JP2018002502A - Manufacturing method of silicon carbide powder - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a manufacturing method capable of efficiently removing impurities and capable of manufacturing high-purity silicon carbide powder. SOLUTION: A first step of obtaining chloride-containing amorphous silica by immersing amorphous porous silica having a porosity of 10 to 50% in an aqueous solution of chloride of an alkali metal or hydrochloric acid, and chloride-containing amorphous silica, A second step of mixing with a carbonaceous raw material and heating, and in the first step, the alkali metal is adjusted so that chlorine in the amorphous porous silica has a chlorine content represented by the following formula (1) or more. The method for producing a silicon carbide powder by immersing it in an aqueous chloride solution or hydrochloric acid. ##EQU1## [C: the content (mg/kg) of each specific metal impurity element in the porous silica, in the order of increasing content, up to a predetermined rank, k: of each metal impurity element Mass ratio of chlorine to metal impurity elements in chloride] [Selection diagram] None

Description

  The present invention relates to a method for producing silicon carbide powder, and more specifically to a production method for obtaining high-purity silicon carbide powder applicable to raw materials for electronic materials such as power semiconductors.

  Silicon carbide (SiC) has been widely used as industrial materials such as polishing / grinding materials, ceramic sintered bodies, and conductive materials. In particular, recently, high-purity silicon carbide has been demanded as a single crystal material used for power semiconductors and the like due to social backgrounds such as an increase in energy saving orientation and the expectation for utilization of natural regenerative energy by denuclearization.

  As a technique for industrially mass-producing silicon carbide, a siliceous raw material containing silicon (Si) (for example, cinnabar) and a carbonaceous raw material containing carbon (C) (for example, petroleum coke) are used as raw materials, and 1600 ° C. in an Atchison furnace. A method for producing silicon carbide by direct reduction reaction by heating as described above is known. In the conventional production using the Atchison furnace, the impurity content in the raw material is high, and it is difficult to control the impurities, so that high-purity silicon carbide cannot be produced.

  Therefore, as a technique for removing impurities from the silicon carbide powder, a technique for removing with an acid and a technique for adding an alkali metal chloride such as sodium chloride are known. The technology for removing with acid is a technology for dissolving and removing impurities in acid by immersing silicon carbide powder in a mixed acid in which hydrofluoric acid and nitric acid are mixed at a certain ratio (see, for example, Patent Document 1). . In order to dissolve the impurity in the acid, the impurity needs to contact the acid. For this reason, although this technique can remove the impurity which exists in the particle | grain surface of a silicon carbide, the impurity taken in the inside of a particle | grain cannot be removed, and it cannot fully refine.

  On the other hand, the technique of adding chlorides such as sodium chloride is to generate chlorides of impurity elements contained in silica and carbon, which are raw materials of silicon carbide, using chlorine gas generated from chlorides, and volatilize these chlorides. This is a technique for reducing the amount of impurities in silicon carbide (see, for example, Non-Patent Document 1). In the present technology, the amount of chloride added is determined according to the amount of impurities in the raw material. In order to obtain silicon carbide with high purity, a large amount of chloride is required. As a result, a large amount of chlorine gas is generated, and there is a problem in the working environment. There was a limit to reduction.

  On the other hand, in recent years, with higher performance of power semiconductors, there has been a demand for higher purity of silicon carbide powder. Therefore, as a method for producing silicon carbide of higher purity, a solid content containing a mixture of silica and carbon is mixed with an aqueous solution containing an alkali metal or alkaline earth metal chloride, and the resulting mixture is solidified. There has been proposed a production method in which liquid separation is performed and the obtained solid content (containing a mixture of silica and carbon and an alkali metal or alkaline earth metal chloride) is heated (for example, see Patent Document 2). ). According to this manufacturing method, silicon carbide powder having a higher purity than that of the prior art can be obtained.

JP 2000-281328 A JP 2014-125407 A

Japan Society for the Promotion of Science, High Temperature Ceramics Material 124th Committee, “Recent Developments of New SiC-Based Ceramic Materials”, Uchida Otsukuraku, February 28, 2001, p121

  However, in the production method described in Patent Document 2, carbon having higher adsorption ability than silica is interposed, and the chloride cannot be uniformly present. As a result, the amount of chloride added must be increased, The above problem was not solved. The same applies when hydrochloric acid is added instead of chloride.

