Calcium silicate board with enhanced thermal stability and preparation method thereof

Abstract

The invention relates to the technical field of building materials, in particular to a calcium silicate board with enhanced thermal stability and a preparation method thereof. The calcium silicate board is prepared from 300 to 400 parts of calcined quicklime, 450 to 750 parts of dry quartz powder, 50 to 150 parts of modified alumina short fibers and 160 to 260 parts of deionized water. The modified aluminum oxide short fiber is grafted with a polymer on the surface and zinc borate is introduced, so that generation and expansion of microcracks are effectively inhibited. The calcium silicate board shows excellent crack resistance and thermal stability in a high-temperature thermal shock environment, and is suitable for development and application of building materials under high-temperature working conditions.

Description

Technical Field

[0001] The present invention relates to the technical field of building materials, and in particular to a calcium silicate board with enhanced thermal stability and a preparation method thereof. Background Art

[0002] Calcium silicate board, an important inorganic non-metallic material, is widely used in buildings, industrial equipment, and thermal insulation and protection in high-temperature environments due to its excellent fire resistance, thermal insulation, and mechanical properties. However, as modern industry continues to demand higher performance from materials, the performance limitations of traditional calcium silicate board in high-temperature thermal shock environments are becoming increasingly apparent. Especially under extreme temperature fluctuations, calcium silicate board is prone to microcracks due to concentrated thermal stress, leading to a degradation of the material's mechanical properties and structural instability, seriously impacting its service life and safety.

[0003] To improve the thermal stability and mechanical properties of calcium silicate boards, researchers have attempted to optimize the material structure through methods such as fiber reinforcement, ceramic phase modification, and polymer composites. For example, fiber reinforcement technology incorporates inorganic fibers (such as glass fibers, carbon fibers, or alumina fibers) into a calcium silicate matrix to enhance the material's tensile strength and crack resistance. However, due to insufficient interfacial bonding between the fibers and the matrix, the fiber reinforcement effect is often difficult to maintain in high-temperature environments. Furthermore, the difference in thermal expansion coefficients between the fibers and the matrix leads to interfacial thermal stress concentration, further exacerbating the initiation and propagation of microcracks.

[0004] Ceramic phase modification is another common reinforcement method. This involves introducing oxide ceramic particles (such as alumina, zirconia, or silicon carbide) into a calcium silicate matrix to improve the material's high-temperature strength and thermal shock resistance. However, while the introduction of ceramic particles can inhibit crack propagation to a certain extent, their rigidity can reduce the material's overall toughness, making it difficult to meet performance requirements in complex thermal shock environments. Furthermore, the uniformity of the ceramic particles' dispersion within the matrix and the quality of their interfacial bonding also directly impact the reinforcement effect. Summary of the Invention

[0005] In view of this, the purpose of the present invention is to provide a calcium silicate board with enhanced thermal stability and a preparation method thereof, so as to solve the problem that the existing calcium silicate board is prone to microcrack expansion under high temperature thermal shock environment, resulting in mechanical performance degradation and structural instability.

[0006] Based on the above objectives, the present invention provides a calcium silicate board with enhanced thermal stability, which is prepared from the following raw materials, by weight: 300-400 parts of calcined quicklime, 450-750 parts of dry quartz powder, 50-150 parts of modified alumina short fibers and 160-260 parts of deionized water.

[0007] Furthermore, the preparation steps of the modified alumina short fibers are as follows: S1: adding alumina short fibers to a mixture of deionized water and ethanol, stirring under ultrasonication for 20-40 minutes, then adding vinyltrimethoxysilane, heating to 50-60°C, stirring for 5-7 hours, centrifuging, washing, and drying to obtain olefinated alumina short fibers; S2: Add butyl acrylate, methacrylic acid, 2-hydroxyethyl acrylate, and Span 80 to a mixed solution of deionized water and anhydrous ethanol, stir for 20-40 minutes, and adjust the pH to 3.8-4.2 with hydrochloric acid to form a pre-emulsion; S3: Add zinc nitrate to deionized water, stir for 8-12 minutes, add ammonium persulfate, and continue stirring for 20-40 minutes to obtain an initiating solution; S4: Under a nitrogen atmosphere, add olefinated alumina short fibers to the initiator solution, raise the temperature to 60-70°C, add the pre-emulsion dropwise during stirring, stir and react for 2.5-3.5 hours after the addition is completed, then add an 8-12wt% boric acid aqueous solution, continue stirring for 20-40 minutes, centrifuge, wash, and dry to obtain modified alumina short fibers.

[0008] Preferably, the alumina short fibers in step S1 have a composition of 85 wt% alumina and 15 wt% silica, an average diameter of 10-15 μm, and an average length of 40-60 mm.

[0009] Preferably, in step S1, the weight ratio of alumina short fibers, deionized water, ethanol and vinyltrimethoxysilane is 50-150:250-750:500-1500:5-20.

