KR20190048811A - Method for manufacturing silicon carbide dense bodies having excellent thermal conductivity and thermal durability - Google Patents

Abstract

(A) a silicon carbide (SiC) powder, boron carbide (B ₄ C), and a carbon-based additive are weighed, mixed and crushed to obtain 90 to 96% by weight of silicon carbide; 1 to 5% by weight of boron carbide; And carbon (C) in an amount of 3 to 5% by weight; (b) preparing a shaped body from the ceramic mixed powder; And (c) sintering the shaped body at a temperature of 2000 to 2400 캜 under normal pressure. The present invention relates to a method for producing a silicon carbide-
According to the present invention, in producing a silicon carbide sintered body by pressureless sintering, the densified silicon carbide sintered body having a high thermal conductivity of at least 97.3% is manufactured by optimizing the amount of boron carbide (B ₄ C) and carbon added .

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention [0001] The present invention relates to a method of manufacturing a silicon carbide sintered body having excellent thermal conductivity and thermal durability,

The present invention relates to a method for producing a silicon carbide ceramic sintered body used for high-temperature parts for heat transfer and the like.

 Silicon carbide is a typical ceramic material for non-arsenic high-temperature structural ceramics. It is a ceramic material that is applied to various fields because it has excellent physical properties such as oxidation resistance, high temperature strength, hardness and abrasion resistance, which are represented by covalent bonding between silicon and carbon elements.

Currently, typical applications of silicon carbide include high-temperature interior and special refractories, bearing materials, blast nozzles, mechanical seals, ceramic ballistic materials, grinding / abrasives and cutting tools, And the like are also used as composite ceramics materials.

Also, due to its excellent thermal and physical properties, it is widely applied to energy fields such as radiant tubes, heat exchangers and heating elements.

On the other hand, silicon carbide has a high melting point due to its strong covalent bonding property and has a low self-diffusion coefficient inside the lattice. Therefore, in order to densify the sintering furnace by normal pressure sintering, Densification processes such as liquid sintering using crude, reaction sintering through silicon impregnation, and pressure sintering to apply additional pressure from outside are widely used.

Among them, pressure sintering is usually performed by using a hot press, and external pressure is used in addition to temperature by densifying driving force. In order to suppress grain growth at high temperature and to utilize the fine mechanical characteristics, a rapid sintering method such as spark plasma sintering It is widely used and the shape of the sintered body is restricted because it uses a mold for pressurization.

Reaction-bonded silicon carbide (RBSC) is a siliconized silicon carbide (SiC) process in which liquid silicon is impregnated into a recrystallized silicon carbide (SiC) skeleton partially annealed by heat treating SiC powder at a temperature of 2000 ° C. or higher It is SiC material densified by applied process. The difference between SiC and SiC is that the liquid Si is impregnated into the SiC and the C-shaped body, so that C and Si react to synthesize the second SiC to lower the process temperature required for complete densification. It is widely used industrially because it is possible to manufacture parts, but there is a limitation on high temperature use temperature depending on the content of residual silicon.

Therefore, there is a growing need for a technique for maximizing densification by optimizing the addition amounts of representative boron carbide and carbon among sintering aids used in the conventional pressure sintering.

Japanese Laid-Open Patent No. 2011-528312 (published on November 17, 2011). Japanese Patent No. 5540318 (Registered on May 31, 2014) Japanese Laid-Open Patent Application No. 2015-193534 (Publication Date: November 5, 2015)

 K. Schwetz: Silicon Carbide Based Hard Materials, R. Riedel (Ed.), Wiley-VCH, New York (2000) 683.  F. L. Riley: Structural Ceramics - Fundamentals and Case Studies, Cambridge, United Kingdom (2009) 175.

SUMMARY OF THE INVENTION The present invention provides a method of manufacturing a silicon carbide sintered body having maximum densification by controlling a composition and a content of a sintering auxiliary used in atmospheric pressure sintering, and a silicon carbide sintered body produced by the method.

