KR102526779B1 - Composition of high temperature ceramic thermal insulators with multiple thermal resistance induced extremely low thermal conductivity, thermal insulators and manufacturing method of the same - Google Patents

Abstract

The present invention relates to an ultra-low thermal conductivity ceramic high-temperature insulation material, a composition thereof, and a method for manufacturing the ultra-low thermal conductivity ceramic high-temperature insulation material.
More specifically, it includes SiC core/ SiO ₂ shell structure particles, porosity of 65 to 95%, thermal conductivity of 0.010 to 0.090 W/mK, and specific compressive strength in the range of 2 to 20 MPa.cm ³ /g. Provides an ultra-low thermal conductivity ceramic high-temperature insulation having a.
In addition, in order to manufacture the ultra-low thermal conductivity ceramic high-temperature insulation material, when the total inorganic material is 100% by weight, 20 to 60% by weight of nano SiC, 10 to 45% by weight of nano silica, 30 to 60% by weight of nano carbon and additional organic binder 1 It provides a composition for preparing ultra-low thermal conductivity ceramic high-temperature insulation containing ~5% by weight.
In addition, it provides a manufacturing process of the ultra-low thermal conductivity ceramic high-temperature insulation material, characterized in that it comprises particles of the SiC core / SiO ₂ shell structure.

Description

Composition of high temperature ceramic thermal insulators with multiple thermal resistance induced extremely low thermal conductivity, thermal insulators and manufacturing method of the same}

The present invention relates to a composition for ultra-low thermal conductivity ceramic high-temperature insulating material, a high-temperature insulating material, and a method for manufacturing the same, which have excellent specific compressive strength and thermal insulation properties.

High-temperature insulation materials for lightweight automobiles and aircraft, insulation materials for defense and space industries such as missiles, spacecraft, and satellites, insulation materials for LNG carriers, and industrial high-temperature insulation materials, etc. The need for a new high-temperature insulation material with excellent structural stability and strength to density (i.e., specific compressive strength) is emerging.

Due to its excellent properties, such as high specific surface area, controllable porosity, excellent thermal shock resistance, excellent chemical stability and low thermal conductivity, along with a controllable porous network, porous ceramics are widely used in insulation materials, ceramic filters, catalyst supports, fuel cell electrodes, and lightweight vacuums. It is widely used in fields such as panel cores and industrial flooring materials.

Porous insulating ceramics require low thermal conductivity and excellent strength, but porous insulating ceramics have inherent brittleness, which often limits their structural applications, and when mechanical strength is increased, thermal insulation performance may deteriorate. Accordingly, research has been actively conducted to develop a high-performance insulator having excellent thermal insulation properties while satisfying excellent mechanical properties.

In general, strategies for manufacturing ceramics with excellent thermal insulation properties include (1) selection of materials with low intrinsic thermal conductivity, (2) maximization of porosity, and (3) phonon scattering at the interface between pores and struts. ) methods such as reinforcement have been proposed.

In previous studies, the following strategies were proposed to maximize porosity in porous SiC-based ceramics with excellent high-temperature stability.

(1) Production of high porosity porous SiC ceramics using direct foaming [H.D. Kim, Y.W. Kim, and C.B. Park, “Microporous Ceramic Materials and The Producing Method of the Same,” US Patent 7,008,576 (March 7, 2006)]

(2) Manufacture of high porosity porous SiC ceramics using the gel freezing method [M. Fukushima, M. Nakata, Y. Zhou, T. Ohji, YI Yoshizawa, Fabrication and properties of ultra highly porous silicon carbide by the gelation-freezing method, J. Eur. Ceram. S°C. 30 (2010) 2889-2896, https://doi.org/10.1016/j.jeurcerams℃.2010.03.018 .]

(3) Manufacture of low thermal conductivity room temperature insulator using supercritical drying process [L. Su, H. Wang, M. Niu, X. Fan, M. Ma, Z. Shi, SW Guo, Ultralight, recoverable, and high-temperature-resistant SiC nanowire airgel, ACS Nano 12 (2018) 3103-3111, https ://doi.org/10.1021/acsnano.7b08577 .]

(4) Manufacture of a porous material having nanopores [P. Wan, Z. Wu, H. Zhang, L. Gao, J. Wang, Porous nano-SiC as thermal insulator: wisdom on balancing thermal stability, high strength and low thermal conductivity, Mater. Res. Lett. 4 (2016) 104-111, https://doi.org/10.1080/21663831.2015.1121167.].

