JP7056534B2 - Amorphous aluminum hydroxide and its manufacturing method, and α-alumina powder manufacturing method - Google Patents

Description

The present invention relates to amorphous aluminum hydroxide and a method for producing the same, and a method for producing α-alumina powder.

Since α-alumina (α-Al ₂ O ₃ ) is excellent in insulation, heat resistance, wear resistance, corrosion resistance, etc., refractories, abrasives, insulators, electronic parts, spark plugs, fillers, catalyst carriers, etc. Widely used in. By the way, α-alumina powder used for applications such as low-temperature sintered ceramics and composite materials is required to be fine particles. Further, the α-alumina powder is required to have a small amount of intermediate alumina such as χ-type, κ-type, and θ-type other than α-type, that is, a high degree of pregelatinization. The α-alumina powder, which is fine and has a high degree of pregelatinization, has excellent sinterability. Therefore, by using this α-alumina powder, it is possible to reduce the manufacturing cost of products such as ceramics and improve the quality of the products.

Various methods are known as methods for obtaining α-alumina powder. Among them, the Bayer process has the advantages that the raw materials are inexpensive and the manufacturing is easy. In the Bayer process, aluminum hydroxide is extracted from bauxite, which is an aluminum ore, with a caustic soda solution. The aluminum hydroxide obtained here is usually gibbsite (Al (OH) ₃ ). Then, this aluminum hydroxide (Al (OH) ₃ ) is heat-treated to undergo a crystal transition to α-alumina.

In order to crystallize aluminum hydroxide to α-alumina, a high temperature heat treatment of about 1100 to 1200 ° C. is usually required. For example, when gibbsite (Al (OH) ₃ ), which is a trihydrate, is heat-treated, it becomes χ-alumina at 200 to 300 ° C, κ-alumina at 900 to 1000 ° C, and finally α- at 1100-1200 ° C. Crystal transition to alumina. When boehmite (AlOOH), which is a monohydrate, is heat-treated, it becomes γ-alumina at 400 to 500 ° C, δ-alumina at 800 to 900 ° C, θ-alumina at 1000 to 1100 ° C, and finally 1200. Crystal transition to α-alumina at ° C.

With such a high temperature heat treatment, it is difficult to obtain α-alumina powder having excellent sinterability. This is because during the heat treatment, alumina grows into grains and becomes coarse. On the other hand, if the heat treatment temperature is lowered to prevent coarse graining, the crystal transition becomes insufficient, and as a result, the degree of pregelatinization of the obtained α-alumina powder is lowered. Therefore, it is required to produce α-alumina powder having fine particles and excellent sinterability with a high degree of pregelatinization while taking advantage of the Bayer process in which raw materials are inexpensive and easy to manufacture.

Various methods have been proposed to deal with this problem. For example, Patent Document 1 discloses a method for producing easily sinterable alumina particles, which comprises firing aluminum hydroxide by the Bayer process, adding magnesium oxide or magnesium hydroxide to the obtained alumina, and then mixing and pulverizing the mixture. Has been done. Patent Document 2 describes a method for producing ultra-easily sinterable alumina using aluminum hydroxide as a raw material by the buyer method. When α-alumina is added as a seed when crushing aluminum hydroxide precipitated particles, intermediate alumina to α-alumina is described. It is disclosed that the temperature of transition to aluminum decreases. Patent Document 3 describes a method for producing α-alumina by calcining an aluminum hydrate powder such as gibsite. It is said that α-alumina powder having excellent sinterability and reactivity can be obtained by adding a certain amount of powder as seeds.

Japanese Patent No. 4890758 Japanese Unexamined Patent Publication No. 6-144830 Japanese Unexamined Patent Publication No. 10-101329

However, the methods disclosed in Patent Document 1 and Patent Document 2 are insufficient to obtain α-alumina powder having fine particles and a high degree of pregelatinization. In the method disclosed in Patent Document 1, the firing temperature of aluminum hydroxide is set to 1100 to 1400 ° C. in order to transfer crystals to α-alumina. Such high-temperature heat treatment cannot sufficiently atomize α-alumina. Moreover, in this method, magnesium oxide and magnesium hydroxide are added to alumina, which causes a problem in terms of purity. Further, in the method disclosed in Patent Document 2, the firing temperature is 1000 to 1200 ° C., and the heat treatment temperature is still high.

In the method disclosed in Patent Document 3, the α-alumina powder is almost completely transitioned to α-alumina at about 900 ° C. to 1000 ° C., and is about 100 to 300 ° C. lower than the conventional transition temperature to α-alumina. It is said that it will be possible to manufacture. However, in the method disclosed in Patent Document 3, it is necessary to prepare α-alumina powder or diaspore powder in which a part of the particles is hydrated, which is inferior in convenience. In Patent Document 3, in order to obtain α-alumina powder obtained by hydrating a part of particles, a method of treating with a wet pulverizer using an α-alumina ball mill or a liner is adopted. Such wet treatment requires a filtration device, a drying facility, and the like, and has a long process cycle. There are synthetic and natural diaspores, and regardless of which one is used, it is necessary to synthesize or purify the diaspores.

Therefore, an object of the present invention is to provide atypical aluminum hydroxide and a method for producing the same, which can obtain α-alumina powder having fine particles and excellent sinterability with a high degree of pregelatinization by a simple method. .. Another object of the present invention is to provide a method for producing α-alumina powder having fine particles and excellent sinterability with a high degree of pregelatinization by a simple method.

