Water-based lubrication is an effective method to achieve superlubricity,which implies a friction coefficient in the order of 10−3 or lower.Recent numerical,analytical,and experimental studies confirm that the surface...Water-based lubrication is an effective method to achieve superlubricity,which implies a friction coefficient in the order of 10−3 or lower.Recent numerical,analytical,and experimental studies confirm that the surface force effect is crucial for realizing water-based superlubricity.To enhance the contribution of the surface force,soft and plastic materials can be utilized as friction pair materials because of their effect in increasing the contact area.A new numerical model of water-based lubrication that considers the surface force between plastic and elastic materials is developed in this study to investigate the effect of plastic flow in water-based lubrication.Considering the complexity of residual stress accumulation in lubrication problems,a simplified plastic model is proposed,which merely calculates the result of the dry contact solution and avoids repeated calculations of the plastic flow.The results of the two models show good agreement.Plastic deformation reduces the local contact pressure and enhances the function of the surface force,thus resulting in a lower friction coefficient.展开更多
The micro crack of aluminum sheet during cold rolling lubricated with emulsions is investigated. Experi-ments show that micro cracks occur after cold rolling process and this is attributed to various parameters, for i...The micro crack of aluminum sheet during cold rolling lubricated with emulsions is investigated. Experi-ments show that micro cracks occur after cold rolling process and this is attributed to various parameters, for instance, the thin oxide film formed at the sheet surface. The micro crack spacing thus becomes an important parameter which deserves more concerns. The aspect ratio of these micro cracks is then analyzed theoreti-cally, which takes into consideration of the oxide fracture process. The good agreement between the obser-vations and the theoretical predictions validates the analysis. The approach can shed some new lights on the mechanical process of aluminium sheet during cold rolling.展开更多
Polyether ether ketone(PEEK)is a widely used material for friction pairs due to its excellent mechanical strength,good wear resistance,and chemical inertness.However,some modifications are necessary when PEEK is used ...Polyether ether ketone(PEEK)is a widely used material for friction pairs due to its excellent mechanical strength,good wear resistance,and chemical inertness.However,some modifications are necessary when PEEK is used as a water-lubricated friction pair.In this study,a novel sulfonation method was developed to design a water-lubricated friction pair with ultralow friction,good wear resistance,and high loading capacity.PEEK powders were sulfonated using ClSO3H and sintered to form bulk plastic.The sulfonated PEEK(SPEEK)plastic exhibited good tribological properties.At a low sliding speed,the friction coefficient was smaller than 0.02 when a 3 wt% NaCl solution was used as the lubricant.The order of magnitude of the wear rate was as low as 10^(-8) mm^(3)/(N·m).The mechanism of friction reduction was mainly hydration lubrication.The negatively charged -SO_(3)^(-) groups on the friction pair can adsorb hydrated Na+cations by electrostatic interactions.These hydrated Na+cations have a high load capacity and low shearing resistance.The ultralow wear mechanism observed in this study is possibly due to ultralow friction properties of the friction pairs prepared through the proposed sulfonation and thermoforming procedures.展开更多
Achievement of steady and reliable super-low friction at the steel/steel contact interface,one of the most tribological systems applied for mechanical moving parts,is of importance for prolonging machine lifetime and ...Achievement of steady and reliable super-low friction at the steel/steel contact interface,one of the most tribological systems applied for mechanical moving parts,is of importance for prolonging machine lifetime and reducing energy consumption.Here we reported that the superlubricity performance of the steel/steel sliding interface lubricated with tiny amounts of diketone solution strongly depends on the oxygen content in surrounding environment.The increase of oxygen not only significantly shortens the initial running-in time but also further reduces the stable coefficient of friction in superlubricity stage due to the enhancement of tribochemical reactions.On the one hand,more severe oxidation wear occurring at higher oxygen content facilitates material removal of the contact interface,lowering the contact pressure and the corresponding initial friction.On the other hand,the growth of iron ions during the shear process in high oxygen environment promotes the formation of chelate which acted as an effective lubricated film chemisorbed at the steel/steel friction interface to further lower the interfacial friction.The results provide a new opportunity to further optimize the tribological performance of diketone superlubricity system,especially towards the lubrication of mechanical engineering materials.展开更多
