JPH01183403A - Production of compounded inorganic substance powder - Google Patents

Abstract

PURPOSE:To efficiently obtain a large amount of truly spherical compounded inorganic substance powder at a low cost, by mixing a specific colloidal solution or sol of an inorganic oxide solution with an aqueous solution of a metallic salt, flocculating colloidal particles and spray-drying the mixture containing the formed flocculates. CONSTITUTION:A colloidal solution or sol of an inorganic oxide is mixed with an aqueous solution of a metallic salt to flocculate colloidal particles. The mixture containing the resultant flocculates is then spray-dried to produce the aimed compounded inorganic substance powder. Furthermore, if colloidal particles are not directly flocculated in mixing the abovementioned colloidal solution or sol of the inorganic oxide with the aqueous solution of the metallic oxide, pH of the resultant mixture is adjusted to flocculate the colloidal particles. The mixture containing the flocculates is subsequently spray-dried to produce the compounded inorganic substance powder. A polar solvent, such as water or alcohol, can be used as a solvent and water is especially preferably used.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a method for producing composite inorganic powder, and more particularly to a method for efficiently producing substantially spherical composite inorganic powder in large quantities at low cost.

[Prior Art and Problems to be Solved by the Invention] Generally, inorganic powders used as resin fillers, abrasives, catalyst carriers, coating raw materials, etc. are preferably as close to true spheres as possible.

As a method for producing such a perfectly spherical or nearly perfectly spherical inorganic powder, a method of spray drying an inorganic oxide sol is known (Japanese Unexamined Patent Publication No. 61-270201). However, the particles obtained by this method had drawbacks such as being hollow and having some dents.

By the way, the Metsuki method is used to compound inorganic particles.

Impregnation method or CV D (Che+5ical Va
Methods such as chemical vapor deposition methods such as por deposition methods are known. However, the plating method and the impregnation method have the drawback that unless the powder used as a raw material is perfectly spherical, the composite inorganic material produced will not be perfectly spherical, and the reaction requires a considerable amount of time. On the other hand, the CVD method has problems in that raw materials are expensive and it is not suitable for mass production.

In recent years, as an improvement to the above method, a mixture of an inorganic powder and an inorganic sol has been spray-dried.1. A method of firing and/or classifying as necessary has been proposed (Japanese Unexamined Patent Publication No. 79841/1984).

According to this method, composite inorganic powder can be obtained, but since the inorganic powder used as a raw material is limited to metal oxides and insoluble metal salts, only a limited number of types of composite inorganic powder can be produced. Can not do it. Also,
Since the spray drying temperature is as low as 0 to 100°C, the work efficiency is poor, and furthermore, the composite inorganic powder obtained does not have sufficient sphericity, and an improvement in the layer quality has been desired.

[Means to solve the problem]

The present inventors have conducted extensive research in order to solve the above-mentioned problems and to develop a method for efficiently producing a wide variety of composite inorganic powders with high sphericity. As a result, by mixing an inorganic oxide colloidal solution or an inorganic oxide sol with an aqueous metal salt solution to once aggregate colloidal particles, and then spray-drying the resulting aggregate-containing mixture,
We have found that the above problems can be solved.

The present invention was completed based on such knowledge.

That is, the present invention provides a composite inorganic powder characterized by mixing an inorganic oxide colloidal solution or an inorganic oxide sol with an aqueous metal salt solution to aggregate colloidal particles, and spray-drying the resulting aggregate-containing mixture. In addition to providing a manufacturing method, if the colloidal particles do not aggregate when the inorganic oxide colloidal solution or inorganic oxide sol and metal salt aqueous solution are mixed as is, the DH of the resulting mixture is adjusted to form the colloid. There is also provided a method for producing a composite inorganic powder by agglomerating the particles and then spray drying the mixture from the resulting agglomerate platform.

