Indiana University-Purdue University Indianapolis (IUPUI) / Provisional restorative treatment is an essential part of fixed prosthodontics. Incorporation of adequately constructed provisional restorations will enhance the success rate of definitive restorations. Repairing or replacing failed provisional restorations is a concern for both clinicians and patients. The objective of this investigation was to study the effects of alumina nanofibers reinforcement on the mechanical properties of commercially available provisional fixed partial denture PMMA material. The hypothesis was that the addition of alumina nanofibers to commercially available PMMA resin will significantly increase its flexural strength, fracture toughness, and microhardness. Alumina nanofibers at 0.0 wt %, 0.5 wt %, 1.0 wt %, and 2.5 wt % were added to commercially available provisional fixed partial material (Jet Tooth Shade). A quaternary ammonium acetate dispersant (CC-59, Goldschmidt, Janesville, WI) was added to the acrylic monomer at 0.0 wt %, 1.0 wt %, 2.0 wt % and 5.0 wt % of the nanofiber weight (12 test groups, 1 control). Samples from each group were evaluated for flexural strength, flexural modulus, fracture toughness, and microhardness. The samples were tested after storing in distilled water for 24 hours and 7 days at 37ºC. Two-way analysis of variance (ANOVA) was used to test the effects of storage time and combinations of alumina nanofiber level and quaternary ammonium acetate dispersant level on the flexural strength, fracture toughness, and microhardness of the provisional PMMA resin. Pair-wise comparisons between groups were performed using Tukey’s multiple comparisons procedure to control the overall significance level at 5 percent. Three fracture toughness samples/group were randomly selected for Energy Dispersive Spectrometry (EDS) to qualitatively evaluate the dispersion of the fibers. The data obtained from this study showed that control sample values were in the acceptance range compared with previous research. The experimental samples did not reinforce the provisional resin in the flexural strength, modulus, fracture toughness, or microhardness. There are several factors may attribute to these results, such as poor bonding at the filler/matrix interface. The more homogeneous the mixture of PMMA and fiber, the stronger the acrylic resin. In fact, the presence of poorly bonded fibers, to which little load is transferred, can be almost equivalent to voids. In addition, as seen with EDS images, alumina nanofibers had a tendency to agglomerate. The use of a magnetic stirrer was not effective in physically separating nanofibers agglomerates. Direct dispersion of alumina nanofibers in methyl methacrylate monomer and quaternary ammonium acetate dispersant was not effective in separating the nanofibers into nano-scaled single crystals. The presence of fiber agglomerates acts as a structural defect that detrimentally affects the mechanical properties. Further studies are needed to evaluate the effectiveness of fibers, dispersion techniques, and coupling agents to enhance the mechanical properties of the provisional PMMA resin.

One of the most sustainable pathways of sewage sludge treatment in recent years has been thermal conversion. The benefits of thermal treatment of sewage sludge are the recovery of energy or valuable chemical products, the destruction of harmful organic compounds, the separation of heavy metals from the P-rich coarse ash fraction, and the decreased and sanitized ash volume. The ashes created by these thermal conversion processes of sewage sludge are often rich in P that is mostly present in minerals with low plant-availability such as apatite. Due to the enrichment of P in the created ashes, a variety of post-processing steps have been developed to recover P from sewage sludge ashes. One proven way for the sus-tainable recovery of P from such ashes is thermal post-processing with alkaline salts, e.g., Na2SO4 or K2CO3, which was able to transform less plant-available phosphates in the sewage sludge into more plant-available alkali-bearing phos-phates. Based on these results, one could facilitate creating these phosphates with enhanced plant-availability by providing the chemical potential to form them already during the thermal conversion process of sewage sludge.   