JP6321357B2 - Method for producing finely baked alumina powder - Google Patents

Description

  The present invention relates to an alumina fine powder fired product and a method for producing the same.

  Here, “sintering” refers to high-temperature treatment at a temperature (for example, 700 ° C.) or higher at which an alumina precipitated crystal that forms a porous alumina layer on the surface of fine alumina powder particles is obtained. However, complete sintering that completely closes the pores of the porous alumina layer is not included.

  In the following description, “%” and “part” indicating a blending unit mean “% by mass” and “part by mass”, respectively, unless otherwise specified.

  Each characteristic value is defined as follows.

    “Average particle diameter” means a median diameter and is a value measured by a laser diffraction method (average particle diameter of less than 50 μm) or a value obtained by JIS standard mesh screen (average particle diameter of 50 μm or more).

    “Specific surface area”: Value measured according to JIS Z 8830 “Method for measuring specific surface area of powder by gas adsorption”.

    “Size of precipitated crystal” —Arithmetic average (biaxial average diameter) of major and minor diameters of a precipitated crystal measured by a scanning electron microscope (SEM) (n = 10).

  Alumina fine powder fired products, in particular α-alumina fine powder fired products, are widely used based on their high heat resistance and low reactivity. In addition, the alumina fine powder fired product is used as a material for functional products in various applications, catalyst carriers, microorganism fixed beds, culture beds, and filtration media. The alumina fine powder fired product is required to have as low a soda component as possible and a large specific surface area in order to correspond to the above-mentioned use.

  However, the specific surface area of the alumina fine powder fired product is determined by its particle size distribution, and it was usually necessary to change the particle size distribution in order to obtain a specific surface area above a certain level.

The alumina fine powder fired product is usually fired (calcined) using boehmite (aluminum hydroxide) produced by a Bayer method in which bauxite is dissolved in a NaOH aqueous solution as a raw material. Aluminum hydroxide produced by this Bayer method contains a considerable amount of impurities such as soda component (Na ₂ O) (Patent Document 1, paragraph 0003). When an alumina fine powder fired product is produced with these impurities contained, it is difficult to obtain a high-quality α alumina fine powder fired product. For example, when used as a catalyst carrier, impurities such as soda components become catalyst poisons.

  Therefore, in Patent Document 1, instead of the Bayer method, aluminum alkoxide is hydrolyzed to produce boehmite and then calcined to produce γ-alumina. A method of adding water and a specific organic carboxylic acid has been proposed.

  In Patent Document 2, wet powder aluminum hydroxide prepared by adding water or lower alcohol to the first dry powder aluminum hydroxide obtained by the aluminum alkoxide method is dried by a stirring type drying method. Thus, there has been proposed a method of obtaining a dry powdery second aluminum hydroxide and firing the second aluminum hydroxide to obtain a finely fired alumina powder.

  Furthermore, in Patent Document 3, an easily sinterable alumina produced by treating aluminum hydroxide and intermediate alumina with an aqueous spineling agent solution, calcining at 1000 to 1400 ° C., and subsequently washing with a dilute acid or dilute base as desired. The manufacturing method of this is proposed.

Special table 2008-534416 gazette (summary etc.) JP 2010-168271 A (summary etc.) JP-A-6-135714 (Summary, etc.)

  However, the method that uses the aluminum alkoxide method instead of the Bayer method described in Patent Documents 1 and 2 has complicated processes and is likely to be expensive to manufacture. Similarly, the method of treating with a spilling agent aqueous solution of Patent Document 3 is also complicated in the process, and the production cost is easily increased.

  An object (problem) of the present invention is to provide an alumina fine powder fired product that can reduce a soda component and relatively increase a specific surface area by a simple method and a method for producing the same.

  As a result of diligent development to solve the above-mentioned problems, the present inventors have conceived an alumina fine powder fired product (1) having the following constitution and a production method (2) thereof.

