Inorganic oxide particle synthesis apparatus and inorganic oxide particle synthesis method

Abstract

To provide an inorganic oxide particle synthesis apparatus capable of downsizing a particle diameter of an inorganic oxide particle to be synthesized.SOLUTION: An inorganic oxide particle synthesis apparatus includes: raw material jetting means configured to jet a raw material containing an inorganic substance; a burner configured to form a flame so as to cover the raw material jetted out from the raw material jetting means; a cylindrical member configured to cover the flame and equipped with an air introduction port configured to introduce ambient air to an inside; and a guide member disposed inside the cylindrical member and configured to guide a flow of the ambient air to the flame. Between an outer surface of the guide member and an inner peripheral surface of the cylindrically member, there is a gap communicating in a direction along a central axis of the cylindrical member.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to an apparatus for synthesizing inorganic oxide particles and a method for synthesizing inorganic oxide particles. [Background technology]

[0002] Conventionally, an inorganic oxide particle synthesis device has been known which is equipped with a nozzle for spraying powdered, liquid, or gaseous raw material containing inorganic substances such as metals, and a burner for forming a flame around the nozzle, and which sprays the raw material from the nozzle into the flame to synthesize inorganic oxide particles.

[0003] For example, Patent Document 1 discloses a metal oxide manufacturing apparatus including a raw material supplying means for supplying raw material to a burner, an oxidizing gas supplying means for ejecting an oxidizing gas from the burner together with the raw material, a mixed gas supplying means for supplying a mixed gas, which is a mixture of a combustible gas and a combustion-supporting gas, to the burner, and a reaction vessel in which the burner is disposed. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2009-46384 A Summary of the Invention [Problem to be solved by the invention]

[0005] However, in conventional inorganic oxide particle synthesis devices, when the size of the device is increased according to the production amount of inorganic oxide particles, the flame formed from the burner also becomes larger and the length of the flame becomes longer. Therefore, when synthesizing inorganic oxide particles having a particle size smaller than a predetermined particle size (e.g., particle size of 1 μm), the raw material injected into the flame is difficult to cool after generating nuclei, and the nuclei coalesce or aggregate to promote particle growth, making it difficult to synthesize inorganic oxide particles having a particle size smaller than the predetermined particle size.

[0006] An object of one aspect of the present invention is to provide an apparatus for synthesizing inorganic oxide particles that can reduce the particle size of inorganic oxide particles to be synthesized even if the apparatus is enlarged. [Means for solving the problem]

[0007] An inorganic oxide particle synthesis apparatus according to one embodiment of the present invention comprises a raw material injection means for injecting raw material containing an inorganic substance, a burner for forming a flame so as to cover the raw material injected from the raw material injection means, a cylindrical member for covering the flame and having an air inlet for introducing air into the inside, and a guide member provided inside the cylindrical member for guiding the flow of air toward the flame, and a gap is formed between the outer surface of the guide member and the inner surface of the cylindrical member, the gap communicating in a direction along the central axis of the cylindrical member. Effect of the Invention

[0008] According to an inorganic oxide particle synthesis apparatus according to one aspect of the present invention, the particle size of the synthesized inorganic oxide particles can be made small even if the apparatus is enlarged. [Brief description of the drawings]

[0009] [Figure 1] 1 is a schematic diagram of an inorganic oxide particle synthesis apparatus according to an embodiment. [Diagram 2] FIG. 2 is a plan view showing the tip surface of the burner. [Diagram 3] FIG. 2 is an enlarged view of a main part of FIG. [Figure 4] FIG. 4 is a perspective view of a guide member and a fixing member. [Diagram 5] 13 is a perspective view showing another example of the guide member and the fixing member. FIG. [Figure 6] FIG. 2 is a diagram showing the flame nucleation position and the reaction stop position in the inorganic oxide particle synthesis apparatus of Example 1 and Comparative Example 1. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0010] Hereinafter, the embodiments of the present invention will be described with reference to the drawings. In order to facilitate understanding of the description, the same components in each drawing are given the same reference numerals, and duplicated descriptions may be omitted. In this specification, unless otherwise specified, "to" indicating a numerical range means that the numerical values ​​before and after it are included as the lower and upper limits.

[0011] <Inorganic oxide particle synthesis device> FIG. 1 is a schematic diagram of an inorganic oxide particle synthesis apparatus according to an embodiment. In FIG. 1, the arrow indicates the direction of the air flow. As shown in FIG. 1, the inorganic oxide particle synthesis apparatus 10 includes a raw material injection means 2 for injecting a raw material 1 containing an inorganic substance, a burner 3 for forming a flame F so as to cover the raw material 1 injected from the raw material injection means 2, and a cylindrical member 4 having an air inlet 41 for covering the flame F and introducing air into the inside. The inorganic oxide particle synthesis apparatus 10 also includes a guide member 5 provided inside the cylindrical member 4 for guiding the flow of air introduced from the air inlet 41 into the inside of the cylindrical member 4 toward the flame F, and a gap G is formed between the outer surface of the guide member 5 and the inner peripheral surface of the cylindrical member 4, communicating in a direction along the central axis of the cylindrical member 4. The guide member 5 functions as a guide plate for changing the direction of the flow of air introduced into the inside of the cylindrical member 4.

[0012] First, the process of forming inorganic oxide particles when flame F is used will be described. Raw material 1 injected from raw material injection means 2 is sublimated by a combustion reaction in flame F formed by burner 3, and raw material 1 becomes vapor. The temperature of vaporized raw material 1 decreases as it flows downstream of flame F, and when the concentration of raw material 1 reaches the critical supersaturation, the vapor of raw material 1 is condensed and inorganic nuclei are generated. The position where the nuclei are generated, which is the furthest position from the tip surface 32 of burner 3 on the central axis C of burner 3, is called nucleation position F1. After that, when the solubility reaches saturation downstream of nucleation position F1, the coalescence of the nuclei and the aggregation reaction stop. The position where the coalescence and aggregation reaction stop, which is the furthest position from the tip surface 32 of burner 3 on the central axis C of burner 3, is called reaction stop position F2.

