The Experts below are selected from a list of 42207 Experts worldwide ranked by ideXlab platform
R B Rastogi - One of the best experts on this subject based on the ideXlab platform.
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zinc oxide and magnesium doped zinc oxide decorated nanocomposites of reduced graphene oxide as Friction and wear modifiers
ACS Applied Materials & Interfaces, 2019Co-Authors: Dinesh K Verma, Bharat Kumar, R B RastogiAbstract:Zinc oxide (ZnO) and magnesium-doped zinc oxide nanoparticles, Zn0.88Mg0.12O (ZMO), were prepared by autocombustion method. Further, nanocomposites of the as-prepared nanoparticles with microwave-synthesized reduced graphene oxide (rGO) nanosheets, ZnO–rGO and ZMO–rGO, have also been prepared with a view to see the effect of doping of magnesium in zinc oxide on the tribological properties of the nanocomposite. Morphologies of nanoparticles/nanosheets and their nanohybrids have been studied by employing scanning electron microscopy (SEM)/high-resolution (HR) SEM with energy-dispersive X-ray (EDX), transmission electron microscopy (TEM)/HR-TEM, X-ray diffraction, Fourier transform infrared, UV–visible, Raman, and X-ray photoelectron spectroscopy (XPS) techniques. Triboactivity of the additives in paraffin oil has been interpreted considering the parameters mean wear scar diameter, coefficient of Friction, Load-carrying capacity, and wear rates obtained from ASTM D4172 and ASTM D5183 tests using a four-ball ...
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Zinc Oxide- and Magnesium-Doped Zinc Oxide-Decorated Nanocomposites of Reduced Graphene Oxide as Friction and Wear Modifiers
2018Co-Authors: Dinesh K. Verma, Bharat Kumar, R B RastogiAbstract:Zinc oxide (ZnO) and magnesium-doped zinc oxide nanoparticles, Zn0.88Mg0.12O (ZMO), were prepared by autocombustion method. Further, nanocomposites of the as-prepared nanoparticles with microwave-synthesized reduced graphene oxide (rGO) nanosheets, ZnO–rGO and ZMO–rGO, have also been prepared with a view to see the effect of doping of magnesium in zinc oxide on the tribological properties of the nanocomposite. Morphologies of nanoparticles/nanosheets and their nanohybrids have been studied by employing scanning electron microscopy (SEM)/high-resolution (HR) SEM with energy-dispersive X-ray (EDX), transmission electron microscopy (TEM)/HR-TEM, X-ray diffraction, Fourier transform infrared, UV–visible, Raman, and X-ray photoelectron spectroscopy (XPS) techniques. Triboactivity of the additives in paraffin oil has been interpreted considering the parameters mean wear scar diameter, coefficient of Friction, Load-carrying capacity, and wear rates obtained from ASTM D4172 and ASTM D5183 tests using a four-ball lubricant tester at optimized concentration (0.125% w/v). The performance of base lube and its admixtures has been found to lie in the order ZMO–rGO > ZnO–rGO > ZMO > ZnO > rGO > paraffin oil. Outstanding enhancement in triboactivity of nanocomposites, particularly that of ZMO–rGO indicates that nanoparticles are irrefutably instrumental in reinforcement of rGO, and on the other hand, rGO is associated with abatement of agglomeration of the nanoparticles. Thus, interactions between rGO and nanoparticles are vehemently synergic in nature. It is noteworthy that the best results were obtained with the following optimized concentrations: ZnO/ZMO 0.25%; rGO 0.15% and composites 0.125% w/v. Morphological studies of the wear track lubricated with different additives have been performed using SEM and contact mode atomic force microscopy. Results are in conformity with the order given above. The EDX analysis of ZMO–rGO exhibits the presence of zinc and magnesium on the worn surface, supporting their role in the formation of in situ tribofilm. Their role is further corroborated by XPS studies. Owing to their excellent tribological behavior, these sulfur- and phosphorus-free composites may be recommended as potential wear and Friction modifiers
Graham J. Leggett - One of the best experts on this subject based on the ideXlab platform.
