A heat insulation board with a low-dimensional SiO2-expanded vermiculite composite gradient structure and its preparation method

Abstract

The application discloses a kind of low-dimensional SiO2-expansion vermiculite composite gradient structure heat insulation plate and preparation method thereof, belong to heat insulation material technical field.The heat insulation plate includes the following mass parts of raw materials: expansion vermiculite 20~50 parts, including 4~6, 10~40 and 40~60 three particle size levels;Low-dimensional SiO2micro powder 13~33 parts, including 300~500nm and 100~200nm two components;CaO-MgO-SiO2quality refractory fiber 3~10 parts;Water glass 6~15 parts;Silica sol 3~8 parts;Kaolin 2~6 parts;Silicon ethyl ester 3~10 parts;Silicone-acrylic resin emulsion 3~10 parts;Sodium fluorosilicate 0.5~2 parts;Silane coupling agent 0.2~1 part.The heat insulation plate of the application thermal conductivity≤0.028W / (m·K), compressive strength≥8.5MPa, 24h water absorption≤5.0%.

Description

Technical Field

[0001] This invention relates to the field of thermal insulation materials technology, and in particular to a thermal insulation board with a low-dimensional SiO2-expanded vermiculite composite gradient structure and its preparation method. Background Technology

[0002] Vermiculite is a layered hydrated aluminosilicate mineral rich in interlayer water. When heated, it loses water and expands, increasing in volume rapidly by 8 to 15 times, and up to 30 times. This expanded vermiculite is called expanded vermiculite. Expanded vermiculite has advantages such as fire resistance, light weight, sound absorption, and low thermal conductivity, making it an excellent fireproof and heat-insulating material.

[0003] Vermiculite boards, made primarily from expanded vermiculite, are widely used in building exterior wall insulation, fireproof door cores, steel structure fire protection, and high-temperature pipeline insulation due to their non-combustible (fire resistance rating can reach over 4 hours), smokeless, non-toxic, and low thermal conductivity properties. Currently, the common preparation method for vermiculite boards involves using expanded vermiculite as aggregate and water glass (sodium silicate or potassium silicate) as a binder, followed by mixing, pressing, curing, and drying processes to obtain the finished product.

[0004] Chinese invention patent CN102173718B discloses a composite board made of kaolin and expanded vermiculite. This patent uses kaolin and expanded vermiculite as the main raw materials, water glass as a binder, and potassium fluorosilicate as a curing accelerator. The process involves mixing, hot pressing (180℃, 0.5MPa, holding pressure for 180 minutes), and demolding to produce a fire-resistant and heat-insulating composite board product. The loose bulk density of the expanded vermiculite is 90–130 kg / m³. 3 The water glass is sodium-type or potassium-type water glass with a solid content of 30-40% and a modulus of 3.0-4.0. This patent improves the strength and fire resistance of vermiculite products by introducing kaolin, utilizing its plasticity, dispersibility, and high-temperature resistance. Its thermal conductivity is 0.09-0.12 W / (m·K), bulk density is 460-820 kg / m³, compressive strength is 4.0-8.0 MPa, and water absorption (GB5486-2008) is 5-35%.

[0005] However, the aforementioned existing technologies and currently available vermiculite board products still have the following shortcomings:

[0006] I. High Thermal Conductivity, Insulation Performance Needs Further Improvement. While the aforementioned composite panels possess fire-resistant and heat-insulating properties, their thermal conductivity typically ranges from 0.09 to 0.12 W / (m·K). This is primarily due to the numerous micron-sized pores between vermiculite particles, resulting in significant convective and radiative heat transfer from the air, making it difficult to further reduce the thermal conductivity. Furthermore, studies have shown that vermiculite-based fire-resistant and heat-insulating products prepared from expanded vermiculite, water glass, potassium fluorosilicate, and silicone-acrylic resin have a thermal conductivity of 0.084 W / (m·K), which remains relatively high.

[0007] Second, the mechanical strength is relatively low, limiting its application scenarios. The compressive strength of existing vermiculite boards is 4.0–8.0 MPa, and the flexural strength is 1.4–2.9 MPa. Although the strength of vermiculite products has been improved by introducing kaolin, there is still room for further improvement in strength for some applications that require bearing higher loads.

[0008] Third, poor water resistance and susceptibility to moisture absorption and powdering. Existing vermiculite boards generally use water glass as a binder. Water glass dissolves and is lost when exposed to water or prolonged exposure to high humidity. The water absorption rate of the composite board (GB5486-2008) ranges from 5% to 35%. This range is relatively wide; a low value (5%) is acceptable, but a high value (35%) indicates that under certain formulation or process conditions, the board's water resistance remains poor. This is mainly because water glass dissolves and is lost when exposed to water or prolonged exposure to high humidity, leading to a sharp drop in board strength or even powdering, severely limiting its application in humid environments.

[0009] Fourth, insufficient high-temperature stability. The maximum service temperature of existing vermiculite boards is usually around 800℃. Above this temperature, the linear shrinkage rate of the board increases sharply and the strength decreases significantly, limiting its application in higher temperature conditions.

