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The tribological behavior of 316L stainless steel/CoCrMo alloy contacts under aqueous lubrication was investigated in this work. Three types of microgels including poly(N-isopropylacrylamide) (PNIPAM), polyacrylic acid (PAA), and poly(N-isopropylacrylamide-co-acrylic acid) (PNIPAM-co-PAA) were prepared and used as lubricant additives in aqueous solutions. Tribological tests were conducted using a ball-on-disk reciprocating tribometer, over a range of temperatures, pH, and concentrations of the microgels. The PNIPAM-co-PAA microgels were proven to have excellent anti-friction and anti-wear properties, depending on the temperature and pH values of the solutions. The maximum friction coefficient coincided with the lower critical solution temperature of the PNIPAM-co-PAA microgels at 32 °C. At the same time, the friction coefficient increased with the increase in pH value of the lubricant solution with the PNIPAM-co-PAA microgels. The unique thermal- and pH-sensitive properties of the PNIPAM-co-PAA microgels provided a new strategy for controlling the friction and wear of steel/CoCrMo alloy contacts under aqueous lubrication.

Purpose This paper aims to offeri novel nano-additives polymer microgels to precisely improve the lubrication properties of titanium alloy under different temperatures. Design/methodology/approach The surfactant-free emulsion polymerization method was used to prepare Poly(N-isoprolylacrylamide) (PNIPAM) microgels. A ball-on-disk tribometer was applied to investigated the temperature-sensitive lubrication behavior of PNIPAM microgels. Findings The results show that the as-prepared microgels are ball-like nanoparticles with the size of 50–900 nm. In addition, potassium persulfate as initiator, complete mixing technic and high sodium dodecyl sulfate (SDS) concentration contribute to the formation of microgels with small size. The tribosystem shows a lower friction coefficient with the lubrication of PNIPAM microgels as aqueous solution additives when the temperature exceeding the critical temperature. Originality/value This work reports the temperature-sensitive lubrication of PNIPAM microgels. The critical temperature of PNIPAM microgels could be regulated by the addition of SDS in the solutions. This offers an effective and facile strategy for regulation of the critical temperature of smart microgels, which is helpful for the smart lubrication in the future.

The mechanochemical reaction kinetics of sulfur with copper to form a metastable copper sulfide phase at room temperature is investigated in ultrahigh vacuum by modifying the properties of the copper during cleaning in vacuum. The measured kinetics is in agreement with a theory first proposed by Karthikeyan and Rigney that predicts that the rate depends linearly both on the contact time and on the strain-rate sensitivity of the substrate. The mechanism for this process was investigated using thin samples of copper fabricated using a focused-ion-beam and by measuring the crystal structure and elemental composition of the copper subsurface region by electron microscopy after reaction. The measured sulfur depth distributions produced by shear-induced surface-to-bulk transport were in good agreement with values calculated using rate constants that also model the reaction kinetics. Sulfur was found both in crystalline regions and also concentrated along grain boundaries, implying that formation of metastable phases is facilitated by both the presence of dislocations and by grain boundaries.

In the present work, two types of novel nano additives, titanium sulfonate ligand/black phosphorus (TiL4/BP) and titanium dioxide/black phosphorus (TiO2/BP) nanocomposites, were prepared. The tribological behavior of the steel/steel friction pairs lubricated by polyalphaolefins type 6 (PAO6) containing the nanocomposites under boundary lubrication was studied. The worn surfaces were analyzed using modern surface techniques. The experimental results show that the rubbed surfaces became smooth and showed little wear with the addition of the nanocomposites. TiO2/BP nanocomposites can significantly improve the lubricity of BP nanosheets under high contact stress. The synergistic roles of the load-bearing abilities and rolling effect of TiO2 nanoparticles, the slip induced by the BP with its layered structure, and the establishment of a tribofilm on the sliding interface are the basis of the tribological mechanisms.

