JP3070092B2 - Method and apparatus for producing oxide superconducting fine particles - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial applications]

The present invention relates to a method and an apparatus for producing oxide superconducting fine particles, and more particularly to an improved technique of a spray drying method.

[Prior art]

When producing an oxide superconducting film or wire, oxide superconducting fine particles in which the constituent elements are blended in a desired ratio are manufactured in advance, and the oxide superconducting fine particles are coated on a substrate by a coating method, a thermal spraying method, or the like. Has been adopted. Conventionally, there is a so-called spray drying method as one of the methods for producing oxide superconducting fine particles. The spray drying method is described in, for example, a publication, [Chemical Industry], Vol. 53, No. 7 (19
89), pages 512 to 514, as introduced under the title of [Production of oxide superconducting fine particles by spray pyrolysis method], Y (NO ₃ ) ₂ , Ba (NO ₃ ) ₂ , Cu (NO ₃ ) An aqueous solution containing constituent elements such as ₂ in a desired ratio is prepared, an aqueous solution containing the constituent elements is mist-formed by means such as a sprayer, and the mist of the aqueous solution is heated and fired in an oxygen gas atmosphere. It is intended to obtain the desired oxide superconducting fine particles. According to the spray-drying method, a mist of an aqueous solution containing the constituent elements in which the above-mentioned materials are blended is heated and fired, so that fine particles having a uniform blending ratio and small particle size can be obtained, and the particle size can be reduced. By doing so, the composition can be made uniform, and the expectation for improving the superconducting properties of the oxide superconductor increases.

[Problems to be solved by the invention]

However, even in the spray drying method described above,
The particle size of the fired oxide superconducting fine particles is, for example, about 1 μm to 0.15 μm. In order to improve the superconducting properties, it is considered effective to reduce the particle size of the oxide superconducting fine particles to a smaller particle size or to increase the purity.
It is difficult to meet such demands, and it is recognized that the oxide superconducting fine particles tend to be deteriorated during the manufacturing process of the oxide superconducting fine particles under the influence of moisture and other coexisting gases. The present invention solves such a problem,
An object of the present invention is to further reduce the particle size, facilitate the control of the particle size, obtain high-purity oxide superconducting fine particles, and the like.

[Means for Solving the Problems]

The present invention proposes two means for solving the above problems. The first means includes a step of misting an aqueous solution containing the constituent elements with a carrier gas such as O ₂ , a step of classifying the mist to select a mist having a small particle size, and a step of separating the mist of the selected small-diameter mist. In the method for producing oxide superconducting fine particles, comprising a step of removing the moisture and a step of heating the small-diameter mist from which water has been removed and baking the oxides of the constituent elements,
The method for producing oxide superconducting fine particles, wherein an aqueous solution containing constituent elements is a nitrate aqueous solution, and a step of contacting and diffusing and adsorbing NOx to an alkali layer is added after the step of baking the oxide of the constituent elements. And how to do it. The second means is a mist-forming means for converting an aqueous solution containing the constituent elements into mist with a carrier gas such as O ₂ , and a classification means connected to the mist-forming means for classifying the mist and selecting a mist having a small particle diameter. A moisture absorbing means connected to the classifying means for removing moisture of the classified small-diameter mist; and a baking means connected to the moisture absorbing means for heating the small-diameter mist from which moisture has been removed and firing the oxide of the constituent element. In the apparatus for producing oxide superconducting fine particles, the aqueous solution containing the constituent element to be misted by the mist forming means is a nitrate aqueous solution, and the baking means is connected to the NOx removing means for bringing NOx into contact with the alkali layer to diffuse and adsorb the NOx. An apparatus for producing oxide superconducting fine particles.

[Action]

In the first means and the second means, although an aqueous solution containing the constituent elements is prepared and mist is formed, a mist having a varied particle size is generated. Is transferred to the mist at the same mixing ratio. Even when only small mist particles having a small particle size are selected from a large number of mist particles having a large particle size, each selected mist having a small particle size has a desired compounding ratio. When the water content of the mist is removed, the dried mist particles become less likely to be attracted to each other by the drying of the mist particles,
The constituent elements in each grain are easily brought into contact with the O ₂ gas, and calcination is performed in a state where the oxygen concentration is increased, whereby uniform oxide superconducting fine particles are generated. In the first means and the second means, the aqueous solubility of the constituent elements is further increased by using an aqueous nitrate solution as the aqueous solution containing the constituent elements, and the oxide formation reaction of the constituent elements during firing is performed. Is promoted. In addition, NOx generated by oxidation of nitrate is diffused and adsorbed to the alkali layer, thereby preventing NOx from being adsorbed to the oxide and improving the purity of the oxide superconducting fine particles.

