Techn. Hochsch., Diss., 2003--Aachen.

O καρκίνος του μαστού είναι μια από τις κυρίες αιτίες θανάτου στις γυναίκες. Καθώς η επιτυχής αντιμετώπιση του συνδέεται με τη φάση της νόσου η έγκαιρη διάγνωση του είναι πολύ σημαντική για τους ασθενείς. Ως τεχνική έγκαιρης διάγνωσης αλλά και πληθυσμιακού έλεγχου χρησιμοποιείται η μαστογραφία με χρήση ακτινών-Χ. Η αποτελεσματικότητα της μαστογραφίας στηρίζεται στην υψηλή ποιότητα απεικόνισης του μαστού αλλά και στο όσο το δυνατόν μικρότερη δόση που εναποτίθεται στον μαστό. Ένα από τα βασικότερα χαρακτηριστικά ποιότητας ενός μαστογραφικου συστήματος που επηρεάζει την ικανότητα απεικόνισης ανομοιογενειών μικρών διαστάσεων (π.χ. αποτιτανώσεων) είναι η χωρική διακριτική ικανότητα. Το κατώτερο αποδεκτό όριο είναι 12 lp/mm για μαστογραφία επαφής. H εστία και ο βαθμός φθοράς της σχετίζεται άμεσα με την χωρική διακριτική ικανότητα και την ποιότητα εικόνας. Σκοπός αυτής της μελέτης ήταν να εξετάσουμε την επίδραση της φθοράς της μαστογραφικής ανόδου, στην χωρική ικανότητα υπό συμβατική και μεγεθυντική γεωμετρία. Μια τέτοια μελέτη δεν ήταν δυνατόν να γίνει πειραματικά σε κλινικές συνθήκες. Για αυτό τον λόγο έγινε χρήση ενός προγράμματος προσομοίωσης σε υπολογιστικό περιβάλλον που στηρίζεται στην τεχνική τυχαίας δειγματοληψίας και στην μέθοδο Monte Carlo (MASTOS Code). Η σημαντική παράμετρος η οποία επιλέχτηκε να εκφράζει τον βαθμό φθοράς της ανόδου είναι η κατανομή της έντασης των φωτονίων της εστίας. Τυπικά υπάρχουν τρεις αντιπροσωπευτικές κατανομές φωτονίων της εστίας, η ομοιόμορφη, η απλή κανονική κατανομή (Gaussian), και η διπλή κανονική ή κανονική κατανομή δύο κορυφών(Double Gaussian). Μια άνοδος χωρίς φθορά αρχικά θεωρήθηκε να έχειμια σχεδόν κανονική κατανομή ένταση φωτονίων και μόλις η καταστροφή αρχίζει η απλή κανονική κατανομή μετατρέπεται σε διπλή κανονική. Αυτή η φθορά της ανόδου οφείλεται κυρίως στην υπερβολική χρήση της και στα υψηλά θερμικά φορτία . Για τη μελέτη της χωρικής διακριτικής ικανότητας χρησιμοποιήθηκε απότομη αιχμή(edge) πάχους 4 cm αποτελούμενη από μόλυβδο, μη διαπερατή από ακτίνες-χ, τοποθετημένη στο κέντρο του πεδίου με την κεντρική ακτίνα της δέσμης κάθετη στην αιχμή και την επιφάνεια του ακτινοβολούμενου αντικειμένου. Έπειτα για τον υπολογισμό της χωρικής διακριτικής ικανότητας υπολογίστηκε αρχικά μία συνάρτηση διασποράς ορίου (ESF) για κάθε εικόνα. Για το σκοπό αυτό μία ορθογώνια περιοχή ενδιαφέροντος επελέγη περιλαμβάνοντας 2 mm από κάθε πλευρά της αιχμής. Το προφίλ του κάθετα υπολογισμένου μέσου όρου των τιμών του grey level κατά μήκος αυτής της απόστασης αντιστοιχεί στη συνάρτηση διασποράς ορίου. Από μαθηματική παραγώγηση της συνάρτησης αυτής προέκυψε η συνάρτηση διασποράς γραμμής (LSF) και με εφαρμογή σε αυτή μετασχηματισμού Fourier καταλήγουμε στη συνάρτηση μεταφοράς διαμόρφωσης (MTF). Οι προκύπτουσες συναρτήσεις μεταφοράς διαμόρφωσης προσαρμόστηκαν με τμήμα κανονικής καμπύλης και η χωρική διακριτική ικανότητα σε lp/mm εξήχθη από αυτές, θεωρώντας ότι αντιστοιχεί στο 5% της MTF. Η συγκεκριμένη μέθοδος μέτρησης της συνάρτησης μεταφοράς διαμόρφωσης είναι πολύ δημοφιλής τελευταία λόγω της απλότητάς της και της καταλληλότητάς της, ειδικά στην ψηφιακή απεικόνιση. Μελετήσαμε την επίδραση της φθοράς της ανόδου στην χωρική διακριτική ικανότητα για δυο μεγέθη εστίας, μια 0.1mm η οποία χρησιμοποιείται στα περισσότερα μαστογραφικά μηχανήματα σήμερα και μια με μεγάλες διαστάσεις όπως 0.5mm. Η μελέτη αυτή έγινε μεταβάλλοντας κάθε φορά τα χαρακτηριστικά της απλής και διπλής κανονικής κατανομής έντασης φωτονίων της εστίας. Ουσιαστικά μεταβάλλαμε την απόσταση μεταξύ των δυο κορυφών (δμ) και την τυπική απόκλιση (σ).