JP2000016872A - Porous silicon carbide sintered body and its production - Google Patents

Abstract

PROBLEM TO BE SOLVED: To facilitate control of the pore diameter and produce sintered body of high mechanical strength by admixing a powder of α-type or β-type silicon carbide to an α-type silicon carbide powder of which the average particle size is specified to a certain value larger than that of the α- or β-type silicon carbide to be admixed. SOLUTION: To 100 pts.wt. of an α-type silicon carbide with an average particle size of 5-100 μm, are homogeneously admixed 10-70 pts.wt. of an α- or β-type silicon carbide powder with an average particle size of 0.1-1 μm. This mixture is molded, fired at 1,700-2,300 deg.C to give a porous silicon carbide sintered body. The sintered body has an average crystalline grain size of 5-100 μm, a pore diameter of 1-30 μm and a porosity of 20-60%. Through such process, the sintering temperature can be linearly and gently correlated to the pore diameter of the sintered body to facilitate the control of firing temperature for giving desired pore diameter. In addition, the bonding force between crystals is increased with increase of the contacting area between crystals and the mechanical strength is increased as a whole of the porous body.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a porous silicon carbide sintered body and a method for producing porous silicon carbide.

[0002]

2. Description of the Prior Art Conventionally, silicon carbide has high hardness, excellent wear resistance, excellent oxidation resistance, excellent corrosion resistance, good thermal conductivity, low thermal expansion coefficient, high thermal shock resistance and high heat resistance at high temperatures. Has excellent chemical and physical properties of strength, wear-resistant materials such as mechanical seals and bearings, refractory materials for high-temperature furnaces, heat-resistant structural materials such as heat exchangers and combustion tubes, and strong materials such as acids and alkalis. It is a material that can be widely used as a corrosion-resistant material for pump parts of corrosive solutions.

Accordingly, a silicon carbide sintered body having these excellent properties, that is, a porous silicon carbide sintered body having open pores, that is, pores having air permeability to the outside (hereinafter simply referred to as pores), Taking advantage of the characteristics of the silicon carbide,
Filter filter used in high temperature atmosphere, oxidizing atmosphere and / or corrosive atmosphere, material that can be used as catalyst or catalyst carrier for oxidative exothermic reaction or chemical reaction under high temperature. It is conceivable that the filter can be used as a filter used for removing foreign particles mixed in corrosive liquid such as sludge or sulfuric acid or hydrochloric acid.

[0004] For the use of the filter as described above, not only heat resistance and corrosion resistance are required, but also resistance at the time of passage of a fluid is small, and foreign matter particles can be removed with high efficiency. Are required. On the other hand, for applications such as catalysts, catalyst carriers, heat exchangers, etc., it is necessary that the surface area for effective generation of chemical reaction, heat transfer or mass transfer be large.

[0005] Conventionally, a silicon carbide sintered body is formed by molding a raw material obtained by mixing an organic resin binder, a plasticizer, and the like with β-type silicon carbide powder, and firing the formed body to reduce silicon carbide fine particles. It has been produced by growing plate crystals and sintering them together. A sintered body having such a plate-like crystal structure has characteristics of a large porosity, a relatively uniform pore diameter, and a low pressure loss (or exhaust resistance) when used as an exhaust gas filter. I was

However, β-type silicon carbide powder tends to grow abnormal grains during sintering, and it is necessary to control the temperature in an extremely narrow temperature range in order to obtain a sintered body having a desired pore diameter. Also, for the same reason, it was difficult to make the pore diameter uniform. Furthermore, in this method, the porous silicon carbide sintered body is mainly composed of a plate crystal,
There is a problem that the number of bonding points between crystals is small and the mechanical strength of the porous body is low.

[0007]

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems, and an object of the present invention is to make it possible to easily control the pore diameter at the time of manufacturing a sintered body and to obtain a desired structure. An object of the present invention is to obtain a sintered body having a relatively uniform pore size and excellent mechanical strength, as well as reliably producing a sintered body having a pore diameter.

