Zirconium oxide

Диссертации "Моделирование процессов перелома кинетики окисления и переориентации гидридов в циркониевых оболочках твэлов". Диссертация на соискание кандидата технических наук по специальности 05.14.03 "Ядерные энергетические установки, включая проектирование, эксплуатация и вывод из эксплуатации" была представлена к защите 18 сентября 2018 в НИЦ "Курчатовский институт".

PhD thesis (in Russian) Modeling of oxidation kinetic transition and hydrides reorientation in zirconium claddings of fuel rods

The following article is a review of the dental literature available, which is aiming to provide the clinician the up-to-date information about the ceramic metal-free dental materials available in Latin-America. Some clinical aspects are mentioned, as well as, classification, indications, contraindications, advantages and disadvantages of the materials specifically selected for single complete crowns. During the literature search, the articles of clinical research were selected, as well as, the articles dedicated to publish the results in vitro research.
This article is intended to be a guide in order to select a metal-free system for complete crowns based on physical properties and according to the specific esthetic and functional needs of each patient.

Key words: Metal-free, full-porcelain, allceramic, crown, ceramic, porcelain, aesthetic.

Palabras clave: Libre de metal, corona, cerámica, porcelana, estética.

An efficient gain-flattened C-band optical amplifier is demonstrated using a hybrid configuration with a Zirconia-based Erbium-doped fibre (Zr-EDF) and a semiconductor optical amplifier (SOA). The amplifier utilizes a two-stage structure with a midway isolator to improve flat gain characteristic and reduce noise figure. At input signal power of -30 dBm, a flat gain of 28 dB is obtained from wavelength region of 1530 to 1560 nm with gain variation of less than 4 dB. The noise figure is maintained below 11 dB at the flat-gain region. This amplifier has the potential to be used in the high channel count dense wavelength division multiplexing system due to its simplicity and compact design. © 2011 Pleiades Publishing, Ltd.

http://link.springer.com/article/10.1134/S1054660X11010099

Abstract- As expensive and common material the zircon (ZrSiO4) contributes opacity to sanitaryware white opaque glazes and promotes whiteness of glaze surface by its high optical refractive index. The high optical refractive index of zirconium silicate is necessary to obtain acceptible white camouflage influence to cover the dark beige color of the soft porcelain sanitaryware body. As known, as an opacifier the zircon has highest cost level in sanitaryware glaze recipes. There are many studies on decrease of usage percentage of zirconium silicate in opaque glaze recipes. The calsined caolin adapted alternative glaze recipes have been tried to obtain acceptible opaque sanitary glaze avoid high recipe cost in this study. Alternative recipe combinations have been tried to provide lower cost sanitary opaque glaze of R2O-RO-(ZrO2)-B2O3-Al2O3-SiO2 glass and ceramic systems. As a result, the notable zircon usage reduction has been achieved without any technical spesification lost or obstacle in industrial base.
Keywords : Zirconium Silicate, Opaque White Glaze, Sanitaryware, Calsined Caolin

Автореферат диссертации "Моделирование процессов перелома кинетики окисления и переориентации гидридов в циркониевых оболочках твэлов". Диссертация на соискание кандидата технических наук по специальности 05.14.03 "Ядерные энергетические установки, включая проектирование, эксплуатация и вывод из эксплуатации" была представлена к защите 18 сентября 2018 в НИЦ "Курчатовский институт".

