KR20170044485A - A SiC Slurry and Manufacturing method of the same - Google Patents

Abstract

The present invention relates to silicon carbide slurry having improved dispersibility to be produced at a high concentration, and a manufacturing method thereof. The silicon carbide slurry comprises: silicon carbide synthetic powder; and a dispersant, wherein the content of the dispersant is 0.5 to 2 wt% when the silicon carbide synthetic powder is 100 wt%.

Description

[0001] The present invention relates to a silicon carbide slurry and a method for producing the same,

The present invention relates to a silicon carbide slurry and a method for producing the same, and more particularly, to a silicon carbide slurry which can be produced at a high concentration by improving dispersibility and a method for producing the same.

Silicon carbide (SiC) is a reinforcing material with high tensile strength. If alumina (Al ₂ O ₃ ) is a representative of oxide ceramics, silicon carbide is a representative of non-oxide ceramics.

Silicon carbide is highly utilizable because it has excellent physical properties such as mechanical properties representative of abrasion resistance, thermal properties representing high temperature strength and creep resistance, chemical resistance typified by oxidation resistance and corrosion resistance, and silicon carbide Is widely used for 'mechanical seal', 'bearing', 'various nozzle', 'hot cutting tool', 'fireproof plate', 'abrasive material', 'steelmaking reducing material', 'arrester'.

However, silicon carbide exhibits excellent mechanical properties. However, because of its high hardness, a large amount of diamond abrasive must be used for processing, and the increase in parts cost due to high processing cost is one of the main factors inhibiting the use of silicon carbide materials It is one.

To solve this problem, various near-net shaping processes such as slip casting, gel casting, and freeze casting have been developed after manufacturing high-density SiC slurry.

In order to produce a shaped body having high strength, density and uniformity by a slurry process, it is necessary to prepare a stable slurry having a high concentration and a low viscosity.

It has been reported that other ceramic powders can be produced at a high concentration of 60 vol% or more.

For example, it has been reported that a high concentration slurry of 62 vol% is produced in the case of Al ₂ O ₃ , and a high concentration slurry of 68 vol% is produced in the case of SiO ₂ .

However, in the case of SiC, it is reported that a slurry with a maximum of 57 vol% is produced when using relatively coarse 0.6 ㎛ powder, which is lower than other powders.

This is because SiC is one of the materials with the highest Hamaker constant among the ceramics, and therefore receives a high Van der Walls force when dispersed in water.

The Hamaker constants of various ceramic powders in water were 4.72, 6.57, 0.71, 5.65 and 3.85 for Al ₂ O ₃ , β-Si ₃ N ₄ , SiO ₂ , TiO ₂ and Y ₂ O ₃ , SiC is 11.9, which is much higher than those ceramics (Bergstrom, L., Hamaker constants of inorganic materials, Adv. Colloid Interface Sci., 70, 125-169 (1997).)

Therefore, a variety of researches have been conducted, such as the formation of SiO ₂ by oxidizing the surface to disperse Si ₃ N ₄ or SiC, which is difficult to disperse, or the formation of a thin coating on the powder surface with Al ₂ O ₃ .

However, these methods have a drawback in that impurities must be introduced into the raw material powder in order to improve dispersibility.

Therefore, there is a demand for development of a technique capable of improving the dispersibility and producing a high concentration silicon carbide slurry.

SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and it is an object of the present invention to provide a high concentration silicon carbide slurry with improved dispersibility and a method for producing the same.

The objects of the present invention are not limited to the above-mentioned objects, and other objects not mentioned can 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 synthetic powder; And a dispersant, wherein the content of the dispersant is 0.5 to 2 wt% based on 100 wt% of the silicon carbide synthetic powder.

Also, the present invention provides the silicon carbide slurry, wherein the silicon carbide synthetic powder comprises a sintering aid, and the sintering aid is at least one selected from the group consisting of Al-C, Al-B-C and B-C.

The present invention also provides a silicon carbide slurry wherein the dispersant is polyethyleneimine (PEI) or Tetramethyl ammonium hydroxide (TMAH).

