The tribological tests were performed using Nitinol 60 alloy pin sliding over GCr15 steel disc in the tribometer system. Four kinds of oils were experimentally investigated as lubrication oils for lubricating Nitinol ...The tribological tests were performed using Nitinol 60 alloy pin sliding over GCr15 steel disc in the tribometer system. Four kinds of oils were experimentally investigated as lubrication oils for lubricating Nitinol 60 alloy in the boundary lubrication regime. The experimental results were compared with a reference dry friction. It was found that Nitinol 60 alloy can be lubricated significantly and has shown remarkable lubrication performance. A superlubricity behavior of Nitinol 60 alloy was observed under castor oil lubrication. An ultra-low coefficient of friction of Nitinol 60 alloy about 0.008 between Nitinol 60 alloy and GCr15 steel was obtained under castor oil lubrication condition after a running-in period. Accordingly, the present study is focused on the lubrication behaviors of castor oil as potential lubrication oil for Nitinol 60 alloy. In the presence of castor oil, coefficient of friction is kept at 0.008 at steady state, corresponding to so-called superlubricity regime （when sliding is then approaching pure rolling）. The mechanism of superlubricity is attributed to the triboformed OH-terminated surfaces from friction-induced dissociation of castor oil and the boundary lubrication films formed on the contact surface due to high polarity and long chain of castor oil allowing strong interactions with the lubricated surfaces.展开更多
The continuous reduction in sulfur content of fuels would lead to diesel fuel with poor lubricity which could re- sult in engine pump failure. In the present work, fatty acids were adopted as lubricity additives to lo...The continuous reduction in sulfur content of fuels would lead to diesel fuel with poor lubricity which could re- sult in engine pump failure. In the present work, fatty acids were adopted as lubricity additives to low-sulfur diesel fuel. It was attempted to correlate the molecular structures of fatty acids, such as carbon chain length, degree of saturation and hy- droxylation, to their lubricity enhancement, which was evaluated by the High-Frequency Reciprocating Rig （HFRR） meth- od. The efficiency order was supported by the density functional theory （DFT） calculations and the molecular dynamics （MD） simulations. The lubricity enhancing properties of fatty acids are mainly determined by the cohesive energy of adsorbed films furmed on iron surface. The greater the cohesive energy, the more efficiently the fatty acid would enhance the lubricity of low-sulfur diesel fuel.展开更多
In this work,fatty acid and its derivatives were adopted as lubricity additives for low sulfur diesel.Tribological evaluation obtained from the High-Frequency Reciprocating Rig(HFRR)apparatus showed that the lubricati...In this work,fatty acid and its derivatives were adopted as lubricity additives for low sulfur diesel.Tribological evaluation obtained from the High-Frequency Reciprocating Rig(HFRR)apparatus showed that the lubricating performance of the additives increased in the following order:stearic acid>glycol monopalmitate>stearyl alcohol>ethyl palmitate>cetyl ethyl ether.The adsorption behavior of the additives on Fe(110)surface and Fe2O3(001)surface was investigated by molecular dynamics(MD)simulations to verify their lubricity performance.The results suggested that adsorption energies of the additives on Fe(110)surface are determined by the van der Waals forces,while adsorptions on Fe2O3(001)surface are significantly attributed to the electrostatic attractive forces.Higher values of adsorption energy of the additives on Fe2O3(001)surface indicate that the additive has more efficient lubricity enhancing properties.展开更多
A super-low friction coefficient of 0.0028 is measured under a pressure of 300MPa when the friction pair(the silicon nitride ball sliding on the silicate glass)is lubricated by the mixed aqueous solution of glycerol a...A super-low friction coefficient of 0.0028 is measured under a pressure of 300MPa when the friction pair(the silicon nitride ball sliding on the silicate glass)is lubricated by the mixed aqueous solution of glycerol and boric acid.The morphorlogies of the hydroxylated glass plate are observed by an atomic force microscope(AFM)in deionized water,glycerol,boric acid and their mixed aqueous solution.Bonding peaks of the retained liquids adhered on the surface of the sliding track are detected by an infrared spectrum apparatus and a Raman spectrum apparatus.The mechanism of the superlubricity of the glycerol and boric acid mixed aqueous solution is discussed.It is deduced that the formation of the lubricant film has enough strength to support higher loads,the hydration effect offering the super lower shear resistance.展开更多
Since the 1990 s, the kerosene fuel(code: JP-8) had been applied in the ground equipment provided with direct injection compression ignition engines in the U.S. Army, resulting in increased occurrence of injection pum...Since the 1990 s, the kerosene fuel(code: JP-8) had been applied in the ground equipment provided with direct injection compression ignition engines in the U.S. Army, resulting in increased occurrence of injection pump failures. Anti-wear additives must be used in the single fuel due to its poor lubricity. In the present work, lubricity improvers were selected on the basis of molecular simulation theoretically and these agents were evaluated to improve the lubricity of jet fuel using the high frequency reciprocating rig(HFRR) apparatus and the ball-on-cylinder lubricity evaluator(BOCLE). It was revealed that dimer acid with higher value of adsorption energy on the Fe(110) plane surface had more efficient lubricity promoting properties than that of naphthenic acid. The experimental results suggested that the dimer acid had a better tribological behavior compared with that of naphthenic acid used as lubricity improver of jet fuel. And addition of anti-wear additives at a dosage of 15 μg/g was able to promote the lubricity of jet fuel to a required level on BOCLE, while a higher concentration over 80 μg/g was needed to improve the lubricity to a demanded value of diesel on HFRR.展开更多
The lubricities of fifteen rare earth compounds of lanthanum, praseodymium, samarium, europium and gadolinium are evaluated on a four ball tester and compared with that of ZDDP(Zinc Dialkyldithiophosphate). Results s...The lubricities of fifteen rare earth compounds of lanthanum, praseodymium, samarium, europium and gadolinium are evaluated on a four ball tester and compared with that of ZDDP(Zinc Dialkyldithiophosphate). Results show that some of rare earth compounds provide much better lubricities than ZDDP, and the hexagonal type of rare earth metal compounds exhibit better lubricites than the body centered cubic type of metal compounds.展开更多
Graphite nanoplatelets were prepared by a novel magnetic-grinding method using self-made equipments. Under a variant magnetic field, magnetic needles collided at a high rotating speed and exfoliated pristine graphite ...Graphite nanoplatelets were prepared by a novel magnetic-grinding method using self-made equipments. Under a variant magnetic field, magnetic needles collided at a high rotating speed and exfoliated pristine graphite into graphite nanoplatelets with high efficiency. The obtained graphite nanoplatelets are highly crystalline, and the thickness is less than 10 nm. Moreover, the surface area could reached 738.1 m^2/g with a grinding time of 4 h. Silanized graphite nanoplatelets can disperse well in SG 15W-40 engine oil and serve as lubricant additive. Tribological results indicate that the friction coefficient and wear-scar of the friction pairs are lower than 76% and 41%, respectively, by adding 1.5‰(mass fraction) of silanized graphite nanoplatelets. Notably, the functionalized graphite nanoplatelets can realize large-scale production and commercial application.展开更多
