Download or read book Surface Characterization and Measurements of Adhesion Force Between Graphite Clustered Particles and Hastelloy X Surface Using an Atomic Force Microscope written by Naphtali Mokgalapa and published by . This book was released on 2011 with total page 81 pages. Available in PDF, EPUB and Kindle. Book excerpt: In this project, adhesion forces between a graphite cluster probe and Hastelloy X samples using an Atomic Force Microscope (AFM) with an attached graphite cluster on a probe are studied. The graphite particle was directly in and out of contact with Hastelloy X and produced a force curve from which the adhesion force was obtained. Hastelloy X surfaces with different grades of roughness due to oxidation were studied. The adhesion force was established using the Johnson, Kendall and Robert (JKR) theory. The irregular graphite cluster used as the probe was approximately 6 micrometer in diameter. The lift-off force of graphite cluster from Hastelloy X and MICA surface was determined in air. Also, the surface of the representative samples was characterized with AFM to determine surface roughness due to the oxidation. The high temperature surface oxidization plays important role in determining the structural integrity of materials over a long period of time, especially, materials of importance for the construction of VHTR systems. The oxidation of the surfaces would affect various properties, such as the emissivity and decay heat removal, as well as, the adhesion of particles on the surface, particularly under accident conditions. Surface characterizations were carried out at 800°C and a pressure of 10-6 torr, and their effects on the adhesion of graphite particles to surface are also discussed.

Download or read book Measurements of Adhesion Force Between Single Particles and Clusters Interacting with Some VHTR Structural Steels written by Naphtali Malesela Mokgalapa and published by . This book was released on 2016 with total page 130 pages. Available in PDF, EPUB and Kindle. Book excerpt: The adhesion force and work of adhesion between aerosols (graphite and silver) generated in very high temperature reactors (VHTRs) and interacting with structural materials are presented. The method involves using Atomic Force Microscopy (AFM) in an air environment glove box.The adhesion force data were obtained for a silver particle and a graphite cluster separately interacting with structural materials including Haynes 230, Inconel 617, and Hastelloy X under four different surface conditions including as received and after oxidation for five, 10, and 15 minutes, respectively. It was found that the Johnson, Kendall, and Roberts model (JKR) enabled the prediction of values that were up to three orders of magnitude higher than the experimental data when silver interacted with structural materials. The difference in order of magnitude between experimental data and theory for graphite in particular varied between one and three. In contrast, the inclusion of surface roughness of the silver particle and surface features of structural materials in calculations produced results that were one order of magnitude higher than the experimental data. These comparisons serve to provide insight into the significant influence that surface roughness has on adhesion force. Data produced in this work may be important in understanding the adhesion of silver and reactor grade graphite aerosols to structural materials and can contribute to particle resuspension calculations.

Download or read book Fundamental and Applied Studies of Particle surface Adhesion Forces Measured by Atomic Force Microscopy written by Elvin R. Beach (III.) and published by . This book was released on 2001 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Community Council Guidelines on Reform of the Common Fisheries Policy written by and published by . This book was released on 1992 with total page 3 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Particle Adhesion written by David J. Quesnel and published by CRC Press. This book was released on 2002-02-07 with total page 546 pages. Available in PDF, EPUB and Kindle. Book excerpt: Whenever a curved surface interacts with another surface, the principles of adhesion are at work. From the cells in your body to the dust on your glasses, intermolecular forces cause materials to attract one another. Elastic deformations resulting from these adhesive interactions store strain that can be liberated during particle detachment. Time dependent changes in adhesion can result from plastic deformation that both increases the real effective contact area and reduces the stored energy available to assist in particle removal. Processes such as these, based on the fundamentals tenets of particle adhesion, are now finding applications across many disciplines leading to a rich and rapid development of knowledge. This book documents the use of particle adhesion concepts in a variety of disciplines. Fields as varied as the cleaning of semiconductors, to the controlling of cancer metastasis, to the abatement of environmental pollution all benefit from applications of particle adhesion concepts.

