JP3656355B2 - Fine particle titanium oxide powder with low chlorine content and process for producing the same - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a fine particle titanium oxide (TiO ₂ ) powder and a method for producing the same, and more specifically, is a fine particle titanium oxide powder obtained by a vapor phase method using titanium tetrachloride as a raw material, and a perovskite compound containing TiO ₂ . The present invention relates to a fine titanium oxide powder having a low chlorine content suitable for production and a production method thereof.
[0002]
[Prior art]
The production methods of 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, titanium oxide powder produced by the vapor phase method has few of these drawbacks, but has the 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]
[Problems to be solved by the invention]
Titanium oxide powder is used in cosmetics, pigments, resin fillers, dielectric materials, and the like, and recently has attracted attention as a high-performance dielectric material.
As a dielectric, for example, BaTiO ₃ is obtained by the following reaction under heating.
BaCO ₃ + TiO ₂ → BaTiO ₃ + CO ₂
In order to improve the dielectric properties of BaTiO ₃ , it is first necessary to make BaTiO ₃ particles fine. The above reaction is a solid-phase reaction, and at that time, BaCO ₃ is first decomposed at a high temperature to produce BaO, and BaO is said to diffuse and dissolve in TiO ₂ particles to become BaTiO ₃ . Accordingly, the size of the BaTiO ₃ particles is governed by the size of the TiO ₂ particles.
[0004]
Chlorine contained in the TiO ₂ particles is adsorbed on the very surface layer of the particles and reacts with BaO generated during heating to produce BaCl ₂ . The BaCl ₂ melts and acts as a flux, causing aggregation of TiO ₂ particles and BaTiO ₃ particles. Also, the melted flux is likely to be localized, and the localized portion is more agglomerated, resulting in variations in quality with other portions. Further, when the particles are aggregated, crystals of BaTiO ₃ particles grow to become abnormal particles, and the dielectric properties of BaTiO ₃ are lowered.
Furthermore the presence of chlorine in the TiO ₂ causes that Kuruwasu the BaO and TiO ₂ in the raw material composition ratio. In high-performance dielectrics, the BaO to TiO ₂ ratio must be strictly controlled to 1: 1. However, when chlorine is present, a portion of BaO becomes BaCl ₂ , resulting in a deviation in the composition ratio. Leading to a decline.
[0005]
As a result of studying the existence form and amount of chlorine contained in the titanium oxide powder by the vapor phase method, the present inventor has found the following.
Chlorine is adsorbed on the surface layer of the titanium oxide particles, and therefore there is a strong correlation between the specific surface area of the powder and the chlorine content.
The correlation diagram is shown in FIG. In FIG. 1, the abscissa indicates the specific surface area α (m ² / g) of the powder, the ordinate indicates the chlorine content X (ppm) of the powder, and the ordinate indicates a logarithmic scale.
[0006]
In general, a heating method is used for the desorption of chlorine. However, when heated at a very high temperature, TiO ₂ particles grow, so the heating temperature is limited, and simply heating in the atmosphere within that temperature range. The chlorine content cannot be lowered sufficiently, and therefore, the vapor phase TiO ₂ powder is used while containing chlorine to some extent.
An object of the present invention is to reduce the chlorine content particularly in fine titanium oxide powders produced by a gas phase method with high purity and less particle aggregation. Yet another object is to obtain a powder having a fine particle size and a sharp particle size distribution.
[0007]
[Means for Solving the Problems]
As a result of various studies on the reduction of the chlorine content of the titanium oxide particles, the present inventor obtained fine titanium oxide powder having a lower chlorine content than the conventional one in the correlation between the specific surface area of the powder and the chlorine content. It has been successful.
That is, according to the present invention, when the specific surface area of the powder measured by the BET method is α (m ² / g) and the chlorine content is X (ppm), the chlorine content X is X = 35E0.02α. It is a fine particle titanium oxide powder with a low chlorine content obtained by a vapor phase method characterized by being lower than the indicated numerical value.
[0008]
Further, the invention of the method includes a first step of producing a crude titanium oxide powder by high-temperature oxidation of titanium tetrachloride using oxygen, water vapor, or a mixed gas thereof, and the powder in a cylindrical rotary heating furnace. This is a method for producing fine titanium oxide powder having a low chlorine content, comprising the second step of dechlorination while rolling.
