Download or read book The Nature of Unstable Oxide Growth in Zirconium and Zirconium Alloys written by Brendan Ensor and published by . This book was released on 2016 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: Zirconium alloys are commonly used as fuel claddings in nuclear reactors due in part to theirsuperior corrosion resistance. The addition of small concentrations of alloying elements prevents thecladding material from undergoing unstable oxide growth under the operating conditions of a nuclearreactor. Unstable oxide growth can also occur due to the presence of hydrides or exposure to neutron flux.The role of alloying elements in avoiding the transition from stable to unstable growth is examined in thisthesis. The goal is to determine the mechanism whereby oxide stabilization occurs.To accomplish this goal, a variety of experiments were performed, and the resulting oxide layerscharacterized with various techniques. Ten model Zr alloys were fabricated and tested in furnace at 600Cfor 40 hours in oxygen and in autoclave at 360C for up to 70 days to determine the causes of breakawayoxidation in pure Zr (and Zr alloys with small concentrations of alloying elements) and the role that alloyingelements play in causing this phenomenon. These alloys were carefully selected and included crystal barZr, sponge Zr, and alloys with small concentrations of Sn, Fe, and Cr. After testing, the alloys werecharacterized using scanning electron microscopy (SEM), Raman spectroscopy, and synchrotron -X-rayfluorescence (XRF) to determine how the structure of the oxide, tetragonal phase content, and alloyingelement distribution affected the formation of unstable oxide. Heterogeneous distribution of alloyingelements was linked to regions of unstable oxide (either nodule-like, grain boundary penetration, ordifferential grain-to-grain growth) and hypothesized to cause breakaway corrosion.The examination of stable oxide layers was then used as a baseline for comparison to cases ofunstable oxide growth in Zr and Zr alloys. One of the primary modes of examination of stable oxide layersformed on Zr alloys was microbeam synchrotron X-ray radiation diffraction and fluorescence, performedat the Advanced Photon Source (APS) at Argonne National Laboratory. This synchrotron X-ray source wasused to perform -X-ray diffraction (XRD), XRF, and 3D Laue spectroscopy. The XRD technique wasused to determine the oxide layer phase content, strain, and grain size as a function of corrosion temperatureand oxide thickness. The XRF technique was used to perform Fe X-ray absorption near-edge spectroscopyiv(XANES) to determine the oxidation state of Fe in the metal as a function of distance from the metal-oxideinterface for various corrosion temperatures. The 3D Laue spectroscopy technique was used to determineplastic deformation and elastic strain in the metal as a function of distance from the metal-oxide interface,corrosion temperature, and oxide thickness for crystal bar Zr and Zircaloy-4.Additionally, Zircaloy-4 samples were corroded in autoclave at 360C for up to 2804 days in andwere periodically weighed to determine oxide thickness. These samples had different coupon thicknessesthat altered the surface-to-volume ratio and led to a higher concentration of hydrogen for a given amountof oxide layer growth. The concentration of hydrogen was measured in archived samples to determine theeffect of hydrogen concentration on corrosion rate. It was observed that the corrosion rate of Zircaloy-4increased with increasing hydrogen concentration above the terminal solid solubility (TSS) of the material(and thus the precipitation of hydrides). More hydrogen caused earlier kinetic transition and areas ofadvanced oxide growth were associated with the locations of hydrides in the metal. It was hypothesizedthat the hydrides hardened the metal ahead of the interface and that the metal was then less able toaccommodate oxide growth stresses leading to earlier kinetic transition and mechanical cracking of theoxide.Finally, eleven Zircaloy-4 samples exposed to various temperatures (272-355C) and neutron fluxlevels (0-11.48 x 1013 n/cm2/s, E > 1 MeV) were examined using XRD and XRF to determine the effectof irradiation on oxide grain size, phase content, and the oxidation of Fe at the APS. With increasing neutronfluence, the grain size of the oxide increased, leading to less tetragonal phase in the oxide away from themetal-oxide interface. At the metal-oxide interface, higher amounts of tetragonal phase were observed withincreasing neutron fluence. This could be caused by the redistribution of Fe from second phase particles(SPPs) into the matrix or due to the hardening of the Zr matrix caused by the exposure to neutrons.The cases of unstable oxide growth examined here were linked to both the distribution and presenceof alloying elements in Zr and Zr alloys and to the level of stress in the oxide. These two phenomena appearto be the primary causes leading to regions of advanced oxide growth and careful consideration should begiven to them when designing and using future Zr alloys in advanced nuclear reactor concepts.
