Insights into the Mechanism of the Mechanochemical Formation of Metastable Phases

Rana, Resham; Long, Daniel; Kotula, Paul Gabriel; Xu, Yufu; Olson, Dustin; Galipaud, Jules; LeMogne, Thierry

doi:10.1021/acsami.0c18980

Cited by 13 publications

(10 citation statements)

References 61 publications

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“…The pin was attached to an arm with attached strain gauges to enable the normal and lateral forces to be measured. The arm was mounted to a rotatable Conflat flange to allow the pin to be rotated to face a cylindrical-mirror analyzer (CMA) to enable Auger spectra of the pin surface to be obtained [34].…”

Section: Experimental and Theoretical Methodsmentioning

confidence: 99%

Inducing High-Energy-Barrier Tribochemical Reaction Pathways; Acetic Acid Decomposition on Copper

2021

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The surface tribological chemistry of acetic acid on copper is studied using an ultrahigh vacuum tribometer, supplemented by first-principles density functional theory calculations of the surface structure and reaction pathways. Acetic acid forms η 2 -acetate species on bridge sites at room temperature as identified by reflection-absorption infrared spectroscopy. Rubbing the surface with a tungsten carbide ball reduces the amount of carbon and oxygen in the rubbed region at the same rates to leave some carbon and oxygen on the surface. This is different from the thermal decomposition pathway, where heating to ~ 580 K removes all oxygen, but leave a small amount of carbon on the surface. It is postulated that this arises because sliding along a direction aligned within the plane of the adsorbed acetate species can induce a high-energy-barrier pathway in which the η 2 -acetate tilts to form an η 1 -acetate that can react to form a bent CO 2 δ− species that decomposes to evolve carbon monoxide and deposit atomic oxygen on the surface. Repeated acetic acid dosing and rubbing reduces the total amount of acetic acid that can adsorb on the surface by ~ 50% after ~ 4 cycles, resulting is a stable, low-friction film. At this point, the adsorbed acetic acid is completely tribochemically removed. This suggests that adsorbed acetic acid can form a selfhealing film in which any wear of the low-friction film will then allow it to be replenished by shear-induced decomposition of adsorbed acetate species.

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Section: Experimental and Theoretical Methodsmentioning

confidence: 99%

Inducing High-Energy-Barrier Tribochemical Reaction Pathways; Acetic Acid Decomposition on Copper

2021

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“…This has been accomplished for simple mechano-active adsorbates in ultrahigh vacuum (UHV) . For example, the mechano/tribochemical reaction pathways of methyl thiolate species on copper have been extensively investigated − and been found to proceed by the adsorbed methyl thiolate species tilting toward the surface to induce C–S bond scission to evolve small gas-phase hydrocarbons and deposit sulfur on the surface. ,, This is followed by a process in which shear causes the sulfur to be driven into the subsurface region to regenerate a clean surface, as illustrated in Scheme , where k 1 and k 2 are the rate constant for the mechanochemical reaction steps and they have been measured. The methyl thiolate tilting that occurs as the reaction proceeds is intuitively expected to cause the reaction to accelerate by the imposition of both normal and lateral forces, and the increase in reaction rate found by just a normal stress agrees with this idea …”

Section: Introductionmentioning

confidence: 99%

Anisotropy of Shear-Induced Mechanochemical Reaction Rates of Surface Adsorbates; Implications for Theoretical Models

