JPH0684243B2 - Method for producing inorganic composite powder - Google Patents

Description

TECHNICAL FIELD The present invention relates to a method for producing an inorganic composite powder. More specifically, it relates to a method for producing an inorganic composite powder in which the inorganic powder is coated with an inorganic material having a composition different from that of the inorganic powder.

(Problems to be Solved by Conventional Techniques and Inventions) An inorganic composite powder obtained by coating an inorganic powder with an inorganic material having a composition different from that of the inorganic powder is used as both an inorganic powder serving as a core and an inorganic material serving as a coating layer. It is possible to combine the characteristics of, and a wide range of application fields are expected by utilizing the characteristics.

For example, silica-coated alumina in JP-A-61-266456, or PLbT-coated PLZT (a compound in which lanthanum is dissolved in lead zircon titanate) in JP-A-59-25901,
Applications to the electronic material field are also active. Further, it is possible to apply the inorganic composite powder to the field of dental materials, and as an example thereof, application to the powder component of dental glass ionomer cement can be considered.

The glass ionomer cement is a cement based on an acid-base reaction of kneading and curing an ion-exchangeable aluminosilicate glass powder and an acrylic acid-based polymer electrolyte aqueous solution, and is damaged by caries or the like. The missing tooth is filled in as a substitute for the tooth substance. In this case, in clinical dentistry, X-ray imaging is often performed to confirm the position and depth of the cement filled in the tooth. At this time, the higher the X-ray contrast property of the cement, the easier the confirmation. Therefore, for example, by coating an aluminosilicate glass having ion exchangeability with an inorganic substance having a high X-ray contrast property such as zirconia to form a composite powder, a high X-ray contrast property which cannot be realized by a conventional aluminosilicate glass is obtained. It is possible to obtain a glass ionomer cement having

As mentioned above, the inorganic composite powder can be used for various purposes. Taking the above-mentioned inorganic composite powder used for the dental glass ionomer cement as an example, the composition of the coating layer is a multi-component aluminosilicate glass. System, the thickness of the coating layer is sufficient to supply sufficient ions for reaction with the polymer electrolyte, 3, the core inorganic powder particles are coated in a dispersed state Fourth, it is an important requirement that the coating layer be uniformly formed on the surface of the particles. The above requirements 1 and 2 are necessary for the hardening of the glass ionomer cement. Further, the requirement of 3 is necessary for the prevention because when the inorganic powder particles are coated in an agglomerated state, an undesirably large inorganic composite powder is generated and the operability is deteriorated when kneading with the polymer electrolyte solution. The requirement of 4 causes the reaction with the polyelectrolyte to occur uniformly on the powder surface,
It is necessary to keep the strength of the cured glass ionomer cement high.

Due to the above circumstances, the production of an inorganic composite powder in which the composition and thickness of the coating layer can be arbitrarily adjusted and a uniform coating layer can be formed on the surface of the inorganic powder in a dispersed state A method is required.

Conventionally, there have been some reports on methods for producing inorganic composite powders, but they are roughly classified into the following three types.

1 Method in which the raw material of the coating layer passes through the gas phase 2 Method in which the raw material of the coating layer passes through the liquid phase 3 Method in which the raw material of the coating layer is a special powder First, regarding the method 1 above, vacuum deposition, metal chloride Examples of the method include a method by thermal decomposition precipitation of a material, but in all of these methods, the raw material components of the coating layer are limited, and it is difficult to form a multi-component coating layer such as aluminosilicate glass.

Next, as the second method, there is known a method of suspending a core inorganic powder in a solution of metal alkoxide, adding water thereto to hydrolyze, and then calcining the powder. The coating layer of the inorganic composite powder obtained by this method was extremely thin, and if a thick coating layer was required, the operation had to be repeated many times.

Further, as a method of No. 3, a method of adhering a special gel hydroxide to silicon nitride and then calcining it is shown in No. 61-91066. Such a method is based on the gel hydroxide. Since the adhesive force is used, there is a drawback that the raw material of the coating layer is limited to a specific gel hydroxide.

As described above, the composition of the coating layer can be arbitrarily selected, a relatively thick coating layer can be formed, and a uniform coating layer is formed on the surface of the core in the state where the inorganic powder is dispersed. A technique for producing an inorganic composite powder capable of forming a powder has not been developed yet, and it is an important technical issue at present.

