KR101124708B1 - Fabrication Method of Silicon Powder by Combustion Synthesis using Molten Salt - Google Patents

Abstract

The present invention relates to a method for producing a high-purity silicon powder, and more specifically, silicon dioxide having a high purity and even granularity by autogenous combustion using silicon dioxide and a reducing metal, by combustion reaction of alkali salts with a particle growth inhibitor. It relates to a manufacturing method. The present invention for this purpose is a method for producing a silicon powder, characterized in that the raw material containing silicon dioxide, a metal reducing agent, and an alkali salt is subjected to a self-burning reaction in the method for producing a silicon powder. The metal reducing agent is preferably selected from the group consisting of calcium, barium, vanadium, and a mixture of magnesium and zinc having a molar ratio of 2: 1 to 1: 2, wherein the molar ratio of silicon dioxide to metal reducing agent is 1: Preferably it is 1.5 to 1: 2.5, the alkali salt is preferably 1 to 5% by weight of the total raw material, the alkali salt is selected from the group consisting of LiCl, NaCl and KCl, or from a mixed salt of the group It is preferable to be.

Silicon, powder, auto combustion, high purity, particle size

Description

Fabrication Method of Silicon Powder by Combustion Synthesis using Molten Salt}

The present invention relates to a method for producing a high-purity silicon powder, and more specifically, silicon dioxide having a high purity and even granularity by autogenous combustion using silicon dioxide and a reducing metal, by combustion reaction of alkali salts with a particle growth inhibitor. It relates to a manufacturing method.

Silicon (Si) is a representative semiconductor material along with germanium, and is used in the manufacture of various device parts such as aluminum alloys, welding rods, and solar cell elements, in addition to the semiconductor field. When silicon powder is added to aluminum, it increases the fluidity of aluminum and improves castability. Therefore, it is an indispensable material for the production of aluminum alloys of the 4XXX series used for casting, and is widely used as a reducing agent in steel mills. In addition to these basic materials, a large amount of silicon is also used in the manufacture of various parts such as welding rods and VTR head drums. In recent years, the use of semiconductor materials is increasing rapidly. In particular, as miniaturization of electronic devices is required, integrated circuits must be made on high-purity silicon substrates, and silicon single crystals of larger diameters are required. Therefore, in order to make high purity single crystal silicon material, high purity silicon powder must be made as a raw material.

The most common method for the production of silicon is to break down and pulverize the silica and reduce it in an electric furnace with coke to obtain about 97-98% of silicon. Since this method reacts for a long time at high temperature and reduces to coke, it is inevitable to produce chemically very stable silicon carbide. In order to obtain a more pure thing, about 99.97% of thing can be obtained by the DuPont method which distills refine | purified silicon tetrachloride to high-purity zinc at high temperature. However, due to the nature of silicon tetrachloride, since it exists as a gas above 57 ℃, there is a limit in mass production.

On the other hand, the auto-combustion synthesis method uses exothermic reaction heat of the reactants. In the case of a large reaction heat material, the reaction propagates spontaneously even without supplying energy from the outside, and thus solid-solid, solid-liquid and solid- It is a method of synthesizing ceramic or intermetallic compounds such as silicides, carbides, nitrides and borides by causing a reaction between gases. The auto-combustion synthesis technique has several characteristics compared to other methods, and the purity of the product is likely to increase due to volatilization of impurities. In addition, the progress of the reaction is very fast, the heating device is generally not necessary, the productivity is high, and the structure of the reactor is simple. However, the reaction is very fast and the temperature is high, it is difficult to precisely control the reaction rate, reaction temperature, gas generation. In addition, it is important to control the proper ratio of the material used as the reducing agent, the reaction conditions, and the particle size. This is because the intermediate used to obtain the desired substance can act as an impurity to lower the purity, and is also necessary to obtain more even particles. There is still a need for a method for mass production of safer, more economical and environmentally friendly finer silicon powder with better crystallinity and purity.

