JP7095885B2 - Silicon manufacturing method - Google Patents

Description

The present invention relates to a method for producing high-purity silicon by using silica, aluminum, calcium oxide, and calcium fluoride as raw materials, melting the raw materials by a thermite reaction, and reducing silica. In particular, the present invention relates to an effective method for producing high-purity (9N) silicon suitable for photoelectric conversion cells, and preferably one of the raw materials is high-purity silica extracted from diatomaceous earth and subjected to high-purity treatment. The present invention relates to a method for producing high-purity solar-grade silicon, that is, silicon suitable for solar cell applications with high photoelectric conversion efficiency, by reducing silica by a thermite reaction without using a carbon raw material.

The production of fossil-based energy is an outgassing source of carbon-containing gases. This leads to global warming of the earth due to greenhouse gases such as CO ₂ gas. This greenhouse gas is one of the major factors leading to global warming. It is generated in all processes that utilize coal as an energy source. On a global scale, 250 billion tonnes of CO ₂ were generated in 2018. Of these, China is 30%, the United States is 15%, India is 7%, and Russia is 5%. On the other hand, some methods for producing CO ₂ alternative clean energy have been proposed and used. Among the alternative energies, the use of solar energy, which is known as a photovoltaic power generation means, has been remarkably advanced in recent years, solar energy is abundant, and photovoltaic power generation equipment is a device used in the process. It has a size that does not cause any problems.

Among the solar power generation devices, the solar cell is the most important part representing the conversion of solar energy and electricity using a silicon wafer. In order to increase the photoelectric conversion efficiency, silicon purity at the same level as the purity of semiconductor silicon is preferable. As for the purity of semiconductor silicon, high purity starting from 10N has been studied. Therefore, in the case of silicon of a solar cell, it is preferable to have a purity close to or equivalent to that in order to obtain high conversion efficiency of the solar cell.

Silicon-based solar cells are the most commonly commercialized and used solar cells, accounting for more than 90% of the solar market. The quality of the silicon material is directly related to the quality effect such as the conversion efficiency of the solar cell. This conversion efficiency is highly dependent on the morphology of silicon, from single crystal to polycrystal. Currently, silicon materials classified as solar grade silicon used in solar cell applications require a minimum purity of 6N.

The raw materials used to make semiconductor silicon are equivalent to the raw materials used to make solar grade silicon. Therefore, the rise and fall of prices in the solar grade silicon manufacturing industry strongly depends on the rise and fall of prices in the semiconductor silicon manufacturing industry. And it tightens the procurement of raw materials for solar grade silicon.

Therefore, in order to solve the shortage of raw materials for manufacturing solar grade silicon, various interests have been focused on increasing the purity of metallic grade silicon known as metallic silicon (2 to 3N). Major impurities in metallic grade silicon include metallic impurities such as calcium, aluminum and iron and non-metallic impurities such as phosphorus and boron. Metal impurities such as iron and aluminum are easy to handle because the metal impurities are easily segregated at the solidification stage and have an extremely low solidification partition coefficient as compared with silicon. However, the non-metal impurities boron and phosphorus act as dopants in silicon and have a high solidification partition coefficient. In the case of boron, the solidification partition coefficient is 0.8, which makes it difficult to remove boron through solidification segregation.

Various alternatives to solidification segregation have been developed to solve the problems of removing non-metallic impurities in order to purify metallic silicon to solar grade silicon. For example, Patent Document 1 discloses a plasma frame dissolution method for boron and phosphorus. Further, Patent Document 2 discloses the removal of atomization of phosphorus. Despite various proposed alternatives for purifying metallic silicon, reaching the purity level of semiconductor grade silicon is due to the lack of an efficient method for achieving high purity. Has not been realized yet.

