The frictional anisotropy of diamond

1981 ◽  
Vol 373 (1755) ◽  
pp. 405-417 ◽  
Keyword(s):  
Critical Load ◽  
Surface Damage ◽  
Diamond Surface ◽  
Radius Of Curvature ◽  
Type I ◽  
Diamond Surfaces ◽  
A Value ◽  
The Coefficient Of Friction ◽  
Contact Pressures ◽  
Critical Contact

This paper describes a study of the friction, in air, of a spherically tipped diamond stylus over the {100} face of a flat diamond surface. The results show that in general the friction is greater when sliding occurs along the <100> direction than along the <110> direction. This cannot be explained in terms of a Coulomb frictional mechanism where the friction is attributed to the climbing of one surface over the asperities on the other, for in that case the coefficient of friction is determined solely by the surface topography and is independent of load. By contrast, the experiments described in this paper show that below a critical load Wc the frictional anisotropy virtually disappears. This critical load is proportional to R 2 , where R is the radius of curvature of the stylus, implying, for Hertzian deformation, a critical contact pressure. For both type I and type II diamonds this critical pressure has a value of the order of 20 GN m -2 . At these and larger contact pressures cathodoluminescent studies of the flat diamond surfaces indicate that the frictional anisotropy is largely due to surface and sub-surface damage produced in preferred crystallographic directions by the sliding process itself. The results are discussed in terms of crack formation and plastic deformation. However, the results do not, as yet, provide an unequivocal account of the mechanism of energy dissipation.

Nano-Hardness, Nano-Friction and Nano-Wear of Ultra-Thin Overcoats

1994 ◽  
Vol 356 ◽  
Author(s):  
D. B. Bogy ◽  
Zhaoguo Jiang
Keyword(s):  
Critical Load ◽  
Normal Load ◽  
Wear Test ◽  
Indentation Hardness ◽  
Fatigue Wear ◽  
A Value ◽  
Hardness Tests ◽  
The Coefficient Of Friction ◽  
Protective Overcoats ◽  
Made In

AbstractThin film magnetic disks require protective overcoats, usually some form of carbon, to guard against corrosion and wear from interaction with the read/write transducer. In current products these films are less than 25 nm in thickness. This paper summarizes developments using scanning probe microscopes with sharp diamond tips (15 – 100 nm radius) to obtain indentation hardness tests with 5 nm deep indentations. We discuss an accelerated wear test that can measure wear at depths on the order of 1 nm. Finally material characterizations related to friction over sub-micron scans are discussed.A novel observation has been made when studying the dependence of friction coefficient on normal load: below a critical load, which is material and tip dependent, no observable wear occurs, and the coefficient of friction is about 0.05. Above the critical load the coefficient is load dependent and increases to a value more usually associated with the materials being tested. A study of fatigue wear was made in the “no-wear” regime with three different results. For some materials, fatigue wear occurred with multiple passes, when none was apparent for a single pass. Other materials showed no fatigue wear, and one material, silicon, showed a build-up or “negative-wear” under multiple passes. Interpretations and implications of these results are discussed.

Field-assisted ionization theory for microscopists

1994 ◽  
Vol 52 ◽  
pp. 820-821
Author(s):  
Patrick P. Camus
Keyword(s):  
Electric Field ◽  
Electron Tunneling ◽  
Ionization Probability ◽  
Critical Distance ◽  
Tunneling Probability ◽  
Field Ionization ◽  
Radius Of Curvature ◽  
Field Evaporation ◽  
A Value ◽  
Ion Emission

The theory of field ion emission is the study of electron tunneling probability enhanced by the application of a high electric field. At subnanometer distances and kilovolt potentials, the probability of tunneling of electrons increases markedly. Field ionization of gas atoms produce atomic resolution images of the surface of the specimen, while field evaporation of surface atoms sections the specimen. Details of emission theory may be found in monographs.Field ionization (FI) is the phenomena whereby an electric field assists in the ionization of gas atoms via tunneling. The tunneling probability is a maximum at a critical distance above the surface,xc, Fig. 1. Energy is required to ionize the gas atom at xc, I, but at a value reduced by the appliedelectric field, xcFe, while energy is recovered by placing the electron in the specimen, φ. The highest ionization probability occurs for those regions on the specimen that have the highest local electric field. Those atoms which protrude from the average surfacehave the smallest radius of curvature, the highest field and therefore produce the highest ionizationprobability and brightest spots on the imaging screen, Fig. 2. This technique is called field ion microscopy (FIM).

