Coating of graphite by polyimide and its gas permeability

Abstract

Gas permeability of a high-density isotropic graphite block was reduced by coating the carbonization of aromatic polyimide by using a solution of polyamic acid. Imidization at 400°C in nitrogen atmosphere after the solvent was vaporized out was essential for good adhesion with graphite substrate. By repetition of coating, imidization at 400°C, and carbonization at 1000° C, the permeability was reduced to 2.4 × 10 −4 cm 2/ sec from 1.3 × 10 −1 cm 2/ sec for the original. The carbonization at 450°C gave much lower permeability of 5.0 × 10 −6 cm 2/ sec with pure slip flow.