JP6839442B2 - Aluminum titanate powder and its manufacturing method - Google Patents

Description

The present invention relates to aluminum titanate powder and a method for producing the same.

Aluminum titanate (Al ₂ O ₃ · TiO ₂ or Al ₂ TiO ₅ ) has a high melting point of 1800 ° C. or higher, a low coefficient of thermal expansion, and excellent thermal shock resistance. Utilizing these characteristics, aluminum titanate is used, for example, as a catalyst carrier for exhaust gas treatment of automobiles (Patent Document 1).

Conventionally, aluminum titanate is produced by mixing a powdered titanium source and a powdered aluminum source, compression molding the obtained mixed powder to prepare a molded product, and firing the molded product. There is. The aluminum titanate powder is produced by pulverizing the molded product thus obtained (Patent Document 2).

Patent Document 3 discloses a method of calcining a precursor mixture containing a titanium source powder, an aluminum powder and a silicon source powder, and pulverizing and classifying the precursor mixture to produce an aluminum titanate-based ceramic powder. Patent Document 3 states that an aluminum titanate-based ceramic powder having an average particle size of more than 20 μm was obtained by the production method.

Patent Document 4 describes _{aluminum titanate by pressure-molding a mixture containing Al 2} O ₃ , TiO ₂ , iron oxide and organic powder, and then firing and pulverizing the mixture in a closed container at 1600 ° C to 1700 ° C. A method for producing a powder is disclosed.

Japanese Unexamined Patent Publication No. 8-72038 WO2005 / 105704 WO2010 / 041648 Japanese Unexamined Patent Publication No. 11-60240

In recent years, in order to improve the performance of final products using aluminum titanate powder, aluminum titanate powder having a small particle size and a sharp particle size distribution has been desired.

In the production of aluminum titanate powder, in the method of producing a molded body of aluminum titanate and then crushing the molded body, there is a limit to the minimum particle size that can be reached, and the variation in particle size becomes large, so that the particle size becomes large. There is a problem that the distribution tends to be broad. Further, the manufacturing method of firing at a high temperature exceeding 1600 ° C. as in Patent Document 4 has a problem that the manufacturing cost is high.

An object of the present invention is to provide an aluminum titanate powder having a small particle size and a small variation in particle size, and a method for producing the same.

The features of the aluminum titanate powder of the present invention and the method for producing the same are as follows.
(Item 1)
The cumulative 50% diameter of the volume standard in the laser diffraction / scattering type particle size distribution measurement is 0.5 μm to 4.0 μm, and the coefficient of variation of the particle size distribution is 60% or less.
It is characterized by aluminum titanate powder.
(Item 2)
It has a rounded particle shape in which the ratio (S1 / S2) of the BET specific surface area (S1) to the specific surface area (S2) of the spherical particles having a cumulative diameter of 50% is less than 2.0.
The aluminum titanate powder according to item 1.
(Item 3)
The BET specific surface area ^is 0.3m ² /g~3.0m 2 / g,
The aluminum titanate powder according to item 2.
(Item 4)
Cumulative 99% diameter is less than 10 μm,
The aluminum titanate powder according to any one of items 1 to 3.
(Item 5)
Composition formula: represented by xAl ₂ O ₃ · TiO ₂ (x = 0.7 to 1.2),
The aluminum titanate powder according to any one of items 1 to 4.
(Item 6)
L ^* a ^* b ^{* Brightness L *} in the color system is 90 or more,
The aluminum titanate powder according to any one of items 1 to 5.
(Item 7)
Further containing 3.0 mol% or less (not including 0) magnesium,
The aluminum titanate powder according to any one of items 1 to 6.
(Item 8)
The decomposition rate after heating at 1100 ° C. for 10 hours in the air atmosphere is 1% or less.
Item 7. The aluminum titanate powder according to item 7.
(Item 9)
The method for producing aluminum titanate powder according to any one of items 1 to 8.
Baking boehmite powder coated with titanium compound,
A method for producing aluminum titanate powder.
(Item 10)
The firing temperature is 1300 ° C to 1500 ° C.
The method for producing an aluminum titanate powder according to item 9.
(Item 11)
At least one of the three-dimensional lengths of the major axis, minor axis or thickness of the boehmite powder is less than 0.5 μm.
The method for producing an aluminum titanate powder according to item 9 or 10.
(Item 12)
The titanium compound is produced from titanyl sulfate, titanium tetrachloride or tetraisopropyl orthotitanate.
The method for producing an aluminum titanate powder according to any one of items 9 to 11.
(Item 13)
The blending ratio of the boehmite powder and the titanium compound is adjusted so that the molar ratio of _{Al 2} O ₃ and TiO _{2 (Al 2} O ₃ / TiO ₂ ) is 1.
The method for producing an aluminum titanate powder according to any one of items 9 to 12.
(Item 14)
The boehmite powder contains magnesium,
The method for producing an aluminum titanate powder according to any one of items 9 to 13.

