KR102414539B1 - A SiC powder, SiC sintered body and Manufacturing method of the same - Google Patents

Abstract

The present invention comprises the steps of preparing a silicon carbide raw material and a sintering aid raw material into a synthetic powder by a mechanical alloying process; and sintering the synthetic powder, wherein the sintering aid is at least one selected from the group consisting of Al-C-based, Al-B-C-based and B-C-based. It relates to a silicon carbide sintered compact, which is densified while being sintered at a low temperature, and it is possible to manufacture a silicon carbide sintered compact having high strength and electrical conductivity.

Description

Silicon carbide powder, silicon carbide sintered body, and manufacturing method thereof {A SiC powder, SiC sintered body and Manufacturing method of the same}

The present invention relates to a silicon carbide powder having high strength and electrical conductivity, a silicon carbide sintered body, and a manufacturing method thereof, and more particularly, to a silicon carbide powder, a silicon carbide sintered body that is densified while sintered at a low temperature, and has high strength and electrical conductivity and to a method for manufacturing the same.

Silicon carbide (SiC) is a reinforcing material having a high tensile modulus. If alumina (Al ₂ O ₃ ) is representative of oxide ceramics, silicon carbide can be said to be representative of non-oxide ceramics.

Silicon carbide has excellent physical properties, such as mechanical properties representing wear resistance, thermal properties representing high temperature strength and creep resistance, and chemical resistance representing oxidation resistance and corrosion resistance, etc. is widely used in 'mechanical seals', 'bearings', 'various nozzles', 'hot cutting tools', 'fireproof plates', 'abrasives', 'reducing materials for steel making', 'arrestors', etc.

However, the manufacturing cost is very high because the process of manufacturing the silicon carbide sintered body is not simple or easy, and therefore there is a limit that it cannot be used more actively. .

In manufacturing such a silicon carbide sintered body, a sintering aid is essentially used. As such a sintering aid, a yttria-alumina series, a metal/iron/aluminum mixture, a beryllium compound, a boron compound, etc. are used.

However, even in the case of using such a sintering aid, in manufacturing a silicon carbide sintered body having excellent physical properties at about 1600 ° C. .

In particular, as a method for producing a silicon carbide sintered compact having excellent high temperature strength by the current liquid phase sintering method, high results have been reported (Kim et al. Acta Mater., 2007), and the sintered compact is sintered at 2000° C. for 6 hours. and Sc ₂ O ₃ -Ru ₂ O ₃ -AlN was used as a sintering aid, and the tensile strength at room temperature was 644 MPa and the tensile strength at 1600° C. was measured to be 600 MPa.

Silicon carbide ceramics manufactured by liquid phase sintering at a lower temperature showed a sharp decrease in strength below 1500℃ in many cases. For example, when using an Al ₂ O ₃ -Y ₂ O ₃ sintering aid, sintering at 1950℃ It is possible, but there was a problem in that a strong plastic deformation was observed with a decrease in strength when the flexural strength was measured at 1400°C (AL Ortiz et al., J. Europ. Ceram. Soc., 24, 3245-3249 (2004)).

In addition, solid-phase sintered silicon carbide using B ₄ C and C as sintering aids maintained superior strength than room temperature up to 1500°C, but there was a problem in that a high sintering temperature of 2150°C was required for densification (G. Magnani et al. ., J. Europ. Ceram. Soc., 21, 633-638 (2001)).

That is, the silicon carbide sintered compact showing excellent high-temperature physical properties with little decrease in strength up to 1500° C. still has a problem that the sintering temperature is very high and requires a long sintering holding time.

In particular, a high sintering temperature requires a lot of energy, which has a problem that leads to an increase in the manufacturing cost of the silicon carbide sintered body. , Accordingly, there is an urgent need for the development of a densified silicon carbide sintered body while being sintered at a low temperature.

In addition, recently, research results on a silicon carbide sintered body having high electrical conductivity have been actively reported.

Silicon carbide having such high electrical conductivity is expected to be utilized in various fields such as high-temperature heating elements and high-energy devices.

For example, it has been reported that the resistivity value is reduced to 1.8×10 ^-4 Ω·cm through a method of adding TiN having high electrical conductivity to SiC as a secondary phase, but in this case, the coefficient of thermal expansion with the secondary phase Residual stress problems may occur due to the difference, and there is a disadvantage that sintering is required for a relatively long time at high temperature and high pressure with sintering conditions of 2000° C., 40 MPa, and 3 hours.

Therefore, there is a demand for the development of silicon carbide powders and sintered compacts that are sintered for a short time at a lower temperature and pressure than before, and exhibit high electrical conductivity while being densified.

The problem to be solved by the present invention is to solve the problems of the prior art described above, and to provide a silicon carbide powder, a silicon carbide sintered body, and a method for manufacturing the same, which are densified while sintered at a low temperature, and have high strength and electrical conductivity.

Objects of the present invention are not limited to the objects mentioned above, and other objects not mentioned will be clearly understood by those skilled in the art from the following description.

In order to solve the above-mentioned problems, the present invention provides a silicon carbide sintered body including a sintering aid, wherein the sintering aid contains Al, and the silicon carbide sintered body contains 0.97 to 4.38 wt% of Al inside the grains. It provides a silicon carbide sintered body comprising.

