The sustainability of biolubricants as green alternatives for industrial and machinery lubrication is questionable due to their unreliable oxidative stability, high pour point, and easy accumulation of contaminants that affect their tribological performance. Bio-based ionic liquid (IL) lubricants, which are environmentally friendly liquid state salts, have overcome these concerns related to conventional biolubricants. The present study investigates the effect of varying cation–anion moieties in ILs to understand their tribological performance and industrial viability. The industrial viability was analyzed by scaling their friction and wear behaviors against conventional biolubricants, and petroleum-based oils. The study investigated both bio- and nonbio-based ILs. Among the ILs examined, P 666,14 Saccharinate, P 666,14 Salicyate, and P 666,14 Benzoate were found to have superior tribological properties. The presence of large alkyl cation chain length and large aromatic anion ring size in ILs can effectively reduce friction and wear. This study details the mechanism by which the structural combinations of anion and cation in ILs define the tribological behavior of the bulk IL. Additionally, this study also highlights the environmentally benign nature of IL lubricants for possible industrial applications.

Three kinds of S- and P-free borate esters containing N with different alkyl chain lengths were prepared by using boric acid, ethanolamine, and alkyl-alcohol as the starting materials. The chemical structure of the products was analyzed by means of Fourier transformation infrared spectrometry, elemental analysis, and so on. The thermal stability of the products was evaluated by thermogravimetric analysis. The tribological properties of the synthesized borate esters as lubricating oil additives in liquid paraffin were evaluated using a four-ball friction and wear tester while the morphologies of the worn scars of the steel balls were observed using a scanning electron microscope. The chemical components on the worn surfaces of the steel balls were analyzed using an X-ray photoelectron spectroscopy. Results show that all the three kinds of synthetic borate esters as additives in liquid paraffin possess good antiwear performance and may be used as promising S- and P-free environmentally acceptable lubricating oil additives. Particularly, borate ester with short alkyl chain length at a low concentration in liquid paraffin was more effective in reducing wear, and the antiwear ability of the additives decreased with increasing alkyl chain length. The antiwear ability of the N-containing borate esters as additives in liquid paraffin might be closely related to the formation of hydrogen bonds via N with a high electronegativity and small atomic radius and the easy permeation of electron-deficient B on the rubbing steel surfaces.

Addressed is the mechanism of finishing processes for a workpiece surface using hard abrasive tools such as grinding, abrasive paper, and filing. The mechanism is intended to monitor the gradual changes of the workpiece surface state roughness as the tool is applied for several strokes. Based on a number of common features, the present study simulates each rubbing stroke as a Markov process, and each set of several strokes as a Markov chain. In the simulating model, the discrete probabilistic properties of a specific tool abrasive surface can be expressed in terms of a corresponding Markov matrix operator. Thus, the tool action after one rubbing stroke is obtained via a matrix mapping from a given state roughness to a subsequent state roughness of the workpiece surface. Although the suggested model is capable to handle a comprehensive finishing mechanism, the study focuses on the simple case of zero feeding using a hard abrasive tool, in which the Markov matrix shrinks to a special triangular form. Main findings show that major aspects of the tool surface are transferred to the stepwise roughness state of the workpiece immediately after the first stroke. In addition, regardless of the initial roughness state of the workpiece surface, whether with flat or randomly distributed heights, the ultimate state roughness is unique and definitely features the theoretical case of a plain flat surface. However, this theoretical case is infeasible since it can only be reached after infinite number of strokes.

The tribological properties of Mo S 2 microsized spheres ( MS - Mo S 2 ) with diameter of 0.5 – 3 μ m modified by self-prepared surfactant quaternary ammonium salt of 2-undecyl-1-dithioureido-ethyl-imidazoline (SUDEI) as an additive in base oil 500 SN were investigated and compared with those of commercial colloidal Mo S 2 ( CC - Mo S 2 ) on a four-ball tester and an Optimol SRV oscillating friction and wear tester in a ball-on-disk contact configuration. The worn surfaces of the bottom flat disk were examined with scanning electron microscopy and X-ray photoelectron spectroscopy. It was found that the Mo S 2 microsized spheres product was a much better extreme-pressure additive and antiwear and friction-reduction additive in 500 SN than commercial colloidal Mo S 2 ( CC - Mo S 2 ) . Under the appropriate concentration of 0.1% and 0.25% for MS - Mo S 2 and CC - Mo S 2 and the load of 400 N , the friction coefficient of MS - Mo S 2 /oil and CC - Mo S 2 /oil decreased about 25.0% and 12.5% and the wear volume loss decreased about 50.4% and 12.9% compared with the pure base stock. The boundary lubrication mechanism could be deduced as the effective chemical adsorption film formed by the long chain alkyl ( C 11 H 23 ) and active elements (S and N) in the surfactant SUDEI and tribochemical reaction film composed of the tribochemical reaction products.

