Tribological performance of pullulan additives in water-based lubricant

Water can be used as an ecological lubricant base if the water-based additives are properly developed to modify its tribological properties. Additionally, those additives should be friend both to human and nature. Pullulan is a naturally occurring polysaccharide, which is biodegradable and non-toxic and widely used in food and nonfood applications. We focus here on understanding the lubrication properties of pullulan, in aqueous solution in absence and presence of sodium salts. Lubrication is studied using a ball-on-disk tribometer with steel–steel surfaces and the friction coefficient and wear are measured in the boundary lubrication regimes. The adsorption of pullulan molecules onto steel surface is determined by measuring wettability of friction couples. It was found that the addition of pullulan improves the lubricating properties of water. The lubricating performance of Pullulan solution could be further improved if sodium chloride or sodium fluoride is added. The tribological results obtained were correlated with the adsorption capacity of pullulan molecules onto steel surface.     

Tribological behaviors of surface-coated serpentine ultrafine powders as lubricant additive

The effect of surface-coated ultrafine powders (UFPs) of serpentine suspended in lubricants on the tribological behaviors of a mated 1045 steel contact was investigated. Through the addition of serpentine UFPs to oil, the wear resistance ability was improved and the friction coefficient was decreased. The addition of 1.5 wt% serpentine to oil is found most efficient in reducing friction and wear. The nano-hardness and the ratio of hardness to modulus of friction surface are observably increased. Such effects can be attributed to the formation of a tribofilm of multi-apertured oxide layer, on which the micrometric alumina particles embedded and serpentine nano-particles adsorbed.     

Ionic liquid modified multi-walled carbon nanotubes as lubricant additive

Multi-walled carbon nanotubes (MWCNTs) were modified by imidazolium-based ionic liquid (IL), 1-hydroxyethyl-3-hexyl imidazolium tetrafluoroborate and used as an additive in base stock IL 1-methyl-3-butylimidazolium tetrafluoroborate as the base lubricant. The effectiveness of using the IL- modified MWCNTs as lubricant additive was evaluated using a ball-on-plate configuration on an Optimol SRV oscillating friction and wear tester. The worn surfaces were examined using scanning electron microscope and the chemical composition on wear tracks was analyzed on an X-ray photoelectron spectrometer. Results suggest excellent anti-wear properties for the IL-modified MWCNTs as lubricant additive.     

Tribological properties of some water-based lubricants containing polyethylene glycol under boundary lubrication conditions

The metal-working industry is increasingly interested in synthetic metalworking fluids and coolants. The excellent lubricating properties of polyalkylene glycols have been recognised in areas such as gear lubricants, hydraulic fluids, and compressor lubricants. The main purpose of the present work was to investigate the friction and wear properties of several polyethylene glycols and their synergy with a common water-soluble EP additive, using four-ball and ball-on-plate tribometers.     

Tribological behaviors and wear mechanisms of ultrafine magnesium aluminum silicate powders as lubricant additive

The ultrafine attapulgite powders (UAP) were prepared using natural attapulgite powders (NAP) by the ball-milling dispersion method. The tribological behaviors of surface-modified NAP and UAP dispersed into mineral base oil were investigated. SEM, EDS, XPS and a microhardness tester were utilized to analyze the tribofilm formed on the worn surfaces. It is found that both the additives can improve the friction-reduction and anti-wear properties of the base oil. A tribofilm mainly composed of FeO, Fe₂O₃, FeOOH and SiO formed on the worn surface lubricated with oil containing NAP and UAP. And the content of iron oxides and SiO formed on the worn surface lubricated with oil containing UAP is much higher, which is responsible for the better friction-reduction and anti-wear properties of UAP.     

Tribological properties of h‐BN nanoparticles as lubricant additive on cylinder liner and piston ring

Friction and wear behaviour of different concentrations of hex‐boron nitride (h‐BN) nanoparticles in engine oil of grade SAE 20W50 were studied at various loads. These tribological studies were conducted using a four‐ball wear test machine and a pin‐on‐disc universal tribometer. Anti‐wear properties of SAE 20W50 + h‐BN were studied on the four‐ball wear test machine as per ASTM D4172 standard. Friction and wear properties of SAE 20W50 + h‐BN on piston ring and cylinder liner tribo‐pair were studied using the universal tribometer. Nanoparticles of h‐BN mixed in lubricant showed excellent tribological performance. In most of the cases, h‐BN nanoparticles as additive reduced the wear loss by 30–70% at various loads. The minimum value of coefficient of friction (0.0401) was found with SAE 20W50 + 3 wt% of h‐BN at normal load of 100 N. Scanning electron microscopy and Raman spectroscopy were used for characterisation of h‐BN and wear scars. Copyright © 2016 John Wiley & Sons, Ltd.     

