JPH0873214A - Fibrous hydrated alumina and its production - Google Patents

Abstract

PURPOSE: To conveniently and inexpensively produce an alumina fiber excellent in fiber shape retaining property and useful as a reinforcing material, adsorbent, fire resistant additive and fibrous material precursor by subjecting a fibrous aluminum salt to oxidation treatment with a chloric acid aq. soln. CONSTITUTION: The fibrous hydrated alumina having 20-35wt.% Al content is obtained by subjecting the fibrous aluminum salt to the oxidation treatment with the chloric acid aq. soln. In a production of this fibrous hydrated alumina, for example, the fibrous aluminum salt such as fibrous aluminum sulfate and fibrous aluminum carbonate is subjected to the oxidation treatment with the chloric acid aq. soln. preferably. This fibrous hydrated alumina is a new one having 20-35wt.% aluminum content and rich in adsorptivity of other substance and useful as fibrous aluminum based multiple oxides.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to fibrous hydrated alumina and a method for producing fibrous hydrated alumina and fibrous aluminum oxide.

[0002]

2. Description of the Related Art The present inventors have conducted research and development for many years on inorganic fiber materials such as alkali metal titanate whiskers, and their synthesis, modification and modification methods, and further inorganic fibers obtained by these methods. We have proposed new technologies for material application development. At present, the industrial applicability of inorganic fiber materials has attracted widespread attention. As a result, various natural and synthetic inorganic fiber materials have been proposed and widely used as reinforcing agents for metals and ceramics including resin composite materials. .

Among these inorganic fiber materials, α-alumina has the characteristics of high thermal conductivity, hardness and mechanical strength and excellent chemical stability and electrical insulation, so that it is heat resistant material, electronic industrial material, and electrical material. Widely used for applications such as insulating materials. However, a fiber-shaped material for use as a reinforcing agent for various materials has not been known sufficiently.

At present, aluminum silicate whiskers and aluminum silicate whiskers are available as alumina type whiskers. However, all of these whiskers require complicated reactions requiring advanced technology for synthesis or long-term growth reactions at high temperatures, and in addition, it is difficult to adjust the fiber shape and requires high skill and mass production. Is difficult, expensive, and cannot be used for various purposes.

Alumina fibers have been developed and studied for a long time and are gradually being used. Conventionally, a polycrystalline alumina fiber by the precursor fiber method has been proposed, but this is difficult to shorten the fiber, the manufacturing process is complicated, and when the shape variation is large and it is used for a fiber reinforcement application. I was not completely satisfied.

As the fibrous aluminum compound, JP-A-50-62897, JP-A-51-21600 and JP-A-60-166220 disclose methods for producing aluminate (AlOOH). However, the fiber shape is only about several μm at the most, and the heat treatment at 1200 ° C. or higher is required for the α-aluminization, so that the utility is not yet satisfactory.

Further, Al (NH ₄ ) CO ₃ (OH) ₂ having a fiber length of 0.1 to 3 μm is disclosed in JP-A-63-147820 and JP-B-63-147821. JP-A-58-95612, JP-A-58-
185434 and JP 58-185435 issue Publication _{Al (OH) a (SO 4} ) b · nH 2 O (2.3
There have been proposed fibrous aluminum compounds such as 2 ≦ a <2.44, 0.28 <b ≦ 0.34) and a method for producing fibrous alumina by firing these. However, these manufacturing methods have a drawback that carbonate radicals and sulfate radicals tend to remain unless the firing method is taken into consideration. Since these carbonate radicals and sulfate radicals decompose at relatively high temperatures, if they remain in the target product, they may cause deterioration of the shape during firing, which is not preferable.

[0008]

Generally, a flux method using a solvent or a vapor phase growth method is used for synthesizing a whisker material, but both require a large amount of energy at a high temperature and a high temperature homogeneous heating. Development of manufacturing technology,
The development of complicated reaction control technology accompanying the gas phase reaction is required, and the establishment of a simple synthetic method has been awaited.

An object of the present invention is to have excellent fiber shape retention,
It is an object of the present invention to provide a novel alumina fiber useful as a reinforcing material, an adsorbent, a flame retardant, and a fibrous material precursor, and a method capable of easily and inexpensively producing the alumina fiber by a wet chemical reaction.

[0010]

That is, the present invention relates to fibrous hydrated alumina having an Al content of 20 to 35% by weight.

The present invention also relates to a method for producing fibrous hydrated alumina having an Al content of 20 to 35% by weight, which is characterized by oxidizing a fibrous aluminum salt with a chloric acid aqueous solution.

