JP6281900B2 - Method for forming functional sintered dense film and method for synthesizing nanoparticles - Google Patents

Description

The present invention relates to a method for forming a functional sintered dense film and a nanoparticle synthesis method . More specifically, the present invention relates to a method for forming a functional sintered dense film formed by sintering nanoparticles using press pressure, and a nanoparticle synthesis method suitable for forming a functional sintered dense film.

  Nanoparticles have a lower melting point than bulk due to their size effect. By utilizing this melting point lowering phenomenon, metal wiring is sintered at a low temperature using printed electronics or the like (see, for example, Patent Document 1).

JP 2012-140669 A JP2013-247181A JP 2013-230416 A

  However, since metal nanoparticles have high activity due to the size effect, they are easily oxidized, especially in the case of base metal nanoparticles. In addition, the nanoparticle surface is coated with a protective dispersant for particle size control, dispersibility control, and oxidation prevention, thereby inhibiting the sintering of the nanoparticles. For this reason, the conventional nanoparticle sintering method has a problem that it is difficult to synthesize a dense film in addition to the aforementioned oxidation problem. In addition, the conventional nanoparticle sintering method has a problem that the cost increases because it is fired in an inert atmosphere or the oxidized film is heat-treated again in a reducing atmosphere to prevent oxidation. It was.

The present invention has been made in view of the above-described problems of the prior art, and can form a functional sintered dense film using nanoparticles easily at a lower temperature and in a shorter time while preventing nanoparticle oxidation. An object is to provide a method for forming a functional sintered dense film and a method for synthesizing nanoparticles .

  Therefore, the inventor of the present application has conducted various studies to achieve the above object, and as a result, regarding the sintering of nanoparticles, the nanoparticles are sintered at room temperature by press-pressing the nanoparticles, and further, It has been found that by heating, sintering proceeds and a functional sintered dense film is obtained. In addition, regarding the sintering of metal nanoparticles, the inventor of the present application remarkably accelerates sintering by adding a flux during sintering, thereby obtaining a functional sintered dense film at a low temperature and in a short time. I found out that The inventor of the present application has also found that a metal functional sintered dense film can be obtained without being oxidized in the atmosphere by press-pressing the metal nanoparticles. Furthermore, the present inventor has found a new method for synthesizing metal nanoparticles that does not use a protective dispersant that inhibits effective sintering during metal nanoparticle sintering in the production of a functional sintered dense film.

The present invention has been made on the basis of the above knowledge, and the method for forming a functional sintered dense film according to the present invention uses the press pressure to directly apply the entire nanoparticles composed of chromium using a press die. A functional sintered dense film is formed by sealing and sintering the nanoparticles. Thereby, the nanoparticle can be sintered at a low temperature by the phenomenon of the melting point lowering of the nanoparticles and the application of energy by pressurization to form a functional sintered dense film.

  In the method for forming a functional sintered dense film according to the present invention, the functional sintered dense film may be formed in an air atmosphere. Since the densification is promoted by applying the press, the nanoparticle surface is blocked from the atmosphere, so that the oxidation of the nanoparticle surface is suppressed and the sintering is promoted.

  In the method for forming a functional sintered dense film according to the present invention, the sintering of the nanoparticles may be promoted using a flux. Since the oxide layer on the surface of the nanoparticles that inhibits sintering can be removed by flux, a functional sintered dense film can be obtained at a low temperature and in a short time.

  In the method for forming a functional sintered dense film according to the present invention, the functional sintered dense film may be formed using a sealing material. Since the pressure can be efficiently transmitted using the sealing material during press pressurization, the sinterability / denseness of the functional sintered dense film can be further improved.

Functional sintered dense film related to the present invention are those obtained by the method for forming a functional sintered dense film according to the present invention described above, for example, the wiring in the electronics field and electrodes, or the hardness It is suitable for a hard coating film or the like that is required.

The nanoparticle synthesis method according to the present invention is a nanoparticle synthesis method used in the method for forming a functional sintered dense film according to the present invention described above, and the nanoparticle raw material is used without using a protective dispersant. Nanoparticles are synthesized by introducing and reducing to a solvent. Thereby, nanoparticles can be synthesized without using a protective dispersant. In addition, it is possible to avoid a situation in which the protective dispersant hinders the sintering of the nanoparticles and inhibits the densification of the sintered film.

Nanoparticles with the present invention is a nanoparticle obtained by nanoparticle synthesis method according to the present invention described above, the nanoparticle is a single nanometer size. A functional sintered dense film can be reliably formed by performing the method for forming a functional sintered dense film according to the present invention described above using such single nanometer-sized nanoparticles. .

