Relationship Between Chemical Structure and Effectiveness of Some Metallic Dialkyl and Diaryldithiophosphates in Different Lubricated Mechanisms

The antiwear (AW) and extreme-pressure (EP) properties of some metallic dialkyl and diaryidithiophosphates (MDTP), including zinc, have been studied in different metal/metal contact conditions : four-ball and FZG rigs. We have noted :- With pure dialkyldithiophosphates of different divalent metals (Zn, Cd, Cu, Pb, Ni, Co), prepared from the same alcohol :(a) On the four-ball rig, EP results, expressed in terms of load-wear index, show that the highest performances are obtained with ZnDTP, but statistically the higher the ionic radius of the metal, the better the performance. EP results, expressed in terms of weld load, do not show any difference between these MDTP. (b) On the four-ball rig, AW results, expressed in terms of wear scar, show that the highest performances are obtaine with ZnDTP; beyond a certain value these performances with Zn and Pb are almost independent of the concentration. For the other metallic DTP, there is a very close relationship between performance and concentration. (c) On the FZG gear rig, EP-AW results, expressed in terms of failure load stage and specific wear, show that statistically, the higher the ionic radius of the metal, the better the performance. - With ZnDTP :(a) On the four-ball rig, EP results, expressed in terms of load wear index, do not depend on the chemical structure of the alcohol used for synthetized ZnDTP, but if results are expressed in terms of weld load, better performances are obtained with ZnDTP synthetized from secondary alcohols. AW results show that the effectiveness of ZnDTP from secondary alcohols is slightly higher when the alcohols used contain less than six carbon atoms. Beyond six carbon atoms in primary or secondary alcohol molecules, performances decrease. (b) On the FZG gear rig, EP-AW results show that performances do not depend on the primary or secondary nature of the alcohols used, and that the smaller the hydrocarbon chain of these alcohols, the better the performances. The results of this work indicate that ZnDTP is the most effective of the MDTP we have studied. For ZnDTP prepared from different alcohols and alkylphenols the performances depend not only on the chemical structure of the additive, but also on contact conditions (kinematic, material types, etc. ), and on the criteria considered (seizure load, weld load, wear, etc.