scholarly journals Ab initio thermodynamics reveals the nanocomposite structure of ferrihydrite

2021 ◽  
Vol 4 (1) ◽  
Author(s):  
Michel Sassi ◽  
Anne M. Chaka ◽  
Kevin M. Rosso
Keyword(s):  
Ab Initio ◽  
Water Pressure ◽  
Critical Role ◽  
Ambient Conditions ◽  
Structural Water ◽  
X Ray ◽  
Distinct Structure ◽  
Wide Range ◽  
Lower Temperature ◽  
Individual Nanoparticles

AbstractFerrihydrite is a poorly crystalline iron oxyhydroxide nanomineral that serves a critical role as the most bioavailable form of ferric iron for living systems. However, its atomic structure and composition remain unclear due in part to ambiguities in interpretation of X-ray scattering results. Prevailing models so far have not considered the prospect that at the level of individual nanoparticles multiple X-ray indistinguishable phases could coexist. Using ab initio thermodynamics we show that ferrihydrite is likely a nanocomposite of distinct structure types whose distribution depends on particle size, temperature, and hydration. Nanoparticles of two contrasting single-phase ferrihydrite models of Michel and Manceau are here shown to be thermodynamically equivalent across a wide range of temperature and pressure conditions despite differences in their structural water content. Higher temperature and water pressure favor the formation of the former, while lower temperature and water pressure favor the latter. For aqueous suspensions at ambient conditions, their coexistence is maximal for particle sizes up to 12 nm. The predictions inform and help resolve different observations in various experiments.

scholarly journals Ab Initio Thermodynamics Reveals the Nanocomposite Structure of Ferrihydrite

2021 ◽  
Author(s):  
Michel Sassi ◽  
Anne Chaka ◽  
Kevin Rosso
Keyword(s):  
Ab Initio ◽  
Water Pressure ◽  
Critical Role ◽  
Ambient Conditions ◽  
Structural Water ◽  
X Ray ◽  
Distinct Structure ◽  
Wide Range ◽  
Lower Temperature ◽  
Individual Nanoparticles

Abstract Ferrihydrite is a poorly crystalline iron oxyhydroxide nanomineral that serves a critical role as the most bioavailable form of ferric iron for living systems. However, its atomic structure and composition remain unclear due in part to ambiguities in interpretation of X-ray scattering results. Prevailing models so far have not considered the prospect that at the level of individual nanoparticles multiple X-ray indistinguishable phases could coexist. Using ab initio thermodynamics we show that ferrihydrite is likely a nanocomposite of distinct structure types whose distribution depends on particle size, temperature, and hydration. Nanoparticles of two contrasting single-phase ferrihydrite models of Michel and Manceau are here shown to be thermodynamically equivalent across a wide range of temperature and pressure conditions despite differences in their structural water content. Higher temperature and water pressure favor the formation of the former, while lower temperature and water pressure favor the latter. For aqueous suspensions at ambient conditions, their coexistence is maximal for particle sizes up to 12 nm. The predictions can be connected to and help resolve different observations in various experiments.

Synthesis Of Highly Ordered Macroporous Minerals: Extension of the Synthetic Method to Other Metal Oxides and Organic-Inorganic Composites

1998 ◽  
Vol 549 ◽  
Author(s):  
C.F. Blanford ◽  
T.N. Do ◽  
B.T. Holland ◽  
A. Stein
Keyword(s):  
Electron Microscopy ◽  
Metal Oxides ◽  
Three Dimensional ◽  
X Ray Diffraction ◽  
X Ray ◽  
Selected Area Electron Diffraction ◽  
Transmission Electron ◽  
Wide Range ◽  
Ordered Macroporous ◽  
Lower Temperature

