JPH0261408B2 - - Google Patents

Description

[Detailed description of the invention]

"Industrial Application Field" The present invention has a multilayer structure consisting of a core of inorganic material and a coating layer of different types of inorganic materials formed around the core, and has excellent workability in press molding and the density of molded products. This invention relates to a method for granulating powder raw materials that increases the ``Prior art'' As a granulation method for inorganic powder raw materials exhibiting this type of multilayer structure, ceramic raw material powders subjected to lipophilic surface treatment are emulsified and dispersed in a water-insoluble organic solvent, and the oil-based An aqueous slurry W in which powder of a metal or a metal compound to be metallized by reduction firing is dispersed in water is dispersed in the slurry O to form a W/O emulsion, and then the above-mentioned slurry is formed by spray drying. The present applicant has proposed a patent application filed in 1983 for a raw material powder for press molding of highly thermally conductive ceramics, which has a multi-layered structure consisting of a metal or metal compound powder as a core and covered with ceramic raw material powder.
It is disclosed in Japanese Patent Application Laid-Open No. 175597 and Japanese Patent Application Laid-open No. 1983-69468. "Problems to be Solved by the Invention" The granules with a layered structure granulated by the above spray drying have a spherical shape and are highly fluid in the mold.
Although the packing density is high, granules are formed by agglomerating primary particles by curing organic binder and inorganic caking body used depending on the composition during spray drying, so they are essentially hard and cannot be press-formed. There was an overwhelming sense of dissatisfaction. "Means for Solving the Problem" A metal alkoxide dissolved or dispersed in oil made by emulsifying an aqueous slurry containing inorganic particles is subjected to a hydrolysis reaction by the water in the aqueous slurry, and then the reaction is carried out. The product is separated from the oil and taken out. "Function" The metal alkoxide dissolved or dispersed in the oil emulsified from the aqueous slurry causes a hydrolysis reaction at the oil-water interface, and the hydrolysis reaction product destroys the emulsified inorganic particles in the oil. However, due to the surface tension of water, which is higher than that of oil, the emulsified aqueous slurry becomes spherical, and a coated structure made by coating this with a hydrolysis reaction product is also used. It has a spherical shape. "Effects of the Invention" As described above, the present invention cleverly utilizes the hydrolysis reaction of metal alkoxide to granulate an inorganic powder raw material consisting of a spherical layered structure. Unlike those obtained by heating and curing inorganic binders, the body raw material is easily crushed and has a spherical shape, so it is possible to increase both the fluidity in the mold and the packing density in press molding to obtain a dense product. Can be done. "Example" Example 1 Add 150ml of turpentine oil to a magnetic stirrer.
While stirring at 1800 RPM, add 129 g of ferrous oxide (FeO, first class reagent), 1 g of inorganic binder polyvinyl alcohol, and 40 ml of water to a 15 mm diameter alumina ball.
500g in a polyethylene container with an internal volume of 500ml
An aqueous slurry obtained by pulverizing and mixing at 120 RPM for 48 hours is poured into the slurry at a rate of about 2 ml per second to emulsify and disperse it, thereby obtaining an oil-based slurry 1. The average particle size of the water-based slurry emulsified in this oil-based slurry 1 was about 20 μm. Separately, 26 g of tetramethoxysilane [Si(OCH ₃ ) ₄ ] and 35 g of magnesium ethoxide [(C ₂ H ₅ O) ₂ Mg] were converted into forsterite 2MgO・SiO ₂ .
Dissolve in 150 ml of turpentine oil and use this as oil-based slurry 2. Next, while stirring the former oil-based slurry 1 with a magnetic stirrer at 600 RPM, the latter oil-based slurry 2 was poured into it at a rate of about 3 c.c. per second.
Stirring was continued for a minute. As a result of this stirring, on the surface of the aqueous slurry containing the ferrous oxide and emulsified to an average particle size of about 20μ, the hydrolysis product Si(OH) of tetramethoxysilane in the oil slurry 2 is formed. A layer of Mg(OH) ₂ , a hydrolysis product of ₄ and magnesium ethoxide, was formed. The average particle size of the spheres containing this hydrolysis product layer was about 30μ. With continued stirring, the slurry was cooled to about -5°C below zero, at which the turpentine oil did not freeze and the spheres froze, and then passed through a 350 mesh sieve to separate and collect granules consisting of frozen spheres. The granules collected in this way were freeze-dried for about 2 hours (equipment: Tokyo Rika Kikai Co., Ltd.: vacuum degree 0.2).
mmHg) to evaporate and volatilize the internal moisture, and the average particle size is approximately 28μ [FeO core approximately 19μ, Si (OH) ₄ and Mg
The desired powder raw material consisting of a dried spherical layered structure with a coating layer of approximately 0.5μ consisting of (OH) ₂ was obtained. This powder raw material was molded into 5 plate-shaped elements of 5 x 12 x 36 mm using a mold press at 1500 kg/cm ² and fired at 1360°C for 1 hour at a dew point of 20°C in an ammonia decomposition gas atmosphere. A sintered product measuring 3.8 x 9.2 x 27.7 mm was obtained. This sintered product is sintered in a powder metallurgical manner, and consists of numerous polyhedrons of 13 to 15μ in size made of fine Fe powder that flatten from the bottom (the contact part of the mold receiver) to the top. It exhibited a dense cross-sectional shape that was firmly bonded to the insulating layer of sintered forsterite with a thickness of 2 to 4 microns through a metallization reaction. Table 1 shows the various characteristic values in comparison with standard values of forsterite compositions.

