JP2010159177A - Nanocrystal aggregate and method for producing the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a nanocrystal aggregate where nanocrystals are aggregated and a method for producing the same. <P>SOLUTION: The nanocrystal aggregate where the nanocrystals of single crystal particles having a particle diameter of 1-20 nm are aligned and gathered toward a specific crystal direction by irradiating a mixed solution containing one or more metal ions and a colloidal dispersion solution with ultrasonic waves and where the particle diameters of the aggregate are uniform in the range of 100 nm and 50 μm is produced. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a nanocrystal aggregate in which nanocrystals are assembled, and a method for producing the same.

  Ceramic materials have been reduced in size and performance, and various materials have been developed. In addition, harmless materials with low environmental impact and low-temperature manufacturing technology are required. Under such circumstances, a ceramic powder having a small particle size and a narrow particle size distribution that can be sintered at a low temperature is attracting attention as a material for electronic components.

  When a powder having such a small particle size and a narrow particle size distribution is used as the dielectric material, the capacity of the multilayer capacitor can be increased. In addition, when used as a piezoelectric material, huge piezoelectric characteristics can be derived by using domains and interfaces.

  The powder having such a small particle size and a narrow particle size distribution can be synthesized by, for example, an aqueous solution reaction (hydrothermal reaction) under pressure or a thermal decomposition reaction of sprayed droplets.

  Patent Document 1 discloses a method for producing plate-like calcium hydroxide, Patent Document 2 discloses a colloidal particle precipitation / floating method and a processing apparatus using the method, and Patent Document 3 discloses a method for producing a ceramic raw material powder. It is disclosed.

JP 2000-7329 A JP 2008-229427 A JP 2005-298278 A

  In general, a small particle having a particle size of submicron or less has a large surface ratio with respect to its volume, and the surface is active. Therefore, it is difficult to control the aggregation state. That is, the number of fine particles constituting the aggregated grains, the crystal orientation, and the size and shape of the entire aggregate cannot be adjusted. For this reason, the particle size and shape of the aggregated particles cannot be arbitrarily arranged. As a result, even if it is possible to synthesize particles having a small particle size on the order of nanometers, it is not possible to sinter dense ceramics at low temperatures by taking advantage of the characteristics.

  On the other hand, research on chemical reactions using ultrasonic waves has attracted attention as sonochemistry. When a liquid is irradiated with ultrasonic waves, the generation and disappearance of bubbles generated in the liquid are related to the chemical reaction, and the cavitation caused by the change in pressure when ultrasonic waves propagate in the liquid is destroyed. As a result, a high-temperature state appears in a minute region and the chemical reaction proceeds. The reaction field at this time is considered to be an ultra-high temperature reaction field (about 5000 ° C., 100 atm). When the solvent is water, the appearance of hydrogen peroxide and OH radicals is also detected. In a chemical reaction using ultrasonic waves, the reaction is not accelerated by a temperature rise as in a normal chemical reaction, but is mainly related to the nature of the solvent.

  An object of the present invention is to provide a nanocrystal aggregate in which nanocrystals are assembled, and a method for producing the same.

  In order to solve the above problems, the present inventors have found that a nanocrystal aggregate can be obtained by irradiating a mixed solution containing metal ions with ultrasonic waves. That is, according to the present invention, the following nanocrystal aggregates and methods for producing the same are provided.

[1] A method for producing a nanocrystal aggregate in which a nanocrystal aggregate in which nanocrystals are aggregated is produced by irradiating a mixed solution containing metal ions with ultrasonic waves.

[2] The method for producing a nanocrystal aggregate according to [1], wherein the mixed solution is a colloidal dispersion solution containing one or more metal ions.

[3] The mixed solution containing the metal ions is obtained by dissolving or dispersing any one of an inorganic salt, an organic acid, and an organometallic compound in any of water, alcohol, and an organic solvent. Or the manufacturing method of the nanocrystal aggregate | assembly as described in [2].

[4] The method for producing a nanocrystal aggregate according to any one of [1] to [3], wherein an ultrasonic frequency in the reaction step by the ultrasonic irradiation is 10 kHz to 1000 kHz.

