JPH09278443A - Titanium oxide particulates and its production - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide titanium oxide particulates having a particle diameter and a specific surface area suitable for sintering and small in aggregation at the time of heating. SOLUTION: This titanium oxide particulates have 0.1-0.5μm average particle diameter and 40-95m<2> /g specific surface area and have a property that the specific surface area becomes 10-30m<2> /g in the case of heating the particulates at 800 deg.C for 30min. The particulates are produced by preparing a mixed solution of titanium tetrachloride and water with a polycarboxylic acid at <50 deg.C, heating to the hydrolyzing temp. of titanium tetrachloride and filtering, drying and heat treating the resultant precipitate. In such a case, the hydrolyzing reaction is executed preferably while suppressing the releasing of generated hydrogen chloride gas by providing a reflux condenser 3.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to fine particles of titanium oxide having excellent dispersibility and a method for producing the same, and more particularly to electronic ceramic materials for high-performance capacitors, thermistors, solar cells, high-grade cosmetic materials, and plastic additives. , Fine particles of titanium oxide having excellent dispersibility, which are suitable as raw materials for chemicals such as paints, inks and deodorants, and a method for producing the same.

[0002]

2. Description of the Related Art When titanium oxide particles are used for a sintered material such as a capacitor dielectric or a thermistor material, the particles should be small, and even if they have the same particle size, the specific surface area should be large. This is because, for example, in a capacitor, titanium oxide and, for example, barium oxide are reacted and sintered, but the larger the specific surface area is, the higher the reactive sintering property is.

The method of making the particles of titanium oxide into very small particles is roughly classified into a dry method of oxidizing and decomposing titanium tetrachloride in the gas phase, and an alcoside compound of titanium (JP-A-62-2).
26814) and titanium tetrachloride (JP-A-60-18641).
There is a wet method of hydrolyzing 8). Titanium oxide fine particles obtained by the dry method have a sufficiently small particle size, but since the surface is smooth, the specific surface area is not so large relative to the particle size, and it cannot be said that they are excellent as a sintering material. Therefore, many wet methods have been proposed for obtaining fine particles having a large specific surface area. For example, in the above-mentioned JP-A-60-186418, very fine particles having a particle size of 0.05 to 0.5 μm are obtained.

[0004]

The fine particles of titanium oxide are highly active and tend to agglomerate. When the fine particles aggregate, the characteristics of the fine particles are lost, which is inconvenient not only when the fine particles are used as a sintering material but also as various additives and paints. The cohesiveness based on the activity of titanium oxide and fine particles also appears in the heating process during reactive sintering using titanium oxide fine particles. As a result, the powder consisting of titanium oxide fine particles is mixed with other raw materials even if they are not aggregated,
During reaction sintering, titanium oxide fine particles agglomerate and sinter before the sintering, and at the same time, there occurs a portion where other raw materials also sinter themselves, so a uniform reaction sintered body cannot be obtained. .

The fine particles produced by the method of the above patent are not good in avoiding aggregation during this heating process. As another method for reducing the surface activity of titanium oxide fine particles, there is JP-A-57-145007. This method is a method in which a polyamino acid salt such as polyaspartate is adsorbed on the surface of titanium oxide fine particles and then treated with an acidic substance. However, such a method of adsorbing a salt is a method of treating particles that are usually produced, and it is necessary to uniformly disperse the particles into primary particles, which is technically difficult. As a result, the uniform adsorption treatment is not sufficiently performed, so that when the sintered material is used as in the present invention, abnormal grain growth is observed, which is not preferable.
From these facts, the characteristics required for the titanium oxide fine particles are that the particle size is small from the top in order to enhance the reaction sinterability,
In addition, the specific surface area is large, the particles are so small that they are not aggregated, that is, the dispersibility is good, and the aggregation is small when the particles are used as a reactive sintering material and heated. Is. An object of the present invention is to provide titanium oxide fine particles having the above characteristics.