Με τον τρόπο αυτό πήραμε εικόνες που αντιστοιχούν κάθε φορά σε διαφορετική κατανομή των φωτονίων στην εστία και επομένως σε διαφορετικό βαθμό φθοράς της ανόδου. Όταν η απόσταση των δυο κορυφών της διπλής κανονικής κατανομής ήταν μηδέν τότε είχαμε κανονική κατανομή η οποία αντιστοιχούσε σε μια άνοδο χωρίς φθορά ενώ όταν η απόσταση των δυο κορυφών της διπλής κατανομής αυξανόταν τότε αντιστοιχούσε σε άνοδο με μεγαλύτερο βαθμό φθοράς. Τέλος διατηρώντας σταθερή την απόσταση τον δυο κορυφών μεταβάλαμε την τυπική απόκλιση της κατανομής (σ) με αποτέλεσμα και σε αυτή την περίπτωση να έχουμε ασυμπτωτική προσέγγιση τηςδιπλής κανονικής κατανομής στην απλή κανονική κατανομή της έντασης των φωτονίων της εστίας. Όταν η εστία είναι καινούργια ακόμα και με διαστάσεις 0.5 mm x 0.5 mm (οι οποίες είναι πάνω από τις τυπικές μαστογραφικές τιμές) τότε η χωρική ικανότητα είναι υψηλή και πάνω από το αποδεκτό όριο των 12 lp/mm για την συμβατική μαστογραφία και καθώς αρχίζει η φθορά της η χωρική διακριτική ικανότητα μειώνεται σε ποσοστό 4% με 8%. Αντίθετα για μεγεθυντικές λήψεις όταν αρχίζει η φθορά της ανόδου λόγο της χρήσης της η χωρική διακριτική ικανότητα γίνετε πολύ μικρή με τιμές που κυμαίνονται γύρω στο 5 lp/mm . Επομένως εστίες με μεγάλες διαστάσεις όπως 0.5 mm δεν είναι κατά κανόνα κατάλληλες για μεγεθυντική λήψη καθώς η χωρική διακριτική ικανότητα είναι πολύ μικρή ειδικά όταν αρχίζει η φθορά τους. Για την ονομαστική εστία 0.1 mm x 0.1 mm. τα αποτελέσματα καθορίζουν ότι μια φθαρμένη άνοδος δεν επηρεάζει σημαντικά την ποιότητα εικόνας στην συμβατική μαστογραφία. Η χωρική διακριτική ικανότητα διατηρείται σε υψηλές τιμές(21 lp/mm) με ασήμαντη διακύμανση (περίπου 2% με 5%) μεταξύ των αποτελεσμάτων κατά τη διάρκεια της φθοράς της. Παρόλα αυτά μια φθαρμένη άνοδος έχει σημαντικό αντίκτυπο στη χωρική διακριτική ικανότητα υπό μεγεθυντικές συνθήκες. Όταν η απόσταση των δυο κορυφών της διπλής κατανομής αυξάνει (που αντιστοιχεί σε μεγαλύτερο βαθμό φθοράς ), η χωρική διακριτική ικανότητα μειώνεται σημαντικά ακόμα και κάτω από το αποδεκτό όριο των 12 lp/mm που συνήθως χρησιμοποιείται σε κλινική πρακτική. Για τον μέγιστο βαθμό μεγέθυνσης (m=2) η σχετική υποβάθμιση ης χωρικής διακριτικής ικανότητας φτάνει το 66%. Όταν η τυπική απόκλιση (σ) των δυο κορυφών αυξάνει σε μια διπλή κατανομή με σταθερή απόσταση (δμ) μεταξύ των δυο κορυφών, τότε το αποτέλεσμα είναι η υποβάθμιση της χωρικής διακριτικής ικανότητας σχεδόν 40% (για m= 1.6 κ εστία 0.1 mm). Η επίδραση της φθοράς της ανόδου στην χωρική διακριτική ικανότητα είναι σημαντική ειδικά για μεγάλους βαθμούς μεγέθυνσης (1.6, 1.8, 2.0). Χαρακτηριστικό είναι το γεγονός ότι μια καινούργια άνοδος προκαλεί μείωση της χωρικής διακριτικής ικανότητας κατά 27%, ενώ μια φθαρμένη άνοδος προκαλεί μείωση που φτάνει το 75% καθώς αυξάνουμε την μεγέθυνση από 1 έως 2 με βήμα 0.2. Επομένως η χωρική διακριτική ικανότητα επηρεάζεται ευθέως από την μορφή την κατανομή της έντασης των φωτονίων στην εστία, η οποία προσδιορίζει και την κατάσταση που βρίσκεται η άνοδος , το μέγεθος της εστίας και την μεγέθυνση. Σανσυμπέρασμα μπορούμε να πούμε ότι μόνο εστίες με μικρές διαστάσεις όπως 0.1 mm είναι κατάλληλες για μεγεθυντική μαστογραφία. Μια φθαρμένη άνοδος με εστία 