Marcel van Eijk - Academia.edu (original) (raw)
Papers by Marcel van Eijk
Steinkopff eBooks, Oct 3, 2007
ABSTRACT The adsorption kinetics of the polysaccharide xanthan from aqueous solution on zirconium... more ABSTRACT The adsorption kinetics of the polysaccharide xanthan from aqueous solution on zirconium oxide were studied as a function of pH and ionic strength. The adsorption was monitored by reflectometry in a stagnation-point flow setup. At intermediate pH and ionic strength, xanthan is present in a helical form and it can be viewed as a semi-flexible polymer under these conditions. By lowering the salt concentration or increasing the pH a helix-coil transition takes place. This transition is caused by the mutual electrostatic repulsion of the short side chains of xanthan. The so-formed coil can be considered as a Gaussian chain, with a large radius of gyration. The conformation of the polysaccharide is roughly reflected in the adsorption behavior. It is, however, deduced that the electrostatic interaction between polymer and surface influences the stability of the helix. The adsorption process can be divided in two regimes. At low surface coverage the rate of adsorption is transport-limited, which in a stagnation-point flow leads to a linear time dependence of the adsorbed amount. The adsorption rate in this regime hardly changes with ionic strength or pH. The time range over which it holds, however, does, which can be understood in terms of electrostatic effects. At higher surface coverage two types of behavior are observed. At low ionic strength and on a highly charged surface the adsorbed amount saturates abruptly. This kind of kinetics resemble those of flexible polymers. In this case the xanthan presumably adsorbs in a coil-like conformation, because the helix becomes unstable in the vicinity of the surface. At higher ionic strength and on a weakly charged surface, the adsorbed amount increases gradually over very long times. Under these conditions, the helix conformation is more stable so that we ascribe this slow process to tentatively rearrangement and alignment processes of the stiff chains on the surface.
Wear, Jul 1, 2016
This is a repository copy of An experimental and analytical study of the effect of water and its ... more This is a repository copy of An experimental and analytical study of the effect of water and its tribochemistry on the tribocorrosive wear of boundary lubricated systems with ZDDP-containing oil.
Tribology International, 2017
A novel polymer grease micro-structure is revealed using scanning electron microscopy (SEM), cryo... more A novel polymer grease micro-structure is revealed using scanning electron microscopy (SEM), cryogenic scanning electron microscopy (cryo-SEM) and transmission electron microscopy (TEM). The structure consists of amorphous polypropylene nano-particles uniformly distributed in the base oil. This novel microstructure has never been documented before. Rheology shows that there is no irreversible shear-thinning. The grease shows excellent stability and flow behaviours. In the absence of crystallization and a network thickener structure, it has a potential for use at extremely low start-up temperatures. Spherical roller bearing (SRB) testing shows excellent lubricating performance and the potential for lowering friction in comparison with benchmark greases. It is hypothesized that the grease behaves as a highly stable nano-fluid allowing abundant oil replenishment into the rolling contact, whereby nanoparticles are released with the base oil in the contact.
European Physical Journal B, Feb 1, 1998
Page 1. Eur. Phys. J. B 1, 233244 (1998) THE EUROPEAN PHYSICAL JOURNAL B c EDP Sciences Springer... more Page 1. Eur. Phys. J. B 1, 233244 (1998) THE EUROPEAN PHYSICAL JOURNAL B c EDP Sciences Springer-Verlag 1998 Adsorption and spreading of polymers at plane interfaces; theory and molecular dynamics simulations ...
gemini croscopy from ran gion. Th found to length. bromide length s the comp at rough concentr a ... more gemini croscopy from ran gion. Th found to length. bromide length s the comp at rough concentr a single-two-taile DNA. A with a α changin on diast α,ω-diam showed effects. T similar t being m Key W therapy; Gene Th The p their ori the “sic new gen The pro tion) inv membra
Tribology International, 2019
This is a repository copy of The multiple roles of a chemical tribofilm in hydrogen uptake from l... more This is a repository copy of The multiple roles of a chemical tribofilm in hydrogen uptake from lubricated rubbing contacts.