According to the present inventor, atypical aluminum hydroxide having a crystal water content and an exothermic peak temperature within a specific range has a remarkably low crystal transition temperature to α-alumina, and as a result, easily sintered α-alumina. It has been found that it is useful as a raw material for powder production and that the amorphous aluminum hydroxide can be obtained by a simple method using a dry bead mill. The present invention has been completed based on such findings, and provides an amorphous aluminum hydroxide and a method for producing the same, and a method for producing α-alumina powder. Specifically, the following are provided.

(1) The present invention is amorphous aluminum hydroxide having a water of crystallization content of 21.0% by mass or less and showing an exothermic peak in the temperature range of 750 to 850 ° C. by differential scanning calorific value analysis.

(2) The present invention is further the amorphous aluminum hydroxide according to (1) above, wherein the content of the water of crystallization is 17.0% by mass or less.

(3) The present invention is the amorphous aluminum hydroxide according to (1) or (2) above, which further exhibits an exothermic peak in the temperature range of 810 to 830 ° C. by differential scanning calorimetry.

(4) The present invention further comprises the amorphous aluminum hydroxide according to any one of (1) to (3) above, wherein the sodium content is 0.01% by mass or less and the zirconium content is 0.05% by mass or less. Is.

(5) The present invention further comprises a step of mixing α-alumina seeds with aluminum hydroxide powder to prepare an aluminum hydroxide mixed raw material containing 10 to 20% by mass of the α-alumina seeds.
The method for producing amorphous aluminum hydroxide according to any one of (1) to (4) above, which comprises a step of subjecting the aluminum hydroxide mixed raw material to a mechanochemical treatment using a dry bead mill.

(6) The present invention is a method for producing α-alumina powder, which further heat-treats the amorphous aluminum hydroxide according to any one of (1) to (4) at a temperature in the range of 900 to 1000 ° C. ..

(7) The present invention is a method for producing α-alumina powder, which further heat-treats the amorphous aluminum hydroxide produced by the method (5) above at a temperature in the range of 900 to 1000 ° C.

The amorphous aluminum hydroxide of the present invention has a significantly low crystal transition temperature to α-alumina. Therefore, it can be used as a raw material for producing α-alumina powder having fine particles and a high degree of pregelatinization. Further, according to the method for producing amorphous aluminum hydroxide of the present invention, the amorphous aluminum hydroxide can be easily obtained. Further, according to the method for producing α-alumina powder of the present invention, α-alumina powder having fine particles and a high degree of pregelatinization and high quality can be obtained by a simple method. Therefore, it is possible to produce α-alumina powder with easy sinterability and high quality at low cost. By using this α-alumina powder, it becomes possible to manufacture high-quality ceramics and other products at low cost.

The X-ray diffraction pattern of the mixed raw material is shown. The X-ray diffraction pattern of the dry-processed powder is shown. The X-ray diffraction pattern of the dry-processed powder is shown. The X-ray diffraction pattern of the dry-processed powder is shown. The X-ray diffraction pattern of the mixed raw material is shown. The X-ray diffraction pattern of the dry-processed powder is shown. The DSC curve of the mixed raw material and the dry-processed powder is shown. The DSC curve of the dry-processed powder is shown. The DSC curve of the dry-processed powder is shown. The DSC curve of the dry-processed powder is shown. The SEM image of the dry-processed powder is shown. The SEM image of the dry-processed powder is shown. The X-ray diffraction pattern of the dry-processed powder after the heat treatment is shown. The X-ray diffraction pattern of the dry-processed powder after the heat treatment is shown. The X-ray diffraction pattern of the aluminum hydroxide powder after the heat treatment is shown. The X-ray diffraction pattern of the aluminum hydroxide powder after the heat treatment is shown. The degree of pregelatinization of the dry treated powder and the aluminum hydroxide powder after the heat treatment is shown. The X-ray diffraction intensity of the dry-type treated powder and the aluminum hydroxide powder after the heat treatment is shown. The SEM image of the dry treated powder (α-alumina powder) after the heat treatment is shown. The particle size distribution of the dry-type treated powder (α-alumina powder) after the heat treatment is shown.

Atypical Aluminum Hydroxide The amorphous aluminum hydroxide of the present invention is mainly composed of atypical aluminum hydroxide. Aluminum hydroxide is a compound having a composition such as gibbsite (Al (OH) ₃ ) in a completely crystalline state. In the amorphous aluminum hydroxide, the crystallinity of aluminum hydroxide has disappeared or decreased, and a part of water of crystallization has escaped. Therefore, the amorphous aluminum hydroxide is different from aluminum hydroxide, which is in a completely crystalline state, in the crystalline state and the amount of crystalline water. The degree of amorphization can be evaluated by the intensity (CPS) of the crystal peak (002) plane of the gibsite measured by X-ray diffraction and the water of crystallization (LOI). In the present invention, the amorphous aluminum hydroxide means that the intensity of the crystal peak (002) plane of gibbsite measured by X-ray diffraction is 350 CPS or less and the amount of crystal water is 21.0% by mass or less. On the other hand, the amount of crystalline water of the non-amorphized gibbsite is about 34.7% by mass.

