Multialkylated Cyclopentanes Research Articles

Modification of POSS and their tribological properties and resistant to space atomic oxygen irradiation as lubricant additive of multialkylated cyclopentanes

Developing functional additive resistant to space atomic oxygen (AO) irradiation through simple molecular design and chemical synthesis to enhance the lubricating performance of multialkylated cyclopentanes (MACs) oil is a significant challenge. Herein, sulfur-containing polyhedral oligomere silsesquioxane (POSS) were synthesize via a click-chemistry reaction of octavinyl polyhedral oligomeric with alkyl sulfide. The reduce-friction (RF), anti-wear (AW) properties and anti-AO irradiation of POSS-S-R as MACs base oil additives in atmospheric and simulated space environments were systematically investigated for the first time. Results demonstrate that POSS-S-R not only possesses outstanding anti-AO irradiation capacity but also effectively improves the RF and AW of MACs in atmospheric or simulated space surroundings. This improvement is due to the excellent anti-AO irradiation properties of the POSS structure itself and the high load-carrying ability of silicon-containing and sulfur-containing compounds generated by tribo-chemical reactions, which effectively separates the direct contact of the friction interface. We believe that this synthesized POSS-S-R is a promising additive for space lubricants.

MoS2 Lubricating Film Meets Supramolecular Gel: A Novel Composite Lubricating System for Space Applications.

In the field of space mechanical lubrication, to improve the reliability and life of space lubrication, solid lubricating film-liquid lubricant composite lubrication has been used in recent years. This lubrication method can improve the durability of sliding friction mating surfaces, reduce equipment wear, and extend the service life of motion mechanisms. However, due to unstable factors such as volatilization and creeping of liquid lubricants in microgravity and ultra-high-vacuum environments, the solid lubricating film wears out after long-term use and produces wear debris and other unfavorable factors. To solve the above problems, this study proposes a novel composite lubrication system constituting a MoS2 film in combination with a supramolecular gel. The tribological performance of this lubrication system establishes an extended service life with a lower wear rate compared to the MoS2 film, regardless of functioning in vacuum or atmospheric conditions. More importantly, the results of the irradiation experiment demonstrate that MoS2-gel exhibits better anticreep performance as compared to MoS2-oil when exposed to atomic oxygen and ultraviolet light for 4 h. The analysis of this composite lubrication mechanism also reveals the formation of a continuous transfer film on the surface of the friction pairs by virtue of the outstanding synergistic effect between the MoS2 film and the gel. MoS2 debris is present in the gel as an additive, and the gel is capable of replenishing automatically once the MoS2 film is depleted. Moreover, the strong anticreep properties of the gel are attributable to the multialkylated cyclopentane oil being trapped by the intricate reassembling of the gelator network. It is firmly believed that this novel MoS2-gel composite lubrication system may have good prospective applications in space and special machinery domains.

Tribochemical degradation of vacuum‐stable lubricants: A comparative study between multialkylated cyclopentane and perfluoropolyether in a vacuum ball‐on‐disc and full‐bearing tests

AbstractIn this study, the decomposition of a multialkylated cyclopentane (MAC) and a perfluoro‐poly‐ether (PFPE) lubricant was investigated in a ball‐on‐disc sliding test under vacuum and in a rolling contact fatigue (RCF) test on full bearings. In situ mass spectrometry was conducted to study the tribochemical formation of hydrogen in a steel‐on‐steel ball‐on‐disc sliding contact. Further investigations on lubricant degradation in rolling‐sliding contact indicated fragmentation and oxidation reaction of the MAC oil by interaction with the oxide layer and the nascent bearing steel.Finite element method (FEM) analysis was carried out to model the contact in the ball‐on‐disc experiments and to extract contact surface temperature fields.Post‐RCF hydrogen analysis of bearing components indicated increased hydrogen content in the samples lubricated with the MAC fluid. The RCF tests with PFPE did not indicate any signs of surface damage.