Download or read book The Importance of Oxide Morphology for the Oxidation Rate of Zirconium Alloys written by E. Ahlberg and published by . This book was released on 1996 with total page 19 pages. Available in PDF, EPUB and Kindle. Book excerpt: The oxide growth rate of zirconium alloys, e.g., Zircaloy-2 and Zircaloy-4, has been proposed to be controlled mainly by the transformation of the zirconium oxide from tetragonal to monoclinic structure at some distance from the metal-oxide interface, leading to cracking. This oxide growth rate model is inconsistent with our results. Zirconium alloys of varying chemical composition but with identical manufacturing process had markedly different oxide growth and hydriding properties in autoclave testing (400°C steam). The materials were characterized by several methods, e.g., electron microscopy (SEM), X-ray diffraction (XRD), and electrochemical impedance (EIS). The SEM and some of the XRD investigations of the oxide were performed on the metal-oxide interface after dissolution of the metal. The oxide growth developed through three different stages with an altered oxide morphology at the metaloxide interface at each stage. The developments of the stages were correlated with the oxide growth rate. Impedance measurements suggested that the oxide film had three layers, the outermost being extensively porous. Relaxation of the oxide film stress showed that the compressive stress in the oxide was not essential for retention of a significant amount of the tetragonal phase.
Download or read book Oxidation of Zirconium and Zirconium Alloys in Liquid Sodium written by T. L. Mackay and published by . This book was released on 1962 with total page 26 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Recent Studies of the Growth and Breakdown of Oxide Films on Zirconium and Its Alloys written by J. N. Wanklyn and published by . This book was released on 1964 with total page 18 pages. Available in PDF, EPUB and Kindle. Book excerpt: Several attempts to develop zirconium alloys suitable for use in superheated steam have been described (1-4). Assessment (5,6) of the results suggested that although a number of alloying additions can have a beneficial effect, great variability confuses the results, which, moreover, are no better than would be achieved by unalloyed zirconium in dry oxygen. Further, it appeared that only a low concentration of the added elements, provided it was distributed appropriately in the oxide film, might suffice to give corrosion resistance (2); it was also suggested (6) that the significant film breakdown in steam occurred on a very small scale. The behavior of resistant alloys was pictured in terms of a balance between film growth and film breakdown, leading beyond weight gains of 100 mg/dm2 to a more or less linear rate of corrosion. This paper reports recent attempts to study these two processes more intimately, using thinner films on unalloyed zirconium, and exploring some newer techniques. It may be said that zirconium, quite apart from its nuclear interest, is a rather suitable metal for such studies, forming but one oxide and having only a single valence. Moreover, although the entry of small amounts of hydrogen into the oxide is important, the complication of hydrated oxides is absent. Inasmuch as the aim is to give an up-to-date report of current work and thought, loose ends and tentative explanations may be expected in the following account.
Download or read book Identification and Growth of Oxide Films on Zirconium in High temperature Water written by C. M. Schwartz and published by . This book was released on 1955 with total page 28 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Oxide Growth Mechanism on Zirconium Alloys written by F. Garzarolli and published by . This book was released on 1991 with total page 21 pages. Available in PDF, EPUB and Kindle. Book excerpt: In order to get a better understanding of the mechanisms governing corrosion of Zr-based alloys, several examinations have been performed on a variety of samples with uniform and nodular corrosion and different oxide layer thicknesses.
Download or read book Corrosion of Zirconium and Zirconium Alloys written by Boris Grigorevich Parfenov and published by . This book was released on 1969 with total page 204 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book An Investigation of the Effect of Tin on Zirconium Alloy Oxide Morphology written by Jessica Gee and published by . This book was released on 2015 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: This study aims to investigate oxide formation in zirconium-tin binary alloys as compared to pure zirconium corroded in an oxygen environment. An analysis of oxide morphology with a focus on the metal-oxide interface is meant to establish the influence of tin content on the formation of instabilities in zirconium oxide, leading to breakaway corrosion. The oxide formed on three alloys of varying tin content are compared with those formed on zirconium crystal bar and zirconium sponge to characterize the role tin plays in altering the formation of oxide in these metals. Optical microscopy as well as field emission scanning electron microscopy (FESEM) imaging are used to observe the cross-sectional oxide growth. Increasing tin content increases the oxide thickness. The comparison between these alloys allows for the examination of stable, unstable, and breakaway oxide behavior. Preferential oxide growth occurs at grain boundaries, and develops into instabilities that permeate into grains within the metal. Breakaway behavior causes a dramatic increase in oxidation rate.
Download or read book Oxidation of Zirconium and Zirconium Alloys written by and published by . This book was released on 1959 with total page 48 pages. Available in PDF, EPUB and Kindle. Book excerpt: The oxidation rate was found to be relatively insensitive to various types of surface preparations in the temperature range 400 to 700 deg C. No dependence of reaction rate on oxygen pressure was observed. The cubic rate law also was obeyed by foil specimens at 700 deg C; however, the rate constants were slightly larger than values obtained from parallelepiped samples.
