High temperature oxidation stability of automotive crankcase oils and their base oils

A modified open test tube type of apparatus has been used to assess the high-temperature oxidation stabilities of two grades of automotive crankcase oils and their base oils under conditions that simulate those encountered in the internal combustion engines. The method involved keeping the oil temperature at 180°C with an air flow of 1.0 L/min for 65 hours and evaluating the soluble oil acidity, pentane insolubles, volatile acidity and total oxidation products formed. The procedure detected that the oil acidity increased exponentially and sludge formation started after a threshold level of oxidation products had been formed. Volatility losses were found to be appreciable, and the antioxidant additives were quickly used up under the simulated conditions. Therefore only a mineral oil of high natural antioxidant capability could provide improved performance at high temperatures. The total oxidation product proved to be a valuable source of information on the extent of oil oxidation and oxidation stability study.     

An evaluation of antioxidants for vegetable oils at elevated temperatures

The antioxidant efficacy of various oxidation inhibitors in low erucic acid rapeseed oil has been studied in a screening test at 130°C by an induction period method. Hindered monophenols, sulphides, phosphites, aromatic amines and zinc dithiophosphates yielded no or only marginal stabilising effects. Remarkably increased oxidation stabilities were observed with certain hindered bisphenols, polyhydroxybenzenes, zinc and bismuth dithiocarbamates. In high oleic sunflower oil with a lesser portion of multiple unsaturation, these additives induced relatively longer induction periods. Mixtures of zinc dithiocarbamates and 4,4′-methylenebis-(2, 6-di-tert-butylphenol) or octylated di-phenylamine, as well as compositions of all three compounds, exhibited synergistic effects. Under the conditions employed these additives were distinctly superior to commercially recommended formulations. A mechanistic concept of the antioxidant action of zinc dithiocarbamate is briefly discussed.     

The relationship between oxidation stability and antioxidant depletion in turbine oils formulated with Groups II,III and IV base stocks

Using simple turbine oil formulations, we studied the effects of different antioxidant systems on oxidation behaviour. Fourier transform infrared was used as a sensitive probe to monitor the depletion of different antioxidant types present in turbine oils based on Group II, III and IV base stocks. It was found that the depletion of alkylated diphenylamine antioxidants from turbine oil systems is generally slower when hindered phenolics are present in the formulation. Furthermore, the type of hindered phenolic used in the formulation is critical for preserving this amine activity, with the bis‐phenolic 4,4‐methylenebis(2,6‐di‐tert‐butylphenol) showing superior performance over a phenolic ester of approximately the same molecular weight. This effect was explained by the higher hindered phenolic activity of the bis‐phenolic relative to the phenolic ester. The ability of the bis‐phenolic to preserve or protect the amine antioxidant, combined with its higher hindered phenolic activity, was shown to improve the oxidation resistance of turbine oils. The results also showed a surprisingly high oxidation stability for turbine oils formulated with Group III base stock, with the oxidation resistance of the Group III systems exceeding that of the equivalent Group II and Group IV systems. Copyright © 2007 John Wiley & Sons, Ltd.     

The influence of chemical structure on the physical properties and antioxidant response of hydrocracked base stocks and polyalphaolefins

This study was conducted to determine the effect of hydrocracked base stock chemical composition on lubricant properties, oxidation performance, and antioxidant additive response. Fifteen hydrocracked base stocks and polyalphaolefins were analysed by mass spectrometry for paraffinics, and single‐, double‐, and multi‐ring naphthenics. Low levels of aromatics were confirmed in all the base oils. A linear relationship was found between certain naphthenic structures in the base stocks and properties, such as viscosity index, aniline point, and volatility. Additivated versions of the base stocks were also screened in the rotary bomb oxidation test (ASTM D 2272) and the thin‐film oxygen uptake test (ASTM D 4742). A relationship between the types of naphthenic structures in the additivated base stocks and oxidative stability was found. Base oils containing low levels of condensed multi‐ring naphthenic structures exhibited superior oxidation performance, lower volatility, and poorer solvency. Furthermore, antioxidant structure had a profound effect on oxidative stability as the level of multi‐ring naphthenic structures in the base oils decreased. These results suggest that deeper knowledge of chemical composition could help in selecting base stocks and additives to meet future product specifications.     

