A method for preparing spherical alumina powder by flame fusion

Abstract

The present invention relates to a preparation process for spherical alumina micropowder by flame melting. The preparation process for spherical alumina micropowder by flame melting comprises: preparation of alumina powder: preparing an aluminum nitrate solution, adding a dispersant and seed crystals to the solution, dripping an ammonia aqueous solution thereto, adjusting the pH to obtain a precursor precipitate, filtering the precursor precipitate, washing, drying, and sieving the dried powder to obtain a precursor powder, calcining, cooling with the furnace, and obtaining alumina powder. Preparation of spherical alumina micropowder: using a powder feeder to introduce the pretreated alumina powder into the flame temperature field, the alumina powder is heated and accelerated by the flame flow in the burner, and continues to be heated and melted when flying through the spheroidizing furnace. The molten particles fly out of the high temperature zone and are rapidly cooled to obtain molten spherical alumina, which are then classified and collected to obtain alumina micropowder with high purity and uniform particle size. The present invention has the advantages of low particle wear, long service life, and high spheroidization degree.

Description

Technical Field

[0001] The invention relates to a preparation process of spherical alumina micropowder by a flame melting method. Background Art

[0002] Driven by the rapid development of global industry, spherical alumina powders have been extensively studied in recent years. Synthesized spherical alumina is primarily used in catalysts and catalyst supports, ceramic powders, and optical materials. The diverse crystal forms and unique physical and chemical properties of alumina and its hydrates have led to their widespread application in fields such as petrochemicals, electronics, refractories, ceramics, abrasives, pharmaceuticals, and aerospace. The performance of alumina products in these diverse fields is significantly influenced by the morphology and size of the raw powder particles. Among powder particles of varying shapes, spherical particles exhibit a regular morphology, a smaller specific surface area, a higher bulk density, and superior flow properties, significantly enhancing the product's performance.

[0003] Spherical alumina, due to its unique properties, can effectively enhance its physical and chemical properties when combined with inorganic materials. High thermal conductivity gaskets, a typical thermal interface material, effectively improve heat dissipation. By replacing traditional metal powders with spherical alumina and synthesizing it with an organic silicone grease composite material, a high thermal conductivity and high insulation gasket composite material is produced.

[0004] Spherical aluminum oxide as a surface coating exhibits excellent performance characteristics, such as high hardness, low thermal conductivity and chemical resistance. Therefore, it is generally sprayed on the surface of plastics or metals to improve surface hardness, corrosion resistance, wear resistance and fire resistance.

[0005] Spherical alumina materials can be sintered into transparent ceramics, used as high-pressure lamp materials or compounded with rare earth phosphors to form new luminous functional materials, which can not only reduce costs but also extend service life.

[0006] When spherical alumina is used as a catalyst or catalyst carrier, the balls are evenly stacked through point contact, which can effectively reduce bed resistance and thus improve mass transfer and catalytic effects.

[0007] The various advantages of spherical alumina powder have led to its widespread application in high-tech fields. However, the current preparation technology and application of spherical alumina powder still face numerous problems, including suboptimal particle shape, low production efficiency, difficult to control process parameters, complex structure, difficult to resolve product agglomeration problems, wide product particle size distribution, harsh conditions, high cost, and poor repeatability of the preparation process. Summary of the Invention

[0008] The purpose of the present invention is to solve the existing problems of large particle size, wide particle size distribution, agglomeration and spherical merging of spherical alumina powder, and finally obtain alumina powder with good spherical regularity, good dispersion and fine particle size.

[0009] The above technical objectives of the present invention are achieved through the following technical solutions:

[0010] (1) Alumina preparation

[0011] A certain concentration of aluminum nitrate solution is prepared, and a dispersant and seed crystals are added to the solution, an ammonia solution is added dropwise thereto, the pH is adjusted to obtain a precursor precipitate, the solution is stirred and ultrasonically treated, and then aged at room temperature. The precursor precipitate is filtered, washed, and dried, and the dried powder obtained is sieved to obtain a precursor powder. The prepared precursor powder is calcined and cooled to room temperature with the furnace to obtain alumina powder.

[0012] (2) Preparation of spherical alumina

[0013] Alumina powder is used as raw material. After pretreatment, it is introduced into the flame temperature field using a powder feeder, heated and melted. The molten particles then fly out of the high-temperature zone and are rapidly cooled to produce molten spherical alumina. After classification, they are collected to obtain high-purity and uniform-size alumina micropowder.

