Nanocomposites and nanomaterials 
Investigation of thermodynamic features of ultrapure graphite obtaining by the method of high-temperature concentrating 
Strativnov E.V.1, Khovavko A.I.1, Kozhan A.P.1
1 Department of Thermo-chemical Processes and Nanotechnologies,
Gas Institute of the NAS of Ukraine. 
Degtyarivska, 39, Kyiv-03113, Ukraine. 
E-mail: estrativnov@gmail.com
Purity of graphite determines its consumer properties in metallurgy, nuclear-power engineering, electronics, precision engineering etc. There are several ways to beneficiate graphite: mechanical (dry), gravity (wet) and microbiological. There are also high-temperature purification methods, which consist in graphite processing up to 1600…1800 ºС by hazardous compounds of fluorine or chlorine. These methods gives possibility to obtain purity of 99.0…99.8%. For deeper cleaning (more than 99.8%) vacuum refining is used. However, the subtle physicochemical mechanism of this phenomenon has not been studied. So, thermal technology for graphite purification at high temperatures is more often used now. Despite wide popularity of this technology, the essence of the ongoing reactions is studied insufficiently. For thermodynamic studies we used the sample of flaky graphite of commercial batches produced at Zavalye graphite plant (Ukraine), with purity 94.33%. The study was conducted using the software program "Terra". The results of calculations are presented in the equilibrium compositions of condensed and gaseous phases. It is shown that with temperature increasing the oxide impurities are reduced and react between themselves, forming intermediate compounds of the type Fe3C, MgSi03, MgAI204, CaSi03, AI4O4 etc. The graphs show that aluminum, magnesium and calcium containing impurities disappear at temperatures 2300, 2400, 2450 K respectively. Iron-containing impurities disappear at 2800 K, and silicon at 3000 K. Removal of oxides occurs by reducing them to metals, with formation of a more stable double oxides. The obtained data give a complete picture of transformations in beneficiated sample, including formation of intermediate compounds and evaporation of reduced metals. Approximately 99.94% purity of graphite is achieved at temperatures of 2900-2950 K.