JPH07206431A - Production of alpha-alumina powder - Google Patents

Abstract

PURPOSE:To industrially and advantageously produce alpha-alumina powder made of hardly flocculated uniform polyhedral particles from various starting materials for alumina. CONSTITUTION:When transition alumina or starting material for alumina convertible into transition alumina by heat treatment is continuously fired in an atmosphere contg. >=1vol.% gaseous hydrogen halide and/or halogen in a firing furnace, a solid or liq. source for gaseous hydrogen halide and/or a solid or liq. source for gaseous halogen is directly fed into the firing furnace.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to a method for producing α-alumina powder.

[0002]

2. Description of the Related Art α-Alumina powder is widely used as an abrasive, a raw material for a sintered body, a plasma spray material, a filler and the like. The α-alumina powder obtained by a conventional general production method has a problem that it is a polycrystalline body having a non-uniform shape, contains many agglomerated particles, has a wide particle size distribution, and has a low alumina purity depending on the application. It was To overcome these problems, in certain applications, α
-Alumina powder has been used. However, even by such a method, the shape and particle size of α-alumina cannot be arbitrarily controlled, and α-alumina having a narrow particle size distribution has hitherto been used.
It was difficult to produce alumina powder.

As a special method for producing α-alumina powder, a method of hydrothermal treatment of aluminum hydroxide (hereinafter, referred to as
Known methods include a hydrothermal treatment method), a method of adding flux to aluminum hydroxide to melt and precipitate (hereinafter referred to as a flux method), a method of firing aluminum hydroxide in the presence of a mineralizer, and the like.

First, as a hydrothermal treatment method, Japanese Patent Publication No. 57-
No. 22886 discloses a method of controlling the particle size by adding corundum as a seed crystal, but it is a synthesis under high temperature and high pressure, and there is a problem that the obtained α-alumina powder becomes expensive. .

Next, the flux method has been proposed as a method of controlling the shape and particle size of α-alumina powder for the purpose of using it as an abrasive, a filler and the like. For example, JP-A-3-
Japanese Patent No. 131515 discloses that aluminum hydroxide is calcined in the presence of a fluorine-based flux having a melting point of 800 ° C. or less, so that the average particle size is 2 to 20 μm, and the hexagonal close-packed lattice of α-alumina is hexagonal. Let D be the maximum particle size parallel to the lattice plane and H be the particle size perpendicular to the hexagonal lattice plane.
A method for producing hexagonal plate-shaped α-alumina particles having a / H ratio of 5 to 40 is disclosed. However, with this method, a fine α-alumina powder having a particle size of 2 μm or less cannot be formed, and the shape is all plate-like, and it is impossible to arbitrarily control the shape and particle size. Further, the obtained α-alumina powder was not always sufficient for use as an abrasive, a filler, a raw material for a single crystal and the like.

The most common and cheapest method for producing α-alumina powder is the Bayer method. In the Bayer method, aluminum hydroxide or transition alumina is obtained in the intermediate step of producing α-alumina powder from the raw material bauxite. The α-alumina powder is produced by firing aluminum hydroxide or transition alumina in the atmosphere.

Aluminum hydroxide or transition alumina, which is industrially inexpensively obtained in this intermediate stage, is usually
The α-alumina obtained by calcining these aluminum hydroxides or transition aluminas in the air contains agglomerated coarse particles, though the particle size is larger than 10 μm.
The powder was amorphous in shape.

Several proposals have been made to solve such problems. For example, British Patent No. 990801
In the specification, by burning sodium hydroxide contaminated with sodium in the coexistence of a chlorine-containing substance and a fluorine-containing substance, soda in the aluminum hydroxide is reduced, and an average crystal size in the range of 5 to 12 μm. A method of obtaining substantially 100% crystalline alpha-alumina having a is described. However, α-alumina obtained by this method has a wide particle size distribution having large particles that greatly exceed the average crystal particle size. Further, since a large amount of gas containing chlorine and fluorine compounds is used, the cost of treating the waste gas is high, which is disadvantageous as an industrial process.

