2016-Sustainable Industrial Processing Summit
SIPS 2016 Volume 9: Molten Salts and Ionic Liquids, Energy Production
| Editors: | Kongoli F, Gaune-Escard M, Turna T, Mauntz M, Dodds H.L. |
| Publisher: | Flogen Star OUTREACH |
| Publication Year: | 2016 |
| Pages: | 390 pages |
| ISBN: | 978-1-987820-24-9 |
| ISSN: | 2291-1227 (Metals and Materials Processing in a Clean Environment Series) |
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Thermodynamical Substantiation of Metallothermic and High-Temperature Electrochemical Synthesis of Chromium Silicides
Angelina Gab1; Liliia Molotovska2; Viktor Malyshev3; Alla Sushchenko2; Marcelle Gaune-Escard4;1NATIONAL TECHNICAL UNIVERSITY OF UKRAINE, Kyiv, Ukraine; 2V.I. VERNADSKY INSTITUTE OF GENERAL AND INORGANIC CHEMISTRY OF THE NATIONAL ACADEMY OF SCIENCES OF UKRAINE, Kyiv, Ukraine; 3IGIC NASU, Kyiv, Ukraine; 4AIX-MARSEILLE UNIVERSITé/POLYTECH, CNRS/IUSTI UMR7343, Marseille, France;
Type of Paper: Regular
Id Paper: 203
Topic: 13
Abstract:
The aim of the present study is theoretical backgroundation of the possibility of high-temperature electrochemical synthesis (HTES) and metallothermic synthesis of chromium silicides for the practical implementation of these processes.<br />Methods: thermodynamical calculations, cyclic voltammetry, potentio- and galvanostatic electrolysis, X-ray phase analysis.<br />At a temperature of electrolysis 1000 K, silicon containing compounds can be arranged in the order of descending equilibrium isolation potential of silicon as follows:<br />SiF4 >Na2SiO3 >Li2SiO3 >Mg2SiO4 >Na2Si2O5 >Li2Si2O5 >MgSiO3 >SiO2 <br />From the decomposition voltage values, it follows that the most energetically profitable process is the direct silicon deposition process. However, it will depend on the kinetic characteristics of the process, which reaction will take place.<br />Deposition potentials for chromium (-0.7-1.0 V) and for silicon (-1,6-1,9 V) differ substantially. Therefore, the electrochemical synthesis of chromium silicide is possible only in kinetic mode.<br />HTES of chromium silicides was realized from the molten KCl-Na3AlF6-K2CrO4-SiO2 mixture. Volt-ampere dependencies show reduction waves for oxyfluoride complexes of Cr and Si at potentials -0.7 ÷ -0.9 and -1.6 ÷ -1.9 V, respectively, which is congruent with thermodynamical calculations results. Depending on the electrolyte composition and parameters of electrolysis, phases of Cr2O3, higher silicide CrSi2, and silicide Cr3Si mixed with aluminum compounds were obtained.<br />To optimize the yield of chromium silicides, HTES was performed in the KCl-KF-K2SiF6-K2CrO4 system. At the current-voltage dependencies for this system, waves were also found for the reduction of oxyfluoride complexes of Cr and Si at the significantly different potentials. Depending on the electrolyte composition and parameters of electrolysis, both individual Cr2O3, Cr3Si, and CrSi2 phases and mixtures of these phases with low silicon content were obtained.<br />Experimental data on the phase composition of the electrolysis products show that the process of silicothermic reduction of Cr2O3 depends on several factors including the crucial role played by the temperature and duration of the process.<br />Thermodynamic background of metallothermic reduction of halogen containing compounds of chromium and silicon allowed to classify the process conditions by metals-reducers and silicides of different composition. It was confirmed experimentally that obtaining of CrSi2 nanopowders is possible using the method of metallothermic reduction of chromium chloride and sodium fluorosilicate by metals-reducers (Na, K, Mg, Ca).<br />Keywords: chromium silicides, thermodynamics, metallothermic synthesis, electrochemical synthesis.
Keywords:
Molten Salt Chemistry and Thermodynamics;References:
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