The Friction Reducing Properties of Molybdenum Dialkyldithiocarbamate Additives: Part II - Durability of Friction Reducing Capability

Graham, J. M. R.; Spikes, H. A.; Jensen, R. K.

doi:10.1080/10402000108982505

Cited by 49 publications

(37 citation statements)

References 16 publications

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“…XPS and Raman have subsequently become widely used tools to study organo-molybdenum additive tribofilms [145][146] Figure 12. AFM lateral force map of surface rubbed in MoDTC solution showing low (dark) lateral force nanosheets [144] A recurrent theme in the literature is the existence of a "synergy" between MoDTC and ZDDP, where a combination of both types of additive in solution gives lower friction than MoDTC alone and/or lower wear than ZDDP alone [137] [147][148][149][150][151]. It is certainly the case that the rate of onset of friction reduction and in particular the longevity of friction reduction by MoDTC appears to be increased when ZDDP is present, although the actual occurrence of additive synergy, a quantitative concept based on the combined concentrations of pairs of additives [152] A significant practical problem associated with the use of organo-molybdenum FMs in engine lubricants is that their ability to reduce friction can be quite rapidly lost when they operate in oxidising environments at elevated temperature, such as in crankcase engines [157].…”

Section: Research On Oil-soluble Molybdenum Fmsmentioning

confidence: 99%

Friction Modifier Additives

2015

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The need for energy efficiency is leading to the growing use of additives that reduce friction in thin film boundary and mixed lubrication conditions. Several classes of such friction modifier additive exist, the main ones being organic friction modifiers, functionalised polymers, soluble organo-molybdenum additives and dispersed nanoparticles. All work in different ways. This paper reviews these four main types of lubricant friction modifier additive and outlines their history, research and the mechanisms by which they are currently believed to function. Aspects of their behaviour that are still not yet fully understood are highlighted.

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Section: Research On Oil-soluble Molybdenum Fmsmentioning

confidence: 99%

Friction Modifier Additives

2015

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“…Formation of MoDTC tribofilms is affected by parameters such as temperature, MoDTC concentration, the presence of antioxidants and other lubricant additives as well as contact parameters such as the stroke length, sliding speed, slide-roll ratio and surface roughness of the sliding pair which in turn affect the friction performance of the additive [6][7][8][9][10][11][12]. Although there is a consensus within the research community that MoDTC reduces friction by formation of MoS 2 within the contact region, there is still no mechanistic model that links additive chemistry in a dynamic tribological system to friction and wear performance.…”

Section: Introductionmentioning

confidence: 99%

A methodology for Raman characterisation of MoDTC tribofilms and its application in investigating the influence of surface chemistry on friction performance of MoDTC lubricants

2015

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In this study, Raman spectroscopy has been employed to understand the influence of surface chemistry on friction in a tribocontact. Tribotests were conducted using molybdenum dialkyldithiocarbamate (MoDTC) lubricant in a steel/steel sliding contact. Firstly, surface chemistry in the high friction regime, at the beginning of the test, and in the low friction regime, after longer test duration is investigated. Secondly, the influence of temperature on the surface chemistry of the resulting wear scars is investigated. Results show that at the beginning of tribotests with MoDTC lubricant, iron oxides are formed in the tribocontact which result in high friction. At longer test durations, adsorbed MoDTC on the ferrous surface decomposes to form MoS 2 and low friction is observed. Surface chemistry at the tribocontact has been found to vary depending on the test temperature. At high temperatures, MoS 2 is formed which provides friction reduction while at low temperatures, molybdenum oxide and amorphous sulphur-rich molybdenum (MoS x ) compounds are formed which do not provide friction reduction. Furthermore, it has been shown that MoS 2 formed within the tribocontact at high temperatures has a slightly disordered crystal structure as a result of tribological processes.

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“…At high temperature (160°C), MoDTC did not act to trap free radicals but nevertheless possessed some oxidation inhibitor properties, which probably reflects a peroxide decomposing activity. Graham also showed that the addition of hydroperoxide to MoDTC oil followed by storage for 24 h at room temperature resulted in almost complete loss of both MoDTC and its friction-reducing ability, suggesting a peroxide decomposing behaviour [10].…”

Section: Discussionmentioning

confidence: 95%

“…MoDTC then only lost its friction-reducing effectiveness when all the ZDDP was used up. Research also showed that radical inhibitor-type antioxidants and sulphur-containing peroxide decomposer antioxidants could slow the rate at which MoDTC is lost while other engine oil additives and also base oil type could influence durability of the friction-reducing properties of MoDTC [7,8,10,11].…”

Section: Introductionmentioning

confidence: 99%

“…Graham et al [10] combined an air/NO x -based oil oxidation test, reverse-phase high-pressure liquid chromatography (HPLC) and HFRR friction measurements to study the influence of oil ageing on MoDTC degradation. They found that the rate of MoDTC loss as measured by HPLC and the oxidation time needed to lose friction-reducing capability both varied depending on the MoDTC structure and purity.…”

Section: Introductionmentioning

confidence: 99%

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Influence of NO x and Air on the Ageing Behaviour of MoDTC

et al. 2017

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Molybdenum dialkyldithiocarbamates (MoDTCs) are very effective friction modifier additives for use in engine oils and other lubricants. However, as engine oils age during extended drain intervals, MoDTCs can lose some or all of their ability to reduce friction and this is generally believed to result from their oxidative degradation. In this study, MoDTC solutions in base oil have been subjected to oil ageing in a controlled NO x /air flow rate, controlled temperature test apparatus and the effect of ageing on the ability of the MoDTC to reduce friction has been explored. As shown in previous studies, the additive's friction-reducing properties are completely lost after a quite short period of ageing at 160°C. However, it was found that at this temperature the presence of NO x has little if any influence on the rate of friction loss, indicating that the latter is controlled primarily by the rate of reaction of oxygen with the base oil and thus the rate of consumption of MoDTC as a peroxide decomposer. By contrast, when ageing tests are carried out at lower temperatures it is found that NO x has a very strong effect on the rate at which MoDTC loses its ability to reduce friction, so that at 100°C NO x accelerates this rate by two orders of magnitude compared to air alone. This suggests that at low temperatures the rate at which MoDTC is consumed is controlled by its reaction as a radical inhibitor with NO x species.

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The Friction Reducing Properties of Molybdenum Dialkyldithiocarbamate Additives: Part II - Durability of Friction Reducing Capability

Cited by 49 publications

References 16 publications

Friction Modifier Additives

Friction Modifier Additives

A methodology for Raman characterisation of MoDTC tribofilms and its application in investigating the influence of surface chemistry on friction performance of MoDTC lubricants

Influence of NO x and Air on the Ageing Behaviour of MoDTC

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