[0008]

Means for Solving the Problems The inventor of the present invention has conducted intensive studies to solve the above problems, and as a result, has reached the following invention. That is, the invention of claim 1 has an average crystal grain size of 5
１００100 μm, pore size 1-30 μm, porosity 20-
It is a porous silicon carbide sintered body characterized by being 60%. Further, the invention of claim 2 includes the following first to third steps.
The average value of the crystal grain size consisting of the process sequence is 5 to 1
00 μm, pore size 1-30 μm, porosity 20-60
% Of the porous silicon carbide sintered body. First Step The average particle diameter is 0.1 to 1 μm with respect to 100 parts by weight of α-type silicon carbide powder having an average particle diameter of 5 to 100 μm.
A step of uniformly mixing 10 to 70 parts by weight of α-type or β-type silicon carbide powder of the above; a second step of forming a mixture obtained in the first step; and a third step obtained by the second step. 17
Baking in a temperature range of 00 to 2300 ° C;

By doing so, the correlation between the sintering temperature and the pore diameter of the sintered body obtained by sintering can be made linear and gradual, and the sintering temperature can be controlled to a desired size. Becomes easier. In addition, since the granular crystals participate in sintering, the contact area between the crystals increases, the bonding force between the crystals increases, and the mechanical strength of the entire porous body improves.

On the other hand, at the grain boundary when β-type silicon carbide powder is used as a starting material as in the related art, a relatively abnormal platelet crystal tends to be generated in a certain temperature range, so that a relatively coarse plate-like crystal is formed. Generated. Therefore, in the crystal structure of the porous sintered body, coarse plate-like crystals form the main skeleton of the sintered body, and relatively large pores are formed in the gaps between them. Therefore, the bonding strength between the crystals is reduced, and the mechanical strength of the entire porous body is reduced.

The raw material silicon carbide powder contains 10 parts by weight of α-type or β-type silicon carbide having an average particle size of 0.1 to 1 μm per 100 parts by weight of α-type silicon carbide powder having an average particle size of 5 to 100 μm. It is preferable to mix it in an amount of 70 parts by weight. When the average particle size of the α-type or β-type silicon carbide is less than 0.1 μm, not only is it difficult to control the grain growth, but also it is difficult to obtain and expensive, and it is not practical. On the other hand, if it is larger than 1 μm, the activity of the powder is low, so that it is difficult to suitably obtain a porous body.

When the average particle size of the α-type silicon carbide powder is less than 5 μm, the effect of suppressing abnormal grain growth of α-type or β-type silicon carbide is low. On the other hand, if it is larger than 100 μm, not only the moldability becomes poor, but also the strength of the obtained porous body deteriorates.

When the amount of the α-type or β-type silicon carbide powder exceeds 70 parts by weight, rapid abnormal grain growth is not effectively reduced, and relatively coarse silicon carbide crystals are formed. An excellent sintered body cannot be obtained. If the amount is less than 10 parts by weight, the sintering temperature must be extremely high to obtain a desired pore diameter, which is disadvantageous in cost.

According to the above conditions, α-type silicon carbide powder is
By appropriately setting the proportion of the α-type or β-type silicon carbide powder, the size of the pore diameter of the sintered body can be easily and reliably controlled in the range of 1 to several tens μm.

The raw material powder of the present invention is mixed with a molding binder and, if necessary, a dispersing solvent to obtain a slurry-like molding material, which is formed into a desired shape.
By firing, a porous silicon carbide sintered body is manufactured.

Examples of the molding binder include polyvinyl alcohol, methyl cellulose, carboxymethyl cellulose, hydroxyethyl cellulose, polyethylene glycol, phenol resin, epoxy resin, acrylic resin and the like. The mixing ratio of the molding binder is generally 1 to 100 parts by weight of the total of the silicon carbide powder.
A range of from 10 to 10 parts by weight is preferred. If the blending ratio is less than 1 part by weight, the strength of the molded body becomes insufficient, and if it exceeds 10 parts by weight, cracks tend to occur in the molded body when the binder is removed.

As the dispersing solvent to be mixed with the raw material powder, an organic solvent such as benzene, alcohol such as methanol, water and the like can be used, and the compounding amount is adjusted according to the viscosity of the raw material slurry. The raw material slurry is mixed by an attritor or the like, and then sufficiently kneaded by a kneader or the like to be prepared and formed into a desired shape.

When firing the dried compact, the firing temperature is preferably from 1700 to 2300 ° C.
In this case, it is desirable to perform firing in a non-oxidizing atmosphere. This is to prevent the carbonaceous material from burning and disappearing due to heat during firing. This combustion temperature is 1
If the temperature is lower than 700 ° C., the growth rate of the silicon carbide fine particles is extremely low, and the sintering at the contact portion between the particles becomes insufficient, so that a sintered body having excellent strength cannot be obtained. On the other hand, if the firing temperature is 2
When the temperature exceeds 300 ° C., the fuel consumption increases, which is not only disadvantageous in terms of cost, but also the sublimation of silicon carbide becomes remarkable, and the mechanical strength of the sintered body decreases.

[0019]

Next, the present invention will be described with reference to examples and comparative examples.