  Accordingly, an object of the present invention is to provide a method for producing silicon carbide powder including a step of removing impurities of silicon carbide powder by addition of alkali metal chloride or hydrochloric acid, even if the addition amount of chloride or hydrochloric acid is small. An object of the present invention is to provide a production method capable of efficiently removing impurities and producing a high-purity silicon carbide powder.

The method for producing silicon carbide powder of the present invention includes a first step of immersing amorphous porous silica having a porosity of 10 to 50% in an alkali metal chloride aqueous solution or hydrochloric acid to obtain chloride-containing amorphous silica, and A second step of mixing and heating the chloride-containing amorphous silica and the carbonaceous raw material,
In the first step, the amorphous porous silica is immersed in the alkali metal chloride aqueous solution or hydrochloric acid so that the chlorine content is not less than the chlorine content represented by the following formula (1).

[However, C is a metal impurity element of the 3rd to 4th periods and 2 (2A group)-13 (3B) group in the said amorphous porous silica, Comprising: The content (mg / kg) of each element up to the upper predetermined order is shown, k is the mass ratio of chlorine to the metal impurity element in the chloride of each metal impurity element, Σ is the content of the metal impurity element Indicates that the values of each kC are added. ]
Here, the third period, the fourth period, the 2 (2A group), and the 13 (3B) group are periods and groups in the long-period periodic table.

  In the method for producing silicon carbide powder of the present invention, amorphous porous silica having a predetermined porosity is used, so that the internal voids can be impregnated with chloride or hydrochloric acid, and chloride or hydrochloric acid can be uniformly introduced into the raw material. Hydrochloric acid can be dispersed. Therefore, impurities can be effectively removed even with a small amount of chloride or hydrochloric acid. In addition, since the amount of chloride or hydrochloric acid is very small, a large amount of white smoke resulting from them can be suppressed, and firing in consideration of the environment becomes possible. Furthermore, unlike the invention described in Japanese Patent Application Laid-Open No. 2014-125407, in which sodium chloride is mixed with carbon-containing silica, there is no carbon having higher adsorption capacity than silica, so that chloride or hydrochloric acid is uniformly present in the silica particles. As a result, the effect is exhibited even in a smaller amount than the invention described in the above publication.

  The method for producing silicon carbide powder of the present invention includes a first step of immersing amorphous porous silica having a porosity of 10 to 50% in an alkali metal chloride aqueous solution or hydrochloric acid to obtain chloride-containing amorphous silica, and A second step of mixing and heating the chloride-containing amorphous silica and a carbonaceous raw material, wherein the chlorine in the amorphous porous silica is represented by the following formula (1) in the first step: It is characterized by immersing in the alkali metal chloride aqueous solution or hydrochloric acid so as to be more than the content.

In the formula (1), C is a metal impurity element in the third period to the fourth period and in the 2 (group 2A) to group 13 (3B) group in the amorphous porous silica, Indicates the content (mg / kg) of each element up to the upper predetermined order in the descending order, k indicates the mass ratio of chlorine to the metal impurity element in the chloride of each metal impurity element, and Σ indicates the metal It shows that the value of each kC of the impurity element is added.
Below, each process of the manufacturing method of this invention is demonstrated.

[First step]
In the first step, an amorphous porous silica having a porosity of 10 to 50% (hereinafter also simply referred to as “porous silica”) is also referred to as an alkali metal chloride aqueous solution (hereinafter simply referred to as “chloride aqueous solution”). Or soaking in hydrochloric acid to obtain chloride-containing amorphous silica. First, each component used in this step will be described.

(Amorphous porous silica)
Amorphous porous silica having a porosity of 10 to 50% is used. By using one having a porosity of 10 to 50%, a sufficient amount of an aqueous chloride solution or hydrochloric acid can be impregnated in the void, and chloride and the like can be uniformly dispersed in the raw material. As a result, impurities can be sufficiently removed even with a very small amount of chloride aqueous solution. When the porosity of the porous silica is less than 10%, the amount of the chloride aqueous solution or hydrochloric acid to be impregnated becomes small, and as a result, the impurity removal effect of silicon carbide cannot be obtained. If it exceeds 50%, the amount of the chloride aqueous solution increases, and a predetermined amount or more of the chloride aqueous solution or the like is impregnated, leading to deterioration of the working environment. The porosity is preferably 12.5 to 40%, and more preferably 15 to 35%.

