KR100785058B1 - Fabrication method of uniform alumina powder with low-agglomeration using microwave synthesis - Google Patents

Abstract

A method for producing alumina powder is provided to obtain multi-phase alumina powder or alpha-alumina composite powder having a fine particle size and causing little agglomeration, to improve the time- and cost-efficiency, and to obtain a material useful as a catalytic material, biochemical material, sensor or laser material. A method for producing alumina powder with low agglomeration comprises a step of treating ammonium aluminum carbonate in a microwave furnace by way of thermal decomposition and phase transition to provide alumina or alumina composite powder. The ammonium aluminum carbonate is prepared by mixing an aqueous solution containing an aluminum salt with an aqueous solution of ammonium hydrogen carbonate. The treatment in a microwave furnace is carried out under an atmosphere of air, nitrogen, argon, hydrogen or a combination thereof at 300-1200 deg.C for at least 5 minutes.

Description

FABRICATION METHOD OF UNIFORM ALUMINA POWDER WITH LOW-AGGLOMERATION USING MICROWAVE SYNTHESIS

1 is a schematic view showing a manufacturing process of an alumina powder or an alumina composite powder according to an embodiment of the present invention,

2 is an X-ray diffraction pattern of alumina composite powder synthesized according to the temperature of ammonium aluminum carbonate in a microwave synthesis furnace in the atmosphere of air,

3 is an X-ray diffraction pattern of the alumina composite powder synthesized according to the temperature of the ammonium aluminum carbonate in an electric furnace in the atmosphere,

4 is a comparison of the crystal phase size of the alumina composite powder at a temperature at which the alumina aluminum carbonate is synthesized in a microwave synthesis furnace at different temperatures.

The present invention relates to a method for producing an alumina powder, and more particularly, to a method for producing an alumina powder or alumina composite powder with uniform and almost no aggregation using microwave synthesis.

In general, alumina has physicochemical properties such as high melting point, abrasion resistance, insulation, oxidation resistance, etc., and thus has been spotlighted as a functional catalyst, high temperature structure, high strength light-transmitting ceramic material and biomaterial used in various advanced technologies. These ceramic materials used in high-tech industries should be made of fine particles with a purity of 99.99% or more, with chemical homogeneity and uniform microstructure.

A conventional ceramic synthesis method for producing alumina powder by such a method is to have a ball milling method which is a mechanical grinding method. However, the ball milling method has a disadvantage in that impurities are easily mixed and are synthesized with alumina having a high content of impurities, and the particle size of the alumina powder is not uniform, so that the particle size distribution is wide.

Alternatively, the sol-gel method for producing alumina powder is a mass production is possible, but there is a problem in that the aggregation of particles occurs because the crystallization process is required for a long time in an electric furnace at a high temperature.

As another method, a method for producing spherical alumina powder has been recently published by a metal alkoxide method or a hydrolysis control method. Since the hydrolysis rate of aluminum alkoxide cannot be properly controlled, a uniform particle size distribution can be obtained. It was difficult to obtain spherical alumina microparticles with an excitation.

Since all of the above-described conventional synthesis methods are synthesized in an electric furnace, crystallization is performed for a long time and aggregation between particles occurs, which makes it difficult to synthesize high purity alumina powder having a particle size of 100 nm or less.

In particular, since high temperature alpha alumina is synthesized after maintaining for at least 1200 ° C. for several hours, it is still difficult to manufacture a large amount of highly dispersible nano alumina.

Accordingly, there is an urgent need for a new synthesis method for shortening the process of long-term crystallization at high temperature to synthesize nano-sized alumina in a short time at low temperature.

The present invention is to solve the above problems, to provide a method for synthesizing nano-sized alumina to alumina composite powder from alumina precursor using a microwave synthesis furnace having a uniform heating and rapid heating effect. There is this.

In order to achieve this object, the present invention provides a method for synthesizing alumina powder or alumina composite powder by pyrolysis and phase transition using microwaves from a precursor of alumina (eg, ammonium aluminum carbonate).

Accordingly, secondary aggregation between powders may be reduced through rapid phase change at low temperature, and nano-sized multiphase alumina powder or alpha alumina composite powder may be synthesized.

More specifically, the present invention uses ammonium aluminum carbonate (Ammonium Aluminum Carbonate Hydroxide) as a precursor of alumina or composite alumina, and the precursor has a uniform particle size at low temperature and 100 nm or less at low temperature by thermal decomposition and promotion of phase transition using microwave. Alumina powder or alpha alumina composite powder (eg, magnesium aluminate spinel-alpha alumina composite powder) having amorphous, gamma, theta, and alpha phases having a fine particle size is prepared.

Compared with the conventional synthesis method using an electric heating furnace for synthesizing the alumina powder, the production method of the present invention has the advantage of being able to synthesize the alumina powder in a very short time with little secondary aggregation.

Figure 1 is a schematic diagram showing the manufacturing process of the alumina powder or alumina composite powder according to an embodiment of the present invention.

