Inorganic oxide hollow particles

Abstract

To provide an inorganic oxide hollow particle having a low bulk density and a high compressibility ratio.SOLUTION: An inorganic oxide hollow particle contains, as inorganic oxides, 60 mass% or more silicon oxide, 20 mass% or less boron oxide, 12 mass% or less magnesium oxide and 15 mass% or more aluminum oxide.SELECTED DRAWING: None

Description

[Technical field]

[0001] The present invention relates to inorganic oxide hollow particles. [Background technology]

[0002] Inorganic oxide hollow particles are used in the fields of heat insulation materials, heat shielding materials, soundproofing and absorbing materials, catalyst carriers, building materials, and electronic materials. For example, it has been reported that ceramic thick-skinned hollow particles, which have an outer diameter of 7 to 20 mm, a hollow diameter of 3 to 12 mm, a skin thickness of 2 mm or more, a static fracture strength of 2000 N or more, and an impact fracture strength of 40 N or more, can stably impart a heat shielding effect to the structure itself while being an aggregate to be mixed in an artificial structure (Patent Document 1). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2014-141371 A Summary of the Invention [Problem to be solved by the invention]

[0004] Since inorganic oxide hollow particles have cavities surrounded by an outer shell, they are lighter than non-hollow particles. A low bulk density is advantageous for making inorganic oxide hollow particles lighter. However, when the bulk density of inorganic oxide hollow particles is low, the volume increases, which increases the effort and cost required for transportation. In this case, if the inorganic oxide hollow particles can be compressed without being damaged, the volume can be reduced, thereby reducing the load during transportation. An object of the present invention is to provide inorganic oxide hollow particles having a low bulk density and a high compressibility. [Means for solving the problem]

[0005] The present inventors conducted research in light of the above problems and found that inorganic oxide hollow particles containing a specific amount of a specific compound as an inorganic oxide can have a lower bulk density and a higher compressibility than conventional particles.

[0006] That is, the present invention provides the following [1] to [4]. [1] Inorganic oxide hollow particles containing, as inorganic oxides, 60 mass% or more of silicon oxide, 20 mass% or less of boron oxide, 12 mass% or less of magnesium oxide, and 15 mass% or more of aluminum oxide. [2] Bulk density is 0.015g / cm 3 The inorganic oxide hollow particles according to [1] above, having a compressibility of 85% or more. [3] The inorganic oxide hollow particles according to [1] or [2] above, having a circularity of 0.70 or less. [4] The inorganic oxide hollow particles according to any one of the above [1] to [3], which have an angle of repose of 50° or more. Effect of the Invention

[0007] According to the present invention, it is possible to provide inorganic oxide hollow particles having a low bulk density and a high compressibility. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0008] In this specification, the term "hollow particles" refers to particles having a cavity (hollow structure) inside. The cavity is surrounded by an outer shell, and the number of cavities may be one or more. Therefore, hollow particles are different from porous particles having multiple pores extending from the surface of the particle to the inside. Note that hollow particles can be clearly distinguished from porous particles by scanning electron microscope (SEM) images.

[0009] The inorganic oxide hollow particles of the present invention have a shell made of a specific inorganic oxide. Specifically, the inorganic oxides constituting the shell include silicon oxide, boron oxide, magnesium oxide, and aluminum oxide. This allows the bulk density to be lowered and the compression ratio to be higher than in the past.

[0010] As the silicon oxide, SiO2 is preferred from the viewpoint of low bulk density and high compressibility. As the boron oxide, B2O3 is preferred from the viewpoints of low bulk density and high compressibility. As the magnesium oxide, MgO is preferred from the viewpoints of low bulk density and high compressibility. As the aluminum oxide, Al2O3 is preferable from the viewpoint of low bulk density and high compressibility.

