The production and properties of filamentous carbon

Carbon filaments have been produced by the cobalt catalysed decomposition of 60 torr acetylene at 725°C. An upper pressure limit of 200 torr is set by polymerisation of acetylene. Pre-heating the acetylene increases filament yield, particularly at either 550 or 650°C. Addition of hydrogen to the acetylene produced a similar but somewhat smaller effect when it was pre-heated to these temperatures. The surface areas of many batches of filaments have been measured by adsorption of radioactive xenon at ?196°C. The values range from 9 to 153 m² · g^?1 depending on the preparation conditions and whether the measurement is made on filaments still bonded to the steel mesh support or on base filaments (when there is access to the inner cores of the filaments). The densities, 2°48 g · cm^?3, indicate that a significant amount of catalyst metal is retained in the filaments. Controlled atmosphere electron microscopy has been used to follow the absorption of water vapour by filaments at ambient temperature.