A study in EP activity evaluation of some new oil-soluble Mo-S complexes

0.5% (w/v) solutions of bis(1,5-diaryl-2,4-dithiomalonamido) dioxomolybdenum complexes in paraffin oil were found to reduce significantly wear and friction of the steel balls in a four-ball test. The additive, bis(1,5-di-p-methoxyphenul-2,4-dithiomalonamido) dioxomolybdenum (VI) afforded higher values of initial seizure load (ISL, 112 kgf), 2.5 second seizure delay load (2.5 s SDL, 126 kgf), weld load (WL, >500 kgf), flash temperature parameter (FTP, 296) and mean Hertz load (MHL, 84 kgf) as compared with the plain paraffin oil and a sulphur-phosphorus additive. The tribological end effects were studied by scanning electron microscopy (SEM) and Auger electron spectroscopy (AES) techniques respectively.     

EP/AW performance evaluation of some zinc alkyl/dialkyl/alkylaryl‐dithiocarbamates in four‐ball tests

Tribochemistry, the chemistry of interacting surfaces under the influence of a lubricant, helps in the appropriate selection of suitable lubricant additives for specific uses. Modern lubricants are usually formulated from a range of petroleum base oils or synthetic fluids incorporating a variety of chemical additives for performance enhancement. Extreme‐pressure (EP) and anti‐wear (AW) additives are used extensively in lubricants for hypoid gears and metal cutting and forming operations to reduce wear, modify friction, and prevent scuffing of moving metallic parts. The present paper includes the synthesis and the evaluation of the tribological properties of 0.5% (w/v) solutions of some zinc bis‐(alkyl/dialkyl/alkylaryldithiocarbamates) in paraffin oil using 12.7 mm diameter steel bearing ball specimens in four‐ball tests. All the synthesised zinc dithiocarbamate additives in general, and zinc bis‐(morpholinodithio‐carbamate) (A₄) in particular, exhibited good AW, EP, and friction‐reducing properties. Additive A₄ especially gave low values of wear‐scar diameter and coefficient of friction at higher loads and higher values of load wear index and flash temperature parameter during EP tests (ASTM D 2783) and afforded lower values of wear‐scar diameter in a one‐hour wear test (ASTM D 2266–67). The surface topography of the wear‐scar matrix of the used ball specimens was investigated by scanning electron microscopy.     

用红外光谱法测定润滑油中MoDTC含量的研究

二烷基二硫代氨基甲酸钼(MoDTC)的减摩效果与其在润滑油中的含量直接相关,为探索快速准确的润滑油新油和在用油中MoDTC含量的检测方法,采用红外光谱分析MoDTC在成品发动机油和减速箱油中的吸收峰特征。选取波数为1 515 cm-1的吸收峰为定量基准,分别用差谱法和直接趋势法建立发动机油和减速箱油中MoDTC含量的测定方法。该方法回归曲线相关系数高,计算误差小。用建立的方法考察发动机油中MoDTC在四球试验时的消耗情况,结果发现MoDTC的消耗趋势与四球试验摩擦因数和磨斑直径的变化趋势有很好的对应关系,验证了该方法对检测新油和在用油中的MoDTC含量均有很好的效果。     

Tribological studies of 1-alkyl-2,5-dithiohydrazodicarbonamides and their Mo–S complexes as EP and multifunctional additives

This communication reports a comparative study of the anti-wear, extreme pressure and friction reducing properties of 0.5% (w/v) admixtures of paraffin oil with 1-alkyl-2,5- dithiohydrazodicarbonamide ligands and their Mo–S complexes, i.e. μ-hydroxo-μ-(1-alkyl-2,5-dithiohydrazodicarbonamido)-bis-[dioxohydroxo molybdenum VI] using 12.7 mm diameter steel bearing balls in a four-ball test. In particular, the additive μ-hydroxo-μ-(1-n-butyl-2,5-dithiohydrazodicarbonamido)-bis-[dioxohydroxo molybdenum VI] exhibits an increase in the load carrying capacity of the lubricant and a decrease in the values of wear and coefficient of friction. The surface analysis of the wear-scar matrix of the used ball specimen has been investigated by SEM and AES techniques.     

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.     

