Search results for "quartz"
showing 10 items of 239 documents
Petrogenesis of synorogenic diorite–granodiorite–granite complexes in the Damara Belt, Namibia: Constraints from U–Pb zircon ages and Sr–Nd–Pb isotop…
2015
The synorogenic Palmental complex (central Damara Belt, Nambia) consists of ca. 545 Ma old quartz diorites and rare granodiorites and ca. 520 Ma-old leucogranites, representing one of the earliest and most primitive phase of crustal plutonism predating the main high-T regional metamorphism. Most quartz diorites and one granodiorite evolved through multistage, polybaric evolutionary processes involving fractionation from a lithospheric mantle-derived melt, followed by fractional crystallization of mainly hornblende, plagioclase and apatite which is shown by decreasing MgO, FeO, CaO, TiO2 and P2O5 with increasing SiO2. Assimilation of felsic basement gneisses was also important during formati…
Structure and Doping Determined Thermoelectric Properties of Bi2Se3Thin Films Deposited by Vapour–Solid Technique
2019
In this work, a simple catalyst-free vapour-solid deposition method was applied for controlled deposition of two types (planar and disordered) of continuous Bi 2 Se 3 nanostructured thin films on different (fused quartz/glass, mica, graphene) substrates. Characterisation of electron transport (type, concentration and mobility of the main charge carriers) and thermoelectric properties (Seebeck coefficient and power factor) showed that proposed in this work deposition method allows to obtain Bi 2 Se 3 thin films with power factor comparable and even higher than reported for the Bi 2 Se 3 thin films grown by molecular beam epitaxy technique. Power factor of the best obtained thin films can be …
Structure-determined thermoelectric properties of Bi2Se3 thin films deposited by vapour-solid technique
2018
International audience; In this work, a simple catalyst-free vapour-solid deposition method is applied for controlled obtaining of two types (planar and disordered) continuous Bi2Se3 nanostructured thin films on different (fused quartz/glass, mica, graphene) substrates. Performed for the deposited thin films transport and thermoelectric characterization (type, concentration and mobility of the main charge carriers, Seebeck coefficient and power factor) showed that proposed deposition method allows to fabricate “low-doped” Bi2Se3 thin films with power factor comparable and even higher than reported for the Bi2Se3 thin films fabricated by molecular beam epitaxy technique.
Radiation induced generation of non-bridging oxygen hole center in silica: Intrinsic and extrinsic processes
2007
Abstract The generation of non-bridging oxygen hole center ( Si–O ) was investigated in a wide variety of natural (fused quartz) and synthetic silica samples exposed to different γ- and β-irradiation doses by looking at its optical bands. We distinguish two different generation processes: intrinsic associated with the cleavage of Si–O bond and characterized by a sublinear law and extrinsic due to the conversion of OH precursor characterized by a growth curve with a saturating tendency. The interplay between the two processes and the role of H are discussed.
Growth of paramagnetic defects by gamma rays irradiation in oxygen-deficient silica
2005
Abstract We report an electron paramagnetic resonance (EPR) study of gamma rays irradiation effects on an oxygen-deficient silica obtained from fused quartz. We have found that three types of E′ centers, E α ′ , E γ ′ and E δ ′ , and a paramagnetic defect in a spin triplet state (S = 1) are induced. The EPR signals dependence on the microwave power have been investigated. The concentrations of these centers as a function of gamma ray irradiation show that for high dose a limit value is reached suggesting a generation process from precursors.
Polish is quantitatively different on quartzite flakes used on different worked materials.
2020
Metrology has been successfully used in the last decade to quantify use-wear on stone tools. Such techniques have been mostly applied to fine-grained rocks (chert), while studies on coarse-grained raw materials have been relatively infrequent. In this study, confocal microscopy was employed to investigate polished surfaces on a coarse-grained lithology, quartzite. Wear originating from contact with five different worked materials were classified in a data-driven approach using machine learning. Two different classifiers, a decision tree and a support-vector machine, were used to assign the different textures to a worked material based on a selected number of parameters (Mean density of furr…
An electrochemical quartz crystal microbalance study of lithium insertion into thin films of tungsten trioxide II. Experimental results and compariso…
1995
Abstract Lithium insertion into amorphous thin films of tungsten trioxide (a-WO 3 ) prepared by thermal vacuum evaporation of WO 3 powder has been studied experimentally by chronoamperometry, cyclic voltammetry and ac impedance spectroscopy associated with electrochemical quartz crystal microbalance (EQCM). During cathodic polarization of the electrode and at short times two antagonistic processes occur. One is a non faradaic process and is associated with the expulsion of anions from the electrode surface under the effect of the electric field built in the electrolyte when a potential difference is imposed between the electrodes. The other one is the faradaic insertion of non-solvated lith…
An electrochemical quartz crystal microbalance study of lithium insertion into thin films of tungsten trioxide I. Modeling of the ionic insertion mec…
1995
A theoretical description of the mechanism of lithium insertion into amorphous thin films of tungsten trioxide (a-WO3) prepared by thermal vacuum evaporation of WO3 powder is presented. The model developed is based on the experimental results obtained by chronoamperometry and ac impedance spectroscopy associated with electrochemical quartz crystal microbalance (EQCM). The electrode mass change and the current flowing through the electrochemical cell during cathodic polarization are simulta neously recorded. As expected, it can be observed that the insertion process is associated with a gain of mass of the inserted electrode at long times (t > 1 s). On the other hand at short times (t < 1 s)…
Polymer dynamics in thin p-type conducting films investigated by ac-electrogravimetry. Kinetics aspects on anion exclusion, free solvent transfer, an…
2015
A new transfer model is proposed to explain ac-electrogravimetry response of p-doped films. This model takes into account the exclusion effect occurring as a result of the anion transfer. The insertion/expulsion of anions inside a film involves simultaneously the expulsion/insertion of free solvent molecules. The number of solvent molecules excluded depends on the volume of anion transferred. Solvent transfer stimulated by the conformational changes of films constitutes the remaining electrogravimetric response when the exclusion process cannot explain by itself this response. Consequently, the kinetics of this free solvent transfer can be directly related to the kinetics of conformational …
A late Eemian aridity pulse in central Europe during the last glacial inception
2005
How do ice ages begin? It's an obvious question to ask as we enjoy the relative luxury of an interglacial, but a hard one to answer. A look at past transitions may give some clues as to how this period will one day come to an end. A climate reconstruction based on sediments found beneath a lake in the Eifel mountains in Germany provides evidence of an extreme climate event lasting 468 years right at the end of the last interglacial. Dust storms, aridity, bushfires and the loss of trees associated with a warm climate coincided with a southward shift of the warm waters of the North Atlantic drift. In terms of insolation — the rate of delivery of the Sun's radiation to Earth — conditions then …