Traditionally, solar grade silicon has been manufactured by a traditional method consisting of a series of two major steps. This method first uses a carbon material and heats it to 2000 ° C. in an arc furnace to convert silica to silicon. After that, a step of purifying the obtained silicon by a chemical method called the Siemens method disclosed in Patent Document 3 is continued. However, this method has a problem that it is expensive and CO ₂ that causes climate change is released into the air at a high level. For this reason, at the industrial level near 2017, the global warming of 1 ° C has been brought about.

Various alternatives have been developed to remedy the major drawbacks of the traditional Siemens method. One of them is the Elchem method described in Patent Document 4, in which CO ₂ emissions are reduced until the CO ₂ emission amount reaches 50,000 tons per 5000 tons of SoG-Si. Therefore, it can be said that this method is greatly improved as compared with the Siemens method. However, the amount of CO ₂ released by the Elchem method is still at an extremely high level, which is a level at which a temperature rise of 0.2 ° C. occurs in the last 10 years. Increased CO ₂ emissions in the coming years are expected to be fatal to the Earth's environment and human survival. Therefore, in order to accelerate the use of renewable energy and the good conservation of the global environment in the future, as a method of producing solar grade silicon, a zero emission process that does not emit carbon dioxide or a CO ₂ -free society is possible. It is required to realize it promptly.

WO2010 / 024310A1 CN101252136A US2008 / 0206970A1 US Patent 6861040B1 US Patent 51582830 WO2006 / 041271 WO2013 / 078220 WO2004 / 101434A1

Currently, there is no ideal method for producing high-purity silicon for solar cell applications without the use of carbonaceous materials. Therefore, as a method for producing high-purity silicon for solar cells, there is a demand for the development of a production method with strict zero carbon emission. It should be noted that thermal carbon reduction requires substantial consumption of electrical energy, and if a second-generation solar cell as self-power is used, the zero emission process will occur in that part and the amount of carbon emission will be reduced. Can be done. However, thermite reduction using the thermite reaction does not result in high levels of CO ₂ emissions. It can be said that the thermite reaction using aluminum as a reducing agent is a CO ₂ -free step for reducing a material containing oxygen (Patent Document 5). In addition, although it is not a thermite reaction, there are those disclosed in Patent Documents 6 to 8 as a method for producing high-purity silicon which is not based on the Siemens method and the Elken method.

Patent Document 5 discloses a method for producing a pure metal or an alloy metal by a thermite reaction after charging a mixture of a metal oxide powder and a reducing agent into a reaction furnace. Patent Document 6 discloses a method for producing high-purity silicon by reducing silicon dioxide by an aluminum thermal reduction method. Patent Document 7 is a method for producing solar grade silicon, in which silica is preheated to a temperature of 1300 to 1400 ° C. and brought into contact with aluminum to melt aluminum to form an aluminum-silicon alloy. Is. In Patent Document 8, high-purity silicon powder is obtained by a chemical treatment including thermal carbon reduction of quartzite and a treatment with an aqueous solution of an inorganic acid.

However, there is a clean method that reduces silica to obtain high _- purity silicon without emitting carbon dioxide and uses the obtained high-purity silicon for solar power generation to convert solar energy into electrical energy. Although it contributes to the realization of an ideal society, a method capable of reducing and producing this high-purity silicon with high efficiency has not yet been realized.

The present invention has been made in view of the above problems, and by reducing silica with aluminum by a thermite reaction, high efficiency is achieved without using a carbonaceous material and without releasing carbon dioxide gas in the manufacturing process. It is an object of the present invention to provide a method for producing silicon, which is capable of producing high-purity silicon. In particular, the present invention produces high-purity silicon having a purity of 9N level for solar cell use by reducing a relatively high-purity silica raw material of 3N or more, more preferably 4N or more, with aluminum by a thermite reaction. The purpose is to provide a way to do this.

According to the present invention, for example, raw material silica obtained by purifying diatomaceous earth, which is abundant in the world, is reduced by a thermite reaction in a graphite heater using aluminum as a reducing agent to produce high-purity silicon. Manufactured. This high-purity silicon can be purified to obtain high-purity solar-grade silicon by removing the slag generated during the thermite reaction.

