CN102976758B - Preparation method of macroporous interconnection SiC ceramics - Google Patents

Abstract

The invention relates to the technical field of ceramic materials, in particular to a method for preparing macroporous interconnected SiC ceramics. The binder polyvinyl alcohol aqueous solution is mixed to form a uniform slurry, and the slurry is shaken by hand or mechanically to introduce air bubbles; the uniform slurry after foaming is put into a closed container, and the controlled decompression process is carried out; the expanded After the slurry is frozen with the container at -17°C for 4~12h, it is extracted in absolute ethanol or industrial ethanol at room temperature or under freezing conditions, and then immersed in a 7% mass fraction of phenolic resin ethanol solution. The sample is kept at 50~120°C Dry for 4 hours under low temperature, and in an inert atmosphere, keep the temperature at 1950~2100℃ for 0.5~2h to complete sintering. The invention adopts a decompression process to increase the pore diameter of the SiC ceramic from the submillimeter level to the millimeter level, and has low production cost and simplified process.

Description

A preparation method of macroporous interconnected SiC ceramics

technical field

The invention relates to the technical field of ceramic materials, in particular to a method for preparing large-pore interconnected SiC ceramics.

Background technique

Macroporous silicon carbide has the characteristics of high temperature resistance, corrosion resistance, metal melt erosion resistance, high strength, high flux rate, and large specific surface area. It is used in the field of metallurgical casting to filter and stabilize molten metal liquid and gas, and can be used as a catalyst carrier.

For the preparation of silicon carbide porous ceramics with large pores, domestic and foreign researches mainly focus on the hard template method, that is, by using precursors, such as polymer particles, organic foams and inorganic salts, as templates to mix with ceramic raw material powders, and then in the preparation The template is removed during the process to form a porous ceramic. For example: by mixing carbon powder and silicon carbide powder in a certain proportion, press molding, sintering at high temperature, and then air burning to remove carbon particles, silicon carbide porous ceramics with large pores can be prepared; polymer microspheres are used as templates, Such as using starch gel sponge, polyurethane sponge (Yao Xiumin, etc., the influence of secondary slurry viscosity on the performance of reticulated porous silicon carbide ceramics, Ceram.Inter.32(2006), 137, using MgO-Al ₂ O ₃ -SiO ₂ As a sintering agent, low-temperature sintering network porous silicon carbide ceramics J. Mater. Sci 42 (2007) 4960), carbon sponge (Guo Quangui et al., Effect of nano-AlN content on the microstructure and mechanical properties of porous silicon carbide prepared by silicon carbide foam, J. . Eur. Ceram. Soc.30 (2010) 113, Preparation of foamed porous silicon carbide from the silicification reaction of mesoporous pitch and nano silicon carbide mixture, Mater. Sci. Eng. A 488 (2008) 514) etc. , drying and subsequent sintering can prepare macroporous silicon carbide ceramics; in addition, wood with a macroporous structure can also be used as a carbon source to prepare macroporous silicon carbide ceramics with a bionic structure.

However, for the current preparation methods that mainly rely on hard templates or macroporous framework materials for the preparation of macroporous silicon carbide, the disadvantages are also obvious: first, the pore size and pore type depend on the pore size and pore type of the template, and cannot be adjusted and modified Secondly, the synthesis steps are relatively cumbersome. In addition to the sintering steps of ceramics, some also involve template preparation and pretreatment, including steps such as pore formation and carbonization; especially using various sponges as templates, it is easy to generate wall pores (sponge skeleton left after decomposition) (Yao Xiumin, etc., the influence of secondary slurry viscosity on the performance of reticulated porous silicon carbide ceramics, Ceram. Inter.32 (2006) 137), which is unfavorable for improving the mechanical properties of ceramics after sintering . Therefore, these methods all have disadvantages such as complex process, high cost, and closed pores, and are limited in use. It is of great application value to study a low-cost method for preparing macroporous silicon carbide materials whose structure can be designed and adjusted.