(Means for Solving the Problems) As a result of intensive research to overcome the above technical problems, the present inventors have found that an inorganic powder and an inorganic fine powder having a particle size smaller than that have a specific property. Moreover, they have found that such an object can be achieved by mixing them in the presence of a specific amount of liquid binder and then heating them, and have completed the present invention.

That is, the present invention is: (1) 100 parts by weight of inorganic powder having a particle size of 1 μm or more (2) Melting point is 200 ° C. higher than the melting point of the inorganic powder or less, and particle size is 0.2 or less with respect to the inorganic powder. And 1 to 100 parts by weight of an inorganic fine powder having a composition different from that of the inorganic powder, and (3) a liquid binder having an affinity for the above-mentioned inorganic fine powder and having a viscosity of 20 Boise or less, represented by the following formula: (X) 2 × 10 ⁻³ GM ≦ X ≦ 1.2 × 10 ⁻² GM (where X: amount of liquid binder (parts by weight) G: oil absorption of the above inorganic fine powder (%) M : Amount of the above inorganic fine powder (parts by weight)) to obtain a composite powder, and then melting the particle surface of the composite powder, to a method for producing an inorganic composite powder.

The above-mentioned inorganic powder (1) used in the present invention (hereinafter referred to as powder (A)) serves as a core of the inorganic composite powder, and is known according to the intended function of the composite powder. Inorganic powder is used as appropriate. Generally preferable examples include powders of inorganic oxides, inorganic carbides, inorganic nitrides, etc. In particular, inorganic oxide powders are preferably used because they are stable in melting described later. Examples of the inorganic oxide powder include metal oxides, solid solutions thereof, complex oxides, silicate compounds, phosphate compounds, glass, and the like. Specific examples thereof include magnesium oxide. , Calcium oxide, strontium oxide, barium oxide, scandium oxide, yttrium oxide, lanthanum oxide, titanium oxide, zirconium oxide, vanadium oxide,
Tantalum oxide, chromium oxide, molybdenum oxide, manganese oxide, iron oxide, cobalt oxide, nickel oxide, copper oxide,
Zinc oxide, aluminum oxide, gallium oxide, indium oxide, silicon dioxide, germanium oxide, oxides such as tin oxide or their solid solutions, ilmenite, spinel, garnet, complex oxides such as perovskite, mullite,
Silicate compounds such as cordierite, forsterite, zircon, eucryptite, spodumene, olivine, phosphate compounds such as apatite, aluminosilicate glass, borosilicate glass, germanate glass,
Examples include glass such as crystallized glass.

As the above-mentioned powder (A), it is preferable to use one that exhibits a function in a coated state, and those functions include magnetism, X-ray contrast, lightness and the like.

Further, in the present invention, the particle diameter of the powder (A) must be 1 μm or more. That is, when the particle diameter is smaller than the above value, the powder (A) is likely to aggregate during mixing, and it becomes difficult to uniformly attach the inorganic fine powder to each surface of the powder (A). Generally 1 to 100 μm, preferably 1 to 50
μm is preferred.

Further, the powder (A) generally does not easily absorb the liquid binder, though it depends on the mixing method with the liquid binder described later.
That is, it is preferable to use one having a small oil absorption amount. The reason for this is that when the powder (A) is mixed with a liquid binder at the same time as the inorganic fine powder described later, the liquid binder is absorbed by the powder (A), and the inorganic fine powder adheres to the surface of the powder (A). This is because the liquid binder may remain inside or may not adhere sufficiently when the particle surface of the composite powder is melted. The preferable oil absorption of the powder (A) is 50% or less.

The inorganic fine powder (2) used in the present invention (hereinafter referred to as powder (B)) forms a uniform molten layer on the surface of powder (A), and powder (B) is It must have a composition different from that of the powder (A). The different composition here means
It includes the case where some or all of the components are different, and the case where the components are the same but the ratio of each component is different.

Further, the melting point of the powder (B) (the flow temperature when the powder (B) is glass) must be 200 ° C. or higher than the melting point of the inorganic powder, and more preferably the powder. (A)
Is equal to or lower than the melting point (the flowing temperature when the powder (A) is glass). That is, when the melting point of the powder (B) is higher than the above range, when the powder (B) is melted, the powder (A) inside the powder (B) is melted.
This is because the powder (B) that will be the coating layer will be compatible with the powder (A) that will be the core, and its properties may change.

