JPH0229637B2 - - Google Patents

Description

[Detailed description of the invention]

[Industrial Field of Application] The present invention relates to a silicon carbide composite having excellent sliding properties in which the open pores of a porous silicon carbide sintered body are filled with a synthetic resin. Traditionally, silicon carbide is known for its chemical properties such as high hardness, good wear resistance, good oxidation resistance, good corrosion resistance, good thermal conductivity, low coefficient of thermal expansion, high thermal shock resistance as well as high strength at high temperatures. It has excellent physical properties and can be widely used as wear-resistant materials such as mechanical seals and bearings, pump parts for highly corrosive solutions such as acids and alkalis, and corrosion-resistant materials such as water pipe packing. It is a material that can be used. [Prior Art] By the way, silicon carbide sintered bodies have high hardness and excellent wear resistance, but they have poor self-lubricating properties, and are particularly difficult to use as mechanical components that involve friction phenomena, such as mechanical seals and bearings. However, there were problems with the durability and reliability of the equipment. As a material to solve the above-mentioned problems, JP-A-Sho
No. 58-161982 discloses an invention related to a "ceramics composite in which a fluorine-containing polymer is bonded to ceramics," and the specification of the publication discloses a composite of a silicon carbide sintered body and a fluororesin. body is described. However, the above-mentioned invention does not describe any characteristics of the silicon carbide sintered body suitable for compounding with a fluororesin. [Problems to be Solved by the Invention] By the way, porous silicon carbide sintered bodies are used for the above-mentioned composites with synthetic resins, but the conventional production of porous silicon carbide sintered bodies is difficult. As a method, JP-A No. 48-39515 describes a method in which a carbonaceous binder is added to silicon carbide powder with or without carbon powder, and the theoretical amount of carbon that reacts with this carbon powder and free carbon from the binder produced during firing is described. Homogeneous porous recrystallization carbonization characterized by adding siliceous powder to form the molded body, and then heating the molded body to 1900 to 2400°C in the carbon powder to silicify the carbon content in the molded body. ``Method for manufacturing a silicon body.'' is disclosed. However, the structure of the porous body produced by the above method is shown in Figure 2 as a model, and the bond between the crystals is weak, so the crystal particles tend to separate easily. . The present invention provides a porous silicon carbide body that eliminates and improves the drawbacks of the previously known porous silicon carbide sintered body as described above, that is, a silicon carbide sintered body that is suitable for compounding with synthetic resins such as fluororesins. The purpose of the present invention is to provide a silicon carbide composite material with excellent sliding properties by applying a silicon carbide material to the silicon carbide composite material. [Means for Solving the Problems] For the above-mentioned purpose, the present inventors have conducted various studies and found that the present inventors have developed a material having an average aspect ratio of 3 to 50 and an average length in the major axis direction of 0.5 to 1000 μm. By newly discovering a porous silicon carbide sintered body having a three-dimensional network structure mainly composed of silicon carbide plate-like crystals, and filling the open pores of this porous silicon carbide sintered body with synthetic resin. The inventors came up with the idea that the above-mentioned problems could be solved, and completed the present invention. The present invention will be explained in detail below. The porous silicon carbide sintered body of the present invention (hereinafter referred to as a porous body) has an average aspect ratio of 3 to 50 and an average length of 0.5 to 1000 μm in the long axis direction, and is mainly a silicon carbide plate-like body. It is necessary that it is composed of crystals and has a three-dimensional network structure with open pores. The reason why it is necessary for the average aspect ratio of the porous body to be 3 to 50 is that by setting the average aspect ratio to 3 or more, the pores composed of the silicon carbide plate crystals are reduced in volume occupied by the crystals. This is because it can be made into a relatively large and high-strength porous body, that is, a high-strength porous body with a high porosity. This is because there are few joints between the crystals, so the strength of the porous body itself is low, and the strength of the silicon carbide composite is low. More preferably, the porous body has an average aspect ratio of 5 to 30. Note that the aspect ratio here is the ratio of the long axis to the short axis of each crystal observed in an arbitrary cross section of the sintered body. Also, the average length of the plate-like crystals in the long axis direction is
