High-strength low-thermal-conductivity insulating layer castable for rotary kiln and preparation process thereof

Abstract

The application relates to a high-strength low-thermal-conductivity thermal-insulation layer castable for a rotary kiln and a preparation process thereof, and belongs to the technical field of refractory materials. The high-strength low-thermal-conductivity thermal-insulation castable for the rotary kiln comprises the following components in parts by mass: modified mullite hollow spheres 40-50 parts, alumina hollow spheres 15-25 parts, active alpha-Al2O3 micropowder 7-10 parts, silicon micropowder 5-10 parts, a reinforcing agent 3-5 parts, a water reducing agent 0.1-0.2 parts, a binding agent 20-30 parts and explosion-proof fiber 0.1 part. The reinforcing agent is added in the light thermal-insulation layer castable, the high-temperature resistance of the castable is increased while the heat insulation effect is ensured, cracks, falling or damage of the thermal-insulation layer slurry of the conventional light castable under the high-temperature and cold-heat-alternating environment of the rotary kiln are avoided, the heat insulation effect is influenced, and the service life of the rotary kiln is prolonged.

Description

Technical Field

[0001] This invention belongs to the field of refractory materials technology, specifically relating to a high-strength, low-thermal-conductivity insulation layer castable for rotary kilns and its preparation process. Background Technology

[0002] Rotary kilns, as core thermal equipment in industries such as building materials, metallurgy, and chemicals, directly impact production costs and environmental protection through their energy consumption. During long-term high-temperature operation, the kiln shell dissipates significant heat due to the scouring effect of the internal high-temperature airflow and material abrasion, leading to energy waste and excessively high surface temperatures, affecting equipment safety and increasing production costs. Due to the torque generated during operation and the deformation caused by its own weight, ceramic fiberboard and ordinary lightweight insulation materials cannot be used for the kiln lining. This is because while ceramic fiberboard and ordinary lightweight insulation materials have excellent insulation performance, their own strength is extremely low; if used inside a rotary kiln, they would crack, causing damage to the working lining material. Therefore, there is an urgent need for an insulation layer castable that combines good insulation, high-temperature resistance, and high high-temperature strength. Summary of the Invention

[0003] The first objective of this invention is to provide a high-strength, low-thermal-conductivity insulation layer castable for rotary kilns to solve the technical problem that existing lightweight insulation castables cannot simultaneously possess good insulation properties, good high-temperature resistance, and high-temperature strength.

[0004] The second objective of this invention is to provide a preparation process for a high-strength, low-thermal-conductivity insulation layer castable for rotary kilns.

[0005] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0006] A high-strength, low-thermal-conductivity insulating castable for rotary kilns comprises, by weight: 40-50 parts modified mullite hollow spheres, 15-25 parts alumina hollow spheres, 7-10 parts active α-Al2O3 micro powder, 5-10 parts silica micro powder, 3-5 parts reinforcing agent, 0.1-0.2 parts water-reducing agent, 20-30 parts binder, and 0.1 parts explosion-proof fiber.

[0007] Furthermore, the preparation method of the reinforcing agent includes the following steps: mixing BN-BAS ceramic powder, ZrSiO4 powder, and TiZrNi powder to obtain a mixed powder; adding a solvent to the mixed powder; ball milling and mixing to obtain a slurry; adding a foaming agent and a foam stabilizer to the slurry; mixing evenly; drying; and sintering under an inert gas to obtain the reinforcing agent; the particle size of the reinforcing agent is 25-40 μm.

[0008] Furthermore, the mass ratio of the BN-BAS ceramic powder, ZrSiO4 powder, and TiZrNi powder is 1:0.2-0.5:0.1-0.2; the TiZrNi powder comprises, by weight percentage: 12-18% Zr, 1-5% Ni, and the remainder Ti.

[0009] Furthermore, the foaming agent is a protein-based foaming agent, and the foam stabilizer is dextrin; the foaming agent accounts for 3-5% of the mass of the mixed powder, and the foam stabilizer accounts for 1-3% of the mass of the foaming agent; the solvent is ethanol.

[0010] Furthermore, the inert gas is argon or nitrogen, the sintering temperature is 1400-1550 ℃, the sintering time is 1-3 h, and the sintering pressure is 18-20 MPa.

[0011] Furthermore, the preparation method of the modified mullite hollow spheres includes the following steps: mixing silica sol and aluminum sol evenly to obtain a silica-alumina composite sol, adding mullite hollow spheres and stirring evenly, then adding propylene oxide and formamide to obtain a silica-alumina composite gel, allowing the silica-alumina composite gel to stand for 12-24 h, adding alcohol solvent for aging for 24-48 h, and obtaining modified mullite hollow spheres by supercritical drying.