et al. 2022

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Mechanochemical reactions occur by an applied force modifying and ideally accelerating the rate of reaction of a mechanically active species, a mechanophore. Thermal reactions are described by the steepest descent pathway (SDP) of the potential energy surface (PES) from the transition state to the reactant state, which are stationary points on the SDP. The activation energy is calculated from the energy difference between these two points. The PES is modified by an imposed force to yield a reaction pathway given by the force-displaced stationary points (FDSPs), which depend on the magnitude and direction of the force and shape of the PES. However, the SDP has zero force in a direction perpendicular to it so that the PES can be visualized as a “harmonic valley” that forms a potential energy trough about the SDP. If the walls of the potential trough are sufficiently steep, a mechanochemical reaction should be constrained to occur along the SDP, and the influence of an applied force should depend only on the component of the force along it. If this is the case, it should be possible to use just the shape of the PES around the initial and transition states to calculate the effect of an imposed force or stress on mechanochemical reaction rates. The postulate is tested for the mechanically induced decomposition of an adsorbed methyl thiolate species on a Cu(100) single-crystal surface by measuring the azimuthal angular dependence of the mechanochemical methyl thiolate decomposition rate by varying the sliding direction of a sharp atomic force microscope tip over the surface in ultrahigh vacuum. The concept is also illustrated using a model 4-fold potential using a Remoissenet–Peyrard function to mimic the potential of a Cu(100) surface. This yields an angular dependence that agrees well with the prediction from the above postulate. This simplification will facilitate the analysis of mechanochemical rates of both surface and bulk reactions.

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“…The arm was mounted to a rotatable 2 3 4 " Conflat flange to allow the pin to be rotated to face a cylindrical mirror analyzer (CMA) to enable Auger spectra of the pin surface to be obtained. Additional experiments were carried out by analyzing the tungsten carbide pin by X-ray photoelectron spectroscopy after argon ion bombardment using a spectrometer containing a hemispherical analyzer built by ThermoFisher (220i) with a focused monochromatic X-Ray source [12].…”

Section: Experimental and Theoretical Methodsmentioning

confidence: 99%

“…It is becoming increasingly clear that the chemistry of lubricant additives is dominated by mechanochemical processes [1][2][3][4][5][6][7][8] in which the potential energy surface is modified to change the rate of reaction [9][10][11][12][13]. This implies that the nature and stereochemistry of the chemical functionality at the sliding interface might be expected to influence the tribo/mechanochemical reaction rate.…”

Section: Introductionmentioning

confidence: 99%

Influence of the Nature and Orientation of the Terminal Group on the Tribochemical Reaction Rates of Carboxylic Acid Monolayers on Copper

et al. 2021

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The effect of changing the terminal functional group of C 7 and C 8 carboxylate species adsorbed on copper on the rate of tribochemical decomposition is investigated both in an ultrahigh vacuum tribometer and using an atomic force microscopy (AFM) tip, where the conditions are selected to provide similar normal stresses for both experiments. The carbon chains are terminated by alkyl, vinyl and acetylide groups, where the different chain lengths are selected to modify the orientation of the terminal π-orbitals. The pull-off forces measured by AFM are in accord with the calculated molecular structure but, despite this, the rates of tribochemical decomposition of all the adsorbed carboxylates are identical. However, the carbon is lost from the surface at different rates and this is ascribed to the different reactivities of the resulting carbonaceous species that are tribochemically produced at room temperature, but form thermally at ~ 650 K. This results in lower-energy barrier pathways, such as β-hydride elimination reactions, occurring preferentially compared to higher-activation-energy ones, such as coupling reactions. It is proposed that these rates are influenced by the ability of the terminal groups to access the copper surface and accounts for the relative reaction rates and the amount of carbon deposited onto the surface.

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Insights into the Mechanism of the Mechanochemical Formation of Metastable Phases

Cited by 13 publications

References 61 publications

Inducing High-Energy-Barrier Tribochemical Reaction Pathways; Acetic Acid Decomposition on Copper

Inducing High-Energy-Barrier Tribochemical Reaction Pathways; Acetic Acid Decomposition on Copper

Anisotropy of Shear-Induced Mechanochemical Reaction Rates of Surface Adsorbates; Implications for Theoretical Models

Influence of the Nature and Orientation of the Terminal Group on the Tribochemical Reaction Rates of Carboxylic Acid Monolayers on Copper

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