[0010] Preferably, in step S2, the weight ratio of butyl acrylate, methacrylic acid, 2-hydroxyethyl acrylate, Span 80, deionized water and anhydrous ethanol is 25-75:15-45:10-35:1.5-4.5:250-750:150-450.

[0011] Preferably, in step S3, the weight ratio of zinc nitrate, deionized water and ammonium persulfate is 6-18:50-150:0.8-2.4.

[0012] Preferably, in step S4, the weight ratio of the olefinated alumina short fibers, the initiating solution, the pre-emulsion and the boric acid aqueous solution is 50-150:50-150:450-1300:60-100.

[0013] Preferably, the calcined quicklime is obtained by calcining quicklime at 960-1000° C. for 2-3 hours and grinding it through a 250-300 mesh sieve.

[0014] Preferably, the dry quartz powder is obtained by drying quartz powder at 100-110° C. for 10-15 hours and grinding it through a 250-350 mesh sieve.

[0015] Furthermore, the present invention provides a method for preparing a calcium silicate board with enhanced thermal stability, comprising the following steps: (1) Mix calcined quicklime, dry quartz powder, modified alumina short fibers and deionized water, and stir at 250-350 rpm for 12-18 minutes to obtain a slurry; (2) The slurry is flow-formed through a flow-forming plate-making machine to obtain a green blank; (3) placing the green blank in an autoclave and autoclaving to obtain a sheet; (4) The steam-cured board is placed in a muffle furnace, calcined under a nitrogen atmosphere, and cooled to obtain a calcium silicate board with enhanced thermal stability.

[0016] Preferably, the flow forming temperature in step (2) is 38-42° C., and the vacuum degree is -0.07±0.01 MPa.

[0017] Preferably, the autoclaving step in step (3) is as follows: heating to 155-165°C at a rate of 1-10°C / min under a saturated steam pressure of 0.6-1 MPa, keeping the temperature for 6-10 hours, then heating to 190-200°C at a rate of 1-1.5°C / min under a saturated steam pressure of 1.4-1.6 MPa, and keeping the temperature for 5-7 hours.

[0018] Preferably, the calcination step in step (4) is as follows: heating to 580-620°C at 4-6°C / min, keeping the temperature for 1.5-2.5h Beneficial effects of the present invention: The present invention achieves a synergistic improvement in the mechanical properties and thermal stability of the material by constructing a fiber-polymer-ceramic multiphase synergistic reinforcement system. The polymer grafted onto the fiber surface forms a gradient transition structure of nanocarbon layer and ceramic phase during pyrolysis, effectively filling the micro defects of the matrix and enhancing the efficiency of interfacial stress transfer. The in-situ generated borosilicate glass phase repairs thermal cycle damage through viscous flow, forming a dynamic self-healing protective layer. The multi-scale reinforcement mechanism enables the material to effectively disperse mechanical loads and thermal stresses during thermal shock, inhibiting the initiation and expansion of microcracks.

[0019] The present invention utilizes the synergistic effect of flexible polymer segments and rigid ceramic phases to provide the reinforcement system with both stress buffering and load-bearing functions. The thermal expansion coefficient transition layer formed by the gradient carbonization structure significantly reduces the interfacial thermal stress between the fiber and the matrix. The zinc borate formed on the fiber surface effectively induces microcrack deflection, extending the crack propagation path and consuming fracture energy. Furthermore, the catalytically formed graphitized carbon network improves the material's thermal conductivity, accelerating heat diffusion and preventing local overheating.

[0020] The calcium silicate board with enhanced thermal stability provided by the present invention can still maintain a stable microstructure and excellent mechanical properties under extreme temperature alternation environments, providing an innovative solution for the development of building materials for high-temperature working conditions. DETAILED DESCRIPTION

[0021] In order to make the objectives, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below with reference to specific embodiments.

[0022] In the specific embodiment of the present invention, the alumina short fibers were purchased from Suzhou Baird New Material Technology Co., Ltd., model number Nextel720, with a composition of 85 wt% alumina and 15 wt% silica, an average diameter of 11.4 μm, and an average length of 51.6 mm.

