Initial steps in the surface chemistry of vapor phase lubrication by organophosphorus compounds

The surface chemistry of trimethylphosphite (CH₃O)₃P has been studied on Cu(111) and Ni(111) surfaces in order to model the initial steps in the reactions of vapor phase lubrication by organophosphorus compounds. The initial reactions involve scission of the P–O bonds to deposit methoxy groups (CH₃O_(ad)) on the surfaces. On the Cu(111) surface the formation of CH₃O_(ad) species occurs only after oxidation of the surface. The CH₃O_(ad) groups on Cu(111) decompose by β‐hydride elimination to produce formaldehyde (O=CH₂) and adsorbed hydrogen. CH₃O_(ad) groups are formed from (CH₃O)₃P on the clean Ni(111) surface and decompose by complete dehydrogenation to CO and adsorbed hydrogen atoms. This chemistry is very similar to that observed for CH₃OH on these surfaces. These results suggest that alkoxides are important intermediates in the decomposition of vapor phase lubricants on metal surfaces. This revised version was published online in July 2006 with corrections to the Cover Date.     

Activation of the SiC surface for vapor phase lubrication by Fe chemical vapor deposition from Fe(CO)5

The feasibility is demonstrated of a new approach to the vapor phase lubrication of ceramics using organophosphorus compounds. The surface of SiC is shown to be unreactive for the decomposition of trimethylphosphite, (CH₃O)₃P, a simple model for organophosphorus vapor phase lubricants such as tricresylphosphate. In order to activate the surface of SiC it has been exposed to Fe(CO)₅ at a temperature of 600 K. Chemical vapor deposition serves as a means of depositing Fe on the SiC surface. The Fe-modified SiC surface is then shown to induce the decomposition of adsorbed (CH₃O)₃P. The mechanism of (CH₃O)₃P decomposition is similar to that observed on Fe(110) surfaces modified by the presence of oxygen. It is initiated by P–O bond cleavage to produce adsorbed methoxy groups, CH₃O_(ad), which then decompose by -hydride elimination resulting in H₂, CO, H₂CO, and CH₃OH desorption. It is suggested that chemical vapor deposition of metals using high vapor pressure metal-containing compounds such as Fe(CO)₅ can serve as a mechanism for continuous, in situ activation of ceramic surfaces for vapor phase lubrication in high temperature engines.     

The surface chemistry of alkyl and arylphosphate vapor phase lubricants on Fe foil

The surface chemistry of tributylphosphate (TBP) and tricresylphosphate (TCP) on a polycrystalline Fe surface was studied using temperature programmed reaction spectroscopy and Auger electron spectroscopy to illustrate some of the initial steps in the reaction mechanisms of alkyl and arylphosphate vapor phase lubricants. During heating, TBP [(C₄H₉O)₃P=O] adsorbed on the Fe surface decomposes via C–O bond scission to give butyl surface intermediates [C₄H₉–] that react via β-hydride elimination to desorb as 1-butene [CH₃CH₂CH=CH₂] and H₂ without appreciable carbon deposition onto the surface. The thermal decomposition of 1-iodobutane [I-C₄H₉] on Fe was observed to proceed via the same β-hydride elimination mechanism. In contrast to tributylphosphate, meta-tricresylphosphate (m-TCP) [(CH₃–C₆H₄O)₃P=O] decomposes on Fe via P–O bond scission to produce methylphenoxy intermediates [CH₃–C₆H₄O–]. During heating to 800 K, methylphenoxy intermediates either desorb as m-cresol [CH₃–C₆H₄–OH] via hydrogenation or decompose further to generate tolyl intermediates [CH₃–C₆H₄–]. Some of the tolyl intermediates desorb as toluene [CH₃–C₆H₅] via hydrogenation but the majority decompose resulting in H₂ and CO desorption and carbon deposition onto the Fe surface. The P–O bond scission mechanism of m-TCP was verified by showing that the temperature programmed reaction spectra of m-cresol yield products that are almost identical to those of m-TCP. These results provide insight into the origin of the differences in the performance of alkyl and arylphosphates as vapor phase lubricants. The alkylphosphates decompose via alkyl intermediates that readily undergo β-hydride elimination and desorb into the gas phase as olefins, thus removing carbon from the surface. In contrast, the arylphosphates generate aryloxy intermediates by P–O bond scission and aryl intermediates by further C–O bond scission. Neither of these intermediates can undergo β-hydride elimination and thus they decompose to deposit carbon onto the Fe surface. The higher efficiency for carbon deposition may be the primary reason for the superior performance of the arylphosphates over alkylphosphates as vapor phase lubricants.     

