Xonotlite composite thermal insulation material and preparation method thereof

Abstract

The invention belongs to the technical field of thermal insulation materials, and relates to a xonotlite composite thermal insulation material and a preparation method thereof. The xonotlite composite thermal insulation material is prepared from the following raw materials: biomass ash, a calcium raw material, a reaction accelerator, a temperature-resistant modifier, porous minerals and deionized water. According to the method, the biomass ash is used as a silicon source, the C-S-H seed crystal is used as a reaction accelerant and reacts with the calcium raw material to form xonotlite, so that recycling and high-value utilization of agricultural wastes are realized, and the cost of the raw materials is reduced.

Description

Technical Field

[0001] This invention belongs to the technical field of thermal insulation materials, and in particular relates to a hard silica-calcium stone composite thermal insulation material and its preparation method. Background Technology

[0002] Driven by both global energy transition and rapid industrial development, my country's economy has maintained steady growth, with heavy industries such as aerospace, metallurgy, and chemical energy experiencing particularly rapid development. This rapid expansion has led to a year-on-year increase in total energy consumption, highlighting the growing imbalance between energy supply and demand. Under these challenging circumstances, improving comprehensive energy utilization and reducing energy losses have become crucial for achieving sustainable development.

[0003] In high-temperature industrial production scenarios, such as metallurgical furnaces, chemical reactors, and thermal power generation equipment, a large amount of heat energy is lost into the environment through the equipment surface, resulting in energy waste. To effectively reduce heat loss, the application of thermal insulation materials has become an important technical means. Traditional inorganic thermal insulation materials, such as rock wool boards, foamed cement boards, and expanded perlite boards, once held an important position in the building and industrial insulation fields due to their wide availability and relatively low cost. However, these materials have revealed many drawbacks in practical applications: rock wool boards, when exposed to humid environments for extended periods, easily absorb water and swell, leading to board deformation and a significant decrease in insulation performance. Simultaneously, the fibers are prone to detachment, posing health and safety hazards. Foamed cement boards have uneven internal pore structures, making them highly susceptible to cracking under drastic temperature changes or mechanical stress, thus compromising the overall insulation effect. Expanded perlite boards have low strength, are easily damaged during handling and construction, and are highly hygroscopic, with a significantly increased thermal conductivity after absorbing moisture, making it difficult to meet long-term stable insulation requirements. These defects not only severely shorten the service life of materials, but also increase maintenance costs and resource consumption due to frequent replacements, making it difficult to meet the stringent requirements of modern industry for high-efficiency and energy-saving materials.

[0004] Hard calcium silicate is a layered, chain-like calcium silicate crystal. Due to its excellent high-temperature resistance, low thermal conductivity, and high flame retardancy, it is widely used in chemical pipeline insulation, industrial kiln insulation, and ship bulkheads. Its porous structure formed by interwoven microfibers endows the material with lightweight properties. However, traditional methods for synthesizing hard calcium silicate suffer from drawbacks such as high raw material costs, low strength, and insufficient porosity control, limiting its large-scale application. Summary of the Invention

[0005] In view of this, the purpose of this invention is to provide a hard silica-calcium stone composite thermal insulation material and its preparation method, which can reduce the cost of thermal insulation materials.

[0006] The technical solution adopted in this invention is as follows: A hard silica-calcium stone composite thermal insulation material, characterized in that, by weight, the raw materials used include: 10-15 parts biomass ash, 8-20 parts calcium raw materials, 0.1-0.3 parts reaction accelerator, 0.1-0.3 parts temperature-resistant modifier, 10-20 parts porous minerals, and 400-600 parts deionized water.

[0007] The biomass ash is one or more of rice husk ash, bamboo fiber ash, and straw ash, with a particle size of 50-100μm.

[0008] Rice husk ash, bamboo fiber ash, and straw ash are substances produced after burning rice husks, bamboo fibers, and straw, respectively.

[0009] The calcium-based raw material is one of quicklime, carbide slag, or a mixture thereof, with a particle size of 50-500 μm.

[0010] The reaction promoter is a CSH seed crystal with a particle size of 50-200 nm.

[0011] The temperature-resistant modifier is one or more of zirconium nitrate, cerium nitrate, and lanthanum nitrate, with a particle size of 1-100 μm.

