Graphite carbon foam films prepared from porous polyimide with in situ formed catalytic nickel particles

This article describes the preparation of porous polyimide composites and carbon foam films with uniform and controllable porous structures, using nickel oleate as a pore-forming agent and as a precursor for catalyst formation for the carbonization process. Pore formation occurs by a phase separation initially producing a dispersion of nickel oleate liquid in the polyamide acid film. Subsequent heat treatment induces decomposition of the nickel oleate accompanied by the evolution of foam forming gas. Small nickel particles, formed by the decomposition of nickel oleate, melt as the process temperature rises above 1200°C and these molten nickel particles then play an important catalytic role in promoting the graphitization of the polyimide composites as part of a dynamic process forming pores proceeding through the thickness of the film. These porous structures are maintained after the removal of the nickel by pyrolysis. The thermal behavior and structure of the porous polyimide films were examined and the porosity and stacking structures of the carbon foam films formed by polyimide pyrolysis were investigated. The results indicate that the pore size of the carbon foams could be controlled over a broad range by varying the nickel oleate content participating in the polymerization reaction.