[0011] The contents of each of the inorganic oxides constituting the inorganic oxide hollow particles of the present invention are as follows. In this specification, the contents of each of the inorganic oxides are values ​​measured in terms of oxides by fluorescent X-ray analysis and the chemical components are calculated. Then, each chemical component is calculated by correcting according to the following formula so that the total value of the oxides of the elements to be analyzed is 100%. For example, a ZSX primus II (manufactured by Rigaku Corporation) can be used as the fluorescent X-ray analyzer.

[0012] Chemical composition (after correction) (%) = Chemical composition (before correction) × 100 / (100-impurities (%)) (In the formula, the impurity (%) is calculated by subtracting the total value of the above-mentioned chemical composition of the oxide from 100.)

[0013] The silicon oxide content is 60% by mass or more, and from the viewpoints of low bulk density and high compressibility, it is preferably 61% by mass or more, more preferably 63% by mass or more, even more preferably 65% ​​by mass or more, and is preferably 80% by mass or less, more preferably 79% by mass or less, and even more preferably 78% by mass or less. The content of boron oxide is 20% by mass or less, and from the viewpoint of low bulk density and high compressibility, it is preferably 19% by mass or less, more preferably 15% by mass or less, and even more preferably 12% by mass or less. The lower limit of the content of boron oxide is not particularly limited and may be 0% by mass, but is preferably 0.1% by mass or more, more preferably 0.3% by mass or more, and even more preferably 0.5% by mass or more. The content of magnesium oxide is 12% by mass or less, and from the viewpoint of low bulk density and high compressibility, it is preferably 10% by mass or less, more preferably 8% by mass or less, and even more preferably 6% by mass or less. The lower limit of the content of magnesium oxide is not particularly limited and may be 0% by mass, but from the viewpoint of low bulk density and high compressibility, it is preferably 0.5% by mass or more, more preferably 1% by mass or more, and even more preferably 2% by mass or more. The aluminum oxide content is 12% by mass or more, and from the viewpoints of low bulk density and high compressibility, it is preferably 13% by mass or more, more preferably 15% by mass or more, even more preferably 17% by mass or more, and is preferably 25% by mass or less, more preferably 23% by mass or less, and even more preferably 21% by mass or less.

[0014] The inorganic oxide hollow particles of the present invention may further contain an inorganic oxide other than the above four types as the inorganic oxide constituting the outer shell, such as an oxide of a Group 1 element, an oxide of a Group 2 element other than magnesium oxide, or an oxide of a Group 4 element. Examples of Group 1 element oxides include Li2O, Na2O, K2O, Rb2O, and Cs2O. Examples of Group 2 element oxides other than magnesium oxide include CaO, SrO, BaO, and RaO. Examples of Group 4 element oxides include TiO2, ZrO2, and HfO2. The content of inorganic oxides other than the above four types can be appropriately selected within a range that does not impair the effects of the present invention. From the viewpoint of low bulk density and high compressibility, however, the content is preferably 10 mass % or less, more preferably 5 mass % or less, even more preferably 1 mass % or less, and even more preferably does not contain inorganic oxides other than the above four types.

[0015] From the viewpoint of low bulk density and high compressibility, the inorganic oxide hollow particles of the present invention preferably have a total content of silicon oxide and aluminum oxide of 70 mass% or more, more preferably 75 mass% or more, even more preferably 80 mass% or more, and even more preferably 85 mass% or more, with the remainder being at least one selected from boron oxide and magnesium oxide, and preferably containing at least magnesium oxide. In addition, from the viewpoint of low bulk density and high compressibility, the inorganic oxide hollow particles of the present invention preferably have a mass ratio of silicon oxide to aluminum oxide (aluminum oxide / silicon oxide) of 0.2 to 3, more preferably 0.21 to 0.28, and even more preferably 0.23 to 0.26.

