DE102012223195A1 - Preparing semi-metal nitride/carbide powders by reacting gaseous semi-metal hydrogens and halides containing gaseous carbon and hydrogen-containing compounds and hydrogen and nitrogen-containing compounds in non-thermal plasma - Google Patents

Abstract

Preparing powders of semi-metal nitrides or semi-metal carbides, comprises introducing gaseous semimetal hydrogens and/or semimetal halides containing gaseous carbon and hydrogen containing compounds and gaseous hydrogen and nitrogen containing compounds in a non-thermal plasma, and then reacting. An independent claim is included for a reactor for carrying out chemical reactions in the non-thermal plasma, comprising: a reactor enclosure (1) which defines an evacuable reaction chamber (2) at an interior; at least one conduit for introducing the reaction components in a plasma reaction chamber (5) located at the interior of the reaction chamber, where the conduit is conducted through the reactor enclosure; at least conduit for discharging gases from the reaction chamber which is passed through the reactor enclosure; a side of arc-shaped electrodes (6, 7) arranged at the interior of the reaction chamber for generating a non-thermal plasma, where the arc-shaped surfaces face each other, so that the non-thermal plasma is formed between surfaces of the plasma reaction chamber; a reactor section (14) located in the lower part of the reactor to form a portion of the reaction chamber and undergoing a continuous reduction of its cross section along longitudinal direction of the reactor; and a lock arranged at the lower end of the reactor for discharging the reaction product from the reactor.

Description

The present invention relates to a process for producing high-purity powders of semimetal carbides or nitrides, the products produced therewith and a plasma reactor suitable therefor.

Semi-metal carbides and nitrides, particularly silicon carbide (hereinafter also called "SiC") and silicon nitride (hereinafter also called "Si ₃ N ₄ "), are important substances in the ceramic industry. Of particular importance are SiC and Si ₃ N ₄ as high-purity species in the photovoltaic or semiconductor industry, in particular in a highly pure form.

Furthermore, SiC material with high purity is characterized by a high resistance to other chemical reagents even at high temperatures. The high stability at high temperatures has made SiC very popular in the applications of support for wafer tray supports and paddles in semiconductor (diffusion) furnaces. The semiconductive electronic properties of SiC, which is achieved by doping according to the applications, are used in heating elements for industrial furnaces. High purity powdery SiC is also a key material for the production of temperature variable resistors and varistors.

Si ₃ N ₄ is an electrical insulator and is characterized by a high stability against molten metal. Silicon nitride is a fairly expensive material and its cost-benefit ratio is very good. Applications are in the field of ceramics, the coating of crucibles in silicon processing and other metal melt processing processes. Furthermore, it is an excellent electro-technical functional material with best high-temperature insulation properties (Source: http://accuratus.com/silinit.html ).

The production of semimetal carbides and nitrides is known.

• – durch direkte Nitridierung von Silicium in Stickstoffatmospäre,
• – durch carbothermische Nitridierung von Siliciumdioxid und Kohlenstoff in Stickstoffatmosphäre,
• – durch Diimid-Synthese von Siliciumchlorid in Ammoniakatmosphäre und anschließender Zersetzung des gebildeten Siliciumdiimids, oder
• – oder durch chemische Gasphasenabscheidung (CVD) von Silan-/Ammoniak-Gemischen an heißen Oberflächen hergestellt werden.

For example, silicon nitride

• By direct nitridation of silicon into a nitrogen atmosphere,
• By carbothermal nitridation of silica and carbon in a nitrogen atmosphere,
• By diimide synthesis of silicon chloride in an ammonia atmosphere and subsequent decomposition of the silicon diimide formed, or
• Or by chemical vapor deposition (CVD) of silane / ammonia mixtures on hot surfaces.

• – durch das Acheson-Verfahren, bei dem Siliziumdioxid und Kohlenstoff zu α-Siliciumcarbid und Kohlenmonoxid umgesetzt werden, oder
• – durch das CVD-Verfahren, beispielsweise durch thermische Zersetzung von chlorhaltigen Carbosilanen in Wasserstoff enthaltender Atmosphäre an heißen Oberflächen erzeugt werden.