The amorphous aluminum hydroxide of the present invention has a water of crystallization (LOI) of 21.0% by mass or less. Amorphous aluminum hydroxide has a smaller amount of crystalline water than aluminum hydroxide, which is in a completely crystalline state. As will be described later, the amorphous aluminum hydroxide of the present invention is produced by subjecting a mixed raw material composed of aluminum hydroxide powder and α-alumina seeds to a mechanochemical treatment (atypical treatment) using a dry ball mill. be able to. During the amorphization treatment using a dry bead mill, the primary particles constituting the aluminum hydroxide crystals such as gibbsite are crushed to a fine region, and the water of crystallization contained therein is discharged to the outside. It is speculated that it will be possible to sufficiently lower the crystal transition temperature to α-alumina by proceeding with pulverization until the amount of crystal water becomes small and forming sufficiently fine primary particles.

From the viewpoint of promoting amorphousness, the water of crystallization content is preferably 17.0% by mass or less. The lower limit of the water of crystallization content is not particularly limited, but may be typically 15.0% by mass or more.

The amorphous aluminum hydroxide of the present invention shows an exothermic peak in the temperature range of 750 to 850 ° C. by differential scanning calorimetry. This exothermic peak corresponds to the crystal transition to α-alumina (α-alumination). Ordinary aluminum hydroxide has a crystal transition temperature of 1100 to 1200 ° C. to α-alumina. On the other hand, the amorphous aluminum hydroxide of the present invention has an extremely low crystal transition temperature of 750 to 850 ° C. Amorphous aluminum hydroxide preferably exhibits an exothermic peak in the temperature range of 810 to 830 ° C.

The BET specific surface area of the amorphous aluminum hydroxide is not particularly limited, but is typically 15 to 50 m ² / g. The BET specific surface area can be measured using an automatic specific surface area measuring device (Micromeritex Co., Ltd., Flowsorb II2300 type) based on JIS1626.

The amorphous aluminum hydroxide of the present invention preferably has a content of elements other than aluminum (Al), oxygen (O) and hydrogen (H) of 0.1% by mass or less. In particular, it is preferable that the sodium (Na) content is 0.01% by mass or less and the zirconium (Zr) content is 0.05% by mass or less. Sodium and zirconium are components that inhibit sintering in the production of the final product, easily sintered ceramics, and it is desirable that the amount is as small as possible. In the amorphous aluminum hydroxide of the present invention, even if aluminum hydroxide such as gibbsite having a high sodium content is used as a raw material at the time of its production, the sodium contained in the crystals is removed during the amorphous treatment. As it comes out, it can be easily cleaned and removed. Further, if a raw material having a low sodium content is used, the sodium content of the amorphous aluminum hydroxide can be naturally reduced.

The amorphous aluminum hydroxide of the present invention has an extremely low crystal transition temperature of 750 to 850 ° C. to α-alumina. Therefore, by heat-treating this amorphous aluminum hydroxide at a low temperature, it is possible to obtain α-alumina powder having fine particles and a high degree of pregelatinization. As described above, an aluminum hydroxide-based material having an extremely low crystal transition temperature has not been known so far. For example, the aluminum hydroxide disclosed in Patent Document 1 and Patent Document 2 has a firing temperature of 1000 ° C. or higher because it undergoes crystal transition to α-alumina. Further, in Patent Document 3, it is stated that α-alumina powder can be produced at a temperature as low as 100 to 300 ° C. than the conventional transition temperature. However, the results of thermal analysis (TG / DTA) show that α. -The exothermic peaks corresponding to the transition temperature to alumina exist at about 960 ° C and about 1200 ° C (FIG. 4 (C) of Patent Document 3).

Method for producing amorphous aluminum hydroxide In the method for producing amorphous aluminum hydroxide of the present invention, α-alumina seeds are mixed with aluminum hydroxide powder, and aluminum hydroxide containing 10 to 20% by mass of the α-alumina seeds. It includes a step of using the mixed raw material and a step of subjecting the aluminum hydroxide mixed raw material to a mechanochemical treatment using a dry bead mill.

First, aluminum hydroxide powder is prepared as a raw material. As the aluminum hydroxide powder, gibbsite, buyer light and the like can be used. However, gibbsite is preferable in view of manufacturing cost. Further, the aluminum hydroxide powder may be produced by any method, but those produced by the Bayer process are preferable.

From the viewpoint of the fluidity and ease of handling of the powder, the aluminum hydroxide powder preferably has a Dp50 (average particle size) of 3 to 50 μm and a BET specific surface area of 0.2 to 5.0 m ² / g. The general-purpose aluminum hydroxide powder has a Dp50 and a BET specific surface area within the above range. In the production method of the present invention, a general-purpose aluminum hydroxide powder raw material can be used, and as a result, the advantages of reduction in production cost and simplicity can be maximized.

Next, α-alumina seeds are mixed with the aluminum hydroxide powder to obtain an aluminum hydroxide mixed raw material. The mixing amount of α-alumina seeds is adjusted so that the content of α-alumina seeds in the aluminum hydroxide mixed raw material is 10 to 20% by mass. By adding α-alumina seeds, it becomes possible to fully exert the effect of lowering the crystal transition temperature of the obtained amorphous aluminum hydroxide.

The decrease in crystal transition temperature due to α-alumina seeds is estimated as follows. That is, the phenomenon that the pregelatinization transition temperature is lowered by adding a small amount of α-alumina as a seed to the aluminum hydroxide raw material has been known for a long time. In the present invention, aluminum hydroxide (gibbsite or the like) and α-alumina seeds, which are raw materials, are first prepared into a mixed raw material powder, and at the same time, subjected to mechanochemical treatment to crush them so as to be significantly smaller. Therefore, the amorphous aluminum hydroxide primary particles having an increased specific surface area and the α-alumina seeds are closely aggregated at the particle interface, and the desired interaction is made more uniform. As a result, it is considered that amorphous aluminum hydroxide can undergo pregelatinization transition in a low temperature region where phase transition does not normally occur without passing through an intermediate alumina phase such as χ alumina.