In this study,we address the superlubricity behavior of sapphire against ruby(or sapphire against itself)under phosphoric acid solution lubrication.An ultra-low friction coefficient of 0.004 was obtained under a very ...In this study,we address the superlubricity behavior of sapphire against ruby(or sapphire against itself)under phosphoric acid solution lubrication.An ultra-low friction coefficient of 0.004 was obtained under a very high contact pressure,with a virgin contact pressure up to 2.57 GPa.Related experiments have indicated that the load,sliding speed,and humidity of the test environment can affect superlubricity to some degree,so we tested variations in these conditions.When superlubricity appears in this study a thin film is present,consisting of a hydrogen bond network of phosphoric acid and water molecules adsorbed on the two friction surfaces,which accounts for the ultra-low friction.Most significantly,the wear rate of the sapphire and ruby in the friction process is very slow and the superlubricity state is very stable,providing favorable conditions for future technological applications.展开更多
In this work,a super-low friction coefficient of 0.003 was found between a silicon nitride ball and a sapphire plate lubricated by phosphoric acid solution.The wear mainly occurred in the running-in period and disappe...In this work,a super-low friction coefficient of 0.003 was found between a silicon nitride ball and a sapphire plate lubricated by phosphoric acid solution.The wear mainly occurred in the running-in period and disappeared after superlubricity was achieved.The friction coefficient was effectively reduced from 0.3 to 0.003 at a constant speed of 0.076 m/s,accompanied by a 12-nm-thickness film.The lubrication regime was indicated to change from boundary lubrication in the running-in period to elastohydrodynamic lubrication in the superlubricity period,which is also supported by the results of the friction coefficient versus sliding speed.In addition,the experimental results showed good agreement with theoretical calculations based on the elastohydrodynamic lubrication theory,suggesting a significant hydrodynamic effect of phosphoric acid on superlubricity.展开更多
Graphene is a promising material as a lubricant additive for reducing friction and wear.Here,a dispersing method which combines chemical modification of graphene by octadecylamine and dicyclohexylcarbodiimide with a k...Graphene is a promising material as a lubricant additive for reducing friction and wear.Here,a dispersing method which combines chemical modification of graphene by octadecylamine and dicyclohexylcarbodiimide with a kind of effective dispersant has been successfully developed to achieve the remarkable dispersion stability of graphene in base oil.The stable dispersion time of modified graphene(0.5 wt%)with dispersant(1 wt%)in PAO-6 could be up to about 120 days,which was the longest time reported so far.At the same time,the lubricant exhibits a significant improvement of tribological performance for a steel ball to plate tribo-system with a normal load of 2 N.The coefficient of friction between sliding surfaces was~0.10 and the depth of wear track on plate was~21 nm,which decreased by about 44%and 90%when compared to pure PAO-6,respectively.Furthermore,the analysis of the lubricating mechanisms in regard to the sliding-induced formation of nanostructured tribo-film has been contacted by using Raman spectra and TEM.展开更多
High-temperature solid lubricants play a significant role in the hot metal forming process.However,preparing high-temperature solid lubricant is formidably challenging due to the stern working conditions.Here we succe...High-temperature solid lubricants play a significant role in the hot metal forming process.However,preparing high-temperature solid lubricant is formidably challenging due to the stern working conditions.Here we successfully develop a new type of eco-friendly high-temperature graphite-based solid lubricant by using amorphous silica dioxide,aluminum dihydrogen phosphate,and solid lubricant graphite.The solid lubricating coating exhibits excellent tribological properties with a very low friction coefficient and good wear protection for workpiece at high temperature under the air atmosphere.An array of analytical techniques reveals the existence of solid lubricant graphite in the lubricating coating after the high-temperature friction test.A synergistic effect between the protective surface film and the solid lubricant graphite is proposed to account for such superior lubricating performance.This work highlights the synergistic effect between the protection layer and the lubricant graphite and further provides the insight in designing the high-temperature solid lubricant.展开更多
