Cordierite-based foamed ceramic prepared from industrial solid waste and preparation method thereof

Abstract

The invention relates to the technical field of inorganic non-metallic materials, in particular to cordierite-based foamed ceramic prepared from industrial solid waste and a preparation method thereof.The cordierite-based foamed ceramic is prepared by taking coal gangue, fly ash and red mud as main raw materials, adding light calcined magnesia, potassium feldspar and a silicon carbide foaming agent, mixing, forming and sintering. The preparation method of the cordierite-based foamed ceramic prepared from the industrial solid waste is low in cost and stable in process, and the obtained cordierite-based foamed ceramic has high porosity, uniform pore size and excellent mechanical properties and is suitable for building thermal insulation materials.

Description

Technical Field

[0001] This invention relates to the field of building materials technology, specifically to a cordierite-based foamed ceramic prepared using industrial solid waste and its preparation method. Background Technology

[0002] With the acceleration of industrialization, the accumulation of industrial solid waste, such as coal gangue, fly ash, and red mud, is becoming increasingly serious, not only occupying large amounts of land but also potentially causing environmental pollution. How to efficiently utilize these wastes has become a current research hotspot. Foamed ceramics, due to their excellent properties such as lightweight, heat insulation, sound insulation, and fire resistance, have broad application prospects in the field of building materials. However, the traditional preparation of foamed ceramics largely relies on mineral and industrial raw materials, resulting in high costs, and their performance needs further improvement.

[0003] In the existing technology, some studies have attempted to prepare foamed ceramics using industrial solid waste, but the following problems exist: foamed ceramics prepared by relying on only a single waste (such as coal gangue or fly ash) have low porosity and insufficient mechanical properties; improper selection and dosage control of foaming agent lead to uneven pore size distribution or decreased mechanical strength; and the sintering temperature range is narrow, resulting in poor process stability. Summary of the Invention

[0004] To address the shortcomings of the existing technologies, the present invention aims to provide a cordierite-based foamed ceramic prepared from industrial solid waste and its preparation method. The method has the advantages of low cost, high performance, and stable process, thereby realizing the resource utilization of industrial solid waste. Furthermore, by optimizing the raw material ratio and process parameters, the foamed ceramic can achieve high porosity, uniform pore size distribution, and excellent mechanical properties.

[0005] To solve the above-mentioned technical problems, the present invention adopts the following technical solution: A method for preparing cordierite-based foamed ceramics using industrial solid waste includes the following steps: The raw materials are coal gangue, fly ash, lightly calcined magnesium oxide, potassium feldspar and red mud, with silicon carbide foaming agent added. The mixture is ball-milled, dried and granulated to form raw material particles.

[0006] The raw material granules are dry-pressed into blanks.

[0007] After sintering the green body, it is naturally cooled to obtain foamed ceramics with cordierite as the main crystalline phase.

[0008] In a preferred embodiment of the present invention, the mass fraction of coal gangue in the basic raw materials is 45% to 55%, the mass fraction of fly ash is 25% to 35%, the mass fraction of lightly calcined magnesia is 12% to 18%, the mass fraction of potassium feldspar is 3% to 7%, and the mass fraction of red mud is 3% to 7%, and the silicon carbide foaming agent accounts for 0.5% to 1.5% of the total amount of the above basic raw materials.

[0009] In a preferred embodiment of the present invention, the particle size of the silicon carbide foaming agent is 20μm to 75μm and the purity is ≥98%.

[0010] In a preferred embodiment of the present invention, the mixture is ball-milled until the particle size is D90≤75μm, and the particle size after granulation is 0.5mm~2mm.

[0011] In a preferred embodiment of the present invention, the sintering conditions for the green body are as follows: heating at 5°C / min to 10°C / min to a temperature of 1190°C to 1210°C, holding for 55 min to 65 min, and further holding for 60 min.

[0012] Furthermore, the raw material ratio is as follows: coal gangue: 50wt%, fly ash: 30wt%, lightly calcined magnesia: 15wt%, potassium feldspar: 5wt%, red mud: 5wt%, and silicon carbide foaming agent content is 1wt%.

[0013] Further, raw material processing: crush and grind coal gangue, fly ash and red mud to a particle size ≤100μm, mix all raw materials in proportion, add an appropriate amount of water and stir evenly to form a billet.

[0014] Further, forming and drying: the blank is pressed into shape and dried until the moisture content is ≤2%.

