JP5093639B2 - Method for producing carbon / ceramic composite material - Google Patents

Description

  The present invention relates to a technique for producing a composite material having heat resistance, oxidation resistance, and molten metal resistance used in metallurgical and glass production. More specifically, the present invention relates to a technique for producing a high-density carbon / ceramic composite material produced using pitch, a thermosetting resin, and ceramic powder.

  The carbon / ceramic composite material according to the present invention has a life of about 10 times that of a flammable carbon material, and has heat resistance and the like particularly in the field of a member handling a molten metal such as metallurgy or a member for manufacturing a glass bottle. Widely used as a material. However, the carbon / ceramic composite material is difficult to machine as compared with the general carbon material, and therefore, the problem is that the processing cost is high for processing to the shape of the final product. Therefore, if it is molded from the beginning into the shape of the final product, the subsequent machining process can be reduced. However, in the current manufacturing method, in order to obtain a high-density composite material, Molded with a high pressure of 150 MPa or more, or molded by pressing with a rubber press. This is because raw coke that does not soften or melt is used as the carbon raw material, so that the compacted body is not sintered or densified during firing, and the density of the formed body before firing must be increased in advance. .

  On the other hand, a technique is also known in which a mixed powder of raw coke and ceramic is pre-fired at 800 ° C., and then formed into a slurry without pressure and fired to produce a carbon / ceramic composite material ( Patent Document 1). However, in the molding method described in Patent Document 1, the carbon raw material of the mixed powder is already carbonized before being slurried and cannot be a driving force for sintering. It becomes power. This is because the continuous phase during sintering is ceramics, and the carbon component tends to exist in isolation. Therefore, it is different from this composite material in terms of physical properties such as electrical characteristics.

  As described above, there is a problem that raw coke used as a carbon raw material does not soften or melt, but on the other hand, in the carbonization process of organic matter, pitches before becoming raw coke are about 150 to 300 ° C. Softens with temperature. However, if this is used as it is as a precursor of carbon, foaming or the like is generated due to shape loss due to softening of pitch during firing or generation of a large amount of volatile matter. In a composite material mainly composed of a fibrous material such as a carbon / carbon fiber composite material, the pitch can be used as a carbon raw material because the shape can be maintained by softening or foaming the pitch. This product is porous, so pitch impregnation and firing are repeated to increase the density of the carbon material.

  In addition, although carbon fiber reinforced carbon composites using a thermosetting resin and pitch in part are also seen, despite using a molding pressure of 10 MPa or less and using short carbon fibers as a reinforcing material, The bending strength is 50 MPa or less, which is 1/3 or less of the composite material according to the present invention. However, in the production of a carbon / ceramic composite material, the pitch is not used as the main component of the carbon raw material as it is due to the collapse of the shape of the molded body or foaming.

  As described above, since it was difficult to use pitch as a main component of the carbon raw material of the carbon / ceramic composite material, raw coke obtained by further heat-treating the pitch is used as the carbon raw material, which is 150 MPa. Very high molding pressure is essential. Recently, for example, as seen in Patent Document 2, it has been proposed to infusibilize the pitch to obtain a carbon raw material. However, this method requires a complicated process of infusibilizing the pitch, and also requires a pressure of around 50 MPa when forming, and a dense composite material has not been obtained, so it is free in a slurry state. Molding is impossible.

  Further, in the production of a carbon / ceramic composite material, it is also conceivable to use a thermosetting resin such as a phenol resin as a carbon raw material. The thermosetting resin has a relatively high carbon yield by heat treatment, and can be a carbon material as it is without being softened or melted. However, thermosetting resins have extremely large dimensional shrinkage during heat treatment, and cracks are unavoidable. This is particularly the case with thick molded bodies, and only a few millimeters can be obtained. Therefore, the thermosetting resin is not used as it is as the carbon raw material of the carbon / ceramic composite material.

  For example, as seen in Patent Document 3, a method of pressureless molding as a slurry in a carbon-based composite material is also disclosed, but this is a matrix is a metal, and therefore heat resistance is significantly inferior. / Not within the category of ceramic composites.

Japanese Patent Publication No.2-7907 JP 2005-8476 A JP 2002-69548 A

  The carbon / ceramic composite material has some advantages as described above and is used effectively. However, this carbon / ceramic composite material is usually manufactured by high-pressure molding, and therefore, it is difficult to make a free-form product, and since it contains high-hardness ceramics, it is difficult to machine. For this reason, in order to process to the shape of the final product, the current situation is that the cost becomes high.

  Therefore, there are many restrictions on molding a product having an arbitrary shape such as casting or slip casting, and the cost is high. Furthermore, as described above, a technique for producing a composite material under normal pressure is also disclosed. However, a material for manufacturing a composite material that constitutes a part of the structure uses a metal as a matrix, and the heat resistance of the composite material is insufficient. Moreover, in the manufacturing technology using resin, it has been developed for special applications and is not a composite material that forms a structure as a non-metallic substance. What constitutes a part of the structure is required to have heat resistance and high rigidity, and therefore must be a high-density material.

