bluuebunny/crossref_metadata_2025 huggingface dataset:
The influence of application and additives on ecotoxicity and biodegradability of environmentally acceptable ester‐based lubricants
Authors: Hahn S. , Dott W. , Eisentraeger A.
Published: July 2006

The main advantages of lubricants based on synthetic esters are their good biodegradability and low toxicity. Most of them are classified as non‐water polluting. Also, the lubricants should be stable for a long time, while operating under varying conditions. In the work presented here ‐ part of a research project

SFB 442, University of Aachen, see acknowledgement.

to improve the ecological and technical properties of these types of lubricant by chemical modification of the base fluids, variation of the type and concentration of additives, and application of new coating technologies for tools with which the lubricants are used ‐ the effects of different operating conditions on toxicity, biodegradability, and chemical characteristics are assessed using biological and chemical methods. Water‐extractable toxicity is determined using a modified extraction technique and several bioassays, which allow one to distinguish between the toxic potential of the base fluids and that of the base fluids with additives. Biodegradability is determined using an optimised test system, changes in the chemical composition of the lubricants are quantified, and it is shown how the addition of additives, and the changes in the lubricants during use, affect the ecological characteristics.
Tribological properties of phosphate esters as additives in rape seed oil
Authors: Jiusheng Li , Wenqi Rao , Tianhui Ren , Xingguo Fu , Weimin Liu
Published: July 2006

With the growing concern about environmental pollution, vegetable oils have begun to be applied as base oils for environmentally friendly lubricants. Additives containing phosphorus can be used for their excellent antiwear properties and low toxicity. In view of this, a study of a series of phosphate esters as additives in rape seed oil (RSO) was carried out using a four‐ball tester. The results indicate that phosphate esters possess very good load‐carrying capacity and good antiwear and friction‐reducing properties compared with RSO by itself. Surface analysis of the worn balls was carried out using X‐ray photoelectron spectroscopy (XPS) and scanning electron microscopy (SEM). The tribological mechanism of the additives is discussed on the basis of the experimental results.
Lubricating properties of vegetable oils and paraffinic oils with unsaturated fatty acids under high‐contact‐pressure conditions in four‐ball tests
Authors: Murakami Teruo , Sakamoto Hiroshi
Published: July 2006

The tribological properties of three kinds of vegetable oils of different composition under high‐contact‐pressure conditions were evaluated in four‐ball tests to elucidate the lubrication mechanism of vegetable oils. The types of fatty acids composing the triglycerides and the concentration of dissolved oxygen appeared mainly to control the lubricating performance. Therefore, glycerol and a paraffinic oil containing fatty acids were tested as a comparison. Further, the influences of fatty acid types, antioxidant additives, and dissolved oxygen in the oils on the lubricating performance were examined. It was shown that linolenic acid with three double bonds was the most effective at higher temperature, where the formation of a friction polymer was observed, although the addition of antioxidant additives suppressed the formation of the friction polymer but reduced the load‐carrying capacity.
Tribocarbonisation of a synthetic engine oil in lubricated piston ring/cylinder bore sliding contact and its relation to friction and wear
Authors: Li S. H. , Zhang R. J. , Jin Y. S. , Wang Y. C. , Tung S. C.
Published: July 2006

Tribocarbonisation of a fully formulated synthetic engine oil, an API SJ/SAE 5W‐30 containing an organic molybdenum friction modifier, was investigated in an Optimal SRV® tribotester, with a Mo‐coated piston ring and a cast iron cylinder bore tribopair in lubricated sliding contact and under stepwise heating conditions. The friction characteristics were determined by the friction coefficient curve which showed that two local minimum values occurred as the temperature increased stepwise. The local minimum friction coefficient at the lower temperature of 290°C was the result of the formation of MoS2 and MoO3, tribochemically generated by MoDTC and ZDTP. For the other local minimum friction coefficient at the higher temperature of 400°C, FT‐IR and Raman spectroscopic examinations of the worn tracks on the cylinder bore samples indicated that tribopyrolysis of the oil components and simultaneous polycondensation into carbonaceous species had occurred. Detailed Raman analyses showed that the carbonaceous species included a disordered phase and an ordered phase characterised, respectively, by the D‐line (1370 cm−1) and G‐line (1580 cm−1). The peak positions and sizes of the graphite crystallites involved varied according to temperature, and were related to the specific points on the friction coefficient versus temperature curve. Tribochemistry could enhance pyrolysis of the oil and facilitate the production of the carbonaceous species and growth of the graphite crystallites.
Tribological performance of an ionic liquid as a lubricant for steel/aluminium contacts
Authors: Chen  , Yunxia  , Ye  , Chengfeng  , Wang  , Haizhong  , Liu  , Weimin
Published: July 2006

