JP2981869B2 - Fibrous AlNH4CO3 (OH) 2 single crystal particles and fired product, and methods for producing them - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] The present invention relates to a compound having a fibrous form, AlNH ₄ CO ₃ (OH) ₂ (hereinafter referred to as AAC).
H) and a fired product thereof, and a method for producing them efficiently and with good reproducibility.

[0002]

2. Description of the Related Art Currently known AACH particles are relatively close to isotropic shapes such as spherical, rice-granular, and needle-like particles, and among them, spherical particles are industrially used as starting materials for producing ceramics. It is manufactured and used in large quantities. In the conventional ceramic manufacturing technology, many methods such as press molding and casting are used when molding a powder, and in this case, spherical particles are required. However, at present, hydrostatic pressing,
With the development of methods using hot isostatic pressing and the like, it has become possible to produce dense compacts and sintered bodies using anisotropic particles. In addition, with the development of science and technology and manufacturing technology, design of new materials that combine functions and compositions by combining multiple materials, as well as single-composition and single-structure materials that have been used conventionally. , Development is underway. For this purpose, a ceramic material having an anisotropic needle-like or fibrous form is required as a necessary material.

At present, whiskers and long fibers of relatively limited types such as silicon nitride, silicon carbide and carbon are produced on an industrial scale as materials having a form suitable for this purpose. There are few examples. However, in order to manufacture a composite material of oxide ceramics, acicular or fibrous particles of oxide ceramics or α-alumina whiskers are required from the viewpoint of compatibility of chemical properties.

AACH particles began to attract industrial attention around 1977, and were relatively new. Since then, few experimental attempts have been made to develop the shape of the particles anisotropically. Only patents can be seen. For example,
Kato et al. Reported that ammonium aluminum sulfate, AlNH ₄
(SO ₄ ) ₂ (hereinafter referred to as AA), ammonium bicarbonate, NH ₄ HCO ₃ (hereinafter referred to as AHC)
A large number of needle-like particles grow radially and take a coherent aggregate form when the aqueous solution reaction at 55-65 ° C. is performed (Shuzo Kato, Takeo Iga, Shogo Hatano, Yuichi Izawa, Journal of the Ceramic Industry Association, 84, 215-220 (197
6)). Several patents have been disclosed for producing needle-like or rod-like particles. That is, a method of gradually reacting a concentrated aqueous solution of ammonium bicarbonate with a dilute aqueous solution of aluminum chloride (Japanese Patent Application Laid-Open No. 58-26029), and a method of producing crystalline ammonium dawsonite, wherein water-insoluble basic aluminum sulfate and ammonium hydrogen carbonate are used Reaction method (Yazawa and Hatano, Tokuhei 2-58205)
No.), a method of aging an aluminum hydroxide or its hydrate at a temperature of 60 ° C. or more in an aqueous solution of ammonium hydrogen carbonate (Murase and Iga, Tokuhei 2-62485)
No.), a method of preliminarily adding an acid or a base to an aging solution when the reaction product of an aqueous solution of an aluminum salt and ammonium bicarbonate is heated and aged in an aqueous ammonium bicarbonate solution (Murase and Iga, Tokuho 4-36093) It has been reported that needle-like or rod-like AACH particles can be obtained by the method described in US Pat. Comprehensively judging these facts, AACH
It is evident that the particles can grow anisotropically to become needle-like particles, and that if the production conditions are appropriately selected, it is possible to produce very long AACH particles which can be said to be fibrous. Can be

The following methods are known for directly obtaining α-alumina needle-like particles or whiskers.
When a high temperature gas phase reaction of 1500 to 2000 ° C. is used, α
Alumina whiskers can be formed on the substrate. There is also known a method of producing an α-alumina fiber by drawing a melt of α-alumina from a small-diameter nozzle and solidifying the melt. In these methods, the reaction conditions are strictly controlled, the yield is low, or high temperature conditions are required.

