Molten chloride salts have been proposed to be used as the primary coolant in molten salt reactors, and as the heat transfer fluid in concentrated solar power plants in next generation energy system design. The corrosive properties of molten chloride salts make it challenging to find appropriate structural materials for plant/system realization. In this work, two corrosion mitigation strategies are investigated to determine the relative corrosion performance of high temperature alloys in molten chloride salt mixtures: (1) chemical purification of salt mixture using a Mg sacrificial anode and (2) developing a protective oxide layer on the surface of high temperature alloys after pre-oxidation. These corrosion inhibitors are studied in combination with each other to determine the relative corrosion performance of three high temperature alloys: Incoloy 800H (chromia former), Haynes 214 (alumina former), and Noram SX (silica former). The unprotected and pre-oxidized alloys were exposed to molten chloride salt (62.5 wt % KCl + 37.5 wt % MgCl2·6H2O) with and without 1.7 wt % Mg as a corrosion inhibitor for 100 h at 700 °C under inert Ar atmosphere. SEM-EDS characterization was used to compare cross-sections and surfaces of each alloy exposed to molten salt with and without Mg additions. SEM-EDS cross-sectional characterization revealed significant Cr depletion in each unprotected alloy, and reduced Cr depletion in alloys immersed in molten chloride salt mixtures with chemical purification included. The addition of Mg metal to the salt mixture resulted in the precipitation of MgO on the alloy surfaces. The oxide deposition of MgO on components may impact the thermal and mechanical performance of the system. Therefore, the addition of Mg should be optimized for use in an operational system. Cross-sectional analysis identified the dissolution of Cr2O3 and SiO2 oxide scales and a stable Al2O3 oxide scale post-exposure. / Thesis / Master of Applied Science (MASc)

Made available in DSpace on 2014-06-11T19:29:13Z (GMT). No. of bitstreams: 0 Previous issue date: 2007-08-16Bitstream added on 2014-06-13T20:38:39Z : No. of bitstreams: 1 cesco_dd_me_ilha.pdf: 575055 bytes, checksum: 812d7bbf5c5a525f1a7625caabd57c5c (MD5) / A cloração das águas na presença de precursores da formação de SPDs, oriundos da MON forma entre estes os THMs, cujos principais compostos são o clorofórmio, bromodiclorometano, dibromoclorometano e bromofórmio, potencialmente cancerígenos ao ser humano. No ano de 1974, os THMs foram detectados na água potável nos Estados Unidos e estudos da época apresentaram as primeiras indicações da existência de correlação entre água de abastecimento, THMs e câncer e, estudos posteriores, levaram à fixação de valores limites dos mesmos. No Brasil o valor máximo para os THMs está fixado em 100 g/L na água para consumo humano, de acordo com a Portaria nº. 518/04 (BRASIL, 2004), mas estes valores limites são variáveis em outros países. O presente estudo buscou identificar a formação de THMs, gerados a partir da reação do cloro com a MON, avaliando a formação com e sem a pré-oxidação com cloro na ETA da SABESP de Presidente Epitácio SP, em escala real, onde as concentrações da MON foram reduzidas pelas etapas do processo de tratamento (coagulação, floculação, decantação e filtração), com a mudança do coagulante de cloreto férrico para PAC e, avaliou-se a formação de THM na rede de distribuição. A quantificação de THM foi realizada pelas técnicas de cromatografia gasosa e da MON através da leitura da absorbância à radiação ultravioleta visível no comprimento de onda a 254 nm em espectrofotômetro UV254, parâmetro indireto com filtração da amostra. As análises da MON mostraram que o sistema de tratamento de água não removeu todos compostos orgânicos naturais, que na presença do cloro residual disponível na rede, mostrou tendência de aumentar a formação de THM durante o seu percurso. / The chlorination of the water, when the presence of disinfections by-products are formed, resulting from Natural Organic Matter (NOM), forms among them the trihalomethanes (THMs), which is mainly composed by chloroform (CHCl3), bromodichloromethane (CHBrCl2), dibromochloromethane (CHBr2Cl) and bromoform (CHBr3), that are potentially cancerous to humans. In 1974, the THMs were detected in the drinking water in the USA and studies, at the time, showed the first indications of the drinking water correlation, THMs and cancer disease and, further studies brought to fixation of limits for them. In Brazil, the maximum value for the THMs is fixed in 100μg/l in the drinking water, according to government act nº 518/04 (BRASIL, 2004), however those limits varied from country to country. The present research identified the formation of THMs, generated from the reaction of the chlorine with NOM, evaluating the formation with or without the pre-oxidation with chlorine in the SABESP Water Treatment Plant at the Presidente Epitacio city (São Paulo State), in full scale, where the concentrations of the NOM were reduced by the different phases of the treatment process (coagulation, flocculation, decantation and filtration), with the change of the coagulant from iron chloride to Poli Aluminum Chloride (PAC) and, the formation of THM was found at the distribution net. The quantification of THM was made by the gas chromatography technique and NOM are reading in the 254 nm absorbance radiation wave length in an UV spectrophotometer, indirect sample with filtration. The analysis of the NOM showed that the water treatment system did not remove all the natural organic compounds, that in the presence of residual chlorine available in the net, showed increasing tendency to form THM.

