KR20100024663A

KR20100024663A - Method and plasma torch for direct and continous synthesis of nano-scaled composite powders using thermal plasmas

Info

Publication number: KR20100024663A
Application number: KR1020080083334A
Authority: KR
Inventors: 백광현; 주원태
Original assignee: (주) 플라즈닉스
Priority date: 2008-08-26
Filing date: 2008-08-26
Publication date: 2010-03-08

Abstract

PURPOSE: A method for directly and continuously synthesizing nanocomposite powder using thermal plasma and a plasma torch are provided to improving a property of an end-product using the nanocomposite powder for a raw material. CONSTITUTION: A method for synthesizing nanocomposite powder using thermal plasma comprises: a step of mixing a raw material; a step of injecting the compound to inner part of thermal plasma flame of high temperature; a step of melting and vaporizing the injected compound in the thermal plasma flame of the high temperature; a step of cooling the vaporized compound; and a step of making the raw material in a granule form.

Description

METHOD AND PLASMA TORCH FOR DIRECT AND CONTINOUS SYNTHESIS OF NANO-SCALED COMPOSITE POWDERS USING THERMAL PLASMAS}

The present invention relates to a method of directly synthesizing nano-sized composite powder from individual raw materials using thermal plasma.

Recently, small-sized, spherical shaped multicomponent composite powders (eg, glass powder) have been used as materials for multilayer ceramic capacitors (MLCCs) or plasma display panels (PDPs). Conventionally, a method of synthesizing a composite powder, such as glass powder, is typically a mixture of raw materials of various components, and then dissolved at a high temperature using a crucible such as platinum, and then reduced in size by mechanical milling of the cullet obtained through rapid quenching. This method has the advantage that it can be easily mass-produced, but there is a limit in obtaining fine powder of 1 micron or less simply by mechanical milling. The powder shape after milling is also irregular and has difficulty in continuous process. In addition, certain components, such as bismuth, have difficulty in controlling impurities such as eluting a material used as a crucible such as platinum at a high temperature or mixing a liquid material during wet milling.

As another method for obtaining a composite powder having a size of 1 micron or less, there is a method of synthesizing using a sol-gel method. In this case, agglomeration of the synthesized powder is severe, and powder characteristics are poor and precursor materials are There is a fatal weakness that is expensive and difficult to industrialize.

An object of the present invention for solving the above problems is to provide a method of directly and continuously synthesizing a nano-sized composite powder by melting and vaporizing the mixed raw material using a high temperature thermal plasma, and then cooling. By eliminating the high temperature crucible to support the raw material and synthesizing the nano-sized composite powder directly in the gas phase, the secondary crushing process can be omitted, so impurities can be easily controlled and the continuous process is possible for quality control and It also has many advantages in terms of productivity.