[0012] Furthermore, the silica sol is prepared by mixing tetraethyl orthosilicate, alcohol, and water in a molar ratio of 1:2-12:1-10; the aluminum sol is prepared by mixing aluminum nitrate, alcohol, and water in a molar ratio of 1:4-15:8-20; the volume ratio of silica sol to aluminum sol is 20-25:15-20; wherein the molar ratio of aluminum atoms to formamide in the aluminum sol is 1:0.8, and the molar ratio of aluminum atoms to propylene oxide is 1:8; the mass ratio of the silica-alumina composite sol to the mullite hollow spheres is 1:1-2.

[0013] Furthermore, the mullite hollow spheres, calculated by mass percentage, comprise: 10-40% mullite hollow spheres with a particle size of 5-3 mm, 10-40% mullite hollow spheres with a particle size of 3-2 mm, 10-40% mullite hollow spheres with a particle size of 2-1 mm, and 10-30% mullite hollow spheres with a particle size of 1-0.2 mm.

[0014] Furthermore, the hollow alumina spheres contain ≥98% Al2O3 by weight; the hollow alumina spheres, by mass percentage, comprise: 20-35% hollow alumina spheres with a particle size of 3-5 mm and 65-80% hollow alumina spheres with a particle size of 3-0.2 mm; the silica powder contains >94% SiO2 by weight; the active α-Al2O3 powder contains ≥99% Al2O3 by weight and has a median diameter of less than 1.5 μm; and the binder is aluminate cement.

[0015] A preparation process for a high-strength, low-thermal-conductivity insulation layer castable for rotary kilns includes the following steps: mixing the modified mullite hollow spheres, alumina hollow spheres, active α-Al2O3 micro powder, silica micro powder, reinforcing agent, explosion-proof fiber, water-reducing agent, and binder in the specified amounts evenly, stirring for 8-12 minutes, casting into shape, and then naturally drying at 25-30 ℃ for 24 h before demolding, followed by drying at 100-110 ℃ for 24 h to obtain the final product.

[0016] The beneficial effects of this invention are:

[0017] This invention adds a reinforcing agent to the lightweight insulation layer castable, which increases the high temperature resistance of the castable while ensuring the insulation effect. This avoids the cracking, peeling or damage of the insulation layer slurry caused by conventional lightweight castables in the high temperature and alternating hot and cold environment of rotary kiln, which affects its insulation effect and increases the service life of rotary kiln.

[0018] BN-BAS ceramics have excellent high-temperature resistance, but their thermal conductivity is relatively high. This invention improves the thermal conductivity of BN-BAS ceramics by adding ZrSiO4 and TiZrNi, while further increasing the mechanical properties of BN-BAS ceramics. This makes the high-strength, low-thermal-conductivity insulation layer castable for rotary kilns of this invention both low thermal conductivity and high-temperature resistance.

[0019] Mullite hollow spheres have extremely low thermal conductivity but poor strength. This invention modifies mullite hollow spheres by filling their pores with aerogel. The aerogel bears part of the load, significantly improving the compressive and flexural strength of the modified mullite hollow spheres compared to unmodified ones. Simultaneously, the aerogel filling the pores further reduces the surface porosity of the mullite hollow spheres, further decreasing their thermal conductivity. Detailed Implementation

[0020] The present invention will be further described below with reference to embodiments.

[0021] BN-BAS ceramics were prepared using existing methods. The specific preparation process was as follows: 10 kg of h-BN was mixed with 70 kg of ethanol, and 0.5 kg of stearic acid was added. After ultrasonic dispersion for 2 h, an ethanol suspension of h-BN was obtained. γ-AlOOH sol, pre-hydrolyzed TEOS, and (CH3COO)2Ba solution were sequentially added to the h-BN ethanol suspension with continuous stirring. Dilute NH3·H2O was added dropwise to adjust the pH to 8, and the mixture was stirred for 24 h. Subsequently, it was dried at 150 ℃ for 24 h and calcined at 700 ℃ for 3 h to obtain BN-BAS composite powder. The BN-BAS composite powder was then hot-pressed and sintered under a nitrogen atmosphere of 0.1 MPa. The hot-pressing sintering conditions were as follows: The temperature was first raised from 25 °C to 1200 °C at a rate of 20 °C / min, held at 1200 °C for 5 min, and then slowly pressurized to 25 MPa. Subsequently, the temperature was raised from 1200 °C to 1700 °C at a rate of 10 °C / min, held at 1700 °C for 1 h, and then cooled to 1200 °C to begin depressurization. The weight percentage of h-BN to BAS in the BN-BAS ceramic was 60%:40%.

[0022] Example 1

[0023] The high-strength, low-thermal-conductivity insulation layer castable for rotary kilns in Example 1 includes the following raw materials: 40 kg of modified mullite hollow spheres, 18 kg of alumina hollow spheres, 7 kg of active α-Al2O3 micro powder, 8 kg of silica micro powder, 4 kg of reinforcing agent, 0.1 kg of polycarboxylate superplasticizer, 25 kg of aluminate cement, and 0.1 kg of explosion-proof fiber.

