JPS6131315A - Production of alumina balloon - Google Patents

Abstract

PURPOSE:To obtain a uniform alumina balloon having excellent heat insulating property and strength and high purity with good yield by coating a specific mixture around the combustible nucleus then subjecting the same to combustion by heating and sintering. CONSTITUTION:An aq. slurry or org. solvent slurry contg. the Al(OH)3 and/or Al2O3 of <=50mum obtd. by a Bayer process, org. binder (e.g.: PVA) and Al inorg. binder (e.g.: polyaluminum chloride) is sprayed around the combustible nucleus (e.g.: activated carbon grain) and is coated thereon by using a pan coater, etc. by which the granular material is obtd. Said material is then heated to 200- 700 deg.C to burn away the above-described combustible nucleus and to obtain the hollow alumina body and thereafter the temp. is increased to 1,300-1,800 deg.C which is the sintering temp. of alumina. The alumina balloon having 0.05 - several 10mm. diameter is thus obtd.

Description

[Detailed description of the invention] The present invention relates to a method for manufacturing an alumina balloon.

Alumina balloons, which have uses such as heat-insulating refractory materials, non-combustible fillers, filtration materials, catalyst carriers, and fishing floats, are made by melting the raw material alumina in an electric furnace and then draining it from the electric furnace. It is usually produced by the so-called melt spraying method, in which high-pressure gas is sprayed toward the molten metal, and the liquid is scattered as hollow globules (chemical technology magazine MOL 1933).
(See page 26 of the June issue). This melt spraying method is 99%
It has the advantage that a high-purity alumina balloon made of the alumina described above can be obtained, but on the other hand (a) it requires a large amount of energy to melt the raw materials and blow high-pressure gas to the melt, and (b) the viscosity of molten alumina is low. Conditions such as surface tension and wind pressure of high-pressure air greatly affect the properties of the resulting alumina balloon, and optimization of these conditions is not easy; (c) a step of removing coarse particles and fine particles with II;
In order to remove iron powder mixed in during handling and iron attached to the balloon, iron is removed through a powerful electromagnetic iron removal device, and broken balls in the shape of hemispheres and flakes are removed to below a certain ratio using a ball sorting machine. Excluding (
This method has drawbacks such as requiring steps and complicated operations.

SUMMARY OF THE INVENTION An object of the present invention is to provide a method for manufacturing alumina balloons that overcomes the drawbacks of the prior art described above and has advantages in terms of manufacturing operations and product quality.

The method for producing an alumina balloon according to the present invention is to combine an organic binder and an aluminum-based inorganic binder with alumina and/or an aluminum-based inorganic binder.
or after addition to aluminum hydroxide, the resulting mixture is coated around the combustible core and then heated to a temperature at which the combustible core can burn, after which the alumina is It is characterized by sintering alumina by heating it to m degrees that can be sintered.

Alumina is used as a raw material in the method of the present invention to achieve this. As this alumina, one obtained by firing aluminum hydroxide obtained by the Bayer process at a temperature of, for example, 1250° C. is preferably used. As will be described later, a thin alumina film before sintering of alumina tends to collapse after combustion of combustible cores, so in order to prevent this collapse as much as possible, it is preferable that the particle size of the raw material alumina be as small as possible. A desirable particle size is 50 μm or less, and a particularly desirable particle size is 20 μm or less. Since aluminum hydroxide is converted to alumina under the heating conditions employed in the process of the invention (combustible core combustion conditions and alumina sintering conditions), aluminum hydroxide can be used together with or instead of said alumina. You can also use

In the present invention, it is necessary to use both an organic binder and an aluminum-based inorganic binder simultaneously as the binder added to and mixed with alumina and/or aluminum hydroxide. The reason for this is that the organic binder increases the mechanical strength of the granules before heat treatment and works to prevent the granules from chipping or breaking due to impact etc. before heat treatment. The inorganic binder is heated at a temperature (usually 300 to 100°
This is because the following defects will occur if one of these is absent:

(i) If only an organic binder is used, the mechanical strength of the granules before heat treatment is maintained as described above, but since the organic binder burns at the same time as the combustible cores, the flammable After the combustion of the core, the collapse of the thin alumina film before alumina sintering cannot be prevented.

(ii) Since aluminum-based inorganic binders have inferior adhesive properties compared to organic binders, the mechanical strength of the granules before heat treatment is lower when using only aluminum-based inorganic binders than when using only organic binders. Since it is not possible to increase the temperature, the granules are likely to be damaged or destroyed before heating.