[0012] The porous mineral is one or more of volcanic rock, zeolite, and expanded perlite, with a particle size of 50-500 μm.

[0013] A method for preparing hard silica-calcium stone composite thermal insulation material includes the following steps: 1) Biomass ash is soaked in dilute acid, washed, dried and then calcined to obtain pretreated biomass ash; 2) Mix and stir the pretreated biomass ash, calcareous raw materials, reaction accelerator, temperature resistant modifier, porous minerals, and deionized water (stirring speed 300-500 r / min, stirring time 1-2h) until uniform to obtain a mixed slurry; 3) The mixed slurry is heated to react. After the reaction is completed, it is cooled, filtered and molded, and dried to obtain hard silica-calcium stone composite thermal insulation material.

[0014] In step 1), the mass fraction of dilute acid is 3-8%, the soaking time is 12-24 hours, and the filtrate is washed until the pH is 6.5-7.5.

[0015] In step 1), the drying temperature is 50-70℃ and the drying time is 4-6h; the calcination temperature is 550-700℃ and the calcination time is 1.5-2.5h.

[0016] In step 3), the reaction temperature is 200-230℃ and the time is 6-10h.

[0017] In step 3), the pressure of the hydrothermal synthesis reactor used in the reaction process is 1.5-3.0 MPa; stirring is maintained during the reaction process at a stirring rate of 150-250 r / min.

[0018] In step 3), the product is placed in a forced-air drying oven and dried at 90-110℃ for 12-24 hours.

[0019] Compared with the prior art, the beneficial technical effects of the present invention are: In this invention, biomass ash is used as a raw material. Biomass ash is an agricultural waste that is widely available and inexpensive. After pretreatment with dilute acid and calcination, metallic impurities (such as Fe) in the biomass ash are effectively removed. 3+ Al 3+ (etc.) and residual organic matter, transforming biomass ash into amorphous SiO2 templates with high specific surface area and abundant three-dimensional interconnected channels. This not only realizes the resource utilization and high-value utilization of agricultural waste and reduces raw material costs, but also conforms to the development direction of green chemical industry.

[0020] In this invention, biomass ash serves as the silicon source, reacting with calcium-based raw materials to form hard calcium silicate. During the synthesis process, lanthanum nitrate, cerium nitrate, or zirconium nitrate are incorporated as temperature-resistant modifiers. By replacing some calcium ions to form stronger lanthanum-oxygen, cerium-oxygen, and zirconium-oxygen bonds, the stability of hard calcium silicate is improved, thereby enhancing its temperature resistance. Furthermore, the introduction of these lanthanum, cerium, and zirconium ions alters the crystal structure of hard calcium silicate, creating lattice distortion. Lattice distortion increases the defect concentration within the crystal, and these defects effectively scatter phonons, reducing their propagation speed and thus decreasing the material's thermal conductivity.

[0021] CSH seed crystals are used as reaction promoters. CSH seed crystals possess extremely high specific surface area and abundant surface active sites, providing numerous nucleation centers for the growth of hard silicate crystals. The presence of CSH seed crystals allows calcium and silicate ions in the solution to rapidly aggregate and precipitate on the seed crystal surface, significantly reducing the activation energy required for nucleation and thus accelerating the nucleation process of hard silicate crystals.

[0022] The introduction of porous minerals (volcanic rocks, zeolites, expanded perlite, etc.) into the composite of hard calcium silicate has brought about a multifaceted synergistic effect. From the perspective of thermal insulation performance, these porous minerals themselves have a rich pore structure, which increases the porosity of the hard calcium silicate composite insulation material, further enhancing the overall thermal insulation effect of the material. In terms of the mechanical properties of the material, porous minerals have high hardness and strength. They are uniformly dispersed in the hard calcium silicate matrix, acting as a reinforcing skeleton and effectively improving the compressive and flexural strength of the material. At the same time, these porous minerals are abundant in nature and inexpensive, and large-scale application will not cause excessive consumption of resources, which is in line with the development trend of green building materials.