The effects of wall surface features on the rheological properties and phase orientation of liquid crystalline polymer (LCP) melts flowing in a nanochannel have been first investigated by molecular dynamics (MD) simulations. The surfaces are modeled as rough atomic serrated walls whereby the roughness is characterized by the period and amplitude of serration. The molecular chains of LCPs are depicted by a newly developed molecular model named the GB-spring-bead model. Through simulating the phase formation of LCP melts, the new model was evaluated and the results have shown the new model is efficient and accurate to describe semi-flexible main-chain LCP molecules. MD simulations of the effect of wall surface features on the LCP shear flow were conducted and the results have revealed the surface features affect greatly the rheological properties and phase orientations of LCP melts in a nanochannel (the distance between the upper wall and the lower wall is 12.8 nm ). Findings in this study provide very useful information in the injection molding of plastic products with nanofeatures.

In this paper Spartan 02, a molecular dynamics software, is used to analyze and predict the tribological properties of coconut oil in a qualitative manner on the basis of carbon chain length of the constituent fatty acids, their polarity (net electrostatic charge, Q r ), the energies of the molecular orbitals E _ H O M O (energy of the highest occupied molecular orbital), and E _ L U M O (energy of the lowest unoccupied molecular orbital), and the heats of formations ( H-Form ) of the iron soaps of respective fatty acids. Tribological properties of the constituent fatty acids of coconut oil were evaluated using a four-ball tester as per ASTM D4172 method. The experimental results showed good correlation to the selected quantum chemical descriptors. The influence of an anti-wear additive on the tribological performance of coconut oil and the optimum additive concentration were also evaluated experimentally.

Wear of ultra-high molecular weight polyethylene (UHMWPE) continues to be a major obstacle limiting the longevity of total joint replacements. Efforts to solve the wear problem in UHMWPE have resulted in numerous studies dealing with the microstructure, morphology, and mechanical properties of this polymer. However, the fundamental wear mechanisms at different material length scales in total joint replacements remain elusive. Consequently, a systematic investigation of the initial stage of the wear process was performed in this study in order to obtain insight into the origins of wear in UHMWPE at submicrometer scales. Sliding experiments were performed with both unmodified and crosslinked (by gamma radiation treatment) UHMWPE subjected to reciprocating sliding against Co-Cr alloy in a bath of bovine serum under ranges of mean contact pressure and sliding speed typical of knee joints. Nanoindentation and optical, scanning electron, and transmission electron microscopy were used to examine the effect of crosslinking on the nanomechanical properties, dominant wear mechanisms, and microstructure of UHMWPE. The fundamental wear micromechanisms of unmodified and crosslinked UHMWPE are interpreted in the context of coefficient of friction, wear factor, creep, adhesion force, and microstructure results.

Chemical degradation of lubricant fluids of perfluoropolyether (PFPE), such as Fomblin Z-DOL, Fomblin AM-2001, Fomblin Z-25, Demnum SP-3, and Demnum SA, with bivalent metal ions was examined. The respective reaction mechanisms involve an ether cleavage process which is caused by the coordination of metal ions with oxygen atoms in the main chains of the PFPE. Metal ions were evaluated for their ability to degrade the PFPE, and the results demonstrate that the ions ranking in terms of this ability is as follows: Cu 2+ > Ni 2+ > Co 2+ > Fe 2+ > Mn 2+ > Mg 2+ . This trend can be explained by the ionization potentials of the metal atoms. For an identical metal ion, the Demnum lubricants showed a greater stability than the Fomblin lubricants.

The study of bearings subjected to impulsive loads have previously showed that inertia effects and surface accelerations play an important role in the bearing response. Although the lubricant was considered Newtonian, this assumption is no longer valid with modern lubricant. In industrial applications, mineral lubricants are added to several long soluble chains of polymer in order to conserve optimum properties under different operating conditions. The addition of these polymers results in the drop of viscosity under high shear-rate, in the range of 10 −6 –10 −8 s −1 . This study presents a continuation of previous works. It examines the influence of both effects, the decrease in viscosity and the fluid inertia, in a journal bearing under impulsive loads. Using the power-law model, the results show important differences in shaft responses compared to the Newtonian cases. Furthermore, in high shear-thinning effects, a reduction of lubricant capacity to absorb sudden dynamic loads is observed.

In order to examine the fundamental boundary lubrication properties of ceramics, reciprocating friction experiments of silicon based ceramics such as silicon carbide and silicon nitride were conducted with trialkyl phosphites and other oil additives. When ceramics were slid against ceramics, trialkyl phosphites with long carbon chains reduced the friction of silicon nitride markedly; the friction coefficients decreased with an increase in the carbon chain length. Other oil additives, however, did not greatly affect the friction. When ceramics were slid against metals, additives containing chlorine or sulfur increased friction of certain sliding couples. On the other hand, a trialkyl phosphite reduced friction and the friction coefficients increased with an increase in the maximum Hertzian contact pressure.

