A method for preparing a series of mullite materials based on a coal gangue electric melting method

Abstract

This invention provides a method for preparing a series of mullite materials based on the electrofusion method of coal gangue, belonging to the field of dielectric materials technology. This invention uses coal gangue as raw material to prepare mullite materials. By controlling the amount of carbonaceous reducing agent added and the cooling rate, the content and occurrence form of iron in the mullite materials can be controllably adjusted, thereby preparing a series of mullite materials that meet different dielectric performance requirements.

Description

Technical Field

[0001] This invention belongs to the field of dielectric materials technology, specifically relating to a method for preparing a series of mullite materials based on the coal gangue electrofusion method. Background Technology

[0002] Coal gangue, an industrial solid waste rich in SiO2, Al2O3, and Fe2O3, has always been a research hotspot in the fields of materials and environment for resource utilization. Among these efforts, the preparation of mullite from coal gangue is an important pathway for solid waste resource utilization. Mullite is valued for its excellent thermal stability, chemical stability, and dielectric properties, such as its low dielectric constant (6-8) and extremely low dielectric loss (10⁻⁶). -3 ~10 -4 With its extremely high dielectric strength (15~40kV / mm), Fe2O3 is widely used in high-temperature ceramics, capacitors, microwave devices, and other fields. Fe2O3 is a typical semiconductor material. Due to its semiconductor properties, it exhibits non-negligible conductivity, resulting in typically high dielectric loss and a dielectric constant much higher than that of traditional insulators. Furthermore, its dielectric properties are extremely sensitive to factors such as frequency, temperature, crystal structure, microstructure, stoichiometry, and defects. In existing technologies for preparing mullite from coal gangue, Fe2O3 is considered an impurity, typically requiring pretreatment (such as magnetic separation and acid leaching) to remove iron. This process is complex, causes secondary pollution, and wastes iron resources. Summary of the Invention

[0003] The purpose of this invention is to provide a method for preparing a series of mullite materials based on the electrofusion method of coal gangue. The method provided by this invention allows for controllable adjustment of the iron content and morphology in mullite materials, resulting in a series of dielectric materials with different dielectric constants and dielectric loss characteristics.

[0004] To achieve the above-mentioned objectives, the present invention provides the following technical solution: This invention provides a method for preparing a series of mullite materials based on the electrofusion method of coal gangue, comprising the following steps: (1) Coal gangue, aluminum supplement and carbonaceous reducing agent are mixed and smelted to obtain mullite melt; the amount of carbonaceous reducing agent added is m C Calculated according to formula I: m C = (0~1.5)m C-th Equation I, where m C-th =0.225×m Fe2O3 m Fe2O3 The average total mass of Fe2O3 in coal gangue and aluminum supplement calculated based on multi-point sampling and testing is ±5%. When m C =(0~0.99)m C-thAt that time, the molar ratio of Al2O3 to SiO2 in the coal gangue and aluminum supplement is (1.2~1.3):1; when m C =(1.0~1.5)m C-th At that time, the molar ratio of Al2O3 to SiO2 in the coal gangue and aluminum supplement is (1.4~1.5):1; (2) Cool the mullite melt obtained in step (1) to obtain mullite material; when m in step (1) C =(0~0.3)m C-th When the cooling rate is ≤10℃ / min; when m in step (1) C = (0.31~0.99)m C-th When the cooling rate is ≥30℃ / min; when m in step (1) C =(1.0~1.5)m C-th When the cooling rate is ≤10℃ / min, the cooling rate is the average cooling rate of the mullite melt within the range of 1850~1200℃.

[0005] Preferably, the aluminum supplement in step (1) includes aluminum oxide or bauxite.

[0006] Preferably, in step (1), when m C =(0~0.99)m C-th At that time, the molar ratio of Al2O3 to SiO2 in the coal gangue and aluminum supplement is 1.2:1; when m C =(1.0~1.5)m C-th At that time, the molar ratio of Al2O3 to SiO2 in the coal gangue and aluminum supplement is 1.5:1.

[0007] Preferably, the carbonaceous reducing agent in step (1) includes coke, graphite or anthracite.

