阅读说明：本技术 采用放电等离子烧结制备氮掺杂导电碳化硅陶瓷的方法 (Method for preparing nitrogen-doped conductive silicon carbide ceramic by adopting spark plasma sintering ) 是由 李华鑫 沈伟健 杨建国 贺艳明 郑文健 闾川阳 马英鹤 郑勇 魏连峰 于 2021-10-20 设计创作，主要内容包括：本发明公开了采用放电等离子烧结制备氮掺杂导电碳化硅陶瓷的方法,包括如下步骤：1)球磨混料：在氧化锆球磨罐中用氧化锆球对氧化铝、氧化钇和碳化硅粉末进行湿法球磨；2)粉末干燥与装配：2.1)球磨后的混合粉末进行过滤筛分,倒入玻璃容器内,然后置于干燥箱中于50～70℃下干燥6h,干燥以后的粉末再用研钵进行手工粉碎；2.2)将混合干燥以后的粉末进行装配,装配容器包括石墨模具和石墨压头；2.3)采用压片机对装配好后的粉末进行预压；3)高温烧结：将预压后的粉末置于放电等离子烧结炉中进行高温烧结。本发明采用放电等离子烧结方法,不仅在较短时间内便可制备出低电阻率和力学性能优良的碳化硅陶瓷,并且可以实现电阻率的精确调控。(The invention discloses a method for preparing nitrogen-doped conductive silicon carbide ceramic by adopting spark plasma sintering, which comprises the following steps: 1) ball milling and mixing: wet ball milling of alumina, yttria and silicon carbide powder with zirconia balls in a zirconia ball milling tank; 2) powder drying and assembling: 2.1) filtering and screening the mixed powder subjected to ball milling, pouring the filtered mixed powder into a glass container, then placing the glass container into a drying oven, drying the glass container for 6 hours at the temperature of 50-70 ℃, and manually crushing the dried powder by using a mortar; 2.2) assembling the mixed and dried powder, wherein the assembling container comprises a graphite die and a graphite pressure head; 2.3) prepressing the assembled powder by adopting a tablet press; 3) and (3) high-temperature sintering: and placing the pre-pressed powder in a discharge plasma sintering furnace for high-temperature sintering. The invention adopts the spark plasma sintering method, can prepare the silicon carbide ceramic with low resistivity and excellent mechanical property in a short time, and can realize the precise regulation and control of the resistivity.)

1. The method for preparing the nitrogen-doped conductive silicon carbide ceramic by adopting spark plasma sintering is characterized by comprising the following steps of:

1) ball milling and mixing:

wet ball milling of alumina, yttria and silicon carbide powder with zirconia balls in a zirconia ball milling tank;

2) powder drying and assembling:

2.1) filtering and screening the mixed powder subjected to ball milling, pouring the filtered mixed powder into a glass container, then placing the glass container into a drying oven, drying the glass container for 6 hours at the temperature of 50-70 ℃, and manually crushing the dried powder by using a mortar;

2.2) assembling the mixed and dried powder, wherein the assembling container comprises a graphite die and a graphite pressure head;

2.3) prepressing the assembled powder by adopting a tablet press, wherein the prepressing pressure is 5-10 MPa;

3) and (3) high-temperature sintering:

and placing the pre-pressed powder in a discharge plasma sintering furnace for high-temperature sintering, wherein the sintering atmosphere is nitrogen, the heating rate is 50-100 ℃/min, the sintering temperature is 1850-2000 ℃, the sintering time is 1-10 min, and the sintering pressure is 40-50 MPa.

2. The method for preparing nitrogen-doped conductive silicon carbide ceramic by spark plasma sintering according to claim 1, wherein in the step 1), the total content of the alumina and the yttria is 2-6 wt%, and the mass ratio of the alumina to the yttria is 3: 2.

