阅读说明：本技术 一种AlN晶须增强层状多孔SiC陶瓷及其制备方法 (AlN whisker reinforced layered porous SiC ceramic and preparation method thereof ) 是由 史国栋 周文雅 武湛君 王亨利 宋健 于 2019-09-06 设计创作，主要内容包括：本发明公开了一种AlN晶须增强层状多孔SiC陶瓷及其制备方法,属于多孔陶瓷技术领域。所述的AlN晶须增强层状多孔SiC陶瓷采用平行排列的SiC基陶瓷层作为基体,SiC基陶瓷层间存在层状贯通孔,大量AlN晶须端部粘附在SiC基陶瓷层表面并向层状贯通孔中伸出。这些AlN晶须相互交叉在层状贯通孔中形成三维网状结构,从而能够提高层状多孔SiC陶瓷的比表面积,并可以实现对SiC基陶瓷层的有效支撑,增加层状多孔SiC陶瓷的强度。本发明的AlN晶须增强层状多孔SiC陶瓷的比表面积和压缩强度明显增加,能显著提高层状多孔SiC陶瓷的使用价值。(the invention discloses an AlN whisker reinforced layered porous SiC ceramic and a preparation method thereof, belonging to the technical field of porous ceramics. The AlN whisker reinforced laminated porous SiC ceramic adopts SiC-based ceramic layers which are arranged in parallel as a matrix, laminated through holes exist among the SiC-based ceramic layers, and a large number of AlN whisker ends are adhered to the surface of the SiC-based ceramic layers and extend out of the laminated through holes. The AlN whiskers are intersected with each other to form a three-dimensional network structure in the layered through holes, so that the specific surface area of the layered porous SiC ceramic can be increased, the SiC-based ceramic layer can be effectively supported, and the strength of the layered porous SiC ceramic can be increased. The AlN whisker reinforced laminated porous SiC ceramic has obviously increased specific surface area and compression strength, and can obviously improve the use value of the laminated porous SiC ceramic.)

1. An AlN whisker reinforced laminated porous SiC ceramic is characterized in that an SiC-based ceramic layer which is arranged in parallel is used as a matrix of the AlN whisker reinforced laminated porous SiC ceramic, laminated through holes exist among the SiC-based ceramic layers, and a large number of AlN whisker ends are adhered to the surface of the SiC-based ceramic layer and extend out of the laminated through holes; these AlN whiskers intersect with each other to form a three-dimensional network structure in the layered through-hole;

the SiC-based ceramic layer is mainly composed of SiC and Al ₂ O ₃.

2. A preparation method of AlN whisker reinforced layered porous SiC ceramic is characterized by comprising the following specific steps:

(1) dispersing SiC powder, a dispersing agent accounting for 0.2-2.0 wt.% of the mass of the SiC powder and sintering aid powder accounting for 0-30 wt.% of the mass of the SiC powder into deionized water together to obtain ceramic particle dispersion liquid with the solid phase content of 5-30 vol.%; the solid phase comprises SiC and a sintering aid;

The dispersant is one or more of polyethylene glycol, sodium silicate, sodium carboxymethylcellulose, tetramethylammonium hydroxide, ammonium polymethacrylate, polyethyleneimine, sodium dodecyl benzene sulfonate and sodium dodecyl sulfate;

The sintering aid is Al ₂ O ₃;

(2) Placing the ceramic particle dispersion liquid obtained in the step (1) into a polytetrafluoroethylene container, wherein the wall thickness of the container is 3-8 mm, then placing the polytetrafluoroethylene container on an entity metal block, immersing the lower half part of the metal block into a refrigerant, and directionally freezing an alumina suspension mixed with a sintering aid through heat transfer of the metal block until the suspension is completely frozen to obtain an ice block containing a ceramic particle assembly;

The metal block is made of copper or aluminum;

The refrigerant is liquid nitrogen;

(3) drying the ice blocks containing the ceramic particle assembly obtained in the step (2) for 24-72h under the conditions that the temperature is lower than minus 18 ℃ and the air pressure is lower than 600Pa to remove ice, and obtaining a layered porous ceramic body; sintering the obtained layered porous ceramic blank at the temperature of 1500-2000 ℃ for 2h to prepare layered porous SiC ceramic;

(4) placing Al-Mg alloy with the volume equal to the pore volume of the laminated porous SiC ceramic on the laminated porous SiC ceramic, placing the Al-Mg alloy and the laminated porous SiC ceramic into a high-temperature furnace, firstly infiltrating for 1h under the condition of 800 ℃, then heating for 1-3h under the conditions of nitrogen atmosphere and 1080-1200 ℃, so that Al reacts with N ₂, and growing AlN whiskers in pores of the laminated porous SiC ceramic to prepare AlN whisker reinforced laminated porous SiC ceramic;

The content of Mg in the Al-Mg alloy is 8-30 wt.%.

