JP2020142949A - Producing method of inorganic oxide particle - Google Patents

Abstract

To provide a producing method of an inorganic oxide particle solidification of which is prevented at a tip of a nozzle, and which has a sharp particle size distribution.SOLUTION: The producing method of the inorganic oxide particle includes a step of spraying, for thermal decomposition, mist from a nozzle into an internal combustion type spray thermal decomposition apparatus that is provided with the nozzle for spraying the mist of a solution of a compound containing elements constituting the inorganic oxide, and a combustion burner as a heating source for the sprayed mist, in which the combustion burner is arranged so that flame of the combustion burner does not come into direct contact with the mist, a ratio of a spray velocity of the mist sprayed from the nozzle to a flow velocity of a combustion gas generated by the combustion burner (spray velocity/combustion gas flow velocity) is 1 to 5, and a heating temperature is 400 to 1800°C.SELECTED DRAWING: None

Description

The present invention relates to a method for producing inorganic oxide particles.

As a method for producing inorganic oxide particles, for example, a spray pyrolysis method is known. The spray pyrolysis method is a manufacturing method in which heat is applied to the mist sprayed in the spray pyrolysis apparatus and particles are synthesized by thermal decomposition. A spraying device generally called a two-fluid, three-fluid or four-fluid nozzle is used to form the mist, and the mist is atomized by discharging the raw material solution from the tip at the same time as compressed air. Then, the mist is blown into the spray pyrolysis apparatus and treated with a heat source (hot air) generated by a heater, a burner, or the like to synthesize inorganic oxide particles (Patent Document 1). In addition, it is possible to produce inorganic oxide hollow particles in which voids exist inside the particles by the spray pyrolysis method, but the inorganic oxide hollow particles are lighter in weight and have heat insulation and heat shielding properties as compared with dense particles. Since it has excellent properties such as sound insulation and light scattering, it is widely used as a heat insulating / heat insulating material filler, a sound insulating material filler, and a reflective material filler (Patent Document 2).

Japanese Unexamined Patent Publication No. 2011-98867 Japanese Unexamined Patent Publication No. 2018-065078

However, when inorganic oxide particles are produced by a general spray pyrolysis device, the mist sprayed from the spray device is tilted by the hot air, and the mist and particles adhere to the furnace wall and the nozzle discharge port, and the nozzle tip Solidification may occur in the part. In addition, there is a problem that the mists fanned by hot air interfere with each other during drying, the particles adhere to each other, and the particle size distribution becomes broad.
An object of the present invention is to provide a method for producing inorganic oxide particles having a sharp particle size distribution while preventing consolidation at the tip of a nozzle.

As a result of studies to solve the above problems, the present inventors have found that the raw material solution sprayed from the nozzle in an internal combustion type spray thermal decomposition apparatus provided with a combustion burner arranged so that the flame does not come into direct contact with the mist. By controlling the ratio of the mist spraying speed to the combustion gas flow velocity generated by the combustion burner (spraying speed / combustion gas flow velocity) and the heating temperature within a specific range, solidification at the nozzle tip is prevented. It was also found that inorganic oxide particles having a sharp particle size distribution can be produced.

That is, the present invention provides the following [1] to [3].
[1] From the nozzle into an internal combustion type spray thermal decomposition apparatus including a nozzle for spraying a mist of a solution of a compound containing an element constituting an inorganic oxide and a combustion burner as a heating source of the sprayed mist. A method for producing inorganic oxide particles, which comprises a step of spraying the mist and thermally decomposing the mist.
The combustion burner is arranged so that the flame of the combustion burner does not come into direct contact with the mist.
The ratio (spraying speed / combustion gas flow velocity) between the spraying speed of the mist sprayed from the nozzle and the flow velocity of the combustion gas generated by the combustion burner is 1 to 5.
The heating temperature is 400-1800 ° C.
Method for producing inorganic oxide particles.
[2] The compound containing the element constituting the oxide is one selected from aluminum salt, titanium salt, magnesium salt, calcium salt, sodium salt, borate, aluminosilicate, aluminum alkoxide and silicate alkoxide. The method for producing inorganic oxide particles according to [1], which is two or more kinds.
[3] The method for producing inorganic oxide particles according to [1] or [2], wherein the solution is an aqueous solution.

