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Glass Composition (glass + composition)
Selected AbstractsQuaternary tephra marker beds and their potential for palaeoenvironmental reconstruction on Chatham Island, east of New Zealand, southwest Pacific Ocean,JOURNAL OF QUATERNARY SCIENCE, Issue 7 2010Katherine A. Holt Abstract Tephras provide one of the most reliable methods of time control and synchronisation within Quaternary sequences. We report on the identification of two widespread rhyolitic tephras , the Kawakawa and Rangitawa tephras , preserved in extensive peat deposits on Chatham Island ,900,km east of New Zealand. The tephras, both products of supereruptions from the Taupo Volcanic Zone, occur as pale, fine-ash dominated layers typically 10,150,mm thick. Mineralogically they are dominated by rhyolitic glass, together with subordinate amounts of quartz, feldspar, hypersthene, hornblende, Fe,Ti oxides and zircon. Phlogopite/biotite was identified additionally in Rangitawa Tephra. Ages for each tephra were obtained via mineralogical and major element glass composition-based correlation with well-dated equivalent deposits on mainland New Zealand, and we also obtained a new zircon fission-track age for Rangitawa Tephra (350,±,50,ka) on Chatham Island. Both tephras were erupted at critical times for palaeoenvironmental reconstructions in the New Zealand region: the Kawakawa at ca. 27 cal. ka, near the beginning of the ,extended' LGM early in marine isotope stage (MIS) 2; and the Rangitawa at ca. 350 ka near the end of MIS 10. The time constraints provided by the tephras demonstrate that Chatham Island peats contain long-distance pollen derived from mainland New Zealand, which provides a reliable proxy for identifying glacial,interglacial climate conditions, in this case during the MIS 11,10 and MIS 2,1 cycles. The two tephras thus provide important chronostratigraphic tie-points that facilitate correlation and synchronisation not only across the Quaternary deposits of the Chatham Islands group but also with climatically significant terrestrial and marine records in the wider New Zealand region. Copyright © 2010 John Wiley & Sons, Ltd. [source] Aqueous Corrosion of the GeSe4 Chalcogenide Glass: Surface Properties and Corrosion MechanismJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 8 2009Yi-Fan Niu The aqueous corrosion behavior of the GeSe4 glass composition has been studied over time under various conditions (temperature and pH). The evolution of the surface topography by atomic force microscopy and properties such as surface hardness and reduced modulus, as well as the optical transmission in the 1,16 ,m window, have been measured as a function of time spent in the corrosive solution. It was found that even if the glass reacts at room temperature, its optical transparency was barely affected. Nevertheless, the durability of GeSe4 was found to be drastically affected by an increase of both temperature and pH. Furthermore, pure selenium nanoparticles were formed during the corrosion process, and the nature of these nanoparticles,amorphous or crystallized (hexagonal phase),depends on temperature. A reaction mechanism was proposed, and the activation energy of the reaction of corrosion in deionized water (47 kJ/mol) was determined from an original technique that relies on the temporal optical loss variation of a GeSe4 optical fiber placed in water at different temperatures. [source] High-Temperature Oxidation Behavior of High-Purity ,-, ,-, and Mixed Silicon Nitride CeramicsJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 2 2002M. Backhaus-Ricoult High-temperature oxidation behavior, microstructural evolution, and oxidation kinetics of additive-free ,-, ,-, and mixed silicon nitride ceramics is investigated. The oxidation rate of the ceramics depends on the allotropic ratio; best oxidation resistance is achieved for ceramics rich in ,-phase. Variations in the oxidation kinetics are directly related to average grain size and glass distribution in the oxidation scale. The oxygen contents incorporated into the Si3N4 phase before its dissolution at the oxidation front affects the local glass composition and thereby yields nucleation and growth rates of SiO2 crystallites within the glass phase and a final oxidation scale microstructure, which depend on the incorporated oxygen contents. For the ,-polymorph, the dynamic oxygen solubility is found to remain negligible; therefore, a nitrogen-rich glass forms at the oxidation front, which promotes devitrification and yields a scale with small grain size and thin intergranular glass films. ,-Si3N4 is observed to form oxygen-rich solid solutions on oxidation, which are in contact with silicon oxynitride or oxygen-rich glass. Nucleation of cristobalite in the latter is sluggish, yielding coarse-grained oxidation scales with thick intergranular glass film. [source] Crystallization of Lead Niobate Glass by Mechanical ActivationJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 11 2001Junmin Xue Mechanical activation-triggered crystallization in PbNb2O6 -based glass was dependent on the initial presence of nuclei. The crystallization cannot be initiated by mechanical activation in a highly amorphous glass composition quenched from 1350°C where PbNb2O6 nuclei did not exist. The steady growth of nanocrystallites of PbNb2O6 was