Synergistic lubricating effect of several ashless dithiocarbamates with Mo-donor additives

Several kinds of alkylenebis(dialkyldithiocarbamates) were synthesized and the tribological properties as additives in base oil (100N) and Li-soap greases were evaluated using 4-ball tester and SRV tester (Schwingreibverschleissprüfung für Schmierstoffe). The results show that all additives reduce wear. Especially, when Mo(Zn)-donor additives such as Mo-DTC, Zn-DTP, and a vegetable oil modified organomolybdenum complex were blended in base oil containing methylenebisdibutyldithiocarbamate as sulfur donor, synergism was seen both in terms of oxidation stability through thermo gravimetric analysis (TGA) and wear properties using a 4-ball tester. TGA showed that oils containing sulfur-donor and Mo(Zn)-donor additive mixtures possess improved oxidation stabilities. Also, these oils have good antiwear properties under mild pressure conditions. The elemental composition of the antiwear films generated on steel counterfaces were investigated with scanning electron microscopy (SEM), and energy dispersive X-ray spectroscopy (EDX). It was found that sulfur-donor and Mo-donor additives reacted with the counterface metal and generated a surface protective film consisting of FeS and MoS₂.     

Low sulfur,phosphorus and metal free antiwear additives: Synergistic action of salicylaldehyde N(4)-phenylthiosemicarbazones and its different derivatives with Vanlube 289 additive

With a view to develop metal free, low SAPs antiwear additives, the antiwear properties of salicylaldehyde N(4)-phenylthiosemicarbazone and its p-methylphenyl, p-methoxyphenyl and p-chlorophenyl derivatives(1%w/v) and their synergistic/antagonistic behavior with Vanlube 289(1%w/v) additive were tested in base oil using four-ball lubricant tester and ZDDP as a reference additive. Antiwear testing of additives(1%w/v) was done by varying load and time. The performance of antiwear additives has been compared on the basis of tribological parameters. An appreciable synergistic activity is observed between 1% concentrations of the thiosemicarbazones and Vanlube289. The efficiencies of the synergistic formulations are far better than that of ZDDP. The topography and composition of the wear scar were analyzed by AFM and SEM with EDX. The synergistic formulations cause enormous reduction in surface roughness. The EDX analysis of the wear scar in the case of base oil with additive exhibits presence of sulfur and nitrogen.     

水溶性LaF3纳米颗粒的制备及其摩擦学行为研究

以柠檬酸为修饰剂在水溶液中合成表面修饰LaF3纳米微粒,通过X射线衍射(XRD)、傅立叶变换红外光谱(FTIR)、热重分析(TG-DTA)、激光粒度分布仪、透射电子显微镜(TEM)、X射线光电子能谱仪(XPS)等测试手段对其结构和形貌进行表征;采用四球摩擦磨损试验机考察LaF3纳米微粒作为添加剂时的摩擦学行为;采用X射线光电子能谱仪(XPS)分析钢球磨损表面的元素组成。结果表明,柠檬酸修饰的LaF3纳米微粒,平均粒径约为4 nm;LaF3纳米微粒在水中的分散性良好,作为水基添加剂,在摩擦过程中可在钢摩擦副表面的形成由Fe2O3、La2O3等为主要组成部分的边界润滑膜,因此表现出极好的抗磨减摩性能,具有很好的应用前景。     

Tribological behavior of some antiwear additives in vegetable oils

There has been a growing concern for the use of mineral oils because of the worldwide interest in environmental issues. This has promoted the use of vegetable oils as the alternative base fluids, environmental friendly lubricants. In view of this, a study of the effect of antiwear additives in vegetable oils was carried out using a four-ball wear tester. The newly synthesized additive, di-butyl 3·5-di-t-butyl 4-hydroxy benzyl phosphonate (DBP) showed excellent antiwear performance compared with the conventional additive, TCP under high speed and temperature conditions. To investigate the scavenging role of free hydrogen radicals of the DBP additive, a thermal degradation test was conducted to identify physico-chemical reactions using a differential scanning calorimeter (DSC). The surface analysis of worn balls was carried out using an optical microscopy and EDAX. On the basis of the experimental results, the new additive showed the dual function of hydrogen scavenging and protective film formation, and was found to be a effective antiwear additive in various lubrication systems.     