The inorganic oxide colloidal solution or inorganic oxide sol used in the present invention preferably has a Si0g content of 1 to 50
wt % wt % wt % silicate sol (Coloyta lLt'y silica, Aj!zOs content is preferably 1 to 50 wt % wt % s lumina sol, Ti0z content is preferably 1 to 50 wt % wt % wt % sebum tania sol, ZrOz content is preferably is 1
-50% by weight of laconic acid. Although polar solvents such as water and alcohol can be used as the solvent, it is particularly preferable to use water.

Various metal salts can be used as the metal salt in the metal salt aqueous solution to be mixed with the inorganic oxide colloidal solution or inorganic oxide sol, and examples include Cr and M.

Group VIa metals of the periodic table, such as group VIa metals such as Mn, group IIa metals such as Mn,
Examples include nitrates, sulfates, and chlorides of group I metals such as Fe, Co, and Ni, group Ib metals such as Cu, and group Nb metals such as Zn. Specific examples include nickel nitrate, iron nitrate, cobalt nitrate, copper nitrate, chromium nitrate, copper sulfate, iron sulfate, and iron chloride. Among these metal salts, Group (1) metal salts are preferred, particularly nickel nitrate.

Iron nitrate, cobalt nitrate, iron sulfate, iron chloride, etc. are preferably used.

The metal salt concentration in the metal salt aqueous solution is not particularly limited as long as it is below the saturation concentration, but generally it is preferably in the range of 0.1 mol/2 or more and below the saturation concentration.

According to the method of the present invention, the inorganic oxide colloidal solution or inorganic oxide sol and the metal salt aqueous solution are mixed to aggregate colloidal particles. There is no particular restriction on the mixing ratio of the inorganic oxide colloidal solution or inorganic oxide sol to the metal salt aqueous solution, but usually the metal content in the resulting composite inorganic powder is 0.
What is necessary is just to mix so that it may be 1-50 weight% of weight%.

Note that colloidal particles may coagulate simply by mixing an inorganic oxide colloidal solution or an inorganic oxide sol with a metal salt aqueous solution, but if they do not coagulate, an alkali metal hydroxide aqueous solution such as a sodium hydroxide aqueous solution, ammonia PTT by adding po regulators such as water, basic buffer solution, etc.
is adjusted to produce a metal hydroxide, and colloidal particles can be agglomerated by the aggregation effect of this metal hydroxide.

Conversely, if the agglomeration progresses too much and the viscosity of the aggregate-containing mixture becomes too high, this mixture cannot be fed to the spray dryer, so a solvent, preferably an inorganic oxide colloidal solution or an inorganic oxide colloid solution, the same solvent as the sol,
For example, add water to disperse the aggregates and reduce the viscosity to 2 at room temperature.
It is preferable to lower the amount to 00 cp (centivoise) or less, particularly 100 cp or less, because supply operations etc. become easier.

In the method of the present invention, the aggregate-containing mixture obtained by the above-mentioned agglomeration treatment is spray-dried by a method such as introducing it into a spray drying device. As an apparatus used for this spray drying process, an apparatus generally used for spray drying can be used. Spray drying treatment conditions are not particularly limited and can be carried out under conditions commonly used in the past. The hot air inlet temperature can be selected within the range of 70 to 500°C, but from the point of view of work efficiency it is preferably set to 100"C or higher, especially 150"C or higher.The mixture supply rate is 3kg/hour (moisture content The rotation speed of the nozzle is preferably 50,000 rps or less, preferably 10,000 to 30,000 rpa+.If it exceeds 50,000 rps+, the dry powder will collide with the wall of the drying chamber. It is difficult to maintain a true spherical shape.

Note that the average particle diameter of the composite inorganic powder obtained by the method of the present invention can be adjusted by changing the number of rotations of the nozzle.
When the rotation speed is set to rp-, the average particle diameter is approximately 100 μm, and when the rotation speed is set to 50,000 rpm, the average particle diameter is approximately 5 μm.

The mechanism by which composite inorganic powder having a true spherical shape or a shape close to it can be efficiently obtained by carrying out the agglomeration treatment as in the present invention is not necessarily clear, but it is speculated as follows.

