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Mean Grain Size (mean + grain_size)
Selected AbstractsMagnetic study of Hitperm alloys (Fe0.5Co0.5)1,x ,y ,zMxByCuz (M = Hf, Zr, Nb)PHYSICA STATUS SOLIDI (A) APPLICATIONS AND MATERIALS SCIENCE, Issue 7 2006Abstract A family of the Hitperm alloys (Fe0.5Co0.5)1,x ,y ,zMxByCuz (M = Hf, Zr, Nb) produced in an argon atmosphere as amorphous ribbons with 0.025 mm thickness are investigated up to 1200 K. The partial replacement of Fe by Co with optimal Fe0.5Co0.5 ratio increases the Curie temperature of the amorphous phase and the magnetic moment per formula unit. The early stages of crystallization can be observed by magnetization measurements. Alloys subjected to the first controlled crystallization stage are built of bcc-(Fe,Co) nanocrystals that are homegeneously embedded in the amorphous matrix. Mean grain sizes are about 11 nm. These two-phase alloys exhibit good soft magnetic properties with the relatively low coercive fields up to 50 A/m. Hafnium and hafnium/zirconium mixture are found to be the best inhibitors of the nanograin growth resulting in the best soft magnetic parameters. Alloys with niobium exhibit lower thermal stability and higher coercive fields. The correlation between the structure evolution and the magnetic properties is analysed and discussed. Conditions for optimum heat treatment are also determined. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] The Optimal Grain Sized Nanocrystalline Ni with High Strength and Good Ductility Fabricated by a Direct Current Electrodeposition,ADVANCED ENGINEERING MATERIALS, Issue 6 2008X. Shen In this work, six pure Ni specimen which mean grain sizes spans a broad range from ultra-fine to nanometer were fabricated by direct current electrodeposition and a coarse grain Ni was obtained by annealing. A gradual transition of the crystallographic preferred orientation of the deposited Ni from (200) texture to isotropic or random orientation with decreasing the mean grain size was revealed by XRD. [source] High-strain-rate Superplasticity in a Nanostructured Al-Mg AlloyADVANCED ENGINEERING MATERIALS, Issue 4 2005B. Q. Han In this work, the authors report high-strain-rate superplasticity in a nanostructured Al-7.5%Mg alloy with a mean grain size of 90 nm processed via consolidation of cryomilled Al-Mg powders. Tensile ductility with an elongation of 291% was observed at a strain rate of 10-1 s-1 and at a temperature of 573 K. Noteworthy is the fact that the microstructure is essentially stable during testing at 573 K. Grain boundary sliding is suggested to be the dominant deformation mechanism in the superplastic deformation of the nanostructured Al-Mg alloy. [source] Structural patterns in coarse gravelriver beds: typology, survey and assessment of the roles of grain size and river regimeGEOGRAFISKA ANNALER SERIES A: PHYSICAL GEOGRAPHY, Issue 1 2002Lea Wittenberg The concept of river-bed stability as indexed by the occurrence of stable bed forms was examined in humid-temperate perennial streams and in Mediterranean ephemeral streams. The study examined the structural patterns of bed forms and their spatial distribution between temperate-humid and Mediterranean streams. Study sites in Northumberland, UK, and Mt. Carmel, Israel, were selected for their morphometric similarity, despite the contrast in climate, vegetation and hydrological regime. Fieldwork was based on a large number of Wolman grain size distributions and structure measurements along cross-sections at seven sites; Differences in mean grain size of bed structures were estimated using the general linear model (GLM) procedure and Duncan's multiple range test. Based on field evidence, river-bed configurations were divided into structural categories, according to the depositional setting of each measured particle on the river bed. Statistical analysis confirmed former qualitative descriptions of small-scale bed forms. The study identified spatial segregation in bed form distribution. In general, 30,40%of the bed material in the surveyed perennial streams was clustered, in contrast to approximately 10%in the ephemeral counterparts. The sorting index revealed higher values for the perennial streams, namely 2.39,3.59 compared with 1.73,2.07 for the ephemeral counterparts. It is suggested that the degree of sediment sorting and the proportion of clusters are strongly related. Sediment sorting, sediment supply and the hydrological regime explain the mechanism of cluster formation. It is assumed that climate shifts or human interference within river basins might affect the regional characteristic flood hydrograph, and