Evaluation of ball and disc wear scar data in the HFRR lubricity test

The high‐frequency reciprocating rig (HFRR) lubricity tester has become a widespread method for determining the lubricity of diesel fuels. The test is a ball‐on‐disc method, in which a steel ball scrapes over a steel disc immersed in the liquid to be tested. According to standards, the wear scar generated on the ball, in the form of the average of the x‐ and y‐axes, is used for evaluating the lubricity of the sample. Generally, the smaller the wear scar, the greater the lubricity of the sample. However, a wear scar is also generated on the disc. The size of the wear scar on the disc also depends on the lubricity of the sample. In this work, the wear scar data of the balls and discs of 230 samples related to the testing of biodiesel and related compounds with petrodiesel were evaluated. Data comparisons for all wear scar combinations correlated well by linear regression. Although correlations are slightly better when using only ball wear scar data (r² > 0.99), other wear scar data, including those generated on the disc, appear just as useable (r² ≈ 0.97–0.99) for evaluating lubricity by the HFRR test. The wear scars on the disc have the advantage of being more easily measurable and recognisable under the microscope, especially if the wear scars are small. Limits for all wear scar values corresponding to current limits for average ball wear scar data in standards are presented. Published in 2007 by John Wiley & Sons, Ltd.     

Comparison of boundary lubrication films formed under four‐ball friction test conditions with different AW/EP Additives‐an X‐ray photoelectron spectroscopy study

The antiwear and extreme‐pressure properties of six different types of additive (molybdenum dialkyldithiophosphate, dibenzyl disulphide, molybdenum dialkyldithiocarbamate, zinc dialkyldithiophosphate, chlorinated paraffin wax, and triaryl phosphate) were evaluated by standard four‐ball friction and wear tests. This was followed by scanning electron microscopy (SEM), X‐ray photoelectron spectroscopy (XPS), and X‐ray photoelectron imaging (XPI) analyses of the worn surfaces to determine the structure of the boundary lubrication film and the mechanism of the tribochemical reaction occurring during the friction process. The presence of the additives in the base oil significantly increased the weld load and drastically reduced the wear‐scar diameter, suggesting antiwear and extreme‐pressure properties of the additives. The enhanced antiwear and loadcarrying capacity of the additive‐containing oils was attributed to the formation of a complex boundary lubrication film formed between the surfaces during the friction process as a result of the tribochemical reaction. The antiwear and extreme‐pressure properties of the additives were explained based on the XPS data. The studies indicated that the lubricating properties of the additives depend on their chemical nature and reactivity with metal surfaces.     

Tribological properties of P‐ and N‐containing organic compounds as potential extreme‐pressure and antiwear additives

An amine salt of an alkoxylphosphate (a P‐ and N‐containing organic compound, PN) was synthesised. Its extreme‐pressure, antiwear, and friction‐reducing properties were evaluated as an additive in liquid paraffin and a mineral oil. Tests were performed on a four‐ball friction and wear tester with an AISI 52100 steel ball self‐mated pair and the results were compared with those of sulphurised olefin (SO), zinc di‐n‐butyldithio‐phosphate (ZDDP), and dibutylphosphite (DBP). The morphologies of the worn steel surfaces were observed using a scanning electron microscope, while the binding energies of some typical elements on the worn surfaces were determined using X‐ray photoelectron spectroscopy. The additives were found to increase the load‐carrying capacity and to reduce wear and friction coefficient considerably. PN as an additive exhibits better load‐carrying, antiwear, and friction‐reducing properties than SO, ZDDP, and DBP under the same test conditions.     

有机钼型复合润滑油添加剂的高温摩擦学性能

以全配方矿物基50CC 柴油机油和 SF/15W-40型汽油机油作为基础润滑油,采用微动、滑动磨损试验机考察了有机钼复合添加剂对45钢/GCr15轴承钢摩擦副的高温微动、滑动磨损性能的影响.结果表明:有机钼添加剂通过分解、吸附和摩擦化学反应,在金属表面形成了吸附的磷酸盐和含 FeS,MoS_2的化学反应膜共同组成的复合表面保护膜,从而有效地改善45钢/GCr15轴承钢摩擦副的高温微动、滑动磨损性能,并具有明显的减摩效果.     

碳酸酯对Ti6Al4V/钢摩擦副摩擦磨损性能的影响

采用SRV型微动摩擦磨损实验机分别考察了Ti6Al4V-钢摩擦副在2种碳酸酯润滑下的摩擦磨损性能,并利用扫描电子显微镜和X射线光电子能谱仪分析了Ti6Al4V磨斑表面形貌和典型元素的化学状态。结果表明,2种碳酸酯作为Ti6Al4V/钢摩擦副的润滑剂所表现出的减摩抗磨和承载能力优于其相对应的脂肪醇;载荷和频率明显影响Ti6Al4V/钢摩擦副在碳酸酯润滑下的摩擦磨损行为;碳酸二-2-乙基己酯所表现出的减摩抗磨和承载能力明显优于碳酸二辛酯;2种碳酸酯对Ti6Al4V/钢摩擦副的润滑机制为在Ti6Al4V磨损表面形成吸附膜,从而起到减摩抗磨的作用。     