(1) In the alumina fine powder fired product according to the present invention, a porous alumina layer composed of alumina precipitated crystals is formed on the surface of alumina fine particles (supported particles) . It is characterized by being.

That is, an increase in specific surface area can be expected by forming a porous alumina layer composed of alumina precipitated crystals on the surface of alumina fine particles (supported particles). And by passing through a baking process, the reduction | decrease of a soda component can also be anticipated. Aluminum lactate has a high solubility (25 ° C .: 30%), and it is easy to prepare a crystal precipitation agent (a spray solution).

(2) The method for producing the alumina fine powder fired product according to the present invention comprises spraying a crystal precipitation agent (aluminum lactate dispersion) on a raw material made of alumina fine particles (alumina fine powder) while crushing the raw material. Forming a coating layer of a crystal precipitation agent on the surface of the alumina fine particles and adjusting the particle size; firing the post-spraying raw material; and using the aluminum lactate in the coating layer of the crystal precipitation agent as alumina precipitation crystals, the porous seen including a firing step of forming the quality alumina layer, wherein the spray with respect to the raw material of the crystal precipitating agent, continuously or intermittently feed was introduced into the rotary disc which is inclined in the tumbling granulator during operation, It is characterized in that it is carried out at the outer peripheral part of the rotating dish while crushing the raw material by rolling circulation .

  The alumina fine powder fired product according to the present invention can be produced with a small number of man-hours by spraying the alumina crystal precipitating agent while pulverizing the raw material, and adjusting the size and firing.

It is model sectional drawing of the process in the manufacturing method of the alumina fine powder baking products of this invention. It is a model side view of the rotating plate of the rolling granulator used for this invention. It is an operation explanatory top view of a rotating plate similarly. It is model explanatory drawing of the fluidized bed apparatus provided with the crushing mechanism used for this invention. A and B are SEM photographs of each fired product in Example 1 and Comparative Example 1. FIG. A and B are SEM photographs of the fired products in Example 2 and Comparative Example 2, respectively.

  Hereinafter, the alumina fine powder fired product of the present invention and the production method thereof will be described with reference to the drawings.

  The alumina fine powder fired product (product) 11A of the present embodiment is such that a porous alumina layer 15A composed of alumina precipitated crystals 15a is formed on the surface of alumina fine particles (supported particles) 13 (FIG. 1 (2)). FIG. 5 (A) and 6 (A)). The practical particle size, specific surface area, and cross-sectional size of precipitated crystals of this product are shown below.

1) Average particle diameter (median): 0.1 to 500 μm,
2) Specific surface area (BET): 0.1-20 m ² / g,
3) Alumina precipitated crystal size: 0.1-5 μm.

  The method for producing an alumina fine powder fired product of the present invention basically includes the following spraying step and firing step.

<Spraying process>
A raw material (alumina fine powder) made of alumina fine particles is sprayed with an alumina crystal precipitating agent (aluminum compound aqueous dispersion) while being pulverized. In this step, as shown in FIG. 1 (1), a coating layer 15 of a crystal precipitation agent is formed on the surface of alumina fine particles (supported particles) 13.

<Baking process>
The raw material after spraying is fired. In this step, the aluminum compound in the coating layer 15 becomes alumina precipitated crystals (usually γ to α) 15a, and the porous alumina layer 15A is formed on the surface of the alumina fine particles (supported particles) 13.

  In the present invention, the alumina fine powder used as a raw material is usually an inexpensive calcined alumina fine powder. Even if it is not a refined fine powder, it is possible to use a coarse alumina fine powder as long as the impurities contained in the support particles 11 disappear in the subsequent firing step. This is because the Na component disappears as described below.

For example, Na ₂ O is thermally decomposed at 400 ° C. or higher, and Na is vaporized at 892 ° C. Further, _Na 2 _{O 2} produced by thermal decomposition of Na ₂ O is a _Na 2 CO ₃ reacts with carbonate, the _Na 2 CO ₃ decomposes at below 1000 ° C..

