CN120225465A - Silicon carbide powder and method for producing same - Google Patents
Silicon carbide powder and method for producing same Download PDFInfo
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- CN120225465A CN120225465A CN202380079349.6A CN202380079349A CN120225465A CN 120225465 A CN120225465 A CN 120225465A CN 202380079349 A CN202380079349 A CN 202380079349A CN 120225465 A CN120225465 A CN 120225465A
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Abstract
The purpose of the present invention is to provide a silicon carbide powder which is highly reduced in both silicon-based impurities and free carbon. The method for producing a silicon carbide powder by mixing a metal silicon powder and a carbon powder and performing self-propagating high-temperature synthesis is characterized by comprising a mixing step of mixing a metal silicon powder and a carbon powder to obtain a raw material for producing a silicon carbide, and a production step of obtaining a silicon carbide powder by performing self-propagating high-temperature synthesis of the metal silicon powder and the carbon powder after mixing in an inert gas atmosphere so that the bulk density of the metal silicon powder and the carbon powder after mixing in the mixing step is twice or more the bulk density of the metal silicon powder and the carbon powder before mixing.
Description
Technical Field
The present invention relates to a method for producing silicon carbide powder and silicon carbide powder. More specifically, the present invention relates to a method for producing a silicon carbide powder having a reduced carbon content and a reduced metal impurity content, which can be used as a raw material for a semiconductor wafer, and to a silicon carbide powder.
Background
Silicon carbide (SiC) has excellent properties such as high hardness, high strength, high heat resistance, and high thermal conductivity, and is therefore used for abrasives, refractory materials, heating elements, and the like. In recent years, demand for a raw material for SiC semiconductor wafers has increased. In producing silicon carbide powder suitable for these applications, it is particularly required that the silicon carbide powder has high purity as a raw material for SiC semiconductor wafers, a raw material for SiC sintered bodies for semiconductor production, and the like. As a cause of the decrease in purity of the silicon carbide powder, it is known that unreacted silicon and carbon derived from raw materials at the time of production exist, and that when the silicon carbide powder containing these components is used as a raw material, the product is adversely affected. For example, patent document 1 discloses that when silicon carbide powder as a raw material for producing a SiC single crystal by a sublimation recrystallization method contains unreacted carbon (free carbon), carbon enters the SiC single crystal and causes defects. Further, patent document 2 discloses that when the silicon carbide powder as a raw material for producing a silicon carbide sintered body contains free silicon, sintering is hindered or defect generation in the sintered body is caused.
As a method for producing silicon carbide, there are known (1) an acheson method in which silica sand and coke are heated at a high temperature by electric heating (for example, patent documents 1 and 3), (2) a method in which a mixture of silica and carbon powder is externally heated to undergo a reduction and carbonization reaction (for example, patent document 4), (3) a method in which a mixture of metal silicon powder and carbon powder is externally heated to undergo carbonization (for example, patent document 5), and (4) a method in which a mixture of metal silicon powder and carbon powder is preheated and then a part of a sample is ignited and burned (also referred to as a self-propagating high-temperature synthesis method or a combustion synthesis method; for example, patent document 6).
(1) The method of (2) is the most commonly used method for producing silicon carbide powder, and can be produced relatively inexpensively using a large-scale apparatus, but free silicon and free carbon are easily produced due to the presence of temperature unevenness in the furnace, and it is difficult to obtain a high-purity product. (2) The method of (2) uses high purity silica and carbon powder as raw materials, and silicon carbide powder with higher purity is easily obtained, but silica tends to produce free SiO 2 as raw materials. (3) The method of the present invention uses high purity metal silicon powder and carbon powder as raw materials, and is easy to obtain silicon carbide powder with higher purity, but silicon volatilizes during high temperature firing, and free carbon cannot be reduced to a high degree. (4) The production method of (2) can be synthesized at a lower temperature than (3), and therefore, volatilization of silicon can be suppressed, but the low reaction temperature suppresses the conversion rate into silicon carbide, and free silicon and free carbon increase. The free carbon can be removed easily by performing the heat treatment in an air atmosphere, but the silicon-based impurity requires a treatment with hydrofluoric acid or the like. When the content of free carbon is high, the content of relative silicon-based impurities increases, so that lowering the content of free carbon after the reaction is extremely important for improving the purity of the silicon carbide powder.