Technical Field

The invention belongs to the technical field of porous ceramics, and particularly relates to an AlN whisker reinforced layered porous SiC ceramic and a preparation method thereof.

Background

Porous ceramics are ceramic materials having a large number of through and non-through channel structures. The high porosity makes it have the advantages of low density, good thermal insulation, high specific surface area, low dielectric constant, good permeability, etc. Silicon carbide (SiC) is a ceramic material with excellent properties. The porous SiC ceramic material has the advantages of common porous ceramics such as higher porosity, small volume density, large specific surface area and the like, and also has the characteristics of high strength, corrosion resistance, high temperature resistance, low thermal expansion coefficient, good thermal shock resistance and biocompatibility and the like. The excellent properties enable the porous SiC ceramic to have wide application prospects in the fields of filter materials, catalyst carriers, biological materials and composite material framework materials, and have huge application requirements in various fields of environmental protection, aerospace, biomedical treatment, electronic devices, energy chemical industry and the like. Therefore, the development of high-performance porous SiC ceramics and preparation technology can bring huge economic value and good social significance.

The preparation method of the porous ceramic mainly comprises a pore-forming agent adding method, a foaming method, a particle stacking method, an organic foam impregnation method, an ice template method and the like. The ice template method is to freeze water dispersion containing ceramic grains with ice as pore creating template, to push the ceramic grains to the gaps between the ice grains with the tips of the ice crystals growing during the condensation of water into ice, to assemble the ceramic grains into specific structure under the action of the ice template, to sublimate and eliminate the ice crystals after freeze drying, to form pores in the positions occupied by the original ice crystals, so that the pore structure in the freeze cast porous ceramic is the duplication of the ice crystal morphology. Compared with other preparation methods, the ice template method has the advantages of simple and flexible process (being suitable for various materials such as metal, ceramic, organic matter and the like), environmental protection and the like; in addition, the porous ceramic prepared by the method has higher strength, and the pore structure of the porous ceramic has good controllability. The method can prepare a porous structure with a complex shape and a fine structure and a lamellar or honeycomb through hole with a great length. The characteristics lead the ice template porous ceramic to have excellent use value and market prospect.

the brittle and porous characteristics enable the mechanical properties of the porous ceramics to be generally poor and the porous ceramics to be easily damaged in the using process, so that the improvement of the strength of the porous ceramics has important significance for reducing the damage of the porous ceramics in application and improving the service performance and the value of the porous ceramics. And for porous ceramics used as catalyst carriers, heat exchangers, gas sensors and other devices, the improvement of the surface area of the porous ceramics has important significance for improving the service performance of the porous ceramics. The strength and specific surface area of the porous SiC ceramic prepared by the current ice template method are still not high enough, so that the application value of the porous SiC ceramic is limited.

disclosure of Invention

Aiming at the current situation that the strength and the specific surface area of porous SiC ceramics in the prior art are not high, the invention provides an AlN whisker reinforced layered porous SiC ceramics and a preparation method thereof. The preparation process of the porous ceramic comprises the following steps: firstly, preparing laminated porous SiC ceramic by adopting the existing ice template method, then filling Al-Mg alloy into the pores of the laminated porous SiC ceramic, and heating at high temperature in a nitrogen environment to enable Al to react with nitrogen and grow AlN whiskers on the surface of the SiC ceramic layer of the laminated porous SiC ceramic, thereby finally forming the AlN whisker reinforced laminated porous SiC ceramic. The AlN whiskers have high strength and high specific surface area, so the strength and the specific surface area of the laminated porous SiC ceramic can be effectively improved by introducing the AlN whiskers into the surface of the SiC ceramic layer of the laminated porous SiC ceramic.