consequently alter the sedimentary character of the river bed. In the case where river bed stability is reduced owing to changes in cluster bed form distribution, rivers that normally do not yield a significant amount of sediment might be subject to notable sedimentation problems. [source] Climatic change during the last 4000 years in the southern Tarim Basin, Xinjiang, northwest China,JOURNAL OF QUATERNARY SCIENCE, Issue 7 2007Wei Zhong Abstract In this study, a ca. 4000,cal. yr ancient lacustrine (or wetland) sediment record at the southern margin of Tarim Basin is used to reconstruct the history of climate change. Six radiocarbon dates on organic matter were obtained. ,18O and ,13C of carbonate, pollen and sediment particle size were analysed for climate proxies. The proxies indicate that a drier climate prevailed in the area before ca. 1010 BC and during period 1010 BC,AD 500 climate then changed rapidly and continuously from dry to moist, but after about AD 500 climate generally shows dry condition. Several centennial-scale climatic events were revealed, with the wettest spell during AD 450,550, and a relatively wetter interval between AD 930,1030. Pollen results show that regional climate may influence human agricultural activities. Spectral analysis of mean grain size (MGS) proxy reveals statistically pronounced cyclic signals, such as ca. 200,yr, ca. 120,yr, ca. 90,yr, ca. 45,yr and ca. 33 or 30,yr, which may be associated with solar activities, implying that solar variability plays an important role in the decadal- and centennial-scale climate variations in the study area. Copyright © 2007 John Wiley & Sons, Ltd. [source] Barium Holmium Zirconate, A New Perovskite Oxide: II, Synthesis as Nanoparticles through a Modified Combustion ProcessJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 10 2002Rajan Jose Nanoparticles of barium holmium zirconate, a new complex perovskite ceramic oxide, has been synthesized using a modified self-propagating combustion process. The solid combustion products obtained were characterized by X-ray diffraction (XRD), electron diffraction, differential thermal analysis, thermogravimetric analysis, infrared spectroscopy, particle size analysis, surface area determination, and high-resolution transmission electron microscopy. The XRD and electron diffraction studies have shown that the as-prepared powder is phase pure Ba2HoZrO5.5 and has a complex cubic perovskite (A2BB,O6) structure with a lattice constant a= 8.428 Å. The transmission electron microscopic investigation has shown that the particle size of the as-prepared powder was in the range 4,16 nm with a mean grain size of 8.2 nm. The nanoparticles of Ba2HoZrO5.5 obtained by the present method could be sintered to 98% theoretical density at 1500°C. [source] A comparative study of laser- and electric-field-induced effects on the crystallinity, surface morphology and plasmon resonance of indium and gold thin filmsPHYSICA STATUS SOLIDI (A) APPLICATIONS AND MATERIALS SCIENCE, Issue 4 2010Prashant Kumar Abstract The effects of post-deposition treatment of In and Au thin films by excimer laser and electric field are reported. The films were subjected to an electric field in the range of 0.1,3.3,kV/cm and laser irradiation in the range from 0.01 to 0.1,J/cm2. The effect of this treatment on the morphology and crystallinity of indium and gold thin films (10,100,nm thickness) is investigated. Indium films exhibited a three-fold grain growth at an electric field of 3.3,kV/cm. Gold thin film, on the other hand, showed significant grain growth at a much lower field of 0.6,kV/cm. The as-deposited thin films of indium and gold were amorphous but turned nanocrystalline with average crystallite sizes of 57,nm at 3.33,kV/cm and 35,nm at 0.66,kV/cm, respectively. When indium thin films were laser irradiated, flat disc-shaped grains for as-deposited thin films were transformed to spherical grains at a laser fluence of 0.02,J/cm2 and cubical grains at 0.05,J/cm2. At 0.05,J/cm2, as-deposited amorphous indium and gold thin films turned nanocrystalline with crystallite sizes of 50,nm and 10,nm, respectively. Significantly, laser treatment causes the grain-size distribution to become narrower with a shift in mean size to larger values. Electric-field treatment on the other hand leads to a shifting of the mean grain size to larger values without affecting the distribution. [source] The Optimal Grain Sized Nanocrystalline Ni with High Strength and Good Ductility Fabricated by a Direct Current Electrodeposition,ADVANCED ENGINEERING MATERIALS, Issue 6 2008X. Shen In this work, six pure Ni specimen which mean grain