The aluminum titanate powder of the present invention has a small particle size and a sharp particle size distribution.

In the method for producing aluminum titanate powder of the present invention, aluminum titanate powder can be produced from a powdery raw material, and it is not necessary to produce a molded product of aluminum titanate. Therefore, of course, it is not necessary to crush the molded product of aluminum titanate. In the conventional breakdown method in which an aluminum titanate molded product is pulverized to produce a powder, the particle size distribution of the obtained powder tends to be broad, and a classification step is required to sharpen the particle size distribution. There are many. In this respect, the production method of the present invention can obtain a sharp particle size distribution without a classification step. Further, the particle size of the obtained aluminum titanate powder can be easily controlled by changing the particle size of the boehmite powder which is the base material. Further, since the boehmite powder is coated with the titanium compound, the contact area between the aluminum source and the titanium source is increased, and the reaction is facilitated. As a result, it is possible to suppress the residual unreacted raw material and the production ratio of by-products.

Scanning electron microscope (SEM) images of Examples 1, 3 to 5 and Comparative Example 1, (a) is an image having a magnification of 3000 times, and (b) is an image having a magnification of 5000 times.

Hereinafter, the characteristics of the aluminum titanate powder of the present invention will be described first, and then the method for producing the aluminum titanate powder will be described.

<Aluminum titanate powder>
The aluminum titanate powder of the present invention is characterized in that the cumulative 50% diameter (D ₅₀ ) of the volume standard measured by the laser diffraction scattering type particle size distribution measurement is in the range of 0.5 μm to 4.0 μm. .. The upper limit of the cumulative 50% diameter is preferably less than 3.5 μm.

In the aluminum titanate powder of the present invention, the coefficient of variation CV of the particle size distribution obtained by the laser diffraction / scattering type particle size distribution measurement is preferably 60% or less, and more preferably 56% or less. The coefficient of variation CV (%) can be calculated by the following formula 1 from the standard deviation SD (μm) of the particle size distribution and the volume mean diameter MV (μm). Here, the standard deviation SD is a value defined by Equation 2 from the _{cumulative 84% diameter (D 84} ) and the cumulative 16% diameter (D _16). The coefficient of variation is a value representing the relative variation of each particle size with respect to the volume mean diameter, and the smaller the coefficient of variation is, the smaller the variation of each particle size with respect to the volume mean diameter is, and the sharper the particle size distribution is. ..

In the aluminum titanate powder of the present invention, the cumulative 99% diameter (D ₉₉ ) is preferably less than 10 μm, more preferably less than 9.5 μm. The cumulative 90% diameter (D ₉₀ ) is preferably less than 6.0 μm.

The difference (D _99- D ₁₀ ) between the cumulative 99% diameter and the cumulative 10% diameter (D ₁₀ ) is preferably 2 μm to 9 μm. The upper limit of D _99- D ₁₀ is more preferably less than 8.5 μm. The difference between the cumulative 90% diameter and the cumulative 10% diameter (D _90- D ₁₀ ) is preferably 1 μm to 5 μm. It can be said that the smaller D _99- D ₁₀ and D _90- D _{10, the sharper the particle size distribution.}

In the aluminum titanate powder of the present invention, the _{value calculated by (standard deviation SD / cumulative 50% diameter D 50} ) × 100 is preferably 60% or less. It can be said that the smaller this value is, the smaller the variation of each particle size with respect to the cumulative 50% diameter is, and the sharper the particle size distribution is.

The particle shape of the aluminum titanate powder of the present invention is preferably rounded. The aluminum titanate powder of the present invention has an ideal spherical particle having a measured BET specific surface area S1 (m ² / g) and a cumulative 50% diameter (D ₅₀ ) as a diameter (that is, a diameter D ₅₀ ). ^{However, the ratio (S1 / S2) to the specific surface area S2 (m 2} / g) of the particles (particles assumed to have a spherical shape) is preferably greater than 0 and less than 2.0, preferably 0.5 or more. It is more preferably 1.5 or less, and most preferably 1.0. S1 / S2 are parameters for determining whether or not the particle shape is close to a sphere. The closer the specific surface area S1 of the particles actually measured by the BET method is to the specific surface area S2 of the ideal spherical particle (that is, the closer S1 / S2 is to 1.0), the more spherical the particle shape is. It can be said that it is close to.