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Nanoscale Contact Mechanics of Biocompatible Polyzwitterionic Brushes
2016Co-Authors: Zhenyu Zhang, Andrew J. Morse, Steven P. Armes, Andrew L. Lewis, Mark Geoghegan, Graham J. LeggettAbstract:Friction force microscopy has been used to demonstrate that biocompatible, lubricious poly(2-(methacryloyloxy)ethylphosphorylcholine) (PMPC) brushes exhibit different Frictional properties depending on the medium (methanol, ethanol, 2-propanol, and water; the latter also with different quantities of added salt). The chemical functionalization of the probe (amine-, carboxylic acid-, and methyl-terminated probes were used) is not as important as the medium in determining the contact mechanics. For solvents such as methanol, where the adhesion between AFM probe and PMPC brushes is negligible, a linear Friction–Load relationship is observed. In contrast, the Friction–Load plot is nonlinear in ethanol or water, media in which stronger adhesion is measured. For ethanol, the data indicate Johnson–Kendall–Roberts (JKR) mechanics, whereas the Derjaguin–Muller–Toporov (DMT) model provided a good fit for the data acquired in water. Contact mechanics on zwitterionic PMPC brushes immersed in aqueous solutions of varying ionic strength followed the same trend, with high adhesion energies being correlated with a nonlinear Friction–Load relationship. These results can be rationalized by treating the Friction force as the sum of a Load-dependent term, attributed to molecular plowing, and an area-dependent shear term. In a good solvent for PMPC such as methanol, the shear term is negligible and the sliding interaction is dominated by molecular plowing. However, the adhesion energy is significantly larger in water and ethanol and the shear term is no longer negligible
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Nanoscale Contact Mechanics between Two Grafted Polyelectrolyte Surfaces
2015Co-Authors: Maryam Raftari, Graham J. Leggett, Zhenyu J. Zhang, Steven R. Carter, Mark GeogheganAbstract:The adhesive and Frictional behavior of end-grafted poly[2-(dimethylamino)ethyl methacrylate] (PDMAEMA) films (brushes) in contact with atomic force microscope tips from which PDMAEMA or poly(methacrylic acid) (PMAA) were grafted has been shown to be a strong function of pH in aqueous solution. The interaction between the brush-coated surfaces is determined by a combination of electrostatic and noncovalent interactions, modulated by the effect of the solvation state on the brush and the resulting area of contact between the probe and the surface. For cationic PDMAEMA–PDMAEMA contacts at low pH, the brushes are highly solvated; a combination of electrostatic repulsion and a high degree of solvation (leading to a significant osmotic pressure) leads to a small area of contact, weak adhesion, and energy dissipation through plowing. As the pH increases, the electrostatic repulsion and the osmotic pressure decrease, leading to an increase in the area of contact and a concomitant increase in the strength of adhesion through hydrophobic interactions; as a consequence, the Friction–Load relationship becomes nonlinear as shear processes contribute to Friction and the mechanics are fitted by DMT theory and, at higher pH, by the JKR model. For PDMAEMA–PMAA, the electrostatic interaction is attractive at neutral pH, leading to a large adhesion force, a large area of contact, and a nonlinear Friction–Load relationship. However, as the pH becomes either very small or very large, a significant charge is acquired by one of the contacting surfaces, leading to a large amount of bound solvent and a significant osmotic pressure that resists deformation. As a consequence, the area of contact is small, adhesion forces are reduced, and the Friction–Load relationship is linear, with energy dissipation dominated by molecular plowing
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Relationship Between Molecular Contact Thermodynamics and Surface Contact Mechanics