The particle size of the powder (B) is 0.2 or less, and preferably 0.1 or less with respect to the powder (A). When the particle diameter of the powder (B) is larger than the above range, it becomes difficult for the powder (B) to uniformly adhere to the surface of the powder (A), and it becomes difficult to obtain the target composite powder.

As the powder (B), the material is not particularly limited as long as it satisfies the above requirements, and a known material is appropriately used according to the purpose. Fine powders of inorganic oxides, inorganic carbides, inorganic nitrides, and the like can be given as examples of materials generally suitably used, and inorganic oxide fine powders are particularly preferable.
Examples of the inorganic oxide fine powder include metal oxides, solid solutions thereof, complex oxides, silicates, phosphates and glasses, and specific examples thereof include gallium oxide and oxides. Chromium, silicon dioxide, tin oxide,
Oxides such as thallium oxide, tungsten oxide, tantalum oxide, titanium oxide, iron oxide, copper oxide, lead oxide, bismuth oxide, manganese oxide and molybdenum oxide, or solid solutions thereof, complex oxides such as ilmenite, spinel, garnet and perovskite. , Mullite, cordierite, forsterite, zircon, eucryptite, spodumene, olivine and other silicate compounds, apatite and other phosphate compounds, and aluminosilicate glass, borosilicate glass, germanate glass, crystallized glass, etc. There is glass etc. In particular, when the composite powder of the present invention is used for dental glass ionomer cement, aluminosilicate glass is preferably used.

Further, it is also possible to use a substance having the above composition by heating, for example, a metal carbonate,
There are hydroxides and hydrous oxides. It is also possible to use two or more of the above-mentioned powders (B) in combination.

If the powder (B) is considered to be a functional material, its functions are acid resistance, alkali resistance, oxidation resistance, abrasion resistance, insulation, conductivity, semiconductivity, thermal conductivity, ion exchangeability. And so on.

In the present invention, the addition amount of the powder (B) is 100% of the powder (A).
1 to 100 parts by weight, preferably 1 to 5 parts by weight
0 parts by weight. If the amount added is larger than the above range, the powder (B) will not adhere to the surface of the powder (A) and aggregates of only the powder (B) will be easily generated. If the amount is smaller than the above range, it becomes difficult to uniformly adhere to the surface of the powder (A).

The liquid binder (3) used in the present invention is a powder (A).
This is for attaching the powder (B) to the surface. Therefore, it is necessary that the liquid binder has an affinity for the powder (A) and the powder (B), and generally has hydrophilicity. As the liquid binder having hydrophilicity, one having a hydrophilic group is generally used. Examples of those which are preferably used as the hydrophilic group include a hydroxyl group, an ether group,
There are carbonyl group, carboxyl group, ester group, amino group, amide group and the like. If the liquid binder does not have an affinity for the powder (A) and the powder (B), the wetness of the binder to the powder is poor, and the powder (B) is present on the surface of the powder (A). It becomes difficult to adhere.

Further, it is necessary that the viscosity of the above liquid binder is 20 or less, preferably 10 or less. That is, when the viscosity of the liquid binder is larger than the above range, the dispersion becomes poor when the powder (A) and the powder (B) are mixed, and the powder (B) hardly adheres to the surface of the powder (A). Become.

In the present invention, a liquid binder which is preferably used in the present invention is specifically exemplified by methanol, ethanol, propanol, butanol, pentanol, ethylene glycol,
Alcohols such as diethylene glycol, triethylene glycol and glycerin, ethers such as dioxane, tetrahydrofuran and tetrahydropyran, acetone,
Examples thereof include ketones such as acetonylacetone and methyl ethyl ketone, organic acids such as formic acid, acetic acid and propionic acid, amides such as formamide and dimethylformamide, and water.

Further, the liquid binder is an amount (X) represented by the following formula.
Used in.

