Search results for "Glass"
showing 10 items of 1153 documents
Upconversion luminescence of a transparent glass ceramics with hexagonal Na(Gd,Lu)F4 nanocrystals
2017
Novel Er3+ doped transparent glass ceramics containing hexagonal Na(Gd,Lu)F4 nanocrystals were prepared from oxyfluoride glasses. The distribution of rare earth ions in the crystalline and glassy phase has been analyzed by X-ray diffraction and erbium luminescence decay kinetics measurement. A strong deviation of rare earth ion content in fluoride nanocrystals in comparison to the base glass has been observed. Preferential incorporation of Gd3+ over Lu3+ ions in the fluoride lattice leads to the stabilization of hexagonal Na(Gd,Lu)F4 structure and prevents the formation of cubic fluorite type solid solutions. A considerable enhancement of upconversion luminescence correlates with the format…
Electron paramagnetic resonance and photoluminescence investigation of europium local structure in oxyfluoride glass ceramics containing SrF2 nanocry…
2017
Different compositions of europium doped aluminosilicate oxyfluoride glass ceramics prepared in air atmosphere have been studied by electron paramagnetic resonance (EPR) and optical spectroscopy methods. X-ray diffraction (XRD) and transmission electron microscopy (TEM) measurements show presence of homogenously distributed SrF2 nanocrystals after the heat treatment of the precursor glass. Efficient Eu3+ incorporation in the high symmetry environment of glass ceramics is observed from the photoluminescence spectra. EPR spectra indicate Eu3+ → Eu2+ reduction upon precipitation of crystalline phases in the glass matrix. For composition abundant with Eu2+ in the glassy state such behaviour is …
Līvānu stikla fabrikas vēsture no 1970. gada līdz 1995. gadam
2019
Bakalaura darba temats ir “Līvānu stikla fabrikas vēsture no 1970. gada līdz 1995. gadam”. Šī bakalaura darba galvenais mērķis ir apkopot informāciju par Līvānu stikla fabriku dokumentos, publikācijas un mutvārdu vēstures stāstos laika posmā no 1975. gada līdz 1992. gadam un salīdzināt galvenos procesus un notikumus, kas notikuši fabrikas vēsturē. Tā rezultātā noskaidrot Līvānu stikla fabrikas nozīmi. Pētījuma rezultātā tapis bakalaura darbs, kur tika izpētīta un apzināta informācija par Līvānu stikla fabriku, tās vēsturi, galvenajiem attīstības posmiem, sabiedrisko dzīvi un norieta periodu. Pētījumā izmantoti Līvānu novada Centrālās bibliotēkās pieejamie novadpētniecības materiāli. Padziļi…
In situobservation of the generation and annealing kinetics of E ′ centres induced in amorphous SiO2by 4.7 eV laser irradiation
2011
The kinetics of E' centers induced in silica by 4.7eV laser irradiation was investigated observing in situ their optical absorption band at 5.8 eV. After exposure the defects decay due to reaction with diffusing molecular hydrogen of radiolytic origin. Hydrogen-related annealing is active also during exposure and competes with the photo-induced generation of the centers until a saturation is reached. The concentrations of E' and H2 at saturation are proportional, so indicating that the UV-induced generation processes of the two species are correlated. These results are consistent with a model in which E' and hydrogen are generated from a common precursor Si-H.
Static Properties of a Simulated Supercooled Polymer Melt: Structure Factors, Monomer Distributions Relative to the Center of Mass, and Triple Correl…
2004
We analyze structural and conformational properties in a simulated bead-spring model of a non-entangled, supercooled polymer melt. We explore the statics of the model via various structure factors, involving not only the monomers, but also the center of mass (CM). We find that the conformation of the chains and the CM-CM structure factor, which is well described by a recently proposed approximation [Krakoviack et al., Europhys. Lett. 58, 53 (2002)], remain essentially unchanged on cooling toward the critical glass transition temperature of mode-coupling theory. Spatial correlations between monomers on different chains, however, depend on temperature, albeit smoothly. This implies that the g…
Feasible glass‐melting process assisted by microwaves
2019
[EN] The advantages of microwave (MW) energy processing have been verified in the sintering of a ceramic frit at a pre-industrial scale. The challenge of achieving high temperature using MW energy at such dimensions was overcome and a mix of natural raw materials was heated until its fluxing point. Changes in dielectric properties of the raw materials mix were also measured in situ with the increase in temperature, being in accordance to thermal processes of a conventional heating process. The properties of the resulting ceramic frit were compared with the same frit obtained by the conventional sintering method. Both frits showed similar thermal behavior regarding DTA-TGA, heating microscop…
Mechanical properties, internal structure and transport mechanism of oxygen in cork
2015
During the post bottling aging, premature oxidation reactions could occur and the oxygen barrier properties of the stopper are often pointed out. Nowadays, the internal structure of this material or the effect of hydration on its mechanical properties are still undetermined. Moreover, regarding the barrier properties, the limiting step of the oxygen transfer was not yet fully understood as well as the effect of compression or the role of the glass/cork interface in a bottleneck. The study of the internal structure of cork stopper allowed us to visualize the macroporosity of the material and conclude that there is no interconnectivity between lenticels, for the two qualities studied. The eff…
The Pratz le Curtillet settlement
2016
Among the earliest habitats of the early Middle Ages studied in Franche-Comté, the Pratz le Curtillet a settlement sets itself apart by its location in the Jura highlands, renowned for its remoteness and inhospitable landscapes. On the Lizon plateau, the scope of the archaeological work explored on the 16 hectares and the quality of the remains still constitute an exceptional complex today. An imposing 16m by 13m stone building flanked by an annex forms the residential part of the estate, while sheltering fodder and livestock, while the second building houses a forge. Domestic and artisanal equipment provide ample documentation on the living conditions of this small community of high status…
Molecular dynamics near the glass transition
1993
Solid state 13C NMR spectroscopy has been applied to investigate the time scale and the geometry of rotational motions near the glass transition of the low-molar-mass van der Waals glass former 1,3,5-tri-α-naphthylbenzene (T g = 342 K). Two-dimensional 13C exchange spectra were taken between 347 and 372 K. With the principal values of the 13C chemical shift tensors determined from 13C CP/MAS spectra and static one-dimensional 13C spectra, the two-dimensional spectra are interpreted according to the isotropic rotational diffusional model to yield mean correlation times τ0 in the range 10 ms ˇ- τ0 ˇ- 50 s, and a log-Gaussian distribution of correlation times with a width of 1·5 decades. The m…
From strong to fragile glass formers: secondary relaxation in polyalcohols.
2002
We have studied details of the molecular origin of slow secondary relaxation near T(g) in a series of neat polyalcohols by means of dielectric spectroscopy and (2)H NMR. From glycerol to threitol, xylitol, and sorbitol the appearance of the secondary relaxation changes gradually from a wing-type scenario to a pronounced beta peak. It is found that in sorbitol the dynamics of the whole molecule contributes equally to the beta process, while in glycerol the hydrogen bond forming OH groups remain rather rigid compared to the hydrogens bonded to the carbon skeleton.