KR101659823B1 - A HfC Composites and A Manufacturing method of the same - Google Patents

Abstract

The present invention relates to a method for producing a sintered body, comprising: mixing HfC, a sintering aid and a carbon source; Heat treating the carbon source to produce a carbon powder; And sintering a mixture comprising the HfC, the sintering aid and the carbon, wherein the sintering aids are selected from the group consisting of zirconium silicide (Zr _x Si _y ), hafnium silicide (Hf _x Si _y , Hafnium silicide The present invention relates to a method for producing a HfC composite and a HfC composite according to the present invention, wherein a zirconium silicide group (Zr _x Si _y , Zirconium silicides, or hafnium silicides (Hf _x Si _y , Hafnium silicides), it is possible to manufacture HfC composites having a finer grain size and uniform distribution of SiC by preventing local concentration of chemical composition.

Description

HfC composites and their manufacturing methods.

More particularly, the present invention relates to a high purity HfC-SiC composite material having a fine particle size and a uniform secondary phase distribution and densely sintered, and a method for producing the same.

HfC has a very high melting point of about 3800 ° C, has excellent mechanical properties such as excellent strength and hardness characteristics, has a wide range of applications in industry, and many researches have been carried out especially for military and aerospace applications .

Especially, ZrB ₂ is superior to ZrB ₂ which has undergone much research in the past.

However, in the case of HfC, there are many limitations in industrial applications due to ovoid formation, which is a characteristic of high melting point materials, and low oxidation resistance at a working temperature range of 800 to 1500 ° C.

In order to overcome this ovarian formation, a method of applying an additive to HfC has been applied.

More specifically, when 20 to 40% by weight of SiC as an additive is added to the total weight of HfC-SiC, the sinterability of HfC is improved, the oxidation resistance at 900 to 1500 ° C is improved, and the mechanical properties such as strength are improved [1]

However, in this case, the SiC should be uniformly distributed in the HfC base so as to exhibit the strength enhancement and the oxidation inhibition effect.

Therefore, to improve the sinterability of HfC powder and uniformly mix with SiC, commercial HfC powder is mixed with SiC by using wet milling method using high grinding apparatus such as attrition mill and planetary mill and liquid dispersion medium I am using it.

However, since HfC has a high elastic modulus, hardness and fracture toughness, it is not easy to grind, and there is a problem that a large amount of contaminants are introduced from a ball for grinding and a grinding container at the time of grinding.

In addition, SiCs tend to be re-agglomerated during the process of mixing HfC and SiC by wet mixing method, and it is difficult to manufacture HfC-SiC composite material with uniform distribution of SiC. [3]

In order to solve the problem of such uniformity and the problems of incorporation of impurities through long pulverization and mixing processes, there have been reported examples of producing HfC-SiC composite materials using Hf, Si and C, which are components of the composite material as a starting material [4] [5]

However, in these studies, due to the local concentration of the chemical composition, the HfC and SiC formed grow to a size similar to that of the starting materials Hf and Si, and thus the composite materials produced by these methods have grain sizes of 3 to 10 Mu m and relatively coarse.

Also, since Hf powder as a starting material is highly reactive with air, there is a danger of explosion when exposed to air in a powder state, and all experiments must be performed in an expensive inert atmosphere, which makes industrialization difficult.

[1] J. X. Liu et al., J. Am. Ceram. Soc., 96 [6], 1751-1756 (2013). [2] C. Heiligers et al., Int. J. Ref. Met. Hard Mater., 25 [4], 300-309 (2007). [3] S. Kim et al., Ceramics International, 40 [2], 3477-3483 (2014). [4] D. L. Hu et al., J. Eur. Ceram. Soc., 34 [3], 611-619 (2014). [5] Y. D. Blum et al., J. Mater. Sci., 39 [19], 6023-6042 (2004).

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems of the prior art, and it is an object of the present invention to provide a high-purity HfC-SiC composite material having a fine particle size and a uniform secondary phase distribution and densely sintered, .

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 method of manufacturing a carbon nanotube, comprising: mixing HfC, a sintering aid and a carbon source; And a step of sintering a mixture containing the HfC, the sintering aid and the carbon source, wherein the sintering aid is selected from the group consisting of Zr _x Si _y , Zirconium silicide, and hafnium silicide (Hf _x Si _y , Hafnium silicide ) Is used as a solvent for the HfC composite.

