Preparation method of red-mud-based pneumatic silencer

Abstract

The invention discloses a red mud-based pneumatic silencer and a preparation method thereof, the method takes red mud, waste aluminum oxide ceramic substrate powder, waste glass powder and other industrial solid wastes as raw materials, and the high-performance pneumatic silencer is prepared through the processes of mixing, burdening, grinding and powdering, melting, atomizing and balling and sinter molding. The preparation method comprises the following specific steps: mixing 20-50 parts of red mud, 10-30 parts of waste aluminum oxide ceramic substrate powder, 1-7 parts of lithium tetraborate, 1-3 parts of lithium metaborate, 5-15 parts of waste glass powder, 5-15 parts of quartz sand and 10-20 parts of kaolin, and grinding until the 325-micron screen residue is less than 1%; melting at the temperature of between 1,300 and 1,700 DEG C; carrying out atomization under the pressure of 0.5-2.0 MPa, and preparing 18-88 [mu] m glass spheres at the cooling rate of 100-500 DEG C / s; and sintering at the temperature of 1000-1200 DEG C for 1-3 hours. The prepared silencer has a communicated pore structure, the silencing capacity reaches 21-30dB (A), the silencer is not damaged under the radial load of 260-350N, and meanwhile, the silencer has excellent acid and alkali corrosion resistance and high-temperature stability. High-value utilization of industrial solid waste is achieved, and the problems that a traditional metal silencer is prone to corrosion and short in service life are solved.

Description

Technical Field

[0001] This invention relates to the fields of solid waste resource utilization and noise control technology, and in particular to a red mud-based pneumatic silencer and its preparation method. Background Technology

[0002] Red mud is a major industrial solid waste generated during alumina production, with an annual output exceeding 150 million tons. Its storage not only occupies a large amount of land but also poses environmental risks such as highly alkaline pollution. In recent years, the resource utilization of red mud has become a research hotspot, especially in the fields of building materials and environmental protection materials.

[0003] Current technologies for the resource utilization of red mud mainly focus on the building materials sector, such as sound-absorbing panels, ceramic bricks, thermal insulation bricks, and ceramsite, with limited application in industrial silencers. While traditional metal silencers (such as copper and stainless steel silencers) possess certain noise reduction properties, they are prone to corrosion or oxidation failure in harsh environments such as acidic and alkaline industrial waste gases and high-temperature flues, resulting in short service life and high maintenance costs. Existing red mud-based ceramic materials, although possessing advantages in corrosion resistance and high-temperature resistance, are mostly produced using conventional granulation-pressing-sintering processes. This leads to insufficient uniformity of the porous structure and precise pore size control, making it difficult to simultaneously meet the stringent requirements of industrial silencers in terms of noise reduction performance and mechanical strength. Furthermore, current technologies have limited capacity for high-value utilization of industrial waste such as red mud, lacking red mud-based noise-reducing materials and efficient preparation methods that combine environmental adaptability, high mechanical strength, and excellent noise reduction performance. Summary of the Invention

[0004] This invention addresses the problems existing in the prior art by providing a red mud-based pneumatic silencer and its preparation method.

[0005] To solve the above-mentioned technical problems, the present invention proposes the following technical solution:

[0006] A method for preparing a red mud-based pneumatic silencer, characterized by comprising the following steps:

[0007] (1) Mixing ingredients: By weight, mix 20-50 parts of red mud, 10-30 parts of waste alumina ceramic substrate powder, 1-7 parts of lithium tetraborate, 1-3 parts of lithium metaborate, 5-15 parts of waste glass powder, 5-15 parts of quartz sand, and 10-20 parts of kaolin, so that the chemical composition of the mixture meets the requirements of 20-45% silicon dioxide, 20-50% alumina, 3-10% calcium oxide, 1.5-5% iron oxide, and 2-7% sodium oxide.

[0008] (2) Grinding and powdering: Grind the mixture from step (1) until the residue on a 325μm sieve is less than 1%;

[0009] (3) Melting: The mixed powder from step (2) is fed into a glass melting pool for melting at a temperature of 1300-1700℃ to obtain a high-temperature molten liquid;

[0010] (4) Atomization into spheres: The high-temperature molten liquid from step (3) is sprayed through an atomizer with an atomization pressure of 0.5-2.0 MPa and a cooling rate of 100-500 °C / s to prepare glass spheres with a particle size of 18-88 μm.

