JP2015218071A - Fine mullite hollow particle - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a fine mullite hollow particle which can be used widely as heat insulation material, heat shielding material or the like.SOLUTION: A fine mullite hollow particle has a shell that partitions a hollow chamber. The fine mullite hollow particle is characterized in that an average circularity is 0.85 or more, an average particle diameter is 0.5 μm-20 μm, the shell thickness is 500 nm or less, and 95% or more of the particle constituting component is mullite with AlOcontent 60-80 mass% and SiOcontent 20-40 mass%.

Description

  The present invention relates to fine mullite hollow particles.

  Oxide hollow particles and oxide porous materials are used in fields such as heat insulating materials, heat shielding materials, catalyst carriers, and building materials. For example, (Patent Document 1, Non-Patent Documents 1 and 2) fly ash hollow particles are used as a component of a cement-based heat insulator. However, since fly ash hollow particles have a large particle size and are colored, they have not been applied in the fields of heat insulating materials, plastic fillers, sensitizers and the like that require a thin film. Further, fly ash hollow particles have a higher thermal conductivity than mullite and are inferior in heat insulation.

JP 2005-536333 A

Coal ash handbook (4th edition), II-83 to II-85 (Environmental Technology Association, Japan Fly Ash Association) Functional filler development technology, pages 209-212 (issued by CMC Co., Ltd.)

  An object of the present invention is to provide new oxide hollow particles having a small particle diameter and excellent heat insulating properties and heat shielding properties.

Therefore, the present inventor has produced mullite hollow particles by spray pyrolysis, and has been variously studied on the particle diameter, thickness, shape, etc., and the average circularity is 0.85 or more and the average particle diameter is 0.5 μm. -20 μm, shell thickness is 500 nm or less, and the constituent mullite has an Al ₂ O ₃ content of 60 to 80% by mass and an SiO ₂ content of 20 to 40% by mass. The present inventors have found that fine mullite hollow particles having low thermal conductivity and excellent heat insulation can be obtained.

That is, the present invention relates to the following [1] to [6].
[1] A micro mullite hollow particle having a shell defining a hollow chamber, having an average circularity of 0.85 or more, an average particle diameter of 0.5 μm to 20 μm, and a thickness of the shell of 500 nm or less. Fine mullite hollow particles characterized in that 95% or more of the components are mullite having an Al ₂ O ₃ content of 60 to 80 mass% and an SiO ₂ content of 20 to 40 mass%.
[2] The fine mullite hollow particles according to [1], having a thermal conductivity of 0.005 to 0.1 W / m · K.
[3] The fine mullite hollow particles according to [1] or [2], wherein the bulk density is 0.01 to 0.3 g / cm ³ .
[4] The fine mullite hollow particles according to any one of [1] to [3], wherein the particle strength is 0.3 to 480 MPa.
[5] The fine mullite hollow particles according to any one of [1] to [4], which are produced by a spray pyrolysis method in which an aluminum and silicon-containing solution is sprayed with a spray nozzle.
[6] The fine mullite hollow particles according to any one of [1] to [5], which are obtained by heat-treating hollow particles obtained by a spray pyrolysis method.

  The fine mullite hollow particles of the present invention have a low thermal conductivity and excellent thermal stability, and are therefore useful as fillers for heat insulating materials and heat shielding materials that require a thin film.

It is a figure which shows the scanning electron microscope (SEM) image of this invention micro mullite hollow particle. It is a figure which shows the transmission electron microscope (TEM) image of this invention micro mullite hollow particle. It is a figure which shows the powder X-ray-diffraction spectrum of this invention micro mullite hollow particle. It is a figure which shows the particle size distribution of this invention micro mullite hollow particle.

The micro mullite hollow particle of the present invention is a micro mullite hollow particle having a shell defining a hollow chamber, having an average circularity of 0.85 or more, an average particle diameter of 0.5 μm to 20 μm, and a thickness of the shell of 500 nm. Hereinafter, 95% or more of the components constituting the particles are mullite (Al ₂ O ₃ content 60 to 80% by mass, SiO ₂ content 20 to 40% by mass).