【Example】

An embodiment of a method and an apparatus for producing oxide superconducting fine particles according to the present invention will be described below with reference to FIGS. 1 to 4. 1 to 3, reference numeral 1 denotes an aqueous solution supply unit, 2 denotes a carrier gas supply unit, 3 denotes a mist generation unit (nebulizer), 4 denotes a classification unit (mist selection unit), and 5 denotes a water evaporation unit (water evaporation). , 6 is a moisture absorbing means (diffusion dryer), 7 is a heat retaining means, 8 is a firing means (firing furnace), and 9 is a NOx removing means. To explain these details, the aqueous solution supply means 1 mixes constituent elements such as Y, Ba, and Cu at a desired mixing ratio, and converts a nitrate aqueous solution (superconducting solution) R containing nitrate, for example, into a mist forming means 3. The apparatus comprises a sample tank 11 for storing the aqueous solution, a transfer pump 12 for transferring the stored liquid in the sample tank 11 to the mist generating means 3, and a spray liquid supply pipe 13. The carrier gas supply means 2 is connected to the mist generation means 3 and supplies oxygen gas as a carrier gas. The carrier gas supply means 2 includes an oxygen gas supply source 21 such as an oxygen cylinder, a flow controller 22 for adjusting the amount of oxygen gas, And an oxygen gas supply pipe 23. The mist forming means 3 converts the aqueous solution containing the constituent elements into a mist, and the classifying means 4 is connected to the mist forming means 3 and classifies the mist to select mist having a small particle size, as shown in FIG. Thus, the structure has mutual relations. That is, the mist generating means 3 is provided with the carrier gas supply pipe 23.
And an orifice portion 31 in which the flow path is sandwiched to, for example, a hole diameter of about 10 μm, and a merging portion 32 which communicates with the orifice portion 31 and the spray liquid supply pipe 13 to mist the aqueous solution.
And a spouting section for spouting the mist converted into mist at the merging section 32
33. Further, the classifying means 4 is installed in a state close to the mist generating means 3 and forms a mist separating sleeve 41 forming a space S for discharging the mist, and a position of the mist separating sleeve 41 above and close to the jetting portion 33. And a mist separating sleeve 41 provided on the
A classifying section 43 provided at a position facing the ejection section 33 on the side wall of the classifying section 43 for liquefying the mist having a large particle size by dispersing the mist and dispersing the mist having a small particle size. A collision unit 44 provided to prevent the mist having a large particle diameter from moving upward; an aqueous solution collection tube 45 for flowing down the aqueous solution liquefied by contacting the classification unit 43 and the collision unit 44; and an aqueous solution collection tube 45. , A pump 46 for transferring the aqueous solution stored in the trap 46, and an aqueous solution return pipe 48 connecting the pump 47 and the sample tank 11. The water evaporation means 5 includes a heat transfer tube 52 connected to the mist separation sleeve 41 of the classification means 4 in a casing 51.
A heater 53 for heating the heat transfer tube 52;
A temperature sensor 54 for detecting the temperature of the heater 53 is provided, and the controller 55 adjusts the amount of heat of the heater 53 based on the temperature detection data of the temperature sensor 54. The moisture absorbing means (diffusion dryer) 6 is connected to the heat transfer pipe 52 in the moisture evaporating means 5 to remove moisture in the gaseous fluid to be inserted. Are arranged in a penetrating state,
In this structure, a moisture absorbing layer 63 filled with silica gel particles is provided around the ventilation sleeve 62. The heat retaining means 7 has a structure in which a heat retaining layer 72 is arranged around a gaseous fluid transfer pipe 71 connecting the moisture absorbing means 6 and the firing means 7. The sintering means 8 is constituted by a pre-heating unit (pre-heating furnace) 8A in the former stage and a sintering unit (firing furnace) 8B in the latter stage, and heats the mist in a dehumidified state to sinter the oxides of the constituent elements.
A heating and firing tube 81 arranged in a connected state between the gaseous fluid transfer pipe 71 in the heat retaining means 7 and the NOx removing means 9 at the subsequent stage;
Heater units 82A and 82B for heating the heating and firing tube 81
And a temperature sensor 83 for detecting the temperature of the heating and firing tube 81
A and 83B are provided, and the preheating temperature controller 84 and the firing temperature controller 85 adjust the heat quantity of both heater sections 82A and 82B based on the temperature detection data of the temperature sensors 83A and 83B. The NOx removing means 9 is connected to the subsequent stage of the firing means 8 to remove NOx and water vapor in the gaseous fluid, and a mesh-shaped ventilation sleeve 92 is disposed in a storage container 91 in a penetrating state. In this structure, an alkali layer 93 filled with NaOH particles is provided around the ventilation sleeve 92. In addition, in the lower stage of the NOx removing means 9,
4 is connected, a particle storage container 95 is disposed below the particle take-out tube 94, and a particle diameter measuring device 96 is connected to the particle take-out tube 94.