3. the method for preparing nitrogen-doped conductive silicon carbide ceramic by spark plasma sintering according to claim 1 or 2, wherein in step 1), the purity of the powder is up to 99.9%, wherein the particle size of the alumina and yttria powder is micron-sized, the silicon carbide powder is nano-sized beta-SiC, and the medium of wet ball milling is preferably acetone.

4. The method for preparing nitrogen-doped conductive silicon carbide ceramic by spark plasma sintering according to claim 1, wherein in the step 1), the ball milling equipment is an all-directional planetary ball mill, and the ball milling equipment is operated for 4-8 hours in a single direction at a rotating speed of 200-400 r/min.

5. The method for preparing nitrogen-doped conductive silicon carbide ceramic by spark plasma sintering as claimed in claim 1, wherein in step 2.2), the graphite mold is made of high-strength graphite material.

6. The method for preparing nitrogen-doped conductive silicon carbide ceramic by spark plasma sintering as claimed in claim 1, wherein the nitrogen pressure in step 3) is always lower than 0.5 MPa.

7. The method for preparing nitrogen-doped conductive silicon carbide ceramic by spark plasma sintering as claimed in claim 1, wherein in the step 3), after the sintering process is finished, the procedure is directly closed and natural cooling is carried out to room temperature.

8. The method for preparing nitrogen-doped conductive silicon carbide ceramic by spark plasma sintering as claimed in claim 1, wherein the resistivity of the silicon carbide ceramic prepared in step 3) is 10^-3～10¹Omega cm, the density is more than 96%, the hardness is 14.58-24.69 GPa, the elastic modulus is 310.97-400.12 GPa, and the fracture toughness is 1.97-2.69 MPa m^1/2MPa·m^1/2The nitrogen content in the material is 0.17-1.95 wt%.

Technical Field

The invention relates to the technical field of conductive silicon carbide ceramics, and relates to a method for preparing nitrogen-doped conductive silicon carbide ceramics by adopting spark plasma sintering.

Background

Silicon carbide (SiC) ceramics and their composites have many technical advantages such as high strength, high hardness, good oxidation and corrosion resistance, high thermal conductivity, and low thermal expansion coefficient. Based on these advantages, SiC and its composite materials are widely used as high-temperature structural ceramics in heat exchanger parts, gas turbine parts, nuclear reactors, and the like. However, the SiC ceramic has a great limitation in its application because it is difficult to process the material into a complicated shape due to its high resistivity, hardness and brittleness. Whereas for materials with low resistivity (<100 Ω · cm), complex shapes can be machined precisely by wire Electrical Discharge Machining (EDM). Therefore, the preparation of conductive SiC ceramics that can be electro-discharge processed can effectively solve this problem.

The method for preparing the conductive SiC ceramic mainly comprises element doping (Al, B, N and the like) and adding a conductive second phase (such as ZrB)₂TiN, TiC, etc.). Compared with the addition of the conductive second phase, the element doping mode can prepare the SiC ceramic with low resistivity under the condition of doping a very small amount of elements, thereby retaining the original excellent physical and chemical properties of the silicon carbide ceramic. The doping element species are mainly divided into n-type dopants and p-type dopants, wherein the n-type doping can reduce the resistivity of the ceramic to 10^-3Omega cm, n-type dopant is the first choice for preparing conductive silicon carbide ceramicHowever, nitrogen is one of the most widely used n-type dopants.

Compared with the traditional sintering mode (pressureless and hot-pressing sintering mode) which needs long-time heat preservation, the Spark Plasma Sintering (SPS) can prepare the silicon carbide ceramic in extremely short heat preservation time (less than 10min), and can effectively control the growth of crystal grains of the material, so that the silicon carbide ceramic material with excellent mechanical property can be prepared. In conclusion, the preparation of the conductive SiC ceramic with low resistivity and high strength by adopting spark plasma sintering has important research significance.

Disclosure of Invention

Aiming at the technical problems in the prior art, the application aims to provide a method for preparing nitrogen-doped conductive silicon carbide ceramic by adopting spark plasma sintering, which is used for overcoming the defect that high-resistivity silicon carbide ceramic in the prior art is difficult to process, and meanwhile, the conductive silicon carbide ceramic is low in preparation difficulty and simple in process.

