JP7224997B2 - Al4SiC4 powder - Google Patents

Description

The present invention relates to Al ₄ SiC ₄ powder. More specifically, the present invention relates to Al ₄ SiC ₄ powders used for thermal barrier coatings and the like.

In recent years, due to the effects of global warming, temperature rise and deterioration of structures due to heat rays such as sunlight (infrared rays) have become a problem. BACKGROUND ART In buildings, heat-shielding paints are often used to prevent an increase in room temperature due to direct sunlight by coating the outer walls and roofs of the buildings. There is a demand for a heat-shielding paint that has a high reflectance in the infrared region. In order to impart infrared reflectivity, heat-shielding paints to which additives such as titanium oxide and aluminum oxide are added have been studied.

Japanese Patent No. 6302518 (Patent Document 1) proposes a heat-shielding paint containing large-diameter titanium oxide, small-diameter titanium oxide, and hollow particles made of acrylonitrile-based resin. Japanese Patent Application Laid-Open No. 2017-194632 (Patent Document 2) discloses a heat-shielding paint for suppressing temperature rise of an optical device due to sunlight. This heat-shielding paint contains void-containing particles and high-refractive-index particles in a solution in which a predetermined resin is dissolved in a solvent.

Japanese Patent No. 6311135 (Patent Document 3) proposes a coating liquid to be applied to a refractory used for the inner wall of a heating furnace or the like. This coating liquid contains ceramic fibers and/or ceramic powder as a radiation scattering material. Japanese Patent No. 5315589 (Patent Document 4) discloses an infrared reflective black pigment composed of a composite oxide containing Fe, Co and Al. In Japanese Patent No. 6131625 (Patent Document 5), the Al ₄ SiC ₄ powder mentioned as a radiation scattering material in Patent Document 3 is used as an antioxidant for refractories.

Japanese Patent No. 6302518 JP 2017-194632 A Japanese Patent No. 6311135 Japanese Patent No. 5315589 Japanese Patent No. 6131625

Various materials have been investigated to impart infrared reflectivity to heat-shielding paints, but their performance is not sufficiently satisfactory. The Al ₄ SiC ₄ powder proposed in Patent Document 3 has been studied as an antioxidant for refractories, but sufficient studies have not been conducted to improve the infrared reflective properties. Moreover, since the black pigment proposed in Patent Document 4 contains Co, which is a rare metal, there is also the problem that it is not preferable from the viewpoint of raw material supply and cost. Additives for imparting infrared reflectivity to heat-shielding paints are required to be further improved.

SUMMARY OF THE INVENTION An object of the present invention is to provide an Al ₄ SiC ₄ powder having excellent infrared reflective properties.

As a result of intensive studies, the present inventors have found that Al ₄ SiC ₄ powder having a predetermined pore size distribution can impart remarkably excellent infrared reflective properties, thereby completing the present invention. .

That is, the Al ₄ SiC ₄ powder according to the present invention has a mode diameter of 12.0 μm or less and a mode volume of 1.40×10 ⁻³ m ³ · in the pore distribution measured by the mercury intrusion method. kg ⁻¹ or less.

Preferably, the Al ₄ SiC ₄ powder has a total pore volume of 0.70×10 ⁻³ m ³ ·kg ⁻¹ or less and an inflection point diameter of is 15.0 μm or less.

Preferably, the Al ₄ SiC ₄ powder has an intra-particle void volume of 0.55×10 ⁻³ m ³ ·kg ⁻¹ or less in the pore size distribution measured by mercury porosimetry.

Furthermore, the present invention relates to an additive for thermal barrier paint containing this Al ₄ SiC ₄ powder.

The infrared reflectance by the Al ₄ SiC ₄ powder according to the invention is high. By blending this Al ₄ SiC ₄ powder as an additive, it is possible to obtain a heat-shielding paint with excellent infrared reflective properties.

The present invention will now be described in detail based on preferred embodiments.

