Advances in Oxidation Stability of Lubricants

A composition for improving lubricants that contains a minimally toxic antioxidant and a biobased multifunctional additive. The antioxidant is a specific compound with a defined structure to enhance oxidative stability of biobased lubricants. The additive improves other lubricant properties like viscosity, pour point, and demulsification. The composition enables formulating environmentally acceptable lubricants (EALs) that are biodegradable, minimally toxic, and perform similarly to petroleum lubricants.

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Antioxidant composition for stabilizing polyols and polyurethanes, particularly polyurethane foams, comprising a first derivatized phenolic antioxidant, a second phenolic antioxidant, and a hindered amine light stabilizer. The composition provides improved scorch protection, color stability, and reduced VOC emissions compared to conventional antioxidant blends.

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Introducing an additive is a practical approach to improve the lubrication performance of base oil in the field of tribology. Herein, a series of sulfoximine derivatives was synthesized and incorporated into base oil A51 as additives. The tribological properties of these lubricants were evaluated at both room and high temperatures, and the result demonstrated that they displayed excellent friction reduction and wear resistance in the friction process under both test conditions. Moreover, the chemical composition of the worn scar surface was inspected using EDS, XPS and TOF-SIMS to explore the lubricating mechanism. It is reasonable to conclude that the synergistic interaction between the aromatic ring scaffolds and elements like N, F, and S facilitated the adsorption of lubricant on the steel block surfaces and forming a tribofilm during the friction process. This tribofilm has a dominant impact on the systems lubrication performance. This research provides novel oil-soluble lubricant additives, offering a facile approach to formulating high-quality lubricants.

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A lubricating oil composition with low evaporation loss and viscosity, comprising a poly-α-olefin and an antioxidant, wherein the antioxidant is present in an amount of 0.05% by mass or more with respect to the poly-α-olefin, and the evaporation loss by the Noack method is 4.9% by mass or less.

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Aminophenol antioxidants for inhibiting oxidation of natural oils and materials derived therefrom, such as biodiesel and biolubricants. The antioxidants, represented by Formula I, provide excellent protection against oxidation while maintaining the properties of the natural oil-derived materials. They can be added to biodiesel and biolubricants to prevent degradation and maintain performance characteristics.

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Lubricating oil composition with high viscosity index, comprising a base oil with a kinematic viscosity of 2.0-7.0 mm2/s at 100°C and a polymer with a specific molecular structure, wherein the polymer has a ratio of peak integral values at 10.0-11.0 ppm to 13.5-14.5 ppm of 0.05 or more as determined by 13C-NMR analysis.

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Solid lubricants are those materials that are used to lubricate mainly in dry circumstances. Its main role is similar to that of oils and greases, which is used to create a continuous and adherent lubricant film on the tribological pair surfaces for minimising friction and wear [1]. These coatings are typically employed in situations where liquid lubricants cannot be used or do not offer expected lubrication, such as in high or cryogenic temperatures, high vacuum, ultrahigh-radiation, reactive environments and in extreme contact pressure conditions [2]. Different types of solid lubricants, including graphite, have been extensively used since the middle of the 20th century [3]. From 1950 onwards, development in aeronautics industries emphasised the research and development of advanced solid lubricants. They can be classed based on their crystalline structure, features, properties, or functions, among other things. Different types of solid lubricant coating are shown in Fig. 1 [1].

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Lubricating oils are derived from petroleum and are widely used in the industrial sector, with the aim of reducing wear caused by friction on metal parts. Currently, mineral lubricants are commercially the most used throughout the world, they are a complex mixture of paraffinic, olefinic, naphthenic and aromatic hydrocarbons with 20 to 50 carbon atoms. These are products of the union of two main components: chemical additives and base oil. The base oil is extracted from the petroleum refining process and the chemical additive is used to modify, preserve and intensify the physical and chemical characteristics of the product. They have greater oxidation stability and are cheaper than other types of lubricants. However, mineral lubricants have low biodegradability and release toxic materials into the environment (Karmakar et al., 2017).

