scholarly journals Metallic lead nanospheres discovered in ancient zircons

2015 ◽  
Vol 112 (16) ◽  
pp. 4958-4963 ◽  
Author(s):  
Monika A. Kusiak ◽  
Daniel J. Dunkley ◽  
Richard Wirth ◽  
Martin J. Whitehouse ◽  
Simon A. Wilde ◽  
...  
Keyword(s):  
High Temperature ◽  
Melt Inclusions ◽  
Metallic Lead ◽  
Geological Processes ◽  
Transmission Electron ◽  
Wide Range ◽  
Scanning Transmission ◽  
High Grade Metamorphism ◽  
High Temperature Metamorphism ◽  
Ultra High Temperature

Zircon (ZrSiO4) is the most commonly used geochronometer, preserving age and geochemical information through a wide range of geological processes. However, zircon U–Pb geochronology can be affected by redistribution of radiogenic Pb, which is incompatible in the crystal structure. This phenomenon is particularly common in zircon that has experienced ultra-high temperature metamorphism, where ion imaging has revealed submicrometer domains that are sufficiently heterogeneously distributed to severely perturb ages, in some cases yielding apparent Hadean (>4 Ga) ages from younger zircons. Documenting the composition and mineralogy of these Pb-enriched domains is essential for understanding the processes of Pb redistribution in zircon and its effects on geochronology. Using high-resolution scanning transmission electron microscopy, we show that Pb-rich domains previously identified in zircons from East Antarctic granulites are 5–30 nm nanospheres of metallic Pb. They are randomly distributed with respect to zircon crystallinity, and their association with a Ti- and Al-rich silica melt suggests that they represent melt inclusions generated during ultra-high temperature metamorphism. Metallic Pb is exceedingly rare in nature and previously has not been reported in association with high-grade metamorphism. Formation of these metallic nanospheres within annealed zircon effectively halts the loss of radiogenic Pb from zircon. Both the redistribution and phase separation of radiogenic Pb in this manner can compromise the precision and accuracy of U–Pb ages obtained by high spatial resolution methods.

PROCESSING OF ULTRA-HIGH TEMPERATURE CERAMIC MATRIX COMPOSITES (UHTCMCS) THROUGH RF ENHANCED CHEMICAL VAPOUR INFILTRATION (RF-CVI)

2021 ◽  
Author(s):  
VINOTHINI VENKATACHALAM, ◽  
JON BINNER ◽  
THOMAS REIMER ◽  
BUCKARD ESSER ◽  
STEFANO MUNGIGUERRA ◽  
...  
Keyword(s):  
High Temperature ◽  
Carbon Fibre ◽  
Chemical Vapor Infiltration ◽  
Matrix Composites ◽  
Carbon Fibres ◽  
Temperature Oxidation ◽  
Ceramic Phase ◽  
Wide Range ◽  
The University ◽  
Ultra High Temperature

Carbon fibre (Cf) reinforced Ultra High Temperature Ceramic (UHTC) Matrix Composites (UHTCMCs) have proven to be excellent materials that can survive nearly 3000°C in highly oxidizing environments along with a good specific strength. Consequently, they have excellent potential for use in aerospace applications such as rocket nozzle throats and thermal protection systems (TPS). Due to the presence of the carbon fibres, UHTCMCs offer high strength and modulus combined with excellent thermal shock behaviour whilst the presence of the ultra-high temperature ceramic phase protects the carbon fibres at the application temperatures. High temperature oxidation, thermal ablation behaviour and mechanical properties of the UHTCMC’s relies heavily on the bonding between the carbon fibre and matrices especially the oxides formed to avoid any progressive failure and predict the life of the components. In the present investigation, a radio frequency assisted chemical vapor infiltration (RF-CVI) technique has been used to make the 2.5D Cf reinforced ZrB2, ZrB2/carbon matrices composites with various interphase materials. The advantage of RF heating is that it creates an inverse temperature profile in the sample, which means that the infiltration starts from inside and progresses outwards. This allows the time needed for processing to be reduced very significantly compared to the conventional CVI process. This presentation will report on the latest results from the research that has been undertaken at the University of Birmingham, including the results from a wide range of testing that has been undertaken at both DLR in Germany and the University of Naples in Italy.

Ultra-high temperature metamorphism recorded in Fe-rich olivine-bearing migmatite from the Khondalite Belt, North China Craton

2017 ◽  
Vol 36 (3) ◽  
pp. 343-368 ◽  
Author(s):  
Cyril Lobjoie ◽  
Wei Lin ◽  
Pierre Trap ◽  
Philippe Goncalves ◽  
Qiuli Li ◽  
...  
Keyword(s):  
High Temperature ◽  
North China Craton ◽  
North China ◽  
Khondalite Belt ◽  
High Temperature Metamorphism ◽  
Ultra High Temperature

scholarly journals Dynamic behavior of reversible oxygen migration in irradiated-annealed high temperature superconducting wires