The technical scheme of the invention is as follows:

the method for preparing the nitrogen-doped conductive silicon carbide ceramic by adopting spark plasma sintering comprises the following steps:

1) ball milling and mixing:

wet ball milling of alumina, yttria and silicon carbide powder with zirconia balls in a zirconia ball milling tank;

2) powder drying and assembling:

2.1) filtering and screening the mixed powder subjected to ball milling, pouring the filtered mixed powder into a glass container, then placing the glass container into a drying oven, drying the glass container for 6 hours at the temperature of 50-70 ℃, and manually crushing the dried powder by using a mortar;

2.2) assembling the mixed and dried powder, wherein the assembling container comprises a graphite die and a graphite pressure head;

2.3) prepressing the assembled powder by adopting a tablet press, wherein the prepressing pressure is 5-10 MPa;

3) and (3) high-temperature sintering:

and placing the pre-pressed powder in a discharge plasma sintering furnace for high-temperature sintering, wherein the sintering atmosphere is nitrogen, the heating rate is 50-100 ℃/min, the sintering temperature is 1850-2000 ℃, the sintering time is 1-10 min, and the sintering pressure is 40-50 MPa.

Further, in the step 1), the total content of the aluminum oxide and the yttrium oxide is 2-6 wt%, and the mass ratio of the aluminum oxide to the yttrium oxide is always kept between 3: 2.

further, in the step 1), the powder purity reaches 99.9%, wherein the particle sizes of the aluminum oxide powder and the yttrium oxide powder are micron-sized, the selected silicon carbide powder is nano-sized beta-SiC, and acetone is preferably used as a medium for wet ball milling.

Further, in the step 1), the ball milling equipment is an all-directional planetary ball mill, and the ball milling equipment runs for 4-8 hours in a single direction at a rotating speed of 200-400 r/min.

Further, in the step 2.2), the graphite mold is made of a high-strength graphite material.

Further, in the step 3), the nitrogen pressure is always lower than 0.5 MPa;

further, in the step 3), after the sintering process is finished, the procedure is directly closed, and the temperature is naturally reduced to the room temperature.

Further, in the step 3), the resistivity of the prepared silicon carbide ceramic is 10^-3～10¹Omega cm, the density is more than 96%, the hardness is 14.58-24.69 GPa, the elastic modulus is 310.97-400.12 GPa, and the fracture toughness is 1.97-2.69 MPa m^1/2The nitrogen content in the material is 0.17-1.95 wt%.

The invention has the beneficial effects that: compared with other methods for preparing the conductive silicon carbide ceramic, the method adopts a discharge plasma sintering method, can prepare the silicon carbide ceramic with low resistivity and excellent mechanical property in a short time, can realize accurate regulation and control of the resistivity, and simultaneously can well retain the excellent physicochemical property of the original silicon carbide ceramic due to the extremely low content of the sintering aid and the nitrogen doping amount, so the method is also suitable for the field of high-temperature structural ceramics.

Drawings

FIG. 1 is a process flow diagram of the present invention;

FIG. 2 is a scanning electron micrograph of the conductive silicon carbide ceramic prepared according to the present invention;

in fig. 2: a, b, c and d represent the surface morphology of the conductive silicon carbide ceramic obtained by heat preservation at sintering temperatures of 1850 ℃, 1900 ℃, 1950 ℃ and 2000 ℃ for 5min, respectively, when the total content of the sintering aid is 2 wt%.

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 derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention. In addition, the technical solutions in the embodiments of the present invention may be combined with each other, but it must be based on the realization of those skilled in the art, and when the technical solutions are contradictory or cannot be realized, such a combination of technical solutions should not be considered to exist, and is not within the protection scope of the present invention.

The drugs/reagents used are all commercially available without specific mention.

