No description available.

No description available.

While it has long been known that water flow can influence non-uniform corrosion of copper pipe (Rushing 2002, Marshall 2004), it has never previously been considered a primary contributor to the problem. This work is the first to describe a fundamentally important phenomenon in aqueous non-uniform corrosion: flow electrification. A conceptual framework for flow electrification was developed from prior work on non-aqueous fluid flow in pipes, where the primary concern was prevention of electrical explosions. Thereafter, a series of experiments was aimed at monitoring flow electrification, quantifying its practical effects, and examining aspects of non-uniform copper corrosion in real situations. Under conditions with little or no flow, in a high pH and high chlorine water known to cause pinholes in copper pipes, while water chemistry influenced corrosion, non-uniform corrosion was not sustained. But when flowrates were higher, flow electrification contributed to severe and sustained non-uniform corrosion, with the most serious attack manifested in the first section of pipe that encountered the flowing water. The magnitude of flow electrification increased with chlorine concentration, pH and flowrate. Containers dosed with inhibitors such as zinc or phosphate experienced lower electrification, current, voltage, scale resistance, and corrosion potential measurements when compared to a control without an inhibitor. Additionally, systems dosed with inhibitors had reduced rate of chlorine decay, weight loss, pit density and/or maximum depth. Zinc orthophosphate had the largest positive impact on electrochemical measures of pitting. However, experimental studies suggested that if zinc orthophosphate was dosed to a system for a period of time, and dosing was then stopped, very serious pitting could occur. A practical case study seemed to strongly confirm this hypothesis in one system. The presence of sulfides caused the separation of anode and cathode along a pipe section, from electrification, to reverse relative to what was observed in the system with high chlorine and high pH. Below a certain level of sulfides, electrification ceased. It seems likely, based on measurement of electrochemical potential (Ecorr) in waters of this type as a function of sulfide concentration, that the onset of pitting would be associated with decreasing Ecorr with time. If so, the fundamental basis of tracking Ecorr rise with time to predict pitting propensity would be invalidated. Electrochemical noise programs were applied to try to differentiate between systems of low and high pitting propensity. Amplitudes of potential noise and current noise measurements drastically increased with the presence of sulfides or chlorine, confirming that tracking electrochemical noise may indicate the presence of a pitting agent. However, the electrochemical noise measurements are at best, an indirect indicator of copper pitting, and their interpretation is complicated by the co-occurrence of flow electrification. Attempts were made to apply these insights to a case study examining pitting in two real waters in Maryland and to examine the effects of orthophosphate, chlorination, chloramination and enhanced coagulation on copper pitting propensity. Tracking of Ecorr suggested that the control water (without phosphate) had the greatest pitting propensity. The free chlorine system with orthophosphate maintained Ecorr values below the control signifying that the presence of phosphate lowered the corrosion propensity. Waters with chloramine and phosphate had the lowest Ecorr values and also had the least variability in Ecorr due to the stability of the disinfectant. There is considerable ambiguity in the results, since the copper pipes exposed to the waters in question did not develop serious pitting over the several months of the study. / Master of Science

