Effect of preparation conditions on gas permeability and sealing efficiency of graphite foil

Nitrogen permeability of graphite foil (GF) based on expandable graphite with different oxidation degrees was measured. Expandable graphite was obtained by the chemical interaction of graphite and nitric acid with the formation of graphite nitrate of II, III, IV stages and by the electrochemical oxidation of graphite in HNO₃ solution followed by water washing. The expandable graphite samples were heat-treated at 800 °C with the formation of exfoliated graphite followed by pressing the exfoliated graphite into GF. The samples of exfoliated graphite and graphite foil were investigated by XRD, SEM, Raman spectroscopy and mercury porosimetry methods. GF nitrogen permeance decreases from 19.7 × 10⁻¹⁰ to 6.7 × 10⁻¹⁰ mol m⁻² s⁻¹ Pa⁻¹ with decreasing a stage number of graphite nitrate from IV to II. Gas permeance of GF based on electrochemical expandable graphite decreases by an order of magnitude up to 0.2 × 10⁻¹⁰ mol m⁻² s⁻¹ Pa⁻¹ in comparison with GF based on graphite nitrate of II stage. Thus, it is possible to produce the graphite foil material with a wide range of permeability and, respectively, the different sealing efficiency by varying the oxidation degree of the initial graphite matrix in the step of obtaining graphite intercalation compounds and expandable graphite.