A method for preparing low thermal conductivity silicon-mullite bricks by using basalt fibers in cooperation with ceramic powder

Abstract

The present application relates to the technical field of silica mullite brick, and particularly relates to a method for preparing low-thermal-conductivity silica mullite brick by using basalt fiber and ceramic powder; the method comprises the following steps: S1, raw material preparation, S2, functional layer preparation, S3, heat preservation layer preparation, and S4, pressing forming; the corrosion resistance and heat preservation performance of the low-thermal-conductivity silica mullite brick are further optimized and improved through the synergistic effect of the basalt fiber and the ceramic powder; aiming at the problem that the basalt fiber is easily pulled out when subjected to stress, affecting the performance of the composite material, the ceramic powder with a core-shell structure can significantly improve the mechanical properties of the basalt fiber composite material, further improving the mechanical properties of the low-thermal-conductivity silica mullite brick and optimizing the salt-alkali resistance and heat preservation effect.

Description

Technical Field

[0001] This invention relates to the field of silicon-mullite brick technology, specifically to a method for preparing low thermal conductivity silicon-mullite bricks using basalt fibers in conjunction with ceramic powder. Background Technology

[0002] Basalt fiber (BF) is hailed as a pollution-free green industrial raw material. It is a continuous fiber made from natural basalt through rapid drawing under high temperature conditions. Its main chemical components are silicon dioxide, aluminum oxide, titanium dioxide, and ferric oxide. BF is characterized by good chemical stability, mechanical properties, high temperature resistance, acid and alkali corrosion resistance, and low cost. It is widely used as a reinforcing filler in polymer composites such as rubber and epoxy resin. Low thermal conductivity refers to the material's low thermal conductivity, meaning that less heat is transferred per unit area per unit time.

[0003] However, basalt fiber (BF) has a smooth surface, low surface energy, and small specific surface area, making it difficult to react with the polymer matrix. It is also easily extracted under stress, affecting the performance of the composite material. Furthermore, the salt and alkali resistance of existing low thermal conductivity silica-mullite bricks is limited. To address these issues, this invention provides a method for preparing low thermal conductivity silica-mullite bricks using basalt fiber in conjunction with ceramic powder. Summary of the Invention

[0004] To address the aforementioned problems, this invention provides a method for preparing low thermal conductivity silicon-mullite bricks using basalt fibers in conjunction with ceramic powder.

[0005] The technical solution of this invention is: a method for preparing low thermal conductivity silicon-mullite bricks using basalt fiber and ceramic powder, comprising the following steps:

[0006] S1. Raw material preparation

[0007] Microporous mullite, silicon carbide powder, basalt fiber and ceramic powder are used as ceramic aggregates, agar powder is used as a forming agent, water is used as a solvent, ammonium bicarbonate is used as a pore-forming agent, pulp waste liquor is used as a binder, and silon powder and rigid polyurethane foam are used as additives to prepare each material separately.

[0008] The mass percentages of each component are as follows: silicon carbide micro powder 25-35%, microporous mullite 15-25%, basalt fiber 3-7%, ceramic powder 8-12%, agar powder 2-8%, ammonium bicarbonate 2-3%, pulp waste liquor 5-12%, silane powder 2-4%, rigid polyurethane foam 2-3%, and water as the balance; the ceramic powder and the pulp waste liquor are divided into 2-3 equal parts.

[0009] S2, Functional Layer Preparation

[0010] Take one portion of ceramic powder and mix the silicon carbide micro powder, basalt fiber, agar powder, and ammonium bicarbonate evenly to obtain a mixed powder. Then, add silon powder to water and stir to make a mixed solvent. Finally, add the mixed solvent and one portion of pulp waste liquid to the mixed powder in sequence and mix and grind for 10-15 minutes to obtain the functional layer.

[0011] S3, Insulation Layer Preparation

[0012] Take microporous mullite, the remaining ceramic powder and rigid polyurethane foam and mix them evenly. Then pour in the remaining pulp waste liquid and mix and knead for 10-15 minutes to obtain the insulation layer mud, which is the insulation layer.

[0013] S4, Compression Molding

[0014] The functional layer and the insulation layer are pressed together to form a brick blank, which is then naturally dried at 25-30℃ for 20-24 hours, then dried at 100-130℃, and then fired at 1300-1450℃ for 5-10 hours. After cooling, the low thermal conductivity silicon molybdenum brick is obtained.

[0015] Explanation: Ammonium cyanate, as a pore-forming agent, can decompose during sintering to generate a large amount of gas, forming a uniform pore structure, improving the thermal insulation performance of the material. At the same time, it can improve the compatibility of basalt fiber and ceramic powder, promote their bonding, and enhance the internal structure of low thermal conductivity silica-mullite bricks. In addition, compared with other pore-forming agents, ammonium cyanate, as a pore-forming agent, also has the ability to adjust the pH value of low thermal conductivity silica-mullite bricks, which can improve their resistance to salt and alkali, enhance their durability in harsh environments, further improve the thermal conductivity of low thermal conductivity silica-mullite bricks, reduce their thermal conductivity coefficient, and improve the thermal insulation effect.