In addition, the present invention provides a silicon carbide sintered compact further comprising 0.1 wt% or more of B in the grain (grain) of the silicon carbide sintered compact.

In addition, the present invention provides a silicon carbide sintered body, characterized in that the specific resistance value of the silicon carbide sintered body is 1 ~ 10 ^-4 Ω·cm.

In addition, the present invention comprises the steps of preparing a silicon carbide raw material and a sintering aid raw material into a synthetic powder by a mechanical alloying process; and sintering the synthetic powder, wherein the sintering aid is at least one selected from the group consisting of Al-C-based, Al-B-C-based and B-C-based It provides a method of manufacturing a sintered silicon carbide body .

In addition, the present invention comprises the steps of preparing the silicon carbide raw material and the sintering aid raw material into a synthetic powder by a mechanical alloying process, mixing the silicon carbide raw material and the sintering aid raw material; And it provides a method of manufacturing a silicon carbide sintered compact, characterized in that the step of manufacturing a mixture including the silicon carbide raw material and the sintering aid raw material into a synthetic powder by a mechanical alloying (mechanical alloying) process.

In the present invention, the silicon carbide raw material includes Si and a first carbon source, and the sintering aid raw material includes at least one material selected from the group consisting of Al, B, and B ₄ C and a second carbon source. It provides a method for manufacturing a silicon carbide sintered compact.

In addition, the present invention provides a method for producing a silicon carbide sintered body, characterized in that the sintering temperature of the sintering step is 1550 to 2100 ℃.

In addition, the present invention provides a method for producing a silicon carbide sintered body, characterized in that the content of the sintering aid is 2 to 13wt%.

In addition, the present invention synthesizes at least one material selected from the group consisting of Si, Al, B, and B ₄ C and a carbon source by a mechanical alloying process, and a SiC-based synthesis in which a sintering aid is distributed therein. preparing a powder; and sintering the synthetic powder, wherein the sintering aid is at least one selected from the group consisting of Al-C-based, Al-BC-based and BC-based. It provides a method of manufacturing a sintered silicon carbide body .

In addition, the present invention provides the step of synthesizing at least one material selected from the group consisting of Si and Al, B, and B ₄ C and a carbon source by a mechanical alloying process, Si and Al, B, and Mixing at least one material selected from the group consisting of B ₄ C and a carbon source; And it provides a method of manufacturing a silicon carbide sintered body, characterized in that the step of manufacturing the mixture into a synthetic powder by a mechanical alloying (mechanical alloying) process.

In addition, the present invention provides a method for producing a silicon carbide sintered body including each of the SiC-based synthetic powder contains 0.5 wt% or more of Al and 0.1 wt% or more of B therein.

In addition, the present invention provides a method for producing a silicon carbide sintered body, characterized in that the sintering temperature of the sintering step is 1550 to 2100 ℃.

In addition, the present invention provides a silicon carbide sintered body, characterized in that the specific resistance value of the silicon carbide sintered body is 1 ~ 10 ^-4 Ω·cm.

In the present invention as described above, it is possible to manufacture a sintered silicon carbide body that is densified while sintered at a low temperature and has high electrical conductivity.

In addition, in the present invention, it is possible to secure a densified silicon carbide sintered compact with only a small amount of 2 to 13wt% of a sintering aid, thereby manufacturing a silicon carbide sintered compact having a high strength value.

1 is a flowchart illustrating a method for manufacturing a silicon carbide sintered body according to the present invention.
2A to 2C are graphs showing XRD data of SiC powder synthesized under various compositions and milling conditions.
Figure 3a is a TEM image of the powder synthesized according to the SiCA13C1 condition, Figure 3b is a TEM image of the powder synthesized according to the SiCAl7C1 condition.
4 is a graph showing the particle size distribution of the synthesized powder.
5 is a HR-TEM (High Resolution-Transmission Electron Micrograph) of the powder synthesized according to the SiCAL7C1 condition.
6 is a TEM image of the powder synthesized according to the SiCAl5C1 condition.
7A is a TEM image of silicon carbide powder sintered according to the SiCA17C1 condition, and FIG. 7B is an EDS mapping result of Al element in the silicon carbide powder sintered according to the SiCAI7C1 condition.
Figure 8a is an image showing the microstructure of silicon carbide powder sintered under the conditions of 1800 ° C and 20 MPa by applying the Al3C1 composition, 8b is the microstructure of the specimen sintered at 1650 ° C. and 20 MPa by applying the Al12.5C1 composition It is an image shown.
9 is a view showing the SEM and EDS analysis results of the specimens sintered at various temperatures while increasing the content of the sintering aid.

Advantages and features of the present invention and methods of achieving them will become apparent with reference to the embodiments described below in detail in conjunction with the accompanying drawings. However, the present invention is not limited to the embodiments disclosed below, but will be implemented in a variety of different forms, and only these embodiments allow the disclosure of the present invention to be complete, and common knowledge in the technical field to which the present invention belongs It is provided to fully inform the possessor of the scope of the invention, and the present invention is only defined by the scope of the claims.

With reference to the accompanying drawings will be described in detail for the implementation of the present invention. Irrespective of the drawings, like reference numbers refer to like elements, and "and/or" includes each and every combination of one or more of the recited items.