[0008] Preferably, the melting temperature in step (1) is 1800~2000℃.

[0009] Preferably, the melting time in step (1) is 1 to 3 hours.

[0010] Preferably, the particle size of the coal gangue in step (1) is ≤10mm.

[0011] Preferably, the particle size of the aluminum supplement in step (1) is ≤10mm.

[0012] Preferably, the particle size of the carbonaceous reducing agent in step (1) is 3~5 mm.

[0013] This invention provides a method for preparing a series of mullite materials based on the electrofusion method of coal gangue, comprising the following steps: (1) mixing coal gangue, aluminum supplement and carbonaceous reducing agent, and smelting to obtain mullite melt; wherein the amount of carbonaceous reducing agent added is m C Calculated according to formula I, m C = (0~1.5)m C-th Equation I, where m C-th =0.225×m Fe2O3 m Fe2O3 The average total mass of Fe2O3 in coal gangue and aluminum supplement calculated based on multi-point sampling and detection is ±5%; when m C =(0~0.99)m C-th At that time, the molar ratio of Al2O3 to SiO2 in the coal gangue and aluminum supplement is (1.2~1.3):1; when m C =(1.0~1.5)m C-th When the molar ratio of Al2O3 to SiO2 in the coal gangue and aluminum supplement is (1.4~1.5):1; (2) the mullite melt obtained in step (1) is cooled to obtain mullite material; when m in step (1) C =(0~0.3)m C-th When the cooling rate is ≤10℃ / min; when m in step (1) C = (0.31~0.99)m C-th When the cooling rate is ≥30℃ / min; when m in step (1) C =(1.0~1.5)m C-th When the cooling rate is ≤10℃ / min, the cooling rate is the average cooling rate of the mullite melt within the range of 1850~1200℃. This invention controls the cooling rate to adjust the occurrence morphology of iron in mullite, when m C =(0~0.3)m C-th At this temperature, Fe2O3 in the raw material is hardly reduced, and excess SiO2 forms a silicon-rich liquid phase network at high temperature, providing channels for the migration and aggregation of iron ions. Slow cooling at a rate ≤10℃ / min facilitates the supersaturated precipitation of iron from the liquid phase, which then nucleates and grows at the mullite grain boundaries in the form of a second phase (such as iron spinel FeAl2O4, fir olivine Fe2SiO4, etc.), constructing a micron-sized dispersed conductive / magnetic loss network, thereby preparing a high-iron-content mullite material with electromagnetic wave absorption properties; when m C = (0.31~0.99)m C-thAt this time, only a portion of Fe2O3 in the raw material is reduced, and the remaining iron ions dissolve in the silicon-rich liquid phase. Controlling the cooling rate to ≥30℃ / min facilitates rapid cooling, which helps to "freeze" the iron atoms. Part of the iron replaces aluminum in the mullite lattice as a solid solution, while the other part is trapped in the iron-containing glassy phase between the grains, forming a multiphase structure of solid solution + iron-containing glassy phase. This enhances the polarization effect of the material, resulting in a high dielectric constant mullite material with medium iron content. When m C =(1.0~1.5)m C-th At this time, the Fe2O3 in the raw material is almost completely reduced, and the iron content in the mullite melt is very low. By controlling the cooling rate and cooling slowly at a rate of ≤10℃ / min, the residual intergranular glass phase is minimized, the complete development of mullite crystals is promoted, and lattice defects are eliminated, thereby obtaining a low-iron content mullite material with low dielectric loss and high refractoriness.

[0014] Based on the dielectric properties requirements of the target product, this invention divides the process parameters into three specific windows: (1) High-temperature insulating mullite material: for low dielectric loss (tanδ≤5×10 -4 (2) High dielectric constant mullite material: For substrates or energy storage applications with high dielectric constant (ε≥10), the ratio of Al2O3:SiO2 in the raw materials is controlled to be (1.4~1.5):1, the carbonaceous reducing agent coefficient k=1.0~1.5, and a slow cooling process of ≤10℃ / min is adopted. This combination ensures the high purity and integrity of the mullite crystal phase and minimizes glass phase and impurity defects. (3) Electromagnetic Absorbing Mullite Material: For microwave absorption applications requiring synergistic high dielectric and magnetic losses, the molar ratio of Al2O3:SiO2 in the raw materials was controlled at 1.2:1, the carbonaceous reducing agent coefficient k = 0~0.3, and a slow cooling process of ≤10℃ / min was adopted. This process promoted the full precipitation and growth of iron-based spinel or olivine second phase in the silicon-rich grain boundary network, constructing an effective electromagnetic dissipation network. Detailed Implementation

