Aluminum oxide microsphere preparation method based on surface layer flame spray melting technology

Abstract

The invention belongs to the field of preparation of alumina microspheres, and particularly relates to a preparation method of micron-scale spherical alumina. According to the invention, dedusting powder generated in the crushing process of fused white corundum is used as a main raw material, auxiliary materials are added, sintering and crushing are carried out, and then flame spray melting is carried out. The method has the advantages of low raw material cost, low sintering temperature in the intermediate link, easy breakage of the sintered product, high speed in the flame spray melting stage, effective utilization of the dedusting powder by-product in the production process of the fused white corundum, energy saving and environmental protection.

Description

Technical Field

[0001] The invention belongs to alumina microsphere preparation technology, and specifically relates to energy-saving preparation of alumina microsphere and recycling of dust removal powder generated in the process of crushing fused white corundum. Background Art

[0002] As a high-performance inorganic material, alumina microspheres have excellent properties such as high mechanical strength, high temperature resistance, good filling fluidity, and acid and alkali corrosion resistance. In addition, due to the small contact area of ​​the spheres, the stacked alumina microspheres have a large porosity, so the overall specific surface area is large, which is particularly suitable for use as catalyst carriers and adsorbents. At present, alumina microspheres have been widely used in catalyst carriers, electronic material processing, biomedicine, 3D printing and new energy fields.

[0003] There are several common methods for producing alumina microspheres: (1) the sol-gel method, which is to dissolve aluminum salt (such as aluminum nitrate) in water, add a gelling agent (such as ammonia water) to form a sol, and then dry and calcine to obtain alumina microspheres; (2) the spray drying method, which is to spray the alumina precursor solution into small droplets, dry it with hot air to form microspheres, and then calcine; (3) the hydrothermal method, which is to generate alumina microspheres through a hydrothermal reaction of an aluminum salt solution under high temperature and pressure; (4) the template method, which is to use a template (such as polymer microspheres) to guide the alumina precursor to form a sol. The main method is to deposit the alumina precursor on its surface, and then remove the template to obtain microspheres; (5) the emulsion method is to mix the alumina precursor solution with the oil phase to form an emulsion, and then obtain microspheres through solidification, separation and calcination; (6) the fluidized bed method is to suspend the alumina precursor powder through air flow and heat it in the fluidized bed to form microspheres; (7) the chemical vapor deposition method is to decompose the gaseous aluminum compound and deposit it on the substrate at high temperature to form alumina microspheres; (8) the electrochemical method is to deposit alumina on the electrode surface through electrochemical reaction, and then obtain microspheres after treatment. At present, the domestic companies that have alumina microsphere products mainly include Aluminum Corporation of China, Shandong Aluminum Corporation, Henan Zhongfu Industrial Co., Ltd. and Jiangsu Pengfei Group Co., Ltd., and the foreign companies mainly include Alcoa, Rhodia, Nippon Light Metal and Martinswerk.

[0004] It can be seen that the development of alumina microspheres has become mature both in terms of production methods and products. If a new alumina microsphere production technology is to be developed and industrialized, it is also necessary to consider competing with existing products on the market and making profits, which is very difficult. On the other hand, although the current alumina microsphere products and production technologies are relatively mature, there are generally problems such as high energy consumption in the production process, complex production process, and high product prices. If the relevant resources of the alumina industry chain can be reasonably utilized, the production cost can be reduced, and at the same time, an application outlet can be found for some difficult-to-digest by-products.

