CN113831144A

CN113831144A - Method for preparing ceramic material by multi-field coupling ultra-fast sintering

Info

Publication number: CN113831144A
Application number: CN202111244701.6A
Authority: CN
Inventors: 徐晨; 白彬
Original assignee: Institute of Materials of CAEP
Current assignee: Institute of Materials of CAEP
Priority date: 2021-10-26
Filing date: 2021-10-26
Publication date: 2021-12-24
Anticipated expiration: 2041-10-26
Also published as: CN113831144B

Abstract

The invention provides a method for preparing a ceramic material by multi-field coupling ultra-fast sintering, belonging to the technical field of preparation of ceramic materials. The method comprises the steps of filling ceramic powder or ceramic green bodies into an ultrathin graphite mold with the wall thickness of 1-20mm, applying a power supply and a microwave-assisted heating or induction-assisted heating multiple heat sources to the ultrathin graphite mold, enabling the ceramic powder or ceramic green bodies to be heated up at a heating rate of 500-2000 ℃/min under the combined action of the multiple heat sources and the ultrathin graphite mold in an ultra-fast mode, achieving the effect of jumping over a grain rapid growth temperature region in an ultra-fast mode and directly entering a sintering densification temperature region, cooling and demolding after sintering is completed, and taking out sintered and molded blocks from the ultrathin graphite mold. The heating rate of the invention can reach 2000 ℃/min at most, the sintering temperature of densification is 500 ℃ and above lower than the ordinary pressureless sintering temperature, the temperature difference of a temperature field can be effectively reduced, the cracking of a large-size sample caused by nonuniform temperature is reduced, and the sintering densification of the large-size sample is facilitated.

Description

Method for preparing ceramic material by multi-field coupling ultra-fast sintering

Technical Field

The invention belongs to the technical field of ceramic material preparation, and particularly relates to a method for preparing a ceramic material by multi-field coupling ultra-fast sintering.

Background

Rapid sintering is the mainstream trend of the ceramic sintering technology in the world in recent years. The current sintering technologies meeting the requirements of ultra-fast sintering include Spark Plasma Sintering (SPS), Flash Sintering (FS), microwave sintering and the like. The plasma is a dissociated high-temperature conductive gas and has a high reaction activity. Because the temperature of the plasma is generally 4000-10999 ℃, the gaseous molecules and atoms are in a highly activated state, and the ionization degree in the plasma gas is very high, the properties make the plasma become a very important material preparation and processing technology. The sintering method utilizes pulse current to enable particles to generate Joule heat uniformly and enable the surfaces of the particles to be activated into discharge plasma, and accelerates the diffusion process, so that the ceramic particles are bridged more easily, and the powder is sintered to be compact at a lower temperature.

The SPS technology has the advantages of ultra-fast speed, low temperature, high efficiency, and the like, and can be used for preparing metals, ceramics, nano materials, amorphous materials, coupling materials, gradient materials, and the like, so that a great deal of attention and research in the academic world and the industry are obtained in recent years. The most studied of them are functional materials, including thermoelectric materials, magnetic materials, functionally graded materials, coupled functional materials, nano functional materials, etc. In addition, attempts have been made to produce amorphous alloys, shape memory alloys, diamonds, etc. from SPS. At present, many researches on the preparation of new materials by using SPS are carried out abroad, especially in Japan, and part of products are put into production. However, the sintering mechanism of SPS is not completely understood at present, and a great deal of practical and theoretical research is needed to complete the sintering mechanism. The existing SPS can not be sintered to a product with the size of more than 300mm to achieve complete compactness due to the capacity limitation of pulse current and uneven distribution of a temperature field. Moreover, the current design of SPS cannot produce complex shaped products. In addition, SPS is expensive, and although there are industrial products, the sintering cost is high, and it is not yet applied to the production of practical ceramic products.

Flash fever was first discovered in 3YSZ in 2010 by professor Rishi Raj of University of Colorado (University of Colorado), usa. The research shows that the compound hasCeramic materials of specific electrical properties are heated and loaded with a constant voltage, and when the furnace temperature is raised to a characteristic temperature, the material shows electroluminescence and rapidly densifies (fig. 1). Compared with other sintering technologies, flash sintering has the characteristics of low sintering temperature (generally lower than pressureless sintering temperature by more than 400 ℃) and short time, can effectively improve sintering efficiency and inhibit coarsening of crystal grains, and has a wider application prospect. Early flash firing research focused on oxide ceramics, such as Al₂O₃、Y₂O₃、TiO₂And the like. Subsequent studies have found that flash firing techniques can also be applied to carbide and boride ceramics, such as SiC, B₄C、ZrB₂And the like. However, in flash firing, the direct current electric field distribution is difficult to achieve complete uniformity, so that a large-size sample with uniform density is difficult to prepare.