Hypericin(C30H16O8)is a naturally occurring substance,an anthraquinone derived from St.John’s wort,possessing outstanding antiviral,antitumor,antibacterial,and antioxidant properties.Today,hypericin is primarily used...Hypericin(C30H16O8)is a naturally occurring substance,an anthraquinone derived from St.John’s wort,possessing outstanding antiviral,antitumor,antibacterial,and antioxidant properties.Today,hypericin is primarily used in medicinal applications.It is a small,flat organic molecule with a graphene-like core surrounded by oxidized functions,suggesting it could act as a graphene precursor in tribological contacts.Therefore,we investigated the lubrication properties of hypericin as an additive in glycerol,used as a base oil.It is well established that glycerol is superlubricious under full and thin film elastohydrodynamic(EHD)lubrication regimes but generally fails with steel under more severe conditions(mixed and boundary regimes).We studied the effect of hypericin added to glycerol for steel-on-steel and steel-on-silicon friction pairs.For the steel-on-steel configuration,results show that hypericin is a strong anti-wear additive due to its antioxidant properties that scavenge OH radicals.Moreover,hypericin is also an efficient friction-reducing agent,providing a steady state and robust ultralow friction coefficient(0.02–0.03).Thus,it outperforms most traditional additive formulations under the same conditions,although it does not achieve superlubricity(coefficient of friction(CoF)<0.01)under more severe conditions.For steel-on-silicon,hypericin significantly extends the superlubricity regime of glycerol to lambda ratios well below unity(low sliding speeds).The mechanism of superlubricity is attributed to the friction-induced formation of graphene layers from hypericin molecules,smoothing friction surfaces,and operating a hybrid liquid–solid superlubricious system.展开更多
Lithography-based techniques for cross-scale nanopore array fabrication are expensive,and the design of nanoporous structures relative to wettability or lubricity is intricate.This study presents a low-cost strategy i...Lithography-based techniques for cross-scale nanopore array fabrication are expensive,and the design of nanoporous structures relative to wettability or lubricity is intricate.This study presents a low-cost strategy integrating the anodization and pore-widening processes to successfully fabricate anodic aluminum oxide(AAO)nanoporous structures with pore diameters ranging from 40 to 330 nm and interpore distances ranging from 60 to 335 nm.This study reveals the synergistic regulation mechanism of pore characteristics on surface wettability and lubricity.Results showed that both pore diameter and interpore distance increase with applied voltage,and a minimum pore diameter of 40 nm achieves a low voltage(i.e.,40 V)and short anodization time.The pore-widening process significantly enhances pore uniformity.The AAO surface exhibits excellent lubricating properties with a minimum coefficient of friction of 0.05 after pore widening.In addition,the wettability of AAO can be precisely controlled by adjusting pore diameter and porosity.A small pore diameter of 40 nm exhibits hydrophobicity(contact angle of approximately 100°).The pore-widening process helps enhance the hydrophobicity of the AAO surface,where an appropriate pore diameter of 100 nm exhibits near superhydrophobicity(contact angle of approximately 141°).However,a large pore diameter of 330 nm exhibits superhydrophilicity(contact angle of approximately 4°).This study provides valuable insights into understanding the interaction between the structural characteristics and the surface properties of AAO,contributing to the development of high-performance nanopore array templates.展开更多
The mixed lubricant prepared by mixing 1-(4-ethylphenyl)-nonane-1,3-dione(0206)and chelate(0206-Fe)in a ratio of 4:6 had better tribological properties than 0206.In this study,it was found that the mixed lubricant pre...The mixed lubricant prepared by mixing 1-(4-ethylphenyl)-nonane-1,3-dione(0206)and chelate(0206-Fe)in a ratio of 4:6 had better tribological properties than 0206.In this study,it was found that the mixed lubricant prepared by mixing alkane lubricants with 0206-Fe(60%)at a ratio of 2:8 can not only achieve superlubricity,but also reduce the wear scar diameter(WSD)of the friction pairs.The mixed solution prepared by the four polar solutions with 0206-Fe(60%)cannot achieve superlubricity.The results of surface analysis and molecular dynamics(MD)simulation showed that the four polar molecules were preferentially adsorbed on the metal surface,occupying the diketone adsorption sites,and the adsorption layer formed by them cannot produce synergistic lubrication with the chelates.展开更多
Polymers have complex molecular structures that often lead to interchain friction and hinder movement,making it difficult to achieve superlubricity.However,in the field of hydration lubrication,the electronegative int...Polymers have complex molecular structures that often lead to interchain friction and hinder movement,making it difficult to achieve superlubricity.However,in the field of hydration lubrication,the electronegative interface of ceramics readily adsorbs water molecules,creating a protective water film that covers the frictional interface and effectively reduces friction.To achieve hydration lubrication,it is essential to create a continuous lubricating film by selectively enriching specific functional groups of adsorbed water molecules from the polymer solution onto the ceramic surface.By adsorbing a hydrophilic layer composed of polyvinylpyrrolidone with pyrrolidone groups onto a negatively charged Si_(3)N_(4)/sapphire interface,we formed a continuous lubricating film.Research has shown that the interaction between the polymer chain structure of polyvinylpyrrolidone molecules(such as PVP10000)in solution and water molecules could result in excellent superlubricity.When the contact pressure exceeds 198 MPa,the coefficients of friction(COF)can be reduced to 0.004-0.007.Through detailed surface analyses and sophisticated simulations,we uncovered the underlying mechanism involved.The pyrrolidone moieties of polyvinyl pyrrolidone(PVP)formed hydrogen bonds with the Si_(3)N_(4) surface,transforming the initially difficult frictional interface into a PVP/sapphire interface with significantly reduced sliding energy barriers.These findings highlight the vital role of PVP in superlubricity and hydration lubrication and provide a theoretical and experimental basis for the design of materials and lubricants with exceptional lubricating properties.展开更多