Silicon carbide, for example, by the

• By the Acheson process, in which silica and carbon are converted to α-silicon carbide and carbon monoxide, or
• Be produced by the CVD process, for example by thermal decomposition of chlorinated carbosilanes in hydrogen-containing atmosphere on hot surfaces.

DE 10 2006 003 820 A1 describes the production of ceramic moldings with high-purity Si ₃ N ₄ coating by thermal treatment of a dispersion applied to a ceramic shaped body containing fine high-purity silicon particles and a dispersant in a nitrogen-containing atmosphere.

DE 698 13 648 T2 describes the application of a thin layer of Si ₃ N ₄ or oxynitride on a glass substrate by pyrolysis of a Si precursor compound and an N-precursor compound in the gas phase ("CVD method"). Si-precursor compounds are called silanes, alkylsilanes and silazanes. N-precursor compounds are called amines.

Out DE 695 21 409 T2 the production of Boraluminiumnitridschichten is known. These layers are deposited by sputtering.

DE 691 19 816 T2 describes nitride products and a process for their production in which a combustible mixture is burned in a reactor and reactants are introduced into the generated hot plasma for the production of nitride compounds. In addition to the desired nitrides, this process also produces certain proportions of carbides.

DE 690 31 859 T2 also describes nitride products and a process for their preparation.

As in the aforementioned document, a combustible mixture is burned in a reactor and introduced into the hot plasma generated reactants for the production of nitride compounds. In this process, carbides are formed in addition to the desired nitrides.

In the DE 101 43 685 A1 Structured silicon carbide particles in the form of primary and secondary particles and processes for their preparation are described. The secondary particles are essentially composed of the primary particles and correspond in morphology and structure of the particles of the starting material Kiesel-gur or diatomaceous earth. The reactants kieselguhr or diatomaceous earth and carbon are reacted in a reaction space at high temperatures, in which the reactants are heated at high speed.

DE 39 39 048 A1 describes a process for producing silicon carbide or silicon nitride whiskers or powders in which silicon fluoride and ammonia or hydrocarbon are reacted together at elevated temperatures. The products produced contained a relatively large amount of elemental silicon.

DE 39 13 716 C2 describes a method of coating a substrate in a plasma formed in a sealed vacuum chamber.

The formation of layers of silicon nitride is described by way of example.

In the DE 1 767 938 A describes a method for performing chemical reactions in a plasma. The reaction of boron halides with hydrogen to form elemental boron is mentioned. Another reaction described is the reaction of halides of metals or semimetals with ammonia, for example the production of aluminum nitride. Further, the reaction of metals or semimetals with ammonia, halogenated hydrocarbons, hydrogen sulfide or phosphorus halides to the corresponding nitrides, carbides, sulfides or phosphides is disclosed. In this document, no representation of carbides or nitrides starting from high-purity hemi-metal hydrides and compounds containing carbon and hydrogen or compounds containing hydrogen and nitrogen is disclosed. The plasma used is in thermal equilibrium since it is formed by inductive coupling with high frequency energy.

The preparation of the high-purity powdered Halbmetallcarbid- and Halbmetallnitridverbindungen with the known manufacturing technologies, eg. As the Acheson process, even at acceptable cost, not possible.

It was therefore an object to develop a production process for pulverulent semimetal carbides and nitrides, preferably for SiC or Si ₃ N ₄ , which makes these substances economically available in highly pure form. In addition, a manufacturing process for powdered semimetal carbides and nitrides is to be provided, which allows high throughputs in the production of these compounds.

This could be achieved completely surprisingly by the use or use of a non-thermal plasma, in particular a non-thermal plasma generated by a gas discharge, to a mass flow containing the required reaction components.

The invention relates to a process for the production of pulverulent and highly pure semi-metal nitrides or of semimetal carbides by introducing gaseous semimetal hydrogens and / or semimetal halides and compounds containing gaseous carbon and hydrogen or compounds containing gaseous hydrogen and nitrogen into a non-thermal plasma and reacting them Connections in it.

