RU2616058C2 - Method of elements carbides and element-carbon compositions obtaining - Google Patents

Abstract

FIELD: metallurgy.

SUBSTANCE: method of producing of metal-carbon systems nanopowders consisting of metal carbides and metal-carbon compositions from chloride and oxide metals and hydrocarbons compounds in a thermal electrical discharges plasma, in which the process is carried out in a mixture plasma of saturated hydrocarbons with oxygen at the atomic ratio of elements in the mixture - carbon (C plasmas) and oxygen (O plasmas), which corresponds to the condition of C plasmas/O plasmas = 1.

EFFECT: developed method for the formation of metal-carbon systems nanopowders makes it possible to reduce the energy expenditure on the generation of a thermal plasma flow.

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Description

The invention relates to powder metallurgy. Metal carbides and metal-carbon compositions are widely used to create solid, anti-friction, electrical and other materials and coatings.

Numerous methods are known for producing powders of carbides of elements and element-carbon compositions, including in flows of thermal plasma of electric discharges, in the form of nanopowders with particle sizes less than 100 nm.

The synthesis of titanium carbide was carried out in a three-jet plasma reactor during the reduction of titanium oxide TiO _{2 with} methane and methane carbidization of titanium metal in a nitrogen plasma stream (A.K. Garbuzova et al. Plasma synthesis of titanium carbide: scientific justification, technology, economic evaluation. Bulletin of the mining and metallurgical industry section of the Russian Academy of Natural Sciences, Department of Metallurgy, Issue 32, pp. 122-136, 2014). The obtained titanium carbide nanopowder consisting of cubic particles with an average size of 35 nm. Titanium carbide contains impurities of free carbon (1.2-1.6 wt.%), As well as titanium dioxide (6.5 wt.%) Or titanium (5.5 wt.%) Depending on the type of raw material used. The presence of a significant amount of impurities in the resulting titanium carbide is a serious disadvantage of the process.

Tungsten carbide WC _1-x with a particle size of less than 20 nm was obtained by the interaction of ammonium paratungstate with methane in a stream of hydrogen-argon plasma generated in an electric arc plasma torch (Taegong Ryu etal, Plasma Synthesis of Tungsten Carbide Nanopowder from Ammonium Paratungstate, J. Am. Soc., 2009, 92, 3, pp. 655-660). The disadvantages of the process include the use of an inert argon gas to generate thermal plasma, which leads to an increase in the cost of the resulting product due to the need to heat argon to high temperatures and, consequently, increase energy consumption.

Silicon carbide nanopowders SiC were obtained in a thermal plasma of an argon-hydrogen mixture generated in an RF plasmatron by the interaction of silicon tetrachloride SiCl ₄ and ethylene C ₂ H ₄ (KlotzH.-D., MachR., Oleszak F., Szulzewsky K., Kramer W.,. Schierhorn E. Nanocrystalline Ceramic SiC, TiCand SiC-TiCPowders Producedinan RFInductionPlasma, ISPC-12, Minneapolis, USA, 1995, pp. 1147-1152). The powders synthesized under these conditions consisted mainly of β-SiC nanoparticles with an average size of 20-50 nm. As in the previous version of the production of tungsten carbide, the disadvantage of the process is the use of argon, which leads to an increase in the cost of electricity.

The closest to the proposed technical essence and the achieved result is a method for producing nanopowders of element-carbon systems (RF patent No. 2434807, 2010), in which the process is carried out in thermal plasma of a mixture of hydrocarbon with one of the components or a mixture of components from the group: water vapor , carbon dioxide. In the reacting system, the total atomic content of carbon elements C _total , oxygen O _total and element E1 total, forming the element-carbon system that meets the condition (C _total -O _total ) / E1 _total > K, where K is the number of carbon atoms per one atom of an element in the gross formula of the resulting nanopowder of element-carbon systems. EFFECT: invention allows to obtain target nanopowders without using additional gases not involved in chemical reactions for plasma production.

The disadvantage of this method is the use of water vapor (carbon dioxide) - hydrocarbon mixtures for plasma generation, when heated to high temperatures, strongly pronounced endothermic reactions occur that increase the energy consumption for carrying out the process at the required temperature.

The technical result is achieved by the fact that in the method of producing nanopowders of the metal-carbon system, consisting of metal carbides and metal-carbon compositions, from chloride and oxide compounds of metals and hydrocarbons in thermal plasma of electrical discharges, according to the invention, the process is carried out in a plasma of a mixture of saturated hydrocarbons with oxygen when the atomic ratio of elements in a mixture of carbon (C plasmas) and oxygen (O plasmas) satisfying the condition C plasmas / O plasmas = 1.