The unusual chromosome 11q23.3 harboring the apolipoprotein(APO)gene cluster has been well documented for its essential roles in plasma lipid-related traits and atherosclerotic cardiovascular diseases.However,its gene...The unusual chromosome 11q23.3 harboring the apolipoprotein(APO)gene cluster has been well documented for its essential roles in plasma lipid-related traits and atherosclerotic cardiovascular diseases.However,its genetic architecture and the potential biological mechanisms underlying complex phenotypes have not been well assessed.We conducted a study for this target region in a Han Chinese population through a stepwise forward framework based on massive parallel sequencing,association analyses,genetic fine mapping,and functional interpretation.The present study identified new meaningful genetic associations that were not simply determined by statistical significance.In addition to the APOA5 gene,we found robust evidence of the genetic commitments of APOC3 and APOA1 to blood lipids.Several variants with high confidence were prioritized along with the potential biological mechanism interpretations in the wake of adaptive fine-mapping analyses.rs2849174 in the APOC3 enhancer was discovered with an unrivaled posterior probability of causality for triglyceride levels and could mediate APOC3 expression through enhancer activity modulated by a combination of histone modifications and transcription factor accessibility.Similarly,multiple lines of evidence converged in favor of rs3741297 as a causal variant influencing high-density lipoprotein cholesterol.Our findings provided novel insights into this genomic locus in the Chinese population.展开更多
This note presents the principle and structure of a tribological measure for floppy disks. The precision of the force measuring system is 1 mN in loading and 3×10-6 N in friction. The resolution of the film thick...This note presents the principle and structure of a tribological measure for floppy disks. The precision of the force measuring system is 1 mN in loading and 3×10-6 N in friction. The resolution of the film thickness between head and floppy disk is 0.5 nm in the vertical and 1.5 nm in the horizontal direction. in order to investigate the tribological characteristics of floppy disks, six types of floppy disks have been tested and the floating properties of these disks are also studied with film measuring system. The experimental results of the surface morphology and friction coefficient of these floppy disks using the atomic force microscope/friction force mcroscope (AFM/FFM) are in accordance with the conclusion made by our own measuring system. The experimental results show that the air film thickness between head and disk is of the same order as the surface roughness of floppy disks.展开更多
Hydrogenated amorphous carbon(a-C:H)films are capable of providing excellent superlubricating properties,which have great potential serving as self-lubricating protective layer for mechanical systems in extreme workin...Hydrogenated amorphous carbon(a-C:H)films are capable of providing excellent superlubricating properties,which have great potential serving as self-lubricating protective layer for mechanical systems in extreme working conditions.However,it is still a huge challenge to develop a-C:H films capable of achieving robust superlubricity state in vacuum.The main obstacle derives from the lack of knowledge on the influencing mechanism of deposition parameters on the films bonding structure and its relation to their self-lubrication performance.Aiming at finding the optimized deposition energy and revealing its influencing mechanism on superlubricity,a series of highly-hydrogenated a-C:H films were synthesized with appropriate ion energy,and systematic tribological experiments and structural characterization were conducted.The results highlight the pivotal role of ion energy on film composition,nanoclustering structure,and bonding state,which determine mechanical properties of highly-hydrogenated a-C:H films and surface passivation ability and hence their superlubricity performance in vacuum.The optimized superlubricity performance with the lowest friction coefficient of 0.006 coupled with the lowest wear rate emerges when the carbon ion energy is just beyond the penetration threshold of subplantation.The combined growth process of surface chemisorption and subsurface implantation is the key for a-C:H films to acquire stiff nanoclustering network and high volume of hydrogen incorporation,which enables a robust near-frictionless sliding surface.These findings can provide a guidance towards a more effective manipulation of self-lubricating a-C:H films for space application.展开更多
