CN101805201B - Preparation method of porous silicon carbide ceramics with high thermal shock resistance - Google Patents

Abstract

The invention belongs to the technical field of disclosing the preparation of porous silicon carbide ceramics, and relates to a method for preparing porous silicon carbide ceramics with high thermal shock resistance. The silicon-resin core-shell structure precursor powder, alumina, silicon dioxide and yttrium oxide prepared by the existing inclusion mixing process are mixed according to the mass ratio range of 100: (0.5-10): (0.1-5), and the mixed powder After the body is subjected to pressure forming, carbonization treatment and sintering treatment, a porous silicon carbide ceramic with high thermal shock resistance is obtained. The invention reduces the sintering temperature to 1200-1800 DEG C, significantly increases the thermal conductivity of ceramics, improves the thermal shock resistance, and loses 6.5-30% of the strength after 30 thermal shocks at 800 DEG C. The prepared porous silicon carbide ceramic has a high porosity greater than 80 percent, an average pore size of 100-300 μm and uniform pore size distribution. The method has the advantages of simple process, less auxiliary additives and obvious effect.

Description

A kind of preparation method of porous silicon carbide ceramics with high thermal shock resistance

technical field

The invention belongs to the technical field of preparing porous silicon carbide ceramics, and in particular relates to a preparation method of porous silicon carbide ceramics with high thermal shock resistance.

Background technique

Porous silicon carbide ceramics have the following characteristics: uniform three-dimensional network structure, high porosity, large continuous pores, small pressure loss, and heat generation when energized (small specific resistance, the resistivity is generally 1-2Ω cm at room temperature ), good high temperature resistance, high thermal conductivity, excellent chemical corrosion resistance, easy cold processing such as cutting and drilling, large contact area with liquid, and micropores in the skeleton (the skeleton volume accounts for about 30%).

Porous silicon carbide ceramics will be more and more widely used in some harsh fields (such as strong corrosive media, high temperature, high radiation, etc.). For example, in the field of metallurgy, it can be used as a molten metal filter, tapping trough, steel tapping hole, cold slide rail and still; Lining and saggers, etc.; in the chemical industry, it can be used as oil and gas generators, garbage incinerators and petroleum gasifiers; in space technology, it can be used as rocket nozzles and high-temperature gas turbine blades; in the field of nuclear energy, especially The high-temperature gas-cooled reactor independently developed by Tsinghua University can be used as a filter to filter the radioactive waste liquid produced during the preparation of high-temperature gas-cooled reactor fuel elements and the high-temperature helium containing graphite particles in the high-temperature gas-cooled reactor. Porous silicon carbide ceramics can combine the excellent properties of porous ceramics and silicon carbide materials. It is an important functional material and can be widely used in fluid filtration. It is especially considered as one of the best candidate materials for diesel exhaust filters. .

The preparation method of porous silicon carbide has been reported in the literature both at home and abroad. For example, Chinese patent (application number: 200610119233.9) has reported a method for preparing silicon carbide porous ceramics by gel encapsulation-freeze drying process. The porous silicon carbide ceramics obtained by this method has a directional and interconnected pore structure, and the porosity is relatively high, but The process is complicated and the purity is not high. "Materials Characterization, 2008, 59(2): 140-143" reported a method of using Al ₂ O ₃ as an additive at 1400-1550 ° C to make the surface of silicon carbide oxidized to form silicon dioxide and aluminum oxide. The mullite forms a sintering neck, and a silicon carbide porous ceramic with a narrow pore size distribution and an average pore size of 1.9 μm is obtained. Increasing the sintering temperature can increase the strength of porous ceramics, but it will reduce the open porosity, and the purity of the porous ceramics obtained by this method is not high. Chinese patent (application number: 200510076993.1) prepared a precursor powder with a silicon-resin core-shell structure by an inclusion mixing process, and then prepared porous silicon carbide with high porosity (more than 80%) through molding, carbonization and high-temperature sintering reactions ceramics. The method has the advantages of simple process, high production efficiency, energy saving, and good environmental compatibility. It is a method capable of preparing porous silicon carbide ceramics with high porosity, but the sintering temperature is high and the thermal shock resistance of the product is poor.

