scholarly journals Grain-size evolution of polar firn: a new empirical grain growth parameterization based on X-ray microcomputer tomography measurements

2012 ◽  
Vol 58 (212) ◽  
pp. 1245-1252 ◽  
Author(s):  
Stefanie Linow ◽  
Maria W. Hörhold ◽  
Johannes Freitag
Keyword(s):  
Grain Size ◽  
Grain Growth ◽  
Microwave Frequency ◽  
Effective Radius ◽  
Spherical Approximation ◽  
Large Variability ◽  
Near Surface ◽  
X Ray ◽  
Size Evolution ◽  
Grain Properties

AbstractFirn microstructure properties from six different sites in Greenland and Antarctica are investigated by means of X-ray microcomputer tomography. The optical effective radius is calculated from the specific surface area (SSA) and used as a measure of grain size. It is shown that the recently introduced spherical approximation of firn grains using the effective radius Reff is representative of grain size in the microwave frequency region. The measured profiles show the well-known increase of grain size with depth at all sites, where the increase is largest at near-surface depths. A large variability in grain size on the decimeter-to-centimeter scale as a result of different grain properties of single layers is superimposed on the overall trend at each site. A simple empirical parameterization of grain-size evolution is developed which allows the rapid grain growth in the uppermost layers of the firn to be predicted. The growth is driven by strong seasonal and diurnal temperature gradients. The model can be used to simulate grain-size profiles required by models of firn/microwave interaction (e.g. for retrieval of accumulation rates from satellite microwave sensors) in a more realistic fashion.

scholarly journals Generating porosity during olivine carbonation via dissolution channels and expansion cracks

Solid Earth ◽  
2018 ◽  
Vol 9 (4) ◽  
pp. 879-896 ◽  
Author(s):  
Tiange Xing ◽  
Wenlu Zhu ◽  
Florian Fusseis ◽  
Harrison Lisabeth
Keyword(s):  
Grain Size ◽  
Carbon Sequestration ◽  
Confining Pressure ◽  
Coarse Grained ◽  
Structure Evolution ◽  
Etch Pits ◽  
Carbonation Reaction ◽  
Near Surface ◽  
X Ray ◽  
Mean Grain Size

Abstract. The olivine carbonation reaction, in which carbon dioxide is chemically incorporated to form carbonate, is central to the emerging carbon sequestration method using ultramafic rocks. The rate of this retrograde metamorphic reaction is controlled, in part, by the available reactive surface area: as the solid volume increases during carbonation, the feasibility of this method ultimately depends on the maintenance of porosity and the creation of new reactive surfaces. We conducted in situ dynamic X-ray microtomography and nanotomography experiments to image and quantify the porosity generation during olivine carbonation. We designed a sample setup that included a thick-walled cup (made of porous olivine aggregates with a mean grain size of either  ∼  5 or  ∼  80 µm) filled with loose olivine sands with grain sizes of 100–500 µm. The whole sample assembly was reacted with a NaHCO3 aqueous solution at 200 °C, under a constant confining pressure of 13 MPa and a pore pressure of 10 MPa. Using synchrotron-based X-ray microtomography, the three-dimensional (3-D) pore structure evolution of the carbonating olivine cup was documented until the olivine aggregates became disintegrated. The dynamic microtomography data show a volume reduction in olivine at the beginning of the reaction, indicating a vigorous dissolution process consistent with the disequilibrium reaction kinetics. In the olivine cup with a grain size of  ∼  80 µm (coarse-grained cup), dissolution planes developed within 30 h, before any precipitation was observed. In the experiment with the olivine cup of  ∼  5 µm mean grain size (fine-grained cup), idiomorphic magnesite crystals were observed on the surface of the olivine sands. The magnesite shows a near-constant growth throughout the experiment, suggesting that the reaction is self-sustained. Large fractures were generated as the reaction proceeded and eventually disintegrated the aggregate after 140 h. Detailed analysis show that these are expansion cracks caused by the volume mismatch in the cup walls, between the expanding interior and the near-surface which keeps a nearly constant volume. Nanotomography images of the reacted olivine cup reveal pervasive etch pits and wormholes in the olivine grains. We interpret this perforation of the solids to provide continuous fluid access, which is likely key to the complete carbonation observed in nature. Reactions proceeding through the formation of nano- to micron-scale dissolution channels provide a viable microscale mechanism in carbon sequestration practices. For the natural peridotite carbonation, a coupled mechanism of dissolution and reaction-induced fracturing should account for the observed self-sustainability of the reaction.