[0015] This invention provides a method for preparing a series of mullite materials based on the electrofusion method of coal gangue, comprising the following steps: (1) Coal gangue, aluminum supplement and carbonaceous reducing agent are mixed and smelted to obtain mullite melt; the amount of carbonaceous reducing agent added is m C Calculated according to formula I: mC = (0~1.5)m C-th Equation I, where m C-th =0.225×m Fe2O3 m Fe2O3 The average total mass of Fe2O3 in coal gangue and aluminum supplement calculated based on multi-point sampling and testing is ±5%. When m C =(0~0.99)m C-th At that time, the molar ratio of Al2O3 to SiO2 in the coal gangue and aluminum supplement is (1.2~1.3):1; when m C =(1.0~1.5)m C-th At that time, the molar ratio of Al2O3 to SiO2 in the coal gangue and aluminum supplement is (1.4~1.5):1; (2) Cool the mullite melt obtained in step (1) to obtain mullite material; when m in step (1) C =(0~0.3)m C-th When the cooling rate is ≤10℃ / min; when m in step (1) C = (0.31~0.99)m C-th When the cooling rate is ≥30℃ / min; when m in step (1) C =(1.0~1.5)m C-th When the cooling rate is ≤10℃ / min, the cooling rate is the average cooling rate of the mullite melt within the range of 1850~1200℃.

[0016] This invention involves mixing coal gangue, aluminum supplement, and carbonaceous reducing agent, and then smelting them to obtain mullite melt.

[0017] The present invention does not have any special limitation on the source of the coal gangue, and any coal gangue known to those skilled in the art can be used.

[0018] In one embodiment, the main chemical composition of the coal gangue may specifically be 28wt% Al2O3, 55wt% SiO2, and 5wt% Fe2O3, with the remainder being loss on ignition.

[0019] In this invention, the coal gangue is preferably crushed and dried sequentially before use.

[0020] The present invention does not impose any special limitations on the crushing operation; any technical solution known to those skilled in the art can be used to ensure that the particle size of the coal gangue is within the required range.

[0021] The present invention does not impose any special limitations on the drying operation; any technical solution known to those skilled in the art can be used to ensure that the moisture content of the coal gangue is within the required range.

[0022] In this invention, the particle size of the coal gangue is preferably ≤10mm; the moisture content of the coal gangue is preferably ≤1wt%.

[0023] In this invention, the aluminum supplement preferably includes alumina or bauxite.

[0024] In one embodiment, the alumina may be industrial alumina (Al2O3 99wt%); the bauxite may be 70 bauxite; the main chemical composition of the 70 bauxite may specifically be Al2O3 70wt%, SiO2 16wt%, Fe2O3 2.5wt%, and TiO2 2.5wt%.

[0025] In this invention, the aluminum supplement is preferably crushed and dried sequentially before use.

[0026] The present invention does not impose any special limitations on the crushing operation; any technical solution known to those skilled in the art can be used to ensure that the particle size of the aluminum supplement is within the required range.

[0027] The present invention does not impose any special limitations on the drying operation. As long as the water content of the aluminum supplement is within the required range, a technical solution known to those skilled in the art can be used.

[0028] In this invention, the particle size of the aluminum supplement is preferably ≤10mm; the water content of the aluminum supplement is preferably ≤1wt%.

[0029] In this invention, the carbonaceous reducing agent preferably includes coke, graphite, or anthracite.

[0030] In this invention, the particle size of the carbonaceous reducing agent is preferably 3-5 mm.

[0031] In this invention, the amount of carbonaceous reducing agent added is m C Calculated according to formula I: m C = (0~1.5)m C-th Formula I, Where m C-th =0.225×m Fe2O3 m Fe2O3 The value is ±5% of the average total mass of Fe2O3 in coal gangue and aluminum supplement calculated based on multi-point sampling and testing.