Contents of the invention

The purpose of the present invention is to provide a method for preparing porous silicon carbide ceramics with high thermal shock resistance. Add alumina, silicon dioxide and yttrium oxide as additives, wherein the mass ratio range of precursor powder, alumina, silicon dioxide and yttrium oxide is 100:(0.5～10):(0.1～5):(0.1 ~5), after four steps of powder mixing, pressure forming, carbonization treatment and sintering, a porous silicon carbide ceramic with high thermal shock resistance is obtained. The specific process steps are as follows:

(1) The silicon-resin core-shell structure precursor powder prepared by the existing encapsulation process and alumina, silicon dioxide and yttrium oxide are in the mass ratio range of 100: (0.5-10): (0.1-5): (0.1 to 5) mixing, the mixing method is manual or mechanical stirring, ball milling or shaking to make it uniform, and the mixing time is 5 minutes to 24 hours;

(2) The mixed powder is pressure-formed to obtain a ceramic green body, and the pressure-forming process conditions are: the forming temperature of the mixed powder is 50-140°C, the forming pressure is 0.5-50 MPa, and the holding time is 20-120 minutes;

(3) The ceramic green body is carbonized, and the carbonization process conditions are as follows: the carbonization temperature is 600-1000°C, the heating rate is 0.3-3°C/min; the argon flow rate is 5-200ml/min, and the holding time is 1-2 4h.

(4) Sintering after carbonization, sintering in argon atmosphere or vacuum, air pressure: 0-20MPa, heating rate: 1-20℃/min, sintering temperature: 1200-1800℃, holding time: 1-4 hours , to obtain porous silicon carbide ceramics with high thermal shock resistance.

The silicon-resin core-shell structure precursor powder prepared by the existing encapsulation process uses silicon powder, phenolic resin and alcohol as raw materials. Mixing process is carried out to obtain silicon-resin core-shell structure precursor powder with the surface of silicon powder fully coated and incompletely coated with resin. For the specific preparation process, please refer to the steps of preparing the powder body of silicon powder coated with phenolic resin in the patent application number 200510076993.1. The silicon-resin core-shell structure precursor powder is prepared for use.

The beneficial effects of the present invention are as follows: the present invention is based on the preparation of the precursor powder with a silicon-resin core-shell structure by the inclusion mixing process, adding the additives alumina, silicon dioxide and yttrium oxide, and using the liquid formed by the additives at high temperature The phase promotes the sintering reaction, reduces the sintering temperature (1200-1800°C), and forms a new solid phase after cooling, which significantly increases the thermal conductivity of the ceramic, thereby improving its thermal shock resistance (800°C heat After 30 shocks, the strength loss is 6.5-30%. However, the advantages of high porosity (greater than 80%), average pore size of 100-300 μm and uniform pore size distribution of the original technology are retained.

The invention reduces the reaction sintering temperature, and obtains the porous silicon carbide ceramics which maintain the advantages of high porosity and controllable pore size of the original product, and has higher thermal conductivity and better thermal shock resistance. The method has the advantages of simple process, less auxiliary additives and obvious effect.

Detailed ways

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

Example 1

Mix the silicon-resin core-shell precursor powder prepared by the inclusion mixing process with alumina, silicon dioxide, and yttrium oxide at a mass ratio of 100:0.5:0.1:0.1, and use a ball mill to mix for 24 hours. Then the mixed powder was kept at 100°C and 1 MPa for 20 minutes to obtain a green body. Next, the green body was carbonized under an argon atmosphere, the argon gas flow rate was 5ml/min, the heating rate was 0.5°C/min, the carbonization temperature was 600°C, and the temperature was kept for 4 hours. Finally, the green body is vacuum sintered in a furnace washed with high-purity argon, the heating rate is 5°C/min, the sintering temperature is 1200°C, and the temperature is kept for 4 hours. After cooling in the furnace, a high-porosity porous material with high thermal shock resistance is obtained. Silicon carbide ceramics.

Example 2

Mix the silicon-resin core-shell precursor powder prepared by the inclusion mixing process with alumina, silicon dioxide, and yttrium oxide at a mass ratio of 100:2:0.3:0.1, and use a ball mill to mix for 24 hours. Then the mixed powder was kept at 80° C. and 5 MPa for 30 minutes to obtain a green body. Next, the green body was carbonized under an argon atmosphere, the argon gas flow rate was 5ml/min, the heating rate was 0.5°C/min, the carbonization temperature was 600°C, and the temperature was kept for 3 hours. Finally, the green body is vacuum sintered in a furnace washed with high-purity argon, the heating rate is 2°C/min, the sintering temperature is 1300°C, and the temperature is kept for 4 hours. After cooling in the furnace, a high-porosity porous material with high thermal shock resistance is obtained. Silicon carbide ceramics.

Example 3

Mix the silicon-resin core-shell precursor powder prepared by the inclusion mixing process with alumina, silicon dioxide, and yttrium oxide at a mass ratio of 100:2:0.3:0.3, and use a ball mill to mix for 24 hours. Then the mixed powder was kept at 140°C and 7.5MPa for 40 minutes to obtain a green body. Next, the green body was carbonized under an argon atmosphere, the argon gas flow rate was 15ml/min, the heating rate was 1°C/min, the carbonization temperature was 700°C, and the temperature was kept for 3 hours. Finally, the green body is sintered at a high temperature in an argon atmosphere, the air pressure is one atmosphere, the argon flow rate is 100ml/min, the heating rate is 10°C/min, the sintering temperature is 1400°C, and the heat preservation is 4 hours, and the thermal shock resistance is obtained by cooling with the furnace. High porosity porous silicon carbide ceramics.