0.1 mm δεν επηρεάζει σημαντικά την χωρική διακριτική ικανότητα στην μαστογραφία επαφής, ενώ αντίθετα για την μεγεθυντική μαστογραφία(κυρίως μεγάλους βαθμούς μεγέθυνσης) η υποβάθμιση της χωρικής διακριτικής ικανότητας είναι σημαντική. Αυτό το γεγονός είναι σημαντικό για υψηλούς βαθμούς μεγέθυνσης και έτσι η αντικατάσταση της λυχνίας ακτινών–x όταν η εστία αρχίζει να φθείρεται είναι πολύ κρίσιμη καθώς μπορεί να οδηγήσει στον υποβιβασμό της χωρικής διακριτικής ικανότητας. / The aim of this study was to examine the influence of mammographic anode aging, from the construction of a perfect anode up to total damage, on spatial resolution under contact and magnification geometries. The crucial parameter that was selected to reflect the degree of damaging of the anode is the type of the x-ray intensity distribution of the focal spot. Typically, there are three representative focal spot distributions, the uniform, the Gaussian and double-peaked Gaussian. A new anode is initially considered to have an almost Gaussian intensity distribution and when the destruction starts the Gaussian distribution turns to double Gaussian distribution. This damage of anode is owed to its extended use and high thermal loads (melting), which is more apparent in the central area of the focal spot. In order to study this aging effect, the Edge Spread Function (ESF) method was utilized, with a thick sharp edge consisting of lead, no transparent to x-rays imaged under various conditions, and following the corresponding spatial resolution was calculated through the modulation transfer function (MTF). In this study we used two focal spot sizes, a 0.1mm which is using in most mammographic units today and a focal spot with big dimensions such 0.5mm. When the focal spot with dimensions 0.5mm by 0.5mm is new then the resolution is high for contact mammography, but when the anode starts damaged, the 0.5mm focal spot is unsuitably because the resolution is maintained under 10 lp/mm, especially for magnification views. Therefore focal spots with big dimensions such 0.5mm are not suitable for clinical practise and magnifications views. Results for nominal focal spot sizes of 0.1mm by 0.1mm demonstrate that a damaged anode does not significantly affect the spatial resolution in contact mammography, since even in this case the spatial resolution is maintained in high degrees with insignificant variation between the results. Nevertheless, a damage anode has important repercussions on the spatial resolution under magnification conditions. When the distance of the two peaks of double Gaussian is increased (corresponding to higher degrees of destruction) the spatial resolution is significantly decreased even under the acceptable limit of 12 lp/mm that is usually utilized in clinical practice. Furthermore, when for a double Gaussian with fixed distance (δμ) between the two peaks, the standard deviation (σ) of two peaks is increasing then it leads to the reduction of spatial resolution of almost 40% for magnification equal 1.6 and focal spot 0.1mm. Accordingly, the resolution is directly affected by the form of the intensity distribution of the anode and the magnification. This effect is dominant for high magnification degrees, and thus the replacement of the x-ray tube when the focal spot starts being destroyed is very crucial, as the tube aging can potentially lead to the degradation of spatial resolution.