Exploring Lubrication Function of MACs Greases for TC4 Alloy Under Sliding and Fretting Conditions

Lubrication function of multialkylated cyclopentanes (MACs) greases for the contact TC4/Steel was investigated in detail under the sliding and fretting conditions, and the worn tracks were measured by surface/interface analysis techniques to explore the friction mechanisms. The results demonstrate that these lubricating greases have good friction-reducing function under fretting and sliding conditions, and their friction reduction is superior to wear resistance, especially calcium sulfonate complex grease. Good lubrication function of MACs greases under sliding friction mainly depends on synergies of grease-film and friction-induced chemical reaction film. Fretting behaviors depend on not only grease-film and chemical reaction film, but also fretting wear mechanisms including abrasion, oxidation, and delamination.

Comparing space adaptability of diamond-like carbon and molybdenum disulfide films toward synergistic lubrication

Space irradiation-induced damage to onefold lubricants including four multialkylated cyclopentanes (MACs) space greases, Chromium doped diamond-like carbon (Cr-DLC) and molybdenum disulfide (MoS2) films was first investigated under simulated space environment (atomic oxygen (AO) and proton (PR)). Then solid-grease synergistic lubrication systems were prepared via spinning four space greases on Cr-DLC and MoS2 film, and their tribological behaviors were evaluated under simulated space environment including ultra-vacuum, AO and PR irradiation, low temperature (−100 °C). The irradiated damage mechanism and friction mechanism were explored by surface/interface analysis techniques. The results demonstrates that Cr-DLC film have better space adaptability than MoS2 film because irradiation induced partial transition of Cr-DLC’s micro-structure with the decrease in ID/IG ratio from 1.50 to 1.26 and the increase of sp3 content from 0.24 to 0.59, while the surface morphology and micro-structure of MoS2 film have dramatically changed. Solid-grease synergistic lubrication systems provide excellent friction-reducing and anti-wear behaviors (friction coefficient can be reduced up to below 0.05 under the special working conditions). Such excellent tribological performance of Cr-DLC-grease lubrication coatings is attributed to the friction-induced graphitization at the sliding interface, while that of MoS2 film mainly depends on its original structure/merits under greases lubrication.

Probing the effect of thickener on tribological properties of lubricating greases

Abstract To evaluate the effect of thickener on tribological properties of lubricating greases, four multialkylated cyclopentanes (MACs) greases were prepared by using lithium complex soap, polyurea, sulfonate calcium complex soap and polytetrafluoroethylene (PTFE). The physical properties and tribological behaviors of four MACs greases were investigated in detail, the worn surfaces were also investigated for understanding the friction mechanism. The results show that calcium sulfonate complex grease (CSCG) has impressive and comprehensive performance including high dropping point, good thermal and oxidative stability, excellent lubrication behaviors, which is mainly attributed to the nature and structure of thickener and the synergies of grease-film and tribo-chemical reaction film comprised of sulfates and complicated oxides.

AntiWear Effect of Mo and W Nanoparticles as Additives for Multialkylated Cyclopentanes Oil in Vacuum

This work examined friction-reducing and antiwear behaviors of multialkylated cyclopentanes (MACs) oil with Mo and W nanoparticles as additives under vacuum condition (∼10−4 Pa). The tribological evaluation was conducted on a vacuum four-ball tribometer. The results suggested that the MACs oil exhibited the transient high friction in vacuum, resulted into severe adhesive wear to the steel friction pairs. The Mo and W nano-additives could effectively eliminate the severe adhesive wear. When added with Mo nanoparticles, the lubricating life of MACs oil could be prolonged due to the retarded decomposition of MACs, which should be ascribed to the formation of Mo metallic boundary films on steel ball surfaces that was confirmed by the surface analysis. As for W nanoparticle additives, the rolling effect as nano-bearings and the abrasive wear of larger particles due to the aggregation of W nanoparticles are the dual tribological mechanisms.

