JPH0222003B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION <Industrial Application Field> The present invention relates to a method for producing alumina, zirconia, titania or zinc oxide spherical fine powder having electrical conductivity. To be more specific, the present invention has microscopic, almost perfect spherical particles with an average particle size in the range of 0.02 to 10 μm, a monodisperse particle size distribution, and a uniform mixture of multicomponent metal oxides. ,
Alumina, which can effectively exhibit conductivity even at room temperature,
The present invention relates to a method for producing zirconia, titania or zinc oxide fine powder.

<Prior Art> Ceramics such as silicon carbide, lanthanum chromate, and zirconia have extremely high electrical resistance at room temperature, and must be heated to a high temperature of 300°C to 500°C to be used as a conductive material. In order to solve this problem, for example, zirconia ceramics have been added to chromium oxide (Japanese Patent Laid-Open No. 59-232966), niobium oxide (Japanese Patent Laid-Open No. 59-57958), and even bismuth oxide (Japanese Patent Laid-Open No. 59-182271). ), etc., and molding the mixture to try to impart conductivity at low temperatures has been proposed.

In addition, attempts have been made to create composite conductive elements by utilizing the mechanical strength and heat resistance of ceramics such as alumina and titania, which exhibit almost no conductivity when used alone, that is, insulating ceramics (for example, JP (See Publication No. 59-78973, etc.).

The raw materials for these composite ceramics are:
In many cases, a powder obtained by pulverizing individually prepared metal oxides and mixing them in solid form, or a powder obtained by co-precipitation from an aqueous solution of multiple metal salts is used. Therefore, the powder thus obtained has a large particle diameter and a wide diameter distribution. Moreover, the shape of the particles is irregular, and in particular, the particles are agglomerated in an irregular shape, and furthermore, each component is unevenly distributed and the uniformity of the composition is low.

When such powder is used as a raw material, there are many problems such as poor sinterability and a molded body with low conductivity.

<Problems to be Solved by the Invention> The present invention has been made in order to eliminate the above-mentioned drawbacks found in conventional composite ceramic raw material powders. The object of the present invention is to provide a fine powder having a substantially monodisperse particle size distribution.

That is, the gist of the present invention is specified as follows.

(1) A water-soluble compound of at least one metal selected from the group consisting of aluminum, zirconium, titanium, and zinc, and a metal capable of imparting conductivity to an oxide of the metal and/or itself in a metallic state or A solid substance produced by mixing an aqueous liquid containing a metal compound having conductivity in an oxide state with a water-insoluble organic solvent to form a W/O emulsion, and then mixing the emulsion with an alkaline substance. 1. A method for producing conductive spherical fine powder, which comprises separating, drying, and oxidizing and/or reducing firing.

(2) A water-soluble compound of at least one metal selected from the group consisting of aluminum, zirconium, titanium, and zinc, and a metal capable of imparting conductivity to an oxide of the metal and/or itself in a metallic state or A solid substance produced by mixing an aqueous liquid containing a metal compound having conductivity in an oxide state with a water-insoluble organic solvent to form a W/O emulsion, and then mixing the emulsion with an alkaline substance. Conductive spherical fine powder characterized by dispersing it in an organic solvent that can be azeotroped with water, dehydrating the solid by heating and distilling it, drying it, and subjecting it to oxidation firing and/or reduction firing. manufacturing method.

<Means> The present invention can be specified as described above, but specifically, it is formed using the following steps.

(1) An aqueous solution containing a water-soluble compound of at least one metal among aluminum, zirconium, titanium, and zinc and a compound of the metal that produces an inorganic substance capable of increasing or developing electrical conductivity, and preferably a water-insoluble organic solvent. are mixed in the presence of a surfactant to prepare a W/O emulsion.

(2) Next, the W/O emulsion and an alkaline substance are mixed and brought into contact to form a precipitate within the micelles.

(3) The precipitate thus obtained is dried and calcined in an oxygen atmosphere or reduced and calcined in a hydrogen, nitrogen, or carbon atmosphere to obtain a conductive spherical fine powder. Furthermore, as an alternative method, (4) the precipitate obtained in (2) is dispersed in an organic solvent that can be azeotroped with water, and the precipitate is dehydrated by heating and distilling the precipitate. things above
If you operate in the same way as (3), you will get good results.

Water-soluble salts of aluminum, zirconium, titanium, and zinc include chlorides such as aluminum chloride, zirconium chloride, and titanium tetrachloride; nitrates such as aluminum nitrate and zinc nitrate;
Other salts include water-soluble nitrates, oxymetal salts, organic carboxylates, etc., but these salts are sparingly soluble or insoluble in the water-insoluble organic solvent used in preparing the emulsion.

Conductivity-imparting elements include chromium, tin, bismuth, ruthenium, antimony,
These include copper, silver, cobalt, nickel, vanadium, cerium, indium, iron, tellurium, and tantalum, which may be incorporated into the micelles in the form of water-soluble compounds similar to those mentioned above, or may be incorporated into the micelles in the form of water-soluble compounds similar to those mentioned above. It can also be effectively used in the form of hydrosols, hydrogels, etc., which can be dispersed in water.