[0013] The nucleation position F1 corresponds to the position of the nucleation temperature of the inorganic substance, and the reaction stop position F2 corresponds to the position of the reaction stop temperature of the coalescence and aggregation reaction of the inorganic substance nuclei, and therefore the nucleation position F1 and the reaction stop position F2 can be identified by measuring the temperature distribution of the flame F. In the flame F, inorganic nuclei are generated in the region inside the contour line R1 of the region where the concentration of raw material 1 is at or above the temperature where the concentration of raw material 1 is at the critical supersaturation, and the coalescence and aggregation reaction of the nuclei stops in the region outside the contour line R2 of the region where the concentration of raw material 1 is at or above the temperature where the concentration of raw material 1 is at the saturated solubility.

[0014] Until the temperature is cooled to the reaction stop position F2, the particles grow larger due to the progress of crystal growth, particle coalescence, and aggregation reactions. In particular, when the apparatus is enlarged to synthesize a large amount of inorganic oxide particles, the flame size also becomes larger, and the time required to reach the reaction stop position F2 from the nucleation position F1 is also longer. Therefore, when the apparatus is enlarged, the particle growth is promoted and inorganic oxide particles with a relatively large diameter tend to be formed. Here, the enlargement of the apparatus refers to an apparatus with a combustion amount of the burner 3 of 10,000 kcal / h or more. As can be seen from this, the shorter the distance from the nucleation position F1 of the raw material 1 to the reaction stop position F2 and the shorter the transit time (ms), the more the particle growth is suppressed, and it becomes possible to synthesize inorganic oxide particles with a small diameter even if the combustion amount of the burner 3 is increased to increase the production amount.

[0015] With this configuration, a portion of the air introduced from the air inlet 41 into the inside of the cylindrical member 4 collides with the guide member 5 and flows toward the flame F, efficiently cooling the flame F from the nucleation position F1 to the reaction stop position F2. Therefore, the inorganic oxide particle synthesis apparatus 10 can quickly cool the nuclei after the inorganic matter contained in the raw material 1 injected into the flame F generates nuclei, and can suppress the growth of particles due to the coalescence or aggregation of the nuclei. As described above, the inorganic oxide particle synthesis apparatus 10 can reduce the particle size of the inorganic oxide particles to be synthesized. The inorganic oxide particle synthesis apparatus 10 can synthesize inorganic oxide particles having a particle size of, for example, nanometer order.

[0016] Furthermore, the distance between the nucleation position F1 and the reaction stop position F2 of the flame F can be adjusted by circulating another part of the air introduced inside the cylindrical member 4 through the gap G between the outer surface of the guide member 5 and the inner peripheral surface of the cylindrical member 4. By reducing the area of ​​the gap G, the distance between the nucleation position F1 and the reaction stop position F2 becomes shorter, and by increasing the area of ​​the gap G, the distance between the nucleation position F1 and the reaction stop position F2 becomes longer. Therefore, the area of ​​the gap G may be adjusted within a range in which the desired particle size of the inorganic oxide particles can be obtained. Here, the area of ​​the gap G means the minimum area of ​​the cross section of the gap G perpendicular to the central axis of the cylindrical member 4.

[0017] In addition, since the air flows through the gap G, the inorganic oxide particles remaining in the space downstream of the narrowed portion 52 of the guide member 5 relative to the air introduction direction also flow along the air introduction direction, which has the effect of preventing the inorganic oxide particles from adhering to or accumulating on the inner surface of the cylindrical member 4 or the outer surface of the guide member 5, etc.

[0018] The state of the raw material 1 injected from the raw material injection means 2 is not particularly limited, and may be liquid or powder, and is preferably in a state in which an aerosol can be formed by spraying or the like. Note that the aerosol means a mixture of minute liquid or solid particles suspended in gas and the surrounding gas. The gas used in the raw material injection means 2 is often an oxidizing gas so as not to lower the temperature of the flame F, but is not limited thereto, and an inert gas may also be used.

[0019] An example of the inorganic oxide particles synthesized in this embodiment is a composite tungsten oxide, which is represented by the general formula M x W y O zThe element M in the above general formula can be, for example, one or more elements selected from among alkali metal elements, alkaline earth metal elements, rare earth elements, Mg, Zr, Cr, Mn, Fe, Ru, Co, Rh, Ir, Ni, Pd, Pt, Cu, Ag, Au, Zn, Cd, Al, Ga, In, Tl, Si, Ge, Sn, Pb, Sb, B, F, P, S, Se, Br, Te, Ti, Nb, V, Mo, Ta, Re, Be, Hf, Os, Bi, and I. In addition, W represents tungsten, and O represents oxygen.

[0020] Examples of the alkali metal elements include Li, Na, K, Rb, Cs, and Fr. Examples of the alkaline earth metal elements include Ca, Sr, Ba, Ra, and Mg. Examples of the rare earth elements include Sc, Y, La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, and Lu.

[0021] The inorganic substance contained in the raw material 1 may be one or more kinds of elemental substances selected from the metals listed above, or salts or compounds thereof.

[0022] When the raw material 1 is a liquid, the raw material 1 can be a solution in which one or more salts of the above-mentioned elements are dissolved in an organic solvent. The type of salt is not particularly limited, and one or more salts selected from carbonates, acetates, nitrates, hydroxides, oxides, etc. can be used. As the organic solvent, for example, mineral spirits, ethanol, tetrahydrofuran, acetone, ethylene glycol, methanol, etc. can be used. Citric acid, ammonia, etc. can be used to adjust the pH of the raw material solution.

[0023] The raw material injection means 2 has a storage section 21 in which the raw material 1 is stored, and a raw material supply pipe 22 that supplies the raw material 1 to the burner 3, and may further have a carrier gas supply pipe 23 that supplies a carrier gas such as oxygen, air, nitrogen, argon, etc. to the burner 3, a compressor, a pump, etc. When the raw material 1 is a liquid, it may have an atomization section for atomizing the liquid by ultrasonic vibration, etc., and a stirring section for dispersing solids in the liquid, etc.