[0015] Further, the sintering process: the dried green body is placed in a high-temperature furnace and heated to 1200℃ (preferred temperature) at a rate of 5℃ / min-10℃ / min, held at that temperature for 1 hour, and then cooled to room temperature with the furnace.

[0016] Furthermore, the optimal solution is to use silicon carbide foaming agent with a particle size of 20μm-75μm to optimize the foaming effect; and to use a sintering temperature of 1200℃, at which point the pore distribution is uniform, the pore wall structure is stable, and there are no cracks.

[0017] Another object of the present invention is to provide a cordierite-based foamed ceramic prepared from industrial solid waste using any of the above-described preparation methods, with a bulk density of 1.27 g / cm³. 3 ~1.84g / cm 3The porosity is 20%–45%, the compressive strength is ≥5MPa, the thermal conductivity at room temperature is ≤0.026W / (m·K), the main crystalline phase is cordierite, there is no SiC phase, and the pore structure is mainly closed pores; the total amount of industrial solid waste in the foamed ceramic is ≥80wt.%.

[0018] The cordierite-based foamed ceramics described in this invention have a pore size of 0.5 mm to 2 mm and a porosity of 20% to 45%.

[0019] This invention relates to the application of cordierite-based foamed ceramics prepared from industrial solid waste in the preparation of building insulation, fireproofing, and sound insulation materials.

[0020] Compared with the prior art, the beneficial effects of the present invention are: 1. This invention uses coal gangue, fly ash, lightly calcined magnesium oxide, potassium feldspar, and red mud as basic raw materials, and adds silicon carbide foaming agent. The materials are ball-milled and mixed, dried and granulated to form raw material particles. The raw material particles are then dry-pressed into green bodies. After sintering the green bodies, they are naturally cooled to obtain foamed ceramics with cordierite as the main crystalline phase. Using industrial solid waste as the main raw material, the cost is low and resource recycling is achieved.

[0021] 2. This invention improves sintering performance and enhances the strength and thermal stability of ceramics by adding lightly calcined magnesium oxide and potassium feldspar.

[0022] 3. This invention optimizes the amount of silicon carbide and the sintering temperature to obtain foamed ceramics with high porosity (20%~45%) and excellent mechanical properties (compressive strength ≥5MPa); the cordierite-based foamed ceramics prepared by this invention using industrial solid waste have lightweight, heat insulation, sound insulation and fireproof properties, and are suitable for building insulation materials. Attached Figure Description

[0023] Figure 1 (a) shows the XRD patterns of foamed ceramics with a silicon carbide content of 0.5 wt% at different sintering temperatures (1190℃, 1200℃, 1210℃) according to the present invention, and (b) shows the XRD patterns of foamed ceramics with different silicon carbide contents (0.5 wt%, 1 wt%, 1.5 wt%) at a sintering temperature of 1200℃ according to the present invention.

[0024] Figure 2 The images show the SEM microstructure of the foamed ceramics of the present invention at different sintering temperatures (1190℃, 1200℃, and 1210℃). Among them, AC is the SEM microstructure of the present invention at a sintering temperature of 1190℃, DF is the SEM microstructure of the present invention at a sintering temperature of 1200℃, and GI is the SEM microstructure of the present invention at a sintering temperature of 1210℃.

[0025] Figure 3The images show the SEM and EDS microstructures of the foamed ceramics of the present invention with different silicon carbide contents (0.5wt%, 1wt%, 1.5wt%). AC is the SEM microstructure of the present invention with a silicon carbide content of 0.5wt%, DF is the SEM microstructure of the present invention with a silicon carbide content of 1wt%, GI is the SEM microstructure of the present invention with a silicon carbide content of 1.5wt%, J is the EDS elemental distribution map of the present invention with a silicon carbide content of 1wt%, and K is the elemental distribution map of the present invention with a silicon carbide content of 1wt%.

[0026] Figure 4 This is the XRD pattern of the raw material of this invention. Detailed Implementation

[0027] The following detailed description, in conjunction with embodiments of the present invention and accompanying drawings, provides a clear and complete illustration of the technical solutions in these embodiments. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of them. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0028] It should be noted that all technical terms used in this invention are for the purpose of describing specific embodiments only and are not intended to limit the scope of protection of this invention. Unless otherwise specified, all raw materials, reagents, instruments and equipment used in the following embodiments of this invention can be purchased from the market or prepared by existing methods.