Molecular Design of Environmentally Adapted Lubricants: Antiwear Additives Derived from Natural Amino Acids

Novel environmentally adapted lubricant additives were synthesized from cystine (Cys ₂ ), an essential amino acid obtained from natural sources. The structural feature of cystine is a dimeric amino acid with a central disulfide bond. The carboxyl groups in Cys ₂ were converted to corresponding esters by reaction with long-chain alcohols. The resultant diesters were soluble in poly-alpha-olefin (PAO) and ester-type synthetic oils. The structural features of the new additives include multifunctional groups on the same molecule, such as disulfide as a tribologically active moiety and polar functional groups as anchors to friction surfaces. The additives consist of hydrogen, carbon, nitrogen, oxygen, and sulfur; they are free of phosphorus, chlorine, and metals. The tribological properties of the additives in a solution of synthetic oil were evaluated by performing laboratory tribotests under boundary conditions. The Cys ₂ -derived additives exhibited comparable antiwear properties to the conventional additive zinc dialkyldithiophosphate (ZnDTP). The additives showed good antiwear properties even at low concentrations of sulfur (160 ppm) in synthetic hydrocarbons such as PAOs. A high concentration of sulfur (640 ppm) was required to obtain an optimized antiwear performance of the synthetic esters as a base oil. The new additives reduced the friction coefficient of PAOs and synthetic esters. A saturated ester of Cys ₂ reduced the friction of PAOs and synthetic esters up to oil temperatures of 150°C. The lubrication mechanism was discussed with respect to the role of functional groups in the additive molecule. The use of amino acids as versatile building blocks for the synthesis of environmentally adapted additives was also pointed out.     

无机盐对水溶性稀土络合物添加剂性能的影响

本文简述了水溶性极压抗磨添加剂存在的问题，合成了水溶性十二烷基聚氧乙烯醚磷酸酯稀土络合物，考察了该类络合物添加剂在水中的极压抗生，提出一套衡量与比较添加剂抗磨和极压性能优劣的参数，并且针对实际应用中水质的不同，研究了阴阳离子对其在水中的摩擦学性能的影响。     

Oil-Soluble Fluorinated Compounds as Antiwear and Antifriction Additives

Many studies have been published on the use of solid fluorinated compounds as lubricants and lubricant additives, but much less has been done with oil-soluble fluorinated additives.

This paper describes a study of fluorinated telomers, especially fatty acids and their amine salts, for boundary lubrication (antiwear conditions). The antiwear effectiveness of these fluorinated compounds is compared with a commercial additive, zinc di-n-butyl dithiophosphate (ZDTP).

Modern analytical tools are used to study surface layers (XPS, automatic wetting balance), and wear particles (IR) to determine their antiwear mechanism. Special attention is given to fluorinated reaction film formation.     

Evaluation of Tribological Properties of Sulfur- and Phosphorous-Free Quinolinium Salts and Their Correlation with Quantum Chemical Parameters