Download or read book Atomic Scale Friction and Microfriction of Graphite and Diamond Using Friction Force Microscopy written by and published by . This book was released on 1993 with total page 39 pages. Available in PDF, EPUB and Kindle. Book excerpt: Friction of graphite and diamond surfaces against a sharp silicon nitride tip was measured using a friction force microscope (FFM). Atomic-scale friction of a freshly cleaved highly oriented pyrolytic graphite (HOPG) exhibited the same periodicity as that of corresponding topography. However, the peaks in friction and those in corresponding topography profiles were displaced relative to each other. Using Fourier expansion of the interaction potential, we have calculated interatomic forces between the FFM tip and graphite surface. We have shown that the variations in atomic-scale friction and the observed displacement between the peaks in friction and those in corresponding topography can be explained by the variations in interatomic forces in the normal and lateral directions. At large scan sizes (50 nm x 50 nm or larger), the variation of friction for graphite and a single-crystal (IIa) diamond was found to follow the local slope of the sample surface, suggesting that a ratchet mechanism is operative in microscale friction.

Download or read book Surface Force and Friction Measurements with an Atomic Force Microscope written by Anders Meurk and published by . This book was released on 1999 with total page 28 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Advances in Particle Adhesion written by Rijmai and published by CRC Press. This book was released on 1996-03-18 with total page 228 pages. Available in PDF, EPUB and Kindle. Book excerpt: In recent years, there has been an upsurge of interest in using techniques drawn from probability to tackle problems in analysis. These applications arise in subjects such as potential theory, harmonic analysis, singular integrals, and the study of analytic functions. This book presents a modern survey of these methods at the level of a beginning Ph.D. student. Highlights of this book include the construction of the Martin boundary, probabilistic proofs of the boundary Harnack principle, Dahlberg's theorem, a probabilistic proof of Riesz' theorem on the Hilbert transform, and Makarov's theorems on the support of harmonic measure. The author assumes that a reader has some background in basic real analysis, but the book includes proofs of all the results from probability theory and advanced analysis required. Each chapter concludes with exercises ranging from the routine to the difficult. In addition, there are included discussions of open problems and further avenues of research.

Download or read book Molecular Adhesion and Its Applications written by Kevin Kendall and published by Springer Science & Business Media. This book was released on 2007-05-08 with total page 433 pages. Available in PDF, EPUB and Kindle. Book excerpt: At the beginning of the twentieth century, engineers and technologists would have recognized the importance of adhesion in two main aspects: First, in the display of friction between surfaces — at the time a topic of growing importance to engineers; the second in crafts requiring the joining of materials — principally wood—to form engineering structures. While physical scientists would have admitted the adhesive properties of glues, gels, and certain pastes, they regarded them as materials of uncertain formulation, too impure to be amenable to precise experiment. Biological scientists were aware also of adhesive phenomena, but the science was supported by documentation rather than understanding. By the end of the century, adhesion and adhesives were playing a crucial and deliberate role in the formulation of materials, in the design and manufacture of engineering structures without weakening rivets or pins, and in the use of thin sections and intricate shapes. Miniaturization down to the micro- and now to the nano-level of mechanical, electrical, electronic, and optical devices relied heavily on the understanding and the technology of adhesion. For most of the century, physical scientists were aware that the states of matter, whether gas, liquid, or solid, were determined by the competition between thermal energy and int- molecular binding forces. Then the solid state had to be differentiated into crystals, amorphous glasses, metals, etc. , so the importance of the molecular attractions in determining stiffness and strength became clearer.

Download or read book Surface Characterization of Carbon Fibers by Atomic Force Microscopy written by and published by . This book was released on 2017 with total page 0 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Atomic scale Simulation of Adhesion Between Metallic Surfaces written by and published by . This book was released on 1990 with total page 11 pages. Available in PDF, EPUB and Kindle. Book excerpt: We have performed MD simulations of adhesive phenomena, on an atomic scale, between metals possessing both smooth and stepped-surfaces. Studies of adhesion between identical metals, consisting of either Au, Cu, or Ni, with (001) or (111) orientations, reveal the existence of adhesive avalanches as the bodies are brought to within a critical separation ((approximately)2 Å). That is, as the surfaces approach one another, one or both surface layers becomes unstable, and abruptly moves toward the other. This signals a transition from an initial system with two distinct surfaces to one possessing no identifiable surfaces. The presence of adhesive avalanches will pose difficulties in determining adhesive forces and energies by means of atomic force microscopy at sub-nanometer separations of probe tip and sample surface. 7 refs., 3 figs.