Further, in the second step of the production method, the chlorine content is made lower than the value of X represented by the above relational formula by bringing the powder into contact with water vapor. .
[0009]
DETAILED DESCRIPTION OF THE INVENTION
As shown in FIG. 1, the chlorine content of the TiO ₂ powder by the vapor phase method using titanium tetrachloride as a raw material has a correlation with the size of the TiO ₂ particles, and the finer the particles, the higher the chlorine content. The chlorine content X (ppm) of the conventional TiO ₂ powder was higher than the value represented by the formula X = 35E0.02α (straight line in FIG. 1) in FIG. 1 (white circles in FIG. 1). Here, α is the specific surface area (m ² / g) of the TiO ₂ powder. The fine 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, the chlorine content is lower than the amount represented by X = 30E0.02α. The specific surface area α is preferably 5 (m ² / g) or more.
[0010]
As described above, the chlorine content increases as the TiO ₂ particles become finer. However, when used as a dielectric material, the finer the particles, the better the particles are generally fine. Preferably, D ₉₀ is 2 μm or less, ie, 90% (weight) or more of the powder. Is 0.2 μm or less.
The particles in the powder should have the same size as possible. In the present invention, this is defined by the distribution constant (n) representing the uniformity of the particle size using the Rosin-Ramler equation known as the equation for the particle size distribution of the powder.
Rosin-Rammler type (literature name: ceramic engineering handbook (edited by the Ceramic Society of Japan, 1st edition, pages 596 to 598) is described.)
R = 100exp (−bD ⁿ ) (1)
Here, R is the percentage of particles larger than D (particle size).
If b = 1 / De ⁿ , the equation (1) is R = 100exp {(D / De) ⁿ } (2)
Here, De is a particle size characteristic number, and n is a constant called a distribution constant.
From the equation (1), log {log (100 / R)} = nlogD + C (3)
C = loglog-nlogDe
[0011]
From the equation (3), when the relationship is plotted on a Rosin-Rammler diagram with log D on the x-axis and log {log (100 / R)} on the y-axis, a straight line is obtained. The gradient n represents the uniformity of the particle size, and the uniformity increases as n increases. Since R = 36.8% when D = De, De can be obtained by reading the particle size of R = 36.8% in the figure.
In the fine particle titanium oxide powder of the present invention, when the particle diameter D is plotted on the above diagram, the value of n is preferably 1.5 or more.
[0012]
Next, the invention of the manufacturing method will be described.
The production method of crude titanium oxide powder before reducing 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 water vapor. It is. To Normal TiCl ₄ 1 mole (in the case of H ₂ O O ₂ conversion in H ₂ O) O ₂ is used about 1.0 to 10 mol. The apparatus is generally a reaction tube made of quartz glass or the like.
The titanium oxide powder obtained by this method usually contains about 0.1 to 2% by weight of chlorine, and the amount is finer as the particle size is finer. 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 particle coarsening due to the growth of powder particles.
[0013]
However, according to the study of the present inventor, simply heating the coarse powder does not sufficiently reduce the chlorine content in the powder. Therefore, in the conventional commercial product, the X = 35E0.02α line as shown in FIG. It was on.
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 furnace in the second step.
By dechlorinating while rolling, the dechlorination rate is considerably higher than dechlorination in a stationary state. For example, a titanium cylindrical rotary furnace is used as the dechlorination apparatus. If the temperature of dechlorination is too high, crystal growth occurs, and if it is low, the efficiency of dechlorination decreases, so the range of 150 to 650 ° C. is preferable. A suitable heating time is a residence time in the rotary furnace of 0.1 to 3 hours.
[0014]
The atmosphere of the rotary heating furnace may be in the air, which also reduces the chlorine content, but in order to increase the effect of reducing chlorine, it is better to inject water vapor, especially lower than the above formula X = 35E0.02α In order to obtain a chlorine content, it is necessary to blow water vapor into the heating furnace to bring TiO ₂ and H ₂ O into contact with each other. In the case of mixing air and water vapor, it is preferable to contain 0.1% by volume or more of water vapor. The reactivity of surface adsorbed chlorine with oxygen is higher with oxygen. For this reason, it is thought that efficient dechlorination advances by making water vapor contact titanium oxide powder particles.
