JPH10251021A - Superfine titanium oxide powder small in chlorine content and its production - Google Patents

Abstract

PROBLEM TO BE SOLVED: To produce a superfine titanium oxide powder small in chlorine content and suitable as a producing raw material of a dielectric such as BaTiO3 . SOLUTION: This superfine titanium oxide powder is produced by a vapor phase method and has X lower than a value expressed by an equation, X=35E0.02α, when the specific surface area of powder measured by BET method is expressed by α(m<2> /g) and the chlorine content is expressed by X(ppm). The producing method of the titanium oxide powder is by oxidizing titanium tetrachloride with oxygen, steam or the gaseous mixture at a high temp. to produce a crude titanium oxide powder and dechlorinating the powder while rolling in a cylindrical rotary heating furnace preferably with steam blown by controlling the temp. of the max. heated area of the powder to 150-650 deg.C.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION The present invention is fine particles of titanium dioxide (TiO ₂₎ relates to powder and its manufacturing method, and more particularly to a titanium tetrachloride as a raw material, a fine titanium oxide powder obtained by the gas phase method, The present invention relates to a fine titanium oxide powder having a low chlorine content suitable for producing a TiO ₂ -containing perovskite compound and a method for producing the same.

[0002]

2. Description of the Related Art Methods for producing titanium oxide powder are roughly classified into a gas phase method in which titanium tetrachloride is reacted with oxygen or water vapor at a high temperature, and a liquid phase method in which titanium tetrachloride or titanium sulfate is hydrolyzed. The titanium oxide powder produced by the liquid phase method is good in that it can be produced under relatively mild conditions, but has disadvantages such as poor purity and easy aggregation of particles. On the other hand, the titanium oxide powder produced by the gas phase method has few of these disadvantages, but has a disadvantage that chlorine is contained in the powder because titanium tetrachloride is used as a raw material. In particular, the finer the powder particles, the higher the chlorine content.

[0003]

Titanium oxide powder is used for cosmetics, pigments, fillers for resins, raw materials for dielectrics, and the like. Recently, however, it has been particularly noted as a high-performance dielectric raw material. As a dielectric, for example, BaTiO ₃ is obtained by the following reaction under heating. BaCO ₃ + TiO ₂ → BaTiO ₃ + C
In order to enhance the dielectric properties of O ₂ BaTiO ₃ ,
It is necessary to make the TiO ₃ particles fine. It is said that the above reaction is a solid-phase reaction, in which BaCO ₃ is firstly decomposed at a high temperature to produce BaO, and BaO is diffused and dissolved in TiO ₂ particles to form BaTiO ₃ . Therefore B
The size of the aTiO ₃ particles is governed by the size of the TiO ₂ particles.

[0006] Chlorine contained in TiO ₂ particles is present by being adsorbed on a very surface layer of the particles.
Reacts with O to produce BaCl ₂ . This BaCl ₂ melts and acts as a flux, and TiO ₂ particles and BaT
Causes agglomeration of iO ₃ particles. Further, the molten flux is likely to be localized, and the localized portion has a large amount of agglomeration, resulting in a variation in quality between other portions. When the particles aggregate, crystals of BaTiO ₃ particles grow and become abnormal particles, which lowers the dielectric properties of BaTiO ₃ . Furthermore, the presence of chlorine in TiO ₂ is due to BaO and Ti
This causes the raw material composition ratio of O ₂ to change. In a high-performance dielectric, the ratio of BaO to TiO ₂ must be strictly controlled to 1: 1.
Since it becomes aCl ₂ , a shift occurs in the composition ratio, which leads to quality deterioration.

The present inventor has studied the existence form and amount of chlorine contained in titanium oxide powder by a gas phase method, and has found the following. Chlorine is adsorbed on the surface layer of the titanium oxide particles, and therefore has a strong correlation between the specific surface area of the powder and the chlorine content. FIG. 1 shows the correlation diagram. In FIG. 1, when the horizontal axis is the specific surface area α (m ² / g) of the powder, the vertical axis is the chlorine content X (ppm) of the powder, and the vertical axis is a logarithmic scale, it has a substantially linear relationship.

A heating method is generally used for desorption of chlorine. However, heating at an excessively high temperature causes TiO ₂ particles to grow, so that the heating temperature is limited. It is not possible to sufficiently reduce the chlorine content by just doing so, and at present, the vapor phase TiO ₂ powder is used while containing chlorine to some extent. SUMMARY OF THE INVENTION An object of the present invention is to reduce the content of chlorine, particularly, in a fine particle titanium oxide powder obtained by a gas phase method with high purity and less aggregation of particles. Still another object is to obtain a powder having a fine particle size and a sharp particle size distribution.

