Afin de répondre aux problématiques écologique et économique du traitement des Matériaux Contenant de l’Amiante (MCA), un procédé complet permettant de traiter de manière optimale ces déchets a été proposé. Pour cela, trois types de déchets ont d’abord été analysés par plusieurs techniques de caractérisation complémentaires (diffraction des rayons X, microscopie électronique à balayage, infrarouge et RMN du solide). Ces analyses ont permis l’identification des différentes phases présentes au sein des déchets. Cette identification est nécessaire, car elle permet d’adapter de manière optimale le procédé de destruction au déchet. La première étape de ce procédé est le traitement en température des MCA dans une solution d’acide nitrique. Elle permet la dissolution de la matrice du déchet et la dénaturation des fibres de chrysotile qui sont présentes dans 95 % des déchets amiantés. Deux phases sont alors récupérées à l’issue de ce traitement : une phase solide composée de silice pure et une phase liquide contenant, notamment, du calcium, du magnésium et du fer. Si les déchets contiennent des fibres de type amphibole (5 % des MCA) ils sont ensuite traités par voie hydrothermale dans un autoclave contenant une solution de soude. Cette étape mène à la dissolution complète du déchet. Une solution basique contenant du silicium est ainsi récupérée. Différentes voies de valorisations ont été développées. Les ions présents dans la solution acide sont récupérés par précipitation sélective des hydroxydes. Une autre voie consiste à synthétiser une zéolithe à partir de la silice pure et de la solution basique. Les isothermes d’adsorption de cette dernière ont été tracés afin de déterminer sa capacité d’adsorption de certains cations métalliques polluants. Pour terminer, une étude fondamentale a été menée sur les nanotubes de silice obtenus avec le traitement de fibres d’amiante pures et différentes applications de ces nanotubes de silice ont été évoquées. / To answer the ecological and economic problems of the treatment of Materials Containing Asbestos (MCA), a complete process allowing to handle in an optimal way these waste was proposed. For that purpose, three types of waste were analyzed by several complementary techniques of characterization (X-rays diffraction, Scanning Electron Microscopy, infrared and NMR spectroscopy). These analyses allowed the identification of the present various phases within waste. This identification is necessary, because it allows to adapt in the optimal way for the destruction of the waste. The first stage of the process is a treatment in temperature of the MCA in a solution of nitric acid leading to the dissolution of the matrix of the waste and the denaturation of the fibers of chrysotile which are present in 95 % of MCA. Two phases are then got back at the end of this treatment: a solid phase of pure silica and a liquid phase containing, in particular, calcium, magnesium and iron ions. If previous waste contains fibers of amphibole type (5 % of the MCA) they are then treated through a hydrothermal process in an autoclave containing a solution of soda. This stage leads to the complete dissolution of the waste. The basic solution containing some silicon is so got back. Various ways of valuations were then developed. The present ions in the acid solution are chemically sorted out by a selective precipitation of hydroxides. Another way consists in synthesizing a zeolite from the pure silica coming from the acid treatment and from the basic solution after hydrothermal treatment. The isotherms of adsorption of this synthesized zeolite were established to determine its capacity of adsorption of certain polluting metallic cations. To finish, a fundamental study was led on the nanotubes of silica obtained after the acid treatment of pure asbestos fibers and diverse applications of these nanotubes of silica were evoked.