[0010] Fifth, the homogeneous structure makes it difficult to balance performance. Existing vermiculite boards are all homogeneous in structure, with the same density in all parts of the same board. In practical applications, the surface of the board needs high strength and wear resistance to resist external damage, while the core layer needs low density and thermal conductivity to achieve good insulation effect—the homogeneous structure makes it difficult to balance surface strength and core insulation performance. Summary of the Invention

[0011] To overcome the shortcomings of the prior art, the present invention adopts the following technical solution:

[0012] A low-dimensional SiO2-expanded vermiculite composite gradient structure heat insulation board, comprising the following raw materials in parts by weight:

[0013] 20-50 parts of expanded vermiculite, wherein the expanded vermiculite comprises three particle size grades: 4-6 mesh, 10-40 mesh, and 40-60 mesh;

[0014] 13 to 33 parts of low-dimensional SiO2 micro powder, wherein the low-dimensional SiO2 micro powder comprises a first component with an average particle size of 300 to 500 nm and a second component with an average particle size of 100 to 200 nm;

[0015] 3-10 parts of CaO-MgO-SiO2 refractory fiber;

[0016] 6-15 parts water glass;

[0017] 3-8 parts of silica sol;

[0018] 2-6 parts of kaolin;

[0019] 3-10 parts of ethyl silicate;

[0020] 3-10 parts of silicone-acrylic resin emulsion;

[0021] Sodium fluorosilicate 0.5–2 parts;

[0022] 0.2 to 1 part of silane coupling agent;

[0023] The heat insulation board has a five-layer gradient density structure, which consists of a bottom layer, a first transition layer, a core layer, a second transition layer, and a surface layer along the thickness direction. The density of the surface layer and the bottom layer is higher than that of the core layer.

[0024] The thermal conductivity of the insulation board is ≤0.028W / (m·K), the compressive strength is ≥8.5MPa, and the water absorption rate is ≤5% in 24h.

[0025] Furthermore, the linear shrinkage rate of the heat insulation board under the condition of 900℃×3h is ≤1.5%.

[0026] Furthermore, the first component of the low-dimensional SiO2 micro powder is 8 to 18 parts, and the second component of the low-dimensional SiO2 micro powder is 5 to 15 parts.

[0027] Furthermore, the core layer also contains 3 to 8 parts of expanded perlite.

[0028] Furthermore, the surface of the heat insulation plate is also provided with a hydrophobic treatment layer formed by an organosilane hydrophobic agent.

[0029] A method for preparing a heat insulation board with a low-dimensional SiO2-expanded vermiculite composite gradient structure includes the following steps:

[0030] S1. Preparation of low-dimensional SiO2 premix: According to the above mass parts, low-dimensional SiO2 micro powder with an average particle size of 300-500nm, low-dimensional SiO2 micro powder with an average particle size of 100-200nm and CaO-MgO-SiO2 refractory fiber are mixed evenly to obtain low-dimensional SiO2 premix.

[0031] S2. Preparation of silica sol precursor solution: Mix 3-10 parts of ethyl silicate, 3-10 parts of ethanol, 2-5 parts of water and hydrochloric acid, and hydrolyze at 40-60℃ for 30-60 minutes to obtain silica sol precursor solution.

[0032] S3. Preparation of organic-inorganic composite binder: Mix water glass, silica sol and silicone-acrylic resin emulsion evenly, add silane coupling agent to obtain organic-inorganic composite binder;

[0033] S4. Preparation of coarse mixture: Mix 4-6 mesh and 10-40 mesh expanded vermiculite, 70-90% of the total amount of low-dimensional SiO2 premix obtained in S1, kaolin, and sodium fluorosilicate evenly. Then add 70-90% of the total amount of organic-inorganic composite binder obtained in S3 and 70-90% of the total amount of silica sol precursor solution obtained in S2, and continue to mix evenly to obtain coarse mixture.

[0034] S5. Preparation of fine mixture: Mix 40-60 mesh expanded vermiculite with 10-30% of the total amount of low-dimensional SiO2 premix obtained in S1, add 10-30% of the total amount of organic-inorganic composite binder obtained in S3 and 10-30% of the total amount of silica sol precursor solution obtained in S2, mix evenly to obtain fine mixture.

[0035] S6. Laying the mixture: In the mold, the bottom layer composed of the fine mixture, the first transition layer composed of the fine mixture and the coarse mixture in a 1:1 ratio, the core layer composed of the coarse mixture, the second transition layer composed of the fine mixture and the coarse mixture in a 1:1 ratio, and the surface layer composed of the fine mixture are laid in sequence to form a five-layer gradient structure.

[0036] S7. Compression molding: Compression molding is carried out under a pressure of 2.5 to 3.5 MPa to obtain a wet sheet material;

[0037] S8. Aging and sintering: The coated board is left to stand to allow the silica sol precursor solution to gel, then aged at 40-60°C, and the aged board is sintered at 800-900°C for 0.5-1 hour.

[0038] S9. Hydrophobic treatment: After the board is fired and cooled to room temperature, an alcohol solution of organosilane hydrophobic agent is sprayed onto the surface. The alcohol solvent is allowed to evaporate naturally by standing. The organosilane undergoes in-situ hydrolysis, condensation and cross-linking on the surface of the board and within a depth of 0.5 to 2 mm near the surface to form a hydrophobic treatment layer.

[0039] Furthermore, in S6, the thickness of each layer in the five-layer gradient structure accounts for the proportion of the total thickness of the board as follows: bottom layer 15-20%, first transition layer 10-15%, core layer 30-50%, second transition layer 10-15%, and surface layer 15-20%.

[0040] Furthermore, after S7 and before S8, the process also includes spraying ultrafine inorganic fiber adhesive: spraying ultrafine inorganic fiber adhesive onto the surface of the wet plate.