This thesis aims to increase the current knowledge about the ash transformation processes of P and to suggest suitable process parameters for the alteration of the phosphate speciation in sewage sludge ashes by co-conversion with alkaline-rich agricultural residues. More specifically, the possibility of incorporating K derived from agricultural residues in phosphate structures derived from sewage sludge was evaluated with respect to the influence of the process temperature, the conver-sion atmosphere, and the fuel mixture. The studied parameters were chosen to generate knowledge relevant for fluidized bed gasification processes, with a spe-cial focus on dual fluidized bed (DFB) gasification systems. The applicability of feldspar bed materials in fluidized bed gasification systems was investigated to enable the substitution of the commonly used olivine, which often contains heavy metals (potentially contaminating recovered ashes), and quartz, which is very reactive towards fuel-derived K and potentially leads to bed material fragmentation and bed agglomeration (Paper I & II). Subsequently, the thermodynamic potential for the alteration of the P-species in sewage sludge ash during co-combustion and co-gasification processes with agricultural residues was investigated (Paper III). Thereafter, an experimental evaluation of the ash transformation chemistry in thermal conversion processes of sewage sludge with different types of alkali-rich agricultural residues in temperatures relevant for flu-idized bed technology was conducted (Paper IV & V). The methodology employed was chosen with respect to the state of technology of the specific investigated process. Paper I & II applied SEM, EDS, XRD, and thermodynamic equilibrium modeling for bed material samples derived from an industrial indirect gasifier. Paper III applied thermodynamic equilibrium calcula-tions to theoretically evaluate ash compositions resulting from co-conversion of sewage sludge and agricultural residues. Paper IV & V employed SEM, EDS, ICP-AES/MS, XRD, and thermochemical modeling on ash samples derived from single pellet lab-scale experiments. The results obtained by analysis of bed material from indirect wood gasification showed the difference in interaction mechanism for K-feldspar and Na-feldspar, most notably the enhanced disintegration of Na-feldspar by K originating from the fuel (Paper I & II). Thermodynamic models employed for fuel mixtures of sewage sludge and agricultural residues showed the thermodynamic preference for the formation of the desired alkali-bearing phosphates (Paper III). Experi-ments conducted with these fuel mixtures (Paper IV & V) supported the theo-retical findings, and the influence of temperature and process conditions could be obtained. However, practical investigations also showed that attainment of the desired ash composition is subject to significant restrictions. Derived from the elaborated results and discussions, it was possible to assess the critical process and fuel parameters for the development of up-scaled gasification processes focusing on the conversion of sewage sludge with the aim of creating improved phosphate formation in the ash. The selection of a suitable bed material in fluidized bed conversion and the transformation mechanisms defining the ash chemistry were found to be of vital importance for future applications. The pur-suit of the predefined aims in reference to P-recovery from sewage sludge has led to a multitude of suggestions for suitable process parameters that must be ad-dressed in future bench- and pilot-scale experimental runs.

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No description available.

Las Percepciones de las Capacidades para la Gestión de la Sostenibilidad del Estudiantado del Grado de ADE de la UPV y la UCV: Análisis Comparado. El propósito de la investigación doctoral es comprender las percepciones y predecir los comportamientos como gestor de Sostenibilidad del estudiantado de Administración y Dirección de Empresas de dos universidades: Universidad Politécnica de Valencia y Universidad Católica de Valencia. Para ello, los objetivos que la vertebran son: 1) Argumentar críticamente una Teoría que, además de ser aceptada por la comunidad científica, sea potente para la comprensión y el aprendizaje de la Gestión de la Sostenibilidad; 2) Seleccionar una Teoría psicosocial, aceptada por la comunidad científica, para comprender y predecir el comportamiento del estudiantado hacia la Gestión de la Sostenibilidad; 3) Construir un cuestionario-escala, a partir de la Teoría seleccionada, siguiendo los procedimientos establecidos por la comunidad de los