Antiseizure properties of aqueous solutions of compounds forming liquid crystalline structures

Amphiphilic compounds composed of a hydrophilic part and a hydrophobic alkyl chain were investigated. The compounds—sodium lauryl sulfate (SLS) and ethoxylated sodium lauryl sulfate (ESLS)—exhibit strong affinity for solid surfaces and form liquid crystalline structures in water. It is expected that they may become effective additives that could significantly modify antiseizure properties of water. They may extend the possibilities for applying water as an ecological base for lubricating substances. Rheological and structural X-ray studies as well as measurements of conductance and wetting angle were carried out. Their aim was to verify and validate the structures being formed in aqueous solutions of the compounds studied. Tribological studies were conducted to measure friction torque as a function of linearly increasing load by means of a four-ball apparatus. The tests were followed by measurement of the wear scar diameter on the balls. Based on the results obtained, antiwear properties were characterized by seizure and scuffing loads as well as by limiting pressure of seizure. The test results are highly surprising. The systems in which simple one-component aqueous solutions were the lubricating substance did not undergo seizure up to the maximum load of 8 kN designed for the tribological tester used. A number of typical antiwear additives in suitable oil bases do not exhibit such good characteristics. Also, the quantities characterizing seizure show relatively high values. Local maxima for the two compounds tested are formed in the area of low concentrations in the dependences of antiseizure properties as a function of concentration. It can be assumed that this is due to ordered structures being formed in the surface phase. The hexagonal phase of high viscosity of the order of several thousand Pa·s which forms in the bulk phase for ESLS and SLS solutions has no visible effect on antiseizure properties, whereas the existence of the lamellar phase for a 70% solution of ESLS affects an increase in the values being measured.     

The effect of emulsifier concentration on the lubricating properties of oil-in-water emulsions

Although the use of oil-in-water (O/W) emulsions as metalworking fluids is widespread, the mechanisms of emulsion lubrication are not yet well understood. Several theories have been proposed but there is not a clear agreement about the effect of different operating conditions and emulsion properties on the lubricating performance of O/W emulsions. In the present study, the film forming ability of O/W emulsions as a function of emulsifier concentration is studied. The emulsifier content exerts a strong influence on all the emulsion properties, such as stability, droplet size distribution, surface and interfacial tension, wetting ability, etc., as well as on the lubricating behaviour, so it has been used to ascertain the relationship between all the properties involved. Three different emulsifiers—anionic, nonionic and cationic—were used at different concentrations in the design of lubricant O/W emulsions. Experimental results show that the work of adhesion of oil droplets on the metal surface is a valuable parameter to predict the ability of emulsions to form thick films in elastohydrodynamic (EHD) contacts. The influence of pH value of O/W emulsions on their lubricating behaviour is also verified. The overall conclusion is that the interactions between metal and oil droplets rule the mechanism of lubrication and that this interaction is primarily controlled by emulsifier concentration.     

Interaction between friction surfaces and lubricating materials of the 2H-MoS2 type

The paper presents an analysis of investigations concerning the concept of the molecular-mechanical origin of the friction and fatigue mechanism as applied to solid lubricants having a structure of the 2H-MoS₂ type.     

Effect of the chemical structure of fluorinated esters on the tribological properties of a steel‐on‐steel system

The effect of the chemical structure of fluorinated esters on the friction and wear behaviour of a steel‐on‐steel system was investigated. The friction and wear testing of a steel disc sliding against a counterpart ball of the same steel was carried out using an Optimal SRV oscillating friction and wear tester. The chemical features of the worn steel surfaces were analysed by means of X‐ray photoelectron spectroscopy, and the morphologies and elemental compositions of the worn steel surfaces observed and determined using scanning electron microscopy. The results indicate that a fluorinated ester with methylene groups that are not substituted by fluorine in the acid structure gives the best friction‐reducing behaviour and a keto‐ester shows the best antiwear properties.     

Tribological properties of some water-based lubricants containing polyethylene glycol under boundary lubrication conditions

The metal-working industry is increasingly interested in synthetic metalworking fluids and coolants. The excellent lubricating properties of polyalkylene glycols have been recognised in areas such as gear lubricants, hydraulic fluids, and compressor lubricants. The main purpose of the present work was to investigate the friction and wear properties of several polyethylene glycols and their synergy with a common water-soluble EP additive, using four-ball and ball-on-plate tribometers.     

