Method and apparatus for manufacturing a silicon-containing material

Abstract

To provide a process of producing silicon-containing materials.SOLUTION: A process comprises (a): converting a gas to a superheated state in which it is at least partly in plasma form and (b): contacting the superheated gas with a silicon-containing first starting material to form a mixture comprising the gas and silicon, wherein the silicon-containing materials are produced by (c): adding to the mixture a second starting material that can enter into a chemical reaction directly with the silicon in the mixture, or breaks down thermally on contact with the superheated gas and / or the mixture, and (d): the steps (a) and (b) are effected spatially separately from one another.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention described below relates to a method and an apparatus for producing a silicon-containing material.

Background Art

[0002] Silicon-containing materials are extremely important in many technical fields. For example, silicon nitride has found use as a material for components that are subject to thermal shock. Silicon carbide, because of its hardness, is suitable as an abrasive for the production of machine components including composite materials or as a semiconductor material. Carbon-coated nano- or microscale silicon particles have found use as an anode material in lithium-ion batteries.

[0003] The production of the aforementioned silicon-containing materials is carried out from a very diverse range of starting materials. Carbon-coated silicon particles are produced by grinding silicon blocks, and the resulting particles can be directly coated with carbon black or other modifications of carbon. Alternatively, the particles can be coated with an organic polymer, which is then carbonized under oxygen-free conditions. Silicon nitride is usually obtained by reacting nitrogen with pure silicon at a temperature higher than 1000°C. Silicon carbide is usually made by the Acheson process or by vapor-phase deposition using chlorosilane as a starting material.

[0004] The aforementioned production examples are, in principle, suitable for the industrial production of the aforementioned materials. However, it is desirable that it be possible to proceed from the same starting material in the production of each of the materials.

[0005] Furthermore, the known methods do not necessarily provide the aforementioned silicon-containing materials at the required level of purity, especially in the case of silicon carbide, and thus it would be desirable to provide an improved production method in this regard.

[0006] In the case of manufacturing carbon-coated nano- or micro-scale silicon particles, it would be desirable that the starting particles to be coated do not need to be obtained by a grinding operation first.

[0007] Furthermore, it would be desirable to optimize the manufacturing of the aforementioned materials from an energy perspective.

Summary of the Invention

[0008] The object of the present invention described below is to provide a solution for this purpose. This solution should be suitable for manufacturing silicon-containing materials as described above on an industrial scale.

[0009] To achieve this object, the present invention proposes a method having the features specified in claim 1 and an apparatus having the features specified in claim 12. Development examples of the present invention are the subject matter of the dependent claims. Specifically, according to the present invention, the following configurations [1] to

[15] are provided. [1] A method for manufacturing a silicon-containing material, the method comprising: (a) a step of converting a gas into a superheated state in which the gas is at least partially in plasma form; (b) a step of bringing the superheated gas into contact with a first starting material containing silicon to form a mixture containing the gas and silicon; comprising, wherein the silicon-containing material is (c) a step of adding to the gas or the mixture a second starting material that can react directly with silicon in the mixture or thermally decomposes when in contact with the superheated gas and / or the mixture; produced by (d) steps (a) and (b) being carried out spatially separated from each other; a method characterized by. [2] The method according to [1], having the following additional steps: (a) a step of bringing the superheated gas into contact with a first starting material containing silicon at a contact temperature higher than the decomposition temperature of the silicon-containing material to be produced to form a mixture containing the gas and silicon; (b) contacting the silicon in the mixture with a second starting material at a contact temperature higher than the decomposition temperature of the silicon-containing material to be produced; (c) cooling the mixture resulting from the contact of the silicon and the second starting material to a temperature lower than the decomposition temperature of the silicon-containing material to be produced for the production of particles of the silicon-containing material. [3] The method according to [2], having at least one of the following additional steps and / or features: (a) the first starting material being metallic silicon or monosilane in particulate form, in particular monosilane; (b) the second starting material being a carbon source that releases carbon when contacted with a superheated gas. [4] The method according to [2], having at least one of the following additional steps and / or features: (a) the first starting material being metallic silicon or monosilane in particulate form, in particular monosilane; (b) the second starting material being a nitrogen source or nitrogen that releases nitrogen when contacted with a superheated gas. [5] The method according to [1], having the following additional steps: (a) contacting a superheated gas with a first starting material containing silicon at a contact temperature higher than the boiling point of silicon to form a mixture containing the gas and silicon; (b) cooling the mixture containing the gas and silicon to a temperature lower than the melting point of silicon to produce silicon particles for contact with the second starting material; (c) contacting the silicon particles with the second starting material at a contact temperature higher than the decomposition temperature of the second starting material and lower than the melting point of silicon. [6] The method according to [5], having at least one of the following additional steps and / or features: (a) the first starting material being metallic silicon or monosilane in particulate form, in particular metallic silicon in particulate form; (b) the second starting material being a carbon source that releases carbon when contacted with the silicon particles. [7] The method according to [1], having the following additional steps: (a) At a temperature higher than the melting point of silicon, bringing the superheated gas into contact with the silicon-containing first starting material to form a mixture containing the gas and silicon; (b) Cooling the mixture containing the gas and silicon to a temperature lower than the melting point of silicon to produce silicon particles for contact with the second starting material; (c) Contacting the silicon particles with the second starting material at a temperature higher than the decomposition temperature of the second starting material and lower than the melting point of silicon. [8] The method according to [7], having at least one of the following additional steps and / or features: (a) The first starting material is monosilane; (b) The second starting material is a carbon source that releases carbon when in contact with the silicon particles. [9] The method according to [1], having the following additional step: (a) At a contact temperature higher than the melting point of silicon, bringing the superheated gas into contact with the silicon-containing first starting material to form a mixture containing the gas and silicon; (b) Contacting the silicon in the mixture with the second starting material at a contact temperature lower than the decomposition temperature of the produced silicon-containing material, particularly at a temperature lower than the decomposition temperature of the produced silicon-containing material and higher than the melting point of silicon.