[Table] From the above table, it can be seen that the sample using the powder raw material granulated according to the above-mentioned Example 1 of the present invention did not significantly deteriorate the electrical properties, which was a concern, compared to the forsterite composition. , it has been shown that other properties, especially thermal conductivity, can be greatly enhanced. In this example, the metal alkoxide to be dissolved in oil-based slurry 1, which is an emulsified water-based slurry containing FeO, was dissolved in another oil in advance and added as oil-based slurry 2. The above two types of metal alkoxides produced, 26
The purpose is to mix g of tetramethoxysilane and 39 g of magnesium ethoxide evenly.
If both can be mixed accurately, they may be directly blended into the oil-based slurry 1 without being made into a slurry, and when used as the oil-based slurry 2, the oil medium is the same as the oil-based slurry 1, or It is preferable to use oils with high affinity. Example 2 200 g of colloidal silica (Snowtex O, Nissan Chemical) in which 1 g of organic binder polyvinyl alcohol was dissolved in 300 ml of diesel oil was stirred with a magnetic stirrer at 1900 RPM as a water-based slurry.
Emulsify and disperse. The average particle size of the aqueous slurry containing emulsified colloidal silica was about 30μ. The stirring of the above magnetic stirrer was lowered to 700 RPM, and 107 g of calcium ethoxide (C ₂ H ₅ O) ₂ Ca was added thereto to react with the above colloidal silica to obtain wollastonite porcelain composition CaSiO ₃ , and after about 10 minutes. In the above average particle size of about 30μ
The surface of an aqueous slurry containing colloidal silica emulsified in an oil-based slurry containing spheres with an average particle diameter of about 50μ is coated with a layer of Ca(OH) ₂ , a hydrolysis product of calcium ethoxide. Obtained. While continuing to stir, this slurry was cooled to -3°C below zero, where the light oil did not freeze but the above-mentioned spheres dispersed in the slurry were frozen, and then passed through a 300 mesh sieve to obtain granules made of frozen spheres. Separated and collected. The granules collected in this way were freeze-dried in the same manner as in the previous example, and the average particle size was approximately 47μ, and the internal Ca
The desired powder raw material consisting of a multilayer structure of dry spheres with a coating layer of (OH) ₂ of about 9 μm was obtained. Next, to obtain the same wollastonite (CaSiO ₃ ) composition as the final product, 500 g of wollastonite (average particle size 1 μ, purity 99%, manufactured by Maruwa Biochemical Co., Ltd.), 4 g of polyvinyl alcohol as an organic binder, Put 300ml of water together with 2kg of 15mmφ alumina ball into an alumina ball mill with an internal volume of 2.
Mixing and pulverizing at 7200 RPM for 48 hours, the resulting slurry was spray-dried at a gas temperature of 170°C, an atomizer diameter of 110 mmφ, and a flow rate of 5 ml per second, resulting in an average particle size of 50 μ.
It was granulated into granules using the conventional method. The two types of granular raw material powders granulated in this way were ^both 5×12
Table 2 shows the results of a comparison of various properties of samples produced by manufacturing five 36 mm x 36 mm plate-shaped elements and firing them in an electric furnace.