Lubricant oils additivated with polymers in EHD contacts: Part 2. Tests using a four‐ball machine

A mineral oil of low viscosity was additivated with different concentrations of low‐density polyethylene. The wear behaviour of the additivated samples and the base oil was evaluated using a four‐ball wear tester at constant speed and variable load. Steel and ceramic (silicon nitride) were chosen for the balls. The scuffing resistance of the ceramic balls was higher than that of the steel balls. No scuffing appeared in the case of an upper steel ball in contact with lower ceramic balls. As far as the minimum wear‐scar diameter on the lower balls was concerned, an optimum concentration of polymer added to the base oil was found from the experimental data, for both types of ball. For the systems investigated, the optimum concentration was about 1.0% polyethylene.     

A study of the synergistic effect of a triazine‐dithiocarbamate derivative with tcp in vegetable oil

A novel, potential ashless S—N‐style additive, 2‐(N,N‐dibutylamino)‐4,6‐bis‐(dibutyldithiocarbamate)‐1,3,5‐triazine (DBTT), was synthesised and its synergistic tribological effect with a traditional additive, tricresyl phosphate (TCP), in rape seed oil was evaluated using a four‐ball tester. The results show that the load‐carrying capacity of the vegetable oil could be improved greatly by the presence of the TCP and/or DBTT additives; at certain mass ratios TCP and DBTT show a good synergistic effect in improving the tribological performance of the base oil. The elemental composition and chemical nature of antiwear films generated at a steel interface were investigated using Kevex energy dispersive X‐ray analysis and X‐ray photoelectron spectroscopy. Scanning electron microscopy was also used to study the rubbed surface morphology. It was found that FeS, organosulphur compound, sulphate, phosphate, and nitrogen‐containing compounds were present in the complex boundary lubrication film.     

含纳米PTFE颗粒润滑脂的润滑性能研究

在四球摩擦磨损试验机上考察纳米PTFE颗粒作为添加剂对复合钛基润滑脂摩擦磨损性能的影响,采用扫描电子显微镜分析试验钢球磨斑的表面形貌,并利用X射线光电子能谱仪检测磨斑表面化学元素的组成及状态。结果表明,在一定添加量范围内,纳米PTFE可以改善复合钛基润滑脂的摩擦磨损性能,其中纳米PTFE质量分数为3%时,复合钛基润滑脂具有最佳的抗磨、减摩性能,可使摩擦因数、磨斑直径分别降低约25.4%和18.9%。纳米PTFE颗粒在钢球表面发生摩擦化学反应,生成了一层金属氟化物,有效地抑制了摩擦表面的黏着磨损和接触疲劳。     

Tribological characteristics of bisphenol S bis(diphenyl phosphate) as a high‐performance antiwear additive in lubricating greases at elevated temperature

Bisphenol S bis(diphenyl phosphate) (BSDP) was synthesised and characterised, and its tribological behaviours as additives in polyurea grease and lithium complex grease were evaluated for steel/steel contact at 200 °C. The results indicated that BSDP could dramatically reduce the friction and wear of sliding pairs in the base grease of polyurea, and the tribological performances of BSDP in polyurea grease were significantly superior to the normally used molybdenum disulfide‐based additive package. Furthermore, BSDP in polyurea grease has better tribological behaviour than that in lithium complex grease at a constant load of 100 N. X‐ray photoelectron spectroscopy analysis indicated that boundary lubrication films composed of Fe(OH)O, Fe₂O₃, Fe₃O₄ and FePO₄ compounds containing the P–O bonds and nitride compounds were formed on the worn surface, which resulted in excellent friction reduction and antiwear performance. Copyright © 2016 John Wiley & Sons, Ltd.     

Transient processes of MoS2 tribofilm formation under boundary lubrication

A tribochemistry study that involves the application of Raman spectroscopy surface analysis has been undertaken to understand the time‐dependent tribochemical reactions, for lubrication by Molybdenum dialkyl‐dithiocarbamate (MoDTC) occurring in boundary lubricated conditions. Under the conditions of rubbing and high temperature, time‐resolved Raman spectroscopy results show the intermediate steps that lead to the MoDTC additive to be tribochemically structured on the wear scar of the contacting surface. A MoS₂ tribofilm with a lattice layer structure is observed on the wear scar whenever the lowest friction was achieved. An apparent shift of the A_1g and E_2g Raman modes, indicating qualitative and quantitative information on the MoS₂ tribofilm formed, is observed to be related to low friction. Detailed analyses of Raman spectra obtained on wear scars at different test durations and temperatures indicate that both temperature and rubbing are needed for the formation of low friction MoS₂ tribofilm. Copyright © 2016 John Wiley & Sons, Ltd.     

