Scanning electron microscopy studies of wear in LM13 and LM13-graphite particulate composite

Examination of the structure of worn surfaces has shown that the wear of LM13 and LM13-graphite particulate composite is controlled by the nature and extent of subsurface deformation. The addition of graphite influences the wear characteristics by affecting the plastically deformed zone. The possible mechanisms of wear are discussed.

f-Gravity and the masses of elementary particles

Abstract is not available.

Dry wear of al-graphite particle composites

Under lubricated conditions, Al-graphite particle composite is a good antiseizure bearing and antifriction material possessing properties which inhibit excessive temperature rise in bearings. The present study characterizes the dry wear properties of the composite. The dry wear characteristics of the Al-(2.7%–5.7% graphite particle) (50–200μm) composite were found to deteriorate with the addition of graphite, load and sliding distance. Both micro structural and microhardness studies of the worn subsurfaces and analysis of wear debris show that the reductions in strength and ductility of the composite due to graphite addition are the most likely causes of deterioration in the wear properties of the composite.

Studies on electrical conductivity of insulator-conductor composites

The variation of electrical resistivity of an insulator-conductor composite, namely, wax-graphite composite, with parameters such as volume fraction, grain size, and temperature has been studied. A model is proposed to explain the observed variations, which assumes that the texture of the composite consists of insulator granules coated with conducting particles. The resistivity of these materials is controlled mainly by the contact resistance between the conducting particles and the number of contacts each particle has with its neighbors. The variation of resistivity with temperature has also been explained with the help of this model and it is attributed to the change in contact area. Journal of Applied Physics is copyrighted by The American Institute of Physics.

The Electronic Structure of Graphite from Compton Profile Measurements

Compton profile data are used to investigate the ground state wavefunction of graphite. The results of two new $\gamma$-ray measurements are reported and compared with the results of earlier $\gamma$-ray and electron scattering measurements. A tight-binding calculation has been carried out and the results of earlier calculations based on a molecular model and a pseudo-potential wavefunction are considered. The analysis, in terms of the reciprocal form factor, shows that none of the calculations gives an adequate description of the data in the basal plane although the pseudo-potential calculation describes the anisotropy in the plane reasonably well. In the basal plane the zero-crossing theorem appears to be violated and this problem must be resolved before more accurate models can be derived. In the c-axis direction the molecular model and the tight binding calculation give better agreement with the experimental data than does the pseudopotential calculation.

A world of Bose particles

Editor's Note: Satyendranath Bose, known primarily as one of the co–founders of quantum statistics, died on 4 February 1974, a few weeks after a symposium in honor of his 80th birthday was held at the Saha Institute for Nuclear Physics in Calcutta. The following paper, originally prepared in that connection, reviews some of the more important developments in particle physics which followed from the fundamental insight contained in a four–page paper published by Bose exactly fifty years ago. At the request of the editors of the AJP, Professor Sudarshan has kindly consented to adapt his paper for reproduction here. We would like to thank William Blanpied for bringing this paper to our attention.

Assembly of physalis mottle virus capsid protein in Escherichia coli and the role of amino and carboxy termini in the formation of the icosahedral particles

The coat protein gene of physalis mottle tymovirus (PhMV) was over expressed in Escherichia coli using pET-3d vector. The recombinant protein was found to self assemble into capsids in vivo. The purified recombinant capsids had an apparent s value of 56.5 S and a diameter of 29(±2) nm. In order to establish the role of amino and carboxy-terminal regions in capsid assembly, two amino-terminal deletions clones lacking the first 11 and 26 amino acid residues and two carboxy-terminal deletions lacking the last five and ten amino acid residues were constructed and overexpressed. The proteins lacking N-terminal 11 (PhCPN1) and 26 (PhCPN2) amino acid residues self assembled into T = 3 capsids in vivo, as evident from electron microscopy, ultracentrifugation and agarose gel electrophoresis. The recombinant, PhCPN1 and PhCPN2 capsids were as stable as the empty capsids formed in vivo and encapsidated a small amount of mRNA. The monoclonal antibody PA3B2, which recognizes the epitope within region 22 to 36, failed to react with PhCPN2 capsids while it recognized the recombinant and PhCPN1 capsids. Disassembly of the capsids upon treatment with urea showed that PhCPN2 capsids were most stable. These results demonstrate that the N-terminal 26 amino acid residues are not essential for T = 3 capsid assembly in PhMV. In contrast, both the proteins lacking the C-terminal five and ten amino acid residues were present only in the insoluble fraction and could not assemble into capsids, suggesting that these residues are crucial for folding and assembly of the particles.

Mechanics of Deformation under Traction and Friction of a Micrometric Monolithic MoS2 Particle in Comparison with those of an Agglomerate of Nanometric MoS2 Particles

Tribology of small inorganic nanoparticles in suspension in a liquid lubricant is often impaired because these particles agglomerate even when organic dispersants are used. In this paper we use lateral force microscopy to study the deformation mechanism and dissipation under traction of two extreme configurations (1) a large MoS2 particle (similar to 20 mu m width) of about 1 mu m height and (2) an agglomerate (similar to 20 mu m width), constituting 50 nm MoS2 crystallites, of about 1 mu m height. The agglomerate records a friction coefficient which is about 5-7 times that of monolithic particle. The paper examines the mechanisms of material removal for both the particles using continuum modeling and microscopy and infers that while the agglomerate response to traction can be accounted for by the bulk mechanical properties of the material, intralayer and interlayer basal planar slips determine the friction and wear of monolithic particles. The results provide a rationale for selection of layered particles, for suspension in liquid lubricants.