In the applicant's authorized patent (patent number: 201010580712.7), we introduced a method for preparing macroporous interconnected silicon carbide with the help of the cold-induced gelation properties of polyvinyl alcohol. The pore diameter is between 0.1 and 0.4 mm. Some applications that require larger pore sizes, such as molten metal filtration, are not advantageous. It is of great application value to develop a preparation method for interconnected SiC ceramics with larger apertures (0.5-2 mm).

Contents of the invention

Aiming at the deficiencies in the prior art, the invention provides a method for preparing large-pore interconnected SiC ceramics with low production cost, simplified process and enlarged pore diameter.

A method for preparing a macroporous interconnected SiC ceramic of the present invention comprises the following steps:

(1) Mix SiC powder and boron carbide powder evenly to form a SiC mixture. The SiC mixture contains 98.92% of SiC powder and 1.08% of boron carbide powder by weight percentage;

(2) Mix the SiC mixture, cationic surfactant, and binder polyvinyl alcohol aqueous solution in a weight ratio of (7~17): (0~3×10 ^-3 ): 44 to form a uniform slurry. Shake or mechanically stir the slurry to introduce air bubbles; put the uniform slurry after bubble induction into a closed container for controlled decompression process;

(3) After the slurry expands to 2~4 times of the initial volume, it is frozen with the container at -17℃ for 4~12h, then extracted in absolute ethanol or industrial ethanol at room temperature or -17℃ for 4~24h , repeated 1 to 3 times, and then immersed in ethanol solution of phenolic resin with a mass fraction of 7%, the sample was dried at 50-120°C for 4 hours, and kept at 1950-2100°C for 0.5-2 hours in an inert atmosphere to complete sintering.

Wherein, the average particle size of the SiC powder described in step (1) is 1.0 μm, and the average particle size of the boron carbide powder is 4.1 μm;

The binder polyvinyl alcohol aqueous solution described in step (2) has a degree of polymerization of polyvinyl alcohol of 2000, a degree of alcoholysis of 99%, a solution concentration of 6.5 to 7.0 wt% or a degree of polymerization of polyvinyl alcohol of 1700, The alcoholysis degree is 99%, and the solution concentration is 7.0-8.0wt%;

The cationic surfactant described in step (2) is sodium lauryl sulfate;

The bubble introduction described in step (2) is to introduce air bubbles by shaking by hand or mechanical stirring;

The decompression process described in step (2) is to expand the homogeneous slurry after decompression in a closed container, thereby increasing the size of the bubbles;

The phenolic resin described in step (3) is Resole type with a molecular weight of 600 and is mainly used for carbon induction.

Features and beneficial effects of the present invention are:

(l) The present invention uses a decompression process to expand the bubbles in a closed container through decompression, thereby increasing the size of the bubbles, so that the pore diameter is significantly increased on the basis of the size reported in the authorized patent, that is, from submillimeters to millimeter level;

(2) The present invention uses polyvinyl alcohol as a binder, which has a long-term stabilizing effect on the air bubbles introduced by oscillation, and its cryogel properties play a role in fixing the air bubbles, so that it can be realized without very harsh freezing conditions gel;

(3) The pore type, pore size, porosity and connectivity of macroporous SiC ceramics can be adjusted conveniently and effectively through the use of trace surfactants;

(4) Ethanol is used to extract the sample, so the maintenance of the pore structure and the drying of the sample can be realized without using expensive freeze-drying equipment and long drying time, making the method of the present invention easy to organize production, and the extracted ethanol and water The mixture can be reused after simple distillation;

(5) Since polyvinyl alcohol is easy to obtain and does not involve complex chemical reactions and the use of sacrificial templates except for the sintering process and preparation route, the present invention is easy to organize and produce, and the cost is low.