On the other hand, it is known to obtain α-alumina needle-like particles by using an aluminum compound having a needle-like morphology and subjecting it to thermal decomposition. That is, when the surface is coated with about 1% by weight of a silica-containing compound using needle-like particles of the compound AACH which becomes alumina after thermal decomposition and then thermally decomposed, γ-alumina or α-alumina is obtained depending on the temperature. And the shape of the particles retains a needle shape (Murase and Iga, Tokuhei 8-11689).
issue). When the boehmite gel film in which the α-alumina fine particles are dispersed is thermally decomposed, α-alumina whiskers grow starting from the added α-alumina fine particles (S. Jagota and R. Raj, J. Cry).
stal Growth, 85, 527-534 (19
87)). These are considered to be suitable for industrial-scale production because the temperature required for the reaction is lower than in the direct method described above and a high yield is expected. However, at present, there is a disadvantage that the particles obtained in the final state are short because the length of the particles in the starting state is short. Therefore, based on the state of the art, there is a need for a method for producing fine and long fine particles of an aluminum compound. In addition, extremely long fibrous fine particles can be used not only as starting materials for whiskers, but also as porous membranes, filters, filters, catalyst carriers, and functional membranes. Not only a simple substance but also a fiber such as a mullite or a spinel compound or a zirconia composite can be used.

[0007]

Under these circumstances, a fibrous aluminum compound AACH and its optimum for producing α-alumina single crystal particles having a fibrous morphology and alumina-based oxide fibers are disclosed. There is a need to provide fired products and to provide a method capable of producing them on an economical scale with good reproducibility by using simple devices and simple operations.

[0008] AACH particles are produced on an industrial scale using an aqueous solution reaction of AA and AHC, and are used as a starting material for producing alumina powder having high purity and easy sintering. For the production, the concentration of the reaction reagent, the pH of the reaction solution, the stirring speed of the reaction solution, the addition speed of the reagent, the reaction temperature,
The ripening conditions of the precipitation are examined, and for the time being, the conditions for obtaining isotropically shaped fine particles are set. Therefore,
The reaction between AA and AHC is not completely understood, and particularly the reaction conditions for synthesizing fibrous particles are hardly clear.

Therefore, the AACH particles grow preferentially in one direction by organizing and comprehensively judging the experimental facts that have been clarified up to now and accumulating experimental facts by repeating new experiments. I tried to find the best condition. Specifically, AHC in the synthesis of compound AACH
Focusing on the effect of the CO ₃ ^2- ion concentration in the aqueous solution,
As for the aging of the precipitate, the aging temperature was expanded to 200 ° C., which is higher than the conventionally studied temperature, and as a result of detailed examination, A
In order to grow ACH crystal particles into fibrous form, AACH
It has become clear that the concentration of CO ₃ ^2- ions in the aqueous solution needs to be sufficiently high during the formation and growth of crystals, and it is particularly necessary to keep the temperature in the growth process at 100 ° C. or higher.

Furthermore, even when the AACH precipitate is aged under the condition that the unreacted aluminum ion is hardly present in the solution after the AACH generation reaction is completed, or when the AACH fine particles are aged in the AHC aqueous solution, the aging time is reduced. It was also found that AACH particles grow elongated.
This fact means that some of the AACH particles were dissolved and the aluminum component was used to grow other particles into fibers. Based on the above findings, fibrous AA
The conditions for generation and ripening required for synthesizing CH particles can be set, and the present invention has been completed. That is, the present invention relates to a compound AA having a fibrous form.
An object of the present invention is to provide a single crystal particle of CH and a calcined product thereof, and a method for producing them efficiently and with good reproducibility.

[0011]