[10] The method according to [2], having at least one of the following additional steps and / or features: (a) The first starting material is metallic silicon or monosilane in particulate form, particularly monosilane; (b) The second starting material is a carbon source that releases carbon when in contact with the mixture.

[11] The method according to [2], having at least one of the following additional steps and / or features: (a) The first starting material is metallic silicon or monosilane in particulate form, particularly monosilane; (b) The second starting material is a nitrogen source or nitrogen that releases nitrogen when in contact with the mixture.

[12] An apparatus (100) for producing a granular Si-containing material in the method according to any one of [1] to

[11] , having the following features: (a) The apparatus (100) includes means (106, 107) capable of converting a gas into a superheated state in which the gas is at least partially in plasma form. (b) The apparatus (100) includes a reaction space (101) and a first supply section (105) for the superheated gas that opens therein. (c) The apparatus (100) includes a second supply section (108) that opens directly into the reaction space (101), and a silicon-containing first starting material can be supplied into the reaction space (101) through the second supply section (108) to form a mixture containing gas and silicon. (d) The apparatus (100) includes a third supply section (112), and a second starting material that can react directly with silicon in the mixture or thermally decompose when contacting the superheated gas and / or the mixture can be supplied to the apparatus (100) through the third supply section (112).

[13] The apparatus according to

[12] , having the following additional steps: (a) The third supply section opens into the reaction space.

[14] The apparatus according to

[12] or

[13] , having the following additional steps: (a) The apparatus includes cooling means (110, 111), whereby the mixture formed in the reaction space (101) can be cooled.

[15] The apparatus according to

[14] , having the following additional steps: (a) The third supply section (112) opens into the space (103), and the mixture cooled by the cooling means flows through the space (103).

[0010] The method according to the present invention is universally applicable and suitable for the production of various silicon-containing materials, which makes it possible to produce materials starting from the same starting materials in each case. This method always includes the following steps: (a) A step of converting a gas into a superheated state in which the gas is at least partially in plasma form. (b) A step of bringing the superheated gas into contact with a silicon-containing first starting material to form a mixture containing gas and silicon. (c) A step of producing a silicon-containing material by adding a second starting material to a gas or a mixture.

[0011] Steps (a) and (b) are useful for the provision of silicon, but potential co-reactants are provided in step (c), which can react with silicon or form a composite material. The second starting material is selected such that it can react directly with silicon in the mixture or thermally decompose when contacted with a heated gas and / or mixture.

[0012] In the latter case, the decomposition releases substances or chemical elements that can react with silicon or form a composite material with silicon.

[0013] A feature of the method of the present invention is that (d) steps (a) and (b) are carried out spatially separated from each other.

[0014] DE102008059408A1 discloses injecting monosilane (SiH 4 ) into a reaction space into which a heated gas stream is also introduced. When contacted with the gas stream, monosilane decomposes into its elemental components. The formed vapor silicon can be condensed. The condensation forms small droplets of liquid silicon. The droplets are collected and the liquid silicon thus obtained can be further processed directly, i.e., without immediate cooling, and can be converted into single-crystalline silicon, for example, by the float zone method or the Czochralski method.

[0015] The present invention constructs this method, and the purpose of this method is no longer the production of pure silicon. Instead, the silicon provided by this method is further processed directly to provide a silicon-containing material. According to the present invention, this method serves as a uniform starting point for the production of many silicon-containing materials.

[0016] The basic principle for the production of silicon is adopted from DE102008059408A1. The overheated gas is brought into contact with a first starting material containing silicon in a reaction space, where the gas, depending on its properties when coming into contact with the starting material, must have a temperature high enough to decompose it, or melt it, or evaporate it. The silicon formed is further processed directly by utilizing the energy that in each case has to be expended in order to directly provide the silicon in an energy - advantageous way to give the silicon - containing material desired in each case.

[0017] According to the invention, the heating of the gas here, in particular the plasma formation, is not carried out within the reaction space where the contact with the first silicon - containing starting material takes place. Instead, according to the invention, the plasma formation and the contact of the silicon - containing first starting material with the overheated gas are carried out spatially separated from each other, as already described in DE102008059408A1.

[0018] To convert the gas into an overheated state, corresponding means are provided, which are preferably plasma - generating means. This can be selected depending on the desired purity of the silicon to be formed. For example, suitable means are for the production of inductively coupled plasmas, in particular for the production of high - purity silicon. On the other hand, obtaining low - purity silicon can be achieved with DC plasma - generating means. In the latter case, the arc formed between the electrodes ensures that energy is input into the gas to convert it into an overheated state.

[0019] The DC plasma - generating means can have a very simple design. In the simplest case, they can include electrodes for the generation of an optical arc and a suitable voltage supply, and the electrodes can be arranged in a space or opening through which the gas to be heated flows.

[0020] When DC plasma generating means are used, what is particularly meant by the aforementioned preferred spatial separation between heating and the contact of the silicon-containing first starting material with the superheated gas is that the gas first flows through an arc, which heats the gas or converts it into plasma, and then the gas is brought into contact with the silicon-containing first starting material beyond the arc in the flow direction. In terms of structure, this is preferably achieved by arranging the electrodes of the DC plasma generating means in the supply part that opens into the reaction space, or by connecting the DC plasma generating means upstream of this supply part. What this achieves is that the heating or plasma generation of the gas is separated from the supply of the silicon-containing first starting material and is not adversely affected by this supply. According to the applicant's knowledge, this is essential due to the high throughput required in industrial-scale processes.