BET specific surface area of porous silica is preferably 400~50000cm ² / g, more preferably 600~25000cm ² / g. When the BET specific surface area is 400 to 50000 cm ² / g, since the voids in the porous silica are fine, an aqueous chloride solution or the like can be effectively and uniformly impregnated in the porous silica.

(Alkali metal chloride aqueous solution or hydrochloric acid)
Examples of the alkali metal chloride include lithium chloride, sodium chloride, and potassium chloride. Among these, sodium chloride and potassium chloride are preferably used. When porous silica is immersed in these aqueous chloride solutions or hydrochloric acid, the aqueous porous chloride solution or hydrochloric acid is impregnated in the voids of the porous silica.

  The above chloride aqueous solution or hydrochloric acid adjusts conditions such as concentration and immersion time so that the chlorine content of the porous silica has the chlorine content calculated by the above formula (1). By applying the aqueous chloride solution or hydrochloric acid to the porous silica in this way, the amorphous porous silica voids can be impregnated with a sufficient amount of chloride (chlorine ions) to remove impurities.

  In the above formula (1), C is the third to fourth period in the porous silica, and is a metal impurity element of 2 (2A group) to 13 (3B) group, and in descending order of content. The content (mg / kg) of each element up to the upper predetermined order. The metal impurity element is Mg, Al, Ca, Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, or Ga.

  In the content (mg / kg) of each of the elements up to the upper predetermined rank in order of increasing content, the predetermined rank is preferably up to 10th, more preferably up to 8th, and up to 5th. More preferably.

  If the metal impurity element and its content in the porous silica used as a raw material are known, C can be obtained for each content concentration based on each element in the upper predetermined order and its content in descending order of content. On the other hand, when the metal impurity element and the content thereof are unknown, the porous silica is dissolved with a mixed acid of hydrofluoric acid and nitric acid, and then measured by ICP-AES analysis method. Each content concentration C can be obtained based on each element and its content.

  k is a coefficient for calculating the chlorine content necessary for removing each metal impurity element, and indicates the mass ratio of chlorine to the metal impurity element in the chloride of each metal impurity element. That is, the chlorine content (mg) necessary to remove the metal impurity element in the porous silica by multiplying k, which represents the content (mg / kg) of the predetermined metal impurity element in the porous silica, by k. / Kg) is calculated.

  Specifically, k is calculated by the equation: (atomic weight of chlorine × number of chlorine atoms in one molecule of chloride of metal impurity element) / atomic weight of metal impurity element. For example, in the case of aluminum chloride, k = 35.45 × 3 / 26.98 = 3.94, and in the case of calcium chloride, k = 35.45 × 2 / 40.08 = 1.77.

  In the present invention, the porous silica is immersed in an aqueous alkali metal chloride solution or hydrochloric acid so that the chlorine content in the porous silica is not less than the chlorine content represented by the following formula (1). The upper limit of chlorine is preferably 1.5 times the chlorine content calculated by the formula (1), more preferably 1.2 times. If the chlorine content exceeds 1.5 times, the amount of generated chlorine increases, which may cause environmental load problems.

  In the present invention, after preparing the porous silica as described above and the chloride aqueous solution or hydrochloric acid whose concentration is adjusted as described above, the porous silica is immersed in the chloride aqueous solution or hydrochloric acid to be chlorinated. A product-containing amorphous silica is obtained. The immersion time for immersing the porous silica in the chloride aqueous solution or hydrochloric acid is preferably 1 to 3 hours, and the alkali metal chloride aqueous solution or hydrochloric acid is at room temperature (for example, 20 ° C.) or higher. Good.