In the present invention, the group of the zirconium silicide group (Zr _x Si _y , Zirconium silicide) is preferably selected from the group consisting of ZrSi ₂ , ZrSi, Zr ₅ Si ₄ , Zr ₅ Si ₃ , Zr ₃ Si ₂ , Zr ₂ Si and Zr ₃ Si (Hf _x Si _y , Hafnium silicide) is at least one or more selected from the group consisting of HfSi ₂ , HfSi, Hf ₅ Si ₄ , Hf ₃ Si _2, and Hf ₂ Si ≪ RTI ID = 0.0 > HfC < / RTI >

The present invention also provides a method for producing an HfC composite, wherein the carbon source is at least one selected from the group consisting of graphite, carbon black and activated carbon.

Further, the present invention provides a method for producing a carbon nanotube, comprising: mixing the HfC, the sintering aid and the carbon source; And sintering the mixture comprising HfC, the sintering aids and the carbon source comprises: mixing HfC, sintering aids and carbon source; Heat-treating the carbon source to produce a heat-treated carbon source; And sintering a mixture containing the HfC, the sintering aid and the heat-treated carbon source, wherein the carbon source is at least one selected from the group consisting of phenol resin, pitch, sucrose, and poly acrylonitrile (PAN) Wherein the HfC complex is produced by a method comprising the steps of:

Further, the present invention provides a method for producing a carbon nanotube, comprising: mixing the HfC, the sintering aid and the carbon source; And sintering the mixture comprising HfC, the sintering aid, and the carbon source comprises: heat treating the carbon source to produce a heat treated carbon source; HfC, a sintering aid, and the heat-treated carbon source; And sintering a mixture containing the HfC, the sintering aid and the heat-treated carbon source, wherein the carbon source is at least one selected from the group consisting of phenol resin, pitch, sucrose, and poly acrylonitrile (PAN) Wherein the HfC complex is produced by a method comprising the steps of:

In addition, the present invention provides a method for producing the HfC composite, wherein the HfC, the sintering aid, and the carbon source are mixed using a planetary mill, an attrition mill, a spes mill or a high energy ball mill.

Further, the present invention provides a method for producing an HfC composite, wherein the sintering step is a pressurizing sintering method, and the pressing force in the pressure sintering method is in a range of a pressing force of 20 to 120 MPa.

Further, the present invention provides a method for producing an HfC composite, wherein the sintering temperature in the above pressure sintering method is 1650 to 2000 ° C.

In addition, the present invention provides the HfC complex produced by the above production method.

The present invention also provides an HfC composite characterized in that the HfC composite has a grain size of 700 nm or less and ZrC and SiC or HfC and SiC are uniformly distributed.

In the present invention as described above, a zirconium silicide group (Zr _x Si _y , Zirconium silicides) or a hafnium silicide group (Hf _x Si _y , Hafnium silicides) in which Zr or Hf and Si are uniformly mixed at a molecular unit level, , It is possible to prevent the local concentration of the chemical composition and to produce HfC composites having a finer grain size than that of the prior art and uniformly distributing SiC.

Further, in the present invention, by mixing the zirconium silicide group or the hafnium silicide group as the Si source with the source of carbon, it is possible to produce a high purity HfC composite having a fine grain size and a uniform microstructure in spite of sintering at a low temperature have.

Also, in the present invention, the sintering step is carried out by using the pressure sintering method instead of the atmospheric pressure sintering method to prevent coarsening of particles generated at a high temperature, and a sintering process using low temperature deformation of the zirconium silicide group and the hafnium silicide group is faithfully performed The HfC complex is formed at an extremely low temperature as compared with the conventional method. Therefore, the HfC composite can be manufactured which minimizes grain growth and maximizes densification.

FIG. 1A is a flow chart for explaining a method of manufacturing the HfC composite according to the first embodiment of the present invention, FIG. 1B is a flowchart for explaining a method of manufacturing the HfC composite according to the second embodiment of the present invention, Is a flowchart for explaining a method of manufacturing the HfC composite according to the third embodiment of the present invention.
2A is a graph showing a discharge plasma sintering behavior of a high purity nano HfC powder without using a sintering aid, and FIG. 2B is a photograph showing the microstructure of the HfC sintered body obtained according to the result of FIG. 2A.
3 is a graph showing the image formation behavior with increasing temperature of HfSi ₂ and C mixed powder mixed with the spesific mill.
4 is a photograph showing the microstructure of the nanocomposite prepared by HSC composition according to the sintering temperature change.
FIG. 5 is a photograph showing the composition distribution of the nanocomposite prepared by HSC composition analyzed by energy dispersive spectroscopy (EDS) mapping.
6 is XRD data according to the sintering temperature change after sintering of the HCHSC composition material.
7 is a graph showing the sintering shrinkage behavior in the discharge plasma sintering of the HSHSC composition material.
8 is a photograph showing a change in the microstructure of the nano-HfC-SiC composite according to the sintering aid amount.
9 is a photograph showing the microstructure change of the HCHSC composite according to the sintering temperature change.