The wear and friction behaviour of an ionic liquid 1‐ethyl‐3‐hexylimidazolium tetrafluoroborate (L206) was investigated as a lubricant for steel/aluminium contacts using an Optimol SRV® oscillating friction and wear tester. The elemental composition and chemical nature of the antiwear films generated on the aluminium surface were analysed using a scanning electron microscope with a Kevex energy dispersive X‐ray analyser attachment (SEM/EDS) and X‐ray photoelectron spectroscopy (XPS). A low friction coefficient (˜0.05) was recorded when lubricating with L206; a small amount of water (5 wt. %) in L206 effectively reduced the wear volume and greatly increased the microhardness of the aluminium alloy, but had little effect on the friction coefficient. The SEM/EDS results showed that severe corrosive wear occurred on the aluminium alloy when lubricating with neat L206, which could be avoided by the addition of water in L206. The XPS results indicated that the species AlF3, Al2O3, AlO(OH), and Al(OH)3 formed during friction; there was no indication of boron on the worn surfaces.
Investigations into the epoxidation and alcoholysis of oleochemicals for use as lubricants
Authors: Hölderich W. F. , Rios L. A. , Weckes P. P. , Schuster H.
Published: July 2006

Most lubricants and functional fluids worldwide are based on mineral oil. These fluids contain up to 10% of a wide variety of additives for the improvement of their tribological properties. Several of these are still ecologically hazardous.

From an environmental point of view, the use of renewable feedstock is of great interest. In Europe rape seed oil is available in substantial amounts and its esters (triglycerides, esters with saturated or partly unsaturated acids) to some extent display better tribological properties than conventional lubricants. The aim of the work which is presented here has been to improve the stability of these types of ester and their derivatives with regard to oxidation and hydrolysis. This can be done by the addition of different carboxylic acids and alcohols, of various complexities, to the double bonds. This paper deals with the indirect addition of different alcohols, such as methanol, isobutanol, and neopentanol, to the double bond of methyl oleate, and the addition of methanol to the double bonds of glycerin trioleate using the corresponding epoxides as intermediates. The reactions were carried out with environmentally friendly heterogeneous catalysts. Several tests, such as for viscosity, oxidation stability, and biodegradability, were carried out to demonstrate the potential of these newly developed fluids for use as lubricants.
The tribological properties of several silahydrocarbons for use in space mechanisms
Authors: Jones W. R. , Jansen M. J. , Gschwender L. J. , Snyder C. E. , Sharma S. K. , Predmore R. E. , Dube M. J.
Published: July 2006

Silahydrocarbons are members of a relatively new class of liquid lubricants with great potential for use in space mechanisms. They are unimolecular species consisting of silicon, carbon, and hydrogen. They possess unique wear, viscosity, and volatility properties while retaining the ability to solubilise conventional additives. The tribological properties of several members of this class, including tri‐, tetra‐, and penta‐compounds, are presented. These properties include viscosity‐temperature, viscosity—pressure, vapour pressure, lubricant life, traction, and reciprocating and four‐ball wear rates. Lubricant lifetimes were determined using a vacuum ball bearing simulator, the spiral orbit tribometer. Wear was measured using a Cameron Plint reciprocating tribometer and wear rates with a vacuum four‐ball tribometer. Conventional viscometry was used for viscosity—temperature measurements and a Knudsen cell for vapour pressure. Thermogravimetric analysis was also used for volatility measurements. Pressure—viscosity coefficients (α—values) were estimated from elastohydrodynamic lubrication film thickness measurements. These properties are compared to those of existing state‐of‐the‐art space lubricants.
High‐pressure rheology of eight synthetic lubricants based on phase diagrams
Authors: Rahman Md. Ziaur , Ohno Nobuyoshi
Published: July 2006

New sets of equations have been constructed from the density‐pressure‐temperature and viscosity‐pressure‐temperature relationships to determine the rheology of synthetic lubricants at high pressure. A phase diagram was first plotted for the oils up to a pressure of 1.2 GPa and temperatures from 303 to 353 K using high‐pressure density experimental results and others. For the oils at temperatures of 313, 333, and 353 K, the high‐pressure viscosity experiment was done up to a viscosity of 104 Pa s and up to a pressure of 0.4 GPa. A relationship, based on free volume theory, between pressure and temperature with varying density and viscosity was proposed. It was found that the new equations from these relationships could predict the high‐pressure rheology more closely than those of previous researchers. Moreover, it was shown that the Ehrenfest equation or the gradient of the phase diagram is closely related to the expansion coefficient of free volume.
Biobased dry‐film metalworking lubricants
Authors: Biresaw G.
Published: July 2006

Metalworking lubricants must allow the manufacture of acceptable products at competitive cost without causing harm to operators or the environment. One way of attaining such a goal is through the use of biobased raw materials in lubricant formaulations. Biobased materials are generally non‐toxic, easily biodegradable, and abundantly available from renewable agricultural sources. However, successful application of biobased marterials in lubrication requires a thorough understanding of the tribochemical properties of these agricultural products. Recent studies have shown that biobased lubricants comprising starch and vegetable oils have promising lubrication properties. This paper discusses investigations into the effect of film thickness on the friction properties of dry‐film lubricants formulated from starch‐soybean oil composites.
Modification of the chemical structure of an environmentally‐friendly castor oil lubricant
Authors: Di‐Hua Tao , Bin Ye
Published: July 2006

Widely used mineral‐oil based lubricants are often released into the environment and cause pollution. Therefore importance is attached to developing environmentally‐friendly lubricants. Vegetable oils have been used as lubricants since ancient times. These materials, similar to synthetic esters, have better biodegradability than mineral oils. They are also renewable. Vegetable oils have some shortcomings, such as a higher pour point and a lower viscosity index than synthetic esters. They have a limited viscosity range and lower oxidative stability due to the presence of unsaturated bonds. Therefore vegetable oils as such cannot satisfy all the requirements of modern machine lubrication. In this paper, the chemical structure of natural castor oil is modified by an isomerisation reaction and by extending the carbon chain, so as to lower the pour point and improve the viscosity index.