[Production example of oxide superconducting fine particles]

An example of the production of oxide superconducting fine particles by the apparatus for producing oxide superconducting fine particles configured as described above will be described. FIG. 3 is a model diagram showing the concept of the steps of the method for producing oxide superconducting fine particles according to the present invention. <Preparation of Aqueous Solution> As described in the related art, as an aqueous solution containing constituent elements in a desired ratio, Y (NO ₃ ) ₂ , Ba (NO ₃ ) ₂ , Cu
(NO) A nitrate aqueous solution R such as ₂ is prepared. By preparing an aqueous solution of a nitrate containing a constituent element, an aqueous solution containing the constituent element in a desired ratio and concentration can be easily obtained as shown by modeling in FIG. Example of Concentration As shown in FIG. 4, a sample having a concentration of XBa ₂ Cu ₃ Ox in the range of 0.0033 mol to 0.0714 mol per liter of solution was used. <Supply of aqueous solution> By operating the transfer pump 12 in the aqueous solution supply means 1, the nitrate aqueous solution R stored in the sample tank 11 is sent to the mist formation means 3 via the spray liquid supply pipe 13. <Supply of carrier gas> By the operation of the carrier gas supply means 2, the oxygen gas is supplied from the oxygen gas supply source 21 to the flow regulator 22 and the oxygen gas supply pipe.
It is sent to the mist generating means 3 via 23. In this case, the carrier gas was 100% O ₂ gas and 2 liters per minute. <Generation of mist> The oxygen gas fed from the oxygen gas supply pipe 23 is jetted out of the orifice section 31 in a jet stream, thereby turning the nitrate aqueous solution R supplied to the junction section 32 into a mist. Mist separation sleeve from spout 33
Spout into the space S inside 41. By this mist formation, the composition of the constituent elements in the nitrate aqueous solution R is transferred to the mist at the same ratio, and the mist in this case is reduced by reducing the diameter of the orifice portion 31 or increasing the ejection speed. Although the diameter can be reduced, large and small particle sizes are mixed. <Classification of mist> When the mist is fed into the space S of the mist separating sleeve 41 from the ejection part 33 of the mist forming means 3, the mist is guided by the guide 42 so that the mist is directly sent to the water evaporation means 5. While preventing that, all the mist is applied to the classification part 43 and dispersed, and for the mist with a large particle size, liquefaction is promoted,
The mist having a small particle size is made to float in the carrier gas. Further, when the mist collides with the classifying section 43, it is likely to be dispersed upward in FIG. To prevent By these classifications, only the mist having a small particle size is selected and put on a carrier gas and sent to the water evaporation means 5. As shown in FIG. 3 by modeling with a magnifying glass, it was confirmed that the particle size of the mist was approximately 0.3 to 1 μm. In this case, each of the selected small-diameter mist has a desired mixing ratio in a state where the mixing ratio of the constituent elements in the aqueous solution is inherited. <Recovery of Large Particle Size Mist> When large and small mist hits the classification unit 43 and the collision unit 44, and the mist having a large particle size is liquefied, the liquid flows down by an aqueous solution recovery pipe 45 and is trapped by a trap 46. Is collected and stored, and the stored liquid is returned to the sample tank 11 via the aqueous solution return pipe 48 by the operation of the pump 47. <Moisture evaporation of mist> The classified small-sized mist is supplied to the heat transfer tube 52 of the moisture evaporation means 5.
When the heater 53 is actuated, the carrier gas inserted by heat transfer from the heat transfer tube 52
Heating to a temperature of 0 ° C. to 120 ° C. promotes evaporation of the water content of the mist, which is a nitrate solution, so that water vapor is separated from the mist. In this case, a heat transfer tube 52 having an inner diameter of 20 mm and a length of 600 mm was used. <Drying of the mist> The heated mist forms a ventilation sleeve in the moisture absorbing means 6.
When sent to the mist 62, the water vapor separated from the mist is diffused and absorbed by the moisture absorbing layer 63, and the ions and nitrates of the respective constituent elements dissolved in one mist are condensed into constituent elements and the like in one mist unit. It becomes a dried mist in a wet state. Then, in a state where mutual adsorption of the dry mist is hindered by the drying, the lower heat retaining means 7 is provided by the carrier gas.