In the context of this description, semimetal are the elements boron, silicon, germanium, arsenic, selenium, antimony and tellurium. Preference is given to germanium and especially silicon. The process according to the invention is particularly preferably used for the production of silicon carbide and silicon nitride Si ₃ N ₄ .

As a semi-metal hydrogen for use in the method of this invention of formula MeH _n or Me ₂ H _2n-2 are generally suitable compounds, wherein Me stands for the semi-metal and n is an integer corresponding to the valence of the semi-metal. Preference is given to using semimetal hydrogens of the formula MeH _n . In the case of silicon, this is preferably SiH ₄ .

Suitable half-metal halides for use in the process according to the invention are generally compounds of the formula MeHal _n or Me ₂ Hal _2n-2 , in which Me is the semimetal and Hal is halogen and n is an integer which corresponds to the valency of the semimetal. Hal may be fluorine, chlorine, bromine or iodine, preferably chlorine. Semi-metal chlorides of the formula MeCl _n are preferably used. In the case of silicon, this is preferably SiCl ₄ .

Suitable compounds containing carbon and hydrogen for use in the process according to the invention are aliphatic, cycloaliphatic, araliphatic or aromatic hydrocarbons which optionally contain nitrogen and / or sulfur as heteroatoms, or else hydrocyanic acid, isocyanic acid, nascent acid or isothiocyanic acid. Aliphatic hydrocarbons are preferably used in the process according to the invention, in particular those having one to ten carbons. Methane or ethane are particularly preferably used.

Suitable nitrogen and hydrogen-containing compounds for use in the process according to the invention are ammonia, hydrazine or hydrazoic acid. Preferably, ammonia is used.

In a preferred variant of the method according to the invention is set High purity starting materials. By this it is meant that the compounds containing carbon and hydrogen, the compounds containing hydrogen and nitrogen, the semi-metallic hydrogens and the semi-metal halides each contain impurities of less than 1 mass ppm, preferably less than 0.1 mass ppm.

In a particularly preferred variant of the process according to the invention, silicon hydride SiH ₄ and ammonia or silicon hydride SiH ₄ and aliphatic C ₁ -C ₄ -hydrocarbons are introduced into the non-thermal plasma and reacted therein. For the production of the non-thermal plasma, a number of conventional methods are available to the person skilled in the art.

The non-thermal plasma used in the method according to the invention is characterized in that it contains electrons and heavy particles, wherein the electrons have a higher energy than the heavy particles, for example N, N ₂ , N ₂₊ , N +, Si, SiH, SiH ₂ + , C, H, H ₂ , or NH). The non-thermal plasma generally has electrons having an energy in the range of 0.1 to 100 eV, especially 1 to 50 eV, and heavy particles having an energy in the range of 1 to 10 eV, especially 0.5 to 1 eV ,

Non-thermal plasmas used according to the invention are generated, for example, by a gas discharge or by irradiation of electromagnetic energy, such as by irradiation of radio or microwaves, into a vacuum chamber. The generation of the plasma does not take place as in thermal plasmas by high temperatures, but by non-thermal ionization processes. The person skilled in such plasmas are known.

The process according to the invention is generally carried out in non-thermal plasmas which have temperatures of from 500 to 1500.degree. C., preferably from 800 to 1000.degree.

By means of the invention, high-purity semi-metal nitride or semimetal carbide powders can be produced in a simple and cost-effective manner.

The invention also relates to pulverulent and high-purity semimetal nitrides or semimetal carbides whose proportion of impurities is less than 1 ppm by weight, in particular less than 0.1 ppm by weight.

Preferably, these powders are silicon carbide or silicon nitride Si ₃ N ₄ . Particles which form these powders may be spherical or non-spherical, eg in the form of whiskers. In the case of the following diameter data, for non-spherical particles, reference is made to the diameter with the greatest value. Preference is given to powders of semimetal carbides or semimetal nitrides whose particles have diameters in the range from 2 to 2500 nm, in particular from 2 to 500 nm, and very particularly preferably from 10 to 200 nm.