[0023] Example

[0024] (1) 50 g of alumina short fibers were added to a mixture of 250 g of deionized water and 500 g of ethanol, and ultrasonically stirred for 20 min. 5 g of vinyltrimethoxysilane was then added, and the mixture was heated to 50 °C and stirred for 5 h. The mixture was centrifuged, washed, and dried to obtain olefinated alumina short fibers. (2) 25 g of butyl acrylate, 15 g of methacrylic acid, 10 g of 2-hydroxyethyl acrylate and 1.5 g of Span 80 were added to a mixed solution of 250 g of deionized water and 150 g of anhydrous ethanol, stirred for 20 min and the pH was adjusted to 3.8 with hydrochloric acid to form a pre-emulsion; 6 g of zinc nitrate was added to 50 g of deionized water, stirred for 8 min, 0.8 g of ammonium persulfate was added and the stirring was continued for 20 min to obtain an initiating solution; under a nitrogen atmosphere, 50 g of olefinated alumina short fibers were added to 50 g of the initiating solution, the temperature was raised to 60 ° C, 450 g of the pre-emulsion was added dropwise during the stirring process, and the reaction was stirred for 2.5 h after the addition was completed, and 60 g of an 8 wt% boric acid aqueous solution was added and the stirring was continued for 20 min. The mixture was centrifuged, washed and dried to obtain modified alumina short fibers; (3) The quartz powder was dried at 100°C for 10 hours, ground and passed through a 250-mesh sieve to obtain dry quartz powder, and quicklime was calcined at 960°C for 2 hours, ground and passed through a 250-mesh sieve to obtain calcined quicklime; (4) 300 g of calcined quicklime, 450 g of dry quartz powder, 50 g of modified alumina short fibers, and 160 g of deionized water were mixed and stirred at 250 rpm for 12 min to obtain a slurry; (5) The slurry is formed by a flow plate making machine at a temperature of 38°C and a vacuum degree of -0.06 MPa to obtain a green blank; (6) Place the green billet in an autoclave, heat it to 155°C at a rate of 1°C / min under a saturated steam pressure of 0.6 MPa, keep it warm for 6 h, then heat it to 190°C at a rate of 1°C / min under a saturated steam pressure of 1.4 MPa, keep it warm for 5 h, and obtain a sheet; (7) The steam-cured board was placed in a muffle furnace, heated to 580°C at a rate of 4°C / min in a nitrogen atmosphere, kept warm for 1.5 h, and cooled to obtain a calcium silicate board with enhanced thermal stability.

[0025] Example

[0026] (1) 100 g of alumina short fibers were added to a mixture of 500 g of deionized water and 1000 g of ethanol, and ultrasonically stirred for 30 min. 10 g of vinyltrimethoxysilane was then added, and the mixture was heated to 55 °C and stirred for 6 h. The mixture was centrifuged, washed, and dried to obtain olefinated alumina short fibers. (2) 58 g of butyl acrylate, 32 g of methacrylic acid, 25 g of 2-hydroxyethyl acrylate and 3 g of Span 80 were added to a mixed solution of 500 g of deionized water and 300 g of anhydrous ethanol, stirred for 30 min and adjusted to pH 4.0 with hydrochloric acid to form a pre-emulsion; 12.5 g of zinc nitrate was added to 100 g of deionized water, stirred for 10 min, 1.7 g of ammonium persulfate was added, and stirring was continued for 30 min to obtain an initiating solution; under a nitrogen atmosphere, 100 g of olefinated alumina short fibers were added to 100 g of the initiating solution, the temperature was raised to 65 ° C, 900 g of the pre-emulsion was added dropwise during the stirring process, and the reaction was stirred for 3 h after the addition was completed, and 80 g of a 10 wt% boric acid aqueous solution was added, and stirring was continued for 30 min. The mixture was centrifuged, washed, and dried to obtain modified alumina short fibers; (3) The quartz powder was dried at 105°C for 12 hours, ground and passed through a 300-mesh sieve to obtain dry quartz powder, and quicklime was calcined at 980°C for 2.5 hours, ground and passed through a 300-mesh sieve to obtain calcined quicklime; (4) 350 g of calcined quicklime, 600 g of dry quartz powder, 100 g of modified alumina short fibers, and 210 g of deionized water were mixed and stirred at 300 rpm for 15 min to obtain a slurry; (5) The slurry is formed by a flow forming machine at a temperature of 40°C and a vacuum degree of -0.07 MPa to obtain a green blank; (6) Place the green billet in an autoclave, heat it to 160°C at a rate of 5°C / min under a saturated steam pressure of 0.8 MPa, keep it warm for 8 h, then heat it to 195°C at a rate of 1.2°C / min under a saturated steam pressure of 1.5 MPa, keep it warm for 6 h, and obtain a sheet; (7) The steam-cured board was placed in a muffle furnace, heated to 600°C at a rate of 5°C / min in a nitrogen atmosphere, kept at this temperature for 2 h, and cooled to obtain a calcium silicate board with enhanced thermal stability.