Generally, in the spray drying of a colloidal solution, in the early stage of drying, along with the movement of water, fine particles among the colloidal particles move to the surface of the droplet, as schematically shown in Figure 6 (a). A surface layer of fine particles is formed. This surface layer tends to dry quickly compared to the inside of the droplet, which is made up of coarse particles, and when it solidifies by drying, the internal moisture moves to the surface. When the evaporation rate becomes greater than the rate at which it is released to the outside through the surface layer, the vapor breaks through the weak part of the surface solid layer and escapes, forming hollow particles with dents, as shown in Figure 6 (b). will be generated.

On the other hand, when agglomeration treatment is applied as in the present invention, the interparticle forces in the generated aggregates are strong, so it is rare for fine particles to move to the surface with the movement of water. No such surface layer is formed.

The droplets are also thought to have a polymer-like network structure,
The speed at which moisture moves to the surface is also fast (and unobstructed).Therefore, not only does the surface solid layer not break through and the internal moisture evaporates, but the internal moisture remains until the late stage of drying. As a result, it is thought that a powder having a solid, true spherical shape or a shape close to it can be obtained.

The true spherical composite inorganic powder obtained as described above is
It is preferable to further calcinate the powder to remove impurities and anions such as chloride ions, nitrate ions, and sulfate ions. This firing process can be carried out at a temperature of 200 to 600°C, but is preferably carried out at a temperature of 450 to 600''C.Furthermore, following this baking process, the powder is classified to obtain powder with uniform particle sizes. You can also get it.

In addition, the fact that the powder obtained by the method of the present invention is a composite inorganic powder means that the obtained powder is E P MA (
Electron Probe Micro-Anal
This was confirmed by surface observation using a microcomputer (ysis). For example, when the surface of powder finally obtained from a mixture of silica sol and nickel nitrate by the method of the present invention was observed using EPMA, it was found that Si and Ni were present in each powder, and S
It was confirmed that a composite of iOz and NiO could be obtained as a single powder.

In addition, in the present invention, the longest diameter and shortest diameter of each particle are measured from a photograph of the obtained powder magnified 1000 times with a scanning electron microscope (SEM), and the sphericity is determined according to the following formula. I asked for it.

Sphericity - Shortest diameter/Longest diameter According to the method of the present invention, it is possible to obtain a powder containing at least 90% of particles having a sphericity of 0.9 to 1.0. The term "perfectly spherical powder" as used herein means a powder having such a sphericity distribution.

In addition, items with particles attached to each other or items with depressions,
Even if it is perfectly spherical, it is not very desirable.

〔Example〕

Next, the present invention will be explained in more detail with reference to Examples and Comparative Examples.

Example 1 Colloidal silica aqueous solution (Sift 17wt%) 1.0
6 kg and nickel nitrate aqueous solution (1.34 mol/1) 20
0d was mixed. This mixture coagulates quickly and is highly viscous, so add 1! In addition, it was homogenized. The viscosity at this time is 2
It was 100 cp at 5°C.

This mixture was dried using a spray dryer (L-8 type spray dryer manufactured by Okawara Kakoki ■, rotating disk diameter 50 mm, drying wall 80 mm).
0s (inner diameter) x 1200111m (length).

Nozzle rotation speed 15. OOOrpm, temperature 250° C., feed rate 2.5 kg/hour). The obtained powder was calcined at 450°C for 2 hours, and then subjected to scanning electron microscopy (S
When observed by EM), it was found to be solid and truly spherical. A 52M photograph of this particle structure (shape) is shown in FIG.

Further, this powder was measured with a laser diffraction particle size analyzer and the average particle size was 2.5 μm. Its composition is 90t% SiOz and 10-t% NiO.
Met.

Example 2 Colloidal silica aqueous solution (Sift 17wt%) 17
5 g of iron nitrate aqueous solution (0.67 mol A010d) were mixed. 15II11 of 5% ammonia water was added to this mixture to coagulate the solution. 100d of water was added to this, and the viscosity was reduced to 7.
Spray drying was carried out in the same manner as in Example 1 at 0 cp (25''C).