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.

The terms spatially relative, "below", "beneath", "lower", "above", "upper" And can be used to easily describe a correlation between an element and other elements. Spatially relative terms should be understood in terms of the directions shown in the drawings, including the different directions of components at the time of use or operation. For example, when inverting an element shown in the figures, an element described as "below" or "beneath" of another element may be placed "above" another element . Thus, the exemplary term "below" can include both downward and upward directions. The components can also be oriented in different directions, so that spatially relative terms can be interpreted according to orientation.

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

FIG. 1A is a flow chart for explaining a method of manufacturing the HfC composite according to the first embodiment of the present invention.

1A, a method of manufacturing an HfC composite according to a first embodiment of the present invention includes mixing a raw material powder HfC, a sintering assistant, and a carbon source (S110)

In this case, the sintering aid in the present invention are zirconium silicide group (Zr _x Si _y, Zirconium silicide) or hafnium silicide group, and characterized by using a (Hf _x Si _y, Hafnium silicides), zirconium silicide group (Zr _x Si _y , Zirconium silicide) according to the ratio of Zr and Si, at least one selected from the group consisting of ZrSi ₂ , ZrSi, Zr ₅ Si ₄ , Zr ₅ Si ₃ , Zr ₃ Si ₂ , Zr ₂ Si and Zr ₃ Si Or hafnium silicides (Hf _x Si _y , Hafnium silicides) are selected from the group consisting of HfSi ₂ , HfSi, Hf ₅ Si ₄ , Hf ₃ Si ₂ and Hf ₂ Si depending on the ratio of Hf and Si And may include at least one or more.

The zirconium silicide group (Zr _x Si _y , Zirconium silicide) or the hafnium silicide group (Hf _x Si _y , Hafnium silicides) has a melting point ranging from 1620 to 2500 ° C. over a wide range, and Zr and Si, or Hf and Si, , HfC and SiC of nanometer size can be formed at the same time when reacting with the carbon source.

That is, in the present invention, a zirconium silicide group (Zr _x Si _y , Zirconium silicides) in which Zr and Si are uniformly mixed at a molecular unit level or a hafnium silicide group (Hf _x Si _y , Hafnium silicides), it is possible to manufacture a HfC composite having finer grain size and SiC uniformly distributed by preventing local concentration of chemical composition.

The carbon source may be at least one selected from solid carbon species such as graphite, carbon black, and activated carbon.

The mixing of the HfC, the sintering aid and the carbon source may be performed using a planetary mill, an attrition mill, a Spex mill, or a high energy ball mill operating on a similar principle. For example, , It may be mixed for 0.1 to 3 hours by a dry method. However, the mixing method of the HfC, the sintering auxiliary, and the carbon source is not limited in the present invention.

On the other hand, when the HfC, the sintering aid, and the carbon source are used as a Spex mill, it is possible to prevent incorporation of impurities caused in the production of the HfC composite according to the present invention, as compared with other mixing methods.

That is, in the case of the attrition mill and the planetary mill, a large amount of contaminants may be introduced from the crushing ball and the crushing vessel upon crushing. However, in the case of the specs mill, such problems can be minimized.

Next, a method for manufacturing the HfC composite according to the first embodiment of the present invention includes a step of sintering the mixture containing the HfC, the sintering aid, and the carbon source (S120).

In the present invention, the sintering temperature in the sintering step may be in the range of 1650 to 2000 ° C, and the sintering atmosphere may be vacuum, argon (Ar), nitrogen atmosphere, and may be spark plasma sintering For 5 to 120 minutes.

Meanwhile, in the sintering step, the chemical reaction formula of the sintering aid and the carbon source is as follows.

Zirconium silicides + C? ZrC + SiC (Scheme 1)

Hafnium silicides + C? HfC + SiC (Scheme 2)

As shown in Reaction Scheme 1 and Reaction Scheme 2, in the sintering step, ZrC, HfC and SiC can be formed through the reaction of the sintering assistant and the carbon source.