[0032] Based on the reaction formula Fe₂O₃ + 3C = 2Fe + 3CO, the theoretically required mass of carbon for the complete reduction of Fe₂O₃ is m. C-th =0.225×m Fe2O3 .

[0033] In this invention, when m C =(0~0.99)mC-th When the molar ratio of Al2O3 to SiO2 in the coal gangue and aluminum supplement is (1.2~1.3):1, preferably 1.2:1; when m C =(1.0~1.5)m C-th When the amount of Al2O3 and SiO2 in the coal gangue and aluminum supplement is (1.4~1.5):1, preferably 1.5:1.

[0034] In this invention, when m C =(1.0~1.5)m C-th At this time, the Fe2O3 in the raw material is almost completely reduced, and the iron content in the mullite melt is very low. By controlling the cooling rate and cooling slowly at a rate of ≤10℃ / min, the residual intergranular glass phase is minimized, the complete development of mullite crystals is promoted, and lattice defects are eliminated, thereby obtaining a low-iron content mullite material with low dielectric loss and high refractoriness, with an iron removal rate of ≥90%.

[0035] In this invention, when m C = (0.31~0.99)m C-th During this process, only a portion of Fe2O3 in the raw material is reduced, while the remaining iron ions dissolve in the silicon-rich liquid phase. Simultaneously, the subsequent cooling rate is controlled to achieve rapid cooling at a rate of ≥30℃ / min, which helps to "freeze" the iron atoms. Part of the iron replaces the aluminum in the mullite lattice in the form of a solid solution, while another part of the iron is captured in the iron-containing glass phase between the crystals, forming a multiphase structure of solid solution + iron-containing glass phase. This enhances the polarization effect of the material, resulting in the preparation of a mullite material with high dielectric constant and medium iron content, with an iron removal rate between 20% and 90% (excluding 90%).

[0036] In this invention, when m C =(0~0.3)m C-th At this stage, Fe2O3 in the raw material is hardly reduced, and excess SiO2 forms a silicon-rich liquid phase network at high temperature, providing channels for the migration and aggregation of iron ions. Simultaneously, controlling the subsequent cooling rate to a slow cooling rate of ≤10℃ / min facilitates the supersaturation precipitation of iron from the liquid phase. Iron then nucleates and grows at the mullite grain boundaries in the form of a second phase (such as iron spinel FeAl2O4, fir olivine Fe2SiO4, etc.), constructing a micron-sized dispersed conductive / magnetic loss network. This process yields a high-iron-content mullite material with electromagnetic wave absorption properties, with an iron removal rate of <20%.

[0037] The present invention does not impose any special limitations on the operation of mixing the coal gangue, aluminum supplement and carbonaceous reducing agent, and any mixing technical solution known to those skilled in the art can be used.

[0038] In one embodiment, the mixing is a dry mixing; the mixing is carried out in a mixer; and the mixing time is 30-60 minutes.

[0039] In this invention, the preferred melting temperature is 1800~2000℃; the preferred melting time is 1~3h. As one embodiment, the melting temperature can specifically be 1800℃, 1850℃, 1900℃, 1950℃, or 2000℃; the melting time can specifically be 1h, 1.5h, 2h, 2.5h, or 3h. By controlling the melting temperature and time within the above ranges, this invention enables the raw materials to fully melt and undergo mullitization and possible Fe2O3 and SiO2 reduction reactions, as well as Fe and Si alloying reactions.

[0040] In this invention, when the content of carbonaceous reducing agent is not 0, Fe2O3 and SiO2 reduction reactions and Fe and Si alloying reactions will occur during the smelting process. When the content of ferrosilicon alloy is relatively high, after smelting, the mullite matrix and ferrosilicon alloy will separate into layers due to the large density difference, with the upper layer being mullite melt and the lower layer being ferrosilicon alloy melt. When the content of carbonaceous reducing agent is 0, Fe2O3 and SiO2 reduction reactions and Fe and Si alloying reactions will not occur during the smelting process, resulting in segregation after smelting, but without the formation of layers.

