Tribochemical Mechanisms of Trimethyl and Triethyl Phosphite on Oxidized Iron in Ultrahigh Vacuum

Rana, Resham

doi:10.1007/s11249-019-1205-4

Cited by 11 publications

(18 citation statements)

References 46 publications

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“…The δ + charge on the Fe ion on the bare oxide is + 1.42 electrons, but the charge on the iron decreases for the phosphoruscontaining fragments in the same order as the increase in positive charge on the phosphorus. This indicates that there is charge transfer to the iron from the phosphorus, which contradicts the conclusion arrived at previously [16], where the predicted charge transfer was from iron to phosphorus. The charges on oxygen and carbon atoms were calculated and are summarized in Table 3.…”

Section: Adsorption Of Trimethyl Phosphite On Fe 3 Ocontrasting

confidence: 89%

“…This resulted in a coverage of one adsorbate per 16 octahedral sites on the oxide surface. Since the experimental desorption temperatures did not vary with coverage [16], only a single coverage was investigated using DFT. Adsorption energies were calculated using where E ads is the adsorption energy, E (molecule+Fe3O4slab) is the energy of the Fe 3 O 4 slab with a molecular adsorbate, E Fe 3 O 4 slab is the energy of the Fe 3 O 4 slab alone, and E molecule is the energy of the isolated adsorbate.…”

Section: Theoretical Methodsmentioning

confidence: 99%

“…Compounds containing phosphorus such as phosphate and phosphite esters are used to lubricate Fe (III) oxide surfaces where phosphate films grow during the tribological process [2][3][4][5][6][7]. It appears that the chemistry of phosphate and phosphite esters is controlled by whether molecular decomposition is initiated by P-O or C-O bond scission, where the reaction is dominated by C-O cleavage on metallic iron [8][9][10][11][12][13] but is controlled by P-O bond breakage on iron oxide [14,15] and the surface chemistry of triethyl phosphite (TEPi) and trimethyl phosphite (TMPi) on oxidized iron in ultrahigh vacuum (UHV) has been correlated with the tribological behavior [16]. It is found that the phosphite esters adsorb onto a thin Fe 3 O 4 film grown on an iron substrate by electron donation from the substrate to the phosphorus atom, leading to a binding energy that increases in the order TMPi > TEPi [17], and correlates well with the location of the vacant LUMO energy.…”

Section: Introductionmentioning

confidence: 99%

“…Because the alcohol and aldehyde form simultaneously, this suggests that the hydrogen required to yield the alcohol derives from the alkoxy dehydrogenation to form the aldehyde. A portion of the phosphate esters desorb molecules at relatively low temperatures (~ 290 K) leading to estimated desorption energies from a Redhead analysis [18] of ~ 67 (0.69 eV) for TEPi and ~ 71 (0.73 eV) kJ/mol for TMPi [16]. Note that the decomposition products referred above desorb at temperatures as high as ~ 600 K, so that there are more strongly bound species on the surface that remain to much higher temperatures.…”

Section: Introductionmentioning

confidence: 99%

“…Since activation energies for the sequential removal of alkoxy species have been measured experimentally [16], the experimental activation energies for the simultaneous desorption of alcohols and aldehydes are compared with the heats of reaction to test whether the surface processes obey the Evans-Polanyi free-energy relations [21] and to confirm that alkoxide removal from the phosphate and phosphite esters is the rate-limiting step in their formation.…”

Section: Introductionmentioning

confidence: 99%

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Adsorption and Reaction of Trimethyl and Triethyl Phosphite on Fe3O4 by Density Functional Theory

Rana

Hopper

2020

Tribol Lett

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First-principle density functional theory (DFT) calculations are used to calculate the most stable structures and heats of adsorption of trimethyl and triethyl phosphites on an Fe 3 O 4 surface in order to understand their behavior as lubricant additives. Previous surface science studies of phosphate and phosphite esters on iron oxide surface have shown that they react by sequentially desorbing the corresponding alcohol and aldehyde in equimolar amounts. This implies that the reactions are limited by the rate of alkoxide removal, followed by a rapid reaction to form the alcohol and aldehyde. It is found that the trialkyl phosphites, dialkyl phosphite, and monoalkyl phosphite all adsorb with the phosphorus atoms bound to surface Fe 3+ ions, with the alkoxy groups close to parallel to the surface. The heat of adsorption increases as the alkoxide groups are removed. The postulate that the rate-limiting step in the decomposition of the phosphate esters is the sequential removal of the alkoxide group is tested by plotting the experimental activation energy obtained from temperature-programed desorption experiments versus the corresponding heats of adsorption calculated by DFT. A linear dependence shows that the reaction obeys the so-called Evans-Polanyi relation, thereby confirming the above postulate. The slope of the plot is close to unity and thus implies that the structure of the transition state of the reaction resembles the product.