Artificial joint cartilage materials are central to arthroplasty for the treatment of osteoarthritis.Hydrogels are highly promising materials for fabricating artificial cartilage owing to their excellent biocompatibil...Artificial joint cartilage materials are central to arthroplasty for the treatment of osteoarthritis.Hydrogels are highly promising materials for fabricating artificial cartilage owing to their excellent biocompatibility and lubricity.Inspired by natural articular cartilage,in this study,we designed a modification strategy to enhance the lubricity of double-network(DN)hydrogels.Specifically,two lubricating substances,nonionic surfactant Tween 80 and hydrogenated soybean phosphatidylcholine(HSPC),were incorporated into a DN hydrogel.Lubricity-enhanced DN hydrogel exhibited superlubricity through the synergistic effect of Tween 80 and HSPC,with a low coefficient of friction of 0.008,which remained stable after 6 h of continuous tribological testing.In addition,the mechanical properties of lubricity-enhanced DN hydrogel were greater than those of unmodified DN hydrogel,with a 29%increase in fracture strain and a 1.7-fold increase in toughness.Tween 80 micelles reinforced the physically cross-linked network through hydrogen bonding with the DN hydrogel,whereas HSPC vesicles encapsulated in the polymer network served as reinforcement nodes to enhance the chemically cross-linked network.As a result,lubricity-enhanced DN hydrogel exhibited both excellent lubricity and mechanical properties.This study demonstrates an innovative way to design hydrogels exhibiting both superlubricity and excellent mechanical properties,broadening the applications of DN hydrogels in the field of artificial joint cartilage.展开更多
Macroscale rolling/sliding conditions are in the superlubricity,a little-studied topic so far.The purpose of this paper is to examine the formation of elastohydrodynamic lubrication(EHL)films by water-based lubricants...Macroscale rolling/sliding conditions are in the superlubricity,a little-studied topic so far.The purpose of this paper is to examine the formation of elastohydrodynamic lubrication(EHL)films by water-based lubricants(glycerol and polyethylene glycol(PEG)),providing superlubricous friction.Experiments were carried out on an optical ball-on-disc tribometer under rolling/sliding conditions.The film thickness was measured by the thin film colorimetric interferometry,and the viscosity of liquids was measured by rotational and high-pressure falling body viscometers.The results show that tribochemical reactions are not the mandatory reason for friction to reach the superlubricity level when using the water-based lubricants.The studied liquids themselves are almost Newtonian.With the addition of water,the signs of shear thinning behavior disappear even more.Suitable conditions for this type of lubricant can be predicted using the known Hamrock–Dowson equations.An anomaly in the thickness of the lubricants was observed as an abrupt change at certain conditions.The more PEG there is in the lubricant,the higher the thickness at the beginning of the jump.展开更多
1-(4-ethylphenyl)-nonane-1,3-dione(0206)is an oil-soluble liquid molecule with rod-like structure.In this study,the chelate(0206-Fe)with octahedral structure was prepared by the reaction of ferric chloride and 1,3-dik...1-(4-ethylphenyl)-nonane-1,3-dione(0206)is an oil-soluble liquid molecule with rod-like structure.In this study,the chelate(0206-Fe)with octahedral structure was prepared by the reaction of ferric chloride and 1,3-diketone.The experimental results show that when using 0206 and a mixed solution containing 60%0206-Fe and 40%0206(0206-Fe(60%))as lubricants of the steel friction pairs,superlubricity can be achieved(0.007,0.006).But their wear scar diameters(WSD)were very large(532µm,370µm),which resulted in the pressure of only 44.3 and 61.8 MPa in the contact areas of the friction pairs.When 0206-Fe(60%)was mixed with PAO6,it was found that the friction coefficient(COF)decreased with increase of 0206-Fe(60%)in the solution.When the ratio of 0206-Fe(60%)to PAO6 was 8:2(PAO6(20%)),it exhibited better comprehensive tribological properties(232.3 MPa).Subsequent studies have shown that reducing the viscosity of the base oil in the mixed solution helped to reduce COF and increased WSD.Considering the COF,contact pressure,and running-in time,it was found that the mixed lubricant(Oil3(20%))prepared by the base oil with a viscosity of 19.7 mPa·s(Oil3)and 0206-Fe(60%)exhibited the best tribological properties(0.007,161.4 MPa,3,100 s).展开更多
Superlubricity is an ideal lubrication state where friction nearly vanishes between contact interfaces. It has become one of the most important research topics and approaches owing to its significance in reducing ener...Superlubricity is an ideal lubrication state where friction nearly vanishes between contact interfaces. It has become one of the most important research topics and approaches owing to its significance in reducing energy consumption and preventing device failures. As an efficient and universal lubricating principle capable of achieving superlubricity, rolling lubrication has attracted widespread attention in recent years. In this review, the theoretical concept of rolling lubrication and the experimental research progress of spherical/scroll structures are summarized. The review focuses on the possibility of achieving rolling lubrication using spherical/scroll structures(such as spherical fullerenes, carbon nanotubes, and formed and constructed spherical/scroll structures). The challenges in achieving rolling lubrication are summarized, and the possibility of molecular rolling lubrication,as well as its potential applications in superlubrication, are discussed.展开更多
Insufficient hole cleaning,cutting suspension,clay swelling,and filtrate invasion of the formation might result from inadequate drilling mud properties.For effective drilling and wellbore stability,water-based mud(WBM...Insufficient hole cleaning,cutting suspension,clay swelling,and filtrate invasion of the formation might result from inadequate drilling mud properties.For effective drilling and wellbore stability,water-based mud(WBM)rheology,lubricity,filtration,and shale inhibition must be optimized and controlled.WBMs react with clays and cause time-dependent borehole issues,which is their principal drawback.Moreover,prolonged exposure destroys certain WBM components,resulting in minimal mud properties.These indicate the need for multifunctional additives to improve WBMs.Thus,this study developed WBM systems employing graphene nanoplatelets(GNPs)and locally acquired discarded coconut shells to overcome severe drilling challenges.By adding triton-X100 to coconut shell-based graphene(GN-CS),a greater dispersion of modified graphene(GN-TX)particles was produced.Characterization,rheology,lubricity,inhibition,and filtration tests were performed on these GN-CS and GN-TX at concentrations of 0.125,0.25,0.375,and 0.50 wt%.Furthermore,biotoxicity,biodegradability,and heavy metal content experiments were performed to study the environmental impact of GN-CS and GN-TX.The results showed that GN-TX had good thermal resistance up to 300℃ with only a 10%loss in weight.Both EDX and FTIR tests showed that the epoxy,carboxyl,and hydroxyl groups are in the GNP-based materials'basal plane.The GN-CS and GN-TX had better fluid properties,including better lubricity,rheology,filtration,and inhibition over the base mud,and the optimal rheological model of the drilling muds was the Herschel Buckley model.The GN-TX(modified)decreased the fluid loss to 20.6e14.3 mL from 24.6 mL at 353 K,whereas the GN-CS(unmodified)reduced it to 21.3e16.7 mL.GN-TX and GN-CS decreased the coefficient of friction of WBM from 0.47 to 0.55 to 0.25e0.41 and 0.33e0.44,respec-tively,from 298 to 353 K.In addition,0.50 wt%of GN-CS and GN-TX reduced the shale pellet swelling height to 5.4%and 5.6%,respectively,from 8.8%.Moreover,the EC 50 values for GN-CS and GN-TX were about 54,000 mg/L and the BOD/COD ratio was about 47%.These results show that the GNP-based products are safe and biodegradable.The GNP-based materials have promising prospects for drilling in environmentally sensitive formations.展开更多