[0014] Preferably, the aluminum oxide preparation comprises: preparing an aluminum nitrate solution having a concentration of 1 mol / L to 2 mol / L by using Al(NO₃)₃·9H₂O with deionized water as a solvent; placing the prepared aluminum nitrate solution in a conical flask, adding a dispersant and seed crystals; magnetically stirring the solution at varying ammonia droplet rates of 0.5 mL / min to 3 mL / min and stirring speeds of 500 rpm to 2000 rpm; adjusting the pH to various values ​​between 3 and 9; stirring and ultrasonically treating the solution; and precipitating the solution in a constant temperature water bath at various temperatures between 30°C and 80°C to obtain a precursor precipitate. The solution is then aged at room temperature for 8 to 24 hours, washed three times with deionized water and twice with anhydrous ethanol, and dried in an electrically heated constant temperature forced air drying oven at 80°C for 8 hours. The dried precursor is sieved through a 200-mesh standard sieve to obtain a precursor powder. The prepared precursor powder is placed in a high-temperature box-type resistance furnace for calcination, and is cooled to room temperature along with the furnace to obtain alumina powder.

[0015] Among them, when aluminum nitrate is used as the raw material, the powder agglomerates are mostly soft agglomerates, and the nitrogen generated after high-temperature heat treatment is conducive to the foaming of the gel, making the product have good dispersibility.

[0016] Using deionized water as the solvent, at low concentrations, the particles are evenly distributed without agglomeration; at high concentrations, agglomeration occurs between particles.

[0017] When the reaction is carried out in a hot solution, increasing the reaction temperature increases the solubility of the precipitate in the solution, reduces the solution's supersaturation, and slows the rate of nucleation. At the same time, the molecules in the solution increase their kinetic energy due to heating, which is not conducive to the formation of stable nuclei, but is conducive to accelerating the rate of nucleus growth. When the reaction temperature rises, the impurities adsorbed in the precipitate are greatly reduced, but the loss caused by the increased solubility is aggravated, so the hot solution needs to be aged.

[0018] Preferably, the preparation of spherical alumina includes: using alumina powder as raw material, subjecting it to pre-treatment such as ball milling and screening, that is, the alumina powder is ball milled in a ball mill, and after pre-treatment, it is screened to a suitable particle size; using a powder feeder to introduce the alumina powder into the flame temperature field, the alumina powder is heated and accelerated by the flame flow in the burner, and flies through the spheroidization furnace to continue to be heated and melted, shrinking into balls under the action of surface tension, and then the molten particles fly away from the high temperature zone and are rapidly cooled to obtain molten spherical alumina, which is collected after grading to obtain high-purity and uniform particle size alumina micropowder.

[0019] Among them, methane, natural gas and other gases are used as the heat source for melting powder. The flame is clean and pollution-free. Alumina powder of suitable particle size is melted instantly at high temperature by high-temperature flame melting beading method, and then quickly cooled and spheroidized to obtain high-purity and uniform particle size alumina micropowder.

[0020] Preferably, the heating rate during the calcination process is 5-8°C / min, the calcination temperature is usually 800-1200°C, and the calcination time is usually 2-4h.

[0021] Preferably, during the ball milling treatment, the sieved precursor or pre-calcined powder, grinding balls, and anhydrous ethanol are added to a 250 mL ball mill at a ratio of 1:2:3-5:6:7, and the mixture is ball milled for 24 hours.

[0022] Preferably, the dispersant is one of polyethylene glycol (PEG), polyvinyl pyrrolidone (PVP), polyvinyl alcohol (PVA) and sodium hexametaphosphate (NaPO3)6.

[0023] Among them, polyethylene glycol 400 (PEG-400) does not dissociate into ions in aqueous solution, but exists as a snake-shaped molecule in the aqueous solution, forming strong hydrogen bonds with the surface of aluminum hydroxide colloid particles. These molecules form a thin film of considerable thickness on the surface of the colloid particles and adsorb onto them. This protective film separates the aluminum hydroxide particles from each other in the liquid phase, preventing them from agglomerating and resulting in excellent particle dispersion. Furthermore, PEG-400 forms a charged protective layer around the particles. Therefore, when like-charged particles approach, the combined electrostatic repulsion and steric hindrance significantly reduce the particle size.

[0024] Preferably, the seed crystal is a-Al2O3.

[0025] As a preferred method, the main component of natural gas is methane, and oxygen is used as carrier gas and combustion-supporting gas. Methane and more than 99.5% pure oxygen are burned in a ratio of 1:1-1:3 as the heat source for molten alumina powder. The carrier gas volume is generally 80-160m 3 / h, temperature is 2000-2600℃.

[0026] Preferably, in step (1) of preparing alumina, the prepared precursor powder is fed through a multi-position uniform distribution feeding device and then calcined, and then cooled to room temperature with the furnace to obtain alumina powder; the multi-position uniform distribution feeding device comprises: a rotating plate having a circular structure, and an annular plate is concentrically fixedly provided on the top of the rotating plate;

[0027] A plurality of dispersion plates are longitudinally fixed to the rotating plate, the plurality of dispersion plates are equidistantly distributed in a circular shape, the dispersion plates are arc-shaped structures, a chamber is provided inside the dispersion plates and the bottom end is open, a plurality of through holes are equidistantly arranged in an area of ​​the inner arc surface of the dispersion plates above the rotating plate, a guide plate is fixedly provided at one centripetal end of the dispersion plates, and the centripetal ends of the plurality of guide plates are fixedly connected;

[0028] The material conveying pipe is fixedly installed on the top of multiple guide plates;

[0029] A support plate is provided with a rotation hole running through the support plate in the longitudinal direction, and the feed pipe passes through the rotation hole vertically and is rotatably mounted at the rotation hole;

[0030] A bevel gear ring is fixed on the circumferential outer wall of the feed pipe, and the bevel gear ring is located above the support plate. A motor is fixed on the top of the support plate, and an output shaft is provided at the output end of the motor. A bevel gear is fixed on the end of the output shaft facing away from the motor, and the bevel gear is meshed with the bevel gear ring.

