CN101323524A - A preparation method of silicon carbide porous ceramics with aligned pores - Google Patents

Abstract

The invention discloses a preparation method of silicon carbide porous ceramics with oriented arrangement holes. Firstly, 0-30% of carbon powder, 0-50% of silicon powder and silicon oxide powder are added to 10-100% of basic raw material silicon carbide according to weight percentage. 0-60%; the particle size of silicon carbide is W3.5-P220, using one particle size or two particle size gradations; then use powder accumulation or ceramic conventional forming process to make the green body from the uniformly mixed ingredients, and place it in graphite In a crucible or sagger; put the crucible or sagger into a vacuum atmosphere sintering furnace with a temperature gradient of 15-30°C/cm, and raise the temperature to ^1900-1900- 2500°C, keep warm for 0.5-3 hours; finally cool down naturally under gas protection, take out the sintered body, and obtain a recrystallized silicon carbide porous ceramic with an oriented arrangement of open pores.

Description

A preparation method of silicon carbide porous ceramics with aligned pores

technical field

The invention relates to a preparation method of a recrystallized silicon carbide porous ceramic with a directional arrangement pore structure that can be used as a filter product or a catalyst carrier.

Background technique

Silicon carbide ceramic material has hardness second only to diamond, extremely high thermal conductivity, relatively low thermal expansion coefficient, excellent thermal shock resistance and creep resistance, high temperature strength and wear resistance, high chemical stability, It is insoluble in common acids and mixed acids, and does not react with boiling hydrochloric acid, sulfuric acid, and hydrofluoric acid. Silicon carbide also has semiconductor properties and has the characteristics of a negative temperature coefficient. Therefore, as a high-temperature ceramic with excellent performance, it has broad application prospects in industrial fields related to thermal engineering, combustion, chemical industry, and environmental protection.

Porous ceramic is a kind of functional ceramic material which is fired at high temperature and has a large number of pores in the sintered body that communicate with each other and the surface of the material. It can be widely used in the fields of molten metal filtration, catalyst carrier, automobile exhaust purification, sound absorption and noise reduction, sensors, biological materials, aerospace materials and other fields. Most of the existing porous ceramics are made of oxide ceramics, but oxide ceramics are difficult to compare with silicon carbide ceramics in terms of hardness and wear resistance, heat conduction and thermal shock resistance, corrosion resistance, and electrical conductivity. In many special applications, new technical requirements are put forward for the performance of porous ceramic materials. These requirements are well matched with the advantages that silicon carbide material itself has. At present, commercialized porous silicon carbide ceramic materials have been developed for automobile exhaust filters, as well as high-temperature metal melt casting filters.

The pore-making technology of existing porous silicon carbide ceramics is mainly by adding carbon powder, starch, and various organic colloids as pore-forming agents; or using wood and polyurethane foam as a porous (foam) template; or using resins with high carbon-fixing content , Resin+silicon carbide, or resin+silicon powder is formed, and the porous green body is formed by high temperature cracking as a precursor. The sintering of porous SiC ceramics is by adding oxides to form a low-melting point phase bonded silicon carbide at high temperature; or adding silicon (also can be added to the green body) during sintering, and the gas phase or liquid phase silicon reacts with carbon during sintering to form The silicon carbide bonded the original silicon carbide in the green body, or directly generated silicon carbide porous body.

Using pore forming agent, foaming method or template method to form pores not only needs to select the appropriate pore forming agent, foaming agent and template, but also most of the removal of pore forming agent, foaming agent or template needs to be carried out under oxidative conditions, which is easy It causes the oxidation of silicon carbide raw material particles, so it is mostly used in the preparation of oxide-bonded silicon carbide porous ceramics. The inherent excellent performance of silicon carbide cannot be fully utilized.

During the preparation process of reaction sintering, it is difficult to obtain a material with high porosity due to the volume expansion of silicon carbide produced by the reaction, or the filling of the pores of the green body by excess reactants (such as metal silicon), and the use temperature of the material is limited. The pore structure of the porous (foam) silicon carbide ceramics prepared in the prior art is all randomly oriented, and the relevant properties of the material are isotropic.

