JPS58135174A - Manufacture of alumina formed body - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed description of the invention] The present invention relates to a method for producing an alumina-based molded body.

More specifically, the main ingredients are paste-like or powder-like alumina hydrate containing a specific amount of water obtained by conditioning colloidal alumina hydrate, or alumina mixed with silicon or magnesium compounds. This method is characterized by press-forming and post-sintering an alumina-based hydrate humidity control product, which has a uniform shape and is free from physical defects such as pinholes, dents, and cracks. It is possible to produce an alumina-based molded body with no heat resistance, high insulation properties, and excellent chemical resistance.

Alumina molded bodies have the heat resistance and high insulation properties of alumina.
By taking advantage of its characteristics such as chemical stability, abrasion resistance, and optical transparency, we can manufacture high-temperature reaction tubes, protection tubes, furnace core tubes, IC boards, resistors,
A wide range of industrial products such as condensers, crucibles, chemical-resistant containers, catalyst carriers, abrasive materials, high-hardness tools, sliding part coating materials, IJ Umlumb luminescent inner tubes, ultraviolet and infrared transmitting materials, window materials for high-temperature furnaces, etc. It is used for a purpose.

Such alumina-based molded bodies are currently obtained mainly by adding a binder to alumina powder, press-molding the mixture, and then sintering it at a high temperature of about 1800° C. or higher.

In particular, so-called translucent alumina sintered bodies that require translucency are
After adding a binder, a magnesium compound, etc. to high-purity alumina powder with a uniform particle size and extremely fine particles and molding it, the molded product is fired to suppress the growth of alumina crystals and eliminate pores in the molded product.

When forming into a thin film, a binder, a plasticizer, and a solvent are added to the alumina powder to form a slurry, and this slurry is spread onto a steel belt or plastic film to a certain thickness using a device such as a doctor blade. Methods of coating, drying and then firing are also known.

Recently, a method for producing a sialumina thin film by forming a film of polyaluminoxane having material residues, halogen, and hydroxyl groups as a precursor film and firing this precursor film (Japanese Patent Publication No. 56-369), The alkoxide is hydrolyzed and peptized with acid to form an alumina hydrate colloid, and this colloid is dried by methods such as natural drying, heat drying, and vacuum drying to form a thin film or block. A method of obtaining a sialumina thin film or alumina lump by subsequent firing has been reported (Japanese Patent Publication No. 54-25520).

However, the method using alumina powder, which is currently widely used, requires sintering at a high temperature of close to 2000°C to obtain a molded body, and it is not a foolproof method that has large restrictions on equipment such as furnace materials. , it is not economical as it consumes a large amount of energy.

In addition, in order to obtain a translucent molded body using this method, the raw alumina must be purified to an extremely high purity and must be extremely fine with a particle size of 1 micron or less. This requires sophisticated technology, such as the need to suppress grain growth, and as a result, it is not easy to produce a molded body.

Regarding thin film forming, in the doctor blade method mentioned above, the processing accuracy of the doctor blade, as well as the surface defects and thickness accuracy of the steel belt, plastic film, etc. used as the moving carrier, are directly reflected in the thickness of the product alumina thin film. There is a large variation in thickness, and it is not only possible to manufacture a thin film with a thickness of about several tens of microns, but in reality, the limit is a film with a thickness of about 0.2 microns.

In the method using polyaluminoxane, the raw material polyaluminoxane is obtained by hydrolysis of aluminum alkoxide, so polyaluminoxane retains a large amount of organic groups, and furthermore, polyaluminoxane itself has the property of being hydrolyzed, so the firing edge The thin film tends to contain residual organic components and residual carbon, and there are also problems in controlling the degree of polyaluminoxane polymerization and in the stability of polyaluminoxane.

If an alumina thin film or alumina molded product contains residual carbon, not only will the appearance deteriorate due to a decrease in translucency and whitening, but also the electrical properties such as insulation will be significantly impaired. The uses of the molded body are limited.

On the other hand, aluminum alkoxide is completely hydrolyzed,
The colloidal alumina hydrate obtained by deflocculation is
In the method of spreading on a substrate such as a film, drying, and firing, it is possible to produce a relatively thin film that does not easily contain organic residues, but in this case, the sol used for molding is required to have fluidity. Since the sol seat is low and contains a large amount of water, it takes a long time and a lot of energy to form a dry film, and since the direction of water volatilization during drying is limited, the thin film is easy to bend, and warpage can be corrected. It is difficult to obtain a film free from physical defects due to cracks in the film. In addition, this method requires
Dry molding requires a longer time and a large amount of energy, which is a major technical disadvantage.

