Monica Ratoi

Monica Ratoi
University of Southampton · Faculty of Engineering and the Environment

PhD DIC

About

45
Publications
6,356
Reads
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1,336
Citations
Additional affiliations
May 2009 - present
University of Southampton
Position
  • Lecturer
March 2006 - April 2009
University of Oxford
Position
  • Research Associate
November 1992 - December 2006
Imperial College London
Position
  • Research Associate

Publications

Publications (45)
Article
Full-text available
The rapid adoption of the advantageous PEEK and its composites paired with steel counterparts in many tribological applications has prompted intense research to investigate their tribological properties under lubrication. This study investigated the effect of oil-lubrication and proposed a mechanism of action. Compared to the dry conditions, oil-lu...
Article
Full-text available
Bearing steels suffer from degradation of mechanical properties when atomic hydrogen diffuses into the steel from the contact surface. In rolling contact fatigue tests this can lead to a significant reduction in fatigue life of the specimens as the amount of hydrogen diffused into the steel increases. To mitigate this challenge, synthetic oils of d...
Data
Video showing pressure induced alignment of lamellar phase lyotropic liquid crystals in a PCS Instruments EHD tribometer. If this interests you I have 200+ GB of videos showing liquid crystal alignments in static and dynamic conditions with normal and oblique polarised light microscopes.
Article
Full-text available
The rapid adoption of the advantageous PEEK/steel pairing in many tribological applications has prompted intense research to optimize its lubrication. Thus, the role of organic friction modifiers (OFMs) in improving the lubrication of PEEK-steel contacts has been studied and their mechanism explained. Their effect on friction and wear depends on th...
Technical Report
Full-text available
A novel experimental project adapted from my undergraduate thesis investigating the uses of polarised light microscopy techniques and single-wavelength ellipsometry for understanding the structure of smectic/lamellar liquid crystal structures in an EHD contact. The layered, lamellar phase of lyotropic liquid crystals (LLCs) display promising trib...
Article
Full-text available
While it is well known that during RCF tests the formation of nascent catalytic sites on the wear track can break down hydrocarbon molecules to release atomic hydrogen, the potential of the hydrogen environment in fuel cells to hydrocrack the hydrocarbon lubricant in high pressure rolling contacts has so far been ignored. Here we investigate for th...
Article
Poly-Ether-Ether-Ketone (PEEK) has been widely used for tribological applications with steel counterparts because of its superior mechanical and self-lubricating properties. Lubrication has the potential to further improve its performance. However, lubrication can have positive or negative effects depending on the operating conditions and little is...
Data
Undergraduate thesis which formed the background/initial feasibility efforts for the Visualisation Of Structured Lubricants In Tribological Contacts E. Richard Booser Scholarship report. Some of the background and theory in this document are underdeveloped so read judiciously, but this document is an interesting read for the experimental methods (a...
Article
Full-text available
In this study, stainless steel and titanium (Ti) tubes obtained from a turbofan engine after the end of its lifetime were analyzed in order to compare the amount of pyrolytic coke present and its influence on the parent, base material. Various analytical techniques including microhardness and topographical evaluations, optical emission spectrometry...
Poster
Full-text available
WS2 nanoparticles (NPs) are some of the most successful lubricant additives for high pressure, high temperature tribological applications and a potential replacement for the antiwear ZDDP and friction modifier additives. Ferrofluids offer a variety of properties such as friction and wear reduction, vibration damping, and cooling that can make them...
Article
Full-text available
Due to their mechanical and physical properties, aluminium alloys possess wide potential in the automotive industry, particularly in hot reciprocating applications such as pistons for diesel and petrol engines. WS2 particle-reinforced composites could bring further improvements by reducing friction and wear between moving parts. Reducing friction i...
Article
Full-text available
The chemical interactions between the kerosene compounds and the stainless steel structure of the tubular components, through which kerosene is transported, develop a degradation phenomenon, causing intergranular contamination from the surface to the inner part (process based also on mass transport, i.e. diffusion at low temperatures). This is the...
Article
Tungsten dichalcogenides such as WS2 and WSe2 have remarkable friction reducing properties in tribological applications due to their layered structure which exfoliates easily under shear. 2H-WS2 nanoparticles (NPs) have recently been shown to possess excellent antiwear properties in high temperature applications due to their ability to react with t...
Article
Hydrogen is one of the cleanest available vehicle fuels but its small atomic size allows it to diffuse readily through the lattice of solid materials, which can cause catastrophic failure in high strength steels. Metal embrittlement has been identified as a major consequence of hydrogen uptake and represents an extra challenge for lubricated tribol...
Article
In high-pressure, high-temperature sliding contacts, WS2 nanoadditives react with the metal substrate to generate 100+ nm chemical tribofilms with a layered structure and excellent tribological properties. The friction, wear and micromechanical properties of WS2 tribofilms are compared with those of tribofilms formed by the zinc dialkyldithiophosph...
Article
Full-text available
The importance of nanoparticle characterization for nanotoxicology has been extensively emphasized and it has been universally agreed that the most important parameters for characterizing nanomaterials are specific surface area and surface properties (chemistry, hydro-philicity/phobicity, charge etc.). This study is proposing the use of enthalpy of...
Conference Paper
Organic friction modifiers (OFMs) are important additives in the lubrication of machines and especially of car engines where performance improvements are constantly sought-after. Together with zinc dialkyldithiophosphates (ZDDPs) antiwear additives, OFMs have a predominant impact on the tribological behaviour of the lubricant. In the current study,...
Article
Organic friction modifiers (OFMs) are important additives in the lubrication of machines and especially of car engines where performance improvements are constantly sought-after. Together with zinc dialkyldithiophosphate (ZDDP) antiwear additives, OFMs have a predominant impact on the tribological behaviour of the lubricant. In the current study, t...
Article
Full-text available
Because of their excellent tribological properties and potential to replace problematic lubricant additives currently in use, WS2 nanoparticles have spurred considerable interest over the last two decades from academia and industry to decipher their mechanism of action. To elucidate the mechanism, this study carried out tribological tests at low an...
Article
Transmission electron microscopy (TEM) is the only technique which can give accurate information on the individual size, shape and composition of NPs. However, in dilute forms it is difficult to collect a sufficient number of NPs on an electron microscope grid for TEM analysis without some means of concentrating the dispersion of NPs. This study in...
Article
Professor Spencer opened the discussion of the paper by Professor Evans: Presumably the profilometry data were measured by some kind of mechanical profilometer, with a well-defined cutoff length corresponding to the size of the stylus. Of course you could have used other methods to include shorter size-scale roughness features. What is the sensitiv...
Article
Full-text available
Quantum dots (QDs) have numerous possible applications for in vivo imaging. However, toxicity data are scarce. To determine the acute in vivo toxicity of QDs with carboxyl surface coating (carboxyl-QDs) and QDs with amine surface coating (amine-QDs), we investigated the inflammatory properties, tissue distribution, and prothrombotic effects after i...
Article
A novel tribometer capable of measuring low friction forces and low loads at high speeds has been employed to measure the friction coefficient in a pure sliding, ball-on-flat contact in hydrodynamic lubrication conditions. The tribometer was custom-built for measuring friction at low loads, to allow the authors to investigate the feasibility of usi...
Article
Although the use of oil-in-water (O/W) emulsions as metalworking fluids is widespread, the mechanisms of emulsion lubrication are not yet well understood. Several theories have been proposed but there is not a clear agreement about the effect of different operating conditions and emulsion properties on the lubricating performance of O/W emulsions....
Conference Paper
This research aims to exploit the physical phenomenon of simple liquids slipping against very smooth solid surfaces, to create a new type of bearing where the lubricant slips against one surface but not the other. To demonstrate the feasibility of this idea, a special test rig capable of measuring milli-Newton forces has been employed to measure fr...
Article
The effect of dispersed soot in engine oils is an increasingly important issue in terms of both engine durability and fuel efficiency. Using carbon black as a soot analogue, a study has been carried out to investigate the main factors that determine the impact of soot on friction and ZDDP film formation in formulated oils. It has been found that di...
Article
Full-text available
In this work, we have explored the application of poly(L-lysine)-g-poly(ethylene glycol) (PLL-g-PEG) as an additive to improve the lubricating properties of water for metal-oxide-based tribo-systems. The adsorption behavior of the polymer onto both silicon oxide and iron oxide has been characterized by optical waveguide lightmode spectroscopy (OWLS...
Article
Full-text available
In this work, we have explored the application of poly(L-lysine)-g-poly(ethylene glycol) (PLL-g-PEG) as an additive to improve the lubricating properties of water for metal-oxide-based tribo-systems. The adsorption behavior of the polymer onto both silicon oxide and iron oxide has been characterized by optical waveguide lightmode spectroscopy (OWLS...
Article
Ultrathin film interferometry has been used to measure the film thickness of deposited Langmuir-Blodgett layers of stearic acid in a rolling, high pressure, ball on flat contact.Deposited multilayers up to five monolayers thick have been found to remain in a vertically-oriented configuration in static contact up to Hertzian pressures of at least 0....
Article
There has been debate for many years as to whether long-chain surfactant friction modifier additives reduce friction by forming adsorbed films of monolayer thickness or whether they form films equivalent to several or many multilayers thick. In the work described in this paper, a series of metal oleate friction modifier additives has been synthesiz...
Article
This paper concerns lubrication in aqueous surfactant systems where the surfactants adsorb at surfaces, in relative motion, forming either a surfactant monolayer or a multi- (liquid crystalline) layer. The surfactants were of two kinds, viz., a double chain cationic surfactant, didodecyldimethylammonium bromide, DDAB, and a single chain cationic su...
Article
A number of recently-developed experimental techniques, such as force balance, atomic force microscopy and ultrathin film interferometry have enabled the direct study of the properties of very thin liquid lubricating films between solid surfaces. These have been used to demonstrate the structure and rheology, and thus the lubricating ability, of mo...
Conference Paper
Full-text available
The boundary lubricating properties of long chain carboxylic acid additives in solution have been studied using a combination of optical interferometry, friction measurement and electrochemistry. This shows that thin, monolayer-scale films are formed under reducing conditions. These films are very effective at limiting friction and wear. In oxidisi...
Conference Paper
A range of metal carboxylate friction modifier additives has been synthesised and their film-forming properties studied using ultrathin film interferometry. It has been found that some of these additives form thick boundary films while others do not. The differences in behaviour are ascribed to the differing electronegativities of the metals in the...
Article
Ultrathin film interferometry has been used to measure the boundary film-forming behaviour of long chain, carboxylic acid oiliness additives. It has been shown that in dry conditions, these acids form very thin films of around 2–3 nm thickness. However when water is present, some acids form significantly thicker films, around 10 nm in thickness. Th...
Article
This paper describes a study of the elastohydrodynamic and boundary film-forming properties of solutions of simple surfactants in water. Such solutions are finding increasing use both as highly fire-resistant and environmentally-friendly hydraulic fluids. They also provide a vehicle to help clarify the origins of the film-forming behavior of oil-in...
Article
Oil-in-water (O/W) emulsions are widely used in metal rolling and cutting and also as fire-resistant hydraulic fluids. For both of these applications they require a reasonable degree of lubricating ability—in metal rolling to protect the surfaces against wear and seizure and to provide a controlled value of friction, and in hydraulics to limit the...
Article
Oil-in-water emulsions, as used in metal working and fire-resistant hydraulic fluids, often show poor lubricating performance and one reason for this is their inability to form effective elastohydrodynamic films. This paper considers how the composition of an oil-in-water emulsion contributes to its lubricating properties. A key factor in oil-in-wa...
Chapter
Fire resistant hydraulic fluids tend to show significantly poorer ribological performance in hydraulic systems than conventional mineral oil-based fluids. There have recently been performance problems associated with increases of operating temperatures of mining hydraulics. This paper describes measurements of the elastohydrodynamic and boundary fi...

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