2015Co-Authors: Nikolaos Nikogeorgos, Christopher A. Hunter, Graham J. LeggettAbstract:Measurements have been made of the adhesion and Friction forces between organic monolayers in heptane/acetone mixtures using an atomic force microscope (AFM). It has been found that the contact mechanics are best modeled by treating the Friction force as the sum of a Load-dependent term (attributed to “molecular plowing”) and an area-dependent term attributed to shearing (adhesion). The relative contributions of plowing and shearing are determined by the coefficient of Friction, μ, and the surface shear strength τ. The transition from adhesion- to Load-determined Friction is controlled by the solvation state of the surface: solvated surfaces represent a limiting case in which the shear term approaches zero, and the Friction-Load relationship is linear, while in other circumstances, the Friction-Load relationship is nonlinear and consistent with Derjaguin–Muller–Toporov mechanics. A striking correlation has been observed between the concentration-dependence of the association constant (Ka) for the formation of 1:1 hydrogen-bonded complexes and the pull-off force Fa and surface shear strength τ for the same molecules when one partner is immobilized by attachment to an AFM probe and the other is adsorbed to a surface. Analysis of the concentration-dependence of Fa and τ enables the prediction of KS with remarkably high precision, indicating that for these hydrogen bonding systems, the tip–sample adhesion is dominated by the H-bond thermodynamics. For mixed monolayers, H-bond thermodynamics dominate the interaction even at very low concentrations of the H-bond acceptor. Even for weakly adhering systems, a nonlinear Friction-Load relationship results. The variation in τ with the film composition is correlated very closely with the variation in Fa. However, the coefficient of Friction varies little with the film composition and is invariant with the strength of tip–sample adhesion, being dominated by molecular plowing and, for sufficiently large concentrations of hydroxyl terminated adsorbates, the disruption of intramonolayer hydrogen bonding interactions
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influence of solvent environment and tip chemistry on the contact mechanics of tip sample interactions in Friction force microscopy of self assembled monolayers of mercaptoundecanoic acid and dodecanethiol
Langmuir, 2007Co-Authors: Tracie J. Colburn, Graham J. LeggettAbstract:Friction force microscopy measurements have been made for self-assembled monolayers of mercaptoundecanoic acid (C10COOH) and dodecanethiol (C11CH3) in different liquid media. In perfluorodecalin, the Friction−Load relationship was nonlinear and consistent with adhesion-controlled sliding. The effective range of the attractive force was controlled by using AFM tips functionalized with alkanethiols (chemical force microscopy). Like pairs of interacting molecules yielded data that were characterized by the Johnson−Kendall−Roberts model of contact mechanics, whereas the interaction between dissimilar pairs of molecules fitted the behavior predicted by the Derjaguin−Muller−Toporov model. In ethanol, the adhesive force was much smaller, and sliding was not adhesion-controlled. Under this condition of low adhesion, the Friction force varied linearly with the applied Load.
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influence of the solvent environment on the contact mechanics of tip sample interactions in Friction force microscopy of poly ethylene terephthalate films
Langmuir, 2006Co-Authors: Claire R. Hurley, Graham J. LeggettAbstract:Friction force microscopy measurements have been carried out on free-standing films of poly(ethylene terephthalate) in a variety of different media. In ethanol, the adhesion force was small, and the Friction-Load relationship was linear. In perfluorodecalin, nonlinearity was observed in the Friction-Load relationship, and the data have been found to fit the Johnson-Kendall-Roberts model of contact mechanics. The behavior in hexadecane was also characterized by a single-asperity contact model, but in this case, the data were found to fit the Derjaguin-Muller-Toporov model. It is suggested that these differences are due to the different strengths of tip-sample adhesion, which arise from the differences in the dielectric constants of the media: in ethanol, which has a high dielectric constant, the Friction force varies linearly with the Load, whereas in media of low dielectric constant, adhesion-limited behavior is observed.
Dinesh K Verma - One of the best experts on this subject based on the ideXlab platform.