Download or read book Atomic Scale Friction Measurements Using Friction Force Microscopy Part 2 Application to Magnetic Media written by and published by . This book was released on 1993 with total page 39 pages. Available in PDF, EPUB and Kindle. Book excerpt: Atomic Force/Friction Force Microscopes (AFM/FFM) were used to study tribological properties of metal-particle tapes with two roughnesses, Co-gamma Fe2O3 tapes (unwiped and wiped), and unlubricated and lubricated thin-film magnetic rigid disks (as-polished and standard textured). Nanoindentation studies showed that the hardness of the tapes through the magnetic coating is not uniform. These results are consistent with the fact that the tape surface is a composite and is not homogeneous. Nanoscratch experiments performed on magnetic tapes using silicon nitride tips revealed that deformation and displacement of tape surface material occurred after one pass under light loads (approx. 100 nN). A comparison between friction force profiles and the corresponding surface roughness profiles of all samples tested shows a poor correlation between localized values of friction and surface roughness. Detailed studies of friction and surface profiles demonstrate an excellent correlation between localized variation of the slope of the surface roughness along the sliding direction and the localized variation of friction. Atomic-scale friction in magnetic media and natural diamond appears to be due to adhesive and ratchet (roughness) mechanisms. Directionality in the local variation of atomic-scale friction data was observed as the samples were scanned in either direction, resulting from the scanning direction and the anisotropy in the surface topography. Atomic-scale coefficient of friction is generally found to be smaller than the macro coefficient of friction as there may be less ploughing contribution in atomic-scale measurements.

Download or read book Advanced Techniques for Surface Engineering written by W. Gissler and published by Springer Science & Business Media. This book was released on 2013-04-17 with total page 402 pages. Available in PDF, EPUB and Kindle. Book excerpt: Today's shortages of resources make the search for wear and corrosion resistant materials one of the most important tasks of the next century. Since the surface of a material is the location where any interaction occurs, it is that there the hardest requirements on the material are imposed: to be wear resistant for tools and bearings; to be corrosion resistant for turbine blades and tubes in the petrochemical industry; to be antireflecting for solar cells; to be decorative for architectural panels and to combine several of these properties in other applications. Surface engineering is the general term that incorporates all the techniques by which a surface modification can be accomplished. These techniques include both coating and modification of the surface by ion implantation and laser beam melting. In recent years a continuously growing number of these techniques were developed to the extent that it became more and more difficult to maintain an overlook and to understand which of these highly differentiated techniques might be applied to resolve a given surface engineering problem. A similar development is also occuring for surface characterization techniques. This volume contains contributions from renowned scientists and engineers to the Eurocourse the aim of which was to inform about the various techniques and to give a comprehensive survey of the latest development on this subject.

Download or read book Atomic Scale Friction Measurements Using Friction Force Microscopy Part II Application to Magnetic Media written by and published by . This book was released on 1993 with total page 9 pages. Available in PDF, EPUB and Kindle. Book excerpt: Atomic Force/Friction Force Microscopes (AFM/FFM) were used to study tribological properties of metal-particle tapes with two roughnesses, Co gamma Fe2O3 tapes (unwiped and wiped), and unlubricated and lubricated thin-film magnetic rigid disks (as-polished and standard textured). Nanoindentation studies showed that the hardness of the tapes through the magnetic coating is not uniform. These results are consistent with the fact that the tape surface is a composite and is not homogeneous. Nanoscratch experiments performed on magnetic tapes using silicon nitride tips revealed that deformation and displacement of tape surface material occurred after one pass under light loads approx. 100 nN). A comparison between friction force profiles and the corresponding surface roughness profiles of all samples tested shows a poor correlation between localized values of friction and surface roughness.