In order to achieve the purpose of improving the strength and the specific surface area of the porous SiC ceramic, the technical scheme of the invention is as follows:

An AlN whisker reinforced laminated porous SiC ceramic which uses SiC-based ceramic layers arranged in parallel as a substrate, laminated through holes are present between the SiC-based ceramic layers, and a large number of AlN whisker ends are adhered to the surface of the SiC-based ceramic layer and protrude into the laminated through holes. The AlN whiskers are intersected with each other to form a three-dimensional network structure in the layered through holes, so that the specific surface area of the layered porous SiC ceramic can be increased, the SiC-based ceramic layer can be effectively supported, and the strength of the layered porous SiC ceramic can be increased.

the SiC-based ceramic layer is mainly composed of SiC and Al ₂ O ₃.

a preparation method of AlN whisker reinforced layered porous SiC ceramics comprises the following specific steps:

(1) And dispersing SiC powder, a dispersing agent accounting for 0.2-2.0 wt.% of the mass of the SiC powder and sintering aid powder accounting for 0-30 wt.% of the mass of the SiC powder into deionized water together to obtain ceramic particle dispersion liquid with the solid phase content of 5-30 vol.%. The solid phase comprises SiC and a sintering aid.

The dispersant is one or more of polyethylene glycol, sodium silicate, sodium carboxymethylcellulose, tetramethylammonium hydroxide, ammonium polymethacrylate, polyethyleneimine, sodium dodecyl benzene sulfonate and sodium dodecyl sulfate.

The sintering aid is Al ₂ O ₃.

(2) Placing the ceramic particle dispersion liquid obtained in the step (1) into a polytetrafluoroethylene container, wherein the wall thickness of the container is 3-8 mm, then placing the polytetrafluoroethylene container on an entity metal block (used as a cold finger), immersing the lower half part of the metal block into a refrigerant, and directionally freezing the alumina suspension mixed with the sintering aid through the heat transfer of the metal block until the suspension is completely frozen, thus obtaining the ice block containing the ceramic particle assembly.

The metal block is made of copper or aluminum;

the refrigerant is liquid nitrogen.

(3) drying the ice blocks containing the ceramic particle assembly obtained in the step (2) for 24-72h under the conditions that the temperature is lower than minus 18 ℃ and the air pressure is lower than 600Pa to remove ice, and obtaining a layered porous ceramic body; sintering the obtained layered porous ceramic blank at the temperature of 1500-2000 ℃ for 2h to prepare the layered porous SiC ceramic.

(4) Placing Al-Mg alloy with the volume equal to the pore volume of the laminated porous SiC ceramic on the laminated porous SiC ceramic, placing the Al-Mg alloy and the laminated porous SiC ceramic into a high-temperature furnace, firstly infiltrating for 1h under the condition of 800 ℃, then heating for 1-3h under the conditions of nitrogen atmosphere and 1080-1200 ℃, so that Al reacts with N ₂, and growing AlN whiskers in the pores of the laminated porous SiC ceramic to obtain the AlN whisker reinforced laminated porous SiC ceramic.

The content of Mg in the Al-Mg alloy is 8-30 wt.%.

The preparation method has the beneficial effects that in the prepared AlN whisker reinforced laminated porous SiC ceramic, AlN whiskers form a three-dimensional network structure in pores among ceramic layers of the laminated porous SiC ceramic. Compared with the laminated porous SiC ceramic without AlN whisker reinforcement, the AlN whisker reinforced laminated porous SiC ceramic provided by the invention has the advantages that the specific surface area and the compressive strength are obviously increased, and the use value of the laminated porous SiC ceramic can be obviously improved.

The reason why the AlN whiskers are selected to reinforce the porous SiC ceramic instead of other whiskers is that compared with other commonly used whisker materials (such as Al ₂ O ₃ whiskers, Si ₃ N ₄ whiskers, ZnO ₂ whiskers and the like), the AlN whiskers have higher use temperature and thermal conductivity, have a thermal expansion coefficient which is closer to that of SiC, can be better matched with a SiC matrix and realize better comprehensive performance.

drawings

FIG. 1 is a schematic view of an apparatus for carrying out step 2 of the present invention;

FIG. 2a is a typical microstructure diagram of an AlN whisker reinforced layered porous SiC ceramic prepared according to the present invention;

Fig. 2b is a partially enlarged view of the box-labeled region in fig. 2 a. Wherein the position pointed by the reference number 6 is AlN whisker; the position indicated by reference numeral 7 is a SiC ceramic layer.

In the figure: 1. a container; 2. a refrigerant; 3. a metal block; 4. a ceramic particle dispersion liquid; 5. a polytetrafluoroethylene container.

Detailed Description

In order to make the objects, features and advantages of the present invention more obvious and understandable, the present invention is further described below with reference to the accompanying drawings in combination with the embodiments so that those skilled in the art can implement the present invention by referring to the description, and the scope of the present invention is not limited to the embodiments. It is to be understood that the embodiments described below are only some embodiments of the present invention, and not all 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.