To implement the method, the known method for producing nanopowders of element-carbon systems (element carbides, element-carbon and element-carbide-carbon compositions) from elements and their compounds in an electric discharge plasma is proposed to be carried out using mixtures of hydrocarbons as plasma-forming gases (natural, liquefied gas , vapors of liquid fuel) with oxygen at a certain atomic ratio of total carbon (C) and total oxygen (O) in a mixture that meets the condition C / O = 1. For the implementation of the method, the most preferred should include saturated hydrocarbons, which are the basis of natural gaseous hydrocarbon raw materials (natural and liquefied gas), as well as gasoline.

These gaseous reactants are supplied to the plasma generator at an atomic ratio C / O = 1, where when passing through an electric discharge they are heated to a temperature of 2500-6000 K and form a high-temperature stream consisting of dissociated hydrogen and carbon monoxide. The processed raw materials as well as hydrocarbons are introduced into the obtained high-temperature plasma stream. The ratio of C / O elements in the composition of the plasma-forming gas should be equal to unity. At a C / O ratio> 1, the formation of carbon deposits on the walls of the discharge channel is possible in the plasma generator, leading to a disruption of its operation mode; at a C / O ratio <1, oxidizing components will be present in the composition of the high-temperature flow in the form of dissociation products of carbon dioxide and water molecules a pair of (O, OH), preventing the formation of the target products.

To generate plasma, one can use electric arc, high-frequency, or microwave plasmatrons, as well as combined circuits based on them.

A distinctive feature and advantage of the proposed process is the use of hydrocarbon-oxygen mixtures as a plasma-forming gas, the atomic ratio of elements in which satisfies the condition C / O = 1, while the generation of thermal plasma does not require the use of additional inert or neutral components, which leads to an increase in energy costs to heat them to high temperatures.

The achievement of minimum energy costs when using hydrocarbon-oxygen mixtures as a plasma-forming gas is confirmed by the results of calculations of the equilibrium compositions and energy characteristics of the interaction of methane and propane with oxygen, air, carbon dioxide and water vapor at an atomic ratio of elements C / O = 1. Table 1 and 2 shows the energy costs (kJ) required to obtain 1 mole of a mixture of reducing agents (CO + H ₂ + H) from methane (table 1) and propane (table 2) in the temperature range 2000-6000 K. These components are prevailing in the equilibrium system С-Н-О at the atomic ratio of elements С / О = 1 in the considered temperature range.

As follows from the tables, the minimum energy consumption for obtaining a mixture of reducing components in the entire temperature range considered is provided for the initial mixtures of methane (propane) - oxygen. Similar results are characteristic of other hydrocarbons.

The proposed process is implemented as follows.

As the feedstock, various metal compounds can be used - oxides, halides, oxyhalides, organoelemental compounds in powder, liquid or gaseous state, while the type of feed is not limited to these groups, however, the oxide or chloride feedstock currently used in industrial scale. The composition of the feedstock may include compounds of various metals.

Hydrocarbons in a gaseous state and oxygen are supplied to a plasma generator, where when passing through an electric discharge - arc, high-frequency, microwave, combined - it is heated to a temperature of at least 2500 K to provide targeted physicochemical transformations leading to the formation of hydrogen and carbon monoxide. Hydrocarbons and oxygen must be supplied to the plasma generator in separate streams to prevent the formation of explosive mixtures.

The feedstock and hydrocarbon are introduced into the plasma stream in quantities that ensure the formation of the target products — nanopowders of metal-carbon systems (element carbides, metal-carbon compositions). The obtained gas-dispersed stream is cooled and then goes to a separation unit, for example, a filter, where gaseous and dispersed reaction products are separated.

The implementation of the method is presented by the following examples.

Example No. 1

A mixture of methane (67.7 mol%) and oxygen (33.3 mol%) with a total flow rate of 1.3 m ³ / h (normal conditions) is introduced into the thermal plasma stream obtained by heating in an electric arc plasma generator a tungsten trioxide powder WO ₃ with a flow rate of 0.15 kg / h and methane with a flow rate of 0.3 m ³ / h (normal conditions).

The atomic C / O ratio in the composition of the plasma-forming gases is unity, the mass-average enthalpy of the plasma jet at the exit of the plasma generator is 4.7 kWh / nm ³ .

The resulting nanopowder consists of particles with sizes less than 30 nm, the predominant phases in it are tungsten carbides W ₂ C, WC _1-x with the presence of tungsten metal and free carbon.