Description of drawings

Fig. 1 is the schematic diagram of slurry decompression expansion to form holes;

Figure 2 is the optical microscope photo of the macroporous silicon carbide ceramic body prepared in Example 1 before (a) and after sintering (b), (c) is the enlarged scanning electron micrograph of the circle in (b), (d ) is the pore size distribution diagram after sintering;

Fig. 3 is the optical microscope photo of the macroporous silicon carbide ceramics prepared in Example 2 before sintering (a) and after sintering (b) and the pore size distribution diagram (c) after sintering;

Fig. 4 is an optical microscope photo (a) and a pore size distribution diagram (b) of the macroporous silicon carbide ceramic green body obtained in Example 3 after sintering;

Fig. 5 is an optical microscope photo (a) and a pore size distribution diagram (b) of the macroporous silicon carbide ceramic green body obtained in Example 4 after sintering;

Fig. 6 is an optical microscope photo (a) and a pore size distribution diagram (b) of the sintered macroporous silicon carbide ceramic green body prepared in Example 5.

Detailed ways

The present invention will be further described below in conjunction with embodiment.

The microscope model used in this embodiment is a USB Digital microscope, and the scanning electron microscope model is a S3400N scanning electron microscope.

Example 1

(1) Mix SiC powder and boron carbide powder evenly to form SiC mixture, wherein the average particle size of SiC powder is 1.0 μm, and the average particle size of boron carbide powder is 4.1 μm; the SiC mixture contains 98.92% of SiC powder by weight percentage , containing boron carbide powder 1.08%;

(2) Use polyvinyl alcohol aqueous solution 20-99 with a concentration of 6.75wt% as the binder, mix the SiC mixture and the binder polyvinyl alcohol aqueous solution at a weight ratio of 7.58:44 to form a uniform slurry, and mechanically Stir the slurry and introduce air bubbles; put the homogeneous slurry after bubble induction into a closed container, and perform a controlled decompression process to make the slurry uniformly expand to three times the initial volume;

(3) After the expanded slurry is frozen with the container at -17°C for 9 hours, the frozen sample is directly transferred to industrial ethanol for extraction for 5 hours, repeated 1 to 3 times, and then immersed in phenolic formaldehyde with a mass fraction of 7%. Resin ethanol solution, the sample was dried at 80°C for 4h; in an inert atmosphere, kept at 2000°C for 0.5h to complete sintering, and the heating rate was 5°C/min.

Figure 2 is the optical microscope photo of the macroporous silicon carbide ceramic body prepared in this example before (a) and after sintering (b) and the scanning electron microscope photo of the pore wall after sintering (c) and the pore size distribution diagram after sintering ( d). The pore diameter of the macroporous silicon carbide ceramic body obtained in this example is 0.6±0.2mm, and the average pore diameter is 0.6mm, which is about twice the pore diameter of the previous patent report (patent number: 201010580712.7), and the macropores are connected by communicating holes. SEM pictures after sintering show that the SiC particles have been interconnected by sintering.

Example 2

(1) Mix SiC powder and boron carbide powder evenly to form SiC mixture, wherein the average particle size of SiC powder is 1.0 μm, and the average particle size of boron carbide powder is 4.1 μm; the SiC mixture contains 98.92% of SiC powder by weight percentage , containing boron carbide powder 1.08%;

(2) Use polyvinyl alcohol aqueous solution 20-99 with a concentration of 6.75wt% as the binder, mix the SiC mixture and the binder polyvinyl alcohol aqueous solution at a weight ratio of 14.19:44 to form a uniform slurry, and mechanically Stir the slurry and introduce air bubbles; put the homogeneous slurry after bubble induction into a closed container, and perform a controlled decompression process to make the slurry uniformly expand to three times the initial volume;

(3) After the expanded slurry is frozen with the container at -17°C for 9 hours, the frozen sample is directly transferred to industrial ethanol for extraction for 5 hours, repeated 1 to 3 times, and then immersed in phenolic formaldehyde with a mass fraction of 7%. Resin ethanol solution, the sample was dried at 80°C for 4h; in an inert atmosphere, kept at 2000°C for 0.5h to complete sintering, and the heating rate was 5°C/min.

