Influence of expansion conditions and precursor flake size on porous structure of expanded graphite

Abstract

Expanded graphite is a highly porous vermicular-structured functional material which is promising as a fire-retardant material, precursor material for graphene production, support material for catalysts, phase-change materials, and battery applications. However, since each application field may require EG with a different expansion potential, tailoring the morphology of EG in terms of its pore amount and size, and selecting the appropriate EG for a specific application are crucial. In this study, the relationship between the expansion ratio and the pore structure of EG was investigated by altering the expansion conditions of expandable graphites with different flake sizes. EG materials with various expansion ratios were prepared. While EG obtained from +325 mesh (>44 μm) expandable graphite exhibited a poor intercalation due to relatively small lateral size of the flakes, which resulted in a significantly low expansion ratio, EG prepared from −10 mesh (<2 mm) expandable graphite resulted in relatively higher expansion ratios at expansion temperatures between 600 and 1150 °C. The highest expansion ratio of 10 mesh sample was obtained at 1150 °C as 80 ml/g. On the other hand, +50 mesh (>300 μm) commercial expandable graphite exhibited an expansion ratio of ∼400 ml/g at 1150 °C in a closed-lid crucible. N₂ sorption analyses revealed a predominantly mesoporous structure for this material, as well as some macro- and micropores. The pore volume increased significantly with increasing expansion temperature. High amount of pores in this material are highly advantageous for adsorbing high amount of particles/molecules onto EG for carbon support, catalyst, and battery applications.

Keywords:

• Expanded graphite
• porous structure
• carbon support