  According to the present invention, in the sintering of nanoparticles, for example, nanoparticles obtained by removing the oxide film on the surface using a flux, or nanoparticles not containing a protective dispersant are sintered at a low temperature using pressurization. By doing so, a functional sintered dense film can be formed without oxidizing at a lower temperature and in a shorter time than conventional. The functional sintered dense film thus formed is suitable, for example, for wiring and electrodes in the electronics field, or a hard coating film requiring hardness.

2 is a SEM photograph of the surface of the film obtained in Example 1 of the method for forming a functional sintered dense film according to an embodiment of the present invention. 4 is a SEM photograph of the surface of the film obtained in Example 2 of the method for forming a functional sintered dense film according to an embodiment of the present invention. 4 is an SEM photograph of the surface of the film obtained in Example 3 of the method for forming a functional sintered dense film according to an embodiment of the present invention. 3 is an XRD pattern of the surface of the film obtained in Example 3 and Comparative Example 1 of the method for forming a functional sintered dense film according to the embodiment of the present invention. It is an optical microscope photograph of the surface of the film | membrane obtained in Example 4 of the formation method of the functional sintered dense film which concerns on embodiment of this invention. 6 is a SEM photograph of the surface of the film obtained in Example 5 of the method for forming a functional sintered dense film according to an embodiment of the present invention. 6 is a SEM photograph of the surface of the film obtained in Example 6 of the method for forming a functional sintered dense film according to an embodiment of the present invention. SEM photograph of nanoparticles obtained in Example 7 when (a) 1-decanol and (b) dimethylimidazole (imidazolidinone) are used as solvents in the nanoparticle synthesis method according to the embodiment of the present invention. It is a graph which shows a particle size distribution. 10 is a SEM photograph of the surface of the film obtained in Example 8 of the method for forming a functional sintered dense film according to an embodiment of the present invention. 10 is a SEM photograph of the surface of the film obtained in Example 9 of the method for forming a functional sintered dense film according to an embodiment of the present invention. It is the SEM photograph and hardness (HV) of the surface of the film | membrane obtained in Example 10 of the formation method of the functional sintered dense film which concerns on embodiment of this invention.

Hereinafter, a method for forming a functional sintered dense film and a method for synthesizing nanoparticles according to an embodiment of the present invention will be described.
In the method for forming a functional sintered dense film according to this embodiment, the functional sintered dense film is formed by sintering the nanoparticles using press pressure. Thereby, the nanoparticle can be sintered at a low temperature by the phenomenon of the melting point lowering of the nanoparticles and the application of energy by pressurization to form a functional sintered dense film.

  At this time, a functional sintered dense film can be formed without being oxidized even in an air atmosphere. That is, since densification is promoted by applying a press, the nanoparticle surface is shielded from the atmosphere, so that oxidation of the nanoparticle surface is suppressed and sintering is promoted.

  In addition, in this embodiment, the process of promoting sintering of a nanoparticle may be further included separately from press pressurization. Examples of other processes for promoting the sintering of the nanoparticles include a heating process, a process for adding a solvent for promoting diffusion, and a process for adding a flux for activating the nanoparticle surface.

In the present embodiment, the nanoparticles used as the raw material for the functional sintered dense film are, for example, ceramic nanoparticles made of oxide, nitride, sulfide, boride, or the like, or noble metal nano-particles such as gold, silver, or platinum. Particles, base metal nanoparticles such as chromium, nickel or copper, or mixed nanoparticles thereof may be used.
The average particle diameter of the nanoparticles may be, for example, about 1 to 100 nm.

Here, the particle diameter of the raw material may be one of the particle diameters of the multimodal particles. When the multimodal particles or mixed nanoparticles have a particle size of submicron or more, one or more kinds of metal nanoparticles having a particle size of about 1 to 100 nm may be included.
The applied pressure when filling or applying the raw material nanoparticles as described above in a press mold and applying energy by pressurization may be, for example, 30 MPa to 600 MPa.

  Further, in the present embodiment, it is possible to improve the sinterability / denseness of the functional sintered dense film by shortening the film formation time by heating when press-pressing at room temperature. . Here, as heating temperature, about 40-400 degreeC may be sufficient, for example.

  In addition, when metal nanoparticles are heated, oxidation of the metal nanoparticles becomes a problem, but in this embodiment, since the whole nanoparticles are sealed with a press mold, it is possible to sinter at a short time and at a low temperature. In addition, the sintering can be further promoted by preventing / suppressing oxidation.

