SiC manufacturing method
Patent Information
- Authority / Receiving Office
- JP · JP
- Patent Type
- Applications
- Current Assignee / Owner
- TOHOKU UNIV
- Filing Date
- 2025-01-17
- Publication Date
- 2026-07-30
Smart Images
Figure 2026123394000002 
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Abstract
Description
Technical Field
[0001] The present invention relates to a method for manufacturing SiC using microwave irradiation.
Background Art
[0002] Silicon carbide (SiC) is industrially manufactured by the Acheson method (Figure 2). In the Acheson method, between paired fixed electrodes, a raw material layer composed of silica and a carbon reducing agent blended in a predetermined ratio is used to cover the core part made of black soot powder particles. By passing an electric current through this, a heating reaction is carried out over about 10 days using the Joule heat generated in the core part to synthesize silicon carbide (SiO2 + 3C → SiC + 2CO). However, the Acheson method has drawbacks such as non-uniform properties of the produced SiC. The reasons for this are that it uses a large amount of electric power of 14 MWh or more per ton of SiC, emits more than four times the weight of SiC in CO, and there is a temperature gradient from the core part towards the outer periphery.
[0003] As a method for solving these problems, Patent Document 1 discloses a method for manufacturing SiC by irradiating Si and CO2 gas (100%) as starting materials with microwaves. According to this method, SiC can be manufactured by absorbing CO2 in a relatively short time (on the order of minutes).
Prior Art Documents
Patent Documents
[0004]
Patent Document 1
Summary of the Invention
Problems to be Solved by the Invention
[0005] Previously, it was believed that under conditions using a raw material gas with a low CO2 concentration, such as combustion exhaust gas, the oxygen concentration in the raw material gas would relatively increase. As a result, the reaction Si + O2 → SiO2 would easily produce impurity SiO2 instead of the desired SiC, making efficient SiC production difficult.
[0006] The inventors conducted various tests and found that efficient SiC production is possible even when oxygen gas is present in the raw material gas, thus completing the present invention. The present invention aims to provide a method for producing SiC using a raw material gas containing oxygen. [Means for solving the problem]
[0007] The present invention includes the following embodiments. [1] A method for producing SiC, comprising heating Si powder by irradiating it with microwaves in a raw material gas containing oxygen gas and CO2 gas (except when the raw material gas consists only of air of atmospheric composition). [2] The method for producing SiC according to [1], wherein the oxygen gas concentration relative to the total volume of the raw material gas is 2 to 21 volume%. [3] The method for producing SiC according to [1] or [2], wherein the oxygen gas concentration relative to the total volume of the raw material gas is 8 to 21 volume%. [4] The method for producing SiC according to any one of [1] to [3], wherein the CO2 gas concentration relative to the total volume of the raw material gas is 10 to 15 volume percent. [5] The method for producing SiC according to any one of [1] to [4], wherein the raw material gas contains nitrogen gas, and the concentration of nitrogen gas relative to the total volume of the remaining gas after removing oxygen gas and CO2 gas from the raw material gas is 90% by volume or more. [Effects of the Invention]
[0008] According to the SiC manufacturing method of the present invention, SiC can be efficiently produced even when using a raw material gas containing oxygen. SiC can be efficiently produced by heating Si powder with microwaves in a raw material gas containing oxygen and CO2 gases. In this invention, raw material gas (exhaust gas, described later) in the low-oxygen region, excluding the oxygen gas concentration of the atmospheric composition, can be effectively utilized. [Brief explanation of the drawing]
[0009] [Figure 1] This graph shows the test results for Example 1. [Figure 2] This is a conceptual diagram of an apparatus for manufacturing SiC using the Acheson process. [Modes for carrying out the invention]
[0010] In this specification and in the claims, a numerical range represented by "~" means a numerical range where the numbers before and after "~" are the lower and upper limits. Furthermore, in this specification, when describing the content, physical properties, etc. of components by setting multiple numerical ranges in stages, the upper and lower limits forming the numerical range are not limited to the specific combinations described before and after "~", and the numerical values of the upper and lower limits forming each numerical range can be combined as appropriate.