[0006]

As a result of various studies on the hydrolysis method of titanium tetrachloride, the present inventor discovered that the desired titanium oxide fine particles can be obtained by hydrolysis under specific conditions. Then, the present invention has been reached. That is, the titanium oxide fine particles of the present invention have an average particle size of 0.1 to 0.1.
0.5 [mu] m, specific surface area of 40~95m ² / g, the specific surface area when heated for 30 minutes the fine particles to 800 ° C. is one that has a characteristic to be 10 to 30 m ² / g. This method for producing titanium oxide fine particles is the same as the method for producing titanium oxide fine particles by hydrolyzing an aqueous solution of titanium tetrachloride, in which titanium tetrachloride, water and polycarboxylic acid are mixed at a temperature of less than 50 ° C., and then the mixture is heated. Then, a hydrolysis reaction is carried out to produce titanium oxide, which is then filtered, dried and heat-treated in a conventional manner.

[0007]

BEST MODE FOR CARRYING OUT THE INVENTION The titanium oxide fine particles of the present invention have an average particle diameter of 0.1 to 0.5 μm and a specific surface area of 40 to 95 m.
^It consists of ² / g. The fine particles are aggregated to form a powder. It is preferable that the number of fine particles having the above-mentioned particle size and specific surface area contained in this powder is large, but if the whole is not the fine particles, most of them, for example, the number of particles is 80.
If at least 100% of the fine particles are used, it is suitable for the purpose of the present invention. In the above, the average particle diameter of the titanium oxide fine particles is 0.
If it is less than 1 μm, aggregation is likely to occur, and particularly during heating, the aggregation becomes large. On the other hand, if it exceeds 0.5 μm, it is inferior in microscopic uniform mixing when mixed with other raw materials, and the surface area becomes small, so that the reaction sinterability is poor.

The specific surface area of the fine particles generally has a correlation with the particle size, but also has a relationship with the surface state of the particles, pores and the like. Therefore, even if the particle size is the same, the reaction sinterability and the cohesiveness are different.
The specific surface area of the titanium oxide fine particles of the present invention is 40 to 95 m.
² / g. The specific surface area is not sufficient homogeneity of the reaction and 40 m ² / g less, also 95m and aggregation properties exceeds ² / g, made especially easily caused aggregation during heating. The average particle diameter and the specific surface area of the titanium oxide fine particles are those of the fine particles which are heat-treated after titanium oxide is produced by the wet method. When titanium oxide fine particles are obtained by a wet method, it is generally in the range of 200 to 700 ° C. after drying, often 3
Heat treatment is performed in the temperature range of 00 to 500 ° C.

One of the features of the titanium oxide fine particles of the present invention is that the cohesiveness when heated is smaller than that of the conventional one. According to the research conducted by the present inventor, it has been found that even the fine particles having the same average particle diameter and specific surface area have different aggregation properties. It seems that other factors besides the particle size and the specific surface area are related to the factor, but since the factor is not clear, in the present invention, the specific surface area when heated under predetermined conditions is measured. The value was used as a measure of the agglomeration property upon heating. As the predetermined condition, heating in air at 800 ° C. for 30 minutes was selected. The temperature of 800 ° C is the result of reaction sintering.
In many cases, agglomeration during the temperature rising process up to 800 ° C. is a problem.

The titanium oxide fine particles of the present invention are the above 800.
The specific surface area when heated in the air at 30 ° C for 30 minutes is 10
It is 30 m ² / g. The larger this specific surface area is, the more preferable, but it is difficult to make it larger than 30 m ² / g. Also, if it is less than 10 m ² / g, it is insufficient from the viewpoint of avoiding aggregation. The specific surface area after heating is considerably smaller than the specific surface area of the titanium oxide fine particles used for heating because the surface of the particles becomes smooth and the pores disappear. The titanium oxide fine particles of the present invention are 80
When heat-treated at 0 ° C. and observed with a microscope, it can be seen that aggregation is small.

