JP2013103868A - METHOD FOR PRODUCING α-ALUMINA FIRED BODY AND SAPPHIRE SINGLE CRYSTAL - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a means for obtaining a low-cost and high-purity α-alumina.SOLUTION: The flow 1 of the method for producing an α-alumina fired body includes: a step 101 to add water to boehmite; a kneading step 102; a deaerating step 103; an extrusion molding step 104; and a firing step 105. Because a gas existing in boehmite is exhausted by deaerating and extrusion-molding boehmite with high pressure in the steps 103 and 104, an α-alumina fired body with high bulk density required for a raw material of a sapphire single crystal is produced only by firing of once in the step 105.

Description

  The present invention relates to an α-alumina sintered body and a method for producing a sapphire single crystal.

  In recent years, attention has been focused on LEDs (light emitting diodes), and artificial sapphire single crystals of sapphire are increasingly used as substrates for electronic circuits. Since sapphire single crystal is optically transparent and has high chemical stability, high mechanical strength, insulation and thermal conductivity, it is effective as a heat sink when used in electronic circuits. High chip durability is given as an LED chip.

  By the way, the sapphire single crystal is made of α-alumina which is an oxide of aluminum. Various methods have been proposed for producing α-alumina.

  As one of them, a technique for producing α-alumina by baking boehmite is known. Here, a method for producing boehmite as a raw material described in this specification will be briefly described.

  As an example of a method for producing boehmite, boehmite is produced in the course of a method for producing α-alumina called an alkoxide method.

  More specifically, high-purity aluminum metal (99.99 percent or more) is first reacted with alcohol to produce an aluminum alkoxide (solution). Next, the aluminum alkoxide is distilled and purified to produce the alkoxide. Further, water is added to the alkoxide for hydrolysis to produce boehmite AlO (OH).

  In the prior art (alkoxide method), this boehmite is fired to form α-alumina powder, the α-alumina powder is subjected to processing such as molding, refired and sintered (to increase the density), and a sapphire single crystal As a raw material. That is, in the prior art, a process of baking the material twice is required.

  In addition, it is necessary to bake the material twice in order to increase the bulk density of α-alumina, which is a raw material of the sapphire single crystal, and to increase the yield of sapphire single crystal production.

  The technique disclosed in Patent Document 1 states that a relatively high-purity α-alumina fired body can be obtained by forming pseudo-boehmite at a high pressure and baking it at 1500 degrees Celsius for 2 hours.

JP 63-55114 A

  By the way, the fact that the step of baking the material twice in the above-described alkoxide method means that the production cost becomes high. In addition, since processing such as molding is performed using α-alumina powder that is hard and highly wearable, there is a problem that non-volatile impurities are mixed into α-alumina due to wear of the apparatus in the process.

  In addition, the α-alumina obtained by the technique disclosed in Patent Document 1 described above has a problem that the surface of the surrounding container is scraped off in the process of forming pseudo-boehmite at a high pressure and the content of nonvolatile impurities is large. There is.

  Therefore, an object of the present invention is to provide means for obtaining a high-density α-alumina sintered body that is low in cost and high in purity.

The present invention has been conceived in view of the above object,
Adding water to boehmite;
Kneading the boehmite hydrolyzed in the hydrating step;
After the step of kneading or in the step of kneading, pressurizing the hydrated and kneaded boehmite at a predetermined pressure or more;
A method of producing an α-alumina fired body comprising the step of firing the hydrated, kneaded and pressurized boehmite only once at a temperature of 1300 degrees Celsius or higher (first embodiment).

In the first embodiment described above,
The pressurizing step may employ a configuration including a step of extruding the hydrated and kneaded boehmite (second embodiment).

In the second embodiment,
A configuration may be adopted that includes a step of degassing the boehmite in an environment of a predetermined atmospheric pressure or lower at any timing from the start of the kneading step to the end of the extrusion molding step (third) Embodiment).

