Friction and Cleavage of Lamellar Solids in Ultrahigh Vacuum

Abstract

This paper contains the results of measurements of sliding friction on copper surfaces at 10⁻⁶−10⁻⁹ torr for five lamellar solids, namely, molybdenum sulfide, tungsten sulfide, cadmium iodide, bismuth iodide, and phthalocyanine. There is no evidence that the sliding behavior of any of these materials is improved by the presence of gas or vapors. Each evolved considerable Quantities of gas during sliding. Molybdenite and surface-nucleated pyrolytic graphite have been cleaved in an ultrahigh vacuum apparatus built for this purpose. The graphite specimens were in both as-deposited and annealed forms. The predominant gas given off for all three materials was methane.