Physico-Chemical nanomaterials science

VI-B group metals silicides nanopowders obtaining by metallothermic synthesis
Rozhalovets K.S.1, Shakhnin D.B.1, Malyshev V.V.1
1 Institute for Engineering & Technology, University “Ukraine”. Lvivska St. 23, Kyiv-03115, Ukraine. 
E-mail: rozhalovets@meta.ua

For chromium disilicide metallothermic synthesis realization, 0.02 mol of anhydrous chromium trichloride and 0.04 mol of sodium fluorosilicate are placed into quartz glass container. After addition of 0.22 mol of potassium metal, container was placed into stainless steel reactor under argon atmosphere. Reactor was heated up to 650-750 °C during 10-15 h. After cooling reactor to room temperature, synthesis products were washed and dried for impurities removing. 
Generally, metallothermic reduction reaction process should be represented as follows. At temperature higher then 450°C, sodium fluorosilicate decomposes into sodium fluoride NaF and gaseous silicon fluoride SiF4. Chromium disilicide metallothermic synthesis reaction is based upon interaction of chromium and silicon formed during reduction of chromium (III) chloride and silicon (IV) fluoride by potassium metal.
We estimated the possibility of molybdenum and tungsten dicilicides obtaining by metallothermic reduction of metal chlorides and sodium fluorosilicate by potassium. As molybdenum and tungsten sources, MoCl3 и WCl6 were used. 
Nascent powders thermal stability was determined in air flow at temperature up to 1000°C. According to thermogravimetric analysis (TGA) data, obtained disilicides mass does not change practically up to 700°C. Within temperature range 700- 1000 °C, synthesized powders mass is increased gradually (up to 6.8% for powders obtained by high-temperature electrochemical synthesis method and up to 7.4% for powders obtained by metallothermic method). The difference in mass increasing can be explained by different fineness of powders. At DTA curves, there is one significant exothermic peak at 815-820°C. DTA and TGA data correlation allows to assume that, up to 700°C, synthesized powders do not oxidize. During further temperature increase, significant oxidation of powders surface is observed. Oxidation process becomes intensive at 815-820°C. During further heating, protective oxide layer is formed at powders surface.