserving heat for 1-2h to obtain the porous ceramic.

Wherein the shape of the porous ceramic is sheet or block, the length or diameter of the porous ceramic is more than 350mm, and the thickness is less than 5mm; the porous ceramic has pore diameter of 10-300 μm and porosity of 25-40%.

The technical solution of the present invention is further illustrated by the following specific examples:

example 1

The preparation method of the porous ceramic comprises the following steps:

a mold was designed and fabricated, and the mold size was 360 × 4.5 (unit mm) in this example, and a 359.9 × 0.12 (unit mm) film was fabricated, which is schematically shown in fig. 1.

Mixing alumina powder with the particle size of 200 microns and clay with the particle size of 15 microns as main materials according to the mass ratio of 1:0.2, putting the mixture into a double-cone mixer, then adding yttrium oxide accounting for 0.3 percent of the weight of the main materials and coke accounting for 1 percent of the weight of the main materials, mixing for 3.5 hours, then taking out the dry materials, putting the dry materials into a double-motion mixer, adding deionized water accounting for 5 percent of the total weight of the dry materials, stirring at a high speed for 2.5 hours, and removing impurities to obtain the compound.

Spray granulation of the compound was carried out, the drying tower rotation speed was adjusted to 12000rpm, the negative pressure was set to 120Pa, the inlet temperature was set to 130 ℃ and the outlet temperature was set to 70 ℃ to obtain granulated powder.

Putting the granulated powder on a film which is assembled in advance with a forming die, spreading uniformly, jolting and leveling, laying a layer of film on the upper surface of the leveling material, assembling the die, then putting the die in an oil press for prepressing with the prepressing pressure of 10MPa and the pressure maintaining time of 8s, after the prepressing is finished, pressing again with the pressing pressure of 20MPa and the pressure maintaining time of 120s, releasing the pressure and demoulding to obtain the formed ceramic wet blank.

And (3) placing the formed wet ceramic blank on a tray, and then carrying out microwave hot air circulation drying with the microwave power of 25kW, the temperature of 70 ℃ and the drying time of 1.5h to obtain a dried blank body, wherein the water content of the dried blank body is 0.8%.

And placing the dried blank body in a high-temperature furnace, burying sand, heating to 450 ℃ at the speed of 19 ℃/h, preserving heat for 1.5h, heating to 1300 ℃ at the speed of 36 ℃/h, preserving heat for 2h, and slowly cooling to room temperature within 36h to obtain the porous ceramic.

The porous ceramics prepared in the example were tested: the yield of the porous ceramic is 95%, the porosity is 38%, and the bending strength is 85MPa; the SEM image is shown in FIG. 4, which shows that: the cross section of the ceramic is a loose porous structure, and the average pore diameter is 180 mu m.

Example 2

The preparation method of the porous ceramic comprises the following steps:

a mold was designed and fabricated, and the mold size was 380 × 4 (unit mm) for this example, and a 379.9 × 0.15 (unit mm) film was fabricated, which is schematically shown in fig. 2.

Mixing the main materials with alumina powder with the particle size of 80 microns and clay with the particle size of 10 microns according to the mass ratio of 1:0.25, putting the mixture into a double-cone mixer, then adding yttrium oxide accounting for 0.26 percent of the weight of the main materials and walnut shells accounting for 1.2 percent of the weight of the main materials, mixing for 4 hours, then taking out the dry materials, putting the dry materials into a double-motion mixer, adding deionized water accounting for 4 percent of the total weight of the dry materials, stirring at a high speed for 3 hours, and removing impurities to obtain the compound.

And (3) carrying out spray granulation on the mixture, and adjusting the rotation speed of a drying tower to 14000rpm, setting the negative pressure to 100Pa, setting the inlet temperature to 160 ℃ and setting the outlet temperature to 60 ℃ to obtain granulated powder.

Putting the granulated powder on a film which is assembled in advance with a forming die, spreading uniformly, jolting and leveling, laying a layer of film on the upper surface of the leveling material, assembling the die, then putting the die in an oil press for prepressing with the prepressing pressure of 12MPa and the pressure maintaining time of 6s, after the prepressing is finished, pressing again with the pressing pressure of 28MPa and the pressure maintaining time of 150s, releasing the pressure and demoulding to obtain the formed ceramic wet blank.