[0027] Example

[0028] (1) 150 g of alumina short fibers were added to a mixture of 750 g of deionized water and 1500 g of ethanol, and ultrasonically stirred for 40 min. 20 g of vinyltrimethoxysilane was then added, and the mixture was heated to 60 °C and stirred for 7 h. The mixture was centrifuged, washed, and dried to obtain olefinated alumina short fibers. (2) 75 g of butyl acrylate, 45 g of methacrylic acid, 35 g of 2-hydroxyethyl acrylate and 4.5 g of Span 80 were added to a mixed solution of 750 g of deionized water and 450 g of anhydrous ethanol, stirred for 40 min and adjusted to pH 4.2 with hydrochloric acid to form a pre-emulsion; 18 g of zinc nitrate was added to 150 g of deionized water, stirred for 12 min, 2.4 g of ammonium persulfate was added, and stirring was continued for 40 min to obtain an initiating solution; under a nitrogen atmosphere, 150 g of olefinated alumina short fibers were added to the 150 g initiating solution, the temperature was raised to 70 ° C, 1300 g of the pre-emulsion was added dropwise during the stirring process, and the reaction was stirred for 3.5 h after the addition was completed, and 100 g of a 12 wt% boric acid aqueous solution was added, and stirring was continued for 40 min. The mixture was centrifuged, washed, and dried to obtain modified alumina short fibers; (3) The quartz powder was dried at 110°C for 15 hours, ground and passed through a 350-mesh sieve to obtain dry quartz powder, and quicklime was calcined at 1000°C for 3 hours, ground and passed through a 300-mesh sieve to obtain calcined quicklime; (4) Mix 400 g of calcined quicklime, 450-750 g of dry quartz powder, 50-150 g of modified alumina short fibers, and 160-260 g of deionized water, and stir at 350 rpm for 18 min to obtain a slurry; (5) The slurry is formed by a flow plate making machine at a temperature of 40°C and a vacuum degree of -0.08 MPa to obtain a green blank; (6) Place the green billet in an autoclave, heat it to 165°C at a rate of 10°C / min under a saturated steam pressure of 1 MPa, keep it warm for 10 h, then heat it to 200°C at a rate of 1.5°C / min under a saturated steam pressure of 1.6 MPa, keep it warm for 7 h, and obtain a sheet; (7) The steam-cured board was placed in a muffle furnace, heated to 620°C at a rate of 6°C / min in a nitrogen atmosphere, kept warm for 2.5 h, and cooled to obtain a calcium silicate board with enhanced thermal stability.

[0029] Comparative Example 1: The difference between Comparative Example 1 and Example 2 is that the olefinated alumina short fibers in (2) are replaced with alumina short fibers; The specific steps are as follows: (1) 58 g of butyl acrylate, 32 g of methacrylic acid, 25 g of 2-hydroxyethyl acrylate and 3 g of Span 80 were added to a mixed solution of 500 g of deionized water and 300 g of anhydrous ethanol, stirred for 30 min and adjusted to pH 4.0 with hydrochloric acid to form a pre-emulsion; 12.5 g of zinc nitrate was added to 100 g of deionized water, stirred for 10 min, 1.7 g of ammonium persulfate was added, and stirring was continued for 30 min to obtain an initiating solution; under a nitrogen atmosphere, 100 g of alumina short fibers were added to 100 g of the initiating solution, the temperature was raised to 65 ° C, 900 g of the pre-emulsion was added dropwise during the stirring process, and the reaction was stirred for 3 h after the addition was completed, and 80 g of a 10 wt% boric acid aqueous solution was added, and stirring was continued for 30 min. The mixture was centrifuged, washed, and dried to obtain modified alumina short fibers; (2) The quartz powder was dried at 105°C for 12 hours, ground and passed through a 300-mesh sieve to obtain dry quartz powder, and quicklime was calcined at 980°C for 2.5 hours, ground and passed through a 300-mesh sieve to obtain calcined quicklime; (3) 350 g of calcined quicklime, 600 g of dry quartz powder, 100 g of modified alumina short fibers, and 210 g of deionized water were mixed and stirred at 300 rpm for 15 min to obtain a slurry; (4) The slurry is formed by a flow forming machine at a temperature of 40°C and a vacuum degree of -0.07 MPa to obtain a green blank; (5) Place the green billet in an autoclave, heat it to 160°C at a rate of 5°C / min under a saturated steam pressure of 0.8 MPa, keep it warm for 8 h, then heat it to 195°C at a rate of 1.2°C / min under a saturated steam pressure of 1.5 MPa, keep it warm for 6 h, and obtain a sheet; (6) Place the steam-cured board in a muffle furnace, raise the temperature to 600°C at 5°C / min in a nitrogen atmosphere, keep it at that temperature for 2 hours, and cool it to obtain a calcium silicate board.