The specific surface area S2 can be calculated by the following formulas 3 to 5 using the cumulative 50% diameter D ₅₀ (μm) and the density of aluminum titanate (ρ = 3.702 × 10 ⁶ g / m ^3). ..

The BET specific surface area of the aluminum titanate powder of the present invention ^{is preferably 0.3 m 2} / g or more. The upper limit of the BET specific surface area ^{is preferably 3.0 m 2} / g or less, ^{more preferably 2.5 m 2} / g or less, and 2.0 m ² / g or less from the viewpoint of ease of manufacture. It is more preferable to have.

The aluminum titanate powder of the present invention preferably has a composition formula represented by xAl ₂ O ₃ · TiO ₂ (x = 0.7 to 1.2). That is, the ratio _{of Al 2} O ₃ to TiO _{2 in aluminum titanate (Al 2} O ₃ / TiO ₂ ) is preferably 0.7 to 1.2. In the composition formula, x = 0.85 to 1.2 is more preferable, and x = 1 is most preferable.

In the aluminum titanate powder of the present invention, the lightness L ^{* in the L *} a ^* b ^* color system is preferably 90 or more, and more preferably 93 or more. The closer the lightness L ^* is to 0, the closer it is to black, and the closer it is to 100, the closer it is to white. When the lightness L ^{* of the} aluminum titanate powder is 90 or more, the color of the aluminum titanate powder is close to white, and when the final product is produced using the aluminum titanate powder, a final product close to white is obtained. Be done.

In the aluminum titanate powder of the present invention, the color difference ΔE ^{* with} respect to the white calibration plate (L ^* : 96.6, a ^* : -0.1, b ^{* : -0.3) in the L *} a ^* b ^{* color system.} Is preferably 4.0 or less. The color difference ΔE ^* is a value defined by the following equation 6 when the difference in brightness and saturation between the white calibration plate and the aluminum titanate powder is ΔL ^* , Δa ^* , and Δb ^{*. If the color difference ΔE * of the} aluminum titanate powder with respect to the white calibration plate is 4.0 or less, the color of the aluminum titanate powder is close to white, and when the final product is manufactured using the aluminum titanate powder, it is white. A final product close to is obtained.

In the aluminum titanate powder of the present invention, the proportion of by-products contained in the aluminum titanate powder is preferably less than 15%. _{It is known that, for example, Al 2} O ₃ (corundum) and TiO ₂ (rutile) are produced as by-products, although it depends on the raw materials used for the aluminum source and the titanium source.

The aluminum titanate powder of the present invention may contain any other metal element in addition to Al and Ti. Examples of other metal elements include magnesium (Mg). _{Aluminum titanate powder is known to decompose into Al 2} O ₃ (corundum) and TiO ₂ (rutile) when heated at 900 ° C to 1300 ° C, and in particular, it decomposes most when heated at 1100 ° C. It is known to be easy. By adding Mg, the decomposition of aluminum titanate can be suppressed. The amount of Mg is larger than 0 mol%, 3.0 mol% or less, preferably 2.0 mol% or less, and more preferably 0.5 mol% or less. The amount of Mg may be greater than 3.0 mol%, but since Mg affects the physical and chemical properties of the synthesized aluminum titanate, the upper limit of the amount of Mg is the desired physical of aluminum titanate. Determined as appropriate, taking into account properties and chemical properties.

The Mg-containing aluminum titanate powder of the present invention preferably has a decomposition rate of 1% or less after heating at 1100 ° C. for 10 hours in an air atmosphere. Further, the decomposition rate after heating at 1100 ° C. for 100 hours in an atmospheric atmosphere is preferably 4% or less, and more preferably 3.5% or less. The decomposition rate (%) can be calculated from the following formula 7. By suppressing the decomposition of aluminum titanate, the content of by-products is low when the aluminum titanate is reheated to produce a product, such as when a sintered body is produced from aluminum titanate powder. Moreover, it is possible to produce a product in which the physical and chemical properties of aluminum titanate are not impaired.