Example 1 α-type silicon carbide powder 1 having an average particle size of 10 μm as a starting material
45 parts by weight of α-type silicon carbide powder having an average particle size of 0.7 μm were mixed with 00 parts by weight.

With respect to 100 parts by weight of the silicon carbide fine powder,
5 parts by weight of polyvinyl alcohol and 300 parts by weight of water were mixed, mixed in a ball mill for 5 hours, and dried. An appropriate amount of the dried mixture was collected, granulated, and then molded at a pressure of 600 kg / cm ² using a metal stamping die. The density of this green compact was 2.0 g / cm ³ . The green compact was placed in a graphite crucible capable of shutting off outside air, and fired in a 1-atmosphere argon gas atmosphere using a Tamman-type firing furnace. In the firing, the temperature was raised to 2200 ° C. at a rate of 10 ° C./min and kept at a maximum temperature of 2200 ° C. for 2 hours. The crystal structure of the obtained sintered body has an average crystal grain size of 10 μm.
m, average pore diameter measured by mercury porosimeter is 7
μm and porosity was 38%.

Example 2 α-type silicon carbide powder 1 having an average particle size of 30 μm as a starting material
30 parts by weight of β-type silicon carbide powder having an average particle diameter of 0.3 μm were mixed with 00 parts by weight.

With respect to 100 parts by weight of the silicon carbide fine powder,
5 parts by weight of polyvinyl alcohol and 300 parts by weight of water were mixed, mixed in a ball mill for 5 hours, and dried. An appropriate amount of the dried mixture was collected, granulated, and then molded at a pressure of 600 kg / cm ² using a metal stamping die. The density of this green compact was 2.0 g / cm ³ . The green compact was placed in a graphite crucible capable of shutting off outside air, and fired in a 1-atmosphere argon gas atmosphere using a Tamman-type firing furnace. In the firing, the temperature was raised to 2150 ° C. at a rate of 10 ° C./min and kept at a maximum temperature of 2150 ° C. for 2 hours. The crystal structure of the obtained sintered body has an average crystal grain size of 30 μm.
m, average pore size measured by mercury porosimeter is 12
μm and porosity was 38%.

Comparative Example 1 α-type silicon carbide powder 10 having an average particle size of 3 μm as a starting material
45 parts by weight of α-type silicon carbide powder having an average particle diameter of 0.7 μm was mixed with 0 parts by weight.

With respect to 100 parts by weight of the silicon carbide fine powder,
5 parts by weight of polyvinyl alcohol and 300 parts by weight of water were mixed, mixed in a ball mill for 5 hours, and dried. An appropriate amount of the dried mixture was collected, granulated, and then molded at a pressure of 600 kg / cm ² using a metal stamping die. The density of this green compact was 1.6 g / cm ³ . The green compact was placed in a graphite crucible capable of shutting off outside air, and fired in a 1-atmosphere argon gas atmosphere using a Tamman-type firing furnace. In the firing, the temperature was raised to 1650 ° C. at a rate of 10 ° C./min and kept at a maximum temperature of 1650 ° C. for 2 hours. The crystal structure of the obtained sintered body has an average crystal grain size of 2.0 μm.
m, average pore diameter measured by mercury porosimeter is 2μ
m, the porosity was 50%.

[0026]

As described above, according to the porous silicon carbide sintered body and the method for manufacturing a porous silicon carbide sintered body of the present invention, it is possible to easily and surely control the pore diameter at the time of producing a crystal. Can be produced, the pore size is relatively uniform, it is possible to produce a sintered body having excellent mechanical strength, the average value of the crystal grain size is 5 to 100 μm, the pore size is 1 to 30 μm,
A porous silicon carbide sintered body having a porosity of 20 to 60% can be obtained.

Claims (2)

[Claims] 1. A porous silicon carbide sintered body having an average crystal grain size of 5 to 100 μm, a pore size of 1 to 30 μm, and a porosity of 20 to 60%. 2. A porous material comprising a sequence of the following first to third steps, having an average crystal grain size of 5 to 100 μm, a pore size of 1 to 30 μm, and a porosity of 20 to 60%. A method for producing a silicon carbide sintered body. First Step The average particle diameter is 0.1 to 1 μm with respect to 100 parts by weight of α-type silicon carbide powder having an average particle diameter of 5 to 100 μm.
A step of uniformly mixing 10 to 70 parts by weight of α-type or β-type silicon carbide powder of the above; a second step of forming a mixture obtained in the first step; and a third step obtained by the second step. 17
Baking in a temperature range of 00 to 2300 ° C;