The transition from atomic stick-slip to continuous sliding has been observed in a number of ways.If extended contacts are moved in different directions,so-called structural lubricity is observed when the two surface ...The transition from atomic stick-slip to continuous sliding has been observed in a number of ways.If extended contacts are moved in different directions,so-called structural lubricity is observed when the two surface lattices are non-matching.Alternatively,a“superlubric”state of motion can be achieved if the normal force is reduced below a certain threshold,the temperature is increased,or the contact is actuated mechanically.These processes have been partially demonstrated using atomic force microscopy,and they can be theoretically understood by proper modifications of the Prandtl−Tomlinson model.展开更多
The polyionic liquid poly-PEGMA-r-METAC(PPM)with quaternary ammonium has been synthesized and evaluated as additive in aqueous lubricating fluids.The rheological behavior of aqueous lubricating fluids with PPM has bee...The polyionic liquid poly-PEGMA-r-METAC(PPM)with quaternary ammonium has been synthesized and evaluated as additive in aqueous lubricating fluids.The rheological behavior of aqueous lubricating fluids with PPM has been characterized to confirm PPM’s function as a viscosity modifier.The tribological behavior of aqueous lubricating fluids with PPM has been investigated on SRV-V and MTM testing machines.It was found that PPM has excellent viscosity-increasing,lubricating,and anti-wear properties as an additive for aqueous,which can be attributed to the ability of PPM to form the protective film and boundary tribofilm generated from complex tribochemical reaction on rubbing surface.The obtained PPM with dual functions of anti-corrosion additives and viscosity index improver can play an important role in diverse lubrication regimes.展开更多
The boundary lubrication mechanism at the articulating surface of natural synovial joints has been the subject of much discussion in tribology.In this study,to elucidate the lubricating function of the superficial are...The boundary lubrication mechanism at the articulating surface of natural synovial joints has been the subject of much discussion in tribology.In this study,to elucidate the lubricating function of the superficial area of articular cartilage and synovial fluid(SF),cartilage specimens were processed with four different treatments:gentle and severe washing with detergent,incubation in NaCl solution,and trypsin digestion to selectively remove certain constituents from the cartilage surface.Subsequently,the frictional characteristics were examined in phosphate-buffered saline(PBS)and SF against glass.Angularly reciprocating sliding tests with a spherical glass probe and square articular cartilage specimens were performed at low contact loads in the mN range to extract the frictional behavior in the superficial area of the cartilage specimens.Meanwhile,the cartilage surface was observed to confirm the effects of treatments on the morphology of the cartilage surface using a fluorescence microscope and water-immersion methods.The coefficient of friction(COF)of the prepared cartilage specimens was varied from 0.05 to over 0.3 in PBS.However,a certain group of cartilage specimens exhibited a low COF of less than 0.1 with limited variation.For the low COF group of specimens,all four treatments increased the COF in PBS to different extents,and fluorescence microscopy revealed that the integrity of the cartilage surface was deteriorated by treatments.This means that the intact cartilage surface had lubricating constituents to maintain low friction,and the removal of such constituents resulted in the loss of the intrinsic boundary lubricity of the cartilage surface.The variation in the COF of the cartilage specimens was suppressed in SF because it had a clear boundary lubrication effect on the cartilage surface.The lubricating effect of SF could be confirmed even after degenerative treatment.展开更多
The term“structural lubricity”denotes a fundamental concept where the friction between two atomically flat surfaces is reduced due to lattice mismatch at the interface.Under favorable circumstances,its effect may ca...The term“structural lubricity”denotes a fundamental concept where the friction between two atomically flat surfaces is reduced due to lattice mismatch at the interface.Under favorable circumstances,its effect may cause a contact to experience ultra-low friction,which is why it is also referred to as“superlubricity”.While the basic principle is intriguingly simple,the experimental analysis of structural lubricity has been challenging.One of the main reasons for this predicament is that the tool most frequently used in nanotribology,the friction force microscope,is not well suited to analyse the friction of extended nanocontacts.To overcome this deficiency,substantial efforts have been directed in recent years towards establishing nanoparticle manipulation techniques,where the friction of nanoparticles sliding on a substrate is measured,as an alternative approach to nanotribological research.By choosing appropriate nanoparticles and substrates,interfaces exhibiting the characteristics needed for the occurrence of structural lubricity can be created.As a consequence,nanoparticle manipulation experiments such as in this review represent a unique opportunity to study the physical conditions and processes necessary to establish structural lubricity,thereby opening a path to exploit this effect in technological applications.展开更多
基金Project(51305331)supported by the National Natural Science Foundation of ChinaProject(2012M511993)supported by China Postdoctoral Science FoundationProject(TPL1202)supported by the Open Fund Program of the State Key Laboratory of Traction Power,Southwest Jiaotong University,China
文摘The tribological tests were performed using Nitinol 60 alloy pin sliding over GCr15 steel disc in the tribometer system. Four kinds of oils were experimentally investigated as lubrication oils for lubricating Nitinol 60 alloy in the boundary lubrication regime. The experimental results were compared with a reference dry friction. It was found that Nitinol 60 alloy can be lubricated significantly and has shown remarkable lubrication performance. A superlubricity behavior of Nitinol 60 alloy was observed under castor oil lubrication. An ultra-low coefficient of friction of Nitinol 60 alloy about 0.008 between Nitinol 60 alloy and GCr15 steel was obtained under castor oil lubrication condition after a running-in period. Accordingly, the present study is focused on the lubrication behaviors of castor oil as potential lubrication oil for Nitinol 60 alloy. In the presence of castor oil, coefficient of friction is kept at 0.008 at steady state, corresponding to so-called superlubricity regime （when sliding is then approaching pure rolling）. The mechanism of superlubricity is attributed to the triboformed OH-terminated surfaces from friction-induced dissociation of castor oil and the boundary lubrication films formed on the contact surface due to high polarity and long chain of castor oil allowing strong interactions with the lubricated surfaces.