2 × 10 ⁻³ GM ≦ X ≦ 1.2 × 10 ⁻² GM (where X: amount of liquid binder (parts by weight) G: oil absorption of the above inorganic fine powder (%) M: amount of the above inorganic fine powder ( Furthermore, a more preferable amount (X) of the liquid binder is in the range of 3 × 10 ⁻³ GM ≦ X ≦ 1.0 × 10 ⁻² GM. When the amount of liquid binder exceeds the above range,
When the powder (B) is dispersed in the liquid binder and does not easily adhere to the surface of the powder (A), and when the addition amount of the liquid binder is smaller than the above range, the powder of the powder (B) is obtained. (A)
In this case, not only is it impossible to form a uniform coating layer, but it is difficult to form a coating layer having a thickness corresponding to the blending amount of the powder (B).

Further, as the liquid binder, it is preferable to select one that is completely decomposed or volatilized when the powder (B) existing on the particle surface of the powder (A) is melted. Therefore, when the liquid binder described above is an organic substance, one having a carbon number of 10 or less, more preferably 6 or less, is preferably used.

The method of mixing the powder (A), the powder (B) and the liquid binder in the present invention is not particularly limited, and ordinary industrial means can be used. Examples of these include a ball mill, a vibrating ball mill, a Henschel mixer, and a liquor machine.

In this case, the mixing order of the powder (A), the powder (B) and the liquid binder is not particularly limited, but when the oil absorption of the powder (A) is large, the powder (B) and the liquid binder are mixed. It is preferable to premix and then mix with the powder (A).

In the present invention, the method of melting the particle surface of the composite powder obtained by mixing the powder (A), the powder (B) and the liquid binder is not particularly limited, and a known heating method can be used. Examples of generally suitable heating means include flames, electric resistance heating elements, and high frequencies. Among them, the method of heating the composite powder by contacting it with a flame or the like in a state of being dispersed in the gas phase can form an extremely uniform molten layer on the surface of the inorganic powder, and is therefore preferably used. To be done.

Further, the temperature required for the heating needs to be higher than the temperature at which the powder (B) forms a molten layer. Moreover, the time required for the heating may be appropriately determined in relation to the heating temperature.

(Effect) According to the method of the present invention, the composition of the coating layer of the composite powder can be changed, a relatively thick coating layer can be formed, and the core inorganic powder is dispersed. It is possible to form a uniform coating layer on the surface. Therefore, according to the method of the present invention, it is possible to produce many kinds of composite powders having the functions of both the core powder and the coating layer on the surface thereof. For example, by coating a powder having a high X-ray contrast property with aluminosilicate glass, a composite powder for glass ionomer cement having a high X-ray contrast property can be obtained. In addition, a substance having magnetism, X-ray contrast property, etc. is used as a core, and its surface has acid resistance, alkali resistance, oxidation resistance, abrasion resistance,
It is also possible to produce a composite powder coated with a substance having high insulation, conductivity, semiconductivity, heat conductivity, and the like.

(Examples) Hereinafter, the present invention will be specifically described with reference to examples, but the present invention is not limited to these examples.

Example 1 To a mixed solution of 24 ml of 0.01 N hydrochloric acid and 320 ml of ethanol was added 333 g of tetraethyl silicate (manufactured by Nippon Corcoat Co., Ltd.), and the mixture was refluxed at 80 ° C. for 2 hours. 55 g of aluminum tree sec-butoxide (manufactured by Tokyo Kasei) and 58 g of triethyl phosphate (manufactured by Wako Pure Chemical Industries) were added to the solution, and the mixture was further refluxed for 1 hour. This solution is referred to as solution A. When 19.2 g of granular metallic calcium (manufactured by Wako Pure Chemical Industries, Ltd.) was added to 4 l of ethanol and refluxed at 60 ° C. for 2 hours, calcium reacted with ethanol to produce calcium ethoxide and dissolved in ethanol. This reaction solution is designated as solution B. 80 ° C after adding solution A to solution B
It was refluxed for 1 hour and the solution was cooled to room temperature.

The liquid thus obtained was gradually added dropwise to a mixed solution of 1.7 l of ammonia water (manufactured by Wako Pure Chemical Industries, Ltd.), 6.7 l of ion-exchanged water, and 16 g of sodium hydroxide (manufactured by Wako Pure Chemical Industries, Ltd.).