According to the present invention, it is possible to prevent solidification at the tip of the nozzle and to produce inorganic oxide particles having a sharp particle size distribution by a simple operation.

It is the schematic (side view, AA line sectional view) which shows an example of the spray pyrolysis apparatus applicable to the manufacturing method of this invention. It is the schematic (side view, AA line sectional view) which shows the other spray pyrolysis apparatus applicable to the manufacturing method of this invention. It is a figure which shows the particle size distribution of the inorganic oxide hollow particle obtained in Example 1. FIG. It is a figure which shows the particle size distribution of the inorganic oxide hollow particle obtained in the comparative example 2. FIG.

Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. In the description of the drawings, the same elements are designated by the same reference numerals, and duplicate description will be omitted. Further, for convenience of illustration, the dimensional ratios in the drawings do not always match those described.
FIG. 1 is a schematic view showing an example of a spray pyrolysis apparatus applicable to the production method of the present invention. The spray pyrolysis apparatus 10 is an internal combustion type, and as shown in FIG. 1, a nozzle 3 for spraying a mist (droplet) 1 of a raw material solution into a pyrolysis furnace 2 and a sprayed mist are used. It has a combustion burner 4 and an auxiliary heat source 5 which are heating sources for thermal decomposition.

First, the configuration of the spray pyrolysis apparatus will be described.
Any material used as the furnace material can be used as the pyrolysis furnace, and the pyrolysis furnace may be selected in consideration of the heating temperature and the like. Further, it is common to use refractory bricks, heat insulating bricks, castables, etc. alone, in layers, or in combination thereof on the inner wall of a metal shell.
The shape of the pyrolysis furnace is preferably a rigid cylindrical shape in that a swirling flow can be generated in the pyrolysis furnace. The size of the pyrolysis furnace can be appropriately selected depending on the production scale.

The nozzles are arranged so as to spray the mist of the raw material solution upward to the bottom of the pyrolysis furnace, as shown in FIG. One nozzle or two or more nozzles may be installed. Further, the nozzle may be protected by a heat insulating material or the like, if necessary, in consideration of heat resistance.

The nozzle is not particularly limited as long as it has a gas supply port for supplying gas and a discharge port for spraying the raw material solution, and examples thereof include a two-fluid nozzle, a three-fluid nozzle, and a four-fluid nozzle. it can. The nozzle method includes an internal mixing method in which the gas supplied to the gas supply port and the raw material solution are mixed inside the nozzle and sprayed from the discharge port, a gas supplied to the gas supply port, and a discharge port. There is an external mixing method in which the sprayed raw material solution is mixed outside the nozzle, and any of them can be adopted, but the external mixing method is preferable from the viewpoint of preventing solidification at the tip of the nozzle and production efficiency. As the gas supplied to the nozzle, for example, air, an inert gas such as nitrogen or argon, or the like can be used. Above all, air is preferable from the viewpoint of economy.

One to four combustion burners can be installed. The spray pyrolysis apparatus shown in FIG. 1 is equipped with two combustion burners. When a plurality of combustion burners are installed, they are arranged diagonally at approximately the same distance from the bottom of the pyrolysis furnace and in the tangential direction inside the pyrolysis furnace (see the sectional view taken along line AA). In this case, they may be arranged upward at an angle of 0 ° to 60 °, and from the viewpoint of efficiently generating a swirling flow, it is preferable that both of the two to four units have the same angle.