[0029] Table 1 shows the sintering temperature and foaming agent dosage for Examples 1-9. Table 2 shows the mass fraction of each chemical component of the main raw materials. Example 1 A method for preparing cordierite-based foamed ceramics using industrial solid waste includes the following steps: (1) Weigh 50g of coal gangue, 30g of fly ash, 15g of lightly calcined magnesium oxide, 5g of potassium feldspar, 5g of red mud, and 0.5wt% of silicon carbide, mix them by ball milling, dry them and granulate them to form raw material particles.

[0030] (2) The raw material particles are dry-pressed into shape, and then dried.

[0031] (3) The green body is sintered by heating to 1190℃ at 8℃ / min, holding for 60min, and finally cooling naturally to obtain foamed ceramic with cordierite as the main crystalline phase.

[0032] (4) Performance test: Porosity: 19.9%; compressive strength: 9.7MPa.

[0033] Example 2 The amount of silicon carbide was adjusted to 1 wt%, and the rest was the same as in Example 1.

[0034] Performance testing: Porosity increased to 31.4%, and compressive strength decreased to 8.3 MPa.

[0035] Example 3 The amount of silicon carbide was adjusted to 1.5 wt%, and the rest was the same as in Example 1.

[0036] Performance testing: Porosity further increased to 33.6%, and compressive strength decreased to 5.7 MPa.

[0037] Example 4 The sintering temperature was adjusted to 1200℃, the amount of silicon carbide was 0.5wt%, and the rest was the same as in Example 1.

[0038] Performance testing: Cracks appeared in the pore walls, the porosity increased to 22.3%, and the strength decreased to 8.3 MPa.

[0039] Example 5 The sintering temperature was adjusted to 1200℃, the amount of silicon carbide was 1wt%, and the rest was the same as in Example 1.

[0040] Performance test: Porosity increased to 28.4%, pore distribution was uniform, pore wall structure was stable and there were no cracks, and strength decreased to 7.5 MPa.

[0041] Example 6 The sintering temperature was adjusted to 1200℃, the amount of silicon carbide was 1.5wt%, and the rest was the same as in Example 1.

[0042] Performance testing: Porosity continued to increase to 36.4%, and strength decreased to 6.3 MPa.

[0043] Example 7 The sintering temperature was adjusted to 1210℃, the amount of silicon carbide was 0.5wt%, and the rest was the same as in Example 1.

[0044] Performance testing: Porosity increased to 20.3%, and strength decreased to 7.2 MPa.

[0045] Example 8 The sintering temperature was adjusted to 1210℃, the amount of silicon carbide was 1wt%, and the rest was the same as in Example 1.

[0046] Performance testing: Porosity increased to 37.6%, while strength decreased to 6.3 MPa.

[0047] Example 9 The sintering temperature was adjusted to 1210℃, the amount of silicon carbide was 1.5wt%, and the rest was the same as in Example 1.

[0048] Performance testing: Porosity continued to increase to 41%, while strength decreased to 5.5 MPa.

[0049] Conclusion: The optimal process parameters are 1 wt% silicon carbide and 1200℃ sintering temperature.

[0050] Figure 1 (a) shows the XRD patterns of foamed ceramics with a silicon carbide content of 0.5 wt% at different sintering temperatures (1190℃, 1200℃, 1210℃) according to the present invention; (b) shows the XRD patterns of foamed ceramics with different silicon carbide contents (0.5 wt%, 1 wt%, 1.5 wt%) at a sintering temperature of 1200℃ according to the present invention. Figure 1 It can be seen that under different conditions, the types of phases formed in the sintered samples are almost the same, with the main crystalline phase being cordierite. For example... Figure 1 In (a), at temperatures of 1190 ℃, 1200 ℃, and 1210 ℃, the characteristic peaks in the diffraction patterns of cordierite remained intact, indicating that this material exhibits excellent thermal stability in this temperature range, making it an ideal matrix for preparing porous ceramics. With increasing temperature, the diffraction peak intensity showed a slight increasing trend, suggesting that high temperatures are beneficial for grain growth and increased crystallinity, potentially improving the mechanical properties of porous ceramics. The baseline of the diffraction patterns was relatively flat, and no particularly prominent amorphous peaks were detected, indicating that high-temperature treatment did not induce a glass transition in cordierite, and the system remained predominantly crystalline.