In particular, among the inexpensive calcined alumina fine powders, those marketed as low soda alumina fine powders (α alumina) can be suitably used. This is to reduce the content of the soda component in the alumina fine powder fired product (product) as much as possible. Specifically, a soda (Na ₂ O standard) content is 0.3% or less, further 0.1% or less, and a particle size (median) of 0.1 to 100 μm, and further 1 to 5 μm is used. It is desirable. The raw material may be β alumina or γ alumina (including ρ, χ, η, and δ). The supported particles include not only primary particles but also secondary particles (aggregated particles).

  As the aluminum compound used as the dispersoid of the crystal precipitation agent, the crystal precipitation agent (liquid) coating layer 15 formed by spraying is dried at the time of granulation after spraying, so that the aluminum compound precipitates and grows. As long as it becomes an α-alumina precipitated crystal, it is not limited to an organic type or an inorganic type. Specific examples of the aluminum compound include the following.

Examples of the organic system include aluminum lactate, aluminum alkoxide, alkylaluminum (methylaluminum (Al ₂ (CH ₃ ) ₆ ), ethylaluminum (Al ₂ (C ₂ H ₅ ) ₆ ), aluminum acetate, and the like. Aluminum nitrate, aluminum chloride, and the like can be suitably used.

  Among these aluminum compounds, an organoaluminum compound, particularly aluminum lactate, is desirable because it has a high solubility (25 ° C .: 30%) and a crystal precipitation agent (a spray solution) can be easily prepared. This aluminum lactate concentration is appropriately adjusted in the range of 1 to 30%, desirably 5 to 30%, depending on the required properties (specific surface area, compressive strength, etc.). The crystal precipitation agent is preferably a solution, but may be a suspension or an emulsion.

  One aspect of spraying the crystal precipitation agent on the raw material is to continuously or intermittently feed the raw material into the rotating dish 17 using a rolling granulator equipped with the rotating dish 17, and the raw material is supplied by the rotating dish 17. It is performed at the outer peripheral part of the rotating dish 17 while being circulated by rolling.

  More specifically, it is performed as follows. In the following description, the unit of the spray amount per unit: part / min is for 100 parts of the alumina raw material powder.

  The rolling granulator is provided with one two-fluid atomizer (sprayer) for mixing and spraying the crystal precipitation agent and air. Then, on the inclined diameter D (inclination angle of 30 to 45 °) connecting the raw material input portion at the outer peripheral portion of the rotating dish 17 and the discharge portion to which the product discharge chute 19 is attached, the raw material input portion side is crystallized. The A band for spraying the agent is used, and the processing raw material discharge site side of the A band is the B band. In this embodiment, since granulation is not aimed, spraying of a binder (for example, PVAL) usually performed in the B band is not performed.

1) A raw material that is alumina fine powder (preferably low-soda calcined alumina fine powder) is charged into the rotating dish 17 during operation from the raw material charging portion (upper part of the A band). At this time, the operating conditions of the rotating pan are the rotational speed: 10 to 60 min ⁻¹ , desirably 10 to 45 min ⁻¹ , and the tilt angle 20 to 70 °, desirably 40 to 70 °. Select appropriately according to the degree of crushing. Outside these tilt angle ranges, it is difficult to roll the particles appropriately. When the fine powder is wet (damp), the angle of repose increases, so the tilt angle must be set large.

  As shown in FIG. 3, the input raw material circulates in a primary rolling manner along the outer peripheral portion (inside the rim portion 17 a) of the rotating dish 17. In other words, after being lifted by the centrifugal force along the outer periphery of the rotating dish, through the lower end outer peripheral part of the rotating dish and beyond the upper end of the rotating dish to the position above the A band, the gravity is reversed by surpassing the centrifugal force. Then, draw a large arc and perform primary rolling circulation through the A band.

  A crystal precipitation agent is sprayed on the charged raw material in the A band (reverse side part of the rolling circulation, desirably the part immediately after reversal), that is, the outer peripheral part of the rotating dish.