The results show that structurally modified castor oil has very good lubrication characteristics. Its viscosity at 40°C is 150 mm2/s, its pour point is −40°C, and its viscosity index is improved. The antiwear and friction characteristics are better than those of mineral oil of the same viscosity and comparable to pentaerythritol esters and diisocapryl sebacate.
A study of the tribological behaviour and action mechanism of thiophosphates in rape seed oil
Authors: Weimin Liu , Qingye Gong , Wanren He
Published: July 2006

Tri‐n‐butyl phosphate and two thiophosphates, tri‐n‐butyl thiophosphate and tri‐n‐octyl thiophosphate, were synthesised. The tribological properties of the compounds as additives in rape seed oil for a steel‐steel friction pair were investigated with two four‐ball machines. The worn surfaces of the steel balls lubricated with the additive‐containing rape seed oil were analysed by means of X‐ray photoelectron spectrometry and scanning electron microscopy. Typical elemental distributions in the worn steel surfaces were analysed with an electron probe micro‐analyser. It was found that rape seed oil containing thiophosphates as additives at appropriate concentrations demonstrated better tribological properties than tri‐n‐butyl phosphate. Tribochemical reactions were found to be involved for the steel‐steel friction pair lubricated with the rape seed oil containing the synthetic phosphates, with the formation of a boundary lubricating film composed of a glyceride of the rape seed oil and the tribochemical reaction products of the additives. This is assumed to contribute to the improvement of the tribological properties of the rape seed oil base stock. The action mechanism of the additives is also discussed.
Some comments on micro‐abrasion interactions of pure metals in bio‐oils
Authors: Mathew M. T. , Stack M. M.
Published: July 2006

An attempt has been made to study the effect of bio‐oils on the two‐ and three‐body abrasion process of pure metals and steel. The equipment used was a micro‐abrasion tester (TE‐66, Phoenix Tribology (Plint)). The materials considered were mild steel, copper, and aluminium, being the most usable and basic materials for industrial applications such as bearings and gear assemblies. The results were used to identify transitions between wear regimes as a function of sliding speed and load. The effect on the abrasion process in the presence of various lubricant oils was also assessed. The mechanisms of abrasion with and without particles were characterised.
The synthesis and tribological behaviour of boron‐nitrogen‐modified fatty acid water‐based lubricant additives
Authors: Hua Fang Jin , Bo‐Shui Chen , Lin Dong , Jiu Wang , Wei‐Jiu Huang
Published: July 2006

A new type of boron‐nitrogen‐midified fatty acid as a water‐based lubricant additive was prepared and the chemical structure characterised by infrared spectroscopy. The tribological properties of the additive in water were evaluated using friction testers. The morphologies and tribochemical species of worn surfaces were analysed by means of X‐ray photoelectron spectroscopy (XPS). The results show that the additive is very good at increasing the losdcarrying capacity and the antiwear and friction‐reducing properties of wter. A lubrication mechanism is inferred in which a lhigh‐strength adsorption film and a tribochemical reaction film form on the rubbing surfaces as a resuly of the carrier effect of long‐chain fatty acid molecules, the high reaction activities of nitrogen, and the electron deficiency of boron, as well as the interactions of these factors.
Synergistic effect of antiwear additives and antioxidants in vegetable oil
Authors: Minami I. , Mimura K.
Published: July 2006

Certain vegetable oils have been recognised as promising candidates for environmentally friendly lubricants. Their lubricity can be optimised using antiwear additives. However, decomposition of the additives, accompanied by auto‐oxidation of the vegetable oils, has been found to occur. In other words, the antiwear additives may degrade in vegetable oils, and give less oxidative stability. In order to understand the mechanism, oxidation testing of a vegetable oil was performed by monitoring the peroxide value (POV). It was observed that POV increases as soon as oxidation starts. The value reached 1400–1500 ppm within 50 h of reaction time. Then it decreased to an equilibrium value of 400–500 ppm within 200 h. Antioxidants to prevent peroxide generation were examined. Phenolic antioxidants and zinc dialkyldithiocar‐bamate exhibited good results with regard to preventing peroxide generation, whereas aromatic amines gave poor results. A synergistic effect that prevents the decomposition of the antiwear additives was found.
The effects of lubricant additives on wear and scuffing resistance of copper alloys under boundary conditions
Authors: Sheng Yu Meng , Rao Ming Yuan
Published: July 2006