científicos sociales; 4) Analizar, comentar y discutir los resultados de las respuestas dadas por la población objeto de la investigación; 5) Comparar los resultados obtenidos entre las diversas poblaciones investigadas y establecer semejanzas y diferencias sobre la Gestión de la Sostenibilidad. Las hipótesis son las siguientes: 1) El estudiantado de ambas Universidades es mayoritariamente favorable al aprendizaje de la Gestión de la Sostenibilidad en todos los elementos que configuran las percepciones; 2) Las mujeres muestran percepciones significativamente más positivas que los varones respecto a la Gestión de la Sostenibilidad; 3) Existen diferencias en las percepciones para la Gestión de la Sostenibilidad entre el alumnado de la Universidad Católica de Valencia y el de la Universidad Politécnica de Valencia. Para alcanzar los objetivos propuestos, el proceso de investigación ha cumplimentado las siguientes fases: a)la argumentación de la importancia del problema que se investiga a la que se ha dedicado el capítulo 2º; b)la revisión del estado actual del conocimiento sobre el problema investigado; a ello se ha dedicado el capítulo 1º; c) la justificación de la perspectiva teórica que se adopta,el enfoque del Desarrollo de las Capacidades Humanas,a la que se dedica el capítulo 3º; d) la selección argumentada de la Teoría dela Acción Planificada de Azjen, en el capítulo 4º; e) la presentación crítica de la metodología de la investigación, en el capítulo 5º, que utiliza de forma complementaria la perspectiva empírico-analítica, que permite explicar y predecir el comportamiento del estudiantado; la hermenéutico-interpretativa, que facilita la comprensión de los significados de las intenciones y acciones del alumnado y el método comparado entre el alumnado de una Universidad y la otra; f) la aplicación del cuestionario-escala, análisis de los datos y comentarios de los resultados de las respuestas del alumnado de la Universidad Católica de Valencia (capítulo 6º), del alumnado de la Universidad Politécnica de Valencia (capítulo 7º) y de la comparación entre el alumnado de ambas universidades (capítulo 8ª). Conclusiones: a)la hipótesis 1. El estudiantado de ambas Universidades es mayoritariamente favorable al aprendizaje de la Gestión de la Sostenibilidad en todos los elementos del sistema de actitudes. La hipótesis 1 queda confirmada en 5 de las 8 sub-hipótesis y parcialmente confirmada en las tres restantes; b) la hipótesis 2. Las mujeres muestran un sistema de actitudes significativamente más positivas que los varones respecto a la Gestión de la Sostenibilidad. La hipótesis 2 queda confirmada; c) la hipótesis 3. Existen diferencias en el sistema de actitudes para la Gestión de la Sostenibilidad entre el alumnado de la Universidad Católica de Valencia y el alumnado de la Universidad Politécnica de Valencia. La hipótesis 3 queda confirmada en 7 de sus 9 sub-hipótesis, parcialmente c / Les Percepcions de les Capacitats per a la Gestió de la Sostenibilitat de l'Estudiantat del Grau d'ADE de la UPV i la UCV: Anàlisi Comparada. El propòsit de la investigació doctoral és comprendre les percepcions i predir els comportaments com a gestor de Sostenibilitat de l'estudiantat d'Administració i Direcció d'Empreses de dues universitats: Universitat Politècnica de València i Universitat Catòlica de València. Per a això, els objectius que la vertebren són: 1) Argumentar críticament una Teoria que, a més de ser acceptada per la comunitat científica, siga potent per a la comprensió i l'aprenentatge de la Gestió de la Sostenibilitat; 2) Seleccionar una Teoria psicosocial, acceptada per la comunitat científica, per a comprendre i predir el comportament de l'estudiantat cap a la Gestió de la Sostenibilitat; 3) Construir un qüestionari-escala, a partir de la Teoria seleccionada, seguint els procediments establerts per la comunitat dels científics socials; 4) Analitzar, comentar i discutir els resultats de les respostes donades per la població objecte de la investigació; 5) Comparar els resultats obtinguts entre les diverses poblacions investigades i establir semblances i diferències sobre la Gestió de la Sostenibilitat. Les hipòtesis són les següents: 1) L'estudiantat d'ambdues Universitats és majoritàriament favorable a l'aprenentatge de la Gestió de la Sostenibilitat en tots els elements que configuren les percepcions; 2) Les dones mostren percepcions significativament més positives que els homes respecte a la Gestió de la Sostenibilitat; 3) Existeixen