abstract: The wide-scale use of green technologies such as electric vehicles has been slowed due to insufficient means of storing enough portable energy. Therefore it is critical that efficient storage mediums be developed in order to transform abundant renewable energy into an on-demand source of power. Lithium (Li) ion batteries are seeing a stream of improvements as they are introduced into many consumer electronics, electric vehicles and aircraft, and medical devices. Li-ion batteries are well suited for portable applications because of their high energy-to-weight ratios, high energy densities, and reasonable life cycles. Current research into Li-ion batteries is focused on enhancing its energy density, and by changing the electrode materials, greater energy capacities can be realized. Silicon (Si) is a very attractive option because it has the highest known theoretical charge capacity. Current Si anodes, however, suffer from early capacity fading caused by pulverization from the stresses induced by large volumetric changes that occur during charging and discharging. An innovative system aimed at resolving this issue is being developed. This system incorporates a thin Si film bonded to an elastomeric substrate which is intended to provide the desired stress relief. Non-linear finite element simulations have shown that a significant amount of deformation can be accommodated until a critical threshold of Li concentration is reached; beyond which buckling is induced and a wavy structure appears. When compared to a similar system using rigid substrates where no buckling occurs, the stress is reduced by an order of magnitude, significantly prolonging the life of the Si anode. Thus the stress can be released at high Li-ion diffusion induced strains by buckling the Si thin film. Several aspects of this anode system have been analyzed including studying the effects of charge rate and thin film plasticity, and the results are compared with preliminary empirical measurements to show great promise. This study serves as the basis for a radical resolution to one of the few remaining barriers left in the development of high performing Si based electrodes for Li-ion batteries. / Dissertation/Thesis / Appendix H - Movies (zipped) / M.S. Mechanical Engineering 2011

Alumínio Pulverizado Termicamente (TSA) é amplamente utilizado em instalações offshore como revestimento de ânodo de sacrifício em tubulações de aço carbono. O transporte e a instalação desses componentes podem levar a pequenos danos no revestimento, o que pode expor a superfície do aço à água do mar. Sabe-se que o depósito calcário é formado na superfície do aço polarizado catodicamente. Assim, esta pesquisa avaliou o TSA aplicado por sistema de pulverização de arco duplo (TWAS) no aço ao carbono S355J2 + N quando ocorrem danos (holidays) para estudar a formação de depósitos calcários no aço e adquirir dados sobre o desempenho do TSA sob altas temperaturas. A aplicação de diferentes condições também foi considerada: presença de selantes; liga do revestimento (99,5% de Al e Al-5% de Mg) e condições enterradas/não enterradas. Dois tipos de experimentos foram realizados: i) testes em potencial livre sob temperaturas constantes (30, 60 e 90°C) e diferentes tamanhos de holidays (expondo 5, 10 e 20% da superfície do aço) e ii) testes sob gradient térmico onde óleo a ~125°C foi adicionado em uma torre polimérica e água externa a ~10°C ficou em contato com a superfície das amostras (tanto potencial livre como polarização de -950 mVAg/AgCl foram aplicados). Análises incluíram inspeção visual, microscópio eletrônico de varredura e difração de Raio-X. A partir dos testes em temperaturas constante, o TSA atingiu um bom potencial de proteção (-800 a -900 mVAg/AgCl) e pouca diferença nos resultados devido à diferença na composição doTSA e no tamanho do holiday foi observada. As taxas de corrosão foram mantidas entre 0,02 e 0,01 mm/ano. No ensaio sob gradiente térmico e potencial livre, a perda de revestimento e as taxas de corrosão foram de 0,4 a 0,002 mm/ano. Além disso, o potencial alcançado foi de uma faixa menor do que a obtida anteriormente (-745 a -835 mVAg/AgCl). No entanto, quando o TSA foi combinado com proteção catódica externa e gradiente térmico, a espessura do TSA foi satisfatório e as taxas de corrosão obtidas foram inferiores a 0,076 mm/ano. O depósito calcário formado no holiday protegeu o aço contra a corrosão e seu mecanismo de crescimento baseado nesta pesquisa foi construído. / Thermally Sprayed Aluminium (TSA) is widely used in offshore facilities as sacrificial anode coating for carbon-steel risers and pipelines. Transportation and installation of those components can lead to small damages in the coating, which can expose the steel surface to the seawater. It is known that calcareous deposit is formed on the cathodically polarised steel surface. Thus, this research evaluated the TSA applied by twin wire arc spray system (TWAS) on S355J2+N carbon-steel when damage (holidays) is present in order to study the calcareous deposit formation on steel and acquire data regarding the TSA performance at high temperatures. Application of different conditions was also considered: presence of sealing; coating alloy (99.5%Al and Al-5%Mg) and buried/unburied conditions. Generally, two types of experiment were conducted – i) tests at free potential at steady temperatures (30, 60 and 90°C) and different holiday sizes (exposing 5, 10 and 20% of the steel surface) and ii) tests under thermal gradient where oil at ~125°C was added in polymeric tower and external water at ~10°C was in contact with the samples surface (both free potential and polarisation of -950 mVAg/AgCl were applied). Methodology of analyses included visual inspection, scanning electron microscope and X-ray Diffraction. From the tests at steady temperatures, the TSA reached a very good protective potential (-800 to -900 mVAg/AgCl) and little difference in results due to difference in TSA composition and holiday size was observed. Corrosion rates were kept between 0.02 and 0.01 mm/year. From the thermal gradient test under free potential, the coating loss and corrosion rates were 0.4 to 0.002 mm/year. Also, the potential achieved was in a lower range than previously obtained (-745 to -835 mVAg/AgCl). However, when TSA was combined with external cathodic protection and thermal gradient, the thickness of the TSA was satisfactory and corrosion rates obtained were below 0.076 mm/year. The calcareous deposit formed within the holiday protected the steel substrate against corrosion and its growth mechanism based in this research was built.