The present invention is to solve the above-mentioned problems, without using a high temperature furnace (furnace), difficult to handle gas, etc., the process is short, excellent thermal efficiency and productivity can greatly reduce the manufacturing cost, crystallinity And to provide a method for producing a high purity silicon powder. In particular, it is to provide a method for producing a higher quality silicon powder through the control of the particle size, together with the conditions such as the optimum mixing ratio of the raw materials used.

The present invention for this purpose is a method for producing a silicon powder, characterized in that the raw material containing silicon dioxide, a metal reducing agent, and an alkali salt is subjected to a self-burning reaction in the method for producing a silicon powder. The metal reducing agent is preferably selected from the group consisting of calcium, barium, vanadium, and a mixture of magnesium and zinc having a molar ratio of 2: 1 to 1: 2, and the average particle size of the silicon dioxide is 10 to 40 Μm, the average particle size of calcium is 10 to 80 μm, the average particle size of barium is 10 to 60 μm, the average particle size of magnesium is 10 to 80 μm, and the average particle size of zinc is 10 to 60 μm. It is preferable that the average particle size of vanadium is 10-80 micrometers.

The molar ratio of silicon dioxide to metal reducing agent is preferably 1: 1.5 to 1: 2.5, and the alkali salt is preferably 1 to 5% by weight of the total raw material, and the alkali salt is LiCl, NaCl and KCl. It is preferably selected from the group consisting of or from mixed salts of the above groups.

In addition, the present invention comprises the steps of (a) mixing the raw material containing silicon dioxide, a metal reducing agent and an alkali salt to form a pellet; (b) charging the pellets to a rotating combustion reactor, followed by localized instantaneous heating and ignition in a vacuum or inert gas atmosphere to autorotate the reaction; And (c) after pulverizing the reaction product of step (b), leaching with an acidic solution and washing with water. 2. The metal reducing agent is preferably calcium or a mixture of magnesium and zinc having a molar ratio of 2: 1 to 1: 2, and the alkali salt is selected from the group consisting of LiCl, NaCl and KCl, or a mixed salt of the group. The alkali salt is preferably 1 to 5% by weight of the total raw material.

The production method according to the present invention can produce the silicon powder without using a high temperature furnace (furnace), difficult to handle gas, etc., the process is simple, the process time is short, the thermal efficiency and productivity is excellent, the production cost It is possible to greatly reduce the, can be adjusted to the average particle size in the micro to sub-micro, in particular, there is an advantage that can produce a high-purity (more than 99%) silicon powder containing no other phase (phase).

Hereinafter, the present invention will be described in more detail, and in describing the present invention, detailed descriptions of related well-known technologies or configurations are omitted in order not to obscure the subject matter of the present invention. In addition, since the following implementation method is only for illustrating the spirit of the present invention, it can be changed to other embodiments equivalent to substitutions and equivalents within the scope without departing from the technical spirit of the present invention. It will be evident to those who have knowledge of.

The method for producing high purity silicon powder according to the present invention is to produce silicon (Si) powder by subjecting a raw material containing silicon dioxide and a metal reducing agent to self-propagating high-temperature synthesis (SHS) in a vacuum or inert gas atmosphere. There is a characteristic. The raw material is characterized by further containing an alkali salt which is a particle growth inhibitor, in order to control the particle size of the silicon powder. The alkali salts can suppress mass transfer during the autogenous combustion reaction to obtain fine silicon particles. The raw materials are charged into a self-burning reactor and mixed appropriately before reacting. These may be formed into powder compacts, or preferably molded into pellets. The mixing may be performed using a ball mill, and preferably 3 to 10 hours at 100 to 300 rpm using a diameter cone ball.