Fig. 3 is an optical microscope photograph of the macroporous silicon carbide ceramic prepared in this example before (a) and after (b) sintering and a pore size distribution diagram (c) after sintering. Compared with Example 1, this example increases the mass ratio of SiC composite powder to PVA solution without changing other conditions, which can significantly increase the size of macropores. The large holes are connected by connecting holes, the hole diameter is about 0.05~0.2mm, and the hole wall is thickened. Obviously, through the present invention, the pore diameter of the three-dimensional interconnected macroporous silicon carbide can be further increased to millimeter level.

Example 3

(1) Mix SiC powder and boron carbide powder evenly to form SiC mixture, wherein the average particle size of SiC powder is 1.0 μm, and the average particle size of boron carbide powder is 4.1 μm; the SiC mixture contains 98.92% of SiC powder by weight percentage , containing boron carbide powder 1.08%;

(2) Using polyvinyl alcohol aqueous solution 20-99 with a concentration of 6.75wt% as a binder, the SiC mixture, sodium lauryl sulfate and binder polyvinyl alcohol aqueous solution are in a weight ratio of 14.19: 2×10 ^-3 : 44 mix evenly to form a uniform slurry, mechanically stir the slurry, and introduce air bubbles; put the uniform slurry after bubbling into a closed container, and perform a controlled decompression process to make the slurry evenly expand to the initial three times the volume;

(3) After the expanded slurry is frozen with the container at -17°C for 9 hours, the frozen sample is directly transferred to industrial ethanol for extraction for 5 hours, repeated 1 to 3 times, and then immersed in phenolic formaldehyde with a mass fraction of 7%. Resin ethanol solution, the sample was dried at 80°C for 4h; in an inert atmosphere, kept at 2000°C for 0.5h to complete sintering, and the heating rate was 5°C/min.

Fig. 4 is an optical microscope photo (a) and a pore size distribution diagram (b) of the sintered macroporous silicon carbide ceramic green body prepared in this example. Compared with Example 2, this example does not change other conditions, adding a small amount of surfactant SDS, the pore size of the macroporous silicon carbide is about 0.8±0.4mm and the uniformity is improved, and the connectivity between the macropores is also significantly improved. , Unicom hole size in 0.2 ± 0.1mm. This is similar to the principle of action of the surfactant (OP-10) described in the granted patent (patent number: 201010580712.7).

Example 4

(1) Mix SiC powder and boron carbide powder evenly to form SiC mixture, wherein the average particle size of SiC powder is 1.0 μm, and the average particle size of boron carbide powder is 4.1 μm; the SiC mixture contains 98.92% of SiC powder by weight percentage , containing boron carbide powder 1.08%;

(2) Use polyvinyl alcohol aqueous solution 20-99 with a concentration of 6.75wt% as the binder, mix the SiC mixture and the binder polyvinyl alcohol aqueous solution at a weight ratio of 14.19:44 to form a uniform slurry, and mechanically Stir the slurry and introduce air bubbles; put the homogeneous slurry after bubble induction into a closed container, and perform a controlled decompression process to make the slurry uniformly expand to twice the original volume;

(3) After the expanded slurry is frozen with the container at -17°C for 9 hours, the frozen sample is directly transferred to industrial ethanol for extraction for 5 hours, repeated 1 to 3 times, and then immersed in phenolic formaldehyde with a mass fraction of 7%. Resin ethanol solution, the sample was dried at 80°C for 4h; in an inert atmosphere, kept at 2000°C for 0.5h to complete sintering, and the heating rate was 5°C/min.

Fig. 5 is an optical microscope photo (a) and a pore size distribution diagram (b) of the sintered macroporous silicon carbide ceramic green body prepared in this example. Compared with Example 2, this embodiment does not change other conditions, reduces the volume of expansion, and can reduce the size of the large pores. The size of the large pores is reduced from about 1.2±0.3mm to about 0.4±0.2mm, and the large pores are connected by The holes are connected, and the hole diameter is about 0.05~0.1mm.