[0023] This invention fully utilizes industrial solid waste such as calcium carbide slag as a calcium-based raw material, achieving a dual improvement in environmental and economic benefits. Calcium carbide slag is the main solid waste generated during the calcium carbide process for producing polyvinyl chloride (PVC). Its large-scale accumulation not only occupies a significant amount of land resources but also causes serious pollution to soil, water, and the atmosphere. Applying calcium carbide slag to the preparation of hard silica-calcium stone composite insulation materials not only effectively solves the problem of calcium carbide slag disposal and reduces environmental pollution but also achieves high-value-added utilization of industrial solid waste. Attached Figure Description

[0024] Figure 1 This is a diagram showing the appearance of the reaction products; Figure 2 The image shows the XRD pattern of the reaction products. Detailed Implementation

[0025] The following examples illustrate specific implementations of the present invention. However, these examples are merely for illustrative purposes and do not limit the scope of the invention in any way.

[0026] Example 1: A method for preparing a hard silica-calcium stone composite thermal insulation material includes the following steps: 1) Weigh out 100g of rice husk ash, 80g of quicklime, 1g of CSH seed crystals, 1g of zirconium nitrate, 100g of volcanic rock, and 4000g of deionized water; 2) Soak rice husk ash in 3% dilute hydrochloric acid for 12 hours, wash with water until the pH of the filtrate is 7.0, dry at 50℃ for 4 hours, and then calcine in a muffle furnace at 550℃ for 1.5 hours to obtain pretreated rice husk ash. 3) Mix the pretreated rice husk ash with other raw materials and stir at a stirring rate of 300 r / min for 1 hour to obtain a mixed slurry; 4) Place the mixed slurry in a hydrothermal synthesis reactor and react at 200℃ for 6 hours. During the reaction, the pressure of the hydrothermal synthesis reactor is 1.5MPa, and the stirring rate is maintained at 150r / min. 5) After the reaction is complete, allow it to cool naturally. After pressing and filtration, place it in a forced-air drying oven and dry at 90℃ for 12 hours to obtain hard silica-calcium stone composite insulation material. The pressed and filtered material is in plate shape, which is the hard silica-calcium stone composite insulation board.

[0027] The appearance of the product after the reaction is shown in the figure. Figure 1 As shown, the hard calcium silicate prepared using rice husk ash as the silicon source is a black powder, which differs from the white hard calcium silicate prepared using pure silica as the silicon source. This difference may be due to the presence of impurity ions (such as Fe) that were not completely removed in the rice husk ash. 3+ Mn 2+ (etc.), the product was subjected to XRD detection, and the results are as follows: Figure 2 As shown, by Figure 2 It can be seen that the main phase of the hard silicate calcium stone composite insulation material obtained by the reaction is hard silicate calcium stone, and it has good crystallinity and high peak intensity.

[0028] Example 2 A method for preparing a hard silica-calcium stone composite thermal insulation material includes the following steps: 1) 100g bamboo fiber ash, 90g quicklime, 2g CSH seed crystals, 1g cerium nitrate, 120g zeolite, 5000g deionized water; 2) Soak bamboo fiber ash in 5% dilute hydrochloric acid for 12 hours, wash until the pH of the filtrate is 7.0, dry at 60℃ for 4 hours, and then calcine in a muffle furnace at 600℃ for 2 hours to obtain pretreated bamboo fiber ash. 3) Mix the pretreated bamboo fiber ash with other raw materials and stir at a stirring rate of 400 r / min for 1.5 h to obtain a mixed slurry; 4) Place the mixed slurry in a hydrothermal synthesis reactor and react at 210℃ for 8 hours. During the reaction, the pressure in the hydrothermal synthesis reactor is 2MPa, and the stirring rate is maintained at 200r / min. 5) After the reaction is complete, allow it to cool naturally. After pressing and filtration, place it in a forced-air drying oven and dry at 100℃ for 18 hours to obtain hard silica-calcium stone composite insulation material. Press and filter it into a plate shape, which is the hard silica-calcium stone composite insulation board.

