Effect of pressure and temperature on the molecular interaction of polar lubricant containing oleic acid in polypropylene glycol observed by infrared spectroscopy

In this work, we have investigated the infrared spectra of polar lubricant in order to explore the molecular interaction under high pressure and temperature conditions using diamond anvil cell. Polypropylene glycol and oleic acid were used as base oil and additive, respectively. Stretching vibration mode of polar functional groups, such as ν _O–H and ν _C═O, was found to be sensitive to pressure and temperature. The peak positions of the vibration mode were shifted clearly to lower wavenumber as pressure increases, and temperature increase induced a slight shift to higher wavenumber. These results indicate that hydrogen bonding between lubricant molecules of base oil and additive was influenced by pressure and temperature. And furthermore, the dependency of the peak shift was discontinuous and affected mainly by pressure. These results imply a structural change on the basis of the molecular interaction of the lubricating molecules at elastohydrodynamic lubrication contacts. Copyright © 2013 John Wiley & Sons, Ltd.     

Friction and wear behaviors of C/C-SiC composites containing Ti3SiC2

In the present paper, friction and wear behaviors of a carbon fiber reinforced carbon–silicon carbide–titanium silicon carbide (C-SiC–Ti₃SiC₂) hybrid matrix composites fabricated by slurry infiltration and liquid silicon infiltration were studied for potential application as brake materials. The properties were compared with those of C/C-SiC composites. The composites containing Ti₃SiC₂ had not only higher friction stability coefficient but also much higher wear resistance than C/C-SiC composites. At an initial braking speed of 28 m/s under 0.8 MPa pressure, the weight wear rate of the composites containing 5 vol% Ti₃SiC₂ was 5.55 mg/cycle, which was only one-third of C/C-SiC composites. Self-lubricious film-like debris was formed on the composites containing Ti₃SiC₂, leading to the improvement of friction and wear properties. The effect of braking speed and braking pressure on the tribological properties of modified composites were investigated. The average friction coefficient was significantly affected by braking speed and braking pressure, but the wear rate was less affected by braking pressure.     

The effect of gasses on the viscosity of dimethyl ether

Dimethyl ether (DME) has been recognised as a clean substitute for diesel oil as it does not form soot during combustion. DME has a vapour pressure of 6 bar at 25 °C; so pressurisation is necessary to keep DME liquid at ambient temperature. Inert gases are good candidates as pressurising media, but their effect on DME viscosity is unknown.Argon (Ar), nitrogen (N₂), carbon dioxide (CO₂), hydrogen (H₂) and propane (C₃H₈) have been investigated at pressure levels of 12–15 bar. A Cannon-Manning semi-micro capillary glass viscometer, size 25, enclosed in a cylindrical pressure container, of glass, submerged completely in a constant temperature bath, has been used. A distinct reduction of efflux times was found only for the gas, CO₂. The reduction in efflux time was about 9%.The kinematic viscosity of pure DME was determined to be: 0.188±0.001 cSt, 25 °C. A previously reported viscosity of pure DME has been corrected for the surface tension effect. Viscosity determination was initially based on a direct comparison of efflux times of DME with that of distilled water. The calculation gave a revised viscosity of 0.186±0.002 cSt, 25 °C, consistent with the above experimental result.     

Study of the tribological performance of zirconia-based materials in pair with VT-9 titanium alloy

The paper presents a study of the possibility of using composite nanostructured ceramic materials and crystals based on zirconia as bearing materials for dry operation at temperatures of up to 150°C. The results of experimental study of the dry friction of the materials in pair with alpha-titanium alloy VT-9 are presented. It is shown that at a sliding velocity of 0.004 m/s, contact pressure of 3.3 MPa, and temperature of 150°C, their antifriction properties do not differ significantly. ZrO₂ crystals have a slight superiority in wear resistance because of their higher microhardness. The wear resistances of the alpha-alloy in pair with the ceramics and the crystal are practically the same. A power pattern of the dependence of the wear rate on the pressure for the ZrO₂ crystal and the VT-9 (α) alloy is confirmed.     