[0041] Furthermore, in S7, the pressing and molding process employs step-by-step pressurization: first, pre-pressing at 0.3–0.5 MPa for 30 seconds, then applying main pressure at 2.5–3.5 MPa for 60–120 seconds, with a depressurization rate ≤0.5 MPa / s.

[0042] Furthermore, in S8, the firing process includes three stages: first, drying at 80-120°C for 2-4 hours, then heating to 800-900°C and holding for 0.5-1 hour, and finally cooling with the furnace.

[0043] Furthermore, in S9, the coating amount for the surface spraying is 100–300 g / m². 2 The settling time is 20 to 60 minutes.

[0044] Compared with the prior art, the beneficial effects of the present invention are:

[0045] 1. This invention introduces low-dimensional SiO2 micropowder with average particle sizes of 300–500 nm and 100–200 nm into the micron-level pores between expanded vermiculite particles, forming a micro-nano multi-level stacked structure. This extends the solid-phase heat transfer path and suppresses air convection heat transfer. Simultaneously, SiO2 aerogel with a nanoporous network structure is generated in situ within the expanded vermiculite pores via a sol-gel method using tetraethyl orthosilicate. This aerogel forms a dual-scale filling with the low-dimensional SiO2 micropowder, further suppressing heat conduction. According to Example 1, the thermal conductivity of the insulation board of this invention can be as low as 0.026 W / (m·K).

[0046] 2. This invention utilizes the lightweight filling of low-dimensional SiO2 micropowder, the high porosity characteristics of in-situ generated SiO2 aerogel, and the structural design that retains macroscopic pores between coarse particles in the core layer. According to Example 1, the average density of the insulation board of this invention is reduced to 255 kg / m³. 3 .

[0047] 3. This invention significantly improves the compressive and flexural strength of the insulation board through the synergistic effects of low-dimensional SiO2 micropowder filling reinforcement, CaO-MgO-SiO2 refractory fiber bridging toughening, an interpenetrating network structure formed by an organic-inorganic composite binder, and high-pressure molding at 2.5–3.5 MPa and low-temperature firing at 800–900℃. According to Example 1, the compressive strength of the insulation board of this invention can reach 10.2 MPa, and the flexural strength can reach 8.0 MPa.

[0048] 4. This invention uses silicone-acrylic resin emulsion, water glass, and silica sol to form an organic-inorganic interpenetrating network (IPN) structure adhesive. This structure combines the high heat resistance of inorganic materials with the water resistance of organic materials. Simultaneously, low-temperature firing at 800–900℃ allows the adhesive to fully cross-link and cure, further improving the water resistance of the board. According to Example 1, the 24-hour water absorption rate of the insulation board of this invention is only 2.8%. Example 3 further shows that after hydrophobic treatment, the 24-hour water absorption rate can be as low as 1.5%, and the compressive strength retention rate after 24-hour immersion in water can reach 96%.

[0049] 5. This invention utilizes a low-temperature sintering process of 800–900℃ to sinter and solidify low-dimensional SiO2 micropowder and fully condense the silicate binder, forming a stable ceramic bonding phase. This significantly improves the high-temperature dimensional stability and residual strength of the board. According to Example 1, the linear shrinkage rate of the insulation board of this invention is only 0.8% under conditions of 900℃ × 3 hours; the maximum operating temperature can reach 1000℃.

[0050] 6. This invention employs a five-layer gradient density structure; the surface and bottom layers use a fine mixture to form a high-density layer (approximately 380 kg / m³), providing high strength and good surface wear resistance; the core layer uses a coarse mixture to form a low-density layer (approximately 200 kg / m³), providing excellent thermal insulation performance; the transition layer achieves a smooth transition in density. Based on a comparison of Example 1 and Comparative Example 4, under the same raw materials and process conditions, Example 1, employing a five-layer gradient density structure, compared to the homogeneous structure of Comparative Example 4, shows a decrease in average density (from 270 kg / m³ to 255 kg / m³) while simultaneously increasing compressive strength from 7.5 MPa to 10.2 MPa. This achieves simultaneous reduction in density and increase in strength, effectively solving the technical problem of existing homogeneous vermiculite boards struggling to balance surface strength and core insulation performance. Detailed Implementation

[0051] The present invention will be further described in detail below with reference to the embodiments, but the implementation of the present invention is not limited thereto.

[0052] The raw materials used in the examples and comparative examples are all commercially available industrial-grade products, as detailed below:

[0053] The expanded vermiculite is industrial grade, with a bulk density of 80–120 kg / m³. 3 The particle size range of expanded vermiculite is 3.35–4.75 mm for 4–6 mesh, 0.425–2.00 mm for 10–40 mesh, and 0.250–0.425 mm for 40–60 mesh.

[0054] The low-dimensional SiO2 micro powder is an industrial-grade SiO2 micro powder. The average particle size of its first component is 300-500 nm, and the SiO2 mass fraction is ≥99.0%. The average particle size of the second component is 100-200 nm, and the SiO2 mass fraction is ≥99.0%.

[0055] CaO-MgO-SiO2 refractory fiber is an industrial-grade refractory fiber with a fiber length of 3-5 mm, a fiber diameter of 2-5 μm, and a maximum service temperature of 1200℃.

[0056] The water glass is industrial-grade sodium silicate water glass with a modulus of 3.0–3.8 and a Baume degree of 38–42.

[0057] The silica sol is an industrial-grade alkaline silica sol with a solid content of 30% and a pH value of 9.0–10.5.

[0058] The kaolin is calcined kaolin with a fineness of 325 mesh and a whiteness of ≥85%.