In addition, the present invention provides a silicon carbide slurry having a content of the sintering assistant of more than 0 and 13 wt% or less with respect to 100 wt% of the silicon carbide synthetic powder.

The present invention also relates to a method for producing a silicon carbide raw material and a sintering starting raw material, which comprises the steps of: preparing a synthetic powder by a mechanical alloying process; And mixing a dispersion medium and a dispersant in the synthetic powder, wherein the sintering assistant is at least one selected from the group consisting of Al-C series, Al-BC series and BC series. ≪ / RTI >

The present invention also relates to a process for producing a SiC-based composite material by synthesizing 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, Preparing a powder; And mixing a dispersion medium and a dispersant in the synthetic powder, wherein the sintering assistant is at least one selected from the group consisting of Al-C series, Al-BC series and BC series. ≪ / RTI >

The mixing of the dispersion medium and the dispersant in the synthetic powder preferably further comprises mixing the synthetic powder, the dispersion medium and the dispersant by stirring, and an ultrasonic dispersion step of accelerating dispersion of the dispersant, Thereby producing a slurry.

Further, the present invention provides a method for producing a silicon carbide slurry, which further comprises a step of mixing a dispersion medium and a dispersant in the synthetic powder, followed by a treatment of a ball mill or a planetary mill.

In the present invention as described above, it is possible to produce a silicon carbide slurry with a high concentration and improved dispersibility.

Also, in the present invention, a synthetic powder is prepared by mixing a silicon carbide raw material and a raw material for sintering auxiliary raw material and mechanically alloying the raw material so that a sintering aid required for producing the silicon carbide slurry having a high concentration is formed in the silicon carbide powder It can be produced so as to be relatively uniformly distributed, so that a high concentration silicon carbide slurry having a high solid content can be easily produced.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a flow chart showing a method for producing a silicon carbide slurry according to the present invention. FIG.
2A to 2C are graphs showing XRD data of SiC powder synthesized under various composition and milling conditions.
FIG. 3A is a TEM image of a powder synthesized according to the conditions of SiCAl3C1, and FIG. 3B is a TEM image of a powder synthesized according to the conditions of SiCAl7C1.
4 is a graph showing the particle size distribution of the synthesized powder.
FIG. 5 is a HR-TEM (High Resolution-Transmission Electron Micrograph) of a powder synthesized according to the conditions of SiCAl7C1.
6 is a TEM image of the powder synthesized according to the conditions of SiCAl5C1.
7a is a graph showing the zeta potential change according to various PEI contents, Fig. 7b is a graph showing the sedimentation behavior of the slurry according to the PEI content change, and Fig. 7c is a graph showing the sedimentation behavior of the slurry with a solid content of 55 vol% 2 is a graph showing the viscosity change of the SiC slurry.
FIG. 8 is a photograph showing the microstructure of a 10 wt% SiC slurry according to a change in PEI content. FIG. 8A shows a case where the PEI content is 0 wt%, FIG. 8B shows the case where the PEI content is 0.5 wt% 8c shows the case where the PEI content is 1 wt%, and FIG. 8d shows the case where the PEI content is 2 wt%.
FIG. 9 is a graph showing particle size distribution change according to PEI content change. FIG.
10 is a graph showing a change in viscosity with an increase in the solid charge amount of the slurry.
11 is a graph showing viscosity change when redispersing 60 vol% slurry dispersed by stirring and ultrasonic waves by high energy milling.
Figure 12a is a content of a showing the viscosity behavior of a 60 vol% slurry produced by using a SiC powder and an Al-containing C as a sintering aid graph, Figure 12b is a fixed shear rate as 215.2s ^-1 and a sintering aid And a graph showing the change in viscosity when the viscosity is changed.
13 is a graph showing viscosity changes when redispersing a 60 vol% slurry in which SiC powder containing 5.1 wt% of Al and C as sintering aids are dispersed by stirring and ultrasonication by high energy milling.
14 is a graph comparing the viscosity of a slurry of 40 vol% of powder synthesized by commercial SiC powder (commercial SiC) and mechanical alloying (MA) process according to the present invention.
15 is a graph comparing the viscosities of slurries of 60 vol% according to various compositions.