The reason why it needs to be 0.5 to 1000 μm is that if the average length in the long axis direction is smaller than 0.5 μm, the pores formed by the plate crystals will be small, and in some cases, some of the pores will be This is because the pores may become independent, making it difficult to fill with synthetic resin. On the other hand, if the length is longer than 1000 μm, the strength of the joints of plate crystals is low, and the strength of the porous body itself is low. be. Among these, it is more preferable that the average length of the plate crystals in the major axis direction is 1 to 800 μm. The porous body of the present invention preferably has an open air light rate of 10 to 70% by volume. The reason is that if the open porosity is lower than 10% by volume, it is not only difficult to fill with synthetic resin;
This is because it is difficult to improve the sliding properties because the filling amount of synthetic resin is practically small;
This is because if it is higher than 70% by volume, the strength of the porous body will be low, and the particles will not only be easily detached, but also the thermal conductivity of the composite will be low, making it easy to seize due to frictional heat. In addition, the average cross-sectional area of the open pores in the network structure is
It is preferably 0.01 to 250000 μm ² . The reason for this is that if the average cross-sectional area of open pores is smaller than 0.01 μm ² , it is difficult to fill with synthetic resin, whereas if the average cross-sectional area of open pores is larger than 250000 μm ² , the strength of the porous body itself will decrease. Among them, the average cross-sectional area of the open pores of the network structure is 0.25 to 90000μ.
Advantageously, ^m2 . And from 3 to 100 weight of the crystals of the porous body
Plate crystals with an aspect ratio of 50 are at least 20
Preferably, it accounts for parts by weight. Incidentally, the content of the plate crystals can be determined by analyzing a structural photograph of the crystals. Here, the porous body is 20
The reason why it is preferable that the plate-shaped crystals have an aspect ratio of 3 to 50 parts by weight or more is because if the plate-shaped crystals are less than 20 parts by weight, a large amount of silicon carbide crystals with a small aspect ratio will be included. This is because it becomes difficult to fill with synthetic resin. In particular, it is advantageous for the plate-like crystals to account for at least 40 parts by weight out of 100 parts by weight of the crystals in the porous body. The specific surface area of the porous body is at least
Advantageously, it is 0.05 m ² /g. Here, the specific surface area is a value determined by the BET method using nitrogen adsorption. The reason why a specific surface area of 0.05 m ² /g or more is preferable is that the bonding area with the synthetic resin is large and a higher strength composite can be formed, and in particular, a specific surface area of 0.2 m ² /g or more is preferable. can be used most preferably. The synthetic resins used in the present invention include acetal resin, nylon resin, polyethylene resin, polycarbonate resin, polybutylene terephthalate resin, styrene acrylonitrile resin,
Resins selected from polypropylene resins, polyurethane resins, polyphenylene sulfide resins, epoxy resins, silicone resins, and fluororesins can be used alone or in combination, and among them, acetal resins, nylon resins, polyethylene resins, Polybutylene terephthalate resin and fluororesin have excellent self-lubricating properties and can significantly improve sliding properties. Methods for filling the synthetic resin into the gas of the porous body include heating the resin to melt it and impregnating it, dissolving the resin in a solvent and impregnating it, and impregnating the resin in a monomer state and then turning it into a polymer. Alternatively, a method of dispersing a finely divided resin in a dispersion medium, impregnating a porous body with this dispersion, drying, and then baking the resin at the melting temperature of the resin can be applied. Next, a method for manufacturing the porous body used in the present invention will be explained. It has a three-dimensional network structure mainly composed of silicon carbide plate crystals with a flat length in the long axis direction of 10 to 1000 μm and an average aspect ratio of 3 to 50. Area is 400~
The porous body having an average cross-sectional area within the range of 250000 μm ² is: (a) silicon carbide powder having an average particle size of 10 μm or less and containing at least 60% by weight of β-type, 2H-type and amorphous silicon carbide; The process of molding the contained silicon carbide powder into a desired shape; and (b) the molded product obtained in step (a) is charged into a heat-resistant container and heated for 1900 minutes while blocking the intrusion of outside air.
It can be obtained by a step of firing within a temperature range of ~2300°C. The starting material contains at least 60% by weight of β form, 2H
Advantageously, one of the starting materials is silicon carbide containing a mold and an amorphous silicon carbide sintered body. The reason for this is that β-type crystals, 2H-type crystals, and amorphous silicon carbide crystals are low-temperature stable crystals that are synthesized at relatively low temperatures.