[pt] Aços inoxidáveis duplex (AIDs) são aços que apresentam boas propriedades mecânicas e de resistência à corrosão, devido a microestrutura composta de, aproximadamente, partes iguais de austenita e ferrita. A exposição dos AIDs a altas temperaturas, durante um processo de soldagem por exemplo, pode resultar na formação de intermetálicos numa faixa de temperatura entre 1000 e 600 C, bem como numa mudança microestrutural na faixa de temperatura de 1200 e 800 C. Estes podem reduzir as propriedades da junta soldada principalmente zona termicamente afetada pelo calor (ZTA), como por exemplo em corrosão em meio cloreto. No entanto, durante processos de fabricação ou de manutenção, tratamentos térmicos ou soldagem, as propriedades do material podem ser alteradas, bem como a resistência à corrosão por pites. O presente estudo tem como objetivo correlacionar as microestruturas obtidas por diferentes taxas de resfriamento, sendo estas microestruturas obtidas por simulação, equivalente aquela obtida em soldagem, a qual corresponde a um regime de não-equilíbrio, com a microestrutura obtida em um regime de equilíbrio e determinar como estas transformações afetam a resistência a corrosão. O estudo foi realizado para dois tipos de AIDs: o UNS S32304 e o UNS S32750. Foram obtidas microestruturas equivalentes a zona termicamente afetada (ZTA) por meio do simulador Gleeble utilizando dois aportes de calor 1,0 e 3,0 KJ/mm, e por tratamentos térmicos realizados a 1000 e 1100 C por 24, 72 e 240 horas seguidas de têmpera em água. A análise microestrutural foi realizada por meio de microscopia ótica (MO) e microscopia eletrônica de varredura (MEV), para caracterização da morfologia de fases, quantificação das fases e caracterização química das fases. Foi determinada a microdureza das fases, a dureza e realizado ensaio de corrosão (ASTM G48). A fração volumétrica da fase austenita das amostras que foram tratadas termicamente reduziu com o aumento do tempo e da temperatura de tratamento, enquanto para as amostras simuladas termicamente diminuiu com a diminuição do aporte térmico para ambos os AIDs. Na avaliação da resistência a corrosão por pites foi observado que o aumento da temperatura de tratamento térmico igualou os valores de Pitting Resistance Equivalent Number (PREN) das fases (austenita e ferrita) devido ao equilíbrio termodinâmico dos elementos nas fases, desta forma a amostra tratada termicamente na temperatura de 1250 C por 24 horas obteve melhor resistência à corrosão por pites para ambos AIDs. Para as amostras simuladas termicamente, o aporte de 3 KJ/mm obteve melhor resultado de resistência à corrosão por pites em ambos os AIDs. / [en] Duplex stainless steels (DSSs) are steels that have good mechanical properties and corrosion resistance due to the microstructure comprised of about equal parts of austenite and ferrite. Exposure of DSSs to high temperatures, during a welding process for example, result in formation of intermetallics in the temperature range of 1000 to 600 C, including a microstructural change between 1200 to 800 C. These can reduce the properties of the welded joint, especially the heat affected zone (HAZ), such as corrosion in chloride environment. However, during manufacturing or maintenance processes, either by heat treatment or welding processes, the properties of the material can be together with the pitting resistance corrosion. The present study aims to correlate the microstructures obtained by different cooling rates, being these microstructures obtained by simulation, equivalent to that obtained in welding, which is equivalent to a non-equilibrium regime, with the microstructure obtained in an equilibrium regime and to determine how these transformations affect the corrosion resistance. The study was conducted for two DSSs: UNS S32304 and UNS S32750. HAZ equivalent microstructures were obtained by the Gleeble simulator for two heat inputs 1.0 and 3.0 KJ/mm, and the heat treatments were performed at 1000, 1100 and 1250 C for 24, 72 and 240 hours followed by quenching in water. Microstructural analysis was performed by optical microscopy and scanning electron microscopy (SEM) to characterize the phase morphology, quantification and chemical composition. The microhardness of the phases, the hardness and corrosion test (ASTM G48) were determined. The volumetric fraction of the austenite phase of the samples that were heat treated decreased with increasing time and temperature treatment, while for the thermally simulated samples it decreased with the decrease of the heat input for both DSSs. The evaluation of the pitting corrosion resistance it was observed that the increase of the heat treatment temperature equaled the phases (austenite and ferrite) Pitting Resistance Equivalent Number (PREN) values due to the thermodynamic balance of the elements in the phases, thus the heat-treated sample at 1250 C for 24 hours showed better pitting corrosion resistance for both AIDs. For the thermally simulated samples, the heat input of 3 KJ/mm obtained better result of pitting corrosion resistance in both AIDs.