In JP-A-59-97528, aluminum hydroxide is added to a temperature higher than that required for the conversion to α-alumina by adding a mineralizer in the form of a compound containing boron and / or fluorine. In the method for producing α-alumina by baking, aluminum hydroxide has a Na ₂ O concentration of 0.1% by weight or less, preferably 0.05% by weight or less based on Al ₂ O _3. A method for producing crystalline alumina is described, which is characterized in that it has a mineralizing agent containing molybdenum and containing ammonium (NH ₄ ⁺ ). The α-alumina obtained by this method has equiaxed crystals, but has a drawback that it is an agglomerate that needs to be ground by a vibration mill. Further, the addition of the mineralizing agent is carried out by mixing it with a pre-dried product of aluminum hydroxide or by adding it directly to the firing furnace. In the former case, the mineralizer is transferred in the countercurrent direction of the atmosphere gas in the furnace, so the concentration of the mineralizer in the atmosphere gas is low, and α-alumina powder with less agglomeration cannot be obtained. In this case, since a large amount of gas to which a mineralizer is added is used, the waste gas treatment cost becomes high, which is disadvantageous as an industrial process. Therefore, a method for industrially producing an α-alumina powder composed of uniform polyhedral particles with less aggregation has not been found yet.

[0010]

Therefore, an object of the present invention is to provide a method for industrially advantageously producing an α-alumina powder composed of uniform polyhedral particles having a small amount of aggregation, starting from various alumina raw materials. To do.

[0011]

The present invention comprises the following inventions. 1. In a method of continuously calcining a transition alumina and / or an alumina raw material which becomes a transition alumina by heat treatment in an atmosphere containing a hydrogen halide gas and / or a halogen gas in an amount of 1% by volume or more, solid or liquid hydrogen halide A method for producing α-alumina powder, which comprises directly supplying a gas source and / or a halogen gas source into a firing furnace. 2. Item 2. The method for producing α-alumina powder according to Item 1, wherein a seed crystal and / or a shape control agent is added to the transition alumina and / or the alumina raw material which becomes the transition alumina by heat treatment. 3. Supply of a solid or liquid hydrogen halide gas source and / or a halogen gas source, which is produced by decomposing a hydrogen halide gas and / or halogen gas produced by transition, into transition alumina and / or an alumina raw material which becomes a transition alumina by heat treatment. The method for producing α-alumina powder according to the above item 1, wherein the α-alumina powder is flowed in a direction parallel to the direction. 4. The solid or liquid hydrogen halide gas source and / or halogen gas source are mixed in advance with transition alumina and / or an alumina raw material to be transition alumina by heat treatment, and the mixture is directly supplied into the firing furnace. Item 1. A method for producing an α-alumina powder according to item 1.

5. 2. The method for producing α-alumina powder according to the above 1, wherein the hydrogen halide gas source is ammonium halide. 6. 5. The method for producing α-alumina powder according to the above item 4, wherein the ammonium halide is ammonium chloride. 7. The method for producing an α-alumina powder according to the above item 1, wherein the firing temperature is 600 ° C. or higher and 1400 ° C. or lower. 8. The method for producing α-alumina powder according to the above item 1, wherein an electric heating type or indirect gas heating type tunnel furnace is used. 9. The method for producing an α-alumina powder according to the above item 1, wherein the primary particles of the α-alumina powder have a polyhedral shape with an average particle diameter of 0.1 to 30 μm.

The present invention will be described in detail below. In the method for producing α-alumina powder of the present invention, transition alumina is used as a raw material and / or an alumina raw material which becomes transition alumina by heat treatment is used. By transitional alumina is meant all of the alumina having the polymorphic form represented by Al ₂ O ₃ except the α form. Specific examples include γ-alumina, δ-alumina, and θ-alumina.

The alumina raw material which becomes the transition alumina by the heat treatment means a precursor of the transition alumina which gives the desired powdery α-alumina via the transition alumina in the firing step of the production method of the present invention. In particular,
Aluminum hydroxide, aluminum sulphate (sometimes abbreviated as van sulphate), so-called light vanes such as potassium aluminum sulphate and ammonium aluminum sulphate, ammonium aluminum carbonate, as well as alumina gel, for example, alumina gel by aluminum underwater discharge method. Etc. can be mentioned.

The method for synthesizing the transition alumina or the alumina raw material which becomes the transition alumina by heat treatment is not particularly limited. For example, aluminum hydroxide can be obtained by the Bayer method, the hydrolysis method of an organic aluminum compound, or the method of synthesizing an aluminum compound obtained from an etching waste liquid such as a capacitor as a starting material.

According to the method of the present invention, aluminum hydroxide or transition alumina having a particle size of 10 μm or more obtained by an industrially inexpensive method such as the Bayer method is used as a raw material, and the desired powdery α is obtained. -Alumina can be obtained. The transition alumina can be obtained by a method of heat-treating aluminum hydroxide, a method of decomposing aluminum sulfate, a method of decomposing light vane, a vapor phase decomposition method of aluminum chloride or a method of decomposing ammonium aluminum carbonate.