[0005] During the production and crushing process of fused white corundum, a byproduct called "dust powder" is produced. It is an alumina corundum powder with a particle size ranging from several microns to tens of microns. Specifically, during the production process of fused white corundum, the raw materials (usually high-purity alumina) are melted at high temperature in an electric arc furnace, and a large amount of dust is generated during the cooling, crushing, screening and other processes. These dusts are collected by dust removal equipment to form "dust powder". Due to its particle size, the market demand for grinding materials of this scale is not large, and its particles are too large when used as a powder raw material for the production of ceramic corundum abrasives. If it is ground and crushed into smaller particles for reuse, it has no advantage in production cost. Therefore, many manufacturers currently use it as a raw material for fused corundum remelting or as a whitening filler in the production of some paper or plastics. However, whether it is used as a fused white corundum remelting or as an additive for other products such as paper, it has no advantages in product characteristics and production costs. In addition, the amount of dust removal powder, a byproduct, produced during the production and crushing process of fused white corundum abrasive is not very high, usually less than 5%, so there are few designs and applications that use this byproduct as a raw material to produce certain products. Based on the above reasons, this patent targets the characteristics of dust removal powder, a byproduct produced during the production of fused white corundum abrasive, and performs simple pulping, drying, sintering, crushing and flame spraying on it to produce alumina microspheres with a particle size of less than 200μm, thereby achieving the upgrading and recycling of this material and enriching the product types and technical reserves of related enterprises. Summary of the invention

[0006] The problem to be solved by the present invention is to produce aluminum oxide microsphere products with a particle size of less than 200 μm using dust removal powder generated in the process of producing fused white corundum abrasive as the main raw material. The raw material cost is low, resources are recycled, the equipment is simple, and energy consumption is saved.

[0007] The method for preparing alumina microspheres based on surface flame spraying technology of the present invention comprises the following steps: (1) Using the dust removal powder produced in the production process of fused white corundum as the main raw material, adding CaF 2 and Na 2 SiO 3As a sintering aid, water and polyethylene glycol are added and mixed evenly to form a slurry; (2) After the slurry is dried, it is transferred into a high-temperature kiln and sintered at about 1300°C to form a block of alumina sintered body; (3) crushing the obtained alumina sintered body to form particles with a particle diameter of less than 200 μm; (4) Using an oxyacetylene flame, the particles are surface-molded to obtain alumina microspheres after cooling.

[0008] Further, the slurry is prepared by the steps of: The dust removal powder and the sintering agent CaF 2 、Na 2 SiO 3 Mixed with polyethylene glycol as a bonding shrinkage aid, and the sintering aid is 1-3% by mass of CaF 2 and 5~10%Na 2 SiO 3 The slurry bonding shrinkage aid is 0.2~0.5% polyethylene glycol. Add water in a mass ratio of 1:1 and stir thoroughly to form a slurry.

[0009] The dust removal powder used in the present invention is a by-product collected by a fused white corundum abrasive manufacturer during the crushing process of fused corundum production, and has a lower cost than the raw materials purchased by a company specializing in the production of alumina microspheres.

[0010] Furthermore, the particle size of the dust removal powder is required to be less than 50 μm, but this requirement is not absolutely strict. Generally speaking, the requirement is met if the proportion of particles with a particle size greater than 50 μm in the dust removal powder does not exceed 5%.

[0011] Furthermore, the drying temperature of the slurry can be selected between 60 and 90°C in combination with production conditions. Note that too low a drying temperature will affect the drying efficiency, while too high a temperature will affect the density of the block aggregates.

[0012] Furthermore, the sintering process temperature needs to be controlled between 1270 and 1330°C. If the temperature is too low, it will affect the density of the slurry particles. If the temperature is too high, the energy consumption will increase and it will be unfavorable for subsequent crushing.

[0013] Furthermore, the sintered alumina sintered body is crushed to a particle diameter less than 200 μm.

[0014] Further, the flame spraying step is: The crushed alumina sintered body particles are slowly dropped into the zirconia refractory tube below through the feeding funnel (see attached). Figure 1Schematic diagram of flame spraying device), several oxyacetylene flame nozzles are symmetrically arranged in the middle of the refractory tube, and the spraying direction of the flame nozzles is adjusted so that the intersection of several flames forms a flame vortex at the central axis of the refractory tube and diffuses in a section of the refractory tube to form a flame zone. After the particles falling from the feeding funnel reach the flame vortex, they will stay in the flame zone for a short time under the action of the flame and the upward rotating airflow. 2 and Na 2 SiO 3 Under the fluxing effect and high temperature burning of the oxyacetylene flame, the surface of the particles will melt quickly. Under the action of the surface tension of the liquid, the molten surface will wrap around the particles in a spherical shape and cool and solidify in the process of falling away from the flame spraying zone to obtain alumina microspheres.

