CN110981528B - Directional porous aluminum nitride ceramic and rapid preparation method thereof - Google Patents
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Abstract
The invention discloses a directional porous aluminum nitride ceramic and a rapid preparation method thereof, wherein tert-butyl alcohol is used as a solvent, citric acid is used as a dispersing agent to freeze-dry aluminum nitride powder and a sintering aid, and the dried green body is placed into a discharge plasma sintering furnace to be rapidly sintered under no pressure, so that the directional porous aluminum nitride ceramic with high porosity and compressive strength can be obtained. The method for preparing the directional porous aluminum nitride ceramic has the characteristics of simple process, short period, good repeatability, low cost and the like. The prepared directional porous aluminum nitride ceramic has wide application prospect in the fields of metal filtration, catalyst carriers, polymer reinforced phases, automobile industry, solar power generation and the like.
Description
Technical Field
The invention belongs to the technical field of preparation of inorganic non-metallic materials, and relates to directional porous aluminum nitride ceramic and a rapid preparation method thereof.
Background
The porous AlN ceramic has a series of excellent characteristics of high thermal conductivity, low thermal expansion coefficient, excellent mechanical property, high chemical stability and the like, so the porous AlN ceramic is widely applied to the fields of molten metal filtration, catalyst carriers, polymer reinforced phases, heat exchange components and the like. The key to improving the thermal physical property and the mechanical property of the porous AlN ceramic is to regulate and control the relationship among the porosity, the pore morphology and the pore structure.
At present, the method for preparing the porous ceramic mainly comprises the following steps: organic foam impregnation, foaming, sol-gel, extrusion, and the like. However, these methods have problems of high energy consumption, long preparation period, low strength, uncontrollable pore structure, etc. For example, the preparation method of the porous aluminum nitride ceramic material disclosed in the patent publication No. CN105503236B requires not only many high-temperature sintering processes but also a complicated preparation process, which results in high energy consumption and long preparation period. The invention patent with publication number CN105489714B 'a porous AlN composite substrate and application thereof in epitaxial growth of high-quality gallium nitride films', the porous AlN layer is grown on the substrate by an MOCVD system, and the defects of complex preparation process, low yield of porous AlN ceramics, difficult control of pore structure and the like exist.
Disclosure of Invention
The invention aims to provide a directional porous aluminum nitride ceramic and a rapid preparation method thereof, which can overcome the defects of long preparation period, low production efficiency, difficult control of a pore structure and the like of the porous AlN ceramic prepared by the traditional method.
In order to achieve the purpose, the invention adopts the following technical scheme to realize the purpose:
the invention discloses a directional porous aluminum nitride ceramic and a rapid preparation method thereof, which comprises the following steps:
1) taking aluminum nitride powder, yttrium oxide powder, calcium fluoride powder and citric acid as raw materials, taking tert-butyl alcohol as a solvent, and fully and uniformly mixing to prepare slurry;
2) freezing the slurry, and then carrying out vacuum freeze drying to obtain a green body;
3) and placing the green body in a discharge plasma pressureless rapid sintering furnace, vacuumizing until the air pressure is less than 10Pa, heating to 1100-1400 ℃ from room temperature at the heating rate of 100-300 ℃/min, preserving the temperature for 3-7min, stopping heating, naturally cooling the temperature in the furnace to below 100 ℃, and taking out a white block in the furnace, namely the directional porous aluminum nitride ceramic.
Preferably, in step 1), the aluminum nitride powder and the tert-butyl alcohol are mixed according to the following volume percentages: 10% -35%: 65-90 percent of the total weight of the aluminum nitride powder, 1-3 percent of the weight of yttrium oxide powder, 3-5 percent of the weight of calcium fluoride powder and 1-5 percent of the weight of aluminum nitride powder.
Preferably, in the step 1), aluminum nitride powder, yttrium oxide powder, calcium fluoride powder, citric acid and tert-butyl alcohol are placed into a ball milling tank for mixing, the ball milling time is 2-12 hours, the material-ball ratio is 4:1, and the rotating speed is 400 r/min.