2020 ◽  
Vol 10 (1) ◽  
Author(s):  
Yi Zhang ◽  
M. W. Rupich ◽  
Vyacheslav Solovyov ◽  
Qiang Li ◽  
Amit Goyal
Keyword(s):  
High Temperature ◽  
Annealing Treatment ◽  
Atomic Scale ◽  
Vacancy Defects ◽  
Superconducting Wires ◽  
High Temperature Superconducting ◽  
Transmission Electron ◽  
Scanning Transmission ◽  
Effect Of Oxygen ◽  
Electron Energy Loss

Abstract We use atomically resolved scanning transmission electron microscopy and electron energy loss spectroscopy to determine the atomic-scale structural, chemical and electronic properties of artificial engineered defects in irradiated-annealed high temperature superconducting wires based on epitaxial Y(Dy)BCO film. We directly probe the oxygen vacancy defects in both plane and chain sites after irradiation with 18-meV Au ions. The plane site vacancies are reoccupied during post-annealing treatment. Our results demonstrate the dynamic reversible behavior of oxygen point defects, which explains the depression and recovery of self-field critical current and critical temperature in irradiation-annealing process. These findings reveal the strong effect of oxygen vacancies in different sites on the superconductivity properties of irradiated Y(Dy)BCO film, and provide important insights into defects engineering of 2G HTS coil wires.

Granulites and charnockites of the Gruf Complex: Evidence for Permian ultra-high temperature metamorphism in the Central Alps

Lithos ◽  
2011 ◽  
Vol 124 (1-2) ◽  
pp. 17-45 ◽  
Author(s):  
A. Galli ◽  
B. Le Bayon ◽  
M.W. Schmidt ◽  
J.-P. Burg ◽  
M.J. Caddick ◽  
...  
Keyword(s):  
High Temperature ◽  
Central Alps ◽  
Gruf Complex ◽  
High Temperature Metamorphism ◽  
Ultra High Temperature

scholarly journals Characterization of Sc2O3&CeO2-Stabilized ZrO2 Powders Via Co-Precipitation or Hydrothermal Synthesis

2013 ◽  
Vol 19 (S5) ◽  
pp. 29-32 ◽  
Author(s):  
Justyna Grzonka ◽  
Victor Vereshchak ◽  
Oleksiy Shevchenko ◽  
Oleksandr Vasylyev ◽  
Krzysztof J. Kurzydłowski
Keyword(s):  
High Temperature ◽  
Hydrothermal Synthesis ◽  
Hydrothermal Reaction ◽  
Scanning Transmission Electron Microscope ◽  
Cubic Phase ◽  
Precipitation Technique ◽  
Transmission Electron ◽  
Scanning Transmission ◽  
Co Precipitation

AbstractAs the presence of Sc2O3 and CeO2 is known to largely enhance the ionic conductivity in the temperature range of 600–800°C, compared with the conventional yttria-stabilized ZrO2, Sc2O3&CeO2-stabilized ZrO2 provide its applicability as electrolytes in solid oxide fuel cells. The current study introduces the methodology to synthesize Sc2O3&CeO2-stabilized ZrO2 powders by using co-precipitation technique or high-temperature hydrothermal reaction, and further describes the structural characterization of the zirconia powders synthesized by the above-mentioned two methods. The co-precipitation technique was found to allow obtaining powders of cubic phase, whereas high-temperature hydrothermal synthesis results in the presence of a monoclinic phase as well. The scanning transmission electron microscope observations also confirm that the size of the synthesized ZrO2 powders in this study is found to be much smaller than that of commercially available powders.

scholarly journals ZnCr2O4 Inclusions in ZnO Matrix Investigated by Probe-Corrected STEM-EELS

Materials ◽  
2019 ◽  
Vol 12 (6) ◽  
pp. 888
Author(s):  
Wei Zhan ◽  
Andrey Yurievich Kosinskiy ◽  
Lasse Vines ◽  
Klaus Magnus Johansen ◽  
Patricia Almeida Carvalho ◽  
...  
Keyword(s):  
Band Gap ◽  
Chromium Oxide ◽  
Gas Sensing ◽  
Waste Water Treatment ◽  
Transmission Electron ◽  
Wide Range ◽  
Scanning Transmission ◽  
Potential Applications ◽  
Photocatalytic Material ◽  
Electron Energy Loss

The ZnCr2O4/ZnO materials system has a wide range of potential applications, for example, as a photocatalytic material for waste-water treatment and gas sensing. In this study, probe-corrected high-resolution scanning transmission electron microscopy and geometric phase analysis were utilized to study the dislocation structure and strain distribution at the interface between zinc oxide (ZnO) and embedded zinc chromium oxide (ZnCr2O4) particles. Ball-milled and dry-pressed ZnO and chromium oxide (α-Cr2O3) powder formed ZnCr2O4 inclusions in ZnO with size ~400 nm, where the interface properties depended on the interface orientation. In particular, sharp interfaces were observed for ZnO [2113]/ZnCr2O4 [110] orientations, while ZnO [1210]/ZnCr2O4 [112] orientations revealed an interface over several atomic layers, with a high density of dislocations. Further, monochromated electron energy-loss spectroscopy was employed to map the optical band gap of ZnCr2O4 nanoparticles in the ZnO matrix and their interface, where the average band gap of ZnCr2O4 nanoparticles was measured to be 3.84 ± 0.03 eV, in contrast to 3.22 ± 0.01 eV for the ZnO matrix.

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