Although the first, second, etc. are used to describe various elements, these elements are not limited by these terms, of course. These terms are only used to distinguish one component from another. Accordingly, it goes without saying that the first component mentioned below may be the second component within the spirit of the present invention.

The terminology used herein is for the purpose of describing the embodiments and is not intended to limit the present invention. In this specification, the singular also includes the plural unless specifically stated otherwise in the phrase. As used herein, “comprises” and/or “comprising” does not exclude the presence or addition of one or more other components in addition to the stated components.

Unless otherwise defined, all terms (including technical and scientific terms) used herein may be used with the meaning commonly understood by those of ordinary skill in the art to which the present invention belongs. In addition, terms defined in a commonly used dictionary are not to be interpreted ideally or excessively unless clearly defined in particular.

Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings.

1 is a flowchart illustrating a method for manufacturing a silicon carbide sintered body according to the present invention.

Referring to FIG. 1 , the method for manufacturing a silicon carbide sintered body according to the present invention includes mixing a silicon carbide raw material and a sintering aid raw material (S100).

The silicon carbide raw material may be understood as a starting material for manufacturing silicon carbide, and the sintering aid raw material may be understood as a starting material for manufacturing a sintering aid.

In addition, the silicon carbide raw material includes Si and a first carbon source, and the sintering aid raw material may include at least one material selected from the group consisting of Al, B, and B ₄ C and a second carbon source. .

In this case, the first carbon source and the second carbon source may be solid carbons such as graphite, graphite, carbon black, activated carbon, etc. However, the type of the carbon source is not limited in the present invention.

Next, the method for manufacturing a silicon carbide sintered body according to the present invention includes the step of preparing a mixture including the silicon carbide raw material and the sintering aid raw material into a synthetic powder by a mechanical alloying process ( S110).

That is, after preparing a mixture by mixing the silicon carbide raw material and the sintering aid raw material, a synthetic powder may be manufactured by a mechanical alloying process.

In this case, in the present invention, through the mechanical alloying process, the SiC-based synthetic powder in which the sintering aid is uniformly distributed therein can be manufactured.

Meanwhile, in the present invention, for convenience of explanation, it is described that steps S100 and S110 are sequentially performed, but, unlike this, steps S100 and S110 may be performed simultaneously.

That is, the mixing process of the silicon carbide raw material and the sintering aid raw material in step S100 may be simultaneously performed in the step of manufacturing the synthetic powder by the mechanical alloying process of step S110. Therefore, the present invention In the S100 and S110 steps, the silicon carbide raw material and the sintering aid raw material are manufactured into a SiC-based synthetic powder in which the sintering aid is uniformly distributed therein by a mechanical alloying process. have.

In this case, the mechanical alloying process may use a planetary mill, an attrition mill, a Spex mill, and a high energy ball mill operating on a similar principle, but , the type of the mechanical alloying process is not limited in the present invention.

Meanwhile, in the present invention, it is preferable to use a ball and a jar made of SiC material and a jar made of SiC material as the balls and jars used in the mechanical alloying process, respectively.

That is, by using a ball made of SiC and a jar made of SiC, it is possible to prevent mixing of impurities introduced from the ball and jar in the milling process.

However, in the present invention, the material of the ball and the jar is not limited. For example, in the case of using a ball of WC material, WC is added to the synthesized SiC-based powder after milling. Although mixed, it was confirmed that even when this powder was used, it exhibited similar low-temperature sintering behavior and high electrical conductivity to the powder synthesized using SiC jars and balls.

On the other hand, the chemical reaction formula expected in the synthetic powder manufacturing step is as follows.

Si + C → SiC (Scheme 1)

According to Scheme 1, silicon carbide according to the present invention is synthesized, and at this time, the sintering aids added by high milling energy are relatively homogeneously mixed into the synthesized silicon carbide.

That is, in the present invention, by the step of preparing the synthetic powder, silicon carbide, that is, SiC is synthesized, and also a sintering aid, for example, Al-C, is relatively uniformly mixed into the synthesized SiC, and then By the process of, the sintering process of the silicon carbide powder mixed with the sintering aid, a silicon carbide sintered body having high electrical conductivity can be manufactured.

On the other hand, as described above, the sintering aid raw material may include at least one material and a second carbon source selected from the group consisting of Al, B, and B ₄ C. Therefore, in the present invention, the sintering aid is Al- It corresponds to at least one consisting of C-based, Al-BC-based, and BC-based, and may correspond to, for example, Al-C, Al-BC, Al-B ₄ CC, BC and/or B ₄ CC.

The sintering aid may be relatively uniformly distributed in the synthesized silicon carbide powder, and in this case, the content of the sintering aid in the synthetic powder may be 1.5 to 15 wt%.

That is, in the present invention, the silicon carbide raw material and the sintering aid raw material are mixed, and the synthetic powder is prepared by a mechanical alloying process. In this case, since the sintering aid can be prepared to be relatively uniformly distributed inside the silicon carbide powder, it is possible to reduce the amount of the sintering aid or achieve densification of the silicon carbide at a lower temperature or a lower pressure than before.