Combined Effect of Phosphate Ester and OBCS on Tribochemical Decomposition of Hydrocarbon Oil on Nascent Steel Surfaces

Combined effect of additives, over-based calcium sulfonate (OBCS) and phosphate ester were investigated on the decomposition of multi-alkylated cyclopentane (MAC). The decomposition processes of the lubricants on the nascent surface of bearing steel AISI52100 were investigated using a ball-on-disk friction tester in a vacuum chamber with a quadrupole mass spectrometer. According to our previous report, the decomposition reaction can be deactivated by the effect of lubricant additives such as organic sulfides and organic phosphates. In this report, the order of efficiency in decreasing the decomposition rate was: OBCS < phosphate ester < phosphate ester + OBCS. The mixed additive was more effective and stable for suppression of the tribochemical decomposition under severe contact conditions of high load and high sliding speed. The critical load for the decomposition which is the lowest load to detect the gas evolution due to the decomposition increased with the mixed additive. XPS and TOF–SIMS analysis revealed that additive molecules competitively chemisorbed on the steel surface and reaction occurred by the formation of calcium phosphate, which covered the steel surface and deactivated the catalytic activity of active sites leading to deactivation. As a result, decomposition of MAC decreased significantly by the combined effect of the additives.

Friction and wear performance of dual lubrication systems combining WS2–MoS2 composite film and low volatility oils under vacuum condition

In the present work, WS2–MoS2 nanocomposite films were sputtered, based on which solid/liquid-lubrication systems were realized by combining the WS2–MoS2 films with space oils including MACs (multialkylated cyclopentanes) and CPSO (chlorinated-phenyl with methyl-terminated silicone oil). The tribological behaviors of the solid/liquid systems were investigated in vacuum. It was revealed that in comparison to pure WS2 film, the WS2–MoS2 composite film exhibited an enhanced tribological performance. Moreover, our results identified that the WS2–MoS2/MACs system integrated better the advantages of the solid and liquid lubrications and thereby a synergistic lubricating effect was generated. A tribological model was established to explain the synergistic lubricating mechanism.

The Effect of the Chemical Structures of Synthetic Hydrocarbon Oils on Their Tribochemical Decomposition

Under boundary lubrication conditions, the formation of a highly active nascent surface can catalyze the decomposition of lubricant oils. Extreme pressure additives can reduce this decomposition but have undesirable environmental impacts, and so it is necessary to develop eco-friendly lubricants. The following study investigated the effects of the chemical structures of hydrocarbon oils on their tribochemical decomposition by comparing an alkyldiphenylether (ADE) to a multialkylated cyclopentane. The analysis of gaseous decomposition products via mass spectrometry during the application of friction showed that the multialkylated cyclopentane decomposed after an induction period of 1.95 km while the ADE did not degrade, even at a distance of 57.5 km, under the same mechanical contact conditions, and exhibited superior anti-wear properties. However, a high concentration of the ADE was necessary to extend the induction period for lubricant decomposition when it was used as an additive. Although the ADE showed high stability in response to friction, it was prone to decomposition once a nascent steel surface was formed. These decomposition characteristics of the ADE are closely related to its chemical structure, because the ether group in the ADE molecule preferentially adsorbs on metal oxide surfaces, forming a dense and robust film. In contrast, the weak bonding between adjacent alkyl groups reduces the shear strength at the interface. Both the benzene and alkyl groups of ADE molecules were found to detach, followed by the further rupture of C–C, C–H, and C–O bonds, catalyzed by active sites on the nascent surface such as surface defects.

In-situ detection of hydrogen evolution in a lubricated sliding pin on disk test under high vacuum

In the present study the decomposition mechanisms of a multi-alkylated cyclopentane (MAC) lubricant on a steel surface were investigated in a ball-on-disk sliding test under vacuum. The lubricant was analyzed in-situ using a mass-spectrometer to study possible tribochemical reactions with the metal surface. The degradation of the lubricant was correlated with the formation of gaseous reaction products including hydrogen and various alkanes and alkenes. An increased carbon concentration was detected using XPS up to a depth of 1µm below the surface of the wear track. This was attributed to reactions between the lubricant and the metal surface involving carbon chain cracking and fragmentation of the lubricant. An oxidation reaction between the lubricant and metal oxides was also identified. From the sliding test results it was shown that the rate of formation of gaseous reaction products increased with increasing load and sliding speed. Flash temperatures were calculated according to the Kuhlmann-Wilsdorf model. Finally, a correlation between the frictional power density and the evolution of hydrogen was established.

Graphene with outstanding anti-irradiation capacity as multialkylated cyclopentanes additive toward space application.

