Home About us Contact
|
Home About us Contact | ||
|
|
||
Single Grains (single + grain)
Selected AbstractsFrom Single Grains to TextureADVANCED ENGINEERING MATERIALS, Issue 10 2009Kun Yan Abstract Structural materials, such as metals, ceramics, and their composites are most often polycrystalline. The nature, morphology, and composition of their microstructure determine in large measure the mechanical properties of the final product, and the art to design novel materials is to find particular arrangements which make them harder, more shock absorbing, heat resistant, or self-recovering upon damage and aging. The understanding of the basic processes and their interplay in a polycrystalline structure are most important for improved simulation of plastic deformation and to predict their thermo-mechanical behavior. [source] Advances in optically stimulated luminescence dating of individual grains of quartz from archeological depositsEVOLUTIONARY ANTHROPOLOGY, Issue 6 2007Zenobia Jacobs Abstract Paleoanthropologists and archeologists interested in occupation histories, faunal remains, and objects of material culture have become increasingly reliant on optically stimulated luminescence (OSL) dating to construct Quaternary chronologies. In part, the increased use of OSL dating reflects its capacity to date events beyond the range of radiocarbon dating and in contexts where suitable organic materials are absent. An earlier review in Evolutionary Anthropology by Feathers1 provides a general account of the principles of luminescence dating. Since then, however, important advances have been made in OSL dating of quartz, so that it is now possible to date individual sand-sized grains and thereby resolve issues of postdepositional mixing of archeological sediments. In this review, we discuss the most important of these advances and their implications with regard to improved age control of archeological sites. We cover aspects of instrumental and methodological development that have facilitated the widespread measurement of single grains related to archeological questions and illustrate our review with some examples of where archeological problems have been resolved using single-grain OSL dating. We do not propose single-grain dating as a panacea, because there are instances where it is not straightforward to use or the results may be difficult to interpret; dating in such contexts remains the subject of continuing research. [source] Time,Temperature,Transformation (TTT) Diagrams for Crystallization of Metal Oxide Thin FilmsADVANCED FUNCTIONAL MATERIALS, Issue 17 2010Jennifer L. M. Rupp Abstract Time,temperature,transformation (TTT) diagrams are proposed for the crystallization of amorphous metal oxide thin films and their specific characteristics are discussed in comparison to glass-based materials, such as glass-ceramics and metallic glasses. The films crystallize from amorphous to full crystallinity in the solid state. As an example the crystallization kinetics for a single-phase metal oxide, ceria, and its gadolinia solid solutions are reported made by the precipitation thin-film method spray pyrolysis. The crystallization of an amorphous metal oxide thin film generally follows the Lijschitz,Sletow,Wagner (LSW) Ostwald ripening theory: Below the percolation threshold of 20 vol% single grains crystallize in the amorphous phase and low crystallization rates are measured. In this state no impact of solute on crystallization is measurable. Once the grains form primary clusters above the threshold the solute slows down crystallization (and grain growth) thus shifting the TTT curves of the doped ceria films to longer times and higher temperatures in comparison to undoped ceria. Current views on crystallization of metal oxide thin films, the impact of solute dragging, and primary TTT diagrams are discussed. Finally, examples on how to use these TTT diagrams for better thermokinetic engineering of metal oxide thin films for MEMS are given, for example, for micro-Solid Oxide Fuel Cells and resistive sensors. In these examples the electrical properties depend on the degree of crystallinity and, thereby, on the TTT conditions. [source] Amphibolite facies retrograde metamorphism of the Zhujiachong eclogite, SE Dabieshan: 40Ar/39Ar age constraints from argon extraction using UV-laser microprobe, in vacuo crushing and stepwise heatingJOURNAL OF METAMORPHIC GEOLOGY, Issue 5 2010H.-N. QIU Abstract The Zhujiachong eclogite in the south-eastern Dabieshan ultra-high- P terrane has been overprinted during retrograde metamorphism, with the development of garnet-amphibolite mineral assemblages in most rocks in the outcrop. This study is focused on providing age constraints for the retrograde amphibolite facies and greenschist facies mineralogy by 40Ar/39Ar dating. By applying a novel approach of combining three different techniques for extracting argon: laser stepwise heating of single grains and small separates, a spot fusion technique by UV-laser ablation microprobe on polished sections and an in vacuo crushing technique for liberating radiogenic argon from fluid inclusions, it is demonstrated that an internally consistent thermal history can be derived. The 40Ar/39Ar ages indicate that phengite formed before 265 Ma, probably during the ultra-high- P event. Ages associated with amphibolite facies retrograde metamorphism range from 242 to 217 Ma by the analyses of amphibole. Ages of c. 230 Ma were found for the symplectite matrix that formed during retrogression from eclogite pyroxene. Late stage hydrothermal activity leading to the formation of coarse-grained paragonite and fluid