It is preferable that the aluminum titanate powder of the present invention does not substantially contain silicon (Si). In addition, "substantially free of Si" means that Si is not intentionally added, and it is permissible to contain Si as an unavoidable impurity. Si is usually added to suppress the decomposition of aluminum titanate. However, there is a problem that the addition of Si lowers the fire resistance of aluminum titanate (for example, paragraph 0005 of JP-A-2002-145569). Since the aluminum titanate powder of the present invention does not substantially contain Si, the decrease in fire resistance due to the addition of Si does not occur.

<Manufacturing method of aluminum titanate powder>
Next, the method for producing the aluminum titanate powder of the present invention will be described. The production method of the present invention is characterized in that an aluminum titanate powder is produced by using a powdery raw material without producing a molded product of aluminum titanate. More specifically, the production method of the present invention is characterized in that aluminum titanate powder is produced by firing an aluminum source powder coated with a titanium source.

Boehmite (Al ₂ O ₃ · H ₂ O) powder is preferably used as the aluminum source powder. As the aluminum source powder, transition alumina powder or the like can be used in addition to boehmite powder.

The particle shape of the boehmite powder is not particularly limited, and for example, needle-shaped boehmite, scaly boehmite, cubic boehmite, and the like can be used, and two or more kinds of boehmite powders having different shapes can be mixed and used.

The length of at least one side of the boehmite particles is preferably less than 0.5 μm. For example, in the case of needle-shaped boehmite, the major axis is less than 0.5 μm (in this case, the minor axis is naturally less than 0.5 μm), or the major axis is 0.5 μm or more and the minor axis is less than 0.5 μm. Is preferable. In the case of scaly boehmite, it is preferable that the major axis is less than 0.5 μm (in this case, the thickness is naturally less than 0.5 μm), or the major axis is 0.5 μm or more and the thickness is less than 0.5 μm. In the case of cubic boehmite, the length of one side is preferably less than 0.5 μm. The major axis and minor axis of needle-shaped boehmite and the major axis and thickness of scaly boehmite are arithmetic mean of the measured values of 100 particles arbitrarily selected from the SEM image. The length of the cubic boehmite is a cumulative 50% diameter based on the volume measured by laser diffraction / scattering particle size distribution measurement.

The boehmite may contain any other metallic element other than Al. Examples of other metal elements include Mg. It is preferable to use Mg-containing boehmite powder, particularly Mg-containing needle-shaped boehmite powder, as the aluminum source because the decomposition of the synthesized aluminum titanate at high temperature can be suppressed. As the Mg-containing boehmite powder, for example, boehmite powder in which fine particles of an Mg compound (MgO or the like) are dispersed can be used. Alternatively, as the Mg-containing boehmite powder, a boehmite powder in which Mg is mixed with boehmite at the atomic level, such as a solid solution of boehmite and an Mg compound (MgO or the like), can be used. Examples of such boehmite powder include boehmite powder in which Mg is intercalated in boehmite, and boehmite powder in which Mg is doped into Al-site of boehmite.

The titanium source is not particularly limited, but an inorganic titanium compound such as titanium oxide can be used, and two or more kinds of titanium compounds can be used in combination. The titanium compound may be produced by chemically reacting a titanium compound precursor in the step of coating the boehmite powder. For example, compounds (titanium compounds) such as titanyl sulfate (TIOSO ₄ · nH ₂ O, 1 <n <2), titanium tetrachloride (TiCl ₄ ) or tetraisopropyl orthotitanate ([(CH ₃ ) ₂ CHO] _{4 Ti).} The precursor) is known to produce titanium oxide by a hydrolysis reaction when mixed with water and heated as needed. By utilizing this chemical reaction and mixing and heating the boehmite powder and the titanium compound precursor as described above in water, the boehmite powder can be coated with titanium oxide produced from the titanium compound precursor.

The method for coating the titanium compound on the boehmite powder is not particularly limited, but from the viewpoint of uniformly and evenly coating the entire boehmite powder as much as possible, it is preferable to carry out the wet method. Examples of the method of wet-coating the titanium compound on the boehmite powder include a method of spraying the titanium compound-containing solution on the boehmite powder and a method of mixing the boehmite slurry and the titanium compound-containing solution. In particular, a method in which a boehmite slurry and an aqueous solution containing a water-soluble titanium compound precursor are mixed, heated and stirred at a predetermined temperature (for example, 100 ° C. or lower) as necessary, and coprecipitated is produced from the titanium compound precursor. It is preferable because the surface of the boehmite powder can be uniformly coated with the titanium compound. If necessary, a step of filtering and washing the slurry of the titanium compound-coated boehmite powder until the pH of the filtrate becomes around 7 may be included. The titanium compound-coated boehmite powder prepared by the wet method is calcined through a drying step.

