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Solid Precursors (solid + precursor)

Distribution by Scientific Domains
Physics and Astronomy75%

Selected Abstracts

FMR study of strain-induced magnetic anisotropies in CrO2 thin films

PHYSICA STATUS SOLIDI (A) APPLICATIONS AND MATERIALS SCIENCE, Issue 15 2004
B. Z. Rameev
Abstract Epitaxial CrO2 thin films were grown on TiO2 (100) single-crystalline substrates by chemical vapour deposition (CVD) process with use of CrO3 solid precursor. The films with different thickness (27,530 nm) were studied by Ferromagnetic Resonance (FMR) technique. Strong dependence of FMR signal on the film thickness was observed in the series of CrO2 films deposited onto the pre-etched TiO2 substrates. It is shown that the magnetic behaviour of the CrO2 films arises from competition between magnetocrystalline and strain anisotropies that favour the [001] and [010] magnetization directions, respectively. For the thinnest film the strain anisotropy dominates, and the magnetic easy axis switches from [001] to the [010] direction. On the contrary, the CrO2 film grown on the unetched substrate demonstrates essentially strain-free magnetic anisotropy behaviour. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

Nanoparticle formation through solid-fed flame synthesis: Experiment and modeling

AICHE JOURNAL, Issue 4 2009
W. Widiyastuti
Abstract The preparation of silica nanoparticles through solid-fed flame synthesis was investigated experimentally and theoretically. Monodispersed submicrometer- and micrometer-sized silica powders were selected as solid precursors for feeding into a flame reactor. The effects of flame temperature, residence time, and precursor particle size were investigated systematically. Silica nanoparticles were formed by the nucleation, coagulation, and surface growth of the generated silica vapors due to the solid precursor evaporation. Numerical modeling was conducted to describe the mechanism of nanoparticle formation. Evaporation of the initial silica particles was considered in the modeling, accounting for its size evolution. Simultaneous mass transfer modeling due to the silica evaporation was solved in combination with a general dynamics equation solution. The modeling and experimental results were in agreement. Both results showed that the methane flow rate, carrier gas flow rate, and initial particle size influenced the effectiveness of nanoparticle formation in solid-fed flame synthesis. © 2009 American Institute of Chemical Engineers AIChE J, 2009 [source]

The Fountain Hills unique CB chondrite: Insights into thermal processes on the CB parent body

METEORITICS & PLANETARY SCIENCE, Issue 6 2009
Dante S. LAURETTA
This meteorite is closely related to the CBa class. Mineral compositions and O-isotopic ratios are indistinguishable from other members of this group. However, many features of Fountain Hills are distinct from the other CB chondrites. Fountain Hills contains 23 volume percent metal, significantly lower than other members of this class. In addition, Fountain Hills contains porphyritic chondrules, which are extremely rare in other CBa chondrites. Fountain Hills does not appear to have experienced the extensive shock seen in other CB chondrites. The chondrule textures and lack of fine-grained matrix suggests that Fountain Hills formed in a dust-poor region of the early solar system by melting of solid precursors. Refractory siderophiles and lithophile elements are present in near-CI abundances (within a factor of two, related to the enhancement of metal). Moderately volatile and highly volatile elements are significantly depleted in Fountain Hills. The abundances of refractory siderophile trace elements in metal grains are consistent with condensation from a gas that is reduced relative to solar composition and at relatively high pressures (10,3bars). Fountain Hills experienced significant thermal metamorphism on its parent asteroid. Combining results from the chemical gradients in an isolated spinel grain with olivine-spinel geothermometry suggests a peak temperature of metamorphism between 535 °C and 878 °C, similar to type-4 ordinary chondrites. [source]

Ferrous silicate spherules with euhedral iron-nickel metal grains from CH carbonaceous chondrites: Evidence for supercooling and condensation under oxidizing conditions

METEORITICS & PLANETARY SCIENCE, Issue 6 2000
A. N. KROT
The silicate portions of the spherules are highly depleted in refractory lithophile elements (CaO, Al2O3, and TiO2 <0.04 wt%) and enriched in FeO, MnO, Cr2O3, and Na2O relative to the dominant, volatile-poor, magnesian chondrules from CH chondrites. The Fe/(Fe + Mg) ratio in the silicate portions of the spherules is positively correlated with Fe concentration in metal grains, which suggests that this correlation is not due to oxidation, reduction, or both of iron (FeOsil , Femet) during melting of metal-silicate solid precursors. Rather, we suggest that this is a condensation signature of the precursors formed under oxidizing conditions. Each metal grain is compositionally uniform, but there are significant intergrain compositional variations: about 8,18 wt% Ni, <0.09 wt% Cr, and a sub-solar Co/Ni ratio. The precursor materials of these spherules were thus characterized by extreme elemental fractionations, which have not been observed in chondritic materials before. Particularly striking is the fractionation of Ni and Co in the rounded-to-euhedral metal grains, which has resulted in a Co/Ni ratio significantly below solar. The liquidus temperatures of the euhedral Fe, Ni metal grains are lower than those of the coexisting ferrous silicates, and we infer that the former crystallized in supercooled silicate melts. The metal grains are compositionally metastable; they are not decomposed into taenite and kamacite, which suggests fast postcrystallization cooling at temperatures below 970 K and lack of subsequent prolonged thermal metamorphism at temperatures above 400,500 K. [source]