Here, maximizing the porosity is the main method of reducing thermal conductivity, but increasing the porosity often accompanies a decrease in mechanical properties. Porous silica ceramics used as one of the materials for insulation are highly evaluated due to their excellent insulation performance, but their application to moving vehicles (aircraft, spacecraft, advanced vehicles, missiles, etc.) is limited because of their weak mechanical strength.

Over the past decades, various attempts have been made to enhance the mechanical properties of porous silica-based ceramics having low thermal conductivity. For example, reinforcement may be attempted through addition of various fibers such as carbon fibers, silica fibers, glass fibers, mullite or alumina fibers, addition of silicon nitride or alumina particles, and addition of crosslinkable ceramic precursors. . Although these attempts have been able to improve mechanical properties to a certain level, there is a disadvantage in that insulation efficiency is lowered due to an increase in a heat transfer area due to an increase in fiber or particle reinforcing materials in porous ceramics.

In particular, in recent years, demands for lightweight insulation materials as well as low thermal conductivity and excellent mechanical strength are increasing in the aerospace and defense fields, such as high-tech carriers (LNG carriers, supersonic aircraft, future vehicles, etc.), missiles, spacecraft, and satellites, and mechanical strength The need for an ultra-low thermal conductivity high-temperature insulator with increased specific strength divided by density is emerging. However, a state-of-the-art ultra-low thermal conductivity insulator with both very low thermal conductivity and high specific strength properties has not yet been reported.

The present invention is to solve the above-mentioned problems of the prior art, and an object of the present invention is to provide a heat insulating ceramic having a hierarchical pore structure with excellent specific compressive strength as well as heat insulating properties and a composition thereof, and It is to provide a manufacturing method thereof.

However, the problem to be solved by the present invention is not limited to the problems mentioned above, and other problems not mentioned will be clearly understood by those skilled in the art from the description below.

In order to achieve the above object, the present invention includes silicon carbide, silica and carbon particles, and the surface of the silicon carbide is partially oxidized to form a structure of a silicon carbide core / silica shell (SiC core / SiO ₂ shell) , The silicon carbide, silica and carbon particles are characterized in that they have a size of 1 nm or more and less than 300 nm, and provides a composition for ultra-low thermal conductivity ceramic high-temperature insulation.

When the total amount of the silicon carbide, silica and carbon particles is 100% by weight, it is preferable that the silicon carbide is 20 to 60% by weight, the silica is 10 to 45% by weight, and the carbon is 30 to 60% by weight.

An organic binder is further added to the silicon carbide, silica, and carbon particles, and the organic binder is preferably 1 to 5% by weight based on the total weight of the composition.

In addition, the present invention (a) preparing a mixture by mixing silicon carbide having a size of 1 nm or more and less than 300 nm, silica having a size of 1 nm or more and less than 300 nm, and carbon having a size of 1 nm or more and less than 300 nm and an organic binder; (b) preparing a molded body using the mixture; (c) sintering the molded body in an atmosphere containing air or oxygen; provides a method for manufacturing an ultra-low thermal conductivity ceramic high-temperature insulation material comprising a.

In step (a), when the total amount of silicon carbide, silica and carbon particles is 100% by weight, 20 to 60% by weight of silicon carbide, 10 to 45% by weight of silica, and 30 to 60% by weight of carbon, Here It is preferable to further include 1 to 5% by weight of an organic binder.

In step (c), the sintering is preferably normal pressure sintering.

The sintering of the step (c) is preferably performed in an atmosphere containing oxygen for 0.5 to 4 hours at a temperature range of 600 to 1200 ° C.

In addition, the present invention is prepared by the above-described method, includes silicon carbide particles having a silicon carbide core / silica shell structure, and has a porosity of 65 to 95%, a thermal conductivity of 0.010 to 0.090 W / mK, and specific compressive strength (specific compressive strength). ) It provides an ultra-low thermal conductivity ceramic high-temperature insulation material, characterized in that it has a range of 2 ~ 20 MPa.cm ³ /g.

The silica shell is amorphous silica, and the silica shell is partially sintered with silica powder having a size of 1 nm or more and less than 300 nm to increase strength, and carbon having a size of 1 nm or more and less than 300 nm is oxidized during sintering in an oxidizing atmosphere to form macro pores. It is desirable to form

The porous ceramic high-temperature insulation material including SiC core/SiO ₂ shell particles of the present invention is prepared by mixing nano-silicon carbide, nano-silica, and nano-carbon in a certain ratio, thereby forming a layer composed of nano, meso, and macro pores. Excellent non-compressive strength properties can be realized along with excellent insulation properties with a pore structure.

Moreover, by sintering in an oxidizing atmosphere at a relatively low temperature, it is possible to improve economic efficiency as well as process efficiency.