Preferably, in the step 2), the freezing temperature is-100 to-25 ℃, and the vacuum freeze-drying temperature is-100 to-20 ℃.
Preferably, in step 2), the slurry is poured into a cylindrical silicon rubber mold for freezing, and the bottom of the silicon rubber mold is a copper column partially immersed in liquid nitrogen.
The invention discloses oriented porous aluminum nitride ceramic prepared by the rapid preparation method, which is of a honeycomb structure, wherein the pore diameter of a honeycomb is 12-50 mu m, the wall thickness is 10-20 mu m, the porosity is 60-87%, and the compressive strength is 0.1-10 MPa.
Compared with the prior art, the invention has the following beneficial effects:
the invention adopts a method combining freeze drying and spark plasma non-pressure sintering (SPS) to rapidly prepare the oriented porous AlN ceramic, adopts tert-butyl alcohol as a freeze drying solvent, citric acid as a dispersing agent and yttrium oxide and calcium fluoride as sintering aids, uniformly mixes the four raw materials and AlN powder by ball milling, performs freeze drying, and puts a dried sample into an SPS rapid sintering furnace for rapid sintering under a vacuum condition to prepare the oriented porous AlN ceramic. Compared with the traditional preparation process, the preparation method has the advantages of low energy consumption, short preparation period, controllable pore structure and the like, does not need high-energy-consumption processes such as high-temperature long-time heat preservation and the like, and can effectively improve the strength and the production efficiency of the porous AlN ceramic.
The directional porous AlN ceramic prepared by the method has uniform internal pore structure, controllable appearance and high repeatability, and has wide application prospect in the fields of metal filtration, catalyst carriers, polymer reinforced phases, automobile industry, solar power generation and the like.
Drawings
FIG. 1 is a schematic view of a freeze-drying process;
FIG. 2 is a schematic view of a discharge plasma pressureless rapid sintering apparatus;
FIG. 3 is an XRD pattern of an oriented porous AlN ceramic;
FIG. 4 is an SEM image of an oriented porous AlN ceramic; wherein, (a) is an SEM image parallel to the freezing direction, and (b) is an SEM image perpendicular to the freezing direction.
Wherein: 1-slurry; 2-a silicon rubber mold; 3-copper columns; 4-green body; 5-oriented porous AlN ceramic; 6-graphite cushion blocks; 7-pressure head; 8-graphite mold; 9-sample; 10-electrode.
Detailed Description
In order to make the technical solutions of the present invention better understood, 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.
It should be noted that the terms "first," "second," and the like in the description and claims of the present invention and in the drawings described above are used for distinguishing between similar elements and not necessarily for describing a particular sequential or chronological order. It is to be understood that the data so used is interchangeable under appropriate circumstances such that the embodiments of the invention described herein are capable of operation in sequences other than those illustrated or described herein. Furthermore, the terms "comprises," "comprising," and "having," and any variations thereof, are intended to cover a non-exclusive inclusion, such that a process, method, system, article, or apparatus that comprises a list of steps or elements is not necessarily limited to those steps or elements expressly listed, but may include other steps or elements not expressly listed or inherent to such process, method, article, or apparatus.
