JP7675588B2 - Inorganic oxide hollow particles - Google Patents

Description

The present invention relates to inorganic oxide hollow particles.

Inorganic oxide hollow particles are used in the fields of heat insulation materials, heat shielding materials, soundproofing and sound absorbing materials, catalyst carriers, building materials, and electronic materials. For example, ceramic thick-skinned hollow particles with 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 have been reported to be aggregates mixed into artificial structures, yet can stably impart a heat shielding effect to the structures themselves (Patent Document 1).

JP 2014-141371 A

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.

The inventors conducted research in light of the above problems and discovered that hollow inorganic oxide particles containing a specific amount of a specific compound as an inorganic oxide can achieve a lower bulk density and a higher compression ratio than conventional particles.

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] The inorganic oxide hollow particles according to [1] above, which have a bulk density of 0.015 g/cm ³ or less and 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 [1] to [3] above, having an angle of repose of 50° or more.

The present invention provides hollow inorganic oxide particles that have a low bulk density and a high compression ratio.

In this specification, "hollow particles" refers to particles that have a cavity (hollow structure) inside. The cavity is surrounded by an outer shell, and there may be one or more cavities. Therefore, hollow particles are different from porous particles that have 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.

The inorganic oxide hollow particles of the present invention have an outer shell made of a specific inorganic oxide. Specifically, the inorganic oxides that make up the outer shell include silicon oxide, boron oxide, magnesium oxide, and aluminum oxide. This allows the bulk density to be lower and the compression ratio to be higher than ever before.

As the silicon oxide, _SiO2 is preferred from the viewpoint of low bulk density and high compressibility.
As the boron oxide, B ₂ O ₃ 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, Al ₂ O ₃ is preferred from the viewpoints of low bulk density and high compressibility.

The content of each of the inorganic oxides constituting the inorganic oxide hollow particles of the present invention is as follows. In this specification, the content of each of the inorganic oxides is a value obtained by measuring in oxide equivalent using X-ray fluorescence analysis and calculating the chemical components. Then, each chemical component is calculated by correcting using 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 X-ray fluorescence analyzer.

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

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.

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 viewpoints of low bulk density and high compressibility, 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 any inorganic oxides other than the above four types.

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.

The inorganic oxide hollow particles of the present invention are characterized by having a lower bulk density than conventional particles. Specifically, the bulk density of the inorganic oxide hollow particles of the present invention is preferably 0.015 g/cm ³ or less, more preferably 0.013 g/cm ³ or less, and even more preferably 0.012 g/cm ³ or less. 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/cm ³ or more, more preferably 0.0005 g/cm ³ or more, and even more preferably 0.001 g/cm ³ or more. In this specification, the term "bulk density" means "loose bulk density" and is measured in accordance with JIS R 1628-1997.

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 degree of compression 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.

Compression rate c (%) = (ρ _p −ρ _A )/ρ _p ×100 (1)
(In the formula, ρ _A represents the loose bulk density, and ρ _p represents the hard bulk density.)

The inorganic oxide hollow particles of the present invention preferably have a non-spherical shape. By making the particles non-spherical, it is possible to suppress an increase in volume even if the bulk density is low, thereby reducing the effort and cost involved in transportation.

The particle shape of the inorganic oxide hollow particles of the present invention can be judged to be non-spherical 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. In addition, when the circularity is 0.85 or more, it is usually judged to be approximately 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 PM=2πr and B= ^πr2 , respectively, so that B=π×(PM/2π) ² , and the circularity of this particle is calculated as 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.

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.

The inorganic oxide hollow particles of the present invention preferably have an area of 15 ^m2 /g or more, more preferably 20 ^m2 /g or more, and even more preferably 25 ^m2 /g or more. The upper limit of the BET specific surface area is not particularly limited, but from the viewpoint of increasing the amount of surface pores and decreasing the particle strength, it is preferably 45 ^m2 /g or less, more preferably 40 ^m2 /g or less, and even more preferably 35 ^m2 /g or less. In this specification, the "BET specific surface area" means 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, using a flow type automatic specific surface area measuring device (FlowSorb III 2305, manufactured by Shimadzu Corporation).

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 density meter 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 or above the melting point for 6 hours in order to remove the hollow parts, cooling them, and measuring them with a dry automatic density meter. For example, an Accupic (Shimadzu Corporation) can be used as the dry automatic density meter.

Hollowness ratio (%) = 1-(particle density/true density) x 100

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 the 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/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/scattering method.

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 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.

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, a Bruker D8 advance (manufactured by Bruker AXS K.K.) can be used as the X-ray diffraction device.

The inorganic oxide hollow particles of the present invention have the characteristics described above and can be used in a variety of applications. For example, they can be used in fields such as heat insulating materials, heat shielding materials, soundproofing and absorbing materials, catalyst carriers, building materials, and electronic materials. Since they have a low bulk density and a high compression ratio, they are useful as fillers for heat insulating materials, heat shielding materials, soundproofing and absorbing materials, building materials, electronic materials, etc.

The method for producing the 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.