AbstractThe facile synthesis of three-dimensional macroporous arrays of titania, zirconia and alumina was recently reported [1]. The synthesis of these materials has now been extended to the oxides of iron, tungsten, and antimony, as well as a mixed yttrium-zirconium system and organically modi- fied silicates. These materials were characterized by Fourier-transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), transmission electron microscopy (TEM), selected area electron diffraction (SAED), X-ray energy dispersive spectrometry (EDS), and powder X-ray diffraction (XRD). Ordered structures of iron, tungsten, and antimony were formed from alkoxide precursors as in the originally reported synthesis, but the template was removed at a lower temperature. Samples of vinyl- and 2-cyanoethyl-modified silicates were formed from a mixture of organotrialkoxysilane and tetraalkoxysilane precursors; the polystyrene template was removed by extraction with a THF/acetone mixture. These results show the ease of extending the original syn- thesis to a wide range of systems. Also, the ability to form homogenous mixed-metal oxides will be important for tailoring the dielectric and photonic properties of these materials.

Characterization of Ge1-x-ySixSny Ternary Alloy Surfaces and Ni/Ge1-x-ySixSny Bilayer Reactions by X-Ray Techniques

2015 ◽  
Vol 1770 ◽  
pp. 19-24 ◽  
Author(s):  
Gordon J. Grzybowski ◽  
Arnold Kiefer ◽  
Bruce Claflin
Keyword(s):  
Photoelectron Spectroscopy ◽  
Chemical Shifts ◽  
Surface Oxidation ◽  
Device Fabrication ◽  
Ternary Alloys ◽  
Ambient Conditions ◽  
X Ray ◽  
Wide Range ◽  
Xps Characterization

ABSTRACTInterest in next generation devices that integrate photonic and electronic functionality is focused on extending the capability of existing group IV material systems while maintaining compatibility with existing processing methods and procedures. One such class of materials which has been recently developed, Ge1-x-ySixSny ternary alloys, is being investigated for integrated Si photonics, solar cell materials, telecommunication applications, and for IR photodetectors. These alloys afford the opportunity to decouple the band gap energies and lattice constants over a wide range of values, potentially yielding direct and indirect character that can be coupled with a variety of different substrates dependent on composition.In the present work, we report X-ray photoelectron spectroscopy (XPS) characterization of Ge1-x-ySixSny alloys grown by gas-source molecular beam epitaxy (GS-MBE) and investigate Ni- Ge1-x-ySiySny bilayer reactions with x-ray diffraction (XRD). The surface oxidation of samples stored in ambient conditions were measured with XPS. High resolution spectra showed chemical shifts of Ge, Si and Sn peaks consistent with Ge-O, Si-O and Sn-O bond formation. Depth profiling indicates a homogeneous composition throughout the bulk of the sample with surface oxidation confined to the top few nanometers. A highly tin-enriched layer was indicated at the surface of the material, while silicon was observed to be either enriched or depleted at the surface depending on the sample.To study the interaction of the ternary with an ohmic contact commonly used in device fabrication processes today, nickel layers 30 nm thick were evaporated onto the alloys and were annealed in nitrogen up to 400 °C for periods as long as 1 hour. The XRD data show that the Ni2(Ge1-x-ySixSny) phase forms first followed by Ni(Ge1-x-ySixSny).

scholarly journals Structures of furanosides: geometrical analysis of low-temperature X-ray and neutron crystal structures of five crystalline methyl pentofuranosides

2001 ◽  
Vol 57 (2) ◽  
pp. 213-220 ◽  
Author(s):  
Artem Evdokimov ◽  
A. Joseph Gilboa ◽  
Thomas F. Koetzle ◽  
Wim T. Klooster ◽  
Arthur J. Schultz ◽  
...  
Keyword(s):  
Hydrogen Bonding ◽  
Crystal Structures ◽  
Critical Role ◽  
Chair Conformation ◽  
Geometrical Analysis ◽  
X Ray ◽  
Wide Range ◽  
First Time ◽  
Ring Conformations