Download or read book How Surface Roughness Affects Adhesion written by Antoine Sanner and published by . This book was released on 2023 with total page 0 pages. Available in PDF, EPUB and Kindle. Book excerpt: Abstract: At atomic scales, all molecules attract each other, but macroscopic objects usually do not stick.The explanation for this apparent paradox is that most surfaces are rough, so that elastically stiff objects only touch on the top of their asperities. Geckos and insects have compliant fibrillar structures or soft pads at the tip of their feet that conform to surface roughness, sustaining enough adhesion to climb vertical walls. Understanding the role of surface roughness in adhesion is a challenge because surfaces exhibit roughness down to the atomic scale. In this thesis, my collaborators and I investigate the effect of surface roughness on adhesion in both stiff and compliant contact systems. I model adhesion theoretically, and I help experimentalists analyze surface topography over multiple scales. The combination of my new models and of the comprehensive surface topography characterization by Abhijeet Gujrati (University of Pittsburgh), allows us to unravel the role of surface roughness in adhesion experiments. Stiff materials do not stick because roughness prevents most of the surfaces to come into the range of molecular attraction. A recent theory quantifies this effect based on an approximate expression for the distribution of interfacial gaps near the contact edge. Joe Monti (Johns Hopkins University) and I benchmark this expression against gap distributions extracted from finely resolved numerical simulations. The theory is valid provided that adhesive stresses are weak and act over a range shorter than a geometrical parameter determined by small-scale roughness. Elastically soft (jelly-like) objects stick because the elastic penalty to deform into intimate contact is small compared to the gain in surface energy. However, theories based on this simple thermodynamic argument cannot explain the fact that in experiments, the force measured during retraction is often much higher than during indentation. This adhesion hysteresis can be caused by material specific irreversibility or elastic instabilities triggered by surface roughness. The role of these instabilities in adhesion hysteresis remains poorly understood because existing numerical and theoretical models cannot account for realistic roughness in soft contacts. I introduce an efficient crack-perturbation model for the contact of rough spheres, enabling large scale simulations with realistic surface roughness. By clarifying the link between adhesion hysteresis and classic pinning problems (for example fracture of heterogeneous materials and wetting angle hysteresis), this model allows me to derive a simple theoretical model linking adhesion hysteresis to surface roughness. In combination with the characterization of surface roughness over multiple scales, my models shed light on the role of elastic instabilities in adhesion experiments. Surfaces are rough from the macroscopic scale down to the atomic scale, and the lack of comprehensive roughness characterization is the major obstacle towards bringing theory and experiments together. Abhijeet Gujrati and collaborators measured the roughness of four diamond coatings over eight decades of length scales, enabling the application of adhesion theories on experiments performed with these samples. Besides the experimental challenge of determining roughness down to the atomic scale, an additional obstacle to the documentation of roughness is the technical complexity of established multiscale roughness measures such as the power spectral density. My collaborators and I address this problem by introducing the scale-dependent roughness parameters (SDRPs), a new analysis framework that is easy to interpret and to implement. This new analysis, together with several established techniques, is available to use through our web-service contact.engineering. We thereby encourage the community to measure, analyze and publish roughness over multiple length scales. The SDRP analysis computes the fluctuations of slopes and curvatures as a function of the lateral length scale. Slopes and curvatures are important ingredients for rough contact theories, but it remains unclear at which scales they matter. Luke Thimons (University of Pittsburgh) and I show that in macro-scale contacts between ruby spheres and diamond coatings, the roughness that critically affects adhesion is between lateral length scales of 43~nm to 1.8~μm. The large-scale cutoff is related to the finite radius of the spherical indenter, while the unimportance of small scales is due to plastic deformations and the long range of the adhesive interaction (5~nm). To determine the critical range of length scales, as well as the parameters of the adhesive interaction, we analyzed the experimental pull-off forces by combining surface topography characterization and numerical simulations. Adhesion is critical in applications such as microelectromechanical systems (MEMS), soft robotics and skin adhesives. Our insights provide guidance for practitioners which scales of roughness to control in order to tune adhesion, and our framework for surface topography characterization will allow a better overall understanding of surface topography across the community