[0016] The Al and O elements in silon powder can interact with the Si-O structure in basalt fibers to form a more stable network structure, thereby improving the corrosion resistance of the fibers in salt solutions. In salt solutions, silon powder promotes the formation of a protective compound film on the fiber surface, which can block the erosion of the fibers by salt ions and reduce the loss of fiber performance. The high-temperature stability of silon powder helps basalt fibers maintain structural integrity in high-temperature environments, which is particularly important for resisting corrosion from salt solutions at high temperatures. Through multiple effects such as strengthening the fiber network structure, forming a protective layer, improving the pore structure, and improving thermal stability, silon powder can effectively promote the salt and alkali resistance of basalt fibers. Rigid polyurethane foam has the function of preventing structural collapse at high temperatures, which can further improve the high-temperature service life of the brick.

[0017] Furthermore, the length of the basalt fibers is 0.5–12 mm;

[0018] Note: When the fiber length is moderate, it can effectively reduce interconnected pores and bleeding channels in cement concrete, forming a spatial network structure, increasing the density of the concrete, and thus improving its impermeability. However, if the fiber length is too long, it may be difficult to distribute evenly and maintain a straight state within the concrete, resulting in more weak areas and ultimately reducing impermeability. Furthermore, excessively long fibers are not easily dispersed during concrete mixing, potentially introducing too many air bubbles, further reducing the density and impermeability of the concrete, thereby weakening the strength and durability of the low thermal conductivity silica-mullite bricks.

[0019] Furthermore, the silon powder is silon powder doped with 0.5 to 2 wt.% yttrium ions or ytterbium ions;

[0020] Note: Doping with yttrium or ytterbium ions can improve the thermal stability of silane powder, thereby enhancing the heat resistance of basalt fiber at high temperatures and improving the service life of low thermal conductivity silica-mullite bricks; it can also optimize the crystal structure and microstructure of silane powder, thereby improving the strength and toughness of basalt fiber and enhancing the tensile strength of low thermal conductivity silica-mullite bricks.

[0021] Furthermore, the ceramic powder has a core-shell structure, consisting of a core, a middle layer, and an outer shell from the inside out. The core is composed of porous alumina material, the middle layer is composed of silicon nitride and aluminum nitride materials in equal mass ratios, and the outer shell is composed of iron oxide and titanium oxide materials in equal mass ratios.

[0022] Note: Iron in basalt fibers exists in both divalent and trivalent forms, with trivalent iron (Fe) being the most abundant. 3+ The content of Fe has a significant impact on the tensile strength of fibers. 3+ / Σ(Fe 2+ +Fe 3+ When the ratio increases, crystals are more likely to precipitate in the fiber during the drawing process, increasing defects on the fiber surface and thus reducing tensile strength. Iron elements in the outer shell can adjust the form and content of iron elements in the fiber through chemical reactions, which helps to optimize the network structure connection of the fiber and improve tensile strength.

[0023] Furthermore, the core has a diameter of 15–55 nm, the intermediate layer has a thickness of 25–40 nm, and the outer shell has a thickness of 15–30 nm.

[0024] Note: The ceramic powder obtained at the above thickness not only has a better thermal insulation effect, but also effectively improves the service life of low thermal conductivity silicon-mullite bricks in extreme environments, such as high temperature, high pressure and strong corrosive media, thus broadening its application fields.

[0025] Furthermore, the method for preparing the ceramic powder is as follows:

[0026] S1: Preparation of outer shell layer mixture: Iron oxide and titanium dioxide are mixed in a nitrogen atmosphere for 45-60 min to obtain outer shell layer mixture;

[0027] S2: Preparation of intermediate layer mixture: Mix silicon nitride and aluminum nitride materials in a nitrogen atmosphere for 45-60 min to obtain intermediate layer mixture;

[0028] S3: Core preparation: Take 25-45 wt% macroporous alumina ceramic particles with a particle size of 100-150 μm, 30-40 wt% mesoporous alumina ceramic particles with a particle size of 50-100 μm, and the balance microporous alumina ceramic particles with a particle size of 10-50 μm to mix them to obtain the core mixture. Put it into a boron nitride crucible, then transfer it into a carbon tube furnace. Under the protection of nitrogen atmosphere, it is first calcined at high temperature, and then after plasma ball milling, it is calcined at low temperature by introducing air at a rate of 5-10 L / min to form the core.

[0029] S4: Preparation of ceramic powder: Under nitrogen protection, the intermediate layer mixture is plasma sprayed onto the core surface, and then kept at 900-1100℃ for 3-5 hours to obtain a ceramic semi-finished product. Then, the outer shell layer mixture is deposited on the surface of the ceramic semi-finished product by vacuum deposition, and kept at 900-1100℃ for 3-5 hours to obtain ceramic powder.