The effects of the present invention are not limited to the above effects, and should be understood to include all effects that can be inferred from the detailed description of the present invention or the configuration of the invention described in the claims.

1 shows a schematic diagram and a thermal resistance circuit diagram showing multiple thermal resistances of ultra-low thermal conductivity ceramic high-temperature insulation materials.
2a and 2b are according to an embodiment of the present invention It shows the microstructure of ultra-low thermal conductivity ceramic high-temperature insulation.
3 is a graph showing a hierarchical pore structure composed of nano, meso, and macro pores of an ultra-low thermal conductivity ceramic high-temperature insulation material according to an embodiment of the present invention.
4 is a high-resolution transmission electron micrograph of an ultra-low thermal conductivity ceramic high-temperature insulation material according to an embodiment of the present invention.

Hereinafter, the present invention will be described in more detail based on preferred embodiments and accompanying drawings.

In ceramics, heat is transmitted by phonons. In order to maximize the scattering of phonons in the passage of heat transfer, the present invention uses nano SiC and nano SiO ₂ powders as raw materials that have stability at high temperatures and do not react below 1600 ° C. In addition, by using nano-carbon particles capable of forming nano-pores as a pore-forming material and sintering in an oxidizing atmosphere at a low temperature of 600 ~ 1200 ℃, nanopores (2 nm or less), mesopores (2 ~ 50 nm) and macropores (50 nm) Above) while having a hierarchical pore structure composed of SiC core / SiO ₂ Shell (shell) particles, an ultra-low thermal conductivity porous ceramic high-temperature insulation material was prepared.

In the porous ceramic high-temperature insulation material including the SiC core/SiO ₂ shell particles, since the starting material is nano-sized, nanopores are formed in the voids between the starting particles, and mesopores are formed between the aggregates of the starting material and the aggregates, as a pore-forming material. The added nano-carbon is thermally oxidized during sintering in an oxidizing atmosphere, and is scattered as CO or CO ₂ to form macropores.

In this regard, Figures 2a and 2b according to an embodiment of the present invention The microstructure of ultra-low thermal conductivity ceramic high-temperature insulation is shown, and the existence of intra-aggregate pores with mesopore sizes and macro-pores (inter-aggregate pores) between aggregates due to oxidation of the pore-forming material are shown. show In FIG. 3, the hierarchical structure of such pores is well represented in a graph.

The hierarchical pore structure composed of the nano, meso, and macro pores maximizes phonon scattering to achieve ultra-low thermal conductivity, and the SiC core/SiO ₂ shell particles form a SiC core-SiO ₂ shell heterogeneous interface in one nanoparticle. Porous ceramics high-temperature insulation including SiC core / SiO ₂ shell particles having very excellent compressive strength because there are no macropores that cause scattering of phonons, implement low thermal conductivity, and reduce the mechanical strength of porous ceramics. Provided.

In addition, the present invention maximizes the porosity of the porous ceramic high-temperature insulation material to 65% or more by controlling the content of the pore former and the sintering temperature to achieve weight reduction, and has a very good specific compressive strength due to low density and high compressive strength. Provided is a ceramic high-temperature insulating material having low thermal conductivity.

In addition, the present invention provides a composition for preparing a ceramic high-temperature insulating material having the excellent specific compressive strength and ultra-low thermal conductivity.

In addition, the present invention provides a manufacturing process of the ceramic high-temperature insulating material having the excellent specific compressive strength and ultra-low thermal conductivity.

The composition of the ceramic high-temperature insulating material having ultra-low thermal conductivity and high specific compressive strength of the present invention is 20 to 60% by weight of nano silicon carbide particles and nano silica (SiO ₂ ) particles when the total amount of inorganic materials in the composition is 100% by weight 10 to 45% by weight, 30 to 60% by weight of nano-carbon as a pore-forming material, and preferably 1 to 5% by weight of an organic binder for the molding process.

Silicon carbide powder, silica powder, and carbon powder used as main raw materials in the composition are preferably nanopowder having an average particle size of 1 nm or more and less than 300 nm.

The surface of the nano-silicon carbide powder of the present invention is partially oxidized during sintering in an oxidizing atmosphere to form amorphous silica (amorphous SiO ₂ ) on the surface to form SiC core/SiO ₂ shell nanoparticles, and amorphous silica on the surface of the SiC particles. Partial sintering occurs with the added nano-silica powder to form a solid structure to impart strength, and nano-carbon is oxidized during sintering in an oxidizing atmosphere to form macropores and achieves light weight, so that it has very low thermal conductivity and high Provides an ultra-low thermal conductivity ceramic high-temperature insulation material comprising SiC core / SiO ₂ shell particles having specific compressive strength.