[0024] The burner 3 has a two-fluid nozzle 31. The two-fluid nozzle 31 forms an aerosol from the supplied solution of the raw material 1 and the carrier gas. The burner 3 also injects a mixed gas, for example, a mixture of a combustion-supporting gas such as oxygen and a flammable gas such as city gas (13A, etc.) or liquefied petroleum gas, from a mixed gas outlet 34 described later. The burner 3 may inject a mixed gas in which the combustion-supporting gas and the flammable gas are mixed in advance through a mixed gas supply pipe 35, or may inject the mixed gas from a supply pipe (not shown) that supplies the combustion-supporting gas and the flammable gas, respectively, at the tip of the burner 3. The mixed gas is a gas that burns around the raw material 1 and promotes the oxidation reaction of the raw material 1. The organic solvent contained in the aerosol injected from the two-fluid nozzle 31 is burned and decomposed by the flame F. The heat generated by this combustion contributes to the sublimation reaction of the raw material 1.

[0025] In this embodiment, the means for forming the aerosol is the two-fluid nozzle 31, but the means for forming the aerosol may be various atomizers such as a centrifugal atomizer and an ultrasonic atomizer. When the raw material 1 is a powder, the means for forming the aerosol may be an aerosol forming device that forms a state in which the powder, which is the raw material 1, is dispersed and supplies the powder into an airflow. The aerosol forming device for aerosolizing the powder includes, for example, a stirring unit having a rotating brush or stirring blade, and a powder supply unit including a piston or a screw feeder that sends the raw material 1 to the stirring unit. The powder, which is the raw material 1, supplied from the powder supply unit is dispersed by the stirring unit, and each dispersed particle is sent to a carrier gas to form an aerosol containing the powder, which is the raw material 1. It is preferable that the stirring unit rotates a brush, stirring blade, or the like at high speed to disperse the powder, which is the raw material 1.

[0026] Fig. 2 is a plan view showing the tip face 32 of the burner 3. As shown in Fig. 2, the burner 3 may have a raw material ejection hole 33 provided in the center of the tip face 32 for ejecting the raw material 1 and a carrier gas, and a plurality of mixed gas ejection holes 34 provided at equal intervals in the circumferential direction around the raw material ejection hole 33 of the tip face 32 for ejecting the mixed gas. In the example shown in Fig. 2, the number of raw material ejection hole 33 is one and the number of mixed gas ejection holes 34 is 30, but the number is not limited to this and may be any number.

[0027] The diameter of the raw material ejection hole 33 and the diameter of the mixed gas ejection hole 34 may be, for example, 0.5 mm to 5 mm. In the tip surface 32 of the burner 3, the distance between the center of the tip surface 32 of the burner 3 and the center of the mixed gas ejection hole 34 may be, for example, 15 mm to 30 mm.

[0028] FIG. 3 is an enlarged view of a main part of FIG. 1. The cylindrical member 4 constitutes a reaction field for the raw material 1 to form inorganic oxide particles, and inside the cylindrical member 4, a guide member 5 is arranged, which functions as a guide plate for changing the direction of the flow of air introduced into the cylindrical member 4. The air inlet 41 is, for example, an opening formed at one end of the cylindrical member 4, and is preferably provided upstream of the tip surface 32 of the burner 3 with respect to the advancing direction of the flame F, as shown in FIG. 3. For example, the tip of the burner 3 is inserted into the inside of the cylindrical member 4 from the opening at one end of the cylindrical member 4, and the gap between the outer peripheral surface of the burner 3 and the inner peripheral surface of the cylindrical member 4 constitutes the air inlet 41, and the air is introduced along the advancing direction of the flame F. With this configuration, the air introduced from the air inlet 41 avoids directly hitting the flame F, collides with the guide member 5, and flows toward the flame F, thereby cooling the flame F. Therefore, the inorganic oxide particle synthesis apparatus 10 can stably maintain the flame F, and can quickly cool the nuclei after the inorganic matter contained in the raw material 1 injected into the flame F generates nuclei. As described above, the inorganic oxide particle synthesis apparatus 10 can stably reduce the particle size of the inorganic oxide particles to be synthesized.

[0029] The other end of the cylindrical member 4 is connected to a cooling section 6 that cools the formed inorganic oxide particles.

[0030] When the air inlet 41 is provided upstream of the tip surface 32 of the burner 3 in the direction of progression of the flame F, the distance between the outer circumferential surface of the burner 3 and the inner circumferential surface of the cylindrical member 4 can be, for example, 10 mm to 500 mm.

[0031] The cylindrical member 4 may have a cooling device 42 provided on the outer circumferential surface. An example of the cooling device 42 is a pipe through which cooling water circulates. The cooling device 42 may further be provided on the outer circumferential surface of the cooling section 6.

[0032] As shown in Figs. 1 and 3, the guide member 5 is disposed between the inner circumferential surface of the cylindrical member 4 and the flame F in a direction perpendicular to the central axis of the cylindrical member 4, in part or in whole. Fig. 4 is a perspective view of the guide member 5. As shown in Figs. 3 and 4, the guide member 5 is cylindrical, and has an opening 51 provided at one end and a narrowed portion 52 located downstream of the opening 51 with respect to the traveling direction of the flame F and having an inner diameter smaller than the diameter of the opening 51. The inorganic oxide particle synthesis device 10 preferably includes a fixing member 9 for fixing the guide member 5 to the inner circumferential surface of the cylindrical member 4. With this configuration, the air introduced into the inside of the cylindrical member 4 collides with the guide member 5 and flows toward the flame F by converging through the narrowed portion 52, so that the distance from the nucleation position F1 of the flame F to the reaction stop position F2 located downstream is shortened, and the flow speed of the gas and nuclei that have passed through the narrowed portion 52 is increased, so that the time it takes for the nuclei to pass from the nucleation position F1 to the reaction stop position F2 is also shortened. Therefore, the inorganic oxide particle synthesis apparatus 10 can cool the nuclei more quickly after the inorganic matter contained in the raw material 1 injected into the flame F forms nuclei, thereby making it possible to reduce the particle size of the inorganic oxide particles synthesized.

[0033] Furthermore, the fixing member 9 can form a gap G between the outer surface of the guide member 5 and the inner peripheral surface of the cylindrical member 4, which communicates in a direction along the central axis of the cylindrical member 4. Another part of the air introduced into the inside of the cylindrical member 4 flows through the gap G, and flows into the space downstream of the guide member 5 with respect to the introduction direction of the air. Therefore, the inorganic oxide particle synthesis device 10 can freely adjust the distance between the nucleation position F1 of the flame F and the reaction stop position F2, and can synthesize inorganic oxide particles of a desired particle size. In addition, it is possible to prevent the synthesized inorganic oxide particles from remaining in the gap G and the space downstream thereof.