Preference is furthermore given to powders of semimetal carbides or semimetal nitrides whose particles have an average diameter d ₅₀ (measured by TEM evaluation, TEM = transmission electron microscope) in the range from 5 to 550 nm, preferably from 50 to 150 nm.

Preference is furthermore given to powders of semimetal carbides or semimetal nitrides whose particles are spherical or in the form of whiskers.

Whether the particles form spherically or in the form of whiskers depends, inter alia, on the H ₂ concentration in the representation. In the 1 and 2 TEM / SEM micrographs of silicon nitride particles produced at different hydrogen plasma concentrations are shown. The bar in these figures means a length of about 1 micron. In the 1 For example, a product made at low hydrogen concentration is shown, as it is in the wall sections of the reactor. In the 2 however, a product is shown which has been prepared at high hydrogen concentration and preferably forms spherical particles or aggregates thereof.

A preferred embodiment of the method according to the invention involves the introduction of hydrogen into the non-thermal plasma.

Quite surprisingly, it was found that the particle size can be adjusted not only by the hydrogen content but also by selective addition and mixing with nitrogen. In the case of nitrides, nitrogen appears to inhibit the decomposition of half metal nitride precursors, such as SiN, at high temperatures, in the case of silicon, at temperatures above 1700 ° C, preferably at temperatures above 2050 ° C. In contrast, in the production of carbides by driving at high temperatures, in the case of silicon at temperatures above 1750 ° C, it can be prevented that nitrogen is incorporated in the solid state.

A further preferred embodiment of the method according to the invention comprises introducing nitrogen into the non-thermal plasma, which in particular has temperatures of more than 1700 ° C., preferably of more than 2050 ° C.

Of course you can work with lower temperatures in the syntheses. It is expedient to use an inert gas, for example a noble gas or a mixture of noble gases, for example argon with small amounts of helium. Other gas mixtures are known in the art or can be found in relevant textbooks.

A further preferred embodiment of the method according to the invention comprises introducing noble gas or noble gas mixtures into the non-thermal plasma, which in particular has temperatures of less than 1700.degree.

• A) Reaktorhülle (1), welche im Innern einen evakuierbaren Reaktionsraum (2) definiert,
• B) mindestens eine Leitung (3, 4) zum Einbringen von Reaktions-komponenten in einen Plasma-Reaktionsraum (5), der sich im Innern des Reaktionsraums (2) befindet, wobei Leitung (3, 4) durch die Reaktorhülle (1) geführt wird,
• C) mindestens eine Leitung (8, 9) zum Abführen von Gasen aus dem Reaktionsraum (2), welche durch die Reaktorhülle (1) geführt wird,
• D) zwei im Innern des Reaktionsraumes (2) angeordnete auf einer Seite jeweils bogenförmig ausgestaltete Elektroden (6, 7) zum Erzeugen eines nicht-thermischen Plasmas, deren bogenförmige Oberflächen einander gegenüber stehen, so dass sich zwischen diesen Oberflächen der Plasma-Reaktionsraum ausbildet, in dem das nicht-thermische Plasma gebildet wird,
• E) einen Raumabschnitt (14), der sich im unteren Teil des Reaktors befindet, einen Teil des Reaktionsraumes (2) bildet und der in Längs-richtung des Reaktors auf die untere Begrenzung zu betrachtet eine kontinuierliche Verringerung seines Querschnitts erfährt, und
• F) am unteren Ende des Reaktors eine Schleuse (15), über die Reaktionsprodukt aus dem Reaktor ausgeschleust werden kann.