observed with an increasing degree of mechanical activation in the glass quenched from 1300°C, where a density of PbNb2O6 nuclei existed before mechanical activation. The inability to nucleate in the highly amorphous oxide glass by mechanical activation is consistent with the much higher structural stability as compared with that of metallic glasses, such as Fe-Si-B. The mechanical activation-grown PbNb2O6 nanocrystals were 10,15 nm in size as observed using HRTEM and their crystallinities were further improved by thermal aging at an elevated temperature in the range of 550° to 650°C. [source] Grain-Boundary Viscosity of BaO-Doped SiCJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 3 2000Giuseppe Pezzotti Internal friction characterization of the viscosity of a residual SiO2/BaO glass, segregated to grain boundaries of polycrystalline SiC, is presented. The anelastic relaxation peak of internal friction, arising from viscous slip along grain boundaries wetted by a glass phase, is analyzed. Two SiC polycrystals, containing SiO2/BaO glasses with different compositions, are studied and compared with a SiC polycrystal containing only pure SiO2. The internal friction peak is first analyzed with respect to its shift upon frequency change. This analysis allows quantitative assessment of both the intrinsic viscosity and the activation energy for viscous flow of the grain-boundary phase. Both parameters markedly decrease with increasing amounts of BaO dopant, which is consistent with data reported in the literature on SiO2 and SiO2/BaO bulk glasses with the same nominal composition. Analysis of the peak morphology is also attempted, considering the evolution of peak width while varying the grain-boundary glass composition. Moreover, the role of microstructural parameters, such as the distributions of grain size and grain-boundary angles, on the broadening of the internal friction peak is addressed, and a procedure is proposed that allows quantitative evaluation of the activation energy for viscous flow of intergranular glass merely from the width of the internal friction peak. [source] DEEPLY COLOURED AND BLACK GLASS IN THE NORTHERN PROVINCES OF THE ROMAN EMPIRE: DIFFERENCES AND SIMILARITIES IN CHEMICAL COMPOSITION BEFORE AND AFTER ad 150*ARCHAEOMETRY, Issue 5 2009V. VAN DER LINDEN In this work we attempt to elucidate the chronological and geographical origin of deeply coloured and black glass dating between 100 bc and ad 300 on the basis of their major and trace element compositions. Samples from the western and eastern parts of the Roman Empire were analysed. Analytical data were obtained by means of a scanning electron microscope , energy-dispersive system (SEM,EDS, 63 samples analysed) and laser ablation , inductively coupled plasma , mass spectrometry (LA,ICP,MS, 41 samples analysed). Among the glass fragments analysed, dark brown, dark purple and dark green hues could be distinguished. Only among the dark green fragments could a clear compositional distinction be observed between fragments dated to the periods before and after ad 150. In the early samples (first century bc to first century ad), iron, responsible for the green hue, was introduced by using impure sand containing relatively high amounts of Ti. In contrast, a Ti-poor source of iron was employed, containing Sb, Co and Pb in trace quantities, in order to obtain the dark green colour in the later glass samples. The analytical results obtained by combining SEM,EDS and LA,ICP,MS are therefore consistent with a differentiation of glassmaking recipes, detectable in glass composition, occurring in the period around ad 150. [source] The Relationship Between 27Al Quadrupolar Parameters and AlF63, Octahedron Connectivity in Crystalline and Glassy Fluoroaluminates,EUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 14 2007Monique Body Abstract 27Al SATRAS and MQ-MAS spectra were recorded for eight crystalline compounds, from the CaF2,AlF3 and BaF2,AlF3 binary and BaF2,CaF2,AlF3 ternary systems, and four glass compositions with different CaF2/BaF2/AlF3 contents. For the crystalline phases, the reconstruction of the spectra leads to the precise determination of the NMR parameters. For the glassy phases, the 27Al SATRAS spectra have been reconstructed using quadrupolar parameter distributions. The main finding of this study is the dependence of the quadrupolar frequency on the type of AlF63, octahedron connectivity. For crystalline phases the experimental ,Q values range between 75 kHz and 510 kHz for structures built up from isolated octahedra, and are between 560 kHz and 1250 kHz for structures built up from isolated chains of cis -connected octahedra, and are between 1530 kHz and 1580 kHz for structures built up from isolated chains of trans -connected octahedra. In the glassy phases the maximum of the quadrupolar frequency distribution shifts toward larger values and its width increases with increasing AlF3 content, and subsequently with the number of connected octahedra. The range of the ,Q values seems to indicate that when the octahedra are connected, cis connections occur most frequently. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007) [source] Sol,Gel Synthesis of PZT,Glass Nanocomposites Using a Simple System and CharacterizationINTERNATIONAL JOURNAL OF APPLIED CERAMIC TECHNOLOGY, Issue 5 2006V. Kumar A simple inorganic system has been developed for the sol,gel synthesis of piezoelectric PZT,glass nanocomposites. Nanocrystalline PZT are nucleated from the amorphous xerogel through controlled heat treatment at 600°C. The formation of the crystalline phase, particle size, morphology, kinetics, and mechanism of crystallization of PZT in the glass matrix have been studied using X-ray diffraction, scanning electron microscopy, and differential thermal analysis. The piezoelectric characteristics of the PZT,glass compositions have been determined, and are correlated with the microstructure and the crystalline phase of PZT. [source] Glass-to-Metal Seal Interfacial Analysis using Electron Probe Microscopy for Reliable Solid Oxide Fuel CellsJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 4 2009Scarlett J. Widgeon The chemical compatibility between sealing glasses and interconnect materials for solid oxide fuel cells (SOFCs) has been studied in SOFC environments. Two borate-based glass compositions were sealed to interconnect materials, 441 stainless-steel (441SS) and Mn1.5Co1.5O4 -coated 441SS. The Mn1.5Co1.5O4 -coated 441SS coupons were analyzed as-received using X-ray diffraction (XRD) and electron probe microanalysis (EPMA) to obtain structural information and concentration profiles, respectively. The concentration profiles and the lack of Fe-containing phases present in the XRD spectrum show Fe is present throughout the coating, suggesting that Fe is partially substituted in the Mn1.5Co1.5O4 spinel. The glass,metal coupons were heat treated in air at 750°C for 500 h. The specimens were analyzed by EPMA and scanning electron microscope (SEM) to obtain images of the glass microstructure at the interface, to verify seal adherence, and to record concentration profiles across the glass,metal interface, with an emphasis on Cr. In total, four seal configurations were tested and analyzed, and in all cases the glasses remained well adhered to the metal and coating, and there was no microstructural evidence of new reaction phases present at the interface. There was slight diffusion of Cr from the 441SS into the sealing glasses, and Cr diffusion was hindered by the coating on the coated 441SS samples. [source] Phase Equilibrium in the Fluorapatite,Anorthite,Diopside SystemJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 12 2000Dilshat Ubaydullayevich Tulyaganov The binary systems Ca5[PO4]3F,CaAl2Si2O8 and Ca5[PO4]3F,CaMgSi2O6 have been investigated, via annealing and quenching in the experimental method, direct observation of the melting behavior of the samples, X-ray diffraction analysis, petrography, and transmission electron microscopy. Phase equilibrium in the ternary system Ca5[PO4]3F,CaAl2Si2O8,CaMgSi2O6 was determined by combining information from the structure of the binary boundary systems and additional experimental data that were obtained from ternary compositions. The glass-formation region of the fluorapatite,anorthite,diopside system was studied, and the glass compositions for the development of glass-ceramics for technical and medical applications were identified. [source] Geochemistry of Darwin glass and target rocks from Darwin crater, Tasmania, AustraliaMETEORITICS & PLANETARY SCIENCE, Issue 3 2008Kieren T. Howard Target rocks at Darwin crater are quartzites and slates (Siluro-Devonian, Eldon Group). Analyses show 2 groups of glass, Average group 1 is composed of: SiO2 (85%), Al2O3 (7.3%), TiO2 (0.05%), FeO (2.2%), MgO (0.9%), and K2O (1.8%). Group 2 has lower average SiO2 (81.1%) and higher average Al2O3 (8.2%). Group 2 is enriched in FeO (+1.5%), MgO (+1.3%) and Ni, Co, and Cr. Average Ni (416 ppm), Co (31 ppm), and Cr (162 ppm) in group 2 are beyond the range of sedimentary rocks. Glass and target rocks have concordant REE patterns (La/Lu = 5.9,10; Eu/Eu* = 0.55,0.65) and overlapping trace element abundances. 87Sr/86Sr ratios for the glasses (0.80778,0.81605) fall in the range (0.76481,1.1212) defined by the rock samples. ,-Nd results range from ,13.57 to ,15.86. Nd model ages range from 1.2,1.9 Ga (CHUR) and the glasses (1.2,1.5 Ga) fall within the range defined by the target samples. The 87Sr/86Sr versus 87Rb/86Sr regression age (411 ± 42 Ma) and initial ratio (0.725 ± 0.016), and the initial 43Nd/144Nd ratio (0.51153 ± 000011) and regression age (451 ± 140 Ma) indicate that the glasses have an inherited isotopic signal from the target rocks at Darwin crater. Mixing models using target rock compositions successfully model the glass for all elementsexcept FeO, MgO, Ni, Co, and Cr in group 2. Mixing models using terrestrial ultramafic rocks fail to match the glass compositions and these enrichments may be related to the projectile. [source] COMPARING GLASS COMPOSITIONAL ANALYSES*ARCHAEOMETRY, Issue 3 2006M. J. BAXTER In a recently published study of Romano-British colourless glass compositions, using inductively coupled plasma spectroscopy, 28 glasses from Colchester sampled in a previous study were resampled. This was done deliberately, with a view to examining the repeatability of results from sampling on different occasions. We report on our results here, developing in the process some simple statistical methodology that could be applied in similar situations. The potential for combining analyses undertaken at different times is discussed and illustrated. [source] | |||||||||||||