Philosophiae Doctor - PhD (Chemistry) / Nanomaterials have been found to undeniably possess superior properties than bulk structures across many fields of study including natural science, medicine, materials science, electronics etc. The study of nano-sized structures has the ability to address the current world crisis in energy demand and climate change. The development of materials that have various applications will allow for quick and cost effective solutions. Nanomaterials of Sn and Bi are the core of the electronic industry for their use in micro packaging components. These nanomaterials are also used as electrocatalysts in fuel cells and carbon dioxide conversion, and as electrodes for rechargeable sodium ion batteries. There are various methods used to make these nanostructures including solid state methods, hydrothermal methods, sputtering, and vacuum deposition techniques. These methods lack the ability to control the structure of material at an atomic level to fine tune the properties of the final product. This study aims to use E-ALD technique to synthesis thin films of Sn and Bi for various energy applications, and reports the use of E-ALD in battery applications for the first time. Thin films were synthesised by developing a deposition sequence and optimising this deposition sequence by varying deposition parameters. These parameters include deposition potential, and concentration of precursor solution. The thin films were characterised using cyclic voltammetry, linear sweep voltammetry, chronoamperometry for electrochemical activity. These were also characterised using scanning electron microscope for morphology, x-ray diffraction for crystal phases, energy dispersive spectroscopy for elemental mapping, and focused ion beam scanning electron microscope for thickness. The elemental content was analysed using electron probe micro analysis and inductively coupled plasma mass spectrometry. The electrochemical impedance charge and discharge profile were used for electrochemical battery tests.

Lithium-ion batteries (LIBs) are an integral part of consumer electronic devices and electric vehicles. There is a growing need for LIBs with higher capacity, rate performance and cycling stability. At the anode electrode these challenges are being addressed for instance by utilising materials with higher theoretical capacity compared to graphite (372 mAh/g) or by optimising the morphology of materials through nanostructuring of the electrode. In this thesis the former is investigated by synthesising a reduced graphene oxide (rGO) tin sulphide (SnS2) hybrid, and the latter by self-assembly of rGO sodium titanate and rGO titanium dioxide (TiO2) nanorods. In Chapter 2, SnS2 is investigated due to its high theoretical capacity as an anode material (645 mAh/g), low cost and environmental benignity. SnS2 nanoparticles were grown directly on rGO sheets which provide a conductive framework and limit the detachment of tin particles which undergo large volume changes during alloying reactions. However, a fast decrease in capacity was observed. Post-mortem analysis of the electrodes showed that rGO becomes irreversibly passivated suggesting that additional measures to retain effective charge transport between the low weight percent conductive additive and the active phase during cycling are required. An alternative material system based on nanorods of intercalation materials (sodium titanate and TiO2) wrapped by rGO sheets was chosen to investigate self-assembly in anodes to address the low packing density of nanomaterials. A drop-casting method was used to align rGO-sodium titanate nanorods through evaporation driven self-assembly (Chapter 3) which relies on a combination of electrostatic repulsive forces originating from the rGO coating, and liquid crystal phase formation at high concentrations, facilitated by the high aspect ratio nanorods. As reference, non-aligned films were prepared by adjusting the pH of the nanorod dispersion. Freestanding aligned and non-aligned films were converted to rGO-TiO2 (Chapter 4). The volumetric capacity of the self-assembled films was double that of non-aligned films, and up to 4.5 times higher than traditional casted electrodes using the same material. Further, up to rates of 4 C, the self-assembled films outperformed the non-aligned films. These films showed no sign of capacity fading up to 1000 cycles, which together with post-mortem analysis confirms that these assembled structures are maintained during battery cycling.