Therefore, as described above, the content of the sintering aid in the synthetic powder is 2 to 13wt%, and a densely sintered silicon carbide sintered body can be manufactured through a small amount of the sintering aid.

Meanwhile, steps S100 and S110 according to the present invention may be expressed as follows.

In the above, for convenience of explanation, in step S100, the first carbon source and the third carbon source are separately described, but when they are mixed, they may correspond to one carbon source.

Therefore, the step S100 may be expressed as a step of mixing Si and at least one material selected from the group consisting of Al, B, and B ₄ C and a carbon source, and the carbon source is a solid phase such as graphite, carbon black, activated carbon, etc. It may be a carbon type of.

In this case, in step S110 according to the present invention, a mixture containing at least one material selected from the group consisting of Si and Al, B, and B ₄ C and a carbon source is prepared as a synthetic powder by a mechanical alloying process It can be expressed in stages.

In addition, as described above, step S100 and step S110 according to the present invention may be performed simultaneously, and in this case, in the present invention, step S100 and step S110 is selected from the group consisting of Si and Al, B, and B ₄ C It may be expressed as a step of preparing at least one material and a carbon source to be used as a synthetic powder by a mechanical alloying process.

Continuingly, referring to Figure 1, the method of manufacturing a silicon carbide sintered body according to the present invention includes the step of sintering the synthetic powder (S120).

The sintering refers to a process of densifying a molded body made by using powder as a raw material at a high temperature, and densification and particle growth are representative sintering phenomena.

The sintering may be classified into normal pressure sintering, pressure sintering, spark plasma sintering, and the like according to a technical method of densification.

Atmospheric pressure sintering is a method of densifying the compact by heat treatment at a high temperature in atmospheric air or inert atmosphere as a normal sintering process. It refers to a method of densification at low temperature by flowing a high current pulse at the same time as it is applied.

In the present invention, the step of sintering the synthetic powder may use a normal pressure sintering method, a pressure sintering method, a spark plasma sintering method, however, in the present invention, The sintering method is not limited.

At this time, the sintering temperature of the sintering step may be 1550 to 2100 ℃, the sintering atmosphere may be a vacuum, argon (Ar) and nitrogen atmosphere, also, for example, spark plasma sintering (spark plasma sintering) method The reaction can proceed by maintaining it for 5 to 120 minutes.

Thus, it is possible to manufacture the silicon carbide sintered body according to the present invention (S130).

Hereinafter, preferred experimental examples according to the present invention will be described, but the present invention is not limited to the above experimental examples.

[Experimental example]

First, in the present invention, Al, Si, B ₄ C and Carbon black were used as raw materials. That is, as described above, in the present invention, the silicon carbide raw material includes Si and the first carbon source, and the sintering aid raw material is at least one material selected from the group consisting of Al, B, and B ₄ C and the second A carbon source may be included, and a portion of the carbon black may be used as the first carbon source, and another portion may be used as the second carbon source.

Compositions and abbreviations of raw materials used in each experiment are shown in Table 1 below.

In Table 1, for example, "Al3" is the ratio of Al:Si:C as a sintering aid while the ratio of Si:C is fixed to 1:1 for the synthesis of SiC, and the molar ratio of Al:Si:C is the same as that of the compound Al ₄ SiC ₄ Phosphorus was 4:1:4, meaning that the amount was adjusted to 3wt%, and "Al5C1" in "Al5" are Al as a sintering aid while the ratio of Si:C is fixed at 1:1 for the synthesis of SiC. The molar ratio of :Si:C was 4:1:4 and the amount was adjusted to 5wt%. “C1” means that 1wt% of excess carbon is additionally included, and “B1C1” means Si for the synthesis of SiC. While the ratio of :C was fixed at 1:1, it means that the amounts of B ₄ C and C were added by 1wt% each as a sintering aid.

Therefore, in the case of the Al2C1 composition, the actual auxiliary content is 2.17 wt%, and in the case of the Al20C1 composition, the auxiliary content is 12.73 wt%.

Meanwhile, the amounts of Al, C and B ₄ C excluding the amount of SiC among the added sintering aids were separately indicated.

Next, the mixture of the raw material composition as described above was prepared as a synthetic powder by a mechanical alloying process. Specifically, in order to minimize contamination, a planetary mill using a SiC jar and a SiC ball was used at 360 rpm and 400 rpm for 72 hours. was mixed. At this time, the ratio of the balls to the raw material composition powder was 1:6.67, and in order to prevent oxidation of the powder during the milling process, the jar used in the planetary mill was sealed in a glove box in an Ar atmosphere. In addition, the synthesized powder was filtered using a 150 mesh sieve inside the glove box of Ar atmosphere.

Hereinafter, the characteristics of the synthetic powder prepared by the mechanical alloying process will be described.

The degree of contamination from the balls and jars during the milling process is shown in Table 2 below by investigating and calculating the change in the mass of the balls before and after the experiment.

Abbreviation rpm ball contamination SiC (%) Al (%) SiCAL3C1 360 1.93 0.19 400 6.7 0.67 SiCAL7C1 360 2.6 0.26 400 6.3 0.63

Referring to Table 2, as a result of EDS analysis, it was found that the commercial SiC ball contained Al, and its content was about 10 wt%. Therefore, the amount of contamination of Al added during milling was relatively low at about 0.2 to 0.3 wt% when the rotation speed of the planetary mill was 360 rpm, but it was found that the contamination increased to about 0.6 to 0.7 wt% at 400 rpm. On the other hand, the jar is reaction-bonded silicon carbide (RBSC), and there is almost no Al contamination from the jar.