Molecular tribology of lubricants and additives

Knowledge of the bulk viscosity provides little guidance to predict accurately the interfacial shear strength and effective viscosity of a fluid in a lubricated contact. To quantify these differences between bulk and thin-film viscosity, an instrument was developed to measure the shear of parallel single crystal solids separated by molecularly-thin lubricant films. The effective shear viscosity is enhanced compared to the bulk, relaxation times are prolonged, and nonlinear responses set in at lower shear rates. These effects are more prominent, the thinner the liquid film. Studies with lubricant additives cast doubt on the usefulness of the concept of a friction coefficient for lubricated sliding.     

N-酰基苯丙氨酸的合成及其在水基中润滑和防锈性能研究

将脂肪酸酰氯和苯丙氨酸在碱性溶液中反应得到的N-酰基苯丙氨酸，用红外光谱对其结构进行表征；用四球摩擦磨损试验机考察了N-酰基苯丙氨酸以三乙醇胺为助溶剂时在水溶液中的摩擦磨损性能，并用俄歇电子能谱研究了磨斑表面边界膜的化学组成和元素分布。结果表明：N-酰基苯丙氨酸的水溶液表现出很好的抗磨和减摩特性，这可能是N-酰基苯丙氨酸三乙醇胺盐中的极性基团吸附在钢球的表面，长碳链疏水性的烃基在金属表面形成较厚的保护膜，在较高载荷运行下，发生化学反应形成高强度的摩擦化学反应膜；N-酰基苯丙氨酸三乙醇胺盐还有较好的防锈性。经细菌试验表明其具有较好的抗菌能力。     

Tribological behaviours of Cu nanoparticles recovered from electroplating effluent as lubricant additive

Nowadays, many efforts have been made to minimise the pollution risks of copper electroplating effluent, such as chemical methods, physical methods, etc. Among them, chemical reduction has been used in this paper for its simplicity and potential for industrial production, and the recovered Cu nanoparticles (CuNPs) were innovatively used as a lubricant additive to prolong the lifetime of lubrication equipment and enhance energy conservation via emission reduction. In this paper, the relationships of the remaining Cu²⁺ concentration ([Cu²⁺]) with NaBH₄/CuSO₄ mole ratio, reaction time and reaction temperature were discussed separately. Then, L₉(3³) orthogonal experiment was carried out to determine optimal reaction conditions. Finally, the tribological behaviours [e.g. friction coefficients (FCs) and wear scar diameter (WSD)] of base oil samples with and without addition of the recovered CuNPs were investigated. Results indicate that the optimal reaction conditions were as follows: NaBH₄/CuSO₄ (4∶6) react at 30°C for 25 min, under which [Cu²⁺] was minimised to 0·2 mg L^?1 with a mean particle size of 33 nm. The FC and WSD of oil with 0·3 wt-%CuNPs were decreased by 33·4 and 19% respectively compared with the base oil. This compound oil was much more suitable for moderate load and high load than for low load. This paper provides a new idea on dealing with the copper electroplating effluent.     

Tribological properties of few-layer graphene oxide sheets as oil-based lubricant additives

The performance of a lubricant largely depends on the additives it involves. However, currently used additives cause severe pollution if they are burned and exhausted. Therefore, it is necessary to develop a new generation of green additives. Graphene oxide (GO) consists of only C, H and O and thus is considered to be environmentally friendly. So the tribological properties of the few-layer GO sheet as an additive in hydrocarbon base oil are investigated systematically. It is found that, with the addition of GO sheets, both the coefficient of friction (COF) and wear are decreased and the working temperature range of the lubricant is expanded in the positive direction. Moreover, GO sheets has better performance under higher sliding speed and the optimized concentration of GO sheets is determined to be 0.5wt%. After rubbing, GO is detected on the wear scars through Raman spectroscopy. And it is believed that, during the rubbing, GO sheets adhere to the sliding surfaces, behaving like protective films and preventing the sliding surfaces from contacting with each other directly. This paper proves that the GO sheet is an effective lubricant additive, illuminates the lubrication mechanism, and provides some critical parameters for the practical application of GO sheets in lubrication.     

高水基液压阀陶瓷摩擦副摩擦学性能研究

为选择适合的高水基乳化液液压阀摩擦副材料,探讨ZrO2与不同结构陶瓷组成的摩擦副在高水基乳化液润滑状态下的摩擦磨损特性。采用摩擦磨损试验机,在不同载荷和滑动速度下,研究在高水基乳化液介质中4种不同陶瓷材料（ZrO2、Al2O3、Si3N4和SiC）分别与ZrO2配副的摩擦学性能,并探讨不同组合陶瓷摩擦副的磨损机制。结果表明：在高水基乳化液中,各陶瓷的摩擦因数均随着滑动速度的增大而降低,其中Al2O3陶瓷的摩擦因数最小;ZrO2、Al2O3和Si3N4陶瓷的摩擦因数受载荷的影响较小,SiC陶瓷的摩擦因数则随着载荷的增大而骤增;各陶瓷的磨损体积都随着速度和载荷的增大而增大,其中Al2O3/ZrO2陶瓷摩擦副的磨损体积最小,其磨损机制以磨粒磨损和微疲劳磨损为主。研究表明,在不同工况下,Al2O3与ZrO2陶瓷配副的摩擦因数和磨损体积均为最低值,更适合作为高水基乳化液液压阀的摩擦副材料。     