[0031] Alumina micropowder is a kind of material with high chemical stability, high purity, true specific gravity, low density, good insulation performance, acid and alkali resistance, high mechanical strength, wear resistance and impact resistance. Flame melting method is a relatively common method for preparing alumina micropowder. The specific steps are: in the calcining furnace, the raw materials for preparing alumina micropowder are fed from top to bottom, so that the raw materials meet the burning flame, and the irregular edges of the micropowder are melted in a very short time. Under the action of surface tension and other factors, spherical micropowder particles are formed to achieve the preparation of alumina micropowder;

[0032] However, the existing flame fusion method for preparing alumina micropowder has certain defects: the raw materials are prone to local accumulation and agglomeration during the process of flowing from top to bottom in the calcining furnace, which makes the raw materials not dispersed enough when in contact with the burning flame, resulting in uneven distribution of the raw materials, and ultimately leads to insufficient contact between the raw materials and the burning flame, affecting the quality of the alumina micropowder.

[0033] By adopting the multi-position uniform distribution feeding device of the present invention, the raw materials are subjected to centrifugal dispersion motion under the action of the rotating plate, and then are subjected to the action of the arc-shaped dispersion plate. The raw materials are dispersed and spread flat on the inner arc surface of the dispersion plate, enter the dispersion plate from the through holes on the dispersion plate, and are finally discharged evenly from the bottom opening of the dispersion plate. As the rotating plate continues to rotate, the raw materials are discharged evenly, and the raw materials are evenly dispersed when in contact with the burning flame. The raw materials are in more sufficient contact with the burning flame, thereby improving the quality of the alumina micropowder.

[0034] Preferably, a shock-absorbing pad is fixedly arranged between the bottom end of the motor and the top end of the support plate.

[0035] Preferably, the top ends of the multiple guide plates are all conical structures.

[0036] Preferably, it also includes a material box, which is fixed above the support plate through an external mounting frame. A accommodating cavity is provided inside the material box and the top is open. A discharge port is provided at the bottom of the material box, and the top output end of the feed pipe is connected to the discharge port.

[0037] Preferably, a material level hole is provided on the side wall of the material box, and a transparent plate is provided at the material level hole.

[0038] Preferably, support plates are symmetrically arranged on both sides of the top of the support plate, and threaded mounting holes are arranged on the support plates. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] Figure 1 It is an isometric perspective view of the overall structure of the multi-position uniform distribution feeding device of the present invention;

[0040] Figure 2 It is an isometric perspective view of the split structure of the rotating plate, multiple dispersion plates and multiple guide plates of the multi-position uniform distribution feeding device of the present invention;

[0041] Figure 3 It is a top structural plan view of multiple dispersion plates and multiple guide plates of the multi-position uniform distribution feeding device of the present invention;

[0042] Figure 4 It is an isometric perspective view of one of the plurality of dispersing plates and the guide plate connected thereto in the multi-position uniform distribution feeding device of the present invention;

[0043] Figure 5It is an isometric perspective view of the motor, bevel gear ring and bevel gear of the multi-position uniform distribution feeding device of the present invention;

[0044] Figure 6 The invention relates to a preparation process of spherical alumina micropowder by flame fusion method.

[0045] Figure numerals: 1. rotating plate; 2. annular plate; 3. dispersion plate; 4. through hole; 5. guide plate; 6. material conveying pipe; 7. support plate; 8. bevel gear ring; 9. motor; 10. output shaft; 11. bevel gear; 12. shock-absorbing pad; 13. material box; 14. material level hole; 15. support plate. DETAILED DESCRIPTION

[0046] Example 1

[0047] Al(NO₃)₃·9H₂O was prepared into a 1 mol / L aluminum nitrate solution using deionized water as the solvent. The prepared aluminum nitrate solution was placed in an Erlenmeyer flask, and polyethylene glycol (PEG) and a-Al₂O₃ seed crystals were added. The solution was magnetically stirred at varying ammonia addition rates of 0.5 mL / min and a stirring speed of 500 r / min. The pH was adjusted to 9 at various pH values, followed by stirring and ultrasonic treatment. The resulting precursor precipitates were then placed in a constant-temperature water bath at 30°C and aged at room temperature for 8 h. The precipitates were then washed three times with deionized water and twice with anhydrous ethanol. The washed precursor precipitates were then dried in an electrically heated constant-temperature forced-air drying oven at 80°C for 8 h. The dried precursor was sieved through a 200-mesh standard sieve to obtain a precursor powder. The prepared precursor powder is introduced into a calcination device through a multi-position uniform distribution feeding device, heated at 5°C / min, calcined at 800°C for 2h, and cooled to room temperature in the furnace to obtain alumina powder.