Contents of the invention

The purpose of the present invention is to provide a preparation method of silicon carbide porous ceramics with oriented pore structure, which does not need to add pore-forming agent and sintering second phase, and only needs to obtain porous silicon carbide by controlling the high-temperature recrystallization sintering process. Ceramic sintered body, in which the silicon carbide particles are bonded by pure silicon carbide formed during the recrystallization process, and the silicon carbide particles are oriented through the preferred orientation, and at the same time an oriented pore structure is formed between the grains.

To achieve the above object, the present invention takes the following technical solutions to achieve:

A preparation method of oriented hole silicon carbide porous ceramics, comprising the following steps:

The first step is to add 0-30% of carbon powder, 0-50% of silicon powder and 0-60% of silicon oxide powder to 10-100% of the basic raw material silicon carbide by weight percentage; wherein the particle size of silicon carbide is W3.5- P220, using one grain size or two grain size gradations;

The second step is to use powder accumulation or conventional ceramic forming technology to make the uniformly mixed ingredients into a green body, and place it in a graphite crucible or a sagger;

The third step is to put the crucible or sagger into a vacuum atmosphere sintering furnace with a temperature gradient of ^15-30 °C/cm, and ^raise the temperature to 1900～2500℃, keep warm for 0.5-3 hours;

In the fourth step, the temperature is naturally lowered and cooled under the protection of the gas in the third step, and the sintered body is taken out to obtain a recrystallized silicon carbide porous ceramic with an aligned pore structure.

In the above scheme, the method of adopting two particle size gradations for the silicon carbide is that the weight ratio of the silicon carbide with a particle size of P120 to the silicon carbide with a particle size of P180 is 4/6 or 3/7 or 6/4; the particle size is P60 The weight ratio of silicon carbide with particle size P120 is 4/6; the weight ratio of silicon carbide with particle size W14 to silicon carbide with particle size W3.5 is 4/6. The temperature gradient is distributed vertically or radially along the furnace body. The powder accumulation is that the ingredients are evenly mixed and then directly loaded into a graphite crucible or a sagger of a product with a required shape and shaken.

The basic principle of the present invention is to use the decomposition reaction of silicon carbide at 1900-2500°C to control the decomposition, sublimation, gas phase transmission, and gas phase recrystallization process to realize directional recrystallization and sintering between silicon carbide particles. Recrystallized silicon carbide porous ceramics with directional openings, or hollow radial or axial opening structures.

Compared with prior art, the beneficial effect of the present invention is:

1. A temperature field with a temperature gradient (vertical or radial temperature field) is used in the sintering furnace, which can control the evaporation-condensation direction of silicon carbide during high-temperature sintering, and obtain the heavy weight of the open-pore structure in the axial or radial direction. Crystalline silicon carbide porous ceramic articles.

2. By rationally selecting the particle size and gradation of silicon carbide, and the addition of other components, recrystallized silicon carbide porous ceramic products with directional arrangement and open-pore structure can be obtained with different porosity and pore size requirements.

3. By controlling the atmosphere pressure during sintering and adjusting the evaporation-condensation rate during high-temperature sintering of silicon carbide, the porosity and pore size of recrystallized silicon carbide porous ceramic products with directional arrangement and open-pore structure can be adjusted.

4. The control of the density of the green body when using a binder to form the green body, or the control of the tap density of the loose-packed green body when not using a binder, can also assist in adjusting the pores of recrystallized silicon carbide porous ceramic products with directional arrangement and opening structure rate and aperture size.

The crystal structure of the prepared silicon carbide porous ceramics is pure α-phase silicon carbide, and the bonding between crystals is realized through recrystallization. The direction of pores can be distributed along the axial or radial direction according to the temperature gradient of the temperature field of the sintering furnace. It has a high degree of directionality, and can obtain silicon carbide porous ceramics with a porosity of 30-70% and a pore size of 2 microns to 2 mm. Its physical and chemical properties are stable and can meet specific application requirements. For example, it can be used as a support material for a permeable membrane or other functional materials. It has the advantages of a wide temperature range and a wide range of applications.

Description of drawings

The present invention will be further described in detail below in conjunction with the accompanying drawings and specific embodiments.

Fig. 1 is the structure and microstructural morphology of pores of sample 3-1 of Example 3 of the present invention. Figure 1(a) and (b) are photomicrographs of different magnifications respectively. It can be seen from Fig. 1 that the microstructure of the porous ceramic of the present invention is composed of rod-shaped pores and silicon carbide particles arranged in an orientation, and the internal and external structures are basically uniform, and the connection between the silicon carbide particles is tight.