[0034] The outer periphery of one end of the guide member 5 on the opening 51 side may be connected to the cylindrical member 4 via a fixed member 9 downstream of the tip surface 32 of the burner 3 with respect to the traveling direction of the flame F, or may be connected to the cylindrical member 4 via a fixed member 9 upstream of the tip surface 32 of the burner 3. The narrowed portion 52 may be provided between one end and the other end of the guide member 5 in the direction along the axis of the guide member 5, or may be an opening provided at the other end of the guide member 5.

[0035] The guide member 5 is preferably in the shape of an inverted truncated cone that tapers along the direction of travel of the flame F. That is, the guide member 5 has a peripheral wall 53 in the shape of an inverted truncated cone that tapers along the direction of travel of the flame F, an opening 51 formed in the large diameter portion, and a narrowed portion 52 corresponding to the small diameter portion. This ensures a sufficient area for the air introduced into the inside of the cylindrical member 4 to collide, and the air introduced into the inside of the cylindrical member 4 can be efficiently collected in the narrowed portion 52. Therefore, the air introduced into the inside of the cylindrical member 4 flows more convergently toward the flame F, so that the flame F is cooled more. As described above, the inorganic oxide particle synthesis device 10 can quickly cool the nuclei after the inorganic substance contained in the raw material 1 injected into the flame F generates nuclei, and can reduce the particle size of the inorganic oxide particles to be synthesized.

[0036] In this configuration, the fixing member 9 connects the outer peripheral surface of the peripheral wall 53 and the inner peripheral surface of the cylindrical member 4. The outer peripheral surface of the peripheral wall 53 is separated from the inner peripheral surface of the cylindrical member 4. The fixing member 9 can form a gap G between the outer peripheral surface of the peripheral wall 53 of the guide member 5 and the inner peripheral surface of the cylindrical member 4, which communicates in a direction along the central axis of the cylindrical member 4. Another part of the air introduced inside the cylindrical member 4 flows through the gap G, and flows into the space downstream of the guide member 5 with respect to the introduction direction of the air. Therefore, the inorganic oxide particle synthesis device 10 can freely adjust the distance between the nucleation position F1 of the flame F and the reaction stop position F2, and can synthesize inorganic oxide particles of a desired particle size. In addition, it is possible to suppress the synthesized inorganic oxide particles from staying in the gap G and the space downstream thereof.

[0037] FIG. 5 is a perspective view showing another example of the guide member 5 and the fixed member 9. As shown in FIG. 5, the guide member 5 may have a shape obtained by cutting a truncated cone from a cylinder. In this case, the peripheral wall 53 of the guide member 5 includes an outer peripheral surface in the shape of a cylindrical surface and an inner peripheral surface in the shape of an inverted truncated cone surface. The guide member 5 has an opening 51 provided at one end, an annular bottom surface 54, and a narrowed portion 52 which is an opening formed in the bottom surface 54. In this configuration, the fixed member 9 connects a part of the outer peripheral surface of the peripheral wall 53 and a part of the inner peripheral surface of the cylindrical member 4. The outer peripheral surface of the peripheral wall 53 is separated from the inner peripheral surface of the cylindrical member 4. The fixed member 9 can form a gap G between the outer peripheral surface of the peripheral wall 53 of the guide member 5 and the inner peripheral surface of the cylindrical member 4, which communicates in a direction along the central axis of the cylindrical member 4. 4. Therefore, the inorganic oxide particle synthesis apparatus 10 having the guide member 5 shown in FIG. 5 also has the same effects as the inorganic oxide particle synthesis apparatus 10 having the guide member 5 shown in FIG.

[0038] The projected area of ​​the gap G as seen from the burner 3 side is S2, and the area of ​​the cross section perpendicular to the central axis of the cylindrical member 4 at the inner diameter part of the cylindrical member 4 is S O In this case, it is preferable to satisfy the following relational expression (3). S2≦ 0.5×S O (3) More preferably, 0.01×S O≦ S2 ≦ 0.5 × S O It is.

[0039] By satisfying the above formula (3), it is possible to sufficiently ensure both the flow rate of the air flowing toward the flame F by colliding with the guide member 5 and the flow rate of the air flowing through the gap G between the outer surface of the guide member 5 and the inner circumferential surface of the cylindrical member 4. Therefore, the inorganic oxide particle synthesis device 10 can freely adjust the distance between the nucleation position F1 of the flame F and the reaction stop position F2, and can synthesize inorganic oxide particles of a desired particle size. In addition, the particle size of the inorganic oxide particles to be synthesized can be made smaller, and the synthesized inorganic oxide particles can be more effectively prevented from remaining in the gap G and the space downstream thereof.

[0040] The fixing member 9 may be a plate-like member extending in a direction along the central axis of the cylindrical member 4. This reduces the area where a part of the air introduced inside the cylindrical member 4 collides with the fixing member 9 when flowing through the gap G, and suppresses a decrease in the flow rate of the introduced air. Therefore, the synthesized inorganic oxide particles tend to flow along the air introduction direction in the space downstream of the guide member 5 with respect to the air introduction direction, so that the inorganic oxide particle synthesis device 10 can freely adjust the distance between the nucleation position F1 of the flame F and the reaction stop position F2, and can synthesize inorganic oxide particles of a desired particle size. In addition, it is possible to further suppress the synthesized inorganic oxide particles from stagnation.

[0041] When the fixing member 9 is a plate-shaped member extending in a direction along the central axis of the cylindrical member 4, the shortest distance between the outer surface of the guide member 5 and the inner surface of the cylindrical member 4 with respect to the inner diameter of the cylindrical member 4 described above may be the length of the fixing member 9 in the radial direction of the cylindrical member 4.