This is because not only does it easily undergo a phase transition to high-temperature stable α-type crystals such as 4H, 6H, or 15R types, forming plate-shaped crystals, but it also has excellent crystal growth properties. It is advantageous to use a starting material consisting of more than % by weight of β-type silicon carbide. Advantageously, the starting material is a fine powder with an average particle size of 10 μm or less. Powders with an average particle size of less than 10 μm have relatively many contact points between particles, and at the firing temperature of silicon carbide, the thermal activity is large and the movement of atoms between silicon carbide particles is extremely large. , bonding between silicon carbide particles is extremely likely to occur. Therefore, the growth of plate crystals is extremely high. In particular, it is preferable that the average particle size of the starting material is 5 μm or less, which gives more favorable results for the growth of plate crystals. Then, the silicon carbide molded body formed into the desired shape using the starting material is placed in a heat-resistant container made of graphite, silicon carbide, etc., and kept within a temperature range of 1900 to 2300°C while blocking the intrusion of outside air. It is fired in The reason why the material is charged in a heat-resistant container and fired while blocking the intrusion of outside air is that it allows adjacent silicon carbide crystals to fuse together and promotes the growth of plate-shaped crystals. . The reason why adjoining silicon carbide crystals can be fused together and the growth of plate-like crystals can be promoted by charging the silicon carbide crystals in a heat-resistant container and firing them while blocking the intrusion of outside air as described above is because the carbonization This is thought to be because movement of silicon carbide atoms between silicon particles by evaporation-recondensation and/or surface diffusion can be promoted. In contrast, when conventional pressureless sintering, atmospheric pressure sintering, or sintering under reduced pressure was tried, not only was it difficult to grow plate-shaped crystals, but the joints of silicon carbide particles were The sintered body had a constricted shape, and the strength of the sintered body decreased. As the heat-resistant container, a heat-resistant container made of at least one material selected from graphite, silicon carbide, tungsten carbide, molybdenum, and molybdenum carbide can be used. Furthermore, it is advantageous to charge the formed body into a heat-resistant container that can block outside air and fire it, so that the volatilization rate of silicon carbide during firing is 5% by weight or less. By the way, in order to obtain a porous body having open pores with a relatively large average cross-sectional area, the heating rate during firing must be relatively slow, the maximum temperature must be relatively high, and/or It is advantageous to increase the holding time at the maximum temperature. Under these conditions, individual silicon carbide plate crystals can be grown to a large size, and as a result, a porous body having a large pore cross-sectional area can be obtained. On the other hand, in order to obtain a porous body having open pores with a relatively small average cross-sectional area, the heating rate during firing should be relatively fast, the maximum temperature should be relatively small, and/or the holding time at the maximum temperature should be It is advantageous to make it short. This is because, under these conditions, individual plate-shaped crystals of silicon carbide are not allowed to grow much. Furthermore, the reason why the formed body is fired in the temperature range of 1900 to 2300°C is that if the firing temperature is lower than 1900°C, the growth of particles will be insufficient and it will be difficult to obtain a porous body with high strength. , when the temperature is higher than 2300℃, the sublimation of silicon carbide increases,
This is because the developed plate-like crystals become thinner and thinner, making it difficult to obtain a porous body with high strength. Among these, it is more preferable to sinter at a temperature between 1950 and 2250°C. be. On the other hand, it has a three-dimensional network structure mainly composed of silicon carbide plate crystals with an average length in the major axis direction of 0.5 to 200 μm and an average aspect ratio of 3 to 50, and has an average cross section of open pores in the network structure. Area is 0.01
The porous body having an average cross-sectional area in the range of ~10000 ^μm2 is (a) silicon carbide having an average particle size of 10 μm or less, and the powder is composed of α-type, β-type and/or amorphous silicon carbide; The starting material is silicon carbide powder consisting of unavoidable impurities, and this powder
Per 100 parts by weight, aluminum, aluminum diboride, aluminum carbide, aluminum nitride, aluminum oxide, boron, boron carbide, boron nitride, boron oxide, calcium oxide, calcium carbide, chromium, chromium boride,