Next, the method for producing the titanium oxide fine particles of the present invention will be described. The production method of the present invention is a method for hydrolyzing an aqueous solution of titanium tetrachloride. At that time, a polyvalent carboxylic acid is added, and a mixture of titanium tetrachloride, water and a polyvalent carboxylic acid is added at a temperature of less than 50 ° C. It is characterized by preparing. It is known to add a polycarboxylic acid by a hydrolysis method of an aqueous titanium tetrachloride solution, as described in JP-A-2-196029. In the method of this patent, the specific surface area is made particularly large by increasing the pores of the titanium oxide fine particles. The titanium oxide fine particles obtained here have A
Ultrafine particles such as g, Cu, Zn, etc. are carried and used for sterilization and antibacterial. The method for producing titanium oxide fine particles of this patent is characterized in that an aqueous solution in which a polycarboxylic acid is dissolved is first heated to 50 ° C. or higher, and titanium tetrachloride is gradually added thereto. Particles composed of a reaction mixture of hydrated titanium oxide and organic acid, which is hydrolyzed by the addition of titanium tetrachloride and is generated, are heated to a temperature of 200 to 400 ° C. to evaporate the organic acid and water contained in the particles. , The pores are generated as traces of the dissociated gas.

According to the research conducted by the present inventor, as in this patent, a polyvalent carboxylic acid aqueous solution is preheated to 50 ° C. or higher, and titanium tetrachloride is added to this, and water,
It was found that when a mixed solution of titanium tetrachloride and polyvalent carboxylic acid was prepared at a temperature of less than 50 ° C. and heated to the hydrolysis temperature and hydrolyzed, the obtained titanium oxide fine particles were different. Since the titanium oxide fine particles are used for sterilization or the like, the method of the above patent is excellent in order to maximize the surface area. According to this method, the specific surface area is 10
0 m ² / g or more. However, the titanium oxide fine particles obtained by this method have a large decrease in specific surface area due to heating.
That is, the specific surface area by heating at 800 ° C. for 30 minutes is smaller than the specific surface area of the titanium oxide fine particles of the present invention described above. In fact, it is confirmed that the cohesiveness is higher than that of the fine particles of the present invention.

When the difference between the above two is further examined, the hydration reaction is preferentially performed in the above method because titanium tetrachloride is added to the high temperature aqueous solution of polycarboxylic acid. On the other hand, in the method of the present invention, it is presumed that in the mixed solution of water, titanium tetrachloride and polyvalent carboxylic acid, the complexation reaction first occurs and then the hydration reaction occurs. For example, the X-ray analysis of the reaction products at about 104 ° C. in both shows that they are different as described later.
In the present invention, the polyvalent carboxylic acid forms irregularities on the surface of the titanium oxide fine particles and forms pores in the particles, has the effect of increasing the specific surface area, and reduces the aggregation in the heating process of the fine particles due to the production conditions as described above. Acting to do. In the present invention, the mixing of water, titanium tetrachloride and polycarboxylic acid is carried out at a temperature of less than 50 ° C, and the lower limit of the temperature is not particularly limited and may be room temperature, for example. Regarding the mixing ratio, titanium tetrachloride is preferably 0.1 to 2 mol / liter in the mixed solution of the three. When the amount of titanium tetrachloride is less than 0.1 mol / liter, the productivity is poor, and the amount of titanium tetrachloride is 2 mol / liter.
When it exceeds liter, the titanium oxide fine particles produced are aggregated to reduce the specific surface area. The amount of polyvalent carboxylic acid is preferably 0.025 to 0.5 mol / liter in the mixed solution of the three. If it is less than 0.025 mol / liter, the specific surface area of the titanium oxide fine particles becomes small, and the above-mentioned effect of addition is small. On the other hand, if it exceeds 0.5 mol / liter, complexation progresses a lot and conversely, aggregates are formed and the specific surface becomes small.

Examples of the polycarboxylic acid used include dibasic or tribasic organic compounds having two or more carboxyl groups such as oxalic acid, malonic acid, succinic acid, malic acid, tartaric acid, citric acid and gluconic acid. It is a polycarboxylic acid. You may use these in mixture of 2 or more types. Even carboxylic acids, for example acetic acid with one carboxyl group are not suitable. The reason is considered that titanium tetrachloride and a complex compound are not formed. A mixed solution of titanium tetrachloride, water and a polycarboxylic acid below 50 ° C. is then heated and hydrolyzed. Hydrogen chloride is generated by hydrolysis and the aqueous solution becomes cloudy. It seems that titanium oxide hydrate and complex compounds are generated in the aqueous solution. The hydrolysis temperature is preferably 60 ° C. or higher and up to the boiling point of the aqueous solution. If the temperature is lower than 60 ° C, the hydrolysis takes a long time, and if the temperature exceeds the boiling point, a high pressure resistant device is required. The hydrolysis is carried out in the above temperature range for about 1 to 5 hours. The above time may be short when the hydrolysis temperature is high, and long when the temperature is low.