[0048] like Figure 1-Figure 5 As shown, a multi-position uniform distribution feeding device comprises: a rotating plate 1 of a circular structure, with an annular plate 2 fixedly provided concentrically on the top of the rotating plate 1; a plurality of dispersion plates 3, which penetrate and are fixed on the rotating plate 1 in the longitudinal direction, and are equidistantly distributed in a circular shape. The dispersion plates 3 are of an arc-shaped structure, and a chamber is provided inside the dispersion plates 3 and is open at the bottom end. A plurality of through holes 4 are provided in an equidistant array in the area of ​​the inner arc surface of the dispersion plates 3 located above the rotating plate 1; a guide plate 5 is fixedly provided on one centripetal end of the dispersion plate 3, and the centripetal ends of the plurality of guide plates 5 are fixedly connected; a material conveying pipe 6 is fixedly mounted on the top of the plurality of guide plates 5;

[0049] More specifically, the centrifugal ends of the multiple dispersion plates 3 are fixedly connected to the circumferential inner wall of the annular plate 2, the feed pipe 6 rotates about its own axial direction, the bottom end of the guide plate 5 is fixedly connected to the top of the rotating plate 1, and the thickness of the guide plate 5 gradually decreases from the centrifugal end to the centripetal end. It should be specifically noted that although the feed pipe 6 is fixed to the top of the multiple guide plates 5, the multiple guide plates 5 do not block the raw materials discharged from the bottom output end of the feed pipe 6. After the raw materials are discharged from the bottom output end of the feed pipe 6 onto the rotating plate 1, the raw materials are distributed in the space between two adjacent guide plates 5.

[0050] Its specific working principle is as follows: the raw material enters the conveying pipe 6 from the top input end and is discharged from the bottom output end of the conveying pipe 6 to the rotating plate 1. At this time, the raw material is distributed in the space between the two adjacent guide plates 5. A rotational driving force is applied to the conveying pipe 6. The conveying pipe 6 drives multiple guide plates 5, multiple dispersion plates 3 and the rotating plate 1 to rotate simultaneously with the axis of the conveying pipe 6 as the axis. Under the action of the centrifugal force generated by the rotation of the rotating plate 1, the raw material on the rotating plate 1 undergoes centrifugal motion. When the dispersion plate 3 rotates with the axis of the conveying pipe 6 as the axis, the inner arc surface of the dispersion plate 3 is located at the front side and undergoes centrifugal motion. The raw material first contacts the inner arc surface of the dispersion plate 3, and continues to perform centrifugal motion under the action of the rotation of the rotating plate 1. During this process, the raw material is evenly dispersed on the inner arc surface of the dispersion plate 3 from the centripetal end to the centrifugal end, and the raw material enters the chamber inside the dispersion plate 3 through the multiple through holes 4 on the dispersion plate 3 and falls out from the bottom end opening of the dispersion plate 3, so that the raw material is evenly discharged from the bottom end opening of the dispersion plate 3. As the rotating plate 1 continues to rotate, the raw material is evenly discharged, so that the raw material is evenly dispersed when it contacts the burning flame, and the raw material contacts the burning flame more fully, thereby improving the quality of the alumina powder.

[0051] Based on the above embodiment, it further includes a support plate 7, a rotation hole is longitudinally provided on the support plate 7, and the feed pipe 6 vertically passes through the rotation hole and is rotatably installed at the rotation hole;

[0052] During the specific implementation process, the feed pipe 6 and the support plate 7 are in a rotationally connected relationship. The support plate 7 supports the feed pipe 6. The support plate 7 facilitates the installation of the feed pipe 6 and components such as the rotating plate 1 in the external calcining furnace, which is convenient for operation.

[0053] Furthermore, a bevel gear ring 8 is fixedly provided on the circumferential outer wall of the feeding pipe 6. The bevel gear ring 8 is located above the support plate 7. A motor 9 is fixedly provided on the top of the support plate 7. An output shaft 10 is provided at the output end of the motor 9. A bevel gear 11 is fixedly provided at the end of the output shaft 10 facing away from the motor 9. The bevel gear 11 is meshed with the bevel gear ring 8.

[0054] During operation, the motor 9 is powered on and drives the bevel gear 11 to rotate through the output shaft 10. The bevel gear 11 drives the feed pipe 6 to rotate through the bevel gear ring 8. The rotation of the feed pipe 6 drives the rotating plate 1 to rotate, thereby achieving dispersed feeding of the raw materials, uniform dispersion of the raw materials, and improving reliability.