Resumo: A cloração das águas na presença de precursores da formação de SPDs, oriundos da MON forma entre estes os THMs, cujos principais compostos são o clorofórmio, bromodiclorometano, dibromoclorometano e bromofórmio, potencialmente cancerígenos ao ser humano. No ano de 1974, os THMs foram detectados na água potável nos Estados Unidos e estudos da época apresentaram as primeiras indicações da existência de correlação entre água de abastecimento, THMs e câncer e, estudos posteriores, levaram à fixação de valores limites dos mesmos. No Brasil o valor máximo para os THMs está fixado em 100 g/L na água para consumo humano, de acordo com a Portaria nº. 518/04 (BRASIL, 2004), mas estes valores limites são variáveis em outros países. O presente estudo buscou identificar a formação de THMs, gerados a partir da reação do cloro com a MON, avaliando a formação com e sem a pré-oxidação com cloro na ETA da SABESP de Presidente Epitácio SP, em escala real, onde as concentrações da MON foram reduzidas pelas etapas do processo de tratamento (coagulação, floculação, decantação e filtração), com a mudança do coagulante de cloreto férrico para PAC e, avaliou-se a formação de THM na rede de distribuição. A quantificação de THM foi realizada pelas técnicas de cromatografia gasosa e da MON através da leitura da absorbância à radiação ultravioleta visível no comprimento de onda a 254 nm em espectrofotômetro UV254, parâmetro indireto com filtração da amostra. As análises da MON mostraram que o sistema de tratamento de água não removeu todos compostos orgânicos naturais, que na presença do cloro residual disponível na rede, mostrou tendência de aumentar a formação de THM durante o seu percurso. / Abstract: The chlorination of the water, when the presence of disinfections by-products are formed, resulting from Natural Organic Matter (NOM), forms among them the trihalomethanes (THMs), which is mainly composed by chloroform (CHCl3), bromodichloromethane (CHBrCl2), dibromochloromethane (CHBr2Cl) and bromoform (CHBr3), that are potentially cancerous to humans. In 1974, the THMs were detected in the drinking water in the USA and studies, at the time, showed the first indications of the drinking water correlation, THMs and cancer disease and, further studies brought to fixation of limits for them. In Brazil, the maximum value for the THMs is fixed in 100μg/l in the drinking water, according to government act nº 518/04 (BRASIL, 2004), however those limits varied from country to country. The present research identified the formation of THMs, generated from the reaction of the chlorine with NOM, evaluating the formation with or without the pre-oxidation with chlorine in the SABESP Water Treatment Plant at the Presidente Epitacio city (São Paulo State), in full scale, where the concentrations of the NOM were reduced by the different phases of the treatment process (coagulation, flocculation, decantation and filtration), with the change of the coagulant from iron chloride to Poli Aluminum Chloride (PAC) and, the formation of THM was found at the distribution net. The quantification of THM was made by the gas chromatography technique and NOM are reading in the 254 nm absorbance radiation wave length in an UV spectrophotometer, indirect sample with filtration. The analysis of the NOM showed that the water treatment system did not remove all the natural organic compounds, that in the presence of residual chlorine available in the net, showed increasing tendency to form THM. / Orientador: Tsunao Matsumoto / Coorientador: Edson Pereira Tangerino / Banca: Milton Dall'Aglio Sobrinho / Banca: Marcelo Libânio / Mestre