In addition, in order to analyze the phase of the synthesized powder, it was measured under Cu Ka conditions using an X-ray diffraction analyzer, and the microstructure and chemical composition of the powder were observed using a high magnification transmission electron microscope (TEM) with EDS attached. .

In addition, the particle size distribution of the synthesized powder was measured using a particle size analyzer, and the average size of crystal grains present in the powder was measured using an image analyzer (nano measurer).

2A to 2C are graphs showing XRD data of SiC powder synthesized under various compositions and milling conditions.

2a to 2c, for example, Al3C1_360rpm is 3wt% of the Al-Si-C sintering aid having the Al ₄ SiC ₄ composition, the amount of the carbon sintering aid is 1 wt%, and the rpm in the milling process is 360 Al5C1_400rpm means that the amount of Al-Si-C sintering aid having an Al ₄ SiC ₄ composition was adjusted to 5 wt%, the amount of carbon sintering aid was adjusted to 1 wt%, and the rpm in the milling process was controlled to 400 .

2a to 2c, when the content of the sintering aid is changed to 3 to 7wt% or the content of the third carbon source, which is excess carbon, is increased to 0.5 and 1wt%, in addition, the rpm in the milling process is 360 to 400 No significant difference was found in the XRD data even when the powder was changed to

The mechanism in which Si and C are synthesized into SiC through mechanical alloying is that the C atom directly replaces the Si site and exists in the form of amorphous Si containing C. As the milling process proceeds, the particles becomes finer, and chemically active defect sites increase to form SiC.

As a result of XRD analysis, Al, B ₄ C and carbon peaks were not seen, which is thought to be because the components were uniformly distributed in SiC due to high energy milling.

In addition, since SiC balls and SiC jars were used, other secondary phases due to contamination were not observed. The SiC peak has a broad shape, because the crystallite size was greatly reduced through high energy milling. As a result of calculating the crystallite size of the powder synthesized at 360 and 400 rpm using Sherrer's formula, it was 17.6 and 12.7 nm, respectively.

In addition, until the Al12.5C1 composition, no significant change in powder properties was observed with the increase in the amount of sintering aid, but in the case of the Al15C1 composition, powder agglomeration was observed. difficulties appeared. However, as the result of sintering the obtained powder, the sintering density at 1550° C. increased as the content of the auxiliary increased. Therefore, in the present invention, it is preferable that the amount of the Al-Si-C-based sintering aid is 20 wt% or less, that is, the amount of the total sintering aid is 13 wt% or less.

3a is a TEM image of the powder synthesized according to the SiCAl3C1 condition, and FIG. 3b is a TEM image of the powder synthesized according to the SiCAl7C1 condition.

Referring to FIGS. 3A and 3B , the particles were spherical, and the primary SiC particles of 10 to 20 nm and Si-C phases in an amorphous state were agglomerated to have a particle size of about 100 nm. This agglomeration is thought to be due to cold welding during high energy ball milling. In addition, the areas formed as dark spots inside the powder indicate that the SiC was partially crystallized. At this time, when the Al content was changed with the Al3C1 and Al7C1 compositions, no difference in particle size was observed.

4 is a graph showing the particle size distribution of the synthesized powder.

Referring to FIG. 4 , a bimodal form in which a primary peak in the region of 100 to 200 nm and a secondary peak around 1 μm exist was shown. It was found that most of the particle sizes were less than 300 nm.

5 is a HR-TEM (High Resolution-Transmission Electron Micrograph) of the powder synthesized according to the SiCAL7C1 condition.

Referring to FIG. 5 , it can be seen that SiC particles crystallized inside the amorphous Si and C matrix phases. Particles as small as 2 nm in size of crystallized particles were also observed. In addition, it was found that the surface of the particles having a size of about 100 nm exists in an amorphous state. Due to the amorphous phase on the surface, the reaction interface increased with high sintering driving force and diffusion rate, which can promote low-temperature sintering of SiC.

6 is a TEM image of the powder synthesized according to the SiCAl5C1 condition, and Table 3 below shows the element content according to the points in FIG.

point Elemental content (wt%) C O Al Si 003 37.3 1.57 1.94 59.2 004 40.24 2.48 1.83 55.44 005 29.91 2.28 1.69 66.12 006 42.88 3.93 2.17 51.01

Referring to FIG. 6 and Table 3, it can be seen that, in the element content of Al measured in various powders synthesized according to the Al5C1 condition, there is no significant deviation in the Al content between the various powders. It is well known that the sintering properties of the powder are improved when the sintering aid is uniformly distributed inside the powder. When making oxide powder by sol-gel method or co-precipitation method, if the sintering aid is uniformly distributed in the oxide powder, densification is completed at a lower temperature than when the powder and sintering aid are separately synthesized and mixed later. this is being reported

It is known that the solubility limit of Al and B in SiC is 0.5wt% and 0.1wt%, respectively, but the SiC powder synthesized by the above method may contain Al and B above the solidsolution limit therein as shown in FIG. 6 and Table 1, , which can be said to be one of the main features of the present invention.

