Molybdenum Dithiocarbamate Research Articles

Tribological evaluation and tribochemistry of some dialkyldithiomalonamides and their Mo-S complexes as EP additives

The reported use of molybdenum dithiocarbamates and molybdenum dithiophosphates as antiwear and EP additives has led to attempts by the authors to synthesise certain novel Mo-S complexes, and evaluate their effectiveness. In the present paper, the synthesis of certain 1,5-dialkyl-2,4-dithiomalonamides and their Mo-S complexes, namely, bis(1,5-dialkyl-2,4-dithiomalonamido)-dioxo-molybdenum (VI), and the tribological evaluation of their 0.5% w/v admixtures in paraffin oil by a four-ball test are reported, and the results compared with a dioxo-bis(N,N-diethyldithiocarbamato)-molybdenum(VI) reference additive. The additive, bis(1,5-diethylhexyl-2,4-dithiomalonamido)-dioxo-molybdenum(VI), has been found to reduce significantly both coefficient of friction and wear-scar values, and to give higher load wear index values and flash temperatures, and has been found to be equally effective with alloy steel balls of three different compositions. However, all the Mo-S complexes afforded smaller wear-scar diameters in a one-hour wear test. The wear spots on the used steel ball specimens were subjected to SEM and AES surface analysis for understanding the additive-metal interaction tribochemistry.

Effect of Molybdenum Dithiocarbamate on Friction and Wear Properties between Aluminum Alloy and Steel

The effect of molybdenum dithiocarbamate (MoDTC) on the friction and wear properties between aluminum alloy and steel was investigated. Large adhesive wear of the aluminum alloy is caused by the transfer of aluminum to the steel when an oil without MoDTC is used. MoDTC can prevent the adhesive wear of aluminum alloy by generating a surface film in the higher sliding speed range. The surface film reduces specific wear of the aluminum alloy to less than approximately 10−9 mm2·N−1, but increases that of the steel to 10−9 mm2·N−1. The corrosive wear of the steel was apparently caused by sulfur originating from MoDTC. Presented as a Society of Tribologists and Lubrication Engineers Paper at the STLE/ASME Tribology Conference in Orlando, Florida, October 11–13, 1999

Tribochemical interactions between Zndtp, Modtc and calcium borate

Tribochemical interactions between antiwear zinc dithiophosphate (Zndtp), friction modifier molybdenum dithiocarbamate (Modtc) and overbased detergent calcium borate (OCB) lubricant additives have been investigated. Friction tests were performed in mild wear conditions under boundary lubrication, in order to enhance tribochemical surface effects. The nature of tribofilms formed was studied by coupling high‐resolution TEM on wear fragments and inside‐wear‐scar, micro‐spot XPS in the same location of the wear track (so‐called dual analysis). The performance of the Modtc/Zndtp mixture is mainly due to the generation of MoS2 single sheets and the digestion of MoO3 in the zinc polyphosphate glass formed. The final result of the tribochemical reaction is a two‐phase tribofilm composed of (i) non‐oriented MoS2 sheets (friction modifier) embedded in a carbon‐rich phase and (ii) a mixed Zn/Mo polyphosphate glass (antiwear). The Modtc/OCB mixture has a similar antiwear mechanism except that the oxide is not completely eliminated, due to the softer action of borate anion compared with phosphate one. Compared to the data obtained with binary combinations (Modtc/Zndtp, Modtc/OCB and Zndtp/OCB), we show here that the ternary system Modtc/Zndtp/OCB provides both a low wear rate and an ultralow friction value, while adding detergent and anti‐corrosive properties to the formulation. Our analytical data indicate that the synergistic effect can be attributed to an outstanding nanostructure of the tribofilm formed. It is composed of a single‐phase material containing perfectly oriented MoS2 single sheets embedded in a calcium and zinc borophosphate glass. The ternary system produces a smart material in the interface, because both functions (antiwear and friction reduction) are correlated. Compared to phosphate alone, the mechanism by which MoS2 sheets have been oriented in the borophosphate could be related to aligned molecules of the glassy polymer in the direction of sliding.

Synergistic effects in binary systems of lubricant additives: a chemical hardness approach

Tribochemical interactions between antiwear zinc dithiophosphate (Zndtp), friction modifier molybdenum dithiocarbamate (Modtc) and detergent overbased calcium borate (CB) lubricant additives have been investigated by coupling analytical TEM and micro‐spot XPS in the tribotester Optimol of SRV GmbH (mild wear conditions in boundary lubrication). Synergistic effects have been observed on both friction and wear data, especially in the Modtc/Zndtp combination. Results have been interpreted on the basis of a chemical hardness concept: the hard and soft acids and bases (HSAB) principle, stabilisation of hard–hard pairs and the maximum hardness principle. The performance of the Modtc/Zndtp mixture is mainly due to the generation of MoS2 single sheets and the digestion of MoO3, which is also formed, by the zinc polyphosphate glass. The final result of the tribochemical reaction is a tribofilm composed of MoS2 sheets embedded in a mixed Mo/Zn polyphosphate glass. The CB/Modtc mixture has a similar mechanism except that the oxide is not completely eliminated, due to the softer borate anion compared with the phosphate one.