[0021] When an inductively coupled plasma is used, for the same reason, the contact with the silicon-containing first starting material is carried out outside the active range of the induction coil used. More preferably, the gas first flows through the induction coil, which heats it, and then the gas is brought into contact with the silicon-containing first starting material beyond the induction coil in the flow direction.

[0022] In some preferred embodiments according to the present invention, the superheated gas is actually cooled by suitable technical means such as the mixing of a temperature-controlled gas having a relatively low temperature and the superheated gas after being heated and before being brought into contact with the silicon-containing first starting material. This is because depending on the type of the silicon-containing first starting material used, the temperature of the plasma is not necessarily required for its evaporation or decomposition. The temperature-controlled gas can be mixed into the superheated gas through an appropriate supply point of the supply part provided for the superheated gas to the reaction space.

[0023] Furthermore, it is preferable to cool the mixture resulting from step (b) or the mixture resulting from step (c) after the addition of the second starting material with the help of the temperature-controlled gas.

[0024] The gas to be converted to a superheated state is preferably hydrogen or a noble gas such as argon or nitrogen or a mixture of said gases. A preferred example is a mixture of argon and hydrogen, for example in a ratio of 10% by volume to 90% by volume.

[0025] With the aid of a device for generating a superheated gas, the gas is preferably heated to a temperature in the range of 1500 °C to 24000 °C, preferably 2000 °C to 20000 °C, more preferably 2000 °C to 15000 °C.

[0026] The temperature control gas used can be, for example, a noble gas such as hydrogen or argon or nitrogen or a mixture of the aforementioned gases.

[0027] The spatial separation between the heating of the gas and the contact of the gas with the silicon-containing starting material ensures that a large amount of the silicon-containing starting material can be converted without impairing the stability of the plasma.

[0028] The first silicon-containing starting material can also be selected depending on the desired purity. For the production of materials with high physical purity, suitable first silicon-containing starting materials are, in particular, gaseous silicon-containing starting materials such as the above-mentioned monosilane or trichlorosilane (SiHCl 3 ). The latter has the disadvantage that it forms chemically aggressive decomposition products upon contact with the superheated gas compared to monosilane. The decomposition of monosilane, in contrast, forms only silicon and hydrogen.

[0029] In many cases, it is also possible to proceed from granular metallic silicon as the first starting material. This can in particular be particles of metallurgical silicon. If a material with high physical purity is to be produced, the metallic silicon used can alternatively be polysilicon or crystalline silicon. Metallic silicon melts or evaporates upon contact with a superheated gas, in particular a plasma. For example, granular silicon can be fed into the reaction space with the aid of a carrier gas stream, for example hydrogen.

[0030] The granular silicon-containing starting material used can also be quartz in particulate form. Quartz can be reduced to metallic silicon when contacted with hydrogen plasma.

[0031] In principle, it is also possible to use a granular silicon alloy, such as ferrosilicon in granular form, as the granular silicon-containing starting material.

[0032] "Granular" should preferably be understood to mean that the first starting material containing silicon is in the form of particles having an average size of 10 nm to 100 μm. The first starting material containing granular silicon preferably does not contain particles having a size exceeding 100 μm.

[0033] As is apparent from the above observations, silicon is preferably in vapor form in the mixture resulting from the contact of the silicon-containing first starting material with the superheated gas and, depending on the contact conditions, is preferably at least partly in the form of very small droplets.

[0034] Regarding the above steps (b) and (c) where the superheated gas is brought into contact with the first starting material and the second starting material is added to the gas or mixture, there are a number of preferred methods: · In a preferred method, the first and second starting materials are brought into contact with the superheated gas and are, for example, simultaneously fed into the flow of the superheated gas. The resulting mixture then contains not only silicon and the superheated gas, but also the second starting material and / or its decomposition products, and possibly compounds from the reaction of silicon with the second starting material. At the same time · In an even more preferred method, a mixture of silicon and the superheated gas is first formed and the second starting material is added to it in a subsequent step. · In principle, it is possible to first form a mixture of the second starting material and the superheated gas and add the first starting material only in a subsequent step. This may be preferred especially when the second starting material can enter directly into a chemical reaction with silicon, i.e., when there is no need for thermal decomposition upstream of the second starting material.​ · In one preferred method, it is also possible that the gas to be converted to the overheated state is the second starting material, or that the second starting material is at least partially added to the gas. In that case, the contact with silicon is carried out immediately after the contact of the silicon-containing first starting material with the overheated gas.

[0035] In a first particularly preferred variant of the method which is particularly suitable for the production of silicon carbide and silicon nitride, the method comprises at least one of the following steps (a) to (c): (a) A step of bringing an overheated gas into contact with a silicon-containing first starting material to form a mixture containing gas and silicon, which is carried out at a contact temperature higher than the decomposition temperature of the silicon-containing material to be produced. (b) A step of bringing the silicon in the mixture into contact with a second starting material at a contact temperature higher than the decomposition temperature of the silicon-containing material to be produced. (c) A step of cooling the mixture resulting from the contact of silicon and the second starting material to a temperature lower than the decomposition temperature of the silicon-containing material to be produced for the production of particles of the silicon-containing material.

[0036] More preferably, the above features (a) to (c) are carried out in combination with each other.

[0037] Steps (a) and (b) can be carried out (A) simultaneously or continuously as described above. In the latter case, (B) first the first starting material is added to the overheated gas, and then the second starting material is supplied into the mixture resulting from step (a), or (C) the second starting material is at least part of the overheated gas when it is brought into contact with the first starting material.

[0038] In case of (A), the contact temperature in steps (a) and (b) means the temperature of the mixture resulting from the contact of the first and second starting materials with the overheated gas.

[0039] In case (B), the contact temperature in step (a) means the temperature of the mixture resulting from step (a), and the contact temperature in step (b) means the temperature of the mixture resulting from step (b). Preferably, the contact temperatures in steps (a) and (b) are essentially the same.