The invention also relates to a reactor for carrying out chemical reactions in a non-thermal plasma comprising the elements:

• A) Reactor shell ( 1 ), which inside an evacuable reaction space ( 2 ) Are defined,
• B) at least one line ( 3 . 4 ) for introducing reaction components into a plasma reaction space ( 5 ) located in the interior of the reaction space ( 2 ), where line ( 3 . 4 ) through the reactor shell ( 1 ) to be led,
• C) at least one line ( 8th . 9 ) for removing gases from the reaction space ( 2 ), which through the reactor shell ( 1 ) to be led,
• D) two in the interior of the reaction space ( 2 ) arranged on one side in each case arch-shaped electrodes ( 6 . 7 ) for producing a non-thermal plasma whose arcuate surfaces face each other so that the plasma reaction space is formed between these surfaces, in which the non-thermal plasma is formed,
• E) a room section ( 14 ), which is located in the lower part of the reactor, a part of the reaction space ( 2 ) and viewed in the longitudinal direction of the reactor to the lower boundary considered to undergo a continuous reduction in its cross-section, and
• F) at the lower end of the reactor a lock ( 15 ), can be discharged via the reaction product from the reactor.

A preferred embodiment relates to a reactor with the above-defined elements A) to F), which as element G) additionally a line ( 16 ), via which a gas in the reaction space ( 2 ), whereby line ( 16 ) through the upper side of the reactor wall ( 1 ) and wherein the reactor-side mouth of line ( 16 ) by a positioning device in the reaction space ( 2 ), and preferably into the plasma reaction space ( 5 ) opens.

A further preferred embodiment relates to a reactor with the above-defined elements A) to F) and preferably G), in which in the upper part in the interior of a nozzle ( 17 ), preferably a Venturi nozzle, is attached.

In a further preferred embodiment of the reactor according to the invention, longitudinal extent of the reaction space is ( 2 ) is greater than its transverse extension.

In a further preferred embodiment of the reactor according to the invention, this two lines ( 3 . 4 ) for introducing reaction components, each by two opposite transverse walls of the reactor shell ( 1 ) are guided.

The plasma in the discharge zone, the plasma reaction space ( 5 ), can be generated by high voltage pulses in a simple manner as plasma in nonthermal equilibrium. The temperatures of the heavy particles (atoms, ions) as well as the light particles (electrons) depend on reaction-technical requirements. For example, temperatures above 1750 ° C. are to be avoided in SiN production for high yields. If the target direction is the desire for smaller particles, then it can be beneficial to drive carefully into this temperature regime. As a result, the nucleation is kinetically inhibited and so surprisingly small particles are formed in the reaction space in a surprising manner.

A reactor is preferred in which the mouth of the at least one line ( 3 . 4 . 16 ) for introducing components into the reaction space ( 2 ) can be positioned.

The following examples illustrate the invention without limiting it. Example 1: Process for integrated production of SiC In a plasma reactor, methane as a carbon source (which is converted to acetylene in the plasma) and monosilane SiH ₄ as a silicon source are reacted in a thermal non-equilibrium gas discharge. The target product SiC was produced.

The reaction took place via all stages according to the following reaction equation: SiH ₄ + CH ₄ -> SiC + 4H ₂

Example 2: Process for the preparation of Si ₃ N ₄

Ammonia as a nitrogen source and monosilane SiH ₄ as a silicon source in the plasma were converted into a plasma reactor, thereby producing the target product Si ₃ N ₄ .

The reaction was carried out according to the following reaction equation: SiH ₄ + 4 NH ₃ -> Si ₃ N ₄ + 12 H ₂

The surface area of the material powder produced in a simple hand trial was about 46 2 to 100 m / g, the particle size being distributed around 20 to 200 nm. The plasma reactor was operated at 0.45 kW and approximately 14 kHz with high-voltage pulses having a half-width of t (50) 567ns and a mass flow of 43 NL / min.

For the above procedures, non-thermal equilibrium gas discharges were used. Non-thermal means in the inventive sense that the electrons as energy-mediating species have a higher temperature than the heavy particles (N, N ₂ , N ₂₊ , N + Si, SiH, SiH ₂ + ... C, H, H ₂ , NH, .. .). These were produced by the expert known or familiar power supplies.

