A method for the preparation of an alumina spray granulated powder

Abstract

The application discloses a preparation method of an alumina spray granulation powder, and belongs to the technical field of spray granulation, and comprises the following steps: S1, slurry preparation: adding alumina raw material powder into deionized water, then adding a composite dispersing agent, high-speed stirring and ball milling to obtain a slurry, adding a composite bonding-plasticizing agent system into the slurry and continuously ball milling and stirring to obtain a special slurry for spray granulation; S2, atomization and drying: conveying the special slurry for spray granulation to a centrifugal atomizer, matching the feeding speed with the rotating speed, and ensuring that the special slurry for spray granulation is sheared by centrifugal force to form liquid drops with uniform sizes; the liquid drops are sprayed into a spray drying tower and dried by contacting hot air, and a three-stage temperature field control is adopted in the drying process; S3, collection and post-treatment: collecting the granules after drying, aging the collected granule powder in an oven at 60-80 DEG C for 6-24 hours, and finally screening, and taking the granules with a particle size in the range of 32-125 mu m as products.

Description

Technical Field

[0001] This invention relates to the field of spray granulation technology, and in particular to a method for preparing alumina spray granulation powder. Background Technology

[0002] Spray granulation is a process that atomizes ceramic slurry into tiny droplets and then instantly dries them in hot air to obtain spherical particles with good flowability. It is a key step connecting powder synthesis and dry forming. High-quality spray-granulated powder is essential for achieving high uniformity, high density, and complex shape forming of ceramic green bodies.

[0003] However, traditional alumina spray granulation technology has the following common problems that limit the preparation of high-performance ceramics:

[0004] The contradiction between particle strength and flowability: To achieve high flowability, high particle sphericity and smooth surface are required. This usually requires a high solids content in the slurry and a moderate amount of binder. However, high solids content slurries have high viscosity and are difficult to atomize; while too much or inappropriate binder will result in overly hard particles that cannot be effectively broken and rearranged during subsequent dry pressing, leading to defects; too little binder results in low particle strength and the generation of fine powder during transportation and filling.

[0005] Internal structural defects in particles: Particles prepared by traditional processes often exhibit "hollow spheres" or "large pores." This is due to the rapid formation of a hard shell on the surface during drying, which hinders the evaporation of the internal solvent. This hollow structure is prone to breakage during molding, resulting in irregular large particles, or it may remain as a source of defects within the green body.

[0006] Wide particle size distribution: Conventional pressure or centrifugal atomization methods struggle to produce highly uniform droplets, resulting in a wide particle size distribution in the granulated powder. This wide distribution leads to a decrease in powder bulk density, and the pattern of small particles filling the gaps between large particles during molding becomes complex, affecting the uniformity of the green body.

[0007] Organic residues and debinding issues: If commonly used binders and plasticizers are not completely decomposed in the subsequent debinding stage, carbon residues are easily generated, which affects the performance of the sintered body. Summary of the Invention

[0008] The technical problem to be solved by the present invention is to provide a method for preparing alumina spray granulated powder, which prepares granulated powder with high sphericity, high fluidity, low porosity, narrow particle size distribution and suitable crushing strength.

[0009] To solve the above-mentioned technical problems, the technical solution of the present invention is as follows:

[0010] A method for preparing alumina spray-granulated powder, the method comprising the following steps:

[0011] S1. Slurry preparation:

[0012] Alumina raw material powder is added to deionized water to prepare an initial suspension with a solid content of 45-65%. Then, a composite dispersant is added at a rate of 0.3-1.5% of the alumina raw material powder mass. The mixture is stirred at high speed and ball-milled for 2-12 hours to obtain a stable and uniform slurry. A composite binder-plasticizer system is then added to the slurry. The composite binder-plasticizer system includes:

[0013] The main binder is polyvinyl butyral or hydroxypropyl methylcellulose, and the addition amount is 0.5-3.0 wt% of the alumina raw material powder.

[0014] The auxiliary binder and plasticizer are polyethylene glycol and / or glycerin, added at a rate of 0.5–2.5 wt% of the alumina raw material powder.

[0015] The pore structure regulator is soluble starch or microcrystalline cellulose, added at a rate of 0.1–1.0 wt% of the alumina raw material powder.

[0016] After adding the composite binder-plasticizer system, continue ball milling and stirring for 2 to 6 hours to ensure that the organic matter is completely dissolved and dispersed, and obtain a spray granulation slurry with a viscosity in the range of 300 to 1500 mPa·s.