Chemical disinfection is the cornerstone of safe drinking water. However, the use of chemical disinfection results in the unintentional formation of disinfection by-products (DBPs), an outcome of reactions between the disinfectant and natural organic matter (NOM) present in the native (raw) water. DBPs are suspected carcinogens, and as such, have been regulated by the U.S. Environmental Protection Agency (USEPA) under the Safe Drinking Water Act (SDWA). This document reports the results of a study that investigated the use of chlorine dioxide pre-oxidation for the reduction of DBP precursors, and subsequently, DBP formation potential (FP). To determine the effectiveness of the chlorine dioxide pre-oxidation process, two surface waters were studied: raw water from Lake Claire (Orlando, FL) and raw water from the East Maui Watershed (Makawao, HI). Lake Claire water contains approximately 11-12 mg/L of NOM and 35 mg/L as CaCO3 of alkalinity, while the Maui source water typically ranges between 7-8 mg/L of NOM with 2-10 mg/L as CaCO3 of alkalinity. Two chlorine dioxide doses were investigated (0.75 mg/L and 1.5 mg/L) and compared to a control to quantify the effectiveness of this advanced pre-treatment oxidation process. Water collected at each site was subject to the following treatment process: oxidation, coagulation, flocculation, sedimentation, ultrafiltration, and disinfection with free chlorine. Disinfection by-product formation potential (DBPFP) analysis showed that ClO2 pre-oxidation, in general, increased the 7-day DBPFP of the East Maui water, and decreased the 7-day DBPFP of the Lake Claire source water. For the Lake Claire water at the higher ClO2 dose, total trihalomethanes (TTHM) were decreased by 37 percent and the five regulated haloacetic acids (HAA5) by 23 percent. For the East Maui source water at the higher ClO2 dose, TTHM’s were increased by 53 percent and HAA5’s by 60 percent. Future research should determine the effect of alkalinity on DBPFP, which could be the reason why chlorine dioxide pre-oxidation caused one water source’s DBPFP to decrease and the other to increase.

La nitruration gazeuse de pièces en acier de construction est un procédé thermochimique permettant de générer un gradient de propriétés mécaniques à la surface des pièces par diffusion d’atomes d’azote. Les pièces traitées présentent un fort gradient de contraintes résiduelles et de dureté, optimales pour les applications de transmission de puissance utilisées dans les domaines de l’aéronautique ou l’automobile de compétition. L’enrichissement en azote est issu de la décomposition catalytique de l’ammoniac à la surface des pièces en acier. Cependant, le procédé reste extrêmement sensible à l’état de surface des pièces, qui inclue les caractéristiques géométriques, mécaniques mais également chimique, pouvant inhiber les propriétés de décomposition catalytique ainsi que la diffusion de l’azote. Cette désactivation peut avoir différentes origines, comme l’adsorption d’un élément poison de la réaction ou l’encrassement de la surface des pièces. Le phénomène de désactivation catalytique est étudié depuis quelques dizaines d’années. Cependant, peu de publications sont disponibles au sujet de son application dans le cas particulier de la nitruration d’aciers de construction. Comprendre l’inhibition de la nitruration permettrait d’améliorer la fiabilité industrielle de ce procédé. Afin de répondre à cette demande, une démarche expérimentale, basée sur des études de cas industriels et sur une étude bibliographique, a été mis en place. Une étude de pollution issue de résidus d’huile de coupe, de dépôt de carbone et d’empoisonnement au soufre est proposée. De plus, une démarche expérimentale visant à déterminer l’impact de pollutions mécaniques (état mécanique initial) sur le procédé de nitruration est proposée. Des analyses thermogravimétriques couplées à des observations et à la détermination des propriétés mécaniques générées par nitruration permettent d’approfondir la compréhension de ces phénomènes de désactivation des surfaces nitrurées. Suite à cette étude, la capacité d’activation de surface de trois éléments de préparation in-situ, que sont l’oxydation, l’urée et le chlorure d’ammonium, a été déterminé sur les pollutions précédemment étudiées. / The gaseous nitriding of steel parts is a thermochemical process that generates a mechanical properties gradient at the surface by nitrogen diffusion. The treated parts indicate an important residual stress and hardness gradient, optimized for power transmission applications used in aeronautics and motor sports. The increase of nitrogen concentration is due to the catalytic decomposition of ammonia at the iron-based surface of parts. However, the process is extremely sensitive to the surface state of parts that includes geometrical, mechanical but also chemical properties. This state can