Download or read book Influence of Hydride Precipitation on the Corrosion Kinetics of Zircaloy 4 written by Michael Jublot and published by . This book was released on 2018 with total page 35 pages. Available in PDF, EPUB and Kindle. Book excerpt: Hydride precipitation at the oxide-metal interface is frequently proposed as causing the corrosion acceleration of Zircaloy-4 at high burnup in pressurized water reactors (PWRs). In order to identify the local mechanisms possibly involved, we studied the nanostructure of oxides formed on massive zirconium hydrides and reference Zircaloy-4 with an innovative grain mapping technique with the use of transmission electron microscopy (TEM). In autoclave PWR conditions, the presence of a precipitated hydride phase, previously formed by a cathodic charging technique at the surface of Zircaloy-4, clearly increased the corrosion rate, and a higher oxygen diffusion flux along oxide grain boundaries is observed compared with the reference Zircaloy-4. The texture, grain size, and adjacent grain misorientation in the oxide layer were studied in detail along the direction of the oxide growth using an automated crystal orientation mapping technique associated with TEM for both prehydrided and reference Zircaloy-4 samples. The texture in the growth direction is similar on prehydrided and reference samples, but the grain-to-grain misorientations showed differences. Indeed, on the prehydrided sample, the misorientation of 90° with respect to the [001] monoclinic axis is less probable than in the reference oxide, and more misorientations of 50-70° and 120-150°, corresponding to larger mismatches between neighboring grain boundaries, are observed. A smaller average diameter of the columnar monoclinic grains is also clearly revealed for the oxide grown on the prehydrided sample that leads to a larger number of diffusion paths for oxidizing species. These results are discussed and used for simulating oxygen diffusion flux through the polycrystalline microstructure of the oxide layer as a function of the grain size.
Download or read book Microstructure of the Oxide Films Formed on Zirconium Based Alloys written by GP. Airey and published by . This book was released on 1974 with total page 14 pages. Available in PDF, EPUB and Kindle. Book excerpt: Microstructural characterization of oxide films formed on zirconium-based alloys was performed by use of scanning and transmission electron microscopy. Examination of pre-transition films formed on Zircaloy-4 oxidized in 360°C (680°F) water revealed a small grain size of approximately 100 Å (10 nm) diameter. In addition, a gradation of grain size was observed throughout the film thickness, such that at the oxide-water surface (oldest oxide), a grain size of less than 50 Å (5nm) was observed, and at the metal-oxide surface (newest oxide), the grain size was approximately 200 Å (20 nm). In post-transition films the outermost oxide still possessed the very fine 50 Å (5 nm) diameter grain size. However, the newest oxide of post-transition films consisted of relatively large grains, with grain diameters of 1000 to 5000 Å (100 to 500 nm). At the midthicknesses of these oxides intermediate grain sizes were observed. The bulk of the post-transition films was highly porous. Pore sizes ranged from approximately 10 to 150 Å (1 to 15 nm), and many connected pores were concentrated at the grain boundaries. Under more severe oxidizing conditions, imposed by increasing the corrosion temperature to 427°C (800°F), the growth of large grains at the metal-oxide interface was unstable and film growth proceeded by the nucleation of finer grains.
Download or read book Zirconium in the Nuclear Industry Tenth International Symposium written by A. M. Garde and published by ASTM International. This book was released on 1994 with total page 805 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Enhanced Low Temperature Oxidation of Zirconium Alloys Under Irradiation written by B. Cox and published by . This book was released on 1989 with total page 21 pages. Available in PDF, EPUB and Kindle. Book excerpt: The linear growth of relatively thick (>300 nm) interference-colored oxide films on zirconium alloy specimens exposed in the Advanced Test Reactor (ATR) coolant at ?55°C was unexpected. Initial ideas were that this was a photoconduction effect. Experiments to study photoconduction in thin anodic zirconium oxide (ZrO2) films in the laboratory were initiated to provide background data. It was found that, in the laboratory, provided a high electric field was maintained across the oxide during ultraviolet (UV) irradiation, enhanced growth of oxide occurred in the irradiated area. Similarly enhanced growth could be obtained on thin thermally formed oxide films that were immersed in an electrolyte with a high electric field superimposed. This enhanced growth was found to be caused by the development of porosity in the barrier oxide layer by an enhanced local dissolution and reprecipitation process during UV irradiation. Similar porosity was observed in the oxide films on the ATR specimens. Since it is not thought that a high electric field could have been present in this instance, localized dissolution of fast-neutron primary recoil tracks may be the operative mechanism. In all instances, the specimens attempt to maintain the normal barrier-layer oxide thickness, which causes the additional oxide growth. Similar mechanisms may have operated during the formation of thick loosely adherent, porous oxides in homogeneous reactor solutions under irradiation, and may be the cause of enhanced oxidation of zirconium alloys in high-temperature water-cooled reactors in some water chemistries.
Download or read book Corrosion of Zirconium Alloys in 900 Steam written by J. Paul Pemsler and published by . This book was released on 1958 with total page 26 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Evolution of the Oxide Microstructure and Oxide Growth Induced Residual Strains During Waterside Corrosion of Zirconium Alloys written by David J. Spengler and published by . This book was released on 2012 with total page 177 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book The Mechanism of Oxide Film Growth and Breakdown on Zirconium and Zircaloy 2 written by B. Cox and published by . This book was released on 1959 with total page 10 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Nuclear Science Abstracts written by and published by . This book was released on 1974 with total page 852 pages. Available in PDF, EPUB and Kindle. Book excerpt:
