scholarly journals Influence of Oxidation Media on the Transport Properties of Thin Oxide Layers of Zirconium Alloys

10.14311/1002 ◽  
2007 ◽  
Vol 47 (6) ◽  
Author(s):  
H. Frank
Keyword(s):  
Activation Energy ◽  
Zirconium Alloys ◽  
Bottom Layer ◽  
Oxide Layers ◽  
Air Samples ◽  
Ag Electrodes ◽  
Order Of Magnitude ◽  
Injection Currents ◽  
Space Charge Limited Currents ◽  
Equal Thickness

Two batches of tubes of Zr1Nb and of Zry-4W were oxidized for 30 days at 425 °C in steam, and for 360 days at 500 °C in air, respectively. The analysis of the I-V characteristics at constant temperatures up to 220 °C of oxide layers of nearly equal thickness gave an activation energy of 1,3 eV for the grey homogeneous steam samples, and of 0.4 eV for the white surface layer, and of 1.3 eV at temperatures over 140 °C, for the grey bottom layer of the air samples, respectively. The I-V characteristics were sub-linear in the air samples, the current growing less at rising voltages, but staightening to super-linear space-charge limited currents at higher temperatures. The injection currents flowing when voltage was applied did not reach constant equilibrium, but at a bend, continued with a lesser slope. The resistivity was about one order of magnitude greater in air samples and greater in Zry-4W. The relative permittivity was greater in the steam samples and greater in Zr1Nb. The currents of the air samples were greater with Au electrodes than with Ag electrodes. 

scholarly journals SYNTHESIS AND ELECTRICAL CONDUCTIVITY OF SOLID SOLUTIONS OF THE SYSTEM RbF-PbF2-SnF2

2019 ◽  
Vol 85 (5) ◽  
pp. 60-68
Author(s):  
Yuliay Pogorenko ◽  
Anatoliy Omel’chuk ◽  
Roman Pshenichny ◽  
Anton Nagornyi
Keyword(s):  
Activation Energy ◽  
Electrical Conductivity ◽  
Temperature Dependence ◽  
Solid Solutions ◽  
Basic Structure ◽  
Elementary Cell ◽  
Initial Structure ◽  
Fluoride Ions ◽  
Temperature Range ◽  
Order Of Magnitude

In the system RbF–PbF2–SnF2 are formed solid solutions of the heterovalent substitution RbxPb0,86‑xSn1,14F4-x (0 < x ≤ 0,2) with structure of β–PbSnF4. At x > 0,2 on the X-ray diffractograms, in addition to the basic structure, additional peaks are recorded that do not correspond to the reflexes of the individual fluorides and can indicate the formation of a mixture of solid solutions of different composition. For single-phase solid solutions, the calculated parameters of the crystal lattice are satisfactorily described by the Vegard rule. The introduction of ions of Rb+ into the initial structure leads to an increase in the parameter a of the elementary cell from 5.967 for x = 0 to 5.970 for x = 0.20. The replacement of a part of leads ions to rubium ions an increase in electrical conductivity compared with β–PbSnF4 and Pb0.86Sn1.14F4. Insignificant substitution (up to 3.0 mol%) of ions Pb2+ at Rb+ at T<500 K per order of magnitude reduces the conductivity of the samples obtained, while the nature of its temperature dependence is similar to the temperature dependence of the conductivity of the sample β-PbSnF4. By replacing 5 mol. % of ions with Pb2+ on Rb+, the fluoride ion conductivity at T> 450 K is higher than the conductivity of the initial sample Pb0,86Sn1,14F4 and at temperatures below 450 K by an order of magnitude smaller. With further increase in the content of RbF the electrical conductivity of the samples increases throughout the temperature range, reaching the maximum values at x≥0.15 (σ573 = 0.34–0.41 S/cm, Ea = 0.16 eV and σ373 = (5.34–8.16)•10-2 S/cm, Ea = 0.48–0.51 eV, respectively). In the general case, the replacement of a part of the ions of Pb2+ with Rb+ to an increase in the electrical conductivity of the samples throughout the temperature range. The activation energy of conductivity with an increase in the content of RbF in the low-temperature region in the general case increases, and at temperatures above 400 K is inversely proportional decreasing. The nature of the dependence of the activation energy on the concentration of the heterovalent substituent and its value indicate that the conductivity of the samples obtained increases with an increase in the vacancies of fluoride ions in the structure of the solid solutions.

