Shear activation of ZDDP reaction films in the presence and absence of nanodiamonds

We explore the impact of shear stress and nanodiamond (ND) additives on the formation temperatures of thermal- and tribo-reaction films of steel samples immersed in basestock oils containing zinc dialkyl dithiophosphate (ZDDP) additives. The measurements were performed in-situ using a quartz crystal microbalance (QCM) immersed in oil, oil plus ZDDP, and oil plus ZDDP-ND blends over the temperature range 25 200 degrees C. ZDDP reaction film formation temperatures were observed to decrease with contact stress and be similar in value to ZDDP-ND blends. ND were observed to be embedded in the reaction films, consistent with prior observations for Tricresyl phosphate (TCP) ND blends, and also consistent with the presence of both primary and secondary reaction products in the films. In addition, the ZDDP+ND reaction tribofilms were observed to be thicker, rougher and more adhesive than those formed with only ZDDP.

Automated summary

This study investigates the effect of shear stress and nanodiamond additives on the formation temperatures of thermal- and tribo-reaction films on steel samples immersed in basestock oils containing zinc dialkyl dithiophosphate (ZDDP) additives. In-situ measurements using a quartz crystal microbalance (QCM) were conducted over a temperature range of 25-200 degrees C in oil, oil plus ZDDP, and oil plus ZDDP-ND blends. The results show that the formation temperatures of ZDDP reaction films decrease with contact stress and are similar to those of ZDDP-ND blends. Nanodiamonds were found to be embedded in the reaction films, consistent with previous observations for Tricresyl phosphate (TCP) and ND blends, indicating the presence of both primary and secondary reaction products in the films. Furthermore, the ZDDP+ND reaction tribofilms were observed to be thicker, rougher, and more adhesive compared to those formed with only ZDDP.