Preparation process of environment-friendly ceramic composite material

Abstract

This invention discloses a preparation process for an environmentally friendly ceramic composite material, specifically relating to the field of environmentally friendly ceramic materials technology. The process includes S1, raw material pretreatment; S2, mixing and addition; S3, wet molding; S4, gradient debinding; and S5, low-temperature sintering. This invention enables the production of high-strength, porous ceramic materials with controllable pore structure under low-temperature sintering conditions. It achieves in-situ mullite formation through the synergistic promotion of diatomaceous earth and rice husk ash, and optimizes the pore structure and interface bonding using composite pore-forming agents and coupling agents. This results in ceramic materials with three-dimensional interconnected open pores, high porosity, low thermal conductivity, and excellent high-temperature stability. Simultaneously, the mineral phases and interface structures formed during sintering synergistically fix heavy metals, significantly reducing the risk of environmental leaching. This allows the product to meet the environmental protection requirements of green building materials and is suitable for building insulation and industrial thermal insulation applications.

Description

Technical Field

[0001] This invention relates to the field of environmentally friendly ceramic materials technology, and more specifically, to a preparation process for an environmentally friendly ceramic composite material. Background Technology

[0002] Currently, using industrial solid wastes such as fly ash and bauxite to prepare porous ceramics is an important way to achieve resource recycling. However, existing processes generally have high sintering temperatures (usually ≥1200℃) and high energy consumption. Furthermore, due to insufficient activity of raw materials, the strength of the resulting ceramics is relatively low (generally <30MPa), which makes it difficult to meet the mechanical requirements of building insulation or filter carriers. In addition, the decomposition of traditional pore-forming agents (such as starch and silicon carbide) is uncontrollable, resulting in wide pore size distribution and high closed-pore rate, which seriously affects the functionality and consistency of the material.

[0003] Although existing studies have attempted to improve performance by adding reinforcing phases or lowering sintering temperatures, these methods often involve expensive additives or sacrificing porosity, resulting in high costs and complex processes. Furthermore, most processes fail to effectively immobilize heavy metals in solid waste, which are prone to migration at high temperatures, leading to excessive leaching toxicity and limiting their application in civilian or environmentally sensitive scenarios.

[0004] In view of the above situation, the present invention provides a preparation process for an environmentally friendly ceramic composite material. Summary of the Invention

[0005] In order to overcome the above-mentioned defects of the prior art, the present invention provides a preparation process for an environmentally friendly ceramic composite material to solve the problems mentioned in the background art.

[0006] To achieve the above objectives, the present invention provides the following technical solution: a preparation process for an environmentally friendly ceramic composite material, specifically including the following steps: S1. Raw material pretreatment: Mix 50-60 parts by weight of fly ash, 20-25 parts by weight of bauxite and 8-12 parts by weight of diatomaceous earth and place them in a ball mill. Use zirconia balls as the medium, with a ball-to-material ratio of 4:1, and ball mill at 280 rpm for 4.5-5 hours to obtain composite powder with D50≤12μm. S2. Adding the mixture: Add 4-7 parts by weight of rice husk ash, 3-5 parts by weight of a low-temperature composite pore-forming agent composed of polymethyl methacrylate microspheres and calcium carbonate in a mass ratio of 3:2, and 1.5-2.5 parts by weight of γ-glycidyl oxypropyltrimethoxysilane coupling agent to the powder obtained in S1. Mix in a V-type mixer at 25 rpm for 40-42 min. S3, wet molding: add 9% of deionized water by mass of total solid phase to the mixture obtained in S2, stir into a slurry, pour into a mold, and cold isostatically press at 40MPa to obtain a green body. S4. Gradient debinding: The green body is heated to 550℃ at a rate of 1.8℃ / min and held for 1.2h to allow the organic pore-forming agent to fully decompose without producing cracks. S5. Low-temperature sintering: Continue heating at 2.2℃ / min to 1050℃, hold for 1.5h, and complete sintering in air atmosphere. Cool to room temperature with the furnace to obtain the environmentally friendly ceramic composite material.

[0007] Preferably, in step S1, the fly ash is fly ash from a secondary or higher-level coal-fired power plant, with a silica and alumina content ≥80wt% and an iron oxide content ≤3wt%; the diatomaceous earth has a specific surface area ≥20m² / g, and its main mineral phase is amorphous silica.