[0030] Comparative Example 2: The difference between Comparative Example 2 and Example 2 is that butyl acrylate is not added in step (2); The specific steps are as follows: (1) 100 g of alumina short fibers were added to a mixture of 500 g of deionized water and 1000 g of ethanol, and ultrasonically stirred for 30 min. 10 g of vinyltrimethoxysilane was then added, and the mixture was heated to 55 °C and stirred for 6 h. The mixture was centrifuged, washed, and dried to obtain olefinated alumina short fibers. (2) 32 g of methacrylic acid, 25 g of 2-hydroxyethyl acrylate and 3 g of Span 80 were added to a mixed solution of 500 g of deionized water and 300 g of anhydrous ethanol, stirred for 30 min and adjusted to pH 4.0 with hydrochloric acid to form a pre-emulsion; 12.5 g of zinc nitrate was added to 100 g of deionized water, stirred for 10 min, 1.7 g of ammonium persulfate was added, and stirring was continued for 30 min to obtain an initiating solution; under a nitrogen atmosphere, 100 g of olefinated alumina short fibers were added to 100 g of the initiating solution, the temperature was raised to 65 ° C, 900 g of the pre-emulsion was added dropwise during the stirring process, and the reaction was stirred for 3 h after the addition was completed, and 80 g of a 10 wt% boric acid aqueous solution was added, and stirring was continued for 30 min. The mixture was centrifuged, washed, and dried to obtain modified alumina short fibers; (3) The quartz powder was dried at 105°C for 12 hours, ground and passed through a 300-mesh sieve to obtain dry quartz powder, and quicklime was calcined at 980°C for 2.5 hours, ground and passed through a 300-mesh sieve to obtain calcined quicklime; (4) 350 g of calcined quicklime, 600 g of dry quartz powder, 100 g of modified alumina short fibers, and 210 g of deionized water were mixed and stirred at 300 rpm for 15 min to obtain a slurry; (5) The slurry is formed by a flow forming machine at a temperature of 40°C and a vacuum degree of -0.07 MPa to obtain a green blank; (6) Place the green billet in an autoclave, heat it to 160°C at a rate of 5°C / min under a saturated steam pressure of 0.8 MPa, keep it warm for 8 h, then heat it to 195°C at a rate of 1.2°C / min under a saturated steam pressure of 1.5 MPa, keep it warm for 6 h, and obtain a sheet; (7) Place the steam-cured board in a muffle furnace, heat it to 600°C at 5°C / min in a nitrogen atmosphere, keep it warm for 2 hours, and cool it to obtain a calcium silicate board.

[0031] Comparative Example 3: The difference between Comparative Example 3 and Example 2 is that: methacrylic acid is not added in step (2); The specific steps are as follows: (1) 100 g of alumina short fibers were added to a mixture of 500 g of deionized water and 1000 g of ethanol, and ultrasonically stirred for 30 min. 10 g of vinyltrimethoxysilane was then added, and the mixture was heated to 55 °C and stirred for 6 h. The mixture was centrifuged, washed, and dried to obtain olefinated alumina short fibers. (2) 58 g of butyl acrylate, 25 g of 2-hydroxyethyl acrylate and 3 g of Span 80 were added to a mixed solution of 500 g of deionized water and 300 g of anhydrous ethanol, stirred for 30 min and adjusted to pH 4.0 with hydrochloric acid to form a pre-emulsion; 12.5 g of zinc nitrate was added to 100 g of deionized water, stirred for 10 min, 1.7 g of ammonium persulfate was added, and stirring was continued for 30 min to obtain an initiating solution; under a nitrogen atmosphere, 100 g of olefinated alumina short fibers were added to 100 g of the initiating solution, the temperature was raised to 65 ° C, 900 g of the pre-emulsion was added dropwise during the stirring process, and the reaction was stirred for 3 h after the addition was completed, and 80 g of a 10 wt% boric acid aqueous solution was added, and stirring was continued for 30 min. The mixture was centrifuged, washed, and dried to obtain modified alumina short fibers; (3) The quartz powder was dried at 105°C for 12 hours, ground and passed through a 300-mesh sieve to obtain dry quartz powder, and quicklime was calcined at 980°C for 2.5 hours, ground and passed through a 300-mesh sieve to obtain calcined quicklime; (4) 350 g of calcined quicklime, 600 g of dry quartz powder, 100 g of modified alumina short fibers, and 210 g of deionized water were mixed and stirred at 300 rpm for 15 min to obtain a slurry; (5) The slurry is formed by a flow forming machine at a temperature of 40°C and a vacuum degree of -0.07 MPa to obtain a green blank; (6) Place the green billet in an autoclave, heat it to 160°C at a rate of 5°C / min under a saturated steam pressure of 0.8 MPa, keep it warm for 8 h, then heat it to 195°C at a rate of 1.2°C / min under a saturated steam pressure of 1.5 MPa, keep it warm for 6 h, and obtain a sheet; (7) Place the steam-cured board in a muffle furnace, heat it to 600°C at 5°C / min in a nitrogen atmosphere, keep it warm for 2 hours, and cool it to obtain a calcium silicate board.