The present inventors have developed a 120
It can be fired at a low temperature of around 0℃, does not easily contain impurities such as carbon, can be easily molded, has a uniform thickness, and has no physical defects such as warps, pinholes, or cracks. The present invention was developed as a result of extensive research into methods for producing various alumina-based molded bodies made of homogeneous alumina, silica-alumina, magnesia-alumina, and silica-magnesial alumina.

That is, the present invention is consistent with the scope of the claims, but the technical point is that 915 to 8 parts per 100 parts by weight of anhydrous alumina obtained by conditioning colloidal alumina hydrate.
This is a method for producing an alumina-based molded body, which is characterized in that a paste-like or powder-like alumina hydrate humidity control product containing 0 parts by weight of water is formed, pressure-molded, and then fired. Then, if necessary, silica and magnesia are further added and mixed with compounds to be converted into these by firing, either before or after adding and mixing the colloidal alumina hydrate.
It is also possible to perform pressure molding and firing.

The colloidal alumina hydrate used in the present invention is one in which fine particles of crystalline or amorphous alumina hydrate are uniformly dispersed in water or water containing an organic solvent,
If the particle size is large, it is difficult to further refine the particles during the steps of concentration or drying for humidity control, crushing, molding, and baking, which tends to cause non-uniformity in the molded product. If the particle size is about 1 micron or less, the requirement for uniformity can be easily satisfied, which is advantageous in bringing about the effects of the present invention.

Various alcohols, ethers, etc. can be used as the organic solvent.

Common methods for obtaining colloidal alumina hydrate include (1) gel-like alumina hydrate produced by adding an alkali to aluminum salt, or gel-like alumina hydrate produced by electrolyzing aluminum as an anode in an electrolyte solution; Crystalline or amorphous alumina hydrate, such as alumina hydrate or alumina hydrate obtained by hydrolyzing aluminum alkoxide, etc., is treated with nitric acid, hydrochloric acid, bromic acid, iodic acid, formic acid, or acetic acid. acids such as iron chloride,
A method of peptizing by adding one or more salts such as aluminum chloride.

(2) A method of electrically dispersing aluminum in water.

(3) a method of treating aluminum with hot water in the presence of oxygen, or a method of fusion of red-hot aluminum with water;
A method of obtaining aluminum from metal, such as a method of reacting water and aluminum under pressure.

(4) Method by hydrolysis of aluminum salt.

(5) A method of double decomposition by adding various carbonates, oxides, hydroxides, etc. to an aluminum chloride aqueous solution.

It can be obtained by various methods such as. Among these various methods, the colloidal alumina hydrate obtained by the method (1) above, in which organic aluminum such as aluminum alkoxide is hydrolyzed and peptized, has a high purity because the raw material can be purified by operations such as distillation. This is suitable in the present invention, which also aims to obtain a molded article with a high temperature.

When the present invention is carried out using colloidal alumina hydrate as a raw material, it has the advantage that it is easy to obtain a highly uniform molded body because the colloidal particles are fine. It is possible to obtain an alumina-based molded body having a uniformity of light transmittance that is difficult to obtain.

In the present invention, the steps of concentration, drying, and pulverization can be performed before firing, but as will be described later, the colloid particles do not become coarse even after these steps, and these steps result in a uniform compact. There is no obstacle to obtaining.

Humidity control in the present invention involves concentration and drying, removal of the dispersion medium in colloidal alumina hydrate by heating, reduced pressure, or other methods, or electrophoresis, colloidal alumina hydrate, etc. It is also referred to as concentrating the alumina hydrate and adjusting the colloidal alumina hydrate to a state containing 915 to 80 parts by weight of water per 100 parts by weight of anhydrous alumina.

The colloidal alumina hydrate may be suitably dried once, and the water content may be adjusted again to a range containing 915 to 80 parts by weight of water per 100 parts by weight of anhydrous alumina.

If the moisture after drying exceeds 980% by weight of anhydrous alumina, the fluidity is too high and it is difficult to form a molded product during the next step of pressure molding, and the amount of volatilized water is high, resulting in warpage after molding. It is easy to cause deformation such as strain, but it is not an obstacle to achieving the object of the present invention. On the other hand, if it is less than 15%, it becomes a mixture of alumina water and alumina, which causes non-uniformity after the molding process.

The paste-like or powder-like alumina hydrate humidity-conditioned product obtained by humidity-conditioning the colloidal alumina hydrate according to the present invention does not cause precipitation or undissolved matter even if it is re-dispersed in water, and can be easily obtained. Redisperses to colloidal state.

This suggests that the colloidal particles do not aggregate or become coarse even after undergoing processes such as drying, concentration, and pulverization.