PhD thesis abstract (in Russian) Modeling of oxidation kinetic transition and hydrides reorientation in zirconium claddings of fuel rods

As a cladding material used to encapsulate nuclear fuel pellets, zirconium alloys are the primary barrier separating the fuel and a pressurised steam or lithiated water environment. Degradation mechanisms such as oxidation can be the limiting factor in the life-time of the fuel assembly. Key to controlling oxidation, and therefore allowing increased burn-up of fuel, is the development of a mechanistic understanding of the corrosion process. In an autoclave, the oxidation kinetics for zirconium alloys are typically cyclical, with periods of accelerated kinetics being observed in steps of ∼2 μm oxide growth. These periods of accelerated oxidation are immediately preceded by the development of a layer of lateral cracks near the metal-oxide interface, which may be associated with the development of interface roughness. The present work uses scanning electron microscopy to carry out a statistical analysis of changes in the metal-oxide interface roughness between three different alloys at different stages of autoclave oxidation. The first two alloys are Zircaloy-4 and ZIRLO™ for which analysis is carried out at stages before, during and after first transition. The third alloy is an experimental low tin alloy, which under the same oxidation conditions and during the same time period does not appear to go through transition. Assessment of the metal-oxide interface roughness is primarily carried out based on the root mean square of the interface slope known as the Rdq parameter. Results show clear trends with relation to transition points in the corrosion kinetics. Discussion is given to how this relates to the existing mechanistic understanding of the corrosion process, and the components required for possible future modelling approaches.

Zirconia (ZrO2) is a well known oxide refractory material, possessing high strength and high melting point. Black zirconia is a variant of conventional zirconia obtained by the addition of a pigments percentage which changes its color from white to black. The present work shows, for the first time to the best of our knowledge, optical spectra of black ZrO2 in the range 0.3–16.3 µm, comparing them to those of a conventional white stoichometric sample. Moreover, preliminary data on the high temperature emittance of black ZrO2 are shown as well.

Recently, considerable attention has been focused on zirconium oxide (ZrO2) which exhibits many desirable structural and electronic properties and has been used in many applications. For example it is a very attractive and promising material for low-voltage and short-wavelength electro-optical devices such as light emitting diodes and laser diodes; it also has other applications such as gas sensors and varistors [1-4]. This study is related to the preparation of boron doped ZrO2 material. The first step was the preparation of composite by mixing zirconium acetate with polyvinyl alcohol (PVA) at a suitable temperature [5]. The resulting composite polymer was doped with boron using boric acid as boron source and then electrospun giving nano fibers. Finally, the resulting nano fibers were subjected to a thermal treatment at 250 oC, 500 oC, 800 oC to elucidate their morphological properties. The conductivity of the nano fibers obtained was measured with four probe technique and the boron supported polymer was observed to have a higher conductivity. The Differential Scanning Calorimetry (DSC) results indicate that the glass transition (Tg) and melting temperatures (Tm) showed great change with the addition of boron and boron doped fibers were observed to degrade at higher temperatures. The SEM appearance of the fibers showed that the addition of boron resulted in the formation of cross linked bright surfaced fibers.

Zirconium based alloys are commonly used as material for fuel claddings in the light water reactors. Claddings act as first metallic barriers against loss of fission products during the nuclear power plant operation, intermittent storage or final dry storage. The integrity of claddings is always critical issue during reactor operation and during storage of spent fuel. In this work, ring compression testing method developed was applied to study hydrogen embrittlement, to evaluate the stress strain behaviour and hoop fracture properties of E110 (Zr-based) fuel claddings. The results show that the collapse load and the tensile strength values depend strongly on hydrogen concentration. In particular, tensile strength experiment data shows significant change in its trend after reaching the maximum hydrogen solubility limit.

Nano Co3O4-ZnO-ZrO2 mixed metal oxides were synthesized by wet chemical method by mixing of equimolar solutions of cobalt chloride, zinc sulfate and zirconium oxychloride in aqueous sodium hydroxide and refluxed at elevated temperature. The synthesized mixed nano oxides were characterized by FT-IR, XRD, UV-Vis DRS, TEM, SAED, SEM, EDAX and AFM. The FTIR spectra exposed the presence of M-O bonds (M = Co, Zn, Zr). From XRD studies, the size of the Co3O4-ZnO-ZrO2 NPs are found to be 28.11-52.36 nm through Scherrer's formula. The XRD patterns also reveal that the particle size is drastically increased with increasing concentration of precursors. From UV-Vis diffuse reflectance spectra (DRS), band gap energies of the (0.1-0.5 M) Co3O4-ZnO-ZrO2 NPs are found to be in the range of 2.41-2.68 eV. The TEM, SEM and AFM micrographs of 0.1 M Co3O4-ZnO-ZrO2 NPs display irregular shape with size ranging from 20-45 nm. SAED pattern confirms the crystalline nature of these nanoparticles. EDAX analysis indicates the presence of Co, Zn, Zr and O.

