A diatomite low-density board and a method for manufacturing the same

Abstract

The present disclosure relates to the technical field of building materials, and particularly relates to a diatomite low-density board and a preparation method thereof, which comprises the following steps: S1, performing cutinization pretreatment on wood fibers to reduce hydrophilicity to obtain cutinization wood fibers, and then mixing the cutinization wood fibers with diatomite and auxiliary materials to pulp and form a board blank; S2, performing pre-curing on the board blank to generate an initial calcium source, first performing carbonization curing at a first CO2 concentration to convert the initial calcium source on the surface of the board blank into calcium carbonate to form a calcium carbonate layer, adding an alkaline calcium source, performing pre-curing again, then performing carbonization curing at a second CO2 concentration, and the second CO2 concentration is greater than the first CO2 concentration, thereby forming a calcium carbonate-hydrated calcium silicate gradient composite phase in the board blank to obtain a cured board blank; and S3, cooling the cured board blank to room temperature to obtain the diatomite low-density board, and through the synergy of the wood fiber cutinization pretreatment and the two-stage carbonization and re-pre-curing, the low-density board realizes the balance between high strength and low water absorption.

Description

Technical Field

[0001] This disclosure relates to the field of building materials technology, and more particularly to a diatomaceous earth low-density board and its preparation method. Background Technology

[0002] Low-density fiber cement boards are widely used in prefabricated wall systems and floor decking due to their ability to reduce building loads and facilitate construction and installation. To reduce the density of the boards, existing technologies typically use lightweight fillers such as perlite and diatomaceous earth to replace some of the cementitious materials. However, while porous fillers like perlite can reduce density, they also result in a loose matrix structure, with dry flexural strength generally only 6–8 MPa and even lower impact strength. Furthermore, the high water absorption of these fillers often leads to a water absorption rate exceeding 30%, causing severe swelling and shrinkage, and insufficient long-term durability. In addition, perlite requires high-temperature calcination for expansion, resulting in high energy consumption and cost, which does not align with the concept of green and low-carbon development.

[0003] To improve the reinforcement and water resistance of wood fibers, existing technologies propose using waste heat steam from an autoclave combined with diluted lime water for circulating cleaning of the wood fibers, and introducing chemical activators such as potassium peroxide and lithium aluminum hydride to generate lithium silicate and potassium silicate in situ on the fiber surface under autoclaving conditions, thereby achieving reinforcement and hydrophobicity. However, this approach still has the following technical problems in special usage environments: 1. The high-temperature, high-pressure steam environment of autoclaving is not conducive to the directional aggregation of alkali metal ions on the fiber surface and the reaction to form a stable hydrophobic layer; 2. Strong oxidizing or reducing activators can cause degradation of the cellulose molecular chains of wood fibers under alkaline autoclaving conditions, thus weakening the reinforcement effect; 3. The autoclaving temperature is as high as 180℃ or more, which not only consumes a lot of energy, but also further aggravates the damage to wood fibers in the high-temperature alkaline environment, resulting in a significant decrease in the strength of the board in the later stages. Summary of the Invention

[0004] In view of this, the present invention proposes a diatomaceous earth low-density board and its preparation method, which solves the problem that the introduction of lightweight fillers and the use of high-temperature autoclaving to cure existing low-density fiber cement boards lead to fiber degradation and loose matrix, thus making it difficult to achieve both board strength and waterproofness.

[0005] On the one hand, this disclosure provides a method for preparing diatomaceous earth low-density boards, including the following steps: S1, the wood fiber is pre-treated by keratinization to reduce hydrophilicity, resulting in keratinized wood fiber, which is then mixed with diatomaceous earth and auxiliary materials to form pulp and molded into a board blank; S2, the slab is pre-cured to generate an initial calcium source. First, carbonation curing with a first CO2 concentration is performed to convert the initial calcium source on the slab surface into calcium carbonate, forming a calcium carbonate layer. Then, an alkaline calcium source is added, and pre-curing is performed again. Then, carbonation curing with a second CO2 concentration is performed, and the second CO2 concentration is greater than the first CO2 concentration. A calcium carbonate-hydrated calcium silicate gradient composite phase is formed inside the slab to obtain the cured slab. S3. After curing, the slab is cooled to room temperature to obtain diatomaceous earth low-density board.

[0006] On the other hand, a diatomaceous earth low-density board is provided, which is made by the method for preparing diatomaceous earth low-density board as described in any one of the claims, wherein the diatomaceous earth low-density board comprises keratinized wood fiber, diatomaceous earth, cementing components, aggregates and silicates.

[0007] The surface of the board is a dense calcium carbonate layer, and the interior of the board has a gradient composite phase of calcium carbonate and hydrated calcium silicate. In the gradient composite phase, the calcium carbonate content decreases from the surface of the board to the interior, and the hydrated calcium silicate content increases from the surface to the interior.

[0008] The above technical solution has the following advantages: On the one hand, the use of wood fiber cutinization pretreatment solves the problem of alkaline degradation or thermal damage to wood fibers caused by high-temperature steam curing in existing technologies, avoids the loss of fiber reinforcement effect, and allows the fiber to maintain its reinforcement toughness throughout the entire preparation process; On the other hand, by first pre-curing the slab to generate an initial calcium source, and then performing a first CO2 concentration carbonation curing, the initial calcium source on the slab surface is converted into calcium carbonate, forming a dense calcium carbonate layer; then an alkaline calcium source is added, and pre-curing is performed again to ensure uniform penetration of the alkaline calcium source; finally, a second CO2 concentration carbonation curing is performed, causing the alkaline calcium source to react with diatomaceous earth in a volcanic ash reaction, forming a calcium carbonate-hydrated calcium silicate gradient composite phase inside the slab. In this process, the initial calcium source generated during the first pre-curing provides reactants for the first carbonization. The first CO2 concentration carbonization forms a dense calcium carbonate layer on the surface of the slab, which can both block water penetration and allow subsequent CO2 to enter the interior. The second pre-curing after adding an alkaline calcium source allows the alkaline calcium source to fully penetrate into the interior of the slab, avoiding surface accumulation. During the second CO2 concentration carbonization process, the high concentration of CO2 reacts with the penetrated alkaline calcium source, and at the same time, the alkaline calcium source reacts with diatomaceous earth to generate hydrated calcium silicate, forming a gradient composite phase with a surface rich in calcium carbonate and an interior rich in hydrated calcium silicate. This gradient structure overcomes the problem of existing technologies where the introduction of lightweight fillers leads to a loose matrix and difficulty in balancing strength and water resistance: the dense calcium carbonate layer on the surface blocks water penetration and reduces water absorption, while the hydrated calcium silicate in the interior fills the pores and compacts the matrix to improve strength. Moreover, the entire process does not require high-temperature autoclaving, thus achieving a balance between high strength and low water absorption in low-density boards.

[0009] Finally, the diatomaceous earth low-density board prepared by the above method includes keratinized wood fiber, diatomaceous earth, cementing components, aggregates and silicates. Keratinized wood fiber provides reinforcement and toughness support, diatomaceous earth reduces density and provides an active silicon source, aggregates help reduce density and inhibit water absorption, and silicates react with diatomaceous earth to form hydrated calcium silicate. The components work synergistically in the gradient composite phase structure, so that the board has high dry flexural strength, high impact strength, low water absorption and high flexural modulus while maintaining low density. This solves the defects of existing lightweight filler-type boards, such as low strength, high water absorption and poor durability.