[0030] Explanation: The ceramic powder prepared by the above method provides structural support and low thermal resistance channels through porous alumina, which facilitates heat transfer. The silicon nitride and aluminum nitride materials in the middle layer effectively enhance the overall thermal conductivity of the ceramic particles, and can effectively balance the thermal expansion coefficient and mechanical strength of the material while maintaining high thermal conductivity. The iron oxide and titanium dioxide materials in the outer shell help optimize the fiber network structure and improve tensile strength. The addition of titanium dioxide can reduce the viscosity of basalt melt and promote Al 3+ The TiO2 in the basalt fiber enters the network structure as a network precursor, thereby strengthening polymerization and enhancing the impact resistance of the silicon-mullite brick. In addition, the insoluble titanium hydroxide layer formed by TiO2 in the basalt fiber can reduce corrosion in NaOH solution and improve the alkali resistance of the fiber. Plasma ball milling can increase the active sites of solid-phase reaction of the material, accelerate the mass transfer process, and improve sintering activity, thereby obtaining a ceramic core with good thermal insulation performance at low temperature. High-temperature calcination followed by low-temperature calcination can optimize the rheological properties of ceramic powder and improve processability, thereby obtaining ceramic powder with better thermal insulation performance.

[0031] Furthermore, in step S3, the high-temperature calcination temperature is 1000-1200℃, the high-temperature calcination time is 4-8h, and the high-temperature calcination atmosphere pressure is 5-8MPa; the low-temperature calcination temperature is 300-350℃, the calcination time is 3h, and the low-temperature calcination atmosphere pressure is 1-5MPa.

[0032] Note: Plasma ball milling can form a polymer layer on the powder surface, reducing the surface energy of the powder and decreasing agglomeration, thereby improving the dispersibility of ceramic powder. Ceramic powder treated under the above-mentioned high-temperature calcination parameters can promote material densification, reduce porosity, and thus improve the material's density and mechanical properties, such as hardness and flexural strength. However, if the calcination temperature is too high, it may lead to excessive grain growth, increasing internal defects and forming a dense structure with fewer pores, which may reduce the material's thermal insulation performance and mechanical strength. On the other hand, low-temperature calcination parameters can promote the homogenization of the microstructure in the material, reduce defects, and further optimize the thermal insulation performance of ceramic powder.

[0033] Further, in step S3, the plasma ball milling parameters are: motor speed 500-800 r / min, discharge voltage 4-6 kV, discharge frequency 10-20 kHz, ball milling time 30-50 min, and ball-to-material ratio 5-10:1.

[0034] Note: If the processing parameters of plasma ball milling are too large, it may lead to excessive refinement of ceramic powder particles, limiting grain growth and thus affecting the density and thermal stability of the material. On the other hand, if the processing parameters of plasma ball milling are too small, it may not be sufficient to achieve effective material activation and microstructure optimization. This means that the ceramic powder particles are not fine enough and the grain growth is insufficient, resulting in insufficient density and thermal stability of the material.

[0035] Further, in step S4, the parameters of the plasma spraying are: working current 400-600A, arc voltage 50-75V, argon flow rate 20-50L / min, hydrogen flow rate 5-15L / min, powder feeding rate 2-5L / min, spraying distance 80-120mm, spraying angle 90°, argon as plasma gas and powder feeding gas, and hydrogen as combustion gas;

[0036] The parameters for the vacuum plating are: vacuum degree 3×10 -3 ~5×10 -3 Pa, preheating temperature is 70-150℃, negative voltage applied to the target is 200-600V, and deposition time is 10-20min;

[0037] Note: The deposition effect of the intermediate and outer shell layers within the above parameter range is better, and the effect of optimizing the thermal insulation performance of ceramic powder is better.

[0038] Compared with the prior art, the beneficial effects of the present invention are:

[0039] (1) This invention adds silon powder during the preparation of the functional layer and utilizes the interaction between the Al and O elements in the silon powder and the Si-O structure in the basalt fiber to form a more stable network structure, thereby improving the corrosion resistance of the fiber in salt solution. Furthermore, through multiple effects such as enhancing the fiber network structure, forming a protective layer, improving the pore structure and improving thermal stability, it can effectively promote the salt and alkali resistance of basalt fiber.

[0040] (2) This invention further optimizes and improves the corrosion resistance and thermal insulation performance of low thermal conductivity silica-mullite bricks through the synergistic effect of basalt fiber and ceramic powder. In view of the problem that basalt fiber has a smooth surface, low surface energy, small specific surface area, and is not easy to react with the polymer matrix, and is easily extracted under stress, which affects the performance of composite materials, ceramic powder with core-shell structure can significantly improve the mechanical properties of basalt fiber composite materials. Specifically, the iron element in the outer shell can adjust the form and content of iron element in the fiber through chemical reaction, which helps to optimize the network structure connection of the fiber and improve the tensile strength. Thus, while improving the mechanical properties of low thermal conductivity silica-mullite bricks, it also optimizes their salt and alkali resistance and thermal insulation effect.