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zinc oxide and magnesium doped zinc oxide decorated nanocomposites of reduced graphene oxide as Friction and wear modifiers
ACS Applied Materials & Interfaces, 2019Co-Authors: Dinesh K Verma, Bharat Kumar, R B RastogiAbstract:Zinc oxide (ZnO) and magnesium-doped zinc oxide nanoparticles, Zn0.88Mg0.12O (ZMO), were prepared by autocombustion method. Further, nanocomposites of the as-prepared nanoparticles with microwave-synthesized reduced graphene oxide (rGO) nanosheets, ZnO–rGO and ZMO–rGO, have also been prepared with a view to see the effect of doping of magnesium in zinc oxide on the tribological properties of the nanocomposite. Morphologies of nanoparticles/nanosheets and their nanohybrids have been studied by employing scanning electron microscopy (SEM)/high-resolution (HR) SEM with energy-dispersive X-ray (EDX), transmission electron microscopy (TEM)/HR-TEM, X-ray diffraction, Fourier transform infrared, UV–visible, Raman, and X-ray photoelectron spectroscopy (XPS) techniques. Triboactivity of the additives in paraffin oil has been interpreted considering the parameters mean wear scar diameter, coefficient of Friction, Load-carrying capacity, and wear rates obtained from ASTM D4172 and ASTM D5183 tests using a four-ball ...
Bharat Kumar - One of the best experts on this subject based on the ideXlab platform.
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zinc oxide and magnesium doped zinc oxide decorated nanocomposites of reduced graphene oxide as Friction and wear modifiers
ACS Applied Materials & Interfaces, 2019Co-Authors: Dinesh K Verma, Bharat Kumar, R B RastogiAbstract:Zinc oxide (ZnO) and magnesium-doped zinc oxide nanoparticles, Zn0.88Mg0.12O (ZMO), were prepared by autocombustion method. Further, nanocomposites of the as-prepared nanoparticles with microwave-synthesized reduced graphene oxide (rGO) nanosheets, ZnO–rGO and ZMO–rGO, have also been prepared with a view to see the effect of doping of magnesium in zinc oxide on the tribological properties of the nanocomposite. Morphologies of nanoparticles/nanosheets and their nanohybrids have been studied by employing scanning electron microscopy (SEM)/high-resolution (HR) SEM with energy-dispersive X-ray (EDX), transmission electron microscopy (TEM)/HR-TEM, X-ray diffraction, Fourier transform infrared, UV–visible, Raman, and X-ray photoelectron spectroscopy (XPS) techniques. Triboactivity of the additives in paraffin oil has been interpreted considering the parameters mean wear scar diameter, coefficient of Friction, Load-carrying capacity, and wear rates obtained from ASTM D4172 and ASTM D5183 tests using a four-ball ...