abstract: Microbial electrochemical cells (MXCs) offer an alternative to methane production in anaerobic water treatment and the recapture of energy in waste waters. MXCs use anode respiring bacteria (ARB) to oxidize organic compounds and generate electrical current. In both anaerobic digestion and MXCs, an anaerobic food web connects the metabolisms of different microorganisms, using hydrolysis, fermentation and either methanogenesis or anode respiration to break down organic compounds, convert them to acetate and hydrogen, and then convert those intermediates into either methane or current. In this dissertation, understanding and managing the interactions among fermenters, methanogens, and ARB were critical to making developments in MXCs. Deep sequencing technologies were used in order to identify key community members, understand their role in the community, and identify selective pressures that drove the structure of microbial communities. This work goes from developing ARB communities by finding and using the best partners to managing ARB communities with undesirable partners. First, the foundation of MXCs, namely the ARB they rely on, was expanded by identifying novel ARB, the genus Geoalkalibacter, and demonstrating the presence of ARB in 7 out of 13 different environmental samples. Second, a new microbial community which converted butyrate to electricity at ~70% Coulombic efficiency was assembled and demonstrated that mixed communities can be used to assemble efficient ARB communities. Third, varying the concentrations of sugars and ethanol fed to methanogenic communities showed how increasing ED concentration drove decreases in methane production and increases in both fatty acids and the propionate producing genera Bacteroides and Clostridium. Finally, methanogenic batch cultures, fed glucose and sucrose, and exposed to 0.15 – 6 g N-NH4+ L-1 showed that increased NH4+ inhibited methane production, drove fatty acid and lactate production, and enriched Lactobacillales (up to 40% abundance) above 4 g N-NH4+ L-1. Further, 4 g N-NH4+ L-1 improved Coulombic efficiencies in MXCs fed with glucose and sucrose, and showed that MXC communities, especially the biofilm, are more resilient to high NH4+ than comparable methanogenic communities. These developments offer new opportunities for MXC applications, guidance for efficient operation of MXCs, and insights into fermentative microbial communities. / Dissertation/Thesis / Doctoral Dissertation Biological Design 2015

Alumínio Pulverizado Termicamente (TSA) é amplamente utilizado em instalações offshore como revestimento de ânodo de sacrifício em tubulações de aço carbono. O transporte e a instalação desses componentes podem levar a pequenos danos no revestimento, o que pode expor a superfície do aço à água do mar. Sabe-se que o depósito calcário é formado na superfície do aço polarizado catodicamente. Assim, esta pesquisa avaliou o TSA aplicado por sistema de pulverização de arco duplo (TWAS) no aço ao carbono S355J2 + N quando ocorrem danos (holidays) para estudar a formação de depósitos calcários no aço e adquirir dados sobre o desempenho do TSA sob altas temperaturas. A aplicação de diferentes condições também foi considerada: presença de selantes; liga do revestimento (99,5% de Al e Al-5% de Mg) e condições enterradas/não enterradas. Dois tipos de experimentos foram realizados: i) testes em potencial livre sob temperaturas constantes (30, 60 e 90°C) e diferentes tamanhos de holidays (expondo 5, 10 e 20% da superfície do aço) e ii) testes sob gradient térmico onde óleo a ~125°C foi adicionado em uma torre polimérica e água externa a ~10°C ficou em contato com a superfície das amostras (tanto potencial livre como polarização de -950 mVAg/AgCl foram aplicados). Análises incluíram inspeção visual, microscópio eletrônico de varredura e difração de Raio-X. A partir dos testes em temperaturas constante, o TSA atingiu um bom potencial de proteção (-800 a -900 mVAg/AgCl) e pouca diferença nos resultados devido à diferença na composição doTSA e no tamanho do holiday foi observada. As taxas de corrosão foram mantidas entre 0,02 e 0,01 mm/ano. No ensaio sob gradiente térmico e potencial livre, a perda de revestimento e as taxas de corrosão foram de 0,4 a 0,002 mm/ano. Além disso, o potencial alcançado foi de uma faixa menor do que a obtida anteriormente (-745 a -835 mVAg/AgCl). No entanto, quando o TSA foi combinado com proteção catódica externa e gradiente térmico, a espessura do TSA foi satisfatório e as taxas de corrosão obtidas foram inferiores a 0,076 mm/ano. O depósito calcário formado no holiday protegeu o aço contra a corrosão e seu mecanismo de crescimento baseado nesta pesquisa foi construído. / Thermally Sprayed Aluminium (TSA) is widely used in offshore facilities as sacrificial anode coating for carbon-steel risers and pipelines. Transportation and installation of those components can lead to small damages in the coating, which can expose the steel surface to the seawater. It is known that calcareous deposit is formed on the cathodically polarised steel surface. Thus, this research evaluated the TSA applied by twin wire arc spray system (TWAS) on S355J2+N carbon-steel when damage (holidays) is present in order to study the calcareous deposit formation on steel and acquire data regarding the TSA performance at high temperatures. Application of different conditions was also considered: presence of sealing; coating alloy (99.5%Al and Al-5%Mg) and buried/unburied conditions. Generally, two types of experiment were conducted – i) tests at free potential at steady temperatures (30, 60 and 90°C) and different holiday sizes (exposing 5, 10 and 20% of the steel surface) and ii) tests under thermal gradient where oil at ~125°C was added in polymeric tower and external water at ~10°C was in contact with the samples surface (both free potential and polarisation of -950 mVAg/AgCl were applied). Methodology of analyses included visual inspection, scanning electron microscope and X-ray Diffraction. From the tests at steady temperatures, the TSA reached a very good protective potential (-800 to -900 mVAg/AgCl) and little difference in results due to difference in TSA composition and holiday size was observed. Corrosion rates were kept between 0.02 and 0.01 mm/year. From the thermal gradient test under free potential, the coating loss and corrosion rates were 0.4 to 0.002 mm/year. Also, the potential achieved was in a lower range than previously obtained (-745 to -835 mVAg/AgCl). However, when TSA was combined with external cathodic protection and thermal gradient, the thickness of the TSA was satisfactory and corrosion rates obtained were below 0.076 mm/year. The calcareous deposit formed within the holiday protected the steel substrate against corrosion and its growth mechanism based in this research was built.