Pickering emulsion is a new type of stable emulsion made by ultrafine solid particles instead of traditional surfactants as stabilizers, which has received widespread attention in recent years. The preparation methods of stator-rotor homogenization, high-pressure homogenization, and ultrasonic emulsification were compared with others in this work. The main factors affecting the stability of Pickering emulsion are the surface humidity of the solid particles, the polarity of the oil phase, and the oil–water ratio. These factors could affect the nature of the solid particles, the preparation process of Pickering emulsion, and the external environment. Consequently, the long-term stability of Pickering emulsion is still a challenge. The tribological investigations of Pickering emulsion were summarized, and the multifunctional Pickering emulsion shows superior prospects for tribological applications. Moreover, the latest development of Pickering emulsion offers a new strategy for smart lubrication in the near future.

To enhance the tribological performance of piston ring-cylinder liner pair in engines, Ni-P-TiN coated piston rings were prepared by electroless plating technology, and novel Fe3O4@MoS2 nanocomposites were used as lubricating additives in oil. The tribological behavior of the coated friction pairs was evaluated on a multifunctional piston ring-cylinder liner tribometer. The results show that the concentration of TiN nanoparticles in the coatings has an important effect on the tribological performances. The coated piston ring-cylinder liner contact presented a mild abrasive wear with the concentration of TiN nanoparticles at 1.5 g/L. The coated piston rings did not increase the wear loss the cylinder liner due to the lubricating roles of TiN nanoparticles and the formation of transfer layer. The friction coefficient and wear loss of the Ni-P-1.5TiN coatings reduced by 23.8 ± 3.1 wt% and 64.3 ± 1.8 wt%, respectively, comparing to that of the Ni-P coating. Compared with nano-MoS2 and nano-Fe3O4, the Fe3O4@MoS2 nanocomposites as oil additives have a better effect on reducing the friction and wear of the Ni-P-TiN composite coating, mainly due to the synergistic effects of the coatings and the nanocomposite additives.

The thermo-tribological behaviour of 316L stainless steel/ultrahigh molecular weight polyethylene (UHMWPE) contacts under aqueous lubrication was investigated in this work. Thermo-responsive microgels were prepared and used as lubricant additives in aqueous solutions. Tests were conducted using a reciprocating tribometer, over a range of temperatures and microgel concentrations. The microgels were shown to have temperature-dependent friction-reducing and anti-wear properties. The microgels acted as load bearing particles in the water, rolling and sliding between frictional interfaces. A maximum recorded friction coefficient coincided with a phase-transition in the microgels induced at a lubricant temperature of 32 °C. This was indicative of a thermo-tribological sensitivity in the microspheres, whereby particle size and shape changed with temperature, affecting tribological performance. These changes included structural collapse of the microgels due to dehydration at the critical temperature. This characteristic temperature-sensitivity in the microgels offers new strategies for controlling friction and wear of steel/UHMWPE contacts under aqueous lubrication.

To deal with the corrosive property of bio-oil, laser-induced coatings were synthesized on the typical cylinder liner rubbing surfaces. Two nano-additives including MoS2 nanosheets and graphene were introduced into the coatings. The tribological performances of the coated surfaces were tested on a multifunctional cylinder liner-piston ring tribometer. The surfaces before and after sliding were characterized with modern surface analysis technology including Raman spectra, X-ray diffraction (XRD), scanning electron microscope (SEM), energy dispersive X-ray spectroscopy (EDS) and etc. The results show that the nickel-based coated surfaces can effectively prevent the corrosion of the bio-oil. In addition, the laser-induced coatings had better antifriction and antiwear performances than the corresponding traditional electroless plating coatings. With the introduction of MoS2 nanosheets or graphene, the tribological performances of the coatings were further enhanced. Laser irradiation increased the concentration of the nano-additives in the coatings and the thickness of the tribo-layers, which accounted for their outstanding tribological performances.