Therefore, in the present invention, due to the high Al and B content present in the SiC powder, it exhibits excellent sintering properties at low temperature even with a small amount of sintering aid and has high electrical conductivity.

Through the synthetic powder as described above, the following sintering process was performed.

That is, in order to sinter the synthetic powder, the synthesized powder of each composition is put in a graphite mold and using a spark plasma sintering method (temperature increase rate of 100° C./min) in an Ar atmosphere of 1 atm 20 MPa to 40 MPa It was sintered for 30 minutes at a temperature of 1550 to 2100 °C under uniaxial pressure.

Hereinafter, characteristics of the silicon carbide sintered powder produced through the sintering process will be described.

The density of the silicon carbide sintered specimen was obtained using the Archimedes method, and the theoretical density of the specimen was obtained using the rule of mixture, and then the relative density was obtained.

In addition, the microstructure of the silicon carbide sintered body was observed using a scanning electron microscope (SEM). The surface of the sintered body was polished down to 1 μm to reveal the microstructure. For strength measurement, the specimen was processed into a bar shape of 1.5 × 2 × 25 mm, and then the strength was measured using six specimens using a four-point bending strength machine.

Table 4 below shows the relative densities of the densified specimens under various compositions and sintering conditions.

If there is no indication of pressure and time, sintering was performed at a pressure and holding time of 20 MPa and 30 minutes.

Referring to Table 4, in the case of a composition in which 3, 5, 7, 10 and 12.5 wt% of Al ₄ SiC ₄ is added and 1 wt% of excess carbon is additionally added based on the Al 4 SiC 4 composition, the highest sintering occurs when sintering under a pressure of 20 MPa. The temperatures representing the density were 1800, 1750, 1650, 1650 and 1600° C., respectively. When the sintering temperature is lower than this, densification does not completely occur, and when the sintering temperature is high, a phenomenon in which the density decreases again due to grain growth due to oversintering was observed. When the Al content was 0.59 wt% or less, a dense sintered body could not be obtained even when the sintering temperature, pressure, and holding time were increased to 2100° C., 40 MPa, and 2 hours. On the other hand, in the case of Al12.5C1 composition, as the sintering pressure was increased from 20 MPa to 40 MPa and the holding time was increased from 30 minutes to 4 hours, a dense sintered body was obtained at 1550°C.

In the case of Al12.5C1, Al15C1 and Al20C1 compositions, the relative densities continuously increased to 78.0, 83.4 and 90.4% after sintering at 1550 oC and 20 MPa. Even the composition was found to be effective.

High temperature sintering increases the process cost, but as will be described later, sintering at high temperature can significantly improve the electrical conductivity of the specimen. Under the pressurization condition of 20 MPa, a dense sintered body could not be obtained at 1550°C or lower, and problems in mass production could occur at 2100°C or higher. Accordingly, in the present invention, the sintering temperature in the sintering step is 1550 to 2100° C. under the pressure sintering condition of 20 MPa, which has a critical significance. However, it is self-evident that the minimum sintering temperature can be decreased as the sintering pressure is increased.

In addition, when the amount of sintering aid is fixed to 3 wt% based on Al ₄ SiC ₄ and the content of excess carbon is increased to 0, 0.5 and 1 wt%, the relative densities are 94.5, 94.5 and 96.1%, and 1 wt% of excess carbon is It was found that the sintering of SiC was further promoted. This is thought to be because the addition of excess carbon removes SiO ₂ on the surface of the SiC powder. In the case of Al5C2 composition containing 2wt% of excess carbon, the relative density was lower than that of Al5C1 composition containing 1wt% of excess carbon. Therefore, in the present invention, the mixture preferably contains excess carbon in the range of 0.5 to 2 wt%. On the other hand, the initial sintering stage, in which 3 to 5% shrinkage occurs, is a stage in which fine particles with a size of several tens of nm that are severely distorted and pulverized due to high energy ball milling are rotated and rearranged. In addition, since the rearrangement of particles in the initial sintering stage affects both mid-term and late sintering through mass transport, the initial sintering stage is considered to be very important. As a result of comparing the sintering properties of the powder synthesized at 360 rpm and 400 rpm, the sintering temperature of the powder synthesized at 360 rpm under the pressure condition of 20 MPa was about 50°C lower. When the rpm in the milling process is lower than 360 rpm, it can be seen from XRD analysis that residual Si is present even after 3 days of milling. However, in the present invention, the rpm and milling time in the milling process are not limited, and it is preferable to include process conditions in which residual Si is not present or a small amount is present after milling as a range.

7A is a TEM image of silicon carbide powder synthesized according to the SiCA17C1 condition, and FIG. 7B is an EDS mapping result of Al element in the silicon carbide powder synthesized according to the SiCAI7C1 condition.

Referring to FIGS. 7A and 7B , it can be seen that Al, which is a sintering aid, is spread very evenly inside the SiC powder.

In addition, referring to Table 1, through the very uniform distribution of the sintering aid along with the formation of very fine powder and amorphous Si-C obtained through mechanical alloying, 5wt% at 1650℃-20MPa sintering conditions It was possible to obtain a densified SiC sintered compact with a relative density of 97% or more using only the inner and outer Al and C sintering aids.