The effect of the aromaticity of base stocks on the viscometric properties of multigrade oils

The viscometric properties of multigrade oils containing base stocks with increased aromatic content have been studied. Various types of viscosity index improvers (VIIs) have been incorporated in these formulations. Viscosity measurements were carried out over a wide temperature range (from −10°C to 150°C). The results show that increasing the aromaticity of blends induces a greater thickening effect with all types of VIIs incorporated, but by different magnitudes. This thickening effect is more pronounced at low temperatures. At high temperature and high aromaticity, the VIIs tended to acquire high swelling behaviour, which serves to mask the differences between them. Limited changes were noticed for the viscosity index, thickening tendency, and specific viscosity of the blends tested. The shear stability of the VIIs was found to decrease with the increasing aromaticity of the blends. Such behaviour can be attributed to the swelling of the VIIs and the increase in their molecular volume, which consequently facilitated their shearing.     

An investigation of fretting behaviour of several synthetic base oils

The chemical and physical properties are quite different for mineral oil and synthetic oil. Compared to the investigation of mineral oil, less work on fretting behaviour of synthetic oils was reported. In this paper, a study of typical synthetic base oils such as polyalkylene glycol (PAG), polyalphaolefin (PAO) and silicone oil has been conducted. The contact consisted of a fixed flat specimen (GCr15 steel and 45 steel) opposite to a moving ball specimen (GCr15 steel) with a diameter of 12.3 mm. Other main parameters were as follows: the slip amplitude was ranged from 5 to 80 μm, the frequency was varied from 2 to 5 Hz; the normal load, temperature and relative humidity were respectively 100 N, 23 °C and 60%. Variations in the tangential force versus the displacement as a function of the fretting cycles were recorded. For comparison, fretting tests under dry condition have also been performed. The fretting scars were examined after tests. The evolution of coefficient of friction and wear volume were analyzed and compared at different fretting regimes for different synthetic base oils. The competitions between oil penetration into the interface and self-cleaning by fretting in different fretting regimes, the effect of physical properties such as surface tension, pressure–viscosity coefficient and compressibility on fretting behaviour have been particularly discussed.     

Effect of blended paraffinic base oils on abrasive belt grinding of stainless steel

The effect on grinding performance of blended paraffinic base oils of about the same viscosity was examined experimentally with a newly improved apparatus, in which a pressurized air cylinder is installed as the work infeed system. Stock removal was not affected by the kinds of blended base oil, however, abrasive belt wear decreased with the blended base oil as compared with the single base oil.     

Thermo‐oxidative stability of new‐generation base oils

Thermo‐oxidation of base oils is the primary cause of lubricant degradation and engine failure during use. Degradation is mainly due to high‐temperature oxidation and thermal decomposition near the piston ring zone, forming oxygenated compounds that polymerise to form high‐molecular‐weight insoluble deposits. New‐generation base oils are found to be more stable towards oxidation and deposit formation due to the absence of aromatics and polynaphthenes. However, compatibility with antioxidants and other additives is now of greater concern because of the poor solvency of these oils. With the increase in the purity of the oil, sometimes the oxidation performance is poor in comparison to group I oils, mainly due to the removal of sulphur compounds, which act as natural antioxidants. Thermal techniques, such as differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA), are emerging as fast and accurate methods for determining the thermo‐oxidative stability of base oils and their additive blends, making it possible to measure the oxidation induction time, incipient oxidation temperature, and deposit‐forming tendency. The objective of this work is to evaluate the thermo‐oxidative stability of new‐generation group II/III base oils without antioxidant additives, using DSC and TGA. The kinetics of base oil oxidative degradation are studied using different heating rates. The data obtained from thermal techniques are correlated with the micro‐oxidation data obtained from the Penn State Micro‐Oxidation (PSMO) test. The response of a typical antioxidant additive, zinc dialkyldithiophosphate, towards oxidative degradation of base oils has also been studied.     