[0051] like Figure 1 In (b), the diffraction peaks of the samples with silicon carbide contents of 0.5 wt%, 1 wt%, and 1.5 wt% matched the characteristic peaks of standard cordierite, indicating that as the content of SiC foaming agent increases, the main phase of the porous ceramic remains cordierite, no new phase is introduced, and no characteristic peaks of SiC are observed. The main peak of cordierite does not shift significantly, indicating that the SiC foaming agent does not significantly change the lattice parameters of cordierite. This may be because its content is too low to reach the XRD detection limit, and SiC is consumed by oxidation reaction with air during sintering.

[0052] Figure 2The images show the SEM microstructure of the foamed ceramics at different sintering temperatures (1190℃, 1200℃, and 1210℃) of this invention. AC represents the SEM microstructure at 1190℃, DF at 1200℃, and GI at 1210℃. At 1190℃, the pore size is small, uniformly distributed, and the pore walls are smooth (scale bar 10μm), indicating that the SiC foaming reaction is incomplete at low temperatures, resulting in limited gas release, and that matrix sintering promotes densification. Upon increasing the temperature to 1200℃, the pore size increases, and localized grain growth appears on the pore walls, reflecting that the increased temperature promotes SiC decomposition, increases gas volume, accelerates matrix grain boundary migration, and stabilizes the pore structure. At 1210℃, the pores significantly coarsen, the pore wall thickness is uneven, and intergranular cracks are present, indicating that the violent release of gas at excessively high temperatures leads to instability of the pore structure, while abnormal grain growth weakens the interfacial bonding. With increasing sintering temperature, the pore size gradually increases, forming multiple smaller pores. Numerous small pores of varying sizes exist on the pore walls, primarily forming isolated structures. The porous ceramic structure mainly consists of pores, micropores, and pore walls. As the temperature gradually increases, the sample surface begins to melt and soften, and the release of CO2 gas triggers a foaming process, leading to a significant increase in the number of pores within the sample. The pores within the sample then combine to form pore walls.

[0053] Figure 3The images show the SEM and EDS microstructures of the foamed ceramics of the present invention with different silicon carbide contents (0.5wt%, 1wt%, 1.5wt%). AC represents the SEM microstructure of the present invention with a silicon carbide content of 0.5wt%, DF represents the SEM microstructure of the present invention with a silicon carbide content of 1wt%, GI represents the SEM microstructure of the present invention with a silicon carbide content of 1.5wt%, J represents the EDS elemental distribution map of the present invention with a silicon carbide content of 1wt%, and K represents the elemental distribution map of the present invention with a silicon carbide content of 1wt%. Micropores were observed on the surface of all samples. However, in visible areas, no visible windows were formed on the inner surface of the pores, indicating that closed pores dominate the samples. When the SiC content is 0.5%, the matrix is ​​dense, the pores are sparse and small in size, and appear as isolated spheres, indicating that the foaming efficiency of low SiC content is limited and the gas release is insufficient. The pore structure is most uniform when the SiC content is 1wt%. The continuous fusion of small pores to form interconnected open pores led to an increase in the diameter and number of pores in the sample. The lack of clear interconnection between pores facilitated water molecule penetration, consistent with the effect of SiC content on water absorption. The amount of gas produced by SiC decomposition was moderate, matching the sintering kinetics of the matrix. At a SiC content of 1.5%, excessive pore growth occurred, with some pores merging to form irregular voids; the 10 μm scale bar indicated rough pore walls. Energy scattering spectra of the samples identified the main elements as O, Mg, Al, Si, and K, consistent with the chemical composition analysis results of fly ash, red mud, coal gangue, and potassium feldspar in Table 2. Furthermore, no element enrichment was observed, consistent with the presence of cordierite in XRD analysis, significantly improving the stability of the sample's physical phases.

[0054] from Figure 2 and Figure 3 As can be seen from Table 1, the pores of samples A2, B2, and C2 are more uniform than those of samples A3, B3, and C3. The variations in A2, B2, and C2 are attributed to the inconsistency in SiC distribution and high-temperature melt viscosity, respectively. High temperatures (>1200℃) accelerate the SiC oxidation reaction, but beyond the matrix sintering temperature, the viscosity decreases, leading to an excessively rapid gas escape rate and intensified pore coalescence and coarsening. Furthermore, rapid grain growth and thermal stress accumulation are the main causes of crack initiation. Therefore, 1200℃ was determined as the optimal sintering temperature. The optimal SiC content will be explored based on this 1200℃ temperature.

