JPS6227382A - Manufacture of porous silicon carbide sintered body - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

Detailed Description of the Invention [Field of Industrial Application] The present invention relates to a method for producing a porous silicon carbide sintered body, and in particular, the present invention relates to a porous silicon carbide sintered body having fine open pores uniformly distributed in three dimensions. The present invention relates to a method for producing a quality silicon carbide sintered body.

Traditionally, silicon carbide has chemical and physical advantages such as high hardness, good wear resistance, good oxidation resistance, good thermal conductivity, low coefficient of thermal expansion, high thermal shock resistance and high strength at high temperatures. Wear-resistant materials such as mechanical seals and bearings, heat-resistant structural materials such as heat exchangers and combustion tubes, and pump parts for highly corrosive solutions such as acids and alkalis. It is a material that can be widely used as a corrosion-resistant material.

On the other hand, a porous silicon carbide sintered body consisting of silicon carbide having these properties and open pores (hereinafter simply referred to as pores) having air permeability formed by silicon carbide and its crystals has lubrication in the open pores. By impregnating or filling with the agent, extremely good sliding properties can be imparted, especially for high p
It is conceivable that the present invention can be used for sliding materials used under v-value conditions, such as mechanical seams and bearings.

[Conventional technology]

Conventionally, as a method for manufacturing a porous silicon carbide sintered body, (1)
A method of manufacturing by adding a binder such as vitreous flux or clay to silicon carbide particles serving as an aggregate, molding it, and then baking and hardening the molded product at a temperature where the binder melts (
2) A method in which coarse expanded silicon particles and fine silicon carbide powder are mixed, molded, and then fired at a high temperature of 2000°C or higher, or (3) a method disclosed in JP-A-48-39515. [Formed by adding a carbonaceous binder to silicon carbide powder with or without addition of reconstituted powder, and adding a stoichiometric amount of silicone powder that reacts with the free carbon from the reconstituted powder and the binder produced during firing.] A method for producing a homogeneous porous recrystallized expanded silicon body, which comprises heating the molded body to 1,900 to 2,400"C in the returned powder to siliconize the carbon content in the molded body." etc. are known.

The strength of a porous body produced by adding glassy flux or clay as a binder as described in (1) above is determined by the binder, and it is not possible to obtain a porous body with such high strength. The disadvantage is that it is difficult to use in fields where

On the other hand, if the structure of the porous body created by the methods (2) and (3) above is illustrated as a model, it is shown in Figure 1. Silicon carbide binding material or carbonaceous binding material (B
1 and a gap (C'l).

The strength of the porous body is determined by the bonds between aggregate particles, but since the bonds between the aggregate particles are relatively thin and weak, it is difficult to obtain a porous body with high strength. Met.

Further, the pore diameter in the porous bodies (2) and (3) is controlled by the particle size composition of the aggregate. This method [In order to create a porous body with pores with a relatively small cross-sectional area, it is necessary to mix the particle size of the aggregate appropriately with coarse particles, medium particles, and/or fine particles and form it. ,
As a result, the porosity of the molded article tends to become significantly smaller.

[Problem that the invention seeks to solve]

The present invention eliminates and improves the drawbacks of the above-mentioned prior art, and provides a high-strength porous silicon carbide sintered body in which fine open pores are uniformly distributed in three dimensions and have extremely excellent lubricant retention properties. ,
It is an object of the present invention to provide a method for producing a porous silicon carbide sintered body suitable as a sliding material that can be used particularly under conditions of high pv value.

[Means for solving problems]

According to the present invention, the silicon carbide powder has an average particle size of 10 μm or less, and contains at least 30q6 of β-type crystal silicon carbide.
After forming the starting material mainly containing silicon carbide powder into a desired shape, it is heated for 1 hour in a non-oxidizing gas atmosphere.
Porous silicon carbide sintered, characterized in that it is heated and fired within the range of 700 to 2100°C to form a sintered body with a density of 2.1 to 3.09/min and a strength of 30 kVf/- or more. The above object can be achieved by the method for producing the compact.