The effects of lubricant additives on alloy composition and structure, and on the wear and scuffing resistance of copper alloys, were investigated. The copper alloys used were Sn bronze, Sn‐Zn‐Pb bronze, Al‐Fe bronze, and Si‐Mn brass. The base oil used was straight mineral oil. The additives used were dimer acid, phosphonate ester, sulphide olefine cotton‐seed oil, ZDDP and n‐dibutyl phosphite. The test results revealed that Si‐Mn brass shows the highest resistance to wear and scuffing, and Sn‐Zn‐Pb the lowest. It also revealed that oiliness additives are superior in wear and tear scuffing resistance to EP additives, especially sulphur‐containing additives. The authors also noted that copper alloys show good resistance to wear and scuffing when coupled with a polished steel surface.
Mechanisms of additive effectiveness
Authors: Hsu S. M. , Pei P. , Ku C. S. , Lin R. S. , Hsu S. T.
Published: July 2006

Discusses the nature and extent of base oil‐additive and additive‐additive interactions. The first interaction is in the bulk oil phase, where solution chemistry is involved. The second interaction occurs at the wear surfaces. Various experimental techniques (DSC, TFOUT, FRT, Four ball) were used to measure interactions. In an examination of base oil‐additive‐interactions on oxidation stability, various species of base oils exert a strong influence on the performance of antioxidants. In additive‐additive interactions, the data suggest a strong concentration of dependent interaction patterns among the various additives and the base oils. Mechanistic studies are recommended to elucidate some of the observed phenonema.
Prediction and prolongation of the useful life of industrial oils under operational conditions
Authors: Ivanov S. K. , Aleksandrov V. S.
Published: July 2006

Reports work on increasing the operational life of transformer oils by reducing oxidation, and looks at the possibilities of evaluating the action of metal‐deactivating additives, and new combinations of inhibitors. The paper also examines the possibilities for making predictions of the useful working life of transformer oils in the presence of synergistic inhibitors.
Evaluating thermal and thermooxidation stability for lubricating oils via microscale methods
Authors: El Naga H. H. Abou , Salem A. E. M.
Published: July 2006

Differential thermal analysis (DTA) and thermogravimetry (TG) methods have been developed to evaluate the thermal and thermooxidation stability of different lubricating oils. Measurements are carried out either by heating the oil sample at a constant rate (direct programme) or by keeping it at a fixed high temperature (isothermal programme). Oxygen at a constant flow rate is used for thermooxidation measurements. Tested samples included different viscosity grades: neutral base oils, unadditivated lubricating oil blends, and industrial oils. The mechanism of thermal decomposition for ZDDP and the estimation of its optimum concentration was also considered.
Changes in friction and wear performance caused by interactions among lubricant additives
Authors: Rounds Fred
Published: July 2006

Engine oil additives generally fall into one of two general categories: those that affect bulk oil properties and those that affect the surface properties of lubricated parts. Interactions among surface‐active additives can lead to less‐than‐expected lubricant performance. Laboratory friction and wear test results are presented to illustrate the changes in lubricant performance that interactions among additives can cause. Some possible explanations are proposed.
Additives for metalworking lubricants ‐ a review
Authors: Kajdas C.
Published: July 2006

This paper is presented as an introduction to various specific problems associated with metalworking additives, especially that related to their modes of action. It describes various chemicals used as specific additives for metalworking lubricants. The introductory part of the review deals with general lubricant types for both metal‐forming and metal‐cutting processes. The section dealing with types of additives used for metalworking lubricants is followed by a section on the chemistry of these additives. The detailed review is connected with boundary lubrication additives for water‐based liquids and oil‐based lubricants. Corrosion and antimicrobial agents are discussed as well. Other additives are described more generally.
Elastohydrodynamics and failure prediction
Authors: Cheng H. S.
Published: July 2006

Many rolling and sliding contacts in industrial machineries are lubricated elastohydrodynamically to mitigate friction and wear. Predictions of tribological failures and performance have been greatly enhanced in the past two decades due to advancements in elastohydrodynamics. In this paper, the major physical features and principles of elastohydrodynamic lubrication (EHL) along with the major modes of tribological failures are summarized, first, for these contacts. Brief discussions are given to current predictability of lubricant film thickness, contact pressure, temperature, and friction in elastohydrodynamic contacts, and how these variables are used in predicting contact fatigue life and the threshold conditions for sliding failure.
Oil rheology and journal bearing performance: A review
Authors: Bates T. W.
Published: July 2006

This paper reviews recent work on oil viscosity, volatility and consumption, and describes the conditions under which oil loss occurs, and the processes involved, in automotive engines, generally under fired conditions. Also examined is the evolution of the SAE J300 viscosity classification system, and its relationship to the work going on currently.
Effect of ester/mineral oil compositions on tribochemical reactions of zinc diisobutyldithiophosphate
Authors: Plaza S.
Published: July 2006

Commercially available synthetic lubricants are used in the lubrication of a variety of equipment, but available additives, especially zinc dialkyldithiophosphates (ZDTP) do not respond in some of these as they do in mineral oils.
Structural aspects of European and American diesel engine piston deposits
Authors: Covitch Michael J. , Richardson John P. , Graf Robert T.
Published: July 2006