Bent vs. linear imido ligation at the octahedral molybdenum(VI) dithiocarbamate stabilised centre

Molybdenum(VI) bis(imido) complexes [Mo(NR)2(S2CNEt2)2] 3a–3p have been prepared via two synthetic routes and their structures investigated. Thermolysis of [MoO2(S2CNEt2)2] 1 with 2,6-disubstituted aryl isocyanates affords air-stable bis(imido) complexes 3i–3m in high yields after column chromatography, a route which fails for sterically less demanding isocyanates. A more general preparation involves room temperature addition of two equivalents of [S2CNEt2]– to the labile bis(imido) complexes [Mo(NR)2Cl2(dme)] 2a–2p (dme = 1,2-dimethoxyethane) to afford 3a–3p in high yields. In this manner related complexes [Mo(NR)2(S2CNMe2)2] 4 (R = Ph or But) and [Mo(NPh)2(S2PPh2)2] 5a have also been prepared. Structural and spectroscopic studies have been carried out in order to determine the degree of bending of the imido ligands. Six complexes have been characterised by X-ray crystallography. In all cases one of the imido ligands is linear (Mo–N–C ≥ 160°), while the angle at the second is dependent upon the nature of R and ranges from 180 to 139°. Solid-state 13C CPMAS spectroscopy reveals that the difference in bond angles at the two nitrogen centres (Δ°) correlates closely with the difference in chemical shifts of the ipso-carbon atoms (Δδ). This then has been used to probe the relative bond angles at nitrogen for non-crystallographically characterised complexes. In solution even at low temperatures both imido ligands are equivalent indicating a rapid interconversion between linear and bent bonding modes.

MoS 2 single sheet lubrication by molybdenum dithiocarbamate

The mechanisms by which Modtc reduces friction in the centirange under boundary lubrication have been investigated using analytical tribometry. First, the SRV friction test was coupled with energy-filtering TEM on wear fragments and spatially-resolved XPS inside the wear scars. Second, we performed UHV friction tests on Modtc tribofilms previously created on a large area. The overall data demonstrate that the mechanisms of friction-reduction by Modtc is attributed to the effect of sliding between single layers of MoS 2 only, and not to intra-sliding in MoS 2 3-D crystal. Highly-dispersed MoS 2 sheets are present in a carbon matrix in the tribofilm material. The growth of the 2-D MoS 2 single sheets is thought to be formed by degradation of the Modtc molecule by electron transfer mechanisms activated by the friction process. The lubrication of the uncoated, stationary counterface is attributed to successive transfer of individual sheets towards the friction surface. Practically, in these conditions only a few per cent of dispersed MoS 2 is sufficient to lubricate at the same level as pure MoS 2.

Lubrication of Nonmetallic Materials

With the increased use of ceramic components in passenger cars, there is a need for a lubricant which can be used in ceramic/metal contacts. A recent study by the author showed that molybdenum dithiocarbamate (MoDTC) performed better than zinc dithiophosphate (ZDP) in ceramic/metal contact. Oils containing MoDTC provided lower wear volumes and friction coefficients for a Si3N4/cast iron pair than for a 52100/cast iron pair, while oils containing ZDP showed increased wear volumes for the Si3N4/cast iron pair than the 52100 steel/cast iron pair. In this study, the effect of calcium over-based sulfonate detergent and ashless succinimide dispersant on the antiwear and antifriction performance of MoDTC and ZDP was investigated in Si3N4/cast iron and cast iron/cast iron contacts. The addition of calcium overbased sulfonate or ashless succinimide to MoDTC or ZDP resulted in higher wear volumes for the cast iron/cast iron pair compared to cast iron/cast iron tested with MoDTC and ZDP alone. The addition of calcium overbased sulfonate and ashless succinimide to MoDTC or ZDP showed lower wear volumes than those of the cast iron/cast iron pair tested with MoDTC or ZDP containing calcium overbased sulfonate or ashless succinimide. For cast iron/Si3N4 pairs, the addition of calcium overbased sulfonate and/or ashless succinimide to ZDP increased wear volumes compared to those tested with ZDP alone. However, the addition of calcium overbased sulfonate to MoDTC did not increase the wear volumes, and the addition of calcium overbased sulfonate and ashless succinimide to MoDTC in cast iron/Si3N4 pairs increased wear volumes slightly. A time delay to reach steady-state friction coefficients was observed for cast iron tested against Si3N4 with oils containing MoDTC, calcium overbased sulfonate and ashless succinimide. The wear volumes seem to depend on the time to reach steady-state friction coefficients in cast iron/Si3N4 pairs. Presented as a Society of Tribologists and Lubrication Engineers paper at the World Tribology Congress in London, United Kingdom, September 8–12, 1997

