Esta dissertação, investiga o comportamento em fadiga da liga Ti-6Al-4V após o tratamento superficial denominado oxidação térmica, para aplicação em pinos fusíveis mecânicos. A oxidação térmica controlada do titânio e suas ligas apresenta propriedades interessantes na resistência à corrosão-desgaste, devido a sua alta estabilidade e dureza, contudo, há lacunas na literatura se esse benefício é recíproco nas propriedades da vida em fadiga. Corpos-de-prova foram tratados termicamente em atmosfera de ar ambiente e após foram submetidos a ensaios de rugosidade, metalografia, dureza, tração, fadiga e análise fractográfica. Os resultados obtidos em fadiga foram comparados com a mesma liga não oxidada, mostrando que as propriedades em fadiga não são recíprocas às propriedades de corrosão-desgaste da liga Ti- 6Al-4V, após o tratamento superficial de oxidação térmica. Enquanto para uma determinada condição de tratamento superficial, houve melhora de até 30x na resistência à corrosãodesgaste (redução de 97% na taxa de desgaste), nas propriedades mecânicas houve redução de 18% no limite de resistência à fadiga. / This dissertation investigates the fatigue behavior of thermally oxidized Ti-6Al-4V alloy, applied to break bolts. The controlled thermal oxidation of titanium and its alloys presents interesting properties in fretting-corrosion resistance, especially to the high stability and hardness. However, there are gaps in the literature regarding the effect of this oxide layer on fatigue properties. Thermally Oxidized specimens were tested for roughness, metallography, hardness, tensile strength, fatigue and fractographic analysis. The results were compared with the fatigue results of the same alloy when untreated, showing that the fatigue properties and the fretting-corrosion properties of thermally oxidized Ti-6Al-4V are not reciprocal. While with a given condition for the thermal oxidation, an improvement up to 30x occurred on fretting-corrosion resistance (97% reduction in the rate of wear), the endurance decreased 18%.

Esta dissertação, investiga o comportamento em fadiga da liga Ti-6Al-4V após o tratamento superficial denominado oxidação térmica, para aplicação em pinos fusíveis mecânicos. A oxidação térmica controlada do titânio e suas ligas apresenta propriedades interessantes na resistência à corrosão-desgaste, devido a sua alta estabilidade e dureza, contudo, há lacunas na literatura se esse benefício é recíproco nas propriedades da vida em fadiga. Corpos-de-prova foram tratados termicamente em atmosfera de ar ambiente e após foram submetidos a ensaios de rugosidade, metalografia, dureza, tração, fadiga e análise fractográfica. Os resultados obtidos em fadiga foram comparados com a mesma liga não oxidada, mostrando que as propriedades em fadiga não são recíprocas às propriedades de corrosão-desgaste da liga Ti- 6Al-4V, após o tratamento superficial de oxidação térmica. Enquanto para uma determinada condição de tratamento superficial, houve melhora de até 30x na resistência à corrosãodesgaste (redução de 97% na taxa de desgaste), nas propriedades mecânicas houve redução de 18% no limite de resistência à fadiga. / This dissertation investigates the fatigue behavior of thermally oxidized Ti-6Al-4V alloy, applied to break bolts. The controlled thermal oxidation of titanium and its alloys presents interesting properties in fretting-corrosion resistance, especially to the high stability and hardness. However, there are gaps in the literature regarding the effect of this oxide layer on fatigue properties. Thermally Oxidized specimens were tested for roughness, metallography, hardness, tensile strength, fatigue and fractographic analysis. The results were compared with the fatigue results of the same alloy when untreated, showing that the fatigue properties and the fretting-corrosion properties of thermally oxidized Ti-6Al-4V are not reciprocal. While with a given condition for the thermal oxidation, an improvement up to 30x occurred on fretting-corrosion resistance (97% reduction in the rate of wear), the endurance decreased 18%.