Is transferred to In this case, the dried mist is maintained in a state of inheriting the mixing ratio in the aqueous solution, and the particle size of one mist is reduced by the amount of water removed. As shown, it was observed that the particle size was reduced to approximately 0.1 μm and that water was removed by 90% or more. As the ventilation sleeve 62, one having an inner diameter of 20 mm and a length of 600 mm was used. <Heat keeping of dry mist> In the heat keeping means 7, cooling is prevented by the heat keeping layer 72, and the state of the above-mentioned dry mist is kept at, for example, 120 ° C., and transferred to the subsequent baking means 8. <Firing (Sintering)> The dried mist sent to the firing means 8 is fired by reacting with oxygen in the carrier gas while sequentially passing through the preheating section 8A and the firing section 8B, whereby the oxides of the constituent elements are converted. Generated. That is, by the operation of the heaters 82A and 82B, the carrier gas and the dry mist therein are fired through the heating and firing tube 81. When the particles that have been dried mist in advance are fired, the mist mutual adsorption phenomenon during transfer to the firing step is unlikely to occur, so that the preheated section 8A is maintained while maintaining the state of small particles
And sent to the firing section 8B. In addition, when the dry mist has water removed, the constituent elements are easily brought into contact with the O ₂ gas, and calcination is performed in a state where the oxygen concentration is high, and the oxide generation reaction of the constituent elements is promoted. Homogeneous oxide superconducting fine particles are produced. In this case, the ambient temperature of the preheating section 8A is 1000 ° C, and the firing section 8B
Is set to 950 ° C. or the like. The heating and firing tube 81 used had an inner diameter of 35 mm and a length of 1200 mm. <NOx removal> When the oxide fired in the firing means 8 is sent to the ventilation sleeve 92 in the NOx removing means 9, NOx generated by oxidation of nitrate and NOx adsorbed on the oxide are obtained.
Comes into contact with the alkali layer 93 and is removed from the oxide by diffusion absorption. If any residual moisture adheres to the oxide during the removal of NOx, the moisture is also adsorbed to the alkali layer 93, and the removal of NOx generates oxide superconducting fine particles P to improve the purity. It is. In this case, the alkali layer 93 was 100% NaOH particles. <Measurement of Particle Diameter> As described above, the oxide from which NOx and water have been removed, that is, the oxide superconducting fine particles P are transferred from the fine particle take-out tube 94 to the fine particle storage container 95. By operating the measuring device 96, the particle diameter of the oxide superconducting fine particles P is measured. The oxide superconducting fine particles P manufactured by the above-described manufacturing process have a particle size of, for example, about 0.05 μm as shown in FIG. 3 by modeling with a magnifying glass, and more specifically, FIG. As shown in the figure, although the dispersion is caused by the concentration of the aqueous solution, when the concentration is 0.0333 mol / liter, the particle size of the oxide superconducting fine particles P becomes 0.05 μm when the concentration is lowered when the 50% distribution value is observed. Was observed to be able to further reduce the particle size. Note that the following embodiments can be adopted instead of the embodiments. (1) In the aqueous solution supply means and the aqueous solution preparation step, a carbonate aqueous solution other than a nitrate aqueous solution, an acetate aqueous solution, or the like is used. (2) In the aqueous solution supply means 1 and the aqueous solution preparation step, as shown in FIG. 5, an aqueous solution containing individual constituent elements is pumped up by a pump 12 at the time of preparation of the aqueous solution, supplied at a desired ratio, and passed through a mixer 14 Mist conversion means 3
To change the composition ratio during the production of fine particles. (3) In the NOx removing means and the NOx removing step, the alkali layer is made of an alkali other than NaOH. (4) Production of superconducting fine particles using a solution containing constituent elements other than those described in the example of FIG. (5) The carrier gas is air or the like. (6) Arrangement direction of preheating furnace 8A and firing furnace 8B and insertion direction of gaseous fluid are arbitrary.

