Influences of internal stress arising during carbonization of polycarbodiimide: Part I. Development of inhomogeneous microtexture of the carbon film Original Research Article

Development of inhomogeneous microtexture in a glass-like carbon film from polycarbodiimide (PCDI) has been investigated in relation to the internal stress arising during carbonization. The PCDI films were pre-oxidized through a low-temperature heat-treatment in air and carbonized at temperatures up to 1300°C. Under severe pre-oxidation conditions, the PCDI near the film surface was oxidized intensively and during carbonization, the material in this region showed a larger volume reduction than that taking place in the inner region of the film. Since the material in the outer region could not freely shrink to a larger extent in the direction parallel to the film surface, but was constrained by the material in the inner region, internal stresses arose in the film. As a result, triplicated surface layers were developed in the carbon film. In the skin and the third layers, the carbon layers were preferentially oriented parallel and perpendicular to the film surface, respectively. In the second layer and the central region, the carbon layers were randomly oriented. The inhomogeneous microtexture developed in the pre-oxidized film has also been investigated.