Material‐Dependent Antagonistic Effects between Soot and ZDDP

Abstract

While soot in engine oil is known to accelerate the wear of diesel and gasoline direct‐injection compression‐ignition engines, there is a lack of consensus on the wear mechanism though various hypotheses have been proposed in the literature. Particularly, some recently observed antagonistic effects between soot and a common lubricant antiwear additive, zinc dialkyldithiophosphate (ZDDP), while others did not. The discrepancy is, in part, explained by the strong alloy dependence of such antagonism discovered in this study. Four alloys, 52100 steel and M2, M50, and A2 tool steels, are tested in lubricants containing carbon black (CB, a soot surrogate) with and without ZDDP present. Adding the CB alone to the oil increases the wear rate for all steel alloys as expected. However, distinct wear performance is observed for the four steel alloys when ZDDP is introduced to the CB‐containing oil: while the 52100 steel has notable wear reduction, the three tool steels suffer significant wear increase. Comprehensive tribofilm characterization suggests that the Mo content in the steel alloy and the sulfur from ZDDP strongly influence wear behavior. The combination of CB/Mo‐catalyzed sulfidation and CB‐accelerated abrasion is hypothesized to be responsible for the high wear of the Mo‐alloyed tool steels.

Soot Nanoparticles Generated from Tribofilm Decomposition under Real Engine Conditions for Identifying Lubricant Hazards

“…It should be noted that formation of soot particles is a complex process related to degradation of all components within the engine system. For instance, a recent study has suggested that carbonaceous nanoflakes can encapsulate the fragments of wear particles and inorganic products of mechanochemical reactions . Our current study sheds light on the chemistry occurring within these nanoscopic objects and provides precise information on (i) elemental distribution, (ii) nanoparticle morphology, and (iii) influence on applied operation processes.…”

“…For instance, a recent study has suggested that carbonaceous nanoflakes can encapsulate the fragments of wear particles and inorganic products of mechanochemical reactions. 47 Our current study sheds light on the chemistry occurring within these nanoscopic objects and provides precise information on (i) elemental distribution, (ii) nanoparticle morphology, and (iii) influence on applied operation processes. Given the generally accepted assumption that SNPs are potential toxic specimens, the abovementioned information is critical for toxicity assessment.…”

Using Ionic Liquid Additive to Enhance Lubricating Performance for Low-Viscosity Engine Oil

“…The EF­(ZDDP+IL) tribofilm’s good resistance to contact fatigue micropitting may be attributed to two factors: (i) high content of phosphates and low content of sulfides and (ii) higher thickness (450 nm) to provide a better cushion upon contact. Phosphorus compounds are known to be wear-resistant whereas sulfur compounds could have a detrimental effect on the tribofilm. , The synergistic interaction between ZDDP and IL brings a higher concentration of triboactive elements to the solid–oil interface to form a thick zinc and phosphorus rich but sulfur-less tribofilm. Mechanical properties of the ZDDP, IL, and (ZDDP+IL) generated tribofilms were previously determined by nanoindentation .…”

“…Phosphorus compounds are known to be wearresistant whereas sulfur compounds could have a detrimental effect on the tribofilm. 30,31 The synergistic interaction between ZDDP and IL brings a higher concentration of triboactive elements to the solid−oil interface to form a thick zinc and phosphorus rich but sulfur-less tribofilm. Mechanical properties of the ZDDP, IL, and (ZDDP+IL) generated tribofilms were previously determined by nanoindentation.…”