[0017] S2. Atomization and Drying:

[0018] The spray granulation slurry is fed to a centrifugal atomizer, and the atomizer speed is controlled between 8000 and 20000 rpm. The feed rate is matched with the speed to ensure that the spray granulation slurry is sheared by centrifugal force to form droplets of uniform size.

[0019] The droplets are sprayed into a spray drying tower and dried by contact with hot air. The drying process is controlled by a three-stage temperature field.

[0020] The inlet temperature T1 is 180–220℃;

[0021] The temperature T2 in the middle of the tower is such that the droplets experience the temperature T2 in the middle of the tower during their flight path. The temperature T2 in the middle of the tower is 20 to 50°C higher than the inlet temperature T1, that is, it is controlled between 200 and 270°C.

[0022] The outlet temperature T3 is 90–110℃;

[0023] The hot air flow and the atomized droplet flow are parallel;

[0024] S3. Collection and Post-processing:

[0025] Collect the dried granules, age the collected granule powder in an oven at 60-80℃ for 6-24 hours, and finally sieve them to take the granules with a particle size in the range of 32-125 μm as the product.

[0026] Preferably, in step S1, the alumina raw material powder is α-Al2O3, and the D50 particle size of the alumina raw material powder is 0.3-1.0 μm.

[0027] Preferably, in step S1, the composite dispersant is a mixture of ammonium polyacrylate and polyethylene glycol, and the mass ratio of ammonium polyacrylate to polyethylene glycol is 1:0.2 to 1:1.

[0028] Preferably, in step S1, the stirring speed of the high-speed stirring is greater than or equal to 1000 rpm.

[0029] The above technical solution has the following beneficial effects:

[0030] Optimized strength and flowability: The dense and smooth surface ensures extremely high sphericity and flowability. The moderate microporous structure and plasticizing effect of PEG / glycerol make the particles have suitable "breakage strength" during dry pressing. They can effectively collapse and rearrange under pressure to achieve high green density, rather than producing an arching effect like "hard balls".

[0031] Narrowing particle size distribution: High-speed centrifugal atomization combined with a special slurry can produce highly monodisperse droplets. With the help of a three-stage temperature field, the particles are given a gentle "re-softening" process in the T2 stage, which makes the surface tension of irregular particles that may be caused by uneven drying uniform, further promoting sphericity and narrowing the particle size distribution range.

[0032] Improved glue removal behavior: The selected organic additives have a low thermal decomposition temperature and a narrow range, and have good decomposition synergy with PVB / HPMC, which helps to remove glue quickly and completely in the future and reduce the risk of carbon residue. Detailed Implementation

[0033] The specific embodiments of the present invention will be further described below. It should be noted that these descriptions are for the purpose of aiding understanding the present invention, but do not constitute a limitation thereof. Furthermore, the technical features involved in the various embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

[0034] To overcome the problems of the contradiction between particle strength and flowability, hollow structure and wide particle size distribution in the existing alumina spray granulation technology, a method is provided that has strong process controllability and can stably prepare alumina spray granulated powder with high sphericity, suitable strength, narrow particle size distribution and dense internal structure.

[0035] A method for preparing high-performance alumina spray granulation powder specifically includes the following steps:

[0036] Step S1: Slurry preparation

[0037] Alumina raw material powder is added to deionized water to prepare an initial suspension with a solid content of 45%–65%. The alumina raw material powder is specifically α-Al2O3 with a D50 of 0.3–1.0 μm. The D50 particle size can be 0.3 μm or 1.0 μm. The solid content of the initial suspension is 45% or 65%.

[0038] A composite dispersant, a mixture of ammonium polyacrylate and polyethylene glycol, is added to the initial suspension prepared above. The mass ratio of ammonium polyacrylate to polyethylene glycol is 1:0.2 to 1:1, and the total addition amount is 0.3 to 1.5 wt% of the alumina raw material powder. The mixture is first stirred at high speed and ball-milled for 2 to 12 hours to obtain a homogeneous slurry with low viscosity and high stability. Specifically, the mass ratio of ammonium polyacrylate to polyethylene glycol is 1:0.2 or 1:1, and the total addition amount of the composite dispersant is 0.3% or 1.5% of the alumina raw material powder. The mixture is stirred and ball-milled at a speed of 1000 rpm or higher for 2 hours or 12 hours, or 7 hours.

[0039] A composite binder-plasticizer system is added to the slurry prepared above. The composite binder-plasticizer system comprises:

[0040] Main binder: Polyvinyl butyral (PVB) or hydroxypropyl methylcellulose (HPMC), added at a rate of 0.5–3.0 wt% of the alumina raw material powder. Specifically, the amount of the main binder is 0.5 wt% or 3.0 wt% of the alumina raw material powder, or it can be 1.5 wt%.