  Immediately after the reversal, the powder that undergoes primary rolling circulation can be sprayed while the aggregate density of the powder that hardly spreads downward is high, and the spraying efficiency is improved.

  The spraying conditions at this time are appropriately selected within the range of droplet diameter: 10 to 1000 μm, desirably 10 to 300 μm, unit time spray amount: 0.01 to 4.5 parts / min, desirably 1 to 3 parts / min. The total spray amount is 1 to 30 parts, preferably 1 to 25 parts, per 100 parts of the alumina raw material powder.

  If the droplet diameter is too small, it becomes dry mist (non-wetting droplet), and the crystal precipitation agent becomes difficult to adhere to the raw material. Conversely, if the droplet diameter is too large, granulation is likely to occur. In any case, it is difficult to obtain the object of the present invention (alumina fine powder fired product).

  On the other hand, when the spray amount is small, the working time increases, and conversely, when the spray amount is large, an agglomeration phenomenon occurs and granulation tends to occur, making it difficult to obtain the object of the present invention (alumina fine powder fired product).

  Subsequently, the raw material sprayed with the crystal precipitating agent in the A band is reversed at the site in front of the A band due to an increase in the weight of the crystal precipitating agent, and is secondary-rolled and circulated on the side of the discharge chute of the A band. Although it moves to a band (size-regulating band), since the binder spray usually performed in the B-band is not performed, the particle size is adjusted while being crushed by secondary rolling circulation. The raw material after spraying thus prepared is discharged from the discharge chute. An aluminum compound coating layer is formed on the surface of each particle of the raw material after spraying.

  In addition, the particle group which was not coat | covered with the spray liquid is primary-rolled and circulated, reaches A zone, and spraying is repeated.

  And the raw material after spraying prepared above is baked using an electric furnace or the like.

  The firing conditions at this time are the following conditions.

  Temperature increase rate: 100 to 700 ° C./h, desirably 200 to 400 ° C./h. If the rate of temperature rise is too fast, the crystal grain size will be shortened. Conversely, if the rate of temperature rise is too slow, the crystal will be longer.

  Achieving temperature / holding time: When the precipitated crystal is γ-alumina, it is set to 500 to 1000 ° C. × 0.5 to 20 h, preferably 600 to 900 ° C. × 0.5 to 20 h. Further, when the precipitated crystal is α-alumina, it is set to 1000 to 2000 ° C. × 0.1 to 3 h, preferably 1100 to 1300 ° C. × 0.5 to 1 h.

  In addition, another aspect of the spraying of the crystal precipitating agent on the raw material of the present invention is performed while charging the raw material into a fluidized bed apparatus equipped with a crushing mechanism at a fluidized bed forming site and crushing the raw material. It is.

  As the fluidized bed apparatus, for example, a fluidized bed forming portion as shown in FIG. 4 having a crushing mechanism can be suitably used (see FIG. 1 of Japanese Patent No. 4015593).

  Then, the step of spraying the crystal precipitation agent for the raw material of the present invention using the fluidized bed apparatus will be described with appropriate editing correction as appropriate while citing paragraphs 0023 to 0026 of the publication.

  “Alumina fine particles P in the raw material charged into the processing vessel 1 are a gap between the outer periphery of the rotary rotor 4 and the inner wall of the bottom of the processing vessel 1, and between the crushing mechanism 5 and the inner wall of the processing vessel 1. The space part rises on an ascending air current that rises in the space part between the outer periphery of the draft tube 6 and the inner wall of the processing container 1. After the particulate matter P has risen to some extent in the processing container 1, it is caused by its own weight. Then, it receives the above suction effect and flows into the draft tube 6. Then, the granular material particles P that flow into the draft tube 6 descend into the draft tube 6 and enter the crushing mechanism 5. In this way, the secondary agglomerated part and the aggregated part are crushed when passing through the screen 5b having a large number of holes of a predetermined diameter, so as to be in the form of single particles or predetermined particles. Dispersed in particles in diameter It is.