BRIEF DESCRIPTION OF THE DRAWINGS The advantages and features of the present invention, and the manner of achieving them, will be apparent from and elucidated with reference to the embodiments described hereinafter in conjunction with the accompanying drawings. The present invention may, however, be embodied in many different forms and should not be construed as being limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the invention to those skilled in the art. Is provided to fully convey the scope of the invention to those skilled in the art, and the invention is only defined by the scope of the claims.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Reference will now be made in detail to the preferred embodiments of the present invention, examples of which are illustrated in the accompanying drawings. &Quot; and / or "include each and every combination of one or more of the mentioned items. ≪ RTI ID = 0.0 >

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

The terminology used herein is for the purpose of illustrating embodiments and is not intended to be limiting of the present invention. In the present specification, the singular form includes plural forms unless otherwise specified in the specification. The terms " comprises "and / or" comprising "used in the specification do not exclude the presence or addition of one or more other elements in addition to the stated element.

Unless defined otherwise, all terms (including technical and scientific terms) used herein may be used in a sense commonly understood by one of ordinary skill in the art to which this invention belongs. Also, commonly used predefined terms are not ideally or excessively interpreted unless explicitly defined otherwise.

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

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a flow chart showing a method for producing a silicon carbide slurry according to the present invention. FIG.

Referring to FIG. 1, a method of manufacturing a silicon carbide slurry 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 producing silicon carbide, and the raw material for sintering auxiliary raw material may be understood as a starting material for preparing a sintering auxiliary.

Also, the silicon carbide raw material may include Si and a first carbon source, and the sintering 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 .

At this time, the first carbon source and the second carbon source may be solid carbon species such as graphite, graphite, carbon black, activated carbon and the like, but the kind of the carbon source is not limited in the present invention.

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

That is, the silicon carbide raw material and the sintering auxiliary raw material may be mixed to prepare a mixture, and then the synthetic powder may be produced by a mechanical alloying process.

At this time, in the present invention, the SiC-based synthetic powder having the sintering aid uniformly distributed therein can be produced through the mechanical alloying process.

Meanwhile, in the present invention, steps S100 and S110 are sequentially performed for convenience of explanation. Alternatively, steps S100 and S110 may be performed at the same time.

That is, the mixing step of the silicon carbide raw material and the sintering auxiliary raw material in the step S100 can be simultaneously performed in the step of preparing the synthetic powder by the mechanical alloying process of the step S110.

Accordingly, in the present invention, the steps S100 and S110 may include the steps of: preparing a silicon carbide raw material and a raw material for sintering auxiliary raw material by a mechanical alloying process, into a SiC type synthetic powder uniformly distributed in the sintering assistant . ≪ / RTI >

Meanwhile, in the present invention, steps S100 and S110 illustrate that a SiC-based synthetic powder is produced by mixing a silicon carbide raw material and a sintering auxiliary raw material in a mechanical alloying process, The step S100 and step S110 may be expressed as a step of preparing a raw material for silicon carbide as a synthetic powder by a mechanical alloying process.

At this time, the mechanical alloying process may use a high energy ball mill operating with a planetary mill, an attrition mill, a Spex mill, or the like, , But the present invention does not limit the kind of the mechanical alloying process.

In the present invention, it is preferable that balls and jars used in the mechanical alloying process use SiC balls and SiC jars, respectively.

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

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

Meanwhile, the chemical reaction formula expected in the synthetic powder production step is as follows.

Si + C? SiC (Reaction Scheme 1)

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

That is, in the present invention, the silicon carbide, that is, SiC is synthesized and the sintering auxiliary, such as Al-C, is relatively uniformly mixed into the synthesized SiC by the step of preparing the synthetic powder, The silicon carbide slurry having a high solid content can be produced by a process of dispersing the silicon carbide powder mixed with the sintering aid.