[5] The method for producing a nanocrystal aggregate according to any one of [1] to [4], wherein the generated nanocrystal is a single crystal particle having a particle diameter of 1 nanometer to 20 nanometer.

[6] The method for producing a nanocrystal aggregate according to any one of [1] to [5], wherein the nanocrystals are assembled in a specific crystal orientation.

[7] The method for producing a nanocrystal aggregate according to any one of [1] to [6], wherein the nanocrystals are aligned in a specific crystal orientation.

[8] The method for producing a nanocrystal aggregate according to any one of [1] to [7], wherein the nanocrystal aggregate has a particle size of 100 nanometers to 50 micrometers.

[9] A nanocrystal aggregate produced by the method for producing a nanocrystal aggregate according to any one of [1] to [8].

  By irradiating the mixed solution containing metal ions with ultrasonic waves, a nanocrystal aggregate can be produced, and the synthesis time for obtaining the nanocrystal can be shortened. In addition, secondary particles (nanocrystal aggregates) in which primary particles (nanocrystals) are aligned in the same crystal orientation can be synthesized. Furthermore, secondary agglomerated particles having a uniform particle size can be synthesized.

3 is a flowchart showing a procedure for synthesizing barium titanate nanocrystals in Process 1. It is a flowchart which shows the synthetic | combination procedure of the barium titanate nanocrystal of the process 2. 4 is a flowchart showing a procedure for synthesizing barium titanate nanocrystals in Process 3. It is a SEM photograph of the powder synthesize | combined in 20 minutes of ultrasonic irradiation time. It is the TEM photograph (process 1, solution concentration 0.1M) of the powder synthesize | combined in ultrasonic irradiation time 40 minutes. It is the TEM photograph (process 1, solution concentration 0.05M) of the powder synthesize | combined by ultrasonic irradiation time 40 minutes. It is the TEM photograph (process 2, solution concentration 0.1M) of the powder synthesize | combined in ultrasonic irradiation time 40 minutes. It is the electron diffraction pattern (process 1, solution concentration 0.1M) of the powder synthesize | combined by ultrasonic irradiation time 40 minutes, SAED is a photograph which shows a restriction | limiting visual field and an electron diffraction pattern. It is the electron beam diffraction pattern (process 1, solution concentration 0.1M) of the powder synthesize | combined by ultrasonic irradiation time 40 minutes, and 1-6 is a photograph which shows a nano beam irradiation position and a nano beam diffraction pattern. It is the electron diffraction pattern (process 1, solution concentration 0.05M) of the powder synthesize | combined by ultrasonic irradiation time 40 minutes, SAED is a photograph which shows a restriction | limiting visual field and an electron diffraction pattern. It is the electron diffraction pattern (process 1, solution concentration 0.05M) of the powder synthesize | combined by ultrasonic irradiation time 40 minutes, 1-6 is a photograph which shows a nano beam irradiation position and a nano beam diffraction pattern. It is the electron diffraction pattern (process 2, solution concentration 0.1M) of the powder synthesize | combined by ultrasonic irradiation time 40 minutes, SAED is a photograph which shows a restriction | limiting visual field and an electron diffraction pattern. It is the electron beam diffraction pattern (process 2, solution concentration 0.1M) of the powder synthesize | combined by ultrasonic irradiation time 40 minutes, and 1-6 is a photograph which shows a nano beam irradiation position and a nano beam diffraction pattern.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. The present invention is not limited to the following embodiments, and changes, modifications, and improvements can be added without departing from the scope of the invention.

  The method for producing a nanocrystal aggregate according to the present invention is a method for producing a nanocrystal aggregate in which nanocrystals are aggregated by irradiating a mixed solution containing metal ions with ultrasonic waves.

  The nanocrystal aggregate (sometimes referred to as an aggregate) produced by the method for producing a nanocrystal aggregate of the present invention is a collection of nanocrystals. A nanocrystal is a single crystal particle having a particle size of several nanometers to several tens of nanometers. In addition, the gathering of nanocrystals means a state in which a plurality of nanocrystals gather and are in contact with each other.