Example 4

Mix the silicon-resin core-shell precursor powder prepared by the inclusion mixing process with alumina, silicon dioxide, and yttrium oxide at a mass ratio of 100:3:1:0.5, and use a ball mill to mix for 24 hours. Then, the mixed powder was kept at 130°C and 7.5 MPa for 40 minutes to obtain a green body. Next, the green body was carbonized under an argon atmosphere, the argon gas flow rate was 15ml/min, the heating rate was 2°C/min, the carbonization temperature was 800°C, and the temperature was kept for 2 hours. Finally, the green body is sintered at a high temperature in an argon atmosphere, the air pressure is one atmosphere, the argon flow rate is 100ml/min, the heating rate is 10°C/min, the sintering temperature is 1400°C, and the heat preservation is 4 hours, and the thermal shock resistance is obtained by cooling with the furnace. High porosity porous silicon carbide ceramics.

Example 5

Mix the silicon-resin core-shell precursor powder prepared by the inclusion mixing process with alumina, silicon dioxide, and yttrium oxide at a mass ratio of 100:4:2:1, and use a ball mill to mix for 24 hours. Then, the mixed powder was kept at 100°C and 10 MPa for 60 minutes under heat preservation and pressure to obtain a green body. Next, the green body was carbonized under an argon atmosphere, the argon gas flow rate was 15ml/min, the heating rate was 2°C/min, the carbonization temperature was 800°C, and the temperature was kept for 2 hours. Finally, the green body is sintered at a high temperature in an argon atmosphere, the air pressure is one atmosphere, the argon flow rate is 100ml/min, the heating rate is 15°C/min, the sintering temperature is 1500°C, and the temperature is kept for 3 hours, and the thermal shock resistance is obtained by cooling with the furnace. High porosity porous silicon carbide ceramics.

Example 6

Mix the silicon-resin core-shell precursor powder prepared by the inclusion mixing process with alumina, silicon dioxide, and yttrium oxide at a mass ratio of 100:5:3:2, and use a ball mill to mix for 24 hours. Then the mixed powder was kept at 110° C. and 7.5 MPa for 40 minutes to obtain a green body. Next, the green body was carbonized under an argon atmosphere, the argon flow rate was 20ml/min, the heating rate was 3°C/min, the carbonization temperature was 800°C, and the temperature was kept for 2 hours. Finally, the green body is sintered at a high temperature in an argon atmosphere, the air pressure is one atmosphere, the argon flow rate is 100ml/min, the heating rate is 15°C/min, the sintering temperature is 1500°C, and the temperature is kept for 2.5 hours, and the thermal shock resistance is obtained by cooling with the furnace. High porosity porous silicon carbide ceramics.

Example 7

Mix the silicon-resin core-shell precursor powder prepared by the inclusion mixing process with alumina, silicon dioxide, and yttrium oxide at a mass ratio of 100:6:4:3, and use a ball mill to mix for 24 hours. Then, the mixed powder was kept at 50°C and 8 MPa for 120 minutes under heat preservation and pressure to obtain a green body. Next, the green body was carbonized under an argon atmosphere, the argon gas flow rate was 25ml/min, the heating rate was 3°C/min, the carbonization temperature was 900°C, and the temperature was kept for 2 hours. Finally, the green body is sintered at a high temperature in an argon atmosphere, the air pressure is one atmosphere, the argon flow rate is 100ml/min, the heating rate is 15°C/min, the sintering temperature is 1600°C, and the temperature is kept for 2.5 hours, and the thermal shock resistance is obtained by cooling with the furnace. High porosity porous silicon carbide ceramics.

Example 8

The silicone-resin core-shell precursor powder prepared by the inclusion mixing process was mixed with alumina, silicon dioxide, and yttrium oxide at a mass ratio of 100:7:4:3, and mixed for 24 hours using a ball mill. Then, the mixed powder was kept at 60° C. and 8 MPa for 120 minutes under heat preservation and pressure to obtain a green body. Next, the green body was carbonized under an argon atmosphere, the argon gas flow rate was 25ml/min, the heating rate was 3°C/min, the carbonization temperature was 900°C, and the temperature was kept for 2 hours. Finally, the green body is sintered at a high temperature in an argon atmosphere, the air pressure is 1 atmospheric pressure, the argon flow rate is 100ml/min, the heating rate is 20°C/min, the sintering temperature is 1600°C, and the temperature is kept for 2 hours, and the thermal shock resistance is obtained by cooling with the furnace. High porosity porous silicon carbide ceramics.