Figure 8a is an image showing the microstructure of silicon carbide powder sintered under the conditions of 1800 ° C and 20 MPa by applying the Al3C1 composition, 8b is the microstructure of the specimen sintered at 1650 ° C. and 20 MPa by applying the Al12.5C1 composition It is an image shown.

First, referring to FIG. 8a, when 3wt% of Si ₄ AlC ₄ composition and 1 wt% of C are included as a sintering aid, sintering proceeds even at a relatively low temperature of 1800° C. As a result, the dense SiC grain size is about 3 μm. was observed as In FIG. 8b , when the amount of the sintering aid was increased to 12.5 wt% of Si ₄ AlC ₄ composition and 1 wt% of C and densified at 1650° C., the grain size was reduced to 0.5 μm due to the low sintering temperature.

It is known that during sintering, Al is dissolved in SiC to promote a phase change from β-SiC to α-SiC and at the same time promote grain growth in a plate shape with a high ratio.

On the other hand, the 4-point flexural strength value of the specimen obtained by sintering Al3C1 powder under the condition of 1800℃-20MPa for 30min was 651MPa. In this case, the amount of sintering aid added to the specimen is about 2.8 wt% of Al and 1 wt% of C, etc.

That is, referring to Table 1, as a result of the present invention, even using only a small amount of sintering aid of 2.8wt% (Al3C1 condition in Table 1), even at a relatively low temperature condition of 1800℃, 20MPa, the relative density reached 97.6%, A densified silicon carbide sintered compact could be obtained, and the resultant specimen exhibited a high strength value of 651 MPa.

In addition, when the total amount of the sintering aid was increased to 5.1 wt% (Al7C1 in Table 1), the relative density reached 97.0% even under the low-temperature sintering conditions of 1650° C. and 20 MPa, thereby securing a densified silicon carbide sintered body.

As described above, in the present invention, it is possible to manufacture a silicon carbide sintered compact sintered at a low temperature and densified while using a relatively small amount of sintering aid of 2 to 5 wt%, thereby producing a silicon carbide sintered compact having a high strength value. .

9 is a view showing the SEM and EDS analysis results of the specimens sintered at various temperatures while increasing the content of the sintering aid. At this time, Figure 9a is the result of the Al3C1 specimen (1800 ℃-20MPa, 30min), Figure 9b is the result of the Al5C1 specimen (1750 ℃-20MPa, 30min), Figure 9c is the Al7C1 specimen (1650 ℃-20MPa, 30min) The results, and Figure 9d is the result of the Al12.5C1 specimen (1600 ℃ -20 MPa, 30 min).

When the Al content in the raw material powder is 1.76, 2.93, 4.1 and 7.33 wt%, the Al content in the sintered SiC grain analyzed by EDS is partially segregated into the grain boundary by diffusion during sintering and the original powder Although the content of Al was decreased, it was 0.97, 1.55, 2.58 and 4.38 wt%, respectively.

The following literature may be referred to that 0.5 wt% of Al may be included as a solid solution limit in the SiC grain.

- Tana, H., Tajima, Y. and Kingery, W. D., Solid solubility of aluminum and boron in silicon carbide. Commun. Am. Ceram. Soc., 1982, 65(2), C-27–C-29.

As such, when the powder having a high Al and B content produced as a result of the present invention is sintered, Al and B higher than the original solid solution limit value are present even in the grains present in the sintered body, which is a major feature of the present invention. .

On the other hand, B ₄ C and C have been variously used as sintering aids for SiC, and relatively dense sintered bodies can be obtained when atmospheric sintering is performed at 2050° C. for 2 hours or more with the addition of 1.5-3 wt% of sintering aids. In the case of pressure sintering, the sintering temperature decreases and when a pressure of 20 MPa is applied, sintering conditions of 2200 ° C and 30 minutes are reported when 1 wt% B ₄ C is added, and 2020 ° C., 30 minutes in the case of 1 wt% B and 1 wt% C preparations , 1wt% B ₄ C and 1wt% C are reported under conditions of 1950 ℃, 20 MPa.

However, as shown in Table 4, in the case of the SiC powder manufactured through this experiment, densification was completed when sintering for 2 h at 1800 ° C and 30 MPa using 2 wt% of a sintering aid, It can be seen that densification is possible at temperature, which corresponds to the main feature of the present invention.

Table 5 shows the resistivity values of the densified SiC specimens under various compositions and sintering conditions.

Research to fabricate conductive SiC has been actively conducted in recent years. For example, it has been reported that the specific resistance of a SiC sintered compact sintered in a nitrogen atmosphere using various rare earth metals and AlN sintering aid decreases to 1.5×10 ^-2 Ω·cm, and when yttrium nitrate sintering aid is used, it is reported that 2.8×10 It has been reported that SiC having a very low resistivity of ^-3 Ω·cm can be manufactured.

However, in both cases, a long period of sintering for 6-12 hours was required under a high temperature of 2050° C. and a pressure of 20-40 MPa, and sintering under these harsh conditions causes an increase in production cost.