In this regard, FIG. 4 is a high-resolution transmission electron micrograph of an ultra-low thermal conductivity ceramic high-temperature insulation material according to an embodiment of the present invention, in which nano SiC particles are oxidized during sintering to form a SiC core/SiO ₂ shell structure and the SiC core /SiO ₂ It shows a microstructure in which shell particles and nano-silica particles are firmly bonded.

On the other hand, phonon, which is a heat transfer medium in ceramics, causes scattering at the SiC core/SiO ₂ shell interface to improve thermal resistance (making heat transfer difficult), and also causes phonon scattering in nano, meso, and macropores, and also SiO phonon scattering occurs even at the interface between the ₂ shell-added nano SiO ₂ particles, which greatly increases the multiple thermal resistance, enabling the achievement of ultra-low thermal conductivity.

On the other hand, since the starting materials SiC, SiO ₂ and carbon are all nano-sized, there are more interfaces between different materials per unit volume compared to the case of using sub-micron (average particle size of 0.1 μm or more and less than 1 μm) or micron-sized particles. is formed, which causes phonon scattering at each interface to create a higher thermal resistance, and as a result, it is possible to achieve a very low thermal conductivity.

The process of manufacturing a ceramic high-temperature insulation having ultra-low thermal conductivity and high specific compressive strength is

(1) preparing a mixture of a composition comprising silicon carbide, silica, carbon and an organic binder;

(2) preparing a molded article in a predetermined shape using a mixture of the above composition; and

(3) atmospheric pressure sintering of the molded body;

In the present invention, the composition for ceramic high-temperature insulation having a hierarchical pore structure is 20 to 60% by weight of nano silicon carbide particles and 10 to 45% by weight of nano silica particles, pore forming material, when the total weight of ceramic is 100% by weight As the nano-carbon is composed of 30 to 60% by weight, it is preferable that the organic binder additionally contains 1 to 5% by weight for the molding process.

In addition, it is possible to use both alpha phase and beta phase or a mixture thereof as the silicon carbide powder, and it is preferable to use nano-sized (1 nm or more and less than 300 nm) powder. Although silicon carbide particles of less than 1 nm may be used, nanopowders in the range of 1 nm or more and less than 300 nm are suitable from an economic point of view.

The silica powder may be amorphous, crystalline, or a mixture thereof, and it is preferable to use nano-sized (1 nm or more and less than 300 nm) powder. Silica particles of less than 1 nm may be used, but nanopowders in the range of 1 nm or more and less than 300 nm are suitable from an economic point of view.

The carbon particles added as the pore-forming material may be amorphous, crystalline, or mixtures thereof, and it is preferable to use nano-sized (1 nm or more and less than 300 nm) powder. Silica particles of less than 1 nm may be used, but nanopowders in the range of 1 nm or more and less than 300 nm are suitable from an economic point of view.

In the present invention, when nano silicon carbide is used at less than 20% by weight in the total weight of ceramics, the amount of SiC core/SiO ₂ shell particles formed by oxidation of nano silicon carbide is too small, so the thermal resistance is lowered and the thermal conductivity is 0.090 W/mK. There is a disadvantage in that the specific compressive strength is lowered to less than 2 MPa.cm ³ /g because the amorphous silica content on the surface of the nano silicon carbide is too small, and the porosity is lowered to less than 65% when used in excess of 60% by weight. Since the thermal conductivity is higher than 0.090 W / mK, it is preferable to limit the addition amount of nano SiC particles to 20 to 60% by weight.

Adding less than 10% by weight of nano-silica particles to the total weight of the ceramic causes the area of the interface between the SiC core/SiO ₂ shell particles and the added SiO ₂ particles to be too small, resulting in a high thermal conductivity exceeding 0.090 W/mK. And, since the specific compressive strength is lowered to less than 2 MPa.cm ³ /g when the amount of added amount of nano-silica particles exceeds 45% by weight, it is preferable to limit the amount of added amount of nano-silica particles to 10 to 45% by weight. .

When the nano-carbon particles are added at less than 30% by weight in the total weight of the ceramic, the porosity is lowered to less than 65% and the thermal conductivity becomes higher than 0.090 W/mK. A large amount of nano-carbon is oxidized in an oxidizing atmosphere, resulting in too many macropores, and as a result, the specific compressive strength is lowered to less than 2 MPa.cm ³ /g, so the addition amount of nano-carbon particles is limited to 30 to 60% by weight. It is desirable to do

As the organic binder added to facilitate the molding process, one or more organic binders selected from polyethylene glycol, polyvinyl alcohol, polyvinyl butyl alcohol, methyl cellulose, and paraffin may be used, but the material is not limited thereto. That is, any organic binder may be used as long as it is helpful in forming a ceramic high-temperature insulating material having a hierarchical pore structure.