The heating rate of the aqueous solution to be hydrolyzed is 0.2 to 10 ° C./min, preferably 0.5 to 5.0 ° C.
/ Min. The higher the heating rate, the smaller the obtained titanium oxide fine particles tend to be. Hydrolysis can also be carried out using a normal hydrolysis reaction tank while allowing the generated hydrogen chloride gas to escape, but it is desirable to prevent the generated hydrogen chloride gas from leaking out of the reaction tank and use it in an aqueous solution as much as possible. Is to remain. By this method, the titanium oxide fine particles within the scope of the present invention can be easily obtained.

The method of controlling the escape of the hydrogen chloride gas from the reaction tank is not particularly limited, and it is possible to pressurize, for example. However, the easiest and most effective method is to use the hydrolysis reaction tank. In this method, a reflux condenser is installed to carry out hydrolysis. This device is shown in FIG. In the figure, 1 is a reaction tank filled with a solution 2 in which titanium tetrachloride, water and a polycarboxylic acid are mixed at a temperature of less than 50 ° C., and a reflux condenser 3 is installed therein. 4 is a stirrer, 5 is a thermometer, 6
Is a device for heating the reaction tank. Although water and hydrogen chloride vapor are generated by the hydrolysis reaction, most of them are condensed by the reflux condenser and returned to the reaction tank, so that hydrogen chloride hardly escapes from the reaction tank.

After the completion of the reaction, the liquid containing the titanium oxide hydrate precipitate is taken out from the reaction tank and filtered through, for example, a known rotary filter. The filter cake obtained by filtration is washed with water and then dried in air at a temperature of about 100 ° C. Drying can also be performed under reduced pressure. The cake after drying or the powder after crushing is then heat treated. By this heat treatment, the specific surface area of the titanium oxide fine particles can be adjusted and the crystallinity and the like can be increased. Since the heat treatment causes the particles to grow larger as the temperature rises, it is necessary to set the average particle diameter in the range of 0.1 to 0.5 μm, and generally 200 to
700 ° C is suitable, and preferably 300 to 500 ° C.
The heat treatment is also effective for desorbing a small amount of hydrogen chloride present in the particles.

The batch type reaction has been described above.
A mixed solution of titanium tetrachloride, water and polycarboxylic acid is continuously charged from the upper part of the reaction tank, and a liquid containing a precipitate is continuously taken out from the lower part of the reaction tank, or the mixed solution is put into the reaction tube. A continuous system in which the reaction is performed by heating while flowing is also possible. The titanium tetraoxide fine particles of the present invention have the above-mentioned average particle diameter and specific surface area, and even when they are heated, they have little cohesiveness, that is, in terms of specific surface area, the degree of decrease is smaller than that of other titanium oxide fine particles. There are few. The reason is that in the hydrolysis method of titanium tetrachloride, a polyvalent carboxylic acid is added under specific conditions to form a hydrate of titanium oxide and a complex compound, and when the complex compound is heat-treated, the surface of the titanium oxide is It is considered that the surface activity is reduced by being involved in the structure and the like.

[0019]