By the way, the metal nanoparticles currently on the market are in a state where the surface is covered with an oxide film due to their activity, or a state where a dispersion protective agent is covering the surface in order to prevent oxidation. . Metal nanoparticles covered with an oxide film are difficult to sinter because the oxide film layer inhibits the sintering of the metal nanoparticles. Further, in the nanoparticles covered with the dispersion protective agent, the dispersion protective agent inhibits sintering. Dispersion protective agents used in nanoparticle synthesis include polymer-based protective dispersants represented by polyvinyl alcohol and polyvinylpyrrolidone, amine-based organic molecular protective dispersants, and surfactant-based protective dispersions represented by sodium dodecyl sulfate. Agents and the like.
By removing the oxide layer that inhibits sintering with a flux, a functional sintered dense film can be obtained at a low temperature and in a short time.

  As such a flux, an acid such as nitric acid / hydrochloric acid / sulfuric acid, an alkaline substance typified by a hydroxide, or a mixture thereof may be used. You may use the flux generally used with solder material.

  In the present embodiment, in order to further improve the sinterability / denseness of the functional sintered dense film, the pressure may be efficiently transmitted using a sealing material during pressurization. Examples of the seal material include metal seal materials such as nickel, copper, chromium, lead, and solder materials, or organic seal materials such as Teflon (registered trademark) and polyimide. By processing a sheet-like or linear material to be a sealing material into the shape of a functional sintered dense film to be formed, a sealing material suitable for the present invention can be obtained.

  In this embodiment, in order to further improve the sinterability / denseness of the functional sintered dense film, a salt disk may be used so that the pressure is uniformly transmitted during press pressurization.

  Conventionally, when synthesizing nanoparticles by a chemical method, it has been necessary to add a protective dispersant to control the nanoparticle diameter, but as described above, the protective dispersant prevents the nanoparticles from being sintered. Inhibits densification of the sintered film. In order to solve this problem, the present inventor has found a method for synthesizing nanoparticles by introducing a nanoparticle raw material into a solvent and reducing it as a new nanoparticle synthesis method that does not use a protective dispersant. It was. In addition, by this synthesis method, it is possible to synthesize single nanometer size nanoparticles with amorphous-like, and furthermore, this amorphous nanoparticle and commercial nanoparticles (metal crystal nanoparticles) larger in size are mixed. It was found that a good hard functional sintered dense film can be formed by pressure sintering.

  As the nanoparticle raw material (metal source), for example, a metal carbonyl compound, a metal carbonyl hydride, a nitrosyl complex, a phosphine complex, an isocyanide complex, a thiocarbonyl complex, or the like may be used. Such metal sources may be used alone or in combination of two or more.

  As the solvent, for example, various alcohols or ionic liquids may be used. For example, 1-decanol, imidazolidinone (dimethylimidazole) and the like may be used.

  As a reduction method, electric heating, gas heating, microwave heating, ultrasonic irradiation, or the like may be used. When ultrasonic irradiation is used, the nanoparticle raw material can be reduced at a low temperature.

  The temperature of the reduction treatment in the nanoparticle synthesis method according to the present invention may be, for example, 0 to 200 ° C, and more preferably 10 to 40 ° C. When the reduction treatment temperature is lower than the lower limit of 0 ° C., the metal source is not sufficiently reduced. On the other hand, when the upper limit of 200 ° C. is exceeded, the metal source volatilizes and the yield decreases, and the metal nanoparticles grow. However, metal nanoparticles having a desired size cannot be obtained. The synthesis time may be, for example, 5 to 300 minutes, more preferably 10 to 250 minutes, and particularly preferably 30 to 180 minutes. When the synthesis time is less than the lower limit of 5 minutes, unreacted metal compounds tend to remain. On the other hand, when the upper limit of 300 minutes is exceeded, coarse nuclei are generated and metal nanoparticles of a desired size cannot be obtained. .

According to the present embodiment described above, in the sintering of the nanoparticles, for example, the nanoparticles from which the oxide film on the surface has been removed using a flux, or nanoparticles that do not contain a protective dispersant, are pressed. By using and sintering at a low temperature, a functional sintered dense film can be formed without oxidizing at a lower temperature and in a shorter time than conventional. The functional sintered dense film thus formed is suitable, for example, for wiring and electrodes in the electronics field, or a hard coating film requiring hardness. In particular, the method for forming a functional sintered dense film of this embodiment is useful as an alternative technique for Cr plating in which the use of hexavalent chromium is a problem.
Examples of a method for forming a functional sintered dense film and a method for synthesizing nanoparticles according to embodiments of the present invention will be described below.