The Al ₄ SiC ₄ powder according to the invention consists of a large number of particles. The pore distribution of this Al ₄ SiC ₄ powder is proper. This Al ₄ SiC ₄ powder achieves high infrared reflectance due to proper pore distribution.

Herein, the pore size distribution of Al ₄ SiC ₄ powder is measured by mercury porosimetry. Specifically, a cumulative pore volume curve showing the relationship between the pore diameter and the cumulative pore volume of the Al ₄ SiC ₄ powder is obtained by measuring the pore size distribution by mercury porosimetry. The horizontal axis of the cumulative pore volume curve is the pore diameter obtained from the mercury intrusion pressure, and the vertical axis is the cumulative pore volume. The following formula (I) (Washburn's formula) is used for conversion from the mercury intrusion pressure to the pore diameter.
D=−(1/P)·4γ·cos Ψ (I)
Here, D: pore diameter (m), P: intrusion pressure of mercury (Pa), γ: surface tension of mercury (485 dyne cm ^-1 (0.485 Pa m)), Ψ: contact angle of mercury ( 130° = 2.26893 rad).

The Al ₄ SiC ₄ powder according to the present invention has a mode diameter of 12.0 μm or less and a mode volume of 1.40×10 ⁻³ m ³ ·kg ⁻ in the pore size distribution measured by mercury porosimetry. ¹ or less. Modal volume means the maximum value of the log differential pore volume distribution curve. The mode diameter indicates the pore diameter corresponding to the maximum value of the log differential pore volume distribution curve, and means the diameter of the voids between the particles composing the Al ₄ SiC ₄ powder.

In Al ₄ SiC ₄ powder having a mode diameter of 12.0 μm or less and a mode volume of 1.40×10 ⁻³ m ³ ·kg ⁻¹ or less, there is little aggregation between particles, and the surface area in contact with infrared rays is is large. The infrared reflectance by this Al ₄ SiC ₄ powder is high. Furthermore, the Al ₄ SiC ₄ powder, which has less agglomeration of particles, is excellent in mixability with paint. This Al ₄ SiC ₄ powder is evenly dispersed in the paint. A heat-shielding paint obtained by blending this Al ₄ SiC ₄ powder has excellent infrared reflectivity. In particular, this Al ₄ SiC ₄ powder achieves a high reflectance in the far-infrared region around a wavelength of 5500 nm. This Al ₄ SiC ₄ powder can be suitably used as an additive for imparting infrared reflectivity to a heat shield paint.

From the viewpoint of infrared reflectivity, the Al ₄ SiC ₄ powder has a mode diameter of 0.5 μm or more and 11.5 μm or less, and a mode volume of 0.4×10 ⁻³ m ³ ·kg ⁻¹ or more and 1.30× It is preferably 10 ⁻³ m ³ ·kg ⁻¹ or less, the mode diameter is 0.5 μm or more and 11.0 μm or less, and the mode volume is 0.4×10 ⁻³ m ³ ·kg ⁻¹ or more and 1.25×. It is more preferably 10 ⁻³ m ³ ·kg ⁻¹ or less.

Further, the Al ₄ SiC ₄ powder preferably has a total pore volume of 0.70×10 ⁻³ m ³ ·kg ⁻¹ or less and an inflection point diameter of 15.0 μm or less. Total pore volume means the sum of all pore volumes. The inflection point diameter means the pore diameter at the point with the largest pore diameter among the inflection points at which the cumulative pore volume curve rises sharply.

Al ₄ SiC ₄ powder having a total pore volume of 0.70×10 ⁻³ m ³ ·kg ⁻¹ or less and an inflection point diameter of 15.0 μm or less has few voids present therein, Moreover, the diameter of each void is small. In this Al ₄ SiC ₄ powder, a decrease in infrared reflectance due to penetration of infrared rays into the pores is suppressed. From this point of view, the Al ₄ SiC ₄ powder preferably has a total pore volume of 0.65×10 ⁻³ m ³ ·kg ⁻¹ or less and an inflection point diameter of 0.70 μm or more and 14.5 μm or less. More preferably, the total pore volume is 0.60×10 ⁻³ m ³ ·kg ⁻¹ or less, and the inflection point diameter is 0.70 μm or more and 14.0 μm or less. Although the lower limit of the total pore volume is not particularly limited, it is preferably 0.3×10 ⁻³ m ³ ·kg ⁻¹ or more.