inclusions in vein amphibole was dated at c. 200 Ma. These age results agree well with the mineral crystallization sequence observed from thin-sections of the retrograded eclogite: phengite , paragonite and amphibole in matrix , amphibole in the corona. [source] Crystallization environment of Kazakhstan microdiamond: evidence from nanometric inclusions and mineral associationsJOURNAL OF METAMORPHIC GEOLOGY, Issue 5 2003L. F. Dobrzhinetskaya Abstract Nanometric solid inclusions in diamond incorporated in garnet and zircon from felsic gneiss of the Kokchetav massif, Kazakhstan, have been examined utilizing electron microscopy and focused ion beam techniques. Host garnet and zircon contain numerous pockets of multiple inclusions, which consist of 1,3 diamond crystals intergrown with quartz, phengite, phlogopite, albite, K-feldspar, rutile, apatite, titanite, biotite, chlorite and graphite in various combinations. Recalculation of the average chemical composition of the entrapped fluid represented by multiple inclusion pockets indicates that such fluid contained a low wt% of SiO2, suggesting a relatively low-temperature fluid rather than a melt. Transmission electron microscopy revealed that the diamond contains abundant nanocrystalline inclusions of oxides, rare carbonates and silicates. Within the 15 diamond crystals studied, abundant inclusions were found of SiO2, TiO2, FexOy, Cr2O3, ZrSiO4, and single grains of ThxOy, BaSO4, MgCO3, FeCr2O4 and a stoichiometric Fe-rich pyroxene. The diversity of trace elements within inclusions of essentially the same stoichiometry suggests that the Kokchetav diamond crystallized from a fluid containing variable amounts of Si, Fe, Ti, Cr, Zr, Ba, Mg and Th and other minor components such as K, Na, P, S, Pb, Zn, Nb, Al, Ca, Cl. Most of the components in crystals included in diamond appear to have their origin in the subducted metasediments, but some of them probably originate from the mantle. It is concluded that Kokchetav diamond most likely crystallized from a COH-rich multicomponent supercritical fluid at a relatively low temperature (hence the apparently low content of rock-forming elements), and that the diversity of major and minor components suggests interactions between subducted metasediments and mantle components. [source] TOF-SIMS analysis of cometary matter in Stardust aerogel tracksMETEORITICS & PLANETARY SCIENCE, Issue 1-2 2008Thomas Stephan While single grains >1 ,m are highly variable in their chemical composition, nanometer-scale material found in the wall of one track has within a factor of 1.22 bulk CI chondritic element ratios relative to Fe for Na, Mg, A1, Ti, Cr, Mn, and Co. Compared to CI, a depletion in Ca by a factor of four and an enrichment in Ni by a factor of two was observed. These results seem to confirm recent reports of a CI-like bulk composition of Wild 2. The analysis of organic compounds in aerogel samples is complicated by the presence of contaminants in the capture medium. However, polycyclic aromatic hydrocarbons that could possibly be attributed to the comet were observed. [source] Isotopic compositions of different presolar silicon carbide size fractions from the Murchison meteoriteMETEORITICS & PLANETARY SCIENCE, Issue 5 2000Sachiko AMARI Ratios of 12C/13C range from 37 to 42 and 14N/15N ratios from 370 to 520, within the range of single-grain measurements on coarser samples and in agreement with an asymptotic giant branch (AGB) star origin of most of the grains. Variations among size fractions do not show any simple trend and can be explained by varying contamination with isotopically normal material. Silicon isotopic ratios vary only little and, with one exception, lie to the right of the singlegrain mainstream correlation line. This might indicate a higher percentage of the minor populations Y and Z among finer grain-size fractions. All bulk samples have large 26Mg excesses attributed to the presence of short-lived 26Al at the time of grain formation. Inferred 26Al/27Al ratios are much larger than those measured in single larger mainstream grains. This is probably because of the presence of SiC grains of type X; we obtain an estimate of 0.4 for their 26Al/27Al ratio. Our Ca-isotopic measurements, the first made on presolar SiC grains, show excesses in 42Ca and 43Ca, which is in general agreement with theoretical expectations for AGB stars. Calcium-44 excesses are much larger than expected and are probably because of X grains, which have high44Ca excesses because of the decay of short-lived 44Ti produced in supernova explosions. We arrive at an estimate of 0.014 for the initial 44Ti/48Ti ratio of the X grains, within the range obtained from previous single X grain measurements. The Ti-isotopic ratios of the bulk samples show a V-shaped pattern with excesses of all isotopes relative to 48Ti. Isotopes 46Ti, 47Ti, and 50Ti show excesses relative to the correlation between Ti and Si ratios for single grains and are in general agreement with theoretical models of s-process nucleosynthesis in AGB stars. In contrast, 49Ti does not show any excess relative to the singlegrain data; it also fails to agree with theory, which predicts much larger excesses than observed. Measured 53Cr/52Cr and 57Fe/56Fe ratios are normal within errors. The first result is expected even for Cr in AGB star envelopes, but the second result suggests that most of the Fe analyzed originates from contamination. We have found no simple trends in isotopic composition with respect to grain size that can be interpreted in terms of nucleosynthetic origin, unlike the results for Kr, Xe, Ba, and Sr. [source] | ||||||||||