Numerical investigation of three-dimensional cavitation evolution and excited pressure fluctuations around a twisted hydrofoil

Unsteady cavitating turbulent flow around a twisted hydrofoil was analyzed to illustrate the physical mechanism of the cavitygenerated pressure fluctuations. The numerical simulations of cavitating flow were based on the Partially-Averaged Navier-Stokes (PANS) method and a mass transfer cavitation model. The validity of PANS model has been evaluated and confirmed in cavitation simulations by present authors using three different cases, 2D hydrofoil (Ji et al. 2012 [37]), 3D hydrofoil (Ji et al. 2013 [31]) and marine propeller (Ji et al. 2012 [38]), which shows that the PANS model with f _k = 0.2 and f _ε = 1 can obtain more accurate estimates of unsteady cavitating flows with large-scale fluctuations at a reasonable cost. In present paper we intended to shed light on the physical process responsible for the pressure fluctuations excited by cavitation. The cavity volume was analyzed to illustrate the relationship between the cavitation evolution and the pressure fluctuations. The results show that the cavity volumetric acceleration curve tracks remarkably well with the main features of the time-dependent pressure fluctuations except for the high frequency component. Thus, the cavity volumetric acceleration is the main source of the excited pressure fluctuations by cavitation. It is noted that the cavitation induced pressure fluctuations are transmitted along the suction surface of the hydrofoil and are synchronized with those on the pressure surface at the midplane of the twisted hydrofoil. Further, the pressure fluctuations on the pressure surface decrease towards the center from both the leading and trailing edges of the hydrofoil, with a minimum at 60% chord length from the leading edge.     

The effect of body temperature on the accuracy of arterial and end-tidal carbon dioxide measurement

Measurement of carbon dioxide has great clinical significance during mechanical ventilation, in the adjustment of ventilatory parameters and detection of respiratory complications. The main objective is to investigate the correlation between end-tidal carbon dioxide pressure (PetCO₂) and partial pressure of arterial carbon dioxide (PaCO₂) measured at 37 °C and corrected for body temperature in patients with thermal instability. Altogether, 110 measurements were analyzed, and the correlation was statistically more significant for corrected temperature than measured PaCO₂. The difference between corrected and uncorrected PaCO₂ varies from 3% per °C for hypothermic patients and 6.5% per °C for hiperthermic patients. The difference between PaCO₂ measured and PetCO₂ (Pa-etCO₂) resulted in an increase for all temperature degree, reaching a maximum difference of 9 torr. In contrast, Pa-etCO₂ has little variation when corrected PaCO₂ was used for calculation around −2.1 to 3.1 torr for hypo and hiperthermic patients. Thus, PetCO₂ reflects temperature corrected PaCO₂ more adequately than measured PaCO₂.     

An analysis of the catalysis of Fe, Ni or Co on the wear of diamonds

The desorption probability for hydrogen chemisorbed on diamond surface is discussed. A model including the equilibrium partial pressure of H₂O resulting from oxidation of methane by metal oxides allows the wear rate of diamond to be computed based on the assumption that the wear mechanism involves diffusion. The calculated partial pressure of H₂O suggests that diamond–graphite phase transformation occurs at the surface layer of diamond tools cutting Cu, Ni, Co or Fe. The calculated wear amount of diamond agrees well with the experimental data, when the temperatures of the cutting interfaces are assumed 560 °C for the cutting of Fe and 600 °C for Ni.     

Analysis and modeling of exhaust gas temperature in an ethanol fuelled HCCI engine

Low exhaust temperature in homogeneous charge compression ignition (HCCI) significantly limits efficiency of an exhaust aftertreatment system to mitigate high HC and CO emissions in HCCI engines. This article aims to understand the effect of varying input parameters on HCCI exhaust gas temperature (T_exh) for an ethanol fuelled engine. A single cylinder engine is used to collect experimental data at 100 different HCCI conditions. The results indicate that variation in combustion parameters such as start of combustion (SOC), burn duration (BD) and maximum in-cylinder pressure (P_max) are not effectively correlated with variations of Texh, but the indicated mean effective pressure (IMEP) and constant-volume adiabatic flame temperature (T_ad) are strongly related to T_exh. These experimental findings were then used to design an artificial neural network (ANN) model to predict T_exh. The model was validated with the experimental data, indicating an average error less than 4.5°C between predicted and measured T_exh.     

