RU2565182C1 - Method of producing nanosized powder of silicon compounds - Google Patents

Abstract

FIELD: chemistry.

SUBSTANCE: method of producing silicon nitride or silicon carbide powder includes preheating a mixture of monosilane with an inert diluent gas and a precursor. Ammonia gas or acetylene is used as the precursor. The reaction mixture is subjected to adiabatic compression until thermal decomposition, which enables to obtain the corresponding silicon compound.

EFFECT: invention enables to obtain nanosized powders of silicon compounds consisting of monodispersed particles.

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Description

The invention relates to nanotechnology, and in particular to methods for producing silicon chemical compounds by thermal decomposition of monosilane, in particular to producing pure monodispersed nanopowders of silicon compounds in an adiabatic process, and can be used to create technologies for producing new materials of new functional nanomaterials with unique properties.

Known methods for producing powders based on the evaporation of substances with subsequent condensation [1. Gusev A.I. Nanomaterials, nanostructures, nanotechnology. - M .: Fizmatlit, 2005 .-- 416 p .; 2. Patent RU 2359906, IPC СВВ 33/02, 08/31/2007, Method for producing nanocrystalline silicon powders], laser ablation [3. Umezu I., Takata M., Sugimura A / Surface hydrogeneration of silicon nanocrystals during pulsed laser ablation of silicon target in hydrogen background gas // J. Appl. Phys. 2008. V. 103. P. 114309] or by evaporation by electric discharge [4. LiuM, Lu G., Chen J. Synthesis, assambly and characterization of Si nanocrystals and Si-nanocrystal-carbon nanotube hybrid structures // Nanotechnology. 2008. V. 19. P. 265705], [5. Bochkarev A.A., Polyakova V.I. The processes of formation of micro- and nanodispersed systems. - Novosibirsk: Publishing House of the SB RAS, 2010. - 468 p.].

The main disadvantages of such methods are high energy consumption, a wide distribution of particle sizes (from tens to thousands of nm) and a high content of impurities in the resulting product.

Gas-phase synthesis allows to obtain the purest powders [6. Bylinkina N.N., Mushtakova S.L., Oleinik V.A. et al. // Letters in ZhTF. 1996. T. 22. V. 6. S. 43-47], however, it requires large amounts of energy, the use of sophisticated equipment and does not provide purity and monodispersity of the target product.

The known method [7. Pozdnyakov G.A., Saprykin A.I., Yakovlev V.N. Obtaining nanosized silicon powders by decomposition of monosilane in an adiabatic process // DAN T. 456, No. 1, p. 1-4, 2014], selected as a prototype in which nanosized silicon structures are obtained by thermal decomposition of monosilane. The technical implementation of the method consists in the fact that a mixture of gases consisting of argon and monosilane is placed in a reactor having the shape of a cylinder closed on one side with a movable piston and on the other with a removable flange. Moving the piston, the gas mixture is adiabatically compressed, as a result of which its temperature rises to the decomposition temperature of monosilane. Silicon particles formed during the thermal decomposition of monosilane have a close to monodisperse size distribution and form filamentary structures. After that, the target product in the form of "wool" can be removed from the reactor. Depending on the production conditions (temperature, pressure, etc.), silicon nanoparticles can have amorphous or crystalline structures.

The objective of the invention is to provide a method for the synthesis of silicon compounds (nitride or carbide) in the form of nanoscale powders consisting of particles with a given chemical composition, size, morphology and structure.

The technical result of the method is the synthesis of nanosized powders of the target products (silicon nitride or silicon carbide) of increased uniformity in particle size and the ability to control the properties of the target product (size, structure and morphology of particles) by choosing the composition of the gas mixture of the precursors and the operating parameters of the adiabatic compression device used. In addition, the uniformity of conditions inside the adiabatic compression reactor, unlike all known methods, allows you to scale its size and, accordingly, the amount (mass) of the synthesized product.

The technical result is achieved in that in order to obtain silicon nitride or silicon carbide nanopowders, a precursor selected from ammonia gas or acetylene is introduced into a preheated reaction volume filled with a mixture of monosilane with an inert diluent gas, respectively, and the mixture is adiabatically compressed to thermal decomposition, which ensures obtaining the corresponding silicon compound.

Distinctive features of the invention are: obtaining nanopowders of compounds of silicon nitride or silicon carbide by adiabatic compression of the reaction mixture of monosilane with an inert diluent gas and the selected precursor: gaseous ammonia or acetylene, before thermal decomposition of monosilane and the formation of the corresponding silicon compound.

The method is implemented on the layout of the device [8. Yakovlev V.N. Adiabatic compression device. Application for patent of the Russian Federation No. 2013103951, priority dated January 29, 2013] for adiabatic compression of gases (Fig. 1). The installation is based on a pipe (1) placed inside a tubular ohmic heater (2). The pipe is divided by a movable piston (3) into two chambers. The reaction chamber (4) is located between the piston (3) and the flange (8) having a channel for filling the reaction volume with gaseous precursors (10) and a chromel-alumel thermocouple (9) for measuring the temperature in the reaction zone during compression. The chamber (5) is designed for injection of pushing gas, located between the pushing piston and the flange (6) having a channel (11) for connection to a cylinder with compressed gas.