[0029] Example 3 A method for preparing a hard silica-calcium stone composite thermal insulation material includes the following steps: 1) 100g straw ash, 100g quicklime, 3g CSH seed crystals, 1g lanthanum nitrate, 140g expanded perlite, 6000g deionized water; 2) Soak straw ash in 8% dilute hydrochloric acid for 12 hours, wash until the pH of the filtrate is 7.0, dry at 70℃ for 4 hours, and then calcine in a muffle furnace at 700℃ for 2.5 hours to obtain pretreated straw ash; 3) Mix the pretreated straw ash with other raw materials and stir at a stirring rate of 500 r / min for 2 hours to obtain a mixed slurry; 4) Place the mixed slurry in a hydrothermal synthesis reactor and react at 230℃ for 10 hours. During the reaction, the pressure in the hydrothermal synthesis reactor is 3MPa, and the stirring rate is maintained at 250r / min. 5) After the reaction is complete, allow it to cool naturally. After filtration, place it in a forced-air drying oven and dry at 110℃ for 24 hours to obtain the hard silica-calcium stone composite insulation material. Press and filter the material into a plate shape to obtain the hard silica-calcium stone composite insulation board.

[0030] Example 4 A method for preparing a hard silica-calcium stone composite thermal insulation material includes the following steps: 1) Weigh out 100g of rice husk ash, 100g of carbide slag, 1g of CSH seed crystals, a mixture of 0.5g of zirconium nitrate and 0.5g of lanthanum nitrate, 120 parts of volcanic rock, and 4000g of deionized water.

[0031] 2) Soak rice husk ash in 3% dilute hydrochloric acid for 12 hours, wash until the pH of the filtrate is 7.0, dry at 50℃ for 4 hours, and then calcine in a muffle furnace at 550℃ for 1.5 hours to obtain pretreated rice husk ash. 3) Mix the pretreated rice husk ash with other raw materials and stir at a stirring rate of 300 r / min for 1 hour to obtain a mixed slurry; 4) Place the mixed slurry in a hydrothermal synthesis reactor and react at 200℃ for 6 hours. During the reaction, the pressure of the hydrothermal synthesis reactor is 1.5MPa, and the stirring rate is maintained at 150r / min. 5) After the reaction is complete, allow it to cool naturally. After filtration, place it in a forced-air drying oven and dry at 90℃ for 12 hours to obtain the hard silica-calcium stone composite insulation material. Press and filter the material into a plate shape to obtain the hard silica-calcium stone composite insulation board.

[0032] Example 5 Unlike Example 4, the temperature-resistant modifier used was a mixture of 0.5g zirconium nitrate and 0.5g cerium nitrate.

[0033] Example 6 Unlike Example 4, the temperature-resistant modifier used was a mixture of 0.5g lanthanum nitrate and 0.5g cerium nitrate.

[0034] Example 7 Unlike Example 1, the raw materials used are: 100g rice husk ash, 80g quicklime, 1g zirconium nitrate, 100g volcanic rock, and 4000g deionized water.

[0035] Example 8 Unlike Example 1, the raw materials used are: 100g rice husk ash, 80g quicklime, 1g CSH seed crystals, 100g volcanic rock, and 4000g deionized water.

[0036] Example 9 Unlike Example 1, the raw materials used are: 100g rice husk ash, 80g quicklime, 1g CSH seed crystals, 1g zirconium nitrate, and 4000g deionized water.

[0037] Example 10 Unlike Example 1, the raw materials used are: 100g of rice husk ash, 150g of quicklime, 1g of CSH seed crystals, 1g of zirconium nitrate, 100g of volcanic rock, and 4000g of deionized water.

[0038] Example 11 The difference from Example 1 is: Step 4) Place the mixed slurry in a hydrothermal synthesis reactor and react at 250°C for 6 hours. During the reaction, the pressure of the hydrothermal synthesis reactor is 1.5 MPa, and the stirring rate is maintained at 150 r / min.

[0039] Example 12 The difference from Example 1 is: Step 4) Place the mixed slurry in a hydrothermal synthesis reactor and react at 150°C for 6 hours. During the reaction, the pressure of the hydrothermal synthesis reactor is 1.5 MPa, and the stirring rate is maintained at 150 r / min.