The colloidal alumina hydrate humidity-controlled product according to the present invention can be easily molded by pressurization.

The alumina-based molded product of the present invention obtained from this molded product is
The unfired alumina hydrate molded product is sufficiently homogeneous and transparent, and does not contain a large amount of water, so it does not suffer from physical defects such as warping, pinholes, and cracks in the molded product, which were disadvantages of conventional methods. , the deformation and the resulting low yield could be overcome.

The pressure molding method is not particularly limited, but in order to avoid leaving air bubbles in the molded product, it is desirable to perform pressure molding while removing air bubbles and the like under reduced pressure. Also, in order to improve the surface smoothness, the pressurizing surface should be smooth.

The molded product pressure-molded by this method can be easily mechanically processed, and can also be subjected to processing such as polishing, perforation, cutting, etc., and molded products with complex shapes can also be obtained.

Firing as used in the present invention refers to heating a press-molded product of alumina hydrate to a temperature of 500° C. or higher to transform it into an alumina molded product. When firing at a temperature of 500° C. or lower, the transition from alumina hydrate to alumina does not occur sufficiently, and a perfect alumina molded body cannot be obtained.

When attempting to obtain a translucent alumina molded body, the firing temperature is desirably 1.200°C or lower. When fired at a temperature of 1,200° C. or higher, the molded product shrinks, creating relatively large pores in the molded product, resulting in devitrification of the molded product.

By adding silica or magnesia, it is possible to withstand firing at higher temperatures and maintain translucency even when the product is used, compared to the case where silica or magnesia is not used. In order to prevent the molded body from deforming during firing, firing may be performed under pressure.

In the present invention, the substance that becomes silica or magnesia upon firing is preferably one that does not leave any substances other than these.
For example, those having an organic base such as silicate ester and magnesium alkoxide, high purity silica, and magnesia are desirable. The amount of silica or magnesia to be added depends on the use of the resulting molded product, but it is sufficient to add silica or magnesia in an amount that makes it 20% or less by weight.

If it is added in an amount of 20% or more, the heat resistance, insulation properties, chemical stability, and abrasion resistance of the obtained molded product will be lower than that of alumina.

When the obtained molded body is used as a catalyst or a catalyst carrier, a substance containing a metal other than silicon or magnesium may be added as a dopant to an alumina hydrate colloid or an alumina hydrate colloid, and then molded and calcined.

An example of the embodiment of the present invention will be specifically described below with reference to Examples.

Reference Example 1 (Preparation of colloidal alumina hydrate-1) A cooler, stirrer, and thermometer were installed 5! Distilled water at 4000F was placed in a round bottom flask, heated to 90°C while stirring, and coarsely ground aluminum impropoxide 70 was added to it.
0 ff was added, and the mixture was kept at 90'C for 1 hour for hydrolysis to obtain a gel-like alumina hydrate.

After that, 17o2 of hydrochloric acid with a concentration of 2N was added, and the temperature of the solution was reduced to 9.
Maintain at 5-100'C and continue stirring for 100 hours.
A colloidal alumina hydrate was obtained. This product was a slightly cloudy liquid and no solid matter such as precipitate was observed.

Reference Example 2 (Preparation of colloidal silica) Ethyl silicate 20 (1') and distilled water 4001 were added to a 5-e round bottom flask equipped with a condenser, stirrer, and thermometer, and while stirring, ℃ and maintained at the same temperature for 24 hours to perform hydrolysis to obtain colloidal silica.

Example 1 The colloidal alumina hydrate obtained in Reference Example 1 was
11 [1g of anhydrous alumina 10 heated to 50°C under reduced pressure
The mixture was concentrated and solidified to a state containing 50 parts by weight of water per 0 parts by weight, and the obtained lumps were ground in a mortar to prepare 60 mesh powder of hydrated alumina hydrate.

The obtained powder 11 was placed on a polyester film with a diameter of 3 mm.
After uniformly scattering in an uneven circular shape and covering with a polyester film, it was pressed at a pressure of 1000 Kg/Cfl.

The obtained thin film had a circular shape with a thickness of 0.10 II and a diameter of 4e. After peeling off the polyester film, this alumina hydrate thin film was fired in an electric furnace at a temperature of 1000° C. for 30 minutes to obtain an alumina thin film.

The obtained thin film had a thickness of 0.08 mm and a diameter of 3 mm, was transparent, smooth, and had no warps or cracks. Also, when this alumina thin film was analyzed, the purity was 99.9.
It was 9%.

Example 2 4 tons of the powdered hydrated alumina hydrate obtained in Example 1 was uniformly placed in a tablet molding mold with a diameter of 2 mm, and
Pressed with 'OKglcr& pressure.