[0008] Preferably, in step S2, the polymethyl methacrylate microspheres have a particle size of 50-80 μm and a glass transition temperature of 105°C, and decompose in the range of 300-400°C to generate uniform pores.

[0009] Preferably, in step S3, the holding time for cold isostatic pressing is 4.5 to 5.5 minutes, and the relative density of the green blank is ≥55%.

[0010] Preferably, in step S5, during the process of heating to 1050°C, the temperature is held at 900°C for 7–9 minutes to promote the synergistic formation of mullite and cristobalite and improve high-temperature stability.

[0011] The present invention also provides an environmentally friendly ceramic composite material, which is prepared by the above-mentioned preparation process. The ceramic composite material has a three-dimensional interconnected open-pore structure, a porosity of 62% to 68%, an average pore diameter of 45 to 65 μm, a flexural strength ≥36 MPa, and a thermal conductivity ≤0.19 W / (m·K).

[0012] Preferably, the main crystalline phases of the ceramic composite material are mullite and cristobalite, wherein the content of mullite is 30-35 wt% and the content of cristobalite is 15-20 wt%.

[0013] The technical effects and advantages of this invention are as follows: This invention introduces highly active amorphous silica into diatomaceous earth, which, in conjunction with the silicon source in rice husk ash and the alumina released from bauxite, efficiently promotes the in-situ formation of the mullite phase under low-temperature conditions. At the same time, it utilizes silane coupling agents to improve the interfacial bonding between rice husk ash and the ceramic matrix, effectively strengthening the pore wall structure. Thus, it successfully breaks through the technical bottleneck of "high-temperature sintering and low strength" in traditional fly ash-based porous ceramics, achieving a synergistic optimization of low energy consumption and high strength. This invention uses a composite pore-forming agent composed of polymethyl methacrylate microspheres and calcium carbonate, combined with the skeletal support of diatomaceous earth, to effectively avoid the problems of wide pore size distribution and high closed pore rate caused by the uncontrollable decomposition of a single pore-forming agent. The resulting ceramic has a uniform and interconnected three-dimensional open pore network with concentrated pore size distribution and intact pore walls, which not only ensures high porosity but also maintains good structural stability, laying a microscopic foundation for functional applications such as heat insulation and filtration. This invention effectively suppresses gas-phase and solid-phase heat transfer within the material by constructing a uniformly connected open-pore structure and a dense and reinforced pore wall system, significantly improving thermal insulation performance. Simultaneously, the mullite and cristobalite mineral phases formed in situ during sintering, combined with the interface structure improved by the coupling agent, can synergistically fix heavy metal ions in the raw materials, greatly reducing their environmental leaching risk. This enables the resulting ceramic composite material to meet the environmental safety requirements of civil building materials, providing a reliable technical path for the large-scale application of industrial solid waste-based porous ceramics in the field of green building. This invention regulates the synergistic precipitation behavior of mullite and cristobalite by setting a specific temperature range insulation step during the heating process, forming a mutually supportive main crystalline phase structure. This phase combination not only improves the mechanical properties at room temperature, but also endows the material with good high-temperature dimensional stability and thermal shock resistance, enabling it to maintain structural integrity and functional reliability under long-term service conditions at medium and low temperatures. It is suitable for building insulation and industrial thermal insulation applications. Attached Figure Description

[0014] Figure 1 This is a flowchart illustrating the overall process flow of the present invention. Detailed Implementation Example 1

[0015] This embodiment provides a preparation process for an environmentally friendly ceramic composite material, specifically including the following raw materials in parts by weight: 50 parts fly ash, 20 parts bauxite, 8 parts diatomaceous earth, 4 parts rice husk ash, 3 parts composite pore-forming agent, and 1.5 parts coupling agent. The composite pore-forming agent is composed of polymethyl methacrylate microspheres (50 μm in diameter) and calcium carbonate mixed uniformly at a mass ratio of 3:2. The coupling agent is γ-glycidoxypropyltrimethoxysilane.