  In the nanocrystal aggregate of the present invention, the nanocrystals are assembled in a specific crystal orientation. “Aggregating in a specific crystal orientation” means a state in which a plurality of nanocrystals are gathered in the same crystal orientation and are in contact with each other. In the nanocrystal aggregate of the present invention, the nanocrystals are aligned in a specific crystal orientation. “Aligned to a specific crystal orientation” means a state in which they are aligned in the same crystal orientation.

  Examples of nanocrystals that can be produced by the method for producing a nanocrystal aggregate of the present invention include barium titanate.

  The particle size of the nanocrystal aggregate of the present invention is 100 nanometers to 50 micrometers. Furthermore, the particle size distribution of the nanocrystal aggregate is within 30 nanometers centering on the particle size.

  Next, the manufacturing method of the nanocrystal aggregate of this invention is demonstrated. A report on the form control method of nanocrystal aggregates with a unique structure by ultrasonic irradiation, for example, the form control method of barium titanate aggregates, that is, the method of irradiating ultrasonic waves to a mixed solution of barium ions and titanium ions This is a novel synthesis method that has never been seen before.

  The mixed solution containing metal ions is obtained by dissolving and dispersing an inorganic salt, an organic acid, and an organic metal compound in any of water, alcohol, and an organic solvent.

  Inorganic salts include chlorides, nitrates, sulfates, and the like. Examples of the organic acid include acetate and formate. Examples of organometallic compounds include metal alkoxides.

  As the mixed solution, a colloidal dispersion solution containing one or more metal ions can also be used. Examples of the colloid dispersion solution include titanate colloid and titanium hydroxide colloid.

  The frequency of ultrasonic waves in the reaction step by ultrasonic irradiation is preferably 10 kHz to 1000 kHz, and more preferably 20 kHz to 100 kHz. If it is less than 10 kHz, it is difficult to obtain an irradiation effect. On the other hand, if it exceeds 1000 kHz, heat is generated, which is not appropriate.

  The case where a barium titanate aggregate is produced as a nanocrystal aggregate will be described more specifically. In the case of producing barium titanate aggregates, an alkaline solution in which sodium hydroxide is added to a mixed aqueous solution consisting of an aqueous barium chloride solution and an aqueous titanium chloride solution can be used as the mixed solution containing metal ions. It does not exclude mixed solutions containing ions other than.

  When producing a barium titanate aggregate, a sol solution formed by hydrolysis of a metal alkoxide such as titanium tetraisopropoxide can be used as the colloid dispersion solution, but other colloids are included. It does not exclude the solution.

  Moreover, it is preferable to perform ultrasonic irradiation at 80 to 100 degreeC. If the reaction temperature is too low, the solubility of metal ions is lowered and segregation occurs, so that the target crystal cannot be synthesized.

  Moreover, it is preferable to perform ultrasonic irradiation at pH = 13-14 vicinity. If the pH of the solution is too low, the solubility of metal ions is lowered and segregation occurs, so that the target crystal cannot be synthesized. Moreover, the surface potential of the formed nanocrystal can be controlled by adjusting the pH of the solution.

  Next, a specific process for producing a nanocrystal aggregate will be described with reference to FIGS. 1A to 1B, taking as an example the case of producing a barium titanate aggregate.

<Process 1>
As shown in FIG. 1A, distilled water is prepared and bubbled with Ar gas to exclude carbon dioxide in the air. Using this, a BaCl ₂ solution containing Ba ions is prepared at room temperature. Similarly, a TiCl ₄ solution containing Ti ions is prepared. It is preferable that the Ba ions contained in the BaCl ₂ solution and the Ti ions contained in the TiCl ₄ solution be produced in the same number.

  The pH is adjusted by mixing these solutions with an aqueous NaOH solution or the like. The pH is preferably 13 to 14, and more preferably 14.

Next, ultrasonic irradiation is performed at 50 to 200 W / cm ² . At this time, the temperature of the solution is preferably 80 to 100 ° C.

  The produced powder is centrifuged, washed with ion-exchanged distilled water, and dried in a vacuum dryer.