[0011] ≪SiC Manufacturing Method≫ A first aspect of the present invention is a method for producing SiC, in which Si powder is heated by irradiating it with microwaves in a raw material gas containing oxygen gas and CO2 gas to produce SiC. SiC can be produced while contained within the Si powder used as a raw material.
[0012] In this embodiment, the term "exothermic reaction" is used to include combustion synthesis reactions in which combustion spontaneously propagates and the synthesis reaction proceeds.
[0013] By heating the Si powder in an electric field using microwave irradiation, an exothermic reaction between at least a portion of the Si powder and carbon dioxide is initiated. Because this exothermic reaction can be utilized, the energy supplied from an external source for heating can be reduced.
[0014] The reaction between silicon and carbon dioxide in the exothermic reaction of this embodiment is represented by the following reaction formula (1) and / or (2). 2Si + CO2 → SiC + SiO2 ···(1) 3Si + 2CO2 → 2SiC + SiO2 + O2 ···(2)
[0015] For the above reaction formula (1), ΔG is less than 0 within the range of 0 to 2500K under 1 atm. For the above reaction formula (2), ΔG is less than 0 at about 0 to 1200K under 1 atm. That is, reaction formulas (1) and (2) are exothermic reactions even in a high temperature range.
[0016] The SiC produced in this embodiment may be α-SiC or β-SiC. Usually, when an exothermic reaction is carried out by heat of about 500 to 1500 °C, β-SiC is generated. When β-SiC is heated at a temperature exceeding 2000 °C, it undergoes a phase transition to α-SiC.
[0017] The source (emission source) of the CO2 gas contained in the raw material gas of this embodiment is not particularly limited, and examples include thermal power plants, cement plants, steel mills, waste incineration facilities, transportation equipment, chemical manufacturing plants, pulp manufacturing plants, paper manufacturing plants, paper processing product manufacturing plants, food and beverage manufacturing plants, various machinery manufacturing plants, etc. Further, carbon dioxide in the air may be concentrated and used as needed.
[0018] The origin of the oxygen gas contained in the raw material gas of this embodiment is not particularly limited, and examples include oxygen contained in air. However, the raw material gas of this embodiment may contain air, but excludes the case where it consists only of air having the composition in the atmosphere (the case where the raw material gas is composed only of air). As the raw material gas of this embodiment, it is preferable to effectively utilize industrially emitted gas (exhaust gas). Specific examples of the exhaust gas include exhaust gas derived from the above-described sources of CO2 gas.
[0019] <00000The source gas of this embodiment may contain other gases other than CO2 gas and oxygen gas as long as the formation of SiC is not completely or significantly inhibited. Examples of other gases include gases such as nitrogen, noble gas, methane, ethylene, and carbon monoxide.
[0020] From the perspective of enhancing the production efficiency (yield) of SiC, the oxygen gas concentration relative to the total volume of the source gas used in this embodiment is preferably 2 to 21% by volume, more preferably 2 to 20% by volume, still more preferably 6 to 18% by volume, and even more preferably 8 to 16% by volume. Also, the oxygen gas concentration may be 8 to 21% by volume or 8 to 20% by volume.
[0021] From the perspective of enhancing the production efficiency (yield) of SiC in the state where oxygen gas coexists, the CO2 gas concentration relative to the total volume of the source gas used in this embodiment is preferably 6 to 30% by volume, more preferably 8 to 21% by volume, and still more preferably 10 to 15% by volume.