[0024] The reinforcing agent was prepared as follows: 10 kg of BN-BAS ceramic powder, 3 kg of ZrSiO4 powder, and 1 kg of TiZrNi powder were mixed to obtain a mixed powder. 4 kg of anhydrous ethanol was added to the mixed powder as a solvent, and the mixture was then ball-milled at 300 r / min for 18 h to obtain a slurry. 0.42 kg of protein-type foaming agent and 0.004 kg of dextrin were added to the slurry, mixed thoroughly, dried, and sintered at 1450 ℃ for 2 h under a nitrogen atmosphere to obtain the final product. The TiZrNi powder contained 15% Zr, 4% Ni, and 81% Ti by mass. The particle size of the reinforcing agent was 25–40 μm.

[0025] The modified mullite hollow spheres were prepared as follows: 20 kg of tetraethyl orthosilicate, 2 kg of deionized water, and 9 kg of anhydrous ethanol were mixed evenly, and the pH was adjusted to 2 to obtain a silica sol. 20 kg of aluminum nitrate, 8 kg of deionized water, and 10 kg of anhydrous ethanol were mixed to prepare an aluminum sol. The aluminum sol and silica sol were mixed evenly at a volume ratio of 20:15 to obtain a silica-alumina composite sol. Mullite hollow spheres were added and stirred evenly. Subsequently, propylene oxide and formamide were added to obtain a silica-alumina composite gel. The silica-alumina composite gel was allowed to stand for 12 h, aged with anhydrous ethanol for 24 h, and then dried by supercritical drying to obtain modified mullite hollow spheres. The molar ratio of aluminum atoms to formamide in the aluminum sol was 1:0.8, and the molar ratio of aluminum atoms to propylene oxide was 1:8. The mass ratio of the silica-alumina composite sol to the mullite hollow spheres was 1:1.

[0026] The mullite hollow spheres, calculated by weight percentage, comprise: 20% mullite hollow spheres with a particle size of 5-3 mm, 20% mullite hollow spheres with a particle size of 3-2 mm, 30% mullite hollow spheres with a particle size of 2-1 mm, and 30% mullite hollow spheres with a particle size of 1-0.2 mm. The alumina hollow spheres contain ≥98% Al2O3 by weight percentage; calculated by weight percentage, they comprise: 35% alumina hollow spheres with a particle size of 3-5 mm and 65% alumina hollow spheres with a particle size of 3-0.2 mm. The silica micropowder contains >94% SiO2 by weight percentage; the active α-Al2O3 micropowder contains ≥99% Al2O3 by weight percentage, with a median diameter less than 1.5 μm.

[0027] The preparation process of the high-strength, low-thermal-conductivity insulation layer castable for rotary kilns in Example 1 is as follows: the formula amounts of mullite hollow spheres, alumina hollow spheres, active α-Al2O3 micro powder, silica micro powder, reinforcing agent, explosion-proof fiber, polycarboxylate superplasticizer and aluminate cement are mixed evenly, stirred for 10 min, cast into shape, and then naturally dried at 25 ℃ for 24 h before demolding. Subsequently, it is dried at 100 ℃ for 24 h to obtain the final product.

[0028] Example 2

[0029] The high-strength, low-thermal-conductivity insulation layer castable for rotary kilns in Example 2 includes the following raw materials: 48 kg of modified mullite hollow spheres, 15 kg of alumina hollow spheres, 9 kg of active α-Al2O3 micro powder, 5 kg of silica micro powder, 5 kg of reinforcing agent, 0.1 kg of polycarboxylate superplasticizer, 22 kg of aluminate cement, and 0.1 kg of explosion-proof fiber.

[0030] The reinforcing agent was prepared as follows: 10 kg of BN-BAS ceramic powder, 5 kg of ZrSiO4 powder, and 2 kg of TiZrNi powder were mixed to obtain a mixed powder. 5 kg of anhydrous ethanol was added to the mixed powder as a solvent, and the mixture was then ball-milled at 300 r / min for 18 h to obtain a slurry. 0.85 kg of protein-type foaming agent and 0.017 kg of dextrin were added to the slurry, mixed thoroughly, dried, and sintered at 1400 ℃ for 3 h under a nitrogen atmosphere to obtain the final product. The TiZrNi powder contained 18% Zr, 5% Ni, and 77% Ti by mass. The particle size of the reinforcing agent was 25–40 μm.

[0031] The modified mullite hollow spheres were prepared as follows: 20 kg of tetraethyl orthosilicate, 10 kg of deionized water, and 22 kg of anhydrous ethanol were mixed evenly, and the pH was adjusted to 2 to obtain a silica sol. 20 kg of aluminum nitrate, 10 kg of deionized water, and 24 kg of anhydrous ethanol were mixed to prepare an aluminum sol. The aluminum sol and silica sol were mixed evenly at a volume ratio of 24:18 to obtain a silica-alumina composite sol. Mullite hollow spheres were added and stirred evenly. Subsequently, propylene oxide and formamide were added to obtain a silica-alumina composite gel. The silica-alumina composite gel was allowed to stand for 18 h, aged with anhydrous ethanol for 30 h, and then dried by supercritical drying to obtain modified mullite hollow spheres. The molar ratio of aluminum atoms to formamide in the aluminum sol was 1:0.8, and the molar ratio of aluminum atoms to propylene oxide was 1:8. The mass ratio of the silica-alumina composite sol to the mullite hollow spheres was 1:1.