The Chemistry of Antiwear Films Generated by the Combination of ZDDP and MoDTC Examined by X-ray Absorption Spectroscopy

In order to obtain a better understanding of the decomposition mechanisms of antiwear and antioxidant engine oil additives such as zinc dialkyldithiophosphate (ZDDP) and molybdenum dithiocarbamate (MoDTC), tribochemical and thermally deposited films were prepared from oil solutions containing varying concentrations of these two additives. The chemistry of these films was studied by using X-ray absorption (XANES) spectroscopy and X-ray photoelectron (XPS). The antiwear properties were examined on a Plint rubbing machine by measuring the amount of wear as a function of time and the concentrations of the additives. The XANES and XPS spectra indicate that the dominant species from MoDTC in the antiwear films resembles that of a MoS2-like film, and in the thermal films, the dominant species are those of a sulphate and MoO3. The spectra also indicate that the phosphorus from ZDDP forms polyphosphate chains of varying lengths. The combined use of organo-Mo compounds and Zn alkyl dithiophosphates showed a synergistic effect by reducing both friction and wear. Presented as a Society of Tribologists and Lubrication Engineers paper at the World Tribology Congress in London, United Kingdom, September 8–12, 1997

Environmental Effects on the Composition of Surface Films Produced by an Organo-Molybdenum Compound©

The influence, of environments on the properties of the surface films formed, with molybdenum dithiocarbamate (MoDTC) was examined under a reciprocating sliding condition. MoS2 was formed on the rubbing surfaces in air and oxygen, and molybdenum compounds with an oxidation state lower than MoS2 were produced in nitrogen and argon. The surface film composed of MoS2 was effective in reducing the friction and wear, while the molybdenum compound formed in nitrogen or argon had no ability to prevent direct contact between the rubbing surfaces and to reduce the friction. It was a necessary condition for forming the surface film composed of MoS2 that the environment to be rubbed contained oxygen at a concentration above a certain level.

An investigation of the effects of some motor oil additives on the friction and wear behaviour of oil‐soluble organomolybdenum compounds

AbstractThe compatibility of oil‐soluble organomolybdenum compounds with some motor oil additives (detergent, dispersant, rust inhibitor and ZDDP) has been investigated on a four‐ball machine and a SRV tester. Preliminary results indicated that a combination of two agents might have either synergistic or antagonistic effects on the friction and wear performance of the organomolybdenum compounds, although many combinations were shown to be synergistic. The interactions between two agents were primarily determined by the additive types, additive concentrations and test temperatures.It was also found that the presence of calcium sulphonate detergent was particularly beneficial to molybdenum dithiophos‐phate and molybdenum dithiocarbamate in terms of friction reduction and wear reduction at temperatures in a certain range. The induction period of the organomolybdenum compounds was also reduced. Surface analysis results suggested that the synergistic effects were closely related to the formation of thick films, which were rich in molybdenum and sulphur, on rubbing surfaces.

Role of molybdenum carbide and titanium nitride in the sintering of materials containing titanium and chromium carbides: T. Hachisuka, J. Japan Soc. Powder and Powder Metallurgy, Vol 38, No 2, 1991, 145–152, (In Japanese)

A large amount of research has been devoted to the effect of molybdenum dithiocarbamate (MoDTC) additives on the lubricating performances of carbon-based coatings, showing that a high wear rate is produced when the MoDTC is blended with the base oil. However, the mechanisms leading to the coating removal are not fully understood yet.In this work, the friction and wear performances of an amorphous hydrogenated DLC coating doped with silicon and oxygen have been analysed when lubricated by MoDTC-containing oils. Tribological experiments have been conducted with DLC/steel and DLC/DLC contacts under boundary lubrication conditions using a ball-on-flat tribometer. To understand the wear mechanism, the chemical composition of the tribofilm formed on the steel ball counterpart was investigated by X-ray Photoelectron Spectroscopy (XPS). Transmission Electron Microscopy (TEM) coupled with Energy Dispersive X-Ray Spectroscopy (EDX). A new DLC wear model has been proposed and validated.

