Composition Of Individual Grains Research Articles

Grain-to-Grain Compositional Variations and Phase Segregation in Copper-Zinc-Tin-Sulfide Films.

We have performed a rigorous investigation of the structure and composition of individual grains in copper-zinc-tin-sulfide (CZTS) films realized by sulfurization of a sputtered metal stack. Although on average close to the ideal CZTS stoichiometry, elemental analysis shows significant grain-to-grain variations in composition. High-resolution Raman spectroscopy indicates that this is accompanied by grain-to-grain structural variations as well. The intensity from the 337 cm(-1) Raman peak, generally assigned to the kesterite phase of CZTS, remains constant over a large area of the sample. On the other hand, signals from secondary phases at 376 cm(-1) (copper-tin-sulfide) and 351 cm(-1) (zinc-sulfide) show significant variation over the same area. These results confirm the great complexity inherent to this material system. Moreover, structural and compositional variations are recognized in the literature as a factor limiting the efficiency of CZTS photovoltaic devices. This study demonstrates how a seemingly homogeneous CZTS thin film can actually have considerable structural and compositional variations at the microscale, and highlights the need for routine microscale characterization in this material system.

Compositional Structure and Magnetic Properties of $\hbox{CoCrPt-SiO}_{x}$ Perpendicular Recording Medium

The diameter and compositional variations of magnetic crystal grains in a CoCrPt-SiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">x</sub> perpendicular magnetic recording medium were investigated by using a transmission electron microscope equipped with an energy-dispersive X-ray spectrometer. The grain boundary composition was estimated from the average film and the average grain compositions by taking account of their volumes. It has been shown that the composition of individual grain depends little on grain diameter. The variations in the magnetic anisotropy energy and the saturation magnetization are estimated from the compositions of individual magnetic crystal grains. The thermal stability of magnetic crystal grain is discussed on the basis of the estimated <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">K</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">u</sub> <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">V</i> / <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">kT</i> value.

Proveniência sedimentar: métodos e técnicas analíticas aplicadas

The analysis of sedimentary provenance is a tool increasingly used in basin analysis and particularly in the exploration for clastic hydrocarbon reservoirs. The original sand composition directly controls the types and intensity of the diagenetic processes promoting porosity reduction and generation in the sandstones. Therefore, provenance studies identifing the distribution of the original sands composition in time and space are fundamental for the prediction of potential sandstone reservoirs. Provenance analysis provides the mineralogic and lithologic composition of the source areas, infering their geographic location, climate and topography, determining the main routes of sand distribution, and the distance and time of transportation. The diversity of detrital heavy minerals occurring in sandstones and the occurrence in paragenesis diagnostic of specific source rocks make the analysis of heavy minerals the most sensitive and robust technique for provenance studies. The combination of detrital heavy minerals with quantitative whole-rock petrography, feldspars composition, quartz and rock fragments types allows to establish the complex history of the sediments from their source areas to the depositional sites. Furthermore, modern microanalytical techniques allow the precise determination of the chemical composition of individual grains through electron microprobe (e.g. garnets and tourmalines), the ages of zircon, monazite and titanite through SHRIMP (Sensitive High Resolution Ion Microprobe) or ICPMS - LA (Inductively-Coupled Plasma Mass Spectrometry by Laser Ablation). These parameters directly connect the grains of the sandstones with the composition and age of the igneous or metamorphic rocks of the source terrains. Additionally, apatite and zircon fission track studies may determine the main ages of uplift and erosion of the source terrains. Integrated provenance studies of sandstones from specific areas of several Brazilian margin basins (Santos, Campos, Espirito Santo, Jequitinhonha and Pelotas) allowed the identification of the main source-areas and routes of sediment dispersal. These works shall substantially contribute, together with diagenetic studies, for the reduction of risks envolved in the exploration for clastic reservoirs in the Brazilian margin basins.