Meanwhile, as described above, 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. Accordingly, in the present invention, C, Al-BC, and / or B ₄ CC, and may correspond to, for example, Al-C, Al-BC, Al-B ₄ CC, BC and / or B ₄ CC.

Therefore, in the present invention, the sintering aid corresponds to Al-C, Al-BC, Al-B ₄ CC, BC and / or B ₄ CC which are relatively uniformly distributed in the synthesized silicon carbide powder, The content of the sintering aid may be more than 0 and 13 wt% or less.

Meanwhile, as described above, the sintering aid raw material may not be included in the present invention, and thus the silicon carbide synthetic powder may not include the sintering auxiliary agent.

That is, in the present invention, the raw material for silicon carbide and the raw material for sintering auxiliary raw material are mixed, and the synthetic powder is produced by a mechanical alloying process. Thus, the sintering auxiliary required for producing the high-concentration silicon carbide slurry is mixed with the silicon carbide powder It can be produced so as to be relatively uniformly distributed, so that a high concentration silicon carbide slurry having a high solid content can be easily produced.

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

For convenience of description, the first carbon source and the third carbon source are separately described at step S100, but when they are mixed, they may correspond to one carbon source.

Therefore, the step S100 may be represented by mixing at least one material selected from the group consisting of Si, Al, B, and B ₄ C with a carbon source, and the carbon source may be represented by graphite, graphite, carbon black, It can be a solid carbon of the same phase.

In this case, step S110 according to the present invention is a method of manufacturing a composite material containing 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 As shown in FIG.

In addition, as described above, the steps S100 and S110 according to the present invention can be performed simultaneously. In this case, the steps S100 and S110 of the present invention may be selected from the group consisting of Si, Al, B and B ₄ C And at least one material and carbon source may be synthesized into a synthetic powder by a mechanical alloying process.

1, a method for preparing a silicon carbide slurry according to the present invention includes mixing a dispersion medium and a dispersant in the synthetic powder (S120).

The dispersion medium may be water or an alcohol, and polyethyleneimine (PEI) or tetramethyl ammonium hydroxide (TMAH) may be used as the dispersant.

At this time, the amount of the dispersant is preferably 0.5 to 2 wt% based on 100 wt% of the synthetic powder.

The mixing of the dispersion medium and the dispersant into the synthetic powder may be performed by dissolving a predetermined amount of the dispersant in the dispersion medium and then mixing the synthetic powder and the synthetic powder together by intensive stirring.

 Meanwhile, although not shown in the drawing, an ultrasonic dispersing machine can be used in parallel to promote dispersion of the dispersing agent, and dispersion can further be promoted through a ball mill and a planetary milling treatment.

Thus, the silicon carbide slurry according to the present invention can be manufactured (S130).

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

[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 auxiliary raw material includes at least one material selected from the group consisting of Al, B, and B ₄ C, Carbon black, a part of the carbon black may be used as the first carbon source, and a part of the carbon black may be used as the second carbon source.

The composition and abbreviations of the raw materials used in each experiment are shown in Table 1 below.

For example, "Al3" is Si for the synthesis of SiC in Table 1: The ratio of C 1: the same rate and in a molar ratio of C Compound Al ₄ SiC _4: to the holding, the sintering auxiliary fixed with 1 Al: Si The ratio of Si: C was fixed at 1: 1 for the synthesis of SiC, and the content of Al was changed to 3: The ratio of Si: C was adjusted to 1: 1 for the synthesis of SiC, and the molar ratio of Si: C was adjusted to 4: 1: 4 and the amount thereof was adjusted to 5 wt%. Further, "Al7C1" and "Al12C1" Means that the molar ratio of Al: Si: C was adjusted to 4: 1: 4, which is the same ratio as that of Al ₄ SiC ₄ , as the sintering aid, and the amounts thereof were adjusted to 7 and 12.5 wt%, respectively. C1 "means that 1 wt% of excess carbon is additionally contained, and" B1C1 "means the amount of B ₄ C and C in the sintering aid, while the Si: C ratio is fixed at 1: 1wt%, respectively.

Therefore, the actual preparation amount of Al2C1 composition is 2.17wt% and the preparation amount of Al20C1 composition is 12.73wt%.