Diversos anodos para célula a combustível de óxido sólido (SOFC) têm sido estudados devido aos problemas de deterioração dos anodos tradicionalmente usados, os compósitos à base de zircônia estabilizada/Ni (YSZ/Ni). Estudos prévios evidenciaram que a perovskita La0,75Sr0,25Cr0,50Mn0,50O3 (LSCM) possui desempenho similar em SOFCs usando hidrogênio e metano como combustível, tornando essa cerâmica um possível substituto dos compósitos à base de níquel. No presente estudo, foram sintetizados compostos La0,75Sr0,25Cr0,50-xMn0,50- yRux,yO3 (LSCM-Ru) pelo método dos precursores poliméricos. Análises termogravimétrica e térmica diferencial (TG/ATD) simultâneas e difração de raios X (DRX) foram utilizadas para monitorar a evolução térmica das resinas precursoras e a formação de fase dos compostos. As propriedades elétricas de amostras sinterizadas foram estudadas pela técnica de 4 pontas de prova dc na faixa de temperatura entre 25 °C e 800 °C. Os resultados experimentais indicaram a formação de fase única dos compostos LSCM-Ru calcinados a ~1200 °C. Os parâmetros de rede, calculados a partir dos dados de DRX, revelaram que a substituição parcial dos íons Cr ou Mn pelo Ru não altera significativamente a estrutura cristalina do LSCM até x,y ~ 0,10; uma característica consistente com os raios iônicos similares dos cátions Cr, Mn e Ru com número de coordenação seis. Medidas de resistividade elétrica ao ar mostraram que o mecanismo de transporte não é alterado e que o efeito da substituição de Ru nas propriedades elétricas do composto depende do íon substituído (Cr ou Mn) de maneira consistente com suas substituições parciais. Os testes de SOFCs unitárias revelaram que células com os anodos constituídos por uma camada coletora de corrente do anodo cerâmico LSCM-Ru e uma camada funcional de YSZ/Ni têm desempenho superior a células contendo apenas o anodo cerâmico. As células contendo os anodos cerâmicos LSCM-Ru foram testadas em hidrogênio e etanol, entre 800 °C e 950 °C, e mostraram desempenho em etanol superior ao em hidrogênio; uma característica que foi associada às propriedades de transporte eletrônico dos compostos LSCM-Ru em atmosfera redutora. Os resultados sugerem que os compostos LSCM com substituição parcial de Ru são anodos promissores para SOFC operando com etanol. / Several anodes for solid oxide fuel cell (SOFC) have been studied because of serious degradation exhibited by the traditionally used yttria-stabilized zirconia/Ni cermets (YSZ/Ni). Previous studies showed that the perovskite La0.75Sr0.25Cr0.50Mn0.50O3 (LSCM) has similar performance in SOFCs running on hydrogen and methane fuels, making such a ceramic a potential alternative to YSZ/Ni cermets. In the present study, compounds La0.75Sr0.25Cr0.50- xMn0.50-yRux,yO3 (LSCM-Ru) were synthesized by the polymeric precursor method. Simultaneous thermogravimetric and differential thermal analysis (TG/DTA) and X-ray diffraction (XRD) were used to monitor the thermal evolution of the precursor resins and the formation of crystalline phases. The electrical properties of sintered samples were studied by the 4-probe dc technique in the temperature range between 25 °C and 800 °C with controlled atmosphere. The experimental results showed the formation of single phase LSCM-Ru compounds after heat treatment at ~ 1200 °C. Lattice parameters, calculated from the XRD data, revealed that the partial substitution of Cr or Mn by Ru has no significant effect on the crystal structure of LSCM up to Ru x,y ~ 0.10; in agreement with the similar ionic radius of Cr, Mn and Ru with coordination number six. Electrical resistivity measurements showed that the transport mechanism is unchanged and that the effect of Ru addition on the electrical properties of the compound depends on the substituted ion (Cr or Mn). Electrochemical tests of SOFCs demonstrated that single cells comprised of a current collector layer of LSCM-Ru ceramic anode and a functional layer for YSZ/Ni have superior performance when compared to single cells with only one layer of the ceramic anode. Single cells with the LSCM-Ru ceramic anode layer were tested under both hydrogen and ethanol fuels, in the 800 °C - 950 °C temperature range. The main results showed that the single fuel cells exhibited higher performance under ethanol than under hydrogen; a feature that was related to the enhanced electronic transport properties of LSCM-Ru in reducing atmosphere. The experimental results suggest that the LSCM-Ru compounds are promising anodes for ethanol fueled SOFCs.

