Search results for "Metallurgy"
showing 10 items of 1419 documents
Role of Mobile Interstitial Oxygen Atoms in Defect Processes in Oxides: Interconversion between Oxygen-Associated Defects inSiO2Glass
2004
The role of mobile interstitial oxygen atoms (${\mathrm{O}}^{0}$) in defect processes in oxides is demonstrated by interconversion between the oxygen dangling bond and the peroxy radical (POR) in ${\mathrm{S}\mathrm{i}\mathrm{O}}_{2}$ glass. Superstoichiometric ${\mathrm{O}}^{0}$ was created by ${\mathrm{F}}_{2}$ laser photolysis of the interstitial ${\mathrm{O}}_{2}$. On annealing above $300\text{ }\ifmmode^\circ\else\textdegree\fi{}\mathrm{C}$, ${\mathrm{O}}^{0}$ migrated and converted the oxygen dangling bond to POR. Exposure to 5.0 eV light converted POR back to a pair of the oxygen dangling bond and ${\mathrm{O}}^{0}$ (quantum yield: $\ensuremath{\sim}0.1$). These findings suggest that…
Description of hysteresis of Nickel Metal Hydride Battery
2012
A Dynamic Preisach Model for the description of the hysteresis in Nickel Metal Hydride Battery is presented. Both the hysteresis and the dynamical features of charging and discharging cycles are described. The identification of the model is obtained by using a neural network technique developed for magnetic systems. The model is validated by some experimental tests on commercial batteries.
Pattern Formation During Dry Corrosion of Metals and Alloys
1987
About corrosion of metals and alloys, many exciting problems are not entirely solved. One of them concerns some morphological features such as, for example, stratified periodic structures that may appear, for example during the oxidation or sulfidation of metals and alloys. In this context, a high temperature corrosion kinetics is interpreted in terms of a bistable chemical system which can oscillate spontaneously if a feedback effect could exist. Some models analyse these patterning from a theoretical point of view. Stability analyses of the uniform standard steady state point out that it can be unstable by bifurcation and give rise to multilayered scales. Some non linearities, peculiar to…
Observation of a superfluid component within solid helium.
2011
We demonstrate by neutron scattering that a localized superfluid component exists at high pressures within solid helium in aerogel. Its existence is deduced from the observation of two sharp phonon-roton spectra which are clearly distinguishable from modes in bulk superfluid helium. These roton excitations exhibit different roton gap parameters than the roton observed in the bulk fluid at freezing pressure. One of the roton modes disappears after annealing the samples. Comparison with theoretical calculations suggests that the model that reproduces the observed data best is that of superfluid double layers within the solid and at the helium-substrate interface.
1987
The dielectric relaxation properties of a combined main-chain/side-chain liquid-crystalline polymer were investigated. It was found that the rotation of the side chain about the main chain (δ-process) is not as strongly restricted as in side-chain liquid-crystalline polymers. This is attributed to the facts that the side chain is attached to the flexible spacer within the chain backbone and that the concentration of the side chains is comparatively small. Two low-temperature relaxation processes were observed to occur in the glassy smectic and the crystalline state. They are attributed to intramolecular motions with in the mesogenic groups.
Variation of the optical absorption edge in AgGaS2 single crystals at high pressure
2003
In this paper the optical absorption edge of AgGaS 2 is measured as a function of pressure up to 26 GPa in order to verify the effect of the three phases transitions occurring in that pressure domain. The direct energy gap increases linearly with pressure at the rate of about 4.0 x 10 -2 eV GPa -1 up to 10.2 GPa. The absence of any discontinuity in the energy gap in the pressure range of 4.2-10.2 GPa confirms that the volume change, in the chalcopirite to monoclinic second-order transition, if it exists, is very small. When the pressure is raised above 10.2 GPa, the energy gap drops suddenly by about 1.1 eV and the spectral form of the absorption coefficient is typical of semiconductors wit…
Flotation with sedimentation: Steady states and numerical simulation of transient operation
2020
Abstract A spatially one-dimensional model of the hydrodynamics of a flotation column is based on one continuous phase, the fluid, and two disperse phases: the aggregates, that is, bubbles with attached hydrophobic valuable particles, and the solid particles that form the gangue. A common feed inlet for slurry mixture and gas is considered and the bubbles are assumed to be fully aggregated with hydrophobic particles as they enter the column. The conservation law of the three phases yields a model expressed as a system of partial differential equations where the nonlinear constitutive flux functions come from the drift-flux and solids-flux theories. In addition, the total flux functions are …
Analyses of known and new types of polyhalogenated aromatic substances in oven ash from recycled aluminium production
2003
Abstract Persistent aromatic bromine, chlorine and mixed chlorine-bromine compounds were analysed from recycled aluminium smelter (ALS) ashes to explore the impact of brominated flame retardants (BFR) on their formation. Polybrominated diphenyl ethers (PBDE) were the most abundant original BFRs found. Induction furnace ash contained tetra- to octa-BDEs about 2000 ng g −1 in similar congener ratios as the original scrap, but contents of nona- and deca-BDEs were only 25 and 5 ng g −1 indicating their significant degradation in ALS process. In the most non-polar fraction, PCB levels and profiles were similar as earlier ALS ash samples in 1990s. The highest PCB level measured was that of deca-C…
Electrochemical analysis of metallic heritage artefacts: voltammetry of microparticles (VMP)
2013
Abstract: This chapter discusses the application of the voltammetry of microparticles, a solid-state electrochemical technique, to the field of corrosion of archaeological metal. Identification of metals and alloys, identification, mapping and layer-by-layer analysis of corrosion products on metal surfaces using this technique are described. Applications include quantification of components of alloys and corrosion layers, and evaluation of metal conservation and the kinetics of long-term corrosion processes. Specific applications in archaeometry, conservation and restoration include authentication and dating.
Stress-Strain Law for Confined Concrete with Hardening or Softening Behavior
2013
This paper provides a new general stress-strain law for concrete confined by steel, fiber reinforced polymer (FRP), or fiber reinforced cementitious matrix (FRCM), obtained by a suitable modification of the well-known Sargin’s curve for steel confined concrete. The proposed law is able to reproduce stress-strain curve of any shape, having both hardening or softening behavior, by using a single closed-form simple algebraic expression with constant coefficients. The coefficients are defined on the basis of the stress and the tangent modulus of the confined concrete in three characteristic points of the curve, thus being related to physical meaningful parameters. It will be shown that if the v…