[0059] The ethyl silicate is industrial grade tetraethyl orthosilicate with a purity of ≥98.0%.

[0060] The ethanol is industrial-grade anhydrous ethanol with a purity of ≥99.5%.

[0061] The hydrochloric acid is industrial-grade dilute hydrochloric acid with a concentration of 0.1 mol / L.

[0062] The silicone-acrylic resin emulsion is an industrial-grade silicone-acrylic emulsion with a solid content of 45% and a pH value of 7.0–8.0.

[0063] Sodium fluorosilicate is industrial grade sodium fluorosilicate with a purity ≥98.0%.

[0064] The silane coupling agent is γ-aminopropyltriethoxysilane (KH-550) with a purity ≥97.0%.

[0065] The ultrafine inorganic fiber spraying adhesive is a commercially available water-based adhesive specifically for inorganic fiber spraying, with a solid content of ≥25%.

[0066] The organosilane hydrophobic agent is methyltrimethoxysilane or potassium methylsilicate, industrial grade, with a purity ≥98.0%.

[0067] Example 1: A heat insulation board with a low-dimensional SiO2-expanded vermiculite composite gradient structure and its preparation method. The mass ratio of each raw material in the heat insulation board is as follows: 15 parts expanded vermiculite (4-6 mesh), 22 parts expanded vermiculite (10-40 mesh), 10 parts expanded vermiculite (40-60 mesh), 12 parts first component of low-dimensional SiO2 micro powder (300-500 nm), and 100-200 parts second component of low-dimensional SiO2 micro powder. 8 parts of 00nm), 5 parts of CaO-MgO-SiO2 refractory fiber (3-5mm), 10 parts of water glass (modulus 3.2), 5 parts of silica sol (solid content 30%), 4 parts of kaolin (325 mesh), 6 parts of ethyl silicate, 6 parts of ethanol, 1 part of hydrochloric acid (0.1mol / L), 6 parts of silicone-acrylic resin emulsion (solid content 45%), 1 part of sodium fluorosilicate, and 0.5 parts of silane coupling agent (KH-550).

[0068] The method for preparing the low-dimensional SiO2-expanded vermiculite composite gradient structure heat insulation board in this embodiment includes the following steps:

[0069] Step 1: Preparation of low-dimensional SiO2 premix

[0070] According to the above-mentioned mass proportions, 12 parts of low-dimensional SiO2 micro powder with an average particle size of 300-500nm, 8 parts of low-dimensional SiO2 micro powder with an average particle size of 100-200nm, and 5 parts of CaO-MgO-SiO2 refractory fiber were added to a high-speed mixer and dry-mixed at 800rpm for 8min until all components were mixed evenly to obtain 25 parts of low-dimensional SiO2 premix.

[0071] Step 2: Preparation of silica sol precursor solution

[0072] According to the above-mentioned mass proportions, 6 parts of ethyl silicate, 6 parts of ethanol, 4 parts of deionized water and 1 part of hydrochloric acid were added to the reaction vessel and stirred and hydrolyzed for 45 minutes under a water bath at 50°C to obtain a clear and transparent silica sol precursor solution, with a total volume of approximately 17 parts.

[0073] Step 3: Preparation of organic-inorganic composite binder

[0074] According to the above-mentioned mass proportions, 10 parts of water glass, 5 parts of silica sol and 6 parts of silicone-acrylic resin emulsion were added to a stirring container and stirred at 150 rpm for 12 minutes. Then, 0.5 parts of silane coupling agent were added and stirred for another 5 minutes to obtain an organic-inorganic composite binder with a total volume of 21.5 parts.

[0075] Step 4: Preparation of coarse mixture

[0076] According to the above-mentioned mass proportions, 15 parts of 4-6 mesh expanded vermiculite, 22 parts of 10-40 mesh expanded vermiculite, the low-dimensional SiO2 premix obtained in step one (80% of the total amount, i.e., about 20 parts), 4 parts of kaolin, and 1 part of sodium fluorosilicate are added to a mixer and dry-mixed at 300 rpm for 8 minutes. Then, the organic-inorganic composite binder obtained in step three (80% of the total amount, i.e., about 17.2 parts) and the silica sol precursor solution obtained in step two (80% of the total amount, i.e., about 13.6 parts) are added, and the mixture is stirred at 300 rpm for 15 minutes to ensure that all components are fully mixed and homogeneous, thus obtaining a coarse mixture.

[0077] Step 5: Prepare fine mixture

[0078] According to the above-mentioned mass proportions, 10 parts of 40-60 mesh expanded vermiculite and the low-dimensional SiO2 premix obtained in step one (20% of the total amount, i.e., 5 parts) are added to a mixer. The organic-inorganic composite binder obtained in step three (20% of the total amount, i.e., about 4.3 parts) and the silica sol precursor solution obtained in step two (20% of the total amount, i.e., about 3.4 parts) are added. The mixture is stirred at 300 rpm for 15 minutes until it is uniformly mixed to obtain a fine mixture.

[0079] Step Six: Laying the Mixture

[0080] In this embodiment, the thickness of the final product to be prepared is 60 mm. Based on the bulk density, moisture content, and target density of the raw materials, the compression ratio is determined to be 1.8, meaning the total thickness of the spread material should be 1.8 times the thickness of the final product, and the total thickness of the spread material is 108 mm.

[0081] Five layers of the mixture are laid sequentially in a rectangular steel mold (internal cavity dimensions 114mm × 114mm × 108mm):

[0082] Bottom layer: The fine mixture obtained in step five is evenly spread into the bottom of the mold. The thickness of the spread is controlled to be 18% of the total thickness of the spread, i.e., 19.4mm, which is used to form the bottom layer with a thickness of 10.8mm and a thickness of 18% in the final product.