Referring to FIG. 1, first, an aqueous solution including an aluminum salt and an aqueous solution of ammonium bicarbonate (NH ₄ HCO ₃ ) are reacted at a low temperature (eg, 5 to 15 ° C.) to prepare ammonium aluminum carbonate, which is a precursor of alumina. Here, ammonium bicarbonate is used as precipitant. In addition, the aluminum salt may be at least one selected from the group consisting of ammonium alum (NH ₄ Al (SO ₄ ) ₂ ), aluminum nitrate, aluminum sulfide, aluminum chloride. In addition, the aqueous solution containing the aluminum salt may include a sintering additive or a functional additive.

Next, the alumina powder or the alumina composite powder is prepared by pyrolysis and phase transfer reaction by synthesizing the ammonium aluminum carbonate, which is a precursor of the alumina, by microwave. More specifically, by heating the ammonium aluminum carbonate according to the temperature in the microwave synthesis furnace it can be produced alumina powder of a multi-phase (at least one of amorphous, gamma, theta or alpha phase). In addition, when a variety of sintering additives or functional additives such as magnesium nitrate (Mg (NO ₃ ) ₂ ) were added to the aqueous aluminum solution in the previous step, magnesium aluminate spinel (MgAl ₂ O ₄ ) -alpha alumina composite powder by microwave synthesis Can be synthesized.

Hereinafter, specific embodiments of the present invention will be described. However, the present invention is not limited to the following examples.

Example

To the aqueous ammonium hydrogen carbonate solution at which the reaction temperature was maintained at 10 ° C. or lower and the pH was adjusted to about 10 or lower, an aqueous solution of ammonium alum with or without magnesium salt was added at about 10 ml / min using a slurry pump. The reaction was carried out at a rate of min for 30 minutes to form a precipitate. At this time, the molar ratio of ammonium alum and ammonium bicarbonate was approximately 1: 5. After washing the precipitate, the alumina precursor aqueous solution was lyophilized at -54 ℃. Thus, ammonium aluminum carbonate of 10 nm or less was obtained.

Ammonium aluminum carbonate in a microwave synthesis furnace for 10 minutes depending on the temperature from 300 ℃ to 1150 ℃ with single gas or mixture gas of air, nitrogen, argon, hydrogen, hydrogen / nitrogen, hydrogen / argon, nitrogen / argon, nitrogen / air The heat treatment was performed to prepare alumina powder or alumina composite powder of amorphous, gamma, theta and alpha phases. FIG. 2 is an X-ray diffraction pattern of an alumina composite powder synthesized with ammonium aluminum carbonate according to temperature in an atmosphere of atmosphere in a microwave synthesis furnace. The phase of the alumina powder or the alumina composite powder is analyzed using an X-ray diffraction pattern. The results of the 32 examples classified by temperature and ambient gas are shown in Tables 1 and 2 below.

Table 1 Classification of Examples According to Temperature and Atmospheric Gas

Microwave assisted combustion Temperature (℃) Air Ar N ₂ H ₂ H ₂ / N ₂ H ₂ / Ar N ₂ / Ar N ₂ / Air 1000 Example 1 Example 5 Example 9 Example 13 Example 17 Example 21 Example 25 Example 29 1050 Example 2 Example 6 Example 10 Example 14 Example 18 Example 22 Example 26 Example 30 1100 Example 3 Example 7 Example 11 Example 15 Example 19 Example 23 Example 27 Example 31 1150 Example 4 Example 8 Example 12 Example 16 Example 20 Example 24 Example 28 Example 32

Table 1 is a table of the ammonium aluminum carbonate synthesized according to Figure 1 synthesized using a variety of atmospheres in a microwave synthesis furnace in order to obtain the alpha alumina composite powder according to the temperature shown in the table.

TABLE 2 Stable Phases in the Conditions of Each Example

Microwave assisted combustion Temperature (℃) Air Ar N ₂ H ₂ H ₂ / N ₂ H ₂ / Ar N ₂ / Ar N ₂ / Air 1000 γ γ α> γ, θ α α α> γ, θ γ γ 1050 α, γ, θ α> γ, θ α α α α α, γ, θ α, γ, θ 1100 α α α α α α α α 1150 α α α α α α α α

Table 2 is a table showing the powder obtained by varying the atmosphere and temperature in the microwave synthesis furnace according to the embodiment of Table 1 by identifying the alumina crystal phase generated through X-ray diffraction analysis.

Comparative example

Synthesis of ammonium aluminum carbonate in the same manner as described in the above examples, followed by air, nitrogen, argon, hydrogen, hydrogen / nitrogen, hydrogen / argon, nitrogen / argon, Alumina powder or alumina composite powder of nitrogen / air single gas to mixed theta and alpha phases was prepared. 3 is an X-ray diffraction pattern of alumina composite powder synthesized according to the temperature of ammonium aluminum carbonate from the electric furnace to the atmosphere in the atmosphere.

