Mineral Base Oil Research Articles

Grease thixotropy: evaluation of grease microstructure change due to shear and relaxation

Purpose – The thixotropy of lubricating grease thickened with lithium 12-hydroxystearate with mineral base oil was investigated. The thixotropy has a significant influence on the flow resistance and pressure drop in the structural components of lubrication systems, which is of major importance as today the latter are being centralized and automated. The paper aims to discuss these issues. Design/methodology/approach – Rheometer studies on thixotropy were carried out and the grease microstructure was visualized using atomic force microscopy (AFM). Total reflection Fourier transform infrared spectroscopy (ATR-FTIR) was used to study the physicochemical interactions which indicate the disintegration and recovery of the grease microstructure. Findings – A qualitative assessment of the physicochemical interactions between lithium soap floccules was made and a theory of the self-ordering effect of lithium 12-hydroxystearate associated molecules during shearing and their aggregation and flocculation during relaxation has been proposed. Originality/value – Because of the complexity of the disintegration and recovery of the lubricating grease thickener microstructure, there is still limited physical understanding of the mechanism of this process. Therefore, the present research was undertaken to identify the phenomena involved.

Investigation of the effects of alumina nanoparticles on spur gear surface roughness and hob tool wear in hobbing process

Hobbing process is one of the machining methods in manufacturing spur gears. In machining processes, selecting a suitable lubricant is one of the significant factors in enhancing machining productivity and improving the characteristics of manufactured workpieces. This study has used the nanolubricant including alumina nanoparticles dispersed in mineral-based oil 25W-50 in hobbing process. Then, hobbing process using the lubricant including both nanoparticles, and none has been done utilizing with the similar hob tools. Two spur gears with DIN1.7131 material have been manufactured using each of two lubricants. Then, the hob tool wear and surface roughness values of manufactured spur gears were investigated. Comparing the results show that using lubricant including alumina nanoparticles in hobbing process causes an expressive decrease in the hob tool crater and flank wear. Also, arithmetic surface roughness value in spur gears manufactured with nanolubricant has decreased.

English

The paper predicts the exceptional extreme pressure properties of multi walled carbon nano tube as compared with traditional mineral oil which also contained some additives and graphite. The extreme pressure property was predicted by four ball tester. In the test the load bearing capacity of the newly developed nano oil was predicted to have a better value than the commercial available mineral oil. The weld load of the nanolubricant was found to be 200 kgf as compared with the base mineral oil which got welded at 160 kgf. Thus, the finding would be helpful in developing new nanolubricants which would increase the life of the mating parts, reducing the chances of failure of machine and increasing the productivity. Key words: Mineral oil, multi walled carbon nano tube (MWCNT), pass load, weld load, load bearing capacity, Carbon Nano Tubes (CNT).

Deposit formation from lubricant degradation: a uniform layer deposition model

ABSTRACTReported is a new model describing deposit formation and ageing along the so‐called universal mass deposition curve. The penn state micro‐oxidation (PSMO) apparatus produced model deposits at varied test durations in order to study the ageing mechanism of thin film deposits from mineral base oil. Along the ‘universal’ mass deposition curve, mass deposition rates were correlated to film chemistry. Formed by concerted oxidation‐polymerisation reactions, chemical group and elemental content analyses were performed by Fourier transformed infrared spectroscopy‐attenuated total reflectance and energy dispersive spectroscopy, respectively. The results showed that deposit formation initiates as a film — uniform in composition. After an induction period, the film growth accelerates then slows and eventually falls off, with a decrease in mass often observed. These stages reflect underlying physical and chemical changes as the deposit progresses from an initial polymeric, lacquer‐type deposit, towards a final dark, carbonaceous deposit, along the universal mass deposition curve. Carbonyl, hydroxyl and sp3 hybridised carbon were identified as the main functional groups found across all deposit types albeit at different levels. Correlative behaviour was observed between changes in functional group infrared intensities and O‐atom and C‐atom content. These trends are interpreted as reflecting concerted deoxygenation and dehydrogenation processes, throughout the deposit, over the course of ageing, thus providing a foundation for the uniform layer model. Copyright © 2013 John Wiley & Sons, Ltd.