[0041] (3) The ceramic powder prepared in this invention uses porous alumina as the core, which can provide certain structural support and low thermal resistance channels, thus facilitating heat transfer. The silicon nitride and aluminum nitride materials in the middle layer have high thermal conductivity, which can effectively improve the overall thermal conductivity of the ceramic particles. The equal mass ratio of silicon nitride and aluminum nitride as the middle layer can effectively balance the thermal expansion coefficient and mechanical strength of the material while maintaining high thermal conductivity. The iron oxide and titanium dioxide materials in the outer shell can provide additional protection and improve the service life of the ceramic powder. Furthermore, the iron element can adjust the form and content of iron element in the fiber through chemical reaction, which helps to optimize the network structure connection of the fiber and improve tensile strength. The addition of titanium dioxide can reduce the viscosity of basalt melt and promote Al 3+ The TiO2 enters the network structure and acts as a network precursor, thereby enhancing polymerization. In addition, the insoluble titanium hydroxide layer formed by TiO2 in the basalt fiber can reduce corrosion in NaOH solution and improve the fiber's alkali resistance. Detailed Implementation

[0042] To further illustrate the methods and effects of this invention, the technical solution of this invention will be clearly and completely described below in conjunction with experiments.

[0043] Example 1: A method for preparing low thermal conductivity silicon-mullite bricks using basalt fiber and ceramic powder, comprising the following steps:

[0044] S1. Raw material preparation

[0045] Microporous mullite, silicon carbide powder, basalt fiber, and ceramic powder were used as ceramic aggregates, agar powder as a forming agent, water as a solvent, ammonium bicarbonate as a pore-forming agent, pulp waste liquor as a binder, and silon powder and rigid polyurethane foam as additives. The length of the basalt fiber was 5 mm. The silon powder was silon powder doped with 1.2 wt.% yttrium ions.

[0046] The mass percentages of each component are as follows: silicon carbide micro powder 30%, microporous mullite 20%, basalt fiber 5%, ceramic powder 10%, agar powder 5%, ammonium bicarbonate 2.5%, pulp waste liquor 9%, silon powder 3%, rigid polyurethane foam 2.5%, and water balance; the ceramic powder and pulp waste liquor are divided into 3 equal parts; the ceramic powder used in this embodiment is a commercially available product;

[0047] S2, Functional Layer Preparation

[0048] Take one portion of ceramic powder and mix it evenly with silicon carbide micro powder, basalt fiber, agar powder, and ammonium bicarbonate to obtain a mixed powder. Then, add silon powder to water and stir to make a mixed solvent. Finally, add the mixed solvent and one portion of pulp waste liquid to the mixed powder in sequence and mix and grind for 13 minutes to obtain the functional layer.

[0049] S3, Insulation Layer Preparation

[0050] Take microporous mullite, the remaining ceramic powder and rigid polyurethane foam and mix them evenly. Then pour in the remaining pulp waste liquid and mix for 13 minutes to obtain the insulation layer mud, which is the insulation layer.

[0051] S4, Compression Molding

[0052] The functional layer and the insulation layer are pressed together to form a brick blank, which is then naturally dried at 28℃ for 22 hours, then dried at 115℃, and then fired at 1350℃ for 8 hours. After cooling, the low thermal conductivity silicon molybdenum brick is obtained.

[0053] Example 2: Unlike Example 1, the length of the basalt fiber is 0.5 mm.

[0054] Example 3: Unlike Example 1, the length of the basalt fiber is 12 mm.

[0055] Example 4: Unlike Example 1, the silon powder is silon powder doped with 0.5 wt.% yttrium ions.

[0056] Example 5: Unlike Example 1, the silon powder is silon powder doped with 2 wt.% ytterbium ions.

[0057] Example 6: Unlike Example 1, the mass percentages of each component are as follows: silicon carbide micro powder 25%, microporous mullite 15%, basalt fiber 3%, ceramic powder 8%, agar powder 2%, ammonium bicarbonate 2%, pulp waste liquor 5%, silon powder 2%, rigid polyurethane foam 2%, and water balance.

[0058] Example 7: Unlike Example 1, the mass percentages of each component are as follows: silicon carbide micro powder 35%, microporous mullite 25%, basalt fiber 7%, ceramic powder 12%, agar powder 8%, ammonium bicarbonate 3%, pulp waste liquor 12%, silon powder 4%, rigid polyurethane foam 3%, and water balance.

[0059] Example 8: Unlike Example 1, in step S4, the product is naturally dried at 25°C for 20 hours, then dried at 100°C, and then fired at 1300°C for 5 hours.

[0060] Example 9: Unlike Example 1, in step S4, the product is naturally dried at 30°C for 24 hours, then dried at 130°C, and then fired at 1450°C for 10 hours.