Any one selected from chromium nitride, chromium oxide, iron, iron carbide, iron oxide, lanthanum boride, lanthanum oxide, lithium oxide, silicon, silicon nitride, titanium, titanium oxide, titanium dioxide, titanium trioxide, and yttrium oxide A step of uniformly mixing 10 parts by weight or less of one or more types; (b) A step of molding the mixture obtained in step (a) above; and (c) A step of molding obtained in step (b) above. The body is placed in a heat-resistant container to prevent outside air from entering, and the body is heated to 1700~
It can be obtained by a process of firing within a temperature range of 2300°C. Advantageously, the starting material is a fine powder with an average particle size of 10 μm or less. Powders with an average particle size of less than 10 μm have relatively many contact points between particles, and at the firing temperature of silicon carbide, the thermal activity is large and the movement of atoms between silicon carbide particles is extremely large. , bonding between silicon carbide particles is extremely likely to occur. Therefore, the growth of plate crystals is extremely high. In particular, it is preferable that the average particle size of the starting material is 5 μm or less, which gives more favorable results for the growth of plate crystals. The starting materials include aluminum, aluminum diboride, aluminum carbide, aluminum nitride, aluminum oxide, boron, boron carbide, boron nitride, boron oxide, calcium oxide, calcium carbide, chromium, chromium boride, chromium nitride,
Chromium oxide, iron, iron carbide, iron trioxide, lanthanum boride, lanthanum oxide, lithium oxide, silicon, silicon nitride, titanium, titanium oxide, titanium dioxide,
One or more selected from titanium trioxide and yttrium oxide are added. The substance has the function of significantly increasing the rate of crystal growth of silicon carbide, and on the other hand, the substance has the effect of generating vapor of the substance and/or vapor of decomposition products at a firing temperature of 1700 to 2300°C of the silicon carbide molded body. , diffuses to every corner of the silicon carbide molded body, and forms an extremely large number of plate-like crystal nuclei,
This is because plate crystals develop in each part, and as a result, the size of the plate crystals formed is restricted, resulting in a fine, coarsely woven three-dimensional network structure. Among the above compounds, boron, boron carbide, boron nitride, aluminum oxide, aluminum nitride, iron,
Aluminum carbide, aluminum diboride, aluminum can be used advantageously. On the other hand, it is advantageous that the amount of the substance added is 10 parts by weight or less per 100 parts by weight of the starting material mainly composed of silicon carbide. The reason is 10
Even if more than 1 part by weight is added, the vapor partial pressure of the compound and/or its decomposition product hardly changes within the firing temperature range of the silicon carbide molded body. On the contrary, since the amount of the substance remaining in the molded body increases, the original properties of silicon carbide are lost. Furthermore, the amount of the compound suitable for the growth of plate crystals is 100% of the silicon carbide starting material.
The amount is preferably 5 parts by weight or less. Furthermore, the silicon carbide used as the starting material may be any of α-type, β-type and/or amorphous silicon carbide. A carbon source can be added to the starting material that leaves free carbon during calcination. As such a carbon source, any carbon source that exists in the carbon state at the start of sintering can be used, such as phenolic resin, lignin sulfonate, polyvinyl alcohol, cornstarch, molasses, coal tar pitch, and alginate. Various organic substances such as carbon black, pyrolytic carbon such as acetylene black, etc. can be advantageously used. If free carbon is present at the same time as the above substances,
Since it suppresses crystal growth and forms fine silicon carbide plate crystals, it is effective in obtaining a porous body having fine pores. Further, it is advantageous that the free carbon content is 5 parts by weight or less based on 100 parts by weight of the starting material. The reason for this is that even if more than 5 parts by weight is added, the effect remains, but on the contrary, the amount remaining in the porous body increases, reducing the oxidation resistance of the porous body. It is more effective if the amount is less than 30%. The heat-resistant container is selected from graphite, silicon carbide, aluminum nitride, zirconium oxide, tungsten carbide, titanium carbide, magnesium oxide, molybdenum carbide, molybdenum, tantalum carbide, tantalum, zirconium carbide, and a graphite-silicon carbide composite. A container consisting of any one of these can be used. These containers do not melt within the firing temperature range and can maintain their shape, and also prevent the vapors of the additives and/or decomposition products from leaking out of the system. However, the effect of the additive can be spread to every corner of the silicon carbide molded body. Among them, graphite, silicon carbide, graphite-silicon carbide composite, tungsten carbide, aluminum nitride, titanium carbide, molybdenum, and molybdenum carbide can be effectively used. In addition, in order to