The present invention further relates to a method for producing fibrous aluminum oxide, which comprises oxidizing fibrous aluminum sulfate and / or aluminum carbonate with a chloric acid-based aqueous solution, and then heating and firing.

The fibrous hydrated alumina of the present invention is a novel fibrous hydrated alumina having an aluminum content of 20 to 35%, is excellent in the adsorption of other substances, and is a precursor of a fibrous aluminum-based composite oxide. It is useful as a body.

Although the composition of the fibrous hydrated alumina of the present invention is considered to be a hydrate of aluminum oxide, it does not show a remarkable diffraction peak in X-ray analysis, and thus is amorphous containing no crystalline substance. Is considered to be a collection of. EPMA
In the presence of Al, the results of elemental analysis, infrared spectroscopic analysis and thermal analysis revealed that Al ₂ O ₃ · nH ₂ O (3 <n <1
It was confirmed that the compound had a composition represented by 0). The value of n changes variously depending on the manufacturing method, and the value of n becomes smaller by adding an oxidation treatment.

Amorphous fibrous hydrated alumina having such a composition is a novel substance which has not been known so far.

The shape of the fibrous hydrated alumina of the present invention can take various values depending on the shape of the starting material, but many have a fiber diameter of 0.1 to 10 μm and a fiber length of 1 to 100 μm. Generally, the fiber diameter is 0.1 to 1 μm, and the fiber length is 1 to 30 μm. Among them, those having a fiber diameter of 0.1 to 10 μm and a fiber length of 10 to 100 μm are preferable. Regarding the aspect ratio, the aspect ratio of 10 or more can be easily obtained by adjusting the raw material fiber shape, but the aspect ratio of less than 10 is also included.

Next, the method for producing the fibrous hydrated alumina of the present invention will be described.

In the production of the fibrous hydrated alumina of the present invention, fibrous aluminum salts such as fibrous aluminum sulfate and fibrous aluminum carbonate (hereinafter referred to as "raw fiber") are treated with an aqueous chloric acid solution. It is preferable to adopt a method of oxidizing treatment.

As the fibrous aluminum sulfate and fibrous aluminum carbonate, basic aluminum sulfate whiskers and basic aluminum carbonate whiskers which can be synthesized by a hydrothermal synthesis method can be preferably used, but the invention is not limited thereto.

As the chloric acid aqueous solution used for the oxidation treatment of the raw material fibers of the present invention, an aqueous solution of an alkali or alkaline earth metal hypochlorite such as sodium, potassium or calcium is a stable chloric acid aqueous solution. Preferably
Among these, an aqueous solution of an alkali metal hypochlorite having a large solubility is particularly preferable. In the case of calcium salt, there are problems that it takes a long time for the reaction because of its low solubility and that insoluble components are mixed in the product to make separation difficult. On the other hand, the sodium salt is a raw material which has few problems as described above and is easily available, and is usually provided in a concentration of about 10 to 15%.

In the oxidation treatment of the raw material fiber of the present invention,
First, when chloric acid is contacted with the raw material fiber and decomposed to oxidize the surface of the raw material fiber, sulfate ions, carbonate ions, etc. are generated according to the components of the raw material fiber, and then these ions decompose chloric acid. Since a circulating reaction system is employed in which the raw material whiskers are oxidized, the setting of the raw material fiber concentration is particularly important.

In the present invention, the raw material fiber is usually 0.1 to 10% by weight, preferably 2 to 9% by weight with respect to the aqueous chlorate solution.
It is preferably processed to a concentration of wt. In the present invention, if the treated amount of the fiber is less than 2% by weight, the efficiency is poor. On the contrary, if it exceeds 9% by weight, the contact is insufficient and the reaction is slowed, or chlorine is generated due to sulfate ions or carbonate ions generated. Chloric acid is rapidly consumed because the acid tends to decompose and deteriorate without reacting with the raw material.
This is not preferable because it causes insufficient formation of hydrated alumina.

The concentration of the aqueous chloric acid solution used in the present invention is usually preferably a relatively low concentration, and the amount of effective active chlorine is, for example, about 1 to 5%. A high concentration is not preferable because the oxidizing effect is too strong, which may cause damage or dissolution of the raw material fibers and reduce the fiber yield. However, depending on the type of raw material fiber used, good results may be exhibited even at a concentration of more than 5%. According to the knowledge obtained by the present inventors, such a result depends on the amount of water of crystallization contained in the raw material fiber. That is, when the amount of water of crystallization is small, the target fibrous substance can be obtained in a high yield even at a high concentration, whereas when the amount of water of crystallization is large, if the amount of active chlorine is too small, the reaction will reach the whisker core. However, when sodium hypochlorite is used, a complicated product containing sodium, chlorine, sulfate group or carbonate group tends to be produced as a by-product, which is not preferable.