[0011] (5) Sintering: After cooling the glass spheres from step (4), they are placed into a high-temperature mold for sintering. The sintering temperature is 1000-1200℃ and the sintering time is 1-3 hours. After cooling, a red mud-based pneumatic silencer is obtained.

[0012] Furthermore, the atomization pressure of the atomizing generator in step (4) is 1.0-2.0 MPa.

[0013] Furthermore, the cooling rate described in step (4) is 300-500℃ / s.

[0014] Furthermore, the melting temperature in step (3) is 1400-1600℃.

[0015] Furthermore, the sintering temperature in step (5) is 1100-1200℃.

[0016] Furthermore, the particle size of the glass spheres in step (4) is 30-60 μm.

[0017] The present invention has the following beneficial technical effects:

[0018] 1. Achieve high-value utilization of industrial solid waste: Use industrial solid waste such as red mud, waste alumina ceramic substrate powder, and waste glass powder as the main raw materials to transform them into high-performance silencer products, reduce waste accumulation and environmental pollution, and achieve resource recycling.

[0019] 2. Excellent corrosion resistance: Through specific chemical composition design (ensuring the chemical composition of the mixture meets the requirements of 20-45% silicon dioxide, 20-50% aluminum oxide, 3-10% calcium oxide, 1.5-5% iron oxide, and 2-7% sodium oxide) and glassy ceramic composite structure, the product has excellent resistance to acid and alkali corrosion and can work stably for a long time in harsh chemical environments.

[0020] 3. Good high-temperature stability: The glass sphere sintering structure prepared by the melting-atomization-sintering molding process has good high-temperature stability and can withstand long-term use in high-temperature environments.

[0021] 4. High mechanical strength: The porous structure formed by sintering of the glass spheres has high mechanical strength. It does not break, crack or other defects under radial test loads of 260-350N, meeting the load-bearing requirements of industrial applications.

[0022] 5. Excellent noise reduction performance: By precisely controlling the particle size of the glass spheres to 18-88μm, preferably 30-60μm, a porous structure with interconnected pores is formed, achieving a noise reduction of 21-30dB(A), which can effectively reduce noise pollution.

[0023] 6. Significant process innovation: Uniform glass spheres are prepared by melt spraying technology and formed by rapid cooling (100-500℃ / s) to form a stable glassy structure. Compared with traditional granulation and sintering processes and microwave sintering processes, products with more uniform particle size and more stable performance can be obtained, resulting in excellent overall performance. Detailed Implementation

[0024] This invention provides a method for preparing a red mud-based pneumatic muffler. This method makes full use of industrial solid wastes such as red mud, waste alumina ceramic substrate powder, and waste glass powder, and prepares a high-performance pneumatic muffler through a process route of melting-atomization into spheres-sintering.

[0025] Specifically, the following steps are included:

[0026] In the mixing and batching stage, by weight, 20-50 parts of red mud, 10-30 parts of waste alumina ceramic substrate powder, 1-7 parts of lithium tetraborate, 1-3 parts of lithium metaborate, 5-15 parts of waste glass powder, 5-15 parts of quartz sand, and 10-20 parts of kaolin are mixed to ensure that the chemical composition of the mixture meets the following requirements: silicon dioxide 20-45%, alumina 20-50%, calcium oxide 3-10%, iron oxide 1.5-5%, and sodium oxide 2-7%.

[0027] In the grinding and powdering stage, the mixture is ground to a particle size of less than 1% on a 325μm sieve to ensure powder uniformity and reactivity.

[0028] In the melting stage, the mixed powder is fed into a glass melting pool for high-temperature melting at a temperature of 1300-1700℃, preferably 1400-1600℃, to obtain a high-temperature molten liquid with uniform composition and good fluidity.

[0029] In the atomization and spherical formation stage, the high-temperature molten liquid is sprayed through a high-temperature resistant atomizer at an atomization pressure of 0.5-2.0 MPa, preferably 1.0-2.0 MPa. The sprayed droplets are then rapidly cooled at a rate of 100-500℃ / s, preferably 300-500℃ / s. This rapid cooling inhibits crystal growth and forms a glassy structure, resulting in glass spheres with a particle size of 18-88 μm.

[0030] In the sintering stage, the cooled glass spheres are placed into a high-temperature mold for sintering. The sintering temperature is 1000-1200℃, preferably 1100-1200℃, and the sintering time is 1-3 hours. During the sintering process, the surface of the glass spheres softens and bonds to form an integral structure with interconnected pores. After cooling, a red mud-based pneumatic silencer is obtained.