inhibit the catalytic decomposition properties and the nitrogen diffusion. This deactivation can have different origins, such as the adsorption of a poisoning element or the fouling of the surface of the parts. The catalytic deactivation phenomenon is studied since decades. However, few publications are available in the case of its application in the specific case of the gaseous nitriding of steel. A better understanding of the nitriding inhibition would improve the reliability of this industrial process. In order to answer this demand, an experimental approach, based on industrial case and bibliographical study, is proposed. A pollution study obtained from machining oil residues, carbon deposit, or sulfur poisoning is proposed. Moreover, an experimental approach, aiming to determine the impact of initial mechanical properties on the nitriding process is proposed. Thermogravimetric analyses coupled to observations and mechanical properties analyses enable to develop the knowledge of the nitrided surfaces deactivation processes. After this study, the surface activation capacity of three in-situ processes, namely oxidation, urea and ammonium chloride, over the previously studied contaminations is determined.

Made available in DSpace on 2014-12-17T15:03:25Z (GMT). No. of bitstreams: 1 HugoMBE_DISSERT.pdf: 3011454 bytes, checksum: f02eedee61c0464777dbee026e3a93cf (MD5) Previous issue date: 2010-12-17 / Coordena??o de Aperfei?oamento de Pessoal de N?vel Superior / Eutrophication is a growing process present in the water sources located in the northeast of Brazil. Among the main consequences of these changes in trophic levels of a water source, stands out adding complexity to the treatment to achieve water standards. By these considerations, this study aimed to define, on a laboratory scale, products and operational conditions to be applied in the processing steps using raw water from Gargalheiras dam, RN, Brazil. The dam mentioned shows a high number of cyanobacteria, with a concentration of cells / ml higher than that established by Decree No. 518/04 MS. The same source was also considered by the state environmental agency in 2009 as hypereutrophic. The static tests developed in this research simulated direct filtration (laboratory filters) and pre-oxidation with chlorine and powdered activated carbon adsorption. The research included the evaluation of the coagulants aluminum hydrochloride (HCA) and alum (SA). The development of the research investigated the conditions for rapid mixing, the dosages of coagulants and pHs of coagulation by the drawing of diagrams. The interference of filtration rate and particle size of filtering means were evaluated as samples and the time of contact were tested with chlorine and activated carbon. By the results of the characterization of the raw water source it was possible to identify the presence of a high pH (7.34). The true color was significant (29 uH) in relation to the apparent color and turbidity (66 uH and 13.60 NTU), reflecting in the measurement of organic matter: MON (8.41 mg.L-1) and Abs254 (0.065 cm-1). The optimization of quick mix set time of 17", the speed gradient of 700 s-1 in the coagulation with HCA and the time of 20" with speed gradient of 800 s-1 for SA. The smaller particle sizes of sand filtering means helped the treatment and the variation in filtration rate did not affect significantly the efficiency of the process. The evaluation of the processing steps found adjustment in standard color and turbidity of the Decree n? 518/04 MS, taking in consideration the average values found in raw water. In the treatment using the HCA for direct filtration the palatable pattern based on the apparent color can be achieved with a dose of 25 mg L-1. With the addition of pre-oxidation step, the standard result was achieved with a reduced dose for 12 mgHCA.L-1. The turbidity standard for water was obtained by direct filtration when the dose exceeds 25 mg L-1 of HCA. With pre-oxidation step there is the possibility of reducing the dose to 20 mg L-1.The addition of CAP adsorption, promoted drinking water for both parameters, with even lower dosage, 13 mg L-1 of HCA. With coagulation using SA removal required for the parameter of apparent color it was achieved