[0055] Furthermore, a shock-absorbing pad 12 is fixedly provided between the bottom end of the motor 9 and the top end of the support plate 7; the shock-absorbing pad 12 acts as a shock-absorbing and buffering device for the motor 9, thereby reducing the noise during the operation of the motor 9 and improving stability.

[0056] Based on the above embodiment, the top ends of the multiple guide plates 5 are all conical structures; by designing the top ends of the multiple guide plates 5 connected to the bottom output end of the conveying pipe 6 to be conical structures, the raw materials discharged from the bottom output end of the conveying pipe 6 will not accumulate at the top ends of the guide plates 5, so that all the raw materials can be discharged from the bottom output end of the conveying pipe 6 to the rotating plate 1, thereby improving the output efficiency of the raw materials.

[0057] Based on the above embodiment, it further includes a material box 13, which is fixed above the support plate 7 through an external mounting frame. The material box 13 is provided with a receiving cavity inside and has an open top. The bottom end of the material box 13 is provided with a discharge port, and the top output end of the feed pipe 6 is connected to the discharge port.

[0058] During operation, the raw materials are first filled into the material box 13, the raw materials enter the material delivery pipe 6 from the discharge port, and are finally discharged from the bottom output end of the material delivery pipe 6 to the rotating plate 1, and the material box 13 plays a role in centralized storage of the raw materials.

[0059] Based on the above embodiment, a material level hole 14 is provided on the side wall of the material box 13, and a transparent plate is provided at the material level hole 14; the material level hole 14 facilitates observation of the amount of raw materials remaining in the material box 13 and timely replenishment, thereby improving convenience.

[0060] Based on the above embodiment, support plates 15 are symmetrically provided on both sides of the top of the support plate 7, and threaded mounting holes are provided on the support plates 15; the support plates 15 facilitate the fixed installation of the support plate 7 in the external calcining furnace, thereby improving convenience.

[0061] Alumina powder is used as raw material, passed through a 200 mesh sieve, and pre-processed by ball milling. The sieved precursor or pre-calcined powder is added to a 250mL ball mill with grinding balls and anhydrous ethanol in a ratio of 1:2:3 and ball milled for 24 hours. Alumina powder is introduced into the flame temperature field using a powder feeder. Methane and pure oxygen above 99.5% are burned in a ratio of 1:1 as the heat source for melting alumina powder. The carrier gas volume is generally 80m 3 / h, the temperature is 2000 ° C. High-purity and uniform particle size alumina powder is obtained.

[0062] Example 2

[0063] Al(NO₃)₃·9H₂O was prepared into a 1.2 mol / L aluminum nitrate solution using deionized water as the solvent. The prepared aluminum nitrate solution was placed in an Erlenmeyer flask, and polyethylene glycol (PEG) and a-Al₂O₃ seed crystals were added. The solution was then magnetically stirred at varying ammonia addition rates of 1 mL / min and a stirring speed of 1000 r / min. The pH was adjusted to 7 at various pH values, followed by stirring and ultrasonic treatment. The resulting precursor precipitates were then placed in a constant-temperature water bath at 50°C and aged at room temperature for 12 hours. The precipitates were then washed three times with deionized water and twice with anhydrous ethanol. The washed precursor precipitates were then dried in an electrically heated constant-temperature forced-air drying oven at 80°C for 8 hours. The dried precursor was sieved through a 200-mesh standard sieve to obtain a precursor powder. The prepared precursor powder is placed in a high-temperature box-type resistance furnace for calcination, and the temperature is increased at 6°C / min to 900°C for 2h, and then cooled to room temperature in the furnace to obtain alumina powder. Alumina powder is used as raw material, passed through a 200-mesh sieve, and pre-treated by ball milling. The sieved precursor or pre-calcined powder is added to a 250mL ball mill jar with grinding balls and anhydrous ethanol in a ratio of 2:4:5, and ball milled for 24h. Alumina powder is introduced into the flame temperature field using a powder feeder, and methane and more than 99.5% pure oxygen are burned in a ratio of 1:2 as a heat source for melting alumina powder. The carrier gas volume is generally 100m 3 / h, the temperature is 2200 ° C. High-purity and uniform particle size alumina powder is obtained.