[0041] In this invention, when stratification occurs, after melting, the product is preferably stratified to obtain a mullite melt. This invention does not impose any special limitations on the stratification process; any technical solution well-known to those skilled in the art can be used.

[0042] In this invention, when no stratification occurs, mullite melt is obtained after smelting.

[0043] In one implementation, the smelting is carried out in a three-phase electric arc furnace.

[0044] After obtaining the mullite melt, the present invention cools the mullite melt to obtain mullite material.

[0045] In this invention, when m C =(0~0.3)m C-th When the cooling rate is ≤10℃ / min; when m C = (0.31~0.99)m C-th When the cooling rate is ≥30℃ / min; when m C =(1.0~1.5)m C-th When the cooling rate is ≤10℃ / min, the cooling rate is the average cooling rate of the mullite melt within the range of 1850~1200℃.

[0046] When the cooling temperature is below 1200°C, the present invention does not impose any special limitation on the cooling rate; cooling to room temperature can be achieved by using cooling techniques well known to those skilled in the art.

[0047] This invention controls the cooling rate and adjusts the occurrence morphology of iron in mullite, when m C =(0~0.3)m C-th At this temperature, Fe2O3 in the raw material is hardly reduced, and excess SiO2 forms a silicon-rich liquid phase network at high temperature, providing channels for the migration and aggregation of iron ions. Slow cooling at a rate ≤10℃ / min facilitates the supersaturated precipitation of iron from the liquid phase, which then nucleates and grows at the mullite grain boundaries in the form of a second phase (such as iron spinel FeAl2O4, fir olivine Fe2SiO4, etc.), constructing a micron-sized dispersed conductive / magnetic loss network, thereby preparing a high-iron-content mullite material with electromagnetic wave absorption properties; when m C = (0.31~0.99)m C-th At this time, only a portion of Fe2O3 in the raw material is reduced, and the remaining iron ions dissolve in the silicon-rich liquid phase. Controlling the cooling rate to ≥30℃ / min facilitates rapid cooling, which helps to "freeze" the iron atoms. Part of the iron replaces aluminum in the mullite lattice as a solid solution, while the other part is trapped in the iron-containing glassy phase between the grains, forming a multiphase structure of solid solution + iron-containing glassy phase. This enhances the polarization effect of the material, resulting in a high dielectric constant mullite material with medium iron content. When m C =(1.0~1.5)m C-th At this time, the Fe2O3 in the raw material is almost completely reduced, and the iron content in the mullite melt is very low. By controlling the cooling rate and cooling slowly at a rate of ≤10℃ / min, the residual intergranular glass phase is minimized, the complete development of mullite crystals is promoted, and lattice defects are eliminated, thereby obtaining a low-iron content mullite material with low dielectric loss and high refractoriness.

[0048] When the fused melt is cooled from 1800~2000℃, it successively passes through the liquid phase region, the liquid + mullite two-phase region, and the mullite + SiO2 eutectic / solid phase region. The residual SiO2-rich liquid phase tends to form a glassy phase when rapidly cooled (≥30℃ / min), and tends to crystallize into cristobalite, phosphogypsum, or quartz crystals when slowly cooled (≤10℃ / min). Based on this, the present invention designs a differentiated cooling process for mullite melts with different iron contents. Its core lies in controlling the melt in the critical crystallization and phase separation temperature range (1850~1200℃).

[0049] In this invention, a nucleating agent is preferably added during the mixing process of the coal gangue, aluminum supplement, and carbonaceous reducing agent, or when the mullite melt is cooled to 1500~1650°C.

[0050] In this invention, the nucleating agent preferably includes at least one of FeAl2O4, Fe3O4, Fe2SiO4, TiO2, ZrO2 and Cr2O3.

[0051] In this invention, the preferred mass ratio of the nucleating agent to the total mass of coal gangue, aluminum supplement, and carbonaceous reducing agent is (0.5~10):100. By adding a nucleating agent and controlling its type and dosage, this invention provides heterogeneous nucleation sites for the iron-containing second phase, significantly increasing the number of effective nucleation points and inhibiting the coarse growth of the second phase.