The present invention also provides:
A method for producing a sapphire single crystal according to any one of the chocolate lasky method, the kilopross method, and the EFG method,
Provided is a method for producing a sapphire single crystal comprising a step of melting an α-alumina sintered body produced by the method according to any one of the first to third embodiments in a container (fourth embodiment). .

  According to the method for producing an α-alumina fired body according to the first embodiment of the present invention, it is required as a raw material for a sapphire single crystal only by one firing by pressurizing the water-kneaded boehmite. An α-alumina fired body having a high bulk density can be produced. Therefore, the production cost is low compared with the α-alumina fired body produced by the conventional technique that requires a twice baking step. In addition, according to the method for producing an α-alumina fired body according to the first embodiment of the present invention, a relatively soft boehmite hydrate kneaded product is formed. Therefore, a relatively hard α-alumina hydrate kneaded product is formed. Compared with an α-alumina fired body produced by a conventional technique requiring a process, there is less contamination (contamination) in the molding process, and α-alumina having a high purity can be obtained.

  Moreover, according to the method for producing an α-alumina calcined body according to the second embodiment of the present invention, the method includes the step of extruding hydrated and kneaded boehmite. The density can be increased efficiently.

  Moreover, according to the method for producing an α-alumina fired body according to the third embodiment of the present invention, since it includes a step of degassing, α having a higher bulk density than that in the case where degassing is not performed. An alumina fired body can be obtained. As a result, the production yield of sapphire single crystals can be increased.

  Moreover, according to the method for producing a sapphire single crystal according to the fourth embodiment of the present invention, a sapphire single crystal is produced using the α-alumina fired body according to any one of the first to third embodiments as a raw material. Therefore, it is possible to produce a sapphire single crystal having a high purity at a low cost as compared with a sapphire single crystal produced using an α-alumina fired body produced by a conventional technique as a raw material.

FIG. 1 is a diagram showing a flow of a method for producing an α-alumina fired body according to this example which is one specific example of the present invention. FIG. 2 is a photograph of pellets of an α-alumina fired body according to an example which is a specific example of the present invention.

(First embodiment)
Hereinafter, an embodiment which is a specific example of the present invention will be described with reference to the drawings.

  FIG. 1 is a diagram showing a flow 1 of a method for producing an α-alumina fired body according to this example. Increasing the bulk density of the α-alumina sintered body is very important because it leads to an increase in the production yield of sapphire single crystals using the α-alumina as a raw material. Flow 1 is composed of steps 101 to 105. The step of extruding in step 104 is the most important step for increasing the bulk density, and the bulk required as a raw material for the production of sapphire single crystals by this step. Density is obtained. Further, the bulk density is further improved by the degassing step of step 103.

  Hereinafter, each step of the flow 1 will be described. In the following description, “S” is an abbreviation for step.

  S101 is a step of adding water to boehmite. This is done to add water to boehmite and soften it into clay. This is because if it is softened into a clay, the subsequent extrusion process becomes easier.

  S102 is a step of kneading the hydrated boehmite to form clay-like boehmite. By kneading, extrusion molding is facilitated, and variation in density can be suppressed.

  S103 is a step of degassing (kneaded) boehmite. By degassing, the bulk density of the α-alumina fired body, which is the final product of this example, can be increased. As described above, if the bulk density is low, it is inconvenient for an ingot to be a raw material for the sapphire single crystal, so it is very important to increase the bulk density. Note that S103 is generally included in S102 described above or S104 described later.

  S104 is a step of extruding the degassed boehmite. More specifically, the deaerated boehmite is put in a container called a die and extruded from a slight gap having a constant cross-sectional shape at a pressure as high as possible (for example, 600 bar) to form. As described above, this step is most important in increasing the bulk density of the α-alumina fired body, which is the final product of this example. Steps 103 and 104 described above can be performed by, for example, an extrusion molding apparatus disclosed in a patent document (Japanese Patent Laid-Open No. 7-32335).