Collect the resulting gel-like fine powder by filtration and
By drying for an hour, an inorganic fine powder made of a hydrous oxide of sodium-calcium-aluminum-silicon was obtained.
When the inorganic fine powder was observed with a scanning electron microscope (manufactured by JEOL Ltd.), the particle diameter was between approximately 0.2 μm and 0.3 μm. The inorganic fine powder was heated at 800 ° C. to obtain a white powder. Hereinafter, this powder is referred to as an inorganic fine powder (M). The average particle size of this inorganic fine powder (M) is 0.24 μm, and the oil absorption is
It was 180%. The oil absorption was measured according to the method described in JIS-K5101. That is, inorganic fine powder (M) 1.
Take 0g on a glass plate and boiled linseed oil (Showa Varnish)
Was dripped little by little from the buret to the center of the material, and the whole was thoroughly kneaded with a spatula each time. Repeating the dripping and kneading operations, the whole becomes a hard putty-like lump for the first time, and when it reaches the point where it is rolled into a spiral shape with a steel knife, the end point is reached, and the amount of boiled linseed oil used up to that point Was calculated, and the oil absorption amount (%) G was calculated by the following formula.

(However, H: amount of boiled linseed oil (ml) S: amount of material (g)) 15 g of the above inorganic fine powder (M), spherical zirconia (average particle size 10 μm, oil absorption 28%, manufactured by Daiichi Rare Elements Co., Ltd.) 150g and formamide (viscosity 0.04boys) 15g in a ball mill 6
The mixture was mixed for a time to obtain a composite powder in which the inorganic fine powder was attached to the surface of spherical zirconia.

Then, the composite powder was mixed with a multi-tube burner every minute.
Hydrogen (2.3 Nm / hr) as well as oxygen (0.75 Nm / h) at a rate of 25 g
It was fed into the flame formed in r). Subsequently, the powder was cooled down to the cyclone and collected by the cyclone.
As described above, zirconia powder (No. 1) coated with aluminosilicate glass was obtained. An electron micrograph showing the particle structure of the zirconia powder is shown in FIG.

That is, FIG. 1 shows that the composite powder and the monomer (2,2-bis {4 (2-hydroxy-3-methacryloxypropoxy) phenyl} propane) 59.5% by weight, triethylene glycol dimethacrylate 40% by weight, N, N -Azobisisobutyronitrile 0.5% by weight) was kneaded in a mortar and placed in a polymerization vessel pressurized with nitrogen gas to a pressure of 5 kg / cm ² , and heated at 95 ° C for 1 hour to obtain a cured product. The surface of is polished and mirror-finished to prepare a sample for cross-section analysis of composite particles,
3 shows the results of analysis of aluminum existing in the cross section of the composite powder particles by a beam scan mapping method using an X-ray microanalyzer (JEOL, JXA-8600M). This photograph shows that the surface of the obtained inorganic composite powder particles is uniformly coated with aluminosilicate glass. The coating layer had an average thickness of 0.7 μm.

Further, by using the same method as above, by changing the charged amount of the above-mentioned inorganic fine powder, zirconia powder coated with aluminosilicate glass of different thickness (N
o.2 ~ No.4) was obtained. Table 1 shows the production conditions and the thickness of the obtained coating layer.

Example 2 12 g of ultrafine silica (average particle size 0.015 μm, manufactured by Tokuyama Soda Co., Ltd.), 13 g of calcium carbonate (average particle size 0.15 μm, manufactured by Shiraishi Industry Co., Ltd.) and aluminum hydroxide (average particle size)
22 g (0.6 μm, Showa Light Metal Co., Ltd.) were mixed in a mortar. When the oil absorption of the mixed fine powder was measured by the same method as in Example 1, it was 110%.

40 g of the above mixed fine powder and 5 g of sodium methacrylate (manufactured by Wako Pure Chemical Industries, Ltd.) dissolved in 16 g of ion-exchanged water (viscosity 0.0
2 voids) and 160 g of spherical silica (average particle size 8 μm, oil absorption 25%, manufactured by Tokuyama Soda Co., Ltd.) were mixed for 3 hours with a raikai machine to obtain a composite powder having inorganic fine powder adhered to the surface of the spherical silica. .

Then, the composite powder was put into an electric furnace and heated at 950 ° C. for 1 hour. As described above, an inorganic composite powder, which is a silica powder uniformly coated with aluminosilicate glass, was obtained. The coating layer had an average thickness of 0.6 μm.