The method for producing silicon according to the present invention is as follows.
A step of preparing a raw material mixture of silica, aluminum, calcium oxide, and calcium fluoride powder, a step of molding the raw material mixture into pellets or granules using a binder, and the pellets or granules after molding. The step of preheating the raw material mixture consisting of the material to a temperature range of 50 to 150 ° C. to strengthen the pellets or granules, and heating the raw material mixture to 800 ° C. or higher to cause a thermit reaction to initiate the thermit reaction. Later, due to the heat generation phenomenon, the raw material mixture is melted in the process of raising the temperature to 800 to 2000 ° C., and the silica is reduced to form liquid silicon and slag, and the melted material is cooled. It is characterized by having a step of separating and recovering the obtained silicon product.

In other words, the method for producing high-purity silicon of the present invention uses silica, aluminum, calcium oxide, calcium fluoride powder, or the like as a raw material mixture material. Further, this mixture is placed in a graphite crucible and charged in a graphite heater to heat the crucible to 800 ° C. or higher. As a result, a thermite reaction occurs, the crucible contents are heated to 800 to 2000 ° C., the raw material mixture is melted, and silica is reduced to liquid silicon and slag. When the temperature of the reaction material is lowered, the liquid silicon solidifies to obtain a solid silicon product from which impurities are sufficiently removed.

Further, in other words, the present invention relates to a method for preparing high-purity silicon having a small amount of boron and phosphorus without containing a carbonaceous material. This method has a plurality of steps. For example, the raw material silica powder is mixed with a mixture of aluminum powder and calcium oxide with calcium fluoride powder, and the raw material mixture is placed in a rut. Further, when an appropriate temperature is applied to the thermite reaction, the thermite reaction occurs and silica is reduced. Then, the silicon obtained by reduction is recovered in the form of a solid mixture with slag, for example. Then, the final product is purified to obtain a high-purity silicon product.

Further, in other words, the present invention is suitable for producing 9N silicon, which is effective for photoelectrostatic applications. This method uses a thermite reaction that reduces silica without the use of carbonaceous materials. This makes it possible to avoid carbon emissions. The method of the present invention has, for example, the following steps.

(1) A raw material mixture of silica, aluminum, calcium oxide and calcium fluoride is obtained. This may be a mixture of powders of each raw material and then hardened with a binder to form pellets, or a silica pellet obtained by pelletizing silica powder with a binder or an aluminum powder pelleted with a binder. It may be a mixture of pellets of a calcium oxide / calcium fluoride mixture in which a mixed powder of aluminum pellets, calcium oxide and calcium fluoride is pelletized with a binder. In this way, the raw materials are prepared.

(2) The mixture of pellets is charged into a graphite crucible or a BN crucible.

(3) The pellet is preheated to strengthen its structure.

(4) The preheated pellets are heated to activate the thermite reaction in a graphite crucible and reduce silica to silicon.

(5) The temperature of the reaction product is lowered, and the solidified silicon obtained by the thermite reaction is recovered.

According to the present invention, high-purity silicon can be produced without releasing carbon-containing gas such as carbon dioxide gas and carbon monoxide gas. That is, according to the present invention, aluminum is used instead of carbon as the reducing agent, so that carbon emission can be avoided. According to the present invention, carbon dioxide gas and carbon monoxide gas, which are toxic and harmful gases, are not produced in addition to the silicon carbide.

On the other hand, according to the present invention, the ignition point of the thermite reaction is lower than that of the conventional thermal carbon reduction, and therefore the energy consumption is low. Further, the thermite reaction rapidly raises the temperature of the raw material mixture to a high temperature, and the reduction reaction is completed in an extremely short time. Therefore, high-purity silicon can be obtained with high efficiency.

According to the present invention, as compared with the conventional reduction step, the reduction step by the thermit reaction of the present invention is more direct and close to the production of high-purity silicon in the process technique, and there is less waste. , Efficient.