diferències en les percepcions per a la Gestió de la Sostenibilitat entre l'alumnat de la Universitat Catòlica de València i el de la Universitat Politècnica de València. Per a aconseguir els objectius proposats, el procés d'investigació ha cobert les següents fases: a) l'argumentació de la importància del problema que s'investiga a la que s'ha dedicat el capítol 2n; b) la revisió de l'estat actual del coneixement sobre el problema investigat; a això s'ha dedicat el capítol 1r; c) la justificació de la perspectiva teòrica que s'adopta, l'enfocament del Desenvolupament de les Capacitats Humanes, a la qual es dedica el capítol 3r; d) la selecció argumentada de la Teoria de l'Acció Planificada d'Azjen, en el capítol 4rt; e) la presentació crítica de la metodologia de la investigació, en el capítol 5é, que utilitza de forma complementària la perspectiva empíric-analítica, que permet explicar i predir el comportament de l'estudiantat; l'hermenèutica-interpretativa, que facilita la comprensió dels significats de les intencions i accions de l'alumnat i el mètode comparat entre l'alumnat d'una Universitat i l'altra; f) l'aplicació del qüestionari-escala, anàlisi de les dades i comentaris dels resultats de les respostes de l'alumnat de la Universitat Catòlica de València (capítol 6é), de l'alumnat de la Universitat Politècnica de València (capítol 7é) i de la comparació entre l'alumnat d'ambdues universitats (capítol 8a). Conclusions: a) la hipòtesi 1. L'estudiantat d'ambdues Universitats és majoritàriament favorable a l'aprenentatge de la Gestió de la Sostenibilitat en tots els elements del sistema d'actituds. La hipòtesi 1 queda confirmada en 5 de les 8 sub-hipòtesis i parcialment confirmada en les tres restants; b) la hipòtesi 2. Les dones mostren un sistema d'actituds significativament més positives que els homes respecte a la Gestió de la Sostenibilitat. La hipòtesi 2 queda confirmada; c) la hipòtesi 3. Existeixen diferències en el sistema d'actituds per a la Gestió de la Sostenibilitat entre l'alumnat de la Universitat Catòlica de València i l'alumnat de la Universitat Politècnica de València. La hipòtesi 3 queda confirmada en 7 de les seues 9 sub-hipòtesis, parcialment confirmada en 1 sub-hipòtesi i no confirmada en 1 sub-hipòtesi. / Perceptions of the Capacities for Sustainable Management in the Students of "Administration and Business Management" Degree in the Polytechnic University of Valencia and the Catholic University of Valencia: A Comparative Analysis. The purpose of the doctoral research is to understand perceptions and to predict behaviors as Sustainable managers in Administration and Business Management students of two universities: the Polytechnic University of Valencia and the Catholic University of Valencia. To this end, the objectives that underpin are: 1) Critically argue a theory that, in addition to being accepted by the scientific community, is powerful for understanding and learning Sustainability Management; 2) Select a psychosocial theory, accepted by the scientific community, to understand and to predict behavior students towards Sustainability Management; 3) Construct a questionnaire-scale, based on the selected theory, following the procedures established by the community of social scientists; 4) Analyze, comment and discuss the results of the answers given by the population under investigation; 5) Compare the results obtained among different researched populations and establish similarities and differences on Sustainability Management. The hypotheses are: 1) Students of both Universities are mainly favorable to learning Sustainability Management in all the elements that configure the perceptions; 2) Women express significantly more positive perceptions than men with respect to Sustainability Management; 3) There are different perceptions of Sustainability Management among the students in the Catholic University of Valencia and in the Polytechnic University of Valencia. In order to achieve the stipulated objectives, the research process has completed the following phases: a) argumenting the importance of the problem under investigation which is adressed in the 2nd chapter ; b) elaborating the current literature review about the issue under investigation; which is adressed in the 1st chapter; c) justificating the theoretical perspective that is adopted: Development of Human Capacities approach; which is adressed in the 3rd chapter; d) Arguing the selection of Azjen's Theory of Planned Behavior, in the 4th chapter; e) critically