The reaction temperature between the raw material fibers and the chlorate in the present invention can be preferably proceeded at room temperature or in an atmosphere heated to room temperature to 70 ° C. The reaction treatment time is about 5 minutes to 48 hours, usually 1-2.
For example, it can be about 4 hours. In carrying out such a reaction, a pH adjusting agent, a dispersion aid, etc. for adjusting the reaction may be used in combination.

In the reaction of the present invention, since chloric acid is present in excess with respect to the raw material fibers, the concentration of chloric acid hardly changes before and after the reaction, and chloric acid can be reused in the next process. it can.

The fibrous hydrated alumina of the present invention has a shape that is substantially the same as that of the raw material fibers, does not damage the shape when used as a raw material for composite materials, and is extremely excellent in shape retention. By adjusting the shape of the raw material fibers and the like by classification and the like, a homogeneous fibrous substance having a desired shape can be provided, and quality control is easy.

The fibrous alumina of the present invention may be used by appropriately crushing it with a crusher or the like to adjust the aspect ratio, if necessary.

The fibrous hydrated alumina thus prepared does not show a diffraction peak by X-ray analysis,
1, O and H were detected, a hydroxyl group was detected by FTIR analysis, and Al was different depending on reaction conditions and raw materials.
Since the content is 20 to 35% by weight, the oxygen content is 60 to 75% by weight, and the hydrogen content is 3 to 7% by weight, Al ₂ O ₃ ·.
It was confirmed to be hydrated alumina represented by nH ₂ O (3 <n <10).

The fibrous hydrated alumina of the present invention can be used sufficiently as it is, but it still has the following problems. That is, in the method for producing fibrous hydrated alumina of the present invention, a trace amount of aluminum sulfate, carbonate or the like may remain in the core portion depending on the reaction conditions, the shape of the starting raw material fiber and the like. In such a case, although there is no problem in practical use in applications where ionic characteristics do not pose a problem, diffusion of residual components and deterioration of chemical resistance may occur during long-term storage. Further, in the case of exhibiting a composition containing a large amount of bound water, surface hygroscopicity may become large, and properties such as poor chemical resistance and heat resistance may be exhibited, and further improvement in quality is required.

The present invention provides the following stabilization method in order to solve such a problem. That is, the fibrous hydrated alumina of the present invention is further added at 200 to 1300 ° C., preferably 30
Fibrous aluminum oxide may be converted by firing at 0 to 1200 ° C. for 1 to 10 hours. At this time, it is particularly preferable to further oxidize with chloric acid after firing. By such treatment, the fibrous hydrated alumina is stabilized and the following points are observed.

(1) When the fibrous hydrated alumina is fired at about 300 ° C., part of the bound water is desorbed,
The fiber shape and heat deformability are stabilized, and chemical resistance is improved.

(2) Even if a small amount of aluminum sulfate or the like remains on the core, the fiber shape and thermal deformability are stabilized and the chemical resistance is improved by treating again with chloric acid.

(3) If abruptly heating to 1200 ° C. or higher during firing, abrupt Al ₂ O ₃ polycrystallization proceeds throughout the fiber, and α-Al ₂ coarser than X-ray analysis and TEM analysis.
It was confirmed to be an aggregate of O ₃ particles. In this case, the fiber shape is deteriorated, the reinforcing performance is lowered, and the strength of the fiber itself is remarkably lowered, which is not preferable. However, the heat treatment at 1200 ° C. or lower does not have such an effect, and it is in a substantially amorphous state at around 300 ° C.
Also, the Al ₂ O ₃ crystal particles produced during the heat treatment at a relatively high temperature of around 1200 ° C. are fine and do not change in shape, and do not affect the strength or reinforcing property of the fiber itself.

The present invention also includes fibrous aluminum oxide containing fine Al ₂ O ₃ crystals obtained by the above-mentioned stabilization method.

The amorphous fibrous hydrated alumina obtained according to the present invention has a low refractive index, is superior in colorability when formed into a resin composite as compared with crystalline alumina, and is porous so that it is an adsorbent material. It is also suitable for use as an adsorbent, various catalysts, and as a raw material for composite oxide whiskers that adsorb other elements, and has extremely high industrial utility.

[0036]

EXAMPLES The present invention will be further clarified with reference to reference examples, test examples, examples and comparative examples.