Sewage sludge is a by-product of wastewater treatment that simultaneously gathers contaminants, valuable organic matter, and nutrients. The treatment of the increasing amount of sewage sludge is important from both pollution prevention and resource recovery perspectives as i) large shares of mineral phosphorus, listed as a critical raw material, terminate in the sewage sludge, and ii) energy recovery from sewage sludge can cover the energy-intensive demand of the treatment process. Previous research has identified sewage sludge combustion as a suitable treatment approach as it both addresses contaminant destruction and paves the way for efficient phosphorus recovery from the sewage sludge ash. The commercial development of this practice has, however, been slow. Therefore, this thesis aims to investigate the challenges in sustainable sewage sludge management, and to, in more detail, identify the economic viability of energy and phosphorus recovery from sewage sludge through combustion. The thesis’ aim is divided into two objectives addressed in three papers. First, to investigate how different aspects of sewage sludge management, such as contaminants, economic efficiency, technical aspects, and legislation, evolve and interact. This has been done by a review of sewage sludge management research over fifty years (Paper I). Second, to investigate the economic viability of simultaneous energy and phosphorus recovery from sewage sludge by comparing different technology and market scenarios. This has been done for i) new sewage sludge mono-/co-combustion plants (Paper II), and ii) the integration of treatment technologies, mainly anaerobic digestion, hydrothermal carbonization, and combustion, in an existing wastewater treatment plant (Paper III).  Results from the analysis of sewage sludge management research (Paper I) show a narrow-focused perspective that often excludes inseparable aspects such as combination of economic consideration and advanced extraction technology. The investment viability of a new mono-/co-combustion of sewage sludge (Paper II) is highly conditional on heat, electricity, and fertilizer price, and external financial support is often a crucial requirement. Sewage sludge co-combustion with potassium-rich biomasses improves sewage sludge quality and forms usable ash as fertilizer without further need for phosphorus recovery technology. In this case, the economic feasibility of the process is independent of usable ash revenue, which stimulates a competitive selling price for the ash, thereby improving the marketing of sludge-based fertilizer. Avoided disposal costs of sewage sludge for a retrofitted wastewater treatment plant by introducing hydrothermal carbonization (Paper III) shows good economic feasibility while recovering phosphorus. Integrating anaerobic digestion, hydrothermal carbonization, and combustion may also improve investment incentives by improving energy outputs and phosphorus recovery. The economic feasibility is contingent on product (hydrochar, heat, electricity) prices and sensitive to added equipment costs, and costs for sludge transportation and disposal.

Made available in DSpace on 2014-12-17T14:06:57Z (GMT). No. of bitstreams: 1 AntonioNF_DISSERT.pdf: 3720151 bytes, checksum: 9b23d51efb071c929717b8ea4387b379 (MD5) Previous issue date: 2011-06-06 / Coordena??o de Aperfei?oamento de Pessoal de N?vel Superior / Physical-chemical properties of Ti are sensible to the presence of interstitial elements. In the case of thermochemical treatments plasma assisted, the influence of different active species is not still understood. In order to contribute for such knowledge, this work purposes a study of the role played by the active species atmosphere into the Ar N2 CH4 carbonitriding plasma. It was carried out a plasma diagnostic by OES (Optical Emission Spectroscopy) in the z Ar y N2 x CH4 plasma mixture, in which z, y and x indexes represent gas flow variable from 0 to 4 sccm (cm3/min). The diagnostic presents abrupt variations of emission intensities associated to the species in determined conditions. Therefore, they were selected in order to carry out the chemical treatment and then to investigate their influences. Commercial pure Ti disks were submitted to plasma carbonitriding process using pre-established conditions from the OES measurements while some parameters such as pressure and temperature were maintained constant. The concentration profiles of interstitial elements (C and N atoms) were determined by Resonant Nuclear Reaction Analysis (NRA) resulting in a depth profile plots. The reactions used were 15N(ρ,αγ)12C and 12C(α,α)12C. GIXRD (Grazing Incidence X-Ray Diffraction) analysis was used in order to identify the presence of phases on the surface. Micro-Raman spectroscopy was used in order to qualitatively study the carbon into the TiCxN1 structure. It has been verified which the density species effectively influences more the diffusion of particles into the Ti lattice and characteristics of the layer formed than the gas concentration. High intensity of N2 + (391,4 nm) and CH (387,1 nm) species promotes more diffusion of C and N. It was observed that Hα (656,3 nm) species acts like a catalyzer allowing a deeper diffusion of nitrogen and carbon into the titanium lattice. / As propriedades f?sico-qu?micas do Ti s?o sens?veis ? presen?a de intersticiais. No caso do tratamento termoqu?mico auxiliado por plasma, a influ?ncia das diferentes esp?cies ativas ainda n?o ? bem entendida. A fim de colaborar para tal conhecimento, esse trabalho prop?e um estudo das esp?cies ativas do plasma carbonitretante de N2+Ar+CH4. Foi realizado o diagn?stico por espectroscopia de emiss?o ?ptica (OES) do plasma na mistura xAr+yN2+zCH4, onde x, y e z s?o fluxos vari?veis de 0 a 4 sccm (cm3/min.). Esse diagn?stico apresentou varia??es abruptas de intensidades de emiss?o das esp?cies em determinadas condi??es e estas foram selecionadas para realizar o tratamento termoqu?mico e assim investigar suas influ?ncias. Em seguida, discos de Ti comercialmente puros foram submetidos ao processo de carbonitreta??o por plasma com as condi??es pr?-estabelecidas pelo diagn?stico de plasma enquanto que os par?metros de press?o e temperatura foram mantidos constantes. O perfil de concentra??o dos intersticiais, carbono e nitrog?nio, foi determinado por rea??o nuclear ressonante (NRA) resultando numa curva de perfil em profundidade. As rea??es usadas foram 15N(ρ,αγ)12C e 12C(α,α)12C. Utilizou-se difra??o de raios-X em ?ngulo rasante (GIDRX) para identificar as fases presentes na superf?cie. A espectroscopia micro-Raman foi usada para estudar, de forma qualitativa a estrutura do carbono no TiCxN1-xVerificou-se que a densidade das esp?cies influencia, de maneira mais efetiva que o fluxo de g?s, no processo de difus?o e nas caracter?sticas da camada formada. Alta intensidade das esp?cies N2 + (391,4 nm) e CH (387,1 nm) favorecem a difus?o dos intersticiais C e N. Foi observado que o Hα (656,3 nm) atua como catalisador permitindo a difus?o em maiores profundidades desses intersticiais na estrutura do Ti.

