Tribological Properties of TiO2@CTAB Core-Shell Nanopowders as Lubricating Additives

In this experimental investigation, a core-shell-structurednano-lubricating additive was synthesized utilizing the dielectricbarrier discharge plasma (DBDP)-assisted ball grinding technique fora duration of 5 h. The microstructural analysis of the nano-TiO2 powder was performed employing advanced methods such as X-raydiffraction (XRD) and thermogravimetry-differential scanningcalorimetry (TG-DSC). The initial particle size of TiO2 was refined from 1 & mu;m to a range of 150-200 nm, resultingin a remarkable increase in lattice distortion rate by 88.2% and anoil affinity enhancement of 200%. Through the introduction of CTAB'soil-compatible group onto the surface of nano-TiO2 particles,a modified layer with a thickness of 21 nm possessing superior thermalstability and an activation energy (E (a)) of 600 kJ/mol was successfully produced. Molecular dynamics simulationswere conducted to elucidate the mechanism underlying the surface modificationof nano-TiO2 powder facilitated by DBDP-assisted ball grinding,thereby revealing the pivotal role of electrostatic forces in theorganic modification of the TiO2 surface. It was foundthat electrostatic forces dominantly govern the cetyl trimethyl ammoniumbromide (CTAB)-TiO2 composite interface model, contributingto 70% of the total energy with a maximum energy proportion of -187.84kcal/mol. To evaluate the lubrication performance of the compositeoil samples under boundary lubrication conditions, comprehensive assessmentswere carried out using the four-ball method and reciprocating frictionexperiments. The results demonstrated noteworthy enhancements in viscosityindex, dynamic viscosity, and oil film thickness within the compositeoil samples. Particularly, the composite oil containing 0.5 wt % TiO2@CTAB exhibited outstanding extreme pressure resistance, manifestinga significant reduction of 41.7% in the average friction coefficient,a considerable increase of 25.8% in wear spot diameter, and a substantialelevation of 66.9% in maximum nonseizure load. Compared to the baseoil, the incorporation of 0.5 wt % TiO2@CTAB led to a notableincrement of 34.7% in oil film thickness, 6.7% in dynamic viscosity,and 9% in viscosity index. In the tribological experiment simulatingmarine diesel engines, the friction coefficient witnessed a remarkablereduction by 65.8%, accompanied by a substantial decrease of 54.1%in wear rate. This noteworthy improvement in boundary lubricationconditions of the friction pair effectively mitigated friction andwear. For comprehensive characterization of the wear marks, energy-dispersivespectrometry (EDS) and X-ray photoelectron spectroscopy (XPS) techniqueswere employed to analyze the physical structure and chemical composition.The implementation of TiO2@CTAB nano-lubricating additivesresulted in nanobearing and deposition effects, leading to a reductionin contact area and surface roughness, thereby facilitating the restorationof the friction pairs. These findings possess significant implicationsfor extending the service life of diesel engines and ensuring safenavigation. Furthermore, these studies underscore the considerablepotential of core-shell-structured TiO2@CTAB forwidespread application in diesel engines.

Automated summary

A core-shell-structured nano-lubricating additive was synthesized using the DBDP-assisted ball grinding technique. The particle size of nano-TiO2 was refined, resulting in increased lattice distortion rate and oil affinity enhancement. The introduction of a CTAB-compatible group onto the surface of nano-TiO2 particles produced a modified layer with superior thermal stability. The electrostatic forces played a crucial role in the organic modification of the TiO2 surface. The addition of TiO2@CTAB composite oil exhibited improved lubrication performance under boundary lubrication conditions, reducing friction and wear.