[0031] The resulting silencer is made by sintering glass spheres with a particle size of 18-88μm. The chemical composition of the glass spheres includes 20-45% silicon dioxide, 20-50% aluminum oxide, 3-10% calcium oxide, 1.5-5% iron oxide, and 2-7% sodium oxide. The silencer has excellent noise reduction performance with a noise reduction of 21-30dB(A); high mechanical strength, and does not break, crack, or produce other defects under radial test load of 260-350N; it also has excellent resistance to acid and alkali corrosion and high temperature stability.

[0032] Example 1:

[0033] Principle and mechanism: During the high-temperature melting process of industrial solid waste such as red mud, components such as silicon dioxide and aluminum oxide form aluminosilicate melt. Lithium tetraborate and lithium metaborate act as fluxes to reduce the melting temperature and improve the melt fluidity. Waste glass powder provides additional network formation.

[0034] Molten liquid is atomized under high pressure to form micro-droplets. Under rapid cooling (400℃ / s), the droplets solidify into glassy spheres before crystallization, inhibiting crystal growth and ensuring the uniformity and stability of the spheres. During subsequent sintering, the surface of the glass spheres reaches its softening point at 1150℃, where they bond together to form a three-dimensional interconnected pore network with a porosity of approximately 35-40%. This porous structure dampens and dissipates sound waves, achieving a sound attenuation function.

[0035] The specific steps are as follows:

[0036] (1) Mixing and Batching: Weigh out the following ingredients according to weight: 35 parts red mud (byproduct of an alumina plant, particle size <80um, main components: Fe2O3 5-10%, Al2O3 20-28%, SiO2 20-25%, CaO 13-18%, Na2O 8-12%), 20 parts waste alumina ceramic substrate powder (crushed and pulverized product of waste ceramic substrates from the electronics industry, purity >95%, main component Al2O3), 4 parts lithium tetraborate (analytical grade, Li2B4O7, purity >99%), 2 parts lithium metaborate (analytical grade, LiBO2, purity >98%), and 10 parts waste glass powder (recycled glass bottle crushing product, main components: SiO2 55-70%, Na2O 12-15%, CaO). 10-20%), 10 parts of quartz sand (industrial grade, SiO2 content >98%, particle size <0.5mm), 15 parts of kaolin (industrial grade, main components: Al2O3·2SiO2·2H2O, Al2O3 content 30-39%, SiO2 38-46%).

[0037] The above raw materials were added to a V-type mixer in sequence, and the mixing time was set to 30 minutes and the speed to 25 rpm to ensure that each component was fully and uniformly dispersed. After mixing, samples were taken for chemical composition analysis (XRF fluorescence spectroscopy). The measured chemical composition was: SiO2 31.82%, Al2O3 36.04%, CaO 7.03%, Fe2O3 2.92%, Na2O 4.69%, and other oxides 17.5%, which met the requirements of the technical solution.

[0038] (2) Grinding and powder preparation: The mixture is fed into a planetary ball mill in batches with a ball-to-material ratio of 5:1. The grinding balls are alumina ceramic balls (10mm, 15mm, and 20mm in diameter, mixed in a 1:2:1 ratio). An appropriate amount of deionized water is added (material-to-water ratio of 1:0.6) to make a slurry. The ball mill speed is 300 rpm, and the grinding time is 4 hours. The particle size distribution is checked every hour using a laser particle size analyzer.

[0039] After grinding, the material was passed through a 325-mesh (44μm) standard sieve, and the residue was measured. The actual residue rate was 0.8%, meeting the requirement of <1%. The slurry was spray-dried (inlet temperature 220℃, outlet temperature 110℃) to obtain a free-flowing powder with a moisture content of <0.5%.

[0040] (3) Melting Stage: The dried powder is fed into the fused glass melt pool (500L volume, electrode heating) via an automatic feeding system. The melt pool temperature control system uses multi-point thermocouple monitoring, and the melting temperature is set at 1500℃±20℃. The powder feeding rate is controlled at 15kg / h to ensure the stability of the melt composition. During the melting process, the temperature is increased from room temperature to 800℃ at a rate of 10℃ / min, and held for 1 hour for pre-sintering and dehydration; the temperature is then increased to 1500℃ and held for 2 hours to allow all components to fully melt and react, forming a uniform aluminosilicate glass melt. The melt viscosity at 1500℃ is approximately 5-8 Pa·s, exhibiting good fluidity.