Wear Behavior of Titanium Alloy Lubricated with Palm Olein as Bio-Lubricant Using Pin-On-Disk Tester

The wear mechanism of titanium alloy lubricated with fixed amount of palm olein was investigated using modified pin-on-disk tester. Titanium alloy has high strength-to-weight ratio and excellent mechanical properties such as superb corrosion resistance. This make titanium alloy was chosen for the critical or high temperature/pressure application such as turbine engine parts. Palm oil was chosen for the development of bio-lubricant to replace or minimize the usage mineral oil base lubricant. Palm oil is a vegetable oil which is non-toxic to human and has high decomposition rate. These factors give advantages to palm oil to be produce as an industrial lubricant. The experimental works were performed using a pin-on-disk tribotester, using titanium as the material for both flat ended pin and grooved disk. The test were implemented by dripping 5ml of RBD palm olein as a lubricating oil on the sliding surface at constant speed, which was 0.5m/s using different loads, which were 5N, 20N, 40N and 80N. In this study, the wear rate of the pin and friction coefficient were investigated. The weight loss and surface roughness before and after experiment were analyzed. All the results obtained were compared to commercial hydraulic oil and additive-free paraffinic mineral oil. From the analysis, the friction coefficient acquired with lubrication of RBD palm olein was the lowest compared to commercial hydraulic oil and additive-free paraffinic mineral oil at all loads applied. It could be concluded that RBD palm olein has good lubricity performance and has the capability to be developed as a lubricant.

Tribological Performance Evaluation of Task-Specific Ionic Liquids Derived from Amino Acids

Aspartic acid and glutamic acid derived ionic liquids were found to be efficient antiwear and friction-reducing additives for base oils. The tribological performance evaluation of lubricant blends, prepared as 0.15%, 0.3%, 1%, 1.5%, 2%, and 3% concentration by weight into the mineral base oil, was carried out on a four-ball tribotester. The concentration of ionic liquids along with the chain lengths of alkyl groups influenced the tribological performance of the formulated blends. The synthesized ionic liquids exhibited excellent antifriction and antiwear characteristics.

New Insight into the Relationship Between Molecular Effects and the Rheological Behavior of Polymer-Thickened Lubricants Under High Pressure

The effects of temperature, pressure and shear stress on the viscosity of simplified automotive lubricants—polymer-thickened base oil solutions—were investigated. Various polymers—with different molecular weights and conformations (comb, linear and star)—were used at low concentration (1.2 % w/w) in a hydrocracked mineral base oil: a poly(alkylmethacrylate), an olefin copolymer and a poly(isoprene-styrene hydrogenated). Their rheological behavior was studied and modeled with a Vogel-Tamman and Fulcher equation, a modified Williams-Landel-Ferry-Yasutomi relationship and a Carreau-Yasuda-like formula. Then, the Einstein’s law was used to rapidly and simply determine the hydrodynamic radii of polymers as a function of temperature and pressure. Calculations from Flory equations, intrinsic viscosities and direct measurements confirmed the relevance of this methodology. Finally, molecular considerations allowed a good understanding of the rheological response of polymer solutions.