[0007]

As a result of various studies on the reduction of the chlorine content of titanium oxide particles, the present inventor found that the correlation between the specific surface area of the powder and the chlorine content was lower than that of the conventional powder. It succeeded in obtaining a fine amount of fine titanium oxide powder. That is, the present invention is a BET
When the specific surface area of the powder measured by the method is α (m ² / g) and the chlorine content is X (ppm), the chlorine content X is X
= 35E0.02α, which is a fine particle titanium oxide powder having a low chlorine content obtained by a gas phase method, which is lower than the numerical value represented by the relational expression: 35E0.02α.

Further, the invention of the method comprises a first step of producing a coarse titanium oxide powder by oxidizing titanium tetrachloride at a high temperature using oxygen or steam or a mixed gas thereof,
A second step of dechlorinating the powder while tumbling the powder in a cylindrical rotary heating furnace to produce a fine titanium oxide powder having a low chlorine content. Further, in the second step of the production method, a fine particle titanium oxide powder is produced, wherein the chlorine content is made lower than the value of X represented by the above relational expression by bringing water vapor into contact with the powder. .

[0009]

BEST MODE FOR CARRYING OUT THE INVENTION The chlorine content of TiO ₂ powder obtained by a gas phase method using titanium tetrachloride as a raw material is shown in FIG.
There is a correlation with the size of the iO ₂ particles, and the finer the particles, the higher the chlorine content. Then, the chlorine content X (ppm) of the conventional TiO ₂ powder is calculated by the equation X = 35E0.02α in FIG.
It was higher than the value represented by (the straight line in FIG. 1) (open circles in FIG. 1). Here, α is the specific surface area (m ² / g) of the TiO ₂ powder. The particulate titanium oxide powder of the present invention has a chlorine content lower than the value of X represented by the above formula (black circles in FIG. 1). More preferably, X = 30E0.0
The chlorine content is lower than the amount represented by 2α. The specific surface area α is preferably 5 (m ² / g) or more.

As described above, the chlorine content increases as the TiO ₂ particles become finer, but when used as a dielectric material,
Other general particles finer moderately, preferably D ₉₀ of 2
μm or less, that is, 90% (weight) or more of the powder is 0.2 μm
It is as follows. The particles in the powder are preferably as uniform as possible. The present invention discloses that this is known as Rosin-Rammler (Rosi
The distribution constant (n) representing the uniformity of the particle size is determined using the (n-Rammler) equation. Rosin-Rammler formula (Literature: Ceramic Engineering Handbook (edited by The Ceramic Society of Japan, 1st Edition, pp. 596-59)
8) described. R = 100 exp (−bD ⁿ ) (1) where R is the percentage of particles larger than D (particle size).
b = 1 / De ⁿ and put the (1) formula R = 100exp {(D / De ) n} (2) where De is the number of particle size characteristics, n represents a constant called the distributed constant. From equation (1), log {log (100 / R)} = nlogD + C (3) C = loglog−nlogDe

From equation (3), logD is on the x-axis and logD is on the y-axis.
Rosin with g {log (100 / R)} scale
Plotting their relationship on a Ramler diagram results in a straight line. The gradient n indicates the uniformity of the particle size, and the greater the n, the greater the uniformity. When D = De, R = 36.8%
Therefore, if the particle diameter of R = 36.8% is read on the figure, D
e is required. In the particulate titanium oxide powder of the present invention, when the particle diameter D is plotted on the above-mentioned diagram, the value of n is preferably 1.5 or more.

Next, the invention of the manufacturing method will be described. The method for producing crude titanium oxide powder before the reduction of chlorine (first step) is basically a known so-called gas phase method in which titanium tetrachloride is oxidized at a high temperature of about 300 to 1600 ° C. using oxygen or steam. It is. To Normal TiCl ₄ 1 _{mole, O 2 (H 2 O O} 2 conversion in H ₂ O in the case of) one.
About 0 to 10 mol is used. In general, a reaction tube made of quartz glass or the like is used for the apparatus. The titanium oxide powder obtained by this method usually contains about 0.1 to 2% by weight of chlorine, and the amount thereof is larger as the particle size is smaller. This crude titanium oxide powder is dechlorinated. The method is generally a method of heat-treating the powder at about 200 to 700 ° C. in the atmosphere. The upper limit of the temperature is limited in order to prevent coarsening of particles due to growth of powder particles.