The formation of carbonaceous deposits on upper lands and ring grooves of diesel pistons is believed to be at least partially responsible for excessive cylinder bore wear and loss of oil control in field service. A properly formulated diesel lubricant has, among other performance characteristics, the ability to control piston deposits, thereby improving overall engine performance.
A study of grease film thicknesses in elastorheodynamic rolling point contacts
Authors: Bordenet L. , Dalmaz G. , Chaomleffel J‐P , Vergne F.
Published: July 2006

An elastorheodynamic analysis and a numercial solution are presented for grease film thicknesses in rolling point contacts for fully flooded, isothermal and steady state conditions. The contact surfaces are smooth and a grease four‐parameter rheological model is considered. A modified Reynolds equation is established and a complete numerical solution, including surface deformations, piezoviscous, and compressional effects is given.
An ‘in lubro’ study of viscosity index improvers in end contacts
Authors: Wardle R. W. M. , Coy R. C. , Cann P. M. , Spikes H. A.
Published: July 2006

Polymeric viscosity index (VI) improver solutions in oils suffer from both temporary and permanent viscosity losses in high shear hydrodynamic and elastohydrodynamic (EHD) contacts. In some cases in EHD contacts, these losses can be so severe that the additive makes negligible contribution to oil film thickness.

This paper describes the use of a combination of optical interferometry and FTIR micro‐reflectance spectroscopy to measure the effectiveness, and to observe directly the behaviour, of conventional VI improver solutions within rolling and sliding EHD contacts. The study shows the extent to which polymers enter EHD contacts and charts the degradation that they suffer therein.
Application of a new concept to detergency
Authors: Georges J. M. , Loubet J. L. , Alberola N. , Meille G. , Bourgognon H. , Hoornaert P. , Chapelet G.
Published: July 2006

The purpose of this paper is to describe a new concept in the detergency phenomenon for engines. It is well known that oil detergency is associated with additive adsorption, neutralisation of the acid formed, and insoluble encapsulation. However, the literature is poor in relation to the mechanical properties of oxidised oil film created during the coking process. Basic experiments taking a pure base oil and an overbased additivated oil show clearly two different types of mechanical behaviour in the burned oil film. The base oil creates a ductile film very adherent to the substrate. Conversely, the additivated film can be very brittle and shows clearly cohesive cracks followed by adhesive film‐substrate cracks. A physico‐mechanical model is proposed to explain the role played by the internal stress developed in the film during its gel state. This analysis leads to a simple thermooxidation laboratory test, where mechanical behaviour is evaluated by peeling and is correlated with engine detergency.
On the efficiency of additives during boundary lubrication with special regard to the processes of forming reaction layers
Authors: Meyer K. , Dabrowski J. R. , Kloss H.
Published: July 2006

The process of forming reaction layers of selected compounds is investigated regarding the chemical reactivity of different lubricants. The following lubricants were used as test oils: paraffin solutions with DBDS, ZDTP, acenaphthylene and limonene. Their influence on tribological behaviour is described for different conditions of friction. Relations between layer‐forming behaviour and layer properties on the one hand, and tribological properties on the other hand, were shown by chemical layer profile analysis and other methods.
A strategy for the development of optimised lubricants
Authors: Dare‐Edwards M. P. , Gadd P.
Published: July 2006

The design of lubricants has traditionally relied on the use of single dimension constitution / performance or structure / property relationships. In this paper a strategy is described whereby consideration is given to the inherent property / property (physical and chemical) correlations that exist for fluid lubricants. Progress towards the development of optimised lubricants is then achieved by identifying the molecular structural or compositional traits associated with ‘extensions’ to or ‘deviations’ from the mainstream correlations. Some examples of the success of this novel strategy will be provided, and the directions of its further refinement briefly outlined.
Measurement of the influence of sliding velocity on oil film thickness in an elastohydrodynamic point contact
Authors: Isaksson O.
Published: July 2006

Experiments have been carried out to measure the film thickness between a sapphire disc and a polished steel ball when slippage is permitted between the two surfaces. The velocity sum of the two surfaces was kept constant during the measurements. The method used to determine the oil film thickness in the contact zone is optical interferometry.

It was observed that the change in minimum film thickness was slight. When the sliding velocity was increased, the decrease in central film thickness was considerably larger than that of the minimum film thickness. In addition, the two side lobes, in which the minimum film thickness area occurs, were observed to become flatter as the sliding velocity was increased.
The structure of grease via electron microscopy and image analysis
Authors: Shuff P. J. , Clarke L. J.
Published: July 2006

Many of the insolubles that are essential to the structure of lubricating greases are too small to be usefully imaged in the optical microscope. The higher resolution of the electron microscope is necessary to examine the thickener and additive morphology that contribute so much to the performance of modern greases. However, the high vacuum requirements of these instruments mean that the oil component of grease should not be introduced into the microscope at ambient temperatures. Techniques have been developed to remove the oil prior to examination, or to reduce its vapour pressure to a negligible level. A number of such techniques which have proved to be of value for both the scanning (SEM) and transmission (TEM) microscopes are described and illustrated. The distribution of the thickener fibres can now be measured and analysed by an image analysis procedure from the images of freeze‐fracture TEM replicas.
The use of chemiluminescence in determining the thermal and oxidative stability of motor oils
Authors: Ivanov S. K. , Kalitchin Z. D. , Aleksandrov V. S.
Published: July 2006