Prior art literature
Patent literature
Patent document 1 Japanese patent application laid-open No. 2019-151533
Patent document 2 Japanese patent laid-open No. 63-17258
Patent document 3 Japanese patent application laid-open No. 2015-157737
Patent document 4 Japanese patent application laid-open No. 2012-246165
Patent document 5 International publication No. 2012-157293
Patent document 6 Japanese patent laid-open No. 53-25300
Disclosure of Invention
Problems to be solved by the invention
The method (1) is the most commonly used method for producing silicon carbide powder, and has the advantage that it can be produced relatively inexpensively using a large-scale apparatus, and the improvement is that free silicon and free carbon are easily produced due to the presence of temperature unevenness in the furnace, and it is difficult to obtain a high-purity product. (2) The method of (2) uses high purity silica and carbon powder as raw materials, and silicon carbide powder with higher purity is easily obtained, but silica tends to produce free SiO 2 as raw materials. (3) The method of the present invention uses high purity metal silicon powder and carbon powder as raw materials, and is easy to obtain silicon carbide powder with higher purity, but silicon volatilizes during high temperature firing, and free carbon cannot be reduced to a high degree. (4) The production method of (2) can be synthesized at a lower temperature than (3), and therefore, volatilization of silicon can be suppressed, but the low reaction temperature suppresses the conversion rate into silicon carbide, and free silicon and free carbon increase.
Further, as described in patent documents 1 and 4, attempts have been made to improve purity by removing impurities from the produced silicon carbide powder, but there is a limit in improving purity.
As described above, a silicon carbide powder containing less free silicon, si-based impurities such as free SiO 2, and less free carbon is required, but a silicon carbide powder having both of them highly reduced has not been obtained so far. Accordingly, the problem of the present invention is to provide a silicon carbide powder that highly reduces both silicon-based impurities and free carbon.
Solution for solving the problem
The present inventors have conducted intensive studies to solve the above-mentioned problems. As a result of examining the important factors for the generation of free silicon and free carbon in the self-propagating high-temperature synthesis method of the above-mentioned method (4), it has been found that when these raw materials are unevenly mixed, free silicon and free carbon tend to be generated. Based on these findings, a method for producing a mixed powder of a metal silicon powder and a carbon powder by a self-propagating high-temperature synthesis method was repeatedly examined, and as a result, it was found that the present invention was completed by finding out the fact that when a metal silicon powder and a carbon powder were added to obtain a mixed powder thereof, a mixed powder with less mixing unevenness could be obtained by setting the bulk density after mixing to a predetermined range relative to the bulk density before mixing, and then a silicon carbide powder was produced using the mixed powder, whereby the content of free silicon and free carbon could be reduced and the content of metal impurities could be reduced.
Specifically, the first invention is a method for producing a silicon carbide powder by mixing a metal silicon powder and a carbon powder and producing the silicon carbide powder by self-propagating high-temperature synthesis, wherein the method comprises a mixing step of mixing the metal silicon powder and the carbon powder to obtain a raw material for producing silicon carbide, and a production step of obtaining the silicon carbide powder by self-propagating high-temperature synthesis of the metal silicon powder and the carbon powder after mixing in an inert gas atmosphere such that the bulk density of the metal silicon powder and the carbon powder after mixing in the mixing step is twice or more the bulk density of the metal silicon powder and the carbon powder before mixing.
In the first invention described above, the following scheme is preferably employed.
(1) The manufacturing process is performed in an electric furnace.
(2) The temperature in the electric furnace is 900-2050 ℃.
(3) In the mixing step, at least one selected from the group consisting of a ball mill, a planetary ball mill, a jet mill, and a vibration mill is used as a mixing means.
(4) Mixing metal silicon powder having an average particle diameter of 20 μm or less and carbon powder having a primary particle diameter of 100nm or less.
(5) Comprises a heat treatment step of heat-treating the silicon carbide powder obtained in the production step in an oxidizing atmosphere.
(6) In the heat treatment step, the heat treatment temperature is 600-1200 ℃.
The second invention is a silicon carbide powder, wherein the free carbon content is 0.001 to 0.5 mass% and the free metallic silicon content is 0.01 to 1.0 mass%.
In the second invention described above, the following scheme is preferably employed.
(7) B, al, fe, cu, mg, ni, ca has a total metal impurity content of 1ppm or less.
(8) The free carbon content is 0.001 to 0.5 mass%, the free metallic silicon is 0.01 to 1.0 mass%, and the total content of metal impurities of B, al, fe, cu, mg, ni, ca is 1ppm or less.
Effects of the invention
According to the present invention, a high-purity silicon carbide powder having a low unreacted carbon content can be obtained. As a result, when the single crystal is used as a raw material for SiC single crystal produced by sublimation recrystallization, a single crystal with few defects can be produced. In addition, as a raw material for a sintered body, a sintered body having good sinterability and few defects can be produced. The silicon carbide powder obtained by the production method of the present invention has a low content of metal impurities, and can be used as a raw material for SiC semiconductor wafers.
Detailed Description
The present invention is characterized in that, when a silicon carbide powder is produced by mixing a silicon metal powder and a carbon powder and synthesizing the silicon carbide powder by self-propagating high-temperature synthesis, the bulk density of the silicon metal powder and the carbon powder after mixing is made to be twice or more the bulk density of the silicon metal powder and the carbon powder before mixing. By the production method of the present invention, a high-purity silicon carbide powder having a low content of unreacted free silicon, free carbon, and metal impurities can be obtained. The reason why the high purity silicon carbide powder can be obtained by the production method of the present invention is not clear, but the present inventors speculate as follows. That is, the self-propagating high-temperature synthesis method has a tendency to suppress the conversion rate into silicon carbide and to increase the free silicon and free carbon due to the low reaction temperature as described above. This tendency is particularly likely to occur when the mixing of the metallic silicon powder and the carbon powder before the reaction is insufficient. The carbon powder forms agglomerates in a relatively large amount, and there is a tendency that it is difficult to mix them sufficiently to the extent that the carbon powder is added to the metal silicon powder. In the self-propagating high-temperature synthesis method, silicon powder and carbon powder are mixed and then supplied to a reaction, if the mixing is insufficient, the bulk agglomeration of the carbon powder cannot be sufficiently disintegrated, and the bulk density of the mixed powder does not change significantly. Therefore, by mixing the silicon powder and the carbon powder, the volume density of the mixed powder after mixing is increased by performing a sufficient mixing step using a mixing means such as a ball mill to collapse the carbon powder having formed aggregates and simultaneously sufficiently mixing the silicon powder and the carbon powder. Therefore, it is estimated that the silicon powder and the carbon powder can be uniformly mixed by increasing the bulk density of the mixed powder to a predetermined ratio or more relative to the bulk density before mixing. Then, it is estimated that by supplying the uniformly mixed powder to production, a high-purity silicon carbide powder having a low unreacted carbon content and a low metal impurity content can be obtained.
In the present specification, unless otherwise indicated, with respect to the numerical values A and B, the expression "A to B" means "A or more and B or less". In such terms, if a unit is added to the value B alone, the unit should be applied to the value a. The method for producing the silicon carbide powder of the present invention will be described in detail below.
< Method for producing silicon carbide powder >
[ Metal silicon powder ]
In the production method of the present invention, a mixing step is performed to mix metal silicon powder and carbon powder to obtain a mixed powder (hereinafter also referred to as "raw material for silicon carbide production"). From the standpoint of reaction yield and reduction of the content of unreacted metal silicon powder and carbon powder, it is preferable that the Si/C mixing ratio in the raw material for silicon carbide production is mixed so that the Si/C molar ratio is 0.98 or more and 1.02 or less.