The combustion burner is installed so that the flame of the combustion burner does not come into direct contact with the mist. In order to arrange the combustion burner so as not to come into direct contact with the mist, it is preferable to prevent the flame of the combustion burner from entering the pyrolysis furnace (see FIG. 1). If it is desired to prevent the flame of the burner from entering the pyrolysis furnace, it is better to provide a mechanism that can move the burner in the front-rear direction and adjust it as necessary.
By arranging in this way, a strong swirling flow is generated in the pyrolysis furnace by the combustion gas generated from two to four combustion burners in opposite directions. Since this swirling flow travels from the bottom to the top of the pyrolysis furnace, the mist sprayed from the nozzle also rises while swirling due to this swirling flow. Therefore, the mist can stay in the pyrolysis furnace for a longer distance than the length of the pyrolysis furnace without directly contacting the flame generated from the combustion burner, and can undergo a long-term pyrolysis reaction.

Any commercially available combustion burner can be used. Considering the volume, specifications, etc. of the pyrolysis furnace, it is preferable to select a combustion burner of a type suitable for this, or a pyrolysis furnace may be manufactured and used according to the specifications.

The gas used for the combustion burner is not particularly limited as long as it is a gaseous fuel, and examples thereof include gaseous fuels such as LPG, city gas, and vaporized organic substances.

One or more auxiliary heat sources are installed above the combustion burner of the pyrolysis furnace body (Fig. 1). Examples of the auxiliary heat source include a combustion auxiliary burner, a hot air heater, and an electric heater. Further, the number of auxiliary heat sources installed can be set to about 2 to 6 depending on the length of the pyrolysis furnace, for example, as shown in FIG. In the case of an electric heater, it may be provided around the inside of the pyrolysis furnace.
By installing the auxiliary heat source, the amount of heat dissipated from the furnace body can be applied, and the temperature and holding time required for the synthesis of the inorganic oxide particles can be stably secured with good reproducibility.

When a combustion auxiliary burner or a hot air heater is used as the auxiliary heat source, it can be arranged in the tangential direction in the pyrolysis furnace and in the swirling direction of the combustion gas. This is preferable because the swirling flow can be maintained and strengthened without obstructing the swirling flow of the combustion gas generated by the combustion burner.
Further, the combustion auxiliary burner and the hot air heater may be installed at different surfaces and heights in order to adjust the temperature in the furnace and the swirling flow. As shown in FIG. 1, the surfaces to be installed may be arranged facing each other or in the vertical direction of the pyrolysis furnace. The heights to be installed may be the same height (on the same circumference) and different steps.

In addition, when a combustion auxiliary burner is used as an auxiliary heat source, preventing the flame from coming into direct contact with the mist and generated particles prevents excessive reaction of only a part of the mist, melting and deformation of the particles, etc. It is preferable for producing inorganic oxide particles having a sharp particle size distribution. To prevent the flame of the combustion auxiliary burner from coming into direct contact with the mist and generated particles, the flame of the combustion auxiliary burner should be installed so as not to enter the pyrolysis furnace. For example, the combustion auxiliary burner should be installed in the front-rear direction. A movable mechanism may be provided and adjusted according to the length of the flame.

Next, the production method of the present invention will be described.
The raw material solution sprayed from the nozzle is a solution of a compound containing elements constituting the oxide.
The compound containing an element constituting an oxide is not particularly limited as long as it is a compound containing an element constituting an oxide and dissolved in a solvent such as water, and examples thereof include an inorganic salt and a metal alkoxide. it can. More specifically, one or more selected from aluminum salt, titanium salt, magnesium salt, calcium salt, sodium salt, borate, aluminosilicate, aluminum alkoxide and silicate alkoxide can be mentioned. Examples of the aluminum salt include inorganic salts such as aluminum nitrate, aluminum sulfate, aluminum chloride, aluminum phosphate, aluminum hydroxide, aluminum acetate and aluminum oxalate, organic metal compounds such as aluminum secondary butyrate, and aluminum compounds such as aluminum isopropyrate. Dispersed ones can be mentioned. Examples of the silicate alkoxide include tetraethoxysilane and tetramethoxysilane. Further, a solution in which aluminum oxide and silicon oxide are dispersed in a solvent, and a sol solution of aluminum oxide and silicon oxide can also be used as a raw material solution. Furthermore, raw materials of other elements can be added in order to adjust the melting temperature, heat resistance, and particle strength.