[0061] Example 10: Unlike Example 1, the ceramic powder has a core-shell structure, consisting of a core, an intermediate layer, and an outer shell from the inside out. The core is composed of porous alumina material, the intermediate layer is composed of silicon nitride and aluminum nitride in a 1:1 mass ratio, and the outer shell is composed of iron oxide and titanium dioxide in a 1:1 mass ratio. The core has a diameter of 30 nm, the intermediate layer has a thickness of 30 nm, and the outer shell has a thickness of 22 nm.

[0062] The method for preparing ceramic powder is as follows:

[0063] S1: Preparation of outer shell layer mixture: Iron oxide and titanium dioxide are mixed in a nitrogen atmosphere for 52 min to obtain outer shell layer mixture;

[0064] S2. Preparation of intermediate layer mixture: Mix silicon nitride and aluminum nitride materials in a nitrogen atmosphere for 50 min to obtain intermediate layer mixture;

[0065] S3: Core Preparation: 35 wt% macroporous alumina ceramic particles with a particle size of 100-150 μm, 35 wt% mesoporous alumina ceramic particles with a particle size of 50-100 μm, and the remainder microporous alumina ceramic particles with a particle size of 10-50 μm were mixed to obtain the core mixture. The mixture was placed in a boron nitride crucible and then transferred to a carbon tube furnace. Under a nitrogen atmosphere of 7 MPa, the mixture was first calcined at 1100℃ for 6 hours. Then, after plasma ball milling, air was introduced at a rate of 8 L / min for low-temperature calcination at 325℃ for 3 hours. The atmosphere pressure for low-temperature calcination was 3 MPa to form the core. The plasma ball milling parameters were: motor speed 650 r / min, discharge voltage 5 kV, discharge frequency 15 kHz, ball milling time 40 min, and ball-to-material ratio 8:1.

[0066] S4: Preparation of ceramic powder: Under nitrogen protection, the intermediate layer mixture is plasma sprayed onto the core surface, and then kept at 1000℃ for 4 hours to obtain a ceramic semi-finished product. Then, the outer shell layer mixture is deposited on the surface of the ceramic semi-finished product by vacuum deposition, and kept at 1000℃ for 4 hours to obtain ceramic powder.

[0067] The parameters for plasma spraying are as follows: operating current 500A, arc voltage 65V, argon flow rate 30L / min, hydrogen flow rate 10L / min, powder feeding rate 4L / min, spraying distance 80-120mm, spraying angle 90°, with argon used as both the plasma gas and powder feeding gas, and hydrogen used as the combustion gas. The parameters for vacuum plating are: vacuum degree 4×10⁻⁶. -3 Pa, preheating temperature is 100℃, negative voltage applied to the target is 400V, and deposition time is 15min.

[0068] Example 11: Unlike Example 10, the core diameter is 15nm, the thickness of the intermediate layer is 25nm, and the thickness of the outer shell layer is 15nm.

[0069] Example 12: Unlike Example 10, the core diameter is 55nm, the thickness of the intermediate layer is 40nm, and the thickness of the outer shell layer is 30nm.

[0070] Example 13: Unlike Example 10, in S1, iron oxide and titanium dioxide are mixed in a nitrogen atmosphere for 45 minutes to obtain the outer shell layer mixture; in S2, silicon nitride and aluminum nitride materials are mixed in a nitrogen atmosphere for 45 minutes to obtain the middle layer mixture.

[0071] Example 14: Unlike Example 10, in S1, iron oxide and titanium dioxide are mixed in a nitrogen atmosphere for 60 minutes to obtain the outer shell layer mixture; in S2, silicon nitride and aluminum nitride materials are mixed in a nitrogen atmosphere for 60 minutes to obtain the middle layer mixture.

[0072] Example 15: Unlike Example 10, 25 wt% of macroporous alumina ceramic particles with a particle size of 100-150 μm, 30 wt% of mesoporous alumina ceramic particles with a particle size of 50-100 μm, and the remainder of microporous alumina ceramic particles with a particle size of 10-50 μm were mixed to obtain a core mixture.

[0073] Example 16: Unlike Example 10, 45 wt% of macroporous alumina ceramic particles with a particle size of 100-150 μm, 40 wt% of mesoporous alumina ceramic particles with a particle size of 50-100 μm, and the remainder of microporous alumina ceramic particles with a particle size of 10-50 μm were mixed to obtain a core mixture.

[0074] Example 17: Unlike Example 10, high-temperature calcination was first performed under a nitrogen atmosphere of 5 MPa at a temperature of 1000°C for 4 hours. Then, after plasma ball milling, air was introduced at a rate of 5 L / min for low-temperature calcination at a temperature of 300°C for 3 hours. The atmosphere pressure for low-temperature calcination was 1 MPa, forming a core.