Frictional force microscopic detection of anisotropy at NaCl (1 0 0), (1 1 0) and (1 1 1) surfaces

Frictional coefficients were measured at atom-flat NaCl (1 0 0), (1 1 0) and (1 1 1) surfaces with frictional force microscopy. At the electrically neutral (1 0 0) and (1 1 0) surfaces in 15% relative humidity, lower friction was detected along 1 1 0 direction where the same kind of ions are aligned, than along 1 0 0 direction where different ions alternate. Low and isotropic friction was observed at the polar (1 1 1) surface. The results were explained by the gradients of electrostatic interaction potentials between a dipole at the tip and the ions at the surface. Toward higher relative humidity up to 60%, frictions at the (1 0 0) surface decreased indicating lubrication effect by water. The changes observed for the (1 1 0) surface suggested presence of adsorbed water in stripe pattern along the 1 1 0 direction. In the higher humidity range, frictional force increased at all the surfaces, probably due to larger normal force caused by the meniscus force.     

Two-dimensional ordering of pentafluorobenzenethiol self-assembled monolayers on Au(1 1 1) prepared by ambient-pressure vapor deposition

Formation and surface structures of pentafluorobenzenethiol (PFBT) self-assembled monolayers (SAMs) on Au(1 1 1) prepared by ambient-vapor phase deposition were examined by means of scanning tunneling microscopy (STM) as a function of deposition temperature. PFBT SAMs formed at room temperature have disordered phases with bright aggregated domains, which are very similar to benzenethiol SAMs. As deposition temperature increases to 50 °C, partially ordered domains and large aggregated domains appeared. High-resolution STM clearly revealed that PFBT SAMs formed at 75 °C were composed of long-range, two-dimensional (2D) ordered domains, which can be described as a c(2×√3) structure. The results of this study clearly demonstrate that deposition temperature is a crucial factor for obtaining PFBT SAMs on Au(1 1 1) with a high degree of structural order.     

The surface chemistry of chloroform as an extreme-pressure lubricant additive at high concentrations

Carbon tetrachloride is an extremely good extreme-pressure (EP) lubricant additive at low concentrations (<3 wt% chlorine) since it can react to form a high-melting-point Fe₃C antiseizure layer. In contrast, small hydrogen-containing additive molecules (CH₂Cl₂, CHCl₃) decompose to form FeCl₂ which melts at ~940 K and limits the maximum seizure load to ~3500 N as measured hi a pin and v-block apparatus. However, both thermodynamic calculations and results of a Mössbauer analysis of an iron foil heated in CHCl₃ at 830 K indicate that iron carbide can be formed from chloroform. In addition, it is also found in that case that a plot of seizure load versus concentration, after initially forming a plateau, once again increases with higher additive concentrations (>4 wt% chlorine) in accord with the idea that a higher melting point carbide film can be formed. It has been shown previously that asymptotes in the plot of removal rate versus applied load correspond to melting of the interfacial anti-seizure film. When using 9.0 wt% chlorine from chloroform as the additive, a drastic increase in removal rate is found at an interfacial temperature of ~940 K corresponding to the melting of FeCl₂ and an additional asymptote is evident at ~1500 K due to the melting of Fe₃C in accord with the thermodynamic and Mössbauer results.     