Aligned fibres of partially stabilised zirconia (PSZ, 4 mol% Y2O3) and fully stabilised zirconia (FSZ, 8 mol% Y2O3), 3-5 μm in diameter, were blow spun from a sol-gel precursor, and then fired to give the ceramic fibre. Various potential sol precursors were investigated and characterised, the optimum being an aqueous sol made from hydrolysed and peptised zirconium iso-propoxide. The resulting zirconia fibres were characterised and their evolution studied by XRD, DTA/TGA and SEM, and their mechanical properties assessed. It was found that both PSZ and FSZ fibres formed poorly crystalline cubic zirconia at only 200°C, which became fully crystalline after firing to 400°C. The cubic form was the only phase seen in the FSZ fibre, whereas the PSZ fibre formed the tetragonal phase after firing between 1000 and 1200°C/3 h, and all fibres were nanocrystalline (grain diameter<0.1 μm). Unusually the monoclinic form of zirconia was never observed in the PSZ fibres. After firing above 1200°C the fibres had a strain to break of 0.59%, and appeared to be well sintered from shrinkage data. They had superior creep resistance to Saffil zirconia fibres, creeping at temperatures 50°C higher.

In-situ polymerization of pyrrole was carried out with zirconium oxide, in the presence of oxidizing agent ammonium persulphate, to synthesize polypyrrole/zirconium oxide composites, by chemical oxidation method. The polypyrrole/zirconium oxide composites were synthesized with various compositions viz., 10, 20, 30, 40 and 50 wt. % of zirconium oxide in pyrrole. The powder X-ray diffraction spectrographs suggest that they exhibit semicrystalline behavior. Fourier Transform Infra-Red Spectroscopy shows that, the stretching frequencies are shifted towards higher frequency side. The surface morphologies of these composites studied using Scanning Electron Microscopy indicate that zirconium oxide particles are embedded in the polypyrrole (PPy) chain, to form multiple phases. Thermographs of thermal analysis also imply that the polypyrrole/zirconium oxide composites have stronger stability than PPy. The observation of UV-VIS-NIR spectrum is proof of an interaction between polypyrrole/zirco...

Zirconium alloys are used as fuel cladding in light water reactors. Surface preparation techniques that might impair oxidation resistance would limit the lifetime of the cladding and therefore prevent higher burn-up of fuels. The work presented here investigates the impact of surface roughness on the oxida- tion kinetics of Zircaloy-4 in 400◦C steam for exposures up to 275 days. The work shows well defined
differences in oxidation kinetics between sample preparations following ∼84 days oxidation. Scanning electron microscopy (SEM) and image analysis of samples in cross section allows for an assessment of the

Corrosion is a key limiting factor in the degradation of zirconium alloys in light water reactors. Developing a mechanistic understanding of the corrosion process offers a route towards improving safety and efficiency as demand increases for higher burn-up of fuel. Oxides formed on zirconium alloys are composed of both monoclinic and meta-stable tetragonal phases, and are subject to a number of potential mechanical degradation mechanisms. The work presented investigates the link between the tetragonal to monoclinic oxide phase transformation and degradation of the protective character of the oxide layer. To achieve this, Abaqus finite element analysis of the oxide phase transformation has been carried out. Study of the change in transformation strain energy shows how relaxation of oxidation induced stress and fast fracture at the metal–oxide interface could destabilise the tetragonal phase. Central to this is the identification of the transformation variant most likely to form, and understanding why twinning of the transformed grain is likely to occur. Development of transformation strain tensors and analysis of the strain components allows some separation of dilatation and shear effects. Maximum principal stress is used as an indication of fracture in the surrounding oxide layer. Study of the stress distributions shows the way oxide fracture is likely to occur and the differing effects of dilatation and shape change. Comparison with literature provides qualitative validation of the finite element simulations.