Example 3 Ultrafine silica (average particle size 0.015 μm, manufactured by Tokuyama Soda Co., Ltd.) 20 g, alumina (average particle size 10 μm, oil absorption 15%,
Micron) 180g and glycerin (viscosity 0.15boys)
40 g was mixed with a Henschel mixer to obtain a composite powder in which silica was attached to alumina. The oil absorption of ultrafine silica was 260%. Then, the composite powder was heated in the same manner as in Example 1 to obtain an inorganic composite powder which was an alumina powder uniformly coated with silica. The coating layer had an average thickness of 0.6 μm.

Example 4 40 g of the inorganic fine powder (M) obtained in Example 1, spherical silica (average particle size 3 μm, oil absorption 30%, Harima Fire Brick Co., Ltd.)
200 g and 65 g of water were mixed in a ball mill for 6 hours to obtain a composite powder in which the inorganic fine powder (M) was attached to the surface of spherical silica.

Then, the composite powder is heated in the same manner as in Example 1,
A composite powder, which is a silica powder uniformly coated with aluminosilicate glass, was obtained. The average thickness of the molten layer is 0.2 μm
Met.

Example 5 111 g of calcium hydroxide (manufactured by Wako Pure Chemical Industries) and 88 g of phosphoric acid (manufactured by Wako Pure Chemical Industries) were dissolved in 31 ion-exchanged water,
While stirring the calcium hydroxide aqueous solution at a constant temperature of 50 ° C., the phosphoric acid aqueous solution was added dropwise thereto to synthesize hydroxyapatite. After stirring for a further 24 hours, the hydroxyapatite solids are filtered off and dried at 100 ° C for 8 hours, then 700
By firing at ℃ for 3 hours, the primary particle size is about 0.1μm
A hydroxyapatite fine powder of was obtained. The oil absorption of this hydroxyapatite was 80%.

40 g of the hydroxyapatite fine powder, 200 g of spherical zirconia (average particle diameter 10 μm, oil absorption 28%, manufactured by Daiichi Rare Elements Co., Ltd.) and 20 g of water were mixed in a ball mill for 6 hours, and hydroxyapatite fine powder was formed on the surface of the spherical zirconia. A composite powder adhered with was obtained. Next, the composite powder was fed into a flame in the same manner as in Example 1 and collected by a cyclone to obtain an inorganic composite powder which was a zirconia powder uniformly coated with hydroxyapatite. . The thickness of the coating layer was 1.0 μm on average.

Example 6 150 g of cobalt oxide (manufactured by Wako Pure Chemical Industries, Ltd.) and 312 g of aluminum hydroxide were mixed in a Likai machine and heated at 1300 ° C. for 4 hours to obtain aluminum cobalt oxide having a spinel structure. Next, the aluminum cobalt oxide was pulverized with a vibrating ball mill to obtain aluminum cobalt oxide powder having an average particle diameter of 4 μm and an oil absorption of 32%.

Next, 180 g of the powder, ultrafine silica (manufactured by Tokuyama Soda Co., Ltd.)
20 g and 30 g of water were mixed by a ball mill to obtain a composite powder in which silica was attached to aluminum cobalt oxide.

Then, the composite powder is heated in the same manner as in Example 1,
An inorganic composite powder which was an aluminum-cobalt oxide composite powder uniformly coated with silica was obtained. The thickness of the coating layer is 0.3
was μm.

Comparative Example 1 Ultrafine silica (average particle diameter 0.015 μm, manufactured by Tokuyama Soda Co., Ltd.) 20 g, alumina (average particle diameter 0.3 μm, manufactured by Sumitomo Chemical Co., Ltd.) 180 g, and formamide 30 g were mixed for 15 hours on a likai machine. According to a microscope (manufactured by JEOL Ltd.), alumina was not uniformly coated with silica, and the inorganic composite powder obtained by contacting it with a flame was agglomerated.

Comparative Example 2 Alumina (average particle size 0.3 μm, oil absorption 37%, melting point 2020
℃, manufactured by Sumitomo Chemical Co., Ltd.) 50 g, glass beads (average particle size 30 μm, flow temperature about 900 ° C., manufactured by Toshiba Ballotini) 1
50 g and formamide 12 g were mixed in a ball mill for 6 hours to obtain a composite powder in which alumina adhered to the surface of the glass beads. The composite powder was then fed using a multi-tube burner at a rate of 25 g / min into a flame formed of hydrogen (2.3 Nm / hr) as well as oxygen (0.75 Nm / hr). Subsequently, the powder was cooled down to the cyclone and collected by the cyclone. According to an X-ray microanalyzer, it was found that silicon was distributed on the surface of the obtained powder, and the coating layer of alumina was not formed on the surface of the powder.