(Carbonaceous raw material)
Examples of the carbonaceous raw material include crystalline carbon such as natural graphite and artificial graphite, and amorphous carbon such as carbon black, coke, and activated carbon. These are used singly or in combination of two or more. The average particle size of the carbonaceous raw material is appropriately selected depending on the environment during firing, the state of the raw material (crystalline or amorphous), and the reactivity with the aforementioned porous silica.

[Second step]
In the second step, the chloride-containing amorphous silica and the carbonaceous raw material are mixed to prepare a raw material for producing silicon carbide. At this time, the mixing method of the raw materials is arbitrary, and both wet mixing and dry mixing can be employed. The mixing molar ratio (C / Si) of chloride-containing amorphous silica and carbonaceous raw material during mixing is selected in consideration of the environment during firing, the particle size and reactivity of the raw material for silicon carbide production. To do. The term “optimum” as used herein means improving the yield of silicon carbide obtained by firing, and reducing the remaining amount of unreacted chloride-containing amorphous silica and carbonaceous raw material.

  The obtained mixed powder (raw material for producing silicon carbide) is put into an Atchison furnace and baked at 2500 ° C. or higher to obtain bulk silicon carbide.

  The firing atmosphere is preferably a reducing atmosphere. This is because the yield of silicon carbide decreases when fired in an atmosphere with low reducing ability.

By using the Atchison furnace, the reaction represented by the following reaction formula (1) occurs, and a lump made of silicon carbide is obtained.
SiO ₂ + 3C → SiC + 2CO Reaction formula (1)

  When the heating element in the Atchison furnace is heated, silicon carbide is generated from the raw material in the vicinity of the heating element and grows outward. The aspect of silicon carbide is different between the central part and the outer side of the Atchison furnace. The central part has more α-SiC and the outer part has more β-SiC. In the present invention, the proportion of α-SiC in the central portion can be increased.

  The type of the heating element in the Atchison furnace is not particularly limited as long as it can conduct electricity, and examples thereof include graphite powder and carbon rod.

  The form of the substance constituting the heating element is not particularly limited, and examples thereof include powder and lump. In the Atchison furnace, the heating element is preferably arranged near the center of the raw material for producing silicon carbide, but can be appropriately arranged according to the shape of the growing ingot. For example, the heating element is provided so as to have a rod-like shape as a whole so as to connect electrode cores provided at both ends in the energizing direction of the Atchison furnace. Examples of the rod shape here include a columnar shape and a prismatic shape. The electrical resistance of the heating element is determined according to the capability of the power source.

After energization, a lump of silicon carbide is generated in the furnace. Next, air cooling is performed until the inside of the furnace reaches room temperature, and then the obtained mass made of silicon carbide is pulverized. The pulverization method is not particularly limited as long as it is easy to handle, and examples thereof include a method of pulverization using a ball mill, a disk grinder or the like as a pulverizer.
Finally, classification is performed using a sieve according to the desired particle size. For example, by using a sieve having an opening of 2000 μm and 100 μm, the particle size can be classified into a range of 100 to 2000 μm.

  EXAMPLES Hereinafter, the present invention will be described more specifically with reference to examples. However, the present invention is not limited to the following examples.

[Example 1]
300 kg of water glass (water glass No. 3 manufactured by Fuji Chemical Co., Ltd. (SiO ₂ / Na ₂ O (molar ratio) = 3.2)) 12.5 vol% sulfuric acid (concentrated sulfuric acid (98%) manufactured by Sakai Sangyo Co., Ltd.) The solution was added dropwise to 1300 L to obtain amorphous silica. This amorphous silica was further immersed in 720 L of 12.5 vol% sulfuric acid for 6 hours to remove metal element impurities, washed with 3000 L of industrial water, and then dried for 80 hours in a drier to obtain high-purity amorphous porous 40 kg of silica was synthesized. The porosity of this porous silica was 15%, the BET specific surface area was 710 cm ² / g, and the chemical composition was as shown in Table 1. From the amount of impurities of the porous silica and the formula (1) according to the present invention, a 2.0 mass% sodium chloride aqueous solution (sodium chloride: industrial use) so that the chlorine content is 7.6 mg in 1 kg of the porous silica. And 99.5% purity manufactured by Manac Co., Ltd.) for 1 hour. After dipping, the product was dried for 80 hours with a dryer to synthesize chloride-containing amorphous silica.