[0042] A plurality of fixing members 9 are provided, and the plurality of fixing members 9 are preferably arranged rotationally symmetrically with respect to the central axis C1 of the guide member 5. As a result, a part of the air introduced inside the cylindrical member 4 flows through the gap G relatively uniformly, so that the synthesized inorganic oxide particles flow along the introduction direction of the air in the entire space downstream of the guide member 5 with respect to the introduction direction of the air. Therefore, the inorganic oxide particle synthesis device 10 can freely adjust the distance between the nucleation position F1 of the flame F and the reaction stop position F2, and can synthesize inorganic oxide particles of a desired particle size. In addition, it is possible to further suppress the synthesized inorganic oxide particles from staying in the gap G and the space downstream thereof. In the example shown in FIG. 4 and FIG. 5, four fixing members 9 are arranged at positions that are four-fold rotationally symmetric with respect to the central axis C1 of the guide member 5, but the number of fixing members 9 may be one, two, three, or five or more. In addition, the plurality of fixing members 9 are preferably arranged at equal intervals along the outer periphery of the guide member 5.

[0043] When the guide member 5 is cylindrical with a through hole having an inverted truncated cone shape tapered along the direction of progression of the flame F, as in the example shown in Figures 4 and 5, the peripheral wall 53 of the guide member 5 may be curved so as to be convex outward, or may be curved so as to be convex inward.

[0044] The area of ​​the cross section perpendicular to the central axis of the guide member 5 in the narrowed portion 52 is S I , the area of ​​the cross section of the cylindrical member 4 perpendicular to the central axis of the cylindrical member 4 is S O In this case, it is preferable to satisfy the following relational expression (2). 0.1×S O ≦ S I ≦ 0.8 × S O (2)

[0045] As a result, the air introduced into the inside of the cylindrical member 4 converges and flows toward the flame F, and a sufficient amount of air is obtained, shortening the distance between the nucleation position F1 of the flame F and the reaction stop position F2. Therefore, the inorganic oxide particle synthesis apparatus 10 can cool the nuclei more quickly after the inorganic matter contained in the raw material 1 injected into the flame F generates nuclei, and can reduce the particle size of the synthesized inorganic oxide particles.

[0046] However, the area S of the cross section perpendicular to the central axis of the guide member 5 in the narrowed portion 52 I If the intake pressure is reduced, the amount of air that can be introduced will decrease due to pressure loss at the same intake pressure. In order to secure the amount of air and increase the speed at which the raw material passes, it is necessary to increase the intake pressure. In order to increase the intake pressure, the area of ​​the air inlet 41 may be enlarged or a fan may be provided to forcibly introduce air into the air inlet 41.

[0047] It is preferable that the central axis C1 of the guide member 5 passes through the center of the cross-sectional shape of the narrowed portion 52 perpendicular to the central axis of the cylindrical member 4, and coincides with the central axis of the cylindrical member 4 and the central axis C of the burner 3. This enables the inorganic oxide particle synthesis apparatus 10 to efficiently reduce the particle size of the inorganic oxide particles to be synthesized.

[0048] As shown in FIG. 3, the distance between the tip surface 32 of the burner 3 and the position of the nucleation temperature of the raw material 1 in the flame F is L. a The distance between the tip surface 32 of the burner 3 and the narrowed portion 52 is L b In this case, it is preferable to satisfy the following relational expression (1). 0.4 x L a ≦ L b ≦ 1.6×L a (1)

[0049] L a and L bHowever, by satisfying the relational expression (1), the narrowed portion 52 is disposed in the vicinity of the nucleation position F1 of the raw material 1 in the flame F. Thus, the air introduced inside the cylindrical member 4 collides with the guide member 5 and is caused by the narrowed portion 52 to converge and flow toward the vicinity of the nucleation position F1 of the raw material 1 in the flame F, so that the inorganic oxide particle synthesis apparatus 10 can cool the nuclei more quickly after the inorganic matter contained in the raw material 1 forms nuclei. As a result, the inorganic oxide particle synthesis apparatus 10 can reduce the particle size of the inorganic oxide particles to be synthesized.

[0050] As shown in FIG. 3, the distance between the tip surface 32 of the burner 3 and one end of the guide member 5 on the opening 51 side is L c The distance between the tip surface 32 of the burner 3 and the narrowed portion 52 is L b In this case, it is preferable to satisfy the following relational expression (4). L c ≦ 0.8 × L b (4)

[0051] L c and L b However, by satisfying the relational expression (4), a sufficient area is ensured for the air introduced inside the cylindrical member 4 to collide with, and the air introduced inside the cylindrical member 4 can be efficiently collected at the narrowed portion 52. Therefore, the air introduced inside the cylindrical member 4 flows more convergently toward the flame F, so that the flame F is cooled more. As described above, the inorganic oxide particle synthesis apparatus 10 can cool the nuclei more quickly after the inorganic matter contained in the raw material 1 injected into the flame F forms nuclei, and the particle size of the inorganic oxide particles to be synthesized can be made smaller.

[0052] The guide member 5 may be movable along the central axis of the cylindrical member 4 inside the cylindrical member 4. This allows, for example, the position of the cylindrical member 4 to be easily adjusted to satisfy the above-mentioned relational expression (1) or (4), and makes it possible to adjust the distance between the nucleation position F1 of the flame F and the reaction stop position F2. Specifically, the inorganic oxide particle synthesis device 10 may include a support member that is connected to the guide member 5, extends from the air inlet 41 of the cylindrical member 4 to the outside, and is movable along the axis of the cylindrical member 4. That is, the guide member 5 may be suspended by the support member. This allows the position of the guide member 5 to be easily adjusted by moving the support member up and down from the outside of the cylindrical member 4.

[0053] The cylindrical member 4 can be divided into a plurality of cylindrical member units in a direction along the central axis of the cylindrical member 4, and any of the cylindrical member units may be replaceable with the guide member 5 shown in FIG. 5. That is, the peripheral wall 53 of the guide member 5 constitutes a part of the peripheral wall of the cylindrical member 4. The inorganic oxide particle synthesis device 10 can easily adjust the position of the guide member 5 by replacing the cylindrical member unit at a desired position with the guide member 5. In this case, it is preferable that the inner diameter of the cylindrical member 4 and the outer diameter of the peripheral wall 53 of the guide member 5 are the same. Note that the guide member 5 shown in FIG. 5 may be insertable between any of the adjacent cylindrical member units.