[0015] It should be noted that the temperature of the flame spraying zone is affected by many factors such as the ratio of acetylene and oxygen flow in the oxyacetylene flame, the diameter of the refractory tube, the number of flame nozzles and the injection angle, and needs to be matched with the feeding speed of the feeding funnel. The specific parameters should be determined according to the morphological appearance of the collected products. In addition, the size of the flame needs to be adjusted according to the diameter of the refractory tube. If the diameter is too small or the flame is too large, the alumina particles will be blown back and unable to fall smoothly; if the diameter is too large and the flame is too small, larger pores will be formed between the flame zone and the tube wall. The alumina particles cannot stay in the flame zone for enough time, resulting in an inability to form a spherical appearance. Although the above problems can usually be solved by adjusting the length of the refractory tube above the flame or installing a tungsten wire check net above the flame zone, it is also impossible to deal with the situation where the diameter of the refractory tube and the flame flow are obviously incompatible. The flame nozzle can be inserted into the tube by punching a hole in the wall of the refractory tube or as shown in the figure. Figure 1 As shown, a tungsten mesh is used to connect the two ends of the refractory tube, and the tungsten mesh extends into the interior of the refractory tube through the mesh holes of the tungsten mesh.

[0016] The beneficial effects of the present invention are: 1. The dust removal powder produced as a by-product of the fused white corundum crushing process is used as the main raw material, with low production cost, thus achieving the rational utilization of the product and product value-added.

[0017] 2. The temperature of the intermediate sintering process is low, which saves energy. General kilns can meet the production requirements. Enterprises can make full use of existing facilities and reduce equipment investment.

[0018] 3. The flame spraying equipment has a simple structure and is easy to implement; the conversion rate of alumina microspheres is high and the surface finish is good. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 Schematic diagram of flame spraying on the surface of alumina particles; Figure 2 Design diagram of the flame spray melting device on the surface of aluminum oxide particles used in the embodiment; Figure 3Optical microscope transmission photograph of alumina microspheres obtained in Example; Figure 4 Optical microscope reflection photograph of alumina microspheres obtained in Example; Figure 5 X-ray diffraction spectrum of alumina microspheres obtained after spray melting; Figure 6 Optical microscope transmission photograph of dust removal powder (showing particle size and distribution); Figure 7 Optical microscope reflection photograph of dust removal powder (showing particle size and distribution). DETAILED DESCRIPTION

[0020] The present invention will be further described below in conjunction with the embodiments. Example

[0021] The method for preparing alumina microspheres based on surface flame spraying technology described in the present invention comprises the following steps: (1) Preparation of alumina powder slurry: Take 1kg of dust powder produced during the crushing process of fused white corundum and add 20g of CaF 2 and 50g Na 2 SiO 3 As a sintering aid, add 2g of polyethylene glycol as a bonding shrinkage agent, add 1L of water and stir thoroughly to form a slurry.

[0022] (2) Drying and sintering: The slurry was transferred to an oven for drying at 70°C for 8 hours, and the dried solid was placed in a high-temperature furnace for sintering at 1300°C for 90 minutes to obtain a block-shaped alumina sintered body.

[0023] Crushing and screening: The obtained blocky alumina sintered body is placed in a crusher for crushing, and particles with a particle size of less than 200 μm are screened out, and large particles are further crushed until they reach a standard of less than 200 μm.