with pre-oxidation and 22 mgSA.L-1. Despite the satisfactory results of treatment with the alum, it was not possible to provide water with turbidity less than 1.00 NTU even with the use of all stages of treatment / A eutrofiza??o ? um processo cada vez mais presente nos mananciais situados no nordeste brasileiro. Entre as principais conseq??ncias destas altera??es nos n?veis tr?ficos da ?gua de um manancial destaca-se o acr?scimo de complexidade ao tratamento para potabiliza??o. Mediante a estas considera??es, este trabalho teve como objetivo definir, em escala de laborat?rio, produtos e condi??es operacionais a serem empregadas em etapas de tratamento utilizando ?gua bruta do a?ude Gargalheira, RN, Brasil. O a?ude em quest?o demonstra um n?mero de cianobact?rias elevado, apresentando uma concentra??o de c?lulas/ml superior aos n?veis estabelecidos pela Portaria MS n? 518/04. O mesmo, ainda foi considerado pelo ?rg?o ambiental do estado no ano de 2009 como hipereutr?fico. Os ensaios est?ticos desenvolvidos neste trabalho simularam filtra??o direta (filtros de laborat?rio), pr?oxida??o com cloro e adsor??o por carv?o ativado pulverizado. Foram avaliados os coagulantes hidr?xicloreto de alum?nio (HCA) e sulfato de alum?nio granulado (SA). O desenvolvimento da pesquisa buscou otimiza??o das condi??es de mistura r?pida, das dosagens de coagulantes e pHs de coagula??o com a constru??o de diagramas. As interfer?ncias da taxa de filtra??o e a granulometria do meio filtrante foram avaliadas e testaram-se dosagens e tempos de contato com cloro e com o carv?o ativado. Com os resultados da caracteriza??o da ?gua bruta foi poss?vel identificar no manancial a presen?a de um pH elevado (7,34). A cor verdadeira foi significativa (29 uH) em rela??o ? cor aparente e turbidez (66 uH e 13,60 uNT), refletindo-se nas medidas de mat?ria org?nica: MON (8,41 mg.L-1) e Abs254 (0,065 cm-1). A otimiza??o da mistura r?pida definiu o tempo de 17 , gradiente de velocidade de 700 s-1 na coagula??o com HCA e tempo de 20 , gradiente de velocidade de 800 s-1 para o SA. Granulometrias menores da areia do meio filtrante favoreceram o tratamento e a varia??o na taxa de filtra??o n?o interferiu de forma significativa na efici?ncia do processo. A avalia??o das etapas de tratamento verificou a adequa??o aos padr?es de cor aparente e turbidez da Portaria MS 518/2004 tomando como base os valores m?dios encontrados na ?gua bruta. No tratamento utilizando o HCA por filtra??o direta, a potabilidade para a cor aparente pode ser atingida com uma dosagem de 25 mg.L-1. Adicionando a etapa de pr?oxida??o o padr?o foi atingido com dosagem reduzida para 12 mgHCA.L-1. Para a turbidez a potabilidade foi obtida na filtra??o direta quando a dosagem supera 25 mg.L-1 de HCA. Com etapa de pr?oxida??o h? a possibilidade de redu??o da dosagem para 20 mg.L-1 de coagulante. O acr?scimo da adsor??o em CAP, promoveu a potabilidade para os dois par?metros, com dosagem ainda menor, 13 mg.L-1 de HCA. Coagulando com SA a remo??o necess?ria para o par?metro de cor aparente foi atingida com pr?oxida??o e dosagem de 22 mgSA.L-1. Apesar de apresentar bons resultados o tratamento com o sulfato de alum?nio n?o foi capaz de fornecer ?gua com turbidez menor que 1,00 uNT mesmo com a utiliza??o de todas as etapas de tratamento

O presente trabalho apresenta um estudo sistemático sobre a adsorção e a eletrooxidação do CO sobre eletrodos monocristalinos de platina. A partir da análise das intensidades das bandas integradas e das freqüências do Pt(111)-CO, apresenta-se uma interpretação dos efeitos de acoplamento dipolo-dipolo e de interconversão do COads.. Assim, sobre a Pt(111) os espectros de FTIR in situ mostram que o aumento na razão da intensidade das bandas integradas ACOB/ACOL e nas freqüências do νCOB quando θCO,total diminue é devido à redução do acoplamento dipolo-dipolo entre as moléculas do CO em diferentes sítios e, adicionalmente, à interconversão das formas inclinadas dos COL e COB para a forma do COB. No sentido de explicar esta interconversão, propomos um mechanism baseado nas interações dos orbitais de fronteiras do CO e do metal, associado com a retrodoação de elétrons. Nesse modelo, os deslocamentos das formas inclinadas do COL e do COB em direção à