Antiwear Additives in Neopentyl Ester Oils

A variety of organophosphorus and other selected compounds were studied as antiwear additives for neopentyl polyol ester lubricants on 440C stainless steel rubbing surfaces using a four-ball wear test machine. Their effectiveness as additives was compared with that of tricresyl phosphate. Although 440C steel is relatively unreactive, it was possible to improve strikingly its wear and friction characteristics with organophosphorus additives. Some of the best results were obtained with acid phosphates. Alkyl chain length also appeared to be a significant factor. It was demonstrated that small concentrations of extraneous acidic substances are responsible for the antiwear action of phosphites at high load and that larger amounts of such acidic materials are needed as the load increases. Experiments involving addition of amines to neutralize formulations containing an acid phosphate confirmed that free acids promote antiwear action at the higher loads. Vinyl stearate and selected compounds containing chlorine or sulfur proved ineffective as additives for 440C steel in the antiwear region.     

磷酸胺类添加剂的极压抗磨性能研究

采用四球机考察了磷酸胺和磷酸芳胺两种添加剂的极压抗磨性能。结果表明，磷酸胺和磷酸芳胺都是良好的极压抗磨剂，磷酸胺添加剂在基础油中的性能明显好于在水中的性能，磷酸胺的抗磨性能好于磷酸芳胺．但磷酸芳胺的极压性能要好于磷酸胺。     

硫代磷酸酯胺盐抗磨剂的性能及应用

硫代磷酸酯胺盐具有好的热氧化安定性,极压抗磨性,水解安全性,是一种性能较全面的抗磨添加剂。该剂与其他功能添加剂复配,可调制７５Ｗ／９０,８０Ｗ／９０,８５Ｗ／９０重负载车辆齿轮油,多种粘度级别的重负荷工业齿轮油和７０ＴＢＮ船用气缸油。     

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.     

Antiwear Additives for Ester Oils

Esters for lubrication can be classified into two major groups. One is the neopentyl type or the so‐called hindered type. The other is the triglyceride type, which includes vegetable oils. The improvement of the antiwear properties of carboxylic esters by additive technology under boundary lubrication conditions is studied in this paper. Two strategies are considered, based on the structure of the esters. Triglyceride‐type esters are mainly used as rapidly biodegradable fluids. They have carbon‐carbon unsaturated bonds in their molecules, which are susceptible to auto‐oxidation, and this auto‐oxidation has deleterious effects on the antiwear properties. A synergistic effect of antioxidants and antiwear additives on wear reduction was observed. The mechanism is discussed and practical solutions proposed. Neopentyl‐type esters have thermal and oxidative stability. For these oils, the antiwear properties depend on the polarity of the additive and base oil. The effect of molecular structure on the antiwear properties is discussed. Computer simulation is used to understand the mechanism of action. Examples of molecular design of antiwear additives for neopentyl‐type esters are also proposed.     

Wear and Friction Studies of Neopentyl Polyol Ester Lubricants

Wear and friction properties of three representative neopentyl polyol esters, together with the common diester lubricant base, bis(2-ethylhexyl) sebacate, were studied with the four-ball wear machine at 266 F and 5–50 kg load in the presence and in the absence if tricresyl phosphate. The rubbing surfaces were 52100 steel, 440 C stainless steel and M-50 steel. With 52100 low-chromium steel balls, wear rates were largely independent of ester type. Percolated tricresyl phosphate reduced wear moderately at low loads only. Stainless steel 440 C and M-50 steel gave results significantly different from those with 52100 steel at all loads. In the case of the stainless steel wear was greatly increased at a load of 50 kg and tricresyl phosphate (1%) was ineffective at all loads. M-50 steel gave the lowest wear rates. It showed no response to tricresyl phosphate. Average friction coefficients of all the steels showed little change with the variables examined except for a small increase with load and for slightly lower values with M-50 steel.     

Determination of the Ester Composition of Neopentyl Polyol Ester Lubricants

Because of the increasing use of the neopentyl polyol esters as lubricants, an analytical method capable of giving detailed information concerning the composition of these complex ester mixtures is desirable. Methods of gas-liquid chromatography and thin-layer chromatography have been applied in the successful development if such an analytical method. By direct programmed temperature gas chromatography of the lubricants, the components are separated according to volatility; in most cases resolution is adequate for semi-quantitative analysis. Gas-liquid chromatographic analysis of the free acids produced by hydrolysis of the sample reveals the acyl composition. The parent polyols are determined by programmed temperature gas chromatography of their valerate esters. A semi-preparative thin-layer chromatographic method permits the isolation of the three main ester types, trimethylol propane, pentaerythritol, and dipentaerythritol, for further analysis. A combination of these analytical methods permits a detailed study of the changes in composition which occur in these lubricants during service.     

Effects of Microscale Particles as Antiwear Additives in Water-Based Slurries with Abrasives

Abrasive wear is the dominant cause of tool failure in the process of mining and petroleum/gas drilling. This research investigated the effects of two additives, polystyrene and silicon nitride, on the tribological properties of water-based slurries with silicon dioxide or alumina abrasives. A pin-on-disk configuration was utilized to evaluate the performance of the additives for a steel–steel contact. Experimental results showed that polystyrene particles were able to reduce wear but friction increased simultaneously. On the contrary, silicon nitride particles exhibited excellent performance on both wear resistance and friction reduction. Results in this study indicated that the addition of appropriate additives was able to improve the tribological properties of slurries with abrasives.     