The metal reducing agent is preferably selected from the group consisting of calcium, barium, vanadium, and a mixture of magnesium and zinc having a molar ratio of 2: 1 to 1: 2, and the raw materials are average particle sizes of silicon dioxide. Is 10 to 40 µm, the average particle size of calcium is 10 to 80 µm, the average particle size of barium is 10 to 60 µm, the average particle size of magnesium is 10 to 80 µm, and the average particle size of zinc is 10 It is preferably from 60 to 60 µm, and the average particle size of vanadium is from 10 to 80 µm. It is a particle size within an appropriate range to achieve a homogeneous autogenous combustion reaction, the control of the particle size can be carried out in the mixing step of the raw materials, it can be carried out through the grinding and sieving before mixing the raw materials of course .

The molar ratio of silicon dioxide to metal reducing agent is preferably 1: 1.5 to 1: 2.5. The molar ratio based on the silicon dioxide is a ratio for minimizing the amount of calcium oxide, barium oxide, etc. remaining as impurities after the autogenous combustion reaction while completely reducing the silicon dioxide contained in the raw material and reducing the manufacturing cost. In the case of mixing magnesium and zinc, the case where the ratio is 1: 1 is the best effect.

The alkali salt is preferably 1 to 5% by weight of the total raw material, the alkali salt is preferably selected from the group consisting of LiCl, NaCl and KCl, or selected from mixed salts of the group. This is to produce a narrow particle size distribution silicon having an average particle size of several micro to sub micro. The average particle size of the silicon produced can be controlled by adjusting the addition amount of the alkali salt contained in the raw material to the raw material.

The mixed raw material is preferably molded into pellets using a mold. The molding is preferably performed at a pressure of 1 to 10Mpa using a metal or ceramic mold. The molding pressure is a pressure for maintaining the physical strength of the molded body, local ignition occurs smoothly, widen the reaction area to suppress the remaining of unreacted raw materials, and to prevent the risk of extinguishing before the reaction of the entire pellet is completed. .

The pellet (form) is charged to a self-combusting reactor for the auto-combustion reaction, wherein the auto-combustion reactor is composed of a reactor chamber and a peripheral device, which creates a vacuum or inert gas atmosphere in the reactor chamber and is located in the reactor chamber. Any form may be used as long as it can ignite the specimen.

And, looking at the present invention by the reaction step, (a) mixing the raw materials containing silicon dioxide, metal reducing agent and alkali salt to form a pellet; (b) charging the pellets to a rotating combustion reactor, followed by localized instantaneous heating and ignition in a vacuum or inert gas atmosphere to autorotate the reaction; And (c) after pulverizing the reaction product of step (b), leaching with an acidic solution and washing with water. 2. The metal reducing agent is calcium or a mixture of magnesium and zinc having a molar ratio of 2: 1 to 1: 2 is preferable in terms of efficiency and economics, and the alkali salt is selected from the group consisting of LiCl, NaCl and KCl. It is selected from the mixed salt of the said group, It is preferable that the said alkali salt is 1 to 5 weight% of all the raw materials.

Based on Figure 2 will be described a rotating combustion reactor 100 that can be used in step (b). The combustion support 10 is located in the center of the reactor chamber 102 of the autocombustion reactor. The pellet 12 of the stage is located above the combustion support 10. Within the reactor chamber, Ni-Cr filaments (resistance heating elements) for igniting the pellets are located, which Ni-Cr filaments receive current from a power source 24 located outside the reactor chamber.

Since the exothermic reaction occurs during the self-burning reaction, the reactor chamber should preferably be able to withstand the pressure of 250 atm or higher, and preferably made of stainless steel. At the bottom of the reactor chamber is connected a vacuum pipe 29 for establishing a vacuum in the reactor chamber. The vacuum pipe extends with a vacuum pump 28 located outside the reactor chamber. The vacuum pump draws air in the reactor chamber as needed to create a vacuum. In addition, an inert gas supply pipe 31 for injecting inert gas into the reactor chamber is connected to a lower end of the reactor chamber. The inert gas supply pipe extends to an inert gas source 30 located outside the reactor chamber. The inert gas source provides an inert gas such as nitrogen (N 2) or argon (Ar) into the reactor chamber as needed. In addition, the discharge pipe 32 formed on one side of the lower end of the reactor chamber to maintain a constant pressure in the reactor chamber or to discharge the pressure in the reactor chamber to the outside when recovering the pellets after the reaction. An openable closure is located above the outside of the reactor chamber.

