Adsorption of surrounding gas molecules on pure metal surfaces during wear processes

Abstract

A direct measurement of gas consumption was made during the sliding of twenty-seven elemental metals on each other when they were rubbed together in a vacuum chamber with a restricted volume. The gas pressure in the chamber decreased with time through the adsorption of gas molecules on to freshly generated metal surfaces. Using a mass spectrometer, the nature of the specific gases being adsorbed could be determined through measurement of the pressure drop during the wear process. Through a series of experimental studies, the following facts were observed: 1. (1) Generally speaking, oxygen and water molecules were adsorbed on metal surfaces, and hydrogen molecules were desorbed from metal surfaces during sliding. Far more adsorption of oxygen was observed during mild wear than during severe wear. 2. (2) Oxygen adsorption on elemental metal surfaces during wear was governed by the position of the element in the periodic table. The rare earth metals (f-character elements, such as lanthanum, praseodymium, samarium etc.) adsorbed oxygen most actively; transition metals (d-character elements, such as molybdenum, iron, nickel etc.) were next, and the other metals (s, p-elements, such as silver, zinc, tin etc.) adsorbed the least gas during wear processes. 3. (3) When a magnetic field was applied during iron/iron rubbing, oxygen and water adsorption and hydrogen desorption were greatly accelerated compared with the rates under ordinary conditions. From these findings the authors propose that the action of gas molecules on the wearing surfaces of metals is chemisorption, and they also discuss the role of gas chemisorption in the wear of metals.