Chemiluminescence is reviewed as a method of characterising different behaviour of lubricating oils. This includes mineral oils containing additives such as zinc dialkyl‐dithiophosphates, sulphonates, succinamides. alkylphenols and polymers. Using a chemiluminescence apparatus and manometric apparatus, various lubricant oil fractions blended with additives were examined. The basic emitters of chemiluminescence are excited carbonyl compounds, and results are presented showing the measurement of chemiluminescence at elevated temperatures.
Development and application of thermo‐oxidation laboratory tests. Correlations with engine lubricant specifications
Authors: Bourgognon H. , Piquemal A. , Rodes C. , Benard F. , Alberola N. , Vassel A. , Georges J. M.
Published: July 2006

Laboratory simulation tests are an important stage in the selection of engine lubricants. Where these tests are brief and repeatable, they allow numerous studies and can provide a wide range of information. They are all the more valuable if they have a close degree of correlation with a specification test.

The IIID high temperature oxidation test, the ME 1517 oxidation laboratory test and the Renault 30 diesel engine test are examples of specifications for the formulation of engine lubricants. The aim of the present study has been to find or develop a brief, repeatable laboratory test for these specifications and to establish a correlation between the test and the specification.

Data obtained show satisfactory correlations between the TFOUT (Thin Film Oxygen Uptake Test) and the IIID sequence, the open oxidation laboratory test COST (24 h) and ME 1517 (192 h), and the ELF/ECL microcoking test and the Renault 30 turbo diesel test.
The wear behaviour of steel lubricated by some oxygen‐containing derivatives of heterocyclic nitrogen‐containing compounds (HNCC) under boundary lubrication conditions
Authors: Wei D. , Song H.
Published: July 2006

The effect of an oxygen‐containing group on the wear behaviour of heterocyclic nitrogen‐containing compounds (HNCC) have been investigated on a four‐ball machine and a SRV tester. The preliminary results show that the substitution of the hydroxyl group and aldo‐group significantly increases the antiwear effectiveness of the parent compounds. However, the alkyloxyl group involved in some HNCC does not improve the wear performance of HNCC.

In order to get a better understanding of the role of oxygen‐containing groups in wear chemistry, a pair of compounds, quinoline and 8‐hydroxyquinoline, were chosen for further study. The analytical results of worn surfaces, wear debris and deposits showed that the difference in sliding behaviour between quinoline and 8‐hydroxyquinoline can be related to chemical reaction at the rubbing surfaces involving metal, HNCC and a hydroxyl group in HNCC or oxygen dissolved in the base stock. Under the same test conditions, these compounds, which are similar in chemical structure, give quite different reaction products. Quinoline is decomposed and oxidised by oxygen dissolving in the base stock to form a carboxylate function (soap). In the case of 8‐hydroxyquinoline, partial surface products are converted to higher molecular species, probably due to the catalytic action of fresh metal surface being exposed by rubbing. The new species, with higher molecular weight, probably belong to a kind of friction polymer, function as a boundary lubricant, and dramatically increase the antiwear effectiveness of the compound. The antiwear mechanisms of oxygen‐containing derivatives of HNCC are also discussed.
The overbasing of detergent additives: The behaviour of promoters and determination of factors controlling the overbasing reaction
Authors: Belle C. , Gallo R. , Jacquet F. , Hoornaert P. , Roman J. P.
Published: July 2006

The mechanism of overbasing of additives used in lubricating oils is studied. Overbased calcium sulphonates, the most widely used, are examined. Although the geometrical and physical nature of colloidal carbonate particles has been well studied, little is known about the fundamental aspects and mechanism of the overbasing process. In this paper, assessment of the physical and/or chemical nature of the reaction is made from equations related to the chemical engineering model of the shrinking spherical particle. The results show that the overbasing process is under diffusion control, and the chemical reaction is not determining.
Effect of KMnO4 oxidant additive on solid lubrication of lead‐graphite and silver‐graphite composites
Authors: Umeda Kazunori , Enomoto Yuji , Matsumoto Yukio
Published: July 2006

The purpose of this investigation is to understand the role of KMnO4 as an oxidant additive on the lubrication properties of a soft metal + graphite composite system, under flat contact sliding conditions where the sliding surfaces interact less with the atmosphere. The sliding tests were made using a ring‐on‐disk machine, lubricated with Pb or Ag + graphite composite containing different amounts of KMnO4 additive.