The effect of lubricant additives on friction and wear studies of polyphenylene sulphide

Polyphenylene sulphide is a polymer with good thermal stability and high crystallinity. This paper summarizes the results of friction and wear studies of polyphenylene sulphide and its composites made with conventional solid lubricants to ascertain the suitability of the material as a matrix for solid lubricant additives. The polymer itself has a high coefficient of friction. Wear rate increases with load and speed. Addition of solid lubricant additives helps in improving the friction and wear of the polymer. Composites with MoS₂-Sb₂O₃ and PTFE gave better results than composites made by the addition of graphite and MoS₂ graphite. Wear rate of these composites increased with load and speed; but load and speed had little effect on friction.     

Effect of molecular structure of organic borates on their friction and wear properties

Six organic borates of different molecular chain length were synthesised, and the friction and wear properties of these borates as oil additives were evaluated using a Timken Tester. X-ray photoelectron Spectroscopy (XPS) was used to study the surface composition and valence state of boron on the rubbed surfaces. It was found that the antiwear and friction reduction effects of the borates are significantly influenced by the molecular chain length. The longer the chain length, the lower the friction coefficient and wear, and the higher the failure load. XPS analyses of rubbed surfaces revealed that the binding energy of B_IS increased after rubbing, but no pure B(OH)₃ and B₂O₃ was generated. the load-carrying capacity and the antiwear effect are probably related to the ratio of numbers of carbon atoms to numbers of boron atoms on the rubbed surfaces.     

The effect of a friction modifier on piston ring and cylinder bore friction and wear

The addition of friction modifiers to crankcase lubricants has been shown to significantly reduce the mechanical losses of critical components in internal combustion (ic) engine; thereby improving fuel economy.In this study the friction and wear of a piston ring/cylinder bore material combination was studied using a pin-on-plate laboratory tribo-test machine developed to reproduce the wear mechanisms encountered in an ic engine. Two lubricants were evaluated: (i) a standard SAE 30 grade diesel formulation, and (ii) the same formulation with the addition of a 5% soluble MoS₂ friction modifier.Analysis of the wear results identified three periods of wear: (1) running-in, (2) transient wear and (3) terminal wear. Throughout this study particular emphasis has been placed on the simulation of the wear mechanisms occurring within engines. Surface analysis confirmed that both abrasive wear and delamination wear was produced.Friction benefits attributable to the addition of MoS₂ friction modifier were obtained. However, under specific conditions the wear rate increased due to increased abrasion of the plate.     

The influence of lubricating fluid type on the properties of biodegradable greases

The lubricating ability of a grease depends on both the base oil and the thickener. As a result of their intrinsic properties and/or because of their com‐patibility with thickeners and specific additives, base fluids have different influences upon the properties of grease formulations. It is well known that mineral oils are the most widely used lubricant bases due to their inherent lubricity and lower cost, but recent environmental concern has led to consideration of the use of vegetable oils and readily biodegradable synthetic fluids as raw materials in lubricating grease formulations. As well as the base materials, the additives for biodegradable greases should also be biodegradable. This requirement limits the kind of products that may be used in environmentally friendly greases. This paper presents comparative data concerning the tribological and physico‐chemical properties of biodegradable greases formulated with certain vegetable oils, such as rape seed oil, castor oil, and soybean oil or their mixtures, and synthetic esters. The improvement of the load‐carrying properties of biodegradable greases and the antioxidative effect of some suitable additives have also been studied, and the results are presented here.     

The effect of water on the acid-base properties of new and used IC engine lubricating oils

The absolute values of total base number (TBN) were determined for several sets of both fresh and used engine oil samples. Basic and acidic compounds from these oils have been extracted into water, 7% sea water and ethanol-water (1:1, v/v) mixtures. The extracts have been determined by potentiometric titration as pH extracts, TBN (water extract) and alkalinity. The oil formulations are not resistant to the presence of water but basic additives in fresh oil are more resistant than those for used oils. The percentage of TBN extractable into water significantly increases with service life. The presence of significant amounts of water in lubricating oil is serious and should form part of any lubricant condition monitoring system. The case is argued for both the use of dehydration canisters in oil systems and for the development of a new method of water content determination for used formulated lubricating oils which is quick, accurate and suitable for automated condition monitoring systems. The pH of aqueous extracts for condition monitoring of lubricating oils is shown to be only meaningful for TBN values of 2 or less.     