It is a flowchart which shows the manufacturing method of the solar grade silicon of embodiment of this invention. It is a schematic perspective view which shows the inside of the graphite heater used in embodiment of this invention. It is also a vertical sectional view showing the inside thereof.

Hereinafter, embodiments of the present invention will be specifically described with reference to FIGS. 1 to 3. According to the present invention, when the quality of metallurgical grade silicon produced from the thermal carbon reduction of quartz is improved to solar grade and semiconductor grade silicon, the Siemens method, which is a conventional silicon production method, uses a flammable gas such as silane gas. It was developed to solve the problem caused by the chemical treatment of toxic gas and unpleasant odor, that is, the problem of high energy consumption.

Second, the pollution factor is realistic. Climate change is one of the major problems of the earth. Many research projects are being carried out to curb each process of global warming. Among the gases, CO2 gas has a great influence on the destruction of the earth's climate. The silica reduction process for producing conventional metallurgical grade silicon involves the release of large amounts of CO gas and CO2 gas during the reduction reaction.

There is an increasing need for clean, low-cost methods for manufacturing solar-grade and higher-grade silicon. Any further carbon emissions should be avoided in order to improve the shortcomings of conventional silicon manufacturing methods and protect the planet.

The silicon purity target of the present invention is 99.999999% (9N). In the present invention, impurities of boron and phosphorus serve as a reference in describing the purity level of the raw material and thus the resulting silicon product.

FIG. 2 is a perspective view showing a graphite heater used in the present embodiment, and FIG. 3 is a sectional view. The chamber 1 is made of, for example, SUS, and the inner peripheral surface of the chamber 1 is lined with an alumina heat insulating layer 2. Further, a cylindrical graphite protective layer 3 is installed in the space surrounded by the heat insulating layer 2, and a Nica film layer 4 is provided on the inner surface of the graphite protective layer 3. A water-cooled stainless steel jacket 7 for cooling the chamber 1 is embedded in the wall of the chamber 1. A graphite heater 6 is installed in a space surrounded by the Nica film layer 4. Further, a stainless steel support plate 5 is installed on the bottom of the chamber 1 surrounded by the Nica film layer 4, and graphite having an upper end opened in the center of the graphite heater 6 on the support plate 5. The crucible 11 is placed and arranged on a graphite crucible support base 12. A quartz cylinder 10 is arranged so as to surround the graphite crucible 11. Further, an opening is provided in the center of the upper surface of the chamber 1, and a lid member 15 for closing the opening is installed. Two water-cooled copper power supply connection portions 9 are installed on the lid member 15, and a graphite heater 6 is hung via a power supply terminal connection rod 8 connected to the connection portion 9. As a result, the graphite heater 6 is electrically connected to the power supply connection portion 9 via the power supply terminal connection rod 8 and is supplied with power from the power supply connection portion 9. Further, in the center of the lid member 15, a pipe 13 for supplying Ar gas is installed around the graphite crucible 11. The raw material mixture is placed in the graphite crucible 11 and placed on the graphite crucible support base 12. The raw material mixture in the crucible 11 is heated to a temperature of 800 ° C. or higher by a graphite heater 6 via a quartz cylinder 10. At this time, Ar gas is introduced into the chamber 1, and the peripheral portion of the crucible 11 is maintained in the Ar atmosphere. Then, when the aluminum is heated to 800 ° C. or higher, the thermite reaction is started, and the reduction reaction of silica by aluminum occurs.

As shown in FIG. 1, the method of the present invention is a method for producing high-purity silicon. Further, according to the embodiment of the present invention, the method for producing high-purity silicon includes a step of preparing a raw material mixture in which calcium oxide is added to silica and aluminum powder, and the mixture is kept in the range of 800 to 2000 ° C. It comprises a step of heating to the ignition temperature of an existing thermite reaction and a step of melting the reactants and causing the exchange of oxygen between silica and aluminum to produce silicon and slag. Further, following the step of separating the liquid silicon from the residue, the product is cooled to obtain low impurity level silicon.