[0041] (4) Atomization into spheres: The molten liquid continuously flows out from the bottom outlet (8mm in diameter) of the molten pool and enters the high-pressure atomizer. The atomizer adopts a dual-fluid nozzle design, using compressed air as the atomization medium. The atomization pressure is set to 1.5MPa, and the air flow rate is 120Nm³. 3 The high-temperature molten liquid (approximately 1480℃) is torn into fine droplets by a high-speed airflow at the nozzle outlet. The droplet diameter follows a log-normal distribution, with a median diameter of approximately 45 μm. The atomizing tower is 12 m high and filled with circulating cooling air (temperature 25℃, flow rate 2 m / s). The droplets cool rapidly during their descent, with a cooling rate of approximately 400℃ / s based on heat transfer calculations. The droplet surface first solidifies to form a glassy outer shell, followed by internal solidification. The entire cooling process is completed in approximately 0.15 seconds, effectively suppressing crystal precipitation. The solidified glass spheres are collected in a collector at the bottom of the tower and then classified by a cyclone separator and a bag filter. Spheres with a particle size range of 30-60 μm are screened out as the main product, with a yield of approximately 65%. Scanning electron microscopy (SEM) observation shows that the spheres have regular morphology, a sphericity >0.85, and a smooth, dense surface. X-ray diffraction (XRD) analysis showed that the glass spheres were amorphous, and the diffraction pattern showed broadened peaks, confirming the formation of a glassy structure.

[0042] (5) Sintering and shaping: The sieved glass spheres (30-60μm) are sintered to the designed density (approximately 1.2g / cm³). 3The spheres were filled into a tube-shaped high-temperature resistant graphite mold (inner diameter 50mm, height 100mm, wall thickness 10mm). During filling, slight vibration (frequency 50Hz, amplitude 0.5mm, time 3 minutes) was used to ensure uniform and dense stacking of the spheres, eliminating large pores. After sealing the mold, the entire assembly was transferred to a box-type sintering furnace. Sintering process curve: The temperature was increased from room temperature to 600℃ at a rate of 5℃ / min, and held for 30 minutes for preheating and stress release; then the temperature was increased to 1150℃ at a rate of 3℃ / min, and held for 2 hours for sintering. At 1150℃, the surface of the glass spheres reached a viscous flow state (glass transition temperature Tg is approximately 750℃, softening point is approximately 900℃). Adjacent spheres bonded together under the action of capillary force and surface tension, forming a neck connection, while the main body of the spheres maintained its original morphology, thus forming a three-dimensional skeleton structure of sphere stacking and neck bonding. The furnace atmosphere during sintering was air at atmospheric pressure. After the heat preservation is completed, the heating is turned off, and the furnace is cooled to below 200℃ (cooling rate of about 2℃ / min) to prevent thermal stress cracks caused by rapid cooling. After demolding, the finished red mud-based pneumatic silencer is obtained, which is grayish-brown in appearance, with a smooth surface and no obvious cracks or defects.

[0043] (6) Performance characterization: Porosity was determined using the Archimedes displacement method, with an actual open porosity of 38.2%; bulk density was 1.45 g / cm³. 3 The compressive strength was determined using a universal testing machine (loading rate 0.5 mm / min), with a measured compressive strength of 18.5 MPa. Mechanical strength was tested according to the JB / T12705-2016 standard method. The sample was placed in a radial loading device, and radial pressure was applied at a constant rate until failure. The measured radial load was 300 N, with no breakage, cracks, or other defects. Noise reduction was tested according to the JB / T12705-2016 standard, with a measured noise reduction of 25 dB(A). Corrosion resistance was tested using an acid-base immersion test. The sample was immersed in 10% H2SO4 solution and 10% NaOH solution for 168 hours (temperature 80℃). After removal, the mass loss rates were 0.15% and 0.22%, respectively, with no significant change in surface morphology, demonstrating excellent corrosion resistance. High-temperature stability was tested: the sample was kept at 800℃ in air for 100 hours. After cooling, the dimensional change rate was <0.3%, and the strength retention rate was >95%, demonstrating good high-temperature stability.