The present invention will be explained in detail below.

According to the present invention, the silicon carbide powder has an average particle size of 10 μm.
It is necessary that the powder be a fine powder of less than m.

The reason for this is that the formed body formed from powder with an average particle size of 10 μm or less has a relatively large number of contact points between the particles, and the thermal activity at the firing temperature of silicon carbide powder is large, so that there is a large amount of contact between the silicon carbide particles. Since the movement of atoms is extremely large, bonding between silicon carbide particles is extremely likely to occur. Therefore, a high-strength sintered body can be obtained even at a relatively low density. In particular, it is advantageous that the average a diameter of the measured silicon carbide powder is 5 μm or less.

According to the present invention, the silicon carbide powder needs to be a silicon carbide powder containing at least 30% of β-type crystal silicon carbide. The reason for this is that β-type crystals are low-temperature stable crystals that are synthesized at relatively low temperatures, and silicon carbide particles tend to bond with each other during sintering, making it possible to produce high-strength sintered bodies even with relatively low density. This is because β-type crystals′! Advantageously, the silicon carbide powder contains 1-50% or more.

According to the invention, the starting materials include boron, aluminum, aluminum, chromium, lanthanum, titanium, yttrium,
It is preferable that it contains 0.01 to 5.0% by weight of at least one selected from Bium and these compounds.

The reason why it is preferable that the starting material contains the substance is that the substance has the effect of promoting sintering of silicon carbide, and in order to promote the bonding between silicon carbide particles during sintering, it is preferable that the starting material contains the substance. This is because a strong sintered body can be produced, and the content of the substance is reduced to 0.0.
The reason why the content is preferably in the range of 1 to 5.0% by weight is that if the content is less than 0.01% by weight, the effect of promoting bonding between silicon carbide particles during sintering is small; This is because if the amount is more than 0% by weight, the amount of the substance contained in the sintered body increases and the original characteristics of silicon carbide are lost.

According to the invention, a carbon source that leaves free carbon during calcination can be added to the starting material. As such a carbon source, any carbon source that exists in a carbon state at the start of sintering can be used, such as phenol resin, lignin sulfonate, polyvinyl alcohol, cornstarch, am, coal tar ruby, sochi, Various organic substances such as alginates or pyrolytic carbons such as carbon black and acetylene black can be advantageously used.

When free carbon is present at the same time as the above substances, it is effective in suppressing crystal growth and obtaining a porous silicon carbide sintered body having fine pores.

In addition, the content of free carbon is as follows: starting material 1
Advantageously, it is not more than 5 parts by weight relative to 00 parts by weight. The reason is that even if more than 5 parts by weight is added, the effect will not change, but on the contrary, the amount remaining in the sintered body will increase.
This is because the strength of the sintered body deteriorates.

According to the present invention, after the starting material is formed into a green body, it is fired at a temperature of 1700 to 2100°C in a non-oxidizing gas atmosphere, and the density is 2.1 to 3.0 f/M. A sintered body having a strength of 30 kql/1 ttd or more is produced.

The reason why the firing temperature is limited to a range of 1,700 to 2,100°C is that if the firing temperature is lower than 1,700°C, the bonding between particles is insufficient, making it difficult to obtain a sintered body with high strength. This is because if the temperature is higher than 2100''C, the sintered body tends to become dense, making it difficult to obtain a silicon carbide sintered body with the pores 5 that are the object of the present invention.

According to the present invention, the porous silicon carbide sintered body has a density of 2.1
It is necessary that the strength is 30 kflf/, - or more at ~3.09 kd. The reason why the density needs to be within the range of 2.1 to 3° Oy/- is that the density is 2.1 to 3° Oy/-.
A sintered body smaller than 11/cti has fewer bonding points between silicon carbide particles, so it is less than 30k which is the object of the present invention.
This is because it is difficult to form a sintered body with a strength of yf/mA or higher; on the other hand, 3. This is because a sintered body larger than 100% has a smaller proportion of open pores among the pores contained therein. In addition, the strength is 30 kgf/mm2
The reason why it is necessary is that the strength is 30 kf
If it is smaller than if/-, it will be easily damaged during use and cannot be used practically, so it is especially advantageous if it is 40 to 9 f/- or more. Note that the strength in the present invention is an average bending strength.