forma do COB são favoráveis provavelmente porque a retrodoação de elétrons, Ptd → CO2π* (LUMO), aumenta quando θCO,total diminui. Experimentos potenciostáticos sugerem que a cinética de nucleação e crescimento é o melhor modelo para descrever a eletrooxidação do CO. Propomos que no potencial de oxidação, ECO oxi. pode existir uma via muito rápida de formação do precursores oxigenados e que este pode lateralmente colidir com as ilhas de CO, impedindo que ocorra a dissipação das ilhas do COads. no potencial de oxidação, ECO oxi.. Apresentamos a evolução do crescimento e da oxidação de sub-monocamada de CO sobre monocristais de platina facetados. Em baixo grau de recobrimento do CO foi observado que a adsorção dessa molécula ocorre sem ocupação preferencial de sítios quinas ou terraças. Assim, sugerimos que a adsorção é um processo randômico e que depois que as moléculas do CO são adsorvidas estas não apresentam apreciáveis deslocamentos a partir de CO-(111) em direção aos sítios CO-(110). Isto significa que depois da adsorção, as moléculas do CO têm um longo tempo de residência ou que apresentam um coeficiente de difusão muito baixo. Mas, para alto grau de recobrimento por CO, os resultados mostram que é possível que laterais interações desempanham importantes papéis na distribuição de ocupação dos sítios e observamos que durante a eletrooxidação, são liberados simultaneamente sítios quinas e sítios terraços. Quanto à pré-oxidação, foi observado que quatro condições experimentais precisam ser satisfeitas para que ela ocorra sobre os monocristais de platina: (i) alto grau de recobrimento por CO; (ii) que a superfície onde oncorre a oxidação do CO tenha defeitos, como sítios quinas (110); (iii) que a camada do CO seja formada sob potenciais mais negativos do que o potencial de carga total zero do metal; (iv) e que exista pequena quantidade de CO dissolvido. As condições (i) e (ii) precisam ser satisfeitas simultaneamente para promover a pré-oxidação do CO; as condições (iii) e (iv) essencialmente contribuem correspondendo à condição (i). Observamos que a magnitude do pre-pico aumenta com o aumento do grau de recobrimento por CO. Então, isto pode ser indicativo que a pré-oxidação não tem relação com a difusão do CO em superfície porque o aumento do grau de recobrimento reduz a probabilidade de difusão em superfície. O modelo de ilhas comprimidas parece ser mais apropriado para descrever a pré-oxidação do CO. / This work presents a systematic study on the CO adsorption and its oxidation at platinum single crystal electrodes. From analysis of integrated band intensity and band frequency position of the Pt(111)-CO interface in acid, it is presented an interpretation of the dipole-dipole coupling effect and surface site inter-conversions of COads.. Thus, on Pt(111), in situ FTIR data show that the increase in both ratio integrated band intensity ACOB/ACOL and frequency of νCOB when θCO,total reduces it is indicative of reduce in dipole-dipole coupling interactions between CO molecules in different surface active sites and a mechanism where the tilted COL and COB in CO pressed adlayer displace or inter-convert in favor of increase of COB concentration. In order to explain that CO interconversion, we propose a mechanism based in frontier molecular orbitals of CO and the orbitals of the metal associated with the electron back bond donation. Thus, the displacement of tilted COL and COB on the surface towards COB is more stable because probably the back bond electron donation, Ptd → CO2π* (LUMO), increase when θCO,total diminishes. Potentiostatic experiments suggest that the nucleation and growth is the better model to describe the CO oxidation. It is proposed here that close to ECO oxi. might there is a fast pathway toward formation of oxygenated species and it might reach the CO islands by side and this hinder the dissipation of COads. islands at ECO oxi.. We report also time evolution studies of low CO adsorption coverage and oxidative stripping on stepped platinum surfaces. In low CO coverage, it was observed that there is no preferential site occupancy for CO adsorption on step or terrace. It is proposed that CO adsorption onto these surfaces is a random process, and after CO adsorption there is no appreciable