Undersökning av hur elektrolytkontamination på ventilen på prismatiska litiumjonbattericeller påverkar legeringsytan och påverkar batteriets säkerhet. Åldringsstudier utförs för att påskynda interaktionen av elektrolytförorenade batteriventiler vid önskade miljöförhållanden. Materialegenskaper hos elektrolyt och batteriventil studeras. Ytmorfologin och ventilens mekaniska prestanda analyseras. / Investigation of how electrolyte contamination on the vent of prismatic lithium-ion battery cells affects the alloy surface and impacts the safety of the battery. Ageing studies are carried-out to accelerate the interaction of electrolyte contaminated battery vent at desired environmental conditions. Material properties of electrolyte and battery vent are studied. The surface morphology and mechanical performance of the vent are analyzed.

Rolling contacts are utilized in many technical applications, both in bearings and in the contact between gear teeth. These components are often highly loaded, which makes them susceptible to suffer from rolling contact fatigue. This work focuses on the rolling contact fatigue mechanism of pitting. In order to attain a better understanding of why pitting initiates and grows, detailed simulations of rolling contacts have been performed. In particular the contact between two gears in a truck retarder was here used as a case study. The investigated contact experienced elastohydrodynamic lubrication conditions since the load was high enough to causes the surfaces in contact to deform and the viscosity of the lubricant to increase significantly. In Paper A it was investigated if surface irregularities in the size of the surface roughness are large enough to cause surface initiated fatigue. The investigation focused on the pitch line since small surface initiated pits were found here even though there was no slip present. Since there were pits present at the pitch line, it is important that the theories of pitting can explain the development of pits also in the absence of slip. The conclusion of the work was that surface irregularities of the size of normal surface roughness are enough to cause surface initiated fatigue at the pitch line. In Paper B it was investigated why pits are more likely to initiate in the dedendum of pinion gears than in the addendum. In both areas slip is present but in different directions. In the dedendum the friction from slip is against the rolling direction which enhances the risk for pitting. The investigation was performed by studying the effect of the temperature rise in the contact caused by the slip. The conclusion drawn was that the temperature rise in the contact explained why pitting was more common in the dedendum than in the addendum. / Rullande kontakter förekommer i många applikationer, till exempel i lager och mellan kugghjulständer. Både lager och kugghjul utsätts ofta för höga laster vilket gör att dess ytor löper stor risk att utmattas, vilket kallas rullande kontaktutmattning. Denna studie fokuserar på pitting, även kallat spalling, vilket är en typ av rullande kontaktutmattning där en utmattninsspricka växer fram som får delar av ytan att ramla av. För att få en bättre förståelse varför pittingskador uppkommer har noggranna simuleringar utförts av rullande kontakter. Kontakten mellan två tänder på kugghjul i en lastbilsretarder har används som underlag då många pittingskador påträffats på dem.  För att minska friktionen och nötningen i kontakten mellan kuggtänderna användes smörjmedel. De höga lasterna lastbilsretardern utsattes för deformerade kuggarnas ytor elastiskt samtidigt de kraftigt ökade viskositeten hos smörjmedlet. Dessa förhållanden gör att kontakten kallas för elastohydrodynamiskt smord, vilket på engelska förkortas till EHL. I Artikel A undersöktes om små ytojämnheter kan orsaka ytinitierade pittingskador. Eftersom skadan påträffats i friktionslösa kontakter, så som vid rullcirkeln på de undersökta kugghjulen, är det viktigt att teorierna som förklarar uppkomsten inte är beroende av friktion. Undersökningen fokuserade därför på förhållandena vid rullcirkeln.  Slutsatsen från arbetet var att små ytojämnheter, av samma storleksordning som ytojämnheterna på de undersökta kugghjulen, är tillräckligt stora för att orsaka utmattningsskador. I Artikel B undersöktes varför det är vanligare att pitts initieras i dedendum än addendum på drivande kugghjul. Kontakten på båda sidorna om rullcirkeln slirar svagt åt olika håll. Att kontakten slirar skapar friktion som är motriktad rullriktningen i dedendum vilket ökar risken för pittingskador. För att undersöka varför dessa förhållanden ökar risken för skador fördjupades analysen av kontakten genom att inkludera temperaturfältet. Simuleringarna visade att temperaturen ökar genom kontakten vilket orsakar en asymmetrisk spänningsfördelning. Denna asymmetriska spänningsfördelning gör att ytojämnheter i dedendum är troligare att orsaka skador än ytojämnheter i addendum. / <p>QC 20180213</p>

No description available.