And placing the formed wet ceramic blank on a tray, and then performing microwave hot air circulation drying, wherein the microwave power is 20kW, the temperature is set to be 60 ℃, and the drying time is 2 hours, so as to obtain a dried blank body, wherein the water content of the dried blank body is 0.7%.

And (3) placing the dried green body in a high-temperature furnace, burying sand, heating to 500 ℃ at the rate of 21 ℃/h, keeping the temperature for 2.5h, heating to 1300 ℃ at the rate of 34 ℃/h, keeping the temperature for 1.5h, and slowly cooling to room temperature within 48h to obtain the porous ceramic.

The porous ceramics prepared in the example were tested: the yield of the porous ceramic is 92%, the porosity is 29%, and the bending strength is 95MPa; the SEM image is shown in FIG. 5, and it can be seen that: the cross section of the ceramic is a loose porous structure, and the average pore diameter is 60 mu m.

Example 3

The preparation method of the porous ceramic comprises the following steps:

a mold was designed and fabricated, and the mold size of this example was 430 by 4.5 (unit mm), and a film of 430.9 by 0.13 (unit mm) was fabricated, which is schematically shown in fig. 1.

Putting alumina powder with the particle size of 150 microns and clay with the particle size of 15 microns into a double-cone mixer according to the mass ratio of 1.

Spray granulation was performed on the compound, and the drying tower rotation speed was adjusted to 12000rpm, the negative pressure was set to 120Pa, the inlet temperature was set to 130 ℃, and the outlet temperature was set to 70 ℃, to obtain granulated powder.

Putting the granulated powder on a film which is assembled in advance with a forming die, spreading uniformly, jolting and leveling, laying a layer of film on the upper surface of the leveling material, assembling the die, then putting the die in an oil press for prepressing with the prepressing pressure of 12MPa and the pressure maintaining time of 10s, after the prepressing is finished, pressing again with the pressing pressure of 25MPa and the pressure maintaining time of 150s, releasing the pressure and demoulding to obtain the formed ceramic wet blank.

And placing the formed wet ceramic blank on a tray, and then performing microwave hot air circulation drying, wherein the microwave power is 25kW, the temperature is set to be 70 ℃, and the drying time is 1.5h, so as to obtain a dried blank body, wherein the water content of the dried blank body is 0.8%.

The porous ceramics prepared in the example were tested: the yield of the porous ceramic is 90%, the porosity is 36%, and the bending strength is 89MPa; the SEM image is shown in FIG. 6, which shows that: the cross section of the ceramic is a loose porous structure, and the average pore diameter is 110 mu m.

Example 4

The preparation method of the porous ceramic comprises the following steps:

a mold was designed and fabricated, the mold size of this example was 450 x 4 (unit mm), and a 449.9 x 0.15 (unit mm) film was fabricated, which is schematically shown in fig. 2.

Mixing alumina powder with the particle size of 20 microns and clay with the particle size of 10 microns as main materials according to the mass ratio of 1:0.25, putting the mixture into a double-cone mixer, then adding yttrium oxide accounting for 0.26 percent of the weight of the main materials and walnut shells accounting for 1.2 percent of the weight of the main materials, mixing for 4 hours, then taking out the dry materials, putting the dry materials into a double-motion mixer, adding deionized water accounting for 4 percent of the total weight of the dry materials, stirring at a high speed for 3 hours, and removing impurities to obtain the compound.

Putting the granulated powder on a film which is assembled in advance with a forming die, spreading uniformly, jolting and leveling, laying a layer of film on the upper surface of the leveling material, assembling the die, then putting the die in an oil press for prepressing with the prepressing pressure of 18MPa and the pressure maintaining time of 10s, after the prepressing is finished, pressing again with the pressing pressure of 30MPa and the pressure maintaining time of 180s, releasing the pressure and demoulding to obtain the formed ceramic wet blank.

And placing the dried blank body in a high-temperature furnace, burying sand, heating to 500 ℃ at the speed of 21 ℃/h, preserving heat for 2.5h, heating to 1300 ℃ at the speed of 34 ℃/h, preserving heat for 1.5h, and slowly cooling to room temperature within 48h to obtain the porous ceramic.

