Effect of precursor on the pore structure of carbon foams

Carbon foams were prepared from coal tar pitch, petroleum mesophase pitch, and AR pitch. The molecular weights of the precursors were determined by gel permeation chromatography. Foam structure, average pore diameter and pore diameter distribution were investigated by scanning electron and optical microscopy. It was found that coal tar pitch could not be used as-received to prepare useful carbon foams because of their higher quinoline insoluble (QI) fraction. The carbon foams with homogeneous open pores and microscopic domains were obtained from AR pitch and petroleum mesophase pitch. Carbon foams prepared from AR pitch exhibited a smaller average pore diameter ( 212 mu m), thinner cell walls, a narrower pore diameter distribution ( 180 -300 mu m), higher open-cell ratio, and better ligaments compared with those from the other pitches. It is concluded that a precursor with low molecular weight, narrow molecular weight distribution, and low QI content is favorable for the preparation of carbon foams.