This study achieved water‐based superlubricity with the lubrication of H_3PO_4 solution in vacuum(highest vacuum degree <10–4 torr) for the first time by performing a pre‐running process in air before running in...This study achieved water‐based superlubricity with the lubrication of H_3PO_4 solution in vacuum(highest vacuum degree <10–4 torr) for the first time by performing a pre‐running process in air before running in vacuum. The stable water‐based superlubricity was sustainable in vacuum(0.02 torr) for 14 h until the test was stopped by the user for non‐experimental factor. A further analysis suggested that the superlubricity may be attributed to the phosphoric acid–water network formed in air, which can efficiently lock water molecules in the liquid lubricating film even in vacuum owing to the strong hydrogen bond interaction. Such capability to lock water is strongly affected by the strength of hydrogen bond and environmental conditions. The realization of water‐based superlubricity with H_3PO_4 solution in vacuum can lead to its application in space environment.展开更多
Superlubricity,the state of ultralow friction between two sliding surfaces,has become a frontier subject in tribology.Here,a state-of-the-art review of the phenomena and mechanisms of liquid superlubricity are present...Superlubricity,the state of ultralow friction between two sliding surfaces,has become a frontier subject in tribology.Here,a state-of-the-art review of the phenomena and mechanisms of liquid superlubricity are presented based on our ten-year research,to unlock the secrets behind liquid superlubricity,a major approach to achieve superlubricity.An overview of the discovery of liquid superlubricity materials is presented from five different categories,including water and acid-based solutions,hydrated materials,ionic liquids(ILs),two-dimensional(2D)materials as lubricant additives,and oil-based lubricants,to show the hydrodynamic and hydration contributions to liquid superlubricity.The review also discusses four methods to further expand superlubricity by solving the challenge of lubricants that have a high load-carrying capacity with a low shear resistance,including enhancing the hydration contribution by strengthening the hydration strength of lubricants,designing friction surfaces with higher negative surface charge densities,simultaneously combining hydration and hydrodynamic contribution,and using 2D materials(e.g.,graphene and black phosphorus)to separate the contact of asperities.Furthermore,uniform mechanisms of liquid superlubricity have been summarized for different liquid lubricants at the boundary,mixed,and hydrodynamic lubrication regimes.To the best of our knowledge,almost all the immense progresses of the exciting topic,superlubricity,since the first theoretical prediction in the early 1990s,focus on uniform superlubricity mechanisms.This review aims to guide the research direction of liquid superlubricity in the future and to further expand liquid superlubricity,whether in a theoretical research or engineering applications,ultimately enabling a sustainable state of ultra-low friction and ultra-low wear as well as transformative improvements in the efficiency of mechanical systems and human bodies.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
基金National Natural Science Foundation of China(Grant No.51925506)National Key R&D Program of China(Grants No.2020YFA0711003).
文摘Water-based lubrication is an effective method to achieve superlubricity,which implies a friction coefficient in the order of 10−3 or lower.Recent numerical,analytical,and experimental studies confirm that the surface force effect is crucial for realizing water-based superlubricity.To enhance the contribution of the surface force,soft and plastic materials can be utilized as friction pair materials because of their effect in increasing the contact area.A new numerical model of water-based lubrication that considers the surface force between plastic and elastic materials is developed in this study to investigate the effect of plastic flow in water-based lubrication.Considering the complexity of residual stress accumulation in lubrication problems,a simplified plastic model is proposed,which merely calculates the result of the dry contact solution and avoids repeated calculations of the plastic flow.The results of the two models show good agreement.Plastic deformation reduces the local contact pressure and enhances the function of the surface force,thus resulting in a lower friction coefficient.
文摘The micro crack of aluminum sheet during cold rolling lubricated with emulsions is investigated. Experi-ments show that micro cracks occur after cold rolling process and this is attributed to various parameters, for instance, the thin oxide film formed at the sheet surface. The micro crack spacing thus becomes an important parameter which deserves more concerns. The aspect ratio of these micro cracks is then analyzed theoreti-cally, which takes into consideration of the oxide fracture process. The good agreement between the obser-vations and the theoretical predictions validates the analysis. The approach can shed some new lights on the mechanical process of aluminium sheet during cold rolling.
基金financially supported by the National Natural Science Foundation of China(Grant No.51925506).