That is, in the present invention, by mixing the zirconium silicide group or the hafnium silicide group as the Si source with the source of carbon, it is possible to produce a high purity HfC composite having a fine grain size and a uniform microstructure despite heat treatment at a low temperature have.

On the other hand, when Hf and Si raw material powders are used, HfC and SiC formed by the concentration of local Si and Hf composition grow similarly to Hf and Si raw material powders, and as a result, the coarsening tendency of the particles There is a problem as described above.

In addition, ZrSi ₂ and HfSi ₂ are relatively stable in air and can be easily handled, whereas Zr or Hf powder is explosive in air. Therefore, the process using Zr or Hf powder as a raw material has problems in industrialization.

At this time, the mixing ratio of HfC and SiC can be controlled by selecting silicide having a desired composition or using them in a suitable range.

In the present invention, additional HfC and SiC can be added to the mixture of the sintering aid and the carbon source, thereby improving the properties such as controlling the sintering amount, reducing the cost, and promoting sintering.

In this case, SiC can be supplementarily added only when the desired SiC content can not be satisfied by only the zirconium silicide group or the hafnium silicide group.

On the other hand, ZrSi ₂ in the zirconium silicide group has a melting point as low as 1620 ° C. Therefore, when ZrSi ₂ is added at 40 wt% based on the total weight of the composite material, ZrB ₂ , which exhibits a sintering behavior similar to HfC, It can be densified by a normal-pressure sintering furnace.

However, ZrSi _2, or is expected to be a high-temperature physical properties of the HfC sintered body prepared by a melt of ZrSi _2, or HfSi ₂ at a high temperature greatly reduced when it is used as only a sintering aid HfSi _2, is actually the intensity value at 1400 ℃ For ZrB ₂ It is reported that it decreased greatly.

Therefore, in the present invention, the carbon source is included together with the zirconium silicide group or the hafnium silicide group as the sintering aid, that is, when a stoichiometric carbon source (C) is added, ZrSi ₂ or HfSi ₂ reacts ZrC, HfC, and SiC, so that it is possible to suppress the decrease in physical properties at high temperature.

However, the reaction in the above-mentioned Reaction Schemes 1 and 2 is completed before the liquid phase formation temperature of the ZrSi ₂ or HfSi ₂ , which is 1620 ° C. to 1680 ° C., so that the HfC can not be completely densified by the normal pressure sintering method Lt; / RTI >

That is, when zirconium silicide alone is used, ZrSi ₂ has a melting point near 1650 ° C., so that a liquid phase is formed at 1650 ° C., so that atmospheric pressure sintering of ZrB ₂ , which exhibits a sintering behavior similar to HfC, is possible.

However, the components including the carbon source with the zirconium silicide group or hafnium silicide group in the invention, ZrSi ₂ or the HfSi ₂ reacts with these carbon source before it reaches the middle and the ZrSi ₂ or the melting point HfSi ₂ raised ZrC + SiC, or HfC + SiC. As a result, a liquid phase due to ZrSi ₂ or HfSi ₂ is not formed, and therefore, the problem of densification may be insufficient.

Therefore, in the present invention, the sintering is preferably performed using a pressure sintering method, and the pressure sintering method has an advantage that densification can be promoted.

Generally, it is known that the material starts to deform due to the pressure at a temperature range of about 2/3 of the melting temperature.

In the case of the zirconium silicide group or the hafnium silicide group, for example, ZrSi ₂ , this temperature range corresponds to about 1100 ° C., and at 1400 ° C., deformation due to the pressure of ZrSi ₂ is remarkably caused.

Therefore, even in a relatively low temperature region where the reaction of ZrSi ₂ or HfSi ₂ is not completed, the ZrSi ₂ or HfSi ₂ may be deformed by pressurization, so that the densification of HfC can be further accelerated. The residual ZrSi ₂ or HfSi ₂ is extinguished in the process, so that it is possible to suppress the reduction of high-temperature properties of the produced HfC composite.

At this time, the range of the pressing in the pressure sintering method of the present invention can be performed in the range of the pressing force of 20 to 120 MPa.

When the pressing force is less than 20 MPa, the effect of densification due to pressure deformation of zirconium silicides at low temperature is not apparent, and when the pressing force exceeds 120 MPa, the manufacturing is difficult industrially due to limitations of the equipment. Is preferably in the range of a pressing force of 20 to 120 MPa.