Silica used as a raw material is extracted from diatomaceous earth and purified to the vicinity of 99.999% (5N). This diatomaceous earth is abundant worldwide, and the silica extracted from it is low cost. As a method for obtaining high-purity silica from this diatomaceous earth, for example, there are the following. That is, in this method for producing high-purity silica, first, the diatomaceous earth raw material is leached with acid and washed with pure water to remove impurities including alkaline earth metal, alkali metal, transition metal or post-transition metal. , A step of obtaining an aqueous sodium silicate solution from the residue after washing, and passing the aqueous sodium silicate solution through a first column containing an ion chelate specifying agent to remove boron in the aqueous sodium silicate solution. The step, the phosphorus removing step of removing phosphorus in the aqueous solution by passing the aqueous solution from which the boron was removed through a second column containing an anion chelate specificizing agent, and the aqueous solution from which the phosphorus was removed are centrifuged. It comprises a step of recovering silica by filtering.

According to the present invention, the raw material mixture of silica and aluminum contains calcium fluoride powder mainly composed of CaF ₂ in addition to calcium oxide powder. As a result, a flux effect can be obtained, the ignition temperature of the thermite reaction between silica and aluminum can be lowered, and the required energy can be reduced.

As a raw material for the calcium oxide powder, lime having a calcium oxide powder having an appropriate purity of 4N or more and a calcium fluoride powder can be used.

According to the first step of preparing the mixture, the particle size of each component of the raw material mixture is less than 1 mm and in the case of silica less than 50 μm.

The particle size of the raw material has a great influence on the increase in the reaction rate due to the increase in the contact area. Choosing the right particle size for the particles is a key factor in obtaining a high yield reduction reaction.

According to the present invention, the mixing ratio of silica, aluminum, calcium oxide and calcium fluoride in the raw materials is 2: 1: 2: 1 to 6: 3: 6: 2 in molar ratio.

The weight ratio of silica to aluminum is preferably 1/2 to 1/3 in order to ensure total oxidation of aluminum to alumina and prevent the formation of aluminum slag material.

The weight ratio of silica to calcium oxide is in the range of 1/1 to 3/2 depending on the level used to lower the ignition temperature, because the higher the ratio of calcium oxide, the lower the ignition temperature. do.

Further, the viscosity of the melt reaction product can be adjusted by adding calcium fluoride. This calcium fluoride plays a crucial role in separating the final slag product from the silicon product in order to recover the high purity silicon.

According to the present invention, as shown in FIG. 2, an open graphite crucible is installed inside the graphite heater, and the thermite reaction is introduced into the crucible.

The mixture of raw materials in the form of particles, pellets, and powder is uniformly charged inside the graphite crucible so as to obtain sufficient surface contact between different reactants.

The thermite reaction is ignited after the internal temperature of the graphite crucible reaches 800 ° C. or higher.

After the thermite reaction is initiated, silica reacts with aluminum in the presence of calcium oxide and calcium fluoride powder of the flux material.

The following reaction formulas (Chemical formula 1) and (Chemical formula 2) show the thermite reduction chemical reaction for exchanging oxygen between silica and aluminum.

According to the present invention, the reduction process occurs as follows. The mixture of raw materials containing silica pellets, aluminum, calcium oxide and calcium fluoride is heated to a temperature of about 800 ° C. or higher at a constant heating rate of about 20 ° C./min until all the materials are dissolved. The thermite reaction is ignited and initiated at a temperature of 800-1000 ° C. Further, this thermite reaction proceeds to a high temperature of 2000 ° C. or higher.

The temperature range of the thermite reaction causes the exchange of oxygen between silica and aluminum, producing liquid silicon and aluminum oxide (alumina).

The reaction time varies from 20 minutes to 50 minutes depending on the ratio of raw materials to be charged and heating conditions such as temperature and heating pattern.