The results showed that the addition of KMnO4 in the composites reduced the friction in air up to temperatures of 500°C. The coefficient of friction was as low as 0.1. This is probably due to the fact that KMnO4 decomposed during sliding to generate oxygen, which is effective in improving the lubricating ability of graphite. The optimum concentration of KMnO4 in the solid lubricants (graphite + KMnO4) was 5–10 vol.%. After decomposition of all oxidant additive in the composite, the coefficient of friction of the composites, however, rose to 0.2–0.3.
Study of microstructural transformation of overbased calcium sulphonates during friction
Authors: Giasson S. , Espinat D. , Palermo T.
Published: July 2006

Colloidal dispersions of calcium carbonate stabilised by calcium alkylaryl sulphonates are detergent additives used in lubricant oils, and have particular effects on wear processes. In the present work, such additives were investigated using Small Angle X‐ray Scattering technique (SAXS). Different scattering intensity simulation and curve‐fitting programs were used to determine the size of the overbased calcium sulphonate particles and to characterise the interactions between them. In the additive oil (11 wt% CaCO3), the overbased calcium sulphonates appear as polydispersed micelles having an average calcium carbonate core radius of 2.0 nm. Moreover, an attractive potential between the micelles of less than kT has been observed. In order to investigate the effect of friction constraints on the additive, friction tests were performed on a rotative tribometer. Under specific conditions, there was a decrease in friction force arising from the formation of a viscous deposit. According to the differentanalyses, the viscous deposit contained more polydisperse particles, which did not have the same structure as those contained in the original additive. These particles consisted mainly of calcium carbonate. Some sulphonate chains were expelled from the friction zone. Moreover, the particles contained in the deposit interact with a potential on the order of 10 kT. Wide Angle X‐ray Scattering (WAXS) confirmed the presence of highly crystalline calcite. Moreover, the effects of pressure and the presence of water were studied. The pressure contributes neither to an increase in particle size nor to a crystallisation phenomenon. However, the presence of water in the additive oil alters the interactions between the micelles. The potential observed is 8.2 kT and suggests that the water is a responsible parameter for the agglomeration of micelles consisting of the viscous deposit.
Viscometric properties of a multigrade motor oil in relation to its bright‐stock content
Authors: El Naga H. H. Abou , Bendary S. A.
Published: July 2006

Viscometric properties for a multigrade motor oil with SAE 20W/50 viscosity grade were studied in the presence of different viscosity index improvers. The neat base blends contained increasing percentages of a bright‐stock.

Measured viscometric properties for both the neat and VI improved blends included the following: kinematic viscosity, viscosity increase by incorporation of a VI improver, viscosity index, specific viscosity and thickening tendency. These measurements were carried out over a wide temperature range.

Increase of the bright‐stock content showed that most of the VI improvers behave as thickeners. Polyalkylmethacrylate and styrene‐isoprene copolymers were found to be the only exception from such behaviour for the VI improvers.
Lubricant rheological properties at high pressure
Authors: Bair Scott , Winer Ward O. , Qureshi Farrukh
Published: July 2006

Various types of rheometric apparatus have been developed to study and measure the shear stress behaviour of liquid lubricants. Elastohydrodynamic (EHD) lubrication is better studied with a high‐pressure rheometer which allows independent control of temperature, pressure, and shear strain. With this, the authors propose an improved relation for the variation of viscosity through the glass transition, and present refined relations for shear modulus and limiting shear stress.
A new test technique for the laboratory evaluation of energy‐efficient engine oils
Authors: Babu A. V. Suresh , Martin V. , Mehta A. K.
Published: July 2006

Testing lubricants for fuel economy is a significant part of the drive for energy conservation. Generally, the small differences in fuel economy between lubricants make measurements inherently uncertain. Furthermore, precise engine tests for assessment of energy efficiency are expensive and time consuming. There has been a need, therefore, for the development of an effective laboratory screening technique to assess the energy efficiency of engine oils. With this objective in view, a new test technique consisting of two different tests has been developed for measuring lubricant‐related fuel economy.

Fuel economy through the use of engine oil is achieved by reducing boundary friction and viscous friction. Whereas reduction in boundary friction is obtained through the use of friction modifiers in engine oil, viscous friction is reduced through the use of low viscosity oils and by multigrading.

The efficacy of action of friction modifiers in reducing boundary friction has been assessed with a SRV‐Oscillating Friction and Wear Tester, using point and piston ring/liner segment contact. For the measurement of viscous friction, an attempt has been made to find out the reduction in viscous friction by using low viscosity oils and multigrade oils on a SAE No. 2 Machine, with all‐steel clutch plates.
Studies on the tribological behaviour of two oil‐soluble molybdenum compounds under reciprocating sliding conditions
Authors: Gondal A. K. , Sethuramiah A. , Prakash Braham
Published: July 2006

The use of oil‐soluble organo‐molybdenum compounds in engine oils can help in fuel conservation by reducing engine friction and increase durability by improving wear characteristics. The tribological behaviour of molybdenum dialkyldithiophosphate (MoDDP) was studied with a SRV Optimal tester under reciprocating sliding conditions. The studies were conducted under nonconformal contact conditions on En‐31 steel and conformal contact conditions on piston ring and liner materials. The results indicated that the frictional behaviour of these additives is shear sensitive. Shear sensitivity is influenced by materials, operating conditions and the interaction of MoDDP with additives present in the oil. MoDDP when used in base oil was found to increase the scuff resistance of ring and liner materials. The use of the additive reduced friction and wear (running in as well as normal) under nonconformal contact conditions, while under conformal contact conditions its effect was selective and limited.
A study of tribopolymerisation under fretting contact conditions
Authors: Kajdas C. , Lafleche P. M. , Furey M. J. , Hellgeth J. W. , Ward T. C.
Published: July 2006

