Procedure for production of silicon of nano or micro-wave structure

FIELD: metallurgy.

SUBSTANCE: electrolysis is performed in melt containing (wt %): to 65CsCl, 15-50 KCl, 5-50 KF, 10-60 K2SiF6 at temperature 550-750 °C. As anode there is used material containing silicon. Also electrolysis is carried out with variation of cathode density of current from 0.005 to 1.5 A/cm2 and with successive separation of silicon deposit off surface of a cathode-substrate and electrolyte.

EFFECT: high output of finished product at relatively simple hardware implementation of process.

3 cl, 4 ex

 

The invention relates to the field of metallurgy of non-metals, namely the electrolytic production of silicon in the form of nanofibers and microfibers, suitable for use in lithium chemical power sources, load cells, thermoelectric converters, temperature sensors, field emission electronics, composite materials, etc.

Known methods for producing fibrous nano - (micro-size particles) silicon structures from the vapor phase on Agrocomplex mechanism ("vapor - liquid - solid"), when the surface of the substrate are formed nanocable alloy of silicon with the originating metals (Au, Ag, Cu, Pt, Pd, Ni). When saturation of the alloy on the silicon on the surface of the substrate begins to form nanovolume (microfiber) and silicon of the same diameter as the drop of the alloy. Nano - (micro-size particles) drop alloy of silicon with the originating metal remains on top of the silicon nanofibers (microfiber) and consumes silicon from the gas phase.

Known chloride process, i.e. the interaction SiCl4+H2going in the temperature range of 900-1050°C [Givargizov H. / filamentous Growth, and lamellar crystals from the vapor. / Nauka, M., 1977, 304; Wagner, R.S. / sat "single-crystal fiber and reinforced their materials", M., Mir, 1973, p.42].

A known method of transferring silicon vials using yo is a (bromine), when the source is heated to 1100-1200°C, and the substrate to 850-1000°C [Sandalova AV, Epiphany, AS Dronyk M.I. / Reports of USSR Academy of Sciences 153, 82 (1963)].

Developed a method of obtaining nanofibers silicon deposition in a vacuum running in the temperature range 500-1000°C [K.Ishiwatari, T.Oka, K.Akiyama / Japan J Phys Apple 6, 1170 (1967)].

Reported obtaining nanofibers silicon by decomposition of SiH4in the temperature range 550-900°C [G.A.Bootsma, H.G.Gassen / J. Crystal growth 10, 223 (1971); Majumdar A et al / U.S. Patent No. 7569941 from 04.08.2009].

The above methods of obtaining nanofibers or microfibers silicon have complex instrumentation, and, consequently, for their organization requires a large capital investment for the purchase of equipment and large operating costs for its operation.

Relatively high operating temperatures (1000°C) of the above technologies in combination with processes in chemically aggressive halogenated carrier gas of silicon, and the need to create in some cases deep vacuum imposes high requirements (quality and cost) to construction materials that can be used in installations for the operation of the above technologies. This ultimately leads to an increase in the cost of silicon nanofibers.

In addition, all of the above technologies in the teaching of Si nanofibers are toxic silicon-containing gases, are harmful to the environment. Therefore, it is necessary to provide measures (and thus increase energy consumption) to prevent the ingress of toxic substances in the environment.

Finally, the use of noble metals-activators, including: gold, platinum, palladium, and others, leads to an inevitable loss of these metals during long-term operation.

In General, the currently existing technologies for silicon nanofibers have great energy used to produce one kg of elemental silicon, which increases the cost of its production.

Upon receipt of refractory metals and materials a significant gain in energy per unit mass while maintaining the desired purity and quality compared to other metallurgical technology gives the electrolysis of molten salts, and especially the process of electrolytic refining of the above mentioned refractory materials in molten salt. However, the electrolytic method of producing nanofibers or microfibers silicon is not known.

An object of the invention is to develop the electrolytic production of silicon nanocolonies and microfiber structure with a lower cost of electricity and thermal energy.

The problem is solved by the fact that in the inventive production method of silicon nano - or micropaleontol patterns by electrolytic refining material containing silicon, the electrolysis is carried out in the melt, containing (wt.%): up to 65 CsCl, 15-50 KCl, 5-50 KF, 10-60 K2SiF6at a temperature of 550-750°C using as the anode material containing silicon, the variation of cathode current density of 0.005 to 1.5 A/cm2with subsequent sludge separation of silicon from the surface of the cathode substrate and the electrolyte.

As a cathode material used graphite, glass carbon, Nickel, silver or other inert with respect to silicon under the conditions of electrolysis materials. Released at the cathode of the silicon periodically removed from the bath together with replaceable electrode, mechanically cleaned from the cathode and separated from the electrolyte by use of heated hydrochloric acid, a solution of ammonium fluoride and distilled water.