On the other hand, the amounts of Al, C and B ₄ C except for the amount of SiC in the added sintering aids are shown separately.

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

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

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

Abbreviation rpm ball pollution degree 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 above, it was found from the EDS analysis that the commercial SiC ball contains Al and the content thereof is about 10 wt%. Therefore, the contamination amount of Al added during milling was relatively low as about 0.2 to 0.3 wt% when the revolution speed of the planetary mill was 360 rpm, but it was increased to about 0.6 to 0.7 wt% at 400 rpm. On the other hand, Jar was reaction-bonded Silicon Carbide (RBSC), and Al contamination from jar hardly occurred.

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

The particle size distribution of the synthesized powder was measured using a particle size analyzer, and the average size of the crystal grains existing 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 composition and milling conditions.

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

2A to 2C, when the content of the sintering auxiliary agent is changed to 3 to 7 wt% or the content of the third carbon source of excess carbon is increased to 0.5 and 1 wt%, rpm in the milling process is increased to 360 to 400 , No significant difference was found in the XRD data, and it was confirmed that all the powders consisted only of β-SiC (3C-SiC) without residual Si, Al and C.

Mechanism in which Si and C are synthesized into SiC through mechanical alloying exists in the form of amorphous Si in which C atoms directly substitute for Si and contain C, and as the milling process proceeds, And SiC are formed as the number of chemically active defect sites increases.

XRD analysis showed that Al, B ₄ C and carbon peaks were not observed because the components were uniformly distributed in SiC due to high energy milling.

In addition, since SiC ball and SiC jar were used, no other secondary phase due to contamination was observed. The SiC peak is in a broad form because the crystallite size is much reduced by high energy milling. The crystallite size of the powder synthesized at 360 and 400 rpm using Sherrer equation was 17.6 and 12.7 nm, respectively.

In addition, the Al15C1 composition showed powder agglomeration and the Al20C1 composition showed very strong agglomeration after milling after the milling, and the subsequent process Difficulties appeared. However, the sintering density of the powders increased at 1550 ℃ as the content of the additives increased. Therefore, in the present invention, it is preferable that the amount of the Al-Si-C system sintering auxiliary is 13 wt% or less, that is, the total amount of the sintering auxiliary is 13 wt% or less.

FIG. 3A is a TEM image of a powder synthesized according to the conditions of SiCAl3C1, and FIG. 3B is a TEM image of a powder synthesized according to the conditions of SiCAl7C1.

Referring to FIGS. 3A and 3B, primary SiC particles of 10 to 20 nm and amorphous Si-C phases are spherical and have a particle size of about 100 nm. This cohesion is thought to be due to cold welding during high energy ball milling. Also, the portion formed with dark spots inside the powder shows that SiC partially crystallized. At this time, when Al content was changed in the composition of Al3C1 and Al7C1, 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 shape having a primary peak in a range of 100 to 200 nm and a secondary peak in a range of about 1 μm was observed. As a result of SEM and TEM observation, peaks of about 1 μm were formed by aggregation of smaller particles And most of the particle size was less than 300nm.

FIG. 5 is a HR-TEM (High Resolution-Transmission Electron Micrograph) of a powder synthesized according to the conditions of SiCAl7C1.

Referring to FIG. 5, amorphous Si and crystallized SiC grains in the C base matrix can be identified. Particles with very small sizes of crystallized particles of about 2 nm 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 of the surface, the reaction interface has increased with high sintering driving force and diffusion speed, which can promote the low temperature sintering of SiC.

6 is a TEM image of the powder synthesized under the conditions of SiCAl5C1, and Table 3 below shows the element content according to the points of 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

6 and Table 3, it can be seen that the content of Al in the various powders synthesized according to the condition of Al5C1 does not show a large difference in the content of Al among the various powders. It is well known that when the sintering aid is uniformly distributed in the powder, the sintering property of the powder is improved. When the oxide powder is prepared by the sol-gel method or coprecipitation method, when the sintering aid is uniformly distributed in the oxide powder, the powder and the sintering agent are synthesized separately and the densification is completed at a lower temperature than in the case of mixing them later Is being reported.