Further, from the viewpoint of reactivity, the particle diameter of the metal silicon powder is preferably 2.0 μm to 50.0 μm, more preferably 4.0 μm to 35.0 μm. The average particle diameter of the metal silicon powder is preferably 20 μm or less, more preferably 2.0 μm to 10.0 μm. If the particle size of the metal silicon powder is too small, the proportion of the surface oxide film increases, and thus the Si-based impurities and free carbon of the silicon carbide powder tend to increase. If the particle size is too large, it is difficult to uniformly mix the particles with the carbon powder, and the reaction rate is not sufficiently high, so that Si-based impurities and free carbon tend to increase. When the metal silicon contains metal impurities, the metal impurity concentration of the silicon carbide powder also tends to increase, and therefore the total amount of the metal impurity content of B, al, fe, cu, mg, ni, ca in the metal silicon powder is preferably 1ppm or less, more preferably 0.1ppm or less.
[ Carbon powder ]
In the production method of the present invention, the primary particle diameter of the powder used as the carbon powder is preferably 100nm or less, more preferably 10nm or more and 100nm or less. If the particle size of the carbon powder is too small, air and moisture are easily adsorbed, and the purity of the silicon carbide powder tends to be low. If the particle size is too large, it is difficult to uniformly mix the silicon powder, the reaction rate is not sufficiently high, and Si-based impurities and free carbon tend to increase. When the carbon powder contains metal impurities, the metal impurity concentration of the silicon carbide powder tends to increase, and therefore the metal impurity concentration of the carbon powder is 50ppm or less, more preferably 10ppm or less, and still more preferably 1ppm or less. The type of the carbon powder is not particularly limited, and for example, carbon black, graphite, activated carbon, and the like can be used. The carbon black may be produced by various methods such as a furnace method (furnace black), a channel method (channel black), and an acetylene method (acetylene black).
[ Raw Material for silicon carbide production ]
When the silicon powder and the carbon powder are mixed to obtain a raw material for producing silicon carbide, it is particularly preferable to use a metal silicon powder having an average particle diameter of 20 μm or less and a carbon powder having a primary particle diameter of 100nm or less.
[ Other raw materials ]
In the raw material for silicon carbide production, silicon carbide powder may be added as a diluent for the purpose of controlling the reaction temperature or the like, in addition to the metal silicon powder and the carbon powder, within a range that does not impair the effects of the present invention. When silicon carbide powder is used as the diluent, the Si/C molar ratio of the mixed powder also containing the diluent silicon carbide powder is adjusted. The mixing amount of the silicon carbide powder is usually 50 mass% or less of the mixed powder. Further, if the silicon carbide powder as the diluent contains a large amount of metal impurities, the amount of metal impurities in the produced silicon carbide powder also increases, and therefore the metal impurities in the silicon carbide powder are preferably 200ppm or less, more preferably 100ppm or less, and still more preferably 50ppm or less. The silicon carbide powder produced by the production method of the present invention may be used as a silicon carbide powder for a diluent.
[ Mixing procedure ]
In the production method of the present invention, the method of mixing the metal silicon powder and the carbon powder to obtain the raw material for silicon carbide production requires that the bulk density of the raw material powder for silicon carbide production after mixing is twice or more the bulk density of the metal silicon powder and the carbon powder before mixing. As described above, since the carbon powder is agglomerated, the carbon powder is mixed with the silicon powder while being disintegrated, and thus the carbon powder can be uniformly mixed. The method for measuring the bulk density of the mixed raw material for producing silicon carbide was confirmed by filling the mixed raw material for producing silicon carbide into a glass container having an internal volume of 100cc and measuring the weight. In this case, the filling is performed sparsely without tapping or applying pressure. The bulk densities before mixing were calculated by calculating the bulk densities of the metal silicon powder and the carbon powder, respectively, in the same manner as described above, and then weighted-averaging the bulk densities of the powders according to the mixing ratio. In the production method of the present invention, the bulk density of the metal silicon powder and the carbon powder after mixing may be 2 times or more, preferably 2 times or more and 10 times or less, and particularly preferably 2 times or more and 8 times or less, of the bulk density of the metal silicon powder and the carbon powder before mixing.