The blending ratio of the boehmite powder and the titanium compound is preferably selected so that the molar ratio of _{Al 2} O ₃ and TiO _{2 (Al 2} O ₃ / TiO _{2) is 1.} With such a blending ratio, _{aluminum titanate having a composition formula close to Al 2} O ₃ · TiO ₂ (that is, x = 1) can be synthesized.

The firing temperature is not particularly limited as long as it is the temperature at which aluminum titanate is synthesized, but it is preferable to fire at the lowest possible temperature because the manufacturing cost increases when the firing temperature is high. From this point of view, the firing temperature is, for example, 1300 ° C. to 1500 ° C., preferably 1300 ° C. to 1350 ° C., although it varies depending on the boehmite powder and titanium compound used and the firing time.

The firing time is not particularly limited as long as it is the time for synthesizing aluminum titanate, but the longer the firing time, the higher the production cost, so it is preferable to fire in as short a time as possible. From this point of view, the firing time is preferably 5 hours or less, although it depends on the boehmite powder and titanium compound used and the firing temperature.

The method for producing aluminum titanate powder of the present invention may include a step of crushing aluminum titanate powder synthesized by firing. The aluminum titanate powder after firing may form secondary particles by agglutination of primary particles or light sintering. In such a case, the particle size can be adjusted to an appropriate level by crushing the aluminum titanate powder. In addition, crushing is to loosen the agglomeration of the primary particles and to break the neck between the primary particles generated by sintering, so that the secondary particles are converted into primary particles with almost no destruction of the primary particles themselves. It is an operation that distributes to. For crushing, a known crushing means can be used, and for example, a crushing device such as a ball mill can be used. At this time, the crushing force and the crushing time are appropriately adjusted so as not to destroy the primary particles.

Hereinafter, the present invention will be specifically described with reference to Examples, but the present invention is not limited to these Examples.

<Synthesis of aluminum titanate powder>
[Example 1]
(1) 50 g of scaly boehmite powder (manufactured by Kawai Lime Industry Co., Ltd., major axis 2 μm, minor axis 0.05 μm) was added to a beaker containing 1 L of ion-exchanged water and mixed to prepare a boehmite slurry.
(2) 1 L of ion-exchanged water is put into a beaker different from the beaker of (1) above, 117 g of titanyl sulfate (calculated as n = 1.5) is put into the beaker, and titanyl sulfate is completely dissolved in the ion-exchanged water. Then, the mixture was stirred until the liquid became transparent in the beaker. The weights of the scaly boehmite powder and titanyl sulfate were determined so that the molar ratio of _{Al 2} O ₃ and TiO _{2 was 1: 1.}
(3) The aqueous titanyl sulfate solution prepared in (2) above was added dropwise into the beaker of (1) above at a rate of 1 L / h.
(4) The slurry obtained in (3) above was heated and stirred for 6 hours while maintaining the liquid temperature at 80 ° C. In this step, the surface of the boehmite powder is coated with titanium oxide.
(5) The slurry obtained in (4) above was washed with ion-exchanged water by suction filtration until the pH of the filtrate became 7. Soft water may be used instead of the ion-exchanged water.
(6) The slurry obtained in (5) above was dried at 120 ° C. for 15 hours to prepare a boehmite powder coated with titanium oxide.
(7) The powder obtained in (6) above is placed in a heat-resistant container, the heat-resistant container is placed in an electric furnace, and the temperature is raised from room temperature to 1350 ° C., which is the firing temperature, at a heating rate of 200 ° C./h, 1350. It was kept at ° C. for 5 hours and then naturally cooled in an electric furnace.
(8) The powder obtained in (7) above was crushed with a ball mill for 8 hours to obtain the aluminum titanate powder of the present invention.

[Example 2]
The aluminum titanate powder was produced according to the same procedure and conditions as in Example 1 except that the firing temperature of Example 1 was changed to 1300 ° C.

[Example 3]
Aluminum titanate powder according to the same procedure and conditions as in Example 1 except that the scaly boehmite powder of Example 1 was changed to cubic boehmite powder (manufactured by Kawai Lime Industry Co., Ltd., cumulative 50% diameter 0.3 μm). Manufactured.

[Example 4]
Aluminum titanate powder according to the same procedure and conditions as in Example 1 except that the scaly boehmite powder of Example 1 was changed to scaly boehmite powder (manufactured by Kawai Lime Industry Co., Ltd., major axis 9 μm, minor axis 0.45 μm). Was manufactured.