Comparative Example 3 The spherical zirconia used in Example 1 (average particle size 10 μm
m, manufactured by Daiichi Rare Elements Co., Ltd., 150 g, quartz (average particle size 6 μm,
Fine powder (average particle diameter 3 μm, oil absorption 31%) obtained by pulverizing Tatsumori Co., Ltd. with a jet mill, and formamide 1
2 g were mixed in a ball mill for 6 hours. When the obtained powder was observed with an electron microscope, the fine powder was not uniformly attached to the surface of the spherical zirconia.

Comparative Example 4 150 g of the spherical zirconia used in Comparative Example 3, 50 g of the inorganic fine powder obtained in Example 1 and 12 g of toluene having no affinity for these powders were mixed in a ball mill for 6 hours. When the obtained powder was observed with an electron microscope, no inorganic fine powder adhered to the surface of the spherical zirconia.

Comparative Example 5 150 g of the spherical zirconia used in Comparative Example 3, 50 g of the inorganic fine powder obtained in Example 1 and 12 g of polyphosphoric acid (viscosity 50 Void, manufactured by Wako Pure Chemical Industries, Ltd.) were mixed in a ball mill for 6 hours. When the obtained powder was observed with an electron microscope, almost no inorganic fine powder adhered to the surface of the spherical zirconia.

Comparative Example 6 150 g of the spherical zirconia used in Comparative Example 3, 0.3 g of the inorganic fine powder obtained in Example 1 and 0.3 g of formamide were mixed in a ball mill for 6 hours. When the obtained powder was observed with an electron microscope, the surface of the spherical zirconia was not completely covered with the inorganic fine powder, and the inorganic composite powder obtained by contacting this with a flame was also Spherical zirconia as a core was exposed at the part.

Comparative Example 7 150 g of the spherical zirconia used in Comparative Example 3, 200 g of the inorganic fine powder obtained in Example 1 and 150 g of formamide were mixed in a ball mill for 6 hours. After the obtained powder was brought into contact with a flame in the same manner as in Example 1 and observed with an X-ray microanalyzer, the inorganic fine powder could not be adhered to the surface of the spherical zirconia, and an aggregate of the inorganic fine powder was found. Admitted.

Comparative Example 8 150 g of the spherical zirconia used in Comparative Example 3, 50 g of the inorganic fine powder obtained in Example 1 and 10 g of formamide were mixed in a ball mill for 6 hours and then observed with an electron microscope. The inorganic fine powder was not attached.

Comparative Example 9 150 g of the spherical zirconia used in Comparative Example 3, 50 g of the inorganic fine powder obtained in Example 1 and 150 g of formamide were mixed in a ball mill for 6 hours and then contacted with a flame as in Example 1. When the inorganic composite powder was observed with an X-ray microanalyzer, the inorganic fine powder was not uniformly attached to the surface of the spherical zirconia, and aggregates of the inorganic fine powder were recognized.

[Brief description of drawings]

FIG. 1 is an X-ray microanalyzer photograph showing the particle structure of the composite powder obtained by the method of Example 1, No. 1.

Claims (1)

[Claims] 1. An inorganic powder 100 having a particle size of 1 μm or more.
Parts by weight (2) The melting point is not more than 200 ° C. higher than the melting point of the inorganic powder, and the particle size ratio is 0.2 or less with respect to the inorganic powder,
And 1 to 100 parts by weight of an inorganic fine powder having a composition different from that of the inorganic powder, and (3) a liquid binder having an affinity for the above-mentioned inorganic powder and the inorganic fine powder and having a viscosity of 20 VOICE or less is described below. Amount represented by formula (X) 2 × 10 ⁻³ GM ≦ X ≦ 1.2 × 10 ⁻² GM (where X: amount of liquid binder (parts by weight) G: oil absorption of the above inorganic fine powder (%) M: the amount (parts by weight) of the above inorganic fine powder) to obtain a composite powder, and then the surface of the composite powder is melted.