The content of the organic binder is preferably 1 to 5% by weight of the inorganic material. When the organic binder content is less than 1% by weight, molding defects occur, which is not preferable, and when the organic binder content exceeds 5% by weight, the organic binder is decomposed and disappears during the sintering process, so there is no particular advantage. Therefore, the content of the organic binder is preferably limited to 1 to 5% by weight.

In the step of preparing a mixture of the composition for a ceramic high-temperature insulating material having a gradient pore structure including the nano-silicon carbide, nano-silica, nano-carbon, and an organic binder, the solvent in the mixing process is any one capable of dissolving the organic binder to be added. feel free to use Specifically, methanol, ethanol, propanol, butanol, acetone, or water may be used alone or in combination of two or more.

The mixing process may be performed by a conventional ball milling process. At this time, it is preferable to use a silicon carbide ball to prevent contamination, and it is preferable to use a container made of silicon carbide or plastic material. However, any bowl or container may be used as long as it can make a homogeneous mixture of the composition.

The step of forming the ultra-low thermal conductivity ceramic high-temperature insulation having a layered pore structure having a controlled shape using the mixture of the composition for the ultra-low thermal conductivity ceramic high-temperature insulation is uniaxial pressure molding, cold isostatic pressure molding, slip casting, One or two or more molding methods such as extrusion and injection molding may be used in combination, but it is not limited to these methods, and nano silicon carbide, nano silica, nano carbon and organic binders Any method may be used as long as it can mold a mixture containing

The atmospheric pressure sintering of the molded body of the ultra-low thermal conductivity ceramic high-temperature insulating material having a hierarchical pore structure according to the present invention is carried out in an oxidizing atmosphere (air atmosphere or It is preferable to carry out in an atmosphere containing oxygen), and the holding time at the highest temperature is preferably 0.5 to 4 hours. During the sintering process, it is preferable to maintain the temperature range of 300 to 450° C. for 0.5 to 2 hours before reaching the maximum temperature for thermal decomposition of the organic binder.

If the sintering temperature is less than 600 ° C, the formation of SiO ₂ shell particles due to oxidation of nano-SiC particles is not sufficient, so that after sintering, the formation of SiC core / SiO ₂ shell particles, which is the core idea of the present invention, is not sufficient, and the thermal conductivity There is a disadvantage in that the specific compressive strength exceeds 0.090 W/mK or the specific compressive strength is lowered to less than 2 MPa.cm ³ /g, and when the sintering temperature exceeds 1200 ° C, an excessive amount of SiO ₂ shell is formed on the surface of the nano SiC particles, resulting in amorphous Partial densification proceeds by viscous flow on silica, so that the porosity of the ceramic high-temperature insulation is lowered to less than 65%, and the thermal conductivity exceeds 0.090 W/mK. Therefore, the sintering temperature is preferably limited to the range of 600 to 1200 ° C.

In the sintering process, when the holding time at the highest temperature is less than 0.5 hours, the formation of SiO ₂ shell particles on the surface of the nano-SiC particles is insufficient, and when it exceeds 4 hours, an excessive amount of amorphous SiO ₂ shell formed on the surface of the nano-SiC particles There is a disadvantage in that the thermal conductivity exceeds 0.090 W / mK due to partial densification by the viscous flow of . Therefore, the holding time at the highest temperature during the sintering process is preferably limited to a range of 0.5 to 4 hours.

It is preferable to use air as the sintering atmosphere, and a nitrogen or argon atmosphere is not preferable because it inhibits the formation of SiO ₂ shells on the surfaces of nano-SiC particles. Even in an atmosphere containing oxygen, SiO ₂ shells are formed on the surfaces of nano-SiC particles. However, for effective formation of the SiC core/SiO ₂ shell structure during the sintering process, which is one of the key ideas of the present invention, an air atmosphere is most suitable in terms of process economy.

Below, it will be described in detail based on an embodiment of the present invention. The presented examples are illustrative and not intended to limit the scope of the present invention.

<Examples 1 to 4 and Comparative Examples 1 to 4>

In this embodiment, steps 1-1 to 1-3 were performed as follows to manufacture an ultra-low thermal conductivity ceramic high-temperature insulation material using multiple thermal resistance.