In this study, neodymia doped poly(vinyl) alcohol/zirconium–cerium acetate (PVA/Zr-Ce) nanofibers were prepared using the electrospinning technique, and then calcined at 800°C for 2 hours. For this purpose, PVA/Zr-Ce polymer solutions doped with different concentrations of neodymia were prepared using electrospinning technique, and then calcined and sintered at 800°C for 2 hours. The effect of neodymia doping was investigated in terms of solution properties, morphological changes and thermal characteristics. The fibers were characterized by Fourier transform infrared (FT-IR), X-ray diffraction (XRD), and scanning electron microscope (SEM). The measurements showed that the conductivity, pH, viscosity, and surface tension of the hybrid polymer solutions have decreased with increasing Nd acetate content. The FT-IR spectra of the fibers were in good accordance with the literature. The average crystal size values for calcined and sintered samples which were obtained from precursor solutions were calculated. XRD analysis showed that the crystallite size was decreased with increasing Nd content. This result is verified by the calculation of the total areas of the peaks appeared in the XRD spectra. The very sharp and high intense peaks found in the diffraction patterns revealed the crystalline nature of the product. Moreover, the SEM micrograph of the fibers showed that the average fiber diameters decreased with increasing Nd content.

Heterogeneous catalysts are promising for the transesterification reaction of vegetable oils to produce biodiesel. Unlike homogeneous, heterogeneous catalysts are environmentally benign and could be operated in continuous processes. Moreover they can be reused and ...

Heterogeneous catalysts are promising for the transesterification reaction of vegetable oils to produce biodiesel. Unlike homogeneous, heterogeneous catalysts are environmentally benign and could be operated in continuous processes. Moreover they can be reused and regenerated. However a high molar ratio of alcohol to oil, large amount of catalyst and high temperature and pressure are required when utilizing heterogeneous catalyst to produce biodiesel. In this paper, the catalytic activity of several solid base and acid catalysts, particularly metal oxides and supported metal oxides, was reviewed. Solid acid catalysts were able to do transesterification and esterification reactions simultaneously and convert oils with high amount of FFA (Free Fatty Acids). However, the reaction rate in the presence of solid base catalysts was faster. The catalyst efficiency depended on several factors such as specific surface area, pore size, pore volume and active site concentration. © 2009 Elsevier B.V. All rights reserved.

http://ac.els-cdn.com/S0378382009000629/1-s2.0-S0378382009000629-main.pdf?_tid=944422d4-2363-11e4-be00-00000aacb362&acdnat=1407987312_4885f84527f97d6f59c2ddefc0defb50 
http://www.sciencedirect.com/science/article/pii/S0378382009000629

The aim of this paper is to deposit zirconium oxide films by magnetron sputtering process at different argon partial pressure values of 45%, 55%, 62% and 67%. The effect of argon partial pressure on structural, optical and wettability properties of zirconium oxide films is investigated in this research work. The increase in argon partial pressure leads to increase in intensity of (111) peak for zirconium oxide thin films as observed by X-ray Diffraction. The average crystallite size of zirconium oxide films increases from 19nm to 25nm with increase in argon partial pressure. Wettability properties of zirconium oxide films such as contact angle and surface energy were determined by contact angle measuring system. The minimum transmission values above 63% were observed for all zirconium oxide thin films deposited at different argon partial pressure. Band gap and refractive index of zirconium oxide thin films varies as a function of argon partial pressure.

