KR20050079151A - Mass production method for nano-crystal metallic oxide by using ultrasonic spraying heating method - Google Patents

Abstract

The present invention relates to a method for mass-producing oxides of the metals in nanocrystalline size using metal salts, specifically (1) mixing a metal salt solution and a fuel (first step), (2) the first Ultrasonic spraying the mixed solution with the carrier gas (step 2), (3) reacting the sprayed solution in a high temperature reaction zone for a predetermined time (step 3) and (4) reaction in the reaction zone Collecting the resulting powder (fourth step) and characterized in that to perform each step sequentially.

According to the present invention, it is possible to mass-produce nanocrystal-sized powders with less aggregation and spherical shape.

Description

Mass production method of nanocrystalline metal oxide powder using ultrasonic spray combustion method {MASS PRODUCTION METHOD FOR NANO-CRYSTAL METALLIC OXIDE BY USING ULTRASONIC SPRAYING HEATING METHOD}

The present invention relates to a method for producing a nanocrystalline metal oxide powder, and more particularly, to a method for mass production of nanocrystalline metal oxide powder from a metal salt solution using ultrasonic spray combustion.

With the advancement of science and technology, the development of ceramic materials with excellent performance and function is inevitable. ZnO and TiO ₂ are representative examples of such ceramic materials. The manufacture of nano-sized materials increases the hardness, toughness, ductility and structural properties, as well as the electrical and optical properties in the electronics and telecommunications industry. However, manufacturing nanoscale ceramic materials is limited to laboratory scale.

The word nano is about one billionth the size.

Nanotechnology is a comprehensive description of the technology for fabricating and utilizing materials, devices, and systems at the nanometer scale, ie, at the level of atoms, molecules, or macromolecular structures. Nanotechnology has the potential to replace major existing technologies or create new industries and to change typical scientific models in energy, environment, biotechnology, computing, aerospace and materials.

As the nanoparticles become extremely fine, they exhibit unusual mechanical and physical properties that are not found in ordinary powder materials. That is, in the case of solid crystalline, the chemical and physical properties have inherent properties only of the crystal. For example, melting point, boiling point, hardness, strength, and optical properties are inherent to the material alone, and the physical and chemical properties of the crystal are dependent on the crystalline composition and crystal structure regardless of the crystalline form or size. . However, when the size of the material is nanoscale, the crystal size acts as a variable for the material's properties. As the particle size decreases, the nanopowder decreases the bulk property and the surface property rapidly, so that the basic properties of the material are strength, magnetic, electrical properties and absorbency, catalytic performance, and adsorption capacity. The innovative properties of the light and the like, the application of nano-powder material is expected in a variety of industries such as materials, mechanical, electrical, electronics as well as catalyst, medicine and biotechnology.

Examples of the nano powder material having such excellent surface properties include zinc oxide (ZnO), titanium dioxide (TiO ₂ ), cerium dioxide (CeO ₂ ), carbon nanotubes, and the like. Consisting of oxides of metals such as Zn, Ce or Ti (ie, ZnO, CeO ₂ or TiO ₂ ), salts of these metals can be dissolved in water to form aqueous solutions or dissolved in alcoholic solvents to form alkoxides That can be.

Of these, ZnO nanopowders are excellent in electrical, thermal, optical, and catalytic properties, are piezoelectric, have high light transmittance, and are excellent in fluorescence. ZnO is applied to phosphors, photocatalysts, gain medium of UV semiconductor laser, gas sensor, window material in solar cell, etc. It is used in many other applications such as absorbents.

In addition, CeO ₂ is a material that is usefully used in automotive three-way catalysts and chemical mechanical planarization process, the demand is gradually increasing.

TiO ₂ is one of the important nanopowder materials that has been in the spotlight in recent years, and has excellent properties in solar cells, electronic paper, and photocatalytic drug delivery systems.

As described above, the superior properties of the material may not be expressed when the bulk material is formed, and may be implemented in the case of nano-size fine powder. Therefore, in order to manufacture a device having the above excellent characteristics, it is necessary to first develop a process for producing a metal oxide powder of nanocrystals.

There are various methods of manufacturing such nanocrystalline metal oxide powders. Examples of the method of preparing zinc oxide (ZnO), which are typically used as metal oxide nano powders, include French and US methods.