[0016] The inorganic oxide hollow particles of the present invention are characterized by having a bulk density lower than that of conventional particles. Specifically, the bulk density of the inorganic oxide hollow particles of the present invention is 0.015 g / cm 3 Less than 0.013 g / cm is preferable. 3 Less than 0.012 g / cm is more preferable. 3 The lower limit of the bulk density is not particularly limited, but from the viewpoint of ensuring sufficient strength, it is preferably 0.0001 g / cm3 or less. 3 More than 0.0005 g / cm is preferable. 3 More preferably, 0.001 g / cm 3 In this specification, the term "bulk density" means "loose bulk density" and is measured in accordance with JIS R 1628-1997.

[0017] The inorganic oxide hollow particles of the present invention are characterized by a higher compression ratio than conventional ones. Specifically, the compression ratio of the inorganic oxide hollow particles of the present invention is preferably 85% or more, more preferably 86% or more, and even more preferably 87% or more. In addition, the upper limit of the compression degree is preferably 97% or less, more preferably 95% or less, and even more preferably 93% or less, from the viewpoint of ensuring sufficient strength. Here, in this specification, "compressibility" refers to a value calculated by the following formula (1), and the "hardened bulk density" in the following formula (1) is measured in accordance with JIS R 1628-1997. In addition, for example, a tap density meter JV200i (manufactured by COPLEY) can be used to measure the loose bulk density and hardened bulk density.

[0018] Compression rate c(%)=(ρ p -ρ A ) / ρ p ×100 (1) [In the formula, ρ A indicates the loose bulk density, ρ p indicates the compacted bulk density.

[0019] The inorganic oxide hollow particles of the present invention are preferably non-spherical in shape. By making the particles non-spherical, an increase in volume can be suppressed even if the bulk density is low, and therefore the labor and cost required for transportation can be reduced.

[0020] The non-spherical particle shape of the inorganic oxide hollow particles of the present invention can be determined from the circularity. The circularity of the inorganic oxide hollow particles of the present invention is preferably 0.70 or less, more preferably 0.67 or less, and even more preferably 0.65 or less. A circularity of 0.85 or more is usually considered to be substantially spherical. Here, in this specification, "circularity" refers to a value calculated by the following method. That is, when the projected area (A) and perimeter (PM) of a particle are measured from a scanning electron microscope photograph, and the area of ​​a perfect circle relative to the perimeter (PM) is (B), the circularity of the particle is expressed as A / B. Here, the perimeter and area of ​​a perfect circle having the same perimeter as the perimeter (PM) of the sample particle are expressed as PM=2πr and B=πr, respectively. 2 Therefore, B = π × (PM / 2π)2 The circularity of this particle is: Circularity = A / B = A × 4π / (PM) 2 The circularity of 100 particles is then measured, and the average value is taken as the "circularity" of the inorganic oxide hollow particles. In addition, the inorganic oxide hollow particles of the present invention preferably have a non-spherical particle shape, that is, the ratio of particles having a low circularity is a specific ratio. The ratio of particles having a low circularity is a specific ratio, which improves the compressibility. Specifically, when the circularity of the above 100 particles is measured, the ratio of particles having a circularity of 0.5 or less to the total particles is preferably 10% or more, more preferably 20% or more. This ratio may be 100% to the total particles.

[0021] The inorganic oxide hollow particles of the present invention preferably have an angle of repose of 50° or more, more preferably 52° or more, and even more preferably 54° or more. The upper limit of the angle of repose is not particularly limited, but from the viewpoint of improving handleability, it is preferably 70° or less, more preferably 65° or less, and even more preferably 60° or less. In this specification, the "angle of repose" is measured in accordance with ISO 902. For example, a Powder Tester PT-D type (manufactured by Hosokawa Powder Research Institute) can be used to measure the angle of repose.

[0022] The inorganic oxide hollow particles of the present invention have a diameter of 15 mm. 2 / g or more is preferable, and 20m 2 / g or more is more preferable, and 25m 2 Although there is no particular upper limit to the BET specific surface area, from the viewpoint of increasing the amount of surface pores and decreasing the particle strength, it is preferable that the upper limit is 45 m 2 / g or less is preferable, and 40m 2 / g or less is more preferable, and 35m 2 In this specification, the term "BET specific surface area" refers to a surface area measured by the BET method (a method for measuring surface area by utilizing the adsorption of gas molecules), and can be measured, for example, by using an automatic flow type specific surface area measuring device (FrowSorb III 2305, manufactured by Shimadzu Corporation).