Influences of laser welding parameters on the geometric profile of NI-base superalloy Rene 80 weld-bead

In the present study, autogenous laser butt joint welding parameters of Ni-base super alloy Rene 80 has been investigated by using a continuous wave 2.2?kW CO₂ laser. The experiments were performed based on the response surface methodology as a statistical design of experiment approach in order to investigate the effect of parameters on the response variations, achieving the mathematical equations and predicting the new results. Laser power (1,000?C2,200?W), welding speed (120?C360?cm/min), laser beam focal point position (?0.5?C0.5?mm) and inert gas pressure (0.2?C1?bar) were considered as the input process variables while welding surface width (W1), welding pool area (A), width of the weld-bead at the middle depth (W2), undercut welding and drop of welding were considered as the five process responses. Analyzed by statistical techniques, the results show that the welding bead profile is influenced by the laser heat input and input laser process parameters. Welding speed is known as the most important parameter with the reverse effect on process outputs. Inert gas pressure is the next significant parameter, and higher gas pressure causes welding geometry defects. Laser power has a direct influence on all investigated responses.     

The Importance of Variable Speeds under Extreme Pressure Loading in Molybdenum Disulfide Greases Using Four-Ball Wear Tests

There is recent concern regarding grease behavior in extreme pressure applications. The research described here is aimed at providing good friction and wear performance while optimizing rotational speeds under extreme loading conditions. A design of experiment (DOE) was used to analyze molybdenum disulfide (MoS₂) greases and their importance in reducing wear under extreme loading and various speeds conditions (schedule 1 and schedule 2 speeds). The lamellar structure of MoS₂ provides very good weld protection by forming a layer that can be easily sheared under the applications of extreme pressures. An extreme load of 785 N was used in conjunction with different schedules of various rotational speeds to examine lithium-based grease with and without MoS₂ for an equal number of revolutions. A four-ball wear tester was utilized to run a large number of experiments randomly selected by the DOE software. The grease was heated to 75°C and the wear scar diameters were collected at the end of each test.

The results indicated that wear was largely dependent on the speed condition under extreme pressure loading, and thus a lower MoS₂ concentration is needed to improve the wear resistance of lithium-based greases. The response surface diagram showed that the developed molybdenum disulfide greases exhibited both extreme pressure as well as good wear properties under various rotational speeds when compared to steady-state speed. It is believed that MoS₂ greases under schedule 1 speeds perform better and provide an antiwear film that can resist extreme pressure loadings.     

Effect of atmospheric pressure on friction and wear of 0.45% C steel in fretting

Oxidative wear is significant in fretting wear when sufficient oxygen is supplied. In vacuum, however, oxide does not form readily. In this paper friction and wear behaviours were studied at various atmospheric pressures in order to clarify the effect of ambient pressure on them.Experiments were conducted with 0.45% C steel at ambient pressures from 1.0 × 10⁵ to 1.3 × 10^?3 Pa. The load was 14 N, the peak-to-peak slip amplitudes were 35 and 110 μm and the frequency was usually 8.3 Hz.Friction behaviours are characterized into three types according to the ambient pressure: 1.0 × 10⁵ ? 10 Pa, 10 ? 10^?1 Pa and below 10^?1 Pa. The coefficient of friction increases with a decrease in ambient pressure below 1 Pa. The critical pressure in fretting is found to be 10 Pa, above which the oxidation rate is independent of the ambient pressure and α-Fe₂O₃ is formed. Wear decreases with ambient pressure below the critical pressure where Fe₃O₄ is formed. Adhesive transfer of metallic debris occurs below 10^?1 Pa.The relationship between the coefficient of friction and oxide thickness is obtained analytically, and the effect of frequency on the oxidation rate is considered.     

Studies on wear behavior of nano-intermetallic reinforced Al-base amorphous/nanocrystalline matrix in situ composite

Resistance to wear is an important factor in design and selection of structural components in relative motion against a mating surface. The present work deals with studies on fretting wear behavior of in situ nano-Al₃Ti reinforced Al–Ti–Si amorphous/nanocrystalline matrix composite, processed by high pressure (8 GPa) sintering at room temperature, 350, 400 or 450 °C. The wear experiments were carried out in gross slip fretting regime to investigate the performance of this composite against Al₂O₃ at ambient temperature (22–25 °C) and humidity (50–55%). The highest resistance to fretting wear has been observed in the composites sintered at 400 °C. The fretting wear involves oxidation of Al₃Ti particles in the composite. A continuous, smooth and protective tribolayer is formed on the worn surface of the composite sintered at 400 °C, while fragmentation and spallation leads to a rougher surface and greater wear in the composite sintered at 450 °C.     