For developing antiwear additives with high efficiency but with low sulfated ash, phosphorous, and sulfur (SAPS), N-substituted quinolinium halides, [DIP-Q]⁺Br^? [DIP-Q=1-(3-(1,3-dioxoisoindolin-2-yl)propyl)quinolon-1-ium], [DIE-Q]⁺Br^? [DIE-Q=1-(3-(1,3-dioxoisoindolin-2-yl)ethyl)quinolon-1-ium], [P-Q]⁺I^? [P-Q=propylquinolon-1-ium], and [M-Q]⁺I^? [M-Q=methylquinolon-1-ium] have been prepared and characterized by ¹H- and ¹³C-NMR spectroscopic techniques. The tribological performance of these quinolone-based quaternary salts as antiwear additives in paraffin oil has been assessed on a four-ball test rig. The observed results have been compared with those of zinc dialkyldithiophosphate (ZDDP), a high SAPS additive. The tribotesting of these additives has been performed using 1% w/v additives concentration at different loads and times. The potential of these compounds as antiwear additives is evident from their observed tribological data: mean wear scar diameter (MWD), friction coefficient (µ), mean wear volume (MWV), and wear rates. All of the quinolinium derivatives prove to be better antiwear additives than ZDDP. Among the tested synthesized compounds, [DIP-Q]⁺Br^? exhibits the best tribological behavior followed by [DIE-Q]⁺Br^?, [P-Q]⁺I^?, and [M-Q]⁺I^?. The surface topography of worn surface studied by scanning electron microscopy (SEM) and atomic force microscopy (AFM) shows that surface roughness is reduced to a greater extent in case of quinolinium derivatives than lubrication with ZDDP or base oil alone. Energy-dispersive X-ray (EDX) and X-ray photoelectron spectroscopy (XPS) analysis of worn surfaces in the presence of quinolinium additives shows that the tribofilm is composed of FeBr₃, Fe₃O₄, and organic compounds containing carbonyl and imine bonds. Theoretical investigations using quantum chemical calculations are indicative of significant chemical interactions of these quinolinium additives with metal surfaces, which is strongly supported by the observed experimental data.     

水溶性聚乙二醇磷酸酯的合成及润滑与腐蚀性能研究

有机磷酸酯具有良好的润滑性能,被广泛用作润滑油和水基润滑剂的添加剂。以P2O5和聚乙二醇(400)为原料,采用缓释法合成水溶性聚乙二醇磷酸酯,研究聚乙二醇磷酸酯的极压、抗磨和减摩性能。试验结果表明,添加聚乙二醇磷酸酯可以明显提高基础水基润滑剂的极压、抗磨和减摩性能,水基润滑剂的抗腐蚀性能也能满足要求。     

The friction and wear behavior of 2-(n-alkyldithio)-benzimidazole as additives in liquid paraffin

Three 2-(n-alkyldithio)-benzimidazoles were synthesized. The friction and wear behavior of the synthetic compounds as additives in liquid paraffin were examined with a four-ball machine, with emphasis on revealing the relationship between the chain length of the additive and the friction-reducing ability and lubricating mechanism of the additives. The film formed by the additive during the sliding process was investigated by using X-ray photoelectron spectroscopy. It was found that the synthetic compounds as additives in liquid paraffin had good antiwear performance. The longer the chain length of the synthetic compound, the more stable or less volatile is the compound and the more effective it is in improving wear resistance. This revised version was published online in July 2006 with corrections to the Cover Date.     

Effectiveness of Selected CHO Compounds as Antiwear Additives to White Mineral Oils

The objective of this article is to verify the effectiveness of CHO products (mixtures of esters) and their compositions with a lactam-type CHNO compound applied at the concentration ≤1 wt% as antiwear additives to white oils. The research was performed using a ball-on-disk tester and a special four-ball apparatus. The tested CHO and CHNO additives show very good antiwear properties under boundary lubrication conditions. They provide the highest wear reduction when they are introduced at 0.1 wt%. The wear reduction synergism for mixtures comprising 20 wt% of the CHNO compound and 80 wt% of the selected esters is not observed. Additionally, the limiting pressure of seizure, p_s, was determined. It was found that p_s is not improved by esters and the CHNO additive if they are added at 0.1 wt%; the positive influence of some mixtures comprising 20 wt% of the CHNO compound and 80 wt% of the chosen esters is revealed. It was also proved that the oil viscosity influences the tribological properties of applied additives under boundary lubrication and extreme pressure conditions.     