X-ray diffraction analyses of 3D MgO-based replicas of diatom microshells synthesized by a low-temperature gas/solid displacement reaction

2005 ◽  
Vol 20 (4) ◽  
pp. 306-310 ◽  
Author(s):  
M. S. Haluska ◽  
I. C. Dragomir ◽  
K. H. Sandhage ◽  
R. L. Snyder
Keyword(s):  
Grain Size ◽  
Low Temperature ◽  
Crystallite Size ◽  
Gas Phase ◽  
Grain Growth ◽  
Annealing Time ◽  
Displacement Reaction ◽  
X Ray Diffraction ◽  
Fourier Methods ◽  
X Ray

The nanostructural features of the gas-phase displacement reaction 2Mg(g)+SiO2→2MgO(s)+{Si}, where SiO2 is in the form of diatom shells were studied via X-ray diffraction and Fourier methods. Diatomaceous powder heated to 700 °C in a sealed graphite cell in the presence of Mg vapor formed MgO via a displacement reaction. Warren-Averbach analysis performed on samples reacted for different times showed an initial sharp MgO grain size distribution which broadened with time. New MgO crystallization was shown to occur until about 60 min, whereafter only MgO grain growth occurred. Median MgO crystallite size increased from 7.5 to 24.9 nm during this period, whereas microstrain decreased dramatically past 60 min annealing time.

Relaxation and Grain Growth Behavior of Nanocrystalline Iron

1992 ◽  
Vol 272 ◽  
Author(s):  
J. C. Holzer ◽  
R. Birringer ◽  
J. Eckert ◽  
C.E. Krill ◽  
W.L. Johnson
Keyword(s):  
Grain Size ◽  
Grain Growth ◽  
Scanning Calorimetry ◽  
X Ray ◽  
Peak Broadening ◽  
Transmission Electron ◽  
Average Grain Size ◽  
Nanocrystalline Iron ◽  
Grain Growth Behavior ◽  
Kinetics Of

ABSTRACTNanocrystalline Fe has been prepared by inert gas condensation and ball milling. The kinetics of relaxation and grain growth are investigated by differential scanning calorimetry. The development of the microstructure is monitored by x-ray powder diffraction and transmission electron microscopy. Emphasis is placed on the differences observed for samples prepared by the two different techniques. We find that the kinetics of relaxation and grain growth are very sensitive to the sample preparation method. Samples with the same initial average grain size, as determined by the peak broadening in x-ray diffraction, show very different recovery behavior. The differences are discussed in terms of the estimated grain boundary energies and the initial grain size distribution obtained by the two preparation techniques.

Grain Growth in Al-(Cu, Pd, Nb) Thin Films

1993 ◽  
Vol 309 ◽  
Author(s):  
J.D. Mis ◽  
K.P. Rodbell
Keyword(s):  
Thin Films ◽  
Grain Size ◽  
Grain Growth ◽  
Weight Percent ◽  
Size Distributions ◽  
Precipitate Morphology ◽  
X Ray ◽  
Transmission Electron ◽  
Grain Size Distributions

AbstractThe microstructure of 1 μim thick Al films containing 0.5 and 2%Cu (weight percent), 0.3%Pd, and 0.3%Pd-0.3%Nb were investigated by transmission electron microscopy (TEM) and energy dispersive x-ray spectroscopy (EDS) as a function of isochronal and isothermal anneals. The grain size, grain size distribution, and precipitate morphology of these films was measured from 200 to 500ºC, with the activation energy for grain growth (Ea) determined for I h anneals at 200, 300, 400 and 500ºC. Normal grain growth was recorded for the A1Cu films annealed at temperatures ≤400ºC; however secondary grain growth occurred in the AI-2Cu film annealed for I h at 500ºC, with grains as large as 16 μm in diameter observed. Grain growth in the AI-0.3Pd films resulted in strongly bi-modal grain size distributions, with the onset ofsignificant grain growth retarded for I h anneals at temperatures ≤300ºC.The addition of Nb to the AI-0.3Pd film resulted in monomodal grain size distributions over the entire temperature range. The role of crystallographic texture on grain growth in thin films is discussed.