0Cr18Ni9不锈钢焊缝高速铣削表面粗糙度试验研究

采用正交试验方法进行0Cr18Ni9不锈钢焊缝高速铣削试验,分析铣削参数对表面粗糙度的影响规律,并建立表面粗糙度的经验预测模型。结果表明:随着主轴转速的增大,表面粗糙度值减小,而随着进给速度、切削深度的增大,表面粗糙度值增大,进给速度对表面粗糙度的影响较为明显;较高的主轴转速和较低的进给速度的交互作用有利于减小表面粗糙度值,提高表面质量。     

Adsorption and lubricating properties of HFBII hydrophobins and diblock copolymer poly(methyl methacrylate-b-sodium acrylate) additives in water-lubricated copper vs. a-C:H contacts

In a metal forming process the adhesion between the workpiece and the tool needs to be minimised, which can be achieved by use of lubricants and coatings. Here adsorption and lubrication properties of HFBII hydrophobins and diblock copolymer poly(methyl methacrylate-b-sodium acrylate) in water-lubricated copper vs. a-C:H coating contacts were studied by Surface Plasmon Resonance (SPR) and by a pin-on-disc (POD) tribometer. Hydrophobins formed a dense monolayer film on a-C:H surface and reduced friction by 13–30% but increased the wear of copper compared to pure water lubrication. Poly(methyl methacrylate-b-sodium acrylate) formed a sparse lubricating layer compared to HFBII lubricated contacts, but the friction coefficient was lower. HFBII molecules prevented copper oxide tribofilm formation on the copper pin.     

High‐pressure rheology of eight synthetic lubricants based on phase diagrams

New sets of equations have been constructed from the density‐pressure‐temperature and viscosity‐pressure‐temperature relationships to determine the rheology of synthetic lubricants at high pressure. A phase diagram was first plotted for the oils up to a pressure of 1.2 GPa and temperatures from 303 to 353 K using high‐pressure density experimental results and others. For the oils at temperatures of 313, 333, and 353 K, the high‐pressure viscosity experiment was done up to a viscosity of 10⁴ Pa s and up to a pressure of 0.4 GPa. A relationship, based on free volume theory, between pressure and temperature with varying density and viscosity was proposed. It was found that the new equations from these relationships could predict the high‐pressure rheology more closely than those of previous researchers. Moreover, it was shown that the Ehrenfest equation or the gradient of the phase diagram is closely related to the expansion coefficient of free volume.     

Tribological performance evaluation of (1 1 1) preferred oriented TiN duplex coatings

The duplex surface coating of hot work tool steel, which comprises nitriding of a substrate and coating of a TiN layer, has been the subject of a series of studies as a potential surface modification for tools and machine parts. Through sliding experiment against an aluminum alloy without lubrication, it was shown on a wear map that there are two domains depending on sliding conditions: the wear domain and the transfer domain. In this study, focusing on the improvement in the tribological properties of the duplex coating in terms of the wear domain, the effects of film characteristics on film resistance to erosion wear and film life were investigated. Two kinds of duplex coatings with different film characteristics were prepared by hollow cathode discharge ion plating: a newly developed TiN film with a strong (1 1 1) orientation and an ordinary TiN film with (1 1 1) and (2 0 0) orientations. The erosion wear rate of duplex coating was evaluated by a micro slurry jet erosion test. Film life was evaluated by a sliding test against an aluminum alloy as in previous experiments. It was revealed that the duplex coating with the newly developed TiN film (N-coating) shows higher erosion resistance than previously reported duplex coating (C-coating). From the sliding test, it was also revealed that the N-coating whose XRD intensity ratio of (1 1 1) to (2 0 0) is over 100 shows a wear mode with only chipping, with no scratching, which shortens film life. The film life of N-coating increases about twice as long as C-coating, which has shown higher performance than a conventional duplex coating. Possible mechanisms of the improvement in the tribological properties with N-coating are discussed.     

