Reactive Molecular Dynamics Study of Hierarchical Tribochemical Lubricant Films at Elevated Temperatures

Abstract

We have developed a reactive force field (ReaxFF), which is able to reproduce accurately the physical and chemical properties of a comprehensive Fe/Na/P/O system. This ReaxFF was trained systematically using a large number of quantum data of relative energy, heat of formation, partial charges, bulk modulus, and crystal cell parameters of binary, ternary, and quaternary oxides using a robust parallel and multiparameter optimization of genetic algorithm (GA) to achieve the global optimization. The results indicated a substantial improvement upon previous ReaxFFs for systems of Fe x O y , Na x O y , and P x O y crystals. Moreover, an excellent prediction of molecular, electronic, and chemical properties of inorganic alkali polyphosphate (IAP) was found at low and elevated temperatures. An application of this developed ReaxFF in thin film lubrication of IAP confined between hematite surfaces showed a good agreement with experiments which showed that sodium played a vital role at IAP−hematite interfaces. The tribological performance of the sliding interface has been improved due to the formation of a hierarchical structure of the tribofilm.

Tribochemistry: A Review of Reactive Molecular Dynamics Simulations

“…The latter was then used to study sodium pyrophosphate (Na 4 P 2 O 7 ) confined and sheared between iron(III) oxide (Fe 2 O 3 ) surfaces. The simulations revealed shear-driven dissociation of Na 4 P 2 O 7 leading to layering at the liquid-solid interface and diffusion of Na into the surface, in agreement with experimental observations [86].…”

“…Unfortunately, there are few reactive force fields available that include the elements necessary to model iron oxide with lubricants or additives. However, recently, parameters for ReaxFF have been developed for interactions between phosphate esters and iron oxide [52,85] and between inorganic alkali polyphosphates and iron oxide [86]. The latter was then used to study sodium pyrophosphate (Na 4 P 2 O 7 ) confined and sheared between iron(III) oxide (Fe 2 O 3 ) surfaces.…”

“…As additional parameter sets become available, reactive molecular dynamics simulations of more and more complex chemical systems will be possible. For example, recently developed parameter sets enable the simulation of tricresyl phosphate [52] and tetrasodium pyrophosphate [86] on iron oxide. Similar development of potentials for ZDDP or other additives, particularly with ferrous materials, will be extremely valuable.…”

Seven confluence principles: a case study of standardized statistical analysis for 26 methods that assign net atomic charges in molecules

“…94 DDEC6 has been used to construct exible force elds for various materials. [101][102][103][104][105][106][107][108][109][110][111][112] 7. Appendix: mathematical proofs 7.1 Proof that total least squares and orthogonal distance regression yield the same reversible linear model Consider a linear model of the form…”

Tribochemistry and Lubrication of Alkaline Glass Lubricants in Hot Steel Manufacturing

“…It is important to investigate the chemical mechanism of how a glassy lubricant works when it is applied in practice at high temperature and pressure in metal forming. We have carried out some theoretical investigations of the adsorption and thin film lubrication of Na4P2O7 and Na5P3O10 [31][32][33][34], sodium tetraborate (Na2B4O7), and boron oxide (B2O3) molecules [25,35,36], as well as sodium…”