Thermite reaction is an exothermic reaction in which a considerable amount of energy is released as heat. Therefore, when the thermite reaction is activated in the range of 800 to 1000 ° C., an external heat energy source is unnecessary. Therefore, energy consumption is extremely reduced.

During the period from ignition to reaching the maximum temperature of 2000 ° C., liquid silicon is gradually formed as the thermite reaction occurs. Therefore, in the end, the liquid silicon collects as a single mass of liquid silicon.

By assembling the liquid silicon as one mass, it becomes easy to separate the liquid silicon from the slag generated in all the reduction processes.

In embodiments of the invention, the aluminum metal is removed in two ways according to the chemical reaction described above. In the first method, the aluminum metal reacts with oxygen supplied from silica to generate aluminum gas (Al ₂ O ₃ ) and evaporate. Alternatively, in the second method, aluminum is mixed with other metals and solidified to form solid slag having a higher density than silicon. The denser slag generated sinks to the bottom of the graphite crucible. The acid treatment then extracts the entire amount of slag. A path of suppression of aluminum in the reduction process can occur at the same time. This results in the formation of aluminum oxide gas and aluminum slag, which can result in the removal of large amounts of aluminum from the final product.

The reduction of silica to silicon and the oxidation of aluminum to alumina are carried out in the liquid phase to improve the efficiency of surface contact between the reactants.

The reason for initiating the thermite reaction at temperatures as high as 800-1000 ° C is to increase the total dissolution of the reactants, which results in the reaction occurring in a liquid state beneficial for the reduction process.

According to the present invention, the aluminum powder functions as a reducing agent instead of the carbon used in the conventional thermal carbon reduction of silica.

Aluminum may contain impurities such as B and P in low concentrations. These impurities have a significant effect on the final purity level of silicon and thus on the performance of the solar cell. In the case of conventional carbon reduction, the performance of the solar cell is low because it contains high levels of B and P impurities, but in the case of the present invention, the concentration of B and P impurities is low, so a high-performance solar cell can be obtained. Obtainable.

In the present invention, the thermite reaction is a highly exothermic reaction and can be said to be a self-energy supply reaction. Therefore, the present invention consumes less external energy than the conventional reduction process.

According to the present invention, the conversion efficiency of silica to silicon is about 40%, and the ideal conversion efficiency is 47%, so that extremely high conversion efficiency can be obtained. A slag material containing alumina and calcium oxide is produced, and a part of the slag material adheres to the wall of the crucible, resulting in a loss of 7%.

According to the present invention, a slag material is generated by the reaction of a plurality of kinds of materials existing inside a rut such as silica, silicon, aluminum, alumina, calcium and calcium oxide. The complexity of the slag material makes it difficult to identify the structures handled in the purification process to obtain clean silicone products.

Example 1
Silica powder having a purity of 4 N or more and a particle size of 100 μm or less was mixed with aluminum powder, calcium oxide powder and silica stone powder having the same purity and a particle size of 1 mm or less. A mixture of each powder was added with a binder such as PVA as a binder to form pellets or particles of raw material. The ratio used to prepare the raw materials was (SiO ₂ : Al: CaO: CaF ₂ ) = (4: 2: 4: 2) in molar ratio and was well mixed and molded into pellets or particles. Will be done. More specifically, 17.8 g of silica powder is added to 4 g of aluminum powder, 16.6 g of calcium oxide and 11.6 g of silica stone powder, using PVA binder to pellet or pellet with a diameter of 5-10 mm. Molded into particles. The blending amount of each component of this mixed raw material is SiO ₂ : 35.6% by mass, Al: 8.0% by mass, CaO: 33.2% by mass, and CaF ₂ : 23.2% by mass.

The particles were then preheated to a temperature range of 50-150 ° C. for 1-2 hours to enhance the structure of the particles. The preheated particles were charged into an open graphite crucible and placed in a graphite heater chamber. The charged raw material was heated to a temperature of 800 ° C. at a heating rate of 20 ° C./min. The graphite heater supplies the required thermal energy until the ignition of the thermite reaction. This ignition occurs at a temperature of 800 to 1000 ° C.