<Process 2>
As shown in FIG. 1B, distilled water is prepared and bubbled with Ar gas. Using this, a BaCl ₂ solution containing Ba ions is prepared at room temperature. Also, a TiCl ₄ solution containing the same number of Ti ions as Ba ions is prepared and added to the BaCl ₂ solution. Furthermore, pH is adjusted by adding NaOH aqueous solution etc. to this solution and mixing. Next, the ultrasonic wave irradiation at 50~200W / cm ^2.

  The produced powder is centrifuged, washed with ion-exchanged distilled water, and dried in a vacuum dryer.

<Process 3>
As shown in FIG. 1C, distilled water is prepared and bubbled with Ar gas. Using this, a BaCl ₂ solution containing Ba ions is prepared at room temperature. Moreover, pH is adjusted by adding NaOH aqueous solution etc. to this solution and mixing. Further, a TiCl ₄ solution containing the same number of Ti ions as Ba ions is prepared and added to the BaCl ₂ solution. Next, ultrasonic irradiation is performed at 50 to 200 W / cm ² .

  The produced powder is centrifuged, washed with ion-exchanged distilled water, and dried in a vacuum dryer.

  By the production method as described above, a nanocrystal aggregate in which nanocrystals are aligned with the same crystal orientation can be produced.

  EXAMPLES Hereinafter, although this invention is demonstrated further in detail based on an Example, this invention is not limited to these Examples.

(Experimental Examples 1-19)
Titanium chloride (manufactured by Wako Pure Chemical Industries), barium chloride (manufactured by Wako Pure Chemical Industries), and sodium hydroxide were used.

A horn type ultrasonic irradiation device (manufactured by Branson, Sonifier D450 type) was used, and the frequency was 20 kHz and the output was 150 W / cm ² .

  Process 1 of the nanoparticle synthesis procedure is shown in FIG. 1A, process 2 in FIG. 1B, and process 3 in FIG. 1C. Process 1, process 2, and process 3 were applied to adjust the mixing method of the titanium chloride aqueous solution and the barium chloride aqueous solution and the pH change during mixing.

<Process 1>
As shown in FIG. 1A, 50 ml of distilled water was prepared and bubbled with Ar gas for 30 minutes. Therewith, at room temperature, 0.1M (mol / L), to prepare a BaCl ₂ solution containing Ba ions 0.05 M. Similarly, a TiCl ₄ solution containing 0.1 M (mol / L) and 0.05 M Ti ions was prepared. And these solutions and NaOH aqueous solution (5N) were mixed, and it was set to pH14 at room temperature. Next, ultrasonic irradiation was performed at 80 ° C. in air at 150 W / cm ² . The produced powder was centrifuged twice, washed twice with ion-exchanged distilled water, and dried in a vacuum dryer at 100 ° C. for 2 hours.

<Process 2>
As shown in FIG. 1B, 100 ml of distilled water was prepared and bubbled with Ar gas for 30 minutes. Using this, a BaCl ₂ solution containing 0.1 M (mol / L) and 0.05 M Ba ions was prepared at room temperature. Further, to prepare a TiCl ₄ solution containing the Ba ions as many Ti ions, it was added to the BaCl ₂ solution. Furthermore, NaOH aqueous solution (5N) was added and mixed with this solution, and it was set to pH14 at room temperature. Next, ultrasonic irradiation was performed at 80 ° C. in air at 150 W / cm ² . The produced powder was centrifuged twice, washed twice with ion-exchanged distilled water, and dried in a vacuum dryer at 100 ° C. for 2 hours.

<Process 3>
As shown in FIG. 1C, 100 ml of distilled water was prepared and bubbled with Ar gas for 30 minutes. Using this, a BaCl ₂ solution containing 0.1 M (mol / L) and 0.05 M Ba ions was prepared at room temperature. To this solution, an aqueous NaOH solution (5N) was added and mixed to adjust the pH to 14 at room temperature. Further, a TiCl ₄ solution containing the same number of Ti ions as Ba ions was prepared and added to the BaCl ₂ solution. Next, ultrasonic irradiation was performed at 80 ° C. in air at 150 W / cm ² . The produced powder was centrifuged twice, washed twice with ion-exchanged distilled water, and dried in a vacuum dryer at 100 ° C. for 2 hours.

