CN113831144B

CN113831144B - Method for preparing ceramic material by multi-field coupling ultra-fast sintering

Info

Publication number: CN113831144B
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: 2023-01-31
Anticipated expiration: 2041-10-26
Also published as: CN113831144A

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 die with the wall thickness of 1-20 mm, applying a power supply and a microwave-assisted heating or induction-assisted heating multiple heat sources to the ultrathin graphite die, and heating the ceramic powder or the ceramic green bodies at a heating rate of 500-2000 ℃/min in an ultra-fast manner under the combined action of the multiple heat sources and the ultrathin graphite die, so that the effects of skipping a crystal grain rapid growth temperature region in an ultra-fast manner and directly entering a sintering densification temperature region are achieved, cooling and demolding are carried out after sintering is finished, and the sintered and molded block bodies are taken out of the ultrathin graphite die. 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 ultrafast sintering.

Background

Rapid sintering is the mainstream trend of the international ceramic sintering technology 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 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. by 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. Studies have shown that when a ceramic material having specific electrical properties is heated and subjected to a constant voltage, the material exhibits electroluminescence and rapidly densifies when the furnace temperature is raised to a characteristic temperature (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 Al ₂ O ₃ 、Y ₂ O ₃ 、TiO ₂ And the like. Subsequent studies have found that flash firing techniques can also be applied to carbide and boride ceramics such as SiC, B4C, zrB2, and the like. However, in flash firing, it is difficult to obtain a large-size sample with uniform density due to the difficulty in achieving complete uniformity of the dc electric field distribution.

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 kinetic energy and heat energy converted from microwave energy into 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 preparing 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.

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 100-300 ℃/min. 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 properties. 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 uneven sintering density.

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 500-2000 ℃/min by coupling heating of various heating fields and matching with an ultra-thin graphite mould, achieve the effect of ultra-fast skipping over an ultra-fast grain growth temperature region and directly entering a sintering densification temperature region, effectively reduce the temperature difference of a 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 ceramic materials 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 1-20 mm, applying multiple heat sources such as a power supply, microwave auxiliary heating or induction auxiliary 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 over a grain ultra-fast growth temperature region ultra-fast, directly entering a sintering densification temperature region for sintering, cooling and demolding after sintering is finished, and taking out sintered and molded blocks from 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 size of the ceramic powder is 20 nm-10 μm.

Furthermore, 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 into a blank under the pressure of 100-300 MPa by adopting cold isostatic pressing after compression molding or gel injection molding, and the pressure maintaining time is 1-20 min.

Further, the mould pressing pressure for mould pressing forming is 2-10 Mpa, 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 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 mould, 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 the 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 1 ₂ Microscopic morphology of the ceramic pellet;

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

FIG. 3 shows Al prepared in example 3 ₂ O ₃ Microscopic morphology of the ceramic pellet;

FIG. 4 shows ZrO prepared in comparative example 1 ₂ Microscopic morphology of the ceramic pellet;

FIG. 5 is ZrO prepared in comparative example 2 ₂ Microscopic 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 do not limit the invention.

Example 1

With ZrO ₂ Ceramic powder (powder particle size about 100 nm) 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 ZrO ₂ Ceramic blankWhen the body is inductively heated and heated, the power supply is started to apply a pulse electric field at the two ends of the ultrathin graphite die so as to ensure that ZrO can be heated ₂ The ceramic body is heated up 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 C ₂ A ceramic block. After sintering, cooling and demoulding at 300 ℃/min, and cooling to obtain ZrO ₂ A ceramic core block.

Imaging with secondary electrons using a scanning electron microscope for ZrO ₂ The microscopic morphology of the ceramic pellet is characterized, and the result is shown in figure 1: the density is over 97 percent.

Example 2

With UO ₂ Powder (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 reaction ₂ The nano powder is heated by induction heating, and simultaneously, a power supply is started to apply an alternating current electric field (140V, 1A and 50Hz) at two ends of the graphite mold, so that UO is enabled to be in contact with the graphite mold ₂ The nanopowder was sintered at elevated temperature under the conditions of application of alternating current and induction-assisted (5 kW) 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 structure ₂ A ceramic block. After sintering, cooling and demoulding at 300 ℃/min, and cooling to obtain UO ₂ And (3) a core block.