文摘Polyether ether ketone(PEEK)is a widely used material for friction pairs due to its excellent mechanical strength,good wear resistance,and chemical inertness.However,some modifications are necessary when PEEK is used as a water-lubricated friction pair.In this study,a novel sulfonation method was developed to design a water-lubricated friction pair with ultralow friction,good wear resistance,and high loading capacity.PEEK powders were sulfonated using ClSO3H and sintered to form bulk plastic.The sulfonated PEEK(SPEEK)plastic exhibited good tribological properties.At a low sliding speed,the friction coefficient was smaller than 0.02 when a 3 wt% NaCl solution was used as the lubricant.The order of magnitude of the wear rate was as low as 10^(-8) mm^(3)/(N·m).The mechanism of friction reduction was mainly hydration lubrication.The negatively charged -SO_(3)^(-) groups on the friction pair can adsorb hydrated Na+cations by electrostatic interactions.These hydrated Na+cations have a high load capacity and low shearing resistance.The ultralow wear mechanism observed in this study is possibly due to ultralow friction properties of the friction pairs prepared through the proposed sulfonation and thermoforming procedures.
基金grateful for the financial support from the National Natural Science Foundation of China(51875486 and 52122507)Sichuan Science and Technology Program(2021YFSY0017)the Fundamental Research Funds for the Central Universities(2682021ZTPY095).
文摘Achievement of steady and reliable super-low friction at the steel/steel contact interface,one of the most tribological systems applied for mechanical moving parts,is of importance for prolonging machine lifetime and reducing energy consumption.Here we reported that the superlubricity performance of the steel/steel sliding interface lubricated with tiny amounts of diketone solution strongly depends on the oxygen content in surrounding environment.The increase of oxygen not only significantly shortens the initial running-in time but also further reduces the stable coefficient of friction in superlubricity stage due to the enhancement of tribochemical reactions.On the one hand,more severe oxidation wear occurring at higher oxygen content facilitates material removal of the contact interface,lowering the contact pressure and the corresponding initial friction.On the other hand,the growth of iron ions during the shear process in high oxygen environment promotes the formation of chelate which acted as an effective lubricated film chemisorbed at the steel/steel friction interface to further lower the interfacial friction.The results provide a new opportunity to further optimize the tribological performance of diketone superlubricity system,especially towards the lubrication of mechanical engineering materials.
基金supported by the National Key Basic Research and Development Program(973)of China(2013CB934200)Foundation for the Supervisor of Beijing Excellent Doctoral Dissertation(20111000305)the National Natural Science Foundation of China(NSFC)(Nos.51321092,51027007).
文摘In this study,we address the superlubricity behavior of sapphire against ruby(or sapphire against itself)under phosphoric acid solution lubrication.An ultra-low friction coefficient of 0.004 was obtained under a very high contact pressure,with a virgin contact pressure up to 2.57 GPa.Related experiments have indicated that the load,sliding speed,and humidity of the test environment can affect superlubricity to some degree,so we tested variations in these conditions.When superlubricity appears in this study a thin film is present,consisting of a hydrogen bond network of phosphoric acid and water molecules adsorbed on the two friction surfaces,which accounts for the ultra-low friction.Most significantly,the wear rate of the sapphire and ruby in the friction process is very slow and the superlubricity state is very stable,providing favorable conditions for future technological applications.
基金supported by the National Key Basic Research(973)Program of China(No.2013CB934200)the National Natural Science Foundation of China(Nos.51222507,51335005,51321092).
文摘In this work,a super-low friction coefficient of 0.003 was found between a silicon nitride ball and a sapphire plate lubricated by phosphoric acid solution.The wear mainly occurred in the running-in period and disappeared after superlubricity was achieved.The friction coefficient was effectively reduced from 0.3 to 0.003 at a constant speed of 0.076 m/s,accompanied by a 12-nm-thickness film.The lubrication regime was indicated to change from boundary lubrication in the running-in period to elastohydrodynamic lubrication in the superlubricity period,which is also supported by the results of the friction coefficient versus sliding speed.In addition,the experimental results showed good agreement with theoretical calculations based on the elastohydrodynamic lubrication theory,suggesting a significant hydrodynamic effect of phosphoric acid on superlubricity.
