Initiation of lubricant catalytic decomposition by hydrogen evolution fromcontact sliding on CHx and CNx overcoats

Tribochemical studies of the head/disk interface (HDI) were conducted using hydrogenated (CHx) and nitrogenated (CNx) carbon disk samples coated with perfluoropolyether ZDOL lubricant. The studies involved drag tests with unc oated and carbon-coated Al2O3-TiC sliders and thermal desorption experiment s in an ultrahigh vacuum (UHV) tribochamber. We observed that the hydrogen evolution from CHx overcoats initiates lubricant catalytic decomposition wi th uncoated Al2O3/TiC sliders, forming CF3 (69) and C2F5 (119). The generat ion of hydrofluoric acid (HF) during thermal desorption experiments provide s the formation mechanism of Lewis acid, which is the necessary component f or catalytic reaction causing Z-DOL lube degradation. On the other hand, fo r CNx films, lubricant catalytic decomposition was prevented due to less hy drogen evolution from the CNx overcoat.