ACS Applied Materials & Interfaces, 2019
In wind turbine gearboxes, (near-)surface initiated fatigue is attributed to be the primary failu... more In wind turbine gearboxes, (near-)surface initiated fatigue is attributed to be the primary failure mechanism. In this work, the surface fatigue of a hydrogenated tungsten carbide/amorphous carbon (WC/aC:H) thin-film was tested under severe cyclic tribo-contact using PolyAlphaOlefin (PAO) and PAO + Zinc DialkylDithioPhosphate (ZDDP) lubricants. The film was characterised in terms of its structure and chemistry using X-ray diffraction, analytical Transmission Electron Microscopy (TEM) including Electron Energy Loss Spectroscopy (EELS), as well as X-ray Photoelectron Spectroscopy (XPS). The multilayer carbon thin-film exhibited promising surface fatigue performance showing a slight change in the hybridization state of the aC:H matrix. Dehydrogenation of the thin-film and subsequent transformation of cleaved C-H bonds to non-planar sp 2 carbon rings were inferred from EELS and XPS results. Whilst tribo-induced changes to the aC:H matrix were not influenced by a nanometer-thick ZDDP reaction-film, the rate of oxidation of WC and its oxidation state were affected. Whilst accelerating surface fatigue on a steel surface, the ZDDP-tribofilm protected the WC/aC:H film from surface fatigue. In contrast to the formation of polyphosphates from ZDDP molecules on steel surfaces, it appeared that on the WC/aC:H thin film surface ZDDP molecules decompose to ZnO suppressing the oxidative degradation of WC.
Tribology Letters, 2019
Surface reactive additives are crucial in the lubrication of surfaces experiencing cyclic contact... more Surface reactive additives are crucial in the lubrication of surfaces experiencing cyclic contact. The combination of additives in the lubricant, on the material surface and the complex tribo-contact conditions hinders the design of additive packages which can simultaneously protect steel surfaces from wear and fatigue. Amine-based Organic Friction Modifiers (OFMs) influence the tribological performance of steel surfaces. This study investigates the tribochemical impact of three amine-based OFMs in combination with Zinc DialkylDithioPhosphate (ZDDP) on tribological performance, particularly surface fatigue, for steel surfaces in severe rolling-sliding contacts. The thickness of reaction films was tracked throughout experiments and the chemistry of reaction films was examined using X-ray Photoelectron Spectroscopy (XPS). Results highlight the impact of the OFM polar moiety on tribological performance and its influence on chemical composition of tribo-reaction films and their formation kinetics. The combination of selected OFMs with ZDDP reduces frictional forces and can mitigate surface fatigue under certain conditions.
Tribology International, 2019
The behaviour of n-alkanes confined and sheared between iron oxide surfaces has been studied usin... more The behaviour of n-alkanes confined and sheared between iron oxide surfaces has been studied using nonequilibrium molecular dynamics simulations. The molecular extension, orientation, film structure, flow, and friction have been investigated for a range of n-alkanes chain lengths under conditions representative of the elastohydrodynamic lubrication regime. At high pressure, the molecules show strong layering and long-range order, suggesting solid-like films. Conversely, high shear rates result in less elongated, layered, and ordered molecules; indicating more liquid-like films. Although Couette flow is usually observed for short n-alkanes, the flow is often non-linear for long n-alkanes. The friction coefficient increases logarithmically with shear rate, but the slope decreases with increasing pressure such that it becomes insensitive to shear rate for long n-alkanes.
Applied Surface Science, 2017
Understanding the true interfacial mechanisms involved in the growth of tribofilms generated by Z... more Understanding the true interfacial mechanisms involved in the growth of tribofilms generated by Zinc Dialkyl Dithiophosphate (ZDDP) is important because it is the most widely used antiwear additive and there is legislative pressure to find efficient environmentally-friendly replacements. The main focus of this study is to investigate the durability of the ZDDP tribofilm and correlate it to the chemical and physical properties of the glassy polyphosphates. A novel experimental method has been developed to study the effect of lubricant temperature and contact load on tribofilm growth and durability. Results show that physical parameters such as temperature and pressure significantly influence the tribofilm durability. XPS analyses were carried out before suspending the test and after changing the oil to assess the difference in chemical structure of the tribofilm before and after stopping the test. The chemical analyses suggest that there are different chemical properties across the thickness of the tribofilm and these determine the durability characteristics.
Applied Surface Science, 2017
Zinc Dialkyl DithioPhosphate (ZDDP) as a well-known anti-wear additive enhances the performance o... more Zinc Dialkyl DithioPhosphate (ZDDP) as a well-known anti-wear additive enhances the performance of the lubricant beyond its wear-protection action, through its anti-oxidant and Extreme Pressure (EP) functionality. In spite of over thirty years of research attempting to reveal the mechanism of action of ZDDP, there are still some uncertainties around the exact mechanisms of its action. This is especially the case with the role of sulphide layer formed in the tribofilm and its impact on surface fatigue. Although iron sulphide on the substrate is hypothesised in literature to form as a separate layer, there has been no concrete experimental observation on the distribution of the iron sulphide as a dispersed precipitate, distinct layer at the steel substrate or both. It remains to be clarified whether the iron sulphide layer homogeneously covers the surface or locally forms at the surface. In the current study a cross section of the specimen after experiment was prepared and has been investigated with Transmission Electron Microscopy (TEM) and Energy-Dispersive X-ray (EDX) elemental analysis. A 5-10 nm iron sulphide layer is visualised on the interface as a separate layer underneath the phosphate layer with an altered distribution of tribofilm elements near the crack site. The iron sulphide interface layer is more visible near the crack site where the concentration of the sulphur is enhanced. Also, ZDDP elements were clearly detected inside the crack with a varied relative concentration from the crack-mouth to the crack-tip. Sulphur is present inside the crack to a higher extent than in the bulk of the tribofilm.
Journal of Physics D: Applied Physics, 2016
Tribology International, 2017
Hydrogen in mechanical elements can be generated as a result of tribochemical reactions during su... more Hydrogen in mechanical elements can be generated as a result of tribochemical reactions during surface-rubbing causing steel embrittlement. In this study, a new modified Devanathan-Stachurski setup in which a tribological charging cell is incorporated was developed in order to provide an online measurement of hydrogen permeation through steel from a lubricated metal-metal contact. This new technique enables the study of the hydrogen source and the rate of its permeation in a tribocontact. The effect of water contamination and the presence of conventional anti-wear and friction modifier additives in polyalphaolefin base oil on tribologicallyinduced hydrogen uptake were investigated. The results indicate significant influence of water on hydrogen uptake. The ZDDP anti-wear has promoted hydrogen uptake from the tribocontact. Whilst MoDTC friction modifier reduced the hydrogen permeation.
Tribology International, 2017
Wear performance of any tribological system can be influenced in a complex way by water contamina... more Wear performance of any tribological system can be influenced in a complex way by water contamination. Water can be the cause of steel corrosion which, in turn, can accelerate wear. It can decompose the additives in the oil and create a more corrosive environment which leads to the higher wear in the system. A key novelty of this study is to investigate the effect of relative humidity and the tribochemical changes on the tribological performance and tribofilm characteristics of boundary lubricated systems by means of designing a humidity control system integrated to the Mini Traction Machine (MTM) and Spacer Layer Interferometry Method (SLIM) for the first time. The system is capable of simulating rolling-sliding conditions continuously where lubricant can be contaminated with water. This paper is the first part of a two-part study and the theoretical aspects of the work is the subject of the second part of this investigation. It was observed that humidity hinders the tribofilm formation, especially at higher values of relative humidity and lower temperatures and it can significantly affect the wear process. The correlation between tribofilm thickness, water concentration, temperature and wear of the system was studied. The experimental results suggest that the higher the humidity, the higher the wear of the system and it is more noticeable at lower temperatures where the tribofilm in thinner. The surface chemistry of zinc polyphosphates was investigated as a function of humidity.
Tribology International, 2017
Water ingress into the lubricant as a contaminant affects performance leading to an alteration in... more Water ingress into the lubricant as a contaminant affects performance leading to an alteration in wear, corrosion and fatigue behaviour of the tribological components especially in the rolling element bearings. The current study addresses the tribochemical phenomena involved in micropitting in tribocorrosion systems where different levels of dissolved-water are present in a model lubricant. In this study the effect of different temperatures, water concentrations and relative humidities have been investigated on micropitting under rolling/sliding contacts. The influence of free and dissolved water on tribocorrosive micropitting is clarified. The tribochemical change of the reaction films is studied using X-ray Photoelectron Spectroscopy (XPS) which confirmed that the (poly)phosphate chain length and tribofilm thickness are reduced with increased dissolved-water level. 1. Introduction Water is known as an insidious lubricant contaminant [1, 2]. Water can enter into the lubricant through several sources including a humid environment [2-5] by absorption and condensation, leakage from heat exchanger [2], by-product of chemical reactions [2], free-water [2, 6, 7], etc. Depending on the extent of water ingress in the oil, beyond or within the oil saturation level, water can exist as free-water or dissolved-water, respectively. The saturation level of a lubricant, representing its hygroscopicity, depends on the physiochemical characteristics of the base stock, additive package, environmental parameters (relative humidity and temperature) [8] and oil condition [9]. Free-water in the lubricant forms an emulsion which has an inferior load carrying capacity [10] leading to deficient lubricant performance.
The European physical journal. E, Soft matter, 2002
The association behaviour of a number of glucitol amine gemini surfactants has been investigated ... more The association behaviour of a number of glucitol amine gemini surfactants has been investigated by means of molecular dynamics and self-consistent-field calculations. We have shown that the titratable head group of the surfactant is responsible for a micelle-to-membrane transition when changing the pH. Furthermore, the association structure of this group of surfactants is shown to be very sensitive to ionic strength. The combination of a charged head group, a spacer, and the hydrophilic glucitol side chains is responsible for the possible structural transitions in the associates as a function of ionic strength and pH.
Tribology Letters, 2015
Tribochemistry plays a very important role in the behaviour of systems in tribologically loaded c... more Tribochemistry plays a very important role in the behaviour of systems in tribologically loaded contacts under boundary lubrication conditions. Previous works have mainly reported contact mechanics simulations for capturing the boundary lubrication regime, but the real mechanism in which tribofilms reduce wear is still unclear. In this paper, the wear prediction capabilities of a recently published mechanochemical simulation approach (Ghanbarzadeh et al. in Tribol Int, 2014) are tested. The wear model, which involves a time-and spatially dependent coefficient of wear, was tested for two additive concentrations and three temperatures at different times, and the predictions are validated against experimental results. The experiments were conducted using a mini-traction machine in a sliding/rolling condition, and the spacer layer interferometry method was used to measure the tribofilm thickness. Wear measurements have been taken using a white-light interferometry. Good agreement is seen between simulation and experiment in terms of tribofilm thickness and wear depth predictions.
Steinkopff eBooks, Oct 3, 2007
ABSTRACT The adsorption kinetics of the polysaccharide xanthan from aqueous solution on zirconium... more ABSTRACT The adsorption kinetics of the polysaccharide xanthan from aqueous solution on zirconium oxide were studied as a function of pH and ionic strength. The adsorption was monitored by reflectometry in a stagnation-point flow setup. At intermediate pH and ionic strength, xanthan is present in a helical form and it can be viewed as a semi-flexible polymer under these conditions. By lowering the salt concentration or increasing the pH a helix-coil transition takes place. This transition is caused by the mutual electrostatic repulsion of the short side chains of xanthan. The so-formed coil can be considered as a Gaussian chain, with a large radius of gyration. The conformation of the polysaccharide is roughly reflected in the adsorption behavior. It is, however, deduced that the electrostatic interaction between polymer and surface influences the stability of the helix. The adsorption process can be divided in two regimes. At low surface coverage the rate of adsorption is transport-limited, which in a stagnation-point flow leads to a linear time dependence of the adsorbed amount. The adsorption rate in this regime hardly changes with ionic strength or pH. The time range over which it holds, however, does, which can be understood in terms of electrostatic effects. At higher surface coverage two types of behavior are observed. At low ionic strength and on a highly charged surface the adsorbed amount saturates abruptly. This kind of kinetics resemble those of flexible polymers. In this case the xanthan presumably adsorbs in a coil-like conformation, because the helix becomes unstable in the vicinity of the surface. At higher ionic strength and on a weakly charged surface, the adsorbed amount increases gradually over very long times. Under these conditions, the helix conformation is more stable so that we ascribe this slow process to tentatively rearrangement and alignment processes of the stiff chains on the surface.
Wear, Jul 1, 2016
This is a repository copy of An experimental and analytical study of the effect of water and its ... more This is a repository copy of An experimental and analytical study of the effect of water and its tribochemistry on the tribocorrosive wear of boundary lubricated systems with ZDDP-containing oil.
Tribology International, 2017
A novel polymer grease micro-structure is revealed using scanning electron microscopy (SEM), cryo... more A novel polymer grease micro-structure is revealed using scanning electron microscopy (SEM), cryogenic scanning electron microscopy (cryo-SEM) and transmission electron microscopy (TEM). The structure consists of amorphous polypropylene nano-particles uniformly distributed in the base oil. This novel microstructure has never been documented before. Rheology shows that there is no irreversible shear-thinning. The grease shows excellent stability and flow behaviours. In the absence of crystallization and a network thickener structure, it has a potential for use at extremely low start-up temperatures. Spherical roller bearing (SRB) testing shows excellent lubricating performance and the potential for lowering friction in comparison with benchmark greases. It is hypothesized that the grease behaves as a highly stable nano-fluid allowing abundant oil replenishment into the rolling contact, whereby nanoparticles are released with the base oil in the contact.
European Physical Journal B, Feb 1, 1998
Page 1. Eur. Phys. J. B 1, 233244 (1998) THE EUROPEAN PHYSICAL JOURNAL B c EDP Sciences Springer... more Page 1. Eur. Phys. J. B 1, 233244 (1998) THE EUROPEAN PHYSICAL JOURNAL B c EDP Sciences Springer-Verlag 1998 Adsorption and spreading of polymers at plane interfaces; theory and molecular dynamics simulations ...
gemini croscopy from ran gion. Th found to length. bromide length s the comp at rough concentr a ... more gemini croscopy from ran gion. Th found to length. bromide length s the comp at rough concentr a single-two-taile DNA. A with a α changin on diast α,ω-diam showed effects. T similar t being m Key W therapy; Gene Th The p their ori the “sic new gen The pro tion) inv membra
Tribology International, 2019
This is a repository copy of The multiple roles of a chemical tribofilm in hydrogen uptake from l... more This is a repository copy of The multiple roles of a chemical tribofilm in hydrogen uptake from lubricated rubbing contacts.
ACS Applied Materials & Interfaces, 2019
In wind turbine gearboxes, (near-)surface initiated fatigue is attributed to be the primary failu... more In wind turbine gearboxes, (near-)surface initiated fatigue is attributed to be the primary failure mechanism. In this work, the surface fatigue of a hydrogenated tungsten carbide/amorphous carbon (WC/aC:H) thin-film was tested under severe cyclic tribo-contact using PolyAlphaOlefin (PAO) and PAO + Zinc DialkylDithioPhosphate (ZDDP) lubricants. The film was characterised in terms of its structure and chemistry using X-ray diffraction, analytical Transmission Electron Microscopy (TEM) including Electron Energy Loss Spectroscopy (EELS), as well as X-ray Photoelectron Spectroscopy (XPS). The multilayer carbon thin-film exhibited promising surface fatigue performance showing a slight change in the hybridization state of the aC:H matrix. Dehydrogenation of the thin-film and subsequent transformation of cleaved C-H bonds to non-planar sp 2 carbon rings were inferred from EELS and XPS results. Whilst tribo-induced changes to the aC:H matrix were not influenced by a nanometer-thick ZDDP reaction-film, the rate of oxidation of WC and its oxidation state were affected. Whilst accelerating surface fatigue on a steel surface, the ZDDP-tribofilm protected the WC/aC:H film from surface fatigue. In contrast to the formation of polyphosphates from ZDDP molecules on steel surfaces, it appeared that on the WC/aC:H thin film surface ZDDP molecules decompose to ZnO suppressing the oxidative degradation of WC.
Tribology Letters, 2019
Surface reactive additives are crucial in the lubrication of surfaces experiencing cyclic contact... more Surface reactive additives are crucial in the lubrication of surfaces experiencing cyclic contact. The combination of additives in the lubricant, on the material surface and the complex tribo-contact conditions hinders the design of additive packages which can simultaneously protect steel surfaces from wear and fatigue. Amine-based Organic Friction Modifiers (OFMs) influence the tribological performance of steel surfaces. This study investigates the tribochemical impact of three amine-based OFMs in combination with Zinc DialkylDithioPhosphate (ZDDP) on tribological performance, particularly surface fatigue, for steel surfaces in severe rolling-sliding contacts. The thickness of reaction films was tracked throughout experiments and the chemistry of reaction films was examined using X-ray Photoelectron Spectroscopy (XPS). Results highlight the impact of the OFM polar moiety on tribological performance and its influence on chemical composition of tribo-reaction films and their formation kinetics. The combination of selected OFMs with ZDDP reduces frictional forces and can mitigate surface fatigue under certain conditions.
Tribology International, 2019
The behaviour of n-alkanes confined and sheared between iron oxide surfaces has been studied usin... more The behaviour of n-alkanes confined and sheared between iron oxide surfaces has been studied using nonequilibrium molecular dynamics simulations. The molecular extension, orientation, film structure, flow, and friction have been investigated for a range of n-alkanes chain lengths under conditions representative of the elastohydrodynamic lubrication regime. At high pressure, the molecules show strong layering and long-range order, suggesting solid-like films. Conversely, high shear rates result in less elongated, layered, and ordered molecules; indicating more liquid-like films. Although Couette flow is usually observed for short n-alkanes, the flow is often non-linear for long n-alkanes. The friction coefficient increases logarithmically with shear rate, but the slope decreases with increasing pressure such that it becomes insensitive to shear rate for long n-alkanes.
Applied Surface Science, 2017
Understanding the true interfacial mechanisms involved in the growth of tribofilms generated by Z... more Understanding the true interfacial mechanisms involved in the growth of tribofilms generated by Zinc Dialkyl Dithiophosphate (ZDDP) is important because it is the most widely used antiwear additive and there is legislative pressure to find efficient environmentally-friendly replacements. The main focus of this study is to investigate the durability of the ZDDP tribofilm and correlate it to the chemical and physical properties of the glassy polyphosphates. A novel experimental method has been developed to study the effect of lubricant temperature and contact load on tribofilm growth and durability. Results show that physical parameters such as temperature and pressure significantly influence the tribofilm durability. XPS analyses were carried out before suspending the test and after changing the oil to assess the difference in chemical structure of the tribofilm before and after stopping the test. The chemical analyses suggest that there are different chemical properties across the thickness of the tribofilm and these determine the durability characteristics.
Applied Surface Science, 2017
Zinc Dialkyl DithioPhosphate (ZDDP) as a well-known anti-wear additive enhances the performance o... more Zinc Dialkyl DithioPhosphate (ZDDP) as a well-known anti-wear additive enhances the performance of the lubricant beyond its wear-protection action, through its anti-oxidant and Extreme Pressure (EP) functionality. In spite of over thirty years of research attempting to reveal the mechanism of action of ZDDP, there are still some uncertainties around the exact mechanisms of its action. This is especially the case with the role of sulphide layer formed in the tribofilm and its impact on surface fatigue. Although iron sulphide on the substrate is hypothesised in literature to form as a separate layer, there has been no concrete experimental observation on the distribution of the iron sulphide as a dispersed precipitate, distinct layer at the steel substrate or both. It remains to be clarified whether the iron sulphide layer homogeneously covers the surface or locally forms at the surface. In the current study a cross section of the specimen after experiment was prepared and has been investigated with Transmission Electron Microscopy (TEM) and Energy-Dispersive X-ray (EDX) elemental analysis. A 5-10 nm iron sulphide layer is visualised on the interface as a separate layer underneath the phosphate layer with an altered distribution of tribofilm elements near the crack site. The iron sulphide interface layer is more visible near the crack site where the concentration of the sulphur is enhanced. Also, ZDDP elements were clearly detected inside the crack with a varied relative concentration from the crack-mouth to the crack-tip. Sulphur is present inside the crack to a higher extent than in the bulk of the tribofilm.
Journal of Physics D: Applied Physics, 2016
Tribology International, 2017
Hydrogen in mechanical elements can be generated as a result of tribochemical reactions during su... more Hydrogen in mechanical elements can be generated as a result of tribochemical reactions during surface-rubbing causing steel embrittlement. In this study, a new modified Devanathan-Stachurski setup in which a tribological charging cell is incorporated was developed in order to provide an online measurement of hydrogen permeation through steel from a lubricated metal-metal contact. This new technique enables the study of the hydrogen source and the rate of its permeation in a tribocontact. The effect of water contamination and the presence of conventional anti-wear and friction modifier additives in polyalphaolefin base oil on tribologicallyinduced hydrogen uptake were investigated. The results indicate significant influence of water on hydrogen uptake. The ZDDP anti-wear has promoted hydrogen uptake from the tribocontact. Whilst MoDTC friction modifier reduced the hydrogen permeation.