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Zinc Oxide- and Magnesium-Doped Zinc Oxide-Decorated Nanocomposites of Reduced Graphene Oxide as Friction and Wear Modifiers
2018Co-Authors: Dinesh K. Verma, Bharat Kumar, R B RastogiAbstract:Zinc oxide (ZnO) and magnesium-doped zinc oxide nanoparticles, Zn0.88Mg0.12O (ZMO), were prepared by autocombustion method. Further, nanocomposites of the as-prepared nanoparticles with microwave-synthesized reduced graphene oxide (rGO) nanosheets, ZnO–rGO and ZMO–rGO, have also been prepared with a view to see the effect of doping of magnesium in zinc oxide on the tribological properties of the nanocomposite. Morphologies of nanoparticles/nanosheets and their nanohybrids have been studied by employing scanning electron microscopy (SEM)/high-resolution (HR) SEM with energy-dispersive X-ray (EDX), transmission electron microscopy (TEM)/HR-TEM, X-ray diffraction, Fourier transform infrared, UV–visible, Raman, and X-ray photoelectron spectroscopy (XPS) techniques. Triboactivity of the additives in paraffin oil has been interpreted considering the parameters mean wear scar diameter, coefficient of Friction, Load-carrying capacity, and wear rates obtained from ASTM D4172 and ASTM D5183 tests using a four-ball lubricant tester at optimized concentration (0.125% w/v). The performance of base lube and its admixtures has been found to lie in the order ZMO–rGO > ZnO–rGO > ZMO > ZnO > rGO > paraffin oil. Outstanding enhancement in triboactivity of nanocomposites, particularly that of ZMO–rGO indicates that nanoparticles are irrefutably instrumental in reinforcement of rGO, and on the other hand, rGO is associated with abatement of agglomeration of the nanoparticles. Thus, interactions between rGO and nanoparticles are vehemently synergic in nature. It is noteworthy that the best results were obtained with the following optimized concentrations: ZnO/ZMO 0.25%; rGO 0.15% and composites 0.125% w/v. Morphological studies of the wear track lubricated with different additives have been performed using SEM and contact mode atomic force microscopy. Results are in conformity with the order given above. The EDX analysis of ZMO–rGO exhibits the presence of zinc and magnesium on the worn surface, supporting their role in the formation of in situ tribofilm. Their role is further corroborated by XPS studies. Owing to their excellent tribological behavior, these sulfur- and phosphorus-free composites may be recommended as potential wear and Friction modifiers
Gianpaolo Vitale - One of the best experts on this subject based on the ideXlab platform.
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closed loop mras speed observer for linear induction motor drives
IEEE Transactions on Industry Applications, 2015Co-Authors: Angelo Accetta, Maurizio Cirrincione, Marcello Pucci, Gianpaolo VitaleAbstract:This paper presents a closed-loop model reference adaptive system (CL-MRAS) speed observer developed for linear induction motor (LIM) drives. Starting from the structure of the CL-MRAS speed observer developed in the literature for rotating induction motors, a corresponding speed observer for LIMs has been developed here. It is based on the LIM dynamic model taking into consideration its dynamic end effects. In particular, the following aspects are original: 1) It employs the voltage and current models of the LIM considering its dynamic end effects, 2) it proposes a net thrust model including the braking force caused by the dynamic end effects; 3) it models the Friction Load of the LIM drive experimentally obtained with off-line tests. The proposed sensorless technique has been tested on a purposely developed experimental set-up. Results show that the CL-MRAS observer permits the drive to operate down to the speed of 0.01 m/s, i.e., about 0.15% of the rated speed, which is about 20 times lower than the minimum working speed achieved with other observers implemented on the same LIM drive, such as the total least squares (TLS) MRAS observer, the TLS EXIN full-order Luenberger observer, the extended Kalman filter, and, finally, the TLS EXIN Kalman filter.
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closed loop mras speed observer for linear induction motor drives
Energy Conversion Congress and Exposition, 2013Co-Authors: Angelo Accetta, Maurizio Cirrincione, Marcello Pucci, Gianpaolo VitaleAbstract:This paper presents a Closed-Loop Model Reference Adaptive System (CL-MRAS) speed observer developed for linear induction motor (LIM) drives. Starting from the structure of the CL-MRAS speed observer in literature, It is based on a LIM dynamic model taking into consideration the dynamic end-effects. Particularly, the following aspects are original: it employs the voltage and current models of the LIM considering the dynamic end effects, it proposes a net thrust model including the braking force caused by the dynamic end-effects, it considers the Friction Load of the LIM drive experimentally obtained with off-line tests. The proposed sensorless technique has been tested on a purposely developed experimental set-up. Results show that the CL-MRAS observer permits the drive to operate down to the speed of 0.02 m/s, i.e. about 0.03 % of the rated speed, which is about 10 times lower than the minimum working speed achieved with other observers implemented on the same LIM drive, like the TLS EXIN full-order Luenberger Observer and the TLS EXIN Kalman Filter.