The present invention for solving the above-mentioned problems is based on a water-soluble compound such as aluminum sulfate, aluminum chloride, ammonium aluminum sulfate, aluminum hydroxide, aluminum ethoxide, aluminum isopropoxide or aluminum acetylacetonate. Alternatively, an aqueous solution or suspension of an aluminum compound having some solubility in water is mixed with a CO ₃ ^2- ion concentration of 0.01 mol.
/ L or more sufficiently high NH ₄ HCO ₃ solution or CO ₃
^The compound AlNH ₄ CO ₃ (O 2) obtained by injecting into a basic aqueous solution having a sufficiently high ^2- ion concentration and containing NH ₄ ⁺ ions and heating and aging at a temperature of 100 ° C. or higher.
H) ₂ fibrous single crystal particles having an aspect ratio of 10 or more,
Particles having a length of 0.5 μm or more and a thickness of 0.01 μm or more. In addition, the present invention, the fibrous particles as they are or in the form of a film, a tube, a paper, a bulk, etc.
Obtained by heat treatment at 1000 ° C. or higher,
A fired product having alumina as a main component and having a shape such as a needle shape, a fiber shape, a film shape, a tubular shape, a paper shape, or a bulk shape. Further, the present invention is the method for producing the fibrous particles,
Aluminum sulfate, aluminum chloride, ammonium aluminum sulfate, aluminum hydroxide, aluminum ethoxide, aluminum isopropoxide, or an aqueous solution or suspension of an aluminum compound having some solubility in water such as aluminum acetylacetonate. Into a sufficiently high NH ₄ HCO ₃ aqueous solution having a CO ₃ ^2- ion concentration of 0.01 mol / l or more or a basic aqueous solution having a sufficiently high CO ₃ ^2- ion concentration and containing NH ₄ ⁺ ions, and A fibrous single crystal particle of the compound AlNH ₄ CO ₃ (OH) ₂ , characterized by being heated and aged at the above temperature, having an aspect ratio of 10 or more and a length of 0.5 μm.
m or more, and a method for producing particles having a thickness of 0.01 μm or more. Further, the present invention, the above alumina as a main component,
A method for producing a fired product having a form such as a needle shape, a fiber shape, a film shape, a cylindrical shape, a paper shape or a bulk shape, wherein the fibrous particles according to claim 1 are used as they are or in a film shape, a cylindrical shape, or a paper shape. Or after being formed into a bulk form or the like, and further mixed or compounded with other organic or inorganic compounds such as oxides, metals, plastics, etc., in an atmosphere of air, oxygen, inert gas, vacuum, etc.
A method for producing a fired product having a form of a needle, a fiber, a film, a tube, a paper, a bulk, or the like, comprising alumina as a main component, wherein the heat treatment is performed at a temperature of 00 ° C. or higher. is there.

[0012]

Next, the present invention will be described in more detail. The present invention relates to a method of heating a seed of a fibrous particle and an aluminum source for growing the fibrous particle in a basic aqueous solution having a sufficiently high CO ₃ ^2- ion concentration and containing NH ₄ ⁺ ions at a temperature of 100 ° C. or more. It is characterized by holding, specifically, an aqueous solution or a suspension of an aluminum compound having some solubility in water or water, and the solution has a CO ₃ ^2- ion concentration of 0.01 mol / L
Injecting into a sufficiently high NH ₄ HCO ₃ aqueous solution or a basic aqueous solution containing NH ₄ ⁺ ions having a sufficiently high CO ₃ ^2- ion concentration and heating and aging at a temperature of 100 ° C. or more It is. Thereby, the particles grow elongated along with the holding time, and the target fibrous AACH particles are obtained. Here, examples of the water-soluble aluminum compound include aluminum sulfate, aluminum chloride and ammonium aluminum sulfate. Examples of the hardly soluble aluminum compound having some solubility in water include aluminum hydroxide, aluminum ethoxide, and aluminum isopropoxide. An example is aluminum acetylacetonate. These aqueous solutions or suspensions can be prepared by usual methods. Next, these are combined with a sufficiently high NH ₄ HC having a CO ₃ ^2- ion concentration of 0.01 mol / l or more.
O ₃ aqueous solution or CO ₃ ^2- ion concentration is sufficiently high and NH
₄ ⁺ ions are implanted into the basic aqueous solution containing, heats aged at 100 ° C. or higher, wherein, with the injection such as the aqueous solution, means to them to coexist irrespective of their order of addition. Further, in this case, the CO ₃ ^2- ion concentration is set to 0.1.
If the temperature is lower than 01 mol / l, boehmite or an amorphous aluminum compound is generated without generating AACH, which is not preferable. If the heating temperature is lower than 100 ° C., the reaction rate is low and the AACH particles are sufficiently long. May not be obtained, which is not preferred. Further, in the method of the present invention,
The holding time is important. For example, by aging for about 24 to 48 hours, the AACH particles can be grown elongated. As described above, in the present invention, it is necessary to increase the CO ₃ ^2- ion concentration in the liquid to a predetermined level in order to elongate the morphology of the particles into a fibrous form. It is necessary to add aqueous ammonia and / or a compound having the same effect as above (for the purpose of (1)), but there has been no example of using aqueous ammonia for the purpose of elongating particles. NH ₄ HCO
In addition to the ₃ aqueous solution, CO ₃ ^2-ion concentration is sufficiently high N
It is also possible to use a basic aqueous solution containing H ₄ ⁺ ions, for example, ammonia water blown with carbon dioxide. Thus, AACH fibrous single crystal particles having an aspect ratio of 10 or more, a length of 0.5 μm or more, and a thickness of 0.01
Particles of μm or more are obtained. The fibrous AACH particles are compounds that can be converted into alumina when fired in the air, and have characteristics that cannot be obtained from conventional needle-like crystal materials in that particles having an aspect ratio of 50 or more can be easily obtained. Heretofore, no examples have been found for AACH in which particles having such properties have been obtained. A specific method for implementing this will be described in Examples described later.