According to the present invention, the porous silicon carbide sintered body preferably has an open porosity of 5 to 30% by volume. The reason for this is that if the open porosity is lower than 5% by volume, the substantial amount of lubricant impregnated or filled will be small, making it difficult to fully exhibit the lubricating properties; This is because if the value is higher than , the wear resistance of the porous silicon carbide sintered body is low, and it is difficult to use it particularly under conditions where the pv value is high.

As the lubricant to be impregnated or filled into the porous silicon carbide sintered body, fluorine-based oil, silicone-based oil, various other lubricating oils, or various resins having lubricating properties can be used alone or in combination.

Examples of the fluorine-based oil include fluoroethylene, fluoroester, fluorotriazine, perfluoropolyether, and fluorosilicone.

It is advantageous to use one type or a mixture of two or more selected from these derivatives or polymers thereof; one type selected from polymers or f12
It is advantageous to use mixtures of m or more. Note that the fluorine oil and silicone oil are liquid,
It can be used either in the form of grease or wax.

The fluorine-based oil and silicone-based oil have excellent solvent resistance, chemical stability, and heat resistance, and therefore can provide extremely good lubricating properties over a long period of time.

Examples of the resin having lubricating properties include polyacetal resin, polyamide resin, polyethylene resin, polycarbonate resin, polybutylene terephthalate resin, styrene acrylonitrile/L/resin, polyurethane resin, polyurethane resin, polyphenylene resin, fido resin, epoxy resin, Resins selected from silicone resins and fluororesins can be used alone or in combination.

According to the present invention, these lubricants are present in an amount of at least 10 parts by volume of open pores of the porous silicon carbide sintered body.
Volumetric impregnation or filling is advantageous. The reason for this is that if the amount of lubricant impregnated or filled is less than 10 parts by volume, it is difficult to achieve a substantial lubricating effect.

Methods for impregnating or filling the open pores of the porous silicon carbide sintered body with a lubricant include a method of immersing the lubricant in a lubricant that has been melted or reduced in viscosity by heating under vacuum or pressure, A method of immersing it in a lubricant, a method of impregnating it in a 7-mer state and then adding it to a polymer,
Alternatively, a method can be applied in which a finely divided lubricant is dispersed in a dispersion medium, immersed in the dispersion, impregnated, and then baked.

The porous silicon carbide sintered body impregnated or filled with the lubricant is extremely suitable as a sliding material for rolling bearing poles, retainers, raceway rings, mechanical seals, sliding bearing parts, wire tod printer guides, etc. In particular, those impregnated with a lubricant with excellent chemical resistance such as fluorine-based oil: Parts used under extremely harsh conditions, such as those used in diffusion furnaces and etching equipment for semiconductor materials. It is extremely suitable for applications such as sliding materials or bearings for air conditioners.

Next, the present invention will be explained by examples.

Example 1 Average particle size is 0.28 μm, β-type crystal content is 94.6
100 parts by weight of silicon carbide powder, 1 part by weight of boron carbide powder, 2 parts by weight of carbon black powder, 35 parts by weight of polyvinyl vinyl, 300 parts by weight of water,
After mixing in a ball mill for 5 hours, it was spray dried. In addition,
The silicon ash powder contained 0.29% by weight of free carbon, 0.17% by weight of oxygen, 0.3% by weight of iron'io, and 03% by weight of aluminum.

Collect an appropriate amount of this dried material, mold it, and heat it at 1900°C.
A sintered body was obtained by holding in a gas atmosphere for 10 minutes.

The obtained sintered body has a density of 2.591/c and a strength of 45K.
It had fine open pores uniformly distributed three-dimensionally at gf/mm2, and the open porosity was about 16% by volume.

