The transition from severe to mild wear in law alloy steel

The wear rates of sliding surfaces are significantly reduced if mild oxidational wear can be encouraged. It is hence of prime importance in the interest of component life and material conservation to understand the factors necessary to promote mild, oxidational wear, The present work investigates the fundamental mechanism of the running-in wear of BS EN 31!EN 8 steel couples. under various conditions of load. speed and test duration. Unidirectional sliding experiments were carried out on a pin-on~disc wear machine where frictional force, wear rate, temperature and contact resistance were continuously monitored during each test. Physical methods of analysis (x-ray, scanning electron microscopy etc.) were used to examine the wear debris and worn samples. The wear rate versus load curves revealed mild wear transitions, which under long duration of running, categorized mild wear into four distinct regions.α-Fe20s. Fe304, FeO and an oxide mixture were the predominant oxides in four regions of oxidational wear which were identified above the Welsh T2 transition. The wear curves were strongly effected by the speed and test duration. A surface model was used to calculate the surface parameters, and the results were found to be comparable with the experimentally observed parameters. Oxidation was responsible for the transition from severe to mild wear at a load corresponding to the Welsh T2 transition. In the running-in period sufficient energy input and surface hardness enabled oxide growth rate to increase and eventually exceeded the rate of removal, where mild wear ensued. A model was developed to predict the wear volume up to the transition. Remarkable agreement was found between the theoretical prediction and the experimentally-measured values. The oxidational mechanjsm responsible for transitjon to mild wear under equilibrium conditions was related to the formation of thick homogenous oxide plateaux on subsurface hardened layers, FeO was the oxide formed initially at the onset of mild wear but oxide type changed.during the total running period to give an equilibrium oxide whose nature depended on the loads applied

Study on A.C properties of tin selenidethin films

A.c properties of tin selenide thin films prepared by an encapsulated selenization method are investigated. The measurements obtained from al/snse/al sandwich structures showed strong indication of frequency and temperature dependence of capacitance, dielectric loss and conductance over the ranges of 5-200 khz and 228-373 k, respectively. Dielectric behaviour was expected to be due to space charge polarization which contributed to a.c conduction. This was generally explained in terms of hopping of the charge carriers between localized states with activation energies 0.03-0.08 ev. Parameters such as trap binding energy (0.94 ev) and minimum hopping distance (1.01 nm) were also predicte

Growth of binary, ternary and quatenary III-V compounds nanowores by MOCVD

Various III-V compounds semiconductor Nanowires (NWs) have been grown by using vertical camber MOCVD. The morphology of the NWs has been characterized using FESEM and SEM. In addition to binary and ternary NWs such as GaAs, InP, InxGa1- xAs and AlyGa1-yAs NWs, the quaternary compounds InGaAsP NWs have been successfully grown. The growth of NWs has been assisted by gold nanocolloids as seed particles. Besides this technique, seed free-assisted growth of NWs has also been demonstrated. InxGa1-xAs NWs have been successfully grown without gold seedparticle assisted

Glass-formation region of ternary Sn-Sb-Se-based chalcogenide glasses

Tin-antimony-selenium (TAS)-based system belongs to the ternary chalcogenide compounds of IV-V-VI group owing to their heavy elemental masses, their glass formation region was assumed to be small comparing to their counterpart elements in the same group. However, there were rare published reports on their glass structure, while their glass boundary formation region was not yet reported. It was the aim of this paper to map their glass-forming region experimentally using XRD and validate it theoretically using the average co-ordination number, μ, and the fraction of the bond distributions, f, from chemical order model. Theoretically, it was validated that the glass formation was arrested between μ ≤ 2.4 and the fraction of Sn-Se bonds, f sn-se < 44.5%. XRD analyses of 66-as-prepared samples revealed that the glass formation region was located within the predicted area that mapped in structural triangle

The synthesis of cuprous oxide nanowires in the presence of oxygen using a hot tube thermal evaporation method

Cuprous oxide nanowires have been synthesized by heating copper foil in the presence of oxygen rich environment using a hot tube vacuum thermal evaporation method. The effect of growth parameters such as growth time, temperature and oxidative environment on the morphology of the nanowires is investigated. The growth of cuprous oxide nanowires from copper foils thermally oxidized in the presence of oxygen rich at temperatures between 300 and 500 0C. The nanowires were formed within the temperature range of 400 – 500 0C with diameters and length between 25 - 100 nm and length 1 - 4 µm, respectively. This gave an estimate of aspect ratio around 40. Observation from FESEM results revealed the optimal growth of cuprous oxide nanowires which occurred at oxidation times for 1h, 1/2h and 25 minutes and flow rates of oxygen at 0.09 psi, 0.12 psi and 0.08 psi. The atom% of copper and oxygen were measured using EDX and their existence were later confirmed by XRD, essentially indicated by 40% an 60% of copper and oxygen contents, respectively