基金supported by the Fundamental Research Funds for the Central Universities of China(11CX06036A)
文摘The continuous reduction in sulfur content of fuels would lead to diesel fuel with poor lubricity which could re- sult in engine pump failure. In the present work, fatty acids were adopted as lubricity additives to low-sulfur diesel fuel. It was attempted to correlate the molecular structures of fatty acids, such as carbon chain length, degree of saturation and hy- droxylation, to their lubricity enhancement, which was evaluated by the High-Frequency Reciprocating Rig （HFRR） meth- od. The efficiency order was supported by the density functional theory （DFT） calculations and the molecular dynamics （MD） simulations. The lubricity enhancing properties of fatty acids are mainly determined by the cohesive energy of adsorbed films furmed on iron surface. The greater the cohesive energy, the more efficiently the fatty acid would enhance the lubricity of low-sulfur diesel fuel.
基金financially supported by "the Fundamental Research Funds for the Central Universities,China"(11CX06036A)
文摘In this work,fatty acid and its derivatives were adopted as lubricity additives for low sulfur diesel.Tribological evaluation obtained from the High-Frequency Reciprocating Rig(HFRR)apparatus showed that the lubricating performance of the additives increased in the following order:stearic acid>glycol monopalmitate>stearyl alcohol>ethyl palmitate>cetyl ethyl ether.The adsorption behavior of the additives on Fe(110)surface and Fe2O3(001)surface was investigated by molecular dynamics(MD)simulations to verify their lubricity performance.The results suggested that adsorption energies of the additives on Fe(110)surface are determined by the van der Waals forces,while adsorptions on Fe2O3(001)surface are significantly attributed to the electrostatic attractive forces.Higher values of adsorption energy of the additives on Fe2O3(001)surface indicate that the additive has more efficient lubricity enhancing properties.
基金Supported by the National Natural Science Foundation of China under Grant Nos 50721004,50727007 and 51075227the Basic Research Program of Shenzhen(0021539012100521066).
文摘A super-low friction coefficient of 0.0028 is measured under a pressure of 300MPa when the friction pair(the silicon nitride ball sliding on the silicate glass)is lubricated by the mixed aqueous solution of glycerol and boric acid.The morphorlogies of the hydroxylated glass plate are observed by an atomic force microscope(AFM)in deionized water,glycerol,boric acid and their mixed aqueous solution.Bonding peaks of the retained liquids adhered on the surface of the sliding track are detected by an infrared spectrum apparatus and a Raman spectrum apparatus.The mechanism of the superlubricity of the glycerol and boric acid mixed aqueous solution is discussed.It is deduced that the formation of the lubricant film has enough strength to support higher loads,the hydration effect offering the super lower shear resistance.
文摘Since the 1990 s, the kerosene fuel(code: JP-8) had been applied in the ground equipment provided with direct injection compression ignition engines in the U.S. Army, resulting in increased occurrence of injection pump failures. Anti-wear additives must be used in the single fuel due to its poor lubricity. In the present work, lubricity improvers were selected on the basis of molecular simulation theoretically and these agents were evaluated to improve the lubricity of jet fuel using the high frequency reciprocating rig(HFRR) apparatus and the ball-on-cylinder lubricity evaluator(BOCLE). It was revealed that dimer acid with higher value of adsorption energy on the Fe(110) plane surface had more efficient lubricity promoting properties than that of naphthenic acid. The experimental results suggested that the dimer acid had a better tribological behavior compared with that of naphthenic acid used as lubricity improver of jet fuel. And addition of anti-wear additives at a dosage of 15 μg/g was able to promote the lubricity of jet fuel to a required level on BOCLE, while a higher concentration over 80 μg/g was needed to improve the lubricity to a demanded value of diesel on HFRR.
文摘The lubricities of fifteen rare earth compounds of lanthanum, praseodymium, samarium, europium and gadolinium are evaluated on a four ball tester and compared with that of ZDDP(Zinc Dialkyldithiophosphate). Results show that some of rare earth compounds provide much better lubricities than ZDDP, and the hexagonal type of rare earth metal compounds exhibit better lubricites than the body centered cubic type of metal compounds.
基金Project(ZR2011BL005)supported by the Natural Science Foundation of Shandong Province,China
文摘Graphite nanoplatelets were prepared by a novel magnetic-grinding method using self-made equipments. Under a variant magnetic field, magnetic needles collided at a high rotating speed and exfoliated pristine graphite into graphite nanoplatelets with high efficiency. The obtained graphite nanoplatelets are highly crystalline, and the thickness is less than 10 nm. Moreover, the surface area could reached 738.1 m^2/g with a grinding time of 4 h. Silanized graphite nanoplatelets can disperse well in SG 15W-40 engine oil and serve as lubricant additive. Tribological results indicate that the friction coefficient and wear-scar of the friction pairs are lower than 76% and 41%, respectively, by adding 1.5‰(mass fraction) of silanized graphite nanoplatelets. Notably, the functionalized graphite nanoplatelets can realize large-scale production and commercial application.