The French method is a method of obtaining ZnO powder by melting the zinc zinc after melting and oxidizing with air in the vapor state. However, there is a disadvantage that it is very difficult to control the synthesis reaction conditions of the powder required to prepare the particle size to 100nm or less by using the method.

The US method is a method of obtaining zinc hydroxide or zinc carbonate by reducing coal with a disadvantage that when the ZnO powder is produced by the above method, the powder is very difficult to obtain a high purity powder. Therefore, high reliability and high functionality, which are essential for the development of nanoscale ZnO, are lost due to a decrease in purity and thus are not applicable.

In addition to the above methods, various methods such as a wet method, a sol-gel method, a uniform precipitation method, a Sol-gel method, a gas phase oxidation method, a spray pyrolysis method, and a self-ignition combustion method have been proposed and are currently used for each purpose.

The wet method has the advantage that small particles can be produced by depositing basic zinc carbonate by reaction with ZnSO ₄ or ZnCl ₂ solution and Na ₂ CO ₃ solution, filtering, washing with water, and heating to about 400 to make ZnO. However, there are disadvantages in that the shape of the powder particles is irregular in plate and rod shape and cannot make spherical particles.

The sol-gel method is divided into alkoxide or colloidal sol-gel method, and there are three kinds of precursors which are metal organic compounds, metal inorganic compounds and oxides. A sol is a dispersed colloidal suspension in which particles of about 1 to 1000 nm are generally not precipitated due to van der waals attraction or surface charge. It is transferred to the gel by hydration-condensation or removal of the dispersed solvent in which the powdery particles are dispersed. Transfer refers to a relatively rapid change from viscous liquid to viscoelastic solid and finally to an elastic solid. The nanopowder manufacturing process using the wet chemistry method is called sol-gel method, and the sol-gel method is capable of obtaining ceramics having excellent physical properties by removing inhomogeneities generated in the material by controlling the surface or interface in the process. However, ZnO powder made from zinc chloride is difficult to control pH and temperature conditions, and the particles are agglomerated severely, which limits the application of the powder.

The gas phase oxidation method is a metal and ceramic thin film formation process by the reaction of precursor / carrier gas in the CVD process. Fine particles can be obtained, but aggregation occurs severely during the formation and accumulation of particles. The disadvantage is that.

On the other hand, spray pyrolysis can be obtained by spraying zinc nitrate in the form of fine droplets and heating them to instantly evaporate the solvent from the surface of the droplets and pyrolyze to obtain fine spherical particles, but for pyrolysis, decomposition occurs at very high temperatures. It is very low in terms of recovery and therefore possible on a laboratory scale, but has limited production in mass production.

In the case of self-ignition combustion, which induces the synthesis of oxides by self-ignition, metal nitrate and fuel are dissolved and heated in water to evaporate excess water, and the nitrate acts as a complexing agent, causing the enormous exothermic reaction. By using heat to help the reaction of metal ions and oxygen, as a result of obtaining a high-purity powder without the formation of intermediates. However, in the case of applying the general self-ignition combustion method for the production of ZnO powder, the recovery rate is very low because of the high vapor pressure of Zn or ZnO and the very high heat of reaction during the complexing reaction, and the collection of the powder is very difficult due to the explosive reaction. There are many problems to apply to mass production.

Therefore, as can be seen above, the conventional method for producing nanopowders has one or more problems related to particle size and shape control, agglomeration, and productivity, thereby agglomerating nanoparticles having a spherical fine and uniform shape. It is not suitable for high volume production without causing it to happen.

Accordingly, an object of the present invention is to provide a method for producing a large amount of nano-powder having a spherical fine and uniform shape without causing aggregation to solve the above problems.

Another object of the present invention is to provide a method for producing a high purity metal oxide nano powder through a simple and rapid process.

It is another object of the present invention to provide a method for preparing metal oxide nanopowders even at temperatures much lower than those required by conventional spray pyrolysis.

Characteristic configuration of the present invention for achieving the above object

(1) mixing a metal salt solution and a fuel (first step),

(2) ultrasonic spraying the solution mixed in the first step together with a carrier gas (second step),

(3) reacting the sprayed solution for a predetermined time in a high temperature reaction zone (third step),

(4) collecting the powder produced as a result of the reaction in the reaction zone (fourth step), characterized in that to perform each step sequentially.