presentating the research methodology, in the 5th chapter, which uses in a complementary way the empirical-analytical perspective, which allows explaining and predicting student behavior; the hermeneutic-interpretative perspective, which facilitates understanding the meanings of the intentions and actions in the students and the comparative method between the students at one university and at the other; f) applicating the questionnaire-scale, analysing the data and commenting on the results of the responses of the students at Catholic University of Valencia (6th chapter), the students at Polytechnic University of Valencia (7th chapter) and the comparison between the students of both universities (8th chapter). Conclusions: a) hypothesis 1. The students of both Universities are mostly favorable for learning Sustainability Management in all of the elements of the attitude system. Hypothesis 1 is confirmed in 5 of the 8 sub-hypotheses and partially confirmed in the remaining three; b) hypothesis 2. Women show a system of significantly more positive attitudes than men with respect to Sustainability Management. Hypothesis 2 is confirmed; c) hypothesis 3. There are differences in the attitude system for Sustainability Management among the students of the Catholic University of Valencia and the students of the Polytechnic University of Valencia. Hypothesis 3 is confirmed in 7 of its 9 sub-hypotheses, partially confirmed in 1 sub-hypothesis and not confirmed in 1 sub-hypothesis. / Escámez Marsilla, JI. (2018). LAS PERCEPCIONES DE LAS CAPACIDADES PARA LA GESTIÓN DE LA SOSTENIBILIDAD DEL ESTUDIANTADO DEL GRADO DE ADE DE LA UPV Y LA UCV: ANÁLISIS COMPARADO [Tesis doctoral]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/115487

This thesis aims to provide adequate analytical information on the spade shaped iron bars of Norrland and central Sweden. While their significance has been thoroughly debated for decades, analytical research on them has been confined to cases of single artefacts or theoretical interpretations of their value, meaning and origin. In this study a comprehensive approach is taken into consideration. Based on X-Ray fluorescence (XRF), scanning electron microscopy (SEM) and metallographical analysis this thesis seeks to facilitate new interpretations on quality, production centres and usage based on analytical results. Aiming to settle some of the long lasting questions regarding the artefacts while producing results which can further the discussion by raising new questions, previously unasked.

Superaustenitická korozivzdorná ocel typu 22Cr25NiWCoCu určená pro vysokoteplotní aplikace v energetickém průmyslu byla studována za podmínek nízkocyklové únavy při pokojové a zvýšené teplotě. Jednotlivé vzorky byly podrobeny různým zátěžným procedurám, což umožnilo studium materiálové odezvy spolu s mechanismem poškození. Křivky cyklického zpevnění/změkčení, cyklického napětí a Coffin-Mansonovy křivky byly vyhodnoceny. Únavová životnost materiálu byla diskutována s ohledem na uplatňované mechanismy poškození, které se vyvinuly za specifických zátěžných podmínek. Standardní izotermální únavové experimenty byly provedeny při pokojové a zvýšené teplotě. Hysterezní smyčky zaznamenané během cyklického zatěžování byly analyzovány pomocí zobecněné statistické teorie hysterezní smyčky. Pro různé amplitudy napětí byla určena jak distribuce hustoty pravděpodobnosti interních kritických napětí (dále PDF), tak rovněž zjištěn její vývoj během cyklického namáhání. Zjištěné průběhy PDF byly korelovány s vývojem povrchového reliéfu a vnitřního dislokačního uspořádání zdokumentované pro obě teploty pomocí rastrovací elektronové mikroskopie (SEM) vybavené technikou fokusovaného iontového svazku (FIB), která umožnila rovněž efektivní studium nukleace povrchových únavových trhlin. Při cyklickém zatížení při pokojové teplotě byla pozorována lokalizace cyklické plastické deformace do perzistentních skluzových pásů (PSP). V místech, kde tyto PSP vystupují na povrch materiálu byly pozorovány perzistentní skluzové stopy (PSS) tvořené extruzemi a intruzemi. Postupné prohlubování intruzí, zejména na čele nejhlubší intruze, vede k iniciaci únavové trhliny. Odlišný mechanismus tvorby trhlin byl zjištěn při únavové zkoušce při zvýšené teplotě, kde zásadní roli hrál vliv prostředí. Rychlá oxidace hranic zrn a jejich následné popraskání představuje dominantní mechanismus v I. stádiu nukleace trhlin. Aplikace desetiminutové prodlevy v tahové části