The solubility limit of Al and B in SiC is known to be 0.5 wt% and 0.1 wt%, respectively. However, the SiC powder synthesized by the above method may contain Al and B above the solubility limit in the interior of the SiC powder as shown in FIG. 6 and Table 1 , Which is one of the main features of the present invention.

As described above, in the present invention, the sintering aid corresponds to Al-C, Al-BC, Al-B ₄ CC, BC and / or B ₄ CC which are relatively uniformly distributed in the synthesized silicon carbide powder, The content of the sintering auxiliary agent in the synthetic powder may be more than 0 and 13 wt% or less.

Meanwhile, as described above, the sintering aid raw material may not be included in the present invention, and thus the silicon carbide synthetic powder may not include the sintering auxiliary agent.

Accordingly, in the present invention, a raw material for silicon carbide and a sintering aid raw material are mixed and a synthetic alloy powder is produced by a mechanical alloying process, so that a sintering aid required for producing a high-concentration silicon carbide slurry is mixed with a silicon carbide powder It can be produced so as to be relatively uniformly distributed, so that a high concentration silicon carbide slurry having a high solid content can be easily produced.

Through the synthesis powder as described above, the following slurrying process was carried out.

A dispersion medium and a dispersant were mixed with the synthetic powder as described above to prepare a silicon carbide slurry.

Water or alcohol was used as the dispersion medium, and polyethyleneimine (PEI) or tetramethyl ammonium hydroxide (TMAH) was used as the dispersing agent.

Specifically, after a predetermined amount of the dispersant is dissolved in the dispersion medium, the synthetic powder is mixed with the synthetic powder through intensive stirring. In some cases, an ultrasonic disperser is used in parallel to promote dispersion of the dispersant.

Hereinafter, unless otherwise specified, the solvent is used for the dispersion medium and the dispersant is used for the PEI.

Hereinafter, characteristics of the silicon carbide slurry according to the present invention will be described.

7a is a graph showing the zeta potential change according to various PEI contents, Fig. 7b is a graph showing the sedimentation behavior of the slurry according to the PEI content change, and Fig. 7c is a graph showing the sedimentation behavior of the slurry with a solid content of 55 vol% 2 is a graph showing the viscosity change of the SiC slurry.

Referring to FIG. 7A, the zeta potential value was negative at -12 mV in the absence of the dispersant, whereas it was positive when the amount of PEI was increased. It has been found that slurries with a higher zeta potential value typically exhibit a more stable dispersion, and thus the addition of PEI promotes dispersion of the SiC slurry. The highest zeta potential was obtained when 1 wt% of PEI was added and the zeta potential did not change significantly even when the amount of dispersant was increased.

Accordingly, the amount of the dispersing agent in the present invention is preferably 0.5 to 2 wt% based on 100 wt% of the synthetic powder.

Next, referring to FIG. 7B, it can be seen that the sedimentation behavior of the slurry according to the change of PEI content shows the lowest sedimentation amount when 1 wt% of dispersant is added, as in the zeta potential data described above.

Next, referring to FIG. 7C, the viscosity change of the SiC slurry having a solid content of 55 vol% according to the change of the PEI content was the lowest in the case of 1 wt% PEI, as in the zeta potential results described above.

Despite the high concentration of slurry, shear thinning behaviors were shown in all cases because the weakly agglomerated powders were redispersed by the shear force generated in the viscosity measurement.

FIG. 8 is a photograph showing the microstructure of a 10 wt% SiC slurry according to a change in PEI content. FIG. 8A shows a case where the PEI content is 0 wt%, FIG. 8B shows the case where the PEI content is 0.5 wt% 8c shows the case where the PEI content is 1 wt%, and FIG. 8d shows the case where the PEI content is 2 wt%.

8, when the PEI content was 0 and 0.5 wt%, aggregation occurred in the slurry, but when the PEI content was 1 wt%, the aggregation did not occur, and when the PEI content increased to 2 wt% It can be observed that coagulation occurs partially.

