COMPARATIVE STUDY OF SURFACE DEPOSITS AND BEHAVIOUR OF MOS2 PARTICLES AND MOLYBDENUM DIALKYL-DITHIO-PHOSPHATE

The lubricating properties of suspensions of MoS2 particles and solutions of molybdenum dialkyl-dithio-phosphate (MDDP) and zinc dialkyl-dithio-phosphate (ZDDP) have been compared in tests on a Falex lubrication tester and a cam-cam-follower rig. The bearing surfaces were subsequently examined by electron microscopy and diffraction. Amorphous polymeric deposits were detected on surfaces run in MDDP, and crystalline deposits were found only on surfaces run in MoS2 suspensions. The rates of wear of the cam and cam-follower in MoS2 suspensions with or without a dispersant were about half that for MDDP. In Falex tests, the load-carrying capacity of suspensions of MoS2 was superior to that of MDDP and ZDDP but at lower loads MDDP gave the greatest endurance and the lowest rate of wear. The lubricating properties of the two very different compounds of molybdenum are considered to depend upon the nature of their deposits on the bearing surfaces. © 1969.