Tribological investigation of layered sodium silicate as lubricant additives prepared by freezing titration ion exchange

Two layered sodium silicate products were prepared using a new ion exchange method called the freezing titration ion exchange. The tribological properties of the ion exchange products as additives in mineral oil were evaluated using a four-ball tester. The products exhibited excellent friction behavior when used as additives in mineral oil. When 1 wt% was added, the tribological properties of the oils improved: the maximum non-seizure loads increased by over 27% and the wear scar diameter and friction coefficient decreased by over 50% and 25%, respectively. The friction and wear behaviors of the silicates were better than those of the typical lubricant additives.     

油酸基极压水性润滑添加剂的合成及性能研究

为提高水基润滑剂的润滑性以及抗磨减摩性能,合成一种环境友好的含极压元素P、 N的油酸基极压水性润滑添加剂(OWELA)。采用傅里叶变换红外光谱(FTIR)和核磁共振氢谱(1H NMR)对中间体聚合P-N二元醇(PG)和OWELA进行表征,用四球摩擦试验机研究PG和OWELA的润滑性能。利用扫描电镜和X射线光电子能谱对钢球的磨损表面进行分析,探讨其润滑机制。结果表明:相较于PG, OWELA可以显著降低水的摩擦因数和磨痕直径,可使纯水最大无卡咬载荷提高3.5倍,且具有良好防腐性能; OWELA优异的摩擦学性能归因于高活性极压元素P、 N与金属形成高强度的化学反应膜,以及脂肪酸分子在金属表面形成了物理吸附膜,两者起到协同增效作用。     

A study of P–N compound as multifunctional lubricant additive

A novel P–N compound was synthesised, and its tribological and anti‐oxidation behaviours used as lubricant additive for polyalphaolefins (PAO4) were evaluated. The results demonstrate that adding only low amount (<2 wt.%) of P–N compound into PAO4 could improve its anti‐wear performance by 10 times, enhance its load‐carrying capacity and oxidative stability, verifying the P–N compound is a kind of multifunctional and high‐performance additive. The morphology and the chemical composition of the worn surfaces were characterised by scanning electron microscopy and X‐ray photoelectron spectroscopy, indicating that the excellent anti‐wear and load‐carrying performance could be attributed to the forming of boundary lubrication film composed of iron oxide, iron phosphate, organic phosphine and organic amine, and so on. The work reported here is helpful to pave the practical applications and to understand the action mechanism of the multifunctional lubricant additives. Copyright © 2011 John Wiley & Sons, Ltd.     

Recent achievements in the synthesis and application of inorganic nanoparticles as lubricant components

Recent advances made in the chemistry and technology of nano‐metric inorganic particles allow the synthesis of various metal oxides, chalcogenides, phosphates, and so on. Surface modification of nanoparticles in some cases allows the formation of stable dispersions in liquid hydrocarbons. The state of the art in the field of inorganic nanoparticle synthesis and their application in tribology are discussed in this paper. Special attention is paid to the synthesis of surface‐capped and bare molybdenum sulphide nanoparticles and to the testing thereof as friction‐modifying additives for liquid lubricants. Differences in the mechanism of action of MoS_x nanoparticles and molecular molybdenum complexes (e.g., molybdenum dithiocarbamate) are discussed. Future trends in the use of inorganic nanoparticles as lubricant additives are suggested.     

The chemistry,mechanism and function of tricresyl phosphate (TCP) as an anti‐wear lubricant additive

The detailed understanding of the physical and reaction chemistry of engineering lubricants is key to new developments in the future. Here, we draw together the main chemical/engineering literature in the first systematic review of the standard anti‐wear additive used as an aviation lubricant, tricresyl phosphate (TCP), focusing on understanding the links between the surface chemistry, tribology and decomposition of TCP. While there is still debate concerning the mechanism of TCP, it is clear that it is activated by moisture, oxygen or oxidised metal surfaces. Its anti‐wear properties arise from the resulting formation of iron phosphate or polyphosphate on the contact surfaces. Evidence stresses the importance of chemistry at the boundary layer and a mechanism involving pre‐coordination of TCP at the surface, resulting in activation at the P‐centre and subsequent attack by residual H₂O or surface O²⁻. This perspective provides a potential baseline for the development of future phosphorus‐based high‐performance additives. Copyright © 2015 John Wiley & Sons, Ltd.     