  The alumina fine particles P that have passed through the crushing mechanism 5 are returned again to the above-described updraft by the centrifugal effect of the rotating rotor 4. Thus, in the alumina fine particles P in the processing container 1, a gap between the outer periphery of the rotary rotor 4 and the inner wall of the bottom of the processing container 1, a space between the crushing mechanism 5 and the inner wall of the processing container 1. A fluidized bed is formed that rises in the space between the outer periphery of the draft tube 6 and the inner wall of the processing vessel 1 and floats and circulates in the direction of descending along the inside of the draft tube 6.

  The granular particles (raw material particles) P that have been returned to the upward air flow by the centrifugal effect of the rotating rotor 4 are sprayed with the spray liquid (chemical solution) from the spray nozzle 7 at this position. At the same time that the powder particles P are wetted by the mist of the spray liquid sprayed from the spray nozzle 7, the coating base material (aluminum compound) contained in the spray liquid adheres (sprays) to the surface of the powder particles P. Is done. The granular particles P sprayed with the spray liquid are dried when rising in the space between the outer periphery of the draft tube 6 and the inner wall of the processing vessel 1 and flow into the draft tube 6 again. .

  As described above, by continuously performing the cycle of crushing → spraying liquid spray → drying, the alumina fine particles can be coated. For example, in the case of coating treatment, a coating film (aluminum compound coating layer) is formed without causing secondary aggregation on alumina fine particles (supported particles) having a particle size of 100 μm or less, particularly 50 μm or less (for example, about 10 μm). Is possible. (Note: In the present invention, one sentence is deleted because it is not intended for granulation). The spray nozzle 7 may be disposed so as to spray the spray liquid from the upper side to the lower side with respect to the fluidized bed of the granular particles (so-called top spray). "

  Among the spraying conditions of the sprayed drug in the above spraying, the concentration, droplet diameter, and spray amount per hour are the same as in the case of using a rotating dish type rolling granulator. However, the total spray amount with respect to 100 parts of the raw material is 10 to 1000 parts, preferably 30 to 600 parts.

  Then, the post-spraying raw material sprayed with the crystal precipitating agent prepared above and sized is fired using an electric furnace or the like to be fired. The firing conditions at this time are the same as those prepared using a rolling granulator equipped with a rotating dish.

  The case where the support particles are alumina fine particles of alumina fine powder has been described above as an example, but the present invention is a ceramic fine powder fired product (1) having the following constitution in which the alumina fine powder as a raw material is replaced with ceramic fine powder (1) and It extends to the manufacturing method (2).

(1) Ceramic fine powder fired product,
A porous alumina layer made of alumina precipitated crystals is formed on the surface of ceramic fine particles (supported particles).

(2) A method for producing the ceramic fine powder fired product,
A spraying step of spraying a crystal precipitation agent while pulverizing the raw material (ceramic fine powder) made of ceramic fine particles to form a coating layer of the crystal precipitation agent on the surface of each particle and sizing, And a firing step of firing the raw material after spraying and forming the porous alumina layer by using the aluminum compound in the coating layer of each particle as an alumina precipitated crystal.

Examples of the ceramic used as the raw material (ceramic fine powder) include magnesium oxide (MgO), zirconium oxide (ZrO ₂ ), titanium oxide (TiO ₂ ), calcium oxide (CaO), and beryllium oxide (BeO). .

  Examples carried out together with comparative examples to confirm the effects of the present invention will be described below. The rolling granulator used in both Example 1 and Comparative Example 1 was equipped with a rotating dish having an inner diameter of 300 mm. The A band and B band in the rotating dish are as shown in FIG.

  The specifications of the raw materials used and the chemicals are as follows.