[0016] The specific preparation method is as follows: S1. Raw material pretreatment: 50 parts fly ash, 20 parts bauxite and 8 parts diatomaceous earth are put into a ball mill and zirconia balls are used as grinding media (ball-to-material ratio 4:1). The mixture is ball-milled at 280 rpm for 4.5 hours to obtain composite powder with D50 of 12 μm. S2: Adding the mixture, add 4 parts rice husk ash, 3 parts composite pore-forming agent and 1.5 parts coupling agent to the powder obtained in S1, and mix in a V-type mixer at 22 rpm for 40 min. S3: Wet molding. Add 9% of deionized water by mass of the total solid phase to the mixture obtained in S2, stir into a uniform slurry, and then inject into a stainless steel mold. Cold isostatic pressing is performed at 38MPa for 4.5min to obtain a green body with dimensions of 50mm×50mm×10mm. S4: Gradient debinding, placing the green body in a muffle furnace, heating it to 550℃ at a heating rate of 2.0℃ / min, holding it at that temperature for 1.1h to allow the organic matter to decompose fully; S5: Low-temperature sintering. The green body is heated from 550°C to 900°C at a heating rate of 2.2°C / min, held at 900°C for 7 min, and then heated from 900°C to 1050°C at a heating rate of 2.2°C / min, held for 1.5 h, and finally cooled to room temperature in the furnace to obtain the environmentally friendly ceramic composite material. Example 2

[0017] This embodiment provides a preparation process for an environmentally friendly ceramic composite material, specifically including the following raw materials in parts by weight: 60 parts fly ash, 25 parts bauxite, 12 parts diatomaceous earth, 7 parts rice husk ash, 5 parts composite pore-forming agent, and 2.5 parts coupling agent. The composite pore-forming agent is composed of polymethyl methacrylate microspheres (80 μm in diameter) and calcium carbonate mixed uniformly at a mass ratio of 3:2. The coupling agent is γ-glycidoxypropyltrimethoxysilane.

[0018] The specific preparation method is as follows: S1. Raw material pretreatment: 60 parts fly ash, 25 parts bauxite and 12 parts diatomite were put into a ball mill and milled at 280 rpm for 5.5 hours with zirconia balls as grinding media (ball-to-material ratio 4:1) to obtain composite powder with D50 of 10 μm. S2: Adding the mixture, add 7 parts rice husk ash, 5 parts composite pore-forming agent and 2.5 parts coupling agent to the powder obtained in S1, and mix in a V-type mixer at 28 rpm for 42 min. S3: Wet molding. Add 9% of deionized water by mass of the total solid phase to the mixture obtained in S2, stir into a uniform slurry, and then inject into a stainless steel mold. Cold isostatic pressing is performed at 42MPa for 5.5min to obtain a green body with dimensions of 50mm×50mm×10mm. S4: Gradient debinding, heating the green body to 550℃ at 1.6℃ / min and holding for 1.3h; S5: Low-temperature sintering. Continue to heat the green blank from 550℃ to 900℃ at a heating rate of 2.2℃ / min, hold at 900℃ for 9 min, then continue to heat from 900℃ to 1050℃ at a heating rate of 2.2℃ / min, hold for 1.5 h, and then cool to room temperature with the furnace. Example 3

[0019] This embodiment provides a preparation process for an environmentally friendly ceramic composite material, specifically including the following raw materials in parts by weight: 55 parts fly ash, 22 parts bauxite, 10 parts diatomite, 5.5 parts rice husk ash, 4 parts composite pore-forming agent, and 2.0 parts coupling agent. The composite pore-forming agent is composed of polymethyl methacrylate microspheres (particle size 65 μm) and calcium carbonate mixed uniformly at a mass ratio of 3:2. The coupling agent is γ-glycidoxypropyltrimethoxysilane.

[0020] The specific preparation method is as follows: S1. Raw material pretreatment: 55 parts fly ash, 22 parts bauxite and 10 parts diatomite were put into a ball mill and milled at 280 rpm for 5 hours with zirconia balls as the grinding medium (ball-to-material ratio 4:1) to obtain composite powder with D50 of 11 μm. S2: Adding the mixture, add 5.5 parts rice husk ash, 4 parts composite pore-forming agent and 2.0 parts coupling agent to the powder obtained in S1, and mix in a V-type mixer at 25 rpm for 41 min. S3: Wet molding. Add 9% of deionized water by mass of the total solid phase to the mixture obtained in S2, stir into a uniform slurry, and then inject into a stainless steel mold. Cold isostatic pressing is performed at 40MPa for 5 minutes to obtain a green body with dimensions of 50mm×50mm×10mm. S4: Gradient debinding, heating the green body to 550℃ at 1.8℃ / min and holding for 1.2h; S5: Low-temperature sintering. Continue to heat the green blank from 550℃ to 900℃ at a heating rate of 2.2℃ / min, hold at 900℃ for 8 minutes, then continue to heat from 900℃ to 1050℃ at a heating rate of 2.2℃ / min, hold for 1.5 hours, and then cool to room temperature with the furnace.