[0040] In case (C), the contact temperatures in steps (a) and (b) mean the temperature of the mixture resulting from the contact of the superheated gas consisting at least in part of the second starting material with the first starting material.

[0041] More preferably, the contact temperature selected in step (a) is a temperature lower than the boiling point of silicon and higher than the decomposition temperature of the silicon-containing material to be produced.

[0042] In step (c), it is more preferable that the mixture resulting from the contact of silicon with the second starting material is cooled to a temperature lower than the decomposition temperature of the silicon-containing material to be produced and higher than the melting point of silicon.

[0043] The result of the selection of a contact temperature higher than the decomposition temperature of the silicon-containing material to be produced is that the particles of the silicon-containing material can only be formed in step (c). The time period during which the mixture resulting from the contact of silicon with the second starting material is maintained above the decomposition temperature can affect the size of the particles resulting from step (c). The applicable principle is that the size of the particles increases with increasing time. This is probably because the silicon atoms in the mixture accumulate to form larger droplets.

[0044] In order for the temperature not to be lower than the decomposition temperature in steps (a) and (b), attention must be paid to the mixing ratio and starting temperature of the components involved in each case in the above cases.

[0045] Step (c) preferably includes the following two steps: · First, a step of cooling the mixture to a temperature higher than the melting point of silicon and lower than the decomposition temperature of the silicon-containing material to be produced, · Secondly, subsequently, a step of cooling to a temperature lower than the melting point of silicon, for example by rapid cooling.

[0046] In the second step, it is preferable to cool to a temperature below 50°C.

[0047] The cooling is preferably carried out with the aid of a temperature control gas. This can be a neutral gas such as argon or hydrogen, for example.

[0048] In a first preferred development of a first particularly preferred variant of the method, this is characterized by at least one of the following features (a) and (b): (a) The first starting material is a metal silane or monosilane in particulate form, particularly monosilane, (b) The second starting material is a carbon source that releases carbon when in contact with a heated gas.

[0049] More preferably, the above features (a) and (b) are implemented in combination with each other.

[0050] When the first starting material is metal silicon in particulate form, in a first preferred development, the contact temperature in step (a) is more preferably a temperature higher than the boiling point of silicon.

[0051] More preferably, according to the present invention, in this development, silicon is formed from monosilane and carbon from the carbon source, and these react with each other under conditions that give silicon carbide in a variant of this method, preferably in a stoichiometric composition SiC.

[0052] The decomposition temperature of silicon carbide is about 2830°C. Therefore, in this development, the contact temperature is preferably above this value. If the temperature of the mixture containing silicon and carbon drops below this value, the formation of solid silicon carbide begins.

[0053] The carbon source is preferably a hydrocarbon, such as methane, propene, acetylene and / or ethene.

[0054] In a second preferred development of a first particularly preferred variant of the method, this is characterized by at least one of the following features (a) and (b): (a) The first starting material is a metal silane or monosilane in particulate form, in particular monosilane, (b) The second starting material is a nitrogen source or nitrogen that releases nitrogen when in contact with a heated gas.

[0055] More preferably, the above features (a) and (b) are implemented in combination with each other.

[0056] When the first starting material is metal silicon in particulate form, even in this second preferred development, the contact temperature set in step (a) is more preferably a temperature higher than the boiling point of silicon.

[0057] More preferably, according to the present invention, in this development, silicon is formed from monosilane, which is then, under the conditions for providing silicon nitride in a variant of this method, preferably stoichiometric Si 3 N 4 reacts with nitrogen.

[0058] The decomposition temperature of silicon nitride is about 1900 °C. Therefore, the contact temperature in this development is preferably above this value. If the temperature of the mixture containing silicon and nitrogen drops to a value lower than that temperature, the formation of solid silicon nitride begins.

[0059] The nitrogen source is, for example, ammonia.

[0060] Very generally, by the method of the present invention, in particular by the first particularly preferred variant of the above method, it is possible to form particles which do not have sharp corners or edges and which are in particular essentially spherical. If monosilane is used as the first starting material, this is decomposed to form silicon atoms which then condense to form small substantially spherical droplets. Starting from granular metallic silicon as the first starting material, the particles used are melted at least on the surface so that the corners and edges disappear and are preferably completely melted, resulting in substantially spherical droplets. The droplets formed can then react with the second starting material or the components of the second starting material. After cooling, for example, substantially spherical silicon carbide or silicon nitride particles are obtained.

[0061] For the production of particles having a very small diameter (maximum 150 nm or less), in all variants of the method of the present invention, in a preferred embodiment, monosilane is used as the first starting material. For the production of larger particles (10 μm or less), it is preferred to use metallic silicon as the first starting material.

[0062] The silicon carbide and silicon nitride formed in the first particularly preferred variant of the method described above are preferably formed in the form of at least substantially spherical particles having a median size (d50) in the range from 1 μm to 10 μm.

[0063] In a second particularly preferred variant of the method which is particularly suitable for the production of carbon-coated silicon particles, the method comprises at least one of the following steps (a) to (c): (a) A step of bringing a superheated gas into contact with a silicon-containing first starting material at a contact temperature higher than the boiling point of silicon to form a mixture containing the gas and silicon. (b) A step of cooling the mixture containing the gas and silicon to a temperature lower than the melting point of silicon to produce silicon particles for contact with the second starting material. (c) A step of bringing the silicon particles into contact with the second starting material at a contact temperature higher than the decomposition temperature of the second starting material and lower than the melting point of silicon.

[0064] In this modification, steps (a) and (c) can be carried out continuously. Here, after the first starting material is added to the heated gas, the mixture resulting from step (a) is cooled. Only then is the second starting material brought into contact with the first starting material.