Résumé : Pour se propager dans les cellules de son hôte et évader les réponses immunitaires, les virus végétaux ont développé plusieurs stratégies de défense. Ici, nous avons investigué les structures génétiques du Apple stem pitting virus (ASPV). Nous avons aussi étudié la diversité moléculaire des isolats d’ASPV provenant des poires en regardant les séquences des gènes CP et TGB afin de mieux comprendre les mécanismes évolutionnaires utilisés par ASPV. Nos études ont démontré que les mutations, incluant les insertions et les délétions, la sélection purificatrice et la recombinaison furent des facteurs importants dans l’évolution du l’ASPV en Chine et possiblement mondialement. Comme tous les virus végétaux, l’ASPV se défend contre le RNA silencing de l’hôte grâce à un suppresseur de RNA silencing (VSR) et nous avons montré que le VSR de l’ASPV est la protéine de capside (CP) du virus. Nous avons aussi établi que la diversité moléculaire cause non seulement une variété de symptômes chez son hôte, Nicotiana occidentalis. Cependant elle cause aussi de la variabilité antigénique chez différents isolats, ce qui mène à des écarts de réactivité sérologique entre isolats. Les plantes ont développé plusieurs stratégies pour se défendre contre les virus. Ici, nous avons étudié comment la plante Arabidopsis se défend contre le Tobacco rattle virus (TRV) via le RNA silencing. Nous avons constaté que les phénomènes de susceptibilité, récupération et virus induced gene silencing (VIGS) sont des mécanismes séparables. Nous avons démontré que les protéines AGO2 et AGO4 sont nécessaires à la susceptibilité initiale au TRV, tandis qu’AGO1 est importante pour les VIGS, tandis que la récupération est médiée par d’autres acteurs qui n’ont pas encore été identifiés. Nos résultats suggèrent l’existence de complexes distincts ciblant différentes populations d’ARN viral et cellulaire. De plus, nous avons montré que la répression de la traduction est un mécanisme important durant la récupération de la plante suite à une infection virale, et que les complexes de décoiffage et de RNA processing jouent des rôles importants dans la dégradation des ARNs viraux. Finalement, nous avons montré que les plantes ayant une mutation dans le gène DCP2 présentent un niveaux de VIGS accrue, ainsi qu’une augmentation des niveaux d’ARN viral. Puisque DCP2 fait partie des complexes de décoiffage qui se trouvent dans des granules spécialisés nommés processing bodies (PBs), cela suggère que les PBs jouent un rôle important dans l’élimination les virus. / Abstract : To live in host cells or to escape from host immunity, plant viruses involved a series of defense strategies. Here we investigated Apple stem pitting virus (ASPV) population structures and molecular diversity of ASPV pear isolates based on its function important gene CP and TGB in China, so as to infer the evolution mechanisms of ASPV. Our study showed that mutations (including insertions or deletions), purifying selection, and recombination were important factors driving ASPV evolutions in China or maybe even in the world. And also ASPV defends against it hosts by encoding a VSR. We also showed that ASPV molecular diversity not only induced different biological properties on its herbaceous host N. occidentails but also resulted in antigenic variation of different ASPV CP isolates, which leaded to differences in serological reactivity among rCPs of different ASPV isolates. Plants have developed a series of mechanisms to defend themselves against viruses. Here we how Arabidopsis defend against. We show that virus susceptibility, recovery, and virus induced gene silencing (VIGS) appear to be separable phenomena, with AGO2 and AGO4 playing important roles in the initial susceptibility to TRV, AGO1 playing an important role in VIGS, and as yet unidentifid players mediating recovery. These results suggest the existence of distinct RNA-induced silencing complexes that target different RNA populations within the cell and over time. Furthermore, we showed that translational repression of viral RNA is likely to play an important role in virus recovery and that decapping function plays an important role in clearing viral RNA from the cell. We also showed that a decapping mutant (DCP2) displayed an increased VIGS and virus RNA accumulation, an important role for PBs in eliminating viral RNA.

