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

Development of inhomogeneous microtexture in a glass-like carbon film from polycarbodiimide (PCDI) has been investigated in relation to the internal s tress arising during carbonization. The PCDI films were pre-oxidized throug h a low-temperature heat-treatment in air and carbonized at temperatures up to 1300 degreesC. Under severe pre-oxidation conditions, the PCDI near the film surface was oxidized intensively and during carbonization, the materi al in this region showed a larger volume reduction than that taking place i n the inner region of the film. Since the material in the outer region coul d not freely shrink to a larger extent in the direction parallel to the fil m surface, but was constrained by the material in the inner region, interna l 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 carb on layers were randomly oriented. The inhomogeneous microtexture developed in the pre-oxidized film has also been investigated. (C) 2000 Elsevier Scie nce Ltd. All rights reserved.