The invention is described in further detail below with reference to the accompanying drawings:
referring to fig. 1, which is a freeze-drying process diagram in the rapid preparation method of the directional porous aluminum nitride ceramic disclosed by the invention, after raw materials are prepared into slurry, the uniformly mixed slurry 1 is poured into a cylindrical silicon rubber mold 2 for freezing, the bottom of the mold is a copper column 3 partially immersed in liquid nitrogen, a frozen sample is placed in a freeze dryer for vacuum freeze-drying, a green blank 4 is obtained, and the directional porous aluminum nitride ceramic 5 is obtained through sintering treatment. Referring to fig. 2, which is a schematic view of a discharge plasma pressureless rapid sintering furnace (SPS) used in the process of the present invention, in the figure, 6 is a graphite pad, 7-pressure head; 8-graphite mold; 9-sample; 10-electrode. Example 1
Mixing AlN powder 18g, yttrium oxide powder 0.18g, calcium fluoride powder 0.72g, citric acid 0.9g and 50mL of tert-butyl alcohol, and putting the mixture into a sealed alumina ball milling tank for ball milling for 4 hours, wherein the ball-material ratio is 4:1, the rotating speed is 400 r/min. Then, the slurry after ball milling is poured into a silicon rubber mold for freezing, the bottom of the mold is a copper column precooled in liquid nitrogen, the freezing temperature is controlled at-25 ℃, and the frozen sample is placed in a freeze dryer for vacuum freeze drying at-50 ℃. And finally, placing the dried green body into an SPS rapid sintering furnace, vacuumizing until the air pressure is less than 10Pa, heating to 1250 ℃ from room temperature at the heating rate of 200 ℃/min, preserving the temperature for 5min, stopping heating, and taking out a sample after the temperature in the furnace is naturally cooled to be below 100 ℃ to obtain the oriented porous AlN ceramic with the compressive strength of 0.1 MPa.
The resulting product was characterized by X-ray diffractometer (XRD), Field Emission Scanning Electron Microscope (FESEM). FIG. 3 is an XRD spectrum of a product containing hexagonal AlN phase as a main component, a sintering aid and Al2O3CaAl produced by the reaction12O19、Ca3Al12O6、CaAlF5And Y3Al5O12And waiting for the second phase. FIG. 4 is an FESEM photograph of the product, and it can be found that the oriented porous AlN ceramic has a honeycomb structure, has oriented pores vertically arranged inside, a porosity of 87%, a honeycomb pore diameter of 50 μm, and a wall thickness of 10 μm.
Example 2
30g of AlN powder, 0.6g of yttrium oxide powder, 1.5g of calcium fluoride powder, 0.9g of citric acid and 50mL of tert-butyl alcohol are mixed and then put into a sealed alumina ball-milling tank for ball-milling for 2 hours, wherein the ball-material ratio is 4:1, the rotating speed is 400 r/min. Then, the slurry after ball milling is poured into a silicon rubber mold for freezing, the bottom of the mold is a copper column precooled in liquid nitrogen, the freezing temperature is controlled at-100 ℃, and the frozen sample is placed in a freeze dryer for vacuum freeze drying at-50 ℃. And finally, placing the dried green body into an SPS rapid sintering furnace, vacuumizing until the air pressure is less than 10Pa, heating to 1200 ℃ from room temperature at the heating rate of 150 ℃/min, preserving the temperature for 3min, stopping heating, and taking out a sample after the temperature in the furnace is naturally cooled to be below 100 ℃ to obtain the oriented porous AlN ceramic with the compressive strength of 0.2 MPa.
The resulting product was characterized by X-ray diffractometer (XRD), Field Emission Scanning Electron Microscope (FESEM). It can be found that the oriented porous AlN ceramic has a honeycomb structure, has oriented pores vertically arranged inside, has a porosity of 82%, a honeycomb pore diameter of 35 μm and a wall thickness of 12 μm. Other results were the same as in example 1.
Example 3
Mixing 40g of AlN powder, 1.2g of yttrium oxide powder, 1.2g of calcium fluoride powder, 0.8g of citric acid and 50mL of tert-butyl alcohol, and putting the mixture into a sealed alumina ball milling tank for ball milling for 6 hours, wherein the ball-material ratio is 4:1, the rotating speed is 400 r/min. Then, the slurry after ball milling is poured into a silicon rubber mold for freezing, the bottom of the mold is a copper column precooled in liquid nitrogen, the freezing temperature is controlled at minus 50 ℃, and the frozen sample is placed in a freeze dryer for vacuum freeze drying at minus 20 ℃. And finally, placing the dried green body into an SPS rapid sintering furnace, vacuumizing until the air pressure is less than 10Pa, heating to 1200 ℃ from room temperature at the heating rate of 100 ℃/min, keeping the temperature for 6min, stopping heating, and taking out a sample after the temperature in the furnace is naturally cooled to be below 100 ℃ to obtain the oriented porous AlN ceramic with the compressive strength of 1.5 MPa.