Assessing the corrosion–wear behaviours of Hastelloy C276 alloy in seawater

A systematic investigation has been carried out in the present work to study the electrochemical and corrosion–wear behaviours of Hastelloy C276 alloy sliding against Al₂O₃ pin in artificial seawater, using a pin‐on‐disc tribometer integrated with a potentiostat for electrochemical control. It can be observed that the cathodic shift of open circuit potential and three order of magnitude increase of current density formed due to sliding. The total corrosion–wear loss increases with increasing applied potential. Interestingly, the total material loss at the applied potential of 0.5 and 0.9 V is more than two times of that of pure mechanical wear, confirming the synergy between wear and corrosion. And, the contributions of wear‐induced corrosion (ΔK_c) and corrosion‐induced wear (ΔK_w) are dominant, especially at higher applied potentials. Copyright © 2015 John Wiley & Sons, Ltd.     

Wear and Degradation Characteristics of Perfluoroalkylpolyethers (PFPEs) in High Vacuum©

Wear and degradation as exhibited by degassing of three commercially available perfluoroalkylpolyethers, A, straight chain with acetal linkage (OCF₂CF₂)_p(OCF₂)_q;B, straight chain without acetal linkage (CF₂CF₂CF₂O)_n; C, branched chain (CFCF₃CF₂O)_m, were evaluated at 0.025 mis under 1 to 300 N at 10^?5 Pa in a four-ball configuration using 440C and Si₃N₄ balls, Φ:6.35 mm, as test specimens. A quadrupole mass spectrometer having a mass range of 1 to 200 amu was employed to analyze gaseous products released from the sliding surfaces.

Disregarding the gas released, Oil C showed slightly better wear characteristics than B, but far better than A when tested with a 440C ball on 440C balls.

Taking gas evolution into account, Oil B carried the highest load; the initial degassing was detected at the Hertzian pressure of 1 GPa for A, 2 GPa for B, and 1.75 GPa for C when using 440C balls, and at 1.5 GPa for A and 2.75 GPa for C when using Si₃N₄ balls. Oil B evaluated with Si₃N₄ balls did not evolve gases even at 2.75 GPa. The initial outgassing load of sliding pairs of a Si₃N₄ ball against 440C balls and vice versa was closer to that of a 440C ball on 440C balls than to a Si₃N₄ ball on Si₃N₄ balls.

Mass spectra patterns obtained from experiments with a Si₃N₄ ball on Si₃N₄ balls were similar to those from experiments with a 440C ball on 440C balls.

Oil A released more CFO⁺ (m/e = 47) and CF₂O⁺ (m/e = 66) than Oil B or C, which could originate from the acetal linkage of its molecular structure as shown by Mori and Morales (1).     

Coupled model of dual differential pressure (DDP) for two-phase flow measurement based on phase-isolation method

Phase-isolation is a novel ever-increasing multiphase separation technology, which can facilitate the multiphase fluid flowing concurrently with a substantially clear interface between two phases, and the phenomenon is promisingly employed for the separation and measurement of multiphase flows. Phase-isolation can be implemented by different kinds of lateral forces, of which the centrifugal force induced by the swirlers is the most convenient method. The radial pressure drop between pipe wall and pipe center, and the axial pressure drop along the pipe wall occurs at the downstream of the swirler. In the paper, the coupling model of dual differential pressure (DDP) including the radial-axial differential pressure and radial-radial differential pressure was built employing centrifugal phase-isolation for oil-water two-phase flow, and the theoretical measurement models were validated by our experimental data. At certain cross sections downstream of the swirler, the deviations between theoretical and experimental result of the volumetric oil fraction λ_o and mass flowrate Q_m were below ±7.16% and ±1.14% respectively when the radial-axial differential pressure was adopted, while the deviations between theoretical and experimental result of λ_o and Q_m were below ±6.91% and ±1.13% respectively using the radial-radial differential pressure. The acceptable deviation indicates that the DDP model can be the reference for the analysis and application of two-phase flow in the academic research and practical engineering.     