A Theoretical Tribological Comparison Between Soft and Hard Coatings of Spur Gear Pairs

2017 ◽  
Vol 139 (3) ◽  
Author(s):  
Huaiju Liu ◽  
Caichao Zhu ◽  
Zhanjiang Wang ◽  
Ye Zhou ◽  
Yuanyuan Zhang
Keyword(s):  
Surface Deformation ◽  
Tribological Behavior ◽  
Elastohydrodynamic Lubrication ◽  
Spur Gear ◽  
Hard Coatings ◽  
Radius Of Curvature ◽  
Maximum Pressure ◽  
Gear Pair ◽  
The Coefficient Of Friction ◽  
Squeeze Effect

A thermal elastohydrodynamic lubrication (TEHL) model is developed for a coated spur gear pair to investigate the effect of soft coatings and hard coatings on the tribological behavior of such a gear pair during meshing. The coating properties, i.e., the ratio of the Young's modulus between the coating and the substrate, and the coating thickness, are represented in the calculation of the elastic deformation. Discrete convolution, fast Fourier transform (DC-FFT) is utilized for the fast calculation of the surface deformation. The variation of the radius of curvature, the rolling speed, the slide-to-roll ratio, and the tooth load along the line of action (LOA) during meshing is taken into account and the transient squeeze effect is considered in the Reynolds equation. Energy equations of the solids and the oil film are derived. The temperature field and the pressure field are solved iteratively. The tribological behavior is evaluated in terms of the minimum film thickness, the maximum pressure, the temperature rise, the coefficient of friction, and the frictional power loss of the tooth contact during meshing. The results show discrepancies between the soft coating results and hard coating results.

scholarly journals Theoretical studies of the movement of grain moth eggs infected with the trichogram dosing and scattering device of an unmanned aerial vehicle

2020 ◽  
pp. 27-35
Author(s):  
S. O. Maranda ◽  
V. V. Adamchuk
Keyword(s):  
Unmanned Aerial Vehicle ◽  
Coefficient Of Friction ◽  
Particle Motion ◽  
Plant Protection ◽  
Theoretical Research ◽  
Test Material ◽  
Radius Of Curvature ◽  
Theoretical Studies ◽  
The Coefficient Of Friction ◽  
Aerial Vehicle

Annotation Purpose. Determination of the influence of parameters and modes of operation of the dosing and scattering device on the speed characteristics of the movement of grain moth eggs infected with trichogramma. Methods. Theoretical studies of the process of particle motion of the test material by the dosing and scattering device were performed using the basic laws of classical theoretical mechanics. Results. On the basis of the analysis of means for settlement of a trichogram the design of the dosing and scattering device of the unmanned aerial vehicle (UAV) for settlement of a trichogram is defined. According to the results of theoretical studies, it was concluded that in order to achieve high velocity characteristics of the trichogram movement, the length of the diffuser-deflector deflector, the radius of curvature of the deflector and the angle of the deflector sector must have parameters at which the trichogram will be minimally reduced. The material from which the dosing and dispensing device is made must have the lowest possible coefficient of friction. Conclusions 1. According to the results of theoretical research it is established that with increasing: the curvature of the deflector arc from 0.03 m to 0.09 m and the angle of the deflector sector 0° to 90°, the speed of the trichogram varies from 5 m/s to 3.5 m/s. 2. To increase the width of the capture when performing the technological operation of settling the trichogram, the angle of the deflector sector should be in the range of 45–90°. 3. When changing the coefficient of friction from 0.2 to 0.9, the velocity of the particle decreases from 4.61 m/s to 3.5 m/s. With an increase in the coefficient of friction in 2 times the speed decreases by 8%. Keywords: theory of material particle motion, dosing and scattering device, unmanned aerial vehicle, biological plant protection, trichogram settlement, settlement norm, capture width.

The Influence of Diamond Surface Perfection on the Preferential Nucleation of SP2 Carbon During Methane Pyrolysis

1992 ◽  
Vol 280 ◽  
Author(s):  
B. Y. Lin ◽  
C. P. Beetz ◽  
D. W. Brown ◽  
B. A. Lincoln
Keyword(s):  
Natural Diamond ◽  
High Energy ◽  
Diamond Surface ◽  
Structural Defects ◽  
High Energy Electron ◽  
Diamond Surfaces ◽  
Preferential Nucleation ◽  
Cvd Diamond Film ◽  
Surface Morphologies ◽  
Methane Pyrolysis