[0054] The guide member 5 may have a flange provided on the outer periphery of one end of the guide member 5 on the opening 51 side, and the flange may be insertable between any adjacent cylindrical member units. The inorganic oxide particle synthesis apparatus 10 can easily adjust the position of the guide member 5 by inserting the flange of the guide member 5 between adjacent cylindrical member units. In this case, it is preferable that the inner diameter of the cylindrical member 4 and the outer diameter of the flange of the guide member 5 are the same.

[0055] In the example shown in FIG. 1, the burner 3 is arranged along the vertical direction and the flame advance direction is vertically downward, but this is not limited thereto, and the burner 3 may be arranged along the horizontal direction and the flame advance direction may also be along the horizontal direction.

[0056] The inorganic oxide particle synthesis apparatus 10 may include a collection section 7 connected to the cooling section 6 and for collecting inorganic oxide particles. The cooling section 6 may be provided with an air inlet for cooling (not shown) to further lower the temperature of the inorganic oxide particles. By lowering the temperature of the inorganic oxide particles, deterioration of the filter 8 due to high temperature can be suppressed. The collection section 7 may include a filter 8 such as a bag filter provided inside the collection section 7, and a collection pipe 71 provided at the lower part of the collection section 7. The inorganic oxide particles are introduced into the collection section 7, collected by the filter 8, and when they are deposited on the filter 8, they fall under their own weight and are stored in the collection pipe 71. The inorganic oxide particle synthesis apparatus 10 may include a pressure reducing device (not shown), such as an ejector or an exhaust pump, downstream of the collection section 7, and the space inside the cylindrical member 4 can be controlled to a reduced pressure state by the pressure reducing device.

[0057] <Method of synthesizing inorganic oxide particles> The method for synthesizing inorganic oxide particles of this embodiment includes a step of forming an aerosol containing a raw material containing an inorganic substance, and supplying the aerosol to a flame in a reaction field (aerosol formation step), and a step of heat-treating the raw material contained in the aerosol (heat treatment step). In the heat treatment step, air is introduced into the reaction field so as to flow along the direction of the flame, and a part of the air introduced into the reaction field is collided with a member to flow toward the central axis of the flame, and a part of the air introduced into the reaction field is caused to flow along the direction of the flame without colliding with the member.

[0058] According to the method for synthesizing inorganic oxide particles of the present embodiment, a part of the air introduced into the reaction field is collided with a member and circulated toward the central axis of the flame, so that after the inorganic matter contained in the aerosol supplied to the flame generates nuclei, the nuclei can be quickly cooled, and particle growth due to coalescence or aggregation of the nuclei can be suppressed. Therefore, according to the method for synthesizing inorganic oxide particles of the present embodiment, the particle size of the inorganic oxide particles to be synthesized can be made small. According to the method for synthesizing inorganic oxide particles of the present embodiment, for example, inorganic oxide particles having a particle size on the order of nanometers can be synthesized.

[0059] In addition, by allowing the other part of the air introduced into the reaction field to flow along the direction of flame advancement without colliding with the guide member 5, the other part of the introduced air flows through the gap G into the space downstream of the guide member 5 with respect to the air introduction direction, and the synthesized inorganic oxide particles flow along the air introduction direction in the space downstream of the guide member 5. Therefore, according to the method for synthesizing inorganic oxide particles of this embodiment, the distance between the nucleation position F1 of the flame F and the reaction stop position F2 can be freely adjusted, and inorganic oxide particles of a desired particle size can be synthesized. In addition, it is possible to prevent the synthesized inorganic oxide particles from remaining in the gap G and the space downstream thereof.

[0060] In the method for synthesizing inorganic oxide particles of this embodiment, inorganic oxide particles can be synthesized using the inorganic oxide particle synthesis apparatus 10 of this embodiment.

[0061] The method for synthesizing inorganic oxide particles of the present embodiment may include a step of preparing a raw material containing an inorganic substance (raw material preparation step) prior to the aerosol formation step.

[0062] (Raw material preparation process) In the raw material preparation step, a raw material containing an inorganic substance is prepared. The raw material and the inorganic substance are similar to the raw material 1 and the inorganic substance used in the inorganic oxide particle synthesis apparatus 10 described above, and therefore a description thereof will be omitted. When two or more types of inorganic substances are used, the ratio of the various inorganic substances is mixed in a ratio corresponding to the composition of the desired inorganic oxide particles to prepare the raw material 1. The prepared raw material 1 can be stored in the storage section 21 of the inorganic oxide particle synthesis apparatus 10.

[0063] (Aerosol formation process) In the aerosol formation step, for example, an aerosol containing the raw material 1 prepared in the raw material preparation step is formed, and the aerosol is supplied to a flame in a reaction field. The aerosol contains droplets or particles of the raw material 1. In the aerosol formation step, the aerosol may be formed and supplied to the flame at the same time, or the aerosol may be formed in advance, and then the aerosol may be transported by a carrier gas such as oxygen and supplied to the flame.

[0064] In the aerosol forming step, the means and method for forming the aerosol are not particularly limited, but the raw material injection means 2 of the inorganic oxide particle synthesis apparatus 10 can be used. In addition, the cylindrical member 4 of the inorganic oxide particle synthesis apparatus 10 can be used as a reaction field.

[0065] In the aerosol forming step, when droplets of raw material 1 dispersed in a gas are formed, the diameter of the droplets formed is not particularly limited, but is preferably 100 μm or less, more preferably 10 μm or less, and even more preferably 5 μm or less. By making the diameter of the droplets 100 μm or less, it is possible to suppress the obtained inorganic oxide particles from becoming coarse, and to stably synthesize inorganic oxide particles of the nanometer order. The lower limit of the diameter of the droplets of raw material 1 formed in the aerosol forming step is not particularly limited. However, since it is difficult to form droplets that are too small and there is a risk of reducing productivity, the lower limit of the diameter of the droplets of raw material 1 is preferably, for example, 1 μm or more.