The obtained powder was calcined at 450°C for 1 hour. When this powder was observed with a SEM, it was found to be solid and truly spherical. A 52M photograph of this particle structure (shape) is shown in Figure 2. The average particle size of this powder is 20 μm, and the composition is Sin.
g 99 wt% and FezO 31 wt%.

Example 3 Colloidal silica water tri (SiCh 17wt%) 1
00g and nickel nitrate aqueous solution (1.95 mol/f) 50
m was mixed. This mixture was quite agglomerated, but since its viscosity was as low as 100 cp (25°C), it was directly spray-dried in the same manner as in Example 1.

When the obtained powder was fired at 450° C. for 1 hour and observed with SEM, it was found to be solid and perfectly spherical.

A 52M photograph of this particle structure (shape) is shown in FIG. In addition, the average particle size of this powder is 30 μm2 The composition is Sing
70 wt% and NiO 30 wt%.

Comparative example Colloidal silica aqueous solution (S!Ox 17wt%) 530
g and 200 - of iron nitrate aqueous solution (0.63 mol/l1) were mixed. This liquid mixture did not coagulate and was spray-dried in the same manner as in Example 1. The obtained powder was heated to 450°C.
After firing for 2 hours and observing with SEM, it was found that the shape was spherical with many depressions. A 52M photograph of this particle structure (shape) is shown in FIG. In addition, the average particle size of this powder is 34 μm, and the composition is SiOz 90 wt%, F
Eze310wt%.

Example 4 Colloidal silica aqueous solution (SiO□ 17 wt%) 106
g and 20 ml of an aqueous nickel nitrate solution (1.34 mol/i) were mixed. The mixture immediately coagulated and was homogenized by adding too much water. The viscosity was 100 cp at 25°C. This mixture was dried in a spray dryer (nozzle rotation speed 20.00 O
rpm, temperature 110°C.

Drying was carried out at a feed rate of 1.2 kg/hour). The obtained powder was calcined at 450°C for 1 hour. When this powder was observed with a SEM, it was found to be solid and truly spherical. A 52M photograph of this particle structure (shape) is shown in FIG. In addition, the average particle size of this powder is 20μm, and the composition is 5fOz 90wt.
%, Ni0 1011°C%.

〔Effect of the invention〕

According to the method of the present invention, composite inorganic powder having a true spherical shape or a shape extremely close to this can be efficiently obtained. Moreover, by adjusting the nozzle rotation speed of the spray dryer in the spray drying process, the average particle size of the powder can be adjusted to
It can be easily controlled within a range of 100 μm, and the temperature in the spray drying process can be set at 100° C. or higher, so the work efficiency is high and true spherical composite inorganic powder can be obtained in large quantities and at low cost. Furthermore, since a water-soluble metal salt can be used as a raw material, a wide variety of composite inorganic powders can be obtained.

Therefore, since the composite inorganic powder obtained by the present invention has a highly spherical shape and a smooth surface, it can be suitably used as a resin filler, an abrasive, a catalyst carrier, a coating raw material, and the like.

[Brief explanation of the drawing]

1 to 5 show Example 1. Example 2゜Example 3
．． 3 is a scanning electron microscope (SEM) photograph of the particle structure of powders obtained in Comparative Example and Example 4. FIGS. 6(a) and 6(b) schematically show the structure of droplets in a normal colloidal solution and the structure of particles having depressions obtained by spray-drying the droplets, respectively. Figure 11' 2 F・:C::? 3.

Claims (2)

[Claims] (1) A method for producing a composite inorganic powder, which comprises mixing an inorganic oxide colloidal solution or an inorganic oxide sol with an aqueous metal salt solution to aggregate colloidal particles, and spray-drying the resulting aggregate-containing mixture. . (2) In the inorganic oxide colloidal solution or inorganic oxide sol, the inorganic oxide sol is mixed with an aqueous metal salt solution, and then the pH of the resulting mixture is adjusted to aggregate the colloid particles, and then the resulting aggregate-containing mixture is mixed. A method for producing a composite inorganic powder, the method comprising spray drying.