[0040] In Examples 1-12, the filter presses were molded into plates to obtain hard silica-calcium stone composite insulation boards. The room temperature thermal conductivity, porosity, compressive strength, and flexural strength of these boards were measured, and the results are shown in the table below. Group Thermal conductivity (room temperature) Porosity (%) Compressive strength (MPa) Flexural strength (MPa) Example 1 0.055 75 1.9 0.60 Example 2 0.051 81 1.8 0.58 Example 3 0.040 86 1.7 0.55 Example 4 0.052 76 1.7 0.56 Example 5 0.048 83 1.6 0.54 Example 6 0.035 91 1.4 0.52 Example 7 0.065 69 1.2 0.45 Example 8 0.059 72 1.3 0.51 Example 9 0.050 79 0.5 0.22 Example 10 0.062 65 0.7 0.28 Example 11 0.067 62 0.8 0.29 Example 12 0.060 71 1.0 0.29 The results in the table above show that the addition of heat-resistant modifiers can refine the hard silica calcium stone crystals and reduce the thermal conductivity. In particular, when heat-resistant modifiers are added in combination, such as when lanthanum nitrate and cerium nitrate, zirconium nitrate and cerium nitrate, or lanthanum nitrate and zirconium nitrate are used in combination, the thermal conductivity is further reduced and the porosity is increased.

[0041] When the temperature-resistant modifier was absent (Example 8), its thermal conductivity was significantly increased compared to when the temperature-resistant modifier was added, and its porosity was reduced, indicating that the temperature-resistant modifier can improve the thermal insulation ability of hard silicate.

[0042] The reaction promoter has a significant promoting effect on the synthesis of calcareous silica, and can significantly improve the crystallinity of calcareous silica. When the addition of CSH seed crystals is lacking (Example 7), its poor crystallinity results in a significantly higher thermal conductivity than that of Example 1.

[0043] Porous minerals (volcanic rocks, zeolites, expanded perlite) contain numerous pores, resulting in low thermal conductivity. When combined with calcium silicate, they can reduce the overall thermal conductivity of the calcium silicate composite insulation material. Simultaneously, porous minerals possess structural strength, forming a framework within the material to support the overall structure, thereby improving the material's compressive and flexural strength.

[0044] When the addition of porous minerals is absent (Example 9), the porosity is lower than that of Example 1, the thermal conductivity is higher, and the compressive strength and flexural strength are significantly reduced.

[0045] As can be seen from Example 10, the calcium-to-silica ratio is also a key factor in the synthesis of hard calcium silicate. An appropriate increase in the calcium-to-silica ratio helps to increase the pH of the solution and promote the reaction. However, excessive use of quicklime / carbide slag (Ca / Si>1.5) can easily lead to the reaction of excess CaO to generate Ca(OH)2, which has an adverse effect on the thermal insulation performance of the hard calcium silicate composite insulation material.

[0046] As can be seen from the table above, the hydrothermal reaction temperature is an important factor affecting the thermal conductivity and porosity: the 200-230℃ range can better promote the directional growth and interweaving of hard silica calcium stone fibers, forming a denser porous network, which increases the porosity and reduces the thermal conductivity.

[0047] When the temperature is too high (Example 11), the thermal conductivity increases significantly and the insulation performance decreases because the hard silicate decomposes into wollastonite.

[0048] When the temperature is too low (Example 12), the main product is tobermorite, and hard silicate cannot be formed, thus the thermal conductivity increases and the thermal insulation performance decreases.

[0049] This invention uses biomass ash as the silicon source, carbide slag as the calcium source, and additives such as temperature-resistant modifiers, reaction promoters, and porous minerals to prepare a modified hard silica-calcium stone composite insulation material with excellent thermal insulation performance, high compressive strength, and high flexural strength. Its raw material cost is lower than that of the traditional quartz sand-lime process, as shown in the table below (based on the production of one ton of product): Cost items Traditional method (yuan) This invention (RMB) silicon source Quartz sand (400 mesh): 450-700 Rice husk ash, bamboo fiber ash, straw ash: 100-200 Calcium source Quicklime: 250-400 Carbide slag: 15-60 reaction promoters 0 CSH seed crystals: 15-20 Temperature resistance modifier 0 Zirconium nitrate, lanthanum nitrate, cerium nitrate: 25-100 Porous minerals 0 Volcanic rock, zeolite, expanded perlite: 150-300 As can be seen from the table above, the raw material cost is greatly reduced by using biomass ash as the silicon source and carbide slag as the calcium source. Although the reaction promoter and temperature-resistant modifier added in this invention are expensive, the amount used is small, and the overall raw material cost is reduced by about 50%.