[0083] First transition layer: After the fine mixture obtained in step five and the coarse mixture obtained in step four are mixed evenly at a mass ratio of 1:1, it is laid on the bottom layer. The thickness of the layer is controlled to be 12% of the total thickness of the layer, i.e. 13.0 mm, which is used to form the first transition layer with a thickness of 7.2 mm and a thickness of 12% in the final product.

[0084] Core layer: The coarse mixture obtained in step four is laid on the first transition layer. The thickness of the material is controlled to be 40% of the total thickness of the material, i.e., 43.2 mm, which is used to form the core layer with a thickness of 24.0 mm and a thickness of 40% in the final product.

[0085] Second transition layer: After the fine mixture obtained in step five and the coarse mixture obtained in step four are mixed evenly at a mass ratio of 1:1, it is spread on the core layer. The thickness of the spread material is controlled to be 12% of the total thickness of the spread material, i.e., 13.0 mm, which is used to form the second transition layer with a thickness of 7.2 mm and a thickness of 12% in the final product.

[0086] Surface layer: The fine mixture obtained in step five is spread on the second transition layer. The thickness of the spread is controlled to be 18% of the total thickness of the spread, i.e., 19.4 mm, which is used to form a surface layer with a thickness of 10.8 mm and a thickness of 18% in the final product.

[0087] After each layer is laid, the surface is smoothed with a scraper to form a five-layer gradient structure.

[0088] Step 7: Pressing and Shaping

[0089] The mold containing the five-layer gradient structure mixture is placed on a hydraulic press and pressed into shape using a step-by-step pressing method:

[0090] Pre-compression stage: Pre-compress at 0.4MPa for 30s to allow the layers to bond initially and the mixture to be initially compressed;

[0091] Main compression stage: Apply a pressure of 3.0MPa for 90 seconds to densify the board and compress it to the target thickness of 60mm;

[0092] Depressurization stage: Depressurize slowly to atmospheric pressure at a rate of 0.4 MPa / s to prevent interlayer cracking.

[0093] After pressing and molding, the material is demolded to obtain a wet sheet with a thickness of 60mm.

[0094] Step 8: Spraying ultra-fine inorganic fiber adhesive

[0095] The wet board obtained in step seven is placed on a spraying table, and ultrafine inorganic fiber adhesive is evenly sprayed onto both the upper and lower surfaces of the board using air spraying, with a spray thickness of 0.3 mm. The distance between the spray gun and the board surface is preferably controlled at 200–300 mm, and the spraying pressure is preferably 0.3–0.5 MPa (in this embodiment, the spraying distance is 250 mm, and the spraying pressure is 0.4 MPa). The ultrafine inorganic fiber adhesive is used to enhance the surface strength of the board and improve the adhesion between the surface layer and the subsequent hydrophobic treatment layer; this step is optional, and its presence or absence does not affect the overall performance of the five-layer gradient density structure.

[0096] Step Nine: Aging and Sintering

[0097] After spraying in step eight, the substrate was transferred to a sealed curing container and left to stand at room temperature for 4 hours to allow the silica sol precursor solution to fully gel in the pores of the expanded vermiculite. The substrate was then transferred to a constant temperature drying oven and aged at 50°C for 18 hours to stabilize the gel network structure.

[0098] After aging, the sheets are transferred to a high-temperature resistance furnace for firing. The firing process is a three-stage process:

[0099] Drying section: The temperature is increased from room temperature to 120℃ at a rate of 2℃ / min, and then kept at 120℃ for 3 hours to remove free water from the board.

[0100] Firing section: The temperature is increased from 120℃ to 850℃ at a heating rate of 5℃ / min, and held at 850℃ for 0.5h;

[0101] Cooling section: Heating stops, and the furnace cools naturally to room temperature.

[0102] After firing, the board is removed, resulting in a low-dimensional SiO2-expanded vermiculite composite gradient structure insulation board.

[0103] Step 10: Hydrophobic treatment

[0104] After the substrate has been fired and cooled to room temperature in step nine, it is then surface-coated with a methyltrimethoxysilane ethanol solution (methyltrimethoxysilane to anhydrous ethanol volume ratio of 1:10). The coating amount is 200 g / m². 2 After spraying, the board is left to stand at room temperature for 40 minutes to allow the ethanol solvent to evaporate naturally. Methyltrimethoxysilane undergoes in-situ hydrolysis, condensation, and cross-linking on the surface of the board and within a depth of 0.5–2 mm near the surface, forming a hydrophobic treatment layer.

[0105] Product performance tests are as follows:

[0106] The performance of the insulation board prepared in Example 1 was tested in accordance with GB / T 5486-2008 "Test Methods for Inorganic Rigid Insulation Products" and GB / T 10294-2008 "Determination of Steady-State Thermal Resistance and Related Properties of Insulation Materials - Protective Hot Plate Method".

[0107] The sample size is 114mm×114mm×60mm. Five parallel samples are taken for each test group, and the test results are taken as the arithmetic mean.

[0108] Thermal conductivity: determined according to GB / T 10294-2008, using the protective hot plate method, with a test temperature of 25±2℃, a hot surface temperature of 35℃, and a cold surface temperature of 15℃. The test result is a thermal conductivity of 0.026 W / (m·K).