In other words, the combined use of an organic binder and an aluminum-based inorganic binder in the present invention skillfully eliminates the drawbacks of using each alone.

Polyvinyl alcohol (PVA) is used as an organic binder.
), carboxymethylcellulose (CMG), dextrin, gum arabic, alginate (especially sodium salt), lignin sulfonate (especially sodium salt), glue, gelatin, and the like. Two or more of these specific binders may be used in combination.

As the aluminum-based inorganic binder, aluminum oxychloride, aluminum phosphate, aluminum formacetate, alumina sol, aluminum sulfate, polyaluminum chloride, aluminum hydroxychloride, etc. are preferably used. According to the present invention using an aluminum-based inorganic binder, these aluminum-based inorganic binders are decomposed and converted into alumina under the alumina sintering conditions in the method of the present invention, so that impurities are prevented from being mixed into the obtained alumina balloon. There is an advantage that an alumina balloon of high purity (for example, 99% or more alumina) can be obtained. Two or more of these aluminum-based inorganic binders may be used in combination.

Coating around the combustible core with an organic binder, an aluminum-based inorganic binder, and alumina and/or aluminum hydroxide is a process in which both binders and raw materials (alumina and/or aluminum hydroxide) are coated around a flammable core.
or aluminum hydroxide), or by sprinkling the raw material powder while spraying an aqueous or organic solvent solution containing both binders. Alternatively, both binders and raw materials may be dry mixed, and the resulting mixture may be sprinkled around the flammable core while separately spraying water.

Coating equipment includes fluidized bed coating equipment,
A pan coater, a centrifugal flow type granulator (CF Coco), an agitation-mixing type granulator, etc. are selected depending on the desired size of the alumina balloon and the degree of coating method.

The combustible core is preferably spherical or lumpy; examples include lumps obtained by crushing coal with a crusher such as a hammer mill; commercially available activated carbon granules; used activated carbon granules; grains such as millet and barnyard millet. Granular materials - those made by granulating coal powder, powdered activated carbon, used powdered activated carbon, starch, flake powder, etc. in a granulator in the presence of a suitable binder; examples include foamable plastics. Flammable cores are granulated using an agitation-mixing granulator, a pan-type transfer granulator, an extrusion-type granulator, a spherical granulator, etc., and a binder such as water, polyvinyl alcohol, or glue is added as necessary. can be used.

According to the present invention, a granular material obtained by coating a flammable core with an organic binder, an aluminum-based inorganic binder, and a raw material (alumina and/or aluminum hydroxide) is first heated to a temperature at which the flammable core burns. to burn off flammable nuclei. The combustion temperature of the combustible core varies depending on the type of combustible core, but is usually 200 to 700°C.
'After burning the flammable core, the temperature of the obtained alumina hollow body is further increased to reach the sintering temperature of alumina (usually 13
The final product, an alumina balloon, is obtained by sintering the alumina at a temperature of 00 to 1800°C.

As mentioned above, the alumina coating on the hollow body obtained after the combustible cores are burned away is thin and has a thickness of 30% before the alumina is sintered.
Although it is very brittle and easily disintegrates in the temperature range of 0 to 1,000°C, according to the present invention, since the alumina film contains an aluminum-based inorganic binder, the alumina film does not suffer from defects or defects in the temperature range. Collapse is prevented.

Combustion of the combustible core and sintering of the alumina are carried out using conventional equipment such as tunnel kilns, rotary kilns, shuttle kilns, and the like. Combustion of the flammable core and sintering of the alumina may be performed in the same device or in different devices (1° The diameter of the alumina balloon obtained by the method of the present invention is based on the size of the combustible core. It can be adjusted arbitrarily by changing the intensity, but it is usually 0.05 to several 10I.
It is l/l. Further, the bulk specific gravity of the alumina balloon can be controlled by controlling the thickness of the alumina film.

The present invention will be further explained below with reference to Examples, but the present invention is not limited to these Examples.

Example 1 1% by weight of polyvinyl alcohol (based on alumina; the same applies hereinafter), 511% by weight of polyaluminum chloride, and 40% by weight of water were added to alumina obtained by baking aluminum hydroxide obtained by the Bayer method at 1250°C. The slurry was milled for 48 hours in a nylon-lined ball mill and coated on Q, 5 m/lφ activated carbon particles using a pan coater while spraying the slurry.