[0044] Technical Results: The red mud-based pneumatic silencer prepared in this embodiment achieves a noise reduction of 25 dB(A), which is approximately 38.9% higher than that of traditional metal silencers (noise reduction of 15-18 dB(A)). Under a radial test load of 300 N, it does not exhibit any breakage, cracks, or other defects, meeting the requirements for industrial applications. After immersion in a 10% sulfuric acid and 10% sodium hydroxide solution for 168 hours (80°C), the mass loss rate is <0.25%, far superior to copper silencers (mass loss rate >5%) and stainless steel silencers (mass loss rate 1-2%). After being kept at 800°C for 100 hours, the strength retention rate is >95%, demonstrating excellent high-temperature stability. The formation mechanism of glassy ceramic structure: rapid cooling (400℃ / s) solidifies the molten droplets into amorphous glass spheres. The XRD diffraction pattern shows broadened peak characteristics and no obvious crystal diffraction peaks. During sintering, the surface of the spheres softens and bonds but maintains the amorphous structure, forming a three-dimensional skeleton of sphere stacking and neck connection. The open porosity of 38.2% provides a good acoustic damping channel.

[0045] Example 2:

[0046] Mixed ingredients: Weigh out 20 parts by weight of red mud, 30 parts by weight of waste alumina ceramic substrate powder, 1 part by weight of lithium tetraborate, 3 parts by weight of lithium metaborate, 15 parts by weight of waste glass powder, 10 parts by weight of quartz sand, and 10 parts by weight of kaolin. This formula increases the alumina content and the amount of waste glass powder, while reducing the amount of red mud. The measured chemical composition is: SiO2 31.35%, Al2O3 43.48%, CaO 5.90%, Fe2O3 1.8%, Na2O 3.93%, and other oxides 13.54%.

[0047] Grinding and powder preparation: The mixture was fed into a planetary ball mill in batches at a ball-to-material ratio of 5:1, and deionized water was added (material-to-water ratio 1:0.6) to form a slurry. The ball mill speed was 300 rpm, and the grinding time was 4 hours. After grinding, the mixture was passed through a 325-mesh standard sieve, and the measured residue rate was 0.5%. The slurry was spray-dried to obtain a powder with good flowability.

[0048] Melting: The dry powder is fed into a glass melt pool, and the melting temperature is set to 1400℃ and held for 2 hours. Due to the high alumina content, the melt viscosity increases slightly (about 8-12 Pa·s), but it still maintains good fluidity.

[0049] Atomization into spheres: atomization pressure 1.0 MPa, air flow rate 100 Nm³. 3 Glass spheres with a particle size range of 20-50 μm and a median diameter of approximately 35 μm were prepared by cooling at a rate of 300 °C / s per hour. Scanning electron microscopy (SEM) observation showed that the spheres had regular morphology, a sphericity >0.82, and a smooth surface.

[0050] Sintering and Molding: The sieved glass spheres are filled into a high-temperature resistant graphite mold. The sintering temperature is 1100℃, and the sintering time is 3 hours. The reduced bonding speed at lower temperatures is compensated by extending the sintering time. Sintering process curve: The temperature is increased to 600℃ at a rate of 5℃ / min and held for 30 minutes; then increased to 1100℃ at a rate of 3℃ / min and held for 3 hours. The spheres are then demolded after cooling in the furnace to below 200℃.

[0051] Performance characterization: The finished product has a porosity of 40.5% and a bulk density of 1.35 g / cm³. 3 It has a compressive strength of 15.2 MPa and exhibits no breakage, cracking, or other defects under a radial test load of 280 N. Its noise reduction is 22 dB(A). Corrosion resistance test: after immersion in 10% H₂SO₄ and 10% NaOH solutions for 168 hours (80℃), the mass loss rates are 0.18% and 0.25%, respectively. High temperature stability test: after holding at 800℃ for 100 hours, the strength retention rate is >93%.

[0052] Example 3:

[0053] Mixed ingredients: Weigh out 45 parts red mud, 15 parts waste alumina ceramic substrate powder, 6 parts lithium tetraborate, 2 parts lithium metaborate, 8 parts waste glass powder, 8 parts quartz sand, and 12 parts kaolin by weight. The measured chemical composition is: SiO2 29.53%, Al2O3 32.41%, CaO 8.28%, Fe2O3 3.75%, Na2O 5.52%, and other oxides 20.51%.

[0054] Grinding and powder preparation: The same grinding process as in Example 1 was used, with a grinding time of 4 hours and a residue rate of 0.7% on a 325-mesh sieve.

