The adsorption and thermal decomposition of tricresylphosphate (TCP) on iron and gold

Wheeler, Donald R.; Faut, O. D.

doi:10.1016/0378-5963(84)90040-0

Cited by 32 publications

(28 citation statements)

References 22 publications

(8 reference statements)

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“…XPS has been the most popular technique for the identification of tribo-films [2,11] by detecting the presence of phosphorous compounds. In this study, selected worn ball and disc samples were cleaned in a cyclohexane ultrasonic bath at room temperature for 15 min before XPS analysis using the Scienta ESCA-300 at NCESS Daresbury laboratory.…”

Section: Methodsmentioning

confidence: 99%

“…However, it is now widely accepted that the effectiveness of TCP as an anti-wear additive is due to the chemical reactions of phosphorous with iron to form an iron phosphate film or pads. Two possible routes have been proposed [2], i.e. either TCP adsorbs on the metal surface where it reacts directly with metal or other components of the lubricant, or TCP first reacts or decomposes in the lubricant producing products which then react with the metal surface.…”

Section: Introductionmentioning

confidence: 99%

“…Since the 1980s, further properties of TCP have been explored including the adsorption/desorption mechanisms and thermal effect [2,6], surface treatment with phosphate esters for wear reduction [7,8] and the importance of corrosive wear when TCP is present [9]. Over the years, ceramics especially silicon nitride have also attracted interest from researchers [10,11].…”

Section: Introductionmentioning

confidence: 99%

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The influence of contact conditions on surface reaction layers formed between steel surfaces lubricated by an aviation oil

Wang

Wood

2007

Tribology International

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This study focuses on the influence of load and temperature on the formation and stability of tribo-films for bearing steel on bearing steel contacts lubricated with an aviation oil, EXXON Turbo 2380 (TCP based -tricresyl phosphate) at ambient temperatures. Experiments were carried out on a pin-on-disc (POD) tribometer (with a ball-on-flat geometry) under an average loading rate of 0.17 N s À1 and sliding speed of 3 m s À1. The X-ray photoelectron spectroscopy (XPS) analysis on the worn surfaces of ball and disc shows that a tribo-film forms on both surfaces at room temperature. The formation and removal of the tribo-film are faster on the ball due to the nature of contact between the ball and disc. It was found that the tribo-films formed at room temperature are vulnerable to initial disc temperature. The higher the initial temperature the higher the load carrying capacity. The tribo-film growth and contact deterioration have been monitored by acoustic emission (AE) and electrostatic charge (ESP) sensing systems in real time. The results show that both AE and ESP can detect the tribo-film and contact breakdown and have great potential for on-line condition monitoring of lubricated tribo-contacts. r

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Section: Methodsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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The influence of contact conditions on surface reaction layers formed between steel surfaces lubricated by an aviation oil

Wang

Wood

2007

Tribology International

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“…In the absence of metal or metal oxide surfaces, alkyl phosphates typically thermally decompose above around 530 K, while aryl phosphates remain stable up to approximately 640 K. 20 TPD and AES experiments have shown that TNBP molecules begin to dissociate at room temperature on iron oxide surfaces 27 and XPS experiments have indicated that TCP decomposes at higher temperature (400-500 K) on steel surfaces. 87 The onset temperatures for thermal decomposition on Fe3O4(001) in Fig. 6 are thus approximately 100 K higher in the ReaxFF MD simulations than observed experimentally.…”

Section: Simulationsmentioning

confidence: 71%

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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“…These studies used temperature-programmed desorption (TPD) and XPS on the Cu(111), Ni(111), and Fe(111) surfaces and all suggest that it is the P-O bonds that are cleaved in the case of trimethylphosphite to produce adsorbed methoxy groups [CH 3 O-]. Studies on Fe foils using TCP itself are a little bit harder to interpret but suggest that it is the C-O bonds that dissociate to produce adsorbed toluyl groups [CH 3 (C 4 H 4 )-] [86,87]. These investigations are still underway.…”

Section: P=mentioning

confidence: 99%

Surface chemistry in tribology

Gellman

Spencer²

2002

Proceedings of the Institution of Mechanical Engineers, Part J:

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IntroductionIn general, the twentieth century marked the first major incursion of chemists into the world of tribology. Driven partly by the need for improved lubricants for new machines developed in the first few decades of the century, and partly by new analytical capabilities, lubricant chemists and tribochemists were to become full partners in the science of tribology. In this review we cover a number of topics in surface chemistry in tribology, which serve both to illustrate some of the successes in tribochemical research over the past decades, and also to show that much work remains to be done before true, first-principles tribochemistry-based lubricant and tribopair design can begin. Boundary Lubrication and Oiliness AdditivesIn an ideal world, lubricated sliding surfaces are separated by a stable fluid film of lubricant, which effectively lowers friction and prevents wear, holding the surfaces apart by virtue of its fluid-mechanical properties. The friction coefficient in such a hydrodynamically lubricated bearing is proportional to ηU/W, where U is the relative sliding speed of the surfaces, W the normal load supported by the bearing and η the Newtonian viscosity [1]. At low sliding speeds (e.g upon startup) and/or higher forces, however, the friction coefficient varies in a more complex way (Figure 1) and at the lowest speeds and friction forces can be 2 orders of magnitude higher than under hydrodynamic lubrication conditions. This is the regime of "boundary lubrication", where fluid films have given way to thin layers that serve as the active lubricants, and the realm of pure engineering (hydrodynamic lubrication) has given 2 way to the complex world of surface chemistry under confinement. Boundary lubrication is clearly of vital importance, since it is the mechanism in operation under the most extreme of tribological conditions. Understanding boundary lubrication, however, has been a challenge to tribochemists over the last century, with light appearing at the end of the tunnel only quite recently. Monolayers, Multilayers and soapsIt was noticed in the 1920s that certain lubricants possessed a quality designated "oiliness", which, independent of their viscosity, led to better lubrication at low sliding speeds [2][3][4]. Generally, these oily lubricants tended to be those of natural origin, such as castor oil, containing long-chain oxygenated organic compounds (esters and acids), which have surfactant properties, and are not usually present in their mineral oil counterparts. It was shown that these oxygenated molecules could, by themselves, reduce friction considerably between sliding surfaces, their effectiveness depending on their molecular weight [5] (Figure 2). Hardy developed a monolayer theory of boundary lubrication (Figure 3), whereby he postulated that, under boundary conditions, the sliding surfaces were held apart by adsorbed, oriented monolayers of polar molecules, which form a plane of low shear strength, thus lowering friction and affording protection of the surfaces.3 Figure 2. Depe...

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The adsorption and thermal decomposition of tricresylphosphate (TCP) on iron and gold

Cited by 32 publications

References 22 publications

The influence of contact conditions on surface reaction layers formed between steel surfaces lubricated by an aviation oil

The influence of contact conditions on surface reaction layers formed between steel surfaces lubricated by an aviation oil

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

Surface chemistry in tribology

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