CoordenaÃÃo de AperfeiÃoamento de Pessoal de NÃvel Superior / O lÃquido da castanha de caju (LCC) à constituÃdo de uma mistura de fenÃis com uma longa cadeia alquilÃca na posiÃÃo meta, possuindo diferentes graus de insaturaÃÃes. O estudo cinÃtico da degradaÃÃo termooxidativa a 140ÂC de filme de poli(1,4-cis-isopreno) sintÃtico (PIS), na ausÃncia e presenÃa do LCC tÃcnico e natural e seus derivados (Ãcido anacÃrdico, cardol, cardanol, cardanol hidrogenado e cardanol hidrogenado e alquilado), foi monitorado por espectroscopia na regiÃo do infravermelho atravÃs do acompanhamento da absorbÃncia relativa das bandas em 3450 cm-1, 1720 cm-1 e 835 cm-1. O tempo de induÃÃo (τi) e as constantes aparentes de velocidade para a formaÃÃo de produtos contendo hidrÃxido (kOH) e carbonila (kC=O) e para o consumo das ligaÃÃes duplas da cadeia (kC=C) foram os parÃmetros utilizados. Todos os materiais estudados apresentaram efeito estabilizante na degradaÃÃo tÃrmica do PIS, evidenciado pelo aumento do tempo de induÃÃo e a diminuiÃÃo das constantes aparentes de velocidade. AnÃlise das variaÃÃes de kOH, kC=O, kC=C e τi indica que o mecanismo de aÃÃo independe dos derivados do LCC. A maior efetividade dos derivados do LCC tÃcnico à prÃxima a 3 % (m/m), com exceÃÃo do cardol e HAlqcardanol. Por outro lado, a maior efetividade dos derivados do LCC natural (cardol e cardanol) à prÃxima a 2 % (m/m), com exceÃÃo do Ãcido anacÃrdico e do prÃprio LCC. A atividade antioxidante dos derivados do LCC depende da quantidade de material polimerizado presentes neles. Baseado nos parÃmetros cinÃticos, a ordem de atividade antioxidante para os derivados do LCC tÃcnico foi: LCC > cardol >> cardanol ≅ cardanol hidrogenado e alquilado > cardanol hidrogenado. Para os derivados do LCC natural a ordem foi: cardol > cardanol >> LCC natural >> Ãcido anacÃrdico. AnÃlise termogravimÃtrica revela que a adiÃÃo de derivados do LCC provoca estabilizaÃÃo do PIS quando degradado tanto em atmosfera de nitrogÃnio, como em ar sintÃtico. Os antioxidantes comerciais testados: IPPD (N-isopropil-N-fenil-p-fenileno-diamina), DPPD (N,Nâ-fenil-p-fenileno-diamina), Banox H (2,2,4-trimetil-1,2-dihidroquinolina-polimerizado) e Banox S (fenol estirenado) apresentaram uma atividade bastante superior, com exceÃÃo do BHT (2,6-di-terc-butil-4-metil-fenol). Dentre os derivados do β-naftol, o AO-3 (1,6-diamino-β-naftol) apresentou uma atividade antioxidante similar ao IPPD, embora com menores valores de constantes aparentes de velocidade. Por outro lado, os derivados AO-1 (6-N-etil, N-etilamino-β-naftol) e AO-2 (6-N-etil,N-dietilamino-β-naftol) apresentaram uma atividade antioxidante um pouco superior que os derivados do LCC, mas inferior ao AO-3. / Cashew nut shell liquid (CNSL) is a mixture of meta-alkyl-phenols which varies on its degree of unsaturation attached to the benzene nucleus. The kinetic study of the thermal degradation at 140ÂC of synthetic cis-1,4-polyisoprene film, in the absence and presence of technical and natural CNSL and some derivatives (anacardic acid, cardol, cardanol, hydrogenated cardanol and alkylated hydrogenated cardanol) was carried out by infrared spectroscopy through the evolution of the relative absorbance of the bands in 3450 cm-1, 1720 cm-1 and 835 cm-1. The amount of hydroxyl and carbonyl group formed and also of carbon double bond consumed during the degradation was determined. All material studied showed antioxidant activity that was verified by an increase in the induction period and a decrease in the apparent rate constants of thermal-oxidation. The antioxidant effectiveness is higher for the addition of 3% (w/w) of technical CNSL derivatives, except for alkylated cardanol. The antioxidant effectiveness is higher for the addition of 2% (w/w) of natural CNSL derivatives, except for anacardic acid and pure. Based on kinetic parameters the order of antioxidant activity for technical CNSL derivative was: CNSL >> cardanol ≅ hydrogenated and alkylated cardanol >> hydrogenated cardanol. For natural CNSL components the order was: cardol > cardanol >> CNSL >> Anacardic acid. Thermogravimetric analyses reveals that the addition of LCC derivatives provide stabilization of PIS in atmosphere of nitrogen, as well as in synthetic air. The commercial antioxidants: IPPD (N-isopropyl-N-phenil-p-phenilene-diamine), DPPD (N,Nâ-phenil-p- phenilene-diamine), Banox H (2,2,4-trimethyl-1,2-dihidroquinoline-polimerizade) and Banox S (phenol styrened) presented a quite superior activity, except for BHT (2,6-di-terc-buthyl-4-methyl-phenol. Among β-naftol derivatives, AO-3 (1,6-diamine-β-naftol) presented a similar antioxidant activity to IPPD, although with smaller values of the apparent rate constants. On the other hand, the derivatives AO-1 (6-N-ethyl, N-ethylamine-β-naftol) and AO-2 (6-N-ethyl,N-diethylamine-β-naftol) presented a quite superior antioxidant activity when compared to LCC derivatives, but inferior to AO-3.