On the other hand, in the present invention, when sintering is carried out by the pressure sintering method, the sintering temperature range can be extended more than that in the normal pressure sintering method, that is, the sintering temperature in the pressure sintering method may be 1650 to 2000 ° C.

When the sintering temperature is lower than 1650 ° C, the sintering temperature is not densified due to the pressurization of the zirconium suicide. Therefore, when the sintering temperature exceeds 2000 ° C, densification can be performed. However, The sintering temperature in the pressure sintering method of the present invention is preferably 1650 to 2000 ° C.

That is, in the present invention, the sintering step is carried out by using the pressure sintering method instead of the normal pressure sintering method to prevent coarsening of particles generated at a high temperature, and a sintering process using the zirconium suicide group or the low temperature deformation of the hafnium suicide group is faithfully performed The HfC complex is formed at an extremely low temperature as compared with the conventional method. Therefore, the HfC composite can be manufactured which minimizes grain growth and maximizes densification.

Thus, an HfC composite, that is, an HfC-SiC composite can be produced (S130).

FIG. 1B is a flowchart illustrating a method of manufacturing the HfC composite according to the second embodiment of the present invention. The method of manufacturing the HfC composite according to the second embodiment of the present invention may be the same as the method of manufacturing the HfC composite according to the first embodiment described above, except as described below.

Referring to FIG. 1B, a method of manufacturing an HfC composite according to a second embodiment of the present invention includes mixing a raw material powder HfC, a sintering assistant, and a carbon source (S210).

At this time, the carbon source in the method of producing the HfC composite according to the second embodiment of the present invention may be at least one selected from organic materials such as phenol resin, pitch, sucrose, and polyacrylonitrile (PAN) Can be used.

That is, as described above, in the first embodiment of the present invention, solid carbon materials such as graphite, carbon black, and activated carbon can be used as the carbon source. In the second embodiment of the present invention, , sucrose, and polyacrylonitrile (PAN) may be used.

Next, a method of manufacturing the HfC composite according to the second embodiment of the present invention includes a step of heat-treating the carbon source to produce a heat-treated carbon source (S220).

That is, in the second embodiment of the present invention, the carbon source on the organic material is heat-treated, and the carbon source is transformed into a powdery carbon source, so that the reaction with the sintering auxiliary can proceed in the sintering step described later.

At this time, the heat treatment may preferably be performed in a vacuum, nitrogen or Ar atmosphere at a temperature of 600 to 1000 ° C for 1 to 5 hours, but the heat treatment conditions are not limited in the present invention.

Next, the method of manufacturing the HfC composite according to the second embodiment of the present invention includes a step of sintering the mixture containing the HfC, the sintering aid, and the heat-treated carbon source (S230).

Since this is the same as the first embodiment, detailed description will be omitted below.

Thus, an HfC composite, that is, an HfC-SiC composite can be produced (S240).

FIG. 1C is a flowchart illustrating a method of manufacturing an HfC composite according to a third embodiment of the present invention. The method of manufacturing the HfC composite according to the third embodiment of the present invention may be the same as the method of manufacturing the HfC composite according to the second embodiment described above, except as described below.

Referring to FIG. 1C, a method of manufacturing a HfC composite according to a third embodiment of the present invention includes a step of heat-treating a carbon source to produce a heat-treated carbon source (S310).

At this time, the carbon source in the method of producing the HfC composite according to the third embodiment of the present invention may be at least one selected from organic materials such as phenol resin, pitch, sucrose, and poly acrylonitrile (PAN) Can be used.

That is, in the second embodiment and the third embodiment of the present invention, a carbon source such as the above-described organic material can be used as a carbon source.

On the other hand, as described above, the carbon flow on the organic material is transformed into a powdery carbon source, and a heat treatment process is required so that the reaction with the sintering auxiliary can proceed in the sintering step to be described later.

Therefore, in the third embodiment of the present invention, the heat treatment can be preferably performed in a vacuum, nitrogen or Ar atmosphere at a temperature range of 600 to 1000 ° C for 1 to 5 hours. However, in the present invention, .

Next, referring to FIG. 1C, the method of manufacturing the HfC composite according to the third embodiment of the present invention includes mixing the raw powder HfC, the sintering aid, and the heat-treated carbon source (S320).