2-Methylfuran (MF) and 2,5-dimethylfuran’s (DMF) combustion characteristics have confirmed their validity as appropriate gasoline replacement and enhancement fuels. However, the performance of fuel injection equipment is dependant on the tribological performance of these fuels lubricity testing of MF, DMF and their blends with gasoline was undertaken using the high frequency reciprocating rig method, based on ASTM D6079 . Results showed that both MF and DMF possessed greater lubricity and wear resistance characteristics than those of gasoline when tested as pure substances. Their blends with gasoline at 2, 4, 6, 8, 10, 20 and 50 percent volume (%vol) showed improved tribological performance also. DMF was found to possess greater lubricating properties than that of MF. As little as 2%vol reduced the wear scar diameter by 46% and 47% for MF and DMF respectively showing even a small addition of these biofuels could greatly improve the tribological performance of the fuel within the engine. This was mainly due to the polar functional groups of MF and DMF bonding to the bearing surfaces during testing, creating a tribo-film that protected the surface, reducing both wear and friction. These effects were greatest for the DMF blends, with two methyl groups leading to stronger polarity and a resulting higher bonding strength to the metal surfaces. The reduction in friction coefficients with the addition of the biofuels showed that utilisation of these blends would reduce frictional losses along the fuel line, improving the overall engine efficiency.

Fe3O4 nanospheres, MoS2 nanospheres and Fe3O4@MoS2 nanocomposites were used as lubricating oil additives for steel/steel contact and dispersed in PAO4 base oil. Tribological behavior and wear mechanisms of the steel/steel contacts were investigated. The results indicate that the friction coefficient increased with the addition of Fe3O4 nanospheres and decreased with the addition of MoS2 nanospheres. Their wear types belonged to abrasive wear and furrow wear respectively. In addition, Fe3O4@MoS2 nanocomposites as lubricating additive had excellent lubricating performance and energy-saving potential due to the formation of a stable adsorbed film and a robust tribo-film on the rubbing surfaces which resulted in a mild furrow wear for steel/steel contact.

In the pressent work, nanosized poly (N-isopropyl acrylamide) (PNIPAM) microgels were prepared and used as lubricant additives in bovine calf serum (BCS) for titanium alloy/ultra-high molecular weight polyethylene contact. The effects of sliding speed, load, and temperature on the lubrication behavior were studied on a pin-on-disc tribometer. The tribological results showed that the PNIPAM microgels can significantly improve the lubricity of BCS solution. The PNIPAM microgels exhibited notable temperature-sensitive lubrication characteristics. When the temperature was close to the low critical solution temperature of the PNIPAM microgels, the contact had the lowest friction coefficient due to the formation of a good lubricating layer with collapsed microgels and proteins. This discovery contributes to establishing a new strategy for friction-reduction and antiwear of titanium alloy artificial joint materials.

A novel in situ tribocatalytic esterification reaction has been developed driven by frictional processes, to alleviate the corrosion wear induced by the high content of organic acid in bio-oil. Solid superacid (SO42−/γ-Al2O3) was formulated and prepared as the catalyst. Acetic acid was as the base for the bio-oil, and glycerol was used as a modifying agent. The tribological properties of the bio-oil with varying amounts of solid superacid were evaluated on a HDM-20 end-face tribometer. Scanning electron microscope and X-ray photoelectron spectroscopy were employed to measure the micro-morphologies and elemental contents on the worn surfaces after sliding. The effect of tribocatalysis on the composition of the bio-oil was analyzed by Fourier transform infrared spectrometer and Gas chromatography-Mass spectrometry. The results show that when lubricated by pure bio-oil the worn surfaces showed severe furrows and bulk exfoliation of the surface material. With the solid superacid added to the bio-oil, abrasive wear and material exfoliation were alleviated. The reason for the improved tribological properties is that the solid superacid not only could roll on the friction surface and act as lubricating particles, but also catalyzed esterification between acetic acid and glycerol, which simultaneously improved the tribological properties of bio-oil.

A series of tribological experiments have been conducted to characterise and study the formation of tribofilms derived from TiF 3 and FeF 3 catalysts impregnated in soot-contaminated lubricants. Results showed that inorganic fluorides reduced friction and wear in the specimen contaminated lubricants. With the best results observed when TiF 3 was used. There were also indications that the frictional process, when coupled with the fluorides induced a structural change in the soot particles within the contact zones, contributing to the improved tribological performance. The key contributors to the formation of robust tribofilms were adsorption and tribo-chemical reactions. The better tribological response leads to a method for the design of engine lubricants to mitigate against the effects of soot contamination.

