Time Dependent Nucleation in a Bulk Metallic Glass Forming Alloy

1997 ◽  
Vol 481 ◽  
Author(s):  
T. K Croat ◽  
K. F. Kelton
Keyword(s):  
Electron Microscopy ◽  
Transmission Electron Microscopy ◽  
Metallic Glass ◽  
Amorphous Matrix ◽  
Time Dependent ◽  
Glass Forming ◽  
Transmission Electron ◽  
Dependent Model ◽  
Time Dependent Model ◽  
Multiple Step

ABSTRACTThe effect of composition on the time-dependent nucleation rates in Zr65Al7.5Ni10CU17.5 glasses is investigated to better understand nucleation processes in partitioning systems. Asquenched glasses were annealed to produce a homogeneous dispersion of nanocrystals within the amorphous matrix. The nucleation rates were estimated from the number of crystallites produced as function of annealing time, using scanning and transmission electron microscopy. Experimental results for single and multiple-step annealing treatments are presented. The nucleation results are discussed briefly within the time-dependent model of the classical theory of nucleation.

Structural and analytical studies of the silicified macrohairs from the lemma of the grass Phalaris canariensis L

1984 ◽  
Vol 222 (1229) ◽  
pp. 427-438 ◽  
Keyword(s):  
Electron Microscopy ◽  
Transmission Electron Microscopy ◽  
Silica Particles ◽  
Time Dependent ◽  
Energy Dispersive ◽  
X Ray ◽  
Analytical Studies ◽  
Transmission Electron ◽  
Cellular Control ◽  
Phalaris Canariensis

Silicified macrohairs from mature and immature lemmas of the grass Phalaris canariensis L. have been studied by scanning (s.e.m.) and transmission electron microscopy (t.e.m.) and energy dispersive X-ray analysis (e.d.X.a.) at various times after emergence of the inflorescence. Within the macrohairs a variety of morphologies of silica particles was observed. E.d.X.a. revealed the time-dependent concentrations in the macrohairs of the elements K, Cl, P, and S, in addition to Si. Much lower levels of these elements were found in highly silicified mature macrohairs than in the immature macrohairs. It is proposed that the hairs are silicified under strict cellular control.

Oxyhemoglobin-induced apoptosis in cultured endothelial cells

1999 ◽  
Vol 91 (3) ◽  
pp. 459-465 ◽  
Author(s):  
Kotaro Ogihara ◽  
Alexander Y. Zubkov ◽  
David H. Bernanke ◽  
Adam I. Lewis ◽  
Andrew D. Parent ◽  
...  
Keyword(s):  
Electron Microscopy ◽  
Transmission Electron Microscopy ◽  
Endothelial Cells ◽  
Time Dependent ◽  
Dependent Manner ◽  
Content Type ◽  
Aortic Endothelial Cells ◽  
Bovine Aortic Endothelial Cells ◽  
Transmission Electron ◽  
Fine Print

Object. Oxyhemoglobin (OxyHb) is one of the most important spasmogens for cerebral vasospasm that follows aneurysmal subarachnoid hemorrhage. The cytotoxic effect of OxyHb has been documented in endothelial and smooth-muscle cells; however, the pattern of cell death—necrosis or apoptosis—as the final stage of cell damage has not been demonstrated. This study was undertaken to determine if OxyHb induces apoptotic changes in cultured bovine aortic endothelial cells.Methods. Confluent bovine aortic endothelial cells were treated with OxyHb in a concentration- and time-dependent manner. Cell density was assayed by counting the number of cells that attached to culture dishes after exposure to OxyHb. To identify apoptotic changes, the investigators used three specific methods: DNA fragmentation (electrophoreses), the apoptotic body (transmission electron microscopy), and cleavage of poly (adenosine diphosphate ribose) polymerase (PARP [Western blotting]).Conclusions. Oxyhemoglobin decreased cell density in a concentration- and time-dependent manner. Analysis of DNA showed a pattern of internucleosomal cleavage characteristic of apoptosis (DNA ladder). Transmission electron microscopy demonstrated condensation of nuclei and apoptotic bodies in OxyHb-treated endothelial cells. Western blotting with the PARP antibody revealed that the 116-kD PARP was cleaved to the 85-kD apoptosis-related fragment. These results for the first time demonstrated that the OxyHb induces apoptosis in cultured endothelial cells.

Using Fluctuation Microscopy to Characterize Structural Order in Metallic Glasses

2003 ◽  
Vol 9 (6) ◽  
pp. 509-515 ◽  
Author(s):  
Jing Li ◽  
X. Gu ◽  
T.C. Hufnagel
Keyword(s):  
Electron Microscopy ◽  
Transmission Electron Microscopy ◽  
High Resolution ◽  
Metallic Glass ◽  
Metallic Glasses ◽  
The Other ◽  
Structural Order ◽  
Transmission Electron ◽  
Medium Range ◽  
Fluctuation Microscopy

We have used fluctuation microscopy to reveal the presence of structural order on length scales of 1–2 nm in metallic glasses. We compare results of fluctuation microscopy measurements with high resolution transmission electron microscopy and electron diffraction observations on a series of metallic glass samples with differing degrees of structural order. The agreement between the fluctuation microscopy results and those of the other techniques is good. In particular, we show that the technique used to make thin specimens for electron microscopy affects the structure of the metallic glass, with ion thinning inducing more structural order than electropolishing. We also show that relatively minor changes in the composition of the alloy can have a significant effect on the medium-range order; this increased order is correlated with changes in mechanical behavior.

Precipitation of Zr2Cu Stable Crystalline Phase from Zr70Cu27.5Rh2.5 Amorphous Alloy

2006 ◽  
Vol 979 ◽  
Author(s):  
David Cushman ◽  
Junji Saida ◽  
Chunfei Li
Keyword(s):  
Electron Microscopy ◽  
Transmission Electron Microscopy ◽  
Metallic Glasses ◽  
Crystalline Phase ◽  
Crystallization Process ◽  
Amorphous Matrix ◽  
Nucleation Process ◽  
Transmission Electron ◽  
The Stability ◽  
Icosahedral Quasicrystalline

AbstractThe crystallization process of Zr70Cu27.5Rh2.5 metallic glass was studied with Transmission Electron Microscopy (TEM). In contrast to previous studies where the precipitation of metastable icosahedral quasicrystalline (IQC) particles is of the interest, we designed the present work to focus on the nucleation process of the stable Zr2Cu crystalline phase. It has been found that the alloy consists of IQC particles distributed in amorphous matrix prior to the precipitation of the Zr2Cu stable crystalline phase and Zr2Cu nucleates from the amorphous matrix. The encounter of the IQC phase with Zr2Cu transforms the former into the latter so quickly that no interface between them was found in the present experiment. These insights provide the basis for a discussion of the stability of metallic glasses and the IQC particles.

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