zátěžného cyklu vedlo k vývoji vnitřního (kavitačního) poškozování. Mechanismy vnitřního poškozování byly studovány na podélných řezech rovnoběžných s napěťovou osou zkušebních vzorků. Trhliny a jejich vztah k hranicím zrn a dvojčat byly studovány pomocí difrakce zpětně odražených elektronů (EBSD). Vliv prodlevy na únavovou životnost byl korelován s vývojem povrchového reliéfu a vnitřního poškození. Vzorky z uvedené oceli byly rovněž podrobeny zkouškám termomechanické únavy (TMF), při nichž se v čase mění jak zátěžná síla tak i teplota. Termomechanické únavové zkoušky v režimu soufázném (in-phase) a protifázném (out-of-phase) byly provedeny jak s prodlevou, tak i bez ní. Ve všech případech bylo pozorováno rychlé cyklické zpevnění bez ohledu na použitou amplitudu deformace, u vzorků testovaných v out-of-phase režimu byla zjištěna tendence k saturaci. Zkoumáním povrchového reliéfu za pomocí technik SEM a FIB byla odhalena přednostní oxidace hranic zrn a následné praskání těchto hranic kolmo k ose zatížení. Prodlevy v cyklech při maximálním napětí vedly ke zvýšení amplitudy plastické deformace a následně ke creepovému poškození ve formě vnitřních kavit a trhlin. Interkrystalické šíření trhlin bylo pozorováno na vzorcích testovaných v režimu in-phase. Vývoj poškození v režimu out-of-phase nebyl principiálně ovlivněn zařazením prodlevy do zátěžného cyklu. Charakteristickým znakem namáhání v režimu out-of-phase je nukleace několika trhlin v homogenní oxidické vrstvě jdoucích napříč zrny kolmo k ose zatěžování.

Ce travail présente un développement et une analyse des approches numériques déterministes et probabilistes efficaces pour les équations aux dérivées partielles avec des coefficients et données aléatoires. On s'intéresse au problème d'écoulement stationnaire avec des données aléatoires. Une méthode de projection dans le cas unidimensionnel est présentée, permettant de calculer efficacement la moyenne de la solution. Nous utilisons la méthode de collocation anisotrope des grilles clairsemées. D'abord, un indicateur de l'erreur satisfaisant une borne supérieure de l'erreur est introduit, il permet de calculer les poids d'anisotropie de la méthode. Ensuite, nous démontrons une amélioration de l'erreur a priori de la méthode. Elle confirme l'efficacité de la méthode en comparaison avec Monte-Carlo et elle sera utilisée pour accélérer la méthode par l'extrapolation de Richardson. Nous présentons aussi une analyse numérique d'une méthode probabiliste pour quantifier la migration d'un contaminant dans un milieu aléatoire. Nous considérons le problème d'écoulement couplé avec l'équation d'advection-diffusion, où on s'intéresse à la moyenne de l'extension et de la dispersion du soluté. Le modèle d'écoulement est discrétisée par une méthode des éléments finis mixtes, la concentration du soluté est une densité d'une solution d'une équation différentielle stochastique, qui sera discrétisée par un schéma d'Euler. Enfin, on présente une formule explicite de la dispersion et des estimations de l'erreur a priori optimales. / This work presents a development and an analysis of an effective deterministic and probabilistic approaches for partial differential equation with random coefficients and data. We are interesting in the steady flow equation with stochastic input data. A projection method in the one-dimensional case is presented to compute efficiently the average of the solution. An anisotropic sparse grid collocation method is also used to solve the flow problem. First, we introduce an indicator of the error satisfying an upper bound of the error, it allows us to compute the anisotropy weights of the method. We demonstrate an improvement of the error estimation of the method which confirms the efficiency of the method compared with Monte Carlo and will be used to accelerate the method using the Richardson extrapolation technique. We also present a numerical analysis of one probabilistic method to quantify the migration of a contaminant in random media. We consider the previous flow problem coupled with the advection-diffusion equation, where we are interested in the computation of the mean extension and the mean dispersion of the solute. The flow model is discretized by a mixed finite elements method and the concentration of the solute is a density of a solution of the stochastic differential equation, this latter will be discretized by an Euler scheme. We also present an explicit formula of the dispersion and an optimal a priori error estimates.