scholarly journals Temporal dynamics of ikaite in experimental sea ice

2014 ◽  
Vol 8 (4) ◽  
pp. 1469-1478 ◽  
Author(s):  
S. Rysgaard ◽  
F. Wang ◽  
R. J. Galley ◽  
R. Grimm ◽  
D. Notz ◽  
...  
Keyword(s):  
Sea Ice ◽  
Temporal Dynamics ◽  
Metastable Phase ◽  
Bottom Layer ◽  
Co2 Exchange ◽  
Environmental Research ◽  
Spatial And Temporal Dynamics ◽  
Order Of Magnitude ◽  
Frost Flowers ◽  
Snow Conditions

Abstract. Ikaite (CaCO3 · 6H2O) is a metastable phase of calcium carbonate that normally forms in a cold environment and/or under high pressure. Recently, ikaite crystals have been found in sea ice, and it has been suggested that their precipitation may play an important role in air–sea CO2 exchange in ice-covered seas. Little is known, however, of the spatial and temporal dynamics of ikaite in sea ice. Here we present evidence for highly dynamic ikaite precipitation and dissolution in sea ice grown at an outdoor pool of the Sea-ice Environmental Research Facility (SERF) in Manitoba, Canada. During the experiment, ikaite precipitated in sea ice when temperatures were below −4 °C, creating three distinct zones of ikaite concentrations: (1) a millimeter-to-centimeter-thin surface layer containing frost flowers and brine skim with bulk ikaite concentrations of >2000 μmol kg−1, (2) an internal layer with ikaite concentrations of 200–400 μmol kg−1, and (3) a bottom layer with ikaite concentrations of <100 μmol kg−1. Snowfall events caused the sea ice to warm and ikaite crystals to dissolve. Manual removal of the snow cover allowed the sea ice to cool and brine salinities to increase, resulting in rapid ikaite precipitation. The observed ikaite concentrations were on the same order of magnitude as modeled by FREZCHEM, which further supports the notion that ikaite concentration in sea ice increases with decreasing temperature. Thus, varying snow conditions may play a key role in ikaite precipitation and dissolution in sea ice. This could have a major implication for CO2 exchange with the atmosphere and ocean that has not been accounted for previously.

Inferring rock glacier genesis and dynamics from age-layer modelling and borehole age-profile

2021 ◽  
Author(s):  
Gwendolyn J.-M. C. Leysinger Vieli ◽  
Andreas Vieli ◽  
Alessandro Cicoira
Keyword(s):  
Accumulation Rate ◽  
Bottom Layer ◽  
Rock Glacier ◽  
Depth Profiles ◽  
Talus Slope ◽  
Order Of Magnitude ◽  
Rock Glaciers ◽  
Age Profile ◽  
Modelling Approach

