JPH0253389B2 - - Google Patents

Description

[Detailed description of the invention]

INDUSTRIAL APPLICATION FIELD The present invention relates to a method for producing a silicon carbide sintered body having high density and excellent thermal conductivity. Silicon carbide is chemically stable at room temperature and high temperature, and has excellent mechanical properties, so it is beginning to be used as a heat-resistant structural material and a sliding material. In addition, due to its good thermal conductivity, its use as a heat conductive material for heat sinks, heat exchangers, IC boards, etc. is being considered. BACKGROUND ART Conventionally, when silicon carbide is used as such a material, a sintered body is manufactured by molding fine silicon carbide powder and firing it at a high temperature. However, since silicon carbide is inherently difficult to sinter, a sintering aid is added and mixed during firing. For example, (1)β−
SiC powder with less than 0.03~0.1 wt% boron and 0.1~0.1% carbon
Method of mixing 1.0% by weight and firing
Publication No. 155572). (2) Production method of high density and high thermal conductivity silicon carbide by adding BeO to α-SiC powder and hot pressing (Ceramics, 18, P217-23, 1983
year) is known. However, in the method (1), the degree of densification and the thermal conductivity of the sintered body cannot be said to be sufficiently high. In addition, the method (2) above is not preferable from the viewpoint of the working environment because BeO used as a sintering aid is toxic. Purpose of the Invention The present invention was made to improve the drawbacks of these conventional methods, and its purpose is to produce a silicon carbide sintered body with high density and excellent thermal conductivity without impairing the working environment. This is to provide a way to do so. Structure of the Invention In order to achieve the above object, the present inventors have
One or more rare earth elements and carbon are used as sintering aids in silicon carbide powder of 0.5 μm or less,
By varying the amount and type of sintering agents used and sintering under vacuum or inert atmosphere, it was found that 0.01 to 20% by weight of one or more rare earth elements and 0.05 to 10% by weight of carbon were added to the silicon carbide powder. It was discovered that a sintered body with high density and high thermal conductivity can be obtained by using both agents at the same time, and the present invention was completed based on this knowledge. The gist of the present invention is to combine silicon carbide powder with an average particle size of 5.0 μm or less with a rare earth element in an amount of 0.01 to 20% by weight of the silicon carbide powder, or one or more rare earth element compounds containing the same amount of rare earth element. It is characterized by mixing and molding 0.05 to 10% by weight of carbon in the silicon carbide powder or an organic compound that produces the same amount of carbon, and then firing at 1800 to 2400°C in a vacuum or an inert atmosphere. A method for producing a high-density silicon carbide sintered body. The particle size of the silicon carbide powder used in the present invention must be 5.0 μm or less, preferably 1 μm or less. If the particle size is larger than this, the density of the sintered body decreases and the strength also decreases. The crystal forms of silicon carbide contained in the raw material powder are α form,
Either β-form may be used. A mixture of these may also be used. As the sintering aid, one or more rare earth elements and carbon are used. Note that the rare earth elements here are
Yztrium, lanthanum, cerium, praseodymium, neodymium, samarium, europium,
Refers to gadolinium, terbium, dysprosium, holmium, erbium, thulium, ytterbium, and lutetium. Rare earth element sources include rare earth elements or rare earth element-containing compounds;
For example, rare earth oxides are used. The amount of one or more rare earth elements added (in rare earth element-containing compounds, in terms of rare earth elements) must be 0.01 to 20% by weight, preferably 0.1 to 10% by weight, based on silicon carbide. be. If it is less than 0.01% by weight, densification progresses slowly and a high-density sintered body cannot be obtained. Moreover, if it exceeds 20% by weight, a large amount of rare earth elements will remain in the sintered body, resulting in the disadvantage of lowering the mechanical strength of the silicon carbide sintered body. As the carbon source, carbon such as graphite powder or carbon black, or an organic compound such as phenolic resin that generates carbon during firing is used. The amount of carbon (in the case of an organic compound, in terms of carbon) added must be 0.05 to 10% by weight based on silicon carbide. If it is less than 0.05% by weight, sintering will be difficult, and if it exceeds 10% by weight, carbon will remain in the sintered body, resulting in a disadvantage of lowering the mechanical strength of the silicon carbide sintered body. The role of rare earth elements and carbon as sintering aids is not clear. Rare earth elements are a