Lubrication conditions have significant influences on the formation of tribofilms and then affect tribological behavior. In this work, the influence of tribofilm formation on the tribological behavior of textured surfaces with oval shapes was measured using a pin-on-plate tribometer. The results show that, under full lubrication, the adsorbed oil film controlled the friction and wear behavior of steel/steel tribopairs but under starved lubrication, the formation of a tribofilm significantly influenced the tribological behavior. The appropriate textured surfaces with oval-shaped dimples contribute to obtaining excellent antifriction and antiwear behavior. However, excessively high ratios of the major to the minor axis of the oval can result in high contact stresses which can destroy the tribofilm. Fil: Xu, Yufu. Hefei University of Technology; República de China Fil: Zheng, Quan. Hefei University of Technology; República de China Fil: Abuflaha, Rasha. University of Wisconsin; Estados Unidos. Al al-Bayt University; Jordania Fil: Olson, Dustin. University of Wisconsin; Estados Unidos Fil: Furlong, Octavio Javier. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - San Luis. Instituto de Física Aplicada "Dr. Jorge Andrés Zgrablich". Universidad Nacional de San Luis. Facultad de Ciencias Físico Matemáticas y Naturales. Instituto de Física Aplicada "Dr. Jorge Andrés Zgrablich"; Argentina Fil: You, Tao. University of Wisconsin; Estados Unidos Fil: Zhang, Qiangqiang. Hefei University of Technology; República de China Fil: Hu, Xianguo. Hefei University of Technology; República de China Fil: Tysoe, Wilfred T.. University of Wisconsin; Estados Unidos

Rice husk ceramic (RHC) particles were prepared and its effect on the lubrication performance of liquid paraffin (LP) was investigated using a four-ball tribometer to expand the comprehensive utilization of rice husk. The wear and friction mechanisms of RHC particles were also investigated. Results showed that RHC particles can strengthen the antiwear and friction reduction properties of LP in the presence of 2 wt% polyisobutylene succinimide (T154A) at 75 or 100 °C. The friction and wear mechanisms of RHC particles were ascribed to high temperature, which ensures the involvement of RHC particles in the formation of boundary lubrication film.

To improve the dispersing effects of nanoparticles, Fe3O4/MoS2 nanocomposites were fabricated by precipitation of Fe3O4 nanoparticles onto MoS2 nanosheets, and their tribological properties were investigated. The experimental results show that with an increase in the concentration of MoS2 nanosheets and Fe3O4/MoS2 nanocomposites in both aqueous and bio-diesel media, the friction coefficient and wear scar diameters (WSD) of the steel balls decreased significantly. The maximum decrease amounted to 34.6% for friction coefficient and 29.7% for WSD. The excellent lubricating mechanisms are ascribed to the well dispersed Fe3O4 nanoparticles on MoS2 nanosheets; the combined effect of the nanoball bearing role of Fe3O4 nanoparticles, slippery role of MoS2 nanosheets, adsorbed- and tribo-film help to reduce the friction and wear of the tribo-pairs.

The liquefaction mechanisms of the algal biomass to bio-oil were investigated by using Fourier transform infrared spectroscopy, X-ray diffraction, and scanning electron microscopy, respectively. It was found that NaOH was a satisfactory catalyst and contributed to helping the liquefaction of algal biomass. The bio-oil from algal biomass was composed of many compounds, including carbohydrates, alcohol, hydroxybenzene, carboxylic acid, alkene, ester, and others. The mechanism of hydrothermal catalytic liquefaction was discussed. It was found that, comparing with the husk bio-fuel, the algal bio-oil as a promising alternative fuel was more close to the traditional diesel fuel in physicochemical properties. The novel research outcomes contribute to improving the yield of bio-oil from microalgae, reducing the cost of the bio-oil and accelerating the commercial application of the algal bio-oil in the near future.

One kind of novel biodiesel waste cooking oil ethyl ester (WCOEE) was prepared via transesterfication reaction between waste cooking oil and ethanol. The tribological behavior of diesel/WCOEE blend was evaluated with a four-ball tribometer. The wear resistance, extreme pressure, and friction reduction of the blend were improved with increasing WCOEE. The optimal content of WCOEE in the blend was 20 vol%. It was also found that free fatty acids (FFAs) had a positive effect on the wear resistance of blend. The lubrication improvement of the blend was ascribed to the formation of polyester film and high polarity of fatty acid ethyl ester.

