Effects of surface chemistry on the mechanochemical decomposition of tricresyl phosphate

Ogbomo, Egheosa; Bhuiyan, Fakhrul H.; Latorre, Carlos Ayestarán; Martini, Ashlie; Ewen, James P.

doi:10.1039/d3cp05320b

Cited by 4 publications

(1 citation statement)

References 110 publications

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“…However, Khajeh et al 20 found the reactivity of TCP molecules trended as Fe 3 O 4 < Fe < Fe 2 O 3 by surface chemistry simulations and experiments. Recently, Ogbomo et al 25 found that the reactivity of TCP molecules trended as Fe 3 O 4 ⟨100⟩ < Fe 3 C⟨010⟩ ∼ a-Fe⟨110⟩ by tribochemistry simulations and the rate of decomposition of TCP molecules on all surfaces increased exponentially with temperature and shear stress. Moreover, the presence of base oil molecules lowered the rate constant for TCP molecules decomposition.…”

Section: ■ Introductionmentioning

confidence: 99%

Tribological Properties of Phosphate Ester Confined between Iron-Based Surfaces

Yang,

Duan

2024

Langmuir

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Recent studies have revealed that phosphate ester lubricant additives undergo decomposition and polymerization when confined between two iron-based surfaces, forming tribofilms that play a crucial role in antiwear and friction reduction. However, the behaviors of decomposition and polymerization, as well as the mechanisms behind the antiwear and friction-reducing properties of these tribofilms, remain largely unexplored. To address these gaps, we employed reactive force field molecular dynamics (ReaxFF-MD) to investigate the tribochemical reactions and tribological properties of tricresyl phosphate (TCP) and tri-n-butyl phosphate (TNBP) confined between three types of iron-based substrates with varying oxygen content: α-Fe⟨110⟩, amorphous FeO (a-FeO), and amorphous Fe2O3 (a-Fe2O3) surfaces. Our findings indicate that TCP and TNBP molecules primarily undergo dissociation of P–O and C–O bonds, a process influenced by both the oxygen content of the substrates and the molecular structure of the additives. Following the dissociation of these bonds, the released carbon–hydrogen groups adsorb onto the substrates, leading to the formation of adsorbed carbon films on the surfaces. Simultaneously, the dissociation of P–O and C–O bonds triggers polymerization reactions, resulting in the creation of organic polyphosphate iron groups confined between the surfaces coated with adsorbed carbon films. Due to the difference in the contact state and shearing behavior between the carbon films and the organic polyphosphate iron groups, substrates with higher oxygen content exhibit relatively higher friction forces for both TCP and TNBP molecules. Additionally, TCP molecules demonstrate lower friction forces compared to those of TNBP molecules on all three iron-based substrates.

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Section: ■ Introductionmentioning

confidence: 99%

Tribological Properties of Phosphate Ester Confined between Iron-Based Surfaces

Yang,

Duan

2024

Langmuir

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Influences of the spacing between nitrogen atoms on tribological performance of dual active site phosphorus-nitrogen (P-N) ionic liquid

Lou,

Liang,

Zhao

et al. 2024

Tribology International

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Effect of Electric Fields on the Decomposition of Phosphate Esters

Zhu,

Ewen,

Kritikos

et al. 2024

J. Phys. Chem. C

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Phosphate esters decompose on metal surfaces and form protective polyphosphate films. For many applications, such as in lubricants for electric vehicles and wind turbines, an understanding of the effect of electric fields on molecular decomposition is urgently required. Experimental investigations have yielded contradictory results, with some suggesting that electric fields improve tribological performance, while others have reported the opposite effect. Here, we use nonequilibrium molecular dynamics (NEMD) simulations to study the decomposition of tri-n-butyl phosphate (TNBP) molecules nanoconfined between ferrous surfaces (iron and iron oxide) under electrostatic fields. The reactive force field (ReaxFF) method is used to model the effects of chemical bonding and molecular dissociation. We show that the charge transfer with the polarization current equalization (QTPIE) method gives more realistic behavior compared to the standard charge equilibration (QEq) method under applied electrostatic fields. The rate of TNBP decomposition via carbon–oxygen bond dissociation is faster in the nanoconfined systems than that in the bulk due to the catalytic action of the surfaces. In all cases, the application of an electric field accelerates TNBP decomposition. When electric fields are applied to the confined systems, the phosphate anions are pulled toward the surface with high electric potential, while the alkyl cations are pulled to the surface with lower potential, leading to asymmetric film growth. Analysis of the temperature- and electric field strength-dependent dissociation rate constants using the Arrhenius equation suggests that, on reactive iron surfaces, the increased reactivity under an applied electric field is driven mostly by an increase in the pre-exponential factor, which is linked to the number of molecule–surface collisions. Conversely, the accelerated decomposition of TNBP on iron oxide surfaces can be attributed to a reduction in the activation energy with increasing electric field strength. Single-molecule nudged-elastic band (NEB) calculations also show a linear reduction in the energy barrier for carbon–oxygen bond breaking with electric field strength, due to stabilization of the charged transition state. The simulation results are consistent with experimental observations of enhanced and asymmetric tribofilm growth under electrostatic fields.

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Effects of surface chemistry on the mechanochemical decomposition of tricresyl phosphate

Abstract: Surface chemistry influences the mechanochemical decomposition of antiwear additives.

Cited by 4 publications

References 110 publications

Tribological Properties of Phosphate Ester Confined between Iron-Based Surfaces

Tribological Properties of Phosphate Ester Confined between Iron-Based Surfaces

Influences of the spacing between nitrogen atoms on tribological performance of dual active site phosphorus-nitrogen (P-N) ionic liquid

Effect of Electric Fields on the Decomposition of Phosphate Esters

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