[0032] The mullite hollow spheres, calculated by mass percentage, comprise: 40% mullite hollow spheres with a particle size of 5-3 mm, 30% mullite hollow spheres with a particle size of 3-2 mm, 20% mullite hollow spheres with a particle size of 2-1 mm, and 10% mullite hollow spheres with a particle size of 1-0.2 mm. The alumina hollow spheres contain ≥98% Al2O3 by weight percentage; calculated by mass percentage, they comprise: 20% alumina hollow spheres with a particle size of 3-5 mm, and 80% alumina hollow spheres with a particle size of 3-0.2 mm. The silica micropowder contains >94% SiO2 by weight percentage; the active α-Al2O3 micropowder contains ≥99% Al2O3 by weight percentage, with a median diameter less than 1.5 μm.

[0033] The preparation process of the high-strength, low-thermal-conductivity insulation layer castable for rotary kilns in Example 2 is as follows: the formula amounts of mullite hollow spheres, alumina hollow spheres, active α-Al2O3 micro powder, silica micro powder, reinforcing agent, explosion-proof fiber, polycarboxylate superplasticizer and aluminate cement are mixed evenly, stirred for 12 min, cast into shape, and then naturally dried at 30 ℃ for 24 h before demolding. Subsequently, it is dried at 110 ℃ for 24 h to obtain the final product.

[0034] Example 3

[0035] The high-strength, low-thermal-conductivity insulation layer castable for rotary kilns in Example 3 includes the following raw materials: 50 kg of modified mullite hollow spheres, 25 kg of alumina hollow spheres, 10 kg of active α-Al2O3 micro powder, 10 kg of silica micro powder, 3 kg of reinforcing agent, 0.2 kg of polycarboxylate superplasticizer, 30 kg of aluminate cement, and 0.1 kg of explosion-proof fiber.

[0036] The reinforcing agent was prepared as follows: 10 kg of BN-BAS ceramic powder, 4 kg of ZrSiO4 powder, and 1.5 kg of TiZrNi powder were mixed to obtain a mixed powder. 4.8 kg of anhydrous ethanol was added to the mixed powder as a solvent, and the mixture was then ball-milled at 300 r / min for 18 h to obtain a slurry. 0.62 kg of protein-type foaming agent and 0.019 kg of dextrin were added to the slurry, mixed thoroughly, dried, and sintered at 1500 ℃ for 1 h under a nitrogen atmosphere to obtain the final product. The TiZrNi powder contained 12% Zr, 3% Ni, and 85% Ti by mass. The particle size of the reinforcing agent was 25–40 μm.

[0037] The modified mullite hollow spheres were prepared as follows: 20 kg of tetraethyl orthosilicate, 19 kg of deionized water, and 50 kg of anhydrous ethanol were mixed evenly, and the pH was adjusted to 2 to obtain a silica sol. 20 kg of aluminum nitrate, 19 kg of deionized water, and 37 kg of anhydrous ethanol were mixed to prepare an aluminum sol. The aluminum sol and silica sol were mixed evenly at a volume ratio of 25:20 to obtain a silica-alumina composite sol. Mullite hollow spheres were added and stirred evenly. Subsequently, propylene oxide and formamide were added to obtain a silica-alumina composite gel. The silica-alumina composite gel was allowed to stand for 24 h, aged for 30 h with anhydrous ethanol, and then obtained by supercritical drying to obtain modified mullite hollow spheres. The molar ratio of aluminum atoms to formamide in the aluminum sol was 1:0.8, and the molar ratio of aluminum atoms to propylene oxide was 1:8; the mass ratio of the silica-alumina composite sol to the mullite hollow spheres was 1:1.

[0038] The mullite hollow spheres, calculated by mass percentage, comprise: 30% mullite hollow spheres with a particle size of 5-3 mm, 30% mullite hollow spheres with a particle size of 3-2 mm, 30% mullite hollow spheres with a particle size of 2-1 mm, and 10% mullite hollow spheres with a particle size of 1-0.2 mm. The alumina hollow spheres contain ≥98% Al2O3 by weight percentage; calculated by mass percentage, they comprise: 30% alumina hollow spheres with a particle size of 3-5 mm, and 70% alumina hollow spheres with a particle size of 3-0.2 mm. The silica micropowder contains >94% SiO2 by weight percentage; the active α-Al2O3 micropowder contains ≥99% Al2O3 by weight percentage, with a median diameter less than 1.5 μm.