  Table 1 shows the process, solution concentration (concentration of Ba ion and Ti ion), and ultrasonic irradiation time of the prepared sample.

(Evaluation)
Next, the crystal phase and crystallinity of the particles of the prepared sample were evaluated using an X-ray powder diffraction method (XRD, acceleration voltage 40 kV, current 20 mA). The microstructure was observed using a scanning electron microscope (SEM, acceleration voltage 10 kV) and a transmission electron microscope (TEM, acceleration voltage 300 kV). The crystallinity of each particle was analyzed by electron diffraction (restricted field method, nanobeam diffraction). The chemical composition of the particles and the supernatant solution was evaluated by ICP emission analysis.

  From the XRD results of the produced powder, it was found that the crystal phase and crystallinity change depending on the reaction temperature, solution concentration, and ultrasonic irradiation time.

In the powder synthesized at a low temperature of less than 80 ° C. during the ultrasonic irradiation, BaCO ₃ was the main phase regardless of the solution concentration and the ultrasonic irradiation time.

From this, it was found that it is necessary to proceed the reaction at a temperature of 80 ° C. or higher in order to synthesize BaTiO ₃ single phase particles.

  Therefore, comparison is made of changes in the crystal phase and microstructure of the generated particles when the synthesis conditions such as the mixing method (process), solution concentration, and ultrasonic irradiation time are changed at a synthesis temperature of 80 ° C. and a pH of 14 at the time of mixing. did.

As shown in Table 1, it was found that when the solution had a low concentration (0.05 M), the gel remained when the ultrasonic irradiation time was short, and as a result, BaCO ₃ was mixed.

On the other hand, in the case of a high-concentration (0.1M) solution, it was found that BaTiO ₃ single-phase nanoparticles can be obtained even with an ultrasonic irradiation time of 20 minutes.

  FIG. 2 shows scanning micrographs of particles synthesized under the raw material solution mixing method (processes 1, 2, 3), solution concentration (0.1 M, 0.05 M), and ultrasonic irradiation time of 20 minutes.

  As already shown in Table 1, the product obtained from the low-concentration (0.05M) solution in Process 1 was found to contain a mixture of gels and agglomerated particles and the reaction was insufficient.

  On the other hand, the product obtained from the high-concentration (0.1 M) solution has aggregated primary particles having a small particle size to form pseudospherical secondary particles having a relatively uniform particle size. I understood.

  Among them, the product obtained from the low concentration (0.05M) solution in Process 2 had a characteristic structure in which square-shaped secondary particles were aggregated.

  It was found that the particle size of the aggregated particles was smaller as the solution concentration was higher, and the longer the ultrasonic treatment time was, the more the shape of the particles became round.

  Next, transmission electron micrographs of the barium titanate particles synthesized for the processes 1 and 2 using a high-concentration (0.1M) solution under the condition of ultrasonic irradiation time of 40 minutes are shown in FIGS. 3A, 3B, and 3C. 3A shows process 1, solution concentration 0.1M, FIG. 3B shows process 1, solution concentration 0.05M, and FIG. 3C shows process 2, solution concentration 0.1M.

  The particle size of the secondary particles (nanocrystal aggregate) was 250 nm to 400 nm, and had a relatively quasi-spherical shape. Further, according to observation with a high-resolution transmission electron microscope, it was found that the primary particles (nanocrystals) had an irregular shape with a particle size of 5 nm to 10 nm. Furthermore, lattice fringes were observed in the primary particles, which revealed that they were barium titanate nanocrystals.