The mass-average enthalpy of a plasma jet of 4.7 kWh / nm ³ corresponds to an equilibrium temperature of 3500 K, and at this temperature, based on table 1, the energy consumption for obtaining 1 mole of reducing agents (H ₂ + H + CO) from a mixture (CH ₄ +0.5 O ₂ ) constitute 163 kJ, for mixtures of (CH ₄ +0.5 O ₂ +1.88 N ₂ ), (CH ₄ + CO ₂ ) and (CH ₄ + H ₂ O) this value is higher by 40%, 68% and 34%, respectively. The energy costs for obtaining the target products would increase by the same amount, i.e. nanopowder, if methane - oxygen plasma with a temperature of 3500 K were replaced by the other mixtures mentioned above with the same temperature.

Example No. 2

In a stream of thermal plasma obtained by heating a mixture of propane (40 mol%) - oxygen (60 mol%) with a total flow rate of 1.2 m ³ / h (normal conditions), CuCl ₂ powder is introduced at a flow rate of 0.1 kg / h and propane with a flow rate of 0.2 nm ³ / h (normal conditions). The atomic C / O ratio in the composition of the plasma-forming gases is equal to unity, the mass-average enthalpy of the plasma jet at the exit of the plasma generator is 1.7 kWh / m ³ (normal conditions). The resulting product is a composition of nanoparticles of metallic copper with a size of less than 40 nm and carbon with a content of 9 mass%.

The mass-average enthalpy of a plasma jet of 1.7 kWh / nm ³ corresponds to an equilibrium temperature of 3000 K, and at this temperature the energy consumption for obtaining 1 mole of reducing agents (H ₂ + H + CO) from a mixture (C ₃ H ₈ +1.5 O ₂ ) is 80.4 kJ, mixtures (C ₃ H ₈ +1.5 O ₂ +5.62 N _2), (C ₃ H ₈ +3 CO ₂₎ and (C ₃ H ₈ +3 H ₂ O) this value is above 128%, 53% and 42 % respectively. The energy costs for obtaining the target products would increase by the same amount, i.e. nanopowder, if propane - oxygen plasma with a temperature of 3000 K were replaced by other mixtures mentioned above with the same temperature.

Example No. 3

The mixture of methane (67.7 mol%) and oxygen (33.3 mol%) with a total flow rate of 1.3 m ³ / h (normal conditions) is introduced into a thermal plasma stream obtained by heating in an electric arc plasma generator a mixture of titanium tetrachloride vapors TiCl ₄ with a flow rate of 0.3 kg / h and hexane C ₆ H ₁₄ with a flow rate of 0.81 kg / h. The atomic C / O ratio in the composition of the plasma-forming gases is equal to unity, the mass-average enthalpy of the plasma jet at the exit of the plasma generator is 2.7 kWh / m ³ (normal conditions).

The resulting product is a titanium carbide TiC nanopowder with a specific surface area of 17 m ² / g, which corresponds to an average surface particle size of d ₃₂ = 72 nm.

The mass-average enthalpy of a plasma jet of 2.7 kWh / nm ³ corresponds to an equilibrium temperature of 3000 K, and at this temperature, based on table 1, the energy consumption for obtaining 1 mole of reducing agents (H ₂ + H + CO) from the mixture (CH ₄ +0.5 O ₂ ) make up 101 kJ, for mixtures of (CH ₄ +0.5 O ₂ +1.88 N ₂ ), (CH ₄ + CO ₂ ) and (CH ₄ + H ₂ O) this value is 58%, 130% and 60% higher, respectively. The energy costs for obtaining the target products would increase by the same amount, i.e. nanopowder, if methane - oxygen plasma with a temperature of 3500 K were replaced by the other mixtures mentioned above with the same temperature.

Example No. 4

Ammonium paramolybdate powder (NH ₄ ) is introduced into the thermal plasma stream obtained by heating a mixture of gasoline vapors with a gross formula C _7.95 H _17.9 (47 mass%) and oxygen (53 mass%) with a total consumption of 2.26 kg / h in a plasma generator ₆ Mo ₇ O ₂₄ with a flow rate of 0.2 kg / h and gasoline vapors with a flow rate of 0.15 kg / h.

The atomic C / O ratio in the plasma-forming gases — a mixture of gasoline and oxygen — is equal to unity; the mass-average enthalpy of the plasma jet at the exit of the plasma generator is 15.5 MJ / kg, which corresponds to the equilibrium mass-average temperature of 3900 K.

The resulting nanopowder consists of molybdenum carbides Mo ₂ C and MoC _1-x , the particle size of which is less than 40 nm.

Claims (1)

A method of producing nanopowders of metal-carbon systems consisting of metal carbides and metal-carbon compositions, from chloride and oxide compounds of metals and hydrocarbons in thermal plasma of electrical discharges, characterized in that the process is carried out in a plasma of a mixture of saturated hydrocarbons with oxygen at an atomic ratio of elements in a mixture of carbon (C plasmas) and oxygen (O plasmas) corresponding to the condition C plasmas / O plasmas = 1.