  It is common to use high pressure to produce absolutely reliable composite material having these properties for this. However, as described above, this requires a certain amount of equipment, resulting in high costs. Since the carbon / ceramic composite material of the present invention is manufactured using a thermosetting resin that gives hard carbon, the carbon / ceramic composite material contains more hard carbon components than a conventional soft carbon / ceramic composite material. Therefore, what was manufactured by this invention can be said to be a hard carbon / ceramics composite material, and is a composite material different from the past.

  The present invention has been made based on the above-described technical background, and achieves the following objects. An object of the present invention is to provide a technique for producing a carbon / ceramic composite material that is uniform and has a high density, without requiring pressurization when producing a formed body. Another object of the present invention is to provide a technique for producing a carbon / ceramic composite material that can be produced at low cost.

  The present invention takes the following means in order to achieve the object. The present invention provides a dense carbon / ceramic composite material if the pitch is mixed and pulverized at the same time as the phenol resin and the ceramic powder within a specific blending ratio range without any infusibilization treatment. It has been found that can be manufactured. According to this method, it is possible to use a high-pressure when forming a generated shape without pouring high pressure into a mold as a slurry, and to dry and use this as a generated shape. Since the high pressure is not used, the generated shape is porous. However, since large sintering and densification occur during firing, a dense carbon / ceramic composite material is obtained after firing. Moreover, there is no shape collapse or foaming during firing.

In the method for producing a carbon / ceramic composite material according to the first aspect of the present invention, a pitch of carbon yield of 80% or more and a thermosetting resin powder that is a novolac type phenol resin are blended in a range of 60:40 to 50:50 , The mixing powder is further mixed with the ceramic powder so that the volume mixing ratio is in the range of 70:30 to 50:50, and mixed to form the first mixture, and the first mixed in the mixing process. Add a stirring liquid containing 15% by weight or less of alcohol to the mixture, crush and mix to make a slurry, a slurry process to form a second mixture, and a molding process to mold the dried second mixture and dry it And a step of firing the molded and dried second mixture at a predetermined temperature and time at a high temperature.

  The present invention is basically a technique for producing a composite material that enables creation of a shaped product before sintering under normal pressure. According to the present invention, since a high pressure is not required, a generated shape can be created by a mold method, injection molding, or the like, and thus mass production is possible. In the mixing and pulverization process of the raw material powder, composite particles composed of pitch and ceramic particles are generated and mixed with the thermosetting resin, whereby the composite particles are coated with the thermosetting resin and slurried. A composite material is generated with these particles as the main component.

[pitch]
The pitch may be of any type, but it is preferable to use a pitch having a higher carbon yield than that of a normal pitch such as spinning pitch. Pitches show various softening temperatures in the range of 150 to 300 ° C. In the present invention, the carbon yield is more important than the problem of pitch softening temperature, and it is desirable to use pitches with as high a carbon yield as possible.

[Thermosetting resin]
In addition, any thermosetting resin may be used, but if water is used as a medium for mixing and grinding, it is advantageous in terms of cost and handling. For this reason, novolac type phenol is used as the thermosetting resin. A powder form such as resin is preferred. Next, the slurry produced by mixing and pulverization is molded with a mold by a mold method, injection molding, or the like, and dried. After drying, if left in a non-oxidizing atmosphere (in an inert gas atmosphere) at a temperature of about 60 to 70 ° C. for about 24 hours, the thermosetting resin in the molded body undergoes thermosetting and the mechanical strength of the molded body. This is advantageous for subsequent handling, but this treatment is not always necessary.

[Baking]
The primary firing is performed to carbonize the pitch and the resin in the molded body, but this primary firing process requires a moderate temperature increase because volatile components from the pitch and the resin are generated. The temperature should be raised to 10,000 ° C., preferably 1200 ° C., and the volatile matter from the pitch and resin is almost exhausted by this firing, and the pitch and resin are only carbon. Next, high temperature firing, which depends on the type of ceramics to be combined. In the case of simultaneous composite of SiC and B ₄ C, which is most often used for improving the oxidation resistance of the composite material, the temperature is around 2,100 ° C.

  As described above, the present invention is a material capable of producing a component having a complicated shape by a method such as casting at normal pressure without using high pressure molding. For this reason, machining that has been conventionally performed can be reduced, and the cost can be reduced.

  As described in detail above, in the composite material manufacturing technique of the present invention, a pitch is mixed with a thermosetting resin and ceramic powder to create a slurry. The mixed powder slurry can be molded without applying pressure, dried, primary fired, and secondary fired to obtain a high density carbon / ceramic number composite material. In addition, the manufacturing cost is low, and the composite material can be mass-produced.