(A) a silicon carbide (SiC) powder, boron carbide (B ₄ C), and a carbon-based additive are weighed and mixed and pulverized to obtain 90 to 96 wt% of silicon carbide; 1 to 5% by weight of boron carbide; And 3 to 5% by weight of carbon (C); (b) preparing a shaped body from the ceramic mixed powder; And (c) sintering the molded body at a temperature of 2000 to 2400 캜 under normal pressure, thereby producing a silicon carbide sintered body.

Further, the carbon-based additive is one or more selected from the group consisting of a polymer resin, graphite, carbon black, and activated carbon, and proposes a method of producing the silicon carbide sintered body.

The present invention also provides a method for producing a silicon carbide sintered body, wherein the polymer resin is a phenolic resin.

In the step (c), the green body is sintered at atmospheric pressure at a temperature of 2000 to 2200 캜, thereby producing a silicon carbide sintered body.

Further, prior to the step (c), the method further comprises degreasing the shaped body by heating the shaped body to a temperature of 600 to 1000 ° C. The present invention further provides a method for producing a silicon carbide sintered body.

In addition, the present invention proposes a silicon carbide sintered body produced by the above manufacturing method in another aspect of the invention.

Further, the present invention proposes a silicon carbide sintered body having a relative density of 97.3% or more.

According to the present invention, in producing a silicon carbide sintered body by pressureless sintering, the densified silicon carbide sintered body having a high relative density of at least 97.3% is manufactured by optimizing the amount of boron carbide (B ₄ C) and carbon added .

1 is a flow chart of a method of manufacturing a fully densified silicon carbide sintered body according to the present invention.
Fig. 2 is a graph showing relative density versus the theoretical density of molding density after uniaxial pressing in Examples 1 and 2 and Comparative Examples 1 to 4 of the present invention.
FIG. 3 is a graph showing relative density versus the theoretical density of sintered compacts after vacuum sintering at 2070 ° C. for 2 hours in Examples 1 and 2 and Comparative Examples 1 to 4.
4 is a graph showing relative density versus the theoretical density of sintered compacts after vacuum sintering at 2160 ° C for 2 hours in Examples 1 and 2 and Comparative Examples 1 to 4.
5 is a scanning electron microscope (SEM) image showing the cross-sectional microstructure of the sintered body after vacuum sintering at 2160 ° C for 2 hours in Examples 1 and 2 and Comparative Example 4 of the present application.
6 is a graph showing the results of measurement of thermal conductivity of a sintered body specimen vacuum-sintered at 2160 ° C for 2 hours in Example 2 and Comparative Examples 2 and 3 according to temperature.

In the following description of the present invention, a detailed description of known functions and configurations incorporated herein will be omitted when it may make the subject matter of the present invention rather unclear.

Embodiments in accordance with the concepts of the present invention can make various changes and have various forms, so that specific embodiments are illustrated in the drawings and described in detail in this specification or application. It should be understood, however, that the embodiments according to the concepts of the present invention are not intended to be limited to any particular mode of disclosure, but rather all variations, equivalents, and alternatives falling within the spirit and scope of the present invention.

The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. The singular expressions include plural expressions unless the context clearly dictates otherwise. In this specification, the terms " comprises ", or " having ", or the like, specify that there is a stated feature, number, step, operation, , Steps, operations, components, parts, or combinations thereof, as a matter of principle.

Hereinafter, the present invention will be described in detail.

The present invention maximizes the densification of the sintered body by optimizing the addition amounts of typical boron carbide and carbon among the sintering aids used in the conventional pressure sintering so as to produce sintered silicon carbide excellent in thermal properties such as thermal conductivity and thermal durability through pressure sintering I would like to propose a method.