To expand the application of rice husk (RH) resource, this study developed carbon-based RH ceramic (RHC) particles using a common high-temperature carbonization method. The morphology, composition, and structure of the RHC particles were characterized with a series of modern analysis technologies and were then compared with those of the initial RH powder and carbonized RH (CRH) particles. The dry tribological behavior of RHC particle adobes (RHAs) was also investigated. Results showed the sheet-shaped morphology of the RHC particles. The graphitization degree of the RHC particles was lower than that of the CRH particles possibly because the phenolic resin (PR) filled the micro-pores of the RH particles, thereby prompting the formation of amorphous carbon in the RHC particles as a result of high-temperature carbonization. The appearance of a hydroxy function group ( OH) on the surface of the RHC particles was ascribed to the decomposition of PR at 900 °C. The friction coefficients and mass loss rates of the RHAs almost increased with the rise in load and velocity. In addition, the friction coefficients of the RHAs decreased at high load (5 N) and velocity (0.261 m/s) conditions. Such outcome indicated that the variation of contact area between steel ball and RHA at high load and velocity conditions resulted in the abrasive wear or catastrophic wear.

The development of liquid bioenergy bio-oil from microalgae has recently attracted much attention, while most of them focused on single feedstock. In this work, super/subcritical liquefaction was applied for bio-oil production from hybrid microalgae. The effects of liquefaction conditions on yield of products were investigated. The results show that the hybrid microalgae Chlorella and Spirulina with an appropriate mass ratio present synergistic effects for liquefaction. Lanthanum oxide as catalysts in hydrothermal liquefaction system can improve the quality of the bio-oil. Supercritical alcoholic liquefaction systems have much higher bio-oil yield, and the maximum yield of bio-oil reaches 74.71%. The solvent methanol and ethanol in supercritical conditions could upgrade the components of the bio-oils and enhance their combustion performances. The comprehensive properties of the bio-oil from hybrid microalgae under supercritical liquefaction conditions show a potential prospect for application.

Microalgae bio-oil production is related to the sustainable use of world energy in the future. In the present work, catalytic pyrolysis and liquefaction behavior of microalgae for bio-oil production were investigated. The results show that the rare earth compounds as catalysts contributed to significantly accelerating the pyrolysis of microalgae via reducing the activation energy of pyrolysis process. Ce(II)/HZSM-5 presented the optimal catalytic pyrolysis and liquefaction effects by helping cut the microalgae molecule chains. The maximum bio-oil yield amounted to 49.71 wt% at the catalyst concentration of 5 wt%. The chemical components of the Spirulina bio-oil were composed of carboxylic acids, ketones, olefins, amides, ethers, esters, and partially cyclic N-containing compounds. Although the combustion performances of the Spirulina bio-oil are worse than those of the diesel fuel, it is superior to the reported rice husk bio-oil, suggesting a promising potential application prospect.

A photolithography etching technique was used to fabricate textured surfaces on steel samples. The friction and wear behavior of the textured surfaces were studied with surface contact sliding. The influence of the diameter and the density of the dimples were investigated. The results show that the textured surfaces with appropriate diameters and densities had excellent friction reducing and antiwear properties. Large-diameter dimples can destroy the integrity of the lubricating film, and low- or high-density dimples produce more iron sulfates and fewer ferrous sulfides on the rubbing surfaces due to the tribo-reactions, which resulted in higher friction coefficients. The tribo-chemical films, oil micro-reservoir and wear debris-containing roles of the dimples together help the textured surfaces to provide improved antiwear properties.

Solid sphere-like nano-MoS 2 particles were synthesized via a modified chemical method. The as-synthesized nano-MoS 2 could improve the tribological properties of dioctyl sebacate (DOS) more compared with a commercial 2H micro-MoS 2 . The lubrication of micro-MoS 2 in DOS was ascribed to the tribofilm formed by the tribochemical reactions. When the nano-MoS 2 was applied as an additive in DOS, a solid complex adsorption film beside the tribofilm was formed on the friction surface to reduce the friction and wear. The adsorption film was composed of MoS 2 , DOS, and their chemically bonded compounds.