The particle size of the α-alumina powder obtained by the method of the present invention can be controlled. Seed crystals are added to control the particle size. Seed crystals are α-
It means a nucleus for the crystal growth of alumina, and α-alumina grows around the seed crystal as a nucleus. There is no particular limitation as long as it has this function, and any one can be used as a seed crystal. Preferred seed crystals in the present invention are, for example, compounds of aluminum, titanium, vanadium, chromium, iron, nickel and the like. It is one kind or two or more kinds selected from. Examples of the compound include oxides, nitrides, oxynitrides, carbides, carbonitride halides or borides of the above metals. Preferred are oxides and nitrides.

It is also possible to control the particle shape of the α-alumina powder by using a shape control agent. Although the mechanism of action is not clear, the shape-controlling agent is one which acts in the course of crystal growth to change the D / H ratio. The shape controlling agent is not particularly limited as long as it has such a function, but a preferable shape control agent in the present invention is, for example, one or two selected from boron, yttrium, zirconium, lanthanum, cerium, neodymium metal simple substances or compounds thereof. More than a seed. Examples of the compound include oxides, nitrides, oxynitrides, carbides, carbonitride halides or borides of the above metals. It is preferably an oxide.

The method of mixing the transition alumina and / or the alumina raw material which becomes the transition alumina by heat treatment with the seed crystal and / or the shape control agent is not particularly limited, and, for example, a method such as ball mill or ultrasonic dispersion can be used. .
In addition, the abrasion material at the time of mixing the mixing device materials such as the mixing medium can be used as the shape control agent or the seed crystal.
For example, by using a ball made of α-alumina for ball mill mixing, α-alumina wear powder can be used as a seed crystal mixed with the raw material.

In the present invention, the transition alumina and / or the alumina raw material which becomes the transition alumina by the heat treatment is 1% by volume or more, preferably 5% by volume or more, more preferably 5% by volume or more of the hydrogen halide gas with respect to the total volume of the atmosphere. Is supplied by directly supplying a solid or liquid hydrogen halide gas source into the baking furnace so as to form an atmosphere gas containing 10% by volume or more and baking. Here, as the hydrogen halide gas source, a halogen compound such as ammonium halide or hydrogen halide can be used. Examples of ammonium halides include solid ammonium fluoride, ammonium chloride, ammonium bromide and ammonium iodide. Examples of hydrogen halides include liquid hydrofluoric acid, hydrochloric acid, and hydrobromic acid. Ammonium chloride is the preferred source of hydrogen halide gas.

In the present invention, a solid or liquid state is formed so as to form an atmosphere gas containing 1% by volume or more, preferably 5% by volume or more, more preferably 10% by volume or more of a halogen gas with respect to the total volume of the atmosphere. It is also possible to directly supply the above halogen gas source into the firing furnace and perform firing. Here, as the halogen gas source, solid K ₂ N ₂ F ₆ · K is used.
F and solid iodine are mentioned. Examples of the liquid halogen gas source include liquid bromine and liquid bromic acid.
Further, the hydrogen halide gas source and the halogen gas source can be used at the same time.

It is also possible to supply the halogen gas source and the water vapor at the same time. In this case, the pressure of the atmosphere containing the halogen gas and the steam in the firing furnace is not particularly limited, and can be arbitrarily selected within the industrially used range.

In the present invention, the hydrogen halide gas or the halogen gas in the atmosphere in the firing furnace for firing the transition alumina and / or the alumina raw material which becomes the transition alumina by the heat treatment is maintained at the above predetermined concentration. It is sufficient and does not need to be oversupplied or discharged. Therefore, the hydrogen halide gas source or the solid or liquid substance serving as the halogen gas source may be supplied in an amount that maintains the hydrogen halide gas or halogen gas in the atmosphere in the firing furnace at the above concentration.

The hydrogen halide gas source or the solid or liquid substance serving as the halogen gas source is directly supplied into the firing furnace. It can be supplied alone, but can also be supplied as a mixture with an alumina raw material. For example, in the case of a furnace such as a pusher type tunnel furnace which operates continuously, the raw material is intermittently supplied, and the object can be achieved by putting the material into a container for containing the burned material and inserting it into the furnace. As compared with the case where cylinder gas is used, equipment for supplying gas is unnecessary.