That is, in the second embodiment of the present invention, the carbon source is heat-treated after the HfC, the sintering assistant, and the carbon source are mixed. In contrast, in the third embodiment of the present invention, Which corresponds to an embodiment in which the carbon source on the organic material is transformed into a carbon source on the carbon powder and then the heat-treated carbon source is mixed with the HfC and the sintering auxiliary.

Next, the method of manufacturing the HfC composite according to the third embodiment of the present invention includes the step of sintering the mixture containing the HfC, the sintering aids, and the heat-treated carbon source (S330).

Since this is the same as the first embodiment, detailed description will be omitted below.

Thus, an HfC composite, that is, an HfC-SiC composite can be produced (S340).

2A is a graph showing a discharge plasma sintering behavior of a high purity nano HfC powder without using a sintering aid, and FIG. 2B is a photograph showing the microstructure of the HfC sintered body obtained according to the result of FIG. 2A.

Referring to FIG. 2A, although the nano HfC powder is used, it can be seen that the sintering is performed to some extent by maintaining the pressure at 2300 ° C. and 100 MPa for 30 minutes (relative density is 96%).

Also, referring to FIG. 2B, it can be seen that the sintered body obtained as a result of sintering at a high temperature for a long time has very rough crystal grains having an average grain size of 5 μm or more and a considerable amount of pores remain.

From this, it can be seen that HfC is an extremely difficult material to sinter and there is a problem that coarse grains and many pores remain even when densifying by applying high pressure at an ultra-high temperature.

In order to solve this problem, for example, mixed powders of various compositions shown in Table 1 were used in the present invention. However, the composition shown in the following Table 1 is only an example, and the present invention does not limit the following composition.

Experimental Example Abbreviation Furtherance Experimental Example 1 HSC HfSi ₂ + 3C? HfC + 2SiC Experimental Example 2 HCHSC2 HfC + 20Wt% HSC Experimental Example 3 HCHSC3 HfC + 30Wt% HSC Experimental Example 4 HCHSC4 HfC + 40Wt% HSC

3 is a graph showing the image formation behavior with increasing temperature of the HfSi ₂ and C mixed powder (HSC composition in Table 1) mixed with the SPECS mill.

When the sintering temperature was above 1700 ℃, only HfC and SiC phases were observed and no residual HfSi ₂ or C was observed. From this, it can be seen that the reaction according to the reaction formula 2, for example, is completed at 1700 ° C or higher.

Therefore, when the sintering assistant of the component used in this experiment is used, the secondary phase, which can degrade the high-temperature characteristics after sintering, does not remain in spite of sintering at much lower temperature than that of single-phase HfC sintering , Which is one of the main features of this study.

Table 2 below shows the relative density and various mechanical properties of HSC specimens sintered at various temperatures.

Referring to Table 2, it was found that the sintered compact had a very high relative density of 99.5% at 1700 ° C. under a pressure of 40 MPa.

The elastic modulus, hardness and fracture toughness also showed excellent properties among the HfC - based materials, and even when the sintering temperature was increased from 1700 ℃ to 1900 ℃, the elastic modulus and hardness did not change significantly.

However, fracture toughness was significantly increased at 1900 ℃ sintering. As shown in Fig. 4, the sintering temperature of the sintered specimen at 1900 ℃ did not increase significantly until 1800 ℃, but the effect of fracture toughness due to crack deflection was significant .

4 is a photograph showing the microstructure of the nanocomposite prepared by HSC composition according to the sintering temperature change.

Referring to FIG. 4, no grain growth was observed until 1800 ° C., but a sharp grain growth was observed after sintering at 1900 ° C.

From these results, a sintering temperature suitable for producing the composite material according to the present invention can be determined in a temperature range of 1650 ° C to 2000 ° C.

That is, when the sintering temperature is lower than 1650 ° C., the sintered body is not densified to a degree that can be used for commercialization, and the sintered body is too weak in strength. In the case of heat treatment exceeding 2000 ° C., sintering has already been completed. However, The present invention has a critical meaning in the range of the heat treatment temperature as described above.

FIG. 5 is a photograph showing the composition distribution of the nanocomposite prepared by HSC composition analyzed by energy dispersive spectroscopy (EDS) mapping.

Referring to FIG. 5, it can be seen that the composition is a nanocomposite in which HfC and SiC are mixed very uniformly. In the SEM photograph, the bright region is HfC and the dark region is SiC.

It was also observed that C and O exist more in HfC than in SiC. As shown in FIG. 4 and FIG. 5, the microstructure of the resultant product of the present invention is such that very fine HfC and SiC within a few hundred nanometers are uniformly distributed, and HfSi ₂ , which is used as a sintering aid, Because they are uniformly mixed in the unit.