A biomass oil/diesel blend was prepared using an emulsion method and combusted in a diesel engine. An injector was then removed and the morphology, composition, and structure of the carbonaceous deposits on the pintle-type nozzle were characterized using a combination of HRTEM, SEM/EDAX, Raman and XRD. Results showed that the carbon deposition of the emulsified fuel with high crystallinity was greater than that of diesel. The agglomerated particulate diameters of the deposited carbon from diesel and emulsified fuel were approximately 10–30 μm and 50 μm, respectively. The carbon deposition mechanism from the emulsified fuel was attributed to the high oxygen content of the groups leading to increased polymerization and subsequent condensation on the nozzle surfaces that was then carbonised.

Graphene and MoS 2 were dispersed in esterified bio-oil (EBO) and evaluated as lubricants for steel/steel contact. The tribological behaviors of steel/steel pairs were investigated under lubrication of graphene/MoS 2 blends with different mass ratios, loads and rotating speeds. The micro-morphologies of the worn surfaces were observed by optical and Scanning Electron Microscopy (SEM). The components of the additives and chemical valences of the elements on the rubbed surfaces were analyzed using Raman and X-ray Photoelectron Spectroscopy (XPS). A synergistic lubricating effect for both graphene and MoS 2 with contents of 0.5 wt% as additives dispersed in EBO was observed that reduced the friction coefficient and wear of the steel specimens under boundary lubrication regime conditions. This was ascribed to the formation of a thicker adsorbed tribo film containing graphene, MoS 2 and organics from the EBO. Graphene was shown to improve the retention of MoS 2 on the frictional surfaces and prevent oxidation during rubbing. MoS 2 , on the other hand, prevented the graphene from being ground into small and defective platelets.

In order to accelerate the application of bio-oil in the internal combustion engines, homogeneous catalytic esterification technology under vacuum distillation conditions was used to upgrade the crude bio-oil. The lubricities of the crude bio-oil (BO) and refined bio-oil with homogeneous catalytic esterification (RBOhce) or refined bio-oil without catalyst but with distillation operation (RBOwc) were evaluated by a high frequency reciprocating test rig according to the ASTM D 6079 standard. The basic physiochemical properties and components of the bio-oils were analyzed. The surface morphology, contents and chemical valence of active elements on the worn surfaces were investigated by scanning electron microscopy, energy dispersive spectroscopy and X-ray photoelectron spectroscopy, respectively. The results show that RBOhce has better lubricities than those of BO, but RBOwc has worse lubricities than those of BO. The tribological mechanisms of the bio-oils are attributed to the combined actions of lubricating films and factors that will break the film. Compared with BO, plenty of phenols in RBOwc results in corrosion of the substrate and destroys the integrity of the lubricating films, which is responsible for its corrosive wear. However, more esters and alkanes in RBOhce contribute to forming a complete boundary lubricating film on the rubbed surfaces which result in its excellent antifriction and antiwear properties.

The tribological behaviour of pyrolysis bio-oil with a synthesized nano-Lanthanum oxide (La2O3) additive was evaluated using a point contact four ball tribometer under different frictional conditions. Results were compared against a micro (μ)-La2O3 additive and an un-additised bio-oil as a control. The results show that nano-La2O3 impregnated bio-oil had better tribological properties than the control groups. Under the operating loads, the optimum nanoparticle concentration within the bio-oil was investigated. At these levels, the combined action of adsorbed bio-oil films on the worn surfaces and the bearing effects of the nano-La2O3 minimized friction and wear. The tribo-mechanisms were ascribed to adhesive wear as a result of lubrication starvation under high loads, and abrasive wear at high rotational speeds as a result of combined deformation and aggregation of the nano-La2O3 particles.

