STRUCTURAL AND TEXTURAL CHANGES FROM POLYIMIDE KAPTON TO GRAPHITE .1. OPTICAL MICROSCOPY AND TRANSMISSION ELECTRON-MICROSCOPY

Kapton films, 25-mu-m thick, were carbonized and then graphitized at various temperatures up to 3000-degrees-C. They were studied by optical microscopy and transmission electron microscopy and were prepared by thin-sectioning for transmission electron microscopy. The residual embedded blocks were used as polished sections for optical microscopy. Kapton thin film heat-treated at 650-degrees-C showed thin areas of preferred orientation at its two opposite faces. This orientation extends all over the film thickness between 800-degrees-C and 1000-degrees-C. It corresponds to a statistical orientation of small aromatic layer stacks, parallel to the film plane. From 1000-degrees-C up to 2475-degrees-C flattened pores develop everywhere. At 2475-degrees-C, they suddenly collapse and partial graphitization occurs. The Kapton film is completely graphitized between 2820-degrees-C and 3000-degrees-C. The mechanism of graphitization is similar to that of anthracites and also to that of nongraphitizing carbons heat-treated under pressure.