ABSTRACTWe report a set of CH4 pyrolysis experiments in a UHV system on diamond surfaces having varying degrees of surface roughness or perfection. Scanning electron microscopy (SEM), Auger electron spectroscopy (AES) and reflection high energy electron diffraction (RHEED) were used to examine the formation of graphite and the resulting surface morphologies. A (100) type Ha natural diamond having 3 sputtered craters on the surface was used as the substrate, sp2 carbon was formed preferentially on the structurally defective crater surfaces after ∼3×1010 L of CH4 exposure at 900°C, whereas essentially no sp2 carbon was found on the flat portions of the diamond surface. Similar experiments were also carried out on a polycrystalline CVD diamond film and sp2 carbon was formed on that surface afte ∼4×109 L of CH4 exposure at 900°C. These results indicate that structural defects on diamond surfaces are a crucial factor in the preferential nucleation of sp2 carbon during CH4 pyrolysis.

scholarly journals Platelet Adhesion and Thrombus Formation in Microchannels: The Effect of Assay-Dependent Variables

2020 ◽  
Vol 21 (3) ◽  
pp. 750 ◽  
Author(s):  
Mariangela Scavone ◽  
Silvia Bozzi ◽  
Tatiana Mencarini ◽  
Gianmarco Podda ◽  
Marco Cattaneo ◽  
...  
Keyword(s):  
Room Temperature ◽  
Platelet Adhesion ◽  
Storage Temperature ◽  
Thrombus Formation ◽  
Antiplatelet Agent ◽  
Significant Inhibition ◽  
Type I ◽  
Collagen Concentration ◽  
A Value ◽  
Platelet Deposition

Microfluidic flow chambers (MFCs) allow the study of platelet adhesion and thrombus formation under flow, which may be influenced by several variables. We developed a new MFC, with which we tested the effects of different variables on the results of platelet deposition and thrombus formation on a collagen-coated surface. Methods: Whole blood was perfused in the MFC over collagen Type I for 4 min at different wall shear rates (WSR) and different concentrations of collagen-coating solutions, keeping blood samples at room temperature or 37 °C before starting the experiments. In addition, we tested the effects of the antiplatelet agent acetylsalicylic acid (ASA) (antagonist of cyclooxygenase-1, 100 µM) and cangrelor (antagonist of P2Y12, 1 µM). Results: Platelet deposition on collagen (I) was not affected by the storage temperature of the blood before perfusion (room temperature vs. 37 °C); (II) was dependent on a shear rate in the range between 300/s and 1700/s; and (III) was influenced by the collagen concentration used to coat the microchannels up to a value of 10 µg/mL. ASA and cangrelor did not cause statistically significant inhibition of platelet accumulation, except for ASA at low collagen concentrations. Conclusions: Platelet deposition on collagen-coated surfaces is a shear-dependent process, not influenced by the collagen concentration beyond a value of 10 µg/mL. However, the inhibitory effect of antiplatelet drugs is better observed using low concentrations of collagen.

Characterization of the Chromosomalaac(6′)-Iz Gene of Stenotrophomonas maltophilia

1999 ◽  
Vol 43 (10) ◽  
pp. 2366-2371 ◽  
Author(s):  
Thierry Lambert ◽  
Marie-Cécile Ploy ◽  
François Denis ◽  
Patrice Courvalin
Keyword(s):  
Stenotrophomonas Maltophilia ◽  
Type I ◽  
Aminoglycoside Resistance ◽  
Reading Frame ◽  
A Value ◽  
Calculated Mass ◽  
Total Dna ◽  
Good Agreement

ABSTRACT The aac(6′)-Iz gene of Stenotrophomonas maltophilia BM2690 encoding an aminoglycoside 6′-N-acetyltransferase was characterized. The gene was identified as a coding sequence of 462 bp corresponding to a protein with a calculated mass of 16,506 Da, a value in good agreement with that of ca. 16,000 found by in vitro coupled transcription-translation. Analysis of the deduced amino acid sequence indicated that the protein was a member of the major subfamily of aminoglycoside 6′-N-acetyltransferases. The enzyme conferred resistance to amikacin but not to gentamicin, indicating that it was an AAC(6′) of type I. The open reading frame upstream from the aac(6′)-Izgene was homologous to the fprA gene of Myxococcus xanthus (61% identity), which encodes a putative pyridoxine (pyridoxamine) 5′-phosphate oxidase. Pulsed-field gel electrophoresis of total DNA from BM2690 and S. maltophilia ATTC 13637 digested with XbaI, DraI, and SpeI followed by hybridization with rRNA and aac(6′)-Iz-specific probes indicated that the gene was located in the chromosome. Theaac(6′)-Iz gene was detected by DNA-DNA hybridization in all 80 strains of S. maltophilia tested. The MICs of gentamicin against these strains of S. maltophilia were lower than those of amikacin, netilmicin, and tobramycin, indicating that production of AAC(6′)-Iz contributes to aminoglycoside resistance in S. maltophilia.