Furthermore, the Al ₄ SiC ₄ powder preferably has an intra-particle void amount of 0.55×10 ⁻³ m ³ ·kg ⁻¹ or less. The intra-particle void volume is a volume obtained by subtracting the cumulative pore volume at the inflection point from the total pore volume, and indicates the volume of voids smaller than the particle diameter of aggregated particles present inside each particle.

Al ₄ SiC ₄ powder having an intra-particle void volume of 0.55×10 ⁻³ m ³ ·kg ⁻¹ or less has few pores on the surface of each particle. The surface of each particle constituting this Al ₄ SiC ₄ powder is smooth. In this Al ₄ SiC ₄ powder, the smooth surface of each particle improves the infrared reflectance. From this point of view, the Al ₄ SiC ₄ powder preferably has an intra-particle void volume of 0.54×10 ⁻³ m ³ ·kg ⁻¹ or less, more preferably 0.53×10 ⁻³ m ³ ·kg ⁻¹ More preferably: Although the lower limit of the intra-particle void content is not particularly limited, it is preferably 0.1×10 ⁻³ m ³ ·kg ⁻¹ or more.

Preferably, the volume-based cumulative 50% particle diameter (median diameter) of the Al ₄ SiC ₄ powder is 1 μm or more and 50 μm or less. Al ₄ SiC ₄ powder having a volume-based cumulative 50% particle size of 1 μm or more is excellent in handleability. Excessive increases in viscosity are avoided in paints containing this Al ₄ SiC ₄ powder. From this point of view, the volume-based cumulative 50% particle size of the Al ₄ SiC ₄ powder is more preferably 2 μm or more, and even more preferably 3 μm or more.

Also, the Al ₄ SiC ₄ powder having a volume-based cumulative 50% particle size of 50 μm or less is excellent in dispersibility in paint. In the paint containing the Al ₄ SiC ₄ powder, the deterioration of the finish of the coating film due to sedimentation of the Al ₄ SiC ₄ powder is suppressed. From this point of view, the volume-based cumulative 50% particle size of the Al ₄ SiC ₄ powder is more preferably 40 μm or less, and even more preferably 30 μm or less.

The volume-based cumulative 50% particle size of the Al ₄ SiC ₄ powder is measured by a laser diffraction scattering method. Specifically, after Al ₄ SiC ₄ powder is put into methanol, it is dispersed for 3 minutes at 120 W with an ultrasonic homogenizer (trade name “US-300T” manufactured by Nippon Seiki Seisakusho Co., Ltd.) to obtain a measurement sample. and The volume-based cumulative 50% particle size is determined by measuring this measurement sample using a laser diffraction/scattering particle size distribution analyzer (trade name “MT3300” manufactured by Nikkiso Co., Ltd.).

A method for producing Al ₄ SiC ₄ powder according to a preferred embodiment of the present invention will be described below. The method for producing the Al ₄ SiC ₄ powder is not particularly limited as long as the pore distribution described above is formed and the effects of the present invention can be obtained.

The Al ₄ SiC ₄ powder according to the present invention is manufactured by, for example, weighing an aluminum source, a silicon source, a carbon source, and silicon carbide, respectively, thoroughly mixing them, firing the resulting mixture, and pulverizing it. can do.

As the aluminum source, metal Al, aluminum compounds such as aluminum oxide and aluminum hydroxide, and the like can be used. A preferred aluminum source in terms of purity is metallic Al.

As the silicon source, metal Si, silicon compounds such as silicon dioxide, and the like can be used. A preferred silicon source in terms of purity is metallic Si.

As a carbon source, flake graphite, synthetic graphite, carbon black, or the like can be used. Due to cost and availability, the preferred carbon source is flake graphite.