[0032] Comparative Example 4: The difference between Comparative Example 4 and Example 2 is that: 2-hydroxyethyl acrylate is not added in step (2); The specific steps are as follows: (1) 100 g of alumina short fibers were added to a mixture of 500 g of deionized water and 1000 g of ethanol, and ultrasonically stirred for 30 min. 10 g of vinyltrimethoxysilane was then added, and the mixture was heated to 55 °C and stirred for 6 h. The mixture was centrifuged, washed, and dried to obtain olefinated alumina short fibers. (2) 58 g of butyl acrylate, 32 g of methacrylic acid and 3 g of Span 80 were added to a mixed solution of 500 g of deionized water and 300 g of anhydrous ethanol, stirred for 30 min and adjusted to pH 4.0 with hydrochloric acid to form a pre-emulsion; 12.5 g of zinc nitrate was added to 100 g of deionized water, stirred for 10 min, 1.7 g of ammonium persulfate was added, and stirring was continued for 30 min to obtain an initiating solution; under a nitrogen atmosphere, 100 g of olefinated alumina short fibers were added to 100 g of the initiating solution, the temperature was raised to 65 ° C, 900 g of the pre-emulsion was added dropwise during the stirring process, and the reaction was stirred for 3 h after the addition was completed, and 80 g of a 10 wt% boric acid aqueous solution was added, and stirring was continued for 30 min. The mixture was centrifuged, washed, and dried to obtain modified alumina short fibers; (3) The quartz powder was dried at 105°C for 12 hours, ground and passed through a 300-mesh sieve to obtain dry quartz powder, and quicklime was calcined at 980°C for 2.5 hours, ground and passed through a 300-mesh sieve to obtain calcined quicklime; (4) 350 g of calcined quicklime, 600 g of dry quartz powder, 100 g of modified alumina short fibers, and 210 g of deionized water were mixed and stirred at 300 rpm for 15 min to obtain a slurry; (5) The slurry is formed by a flow forming machine at a temperature of 40°C and a vacuum degree of -0.07 MPa to obtain a green blank; (6) Place the green billet in an autoclave, heat it to 160°C at a rate of 5°C / min under a saturated steam pressure of 0.8 MPa, keep it warm for 8 h, then heat it to 195°C at a rate of 1.2°C / min under a saturated steam pressure of 1.5 MPa, keep it warm for 6 h, and obtain a sheet; (7) Place the steam-cured board in a muffle furnace, heat it to 600°C at 5°C / min in a nitrogen atmosphere, keep it warm for 2 hours, and cool it to obtain a calcium silicate board.

[0033] Comparative Example 5: The difference between Comparative Example 5 and Example 2 is that zinc nitrate and boric acid are not added in step (2); The specific steps are as follows: (1) 100 g of alumina short fibers were added to a mixture of 500 g of deionized water and 1000 g of ethanol, and ultrasonically stirred for 30 min. 10 g of vinyltrimethoxysilane was then added, and the mixture was heated to 55 °C and stirred for 6 h. The mixture was centrifuged, washed, and dried to obtain olefinated alumina short fibers. (2) 58 g of butyl acrylate, 32 g of methacrylic acid, 25 g of 2-hydroxyethyl acrylate and 3 g of Span 80 were added to a mixed solution of 500 g of deionized water and 300 g of anhydrous ethanol, stirred for 30 min and the pH was adjusted to 4.0 with hydrochloric acid to form a pre-emulsion; 1.7 g of ammonium persulfate was added to 100 g of deionized water and stirred for 10 min to obtain 100 g of initiating solution; under a nitrogen atmosphere, 100 g of olefinated alumina short fibers were added to the initiating solution, the temperature was raised to 65 ° C, and 900 g of the pre-emulsion was added dropwise during the stirring process. After the addition was completed, the mixture was stirred for 3 h, centrifuged, washed, and dried to obtain modified alumina short fibers; (3) The quartz powder was dried at 105°C for 12 hours, ground and passed through a 300-mesh sieve to obtain dry quartz powder, and quicklime was calcined at 980°C for 2.5 hours, ground and passed through a 300-mesh sieve to obtain calcined quicklime; (4) 350 g of calcined quicklime, 600 g of dry quartz powder, 100 g of modified alumina short fibers, and 210 g of deionized water were mixed and stirred at 300 rpm for 15 min to obtain a slurry; (5) The slurry is formed by a flow forming machine at a temperature of 40°C and a vacuum degree of -0.07 MPa to obtain a green blank; (6) Place the green billet in an autoclave, heat it to 160°C at a rate of 5°C / min under a saturated steam pressure of 0.8 MPa, keep it warm for 8 h, then heat it to 195°C at a rate of 1.2°C / min under a saturated steam pressure of 1.5 MPa, keep it warm for 6 h, and obtain a sheet; (7) Place the steam-cured board in a muffle furnace, heat it to 600°C at 5°C / min in a nitrogen atmosphere, keep it warm for 2 hours, and cool it to obtain a calcium silicate board.