[0010] It should be understood that the foregoing general description and the following detailed description are exemplary and explanatory only, and are not intended to limit this disclosure. Attached Figure Description

[0011] The accompanying drawings, which are incorporated in and form part of this specification, illustrate embodiments consistent with this disclosure and, together with the description, serve to explain the principles of this disclosure. It is obvious that the drawings described below are merely some embodiments of this disclosure, and those skilled in the art can obtain other drawings based on these drawings without any inventive effort. In the drawings: Figure 1 This is a schematic diagram of the preparation method of the diatomaceous earth low-density board according to the embodiments of the present invention; Figure 2 This is a flowchart of step S1 of the method for preparing diatomaceous earth low-density board according to an embodiment of the present invention; Figure 3 This is a schematic diagram of the preparation method of the modified vitrified microspheres according to an embodiment of the present invention; Figure 4 This is a flowchart of step S2 of the method for preparing diatomaceous earth low-density board according to an embodiment of the present invention; Figure 5 This is a flowchart of step S3 of the method for preparing diatomaceous earth low-density board according to an embodiment of the present invention. Detailed Implementation

[0012] Exemplary embodiments will now be described more fully with reference to the accompanying drawings. However, these exemplary embodiments can be implemented in many forms and should not be construed as limited to the examples set forth herein; rather, these embodiments are provided so that this disclosure will be more thorough and complete, and will fully convey the concept of the exemplary embodiments to those skilled in the art.

[0013] Furthermore, the described features, structures, or characteristics can be combined in any suitable manner in one or more embodiments. Numerous specific details are provided in the following description to give a thorough understanding of embodiments of this disclosure. However, those skilled in the art will recognize that the technical solutions of this disclosure can be practiced without one or more of the specific details, or other methods, components, steps, etc., can be employed. In other instances, well-known methods, implementations, or operations are not shown or described in detail to avoid obscuring various aspects of this disclosure.

[0014] The flowcharts shown in the accompanying drawings are merely illustrative and do not necessarily include all content and operations / steps, nor do they necessarily have to be performed in the described order. For example, some operations / steps can be broken down, while others can be combined or partially combined; therefore, the actual execution order may change depending on the specific circumstances.

[0015] This invention provides a diatomaceous earth low-density board, its preparation method, and its application. Specifically, this invention solves the technical problems of existing low-density fiber cement boards, such as the loose matrix caused by the introduction of lightweight fillers, the difficulty in balancing strength and water resistance, and the degradation of wood fibers caused by high-temperature autoclaving. The method involves a wood fiber keratinization pretreatment, a first CO2 concentration carbonation curing to form a dense calcium carbonate layer, a second CO2 concentration carbonation curing and volcanic ash reaction to construct a calcium carbonate-hydrated calcium silicate gradient composite phase, silicate sealing liquid post-treatment and vacuum degassing, and modified vitrified microsphere aggregate. This results in a board with comprehensive performance of low density, high strength, and low water absorption. The board is particularly suitable for non-load-bearing interior partition walls, floor decking, or roof panels in prefabricated buildings, which can significantly reduce building load and improve construction efficiency. The technical solution is described in detail below with specific implementation methods.

[0016] In one implementation, such as Figure 1 As shown, a method for preparing a diatomaceous earth low-density board includes the following steps: S1 involves pre-treating wood fibers with a keratinized coating to reduce their hydrophilicity, resulting in keratinized wood fibers. These fibers are then mixed with diatomaceous earth and auxiliary materials to form pulp, which is then molded into slabs.

[0017] In one implementation, such as Figure 2 As shown, step S1 includes: S1.1, the wood fiber is placed in a 0.1%-0.3% dilute lime water solution, and then circulated with waste heat steam from an autoclave for cleaning. After settling, organic impurities are removed, resulting in purified wood fiber. This is then subjected to 3-5 wetting-drying cycles to complete the keratinization treatment. After the final wetting, the purified wood fiber is rinsed with hot water at 80-100℃ to remove free waxes and fatty acids. Finally, it is dried to obtain the keratinized wood fiber. Specifically, the wetting process involves immersing the wood fiber in hot water at 80-100℃ until the moisture content is ≥80%, and the drying process involves hot air drying at 60-105℃ until the moisture content is ≤10%.

[0018] This step primarily provides a pretreatment method for wood fiber cuticle removal. Specifically, the treatment involves first placing the wood fibers in dilute lime water and circulating waste heat steam from an autoclave for cleaning. The weak alkalinity of the lime water saponifies fatty acids, while the heat from the steam accelerates the dissolution of organic impurities. After settling, suspended impurities are removed. Subsequently, multiple wetting-drying cycles are performed. Each cycle involves thorough immersion in hot water to allow the fiber cell walls to absorb water and swell. Hot air drying then causes irreversible hydrogen bond condensation between cellulose molecular chains, resulting in a more compact arrangement of cell wall microfibrils. A final hot water spray after wetting further removes residual waxes and fatty acids free on the fiber surface. After this treatment, the wood fiber surface becomes clean with moderate reactivity, while the fiber's swelling capacity and hydrophilicity are significantly reduced.

[0019] The technical problems addressed by this pretreatment are: conventional wood fibers contain organic impurities such as waxes, fatty acids, and pectin on their surface, which hinder interfacial bonding with inorganic cementitious materials; and the strong hydrophilicity of the fibers themselves causes the boards to easily absorb moisture and expand, resulting in poor dimensional stability. Furthermore, traditional high-temperature autoclaving causes alkaline hydrolysis and thermal degradation of wood fibers, significantly reducing fiber strength. Through cutinization pretreatment, the equilibrium moisture content of the wood fibers can be effectively reduced, and the cell wall structure becomes denser, making them less prone to degradation during subsequent curing. Simultaneously, the bonding strength with the cementitious matrix is ​​significantly improved, thus achieving the effect of maintaining enhanced toughness throughout the entire preparation process and providing a reliable reinforcing skeleton for the boards.

[0020] S1.2, keratinized wood fiber is mixed with diatomaceous earth, then aggregate, silicate, and cementing components are added and mixed thoroughly. The mixture is then formed using a flow-forming or sheet-making method. The mixing speed is 300-600 r / min, and the mixing time is 3-8 min, to obtain a slab. The cementing components include cement and quicklime; the aggregate is modified vitrified microspheres with a particle size of 0.1-0.5 mm; the silicate includes at least one of sodium silicate and potassium silicate; and the diatomaceous earth accounts for 40%-60% of the raw material mass, with a SiO2 content ≥85% and a specific surface area ≥20 m². 2 / g.

[0021] Diatomaceous earth possesses a naturally porous structure and a high specific surface area. Its amorphous silica serves as the active silicon source for subsequent volcanic ash reactions. Simultaneously, diatomaceous earth's low density makes it a key component in reducing the density of the board material. Controlling its dosage to 40%-60% ensures sufficient silicon source participation in the reaction while avoiding strength reduction due to excessive silicon. Modified vitrified microspheres, used as aggregate, exhibit better compatibility with the cementitious matrix after surface grafting with silane coupling agents. This further reduces board density and water absorption. The selection of stirring speed and time balances uniform fiber dispersion with preventing excessive fiber breakage, ensuring uniform mixing of all components without damaging fiber length.