Grain growth in nanocomposite Ti–B–N films during deposition: The effect of amorphous phase precipitation

2006 ◽  
Vol 21 (1) ◽  
pp. 82-87 ◽  
Author(s):  
Z-J. Liu ◽  
Y.H. Lu ◽  
Y.G. Shen
Keyword(s):  
Grain Size ◽  
Grain Boundaries ◽  
Grain Growth ◽  
Amorphous Phase ◽  
Amorphous Materials ◽  
Film Deposition ◽  
Growth Exponent ◽  
Experimental Investigations ◽  
Phase Precipitation ◽  
X Ray

Experimental investigations by high-resolution transmission electron microscopy, x-ray photoelectron spectroscopy, and x-ray diffraction show that during sputter-deposition of Ti–B–N films amorphous materials, e.g., TiB2 and BN, are found to precipitate at the grain boundaries, resulting in a decrease in grain size when the boron concentration or the amount of amorphous phase increases. To understand these experimental observations, we have used Monte Carlo simulations to investigate the effect of the amorphous phase precipitation on grain growth during film deposition. Our simulations demonstrate that the precipitation of amorphous phase at the grain boundaries can lower the grain growth exponent and thus leads to a low grain growth rate, particularly in the case of large amounts of amorphous phase. As a result, an exponential decay in grain size with the amount of amorphous phase can be observed in our simulations, which is in reasonably good agreement with the experimental results.

Simulating Sintering Process in SmCo5 Magnets

2008 ◽  
Vol 591-593 ◽  
pp. 80-85 ◽  
Author(s):  
José Adilson de Castro ◽  
Marcos Flavio de Campos
Keyword(s):  
Growth Rate ◽  
Particle Size ◽  
Grain Size ◽  
Magnetic Properties ◽  
Grain Growth ◽  
Sintering Process ◽  
Densification Rate ◽  
Size Evolution ◽  
Sintering Conditions ◽  
Crystal Particle

SmCo5 sintered magnets are produced according the following main processing: milling until single crystal particle size, compaction and sintering. It is necessary high density to maximize remanence, but small grain size to maximize coercivity. A sintering model able to incorporate both, the densification rate and the grain growth rate, is described. This makes easier to find the better sintering conditions for optimization of the magnetic properties (coercivity and remanence). The presented model represents a refinement of previous sintering models, because it takes into account the coupled effects of grain size evolution and shrinkage.

scholarly journals Kinetics of grain growth in Ti-2.7Al-5.7Fe-6Mo-6V alloy

2017 ◽  
Vol 53 (3) ◽  
pp. 263-270
Author(s):  
T.D. Mutava ◽  
L.A. Cornish ◽  
I. Sigalas
Keyword(s):  
Heat Treatment ◽  
Grain Size ◽  
Grain Growth ◽  
Solution Treatment ◽  
Beta Transus ◽  
X Ray ◽  
Solution Treated ◽  
Mean Grain Size ◽  
The Mean ◽  
Kinetics Of