The method of adiabatic compression of the reaction mixture is as follows. At the beginning, the reaction volume (4) is pumped out, then, through the channel for filling the reaction volume, gaseous precursors (10) are filled with a mixture of precursors (and, if necessary, inert diluent gases) and heated to the initial temperature (T ₀ ). Preheating the mixture reduces the degree of compression at which the target reaction is initiated and, if necessary, vaporize the liquid precursors. After that, the chamber (5) is filled with pushing gas from the cylinder. The piston is attached to the flange of the compression chamber (6) with a metal cable (7). The pressure of the pushing gas (P _T ) increases until the cable breaks. After that, the piston begins to move, compressing the reaction mixture of gaseous precursors and inert diluent gases. The temperature in the reactor rises rapidly, reaching a temperature (T _max ), at which intense chemical processes occur with the formation of the target product in the form of nanoparticles. The rise time of the temperature to T _max is about 20 ms. The time during which the temperature remains stable is approximately 1 s. The reaction products formed inside the chamber are removed from the reactor through flange 8 in the form of a “cotton wool” consisting of associates of silicon nanoparticles. The fast flow of the process, stability and uniformity of conditions inside the adiabatic compression reactor, in contrast to all known methods, makes it possible to obtain powders of the target products uniform in size of nanoparticles. In addition, the proposed method, compared with the prototype, in which the decomposition of silane with the formation of silicon nanoparticles, allows the synthesis of nanopowders of various silicon compounds using various precursors. The method is applicable for the production of a wide range of monodisperse nanostructured powders of compounds and individual substances. A necessary condition for its implementation is the gas content and stability of the precursors (or mixtures thereof) at the initial temperature T _{0 of the} reactor.

The method is also applicable to the production of nanostructured powders, heterogeneous in composition, and also to obtain mixtures of nanostructured silicon powders, as it allows to sequentially fill the reaction volume with various precursors without extracting the product of the previous synthesis

To determine the chemical composition of nanopowders of silicon nitride and silicon carbide, atomic emission spectrometry with excitation of spectra in a direct current arc (DCT) and a PGS-2 spectrometer (Karl Zeiss, Germany) were used. For structural analysis nanopowders of the silicon nitride and silicon carbide powder X-ray analysis method used in the sliding beam geometry (diffractometer company Shimadzu XRD - 600 SiK _α radiation). To determine the shape and size of the particles, scanning and transmission electron microscopy (scanning electron microscopes: LEO-1430 (Leica Ltd, USA), Zeiss EVO MA 15 (Karl Zeiss, Germany) and transmission electron microscope TITAN 80-300CS (FEI, Netherlands) were used To determine the particle size distribution, the method of photon correlation spectrometry (90Plus refractometer, Brookhaven, USA) was used.

The following examples show the possibility of obtaining nanostructured silicon compounds.

Example 1. Obtaining silicon nitride by adiabatic compression of a mixture of precursors. The reaction volume of the chamber (4) of the adiabatic device is pumped out, then filled with a mixture of SiH ₄ (9%) + Ar (81%) + NH ₃ (10%) through the channel (10) to charge the reaction volume with gaseous precursors and heated to the initial temperature (T ₀ ) = 128 ° C, initial pressure (before compression of the mixture) P ₀ = 0.09 MPa, compression ratio of the mixture n = 7.7. The target reaction product formed inside the chamber 4 is silicon nitride extracted from the reactor through flange 8.

In FIG. 2 (a) shows a typical view of the resulting product - "wool" from nitride nanoparticles obtained by the proposed method.

In FIG. Figures 3a and 3b show images obtained using a transmission electron microscope (PEM image) of nanostructured silicon nitride particles obtained by adiabatic compression with various magnifications. The PEM image shows that the product consists of extended filaments consisting of adhering particles (a). Silicon nitride nanoparticles have an oval or spherical shape with a characteristic size of ~ 50 nm (b). In FIG. 3d shows the luminescence spectrum of the obtained product.

Example 2. Obtaining silicon carbide by adiabatic compression of a mixture of SiH ₄ (9%) + Ar (81%) + C ₂ H ₂ (10%) are carried out analogously to example 1.

Initial parameters: initial pressure of the mixture P ₀ = 0.105 MPa, initial temperature of the mixture of precursors before compression T ₀ = 131 ° C. The compression ratio is n = 7.7.

In FIG. 2b shows a typical form of the obtained product - “wool” from silicon carbide nanoparticles.

The image (Fig. 4a) obtained with a Zeiss EVO MA 15 scanning electron microscope from Karl Zeiss, Germany (CEM image) shows that the product is a cotton wool from adhered nanoparticles. The PEM image (Fig. 4b, c) shows that the particles have almost the same size of ~ 30 nm. The X-ray diffraction pattern (Fig. 4d) and XRD spectrum (Fig. 4e) obtained using a Shimadzu XRD-600 Japan diffractometer show that silicon carbide powder mainly consists of a crystalline phase.

According to the data of atomic emission spectral analysis with excitation of spectra in a DC arc, a PGS-2 spectrometer (Karl Zeiss, Germany), the purity of nanosilicon obtained by adiabatic compression is 99.95 wt. %

Thus, the proposed method allows the selection of certain adiabatic compression modes to obtain nanoparticles of oxide, nitride and silicon carbide with sizes from 30 to 100 nm in amorphous or crystalline form. The method can be quite simply scaled and implemented in production lines, does not require sophisticated equipment and highly qualified staff.

Claims (1)

A method of producing nanosized powders of silicon nitride or silicon carbide, comprising preheating a mixture of monosilane with an inert diluent gas and a precursor selected from gaseous ammonia or acetylene, respectively, and subsequent adiabatic compression of the reaction mixture to thermal decomposition, providing the corresponding silicon compound.

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