Mechanisms of Oxidation of Fuel Cladding Alloys Revealed by High Resolution APT, TEM and SIMS Analysis

2012 ◽  
Vol 1383 ◽  
Author(s):  
Chris R. M. Grovenor ◽  
Na Ni ◽  
Daniel Hudson ◽  
Sean S. Yardley ◽  
Katie L. Moore ◽  
...  
Keyword(s):  
High Resolution ◽  
Metal Oxide ◽  
Oxide Layer ◽  
Electrochemical Impedance ◽  
Complex Structure ◽  
Oxygen Stoichiometry ◽  
Aqueous Environment ◽  
Oxide Interface ◽  
Aqueous Corrosion ◽  
Sims Analysis

ABSTRACTAqueous corrosion of zirconium alloys has become the major factor limiting prolonged fuel campaigns in nuclear plant. Studies using SEM, TEM and electrochemical impedance measurements have been interpreted as showing a dense inner-most oxide layer, and an increased thickness of the layer has been correlated to a better corrosion resistance. Many authors have reported that an ‘intermediate layer’ at the metal oxide interface has a complex structure or/and stochiometry different to that of both the bulk oxide and bulk metal, sometimes claimed to be a suboxide phase. Diffraction evidence has suggested the presence of both cubic ZrO and rhombohedral Zr3O phases, and compositional analysis has revealed similar variations in local oxygen stoichiometry.We have carried out a systematic investigation of the structure and chemistry of the metal/oxide interface in samples of commercial ZIRLO corroded for times up to 180 days. We have developed new experimental techniques for the study of these interfaces both by Electron Energy Loss Spectroscopy (EELS) analysis in the Transmission Electron Microscope (TEM) and by Atom Probe Tomography (APT), and exactly the same samples have been investigated by both techniques. Our results show the development of a clearly defined suboxide layer of stoichiometry close to ZrO, and the subsequent disappearance of this layer at the first of the characteristic ‘breakaway’ transitions in the oxidation kinetics. We can correlate this behaviour with changes in the structure of the oxide layer, and particularly the development of interconnected porosity that links the corroding interface with the aqueous environment. Using high resolution SIMS analysis of isotopically spiked samples we demonstrate the penetration of the oxidising species through these porous outer oxide layers.

Scale Growth on Austenitic Alloys under KCl Deposits at 500°C

2008 ◽  
Vol 595-598 ◽  
pp. 333-342 ◽  
Author(s):  
Petter Andersson ◽  
Mats Norell
Keyword(s):  
Metal Oxide ◽  
Relative Density ◽  
Oxide Layer ◽  
Scale Growth ◽  
Oxide Interface ◽  
Sanicro 28 ◽  
Austenitic Alloys

The scale growth on two austenitic alloys, Alloy 310 and Sanicro 28, under KCl deposits was examined. This is relevant to the long term corrosion of superheater tubes in biofuel combustion. Coupons were encapsulated in tablets so that 1 mm of KCl with a relative density of 91% covered the metal. Samples were tested at 500°C in 5%O2-10%H2O-N2 for 24, 168 and 672 h. After exposure the salt was broken off and the scale was characterised by using SEM-EDX and AES. After 24 h a 50 nm thick oxide surrounded 500 nm thick chromates on the surface. No oxide layer was detected under the chromates and no Cl was found under either layer. The chromate growth requires lateral transportation of Cr along the surface. This reduces the protectiveness of the oxide and accelerates the formation of less protective Fe rich oxides. The formation of chromates also releases HCl inside the KCl tablet. The chromates did not grow significantly between 24 and 168 h, but the oxide grew equally thick beneath and between them and Cl was enriched around the metal oxide interface. After 672 h the oxides were about 5 μm thick and only few chromates were seen. Crystals of KCl formed in areas with thick porous and Fe rich oxides on both alloys.

The Effect of Y and Zr on the Oxidation of NiA1

1994 ◽  
Vol 364 ◽  
Author(s):  
Eckart Schumann ◽  
J. C. Yang ◽  
M. Rühle ◽  
M. J. Graham
Keyword(s):  
High Resolution ◽  
Grain Boundary ◽  
Metal Oxide ◽  
Grain Boundaries ◽  
Oxidation Behaviour ◽  
Oxide Interface ◽  
Analytical Tem ◽  
Outward Transport ◽  
Tracer Experiments

AbstractThe effect of Y and Zr on the oxidation behaviour of NiAl has been investigated using high resolution SIMS and analytical TEM. 18O tracer experiments in conjunction with SIMS showed that Y and Zr reduce the outward transport of cations during the growth of the AI2O3 scale. Complementary STEM-EDS measurements revealed segregation of Y and Zr at the metal/oxide interface as well as the grain boundaries in the AI2O3 scale. The amounts of segregation at both the interface and grain boundary were calculated to be less than one monolayer.