  Here, the pressurizing step which should be originally specified is included in S103 and S104.

  S105 is a step of baking the extruded boehmite (only once) at 1500 degrees Celsius for about 1 hour or more and about 2 hours or less. As a result, an α-alumina fired body, which is the final product of this example, is produced. The temperature and time are determined in consideration of whether or not an α-alumina fired body excellent in manufacturing cost and accuracy is produced.

  In this case, the bulk density of the obtained α-alumina fired body is about 2.5 g / cc or more and about 3.5 g / cc or less.

The chemical formula for baking and dehydrating boehmite is:
2AlO (OH) → Al ₂ O ₃ + H ₂ O
It is.

  The α-alumina fired body produced by Flow 1 having the above-described configuration has a high bulk density and a very high purity (99.99% or more), and is used as an ingot as a raw material for a sapphire single crystal. .

  The α-alumina fired body can be conveniently divided into pellets by dividing it into a size of about 1 cc when used as a raw material in the production process of sapphire single crystals.

  FIG. 2 is an actual pellet of the α-alumina fired body according to the present example, and the photograph on the right side is a microscopic view of the fine structure of the pellet of the α-alumina fired body according to the present example.

(Second embodiment)
Hereinafter, an embodiment which is another specific example of the present invention will be described.
More specifically, an example of a manufacturing method (growing method) of a sapphire single crystal (that is, the final product of this embodiment) using the α-alumina fired body according to the first embodiment will be described.

  As a method for producing a sapphire single crystal, the Kylopoulos (Ky) method, the Choralski (Czochralski, Cz) method, and the EFG (Edge-defined, Film-fed Growth) method are known as widely used methods. Yes. The kilopross method is sometimes referred to as a chocolate skiing method that does not involve rotation, resulting in confusion with the chocolate skiing method.

  The Kilopros method is a method for producing a sapphire single crystal by immersing a seed crystal in a melt of α-alumina, slowly cooling the melt, and pulling the crystal before solidifying the entire crucible. Hereinafter, the flow of production of the sapphire single crystal according to the present example according to the kilopros method will be briefly described.

  In S201, the α-alumina fired body produced in the first embodiment is put in a crucible and heated to melt.

  In S202, the seed crystal of the α-alumina fired body is immersed in the melt.

  In S203, the above melt is gradually cooled.

  In S204, the crystal is pulled up before the above-mentioned melt is solidified to the entire crucible. Thereby, a sapphire single crystal is obtained.

  The chocolate skiing method is a method of producing a sapphire single crystal by immersing a seed crystal in an α-alumina melt in a crucible and pulling the crystal (or crucible) while rotating it. This is also a common industrial method.

  Hereinafter, the production flow of the sapphire single crystal according to the present example according to the chocolate skiing method will be briefly described.

  In S301, the α-alumina fired body produced in the first embodiment is placed in a crucible and heated to melt.

  In S302, the seed crystal of the α-alumina fired body is immersed in the melt.

  In S303, the above melt is gradually cooled.

  In S304, the crystal is pulled up before the above-mentioned melt is solidified to the entire crucible. At this time, the crystal (or crucible) is pulled up while rotating. Thereby, a sapphire single crystal is obtained.

  The EFG method is a method of controlling the shape of a crystal using a capillary phenomenon. A die (die) having a void of a predetermined shape is floated on a melt of α-alumina, and the crystal using the capillary phenomenon of the melt is used. This is a method of producing a sapphire single crystal by pulling up. According to the EFG method, a crystal whose shape is controlled to a rod shape, a plate shape, a tubular shape, or the like according to the shape of the mold can be obtained.

  Hereinafter, the production flow of the sapphire single crystal according to the present example according to the EFG method will be briefly described.

  In S401, the α-alumina fired body produced in the first embodiment is finely cut or crushed.