These conductivity-imparting elements form an oxide (uniformly mixed, not complexed) together with aluminum, zirconium, titanium, and zinc, and are contained in a molar ratio of 5 to 95%, particularly 30 to 90%.

The concentration of the aqueous solution is not particularly limited, but in order to produce fine particle powder that retains its spherical shape even after firing, a high concentration is preferable, and a concentration near saturation is usually used. The organic solvent used to prepare the raw material aqueous solution and the W/O emulsion is preferably a water-insoluble organic solvent, such as hydrocarbons such as benzene, toluene, xylene, heptane, cyclohexane, chlorobenzene, carbon tetrachloride, etc. Halogenated hydrocarbons and the like are preferred. Furthermore, from the viewpoint of stability of the produced W/O emulsion, it is more desirable to select the organic solvent so that the difference in specific gravity between the aqueous solution and the organic solvent does not become too large.

Emulsification is carried out in a customary manner, preferably using surfactants. That is, a surfactant is added to a raw material aqueous solution, an organic solvent is added dropwise to this while stirring,
Prepare a W/O emulsion. Alternatively, it may be prepared by adding a surfactant to an organic solvent and adding the raw material solution dropwise while stirring.

The surfactant used is preferably one that does not contain metal ions, particularly a nonionic surfactant, in order to avoid contamination with metal ions contained in the surfactant.
the type of surfactant or organic solvent used;
As in the case of ordinary emulsification methods, the diameter and distribution of micelles vary depending on the concentration, degree of stirring during emulsion preparation, temperature, etc. There is a correlation between the diameter of the micelles in the emulsion and the particle diameter in the form of powder, and it is necessary to select emulsification conditions to obtain the desired diameter.

To the W/O emulsion, 20% by weight or more of an organic solvent, preferably in the range of 40 to 70% by weight, and a surfactant of 0.5% by weight or more, preferably 5 to 15% by weight, are added to the W/O emulsion. By preparing the above, it is possible to produce spherical fine particle powder having a particle size within the range of 0.02 to 10 μm. At this time, by preparing an emulsion in which the micelles of the emulsion have a uniform diameter and good stability are prepared, spherical fine particle powder with a uniform particle diameter can be produced.

The W/O emulsion thus prepared is mixed with an alkaline substance to cause a neutralization reaction with aluminum, zirconium, titanium, and zinc ions in the micelles or with other metal ions mixed therein. Generate hydroxides of these metals. It is also possible to use ammonia water or ammonium carbonate aqueous solution as the alkaline substance, but in this case micelles may be destroyed and the proportion of spherical hydroxides with a uniform and good particle size distribution will be reduced. A trend is observed. However, it has been found that when ammonia gas is directly blown into the W/O emulsion, the micelles are not destroyed and become spherical hydroxides. The ammonia gas used may be diluted with air or nitrogen gas, but pure ammonia gas may also be used. Aluminum, zirconium, mixed in the aqueous phase
Metal ions other than titanium and zinc do not necessarily have to generate water-insoluble substances such as hydroxides with ammonia gas. If the substance produced by the reaction is not dissolved in the organic solvent that is the continuous phase of the emulsion, the entire amount remains in the other metal hydroxides in each micelle and is retained until after the subsequent drying and heat treatment process. Uniformly dispersed into individual particles.

The spherical precipitated particles containing hydroxide thus obtained are subjected to a drying heat treatment, but it has been recognized that the spherical particles are easily destroyed by ordinary drying methods in air, and a large proportion of particles do not retain their spherical shape. Ta. For this reason, as a result of various studies on drying methods, it was found that the spherical particles were first dispersed in an organic solvent that can be azeotroped with water, dehydrated by heating and distilling, and then dried and calcined. It has been found that a finely divided powder with a retained spherical shape is obtained. As the organic solvent that can be used, any of hydrophilic organic solvents such as ethanol, n-propyl alcohol, and n-butyl alcohol, and hydrophobic organic solvents such as benzene, toluene, xylene, chlorobenzene, and carbon tetrachloride can be suitably used. However, in the present invention, since a water-insoluble hydrophobic organic solvent is used when preparing the W/O emulsion,
Hydrophobic organic solvents are convenient as organic solvents for dehydration. That is, as described above, in a preferred embodiment of the present invention, after blowing ammonia gas to obtain spherical particles, if necessary, add the organic solvent used in preparing the W/O emulsion, and heat distillation. This is a method for dehydrating the spherical particles. In heating distillation, the temperature of the solution is
Continue until the temperature reaches 100°C or higher to distill off the moisture in the system. The thus obtained spherical fine particles are separated from the liquid phase, dried and then calcined at 400 to 1200°C in an oxidizing atmosphere to obtain spherical fine particles in which multi-component metal oxides are uniformly mixed.

Depending on the components, after drying, it can be fired in a non-oxidizing atmosphere, particularly in an atmosphere such as reduction with hydrogen, nitridation with nitrogen, or carbonization with carbon, to impart electrical conductivity.