[0023] The hollow ratio of the inorganic oxide hollow particles of the present invention is preferably 29% or more, more preferably 30% or more, and even more preferably 31% or more. The upper limit of the hollow ratio is preferably 95% or less, more preferably 90% or less, from the viewpoint of ensuring sufficient strength. Here, in this specification, the "hollow ratio" is a value calculated from the particle density and true density of the particles measured using a dry automatic densitometer using the following formula. Since it is difficult to measure each particle, it is the hollow ratio as a particle group. In addition, the "true density" is measured by heating the particles in a box-type electric furnace at a melting point or higher for 6 hours in order to remove the hollow parts, cooling them, and measuring them with a dry automatic densitometer. For example, an Accupyc (Shimadzu Corporation) can be used as the dry automatic densitometer.

[0024] Hollowness ratio (%)=1-(particle density / true density)×100

[0025] The inorganic oxide hollow particles of the present invention are minute particles. More specifically, the particle size distribution can have the following characteristics. Here, in this specification, "particle size distribution" refers to a volume-based particle size distribution measured in accordance with JIS R 1629 "Method for measuring particle size distribution of fine ceramic raw materials by laser diffraction and scattering method". The particle size distribution is represented by a distribution curve with the horizontal axis representing particle size (μm) and the vertical axis representing the volume-based frequency (%). Note that, for example, Microtrac (manufactured by Nikkiso Co., Ltd.) can be used as a particle size distribution measuring device using the laser diffraction and scattering method.

[0026] For example, the cumulative 10% particle size (D10) in the volume-based particle size distribution is preferably 0.05 μm or more, more preferably 0.1 μm or more, even more preferably 0.3 μm or more, and is preferably 3.0 μm or less, more preferably 2.5 μm or less, even more preferably 2.0 μm or less. The cumulative 50% particle size (D50) in the volume-based particle size distribution is preferably 1.0 μm or more, more preferably 1.5 μm or more, even more preferably 2.0 μm or more, and is preferably 7.0 μm or less, more preferably 6.0 μm or less, even more preferably 5.0 μm or less. The cumulative 90% particle size (D90) in the volume-based particle size distribution is preferably 5.0 μm or more, more preferably 7.0 μm or more, even more preferably 9.0 μm or more, and is preferably 20.0 μm or less, more preferably 15.0 μm or less, even more preferably 10.0 μm or less.

[0027] The aluminosilicate hollow particles of the present invention are preferably amorphous. The amorphous nature of the particles can be confirmed by analyzing the X-ray diffraction pattern obtained by an X-ray diffraction device. For example, Bruker D8 advance (manufactured by Bruker AXS Co., Ltd.) can be used as the X-ray diffraction device.

[0028] The inorganic oxide hollow particles of the present invention have the above-described characteristics and can be applied to various applications. For example, they can be applied to fields such as heat insulating materials, heat shielding materials, soundproofing / absorbing materials, catalyst carriers, building materials, electronic materials, etc., and because they have a low bulk density and a high compressibility, they are useful as fillers for heat insulating materials, heat shielding materials, soundproofing / absorbing materials, building materials, electronic materials, etc.

[0029] The method for producing inorganic oxide hollow particles of the present invention is not particularly limited as long as it can produce inorganic oxide hollow particles having the above-mentioned configuration. For example, a method can be mentioned in which a liquid to be sprayed containing a raw material compound is sprayed from a spray device installed in a spray pyrolysis device, and the sprayed droplets (mist) are pyrolyzed.