Film Formation of Non-Phosphorus Wear Inhibitors

The time-dependent film formation of two potential non-phosphorus supplemental wear inhibitors in the presence of secondary zinc dialkyldithiophosphate (ZnDTP) was studied by electrical contact resistance (ECR), auger, and X-ray photoelectron (XPS) spectroscopy. One weight percent of a molybdenum dithiocarbamate or an ashless dithiocarbamate was blended with a secondary ZnDTP, sufficient in quantity to yield 0.05 wt% phosphorus at blend level. A thorough surface examination by auger and XPS, coupled with the ECR results, detailed the deleterious effects that these supplemental antiwear additives had on ZnDTP antiwear film formation. Both carbamates interfered with antiwear film formation by secondary ZnDTP. It is speculated that MoDTC generated a competing molybdenum sulfide film that oxidized over time to form MoO ₃ , which promotes wear in the ECR bench test based on literature insight. Ashless DTC also formed a competing antiwear film but not as good a film as from ZnDTP alone.     

Preparation of Water-Soluble Lanthanum Fluoride Nanoparticles and Evaluation of their Tribological Properties

Water-soluble LaF₃ nanoparticles surface-capped by two kinds of dialkyl polyoxyethylene glycol thiophosphate ester (denoted as DTP-10 and DTP-20) were synthesized via a surface-modification method. The morphology and microstructure of resultant surface-modified LaF₃ nanoparticles (denoted as LaDTP-10 and LaDTP-20) were characterized by means of X-ray powder diffraction, transmission electron microscopy, and Fourier transform infrared spectrometry, and their thermal stability was examined by thermogravimetric analysis. Moreover, the tribological properties of as-synthesized LaF₃ nanoparticles as additives in distilled water were evaluated with a four-ball friction and wear tester, and the morphology of wear scar and the chemical states of some typical elements thereon were investigated by scanning electron microscopy and X-ray photoelectron spectroscopy. It has been found that as-prepared LaDTP-10 and LaDTP-20 nanoparticles have a size of 19.6 and 8.5 nm, respectively, and they have good dispensability in distilled water. Moreover, as-synthesized LaDTP-10 and LaDTP-20 nanoparticles as lubricant additives in distilled water exhibit good friction reducing, antiwear, and extreme pressure properties as well as high load-carrying capacity even at a concentration of 1 % (mass fraction). This is because LaF₃ nanoparticles can be deposited on sliding steel surfaces to afford a surface protective layer, and they may also tribochemically react with rubbing steel surfaces to generate a boundary lubricating film mainly composed of phosphate, sulfide, sulfate, La₂O₃, and LaF₃. Therefore, it is feasible for LaDTP-10 and LaDTP-20 nanoparticles to be used as water-soluble lubricant additives under harsh conditions.     

Friction Reduction and Antiwear Capacity of Engine Oil Blends Containing Zinc Dialkyl Dithiophosphate and Molybdenum-Complex Additives

The efficacy of oil blends containing zinc dialkyl dithiophosphate (ZnDTP) and molybdenum (Mo)-complex additives to improve the tribological properties of boundary-lubricated steel surfaces was investigated experimentally. The performance of oil blends containing three different types of Mo-complex additives of varying Mo and S contents with or without primary/secondary ZnDTP additions were investigated at 100°C. The formation of antiwear tribofilms was detected in situ by observing the friction force and contact voltage responses. Wear volume and surface topography measurements obtained from surface profilometry and scanning electron microscopy studies were used to quantify the antiwear capacity of the formed tribofilms. The tribological properties are interpreted in terms of the tribofilm chemical composition studied by X-ray photoelectron spectroscopy. The results demonstrate that blending the base oil only with the Mo-compound additives did not improve the friction characteristics. However, an optimum mixture of Mo complexes and ZnDTP additive provided sufficient amounts of S and Mo for the formation of antiwear tribofilms containing low-shear strength MoS ₂ that reduces sliding friction. In addition, the formation of a glassy phosphate phase due to the synergistic effect of the ZnDTP additive enhances the wear resistance of the tribofilm. This study shows that ZnDTP- and Mo-containing additives incorporated in oil blends at optimum proportions improve significantly the tribological properties of boundary-lubricated steel surfaces sliding at elevated temperatures.     