These aluminum source, silicon source and carbon source are weighed so that the molar ratio Al:Si:C of the aluminum, silicon and carbon contained in each is 4:1:4.

Silicon carbide (SiC) is added to suppress the formation of Al ₄ C ₃ which deteriorates the water resistance of the resulting Al ₄ SiC ₄ powder. By adding silicon carbide, the molar ratio Al/Si of aluminum and silicon in the entire raw material becomes lower than the aforementioned 4.0. Specifically, silicon carbide is used so that the molar ratio Al/Si of the aluminum contained in the aluminum source and the total amount of silicon contained in the silicon source and silicon carbide is in the range of 3.76 or more and 3.94 or less. Adjust the amount of

A method for mixing the weighed aluminum source, silicon source, carbon source and silicon carbide is not particularly limited, and a known mixing apparatus is appropriately selected and used. Specific examples thereof include container rotating mixers such as V-type mixers, ribbon mixers, Henschel mixers, proshare mixers, super mixers, and dry ball mills. It is preferable to mix as uniformly as possible.

The mixing conditions for the aluminum source, silicon source, carbon source and silicon carbide are appropriately selected according to the mixing apparatus used. For example, when using a dry ball mill, from the viewpoint of uniform mixing, it is preferable to carry out at room temperature for 5 hours or longer.

Next, the obtained mixed raw material is fired to synthesize Al ₄ SiC ₄ . The apparatus used for firing is not particularly limited as long as it can perform firing at 1650° C. to 1900° C. in an inert atmosphere. Known firing furnaces such as box furnaces, crucible furnaces, tubular furnaces, tunnel furnaces, vacuum furnaces, furnace bottom lifting furnaces, resistance heating furnaces, induction heating furnaces, and direct current electric furnaces can be used.

The synthesis reaction of Al ₄ SiC ₄ by sintering proceeds in two stages. First, Al, Si and C react to form Al ₄ C ₃ and SiC. Next, in a temperature range of 1300° C. or higher, Al ₄ C ₃ and SiC react to synthesize Al ₄ SiC ₄ . If the firing temperature is lower than 1650° C., the progress of the reaction in the second step is slow, so Al ₄ C ₃ tends to remain after the reaction. Therefore, the firing temperature is preferably 1650° C. or higher.

On the other hand, if the firing temperature exceeds 1900° C., part of Al ₄ SiC ₄ is thermally decomposed. Therefore, the firing temperature is preferably 1900° C. or lower, more preferably 1800° C. or lower, and even more preferably 1750° C. or lower. The firing time may be appropriately adjusted according to the firing temperature, but is preferably about 1 hour to 10 hours.

If nitrogen is present in the atmosphere in the kiln, this nitrogen may react with metallic Al to produce aluminum nitride (AlN) as a by-product. In order to suppress the production of aluminum nitride, the firing is preferably carried out in an atmosphere of an inert gas such as argon, and more preferably carried out while flowing an inert gas such as argon into the firing furnace. Moreover, before firing, it is preferable to fill the firing furnace to be used with an inert gas in advance to remove remaining nitrogen and carbon.

Al ₄ SiC ₄ obtained by sintering is pulverized using known pulverization means. The Al ₄ SiC ₄ powder according to the present invention can be obtained by adjusting the pulverizing device and pulverizing conditions so as to obtain the above-described pore distribution and particle size distribution.

Examples of crushing equipment include jaw crushers, cone crushers, impact crushers, roll crushers, cutter mills, stamp mills, ring mills, jet mills, hammer mills, pin mills, dry ball mills, vibration mills, bead mills, cyclone mills, and the like.