[0065] The contact temperature in step (a) means the temperature of the mixture resulting from step (a), and the contact temperature in step (c) means the temperature of the mixture resulting from step (c). The contact temperature in step (a) is higher than the contact temperature in step (c) in any case.

[0066] As a result of the selection of the contact temperature in step (a) being higher than the boiling point of silicon, silicon can be formed in the form of vapor and / or in the form of small droplets. Subsequent cooling forms silicon particles, which still have a temperature high enough for the second starting material to decompose on their surface. The carbon formed accumulates on the surface of the silicon particles, forming silicon-carbon composite particles.

[0067] The cooling in step (b) is preferably carried out with the aid of a temperature-controlled gas. This can be a neutral gas such as argon or hydrogen, for example.

[0068] After step (c), it is cooled to a temperature below 50 °C, for example by rapid cooling.

[0069] In a preferred development of a second particularly preferred modification of the method, this is characterized by at least one of the following (a) and (b): (a) The first starting material is metallic silicon or monosilane in particulate form, in particular metallic silicon in particulate form. (b) The second starting material is a carbon source that releases carbon upon contact with silicon particles.

[0070] More preferably, the above characteristics (a) and (b) are implemented in combination with each other.

[0071] More preferably, according to the present invention, in this development example, metallic silicon is melted and / or evaporated in particulate form, and carbon is formed from a carbon source. Silicon and carbon do not react with each other here because they are brought into contact at a relatively low temperature. Instead, a composite material is formed.

[0072] The carbon source is preferably a hydrocarbon such as methane, propene, acetylene and / or ethene.

[0073] The carbon-coated silicon particles formed in the above second particularly preferred variant of the method are preferably formed in the form of at least substantially spherical particles having a maximum diameter of 150 nm.

[0074] Similar to the second variant, in a third particularly preferred variant of the method which is particularly suitable for the production of carbon-coated silicon particles, the method comprises at least one of the following steps (a) to (c): (a) A step of bringing a superheated gas into contact with a first starting material containing silicon at a contact temperature higher than the melting point of silicon to form a mixture containing the gas and silicon; (b) A step of cooling the mixture containing the gas and silicon to a temperature lower than the melting point of silicon to produce silicon particles for contact with a second starting material; (c) A step of bringing the silicon particles into contact with the second starting material at a contact temperature higher than the decomposition temperature of the second starting material and lower than the melting point of silicon.

[0075] Steps (a) and (c) in this variant can also be carried out continuously. Here, the first starting material is first added to the superheated gas, and then the mixture resulting from step (a) is cooled. Only then is the second starting material brought into contact with the first starting material.

[0076] The contact temperature in step (a) means the temperature of the mixture resulting from step (a), and the contact temperature in step (c) means the temperature of the mixture resulting from step (c). The contact temperature in step (a) is higher than the contact temperature in step (c) in any case.

[0077] As a result of the selection of a contact temperature in step (a) that is higher than the melting point of silicon, silicon can be formed in the form of vapor and / or in the form of small droplets. Subsequent cooling forms silicon particles, which still have a temperature high enough for the second starting material to decompose on their surface. The carbon formed accumulates on the surface of the silicon particles, forming silicon-carbon composite particles.

[0078] The cooling in step (b) is preferably carried out with the aid of a temperature-control gas. This can be a neutral gas such as, for example, argon or hydrogen.

[0079] After step (c), it is preferred to cool to a temperature below 50 °C, for example by quenching.

[0080] In a preferred development of a third particularly preferred variant of the method, this is characterized by at least one of the following features (a) and (b): (a) The first starting material is monosilane, (b) The second starting material is a carbon source that releases carbon when it comes into contact with the silicon particles produced in step (b) above by cooling to a temperature lower than the melting point of silicon.

[0081] More preferably, the above features (a) and (b) are implemented in combination with each other.

[0082] More preferably, according to the present invention, in this development, silicon is formed from monosilane and carbon from the carbon source. Silicon and carbon do not react with each other here. Instead, a composite material is also formed here.

[0083] The carbon source is preferably a hydrocarbon, such as methane, propene, acetylene and / or ethene.

[0084] The carbon-coated silicon particles formed in the above-mentioned third particularly preferred variant of the method are likewise preferably formed in the form of at least substantially spherical particles having a maximum diameter of 150 nm.

[0085] In a fourth particularly preferred variant of a method which is particularly suitable for the production of silicon carbide and silicon nitride as in the first variant, the method comprises at least one of the following steps (a) and (b): (a) a step of bringing a superheated gas into contact with a first starting material containing silicon at a contact temperature higher than the melting point of silicon to form a mixture containing the gas and silicon; (b) a step of bringing the silicon in the mixture into contact with a second starting material at a contact temperature lower than the decomposition temperature of the silicon-containing material to be produced, in particular at a temperature lower than the decomposition temperature of the silicon-containing material to be produced and higher than the melting point of silicon.

[0086] More preferably, the above-mentioned features (a) and (b) are carried out in combination with each other.

[0087] Steps (a) and (b) can be carried out (A) simultaneously or continuously, as in Variant 1. In the latter case, (B) the first starting material is first added to the superheated gas and then the second starting material is fed into the mixture resulting from step (a), or (C) the second starting material is at least part of the superheated gas when it is brought into contact with the first starting material.

[0088] In case (A), the contact temperatures in steps (a) and (b) mean the temperature of the mixture resulting from the contact of the first and second starting materials with the superheated gas.

[0089] In the case of (B), the contact temperature in step (a) means the temperature of the mixture resulting from step (a), and the contact temperature in step (b) means the temperature of the mixture resulting from step (b). The contact temperatures in steps (a) and (b) are preferably essentially the same.