Surprisingly, it has been found that such a non-thermal gas discharge can advantageously be generated by dimming over the pulse frequency, wherein advantageously the electrodes are designed as hollow electrodes with preferably porous end faces, for example made of sintered metal, by a two-dimensional parabolic shape. Thus, the gas flow is distributed uniformly over the electrode surface. The two-dimensional mushroom-like surface can be described according to F (r) = r2 (0.1 <r <1.1 cm).

The 3 schematically shows a variant of the reactor according to the invention in longitudinal section.

Shown is the reactor shell ( 1 ), which inside an evacuable reaction space ( 2 ) whose longitudinal extent is greater than its transverse extent. Furthermore, two lines ( 3 . 4 ) for introducing reaction components into a plasma reaction space ( 5 ) intended. The reactor-side ends ( 3a . 4a ) of the lines ( 3 . 4 ) are widened. Through the ends ( 3a . 4a ), two electrodes ( 6 . 7 ) made of sintered metal into the reactor and protrude into the reaction space ( 2 ) into it. The two electrodes ( 6 . 7 ) are each mushroom-shaped and produce a non-thermal plasma. The curved surfaces of the electrodes ( 6 . 7 ) face each other, so that between these surfaces of the plasma reaction space ( 5 ) in which the non-thermal plasma is formed. In addition, the shows 3 Cables ( 8th . 9 ) for discharging gaseous reaction products from the reaction space ( 2 ), which through the reactor shell ( 1 ). That through the lines ( 8th . 9 ) discharged gas comes from two compartments ( 10 . 11 ), which react with the reaction space ( 2 ) via filters ( 12 . 13 ) and with gas from the reaction space ( 2 ) can be filled. In the lower part of the reactor is in a space section ( 14 ) present a part of the reaction space ( 2 ). Room section ( 14 ) experiences in the longitudinal direction of the reactor to the lower boundary to a continuous reduction in its cross-section. At the lower end of the reactor is a lock ( 15 ), via which the reaction product, preferably as a powder, can be discharged from the reactor. Also shown is a line ( 16 ), via which, for example, inert gas enters the reaction space ( 2 ) can be introduced. Not shown is a positioning device, for positioning the mouth of the line ( 16 ) in the reaction space ( 2 ). In the upper part of the reactor is inside a nozzle ( 17 ), preferably a venturi.

QUOTES INCLUDE IN THE DESCRIPTION

This list of the documents listed by the applicant has been generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Cited patent literature

• DE 102006003820 A1 [0008]
• DE 69813648 T2 [0009]
• DE 69521409 T2 [0010]
• DE 69119816 T2 [0011]
• DE 69031859 T2 [0012]
• DE 10143685 A1 [0014]
• DE 3939048 A1 [0015]
• DE 1767938 A [0016, 0018]

Cited non-patent literature

• http://accuratus.com/silinit.html [0004]

Claims (21)