The effect of base oil oxidation on scuffing

In this work, the effect of base oil oxidation on scuffing was investigated. It was found that under mixed lubrication conditions there is a direct relationship between the level of base oil oxidation and the onset of scuffing, i.e., the greater the oxidation the lower the likelihood of scuffing. An oxidised base oil forms, among other products, carboxylic acids, which reduce scuffing failure in comparison with the parent oil. This was confirmed by the addition of a carboxylic acid directly to the base oil operating under the same mixed lubrication conditions. The removal of the carboxylic acids from the oxidised oil via column chromatography resulted in a scuffing failure performance equivalent to the parent oil. This revised version was published online in June 2006 with corrections to the Cover Date.     

Evaluation of antioxidants in rapeseed oils for railway application

In order to evaluate the applicability of biodegradable base-oil lubricants for railway applications, the influence of UV(ultraviolet)-B light (280-320 nm) on oxidation stability and the tribological performance of rapeseed oil (RO) have been investigated. Antioxidant free RO was oxidized immediately under UV-B irradiation at moderate temperature. Three sterically hindered phenolic-type antioxidants, pentaerythritol tetrakis(3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate), octadecyl-3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate, and 2-6-di-tert-butyl-4-methyl phenol were tested in order to increase the oxidation stability of RO. Pentaerythritol tetrakis(3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate) was the most effective, prolonging the oxidation induction time from 3 h of RO to 40 h. The tribological performance of RO could be improved by the addition of metallic detergent (Ca-alkylsalicylate-CaCO₃) and was stable against the UV-B irradiation.     

柴油机油基础油高温清净性能研究

利用L-1A型润滑油清净性能试验机,通过考察不同类型基础油的沉积物质量、形貌,探讨其高温清净性能。结果表明,APIⅠ类基础油高温清净性能优于APIⅡ类基础油;APIⅠ类基础油中中芳烃和重芳烃和硫元素含量明显高于APIⅡ类基础油,因此氧化安定性好,高温下沉积物生成量也少。     

两种合成航空润滑基础油高温氧化衰变机理研究

为研究航空润滑油的热氧化安定性,模拟聚α-烯烃(PAO)和酯类油(DE)两种合成航空润滑基础油在发动机内的高温工况,借助傅里叶红外光谱(FTIR)、气相色谱/质谱(GC/MS)联用等仪器对反应油样的黏度和结构组成进行测试与分析.结果表明,PAO具有较差的热氧化安定性能,在200℃时就发生分解,而DE的分解温度可达到300℃.在两种航空润滑基础油的高温衰变中,均有不同的产物生成.PAO衰变产物主要包括烷烃和烯烃,而DE的衰变产物主要是含氧化合物.最后,根据实验结果分析了航空润滑基础油的高温衰变机理.     

Effect of nonylpolysulphide in different base oils on abrasive belt grinding of stainless steel

Nonylpolysulphide was added to a single paraffinic base oil, P60, and a blended paraffinic base oil, BP60, and its effect was examined experimetally. Adding nonylpolysulphide to a base oil had a greater effect with the single base oil, P60, than with the blended base oil, BP60, if the grinding condition could be correlated to the sulphur concentration. With the blended base oil, nonylpolysulphide was found to improve the grinding performance in a comparatively wide range of sulphur concentrations.     

The effect of aromatic hydrocarbons in lubricant base oils on the efficiency of adsorptive additives

This paper describes a study of the effect of aromatics in lubricant base oils on the efficiency of adsorptive additives in terms of lubrication and rust‐inhibition performance. The additives investigated were sulphurised isobutylene, tricresyl phosphate (TCP), sorbitol monooleate (Span‐80), and alkylene succinic acid. Four‐ball friction and wear tests, a modified ASTM D 665 rust test, an electrochemical test, and X‐ray photoelectron spectroscopy (XPS) were used to reveal the relationship between the aromatics and the additives. The results show that the aromatic hydrocarbons in the base oils reduce the surface activity of the additives; competitive adsorption between the polar compounds and the additives is not a key factor governing the behaviour of the additives under the test conditions.     