[0109] Compressive strength: Tested according to GB / T 5486-2008, with a loading rate of 5 mm / min, and the maximum load at which the specimen failed was recorded. The test result was a compressive strength of 10.2 MPa.

[0110] Bending strength: Determined according to the three-point bending method of GB / T 5486-2008, with a span of 100 mm and a loading speed of 2 mm / min. The test result is a bending strength of 8.0 MPa.

[0111] Density: Determined according to GB / T 5486-2008. The test result is an average density of 255 kg / m³.

[0112] The density of each layer was tested along the thickness direction: the surface layer density was 382 kg / m³, the first transition layer density was 298 kg / m³, the core layer density was 202 kg / m³, the second transition layer density was 296 kg / m³, and the bottom layer density was 380 kg / m³. The densities of the surface layer and the bottom layer were both higher than those of the core layer.

[0113] 24-hour water absorption rate: determined according to GB / T 5486-2008: the sample was immersed in water at (23±2)℃ for 24 hours, then wiped dry with a damp cloth, weighed, and the percentage increase in mass was calculated. The test result was a 24-hour water absorption rate of 2.8%.

[0114] Linear shrinkage rate: Tested according to GB / T 5486-2008 uniform temperature ignition performance test method: The sample was placed in a high-temperature furnace and heated to 900℃ at a heating rate of 5℃ / min, held at that temperature for 3 hours, and then naturally cooled before measuring the linear shrinkage rate. The test result was a linear shrinkage rate of 0.8% under the condition of 900℃×3h.

[0115] Maximum service temperature: Tested at 800℃, 900℃, and 1000℃ according to the above uniform temperature burning performance test method. The highest test temperature with residual compressive strength ≥ 4.0MPa is taken as the maximum service temperature. The test result shows that the maximum service temperature is ≥ 1000℃.

[0116] Example 2 differs from Example 1 in that, during step six, when laying the core layer, 5 parts of expanded perlite (particle size 1-3 mm) are added to the coarse mixture of the core layer to further reduce the core layer density and thermal conductivity. Correspondingly, the composition of the coarse mixture in step four needs to be increased by these 5 parts of expanded perlite, while the remaining raw material ratios and preparation steps are the same as in Example 1.

[0117] The performance test was conducted using the same test method as in Example 1, and the results are as follows:

[0118] Thermal conductivity: 0.024 W / (m·K);

[0119] Compressive strength: 8.5 MPa;

[0120] Flexural strength: 7.2 MPa;

[0121] Average density: 235 kg / m³;

[0122] 24-hour water absorption rate: 3.0%;

[0123] Linear shrinkage rate at 900℃ for 3 hours: 0.9%.

[0124] Example 3 differs from Example 1 in that: in step 3, when preparing the organic-inorganic composite binder, 2 parts of potassium methylsilicate (organosilane hydrophobic agent) are added; and in step 10, during the hydrophobic treatment, a hexamethyldisilazane-hexane solution (volume ratio of hexamethyldisilazane to hexane is 1:8) is used for spraying, with a spraying amount of 250 g / m² and a standing time of 50 min. The remaining raw material ratios and preparation steps are the same as in Example 1.

[0125] The performance test was conducted using the same test method as in Example 1, and the results are as follows:

[0126] Thermal conductivity: 0.028 W / (m·K);

[0127] Compressive strength: 9.8 MPa;

[0128] Flexural strength: 7.8 MPa;

[0129] Average density: 260 kg / m³;

[0130] 24-hour water absorption rate: 1.5%;

[0131] Compressive strength retention rate after 24 hours of immersion in water: 96%;

[0132] Linear shrinkage rate at 900℃ for 3 hours: 0.7%.

[0133] Comparative Example 1 (Traditional Vermiculite Slab)

[0134] Raw material ratio: 45 parts expanded vermiculite (mixed particle size, 4-60 mesh), 15 parts water glass, and 5 parts kaolin. After the above raw materials are mixed evenly, they are put into a mold and pressed into shape under a pressure of 1.0 MPa. After demolding, they are dried at 150℃ for 6 hours to obtain a traditional vermiculite board.

[0135] The performance test was conducted using the same test method as in Example 1, and the results are as follows:

[0136] Thermal conductivity: 0.068 W / (m·K);

[0137] Compressive strength: 2.1 MPa;

[0138] Flexural strength: 0.8 MPa;

[0139] Average density: 345 kg / m³;

[0140] 24-hour water absorption rate: 22.5%;

[0141] Linear shrinkage rate at 900℃ for 3 hours: 6.8%.

[0142] Comparative Example 2 (only low-dimensional SiO2 micro powder added, without in-situ aerogel and sintering)

[0143] The difference between this comparative example and Example 1 is that the preparation of the silica sol precursor solution in step two is omitted, therefore the silica sol precursor solution is not added in steps four and five, i.e., no in-situ aerogel is generated; at the same time, the calcination in step nine is omitted (i.e., calcination at 850°C is not performed, but drying at 150°C for 6 hours is performed instead). The remaining steps are the same as in Example 1.

[0144] The performance test was conducted using the same test method as in Example 1, and the results are as follows:

[0145] Thermal conductivity: 0.052 W / (m·K);

[0146] Compressive strength: 3.5 MPa;

[0147] Flexural strength: 1.8 MPa;

[0148] Average density: 310 kg / m³;

[0149] 24-hour water absorption rate: 18.0%;

[0150] Linear shrinkage rate at 900℃ for 3 hours: 4.2%.