As the anode material, which is subjected to electrolytic refining, you can use relatively cheap technical silicon. Technical silicon receive on an industrial scale by a carbothermic recovery quartz carbon. The purity of its primary substance from 98.0 to 99.0%, the structure is fibrous.

The above lower and upper limits of the parameters of the proposed method were obtained experimentally based on itnyj research and analysis of the experimental results with the achievement of the task and technological results in the production of high-purity silicon powder with nanocolonies and microfiber structure.

The inventive method can be characterized as a method of electrolytic refining of technical silicon to obtain nanovoloknistykh and microfiber precipitation of silicon with high yield, in which the electrolyte is sodium chloride and fluoride salt melt.

Silicon chloride-fluoride melt on the basis of salts of alkali metals, especially potassium and cesium, has a number of advantages.

First, the chloride-fluoride melts due to the formation of solid fluoride-chloride complexes of silicon with large cations of alkali metals (potassium or cesium) allows to reduce the vapor pressure over the melt and to prevent loss of silicon via the gas phase in the process of electrolysis. Secondly, the chloride salt is much easier to clean from undesirable impurities, particularly oxygen-containing impurities, which have a significant impact on the structure of the cathode Deposit.

In addition, the low temperature regime (550-750°C) allows the use of relatively cheap, but stable at this temperature structural materials in cells, though this temperature range is suitable for electrolytic selection of crystalline nanovoloknistykh or microfiber electrolytic precipitation of elemental Si.

The technical result is ablanovo method is the possibility to realize the production of silicon nanocolonies or microfiber structure with a high yield of high quality with relatively simple equipment the registration process.

Example 1. The electrorefining technical grade silicon KR-1, which served as the anode, is carried out in the melt, consisting of 39.3 wt.% potassium chloride, 33.8 wt.% fluoride and potassium 26.9 wt.% potassium fluorosilicate preparation, graphite and glassy carbon cathodes. Cathode current density range 0.005 to 0.1 A/cm2. The temperature of the process support 650°C. the Precipitate is mechanically separated from the cathode surface of the substrate and washed from the electrolyte. Released at the cathode residue on 80% consists of curved fibers of silicon with a diameter of 50 to 500 nm and a length of 100 μm, depending on the terms of refinement.

Example 2. The electrorefining technical grade silicon KR-1 is carried out in the melt, consisting of 42,0 wt.% potassium chloride, 5.0 wt.% fluoride and potassium 53.0 wt.% potassium fluorosilicate preparation, with a graphite cathode, a cathode current density of 0.05 A/cm2and 700°C. the Precipitate is mechanically separated from the cathode surface of the substrate and washed from the electrolyte is Released at the cathode residue on 10% consists of fibers of silicon, having a form of rectilinear cylindrical fibers with a diameter of 50 to 500 nm and a length of 100 ám.

Example 3. The electrorefining technical grade silicon KR-1 is carried out in the melt, consisting of 62.1 wt.% cesium chloride, 14.9 wt.% potassium chloride, 14.1 wt.% fluoride of potassium and 8.9 wt.% Huck is afterselect potassium, Nickel cathode, in the range of cathode current densities from 0.01 to 0.15 A/cm2and at the process temperature of 580°C. the Precipitate is mechanically separated from the cathode surface of the substrate and washed from the electrolyte. Released at the cathode, the sediment consists of 70% of the fibers of silicon, having a form of a curved cylinder with a diameter of from 70 to 1500 nm and a length of 100 μm, depending on the conditions of electrolysis.

Example 4. The electrorefining technical grade silicon KR-1 is carried out in the melt, consisting of 33.6 wt.% potassium chloride, 21.4 wt.% fluoride of potassium and 45 wt.% potassium fluorosilicate preparation, with a silver cathode, a cathode current density of 0.02 A/cm2and the process temperature of 700°C. the Precipitate is mechanically separated from the cathode surface of the substrate and washed from the electrolyte. Released at the cathode, the sediment consists of 50% of the fibers of silicon, having a form of a curved cylinder with a diameter of from 200 to 400 nm and a length of 10 μm, depending on the conditions of electrolysis.

Thus, the above data confirm that the combination of stated characteristics of the method allows to obtain pure electrolytic nanofibers or microfibers of silicon, which are characterized by the content of the main component (silicon) > 99.99 wt.%.

1. A method of producing silicon nano - or microfiber structure by electrolytic refining material, terasawa silicon, characterized in that the electrolysis is carried out in the melt, containing (wt.%) up to 65 CsCl, 15-50 KCl, 5-50 KF, 10-60 K2SiF6at a temperature of 550-750°C using as the anode material containing silicon, the variation of cathode current density of 0.005 to 1.5 A/cm2with subsequent sludge separation of silicon from the surface of the cathode substrate and the electrolyte.

2. The method according to claim 1, characterized in that the material of the cathode-substrate use graphite, glass carbon, Nickel and silver.

3. The method according to claim 1, characterized in that as the material containing silicon, use technical silicon.



 

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