As described in the above characteristic configuration, the present invention supplies the high temperature heat generated by the reaction of oxygen in the fuel supplied with the fuel or the atmosphere or the oxygen supply device to the metal salt solution which is the raw material of the nanocrystalline metal oxide, After pyrolysis has occurred, a method of producing powder and recovering the powder by oxidizing excess oxygen and pyrolyzed metal. Conventional powder manufacturing method is difficult to manufacture nano-powder and the recovery rate is very low, so mass production is difficult, so as to compensate for these disadvantages and increase the recovery rate, the ultrasonic spray combustion method as described above was used. Detailed description of each step of the present invention will be described below.

The first step of the present invention is the step of adding fuel to lower the heat supplied from the reaction zone and react instantaneously to combine the metal ions included in the raw material with the fuel. As said raw material, the solution which melt | dissolved metal in alcohol and made it into the alkoxide state, or the aqueous solution of metal salt is used. The choice of such raw materials can be determined depending on whether the metal salt can form an aqueous solution or an alkoxide. That is, a salt of a metal such as titanium, for example, is more difficult to form a solution when it is in contact with water, rather than to form an aqueous solution, but when dissolved in alcohol, a salt of titanium may form a titanium alkoxide to form a complete solution. The above solution should be formed to allow thermal decomposition of the metal by the heat supplied during the combustion reaction of the reaction zone and the fuel. However, in the case of Zn, since nitrate can be easily dissolved in water to form an aqueous solution, it is preferable to form an nitrate aqueous solution in this case. In this case, the metal nitrate may be used by using an aqueous nitrate solution sold by itself or by reacting the metal hydroxide with nitric acid water. Representative metals for forming an alkoxide include titanium (Ti), and in the case of forming an aqueous solution, nitrates of zinc (Zn) or cerium (Ce) may be mentioned. However, when forming an alkoxide solution, a predetermined amount of nitric acid solution that serves as an oxidant should be added. The fuel may be an organic compound containing an amine (-NH ₂ ) group or a carboxyl (-COOH) group. Examples thereof include glycine (CH ₂ —NH ₂ —COOH), urea, citric acid, and the like.

In the first step, it is preferable to dissolve the fuel dissolved in the alcoholic solution of the metal salt in an appropriate amount of distilled water, and then stir with a stirrer to prepare a metal salt aqueous solution, and mix the fuel with the aqueous solution. The mixing ratio of the fuel is preferably selected in consideration of the stoichiometric ratio with the raw material. When glycine (glycine, CH ₂ -NH ₂ -COOH) is used, the stoichiometric ratio of the metal salt (zinc nitrate can be used. 1.12 mol per mol of zinc nitrate in the case, 2.24 mol per mol of cerium nitrate in the case of cerium nitrate (that is, 0.4 to 0.7 mol when using nitric acid as a raw material, cerium nitrate If so, it is preferable to mix with 0.8-1.4 mol). Here, the stoichiometric ratio refers to the number of moles of fuel required per mole of raw material calculated by considering the oxidizable and reduced valences of the raw materials and fuel. If the fuel is added less than the mixing ratio, the amount of heat generated decreases, and the recovery rate of the metal oxide is reduced. There is a risk of falling directly into the droplet state or falling into a lump. At this time, slight heating (30-50 ° C.) and agitation should be performed at the same time so that the solution is well stirred. The holding time is about 30 minutes.

The particle size of the nanocrystalline metal oxide powder is proportional to the amount of metal salt supplied. In other words, when the amount of the metal salt is large, the amount of the metal that is pyrolyzed is also increased, thereby increasing the particle size of the oxide produced by oxidation. Under the same concentration of this metal salt, it is proportional to the size of the droplets. Therefore, it is very important to prepare droplets of fine size, and to realize this, in the second step, the mixed solution is supplied to the ultrasonic atomizer via a metering pump, so that the mixed solution is ultrasonically at a constant flow rate with constant and fine droplets. It is necessary to be sprayed. At this time, the size of the sprayed droplets is preferably in the range of 20 to 50㎛, the flow rate of the sprayed droplets is preferably in the range of 10 to 120 cc / min.

At this time, since the nanocrystal produced by the present invention is an oxide, it is necessary to supply air or oxygen gas, which is a source of oxygen, as a carrier gas during ultrasonic spraying. In order to control the amount of air introduced, it is preferable to adjust the needle valve to the air or oxygen inlet connected to the ultrasonic spray gun.