Download or read book Mechanics of Hysteretic Adhesive Elastic Mechanical Contact Between Rough Surfaces written by Haneesh Kesari and published by . This book was released on 2011 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: In experiments that involve contact with adhesion between two surfaces, as found in atomic force microscopy or nanoindentation, two distinct contact force (P) vs. indentation-depth (h) curves are often measured depending on whether the indenter moves towards or away from the sample. The origin of this hysteresis is not well understood and is often attributed to moisture, plasticity or viscoelasticity. We present experiments, atomistic simulations and continuum mechanics models that will show that hysteresis can exist without these effects, and that its magnitude depends on surface roughness. We explain the observed hysteresis as the result of a series of surface instabilities, where the contact area grows or recedes by a finite amount. We also demonstrate that when this is the case material properties can be estimated uniquely from contact experiments even when the measured P -h curves are not unique. The hysteresis energy loss during contact is also a measure of the adhesive toughness of the contact interface. We show experimentally that roughness can both increase and decrease the adhesive toughness of the contact interface. We show through numerical simulation of continuum adhesive contact models that the contact interface is optimally tough at conditions at which the contact region is at the cusp of the transition through which it turns form being mostly simply connected to being predominantly multiply connected.

Download or read book Capillary Adhesion and Friction written by Hussein Nasrallah and published by . This book was released on 2011 with total page 0 pages. Available in PDF, EPUB and Kindle. Book excerpt: The aim of this thesis is concerned with the influence of sliding velocity on capillary adhesion at the nanometer scale. In ambient conditions, capillary condensation which is a thermally activated process, allows the formation of a capillary meniscus at the interface between an atomic force microscope (AFM) probe and a substrate. This capillary meniscus leads to a capillary force that acts as an additional normal load on the tip, and affects the adhesion and friction forces. The Atomic Force Microscopy (AFM) offers interesting opportunities for the measurement of surface properties at the nanometer scale. Nevertheless, in the classical imaging mode, limitations are encountered that lead to a non stationary state. These limitations are overcome by implementing a new AFM mode (called Circular AFM mode). By employing the Circular AFM mode, the evolution of the adhesion force vs. the sliding velocity was investigated in ambient conditions on model hydrophilic and hydrophobic surfaces with different physical-chemical surface properties such as hydrophilicity. For hydrophobic surfaces, the adhesion forces or mainly van der Waals forces showed no velocity dependence, whereas, in the case of hydrophilic surfaces, adhesion forces, mainly due to capillary forces follow three regimes. From a threshold value of the sliding velocity, the adhesion forces start decreasing linearly with the logarithm increase of the sliding velocity and vanish at high sliding velocities. This decrease is also observed on a monoasperity contact between a atomically flat mica surface and a smooth probe, thus eliminating the possibility of the kinetics of the capillary condensation being related to a thermally activated nucleation process as usually assumed. Therefore, we propose a model based on a thermally activated growth process of a capillary meniscus, which perfectly explains the experimental results. Based on these results, we focused on directly investigating with the Circular mode the role of capillary adhesion in friction mechanisms. We investigated the influence of the sliding velocity on the friction coefficient, and a decrease following three regimes, similar to the sliding velocity dependence of the capillary adhesion, was observed for hydrophilic surfaces that possess a roughness higher than 0.1 nm. Whereas, an increase of the friction coefficient was observed on hydrophilic (Mica) or hydrophobic (HOPG) atomically flat surfaces that posses a roughness lower than 0.1 nm. However, in this latter case, the three regimes are not established. Finally, on a rough hydrophobic surface, the friction coefficient was sliding velocity independent. A direct comparison with capillary adhesion behavior with the sliding velocity is expected to give new insights to explain this interplay.