From the viewpoint of lowering the temperature of the pregelatinization transition of amorphous aluminum hydroxide, α-alumina seeds preferably have a high degree of pregelatinization and fine particles. The degree of pregelatinization is preferably 90% or more, more preferably 95% or more. The Dp50 is preferably 0.1 to 0.5 μm, and the BET specific surface area is preferably 5 to 15 m ² / g. Further, from the viewpoint of lowering the temperature of the pregelatinization transition, the higher the content of α-alumina seeds is, the more preferable. However, high quality α-alumina seeds are expensive. In the present invention, the content of α-alumina seeds is set to 10 to 20% by mass from the viewpoint of the balance between the effect of lowering the pregelatinization transition and the economic efficiency. The content of α-alumina seeds is preferably 15 to 20% by mass.

Next, the mixed raw material is subjected to mechanochemical treatment to obtain amorphous aluminum hydroxide. When the pulverization operation is continuously performed on the crystal, the number of surface atoms and / or molecules that have lost the joint increases as the number of new surfaces increases, and the disorder of their bonding state extends to the vicinity of the surface layer. As a result, the pulverized particles are activated. Further, in the case of dry pulverization, agglomeration of powder occurs and the apparent surface area is reduced. The active surface of the crushed particles adsorbs moisture and gas in the air on the surface, and the chemical potential decreases and becomes stable. During this series of reactions, various phase transitions occur. Such phenomena and effects are called mechanochemical reactions, and treatments that cause such mechanochemical reactions are called mechanochemical treatments.

In the method for producing amorphous aluminum hydroxide of the present invention, a treatment using a dry bead mill is performed as a mechanochemical treatment. In the dry bead mill treatment, a high pulverization share is applied to the mixed raw material, and a mechanochemical reaction is effectively triggered. The dry bead mill is a kind of medium stirring type crusher, and is composed of a raw material input port, a cylindrical container (vessel), a rotating stirring member (agitator) provided in the cylindrical container, and an outlet of processed powder. Further, the agitator gap in the vessel is filled with a large number of pulverizing media (beads). In the dry bead mill, the agitator rotates at high speed during operation to agitate the beads. At this time, the raw material input from the raw material input port repeatedly collides with the agitator, beads, and the inner wall of the vessel, and is crushed by impact force, shearing force, frictional force, etc. It is discharged from the exit.

The detailed mechanism of the mechanochemical reaction by the dry bead mill treatment is unknown, but it is speculated as follows. During the treatment, the aluminum hydroxide is continuously subjected to a dry pulverization treatment in a high market share state. Therefore, a part of the water of crystallization in the aluminum hydroxide is desorbed. At the same time, the friction between the crushed particles, the beads and the inner wall of the vessel causes the temperature inside the device to rise, and as a result, phase transition phenomena such as partial hydrothermal reaction and dissolution reprecipitation occur in the crushed particles (aluminum hydroxide). Occur. In fact, when gibsite (crystal water content 34.7% by mass) is used as the raw material aluminum hydroxide powder and the mixing amount of α-alumina seeds is 20% by mass, the water of crystallization content of the aluminum hydroxide mixed raw material is. While it is 27.0% by mass or more, the water of crystallization content of the dry-type treated powder after the dry-type bead mill treatment is reduced to 21.0% by mass or less, and in some cases to 17.0% by mass or less. From this, it is understood that water of crystallization is desorbed by the dry bead mill treatment.

The agitator peripheral speed (rotational speed) of the dry bead mill is preferably 5.0 to 6.0 m / s, more preferably 5.0 to 5.5 m / s, and the bead filling amount is preferably 60 to 60 to s. It is 70% by volume, more preferably 60 to 65% by volume. The feed amount is preferably 1.0 to 4.0 kg / h, more preferably 2.0 to 3.0 kg / h. The higher the agitator peripheral speed and the bead filling amount, the more effectively the mechanochemical treatment is performed, and high quality amorphous aluminum hydroxide is obtained. Further, as the feed amount is smaller, the residence time of the mixed raw material becomes longer, and the amorphous formation of aluminum hydroxide is promoted. However, if the peripheral speed of the agitator and the filling amount of beads are excessively high, stable continuous operation becomes difficult. Further, if the feed amount is excessively small, problems such as a decrease in yield due to leakage of pulverized powder become remarkable, and the production efficiency deteriorates. When the agitator peripheral speed, the bead filling amount and the feed amount are within the above numerical ranges, high-quality amorphous aluminum can be obtained with good productivity.

In the mechanochemical treatment, the aluminum hydroxide mixed raw material may be treated once with a dry bead mill (1 pass treatment) or may be treated multiple times (2 pass treatment, 3 pass treatment, etc.). As described above, the smaller the feed amount, the more the amorphization of aluminum hydroxide is promoted, but the lower the production efficiency. In this respect, by processing a large number of times, the same result as in the case of processing once can be obtained even if the feed amount is increased. Therefore, high-quality amorphous aluminum hydroxide can be obtained while maintaining production efficiency. It is preferable to set the feed amount to 2.0 to 3.0 kg / h and perform 2-pass processing.

During the mechanochemical treatment, a pulverizing aid may be added to the aluminum hydroxide mixed raw material, if necessary. Examples of the pulverizing aid include ethanol.