Next, the fibrous AACH particles produced by the above-described method and conditions are converted into an oxidizing gas such as air and oxygen.
Heat treatment to a temperature of 1000 ° C. or more in an atmosphere of an inert gas such as nitrogen and argon,
Alternatively, it is possible to obtain an unprecedented elongated fiber made of θ-alumina. In this case, if the temperature is much lower than 1000 ° C., the strength of the fiber decreases, which is not preferable. The fibrous A
The ACH particles may be in the form of a film, a tube,
After being formed into an appropriate form such as paper, bulk, etc., it is possible to perform a heat treatment, whereby a film (film) form,
A fired product having an appropriate form such as a tubular shape, a paper shape, and a bulk shape can be manufactured. Further, the fibrous AACH particles can be mixed or compounded with other organic or inorganic compounds such as other oxides, metals, plastics, etc., if necessary, whereby α-alumina whiskers, alumina fibers, mullite Fibers, functional oxide fibers, composite materials of α-alumina whiskers and metals, plastics, ceramics, and the like can be manufactured. These fired products are
In terms of high strength, arbitrarily selected from porosity to denseness, and freedom of form, it has characteristics not found in conventional acicular alumina materials and the like. These will be described more specifically.
When the fiber surface is coated with about 1% by weight of silica at the stage of the CH particles or in the middle of the heat treatment, for example, at the stage of γ- and θ-alumina, and then heat-treated at 1300 ° C., α-alumina is obtained. Fibers can be obtained. If the amount of silica used in the silica coating process is increased, mullite fibers can be synthesized depending on the amount. That is, the amount of silica added was 10% by weight.
If more, mullite fibers are obtained. It is also possible to obtain a fiber of a nitride such as aluminum nitride by changing the atmosphere of the heat treatment to ammonia or the like.

[0014] Fibrous AACH particles and other objects, such as α
Heat treatment after mixing alumina, silica, magnesia, zirconia and / or titania;
For example, when the fibrous AACH particles and α-alumina fine particles are mixed and dispersed and then heat-treated at 1000 to 1100 ° C., the AACH particles are converted into γ- or θ-alumina ultrafine particles by thermal decomposition, and dispersed in advance. At the contact point with the α-alumina particles, the γ- and θ-alumina are taken into the α-alumina particles while further converting to the α-alumina structure, and contribute to the growth of the α-alumina particles. By this growth, α-alumina whiskers are obtained. Also in this case, the addition of a small amount of silica is effective for whisker growth.