  A hollow particle means a particle having a shell that defines a hollow chamber, and is different from a simple porous material. It is clear from the SEM image of FIG. 1 and the TEM image of FIG. 2 that the particles of the present invention have such a structure.

As apparent from FIGS. 1 and 2, the shape of the micro mullite hollow particles of the present invention is spherical, and the average circularity is 0.85 or more. Such a shape is achieved by manufacturing by a spray pyrolysis method.
Here, the circularity is determined by measuring the projected area (A) and the perimeter (PM) of a particle from a scanning electron micrograph, and assuming that the area of a perfect circle with respect to the perimeter (PM) is (B) Circularity is expressed as A / B. Therefore, the circumference and area of a perfect circle having the same circumference as the sample particle (PM) are PM = 2πr and B = πr ² , respectively, so that B = π × (PM / 2π) ² . The circularity of the particles is calculated as circularity = A / B = A / 4π / (PM) ² . The circularity is measured for 100 particles, and the average value is defined as the average circularity. The fine mullite hollow particles of the present invention have an average circularity of 0.85 or more, preferably 0.90 or more from the viewpoint of dispersibility and mixing properties when mixed as various fillers.

  The average particle size of the micro mullite hollow particles of the present invention is 0.5 μm to 20 μm, preferably 1 μm to 20 μm, more preferably 2 μm to 15 μm, still more preferably 3 μm to 12 μm, still more preferably. 3 μm to 10 μm. When it exceeds 20 μm, a part may have a circularity of less than 0.85, which is not preferable. In addition, adjustment of an average particle diameter can be performed by changing the nozzle diameter or atomization system of the spray nozzle used for spraying, and a 2 fluid nozzle, a 4 fluid nozzle, an ultrasonic atomization system etc. can be utilized. Here, the particle size can be measured by analysis with an electron microscope, and the average is JIS R 1629 “Method for measuring particle size distribution by laser diffraction / scattering method of fine ceramic raw material”, Particle size distribution measuring device by laser diffraction / scattering method For example, it can be calculated by a micro truck (manufactured by Nikkiso Co., Ltd.).

  The particle size distribution (particle size distribution) of the micro mullite hollow particles of the present invention is preferably as narrow as possible, and 80% or more of the particles are preferably within ± 5.0 μm of the average particle size, and 80% or more of the particles have an average particle size. The average particle diameter is more preferably ± 4.5 μm, and more preferably 80% or more of the particles are within the average particle diameter of ± 4.0 μm.

  The thickness of the shell of the micro mullite hollow particles of the present invention is 500 nm or less, preferably 1 to 400 nm, more preferably 10 to 300 nm, and further preferably 50 to 200 nm. When the thickness of the shell exceeds 500 nm, the hollow chamber is not sufficient, and particles having sufficiently small thermal conductivity are not obtained. If the shell thickness is too small, the strength of the particles may not be sufficient. The thickness of the shell can be measured from a transmission electron microscope (TEM) image.

In the minute mullite hollow particles of the present invention, 95% or more of the components constituting the particles are mullite (Al ₂ O ₃ content 60 to 80% by mass, SiO ₂ content 20 to 40% by mass), and 96% or more. More preferably, it is mullite (Al ₂ O ₃ content 60 to 80% by mass, SiO ₂ content 20 to 40% by mass), and 97% or more is mullite (Al ₂ O ₃ content 60 to 80% by mass, SiO 2 ₂ content is more preferably 20 to 40% by mass). In the case where the component constituting the particles is not mullite having the above structure, it is not preferable in terms of thermal stability and specific surface area. The Al ₂ O ₃ content in mullite is more preferably 65 to 80% by mass, and the SiO ₂ content is more preferably 20 to 35% by mass. As the components other than Al ₂ O ₃ and SiO _2, is inevitable component mixed on raw materials and manufacturing, for example, Fe ₂ O _3, CaO, etc. TiO ₂ and the like. The constituent ratio of mullite and Al ₂ O ₃ and SiO ₂ in mullite can be calculated by fluorescent X-ray analysis.