Dans la perspective de prédire les transformations chimico-minéralogiques possibles d'une bentonite placée en conditions de stockage profond de déchets radioactifs, plusieurs séries d'expériences ont été réalisées utilisant la bentonite MX80 en présence d'une solution chlorurée sodi-calcique, en absence ou en présence de fer (magnétite + hématite ou fer métal + magnétite), à 80 et 300 °C et pour des durées de 1 jour à 9 mois. Les produits de réactions ont fait l'objet de caractérisations multi-échelles et multi-techniques : diffraction des rayons X, microscope électronique à balayage et en transmission (imagerie haute résolution, EDS et EELS), microsonde électronique, spectroscopie Mössbauer et analyse ICP AES et ICP MS des solutions. Le code de calcul EQ3/6 a été utilisé pour simuler les expériences réalisées. Une nouvelle méthode ponctuelle de détermination de la valence du fer dans les argiles au MET par spectroscopie de perte d'énergie des électrons (EELS) a été développée.

<p>Duplex stainless steels are a very attractive alternative to austenitic grades due to their higher strength and good corrosion performance. The austenitic grades can often be welded autogenously, while the duplex grades normally require addition of filler metal. This is to counteract segregation of important alloying elements and to give sufficient austenite formation to prevent precipitation of chromium nitrides that could have a negative effect on impact toughness and pitting resistance. The corrosion performance of the recently-developed lean duplex stainless steel LDX 2101 is higher than that of 304 and can reach the level of 316. This thesis summarises pitting resistance tests performed on laser and gas tungsten arc (GTA) welded LDX 2101. It is shown here that this material can be autogenously welded, but additions of filler metal, nitrogen in the shielding gas and use of hybrid methods increases the austenite formation and the pitting resistance by further suppressing formation of chromium nitride precipitates in the weld metal. If the weld metal austenite formation is sufficient, the chromium nitride precipitates in the heat-affected zone (HAZ) could cause local pitting, however, this was not seen in this work. Instead, pitting occurred 1–3 mm from the fusion line, in the parent metal rather than in the high temperature HAZ (HTHAZ). This is suggested here to be controlled by the heat tint, and the effect of residual weld oxides on the pitting resistance is studied. The composition and the thickness of weld oxide formed on LDX 2101 and 2304 were determined using X-ray photoelectron spectroscopy (XPS). The heat tint on these lean duplex grades proved to contain significantly more manganese than what has been reported for standard austenitic stainless steels in the 300 series. A new approach on heat tint formation is consequently presented. Evaporation of material from the weld metal and subsequent deposition on the weld oxide are suggested to contribute to weld oxide formation. This is supported by element loss in LDX 2101 weld metal, and nitrogen additions to the GTA shielding gas further increase the evaporation.</p><p> </p>