Example 5

(1) Mix SiC powder and boron carbide powder evenly to form SiC mixture, wherein the average particle size of SiC powder is 1.0 μm, and the average particle size of boron carbide powder is 4.1 μm; the SiC mixture contains 98.92% of SiC powder by weight percentage , containing boron carbide powder 1.08%;

(2) Use polyvinyl alcohol aqueous solution 20-99 with a concentration of 6.75wt% as the binder, mix the SiC mixture and the binder polyvinyl alcohol aqueous solution at a weight ratio of 14.19:44 to form a uniform slurry, and mechanically Stir the slurry and introduce air bubbles; put the homogeneous slurry after bubble induction into a closed container, and perform a controlled decompression process to make the slurry uniformly expand to four times the initial volume;

(3) After the expanded slurry is frozen with the container at -17°C for 9 hours, the frozen sample is directly transferred to industrial ethanol for extraction for 5 hours, repeated 1 to 3 times, and then immersed in phenolic formaldehyde with a mass fraction of 7%. Resin ethanol solution, the sample was dried at 80°C for 4h; in an inert atmosphere, kept at 2000°C for 0.5h to complete sintering, and the heating rate was 5°C/min.

Fig. 6 is an optical microscope photo (a) and a pore size distribution diagram (b) of the sintered macroporous silicon carbide ceramic green body prepared in this example. Compared with Example 4, this embodiment does not change other conditions, increases the volume of expansion, and can increase the size of the large pores. The size of the large pores increases from about 0.4±0.2mm to about 0.8±0.3mm. The connecting holes are connected with each other, and the diameter of the holes is about 0.05~0.3mm.

Example 6

(1) Mix SiC powder and boron carbide powder evenly to form SiC mixture, wherein the average particle size of SiC powder is 1.0 μm, and the average particle size of boron carbide powder is 4.1 μm; the SiC mixture contains 98.92% of SiC powder by weight percentage , containing boron carbide powder 1.08%;

(2) Using polyvinyl alcohol aqueous solution 17-99 with a concentration of 8.0wt% as a binder, the SiC mixture, sodium lauryl sulfate and binder polyvinyl alcohol aqueous solution are in a weight ratio of 17:3×10 ^-3 : 44 mixed evenly to form a uniform slurry, shake the slurry by hand, and introduce air bubbles; put the uniform slurry after the bubbles into an airtight container, and carry out controlled decompression process to make the slurry evenly expand to three times the initial volume;

(3) After the expanded slurry is frozen with the container at -17°C for 4 hours, the frozen sample is placed at room temperature, then transferred to absolute ethanol for extraction for 4 hours, repeated 1 to 3 times, and then immersed in the mass fraction It is a 7% ethanol solution of phenolic resin, and the sample is dried at 50°C for 4 hours; in an inert atmosphere, it is kept at 1950°C for 2 hours to complete sintering, and the heating rate is 5°C/min.

Example 7

(1) Mix SiC powder and boron carbide powder evenly to form SiC mixture, wherein the average particle size of SiC powder is 1.0 μm, and the average particle size of boron carbide powder is 4.1 μm; the SiC mixture contains 98.92% of SiC powder by weight percentage , containing boron carbide powder 1.08%;

(2) Use polyvinyl alcohol aqueous solution 20-99 with a concentration of 7.0wt% as the binder, mix the SiC mixture and the binder polyvinyl alcohol aqueous solution at a weight ratio of 7:44 to form a uniform slurry, and mechanically Stir the slurry and introduce air bubbles; put the homogeneous slurry after bubble induction into a closed container, and perform a controlled decompression process to make the slurry uniformly expand to four times the initial volume;

(3) After the expanded slurry is frozen with the container at -17°C for 12 hours, the frozen sample is placed at room temperature, then transferred to absolute ethanol for extraction for 12 hours, repeated 1 to 3 times, and then immersed in the mass fraction It is a 7% ethanol solution of phenolic resin, and the sample is dried at 120 ° C for 4 h; in an inert atmosphere, it is kept at 2100 ° C for 0.5 h to complete sintering, and the heating rate is 5 ° C / min.