[Example 5]
Same as Example 1 except that the scaly boehmite powder of Example 1 was changed to needle-shaped boehmite powder containing 2.8 mol% of Mg (manufactured by Kawai Lime Industry Co., Ltd., major axis 4 μm, minor axis 0.09 μm). Aluminum titanate powder was produced according to the procedure and conditions of.

[Example 6]
The aluminum titanate powder was produced according to the same procedure and conditions as in Example 5 except that the firing temperature of Example 5 was changed to 1300 ° C.

[Example 7]
Example 1 except that the scaly boehmite powder of Example 1 was changed to needle-shaped boehmite powder containing 2.51 mol% of Mg (manufactured by Kawai Lime Industry Co., Ltd., major axis 3.7 μm, minor axis 0.1 μm). The aluminum titanate powder was produced according to the same procedure and conditions as in the above.

[Example 8]
Example 1 except that the scaly boehmite powder of Example 1 was changed to needle-shaped boehmite powder containing 1.67 mol% of Mg (manufactured by Kawai Lime Industry Co., Ltd., major axis 3.2 μm, minor axis 0.3 μm). The aluminum titanate powder was produced according to the same procedure and conditions as in the above.

[Comparative Example 1]
As the aluminum titanate powder of Comparative Example 1, a commercially available aluminum titanate powder (manufactured by AS ONE Corporation) was used. Considering the particle shape in the SEM image, the aluminum titanate powder of Comparative Example 1 is presumed to be a powder produced by a method of producing an aluminum titanate molded product and then crushing the molded product by a pulverizer. .. From the results of energy dispersive X-ray analysis (EDS) described later, it was found that the aluminum titanate powder of Comparative Example 1 contained 13 mol% of Si.

[Comparative Example 2]
(1) 30 g of scaly boehmite powder (manufactured by Kawai Lime Industry Co., Ltd., major axis 2 μm, minor axis 0.05 μm) and 20 g of anatase-type titanium oxide powder (manufactured by Kanto Chemical Co., Inc., reagent) are mixed to prepare a mixed powder. did. The weights of the scaly boehmite powder and the anatase-type titanium oxide powder were determined so that the molar ratio of _{Al 2} O ₃ and TiO _{2 was 1: 1.}
(2) The mixed powder obtained in (1) above is placed in a heat-resistant container, the heat-resistant container is placed in an electric furnace, and the temperature is raised from room temperature to 1350 ° C., which is the firing temperature, at a heating rate of 200 ° C./h. It was kept at 1350 ° C. for 5 hours and then naturally cooled in an electric furnace.

[Comparative Example 3]
The procedure and conditions were the same as those of Comparative Example 2 except that the scaly boehmite powder of Comparative Example 2 was changed to cubic boehmite powder (manufactured by Kawai Lime Industry Co., Ltd., cumulative 50% diameter 0.3 μm).

[Comparative Example 4]
Similar to Comparative Example 2 except that the scaly boehmite powder of Comparative Example 2 was changed to needle-shaped boehmite powder containing 2.8 mol% of Mg (manufactured by Kawai Lime Industry Co., Ltd., major axis 4 μm, minor axis 0.09 μm). It was carried out according to the procedure and conditions of.

<Evaluation method>
[X-ray diffraction measurement]
Using a powder X-ray diffraction measuring device (device name: D2 PHASER manufactured by BRUKER AXS, X-ray: CuKα ray), the identification of aluminum titanate and by-products and their production ratios were investigated. Aluminum titanate and by-products were identified from the X-ray diffraction pattern obtained by powder X-ray diffraction measurement. In addition, using the quantitative analysis software TOPAS attached to the powder X-ray diffraction measuring device, the production ratio (% by weight) of aluminum titanate and by-products was determined using the peak intensity of the X-ray diffraction pattern.

[Measurement of particle size distribution]
The particle size distribution of the aluminum titanate powder was measured. Put the aluminum titanate powder in a container containing an aqueous solution containing 0.1 wt% sodium hexametaphosphate and stir, then put the container in a 30 W ultrasonic generator and irradiate ultrasonic waves to make the aluminum titanate powder. It was dispersed in an aqueous solution. The aqueous solution containing aluminum titanate powder prepared in this manner is injected into a laser diffraction / scattering type particle size distribution measuring device (device name: MT3000 manufactured by Microtrac Bell Co., Ltd.), and the particle size of the aluminum titanate powder is measured by a wet method. The distribution was measured. In measuring the particle size distribution, the refractive index of aluminum titanate was 1.98 (“Material”, Japan Society of Materials Science, Vol. 12, No. 120, p. 656).