As a method for mixing the metal silicon powder and the carbon powder in the production method of the present invention, specifically, preferable means include mixing means by a stirrer, a mixer, and a ball mill. In particular, a method of applying a load to the raw materials at the time of mixing such as a ball mill can increase the homogeneity of the metallic silicon powder and the carbon powder, and is more preferable. For example, in the case of mixing by using a ball mill, the material of the container, ball, or the like for filling the metal silicon powder and the carbon powder is preferably a material which is not easily worn during mixing and is mixed with the raw material, and more preferably high purity silicon carbide. The spherical diameter is preferably 3 to 20mm, and the size of the spherical diameter is selected so that the metal silicon powder and the carbon powder are homogeneously mixed. The rotation speed may be arbitrarily selected, and is preferably 50 to 500rpm. In addition, as in the case of the method in which the raw materials are subjected to a load during the mixing in the ball mill, if the mixing is performed in the presence of oxygen, the newly formed surface of the silicon metal may be oxidized, and there is a concern that the Si-based impurities and free carbon of the silicon carbide powder may increase, so that the mixing is preferably performed in a non-oxidizing atmosphere (in particular, in a rare gas atmosphere such as argon gas), and the mixture is cooled to room temperature and taken out, thereby suppressing oxidation.
[ Manufacturing Process ]
In the production method of the present invention, a production process is performed in which the silicon carbide powder is obtained by self-propagating high-temperature synthesis of the raw material for silicon carbide production. The apparatus is not particularly limited as long as it is capable of self-propagating high-temperature synthesis, and it is preferable to charge the raw material for silicon carbide production into an electric furnace, heat the inside of the electric furnace, and ignite a part of the raw material for silicon carbide production as needed, thereby producing silicon carbide powder by self-propagating high-temperature synthesis.
When silicon carbide powder is produced by the above method, if oxygen is present in the electric furnace, by-products such as silicon oxide are produced by side reactions. In addition, when nitrogen is present in the electric furnace, the nitrogen content in the generated silicon carbide increases. Therefore, the production process is preferably performed under an inert atmosphere or under reduced pressure. The inert atmosphere may be, for example, a rare gas such as helium, neon, or argon. The pressure when the reaction is carried out under an inert atmosphere is not particularly limited, and the reaction may be carried out under an atmospheric pressure or a pressurized atmosphere. After the raw material is placed in the electric furnace, the pressure in the electric furnace is preferably reduced to 0.5Pa or more and 10Pa or less in order to remove oxygen, nitrogen, moisture, and the like in the electric furnace, and then the step of introducing an inert gas and repressing the pressure to a predetermined pressure is preferably performed at least once or more before the temperature of the electric furnace is raised. After the reaction vessel is replaced with the inert gas, the pressure in the reaction vessel may be reduced again to 0.5Pa or more and 10Pa or less, and the raw material for silicon carbide production may be baked by heating to a temperature lower than the production temperature.
In addition, as the heating temperature in the electric furnace, the temperature in the electric furnace is preferably heated to 900 to 2050 ℃, more preferably 1000 to 1800 ℃, and particularly preferably 1200 to 1500 ℃ from the viewpoint of reliably carrying out the silicon carbide production reaction.
The heating method is not particularly limited, and for example, a mixed powder filled in a heat-resistant reaction vessel made of ceramic, graphite or the like is placed in an electric furnace, the atmosphere is adjusted, and the temperature in the electric furnace is raised from room temperature to a production temperature. The heating time is not particularly limited, and it is preferable to heat up over 1 hour or more because it is easy to heat up uniformly. The upper limit of the heating time is not particularly limited, but is preferably 24 hours or less from the viewpoint of efficient production. The self-propagating high-temperature synthesis reaction may be started by ignition immediately after the temperature is raised to the manufacturing temperature, or the self-propagating high-temperature synthesis reaction may be started by ignition after the self-propagating high-temperature synthesis reaction is temporarily maintained at the manufacturing temperature. In the case of starting the self-propagating high-temperature synthesis reaction by once holding at the production temperature and then igniting, the holding time at the heating temperature is preferably 24 hours or less from the viewpoint of high-efficiency production. In addition, a high manufacturing temperature may be set, and self-propagating high-temperature synthesis reaction may be initiated by spontaneous combustion.
