Liquid Adsorption of Organic Compounds on Hematite α-Fe2O3 Using ReaxFF

Chia, Chung Lim; Avendaño, Carlos; Siperstein, Flor R.; Filip, Sorin V.

doi:10.1021/acs.langmuir.7b02374

Cited by 25 publications

(17 citation statements)

References 60 publications

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“…(within 4 %), 39 and Fe3O4 (within 3 %). 58 They have also been shown to perform favourably compared to other many-body force fields in describing the mechanical properties of α-Fe.…”

Section: Force Fieldmentioning

confidence: 73%

Substituent Effects on the Thermal Decomposition of Phosphate Esters on Ferrous Surfaces

et al. 2020

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Phosphate esters have a wide range of industrial applications, for example in tribology where they are used as vapour phase lubricants and antiwear additives. An atomic-level understanding of phosphate ester tribofilm formation mechanisms is required to improve their tribological performance. A process of particular interest is the thermal decomposition of phosphate esters on steel surfaces, since this initiates polyphosphate film formation. In this study, reactive force field (ReaxFF) molecular dynamics (MD) simulations are used to study the thermal decomposition of phosphate esters with different substituents on several ferrous surfaces. The ReaxFF parameterisation was validated for a representative system using density functional theory (DFT) calculations. During the MD simulations on Fe3O4(001) and α-Fe(110), chemisorption interactions between the phosphate esters and the surfaces occur even at room temperature, and the number of molecule-surface bonds increases as the temperature increases from 300 to 1000 K. Conversely, on hydroxylated, amorphous Fe3O4, most of the molecules are physisorbed and some desorption occurs at high temperature. Thermal decomposition rates were much higher on Fe3O4(001) and particularly α-Fe(110) compared to hydroxylated, amorphous Fe3O4. This suggests that water passivates ferrous surfaces and inhibits phosphate ester chemisorption, decomposition, and ultimately polyphosphate film formation. For the alkyl phosphates, thermal decomposition proceeds mainly through CO and C-H cleavage on Fe3O4(001). Aryl phosphates show much higher thermal stability, and decomposition on Fe3O4(001) only occurs through P-O and C-H cleavage, which require very high temperature. The onset temperature for CO cleavage on Fe3O4(001) increases as: tertiary alkyl < secondary alkyl < primary linear alkyl ≈ primary branched alkyl < aryl. This order is consistent with experimental observations for the thermal stability of antiwear additives with similar substituents. The simulation results clarify a range of surface and substituent effects on the thermal decomposition of phosphate esters on steel that should be helpful for the design of new molecules with improved tribological performance.

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“…(within 4 %), 39 and Fe3O4 (within 3 %). 58 They have also been shown to perform favourably compared to other many-body force fields in describing the mechanical properties of α-Fe.…”

Section: Force Fieldmentioning

confidence: 73%

Substituent Effects on the Thermal Decomposition of Phosphate Esters on Ferrous Surfaces

et al. 2020

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“…The interactions between lubricants and surfaces are more fields such as ReaxFF [43], and ab initio MD methods, but the application to large-scale simulations is difficult. A proper account of chemisorption in MD simulations [44,45], and the description of tribochemistry [46,47] are ongoing problems.…”

Section: Simulation Methodsmentioning

confidence: 99%

Molecular adsorption, self-assembly, and friction in lubricants

Apóstolo

Tsagkaropoulou

Camp

2019

Journal of Molecular Liquids

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Lubricants are complex fluids consisting of a base oil and many different additives, and are used to control friction and wear between solid inorganic surfaces in relative motion. A review of recent work on molecular simulations of lubricants is given. It is shown that simulations can be used to uncover a lot of interesting behaviour, including additive adsorption, additive self-assembly, and a competition between the two. The specific examples to be discussed are: the adsorption of stearic acid and oleic acid in squalane on iron-oxide surfaces; the self-assembly of glycerol monooleate in bulk n-heptane; the adsorption and friction of glycerol monooleate in squalane on iron-oxide surfaces; and the conformations of functionalised copolymers in bulk n-heptane. The structures adopted by the additives can be correlated with the observed frictional properties, opening up the possibility of molecular-level design of new lubricants.

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“…35 The point charges on the atoms vary dynamically during the MD simulation and are calculated using the charge equilibration (Qeq) method. [55][56][57] In the ReaxFF parameter file used in the current study (see Supporting Information), the Fe/P/O ReaxFF parameters were developed by Khajeh et al 36 The (within 4 %), 39 and Fe3O4 (within 3 %). 58 They have also been shown to perform favourably compared to other many-body force fields in describing the mechanical properties of α-Fe.…”

Section: Esystem = Ebond + Eover + Eangle + Etors + Evdw + Ecoulomb +mentioning

confidence: 99%

Substituent Effects on the Thermal Decomposition of Phosphate Esters on Ferrous Surfaces

Ewen

Latorre²,

Gattinoni³

et al. 2020

Preprint

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Phosphate esters have a wide range of industrial applications, for example in tribology where they are used as vapour phase lubricants and antiwear additives. To rationally design phosphate esters with improved tribological performance, an atomic-level understanding of their film formation mechanisms is required. One important aspect is the thermal decomposition of phosphate esters on steel surfaces, since this initiates film formation. In this study, ReaxFF molecular dynamics simulations are used to study the thermal decomposition of phosphate esters with different substituents on several ferrous surfaces. On Fe3O4(001) and α-Fe(110), chemisorption interactions between the phosphate esters and the surfaces occur even at room temperature, and the number of molecule-surface bonds increases as the temperature is increased from 300 to 1000 K. Conversely, on hydroxylated, amorphous Fe3O4, most of the molecules are physisorbed, even at high temperature. Thermal decomposition rates were much higher on Fe3O4(001) and particularly α-Fe(110) compared to hydroxylated, amorphous Fe3O4. This suggests that water passivates ferrous surfaces and inhibits phosphate ester chemisorption, decomposition, and ultimately film formation. On Fe3O4(001), thermal decomposition proceeds mainly through C-O cleavage (to form surface alkyl and aryl groups) and C-H cleavage (to form surface hydroxyls). The onset temperature for C-O cleavage on Fe3O4(001) increases in the order: tertiary alkyl < secondary alkyl < primary linear alkyl ≈ primary branched alkyl < aryl. This order is in agreement with experimental observations for the thermal stability of antiwear additives with similar substituents. The results highlight surface and substituent effects on the thermal decomposition of phosphate esters which should be helpful for the design of new molecules with improved performance.

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Liquid Adsorption of Organic Compounds on Hematite α-Fe₂O₃ Using ReaxFF

Cited by 25 publications

References 60 publications

Substituent Effects on the Thermal Decomposition of Phosphate Esters on Ferrous Surfaces

Substituent Effects on the Thermal Decomposition of Phosphate Esters on Ferrous Surfaces

Molecular adsorption, self-assembly, and friction in lubricants

Substituent Effects on the Thermal Decomposition of Phosphate Esters on Ferrous Surfaces

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