The Influence of Processing Conditions on Gas Transport and Thermal Properties of Graphite Foil Compressed from Exfoliated Graphite

Abstract

Graphite foil (GF) compressed from exfoliated graphite (EG) is a sealing material, which is used in nuclear energy and the chemical industry. The preparation of graphite foil is a complex process, which includes the intercalation of graphite, water washing, thermal exfoliation and pressing of intermediate products. The preparation conditions significantly influence the structure of the material and its physicochemical properties. Thus, the aim of work was to reveal the correlation between GF processing conditions, its crystalline structure, porosity and gas permeability as well as thermal stability. Sealability of the material is connected with low value of gas permeability, while thermal stability allows use of the material in high-temperature processes. Optimization of these parameters allow for the obtaining of a reliable material and expanding of the areas of its application. Exfoliated graphite for GF was prepared at different temperatures of 600, 800 and 1000 °C from the H2SO4–graphite intercalation compound (GIC) of II, III, IV stages. The influence of the GF processing conditions (the GIC stage number and the EG preparation temperature) on the main properties (gas permeability and thermal oxidation stability) of the sealing materials was investigated. A decrease in GIC stage number leads to the formation of GF with lower macroporosity and lower nitrogen and hydrogen permeability. However, an increase in GF surface area leads to an increase in the rate of GF oxidation by air oxygen. An increase in the EG preparation temperature from 800 to 1000 oC results in the formation of EG with a developed micro- and mesoporosity and increasing GF gas permeability. A decrease in EG preparation temperature down to 600 °C promotes the formation of new transport macropores in GF. The change of the EG preparation temperature has little effect on GF oxidation stability.