As shown in fig. 1-2, the embodiments of the present invention are as follows:

example 1

A method for preparing nitrogen-doped conductive silicon carbide ceramic by adopting spark plasma sintering comprises the following steps:

step 1: ball milling mixing material

According to the experimental design proportion, wet ball milling is carried out on alumina, yttria and silicon carbide powder by zirconia balls in a zirconia ball milling tank;

step 2: powder drying and assembly

(1) Filtering and screening the mixed powder subjected to ball milling, pouring the mixed powder into a glass container, then placing the glass container into a drying oven, drying the glass container for 6 hours at the temperature of 50-70 ℃, and manually crushing the dried powder by using a mortar;

(2) assembling the mixed and dried powder, wherein the assembling container comprises a graphite die and a graphite pressure head;

(3) prepressing the assembled powder by a tablet press, wherein the prepressing pressure is 5-10 MPa;

and step 3: high temperature sintering

And placing the pre-pressed powder in a discharge plasma sintering furnace for high-temperature sintering, wherein the sintering atmosphere is nitrogen, the heating rate is 50-100 ℃/min, the sintering temperature is 1850-2000 ℃, the sintering time is 1-10 min, and the sintering pressure is 40-50 MPa.

Example 2:

the method for preparing the nitrogen-doped conductive silicon carbide ceramic by adopting the spark plasma sintering is the same as that in the embodiment 1, the difference is that the powder purity reaches 99.9 percent, wherein the aluminum oxide powder and the yttrium oxide powder are micron-sized, the total content is 2-6wt percent, the selected silicon carbide powder is nano-sized beta-SiC, and acetone is preferentially selected as a medium for wet ball milling.

Example 3:

a method for preparing nitrogen-doped conductive silicon carbide ceramic by adopting spark plasma sintering is similar to that in example 1, except that the mass ratio of aluminum oxide and yttrium oxide with the total content of 2-6 wt% is always maintained to be 3: 2.

example 4:

the method for preparing the nitrogen-doped conductive silicon carbide ceramic by adopting spark plasma sintering is the same as that in the embodiment 1, except that the ball milling equipment is an all-directional planetary ball mill, and the ball milling equipment is operated for 4-8 hours in a single direction at the rotating speed of 200-400 r/min.

Example 5:

a method for preparing nitrogen-doped conductive silicon carbide ceramic by adopting spark plasma sintering, which is the same as the embodiment 1, and is characterized in that a graphite mold adopts a high-strength graphite material.

Example 6:

a method for preparing nitrogen-doped conductive silicon carbide ceramic by adopting spark plasma sintering, which is the same as the embodiment 1, and is characterized in that the pressure of nitrogen is always lower than 0.5 MPa.

Example 7:

a method for preparing nitrogen-doped conductive silicon carbide ceramic by spark plasma sintering, which is the same as the method in example 1, and is characterized in that after the sintering process is finished, the procedure is directly closed, and the temperature is naturally reduced to room temperature.

Example 8:

a method for preparing nitrogen-doped conductive silicon carbide ceramic by spark plasma sintering is similar to that in example 1, except that the prepared silicon carbide ceramic has a resistivity of 10^-3～10¹Omega cm, the density is more than 96%, the hardness is 14.58-24.69 GPa, the elastic modulus is 310.97-400.12 GPa, and the fracture toughness is 1.97-2.69 MPa m^1/2The nitrogen content in the material is 0.17-1.95 wt%.

Example 9:

a method for preparing nitrogen-doped conductive silicon carbide ceramic by adopting spark plasma sintering is the same as that in example 1, except that when the total content of aluminum oxide and yttrium oxide is 6 wt%, the sintering temperature is 1900 ℃, and the heat preservation time is 10min, the obtained silicon carbide ceramic has the highest resistivity of 6.62 omega cm, the corresponding density of 97.03%, the hardness of 18.57GPa, the elastic modulus of 400.12GPa, and the fracture toughness of 2.42MPa m^1/2The nitrogen content was 1.95 wt%.