[Table] The sample using the raw material powder granulated according to the present invention has SiO ₂ from colloidal silica as a core,
After press-molding a multi-layered, easily crushed granular raw material powder consisting of a thin film of Ca(OH) ₂ produced by hydrolysis of ursium ethoxide, which coats the SiO ₂ and Ca(OH) ₂
Table 2 shows that this process densifies wollastonite porcelain (Ca・SiO ₃ ), which has recently attracted attention as an electrical insulator for high-frequency applications, and significantly improves its properties compared to those obtained using conventional methods. be done. In this example, colloidal silica was used as an aqueous slurry containing inorganic particles, but silicic anhydride may be dissolved in water. As described above, in the present invention, a metal alkoxide dissolved or dispersed in an oil emulsified with an aqueous slurry containing inorganic particles is subjected to a hydrolysis reaction with water in the aqueous slurry, and the metal alkoxide in the aqueous slurry is It is composed of a core of inorganic particles and a coating layer of a metal alkoxide reaction product, and exhibits a spherical shape with a high packing density in the mold, and is easily crushed by pressure, resulting in a dense final product or sintered body. The sintered body can be produced in various forms. That is, as in Example 1, it consists of a highly thermally conductive core and a covering layer of high-frequency electric insulator, and does not react during sintering, and even if it does react, it remains only at the contact surface and exhibits its excellent properties. In some cases, as in Example 2, the core and the coating layer react to form a highly dense crystal structure. In other words, in the former case, the inorganic particles forming the aqueous slurry are not limited to metal compounds such as ferrous oxide in the example that is metallized by reduction calcination, but can also be used in the form of metal powder, as well as carbides. , non-oxide ceramic raw material powders such as nitrides, and oxide powders are selected depending on the purpose, and are combined with metal alkoxides to form a coating layer by causing a hydrolysis reaction with the water in the water-based slurry. It will be done. In addition, if the sintering temperatures of the above-mentioned inorganic particles and the hydration reaction product of the metal alkoxide to be combined are close to each other, and a compound of both is produced by firing, hot pressing, which sinters in a short time, may be used. The reaction can be stopped near the boundary between the inorganic particles and the coating layer. Table 3 lists preferred metal alkoxides and characteristics of the final product as a coating layer for the cores of the various inorganic particles forming the above-mentioned aqueous slurry.

[Table] In addition to the oxides and non-oxides listed in the above table, a ceramic composition can also be used for the core. For example, using a perovskite structure such as lead titanate, barium titanate, or lead zirconate titanate-based compound as a core, a coating layer of a forsterite composition is formed using magnesium ethoxide and tetramethoxysilane as starting materials. Therefore, it is effective as a high-frequency radio wave absorbing material that utilizes the particularly high dielectric constant of the nucleus. Next, when a crystal structure is produced by reacting the core and the coating layer in the latter example 2, depending on the combination of the core and the metal alkoxide of the coating layer, a two-component system such as forsterite or a crystal structure can be produced. - In addition to three-component systems such as dirite composition, it is effective for high-purity alumina porcelain in which extremely small amounts of alkoxides such as Mg, Sr, and Ca are combined with core alumina. In Examples 1 and 2 above, an organic binder was added to the water-based slurry, but it was not necessary to add the binder, and the water-based slurry was directly mixed into turpentine or light oil. , a small amount of a liquid emulsifier with an HLB value of 6 or less that emulsifies water in these oils, or a solid emulsifier such as talc powder, in the case of the former liquid, 1% or less by weight of the oil medium;
The latter solid content is preferably 2% or less, and the oil medium referred to herein is not limited to the turpentine oil and light oil used in the examples, but is also a liquid that is sparingly soluble in water, such as a higher alcohol or ketone. In addition, as a means of extracting spheres made of inorganic particles as cores and coated with products from the hydrolysis reaction of metal alkoxides from oil-based slurry, the spheres were frozen to give them mechanical strength, but organic caking If the necessary strength is obtained by the agent, it is possible to pass the oil-based slurry through a sieve at room temperature, and if it contains an organic binder, it can be freeze-dried to increase the bond strength between the particles. The drying method is not limited, although it is preferable because it increases the press molding density. Next, the amount of water in the aqueous slurry of the present invention is the amount necessary to hydrolyze the metal alkoxide, for example, in the case of tetramethoxysilane, the chemical formula of the hydrolysis reaction is Si(OCT ₃ )H ₄ +4H ₂ O→ 4CH ₃ As expressed as OH + Si (OH) ₄ , it is 4 mol% for 1 mol% of tetramethoxysilane, and the lower limit is calculated from the chemical formula of the hydrolysis reaction of these metal alkoxides, and the inorganic particles suspended in water are colloidal. It is preferable that the proportion of the water-based slurry emulsified in the oil-based slurry 1 is in the range of 5 to 40% by volume, including the case of silica, and the proportion of the water-based slurry emulsified in the oil-based slurry 1 is preferably in the range of 20 to 60% of the total volume. In addition, the properties of the final product and sintered body are determined by the dimensions of the core made of inorganic particles in the slurry and the coating layer made of the hydrolysis product of metal alkoxide. 30~90
%, and the latter metal alkoxide is preferably in the range of 70 to 10% from the viewpoint of handling of the granulated powder raw material.

Claims (1)

[Claims] 1. One or more metal alkoxides are dissolved or dispersed in an oil made by emulsifying an aqueous slurry containing one or more inorganic particles, and the metal alkoxides are hydrolyzed by the water in the aqueous slurry. After forming an oil-based slurry containing a coated spherical structure consisting of a reaction product and inorganic particles in the aqueous slurry coated with the reaction product, the oil is removed from the slurry. This is a granulation method for inorganic powder raw materials.