In order to achieve the above object, the present invention provides a method for synthesizing a composite powder using thermal plasma, the method comprising: quantifying and mixing a raw material; injecting the mixed material into a high temperature thermal plasma flame; Melting and vaporizing the material in a high temperature thermal plasma flame; and cooling the melted and vaporized mixture to form a composite powder. In addition, the raw material may further comprise the step of making the granules (granule) form. The raw material may be further heated to a temperature lower than the sintering temperature, and may further include a calcining process for removing some of the volatile components. The raw material is a solid state of the powder in the form of metals and metal oxides and the size may be within 1 ~ 10 micrometers. The mixture may be injected into the vicinity of the coil of the torch along a central axis of the torch through an upper end of the high frequency thermal plasma torch together with a gas for generating plasma. The plasma flame has a temperature of 3000K or more, but preferably has a temperature of 5000K ~ 10000K. Cooling the mixture may be providing a cold gas to the lower end of the plasma flame. The raw material may be injected in the form of a slurry in which a liquid material is mixed. The cooling of the mixture may be performed by providing a convergence-diffusion nozzle on the moving path of the mixture and allowing the mixture to pass through the convergence diffusion nozzle to further increase the cooling rate. In addition, there is provided a plasma torch for synthesizing a composite powder, the torch comprising: a mixing device for mixing a plasma generating gas and a mixture material which is a raw material of the composite powder; An injector formed in the axial direction of the torch for injecting mixture material in the axial direction of the torch; A gas inlet for radially injecting gas into an end portion of the flame of the plasma torch to cool the mixture material exiting the plasma flame generated by the plasma torch; It may include. The plasma torch may be any one of a transfer type, a non transfer type, a cavity type, and a high frequency inductive coupling type. The raw material is preferably, but not limited to, powder in the form of metal or oxide of micron size. Thereafter, the degree of oxidation can be controlled by adjusting the thermal plasma generation atmosphere to an oxidation, reduction, inert atmosphere or the like by using gases such as oxygen, hydrogen, argon and nitrogen. In the mixing step of the raw materials, the raw materials may be simply mixed using a mixer or a mixer such as a mill. The raw materials may be compounded (compounded) by a process such as spray drying or calcining in order to minimize the change in composition. It can also be used. In addition, the raw material of the suspension, slurry, liquid phase, gaseous phase may be used to add a raw material that is difficult to realize a solid phase or to uniformly supply the raw material into a thermal plasma flame. Injecting a mixture of solid, liquid, and gaseous phase into the thermal plasma flame may use a conventional means for transporting a substance such as a powder feeder and a mass flow controller. It can be transferred using. High-temperature thermal plasma spark generation method can use the existing thermal plasma generation method such as DC transfer type, DC non-transfer type, cavity type, and high frequency inductive coupling type. Preference is given to using a combined type. Gas for generating thermal plasma can be used in the air, oxygen, hydrogen, argon, helium, nitrogen or a mixture thereof depending on the desired atmosphere. The temperature of the thermal plasma flame is preferably 3,000 K or more so that heat-resistant raw materials such as MgO and Al ₂ O ₃ can be easily melted and vaporized.The higher the temperature, the shorter the residence time required for melting and vaporization. Can also be increased. Thus, the temperature of the plasma itself is very high from a few 1,000K to 10,000K or more, but the chamber itself for synthesis is separately cooled with cooling water to be maintained at a relatively low temperature so that there is no problem such as crucible material eluting in the melting furnace. As such, the raw materials are mixed in the gaseous state by the high temperature and enthalpy of the thermal plasma, and then cooled and synthesized into a nano-sized composite material through nucleation and growth. Since the temperature gradient of the thermal plasma flame is very large, even if the raw material of different melting point and vaporization point is mixed, it can be mostly melted and vaporized in a narrow area, thereby maintaining a uniform composition. The characteristics of the synthesized powder vary greatly depending on the cooling rate. The faster the cooling rate, the smaller the powder size and the greater the degree of amorphousness. Cooling naturally occurs as it moves away from the thermal plasma flame, but if the cooling rate is insufficient, an additional cooling mechanism may be provided at the bottom of the thermal plasma flame to increase the cooling rate. Such a cooling mechanism includes a method of injecting cold gas or liquid from the outside to increase heat transfer to increase a cooling rate. Gases or liquids injected from the outside are suitable inert or non-reactive materials which do not affect the composition, but in some cases, active or reactive materials may be used for organic coatings for controlling oxidation degree or reducing aggregation. The cooling rate may be further increased by depressurizing the reactor by placing a convergent-divergent nozzle on the path of vaporized raw material. 2 is an example of a high frequency inductive coupling type method using a solid phase raw material in a preferred apparatus configuration for practicing the spirit of the present invention described above. The solid raw material is used by simply mixing the micron-sized powder (1) or granule (3) using a spray drying apparatus (2). Alternatively, it may be used after calcining using an electric furnace or the like to improve the bonding force between various raw materials. The mixed raw materials are thus conveyed by the powder feeder 4 and the carrier gas to a powder inlet installed on the top of the high frequency thermal plasma torch 5. As said carrier gas, it is preferable to use the gas for high frequency thermal plasma production | generation. The transferred raw materials are injected along the central axis of the high frequency thermal plasma torch through a powder injection probe 6 inserted up to or near the coil region of the torch. In this way, the raw materials injected into the central axis of the torch are sufficiently filled with the energy required for vaporization while passing through the plasma 7 region of the high temperature (3000 K or more, preferably 5,000 to 10,000 K) formed while widely filling the inside of the torch. You get The vaporized raw material is rapidly lowered by the gas injected through the quench gas inlet 8 as it exits the bottom of the torch and is thus spheroidized composite powder through a series of processes of supersaturation, nucleation and particle growth. ) Is finally obtained. The resulting composite powder 9 may be collected through a general collection system such as cyclone 10 or bag filter 11.