Proveniência sedimentar: métodos e técnicas analíticas aplicadas

The analysis of sedimentary provenance is a tool increasingly used in basin analysis and particularly in the exploration for clastic hydrocarbon reservoirs. The original sand composition directly controls the types and intensity of the diagenetic processes promoting porosity reduction and generation in the sandstones. Therefore, provenance studies identifing the distribution of the original sands composition in time and space are fundamental for the prediction of potential sandstone reservoirs. Provenance analysis provides the mineralogic and lithologic composition of the source areas, infering their geographic location, climate and topography, determining the main routes of sand distribution, and the distance and time of transportation. The diversity of detrital heavy minerals occurring in sandstones and the occurrence in paragenesis diagnostic of specific source rocks make the analysis of heavy minerals the most sensitive and robust technique for provenance studies. The combination of detrital heavy minerals with quantitative whole-rock petrography, feldspars composition, quartz and rock fragments types allows to establish the complex history of the sediments from their source areas to the depositional sites. Furthermore, modern microanalytical techniques allow the precise determination of the chemical composition of individual grains through electron microprobe (e.g. garnets and tourmalines), the ages of zircon, monazite and titanite through SHRIMP (Sensitive High Resolution Ion Microprobe) or ICPMS - LA (Inductively-Coupled Plasma Mass Spectrometry by Laser Ablation). These parameters directly connect the grains of the sandstones with the composition and age of the igneous or metamorphic rocks of the source terrains. Additionally, apatite and zircon fission track studies may determine the main ages of uplift and erosion of the source terrains. Integrated provenance studies of sandstones from specific areas of several Brazilian margin basins (Santos, Campos, Espírito Santo, Jequitinhonha and Pelotas) allowed the identification of the main source-areas and routes of sediment dispersal. These works shall substantially contribute, together with diagenetic studies, for the reduction of risks envolved in the exploration for clastic reservoirs in the Brazilian margin basins.

Chemical forms of calcium in Ca,Zn- and Ca,Cd-containing grains excreted by tobacco trichomes

Tobacco (Nicotiana tabacum L. cv. Xanthi) plants exposed to toxic levels of zinc and cadmium excrete metals through their leaf trichomes (epidermal hairs) as Zn,Ca- and Cd,Ca-containing grains. Little is known about the nature and formation mechanism of these precipitates. The chemical, crystalline, and noncrystalline compositions of individual grains produced by tobacco were studied by scanning electron microscopy coupled with energy dispersive X-ray analysis (SEM-EDX), micro-X-ray diffraction (µXRD), and calcium K-edge micro X-ray absorption near edge structure (µXANES) spectroscopy. Zinc is predominantly incorporated in calcite and cadmium in calcite and vaterite. Aragonite, which occurs occasionally, does not seem to contain trace metals. In addition to being precipitated in its three possible polymorphic forms, calcite, aragonite, and vaterite, calcium is also speciated as amorphous CaCO3 and possibly organic Ca in some grains. Most often, a particular grain consists of two or more crystalline and noncrystalline phases. The observed variability of intra- and inter-grain elemental and phase composition suggests that this biomineralization process is not constrained by biological factors but instead results from thermodynamically and kinetically controlled reactions. This study illustrates the potential of laterally resolved X-ray synchrotron radiation techniques (µXRD and µXANES) to study biomineralization and metal immobilization processes in plants.Key words: biomineralization, detoxification, micro-XANES, micro-XRD.

Scales of equilibrium and disequilibrium during cleavage formation in chlorite and biotite‐grade phyllites, SE Vermont

AbstractDetailed electron microprobe analyses of phyllosilicates in crenulated phyllites from south‐eastern Vermont show that grain‐scale zoning is common, and sympathetic zoning in adjacent minerals is nearly universal. We interpret this to reflect a pressure‐solution mechanism for cleavage development, where precipitation from a very small fluid reservoir fractionated that fluid. Multiple analyses along single muscovite, biotite and chlorite grains (30–200 μm in length) show zoning patterns indicating Tschermakitic substitutions in muscovite and both Tschermakitic and di/trioctahedral substitutions in biotite and chlorite. Using cross‐cutting relationships and mineral chemistry it is shown that these patterns persist in cleavages produced at metamorphic conditions of chlorite‐grade, chlorite‐grade overprinted by biotite‐grade and biotite‐grade. Zoning patterns are comparable in all three settings, requiring a similar cleavage‐forming mechanism independent of metamorphic grade. Moreover, the use of40Ar/39Ar geochronology demonstrates this is true regardless of age. Furthermore, samples with chlorite‐grade cleavages overprinted by biotite porphyroblasts suggest the closure temperatures for the diffusion of Al, Si, Mg and Fe ions are greater than the temperature of the biotite isograd (&gt;∼400 °C). Parallel and smoothly fanning tie lines produced by coexisting muscovite–chlorite, and muscovite–biotite pairs on compositional diagrams demonstrate effectively instantaneous chemical equilibrium and probably indicate simultaneous crystallization.These results do not support theories suggesting cleavages form in fluid‐dominated systems. If crenulation cleavages formed in systems in which the chemical potentials of all major components are fixed by an external reservoir, then the compositions of individual grains defining these cleavages would be uniform. On the contrary, the fine‐scale chemical zoning observed probably reflects a grain‐scale process consistent with a pressure‐solution mechanism in which the aqueous activities of major components are defined by local dissolution and precipitation. Thus the role of fluids was probably limited to one of catalysing pressure‐solution and fluids apparently did not drive cleavage development.