基金funding from the HORIZON-EIC-2021-PATHFINDEROPEN-0 N.101046693,SSLiP project,funded by the European Union.
文摘Hypericin(C30H16O8)is a naturally occurring substance,an anthraquinone derived from St.John’s wort,possessing outstanding antiviral,antitumor,antibacterial,and antioxidant properties.Today,hypericin is primarily used in medicinal applications.It is a small,flat organic molecule with a graphene-like core surrounded by oxidized functions,suggesting it could act as a graphene precursor in tribological contacts.Therefore,we investigated the lubrication properties of hypericin as an additive in glycerol,used as a base oil.It is well established that glycerol is superlubricious under full and thin film elastohydrodynamic(EHD)lubrication regimes but generally fails with steel under more severe conditions(mixed and boundary regimes).We studied the effect of hypericin added to glycerol for steel-on-steel and steel-on-silicon friction pairs.For the steel-on-steel configuration,results show that hypericin is a strong anti-wear additive due to its antioxidant properties that scavenge OH radicals.Moreover,hypericin is also an efficient friction-reducing agent,providing a steady state and robust ultralow friction coefficient(0.02–0.03).Thus,it outperforms most traditional additive formulations under the same conditions,although it does not achieve superlubricity(coefficient of friction(CoF)<0.01)under more severe conditions.For steel-on-silicon,hypericin significantly extends the superlubricity regime of glycerol to lambda ratios well below unity(low sliding speeds).The mechanism of superlubricity is attributed to the friction-induced formation of graphene layers from hypericin molecules,smoothing friction surfaces,and operating a hybrid liquid–solid superlubricious system.
基金support from the National Natural Science Foundation of China(Grant Nos.52405447 and 52275299)the Key Research and Development Program of Jiangxi Province in China(Grant No.20232BBE50011)+1 种基金the National Key Research and Development Program of China(Grant No.2021YFB1716200)the Research Funds for Leading Talents Program(Grant Nos.048000514123686 and 048000514123581).
文摘Lithography-based techniques for cross-scale nanopore array fabrication are expensive,and the design of nanoporous structures relative to wettability or lubricity is intricate.This study presents a low-cost strategy integrating the anodization and pore-widening processes to successfully fabricate anodic aluminum oxide(AAO)nanoporous structures with pore diameters ranging from 40 to 330 nm and interpore distances ranging from 60 to 335 nm.This study reveals the synergistic regulation mechanism of pore characteristics on surface wettability and lubricity.Results showed that both pore diameter and interpore distance increase with applied voltage,and a minimum pore diameter of 40 nm achieves a low voltage(i.e.,40 V)and short anodization time.The pore-widening process significantly enhances pore uniformity.The AAO surface exhibits excellent lubricating properties with a minimum coefficient of friction of 0.05 after pore widening.In addition,the wettability of AAO can be precisely controlled by adjusting pore diameter and porosity.A small pore diameter of 40 nm exhibits hydrophobicity(contact angle of approximately 100°).The pore-widening process helps enhance the hydrophobicity of the AAO surface,where an appropriate pore diameter of 100 nm exhibits near superhydrophobicity(contact angle of approximately 141°).However,a large pore diameter of 330 nm exhibits superhydrophilicity(contact angle of approximately 4°).This study provides valuable insights into understanding the interaction between the structural characteristics and the surface properties of AAO,contributing to the development of high-performance nanopore array templates.
基金financially supported by National Key R&D Program of China(Grant No.2020YFA0711003)the National Natural Science Foundation of China(Grant Nos.51925506 and 52305178)the XPLORER PRIZE.
文摘The mixed lubricant prepared by mixing 1-(4-ethylphenyl)-nonane-1,3-dione(0206)and chelate(0206-Fe)in a ratio of 4:6 had better tribological properties than 0206.In this study,it was found that the mixed lubricant prepared by mixing alkane lubricants with 0206-Fe(60%)at a ratio of 2:8 can not only achieve superlubricity,but also reduce the wear scar diameter(WSD)of the friction pairs.The mixed solution prepared by the four polar solutions with 0206-Fe(60%)cannot achieve superlubricity.The results of surface analysis and molecular dynamics(MD)simulation showed that the four polar molecules were preferentially adsorbed on the metal surface,occupying the diketone adsorption sites,and the adsorption layer formed by them cannot produce synergistic lubrication with the chelates.
基金supported by the National Natural Science Foundation of China(Nos.52275203 and 52105194)the China Postdoctoral Science Special Funding Project(No.2022T150353)the Tribology Science Fund of the State Key Laboratory of Tribology in Advanced Equipment(Nos.SKLTKF23A03 and SKLTKF23A04).
文摘Polymers have complex molecular structures that often lead to interchain friction and hinder movement,making it difficult to achieve superlubricity.However,in the field of hydration lubrication,the electronegative interface of ceramics readily adsorbs water molecules,creating a protective water film that covers the frictional interface and effectively reduces friction.To achieve hydration lubrication,it is essential to create a continuous lubricating film by selectively enriching specific functional groups of adsorbed water molecules from the polymer solution onto the ceramic surface.By adsorbing a hydrophilic layer composed of polyvinylpyrrolidone with pyrrolidone groups onto a negatively charged Si_(3)N_(4)/sapphire interface,we formed a continuous lubricating film.Research has shown that the interaction between the polymer chain structure of polyvinylpyrrolidone molecules(such as PVP10000)in solution and water molecules could result in excellent superlubricity.When the contact pressure exceeds 198 MPa,the coefficients of friction(COF)can be reduced to 0.004-0.007.Through detailed surface analyses and sophisticated simulations,we uncovered the underlying mechanism involved.The pyrrolidone moieties of polyvinyl pyrrolidone(PVP)formed hydrogen bonds with the Si_(3)N_(4) surface,transforming the initially difficult frictional interface into a PVP/sapphire interface with significantly reduced sliding energy barriers.These findings highlight the vital role of PVP in superlubricity and hydration lubrication and provide a theoretical and experimental basis for the design of materials and lubricants with exceptional lubricating properties.