[0151] Comparative Example 3 (with in-situ aerogel and organic-inorganic composite binder added, but without firing)

[0152] The difference between this comparative example and Example 1 is that step nine (firing at 850°C) is omitted (instead, drying at 150°C for 6 hours is performed). The remaining steps (including steps two through eight and step ten) are the same as in Example 1.

[0153] The performance test was conducted using the same test method as in Example 1, and the results are as follows:

[0154] Thermal conductivity: 0.039 W / (m·K);

[0155] Compressive strength: 4.0 MPa;

[0156] Flexural strength: 2.5 MPa;

[0157] Average density: 285 kg / m³;

[0158] 24-hour water absorption rate: 15.5%;

[0159] Linear shrinkage rate at 900℃ for 3 hours: 2.8%.

[0160] Comparative Example 4 (fired, but without gradient structure)

[0161] The difference between this comparative example and Example 1 is that the fine mixing preparation in step five and the layered material distribution in step six (i.e., the five-layer gradient structure is not used) are omitted. All 25 parts of the low-dimensional SiO2 premix obtained in step one are used in step four. 15 parts of 4-6 mesh, 22 parts of 10-40 mesh, and 10 parts of 40-60 mesh expanded vermiculite, all 25 parts of the low-dimensional SiO2 premix, 4 parts of kaolin, 1 part of sodium fluorosilicate, 21.5 parts of all organic-inorganic composite binder, and approximately 17 parts of all silica sol precursor solution are mixed uniformly in one go and directly loaded into the mold for one pressing. The remaining steps (including steps seven to ten) are the same as in Example 1.

[0162] The performance test was conducted using the same test method as in Example 1, and the results are as follows:

[0163] Thermal conductivity: 0.033 W / (m·K);

[0164] Compressive strength: 7.5 MPa;

[0165] Flexural strength: 5.5 MPa;

[0166] Average density: 270 kg / m³;

[0167] 24-hour water absorption rate: 6.5%;

[0168] Linear shrinkage rate at 900℃ for 3 hours: 1.1%.

[0169] Table 1 summarizes the performance comparisons between the examples and comparative examples.

[0170] Table 1 Summary of Performance Test Results

[0171]

[0172] As can be seen from Table 1 above:

[0173] First, comparing Example 1 with Comparative Example 1, it can be seen that the present invention, through the synergistic effect of low-dimensional SiO2 micro powder composite, in-situ generation of SiO2 aerogel, organic-inorganic composite binder, five-layer gradient density structure and low-temperature sintering process, reduces the thermal conductivity of the insulation board from 0.068 W / (m·K) to 0.026 W / (m·K) (a reduction of approximately 61.8%), increases the compressive strength from 2.1 MPa to 10.2 MPa (an increase of approximately 385.7%), and reduces the 24-hour water absorption rate from 22.5% to 2.8% (a reduction of approximately 87.6%).

[0174] Secondly, comparing Example 1 with Comparative Example 2, it can be seen that when only low-dimensional SiO2 micropowder was added without in-situ aerogel formation and low-temperature sintering, the thermal conductivity was 0.052 W / (m·K) and the compressive strength was 3.5 MPa. However, after adding low-dimensional SiO2 micropowder and further performing in-situ aerogel formation and low-temperature sintering (Example 1), the thermal conductivity decreased to 0.026 W / (m·K) and the compressive strength increased to 10.2 MPa. This indicates that there is a synergistic effect between in-situ aerogel formation and low-temperature sintering, and the performance improvement brought about by the combined effect of the two is far greater than the simple sum of their individual effects.

[0175] Third, comparing Example 1 with Comparative Example 3, it can be seen that when in-situ aerogel and organic-inorganic composite binder are added simultaneously but no low-temperature firing is performed, the 24-hour water absorption rate is 15.5%; while after further low-temperature firing (Example 1), the 24-hour water absorption rate decreases to 2.8%. This indicates that low-temperature firing allows the organic-inorganic composite binder to fully cross-link and cure, significantly improving the water resistance of the board.

[0176] Fourth, comparing Example 1 with Comparative Example 4, it can be seen that under the same raw materials and process conditions, the five-layer gradient density structure (Example 1) compared to the homogeneous structure (Comparative Example 4) resulted in a decrease in average density (from 270 kg / m³ to 255 kg / m³) while the compressive strength increased from 7.5 MPa to 10.2 MPa. This demonstrates that the five-layer gradient density structure achieves the functional integration of high strength in the surface layer and low density in the core layer, achieving the technical effect of simultaneously reducing density and increasing strength.

Claims

1. A heat insulation board with a low-dimensional SiO2-expanded vermiculite composite gradient structure, characterized in that, Raw materials comprising the following parts by weight: 20-50 parts of expanded vermiculite, wherein the expanded vermiculite comprises three particle size grades: 4-6 mesh, 10-40 mesh, and 40-60 mesh; 13 to 33 parts of low-dimensional SiO2 micro powder, wherein the low-dimensional SiO2 micro powder comprises a first component with an average particle size of 300 to 500 nm and a second component with an average particle size of 100 to 200 nm; 3-10 parts of CaO-MgO-SiO2 refractory fiber; 6-15 parts water glass; 3-8 parts of silica sol; 2-6 parts of kaolin; 3-10 parts of ethyl silicate; 3-10 parts of silicone-acrylic resin emulsion; Sodium fluorosilicate 0.5–2 parts; 0.2 to 1 part of silane coupling agent; The heat insulation board has a five-layer gradient density structure, which consists of a bottom layer, a first transition layer, a core layer, a second transition layer, and a surface layer along the thickness direction. The density of the surface layer and the bottom layer is higher than that of the core layer. The thermal conductivity of the insulation board is ≤0.028W / (m·K), the compressive strength is ≥8.5MPa, and the water absorption rate is ≤5% in 24h.