[0050] Thermal conductivity, porosity, compressive strength, and flexural strength are determined according to the following standards: Thermal conductivity: The test was conducted according to GB / T 10294-2008 "Determination of steady-state thermal resistance and related properties of thermal insulation materials - protective hot plate method". The test temperature was room temperature (25℃±2℃), the sample size was 50mm×50mm×25mm, and the temperature difference was set to 20℃.

[0051] Porosity: Apparent porosity was determined by vacuum method according to GB / T 2997-2000 "Test Methods for Bulk Density, Apparent Porosity and True Porosity of Dense Shaped Refractory Products". The sample was a cube of 50mm×50mm×50mm and dried to constant weight at 110℃ before testing.

[0052] Compressive strength: Refer to GB / T 5486-2008 "Test Methods for Inorganic Rigid Thermal Insulation Products", use a 50mm×50mm×50mm cube specimen, load it on a pressure testing machine at a speed of 10mm / min until the specimen fails, and calculate the compressive strength.

[0053] Flexural strength: The strength of cement mortar was tested according to the three-point bending method in GB / T 17671-2021 "Test Method for Strength of Cement Mortar (ISO Method)". The sample size was 40mm×40mm×160mm, the span was 100mm, the loading rate was 50N / s, the maximum load at which the sample broke was recorded, and the flexural strength was calculated.

[0054] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit it. Any other modifications or equivalent substitutions made by those skilled in the art to the technical solutions of the present invention, as long as they do not depart from the spirit and scope of the technical solutions of the present invention, should be covered within the scope of the claims of the present invention.

Claims

1. A hard silica-calcium stone composite thermal insulation material, characterized in that, By weight, the raw materials used include: 10-15 parts biomass ash, 8-20 parts calcium raw materials, 0.1-0.3 parts reaction promoter, 0.1-0.3 parts temperature resistant modifier, 10-20 parts porous minerals, and 400-600 parts deionized water.

2. The hard silica-calcium stone composite thermal insulation material according to claim 1, characterized in that: The biomass ash is one or more of rice husk ash, bamboo fiber ash, and straw ash.

3. The hard silica-calcium stone composite thermal insulation material according to claim 1 or 2, characterized in that: The calcium-based raw material is one or both of quicklime and carbide slag.

4. The hard silica-calcium stone composite thermal insulation material according to claim 1 or 2, characterized in that: The reaction promoter is a CSH seed crystal.

5. The hard silica-calcium stone composite thermal insulation material according to claim 1 or 2, characterized in that: The temperature-resistant modifier is one or more of zirconium nitrate, cerium nitrate, and lanthanum nitrate.

6. The hard silica-calcium stone composite thermal insulation material according to claim 1 or 2, characterized in that: The porous mineral is one or more of volcanic rock, zeolite, and expanded perlite.

7. A method for preparing the hard silica-calcium stone composite thermal insulation material according to claim 1, characterized in that, Includes the following steps: 1) Biomass ash is soaked in dilute acid, washed, dried and then calcined to obtain pretreated biomass ash; 2) Mix the pretreated biomass ash, calcareous raw materials, reaction accelerator, temperature-resistant modifier, porous minerals, and deionized water evenly to obtain a mixed slurry; 3) The mixed slurry is heated to react. After the reaction is completed, it is cooled, filtered and molded, and dried to obtain hard silica-calcium stone composite thermal insulation material.

8. The preparation method according to claim 7, characterized in that: In step 1), the mass fraction of dilute acid is 3-8%, the soaking time is 12-24 hours, and the filtrate is washed until the pH is 6.5-7.

5.

9. The preparation method according to claim 7, characterized in that: In step 1), the drying temperature is 50-70℃ and the drying time is 4-6h; the calcination temperature is 550-700℃ and the calcination time is 1.5-2.5h.

10. The preparation method according to claim 7, characterized in that: In step 3), the reaction temperature is 200-230℃ and the time is 6-10h.

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