Further, Fe ₂ O ₃ particles having the same crystal structure as α-alumina can be used for the same purpose as the above-mentioned α-alumina seed particles, and thereby α-alumina whisker And functional composite fibers such as a composite of magnetic fine particles. If fine particles such as magnesia and zirconia are mixed, dispersed, and heat-treated, a composite ceramic material of alumina whiskers and their oxides and reactants such as spinel can be obtained. In the production of these materials mainly composed of alumina whiskers, fibrous AACH particles are formed into a paper or film shape, and then subjected to a process such as folding, bending, cutting, etc. to give a three-dimensional shape, followed by firing. It is also possible to form a film on the surface of a three-dimensional object. Alternatively, a suspension of fibrous particles is molded by casting, injection molding or the like to give a three-dimensional shape, and then fired. Also, a suspension of fibrous particles is formed into a porous sphere by spray-drying, Many known methods can be used, such as firing.

[0016]

EXAMPLES The present invention will be specifically described below based on examples, but the present invention is not limited to the examples. Example 1 AA and AHC aqueous solutions having concentrations of 0.3 and 3.0 mol / l, respectively, were reacted at room temperature of about 30 ° C., and the precipitate formed was collected by filtration, and the pH was adjusted to about 10 by adding aqueous ammonia. It was kept at 120 ° C. for 48 h in a closed vessel together with the adjusted AHC aqueous solution. The resulting white precipitate is AA
The particles were CH particles, the aspect ratio was 200, and the form was fibrous particles having a length of 2 μm and a thickness of 0.01 μm.

Example 2 An AA aqueous solution having a concentration of 0.3 mol / l and an AHC aqueous solution whose pH was adjusted to 10 by adding aqueous ammonia were mixed with 40 aqueous solutions.
The reaction was carried out at a temperature of 150 ° C., and the resulting precipitate was transferred together with the supernatant to a sealed container and kept at 150 ° C. for 24 hours. As a result, the aspect ratio was 1,000, the length was 10 μm, and the thickness was 0.01 μm.
Was obtained.

Example 3 AACH spherical particles prepared in advance and dried were kept at 150 ° C. for 36 hours in an AHC aqueous solution whose pH was adjusted to 10 by adding aqueous ammonia. As a result, similar fibrous particles having an aspect ratio of 500, a length of 5 μm, and a thickness of 0.01 μm were obtained.

Example 4 AHC adjusted to pH 10 by adding aqueous ammonia
Aluminum acetylacetonate crystal powder was added to the aqueous solution, and the reaction was continued at 40 ° C. for about 6 hours while stirring. The obtained white precipitate was adjusted to a pH of about 1 by adding aqueous ammonia.
150 ° C. in a closed container with AHC aqueous solution adjusted to 0
As a result of adding processing for holding for 48 hours, the aspect ratio becomes 5
0, fibrous AA having a length of 0.5 μm and a thickness of 0.01 μm
CH particles were obtained.

Example 5 The fibrous AACH particles obtained in Example 1 were heat-treated at 1000 ° C. in air. As a result, γ-alumina particles having a fibrous form were obtained.

Example 6 Fibrous AACH obtained according to Examples 1 to 3
The particles were immersed in an ethanol solution of ethyl silicate, dried, and then heat-treated at 1300 ° C. in the air. As a result, α-alumina single crystal particles having a fibrous form were obtained.
In this case, the amount of silica added is about 1 wt%.

Example 7 When the amount of silica added in Example 6 was more than 10% by weight, mullite fibers were obtained.

Example 8 The fibrous AACH particles obtained in Example 1 were mixed in an amount corresponding to about 2 wt% of the weight thereof with α of about 0.1 μm in particle size.
-Suspended with fine alumina particles, which were dried in the form of a film.
As a result of heating the dried film to 1100 ° C. in the air,
Aggregates of α-alumina whiskers in film or flocculent form were obtained, the length and width of each whisker being approximately 0.3-3 μm and 0.1 μm, respectively.

Example 9 The fibrous AACH particles obtained in Example 1 were mixed with an α-alumina whisker obtained in Example 8 in an amount corresponding to about 10% by weight of the weight thereof to form a film. Then, as a result of heat treatment at 1100 ° C. in the air, a film-like or cotton-like α-alumina whisker similar to that of Example 8 was obtained.