&lt;p&gt;The genesis of rock glaciers differs fundamentally from &amp;#8216;normal&amp;#8217; glaciers and results in much older landforms that are often reaching ages of several millennia. Recent datings of rock glacier material from boreholes indicate early Holocene ages for rock glaciers and allow the derivation of age-depth profiles at the borehole location. We use here a 2-dimensional numerical modelling approach that calculates age-layers (isochrones) within the rock glacier body and that considers the accretion, melt and flow-advection of rock glacier material. We apply this model to the case of Lazaun rock glacier (Southern &amp;#214;tztal Alps) for which a well dated profile from a borehole exists, with ages at the bottom older than 9000 years (Krainer et al. 2015). With our modelling we are able to reproduce the observed age-depth profiles well and are able to infer a long-term accumulation rate that is around 1 cm/yr which is an order of magnitude higher than a previous estimate that does not account for deformation. The modelling is consistent with the classic rock glacier genesis of material accretion in the upstream talus slope and confirms the dominance of deformation in the shear-zone at the bottom layer of the rock glacier.&lt;br&gt;We conclude that combining age-layer modelling with dated depth-profiles of rock glaciers allows for important new insights into our understanding of rock glacier evolution and dynamics.&lt;/p&gt;&lt;p&gt;REFERENCES &amp;#160;&lt;br&gt;Krainer, K., Bressan, D., Dietre, B., Haas, J., Hajdas, I., Lang, K. &amp; Tonidandel, D. (2015). A 10,300-year-old permafrost core from the active rock glacier Lazaun, southern Oetztal Alps (South Tyrol, Northern Italy). Quaternary Research, 83 , 324-335.&amp;#160;&lt;/p&gt;&lt;p&gt;&amp;#160;&lt;/p&gt;

Microstructure of Oxide Layers Formed During Autoclave Testing of Zirconium Alloys

2009 ◽  
pp. 579-579-20 ◽  
Author(s):  
B Wadman ◽  
Z Lai ◽  
H-O Andrén ◽  
A-L Nyström ◽  
P Rudling ◽  
...  
Keyword(s):  
Zirconium Alloys ◽  
Oxide Layers

scholarly journals Absolute linear instability in laminar and turbulent gas–liquid two-layer channel flow

2013 ◽  
Vol 714 ◽  
pp. 58-94 ◽  
Author(s):  
Lennon Ó Náraigh ◽  
Peter D. M. Spelt ◽  
Stephen J. Shaw
Keyword(s):  
Gas Flow ◽  
Oil And Gas ◽  
Stability Boundary ◽  
Density Ratio ◽  
Bottom Layer ◽  
Linear Instability ◽  
Absolute Instability ◽  
Two Phase ◽  
Order Of Magnitude ◽  
Temporal Modes

AbstractWe study two-phase stratified flow where the bottom layer is a thin laminar liquid and the upper layer is a fully developed gas flow. The gas flow can be laminar or turbulent. To determine the boundary between convective and absolute instability, we use Orr–Sommerfeld stability theory, and a combination of linear modal analysis and ray analysis. For turbulent gas flow, and for the density ratio $r= 1000$, we find large regions of parameter space that produce absolute instability. These parameter regimes involve viscosity ratios of direct relevance to oil and gas flows. If, instead, the gas layer is laminar, absolute instability persists for the density ratio $r= 1000$, although the convective/absolute stability boundary occurs at a viscosity ratio that is an order of magnitude smaller than in the turbulent case. Two further unstable temporal modes exist in both the laminar and the turbulent cases, one of which can exclude absolute instability. We compare our results with an experimentally determined flow-regime map, and discuss the potential application of the present method to nonlinear analyses.

scholarly journals Oxidation of Zirconium Alloys. Crystallographic Texture of Zirconia: Interpretation and Mechanical Consequences

1998 ◽  
Vol 30 (3-4) ◽  
pp. 247-263 ◽  
Author(s):  
M. Parise ◽  
I. Touet ◽  
O. Sicardy
Keyword(s):  
Zirconium Alloys ◽  
Crystallographic Direction ◽  
Pressurized Water Reactors ◽  
Monoclinic Zirconia ◽  
Oxide Interface ◽  
Pressurized Water ◽  
Oxide Layers ◽  
Pole Figures ◽  
Water Reactors ◽  
Anisotropic Elastic

