Effects of lubricant-additives on the kinetics and mechanisms of ZDDP adsorption on steel surfaces

Wu, Yan; Dacre, B.

doi:10.1016/s0301-679x(97)00022-4

Cited by 29 publications

(8 citation statements)

References 10 publications

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“…A further extension of this approach included long linear boundary-active chain molecules with an imposed connectivity constraint. 41 They found out that an optimum molecular packing order and mixture exists for any coherent adsorbed film formed at the solid barriers, which is in accord with the findings of Wu and Dacre 42 and Tung and Gao. 43,44 These reported analyses were applicable to atomically smooth surfaces and should be extended to rough surfaces with asperity adhesion, ploughing and elastoplastic deformation.…”

Section: Introductionsupporting

confidence: 74%

Nanoscale elastoplastic adhesion of wet asperities

Chong

Teodorescu

Rahnejat

2013

Proceedings of the Institution of Mechanical Engineers, Part J:

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Accurate prediction of friction is crucial for design and efficient operation of many devices, comprising various contacts. In practice, contacting surfaces are rough and often wet. There are several mechanisms, which contribute to friction, including viscous shear of a coherent fluid film, as well as that of a thin adsorbed layer of boundary active molecular species. Additionally, adhesion and elastoplastic deformation of asperities on counterface surfaces may occur. Traditional friction models are based on statistical representation of surface topography as well as description of boundary shear films based on the theoretical lubricant film Eyring shear stress. The study reports a more realistic friction model than the traditional ones, which do not take into account the wet nature of the asperities. The fluid-surface interaction is a main contribution of the article, not hitherto reported in literature. It is shown that ignoring the effect of surface wetness can lead to the over-estimation of boundary friction and under-estimation of contact load-carrying capacity.

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Section: Introductionsupporting

confidence: 74%

Nanoscale elastoplastic adhesion of wet asperities

Chong

Teodorescu

Rahnejat

2013

Proceedings of the Institution of Mechanical Engineers, Part J:

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“…It is generally accepted that ZDDPs decompose under normal engine conditions and that the decomposition products form polyphosphate chains that interconnect and grow forming “pads” on engine parts that act as sacrificial riding surfaces, undergoing wear as a result of friction to protect the underlying material. ,− Although thermal, or thermooxidative, decomposition is regarded as the major mechanism of antiwear film formation, the specific steps involved in this process remain unclear. ,, Additionally, the interaction of ZDDP molecules with other species present in the oil, such as peroxides, acids, and water, and the engine surface itself, are not well understood. − …”

Section: Introductionmentioning

confidence: 99%

“…Reaction conditions likely play a critical role in the formation of antiwear films, and it is these same conditions that make obtaining reliable and consistent data difficult, impairing the formulation of a complete mechanism to describe film formation. Indeed, several degradation pathways that exhibit a dependence on parameters such as temperature − and the presence of certain chemical species in oil ,,,, have been proposed in addition to those mentioned above, and it is likely that several competing processes of ZDDP film formation exist. Computational modeling provides a means to examine chemical species and reactions under specified conditions.…”

Section: Introductionmentioning

confidence: 99%

Finite Temperature Structure and Dynamics of Zinc Dialkyldithiophosphate Wear Inhibitors: A Density Functional Theory and ab Initio Molecular Dynamics Study

Mosey

Woo

2003

J. Phys. Chem. A

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The thermal decomposition of several zinc dialkyldithiophosphate (ZDDP) antiwear additives has been explored with both finite temperature gas-phase ab initio molecular dynamics (MD) simulations and static quantum chemical calculations at the density functional (DFT) level of theory. Calculations have been performed on the ZDDP monomers (Zn(S2P(OR)2)2), ZDDP dimers, and the corresponding linkage isomers (LI-ZDDPs) with a variety of substituents (R = H, Me, Et, i Pr, t Bu, Ph). The results show that the monomeric form of ZDDP likely dominates at finite temperatures for all substituents considered and that the LI-ZDDP isomer is nearly thermoneutral with respect to the parent ZDDP monomer. Optimized geometries of the ZDDP monomer give 4-coordinate Zn structures that are consistent with previously reported theoretical calculations. However, ab initio molecular dynamics simulations of the ZDDP monomers at elevated temperatures show that 2- and 3-coordinate complexes are instead favored and that the decrease in coordination number has a significant effect on the electronic structure of the molecule that may affect the reactivity of ZDDPs with other chemical species present in engine oils. The ab initio MD simulations also provide insight into several decomposition pathways of the various ZDDP species that include the loss of either alkyl or alkoxy radicals as well as the elimination of olefins and sulfides from the ZDDP molecule. The results are discussed in terms of how the observed processes will affect the overall abilities of the antiwear film.

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“…Most investigations on additive adsorption have been performed for zinc dialkyldithiophosphates as lubricant additives for ferrous materials. Few publications deal with the adsorption of ZDTP on iron and iron oxide [1,2], soot [3] powders and steel surfaces [4][5][6], but there are no published results on adsorption of ZDTP on ceramics powders.…”

Section: Introductionmentioning

confidence: 99%

The adsorption of zinc dialkyldithiophosphates on partially stabilized zirconia from hydrocarbon solution

et al. 2006

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Kinetics, isotherms and enthalpy of adsorption of zinc di-n-alkyl(di-n-alkylphenyl, di-n-dialkylphenyl)dithiophosphates (ZDTPs) lubricating oil additives on zirconia partially stabilized by yttria (PSZ) powder from hydrocarbon solution at temperatures 25°C and 35°C were done. The adsorption enthalpy has been determined using a Montcal calorimeter. ZDTP adsorption isotherms are Langmuir-like. The adsorption quantities and differential molar enthalpies DH a d À Á of ZDTPs adsorption on PSZ are low for n-alkyl derivatives, the adsorption decreases with the increasing length of the hydrocarbon chain of the additive ZDTP, the unexpectedly for di-n-propyl ZDTP the differential molar enthalpies of adsorption at 25°C are very low, near zero and for di-n-dialkylphenyl ZDTP only at lower coverage ratios are endothermic, at higher surface coverage for this and remaining additives are exothermic. At 35°C all n-alkyl ZDTPs adsorb on PSZ endothermically endothermic, while both aryl ZDTPs exhibit exothermic effects. All ZDTPs are reversibly physisorbed at 25°C and at 35°C except for both mono-and dialkylphenyl ZDTPs, which are weakly chemisorbed.

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Effects of lubricant-additives on the kinetics and mechanisms of ZDDP adsorption on steel surfaces

Cited by 29 publications

References 10 publications

Nanoscale elastoplastic adhesion of wet asperities

Nanoscale elastoplastic adhesion of wet asperities

Finite Temperature Structure and Dynamics of Zinc Dialkyldithiophosphate Wear Inhibitors: A Density Functional Theory and ab Initio Molecular Dynamics Study

The adsorption of zinc dialkyldithiophosphates on partially stabilized zirconia from hydrocarbon solution

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