[0021] Comparative Example 1 This embodiment provides a preparation process for an environmentally friendly ceramic composite material, specifically including the following raw materials in parts by weight: 50 parts fly ash, 20 parts bauxite, and 3 parts ordinary pore-forming agent; The common pore-forming agent is corn starch with a particle size of 50-100 μm.

[0022] The specific preparation method is as follows: S1. Raw material pretreatment: 50 parts fly ash and 20 parts bauxite were put into a ball mill and milled at 280 rpm for 5 hours with zirconia balls as the grinding medium (ball-to-material ratio 4:1) to obtain a mixed powder with a D50 of 14 μm. S2: Adding the mixture, add 3 parts of corn starch to the powder obtained in S1, and mix in a V-type mixer at 25 rpm for 15 minutes; S3: Dry pressing molding, the mixture obtained in S2 is dry pressed under a pressure of 20MPa and the holding time is 3min to obtain a green body with a size of 50mm×50mm×10mm. S4: Direct sintering, the green blank is placed in a muffle furnace and heated directly to 1200℃ at a heating rate of 3.0℃ / min, and held for 2.0h; S5: Cooling, cooling the furnace to room temperature to obtain a comparatively environmentally friendly ceramic composite material.

[0023] Comparative Example 2 This embodiment provides a preparation process for an environmentally friendly ceramic composite material, which specifically includes the following raw materials in parts by weight: 50 parts fly ash, 20 parts bauxite, 8 parts diatomaceous earth, 4 parts rice husk ash, and 3 parts composite pore-forming agent. The composite pore-forming agent is composed of polymethyl methacrylate microspheres (50 μm in diameter) and calcium carbonate mixed uniformly at a mass ratio of 3:2. No coupling agent was added.

[0024] The specific preparation method is as follows: S1. Raw material pretreatment: 50 parts fly ash, 20 parts bauxite and 8 parts diatomite are put into a ball mill and milled at 280 rpm for 5 hours with zirconia balls as the grinding medium (ball-to-material ratio 4:1) to obtain composite powder with D50 of 11 μm. S2: Adding the mixture, add 4 parts rice husk ash and 3 parts composite pore-forming agent to the powder obtained in S1, and mix in a V-type mixer at 25 rpm for 40 minutes. S3: Wet molding. Add 9% of deionized water by mass of the total solid phase to the mixture obtained in S2, stir into a uniform slurry, and then inject into a stainless steel mold. Cold isostatic pressing is performed at 40MPa for 5 minutes to obtain a green body with dimensions of 50mm×50mm×10mm. S4: Gradient debinding, heating the green body to 550℃ at 1.8℃ / min and holding for 1.2h; S5: Low-temperature sintering, the green body is heated from 550℃ to 1050℃ at a heating rate of 2.2℃ / min, without holding at 900℃, and directly held at 1050℃ for 1.5h, and then cooled to room temperature with the furnace to obtain a comparative environmentally friendly ceramic composite material.

[0025] Comparative Example 3 This embodiment provides a preparation process for an environmentally friendly ceramic composite material, specifically including the following raw materials in parts by weight: 58 parts fly ash, 20 parts bauxite, 4 parts rice husk ash, 3 parts composite pore-forming agent, and 1.5 parts coupling agent. Among them, diatomaceous earth was not used, and the amount of fly ash was increased to maintain a consistent total solid phase mass. The composite pore-forming agent is composed of polymethyl methacrylate microspheres (50 μm in diameter) and calcium carbonate mixed uniformly at a mass ratio of 3:2. The coupling agent is γ-glycidoxypropyltrimethoxysilane.