Ellipsometric study of Si1-x Gex alloy

A report on ellipsometric studies of Si0.5 Ge0.5 and Si0.7 Ge0.3 thin films is described. The samples were earlier prepared from SiGe disks of 3” diameter using RF magnetron sputtering and the films were deposited onto glass substrates at room temperature. Some of the optical properties were investigated using an ellipsometer. In this method, we investigate the changes in refractive indices, n and extinction coefficients, k with film thickness as well as the relevant dielectric constant, ε. The results showed that, at a wavelength of 632.80 nm, n was found to increase with an increase of the germanium contents

LIGHT EMITTING GERMANIUM AND SILICON NANOISLANDS GROWN BY RF MAGNETRON SPUTTERING

The role of annealing temperature on the structural and optical properties of Ge and Si nanoislands deposited on Si(100) grown by radio frequency magnetron sputtering technique are studied. Atomic force microscopy confirmed the formation of Si and Ge nanoislands with estimated sizes lower than 100 nm and 45 nm respectively. The room temperature photoluminescence spectra for Si revealed an emission peak at 2.53 eV which is attributed to the formation of Si nanoislands whereas the observed strong luminescence peak at 3.22 eV for Ge nanoislands is attributed to the quantum size effect. A shift in the PL peak is observed upon annealing which is due to effect of quantum confinement and surface passivation by oxygen. The thermal annealing at 600 0 C is found to play an important role in controlling the shape, number density, root mean square roughness and the energy shift of the luminescence band for both Si and Ge nanoislands. The influence of annealing on growth morphology for Ge nanoislands is appeared to be stronger than Si. The growth mechanism and the luminescence is analyzed and compared with other observations

Silicon self-assembled growth of quantum dots grown on corning glass (7059) substrate

Silicon quantum dots have been grown on corning glass(7059) substrate using a self-assembly method of physical vapour deposition. The samples were fabricated at sufficiently low sputtering rate and varying experimental conditions. Apparently, the onset of nucleation took place during the first 5 minutes of deposition, followed by a further growth of stable islands known as quantum dots, with the measured radii comparable to the predicted values. Other measurement results confirmed the existence of these dots, including the bandgap energy ∼ 1.80 eV from PL and a 2% at. silicon from EDX and possible amorphous from XRD. The nucleation parameters were predicted as follows: Free energy change per unit volume ∆Gv = 2.64x104 Jmol-1; Surface energies per unit area, γLN = 1.48 Jm-2, γNS = 20.0 - 90.0 Jm-2 and γLS = 0.42 x 10-2 Jm-2; Critical energies ∆G* = 7.53x10-17 - 8.31x10-14 J; Critical radii r* = 9.0- 97.0 nm. This experimental evidence strongly support the early stage growth model of silicon quantum dot deposited on corning glass substrat

SOI based nanowire single-electron transistors: design, simulation and process development

One of the great problems in current large-scale integrated circuits is increasing power dissipation in a small silicon chip. Single-electron transistor which operate by means of one-by-one electron transfer, is relatively small and consume very low power and suitable for achieving higher levels of integration. In this research, the four masks step are involved namely source and drain mask, Polysilicon gate mask, contact mask, and metal mask. The masks were designed using ELPHY Quantum GDS II Editor with a nanowire length and nanowire width of approximately 0.10µm and 0.010 µm respectively. In addition, the process flow development of SET and the process and device simulation of SET are also explained in this paper. The Synopsys TCAD simulation tools are utilized for process and device simulation. The results from the device simulation showed that the final SET was operating at room temperature (300K) with a capacitance estimated around 0.4297 aF

The formation of nanoscale clusters-nanofilms/quantum dots predicted using a capillary model of nucleation

This paper describes the theoretical and simulation studies of both homogenous and heterogeneous nucleation, the phenomena that refers to the formation of stable nuclei prior to the growth of nanoclusters including nanofilms and quantum dots. Essentially, a single cluster may contain few thousand of atoms, and interaction with the surface may be preceded via processes, such as diffusion, hopping, sorption and coalescences. These complicated physical-chemical phenomena require in-depth theoretical understanding on how the various interacting quantities can be formulated and then resolved using specific mathematical approximation. In the case of a capillary model for heterogeneous nucleation, the nuclei are assumed to be in spherical shapes, which increase in both energies and diameters, and finally reach their critical points and settled to oval shapes prior to dome-like wetting on the substrate, essentially just like water droplet resting on a surface. The net change of energy, ∆G for the formation of cluster is found to be the functions of nucleus volume, surface area of atomic-nucleus interface, surface area of nucleus-surface interface and energy lost at substrate-atomic interface. The results for ∆G, ∆G*, r* and Ω and their respective changes with r, s and T were obtained and experimentally verified using existing data