Chain length of additives in relation to lubricants in thin film and boundary lubrication

Abstract

The paper sets out to study the influence of surface active compounds on lubrication of a slow running four ball machine first noted by Beeck, Givens, Smith & Williams (1940). The lubricants are pure paraffins, mainly hexadecane, and the additives long chain acids, amines and alcohols. It was found that the oil film was markedly influenced by the additive and a sharp peak in the curve of scuffing load against chain length was found when the additive and the carrier were of the same chain length and shape. The surface viscosities were measured by a falling plate viscometer and the same peak was found when complete matching of the chain length occurred. These results lend support to the existence of long range forces. The Langmuir isotherm gives an explanation of the failure of lubrication, which leads to the seizure of the surfaces. This explanation is in terms of the heat of adsorption and of the standard change of entropy of adsorption of the polar compound onto the surface. A reasonable extension of the theory allows the lubricating characteristics of mineral oils to be described.