Oxygen isotope heterogeneity in chondrules from the Mokoia CV3 carbonaceous chondrite

We report a study of the oxygen isotope ratios of chondrules and their constituent mineral grains from the Mokoia, oxidized CV3 chondrite. Bulk oxygen isotope ratios of 23 individual chondrules were determined by laser ablation fluorination, and oxygen isotope ratios of individual grains, mostly olivine, were obtained in situ on polished mounts using secondary ion mass spectrometry (SIMS). Our results can be compared with data obtained previously for the oxidized CV3 chondrite, Allende. Bulk oxygen isotope ratios of Mokoia chondrules form an array on an oxygen three-isotope plot that is subparallel to, and slightly displaced from, the CCAM (carbonaceous chondrite anhydrous minerals) line. The best-fit line for all CV3 chondrite chondrules has a slope of 0.99, and is displaced significantly (by δ 17O ∼ −2.5‰) from the Young and Russell slope-one line for unaltered calcium-aluminum-rich inclusion (CAI) minerals. Oxygen isotope ratios of many bulk CAIs also lie on the CV-chondrule line, which is the most relevant oxygen isotope array for most CV chondrite components. Bulk oxygen isotope ratios of most chondrules in Mokoia have δ 18O values around 0‰, and olivine grains in these chondrules have similar oxygen isotope ratios to their bulk values. In general, it appears that chondrule mesostases have higher δ 18O values than olivines in the same chondrules. Our bulk chondrule data spread to lower δ 18O values than any ferromagnesian chondrules that have been measured previously. Two chondrules with the lowest bulk δ 18O values (−7.5‰ and −11.7‰) contain olivine grains that display an extremely wide range of oxygen isotope ratios, down to δ 17O, δ 18O around -50‰ in one chondrule. In these chondrules, there are no apparent relict grains, and essentially no relationships between olivine compositions, which are homogeneous, and oxygen isotopic compositions of individual grains. Heterogeneity of oxygen isotope ratios within these chondrules may be the result of incorporation of relict grains from objects such as amoeboid olivine aggregates, followed by solid-state chemical diffusion without concomitant oxygen equilibration. Alternatively, oxygen isotope exchange between an 16O-rich precursor and an 16O-poor gas may have taken place during chondrule formation, and these chondrules may represent partially equilibrated systems in which isotopic heterogeneities became frozen into the crystallizing olivine grains. If this is the case, we can infer that the earliest nebular solids from which chondrules formed had δ 17O and δ 18O values around -50‰, similar to those observed in refractory inclusions.

Mechanically alloyed and hot pressed Ni–49.7Ti alloy showing martensitic transformation

Abstract The Ni–49.7Ti (at.%) alloy was prepared by mechanical alloying (MA) and different steps of milling were investigated. An almost fully amorphous alloy was obtained after 32 h of milling. After consolidation by uniaxial hot die pressing and annealing at 1000 °C for 28 h, a complicated multiphase structure composed of Ni3Ti, NiTi2 and NiTi phases was formed. The β-NiTi phase undergoes reversible thermoelastic martensitic transformation (MT) with Ms temperature as high as 172 °C. This phenomenon was explained by Fe and Cr solute content introducing during milling and formation of the 4H martensite structure. The structure observations performed using scanning electron microscopy allowed to conclude that the average chemical composition of individual grains was Ti—49.7, Ni—47.76, Fe—2.54 (all in at.%). The second phase between the rounded β-NiTi grains was identified as the Ni3Ti phase and additionally, in some other places of the sample the Ni3Ti phase was also found. Transmission electron microscopy (TEM) of sintered samples confirmed the presence of 4H martensite within fine grains of the β-NiTi phase.