Detailed ways

The present invention has done 8 embodiments altogether, and the raw material composition of embodiment 1～8 is listed in table 1.

The raw material composition (WT%) of porous silicon carbide ceramics of the present invention of table 1

According to the formulations of Examples 1 to 8 in Table 1, common adhesives for ceramics are added to the raw materials, and phenolic resins with high carbon-fixing content can also be used as adhesives, and conventional forming methods are used to mix the raw materials and adhesives evenly; into green bodies of different densities; after drying, put them into graphite crucibles or saggars; you can also directly shake the mixed powder into graphite crucibles or saggars with required shape products without using binders. Put the crucible or sagger into a high-temperature vacuum atmosphere sintering furnace, and create a vertical or radial temperature gradient in the furnace body through the design of the heating element and the furnace body; the sintering furnace can be heated by resistance or by induction heating. For a general high-temperature vacuum atmosphere sintering furnace, pay attention to the furnace installation position so that the crucible is in a temperature gradient space of 15-30°C. Raise the temperature to 1900-2500°C under the condition of 0.5×10 ⁴ ~1×10 ⁵ Pa argon gas, keep it warm for 0.5-3 hours, and finally cool down naturally under the protection of gas; obtain high-temperature recrystallized porous carbonization with oriented pore structure Silicon sintered body. Two samples were prepared for each embodiment, a total of sixteen samples, the specific forming and sintering process parameters are shown in Table 2.

Table 2 Porous silicon carbide ceramics forming and sintering process parameters of the present invention

The silicon carbide porous ceramic samples of Examples 1 to 8 obtained by firing at high temperature in the present invention were respectively measured with an analytical balance and a SX-2700 scanning electron microscope for their porosity and pore alignment effect, and the results are listed in Table 3.

Table 3 Pore parameters of silicon carbide porous ceramic samples of the present invention

Claims (6)

1. the preparation method of an oriented hole silicon carbide porous ceramic is characterized in that, comprises the steps:

The first step by weight percentage, adds carbon dust 0～30%, silica flour 0～50%, silica powder 0～60% in basic raw material silicon carbide 10～100%; Wherein carborundum granularity is W3.5～P220, adopts a kind of granularity or two kinds of grain size distributions;

In second step, the batching composition that adopts powder accumulation or conventional ceramics forming technology to mix is made green compact, places plumbago crucible or saggar;

The 3rd step, crucible or saggar put into have the vacuum atmosphere sintering oven that thermograde is 15～30 ℃/cm temperature field, be 0.5 * 10 at pressure ⁴～1 * 10 ⁵Be warming up to 1900～2500 ℃ under the argon gas condition of Pa, be incubated 0.5～3 hour;

In the 4th step, sintered compact is taken out in cooling cooling naturally under the gas shield in the 3rd step, obtains having the recrystallized silicon carbide porous ceramics of directional arrangement pore structure.

2. the preparation method of oriented hole silicon carbide porous ceramic according to claim 1, it is characterized in that described silicon carbide adopts the method for two kinds of grain size distributions to be: granularity is that silicon carbide and the granularity of P120 is that the ratio of the silicon carbide weight of P180 is 4/6 or 3/7 or 6/4.

3. the preparation method who aligns the perforate carborundum porous ceramics according to claim 1 is characterized in that, described silicon carbide adopts the method for two kinds of grain size distributions to be: granularity is that silicon carbide and the granularity of P60 is that the ratio of the silicon carbide weight of P120 is 4/6.

4. the preparation method who aligns the perforate carborundum porous ceramics according to claim 1 is characterized in that, described silicon carbide adopts the method for two kinds of grain size distributions to be: granularity is that silicon carbide and the granularity of W14 is that the ratio of the silicon carbide weight of W3.5 is 4/6.

5. the preparation method of oriented hole silicon carbide porous ceramic according to claim 1 is characterized in that, described thermograde along become in the body of heater vertically to or radial distribution.

6. the preparation method of oriented hole silicon carbide porous ceramic according to claim 1 is characterized in that, described powder accumulation is that batching is formed ram-jolt in the plumbago crucible of the profile product that requires of directly packing into after mixing or the saggar.

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