The chemical properties of these elements are very similar, and it is thought that rare earth elements act in the same way regardless of the type. There are some types of X-ray diffraction lines that can be seen. From this, it is thought that the rare earth element-containing compound reacts with carbon and silicon carbide to produce rare earth element carbide, which is involved in promoting the sintering of silicon carbide. Rare earth elements exhibit the effect of promoting densification of silicon carbide when added at the same time as carbon. Addition of rare earth elements alone does not produce a significant effect. The ratio between the amount of rare earth elements added and the amount of carbon is:
This is particularly important in areas where rare earth elements are present in small amounts. Although a sufficient explanation has not yet been given regarding this optimal ratio, it is necessary that the amount of carbon be greater than a certain amount relative to the amount of rare earth elements. Wet mixing using an organic solvent such as ethanol or acetone or water is suitable for mixing the silicon carbide powder, one or more rare earth elements, and carbon. Particularly when using an organic compound as a carbon source, it is desirable to use an organic solvent that dissolves the organic compound. Molding of these mixtures is performed by die molding, rubber press, injection molding, or the like. Alternatively, a method of simultaneously performing molding and sintering such as hot pressing or hot isostatic pressing may be used. Firing is carried out in vacuum or in an inert atmosphere. Inert atmospheres include helium, argon, and the like. It is necessary for this atmosphere to reduce the amount of free oxygen contained as much as possible. Under reduced pressure, the degree of vacuum
It is desirable that the pressure be 10 ^-4 atmospheres or less, and the oxygen concentration contained in the inert atmosphere be 10 ^-6 atmospheres or less.
The use of graphite furnaces and graphite crucibles is also effective. This is because if the atmosphere contains a large amount of oxygen, the surface of the silicon carbide powder will be oxidized and the sinterability will deteriorate. Firing temperature is 1800-2400℃, preferably 1900℃
Perform at 2200℃. If the temperature is lower than 1800°C, sintering progresses slowly and it is difficult to obtain a dense sintered body, and if the temperature exceeds 2400°C, coarsening of crystal grains becomes noticeable and decomposition of silicon carbide occurs, which is not preferable. The sintering method may be any method such as normal pressure sintering, hot pressing, hot isostatic pressing, etc., but if the amount added is small, it is better to use hot pressing or hot isostatic pressing. . Examples Examples 1 to 8 Average particle size 0.3 μm made by reacting SiO ₂ and carbon
A rare earth element oxide and a resol type phenolic resin as carbon were mixed into the β-SiC powder in the proportions shown in Table 1. However, this mixing ratio is a value converted to rare earth elements and carbon, respectively. Ethanol was added to the above mixture and mixed in a ball mill for 10 hours, followed by drying and pulverization to obtain a raw material powder. Next, the mixed powder is placed in a graphite die, heated at a rate of 50°C/min while applying a pressure of 200Kg/cm ² in a vacuum of 10 ^-4 Torr, and hot pressed under the conditions shown in Table 1. As a result, a sintered body having a diameter of 10 mm and a thickness of 2 mm was obtained. The density and thermal conductivity (measured by the laser flash method) of the obtained sintered body are summarized in Table 2.

[Table] * Converted to rare earth elements.

[Table] Comparing the density and thermal conductivity in Table 2 with the silicon carbide sintered body with excellent thermal conductivity disclosed in JP-A-60-155572,
Both the density and thermal conductivity of the examples are equivalent or superior. In the case of silicon carbide ceramics, it is said that the mechanical strength is significantly improved when the density exceeds 3.1 g/cm ³ , so the achievement of the high-density sintered body as in the example is of great significance. Effects of the Invention As described above, according to the method of the present invention, density 3.1
g/cm ³ or more and a thermal conductivity of 100 W/mk or more, resulting in a silicon carbide sintered body with high density and excellent thermal conductivity.

Claims (1)

[Claims] 1 Silicon carbide powder with an average particle size of 5.0 μm or less, one or more of rare earth elements in an amount of 0.01 to 20% by weight of the silicon carbide powder, or one or more compounds of rare earth elements containing the same amount of rare earth elements, and the silicon carbide. 0.05~10 of powder
Production of a high-density silicon carbide sintered body characterized by mixing and shaping organic compounds that produce % by weight of carbon or the same amount of carbon, and then firing at 1800 to 2400°C in a vacuum or in an inert atmosphere. Law.