Abstract While numerous publications deal with the properties and applications of porous silicon (PS), some of the related topics are not complete or could be investigated from different aspects. Therefore, the main objective of this thesis is to provide novel information associated with the optical and chemical properties of PS. For the investigations, various PS samples are manufactured by electrochemical dark etching of boron-doped p+-type Si wafers. Amongst others, (i) the wavelength-dependent refractive indices of freestanding PS monolayers having different porosities were obtained from optical transmission and reflection spectra in the 700–1700 nm wavelength range, and compared to those calculated from Bruggeman's effective medium approximation (EMA). The refractive indices of the PS samples are shown to be described well with the EMA. In addition, optical scattering at the air-PS interface was demonstrated. (ii) Multilayer stacks are created by alternating the porosities of PS layers within the same sample to form Bragg filters. The Bragg conditions of the filters are calculated and compared to optical transmission measurements. (iii) The oxidation of PS membranes in dry air is investigated with emphases on the reaction kinetics and on the structural changes of the porous matter. As revealed, oxidation proceeds faster in PS than in Si bulk. The formed SiO2 is amorphous and causes stress in the lattice of the residual Si skeleton. (iv) The effect of oxidation extent of PS layers on the growth mechanism of multi-walled carbon nanotubes (CNTs) is investigated. The density of the CNT network is found proportional to the oxidation extent of the substrates. (v) Finally, the chemically-reductive nature of PS is studied and exploited via the immersion plating method to deposit palladium and silver nanoparticles in the nanopores and on the surface of PS samples. The presented novel results have potential in silicon-based technologies, including integrated active and passive optical components (waveguides, filters, antireflection coatings, optical gas/liquid sensors), electronic devices (electrochemical gas/liquid sensors, diodes, field effect devices) and selective chemical catalysis (substrates, growth templates).

No description available.

No description available.