[0075] Example 18: Unlike Example 10, high-temperature calcination was first performed under a nitrogen atmosphere of 8 MPa at a temperature of 1200°C for 8 hours. Then, after plasma ball milling, air was introduced at a rate of 10 L / min for low-temperature calcination at a temperature of 350°C for 3 hours. The atmosphere pressure for low-temperature calcination was 5 MPa, forming a core.

[0076] Example 19: Unlike Example 10, the plasma ball milling parameters are: motor speed 500 r / min, discharge voltage 4 kV, discharge frequency 10 kHz, ball milling time 30-50 min, and ball-to-material ratio 5:1.

[0077] Example 20: Unlike Example 10, the plasma ball milling parameters are: motor speed 800 r / min, discharge voltage 6 kV, discharge frequency 20 kHz, ball milling time 50 min, and ball-to-material ratio 10:1.

[0078] Example 21: Unlike Example 10, the ceramic semi-finished product was then kept at 900°C for 3 hours to obtain a ceramic semi-finished product. Then, the outer shell layer mixture was deposited on the surface of the ceramic semi-finished product by vacuum deposition, and the ceramic powder was obtained by keeping it at 900°C for 3 hours.

[0079] Example 22: Unlike Example 10, the ceramic semi-finished product was then kept at 1100℃ for 5 hours to obtain a ceramic semi-finished product. Then, the outer shell layer mixture was deposited on the surface of the ceramic semi-finished product by vacuum deposition, and ceramic powder was obtained by keeping it at 1100℃ for 5 hours.

[0080] Example 23: Unlike Example 10, the parameters for plasma spraying are: operating current 400A, arc voltage 50V, argon flow rate 20L / min, hydrogen flow rate 5L / min, powder feeding rate 2L / min, and spraying distance 80mm.

[0081] Example 24: Unlike Example 10, the parameters for plasma spraying are: operating current 600A, arc voltage 75V, argon flow rate 50L / min, hydrogen flow rate 15L / min, powder feeding rate 5L / min, and spraying distance 120mm.

[0082] Example 25: Unlike Example 10, the vacuum deposition parameters are: vacuum degree 3 × 10⁻⁶. -3 Pa, preheating temperature is 70℃, negative voltage applied to the target is 200V, and deposition time is 10min.

[0083] Example 26: Unlike Example 10, the vacuum deposition parameters are: vacuum degree 5 × 10⁻⁶. -3 Pa, preheating temperature is 150℃, negative voltage applied to the target is 600V, and deposition time is 20min.

[0084] Experimental Example: The description of this experimental example is based on the schemes described in Examples 1 to 26, and aims to illustrate the practical application effect of the present invention.

[0085] To illustrate the performance of the low thermal conductivity silicon-mullite brick prepared by the present invention, the refractory bricks obtained in the examples and comparative examples were tested respectively, and the test methods are as follows:

[0086] Salt and alkali resistance test method: The static crucible method was used to conduct the alkali erosion resistance test. 80mm×80mm×80mm sample blocks were cut from each brick. A cylindrical groove of φ36mm×40mm was drilled in the center to make a crucible. A 60mm×60mm×30mm thin plate was cut to make a crucible lid. The crucible and lid were dried. 20g of pure chemical K2CO3 was added to each crucible. Fire clay was used to seal the crucible lid and the crucible. The entire crucible was dried in an oven at 110℃ for 12h, then placed in an electric furnace and kept at 1100℃ for 5h. After natural cooling, the alkali erosion resistance of the samples was evaluated by observing the appearance of the samples.

[0087] Thermal conductivity determination method: The determination shall be carried out at 800℃ in accordance with the provisions of YB / T 4130;

[0088] Tensile strength test method: Tested according to national standard JC / T 2197-2013;

[0089] 1. Investigate the influence of raw material composition on the properties of low thermal conductivity silica-mullite bricks.

[0090] Blank group 1: Unlike Example 1, only basalt fiber was added.

[0091] Blank group 2: Unlike Example 1, only ceramic powder was added.

[0092] Comparative Example 1: Unlike Example 1, the basalt fiber length is 15 mm.

[0093] Comparative Example 2: Unlike Example 1, the serone powder in the raw material does not contain rare earth ions.

[0094] Table 1. Performance of low thermal conductivity silicon molybdenum bricks prepared in Examples 1-9, Blank Groups 1-2, and Control Examples 1-2

[0095] Example 1 1.2 96 Level 1 Example 2 1.6 93 Level 1 Example 3 1.3 94 Level 1 Example 4 1.4 92 Level 1 Example 5 1.2 95 Level 1 Example 6 1.5 93 Level 1 Example 7 1.3 95 Level 1 Example 8 1.4 94 Level 1 Example 9 1.3 95 Level 1 Blank Group 1 2.1 79 Level 1 Blank Group 2 1.7 83 Level 2 Compare with Example 1 1.9 87 Level 2 Compare with Example 2 1.8 85 Level 1