Amine-Templated Aluminoborates Exhibiting Graphite and Diamond Nets

A solvothermal reaction of Al2O3, H3BO3, pyridine, and H2O at 180 degrees C/7 days in the presence of organic amine molecules gave rise to four new aluminoborates, [(C6H18N2)(AlB6O13H3)], I; [(C5H16N2) (AlB5O10)]center dot 2H(2)O, II; [(C5H16N2)-(AlB5O10)], III; and [(C5H17N3)(AlB5O10)] center dot H2O, IV, with two- and three-dimensional structures. All the structures have been formed by the connectivity involving Al3+ ions and [B5O10] cyclic pentaborate units. In 1, the 3-connected trigonal nodes form a layer that resembles a graphite structure has been observed. The compounds II, III, and IV, have 4-connected nodes that forms a diamond related three-dimensional structure. The formation of solvatomorphs in II and III is noteworthy and has been observed first time in a family of amine template aluminoborates. A comparison of the various aluminoborate structures reveals subtle relationships between the organic amines (length of the amines) and the final framework structures. The compounds have been characterized using a variety of techniques including IR, second-order optical behavior, and MAS NMR studies.

Investigations on the influence of graphite filler on dry sliding wear and abrasive wear behaviour of carbon fabric reinforced epoxy composites

In this experimental study, the dry sliding wear and two-body abrasive wear behaviour of graphite filled carbon fabric reinforced epoxy composites were investigated. Carbon fabric reinforced epoxy composite was used as a reference material. Sliding wear experiments were conducted using a pin-on-disc wear tester under dry contact condition. Mass loss was determined as a function of sliding velocity for loads of 25, 50, 75, and 100 N at a constant sliding distance of 6000 m. Two-body abrasive wear experiments were performed under multi-pass condition using silicon carbide (SiC) of 150 and 320 grit abrasive papers. The effects of abrading distance and different loads have been studied. Abrasive wear volume and specific wear rate as a function of applied normal load and abrading distance were also determined. The results show that in dry sliding wear situations, for increased load and sliding velocity, higher wear loss was recorded. The excellent wear characteristics were obtained with carbon-epoxy containing graphite as filler. Especially, 10 wt.% of graphite in carbon-epoxy gave a low wear rate. A graphite surface film formed on the counterface was confirmed to be effective in improving the wear characteristics of graphite filled carbon-epoxy composites. In case of two-body abrasive wear, the wear volume increases with increasing load/abrading distance. Experimental results showed the type of counterface (hardened steel disc and SiC paper) material greatly influences the wear behaviour of the composites. Wear mechanisms of the composites were investigated using scanning electron microscopy. Wear of carbon-epoxy composite was found to be mainly due to a microcracking and fiber fracture mechanisms. It was found that the microcracking mechanism had been caused by progressive surface damage. Further, it was also noticed that carbon-epoxy composite wear is reduced to a greater extent by addition of the graphite filler, in which wear was dominated by microplowing/microcutting mechanisms instead of microcracking.

Reversible electrochemistry of cytochrome c on recompressed, binderless exfoliated graphite electrodes

The direct electrochemistry of cytochrome c (cyt-c) has been investigated on exfoliated graphite (EG) electrodes. The as-polished and roughened (using SiC emery sheet) EG surfaces are inactive for the direct electron transfer. However, when the EG electrode was sonicated before the experiment, a pair of redox waves were obtained for freely diffusing cyt-c in the solution phase. The formal potential was found to be 0.01 V (vs. SCE) in 0.1 M phosphate buffer at a pH of 7.1. The electrochemical response for the adsorbed cyt-c on sonicated EG electrodes, which is shown to have carbonyl functional groups on its surface, shows nearly reversible voltammograms in the same electrolyte. However, the formal potential in the adsorbed state is more negative than that observed for the solution phase cyt-c. A structure based on an open heme conformation proposed by Hildebrandt and Stockburger is probably present on the EG surface. It is suggested that the electrochemistry at the EG electrode is essentially governed by favourable electrostatic interactions.

Self-Assembly of Biopolymers on Colloidal Particles via Hydrogen Bonding

Fabrication of multilayer microcapsules via layer-by-layer approach through hydrogen bonding has attracted enormous interest due to its strong response to pH. In this communication, we have prepared hydrogen-bonded multilayer microcapsule without using any cross-linking agent by using DNA base pair (adenine and thymine) modified biocompatible polymers. The growth of the self-assembly on colloidal (melamine formaldehyde: MF) particles has been monitored with zeta potential measurement. The capsules were obtained on dissolution of MF particles at 0.1N HCl. The capsules were characterized with scanning electron microscopy. Moreover, we have observed the salt induced microscopic change in self-assembly of this system on the surface of colloidal particles.

Electrochemical insertion of Sr2+ ions onto nano delta-MnO2 particles

Manganese dioxide is known to be an important electroactive material for supercapacitors. Generally, delta-MnO2 is subjected to electrochemical characterization studies in aqueous electrolytes of Na2SO4. It exhibits capacitance behaviour in the potential range between 0 and 1.0 V vs. SCE (saturated calomel electrode). In the present study, it is shown that delta-MnO2 exhibits capacitance behaviour in Sr(NO3)(2) electrolytes also. The suitable potential range in this electrolyte is also found to be 0-1.0 V. Specific capacitancemeasured in Sr(NO3)(2) electrolyte is 192 F g(-1). X-ray photoelectron spectroscopy data confirm that Sr2+ ions get inserted onto delta-MnO2 anoparticles. (C) 2010 Elsevier B.V. All rights reserved.