2. The heat insulation board with a low-dimensional SiO2-expanded vermiculite composite gradient structure according to claim 1, characterized in that, The linear shrinkage rate of the insulation board under the condition of 900℃×3h is ≤1.5%.

3. The heat insulation board with a low-dimensional SiO2-expanded vermiculite composite gradient structure according to claim 1, characterized in that, The low-dimensional SiO2 micro powder contains 8 to 18 parts of the first component and 5 to 15 parts of the second component.

4. The heat insulation board with a low-dimensional SiO2-expanded vermiculite composite gradient structure according to claim 1, characterized in that, The core layer also contains 3 to 8 parts of expanded perlite.

5. The heat insulation board with a low-dimensional SiO2-expanded vermiculite composite gradient structure according to claim 1, characterized in that, The surface of the heat insulation board is also provided with a hydrophobic treatment layer formed by an organosilane hydrophobic agent.

6. A method for preparing a heat insulation board with a low-dimensional SiO2-expanded vermiculite composite gradient structure as described in any one of claims 1 to 5, characterized in that, Includes the following steps: S1. Preparation of low-dimensional SiO2 premix: According to the mass proportions described in claim 1, low-dimensional SiO2 micro powder with an average particle size of 300-500 nm, low-dimensional SiO2 micro powder with an average particle size of 100-200 nm and CaO-MgO-SiO2 refractory fiber are mixed evenly to obtain low-dimensional SiO2 premix. S2. Preparation of silica sol precursor solution: Mix 3-10 parts of ethyl silicate, 3-10 parts of ethanol, 2-5 parts of water and hydrochloric acid, and hydrolyze at 40-60℃ for 30-60 minutes to obtain silica sol precursor solution. S3. Preparation of organic-inorganic composite binder: Mix water glass, silica sol and silicone-acrylic resin emulsion evenly, add silane coupling agent to obtain organic-inorganic composite binder; S4. Preparation of coarse mixture: Mix 4-6 mesh and 10-40 mesh expanded vermiculite, 70-90% of the total amount of low-dimensional SiO2 premix obtained in S1, kaolin, and sodium fluorosilicate evenly. Then add 70-90% of the total amount of organic-inorganic composite binder obtained in S3 and 70-90% of the total amount of silica sol precursor solution obtained in S2, and continue to mix evenly to obtain coarse mixture. S5. Preparation of fine mixture: Mix 40-60 mesh expanded vermiculite with 10-30% of the total amount of low-dimensional SiO2 premix obtained in S1, add 10-30% of the total amount of organic-inorganic composite binder obtained in S3 and 10-30% of the total amount of silica sol precursor solution obtained in S2, mix evenly to obtain fine mixture. S6. Laying the mixture: In the mold, the bottom layer composed of the fine mixture, the first transition layer composed of the fine mixture and the coarse mixture in a 1:1 ratio, the core layer composed of the coarse mixture, the second transition layer composed of the fine mixture and the coarse mixture in a 1:1 ratio, and the surface layer composed of the fine mixture are laid in sequence to form a five-layer gradient structure. S7. Compression molding: Compression molding is carried out under a pressure of 2.5 to 3.5 MPa to obtain a wet sheet material; S8. Aging and sintering: The coated board is left to stand to allow the silica sol precursor solution to gel, then aged at 40-60°C, and the aged board is sintered at 800-900°C for 0.5-1 hour. S9. Hydrophobic treatment: After the board is fired and cooled to room temperature, an alcohol solution of organosilane hydrophobic agent is sprayed onto the surface. The alcohol solvent is allowed to evaporate naturally by standing. The organosilane undergoes in-situ hydrolysis, condensation and cross-linking on the surface of the board and within a depth of 0.5 to 2 mm near the surface to form a hydrophobic treatment layer.

7. The method for preparing the heat insulation plate with a low-dimensional SiO2-expanded vermiculite composite gradient structure according to claim 6, characterized in that, The process after S7 and before S8 also includes spraying ultrafine inorganic fiber adhesive: spraying ultrafine inorganic fiber adhesive onto the surface of the wet plate.

8. The method for preparing the heat insulation plate with a low-dimensional SiO2-expanded vermiculite composite gradient structure according to claim 6, characterized in that, In S6, the thickness of each layer in the five-layer gradient structure accounts for the proportion of the total thickness of the board as follows: bottom layer 15-20%, first transition layer 10-15%, core layer 30-50%, second transition layer 10-15%, and surface layer 15-20%.

9. The method for preparing the heat insulation plate with a low-dimensional SiO2-expanded vermiculite composite gradient structure according to claim 6, characterized in that, In S7, the pressing and molding process adopts a step-by-step pressurization method: first, pre-press at 0.3-0.5MPa for 30 seconds, then apply main pressure at 2.5-3.5MPa for 60-120 seconds, and the depressurization speed is ≤0.5MPa / s.

10. The method for preparing the heat insulation plate with a low-dimensional SiO2-expanded vermiculite composite gradient structure according to claim 6, characterized in that, In S8, the firing process includes three stages: first, drying at 80–120°C for 2–4 hours; then, heating to 800–900°C and holding at that temperature for 0.5–1 hour; and finally, cooling in the furnace. In S9, the coating amount for the surface spraying is 100–300 g / m². 2 The settling time is 20 to 60 minutes.

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