Further, after the thermite reaction is ignited, the temperature rises rapidly, melting the raw material in the temperature range of 1300 to 2000 ° C. Then, liquid silicon is produced by a reduction reaction of silica. Alumina is produced in the process of oxidizing aluminum in addition to the production of slag material. The addition of calcium fluoride flux powder has an important role in separating the resulting liquid silicon from other products such as alumina and slag. The thermite reaction period is 20 to 40 minutes, depending on the state of the chamber. After ignition of the thermite reaction, the energy provided by the graphite heater is reduced, but at a heating rate of 20 ° C./min, it is maintained for 40-45 minutes. After cooling, a layer of solidified silicon floats on top of the other products of the thermite reaction. This facilitates the recovery of the silicon product.

Example 2
The raw material mixture of silica, aluminum, calcium oxide and calcium fluoride powder having the same properties as in Example 1 has a molar ratio of (SiO ₂ : Al: CaO: CaF ₂ ) = (6: 2: 3: 2). Adjusted to. Specifically, 24.4 g of silica powder is added to 3.7 g of aluminum powder, 11.3 g of calcium oxide powder and 10.6 g of calcium fluoride powder, and 5-10 mm using a PVA binder. Formed into pellets or particles of diameter. The blending amount of each component of this mixed raw material is SiO ₂ : 48.8% by mass, Al: 7.4% by mass, CaO: 22.6% by mass, and CaF ₂ : 21.2% by mass.

The particles were then preheated to a temperature range of 50-150 ° C. for 1-2 hours to enhance the structure of the mixture. Further, the preheated particles were charged into an open graphite crucible and placed in a graphite heater chamber. The step of heating the graphite crucible includes a step of heating to a temperature of 800 ° C. at a heating rate of 20 ° C./min to 25 ° C./min. The graphite heater supplies the required thermal energy until the ignition of the thermite reaction. This ignition occurs at a temperature of 800 to 1000 ° C.

35 to 45 minutes after the thermite reaction ignites, the temperature rises from 1300 ° C to 2000 ° C. This dissolves the entire amount of raw material. Liquid silicon, alumina and slag are produced in the reduction process. After cooling, a layer of solidified silicon floats on top of the other products of the thermite reaction. This facilitates recovery of the silicon product.

Example 3
The raw material mixture of silica, aluminum, calcium oxide and calcium fluoride powder having the same properties as in Example 1 has the following molar ratio (SiO ₂ : Al: CaO: CaF ₂ ) = (5: 3: 4: 1). Adjusted with. Therefore, 21.96 g of silica powder is added to 5.93 g of aluminum powder, 16.4 g of calcium oxide powder and 5.71 g of calcium fluoride powder, and a PVA binder is used to make a diameter of 5 to 10 mm. Formed into pellets or particles. The blending amount of each component of this mixed raw material is SiO ₂ : 43.9% by mass, Al: 11.9% by mass, CaO: 32.8% by mass, and CaF ₂ : 11.4% by mass.

The particles were then preheated to a temperature range of 50-150 ° C. for 1-2 hours to enhance the structure of the mixture. Further, the preheated particles were charged into an open graphite crucible and placed in a graphite heater chamber. The step of heating the graphite crucible includes a step of heating to a temperature of 800 ° C. at a heating rate of 20 ° C./min to 25 ° C./min. The graphite heater supplies the required thermal energy until the ignition of the thermite reaction. This ignition occurs at a temperature of 800 to 1000 ° C.

35 to 45 minutes after the thermite reaction ignites, the temperature rises from 1300 ° C to 2000 ° C. This dissolves the entire amount of raw material. Liquid silicon, alumina and slag are produced in the reduction process. After cooling, a layer of solidified silicon floats on top of the other products of the thermite reaction. This facilitates recovery of the silicon product.