[0064] Example 3

[0065] Al(NO₃)₃·9H₂O was prepared into a 1.5 mol / L aluminum nitrate solution using deionized water as the solvent. The prepared aluminum nitrate solution was placed in a conical flask, and polyethylene glycol (PEG) and a-Al₂O₃ seed crystals were added. The solution was magnetically stirred at different ammonia addition rates of 2 mL / min and a stirring speed of 1500 r / min. The pH was adjusted to 5 at different pH values, followed by stirring and ultrasonic treatment. The resulting precursor precipitates were obtained by aging the solution in a constant-temperature water bath at 60°C for 18 hours at room temperature. The precipitates were then washed three times with deionized water and twice with anhydrous ethanol. The washed precursor precipitates were then dried in an electrically heated constant-temperature forced-air drying oven at 80°C for 8 hours. The dried precursor was sieved through a 200-mesh standard sieve to obtain a precursor powder. The prepared precursor powder is placed in a high-temperature box-type resistance furnace for calcination, and the temperature is increased at 7°C / min to 1000°C for 3 hours, and then cooled to room temperature in the furnace to obtain alumina powder. Alumina powder is used as raw material, passed through a 200-mesh sieve, and pre-treated by ball milling. The sieved precursor or pre-calcined powder is added to a 250mL ball mill jar with grinding balls and anhydrous ethanol in a ratio of 4:5:6, and ball milled for 24 hours. Alumina powder is introduced into the flame temperature field using a powder feeder, and methane and more than 99.5% pure oxygen are burned in a ratio of 1:3 as a heat source for melting alumina powder. The carrier gas volume is generally 140m 3 / h, the temperature is 2400 ° C. High-purity and uniform particle size alumina powder is obtained.

[0066] Example 4

[0067] Al(NO₃)₃·9H₂O was prepared into a 2 mol / L aluminum nitrate solution using deionized water as the solvent. The prepared aluminum nitrate solution was placed in an Erlenmeyer flask, and polyethylene glycol (PEG) and a-Al₂O₃ seed crystals were added. The solution was magnetically stirred at varying ammonia addition rates of 3 mL / min and a stirring speed of 2000 r / min. The pH was adjusted to 3 at various pH values, followed by stirring and ultrasonic treatment. The resulting precursor precipitates were then placed in a constant-temperature water bath at 80°C to obtain a precursor. The resulting precursor precipitates were then aged at room temperature for 24 hours. The precursor precipitates were then washed three times with deionized water and twice with anhydrous ethanol. The washed precursor precipitates were then dried in an electrically heated constant-temperature forced-air drying oven at 80°C for 8 hours. The dried precursor was sieved through a 200-mesh standard sieve to obtain a precursor powder. The prepared precursor powder is placed in a high-temperature box-type resistance furnace for calcination, and the temperature is increased at 8°C / min to 1200°C for 4 hours, and then cooled to room temperature in the furnace to obtain alumina powder. Alumina powder is used as raw material, passed through a 200-mesh sieve, and pre-treated by ball milling. The sieved precursor or pre-calcined powder is added to a 250mL ball mill jar with grinding balls and anhydrous ethanol in a ratio of 5:6:7, and ball milled for 24 hours. Alumina powder is introduced into the flame temperature field using a powder feeder, and methane and more than 99.5% pure oxygen are burned in a ratio of 1:3 as a heat source for melting alumina powder. The carrier gas volume is generally 160m 3 / h, the temperature is 2600 ° C. High-purity and uniform particle size alumina powder is obtained.

[0068] Comparative Example 1

[0069] Al(NO₃)₃·9H₂O was prepared into a 1 mol / L aluminum nitrate solution using deionized water as the solvent. The prepared aluminum nitrate solution was placed in an Erlenmeyer flask, and polyvinylpyrrolidone (PVP) and a-Al₂O₃ seed crystal were added. The solution was then magnetically stirred at varying ammonia addition rates of 3 mL / min and a stirring speed of 500 r / min. The pH was adjusted to 9 at various pH values, followed by stirring and ultrasonic treatment. The solution was then placed in a constant-temperature water bath at 30°C to obtain a precursor precipitate. The solution was then aged at room temperature for 8 hours. The precursor precipitate was washed three times with deionized water and twice with anhydrous ethanol. The washed precursor precipitate was then dried in an electrically heated constant-temperature forced-air drying oven at 80°C for 8 h. The dried precursor was sieved through a 200-mesh standard sieve to obtain a precursor powder. The prepared precursor powder is placed in a high-temperature box-type resistance furnace for calcination, and the temperature is increased at 5°C / min to 800°C for 2h, and then cooled to room temperature in the furnace to obtain alumina powder. Alumina powder is used as raw material, passed through a 200-mesh sieve, and pre-treated by ball milling. The sieved precursor or pre-calcined powder is added to a 250mL ball mill jar with grinding balls and anhydrous ethanol in a ratio of 1:2:3, and ball milled for 24h. Alumina powder is introduced into the flame temperature field using a powder feeder, and methane and more than 99.5% pure oxygen are burned in a ratio of 1:1 as a heat source for melting alumina powder. The carrier gas volume is generally 80m 3 / h, the temperature is 2600 ° C. High-purity and uniform particle size alumina powder is obtained.