Interaction of Polyol Esters and Phosphate Esters with Metal Carbides

The need for higher performance in jet turbine engines has led to the development of alloys with greater hardness for use in bearings. The increased hardness is a result of carburizing of the surface which leads to a change in the surface chemistry through the formation of metal carbides. The authors have found that metal carbides react differently with the lubricants and additives than the oxides found on the surface of currently used alloys. Of particular concern is the observed reaction of the ester basestock with metal carbides in the presence of phosphate esters. The authors have found that metal carbides can catalyze the decomposition of hindered esters in the presence of aryl phosphates to give the component acids. Products of the reaction include free acids, phenyl esters, and dehydrogenated esters. This reaction is expected to rapidly degrade the performance of the oil due to both acid formation and viscosity breakdown. Examination of the remaining solid material indicates that phosphorus has been incorporated into the structure, presumable as phosphate.     

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.     

Antiwear and Extreme Pressure Additives for High-Temperature Lubricants

New aircraft engines require new lubricants that will function under extreme conditions. Synthetic lubricants such as polyphenyl ethers are being explored as functional fluids in this new area. Although the thermal and oxidative properties of polyphenyl ethers are quite good, the lubricity properties are not outstanding. This paper summarizes research done in our laboratory on lubricity additives for polyphenyl ethers. A number of additives have been found to be effective. In general they contained a hetero atom (phosphorus, halogen, sulfur) incorporated into an organic structure. The trichloroacetoxy functional group in an organometallic structure gave compounds with very high extreme pressure (EP) weld points. Although no pattern has been established for antiwear additives, several additives were found that reduced wear. These were not limited to one chemical class. Some additives gave good EP weld points and also reduced wear, but no one compound was extremely effective in both areas.     

润滑脂中极压抗磨添加剂的研究进展

综述近年来多种类型的极压抗磨添加剂在润滑脂中的研究成果,包括:层片状、球粒状添加剂、微纳尺度的软、硬质点添加剂、微纳尺度的氧化物及其他化合物添加剂、环保型添加剂。总结其抗磨减摩的作用机制,并针对目前研究存在的问题,提出了润滑脂用极压抗磨添加剂研究的方向。     

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.     

二冲程汽油机油采用减摩抗磨添加剂的试验研究

本文通过对几种典型的发动机润滑油添加剂的对比试验，研究了此类减摩抗磨添加剂在二冲程汽油机油中的使用效果，试验结果表明某些添加剂在专用摩擦磨损试验机上的试验结果和发动机台架试验结果存在明显差异，据此本文提出了选用润滑油添加剂的建议。     

水溶性复合磷酸酯添加剂抗磨性能研究

合成了水溶性复合磷酸酯,利用四球试验机考察了添加到水溶液中的抗磨性能,并优化了复合磷酸酯的配比,用扫描电子显微镜对钢球磨斑形貌和摩擦表面的元素组成进行了分析,四球结果表明,磷酸酯与硫化物硫脲,油性剂油酸三乙醇胺具有良好的协同抗磨效应,并存在一个最佳配比,电镜能谱分析表明,复合磷酸酯水溶液在摩擦表面与Ｆｅ发生化学反应,生成一种含磷富硫的化学反应膜,而且表面膜中硫,磷元素的含量比为２：１时极压抗磨性能     

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     

Research on Mutual Synergy of Antiwear Additives in Lithium Complex Grease

In recent years, with the enhancement of environment awareness, there has been a progressive reduction in permitted phosphorus and sulfur levels in lubricants. Sulfur and phosphorus are the most important elements of antiwear additives. Because of the reaction between additives, less mass of additives may have the same wear reducing properties when used together. However, there is uncertainty regarding the optimum amount and ratio of these additives. In this article, the influence of five kinds of antiwear additives—sulfurized olefin cottonseed oil (T405), sulfurized isobutylene (SIB), tricresyl phosphate (TCP), molybdenum dialkyl dithiophosphates (MoDTC), zinc dialkyl dithiophosphate (ZDDP), and their combination—on lithium complex grease have been studied by single-factor and orthogonal experiments. The single-factor tests show that T405 and SIB work well under low temperature, whereas TCP and MoDTC work well under higher temperature; ZDDP are multifunctional additives. It was proved that base grease has better antiwear properties at 150 than at 75°C. Additionally, sulfurized additives T405 and ZDDP and phosphate agent TCP could react better with lithium complex grease than the additives that have the same functional group. Furthermore, the results of orthogonal experiments show that the abrasion resistance of lithium complex grease is optimally best when T405, TCP, and ZDDP are blended with a ratio of 2:2:1. In addition, a synergistic effect between T405 and TCP is observed at ratios between 1:1 and 2:1. The morphology and element composition of the worn surfaces are examined by scanning electron microscopy (SEM) and energy-dispersive spectrometry (EDS). Based on the two kinds of technology, the friction and wear mechanism of additives also have been studied.     

油酸新戊二醇壬二酸混合酯的润滑性能

以新戊二醇、壬二酸和油酸为原料通过酯化反应合成了一种混合酯,测定了混合酯的流变学性能、生物降解性能和摩擦学性能。结果表明,混合酯的粘度比较高,粘度指数为227,凝点低于-40.5℃,最大无卡咬负荷为784N,其流变学性能、生物降解性能和摩擦学性能优于矿物油。生物降解率大于97%,是一类高粘度的环境友好酯类油。     

油酸新戊二醇邻苯二甲酸复合酯的润滑性能

以邻苯二甲酸酐、新戊二醇和油酸为原料合成了复合酯,测定了复合酯的流变学性能、生物降解性能和摩擦学性能.结果表明,复合酯的粘度范围宽,40℃的粘度在135～331mm2/s之间,粘度指数约为130,凝点低于-38℃,其中聚合度为1.42的复合酯的最大无卡咬负荷为784 N,磨斑直径为0.40 mm,优于矿物油.生物降解率大于75%,热分解温度大于300℃,因此复合酯是一类性能优良的合成酯类油.