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Lubricating oils play an important role in friction-reducing and anti-wear, as well as enhancing mechanical efficiency. To improve the oxidation stability and service life of lubricating oils, the composition and structure of antioxidants should be strategically designed, and these parameters have significantly affected the performance of antioxidants in lubricating oils. Antioxidants are classified into two types based on the substrates they act on: peroxide decomposers and radical scavengers. In this review, the effects of peroxide decomposers (including sulfur compounds, phosphorus compounds, sulfurphosphorus compounds, and sulfurnitrogen compounds) and radical scavengers, such as hindered phenols and aromatic amines, have been discussed as additives in the antioxidant properties of lubricating oils. The results indicate that peroxide decomposers have excellent performances in lubricating oils, but high pollution of S and P is not conducive to their widespread use. On the contrary, radical scavengers also have superior antioxidant properties and no pollution, possessing the pote... Read More

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Controlled vacuum environments as in space applications represent a challenge for the lubrication of tribological components. In addition to common space lubricant requirements like, e.g., low evaporation, a broad operational temperature range and a high stability during operation, long-term-storage (LTS) properties have gained increasing attention recently. The term addresses the time-dependent stability of a lubricant under static conditions, which can mean chemical degradation processes such as oxidation on the one hand, but also the physical separation of oil and thickener in heterogeneous lubricants like greases. Due to the extended storage periods of lubricated components on-ground but also during a space mission for several years, it has to be ensured that a lubricant is still functional after LTS. This article depicts the development of a space lubricant grease with LTS properties. Firstly, LTS requirements and methods for their assessment are discussed. In the following, a systematic approach towards the design of a grease formulation compatible with LTS is described. Finall... Read More

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Lubricating compositions that maintain viscosity stability and prevent oxidative degradation when contaminated with biodiesel, comprising a base oil, sulfurized additives, boronated dispersants, and a detergent system with a specific sodium-to-magnesium ratio and sulfur-to-sodium ratio. The detergent system provides a controlled level of soap content and metal ions, while the sulfurized additives and boronated dispersants contribute to oxidative stability. The composition is particularly effective in preventing viscosity increase when contaminated with up to 30% biodiesel, as demonstrated by passing the GFC Lu-43-A-11 test.

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Lubricating oil composition with improved corrosion resistance, comprising an alkyl hydroxybenzoate detergent derived from isomerized normal alpha olefins and an oxidation inhibitor system containing a molybdenum-containing antioxidant and a diphenylamine antioxidant. The molybdenum-containing antioxidant is present at a level of at least 120 ppm Mo, and the diphenylamine antioxidant is present at a level of 0.5 wt. % or more.

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A sulfurized polyolefin oligomer for extreme pressure lubricants, made by a three-step process involving reaction of an olefin with a sulfur halide, followed by reaction with an alkali metal hydrosulfide and sulfur in an aqueous solution, and final treatment with an aqueous alkaline solution. The oligomer exhibits improved copper corrosion resistance and solubility in both API Group III and IV base oils, while maintaining extreme pressure performance.

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Abstract Aviation lubricating oil, as the blood of machine operation, plays an important role in the lubrication, cooling, cleaning, sealing, rust prevention, and other aspects of aeroengines, thereby ensuring the safe and stable longterm endurance of aeroengines under highspeed and hightemperature conditions. The thermal oxidation of aviation lubricating oil leading to decay is the most important factor causing lubricating oil failure, which will seriously affect the performance of aeroengines and endanger flight safety. Here, we comprehensively summarize the oxidation mechanism of aviation lubricating oil, factors affecting thermal oxidation of aviation lubricating oil, evaluation methods for thermal oxidation of aviation lubricating oil, and antioxidants that inhibit thermal oxidation of aviation lubricating oil. We hope that this review can enhance readers' understanding of the thermal oxidation of aviation lubricating oil, stimulate broader interest, and promote more exciting development in this promising field.