Example 9

Mix the silicone-resin core-shell precursor powder prepared by the inclusion mixing process with alumina, silicon dioxide, and yttrium oxide at a mass ratio of 100:8:4:5, and use a ball mill to mix for 24 hours. Then the mixed powder was kept at 110° C. and 8 MPa for 60 minutes under heat preservation and pressure to obtain a green body. Next, the green body was carbonized under an argon atmosphere, the argon gas flow rate was 25ml/min, the heating rate was 2°C/min, the carbonization temperature was 900°C, and the temperature was kept for 1.5 hours. Finally, the green body is sintered at a high temperature in an argon atmosphere, the air pressure is one atmosphere, the argon flow rate is 100ml/min, the heating rate is 15°C/min, the sintering temperature is 1700°C, and the temperature is kept for 2 hours, and the thermal shock resistance is obtained by cooling with the furnace. High porosity porous silicon carbide ceramics.

Example 10

Mix the silicon-resin core-shell precursor powder prepared by the inclusion mixing process with alumina, silicon dioxide, and yttrium oxide at a mass ratio of 100:9:4:3, and use a ball mill to mix for 24 hours. Then, the mixed powder was kept at 130°C and 8 MPa for 40 minutes under heat preservation and pressure to obtain a green body. Next, the green body was carbonized under an argon atmosphere, the argon gas flow rate was 25ml/min, the heating rate was 1°C/min, the carbonization temperature was 1000°C, and the temperature was kept for 1 hour. Finally, the green body is sintered at a high temperature in an argon atmosphere, the air pressure is one atmosphere, the argon flow rate is 100ml/min, the heating rate is 10°C/min, the sintering temperature is 1700°C, and the heat preservation is 1.5 hours, and the thermal shock resistance is obtained by cooling with the furnace. High porosity porous silicon carbide ceramics.

Example 11

Mix the silicone-resin core-shell precursor powder prepared by the inclusion mixing process with alumina, silicon dioxide, and yttrium oxide at a mass ratio of 100:10:5:5, and use a ball mill to mix for 24 hours. Then, the mixed powder was kept at 140°C and 8 MPa for 20 minutes under heat preservation and pressure to obtain a green body. Next, the green body was carbonized under an argon atmosphere, the argon gas flow rate was 25ml/min, the heating rate was 1°C/min, the carbonization temperature was 1000°C, and the temperature was kept for 1 hour. Finally, the green body is sintered at a high temperature in an argon atmosphere, the air pressure is one atmosphere, the argon flow rate is 100ml/min, the heating rate is 5°C/min, the sintering temperature is 1800°C, and the temperature is kept for 1 hour, and the thermal shock resistance is obtained by cooling with the furnace. High porosity porous silicon carbide ceramics.

Claims (6)

1. the preparation method of a porous silicon carbide ceramics with high thermal shock resistance; It is characterized in that the silicon-resin core shell structure precursor powder that mixes prepared with existing bag is a raw material; And in above-mentioned raw materials, add aluminum oxide, silicon-dioxide and yttrium oxide as additive; After powder mixing, pressure forming, charing processing and four step process of sintering; Obtain porous silicon carbide ceramics with high thermal shock resistance, wherein, the quality of precursor powder, aluminum oxide, silicon-dioxide, yttrium oxide is 100 than scope: (0.5～10): (0.1～5): (0.1～5).

2. the preparation method of porous silicon carbide ceramics with high thermal shock resistance according to claim 1 is characterized in that the powder blending means is manual or mechanical stirring, ball milling or rocks and make it even.

3. the preparation method of porous silicon carbide ceramics with high thermal shock resistance according to claim 1 is characterized in that the powder mixing time is 5 minutes～24 hours.

4. the preparation method of porous silicon carbide ceramics with high thermal shock resistance according to claim 1; It is characterized in that the pressure molding condition is following: mixed powder is 50～140 ℃ through the green compact mold temperature of pressure forming; Compacting pressure is 0.5～50MPa, and soaking time is 20～120min.

5. the preparation method of porous silicon carbide ceramics with high thermal shock resistance according to claim 1, it is characterized in that the charing treatment process condition is following: carbonization temperature is 600～1000 ℃, temperature rise rate is 0.3～3 ℃/min; Argon flow amount is 5～200ml/min, and soaking time is 1～4h.

6. the preparation method of porous silicon carbide ceramics with high thermal shock resistance according to claim 1; It is characterized in that sintering carries out air pressure in argon gas atmosphere or vacuum: 0～20MPa, temperature rise rate: 1-20 ℃/min; Sintering temperature: 1200～1800 ℃, soaking time: 1～4 hour.