Example 8

(1) Mix SiC powder and boron carbide powder evenly to form SiC mixture, wherein the average particle size of SiC powder is 1.0 μm, and the average particle size of boron carbide powder is 4.1 μm; the SiC mixture contains 98.92% of SiC powder by weight percentage , containing boron carbide powder 1.08%;

(2) Use polyvinyl alcohol aqueous solution 20-99 with a concentration of 6.5wt% as the binder, mix the SiC mixture and the binder polyvinyl alcohol aqueous solution at a weight ratio of 10:44 to form a uniform slurry, and hand Shake the slurry to introduce air bubbles; put the uniform slurry after bubble induction into a closed container, and perform a controlled decompression process to make the slurry uniformly expand to four times the initial volume;

(3) After the expanded slurry is frozen with the container at -17°C for 12 hours, the frozen sample is placed at room temperature, then transferred to absolute ethanol for extraction for 24 hours, repeated 1 to 3 times, and then immersed in the mass fraction It is a 7% ethanol solution of phenolic resin, and the sample is dried at 120 ° C for 4 h; in an inert atmosphere, it is kept at 2100 ° C for 0.5 h to complete sintering, and the heating rate is 5 ° C / min.

Example 9

(1) Mix SiC powder and boron carbide powder evenly to form SiC mixture, wherein the average particle size of SiC powder is 1.0 μm, and the average particle size of boron carbide powder is 4.1 μm; the SiC mixture contains 98.92% of SiC powder by weight percentage , containing boron carbide powder 1.08%;

(2) Use polyvinyl alcohol aqueous solution 17-99 with a concentration of 7.0wt% as the binder, mix the SiC mixture and the binder polyvinyl alcohol aqueous solution at a weight ratio of 7:44 to form a uniform slurry, and mechanically Stir the slurry and introduce air bubbles; put the homogeneous slurry after bubble induction into a closed container, and perform a controlled decompression process to make the slurry uniformly expand to twice the original volume;

(3) After the expanded slurry is frozen with the container at -17°C for 12 hours, the frozen sample is placed at room temperature, then transferred to absolute ethanol for extraction for 5 hours, repeated 1 to 3 times, and then immersed in the mass fraction It is a 7% ethanol solution of phenolic resin, and the sample is dried at 120 ° C for 4 h; in an inert atmosphere, it is kept at 2100 ° C for 0.5 h to complete sintering, and the heating rate is 5 ° C / min.

Claims (1)

1. A preparation method of macroporous interconnected SiC ceramics, comprising the following steps: (1) Mix SiC powder and boron carbide powder evenly to form a SiC mixture. The SiC mixture contains 98.92% of SiC powder and 1.08% of boron carbide powder by weight percentage; the average particle size of the SiC powder is 1.0 μm, The average particle size of boron carbide powder is 4.1 μm; (2) Use polyvinyl alcohol aqueous solution 20-99 with a concentration of 6.75wt% as the binder, mix the SiC mixture and the binder polyvinyl alcohol aqueous solution at a weight ratio of 14.19:44 to form a uniform slurry, and mechanically Stir the slurry and introduce air bubbles; put the uniform slurry after bubble induction into a closed container for controlled decompression process; It is characterized by: (3) After the slurry expands to 3 times the initial volume, it is frozen at -17°C for 9 hours together with the container, then extracted in industrial ethanol for 5 hours at room temperature or -17°C freezing, repeated 1 to 3 times, and then immersed in the mass The phenolic resin ethanol solution with a fraction of 7%, the sample was dried at 80°C for 4h, and kept at 2000°C for 0.5h in an inert atmosphere to complete sintering; the phenolic resin was Resole type with a molecular weight of 600, mainly used to induce carbon; The large pores of the interconnected SiC ceramics have a size of 1.2±0.4 mm and an average diameter of 1.0 mm. The large pores are connected by connecting holes with a diameter of 0.05-0.2 mm, and the walls of the pores are thickened.