  4A to 6B show the electron diffraction results of the barium titanate particles synthesized in the process 1 and 2 using a high-concentration (0.1M) solution under the condition of ultrasonic irradiation time of 40 minutes. 4A and 4B are electron diffraction patterns (process 1, solution concentration 0.1 M) of powder synthesized with an ultrasonic irradiation time of 40 minutes, and SAED in FIG. 4A is a limited field of view and electron diffraction pattern, FIG. 1-6 are the nanobeam irradiation position and the nanobeam diffraction pattern. FIGS. 5A and 5B are electron diffraction patterns (process 1, solution concentration 0.05 M) of powder synthesized with an ultrasonic irradiation time of 40 minutes. SAED in FIG. 5A is a limited field of view and electron diffraction pattern, FIG. 1-6 are the nanobeam irradiation position and the nanobeam diffraction pattern. 6A and 6B are electron diffraction patterns (process 2, solution concentration 0.1 M) of the powder synthesized with an ultrasonic irradiation time of 40 minutes. SAED in FIG. 6A is a limited field of view and electron diffraction pattern, FIG. 1-6 are the nanobeam irradiation position and the nanobeam diffraction pattern.

  Secondary particles (aggregates of barium titanate nanocrystal primary particles) synthesized from an electron diffraction pattern (SAED in FIGS. 4A to 6B) obtained by combining a single secondary particle with a limited field stop (Φ150 nm) are: It turned out that all show the pattern similar to a barium titanate single crystal according to a zone axis. From this result, it was suggested that the secondary particles synthesized by ultrasonic irradiation had high crystallinity, and the primary particles (barium titanate nanocrystals) constituting the secondary particles were aligned in the same direction.

  Further, by comparing the electron beam diffraction pattern of the secondary particles with the nanobeam diffraction pattern (nanobeam diameter 1 nm) of the primary particles constituting the secondary particles (1-6 in FIGS. 4B, 5B, and 6B). It was clarified that the primary particles have the same crystal orientation and that the orientation coincides with the crystal orientation of the entire secondary particles.

(Comparative Example 1)
In order to clarify the effect of ultrasonic irradiation, the production process of barium titanate particles by normal mechanical stirring (no ultrasonic irradiation) was compared under the same raw material, process 2, and synthesis temperature (80 ° C.). As a result, in the case of a high-concentration (0.1M) solution, it was found that the product was in a gel form at a stirring time of 40 minutes, and barium carbonate was produced from the X-ray diffraction results.

(Comparative Example 2)
After 8 hours of mechanical stirring, the product became a mixture of cube-like particles and gel, and was found to be a mixed phase consisting of barium titanate and barium carbonate. Further, a relatively large amount of Ba ²⁺ ions remained in the residual liquid (supernatant liquid) after the generated particles were centrifuged.

  The present invention can be used as a method for producing a nanocrystal aggregate having a uniform crystal orientation. The nanocrystal aggregate of the present invention can be used for dielectric materials, piezoelectric materials, and the like.

Claims (9)

  A method for producing a nanocrystal aggregate, wherein a nanocrystal aggregate in which nanocrystals are aggregated is produced by irradiating a mixed solution containing metal ions with ultrasonic waves.   The method for producing a nanocrystal aggregate according to claim 1, wherein the mixed solution is a colloidal dispersion solution containing one or more metal ions.   The mixed solution containing the metal ions is obtained by dissolving or dispersing any one of an inorganic salt, an organic acid, and an organometallic compound in water, alcohol, or an organic solvent. Method for producing a nanocrystal aggregate.   The manufacturing method of the nanocrystal aggregate | assembly of any one of Claims 1-3 which sets the frequency of the ultrasonic wave in the reaction process by the said ultrasonic irradiation to 10 kHz-1000 kHz.   The method for producing a nanocrystal aggregate according to any one of claims 1 to 4, wherein the generated nanocrystal is a single crystal particle having a particle diameter of 1 nanometer to 20 nanometer.   The method for producing a nanocrystal aggregate according to any one of claims 1 to 5, wherein the nanocrystals are assembled in a specific crystal orientation.   The method for producing a nanocrystal aggregate according to any one of claims 1 to 6, wherein the nanocrystals are aligned in a specific crystal orientation.   The method for producing a nanocrystal aggregate according to any one of claims 1 to 7, wherein the nanocrystal aggregate has a particle size of 100 nanometers to 50 micrometers.   The nanocrystal aggregate manufactured by the manufacturing method of the nanocrystal aggregate of any one of Claims 1-8.