Wear resistant coating of cemented carbides and high speed steels by chemical vapour deposition

Ti(N, C, O), which has been chosen as a coating material for cutting tool inserts, was prepared on cemented carbides and high speed steels by chemical vapour deposition via a gas mixture of TiCl₄, H₂, N₂, CH₄ and CO₂ under reduced pressure. This coating layer is characterized by fine grain size and freedom from porosity. The coated tool inserts show excellent cutting performance.     

Wear Initiation of 52100 Steel Sliding Against a Thin Boron Carbide Coating

Boron carbide (B₄C) is well known for its high hardness and wear resistance. It has been found to polish its mating surface and act as a run-in coating if one of the contacting surfaces is coated by B₄C. Employing such run-in coatings demands a thorough understanding of the initiation and development of the polishing process. This paper reports a study on the initiation and development of the surface wear of 52100 steel balls run against B₄C-coated disks. The evolution of the steel surface wear scar and evolution of the contact pressure contours are utilized in connection with changes in the plastically deformed area in order to gain insight into the wear development. Furthermore, variations of fractal parameters of the steel surface and the overall topothesy, which is a measure of the surface anisotropy, are examined in connection with the wear process.     

CO2 LASER PHOTOACOUSTIC SPECTROSCOPY AND ABSOLUTE ABSORPTION COEFFICIENTS OF SHORT CHAIN SATURATED FATTY ACID VAPOURS

Abstract

A resonant photoacoustic cell, capable of contamination free operation at temperatures above that of the ambient, was constructed and used to determine absolute absorption coefficients of C6:0 (hexanoic) and C8:0 (octanoic) fatty acid vapours at CO₂ laser wavelengths. At atmospheric pressure, the maximum absorption coefficients at the 9R(32) line of the CO₂ laser (1085.77cm^?1) are 8.0 atm^?1 cm^?1 (C6:0 at 332K) and 8.9 atm^?1 cm^?1 (C8:0 at 342 K).

     

Low Friction Carbide-Derived Carbon Coating on SiC in Vacuum Achieved by Microstructure Formulation and Solid–Liquid Lubrication

Carbide-derived carbon (CDC) coatings with dimple (CDC@GSiC coating) and loosely dispersive particles structures (CDC@RBSiC coating) were prepared on two kinds of SiC substrates by using chlorination at 1,000 °C in a 5 vol.% Cl₂–Ar gas. Microstructural effect makes the two CDC coatings exhibit different frictional behavior in ambient pressure and in vacuum. For the CDC@RBSiC coating, the friction coefficient was from 0.08 to 0.12 at ambient pressure and is sensitive to evacuation from ambient pressure to 10³ Pa while it was as high as 0.42 up to a pressure of 10^?4 Pa. Progressive evacuation does not vary the friction coefficient of the CDC@GSiC coating up to 10^?3 Pa. The wear of the CDC@GSiC coating was low with a maximum depth of 8 μm and much lower than that of the CDC@RBSiC coating (70 μm). The dimples on the surface and pores in the CDC@GSiC coating are reservoirs for ion liquid (IL), and the IL impregnated CDC@GSiC coating shows very low friction and wear at ambient pressure and in vacuum.     

Ultra High Pressure Tribometer for Testing CO2 Refrigerant at Chamber Pressures up to 2000 psi to Simulate Compressor Conditions

Abstract

The growing interest for using the natural refrigerant carbon dioxide (CO₂) in refrigeration and air-conditioning applications instead of HFC refrigerants, due to environmental concerns, has led to the development of an ultra high pressure tribometer (UHPT) specifically tailored for testing in CO₂ environment. The existing research on tribology related to CO₂ environment has focused on investigations at relatively low chamber pressures due to equipment restrictions. The UHPT is a unique tribometer that has been custom designed and manufactured to allow testing under CO₂ refrigerant at environmental pressures comparable to those found in compressors. A special housing, which surrounds the tribological surfaces subject to testing, is capable of withstanding chamber pressures up to 13.8 MPa (2000 psi) and can be temperature controlled from 0°C to 100°C via a thermal control system. A multi-axis strain gauge force transducer measures the applied load, frictional forces, and moments during friction testing, and computer control permits different loading profiles. Using this machine, experiments were performed at a range of pressures between 1.4 MPa (200 psi) and 6.9 MPa (1000 psi) of CO₂ refrigerant. The results suggest a slightly better tribological performance at higher pressures compared to lower pressures.