Examples of the inorganic oxide obtained from these raw material compounds include oxides composed of metal oxides, alumina, silica, aluminum and silicon. More specifically, examples thereof include oxides composed of alumina, silica, aluminum and silicon, titanium oxides, magnesium oxides, zinc oxides, zirconium oxides, barium oxides, cerium oxides and yttrium oxides. A composite oxide that combines these oxides can also be mentioned.

Examples of the solvent for dissolving or dispersing the compound containing the element constituting the oxide include water and an organic solvent. Of these, water is preferable from the viewpoint of environmental impact and manufacturing cost.

The concentration of the compound containing the elements constituting the oxide in the raw material solution is preferably 0.01 mol / L to a saturated concentration, preferably 0.1 to 1, in consideration of the particle size distribution, density, strength, etc. of the obtained inorganic oxide particles. 1.0 mol / L is more preferable.

The average particle size of the mist is preferably 0.5 to 60 μm, more preferably 1 to 20 μm, and even more preferably 1 to 15 μm. The average particle size of the mist can be adjusted by adjusting the shape of the nozzle discharge port and the air pressure.

The mist sprayed from the nozzle reaches the flame direction generated from the combustion burner, the solvent evaporates from the mist, and the inorganic salt is deposited on the mist surface.
If the spraying speed of the mist sprayed from the nozzle is too slow, the mist is agitated by the hot air of the combustion burner and tilts, and the mist easily adheres to the nozzle discharge port. Further, if the spraying speed of the mist sprayed from the nozzle is too fast, the mist cannot receive sufficient heat, the particles stick to each other, and the uniformity of the particles is impaired, resulting in a sharp (unimodal) particle size. Inorganic oxide particles with distribution cannot be obtained. Therefore, in the present invention, the spraying speed of the mist sprayed from the nozzle and the flow velocity of the combustion gas generated by the combustion burner are controlled. That is, the ratio (spraying speed / combustion gas flow velocity) between the spraying speed of the mist sprayed from the nozzle and the flow velocity of the combustion gas generated by the combustion burner is controlled to 1 to 5. If the ratio of the spray rate / combustion gas flow rate is less than 1, solidification occurs at the tip of the nozzle. Further, when the ratio of the spray rate / combustion gas flow velocity exceeds 5, inorganic oxide particles having a sharp (unimodal) particle size distribution cannot be obtained. From this point of view, the spray rate / gas flow velocity ratio is preferably 1.5 to 4.5, more preferably 2 to 4, and even more preferably 2.5 to 3.5. The flow velocity of the combustion gas generated by the combustion burner can be calculated by the following formula (1).

Combustion gas flow velocity (m / s) = X / Y (1)

[In the formula, X indicates the amount of gas in the pyrolysis (m ³ / s), and Y indicates the cross section (m ² ) of the pyrolysis furnace. ]

The amount of gas X in the pyrolysis furnace is a value calculated by the following formula (2).

Gas amount in the pyrolysis furnace = burning amount x air ratio x theoretical combustion gas amount x volume expansion coefficient (2)

In the formula (2), the amount of fire (m ³ / s) is the amount of gaseous fuel, and the air ratio is the ratio of the theoretical amount of air to the amount of air actually supplied. The theoretical combustion gas amount (m ³ / s) is the amount of gas generated when the fuel is completely burned by giving the theoretical air amount, and can be calculated from the fuel composition. Further, the volume expansion rate is a ratio between the target gas temperature and the gas temperature in the standard state, and can be obtained from the furnace temperature (K) that can be measured by installing a thermocouple in the pyrolysis furnace.

The spraying speed of the mist sprayed from the nozzle is usually 1 to 50 m / s, preferably 10 to 25 m / s, and more preferably 15 to 20 m / s.
The flow velocity of the combustion gas generated by the combustion burner is usually 1 to 50 m / s, preferably 3 to 20 m / s, and more preferably 4 to 10 m / s.