[0026] The specific preparation method is as follows: S1. Raw material pretreatment: 58 parts of fly ash and 20 parts of bauxite were put into a ball mill and milled at 280 rpm for 5 hours with zirconia balls as the grinding medium (ball-to-material ratio 4:1) to obtain a mixed powder with a D50 of 11 μm. S2: Adding the mixture, add 4 parts rice husk ash, 3 parts composite pore-forming agent and 1.5 parts coupling agent to the powder obtained in S1, and mix in a V-type mixer at 25 rpm for 40 min. S3: Wet molding. Add 9% of deionized water by mass of the total solid phase to the mixture obtained in S2, stir into a uniform slurry, and then inject into a stainless steel mold. Cold isostatic pressing is performed at 40MPa for 5 minutes to obtain a green body with dimensions of 50mm×50mm×10mm. S4: Gradient debinding, heating the green body to 550℃ at 1.8℃ / min and holding for 1.2h; S5: Low-temperature sintering. The green body is heated from 550℃ to 900℃ at a heating rate of 2.2℃ / min and held at 900℃ for 8 min. Then, the temperature is increased from 900℃ to 1050℃ at a rate of 2.2℃ / min and held for 1.5 h. The green body is then cooled to room temperature in the furnace to obtain a comparative environmentally friendly ceramic composite material.

[0027] The performance of Examples 1-3 and Comparative Examples 1-3 were tested respectively, and the testing methods are as follows: 1. Porosity: According to GB / T1966-1996 "Test Method for Apparent Porosity and Bulk Density of Porous Ceramics", the Archimedes displacement method was used for determination; 2. Flexural strength: According to GB / T1965-1996 "Test Method for Flexural Strength of Porous Ceramics", the three-point bending method (span 30mm, loading rate 0.5mm / min) was adopted. 3. Thermal conductivity: According to GB / T10295-2008 "Determination of steady-state thermal resistance and related properties of thermal insulation materials", the heat flow meter method was used (test temperature 25℃). 4. Phase composition: The content of each crystalline phase was determined by Rietelveld using an X-ray diffractometer (XRD, CuKα radiation, scanning range 10°–80°, step size 0.02°). 5. Heavy metal leaching toxicity: According to HJ / T299-2007 "Leaching Toxicity of Solid Waste - Leaching Methods - Sulfuric Acid and Nitric Acid Method", the leaching concentrations of As, Pb, and Cr were determined by inductively coupled plasma mass spectrometry (ICP-MS).

[0028] The test results are shown in the table below:

[0029] Summarize: The data in the table above shows that: 1. Breakthrough in Synergistic Effect of Low Temperature and High Strength: Examples 1–3, sintered at a low temperature of 1050℃, achieved a flexural strength of 36.2–38.5 MPa, significantly superior to Comparative Examples 1–3, as detailed below: Comparative Example 1 uses a traditional process of dry pressing with starch as a pore-forming agent and sintering at a high temperature of 1200℃ (this temperature is the conventional sintering temperature of fly ash-based ceramics). The strength is only 26.5MPa, indicating that even if the sintering temperature is increased by 150℃, high strength cannot be obtained. Comparative Example 2 used fly ash, bauxite, diatomaceous earth, rice husk ash and composite pore-forming agent as raw materials, without adding coupling agent. After wet molding and gradient debinding, it was sintered at 1050℃ and the strength was only 31.0MPa, indicating that coupling agent can effectively improve the interfacial bonding between rice husk ash and ceramic matrix. Comparative Example 3 used fly ash, bauxite, rice husk ash, composite pore-forming agent and coupling agent as raw materials, without using diatomaceous earth (to increase the amount of fly ash to maintain the total solid phase mass balance). After wet molding, gradient debinding and holding at 900℃ and then sintering at 1050℃, the strength was only 29.8MPa, which proves that diatomaceous earth has an irreplaceable role in promoting in-situ mullite formation and strengthening the pore wall structure. This invention achieves a breakthrough in the synergistic effect of low-temperature sintering and high strength by modifying composite pore-forming agents and coupling agents with diatomaceous earth, thereby reducing the sintering temperature by 150°C while increasing the strength by more than 44%.