基金supported by the National Natural Science Foundation of China(52350323)the Guangdong Basic Research Foundation(2024A1515012406)+1 种基金the Guangdong Applied Basic Research Foundation(2023A1515110565)the Tribology Science Fund of State Key Laboratory of Tribology in Advanced Equipment(SKLTKF22B13).
文摘Artificial joint cartilage materials are central to arthroplasty for the treatment of osteoarthritis.Hydrogels are highly promising materials for fabricating artificial cartilage owing to their excellent biocompatibility and lubricity.Inspired by natural articular cartilage,in this study,we designed a modification strategy to enhance the lubricity of double-network(DN)hydrogels.Specifically,two lubricating substances,nonionic surfactant Tween 80 and hydrogenated soybean phosphatidylcholine(HSPC),were incorporated into a DN hydrogel.Lubricity-enhanced DN hydrogel exhibited superlubricity through the synergistic effect of Tween 80 and HSPC,with a low coefficient of friction of 0.008,which remained stable after 6 h of continuous tribological testing.In addition,the mechanical properties of lubricity-enhanced DN hydrogel were greater than those of unmodified DN hydrogel,with a 29%increase in fracture strain and a 1.7-fold increase in toughness.Tween 80 micelles reinforced the physically cross-linked network through hydrogen bonding with the DN hydrogel,whereas HSPC vesicles encapsulated in the polymer network served as reinforcement nodes to enhance the chemically cross-linked network.As a result,lubricity-enhanced DN hydrogel exhibited both excellent lubricity and mechanical properties.This study demonstrates an innovative way to design hydrogels exhibiting both superlubricity and excellent mechanical properties,broadening the applications of DN hydrogels in the field of artificial joint cartilage.
基金supported by the Czech Science Foundation(No.21-28352S).
文摘Macroscale rolling/sliding conditions are in the superlubricity,a little-studied topic so far.The purpose of this paper is to examine the formation of elastohydrodynamic lubrication(EHL)films by water-based lubricants(glycerol and polyethylene glycol(PEG)),providing superlubricous friction.Experiments were carried out on an optical ball-on-disc tribometer under rolling/sliding conditions.The film thickness was measured by the thin film colorimetric interferometry,and the viscosity of liquids was measured by rotational and high-pressure falling body viscometers.The results show that tribochemical reactions are not the mandatory reason for friction to reach the superlubricity level when using the water-based lubricants.The studied liquids themselves are almost Newtonian.With the addition of water,the signs of shear thinning behavior disappear even more.Suitable conditions for this type of lubricant can be predicted using the known Hamrock–Dowson equations.An anomaly in the thickness of the lubricants was observed as an abrupt change at certain conditions.The more PEG there is in the lubricant,the higher the thickness at the beginning of the jump.
基金supported by the National Key R&D Program of China(No.2020YFA0711003)the National Natural Science Foundation of China(No.51925506),and the XPLORER PRIZE.
文摘1-(4-ethylphenyl)-nonane-1,3-dione(0206)is an oil-soluble liquid molecule with rod-like structure.In this study,the chelate(0206-Fe)with octahedral structure was prepared by the reaction of ferric chloride and 1,3-diketone.The experimental results show that when using 0206 and a mixed solution containing 60%0206-Fe and 40%0206(0206-Fe(60%))as lubricants of the steel friction pairs,superlubricity can be achieved(0.007,0.006).But their wear scar diameters(WSD)were very large(532µm,370µm),which resulted in the pressure of only 44.3 and 61.8 MPa in the contact areas of the friction pairs.When 0206-Fe(60%)was mixed with PAO6,it was found that the friction coefficient(COF)decreased with increase of 0206-Fe(60%)in the solution.When the ratio of 0206-Fe(60%)to PAO6 was 8:2(PAO6(20%)),it exhibited better comprehensive tribological properties(232.3 MPa).Subsequent studies have shown that reducing the viscosity of the base oil in the mixed solution helped to reduce COF and increased WSD.Considering the COF,contact pressure,and running-in time,it was found that the mixed lubricant(Oil3(20%))prepared by the base oil with a viscosity of 19.7 mPa·s(Oil3)and 0206-Fe(60%)exhibited the best tribological properties(0.007,161.4 MPa,3,100 s).
基金supported by the Strategic Priority Research Program of the Chinese Academy of Sciences (Grant No. XDB0470202)the National Natural Science Foundation of China (Grant No. 52275222)+2 种基金the China Postdoctoral Science Foundation (Grant No. 2022M723224)the Postdoctoral Fellowship Program of CPSF (Grant No. GZB20230779)the Youth Innovation Promotion Association of the Chinese Academy of Sciences (Grant No. Y202084)。
文摘Superlubricity is an ideal lubrication state where friction nearly vanishes between contact interfaces. It has become one of the most important research topics and approaches owing to its significance in reducing energy consumption and preventing device failures. As an efficient and universal lubricating principle capable of achieving superlubricity, rolling lubrication has attracted widespread attention in recent years. In this review, the theoretical concept of rolling lubrication and the experimental research progress of spherical/scroll structures are summarized. The review focuses on the possibility of achieving rolling lubrication using spherical/scroll structures(such as spherical fullerenes, carbon nanotubes, and formed and constructed spherical/scroll structures). The challenges in achieving rolling lubrication are summarized, and the possibility of molecular rolling lubrication,as well as its potential applications in superlubrication, are discussed.