Neste trabalho serão apresentados os resultados obtidos para as degradações eletroquímicas do corante têxtil Alaranjado Remazol 3R. As degradações foram realizadas em uma célula em fluxo do tipo filtro-prensa e foram utilizados três eletrodos diferentes: platina policristalina, ADE® Ti/Ru0,3Ti0,7O2 comercial e um eletrodo preparado pelo método de Pechini (Ti/Pt). Este último eletrodo foi preparado pela deposição de H2PtCl6.6H2O sobre um substrato de Ti e aquecido a 300°C, formando assim um filme de Pt. Este eletrodo apresentou perfil voltamétrico característicos de um eletrodo de platina policristalina, com as regiões de adsorção e dessorção de hidrogênio, região da dupla camada elétrica e região de formação do óxido bem definidas. As caracterizações do corante por voltametria cíclica indicaram que o corante não é eletroativo na superfície dos eletrodos testados. As eletrólises do corante foram realizadas em soluções de H2SO4 0,5 mol L-1, com a aplicação dos potenciais de 1,80 e 2,20 V e a concentração utilizada do corante foi 35 mg L-1. Também foi estudado o efeito da adição do NaCl ao meio (0,004 a 0,017 mol L-1), para que ocorresse a formação eletroquímica do par HOCl/OCl-. Ficou comprovada a necessidade da adição deste sal que para a degradação do corante ocorresse utilizando estes três eletrodos. Quando o sal foi adicionado ao meio, a remoção de cor atingiu mais de 90% utilizando os três eletrodos. A separação entre o ânodo e o cátodo foi realizada por uma membrana IONAC e com isso ocorreu diminuição na remoção de cor, provavelmente pela diminuição da formação de ácido hipocloroso e hipoclorito de sódio. Comparando-se as remoções de cor na presença e na ausência da membrana IONAC, foi observada uma diminuição de 17,6% na remoção de cor quando aplicado o potencial de 1,80 V e 13% com o potencial de 2,20 V. O pH também foi estudado, e de acordo com os resultados, a melhor remoção de cor foi obtida em soluções com pH 1,6 e aplicando o potencial de 2,20 V, no qual foi alcançada uma degradação do corante próxima a 94%. Entretanto, quando o pH foi variado para o valor de 6,3, a remoção de cor atingiu somente 63% e, em pH > 7, a remoção de cor foi menor ainda, atingindo apenas 27% no caso do pH 12. Já no caso do eletrodo de Ti/Pt, a remoção de cor ocorreu em pH = 6,8, não havendo a necessidade da adição de H2SO4. Utilizando-se a Pt como exemplo, foi observado que a melhor remoção de COT (54%) foi obtida no potencial de 1,80 V e na ausência da membrana separadora. Quando o compartimento foi separado, a remoção de COT diminuiu para 44,6% para o potencial aplicado de 1,80 V. Se considerássemos somente a remoção de cor, as melhores condições seriam a aplicação do potencial de 2,20 V e na ausência da membrana separadora. / This paper will present the results obtained for the electrochemical degradation of textile dye Remazol Orange 3R. A filter-press cell was used with different electrodes: platinum polycrystalline, DSA® Ti/Ru0,3Ti0,7O2 and an electrode prepared by the Pechini method (Ti/Pt). The electrode Ti/Pt was prepared by deposition H2PtCl6.6H2O on a Ti substrate and heated to 300°C, producing a Pt film electrode that has voltammetric profile comparable with a polycrystalline platinum electrode, with regions of adsorption and desorption hydrogen, double layer and the region of oxide formation well defined. The characterizations of the dye by cyclic voltammetry indicated that the dye is not electroactive at the surface of the electrodes tested. The electrolysis of the dye were performed in solutions of 0.5 mol L-1 H2SO4, with potential of 1.80 and 2.20 V and the dye concentration used was 35 mg L-1. Also was studied the effect of adding NaCl to the medium (0.004 to 0.017 mol L-1), to the electrochemical formation of HOCl/OCl-. It was necessary to add NaCl in the electrolyte, for the degradation of the dye was effective. When salt was added to the medium, the color removal reached more than 90% using all electrodes. The separation between the anode and cathode was carried out by a membrane IONAC. Thus, there was a decrease in the color removal, probably due to decrease of formation of hypochlorous acid and sodium hypochlorite. Comparing the color removal in the presence and absence of membrane IONAC, it was observed a decrease of 17.6% in the removal of color when applied potential of 1.8 V and 13% with the potential of 2.2 V. The pH was also studied, and according to the results, the best color removal (94%) was obtained in solutions with pH 1.6 and applying the potential of 2.2 V. However, when the pH was varied to the value of 6.3, the color removal reached only 63% and when pH> 7, the removal of color was even lower, reaching only 27% for pH 12. In the case electrode of Ti / Pt, the color removal occurred at pH = 6.8, with no need for the addition of H2SO4. Using the Pt as an example, it was observed that better TOC removal 54%) was obtained in the potential of 1.8 V and in the absence of the membrane separator. When the compartment was separated, the removal of TOC decreased to 44.6% for the applied potential of 1.8 V. If the only focus is the color removal, the better would be the application of the potential of 2.2 V and the absence of the membrane separator.