[0022] In one implementation, such as Figure 3 As shown, the preparation method of the modified vitrified microspheres includes: immersing the vitrified microspheres in an alkaline solution for surface hydroxylation treatment, filtering and washing until neutral, immersing the surface-hydroxylated vitrified microspheres in a silane coupling agent solution, and reacting at room temperature for 6-8 hours to graft the silane coupling agent onto the surface of the vitrified microspheres. After the reaction is complete, filtering, washing with alcohol, and drying are performed to obtain the modified vitrified microspheres. The vitrified microspheres originally have few hydroxyl groups on their surface; immersion in the alkaline solution increases the number of surface-active hydroxyl groups. Subsequently, one end of the silane coupling agent reacts with the hydroxyl groups for grafting, while the other end carries hydrophobic groups such as amino or alkyl groups, thereby endowing the vitrified microspheres with hydrophobicity. Simultaneously, the grafted silane coupling agent can also form chemical bonds with silicates or hydration products in the cementitious material, enhancing the interfacial bonding between the aggregate and the matrix, and avoiding the strength reduction and water absorption increase caused by the weak interface of ordinary vitrified microspheres. The use of these modified vitrified microspheres can improve the dry flexural strength of the board, reduce water absorption, and help enhance the waterproof effect.

[0023] S2. The slab is pre-cured to generate an initial calcium source. First, carbonation curing with a first CO2 concentration is performed to convert the initial calcium source on the slab surface into calcium carbonate, forming a calcium carbonate layer. Then, an alkaline calcium source is added, and pre-curing is performed again. Then, carbonation curing with a second CO2 concentration is performed, and the second CO2 concentration is greater than the first CO2 concentration. A calcium carbonate-hydrated calcium silicate gradient composite phase is formed inside the slab, resulting in a cured slab.

[0024] In one implementation, such as Figure 4 As shown, Figure 4 The preparation method of step S2 is shown, specifically including: S2.1, the slab is sent into the curing room and left to stand for 8-12 hours at a temperature of 15-35℃ and a relative humidity of ≥90% to allow the cementitious components in the slab to hydrate and generate calcium hydroxide. After pre-curing, it is transferred to the carbonization kettle.

[0025] The purpose of the first pre-curing is to allow the cement and quicklime in the slab to fully hydrate and generate calcium hydroxide, which is the initial calcium source. Calcium hydroxide is a direct reactant in the subsequent carbonization reaction. The high humidity environment prevents the slab surface from drying out and cracking, while also promoting the uniformity of the hydration reaction. This pre-curing step ensures that there is enough calcium hydroxide inside the slab to participate in the first carbonization stage.

[0026] S2.2, the pre-cured slab is sent into the carbonization kettle and cured for 30-60 minutes under the conditions of CO2 volume fraction of 10%-15% and temperature of 35-45℃. This CO2 volume fraction is the first CO2 concentration. During the curing process, calcium hydroxide is converted into calcium carbonate, forming a dense calcium carbonate layer on the surface of the slab. The slab after carbonization with the first CO2 concentration is taken out, and an alkaline calcium source is sprayed onto the surface of the slab. The alkaline calcium source is a slurry of calcium hydroxide and sodium silicate.

[0027] The first CO2 concentration carbonization curing method uses a relatively low concentration of CO2, which preferentially reacts with the calcium hydroxide on the surface of the slab. Due to the moderate reaction rate, the resulting calcium carbonate crystals are tightly packed, uniformly covering and sealing the pores on the slab surface, forming a continuous and dense calcium carbonate waterproof barrier. The technical problem solved by this method is that existing lightweight slabs, due to their porous matrix, allow moisture to easily penetrate from the surface, resulting in high water absorption and poor frost resistance. If high-concentration carbonization is directly applied, CO2 will rapidly diffuse into the interior, preventing the formation of an effective dense layer on the surface. Furthermore, the internal carbonization products, clogging the pores, hinder subsequent reactions. Therefore, the first low-concentration carbonization achieves a balance between surface densification and internal permeability. The thickness of the formed calcium carbonate layer is controllable, and the 24-hour water absorption rate is reduced by more than 60% compared to uncarbonized slabs. Simultaneously, it allows subsequent high-concentration CO2 to penetrate into the interior at a controllable rate, avoiding uneven carbonization. In addition, this surface calcium carbonate layer improves the apparent hardness and wear resistance of the slab, facilitating subsequent decorative treatments. The application of alkaline calcium source is to supplement the calcium source required for subsequent deep carbonization and to introduce additional active silicon source sodium silicate to promote the full progress of the internal volcanic ash reaction.

[0028] S2.3, the slab coated with alkaline calcium source is sent back into the curing chamber and kept under a vacuum of -0.05 to -0.08 MPa for 30-60 minutes. After returning to normal pressure, it is left to stand for 1-2 hours at 40-50℃ and relative humidity ≥90% to allow the alkaline calcium source to penetrate evenly. Then it is sent back into the carbonization kettle to increase the CO2 volume fraction to 60%-80%. This CO2 volume fraction is the second CO2 concentration, which is greater than the first CO2 concentration. The temperature is raised to 55-65℃, the pressure is controlled at 0.1-0.3 MPa, and it is cured for 8-16 hours to allow the alkaline calcium source to react with the diatomaceous earth in a volcanic ash reaction, forming a calcium carbonate-hydrated calcium silicate gradient composite phase, thus obtaining the cured slab.

[0029] The second pre-curing combined with negative pressure treatment includes two stages: First, the air in the pores of the slab is extracted under negative pressure, and then normal pressure is restored, so that the alkaline calcium source sprayed on the surface can quickly penetrate into the deep interior of the slab under the combined drive of capillary force and external atmospheric pressure. Then, it is left to stand under high temperature and high humidity conditions to make the water in the slurry evenly distributed, and sodium silicate and calcium hydroxide further diffused, so as to avoid the slurry drying too quickly and forming a skin on the surface.

[0030] The problem addressed by the second pre-curing process is that simply spraying alkaline calcium source can cause the slurry to remain only on the surface of the slab, failing to effectively penetrate the interior, especially for slabs with high density or thickness. If the alkaline calcium source is not evenly distributed inside the slab, the volcanic ash reaction during subsequent high-concentration carbonization will only occur on the surface, the internal diatomaceous earth cannot be fully utilized, the gradient composite phase structure cannot be formed, the interior of the slab remains loose, and the strength improvement is limited. However, by using negative pressure-assisted penetration, the penetration depth of the alkaline calcium source can reach more than half the thickness of the slab, which is particularly suitable for slabs thicker than 10mm. The high-temperature and high-humidity settling after restoring normal pressure further promotes penetration homogenization.

[0031] The effect of this step is that the alkaline calcium source achieves a three-dimensional uniform distribution within the slab, providing sufficient and evenly distributed reactants for the subsequent pozzolanic reaction. Even with a diatomaceous earth content as high as 60%, it can be fully activated, significantly increasing the amount of internal CSH gel generated, thus ensuring the integrity and mechanical properties of the slab.

[0032] The subsequent second CO2 concentration carbonization curing was carried out under high CO2 concentration, medium temperature, and positive pressure conditions. Because a dense calcium carbonate layer already existed on the surface, the CO2 permeation rate was regulated, allowing the internal carbonization reaction and the volcanic ash reaction to occur simultaneously: the permeated CO2 reacted with calcium hydroxide in the alkaline calcium source to generate calcium carbonate, while the sodium silicate in the alkaline calcium source reacted with amorphous silica in the diatomaceous earth to generate hydrated calcium silicate gel. The resulting gradient composite phase exhibited a high calcium carbonate content and low CSH content on the surface, resulting in dense and waterproof properties; while the internal phase had a high CSH content and low calcium carbonate content, exhibiting good toughness and filling pores. The technical problems solved by this structure are: single carbonization products lead to high brittleness and poor impact resistance in the board; single hydration products lead to insufficient surface density and high water absorption; and traditional processes require high-temperature and high-pressure steam curing to promote the volcanic ash reaction, resulting in high energy consumption and fiber damage. This invention achieves a gradient structure with a dense outer layer and a tough inner layer through gradient carbonization-siliconization at medium-low temperatures up to 65°C. Compared to single carbonization, this effectively improves the drying flexural strength and impact strength, exceeding 2.5 kJ / m. 2 It also shows a significant improvement over single carbonization, with a 24-hour water absorption rate of less than 18%, while avoiding the thermal degradation of wood fibers caused by high-temperature steam pressing, and the energy consumption is only one-third of that of steam pressing curing.

