The Characterization of Carbon Deposit Morphologies Using In Situ Scanning Electron Microscopy

Carbon deposits have been grown on heated polycrystalline iron specimens in a gas reaction cell in a scanning electron microscope. The complete range of deposits formed from methane at temperatures between 620°C and 850°C have been surveyed, from the first appearance of solid carbon on the surface to the final structural breakdown of the metal. Four characteristic morphologies have been identified. There are indications that solution-precipitation processes are involved in the growth mechanisms in each case. The importance of structural disorder in the metal is considered and the behaviour of well annealed material is compared to structurally less stable but clean metal surfaces. The processes that occur in the development of particulate deposits have been followed. Auger analysis of individual morphologies has highlighted particular problems in the analysis of carbon deposits after ion etching. The implications of these observations to deposition on less well-defined metal surfaces and gases containing trace impurities is discussed.