Search results for "MINERALOGY"
showing 10 items of 1516 documents
Study of the MAu6(M = Cr, Mo, W) molecular species: A transition from halogenlike to hydrogenlike chemical behavior for gold
2004
Quantum chemical calculations suggest that a series of molecules with the general formula MAu6 are stable, where M is a a group 6 atom, Cr, Mo, W, respectively. These species have a structure analogous to the corresponding MH6 compounds, while they differ from the MX6, where X is a halogen. The further reaction MAu6 + 3Au2 → MAu12 is strongly exothermic.
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…
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…
Kinetics of phase separation in polymer blends for deep quenches
1986
Electro microscopy was used to study the phase separation kinetics of a polystyrene/polyvinylmethylether system subjected to a critical deep quench. The size of the phase-separated domains was found to increase linearly with time, implying that hydrodynamic effects control the rate of growth of the domains in the time scale and temperature range under consideration. From these measurements the growth velocity and approximate diffusion constants can be determined for three different temperatures. Comparison of these results with those obtained by light scattering on other systems and with theoretical predictions is possible by replotting in dimensionless units.
Mineralogical and chemical variability of fluvial sediments 2. Suspended-load silt (Ganga–Brahmaputra, Bangladesh)
2011
Sediments carried in suspension represent a fundamental part of fluvial transport. Nonetheless, largely because of technical problems, they have been hitherto widely neglected in provenance studies. In order to determine with maximum possible precision the mineralogy of suspended load collected in vertical profiles from water surface to channel bottom of Rivers Ganga and Brahmaputra, we combined Raman spectroscopy with traditional heavy-mineral and X-ray diffraction analyses, carried out separately on low-density and dense fractions of all significant size classes in each sample (multiple-window approach). Suspended load resulted to be a ternary mixture of dominant silt enriched in phyllosi…
Accuracy of 210Pb dating in two annually laminated lake sediments with high Cs background
1997
Abstract A low-background gamma ray spectroscopy system has been used for nondestructive determination of 210Pb, 226Ra, 134Cs and 137Cs in lake sediment samples. Two Finnish sediment cores with high 137Cs activity originating from the Chernobyl accident have been analysed and dated using 210Pb. The accuracy of the 210Pb dating method was checked by varve counting of replicate samples. In one lake the 210Pb method gave similar dating results as varves, but in the other lake significant differences were detected. It was found that a high Cs concentration significantly impairs the accuracy of the 210Pb activity measurement. However, tha reliability of the dating result depends mostly on the co…
An experimental approach to efficiency calibration for gamma-ray spectrometric analysis of large air particulate filters
2013
Abstract A full-energy-peak efficiency (FEPE) calibration procedure for gamma-ray spectrometric analysis of air particulate samples collected on large filters is described herein. The experimental results are obtained for an unconventional measurement geometry, termed a “packet-sample”. The sample is obtained from a large cellulose filter (45 cm×45 cm) used to collect air particulate samples that is resized to dimensions suitable for spectrometric measurements (6 cm×6 cm×0.7 cm). To determine the FEPEs, many standards were created, i.e., some filters containing a small amount of ThO 2 and others containing a known amount of KCl. Efficiency curves obtained through best fits to experimental d…
Thermoluminescence properties of AlN ceramics
1998
Abstract The paper describes thermoluminescence (TL) properties of AlN:Y 2 O 3 ceramics irradiated with ionising radiation. A high TL sensitivity of AlN:Y 2 O 3 ceramics to radiation encouraged a study of the AlN ceramics for application as a dosimetric material. The paper presents experimental data on: glow curve, emission spectrum, dose response, energy dependence, influence of heating rate and fading rate. The measured TL characteristics were compared with those of well-known, widely used TLDs, i.e. LiF:Mg,Ti, LiF:Mg,Cu,P and Al 2 O 3 :C. It is concluded that AlN:Y 2 O 3 ceramics showing a radiation sensitivity which is approximately 50 times greater than that of LiF:Mg,Ti is an interest…
Luminescence of cerium doped YAG nanopowders
2007
Abstract Cerium doped YAG nanopowders with grain size ∼ 20 nm have been synthesized by co-precipitation method. Time-resolved luminescence characteristics have been studied. The results obtained have been compared with the luminescence characteristics for well-studied YAG single crystals. In contrast to cerium doped YAG crystals, cerium doped nanocrystal does not reveal luminescence bands due to antisite defects under electron beam pulse and X-ray excitations at 80–300 K temperature range. It was detected that decay kinetic of Ce 3 + related emission in the nanocrystal can be approximated by two exponents with time constants ∼ 9 and ∼ 47 ns at 290 K. It is faster than single exponential dec…