In order to have a better knowledge of the mechanical behaviour of the oxide layers growing on zirconium alloys in pressurized water reactors, the textures of different zirconium alloys and their oxide layers are studied. The results show that the texture of the oxide layers present a feature common to all the layers: the tilt angle of the maximum intensities of the pole figures obtained on the layers is almost quite identical for all the studied substrates. The azimuthal reinforcements depend on the metallurgical state of the substrate.The crystallographic direction of monoclinic zirconia common to all the oxide grains is identified. A computation based on mechanical issues is presented: considering the anisotropic elastic properties of the monoclinic monocrystal, it is shown that the particular crystallographic direction is linked to an isotropic state of strains in the plane of the metal–oxide interface.

scholarly journals Microstructure and texture analysis of δ-hydride precipitation in Zircaloy-4 materials by electron microscopy and neutron diffraction

2014 ◽  
Vol 47 (1) ◽  
pp. 303-315 ◽  
Author(s):  
Zhiyang Wang ◽  
Ulf Garbe ◽  
Huijun Li ◽  
Yanbo Wang ◽  
Andrew J. Studer ◽  
...  
Keyword(s):  
Electron Microscopy ◽  
Neutron Diffraction ◽  
Profile Analysis ◽  
Zirconium Alloys ◽  
Average Density ◽  
Line Profile Analysis ◽  
Hydride Precipitation ◽  
Diffraction Line Profile ◽  
Transmission Electron ◽  
Order Of Magnitude

This work presents a detailed microstructure and texture study of various hydrided Zircaloy-4 materials by neutron diffraction and microscopy. The results show that the precipitated δ-ZrH1.66generally follows the δ(111)//α(0001) and δ[1{\overline 1}0]//α[11{\overline 2}0] orientation relationship with the α-Zr matrix. The δ-hydride displays a weak texture that is determined by the texture of the α-Zr matrix, and this dependence essentially originates from the observed orientation correlation between α-Zr and δ-hydride. Neutron diffraction line profile analysis and high-resolution transmission electron microscopy observations reveal a significant number of dislocations present in the δ-hydride, with an estimated average density one order of magnitude higher than that in the α-Zr matrix, which contributes to the accommodation of the substantial misfit strains associated with hydride precipitation in the α-Zr matrix. The present observations provide an insight into the behaviour of δ-hydride precipitation in zirconium alloys and may help with understanding the induced embrittling effect of hydrides.

Ion Beam Induced Regrowth in GaAs

1988 ◽  
Vol 100 ◽  
Author(s):  
S. T. Johnson ◽  
J. S. Williams ◽  
E. Nygren ◽  
R. G. Elliman
Keyword(s):  
Activation Energy ◽  
Ion Beam ◽  
Gaas Crystal ◽  
Early Stages ◽  
Order Of Magnitude ◽  
Ion Implanted

ABSTRACTIon implanted, amorphous layers on (100) GaAs have been recrystallised epitaxially by 1.5 MeV Ne+ irradiation at temperatures between 75°C and 135°C. The extent of regrowth essentially increases linearly with ion fluence in the early stages of crystallization and the process is characterized by an activation energy of 0.16eV, about an order of magnitude lower than that for thermal - only epitaxy. Beam annealing produces dislocations in the underlying GaAs crystal, the density of which increases with depth up to the Ne+ ion range.

scholarly journals SARS-CoV-2 and Environmental Samples: A Methodological Approach to Have Consistent and Comparable Results

2020 ◽  
Author(s):  
Angelo Robotto ◽  
Paola Quaglino ◽  
David Lembo ◽  
Marcello Morello ◽  
Enrico Brizio ◽  
...  
Keyword(s):  
Environmental Samples ◽  
Methodological Approach ◽  
Sampling Technique ◽  
Complete Information ◽  
Environmental Sampling ◽  
Air Samples ◽  
Order Of Magnitude ◽  
Wastewater Samples ◽  
The Relationship ◽  
Parallel Sampling