Le grippage dans le cas des aciers inoxydables est un phénomène complexe nécessitant une approche multi-échelle et multi-physique. Les 6 nuances d’aciers inoxydables sélectionnées au cours de cette thèse (316L, 316LN, Nitronic60, AISI660, Uranus45N et 17-4PH) ont été étudiées à l’état de réception et après traitements thermochimique de surface de type S3P. Ces matériaux ont subi un essai de grippage selon la norme ASTM G98 et les échantillons qui en résultent ont été caractérisés selon une approche d’abord surfacique (évolution de la morphologie de la surface, observations MEB…) puis en volume, notamment par le biais de l’approche originale de la microstructure (EBSD, DRX et MET notamment). Cette thèse a ainsi permis d’étudier les différents mécanismes intervenant lors du grippage des aciers inoxydables ainsi que d’étudier l’impact de différentes microstructures et composition chimiques sur ce phénomène. / Galling is a complex phenomenon requiring a multi-scale and multi-physical approach. During this thesis, 6 stainless steel grades (316L, 316LN, Nitronic60, AIS1660, Uranus45N et 17-4PH) are studied, both untreated and after S3P thermochemical heat surface treatment. These materials are tested according to ASTM G98 galling test and resulting samples are then characterized. This characterization is at first realized on the surface (surface morphology evolution, SEM investigations...), then on the bulk material, consisting mainly into a microstructural characterization based on EBSD, XRD and TEM investigations. It results from this thesis a better comprehension of the galling mechanisms in the case of stainless steel. The various effects of material composition, microstructure and material properties in general are also discussed.

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / O objetivo deste trabalho é a aplicação de um Planejamento Fatorial Completo, ferramenta estatística que auxiliará a obter dados empíricos para otimizar um tratamento termoquímico, a cementação. Partindo-se de um levantamento da profundidade de camada cementada e da dureza de uma corrente de aço de baixo teor de carbono, usada para amarração, e para resistir à abrasão reproduziu-se uma nova cementação, variando-se seus parâmetros de influência, para se alcançar o ponto ótimo, definindo o melhor aço e o melhor processo. Foram realizados dois planejamentos, um fatorial 2 e dois 2, comparando o comportamento do processo na prática em relação aos resultados teóricos de uma simulação computacional, que permite a obtenção das curvas de enriquecimento de carbono, baseado na segunda Lei de Fick, para várias condições de contorno. Os perfis teóricos de cementação apresentaram valores de profundidade efetiva próximos aos valores obtidos experimentalmente, evidenciando o planejamento realizado.