Tribological properties of the film formed by borated dioctyl dithiocarbamate as an additive in liquid paraffin

This paper discusses the preparation of borated dioctyl dithiocarbamate as an oil-soluble antiwear and extreme pressure additive for lubricants. Its tribological performance when added to liquid paraffin was evaluated on a four-ball tester and a ring-on-block machine. The relationships between its performances and the concentrations are also given, and are compared with these of zinc dialkyldithiophospate (ZDDP). The results show that the novel compound possesses an excellent load-carrying capacity and friction reduction property similar to ZDDP, and exhibits better antiwear property than ZDDP above 392 N. In addition, the novel compound has good anticorrosive property and high thermal stability. The rubbed surface was investigated using X-ray photoelectron spectroscopy, and the antiwear mechanism was discussed.     

二烷基二硫代磷酸镧/铕混合稀土有机化合物在润滑油中的摩擦性能

合成了二烷基二硫代磷酸镧／铕混合稀土有机化合物(La／EuDDP)，加入到30^#齿轮油中，利用四球试验机考察了摩擦磨损性能。结果表明，La／EuDDP作为润滑油添加剂具有良好的抗磨性能和承载能力，并具有一定的减摩能力，加有该添加剂的30^#齿轮油PB值增加了128％，磨斑直径减少了50％以上。     

Tribological properties of nano‐calcium borate as lithium grease additive

Nano‐calcium borate (NCB) with an average particle size of about 70 nm was synthesised via ethanol supercritical fluid drying technique, and the morphology and microstructures of as‐prepared particles were characterised by means of scanning electron microscope (SEM, JEOL LTD., Tokyo, Japan) and X‐ray powder diffraction. The friction and wear behaviour of the NCB as additive in lithium grease were evaluated with an Optimol‐SRV IV (Optimol Instruments Prüftechnik GmbH, Munich, Germany) oscillating friction and wear tester (SRV tester). The morphology and surface composition of the worn surfaces of lower discs after SRV test were analysed by SEM and X‐ray photoelectron spectroscopy (XPS, Physical Electronics, Inc., USA). The result demonstrated that the anti‐wear and load‐carrying capacities of the lithium grease were significantly improved, and the friction coefficient of the lithium grease decreased with the addition of NCB additive. The analytical results of XPS indicate that the good tribological performance of NCB is attributable to the formation of a boundary lubrication film composed of deposited NCB and the tribochemical reaction products such as B₂O₃, CaO and iron oxides on the rubbing surface. Copyright © 2013 John Wiley & Sons, Ltd.     

The effect of ethoxylated esters on the lubricating properties of their aqueous solutions

In many applications strict ecological criteria are crucial. Water is often used in these cases as a lubricant base. Its disadvantageous properties, in particular lubricity, can be modified by introduction of additives. Ethoxylated methyl esters of fatty acids from rapeseed oil were chosen for that purpose. In order to verify tribological properties of aqueous solutions of these compounds, anti-seizure properties under linearly increasing load, friction and wear under 2 kN (four-ball machine) were assessed. Not only radical change of tribological properties as compared to water was observed, but also the results are comparable to the ones obtained for mineral oils, which contained typical, commercial additives. Significant changes in scuffing load (P _t), seizure load (P _oz), limiting pressure of seizure (p _oz) were recorded even at 0.1% wt concentration of the additive. At optimal concentration P _t, P _oz, p _oz, increased even almost 6-, 2- and 3-fold (respectively). The quantities measured increased with ethoxylation degree. Also at constant load, friction (6-fold) and wear (almost 2-fold) were reduced. In this case, however, no influence of concentration and ethoxylation degree on the quantities measured, was observed.The tribological properties can be discussed in terms of results of physical–chemical tests. Ethoxylates are surface active compounds. Within the range of concentrations analyzed, they form micelles in a bulk phase and liquid-crystalline structures in a surface phase. High surface activity of these additives and creation of specific structures in solutions were proved by measuring surface tension, wetting angle and mesophases observation in polarized light. On the basis of the results of the physical–chemical and tribological tests one can conjecture that profitable tribological properties of the lubricating compositions are the result of strong affinity to the surface and their ability to form ordered structures. One can expect that over the cooperating surfaces a deposit is formed. Presence of the deposit increases real contact area and prevents seizure. This hypothesis gives a simple explanation of the unexpected improvement of anti-seizure properties, which accompanies the increase of ethoxylation degree. Ethoxylates with higher number of ethylene oxide attached, reveal smaller surface activity and better solubility in water. On the other hand, they can be characterized by higher dehydratation temperature. This means that at higher temperatures they reveal surface activity. That is why, during seizure tests, at high temperature, under high loads the esters of higher ethoxylation degree protect friction couples against seizure much more efficiently.