Lubrication of particulate magnetic recording media improves their mechanical durability in sliding and flying by several orders of magnitude compared with unlubricated media. Lubricant removal, degradation, and recovery were studied using microslit scanning Fourier transform infrared spectroscopy and microspot scanning X-ray photoelectron spectroscopy. These techniques measure the total and surface lubricant amounts in the porous film, respectively. Lubricant dynamics were compared for two physisorbed polyperfluoroalkylether lubricants of similar molecular weight but different molecular structure—Y with a CF 3 side group and Z with linear chains. The bulk viscosity of Y was about ten times higher than the viscosity of Z. In sliding, the lubricant removal rate of Y was significantly higher than that of Z while in flying the removal rates were reversed. Removal rates in sliding were orders of magnitude higher than those in flying. Effective lateral diffusion coefficients estimated from the rate of lubricant reflow back to the depleted tracks were close to inversely proportional to the bulk viscosity. During sliding and flying both lubricants degraded as evidenced by chemically altered lubricant detected on the surfaces after dissolution of undegraded lubricant.

Experimental investigation of the wear behavior of Magnesia Partially Stabilized Zirconia (Mg-PSZ) rubbed against itself showed that up to three orders of magnitude increase in the wear resistance can be achieved in a particular temperature range that depends on both the sliding speed and the ambient temperature. XRD analysis revealed that thermally induced phase transformation takes place on the frictional interface. Surface analysis show that wear rates at maximum wear resistance are controlled by the crack generation kinetics rather than by crack propagation kinetics. The plastic strain before fracture varies with temperature. The maximum plastic strain was observed at the temperature of maximum wear resistance. A phenomenological model is presented that provides an explanation for the wear temperature behavior of Mg-PSZ. The model is based on the following chain of events that takes place on the frictional interface: spatial overheating of the surface areas, phase transformation of the overheated areas, cooling, volume expansion, and development of a compressive stress field in the near surface volumes.

Experimental results on friction coefficients obtained with a number of model additives in a four ball test apparatus have confirmed a recently proposed model of boundary lubrication. The values of adsorption free energies, calculated from friction coefficient data, agreed very closely with the free energies of adsorption determined by contact potential difference measurements. In general, the ranking order of additives based on the free energy of adsorption was the same as the published literature. The friction coefficient data obtained here were in excellent agreement with the published data on the chain length effect, chain saturation and branching and polar end-group structure. The ranking order within each group of single chain compounds was explained by the chain dispersion interactions. In general, the greater the chain dispersion interaction, the lower the minimum friction coefficient (the friction coefficient at monolayer coverage).

The viscosity-pressure-temperature behavior of a series of 14 siloxane polymers is reported. The series of fluids includes a range of degree of polymerization and of size and nature of side radicals. The variations span the range of siloxane fluids currently available and considered as possible lubricants. The major conclusion is that the pressure viscosity coefficient considered important to elastohydrodynamic lubrication is only influenced by changing the nature of the side radical and not by the degree of polymerization or the size of alkyl side groups on the siloxane chain.

Animal joints are lubricated by two complementary mechanisms. Weeping lubrication carries most of the joint load hydrostatically, leaving only a small fraction of the total to be carried by rubbing of the solid “skeletons” of the two cartilages. This rubbing is, in turn, lubricated by the synovial mucin; i.e., by long chain polymer molecules dissolved in the joint fluid. There is good evidence that the mucin molecules adsorb to the surfaces and provide boundary lubrication. In this paper we examine further this adsorption processs using a bearing whose two surfaces are rubber and glass, respectively. It is found that the lubricating ability of the mucin is good if it is applied to the bearing in a solution with about physiological salt concentration. At higher salt concentrations the lubrication is comparatively poor, while at zero salt concentration it is very bad indeed. If, on the other hand, the mucin is applied at physiological salt concentration, and then the salt and unadsorbed mucin are washed away with distilled water the lubrication remains good, and has, on occasion, even improved. Once the mucin has been adsorbed the entire range of salt concentration can be explored, with the lubrication becoming worse at high salt concentration and then recovering in greater or lesser degree when the salt is washed off. It seems, then, that the salt concentration affects lubrication in two ways. It can upset the adsorption of the lubricating film, and it can change the lubricating effectiveness of the film once it is adsorbed.

In order to make clear the characteristics of externally pressurized gas bearings, several mathematical flow-models are constructed by making proper chains of fundamental and elemental flow-patterns and pressure changes for circular thrust bearings with single central supply hole. The suggested flow-models, which are the combination of rather simple elements to make the mathematical analysis easy, are quite effective to explain the pressure distributions, the load capacity, and the rate of flow observed experimentally over wide operating conditions. And also, these flow-models make it possible to understand the effects of the inherent compensation, the so-called restrictions in series and the occurrence of shock wave.