MoS2 hollow spheres with an average diameter of 165 nm were prepared from Na2MoO4 and CH3CSNH2 at 82 °C. A simple method was used to obtain smaller hollow spheres (70 nm) without any complicated step, except for the addition of TiO2. The tribological properties of MoS2/TiO2 in rapeseed oil were studied using a four-ball tribometer under 350 N at 0.383 m/s. The effects of load and sliding velocity were also investigated. Wear was significantly alleviated by the produced lubricating film as lubricated with MoS2/TiO2, which was composed of MoO3, Fe2O3, Fe2(SO4)3, TiO2 (trace), and carbon-containing compounds. The tribological properties were also improved because of the decrease in the size of MoS2 and the synergistic effect between MoS2 and TiO2.

Nano-additives have attracted lots of attentions in recent years due to their special performances. A traditional lubricating additive MoS2 with nano-scale and a novel additive graphene were reviewed in this chapter. The synthesis methods, properties, and tribological applications of these two kinds of nano-additives dispersed in media have been reported. Nano-MoS2 has three main nanostructures including nano-ball particles, nano-sheets, and nano-tubes. The wide accepted lubricating mechanisms for the MoS2 nano-balls, nano-sheets, and nano-tubes are nano-bearing effects, slippery roles, and combined actions of rolling and sliding, respectively. Exfoliation and transfer seem to be the main pattern for MoS2 nano-balls. For graphene, the adsorption and tribo-reaction account for its lubricating properties. A synergistic lubricating effect for using graphene and MoS2 together dispersed in oil was found. Graphene was proved to extend the retention of MoS2 on the surfaces and prevent the oxidation of MoS2. Simultaneously, MoS2 prevented the graphene from being ground into small and defective platelets. Both of them help to form a thicker adsorbed and tribo-film which result in a lower friction and wear. Other properties and applications of nano-MoS2 and graphene are also reviewed. It shows that these two nano-additives have diverse functions and great potential for industrial applications.

The mechanochemical reaction between copper and dimethyl disulfide is studied under well-controlled conditions in ultrahigh vacuum (UHV). Reaction is initiated by fast S-S bond scission to form adsorbed methyl thiolate species, and the reaction kinetics are reproduced by two subsequent elementary mechanochemical reaction steps, namely a mechanochemical decomposition of methyl thiolate to deposit sulfur on the surface and evolve small, gas-phase hydrocarbons, and sliding-induced oxidation of the copper by sulfur that regenerates vacant reaction sites. The steady-state reaction kinetics are monitored in situ from the variation in the friction force as the reaction proceeds and modeled using the elementary-step reaction rate constants found for monolayer adsorbates. The analysis yields excellent agreement between the experiment and the kinetic model, as well as correctly predicting the total amount of subsurface sulfur in the film measured using Auger spectroscopy and the sulfur depth distribution measured by angle-resolved X-ray photoelectron spectroscopy. Fil: Adams, Heather. University of Wisconsin; Estados Unidos Fil: Miller, Brendan P.. Chevron Oronite Company; Estados Unidos Fil: Furlong, Octavio Javier. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - San Luis. Instituto de Física Aplicada "Dr. Jorge Andrés Zgrablich". Universidad Nacional de San Luis. Facultad de Ciencias Físico Matemáticas y Naturales. Instituto de Física Aplicada "Dr. Jorge Andrés Zgrablich"; Argentina Fil: Fantauzzi, Marzia. INSTM; Italia Fil: Navarra, Gabriele. INSTM; Italia Fil: Rossi, Antonella. INSTM; Italia Fil: Xu, Yufu. Hefei University of Technology; China Fil: Kotvis, Peter V.. University of Wisconsin; Estados Unidos Fil: Tysoe, Wilfred T.. University of Wisconsin; Estados Unidos

The service life of a diesel fuel injector is highly affected by the tribological properties of the fuel. This study aims to investigate the friction and wear behaviors of emulsified bio-oil (EBO), which is a very promising alternative fuel for engines. Sliding wear tests were performed with a ball-on-disk tribometer using a GCr15 steel ball and a flat specimen as a counterpart. In these tests, the total sliding distance was 500 m, the load ranged from 10 to 20 N, and the oscillation frequency ranged from 30 to 50 Hz. Experimental results showed that EBO had better tribological properties than diesel oil and crude bio-oil. Contact load and oscillation frequency significantly influenced friction coefficient, wear volume, and wear damage pattern. The friction coefficient decreased with an increase in load and increased with an increase in oscillation frequency. Furthermore, the wear volume slightly increased with an increase in load or oscillation frequency. The damage mechanism is attributed to adhesive wear under low load and to abrasive wear under high load. The transition in the wear mechanism is related to the adsorption of the molecules in the EBO, the microstructural contact surface, and the mechanical actions.