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Section: Adsorption Of Trimethyl Phosphite On Fe 3 Ocontrasting

confidence: 89%

Section: Theoretical Methodsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Adsorption and Reaction of Trimethyl and Triethyl Phosphite on Fe3O4 by Density Functional Theory

Rana

Hopper

2020

Tribol Lett

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Surface Chemistry at the Solid‐Solid Interface; Selectivity and Activity in Mechanochemical Reactions on Surfaces

et al. 2021

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This paper summarizes the concepts that underpin the way in which forces exerted on chemical systems can either accelerate their rates or induce reaction pathways that cannot be accessed thermally. This was first described in 1935 by Evans and Polanyi who showed how hydrostatic pressure could accelerate the rates of chemical reactions using a thermodynamic analysis of transition-state theory to demonstrate that the reaction rate increased exponentially with pressure, and depends on a socalled activation volume. This is typically~17 Å 3 /molecule and indicates that pressures on the order of GPa's are required to accelerate the rates of chemical reactions, which commonly occur at solid-solid interfaces such as found in a ball mill. We describe how surface mechanochemical reaction mechanisms are studied using the example of the shear-induced decomposition of carboxylates on copper. They thermally decompose on heating to~650 K to evolve carbon dioxide and deposit a hydrocarbon on the surface but shear stresses accelerate the rate of this process so that it occurs at room temperature. However, it is also found that forces parallel to the COO plane induce a non-thermal reaction pathway to evolve carbon monoxide and adsorbed oxygen on the surface. This reaction pathway can be quenched by using adsorbed benzoate species because the larger area of the aryl ring accentuates the tilt of the COO plane towards the surface to increase the rate of the thermal reaction.

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Gas phase lubrication study with an organic friction modifier

Eickworth

Wagner

Daum

et al. 2022

Lubrication Science

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Friction modifier additive technologies play a crucial role in controlling friction and wear of lubricated tribological systems. Novel additives are usually evaluated using formulations of varying concentrations. It can be very difficult to understand the underlying mechanisms in those laboratory tests because of the interaction of base oil with the additives. It thus can be insightful to perform model experiments in a controllable atmosphere. This can be achieved for instance by integrating a tribometer into a vacuum system comprising in-situ surface analytical methods.In this work, a nitrogen containing organic friction modifier is adsorbed from the gas phase onto a Fe2O3 surface. Different coating thicknesses are prepared by varying the duration of the vapor deposition, so that the influence of the coating thickness on the friction behavior can be investigated. The chemical composition of the coated surfaces is also analyzed by coupling to an XPS photoelectron spectrometer.Contrary to the assumption that layers are formed, this friction modifier accumulates in droplets on the Fe2O3 surface. The number of droplets as well as the radii of droplets increase with evaporation time. The chemical composition of the additive does not change as a result of the gas phase deposition. In the friction tests, the smallest friction values are found for a very low coverage of droplets. For larger droplets, friction increases due to a capillary neck of additive that forms between the sliding surfaces and is dragged along during the friction test.Using gas phase adsorption of a nitrogen containing organic friction modifier it was possible to establish a correlation between droplet morphology and the friction behavior.

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Tribochemical Mechanisms of Trimethyl and Triethyl Phosphite on Oxidized Iron in Ultrahigh Vacuum

Cited by 11 publications

References 46 publications

Adsorption and Reaction of Trimethyl and Triethyl Phosphite on Fe3O4 by Density Functional Theory

Adsorption and Reaction of Trimethyl and Triethyl Phosphite on Fe3O4 by Density Functional Theory

Surface Chemistry at the Solid‐Solid Interface; Selectivity and Activity in Mechanochemical Reactions on Surfaces

Gas phase lubrication study with an organic friction modifier

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