Microwave sintering is a method of sintering materials using microwave heating. The microwave sintering technology is a method for realizing densification sintering by utilizing materials to absorb microwave energy and convert the microwave energy into kinetic energy and heat energy of internal molecules so as to uniformly heat the whole materials to a certain temperature, and is an important technical means for quickly preparing high-quality new materials and traditional materials with new properties. Compared with the conventional sintering method, the microwave sintering method has the advantages of rapid heating, low sintering temperature, material organization refinement, material property improvement, safety, no pollution, high efficiency, energy conservation and the like, thereby being called as a new generation sintering method. However, microwave sintering has a high selectivity for samples, and has limitations in preparing materials.

Disclosure of Invention

The invention aims to provide a method for preparing a ceramic material by multi-field coupling ultra-fast sintering, which can realize the integral ultra-fast temperature rise of 500 plus 2000 ℃/min by coupling and heating a plurality of heating fields and matching with an ultra-thin graphite mold, achieve the effect of ultra-fast skipping an ultra-fast grain growth temperature region and directly entering a sintering densification temperature region, effectively reduce the temperature difference of the temperature field, improve the uniformity of the temperature field, reduce the cracking phenomenon of a large-size sample caused by non-uniform temperature, and be beneficial to the sintering densification of the large-size sample.

The purpose of the invention is realized by the following technical scheme:

a method for preparing a ceramic material by multi-field coupling ultra-fast sintering comprises the steps of loading ceramic powder or ceramic green bodies into an ultra-thin graphite mold with the wall thickness of 1-20mm, applying multiple heat sources such as a power supply, microwave-assisted heating or induction-assisted heating to the ultra-thin graphite mold, enabling the ceramic powder or ceramic green bodies to be subjected to ultra-fast temperature rise integrally at the temperature rise rate of 500-2000 ℃/min under the combined action of the multiple heat sources and the ultra-thin graphite mold, skipping an ultra-fast grain growth temperature region at ultra-fast speed, directly entering a sintering densification temperature region for sintering, cooling and demolding after sintering is completed, and taking sintered and molded blocks out of the graphite mold.

Further, the power supply applied to the graphite mold is one of pulse current, direct current or alternating current.

Further, the grain diameter of the ceramic powder is 20nm-10 mu m.

Further, the sintering temperature is 25-1000 ℃, and the sintering time lasts for 0-600 s.

Further, the ceramic green body is obtained by pressing ceramic powder by compression molding or gel film injection molding and then pressing the ceramic powder by cold isostatic pressing at the pressure of 100-300MPa for the pressure maintaining time of 1-20 min.

Further, the molding pressure of the compression molding is 2-10Mpa, and the pressure maintaining time is 2-5 min.

Further, the sintering atmosphere is one of air, hydrogen, a hydrogen-argon mixed gas, nitrogen and a hydrogen-nitrogen mixed gas.

The existing sintered ceramic material needs to be pressureless sintered for more than 5-8 hours at the temperature of 1400-1800 ℃ so as to achieve the density of more than 95%. The sintering temperature required by the preparation of oxide and non-oxide ceramics by the spark plasma field auxiliary sintering is more than 1100 ℃, and the heating rate is 300 ℃/min and 100 ℃. Excessive sintering temperatures and long sintering times generally cause the grains of the ceramic to grow to micron-sized dimensions, which in turn leads to reduced performance. Meanwhile, the discharge plasma field assisted sintering often has the problem of uneven electric field distribution, and generally only a small sample (the diameter size is within 30 cm) can be prepared, and the large-size sample preparation has cracking or stress concentration or uneven performance caused by insufficient uniformity of sintering density.

The invention uses a multi-field coupling sintering technology, assists pulse/direct current/alternating current heating through an external field (microwave/induction heating), combines an ultrathin graphite mold, can obviously improve the uniformity of a temperature field, improves the heating rate of a sample, quickly skips a rapid grain growth temperature region, directly enters a sintering densification temperature region, reduces the sintering temperature of oxide or non-oxide ceramics, shortens the sintering time, simultaneously can effectively refine grains of a ceramic material and regulate and control a phase structure and a microstructure, improves the density and microstructure uniformity of the material, and meets the use requirements.

In addition, the application provides a method for preparing a ceramic material by multi-field coupling ultra-fast, induction auxiliary heating and microwave auxiliary heating are added while a power supply is applied to the ceramic material for sintering, and the specific implementation modes of the induction auxiliary heating and the microwave auxiliary heating are not limited.