Reference Example Aluminum Chloride Hexahydrate (AlCl ₃ .6H ₂ O) 2
41.4 g was poured into 800 ml of water and dissolved under stirring to prepare an aqueous solution. 400 ml of an aqueous solution in which 40.0 g of sodium hydroxide (NaOH) is dissolved in this aqueous solution
Was added dropwise at a rate of 1 ml / min, and after the addition, the mixture was kept under stirring for 12 hours to prepare a uniform basic aluminum sulfate aqueous solution.

With stirring in this 1200 ml of aqueous solution,
1100 ml of an aqueous solution in which 71.0 g of sodium sulfate (NaSO ₄ ) was dissolved was added dropwise at 2.0 ml / min to obtain 2300 ml of a cloudy liquid. This was separated by filtration and washed with water to remove water-soluble chlorides, sulfuric acid compounds and the like, and dried to obtain 8 g of a white powder.

When the obtained white powder was observed with an optical microscope, a transparent and fine fibrous aggregate was formed. As a result of further X-ray diffraction test, this product was amorphous with no diffraction peak. As a result of chemical analysis, this product was confirmed to contain Al 25.5% and SO ₄ 40.8%, and chlorine and sodium were not detected. Thus, fibrous material synthesized in this Example are considered to be basic aluminum sulfate expressed by a composition _{Al (OH) 2.1 (SO 4} ) 0.45.

Test Example The fibrous basic aluminum sulfate obtained in the above reference example was uniformly dispersed on an electron microscope sample stand, and photographed with an electron microscope at a magnification of 1000 times. Further, the caliper (minimum measured value 1/100)
mm), and the average major axis value and the average minor axis value of 500 pieces were defined as the average fiber length and the average fiber diameter of the present fiber. As a result, it was confirmed that the fibrous aluminum sulfate synthesized in the above Reference Example had an average fiber length of 32 μm and an average fiber diameter of 0.4 μm.

Example 1 5 g of fibrous basic aluminum sulfate synthesized in the above reference example was used to obtain an effective chlorine amount (hereinafter simply referred to as "Cl%") 9.3.
Treatment in 100 g of 7% aqueous solution at room temperature for 5 hours with gentle stirring, then filtration, washing with water and drying to obtain 1.8 g.
To obtain a white fibrous substance. As a result of analyzing the filtrate at this time, Cl% was 8.93%.

When the raw material fibers and the obtained white fibrous substance were observed with an electron microscope (hereinafter abbreviated as "SEM observation"), it was confirmed that the fiber shape of the raw material aluminum sulfate was maintained. . In the X-ray diffraction test, a broad result indicating amorphous was obtained. In the elemental analysis, Al was 33.5%, and chlorine, sodium and sulfur were not detected. Also, from the thermal analysis test, 400 ℃
Shows a gradual weight loss up to near, with a total weight loss of 3
At 6.7%, no weight reduction was shown thereafter, and endothermic peaks considered to be dehydration were observed at around 80 ° C and 195 ° C. The fibrous material obtained from the above results is Al ₂ O ₃
It was confirmed to be fibrous hydrated alumina having a composition of 3.3H ₂ O.

The reactants were further added to 800, 1000 and 120.
An X-ray diffraction test was performed on the material that had been fired at each temperature of 0 ° C. for 2 hours, and as a result, γ-Al ₂ O ₃ single phase and γ
-Al ₂ O ₃ and α-Al ₂ O ₃ mixed phase, α-Al ₂ O ₃
It was a single phase. FIG. 3 shows the X-ray diffraction results of the fibrous basic aluminum sulfate, fibrous hydrated alumina, 800 ° C. calcined product, 1000 ° C. calcined product and 1200 ° C. calcined product used in this example. Further, based on the method of the test example, the fibrous hydrated alumina obtained in this example, 800 ° C. calcined product, 1000
As a result of measuring the shape of the ℃ baked product, 1200 ℃ baked product,
Average fiber length is 31μm, 31μm, 29μ respectively
m, 28 μm, and average fiber diameters of 0.4 μm and 0.
It was 4 μm, 0.5 μm, and 0.5 μm, and it was confirmed that the hydrated aluminization and crystallization by calcination performed in this example did not adversely affect the fiber shape.

Examples 2 to 3 and Comparative Examples 1 to 3 5 g of fibrous basic aluminum sulfate synthesized in the same manner as in the above reference example was used, and the amount of hypochlorous acid used, the concentration and the treatment conditions were changed. Tables 1 and 2 show the analysis and test results of Examples and Comparative Examples.

[0045]

[Table 1] Note) The shape was evaluated by SEM. As compared with the raw material fiber, the one that did not change was good, and the one that was damaged and the by-product of the granular material was displayed.