[0033] S3. After curing, the slab is cooled to room temperature to obtain diatomaceous earth low-density board.

[0034] Specifically, in one embodiment, such as Figure 5 As shown, step S3 includes: after stopping the CO2 supply, cooling the cured slab to 40-60°C, spraying a silicate sealing liquid onto the slab surface, and then continuing to cool to room temperature to obtain a diatomaceous earth low-density board. The silicate sealing liquid includes at least one of sodium silicate and potassium silicate. Before spraying the sealing liquid, the slab can also be placed under vacuum conditions for degassing, with a vacuum degree of -0.06 to -0.09 MPa and a degassing time of 20-40 minutes.

[0035] The key to this post-treatment step is that the surface of the slab after carbonization curing may contain microcracks, pinholes, or unreacted active calcium. Direct cooling of these defects can create channels for moisture penetration, leading to decreased durability over long-term use. Furthermore, unreacted CO2 gas may remain inside the slab, escaping with temperature changes and causing blistering or microcracks. After spraying with silicate sealing liquid, sodium silicate or potassium silicate solution penetrates the surface microcracks and pores, reacting with residual calcium hydroxide to form CSH gel, further sealing the defects. After drying, the silicate itself forms a glassy film, increasing the surface contact angle and further improving water resistance. Vacuum degassing removes residual CO2 before spraying, preventing subsequent thermal stress cracking and making it easier for the sealing liquid to be absorbed. After treatment, the surface water absorption rate of the slab is reduced by 70%, and the freeze-thaw cycle resistance increases to over 50 cycles without abnormalities.

[0036] On the other hand, the present invention provides a diatomaceous earth low-density board, which is prepared by the above-described method. The diatomaceous earth low-density board comprises keratinized wood fiber, diatomaceous earth, cementing components, aggregates, and silicates. Keratinized wood fiber provides reinforcement and toughness support; diatomaceous earth reduces the board density and provides an active silicon source; cementing components form the board matrix and participate in carbonization and pozzolanic reactions; aggregates assist in reducing density and water absorption; and silicates react with diatomaceous earth to form hydrated calcium silicate. The surface layer of the board is a dense calcium carbonate layer, and the interior of the board has a gradient composite phase of calcium carbonate and hydrated calcium silicate, in which the calcium carbonate content decreases from the surface to the interior, and the hydrated calcium silicate content increases from the surface to the interior. The density of the board is 0.9-1.15 g / cm³. 3 Dry flexural strength > 14 MPa, impact strength > 2.5 kJ / m 2 The water absorption rate is less than 18% in 24 hours. This board can be widely used in non-load-bearing interior partition walls, floor decking, or roof panels in prefabricated buildings. It is easy to install and has excellent durability.

[0037] The technical solution and effects of the present invention are further illustrated below through specific embodiments and comparative examples. Each embodiment adopts the basic steps of the above-described embodiment, with only adjustments to the parameters, to demonstrate performance under different conditions.

[0038] Example 1: Wood fibers were placed in a 0.2% diluted lime water solution and cleaned with residual heat steam from an autoclave for 30 minutes, followed by 20 minutes of settling to remove organic impurities, resulting in purified wood fibers. The purified wood fibers were then subjected to a four-cycle wetting-drying process: each cycle involved soaking in 90℃ hot water until the wood fiber moisture content was ≥80%, followed by drying with 80℃ hot air until the moisture content was ≤10%; after the final wetting, the purified wood fibers were sprayed with 90℃ hot water to remove free waxes and fatty acids, and then dried to obtain keratinized wood fibers.

[0039] The preparation of modified vitrified microspheres includes the following steps: Vitrified microspheres are immersed in a 1 mol / L NaOH solution for 2 hours for surface hydroxylation treatment, filtered, and washed with deionized water until neutral; the hydroxylated vitrified microspheres are immersed in an ethanol solution of 2% (w / w) silane coupling agent KH-550 and reacted at room temperature for 7 hours; after the reaction is completed, the microspheres are filtered, washed with anhydrous ethanol, and dried to obtain modified vitrified microspheres with a particle size of 0.2 mm.

[0040] Weigh out diatomaceous earth, which accounts for 50% of the total mass of raw materials. Its SiO2 content is 88% and its specific surface area is 25m². 2 The mixture consists of 15% keratinized wood fiber, 10% cement, 8% quicklime, 12% modified vitrified microspheres, and 5% sodium silicate. First, the keratinized wood fiber is mixed with diatomaceous earth. Then, the modified vitrified microspheres, sodium silicate, cement, and quicklime are added, along with deionized water. The mixture is stirred at a speed of 450 rpm for 5 minutes, and then formed into slabs using a flow casting method.

[0041] The slab was placed in a curing chamber and allowed to stand for 10 hours at 25°C and 95% relative humidity to complete the first pre-curing. Afterward, it was transferred to a carbonization autoclave. The pre-cured slab was then cured for 45 minutes at 40°C and 12% CO2 to form a dense calcium carbonate layer on the surface. After removal, a mixed slurry of 5% calcium hydroxide and 3% sodium silicate was sprayed onto the slab surface. The sprayed slab was then returned to the curing chamber and maintained under a vacuum of 0.06 MPa for 40 minutes. After returning to normal pressure, it was allowed to stand for 1.5 hours at 45°C and 95% relative humidity to allow the alkaline calcium source to penetrate evenly. Subsequently, it was reintroduced into the carbonization autoclave, where the CO2 volume fraction was increased to 70%, the temperature was raised to 60°C, and the pressure was controlled at 0.2 MPa for 12 hours of curing. After stopping the CO2 supply, the temperature is lowered to 50°C, and a 10% sodium silicate sealing liquid is sprayed on. The mixture is then allowed to cool naturally to room temperature to obtain a diatomaceous earth low-density board.

[0042] Example 2: Wood fibers were placed in a 0.1% diluted lime water solution and cleaned with residual heat steam from an autoclave for 30 minutes, followed by 20 minutes of settling to remove organic impurities, resulting in purified wood fibers. The purified wood fibers were then subjected to a three-cycle wetting-drying process: each cycle involved soaking in 80°C hot water until the wood fiber moisture content was ≥80%, followed by drying with 60°C hot air until the moisture content was ≤10%; after the final wetting, the fibers were sprayed with 80°C hot water and dried to obtain keratinized wood fibers.

[0043] The preparation of modified vitrified microspheres includes the following steps: Vitrified microspheres are immersed in a 1 mol / L NaOH solution for 2 h for surface hydroxylation treatment, filtered, and washed with deionized water until neutral; the hydroxylated vitrified microspheres are immersed in an ethanol solution of 2% (w / w) silane coupling agent KH-550 and reacted at room temperature for 7 h; after the reaction is completed, the microspheres are filtered, washed with anhydrous ethanol, and dried to obtain modified vitrified microspheres with a particle size of 0.1 mm.

[0044] Weigh out 40% diatomaceous earth, 20% keratinized wood fiber, 12% cement, 5% quicklime, 15% modified vitrified microspheres, and 8% potassium silicate, which constitute the total mass of the raw materials. Mix and prepare the pulp at a speed of 300 r / min for 8 min, and then form it into a slab using the sheet forming method.