Since the beginning of coronavirus disease 2019 (COVID-19) pandemic, large attention has been focused on the relationship between SARS-CoV-2 diffusion and environment. As a matter of fact, clear evidence of the transmission of SARS-CoV-2 via respiratory aerosol would be of primary importance; at the same time, checking the presence of SARS-CoV-2 in wastewater can be extremely useful to control the diffusion of the disease. Up to now, many studies report SARS-CoV-2 concentrations in indoor/outdoor air samples or water/wastewater samples that can differ by order of magnitude. Unfortunately, complete information about the scientific approach of many studies is still missing, relating to: samplers and sampling materials performances, recovery tests, measurement uncertainty, robustness, detection and quantification limits, infectivity of captured virus, virus degradation during sampling, influence of sample pre-treatments (included freezing) on results, effects of inhibitors, sample alterations due to manipulation, validation of methods and processes, quality assurance according to ISO/IEC 17025 requirements.Based on the first experiences focused on the presence of SARS-CoV-2 in environmental samples such as air quality filters, air-liquid impingers and wastewater samples, the present study describes a coherent preliminary approach to SARS-CoV-2 environmental sampling in order to overcome the evident lack of standardization. Three aspects are highlighted here: the first solution to assure quality and consistency to environmental sampling relies on the development of recovery tests using standard materials and investigating sampling materials, sampling techniques, sampling durations, sample conservation and pre-treatments; secondly, in order to overcome the shortcomings of every single sampling technique, coupling different samplers in parallel sampling could be an efficient strategy to collect more information and make data more reliable, in particular for air samples; finally, with regards to airborne virus sampling, the results could be confirmed by simplified emission and dilution models.

scholarly journals Microstructure and Properties of M3B2-Type Boride-Based Cermet Coatings Prepared by Laser Cladding Synthesis

Coatings ◽  
2019 ◽  
Vol 9 (8) ◽  
pp. 476 ◽  
Author(s):  
Zhaowei Hu ◽  
Wenge Li ◽  
Yuantao Zhao
Keyword(s):  
Corrosion Resistance ◽  
Laser Cladding ◽  
Metal Layer ◽  
Surface Hardness ◽  
Electrochemical Corrosion ◽  
Bottom Layer ◽  
Cermet Coatings ◽  
Good Surface ◽  
Order Of Magnitude ◽  
Metal Phases

Although Q235 steel materials are widely used in offshore engineering, the service life is severely shortened by its inferior resistance to wear and corrosion in harsh marine working environments. Boride-based cermet composites could be a good surface-protective coating to enhance surface hardness, wear resistance, and corrosion resistance. M3B2 (M: Mo, Ni, Fe, Cr) boride-based cermet coatings composed of hard ceramics of M3B2-type complex borides and an {Fe, Ni} metal matrix was fabricated on Q235 steels with mixed Mo, Cr, B, and Ni60 powders using a laser cladding synthesis technique. The influences of laser cladding parameters on the microstructure, phase composition, microhardness, and corrosion resistance of the coatings were comprehensively investigated. Results showed that the microstructures of the coatings mainly consisted of three layers, which were, from the top to bottom layer, a metal layer with fewer ceramic phases, a ceramic layer with fewer metal phases, and another metal layer with fewer ceramic phases. The ceramic phases were mainly M3B2-type borides, and the metal phases were mainly {Fe, Ni} alloys. The appearance of Fe-enriching metal phases was due to the supply of Fe elements from Q235 substrates. With squash pretreatment and without a remelting aftertreatment, ceramics uniformly dispersed in the cermet coatings, and their sizes decreased. The results of microhardness showed that the microhardness of the coating first increased and then decreased from the top layer to the bottom layer, and maximum microhardness was obtained in the layer of ceramics with less metal phases. An electrochemical corrosion test showed that the cermet coatings (jcorr = 6.35 μA/cm2) could improve the corrosion resistance of Q235 steels (j = 43.76 μA/cm2) by one order of magnitude.

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