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

the invention provides a method for preparing a ceramic material by multi-field coupling field ultra-fast sintering, which utilizes the principle that ultra-fast temperature rise can directly reach a densification temperature region and shorten sintering time, and carries out ultra-fast temperature rise on the material by a large pulse/direct current/alternating current heating ultra-thin graphite die so as to rapidly finish sintering at a lower furnace temperature, avoid ineffective heating, reduce the sintering temperature by 500 ℃ or more than conventional non-pressure sintering, effectively reduce the sintering temperature, shorten the sintering time and improve the density of a ceramic block prepared by sintering. Meanwhile, under the combined action of various heating field couplings and the ultrathin graphite mold, the temperature difference of the temperature field can be effectively reduced, the uniformity of the temperature field is improved, the cracking phenomenon of a large-size sample caused by nonuniform temperature is reduced, and the sintering densification of the large-size sample is facilitated.

Drawings

FIG. 1 shows ZrO prepared in example 1₂Microscopic morphology of the ceramic pellet;

FIG. 2 is a UO prepared in example 2₂Microscopic morphology of the core block;

FIG. 3 shows Al prepared in example 3₂O₃Microscopic morphology of the ceramic pellet;

FIG. 4 shows ZrO prepared in comparative example 1₂Microscopic morphology of the ceramic pellet;

FIG. 5 shows ZrO prepared in comparative example 2₂Microscopic morphology of ceramic pellets.

Detailed Description

In order to make the objects, technical solutions and advantages of the present invention more apparent, the present invention is further described in detail with reference to the following embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention.

Example 1

With ZrO₂Ceramic powder (powder particle size about 100nm) as raw material, making 100g of the raw material powder into a ring by gel casting method, placing into a graphite mold with wall thickness of 15mm, introducing argon gas, and adding ZrO₂When the ceramic body is heated up by induction heating, a power supply is started to apply a pulse electric field at two ends of the ultrathin graphite die, so that ZrO can be heated up by induction heating₂The ceramic body is heated for sintering under the conditions of applying pulse current (2000A) and heating by induction assistance (10 kW).

Wherein, the heating rate under the conditions of applying pulse current and induction-assisted heating is 1000 ℃/min, and ZrO with compact structure can be obtained by maintaining the temperature for 30s when the temperature is raised to 600 DEG C₂A ceramic block. After sintering, cooling and demoulding at 300 ℃/min, and cooling to obtain ZrO₂A ceramic core block.

Imaging with secondary electrons using a scanning electron microscope for ZrO₂The microscopic morphology of the ceramic pellet is characterized, and the result is shown in figure 1: the compactness is over 97 percent.

Example 2

With UO₂Powder (particle size of about 1 μm) as raw material, placing 20g of the raw material powder in an ultrathin graphite mold with a wall thickness of 2mm, introducing hydrogen gas, and subjecting to UO reaction₂The nano powder is started while being heated by induction heatingThe power supply applies an alternating current electric field (140V, 1A, 50Hz) at two ends of the graphite mold to ensure that UO is applied₂The nanopowder was sintered at elevated temperature under the conditions of application of alternating current and induction-assisted (5kW) heating.

Wherein the heating rate under the conditions of applying alternating current and induction-assisted heating is 800 deg.C/min, and the temperature is maintained for 30s when the temperature is raised to 700 deg.C to obtain UO with compact structure₂A ceramic block. After sintering, cooling and demoulding at 300 ℃/min, and cooling to obtain UO₂And (3) a core block.

Imaging UO with secondary electrons of scanning electron microscope₂The microscopic morphology of the pellets was characterized, and the results are shown in fig. 2: the compactness is over 95 percent.

Example 3

With Al₂O₃Powder (powder particle size about 200nm) is used as raw material. Putting the raw material powder into a ball milling tank, adding zirconium dioxide grinding balls and 15mL of ethanol, and ball milling and mixing for 15h at the rotating speed of 150 r/min.

After mixing, heating, stirring and drying the slurry at the temperature of 90 ℃; and carrying out compression molding on the dried mixed powder, pressing into a biscuit with the mass of about 100g under the axial pressure of 4MPa, and then pressing the biscuit into a compact by adopting cold isostatic pressing under the pressure of 200MPa and the pressure maintaining time of 10 min.

Placing the blank after isostatic cool pressing into a graphite mold with the wall thickness of 10mm, introducing nitrogen, and then carrying out heat treatment on Al₂O₃Starting a power supply to apply direct current (200V, 5A) to two ends of the graphite mold while heating the powder, and simultaneously performing microwave-assisted heating on the graphite mold to enable Al to be heated₂O₃The powder was sintered by heating under DC current and microwave-assisted (2.45 GHz).