[0039] The preparation process of the high-strength, low-thermal-conductivity insulation layer castable for rotary kilns in Example 3 is as follows: the formula amounts of mullite hollow spheres, alumina hollow spheres, active α-Al2O3 micro powder, silica micro powder, reinforcing agent, explosion-proof fiber, polycarboxylate superplasticizer and aluminate cement are mixed evenly, stirred for 8 min, cast into shape, and then naturally dried at 25 ℃ for 24 h before demolding. Subsequently, it is dried at 100 ℃ for 24 h to obtain the final product.

[0040] Example 4

[0041] The high-strength, low-thermal-conductivity insulation layer castable for rotary kilns in Example 4 includes the following raw materials: 43 kg of modified mullite hollow spheres, 15 kg of alumina hollow spheres, 9 kg of active α-Al2O3 micro powder, 7 kg of silica micro powder, 3 kg of reinforcing agent, 0.2 kg of polycarboxylate superplasticizer, 20 kg of aluminate cement, and 0.1 kg of explosion-proof fiber.

[0042] The reinforcing agent was prepared as follows: 10 kg of BN-BAS ceramic powder, 4 kg of ZrSiO4 powder, and 1.5 kg of TiZrNi powder were mixed to obtain a mixed powder. 4.8 kg of anhydrous ethanol was added to the mixed powder as a solvent, and the mixture was then ball-milled at 300 r / min for 18 h to obtain a slurry. 0.62 kg of protein-type foaming agent and 0.019 kg of dextrin were added to the slurry, mixed thoroughly, dried, and sintered at 1500 ℃ for 1 h under a nitrogen atmosphere to obtain the final product. The TiZrNi powder contained 12% Zr, 3% Ni, and 85% Ti by mass. The particle size of the reinforcing agent was 25–40 μm.

[0043] The modified mullite hollow spheres were prepared as follows: 20 kg of tetraethyl orthosilicate, 7 kg of deionized water, and 30 kg of anhydrous ethanol were mixed evenly, and the pH was adjusted to 2 to obtain a silica sol. 20 kg of aluminum nitrate, 15 kg of deionized water, and 14 kg of anhydrous ethanol were mixed to prepare an aluminum sol. The aluminum sol and silica sol were mixed evenly at a volume ratio of 23:15 to obtain a silica-alumina composite sol. Mullite hollow spheres were added and stirred evenly. Subsequently, propylene oxide and formamide were added to obtain a silica-alumina composite gel. The silica-alumina composite gel was allowed to stand for 20 h, aged for 30 h with anhydrous ethanol, and then obtained by supercritical drying to obtain modified mullite hollow spheres. The molar ratio of aluminum atoms to formamide in the aluminum sol was 1:0.8, and the molar ratio of aluminum atoms to propylene oxide was 1:8; the mass ratio of the silica-alumina composite sol to the mullite hollow spheres was 1:1.

[0044] The mullite hollow spheres, calculated by weight percentage, include: 20% mullite hollow spheres with a particle size of 5-3 mm, 20% mullite hollow spheres with a particle size of 3-2 mm, 30% mullite hollow spheres with a particle size of 2-1 mm, and 30% mullite hollow spheres with a particle size of 1-0.2 mm. The alumina hollow spheres contain ≥98% Al2O3 by weight percentage; calculated by weight percentage, they include: 30% alumina hollow spheres with a particle size of 3-5 mm and 70% alumina hollow spheres with a particle size of 3-0.2 mm. The silica micropowder contains >94% SiO2 by weight percentage; the active α-Al2O3 micropowder contains ≥99% Al2O3 by weight percentage, with a median diameter less than 1.5 μm.

[0045] The preparation process of the high-strength, low-thermal-conductivity insulation layer castable for rotary kilns in Example 4 is as follows: the formula amounts of mullite hollow spheres, alumina hollow spheres, active α-Al2O3 micro powder, silica micro powder, reinforcing agent, explosion-proof fiber, polycarboxylate superplasticizer and aluminate cement are mixed evenly, stirred for 8 min, cast into shape, and then naturally dried at 25 ℃ for 24 h before demolding. Subsequently, it is dried at 100 ℃ for 24 h to obtain the final product.

[0046] Example 5

[0047] The high-strength, low-thermal-conductivity insulation layer castable for rotary kilns in Example 5 includes the following raw materials: 45 kg of modified mullite hollow spheres, 18 kg of alumina hollow spheres, 7 kg of active α-Al2O3 micro powder, 7 kg of silica micro powder, 3 kg of reinforcing agent, 0.2 kg of polycarboxylate superplasticizer, 28 kg of aluminate cement, and 0.1 kg of explosion-proof fiber.