[0015]
【Example】
Hereinafter, the present invention will be specifically described with reference to examples. However, 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 11.3 Nm ³ / hr were each preheated to 1000 ° C. and continuously introduced into a quartz glass reactor. After the obtained reaction mixture was rapidly cooled, 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 a residual chlorine of 0.1% (% by weight, the same applies hereinafter).
[0016]
(2) Crude titanium oxide II A mixture of gaseous titanium tetrachloride 5.9 Nm ³ / hr, oxygen 5.2 Nm ³ / hr and water vapor 7.9 Nm ³ / hr was preheated to 900 ° C., respectively, and continuously quartz It was introduced into a glass reactor. The obtained reaction mixture was rapidly cooled, and then the powder was collected with a Teflon bag filter to obtain finely divided 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%.
[0017]
(3) Crude titanium oxide III
A gaseous mixture of gaseous titanium tetrachloride 5.9 Nm ³ / hr, oxygen 2.2 Nm ³ / hr and water vapor 10.3 Nm ³ / hr was preheated to 900 ° C. and continuously introduced into a quartz glass reactor. . The obtained reaction mixture was rapidly cooled, and then the powder was collected with a Teflon bag filter to obtain finely divided 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%.
[0018]
Example 1
Crude titanium oxide I was fed at 30 kg / hr to an externally heated titanium rotary furnace (diameter 200 mm, length 1500 mm, rotation speed 3 rpm). Steam was introduced into the furnace at 1.0 Nm ³ / hr. The maximum temperature zone in the furnace was set to 600 ° C., and the powder was retained in the furnace for 1 hour for 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 3.1 (m ² / g) of the specific surface area α into X = 35E0.02α to obtain X (40 ppm), and the chlorine content of the titanium oxide of Example 1 is given by the above formula. It is lower than the amount expressed.
The particle size distribution D ₉₀ (hereinafter simply referred to as “D _90” ) of the powder by the laser diffraction particle size distribution measurement method (measurement procedure is as follows) is 1.5 μm, and in the RR-diagram (Rosin-Rammler diagram) The n value (hereinafter simply referred to as “n value”) was 2.5.
In the particle size distribution measurement procedure, 0.05 g of pure water and 100 μl of 10% sodium hexametaphosphate aqueous solution are added to 0.05 g of titanium oxide, and ultrasonic irradiation (46 KHz, 65 W) is performed for 3 minutes. This slurry was applied to a laser diffraction particle size distribution measuring device (SALD-2000J, manufactured by Shimadzu Corporation).
The three-point data D ₁₀ , D ₅₀ , and D ₉₀ obtained by laser diffraction are plotted as R = 90%, R = 50%, and R = 10% in the Rosin-Rammler diagram, respectively. A straight line passing through these points is drawn, and the n value is obtained therefrom.
[0019]
Example 2
Crude titanium oxide II was fed to the same rotary furnace as in Example 1 at 20 kg / hr. Dechlorination treatment was performed in the same manner as in Example 1 except that the maximum temperature zone in the furnace was 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. Assuming that α of X = 35E0.02α is 27, X is 121, and the measured chlorine content of the powder is lower than the value of the above formula.
The D ₉₀ is 0.7 [mu] m, n value was 3.5.
[0020]
Example 3
Crude titanium oxide III was fed to the same rotary furnace as in Example 1 at 20 kg / hr. Dechlorination was performed in the same manner as in Example 1 except that the maximum temperature zone in the furnace was 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. When α of X = 35E0.02α is 99, X is 3300, and the measured chlorine content of the powder is lower than the value of the above formula.
The D ₉₀ is 1.3 .mu.m, n value was 2.4.
[0021]
Example 4
The crude titanium oxide II was dechlorinated in the same manner as in Example 2 except that steam was not introduced into the rotary furnace and the atmosphere was in the atmosphere. 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 water vapor was introduced. From this, X is found to be 121 according to X = 35E0.02α, and the actually measured value is slightly higher.
Incidentally, D ₉₀ is 0.9 .mu.m, n value was 3.1.