Wherein the heating rate under the conditions of applying direct current and microwave-assisted heating is 1500 ℃/min, and Al with compact structure can be obtained by maintaining for 30s when the temperature is raised to 700 DEG C₂O₃And (3) a block body. After sintering, cooling and demoulding at 300 ℃/min, and cooling to obtain Al₂O₃A ceramic core block.

Imaging of Al with secondary electrons using a scanning electron microscope₂O₃The microscopic morphology of the ceramic pellet is characterized, and the result is shown in fig. 3: the compactness is over 95 percent, and the grain size is about 1 mu m.

Comparative example 1

With ZrO₂Ceramic powder (the particle size of the powder is about 100nm) is used as a raw material, 100g of the raw material powder is made into a circular ring by a gel casting method, then the circular ring is placed into an ultrathin graphite mold with the wall thickness of 10mm, argon is introduced, a pulse electric field (2000A) is applied to two ends of the graphite mold, and ZrO is enabled to pass through₂The ceramic green body is heated to 1000 ℃ at the speed of 100 ℃/min and then is kept for 30 s.

Imaging with secondary electrons using a scanning electron microscope for ZrO₂The microscopic morphology of the ceramic pellet is characterized, and the result is shown in fig. 4: the density is 90%.

Comparative example 2

With ZrO₂Ceramic powder (powder particle size about 100nm) as raw material, making 100g of the raw material powder into a ring by gel casting method, placing into a graphite mold with wall thickness of 45mm, introducing argon gas, and adding ZrO₂When the ceramic body is heated up by induction heating, a power supply is started to apply a pulse electric field at two ends of the ultrathin graphite die, so that ZrO can be heated up by induction heating₂The ceramic body is heated for sintering under the conditions of applying pulse current (2000A) and heating by induction assistance (10 kW).

Wherein the heating rate is 100 deg.C/min under the conditions of pulse current application and induction-assisted heating, and ZrO with compact structure can be obtained by maintaining 30s when the temperature is increased to 600 deg.C₂A ceramic block. After sintering, cooling and demoulding at 300 ℃/min, and cooling to obtain ZrO₂A ceramic core block.

Imaging with secondary electrons using a scanning electron microscope for ZrO₂The microscopic morphology of the ceramic pellet is characterized, and the result is shown in fig. 5: the compactness is 85%.

The above description is only for the purpose of illustrating the preferred embodiments of the present invention and is not to be construed as limiting the invention, and any modifications, equivalents and improvements made within the spirit and principle of the present invention are intended to be included within the scope of the present invention.

Claims

1. A method for preparing ceramic materials by multi-field coupling ultra-fast sintering is characterized in that ceramic powder or ceramic green bodies are placed into an ultra-thin graphite mold with the wall thickness of 1-20mm, the ceramic powder or ceramic green bodies are subjected to ultra-fast temperature rise integrally at the temperature rise rate of 500 plus materials 2000 ℃/min under the combined action of a power supply and a microwave auxiliary heating or induction auxiliary heating multiple heat source, the ultra-fast temperature rise region of crystal grains is skipped over to directly enter a sintering temperature region for densification for sintering, the temperature is reduced and demolding is carried out after sintering is finished, and sintered and molded blocks are taken out of the ultra-thin graphite mold.

2. The method for preparing a ceramic material by multi-field coupling ultrafast sintering of claim 1, wherein the power applied to the ultra-thin graphite mold is one of a pulse current, a direct current or an alternating current.

3. The method for preparing ceramic material by multi-field coupling ultrafast sintering of claim 1, wherein the particle size of the ceramic powder is 20nm-10 μm.

4. The method for preparing the ceramic material by the multi-field coupling ultra-fast sintering as claimed in claim 1, wherein the sintering temperature is 25-2000 ℃, and the sintering heat preservation time lasts 0-600 s.

5. The method for preparing a ceramic material by multi-field coupling ultrafast sintering of claim 1, wherein the ceramic green body is obtained by compression molding of ceramic powder, or gel casting molding, and then compaction by isostatic cool pressing at a pressure of 100 and 300Mpa and a pressure of 1-20 min.

6. The method for preparing ceramic material by multi-field coupling ultra-fast sintering according to claim 5, wherein the compression molding pressure is 2-10Mpa, and the dwell time is 2-5 min.

7. The method for preparing a ceramic material by multi-field coupling ultrafast sintering as claimed in claim 1, wherein said sintering atmosphere is one of air, hydrogen-argon mixture, nitrogen, hydrogen-nitrogen mixture.