  As the nanoparticles, tin oxide nanoparticles (average particle size 20 nm) were used. 1 g of this tin oxide nanoparticle was filled into a cylindrical press die (inner diameter 10 mm), and a pressure of 50 MPa or more was applied using a press machine. The tin oxide nanoparticles were diffused and dissolved by applying a pressure of 100 MPa and sintered at room temperature to obtain a sintered body (functionally sintered dense film). FIG. 1 shows an electron microscope (SEM) photograph of the film obtained after applying the pressure. As shown in FIG. 1, it was observed that the particles grew large and the nanoparticles were sintered.

  Copper particles (average particle size 50 nm) were used as the nanoparticles. 1 g of this copper nanoparticle was filled into a cylindrical press die (inner diameter 10 mm), and a pressure of 100 MPa and 10 minutes was applied at room temperature using a press machine. FIG. 2 shows an electron microscope (SEM) photograph of the film obtained after applying the pressure. As shown in FIG. 2, it was observed that the particles were partially grown and the nanoparticles were sintered.

  Copper particles (average particle size 50 nm) were used as the nanoparticles. 1 g of this copper nanoparticle was filled into a cylindrical press die (inner diameter 10 mm), and a pressure of 10 MPa at 30 ° C. for 30 minutes was applied using a press machine. FIG. 3 shows an electron microscope (SEM) photograph of the film obtained after applying the pressure. As shown in FIG. 3, it was observed that the particles grew as a whole and the nanoparticles were sintered. The upper part of FIG. 4 shows the result of examining this sintered film by X-ray diffraction (XRD). As shown in the upper part of FIG. 4, it was confirmed that the copper nanoparticles were not oxidized and sintering proceeded despite the high temperature film formation. That is, it was confirmed that the oxidation was suppressed by the press die and the press pressure, and the sintering of the metal nanoparticles proceeded.

(Comparative Example 1)
Copper particles (average particle size 50 nm) were used as the nanoparticles. 1 g of this copper nanoparticle was filled in a cylindrical press die (inner diameter 10 mm), and sintering was performed in the atmosphere at 150 ° C. for 30 minutes without using a press machine. The lower part of FIG. 4 shows an XRD pattern of the sintered film obtained without pressing. As shown in the lower part of FIG. 4, the particles were oxidized as a whole.

  As nanoparticles, chromium particles (average particle size 40 nm) were used. The chromium nanoparticles were filled in 0.2 g in a cylindrical press die (inner diameter 10 mm), and a pressure of 500 MPa and 1 hour was applied at room temperature using a press machine. FIG. 5 shows an optical micrograph of the film obtained after applying the pressure. As shown in FIG. 5, it was observed that the particles partially grew and the nanoparticles were sintered.

  As nanoparticles, chromium particles (average particle size 40 nm) were used. The chromium nanoparticles were filled in 0.2 g in a cylindrical press die (inner diameter 10 mm), and a pressure of 500 MPa at 400 ° C. for 3 hours was applied using a press machine. FIG. 6 shows an electron microscope (SEM) photograph of the film obtained after applying the pressure. As shown in FIG. 6, it was confirmed that despite the high temperature film formation, the chromium nanoparticles were not oxidized and sintering proceeded. That is, it was confirmed that the oxidation was suppressed by the press die and the press pressure, and the sintering of the metal nanoparticles proceeded.

  As nanoparticles, chromium particles (average particle size 40 nm) were used. The chromium nanoparticles were filled in 0.2 g in a cylindrical press die (inner diameter: 10 mm), flux was added, and then a pressure was applied at 400 ° C. for 3 hours at 400 ° C. using a press machine. FIG. 7 shows an electron microscope (SEM) photograph of the film obtained after applying the pressure. As shown in FIG. 7, it was confirmed that despite the high temperature film formation, the chromium nanoparticles were not oxidized and the sintering was progressing by adding the flux. That is, it was confirmed that the oxidation was suppressed by the press die and the press pressure, and that the sintering of the metal nanoparticles proceeded by adding the flux.