1-1. Preparation of a mixture of ultra-low thermal conductivity ceramic high-temperature insulation composition containing silicon carbide, silica, carbon and an organic binder

In the ratios shown in Table 1 below, beta-phase silicon carbide powder having an average particle diameter of 50 nm, amorphous silica powder having an average particle diameter of 25 nm, amorphous carbon particles having an average particle diameter of 70 nm, and 3% by weight of polyethylene glycol as an organic binder were added, followed by 75 weight of distilled water. % as a solvent and ball milled for 24 hours using SiC balls and a polypropylene container in a conventional ball milling process to prepare a mixture slurry of a uniform composition for ultra-low thermal conductivity ceramic high-temperature insulation, and this slurry was prepared in a conventional dryer was dried at 90 °C for 24 hours.

Composition and sintering conditions of mixture for ultra-low thermal conductivity ceramic high-temperature insulation division
(weight%)
Nano Beta Silicon Carbide
(β-SiC) nano silica
(SiO ₂ ) nano carbon
(C) sintering temperature
(℃) sintering time
(h) comparative example One 36.0 24.0 40.0 500 2 2 36.0 24.0 40.0 1,300 2 3 10.0 40.0 50.0 800 2 4 70.0 0 30.0 1,000 2 Example One 36.0 24.0 40.0 600 2 2 30.0 30.0 40.0 600 2 3 36.0 24.0 40.0 800 2 4 50.0 10.0 40.0 1,000 2

1-2. Preparation of a molded body using a mixture of ultra-low thermal conductivity ceramic composition for high-temperature insulation

The mixture of the ultra-low thermal conductivity ceramic high-temperature insulation composition prepared by the method 1-1 was put into a mold mold, and a molded body was prepared at a pressure of 15 MPa to form a molded body of 10 x 10 x 20 mm ³ and a molded body of 40 x 40 x 6 mm ³ A molded body was prepared. A molded body of 10 x 10 x 20 mm ³ was prepared for measuring compressive strength, and a molded body of 40 x 40 x 6 mm ³ was prepared for measuring thermal conductivity.

1.3. Normal pressure sintering of compacts

Thereafter, the molded body was sintered under normal pressure in the air under the sintering conditions of Table 1 to prepare the ultra-low thermal conductivity ceramic high-temperature insulation material of the present invention. In the process of raising the temperature to the highest temperature during the sintering process, it was maintained at 400 ° C. for 1 hour for thermal decomposition of the organic binder, and then heated to the highest temperature shown in Table 1 and subjected to an atmospheric pressure sintering process.

As shown in Table 1 below, in Comparative Example 1, a molded body of the same size was prepared under the same conditions as in Example 1 using the same composition as that of Example 1, but the sintering temperature range was 600 to 600, which is one of the key ideas of the present invention. Atmospheric pressure sintered for 2 hours at 500 ° C out of 1200 ° C.

In Comparative Example 2, as shown in Table 1, a molded body of the same size was prepared under the same conditions as in Example 1 using the same composition as that of Example 1, but the sintering temperature range of 600 Atmospheric pressure sintered for 2 hours at 1300 ° C out of ~ 1200 ° C.

In Comparative Example 3, the amount of nano SiC powder added, which is one of the key ideas of the present invention, is in the range of 20 to 60% by weight. A molded body was prepared in the same manner as in Example 3 by adding 50% by weight, and sintered at atmospheric pressure under the same sintering conditions as in Example 3.

In Comparative Example 4, the amount of nano SiC powder added, which is one of the key ideas of the present invention, is in the range of 20 to 60% by weight. A molded body was prepared in the same manner as in Example 4 by adding 30% by weight, and sintered at atmospheric pressure under the same sintering conditions as in Example 4.

The density of the manufactured ultra-low thermal conductivity ceramic high-temperature insulating material was measured by dividing the mass of the ceramic high-temperature insulating material manufactured using a 40 x 40 x 6 mm ³ molded body by the volume. The compressive strength of the manufactured ultra-low thermal conductivity ceramic high-temperature insulation was measured using an Instron instrument at a crosshead speed of 0.5 mm/min, and the thermal conductivity of the manufactured ultra-low thermal conductivity ceramic high-temperature insulation was measured using a hot disk ) method. The specific compressive strength of the manufactured ultra-low thermal conductivity ceramic high-temperature insulation was calculated by dividing the compressive strength by the density.