The inorganic salt precipitated on the mist surface is thermally decomposed by applying heat by a combustion burner and an auxiliary heat source, and the inorganic salt is oxidized to form inorganic oxide particles.
The heating temperature is 400 to 1800 ° C. If the temperature is lower than 400 ° C., the thermal decomposition becomes insufficient, and inorganic oxide particles having a sharp (unimodal) particle size distribution cannot be obtained. Further, when the temperature exceeds 1800 ° C., even if the particles are discharged to the outside of the pyrolysis furnace on a swirling flow, they are not sufficiently cooled and the particles tend to aggregate with each other. Therefore, inorganic oxidation having a sharp (unimodal) particle size distribution I can't get particles. From this point of view, the heating temperature is preferably 600 to 1500 ° C, more preferably 700 to 1400 ° C, and even more preferably 900 to 1200 ° C.

Inorganic oxide particles generated by the pyrolysis reaction on a swirling flow from the lower part to the upper part in the pyrolysis furnace are recovered from the upper part of the pyrolysis furnace. Here, in order to efficiently recover the inorganic oxide particles, it is preferable to provide a space at the top of the pyrolysis furnace into which cooling air can be introduced, and to introduce cooling air into the space for cooling recovery. As a means for introducing the cooling air, an installation of a cooling air suction unit, a means for sending the cooling air from a fan or a blower, or the like can be adopted, and these may be performed from a plurality of locations. Further, instead of the cooling air, water cooling may be used, and ion-exchanged water, clean water, or the like can be used. A bag filter or the like can be used to recover the target fine particles.

Further, in the present invention, inorganic oxide hollow particles can also be produced as the inorganic oxide particles. When producing hollow particles, the surface of the inorganic oxide particles after thermal decomposition may be melted. As a result, the pores existing on the surface of the inorganic oxide particles are closed, and the inorganic oxide hollow particles having no pores in the outer shell of the particles and having high particle strength can be obtained.
To melt the surface of the inorganic oxide particles, for example, the temperature of the auxiliary heat source is controlled to be higher than the melting temperature of the inorganic oxide particles, or stepwise from the nozzle installation position toward the outlet of the thermal decomposition furnace. The temperature of the auxiliary heat source may be controlled so as to be equal to or higher than the melting temperature of the inorganic oxide particles.

The melting temperature may be any temperature at which the surface of the inorganic oxide particles melts, but is preferably 600 ° C. or higher from the viewpoint of closing the pores on the surface of the inorganic oxide particles. Further, from the viewpoint that the surface of the inorganic oxide particles melts in about 0.1 seconds to 1 minute, 700 ° C. or higher is preferable, 800 ° C. or higher is more preferable, and 900 ° C. or higher is further preferable. From the viewpoint of economy, the melting temperature is usually 1500 ° C. or lower, preferably 1200 ° C. or lower.

Although the inorganic oxide particles can be produced in this way, the inorganic oxide particles produced by the method of the present invention can have a sharp (unimodal) particle size distribution. Here, the “particle size distribution” as used herein refers to a volume-based particle size distribution measured in accordance with JIS R 1629 “Method for measuring particle size distribution by laser diffraction / scattering method for fine ceramic materials”. The particle size distribution is represented by a distribution curve in which the horizontal axis is the particle size (μm) and the vertical axis is the volume-based frequency (%).

Whether or not the produced inorganic oxide particles have a sharp particle size distribution can be determined by the following method. First, a volume-based particle size distribution of inorganic oxide particles is created in accordance with JIS R 1629. Next, the particle diameter (D90) corresponding to 90% of the volume distribution integration curve and the particle diameter (D10) corresponding to 10% are obtained, and the difference between the two (D90-D10) is calculated. Then, if the particle size difference (D90-D10) is usually less than 6.0 μm, preferably 5.5 μm or less, and more preferably 5.0 μm or less, it can be determined that the particle size distribution is sharp. As the particle size distribution measuring device, for example, Microtrack (manufactured by Microtrack Bell) can be used.