Spreading of PFPE lubricants on carbon surfaces: effect of hydrogen and nitrogen content

The spreading of OH-terminated perfluoropolyalkylether (PFPE), Zdol, on amorphous carbon surfaces was studied as a function of hydrogen or nitrogen content in the carbon film, using scanning micro-ellipsometry. A layered structure of the thickness profiles was observed, which remained qualitatively the same for all carbon types. The sharpness of the second layer was gradually eroded as either hydrogen or nitrogen content in the films was increased. The thickness-dependent diffusion coefficient was calculated using the Matano interface method. It was observed that the surface mobility of Zdol increased as hydrogen content increased, but decreased as nitrogen content increased. Implications of these results on the boundary lubrication properties of Zdol on carbon films are discussed. This revised version was published online in August 2006 with corrections to the Cover Date.     

Influence of surface roughness features on mixed‐film lubrication

An optical technique (three‐dimensional spacer layer imaging) has been developed to map accurately lubricant film thickness in thin‐film elastohydrodynamic (EHD) contacts. This experimental technique has been used to study the influence of surface roughness features, asperity height, and slope on EHD film thickness and pressure. Single ridges transverse to the entrainment direction were used to represent asperities. It was found that the ridges with lower slopes generate films of greater minimum thickness. Below a certain entrainment speed, the minimum film thickness declined at a rate dependent on the ridge slope. At low speeds, the ridges with higher slopes entrapped a larger volume of lubricant ahead of the ridge and along the entrainment direction. For all speeds, the highest ridges entrapped the most lubricant. Both ridge slope and ridge height had a negligible effect on mean film thickness in the contact. Asperity pressure increased with higher ridge slope, but was not influenced by entrainment speed. An increase in pressure was found where lubricant is entrapped upstream of a ridge.     

Construction of phase diagram up to 2 GPa and 200°C for thermo‐reversible gel lubricants by diamond anvil cell

The objective of this research was to make the phase diagram up to 2.0 GPa and 200°C of thermo‐reversible gel lubricants (TR Gel‐Lube) using diamond anvil cell (DAC). TR Gel‐Lube consisted of base fluid and gelling agent. The most important characteristic of TR Gel‐Lube is the reversible change of its physical state. The DAC is able to concerning visual observation of the sol/gel and liquid/viscoelastic–solid transition at high pressure and high temperature. DAC enables the visual observation of the photoelastic effect in order to generate local principal stress difference under the compression field for liquid/viscoelastic‐solid transition of base oil poly‐α‐olefin. The direct observation for sol/gel transition of TR Gel‐Lube at high pressure was also made possible. The phase diagram corresponding to transition from liquid to viscoelastic solid for base oil poly‐α‐olefin and sol to gel for TR Gel‐Lube was made by using DAC. Copyright © 2009 John Wiley & Sons, Ltd.     

Reduction of adhesion and friction of silicon oxide surface in the presence of <Emphasis Type="Italic">n</Emphasis>-propanol vapor in the gas phase

The equilibrium adsorption of gas phase alcohol molecules has been proposed as a new means of in-use anti-stiction and lubrication for MEMS devices. Adhesion and friction of silicon oxide surfaces as a function of n-propanol vapor pressure in the ambient gas were invesitigated using atomic force microscopy. As the vapor pressure increases, the adsorbed n-propanol layer thickness increases. The adhesion and friction significantly decrease with very little addition of n-propanol vapor.     