This sintered body has an inner diameter of 20jlj and an outer diameter of 26j111.
After processing into a ring shape with a thickness of 101μ11, the material was impregnated with Verrefluoroalkylpolyate/I/ under vacuum to impregnate approximately 77% by volume of the voids using a ring-on-ring type sliding testing machine. Theoretical density is 9 when using empty sword atmosphere.
Using 8% silicon carbide sintered material as the mating material, all sliding tests were conducted with the sliding speed set at 1.5 m/1see and the end face load varied, and the results shown in Figure 2 were obtained. Obtained.

As can be seen from Figure 2, this material has been found to have extremely excellent sliding properties over a wide range of pv values, making it suitable as a wear-resistant sliding material for mechanical seats, sliding bearings, etc. I understand that.

Example 2, Comparative Example 1 Sintered bodies were obtained in the same manner as in Example 1, except that the firing temperature was changed as shown in Table 1.

The strength of the obtained nine sintered bodies and the strength of the same as in Example 1 were determined.
Refluoroalkyl polyether/I/e containing fiL sliding speed 1.5 m1sec, r+s load 5k
Table 1 shows the results of the sliding properties measured under the conditions of gf/e4.As can be seen from the results shown in Table 1, the sintered body of this example has high strength even at a relatively low density. The sliding properties of the VC were excellent. On the other hand, comparative example 1y)
With the J-body, there was a significant separation phenomenon of particles during sliding, and the wear coefficient could not be measured.

Table 1 Comparative Example 2 Same as Example 1, but using commercially available G as silicon carbide powder.
A sintered body was obtained by using C16000i silicon carbide powder which was further crushed and classified by particle size, and the firing temperature was changed to 2000''C.The silicon carbide powder had an average particle size of 0.5 μm.
1 The content of α-type crystals is almost 100% by weight, and the free M
0.7% by weight of returned element, 0.3% by weight of oxygen, iron't-0
, 02% by weight, and 0.02% by weight of aluminum.

The strength of the obtained sintered body was impregnated with perfluoroalkyl pholyate/L/wo in the same manner as in Example 1, the sliding speed was 1, 5 Tn/866, and the end face load was 15 Icgf.
The results of the sliding properties measured under the conditions of /e4 are shown in Table 1.

As can be seen from the results shown in Table 1, the sintered body of the wood comparison example was compared to the sintered body of the example whose starting material was silicon carbide powder mainly containing β-type crystal silicon carbide powder. It had low strength and poor sliding properties, and the wear during sliding was so great that it was not possible to measure the wear coefficient.

〔Effect of the invention〕

As described above, the present invention provides a sliding material that has extremely excellent lubricant retention properties and can be used particularly under conditions of high pv value, that is, fine open pores that are uniformly dispersed in three dimensions. It is possible to provide a porous silicon carbide sintered body with It is a material that not only can be expanded, but also can significantly improve the durability and reliability of equipment, making it extremely useful industrially.

[Brief explanation of drawings]

FIG. 1 is a schematic diagram showing the structure of a porous silicon carbide sintered body produced by a conventional method, and FIG. 2 is a graph showing the relationship between the friction coefficient and pv value of the sliding material of Example 1. A...Silicon carbide aggregate, B...Binder, C...Gap in porous body.

Claims (1)

[Claims] 1. A silicon carbide powder having an average particle size of 10 μm or less,
After molding a starting material mainly consisting of silicon carbide powder containing at least 30% of β-type crystal silicon carbide into a product of a desired shape,
It is heated and fired within the range of 0℃, and the density is 2.1 to 3.0.
A method for producing a porous silicon carbide sintered body, characterized in that the sintered body has a strength of 30 kgf/mm^2 or more at g/cm^3. 2. The porous silicon carbide sintered body has an open porosity of 5 to 30.
The manufacturing method according to claim 1, which is expressed in volume %. 3. The starting material is at least one selected from boron, aluminum, iron, chromium, lanthanum, titanium, yttrium, erbium, or a compound thereof.
The manufacturing method according to claim 1 or 2, containing 0.01 to 5.0% by weight of seeds.