The Chemical Degradation of Ester Lubricants

Ali, A. B. M. Shawkat; Lockwood, Frances E.; Klaus, E. E.; Duda, J. L.; Tewksbury, E. J.

doi:10.1080/05698197908982924

Cited by 56 publications

(32 citation statements)

References 4 publications

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“…The polycondensation reactions which lead to high molecular weight intermediates (sludge precursors) can be described as follows. In the first step, aldehydes or ketones formed in the primary oxidation phase combine via an acid-or base-catalysed aldol condensation to form α,β-unsaturated aldehydes or ketones [12], Reaction sequence (4.22):…”

Section: Oxidation Of Hydrocarbons At High Temperature (>120 • C)mentioning

confidence: 99%

Oxidative Degradation and Stabilisation of Mineral Oil-Based Lubricants

Aguilar

Mazzamaro

Rasberger

2009

Chemistry and Technology of Lubricants

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Thermally induced hydrocarbon oxidation is a self-accelerating autoxidation process and is divided into 'low'-, 30-120 • C, and 'high'-, >120 • C, temperature phases. The first has four stages -induction of radical chain reactions, propagation, branching and then termination. Mechanisms of these processes are described and discussed. Differences in hydrocarbon reactivity are related to molecular structure. For hydrocarbon oxidation >120 • C, the first stage is the same as low-temperature oxidation but with reduced selectivity and increased reactivity; second, the oxidation phase becomes diffusion controlled as hydrocarbon viscosities increase from progressive polycondensation of higher molecular weight products, causing varnish and sludge formation. Base oil oxidation stabilities depend upon their derivation, whether solvent neutral, hydrocracked or synthetic, and their response to antioxidant treatment. Lubricant oxidation control focuses on radical scavengers and hydroperoxide decomposers and their synergistic mixtures.Engine oils increasingly use phenolic and aminic antioxidants as radical scavengers with organometallic complex antioxidants. Sterically hindered phenols substituted at 2-and 6-positions by t-butyl groups are particularly effective, reacting successively with peroxy radicals to form stable cyclohexadieneone peroxides. Secondary amines as either two aryl or phenyl and naphthyl groups are very effective at eliminating four peroxy radicals per molecule. They are more effective by a ratio of 4:2 than the sterically hindered phenols below 120 • C. At higher temperatures a catalytic cycle is suggested as an extended stabilisation mechanism. Transition metal ions with two valence states, Fe 2+/3+ , Cu 1+/2+ , etc. as trace quantities of metal soaps catalyse/retard autoxidation according to concentration and/or combination of metals. They catalyse or inhibit oxidation by complexing and decomposing hydroperoxides or can also oxidise peroxy radicals and reduce alkyl radicals to inert products. Organomolybdenum complexes such as molybdenum dialkyldithiocarbamates, MDTC, are increasingly used to stabilise engine lubricants particularly because of synergy with other antioxidants such as alkylated diphenylamines. 107 R.M. Mortier et al. (eds.), Chemistry and Technology of Lubricants, 3rd edn.,

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Section: Oxidation Of Hydrocarbons At High Temperature (>120 • C)mentioning

confidence: 99%

Oxidative Degradation and Stabilisation of Mineral Oil-Based Lubricants

Aguilar

Mazzamaro

Rasberger

2009

Chemistry and Technology of Lubricants

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“…However, the oxidation process of ester linkages is different to that of hydrocarbons due to their unique characteristics, and the oxidation mechanism of hydrocarbon oils does not satisfactorily explain the oxidation of synthetic ester oils. Several studies have reported structures of degradative products of diesters, whereas the structural details of polymerized products resulting from oxidation, as well as the polymerization mechanism, remain unclear . Despite the wide range of applications of trimellitate esters (eg, compressor oils, gear oils, and greases), there are few reports concerning their oxidation behavior .…”

Section: Introductionmentioning

confidence: 99%

Comparison of the oxidation resistance of synthetic ester oils DOA and TDTM: Experimental evaluation and theoretical calculation

Jin

Duan

Wei

et al. 2019

Lubrication Science

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The oxidation behavior of the synthetic ester oils di‐isooctyl adipate (DOA) and tri‐isodecyl trimellitate (TDTM) was investigated by analysing the oxidation induction time and oxidation onset temperature via pressure differential scanning calorimetry tests, and the variation in viscosity after oven accelerated oxidation tests. Moreover, theoretical calculations of the fractional free volumes and oxygen diffusion coefficients of DOA and TDTM were performed, and atomistic‐scale insights into the oxidative mechanisms of both oils were proposed based on reactive molecular dynamic (RMD) simulations. Better oxidation resistance for TDTM was confirmed with experimental observations. RMD results indicated that the C―O bonds of the alcohol chain and ester group of DOA were susceptible to oxidation. However, only the dissociation of the C―O bond of the alcohol chain initiated the oxidation of TDTM. Additionally, more degradation fragments for DOA were identified, along with the formation of a polymerized product, while no large molecules formed for TDTM.

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“…Static oxidation tests of hydrocarbon lubricants [6][7][8][9][10][11] have given rise to products with molecular weights up to 50,000 on low carbon steel surfaces as opposed to 580 -860 for the original material.…”

Section: Introductionmentioning

confidence: 99%

“…Oxidation of lubricants has been shown to form viscous films sometimes referred to as "friction polymer" [5][6][7][8][9][10][11]. Static oxidation tests of hydrocarbon lubricants [6][7][8][9][10][11] have given rise to products with molecular weights up to 50,000 on low carbon steel surfaces as opposed to 580 -860 for the original material.…”

Section: Introductionmentioning

confidence: 99%

Exploring Failure Mechanisms of Lubricated 52100 Steel Contacts in High Vacuum and Dry Air

Dugger¹,

Chung²

1988

MRS Proc.

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A vacuum chamber was designed for studying tribological properties of materials under pressures of 5xlO-s Torr to one atmosphere.The chamber is equipped with a pin-on-disk tribometer, in-situ Auger/X-ray photoelectron spectroscopies, a sputter-ion gun and a windowless solid-state X-ray detector.In this paper, we present results of a study using 52100 steel balls sliding on flat disks of the same material in vacuum and in dry air as a function of normal load.The contacts were lubricated with a synthetic hydrocarbon oil (poly-a-olefin).Failure is defined as the point at which the coefficient of friction increases rapidly above the steady state value.As expected, failure occurs much sooner in vacuum than in dry air. Surface analysis (Auger and XPS) shows direct evidence of the occurrence of high temperature flashes on the surface, which allows the formation and maintenance of a thick oxide in the presence of an adequate supply of oxygen. In addition, a brown film is formed in the vicinity of the wear track for tests performed in dry air, while this film is absent in vacuum.The brown film appears to be a combination of iron oxide and oxidized hydrocarbon from XPS measurements.Results of these studies suggest that the maintenance of an oxide is associated with extended contact life in these studies.

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The Chemical Degradation of Ester Lubricants

Cited by 56 publications

References 4 publications

Oxidative Degradation and Stabilisation of Mineral Oil-Based Lubricants

Oxidative Degradation and Stabilisation of Mineral Oil-Based Lubricants

Comparison of the oxidation resistance of synthetic ester oils DOA and TDTM: Experimental evaluation and theoretical calculation

Exploring Failure Mechanisms of Lubricated 52100 Steel Contacts in High Vacuum and Dry Air

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