FIG. 9 is a graph showing particle size distribution change according to PEI content change. FIG.

Referring to FIG. 9, in the case where no dispersant was added, particles of 1.2 탆 area were found to be larger by the aggregation of particles than the original particle size of 170 nm. When the amount of dispersant was 0.5 wt%, the content of fine particles And the amount of agglomerate was decreased. However, it was confirmed that the dispersion was less than that of 1 wt%, and when the amount of dispersant was more than 1 wt%, the particle size distribution was not significantly affected.

10 is a graph showing a change in viscosity with an increase in the solid charge amount of the slurry.

Referring to FIG. 10, as the solid content increases, the viscosity increases but the effect is weak when the solid content is within 55 vol% to 60 vol%. 62 vol%, the viscosity increased and the shear thickening behavior was observed but the fluidity was maintained. The 63 vol% slurry exhibits complete shear thickening, which indicates unstable slurry state.

11 is a graph showing viscosity change when redispersing 60 vol% slurry dispersed by stirring and ultrasonic waves by high energy milling.

Referring to FIG. 11, it was found that the viscosity of 60 vol% slurry dispersed by stirring and ultrasonic wave was redispersed by high energy milling. This is probably due to the fact that strong agglomerates that were not effectively dispersed by ultrasonic waves dispersed during high energy milling and thus decreased viscosity.

Figure 12a is a content of a showing the viscosity behavior of a 60 vol% slurry produced by using a SiC powder and an Al-containing C as a sintering aid graph, Figure 12b is a fixed shear rate as 215.2s ^-1 and a sintering aid And a graph showing the change in viscosity when the viscosity is changed.

12A, the contents of the sintering aids correspond to 0, 5.1, and 8.3 wt%, respectively. When compared with the viscosity behavior of the SiC slurry without the sintering aid, Shear thinning at low shear rate and shear thickening at high shear rate were observed.

At low shear rate, the structure of the particles in the slurry is close to equilibrium because the thermal motion of the particles is larger than the motion caused by the viscosity. Therefore, the aggregates are destroyed by the shear force and the viscosity decreases.

However, at high shear rates, collisions and interactions between particles become more active, causing re-agglomeration. At a specific shear rate, the shear thickening phenomenon occurs as the particle changes from a two-dimensional layered structure to a three-dimensional structure.

Next, referring to FIG. 12B, it can be seen that as the content of the sintering aid in the slurry increases, the viscosity also increases. However, the SiC slurry with a high solids content of 60 vol% could be successfully prepared even when the total amount of the sintering additive was 8.3 wt%.

13 is a graph showing viscosity changes when redispersing a 60 vol% slurry in which SiC powder containing 5.1 wt% of Al and C as sintering aids are dispersed by stirring and ultrasonication by high energy milling.

Referring to FIG. 13, it is found that the viscosity increases when redispersed as opposed to pure SiC. This is probably due to the newly exposed sintering additive on the powder surface during high energy milling to further reduce the dispersion of powder.

14 is a graph comparing the viscosity of a slurry of 40 vol% of powder synthesized by commercial SiC powder (commercial SiC) and mechanical alloying (MA) process according to the present invention.

14, distilled water (water) was used as a dispersion medium and TMAH was used as a dispersant.

14, in the case of using an aqueous system as a dispersion medium and using TMAH as a dispersant, the viscosity of the powder synthesized by a mechanical alloying process according to the present invention is higher than that of a commercial SiC powder Can be confirmed.

15 is a graph comparing the viscosities of slurries of 60 vol% according to various compositions.

In FIG. 15, for example, SC means a slurry containing no sintering aid, 7C1 means composition of Al7C1 in Table 1, and 12.5C1 means Al12.5C1 in Table 1 above.

15, ethanol was used as a dispersion medium and 1 wt% of PEI was used as a dispersant.

15, it can be seen that the viscosity when the sintering auxiliary agent is used is superior to the case where the sintering auxiliary agent is not used, and it is also confirmed that the viscosity characteristics are different depending on the kind of the sintering auxiliary agent in the slurry .