obtain a porous body having open pores with a relatively large average cross-sectional area, the heating rate during firing must be relatively slow, the maximum temperature must be relatively high, and/or It is advantageous to increase the holding time at the maximum temperature. Under these conditions, individual silicon carbide plate crystals can be grown to a large size, and as a result, a porous body having a large pore cross-sectional area can be obtained. On the other hand, in order to obtain a porous body having open pores with a relatively small average cross-sectional area, the heating rate during firing should be relatively fast, the maximum temperature should be relatively small, and/or the holding time at the maximum temperature should be It is preferable to make it short. This is because, under these conditions, individual plate-shaped crystals of silicon carbide are not allowed to grow much. Furthermore, the reason why the formed body is fired in the temperature range of 1700 to 2300°C is that if the firing temperature is lower than 1700°C, the growth of particles will be insufficient, making it difficult to obtain a porous body with high strength. , when the temperature is higher than 2300℃, the sublimation of silicon carbide increases,
This is because the developed plate-like crystals become thin and thin, making it difficult to obtain a porous body with high strength. Among these, it is more preferable to sinter at a temperature between 1750 and 2250°C. be. Next, the present invention will be explained with reference to Examples and Comparative Examples. Example 1 The silicon carbide fine powder used as the starting material was 94.6
% by weight is β-type crystals and the remainder is substantially 2H-type crystals, mainly containing 0.39% by weight of free carbon, 0.17% by weight of oxygen, 0.03% by weight of iron, 0.03% by weight of aluminum, and has a diameter of 0.28 μm. It had an average particle size. 5 parts by weight of polyvinyl alcohol and 300 parts by weight of water were blended with 100 parts by weight of the silicon carbide fine powder, mixed in a ball mill for 5 hours, and then dried. An appropriate amount of this dry mixture was taken, granulated, and then molded using a metal mold at a pressure of 50 kg/cm ² .
The density of this product is 1.2 g/cm ² and the dry weight is 21
It was hot at g. The formed body was placed in a graphite crucible that can be shut off from outside air, and fired in an argon gas atmosphere at 1 atm using a Tammann type firing furnace. The graphite crucible used had an internal volume of 50 ml. For firing, the temperature was raised to 2200°C at a rate of 2.5°C/min, and the maximum temperature of 2200°C was maintained for 6 hours. The weight of the obtained sintered body was 19.6g, and its crystal structure is shown in the scanning electron micrograph (75x magnification) in Figure 1.
As shown in Figure 2, it has a three-dimensional structure in which plate-shaped crystals with an average aspect ratio of 12 and an average length in the major axis direction of 380 μm are intricately intertwined in multiple directions.
The content of plate-shaped crystals having an aspect ratio of was 98% of the total weight of the porous body. Further, the pores of this porous body were non-linear open pores, the open porosity was 64% of the total volume, the specific surface area was 1.2 m ² /g, and the bending strength was 180 Kg/cm ² . After processing this porous body into a ring shape with an outer diameter of 30 mm, an inner diameter of 15 mm, and a thickness of 5 mm, the average particle size was
0.26μm polytetrafluoroethylene fine particles
After being immersed in suspension water in which 60% by weight was dispersed under vacuum, the composite was baked at a temperature of 380 to 400°C to obtain a composite. The amount of polytetrafluoroethylene filled in this composite was 0.85 g, and its proportion in the voids of the porous body was 50.1% by volume. When this composite was subjected to a dry sliding test on stainless steel (SUS304) using the ring-on-ring method at a sliding speed of 500 mm/sec with an end face load of 10 Kgf/cm ² , the friction coefficient was 0.15. ~
0.22, wear coefficient is 3.1×10 ^-4 mm/Km・(Kgf/cm ² )
It was recognized that the material had extremely excellent sliding properties. Note that the wear coefficient (K) is a value determined by the following relational expression. K=h/PVT K: Wear coefficient (mm/Km・(Kgf/cm ² )) h: Wear depth (mm) T: Sliding time (sec) P: End face load (Kgf/cm ² ) V: Sliding speed (Km/sec) Comparative example 1 A sliding test was conducted in the same manner as in Example 1, but without compounding polytetrafluoroethylene, and the friction coefficient was 0.5 to 0.7, and the wear coefficient was 2.3 × ^10-1
mm/Km・(Kgf/cm ² ). Comparative Example 2 A sliding test was carried out on stainless steel (SUS304), a general sliding material in which 30 parts by weight of glass fiber was composited with 70 parts by weight of polytetrafluoroethylene, under the same conditions as shown in Example 1. As a result, the initial coefficient of friction was relatively low at 0.2 to 0.25, but after about an hour the friction surface became abnormally heated and the coefficient of friction ranged from 0.2 to 0.25.