Chromium carbonyl (Cr (CO) ₆ ) powder was used as a chromium nanoparticle raw material, and 1-decanol was used as a solvent. Add 5 mmol of raw material to 50 ml of solvent, perform nitrogen gas bubbling, remove the dissolved oxygen, irradiate ultrasonic waves with a frequency of 50 kHz and 150 W at 40 ° C to synthesize the chromium nanoparticle by thermal decomposition. did. FIG. 8A shows a photograph of the synthesized chromium nanoparticles, and the average particle size and particle size distribution. As shown in FIG. 8 (a), the chromium nanoparticles synthesized using 1-decanol were dispersed in the solution for a long time (one year or more) without a dispersion protective agent. Further, when the particle size of the synthesized chromium nanoparticles was evaluated, when 1-decanol was used, the average particle size was 5.6 nm, and the standard deviation was 0.68. That is, according to this example, it was possible to synthesize particles having a single nanometer size and a very small standard deviation.

  As shown in FIG. 8B, in the case of chromium nanoparticles synthesized using a dimethylimidazole (imidazolidinone) solvent instead of 1-decanol, the average particle diameter was 8.0 nm and the standard deviation was 1.45. It was.

  Moreover, it is estimated that the chromium nanoparticles obtained by ultrasonic irradiation as described above are amorphous like as a result of electron diffraction.

  Sintering was performed using the chromium nanoparticles synthesized in Example 7 as the nanoparticles. The chromium nanoparticles were filled in 0.2 g in a cylindrical press die (inner diameter: 10 mm), flux was added, and then a pressure was applied at 400 ° C. for 3 hours at 400 ° C. using a press machine. FIG. 9 shows an electron microscope (SEM) photograph of the film obtained after applying the pressure. As shown in FIG. 9, it was confirmed that sintering was very advanced due to the absence of the dispersion protective agent. Further, the hardness increased as the sintering progressed.

  As nanoparticles, chromium particles (average particle size 40 nm) were used. The chromium nanoparticles were filled in 0.2 g in a cylindrical press die (inner diameter: 10 mm), flux was added, and then a pressure was applied at 400 ° C. for 3 hours at 400 ° C. using a press machine. A Teflon sheet and a metal washer (two types) were used as a sealing material when applying pressure. FIG. 10 shows an electron microscope (SEM) photograph of the film obtained after applying the pressure. For comparison, FIG. 10 also shows the result of using a Teflon sheet as a sealing material without adding flux. As shown in FIG. 10, it was confirmed that despite the high temperature film formation, the chromium nanoparticles were not oxidized and the sintering proceeded by adding the flux. That is, oxidation is suppressed by the press die and press pressure, and flux is added. It was confirmed that sintering of the metal nanoparticles proceeded by applying pressure efficiently with the sealing material.

  As nanoparticles, chromium particles (average particle size 40 nm) were used. After filling 0.2g of this chrome nanoparticles into a cylindrical press die (inner diameter 5mm) and adding flux, 350MPa at 200 ℃, 300 ℃ and 400 ℃, applying pressure for 2-3 hours using press machine did. When applying pressure, a Teflon sheet and a nickel wire were used as a sealing material. FIG. 11 shows a partial electron microscope (SEM) photograph of the sintered body obtained after applying the pressure. For comparison, FIG. 11 also shows the results without the addition of flux. As shown in FIG. 11, it was confirmed that despite the high temperature film formation, the chromium nanoparticles were not oxidized and the sintering proceeded by adding a flux. Also, the film hardness (HV) was increased by using a flux and a sealing material. That is, it was confirmed that the oxidation of the metal nanoparticles was progressed by suppressing the oxidation by the press die and the press pressure, adding flux, and applying pressure efficiently with the nickel sealant.

The preferred embodiments of the present invention have been described in detail above. However, the present invention is not limited to the specific embodiments, and various modifications and changes can be made within the scope of the gist of the present invention described in the claims. It can be changed.

Claims (5)

The functional sintering is characterized in that a functional sintered dense film is formed by sealing the whole nanoparticles made of chromium directly with a press die using press pressurization and sintering the nanoparticles. Method for forming a dense film. In the method of forming a functional sintered dense film according to claim 1,
A method for forming a functional sintered dense film, comprising forming the functional sintered dense film in an air atmosphere. In the method for forming a functional sintered dense film according to claim 1 or 2,
A method for forming a functional sintered dense film, wherein the sintering of the nanoparticles is promoted using a flux. In the formation method of the functional sintered dense film according to any one of claims 1 to 3,
A method for forming a functional sintered dense film, wherein the functional sintered dense film is formed using a sealing material. A method for synthesizing nanoparticles used in the method for forming a functional sintered dense film according to any one of claims 1 to 4,
A nanoparticle synthesis method comprising synthesizing the nanoparticles by using a nanoparticle raw material in a solvent and reducing without using a protective dispersant .