Non-graphitic Carbons Research Articles

The effect of current on the friction of carbon brush materials

An examination has been made of the decrease in friction and electrical contact resistance obtained when current is passed between carbon brush materials sliding on themselves or on metals. Experiments using crossed cylinders show that the changes are essentially irreversible and occur when the current exceeds a critical value corresponding to a critical contact temperature. This temperature is within the range 560° C to 1350° C, and corresponds to that at which the material begins to oxidize appreciably; the greatest temperatures are required for highly graphitic carbons and the least for non-graphitic carbons. Oxidation affects the coefficient of friction and the contact resistance primarily by reducing the magnitude of the total real area of contact, and, at the same time, increasing the number of individual contact regions. A possible mechanism for this behaviour is suggested.