Example 10 The fibrous AACH particles obtained in Example 1 were mixed with hematite (α-Fe) in an amount corresponding to about 2 wt% of the weight thereof.
_After mixing with ₂ O ₃ ) fine particles, suspending and forming into a film, the dried film was heat-treated at 1100 ° C. in the air, and as a result, a film-shaped example having a magnetic function was obtained. A similar aggregate of α-alumina whiskers was obtained.

Example 11 By combining the α-alumina whisker aggregate obtained in Example 8 and the γ-alumina particles in Example 5, a catalyst carrier having excellent mechanical strength and a large specific surface area can be produced. For example, the α-alumina aggregate according to Example 8 was immersed in an AHC aqueous solution, an AA aqueous solution was added thereto, and further subjected to a heat treatment at 120 to 150 ° C. for 24 hours under hydrothermal conditions. The resulting porous body was heat-treated at 1000 ° C. in the air, and as a result, a porous bulk body composed of α-alumina whiskers and γ-alumina fibers was obtained.

[0027]

According to the method of the present invention, fibrous AACH single crystal particles can be produced with good reproducibility and economical scale by a simple apparatus and a simple operation, and furthermore, they can be subjected to heat treatment. This makes it possible to produce α-alumina whiskers, alumina fibers, mullite fibers, functional oxide fibers, composite materials of α-alumina whiskers and metals, plastics, ceramics, and the like, which can be produced by various molding methods. It can be used as a material such as a film, a film, and a tube.

Claims (4)

(57) [Claims] 1. An aluminum sulfate, aluminum chloride,
Ammonium aluminum sulfate, aluminum hydroxide,
An aqueous solution or suspension of an aluminum compound having water solubility or any solubility in water, such as aluminum ethoxide, aluminum isopropoxide, or aluminum acetylacetonate, has a CO ₃ ^2- ion concentration of 0.03.
It is obtained by injecting into a sufficiently high NH ₄ HCO ₃ aqueous solution of 1 mol / l or more or a basic aqueous solution containing NH ₄ ⁺ ions having a sufficiently high CO ₃ ²⁻ ion concentration and heating and aging at a temperature of 100 ° C. or more. The compound AlNH ₄ CO
₃ (OH) ₂ fibrous single crystal particles with an aspect ratio of 10
As described above, particles having a length of 0.5 μm or more and a thickness of 0.01 μm or more. 2. The fibrous particles according to claim 1 as they are or after being formed into a film, a tube, a paper, a bulk or the like.
Obtained by heat treatment at 1000 ° C. or higher,
A calcined product containing alumina as a main component and having a needle-like, fibrous, film-like, tubular, paper-like, or bulk-like form. 3. The method for producing fibrous particles according to claim 1, wherein said material comprises aluminum sulfate, aluminum chloride, ammonium aluminum sulfate, aluminum hydroxide, aluminum ethoxide, aluminum isopropoxide, or aluminum acetylacetonate. An aqueous solution or suspension of an aluminum compound that is water-soluble or has some solubility in water has a CO ₃ ^2- ion concentration of 0.01 mol.
1 / l or more sufficiently high NH ₄ HCO ₃ aqueous solution or CO
₃ ^2- ion concentration and injected sufficiently high basic aqueous solution containing NH ₄ ⁺ ions, characterized by heat digestion at 100 ° C. or higher, the compound AlNH ₄ CO ₃ (OH)
_2. A method for producing fibrous single crystal particles having a aspect ratio of 10 or more, a length of 0.5 μm or more, and a thickness of 0.01 μm or more. 4. The method for producing a fired product according to claim 2, which is mainly composed of alumina and has a form such as a needle shape, a fiber shape, a film shape, a tubular shape, a paper shape or a bulk shape. After forming the fibrous particles according to 1 as it is or in the form of a film, a tube, a paper, a bulk, or the like, and further mixing or complexing with other oxides, metals, plastics, or other organic or inorganic compounds. Heat treatment at a temperature of 1000 ° C. or more in an atmosphere of air, oxygen, inert gas, vacuum, etc., made mainly of alumina, needle-like, fiber-like, film-like, tubular, paper-like Or a method for producing a fired product having a form such as a bulk shape.