Multialkylated cyclopentanes (MACs), a class of synthetic hydrocarbon fluid have attracted intensive interest as possible space lubricants due to a series of unique physical and chemical properties. Here, we used graphene with high mechanical strength and chemical inertness as lubricant additive to explore its potential for space application. The effects of space irradiation on graphene and the tribological properties of graphene as lubricant additive were firstly investigated in detail under simulated space environment composed of high vacuum, high/low temperature and irradiation. Results demonstrate that graphene not only possesses outstanding anti–irradiation capacity but also significantly improves the space performance and tribological properties of MACs, which depends on the excellent physicochemical properties and high load-carrying ability of graphene as well as more effective separation of the sliding surfaces.

Improving Tribological Properties of Multialkylated Cyclopentanes under Simulated Space Environment: Two Feasible Approaches.

Space mechanisms require multialkylated cyclopentanes (MACs) more lubricious, more reliable, more durable, and better adaptive to harsh space environments. In this study, two kinds of additives were added into MACs for improving the tribological properties under simulated space environments: (a) solid nanoparticles (tungsten disulfide (WS2), tungsten trioxide (WO3), lanthanum oxide (La2O3), and lanthanum trifluoride (LaF3)) for steel/steel contacts; (b) liquid additives like zinc dialkyldithiophosphate (ZDDP) and molybdenum dialkyldithiocarbamate (MoDTC) for steel/steel and steel/diamond-like carbon (DLC) contacts. The results show that, under harsh simulated space environments, addition of the solid nanoparticles into MACs allows the wear to be reduced by up to one order magnitude, while liquid additives simultaneously reduce friction and wear by 80% and 93%, respectively. Friction mechanisms were proposed according to surface/interface analysis techniques, such as X-ray photoelectron spectroscopy (XPS) and time-of-flight secondary ion mass spectroscopy (TOF-SIMS). The role of solid nanoparticles in reducing friction and wear mainly depends on their surface enhancement effect, and the liquid additives are attributed to the formation of tribochemical reaction film derived from ZDDP and MoDTC on the sliding surfaces.

High-performance lubricant additives based on modified graphene oxide by ionic liquids

Graphene oxide (GO) is a layered material bearing a variety of oxygen-containing functional groups on its basal planes and edges, which allow it as a substrate to conduct a variety of chemical transformations. Here modified graphene oxide (MGO) was prepared using alkyl imidazolium ionic liquids (ILs) (1-butyl-3-methylimidazolium tetrafluoroborate (LB104), 1-butyl-3-methyl imidazolium hexafluorophosphate (LP104) and 1-hexyl-3-methylimidazolium bis(trifluoromethylsulfonyl) amide (LF106)) via epoxide ring-opening reaction, cation-π stacking or van der Waals interactions, with LB104 modified graphene (MG) exfoliated from graphite rod by a moderate electrochemical method as a comparison. The stability and tribological properties of MGO and MG as multialkylated cyclopentanes (MACs) additives were investigated in detail. The results show that GO is converted into graphene through the chemical modification using ILs, and MGO with good dispersion and stability in MACs significantly improves the tribological performance (friction and wear were reduced about 27% and 74% with pure MACs as a comparison, respectively). The excellent tribological properties are attributed to the formation of an ILs-containing graphene-rich tribofilm on the sliding surfaces, which as the third body can prevent the sliding surfaces from straight asperity contact and improve friction reducing and anti-wear behaviors.

Novel Fluorine-containing Trisilahydrocarbon Lubricants and Their Antiatomic Oxygen Irradiation under Simulated Space

Abstract The novel fluorine-containing trisilahydrocarbon lubricants with methyl and 3,3,3-trifluoropropyl substituents (named SiFCH) were synthesized. Importantly, as potential aerospace lubricants, their chemical, physical, and tribological properties under simulated atomic oxygen (AO) exposure in space environment were investigated by a laboratory-built simulation multifunctional space tribo-tester system. The results showed that the SiFCH synthetic oils possess good physical properties and favorable tribological performance, which are superior to that of multi-alkylated cyclopentanes (MACs) in terms of frictional reduction and antiwear capacity under vacuum.

