Effects of pH value and fatty acid sodium on friction and wear of alumina under lubrication with water

Alumina shows a high resistance to wear in an environment where molecules with a hydroxyl group such as water and alcohol. The friction characteristic of alumina in water, however, is found significantly inferior to silicon carbide and silicon nitride. So, in order to clarify the friction and wear mechanism of alumina lubricated with water and to improve its characteristics, effects of pH value and the addition of fatty acid sodium were examined using a pin-on-disk sliding tester. The friction coefficient of Alumina was found to show the highest value in pure water, while it decreased in water solutions of acid, alkali and fatty acid sodium. Particularly, the addition of fatty acid sodium reduced the friction coefficient to 0.04. It was found that this reducing effect was attributed to the reactive products formed on the sliding surface by tribochemical reaction.