  The raw material mixed with the above chloride-containing amorphous silica and amorphous carbon (manufactured by SEAST V Tokai Carbon Co., Ltd.) at a mass ratio of 2/1 and graphite for a heating element are filled in an Atchison furnace at 1500 ° C. to 2500 ° C. Energization was performed for 24 hours to obtain massive silicon carbide. The obtained silicon carbide lump was collected for each of the left part, the central part, and the right part and pulverized to 2 mm or less with a top grinder to obtain silicon carbide powder for each part. The content of impurities in the obtained silicon carbide powder was measured by ICP-AES analysis by the pressurized acid analysis method described in “JIS R 1616”. The results are shown in Table 5.

[Example 2]
From the amount of impurities of the porous silica used in Example 1 and the formula (1) according to the present invention, hydrochloric acid (industrial (35 wt%) is used so that the chlorine content is 7.6 mg in 1 kg of amorphous silica in Example 1. ) Toa Gosei Co., Ltd.) for 5 hours. After dipping, the product was dried for 80 hours with a dryer to synthesize chloride-containing amorphous silica.

  Using the chloride-containing amorphous silica, high-purity silicon carbide powder was obtained in the same manner as in Example 1. The content of impurities in the obtained silicon carbide powder was measured by ICP-AES analysis by the pressurized acid analysis method described in “JIS R 1616”. The results are shown in Table 5.

[Example 3]
Commercial amorphous silica (made by Onoda Chemical Industry Co., Ltd.) having a porosity of 35% and a BET specific surface area of 5 m ² / g contains chlorine in 1 kg of amorphous silica from the amount of amorphous silica impurities and the formula (1) according to the present invention. It was immersed in a 25% by mass aqueous sodium chloride solution for 1 hour so that the amount was 900 mg. After the immersion, the product was dried at 120 ° C. with a dryer for 80 hours to obtain a chloride-containing amorphous silica. Table 2 shows the content concentrations of the top five elements in the commercially available amorphous silica used in this experiment.

  A raw material in which the chloride-containing amorphous silica and amorphous carbon are mixed so as to have a mass ratio of 2/1 and graphite for a heating element are filled in an Atchison furnace and energized at 1500 ° C. to 2500 ° C. for 24 hours to form a massive carbonized carbon. Silicon was obtained. The obtained silicon carbide lump was collected for each of the left part, the central part, and the right part and pulverized to 2 mm or less with a top grinder to obtain silicon carbide powder. The content of impurities in the obtained silicon carbide powder was measured by ICP-AES analysis by the pressurized acid analysis method described in “JIS R 1616”. The results are shown in Table 5.

[Comparative Example 1]
Achison furnace filled with amorphous silica (containing no chloride) synthesized in Example 1, raw material in which amorphous carbon is mixed so as to have a mass ratio of 2/1, and graphite for a heating element is filled at 1500 ° C. to 2500 ° C. Energization was conducted at 0 ° C. for 24 hours to obtain massive silicon carbide. The obtained silicon carbide lump was pulverized by 2 mm or less with a top grinder to obtain silicon carbide powder. The content of impurities in the obtained silicon carbide powder was measured by ICP-AES analysis by the pressurized acid analysis method described in “JIS R 1616”. The results are shown in Table 5.

[Comparative Example 2]
A commercially available natural silica powder (KCLA-2 manufactured by Kyoritsu Material Co., Ltd.) was immersed in a 10% by mass sodium chloride aqueous solution (sodium chloride: industrial use, purity 99.5% manufactured by Manac Co., Ltd.) for 1 hour, and then at 120 ° C. It was dried with a dryer for 80 hours. The impurity concentration of commercially available natural silica was as shown in Table 3. As a result of analyzing the obtained natural silica, only 7.6 mg of chlorine is contained per 1 kg of silica, and 31.6 mg of chlorine which is the target amount calculated from the formula (1) according to the present invention can be contained. There wasn't. A raw material obtained by mixing the natural silica and amorphous carbon in a mass ratio of 2/1 and graphite for a heating element are filled in an Atchison furnace, and energized at 1500 ° C. to 2500 ° C. for 24 hours to obtain massive silicon carbide. It was. The obtained silicon carbide lump was collected for each of the left part, the central part, and the right part and pulverized to 2 mm or less with a top grinder to obtain silicon carbide powder for each part. The content of impurities in the obtained silicon carbide powder was measured by ICP-AES analysis by the pressurized acid analysis method described in “JIS R 1616”. The results are shown in Table 5.