Tribological Performance of Silahydrocarbons Used as Steel‐Steel Lubricants under Vacuum and Atmospheric Pressure

The silahydrocarbons of tetraalkylsilanes with different substituted alkyl groups (named as SiCH) were synthesized and evaluated as lubricants for steel‐steel contacts by a home‐made vacuum four‐ball tribometer (VFBT‐4000) under atmospheric pressure and under vacuum pressure (5 × 10−4 Pa). The SiCH oils possess better thermal stability, low temperature fluidity, and lower saturated vapor pressure than those of multialkylatedcyclopentanes (MACs). The tribological performances of the SiCH oils are also superior to those of MACs and PFPE‐Z25 in terms of friction‐reduction ability and antiwear capacity under sliding friction at vacuum. The SEM/EDS and XPS results reveal that the boundary lubricating film consisting of (‐O‐Si‐R‐)n compounds is formed by tribochemical reactions and serious adhesion wear under atmospheric pressure and the film consisting of (‐Si‐R‐Si‐)n compounds is formed on the worn surface under vacuum pressure.

Ag nanoparticle–multiply alkylated cyclopentane composite ultrathin films fabricated by one step dip coating process and its tribological performances

Herein, Ag nanoparticle–multialkylated cyclopentane (MAC) composite ultrathin films (abridged as Ag–MAC) were fabricated by dip-coating method. X-ray diffraction analysis, transmission electron microscopy, Fourier transform infrared spectroscopy, thermal gravimetric analysis, and atomic force microscopy were used to characterize the so-obtained Ag nanoparticles and Ag–MAC films. Their tribological behaviors were investigated by comparing with 3-aminopropyl triethoxysilane self-assembled monolayers (abridged as APS SAMs) and APS–MAC dual-layer film and results showed that Ag–MAC films possessed much better load-bearing capacity and anti-wear ability, which could be due to the combined effects of the high bearing capacity and antiwear ability of Ag nanoparticles and excellent lubricating properties of MACs.

Vacuum tribological performance of phosphonium-based ionic liquids as lubricants and lubricant additives of multialkylated cyclopentanes

The tribological effects of tetraalkylphosphonium phosphate ionic liquids (PP-ILs) as lubricants and lubricant additives of multialkylated cyclopentanes (MACs) was evaluated in vacuum (10−4Pa) by a vacuum four-ball tribometer. Results showed that the transient seizure-like high friction appearing for MACs could be effectively eliminated by neat PP-ILs or by adding the PP-ILs with long alkyl chain into MACs. Confirmed by the surface analysis, the improved tribological performances could be ascribed to the high load-carrying capacity of ionic liquids and the protective films formed on the contact surfaces through the tribochemical reaction between the PP-ILs and fresh steel surfaces under the boundary lubrication.

Anti-wear and friction-reduction mechanism of Sn and Fe nanoparticles as additives of multialkylated cyclopentanes under vacuum condition

The effect of Sn and Fe nanoparticles as additives of multialkylated cyclopentanes (MACs) was investigated in vacuum (∼10−4 Pa) by a vacuum four-ball tribometer. Results showed that the steel balls exhibited the transient seizure-like high friction when lubricated with MACs base oil in vacuum, while introducing Sn and Fe nanoparticles could effectively eliminate it. Moreover, Sn nanoparticles were more effective on friction-reduction and frictional heat reduction, but less effective on anti-wear ability in comparison with Fe nanoparticles. Confirmed by the surface analysis, the improved tribological performances should be ascribed to a protective film with low shear stress and hardness formed on the worn surface.

The anti-seizure effect of Ag nanoparticles additive in multialkylated cyclopentanes oil under vacuum condition

The effect of surface-modified Ag nanoparticles as additives of multialkylated cyclopentanes (MACs) was investigated in air and vacuum by a vacuum four-ball tribometer. The results showed that both the MACs and MACs containing Ag nanoparticles exhibited steady and low friction coefficients and slight wear in air. However, under vacuum conditions, MACs showed the initial seizure-like high friction, while introducing Ag nanoparticles could effectively eliminate it. Confirmed by the surface analysis, the improved tribological performances caused by Ag nanoparticles could be ascribed to the metal Ag boundary film formed on the friction pair surfaces during tests.