Effects of Organic Molybdenum Compounds on the Friction and Wear Observed with ZDP-Containing Lubricant Blends

Combining an organic molybdenum compound with a zinc dialkyl dithiophosphate (ZDP) antiwear additive can significantly reduce kinetic friction at loads in the antiwear regime as determined in laboratory, 4-ball wear tests. Both molybdenum dithiophosphates and dithiocarbamates are effective. The friction and wear benefits are independent of the ZDP present. Adding a high total base number (TBN) metallic detergent can greatly enhance the high load antiwear behavior of the three component blend whereas lower TBN detergents do not. Unfortunately, ashless dispersants can destroy the observed benefits. The performance improvements obtained with organic additives could not be duplicated by adding specific inorganic solids, either singly or in combination. Presented at the 35th STLE/ASME Tribology Conference in Fort Lauderdale, Florida October 16–19, 1989

Friction and Wear Characteristics of Molybdenum Dithiocarbamate and Molybdenum Dithiophosphate

The friction and wear characteristics of molybdenum dithiocarbamate (MoDTC) and molybdenum dithiophosphate (MoDTP) were examined under a reciprocating sliding condition by adding them to a pure hydrocarbon. Both MoDTC and MoDTP reduced the friction and wear. MoDTC formed a surface film composed mainly of MoS2. MoDTP formed less molybdenum compounds in the rubbing surfaces, which were composed mainly of MoS2 and FePO4 at 120 degrees C, und MoS2, MoO3 and FePO4 at 200 degrees C. A surface film containing MoS2 was effective in reducing the friction. The coefficient of friction was decreased with increasing the concentration of MoS2 in the surface film. MoDTC had a higher ability to form MoS2 than MoDTP. Therefore, MoDTC was superior in reducing friction to MoDTP.

Extraction of molybdenum and tungsten with various reagents

The extraction of molybdenum and tungsten thiocyanates and dithiocarbamates, as well as the extraction with HDEHP, α-benzoinoxime and N-benzoyl-N-phenyl-hydroxylamine in 1–10 mol/l HCl, H2SO4, HF, HF-HCl, and HNO3 medium was studied with the aim to compare the extraction efficiencies of different extractants. The optimum extraction conditions for separation of these two elements are given. New perceptions were obtained for the extraction from hydrofluoric acid medium, especially for the extraction of dithiocarbamates.

Improvement of antifriction properties of motor oils

Improvements in the fuel economy of internal combustion engines is achieved by various means, including reduction of the frictional power losses. The authors examine a method of improving the antifriction properties of motor oil in the example of M-10G/sub 2/ oil by the incorporation of additives that influence the frictional force and wear. The additives used in this work were molybdenum dithiophosphate and dithiocarbamate, zinc dithiophosphate, and bis-xanthate disulfide. Zinc dithiophosphate is used as an antiwear additive in formulating motor oils at various quality levels; oil-soluble complex compounds of molybdenum are used as antifriction additives in motor oils; bis-xanthate disulfide is used mainly as an additive in break-in oils (for example, OM-2).

Carbon–sulphur bond cleavage. Structure of [Mo(SCNPr2)(S2CNPr2)]2S2

The molecular structure of a molybdenum dithiocarbamate showed that its formation proceeds via an oxidative carbon–sulphur bond cleavage followed by formation of a molybdenum–carbene bond.

Silicon nitride in the engineering and process industries : Anon., Metallurgia, 80 (479) (1969) 92–94; 4 figs.

A block on ring tribometer employing AISI E52100 steel components, was used to simulate cam and tappet tribology in order to evaluate the tribological performance and evolution (frictional performance, wear coefficients, surface chemistry species/quantification and film structure) on the tribofilms. Lubricants consisted of a mineral base oil containing zinc dialkyl dithiophosphate (ZDDP) plus a full dispersant-detergent-antioxidant package and an identical blend but with the addition of molybdenum dithiocarbamate (MoDTC). Energy Dispersive X-Ray analysis (EDX) and X-ray Photoelectron Spectroscopy (XPS) chemical analysis techniques have been employed, allowing the crucial link between testing duration and film properties to be evaluated. Factors such as the evolution of surface topography due to formation and hence wear protection and friction control offered, are analysed using Atomic Force Microscopy (AFM). The contrasting frictional difference between the two lubricants is correlated to wear, surface roughness effects, structure and surface chemistry. The relationships between the running-in of an in service valve train system and the tribo-chemical parameters analysed in this tribometer based work are discussed. It is found that friction reduction observed is primarily a consequence of tribofilm shear strength changes and not nano-scale tribofilm surface topography, which are comparable in magnitude at different frictional coefficients.