The effect of oxy-nitrided steel surface on improving the lubricating performance of tricresyl phosphate

A ball-on-disc wear tester was employed to study the effects of an oxy-nitrided steel surface on the lubricating performance of oil additive tricresyl phosphate. Mechanisms of the effects were discussed based on the analytical results obtained with several surface analysis methods. It was found that tricresyl phosphate showed much better anti-scuffing and anti-wear properties on an oxy-nitrided steel surface. The main reason for these effects is that the pretreated iron oxide film on an oxy-nitrided steel surface could promote the chemical reaction of tricresyl phosphate with iron to form a thicker and more compact boundary lubrication film on the wear surfaces.     

Effect of Hardness Ratio on the Wear Performance and Subsurface Evolution of Ni3Al Matrix Composites

A favorable hardness ratio (H_disk/H_pin = H_d/H_p) could lead to a transition to mild wear during sliding contact. To determine a more appropriate H_d/H_p value for the sliding wear, the dry sliding pin-on-disk wear tests of Ni₃Al matrix composites (NMCs) with multilayer graphene (MLG) are undertaken at H_d/H_p values of 0.99, 0.83, 0.42, and 0.35 at sliding speeds of 0.1, 0.3, 0.5, and 0.7 m/s. It is found that the tribological properties of NMCs are strongly affected by the various hardness ratios. At 0.1 m/s, the friction coefficient decreases with a decrease in H_d/H_p value. The low friction coefficient is 0.14 and the wear rate is 0.9 × 10^?5 mm³ N^?1m^?1 under the ceramic counterpart with H_d/H_p of 0.35. At 0.7 m/s, the tribological properties show the opposite trend with a decrease in H_d/H_p. At an H_d/H_p of 0.35, the smooth compact layer on the worn surface could decrease the friction at 0.1 m/s, and the improved hardness in the subsurface by strain hardening would play an important role in the improvement of wear resistance. Under the metal counterpart with H_d/H_p of 0.99, plastic deformation only occurs on the contact surface and the MLG could suppress further shear deformation in the subsurface, leading to a low wear rate (2.4 × 10^?5 mm³ N^?1m^?1) and friction coefficient (0.15) at 0.7 m/s.     

The effects of methane-debris molecules on the frictional properties of diamond

Molecular dynamics simulations have been used to examine the friction between two surfaces placed in sliding contact. These simulations show that the presence of methane-debris molecules squeezed between two hydrogen-terminated diamond (111) surfaces significantly reduces the friction compared to the same two surfaces in the absence of debris. These findings are in agreement with macroscopic experiments that have examined the friction of diamond on diamond in the presence of debris. In addition, the friction coefficients are significantly lower compared to the same system with methyl groups chemisorbed to one of the diamond surfaces.     

Effect of aerosil organophilization on tribological properties of low-filled UHMWPE composites

The effect of aerosil on the formation of structure and surface layers of ultrahigh-molecular-weight polyethylene (UHMWPE) and its low-filled composites is studied during friction. Surface modification of aerosil by vinyl triethoxysilane is found to result in elevated crystallinity degree and hardness of the filled polymeric system, and hardening of the composite surface layer under friction. This can be, evidently, attributed to friction-induced grafting of binder macromolecules to the organophilicized aerosil surface. Strengthening of the matrix bonding with the filler is accompanied by worsening of lubricity, growth of wear resistance, and increasing contribution of the adhesive mechanism instead of the abrasive one to the wear of low-filled UHMWPE composites.     

The effect of the chemical structure of polyfluorinated alcohols on the tribological properties of poly-e-caproamide

The paper presents investigation results of tribological properties of model poly-?-caproamide compositions modified by 0.1 wt % polyfluorinated alcohols of the formula H(CF₂CF₂) _n CH₂OH, where n = 1–3. The methods of X-ray photoelectron spectroscopy, X-ray diffraction analysis, the determination of the limiting wetting angle and microhardness, and thermomechanical analysis were used in this work. The plasticizing role of polyfluorinated alcohols and the orientation effect of poly-?-caproamide most expressed in the compositions of polyfluorinated alcohol with n = 1 have been established. The modified poly-?-caproamide displays by far a lower friction coefficient and a higher wear resistance as compared to the original one. The increased amount of-CF₂-CF₂-groups in the alcohol molecules exerts an advantageous effect on improving the tribooxidative stability of the modified poly-?-caproamide.     