  In S402, the finely cut or crushed α-alumina fired body is placed in a crucible and heated to melt.

  In S403, a mold (die) having a predetermined gap is floated on the melt.

  In S404, the crystal is pulled up by utilizing the capillary action of the melt. Thereby, a sapphire single crystal is obtained. If the shape of the mold is tubular, a sapphire single crystal whose shape is controlled to be tubular can be obtained.

  The ingot of the α-alumina fired body according to the first example is mainly used as a raw material for the kilopross method and the chocolate ski method. Further, as described above, if the ingot of the α-alumina sintered body according to the first embodiment is finely formed, it can be used for the EFG method.

  The sapphire single crystal produced by the method as described above is optically transparent and has high chemical stability, mechanical strength, insulation and thermal conductivity. It is effective as (heat sink) and gives high chip durability as an LED chip.

  Taking advantage of the characteristics of the sapphire single crystal as described above, the sapphire single crystal is suitable as a material for an SOS substrate, a semiconductor device, a cutting tool, a watch glass, or the like.

(Modification)
The embodiment described above can be variously modified within the scope of the technical idea of the present invention. Examples of these modifications are shown below.

  For example, the step of extruding in S104 may not be provided if there is no particular problem. However, since it is important to increase the bulk density of the α-alumina fired body as the final product of the first embodiment, if S104 is omitted, the boehmite is high after the kneading step of S102 or simultaneously with the kneading step. It is necessary to pressurize with pressure.

  Further, the extrusion molding step of S104 may be replaced by an injection molding step.

  The degassing step of S103 may be performed at any timing from the start of the kneading step of S102 to the end of the extrusion molding step of S104. More specifically, degassing can be effectively performed during the kneading step or in the extrusion step.

  The degassing step of S103 and the extrusion molding step of S104 are performed by the method described in the above-mentioned patent document (Japanese Patent Laid-Open No. 7-32335), but the present invention is limited thereto. It is not a thing.

  Therefore, the degassing step of S103 may be performed by degassing the boehmite that has been added in S101 and kneaded in S102 in an environment of a predetermined atmospheric pressure or less realized by using a device such as a pump.

  Further, in the step of extruding in S104, for example, the boehmite is extruded at a pressure of 600 bar. However, the present invention is not limited to this, and the boehmite is extruded by any other pressure if there is no particular problem. May be.

  In the baking step of S105, boehmite is baked at 1500 degrees Celsius for about 1 hour or more and about 2 hours or less, but the present invention is not limited thereto.

  Accordingly, the temperature for baking boehmite is preferably 1400 degrees Celsius or more and 1600 degrees Celsius or less, and if there is no particular problem, the temperature may be other than that and 1300 degrees Celsius or more. The temperature and time for baking boehmite are optimized and changed depending on the combination of the above-described S101 to S105 and the environmental conditions in which those steps are executed. That is, the time for baking boehmite is also appropriately determined, and may be, for example, 2 hours or longer.

  Moreover, although the method for producing a sapphire single crystal is any one of the chocolate lasky method, the kilopross method, and the EFG method, the present invention is not limited thereto.

  That is, the sapphire single crystal according to the present invention may be produced by any other method as long as the above-mentioned α-alumina fired body is used as a raw material.

  Moreover, although the bulk density of the α-alumina fired body produced in the first embodiment is about 2.5 g / cc or more and about 3.5 g / cc or less, the present invention is limited thereby. It is not a thing. Therefore, the bulk density of the α-alumina fired body produced in the first embodiment may be a value other than the values described above.

(Experimental result)
In the following, description will be given of experiments carried out in accordance with an embodiment which is a specific example of the present invention and modifications thereof. Experiment 1 to be described later is an experimental example when the extrusion molding machine is not evacuated, and Experiment 2 to be described later is an experimental example when the extrusion molding machine is evacuated. By comparing the results of both, superiority in the case of vacuuming is recognized.