[0096] Conclusions: Comparison of data from Examples 1-3 and Control Example 1 shows that as the length of basalt fibers increases, the thermal conductivity and tensile strength of the resulting low thermal conductivity silica-mullite bricks initially increase and then decrease. This indicates that excessively long fibers are difficult to disperse during concrete mixing, potentially introducing too many air bubbles, further reducing the density and impermeability of the concrete, thus weakening the strength and durability of the low thermal conductivity silica-mullite bricks. Considering all factors, the low thermal conductivity silica-mullite bricks achieve optimal performance under the conditions of Example 1. Comparison of data from Examples 1, 4-5, and Control Example 2 shows that adding rare earth ions can optimize the crystal structure and microstructure of silane powder, thereby improving the strength and toughness of basalt fibers and enhancing the tensile strength of the low thermal conductivity silica-mullite bricks. Comparison of Examples 1-9 and blank groups 1-2 shows that adding basalt fibers and ceramic powder alone can indeed improve the alkali resistance and thermal insulation performance of silica-mullite bricks, but the tensile effect is limited.

[0097] 2. Investigate the effect of ceramic powder preparation methods on the properties of low thermal conductivity silicon-mullite bricks.

[0098] Table 2. Performance of low thermal conductivity silicon-mullite bricks prepared in Examples 1, 10-26, and Comparative Examples 3-5

[0099]

[0100]

[0101] Comparative Example 3: Unlike Example 10, the alumina ceramic particles are microporous alumina ceramic particles of 10-50 μm.

[0102] Comparative Example 4: Unlike Example 10, the titanium dioxide in the outer shell layer was replaced with phosphorus oxide.

[0103] Comparative Example 5: Unlike Example 10, no plasma ball milling treatment was performed between high-temperature calcination and low-temperature calcination.

[0104] Conclusion: Comparison of Examples 1 and Examples 10-26 shows that the ceramic powder manufactured by this method has a positive effect on improving the tensile strength of basalt fibers, while the commercially available ceramic powder used in Example 1 does not have the effect of improving the tensile strength of basalt fibers.

[0105] A comparison of Examples 10, 15-16, and Comparative Example 3 reveals that the thermal insulation and tensile strength of the low thermal conductivity silica-molybdenum brick obtained using only microporous alumina ceramic particles in Comparative Example 3 are both weakened. This is because the particle size limitation of alumina ceramic particles can effectively reduce thermal conductivity by utilizing larger particle sizes. These particles form larger pores in the microstructure, where air or gas is fixed, reducing heat conduction paths and thus improving insulation performance. Furthermore, large-diameter particles can form stronger interparticle bonds at high temperatures. However, excessively large particle sizes may lead to… The concentration of force improves the overall tensile properties; mesoporous particles play a transitional role in thermal insulation performance. They maintain a certain porosity without significantly affecting the structural strength of the material like macroporous particles. The reasonable distribution of mesoporous particles helps improve the toughness of the material, and by optimizing the contact points between particles, the tensile properties are improved; the high density and small pores of microporous particles are conducive to forming a continuous thermal insulation layer, further improving the thermal insulation effect. Small-diameter particles can fill the gaps between large particles, forming a denser structure, improving the overall strength and toughness of the material, thereby enhancing the tensile properties.

[0106] A comparison of Examples 10, 13-14, and Comparative Example 4 reveals that while the addition of phosphorus oxide can promote the formation of an alkali-resistant glassy phase and reduce the corrosive effect of alkali metals, thus enhancing the alkali resistance of silicon-mullite bricks, it also promotes grain growth at high temperatures, which may weaken the tensile properties of the material and limit its tensile strength. In contrast, the addition of titanium dioxide can reduce the viscosity of basalt melt and promote Al... 3+ The TiO2 enters the network structure and acts as a network precursor, thereby strengthening polymerization and enhancing the tensile properties of silicon-mullite bricks. In addition, the insoluble titanium hydroxide layer formed by TiO2 in basalt fibers can reduce corrosion in NaOH solution and improve the alkali resistance of fibers.

[0107] A comparison of Examples 10, 17-18 and Comparative Example 5 shows that the performance of the low thermal conductivity silicon-molybdenum brick obtained in Comparative Example 5 is significantly weakened due to the absence of plasma ball milling. This indicates that plasma ball milling can increase the active sites of solid-phase reactions, accelerate the mass transfer process, and improve sintering activity, thereby obtaining a ceramic core with good thermal insulation performance at low temperatures. High-temperature calcination followed by low-temperature calcination can optimize the rheological properties of ceramic powder and improve its processability, thereby obtaining ceramic powder with better thermal insulation performance.