颗粒增强铝基复合材料干滑动摩擦性能研究进展

综述了近几十年来各国对颗粒增强铝基复合材料(PRA)干滑动摩擦性能的研究成果,对PRA主要参数的测量、影响PRA耐磨性的因素和磨损机制进行了分析和总结,指出了今后的研究方向。     

无石棉制动带摩擦磨损性能预测系统的研究

以实验为基础,利用Matlab软件平台上的BP神经网络工具箱,建立并训练了无石棉制动带复合纤维优化设计中所需的各纤维组分体积百分含量与制动带摩擦磨损性能指标之间的人工神经网络映射模型。研究结果表明,该BP网络映射模型的网络误差小,映射结果与实际实验结果的吻合度高,能较为准确地预测复合纤维组成对应制动带的摩擦磨损性能指标,解决了二者关系无法用显函数表征的问题,为制动带无石棉复合纤维组成的优化设计奠定了基础。     

A comparative study on the microstructure and tribological properties of Si3N4 and TiN films produced by the IBED method

The tribological properties of Si₃N₄ and TiN thin films produced by ion beam enhanced deposition (IBED) were compared on a SRV friction and wear testing machine. The friction coefficient of all thin films shows a descending tendency with increase in load, and is lower than that of 52100 steel. All the IBED films show a much better wear resistance than 52100 steel, especially in the higher load and frequency ranges; it can reach six times that of the latter. In order to understand the reasons for their excellent properties, the microstructure, microhardness and bonding strength with the substrate were analysed by SEM, X-ray diffraction, Knoop hardness and scratching test methods separately. The results show that the TiN(1) film exhibits the best tribological properties, which are closely related with its greater hardness and bonding strength.     

The effect of nitrogen on the scratch resistance of austenitic stainless steels

High nitrogen stainless steels (HNSS) are being considered a new promising class of engineering materials. When nitrogen is added to austenitic steels it can simultaneously improve fatigue life, strength and wear and localized corrosion resistance. In this work, a single pass pendulum scratch test was used to study the effect of nitrogen on the scratch resistance of an UNS S30403 austenitic stainless steel. Samples with increasing nitrogen contents at the surface were obtained through high temperature gas nitriding. The thermochemical treatments were performed at 1473 K in (N₂+Ar) gas atmospheres for 36.0 ks, obtaining fully austenitic cases (surface nitrogen contents up to 0.5 wt%) ca. 1.5 mm in depth. The scratch tests were performed in a single-pass pendulum, equipped with strain gages to measure normal and tangential forces during scratching. The specific absorbed energy was calculated as the ratio between the measured absorbed energy and the amount of mass removed from the specimen. An increase of the specific absorbed energy with increasing nitrogen content was observed. The results of the scratch tests were analyzed taking into account the stress–strain behavior during depth sensing indentation tests and the energy absorbed during Charpy impact tests. The improvement in scratch resistance due to nitrogen alloying was attributed to the strong hardening effect of nitrogen in solid solution, which does not affect significantly work hardening and toughness. A comparison between the scratch resistance and the cavitation-erosion resistance, measured in previous work, was made too.     

激光处理对人牙釉质酸蚀和耐磨性能的影响

以人牙釉质为研究对象,对牙釉质表面进行激光处理,对激光处理前后牙釉质的表面形貌、力学性能和耐磨性能进行分析,旨在探索激光处理对牙齿酸蚀的抑制和修复作用,为激光在牙齿酸蚀抑制方面的临床应用提供理论指导。结果表明,原始牙釉质表面和酸蚀牙釉质表面经激光处理后,其表面硬度均显著提高、抗酸蚀能力增强;但是,激光处理会导致牙釉质表面变得粗糙,出现大量裂纹和孔洞,牙齿表面的弹性模量降低,表面脆性增大,从而使得牙齿耐磨性显著降低,造成的损伤重于酸蚀。