The microstructure in which such a very fine SiC is very uniformly distributed is one of the very important features of the present invention using HfSi ₂ and a carbon-based sintering auxiliary.

6 is XRD data according to the sintering temperature change after sintering of the HCHSC composition material.

Referring to FIG. 6, only HfC and SiC were detected under all conditions, and no residual HfSi ₂ or C was observed.

In the previous research, since sintering aids are used in most cases to sinter the ovoid-formed HfC and SiC, if a secondary phase is detected on the XRD data of the dense sintered body or if an amorphous secondary phase is observed even though it is not detected .

On the other hand, in the case of the sample obtained according to the present invention, only pure HfC and SiC are present in the reaction formula (2) after sintering, so only the HfC and SiC peaks are clearly obtained on the XRD data.

Since the present invention does not have a secondary phase or an amorphous phase that can degrade the ultrahigh-temperature characteristics of the HfC-SiC composite, the composite produced by the present invention is expected to exhibit excellent high-temperature characteristics and XRD data of the densely sintered sintered body It is one of the important features of the present invention that it consists of only pure HfC and SiC.

7 is a graph showing the sintering shrinkage behavior in the discharge plasma sintering of the HSHSC composition material.

Referring to FIG. 7, it can be seen that the sintering shrinkage starting temperature is about 1543 ° C for HCHSC2, about 1508 ° C for HCHSC3, and about 1463 ° C for HSHSC4. Sintering starts from a lower temperature as the amount of sintering aid increases.

Table 3 shows the sintering densities and mechanical properties of the nano HfC-SiC composites obtained under different sintering conditions from different HCHSC compositions.

Table 3 shows that the sintering temperature of 1850 ° C is required for densification with a relatively high density, while the amount of sintering aid is 30wt% (Experiment 3) and 40wt% (Experimental Example 4), high relative density values were obtained even after sintering at 1800 ° C and 1750 ° C, respectively.

The elastic modulus, hardness and fracture toughness showed excellent properties among the HfC-SiC materials, and even when the sintering temperature was increased from 1750 ° C to 1850 ° C, when the relative density was higher than 98.5% It did not appear.

However, fracture toughness was increased at 1850 ℃ sintering specimen, as shown in Fig. 9, which was not observed until 1800 ℃, while the sintering specimen at 1850 ℃ showed fracture toughness due to crack deflection due to grain growth It is because it is clear.

8 is a photograph showing a change in the microstructure of the nano-HfC-SiC composite according to the change of sintering aid amount.

Referring to FIG. 8, it can be seen that the content of SiC increases as the amount of sintering aid is increased. As shown in the present invention, by varying the content of the sintering aid in the composition, It means that the amount of SiC can be controlled without affecting the uniformity of the size and distribution of the formed SiC.

9 is a photograph showing the microstructure change of the HCHSC composite according to the sintering temperature change.

When the sintering temperature was 1750 ℃ and 1800 ℃, the size of grain size remained to be about 200nm, but when the sintering temperature was increased to 1850 ℃, grain growth was observed, which was consistent with the above HSC results.

From these results, it can be seen that HfC-SiC composites with finer grain size of less than 300nm can be prepared by forming HfC and SiC with fine size by reaction between HfSi ₂ + C and HfSi ₂ + .

As described above, there is an example in which Hf, Si and C are mixed and HfC-SiC composite material is sintered at a low temperature as described above. However, due to the strong explosive nature of the Hf powder as a raw material, there is a great problem in commercialization.

In addition, since the uniform distribution of the chemical composition can not be ensured, the composition is locally concentrated, and thus it is difficult to realize a composite material in which the grain size is fine and the secondary phase, SiC, is uniformly distributed. It is impossible to prevent impurities from being mixed in a large amount from the ball and the jar which are mixed media when the raw powders are pulverized and mixed with a strong mechanical force.

However, in the production of the HfC-SiC composite according to the present invention, zirconium silicides and hafnium silicides, which are sintering aids, are relatively stable in air and thus are easy to handle.

Since Zr or Hf and Si are uniformly mixed in the inside of ZrC or HfC and Si, the ZrC or HfC and SiC grains formed after sintering have a size range of 300 nm or less and HfC grains and SiC grains are uniformly distributed as a whole This is a preferable range of size and microstructure as a composite material containing a secondary phase having a minute size.