Computer processing of high-resolution images of periodic specimens

1986 ◽  
Vol 44 ◽  
pp. 2-5
Author(s):  
W. Chiu ◽  
M.F. Schmid ◽  
T.-W. Jeng
Keyword(s):  
High Resolution ◽  
Fourier Transforms ◽  
Complex Structure ◽  
Distribution Functions ◽  
Multiple Image ◽  
Cryo Electron Microscopy ◽  
Structure Factors ◽  
Unit Cells ◽  
High Resolution Images ◽  
Phase Probability Distribution

Cryo-electron microscopy has been developed to the point where one can image thin protein crystals to 3.5 Å resolution. In our study of the crotoxin complex crystal, we can confirm this structural resolution from optical diffractograms of the low dose images. To retrieve high resolution phases from images, we have to include as many unit cells as possible in order to detect the weak signals in the Fourier transforms of the image. Hayward and Stroud proposed to superimpose multiple image areas by combining phase probability distribution functions for each reflection. The reliability of their phase determination was evaluated in terms of a crystallographic “figure of merit”. Grant and co-workers used a different procedure to enhance the signals from multiple image areas by vector summation of the complex structure factors in reciprocal space.

An Effective SIMS Methodology for GOI Contamination Analysis

2013 ◽  
Author(s):  
Yanhua Huang ◽  
Lei Zhu ◽  
Kenny Ong ◽  
Hanwei Teo ◽  
Younan Hua
Keyword(s):  
Oxide Layer ◽  
Secondary Ion Mass Spectrometry ◽  
Gate Oxide ◽  
Sample Surface ◽  
Low Energy ◽  
Cross Contamination ◽  
Common Effect ◽  
Sims Analysis ◽  
Secondary Ion ◽  
Lower Background

Abstract Contamination in the gate oxide layer is the most common effect which cause the gate oxide integrate (GOI) issue. Dynamic Secondary Ion Mass Spectrometry (SIMS) is a mature tool for GOI contamination analysis. During the sample preparation, all metal and IDL layers above poly should be removed because the presence of these layers added complexity for the subsequent SIMS analysis. The normal delayering process is simply carried out by soaking the sample in the HF solution. However, the poly surface is inevitably contaminated by surroundings even though it is already a practice to clean with DI rinse and tape. In this article, TOFSIMS with low energy sputter gun is used to clean the sample surface after the normal delayering process. The residue signals also can be monitored by TOF SIMS during sputtering to confirm the cross contamination is cleared. After that, a much lower background desirable by dynamic SIMS. Thus an accurate depth profile in gate oxide layer can be achieved without the interference from surface.

Chemical Effects at the Reaction Front in Corroding Spent Nuclear Fuel

2006 ◽  
Vol 985 ◽  
Author(s):  
Jeffrey A. Fortner ◽  
A. Jeremy Kropf ◽  
James L. Jerden ◽  
James C. Cunnane
Keyword(s):  
Transition Zone ◽  
Nuclear Fuel ◽  
Spent Nuclear Fuel ◽  
Aqueous Environment ◽  
Spent Fuel ◽  
Aqueous Corrosion ◽  
Reduction Potentials ◽  
Chemical Effects ◽  
Before And After ◽  
X Ray Absorption

AbstractPerformance assessment models of the U. S. repository at Yucca Mountain, Nevada suggest that neptunium from spent nuclear fuel is a potentially important dose contributor. A scientific understanding of how the UO2 matrix of spent nuclear fuel impacts the oxidative dissolution and reductive precipitation of Np is needed to predict the behavior of Np at the fuel surface during aqueous corrosion. Neptunium would most likely be transported as aqueous Np(V) species, but for this to occur it must first be oxidized from the Np(IV) state found within the parent spent nuclear fuel. In this paper we present synchrotron x-ray absorption spectroscopy and microscopy findings that illuminate the resultant local chemistry of neptunium and plutonium within uranium oxide spent nuclear fuel before and after corrosive alteration in an air-saturated aqueous environment. We find the Pu and Np in unaltered spent fuel to have a +4 oxidation state and an environment consistent with solid-solution in the UO2 matrix. During corrosion in an air-saturated aqueous environment, the uranium matrix is converted to uranyl (UO22+) mineral assemblage that is depleted in Np and Pu relative to the parent fuel. The transition from U(IV) in the fuel to a fully U(VI) character across the corrosion front is not sharp, but occurs over a transition zone of ∼ 50 micrometers. We find evidence of a thin (∼ 20 micrometer) layer that is enriched in Pu and Np within a predominantly U(IV) environment on the fuel side of the transition zone. These experimental observations are consistent with available data for the standard reduction potentials for NpO2+/Np4+ and UO22+/U4+ couples, which indicate that Np(IV) may not be effectively oxidized to Np(V) at the corrosion potential of uranium dioxide spent nuclear fuel in air-saturated aqueous solutions.

Surface to bulk charge transfer at an alkali metal/metal oxide interface

2003 ◽  
Vol 547 (1-2) ◽  
pp. L859-L864 ◽  
Author(s):  
R Lindsay ◽  
E Michelangeli ◽  
B.G Daniels ◽  
M Polcik ◽  
A Verdini ◽  
...  
Keyword(s):  
Charge Transfer ◽  
Alkali Metal ◽  
Metal Oxide ◽  
Oxide Interface ◽  
Metal Metal ◽  
Bulk Charge

High temperature behavior of the metal/oxide interface of ferritic stainless steels

2012 ◽  
Vol 59 ◽  
pp. 148-156 ◽  
Author(s):  
Jérôme Issartel ◽  
Sébastien Martoia ◽  
Frédéric Charlot ◽  
Valérie Parry ◽  
Guillaume Parry ◽  
...  
Keyword(s):  
High Temperature ◽  
Metal Oxide ◽  
Stainless Steels ◽  
Temperature Behavior ◽  
Oxide Interface ◽  
Ferritic Stainless Steels ◽  
High Temperature Behavior
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