[0090] In the case of (C), the contact temperatures in steps (a) and (b) mean the temperature of the mixture resulting from the contact of a superheated gas consisting at least partly of the second starting material with the first starting material.

[0091] More preferably, the contact temperature selected in step (a) is a temperature higher than the melting point of silicon and less than 2500 °C. This provides the silicon in step (a), particularly in the form of small droplets and perhaps partly in vapor form.

[0092] The result of the selection of the contact temperature in step (a) lower than the decomposition temperature of the silicon-containing material to be produced is that the particles of the silicon-containing material can be formed immediately after the addition of the second starting material. The time period between the addition of the first starting material and the addition of the second starting material can affect the size of the particles resulting from step (b). The applicable principle is that the size of the particles increases with the increase of the time period. Perhaps because the silicon atoms in the mixture accumulate to form larger droplets.

[0093] After step (c), it is preferable to cool to a temperature below 50 °C, for example by rapid cooling.

[0094] In a first preferred development of a fourth particularly preferred variant of the method, the method is characterized by at least one of the following features (a) and (b): (a) The first starting material is metallic silicon or monosilane in particulate form, particularly monosilane; (b) The second starting material is a carbon source that releases carbon upon contact with the mixture.

[0095] More preferably, the above features (a) and (b) are implemented in combination with each other.

[0096] More preferably, according to the present invention, in this development example, silicon is formed from monosilane and carbon from a carbon source, and these react with each other preferably in a stoichiometric composition of SiC under conditions for providing silicon carbide in a variant of this method.

[0097] The decomposition temperature of silicon carbide is, as already mentioned above, about 2830 °C. Therefore, the preferred contact temperature in step (a) in this development example is preferably lower than this value. In step (b), the contact temperature is preferably set to a maximum value of 2500 °C as well. Therefore, the contact temperatures in steps (a) and (b) in this development example are preferably essentially the same. Cooling between steps (a) and (b) is not required here.

[0098] The carbon source is preferably a hydrocarbon such as methane, propene, acetylene and / or ethene.

[0099] In a second preferred development example of a fourth particularly preferred variant of the method, this is characterized by at least one of the following features (a) and (b): (a) The first starting material is metallic silicon or monosilane in particulate form, in particular monosilane. (b) The second starting material is a nitrogen source or nitrogen that releases nitrogen when contacted with the mixture.

[0100] More preferably, the above features (a) and (b) are implemented in combination with each other.

[0101] More preferably, according to the present invention, in this development example, silicon is formed from monosilane, which then reacts with nitrogen preferably in stoichiometric Si 3 N 4 under conditions for providing silicon nitride in a variant of this method.

[0102] As already mentioned above, the decomposition temperature of silicon nitride is about 1900 °C. Therefore, the contact temperature in step (a) of the described fourth preferred variant is probably higher than this value and has a preferred maximum value of 2500 °C. Therefore, it may be necessary to cool the mixture resulting from step (a) before the contact in step (b) of the fourth variant in order to achieve the contact temperature required for step (b) which is lower than the decomposition temperature of silicon nitride.

[0103] The cooling is preferably carried out with the aid of a temperature control gas. This can be a neutral gas such as, for example, argon or hydrogen.

[0104] The nitrogen source is, for example, ammonia.

[0105] The silicon carbide and silicon nitride formed in the above-described fourth particularly preferred variant of the method are preferably formed in the form of at least substantially spherical particles having a median size (d50) in the range of 1 μm to 10 μm.

[0106] The device according to the present invention An apparatus suitable for the performance of the method is described below. Such an apparatus is characterized by the following features (a) to (d): (a) The apparatus includes means capable of converting a gas into a superheated state in which the gas is at least partially in plasma form. (b) The apparatus includes a reaction space and a first supply for the superheated gas opening therein. (c) The apparatus includes a second supply opening directly into the reaction space, through which a silicon-containing first starting material can be supplied into the reaction space to form a mixture containing gas and silicon. (d) The apparatus includes a third supply, through which a second starting material that can react directly with the silicon in the mixture or thermally decompose upon contact with the superheated gas and / or the mixture can be supplied into the apparatus.

[0107] Means for converting the gas to a superheated state and its possible configurations for the implementation of the spatial separation of the contact and heating of the silicon-containing first starting material with the superheated gas have already been described in connection with the method of the present invention.

[0108] The reaction space in which the silicon-containing first starting material is contacted with the superheated gas must be heat-resistant in order to withstand the thermal stress caused by the superheated gas. For example, the reaction space can be lined or consist of a thermally stable material such as graphite for this purpose. In particular, the walls of the reaction space, in particular the aforementioned side walls and the aforementioned sealing elements, can be at least partially or completely made of such a material. Alternatively or additionally, the reaction space can include a heat-insulating material that thermally shields it from its environment.

[0109] The first supply for the superheated gas does not require any special configuration. It is preferably open into the reaction space in the vertical direction from above. In contrast, the second supply preferably has a special configuration to prevent the opening through which it opens into the reaction space from being blocked by solid silicon deposits.

[0110] It preferably includes a nozzle having a nozzle passage that opens directly into the reaction space through which the first starting material can be supplied into the reaction space. The device preferably includes means for enabling the introduction of an inert gas into the reaction space to protect the mouth opening of the nozzle passage from the thermal stress emerging from the superheated gas. The inert gas forms a kind of thermal barrier that shields the mouth opening of the nozzle passage from the superheated gas and thus prevents the silicon-containing starting material entering the reaction space from decomposing or melting directly at the mouth opening. Instead, the decomposition and / or melting of the silicon-containing starting material can be carried out at a distance from the mouth opening.

[0111] Preferably, according to the present invention, the inert gas used is a gas that cannot react to an extent relevant under the conditions present in the reaction space with the silicon-containing starting material or the silicon formed. Suitable gases are, in principle, the same gases as those heated by means for generating a superheated gas, in particular noble gases such as hydrogen, argon, and mixtures thereof.