[0045] The slab was placed in a curing chamber and allowed to stand for 12 hours at 15℃ and 90% relative humidity to complete the first pre-curing. Afterward, it was transferred to a carbonization autoclave. The pre-cured slab was then cured for 60 minutes at 35℃ and 10% CO2. After removal, a mixed slurry of 4% calcium hydroxide and 4% sodium silicate was sprayed onto the surface. The sprayed slab was then returned to the curing chamber and kept under a vacuum of 0.08 MPa for 30 minutes. After returning to normal pressure, it was allowed to stand for 2 hours at 40℃ and 90% relative humidity to allow the alkaline calcium source to penetrate evenly. Finally, it was returned to the carbonization autoclave, where the CO2 volume fraction was increased to 60%, the temperature was raised to 55℃, and the pressure was controlled at 0.1 MPa for 16 hours of curing. After stopping the CO2 supply, the cured slab is placed in a vacuum drying oven and degassed at 0.08 MPa and 50°C for 30 minutes to remove residual carbon dioxide and free moisture from the slab and promote homogenization of the pore structure. Then, it is cooled to 40°C, sprayed with potassium silicate sealing solution, and allowed to cool naturally to room temperature to obtain diatomaceous earth low-density board.

[0046] Example 3: Wood fibers were placed in a 0.3% diluted lime water solution and cleaned with residual heat steam from an autoclave for 30 minutes, followed by 20 minutes of settling to remove organic impurities, resulting in purified wood fibers. The purified wood fibers were then subjected to five wetting-drying cycles. Each cycle involved soaking the fibers in 100°C hot water until the moisture content was ≥80%, followed by drying with 105°C hot air until the moisture content was ≤10%. After the final wetting, the fibers were rinsed with 100°C hot water and then dried to obtain keratinized wood fibers.

[0047] The preparation of modified vitrified microspheres includes the following steps: Vitrified microspheres are immersed in a 1 mol / L NaOH solution for 2 hours for surface hydroxylation treatment, filtered, and washed with deionized water until neutral; the hydroxylated vitrified microspheres are immersed in an ethanol solution of 2% (w / w) silane coupling agent KH-550 and reacted at room temperature for 7 hours; after the reaction is completed, the microspheres are filtered, washed with anhydrous ethanol, and dried to obtain modified vitrified microspheres with a particle size of 0.5 mm.

[0048] Weigh out 60% diatomaceous earth, 10% keratinized wood fiber, 8% cement, 7% quicklime, 10% modified vitrified microspheres, and 5% sodium silicate, which constitute the total mass of the raw materials. Mix and prepare the slurry at 600 r / min for 3 min, and then form it into a slab using the flow casting method.

[0049] The slab is placed in a curing chamber and left to stand for 8 hours at 35℃ and 95% relative humidity to complete the first pre-curing. Afterward, it is transferred to a carbonization autoclave and cured for 30 minutes at 45℃ with 15% CO2 by volume. Upon removal, a mixed slurry of 6% calcium hydroxide and 2% sodium silicate by mass is sprayed onto the surface of the slab. The sprayed slab is then returned to the curing chamber and maintained under a vacuum of 0.05 MPa for 60 minutes. After restoring to normal pressure, it is left to stand for 1 hour at 50℃ and 95% relative humidity to allow the alkaline calcium source to penetrate evenly. It is then returned to the carbonization autoclave, where the CO2 volume fraction is increased to 80%, the temperature is raised to 65℃, and the pressure is controlled at 0.3 MPa for 8 hours of curing. After stopping the CO2 supply, the temperature is lowered to 60℃, and a sodium silicate sealing liquid is sprayed on. The slab is then allowed to cool naturally to room temperature to obtain a diatomaceous earth low-density board.

[0050] Comparative Example 1: The difference from Example 1 is that in step S1, the wood fibers are not pre-treated with keratinization; instead, they are simply placed in a 0.2% diluted lime water solution, circulated with residual heat steam from an autoclave for 30 minutes, left to stand for 20 minutes to remove organic impurities, and then directly dried without undergoing a wetting-drying cycle or hot water spray rinsing. The specific preparation method is as follows: Wood fibers were placed in a 0.2% dilute lime water solution, and then circulated through a steam autoclave for 30 minutes to clean them. After standing for 20 minutes, the solution was filtered and dried with hot air at 80°C until the moisture content was ≤10%, thus obtaining unkeratinated wood fibers.

[0051] Preparation of modified vitrified microspheres: Vitrified microspheres were immersed in 1 mol / L NaOH solution for 2 h for surface hydroxylation treatment, filtered, and washed with deionized water until neutral; the hydroxylated vitrified microspheres were immersed in an ethanol solution of 2% (w / w) silane coupling agent KH-550 and reacted at room temperature for 7 h; after the reaction was completed, the microspheres were filtered, washed with anhydrous ethanol, and dried to obtain modified vitrified microspheres with a particle size of 0.2 mm.

[0052] Weigh out diatomaceous earth, which accounts for 50% of the total mass of raw materials. Its SiO2 content is 88% and its specific surface area is 25 m². 2 / g, 15% unkeratinated wood fiber, 10% cement, 8% quicklime, 12% modified vitrified microspheres, 5% sodium silicate. First, the unkeratinated wood fiber is mixed with diatomaceous earth, then the modified vitrified microspheres, sodium silicate, cement, and quicklime are added, along with deionized water and stirred. The pulping speed is 450 r / min, and the mixture is stirred for 5 min. The mixture is then formed into slabs using the flow casting method.

[0053] The slab is placed in a curing chamber and left to stand for 10 hours at 25°C and 95% relative humidity to complete the first pre-curing. Afterward, it is transferred to a carbonization autoclave. The pre-cured slab is then cured for 45 minutes at 40°C and 12% CO2 to form a dense calcium carbonate layer on the surface. After removal, a mixed slurry of 5% calcium hydroxide and 3% sodium silicate is sprayed onto the slab surface. The sprayed slab is then placed back into the curing chamber and kept under a vacuum of -0.06 MPa for 40 minutes. After returning to normal pressure, it is left to stand for 1.5 hours at 45°C and 95% relative humidity to allow the alkaline calcium source to penetrate evenly. The material is reintroduced into the carbonization autoclave, where the CO2 volume fraction is increased to 70%, the temperature is raised to 60°C, the pressure is controlled at 0.2 MPa, and the material is cured for 12 hours. After stopping the CO2 supply, the temperature is lowered to 50°C, and a 10% sodium silicate sealing liquid is sprayed on. The material is then allowed to cool naturally to room temperature to obtain a diatomaceous earth low-density board.

[0054] Comparative Example 2: The difference from Example 1 is that the two-stage carbonization curing is cancelled, and only a single high-concentration carbonization is used. That is, the first CO2 concentration carbonization and the second pre-curing are not carried out, and the alkaline calcium source is not sprayed. The specific preparation method is as follows: Wood fibers were placed in a 0.2% diluted lime water solution and cleaned with residual heat steam from an autoclave for 30 minutes, followed by 20 minutes of settling to remove organic impurities, resulting in purified wood fibers. The purified wood fibers were then subjected to a four-cycle wetting-drying process: each cycle involved soaking in 90℃ hot water until the wood fiber moisture content was ≥80%, followed by drying with 80℃ hot air until the moisture content was ≤10%; after the final wetting, the purified wood fibers were sprayed with 90℃ hot water to remove free waxes and fatty acids, and then dried to obtain keratinized wood fibers.