[0041] Auxiliary binder and plasticizer: polyethylene glycol and / or glycerin, added at a rate of 0.5 to 2.5 wt% of the alumina raw material powder. Specifically, the auxiliary binder and plasticizer are added at a rate of 0.5 wt% or 2.5 wt% of the alumina raw material powder. The auxiliary binder and plasticizer are polyethylene glycol or glycerin, or polyethylene glycol and glycerin.

[0042] Pore ​​structure regulator: soluble starch or microcrystalline cellulose, added at a rate of 0.1–1.0 wt% of the alumina raw material powder. Specifically, the amount of soluble starch or microcrystalline cellulose added is 0.1 wt% or 1.0 wt% of the alumina raw material powder.

[0043] After adding the composite binder-plasticizer system, continue ball milling and stirring for 2 to 6 hours to ensure complete dissolution and dispersion of organic matter, and obtain a uniform and stable spray granulation slurry with a viscosity in the range of 300 to 1500 mPa·s. Specifically, after adding the composite binder-plasticizer system, continue ball milling or stirring for 2 or 6 hours to obtain a spray granulation slurry with a viscosity of 300 mPa·s or 1500 mPa·s at 25°C, or even 900 mPa·s.

[0044] Step S2: Atomization and Drying

[0045] The above-mentioned spray granulation slurry is fed to a centrifugal atomizer, and the atomizer speed is controlled at 8000-20000 rpm. The feed rate is matched with the speed to ensure that the slurry is sheared by centrifugal force to form droplets of uniform size. Specifically, the atomizer speed is controlled at 8000 rpm or 20000 rpm, or it can be 12000 rpm.

[0046] The droplets formed above are sprayed into a spray drying tower and dried by contact with hot air. The drying process adopts a three-stage temperature field control of "low temperature-high temperature-low temperature", as detailed below:

[0047] The inlet temperature T1 is set to 180-220℃. Specifically, the inlet temperature T1 is set to 180℃ or 220℃, or it can be 200℃.

[0048] The temperature T2 in the middle of the tower: Through auxiliary heating or tower structure design, the droplets experience a temperature peak in a section of the flight path, with a middle temperature T2. The middle temperature T2 is 20-50°C higher than the inlet temperature T1, that is, the middle temperature T2 is controlled between 200-270°C. Specifically, the middle temperature T2 is 20-50°C higher than the inlet temperature T1, that is, the middle temperature T2 can be 200°C or 270°C.

[0049] The outlet temperature T3 is 90-110℃, specifically 90℃ or 110℃, or even 100℃;

[0050] The hot air flow and the atomized droplet flow are parallel.

[0051] Step S3: Collection and Post-processing

[0052] The dried granules are collected by a cyclone separator;

[0053] The collected powder is aged in an oven at 60-80℃ for 6-24 hours. Specifically, the collected powder is aged in an oven at 60℃ or 80℃ for 6 hours or 24 hours, or it can be aged in an oven at 70℃ for 15 hours.

[0054] After sieving, particles with a diameter between 32 and 125 μm are taken as the product, and alumina ceramics are prepared by dry pressing and sintering.

[0055] The granules prepared by the above method have a dense and smooth surface that ensures extremely high sphericity and flowability (the angle of repose can be less than or equal to 25°). The moderate microporous structure and the plasticizing effect of PEG / glycerol make the granules have suitable "breakage strength" when dry pressing, and can effectively collapse and rearrange under pressure to achieve high green density, rather than producing an arching effect like "hard balls".

[0056] High-speed centrifugal atomization combined with a specially formulated slurry (with suitable viscosity and surface tension) can produce highly monodisperse droplets. With the help of a three-stage temperature field, the particles are given a gentle "re-softening" process in the T2 stage, which makes the surface tension of irregular particles that may be caused by uneven drying uniform, further promoting sphericity and reducing the particle size distribution range (the span D90 / D10 can be less than 1.8).

[0057] The selected organic additives have a low thermal decomposition temperature and a narrow range, and have good decomposition synergy with PVB / HPMC, which helps to quickly and completely remove the adhesive and reduce the risk of carbon residue.

[0058] Example 1

[0059] A method for preparing high-performance alumina spray-granulated powder includes the following steps:

[0060] Step 1: Slurry preparation

[0061] Take 10 kg (dry basis) of α-Al2O3 powder with an average particle size D50=0.5μm, add deionized water and mix to prepare a suspension with a solid content of 55%.