Experimental analysis of stable CuO nanoparticle enhanced lubricants

The tribological properties of a custom-prepared and stable nano-lubricant that consists of CuO nanoparticles (9nm average diameter) suspended in mineral base oil using sodium oleate (SOA) as a surfactant are presented. Nano-lubricants with concentrations of 0.5, 1.0 and 2.0%wt were investigated using a disk-on-disk friction and wear test. It is observed that CuO/SOA nanoparticle additives reduce the friction between the lubricated surfaces in the absence of any other conventional additives. The effect of nanoparticles is more influential at higher loads and concentrations. Also, the steady state temperature of the lubricant is lower in the presence of nanoparticles. Measurements show that the viscosity of the nano-lubricants increases as more nanoparticles are introduced in the lubricant. The Stribeck curve is utilised to generalise the friction, temperature and the viscosity results into a single plot which can help to compare the performance of different nano-lubricants. Wear analysis based on profilometry results suggests that the wear increases with the nanoparticle concentration up to a 1.0%wt and then decreases for a 2.0%wt nano-lubricant. SEM/EDS results suggest that nanoparticles bond to the surface and form protective layers. Based on the results, different possible mechanisms for nanoparticles in the boundary lubrication regime were evaluated and the reduction in the real area of contact was suggested as the possible mechanism for reducing friction.

Synthesis, Characterization, and Performance Evaluation of Some Multifunctional Lube Oil Additives

Eight polymers (two homopolymers and six copolymers with 1-decene) of isodecyl acrylate and isooctyl acrylate were synthesized using benzoyl peroxide as initiator and characterized by spectral analysis, viscometric, and thermogravimetric measurements. Intrinsic viscosity obtained from the viscometric method was used to determine the viscometric molecular weight of the polymers. Pour point (PP) and viscosity index (VI) of the additive-doped base oils were evaluated to check the efficiency of the polymers as pour point depressant (PPD) and viscosity index improver (VII), respectively. Analysis of different properties indicates that the isooctyl acrylate polymers have better lube oil additive property than that of isodecyl acrylate polymers. VI and PP values of the polymers doped in base oils depend on the nature of mineral base oils, polymer type, and also on the concentration of the additives.

Hardness effect of DLC on tribological properties for sliding bearing under boundary lubrication condition in additive-free mineral base oil

Diamond-like carbons (DLC) with different hardness of 47.1, 11.8 and 6.05GPa were coated on SUJ2 rollers, and their tribological properties were investigated under boundary lubrication conditions in an additive-free mineral base oil at different testing oil temperatures of 24, 80 and 160°C. The hardest DLC with 47.1GPa showed the lowest friction coefficient and wear. From the results of the Raman analyses and spectroscopy ellipsometry, we found that the structure changed at oil temperature of thickness of 80°C with the formation of a thick layer of 160nm at the topmost sliding contact surface which provided the lowest friction coefficient of 0.03 in an additive-free mineral base oil.

Wear of sintered HSS under combined squeeze–sliding lubrication

Some mechanical assemblies are subjected to combined impacts and sliding motion, and this leads to complex wear mechanisms. When lubricants are introduced, the friction is reduced and surfaces damage processes are modified. A specially developed impact-sliding tribometer was used to investigate the effect of the different model lubricants on wear behavior of a sintered high-speed steel (M2) under impactsliding. The squeezesliding event was observed using a high-speed camera. An increase of lubricant viscosity was observed to increase the wear depth. In addition, a comparison of wear volumes produced using pure mineral base oil and the same base oil containing an anti-wear, anti-friction additive (ZDDP), shows that this additive has only a weak effect on wear reduction under squeeze–sliding lubrication. A discussion of basic wear mechanisms is presented to explain the observations.

Tribological performance and tribochemical processes in a DLC/steel system when lubricated in a fully formulated oil and base oil