Este trabalho tem por objetivo estudar a eficiência dos oxiânions molibdato (MoO4 2-) e tungstato (WO4 2-) na inibição da corrosão localizada em aços inoxidáveis austeníticos (347 e 304L) em sistemas de água com alto grau de pureza na presença de íons cloreto (Cl-). Para avaliar a ação dos oxiânions estudados foram empregadas técnicas eletroquímicas de monitoramento do potencial de circuito aberto (Eoc), espectroscopia de impedância eletroquímica (EIS), polarização cíclica (PC) e cronoamperometria (CA). Para caracterização superficial foram utilizadas microscopia óptica (MO) e microscopia eletrônica de varredura (SEM). Os ensaios foram realizados em meios contendo somente água pura desoxigenada e água pura desoxigenada contendo íons cloreto (50, 100, 200, 300 e 500 ppm) variando a concentração (0, 10-4, 10-3 e 10-2 M) dos inibidores molibdato e tungstato de sódio. Todos os experimentos foram realizados à temperatura ambiente e em condições hidrodinâmicas controladas, empregando o sistema de eletrodo de disco rotativo (RDE) com velocidade constante de1200 rpm. Os resultados mostraram que os aços inoxidáveis 347 e 304L permanecem passivos em água pura, uma vez que o meio não é agressivo. Entretanto, a adição de íons cloreto tornou-os susceptíveis à corrosão por pites, pois os cloretos atuam como desapassivadores, fragilizando o filme passivo que fornece proteção aos aços inoxidáveis. O aumento da concentração dos íons cloreto no eletrólito aumentou a sua agressividade para os dois aços estudados, sendo observado o precoce aparecimento da corrosão. No entanto, a adição dos inibidores molibdato e tungstato de sódio melhorou a qualidade da camada passiva, aumentando os valores de potencial de pite (Ep) e de módulo de impedância, mantendo a passividade dos aços num amplo intervalo de potenciais. Ensaios cronoamperométricos mostraram que na presença dos oxiânions os valores medidos de densidade de corrente de resposta para os aços inoxidáveis 347 e 304L foram acentuadamente menores em relação aos valores obtidos na ausência dos mesmos, confirmando que os inibidores utilizados atuam na melhora da camada passiva, diminuindo a sensibilidade aos cloretos e conseqüentemente aumentando a resistência contra a corrosão por pites dos aços. O estudo mostrou que os melhores resultados para ambos os aços foram obtidos na presença de 10-2 M de inibidor, tanto para o tungstato quanto para o molibdato, sendo este com eficiência levemente melhor. Além disso, o aço 304L sem partículas incrustadas de alumina mostrou-se menos susceptível aos ataques dos cloretos do que o aço 347. Nas amostras que tiveram a superfície tratada com lixas de abrasivo de alumina, essas partículas foram incrustadas nos aços e isso levou ao desaparecimento de um potencial de pite bem definido. Na presença de alta concentração de cloretos, essas partículas foram arrancadas pelo ataque às regiões deformadas mecanicamente, localizadas ao redor das partículas incrustadas e as propriedades do aço em si puderam ser verificadas. / The aim of this work is to study the efficiency of molibdate (MoO4 2-) and tungstate (WO4 2-) oxianions in the inhibition of the localized corrosion in austenitic stainless steels (347 and 304L) in high purity water systems in the presence of chloride ions (Cl-). In order to evaluate the action of the oxianions electrochemical techniques as open circuit potential (OCP), electrochemical impedance spectroscopy (EIS), cyclic polarization (CP) and chronoamperometry (CA) were accomplished. For surface characterization optical microscopy (OM) and scanning electron microscopy (SEM) were used. The experiments were carried out in deoxygenated pure water and deoxygenated pure water containing chloride ions (50, 100, 200, 300 and 500 ppm) adding different concentrations (0, 10-4, 10-3 and 10-2 M) of molibdate and tungstate ions. All the experiments were performed at room temperature under controlled hydrodynamic conditions using a rotating disk electrode (RDE) at constant rotation speed of 1200 rpm. The results showed that 347 and 304L stainless steels remain passive in pure water, since