[0048] The reinforcing agent was prepared as follows: 10 kg of BN-BAS ceramic powder, 3.5 kg of ZrSiO4 powder, and 1.8 kg of TiZrNi powder were mixed to obtain a mixed powder. 4.5 kg of anhydrous ethanol was added to the mixed powder as a solvent, and then the mixture was ball-milled at 300 r / min for 18 h to obtain a slurry. 0.69 kg of protein-type foaming agent and 0.018 kg of dextrin were added to the slurry, mixed thoroughly, dried, and sintered at 1500 ℃ for 1 h under a nitrogen atmosphere to obtain the final product. The TiZrNi powder contained 12% Zr, 3% Ni, and 85% Ti by mass. The particle size of the reinforcing agent was 25–40 μm.

[0049] The modified mullite hollow spheres were prepared as follows: 20 kg of tetraethyl orthosilicate, 15 kg of deionized water, and 20 kg of anhydrous ethanol were mixed evenly, and the pH was adjusted to 2 to obtain a silica sol. 20 kg of aluminum nitrate, 15 kg of deionized water, and 20 kg of anhydrous ethanol were mixed to prepare an aluminum sol. The aluminum sol and silica sol were mixed evenly at a volume ratio of 23:15 to obtain a silica-alumina composite sol. Mullite hollow spheres were added and stirred evenly. Subsequently, propylene oxide and formamide were added to obtain a silica-alumina composite gel. The silica-alumina composite gel was allowed to stand for 20 h, then aged for 30 h with anhydrous ethanol. Modified mullite hollow spheres were obtained by supercritical drying. The molar ratio of aluminum atoms to formamide in the aluminum sol was 1:0.8, and the molar ratio of aluminum atoms to propylene oxide was 1:8. The mass ratio of the silica-alumina composite sol to the mullite hollow spheres was 1:1.

[0050] The mullite hollow spheres, calculated by mass percentage, comprise: 30% mullite hollow spheres with a particle size of 5-3 mm, 30% mullite hollow spheres with a particle size of 3-2 mm, 30% mullite hollow spheres with a particle size of 2-1 mm, and 10% mullite hollow spheres with a particle size of 1-0.2 mm. The alumina hollow spheres contain ≥98% Al2O3 by weight percentage; calculated by mass percentage, they comprise: 30% alumina hollow spheres with a particle size of 3-5 mm, and 70% alumina hollow spheres with a particle size of 3-0.2 mm. The silica micropowder contains >94% SiO2 by weight percentage; the active α-Al2O3 micropowder contains ≥99% Al2O3 by weight percentage, with a median diameter less than 1.5 μm.

[0051] The preparation process of the high-strength, low-thermal-conductivity insulation layer castable for rotary kilns in Example 5 is as follows: the formula amounts of mullite hollow spheres, alumina hollow spheres, active α-Al2O3 micro powder, silica micro powder, reinforcing agent, explosion-proof fiber, polycarboxylate superplasticizer and aluminate cement are mixed evenly, stirred for 8 min, cast into shape, and then naturally dried at 25 ℃ for 24 h before demolding. Subsequently, it is dried at 100 ℃ for 24 h to obtain the final product.

[0052] Comparative Example 1

[0053] The high-strength, low-thermal-conductivity insulation layer castable for rotary kilns in Comparative Example 1 is largely the same as that in Example 1. The difference between the high-strength, low-thermal-conductivity insulation layer castable for rotary kilns in Comparative Example 1 and Example 1 is that Comparative Example 1 omits the reinforcing agent and makes up the mass according to the proportions of each substance in Example 1.

[0054] Comparative Example 2

[0055] The high-strength, low-thermal-conductivity insulation layer castable for rotary kilns in Comparative Example 2 is largely the same as that in Example 1. The difference between the high-strength, low-thermal-conductivity insulation layer castable for rotary kilns in Comparative Example 2 and Example 1 is that Comparative Example 2 uses BN-BAS ceramic as a reinforcing agent.

[0056] Comparative Example 3

[0057] The high-strength, low-thermal-conductivity insulation layer castable for rotary kilns in Comparative Example 3 is largely the same as that in Example 1. The difference between the high-strength, low-thermal-conductivity insulation layer castable for rotary kilns in Comparative Example 3 and Example 1 is that ZrSiO4 powder is omitted from the reinforcing agent in Comparative Example 3, and the mass is made up according to the ratio of BN-BAS ceramic powder and TiZrNi powder in Example 1.

[0058] Comparative Example 4

[0059] The high-strength, low-thermal-conductivity insulation layer castable for rotary kilns in Comparative Example 4 is largely the same as that in Example 1. The difference between the high-strength, low-thermal-conductivity insulation layer castable for rotary kilns in Comparative Example 4 and Example 1 is that TiZrNi powder is omitted from the reinforcing agent in Comparative Example 4, and the mass is made up according to the ratio of BN-BAS ceramic powder and ZrSiO4 powder in Example 1.

[0060] Comparative Example 5

[0061] The high-strength, low-thermal-conductivity insulation layer castable for rotary kilns in Comparative Example 5 is largely the same as that in Example 1. The difference between the high-strength, low-thermal-conductivity insulation layer castable for rotary kilns in Comparative Example 5 and Example 1 is that the mass of ZrSiO4 powder in the reinforcing agent of Comparative Example 5 is 1.5 kg.