[Comparative Example 3]
In 1 kg of the amorphous silica of Example 1, it was immersed in a 5% by mass aqueous solution of hydrochloric acid for 1 hour so that the chlorine content was 5.0 mg. After dipping, the product was dried for 80 hours with a dryer to synthesize chloride-containing amorphous silica. Using this chloride-containing amorphous silica, a lump of silicon carbide was obtained in the same manner as in Comparative Example 2. The obtained silicon carbide lump was collected for each of the left part, the central part, and the right part and pulverized to 2 mm or less with a top grinder to obtain silicon carbide powder for each part. The content of impurities in the obtained silicon carbide powder was measured by ICP-AES analysis by the pressurized acid analysis method described in “JIS R 1616”. The results are shown in Table 5.

[Comparative Example 4]
27 kg of amorphous carbon was added to 140 kg of water glass and mixed to obtain a carbon-containing water glass. 167 kg of the obtained carbon-containing water glass was dropped into 1300 L of sulfuric acid having a sulfuric acid concentration of 12.5 vol% to synthesize carbon-containing amorphous silica. This carbon-containing amorphous silica is further immersed in 720 L of 12.5 vol% sulfuric acid for 6 hours to remove metal element impurities, washed with 3000 L of industrial water, and then dried for 80 hours in a dryer to obtain high purity carbon. 49.5 kg of containing amorphous silica was synthesized. The amount of impurities in the obtained carbon-containing amorphous silica was as shown in Table 4. From the amount of impurities and the formula (1) according to the present invention, it was immersed for 1 hour in a 10% by mass sodium chloride aqueous solution so that the chlorine content was 35.2 mg in 1 kg of carbon-containing amorphous silica. After soaking, the product was dried for 80 hours with a drier to synthesize chloride and carbon-containing amorphous silica.

  The above-mentioned chloride and carbon-containing amorphous silica and heating element graphite were filled in an Atchison furnace and energized at 1500 ° C. to 2500 ° C. for 24 hours to obtain massive silicon carbide. The obtained silicon carbide lump was collected for each of the left part, the central part, and the right part and pulverized to 2 mm or less with a top grinder to obtain silicon carbide powder for each part. The content of impurities in the obtained silicon carbide powder was measured by ICP-AES analysis by the pressurized acid analysis method described in “JIS R 1616”. The results are shown in Table 5.

  It can be seen that the silicon carbide powders of Examples 1 to 3 have a lower impurity element content than Comparative Examples 1 and 2. Moreover, it turns out that the silicon carbide powder of the comparative example 3 using the porous silica with little chloride amount has much content of an impurity element compared with Examples 1-3. Furthermore, Comparative Example 4 is a silicon carbide powder according to the invention described in JP 2014-125407 A, in which sodium chloride is mixed with carbon-containing silica, but Examples 1 to 3 are more than Comparative Example 4 It can be seen that high-purity silicon carbide powder can be produced.

Claims (1)

A first step of immersing amorphous porous silica having a porosity of 10 to 50% in an alkali metal chloride aqueous solution or hydrochloric acid to obtain chloride-containing amorphous silica; and the chloride-containing amorphous silica and carbonaceous raw material A second step of mixing and heating
Carbonization characterized in that in the first step, the amorphous porous silica is immersed in the alkali metal chloride aqueous solution or hydrochloric acid so that the chlorine content is not less than the chlorine content represented by the following formula (1). A method for producing silicon powder.
[However, C is a metal impurity element of the 3rd to 4th periods and 2 (2A group)-13 (3B) group in the said amorphous porous silica, Comprising: The content (mg / kg) of each element up to the upper predetermined order is shown, k is the mass ratio of chlorine to the metal impurity element in the chloride of each metal impurity element, Σ is the content of the metal impurity element Indicates that the values of each kC are added. ]