In the present invention, when a compound of a metal that is relatively easily reduced is coexisting, spherical particles in which metal is uniformly mixed in alumina, zirconia, titania, and zinc oxide can be produced by reduction treatment, and conductive. A powder with good spherical particles can be obtained.

<Functions and Effects> In the present invention, the stability of the W/O emulsion and the diameter and diameter distribution of the micelles influence the particle diameter and diameter distribution of the obtained spherical fine particle powder. Therefore, the preparation of W/O emulsions, especially the selection and usage of surfactants, are important.

As mentioned above, a multi-component metal salt aqueous solution and ammonia gas can be reacted in the micelles of a W/O emulsion and dehydrated using an organic solvent without being dispersed in water. Even if a compound is produced, as long as it is not dissolved in the organic solvent used, it will be uniformly dispersed in each particle, and a powder with no uneven distribution of composition can be obtained. At this time, salts of aluminum, zirconium, titanium, and zinc react with ammonia gas to form hydroxides that are insoluble in water, which also has the effect of fixing the aqueous phase droplets in the emulsion.

More favorable results are obtained when all the metal salts in the system form insoluble salts upon reaction with ammonia gas.

The present invention relates to a method that maintains a spherical shape even after calcination through dehydration using ammonia gas and an organic solvent, and obtains a spherical fine powder with a uniform mixture of multiple components, which is easy to industrially produce. This is a practical method for producing spherical fine powder.

Example 1 Copper nitrate 1 mol/, aluminum nitrate 2 mol/
Two types of polyoxyethylene alkyl phenyl ether were mixed to give HLB5, and 50 g of the mixture was added to 100 ml of an aqueous solution containing the same amount. While vigorously stirring this solution with a homomixer, add 120% of toluene.
ml was added dropwise over about 30 minutes to prepare a W/O emulsion. Next, 100% ammonia gas was blown into the W/O emulsion at a rate of 1/min (STP) for 30 minutes while stirring gently. 200 ml of toluene was added to the liquid in which the neutralization reaction had been completed, and the water in the system was separated by heating and distillation. This heating was continued until the vapors were collected cold, where no aqueous phase separated. After separating the precipitate
By drying at 150°C for 8 hours and then firing in an electric furnace at 900°C for 2 hours, a spherical fine powder with an average diameter of 6 μm was obtained. The standard deviation was approximately 2 μm.
The powder was further reduced at 150°C in a hydrogen gas atmosphere to obtain a spherical fine powder of alumina mixed with metallic copper. When the powder was pressed and molded at 1.6 t/cm ² , the molded product showed high conductivity.

Example 2 Sorbitan fatty acid ester and polyoxyethylene sorbitan fatty acid ester were mixed to give an HLB of 4.0 and dissolved in 200 ml of chlorobenzene. In addition, yttrium chloride, zirconium oxychloride, and chromium chloride () can be combined with Y ₂ O ₃ , ZrO ₂ ,
Cr ₂ O ₃ was dissolved in water to give a concentration of 3, 87, and 10 mol %, respectively, and an aqueous solution was prepared with a concentration of 2.0 mol/ZrO ₂ . While vigorously stirring the above chlorobenzene solution, 50 ml of this aqueous solution was added dropwise to obtain a W/O emulsion. Ammonia gas was then bubbled through the emulsion at 1/min for 45 minutes. The emulsion, in which the neutralization reaction had thus been completed, was heated and distilled to remove moisture. After separating the precipitate, the solution was dried at 150°C for one day, and then calcined at 700°C for 2 hours, resulting in a chromium oxide-containing zirconia product with an average diameter of 0.7 μm and a standard deviation of 0.16 μm.
m spherical particles were obtained. Add a small amount of organic binder to the powder, press it at 2t/cm ² and shape it.
Sintered at 1500℃. The obtained sintered body showed good conductivity at 400℃.

Claims (1)

[Scope of Claims] 1. A water-soluble compound of at least one metal selected from the group consisting of aluminum, zirconium, titanium, and zinc, and a metal and/or that can impart conductivity to an oxide of the metal. An aqueous liquid containing a metal compound which itself has conductivity in a metallic state or an oxide state is mixed with a water-insoluble organic solvent to form a W/O emulsion, and then the emulsion is mixed with an alkaline substance. A method for producing conductive spherical fine powder, which comprises separating the produced solid matter, drying it, and subjecting it to oxidation firing and/or reduction firing. 2. The metal that can impart conductivity or has conductivity itself is chromium, tin, bismuth, ruthenium, antimony, copper, silver, vanadium, nickel, cerium, cobalt, indium, iron,
The method according to claim 1, characterized in that at least one selected from the group consisting of tellurium and tantalum is used. 3. A water-soluble compound of at least one metal selected from the group consisting of aluminum, zirconium, titanium, and zinc, and a metal and/or itself in a metallic state or oxide that can impart conductivity to the oxide of the metal. An aqueous liquid containing a metal compound having conductivity in the state of Production of a conductive spherical fine powder characterized by dispersing it in an organic solvent that can be azeotroped with the solid substance, dehydrating the solid by heating and distilling it, and further drying and oxidizing and/or reducing calcining. Method.