1) Raw material (calcined alumina fine powder)
・ Low soda alumina fine powder: average particle size: 2.5 μm, Na ₂ O: 0.08%, specific surface area: 1.4 m ² / g
2) Drug ・ Crystal precipitation agent: 30% aqueous solution of aluminum lactate,

<Example 1>
1) After putting 100 g of low-soda alumina fine powder as a raw material into a rotating dish adjusted to an inclination angle of 62 °, the rotating dish is started and the rotation speed is adjusted so that proper rolling occurs in the raw material. The rotation speed at that time was set to 35 min- ¹ .

  2) A spray solution of a crystal precipitating agent is sprayed onto the raw material that has circulated and circulated around the outer peripheral portion to reach the A zone, with the spray pressure and unit time spray amount adjusted so that the droplet diameter is 10 μm. The total spray amount at this time was 50 parts with respect to 100 parts of the raw material. In this example, since the spray amount per unit time was 2.5 parts / min, the total spray time was 20 minutes.

  At this time, the temperature in the rotating pan was adjusted in the range of 28 ° C. to 32 ° C., and the temperature of the spray solution and the spray amount per unit time were adjusted. This is because there is a decrease due to heat of evaporation. The rotating dish itself was also kept warm from the back with an electric heater (non-contact).

  Next, the wet fine powder thus prepared was heated to an ultimate temperature of 900 ° C. at a temperature rising rate of 300 ° C./h and held for 3 hours to obtain a fired fine powder.

<Comparative Example 1>
In the said Example 1, it was crushed without spraying a crystal precipitation agent only by rolling on the same conditions. The crushed raw material thus prepared was fired under the same conditions as in Example 1.

<Example 2>
Using the commercially available fluidized bed granulation / drying apparatus having the same configuration as the fluidized bed granulation / drying apparatus shown in FIG. 3, the same raw material as in Example 1 was put into the processing vessel and pulverized by the pulverization mechanism. However, the crystal precipitant was sprayed from the spray nozzle to the raw material to prepare a post-spray raw material.

Raw material input amount: 1 kg of calcined alumina, crystal precipitation agent: 1000 cc of aluminum lactate 5% aqueous solution, air supply rate: 0.6-3 m ³ / min, impeller rotation speed: 3000 min ⁻¹ , time spray amount 3- 5 cc / min, operation time: 300 min.

  Other raw material conditions (specification / ratio of auxiliary raw materials) and spraying conditions (crystal precipitation agent concentration, droplet diameter, spray amount per hour) were the same as in Example 1. Moreover, the crushed raw material thus prepared was fired under the same conditions as in Example 1.

<Comparative example 2>
In Example 2, the raw material was put into the processing container, and the crushed raw material was prepared only by crushing by the crushing mechanism and without spraying the crystal precipitation agent. The crushed raw material thus prepared was fired under the same conditions as in Example 2.

  The SEM photographs (× 1500 times) of Example 1 / Comparative Example 1 and Example 2 / Comparative Example 2 thus prepared are shown in FIGS. From the SEM photograph, it can be seen that the products of the present invention of Examples 1 and 2 have needle-like crystals in each particle. On the other hand, it can be seen that Comparative Examples 1 and 2 do not have acicular crystals in each particle. The alumina fine powder fired product of the present invention has acicular crystals (acicular crystals) close to perfect crystals inside, so when used as a raw material, improvement in properties such as strength, electrical characteristics, heat resistance, etc. in various products is expected. it can. Furthermore, since it has acicular crystals, it has various characteristics as described below, so the following effects can be expected.

    1) The catalyst particles can be deposited thinly and evenly (the amount of catalyst used can be reduced).

    2) A medium (of microorganisms) can be attached near the surface layer (proliferation of microorganisms can be promoted).

    3) In water purification, fine pollutants can be filtered.

  The same specific surface area and soda component were measured and are shown in Table 1.