Examples of raw material compounds include compounds containing one or more elements selected from silicon, boron, magnesium, and aluminum as elements constituting oxides. 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 elements. Examples of inorganic salts include nitrates, sulfates, carbonates, hydroxides, and halides. Examples of organic salts include formates, acetates, propionates, oxalates, and citrates.

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.

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.

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.

The oxides obtained from these raw material compounds include, for example, silicon oxide, boron oxide, magnesium oxide, and alumina, as well as composite oxides that combine these oxides.

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 can be adjusted appropriately according to the type of raw material compounds so as to obtain hollow inorganic oxide particles of the above-mentioned composition.

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, as the total amount of each element.

The spray pyrolysis device 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.

Examples of spray devices include fluid nozzles such as two-fluid nozzles, three-fluid nozzles, and four-fluid nozzles. Fluid nozzles can be either an internal mixing method in which the gas and raw material solution are mixed inside the nozzle, or an external mixing method in which the gas and raw material solution are mixed outside the nozzle, and either method can be used. Gases that can be supplied to the nozzle include, for example, air, and inert gases such as nitrogen and argon. Among these, air is preferred from the viewpoint of economy. One or more spray devices can be installed.

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.

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.

Examples of the heating device include a combustion burner, a hot air heater, an electric heater, etc. 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., even more 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.

The inorganic oxide hollow particles produced by the pyrolysis reaction are collected downstream of the pyrolysis furnace. The inorganic oxide hollow particles can be collected using a powder collection device that uses a high-performance cyclone powder collection machine or a bag filter.

The following examples are provided to further explain the embodiments of the present invention. However, the present invention is not limited to the following examples.

1. Analysis of Chemical Composition The inorganic oxide hollow particles were molded using a press to prepare briquettes, and the briquettes were measured in terms of oxides using an X-ray fluorescence analyzer (ZSX Primus II, manufactured by Rigaku Corporation) to calculate the chemical components. Each chemical component was calculated by correcting the oxides of the elements to be analyzed ( _SiO2 , _{Al2O3 ,} MgO, _B2O ) using the following formula so that the total value was 100%.

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

2. Measurement of bulk density: Measurement was performed using a tap density meter JV200i (manufactured by Copley) in accordance with JIS R 1628-1997.

3. Measurement of Compressibility The compression ratio was calculated according to the following formula (1).

Compression ratio c (%) = (ρp - ρA) / ρp × 100 (1)
(In the formula, ρA represents loose bulk density, and ρp represents hard bulk density.)

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

Hollowness ratio (%) = (1-particle density/true density) x 100

5. Measurement of Angle of Repose Measurement was performed in accordance with ISO 902 using a Powder Tester PT-D type (manufactured by Hosokawa Powder Laboratory Co., Ltd.).

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 having the same perimeter as the perimeter (PM) of the sample particle are PM=2πr and B= ^πr2 , respectively, so B=π×(PM/2π) ² , and the circularity of this particle is calculated as circularity=A/B=A×4π/(PM) ² . Then, the circularity of 100 particles was measured, and the average value was taken as the "circularity" of the inorganic oxide hollow particles. In addition, the number ratio of particles having a circularity of 0.5 or less was calculated. Note that a JSM-7001F (manufactured by JEOL Ltd.) was used as the scanning electron microscope.

7. Analysis of Crystal Structure Measurement was performed using a powder X-ray diffractometer (Bruker D8 advance, manufactured by Bruker AXS K.K.), and the crystal structure was analyzed from the obtained X-ray diffraction pattern.

8. Measurement of particle size Using a particle size distribution measuring device (MT3000II, manufactured by Microtrackbell Co., Ltd.), a volumetric particle size distribution was prepared in accordance with JIS R 1629, and the cumulative 10% particle size (D10) in the volumetric particle size distribution, the cumulative 50% particle size (D50) in the volumetric particle size distribution, and the cumulative 90% particle size (D90) in the volumetric particle size distribution were determined.

9. Measurement of BET specific surface area The BET specific surface area was measured using a flow type automatic specific surface area measuring device (FlowSorb III 2305, manufactured by Shimadzu Corporation) using a nitrogen/helium mixed gas containing 30% nitrogen.

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 concentrations 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 sending 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 sending 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 recovered using a bag filter. The physical properties of the recovered inorganic oxide hollow particles were analyzed. The results are shown in Table 2.

The inorganic oxide hollow particles of Comparative Example 1 had a high content of boron oxide and magnesium oxide as inorganic oxides, but a low content of silicon oxide, and therefore had a high bulk density and a low compressibility. It can also be seen that the inorganic oxide hollow particles of Comparative Example 1 were approximately spherical, had a low angle of repose, and had a low BET specific surface area.
On the other hand, the inorganic oxide hollow particles of Examples 1 to 3 contained a specific amount of a specific compound as an inorganic oxide, and therefore had a low bulk density and a high compressibility. It is also found that the inorganic oxide hollow particles of Examples 1 to 3 were non-spherical, had a high angle of repose, and had a high BET specific surface area.

Claims (4)

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. The non-spherical inorganic oxide hollow particles according to claim 1, which have a bulk density of 0.015 g/cm ³ or less and a compressibility of 85% or more. 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. 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.