[0055] The preparation of modified vitrified microspheres includes the following steps: Vitrified microspheres are immersed in a 1 mol / L NaOH solution for 2 hours for surface hydroxylation treatment, filtered, and washed with deionized water until neutral; the hydroxylated vitrified microspheres are immersed in an ethanol solution of 2% (w / w) silane coupling agent KH-550 and reacted at room temperature for 7 hours; after the reaction is completed, the microspheres are filtered, washed with anhydrous ethanol, and dried to obtain modified vitrified microspheres with a particle size of 0.2 mm.

[0056] Weigh out diatomaceous earth, which accounts for 50% of the total mass of raw materials. Its SiO2 content is 88% and its specific surface area is 25 m². 2 / g, 15% keratinized wood fiber, 10% cement, 8% quicklime, 12% modified vitrified microspheres, 5% sodium silicate. First, the keratinized wood fiber is mixed with diatomaceous earth, then the modified vitrified microspheres, sodium silicate, cement, and quicklime are added, along with deionized water and stirred. The pulping speed is 450 r / min, and the mixture is stirred for 5 min. The mixture is then formed into slabs using the flow casting method.

[0057] The slabs were placed in a curing chamber and left to stand for 10 hours at 25°C and 95% relative humidity to complete the first pre-curing. Afterward, they were transferred to a carbonization autoclave. The pre-cured slabs were then subjected to a single high-concentration carbonization process: cured for 12 hours at 70% CO2 volume fraction, 60°C, and 0.2 MPa pressure. After stopping the CO2 supply, the temperature was lowered to 50°C, and a 10% sodium silicate sealing solution was sprayed on. The slabs were then allowed to cool naturally to room temperature to obtain diatomaceous earth low-density boards.

[0058] Comparative Example 3: The difference from Example 1 is that no alkaline calcium source is sprayed in step S2.2. The specific preparation method is as follows: Wood fibers were placed in a 0.2% diluted lime water solution and cleaned with residual heat steam from an autoclave for 30 minutes, followed by 20 minutes of settling to remove organic impurities, resulting in purified wood fibers. The purified wood fibers were then subjected to a four-cycle wetting-drying process: each cycle involved soaking in 90℃ hot water until the wood fiber moisture content was ≥80%, followed by drying with 80℃ hot air until the moisture content was ≤10%; after the final wetting, the purified wood fibers were sprayed with 90℃ hot water to remove free waxes and fatty acids, and then dried to obtain keratinized wood fibers.

[0059] The preparation of modified vitrified microspheres includes the following steps: Vitrified microspheres are immersed in a 1 mol / L NaOH solution for 2 hours for surface hydroxylation treatment, filtered, and washed with deionized water until neutral; the hydroxylated vitrified microspheres are immersed in an ethanol solution of 2% (w / w) silane coupling agent KH-550 and reacted at room temperature for 7 hours; after the reaction is completed, the microspheres are filtered, washed with anhydrous ethanol, and dried to obtain modified vitrified microspheres with a particle size of 0.2 mm.

[0060] Weigh out diatomaceous earth, which accounts for 50% of the total mass of raw materials. Its SiO2 content is 88% and its specific surface area is 25m². 2 / g, 15% keratinized wood fiber, 10% cement, 8% quicklime, 12% modified vitrified microspheres, 5% sodium silicate. First, the keratinized wood fiber is mixed with diatomaceous earth, then the modified vitrified microspheres, sodium silicate, cement, and quicklime are added, along with deionized water and stirred. The pulping speed is 450 r / min, and the mixture is stirred for 5 min. The mixture is then formed into slabs using the flow casting method.

[0061] The slab is placed in a curing chamber and left to stand for 10 hours at 25°C and 95% relative humidity to complete the first pre-curing. Afterward, it is transferred to a carbonization autoclave. The pre-cured slab is then cured for 45 minutes at 40°C and 12% CO2 to form a dense calcium carbonate layer on the surface. After removal, without spraying an alkaline calcium source, it is directly returned to the curing chamber and kept under a vacuum of -0.06 MPa for 40 minutes. After returning to normal pressure, it is left to stand for 1.5 hours at 45°C and 95% relative humidity. It is then returned to the carbonization autoclave, where the CO2 volume fraction is increased to 70%, the temperature is raised to 60°C, and the pressure is controlled at 0.2 MPa for 12 hours. After stopping the CO2 supply, the temperature is lowered to 50°C, and a 10% sodium silicate sealing liquid is sprayed on. The slab is then allowed to cool naturally to room temperature to obtain a diatomaceous earth low-density board.

[0062] Comparative Example 4: The difference from Example 1 is that the aggregate used is unmodified ordinary vitrified microspheres, and the specific preparation method is as follows: Wood fibers were placed in a 0.2% diluted lime water solution and cleaned with residual heat steam from an autoclave for 30 minutes, followed by 20 minutes of settling to remove organic impurities, resulting in purified wood fibers. The purified wood fibers were then subjected to a four-cycle wetting-drying process: each cycle involved soaking in 90℃ hot water until the wood fiber moisture content was ≥80%, followed by drying with 80℃ hot air until the moisture content was ≤10%; after the final wetting, the purified wood fibers were sprayed with 90℃ hot water to remove free waxes and fatty acids, and then dried to obtain keratinized wood fibers.

[0063] The aggregate used is commercially available ordinary vitrified microspheres with a particle size of 0.2mm, without any modification treatment.

[0064] Weigh out diatomaceous earth (50% of total raw material mass, SiO2 content 88%, specific surface area 25 m² / g), 15% keratinized wood fiber, 10% cement, 8% quicklime, 12% ordinary vitrified microspheres, and 5% sodium silicate. First, mix the keratinized wood fiber with the diatomaceous earth, then add the ordinary vitrified microspheres, sodium silicate, cement, and quicklime. Add deionized water and stir. The mixing speed is 450 r / min, and the mixture is stirred for 5 minutes. The mixture is then formed into slabs using the flow casting method.

[0065] The slab is placed in a curing chamber and left to stand for 10 hours at 25°C and 95% relative humidity to complete the first pre-curing. Afterward, it is transferred to a carbonization autoclave. The pre-cured slab is then cured for 45 minutes at 40°C and 12% CO2 to form a dense calcium carbonate layer on the surface. After removal, a mixed slurry of 5% calcium hydroxide and 3% sodium silicate is sprayed onto the slab surface. The sprayed slab is then placed back into the curing chamber and kept under a vacuum of -0.06 MPa for 40 minutes. After returning to normal pressure, it is left to stand for 1.5 hours at 45°C and 95% relative humidity to allow the alkaline calcium source to penetrate evenly. The material is reintroduced into the carbonization autoclave, where the CO2 volume fraction is increased to 70%, the temperature is raised to 60°C, the pressure is controlled at 0.2 MPa, and the material is cured for 12 hours. After stopping the CO2 supply, the temperature is lowered to 50°C, and a 10% sodium silicate sealing liquid is sprayed on. The material is then allowed to cool naturally to room temperature to obtain a diatomaceous earth low-density board.

[0066] The diatomaceous earth low-density boards obtained in the examples and comparative examples were subjected to relevant performance tests. The test contents and methods are as follows: Density determination: According to the method of GB / T17671-1999, measure the mass and volume of the dried board and calculate the density.

[0067] Dry flexural strength determination: A universal testing machine was used to conduct a three-point bending test according to the JC / T412.1-2018 standard. The sample size was 160mm×40mm×10mm, the span was 100mm, and the loading rate was 0.5mm / min.

[0068] Impact strength determination: According to GB / T2572-2005, a simply supported beam impact testing machine was used, with unnotched specimens and an impact energy of 2J.

[0069] 24-hour water absorption rate determination: Immerse the dried board sample in water at 20°C for 24 hours, remove it, wipe off the surface moisture, weigh it, and calculate the water absorption rate.