The Frictional Response of VC(100) Surfaces: Influence of 1-Octanol and 2,2,2-Trifluoroethanol Adsorption

In this report, we present ultrahigh vacuum (UHV) atomic-scale measurements of the frictional response of the VC(100) surface and the influence on friction through the adsorption of 1-octanol (CH₃(CH₂)₇OH) and 2,2,2-trifluoroethanol (CF₃CH₂OH). Atomic force microscopy (AFM) has been used to determine the changes in interfacial friction and adhesion, while scanning tunneling microscopy (STM) has revealed changes in surface morphology upon adsorption. X-ray photoelectron spectroscopy (XPS) has been utilized to determine the composition of the surface formed through the reaction of these adsorbates with VC. Adsorption of 1-octanol on the VC(100) surface at room temperature causes a 15% reduction in the friction measured between a clean VC surface and a silicon nitride AFM tip. STM images, combined with XPS results, reveal that 1-octanol does not completely cover the surface and that saturation occurs approximately at a 500L exposure. Adsorption of 2,2,2-trifluoroethanol on the VC(100) surface at room temperature produces a significant increase in friction while at the same time producing a decrease in adhesion. These contrasting results are interpreted in terms of differences in interfacial shear strength, chemical composition, and the molecular details of the adsorbed layer.     

0Cr18Ni9在干切削和微量润滑下表面粗糙度的研究

对0Cr18Ni9奥氏体不锈钢在传统乳化剂、干车削和微量润滑车削条件下进行切削试验。通过设计多因素正交试验方法和分组实验,比较在不同的冷却润滑方式下,背吃刀量、切削速度、进给量等切削用量对工件表面粗糙度的影响,从而为实际的生产加工积累和提供基础数据。     

The study of tribological properties of laser‐textured surface of 2024 aluminium alloy under boundary lubrication

The tribological property of aluminium alloy is critical for its reliable operation in practical applications. In this paper, the tribological performance of laser‐textured 2024 aluminium alloy is studied in unidirectional sliding tests under boundary lubrication. The dimples were produced on the aluminium alloy surface by using a pulse Nd : YAG laser. The topographical microstructures of these laser‐induced textures were characterised by optical and scanning electron microscopy. In comparison with untextured surfaces, a significant improvement in friction behaviour was observed for the textured surfaces. The influences of dimples density on the tribological properties were investigated. Two types of oil with different viscosities were evaluated as lubricants. It was found that the beneficial effects of laser surface texturing are more pronounced at higher speed and load with higher viscosity oil. The optimum dimples density of 8.5% was found to have a lower friction coefficient. On basis of the experimental results, the mechanism of friction reduction and anti‐wear is proposed. Copyright © 2012 John Wiley & Sons, Ltd.     

The effect of surface chemistry in lubrication on the tribological behaviour of steel rollers under rolling-sliding contacts

Experiments were carried out on a wear test machine utilising a gearcam adapter to simulate line-contact lubrication. Due to the formation of a surface adsorption layer on the steel substrate, the tribological performance was detected by measuring the voltage for a lubricant with various additive concentrations. The roller wear rate was found to be strongly dependent upon both the rising rate of voltage in the wear process and the time period needed to create a positive voltage. The antiwear effect of differing additive concentrations was evaluated using the measurements of voltage for various operating conditions. An increase in rotational speed, with a lubricating oil with a low additive concentration, decreases the wear rate. A lubricating oil with a high additive concentration does little to decrease the wear rate at low rotational speeds.     

High-field versus high-pressure: Weakly adsorbed CO species on Pt(1 1 1)

Adsorption of carbon monoxide on a nanosized apex facet of a [1 1 1]-oriented Pt field emitter tip was studied under high electrostatic field conditions (15–20 V/nm) by field ion appearance energy spectroscopy (FIAES). Weakly bound highly mobile CO species have been detected and their possible role in surface reactions such as CO oxidation on Pt was elucidated.     

基于红外热像技术的喷油润滑齿轮齿面温度实验研究

齿轮的齿面温度与齿轮的多种失效形式有关,对齿轮温度进行快速、准确的测量对预测齿轮的失效与改进润滑系统的设计具有重要的实际意义。将红外热像技术应用于齿面温度的测量,提供了一种喷油润滑齿轮红外测温的方法;并在改装后的齿轮试验机上对不同工况下的齿轮齿面温度进行了测量,研究了喷油压力、扭矩载荷及转速对齿面温度的影响关系。