(A) a silicon carbide (SiC) powder, boron carbide (B ₄ C) and a carbonaceous additive are weighed, mixed and crushed to obtain 90 to 96% by weight of silicon carbide; 1 to 5% by weight of boron carbide; And 3 to 5% by weight of carbon (C); (b) preparing a shaped body from the ceramic mixed powder; And (c) sintering the formed body at a temperature of 2000 to 2400 캜.

In the step (a), a step of preparing a ceramic raw material powder for producing a sintered body includes: 90 to 96% by weight of silicon carbide; 1 to 5% by weight of boron carbide; (SiC) powder, boron carbide (B ₄ C) and the carbon-based additive are weighed, mixed and pulverized to obtain a mixed powder containing 3 to 5% by weight of carbon (C)

The carbon-based additive is a component which serves as a carbon source for providing carbon (C) as a sintering aid, and is preferably a polymer resin or graphite capable of decomposing by heating in a sintering step such as a phenol resin to generate carbon, Carbon black, activated carbon, and the like.

Next, the step (b) is a step of producing a molded body using the ceramic mixed powder.

The molding method for producing the molded article in this step is not particularly limited, and for example, this step can be carried out by using the press molding method. The press molding is a method in which a molded body having a desired shape is obtained by, for example, filling and pressurizing the ceramic mixed powder into a mold, and is suitable for obtaining a molded body having a complicated shape.

Further, in this step, CIP (Cold Isostatic Press) molding can be additionally performed after performing normal press molding such as uniaxial pressing if necessary. For example, after the ceramic mixed powder is provided in a conventional press molding, the obtained molded article is pressed using a CIP molding machine. The CIP molding can arrange the press-molded article in a rubber mold having the same shape as the press mold, press uniformly in all directions up, down, left, and right by means of a medium such as water, thereby making it possible to obtain a high-density molded article.

In the step (c), the compact is sintered at a temperature of 2000 to 2400 ° C.

That is, in this step, in order to prevent the decomposition of silicon carbide, a non-oxidizing atmosphere (a vacuum atmosphere, a reducing gas atmosphere, an inert gas (for example, nitrogen gas) Atmosphere, etc.).

 Meanwhile, a degreasing step for removing the organic binder added for the production of the molded body may be additionally carried out by heating the shaped body in a non-oxidizing atmosphere at a temperature of 600 to 1000 ° C, if necessary, before performing the normal pressure sintering in this step have.

When the silicon carbide sintered body obtained through steps (a) to (c) contains a lot of free carbon, the silicon carbide sintered body is heat-treated at a temperature of 400 to 1000 ° C in the air Free carbon can be removed. Here, the free carbon means carbon which is not bound by a chemical bond in the crystal structure of silicon carbide or boron carbide.

According to the manufacturing method of the silicon carbide sintered body according to the present invention as described above, the sintered silicon carbide sintered body can be produced by optimizing the addition amount of boron carbide (B ₄ C) and carbon, Densified silicon carbide sintered body having a high density can be produced.

Hereinafter, the present invention will be described in more detail with reference to preferred embodiments. The embodiments presented are only a concrete example of the present invention and are not provided for the purpose of limiting the scope of the present invention.

<Examples> Preparation of silicon carbide sintered body by pressureless sintering and densification of sintered body

The sintering pressureless sintered silicon carbide was manufactured according to one example of the method of producing the silicon carbide sintered body according to the present invention shown in FIG. 1, and the properties such as the microstructure and thermal conductivity of each sintered specimen were investigated following the densification behavior according to the sintering assistant. Atmospheric pressure sintered silicon carbide material is a material which is mainly sintered with silicon carbide and sintered at a temperature of 2000 ℃ or higher by using a small amount of sintering auxiliary such as B ₄ C or C because high heat conductivity and high temperature strength are required to be applied to a heat exchanger tube .

In order to examine the sintering characteristics of the pressureless sintered silicon carbide and the sintering characteristics according to the sintering temperature, Comparative Examples 1 to 4, in which the sintering additives B ₄ C and C were added at a ratio of 5 mass% The molding densities after uniaxial pressing and the sintered densities after normal pressure sintering at 2070 ° C and 2160 ° C were evaluated for the compositions of Examples 1 and 2, respectively. In the composition, C was added in the form of phenolic resin, and the composition was calculated assuming that the amount of residue was 50%.