As described above, in the present invention, silicon carbide, that is, SiC is synthesized by the step of preparing the synthetic powder, and a sintering aid such as Al-C is relatively uniformly distributed in the synthesized SiC And a silicon carbide slurry having a high solids content can be prepared by a subsequent step of dispersing the silicon carbide powder mixed with the sintering aid.

At this time, the sintering aid corresponds to Al-C, Al-BC, Al-B4C-C, BC and / or B4C-C which are relatively uniformly distributed in the synthesized silicon carbide powder, The content of the sintering aid may be 0.5 to 12.5 wt%.

That is, in the present invention, the raw material for silicon carbide and the raw material for sintering auxiliary raw material are mixed, and the synthetic powder is produced by a mechanical alloying process. Thus, the sintering auxiliary required for producing the high-concentration silicon carbide slurry is mixed with the silicon carbide powder It can be produced so as to be relatively uniformly distributed, so that a high concentration silicon carbide slurry having a high solid content can be easily produced.

Studies on the use of various dispersants have been reported to produce general silicon carbide slurries and it has been reported that the use of polyethylenimine (PEI) and tetramethyl ammonium hydroxide (TMAH) Zhang, Q Xu, F Ye, Q Lin, D Jiang, M Iwasa, Effect of citric acid on the adsorption behavior of polyethylene inmine (PEI) and the related stability of SiC slurries, Colloids and Surfaces A: Physicochemical and Engineering Aspects, 276 [1-3], 168-175 (2006))

Zhang et al. Prepared a single phase, 57 vol% SiC slurry, using relatively coarse 0.6 .mu.m sized commercial powders. On the other hand, when using the method disclosed in this application, using a fine SiC powder with an average particle size of 170 nm, %, Respectively. In particular, when a sintering assistant is included, only a slurry having a maximum volume of 50 vol% can be prepared in the prior art, while in the case of the method disclosed in the present invention, sintering aids Al, B and It is possible to manufacture a nano SiC slurry at a maximum of 60 vol% even when a large amount of C is contained.

While the present invention has been described in connection with what is presently considered to be practical exemplary embodiments, it is to be understood that the invention is not limited to the disclosed embodiments, but, on the contrary, It will be understood. It is therefore to be understood that the above-described embodiments are illustrative in all aspects and not restrictive.

Claims (8)

Silicon carbide synthetic powder; And
Dispersant,
The content of the dispersant is 0.5 to 2 wt% based on 100 wt% of the silicon carbide synthetic powder. The method according to claim 1,
The dispersant is polyethyleneimine (PEI) or Tetramethyl ammonium hydroxide (TMAH). The method according to claim 1,
Wherein the silicon carbide synthetic powder comprises a sintering auxiliary agent,
Wherein the sintering aid is at least one selected from the group consisting of Al-C series, Al-BC series and BC series. The method of claim 3,
Wherein the content of the sintering assistant is more than 0 and not more than 13 wt% with respect to 100 wt% of the silicon carbide synthetic powder. Preparing a silicon carbide raw material and a sintering starting raw material by a mechanical alloying process as a synthetic powder; And
Mixing a dispersion medium and a dispersant in the synthetic powder,
Wherein the sintering aid is at least one selected from the group consisting of Al-C series, Al-BC series and BC series. Synthesizing 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 to produce a SiC-based synthetic powder having a sintering aid dispersed therein ; And
Mixing a dispersion medium and a dispersant in the synthetic powder,
Wherein the sintering aid is at least one selected from the group consisting of Al-C series, Al-BC series and BC series. The method according to claim 5 or 6,
Mixing the dispersion medium and the dispersant in the synthetic powder further comprises a step of mixing the synthetic powder, the dispersion medium and the dispersant by stirring, and an ultrasonic dispersion step of promoting dispersion of the dispersant. 8. The method of claim 7,
After mixing the dispersion medium and the dispersant into the synthetic powder,
A method for producing a silicon carbide slurry, the method further comprising a treatment of a ball mill or a planetary mill.

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