炼油装置腐蚀及应对措施

对我厂炼油装置改炼高硫原油对设备腐蚀问题进行探讨,并提出应对措施。     

Study of some non-edible vegetable oils of Indian origin for lubricant application

Due to growing environmental concerns, eco-friendly processes and materials have become one of the key interests of research and in the area of tribology, natural esters are gaining popularity as lubricants. Natural esters are being used in many applications as eco-friendly lubricant base. In Europe, canola/rapeseed oil and sunflower oil are mainly used, whereas in the USA, soybean oil is in use for formulating environmentally friendly lubricants. Native and genetically modified high oleic varieties of these oils are being widely used. In the Indian scenario, since the above-mentioned oils are scarcely available for industrial applications, there is a need to look for other viable alternatives. Some candidate non-edible vegetable oils of Indian origin were selected which were unexplored or less explored in the field of lubricant application, and their suitability in lubricant application focusing mainly on physico-chemical characteristics, thermo-oxidative stability and lubrication characteristics was studied. These oils were found to be promising candidates for application in lubricants in view of their physico-chemical characteristics and better thermo-oxidative and hydrolytic stability. Copyright © 2007 John Wiley & Sons, Ltd.     

Application of quantitative 13C nuclear magnetic resonance spectroscopy to the characterisation of solvent‐refined aromatic‐rich lubricant base oils

Nuclear magnetic resonance (NMR) spectroscopy has emerged as a powerful technique for studying the molecular composition of base oil matrices. The usefulness of this technique lies in its ability to explain the chemistry involved in the molecular changes observed in various lubricant refining and extraction stages. This paper discusses the use of this technique in understanding the variation of gross properties observed in base oils during lubricant processing steps. The variations in weight percent of sulphur, viscosity index (VI), Conradson carbon residue (CCR), characterisation factor (K_UOP), etc., are explained at the molecular level using high‐resolution quantitative ¹H and ¹³C NMR. A single well‐recorded quantitative spectrum of a sample can be used to generate sufficient information on the different properties used for the specification of base oils.     

Inverse gas chromatographic study of the oxidation stability of lubricating base oil via linear solvation energy relationship

Linear solvation relationship was used as a new approach to follow the oxidation steps of both naphthenic and paraffinic base oils and to compare the resistances of both oils against oxidation. The obtained results demonstrate that the values of solvation of both oils change approximately linearly with the oxidation time at constant temperature. It was found that the values of the constants change by a faster rate on oxidation of the naphthenic base oil compared with their rate of change of paraffinic oil oxidation. The changed values of solvation constants during the course of oxidation can be used to follow the initiation, propagation and termination oxidation steps. Copyright © 2012 John Wiley & Sons, Ltd.     

Evaluation of the oxidative properties of vegetable oils as base stocks for industrial lubricants using spectroscopic and thermogravimetric analyses

This paper presents the study of the oxidative behaviour of vegetable oils using Fourier transform infrared (FTIR), nuclear magnetic resonance (NMR) spectroscopic methods and thermogravimetric analysis/differential thermal analysis (TGA/DTA) techniques. The properties of vegetable oils were determined by their fatty acid (FA) composition. A high content of polyunsaturated FAs, like linoleic and linolenic acids, decreases thermal‐oxidative stability. FTIR spectroscopy can be used as a quick method to measure the degree of unsaturation in vegetable oils in a qualitative manner. NMR spectroscopy can be used to quantitatively evaluate the degree of unsaturation in vegetable oils. TGA/DTA techniques were used to evaluate the oxidative properties of vegetable oils. In the present study, TGA/DTA analyses was performed on different vegetable oils under isothermal conditions at 150 °C for 3 hours. TGA/DTA thermograms showed weight changes and thermal activities in terms of exothermic or endothermic heat flows during the oxidative reactions. The oxidative degradation was evaluated in terms of the weight gain by the respective vegetable oils under the test conditions, due to the formation of oxidative polymerization products and the value of exothermic peaks as obtained from the DTA. The comparative study of the oxidative performance of different vegetable oils showed that the higher the degrees of unsaturation, the higher are the weight gains and the exothermic peaks. The evaluation of the effect of a chosen antioxidant showed marked improvement on the oxidative stability of vegetable oils. Copyright © 2008 John Wiley & Sons, Ltd.     

NMR and DSC studies of base oils

The effect of the composition of a base oil matrix on additive response is an indication of its behaviour in a dynamic system. In this paper, a novel method involving quantitative ¹H and ¹³C NMR to explain the molecular chemistry of base oil is used. Oxidative degradation of base oils (pure as well as additivated) has been studied using DSC. The results are explained in terms of molecular composition of the different base stocks to get a clear understanding of additive response in a matrix of different hydrocarbon oils.