Crystal structures of all five crystalline methyl D-pentofuranosides, methyl α-D-arabinofuranoside (1), methyl β-D-arabinofuranoside (2), methyl α-D-lyxofuranoside (3), methyl β-D-ribofuranoside (4) and methyl α-D-xylofuranoside (5) have been determined by means of cryogenic X-ray and neutron crystallography. The neutron diffraction experiments provide accurate, unbiased H-atom positions which are especially important because of the critical role of hydrogen bonding in these systems. This paper summarizes the geometrical and conformational parameters of the structures of all five crystalline methyl pentofuranosides, several of them reported here for the first time. The methyl pentofuranoside structures are compared with the structures of the five crystalline methyl hexopyranosides for which accurate X-ray and neutron structures have been determined. Unlike the methyl hexopyranosides, which crystallize exclusively in the C 1 chair conformation, the five crystalline methyl pentofuranosides represent a very wide range of ring conformations.

scholarly journals A versatile nanoreactor for complementary in situ X-ray and electron microscopy studies in catalysis and materials science

2019 ◽  
Vol 26 (5) ◽  
pp. 1769-1781 ◽  
Author(s):  
Yakub Fam ◽  
Thomas L. Sheppard ◽  
Johannes Becher ◽  
Dennis Scherhaufer ◽  
Heinz Lambach ◽  
...  
Keyword(s):  
Electron Microscopy ◽  
Materials Science ◽  
Functional Materials ◽  
Ambient Conditions ◽  
Zeolite Sample ◽  
X Ray ◽  
Fluorescence Measurements ◽  
Wide Range ◽  
Modular Platform

Two in situ `nanoreactors' for high-resolution imaging of catalysts have been designed and applied at the hard X-ray nanoprobe endstation at beamline P06 of the PETRA III synchrotron radiation source. The reactors house samples supported on commercial MEMS chips, and were applied for complementary hard X-ray ptychography (23 nm spatial resolution) and transmission electron microscopy, with additional X-ray fluorescence measurements. The reactors allow pressures of 100 kPa and temperatures of up to 1573 K, offering a wide range of conditions relevant for catalysis. Ptychographic tomography was demonstrated at limited tilting angles of at least ±35° within the reactors and ±65° on the naked sample holders. Two case studies were selected to demonstrate the functionality of the reactors: (i) annealing of hierarchical nanoporous gold up to 923 K under inert He environment and (ii) acquisition of a ptychographic projection series at ±35° of a hierarchically structured macroporous zeolite sample under ambient conditions. The reactors are shown to be a flexible and modular platform for in situ studies in catalysis and materials science which may be adapted for a range of sample and experiment types, opening new characterization pathways in correlative multimodal in situ analysis of functional materials at work. The cells will presently be made available for all interested users of beamline P06 at PETRA III.

TIME TO THE END OF PRIMARY CONSOLIDATION (EOP) OF SOFT CLAYEY SOILS: CONCERNING THE EFFECT OF ATTERBERG’S LIMIT AND CYCLIC LOADING HISTORY

2019 ◽  
Vol 128 (2B) ◽  
pp. 29-41
Author(s):  
Trần Thanh Nhàn
Keyword(s):  
Cyclic Loading ◽  
Pore Water ◽  
Pore Water Pressure ◽  
Water Pressure ◽  
Clayey Soils ◽  
Loading History ◽  
Cyclic Shear ◽  
Wide Range ◽  
Primary Consolidation ◽  
Time Required

In order to observe the end of primary consolidation (EOP) of cohesive soils with and without subjecting to cyclic loading, reconstituted specimens of clayey soils at various Atterberg’s limits were used for oedometer test at different loading increments and undrained cyclic shear test followed by drainage with various cyclic shear directions and a wide range of shear strain amplitudes. The pore water pressure and settlement of the soils were measured with time and the time to EOP was then determined by different methods. It is shown from observed results that the time to EOP determined by 3-t method agrees well with the time required for full dissipation of the pore water pressure and being considerably larger than those determined by Log Time method. These observations were then further evaluated in connection with effects of the Atterberg’s limit and the cyclic loading history.

