ИСТИНА

Expanded graphite (EG) is a well-known graphite material that found great application for production non-asbestos packing materials and heat-distributing materials. Recently it was considered as a sorbent for water purification, support for catalyst and electrochemical application. The structure and properties of expanded graphite depend on the way of expandable graphite preparation and on exfoliation conditions. The aim of present work was to find out the correlation between the depth of graphite oxidation and properties of graphite materials. Natural flaky graphite was subjected to intercalation and oxidation in 60% HNO3 using chemical and electrochemical techniques. The depth of graphite oxidation was varied by the time and C:KMnO4 ratio or by the specific quantity of electricity passed through graphite (Q). Exfoliation was carried out at 250 and 900 oC in air. EG prepared from graphite nitrate and thermally reduced graphite oxide (GO) were studied as comparison samples. XRD, Raman spectroscopy, SEM, nitrogen adsorption, DSC and laser flash analysis were applied for all the samples. Even long-term chemical graphite oxidation does not result any changes in graphite structure. The minimum Q necessary for appearance GO phase on XRD patterns and significant change of expandable graphite thermal behavior was estimated. The kinetic model of exfoliation was proposed. Microstructure, porous structure, thermal capacity, and thermal conductivity for all EG samples were determined and correlation between the synthesis conditions and properties was estimated.