UA80951C2 - Electrolyte for silicon powder obtaining - Google Patents

Abstract

The invention relates to the technology for metal silicon obtaining by the electrolysis from liquid melts. An electrolyte for obtaining of silicon powder contains silicon (IV) oxide, potassium chloride, potassium tetrafluoroborate, sodium chloride and sodium hexafluorosilicate at corresponding weight ratio of components. The use of the invention allows to reduce melting temperature of the electrolyte and, correspondingly, to reduce power inputs.

Description

Description of the invention

The invention relates to non-ferrous metallurgy, electrometallurgy of silicon, namely: obtaining silicon 2 powders by electrolysis from salt anhydrous melts and can be used in the production of metal-ceramic products, for obtaining alloys and compounds based on silicon, etc. The purpose of the invention is to optimize the electrolysis process by lowering the crystallization temperature of the oxide-salt molten electrolyte.

An electrolyte with a crystallization temperature of 675 K is proposed, which is 362 lower than previously known. The composition of the proposed low-temperature electrolyte includes the following components:

Potassium chloride, grade "ch. d. a", melting point 1043 K;

Potassium tetrafluoroborate, grade "ch. d. a", melting point 803 K;

Sodium hexafluorosilicate, grade "ch. d. a", melting point 1119K;

Sodium chloride, grade "kh.ch.", melting point 1073 K;

Silicon (IM) oxide (quartz glass), melting point 1685 K. The starting materials were dried in advance at a temperature of 378 - 393 K, and then calcined at 623 K to a constant mass. Silicon (IM) oxide was dissolved in a salt mixture of the following composition, wt. 90:

Sodium hexafluorosilicate 21.5 2;

Potassium chloride 9.4 2;

Potassium tetrafluoroborate 64.0 2;

Sodium chloride 5.1-2.

It should be noted that silicon (IM) oxide dissolves well in the salt melt without a significant increase in the temperature of the beginning of crystallization up to 8 wt. 95, in relation to the mass of the salt mixture, and this amount of it (U is enough to carry out electrolysis from this melt, in which it is a source of silicon.

Electrolysis was performed in galvanostatic and potentiostatic modes using a constant current source B5-43. A glass carbon crucible with a volume of .44d-4 m was used as an electrolytic bath. A plate made of graphite or glass carbon was used as an anode, a steel plate was used as a cathode, the ratio of the size of the surface of the cathode to the anode was 71:5 to reduce the influence of the anodic process. The temperature was adjusted and maintained with a P-111 thermostat and fixed with a platinum-platinum rhodium (Ge) thermocouple and a B7-23 digital voltmeter.

In order to choose the optimal mode of the electrolysis process (current density, voltage, etc.), preliminary studies were conducted to establish the mechanism and kinetics of the silicon electroreduction process, as well as its discharge potential (se). For this, chronovoltammetric studies were carried out in the potentiodynamic mode using a PI-50-1 potentiostat with a PR-8 programmer using a three-electrode circuit (the working electrode is the cathode, the auxiliary electrode is the anode, and the reference electrode is platinum). "

The current density in the galvanostatic mode was maintained in the interval (0.07-01 t-o? A/m2 with an accuracy of 70 4 1a6 A/m?, and the voltage - 22528) V (potentiostatic mode) with an accuracy of MY V. In our experiments, the time not with electrolysis was 9-7 / hours. The cathode deposit is formed in the form of a solid metal salt structure, from the so-called "pear". This structure includes silicon powder (35-50)95 mixed with salt components of the electrolyte.

The purification of silicon powder from impurities of the oxide-salt phase was carried out in two stages: washing of soluble salts in hot distilled water followed by drying of the main product at a temperature of 378 - 393 K; with vacuum-thermal distillation of the product (silicon powder with salt impurities) at a temperature of (735,973) K and a pressure of a-1 0-3 Pa. The phase composition of electrolysis products was determined using a DRON-2.0 diffractometer. o Quantitative analysis of the content of silicon in the cathode deposit was determined by a colorimetric method (FEK-58M) in the form of se) silicon-molybdenum heteropolyacid. The current output was determined using a copper coulometer. In this way, on the basis of complex experimental studies (thermal phase analysis, chronovoltammetry, galvanostatic and potentiostatic electrolysis, X-ray phase analysis) taking into account the analysis of the state diagrams of the corresponding salt and metal systems, an electrolyte was invented for the production of silicon powder, which has a lower crystallization temperature by 36 g, compared to the previously known composition of the electrolyte, and therefore less energy-consuming when conducting electrolysis using it. The prototype should be considered "Melt for the electrolytic production of melalic silicon", (Author's

GF! certificate of the USSR Mo 1546515, m.cl. C2581/00, V.V. Bugaenko, G.Ya. Kasyanenko. - MO 4399308/31-26; Application 11.12.87; Publ. 28.02.90, Bul. Mo 8.). This electrolyte contains: potassium hexafluorosilicate - 9-18wt.9o; o potassium chloride - 9-17wt.9o; potassium tetrafluoroborate - 57-81 wt.bo; silicon (IM) oxide - 1-8wt.9o. The use of a new composition of the electrolyte, which melts at a temperature higher than that previously known (prototype), gives another 60 additional advantages, namely: better solubility of silicon (IM) oxide, a decrease in the corrosion activity of the melt in relation to the materials of the electrolyzer, the possibility of using higher values of current density, which is the basis of increasing the speed of electrochemical processes and, as a result, intensification of the electrolysis process.

The results of experimental studies on establishing the optimal mode of electrolysis and the relationship between the composition of the electrolyte, the parameters of the electrolysis process, the current output and the content of silicon in the cathode deposit are presented in Table 1.

It follows from the results of the study that increasing the content of ZO o" in the melt makes it possible to carry out electrolysis at a higher current density, i.e. at a higher speed, while maintaining the optimal parameters of the silicon content in the precipitate and the current yield. In addition, an increase in the content of 5iO»o in the melt ensures

Reducing the frequency of adjusting the melt and adding additives to it 5iO 5". The phase composition of the cathode product after complex purification in water and purification by the method of vacuum-thermal distillation, determined by X-ray phase analysis, corresponds to the pure phase of silicon without impurities. However, with an increase in the electrolysis current density and, accordingly, a voltage greater than (285 30) V, boron impurities are possible in the electrolysis product. 70 Table 1 mo Content of ZO" in the order, in|tzhf1lo-2dimo| 0.8 |Phase composition) The content of the cathode. sediment, 95 Current output, 90 18 1vvvroom 61lyu dv) in ram

Thus, from the electrolyte of the presented composition with a crystallization temperature of 675 K, which is 36be lower than

A previously known (prototype) powdery product, the phase composition of which corresponds to silicon, is restrained under the specified electrolysis modes.

Claims (1)

The formula of the invention with 7 o Electrolyte for obtaining silicon powder, containing silicon oxide (IM), potassium chloride, potassium tetrafluoroborate, which is distinguished by the fact that it additionally contains sodium chloride and sodium hexafluorosilicate at this ratio of components, wt. 9 o: I o silicon oxide (M) 4.0-8.0 potassium chloride 6.9-109 IS o) potassium tetrafluoroborate 58.1-62.1 F sodium chloride 2.8-6.8 sodium hexafluorosilicate 18.2-22.2. (ав) d) Official Bulletin "Industrial Property". Book 1 "Inventions, useful models, topographies of integrated microcircuits", 2007, M 19, 26.11.2007. State Department of Intellectual Property of the Ministry of Education and Science of Ukraine. " - . and? (ee) («c) se) 1 -th name) 60 b5