Increasing the thermal diffusivity of flexible graphite sheets by superheated steam treatment

Excerpt

Flexible expanded graphite sheets are used as thermal interface materials for heat dissipation in electronic devices such as CPU packages [1] and LEDs [2], because the graphite sheets have a high thermal conductivity, are lightweight, and can conform well to surfaces. Sheets made of natural graphite are generally fabricated by the following process. Natural flake graphite is initially soaked in intercalating agents such as concentrated sulfuric acid and perchloric acid along with potassium dichromate or nitric acid oxidizing agents to intercalate the reagent ions into the interlayer spaces of the graphite. The graphite is then washed with water to remove excess reagent, and dried. Then, the intercalated graphite is expanded significantly by heat treatment above 1000 K, during which the graphene layers are exfoliated by thermal vaporization of the intercalants. Graphite sheets are mechanically formed by roll-compacting the expanded graphite flakes without binders [3, 4]. …