A phenomenon that significantly fluctuated within the range of 0.4 was observed.
In addition, the wear coefficient at this time is 2.2×10 ^-3 mm/Km (Kg
f/cm ² ), and it was observed that the surface of the stainless steel was extremely rough. Comparative Example 3 The same method as in Example 1 was used, but the formed body was sintered without being placed in a crucible, and the average aspect ratio was 1.8.
A porous body with a crystal structure consisting of almost granular silicon carbide with an average length in the major axis direction of 30 μm was obtained. The weight of this porous body was 18.8 g. The open porosity of this porous body was 67% by volume of the total volume,
The bending strength was extremely low at 4 kg/cm ² . Polytetrafluoronithylene was applied to the voids of the porous body in the same manner as in Example 1.
30% composite by volume. The coefficient of friction of this composite is 0.15
Although the value was relatively low at ~0.2, the wear coefficient was 8.5.
×10 ^-3 mm/Km (Kgf/cm ² ), which was significantly inferior. Examples 2 and 3 Same as Example 1, but molding pressure was changed to 3000Kg/
cm ² and 10 Kg/cm ^{2 ,} and impregnated a heated and melted polyacetal resin into a porous body to produce a composite. The properties of the obtained composite are shown in Table 1.

〔Effect of the invention〕

As mentioned above, the silicon carbide composite of the present invention has extremely excellent sliding properties, and can be applied to mechanical components that involve friction phenomena such as bearings and seals of mechanical devices. , the durability and reliability of the device can be significantly improved.

[Brief explanation of drawings]

FIG. 1 is a scanning electron micrograph (75x magnification) showing the crystal structure of the porous material described in Example 1, and FIG. 2 is a schematic diagram showing the structure of a conventional silicon carbide porous material. A...Silicon carbide aggregate, B...Binder, C...
...Gap between porous bodies.

Claims (1)

[Scope of Claims] 1. A porous silicon carbide sintered body having open pores with a three-dimensional network structure, the average aspect ratio of which is 3.
~50, and the average length in the long axis direction is 0.5~1000μm
It mainly consists of a silicon carbide plate-like crystal structure,
A silicon carbide composite comprising the open pores filled with a synthetic resin. 2 The porous silicon carbide sintered body has a content of 10 to 70% by volume.
The silicon carbide composite according to claim 1, having an open porosity of . 3 The average cross-sectional area of the open pores is 0.01 to 250000μ
The silicon carbide composite according to claim 1 or 2, which is m ² . 4. Claims 1 to 3, wherein out of 100 parts by weight of the porous silicon carbide sintered body, plate crystals having an aspect ratio of 3 to 50 account for at least 20 parts by weight.
The silicon carbide composite described in . 5. The synthetic resin is selected from acetal resin, nylon resin, polyethylene resin, polycarbonate resin, polybutylene terephthalate resin, styrene acrylonitrile resin, polypropylene resin, polyurethane resin, polyphenylene sulfide resin, epoxy resin, silicone resin, or fluororesin. The silicon carbide composite according to claims 1 to 4, which is at least one selected from the group consisting of at least one type. 6. The silicon carbide composite according to claim 1, wherein the synthetic resin is filled in an amount of at least 10 parts by volume per 100 parts by volume of open pores of the porous silicon carbide sintered body.