[0034] Performance testing: Flexural strength: According to Article 6.3 of JC / T 564.1-2018, a WAW-1000C microcomputer-controlled electro-hydraulic servo universal testing machine was used with a span of 200 mm and a loading rate of 5 mm / min. The results are shown in Table 1. Compressive strength: According to GB / T 17617-2013, the loading rate is set to 2400N / s until the sample is broken, and the maximum pressure value is recorded. The calculation formula is: C=P / A, where C is the compressive strength (MPa), P is the breaking load (N), and A is the compressive area (mm 2 ), the results are shown in Table 1; Thermal shock stability: The specimens were cut into 100 mm × 100 mm × 10 mm dimensions and dried in a 105°C oven to constant weight. The specimens were then tested using a high-temperature box-type resistance furnace with the initial temperature set at 600°C. The specimens were placed vertically in the center of the furnace preheated to 600°C and kept warm for 30 minutes before being quickly removed. The specimens were immediately immersed in 25±2°C deionized water for rapid cooling. The immersion time was 10 minutes. The specimens were removed and dried with compressed air. The thermal shock cycle was repeated 20 times. The flexural strength was tested and the strength retention rate was calculated. The results are shown in Table 1.

[0035] Table 1 Performance test results

[0036] Data Analysis: As can be seen from the data of Examples 1-3 in Table 1, the enhanced thermal stability calcium silicate board prepared by the present invention has high flexural and compressive strengths and can maintain a stable internal structure and mechanical strength under alternating conditions of high temperature and rapid cooling. This is likely due to the fact that the acrylic copolymer grafted onto the surface of the alumina short fibers forms an interpenetrating network with the calcium silicate hydration products through molecular chains during the autoclaving and curing stage. The nanocarbon layer formed by polymer carbonization during high-temperature pyrolysis and the zinc borate generated in situ on the fiber surface synergistically fill the matrix micro-defects and enhance the fiber-matrix interface. This multi-scale reinforcement mechanism enables the material to effectively disperse stress when subjected to mechanical loads. At the same time, the high-temperature stability of zinc borate provides thermal barrier protection for the material, inhibiting the propagation of microcracks caused by thermal stress.

[0037] From the data of Example 2 and Comparative Example 1 in Table 1, it can be seen that in Example 2, by surface alkenyl modification of alumina short fibers, the flexural strength, compressive strength and post-thermal shock strength retention rate of the calcium silicate board were significantly improved. This is mainly because the alkenyl treatment constructs active grafting sites on the fiber surface through chemical bonding, enabling the subsequent polymer coating to achieve covalent bond anchoring. This strong interfacial bonding can more effectively transfer stress than physical adsorption, avoiding early failure caused by interfacial peeling. At the same time, the molecular chains on the fiber surface can relieve the interfacial stress caused by the difference in thermal expansion coefficient between the fiber and the matrix after carbonization, maintaining structural integrity during thermal shock.

[0038] The data from Example 2 and Comparative Example 2 in Table 1 show that the addition of butyl acrylate in Example 2 significantly improved the mechanical properties and thermal shock stability of the calcium silicate board. The addition of butyl acrylate likely improved the adhesion between the fibers and the matrix, thereby increasing the uniformity and density of the matrix, enabling the material to maintain a high strength retention rate after multiple thermal shock cycles.

[0039] The data from Example 2 and Comparative Example 3 in Table 1 show that the addition of methacrylic acid in Example 2 significantly enhanced the flexural strength, compressive strength, and post-thermal shock strength retention of the calcium silicate board. This is likely due to the carboxylic acid groups on the methacrylic acid promoting the formation of zinc nitrate and boric acid on the fiber surface.

[0040] As can be seen from the data in Example 2 and Comparative Example 4 in Table 1, the addition of 2-hydroxyethyl acrylate in Example 2 significantly improved the overall performance of the calcium silicate board. This is likely due to the hydroxyl functional groups of 2-hydroxyethyl acrylate forming a hydrogen bond network with the calcium silicate hydration products, promoting the fusion of the organic-inorganic interface during the autoclaving curing stage. The flexibility of the ethoxy chain segments enables the polymer layer to form a gradient carbonization structure during thermal decomposition. This gradual interface can effectively alleviate thermal stress concentration. The thermal decomposition products of hydroxyl groups may also participate in the formation of silicate lattice defects, enhancing the toughness of the matrix.

[0041] From the data of Example 2 and Comparative Example 5 in Table 1, it can be seen that the introduction of zinc nitrate and boric acid in Example 2 significantly enhances the mechanical properties and thermal shock stability of the calcium silicate board. This may be because the zinc borate generated by the reaction of zinc nitrate and boric acid forms a nano-whisker structure on the fiber surface, and its anisotropic thermal expansion characteristics can induce microcrack deflection. During the high-temperature pyrolysis process, B2O3 produced by the decomposition of zinc borate forms a borosilicate glass phase with a low expansion coefficient with SiO2. This in-situ generated interface phase not only improves the chemical compatibility between the fiber and the matrix, but also can repair micro-defects generated by thermal cycling through viscous flow. The catalytic effect of zinc ions may promote the graphitization of carbonization products, forming a high thermal conductivity network to accelerate heat diffusion, thereby significantly improving the thermal shock stability of the material.