When treated using a general dry crusher other than the dry bead mill, for example, a dry ball mill, the mechanochemical reaction of the treated powder is insufficient, and amorphous aluminum hydroxide cannot be obtained. Moreover, in such a general dry pulverizer, even if the processing time is lengthened, there is a limit to the atomization of the pulverized particles, and the specific surface area cannot be sufficiently increased. Further, when treated using a wet pulverizer, it is possible to atomize the pulverized particles to 1 μm or less, but the mechanochemical reaction is insufficient. Therefore, amorphous aluminum hydroxide cannot be obtained. In addition, when a wet pulverizer is used, there is a problem that contamination (impurities) increases and productivity is poor. For example, in Patent Document 3, wet pulverization treatment is performed, but the wet pulverization treatment requires an advanced filtration device and a large-scale drying facility.

On the other hand, in the production method of the present invention, the mechanical reaction of the aluminum hydroxide mixed raw material can be made sufficient by the dry bead treatment, which is a dry treatment, and as a result, the crystal transition temperature to α-alumina can be satisfied. Amorphous aluminum hydroxide with a significantly low transition temperature can be easily obtained. In particular, since the manufacturing method of the present invention employs mechanical treatment using a dry beer mill, it is possible to inexpensively obtain amorphous aluminum hydroxide having a high degree of processing difficulty while using general-purpose aluminum hydroxide as a starting material. Therefore, the advanced filtration device and large-scale drying equipment required for the wet pulverization process are not required, and the productivity is excellent. Moreover, when a continuous device is used as the dry bead mill, continuous processing is possible.

Method for Producing α-Alumina Powder In the method for producing α-alumina powder of the present invention, amorphous aluminum hydroxide is heat-treated (baked) at a temperature in the range of 900 to 1000 ° C. Further, if necessary, the heat-treated powder after the heat treatment may be subjected to a crushing treatment. Since the amorphous aluminum hydroxide of the present invention has a remarkably low crystal transition temperature to α-alumina, α-alumina powder having a sufficiently high degree of pregelatinization can be obtained even by heat treatment at a relatively low temperature of 900 to 1000 ° C. Can be done. Further, since the heat treatment temperature is low, it is possible to suppress the growth of crystal grains during the heat treatment. Therefore, fine-grained alumina powder having a high degree of pregelatinization can be obtained. The heat treatment temperature is preferably 900 to 1000 ° C, more preferably 925 to 975 ° C.

The α-alumina powder preferably has a degree of pregelatinization of 80.0% or more, more preferably 90.0% or more. Since the production method of the present invention uses amorphous aluminum hydroxide having a sufficiently low crystal transition temperature to α-alumina, it is possible to obtain alumina powder having a high degree of pregelatinization. The degree of pregelatinization is determined by measuring the X-ray diffraction intensity of the (012) plane and the (116) plane of the α-alumina crystal and comparing it with the X-ray diffraction intensity of the standard sample (pregelatinization degree 100%). be able to.

The α-alumina powder preferably has a Dp50 of 0.1 to 0.5 μm and a BET specific surface area of 5.0 to 15.0 m ² / g. In the production method of the present invention, since the heat treatment temperature is low, fine α-alumina powder can be obtained.

The α-alumina powder preferably has a content of components other than alumina of 0.2% by mass or less, more preferably 0.1% by mass. Although a component such as magnesium oxide is added in Patent Document 1, such an additive component is not necessary in the production method of the present invention. Moreover, even if gibbsite or the like having a high sodium content is used as a raw material, the sodium content can be easily reduced. Therefore, it is possible to obtain α-alumina powder having a low content of sodium and zirconium, which are sintering inhibitory components.

As described above, by the method for producing α-alumina powder of the present invention, it is possible to easily obtain high-quality α-alumina powder having fine particles and a high degree of pregelatinization. This α-alumina powder has excellent sinterability. Therefore, it is possible to manufacture α-alumina powder having excellent sinterability and products such as ceramics using the powder at low cost.

The present invention will be described in detail with reference to the following examples. However, the present invention is not limited to the following examples.

(1) Preparation of dry-processed powder (amorphous aluminum hydroxide)
Example 1 (comparative example)
<Preparation of mixed raw materials>
The aluminum hydroxide mixed raw material was prepared as follows. First, aluminum hydroxide powder and α-alumina seeds were prepared as raw materials. As the aluminum hydroxide powder, B53 (gibbsite) manufactured by Nippon Light Metal Co., Ltd., which is an inexpensive general-purpose product manufactured by the Bayer process, was used. Further, as the α-alumina seed, AHP200 manufactured by Nippon Light Metal Co., Ltd. was used. The α-alumina seed (AHP200) had a degree of pregelatinization of 97.0%.

Next, 20 wt% of α-alumina seeds (AHP200) was added to the aluminum hydroxide powder (B53), and then mixed for 5 minutes using a Henshell mixer to mix raw materials for amorphous aluminum hydroxide raw materials. (Mixed powder).

<Mechanochemical treatment>
Further, the mixed raw material was subjected to mechanochemical treatment using a dry bead mill (Ashizawa Finetech Co., Ltd., SDA-5) for 1 pass (1 pass treatment) to prepare a dry treated powder. The dry bead mill treatment uses PSZ (partially stabilized zirconia) media beads with a diameter of 1.5 mm and a crushing aid (ethanol), and the bead filling rate is 60% by volume, the peripheral speed is 5.5 m / s, and the feed amount is 3.0 kg /. It was done under the condition of h.