Diamond-like carbon (DLC) coatings show extremely good promise for a number of applications in automotive components as they exhibit excellent tribological properties such as low friction and good wear resistance. This can impact on improved fuel economy and durability of the engine components. Much work has been reported on the dry sliding of DLC coatings with less so in lubricated contacts and, as such, there is a need to further understand the tribochemistry of lubricated DLC contacts. Commercially-available oils are normally optimised to work on ferrous surfaces. Previous studies on DLC lubricated contacts have tended to use model oil systems rather than fully formulated lubricants and from this an interesting picture of lubrication mechanisms is emerging. Optimising compatibility between a surface and a set of lubricant additives may lead to excellent durability (wear) as well as increased fuel economy (low friction). In this work, the friction and wear properties of a DLC coating under boundary lubrication conditions have been investigated and the tribological performance compared with that of an uncoated steel system.A pin-on-plate tribotester was used to run the experiments using High speed steel (HSS) M2 grade plates coated with 15at.% hydrogenated DLC (a-C:15H) sliding against cast iron pins. A Group III mineral base oil, fully synthetic Group IV PAO and four different fully formulated oils were used in this study. Furthermore optical and scanning electron microscopes (SEM) were used to observe the wear scar and to assess the durability of the coatings. Energy-Dispersive X-ray analysis (EDX), X-ray Photoelectron Spectroscopy (XPS) and Raman spectroscopy analyses were performed on the tribofilms to understand the tribochemical interactions between oil additives and the a-C:15H coating.This study show that the durability of the a-C:15H coating strongly depends on the selected additive package in the oils. In addition the effect of detergent, dispersant and antioxidants on the performance of the molybdenum-based friction modifier (Mo-FM) and ZDDP anti-wear additive was investigated and results are reported in this paper.

Microstructure, mechanical properties and tribological behavior of tribofilm generated from natural serpentine mineral powders as lubricant additive

Surface-modified serpentine powders with an average size of 1.0μm were dispersed into mineral base oil to improve the lubricating properties of oil, as well as to generate a thin tribofilm on the worn surface. SEM, TEM, nano-indentation and Stribeck testing were performed to study the morphology, microstructure, micromechanical properties and tribological behavior of the tribofilm, respectively. Results show that a nanocrystalline tribofilm, with a thickness of 500–600nm, is formed on the worn surface under the lubrication of oil with 1.5wt% serpentine. The film is mainly composed of Fe3O4, FeSi, SiO2, AlFe and Fe-C compound (Fe3C). A phenomenological model of the tribofilm generated by serpentine was developed based on the experimental results. The excellent mechanical properties, reinforced phase of embedded particles and porous structure of the tribofilm contribute to the reduction of friction and wear, especially in the case of boundary and mixed lubrication.

Determination of Silicon in Vegetable Oil and Biodiesel by High-Resolution Continuum Source Flame Atomic Absorption Spectrometry Using Sample Dilution with Xylene

In this paper, a simple procedure for the determination of Si in vegetable oils and biodiesel of different origins by high-resolution continuum source flame atomic absorption spectrometry is proposed. Samples were diluted with xylene, and external calibration was performed with calibration solutions prepared with xylene and mineral base oil used for viscosity matching. The accuracy was assessed using recovery tests and comparing the results for a set of vegetable oils and biodiesel to those determined by inductively coupled plasma–optical emission spectroscopy (ICP–OES). Recoveries at 3.0 and 5.0 mg L–1 levels using organic Si standard-spiked solutions ranged from 93 to 113%. The limit of detection at the optimized conditions in the original sample was approximately 0.60 mg kg–1, which is adequate for the analysis of vegetable oils and biodiesel according to the Brazilian legislation.

Production and Application Properties of Dispersive Viscosity Index Improvers

Polymeric dispersive viscosity index improvers of lubricating mineral oils based on styrene, dodecyl-methacrylate, octadecyl methacrylate, and N,N-dimethylaminoethyl methacrylate (d-PSAMA) were produced by performing copolymerizations isothermally up to the high conversion in mineral base oil solution, using monofunctional or bifunctional peroxide initiator. The obtained kinetics results reveal the benefits of the usage of a bifunctional peroxide initiator over a monofunctional, because complete conversion of monomers was accomplished in the shorter reaction time, performing the process in a full batchwise mode. When the bifunctional initiator was applied, the required polymerization temperature was slightly higher (105 °C), and copolymers of higher average molecular weight values (Mw = 60–120 kg mol–1) were obtained, while in case of the monofunctional peroxide initiator, the reaction temperature was 100 °C, and average molecular weight values of copolymers were Mw = 30–100 kg/mol. Investigated applicati...