From the obtained particle size distribution measurement results, the cumulative 10% diameter D ₁₀ , the cumulative 50% diameter D ₅₀ , the cumulative 90% diameter D ₉₀ , the cumulative 99% diameter D ₉₉ , the standard deviation SD, and the volume average diameter MV are obtained. Obtained. Using the standard deviation SD and the volume mean diameter MV, the coefficient of variation CV was calculated according to the above equation 1. Further, using the cumulative 50% diameter D ₅₀ , the specific surface area S2 was calculated according to the above formulas 3 to 5.

[Specific surface area measurement]
The BET specific surface area of the aluminum titanate powder was measured. As a pretreatment, aluminum titanate powder was placed in a pretreatment device for adsorption measurement (device name: BELPREP-vacII manufactured by Microtrac Bell Co., Ltd.), and vacuum heating and exhausting was performed at 150 ° C. for 3 hours. After that, the amount of nitrogen adsorbed on the pretreated aluminum titanate powder was measured using a nitrogen adsorption measuring device (device name: BELSORP-miniII manufactured by Microtrac Bell Co., Ltd.) in the vicinity of the liquid nitrogen temperature (77K) in a constant capacity type. It was measured by the gas adsorption method. As the measurement program, the adsorption measurement program mounted on BELSORP-miniII was used. From the measured nitrogen adsorption amount, the specific surface area was calculated by the BET method using the analysis program mounted on BELSORP-miniII.

[SEM observation and EDS measurement]
Using a scanning electron microscope (device name: JSM-7500FA manufactured by JEOL Ltd.) equipped with an energy dispersive X-ray analyzer, observation of the particle shape of aluminum titanate powder and the element ratio (molar ratio) in the powder ) Was measured. The element mapping measurement of EDS was performed under the conditions of a visual field magnification of 3000 times, an acceleration voltage of 15 kV, and an integration number of times: 50 times. The elemental ratio of Al and Ti in aluminum titanate was measured, and the composition formula of aluminum titanate was obtained from the obtained elemental ratio. In addition, the ratio of constituent elements in the aluminum titanate of Comparative Example 1 was measured.

[Brightness and saturation measurement]
The brightness and saturation of the aluminum titanate powder were measured using a spectrophotometer (device name: CM-3600d manufactured by Konica Minolta Japan Co., Ltd.). Aluminum titanate powder is packed in a quartz cell so that there are no voids, and based on the following measurement conditions, L ^* a ^* b ^{* brightness L *} , saturation a ^* , saturation b ^* and saturation in the color system are measured. The color difference ΔE ^* was measured. When measuring, first calibrate using the white calibration plate (L ^* : 96.6, a ^* : -0.1, b ^* : -0.3) attached to the measuring device, and then each aluminum titanate. The powder was measured. Each aluminum titanate powder was measured three times and the arithmetic mean of the three measurements was taken. a ^* and b ^* represent the color direction. The + a ^* direction represents the red direction, the -a ^* direction represents the green direction, the + b ^* direction represents the yellow direction, and the -b ^* direction represents the blue direction. a ^* and b ^* become more colorful as the value (absolute value) increases, and become dull as the value approaches 0. ΔE ^* is the color difference with respect to the white calibration plate.
Measurement method: Simultaneous measurement of SCI (including specularly reflected light) / SCE (removing specularly reflected light) (however, the value measured by the SCE method was adopted)
Measurement wavelength: 360-740 nm
Wavelength interval: 10 nm
Measurement diameter: φ8 mm
Light source: D65

[Heating test]
Aluminum titanate powder in a heat-resistant container was placed in an electric furnace, heated from room temperature to 1100 ° C. at a heating rate of 200 ° C./h, held at 1100 ° C. for 10 hours, and then naturally cooled in the electric furnace. .. X-ray diffraction measurement of the powder after cooling was performed, and the ratio (% by weight) of aluminum titanate in the powder was examined. Then, the decomposition rate was calculated according to the above formula 7 from the ratio of aluminum titanate before heating and the ratio of aluminum titanate after heating. In addition, the decomposition rate of aluminum titanate when held for 100 hours was also measured under the same temperature conditions and procedures.

<Result>
Table 1 shows the evaluation results of the powders obtained from Examples 1 to 8 and Comparative Examples 1 to 4. In addition, "-(hyphen)" is added to the unmeasured part.