In the present invention, the solid or liquid hydrogen halide gas source and / or the hydrogen halide gas and / or halogen gas produced by decomposition of the halogen gas source are transition alumina and / or transition alumina by heat treatment. It is preferable to flow in parallel with the supply direction of the alumina raw material. It is sufficient if the hydrogen halide gas and / or the halogen gas are maintained at the concentration necessary for the reaction, but since the airtightness of the firing furnace may not be sufficient, halogenation may be performed in the highest temperature equalizing zone of the firing furnace. In order to maintain the concentration of hydrogen gas and / or halogen gas more than necessary, it is preferable to allow these gases to flow in parallel with the feed direction of the raw material.

Here, the method of causing the hydrogen halide gas and / or the halogen gas to flow in parallel with the supply direction of the alumina raw material is to flow the gas from the inlet side of the alumina raw material in the direction of the highest temperature equalizing zone in the furnace. It is possible to carry these gases with nitrogen gas, or to suck with a blower from the outlet of the α-alumina powder obtained by firing. The maximum soaking zone is a region in which transition alumina and / or alumina raw material that becomes transition alumina by heat treatment reacts with hydrogen halide gas and / or halogen gas to perform firing, and the temperature here in the furnace is The maximum temperature optimum for the reaction must be maintained. In this way, at least the atmosphere in the region where the firing is performed in the furnace can always be kept at a predetermined concentration.

The firing temperature is preferably 600 ° C. or higher 140
It is 0 ° C or lower, more preferably 700 ° C or higher and 1300 ° C or lower, and further preferably 800 ° C or higher and 1200 ° C or lower. By controlling and firing in this temperature range, the α-alumina particles produced are less likely to aggregate with each other at an industrially advantageous production rate, and α having a narrow particle size distribution immediately after firing is used.
-Powdered α-alumina composed of alumina particles can be obtained.

The appropriate firing time depends on the concentration of the atmospheric gas and the firing temperature and is not necessarily limited, but is preferably 1 minute or longer, more preferably 10 minutes or longer.
It is sufficient to calcine until the alumina raw material grows to α-alumina. The desired α-alumina powder can be obtained in a shorter time than the firing time of the conventional method.

The firing device is not necessarily limited as long as the raw materials can be continuously supplied and the product can be taken out, and a so-called continuous firing furnace can be used. It is desirable that the firing furnace is made of a material that is not corroded by hydrogen halide gas, halogen gas, etc., and further, it is desirable that the firing furnace be provided with a mechanism capable of adjusting the atmosphere. Further, since an acid gas such as hydrogen halide gas or halogen gas is used, it is preferable that the firing furnace be airtight. Therefore, a tunnel furnace, a rotary kiln, or the like can be used, but in the present invention, it is preferable to use an electric heating type or indirect gas heating type tunnel furnace. As the material of the apparatus used in the manufacturing process, it is desirable to use a crucible or sheath made of alumina, quartz, acid-resistant brick or graphite because the reaction proceeds in an acidic atmosphere.

According to the above-mentioned production method, starting from various alumina raw materials, the primary particles have an average particle diameter of 0.1 to 30 μm, α-consisting of uniform and polyhedral particles with less aggregation.
Alumina powder can be produced industrially advantageously.

[0031]

EXAMPLES The present invention will now be described in more detail with reference to examples, but the present invention is not limited to these examples. Various measurements in the present invention were performed as follows. 1. Measurement of number average particle diameter of α-alumina Scanning electron microscope of α-alumina (T-300, manufactured by JEOL Ltd.) 80 to 100 particles were selected from the photograph and image analysis was performed, and the average circle equivalent diameter was calculated. The value and its distribution were obtained. The equivalent circle diameter is a value converted into the diameter of a perfect circle having the same area.

Example 1 Aluminum hydroxide obtained by synthesizing an organoaluminum compound by a hydrolysis method as an alumina raw material is granulated into a spherical shape having a diameter of 2 to 3 mm by using a plate type granulator. The granulated raw material is calcined at 800 ° C. for 1 hour to obtain a transition alumina having a BET specific surface area of 150 m ² / g. 600 g of this transition alumina is placed in a firing container made of alumina, and is supplied at intervals of 17 minutes to a pusher type tunnel furnace in which the maximum soaking zone is maintained at 1100 ° C. by electric heating. Baking container 1
A baking vessel containing 1.2 kg of ammonium chloride is supplied for every 0 pieces. The transit time in the soaking zone is 1 hour. Nitrogen gas is introduced through the gas supply port on the raw material supply side so that hydrogen chloride gas generated by thermal decomposition of ammonium chloride is supplied to the high temperature part of the firing furnace. Alumina obtained after firing is an alumina powder composed of α-alumina particles having a polyhedral shape and a number average particle diameter of 18 μm and easily crushed. The hydrogen chloride concentration in the atmosphere gas in the firing furnace is 18% by volume.