EXAMPLES The present invention will be specifically described below with reference to examples. (Example 1) In a separable flask equipped with a stirrer and a reflux device shown in FIG. 1, 1.25 mol of oxalic acid dihydrate and 1 part of pure water were added.
Charge 000 grams at room temperature to completely dissolve the oxalic acid.
While keeping the temperature of this solution at room temperature, pure water and titanium tetrachloride are added to the solution so that the oxalic acid concentration is 0.25 mol / liter and the titanium tetrachloride concentration is 1.0 mol / liter. . At the end of preparation, the liquid was in a state of no precipitate. Next, this aqueous solution is heated at a temperature rising rate of 5 ° C./min, and after reaching the boiling point (about 104 ° C.), 1
The hydrolysis reaction was carried out completely for a period of time to obtain a precipitate. After cooling, remove the liquid containing the precipitate from the flask,
It filtered using the filter paper with a pore size of 0.1 micrometer. The precipitate on the filter paper was thoroughly washed with water and then dried with a hot air dryer at 105 ° C. Subsequently, the mixture was crushed with a ball mill and heat-treated at 450 ° C. for 1 hour in a muffle furnace in an air atmosphere to obtain titanium oxide fine particles. The specific surface area of the fine particles was 61 m ² / g as measured by the BET method. In addition, as a result of measuring the particle size distribution using the centrifugal sedimentation method, the average particle size is 0.3 μm.
m of fine particles. Further, the titanium oxide fine particles were heat-treated at 800 ° C. for 30 minutes in an air atmosphere using a muffle furnace, and as a result, the specific surface area was 26 m ² / g. When the hot air dried product at 105 ° C. in the middle of the above was crushed by a ball mill and analyzed by X-ray, the diffraction line of FIG. 2 was obtained.

Comparative Example 1 Pure water and oxalic acid dihydrate are charged in a separable flask in the same manner as in Example 1. Then, the solution is heated to raise the temperature of the oxalic acid aqueous solution to 95 ° C. Pure water and titanium tetrachloride were added to this at 1 ml / min. The oxalic acid concentration is adjusted to 0.25 mol / liter and the titanium tetrachloride concentration is adjusted to 1.0 mol / liter.
During this time, the separable flask is heated to raise the temperature of the aqueous solution to 9
Maintain at 5 ° C. A white precipitate was partially seen in the liquid at the end of adjustment. Next, this aqueous solution was heated at a temperature rising rate of 5 ° C./min, and after reaching the boiling point (about 104 ° C.), it was held for 1 hour to carry out the hydrolysis reaction completely to obtain a precipitate. Thereafter, as in Example 1, filtration, drying, crushing, heat treatment at 450 ° C., and heat treatment at 800 ° C. were performed. This 45
The specific surface area of the titanium oxide fine particles heat-treated at 0 ° C. by the BET method was 150 m ² / g, and the average particle diameter was 1.0 μm when the particle size was measured by the centrifugal sedimentation method. Also 80
The specific surface area of the product heat-treated at 0 ° C. was 4 m ² / g. When the hot air dried product at 105 ° C. in the middle of the above was dried by a ball mill and analyzed by X-ray, the diffraction line of FIG. 3 was obtained.

(Example 2) In Example 1, in the mixed solution of water, titanium tetrachloride and oxalic acid dihydrate, the concentration of oxalic acid dihydrate was 0.5 mol / l, and the mixed solution was adjusted. Titanium oxide fine particles were obtained in the same manner as in Example 1 except that the temperature was 45 ° C. The specific surface area of the obtained titanium oxide fine particles was 87 m ² / g, and the average particle diameter was 0.2 μm.
Further, as a result of similarly performing heat treatment at 800 ° C. for 30 minutes, the specific surface area was 20 m ² / g.

Example 3 Example 1 was repeated except that citric acid hydrate was used in place of oxalic acid dihydrate and the concentration of the mixed solution was 0.25 mol / liter.
Titanium oxide fine particles were obtained in the same manner as in. The specific surface area of the obtained titanium oxide fine particles was 88 m ² / g, and the average particle diameter was 0.2 μm. Similarly, as a result of heat treatment at 800 ° C. for 30 minutes, the specific surface area was 15 m ² / g.

(Example 4) The same as Example 1 except that malic acid was used in place of oxalic acid dihydrate and the concentration thereof in the mixed solution was 0.025 mol / liter. Thus, titanium oxide fine particles were obtained. The obtained titanium oxide fine particles had a specific surface area of 97 m ² / g and an average particle diameter of 0.1.
It was 15 μm. Similarly, as a result of heat treatment at 800 ° C. for 30 minutes, the specific surface area was 14 m ² / g.

(Example 5) In Example 1, adipic acid was used in place of oxalic acid dihydrate, and the concentration thereof in the mixed solution was 0.25 mol / liter, but the temperature was adjusted to 40 at the time of adjusting the mixed solution. Titanium oxide fine particles were obtained in the same manner as in Example 1 except that the temperature was changed to ° C. The specific surface area of the obtained titanium oxide fine particles was 90 m ² / g, and the average particle diameter was 0.2 μm. Similarly, as a result of heat treatment at 800 ° C. for 30 minutes,
The specific surface area was 12 m ² / g.

