Search results for "QUENCHING"
showing 10 items of 275 documents
Influence of crystal defects on the electromigration of the hydrogen in palladium
2001
Abstract Electromigration and diffusion of hydrogen in palladium defected through quenching to liquid nitrogen temperature were investigated. It was found that the obtained experimental results cannot be described by means of a single flux of hydrogen which diffuses in a gradient of electric field. In order to effectively explain the obtained results, a theoretical model was elaborated. It assumed the existence of the following two fluxes of hydrogen in the quenched metal: • Ji—of migration, according to the interstitial mechanism, and • Ji–d—of migration, according to the interstitial-defective mechanism. Dependence of effective valences and diffusion coefficients for both mechanisms of tr…
Densified low-hygroscopic form of P2O5 glass
2011
P2O5 compound is an archetypical glass-forming oxide with a record-high hygroscopicity, which makes both the study and potential industrial uses of the glass extremely difficult. We found that the quenching from the P2O5 melt under ultrahigh pressures enables obtaining densified P2O5 glasses with a residual densification up to 12% at normal conditions. These glasses have a low hygroscopicity and can exist under air conditions for several weeks. An examination of the structure of the new form of P2O5 glass reveals a significant increase in neighbors of terminal oxygen atoms in the second coordination sphere and a cardinal decrease of the volume of nanovoids in the glassy matrix. The research…
Ab initiophase diagram of iridium
2016
The phase diagram of iridium is investigated using the Z methodology. The Z methodology is a technique for phase diagram studies that combines the direct Z method for the computation of melting curves and the inverse Z method for the calculation of solid-solid phase boundaries. In the direct Z method, the solid phases along the melting curve are determined by comparing the solid-liquid equilibrium boundaries of candidate crystal structures. The inverse Z method involves quenching the liquid into the most stable solid phase at various temperatures and pressures to locate a solid-solid boundary. Although excellent agreement with the available experimental data (to less than or similar to 65 G…
Exciton recombination dynamics inInAs∕InPself-assembled quantum wires
2005
In this work we investigate the exciton recombination dynamics in InAs/ InP semiconductor self-assembled quantum wires, by means of continuous wave and time resolved photoluminescence. The continuous wave photoluminescence results seem to indicate that the temperature quenching of the emission band seems to be more probably due to unipolar thermal escape of electrons towards the InP barrier. On the other hand, the analysis of time resolved photoluminescence reveals that the temperature dependence of the radiative and nonradiative recombination times is mainly determined by the dynamics of excitons localized by disorder shigh energy tail of the PL bandd and strongly localized slow energy tai…
Nitrogen vacancy type defect luminescence of AlN nanopowder
2020
Abstract Native luminescent defects were investigated in AlN nanopowder (NP) using spectral characterization methods. Photoluminescence and its excitation spectra were studied within a wide temperature range from 8K up to room temperature. It was found that in AlN NP a broad luminescence band appears within a blue spectral region consisting of at least two sub-bands at 415 nm and 390 nm, which can be related to presence of two different but in the same time similar defect types. These luminescent defects are located either inside the bulk material or on the material surface. Interaction of the surface defects with environmental oxygen was found resulting in quenching of the blue luminescenc…
UV-light induced luminescence processes in Al2O3 bulk and nanosize powders
2010
Abstract UV-light induced photoluminescence (PL) and thermoluminescence (TL) have been studied in the alumina (Al2O3) bulk and nanosize powders. It has been found that luminescence properties of the studied alumina powders are determined mainly by presence of the uncontrolled impurities of titanium, iron and chromium. Despite the general similarity of PL characterized by two main emission band around 400 and 750 nm a number of differences has been observed in relative yield and position of the emission bands as well as in the excitation spectrum of the short wavelength band. Essential differences have been observed also in the intensity of the TL signal, TL curves and TL emission spectra re…
Luminescence properties of Tb3+:Y3Al5O12 nanocrystallites prepared by the sol–gel method
2004
Tb 3+ :YAG nanocrystalline powders have been prepared by the sol-gel route. Structure and morphology of the obtained materials have been studied. The average grain sizes have been determined by X-ray powder diffraction measurements. Photo- and cathodoluminescence spectra of the Tb 3+ :Y 3 Al 5 O 12 powders have been measured. It has been found that the samples at low concentration demonstrate emission ascribable to the 5 D 3 →F J and 5 D 4 → 7 F J transitions. In particular, the concentration dependence of the luminescence spectra and lifetimes have been investigated as a function of the YAG grains sizes. It has been shown that the cross-relaxation responsible for the quenching of the 5 D 3…
Extrinsic Effects on the Optical Properties of Surface Color Defects Generated in Hexagonal Boron Nitride Nanosheets
2021
Hexagonal boron nitride (hBN) is a wide-band gap van der Waals material able to host light-emitting centers behaving as single photon sources. Here, we report the generation of color defects in hBN nanosheets dispersed on different kinds of substrates by thermal treatment processes. The optical properties of these defects have been studied using microspectroscopy techniques and far-field simulations of their light emission. Using these techniques, we have found that subsequent ozone treatments of the deposited hBN nanosheets improve the optical emission properties of created defects, as revealed by their zero-phonon linewidth narrowing and reduction of background emission. Microlocalized co…
Study of the long-period changes in samples of isotactic poly(propylene) obtained by quenching from the melt and subsequent annealing at different te…
1997
The structural modifications induced in samples of isotactic poly(propylene) obtained by quenching from the melt at 100°C/s and subsequently annealed at 40, 60 and 80°C for different annealing times have been studied using simultaneous wide-angle and small-angle X-ray scattering at the synchrotron radiation source of DESY. The occurrance of two different long-period values is demonstrated. These values are related to the mesomorphic phase, existing in the starting quenched material, and to the α-monoclinic one, which settles during the annealing process, respectively.
Synthesis of refractory metal nuggets and constraints on the thermal histories of nugget-bearing Ca, Al-rich inclusions
2015
Tiny refractory metal nuggets are mainly observed inside Ca, Al-rich inclusions (CAIs) from chondritic meteorites and are commonly assumed to be condensates from a solar composition gas. However, recent detailed studies of metal nugget compositions and their comparison with predictions from condensation show that the observed abundance patterns are extremely difficult to achieve in this way. As a test for the proposed alternative, precipitation from a silicate liquid, we conducted melting experiments, in which nine different refractory metals (nugget components) were equilibrated with each other along with a CAI-like liquid at reducing conditions. When quenched, minerals similar to those in…