The resulting product was characterized by X-ray diffractometer (XRD), Field Emission Scanning Electron Microscope (FESEM). It was found that the oriented porous AlN ceramic had a honeycomb structure with oriented pores vertically arranged inside, a porosity of 75%, a honeycomb pore diameter of 25 μm and a wall thickness of 14 μm. Other results were the same as in example 1.
Example 4
55g of AlN powder, 0.55g of yttrium oxide powder, 2.2g of calcium fluoride powder, 1.1g of citric acid and 50mL of tert-butyl alcohol are mixed and then put into a sealed alumina ball-milling tank for ball-milling for 10 hours, wherein the ball-material ratio is 4:1, the rotating speed is 400 r/min. Then, the slurry after ball milling is poured into a silicon rubber mold for freezing, the bottom of the mold is a copper column precooled in liquid nitrogen, the freezing temperature is controlled to be-75 ℃, and the frozen sample is placed in a freeze dryer for vacuum freeze drying at-100 ℃. And finally, placing the dried green body into an SPS rapid sintering furnace, vacuumizing until the air pressure is less than 10Pa, heating to 1400 ℃ from room temperature at the heating rate of 300 ℃/min, keeping the temperature for 3min, stopping heating, and taking out a sample after the temperature in the furnace is naturally cooled to be below 100 ℃ to obtain the directional porous AlN ceramic with the compressive strength of 4 MPa.
The resulting product was characterized by X-ray diffractometer (XRD), Field Emission Scanning Electron Microscope (FESEM). It can be found that the directional porous AlN ceramic has a honeycomb structure, the interior of the ceramic is vertically arranged directional holes, the porosity is 70%, the pore diameter of the honeycomb is 18 μm, and the wall thickness is 16 μm. Other results were the same as in example 1.
Example 5
70g of AlN powder, 1.05g of yttrium oxide powder, 2.45g of calcium fluoride powder, 1.4g of citric acid and 50mL of tert-butyl alcohol are mixed and then put into a sealed alumina ball-milling tank for ball-milling for 8 hours, wherein the ball-material ratio is 4:1, the rotating speed is 400 r/min. Then, the slurry after ball milling is poured into a silicon rubber mold for freezing, the bottom of the mold is a copper column precooled in liquid nitrogen, the freezing temperature is controlled at-100 ℃, and the frozen sample is placed in a freeze dryer for vacuum freeze drying at-75 ℃. And finally, placing the dried green body into an SPS rapid sintering furnace, vacuumizing until the air pressure is less than 10Pa, heating to 1300 ℃ from room temperature at the heating rate of 250 ℃/min, preserving the temperature for 4min, stopping heating, and taking out a sample after the temperature in the furnace is naturally cooled to be below 100 ℃ to obtain the directional porous AlN ceramic with the compressive strength of 6 MPa.
The resulting product was characterized by X-ray diffractometer (XRD), Field Emission Scanning Electron Microscope (FESEM). It can be found that the directional porous AlN ceramic has a honeycomb structure, the interior of the ceramic is provided with directional holes which are vertically arranged, the porosity is 65%, the pore diameter of the honeycomb is 14 μm, and the wall thickness is 18 μm. Other results were the same as in example 1.
Example 6
Mixing 88g of AlN powder, 2.64g of yttrium oxide powder, 4.4g of calcium fluoride powder, 0.88g of citric acid and 50mL of tert-butyl alcohol, and putting the mixture into a sealed alumina ball-milling tank for ball milling for 12 hours, wherein the ball-material ratio is 4:1, the rotating speed is 400 r/min. Then, the slurry after ball milling is poured into a silicon rubber mold for freezing, the bottom of the mold is a copper column precooled in liquid nitrogen, the freezing temperature is controlled to be-75 ℃, and the frozen sample is placed in a freeze dryer for vacuum freeze drying at-50 ℃. And finally, placing the dried green body into an SPS rapid sintering furnace, vacuumizing until the air pressure is less than 10Pa, heating to 1100 ℃ from room temperature at the heating rate of 150 ℃/min, keeping the temperature for 7min, stopping heating, and taking out a sample after the temperature in the furnace is naturally cooled to be below 100 ℃ to obtain the oriented porous AlN ceramic with the compressive strength of 10 MPa.
