PLASMA FLUORINATION OF GRAPHITE

Fluorinated graphites are low surface energy, thermally stable solids that have applications as moisture resistant lubricants, water repellents, release agents. and lithium battery cathodes. Conventional methods of synthesizing fluorinated graphite, however, make inefficient use of fluorine feed stocks, are time consuming and limited by safety considerations. In this article, we demonstrate that plasma processing techniques can be used to fluorinate graphite surfaces and thereby reduce the surface free energy from an untreated value of 50 mJ/m to as low as 7 mJ/m2. Pressed graphite pellets and graphite foils are exposed to nitrogen trifluoride and sulfur hexafluoride plasmas. Fluorination is monitored with x-ray photoelectron spectroscopy (XPS), while liquid contact angle measurements are used to assess the free energy of the treated surfaces. Results indicate that significant surface fluorination can be achieved in exposure times of 10-15 min and with only modest plasma energies of 0.2 W/cm2. X-ray photoelectron spectroscopy (XPS) confirms the formation of CF2 and CF covalent bonds. Fluorine depth profiles show that CF2 species predominate on the fluorinated graphite surface, while CF species are found in the subsurface at depths less than 100 angstrom.