As described above, when the synthetic method proposed in the present invention is used, impurities-controlled nanocomposite powder can be produced directly and continuously without post-processing, thereby improving the characteristics of the final product using the raw material, quality control and productivity. It can also contribute to improvement.

Hereinafter, the effects of the present invention will be described in detail through examples.

However, the following examples are for explaining the specific application of the present invention and the scope of the present invention is not limited to the examples.

Example 1 Synthesis of Nano Glass Powder from Raw Materials Consisting of BaO, K ₂ O, B ₂ O ₃ , and SiO ₂

Borosilicate nano glass powder, which can be used as a sintering aid of a multilayer ceramic capacitor, was synthesized using the method proposed by the present invention. FIG. 3 is an electron scanning micrograph showing a mixture of BaO, K ₂ O, B ₂ O ₃ , and SiO ₂ and granulated to 100 μm by spray-drying. FIG. 4 is a raw material and high frequency induction of FIG. 3. Electron scanning micrographs of glass powder synthesized using a coupled plasma (high frequency output 10 kW, argon flow rate 58 lpm). It can be seen that the synthesized glass powder does not exceed 500 nm in size and has a spherical shape.

5 and 6 are graphs showing the X-ray diffraction (XRD) characteristics of the glass powder synthesized with the raw granules. It indicates that the four components included in the raw material were vitrified into an amorphous composite in the course of melting, vaporization and resynthesis by plasma.

Table 1 shows the components of raw materials and synthetic materials and their changes. A slight compositional difference occurs between the raw material and the synthetic material, which is expected to be due to the difference between the melting point and the vaporization point of each raw material, which is controlled by changing the temperature gradient of the plasma or changing the initial composition slightly beforehand. It is expected that the composition of can be obtained.

1 shows a method for producing a composite powder according to the present invention.

2 shows an apparatus for producing a composite powder according to the present invention.

Figure 3 is an electron scanning micrograph showing the granulation of the raw material

4 is an electron scanning micrograph of the glass powder synthesized using the raw material of FIG.

5 and 6 are graphs showing the x-ray diffraction characteristics of the glass powder synthesized with the raw granules

Claims

As a method for synthesizing a composite powder using thermal plasma,

Quantifying and mixing the raw materials;

Injecting the mixed material into a high temperature thermal plasma flame;

Melting and vaporizing the injected mixture in a high temperature thermal plasma flame;

Forming a composite powder by cooling the molten, vaporized mixture

Synthesis of Composite Powder Using Thermal Plasma

The method of claim 1, further comprising the step of making the raw material into a granule form.

The method of claim 1, further comprising a calcining process of removing a portion of the volatile components by heating the raw material to a temperature lower than the sintering temperature.

The method of synthesizing a composite powder using thermal plasma according to claim 1, wherein the raw material is in a solid state of powder in the form of metals and metal oxides and has a size within 1 to 10 micrometers.

The composite powder of claim 1, wherein the mixture is injected into the vicinity of the coil of the torch along a central axis of the torch through an upper end of the high frequency thermal plasma torch together with a gas for generating plasma. Synthesis method

The plasma flame has a temperature of 3000K or more, characterized in that the synthesis method of the composite powder using the thermal plasma

The method of claim 1, wherein the cooling of the mixture comprises providing a cold gas at a lower end of the plasma flame.

The method of claim 1, wherein the raw material is injected in the form of a slurry in which liquid materials are mixed.

The method of claim 1, wherein the cooling of the mixture is further performed by providing a converging-diffusion nozzle on the moving path of the mixture and passing the converging diffusion nozzle to further increase the cooling rate. Synthesis method of composite powder

A plasma torch for synthesizing composite powder,

The plasma torch is a mixing device for mixing a mixture of the plasma generating gas and the raw material of the composite powder;

An injector formed in the axial direction of the torch for injecting mixture material in the axial direction of the torch;

A gas inlet for radially injecting gas into an end portion of the flame of the plasma torch to cool the mixture material exiting the plasma flame generated by the plasma torch; A plasma torch for synthesizing a composite powder, comprising

The plasma torch of claim 1, wherein the plasma torch is any one of a transfer type, a non-transfer type, a cavity type, and a high frequency inductive coupling type.