[0070] Comparative Example 2

[0071] Al(NO₃)₃·9H₂O was prepared into a 1 mol / L aluminum nitrate solution using deionized water as the solvent. The prepared aluminum nitrate solution was placed in an Erlenmeyer flask, and polyvinyl alcohol (PVA) and a-Al₂O₃ seed crystal were added. The solution was magnetically stirred at different ammonia droplet rates of 3 mL / min and a stirring speed of 500 r / min. The pH value was adjusted to 9 at different pH values, and the solution was stirred and ultrasonically treated. The precursor precipitates were obtained by aging in a constant-temperature water bath at 30°C. The precursor precipitates were then washed three times with deionized water and twice with anhydrous ethanol. The washed precursor precipitates were placed in an electric constant-temperature forced-air drying oven and dried at 80°C for 8 h. The dried precursor was sieved through a 200-mesh standard sieve to obtain a precursor powder. The prepared precursor powder was calcined in a high-temperature box-type resistance furnace at 800°C for 2 h at a heating rate of 5°C / min. The calcination was then continued to cool to room temperature to obtain alumina powder. Alumina powder is used as raw material, passed through a 200 mesh sieve, and pre-processed by ball milling. The sieved precursor or pre-calcined powder is added to a 250mL ball mill with grinding balls and anhydrous ethanol in a ratio of 1:2:3 and ball milled for 24 hours. Alumina powder is introduced into the flame temperature field using a powder feeder. Methane and pure oxygen above 99.5% are burned in a ratio of 1:1 as the heat source for melting alumina powder. The carrier gas volume is generally 160m 3 / h, the temperature is 2600 ° C. High-purity and uniform particle size alumina powder is obtained.

[0072] Experimental test of alumina powder obtained in Examples and Comparative Examples:

[0073] Laser particle size analysis

[0074] The sample's particle size and size distribution were measured using a 90 Plus Zeta Nanoparticle Sizer from Brookhaven Instruments (USA). Water or anhydrous ethanol were used as the measuring medium. The instrument can measure particle sizes from 0.3 nm to 10 μm (depending on refractive index, concentration, and scattering angle), and can measure particles of any colloidal size (suspended in a clear liquid).

[0075] Specific surface area analyzer

[0076] A surface area analyzer can be used to measure the specific surface area of ​​powder particles. The specific surface area of ​​the particle samples was tested and analyzed using a Flowsorb 3-2310 surface area analyzer. The sample drying temperature was 200°C.

[0077] Friction coefficient tester

[0078] Friction coefficient meters are commonly used to measure the static and kinetic friction coefficients of sliding materials. This experiment used an MXD-01 friction coefficient meter to measure the friction coefficient of particles before and after grinding.

[0079] Scanning electron microscopy

[0080] Scanning electron microscopy can be used to observe the microscopic morphology and size of powder particles. A NOVANANOSEM-430 field emission scanning electron microscope was used to analyze the particle size and morphology of the particle samples. The test parameters were an accelerating voltage of 15.0 kV and an electron beam current of 80.0 pA.

[0081] Sphericity

[0082] The sphericity of the particles was calculated using the image analysis software Image-Pro Plus 6.0 (developed by MediaCybernetics, USA) combined with scanning electron microscopy images. The formula for calculating the sphericity of a single particle is: Φ = 4πS / p 2

[0083] Where Φ is the particle's sphericity, S is the particle's projected area under the electron microscope image, and p is the particle's projected perimeter under the electron microscope image. The maximum value of Φ is 1. A larger Φ value indicates a greater sphericity and a more spherical particle. The sphericity of 100 randomly selected particles is calculated and then averaged to obtain the average sphericity of the particles.

[0084] Table 1 Alumina particle size

[0085]

[0086] The reaction temperature is correlated with the average particle size, increasing with increasing temperature. The addition rate is also correlated with the average particle size, increasing with increasing addition rate. The reaction pH is also correlated with the average particle size, decreasing with increasing pH. Laser particle size distribution of alumina powder indicates the size of secondary agglomerated particles, i.e., the dispersion of primary particles in the aqueous solution. A smaller average particle size indicates smaller secondary agglomerated particles, indicating better dispersion of the primary particles. Excessively fast ammonia addition can lead to local saturation and overheating. This increases the particle surface energy, causing the particles to aggregate into agglomerates due to van der Waals forces, surface electrostatic forces, and hydrogen bonding. Smaller particle size increases specific surface area, resulting in a relatively greater amount of heat transferred to the powder from the flame temperature field. Furthermore, the melting temperature of a powder is related to its particle size: smaller particles have a lower melting point. Therefore, under the same conditions, smaller alumina particles will melt preferentially. The time required for particle melting and spheroidization is proportional to the particle diameter. Larger particles require longer melting times, meaning they are more difficult to melt. Smaller particles, on the other hand, are easier to melt and spheroidize. Therefore, the particle size of the powder used in spheroidization should not be too large, and the narrower the particle size distribution, the better.

[0087] Table 2 Specific surface area

[0088]

[0089] Compared with the raw alumina particles, the specific surface area of ​​the alumina particles ground from Comparative Example 2 to Example 1 increased to 23.4 m 2 / g, which is due to the obvious reduction in the particle size of the alumina particles. Compared with the alumina particles ground in the control ratio, the specific surface area of ​​the particles ground in different ratios has increased to a certain extent.