Porosity, thermal conductivity, and specific compressive strength of ultra-low thermal conductivity ceramic high-temperature insulation materials division
porosity
(%) thermal conductivity
(W/mK) specific compressive strength
(MPa cm ³ /g) comparative example One The intensity is too weak to be measurable The intensity is too weak to be measurable The intensity is too weak to be measurable 2 47.5 0.450 3.5 3 55.2 0.434 4.2 4 30.4 1.020 12.1 Example One 73.0 0.039 2.4 2 72.7 0.038 3.9 3 71.0 0.041 4.2 4 71.2 0.059 8.0

As shown in Tables 1 and 2, in the case of Comparative Example 1 and Comparative Example 2, which were sintered out of the sintering temperature range of 600 to 1200 ° C, which is one of the key ideas of the present invention, the strength was too weak to measure thermal conductivity and density, or Physical properties unsuitable for application as a high-temperature insulator were obtained, such as a porosity of less than 60% and a thermal conductivity of more than 0.4 W/mK.

In Comparative Example 3 and Comparative Example 4, 10% by weight or 70% by weight of nano-SiC particles were added out of the range (20 to 60% by weight) of the nano-SiC powder, which is one of the key ideas of the present invention, In the case of molding and normal pressure sintering under the same conditions as in 4, the thermal conductivity is too high as 0.400 W/mK or more, and the porosity is very low as less than 60%, so it is not suitable as an ultra-low thermal conductivity ceramic high-temperature insulation material.

Therefore, Comparative Examples 1 to 4 have disadvantages such as too low compressive strength, too high thermal conductivity of 0.400 W/mK or more, or too low porosity of less than 60%, resulting in physical properties of the ultra-low thermal conductivity ceramic high-temperature insulation material of the present invention. are clearly distinguished from

On the other hand, Examples 1 to 4 were prepared by the following process according to the core idea of the present invention. A composition for ultra-low thermal conductivity ceramic high-temperature insulation is prepared by adding 30 to 50% by weight of nano silicon carbide particles, 10 to 30% by weight of nano silica particles, 40% by weight of nano carbon particles, and 3% by weight of an organic binder to prepare a uniformly mixed composition. And, using the composition, a molded body of an ultra-low thermal conductivity ceramic high-temperature insulation material was manufactured by a uniaxial pressure molding method. By sintering the molded body for 2 hours using an air atmosphere at 600 to 1000 ° C., the porosity is 70% or more, the thermal conductivity is in the range of 0.038 to 0.059 W / mK, and the specific compressive strength is in the range of 2.4 to 8.0 MPa.cm ³ /g. An ultra-low thermal conductivity ceramic high-temperature insulation material having insulating properties was prepared.

In addition, although not shown as experimental results here, it was confirmed that within the ranges of raw material content, sintering temperature, sintering time, etc. presented in the present invention, excellent thermal conductivity and specific compressive strength were exhibited in contrast to cases outside these ranges.

<Examples 5 to 8>

In this embodiment, steps 2-1 to 2-3 were performed as follows to manufacture an ultra-low thermal conductivity ceramic high-temperature insulation material using multiple thermal resistance.

2-1. Preparation of a mixture of ultra-low thermal conductivity ceramic high-temperature insulation composition containing silicon carbide, silica, carbon and an organic binder

In the ratios shown in Table 3 below, beta-phase silicon carbide powder having an average particle diameter of 30 nm, amorphous silica powder having an average particle diameter of 25 nm, amorphous carbon particles having an average particle diameter of 40 nm, and 3.5% by weight of polyethylene glycol as an organic binder were added, and 78 weight of distilled water % was added as a solvent and ball milled for 24 hours using SiC balls and a polypropylene container in a conventional ball milling process to prepare a mixture slurry of a uniform composition for ultra-low thermal conductivity ceramic high-temperature insulation, and this slurry was prepared in a conventional dryer was dried at 90 °C for 24 hours.

Composition and sintering conditions of mixture for ultra-low thermal conductivity ceramic high-temperature insulation division
(weight%)
Nano Beta Silicon Carbide
(β-SiC) nano silica
(SiO ₂ ) nano carbon
(C) sintering temperature
(℃) sintering time
(h) Example 5 25 40 35 750 One 6 23 20 57 600 2 7 22 28 50 700 2 8 20 40 40 1,100 One

2-2. Preparation of a molded body using a mixture of ultra-low thermal conductivity ceramic composition for high-temperature insulation

The mixture of the ultra-low thermal conductivity ceramic high-temperature insulation composition prepared by the method 2-1 was put into a mold mold, and a molded body was prepared at a pressure of 20 MPa to form a molded body of 10 x 10 x 20 mm ³ and a molded body of 40 x 40 x 8 mm ³ A molded body was prepared. A molded body of 10 x 10 x 20 mm ³ was prepared for measuring compressive strength, and a molded body of 50 x 50 x 8 mm ³ was prepared for measuring thermal conductivity.