【The invention's effect】

According to the first invention and the second invention, that is, according to the first and second inventions, the following effects can be obtained. (1) Compared with superconducting fine particles manufactured by the conventional spray-drying method by classifying the aqueous solution containing the constituent elements during mist formation, selecting those having a small particle size, and sintering the mist while removing the water content of the mist. Thus, superconducting fine particles having a much smaller particle size can be produced. (2) The particle size of the superconducting fine particles can be arbitrarily controlled in combination with the above-mentioned concentration control of the aqueous solution. (3) Since the baking is performed in a state where water is removed, deterioration of the superconducting fine particles can be suppressed. (4) By using superconducting fine particles whose particle diameter is small and the composition of the constituent elements is controlled in the form of fine particles, it is expected that a superconductor having excellent characteristics will be synthesized. Further, the following effects are obtained. (1) By using a nitrate aqueous solution as the aqueous solution containing the constituent elements, the water solubility of the constituent elements is increased, and homogenization of each superconducting fine particle can be achieved. (2) By drying and baking the nitrate aqueous solution, it is possible to promote the oxide formation reaction of the constituent elements at the time of baking, and to improve the purity of the oxide superconducting fine particles.

[Brief description of the drawings]

FIG. 1 is a partially cutaway front view showing a schematic configuration example of an apparatus for producing oxide superconducting fine particles according to the present invention. FIG. 2 is a front sectional view showing a detailed structure of a chain line II portion in FIG. FIG. 3 is a model diagram showing a concept of a manufacturing process of the oxide superconducting fine particles according to the present invention. FIG. 4 is a distribution diagram showing the relationship between the aqueous solution concentration and the particle size in the oxide superconducting fine particles produced by the method and apparatus for producing oxide superconducting fine particles according to the present invention. FIG. 5 is a front view showing another embodiment of the aqueous solution supply means in FIG.

[Explanation of symbols]

R: nitrate aqueous solution, P: oxide superconducting fine particles, S:
... space, 1 ... aqueous solution supply means, 2 ... carrier gas supply means, 3 ... mist generation means (nebulizer), 4 ...
Classification means (mist sorting means), 5 ... Moisture evaporating means (moisture evaporator), 6 ... Moisture absorbing means (Diffusion dryer), 7 ... Heat keeping means, 8 ... Baking means, 8A ... Preheating unit (Preheating furnace) ), 8B: firing section (firing furnace), 9: NOx removal means, 11: sample tank, 12: transfer pump, 13: spray liquid supply pipe, 21: oxygen gas supply source, 22 ... Flow regulator, 23 ... Oxygen gas supply pipe, 31 ... Orifice part, 32 ...
... Merging part, 33 ... Squirting part, 41 ... Mist separation sleeve, 42 ... Guide, 43 ... Classification part, 44 ... Collision part, 45 ...
... Aqueous solution collection pipe, 46 ... Trap, 47 ... Pumping pump, 48 ... Aqueous solution return pipe, 51 ... Casing, 52 ...
Heat transfer tube, 53 Heater, 54 Temperature sensor, 55 Controller, 61 Container, 62 Vent sleeve, 63
… Moisture absorbing layer, 71… gaseous fluid transfer pipe, 72… thermal insulation layer, 81
…… Heated firing tube, 82A ・ 82B …… Heater section, 83A • 83B ……
Temperature sensor, 84: Preheating temperature controller, 85: Firing temperature controller, 91: Storage container, 92: Vent sleeve, 93: Alkaline layer, 94: Particle extraction tube, 95:
... particle storage container, 96 ... particle size measuring device.

Claims (2)

(57) [Claims] 1. A step of converting an aqueous solution containing a constituent element into a mist with a carrier gas such as O ₂ , a step of classifying the mist and selecting a mist having a small particle size, and a step of separating water of the selected small-diameter mist. A method for producing oxide superconducting fine particles, comprising: a moisture absorption step of removing, and a step of heating a small-diameter mist from which water has been removed and firing an oxide of a constituent element, wherein the aqueous solution containing the constituent element is an aqueous nitrate solution, A method for producing oxide superconducting fine particles, characterized in that a step of bringing NOx into contact with an alkali layer to diffuse and adsorb it is added after the step of baking the oxide. 2. A mist generating means for converting an aqueous solution containing a constituent element into a mist with a carrier gas such as O ₂ , a classification means connected to the mist generating means for classifying the mist and selecting a mist having a small particle size. A moisture absorbing means connected to the classifying means for removing water from the classified small-diameter mist; and a firing means connected to the moisture absorbing means for heating the small-diameter mist from which the moisture has been removed and firing the oxides of the constituent elements. In the manufacturing apparatus of the oxide superconducting fine particles, the aqueous solution containing the constituent element to be misted by the mist forming means is a nitrate aqueous solution, and the baking means is connected to the NOx removing means for bringing NOx into contact with an alkali layer and diffusing and adsorbing the same. An apparatus for producing oxide superconducting fine particles, comprising: