Lubricant Degradation Research Articles

Study of Hard Disk and Slider Surfaces Using X-Ray Photoemission Electron Microscopy and Near Edge X-Ray Absorption Fine Structure Spectroscopy

AbstractX-ray Photo Emission Electron Microscopy (X-PEEM) and Near Edge X-ray Absorption Fine Structure (NEXAFS) spectroscopy were applied to study the properties of amorphous hard carbon overcoats on disks and sliders, and the properties of the lubricant. The modification of lubricants after performing thermal desorption studies was measured by NEXAFS, and the results are compared to thermal desorption data. The study of lubricant degradation in wear tracks is described. Sliders were investigated before and after wear test, and the modification of the slider coating as well as the transfer of lubricant to the slider was studied. The studies show that the lubricant is altered chemically during the wear. Fluorine is removed and carboxyl groups are formed.

Optimized structures and proton affinities of fluorinated dimethyl ethers: an ab initio study

Ab initio methods have been used to investigate the proton affinity and the geometry changes upon protonation for the molecules (CH 3) 2O, (CH 2F) 2O, (CHF 2) 2O, and (CF 3) 2O. Geometry optimizations were performed at the MP2/3-21G level, and the resulting geometries were used for single-point energy MP2/6-31G ∗∗ calculations. The proton affinity calculated for (CH 3) 2O was 7 kJ mol −1 from the experimental value, within the desired variance of ±8 kJ mol −1 for G2 theory, suggesting that the methodology used in this study is adequate for energy difference considerations. For (CF 3) 2O, the calculated proton affinity of 602 kJ mol −1 suggests that perfluorinated ether molecules do not act as Lewis bases under normal circumstances, e.g. degradation of commercial lubricants in tribological applications.

A simplified density functional theory study of triboelectronic lubricant degradation

The degradation of perfluorinated polyether lubricants in computer disk and tape drives is an important factor limiting their lifetimes. One likely path to degradation is through interaction with triboelectrons. We look at two triboelectron degradation mechanisms: dissociative attachment and dipolar dissociation. We carry out total-energy minimization calculations for the triplet excited state and the negatively-charged state of prototypical saturated fluorocarbon molecules. Electron attachment occasionally leads to dissociation, but often does not. Excitation to the triplet excited state uniformly provides the energetics favourable for dissociation.

Lubrication of Slow Rolling Contacts—The NASA Ball on Plate Tribometer

The NASA Ball on Plate Tribometer was built for the investigation of boundary lubricated rolling. Its contact conditions are easily calculated, and can be adjusted to match a range of real hearing applications for stress, surface velocity, pivot, and contact severity. The rig operates under high vacuum at room temperature. Lubricant charge and specimen preparation are well-controlled and well-characterized. Mass spectroscopy instrumentation allows an indication of lubricant degradation during rolling. Other tribological quantities immediately available are contact resistance, friction coefficient, transverse creep, and orbit velocity deficit. Simple specimens allow post-test surface analysis such as FTIR, XPS, microscopy, and profilometry. Here we describe the Tribometer and discuss representative results obtained with liquid, solid, and no lubricant.

Oil ageing ‐ drain period in a petrol engine

The more frequently an engine oil is changed, the more the overhaul life of the engine is extended but with an increase in the cost both of the oil and of the oil drain services. If engine oil is changed less frequently the associated costs will decrease. In order to find the optimum drain interval, it is necessary to establish the relationship between the cost of the oil and oil drain services and the cost of more frequent overhauls. Presents an investigation into the degradation of a proprietary lubricant marketed in Turkey, and the wear rate of a petrol engine driven in urban traffic. Lubricant samples were examined approximately every 2,000km for deterioration of the lubricant and evidence of wear of the engine components. From the experimental results, determines the optimum oil drain period of the engine.

The effect of Lewis acid catalysis on the decomposition of CF 3OCF 3 to COF 2 and CF 4

The CF 3OCF 3 and AlF 3 Lewis acid interaction is investigated by ab initio theory to explain the catalytically enhanced degradation of polyperfluorinated ether lubricants. Thus, an understanding of the Lewis acid interaction in these materials is gained by investigating the optimized geometries of CF 3OCF 3 in the presence and absence of AlF 3. The computed bond parameters and partial atomic charges identify a strong interaction between the aluminum substrate and the CF 3OCF 3 ether oxygen atom. A transition state that connects the reactant CF 3OCF 3 and products COF 2 and CF 4 is identified. The effect of the Lewis acid interaction on the transition state geometry is analyzed. A significant reduction in the activation energy to the transition state via the Lewis acid interaction is computed, providing a quantitative understanding for catalytically induced degradation in these materials.

Degradation of perfluoropolyether lubricants on magnetic recording disks during sliding

Degradation of perfluoropolyether lubricants (Fomblin Z-Dol and Fomblin AM 2001) on the magnetic recording thin-films disks are studied during sliding with an Al2O3-TiC slider under high vacuum. Gaseous products generated from the head/disk interfaces are detected and monitored as a function of sliding distance using a quadrupole mass spectrometer. Effects of overcoats and surface roughnesses of disks on degradation of lubricants and coefficient of friction were also studied. Experimental results show that the gaseous products generated from Z-Dol and AM 2001 lubricants during sliding are quite similar. Degradation of both lubricants is found to take place from the beginning of sliding, and the evolution rate of decomposition fragments decreases with the sliding distance. Removal of the lubricants is accompanied by a rapid rise in the coefficient of friction of the interfaces, followed by gaseous products from the tribochemical reaction of the overcoat material. Surface roughness of the disk has an effect on the sliding distance to failure, but little effect on the decomposition of lubricant.

Characterization of the head-disk interface for proximity recording

Lubricant additives and nitrogenated carbon overcoat are frequently used for the head-disk interface (HDI) of the proximity recording technology. The results show that lubricant degradation can be reduced by lubricant additives such as cyclic phosphazenes but excessive amount of the additive will accumulate on head and form marks on disk surface which is detrimental for the drive performance. Use of nitrogenated carbon for overcoat makes it possible for tailoring the HDI by increasing the overcoat conductivity and modifying the bonded lubricant thickness.

Acoustic emission study of lubricant effect on proximity contact recording

Pseudo-impact contact at the interface between proximity sliders and magnetic rigid disks were investigated by acoustic emission (AE) technique. Under a hot/wet condition of 60/spl deg/C/80%RH and an operation speed of 19.15 m/s., AE responses were collected in real-time to monitor interaction events at the head/disk interface (HDI). The profile of AE responses shows various events at the HDI which can be correlated to the micro-wear of the carbon overcoat and lubricant degradation. These events were also detected by optical surface analysis (OSA). These wear and degradation events indicate the need for choosing the proper lubricant and demonstrate that AE is a suitable tool to detect these events at the head/disk interface.

Tribology of Different Ceramic Sliders on Lubricated Thin-Film Disks©

Seventy-percent straight-rail, taper-flat sliders were made from A12O3-TiC, Mn-Zn ferrite, SiC, Si3N4 and ZrO2 and tested, on lubricated thin-film disks. The tests involved low speed (0.44 m/s) continuous contact drag testing at a fixed radius for a maximum of one. million revolutions or to disk failure. SiC did not cause the disk media, to fail, even, out to five million revolutions, and the friction force had. consistently low modulation throughout the test. Si3N4 did not cause any disk failures but exhibited higher friction force with more modulation. A2O3-TiC, Mn-Zn ferrite and ZrO2 exhibited high failure, rates (>50%), even though the initial friction forces were. low. The failure rates of these ceramics can be explained by the catalytic activity of Al2O3, TiC, Fe2O2 and ZrO2 on the degradation of the disk lubricant. Another explanation is the localized surface oxidation of SiC and Si3N4 sliders resulted, in a softer slider material exhibiting more wear, leading to higher contact area and lower contact stresses at the slider/disk interface. Presented as a Society of Tribologists and Lubrication Engineers paper at the ASME/STLE Tribology Conference in San Francisco, California, October 13–17, 1996

Surface and lubricant/overcoat interface properties of the rigid disks after corrosion

The surface and perfluoropolyether (PPE) lubricant/overcoat properties of magnetic hard disks after corrosion stressed at a temperature of 80/spl deg/C and an 80% relative humidity are studied by time-of-flight secondary ion mass spectrometry. The corrosion stress leads to selective migration of cobalt from the magnetic layer which is dependent on disk overcoat composition and structure. The corrosion also results in evaporation and degradation of the PFPE lubricant.

Degradation of Thin-Film Disk PFPE Lubricants by Ceramic Powders©

Perfluoropolyether lubricants have been the lubricants of choice on thin-film magnetic disks because of their superior properties. However, studies have shown that they can degrade at lower temperatures in the presence of metal oxides such as Al2O3 and Fe2O3. In this paper, the degradation behavior of three widely used disk lubricants which have a Z-backbone structure were studied in the presence of the following ceramic powders: AlN, Al2O3, Fe2O3, SiC, Si3N4, SiO2, TiC, TiO2, and ZrO2. Experiments involved monitoring the weight loss of a continuously stirred mixture of lubricant containing 1 wt% of powder with lime, at a fixed temperature of 250° C. In the case of ZDOL 4000, there was a 10% loss in the first 60 minutes and then a very low and constant rate of weight loss. TiC, AlN and Al2O3were very aggressive in degrading the lubricant while SiC and Si3N4 had no effect at all. ZDOL 2000 exhibited a 60% loss in the first 100 minutes and then a low and constant rate of loss with time. ZrO2, Al2O3, TiC and AlN were very effective in degrading the lubricant, while SiC and Si3N4 had negligible effect. Heating the AM 2001 lubricant alone at 250°C caused the lubricant to quickly turn into a black sludge; however, at 180°C, it exhibited a slow and constant weight loss with time. At 180° C, the presence of ceramic powders did not appear to have any effect on the rate of weight loss. X-ray diffraction of residues left behind after degradation tests showed that, except for the tests with SiC and Si3N4, most of the residues left behind after complete lubricant degradation were found to contain fluorides. Presented as a Society of Tribologists and Lubrication Engineers paper at the STLE/ASME Tribology Conference in Kissimmee, Florida, October 8–11, 1995

Detection of tribochemical reactions using photoelectron emission microscopy

The thermal decomposition of trifluoroacetic acid on a Mo(100) is studied using high resolution electron energy loss spectroscopy. It is found that trifluoroacetic acid (CF3COOH) exposed to the Mo(100) surface at room temperature deprotonates to form a trifluoroacetate species (CF3COO–). Further decomposition of the acetate species is observed resulting in the formation of an intermediate species and possibly ionic fluorine adsorption at elevated temperatures. Dynamic photoelectron emission microscopy images are obtained from a rotating, cylindrical molybdenum sample. This real-time imaging of a rotating sample lays the foundation for imaging various tribo-induced reactions in real time. First experiments employing the rotating cylindrical sample, the adsorption of trifluoroacetic acid and how such experiments may clarify the mechanisms for lubricant degradation are discussed.

Utilization and degradation of an ester-based synthetic lubricant by Acinetobacter lwoffi.

An oil-degrading bacterium, Acinetobacter lwoffi, isolated by elective culture from the Medway estuary, utilized an ester-based synthetic lubricating oil EMKARATE DE 155 as sole carbon and energy source. Analysis of culture supernatants by gas chromatography showed the accumulation of a nondegradable metabolite 1,1,1 Tris (hydroxymethyl)propane in addition to two metabolizable fatty acids, octanoic and decanoic acids as products of the synthetic oil degradation. Esterase activities were subsequently demonstrated in oil and acetate-grown cells. The synthetic oil therefore appears to be partially biodegradable in the environment.

Biodegradable lubricants—studies on thermo-oxidation of metal-working and hydraulic fluids by differential scanning calorimetry (DSC)

In continuation of our study of the thermal-oxidative degradation of lubricants using PDSC, we investigated the biodegradable metal-working and hydraulic fluids that are available on the European market. Isothermal onset times of oxidation were measured at different sample temperatures and plotted against the reciprocal temperatures, giving straight ageing lines which were used to differentiate between the thermal-oxidative stabilities of the oils. The stabilities of metal-working oils and hydraulic fluids vary over a wide range. Synthetic ester oils are more stable than vegetable-based fluids; however, our work demonstrates that the latter can be improved by selected antioxidants to yield equal or even better thermal-oxidative stabilities. Measurements conducted on steel surfaces show a strong catalytic influence compared to an inert aluminium (Al 2O 3) surface for both fluids. We also investigated the stabilities of laboratory-aged hydraulic fluids (ASTM-D-2893). The results, by PDSC alone or in combination with conventional oxidation tests, show that the ageing behaviour of biodegradable lubricants can be assessed effectively. Commercial products are by no means of equal quality in this respect. In our opinion, single PDSC measurement could offer many advantages over the conventional oxidation tests used, such as the Baader test (DIN 51554) or the Rancimat test. Typical results for commercial products based on rapeseed oil and synthetic esters are presented.

Amperometric electrochemical device for remote detection of degradation of fire-resistant fluid lubricants

Ultramicroelectrodes have been used to follow continuously the hydrolysis of triarylphosphate esters, these compounds being envisaged as lubricants of the primary pump motor in nuclear plants. The amperometric ultramicroelectrochemical device gives the expected results in industrial site testing.

Characterization of the Ring Pack Lubricant and its Environment

The performance characteristics of the piston ring-liner assembly and the lubricant within it are critical for the operation of modern internal combustion engines. The ring pack can directly affect engine friction, oil consumption and oil degradation, which in turn can impact upon fuel economy, emissions and engine wear. The operation of this system is complex and no single technique is capable of fully characterizing the processes occurring. This paper outlines the range of both experimental and theoretical methods that are being applied to the study of this system and the lubricant within it. These include the modelling of ring pack gas and oil flows, and direct measurement of piston temperatures, ring belt pressures and piston ring motion. Characterization of lubricant degradation via direct sampling of oil from the top ring groove of an operating engine has also been used. The merits of such a multi-faceted approach are discussed in relation to piston deposit formation.

A Fractal Theory of the Temperature Distribution at Elastic Contacts of Fast Sliding Surfaces

The statistical temperature distribution at fast sliding interfaces is studied by characterizing the surfaces as fractals and considering elastic deformation of the asperities. The fractions of the real contact area in the slow, transitional, and fast sliding regimes are determined based on the microcontact size distribution. For a smooth surface in contact with a rough surface, the temperature rises at the real contact area are determined under the assumption that most of the frictional heat is transferred to one of the surfaces. The interfacial temperature rises are bounded by the maximum temperature rise at the largest microcontact when the fractal dimension is 1.5 or less, and are unbounded when it is greater than 1.5. Higher temperature rises occur at larger microcontacts when the fractal dimension is less than 1.5, and at smaller microcontacts when it is greater than 1.5. For a fractal dimension of 1.5, the maximum temperature rise at a microcontact is independent of its size. The maximum temperature rise at the largest microcontact is expressed as a function of the friction coefficient, sliding speed, elastic and thermal properties, real and apparent contact areas, and fractal parameters. The closed-form solutions for the distribution density function of the temperature rise can be used to calculate the fraction of the real contact area of fast sliding surfaces subjected to temperature rises in any given range. The present theory is applied to boundary-lubricated and dry sliding contacts to determine the fractions of the real contact area where lubricant degradation and thermal surface failure may occur.

Optical Surface Analysis of the Head-Disk-Interface of Thin Film Disks

This paper describes the design, operation, theory, and data interpretation of an Optical Surface Analyzer (OSA). The OSA can measure carbon wear, lubricant depletion/accumulation, surface roughness, and lubricant alteration on carbon coated thin film disks. This device can measure an Angstrom of carbon wear or lubricant depletion/accumulation. The OSA can also measure debris generation and lubricant degradation through a measurement of optical index change. The lateral resolution of the OSA is approximately 5 by 10 microns and the bandwidth of the device is 2 MHz. The small device size allows it to be used within a test stand environment.

Wear Evaluation of Ultra High Molecular Weight Polyethylene Using Pin-On-Flat and Hip Simulation Techniques

AbstractReduction of wear and wear debris is one of the most important areas of research presently in the field of orthopedic devices. It is speculated that wear debris is one of the contributing factors in the cascade of events that lead to osteolysis. In this regard it is very important to be able to evaluate in vitro the wear of UHMWPE produced by various manufacturing methods. Presently the three most common methods of wear testing are: pin-on-flat, pin-on-disk, and hip simulator.Wear evaluation was performed on gamma irradiated UHMWPE that was manufactured by three different processes: extrusion, direct compression molding, and isostatic compression molding. The wear evaluation consisted of pin-on-flat and hip simulator testing.omparison of the results from these two different types of tests show that the two tests would rank the wear resistance of the UHMWPE in the same order. However, there is a variation in the difference of the wear rates between the two tests. The pin-on-flat results show that the direct and isostatic compression molded material had approximately 50% less wear than the extruded material whereas the hip simulator results show that the isostatic compression molded material had 16% less wear than the extruded material. The difference in the results of these two tests are the effects of a combination of factors including the mechanical and material properties of the UHN4WPE, modes of wear that are active, the state of stress (constant vs. cyclic) in the specimens, third body contamination of the lubricant, bacterial degradation of the bovine serum lubricant, etc. Both tests are very important and necessary in the evaluation of wear of orthopedic materials.