[0112] In a preferred development of the present invention, the apparatus is characterized by at least one of the following features (a) to (c): (a) The nozzle is a multiphase nozzle having a nozzle passage for supplying a silicon-containing first starting material as a first nozzle passage. (b) The multiphase nozzle includes a second nozzle passage that opens directly into the reaction space as means for introducing an inert gas. (c) The second nozzle passage opens at the mouth opening and surrounds the mouth opening of the first nozzle passage.

[0113] More preferably, the above features (a) to (c) are implemented in combination with each other. In this way, it is possible to implement heat shielding of the mouth opening in a particularly elegant manner.

[0114] More preferably, the mouth opening of the first nozzle passage is round, particularly circular, and the mouth opening of the second nozzle passage is annular. The inert gas introduced into the reaction space through this opening forms an annular inert gas flow that surrounds the silicon-containing first starting material flowing in the reaction space.

[0115] In a further preferred development of the present invention, the apparatus is characterized by the following feature (a): (a) A third supply part opens into the reaction space.

[0116] This variant is particularly preferred when the first and second starting materials are contacted simultaneously with the superheated gas. If the starting materials are added continuously by contrast, it is probably highly preferred that the third supply part opens into a space downstream of the reaction space rather than in the reaction space, through which the silicon-containing mixture formed in the reaction space flows.

[0117] In a preferred embodiment, the third supply part can be designed similarly to the second supply part and in particular has at least one of the following features (a) to (c): (a) The first supply part includes a multiphase nozzle having a first nozzle passage for supplying the second starting material. (b) The multiphase nozzle includes a second nozzle passage that opens directly into the reaction space. (c) The second nozzle passage opens at the mouth opening and surrounds the mouth opening of the first nozzle, in particular surrounding it in an annular form.

[0118] More preferably, the above features (a) to (c) are implemented in combination with each other.

[0119] In a more preferred development of the invention, the apparatus is characterized by at least one of the following features (a) and (b): (a) The apparatus includes cooling means by which the mixture formed in the reaction space can be cooled. (b) The third supply part opens into a space through which the mixture cooled by the cooling means flows.

[0120] With the help of the cooling means, it is possible to cool the silicon-containing mixture formed in the reaction space before it is contacted with the second starting material in the space connected to the reaction space.

[0121] The cooling means can in particular be a supply part through which a temperature-control gas can be supplied into the mixture emerging from the reaction space. An annular nozzle is particularly suitable, through which the mixture to be cooled flows.

Brief Description of the Drawings

[0122] Further features, details, and advantages of the present invention will be apparent from the claims and the abstract (the texts of both of which are incorporated by reference into the specification), the following description of the preferred embodiments of the present invention, and the drawings. The drawings are shown in schematic form.

Figure 1

Figure 2

Figure 3

Figure 4

DETAILED DESCRIPTION OF THE INVENTION

[0123] The apparatus 100 shown in FIG. 1 includes three consecutive spaces 101, 102, and 103, which are joined on the outside by a wall 104 and connected to each other by passages 101a and 102a.

[0124] Space 101 is a reaction space into which superheated gas is supplied by a supply unit 105. In the supply unit, there is means including an annular electrode 106 and a pin-shaped electrode 107, and an arc can be generated by applying a voltage between these electrodes. If gas flows through the supply unit 105, the arc can provide energy input into the gas and convert the gas into a superheated state.

[0125] The gas heated by the arc enters axially into the reaction space 101, where it can be brought into contact with a first silicon-containing starting material. This can be supplied into the reaction space via a supply unit 108 in the form of a multiphase nozzle. When the superheated gas and the first starting material are brought into contact, a mixture containing gas and silicon is formed in the reaction space 101.

[0126] A second starting material that can enter into a chemical reaction with silicon in the mixture can be supplied into the reaction space 101 via the supply section 109. This can be, for example, ammonia. The supply section 109 can here take the form of a multiphase nozzle, similar to the supply section 108.

[0127] The supply section 109 is utilized to supply the second starting material into the reaction space when it is manufactured according to the above-described first particularly preferred variant of the method of the present invention, which is particularly suitable for the production of silicon-containing materials such as silicon carbide and silicon nitride.

[0128] Alternatively, the supply section 109 can also find use for supplying monosilane, which is preferred for increasing the throughput of the apparatus.

[0129] The supply sections 110 and 111 that enter the space 102 are supply sections for supplying a temperature control gas. This can serve to cool the gas mixture exiting the reaction space.

[0130] The supply section 112 that opens into the space 103 can find use for supplying a second starting material. This applies particularly when the silicon-containing material is manufactured according to the above-described third or fourth particularly preferred variants of the method of the present invention.

[0131] The silicon-containing material manufactured according to the present invention can be removed from the apparatus 100 via the passage 103a.

[0132] The apparatus shown in FIG. 2 differs from the apparatus of FIG. 1 in only a few respects. For example, the supply section 105 for the superheated gas opens into the reaction space 101 not axially but rather tangentially. Further, only one supply section 108 that opens into the reaction space 101 is provided for the silicon-containing first starting material.

[0133] The apparatus 100 shown in FIG. 3 is particularly suitable for the production of carbon-coated silicon particles according to the above-described second particularly preferred variant of the method of the present invention. It is possible here to supply solid silicon particles into the reaction space 101 via the supply section 108 and bring them into direct contact with the superheated gas entering via the supply section 105. The formed mixture can be brought into contact in space 103 with a carbon source supplied via supply section 112, such as methane. However, beforehand, the mixture in space 102 is cooled to a temperature higher than the decomposition temperature of the carbon source and lower than the melting point of silicon. In space 103, the carbon source can be decomposed at the surface of the silicon particles present in the mixture and accumulate there to form a carbon shell.