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Rapid advances in modern industrial tribo-systems under high temperatures and heavy loads generate a growing demand for lubricating materials used in extreme environmental conditions. Metal-based lubricant coatings with excellent mechanical properties and thermal stability are widely used on core parts to reduce friction in harsh environments. This paper reviews the progress on modulating the frictional properties of coatings by designing the components and preparation techniques to prolong the lifetime of metal-based lubrication coatings. The impacts of the microstructural changes on the mechanical performances, including hardness, plasticity, interfacial adhesion, and environmental stability, were essential for the deformation and crack propagation of the coatings. Their performances and lubrication mechanisms were concerned under heavy loads, in a wide range of temperatures, and in corrosive marine environments. Finally, the study concluded the basic requirements of metal-based coatings for extreme environments at this stage. The research challenges and potential problems of metal... Read More

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When exposed to high surface temperatures, engine lubricating oils degrade and may form solid deposits, which cause operational issues and increase shutdown time and maintenance costs. Despite its being a common issue in engine operation, the information available on the mechanics of this phenomenon is still lacking, and the experimental data and conditions must be updated to match the improvements in both lubricant stability and engine efficiency. To this end, an experimental apparatus has been developed to study the mechanisms that lead to the degradation and deposit formation of lubricants at high temperatures. The apparatus is designed to operate at pressures up to 69 bar, surface temperatures up to 650 C, oil bulk temperatures up to 550 C, and flow rates of <14 mL/min. In this apparatus, the oil is cycled through a heated test section, and deposits accumulate on the heated surface. The time required for deposits to start accumulating under the test conditions is determined based on the recorded temperature traces, and collected oil and deposit samples may be analyzed to... Read More

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Vegetable oils as bio-lubricants have poor oxidation stability due to the unsaturated fatty acids in their composition. The oxidation in bio-lubricants can occur because they are exposed to heat, light, and oxygen. In this research, clove oil was used to reduce oxidation in vegetable oils. The effects of blending clove oil (0, 5, and 10% wt) with virgin coconut oil (VCO), hydrogenated coconut oil (HCO), and palm oil that have been exposed to oxygen for 30 days have been investigated. Viscometer and pin-on-disk tests were used to determine the physical and tribological properties of the bio-lubricants. The results show that the addition of clove oil to these oils could reduce the oxidation process. It was indicated by the reduced percentage increase in the dynamic viscosity of 10% wt clove oil in VCO of around 5.41% for 30 days. Results of wear rate indicated that the effect of adding clove oil to VCO and HCO was better than that of palm oil, where the wear rate of VCO and HCO decreased with an increasing clove oil composition. Meanwhile, their coefficients of friction were only affec... Read More

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In this study, the thermo-oxidative stability and tribological behavior of bio-based lubricant samples synthesized from castor oil using isoamyl alcohol were evaluated. Initially, the compositional and physicochemical properties of the obtained samples were assessed using the 1H NMR, FTIR and ASTM methods. Oxidative stability of the samples was evaluated using the Rancimat method at 110 C under air flow. The final biolubricant sample (BL2), obtained after esterification, epoxidation and oxirane rings opening reactions, presented an oxidation stability time (OST) of 14.3 h. The thermal stability was also evaluated by thermogravimetry (TG) from the mass variations under inert and oxidative atmosphere. BL2 showed higher thermal stability compared to the other samples, demonstrating higher decomposition temperatures in both inert (339.04 C) and oxidative (338.47 C) atmospheres, for a mass loss of 50%. The tribological properties of the samples were evaluated using a four-ball tribometer configuration. The BL1 and BL2 samples exhibited lower friction coefficients than the mineral oil s... Read More

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Automotive formulated lubricants are high value products composed of 80% base oil and 20% various additives. During their life service, lubricants are exposed to several factors that will cause degradation over time, such as high temperature, shear, and oxidation. Base oil is a complex combination of hydrocarbons that are relatively sensitive to oxidation. During the initiation phase of oxidation, free radicals are formed, leading to the production of hydroperoxide ROOH and an alkyl radical R. These compounds will react with the base oil molecules to form aldehydes, ketones, and carboxylic acids in the termination phase. Owing to the molecular complexity of these mixtures, Fourier transform mass spectrometry seems to be the most appropriate tool to cover their wide range of compounds due to its ultra-high resolving power and mass accuracy. In this study, a native formulated lubricant and its different oxidized states at 140 C under air flow (3, 5, 7, 8, and 9 days of oxidation) were analyzed by FTICR MS. The combination of atmospheric pressure chemical ionization (APCI) was used to... Read More

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A lubricant composition with improved oxidation resistance, comprising a base oil and a diester of formula (I) R1—O—CO—O—R2, where R1 and R2 are alkyl groups, preferably methyl, ethyl, or propyl. The diester reduces the oxidation level of the lubricant composition, measured by viscosity increase, and extends its service life.

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