Process for the preparation of pulverulent and high-purity semi-metal nitrides or of semimetal carbides by introducing gaseous semimetal hydrogens and / or semimetal halides and compounds containing gaseous carbon and hydrogen or gaseous hydrogen and nitrogen-containing compounds into a non-thermal plasma and by reacting these compounds therein , A method according to claim 1, characterized in that the semi-metal is selected from the group consisting of boron, silicon, germanium, arsenic, selenium, antimony and tellurium. A method according to claim 2, characterized in that the semimetal is silicon. A method according to claim 1, characterized in that the semimetal carbide is silicon carbide and that the semimetal nitride is silicon nitride Si ₃ N ₄ . A method according to claim 1, characterized in that the semimetal hydrogen has the formula MeH _n or Me ₂ H _2n-2 and that the semimetal halide has the formula MeHal _n or Me ₂ Hal _2n-2 , wherein Me for the semimetal and Hal is halogen and n is an integer corresponding to the valency of the semimetal. A method according to claim 1, characterized in that the compound containing carbon and hydrogen is an aliphatic, cycloaliphatic, araliphatic or aromatic hydrocarbon which optionally contains nitrogen and / or sulfur as heteroatoms, or hydrocyanic acid, isocyanic acid, nascent acid or isothiocyanic acid. A method according to claim 1, characterized in that the nitrogen and hydrogen-containing compound is ammonia, hydrazine or hydrazoic acid. A process according to any one of claims 1 to 7, characterized in that the compounds containing carbon and hydrogen, the compounds containing hydrogen and nitrogen, the semi-metallic hydrogens and the semi-metal halides each contain impurities of less than 1 mass ppm. A method according to claim 1, characterized in that silicon hydride SiH ₄ and ammonia or that silicon hydride SiH ₄ and aliphatic C ₁ -C ₄ hydrocarbons are introduced into the non-thermal plasma and reacted therein. Method according to one of claims 1 to 9, characterized in that the non-thermal plasma is generated by a gas discharge or by irradiation of electromagnetic energy in a vacuum chamber, wherein the electrons contained in the non-thermal plasma have a higher energy than that in the plasma contained heavy particles. A method according to claim 10, characterized in that the electrons contained in the non-thermal plasma have an energy of 0.1 to 100 eV and the heavy particles contained in the plasma an energy of 0.5 to 1 eV, with the proviso that the energy the electrons contained in the non-thermal plasma is larger than the energy of the heavy particles contained in the non-thermal plasma. A method according to claim 1, characterized in that hydrogen is introduced into the non-thermal plasma. A method according to claim 1, characterized in that in the non-thermal plasma, nitrogen is introduced and that the non-thermal plasma in particular temperatures of about 1700 ° C, preferably of about 2050 ° C. A method according to claim 1, characterized in that in the non-thermal plasma noble gas or a noble gas mixture is introduced, wherein the non-thermal plasma in particular has temperatures of less than 1700 ° C. Powdered and high-purity semi-metal nitrides or semimetal carbides, characterized in that their proportion of impurities is less than 1 ppm by weight. Semi-metal nitrides or semimetal nitrides according to claim 12, characterized in that their proportion of impurities is less than 0.1 ppm by weight. Semi-metal nitrides or semimetal nitrides according to one of claims 12 or 13, characterized in that they are silicon carbide or silicon nitride Si ₃ N ₄ . Semi-metal nitrides or semimetal nitrides according to any one of claims 12 to 14, characterized in that the particles of the powder are spherical and have diameters in the range of 2 to 500 nm and a mean diameter d ₅₀ in the range of 50 to 150 nm. Reactor for performing chemical reactions in a non-thermal plasma comprising the elements A) Reactor shell ( 1 ), which inside an evacuable reaction space ( 2 ), B) at least one line ( 3 . 4 ) for introducing reaction components into a plasma reaction space ( 5 ) located in the interior of the reaction space ( 2 ), where line ( 3 . 4 ) through the reactor shell ( 1 ), C) at least one line ( 8th . 9 ) for removing gases from the reaction space ( 2 ), which through the reactor shell ( 1 ) D) two in the interior of the reaction space ( 2 ) arranged on one side in each case arch-shaped electrodes ( 6 . 7 ) for producing a non-thermal plasma, the arcuate surfaces of which face each other so that the plasma reaction space is formed between these surfaces, in which the non-thermal plasma is formed, E) a space portion (FIG. 14 ), which is located in the lower part of the reactor, a part of the reaction space ( 2 ) and seen in the longitudinal direction of the reactor to the lower boundary seen to undergo a continuous reduction in its cross-section, and F) at the lower end of the reactor, a lock ( 15 ), can be discharged via the reaction product from the reactor. Reactor according to claim 19, characterized in that this one line ( 16 ), via which a gas in the reaction space ( 2 ), whereby line ( 16 ) through the upper side of the reactor wall ( 1 ) and wherein the reactor-side mouth of line ( 16 ) by a positioning device in the reaction space ( 2 ), and preferably into the plasma reaction space ( 5 ) opens. Reactor according to claim 19, characterized in that in the upper part of the reactor inside a nozzle ( 17 ), preferably a Venturi nozzle, is attached.

Images