[ Heat treatment Process ]
In the production method of the present invention, a heat treatment step may be performed as needed, and the silicon carbide powder obtained in the production step may be subjected to a heat treatment in an oxidizing atmosphere. By the above-described production steps, the silicon powder and carbon powder in the raw material for producing silicon carbide are almost consumed, but a part of unreacted silicon powder and carbon powder may remain. Therefore, by heat-treating the silicon carbide powder after the production process in an oxidizing atmosphere, the residual carbon is oxidized and converted into carbon monoxide and carbon dioxide, and thus a part of the unreacted carbon powder can be consumed. In the production method of the present invention, the heat treatment step may be continued after the production step, or the silicon carbide powder obtained after the production step may be filled into a separate heating furnace to be heat-treated.
In the heat treatment step, an oxidizing atmosphere may be, for example, air, oxygen, or other oxidizing gas. The pressure is not particularly limited, and is preferably atmospheric pressure. The air may be circulated in the heating furnace using a blower, a fan, or the like.
The temperature in the heat treatment step is preferably 600 to 1200 ℃, more preferably 600 to 1000 ℃, and particularly preferably 700 to 900 ℃. If the heating temperature is below the range, oxidation of residual carbon does not proceed sufficiently, and if the heating temperature is above the range, oxidation of silicon carbide proceeds significantly.
The heating time is not particularly limited as long as the heating time is maintained until the carbon powder in the silicon carbide powder obtained in the production process is reacted and completely consumed, and may be, for example, 1 to 10 hours.
[ Pulverizing Process ]
In the production method of the present invention, after the heating step, the particles may be pulverized as needed to adjust the particle size. The pulverizing method is not particularly limited, and preferable examples thereof include pulverization by a vibration ball mill, a rotary ball mill, and a jet mill. The material of the container, the ball, etc. may be a material which is not easily abraded and mixed with the raw material, and more preferably, high purity silicon carbide. Even if impurities are mixed, the impurities can be removed by a cleaning step described later.
[ Cleaning Process ]
In the production method of the present invention, a cleaning treatment may be performed as needed to reduce metal impurities and the like. The washing may be performed using an acidic aqueous solution or an alkaline aqueous solution, and may be performed according to the element to be reduced. For example, hydrochloric acid, hydrofluoric acid, nitric acid, sulfuric acid, phosphoric acid may be used as the acidic aqueous solution, and an aqueous sodium hydroxide solution, an aqueous potassium hydroxide solution, or the like may be used as the alkaline aqueous solution. The cleaning solution may be heated to promote dissolution if desired.
< Silicon carbide powder >
By the production method of the present invention, a high-purity silicon carbide powder having a low free carbon and a low metal silicon content can be obtained. Specifically, the free carbon content of the obtainable silicon carbide powder is 0.5 mass% or less and 1.0 mass% or less, and preferably 0.001 to 0.5 mass% and 0.01 to 1.0 mass% of free metal silicon. The silicon carbide powder of the present invention has extremely low carbon content and is particularly suitable for use in semiconductor applications requiring high purity. The free carbon amount can be calculated from the weight reduction before and after the heat treatment step by performing the heat treatment step. Further, by performing the heating step after the above-described production step, the silicon carbide powder can be obtained with a carbon content of 0.05 mass% or less, preferably 0.001 to 0.05 mass%.
Further, according to the production method of the present invention, a high-purity silicon carbide powder having a total metal impurity content of B, al, fe, cu, mg, ni, ca of 1ppm or less can be obtained. The content of metal impurities can be determined by glow discharge mass spectrometry.
< Use of silicon carbide powder >
The use of the silicon carbide powder of the present invention is not particularly limited, and since Si-based impurities and free carbon are small, the silicon carbide powder can be suitably used as a raw material for SiC single crystals produced by a sublimation recrystallization method, a raw material for SiC sintered bodies for semiconductor production, and the like, which are particularly required to be high-purity silicon carbide powder.
Examples
Hereinafter, the present invention will be described more specifically, but the present invention is not limited to these examples. The physical properties of examples and comparative examples were measured by the following methods.
(1) Concentration of free carbon
The free carbon concentration was calculated from the weight reduction in the heating step. Specifically, the following is performed. About 10g of the silicon carbide powder produced by the production method of the present invention was placed in an aluminum/silica porcelain container having a capacity of 28cc, the weight of which was measured in advance, and the weight was measured. After the porcelain vessel was placed in an electric furnace, the temperature was raised to 800 ℃ under atmospheric pressure, and the vessel was maintained for 2 hours after reaching 800 ℃. Then, the weight was measured after cooling to room temperature, and the free carbon concentration was calculated by dividing the reduced weight before and after the heating step by the weight of the silicon carbide powder supplied after the heating step.