Pulverization conditions are not particularly limited, and the desired pore distribution and particle size distribution can be achieved by appropriately adjusting the number of revolutions during pulverization, treatment time, etc. according to the type of pulverizer used. . For example, when pulverizing using a dry ball mill, the preferred pulverization time is 0.1 hour or more and 24 hours or less. If the pulverization time is shorter than 0.1 hour, the resulting Al ₄ SiC ₄ powder may have a large particle size and may not have a desired pore size distribution. A plurality of Al ₄ SiC ₄ powders with different pore distributions and particle size distributions can be mixed to adjust the desired pore size distribution and particle size distribution. When mixing a plurality of Al ₄ SiC ₄ powders, the mixing method is not particularly limited, and a known mixing apparatus is appropriately selected and used. Specific examples thereof include container rotating mixers such as V-type mixers, ribbon mixers, Henschel mixers, proshare mixers, super mixers, and dry ball mills.

Although the Al ₄ SiC ₄ powder according to the present invention can be manufactured by the above steps, the method for manufacturing the Al ₄ SiC ₄ powder according to the present invention is not limited to the above manufacturing method.

The Al ₄ SiC ₄ powder described above is preferably used as an additive for heat insulating paints. The heat-shielding paint obtained by blending the additive containing this Al ₄ SiC ₄ powder exhibits high infrared reflectivity due to the Al ₄ SiC ₄ powder having an appropriate pore size distribution. This heat-shielding paint additive can be used not only for buildings but also in various other fields to manufacture heat-shielding paints for preventing temperature rise and deterioration due to infrared rays.

The effects of the present invention will be clarified by examples below, but the present invention should not be construed in a limited manner based on the description of these examples. The pore size distribution of the Al ₄ SiC ₄ powders obtained in Synthesis Examples, Examples and Comparative Examples, which will be described later, was measured according to the following method.

[Pore size distribution measurement]
As a mercury intrusion type pore size distribution measuring device, a trade name "Autopore IV9510" manufactured by Micromeritics was used. As mercury, a special grade mercury reagent having a purity of 99.5 mass % or higher and a density of 15.5335×103 kg/m ³ was used. A powder sample cell having a cell internal volume of 5×10 ⁻⁶ m ³ and a stem volume of 0.38×10 ⁻⁶ m ³ was used as the measurement cell. Each Al ₄ SiC ₄ powder as a measurement sample was precisely weighed in a mass range of 0.10×10 ⁻³ to 0.13×10 ⁻³ kg and filled in a measurement cell. After this measurement cell was installed in the apparatus, the inside of the cell was held in a reduced pressure state for 20 minutes at a pressure of 50 μHg (6.67 Pa) or less. Mercury was then filled into the measurement cell to a pressure of 1.5 psia (10342 Pa). After that, mercury was injected at a pressure ranging from 2 psia (13790 Pa) to 60000 psia (413.7 MPa), and the pore distribution was measured.

The following formula (I) was used to convert the mercury injection pressure into the pore diameter.
D=−(1/P)·4γ·cos Ψ (I)
Here, D: pore diameter (m), P: intrusion pressure of mercury (Pa), γ: surface tension of mercury (485 dyne cm ^-1 (0.485 Pa m)), Ψ: contact angle of mercury ( 130° = 2.26893 rad).

[Synthesis Example 1]
Raw materials consisting of metallic Al (purity 99%, particle size 50 μm or less), metallic Si (purity 98%, particle size 50 μm or less), and flake graphite (purity 98%, particle size 100 μm or less) are converted to Al:Si:C = 44 in terms of moles. 44 mol %: 11.11 mol %: 44.44 mol %. Furthermore, SiC (purity 99%, particle size 50 µm or less) was weighed so that the Al/Si molar ratio in the entire raw material was 3.76 or more and 3.94 or less.

The weighed raw materials were dry mixed for 0.5 hours using a super mixer. The obtained mixed raw material was put into a firing furnace and fired at 1800° C. for 5 hours while flowing argon gas. The fired product obtained was pulverized using a dry ball mill. Pulverization by a dry ball mill was performed by putting 1.7 kg of alumina balls and 0.5 kg of the fired product into a pot of 2 L in volume and rotating the powder at 80 rpm. By adjusting the pulverization time so that the mode diameter, mode volume, total pore volume, inflection point diameter, and intra-particle void volume are as shown in Table 1 below, Al ₄ SiC ₄ of Synthesis Example 1 A powder (S1) was obtained.