In this step, the powder compact or the molded pellet in the cylindrical mold is charged to the above-described autocombustion reactor, and after charging, a purging process of repeating the supply of vacuum and an inert gas to remove oxygen in the reactor chamber is performed. do. After sufficient purging has been carried out, a portion of the pellet is partially ignited in a vacuum or inert atmosphere to induce a self-burning reaction. When the autocombustion reaction is carried out in an inert atmosphere, the reactor chamber is preferably 1 ~ 100atm pressure.

When the pellet is locally heated and ignited locally by a local heating means such as a resistance heating element, the heat of reaction generated from the locally generated initial synthesis reaction propagates through the entire pellet itself, and the autogenous combustion reaction is performed. . In the manufacturing method of the present invention, the time required for the reaction is within a few seconds to several minutes due to the characteristics of the auto-combustion reaction. The process is simple by mixing and partial heating, it is eco-friendly because no harmful gases or harmful reactants are produced, and it is economical method that can be mass-produced because it manufactures high hydrothermal silicon powder with cheap raw materials and minimum energy supply. After the step is obtained because the aggregates are agglomerates in which the particles are agglomerated to a certain portion, it is preferable that the grinding step of physically grinding them. Physically pulverizing the powders produced by the reaction may be carried out using a conventional ball mill, roll milling, or the like, preferably using roll milling. The pulverized reaction product contains impurities other than silicon by the reducing agent and the grain growth inhibitor added to the raw materials. The leaching step and washing with an acidic solution are performed to remove this to obtain a high purity silicon powder.

    The leaching step is carried out to remove the oxide of the metal used as the reducing agent, by mixing and stirring the strong acid aqueous solution and the pulverized reaction product, and then performing the separation and recovery of the powder using solid-liquid separation such as filtration It may be repeated one or more times. Preferably the strong acid aqueous solution is an aqueous hydrochloric acid solution of 3 to 10M concentration. Leaching with the acid removes the product (metal oxide) by the metal reducing agent contained in the reaction product.

After the leaching step, washing with water is carried out by mixing and stirring the distilled water and the leached powder, and then separating and recovering the powder, and this washing step may be performed one or more times, and is repeatedly performed 5 to 10 times. It is preferable to sufficiently remove the acid remaining in the remaining powder by the leaching treatment and the grain growth inhibitor remaining in the reaction product. After washing with water, the separated and recovered powder may be dried to obtain a silicon powder of high purity having a controlled average particle size.

Hereinafter, the present invention will be described in more detail based on the following examples.

Example 1

The molar ratio of silicon dioxide (SiO2, Junsei, S0166) and calcium (Ca, Acros, 2011-85000) is weighed to be 1: 2.1 and mixed uniformly in a ball mill, and the mixture is cold-pressed to a pressure of 5 Mpa to obtain a diameter. Pellets of size 30 mm and height 40 mm were prepared. After the prepared pellets were charged into a reactor chamber similar to that of FIG. I was. Thereafter, the pellets were locally ignited using a Ni-Cr resistance heating element to proceed with the combustion reaction. After the completion of the auto-combustion reaction, the product was pulverized using a roll mill, and the pulverized product was mixed with 6.0 M hydrochloric acid solution (50 ° C.), leached for 6 hours, and washed with hydrochloric acid until no hydrochloric acid ion was detected. And filtration was repeated. The filtered powder was dried at 80 ° C. for 24 hours to produce silicon powder.

