RU2526552C1 - Method of obtaining nanosized metal oxides from organometallic precursors - Google Patents

Abstract

FIELD: chemistry.

SUBSTANCE: invention can be used in chemical industry. nanosized metal oxides are obtained by chemical reaction of oxidation of organometallic compound with initiation of processes by energy impact, as such, used is pulsed electron beam with electron energy 100÷500 keV, duration 10÷100 ns and total current of beam 1-10 kA.

EFFECT: claimed invention makes it possible to increase productivity and extend nomenclature of obtained nanosized oxides on the same equipment without changing synthesis mode.

2 tbl, 1 dwg

Description

The invention relates to chemical and technical physics, metallurgy and is intended to obtain nanosized oxides powders.

The known method [Patent RU No. 2153016, IPC7 C22B 34/00, C01B 33/00, H05B 7/00, publ. 07/20/2000] obtaining rare refractory metals, silicon and their compounds. The method consists in the restoration (or decomposition) of gaseous compounds of metals and silicon in the presence of reagents in the zone of low-temperature thermonequilibrium plasma. The method uses an additional introduction into the reaction zone of a combustible mixture (hydrogen and oxygen) and activation of gaseous reactants by ultraviolet radiation.

The known method [Patent RU No. 2264888, IPC7 B22F 9/28, publ. 07/20/2005] obtaining nanosized powders of oxides. The method consists in feeding to the reactor a metal halide and a reducing agent in gaseous states. Before processing the gas mixture, oxygen is supplied to the reactor and a chain chemical process is initiated by pulsed energy exposure with a duration of not more than 10 ^-5 seconds.

The known method [Patent RU No. 2230033, IPC7 C01G 23/07, publ. 06/10/2004] obtaining titanium dioxide. The method includes generating a plasma of oxygen (or oxygen-containing gas) with a temperature of 1300-3600 ° C in an electric arc plasma generator. Then, titanium tetrachloride in a liquid state is introduced into the plasma stream. The titanium tetrachloride is oxidized by lowering the temperature of the reaction products to 1000-1600 ° C, cooling the resulting reaction products and separating the target product.

The disadvantages of these methods is the need for additional introduction into the reaction zone of a combustible mixture (hydrogen and oxygen); inconvenience of using metal halides as initial reagents, reacting under normal conditions with water vapor contained in air, with the formation of hydrogen chloride vapor.

A method is known [Hendrik K. Kammler Sotiris E. Pratsinis Scaling-up the Production of Nanosized SiO ₂ particles in a Double Diffusion Flame Aerosol Reactor // Journal of Nanoparticle Research. - 1999. - vol. 1, No. 4. - pp.467-477] for the preparation of nanosized silica by the oxidation of hexamethyldisiloxane in a flow reactor. The method allows to obtain nanosized silicon dioxide with an average particle size of from 15 to 170 nm. Productivity of the installation is 130 g / hour. However, the method is quite complicated in hardware design.

The known method [Thomas Delclos, Carole Aimé, Emilie Pouget, Aurélie Brizard, Ivan Huc, Marie-Hélène Delville and Reiko Oda. Individualized Silica Nanohelices and Nanotubes: Tuning Inorganic Nanostructures Using Lipidic Self-Assemblies // Nano Lett. - 2008. - N.8. - P.1929-1935] obtaining nanosized silica by the sol-gel method. Tetraethoxysilane was hydrolyzed on the surface of a "template" organic gel. Then the organics were removed by annealing at a temperature of 450 ° C. (C ₂ H ₄ -1,2 - ((CH ₃ ) ₂ N ⁺ C ₁₆ H ₃₃ ) ₂ ) and tetraethoxysilane mixed with benzylamine as a catalyst were used as starting precursors. The disadvantages of this method are the large energy costs associated with the processes of hydrolysis and annealing at certain stages of obtaining the final product in the form of a nanosized powder of silicon dioxide.