[0134] FIG. 4 shows a multiphase nozzle 108 for supplying a silicon-containing starting material, usually monosilane, which can be used in the apparatus shown in FIGS. 1 and 2. The nozzle 108 is integrated into the wall 104 of the apparatus 100 such that the nozzle passage 113 of the nozzle 108, which serves to supply the silicon-containing starting material, opens axially directly into the reaction space 101 (orifice opening 113a) and is spaced from the wall 104 of the reaction space 101. The nozzle 108 is thermally insulated from the wall 104 by an annular insulating element 114 surrounded by a graphite ring 115.

[0135] It is readily apparent that the nozzle 108 projects into the reaction space 101 such that the orifice opening 113a of the nozzle 113 opens into the reaction space 101 spaced by a distance d from the wall 104. This is intended to avoid the formation of a solid silicon deposit around the nozzle 108.

[0136] Similar to the nozzle passage 113, the multiphase nozzle 108 includes a second nozzle passage 116. This also opens axially directly into the reaction space 101 (orifice opening 116a). The nozzle passages 113 and 116 are defined by annular passage walls 108a and 108b in a concentric arrangement.

[0137] During operation, an inert gas (usually hydrogen) is introduced into the reaction space 101 through the orifice 116a of the nozzle passage 116 in the form of an annular gap. This surrounds the flow of the silicon-containing starting material ejected through the annular-shaped nozzle passage 113 and shields the orifice opening 113a of the nozzle passage 113 from the thermal stress within the reaction space 101.

Claims

1. A method for producing a silicon-containing material, the method comprising: (a) converting a gas to a superheated state in which the gas is at least partially in plasma form; (b) contacting the superheated gas with a silicon-containing first starting material to form a mixture comprising the gas and silicon; comprising: The silicon-containing material is produced by: (c) adding to the mixture a second starting material that can react directly with silicon in the mixture or that thermally decomposes upon contact with the superheated gas and / or the mixture; wherein: (d) steps (a) and (b) are carried out spatially separated from each other; (e) the silicon-containing first starting material is introduced into the reaction space through a first passage of a multiphase nozzle; (f) an inert gas is introduced into the reaction space through a second passage of the multiphase nozzle; (g) the first passage of the multiphase nozzle has an orifice opening that is spaced apart from the wall of the reaction space. A method characterized thereby.

2. The method according to claim 1, having the following additional steps: (a) contacting the superheated gas with the silicon-containing first starting material at a contact temperature higher than the decomposition temperature of the silicon-containing material to be produced to form a mixture comprising the gas and silicon; (b) contacting the silicon in the mixture with the second starting material at a contact temperature higher than the decomposition temperature of the silicon-containing material to be produced; (c) cooling the mixture resulting from the contact of silicon and the second starting material to a temperature lower than the decomposition temperature of the silicon-containing material to be produced for the production of particles of the silicon-containing material.

3. The method according to claim 2, having at least one of the following additional steps and / or features: (a) the first starting material is metallic silicon or monosilane in particulate form, in particular monosilane; (b) the second starting material is a carbon source that releases carbon upon contact with the superheated gas.

4. The method according to claim 2, having at least one of the following additional steps and / or features: (a) the first starting material is metallic silicon or monosilane in particulate form, in particular monosilane; (b) the inert gas is a nitrogen source or nitrogen that releases nitrogen upon contact with the superheated gas.

5. The method according to claim 1, having the following additional step: (a) contacting the superheated gas with the silicon-containing first starting material at a contact temperature higher than the boiling point of silicon to form a mixture comprising the gas and silicon. Step of producing silicon particles for contacting with a second starting material by cooling a mixture containing gas and silicon to a temperature lower than the melting point of silicon. Step of contacting the silicon particles with the second starting material at a contact temperature higher than the decomposition temperature of the second starting material and lower than the melting point of silicon. **Claim 6** The method according to claim 5, having at least one of the following additional steps and / or features: (a) The first starting material is metallic silicon or monosilane in particulate form, in particular metallic silicon in particulate form. (b) The second starting material is a carbon source that releases carbon when contacting the silicon particles. **Claim 7** The method according to claim 1, having the following additional steps: (a) Step of contacting a superheated gas with a silicon-containing first starting material at a temperature higher than the melting point of silicon to form a mixture containing gas and silicon. (b) Step of cooling the mixture containing gas and silicon to a temperature lower than the melting point of silicon to produce silicon particles for contacting with the second starting material. (c) Step of contacting the silicon particles with the second starting material at a temperature higher than the decomposition temperature of the second starting material and lower than the melting point of silicon. **Claim 8** The method according to claim 7, having at least one of the following additional steps and / or features: (a) The first starting material is monosilane. (b) The second starting material is a carbon source that releases carbon when contacting the silicon particles. **Claim 9** The method according to claim 1, having the following additional steps: (a) Step of contacting a superheated gas with a silicon-containing first starting material at a contact temperature higher than the melting point of silicon to form a mixture containing gas and silicon. (b) Step of contacting silicon in the mixture with the second starting material at a contact temperature lower than the decomposition temperature of the produced silicon-containing material, in particular at a temperature lower than the decomposition temperature of the produced silicon-containing material and higher than the melting point of silicon. **Claim 10** The method according to claim 2, having at least one of the following additional steps and / or features: (a) The first starting material is metallic silicon or monosilane in particulate form, in particular monosilane. (b) The second starting material is a carbon source that releases carbon when contacting the mixture. **Claim 11** The method according to claim 2, having at least one of the following additional steps and / or features: (a) The first starting material is metallic silicon or monosilane in particulate form, in particular monosilane. (b) The inert gas is a nitrogen source or nitrogen that releases nitrogen when it comes into contact with the mixture.

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