[0070] Table 1: Performance test results of diatomaceous earth low-density boards obtained in the examples and comparative examples.

[0071] As shown in Table 1, the performance test results of the diatomaceous earth low-density boards obtained in Examples 1-3 are better than those in Comparative Examples 1-4, with the density controlled between 0.95-1.10 g / cm³. 3 Between these values, the dry flexural strength is greater than 14 MPa, and the impact strength is greater than 2.5 kJ / m. 2 The 24-hour water absorption rate is less than 18%, demonstrating excellent overall performance. Example 1 exhibits the highest dry flexural strength and the lowest water absorption rate, showing the best performance. Example 2, with the lowest density, optimized internal pore uniformity through a vacuum degassing step in post-treatment, reducing microcracks caused by residual CO2, while still achieving an impact strength of 2.6 kJ / m³. 2 With a water absorption rate controlled at 16.8%, it exhibits excellent balance between lightweight, high strength, and waterproofing. Example 3 still maintains good mechanical properties even with a high diatomaceous earth content.

[0072] Comparative Example 1 did not undergo wood fiber cutinization pretreatment. This was because the wood fiber cell walls were not moistened. The irreversible hydrogen bond condensation during the drying cycle allows the cellulose molecular chains to retain their original hydrophilic structure and high swelling capacity. In the alkaline environment of cement, unkeratinized wood fibers easily absorb water and swell. Simultaneously, hemicellulose and lignin degrade under alkaline conditions, leading to a decrease in fiber strength and a weakening of the interfacial bond between the fiber and the cementitious matrix. Therefore, the flexural strength and impact strength of the board in Comparative Example 1 are significantly reduced during drying, while the water absorption rate is significantly increased. After pre-keratinization, the fiber cell walls become denser and less hydrophilic, thus maintaining their enhanced toughness and resistance to degradation during subsequent carbonization curing.

[0073] Comparative Example 2 omitted the two-stage carbonation curing process, employing only a single high-concentration carbonation. This example skipped the initial CO2 concentration carbonation to form a dense surface calcium carbonate layer, and also omitted the application of an alkaline calcium source and subsequent pre-curing, directly carbonizing at a high CO2 concentration. Due to the lack of the initial low-concentration carbonation, a continuous, dense calcium carbonate waterproof barrier could not form on the slab surface, allowing CO2 to rapidly diffuse into the interior, resulting in a porous and loose surface. Simultaneously, without supplementing the alkaline calcium source, the internal reaction relied solely on a small amount of calcium hydroxide generated during pre-curing, leading to an incomplete volcanic ash reaction and almost no formation of sufficient hydrated calcium silicate gel. Consequently, the strength of the board in Comparative Example 2 decreased significantly, and its water absorption remained high. This comparative result demonstrates that only by following the sequence of low-concentration surface carbonation, followed by calcium source supplementation and subsequent pre-curing, and finally high-concentration internal carbonation, can a dense surface calcium carbonate layer and an internal hydrated calcium silicate gel, forming a gradient composite phase with an outer dense and inner toughness, be achieved. Missing any step will prevent the formation of this structure.

[0074] In Comparative Example 3, no alkaline calcium source was sprayed during the second CO2 concentration carbonation stage. Although a surface calcium carbonate layer was still formed during the first CO2 concentration carbonation, and the vacuum and high-temperature, high-humidity pre-curing treatment was still underway, the total amount of calcium hydroxide generated by the slab itself during pre-curing was limited, and most of it was consumed in the formation of surface calcium carbonate during the first carbonation stage. This resulted in a severe shortage of calcium and silicon sources within the slab. Without external supplementation of alkaline calcium sources, the volcanic ash reaction could hardly occur, and the amount of hydrated calcium silicate gel generated was extremely small. Therefore, the internal pores of the slab were not effectively filled, the matrix was loose, and both strength and water resistance decreased significantly. This demonstrates that relying solely on the calcium hydroxide generated by the slab's own hydration cannot provide sufficient calcium and silicon sources. An additional spray of alkaline calcium source and subsequent pre-curing to ensure uniform penetration are necessary to generate sufficient hydrated calcium silicate gel to fill the internal pores during the second carbonization stage.

[0075] Comparative Example 4 used unmodified ordinary vitrified microspheres. Ordinary vitrified microspheres have few hydroxyl groups on their surface, are highly hydrophilic, and have a smooth surface. They lack chemical bonds with the cementitious silicate matrix, resulting in weak interfacial adhesion. Under stress, the vitrified microspheres easily detach from the matrix, leading to crack propagation. Simultaneously, their porous structure is directly exposed to the environment, allowing moisture to easily penetrate into the board along the aggregate interface. Compared to the modified vitrified microspheres used in the examples, the water absorption rate of the board in Comparative Example 4 increased significantly, and both its dry flexural strength and impact strength decreased. Therefore, using vitrified microspheres grafted with a silane coupling agent, which have a hydrophobic surface and can form chemical bonds with the matrix, helps reduce the water absorption rate of the board and improve its mechanical properties.

[0076] Furthermore, Example 2, compared to Example 1, added a vacuum degassing step in the post-processing stage, maintaining excellent impact resistance and low water absorption even with lower density. This indicates that vacuum degassing can effectively remove residual CO2 and free moisture from the slab, reduce microcrack formation, promote homogenization of pore structure, and thus further improve the overall performance of the slab.

[0077] Application Example 1: The diatomaceous earth low-density board prepared in Example 2 was used in the non-load-bearing interior partition system of prefabricated buildings. The standard size of the board is 2440 mm × 1220 mm × 10 mm, and it can be cut into any size according to actual needs. Since the board adopts wood fiber keratinization pretreatment, the fiber cell wall is densified and the hydrophilicity is significantly reduced. Therefore, the board is not easy to chip during the cutting process, the cut is neat, and the processing adaptability is good.

[0078] The density of the board is 0.9-1.15 g / cm³. 3Its density is significantly lower than that of traditional cement fiberboard. This low-density characteristic mainly stems from the porous structure of diatomaceous earth and the lightweight aggregate of modified vitrified microspheres. The low density significantly reduces the building load, making it particularly suitable for high-rise prefabricated buildings, allowing for a corresponding reduction in beam and column cross-sectional dimensions and saving structural materials.

[0079] The dry flexural strength of the board is greater than 14 MPa, and the impact strength is greater than 2.5 kJ / m. 2 The source of this high strength and high toughness lies in the gradient composite phase structure formed by the dense calcium carbonate layer on the surface, which is formed by carbonization at the first CO2 concentration, and the hydrated calcium silicate gel inside, which is formed by carbonization at the second CO2 concentration and reaction with volcanic ash. The surface calcium carbonate layer gives the board good rigidity, while the hydrated calcium silicate gel inside fills the pores and forms a tight composite with the keratinized wood fibers, so that the board only shows local indentations and no through cracks when subjected to impact, thus possessing both rigidity and toughness.

[0080] The 24-hour water absorption rate of the board is less than 18%. This low water absorption rate is achieved through the waterproof barrier effect of the dense calcium carbonate layer on the surface, the hydrophobic modification of the surface of the modified vitrified microspheres, and the sealing of microcracks by the post-treatment silicate sealing liquid. Therefore, the board exhibits minimal volume change in humid environments or during seasons with fluctuating humidity, preventing cracking at the board seams or peeling of the finishing layer due to moisture absorption and ensuring long-term dimensional stability.