Claims

1. A method for preparing low thermal conductivity silicon-mullite bricks using basalt fiber in conjunction with ceramic powder, characterized in that, Includes the following steps: S1. Raw material preparation Microporous mullite, silicon carbide micro powder, basalt fiber, and ceramic powder are used as ceramic aggregates, agar powder as a forming agent, water as a solvent, ammonium bicarbonate as a pore-forming agent, pulp waste liquor as a binder, and silon powder and rigid polyurethane foam as additives to prepare each material separately; the silon powder is silon powder doped with 0.5~2wt.% yttrium ions or ytterbium ions. The mass percentages of each component are as follows: silicon carbide micro powder 25-35%, microporous mullite 15-25%, basalt fiber 3-7%, ceramic powder 8-12%, agar powder 2-8%, ammonium bicarbonate 2-3%, pulp waste liquor 5-12%, silane powder 2-4%, rigid polyurethane foam 2-3%, and water as the balance; the ceramic powder is divided into 2-3 equal parts, and the pulp waste liquor is divided into 2-3 equal parts. S2, Functional Layer Preparation Take one portion of ceramic powder and mix the silicon carbide micro powder, basalt fiber, agar powder, and ammonium bicarbonate evenly to obtain a mixed powder. Then, add silon powder to water and stir to make a mixed solvent. Finally, add the mixed solvent and one portion of pulp waste liquid to the mixed powder in sequence and mix and grind for 10-15 minutes to obtain the functional layer. S3, Insulation Layer Preparation Microporous mullite, the remaining ceramic powder, and rigid polyurethane foam are mixed evenly, and then the remaining pulp waste liquid is poured in and mixed and kneaded for 10-15 minutes to obtain the insulation layer mud, which is the insulation layer. The ceramic powder has a core-shell structure, consisting of a core, a middle layer, and an outer shell layer from the inside out. The core is composed of porous alumina material, the middle layer is composed of silicon nitride and aluminum nitride materials in equal mass ratio, and the outer shell layer is composed of iron oxide and titanium dioxide materials in equal mass ratio. The core has a diameter of 15~55nm, the intermediate layer has a thickness of 25~40nm, and the outer shell has a thickness of 15~30nm. The method for preparing the ceramic powder is as follows: S1' Preparation of the outer shell layer mixture: Iron oxide and titanium dioxide are mixed in a nitrogen atmosphere for 45-60 minutes to obtain the outer shell layer mixture; S2' Preparation of intermediate layer mixture: Mix silicon nitride and aluminum nitride materials in a nitrogen atmosphere for 45-60 min to obtain intermediate layer mixture; S3' Preparation of the core: Take 25~45wt% macroporous alumina ceramic particles with a particle size of 100~150μm, 30~40wt% mesoporous alumina ceramic particles with a particle size of 50~100μm, and the balance microporous alumina ceramic particles with a particle size of 10~50μm to mix them to obtain the core mixture. Put it into a boron nitride crucible, and then transfer it into a carbon tube furnace. Under the protection of nitrogen atmosphere, it is first calcined at high temperature, and then after plasma ball milling, it is calcined at low temperature by introducing air at a rate of 5~10L / min to form the core. S4' Preparation of ceramic powder: Under nitrogen protection, the intermediate layer mixture is plasma sprayed onto the core surface, and then kept at 900~1100℃ for 3~5h to obtain a ceramic semi-finished product. Then, the outer shell layer mixture is deposited on the surface of the ceramic semi-finished product by vacuum plating, and kept at 900~1100℃ for 3~5h to obtain ceramic powder. S4, Compression Molding The functional layer and the insulation layer are pressed together to form a brick blank, which is then naturally dried at 25~30℃ for 20~24h, then dried at 100~130℃, and then fired at 1300~1450℃ for 5~10h. After cooling, the low thermal conductivity silicon molybdenum brick is obtained. In step S4, the parameters of the plasma spraying are: working current 400~600A, arc voltage 50~75V, argon flow rate 20~50L / min, hydrogen flow rate 5~15L / min, powder feeding rate 2~5L / min, spraying distance 80~120mm, spraying angle 90°, argon as plasma gas and powder feeding gas, and hydrogen as combustion gas; The vacuum plating parameters are: vacuum degree 3x10 -3 -5x10 -3 Pa, preheating temperature 70-150℃, negative voltage applied to the target material 200-600V, deposition time 10-20min; The basalt fibers are 0.5 to 12 mm in length.

2. The method for preparing low thermal conductivity silicon-mullite bricks using basalt fiber and ceramic powder as described in claim 1, characterized in that, In step S3, the high-temperature calcination temperature is 1000~1200℃, the high-temperature calcination time is 4-8h, and the high-temperature calcination atmosphere pressure is 5~8MPa; the low-temperature calcination temperature is 300~350℃, the calcination time is 3h, and the low-temperature calcination atmosphere pressure is 1~5MPa.

3. The method for preparing low thermal conductivity silicon-mullite bricks using basalt fiber and ceramic powder as described in claim 1, characterized in that, In step S3, the plasma ball milling parameters are: motor speed 500~800 r / min, discharge voltage 4~6 kV, discharge frequency 10~20 kHz, ball milling time 30~50 min, and ball-to-material ratio 5~10:1.

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