the environment is not aggressive. However, in the presence of chloride ions they become susceptive to pitting corrosion, with chloride ions acting depassivity agents weakening the passive film that supplies protection to the stainless steels. The increase of chloride ions concentration in the electrolyte enhanced the aggressiveness for both steels evidenced by a precocious accurance of pitting corrosion. On the other hand, the addition of sodium molibdate and tungstate inhibitors improved the quality of the passive layer, increasing the pitting potentials (Ep) and the impedance modulus, improving the the passivity of steels a large of potential range. Chronoamperometric measurements showed that in the presence of oxianions response current density for 347 and 304L stainless steels was strongly diminished in relation to the values obtained in the absence of the inhibitors, confirming that the inhibitors act in the improvement of the passive layer, decreasing its sensitivity to chlorides and consequently increasing the steels resistance against pitting corrosion. Results showed that the best results for both steels were obtained in the presence of 10- 2 M tungstate or molibdate, being this latter with efficiency lightly better. Moreover, the 304L stainless steel showed to be less susceptive to pitting corrosion compared to 347 stainless steel. For stainless steel specimens previously treated with Al2O3 emery papers, Al2O3 particles become embedded in the steel surface and led to the indefinition of the pitting potential values. In the presence of high chloride concentrations, the mechanically affected region of steel in the surrounding of Al2O3 particles was attacked and Al2O3 particles were removed reveling the stainless steel own resistance to chlorides.

Nenhuma / A liga 800GN (grau nuclear) é um material utilizado na fabricação de geradores de vapor para reatores de água pressurizada (PWR) de usinas nucleares devido à sua elevada resistência à corrosão. A resistência à corrosão da liga 800GN é devida ao caráter protetor da película de óxido formada na superfície do tubo em contato com a água pressurizada à alta temperatura. No entanto, a corrosão tem sido a principal causa de falhas nos tubos dos geradores de vapor de usinas nucleares. Os problemas gerados pela corrosão têm sido atribuídos a condições e excursões da química da água do circuito secundário, muitos dos quais resultantes da entrada de água de refrigeração do condensador no circuito secundário. A experiência adquirida em diferentes centrais nucleares mostra que a composição química da água tem um papel importante na manutenção da integridade da película protetora de óxido formada na superfície do tubo. Neste trabalho foi avaliada a resistência à corrosão por pites de tubos da liga 800GN, em meio similar ao do circuito secundário de um reator PWR contendo teores de contaminação por íons cloreto de 250 ppb, 1 ppm, 5 ppm, 10 ppm e 50 ppm. A susceptibilidade dos tubos de liga 800GN ao processo de corrosão por pites foi avaliada em célula eletroquímica à temperatura de 80 C e em autoclave à temperatura de 250 oC, empregando-se a técnica eletroquímica de polarização anódica potenciodinâmica cíclica. A observação da morfologia da superfície das amostras após os ensaios eletroquímicos foi realizada por meio de microscopia ótica e microscopia eletrônica por varredura e microanálise por EDS (Energy Dispersive Spectrometry). A 80 C, a liga 800GN apresentou resistência à corrosão por pites, mesmo quando concentrações 5 ppm de Cl- foram adicionadas ao meio similar ao do ambiente secundário de um reator PWR. Corrosão por pites foi observada somente com a adição de 10 e 50 ppm de Cl-. Os ensaios eletroquímicos a 250 C mostraram que na condição normal de operação de um reator PWR e com a adição de 250 ppb de íons cloreto a liga 800GN exibiu elevada resistência à corrosão por pites, não ocorrendo nenhuma modificação na superfície do material. No entanto, ficou evidenciado que com a adição de 1 ppm de cloreto ao meio PWR iniciou-se uma modificação no filme passivo formado na superfície da liga 800GN.