Antiwear film formation of neutral and basic ZDDP: influence of the reaction temperature and of the concentration

Both synchrotron radiation-based techniques (XANES) and transmission electr on microscopy (EDX, EELS) are used to draw a comparison of antiwear and the rmal films generated from neutral and basic ZDDP salts. Antiwear films were created in a pin-on-flat wear machine and the wear debris was collected. T he analysis of the tribofilms did not show any substantial difference betwe en neutral and basic ZDDPs. The wear scar diameter and the P and S chemical environment in the tribofilm were very similar. The chemical analysis of t he wear debris revealed differences in the chemical composition. Wear debri s from basic ZDDP seems to be mostly composed either of unreacted ZDDP or o f a linkage isomer of ZDDP (LI-ZDDP), and zinc polyphosphate; whereas the w ear debris as far as neutral ZDDP is concerned seems to be exclusively comp osed of zinc polyphosphate (and sulphur species). More iron was also detect ed in the wear debris with basic ZDDP - possibly an indication of the iron content of the tribofilm. Differences in chemical structure could also be d etected in the thermal films. While neutral ZDDP reacted with the surface t o form polyphosphates at 150 degrees C, the same reaction products were obt ained with basic ZDDP at 175 degrees C. The concentration of ZDDP in oil is thought to be the main parameter to explain the differences in the thermal film formation.