[0062] Comparative Example 6

[0063] The high-strength, low-thermal-conductivity insulation layer castable for rotary kilns in Comparative Example 6 is largely the same as that in Example 1. The difference between the high-strength, low-thermal-conductivity insulation layer castable for rotary kilns in Comparative Example 6 and Example 1 is that the mass of ZrSiO4 powder in the reinforcing agent of Comparative Example 6 is 5.5 kg.

[0064] Comparative Example 7

[0065] The high-strength, low-thermal-conductivity insulation layer castable for rotary kilns in Comparative Example 7 is largely the same as that in Example 1. The difference between the high-strength, low-thermal-conductivity insulation layer castable for rotary kilns in Comparative Example 7 and Example 1 is that the mass of TiZrNi powder in the reinforcing agent of Comparative Example 7 is 0.5 kg.

[0066] Comparative Example 8

[0067] The high-strength, low-thermal-conductivity insulation layer castable for rotary kilns in Comparative Example 8 is largely the same as that in Example 1. The difference between the high-strength, low-thermal-conductivity insulation layer castable for rotary kilns in Comparative Example 8 and Example 1 is that the mass of TiZrNi powder in the reinforcing agent of Comparative Example 8 is 2.5 kg.

[0068] Comparative Example 9

[0069] The high-strength, low-thermal-conductivity insulation layer castable for rotary kilns in Comparative Example 9 is largely the same as that in Example 1. The difference between the high-strength, low-thermal-conductivity insulation layer castable for rotary kilns in Comparative Example 9 and Example 1 is that the mass of reinforcing agent added in Comparative Example 9 is 2 kg.

[0070] Comparative Example 10

[0071] The high-strength, low-thermal-conductivity insulation layer castable for rotary kilns in Comparative Example 10 is largely the same as that in Example 1. The difference between the high-strength, low-thermal-conductivity insulation layer castable for rotary kilns in Comparative Example 10 and Example 1 is that the mass of reinforcing agent added in Comparative Example 10 is 6 kg.

[0072] Comparative Example 11

[0073] The high-strength, low-thermal-conductivity insulation layer castable for rotary kilns in Comparative Example 11 is largely the same as that in Example 1. The difference between the high-strength, low-thermal-conductivity insulation layer castable for rotary kilns in Comparative Example 11 and Example 1 is that the mullite hollow spheres in Comparative Example 11 were not modified.

[0074] Comparative Example 12

[0075] The high-strength, low-thermal-conductivity insulation layer castable for rotary kilns in Comparative Example 12 is largely the same as that in Example 1. The difference between the high-strength, low-thermal-conductivity insulation layer castable for rotary kilns in Comparative Example 12 and Example 1 is that the mullite hollow spheres in Comparative Example 11 were not modified, and no reinforcing agent was added in Comparative Example 12. The mass of each substance was supplemented according to the proportions of the substances in Example 1.

[0076] Experimental Example 1

[0077] 1. The bulk density (g / cm³) of the sample was tested according to GB / T2997-2015. 3 );

[0078] 2. Test the compressive strength (MPa) according to YB / T5072-2023.

[0079] 3. Test the flexural strength (MPa) according to YB / T3001-2017;

[0080] 4. Thermal shock stability was tested according to YB / T30873-2014 (times), with water cooling at 1100 ℃;

[0081] 5. Test the thermal conductivity (W / (m·K)) according to GBT4130-2005.

[0082] Table 1. Performance test results of castables in Example 1 and Comparative Examples 1-12

[0083]

[0084] As can be seen from Comparative Example 1, the reinforcing agent can significantly increase the high-temperature resistance of lightweight castables, and increase the flexural strength and compressive strength of lightweight castables at room temperature and high temperature, avoiding the difficulty of traditional lightweight castables in possessing both thermal insulation and thermodynamic properties. As can be seen from Comparative Examples 2-4, although the reinforcing agent without ZrSiO4 powder and TiZrNi powder can also increase the high-temperature resistance of the castables of this invention, there is still a significant difference compared to the effect of Example 1. As can be seen from Comparative Example 4, the thermal conductivity of the castable increases significantly in the absence of TiZrNi powder, and TiZrNi powder can reduce the thermal conductivity of BN-BAS ceramics. As can be seen from Comparative Examples 5-8 and Comparative Examples 9-10, only with the specified proportions of the raw materials in this invention can the castables of this invention possess both high-temperature resistance and thermal insulation properties. As can be seen from Comparative Example 11, the modified mullite hollow spheres can significantly increase the high-temperature resistance of the castables of this invention.