Closest to the proposed method is the method that we selected for the prototype [Motoaki Adachi, Shigeki Tsukui, Kikuo Okuyama Nanoparticle Formation Mechanism in CVD Reactor with Ionization of Source Vapor // Journal of Nanoparticle Research. - 2003. - v.5 (1-2). - pp.31-37]. It consists in chemical vapor deposition of an organometallic precursor (tetraethoxysilane and oxygen) to produce silicon dioxide nanoparticles. To reduce particle agglomeration, energy is used by treating the molecules of an organometallic precursor in a corona discharge in an additional chamber. As a result of this, the van der Waals forces decrease upon mixing in the main chamber of tetraethoxysilane and oxygen molecules having a unipolar charge. The method includes feeding tetraethoxysilane into the preliminary chamber, where its molecules are treated by corona discharge (at different potentials of the high-voltage ionizer electrode from -10 to +6 kV) at high pressure of 0.1-0.3 MPa and are transferred to the reactor. Tetraethoxysilane ions react with oxygen molecules to form silicon dioxide particles. Since particles containing tetroethoxysilane have a large number of ethoxy groups, the authors propose maintaining a temperature of 723–873 K in the reactor. If the temperature of the reactor is less than this range, large particles are synthesized. Also, the particle size in this method is affected by the collection time of the final products (the shorter the time, the smaller the particle size). The initial concentration of tetraethoxysilane 3.4 × 10 ^-5 and 8.60 × 10 ^-6 mol / l, the reactor volume of 100 and 200 cm ³ .

The disadvantage of the prototype method is the complexity of the hardware (an additional chamber for ionizing the molecules of the organometallic compound), the high energy intensity of the process due to the need for constant heating of the reactor to a temperature of 723-873 K, low productivity of the process due to the use of a low concentration of tetraethoxysilane and a small reactor volume, the size dependence obtained oxides from the time of collection of the final product and the potential of the ionizer.

The objective of the proposed solution is to develop an energy-saving method for producing nanoscale metal oxides from an organometallic precursor.

The technical result consists in increasing productivity, expanding the range of obtained nanosized oxides on the same equipment without changing the synthesis mode.

The technical problem is achieved by the fact that in the method of producing nanosized metal oxides from organometallic precursors by conducting a chemical reaction of oxidation of an organometallic compound when processes are initiated by energy exposure, in contrast to the prototype, the mixture is affected by a pulsed electron beam with an electron energy of 100 ÷ 500 keV, duration 10 ÷ 100 ns and with a total beam current of 1-10 kA.

The method for producing nanosized metal oxides from organometallic precursors is based on volumetric excitation of the reaction gas by a pulsed electron beam and the organization of the reaction process in the entire excitation region. The energy consumption of the beam is much lower than the energy released in chemical endothermic reactions and during the formation of oxide particles.

It is advisable to use a pulsed electron beam, the electron energy of which is 100 ÷ 500 keV, as an energy effect. The use of a pulsed electron beam of such energy allows increasing the volume of the reaction chamber to 8 l. It is impractical to use an electron beam with an energy of less than 100 keV due to the fact that the electron beam is introduced into the reaction chamber with a mixture of gases through the exit window, which is an aluminum foil (140 μm thick), so electrons with lower energy will be delayed in the exit window. The use of an electron beam with an energy of more than 500 keV is possible, thereby it is possible to increase the productivity of the installation, however, such installations require additional protection against X-ray bremsstrahlung and their mandatory registration in the SES.

It is advisable to use a beam current of 1-10 kA. In the case when the beam current is less than 1 kA, the number of primary electrons is also smaller, which means that fewer ionization events occur, as a result of which the number of nuclei of the reaction of the synthesis process decreases. The use of an electron beam with a current greater than the specified range is possible, however, this increases the economic costs of creating such an installation.

It is advisable to use an electron beam with a duration of 10 ÷ 100 ns. The use of a beam with a duration of more than 100 ns is impractical, since in this case the lifetime of the active particles will be less than the time of energy exposure to the starting materials. The use of an electron beam with a duration of less than 10 ns requires more complex hardware design, which is not economically feasible.

The figure shows a diagram of a plant for producing nanoscale metal oxides from organometallic precursors.

The installation consists of a reactor 2 with a pipe 1 for supplying an organometallic compound, a pipe 3 for supplying oxygen, a window 4 for performing pulsed energy exposure, a window 5 for collecting powder, a pipe 6 for outputting by-products, and 7 a source of pulsed energy exposure - a pulsed electron accelerator.

The method is as follows, the organometallic compound through the pipe 1 is fed into the volume of the reactor 2, where it is heated to boiling point (from 350 to 450 K), or melting (from 400 to 500 K) using a solid organometallic precursor. Through the pipe 3 in the volume of the reactor 2 serves oxygen. Through the window 4, the gas mixture in the reactor 2 is energized by a pulsed electron beam from the source 7. The reaction products in the form of a nanosized powder are collected at the bottom of the reactor 2 and removed through the window 5. By-products of the reaction in the gaseous state (CO ₂ , H ₂ O) removed through pipe 6.