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

Example 3

With Al ₂ O ₃ Powder (particle size of about 200 nm) 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 15 hours 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 cold isostatic pressing into a graphite mould with the wall thickness of 10mm, introducing nitrogen, and then carrying out heat treatment on Al ₂ O ₃ Heating the powder, starting a power supply to apply direct current (200V, 5A) to two ends of the graphite mold, and simultaneously performing microwave-assisted heating on the graphite mold to enable Al to be heated ₂ O ₃ The 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 C ₂ O ₃ And (3) blocking. After sintering, cooling and demoulding at 300 ℃/min, and cooling to obtain Al ₂ O ₃ A ceramic core block.

Imaging of Al with secondary electrons using a scanning electron microscope ₂ O ₃ The microscopic morphology of the ceramic pellet is characterized, and the result is shown in fig. 3: the density is over 95 percent, and the grain size is about 1 mu m.

Comparative example 1

With ZrO ₂ Ceramic powder (the particle size of the powder is about 100 nm) 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 through ₂ The ceramic green body is heated to 1000 ℃ at the speed of 100 ℃/min and then is kept for 30s.

Imaging ZrO by secondary electrons using scanning electron microscope ₂ The microscopic morphology of the ceramic pellet is characterized, and the result is shown in fig. 4: the density is 90%.

Comparative example 2

With ZrO ₂ Ceramic powder (powder particle size about 100 nm) 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 ZrO ₂ When the ceramic body is inductively heated and heated, the power supply is started to the ultrathin graphite dieApplying a pulse electric field across both ends to allow ZrO to set ₂ The ceramic body is heated up 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.C ₂ A ceramic block. After sintering, cooling and demoulding at 300 ℃/min, and cooling to obtain ZrO ₂ A ceramic core block.

Imaging with secondary electrons using a scanning electron microscope for ZrO ₂ The microscopic morphology of the ceramic pellet is characterized, and the result is shown in fig. 5: the compactness is 85%.

The above description is intended to be illustrative of the preferred embodiment of the present invention and should not be taken as limiting the invention, but rather, the intention is to cover all modifications, equivalents, and alternatives falling within the spirit and scope of the invention.

Claims

1. A method for preparing ceramic materials by multi-field coupling ultra-fast sintering is characterized in that single ceramic powder with the grain size of 20 nm-10 microns or single ceramic powder with the grain size of 20 nm-10 microns is subjected to gel injection molding and then is subjected to isostatic cool pressing to prepare an obtained or compression-molded ceramic green body, the ceramic green body is loaded into an ultra-thin graphite mold with the wall thickness of 1-20 mm, after sintering atmosphere is introduced, current and microwave auxiliary heating or current and induction auxiliary heating are applied to the ultra-thin graphite mold to form a multi-heat source, the ceramic powder or the ceramic green body is subjected to ultra-fast temperature rise under the combined action of the multi-heat source and the ultra-thin graphite mold at the temperature rise rate of 500-2000 ℃/min until the sintering temperature is 600-1000 ℃, the sintering heat preservation time lasts for 30s, so that the ceramic powder or the ceramic green body directly enters a sintering densification temperature zone through an ultra-fast grain growth temperature zone to be sintered, and is subjected to sintering after sintering demolding, and then is cooled at the temperature of 300 ℃/min and then taken out of the ultra-thin graphite mold; the single ceramic powder is ZrO ₂ Or UO ₂ Or Al ₂ O ₃ (ii) a The sintering atmosphere is hydrogen, hydrogen-argon mixed gas, nitrogen and hydrogen-nitrogen mixed gasTo (3) is provided.

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

3. The method for preparing a ceramic material by multi-field coupling ultrafast sintering of claim 1, wherein the cold isostatic pressing pressure is 100-300 Mpa, and the dwell time is 1-20 min.

4. The method for preparing ceramic material by multi-field coupling ultra-fast sintering according to claim 3, wherein the compression molding pressure is 2-10 MPa, and the pressure holding time is 2-5 min.