[0046]

[Table 2] The TG-DTA result of Comparative Example 3 was that the weight loss up to 400 ° C. was 36.2%, the weight loss was 6.8% and the endotherm was 9%.
It was detected in the vicinity of 60 ° C., and residual sulfate was confirmed. From these Comparative Examples and Examples, it was found that damage and elution of fibers occur at high concentration, high temperature and high bath ratio, and conversely untreated sulfate radicals tend to remain at low temperature.

Example 4 The fibrous hydrated alumina obtained in Comparative Example 3 was heated at 800 ° C. for 2 hours.
Heat treatment was performed for an hour. SEM of the same sample after heat treatment
The result of the shape of the observation, the diffraction peak of the damage to the fiber shape from being not X-ray diffraction test results observed γ-Al ₂ O ₃ -
I showed you.

Although a slight amount of sulfate remained in this product, it was found to be γ-Al ₂ O ₃ in the X-ray diffraction test by treating with sodium hypochlorite in the same manner as in Example 1. , TG-DTA also had a weight loss of 0.8% and contained almost no water of crystallization, and fibrous alumina having no endothermic peak of sulfate radical at around 960 ° C. was obtained.

Comparative Example 4 The raw material fibrous basic aluminum sulfate was heat-treated at 800 ° C. for 2 hours. After heat treatment, X for the same sample
When the line diffraction test was performed, it was in a broad state, and TG
In -DTA, the endothermic peak of sulfate was also confirmed, confirming that it was present in the composition of basic aluminum sulfate.

Example 5 Fibrous aluminum carbonate (synthesized according to Example 1 of Japanese Patent Publication No. 4-36093), Al (NH ₄ ) CO ₂ (O
H) ₂ , an average fiber length of 3 μm, and an average fiber diameter of 0.1 μm) were treated in the same manner as in the example, from 5 g of raw material to 4.1 g after treatment.
A fine fibrous product of In this treatment, Cl 9.37% changed to Cl 8.81% before and after the reaction treatment.

As a result of examining this product by elemental analysis, A
It contained 25.6% of 1, N, C, Cl and Na were not detected, and was amorphous by X-ray analysis.
A 1.6% weight loss was confirmed, Al ₂ O ₃ .6H ₂ O
It was confirmed to be fibrous hydrated alumina having the composition of. Also, this product was heated at 300 ° C. for 2 hours and then 8 hours.
By firing at 00 ° C. for 1 hour, γ-Al ₂ O ₃
And the shape did not change before and after firing, and the shape of the raw material was maintained.

[0052]

【The invention's effect】

1. ADVANTAGE OF THE INVENTION According to this invention, the fibrous hydrated aluminum which is excellent in fiber shape retention property and is useful as a reinforcement material and a flame retardant, and its simple manufacturing method are provided.

2. Since the fibrous hydrated alumina and the fibrous aluminum oxide of the present invention have excellent adsorption properties, various compounds such as antibacterial agents and electronic devices can be used in various applications by firing after adsorbing various compounds. It is possible to obtain an applicable composite composite fibrous material.

3. The fibrous hydrated alumina and fibrous aluminum oxide of the present invention are highly amorphous, have excellent transparency, and are useful as a fibrous reinforcing material that can be arbitrarily colored.

[Brief description of drawings]

FIG. 1 is an electron micrograph showing a fiber shape of a raw material fiber synthesized in a reference example.

FIG. 2 is an electron micrograph showing the shape of fibers of the white fibrous material obtained in Example 1.

FIG. 3 Fibrous basic aluminum sulfate used in Example 1, fibrous hydrated alumina, calcined at 800 ° C., 1000 ° C.
It is an X-ray diffraction diagram of a baked product and a 1200 ° C baked product.

Claims (6)

[Claims] 1. A fibrous hydrated alumina having an Al content of 20 to 35% by weight. 2. A fiber diameter of 0.1 to 10 μm and a fiber length of 10
The fibrous hydrated alumina according to claim 1, which has a 100 μm and an aspect ratio of 10 or more. 3. The method for producing fibrous hydrated alumina according to claim 1, wherein one or more fibrous aluminum salts are subjected to an oxidation treatment with an aqueous chloric acid solution. 4. The method for producing fibrous hydrated alumina according to claim 3, wherein the fibrous aluminum salt is fibrous aluminum sulfate and / or fibrous aluminum carbonate. 5. A method for producing fibrous aluminum oxide, which comprises subjecting fibrous aluminum sulfate and / or fibrous aluminum carbonate to oxidation treatment with a chloric acid-based aqueous solution and then heating and firing. 6. The method for producing fibrous aluminum oxide according to claim 5, wherein after the heating and firing, the oxidizing treatment is performed again with a chloric acid-based aqueous solution.