Evaluation of Food Grade Corn Oil for Electrical Applications

Petroleum-based insulating liquids are applied in several items of electrical power equipment, in which they serve as a dielectric as well as a coolant. However, these oils are environmentally toxic and inflammable, require costly fire protection schemes and deluge systems. To overcome this problem, seed-based vegetable oils have been investigated since these are biodegradable, non-toxic, and posses high fire point. In this experimental investigation, a local brand of seed-based corn oil is evaluated so as to be adopted as a viable dielectric fluid. It was characterized through a series of dielectric and physio-chemical properties and compared with mineral insulating oil. Results show that its 60 Hz breakdown strength is much higher than the mineral oil, while tan δ values satisfy IEC-60156 set criteria. Higher values of permittivity will enable favorable field distribution across oil-cellulose composite insulation. Under oxidation in presence of copper catalyst, it exhibits much less degradation than in mineral oil since its acidity is decreased. It therefore offers a more cost effective replacement solution, in particular for electrical applications in under developed and developing countries where the mineral-based oils are expensive due to a price hike in petroleum crudes.

Tribological synergism of surface‐modified calcium borate nanoparticles and sulfurized olefin

PurposeSulfurized olefins have been extensively used in many kinds of gear lubricants as EP additives. However, their commercial applications are not totally satisfactory because of the pungent, obnoxious odor and corrosion of copper and copper alloys. The purpose of this paper is to investigate the synergistic effects of one type of calcium borate nanoparticles modified by oleic acid (code to CaBN) and sulfurized olefin, in a kind of mineral base oil MVIS 250, in order to find a potential substitute for sulfurized olefins.Design/methodology/approachOne kind of calcium borate nanoparticle modified by oleic acid (CaBN) was prepared, and its structures were characterized by inductively coupled plasma atomic emission spectroscopy (ICP‐AES), X‐ray power diffraction (XRD) and transmission electron microscope (TEM). The tribological properties of the complex of CaBN with sulfurized olefins (T321) in base oil were evaluated using four‐ball tribotester and compared with CaBN or T321 as individual component. The worn surfaces were investigated by scanning electron microscope (SEM) and X‐ray photoelectron spectroscopy (XPS). In addition, the corrosion‐inhibiting properties of additives were also studied.FindingsThe results of tests show that there are significant synergistic effects on tribological properties between two kinds of additives. Based on the results of SEM and XPS, it can be deduced that a wear resistance film containing B2O3, FeS, FeS2 and CaO was formed on the worn surfaces during the sliding process. Moreover, CaBN and T321 also show excellent synergistic effect on the corrosion‐inhibiting property.Originality/valueThis paper provides a kind of “green” nanoparticle which possesses excellent synergic effect with sulfurized olefins, and gives another selection for industrial applications in which T321 is needed.