[0066] In the aerosol forming process, when forming particles of the raw material 1 dispersed in a gas, the diameter of the particles is not particularly limited, but is preferably 50 μm or less, more preferably 5 μm or less, and even more preferably 1 μm or less. By making the diameter of the particles 50 μm or less, it is possible to perform heat treatment more reliably to the inside of the particles. The diameter of the particles can be calculated by observing in three fields of view using a transmission electron microscope. Specifically, images of a total of 600 to 700 particles are observed in three fields of view, the cross-sectional area of ​​each particle is calculated, and the circular equivalent diameter of each particle is calculated. The arithmetic average of the circular equivalent diameters of each particle is then taken as the diameter (particle size) of the particle.

[0067] (Heat treatment process) In the heat treatment step, the raw material is heat-treated to form inorganic oxide particles from the raw material. The means and method for heat treatment in the heat treatment step are not particularly limited as long as the raw material is heat-treated at a temperature equal to or higher than the temperature at which nuclei are generated, but the burner 3 of the inorganic oxide particle synthesis device 10 can be used. By performing heat treatment below the temperature at which the reaction stops, the inorganic matter contained in the raw material is thermally decomposed, nuclei are generated, and inorganic oxide particles are formed through particle growth, aggregation, and coalescence reactions.

[0068] The heat treatment temperature may be any temperature as long as it is equal to or higher than the nucleation temperature, and the upper limit of the heat treatment temperature is not particularly limited, but is preferably 4000° C. or lower from the viewpoint of suppressing energy consumption.

[0069] The flame F is formed using a mixed gas containing a combustion-supporting gas and a combustible gas. The combustion-supporting gas can be oxygen gas, and the combustible gas can be propane or city gas.

[0070] In the heat treatment process, a guide member 5 of the inorganic oxide particle synthesis apparatus 10 and a gap G or a fixing member 9 can be used as a member for causing a portion of the air introduced into the reaction field to collide with a member, and for causing a portion of the air introduced into the reaction field to circulate along the direction of flame progression without colliding with a member. EXAMPLES

[0071] The present invention will be described below with reference to specific examples, but is not limited to these examples.

[0072] Cesium tungsten oxide particles were synthesized using the inorganic oxide particle synthesis apparatus 10 shown in Fig. 1, and evaluated by the following method. Specific conditions are described below.

[0073] <Synthesis of inorganic oxide particles> Example 1 In the inorganic oxide particle synthesis apparatus, a guide member 5 in the shape of an inverted truncated cone tapered along the direction of flame advance was provided inside a cylindrical member 4 with an inner diameter of 10.2 cm. The inner diameter of the narrowed portion 52 of the guide member 5 was 4.77 cm. The distance of the gap G between the outer surface of the guide member 5 and the inner peripheral surface of the cylindrical member 4 was 0.92 cm, and four plate-shaped fixing members 9 with a thickness of 5.0 mm were connected to the outer surface of the guide member 5 and the inner peripheral surface of the cylindrical member 4 at equal intervals. In addition, the distance L between the tip surface 32 of the burner 3 and the nucleation position F1 (1000°C) of the raw material 1 was 0.92 cm. a is 56.8 cm, and the distance L between the tip surface 32 of the burner 3 and the narrowed portion 52 of the guide member 5 is b The distance L between the tip surface 32 of the burner 3 and the opening 51 was set to 51.0 cm. c was set at 20.4 cm.

[0074] As raw material 1, a tungsten solution was prepared by dissolving hexacarbonyl tungsten, an inorganic substance, in tetrahydrofuran, an organic solvent. Next, a cesium solution was prepared by dissolving cesium acetate, an inorganic substance, in ethanol, an organic solvent. After that, the tungsten solution and the cesium solution were mixed to produce a cesium tungsten solution (raw material preparation process).

[0075] Next, the raw material solution stored in the storage section 21 was supplied to the two-fluid nozzle 31 together with oxygen as a carrier gas to form an aerosol, which was then supplied into the flame of the burner 3 (aerosol formation process). The supply rate of the raw material solution to the burner 3 was 1 L / h. The flow rate of the oxygen as a carrier gas was 75 L / min. The air flow rate to the air inlet 41 was 280 Nm3 / h~540Nm 3 The temperature was controlled to be within the range of / h.

[0076] Next, the raw material solution contained in the aerosol was heat-treated by the flame formed by the burner 3 (heat treatment process). City gas and oxygen gas were used to form the flame by the burner 3, with the city gas flow rate being 2.8 L / min and the oxygen flow rate being 36.0 L / min. The combustion amount of the burner was 20,000 kcal / h, and the heat treatment was performed at a temperature of 1,500°C or higher. The cesium tungsten oxide particles obtained by the heat treatment were cooled and collected by a filter.

[0077] Comparative Example 1 Inorganic oxide particles were synthesized in the same manner as in Example 1, except that the guide member 5 and the fixing member 9 in the shape of an inverted truncated cone were not provided in the inorganic oxide particle synthesis apparatus.

[0078] <Evaluation> For the inorganic oxide particle synthesis apparatus of Example 1 and Comparative Example 1, the temperature distribution of the flame during heat treatment was measured using a K-type thermocouple, and the contour (outline) shapes of the areas at 1,000°C where nuclei begin to form and 500°C where the reaction stops were confirmed.

[0079] FIG. 6 is a diagram showing the flame nucleation position F1 and the reaction stop position F2 in the inorganic oxide particle synthesis apparatus of Example 1 and Comparative Example 1. The average value of the temperature at each position of the flame was calculated by measuring 10 times, and the point at 1,000°C where the nuclei start to be generated was connected with a line to create a contour line R1, and the point at 500°C where the coalescence and aggregation reaction stops was connected with a line to create a contour line R2. The upper dashed line in Example 1 indicates the position of the opening 51 of the guide member 5, and the lower dashed line indicates the position of the narrowed portion 52 of the guide member 5. As shown in FIG. 6, in the inorganic oxide particle synthesis apparatus of Example 1, the distance from the tip surface 32 of the burner 3 to the nucleation position F1 (1,000°C) was 56.8 cm, and the distance from the tip surface 32 of the burner 3 to the reaction stop position F2 (500°C) was extended to 64.9 cm. That is, in Example 1, the distance from the nucleation position F1 to the reaction stop position F2 was 8.1 cm. In addition, the synthesized cesium tungsten oxide particles were observed using a transmission electron microscope, and the particle size of the cesium tungsten oxide particles synthesized by the inorganic oxide particle synthesis apparatus of Example 1 was 245 nm in terms of D90 of the particle size distribution.