[Synthesis Example 2]
The conditions for dry ball mill pulverization after firing were adjusted so that the mode diameter, mode volume, total pore volume, inflection point diameter, and intra-particle void volume were as shown in Table 1 below. Al ₄ SiC ₄ powder (S2) of Synthesis Example 2 was obtained in the same manner as in Example 1.

[Synthesis Example 3]
The conditions for dry ball mill pulverization after firing were adjusted so that the mode diameter, mode volume, total pore volume, inflection point diameter, and intra-particle void volume were as shown in Table 1 below. Al ₄ SiC ₄ powder (S3) of Synthesis Example 3 was obtained in the same manner as in Example 1.

[Example 1-3 and Comparative Example 1-2]
The Al ₄ SiC ₄ powders (S1) to (S3) obtained in Synthesis Example 1-3 were blended according to the blending ratio (mass ratio) shown in Table 2 below, and Example 1-3 and Comparative Example 1-2. of Al ₄ SiC ₄ powder was obtained. For Examples 2 and 3, mixing was performed with a mixer during compounding. The mode diameter, mode volume, total pore volume, inflection point diameter and intra-particle void volume of Example 1-3 and Comparative Example 1-2 are shown in Table 2 below.

[Measurement of infrared reflectance]
JIS R1693-2: 2012 (Emissivity measurement method for fine ceramics and ceramic composite materials Part 2: Vertical emissivity by reflection method using FTIR) Infrared rays of Example 1-3 and Comparative Example 1-2 Reflectance was measured. An FTIR device (System 2000, manufactured by Perkin Elmer) was used for the measurement. Using an integrating sphere (Labsphere RSA-PE-200-ID), at room temperature (25 ° C.), the spectral reflectance spectrum is measured in the wavelength range of 1667 nm to 25.0 μm, and the reflectance is calculated from the obtained data. Calculated. A case where the reflectance at a wavelength of 5500 nm was 30% or more was rated as ⊚, a case of 20% or more was rated as ◯, and a case of less than 20% was rated as x. The higher the numerical value, the higher the evaluation. The results are shown in Table 2 below.

As shown in Table 2, the Al ₄ SiC ₄ powder obtained in Example 1-3 had a mode diameter of 12.0 μm or less and a mode volume of 1.0 μm in the pore distribution measured by the mercury porosimetry. It was 40×10 ⁻³ m ³ ·kg ⁻¹ or less. In Example 1-3, there was little agglomeration of particles, and the surface area for infrared rays was large, so a high infrared reflectance was achieved.

On the other hand, the Al ₄ SiC ₄ powder of Comparative Example 1-2 has a large mode diameter exceeding 12.0 μm and a large mode volume exceeding 1.40×10 ⁻³ m ³ ·kg ⁻¹ . The results were inferior in reflectance.

As shown in Table 2, the Al ₄ SiC ₄ powder of the example is evaluated higher than the Al ₄ SiC ₄ powder of the comparative example. From this evaluation result, the superiority of the present invention is clear.

The Al ₄ SiC ₄ powder described above is used in various fields as an additive for imparting infrared reflectivity.

Claims (4)

Al ₄ SiC ₄ powder having a mode diameter of 12.0 μm or less and a mode volume of 1.40×10 ⁻³ m ³ ·kg ⁻¹ or less in the pore size distribution measured by mercury porosimetry. Claim 1, wherein the total pore volume is 0.70×10 ⁻³ m ³ ·kg ⁻¹ or less and the inflection point diameter is 15.0 μm or less in the pore distribution measured by the mercury intrusion method. Al ₄ SiC ₄ powder according to . 3. The Al ₄ SiC ₄ powder according to claim 1, wherein the pore size distribution measured by mercury porosimetry has an intra-particle void volume of 0.55×10 ⁻³ m ³ ·kg ⁻¹ or less. An additive for thermal barrier paints, comprising the Al ₄ SiC ₄ powder according to any one of claims 1 to 3.