Crystallization processes in an artificial magma: variations in crystal shape, growth rate and composition with melt cooling history

1995 ◽  
Vol 120 (3-4) ◽  
pp. 412-425 ◽  
Author(s):  
Nelia W. Dunbar ◽  
Gary K. Jacobs ◽  
Michael T. Naney
Keyword(s):  
Growth Rate ◽  
Crystal Shape ◽  
Cooling History ◽  
Melt Cooling

Prediction of Hypoeutectic Gray Iron Microstructure during Solidification and Solid Transformation Using Simple Fourier Model

2010 ◽  
Vol 457 ◽  
pp. 293-298 ◽  
Author(s):  
Mohamed Ahmed Taha Hanafi ◽  
Nahed A. El Mahallawy ◽  
Ahmed M. El-Sabbagh ◽  
Talat El-Benawy ◽  
Hasan F. Hadla
Keyword(s):  
Growth Rate ◽  
Cast Iron ◽  
Solid State ◽  
Rate Constants ◽  
Volume Fraction ◽  
Phase Evolution ◽  
Gray Iron ◽  
Cooling History ◽  
History Of ◽  
Fourier Model

Phases’ evolution during the solidification of a hypoeutectic 3.92% C-equivalence cast iron was modelled by considering the cooling history of the alloy from the melt, thus including both solidification and solid state transformations. Simple Fourier model was used to combine macroscopic heat flow and microscopic kinetics for phase evolution. Different cooling rates were obtained by casting cylinders and stepped plates. Measured number of primary austenitic nuclei, eutectic cells and volume fraction of phases during solidification (graphite, a-ferrite, pearlite and cementite), are correlated with the cooling rate. Growth rate constants for primary austenite, are found to be  = 8.7E-7, and n = 2.3. Growth rate constants for primary graphite (types A, B, and C), are found to be  =5.7E-7, and n = 2. The model matches with the experimental work where the error percent of modelling volume fractions of pearlite, graphite, ferrite and cementite ranges between 0.2 and 1.5%.

scholarly journals A stable ultrastructural pattern despite variable cell size in <i>Lithothamnion corallioides</i>

2021 ◽  
Vol 18 (22) ◽  
pp. 6061-6076
Author(s):  
Valentina Alice Bracchi ◽  
Giulia Piazza ◽  
Daniela Basso
Keyword(s):  
Growth Rate ◽  
Cell Walls ◽  
Environmental Variables ◽  
Coralline Algae ◽  
Ultrastructural Changes ◽  
Depth Range ◽  
Crystal Shape ◽  
Axis Parallel ◽  
Calcification Process ◽  
Early Alteration

Abstract. Recent advances on the mechanism and pattern of calcification in coralline algae led to contradictory conclusions. The evidence of a biologically controlled calcification process, resulting in distinctive patterns at the scale of family, was observed. However, the coralline calcification process has been also interpreted as biologically induced because of the dependency of its elemental composition on environmental variables. To clarify the matter, five collections of Lithothamnion corallioides from the Atlantic Ocean and the Mediterranean Sea, across a wide depth range (12–66 m), have been analyzed for morphology, anatomy and cell wall crystal patterns in both perithallial and epithallial cells to detect possible ultrastructural changes. L. corallioides shows the alternation of tiers of short-squared and long-ovoid/rectangular cells along the perithallus, forming a typical banding. The perithallial cell length decreases according to water depth and growth rate, whereas the diameter remains constant. Our observations confirm that both epithallial and perithallial cells show primary (PW) and secondary (SW) calcite walls. Rectangular tiles, with the long axis parallel to the cell membrane forming a multi-layered structure, characterize the PW. Flattened squared bricks characterize the SW, with roundish outlines enveloping the cell and showing a zigzag and cross orientation. Long and short cells have different thicknesses of PW and SW, increasing in short cells. Epithallial cells are one to three flared cells with the same shape of the PW and SW crystals. Despite the diverse seafloor environments and the variable L. corallioides growth rate, the cell walls maintain a consistent ultrastructural pattern with unaffected crystal shape and arrangement. A comparison with two congeneric species, L. minervae and L. valens, showed similar ultrastructural patterns in the SW but evident differences in the PW crystal shape. Our observations point to a biologically control rather than an induction of the calcification process in coralline algae and suggest a possible new morphological diagnostic tool for species identification, with relevant importance for paleontological applications. Finally, secondary calcite, in the form of dogtooth crystals that fill the cell lumen, has been observed. It represents a form of early alteration in living collections which can have implications in the reliability of climate and paleoclimate studies based on geochemical techniques.