That is, according to the present invention, the sintered HfC-SiC composite has a grain size of 700 nm or less and has a microstructure in which two phases, for example, ZrC and SiC or HfC and SiC are uniformly distributed over the entire range.

In addition, the zirconium silicide group and the hafnium silicide group contribute to the densification of the zirconium silicide group and the hafnium silicide group at a temperature of 1300 DEG C or higher due to the relatively low melting temperature, It is expected that sintering easily occurs at low temperature because ZrC and SiC or HfC and SiC are changed into high temperature stable phase and excellent high temperature properties can be satisfied at the same time.

That is, in the present invention as described above, the zirconium silicide group (Zr _x Si _y , Zirconium silicides) or the hafnium silicide group (Hf _x Si _y (Zr)), in which Zr and Si or Hf and Si are uniformly mixed at the molecular unit level , Hafnium silicides), it is possible to manufacture HfC composites having finer grain size and SiC uniformly distributed by preventing local concentration of chemical composition.

Further, in the present invention, by mixing the zirconium silicide group or the hafnium silicide group as the Si source with the source of carbon, it is possible to produce a high purity HfC composite having a fine grain size and a uniform microstructure in spite of sintering at a low temperature have.

Also, in the present invention, the sintering step is carried out by using the pressure sintering method instead of the atmospheric pressure sintering method to prevent coarsening of particles generated at a high temperature, and a sintering process using low temperature deformation of the zirconium silicide group and the hafnium silicide group is faithfully performed The HfC complex is formed at an extremely low temperature as compared with the conventional method. Therefore, the HfC composite can be manufactured which minimizes grain growth and maximizes densification.

Thus, compared with the prior art, the present invention can achieve better effects in terms of ease of operation, purity, uniform distribution of secondary phase, grain size and sintering temperature.

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 (10)

Mixing HfC, sintering aids and carbon sources; And
Sintering the mixture comprising the HfC, the sintering aids and the carbon source,
The sintering aids may be selected from the group consisting of zirconium silicide (Zr _x Si _y , zirconium silicide) and hafnium silicide (Hf _x Si _y , Hafnium silicide)
The zirconium silicide group (Zr _x Si _y , Zirconium silicide) is at least one selected from the group consisting of ZrSi ₂ , ZrSi, Zr ₅ Si ₄ , Zr ₅ Si ₃ , Zr ₃ Si ₂ , Zr ₂ Si and Zr ₃ Si Wherein the hafnium silicide group (Hf _x Si _y , Hafnium silicide) is at least one selected from the group consisting of HfSi ₂ , HfSi, Hf ₅ Si ₄ , Hf ₃ Si ₂ and Hf ₂ Si. Gt; delete The method according to claim 1,
Wherein the carbon source is at least one selected from the group consisting of graphite, carbon black and activated carbon. The method according to claim 1,
Mixing the HfC, the sintering aid, and the carbon source; And sintering the mixture comprising HfC, the sintering aids and the carbon source,
Mixing HfC, sintering aids and carbon sources; Heat-treating the carbon source to produce a heat-treated carbon source; And sintering the mixture comprising the HfC, the sintering aids and the heat treated carbon source,
Wherein the carbon source is at least one selected from the group consisting of phenol resin, pitch, sucrose, and polyacrylonitrile (PAN). The method according to claim 1,
Mixing the HfC, the sintering aid, and the carbon source; And sintering the mixture comprising HfC, the sintering aids and the carbon source,
Heat-treating the carbon source to produce a heat-treated carbon source; HfC, a sintering aid, and the heat-treated carbon source; And sintering the mixture comprising the HfC, the sintering aids and the heat treated carbon source,
Wherein the carbon source is at least one selected from the group consisting of phenol resin, pitch, sucrose, and polyacrylonitrile (PAN). The method according to claim 1,
Wherein the HfC, the sintering aid, and the carbon source are mixed using a planetary mill, an attrition mill, a spes mill, or a high energy ball mill. The method according to claim 1,
The sintering step may be performed using a pressure sintering method,
Wherein the pressure in the pressure sintering method ranges from 20 to 120 MPa. 8. The method of claim 7,
Wherein the sintering temperature in the pressure sintering method is 1650 to 2000 占 폚. 9. The HfC complex produced by the method of any one of claims 1 to 8. 10. The method of claim 9,
Wherein the HfC composite has a grain size of 700 nm or less and HfC and SiC are uniformly distributed.

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