However, according to the study of the present inventor, simply heating the coarse powder does not sufficiently lower the chlorine content in the powder. Therefore, as shown in FIG.
Above the 35E0.02α line. The production method of the present invention is characterized in that the crude titanium oxide powder is dechlorinated while being rolled in a cylindrical rotary heating furnace in a second step. Dechlorination while rolling makes the dechlorination rate considerably higher than dechlorination at rest. As the dechlorination apparatus, for example, a titanium cylindrical rotary furnace is used. If the temperature of dechlorination is too high, crystal growth occurs, and if the temperature is low, the efficiency of dechlorination decreases, so the range of 150 to 650 ° C is preferable. The heating time is the residence time of 0.1 to 3 in the rotary furnace.
Time is appropriate.

The atmosphere of the rotary heating furnace may be air,
Although the chlorine content is considerably lowered by this, it is preferable to blow steam in order to enhance the effect of chlorine reduction. It is necessary to blow water vapor to bring TiO ₂ and H ₂ O into contact. In the case of mixing air and steam, it is preferable to contain steam at 0.1 volume% or more. The reactivity of chlorine with surface adsorption is higher in water than in oxygen. For this reason, it is considered that efficient dechlorination proceeds by bringing the water vapor into contact with the titanium oxide powder particles.

[0015]

EXAMPLES The present invention will be described in detail below with reference to examples, but the present invention is not limited to the examples. First, crude titanium oxide was produced by the following method. (1) Crude titanium oxide I Gaseous titanium tetrachloride 8.9 Nm ³ / hr and oxygen
³ Nm ³ / hr was preheated to 1000 ° C. and continuously introduced into a quartz glass reactor. After rapidly cooling the obtained reaction mixture, the powder was collected with a Teflon bag filter to obtain fine particle titanium oxide at 30 kg / hr. This titanium oxide had a specific surface area of 3.2 m ² / g, a rutile ratio of 97%, and residual chlorine of 0.1% (% by weight, the same applies hereinafter).

(2) Crude titanium oxide II Gaseous titanium tetrachloride 5.9 Nm ³ / hr, oxygen 5.2
Nm ³ / hr and steam 7.9 nm ³ / hr the mixture gas was preheated to 900 ° C., respectively, were continuously introduced into a quartz glass reactor. After rapidly cooling the obtained reaction mixture, the powder was collected with a Teflon bag filter to obtain fine particle titanium oxide at 20 kg / hr. This titanium oxide had a specific surface area of 28 m ² / g, a rutile ratio of 32%, and a residual chlorine of 1.2%.

(3) Crude titanium oxide III Gaseous titanium tetrachloride 5.9 Nm ³ / hr, oxygen 2.2
Nm ³ / hr and steam 10.3 nm ³ / hr the mixture gas was preheated to 900 ° C., respectively, were continuously introduced into a quartz glass reactor. After rapidly cooling the obtained reaction mixture, the powder was collected with a Teflon bag filter to obtain fine particle titanium oxide at 20 kg / hr. This titanium oxide had a specific surface area of 101 m ² / g, a rutile ratio of 15%, and a residual chlorine of 2.1%.

EXAMPLE 1 A crude titanium oxide I was placed in a titanium external heating rotary furnace (diameter 200 m).
m, length 1500mm, rotation speed 3rpm), 30k
g / hr. 1.0 Nm of steam in the furnace
³ / hr introduced. The maximum temperature zone in the furnace was set to 600 ° C., and the powder was kept in the furnace for 1 hour to perform a dechlorination treatment. As a result, the specific surface area was almost unchanged at 3.1 m ² / g, but the residual chlorine was reduced to 30 ppm. Substituting the value of the specific surface area α of 3.1 (m ² / g) into X = 35E0.02α to obtain X results in 40 (ppm), and the chlorine content of the titanium oxide of Example 1 is calculated by the above equation. It is lower than the amount represented. The particle size distribution D ₉₀ (hereinafter simply abbreviated as D ₉₀ ) of the powder according to a laser diffraction particle size distribution measuring method (measurement procedure is described below) is 1.5 μm, and The n value (hereinafter, simply abbreviated as “n value”) was 2.5. In the particle size distribution measurement procedure, 0.05 cc of titanium oxide, 5.0 cc of pure water and 100 μl of a 10% sodium hexametaphosphate aqueous solution are added, and ultrasonic irradiation (46 KHz, 65 W) is performed for 3 minutes. This slurry is subjected to a laser diffraction particle size distribution analyzer (SA manufactured by Shimadzu Corporation).
LD-2000J). The three-point data, D ₁₀ , D ₅₀ , and D ₉₀ , obtained in the laser diffraction, are respectively represented by R = 90%, R = 50%, and R = in a rosin-Rammler diagram.
Plot as 10%. A straight line passing through these points is drawn, and the n value is determined from this.

