In situ MoS2 formation and selective transfer from MoDPT films

UHV friction tests and complementary analyses using AES, XPS, TEM and EELS give a global view of the friction reduction mechanisms of MoDTP antiwear and friction-reducing additive. The study was performed with MoDTP tribofilms composed mainly of an amorphous phosphate glass containing flexible and highly dispersed MoS2 single sheets. The transfer films created under UHV friction were studied by AES. The hard and soft acids and bases (HSAB) principle was used to exploit the data. We observed that relatively high friction (mu similar to 0.3) was associated with the transfer of the whole tribofilm from the flat to the pin by a chemical reaction between the phosphates present in the tribofilm and the native oxide layer on the pin. When the oxide layer was removed, the MoS2 sheets reacted with the nascent metal surface of the pin. The transfer film observed on the pin is very thin (4 nm) and it can clearly be seen that only a few single sheets of MoS2 are needed to achieve friction at the centirange. (C) 1998 Elsevier Science S.A. All rights reserved.