Example 2 (Example)
During the mechanical treatment, a dry treated powder (amorphous aluminum hydroxide) was produced in the same manner as in Example 1 except that the treatment was completed in the middle of the second pass.

Example 3 (Example)
A dry treated powder (amorphous aluminum hydroxide) was produced in the same manner as in Example 1 except that the mechanochemical treatment was performed in 2 passes (2-pass treatment).

Example 4 (comparative example)
BE033 (gibbsite) manufactured by Nippon Light Metal Co., Ltd. is used as the aluminum hydroxide powder, and the developed product (pregelatinization degree 93.0%) is used as the α-alumina seed. A dry-processed powder was produced in the same manner as in Example 1 except that a bridge breaker (powder clogging clearing device) was installed near the charging port). Here, the bridge breaker is a device for the purpose of preventing powder clogging in the vicinity of the feed port, and by installing the bridge breaker, stable sample collection is possible even in continuous operation.

Example 5 (comparative example)
The dry-processed powder was prepared in the same manner as in Example 4 except that the bridge breaker was not installed.

Example 6 (Example)
A dry treated powder (amorphous aluminum hydroxide) was produced in the same manner as in Example 4 except that the peripheral speed of the dry bead mill was 6.0 m / s.

Example 7 (comparative example)
As α-alumina seeds, a developed product having a different BET specific surface area (pregelatinization degree 90.0%) was used, and the dry-type treatment was carried out in the same manner as in Example 4 except that the feed amount of the dry-type bead mill was 4.0 kg / h. The powder was made.

Example 8 (comparative example)
A dry untreated powder was produced in the same manner as in Example 7 except that the mechanochemical treatment was performed in 2 passes (2-pass treatment).

Example 9 (Example)
A dry treated powder (amorphous aluminum hydroxide) was produced in the same manner as in Example 7 except that the feed amount of the dry bead mill was 2.0 kg / h and the bead filling rate was 65% by volume.

Example 10 (reference example)
Same as Example 9 except that C10 (pseudo-boehmite) manufactured by Nippon Light Metal Co., Ltd. was used as the raw material aluminum hydroxide and AHP200 (pregelatinization degree 97.0%) manufactured by Nippon Light Metal Co., Ltd. was used as the α-alumina seed. , Dry-type treated powder was prepared.

(2) Evaluation of dry-processed powder (amorphous aluminum hydroxide) Various characteristics of Examples 1 to 10 were evaluated as follows.

<Dp50>
The average particle size (Dp50) was measured as follows. That is, a homogenizer (Nissei Tokyo Office, US-600T) was used to disperse the powder to be measured under the conditions of 600 W, 20 kHz, 1 minute, and then a laser diffraction / scattering particle size analyzer (Nikkiso Co., Ltd., Microtrack). The particle size of the sample was measured using MT3300).

<BET specific surface area>
The BET specific surface area was measured using an automatic specific surface area measuring device (Micromeritex, Flowsorb II2300 type) based on JIS1626.

<X-ray diffraction>
The X-ray diffraction pattern of the powder sample was obtained by the powder X-ray diffraction method, and the intensity (CPS) of the crystal peak (002) plane of the gibsite was calculated from this diffraction pattern. For Example 10, the intensity (CPS) of the crystal peak (020) plane of boehmite was calculated from the diffraction pattern.

X-ray diffraction was performed as follows. First, a powder sample was placed on a special sample plate and lightly spread to a size of 20 mm × 20 mm × 0.5 mm to prepare a measurement sample. Next, an X-ray diffraction pattern of the measurement sample was obtained using an X-ray diffractometer.

The conditions for X-ray diffraction were as follows.
-Device: RINT manufactured by Rigaku Co., Ltd. (Sample horizontal type: UltimaII)
-Radioactive source: CuKα wire-Voltage: 40kV
-Current: 40mA
-Scan speed: 4 ° / min
-Sample width: 0.05 °
-Starting angle: 5 °
-End angle: 90 °

<Water of crystallization>
The water of crystallization (LOI) was determined by measuring the ignition loss (%). The measurement of ignition loss was performed as follows. First, the sample was placed in a platinum crucible, and the mass W2 (g) was measured using a weighing bottle. After the measurement, the sample is dried, and then the temperature is raised to 1100 ° C. at a rate of about 100 ° C./15 min, and a strong heat treatment is performed to keep the temperature inside the furnace at 1100 ° C. ± 25 ° C. for 1 hour. rice field. The mass W3 (g) was measured after ignition. Separately, the mass W1 (g) of the platinum crucible and the weighing bottle was measured. Using W1 to W3, the water of crystallization content LOI (ignition loss) is calculated by the formula: LOI = (W2-W3) / (W2-W1) × 100 (%) -adhered water content (%) (where W1 Was determined by the mass (g) of the platinum crucible and the weighing bottle, W2 was determined by the mass of the sample, the platinum crucible and the weighing bottle (g), and W3 was determined by the mass of the sample, the platinum crucible and the weighing bottle after ignition (g).

<Peak temperature of heat generation>
The exothermic peak temperature was determined by performing differential scanning calorimetry (DSC) using a differential scanning calorimeter (manufactured by Rigaku Co., Ltd.). First, in order to exclude the influence of adhered water and the like, a pretreatment of holding the sample at 300 ° C. for 1 hour is performed, and then a measurement is performed at a heating rate of 20 ° C./min to obtain a DSC curve and pregelatinize heat generation. The peak was detected.