[0055] Melting: The melting temperature was set at 1300℃ and held for 3 hours. Due to the low temperature, the holding time needed to be extended to ensure that all components fully melted and reacted. The fluxing effect of lithium tetraborate and lithium metaborate was significant at this temperature, and the melt viscosity was approximately 15-20 Pa·s, which, although high, still allowed for flow.

[0056] Atomization into spheres: atomization pressure 1.2MPa, airflow 110Nm 3 Due to the high viscosity of the melt and the wide distribution of droplet diameter, a cooling rate of 200℃ / s was used to prepare glass spheres with a particle size range of 40-75μm and a median diameter of about 55μm.

[0057] Sintering: Sintering temperature 1150℃, sintering time 2 hours. A higher sintering temperature is used to compensate for the effect of larger spherical particle size on bonding.

[0058] Performance characterization: The finished product has a porosity of 36.5% and a bulk density of 1.50 g / cm³. 3It has a compressive strength of 16.8 MPa, and does not produce any damage, cracks or other defects under a radial test load of 270 N. The noise reduction is 23 dB(A).

[0059] Example 4:

[0060] Mixed ingredients: Weigh out 30 parts red mud, 25 parts waste alumina ceramic substrate powder, 3 parts lithium tetraborate, 1 part lithium metaborate, 12 parts waste glass powder, 12 parts quartz sand, and 15 parts kaolin according to the following weight proportions. The actual chemical composition is: SiO2 33.94%, Al2O3 39.84%, CaO 6.56%, Fe2O3 2.50%, Na2O 4.38%, and other oxides 12.78%.

[0061] Grinding and powdering: The same grinding process as in Example 1 was used, with a 325-mesh sieve residue of 0.6%.

[0062] Melting: The melting temperature was set at 1700℃ and held for 1.5 hours. The melt exhibited excellent fluidity at high temperatures, with a viscosity of approximately 2-4 Pa·s, and all components were fully and uniformly melted.

[0063] Atomization into spheres: atomization pressure 2.0 MPa, airflow 140 Nm³ 3 Due to the good fluidity of the melt, it is easy to atomize into finer droplets. With a cooling rate of 450℃ / s, glass spheres with a particle size range of 25-55μm and a median diameter of about 38μm were prepared. Scanning electron microscopy showed that the spheres had a very regular morphology, a sphericity >0.90, and a smooth and dense surface.

[0064] Sintering: Sintering temperature 1120℃, sintering time 2 hours. Due to the good quality of the spheres, good bonding can be obtained using a medium sintering temperature.

[0065] Performance characterization: The finished product has a porosity of 37.8% and a bulk density of 1.48 g / cm³. 3 It exhibits a compressive strength of 19.2 MPa, and shows no breakage, cracking, or other defects under a radial test load of 320 N. Its noise reduction is 26 dB(A). The corrosion resistance and high-temperature stability test results are comparable to those of Example 1.

[0066] Example 5:

[0067] Mixed ingredients: Weigh out 38 parts by weight of red mud, 18 parts by weight of waste alumina ceramic substrate powder, 5 parts by weight of lithium tetraborate, 2 parts by weight of lithium metaborate, 10 parts by weight of waste glass powder, 11 parts by weight of quartz sand, and 14 parts by weight of kaolin. The measured chemical composition is: SiO2 32.44%, Al2O3 33.69%, CaO 7.53%, Fe2O3 3.1%, Na2O 4.90%, and other oxides 18.52%.

[0068] Grinding and powder preparation: The same grinding process as in Example 1 was used, with a 325-mesh sieve residue of 0.8%.

[0069] Melting: Melting temperature 1480℃, hold for 2 hours, the melt has good fluidity.

[0070] Atomization into spheres: atomization pressure 0.5MPa, airflow 80Nm 3 / h. Due to the low atomization pressure, the resulting droplets have relatively large diameters, ranging from 55-80 μm, with a median diameter of approximately 65 μm. To improve cooling efficiency, the cooling airflow velocity was increased to 3 m / s, achieving a cooling rate of 500 °C / s. Rapid cooling effectively suppressed the crystallization tendency of large-diameter droplets, and XRD analysis confirmed the formation of a glassy structure.

[0071] Sintering: Sintering temperature 1180℃, sintering time 1.5 hours. Due to the large particle size of the spheres, a higher sintering temperature and a shorter sintering time were used to obtain good bonding.