[0030] 2. Precise and controllable pore structure: Examples 1–3 obtained a uniform open pore structure of 48–63 μm (pore size distribution variation coefficient <17%), while Comparative Example 1 had large pores (90 μm) and wide distribution (variation coefficient >35%) due to the use of starch pore-forming agent. Although Comparative Example 3 had smaller pore size, it had a high closed pore rate. This proves that the present invention achieves a microstructure with controllable pore size and high open pore rate through the synergy of composite pore-forming agent and diatomaceous earth. 3. Excellent thermal insulation performance: The thermal conductivity of Examples 1–3 (0.175–0.188 W / (m·K)) is significantly lower than that of Comparative Examples 1–3 (0.210–0.250 W / (m·K)), with a reduction of 11–29%. This proves that the present invention effectively reduces gas phase heat transfer and solid phase heat transfer by synergistically optimizing the pore structure and interface through diatomaceous earth, rice husk ash and coupling agent, thus achieving a breakthrough in thermal insulation performance. It is suitable for building energy conservation and industrial thermal insulation fields. 4. High environmental safety: According to the leaching test of HJ / T299-2007, the As ≤ 0.32 mg / L, Pb ≤ 0.85 mg / L, and Cr ≤ 1.65 mg / L of Examples 1–3 are all far below the hazardous waste identification limits of GB5085.3-2007 (As: 5 mg / L, Pb: 5 mg / L, Cr: 15 mg / L). In contrast, Comparative Examples 1–3, due to the lack of coupling agent or diatomaceous earth, have weak heavy metal fixation ability, and the leaching concentrations of As, Pb, and Cr are significantly increased. This proves that the present invention achieves efficient heavy metal stabilization through the synergistic effect of interface modification and mineral phase solidification.

[0031] In summary, compared with the comparative example, the present invention provides a new route for preparing environmentally friendly ceramic composite materials that combines low energy consumption, high strength, low thermal conductivity, and high environmental friendliness, which has significant technological progress and broad industrialization prospects.

[0032] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A preparation process for an environmentally friendly ceramic composite material, characterized in that: Specifically, the following steps are included: S1. Raw material pretreatment: 50-60 parts by weight of fly ash, 20-25 parts by weight of bauxite, and 8-12 parts by weight of diatomaceous earth are mixed and placed in a ball mill. Zirconia balls are used as the medium, and the ball-to-material ratio is 4:

1. The mixture is ball-milled at 280 rpm for 4.5-5 hours to obtain a composite powder with D50 ≤ 12 μm. The fly ash is fly ash from a secondary or higher-grade coal-fired power plant, with a silica and alumina content ≥ 80 wt% and an iron oxide content ≤ 3 wt%. The diatomaceous earth has a specific surface area ≥ 20 m² / g, and its main mineral phase is amorphous silica. S2. Adding the mixture: Add 4-7 parts by weight of rice husk ash, 3-5 parts by weight of a low-temperature composite pore-forming agent composed of polymethyl methacrylate microspheres and calcium carbonate in a mass ratio of 3:2, and 1.5-2.5 parts by weight of γ-glycidyl etheroxypropyltrimethoxysilane coupling agent to the powder obtained in S1. Mix in a V-type mixer at 25 rpm for 40-42 min. The polymethyl methacrylate microspheres have a particle size of 50-80 μm and a glass transition temperature of 105℃. They decompose in the range of 300-400℃ to produce uniform pores. S3. Wet molding: Add 9% deionized water (by mass of total solid phase) to the mixture obtained in S2, stir to form a slurry, pour into a mold, and cold isostatically press at 40 MPa for 4.5–5.5 min to obtain a green body with a relative density ≥55%. S4. Gradient debinding: The green body is heated to 550℃ at a rate of 1.8℃ / min and held for 1.2h to allow the organic pore-forming agent to fully decompose without producing cracks. S5. Low-temperature sintering: Continue heating at 2.2℃ / min to 1050℃, hold for 1.5h, and complete sintering in air atmosphere. Cool to room temperature with the furnace to obtain the environmentally friendly ceramic composite material. During the process of heating to 1050℃, hold at 900℃ for 7-9min to promote the synergistic formation of mullite and cristobalite and improve high-temperature stability. The environmentally friendly ceramic composite material has a three-dimensional interconnected open-pore structure with a porosity of 62% to 68%, an average pore diameter of 45 to 65 μm, a flexural strength of ≥36 MPa, and a thermal conductivity of ≤0.19 W / (m·K). The main crystalline phases of the ceramic composite material are mullite and cristobalite, wherein the content of mullite is 30 to 35 wt% and the content of cristobalite is 15 to 20 wt%.

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