2.3. Normal pressure sintering of compacts

Thereafter, the molded body was sintered under normal pressure in air under the sintering conditions of Table 3 to prepare an ultra-low thermal conductivity ceramic high-temperature insulation material of the present invention. In the process of raising the temperature to the highest temperature during the sintering process, it was maintained at 410 ° C. for 1 hour for thermal decomposition of the organic binder, and then heated to the highest temperature shown in Table 3 and subjected to an atmospheric pressure sintering process.

The density of the ultra-low thermal conductivity ceramic high-temperature insulator was measured by dividing the mass of the high-temperature insulator manufactured using a 50 x 50 x 8 mm ³ molded body by the volume. The compressive strength of the prepared ultra-low thermal conductivity ceramic high-temperature insulation was measured using an Instron instrument at a crosshead speed of 0.5 mm/min, and the thermal conductivity of the prepared ultra-low thermal conductivity ceramic high-temperature insulation was measured using a hot disk ) method. The specific compressive strength of the manufactured ultra-low thermal conductivity ceramic high-temperature insulation was calculated by dividing the compressive strength by the density.

Porosity, thermal conductivity, and specific compressive strength of ultra-low thermal conductivity ceramic high-temperature insulation materials division
porosity
(%) thermal conductivity
(W/mK) specific compressive strength
(MPa cm ³ /g) Example 5 72.3 0.034 10.5 6 89.5 0.019 3.1 7 82.3 0.026 3.5 8 74.5 0.031 9.8

Examples 5 to 8 prepared according to the core idea of the present invention have a porosity of 72% or more, thermal conductivity in the range of 0.019 to 0.034 W / mK, and specific compressive strength in the range of 3.1 to 10.5 MPa.cm ³ /g. An ultra-low thermal conductivity ceramic high-temperature insulation material is provided.

As described above, although the embodiments have been described with limited examples and drawings, those skilled in the art can make various modifications and variations from the above description. For example, even if the described techniques are performed in a different order from the described method, and/or the described components are combined or combined in a different form than the described method, or substituted or replaced by other components or equivalents. Appropriate results can be achieved.

Therefore, other implementations, other embodiments, and equivalents of the claims are within the scope of the following claims.

Claims (9)

It includes silicon carbide, silica and carbon particles, the surface of which is partially oxidized to form a structure of silicon carbide core / silica shell (SiC core / SiO ₂ shell), and the silicon carbide, silica and carbon particles are 1 nm have a size greater than or equal to 300 nm,
When the total amount of the silicon carbide, silica and carbon particles is 100% by weight, 20 to 60% by weight of silicon carbide, 10 to 45% by weight of silica, and 30 to 60% by weight of carbon Ultra low thermal conductivity ceramic high temperature Composition for insulation. delete According to claim 1,
An organic binder is further added to the silicon carbide, silica and carbon particles, and the organic binder is 1 to 5% by weight based on the total weight of the composition. (a) preparing a mixture by mixing silicon carbide having a size of 1 nm or more and less than 300 nm, silica having a size of 1 nm or more and less than 300 nm, carbon having a size of 1 nm or more and less than 300 nm, and an organic binder;
(b) preparing a molded body using the mixture;
(c) sintering the molded body in an atmosphere containing air or oxygen;
Including,
In step (a), when the total amount of silicon carbide, silica and carbon particles is 100% by weight, 20 to 60% by weight of silicon carbide, 10 to 45% by weight of silica, and 30 to 60% by weight of carbon, Here A method of manufacturing an ultra-low thermal conductivity ceramic high-temperature insulation material, characterized in that it further comprises 1 to 5% by weight of an organic binder. delete According to claim 4,
The sintering in step (c) is a method for producing an ultra-low thermal conductivity ceramic high-temperature insulation material, characterized in that normal pressure sintering. According to claim 4,
The sintering in step (c) is a method for producing an ultra-low thermal conductivity ceramic high-temperature insulation, characterized in that carried out in an atmosphere containing oxygen for 0.5 to 4 hours in the temperature range of 600 ~ 1200 ℃. It is prepared by the method of claim 4,
It contains silicon carbide particles with a silicon carbide core/silica shell structure, and has a porosity of 65 to 95%, thermal conductivity of 0.010 to 0.090 W/mK, and specific compressive strength of 2 to 20 MPa.cm ³ /g. Ultra-low thermal conductivity ceramic high-temperature insulation, characterized in that. According to claim 8,
The silica shell is amorphous silica, and the silica shell is partially sintered with silica powder having a size of 1 nm or more and less than 300 nm to increase strength, and carbon having a size of 1 nm or more and less than 300 nm is oxidized during sintering in an oxidizing atmosphere to form macro pores. Ultra-low thermal conductivity ceramic high-temperature insulation, characterized in that for forming.

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