Comparative Example 2 Titanium oxide fine particles were obtained in the same manner as in Example 1 except that oxalic acid dihydrate was not used. Although the specific surface area of the obtained titanium oxide fine particles was 45 m ² / g and the average particle diameter was 0.35 μm, the specific surface area was 2 m ² / g as a result of heat treatment at 800 ° C. for 30 minutes in the same manner. As shown in Comparative Example 2, the titanium oxide fine particles produced without using the polycarboxylic acid have a small specific surface area, and when heat-treated at 800 ° C., the specific surface area significantly decreases. The main reason for this is that the particles were aggregated by heat treatment. The titanium oxide fine particles of Comparative Example 1 have almost no difference in average particle diameter and specific surface area from those of the present invention when heat-treated at 450 ° C., but when heat-treated at 800 ° C., the degree of decrease in specific surface area becomes larger than that of the present invention. This indicates that the agglomeration of particles by heat treatment at 800 ° C. is larger than that of the present invention.

[0026]

The titanium oxide fine particles of the present invention have a considerably small average particle diameter and a large specific surface area. Nevertheless, there is little aggregation during heating. Therefore, it is particularly suitable as a sintering material. Further, since it has good dispersibility, it can be used not only for sintered materials but also for plastic additives, paints, inks, cosmetic materials, deodorants and the like. A reflux condenser is installed in the hydrolysis reaction of titanium tetrachloride of the present invention, and since hydrogen chloride generated does not go out of the reaction tank, a hydrogen chloride gas collector is not required,
It is also advantageous in terms of equipment.

[Brief description of drawings]

FIG. 1 is a schematic sectional view of a reaction tank used in the method of the present invention.

FIG. 2 is an X-ray analysis diagram of 105 ° C. hot air dried product of the reaction product of the present invention.

FIG. 3 is an X-ray analysis diagram of a 105 ° C. hot-air dried product of the reaction product in Comparative Example 1.

[Explanation of symbols]

 1 Reaction Tank 2 Aqueous Solution Containing Titanium Tetrachloride and Polycarboxylic Acid 3 Reflux Cooler 4 Stirrer 5 Thermometer 6 Heating Device

Claims (8)

[Claims] 1. Titanium oxide fine particles having an average particle diameter of 0.1 to 0.5 μm and a specific surface area of 40 to 95 m ² / g,
Titanium oxide fine particles having a specific surface area of 10 to 30 m ² / g when the fine particles are heated to 800 ° C. for 30 minutes. 2. The titanium oxide fine particles according to claim 1, which are for a sintering material. 3. A method for producing fine particles of titanium oxide by hydrolysis of an aqueous solution of titanium tetrachloride, wherein titanium tetrachloride, water and a polycarboxylic acid are mixed at a temperature of less than 50 ° C., and then the mixed solution is heated to hydrolyze. A method for producing titanium oxide fine particles, which comprises performing a decomposition reaction to generate titanium oxide. 4. The method for producing titanium oxide fine particles according to claim 3, wherein the heating temperature for the hydrolysis is in the range of 60 ° C. to the boiling point of the mixed solution. 5. The concentration of titanium tetrachloride in the mixed solution of titanium tetrachloride, water and polyvalent carboxylic acid is 0.1 mol / liter to 2 mol / liter, and the concentration of polyvalent carboxylic acid is 0.0.
The method for producing titanium oxide fine particles according to claim 3 or 4, wherein the amount is 25 mol / liter to 0.5 mol / liter. 6. The method for producing titanium oxide fine particles according to claim 3, wherein the hydrolysis is carried out while suppressing the escape of hydrogen chloride generated by the hydrolysis from the reaction tank. 7. The method for producing titanium oxide fine particles according to claim 6, wherein a reflux condenser is installed in the hydrolysis reaction tank to suppress the escape of hydrogen chloride generated from the reaction tank. 8. A method for producing titanium oxide fine particles, which comprises heat-treating the fine powder obtained by any one of claims 3 to 7 at 300 to 500 ° C.