  The specific surface area of Examples 1 and 2 is about 4 times or more of Comparative Example 1 and 2 without spraying using the same low soda alumina fine powder as in Examples 1 and 2, and about 3 times or more of the specific surface area of the raw material. Met. It was confirmed that the alumina fine powder fired product of the present invention has a significantly increased specific surface area.

  In addition, it was confirmed that the soda components of Example 1 / Comparative Example 1 and Example 2 / Comparative Example 2 after each firing were all about 0.05%, which was reduced from 0.08% of the raw material.

11 Fine particles of raw material after spraying 11A Fine particles of calcined alumina powder 13 Alumina fine particles (supported particles)
15 Coating layer of crystal precipitation agent 15A Porous alumina layer 15a Alumina precipitation crystal

Claims (10)

A method for producing an alumina fine powder fired product in which a porous alumina layer made of alumina precipitated crystals is formed on the surface of alumina fine particles (supported particles),
A raw material made of alumina fine particles (alumina fine powder) is sprayed with a crystal precipitation agent (aluminum lactate dispersion) while pulverizing the raw material to coat the surface of the alumina fine particles (supported particles) with the crystal precipitation agent. A spraying process for forming a layer and sizing;
Firing the raw material after spraying, and forming the porous alumina layer by using aluminum lactate in the coating layer as an alumina precipitated crystal,
Spraying the crystal precipitating agent on the raw material is continuously or intermittently introduced into an inclined rotating dish of an operating tumbling granulator, and the raw material of the rotating dish is crushed by rolling circulation. A process for producing an alumina fine powder fired product, characterized in that it is carried out at the outer peripheral part. The method for producing a fired product of fine alumina powder according to claim 1, wherein the precipitated alumina crystals include needle-like crystals. The alumina fine powder fired product has an average particle size (median): 0.1 to 500 μm, a specific surface area (BET method): 0.1 to ²⁰ m ² / g, and the size of the alumina precipitated crystals. Is 0.1-5 micrometers, The manufacturing method of the alumina fine powder baked material of Claim 1 or 2 characterized by the above-mentioned. Spray with respect to the raw material of the crystallization agent, according to claim 1, dispersion medium of said crystal precipitating agent from the surface of each particle of the raw material and performing in a volatilizable conditions A method for producing an alumina fine powder fired product. The method for producing a fired product of fine alumina powder according to any one of claims 1 to 4, wherein a droplet diameter of spraying the raw material of the crystal precipitation agent is 10 to 1000 µm. The unit time spray amount of the crystal precipitation agent to the raw material is 0.01 to 4.5 parts min with respect to 100 parts of the raw material. ^-1 The method for producing a fired product of fine alumina powder according to claim 5, wherein: The method for producing an alumina fine powder fired product according to any one of claims 1 to 6, wherein an inclination angle of the rotating dish is 20 to 70 °. The rotation speed of the rotating dish is 10-60 min ^-1 The method for producing an alumina fine powder fired product according to claim 7. The feedstock, Na ₂ O content: 0.3% or less, an average particle diameter (median diameter): any of claims 1-8, characterized in that the calcined alumina powder is 0.1~100μm method for producing a fine alumina powder calcined product according to. A method for producing a ceramic fine powder fired product in which a porous alumina layer made of alumina precipitated crystals is formed on the surface of ceramic fine particles (supported particles),
The raw material consisting of ceramic fine particles (ceramic fine powder) is sprayed with a crystal precipitation agent (aluminum lactate dispersion) while crushing the raw material, and the surface of the ceramic fine particles (supported particles) is coated with the crystal precipitation agent. A spraying process for forming a layer and sizing;
Firing the raw material after spraying, and forming the porous alumina layer by using aluminum lactate in the coating layer of the crystal precipitation agent as alumina precipitation crystals,
The raw material is sprayed onto the raw material continuously or intermittently by using a rolling granulator equipped with an inclined rotating dish, and the raw material is transferred by the rotating dish. A method for producing a fired ceramic fine powder, which is performed at the outer peripheral portion of the rotating dish while being circulated and pulverized.