[0072] Performance characterization: The finished product has a porosity of 35.2% and a bulk density of 1.52 g / cm³. 3 It has a compressive strength of 17.5 MPa, and does not break, crack, or produce other defects under a radial test load of 285 N. The noise reduction is 24 dB(A).

[0073] Example 6:

[0074] Mixed ingredients: 28 parts by weight of red mud, 22 parts by weight of waste alumina ceramic substrate powder, 4 parts by weight of lithium tetraborate, 2 parts by weight of lithium metaborate, 11 parts by weight of waste glass powder, 13 parts by weight of quartz sand, and 16 parts by weight of kaolin. The measured chemical composition is: SiO2 34.32%, Al2O3 36.60%, CaO 6.09%, Fe2O3 2.33%, Na2O 4.06%, and other oxides 16.6%.

[0075] Grinding and powder preparation: The same grinding process as in Example 1 was used, with a 325-mesh sieve residue rate of 0.7%.

[0076] Melting: Melting temperature 1520℃, hold for 2 hours.

[0077] Atomization into spheres: Atomization pressure of 1.3 MPa and cooling rate of 350 °C / s were used to prepare glass spheres with a particle size range of 35-65 μm and a median diameter of about 48 μm.

[0078] Sintering and forming: Sintering temperature 1200℃, sintering time 1 hour. At this temperature, the surface of the glass sphere softens significantly, and bonding is rapid, thus shortening the sintering time. Sintering process curve: Heat to 600℃ at a rate of 5℃ / min, hold for 30 minutes; continue heating to 1200℃ at a rate of 3℃ / min, hold for 1 hour. Demold after cooling to below 200℃ in the furnace.

[0079] Performance characterization: The finished product has a porosity of 34.8% and a bulk density of 1.55 g / cm³. 3 It exhibits a compressive strength of 20.3 MPa, and shows no breakage, cracking, or other defects under a radial test load of 340 N, with a noise reduction of 27 dB(A). The higher sintering temperature ensures more complete bonding of the spheres, significantly improving mechanical strength. Corrosion resistance test: After immersion in 10% H₂SO₄ and 10% NaOH solutions for 168 hours (80℃), the mass loss rates are 0.13% and 0.20%, respectively. High-temperature stability test: After holding at 800℃ for 100 hours, the strength retention rate is >96%.

[0080] Example 7:

[0081] Mixed ingredients: Weigh out 20 parts by weight of red mud, 10 parts by weight of waste alumina ceramic substrate powder, 1 part by weight of lithium tetraborate, 1 part by weight of lithium metaborate, 5 parts by weight of waste glass powder, 5 parts by weight of quartz sand, and 10 parts by weight of kaolin. The measured chemical composition is: SiO2 32.60%, Al2O3 36.35%, CaO 7.21%, Fe2O3 3.08%, Na2O 4.81%, and other oxides 15.95%.

[0082] Grinding and powdering: The same grinding process as in Example 1 was used, with a 325-mesh sieve residue of 0.9%.

[0083] Melting: Melting temperature 1300℃, holding time 3 hours. Due to the use of a relatively low melting temperature, the holding time needs to be appropriately extended to ensure that the mixture is fully melted and uniform.

[0084] Atomization into spheres: Atomization pressure of 0.5 MPa and cooling rate of 100 °C / s were used to prepare glass spheres with a particle size range of 18-28 μm and a median diameter of approximately 22 μm. The relatively low atomization pressure and cooling rate resulted in smaller sphere sizes, but the spheres were uniformly distributed.

[0085] Sintering and shaping: Sintering temperature 1000℃, sintering time 1 hour. Sintering process curve: Heat to 600℃ at a rate of 5℃ / min, hold for 30 minutes; continue to heat to 1000℃ at a rate of 3℃ / min, hold for 1 hour. Demold after cooling to below 200℃ in the furnace.

[0086] Performance characterization: The finished product has a porosity of 42.6% and a bulk density of 1.32 g / cm³. 3It has a compressive strength of 15.8 MPa, and exhibits no breakage, cracking, or other defects under a radial test load of 280 N. The noise reduction is 24 dB(A). The relatively low sintering temperature allows the spheres to maintain a high porosity, facilitating airflow, but resulting in relatively low mechanical strength. Corrosion resistance test: After immersion in 10% H₂SO₄ and 10% NaOH solutions for 168 hours (80℃), the mass loss rates were 0.18% and 0.25%, respectively. High temperature stability test: After holding at 800℃ for 100 hours, the strength retention rate was >92%.