The friction and wear behaviors of catalytic methylesterified bio-oils were compared with those of a conventional crude bio-oil using a reciprocating friction-type tribometer. The microstructure of and typical elements in the worn surfaces were also examined. Results showed that the friction coefficient and wear loss of the frictional pairs significantly decreased after lubrication with the esterified bio-oils. This result can be attributed to the esterified bio-oils having more ester components than the crude bio-oil and to the formation of a chemical adsorption layer on the worn surfaces of the frictional pairs. The tribological mechanisms of the crude and esterified bio-oils can be ascribed to corrosive wear and to boundary lubrication, respectively.

The tribological response of bio-oil derived from Spirulina algae has been assessed, according to the choice of catalyst during esterification. The bio-oil was upgraded over the selected catalysts of KF/HZSM-5 and KF/Al 2 O 3 with ethanol. Physical and chemical properties were assessed throughout with the crystal structure of the catalysts was characterized by X-ray diffraction (XRD), chemical groups and components of the bio-oil by Fourier Transform infrared spectroscopy (FTIR) and Gas Chromatograph–Mass Spectroscopy (GC–MS). Tribological experiments were conducted using a bespoke piston ring-on-cylinder liner tribometer. Worn surfaces were observed by Scanning Electron Microscope (SEM), and the elemental contents and valences were tested by X-ray Energy Dispersive Spectroscopy (EDS) and X-ray Photoelectron Spectroscopy (XPS). It is shown that choice of catalyst used during the upgrading of the bio-oil has a significant effect on tribological performance. Catalytic esterification improved friction resistance and the anti-wear properties of the bio-oil. KF/Al 2 O 3 was a better catalyst for doing this than KF/HZSM, a result of the ester and organic groups present in the KF/Al 2 O 3 upgraded bio-oil. These groups acted to form a protective tribo-film between surfaces.

The autotransformer voltage regulation is divided into two types: on-load voltage regulation and non-excitation voltage regulation. According to the position, it can be divided into medium voltage side line end voltage regulation, neutral point voltage regulation, and series winding end voltage regulation. This paper describes that a certain ODFPS-1000000/1000 transformer uses neutral point voltage regulation to change the magnetic flux for voltage regulation, and gives the magnetic flux, the coil zeta potential and the linear variation of the three-phase voltage, especially the formula for the compensation principle. Derivation and principle analysis.

The commutation structure is a composite insulation structure composed of oil, paper and cardboard. The converter transformer usually adopts positive and negative adjustment, and the polarity selector generates a recovery voltage and a breaking circuit between the opened contacts during the switching process. It is usually necessary to use a tie resistor to make a potential connection to the voltage regulating winding to limit the recovery voltage. At the same time, in order to shorten the time of the potential resistance access and reduce the no-load loss of the transformer, a potential switch is required to be used in conjunction with the tie resistor. In this paper, the characteristics of the floating potential and the capacitor current during the switching of the positive and negative voltage-regulating windings are analysed. The relationship between the arrangement of the commutating windings and the recovery voltage is given. The positive and negative floating suspension breaking capabilities of the contacts are analysed by examples. The calculation basis for the selection of the binding resistor is given, and relevant conclusions are given.

The use of renewable bio-fuel in internal combustion engines is the trend for the near future. However, it is easy to affect the cylinder liner due to the cavitation of the fuels. This study shows definite evidence that the cavitation erosion affects the tribological behaviour of the boron cast iron cylinder liner. The results indicate that the amount of both adsorbed lubricating film and tribo-film on the worn surfaces of the boron cast iron decreased with an increase in cavitation time, which is the direct reason for the increase of the friction coefficient and wear loss of the cylinder liner.