[0062] Add composite dispersant: ammonium polyacrylate (PAA-NH4) and polyethylene glycol (PEG-6000), ball mill for 6 hours. The composite dispersant is 0.9 wt% of the alumina raw material powder, specifically 0.6 wt% ammonium polyacrylate and 0.3 wt% polyethylene glycol, i.e., 0.06 kg of ammonium polyacrylate and 0.03 kg of polyethylene glycol.

[0063] A composite binder-plasticizer system is added, including: polyvinyl butyral, polyethylene glycol (PEG-800), glycerin, and soluble starch. The polyvinyl butyral content is 1.5 wt% of the alumina raw material powder, the polyethylene glycol (PEG-800) content is 1 wt%, the glycerin content is 0.5 wt%, and the soluble starch content is 0.5 wt%. Specifically, the content is: 0.15 kg of polyvinyl butyral, 0.1 kg of polyethylene glycol, 0.05 kg of glycerin, and 0.05 kg of soluble starch.

[0064] Continue ball milling for 3 hours, and the slurry viscosity was measured to be 800 mPa·s (25℃) for spray granulation.

[0065] Step 2: Spray granulation

[0066] A high-speed centrifugal atomizer is used to form uniformly sized droplets at a rotation speed of 15,000 rpm;

[0067] Spray drying tower parameters: inlet temperature T1 is 200℃, a heating ring is set in the middle section of the tower to make the local temperature T2 230℃, outlet temperature T3 is 100℃, and the flow is parallel.

[0068] Step 3: Post-processing

[0069] Collect the powder, age it in an oven at 70℃ for 12 hours, and sieve it to obtain particles with a particle size range of 45-100 μm as the product.

[0070] The embodiments of the present invention have been described in detail above, but the present invention is not limited to the described embodiments. For those skilled in the art, various changes, modifications, substitutions, and variations can be made to these embodiments without departing from the principles and spirit of the present invention, and these variations still fall within the protection scope of the present invention.

Claims

1. A method for preparing alumina spray-granulated powder, characterized in that, The preparation method includes the following steps: S1. Slurry preparation: Alumina raw material powder is added to deionized water to prepare an initial suspension with a solid content of 45-65%. Then, a composite dispersant is added at a rate of 0.3-1.5% of the alumina raw material powder mass. The mixture is stirred at high speed and ball-milled for 2-12 hours to obtain a stable and uniform slurry. A composite binder-plasticizer system is then added to the slurry. The composite binder-plasticizer system includes: The main binder is polyvinyl butyral or hydroxypropyl methylcellulose, and the addition amount is 0.5-3.0 wt% of the alumina raw material powder. The auxiliary binder and plasticizer are polyethylene glycol and / or glycerin, added at a rate of 0.5–2.5 wt% of the alumina raw material powder. The pore structure regulator is soluble starch or microcrystalline cellulose, added at a rate of 0.1–1.0 wt% of the alumina raw material powder. After adding the composite binder-plasticizer system, continue ball milling and stirring for 2 to 6 hours to ensure that the organic matter is completely dissolved and dispersed, and obtain a spray granulation slurry with a viscosity in the range of 300 to 1500 mPa·s. S2. Atomization and Drying: The spray granulation slurry is fed to a centrifugal atomizer, and the atomizer speed is controlled between 8,000 and 20,000 rpm. The feed rate is matched with the speed to ensure that the spray granulation slurry is sheared by centrifugal force to form droplets of uniform size. The droplets are sprayed into a spray drying tower and dried by contact with hot air. The drying process is controlled by a three-stage temperature field. The inlet temperature T1 is 180–220℃; The temperature T2 in the middle of the tower is such that the droplets experience the temperature T2 in the middle of the tower during their flight path. The temperature T2 in the middle of the tower is 20 to 50°C higher than the inlet temperature T1, that is, it is controlled between 200 and 270°C. The outlet temperature T3 is 90–110℃; The hot air flow and the atomized droplet flow are parallel; S3. Collection and Post-processing: Collect the dried granules, age the collected granule powder in an oven at 60-80℃ for 6-24 hours, and finally sieve them to take the granules with a particle size in the range of 32-125 μm as the product.

2. The method for preparing alumina spray-granulated powder according to claim 1, characterized in that, In step S1, the alumina raw material powder is α-Al2O3, and the D50 particle size of the alumina raw material powder is 0.3-1.0 μm.

3. The method for preparing alumina spray-granulated powder according to claim 1, characterized in that, In step S1, the composite dispersant is a mixture of ammonium polyacrylate and polyethylene glycol, and the mass ratio of ammonium polyacrylate to polyethylene glycol is 1:0.2 to 1:

1.

4. The method for preparing alumina spray-granulated powder according to claim 1, characterized in that, In step S1, the stirring speed of the high-speed stirring is greater than or equal to 1000 rpm.