Role of nitrogen in tribochemical interaction between Zndtp and succinimide in boundary lubrication

Tribochemical interactions between zinc dithiophosphate (Zndtp) and polyiso butene succinimide (PIBSI) were studied in the mild wear regime by a dual a nalysis approach. Both TEM analyses of wear fragments and inside wear scar XPS on tribofilms were obtained in the same location of the wear track. In presence of the succinimide, there are notable modifications in the composi tion of the zinc polyphosphate tribofilm which is classically formed in pre sence of Zndtp alone. Apart from amorphous zinc polyphosphate glass, the fi lm contains also large amounts of oxidised species (oxides, sulphates and n itrates) together with residual succinimide function groups. The atomic rat io N/P is about 0.3. Moreover, compared to Zndtp, less tribofilm is produce d due to some competition in adsorption process. The results highlight the role of the tribochemical reaction to explain the antagonism between the tw o additives. The presence of some iran oxide in the tribofilm material indi cates that the anti-abrasive wear mechanism of Zndtp is hindered by the pre sence of the succinimide. The lower content of the tribofilm in sulphide sp ecies also suggests a lower efficiency to control the anti-seizure properti es of the mixture of the two additives. (C) 2000 Elsevier Science Ltd. All rights reserved.