Made available in DSpace on 2016-12-08T17:19:24Z (GMT). No. of bitstreams: 1 Claudinei Franco.pdf: 6129117 bytes, checksum: 6059aaddb2af97db39be8b6299acf549 (MD5) Previous issue date: 2014-10-30 / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / The interest for improvements in tribological properties of materials, more specifically in steels with low and medium carbon content are of great importance for mechanical components life time. In this work, thermochemical treatments were carried out on ABNT 1020 and ABNT 1045 steels, in order to compare and evaluate the tribological behavior and also the phases and layers formed, to the different types of treatments which are: boronizing, nitriding and multi component boronizing (also known as duplex treatment). The specific objectives were to plan the different ways of treatment; evaluate and compare the effect of the substrate according to the microstructure, support and interface of the layers formed through the treatments; characterize the wear mechanisms for the different treatments and compare the results of both materials. The thermochemical treatments were carried out, using as basis previous works performed by the powder metallurgy research group. Boronizing and nitriding treatments were carried out by solid means, multi component boronizing treatment was performed in two ways: in the first one, boronizing was followed by nitriding (BN) and the in the second one, nitriding was followed by boronizing (NB). These duplex treatments were performed with the same conditions of time and temperature used for nitriding and boronizing treatments. Pin-on-disk sliding wear tests were performed using WC-Co (hard metal) balls as counter body. Through the test it was possible to evaluate the tribological behaviour. Friction coefficient, volume of removed material and wear mechanisms were determined. The microhardness of the formed layers was measured at the surface and on the cross section of the specimens. X-ray diffraction was used to confirm the formed compounds on nitriding, boronizing and boron-nitriding (duplex) treatments. The results showed an increase in the hardness of the surface layer and a reduction in the amount of removed material (volume) in all thermochemical treatments comparing with the condition of non-treated samples. Regarding the tribological behavior, by evaluating the thermochemically treated samples, the nitrided samples of ABNT 1020 presented the highest amount of removed material (0,078 mm3) and its hardness was 436 HV0.05. The boronized ABNT 1020 steel presented the lower amount of removed material (0,013 mm3). The boronized ABNT 1045 steel reached the highest mean hardness on the surface (1750 HV0.05) and the NB duplex treatment in this material provided the highest hardness of the formed layer, about 2270 HV0.05. / O interesse por melhorias nas propriedades tribológicas de materiais, mais específico em aços com baixo e médio teor de carbono são de grande importância para a vida útil de componentes mecânicos. Neste trabalho foram realizados diversos tratamentos termoquímicos em aços ABNT 1020 e ABNT 1045, com o objetivo de comparar e avaliar o comportamento tribológico e também as fases e camadas formadas, para as diferentes formas de tratamentos que são: boretação, nitretação e boretação multicomponente (também conhecido como tratamento duplex). Os objetivos específicos foram: planejar as formas de tratamentos; avaliar e comparar o efeito do substrato relacionado à microestrutura, ao suporte e interface das camadas formadas nos tratamentos realizados; caracterizar os mecanismos e formas de desgastes para os diversos tratamentos e comparar entre os dois materiais. Os tratamentos termoquímicos foram realizados, utilizando como base trabalhos anteriores que foram realizados no grupo de pesquisa de metalurgia do pó. Os tratamentos de boretação e nitretação foram realizados por via sólida, o tratamento de boretação multicomponente foi realizado de duas formas: na primeira foi realizada a boretação seguido de nitretação (BN) e a segunda foi a nitretação seguido de boretação (NB), nos tratamentos duplex utilizaram-se os mesmos parâmetros de boretação e nitretação. Foram realizados ensaios de desgaste por deslizamento do tipo pino sobre disco, com esferas de WC-Co (metal duro) como contra corpo. Foram avaliados: o coeficiente de atrito, o volume de material removido e os mecanismos de desgaste. A dureza da camada formada foi avaliada por microdureza na superfície e na seção transversal. Difratometria de raios-X foi utilizada para a comprovação da formação das camadas de nitretos, boretos e boro-nitretos (duplex). Os resultados mostraram melhoras principalmente na dureza da camada superficial e redução no volume de material removido, em todos os tratamentos termoquímicos, quando comparado com amostras sem tratamento. Em relação ao comportamento tribológico, avaliando as amostras tratadas termoquimicamente, as amostras nitretadas do aço ABNT 1020 foram as que apresentaram os piores resultados com volume de material removido de 0,078 mm3 e dureza de 436 HV0,05. Já a boretação no aço ABNT 1020 foi o tratamento que apresentou o melhor desempenho em volume de material removido com 0,013 mm3. O aço ABNT 1045 com tratamento de boretação apresentou a maior dureza média na superfície, com 1750 HV0,05 e o tratamento duplex NB neste mesmo material proporcionou a maior dureza na seção transversal, resultante da camada formada de nitretos-boro com 2270 HV0,05.

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / O objetivo deste trabalho é a aplicação de um Planejamento Fatorial Completo, ferramenta estatística que auxiliará a obter dados empíricos para otimizar um tratamento termoquímico, a cementação. Partindo-se de um levantamento da profundidade de camada cementada e da dureza de uma corrente de aço de baixo teor de carbono, usada para amarração, e para resistir à abrasão reproduziu-se uma nova cementação, variando-se seus parâmetros de influência, para se alcançar o ponto ótimo, definindo o melhor aço e o melhor processo. Foram realizados dois planejamentos, um fatorial 2 e dois 2, comparando o comportamento do processo na prática em relação aos resultados teóricos de uma simulação computacional, que permite a obtenção das curvas de enriquecimento de carbono, baseado na segunda Lei de Fick, para várias condições de contorno. Os perfis teóricos de cementação apresentaram valores de profundidade efetiva próximos aos valores obtidos experimentalmente, evidenciando o planejamento realizado.