[0022]
Comparative Example 1
2 kg of crude titanium oxide II was spread on a titanium vat with a powder thickness of 30 mm. When this was put into an electric furnace and dechlorinated at 550 ° C. for 3 hours, the specific surface area was 26 m ² / g and the residual chlorine was reduced to 380 ppm. When X is 35 with α of X = 35E0.02α being 26, 115 is obtained. Therefore, the residual chlorine is much higher than the value of the above formula.
Further, D ₉₀ is 1.3 .mu.m, n value was 2.8.
[0023]
Comparative Example 2
Analysis of Nippon Aerosil Co., Ltd. ultrafine titanium oxide P-25 revealed that it had a specific surface area of 48 m ² / g and contained 820 ppm of chlorine. When X is calculated from X = 35E0.02α, it is 319, and the residual chlorine is considerably higher than the value of the above formula.
Further, D ₉₀ is 3.1 .mu.m, n value was 1.4.
[0024]
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 chlorine was contained at 60 ppm. When X is calculated from X = 35E0.02α, it becomes 39, and the residual chlorine is higher than the value of the above formula.
Further, D ₉₀ is 3.2 .mu.m, n value was 1.7.
[0025]
【The invention's effect】
According to the present invention, an unprecedented fine powder of a low chlorine content, which is a titanium oxide of a vapor phase method, is obtained. This powder is particularly useful as a raw material for high-performance perovskite compounds containing TiO ₂ as a component.
Moreover, since the particle size is uniform, that is, the particle size distribution is sharp and fine particles can be obtained, it is also 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 the chlorine content.

Claims (15)

When the specific surface area of the powder measured by the BET method is α (m ² / g) and the chlorine content is X (ppm), the chlorine content X is lower than the numerical value represented by the relational expression X = 35E0.02α. A fine titanium oxide powder having a low chlorine content obtained by a vapor phase method. The fine particle titanium oxide powder having a low chlorine content according to claim 1, wherein α is 3.1 or more. The fine particle titanium oxide powder having a low chlorine content according to claim 1, wherein α is 27 or more. The fine titanium oxide powder having a low chlorine content according to claim 1, wherein α is 99 or more. The fine particle titanium oxide powder according to any one of claims 1 to 4 , wherein D ₉₀ is 2 µm or less in a particle size distribution curve measured by a laser diffraction particle size distribution measurement method. The fine particle titanium oxide powder according to any one of claims 1 to 5 , wherein an n value in a rosin-Rammler formula representing a particle size distribution is 1.5 or more. The fine particle titanium oxide powder according to any one of claims 1 to 6, which is used for producing a perovskite compound. A first step of producing crude titanium oxide powder by high-temperature oxidation of titanium tetrachloride using oxygen, water vapor, or a mixed gas thereof, and dechlorination while rolling the powder in a cylindrical rotary furnace preparation of small microparticles of titanium oxide powder chlorine content and a second step of performing. The method for producing fine particle titanium oxide powder according to claim 8 , wherein in the second step of dechlorination, the chlorine content is adjusted to the amount described in claim 1 by bringing water vapor into contact with the powder. The method for producing a fine particle titanium oxide powder according to claim 8 or 9, wherein the temperature of the highest heating zone of the powder in the second step is 150 ° C or higher and 650 ° C or lower. The method for producing a fine particle titanium oxide powder having a low chlorine content according to any one of claims 8 to 10, wherein the first step is an oxidation reaction at 300 to 1600 ° C. The first step is TiCl _Four For 1 mole, O ₂ (H ₂ H for O ₂
O in O ₂ The method for producing finely divided titanium oxide powder having a low chlorine content according to any one of claims 8 to 11, wherein the conversion is a reaction using 1.0 to 10 mol. The method for producing a fine titanium oxide powder having a low chlorine content according to any one of claims 8 to 12, wherein the cylindrical rotary heating furnace is made of titanium. The method for producing a fine particle titanium oxide powder according to any one of claims 8 to 13, wherein the residence time of the powder in the second step is 0.1 to 3 hours. The method for producing fine-particle titanium oxide powder according to any one of claims 9 to 14, wherein a ratio of water vapor is 0.1% by volume or more.

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