[0052] This invention uses coal gangue as raw material to prepare mullite materials. By controlling the amount of carbonaceous reducing agent added and the cooling rate, the content and occurrence form of iron in the mullite materials can be controlled and adjusted, thereby preparing a series of mullite dielectric materials with different dielectric constants and dielectric loss characteristics. These materials can meet the material requirements of different fields and have better flexibility. High-value-added series products can be prepared from industrial solid waste coal gangue, avoiding resource waste and realizing the resource utilization of waste. Moreover, the preparation process does not require magnetic separation or acid leaching to remove iron, making the process simpler and avoiding secondary pollution.

[0053] The technical solutions of this invention will be clearly and completely described below with reference to the embodiments thereof. Obviously, the described embodiments are only a part of the embodiments of this invention, and not all of them. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without creative effort are within the scope of protection of this invention.

[0054] In each embodiment, the main chemical components of the coal gangue are 28wt% Al2O3, 55wt% SiO2, and 5wt% Fe2O3, with the remainder being loss on ignition; the bauxite is 70 bauxite, with the main chemical components being 70wt% Al2O3, 16wt% SiO2, 2.5wt% Fe2O3, and 2.5wt% TiO2; and industrial alumina (99wt% Al2O3).

[0055] Example 1 A method for preparing low-iron-content mullite material based on coal gangue electrofusion: (1) Coal gangue and industrial alumina are crushed and dried sequentially to obtain coal gangue and industrial alumina with a particle size ≤10mm and a water content of 1wt%. (2) The coal gangue and industrial alumina obtained in step (1) are dry-mixed with coke powder (particle size 3~5mm) in a mixer for 45min, wherein the molar ratio of Al2O3 to SiO2 in the coal gangue and industrial alumina is 1.5:1, and the mass m of the coke powder is... C =1.4m C-th m C-th=0.225×m Fe2O3 m Fe2O3 The average total mass of Fe2O3 in coal gangue and industrial alumina was calculated based on multi-point sampling and testing. Then, the mixture was put into a three-phase electric arc furnace and heated to 1900℃ for smelting for 1 hour. After smelting, the upper mullite melt and the lower ferrosilicon alloy were discharged from different outlets to obtain the mullite melt. (3) The mullite melt obtained in step (2) is poured into an insulating sand mold, covered with an insulating material for slow cooling, and its average cooling rate in the temperature range of 1850~1200℃ is controlled to be 8℃ / min. Then, it is allowed to cool naturally to room temperature with the sand mold to obtain low-iron fused mullite material.

[0056] Testing revealed that the low-iron fused mullite material prepared in Example 1 had a total iron content of 0.25 wt%, a dielectric constant of 7.1 at 10 GHz, and a dielectric loss of 4.8 × 10⁻⁶. -4 It exhibits excellent high-temperature insulation properties.

[0057] Example 2 A method for preparing medium-iron content mullite material based on coal gangue electrofusion: (1) Coal gangue and bauxite are crushed and dried sequentially to obtain coal gangue and bauxite with a particle size ≤10mm and a water content of 1wt%; (2) The coal gangue and bauxite obtained in step (1) are dry-mixed with coke powder (particle size 3~5mm) in a mixer for 45min, wherein the molar ratio of Al2O3 to SiO2 in the coal gangue and bauxite is 1.2:1, and the mass m of the coke powder is... C =0.5m C-th m C-th =0.225×m Fe2O3 m Fe2O3 The average total mass of Fe2O3 in coal gangue and bauxite was calculated based on multi-point sampling and testing. The mixture was then placed in a three-phase electric arc furnace and heated to 1900℃ for 1 hour to obtain mullite melt. (3) The mullite melt obtained in step (2) is thin-walled and cast with a thickness of 15 mm. The average cooling rate is controlled at 40 °C / min in the temperature range of 1850~1200 °C. Then it is naturally cooled to room temperature to obtain China Iron & Steel fused mullite material.

[0058] Testing revealed that the total iron content of the ferrofused mullite material prepared in Example 2 was 2.05 wt%, its dielectric constant at 10 GHz was 13.8, and its dielectric loss was 8.1 × 10⁻⁶. -3 It is suitable for substrates or electronic packaging fields that require high dielectric constant and have a certain tolerance for loss.