Table 3 Comparison of Crystal Phase Size and Alumina Phase According to Temperature of Examples and Comparative Examples

Temperature (℃) Crystal phase size (nm) Alumina phase Example 33 1000 7 γ Example 34 1050 8 γ Example 35 1100 28 α Example 36 1150 30 α Comparative Example 1 1000 9 γ Comparative Example 2 1050 10 γ Comparative Example 3 1100 39 γ Comparative Example 4 1150 44 α

Table 3 is an example comparing the crystal phase size of the multi-phase alumina powder obtained by varying the atmosphere and temperature of the ammonium aluminum carbonate synthesized according to FIG. 1 in a microwave synthesis furnace and an electric heating furnace to obtain pure alumina powder. Referring to Table 3, the examples can obtain the α phase at a lower temperature than the comparative examples, thereby obtaining a finer crystal phase size of the alumina powder obtained at each temperature. Since fine powder is obtained due to low temperature synthesis, there is an advantage in requiring high activity such as catalyst or sintering. Particularly, when a dense alumina sintered body is to be manufactured, since the sintering is greatly inhibited due to the phase transition phenomenon of the alumina during sintering, a dense sintered body cannot be obtained using low-temperature alumina. Use has an advantage in producing a compact sintered body.

Table 4 Comparison of Crystal Phase Sizes for Alpha Alumina and Magnesium Aluminate Spinel Powders

α-Al ₂ O ₃ (nm) MgAl ₂ O ₄ (nm) Example 3 28.5 27.2 Example 7 30.4 30.6 Example 10 27.4 27.1 Example 17 26.2 25.1

Table 4 is an example comparing the crystal phase sizes of alpha alumina and magnesium aluminate spinel powders obtained by varying the atmosphere and temperature of ammonium aluminum carbonate in a microwave synthesis furnace, respectively. The crystal phase size of the alpha alumina and magnesium aluminate composite powder can be controlled by adjusting the atmosphere and temperature, and the smallest crystal phase can be obtained in the hydrogen / nitrogen mixed gas atmosphere (Example 17).

4 is a comparison of the crystal phase size of the alumina composite powder at a temperature at which the alumina aluminum carbonate is synthesized in a microwave synthesis furnace at different temperatures. It can be seen that the alpha alumina produced in the hydrogen / nitrogen mixed gas atmosphere having the lowest transition temperature at which a single alpha phase is generated shows the smallest crystal size, and the transition temperature is also greatly affected by the atmosphere.

As described above, since the present invention is accompanied by a fast phase transition at a low temperature, it is possible to prepare a multiphase alumina powder to alpha alumina composite powder with finer particles and less aggregation than the conventional synthesis method. In addition, since the nanopowder is synthesized at a synthesis temperature lower than about 100 ° C. to 200 ° C. and a short synthesis time within 10 minutes, compared to the conventional synthesis method, the process cost is reduced. In addition, since the powder prepared by the present invention is finely and uniformly mixed to 100 nm or less, the laser material, which is used alone or in combination with other oxides, such as a catalytic chemically active material, a biological biochemical material, a sensor material, and a high heat-resistant high-strength structural material And can be used to manufacture highly transmissive ceramic materials.

Although the present invention has been described with reference to the illustrated embodiments, it is merely exemplary, and the present invention may encompass various modifications and equivalent other embodiments that can be made by those skilled in the art. Will understand.

Claims (8)

Microwave synthesis of ammonium aluminum carbonate to produce alumina powder or alumina composite powder by pyrolysis and phase transfer reaction. delete The method of claim 1, The ammonium aluminum carbonate is prepared by mixing an aqueous solution containing an aluminum salt and an aqueous solution of ammonium bicarbonate. The method of claim 3, wherein The aluminum salt is a method for producing a uniform low agglomeration alumina powder, characterized in that at least one selected from the group consisting of ammonium alum (NH ₄ Al (SO ₄ ) ₂ ), aluminum nitrate, aluminum sulfide, aluminum chloride. The method of claim 3, wherein Method for producing a uniform low agglomeration alumina powder, characterized in that the sintering additive is contained in the aqueous solution containing the aluminum salt. The method of claim 3, wherein Magnesium nitrate (Mg (NO ₃ ) ₂ ) is added to the aqueous solution containing the aluminum salt, and uniform low agglomerated alumina powder, characterized in that magnesium aluminate spinel-alpha alumina composite powder is prepared by the microwave synthesis. Manufacturing method. The method of claim 1, The microwave synthesis is a method for producing a uniform low agglomeration alumina powder, characterized in that in the atmosphere of a single gas of air, nitrogen, argon, hydrogen, or a mixed gas thereof. The method of claim 1, Alumina powder or alumina composite powder on amorphous, gamma (γ), theta (θ) or alpha (α) is prepared by microsynthesis of heat treatment at a temperature ranging from 300 ° C. to 1200 ° C. for at least 5 minutes in a microwave synthesis furnace. Method for producing a uniform low agglomeration alumina powder, characterized in that.

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