Cette thèse porte sur l’étude multi-échelle du vieillissement d’assemblages collés à base de colle époxy employés dans le domaine aéronautique. Dans leurs conditions de service, ces matériaux sont soumis à un vieillissement humide, qui peut s’accompagner d’un vieillissement thermique essentiellement lors des phases de décollage des avions. De telles conditions rendent difficiles la prédiction de la durée de vie basée uniquement sur le suivi des propriétés mécaniques des assemblages (par des tests de cisaillement simple ou de clivage) lors d’essais de vieillissement normalisés qui prévalent, pour le moment, dans l’industrie. Notre objectif était donc une étude du vieillissement à l’échelle moléculaire afin d’en dériver, à terme, des lois cinétiques prédisant la vitesse de dégradation. Une première étape a mis en lumière les différences existantes entre le vieillissement humide (rupture adhésive) et thermique (rupture cohésive). La rupture cohésive observée en vieillissement thermique nous a conduits à étudier les mécanismes responsables de la chute de ténacité des époxys. Nous avons ainsi étudié les mécanismes de dégradation de l’adhésif, de deux de ses systèmes « représentatifs » (DGEBA-DDS et TGMDA-DDS). L’analyse des produits de dégradation dans ces réseaux et leurs composées modèles nous a conduits à élaborer un schéma cinétique intégrant la réactivité des principaux sites d’oxydation (sites au voisinage de certains hétéroatomes) qui peut décrire en partie l’oxydation des systèmes simples DGEBA-DDS et TGMDA-DDS mais devra être converti en modèle de co-oxydation (c’est-à-dire intégrant la participation simultanée de plusieurs sites) à la fois pour décrire plus complétement l’oxydation des systèmes simples mais surtout pour traiter des matériaux industriels de formulation complexe. Dans une dernière partie, nous nous sommes intéressés à la spécificité des assemblages collés lors d’un vieillissement humide. Cette dernière partie montre la nécessité de bien comprendre les phénomènes de diffusion à l’interface, et dans des matériaux oxydés, pour pouvoir prédire la durée de vie des adhésifs époxys employés pour les assemblages collés. / This thesis deals with a multi-scale study of the ageing of bonded assemblies based on epoxy adhesive used in the aeronautical field. In service conditions, these materials are subjected to humid ageing, which can be accompanied by thermal ageing essentially during the take-off phases of aircraft. Such conditions make it difficult to predict lifetime based only on the study of the mechanical properties of the assemblies (by single lap shear stress or wedge tests) in standardized ageing tests, which, for the moment, prevail in the industry. Our objective was therefore a study of ageing at the molecular scale in order to derive forward kinetic laws predicting the kinetics of degradation. A first step highlighted the differences between humid ageing (adhesive failure) and thermal aging (cohesive failure). The cohesive rupture observed in thermal ageing led us to study the mechanisms responsible for the decrease in toughness of the epoxies. We studied the mechanisms of degradation of the adhesive as well as two of its "representative" systems (DGEBA-DDS and TGMDA-DDS). The analysis of degradation products in these networks and their model compounds led us to develop a kinetic scheme introducing the reactivity of the main oxidation sites (site near certain heteroatoms) which can partly describe the oxidation of simple systems. In the future, DGEBA-DDS and TGMDA-DDS will have to be converted into a co-oxidation model (that means integrating the simultaneous participation of several sites) to describe entirely the oxidation of simple systems but especially for handled industrial materials of complex formulation. In a last part, we were interested in the specificity of bonded assemblies during humid aging. This last section displays the need to understand diffusion phenomena at the interface, and in oxidized materials, to predict the lifetime of epoxy adhesives used for bonded assemblies.

Les élastomères à base d’Ethylène Propylène Diène Monomère (EPDM) sont utilisés dans les accessoires du réseau de distribution d’électricité sous-terrain pour assurer l’isolation des jonctions de câbles. En effet, la structure chimique de ce polymère est apolaire et induit donc l’hydrophobicité désirée pour cette application. Cependant, en conditions de service, la thermo-oxydation provoque l’incorporation d’atomes d’oxygène (formation de fonctions hydrophiles) aux chaines EPDM. Ainsi, l’objectif de cette thèse était d’étudier l’influence du vieillissement thermo-oxydant sur les propriétés de transport d’eau dans les accessoires en EPDM. Trois formulations d’EPDM sans charges (une réticulée au peroxyde et deux autres réticulées au soufre) ainsi que six formulations industrielles (toutes réticulées au soufre) ont subi un vieillissement thermique accéléré en étuve ventilée d’air entre 90 et 190°C. L’analyse multi-échelle (combinant plusieurs techniques expérimentales) a permis de mettre en évidence les modifications structurales dans les matrices EPDM et d’établir des corrélations entre les propriétés physico-chimiques mesurées au cours du vieillissement. Les propriétés de transport d’eau ont ensuite été caractérisées entre 30 et 70°C et entre 10 et 100 % HR à l’état initial et pour différents états d’oxydation. Ces résultats ont permis d’établir des relations structure/propriété entre les propriétés de transport d’eau et l’incorporation d’oxygène, mais aussi de simuler l’influence cruciale des charges. / Ethylene Propylene Diene Monomer (EPDM) based elastomers are used in the accessories of the underground electrical distribution network for guaranteeing the insulation of cable junctions. Indeed, the chemical structure of this apolar polymer gives the desired hydrophobicity for this application. However, in service conditions, thermo-oxidation causes an incorporation of oxygen atoms (formation of hydrophilic function) into EPDM chains. Thus, this PhD thesis aimed at studying the influence of thermal oxidative ageing on the water transport properties into EPDM accessories. Three unfilled formulations (one peroxide crosslinked and two sulfur vulcanized) and six industrial formulations (all vulcanized) were submitted to an accelerated thermal ageing in air-ventilated ovens between 90 and 190 °C. The multi-scale analysis (combining several experimental techniques) allowed highlighting the structural changes in EPDM matrices and establishing correlations between the physico-chemical properties measured during ageing. Then, the water transport properties were characterized between 30 and 70 °C and between 10 and 100 %RH at the initial state and for different oxidation states. These results allowed establishing structure/property relationships between water transport properties and oxygen incorporation, but also to simulate the crucial influence of fillers.