<Amount of impurities>
The content of impurities (Zr, Na ₂ O) in the sample was measured by the following method. First, after preparing the sample, it was placed in a platinum crucible and set in a high-frequency melting device. Then, preheating at 700 ° C. × 60 sec, melting at 1200 ° C. × 240 sec, and shaking treatment at 1200 ° C. × 120 sec were performed to prepare a glass beaded sample. Next, a glass bead sample was analyzed using a scanning fluorescent X-ray analyzer (Rigaku Co., Ltd., ZSX Primus II). Then, the obtained data was compared with the data of the standard sample for the calibration curve to obtain the measurement result. In addition, the measurement results were rounded according to JIS Z 8401.

(3) Results For Examples 1 to 10, the evaluation results of the raw materials (aluminum hydroxide powder, α-alumina seeds), aluminum hydroxide mixed raw materials and dry-treated powder (atypical aluminum hydroxide) are shown in the table together with the sample preparation conditions. Shown in 1 to 4. The X-ray diffraction patterns of the mixed raw material and the dry-processed powder (amorphous aluminum hydroxide) are shown in FIGS. 1 to 6, and the DSC curves are shown in FIGS. 7 to 10. Further, for Examples 1 to 9, the amounts of impurities (Zr, Na ₂ O) in the raw materials, the mixed raw materials and the dry-processed powder are shown in Tables 5 to 7.

As can be seen from the results of the X-ray diffraction peak intensities shown in Tables 1 to 4 and FIGS. 1 to 6, the peak intensities are remarkably reduced by subjecting the aluminum hydroxide mixed raw material to mechanochemical treatment using a dry bead mill. At the same time, the water of crystallization content was reduced (Examples 1 to 9). In particular, the mixed raw materials of Examples 1 to 9 have a water of crystallization content of 27.7 to 27.9% by mass, whereas the mixed raw materials of the present invention subjected to the dry bead mill treatment (Examples 2, 3, 6 and). The atypical aluminum hydroxide (dry-treated powder) of 9) had a water of crystallization content of 21.0% by mass or less, and in some cases 17.0% by mass or less. From this, it can be seen that the aluminum hydroxide is amorphized by the dry bead mill treatment, the crystallinity disappears or decreases, and a part of the water of crystallization escapes.

Further, as can be seen from the results of the exothermic temperature (DSC curve) shown in Tables 1 to 4 and FIGS. 7 to 10, the mechanochemical treatment significantly reduced the pregelatinized exothermic temperature. In particular, the mixed raw materials of Examples 1 to 9 have a heat generation temperature of 1100 ° C. or higher, whereas the dry-treated powder (atypical aluminum hydroxide) of the examples of the present invention (Examples 2, 3, 6 and 9) has a heat generation temperature of 1100 ° C. or higher. The heat generation temperature dropped to 850 ° C. or lower, and in some cases to 820 ° C. or lower. From this, it can be seen that the amorphous aluminum hydroxide of the present invention has a remarkably low crystal transition temperature to α-alumina.

In Example 4 in which the bridge breaker is installed in the dry-type bead mill, powder clogging near the feed port does not occur during the mechanochemical treatment, and the raw material can be stably supplied according to the feed set amount, and continuous supply is possible. Was possible. Therefore, the sample according to the set conditions could be collected, and a continuously pulverized product could be obtained. On the other hand, in Example 5 in which the bridge breaker was not installed, bridges (powder clogging) frequently occurred near the feed port, and in that case, the powder clogging was manually cleared. Therefore, there is a possibility that the raw material is discontinuously charged into the pulverized portion even though the feed amount is set quantitatively. Therefore, it is considered that the sample was processed for a longer time than the set residence time and was collected discontinuously. Therefore, in Example 5, a pulverized powder (discontinuous pulverized product accompanied by manual operation) that had been subjected to an amorphous treatment exceeding the set value was obtained.

As can be seen from Tables 1, 2 and 5 to 7, as the mechanochemical treatment (amorphous treatment) progresses, the water of crystallization (LOI) decreases and f-Na ₂ O increases. Finally, the value shifted to almost the same value as t—Na ₂ O. Here, t-Na ₂ O is the sodium content contained in the molten sample, which is the sum of the sodium (Na) content incorporated in the aluminum hydroxide crystal and the sodium content adhering to the crystal surface. It is a total amount measurement value of. Further, f—Na ₂ O is a so-called elution-impure sodium content that is attached to the surface and can be easily removed by a washing operation or the like.

The sodium content incorporated in the aluminum hydroxide crystals produced by the Bayer process is extremely difficult to remove by general cleaning operations, and the quality of the alumina particles after firing and the sinterability of the target ceramics are improved. It has a big negative effect. In the present invention, the sodium content incorporated in the crystal is released to the outside of the crystal by the mechanochemical treatment (amorphization treatment), so that f—Na ₂ O can be easily taken out by a general washing operation or the like. It is migrating. Therefore, even when inexpensive and general-purpose aluminum hydroxide having a relatively high sodium content in crystals is used as a raw material, atypical aluminum hydroxide having a reduced amount of sodium in crystals can be easily obtained. Therefore, according to the method for producing amorphous aluminum hydroxide of the present invention, even if gibsite having a high sodium content is used as a raw material, sodium in crystals can be easily removed during mechanical treatment (amorphous treatment). Amorphous aluminum hydroxide with a reduced amount of sodium in crystals can be obtained.