scholarly journals θ13, μτ SYMMETRY BREAKING AND NEUTRINO YUKAWA TEXTURES

2013 ◽  
Vol 28 (24) ◽  
pp. 1350118 ◽  
Author(s):  
BISWAJIT ADHIKARY ◽  
AMBAR GHOSAL ◽  
PROBIR ROY
Keyword(s):  
Symmetry Breaking ◽  
Neutrino Mass ◽  
Charged Lepton ◽  
Heavy Neutrino ◽  
Type I ◽  
Mixing Angles ◽  
Order Analysis ◽  
A Value ◽  
Mass Matrices ◽  
Best Fit

Within the type-I seesaw and in the basis where charged lepton and heavy neutrino mass matrices are real and diagonal, μτ symmetric four and three zero neutrino Yukawa textures are perturbed by lowest order μτ symmetry breaking terms. These perturbations are taken to be the most general ones for those textures. For quite small values of those symmetry breaking parameters, permitting a lowest order analysis, current best-fit ranges of neutrino mass squared differences and mixing angles are shown to be accommodable, including a value of θ13 in the observed range, provided all the light neutrinos have an inverted mass ordering.

The area of real contact and the shear strength of monomolecular layers of a boundary lubricant

1955 ◽  
Vol 227 (1171) ◽  
pp. 500-515 ◽  
Keyword(s):  
Shear Strength ◽  
Molecular Layer ◽  
Tangential Force ◽  
Surface Damage ◽  
Calcium Stearate ◽  
A Value ◽  
Boundary Lubricant ◽  
Tangential Forces ◽  
Monomolecular Layers ◽  
Single Molecular Layer

A method has been developed by which molecularly smooth surfaces may be placed together and the area of contact formed between them measured. Selected sheets of mica were cleaved to be free from cleavage steps on both sides of the sheets. These were bowed up and mounted as crossed cylinders in an apparatus in which normal and tangential loads could be applied. The area of contact formed between the surfaces has been examined using multiple-beam interference techniques. Examination of the hue and intensity of the central region of the interferograms enables a separation of the mica sheets to be detected even if this is of only a few ångströms. This means that the boundary of the region of contact may be determined with a greater precision than has hitherto been possible. Fringes of equal chromatic order provide a sensitive means for the detection of small particles of accidental contamination and have been used to show when the contact is intimate over the whole region. Normal and tangential forces have been applied to the mica specimens, both when in a clean condition and when covered with a monomolecular layer of calcium stearate. The area of contact was observed simultaneously. The area and the force required to shear it being known, the shear strength of the junctions has been calculated. The damage occurring during the process has been examined using reflexion electron microscopy. At certain values of the tangential force smooth sliding takes place on the lubricated surfaces and no surface damage can be detected. Further increase of the tangential force produces a rapid slip causing fragments to be torn out of the surface and some damage occurs. No smooth sliding was detected on unlubricated surfaces of mica and the damage produced during the slip was extensive. The force required to shear the junction formed between clean smooth mica surfaces is very high. A value of 10 Kg/mm 2 has been obtained. For the monomolecular layers of calcium stearate the value obtained is about forty times lower but is by no means negligible. This means that a considerable force is required to shear a film of boundary lubricant and accounts for the otherwise unexplained observation that when metals are lubricated with a single molecular layer of soap or fatty acid the frictional force is reduced by only a factor of 10 while the wear decreases by a factor of 10000 or more.

Molecular-Dynamics Simulations of Collisions of Buckminsterfullerene with Diamond Surfaces

1990 ◽  
Vol 206 ◽  
Author(s):  
R.C. Mowrey ◽  
D.W. Brenner ◽  
B.I. Dunlap ◽  
J.W. Mintmire ◽  
C.T. White
Keyword(s):  
Molecular Dynamics ◽  
Molecular Dynamics Simulations ◽  
Center Of Mass ◽  
Potential Energy Function ◽  
Diamond Surface ◽  
Many Body ◽  
Diamond Surfaces ◽  
Gas Phase Dissociation ◽  
Dynamics Simulations ◽  
Body Potential

ABSTRACTWe have performed molecular dynamics simulations using a recently developed empirical many-body potential energy function to study the collision of the C60 isomer buckmin-sterfullerene with a hydrogen-terminated diamond surface. The simulations indicate that the cluster can react with the surface and has a larger probability of gaining atoms from the surface than of losing atoms to the surface. We have investigated the dependence of the reaction probability on the initial center-of-mass translational velocity of the cluster. The structures and energy distributions of the product clusters have been determined. Both inelastically and reactively scattered clusters have large amounts of internal energy which suggests that gas-phase dissociation is likely.

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