[0081] Furthermore, the board's fire performance rating reaches A2. Because the board contains a large amount of inorganic cementitious components, diatomaceous earth, and modified vitrified microspheres, the keratinized wood fibers are fully encapsulated within the inorganic matrix, making it less susceptible to direct exposure to flames when heated. In the event of a fire, the board does not burn or release toxic fumes, meeting the requirements of building fire protection codes.

[0082] In summary, the diatomaceous earth low-density board and its preparation method provided by this invention, through the synergistic effects of wood fiber cutinization pretreatment, first CO2 concentration carbonization to form a dense surface layer, addition of an alkaline calcium source followed by pre-curing and negative pressure-assisted infiltration and high-temperature and high-humidity homogenization, and second CO2 concentration carbonization triggering a volcanic ash reaction to generate internal hydrated calcium silicate gel, successfully prepares an environmentally friendly board with low density, high strength, and low water absorption. This method avoids the thermal degradation and alkaline hydrolysis of wood fibers caused by traditional high-temperature autoclaving. All reactions are completed under medium and low temperature conditions, conforming to the green and low-carbon concept. The resulting board is suitable for prefabricated wall panels, floor decking, and other building applications.

[0083] Other embodiments of this disclosure will readily occur to those skilled in the art upon consideration of the specification and practice of the invention disclosed herein. This application 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 examples are to be considered exemplary only, and the true scope and spirit of this disclosure are indicated by the following claims.

[0084] It should be understood that this disclosure is not limited to the precise structures described above and shown in the accompanying drawings, and various modifications and changes can be made without departing from its scope. The scope of this disclosure is limited only by the appended claims.

Claims

1. A method for preparing a low-density diatomaceous earth board, characterized in that, Includes the following steps: S1, the wood fiber is pre-treated by keratinization to reduce hydrophilicity, resulting in keratinized wood fiber, which is then mixed with diatomaceous earth and auxiliary materials to form pulp and molded into a board blank; S2, the slab is pre-cured to generate an initial calcium source. First, carbonation curing with a first CO2 concentration is performed to convert the initial calcium source on the slab surface into calcium carbonate, forming a calcium carbonate layer. Then, an alkaline calcium source is added, and pre-curing is performed again. Then, carbonation curing with a second CO2 concentration is performed, and the second CO2 concentration is greater than the first CO2 concentration. A calcium carbonate-hydrated calcium silicate gradient composite phase is formed inside the slab to obtain the cured slab. S3. After curing, the slab is cooled to room temperature to obtain diatomaceous earth low-density board.

2. The method for preparing diatomaceous earth low-density board according to claim 1, characterized in that, Step S1 includes: S1.1, the wood fiber is placed in a 0.1%-0.3% dilute lime water solution, and the residual heat steam from the autoclave is passed through for circulating cleaning. After standing, organic impurities are removed to obtain purified wood fiber. Then, the wood fiber undergoes 3-5 wetting-drying cycles to complete the keratinization treatment. After the last wetting, the purified wood fiber is sprayed with hot water at 80-100℃ to remove free wax and fatty acids. After drying, the pretreated wood fiber is obtained. S1.2, pretreated wood fiber is mixed with diatomaceous earth, then aggregate, silicate and cementing components are added and mixed evenly. The mixture is formed by flow casting or sheet forming. The stirring speed is 300-600 r / min and the stirring time is 3-8 min to obtain a slab.

3. The method for preparing diatomaceous earth low-density board according to claim 2, characterized in that, The temperature of the waste heat steam in the autoclave is 80-100℃, the circulation cleaning time is 20-40min, the wetting is to soak until the moisture content of the wood fiber is ≥80%, and the drying is to dry with hot air at 60-105℃ until the moisture content of the wood fiber is ≤10%.

4. The method for preparing diatomaceous earth low-density board according to claim 2, characterized in that, In step S1, the auxiliary materials include cementitious components, aggregates, and silicates. The cementitious components include cement and quicklime. The aggregates are modified vitrified microspheres with a particle size of 0.1-0.5 mm. The silicates include at least one of sodium silicate and potassium silicate. The diatomaceous earth accounts for 40%-60% of the raw material mass, with a SiO2 content ≥85% and a specific surface area ≥20 m². 2 / g.

5. The method for preparing diatomaceous earth low-density board according to claim 4, characterized in that, The method for preparing the modified vitrified microspheres includes: The vitrified microspheres were immersed in an alkaline solution for surface hydroxylation treatment. After filtration and washing until neutral, the surface-hydroxylated vitrified microspheres were immersed in a silane coupling agent solution and reacted at room temperature for 6-8 hours to graft the silane coupling agent onto the surface of the vitrified microspheres. After the reaction was completed, the microspheres were filtered, washed with alcohol, and dried to obtain the modified vitrified microspheres.

6. The method for preparing diatomaceous earth low-density board according to claim 1, characterized in that, Step S2 includes: S2.1, the slab is sent into the curing room and left to stand for 8-12 hours at a temperature of 15-35℃ and a relative humidity of ≥90% to allow the cementitious components in the slab to hydrate and generate calcium hydroxide. After pre-curing, it is transferred to the carbonization kettle. S2.2, the pre-cured slab is sent into the carbonization kettle and cured for 30-60 minutes under the conditions of CO2 volume fraction of 10%-15% and temperature of 35-45℃, so that calcium hydroxide is converted into calcium carbonate and a dense calcium carbonate layer is formed on the surface of the slab. The slab after carbonization with the first CO2 concentration is taken out and an alkaline calcium source is sprayed onto the surface of the slab. S2.3, the slab after being sprayed with alkaline calcium source is sent back into the curing chamber and kept under a vacuum of -0.05~-0.08MPa for 30-60 minutes. Then, it is allowed to stand for 1-2 hours at normal pressure, 40-50℃ and relative humidity ≥90% to allow the alkaline calcium source to penetrate evenly. It is then sent back into the carbonization autoclave, and the CO2 volume fraction is increased to 60%-80%, the temperature is raised to 55-65℃, the pressure is controlled at 0.1-0.3MPa, and it is cured for 8-16 hours to allow the alkaline calcium source to react with the diatomaceous earth in a volcanic ash reaction to form a calcium carbonate-hydrated calcium silicate gradient composite phase, thus obtaining the cured slab.

7. The method for preparing diatomaceous earth low-density board according to claim 6, characterized in that, The alkaline calcium source is a slurry of calcium hydroxide and sodium silicate, and the mass ratio of calcium hydroxide to sodium silicate in the alkaline calcium source is 1-3:

1.

8. The method for preparing diatomaceous earth low-density board according to claim 1, characterized in that, Step S3 includes: after stopping the CO2 supply, cooling the cured slab to 40-60°C, spraying silicate sealing liquid onto the slab surface, and then continuing to cool to room temperature to obtain diatomaceous earth low-density board, wherein the silicate sealing liquid includes at least one of sodium silicate and potassium silicate.

9. The method for preparing diatomaceous earth low-density board according to claim 8, characterized in that, Before spraying silicate sealing liquid onto the slab surface in step S3, the slab is placed under vacuum for degassing treatment. The treatment conditions are a vacuum degree of -0.06 to -0.09 MPa and a degassing time of 20-40 min.

10. A diatomaceous earth low-density board, manufactured by the method for preparing diatomaceous earth low-density board as described in any one of claims 1-9, characterized in that, The diatomaceous earth low-density board comprises keratinized wood fiber, diatomaceous earth, cementing components, aggregates, and silicates. The surface of the board is a dense calcium carbonate layer, and the interior of the board has a gradient composite phase of calcium carbonate and hydrated calcium silicate. In the gradient composite phase, the calcium carbonate content decreases from the surface of the board to the interior, and the hydrated calcium silicate content increases from the surface to the interior.

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