The particle density of the inorganic oxide particles is usually 0.1 to 2.5 g / cm ³ , preferably 0.2 to 1.0 g / cm ³ , and more preferably 0.3 to 0.6 g / cm. It is ³ . The particle density can be measured by a gas substitution method in accordance with JIS R 1620. As the particle density measuring device, for example, a dry automatic density meter "Accupic (manufactured by Shimadzu Corporation)" can be used.

The present invention has been described in detail above based on the embodiment. However, the present invention is not limited to the above embodiment. The present invention can be modified in various ways without departing from the gist thereof. For example, in the spray pyrolysis apparatus 10, two combustion burners are arranged diagonally in substantially the same direction along the tangential direction in the thermal decomposition furnace, as in the spray pyrolysis apparatus 20 shown in FIG. , One combustion burner may be installed in the tangential direction inside the pyrolysis furnace.

Hereinafter, embodiments of the present invention will be described in more detail with reference to examples. However, the present invention is not limited to the following examples.

1. 1. Evaluation of Caking at Nozzle Tip After manufacturing the inorganic oxide particles, the nozzle tip was visually observed to determine the presence or absence of caking.

2. 2. Measurement of particle size distribution Using Microtrac MT3300EX II (manufactured by Microtrac Bell) as a particle size distribution measuring device by laser diffraction / scattering method, the particle size distribution of inorganic oxide particles is measured by JIS R 1629 "Laser of fine ceramics raw material". It was created on a volume basis in accordance with "Particle size distribution measurement method by diffraction / scattering method". Then, the particle diameter (D90) corresponding to 90% of the volume distribution integration curve and the particle diameter (D10) corresponding to 10% were obtained, and the difference between the two (D90-D10) was calculated. Those having a particle size difference (D90-D10) of less than 6.0 μm were judged to have a sharp particle size distribution.

Example 1
Inorganic oxide particles were produced using the spray pyrolysis apparatus shown in FIG. In the spray pyrolysis apparatus, a combustion burner is installed so that the flame of the combustion burner does not come into direct contact with the mist, and the cross-sectional area of the pyrolysis furnace is 0.1 (m ² ).
First, in 100 L of ion-exchanged water, 1992 g of tetraethyl orthosilicate, 131 g of aluminum nitrate hexahydrate, 455 g of magnesium nitrate hexahydrate, 516 g of calcium nitrate tetrahydrate, 1666 g of sodium tetraborate perhydrate, and 1 L of concentrated nitric acid. Was put into the solution tank of the vertical gas furnace and stirred. Next, the raw material solution is sent to a two-fluid nozzle by a liquid feed pump, and the mist of the raw material solution is sprayed from the two-fluid nozzle into a vertical gas furnace in which the temperature inside the furnace is set to 1050 ° C. at the spraying rate shown in Table 1. , Inorganic oxide hollow particles were produced by controlling the flow velocity of the combustion gas shown in Table 1, and recovered by a bag filter. Then, the presence or absence of consolidation at the tip of the nozzle was visually confirmed. Moreover, the particle size distribution of the inorganic oxide hollow particles was measured, and the particle size difference (D90-D10) was determined. The results are shown in Table 1. In addition, FIG. 3 shows the particle size distribution of the inorganic oxide hollow particles.

Examples 2-5
Inorganic oxide hollow particles were produced by the same operation as in Example 1 except that the mist spraying speed and the combustion gas flow velocity were changed as shown in Table 1, and collected by a bag filter. Then, the presence or absence of consolidation at the tip of the nozzle was visually confirmed. Moreover, the particle size distribution of the inorganic oxide hollow particles was measured, and the particle size difference (D90-D10) was determined. The results are shown in Table 1.

Examples 6 and 7
Inorganic oxide hollow particles were produced by the same operation as in Example 1 except that the temperature in the furnace, the spray rate of mist, and the flow velocity of the combustion gas were changed as shown in Table 1, and the particles were recovered by a bag filter. Then, the presence or absence of consolidation at the tip of the nozzle was visually confirmed. Moreover, the particle size distribution of the inorganic oxide hollow particles was measured, and the particle size difference (D90-D10) was determined. The results are shown in Table 1.