  First, Experiment 1 will be described. Boehmite AlO (OH) produced by hydrolyzing aluminum alkoxide was put into a 2 liter stirring kneader, stirred, and 920 g of pure water was added. In this state, the mixture was kneaded for 15 minutes to obtain clay-like boehmite.

  This clay-like boehmite was put into an extrusion machine FM-30 manufactured by Miyazaki Tekko Co., Ltd., and extrusion-molded with a pressure of 2.5 Mpa (megapascal) to obtain a 5 mm diameter rod-like body.

  The molded article, which is the above-mentioned rod-shaped body, was dried at 110 degrees Celsius and fired in an electric furnace at 1500 degrees Celsius for 2 hours to obtain a sintered body. The result will be described later.

  Next, Experiment 2 will be described. In the same manner as in Experiment 1, boehmite AlO (OH) produced by hydrolyzing aluminum alkoxide was put into a 2 liter stirring kneader, stirred, and 920 g of pure water was added. In this state, the mixture was kneaded for 15 minutes to obtain clay-like boehmite.

  This clay-like boehmite is put into an extruder FM-30 manufactured by Miyazaki Tekko, the degree of vacuum is set to -0.1 Mpa (megapascal), the inside of the extruder is evacuated, and 2.5 MPa (megapascal) is applied. A 5 mm diameter rod-like body was obtained by extrusion molding under pressure.

  The molded article, which is the above-mentioned rod-shaped body, was dried at 110 degrees Celsius and fired in an electric furnace at 1500 degrees Celsius for 2 hours to obtain a sintered body. The results are shown in Table 1 below together with the results of Experiment 1 described above.

  Referring to Table 1, the bulk density of the α-alumina fired body is increased from 2.21 g / cc to 2.85 g / cc by pulling the extruder into a vacuum. This is an important value for increasing the production yield of sapphire single crystals.

  Moreover, as can be seen from Table 1, the purity of the α-alumina fired body was not changed by evacuating the extruder. That is, it was found that the purity of the α-alumina calcined body was the same as that of the raw material boehmite and there was no contamination (contamination).

  As a future policy, it is considered that the bulk density of the α-alumina sintered body can be further increased by optimizing the above-mentioned pressure, degree of vacuum, and amount of water added.

  In addition, the density of Table 1 was measured by the Archimedes method, and the impurity was measured by the ICP-OES method.

  The production method of the α-alumina sintered body of the present invention can produce α-alumina with low contamination and low contamination, and the production method of the sapphire single crystal of the present invention is low in cost and high in yield. Since a sapphire single crystal can be produced, it is effective in many fields including a substrate of a semiconductor electric circuit. Therefore, it can be used in a so-called manufacturing industry.

DESCRIPTION OF SYMBOLS 1 ... Flow, S101 ... Water adding step, S102 ... Kneading step, S103 ... Deaeration step, S104 ... Extrusion molding step, S105 ... Baking step

Claims (4)

Adding water to boehmite;
Kneading the boehmite hydrolyzed in the hydrating step;
After the step of kneading or in the step of kneading, pressurizing the hydrated and kneaded boehmite at a predetermined pressure or more;
And baking the hydrated, kneaded and pressurized boehmite only once at a temperature of 1300 degrees Celsius or higher. The method for producing an α-alumina fired body according to claim 1, wherein the pressurizing step includes a step of extruding the hydrated and kneaded boehmite. The α-alumina firing according to claim 2, further comprising a step of degassing the boehmite in an environment of a predetermined atmospheric pressure or less at any timing from the start of the kneading step to the end of the extrusion molding step. How to produce the body. A method for producing a sapphire single crystal according to any one of the chocolate lasky method, the kilopross method, and the EFG method,
A method for producing a sapphire single crystal comprising a step of melting an α-alumina fired body produced by the method according to claim 1 in a container.