Physical properties of surfaces - III—The surface temperature of sliding metals - The temperature of lubricated surfaces

When one solid body slides over another, most of the work done against the frictional force opposing the motion will be liberated as heat between the surfaces, and will raise the temperature of the bodies. A simple calculation shows that the temperature of the surface atoms may reach a very high value. I of this paper describes an attempt to measure the temperature of the surface layers of the bodies during sliding. The surface temperature was measured by using the rubbing contact of two different metals as a thermocouple, and determining the electromotive force generated on sliding. It is apparent that the electrical contact and the friction occur at the same points where the surfaces touch, so that the measurements should give information about the temperature of the actual surface atoms of the metals where they are rubbing. Experiments showed that the local surface temperature was surprisingly high and could exceed 1000°C, even though the mass of the metal was quite cool. The temperature reached by the sliding surfaces depended upon the load, speed, coefficient of friction and thermal conductivity, and was in good agreement with theory. The behaviour of readily fusible metals showed that the temperature measured was a real one. With metals such as gallium, Wood’s metal or lead, the measured tempera­ture rose to a constant value which could not be exceeded, and which corresponded numerically to the melting temperature of each metal.