[0022] When the source gas used in this embodiment contains nitrogen gas, from the perspective of enhancing the production efficiency (yield) of SiC in the state where oxygen gas and CO2 gas coexist, the concentration of nitrogen gas relative to the total volume of the remaining gas obtained by removing oxygen gas and CO2 gas from the source gas is preferably 50% by volume or more, more preferably 70% by volume or more, still more preferably 90% by volume or more, and may be 100% by volume.
[0023] As an example of an embodiment of this aspect, a configuration may be adopted in which Si powder is placed in a cylindrical reaction vessel in a spread state, the cylinder is kept horizontal, the source gas is introduced from one end of the cylinder, and the source gas is discharged from the other end of the cylinder. This reaction vessel is installed in the internal space of a cavity resonator capable of resonating microwaves, and by irradiating the reaction vessel with microwaves, the Si powder in the reaction vessel can be heated in the source gas. It is preferable that the microwaves form a standing wave (stationary wave) in the resonator. The standing wave is preferably in a single mode.
[0024] The raw material gas in the reaction vessel may remain stationary, but from the viewpoint of improving the efficiency of SiC production, it is preferable to circulate the raw material gas within the reaction vessel. The flow rate of the raw material gas should be appropriately set according to the volume and shape of the reaction vessel used and the amount of Si powder. As an example, for 1 g of Si powder in a cylindrical reaction vessel, a flow rate of 0.1 to 5 L / min is preferred, and 1 to 2 L / min is more preferred.
[0025] The reaction vessel is preferably made of a material that has low microwave absorption and heat resistance; for example, a reaction vessel made of quartz is a good choice.
[0026] It is preferable that the Si powder placed in the reaction vessel has high purity. Higher purity is advantageous when purifying and separating SiC from the Si powder. From this viewpoint, the Si content relative to the total mass of the Si powder is preferably 80% by mass or more, more preferably 90% by mass or more, and even more preferably 95% by mass or more.
[0027] Other materials besides Si that may be contained in Si powder include, for example, SiO2 and SiC. When SiC is purified and separated from the Si powder used in the SiC manufacturing method of this embodiment, and the remaining Si powder is reused as a raw material, SiO2 and SiC generated in the previous use may remain in the reused Si powder.
[0028] The average particle size of the Si particles constituting the Si powder is not particularly limited, but from the viewpoint of uniform heating and efficient contact with the raw material gas, it is preferably 5 mm or less, and more preferably 1 mm or less. It is also preferable to use Si powder that has been passed through a sieve with a desired mesh size (e.g., 45 μm) (e.g., Si powder with an average particle size of 45 μm or less).
[0029] The frequency of the microwaves irradiated onto the Si powder is not particularly limited as long as it can heat the Si powder. Generally, microwave frequencies are 300 MHz to 300 GHz, and within this range, from the viewpoint of heating the Si powder quickly and relatively uniformly, for example, 0.5 GHz to 10 GHz is preferred, and 1 GHz to 5 GHz is more preferred.
[0030] The output power of the microwaves irradiated onto the Si powder is not particularly limited and can be set appropriately according to the volume and shape of the reaction vessel and the amount of Si powder. For example, from the viewpoint of rapidly and relatively uniformly heating the Si powder, 10 to 10 kW is preferred, and 100 to 1000 W is more preferred, per 1 g of Si powder in the reaction vessel. Commercially available industrial microwave heating devices are known to have an output power of, for example, 300 W to 300 kW, and such devices may be applied to the manufacturing method according to this embodiment.
[0031] The heating temperature of the Si powder by microwave irradiation should be any temperature at which the exothermic reaction that generates SiC occurs, such as 100 to 2500°C, with 300 to 2000°C being preferred.
[0032] The heating time of Si powder by microwave irradiation should be as long as necessary for the exothermic reaction that generates SiC to begin, and heating may be continued even after the exothermic reaction has started. For example, when heating 1 g of Si powder with an output of 500 W, the heating time is preferably, for example, 1 to 6000 seconds, more preferably 10 to 3000 seconds, and even more preferably 30 to 600 seconds.