The porous ceramics prepared in the example were tested: the yield of the porous ceramic is 91%, the porosity is 32%, and the bending strength is 110MPa; the SEM image is shown in FIG. 7, which shows that: the cross section of the ceramic is a loose porous structure, and the average pore diameter is 19 mu m.

Comparative example 1

The preparation method of the porous ceramic of the comparative example comprises the following steps:

a mold was designed and fabricated, with the mold size of this example being 360 x 4.5 (units mm).

Mixing alumina powder with the particle size of 200 microns and clay with the particle size of 15 microns as main materials according to the mass ratio of 1:0.2, putting the mixture into a double-cone mixer, then adding yttrium oxide accounting for 0.3 percent of the weight of the main materials and coke accounting for 1 percent of the weight of the main materials, mixing for 3.5 hours, then taking out the dry materials, putting the dry materials into a double-motion mixer, adding deionized water accounting for 5 percent of the total weight of the dry materials, stirring at a high speed for 2.5 hours, and removing impurities to obtain the mixed material.

And putting the granulated powder on a film which is assembled in advance on a forming die, uniformly spreading, jolting and leveling, paving a layer of film on the upper surface of the leveling material, assembling the die, then putting the die into an oil press for prepressing at 10MPa for 8s, releasing pressure and demoulding to obtain a formed ceramic wet blank, wherein the die bonding rate is about 60 percent, and after the prepressing is finished, the pressing pressure is 20MPa, the pressure maintaining time is 120 s.

And (3) placing the formed wet ceramic blank on a glass plate, and then carrying out forced air drying at the temperature of 70 ℃ for 8 hours to obtain a dried blank, wherein the water content of the dried blank is 0.8%.

The porous ceramics prepared in the example were tested: the yield of the porous ceramic is 70%, the porosity is 40%, and the bending strength is 70MPa; the SEM image is shown in FIG. 8, which shows that: the cross section of the ceramic is a loose porous structure, and the average pore diameter is 170 mu m.

The difference between the comparative example and the example 1 is that the air-permeable structure film of the invention is not adopted in the process of preparing the porous ceramic, the microwave hot air circulation drying is not adopted in the drying process of the formed ceramic wet blank, but the blast drying is adopted, and other processes are the same. Through comparison between the porous ceramic material and the porous ceramic material in example 1, the porous ceramic material in comparative example 1 has a die-bonding phenomenon in a wet blank during press forming, the die-bonding rate is about 60%, and the porous ceramic material in example 1 has no die-bonding phenomenon in the wet blank during press forming; comparative example 1, the water content of the dried green body can reach 0.8% only by drying the ceramic wet green body for 8 hours, and example 1 only needs 1.5 hours, compared with comparative example 1, the invention has the advantages of energy saving and high production efficiency; the product yield is 70%, the product yield of the embodiment 1 of the invention is 90%, and is improved by about 28% compared with the comparative example 1, because the product cracking problem is caused by the fact that the comparative example 1 has adhesive film and too long drying time in the process of preparing the porous ceramic; the comparative analysis shows that the preparation method of the invention solves the defect that the wet blank of the porous ceramic is easy to be adhered with a mold and microcrack when the porous ceramic is molded, the yield of the porous ceramic is obviously higher than that of the porous ceramic prepared by the traditional method, and the bending strength performance of the porous ceramic is also better than that of the porous ceramic prepared by the traditional method.

The porous ceramic and the preparation method thereof provided by the invention are described in detail above. The principles and embodiments of the present invention have been described herein using specific examples, which are presented only to assist in understanding the method and its core concepts of the present invention. It should be noted that, for those skilled in the art, without departing from the principle of the present invention, it is possible to make various improvements and modifications to the present invention, and those improvements and modifications also fall within the scope of the claims of the present invention.