Counterfeit Parts Recognition and Detection for Failure Analysts

2010 ◽  
Author(s):  
Katherine V. Whittington
Keyword(s):  
Thermal Cycle ◽  
Visual Inspection ◽  
Acoustic Microscopy ◽  
Scanning Acoustic Microscopy ◽  
3D Measurement ◽  
X Ray ◽  
Wide Range ◽  
Electronic Parts ◽  
Testing Awareness

Abstract The electronics supply chain is being increasingly infiltrated by non-authentic, counterfeit electronic parts, whose use poses a great risk to the integrity and quality of critical hardware. There is a wide range of counterfeit parts such as leads and body molds. The failure analyst has many tools that can be used to investigate counterfeit parts. The key is to follow an investigative path that makes sense for each scenario. External visual inspection is called for whenever the source of supply is questionable. Other methods include use of solvents, 3D measurement, X-ray fluorescence, C-mode scanning acoustic microscopy, thermal cycle testing, burn-in technique, and electrical testing. Awareness, vigilance, and effective investigations are the best defense against the threat of counterfeit parts.

Shooting a Tiger

2018 ◽  
Author(s):  
Vijaya Ramadas Mandala
Keyword(s):  
Critical Role ◽  
Late Nineteenth Century ◽  
Way Of Life ◽  
Colonial India ◽  
British Raj ◽  
Early Colonial ◽  
Wide Range ◽  
Forest Legislation ◽  
Imperial Governance ◽  
North And South

The main contention of Shooting a Tiger is that hunting during the colonial period was not merely a recreational activity, but a practice intimately connected with imperial governance. The book positions shikar or hunting at the heart of colonial rule by demonstrating that, for the British in India, it served as a political, practical, and symbolic apparatus in the consolidation of power and rule during the nineteenth and early twentieth centuries. The book analyses early colonial hunting during the Company period, and then surveys different aspects of hunting during the high imperial decades in the later nineteenth and early twentieth centuries. The book draws upon an impressive array of archival material and uses a wide range of evidence to support its contentions. It examines hunting at a variety of social and ethnic levels—military, administrative, elite, princely India, Indian professional hunters, and in terms of Indian auxiliaries and (sometimes) resisters. It also deals with different geographical contexts—the plains, the mountains, north and south India. The exclusive privilege of hunting exercised by the ruling classes, following colonial forest legislation, continued to be extended to the Indian princes who played a critical role in sustaining the lavish hunts that became the hallmark of the late nineteenth-century British Raj. Hunting was also a way of life in colonial India, undertaken by officials and soldiers alike alongside their everyday duties, necessary for their mental sustenance and vital for the smooth operation of the colonial administration. There are also two final chapters on conservation, particularly the last chapter focusing on two British hunter-turned-conservationists, Jim Corbett and Colonel Richard Burton.

scholarly journals The Degree of Oxidation of Graphene Oxide

Nanomaterials ◽  
2021 ◽  
Vol 11 (3) ◽  
pp. 560
Author(s):  
Alexandra Carvalho ◽  
Mariana C. F. Costa ◽  
Valeria S. Marangoni ◽  
Pei Rou Ng ◽  
Thi Le Hang Nguyen ◽  
...  
Keyword(s):  
Graphene Oxide ◽  
Ab Initio ◽  
State Of The Art ◽  
High Accuracy ◽  
Precise Determination ◽  
Photoemission Spectroscopy ◽  
Pristine Graphene ◽  
X Ray ◽  
Degree Of Oxidation

We show that the degree of oxidation of graphene oxide (GO) can be obtained by using a combination of state-of-the-art ab initio computational modeling and X-ray photoemission spectroscopy (XPS). We show that the shift of the XPS C1s peak relative to pristine graphene, ΔEC1s, can be described with high accuracy by ΔEC1s=A(cO−cl)2+E0, where c0 is the oxygen concentration, A=52.3 eV, cl=0.122, and E0=1.22 eV. Our results demonstrate a precise determination of the oxygen content of GO samples.

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