(2) Concentration of free silicon
The free silicon concentration was determined from the integrated intensity ratio of the 3C silicon carbide (111) peak to the metal silicon (111) peak in the 2θ measurement of X-ray diffraction. Samples were obtained by adding 0.1 to 5.0 mass% of metallic silicon to silicon carbide powder in advance, and samples were prepared at 5 points, and X-ray diffraction measurement (SmartLab manufactured by Rigaku) was performed to obtain a calibration curve of the integrated intensity ratio of the 3C silicon carbide (111) peak to the metallic silicon (111) peak with respect to the metallic silicon content in the 2θ measurement of X-ray diffraction. The integrated intensity ratio of the 3C type silicon carbide (111) peak to the metal silicon (111) peak in the 2θ measurement of the X-ray diffraction of the manufactured silicon carbide powder was substituted into the correction curve, thereby calculating the free silicon concentration in the silicon carbide powder.
(3) Metal impurity amount
The metal impurity amount is the total amount of alkali metal, alkaline earth metal and transition metal with atomic numbers of 3-92 measured by glow discharge mass spectrometry (ThermoFisher Scientific, ELEMENT GD PLUS).
(4) Bulk density of
The bulk density after mixing the metal silicon powder and the carbon powder was calculated by filling the mixed powder in a measuring cylinder having a capacity of 100cc to a scale of 100cc and taking the measured weight as the weight per 100 cc. When the mixed powder is filled, the mixed powder is put into a measuring cylinder placed on an electronic balance by using a medicine spoon, and a sparse filling state is obtained in which no special pressure is applied to the mixed powder.
The bulk density before mixing is obtained by calculating the bulk densities of the metal silicon powder and the carbon powder in the same manner as the bulk density measurement method of the mixed powder, and weight-averaging the bulk densities of the powders according to the mixing ratio.
(5) Particle diameter, average particle diameter and primary particle diameter of carbon powder of metal silicon powder
The particle size and the average particle size of the metal silicon powder were measured by a laser diffraction/scattering particle size measuring apparatus (PARTICA LA-950V2 manufactured by horiba ltd). Ethanol is used for the dispersion medium. The median diameter (D50) obtained was measured as the particle diameter.
The primary particle diameter of the carbon powder was obtained by measuring the length of any particle from an observation image obtained by using a scanning electron microscope (FE-SEM JSM-7800Prime, japan electronics system) at an observation magnification of 10 ten thousand times.
Example 1]
Metal silicon powder having an average particle diameter of 5.0 mu m, B, al, fe, cu, mg, ni, ca and a total amount of metal impurity content of 0.51ppm and acetylene black having a particle diameter of 30nm as a carbon powder were weighed in a molar ratio of 1.00:1.00 (Si/C molar ratio of 1.00) and charged into a ball mill pot. The bulk density before mixing was 0.08g/cm 3. The mixture was mixed at 125rpm for 30 minutes using a ball mill to obtain a raw material for silicon carbide production having a bulk density of 0.35g/cm 3 (the bulk density after mixing was 4.28 times that before mixing). The atmosphere in the mixture was argon, and after cooling, the atmosphere was replaced with air. The grinding ball is made of silicon carbide.
The mixed powder was filled into a graphite crucible and set in an electric furnace. The pressure in the furnace was reduced to 0.5Pa or more and 10Pa or less, and then the operation of introducing argon gas having a purity of 99.999% and repressing the pressure to normal pressure was repeated 2 times. Argon was flowed through the electric furnace at a flow rate of 5 liters/min while maintaining the atmospheric pressure, while raising the temperature from room temperature to 1200 ℃ for 3 hours. Silicon carbide powder is obtained by self-propagating high temperature synthesis with spontaneous combustion during the temperature rise. The free carbon content of silicon carbide is 0.01 mass% and the free silicon content is 0.1 mass% or less. The evaluation results of the obtained silicon carbide powder are shown in table 1.