[0090] Table 3 Sphericity

[0091]

[0092] It can be seen from Table 3 that Example 1 has the largest sphericity and Comparative Example 2 has the smallest. As the airflow rate increases, the sphericity of the alumina micropowder first increases and then decreases. This is because the flame burner power increases with the increase in airflow rate. Another effect is that the flight speed of the particles increases with the increase in airflow rate. With the increase in airflow rate, the energy of the temperature field generated by the flame increases and the temperature rises, which accelerates the heat transfer between the flame and the particles. Another effect is that the flight speed of the particles increases with the increase in airflow rate. As the gas flow rate increases, the flight speed of the particles increases, and the flight time of the particles in the flame and the spheroidization furnace is shortened. The micropowder does not have time to melt, resulting in a decrease in the spheroidization rate.

[0093] Table 4 Friction coefficient of alumina powder

[0094]

[0095] As shown in Table 4, Example 1 has the lowest friction coefficient, while Comparative Example 2 has the highest, gradually increasing. This is because the raw material particles have relatively irregular morphology and low sphericity. After grinding, the sharp corners and edges of the particles are reduced, the sphericity is improved to a certain extent, and the contact surface roughness is relatively reduced, resulting in a decrease in the friction coefficient. In addition, more spherical particles are more likely to undergo rolling friction during the sliding process, which also plays a role in reducing friction, thereby significantly reducing the friction coefficient.

[0096] This specific embodiment is merely an explanation of the present invention and does not limit the present invention. After reading this specification, those skilled in the art can make non-creative modifications to this embodiment as needed, but as long as they are within the scope of the claims of the present invention, they are protected by patent law.

Claims

1. A method for preparing spherical alumina powder by flame fusion, characterized in that: (1) Alumina preparation Al(NO3)3·9H2O was prepared into a 1 mol / L aluminum nitrate solution using deionized water as a solvent. The prepared aluminum nitrate solution was placed in a conical flask, and polyethylene glycol (PEG) and a-Al2O3 seed crystal were added thereto. The solution was magnetically stirred at an ammonia drop rate of 0.5 mL / min and a stirring speed of 500 r / min. The pH value was adjusted to 9, stirred and ultrasonically treated. The precursor precipitate was obtained by placing it in a constant temperature water bath at 30°C, and then aged at room temperature for 8 h. The precursor precipitate was washed 3 times with deionized water and 2 times with anhydrous ethanol. The washed precursor precipitate was placed in an electric constant temperature blast drying oven and dried at 80°C for 8 h. The dried precursor was sieved through a 200-mesh standard sieve to obtain a precursor powder. The prepared precursor powder is introduced into a multi-position uniform distribution feeding device for calcination, the temperature is increased at 5°C / min, calcined at 800°C for 2h, and cooled to room temperature in the furnace to obtain alumina powder; The multi-position uniform distribution feeding device comprises: The rotating plate (1) is a circular structure, and an annular plate (2) is fixedly provided concentrically on the top of the rotating plate (1); A plurality of dispersion plates (3) are fixed on the rotating plate (1) through the longitudinal direction, the plurality of dispersion plates (3) are equidistantly distributed in a circular shape, the dispersion plates (3) are arc-shaped structures, a chamber is provided inside the dispersion plates (3) and the bottom end is open, a plurality of through holes (4) are provided in an equidistant array in the area of ​​the inner arc surface of the dispersion plates (3) located above the rotating plate (1), a guide plate (5) is fixedly provided at one centripetal end of the dispersion plates (3), and the centripetal ends of the plurality of guide plates (5) are fixedly connected; A material delivery pipe (6) is fixedly mounted on the top of the plurality of guide plates (5); A support plate (7) is provided with a rotation hole extending longitudinally therethrough, and the feed pipe (6) vertically passes through the rotation hole and is rotatably mounted at the rotation hole; A bevel gear ring (8) is fixedly provided on the circumferential outer wall of the feed pipe (6), the bevel gear ring (8) is located above the support plate (7), a motor (9) is fixedly provided on the top of the support plate (7), an output shaft (10) is provided at the output end of the motor (9), a bevel gear (11) is fixedly provided at one end of the output shaft (10) facing away from the motor (9), and the bevel gear (11) is meshed with the bevel gear ring (8); (2) Preparation of spherical alumina Alumina powder is used as raw material, passed through a 200-mesh sieve, and pre-treated by ball milling. The sieved precursor, grinding balls, and anhydrous ethanol are added to a 250 mL ball mill at a ratio of 1:2:3 and ball milled for 24 hours. Alumina powder is introduced into the flame temperature field using a powder feeder, and methane and pure oxygen above 99.5% are burned in a 1:1 ratio as a heat source for melting alumina powder. The carrier gas volume is generally 80m 3 / h, the temperature is 2000℃; high-purity and uniform particle size alumina powder is obtained.

2. The method for preparing spherical alumina powder by flame fusion according to claim 1, characterized in that: The top ends of the plurality of guide plates (5) are all conical structures.

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