Example 2 The same transition alumina raw material granulated as in Example 1 is fired under the same conditions as in Example 1 except for the following. After adding 200 g of ammonium chloride to each firing container, 400 g of transition alumina raw material is placed on ammonium chloride and supplied to the firing furnace. Nitrogen gas is not introduced. Alumina obtained after firing is an alumina powder composed of α-alumina particles having a polyhedral shape and a number average particle diameter of 18 μm and easily crushed. The hydrogen chloride concentration in the atmosphere gas in the firing furnace is 25% by volume.

Example 3 Transition alumina (trade name: AKP-G) was used as an alumina raw material.
15, manufactured by Sumitomo Chemical Co., Ltd.), 900 g of α-alumina (trade name: AKP-30, manufactured by Sumitomo Chemical Co., Ltd.) and 1.5 ml of ammonium chloride as seed crystals.
After mixing kg with a V-type blender, a mixing granulator (trade name: vertical granulator, manufactured by Paulec)
Granulate using. After drying at 120 ° C. for 1 hour, 950 g of this mixed granulation raw material was put into a firing container made of alumina, and at a time interval of 8.5 minutes, a pusher tunnel in which the maximum soaking zone was maintained at 1100 ° C. by electric heating. Supply to the furnace. The transit time in the soaking zone is 0.5 hours. Nitrogen gas is introduced from the gas supply port on the raw material supply side so that hydrogen chloride gas generated by thermal decomposition of ammonium chloride is supplied to the high temperature part of the firing furnace. The alumina obtained after calcination is an alumina powder composed of α-alumina particles having a polyhedral shape and a number average particle diameter of 0.8 μm and easily crushed. Hydrogen chloride concentration in the atmosphere gas in the firing furnace is 3% by volume
And

Comparative Example 1 Alumina is fired under the same starting materials and conditions as in Example 1 except that ammonium chloride is not supplied. The alumina obtained after firing is a transition alumina powder mainly composed of δ-alumina.

Comparative Example 2 Comparative Example 1 is repeated under the same conditions except that the soaking zone is heated to 1300.degree. The alumina obtained after firing was an alumina powder composed of α-alumina particles having a non-uniform shape and a number average particle diameter of 0.4 μm and hard agglomeration.

[0037]

EFFECTS OF THE INVENTION According to the present invention, since no hydrogen halide gas or cylinder gas of halogen gas is used, a gas supply facility is not required, and the gas source is easy to handle and supply method. Starting from various alumina raw materials in an advantageous manner, it is possible to produce α-alumina powders which are uniform and polyhedral particles with primary particles having an average particle size of 0.1 to 30 μm and less aggregation.

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification code Internal reference number FI technical display location C04B 35/64 // C04B 35/10

Claims (9)

[Claims] 1. A method of continuously calcining transition alumina and / or an alumina raw material which becomes transition alumina by heat treatment in an atmosphere containing hydrogen halide gas and / or halogen gas in an amount of 1% by volume or more, in a solid or liquid state. -Like hydrogen halide gas source and / or halogen gas source is directly supplied into the firing furnace.
Method for producing alumina powder. 2. The method for producing an α-alumina powder according to claim 1, wherein a seed crystal and / or a shape control agent is added to the transition alumina and / or the alumina raw material which becomes the transition alumina by heat treatment. 3. A solid or liquid hydrogen halide gas source and / or a halogen gas source is decomposed to produce hydrogen halide gas and / or halogen gas, and the transition alumina and / or heat treatment is performed to obtain transition alumina. The method for producing α-alumina powder according to claim 1, wherein the flowing alumina raw material is made to flow in parallel with the supply direction. 4. A solid or liquid hydrogen halide gas source and / or a halogen gas source are mixed in advance with transition alumina and / or an alumina raw material to be transition alumina by heat treatment and directly supplied into a firing furnace. The method for producing α-alumina powder according to claim 1, wherein 5. The method for producing an α-alumina powder according to claim 1, wherein the hydrogen halide gas source is ammonium halide. 6. The method for producing an α-alumina powder according to claim 4, wherein the ammonium halide is ammonium chloride. 7. The method for producing an α-alumina powder according to claim 1, wherein the firing temperature is 600 ° C. or higher and 1400 ° C. or lower. 8. An α-type according to claim 1, wherein an electric heating type or indirect gas heating type tunnel furnace is used.
Method for producing alumina powder. 9. Primary particles of α-alumina powder are 0.1 to 3
The method for producing α-alumina powder according to claim 1, which has a polyhedral shape with an average particle diameter of 0 μm.