The metastable (?Ti) alloy Ti-2.7Al-5.7Fe-6Mo-6V (wt%) was produced by semi-centrifugal casting of blended elemental powders. The phases were identified by X-ray diffraction (XRD), and overall composition was measured by X-ray fluorescence (XRF). The beta transus was determined by differential thermal analysis (DTA) and optical microscopy. The cast alloys were annealed at different temperatures under argon, up to 900oC, where they were in the solution-treated state, and the solution-treated alloys were aged between 400oC and 600oC. The kinetics of grain growth during heat treatment of the as-cast and solution-treated alloys was investigated by metallography, using the grain intercept method. Grain growth depended on whether the matrix was (?Ti) or (?Ti), and on the competing precipitate dissolution, or nucleation and growth processes. The as-cast alloy had a mean grain size of 19 ? 7?m, which increased to 63 ? 21?m after heat treating at 500?C for 2h. The alloy was duplex between 590?C and 800?C, and completely (?Ti) above 800?C. After solution treatment, the mean grain size was 40 ? 16 ?m, which was smaller than at the lower heat treatment temperatures. Following solution treatment, the mean grain size increased with increasing ageing temperature, up to 66 ? 22?m after 2h at 600?C. The growth exponents were lower than the 0.5 for normal grain growth in both cases, and there was an incubation period at 300?C and 400?C when the alloy was not solution-treated. Minimal grain growth was observed close to the beta transus.

Aspects of microanalysis in a transmission electron microscope

1978 ◽  
Vol 36 (1) ◽  
pp. 510-511
Author(s):  
R. Sinclair ◽  
B.E. Jacobson
Keyword(s):  
Grain Size ◽  
Electron Beam ◽  
Electron Microscope ◽  
Chemical Analysis ◽  
Transmission Electron Microscope ◽  
Vapor Deposition ◽  
Critical Currents ◽  
X Ray ◽  
Fine Grain ◽  
Transmission Electron

INTRODUCTIONThe prospect of performing chemical analysis of thin specimens at any desired level of resolution is particularly appealing to the materials scientist. Commercial TEM-based systems are now available which virtually provide this capability. The purpose of this contribution is to illustrate its application to problems which would have been intractable until recently, pointing out some current limitations.X-RAY ANALYSISIn an attempt to fabricate superconducting materials with high critical currents and temperature, thin Nb3Sn films have been prepared by electron beam vapor deposition [1]. Fine-grain size material is desirable which may be achieved by codeposition with small amounts of Al2O3 . Figure 1 shows the STEM microstructure, with large (∽ 200 Å dia) voids present at the grain boundaries. Higher quality TEM micrographs (e.g. fig. 2) reveal the presence of small voids within the grains which are absent in pure Nb3Sn prepared under identical conditions. The X-ray spectrum from large (∽ lμ dia) or small (∽100 Ǻ dia) areas within the grains indicates only small amounts of A1 (fig.3).

scholarly journals Grain Size Evolution and Mechanical Properties of Nb, V–Nb, and Ti–Nb Boron Type S1100QL Steels

Metals ◽  
2021 ◽  
Vol 11 (3) ◽  
pp. 492
Author(s):  
Jan Foder ◽  
Jaka Burja ◽  
Grega Klančnik
Keyword(s):  
Mechanical Properties ◽  
Heat Treatment ◽  
Grain Size ◽  
Hot Forging ◽  
Size Control ◽  
High Strength ◽  
Fatigue Properties ◽  
Titanium Addition ◽  
Austenite Grain Size ◽  
Size Evolution

Titanium additions are often used for boron factor and primary austenite grain size control in boron high- and ultra-high-strength alloys. Due to the risk of formation of coarse TiN during solidification the addition of titanium is limited in respect to nitrogen. The risk of coarse nitrides working as non-metallic inclusions formed in the last solidification front can degrade fatigue properties and weldability of the final product. In the presented study three microalloying systems with minor additions were tested, two without any titanium addition, to evaluate grain size evolution and mechanical properties with pre-defined as-cast, hot forging, hot rolling, and off-line heat-treatment strategy to meet demands for S1100QL steel. Microstructure evolution from hot-forged to final martensitic microstructure was observed, continuous cooling transformation diagrams of non-deformed austenite were constructed for off-line heat treatment, and the mechanical properties of Nb and V–Nb were compared to Ti–Nb microalloying system with a limited titanium addition. Using the parameters in the laboratory environment all three micro-alloying systems can provide needed mechanical properties, especially the Ti–Nb system can be successfully replaced with V–Nb having the highest response in tensile properties and still obtaining satisfying toughness of 27 J at –40 °C using Charpy V-notch samples.

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