EXAMPLE 2 20 kg / h of crude titanium oxide II was placed in the same rotary furnace as in Example 1.
r. Dechlorination was performed in the same manner as in Example 1 except that the maximum temperature zone in the furnace was set to 550 ° C. As a result, the specific surface area was almost unchanged at 27 m ² / g, but the residual chlorine was reduced to 100 ppm. X = 35E0.02
If α of α is 27, X is 121, and the measured chlorine content of the powder is lower than the value of the above equation. Also D
₉₀ was 0.7 μm, and the n value was 3.5.

Example 3 Crude titanium oxide III was placed in the same rotary furnace as in Example 1 at a rate of 20 kg / kg.
hr. Dechlorination was performed in the same manner as in Example 1 except that the maximum temperature zone in the furnace was set to 350 ° C. As a result, the specific surface area was almost unchanged at 99 m ² / g, but the residual chlorine was reduced to 2800 ppm. X = 35E0.
If α of 02α is 99, X is 3300, and the measured chlorine content of the powder is lower than the value of the above equation.
D ₉₀ was 1.3 μm and n value was 2.4.

Example 4 Dechlorination treatment was carried out in the same manner as in Example 2 except that crude titanium oxide II was used in the atmosphere without introducing steam into a rotary furnace. As a result, the specific surface area was almost unchanged at 27 m ² / g, but the residual chlorine was 150 ppm, which was slightly higher than that of Example 2 in which steam was introduced. From this, when X is calculated according to X = 35E0.02α, it becomes 121, and the actually measured value is slightly higher. Incidentally, D ₉₀ is 0.9 .mu.m, n value was 3.1.

Comparative Example 1 2 kg of crude titanium oxide II was placed in a titanium vat with a powder thickness of 3
It was spread at 0 mm. Put this in an electric furnace at 550 ° C,
After dechlorination for 3 hours, the specific surface area was 26 m ² / g.
The residual chlorine was reduced to 380 ppm. X = 35
When X is obtained by setting α of E0.02α to 26, it becomes 115. Therefore, the residual chlorine is much higher than the value of the above equation. D ₉₀ was 1.3 μm and the n value was 2.8.

Comparative Example 2 Ultrafine titanium oxide P-25 from Aerosil Japan
Was analyzed to find that chlorine was reduced to 82 at a specific surface area of 48 m ² / g.
The content was 0 ppm. When X is calculated from X = 35E0.02α, it becomes 319, and the residual chlorine is considerably higher than the value of the above equation. Further, D ₉₀ is 3.1 .mu.m, n value 1.4
Met.

Comparative Example 3 When high-purity titanium oxide manufactured by Toho Titanium Co., Ltd. was analyzed, the specific surface area was 2.2 m ² / g and contained 60 ppm of chlorine. When X is obtained from X = 35E0.02α, 39 is obtained.
And the residual chlorine is higher than the value of the above equation. D ₉₀
Was 3.2 μm, and the n value was 1.7.

[0025]

Industrial Applicability According to the present invention, titanium oxide fine particles having an unprecedented low chlorine content obtained by a gas phase method have been obtained. This powder is particularly useful as a raw material for a high performance perovskite compound containing TiO ₂ as a component. In addition, uniform particle size,
That is, since the particle size distribution is sharp and fine particles can be formed, it is suitable for various uses other than the above compounds.

[Brief description of the drawings]

FIG. 1 is a graph showing the relationship between the particle size of titanium oxide powder and chlorine content.

Claims (7)

[Claims] 1. The specific surface area of a powder measured by the BET method is α
(M ² / g) and when the chlorine content is X (ppm),
The fine particle titanium oxide powder having a low chlorine content obtained by a gas phase method, wherein the chlorine content X is lower than the numerical value represented by the relational expression of X = 35E0.02α. 2. A method for producing a perovskite compound according to claim 1.
The particulate titanium oxide powder as described in the above. 3. The fine particle titanium oxide powder according to claim 1, wherein D ₉₀ is 2 μm or less in a particle size distribution curve measured by a laser diffraction type particle size distribution measuring method. 4. The finely divided titanium oxide powder according to claim 1, wherein an n value in a rosin-Rammler equation representing a particle size distribution is 1.5 or more. 5. A first step of producing titanium oxide powder by high-temperature oxidation of titanium tetrachloride using oxygen, steam, or a mixture thereof, and rolling the powder in a cylindrical rotary heating furnace. And a second step of dechlorination while moving the powder. 6. The chlorine content in the second step of dechlorination by bringing steam into contact with the powder.
The method for producing a fine particle titanium oxide powder according to claim 5, wherein the amount is as described in (1). 7. The method according to claim 5, wherein the temperature of the highest heating zone of the powder in the second step is 150 ° C. or more and 650 ° C. or less.