Pressure sintering  Molding / sintering density values according to sintering additive amount and sintering temperature of silicon carbide Composition (% by mass) Forming density Sintered density (2070 캜) Sintered density (2160 ° C) Serial Number SiC B ₄ C C Forming density
(g / cm ³⁾ Relative density
(%) Sintered density
(g / cm ³⁾ Relative density
(%) Sintered density
(g / cm ³⁾ Relative density
(%) Comparative Example 1 100 0 0 1.64 50.9 1.74 54.0 1.67 51.9 Comparative Example 2 95 5 0 1.59 50.1 1.75 55.1 1.74 54.8 Comparative Example 3 95 0 5 1.73 55.4 2.17 69.5 2.01 64.4 Comparative Example 4 94 5 One 1.65 52.3 2.62 83.0 2.79 88.4 Example 1 92 5 3 1.68 53.9 3.04 97.5 3.10 99.4 Example 2 90 5 5 1.71 55.5 3.00 97.3 3.05 99.0

Table 1 shows the molding density and sintering density according to the composition of the SSC material and the sintering temperature. Molding density was calculated by calculating the volume from the diameter and thickness of the specimen and measuring the mass of the specimen. The relative density is a value obtained from the composition density and the percentage of the sintered density value based on the theoretical density using the mixing ratio from each composition.

Referring to Table 1 and FIG. 2 to FIG. 4, it was revealed that B ₄ C plays a role as a sintering aid during the sintering process when the phenolic resin is contained in the composition and the molding density is secured during the press molding. For example, in the case of a composition in which C or B ₄ C is added singly (Comparative Example 2, Comparative Example 3), the sintered density is not significantly changed from the molding density.

On the other hand, among the specimens having high molding densities, the relative density of 99% or more in the composition including B ₄ C was present (Examples 1 and 2).

FIG. 5 is a scanning electron microscope (SEM) showing the cross-sectional microstructure of the sintered body after vacuum sintering at 2160 ° C. for 2 hours in Examples 1 and 2 and Comparative Example 4 of the present invention, The sintered bodies of Examples 1 and 2, which were confirmed to have a density, showed almost no pores, unlike the sintered bodies of Comparative Example 4.

6 is a graph showing the results of measurement of thermal conductivity of a sintered body specimen vacuum-sintered at 2160 ° C for 2 hours in Example 2 and Comparative Examples 2 and 3. As shown above, The sintered bodies of Example 2 having significantly higher sintered densities than those of Examples 2 and 3 were found to have significantly higher thermal conductivity as expected.

Claims (7)

(a) Weighing silicon carbide (SiC) powder, boron carbide (B ₄ C) and a carbon-based additive, mixing and pulverizing, 90 to 96% by weight of silicon carbide; 1 to 5% by weight of boron carbide; And 3 to 5% by weight of carbon (C);
(b) preparing a shaped body from the ceramic mixed powder; And
(c) sintering the formed body at a temperature of 2000 to 2400 캜 under atmospheric pressure. The method according to claim 1,
Wherein the carbon-based additive is at least one selected from the group consisting of a polymer resin, graphite, carbon black, and activated carbon. 3. The method of claim 2,
Wherein the polymer resin is a phenolic resin. The method according to claim 1,
Wherein the shaped body is sintered at atmospheric pressure at a temperature of 2000 to 2200 ° C in the step (c). The method according to claim 1,
Further comprising degreasing the shaped body by heating the shaped body to a temperature of 600 to 1000 캜 before performing the step (c). A silicon carbide sintered body produced by the manufacturing method according to any one of claims 1 to 5. The silicon carbide sintered body according to claim 6, wherein the silicon carbide sintered body has a relative density of 97.3% or more.

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