[0030] Examples of the raw material compound include compounds containing one or more elements selected from silicon, boron, magnesium, and aluminum as elements constituting an oxide. Such compounds are not particularly limited as long as they are compounds that dissolve in water, and examples include inorganic salts, organic salts, and alkoxides, which may contain one or more of these elements. Examples of inorganic salts include nitrates, sulfates, carbonates, hydroxides, and halides. Examples of organic salts include formates, acetates, propionates, oxalates, and citrates.

[0031] Examples of silicon-containing compounds include silicic acid alkoxides. Examples of silicic acid alkoxides include tetramethyl orthosilicate (TMOS), tetraethyl orthosilicate (TEOS), tetrapropyl orthosilicate (TPOS), and tetrabutoxysilane. In addition, a solution in which silicon oxide is dispersed in a solvent, or a sol solution of silicon oxide can also be used as the raw material compound solution. Examples of the boron-containing compound include metaborates such as sodium borate and potassium borate, tetraborates such as sodium tetraborate and potassium tetraborate, pentaborates such as sodium pentaborate and potassium pentaborate, and boric acid. Examples of magnesium-containing compounds include magnesium nitrate, magnesium sulfate, magnesium chloride, magnesium phosphate, and magnesium hydroxide. Examples of aluminum-containing compounds include inorganic salts such as aluminum nitrate, aluminum sulfate, aluminum chloride, aluminum phosphate, aluminum hydroxide, aluminum acetate, and aluminum oxalate, and aluminum alkoxides such as aluminum methoxide, aluminum ethoxide, and aluminum isopropoxide. In addition, aluminosilicates, solutions in which aluminum oxide is dispersed in a solvent, and sol solutions of aluminum oxide can also be used as the raw compound solutions. Examples of aluminosilicates include sodium aluminosilicate, potassium aluminosilicate, and calcium aluminosilicate.

[0032] In the present invention, the raw material compounds may further contain compounds containing elements other than silicon, boron, magnesium and aluminum. Such compounds are not particularly limited as long as they are water-soluble metal compounds, and may include, for example, one or more selected from lithium salts, potassium salts, titanium salts, calcium salts, strontium salts, zinc salts, zirconium salts, barium salts, cesium salts, and yttrium salts. Examples of salts of these metals include inorganic salts, organic salts, and alkoxides. Specific examples of inorganic salts and organic salts are as described above.

[0033] Examples of the lithium salt include lithium chloride, lithium nitrate, and lithium nitrite. Examples of potassium salts include potassium chloride, potassium nitrate, and potassium sulfate. Examples of titanium salts include titanium nitrate, titanium sulfate, and titanium chloride. Examples of calcium salts include calcium nitrate, calcium chloride, calcium hydroxide, calcium formate, calcium acetate, and calcium propionate. Examples of strontium salts include strontium acetate and strontium propionate. Examples of zinc salts include zinc nitrate, zinc sulfate, and zinc chloride. Examples of zirconium salts include zirconium oxynitrate and zirconium oxychloride. Examples of barium salts include barium nitrate, barium chloride, and barium hydroxide. Examples of cesium salts include cesium nitrate, cesium sulfate, and cesium chloride. Examples of yttrium salts include yttrium nitrate, yttrium sulfate, and yttrium chloride.

[0034] Examples of oxides obtainable from these raw material compounds include silicon oxide, boron oxide, magnesium oxide, and alumina, as well as composite oxides that are combinations of these oxides.

[0035] The liquid to be sprayed can be prepared by mixing the raw material compounds with water or an organic solvent such as ethanol. The mixing ratio of the raw material compounds may be appropriately adjusted according to the type of the raw material compounds so as to obtain hollow inorganic oxide particles having the above-mentioned composition.

[0036] The concentration of the raw material compounds in the liquid to be sprayed is preferably 0.01 mol / L to 2.0 mol / L, and more preferably 0.1 mol / L to 1.0 mol / L, in terms of the total amount of each element.

[0037] The spray pyrolysis apparatus preferably has a pyrolysis furnace with a vertical cylindrical shape, and the size of the pyrolysis furnace can be appropriately selected depending on the production scale.