Tribology International, 2017
Wear performance of any tribological system can be influenced in a complex way by water contamina... more Wear performance of any tribological system can be influenced in a complex way by water contamination. Water can be the cause of steel corrosion which, in turn, can accelerate wear. It can decompose the additives in the oil and create a more corrosive environment which leads to the higher wear in the system. A key novelty of this study is to investigate the effect of relative humidity and the tribochemical changes on the tribological performance and tribofilm characteristics of boundary lubricated systems by means of designing a humidity control system integrated to the Mini Traction Machine (MTM) and Spacer Layer Interferometry Method (SLIM) for the first time. The system is capable of simulating rolling-sliding conditions continuously where lubricant can be contaminated with water. This paper is the first part of a two-part study and the theoretical aspects of the work is the subject of the second part of this investigation. It was observed that humidity hinders the tribofilm formation, especially at higher values of relative humidity and lower temperatures and it can significantly affect the wear process. The correlation between tribofilm thickness, water concentration, temperature and wear of the system was studied. The experimental results suggest that the higher the humidity, the higher the wear of the system and it is more noticeable at lower temperatures where the tribofilm in thinner. The surface chemistry of zinc polyphosphates was investigated as a function of humidity.
Tribology International, 2017
Water ingress into the lubricant as a contaminant affects performance leading to an alteration in... more Water ingress into the lubricant as a contaminant affects performance leading to an alteration in wear, corrosion and fatigue behaviour of the tribological components especially in the rolling element bearings. The current study addresses the tribochemical phenomena involved in micropitting in tribocorrosion systems where different levels of dissolved-water are present in a model lubricant. In this study the effect of different temperatures, water concentrations and relative humidities have been investigated on micropitting under rolling/sliding contacts. The influence of free and dissolved water on tribocorrosive micropitting is clarified. The tribochemical change of the reaction films is studied using X-ray Photoelectron Spectroscopy (XPS) which confirmed that the (poly)phosphate chain length and tribofilm thickness are reduced with increased dissolved-water level. 1. Introduction Water is known as an insidious lubricant contaminant [1, 2]. Water can enter into the lubricant through several sources including a humid environment [2-5] by absorption and condensation, leakage from heat exchanger [2], by-product of chemical reactions [2], free-water [2, 6, 7], etc. Depending on the extent of water ingress in the oil, beyond or within the oil saturation level, water can exist as free-water or dissolved-water, respectively. The saturation level of a lubricant, representing its hygroscopicity, depends on the physiochemical characteristics of the base stock, additive package, environmental parameters (relative humidity and temperature) [8] and oil condition [9]. Free-water in the lubricant forms an emulsion which has an inferior load carrying capacity [10] leading to deficient lubricant performance.
The European physical journal. E, Soft matter, 2002
The association behaviour of a number of glucitol amine gemini surfactants has been investigated ... more The association behaviour of a number of glucitol amine gemini surfactants has been investigated by means of molecular dynamics and self-consistent-field calculations. We have shown that the titratable head group of the surfactant is responsible for a micelle-to-membrane transition when changing the pH. Furthermore, the association structure of this group of surfactants is shown to be very sensitive to ionic strength. The combination of a charged head group, a spacer, and the hydrophilic glucitol side chains is responsible for the possible structural transitions in the associates as a function of ionic strength and pH.
Tribology Letters, 2015
Tribochemistry plays a very important role in the behaviour of systems in tribologically loaded c... more Tribochemistry plays a very important role in the behaviour of systems in tribologically loaded contacts under boundary lubrication conditions. Previous works have mainly reported contact mechanics simulations for capturing the boundary lubrication regime, but the real mechanism in which tribofilms reduce wear is still unclear. In this paper, the wear prediction capabilities of a recently published mechanochemical simulation approach (Ghanbarzadeh et al. in Tribol Int, 2014) are tested. The wear model, which involves a time-and spatially dependent coefficient of wear, was tested for two additive concentrations and three temperatures at different times, and the predictions are validated against experimental results. The experiments were conducted using a mini-traction machine in a sliding/rolling condition, and the spacer layer interferometry method was used to measure the tribofilm thickness. Wear measurements have been taken using a white-light interferometry. Good agreement is seen between simulation and experiment in terms of tribofilm thickness and wear depth predictions.