基金financially supported by the National Natural Science Foundation of China(Grant Nos.51527901 and 51335005)。
文摘Graphene is a promising material as a lubricant additive for reducing friction and wear.Here,a dispersing method which combines chemical modification of graphene by octadecylamine and dicyclohexylcarbodiimide with a kind of effective dispersant has been successfully developed to achieve the remarkable dispersion stability of graphene in base oil.The stable dispersion time of modified graphene(0.5 wt%)with dispersant(1 wt%)in PAO-6 could be up to about 120 days,which was the longest time reported so far.At the same time,the lubricant exhibits a significant improvement of tribological performance for a steel ball to plate tribo-system with a normal load of 2 N.The coefficient of friction between sliding surfaces was~0.10 and the depth of wear track on plate was~21 nm,which decreased by about 44%and 90%when compared to pure PAO-6,respectively.Furthermore,the analysis of the lubricating mechanisms in regard to the sliding-induced formation of nanostructured tribo-film has been contacted by using Raman spectra and TEM.
基金The work is financially supported by the National Key Research and Development Program(No.2018 YFB2002204)the National Natural Science Foundation of China(Grant Nos.51925506 and 51527901).
文摘High-temperature solid lubricants play a significant role in the hot metal forming process.However,preparing high-temperature solid lubricant is formidably challenging due to the stern working conditions.Here we successfully develop a new type of eco-friendly high-temperature graphite-based solid lubricant by using amorphous silica dioxide,aluminum dihydrogen phosphate,and solid lubricant graphite.The solid lubricating coating exhibits excellent tribological properties with a very low friction coefficient and good wear protection for workpiece at high temperature under the air atmosphere.An array of analytical techniques reveals the existence of solid lubricant graphite in the lubricating coating after the high-temperature friction test.A synergistic effect between the protective surface film and the solid lubricant graphite is proposed to account for such superior lubricating performance.This work highlights the synergistic effect between the protection layer and the lubricant graphite and further provides the insight in designing the high-temperature solid lubricant.
基金We gratefully acknowledge all the contributors that made this research possible,all the sample donors for this study,and all the clinicians for their assistance in recruiting participants to the study.This work was supported by the grant from the National Natural Science Foundation of China(31401082).
文摘The unusual chromosome 11q23.3 harboring the apolipoprotein(APO)gene cluster has been well documented for its essential roles in plasma lipid-related traits and atherosclerotic cardiovascular diseases.However,its genetic architecture and the potential biological mechanisms underlying complex phenotypes have not been well assessed.We conducted a study for this target region in a Han Chinese population through a stepwise forward framework based on massive parallel sequencing,association analyses,genetic fine mapping,and functional interpretation.The present study identified new meaningful genetic associations that were not simply determined by statistical significance.In addition to the APOA5 gene,we found robust evidence of the genetic commitments of APOC3 and APOA1 to blood lipids.Several variants with high confidence were prioritized along with the potential biological mechanism interpretations in the wake of adaptive fine-mapping analyses.rs2849174 in the APOC3 enhancer was discovered with an unrivaled posterior probability of causality for triglyceride levels and could mediate APOC3 expression through enhancer activity modulated by a combination of histone modifications and transcription factor accessibility.Similarly,multiple lines of evidence converged in favor of rs3741297 as a causal variant influencing high-density lipoprotein cholesterol.Our findings provided novel insights into this genomic locus in the Chinese population.
文摘This note presents the principle and structure of a tribological measure for floppy disks. The precision of the force measuring system is 1 mN in loading and 3×10-6 N in friction. The resolution of the film thickness between head and floppy disk is 0.5 nm in the vertical and 1.5 nm in the horizontal direction. in order to investigate the tribological characteristics of floppy disks, six types of floppy disks have been tested and the floating properties of these disks are also studied with film measuring system. The experimental results of the surface morphology and friction coefficient of these floppy disks using the atomic force microscope/friction force mcroscope (AFM/FFM) are in accordance with the conclusion made by our own measuring system. The experimental results show that the air film thickness between head and disk is of the same order as the surface roughness of floppy disks.