[0087] Example 8:

[0088] Mixed ingredients: Weigh out 50 parts by weight of red mud, 30 parts by weight of waste alumina ceramic substrate powder, 7 parts by weight of lithium tetraborate, 3 parts by weight of lithium metaborate, 15 parts by weight of waste glass powder, 15 parts by weight of quartz sand, and 20 parts by weight of kaolin. The measured chemical composition is: SiO2 31.54%, Al2O3 35.93%, CaO 6.96%, Fe2O3 2.86%, Na2O 4.64%, and other oxides 18.07%.

[0089] Grinding and powdering: The same grinding process as in Example 1 was used, with a 325-mesh sieve residue of 0.6%.

[0090] Melting: Melting temperature 1700℃, held for 1.5 hours. High-temperature melting causes the raw material to melt rapidly, reducing viscosity and increasing fluidity.

[0091] Atomization into spheres: Atomization pressure of 2.0 MPa and cooling rate of 500 °C / s were used to prepare glass spheres with a particle size range of 70-88 μm and a median diameter of approximately 78 μm. The high atomization pressure and rapid cooling resulted in larger sphere sizes, but with smooth and dense surfaces.

[0092] Sintering and shaping: Sintering temperature 1200℃, sintering time 3 hours. Sintering process curve: Heat to 600℃ at a rate of 5℃ / min, hold for 30 minutes; continue heating to 1200℃ at a rate of 3℃ / min, hold for 3 hours. Demold after cooling to below 200℃ in the furnace. Extending the sintering time allows for full bonding of larger particle sizes.

[0093] Performance characterization: The finished product has a porosity of 28.3% and a bulk density of 1.78 g / cm³. 3 It has a compressive strength of 25.6 MPa, and exhibits no breakage, cracking, or other defects under a radial test load of 380 N. The noise reduction is 22 dB(A). High-temperature, long-term sintering results in a denser sphere bond, maximizing mechanical strength, but relatively reducing porosity. Corrosion resistance test: After immersion in 10% H₂SO₄ and 10% NaOH solutions for 168 hours (80℃), the mass loss rates are 0.09% and 0.14%, respectively. High-temperature stability test: After holding at 800℃ for 100 hours, the strength retention rate is >98%.

Claims

1. A method for preparing a red mud-based pneumatic silencer, characterized in that, Includes the following steps: (1) Mixing ingredients: By weight, mix 20-50 parts of red mud, 10-30 parts of waste alumina ceramic substrate powder, 1-7 parts of lithium tetraborate, 1-3 parts of lithium metaborate, 5-15 parts of waste glass powder, 5-15 parts of quartz sand, and 10-20 parts of kaolin, so that the chemical composition of the mixture meets the requirements of 20-45% silicon dioxide, 20-50% alumina, 3-10% calcium oxide, 1.5-5% iron oxide, and 2-7% sodium oxide. (2) Grinding and powdering: Grind the mixture from step (1) until the residue on a 325μm sieve is less than 1%; (3) Melting: The mixed powder from step (2) is fed into a glass melting pool for melting at a temperature of 1300-1700℃ to obtain a high-temperature molten liquid; (4) Atomization into spheres: The high-temperature molten liquid from step (3) is sprayed through an atomizer with an atomization pressure of 0.5-2.0 MPa and a cooling rate of 100-500 °C / s to prepare glass spheres with a particle size of 18-88 μm. (5) Sintering: After cooling the glass sphere from step (4), it is placed into a high-temperature mold for sintering. The sintering temperature is 1000-1200℃ and the sintering time is 1-3 hours. After cooling, a red mud-based pneumatic silencer is obtained.

2. The method for preparing the red mud-based pneumatic silencer according to claim 1, characterized in that, The atomization pressure of the atomizer in step (4) is 1.0-2.0 MPa.

3. The method for preparing the red mud-based pneumatic silencer according to claim 1 or 2, characterized in that, The cooling rate described in step (4) is 300-500℃ / s.

4. The method for preparing the red mud-based pneumatic silencer according to claim 1 or 2, characterized in that, The melting temperature mentioned in step (3) is 1400-1600℃.

5. The method for preparing the red mud-based pneumatic silencer according to claim 1 or 2, characterized in that, The sintering temperature in step (5) is 1100-1200℃.

6. The method for preparing the red mud-based pneumatic silencer according to claim 1 or 2, characterized in that, The particle size of the glass spheres in step (4) is 30-60 μm.