[0033] After the exothermic reaction has started, heating by microwave irradiation may be stopped or continued. If combustion propagates spontaneously and the synthesis reaction proceeds, the reaction will continue even if heating is stopped. If combustion does not propagate spontaneously, microwave irradiation may be repeated two or more times, either continuously or intermittently.
[0034] From the viewpoint of uniformly heating the Si powder, the Si powder may be mixed during microwave irradiation, or the microwave irradiation may be temporarily stopped, the temperature of the Si powder may be cooled as needed, the Si powder may be mixed, and then the microwave irradiation may be resumed.
[0035] The heating of the Si powder by microwave irradiation may be carried out under atmospheric pressure, or under reduced or increased pressure in the reaction vessel. [Examples]
[0036] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to these examples.
[0037] [Example 1] A quartz cylinder (size: cross-sectional diameter 8 mm, length 70 mm) containing 0.15 g of silicon powder was placed along the central axis of a hollow resonator surrounded by metal walls. Five types of mixed gases (raw material gases containing only CO2 gas, oxygen gas, and nitrogen gas) shown in Table 1 were prepared using a mass flow controller. Under atmospheric pressure, the mixed gases were circulated through a cylinder at a flow rate of 0.2 L / min while a microwave was irradiated into the resonator at 70 W (frequency 2.45 GHz) for 1 minute to form a single-mode standing wave, and the silicon powder inside the cylinder was heated by electric field. The reaction product was allowed to stand until it reached room temperature while the mixed gases continued to flow. After standing, the reaction product was removed from the cylinder and crushed using an alumina mortar. 。 One cycle consisted of microwave irradiation followed by disintegration, and this cycle was repeated three times. From the second cycle onward, the microwave power was set to 90W. After three cycles of disintegration, the reaction products were analyzed by XRD (X-ray diffraction), and Si and SiC were quantified using the RIR (reference intensity ratio) method. Figure 1 shows the results for each of the five mixed gases used as source gases.
[0038] [Table 1]
[0039] The results from Example 1 confirmed that SiC can be produced in a proportion of 1 to 15% or more of the total mass of the reaction product, even when oxygen gas is present in the raw material gas. The reaction that occurred here was 2Si + CO2 → SiC + SiO2, and it is thought that heat of formation was generated when the by-product SiO2 was produced. This secondary heat of formation is presumed to compensate for the relatively low heat of formation derived from CO2 obtained when using the oxygen-containing raw material gas used in this example, compared to the high heat of formation obtained when using a raw material gas containing only CO2.
[0040] In the results of Example 1, the SiC production efficiency was particularly excellent when using raw material gases No. 3 (O2:10%) and No. 4 (O2:15%), where the oxygen gas concentration relative to the total volume of the raw material gas was in the range of 8-21%. [Explanation of Symbols]
[0041] 101... Fixed electrode, 102... Core made of graphite, 103... Raw material layer containing silica and carbon reducing agent
Claims
1. Oxygen gas and CO ２ A method for producing SiC, comprising heating Si powder by irradiating it with microwaves in a raw material gas containing gas (except when the raw material gas consists solely of air with an atmospheric composition) to produce SiC.
2. The method for producing SiC according to claim 1, wherein the oxygen gas concentration relative to the total volume of the raw material gas is 2 to 21 volume percent.
3. The method for producing SiC according to claim 2, wherein the oxygen gas concentration relative to the total volume of the raw material gas is 8 to 21 volume percent.
4. CO2 relative to the total volume of the raw material gas ２ The method for producing SiC according to claim 3, wherein the gas concentration is 10 to 15 volume percent.
5. The aforementioned raw material gas contains nitrogen gas. From the aforementioned raw material gas, oxygen gas and CO2 are obtained. ２ The method for producing SiC according to claim 4, wherein the concentration of nitrogen gas relative to the total volume of the remaining gas after removing the gas is 90% by volume or more.