Cometary and Interstellar Dust Analyzer for comet Wild 2

The Cometary and Interstellar Dust Analyzer (CIDA) instrument analyzes the composition of individual grains in the cometary coma. As each particle impacts a silver plate, the high‐impact energy due to the relative velocity of the spacecraft as it flies through the coma causes the elements and molecular compounds in the particle to become ionized. Using a fast time‐of‐flight mass spectrometer, a complete set of ions are detected for each impact, from a mass range of 1 (atomic hydrogen) up to a few thousand atomic mass units, encompassing all elements in the periodic table and many molecules, such as organic compounds. This experimental technique has already been applied with excellent success at Halley's comet, and the CIDA derivative instrument is flying on the Stardust mission, which will encounter comet Wild 2 in January of 2004. The data returned will give clues to the elemental and chemical composition of the dust component of this comet.

Rhodarsenide, (Rh,Pd)2As, a new mineral

The new mineral rhodarsenide, ideally (Rh, Pd)2As, has been found in concentrates from placers of the Srebrnica river, near the village Veluce in Central Serbia, The associated platinum-group minerals are PGE alloys, Rh-Ir sulpharsenides and sperrylite. Rhodarsenide is present as inclusions (up to 80 x 100 11m) in Pt-Fe and Ru-Os-Ir alloys. In reflected light it is brownish; pleochroism and anisotropy are weak to distinct. Maximum and minimum reflectance values in air for standard wavelengths (470, 546, 589 and 650 nm) are 46.3/45.5, 48.4/47,6, 49.5/48,2 and 51.2/49,8, respectively; values measured in oil are 38,2/32.9 (470), 39.8/35.7 (546),40.4/36.4 (589) and 40.5/36,6 (650). Vickers micro-indentation hardness (VHN2s) is 493-585 kg/mm2, Chemical compositions of individual grains of rhodarsenide vary between Rh 38.53-60,81, Pd 12.10-34.67, Pt 0,00-2,38, Ir 0.09- 0.48, Fe 0,00-0.10, Cu 0.08-0.46, As 23.42-27,96, Sb 0,09-1.60, and Te 0.08-1.20 wt.%, corresponding to: (Rhl.67Pdo.34)L201 ASO.99and (Rhl.07Pdo.94Ptom)L2.04 (ASO.9ISbo.04Teo.0l)m.96. The X-ray powder-diffraction pattern was indexed for an orthorhombic cell with a =5.866 A; b = 3.893 A; c = 7.302 A; a: b: c = 1.507: I: 1.875; V = 166.7 A3, For Z = 4, the calculated density is 11.32 g/cm3, The three strongest lines in the X-ray pattern are 2,237 (10), 2,067 (8) and 2.426 (7) A.

Nanocrystalline titanium aluminide

TiAl has potential of being a strong, light-weight structural material. Nanocrystalline TiAl samples were synthesized by sputtering, particle condensation in inert gas and high-pressure compaction of the powder. Structure and chemical composition of individual grains were investigated by X-ray diffraction, conventional transmission electron microscopy, high resolution electron microscopy and micro-chemical analysis. The grains ranged from 3 to 35 nm in diameter, with most of them measuring less than 10 nm. No ordered intermetallic phase was found. The majority of the grains consisted of disordered hexagonal phase with a composition close to Ti-55 at.% Al.

Re-evaluation of the chemistry of dust grains in the coma of comet Halley

THE bulk chemical composition of the dust grains in the coma of comet Halley has been determined1–11 by examination of data from the PUMA 1 and 2 and PIA mass spectrometers on the Vega and Giotto missions. Although the bulk elemental composition of rock-forming elements (that is, excluding C, H, N and O) seemed to be close to solar (that is, similar to CI carbonaceous chondrites), the ion ratios of some of these elements, such as Mg+/Si+ and Fe+/Si+, are rather different from those in CI chondrites. There has not been, however, a satisfactory investigation of the chemical composition of individual grains as a function of their mass. Here we re-evaluate the PUMA 1 and 2 data to perform such an analysis. We find that the compositions of heavy and light grains are very different, with light grains being magnesium-rich (silicon-deficient), whereas the mean Mg+/Si+ ratio in heavy grains is similar to CI chondritic. The marked difference in composition between light and heavy grains indicates that the origin of the two grain populations might be different.