As can be seen from Tables 5 to 7, the amount of zirconium (Zr) in the dry-treated powder (atypical aluminum hydroxide) is the dry-treated powder even though the zirconia beads are used as the medium during the dry-type bead mill treatment. It is almost the same as the previous mixed raw material. From this, it can be seen that according to the method for producing amorphous aluminum hydroxide of the present invention, an increase in the amount of zirconium is suppressed, and amorphous aluminum hydroxide having a small amount of zirconium can be obtained.

As described above, according to the production method of the present invention, amorphous aluminum hydroxide having a remarkably low crystal transition temperature to α-alumina and a low content of sodium and zirconium, which are sintering inhibitory components, can be obtained. Therefore, according to the present invention, it is possible to obtain amorphous aluminum hydroxide that can obtain α-alumina powder having fine particles and excellent sinterability with a high degree of pregelatinization by a simple method.

(4) Preparation and evaluation of α-alumina powder A heat-treated powder (alumina powder) was prepared by heat-treating (burning) a dry-type treated powder (atypical aluminum hydroxide). Specifically, the dry-type treated powders (amorphous aluminum hydroxide) of Examples 1, 3, 6, 9 and 10 were heat-treated at 400 to 950 ° C. for 5 to 24 hours. For comparison, the aluminum hydroxide powder (BE033) that had not been treated with mechanochemicals was heat-treated at 800 to 1400 ° C. for 10 to 24 hours.

The obtained heat-treated powder was measured for BET specific surface area and true specific gravity, and analyzed by X-ray diffraction method. In addition, the degree of pregelatinization was calculated based on the results of X-ray diffraction analysis. The degree of pregelatinization was determined by comparing the X-ray diffraction intensities of the (012) and (116) planes of the α-alumina crystal with the X-ray diffraction intensities of the standard sample (100% pregelatinization).

The results obtained are shown in Table 8. In Table 8, the heights (peak intensities) and half of the 2θ (25.6) r-plane, 2θ (52.5) r-plane and 2θ (57.5) r-plane obtained by X-ray diffraction analysis are shown. The price range is also shown. Further, for the dry-treated powder (Example 6) and the raw material aluminum hydroxide powder (BE033), the X-ray diffraction patterns after the heat treatment are shown in FIGS. 13 to 16, and the degree of pregelatinization and the X-ray diffraction intensity after the heat treatment (2θ (2θ). 25.6) r-plane) are shown in FIGS. 17 and 18, respectively.

As shown in Table 8, the aluminum hydroxide powder (BE033) started to be pregelatinized at 1000 ° C. or higher, and required high temperature heat treatment as high as 1150 ° C. to reach a pregelatinization degree of 90% or higher. The BET specific surface area at that time was 9.5 m ² / g or less. Further, the dry-type treated powder (Example 1) of the comparative example, which had been subjected to mechanochemical treatment but had an insufficient degree of amorphization, did not reach a degree of pregelatinization of 90% even after the heat treatment at 950 ° C.

On the other hand, the dry-type treated powder (amorphous aluminum hydroxide) (Example 3, Example 6 and Example 9) of Examples having a sufficient degree of amorphousness has a degree of pregelatinization of 90% after heat treatment at 950 ° C. As described above, the BET specific surface area was 11.5 m ² / g or more. From this, it can be seen that the amorphous aluminum hydroxide sufficiently undergoes crystal transition to α-alumina even by low temperature heat treatment. In fact, as can be seen in FIGS. 17 and 18, amorphous aluminum hydroxide has a crystal transition to α-alumina of about 300 ° C. as compared with aluminum hydroxide powder (BE033) which has not been subjected to mechanochemical treatment. It was cold.

19 and 20 show a scanning electron microscope image (SEM image) and a particle size distribution of α-alumina powder prepared by heat-treating atypical aluminum hydroxide at 1000 ° C. As can be seen from this, the α-alumina powder had an average particle size (Dp50) of 0.11 μm, which was very fine and showed a uniform particle size distribution.

As can be understood from the above results, the amorphous aluminum hydroxide of the present invention has a remarkably low crystal transition temperature to α-alumina and a low content of sodium and zirconium, which are sintering inhibitory components. Therefore, by using such amorphous aluminum hydroxide as a raw material for producing α-alumina powder, a high-quality α-alumina powder having fine particles, a high degree of pregelatinization, and easy sinterability can be obtained by a simple method. be able to. By using this α-alumina powder, it becomes possible to manufacture high-quality ceramics and other products at low cost.

Claims (5)

The content of water of crystallization is 21.0% by mass or less, the exothermic peak is shown in the temperature range of 810 to 830 ° C. in the differential scanning calorific value analysis, and the amount of sodium (Na ₂ O) in the crystal is 0.01% by mass. Hereinafter, amorphous aluminum hydroxide having a zirconium content of 0.05% by mass or less and a BET specific surface area of 15 to 50 m ² / g . The amorphous aluminum hydroxide according to claim 1, wherein the content of the water of crystallization is 17.0% by mass or less. A step of mixing α-alumina seeds with aluminum hydroxide powder to prepare an aluminum hydroxide mixed raw material containing 10 to 20% by mass of the α-alumina seeds.
The method for producing amorphous aluminum hydroxide according to claim 1 or 2 , which comprises a step of subjecting the aluminum hydroxide mixed raw material to a mechanochemical treatment using a dry bead mill. A method for producing α-alumina powder, wherein the amorphous aluminum hydroxide according to claim 1 or 2 is heat-treated at a temperature in the range of 900 to 1000 ° C. A method for producing α-alumina powder, wherein the amorphous aluminum hydroxide produced by the method according to claim 3 is heat-treated at a temperature in the range of 900 to 1000 ° C.

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