[0038] Examples of the spraying device include fluid nozzles such as a two-fluid nozzle, a three-fluid nozzle, and a four-fluid nozzle. Here, the type of the fluid nozzle includes an internal mixing type in which the gas and the raw material solution are mixed inside the nozzle, and an external mixing type in which the gas and the raw material solution are mixed outside the nozzle, and either type can be adopted. As the gas to be supplied to the nozzle, for example, air, nitrogen, argon, or other inert gases can be used. Among them, air is preferable from the viewpoint of economy. Incidentally, one or more spraying devices can be installed.

[0039] The flow rate of the liquid to be sprayed is usually 1 to 100 L / h, preferably 3 to 80 L / h, and more preferably 5 to 60 L / h.

[0040] The droplets sprayed from the spray device are heated by a heater in the pyrolysis furnace to form a film containing an inorganic compound, and the film acts as a starting point for the formation of hollow inorganic oxide particles. The droplet ejection speed is usually 1 to 50 m / s, preferably 5 to 35 m / s, and more preferably 10 to 20 m / s.

[0041] Examples of the heating device include a combustion burner, a hot air heater, and an electric heater. One or more heating devices can be installed. Any of the combustion burners, hot air heaters, and electric heaters that are generally available on the market can be used. The temperature of the heating device is preferably 400 to 1800° C., more preferably 600 to 1500° C., further preferably 700 to 1400° C., and even more preferably 800 to 1200° C. At such a temperature, pyrolysis is sufficient, and the particles are less likely to aggregate when discharged outside the pyrolysis furnace.

[0042] The inorganic oxide hollow particles generated by the thermal decomposition reaction are collected from the downstream side of the thermal decomposition furnace using a powder collection device such as a high-performance cyclone powder collection machine or a bag filter. EXAMPLES

[0043] The embodiments of the present invention will be described in more detail below with reference to examples, but the present invention is not limited to the following examples.

[0044] 1. Chemical composition analysis The inorganic oxide hollow particles were pressed into briquettes, which were then measured in terms of oxides using an X-ray fluorescence analyzer (ZSX primus II, Rigaku Corporation) to calculate the chemical components. Each chemical component was calculated by correcting the total value of the oxides of the analyzed elements (SiO2, Al2O3, MgO, and B2O) to 100% using the following formula.

[0045] Chemical composition (after correction) (%) = Chemical composition (before correction) × 100 / (100-impurities (%)) (In the formula, the impurity (%) is calculated by subtracting the total value of the above-mentioned chemical composition of the oxide from 100.)

[0046] 2. Measurement of bulk density The measurement was performed using a tap density meter JV200i (manufactured by COPLEY) in accordance with JIS R 1628-1997.

[0047] 3. Compression ratio measurement The compression ratio was calculated according to the following formula (1).

[0048] Compressibility c(%)=(ρp-ρA) / ρp×100 (1) (In the formula, ρA represents the loose bulk density, and ρp represents the hard bulk density.)

[0049] 4. Measurement of particle density, true density, and hollowness The particle density and true density of the particles were measured using an Accupyc (Shimadzu Corporation) as a dry automatic density meter, and calculated using the following formula: Note that the true density was measured by heating the particles at or above the melting point for 6 hours in a box-type electric furnace to remove hollow parts, then cooling and measuring the true density with the dry automatic density meter.

[0050] Hollowness ratio (%)=(1-particle density / true density)×100

[0051] 5. Measurement of angle of repose The measurements were performed using a Powder Tester PT-D model (manufactured by Hosokawa Powder Laboratory Co., Ltd.) in accordance with ISO 902.