[0059] Example 3 A method for preparing high-iron-content mullite material based on coal gangue electrofusion: (1) Coal gangue and bauxite are crushed and dried sequentially to obtain coal gangue and bauxite with a particle size ≤10mm and a water content of 1wt%; (2) The coal gangue and bauxite obtained in step (1) are dry-mixed in a mixer for 45 minutes, wherein the molar ratio of Al2O3 to SiO2 in the coal gangue and bauxite is 1.2:1, and no coke powder is added, i.e., the mass m of the coke powder is... C =0m C-th m C-th =0.225×m Fe2O3 m Fe2O3 The average total mass of Fe2O3 in coal gangue and bauxite was calculated based on multi-point sampling and testing. Then, the mixture was put into a three-phase electric arc furnace and heated to 1900℃ for smelting for 1 hour. After smelting, mullite melt was obtained. (3) The mullite melt obtained in step (2) is poured into an insulating sand mold, covered with an insulating material for slow cooling, and its average cooling rate in the temperature range of 1850~1200℃ is controlled to be 8℃ / min. Then, it is naturally cooled to room temperature with the sand mold to obtain high-speed rail fused mullite material.

[0060] Tests showed that the total iron content of the high-iron electrofused mullite material prepared in Example 3 was 3.3 wt%, the dielectric constant at 10 GHz was 27.2, the dielectric loss was 0.07, and it exhibited excellent electromagnetic wave absorption performance in the X-band.

[0061] In summary, this invention uses coal gangue as raw material to prepare a series of mullite materials with different iron contents and dielectric properties, which can meet the needs of multiple fields.

[0062] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for preparing a series of mullite materials based on the electrofusion method of coal gangue, comprising the following steps: (1) Coal gangue, aluminum supplement and carbonaceous reducing agent are mixed and smelted to obtain mullite melt; the amount of carbonaceous reducing agent added is m C Calculated according to formula I: m C = (0~1.5)m C-th Equation I, where m C-th =0.225×m Fe2O3 m Fe2O3 The average total mass of Fe2O3 in coal gangue and aluminum supplement calculated based on multi-point sampling and testing is ±5%. When m C =(0~0.99)m C-th At that time, the molar ratio of Al2O3 to SiO2 in the coal gangue and aluminum supplement is (1.2~1.3):1; when m C =(1.0~1.5)m C-th At that time, the molar ratio of Al2O3 to SiO2 in the coal gangue and aluminum supplement is (1.4~1.5):1; (2) Cool the mullite melt obtained in step (1) to obtain mullite material; when m in step (1) C =(0~0.3)m C-th When the cooling rate is ≤10℃ / min; when m in step (1) C = (0.31~0.99)m C-th When the cooling rate is ≥30℃ / min; when m in step (1) C =(1.0~1.5)m C-th When the cooling rate is ≤10℃ / min, the cooling rate is the average cooling rate of the mullite melt within the range of 1850~1200℃.

2. The method according to claim 1, characterized in that, The aluminum supplement in step (1) includes aluminum oxide or bauxite.

3. The method according to claim 1, characterized in that, In step (1), when m C =(0~0.99)m C-th At that time, the molar ratio of Al2O3 to SiO2 in the coal gangue and aluminum supplement is 1.2:1; when m C =(1.0~1.5)m C-th At that time, the molar ratio of Al2O3 to SiO2 in the coal gangue and aluminum supplement is 1.5:

1.

4. The method according to claim 1, characterized in that, The carbonaceous reducing agent in step (1) includes coke, graphite or anthracite.

5. The method according to claim 1, characterized in that, The melting temperature in step (1) is 1800~2000℃.

6. The method according to claim 1 or 5, characterized in that, The melting time in step (1) is 1 to 3 hours.

7. The method according to claim 1, characterized in that, The particle size of the coal gangue in step (1) is ≤10mm.

8. The method according to claim 1, characterized in that, The particle size of the aluminum supplement in step (1) is ≤10mm.

9. The method according to claim 1, characterized in that, The particle size of the carbonaceous reducing agent in step (1) is 3~5mm.