  The thermal conductivity of the micro mullite hollow particles of the present invention is preferably 0.005 to 0.1 W / m · K, more preferably 0.005 to 0.08 W / m · K, and 0.01 to 0.06 W / K. m · K is more preferable. Since the micro mullite hollow particles of the present invention have a low thermal conductivity, they are excellent as heat insulating materials and heat shielding materials. Here, the thermal conductivity can be measured by an unsteady hot wire method using a rapid thermal conductivity meter QTM-500 (manufactured by Kyoto Electronics Industry Co., Ltd.).

The bulk density of the fine mullite hollow particles of the present invention is preferably from 0.01 to 0.3 g / cm ^3, more preferably from 0.02~0.3g / cm ^3, 0.03~0 More preferably, it is ³ g / cm ³ . The bulk density can be measured by a measurement method of JIS R 1628 “Measurement Method of Bulk Density of Fine Ceramics Powder” or a powder mechanical property measurement device such as a powder tester (manufactured by Hosokawa Micron).

  The particle strength of the micro mullite hollow particles of the present invention is preferably 0.3 to 480 (90% survival time) MPa, more preferably 0.3 to 320 MPa, and 0.3 to 40 MPa. Is more preferable. Particle strength can be measured with a mercury intrusion porosimeter in accordance with ASTM D 3102-78.

  The compressive strength of the micro mullite hollow particles of the present invention is preferably 10 to 800 MPa, more preferably 20 to 700 MPa, and further preferably 30 to 500 MPa. Here, the compressive strength can be measured by a micro compression tester MCT-510 (manufactured by Shimadzu Corporation).

The angle of repose of the micro mullite hollow particles of the present invention is preferably 30 to 70 °, more preferably 40 to 60 °, and still more preferably 45 to 55 °.
Here, the angle of repose is important in terms of uniform dispersibility in the base material when the mullite hollow particles are used as a thin-film filler for a heat insulating material or a filler for a heat shielding material. It can be measured by a powder mechanical property measuring apparatus such as

  The fine mullite hollow particles of the present invention can be produced, for example, by a spray pyrolysis method. Specifically, it can be produced by a spray pyrolysis method in which an aluminum and silicon-containing aqueous solution is sprayed with a fluid nozzle such as a two-fluid nozzle or a four-fluid nozzle.

As the raw materials of aluminum and silicon to be used, inorganic salts, oxide particles, oxide particles having a composition in which the composition when forming mullite is 60 to 80% by mass of Al ₂ O _{3 and} 20 to 40% by mass of SiO ₂ are used. Any dispersion and sol solution may be used.

  The aluminum and silicon-containing solution can be prepared by mixing an aluminum compound and a silicon compound with water or an organic solvent such as ethanol. As the solvent, a mixture of water and an organic solvent can also be used. As the aluminum compound, compounds such as aluminum nitrate, aluminum chloride, aluminum sulfate, aluminum isopropoxide, aluminum oxide, and aluminum oxide sol can be used. As the silicon compound, sodium silicate, potassium silicate, tetraethyl orthosilicate, silicon oxide, silica sol and the like can be used. The concentration of the aluminum and silicon-containing solution is preferably 0.01 mol / L to 2.0 mol / L, more preferably 0.1 mol / L to 1.0 mol / L, as the total amount of each metal. An organic acid such as malic acid, citric acid or lactic acid may be added to the aluminum and silicon-containing solution.

  The aluminum and silicon-containing solution is preferably sprayed with a two-fluid nozzle from the viewpoints of particle size adjustment and productivity. Here, the two-fluid nozzle method includes an internal mixing method in which air and aluminum and silicon-containing solution are mixed inside the nozzle, and an external mixing method in which air, aluminum and silicon-containing aqueous solution are mixed outside the nozzle. Can also be adopted.