Comparative Examples 1 and 2
Inorganic oxide hollow particles were produced by the same operation as in Example 1 except that the mist spraying speed and the combustion gas flow velocity were changed as shown in Table 1, and recovered by a bag filter. Then, the presence or absence of consolidation at the tip of the nozzle was visually confirmed. Moreover, the particle size distribution of the inorganic oxide hollow particles was measured, and the particle size difference (D90-D10) was determined. The results are shown in Table 1. Note that FIG. 4 shows the particle size distribution of the inorganic oxide hollow particles obtained in Comparative Example 2.

Comparative Examples 3 and 4
Inorganic oxide hollow particles were produced by the same operation as in Example 1 except that the temperature in the furnace, the spray rate of mist, and the flow velocity of the combustion gas were changed as shown in Table 1, and the particles were recovered by a bag filter. Then, the presence or absence of consolidation at the tip of the nozzle was visually confirmed. Moreover, the particle size distribution of the inorganic oxide hollow particles was measured, and the particle size difference (D90-D10) was determined. The results are shown in Table 1.

The following can be seen from Table 1 and FIGS. 3 and 4.
In Comparative Example 1, it is considered that the mist sprayed from the nozzle was sprayed too slowly, so that the mist was agitated by the hot air of the combustion burner and tilted, and the mist adhered to the nozzle discharge port to cause consolidation.
In Comparative Example 2, since the spraying speed of the mist sprayed from the nozzle is too fast, the mist cannot receive sufficient heat, the particles stick to each other, and the particle size difference (D90-D10) is as large as 6.4. It is considered that the particle size distribution was bimodal (Fig. 4).
In Comparative Example 3, since the temperature inside the furnace was as low as 350 ° C. and the thermal decomposition was insufficient, it is considered that the particle size distribution was bimodal with a large particle size difference (D90-D10) of 7.0.
In Comparative Example 4, the temperature inside the furnace was as high as 1850 ° C., and even if the particles after thermal decomposition were discharged to the outside of the furnace, they were not sufficiently cooled and the particles aggregated, so that the particle size difference (D90-D10) was 6.2. It is considered that the particle size distribution was large and bimodal.
On the other hand, in Examples 1 to 7, the ratio of the spray rate of the mist sprayed from the nozzle to the flow velocity of the combustion gas generated by the combustion burner (discharge rate / combustion gas flow velocity) and the heating temperature are within a specific range. Therefore, the inorganic oxide particles having a sharp (unimodal) particle size distribution shown in FIG. 3 were obtained without causing solidification at the tip of the nozzle.

1 mist (droplet)
2 Pyrolysis furnace 3 Nozzle 4 Combustion burner 5 Auxiliary heat source 10, 20 Spray pyrolysis device

Claims (3)

The mist is sprayed from the nozzle into an internal combustion type spray thermal decomposition apparatus including a nozzle for spraying a mist of a solution of a compound containing an element constituting an inorganic oxide and a combustion burner as a heating source of the sprayed mist. A method for producing inorganic oxide particles, which comprises a step of spraying and thermally decomposing.
The combustion burner is arranged so that the flame of the combustion burner does not come into direct contact with the mist.
The ratio (spraying speed / combustion gas flow velocity) between the spraying speed of the mist sprayed from the nozzle and the flow velocity of the combustion gas generated by the combustion burner is 1 to 5.
The heating temperature is 400-1800 ° C.
Method for producing inorganic oxide particles. One or more compounds containing the elements constituting the oxide are selected from aluminum salt, titanium salt, magnesium salt, calcium salt, sodium salt, borate, aluminosilicate, aluminum alkoxide and silicate alkoxide. The method for producing an inorganic oxide particle according to claim 1. The method for producing inorganic oxide particles according to claim 1 or 2, wherein the solution is an aqueous solution.