文摘Insufficient hole cleaning,cutting suspension,clay swelling,and filtrate invasion of the formation might result from inadequate drilling mud properties.For effective drilling and wellbore stability,water-based mud(WBM)rheology,lubricity,filtration,and shale inhibition must be optimized and controlled.WBMs react with clays and cause time-dependent borehole issues,which is their principal drawback.Moreover,prolonged exposure destroys certain WBM components,resulting in minimal mud properties.These indicate the need for multifunctional additives to improve WBMs.Thus,this study developed WBM systems employing graphene nanoplatelets(GNPs)and locally acquired discarded coconut shells to overcome severe drilling challenges.By adding triton-X100 to coconut shell-based graphene(GN-CS),a greater dispersion of modified graphene(GN-TX)particles was produced.Characterization,rheology,lubricity,inhibition,and filtration tests were performed on these GN-CS and GN-TX at concentrations of 0.125,0.25,0.375,and 0.50 wt%.Furthermore,biotoxicity,biodegradability,and heavy metal content experiments were performed to study the environmental impact of GN-CS and GN-TX.The results showed that GN-TX had good thermal resistance up to 300℃ with only a 10%loss in weight.Both EDX and FTIR tests showed that the epoxy,carboxyl,and hydroxyl groups are in the GNP-based materials'basal plane.The GN-CS and GN-TX had better fluid properties,including better lubricity,rheology,filtration,and inhibition over the base mud,and the optimal rheological model of the drilling muds was the Herschel Buckley model.The GN-TX(modified)decreased the fluid loss to 20.6e14.3 mL from 24.6 mL at 353 K,whereas the GN-CS(unmodified)reduced it to 21.3e16.7 mL.GN-TX and GN-CS decreased the coefficient of friction of WBM from 0.47 to 0.55 to 0.25e0.41 and 0.33e0.44,respec-tively,from 298 to 353 K.In addition,0.50 wt%of GN-CS and GN-TX reduced the shale pellet swelling height to 5.4%and 5.6%,respectively,from 8.8%.Moreover,the EC 50 values for GN-CS and GN-TX were about 54,000 mg/L and the BOD/COD ratio was about 47%.These results show that the GNP-based products are safe and biodegradable.The GNP-based materials have promising prospects for drilling in environmentally sensitive formations.
基金E.M.acknowledges financial support by the Swiss National Science Foundation(SNF)the Commission for Technology and Innovation(CTI),COST Action MP1303 and the Swiss Nanoscience Institute(SNI).E.G.acknowledges the Spanish Ministry of Economy and Competitiveness(MINECO)Project MAT2012-26312.
文摘The transition from atomic stick-slip to continuous sliding has been observed in a number of ways.If extended contacts are moved in different directions,so-called structural lubricity is observed when the two surface lattices are non-matching.Alternatively,a“superlubric”state of motion can be achieved if the normal force is reduced below a certain threshold,the temperature is increased,or the contact is actuated mechanically.These processes have been partially demonstrated using atomic force microscopy,and they can be theoretically understood by proper modifications of the Prandtl−Tomlinson model.
基金support from the National Key R&D Program of China(2021YFA0716304)the Strategic Priority Research Program of the Chinese Academy of Sciences(XDB 0470301),the National Natural Science Foundation of China(U23A20623,21972153,and 52075524)+2 种基金Gansu Province Science and Technology Plan(20JR10RA060,22ZD6GA002,and 22ZD6GA025)Openning Project of State Key Laboratory of Solid Lubrication,LICP(LSL-2004)the Taishan Scholars Program.
文摘The polyionic liquid poly-PEGMA-r-METAC(PPM)with quaternary ammonium has been synthesized and evaluated as additive in aqueous lubricating fluids.The rheological behavior of aqueous lubricating fluids with PPM has been characterized to confirm PPM’s function as a viscosity modifier.The tribological behavior of aqueous lubricating fluids with PPM has been investigated on SRV-V and MTM testing machines.It was found that PPM has excellent viscosity-increasing,lubricating,and anti-wear properties as an additive for aqueous,which can be attributed to the ability of PPM to form the protective film and boundary tribofilm generated from complex tribochemical reaction on rubbing surface.The obtained PPM with dual functions of anti-corrosion additives and viscosity index improver can play an important role in diverse lubrication regimes.
基金support was given by the Grant-in Aid for Scientific Research(A)of Japan Society for the Promotion of Science(21H04535).
文摘The boundary lubrication mechanism at the articulating surface of natural synovial joints has been the subject of much discussion in tribology.In this study,to elucidate the lubricating function of the superficial area of articular cartilage and synovial fluid(SF),cartilage specimens were processed with four different treatments:gentle and severe washing with detergent,incubation in NaCl solution,and trypsin digestion to selectively remove certain constituents from the cartilage surface.Subsequently,the frictional characteristics were examined in phosphate-buffered saline(PBS)and SF against glass.Angularly reciprocating sliding tests with a spherical glass probe and square articular cartilage specimens were performed at low contact loads in the mN range to extract the frictional behavior in the superficial area of the cartilage specimens.Meanwhile,the cartilage surface was observed to confirm the effects of treatments on the morphology of the cartilage surface using a fluorescence microscope and water-immersion methods.The coefficient of friction(COF)of the prepared cartilage specimens was varied from 0.05 to over 0.3 in PBS.However,a certain group of cartilage specimens exhibited a low COF of less than 0.1 with limited variation.For the low COF group of specimens,all four treatments increased the COF in PBS to different extents,and fluorescence microscopy revealed that the integrity of the cartilage surface was deteriorated by treatments.This means that the intact cartilage surface had lubricating constituents to maintain low friction,and the removal of such constituents resulted in the loss of the intrinsic boundary lubricity of the cartilage surface.The variation in the COF of the cartilage specimens was suppressed in SF because it had a clear boundary lubrication effect on the cartilage surface.The lubricating effect of SF could be confirmed even after degenerative treatment.
基金Financial support was provided by the DFG(Project SCHI 619/8-1)the EUROCORES program FANAS of the European Science Foundation,and the EC 6th framework program(Grant No.ERAS-CT-2003-980409)U.S.acknowledges primary financial support by the National Science Foundation through the Yale Materials Research Science and Engineering Center(Grant No.MRSEC DMR-1119826).
文摘The term“structural lubricity”denotes a fundamental concept where the friction between two atomically flat surfaces is reduced due to lattice mismatch at the interface.Under favorable circumstances,its effect may cause a contact to experience ultra-low friction,which is why it is also referred to as“superlubricity”.While the basic principle is intriguingly simple,the experimental analysis of structural lubricity has been challenging.One of the main reasons for this predicament is that the tool most frequently used in nanotribology,the friction force microscope,is not well suited to analyse the friction of extended nanocontacts.To overcome this deficiency,substantial efforts have been directed in recent years towards establishing nanoparticle manipulation techniques,where the friction of nanoparticles sliding on a substrate is measured,as an alternative approach to nanotribological research.By choosing appropriate nanoparticles and substrates,interfaces exhibiting the characteristics needed for the occurrence of structural lubricity can be created.As a consequence,nanoparticle manipulation experiments such as in this review represent a unique opportunity to study the physical conditions and processes necessary to establish structural lubricity,thereby opening a path to exploit this effect in technological applications.