The coated particles were heated in a tunnel kiln at 500° C. for 4 hours to burn out the activated carbon particles.

This is roughly heated to 1700℃ in a rotary kiln.
．． An alumina balloon with a uniform size of 5 i/mφ was obtained.

After intermediate firing and high temperature firing, an alumina balloon with a yield of 95% and high purity (alumina of 95% or more) was obtained.

Comparative Example 1 Example 1 was repeated using the same materials but without the addition of polyaluminum chloride.

The material intermediately fired at 500°C was very brittle, and when it was then fired in a rotary kiln, a good alumina balloon was obtained, but the yield was only 5%.

Example 2 2% by weight of sodium alginate powder and 5% by weight of aluminum sulfate were added to the alumina used in Example 1, and the mixture was ground in a ball mill for 48 hours.

This mixed and pulverized product was coated on polystyrene beads of 5 m/iφ using a marmerizer equipped with a hot air blower while spraying water. The coated grains were fired in the same manner as in Example 1.

As a result, high purity alumina balloons with a uniform size of 3 m/mφ were obtained with a yield of 90%.

Comparative Example 2 Example 2 was repeated using the same materials but without the addition of aluminum sulfate. The material that was intermediately fired at 500°C was very brittle, and when it was then fired in a rotary kiln, it all collapsed and a good alumina balloon could not be obtained.

Example 3 I, O weight percent of gum arabic and 5.0 weight percent of aluminum oxychloride were added and mixed to 0.5 μm fine alumina powder obtained by grinding the alumina used in Example 1 for 48 hours in a ball mill. did. Spray the mixture at 2 m/- while spraying water using a marmerizer equipped with a hot air blower.
It was coated on millet (grain granules) of φ. The coated grains were fired in the same manner as in Example 1.

As a result, a high purity alumina balloon of i vh/mφ was obtained with a yield of 90%.

Example 4 1.0% by weight of dextrin and 5.0% by weight of aluminum formacetate were added and mixed to the alumina fine powder used in Example 3, and the mixture was mixed to 4 m/l in the same manner as in Example 3.
The used spherical activated carbon in a was coated.

The coated grains were fired in the same manner as in Example 1. As a result, high purity alumina balloons of uniform size of 3 r*/a were obtained with a yield of 90%.

According to the present invention, since an organic binder and an aluminum-based inorganic binder are used together, the alumina and/or aluminum hydroxide film surrounding the flammable core is damaged before heat treatment. , the alumina film does not collapse after the combustion of the flammable core and before the alumina film is sintered. Therefore, uniform alumina balloons having various properties such as high heat insulation properties and strength can be obtained at a high recovery rate (yield). Furthermore, since the alumina balloons obtained are free of oxidation, the obtained alumina balloons have the advantage of being of high purity.

Claims (9)

[Claims] (1) After adding an organic binder and an aluminum-based inorganic binder to alumina and/or aluminum hydroxide, the resulting mixture is coated around a flammable core, and then heated to a temperature at which the flammable core can burn. 1. A method for producing an alumina balloon, which comprises burning a flammable core by heating the alumina to a temperature at which the alumina can be sintered. (2) Particle size of alumina and aluminum hydroxide is 50μ
The method according to claim 1, which is: (3) The method according to claim 2, wherein the particle size is 20 μm or less. (4) The temperature at which the flammable core can burn is 200 to 700°C
The method according to claim 1. (5) The temperature at which alumina can be sintered is 1300 to 1800
The method according to claim 1, wherein the temperature is .degree. (6) The organic binder is polyvinyl alcohol (PVA)
), carboxymethylcellulose (CMC), dextrin, gum arabic, alginate, lignosulfonate, glue, and gelatin. (7) The method according to claim 1, wherein the aluminum-based inorganic binder is selected from the group consisting of aluminum oxychloride, aluminum phosphate, aluminum formacetate, alumina sol, aluminum sulfate, polyaluminum chloride, and aluminum hydroxychloride. (8) A lump of combustible core obtained by crushing coal; commercially available activated carbon granules: used activated carbon granules; grain granules: coal powder;
2. The method according to claim 1, wherein the method is selected from the group consisting of powdered activated carbon, used powdered activated carbon, starch, or granulated powder in the presence of a binder; and expandable plastic. (9) The method according to claim 1, wherein a mixture containing an organic binder, an aluminum-based inorganic binder, and alumina and/or aluminum hydroxide is coated around the flammable core as an aqueous slurry or an organic solvent slurry.