基金The authors would like to thank Dongzhou ZHAN for technological support during friction experiment.This work was supported by the National Natural Science Foundation of China(Nos.51925506,51975314,51935006,and 51527901).
文摘Hydrogenated amorphous carbon(a-C:H)films are capable of providing excellent superlubricating properties,which have great potential serving as self-lubricating protective layer for mechanical systems in extreme working conditions.However,it is still a huge challenge to develop a-C:H films capable of achieving robust superlubricity state in vacuum.The main obstacle derives from the lack of knowledge on the influencing mechanism of deposition parameters on the films bonding structure and its relation to their self-lubrication performance.Aiming at finding the optimized deposition energy and revealing its influencing mechanism on superlubricity,a series of highly-hydrogenated a-C:H films were synthesized with appropriate ion energy,and systematic tribological experiments and structural characterization were conducted.The results highlight the pivotal role of ion energy on film composition,nanoclustering structure,and bonding state,which determine mechanical properties of highly-hydrogenated a-C:H films and surface passivation ability and hence their superlubricity performance in vacuum.The optimized superlubricity performance with the lowest friction coefficient of 0.006 coupled with the lowest wear rate emerges when the carbon ion energy is just beyond the penetration threshold of subplantation.The combined growth process of surface chemisorption and subsurface implantation is the key for a-C:H films to acquire stiff nanoclustering network and high volume of hydrogen incorporation,which enables a robust near-frictionless sliding surface.These findings can provide a guidance towards a more effective manipulation of self-lubricating a-C:H films for space application.
基金financial support from the National Natural Science Foundation of China (Nos.51527901,51405256)Self-developed Project of State Key Laboratory of Traction Power (No.2017TPL_Z02)
文摘This study achieved water‐based superlubricity with the lubrication of H_3PO_4 solution in vacuum(highest vacuum degree <10–4 torr) for the first time by performing a pre‐running process in air before running in vacuum. The stable water‐based superlubricity was sustainable in vacuum(0.02 torr) for 14 h until the test was stopped by the user for non‐experimental factor. A further analysis suggested that the superlubricity may be attributed to the phosphoric acid–water network formed in air, which can efficiently lock water molecules in the liquid lubricating film even in vacuum owing to the strong hydrogen bond interaction. Such capability to lock water is strongly affected by the strength of hydrogen bond and environmental conditions. The realization of water‐based superlubricity with H_3PO_4 solution in vacuum can lead to its application in space environment.
基金This work is financially supported by the National Key R&D Program of China(No.2018YFB2002204)the National Natural Science Foundation of China(No.51925506)。
文摘Superlubricity,the state of ultralow friction between two sliding surfaces,has become a frontier subject in tribology.Here,a state-of-the-art review of the phenomena and mechanisms of liquid superlubricity are presented based on our ten-year research,to unlock the secrets behind liquid superlubricity,a major approach to achieve superlubricity.An overview of the discovery of liquid superlubricity materials is presented from five different categories,including water and acid-based solutions,hydrated materials,ionic liquids(ILs),two-dimensional(2D)materials as lubricant additives,and oil-based lubricants,to show the hydrodynamic and hydration contributions to liquid superlubricity.The review also discusses four methods to further expand superlubricity by solving the challenge of lubricants that have a high load-carrying capacity with a low shear resistance,including enhancing the hydration contribution by strengthening the hydration strength of lubricants,designing friction surfaces with higher negative surface charge densities,simultaneously combining hydration and hydrodynamic contribution,and using 2D materials(e.g.,graphene and black phosphorus)to separate the contact of asperities.Furthermore,uniform mechanisms of liquid superlubricity have been summarized for different liquid lubricants at the boundary,mixed,and hydrodynamic lubrication regimes.To the best of our knowledge,almost all the immense progresses of the exciting topic,superlubricity,since the first theoretical prediction in the early 1990s,focus on uniform superlubricity mechanisms.This review aims to guide the research direction of liquid superlubricity in the future and to further expand liquid superlubricity,whether in a theoretical research or engineering applications,ultimately enabling a sustainable state of ultra-low friction and ultra-low wear as well as transformative improvements in the efficiency of mechanical systems and human bodies.
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).