The present work has been produced as part of an on-going collaboration between the University of Manchester and Amec, with the primary aim of furthering mechanistic understanding of corrosion processes in zirconium alloys out-of-reactor. Zirconium alloys are used as cladding material for nuclear fuel pellets, and correct understanding of the corrosion process in autoclave is essential to predicting material behaviour in-reactor. This EngD thesis is composed of five proposed papers that investigate observations and hypotheses under the theme of mechanical degradation in oxides formed on zirconium alloys in autoclave. First investigations concern observed stress relaxation in zirconium oxide. Finite element analysis is used to capture mechanical aspects of the corrosion process and apply this to stress behaviour determined previously using synchrotron x-ray diffraction. The results indicate that a mechanism other than creep or hydrogen induced lattice strain must be present to account for the observed stress relaxation. One such potential mechanism is crack formation; statistical analysis of scanning electron microscopy images has been used to identify a link between the development of roughness at the metal-oxide interface, crack formation in the oxide and transition points or acceleration in the corrosion kinetics. Parameters such as the median radius of curvature and profile slope (Rdq) have been applied, as these parameters do not require the definition of a periodic wavelength or amplitude. These and other parameters are related to information in literature to indicate that for samples of Zircaloy-4 and ZIRLOTM, which go through transition, the interface roughness changes in a way that would increase localised stress concentrations. The third material is an experimental low tin alloy, which under the same oxidation conditions, and during the same time period, does not appear to go through transition and does not develop an interface roughness in the same way. A critical assessment of finite element analysis applied to oxidising non-planar interfaces shows the significant limitations in the existing mechanism for representing oxidation expansion and stress formation. Autoclave oxidation experiments of artificially roughened samples of Zircaloy-4 were carried out to further understand the impact of out-of-plane stress generation. The results indicate a divergence based on surface roughness after ~86 days oxidation. SEM examination of images in cross section highlighted accelerated oxidation above surface roughness peaks, and an increased crack area in rougher samples. Finally, finite element analysis of the tetragonal to monoclinic phase transformation showed that biaxial compressive stress relaxation, or the tri-axial tensile stress associated with an advancing crack tip, could reduce the transformation strain energy and destabilise the tetragonal phase. The volumetric expansion and shear strain associated with the phase transformation produces stress in the surrounding oxide sufficient to generate nano-scale cracks perpendicular to the metal-oxide interface. This would allow fast ingress routes for oxygen containing species, and therefore acceleration in the corrosion kinetics.

Abstract Er 2 O 3 doped calcia stabilized zirconia based inert matrix fuel containing CeO 2 as a surrogate for PuO 2 was fabricated for a wide range of concentration using the polymer-to-ceramic conversion technique via metal acetate preceramic hybrid polymer solutions. Samples were characterized by XRD, SEM and AFM techniques. Nanocrystallite size variation in the samples was evaluated using peak broadening values by means of the Scherrer formula.

In this study, neodymia doped poly(vinyl) alcohol/zirconium–cerium acetate (PVA/Zr-Ce) nanofibers were prepared using the electrospinning technique, and then calcined at 800°C for 2 hours. For this purpose, PVA/Zr-Ce polymer solutions doped with different concentrations of neodymia were prepared using electrospinning technique, and then calcined and sintered at 800°C for 2 hours. The effect of neodymia doping was investigated in terms of solution properties, morphological changes and thermal characteristics. The fibers were characterized by Fourier transform infrared (FT-IR), X-ray diffraction (XRD), and scanning electron microscope (SEM). The measurements showed that the conductivity, pH, viscosity, and surface tension of the hybrid polymer solutions have decreased with increasing Nd acetate content. The FT-IR spectra of the fibers were in good accordance with the literature. The average crystal size values for calcined and sintered samples which were obtained from precursor solutions were calculated. XRD analysis showed that the crystallite size was decreased with increasing Nd content. This result is verified by the calculation of the total areas of the peaks appeared in the XRD spectra. The very sharp and high intense peaks found in the diffraction patterns revealed the crystalline nature of the product. Moreover, the SEM micrograph of the fibers showed that the average fiber diameters decreased with increasing Nd content.