[0042] Those skilled in the art should understand that the discussion of any of the above embodiments is merely illustrative and is not intended to imply that the scope of the present invention is limited to these examples. Within the scope of the present invention, the technical features in the above embodiments or different embodiments may be combined, the steps may be implemented in any order, and there are many other variations of the different aspects of the present invention as described above, which are not provided in detail for the sake of simplicity.

Claims

1. A calcium silicate board with enhanced thermal stability, characterized in that: The preparation method is prepared from the following raw materials in parts by weight: 300-400 parts of calcined quicklime, 450-750 parts of dry quartz powder, 50-150 parts of modified alumina short fibers and 160-260 parts of deionized water; The preparation steps of the modified alumina short fibers are as follows: S1: adding alumina short fibers to a mixture of deionized water and ethanol, stirring under ultrasonication for 20-40 minutes, then adding vinyltrimethoxysilane, heating to 50-60°C, stirring for 5-7 hours, centrifuging, washing, and drying to obtain olefinated alumina short fibers; S2: Add butyl acrylate, methacrylic acid, 2-hydroxyethyl acrylate, and Span 80 to a mixed solution of deionized water and anhydrous ethanol, stir for 20-40 minutes, and adjust the pH to 3.8-4.2 with hydrochloric acid to form a pre-emulsion; S3: Add zinc nitrate to deionized water, stir for 8-12 minutes, add ammonium persulfate, and continue stirring for 20-40 minutes to obtain an initiating solution; S4: Under a nitrogen atmosphere, add the olefinated alumina short fibers to the initiator solution, raise the temperature to 60-70°C, add the pre-emulsion dropwise while stirring, and stir and react for 2.5-3.5 hours after the addition is complete. Then, add an 8-12 wt% boric acid aqueous solution, continue stirring for 20-40 minutes, centrifuge, wash, and dry to obtain modified alumina short fibers; In step S1, the weight ratio of alumina short fibers, deionized water, ethanol, and vinyltrimethoxysilane is 50-150:250-750:500-1500:5-20; In step S2, the weight ratio of butyl acrylate, methacrylic acid, 2-hydroxyethyl acrylate, Span 80, deionized water and anhydrous ethanol is 25-75:15-45:10-35:1.5-4.5:250-750:150-450; In step S3, the weight ratio of zinc nitrate, deionized water, and ammonium persulfate is 6-18:50-150:0.8-2.4; In step S4, the weight ratio of the olefinated alumina short fibers, the initiating solution, the pre-emulsion and the boric acid aqueous solution is 50-150:50-150:450-1300:60-100.

2. The calcium silicate board with enhanced thermal stability according to claim 1, characterized in that: The calcined quicklime is obtained by calcining quicklime at 960-1000° C. for 2-3 hours and grinding it through a 250-300 mesh sieve.

3. The calcium silicate board with enhanced thermal stability according to claim 1, characterized in that: The dried quartz powder is obtained by drying quartz powder at 100-110° C. for 10-15 hours and grinding it through a 250-350 mesh sieve.

4. The calcium silicate board with enhanced thermal stability according to claim 1, characterized in that: The alumina short fibers in step S1 have a composition of 85 wt% alumina and 15 wt% silica, an average diameter of 10-15 μm, and an average length of 40-60 mm.

5. A method for preparing a calcium silicate board with enhanced thermal stability according to any one of claims 1 to 5, characterized in that: The following steps are involved: (1) Mix calcined quicklime, dry quartz powder, modified alumina short fibers and deionized water, and stir at 250-350 rpm for 12-18 minutes to obtain a slurry; (2) The slurry is flowed through a slurry plate-making machine to form a green blank; (3) placing the green blank in an autoclave and autoclaving to obtain a sheet; (4) The steam-cured board is placed in a muffle furnace, calcined under a nitrogen atmosphere, and cooled to obtain a calcium silicate board with enhanced thermal stability.

6. The method for preparing a calcium silicate board with enhanced thermal stability according to claim 6, characterized in that: The temperature of the slurry forming in step (2) is 38-42° C., and the vacuum degree is -0.07±0.01 MPa.

7. The method for preparing a calcium silicate board with enhanced thermal stability according to claim 6, characterized in that: The autoclaving step in step (3) is as follows: heating to 155-165°C at a rate of 1-10°C / min under a saturated steam pressure of 0.6-1 MPa, keeping the temperature for 6-10 hours, and then heating to 190-200°C at a rate of 1-1.5°C / min under a saturated steam pressure of 1.4-1.6 MPa, and keeping the temperature for 5-7 hours.

8. The method for preparing a calcium silicate board with enhanced thermal stability according to claim 6, characterized in that: The calcination step in step (4) is as follows: heating to 580-620°C at a rate of 4-6°C / min and keeping the temperature for 1.5-2.5h.

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