[0055] Table 2 shows the chemical composition of the main raw materials. Figure 4The XRD patterns of the raw materials are shown. The results indicate that the red mud contains high levels of Fe2O3 (36.19 wt%) and Al2O3 (19.44 wt%); coal gangue is essentially a complex mixture of aluminosilicates, mainly composed of silicon and aluminum oxides, rich in unburned carbon, and containing varying amounts of iron, calcium, magnesium, potassium, sodium, and sulfur; fly ash is mainly composed of SiO2 (54.09 wt%) and Al2O3 (30.80 wt%), with relatively low mass fractions of other chemical components. Regarding crystal phase (e.g....), Figure 4 As shown), the main crystalline phases in the red mud are hematite (Fe2O3, PDF#00-001-1053) and pyrophyllite (Al2[Si4O3]). 10 [(OH)2, PDF#00-074-1193]. The main crystalline phases in coal gangue are quartz (SiO2, PDF#00-003-1161) and kaolinite (Al2[(OH)4 / Si2O5], PDF#00-011-0579). The main crystalline phases in potassium feldspar are potassium feldspar phase (K2O·Al2O3·6SiO2, PDF#00-010-0353). The main crystalline phases in fly ash are quartz (SiO2, PDF#00-003-1161) and mullite (3Al2O3·2SiO2, PDF#00-015-0776).

[0056] It should be noted that when numerical ranges are involved in this invention, it should be understood that both endpoints of each numerical range and any value between the two endpoints can be selected. Since the steps and methods used are the same as in the embodiments, preferred embodiments are described here to avoid redundancy. Although preferred embodiments of the invention have been described, those skilled in the art, once they understand the basic inventive concept, can make other changes and modifications to these embodiments. Therefore, the appended claims are intended to be interpreted as including the preferred embodiments as well as all changes and modifications falling within the scope of this invention.

[0057] Obviously, those skilled in the art can make various modifications and variations to this invention without departing from its spirit and scope. Therefore, if these modifications and variations fall within the scope of the claims of this invention and their equivalents, this invention also intends to include these modifications and variations.

Claims

1. A method for preparing cordierite-based foamed ceramics using industrial solid waste, characterized in that, Includes the following steps: Using coal gangue, fly ash, lightly calcined magnesium oxide, potassium feldspar and red mud as basic raw materials, and adding silicon carbide foaming agent, the mixture is ball-milled, dried and granulated to form raw material particles; The raw material granules are dry-pressed into blanks; After sintering the green body, it is naturally cooled to obtain foamed ceramics with cordierite as the main crystalline phase. The basic raw materials consist of 45%–55% coal gangue, 25%–35% fly ash, 12%–18% lightly calcined magnesia, 3%–7% potassium feldspar, and 3%–7% red mud. Silicon carbide foaming agent accounts for 0.5%–1.5% of the total amount of the above basic raw materials.

2. The method for preparing cordierite-based foamed ceramics using industrial solid waste according to claim 1, characterized in that, The particle size of the silicon carbide foaming agent is 20μm~75μm, and the purity is ≥98%.

3. The method for preparing cordierite-based foamed ceramics using industrial solid waste according to claim 1, characterized in that, Ball milling to mix to a particle size of D 90 ≤75μm, the particle size of the raw material particles is 0.5mm~2mm.

4. The method for preparing foamed ceramics according to claim 1, characterized in that, The sintering conditions for the green body are as follows: the temperature is increased from 5℃ / min to 10℃ / min to 1190℃ to 1210℃, and the holding time is 55min to 65min.

5. A cordierite-based foamed ceramic prepared using industrial solid waste, characterized in that, Cordierite-based foamed ceramics are prepared by the preparation method according to any one of claims 1-4, wherein the main crystalline phase of the cordierite-based foamed ceramics is cordierite phase.

6. The cordierite-based foamed ceramic prepared from industrial solid waste according to claim 5, characterized in that, The cordierite-based foamed ceramic has a porous structure, with closed pores as the main component, a pore size of 0.5 mm to 2 mm, and a porosity of 20% to 45%.

7. The application of cordierite-based foamed ceramics prepared from industrial solid waste according to claim 5 in the preparation of building insulation, fireproofing and sound insulation materials.

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