As can be seen from Table 1, in Comparative Examples 2 to 4, the production ratio of aluminum titanate was at most 29.1% by weight. In Comparative Examples 2 to 4, since the production ratio of by-products was higher than the production ratio of aluminum titanate, no evaluation other than X-ray diffraction measurement was performed.

The aluminum titanate powder of the present invention has a smaller coefficient of variation (that is, smaller variation in particle size), a smaller cumulative 99% diameter, and a sharper particle size distribution than the aluminum titanate powder of Comparative Example 1. It was.

As can be seen from FIG. 1, the particles of the aluminum titanate powder of Comparative Example 1 have an angular shape, whereas the particles of the aluminum titanate powder of Examples 1 and 3 to 5 have a rounded shape. doing. As shown in Table 1, the S1 / S2 of the aluminum titanate powder of the present invention is closer to 1.0 than that of the comparative example. Therefore, it can be seen that the aluminum titanate powder of the present invention has a particle shape close to a sphere.

The aluminum titanate powder of the present invention had a lower decomposition rate than the aluminum titanate powder of Comparative Example 1 containing Si. From this, it can be seen that the aluminum titanate powder of the present invention is difficult to decompose and has high high temperature stability even if it does not contain Si for suppressing decomposition. As shown in Examples 5, 7 and 8, aluminum titanate prepared from Mg-containing needle-shaped boehmite decomposes only 3.2% at the maximum even when heated for 100 hours, and has high high-temperature stability. I understand.

The brightness of the aluminum titanate powder of the present invention was higher than that of Comparative Example 1. Further, the color difference of the aluminum titanate powder of the present invention with respect to the white calibration plate was smaller than that of Comparative Example 1. From this, it can be seen that the aluminum titanate powder of the present invention is closer to white than Comparative Example 1.

In the method for producing aluminum titanate powder of the present invention, the produced aluminum titanate particles were not firmly bonded to each other, and could be dispersed to the primary particles by crushing for about 8 hours. Further, aluminum titanate could be synthesized at a firing temperature of 1300 ° C. to 1350 ° C. and a firing time of 5 hours at a lower temperature and in a shorter time than before.

Claims (14)

The cumulative 50% diameter of the volume standard in the laser diffraction / scattering type particle size distribution measurement is 0.5 μm to 4.0 μm, and the coefficient of variation of the particle size distribution is 60% or less.
It is characterized by aluminum titanate powder. It has a rounded particle shape in which the ratio (S1 / S2) of the BET specific surface area (S1) to the specific surface area (S2) of the spherical particles having a cumulative diameter of 50% is less than 2.0.
The aluminum titanate powder according to claim 1. The BET specific surface area ^is 0.3m ² /g~3.0m 2 / g,
The aluminum titanate powder according to claim 2. Cumulative 99% diameter is less than 10 μm,
The aluminum titanate powder according to any one of claims 1 to 3. Composition formula: represented by xAl ₂ O ₃ · TiO ₂ (x = 0.7 to 1.2),
The aluminum titanate powder according to any one of claims 1 to 4. L ^* a ^* b ^{* Brightness L *} in the color system is 90 or more.
The aluminum titanate powder according to any one of claims 1 to 5. Further containing 3.0 mol% or less (not including 0) magnesium,
The aluminum titanate powder according to any one of claims 1 to 6. The decomposition rate after heating at 1100 ° C. for 10 hours in the air atmosphere is 1% or less.
The aluminum titanate powder according to claim 7. The method for producing aluminum titanate powder according to any one of claims 1 to 8.
Baking boehmite powder coated with titanium compound,
A method for producing aluminum titanate powder. The firing temperature is 1300 ° C to 1500 ° C.
The method for producing an aluminum titanate powder according to claim 9. At least one of the three-dimensional lengths of the major axis, minor axis or thickness of the boehmite powder is less than 0.5 μm.
The method for producing an aluminum titanate powder according to claim 9 or 10. The titanium compound is produced from titanyl sulfate, titanium tetrachloride or tetraisopropyl orthotitanate.
The method for producing an aluminum titanate powder according to any one of claims 9 to 11. The blending ratio of the boehmite powder and the titanium compound is adjusted so that the molar ratio of _{Al 2} O ₃ and TiO _{2 (Al 2} O ₃ / TiO ₂ ) is 1.
The method for producing an aluminum titanate powder according to any one of claims 9 to 12. The boehmite powder contains magnesium,
The method for producing an aluminum titanate powder according to any one of claims 9 to 13.