Example 2

After weighing so that the molar ratio of silicon dioxide (SiO 2, Junsei, S0166) and calcium (Ca, acrose, 2011-85000) is 1: 2.1, NaCl (NaCl, Samjeon Chem, S0485) is added to 2% by weight of the total raw materials. Silicon powder was prepared in a similar manner to Example 1 except that the mixture was further added to the ball mill to be uniformly mixed. Figure 3 shows the X-ray diffraction analysis of the powder prepared in Example 1. It can be seen that the single phase of silicon is synthesized by the manufacturing method of the present invention, and it can be seen that other phases other than silicon are not produced. Figure 4 is a scanning electron micrograph of the silicon powder prepared in Example 1, the silicon particles produced by the autogenous combustion reaction has an irregular irregular structure, it can be confirmed that the particle size of 1 ~ 5㎛. It was also found that the particles aggregated to some extent even after pulverization by a roll mill. 5 and 6 show the X-ray diffraction analysis results and SEM images of the silicon powder prepared in Example 2, respectively. As can be seen from FIG. 5, even when an alkali salt, which is a grain growth inhibitor, was added, it was confirmed that a powder composed of a single phase of silicon was obtained. Similarly to Example 1, particles having an irregular irregular structure were prepared, but the particles It could be confirmed that the size is controlled to smaller particles to 0.5 to 1㎛.

As described above, the present invention has been described by specific matters and limited embodiments and drawings, such as a specific device. However, the present invention is provided to help a more general understanding of the present invention, and the present invention is not limited to the above embodiments. For those skilled in the art, various modifications and variations are possible from such description. Accordingly, the spirit of the present invention should not be construed as being limited to the embodiments described, and all of the equivalents or equivalents of the claims, as well as the following claims, belong to the scope of the present invention .

1 is a flow chart showing a manufacturing method of the present invention,

Figure 2 is an apparatus diagram of a rotating combustion reactor that can be used in the production method of the present invention,

Figure 3 shows the X-ray diffraction analysis of the powder prepared in Example 1 of the present invention,

4 is a scanning electron micrograph of the silicon powder prepared in Example 1 of the present invention.

Figure 5 shows the X-ray diffraction analysis of the powder prepared in Example 2 of the present invention,

6 is a scanning electron micrograph of the powder prepared in Example 2 of the present invention.

Claims (9)

delete In the method for producing a silicon powder, the raw material containing silicon dioxide, a metal reducing agent, and an alkali salt is subjected to a self-burning reaction, The metal reducing agent is at least one selected from the group consisting of calcium, barium, vanadium, and a mixture of magnesium and zinc having a molar ratio of 2: 1 to 1: 2, The alkali salt is selected from the group consisting of LiCl, NaCl and KCl, or a method of producing a silicon powder, characterized in that selected from the mixed salt of the alkali salt group. 3. The method of claim 2, The average particle size of the silicon dioxide is 10 to 40㎛, the average particle size of calcium is 10 to 80㎛, the average particle size of barium is 10 to 60㎛, the average particle size of magnesium is 10 to 80㎛, The average particle size of zinc is 10 to 60㎛, the average particle size of vanadium is a method for producing a silicon powder, characterized in that 10 to 80㎛. The method according to any one of claims 2 to 3, The molar ratio of the silicon dioxide: metal reducing agent is 1: 1.5 to 1: 2.5 method for producing a silicon powder, characterized in that. delete The method according to any one of claims 2 to 3, The alkali salt is a method for producing a silicon powder, characterized in that 1 to 5% by weight of the total raw material. (a) mixing a raw material containing silicon dioxide, a metal reducing agent and an alkali salt to form a pellet; (b) charging the pellets to a rotating combustion reactor, followed by localized instantaneous heating and ignition in a vacuum or inert gas atmosphere to autorotate the reaction; And (c) pulverizing the reaction product of step (b), leaching with an acidic solution and washing with water; The metal reducing agent is at least one selected from the group consisting of calcium, barium, vanadium, and a mixture of magnesium and zinc having a molar ratio of 2: 1 to 1: 2, The alkali salt is selected from the group consisting of LiCl, NaCl and KCl, or a method of producing a silicon powder, characterized in that selected from the mixed salt of the alkali salt group. delete The method of claim 7, wherein The alkali salt is a method for producing a silicon powder, characterized in that 1 to 5% by weight of the total raw material.

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