The inventive method allows you to combine the chamber for ionization of the organometallic precursor and the reaction chamber, which improves the efficiency of the transmitted energy to the reagents.

Example 1. The reactor 2, made of quartz glass, with a diameter of 140 mm, with a volume of 6 l, is equipped with a manometer, vacuum gauge, low-inertia pressure sensor for recording fast processes, shut-off and control valves for inlet of the initial reagent mixture and pumping gas. Reactor 2 was pumped out to a pressure of ~ 7 torr before filling the gas mixture, then Si (C ₂ H ₅ O) _{4 was} heated to the boiling point (442 K). Then, tetraethoxysilane and then oxygen are introduced into reactor 2. The concentration of the starting reagents: 2.2 mmol of the organometallic compound Si (C ₂ H ₅ O) ₄ and 26.87 mol of oxygen. When pulsed high-current electron beam parameters: energy of electrons of 450-500 keV, the beam current of 1-10 kA, a pulse duration of 60 ns, to a mixture of organometallic compounds of Si (C ₂ H ₅ O) ₄ and oxygen reactions of organometallic compounds of Si oxidation ( C ₂ H ₅ O) ₄ initiated by electron impact:

The complete conversion of Si (C ₂ H ₅ O) ₄ occurred in one pulse of the electron beam. After the electron beam was injected into the mixture, a nanosized powder was formed in the reactor.

Table 1 shows Examples 2 and 3 of obtaining nanosized powders of titanium and copper oxides under the same synthesis conditions and with a single exposure to a pulsed electron beam on a mixture of starting reagents.

Table 2 shows the effect of subsequent effects of the electron beam on the synthesized particles of metal oxides at a concentration of the starting reagents indicated in table 1.

The process of producing oxide powders can be carried out both in a cyclic mode (gas inlet → irradiation → pumping out reaction by-products in a gaseous state), and in a continuous (flowing mode).

The obtained nanosized particles from an organometallic precursor have an average size of 40-100 nm.

The proposed method is applicable to obtain nanoscale powders of oxides of various metals from organometallic precursors. The method allows to increase the productivity of the process of producing oxides by increasing the volume of the plasma-chemical reactor and the concentration of the starting reagents. In the proposed method, the reaction chamber is heated only to the boiling temperature of the organometallic precursor, which allows not only to reduce energy consumption, but also to increase the purity of the final product, by eliminating process contaminants caused by heating the reactor to the temperatures required for chemical reactions to occur.

Table 1 The obtained metal oxide Starting reagents (organometallic precursor + gas) Basic physicochemical properties of an organometallic precursor The concentration of the starting components The average size of the resulting oxides SiO ₂ Tetraethoxysilane Si (C ₂ H ₅ O) ₄ Si (C ₂ H ₅ O) ₄ = 2.2 mmol 40-80 nm Oxygen T _bale = 442 K O ₂ = 26.87 mol TiO ₂ Tetraethoxy titanium Ti (C ₂ H ₅ O) ₄ Ti (C ₂ H ₅ O) ₄ = 2.2 mmol 50-100 nm Oxygen T _bale = 423 K O ₂ = 26.87 mol CuO Salicylaliminum Copper C ₁₄ H ₁₂ O ₂ N ₂ Cu C ₁₄ H ₁₂ O ₂ N ₂ Cu = 2.2 mmol 60-80 nm Oxygen T _{melting point} = 490 K O ₂ = 26.87 mol

table 2 The obtained metal oxide The concentration of the starting components 1 impulse 5 pulses 10 pulses The average size of the obtained oxides SiO ₂ Si (C ₂ H ₅ O) ₄ = 2.2 mmol 40-80 nm 60-100 nm 120-180 nm O ₂ = 26.87 mol TiO ₂ Ti (C ₂ H ₅ O) ₄ = 2.2 mmol 50-100 nm 70-120 nm 150-200 nm O ₂ = 26.87 mol CuO C ₁₄ H ₁₂ O ₂ N ₂ Cu = 2.2 mmol 60-80 nm 80-100 nm 150-180 nm O ₂ = 26.87 mol

Claims (1)

A method of producing nanosized metal oxides from organometallic precursors by conducting a chemical reaction of oxidation of an organometallic compound when processes are initiated by energy exposure, characterized in that the mixture is exposed to a pulsed electron beam with an electron energy of 100 ÷ 500 keV, a duration of 10 ÷ 100 ns, and with a total beam current of 1 -10 kA.

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