Atomic Force Microscopy and Raman Spectroscopy Investigation of Additive Interactions Responsible for Anti-Wear Film Formation in a Lubricated Contact

Rational formulation of lubricants requires an understanding of additive interactions that impact antiwear film qualities such as thickness, topography, and friction. In an effort to understand the complex additive interactions responsible for formation of anti-wear and friction-reducing films, atomic force microscopy (AFM) in conjunction with Raman microscopy has been used to conduct a nanoscale investigation of the wear tracks formed by a high-frequency reciprocating rig (HFRR) in the presence of various commercial lubricant additives combinations. Of the additives examined, zinc dithiophosphate (ZnDTP)-based additives are found to be solely responsible for the formation of a thick (hundreds of nm) film that exhibits a pitted topography. Addition of a molybdenum-based friction modifier to the lubricant blend reduces the film thickness considerably and reacts to produce MoS ₂ on the surface, suggesting an interaction with the zinc dithiophosphate–based additive that prevents antiwear film formation. Formation of MoS ₂ , found only in the wear track, is consistent with a dramatic reduction of friction coefficient measured in the HFRR. Subsequent addition of borated dispersants to the lubricant reveals a further reduction in friction coefficient and a modest return of anti-wear film. However, addition of detergents to the formulation increases the friction coefficient and also promotes the formation of an anti-wear film. Nanoindentation measurements on the bulk properties of the anti-wear films determined that all of the anti-wear films had similar modulus and hardness measurements which were lower than that of the parent steel material, but did not correlate with the friction measurements obtained from the HFRR. This indicates that nanoscale measurements on material properties of the film are necessary to elucidate friction properties of the interface, and that these properties cannot be determined from macroscale measurements on the bulk film.

     

Antagonistic Interaction of Antiwear Additives and Carbon Black

It is well known that the presence of soot in engine oils can lead to an increase in wear of engine parts. This is a growing problem as soot levels in diesel engine oils are rising due to a combination of extended drain intervals and the various methods employed to reduce NO _x formation such as retarded ignition and exhaust gas recirculation. Several different mechanisms have been proposed by which soot might lead to an increase in wear in mixed lubrication conditions, of which the most widely favoured is abrasion by soot, either of the rubbing metallic parts in engines or of the antiwear additive films formed on rubbing metal surfaces. In this study it is shown that the combination of mixed alkyl ZDDP and carbon black (used as soot surrogate) is strongly antagonistic in terms of wear. In a lubricant containing carbon black, the presence of ZDDP leads to considerably more wear than if ZDDP is left out. A similar, though less severe antagonism is also seen with primary ZDDP and other antiwear and EP additives. By varying the lubricant film thickness it is shown that the effect of carbon black in ZDDP-containing oils is to promote wear up to quite thick hydrodynamic film conditions, approaching the secondary carbon black particle size. It is proposed that the antagonistic wear effect results from a corrosion-abrasive mechanism in which the reaction film formed by antiwear additive and rubbing metal surface is very rapidly and continually abraded by carbon black. At most carbon black concentrations, wear rate then becomes controlled by the rate of initial antiwear additive film formation, which for secondary ZDDP is very rapid, rather than by the kinetics of the abrasive process. From this understanding, strategies for reducing the impact of engine soot on wear can be deduced.     

An Experimental Study of the Wear Caused by Loose Abrasive Particles in Oil

Abrasive powders were added to a highly-refined petroleum oil and run in a vane pump. With no antiwear additive, wear was successive and volumetric efficiency dropped rapidly. With 0.1% oleic acid or stearyl amine added to the oil the abrasive wear of the particles was essentially eliminated. Also, precoating the particles with the antiwear additive before adding to the base oil greatly retarded wear. Oleic acid performed best on iron oxide (basic), stearyl amine best on silica (acidic). No reduction in abrasive wear by oleic acid was observed when a steel ball was loaded against a grinding wheel. It is concluded that the antiwear additives prevent three-body abrasion (abrasion by loose Articles) by preventing the particles from adhering to one of the wing surfaces where they can act like small cutting tools.     