Claims

1. A preparation method of porous ceramics is characterized in that: placing the granulating powder for preparing the porous ceramic on a lower pressing head paved with a lower film, paving an upper film on the surface of the granulating powder, placing an upper pressing head on the upper film, assembling a porous ceramic forming die, and then pressing, drying and sintering at high temperature to prepare the porous ceramic;

the method comprises the following specific steps:

(1) Designing and manufacturing a porous ceramic forming die, wherein the porous ceramic forming die comprises an upper pressing head, a die ring and a lower pressing head; the fit clearance between the upper and lower pressure heads of the porous ceramic forming die and the die ring in the step (1) is 0.1-0.4mm;

(2) Manufacturing an upper film and a lower film according to the sizes of the upper pressure head and the lower pressure head of the porous ceramic forming die in the step (1); the preparation method of the film in the step (2) comprises the following steps: uniformly coating a layer of water-based acrylic glue on a plastic bottom film with the thickness of 80-100 mu m, bonding the plastic bottom film with a metal substrate with the surface roughness Ra of 0.3-1 mu m to prepare a double-layer composite film with the thickness of 100-200 mu m, and rolling micro-airway lines with the width of 10-50 mu m and the depth of 40-100 mu m on the metal substrate to prepare a film; wherein the plastic basement membrane is a polyester basement membrane, a polyvinyl chloride basement membrane or a polyimide basement membrane, and the metal substrate is a copper substrate, an aluminum substrate or a silver-based calendered sheet;

(5) Assembling the lower pressing head and the die ring of the porous ceramic forming die in the step (1), paving a layer of the lower film in the step (2) on the surface of the lower pressing head, then placing the granulating powder in the step (4) on the lower film, paving a layer of upper film on the upper surface of the granulating powder, installing the pressing head, then moving the pressing head into a pressing machine for prepressing, and pressing again after the prepressing is finished to obtain a formed ceramic wet blank; by adopting the film with the micro-air-channel structure, the upper surface and the lower surface of the wet blank are directly contacted with the film with the micro-air-channel structure during compression molding, and air is directly released from the air channel of the film during compression molding;

(7) And (4) burying sand and sintering the dried blank in the step (6) to obtain the porous ceramic.

2. The method for producing a porous ceramic according to claim 1, characterized in that: the main materials in the step (3) comprise alumina powder and clay; the particle size range of the alumina powder is 5-500 mu m, and the particle size range of the clay is 5-20 mu m; the mass ratio of the alumina powder to the clay is 1 (0.15-0.3).

3. The method for producing a porous ceramic according to claim 2, characterized in that: in the step (3), yttrium oxide accounts for 0.2-0.5% of the total mass of the main materials, pore-forming agent accounts for 0.2-2% of the total mass of the main materials, and water accounts for 2-8% of the total mass of the main materials; the pore-forming agent is coke, wood powder or walnut shell.

4. The method for producing a porous ceramic according to claim 3, characterized in that: the parameters of the spray drying tower in the step (4) are the rotating speed of the rotary disc of 7000-14000rpm, the negative pressure of 100-150Pa, the inlet temperature of 140-190 ℃ and the outlet temperature of 50-70 ℃; the prepressing pressure in the step (5) is 5-15MPa, and the pressure maintaining time is 5-20s; the secondary pressing pressure is 10-30MPa, and the dwell time is 120-300s.

5. The method for producing a porous ceramic according to claim 4, characterized in that: in the step (6), the microwave power is 10-30kW, the drying temperature is 40-80 ℃, and the drying time is 1-3h; the water content of the dried green body is not higher than 1%, and the flatness of the tray is lower than 0.1mm.

6. The method for producing a porous ceramic according to claim 5, characterized in that: the sand burying sintering process in the step (7) comprises the steps of heating to 400-600 ℃ at the speed of 17-25 ℃/h, preserving heat for 1-3h, heating to 1250-1550 ℃ at the speed of 27-48 ℃/h, and preserving heat for 1-2h; when the sand is buried and sintered, the flatness of the sand cushion on the bottom surface of the dry blank is lower than 0.1mm, and the granularity number of the sand is 10-30 meshes.

7. The porous ceramic produced by the production method according to any one of claims 1 to 6, characterized in that: the porous ceramic is sheet-shaped or block-shaped; the length or diameter of the porous ceramic is more than 350mm, and the thickness is less than 5mm; the porous ceramic has pore diameter of 10-300 μm and porosity of 25-40%.