Example 2]
Silicon carbide powder was synthesized in the same manner as in example 1, except that the mixing time in the ball mill was 60 minutes. The bulk density of the raw material for producing silicon carbide after mixing was 0.48g/cm 3 (the bulk density after mixing was 5.93 times that before mixing). The free carbon content of the obtained silicon carbide was 0.01 mass% or less, and the free silicon content was 0.1 mass% or less. The evaluation results of the obtained silicon carbide powder are shown in table 1.
Example 3]
Silicon carbide powder was synthesized in the same manner as in example 1, except that the mixing time in the ball mill was 10 minutes. The bulk density of the raw material for producing silicon carbide after mixing was 0.17g/cm 3 (the bulk density after mixing was 2.11 times that before mixing). The free carbon content of the obtained silicon carbide was 0.31 mass% and the free silicon content was 0.7 mass%. The evaluation results of the obtained silicon carbide powder are shown in table 1.
Example 4]
Silicon carbide powder produced in the same manner as in example 1 was filled into an aluminum/silicon dioxide porcelain vessel and placed in an electric furnace. The furnace was kept under atmospheric air and normal pressure, and the temperature was raised to 800℃for 1 hour, and then maintained at 800℃for 2 hours. After maintaining for 2 hours, the mixture was cooled to room temperature to obtain silicon carbide powder. The free carbon content of the obtained silicon carbide was 0.01 mass% or less, and the free silicon content was 0.1 mass% or less. The evaluation results of the obtained silicon carbide powder are shown in table 1.
Comparative example 1]
Silicon carbide powder was synthesized in the same manner as in example 1, except that the mixing time in the ball mill was 5 minutes. The bulk density of the raw material for producing silicon carbide after mixing was 0.12g/cm 3 (the bulk density after mixing was 1.44 times that before mixing). The free carbon content of the obtained silicon carbide was 1.09 mass% and the free silicon content was 2.5 mass%. The evaluation results of the obtained silicon carbide powder are shown in table 1.
Comparative example 2]
The metal silicon powder and acetylene black having a particle diameter of 30nm as a carbon powder were weighed in a molar ratio of 1.00:1.00 (Si/C molar ratio of 1.00), and put into a polyethylene bag with a zipper. Silicon carbide powder was synthesized in the same manner as in example 1, except that a polyethylene bag was shaken up and down for 5 minutes to mix metal silicon powder and carbon powder to obtain a raw material for silicon carbide production. The bulk density of the raw material for producing silicon carbide after mixing was 0.08g/cm 3 (the bulk density after mixing was 1.02 times that before mixing). The free carbon content of the obtained silicon carbide was 1.79 mass% and the free silicon content was 4.2 mass%. The evaluation results of the obtained silicon carbide powder are shown in table 1.
Comparative example 3]
Silicon carbide powder produced in the same manner as in comparative example 1 was charged into an aluminum/silicon dioxide porcelain vessel and placed in an electric furnace. The furnace was kept under atmospheric air and normal pressure, and the temperature was raised to 800℃for 1 hour, and then maintained at 800℃for 2 hours. After maintaining for 2 hours, the mixture was cooled to room temperature to obtain silicon carbide powder. The free carbon content of the obtained silicon carbide was 0.01 mass%, and the free silicon content was 2.5 mass%. The evaluation results of the obtained silicon carbide powder are shown in table 1.
TABLE 1
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| JP2009173501A (en) * | 2008-01-28 | 2009-08-06 | Bridgestone Corp | Method of manufacturing high purity silicon carbide powder for silicon carbide single crystal manufacture and silicon carbide single crystal |
| JP2012240869A (en) | 2011-05-18 | 2012-12-10 | Sumitomo Electric Ind Ltd | Silicon carbide powder and method for producing silicon carbide powder |
| JP2014122131A (en) * | 2012-12-21 | 2014-07-03 | Taiheiyo Cement Corp | Production method of high-purity silicon carbide powder |
| JP6184732B2 (en) * | 2013-04-26 | 2017-08-23 | 株式会社トクヤマ | Silicon carbide granules and method for producing the same |
| CA3199812A1 (en) * | 2014-09-25 | 2016-03-31 | Pallidus, Inc. | Polysilocarb based silicon carbide materials, applications and devices |
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