The third step of the present invention is a step in which the mixed solution and oxygen in the atmosphere react with each other to complex and generate high heat to thermally decompose and oxidize the metal salt in the solution. Unlike spray pyrolysis, the present invention is a method of spontaneously igniting droplets by mixing fuel with a solution to supply heat required for a pyrolysis reaction, and does not need to maintain a high temperature in the reaction zone as in spray pyrolysis. Therefore, only an appropriate temperature range needs to be maintained, but in the method according to the present invention, it is sufficient to maintain the temperature of the reaction zone at 500 to 700 ° C. This temperature is much lower than 1000 ° C., which is the temperature required by the conventional spray pyrolysis method, which improves the durability of the device realizing the method of the present invention and replaces components such as reaction tubes with inexpensive parts that can be used at low temperatures. Make it possible. It is also preferred that the reaction zone consists of a vertical tubular reaction tube in order to increase the heat supply efficiency with the solution and to keep the powder in the reaction zone for as long as possible.

The fourth step is to collect the nano-powder produced in the third step, the powder is collected is very small particle size of the nano-powder is difficult to recover, so special measures are required. First, it is preferable to inhale the nano powder passing through the reaction zone together with the air in the atmosphere and to collect and recover a filter (SUS-filter, HEPA-filter, etc.) in the moving path of the sucked powder.

It is advisable to seal the inside of the furnace completely during each step. The reason for this is that a cover equipped with an ultrasonic spray gun is installed to install an ultrasonic spray gun on the upper part of the furnace.In this case, if the furnace and the cover are not completely sealed, air pressure in the atmosphere is increased due to the gap between the furnace and the cover. This can be inhaled for the reason that the inhaled air affects the laminar flow flow inside the furnace, causing it to turn into turbulent flow, which causes the microdroplets sprayed by the ultrasonic waves to collide with each other. This is because there is a risk of coarsening of the resulting powder.

Hereinafter, the results of observing the advantageous effect of the present invention through a preferred embodiment of the present invention.

However, the following examples are illustrative of the present invention, and the content of the present invention is not limited by the examples.

(Example)

Hereinafter, the preferred embodiment of the present invention will be described in detail. First, the precursor solution 100 for the self-ignition combustion reaction was prepared in the first step. As the precursor solution, an aqueous solution of zinc nitrate (Zn (NO ₃ ) ₂ ), which is an oxidizing agent, was used. Glycine was used as a fuel. In order to prepare the precursor solution, zinc nitrate (Zn (NO ₃ ) ₂ · 6H ₂ O) and fuel were dissolved in distilled water, and then stirred and heated at the same time, and then the mixed solution was vertically mixed using a metering pump 90. It was fed to an ultrasonic atomizer 80 mounted on the furnace. At this time, the amount of distilled water used is not particularly limited, but it is sufficient if the zinc nitrate is completely dissolved and has a viscosity of a certain level or more so that the mixed solution can be easily supplied to the metering pump 90. At this time, in order to examine the correlation between the amount of metal nitrate and the fuel, the fuel was mixed and changed in the ratio of 0 to 1.12 (0 to 1.07 times the stoichiometric ratio) of the number of moles of metal nitrate, and used in the experiment.

Thereafter, as a second step, ultrasonic spraying was performed into the vertical furnace shown in FIG. 1, and sprayed by changing the flow rate of the sprayed droplet to 10 to 120 cc / min, and the sprayed droplet size was 20 to 50 μm. Sprayed in the range.

In order to observe the effect of the temperature change in the reaction zone 20 in the third step process and to control the reaction temperature of the droplets sprayed by the ultrasonic atomizer, the reaction zone was divided into three zones and the K-type thermocouple. And installed the controller. At this time, the experiment was carried out by changing the set temperature to 400 ~ 700 ℃.

As shown in FIG. 1, the fourth step recovery process is performed by suctioning the synthesized powder in a blower and recovering it using a stainless filter installed in the blower 70 and two cyclones-type systems 40 and 50. It carried out in the form to do.

Hereinafter, the experimental results of the present embodiment will be described with reference to FIGS. 2 to 4.

First, referring to FIG. 2, the optimum condition of the mixing ratio of the metal nitrate and the fuel to increase the recovery of the nanopowder was when the molar ratio of the fuel to zinc nitrate was 0.4 to 0.7 (0.36 to 0.63 times the stoichiometric ratio). The temperature of the reaction zone was found to be optimal at 500 to 700 ° C. when the fuel ratio was 0.65.