Example 4
The raw material mixture of silica, aluminum, calcium oxide and calcium fluoride powder having the same properties as in Example 1 has the following molar ratio (SiO ₂ : Al: CaO: CaF ₂ ) = (5: 3: 3: 2). Adjusted with. That is, 21.28 g of silica powder is added to 5.73 g of aluminum powder, 11.92 g of calcium oxide powder and 11.06 g of calcium fluoride powder, and pellets having a diameter of 5 to 10 mm are used with a PVA binder. Or it is molded into particles. The blending amount of each component of this mixed raw material is SiO ₂ : 42.6% by mass, Al: 11.5% by mass, CaO: 23.8% by mass, CaF ₂ : 22.1% by mass.

Then, in order to strengthen the structure of the mixture, the molded particles were preheated to a temperature range of 50 to 150 ° C. for 1 to 2 hours. Further, the preheated particles were charged into an open graphite crucible and placed in a graphite heater chamber. The step of heating the graphite crucible includes a step of heating to a temperature of 800 ° C. at a heating rate of 25 ° C./min to 35 ° C./min. The graphite heater supplies the required thermal energy until the ignition of the thermite reaction. This ignition occurs at a temperature of 800 to 1000 ° C.

35 to 45 minutes after the thermite reaction ignites, the temperature rises from 1300 ° C to 2000 ° C. This dissolves the entire amount of raw material. Liquid silicon, alumina and slag are produced in the reduction process. After cooling, a layer of solidified silicon floats on top of the other products of the thermite reaction. This facilitates recovery of the silicon product.

In this way, the raw material mixture of SiO ₂ , Al, CaO and CaF ₂ is heated by a thermite reaction to reduce SiO ₂ to obtain high-purity silicon. In the examples of Examples 1, 2, 2, 3 and 4, for example, the raw material mixture contains 35 to 50% by mass of SiO ₂ , 7 to 12% by mass of Al: and 20 to 35% by mass of CaO. %, CaF ₂ is 10 to 25% by mass. However, the composition range of the mixed raw material of the present invention is not limited to this, and the effect of the present invention can be exhibited as long as the composition range is such that the thermite reaction occurs.

In the present invention, instead of producing high-purity silicon by conventional thermal carbon reduction, the thermite reaction is used as a heat source and silica is reduced with aluminum to achieve high purity without releasing carbon-containing gas, which is a greenhouse gas. Since silicon can be produced, solar grade silicon for solar cells can be produced with high efficiency without causing deterioration of the global environment. Therefore, the present invention is extremely useful for producing high-purity silicon such as solar grade silicon.

1: Chamber 2: Alumina heat insulating layer 3: Graphite protective layer 4: Nica film layer 5: Support plate 6: Graphite heater 7: Stainless steel cooling jacket 8: Power terminal connection rod 9: Connection part 10: Cylinder 11: Graphite Crucible 12: Graphite crucible support 13: Pipe 15: Lid member

Claims (2)

The process of preparing a raw material mixture of powders of silica, aluminum, calcium oxide, and calcium fluoride, and
The step of molding the raw material mixture into pellets or granules using a binder, and
A step of preheating the raw material mixture consisting of the pellets or granules after molding to a temperature range of 50 to 150 ° C. to strengthen the pellets or granules.
The step of heating the raw material mixture to 800 to 1000 ° C. to cause a thermite reaction, and
After the start of the thermite reaction, the exothermic phenomenon is utilized to raise the temperature of the raw material mixture to a temperature of 1300 to 2000 ° C. , melt the raw material mixture, and reduce the silica to produce liquid silicon and slag . Process and
The process of lowering the temperature of this melted material to separate and recover the obtained silicon product, and
A method for producing silicon, which comprises. The silica according to claim 1, wherein the silica as a raw material is extracted from diatomaceous earth, then boron is removed by an ion chelate specifying agent, and phosphorus is removed by an anion chelating specifying agent to purify the silica. How to make silicon.

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