sizes spans a broad range from ultra-fine to nanometer were fabricated by direct current electrodeposition and a coarse grain Ni was obtained by annealing. A gradual transition of the crystallographic preferred orientation of the deposited Ni from (200) texture to isotropic or random orientation with decreasing the mean grain size was revealed by XRD. [source] Reaction-induced nucleation and growth v. grain coarsening in contact metamorphic, impure carbonatesJOURNAL OF METAMORPHIC GEOLOGY, Issue 8 2010A. BERGER Abstract The understanding of the evolution of microstructures in a metamorphic rock requires insights into the nucleation and growth history of individual grains, as well as the coarsening processes of the entire aggregate. These two processes are compared in impure carbonates from the contact metamorphic aureole of the Adamello pluton (N-Italy). As a function of increasing distance from the pluton contact, the investigated samples have peak metamorphic temperatures ranging from the stability field of diopside/tremolite down to diagenetic conditions. All samples consist of calcite as the dominant matrix phase, but additionally contain variable amounts of other minerals, the so-called second phases. These second phases are mostly silicate minerals and can be described in a KCMASHC system (K2O, CaO, MgO, Al2O3, SiO2, H2O, CO2), but with variable K/Mg ratios. The modelled and observed metamorphic evolution of these samples are combined with the quantification of the microstructures, i.e. mean grain sizes and crystal size distributions. Growth of the matrix phase and second phases strongly depends on each other owing to coupled grain coarsening. The matrix phase is controlled by the interparticle distances between the second phases, while the second phases need the matrix grain boundary network for mass transfer processes during both grain coarsening and mineral reactions. Interestingly, similar final mean grain sizes of primary second phase and second phases newly formed by nucleation are observed, although the latter formed later but at higher temperatures. Moreover, different kinetic processes, attributed to different driving forces for growth of the newly nucleated grains in comparison with coarsening processes of the pre-existing phases, must have been involved. Chemically induced driving forces of grain growth during reactions are orders of magnitudes larger compared to surface energy, allowing new reaction products subjected to fast growth rates to attain similar grain sizes as phases which underwent long-term grain coarsening. In contrast, observed variations in grain size of the same mineral in samples with a similar T,t history indicate that transport properties depend not only on the growth and coarsening kinetics of the second phases but also on the microstructure of the dominant matrix phase during coupled grain coarsening. Resulting microstructural phenomena such as overgrowth and therefore preservation of former stable minerals by the matrix phase may provide new constraints on the temporal variation of microstructures and provide a unique source for the interpretation of the evolution of metamorphic microstructures. [source] Variations in Grain Size Analysis with a Time-of-Transition Laser Sizer (Galai CIS-50) using a Gravitational Flow SystemPARTICLE & PARTICLE SYSTEMS CHARACTERIZATION, Issue 6 2004Björn Bohling Abstract This study deals with grain size analysis with a Laser Sizer Galai CIS-50. This device utilizes the time-of-transition method and is equipped with a module for measurements in the range 0.5 to 150,,m along with a gravitational flow system. Experiments were conducted using natural marine sediments. The aim was to determine possible explanations for discrepancies in the measured results that occurred between different operators of the Galai CIS-50. These discrepancies may be due to differences in the technique of inserting a sub-sample into the measurement system. Furthermore, the influence of the sample concentration and the flow velocity in the device's liquid flow cell is considered, since these factors can act as potential sources of inaccuracies and errors in the experimental setup. Strong variations in the results occurred, which were mainly due to problems in the detection of particles >20,,m. In the range>20,,m gaps appeared in the registration of the size distribution. An improvement in reproducibility was achieved by using a pipette instead of a beaker for the insertion step. Nevertheless, the standard deviation for mean grain sizes of natural marine sediments obtained with the Galai CIS-50 is still about 20%. [source] | |||||||||||||