[0080] On the other hand, in the inorganic oxide particle synthesis apparatus of Comparative Example 1, the distance between the tip surface 32 of the burner 3 and the nucleation position F1 (1,000°C) was 57.3 cm, and the distance between the tip surface 32 of the burner 3 and the reaction stop position F2 (500°C) was extended to 69.6 cm. That is, in Comparative Example 1, the distance from the nucleation position F1 to the reaction stop position F2 was 12.3 cm, which was longer than the distance of 8.1 cm from the nucleation position F1 to the reaction stop position F2 in Example 1. In addition, the particle size of the cesium tungsten oxide particles synthesized by the inorganic oxide particle synthesis apparatus of Comparative Example 1 was 1.8 μm in D90 of the particle size distribution, which was larger than the particle size of Example 1.

[0081] That is, it was confirmed that the distance from the nucleation position F1 to the reaction stop position F2 was shortened by providing the inorganic oxide particle synthesis apparatus with the guide member 5 and the fixing member 9. Since the distance from the nucleation position F1 to the reaction stop position F2 in Example 1 was shortened to about 2 / 3 compared to Comparative Example 1, the time to pass through this region was also shortened to about 2 / 3. Therefore, it was confirmed that by shortening the distance from the nucleation position F1 to the reaction stop position F2 in the heat treatment process, the growth of particles due to the coalescence or aggregation of nuclei after they are generated is suppressed.

[0082] Furthermore, it was confirmed that the inorganic oxide particles formed in the heat treatment process flow along the air introduction direction in the space downstream of the guide member with respect to the air introduction direction.

[0083] Although the embodiment has been described above, the above embodiment is presented as an example, and the present invention is not limited to the above embodiment. The above embodiment can be implemented in various other forms, and various combinations, omissions, substitutions, modifications, etc. can be made without departing from the gist of the invention. These embodiments and their modifications are included in the scope and gist of the invention, and are included in the scope of the invention and its equivalents described in the claims. [Explanation of symbols]

[0084] 1 raw material 2 Raw material injection means 21 Storage area 22 Raw material supply pipe 23 Carrier gas supply pipe 3 Burner 31 Two-fluid nozzle 32 Tip surface 33 Raw material spout hole 34 Mixed gas vent 35 Mixed gas supply pipe 4 Cylindrical members 41 Atmospheric inlet 42 Cooling device 5 Guide member 51 Opening 52 Stenosis 53 Peripheral wall 53a 1st peripheral wall part 53b Second peripheral wall part 54 Bottom 6 Cooling section 7. Collection Section 71 Recovery tube 8 Filters 9 Fixing member 10 Inorganic oxide particle synthesis equipment

Claims

1. A raw material injection means for injecting a raw material containing an inorganic substance; a burner that forms a flame so as to cover the raw material injected from the raw material injection means; A cylindrical member that covers the flame and has an air inlet that introduces air into the inside; a guide member provided inside the cylindrical member and guiding the air flow toward the flame; The inorganic oxide particle synthesizing apparatus has a gap formed between the outer surface of the guide member and the inner peripheral surface of the cylindrical member, the gap communicating in a direction along the central axis of the cylindrical member.

2. The inorganic oxide particle synthesis apparatus of claim 1, wherein the guide member is cylindrical and has an opening at one end and a narrowed portion located downstream of the opening in the direction of flame progression and having an inner diameter smaller than the diameter of the opening.

3. The guide member defines a distance between the tip surface of the burner and the position of the nucleation temperature of the raw material in the flame as L ａ The distance between the tip surface of the burner and the narrowed portion is L ｂ 3. The apparatus for synthesizing inorganic oxide particles according to claim 2, which satisfies the following relational expression (1): 0.4×L ａ ≦ L ｂ ≦ 1.6×L ａ ・・・(1)

4. The area of ​​a cross section perpendicular to the central axis of the guide member in the narrowed portion is S Ｉ , the area of ​​a cross section perpendicular to the central axis of the cylindrical member at the inner diameter portion of the cylindrical member is S Ｏ 3. The apparatus for synthesizing inorganic oxide particles according to claim 2, which satisfies the following relational expression (2): 0.1×S Ｏ ≦ S Ｉ ≦ 0.8×S Ｏ ・・・(2)

5. The projected area of ​​the gap as viewed from the burner side is S ２ , the area of ​​a cross section perpendicular to the central axis of the cylindrical member at the inner diameter portion of the cylindrical member is S Ｏ 3. The apparatus for synthesizing inorganic oxide particles according to claim 1 or 2, which satisfies the following relational expression (3): S ２ ≦ 0.5×S Ｏ ・・・(3)

6. The distance between the tip surface of the burner and one end of the guide member on the opening side is L ｃ The distance between the tip surface of the burner and the narrowed portion is L ｂ 3. The apparatus for synthesizing inorganic oxide particles according to claim 2, which satisfies the following relational expression (4): L ｃ ≦ 0.8×L ｂ ・・・(4)

7. 3. The apparatus for synthesizing inorganic oxide particles according to claim 2, wherein the guide member has an inverted truncated cone shape tapered along the direction in which the flame advances.

8. 3. The inorganic oxide particle synthesis apparatus according to claim 1, wherein the air inlet is provided upstream of a tip surface of the burner with respect to a direction in which the flame advances.

9. 3. The apparatus for synthesizing inorganic oxide particles according to claim 1, further comprising a fixing member for fixing the guide member to an inner circumferential surface of the cylindrical member.

10. The fixing member is provided in plurality, 10. The apparatus for synthesizing inorganic oxide particles according to claim 9, wherein the plurality of fixing members are arranged rotationally symmetrically with respect to a central axis of the guide member.

11. forming an aerosol having an inorganic raw material and supplying the aerosol to a flame in a reaction field; and heat-treating the raw material contained in the aerosol, A method for synthesizing inorganic oxide particles, in which, in the heat treatment step, air is introduced into the reaction field so as to flow along the advancing direction of the flame, and a portion of the air introduced into the reaction field is caused to collide with a component so as to flow toward the central axis of the flame, and a portion of the air introduced into the reaction field is caused to flow along the advancing direction of the flame without colliding with the component.

Images