The sprayed mist is pyrolyzed by passing through a drying zone of 100 to 600 ° C. and then a pyrolysis zone of 600 to 1600 ° C. to form mullite hollow particles. The temperature of the drying zone is preferably 350 to 550 ° C., more preferably 400 to 500 ° C. from the viewpoint of maintaining hollowness. In this drying zone, the outside of the mist is dried to form a film of an inorganic compound, and the internal liquid is dried starting from the film, so that the particles are formed in a hollow shape.
The temperature of the pyrolysis zone is preferably 700 to 950 ° C, more preferably 800 to 900 ° C from the viewpoint of production cost. The pyrolysis zone is a mullite hollow particle having a shell that defines a hollow chamber by advancing a pyrolysis reaction at a high temperature, thereby strengthening the hollow structure formed in the drying zone. Hollow particles having a thickness of 5 mm are obtained.

  The obtained hollow particles may be classified by passing through a filter and the particle diameter may be adjusted. The obtained hollow particles are heated to 1000 ° C. or higher, preferably 1150 to 1250 ° C., to obtain hollow particles made of mullite having the above composition.

  The fine mullite hollow particles of the present invention have a hollow structure as described above and have a low thermal conductivity, and thus are useful as fillers for heat insulating materials and heat shielding materials. Moreover, since it is a fine particle | grain with an average particle diameter of 0.5 micrometer-20 micrometers, it is especially useful as a thin film-form filler for heat insulation materials, and a filler for thermal insulation materials. Therefore, it is advantageous to form a thin film-like heat insulating material and heat insulating material on various containers, partition walls, floors, roofs, etc. that require heat insulating properties and heat insulating properties.

  In order to obtain a heat-insulating composition or a heat-insulating composition, a heat-resistant paint, a heat-resistant resin, or the like can be blended with the fine mullite hollow particles of the present invention. The content of the fine mullite hollow particles in these compositions is preferably 5 to 90% by mass, and more preferably 10 to 80% by mass.

  Next, an Example is given and this invention is demonstrated.

Example 1
0.2 mol / L aluminum in which aluminum nitrate and tetraethyl orthosilicate were dissolved in distilled water and a silicon-containing aqueous solution were charged into the solution tank of the spray pyrolysis apparatus. The introduced aqueous solution was sprayed in the form of a mist through a two-fluid nozzle by a liquid feed pump, and passed through a drying zone (about 450 ° C.) and then a thermal decomposition zone (about 900 ° C.). Hollow particles were collected using a bag filter. The obtained hollow particles were fired at about 1200 ° C. to obtain the desired fine mullite hollow particles.

  A scanning electron microscope (SEM) photograph of the obtained micro mullite hollow particles is shown in FIG. 1, and a transmission electron microscope (TEM) photograph is shown in FIG. 1 and 2, the obtained particles have an average circularity of 0.92, an average particle diameter of about 5.9 μm, and a shell thickness of 50 to 100 nm.

The powder X-ray diffraction spectrum of the obtained fine mullite hollow particles is shown in FIG. FIG. 3 shows that the hollow particles are composed of mullite (Al ₂ O ₂ 60-80% by mass, SiO ₂ 20-40% by mass).

  The measurement result of the particle size distribution of the obtained micro mullite hollow particles is shown in FIG. FIG. 4 shows that the particle size distribution is sharp and the average particle size is 5.9 μm.

  Various characteristics of the obtained micro mullite hollow particles are shown in Table 1.

Claims (6)

A fine mullite hollow particle having a shell defining a hollow chamber, having an average circularity of 0.85 or more, an average particle diameter of 0.5 μm to 20 μm, a thickness of the shell of 500 nm or less, and 95 of the components constituting the particle % Mullite having an Al ₂ O ₃ content of 60 to 80 mass% and an SiO ₂ content of 20 to 40 mass%.   The fine mullite hollow particles according to claim 1, having a thermal conductivity of 0.005 to 0.1 W / m · K. The fine mullite hollow particles according to claim 1 or 2, having a bulk density of 0.01 to 0.3 g / cm ³ .   The fine mullite hollow particles according to any one of claims 1 to 3, wherein the particle strength is 0.3 to 480 MPa.   The fine mullite hollow particles according to any one of claims 1 to 4, which are produced by a spray pyrolysis method in which an aluminum and silicon-containing solution is sprayed with a spray nozzle.   The fine mullite hollow particles according to any one of claims 1 to 5, which are obtained by heat-treating hollow particles obtained by a spray pyrolysis method.