However, in the case of SiC manufactured according to the method presented in the present invention, the specimen sintered at a temperature of around 1750° C. and a pressure of 20 MPa for 30 minutes also showed a very low specific resistance value of 10 ⁻⁴ Ω·cm.

Referring to Table 5, when Al and C are used as sintering aids, the specific resistance exhibited a value in the range of 10 ^-1 to 10 ^-3 Ω·cm, and as the sintering temperature increases and the amount of the sintering aid decreases, the overall It was found that the resistivity value was lowered. The specimens sintered at 1600°C showed the highest resistivity value among the specimens prepared in the present invention at 10 ^-1 Ω·cm, and in the case of the specimens sintered at 2100°C with the Al1C1 composition, even though complete densification was not achieved, 10 It showed a low resistivity value in the range of ^-3 Ω·cm.

This difference is because as the sintering temperature decreases, the average grain size decreases and the density of grain boundaries acting as an insulator increases.

On the other hand, when sintered at high temperature, the electrical conductivity increases due to the decrease in the density of the grain boundary that acts as an insulator due to grain growth. Therefore, it is possible to control the electrical conductivity by the amount of the sintering aid added and the sintering temperature, which corresponds to the main feature of the present invention.

In addition, in the present invention, in the case of the Al-C composition in which B is not included in the sintering aid, it is understood that a small amount of the sintering aid is used for high electrical conductivity and the sintering temperature is increased to 2100° C. to promote densification and grain growth. can

In the case of B05Al2C1 and B1C1 compositions containing B in the sintering aid, it was found that the specific resistance value was very low in the range of 10 ^-3 to 10 ^-4 Ω·cm even after sintering at a low temperature of 1700-1800 ° C. It was found that when a small amount of B was included in the specimen prepared with

It is reported that the specific resistance of SiC obtained after sintering for 5 hours at 2050°C and 20MPa under Ar atmosphere using 1wt% Al or B as a sintering aid in SiC is 10 ³ to 10 ⁵ Ω·cm, respectively. .

This result was obtained using a sintering aid composition similar to the method presented in the present invention, but showed a resistivity value higher than 10 ⁶ Ω·cm compared to the resistivity value obtained in the present invention.

When a sintering aid is added as in the conventional method, only 0.1 and/or 0.5 wt% of the solubility limit of B and Al, respectively, can be included in SiC, whereas in the case of the specimen manufactured through the present invention, 4.3 wt%, which is significantly higher than this. It is determined that the above Al may be included in the SiC grains, thereby greatly improving electrical conductivity.

In addition, it was found that the electrical conductivity increases as the grain boundaries that interfere with the conductivity are reduced by promoting grain growth at high temperatures. In the present invention as described above, for example, by synthesizing Si, Al, and C by mechanical alloying, it is possible to manufacture a SiC composite powder in which Al as a sintering aid is uniformly distributed therein.

Accordingly, in the present invention, since the sintering aid is uniformly distributed in the inside of the SiC composite powder, and Al and B in a high content that is not possible with the conventional method can be included in the SiC grain, compared to the conventional method, Low temperature sintering and high electrical conductivity are possible.

Therefore, when the present sintering aid is added and a single-phase SiC-based powder is synthesized by mechanical alloying of Si and C, low-temperature sintering is possible and a sintered silicon carbide body having high electrical conductivity can be manufactured.

Although embodiments of the present invention have been described with reference to the above and the accompanying drawings, those of ordinary skill in the art to which the present invention pertains can practice the present invention in other specific forms without changing its technical spirit or essential features. You can understand that there is Therefore, it should be understood that the embodiments described above are illustrative in all respects and not restrictive.

Claims (7)

In the silicon carbide sintered body comprising a sintering aid,
The sintering aid contains Al,
The silicon carbide sintered body contains 0.97 to 4.38 wt% of Al in the grain (grain),
The silicon carbide raw material and the sintering aid raw material are manufactured into synthetic powder by a mechanical alloying process,
Manufactured by sintering the synthetic powder,
A silicon carbide sintered body having a specific resistance value of 1 to 10 ^-4 Ω·cm. The method of claim 1,
The silicon carbide sintered compact further comprises 0.1 wt% or more of B in the grain (grain). delete A method for producing the silicon carbide sintered body according to claim 1,
manufacturing a silicon carbide raw material and a sintering aid raw material into a synthetic powder by a mechanical alloying process; and
sintering the synthetic powder;
The sintering aid is a method of manufacturing a silicon carbide sintered body, characterized in that at least one selected from the group consisting of Al-C-based, Al-BC-based and BC-based. A step of synthesizing Si and at least one material selected from the group consisting of Al, B, and B ₄ C and a carbon source by a mechanical alloying process to prepare a SiC-based composite powder having a sintering aid distributed therein ; and
sintering the synthetic powder;
The sintering aid is a method of manufacturing a silicon carbide sintered body, characterized in that at least one selected from the group consisting of Al-C-based, Al-BC-based and BC-based. 6. The method according to claim 4 or 5,
The sintering temperature of the sintering step is a method of manufacturing a silicon carbide sintered body, characterized in that 1550 to 2100 ℃. 6. The method according to claim 4 or 5,
The method for producing a silicon carbide sintered body, characterized in that the content of the sintering aid is 2 to 13wt%.

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