Determination of the supercooling dependence of the (211) facet of BGO crystal on growth rate from the temporal dependence of supercooling at a prescribed melt-cooling rate

2000 ◽  
Vol 45 (5) ◽  
pp. 630-632
Author(s):  
Ya. V. Vasiliev ◽  
V. D. Golyshev ◽  
M. A. Gonik ◽  
É. N. Kolesnikova ◽  
V. B. Tsvetovskii ◽  
...  
Keyword(s):  
Growth Rate ◽  
Cooling Rate ◽  
Temporal Dependence ◽  
Melt Cooling

scholarly journals A stable ultrastructural pattern despite variable cell size in <i>Lithothamnion corallioides</i>

2021 ◽  
Author(s):  
Valentina Alice Bracchi ◽  
Giulia Piazza ◽  
Daniela Basso
Keyword(s):  
Growth Rate ◽  
Cell Walls ◽  
Coralline Algae ◽  
Ultrastructural Changes ◽  
Depth Range ◽  
Crystal Shape ◽  
Zigzag Pattern ◽  
Axis Parallel ◽  
Calcification Process ◽  
Different Thickness

Abstract. Recent advances on the mechanism and pattern of calcification in coralline algae lead to contradictory conclusions. Coralline calcification appears biologically induced, as suggested by the dependency of its elemental composition on environmental variables. However, evidence of a biologically controlled calcification process, resulting in distinctive patterns at the scale of family, was also observed. In order to clarify the matter, five collections of Lithothamnion corallioides from the Atlantic Ocean and the Mediterranean Sea, across a wide depth range (12–66 m) have been analyzed for morphology, anatomy and cell wall crystal patterns of both perithallial and epithallial cells, in order to detect possible ultrastructural changes. L. corallioides shows the alternation of tiers of short-squared and long-ovoid/rectangular cells along the perithallus, forming a typical banding. The perithallial cell length decreases according to water depth and growth-rate, whereas diameter remains constant. Our observations confirm that both epithallial and perithallial cells show primary (PW) and secondary (SW) calcite walls. Rectangular tiles, with the long axis parallel to the cell membrane forming a multi-layered structure, characterize the PW. Flattened squared bricks characterize the SW with roundish outlines enveloping the cell and showing a zigzag pattern. Long and short cells have different thickness of PW and SW, with a thicker SW and PW in short cells. Epithallial cells are one up to three flared cells, with the same shape of the PW and SW crystals. Despite the diverse seafloor environments and the variable L. corallioides growth-rate, the cell walls maintain a consistent ultrastructural pattern, with unaffected crystal shape and arrangement. A comparison with two congeneric species, L. minervae and L. valens, showed similar ultrastructural patterns in SW, but evident differences in the PW crystal shape. Our observations point to a biological control rather than an induction of the calcification process in coralline algae, and suggest a possible new morphological diagnostic tool for species identification, with relevant importance for paleontological application. Finally, secondary calcite, in form of dogtooth crystals that fill the cell lumen, has been observed. It represents a form of early diagenesis in living collections which can have implications in the reliability of climate and paleoclimate studies based on the geochemistry techniques.

The threshold energy for atom displacement in fcc metals

1990 ◽  
Vol 48 (4) ◽  
pp. 530-531
Author(s):  
Wilfried Sigle ◽  
Matthias Hohenstein ◽  
Alfred Seeger
Keyword(s):  
Growth Rate ◽  
Elevated Temperatures ◽  
Threshold Energy ◽  
Dislocation Loops ◽  
Absolute Minimum ◽  
Voltage Electron ◽  
Atom Displacement ◽  
Electron Microscopes ◽  
Fcc Metal

Prolonged electron irradiation of metals at elevated temperatures usually leads to the formation of large interstitial-type dislocation loops. The growth rate of the loops is proportional to the total cross-section for atom displacement,which is implicitly connected with the threshold energy for atom displacement, Ed . Thus, by measuring the growth rate as a function of the electron energy and the orientation of the specimen with respect to the electron beam, the anisotropy of Ed can be determined rather precisely. We have performed such experiments in situ in high-voltage electron microscopes on Ag and Au at 473K as a function of the orientation and on Au as a function of temperature at several fixed orientations.Whereas in Ag minima of Ed are found close to <100>,<110>, and <210> (13-18eV), (Fig.1) atom displacement in Au requires least energy along <100>(15-19eV) (Fig.2). Au is thus the first fcc metal in which the absolute minimum of the threshold energy has been established not to lie in or close to the <110> direction.

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