Example 10:

a method for preparing nitrogen-doped conductive silicon carbide ceramic by adopting spark plasma sintering is the same as that in example 1, except that when the total content of aluminum oxide and yttrium oxide is 4 wt%, the sintering temperature is 1900 ℃, and the heat preservation time is 10min, the obtained silicon carbide ceramic has the resistivity of 3.20 omega-cm, the corresponding density of 98.01%, the hardness of 19.73GPa, the elastic modulus of 330.11GPa, and the fracture toughness of 2.32 MPa-m^1/2The nitrogen content was 1.87 wt%.

Example 11:

a method for preparing nitrogen-doped conductive silicon carbide ceramic by spark plasma sintering is the same as that in example 1, except that when the total content of aluminum oxide and yttrium oxide is 2 wt%, the sintering temperature is 2000 ℃, and the holding time is 5min, the resistivity of the obtained silicon carbide ceramic is the lowest and is 2.77 x 10^-3Omega cm, the corresponding density is 97.46 percentThe hardness was 22.65GPa, the elastic modulus was 330.43GPa, and the fracture toughness was 2.69 MPa.m^1/2Nitrogen content 0.17 wt%;

comparative example:

the traditional method adopts the traditional sintering mode (pressureless and hot-pressing sintering mode).

TABLE 1 comparison of the parameters of the conventional method and the nitrogen-doped conductive SiC ceramics prepared in this patent

Parameter comparison	Conventional methods	This patent
			Sintering time	>1h	<10min
Compactness degree	90～99％	96～99％
			Hardness (GPa)	19.0～26.7	14.58～24.69
Modulus of elasticity (GPa)	50～500	310.97～400.12
			Resistivity (omega cm)	10-3～102	10-3～101

Compared with the long-time pressureless and hot-pressing sintering (the heat preservation time is more than 1h) of the traditional method, the method can quickly prepare the conductive silicon carbide with low resistivity (5min), effectively inhibit the growth of crystal grains (less than 2.5 mu m), and can also obtain good mechanical property;

according to the method for preparing the nitrogen-doped conductive silicon carbide ceramic by adopting spark plasma sintering, a small amount of aluminum oxide and yttrium oxide sintering aid is added (the lower the content of the sintering aid is, the lower the resistivity is, Al in the sintering aid can be partially doped into silicon carbide, so that the concentration of a donor generated by nitrogen doping is reduced, the resistivity is improved), a high-temperature eutectic crystal is formed at 1850 ℃, and therefore the effect of densifying the silicon carbide ceramic is achieved, and meanwhile, nitrogen elements in nitrogen are absorbed, so that nitrogen doping is achieved. By regulating and controlling the sintering temperature, the heat preservation time and the content of the sintering aid, the electrical resistivity (10) with different grades can be obtained^-3～10¹Omega cm) nitrogen doped conductive silicon carbide ceramic to realize accurate regulation and control of resistivity.

The principle of the invention is as follows: firstly, uniformly mixing SiC powder and a sintering aid by mechanical ball milling, and then sintering the mixed powder at high temperature in a nitrogen atmosphere. In a high-temperature environment, the liquid-phase sintering aid can dissolve part of N₂Nitrogen in the atmosphere. The SiC crystal grains grow along a dissolution recrystallization mechanism, and then nitrogen is dissolved into the SiC crystal lattice to form effective nitrogen doping. And nitrogen doping causes ionization of donor impurities, resulting in the donor level of SiC being close to the conduction band edge, thereby imparting conductive characteristics to SiC.

The foregoing shows and describes the general principles and broad features of the present invention and advantages thereof. It will be understood by those skilled in the art that the present invention is not limited to the embodiments described above, which are described in the specification and illustrated only to illustrate the principle of the present invention, but that various changes and modifications may be made therein without departing from the spirit and scope of the present invention, which fall within the scope of the invention as claimed. The scope of the invention is defined by the appended claims and equivalents thereof.