The correlation between results of different model friction tests in terms of an energy analysis of friction and lubrication

A general method for anticipating results of highly complex tests on the basis of simple measurements has not yet been worked out. An energy-based method for determining antiwear and extreme pressure (EP) properties of oils containing additives is described in the present paper. The method allows the parameters characterizing the ability of additive-containing oils to form boundary layers in the antiwear (α_AW) and EP (α_EP) regions to be determined.The parameters α_AW and α_EP make it possible to correlate the results of different friction tests. The correlation between seizure load P_t, welding load P_z, wear load index I_h, four-ball wear test results d₄₀ and results of the FZG tests is presented in this paper.     

A High-Performance Multifunctional Lubricant Additive for Water–Glycol Hydraulic Fluid

A water-soluble boron (B)-containing thiophosphite derivative (BTP) was synthesized, and its tribological, anticorrosion, and antirust properties as an additive for the base liquid of water–glycol hydraulic fluid were evaluated in detail. The results of tests demonstrated that BTP is indeed a high-performance and multifunctional water-soluble lubricant additive that was able to remarkably improve the extreme pressure, friction-reducing, antiwear, anticorrosion, and rust-inhibiting properties of the base liquid when added at a low adding concentration (<3 wt%). Based on a performance comparison of BTP and thiophosphite (TP), whose chemical structure is similar to that of BTP but without B, a number of primary conclusions were drawn. The B element existing as alkanolamine borate group could greatly improve the extreme pressure, antiwear, and antirust performance of BTP, especially the antirust performance, but had only a small effect on the friction-reducing and anticorrosion properties. Based on characterizations and analyses of the worn surfaces, we propose that the antiwear mechanism consists of the prepared compound BTP reacting with the steel surface during the friction process to generate a protective film mainly composed of phosphate, sulfide, sulfate, organic amine, and B₂O₃.     

Chemistry of Antiwear Films from Ashless Thiophosphate Oil Additives

X-ray absorption near-edge structure (XANES) spectroscopy has been combined with atomic force microscopy (AFM) to investigate the interaction of ashless thiophosphate oil additives on steel. Both mono- and dithiophosphates were studied and compared with one another in terms of chemistry and tribological performance. XANES revealed that, thermally, all three thiophosphate additives behaved similarly with steel to form a thermal film at temperatures of 150 °C. The thermal films all consisted of a layered structure comprised of Fe(II) polyphosphate and FeSO₄ in the bulk and iron polyphosphate of various chain length towards the surface. Tribochemical films generated at 5min, 1 h, and 6 h of wear testing revealed that for all three additives, the phosphorus chemistry of an antiwear (AW) film remained chemically consistent throughout all rubbing times. This suggests that the phosphorus chemistry of the AW film is determined in the initial stages of tribofilm formation. The iron polyphosphate chain length remained uniform throughout the AW film with short chain iron polyphosphates found both at the surface and in the bulk of the films. Mild AW conditions produced several different forms of sulfur at the various stages during wear testing. S K-edge XANES spectra for the 5-min tribofilms (both total electron yield and fluorescence yield) showed oxidized and reduced forms of sulfur throughout the films for all three additives. Over extended periods of rubbing (6 h), the more thermodynamically stable product, FeSO₄, was produced and became the major constituent of the tribofilms formed. Iron sulfate was present throughout the films with only traces of reduced sulfur present.AFM imaging of the AW films revealed that the morphology of the films varied from additive to additive and changed over the duration of wear testing. Generally, the AW films were composed of elongated pads orientated in the sliding direction. As rubbing continued, the pads of each AW film became more homogeneous. The larger pads of AW film appeared to have supported most of the load throughout the course of wear testing, resulting in better AW protection to the metal over increased periods of rubbing