Self-assembled monolayer protective films for hybrid sliding contacts

Silicon nitride as an energy efficient material is replacing conventional steels for new generation engineering components such as bearings, cutting tools, electronics and engine parts in automotive, aerospace and wind industries. Compared with steel bearings, silicon nitride bearings can be operated at much higher temperatures and speeds with >60% weight reduction and up to 80% friction reduction. These are all due to its unique material properties, including high wear and corrosion resistance, low density and heat generation. Current lubrication solutions for hybrid contacts, where silicon nitride balls and steel races are used, are mostly relying on the protection film formed on the metal surfaces. Self-assembled monolayers (SAMs) have been found very useful in modifying surfaces, especially for microelectromechanical system and nanoscale applications, e.g. atomic force microscopy tips, etc. This study aims to investigate the feasibility of forming a SAM protection film on industrial grade bearing material silicon nitride to reduce the friction for the oil lubricated hybrid contacts. Four silanes with different functional head groups, including octadecyltrichlorosilane (OTS), octyltrichlorosilane, chlorodimethyloctadecylsilane and octadecyltrimethoxysilane, were initially investigated to form SAMs on industrial grade silicon nitride surfaces. The effects of concentration and immersion time of the silanes on the formation of SAMs on the silicon nitride surface were evaluated using contact angle measurements. The preliminary results show that the wetting properties of the silicon nitride surface can be effectively modified by the formation of SAMs from the silane solutions. OTS can form an order and compact SAM on the silicon nitride surfaces within 2 min at the concentration of 2··5 mM in decane solution, while the other three alkylsilanes can also effectively modify silicon nitride surfaces given sufficient immersion time, e.g. over 1 h. Tribological tests were subsequently carried out on a ball on disc rig where a steel ball and a silicon nitride disc were used. The effect of the formation of alkylsilane SAMs on the friction between the sliding contacts has been evaluated in two different methods. The first method was to test preformed SAM films under dry conditions, and the second was to premix one of the surfactants with Shell Vitrea ISO 32 mineral base oil and then spray the mixture to the contacts during the ball on disc testing. The test results show that an average of over 40 and 30% friction reduction was achieved for the hybrid contact when lubricated with the base oil mixed with OTS (>2··5 mM) and octadecyltrimethoxysilane (5 mM) respectively compared with that of the sliding contact lubricated by the base oil only. Since OTS may produce corrosive byproducts during SAM formation, octadecyltrimethoxysilane may be a more suitable additive for the hybrid contacts.

The efficiency of Co-based single-wall carbon nanotubes (SWNTs) as an AW/EP additive for mineral base oils

This paper describes the tribological behavior of Co-based single-wall carbon nanotubes (SWNTs) and a commercial antiwear (AW) and extreme-pressure (EP) additive to a mineral base oil (SAE 20). Single-wall carbon nanotubes possess interesting tribological properties; therefore, in our investigation, they were used as an AW and EP additive to SAE 20 base oil. Friction and wear were tested using a Pin on Disk C.S.M tribometer, while a four-ball tester was used to evaluate the extreme pressure properties. After friction tests, the rubbed surface was investigated with X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM) and atomic force microscopy (AFM) to understand the mechanism of action on an atomic scale. The single-wall carbon nanotubes were produced by chemical carbon vapor deposition (CCVD) and were characterized suing transmission electron microscopy (TEM). Tube diameter was determined using RAMAN spectroscopy. Used as an additive to base oil, SWNTs are more efficient than a commercial additive (CA) control. In tests, the friction coefficient decreased to 0.087 using only 0.5wt% SWNTs added to SAE 20. A synergistic effect was found between SWNTs and the commercial additive, giving this combination the best tribological properties.

LCA of petroleum-based lubricants: state of art and inclusion of additives

While the application of Life Cycle Assessment (LCA) to lubricants can be considered fully operational for general purposes outside the lubricants industry, where Life Cycle Inventories (LCIs) of mineral and synthetic base oils can be used interchangeably and where additives can be excluded, this is not the case for research and development purposes within the industry. Previous LCAs of base oils are not sufficiently detailed and comprehensive for R&D purposes, and there are no LCAs of lube additives and fully formulated lubricants. The aim of this paper is to integrate and expand previous LCAs of base oils and to investigate on the contribution of lube additives to the environmental impacts of a fully formulated lubricant. This study considers three base oils (mineral, poly-alpha-olefins (PAO) and hydrocracked) and a set of lubricating additives typically used in fully formulated engine oil. The LCA model is based on both industry and literature data. Trends in the lubricants industry towards more sophisticated base oils correspond to remarkably higher environmental impacts per kilogram of product but lead to reduced impacts per kilometre. The contribution of additives to the life cycle impacts of commercial lube oil was found to be remarkably high for some impact categories (nearly 35 % for global warming). As base oil is concerned, this study made the point on data availability and provided a contribution in order to integrate and expand previous LCAs of mineral base oil and PAO. On the side of additives, the main conclusion is that in modern lubricants, the contribution of additives in terms of environmental impact can be remarkably high and, therefore, they should not be excluded.