[0052] 6. Measurement of circularity When the projected area (A) and perimeter (PM) of a particle are measured from a scanning electron microscope photograph, and the area of ​​a perfect circle relative to the perimeter (PM) is (B), the circularity of the particle is expressed as A / B. Here, the perimeter and area of ​​a perfect circle with the same perimeter as the perimeter (PM) of the sample particle are PM=2πr and B=πr, respectively. 2 Therefore, B = π × (PM / 2π) 2 The circularity of this particle is: Circularity = A / B = A × 4π / (PM) 2 The circularity is calculated as follows. The circularity of 100 particles was measured, and the average value was taken as the "circularity" of the inorganic oxide hollow particles. The percentage of particles with a circularity of 0.5 or less was calculated. The scanning electron microscope used was JSM-7001F (manufactured by JEOL Ltd.).

[0053] 7. Crystal Structure Analysis Measurements were performed using a powder X-ray diffractometer (Bruker D8 advance, manufactured by Bruker AXS Co., Ltd.), and the crystal structure was analyzed from the obtained X-ray diffraction pattern.

[0054] 8. Particle size measurement A particle size distribution was prepared based on volume in accordance with JIS R 1629 using a particle size distribution measuring device (MT3000II, manufactured by Microtrack Bell), and the cumulative 10% particle size (D10) in the volume-based particle size distribution, the cumulative 50% particle size (D50) in the volume-based particle size distribution, and the cumulative 90% particle size (D90) in the volume-based particle size distribution were determined.

[0055] 9. Measurement of BET specific surface area The BET specific surface area was measured using an automatic flow type specific surface area measuring device (FlowSorb III 2305, Shimadzu Corporation) using a nitrogen-helium gas mixture containing 30% nitrogen.

[0056] Examples 1 to 3 and Comparative Example 1 The raw material compounds (colloidal silica, tetraethyl orthosilicate, aluminum nitrate nonahydrate, magnesium nitrate hexahydrate, boric acid) were dissolved in 30 liters of distilled water to the molar concentration shown in Table 1, and the raw material compound aqueous solution was charged into a solution tank. The charged aqueous solution was sent to a two-fluid nozzle by a liquid delivery pump, sprayed in a mist form from the two-fluid nozzle, and heated in a furnace (1000°C). The operating conditions of the two-fluid nozzle were set to a nozzle air volume of 100 L / min and a liquid delivery volume of 67 mL / min. Then, the mixture was quenched by a cooling mechanism installed at the outlet of the reaction zone of the furnace, and the inorganic oxide hollow particles were then collected using a bag filter. The physical properties of the collected inorganic oxide hollow particles were analyzed. The results are shown in Table 2.

[0057] [Table 1]

[0058] [Table 2]

[0059] The inorganic oxide hollow particles of Comparative Example 1 have a high content of boron oxide and magnesium oxide as inorganic oxides, but a low content of silicon oxide, so that the bulk density is high and the compressibility is low. It is also found that the inorganic oxide hollow particles of Comparative Example 1 are approximately spherical, have a low angle of repose, and have a low BET specific surface area. On the other hand, the inorganic oxide hollow particles of Examples 1 to 3 contain a specific amount of a specific compound as an inorganic oxide, and therefore have a low bulk density and a high compressibility. It is also found that the inorganic oxide hollow particles of Examples 1 to 3 are non-spherical, have a high angle of repose, and have a high BET specific surface area.

Claims

1. The inorganic oxides include 60% by mass or more of silicon oxide, 20% by mass or less of boron oxide, 4.0% by mass or more and 6% by mass or less of magnesium oxide, and 15% by mass or more of aluminum oxide, The circularity is 0.70 or less. Non-spherical inorganic oxide hollow particles.

2. Bulk density is 0.015 g / cm 3 2. The non-spherical inorganic oxide hollow particle according to claim 1, having a particle size of 0.1 to 1.0 mm and a compressibility of 85% or more.

3. 3. The non-spherical inorganic oxide hollow particles according to claim 1 or 2, which have an angle of repose of 50° or more.

4. 4. The non-spherical inorganic oxide hollow particles according to claim 1, wherein the proportion of particles having a circularity of 0.5 or less is 10% or more of the total number of particles.

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