The resulting product was characterized by X-ray diffractometer (XRD), Field Emission Scanning Electron Microscope (FESEM). It can be found that the oriented porous AlN ceramic has a honeycomb structure, the interior of the AlN ceramic is provided with oriented pores which are vertically arranged, the porosity is 60%, the pore diameter of the honeycomb is 12 mu m, and the wall thickness is 20 mu m. Other results were the same as in example 1.
In conclusion, the method adopts tert-butyl alcohol as a solvent and citric acid as a dispersing agent to freeze-dry the aluminum nitride powder and the sintering aid, and the dried green body is placed into a discharge plasma sintering furnace to be rapidly sintered under no pressure, so that the oriented porous aluminum nitride ceramic with high porosity and compressive strength can be obtained. The method for preparing the directional porous aluminum nitride ceramic has the characteristics of simple process, short period, good repeatability, low cost and the like. The prepared directional porous aluminum nitride ceramic has wide application prospect in the fields of metal filtration, catalyst carriers, polymer reinforced phases, automobile industry, solar power generation and the like.
The above-mentioned contents are only for illustrating the technical idea of the present invention, and the protection scope of the present invention is not limited thereby, and any modification made on the basis of the technical idea of the present invention falls within the protection scope of the claims of the present invention.
Claims (3)
1. A rapid preparation method of directional porous aluminum nitride ceramics is characterized by comprising the following steps:
1) taking aluminum nitride powder, yttrium oxide powder, calcium fluoride powder and citric acid as raw materials, taking tert-butyl alcohol as a solvent, and fully and uniformly mixing to prepare slurry;
wherein the aluminum nitride powder and the tertiary butanol are mixed according to the following volume percentage: 10% -35%: 65-90 percent of the total weight of the aluminum nitride powder, 1-3 percent of yttrium oxide powder, 3-5 percent of calcium fluoride powder and 1-5 percent of citric acid;
fully mixing the aluminum nitride powder, the yttrium oxide powder, the calcium fluoride powder, the citric acid and the tertiary butanol in a ball milling tank for 2-12 hours at a material-ball ratio of 4:1 and a rotation speed of 400 r/min;
2) freezing the slurry, and then carrying out vacuum freeze drying to obtain a green body;
wherein the freezing temperature is-100 to-25 ℃, and the vacuum freeze drying temperature is-100 to-20 ℃;
3) placing the green body in a discharge plasma pressureless rapid sintering furnace, vacuumizing until the air pressure is less than 10Pa, heating to 1100-1400 ℃ from room temperature at the heating rate of 100-300 ℃/min, preserving the heat for 3-7min, stopping heating, naturally cooling the temperature in the furnace to be below 100 ℃, and taking out a white block in the furnace to be directional porous aluminum nitride ceramic, wherein the directional porous aluminum nitride ceramic is of a honeycomb structure, the pore diameter of the honeycomb is 12-50 mu m, the wall thickness is 10-20 mu m, the porosity is 60-87%, and the compressive strength is 0.1-10 MPa.
2. The rapid preparation method of directional porous aluminum nitride ceramic according to claim 1, wherein in step 2), the slurry is poured into a cylindrical silicon rubber mold for freezing, and the bottom of the silicon rubber mold is a copper column partially immersed in liquid nitrogen.
3. The oriented porous aluminum nitride ceramic prepared by the rapid preparation method according to any one of claims 1 to 2 is characterized in that the oriented porous aluminum nitride ceramic is of a honeycomb structure, the honeycomb pore diameter is 12-50 μm, the wall thickness is 10-20 μm, the porosity is 60-87%, and the compressive strength is 0.1-10 MPa.
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