3 and 4 show the X-ray diffraction test results and electron micrographs of the nanopowders prepared by the most preferred embodiment of the present invention. The powder synthesized by the ultrasonic spray combustion showed a distinct ZnO phase with little other impurities as shown in the X-ray diffraction results (see FIG. 3). And, as shown in Figure 4, the shape and size control results also showed a good shape and size as a sphere consisting of a weak aggregate having a primary particle size of 20 ~ 30nm. In addition, the nano powder is a material exhibiting excellent properties by surface properties rather than bulk properties, the more the specific surface area is more advantageous, according to the present embodiment zinc oxide nano powder having a specific surface area of 20 to 25 m ² / g. It could be made (see FIGS. 4A and 4B).

In addition, it can be seen that the mass production rate of the powder produced in this example is about 500 g / hr.

Compared to other processes, the method of the present invention is simpler in manufacturing process and more economical in manufacturing cost, and can produce high quality, high purity zinc oxide in a large amount, which does not require reheating of the powder after synthesis, and the synthesis time is very short. . In particular, since it is a nano-size, it will be used in electric, electronic, communication devices, etc., where characteristics such as small size, light weight, and high reliability are essential. In the present invention, particles having a spherical particle size ranging from 20 to 50 nm are formed, and are easy to disperse as weak aggregates rather than heavy aggregates shown in the conventional method. The high specific surface area value of g is expected to enable applications in photocatalytic applications.

1 is a schematic diagram of an ultrasonic atomizing device and a powder collecting device for realizing the method according to the present invention;

2 is a recovery rate according to fuel and reaction temperature when producing nanocrystalline zinc oxide by the method according to the present invention,

3 is an X-ray diffraction result of nanocrystalline zinc oxide prepared by the method according to the present invention, and

4 is an electron micrograph of the nanocrystalline zinc oxide prepared by the method according to the present invention, 4a is a result of analyzing the form by scanning electron microscope (SEM), 4b is a transmission electron microscope (TEM) This is the result of the form analysis.

Claims (10)

(1) mixing a metal salt solution and a fuel (first step), (2) ultrasonically spraying the solution mixed in the first step together with the carrier gas (second step), (3) reacting the sprayed solution for a predetermined time in a high temperature reaction zone (third step), and (4) A method for mass-producing a nanocrystalline metal oxide powder using an ultrasonic atomizing combustion method comprising the steps (fourth step) of collecting the powder produced as a result of the reaction in the reaction zone and sequentially performing each step. The method of claim 1, wherein the metal salt is a metal salt capable of forming an alkoxide compound or an aqueous metal salt solution. The method of claim 1, wherein the fuel is an organic compound containing at least one of amine (-NH ₂ ) or carboxyl (-COOH) group, characterized in that the mass production of nanocrystalline metal oxide powder using the ultrasonic spray combustion method Way. The method of claim 2 or 3, wherein the mixing ratio of the fuel is 0.36 to 0.63 times the stoichiometric ratio required for the reduction of the metal salt. According to claim 3, wherein the fuel is an organic compound containing at least one of an amine (-NH ₂ ) or carboxyl (-COOH) group, characterized in that at least one selected from glycine, urea and citric acid is used. Mass production method of crystalline metal oxide powder. The method of claim 1, wherein the diameter of the droplets to be ultrasonically sprayed is 20 to 50 ㎛, the flow rate of the droplets is in the range of 10 to 120 cc / min. . The method for mass production of nanocrystalline metal oxide powder using the ultrasonic atomizing combustion method according to claim 1, wherein the temperature of the reaction zone is maintained at 500 to 700 占 폚. The method for mass production of nanocrystalline metal oxide powder using the ultrasonic spray combustion method according to claim 1, wherein the reaction zone is a vertical tubular reaction tube. The method of claim 1, wherein the nanopowder passing through the reaction zone is sucked together with the air in the atmosphere by a method of collecting the nanopowder of the fourth step, and then recovered using a filter installed in the moving path of the sucked powder. A method for mass production of nanocrystalline metal oxide powders using ultrasonic spray combustion. The method of claim 1, wherein the ultrasonic atomizer and the reactor are sealed.