The present study is aimed at determining whether or not tribopolymerisation can occur under conditions of fretting contact. Using a high contact stress system consisting of oscillating metal balls loaded against flat steel discs, effects of various monomers on friction, wear, and surface film formation were determined. Monomers were used at 1% concentration in hexadecane. Under the conditions used (90N load, 40 Hz frequency, 300 μm amplitude, for 1 hour), the monomers tested reduced friction or wear or both. Fourier Transform Infrared (FTIR) analysis of the test specimens showed that organic material is presented in the wear scars and depends on the metal system used, the monomer structure, location within the track, and the method of cleaning the surface after a test. With Al‐on‐steel, the addition of 1% styrene to hexadecane reduced volumetric wear of the disc by 65%; furthermore, positive FTIR evidence of polystyrene in the wear track was obtained. But adimer acid/glycol monomer formed metal soaps, no polymer, and had little effect on wear under these conditions. These results support the hypotheses that addition‐type tribopolymerisation can be initiated by exoelectron emission. Additionally, it was found that not only does methyl methacrylate polymerise under the fretting conditions, but the polymer film formed also reacts with the friction contact surface.

Taken as a whole, the results of this study of possible tribopolymerisation under fretting conditions support both major hypotheses, namely that: (i) for condensation‐type monomers, the most important factor is the temperature of the rubbing surfaces. (ii) For addition‐type monomers, it would appear that the effect of exoelectron emission can initiate surface polymerisation even at relatively low surface temperatures, e.g., 10–40°C above ambient. This is in agreement with the negative‐ion‐radical action mechanism (NIRAM) of boundary lubricant component.

Finally, the results obtained in this study demonstrate that the principle of tribopolymerisation developed by Furey and Kajdas can be used as a novel and effective approach to designing specific molecular structures for boundary lubrication under various rubbing conditions.
Tribological, electrochemical, and spectral analysis of zinc dialkyldithiophosphates (ZDDP) of different thermal stabilities
Authors: Likhterov S. D. , Fufaev A. A. , Kotova G. G. , Shor G. I.
Published: July 2006

The antiwear properties of five zinc dialkyldithiophosphates, which differed in thermal stability, were evaluated in a 4‐ball machine by a preliminary wear track formation method. After testing the additives, the wear resistance of the films formed was measured by the increase in preliminary wear scar diameter over that of the additive‐free oil. IR spectroscopy was then used to study the transformation products of additives after thermostatic testing at between 100 and 240°C on steel surfaces, where the interaction products were evaluated by electrode potential method. The interaction of the decomposition products of dithi‐ophosphates with metal surfaces was found to be followed by a change in electrode potential. For the tested additives, a relationship is shown between antiwear effectiveness of the film on a friction track during tribological tests and the electrode potential value of the steel sample. Different parts of the relationship between the electrode potential and temperature relate to different stages of dithiophosphate decomposition measured by IR spectroscopy. It can be said that chemical modification of the steel surface which produces an improvement of antiwear properties, starts at the decomposition temperature of the dithiophosphate neutral salt.
A study of viscometric properties of multigrade lubricants
Authors: Hassanean M. H. M. , Bartz W. J. , Naga H. H. Abou El
Published: July 2006

The rheological behaviour of several multigrade oils formulated with four different polymer‐type viscosity index (VI) improvers was experimentally studied at different shear rates ranging from 1000S−1 to 35,000S1 and at both VI reference temperatures of 40°C and 100°C. The investigation was an attempt to assess the effect of each polymer addition on the viscosity‐temperature relationship, as related to its chemical type and to the shear rate applied. It was found that the viscosity loss with increasing shear rate is greater for hydrocarbon polymer types than for methacrylate, especially at low temperatures. It was also found that the viscosity index is affected by the shear rate as well as by the type and concentration of polymer additive; its significance is thus linked with the condition under which it is determined and cannot be used as an absolute criterion for the appraisal of multigrade oil performance.
Effects of NOX on inhibition of oxidation by ZDTPS
Authors: Johnson M. D. , Korcek S. , Rokosz M. J.
Published: July 2006

Investigations of the effects of nitrogen oxides (NOX) on liquid phase oxidation and inhibition have been conducted in order to develop an improved understanding of the processes by which NOx accelerates oil degradation in internal combustion engines. Results from studies of the effects of NOx on oxidation of hexadecane (HD) alone, and in combination with a radical trapping (hindered phenol) antioxidant, and preliminary studies with zinc dialkyldithiophosphates (ZDTPs) were presented in previous reports.1‐3 The complexity of reactions involving NOx and the role in lubricant degradation of NOx from blowby were described. Those results suggested that NOx accelerates the rate of consumption of antioxidant additives and, thus, shortens the useful life of the oil. This work describes results of additional investigations with ZDTPs.