The main purpose of this thesis was to compare GAC adsorption method, VOCs incinerationmethod and Non-treatment alternative by using LCA to find which method or alternative isenvironmentally preferable. The LCA framework proposed by ISO 14040 (1997) has beenconsidered in this research. The comparison was made by considering a flue gas contaminatedby toluene (with three different concentration 100, 1000, 2000 mg/m3). The plant locationwhere the polluted flue gas is emitted has been assumed to be located in Borås, Sweden. Theflow rate of emitted flue gas was 10000m3/hr. The present thesis report contains two mainparts.The results of LCA showed that when the toluene concentration is low (< 100 mg/m3), GACadsorption method, Non-treatment alternative and VOCs incineration method are respectivelypreferable from environmental point of view. On the other side, when the tolueneconcentration of inlet stream is high (>1000 mg/m3), the order of GAC adsorption method,incineration and Non-treatment alternative is more desirable. Furthermore, the resultsillustrated that as toluene plays the role of fuel as a hydrocarbon, VOCs incineration methodis much more suitable when toluene concentration is high due to lower demand on additionalfuel. In the other words, high toluene concentration of influent leads to less environmentalimpact when VOCs incineration method is exploited. Conversely, the environmental impactof GAC adsorption method is increased when the inlet concentration of toluene is escalated.In overall, the weighted result showed that GAC adsorption method is the most preferablemethod while Non-treatment alternative is the worst.

The thermal oxidation of titanium alloys is a technique studied to improve the tribological performance, despite its evidences of loss of performance in fatigue. Thermal oxidation treatment of Ti-6Al-4V alloy was performed in air at 600 °C for 2, 5 and 10 h. The fatigue behavior were evaluated and compared with those of the untreated one. The characterization was performed through optical and electronic microscopy, x-ray diffraction, microhardness and roughness measurements. The results of the XRD showed a growth of the rutile peaks when increasing the treatment time from 2 to 10 h. Microhardness and roughness were also elevated by increasing treatment time up to 10 h. There was an increase in mean thickness from 0.12 μm to 1.09 μm, increasing the treatment duration from 2 to 5 h. The results indicated a reduction in the fatigue limit of samples subjected to oxidation. The results indicated a reduction of 35% for oxidized samples for 2 h, 27% for oxidized samples for 5 h and 29% for samples treated for 10 h, in relation to the test with untreated specimens. The detrimental effect caused by the layer formed after oxidation for 2 h was as damaging as that caused by the layer formed after 10 h, even if presented with a higher thickness. The morphology found in the fractured samples indicated embrittlement on the surface of the oxidized samples, contributing to the nucleation of initial cracks in the layer that favored the propagation of fatigue, independent of the layer thickness. / A oxidação térmica de ligas de titânio é uma técnica estudada para melhorar o desempenho tribológico, apesar das evidências de perda de desempenho em fadiga. O tratamento de oxidação térmica da liga Ti-6Al-4V foi realizado ao ar a 600 °C durante 2, 5 e 10 h. O comportamento à fadiga foi analisado e comparado com a condição não tratada. Foi feita caracterização através de análise por microscopia ótica e eletrônica, difração de raios-x, microdureza e medição da rugosidade. Os resultados do DRX demonstraram crescimento dos picos de rutilo ao elevar o tempo de tratamento até 10 h. Observou-se, também, elevação da microdureza e da rugosidade ao elevar o tempo de tratamento até 10 h. Verificou-se um aumento na espessura média da camada formada de 0,12 μm para 1,09 μm ao elevar a duração do tratamento de 2 para 10 h. Os resultados apontaram redução de resistência a fadiga de 35 % para amostras oxidadas durante 2 h, 27 % para amostras oxidadas por 5 h e 29 % para as amostras tratadas durante 10 h, em relação ao ensaio com corpos de prova não submetidos ao tratamento. O efeito prejudicial causado pela camada formada após oxidação de 2 h foi tão danoso quanto o causado pela camada formada após 10 h, apesar da diferença entre as espessuras da camada. A morfologia encontrada nas amostras fraturadas indicou fragilização na superfície das amostras oxidadas, contribuindo para a nucleação de trincas iniciais na camada que favoreceram a propagação de fadiga, independendo da espessura de camada. / São Cristóvão, SE