[0085] Other embodiments of this disclosure will readily occur to those skilled in the art upon consideration of the specification and practice of the disclosure herein. This disclosure is intended to cover any variations, uses, or adaptations of this disclosure that follow the general principles of this disclosure and include common knowledge or customary techniques in the art not disclosed herein. The specification and embodiments are to be considered exemplary only, and the true scope and spirit of this disclosure are indicated by the claims. The above descriptions are merely preferred embodiments of the present invention and are not intended to limit the invention. The patent protection scope of this invention is determined by the claims, and any equivalent structural changes made based on the content of this specification should also be included within the protection scope of this invention.

Claims

1. A high-strength, low-thermal-conductivity insulation layer castable for rotary kilns, characterized in that, The composition by weight is as follows: 40-50 parts modified mullite hollow spheres, 15-25 parts alumina hollow spheres, 7-10 parts active α-Al2O3 micro powder, 5-10 parts silica micro powder, 3-5 parts reinforcing agent, 0.1-0.2 parts water-reducing agent, 20-30 parts binder, and 0.1 parts explosion-proof fiber. The preparation method of the reinforcing agent includes the following steps: mixing BN-BAS ceramic powder, ZrSiO4 powder, and TiZrNi powder to obtain a mixed powder; adding a solvent to the mixed powder; ball milling and mixing to obtain a slurry; adding a foaming agent and a foam stabilizer to the slurry; mixing evenly; drying; and sintering under an inert gas to obtain the reinforcing agent; the particle size of the reinforcing agent is 25-40 μm. The mass ratio of the BN-BAS ceramic powder, ZrSiO4 powder, and TiZrNi powder is 1:0.2-0.5:0.1-0.2; the TiZrNi powder comprises, by weight percentage: 12-18% Zr, 1-5% Ni, and the remainder Ti. The sintering temperature is 1400-1550 ℃, and the sintering time is 1-3 h.

2. The high-strength, low-thermal-conductivity insulation layer castable for rotary kilns according to claim 1, characterized in that, The foaming agent is a protein-based foaming agent, and the foam stabilizer is dextrin; the foaming agent accounts for 3-5% of the mass of the mixed powder, and the foam stabilizer accounts for 1-3% of the mass of the foaming agent; the solvent is ethanol.

3. The high-strength, low-thermal-conductivity insulation layer castable for rotary kilns according to claim 1, characterized in that, The method for preparing the modified mullite hollow spheres includes the following steps: mixing silica sol and aluminum sol evenly to obtain a silica-alumina composite sol, adding mullite hollow spheres and stirring evenly, then adding propylene oxide and formamide to obtain a silica-alumina composite gel, allowing the silica-alumina composite gel to stand for 12-24 h, adding alcohol solvent for aging for 24-48 h, and obtaining the modified mullite hollow spheres by supercritical drying.

4. The high-strength, low-thermal-conductivity insulation layer castable for rotary kilns according to claim 3, characterized in that, The silica sol is prepared by mixing tetraethyl orthosilicate, alcohol, and water in a molar ratio of 1:2-12:1-10; the aluminum sol is prepared by mixing aluminum nitrate, alcohol, and water in a molar ratio of 1:4-15:8-20; the volume ratio of silica sol to aluminum sol is 20-25:15-20; the molar ratio of aluminum atoms to formamide in the aluminum sol is 1:0.8, and the molar ratio of aluminum atoms to propylene oxide is 1:8; the mass ratio of the silica-alumina composite sol to the mullite hollow spheres is 1:1-2.

5. The high-strength, low-thermal-conductivity insulation layer castable for rotary kilns according to claim 3, characterized in that, The mullite hollow spheres, calculated by mass percentage, comprise: 10-40% mullite hollow spheres with a particle size of 5-3 mm, 10-40% mullite hollow spheres with a particle size of 3-2 mm, 10-40% mullite hollow spheres with a particle size of 2-1 mm, and 10-30% mullite hollow spheres with a particle size of 1-0.2 mm.

6. The high-strength, low-thermal-conductivity insulation layer castable for rotary kilns according to claim 1, characterized in that, The hollow alumina spheres contain ≥98% Al2O3 by weight; the hollow alumina spheres comprise, by mass percentage: 20-35% hollow alumina spheres with a particle size of 3-5 mm and 65-80% hollow alumina spheres with a particle size of 3-0.2 mm; the silica powder contains >94% SiO2 by weight; the active α-Al2O3 powder contains ≥99% Al2O3 by weight and has a median diameter of less than 1.5 μm; the binder is aluminate cement.

7. A preparation process for a high-strength, low-thermal-conductivity insulating layer castable for rotary kilns as described in any one of claims 1-6, characterized in that, The process includes the following steps: mixing the modified mullite hollow spheres, alumina hollow spheres, active α-Al2O3 micro powder, silica micro powder, reinforcing agent, explosion-proof fiber, water-reducing agent and binder in the specified amounts until uniform, stirring for 8-12 minutes, casting into shape, and then naturally drying at 25-30 ℃ for 24 hours before demolding, followed by drying at 100-110 ℃ for 24 hours to obtain the final product.

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