THE ROLE OF ENVIRONMENT IN THE FRICTION OF DIAMOND FOR MAGNETIC RECORDING HEAD APPLICATIONS

The coefficient of friction for diamond sliding against diamond and for diamond sliding against a thin-film magnetic disk has been measured at low sliding velocities (millimeters per minute). The experiments were carried out in laboratory air, vacuum (10(-8) Torr) and hydrogen, helium, nitrogen and oxygen gases at pressures ranging from 10(-6) to 10(-4) Torr. For both the sliding systems, the coefficient of friction was found to be highest in vacuum and lowest in air. Intermediate values were obtained in the presence of the other gases. For diamond sliding against diamond, the coefficient of friction decreased with increasing pressure of the gas in the chamber; this decrease was particularly rapid in the presence of excited hydrogen. Values of the friction coefficient close to that measured in the presence of air were also obtained in the presence of helium and excited hydrogen for diamond sliding against thin-film disk. There was no detectable change in the coefficient of friction for the latter system in air when the humidity was varied between 12% and 80%. The variations in the friction coefficient with different environments are explained in terms of the interactions occurring between the gases and the diamond/disk surface.