  Embodiments of the present invention will be described below in place of the following examples.

Spinning pitch (carbon yield: 86%) and novolac type phenol resin powder were blended at a weight ratio of 55:45, and further mixed powder of 1: 1 molar ratio of SiC and B ₄ C was added to these mixed powders. Was added at a volume ratio of 40% with respect to the whole. This was pulverized and mixed in water by a ball mill for 72 hours. At that time, 1% or less of a commercially available surfactant, 5% of ethylene glycol, and 2% of polyvinyl alcohol (all by weight) were added as a binder. The obtained slurry was put into an 80 × 40 × 20 mm mold and left to dry for 2 days. After drying, it was sealed in a plastic bag to prevent oxidation, and allowed to stand at 60 ° C. for one day to cure the phenolic resin in the molded body.

Thereafter, the temperature was raised to 1,200 ° C. at a rate of temperature rise of 1 ° C./min in an argon atmosphere and held for 1 hour. The primary fired compact was further fired at 2,100 ° C. for 30 minutes in a graphitization furnace. The heating rate was 10 ° C./min. When placed in a closed container and allowed to stand at 75 ° C. for 24 hours, a gel-like product was observed. This was dissolved and filtered, and dried by a drier to obtain a powder. The obtained carbon / ceramic composite material had a bulk density of 1.8 g / cm ³ . This number of 1.8 g / cm ³ is sufficiently high density, but in this experimental example, the slurry preparation technique was not sufficient, and bubbles were observed in the slurry. For this reason, it can be predicted that a higher density composite material can be produced if sufficient slurry preparation without bubbles is performed.

Spinning pitch (86% carbon yield), and a novolak type phenolic resin powder, 55: formulated at a weight ratio of 45, further to the mixed powder, the mixed powder of the molar ratio 74:26 of SiC and _{B 4} C It added so that it might become 44% of volume ratio with respect to the whole. This was pulverized and mixed for 96 hours in water containing 5 to 20% by weight of ethanol by a ball mill. The obtained slurry was put in an 80 × 40 × 20 mm mold, dried, and after mold release, left at 60 ° C. for 6 days to be completely dried. Table 1 shows the relationship between the ethanol content in water during raw material mixing and the porosity of the 2,200 ° C. sintered body.

As the ethanol content increases, the porosity of the fired body decreases. However, the bulk density (D) of the fired body is almost constant regardless of the ethanol content. This means that the inclusion of ethanol during pulverization changes the pores in the fired body from open pores to closed pores. Infer that it can be increased. When the ethanol content was 20% by weight, the sample powder adhered to the ball and the mill wall during mixing, and mixing was not successful.

  The same raw material as in Examples 1 and 2 was used. The blending ratio was calculated so that the proportion of the ceramic component in the final sample after the heat treatment was as shown in Table 2 in consideration of the weight loss accompanying the heat treatment of the pitch and the resin. Water containing 15% by weight of ethanol was added to the mixed powder thus mixed, and pulverized for 72 hours by the ball mill used in Example 2. The obtained slurry was poured into an 80 × 40 mm mold, and after die cutting and drying, calcined to 1,200 ° C., and then heat-treated in a Tamman furnace at 2,200 ° C. for 1 hour.

Table 2 shows the bulk density, open area ratio, rebound hardness (Shore hardness), and bending strength. In addition, 5 test pieces (30 * 5 * 1.5mm) were cut out from the same sample, and the bending strength showed the average of those measured values. The porosity was measured by a water impregnation method. When the raw material is blended, if the pitch is large, sample swelling will be observed during heat treatment. This is remarkable in a sample having a small amount of ceramics, but in a sample having a large amount of ceramics, no blister is observed even if the pitch amount is large. In addition, as the pitch amount increases, the sample tends to become denser. Compared with commercially available carbon / ceramic composites according to the catalog, the bulk density of the present invention is small and the open area ratio is large compared with the commercially available bulk density of 2.1 to 2.3 g / cm ³ . However, the bending strength of some commercially available products exceeds 200 Mpa compared to 100 to 200 Mpa, and is not inferior.

Claims (1)

A pitch of carbon yield of 80% or more and a thermosetting resin powder that is a novolac type phenol resin are blended in the range of 60:40 to 50:50 , and ceramic powder is further added to the blended powder in a volume mixing ratio of 70: A mixing step of blending and mixing in a range of 30 to 50:50 to form a first mixture;
A slurry step of adding a stirring liquid containing 15% by weight or less of alcohols to the first mixture mixed in any one of the mixing steps, pulverizing and mixing, and forming a second mixture;
Forming the slurry-formed second mixture, drying and forming,
A method for producing a carbon / ceramic composite material comprising: a step of firing the molded and dried second mixture at a predetermined temperature, a predetermined time, and a high temperature.