Cyclic alkyl disulphides as tribological additives

The use of sulphurised natural oils, fats, hydrocarbons, terpenes and aromatic sulphides, disulphides and poly‐sulphides, as antiwear and extreme‐pressure lubricant additives, has already been established. However, the potential of cyclic disulphides merits attention. The present paper describes the synthesis and evaluation of 0.5% solutions of certain cyclic disulphides as tribological additives, namely 3‐alkylimino‐5‐(N‐methylphenyl)amino‐1,2,4‐dithiazolines, in paraffin oil, on a four‐ball test rig with 12.7 mm diameter steel bearing balls as test specimens. All the additives in general, and 3‐propylimino‐5‐(N‐methylphenyl)amino‐1,2,4‐dithiazoline in particular, exhibited remarkably good antifriction and EP activity, showing a decrease in the coefficient of friction and an appreciable increase in the load‐carrying capacity of the lubricant as indicated by a higher load wear index. The wear surface topography of the used test specimen was studied using scanning electron microscopy.     

Synthetic aluminium complex grease: A tribological evaluation using a four‐ball test

This paper describes the preparation and performance evaluation of a synthetic aluminium complex grease. The aluminium complex grease was prepared in situ by reacting stearic acid and benzoic acid in the presence of a synthetic base oil, polyalphaolefin. The preparation of the soap (aluminium benzoate stearate hydroxide) was monitored using Fourier transform infrared. Two different extreme‐pressure additives blended with the prepared aluminium complex grease were evaluated for their extreme‐pressure activity in four‐ball and Timken tests. These greases exhibited higher Timken OK loads (60 lb), lower values of wear‐scar diameter at higher loads, and higher values of weld load in the four‐ball test than the aluminium complex grease without additive. The blended greases were also found to pass rust and corrosion, oxidation‐stability, and shear‐stability tests. The topography of the specimens after four‐ball testing was studied with scanning electron microscopy.     

2.25Cr1Mo传热管切向微动磨损性能研究

钠冷快堆换热器中的冷却剂与构件之间的流致振动会导致传热管发生微动磨损。以钠冷快堆换热器传热管候选材料2.25Cr1Mo钢为研究对象，研究其在不同法向载荷(10、20、30 N)下的切向微动磨损行为和损伤演变规律；采用光学显微镜(OM)、扫描电镜(SEM)及EDS对磨痕的形貌及摩擦化学反应进行分析；通过白光干涉仪获得传热管的磨损量。结果表明：随着法向载荷的增加，2.25Cr1Mo钢的微动模式由完全滑移转变为部分滑移，摩擦因数、磨损体积随着法向载荷的增加先增加后减小；当载荷为10～20 N时，2.25Cr1Mo钢的主要磨损机制为磨粒磨损、分层剥落以及氧化磨损，当载荷为30 N时，主要磨损机制为黏着磨损、塑性变形和氧化磨损。     

Synthetic polyurea extreme‐pressure greases

This paper describes the preparation of synthetic polyurea greases and evaluates their performance. The polyurea greases were prepared in situ by reacting diisocyanate with monoamines and ethylene diamine in the presence of a synthetic base oil (polyalphaolefin). Two different extreme‐pressure (EP) additives blended with the prepared polyurea greases were evaluated for their EP activity in four‐ball and Timken tests. The additivated greases gave higher loads, and higher values of weld load in the four‐ball test as compared to the polyurea grease without additive. The blended greases were also found to pass rust, corrosion, oxidative stability, and shear stability tests. The topography of the wear‐scar surfaces was investigated using scanning electron microscopy.     

Suspension of molybdenum–sulphur complexes in paraffin oil as extreme pressure lubricants

Molybdenyl aryl thiobiurets were evaluated as extreme pressure lubrication additives in a four ball test using steel balls of 12.7 mm diameter. A comparative account of performance of the tested compounds is presented on the basis of various tribological parameters such as initial seizure load, 2.5 s seizure delay load, weld load, mean Hertz load, flash temperature parameter, pressure wear index, friction coefficient (μ) and wear scar diameter (d), etc. All the tested complexes have been found to possess significant Extreme Pressure (EP) efficiency under the experimental conditions of four ball test. The best performance was shown by p-methoxyphenyl and p-chlorophenyl thiobiurets. The surface topography and tribochemistry of wear scar surface of balls in the presence of p-methoxyphenyl derivative at different loads have been studied by scanning electron microscopy and Auger Electron Spectroscopy (AES). The presence of molybdenum, sulphur, oxygen, nitrogen, etc. on the ball surface, detected by AES, suggests that these compounds act as precursors of tribologically active chemical layers formed under extreme pressure conditions.