[0024] Melt Spraying: The screened particles are transferred into the oxyacetylene flame combustion area in the zirconia refractory tube at a speed of 60g / min through the feeding funnel. For specific parameters, see Figure 2 As shown. The three flame nozzles in the middle of the refractory tube are pointed at the central axis of the refractory tube at an angle of 45° upwards and then offset 5° clockwise with the intersection of the spray gun and the high-temperature tube wall as the fulcrum. The acetylene flow rate of each spray gun is 3L / min and the oxygen flow rate is 6L / min. After the falling alumina particles enter the flame zone, the surface of the particles melts rapidly and forms a sphere under the action of surface tension. After leaving the flame zone and cooling, the particles maintain a spherical appearance to obtain alumina microspheres. Performance test analysis: 1. Morphology observation: Figure 3 and Figure 4 The following are the translucent and reflective photos of alumina microspheres taken under the optical microscope of Zeiss Axioscope 5. It can be seen that the microspheres have a high conversion rate, a smooth surface and good gloss.

[0025] 2.X-ray diffraction spectrum: Figure 5 This is the X-ray diffraction diagram of the prepared microspheres. It can be seen that the alumina microspheres are still α-alumina in the corundum phase after surface spraying.

[0026] 3. Microsphere density: The abrasive density was 3.0 g / cm3 as measured by a hydrostatic balance. 3 , compared with the density of single crystal corundum 4.0g / cm 3 It can be seen that the porosity of the alumina microspheres prepared in this case is 25%.

[0027] The aluminum oxide microspheres prepared by the invention have high yield, good sphericity and smooth surface, and reasonably utilize dust removal powder generated in the production process of fused white corundum abrasives. The process is simple, the equipment investment is low, and the optimal utilization of resources and high value of by-products are achieved.

[0028] According to the content of the invention, a simple adjustment of the process parameters or a simple modification of the spray melting device can also achieve the preparation of alumina microspheres, and show similar results to the above embodiment. The above is an exemplary description of the present invention. It should be noted that any simple modification and equivalent replacement that can be made by those skilled in the art without spending creative labor without departing from the core of the present invention fall within the protection scope of the present invention.

Claims

1. A method for preparing alumina microspheres based on surface flame spraying technology, characterized in that: The following steps are involved: (1) Using the dust removal powder produced in the production process of fused white corundum as the main raw material, adding CaF2 and Na2SiO3 as sintering aids, adding water and polyethylene glycol, and mixing evenly to form a slurry; (2) After the slurry is dried, it is transferred into a high-temperature kiln and sintered at about 1300°C to form a block of alumina sintered body; (3) crushing the blocky alumina sintered body to form particles with a particle diameter of less than 200 μm; (4) Using an oxyacetylene flame, the particles are surface-molded to obtain alumina microspheres after cooling.

2. The method for preparing alumina microspheres based on surface flame spraying technology according to claim 1, characterized in that: The main raw material is dust removal powder with a particle size of less than 50 μm formed in the production process of fused white corundum. The sintering aid in step (1) is 1-3% by mass of CaF2 and 5-10% by mass of Na2SiO3. The slurry bonding and shrinkage aid is 0.2-0.5% by mass of polyethylene glycol.

3. The method for preparing alumina microspheres based on surface flame spraying technology according to claim 1, characterized in that The sintering temperature of the dried alumina is 1270-1330°C and the alumina sintered body needs to be crushed to a particle size less than 200 μm.

4. The method for preparing alumina microspheres based on surface flame spraying technology according to claim 1, characterized in that The crushed qualified alumina sintered particles are passed through a feeding funnel and enter a vertical zirconia refractory tube by their own gravity. Several symmetrically distributed oxyacetylene flame nozzles are arranged in the refractory tube. By adjusting the nozzle angles and the flow rates of oxygen and acetylene, a conical flame vortex is formed in the refractory tube and diffused in a section of the center of the tube to form a flame zone. When the alumina sintered particles pass through the flame zone, their surfaces melt rapidly and they are formed into spheres under the action of the surface tension of the liquid. After falling out of the flame zone, they are cooled to form alumina microspheres.

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