Thermochemische Randschichthärteverfahren ermöglichen eine ausscheidungsfreie Einlagerung von Kohlenstoff bzw. Stickstoff innerhalb des austenitischen Mischkristalls. Im Zusammenhang mit einer Randschichtbehandlung thermisch gespritzter Schichtsysteme stellen die charakteristischen Strukturmerkmale eine bislang weitgehend unerforschte Einflussgröße für die Beurteilung von Diffusionsprozessen dar. Bei der Verarbeitung von randschichtgehärtetem Pulver durch Verfahren des thermischen Spritzens ist die Phasenstabilität des Spritzzusatzwerkstoffs von übergeordneter Bedeutung. Die beiden Möglichkeiten einer Verfahrenskombination werden für hochgeschwindigkeitsflamm- und atmosphärisch plasmagespritzte Schichtsysteme des Werkstoffs EN 1.4404 durch systematische Prozess- und Parametervariation eingehend betrachtet. Für die einzelnen Schichtsysteme werden Einflussfaktoren struktur- und prozessspezifisch sowie in Abhängigkeit vom Anreicherungsmedium erfasst und im Kontext der Massivwerkstoffreferenz eingeordnet. Die daraus abgeleiteten allgemeingültigen Aussagen zu verfahrenstechnischen Wechselwirkungseffekten ermöglichen eine anwendungsorientierte Verfahrensauswahl bzw. Entwicklungsstrategie. / Thermochemical surface hardening enables a precipitation-free solvation of carbon or nitrogen on interstices of the austenitic crystal lattice. However, the interplay of the diffusion mechanisms with the structural properties of thermal spray coatings has not yet been understood. Thermal spraying of surface-hardened powders is a further opportunity, where the phase stability of the feedstock material is of crucial importance. A process and parameter study is conducted on high velocity oxy-fuel and atmospheric plasma spraying of AISI 316L considering both basic concepts. Structural and process-specific influence factors are examined for the different coating systems in comparison to the bulk material reference. Correlation effects are determined allowing for an application-oriented process selection or development strategy.

A solution-hardening of AISI 316L stainless-steel powder was conducted. The expansion of the crystal lattice and a strong increase in the nanoindentation hardness confirm the successful diffusion of carbon and nitrogen in the interstices. A multiphase state of the powder feedstock with phase fractions of the metastable S-phase (expanded austenite) mainly at the particle’s edge, and the initial austenitic phase within the core was found. Thermal spraying using high velocity oxy-fuel (HVOF) and atmospheric plasma spraying (APS) prove the sufficient thermal stability of the Sphase. Microstructural investigations of the HVOF coating reveal the ductility of the S-phase layer, while the higher heat load within the APS cause diffusion processes with the initial austenitic phase. The lattice expansion and the nanoindentation hardness decrease during thermal spraying. However, the absence of precipitates ensures the sufficient heat stability of the metastable S-phase. Even though further efforts are required for the thermochemical treatment of powder feedstock, the results confirm the feasibility of the novel powder treatment approach.

Gas nitriding is known as a convenient process to improve the wear resistance of steel components. A precipitation-free hardening by low-temperature processes is established to retain the good corrosion resistance of stainless steel. In cases of thermal spray coatings, the interstitial solvation is achieved without an additional surface activation step. The open porosity permits the penetration of the donator media and leads to a structural diffusion. An inhomogeneous diffusion enrichment occurs at the single spray particle edges within the coating’s microstructure. A decreasing diffusion depth is found with increasing surface distance. The present study investigates an adjusted process management for low-temperature gas nitriding of high velocity oxy-fuel-sprayed AISI 316L coatings. To maintain a homogeneous diffusion depth within the coating, a pressure modulation during the process is studied. Additionally, the use of cracked gas as donator is examined. The process management is designed without an additional surface activation step. Regardless of surface distance, microstructural investigations reveal a homogeneous diffusion depth by a reduced processing time. The constant hardening depth allows a reliable prediction of the coatings’ properties. An enhanced hardness and improved wear resistance is found in comparison with the as-sprayed coating condition.