A hole with a diameter of 3 m11 was drilled in the obtained cylindrical molded product, and it was fired in an electric furnace at a temperature of 1400°C for 30 minutes.
A cylindrical alumina molded body having a perforation and having a thickness of 4 mm and a diameter of 1.8 om was obtained. No defects such as cracks were observed in the obtained molded body.

Reference Example 2 (Preparation of colloidal alumina hydrate-2) Aluminum isopropoxide powder was placed in a 70 ftk mortar, 0.01N hydrochloric acid 202 was added thereto, kneaded for 30 minutes, and hydrolyzed to produce alumina hydrate. Obtained.

Place the obtained hydrate t-11 in a flask and add 38 mL of distilled water.
After adding 0f and 2N hydrochloric acid 172, the internal temperature was reduced to 95.
The mixture was kept at ~100°C and stirred continuously for 100 hours to form a colloidal alumina hydrate. The obtained colloidal alumina hydrate was in the form of a slightly cloudy liquid, with no residual solid matter such as precipitation.

Example 3 The colloidal alumina aquarium 1002 obtained in Reference Example 1 and the colloidal silica IOf obtained in Reference Example 2 were mixed and heated under reduced pressure to form a state containing 50 parts by weight of water per 100 parts by weight of anhydrous alumina. until dry.

The dried lumps were then crushed and crushed in the same manner as in Example 1.
Molding and firing were carried out (calcination temperature: 1400°C, firing time: 3 hours) to obtain a circular thin film-like alumina-based molded body having a thickness of 0.09 IIB and a diameter of 3.6 mm. This product was transparent and had no physical defects such as scratches or cracks.

Example 4 Powdered hydrated alumina aquarium 1007 prepared in Example 1
Add 0.5S' of powdered magnesium hydroxide gold to the
Mix well, and mold and bake this mixture in the same manner as in Example 1 (however, the baking temperature is 1400°C) to give a thickness of 0.091 mm.
A circular thin film shaped alumina molded body with a diameter of 1 m and 2.7 yen was obtained. This thin film was transparent and no defects such as cracks, warpage, or cracks were observed.

Example 5 The colloidal alumina hydrate obtained in Reference Example 3 was transferred to Example 1.
An alumina hydrate thin film was obtained by processing in the same manner as above. The obtained thin film had a circular shape with a thickness of 0.12111 mm and a diameter of 4 degrees. The thin film was fired at 1000°C for 30 minutes to obtain an alumina thin film. The obtained thin film has a purity of 99.99% and a thickness of 0.0
8 II The diameter was 3 degrees, transparent, smooth and rough, and no cracks were observed.

Comparative Example 1 45 tons of colloidal alumina hydrate obtained in Reference Example 1 was poured into a 106 square Teflon container and air-dried.
An alumina hydrate thin film with a thickness of 0.08 III was obtained.
The thin film was warped after drying, and when a load was applied to correct the warp, it broke, and a thin film with an area of 1 cr/or more could not be obtained. If fired without straightening the grain,
The degree of cracking was large, and cracks also occurred, making it impossible to obtain a smooth thin film.

Comparative Example 2 Put 4000f of distilled water into a 5! round bottom flask, install a cooler, stirrer, and thermometer, heat it to 90℃, add 700f of coarsely ground aluminum impropoxide to the heated water, and heat it to 90℃. A non-colloidal alumina hydrate was obtained by holding and hydrolyzing the alumina hydrate.The obtained alumina hydrate was separated, dried and ground until it had a moisture content of 40% of the alumina, and a powder of 60 mesh baths was obtained. This powder was molded and fired in the same manner as in Example 1, but a transparent thin film could not be obtained after molding, and the thin film after firing was warped and remained opaque.

Patent applicant Mitsui Toatsu Chemical Co., Ltd.

Claims (4)

[Claims] (1) Production of an alumina-based molded body characterized by pressure molding a colloidal alumina hydrate moisture conditioned product in which 15 to 80 parts by weight of water is present per 100 parts by weight of anhydrous alumina and post-sintering. Method. (2) Claim 1, characterized in that the colloidal alumina hydrate humidity control product contains 20 or less silica or magnesha, or a substance that becomes silica or magnesha when fired, in terms of solid matter. Method-0 (3) The method according to claim 1 or 2, wherein the particle size of the colloidal alumina hydrate is 1 micron or less. (4) A patent claim characterized in that the colloidal alumina hydrate is obtained by peptizing alumina hydrate obtained by hydrolyzing aluminum alkoxide with water at a molar ratio of 3 or more. The method according to items 1 to 3 of the scope of the invention.