shift from CO-(111) to CO-(110) sites. This implies that after adsorption, CO molecules either have a very long residence time, or that the diffusion coefficient is much lower than previously thought. But, in high CO coverage, the results show that it is possible that the lateral interaction might play important role in CO site occupancy and it was observed that during the CO electrooxidation the sites released included both terrace (111) and step (110) orientations. Among the CO oxidation a clear CO preoxidation process also occurs. It was observed four experimental conditions which were verified to be fulfilled to promote CO pre-oxidation on platinum single crystal: (i) the CO coverage is should be higher than minimum threshold; (ii) the surface where CO oxidation take place should have defects, such as (110) steps; (ii) the CO monolayer should be formed at potentials below the potential of zero total charge; (iv) and in a small amount of dissolved CO should be present in the electrolyte solution. In both conditions (i) and (ii) are necessary to take place simultaneously to promote CO pre-oxidation, (iii) and (iv) essentially contribute in fulfilling condition (i). It was verified that the magnitude of pre-peak increases with the amount of CO coverage. Thus, this might indicate that the CO pre-oxidation is not having relationship with the CO diffusion on the surface, because the increase of CO coverage diminishes surface diffusion. A picture model of compressed CO islands seems the most to describe CO pre-oxidation.

No presente trabalho foi estudada a utilização do ozônio como auxiliar no pós-tratamento de reatores anaeróbios por reatores de lodos ativados. Foi estudada a influência da ozonização no aumento da biodegradabilidade da matéria orgânica recalcitrante de efluente anaeróbio antes de ser submetido ao tratamento aeróbio. A pesquisa foi dividida em três etapas. Na primeira e segunda etapas foram utilizados quatro amostras, uma bruta e três ozonizadas com dosagens de 5, 10 e 15 mg O3/L. As amostras da primeira e segunda etapa tiveram tempos de ozonização de 30 e 50 minutos, respectivamente. Os reatores de lodos ativados tiveram tempo de retenção celular de 10 dias e tempo de detenção hidráulica de 24 horas. Na terceira etapa foram utilizadas três amostras, uma bruta e duas ozonizadas cuja dosagem de ozônio foi de 15 mg/L, valor que obteve melhores resultados nas etapas anteriores. Os tempos de ozonização de cada amostra foram de 30 e 50 minutos. Nesta fase, o reator de lodos ativados teve tempo de retenção celular de 10 dias e tempo de detenção hidráulica de 12 horas. Entretanto, amostras ozonizadas submetidas a pós-tratamento em reator de lodos ativados, apresentaram aumento da biodegradabilidade quando expostas a maiores tempos de ozonização. A alimentação do reator de lodos ativados com amostras ozonizadas trouxe benefícios ao seu desempenho. / On this research was studied the utilization of ozone as auxiliary on the post-treatment of anaerobics reactors by activated sludges reactors. It was studied the influence of ozonization of anaerobic effluent before being submitted to an aerobic treatment on the increase of the biodegradability of recalcitrant organic matter. The research was divided in three stages. In the first and second stage was used four samples, one brute and three ozonizades with doses of 5, 10 and 15 mg O3/L. The samples used on first and second stages had being ozonization times of 30 and 50 minutes, respectively. The activated sludges reactors had time of cellular retention of 10 days and hydraulic time of detention of 24 hours. On the third stage were used three samples, one brute and two ozonizades whose doses of ozone was of 15 mg/L, this value achieved the best results in the previous stages. The ozonizations times of each sample were of 30 and 50 minutes. On this stage the activated sludges reactors had time of cellular retention of 10 days and hydraulic time of detention of 12 hours. It was observed that ozonizades samples submitted to post-treatment in activated sludges reactors presented increase of the biodegradability when exposed at largest times of ozonization. The feeding of activated sludges reactors with ozonizades samples benefit its perfomance.

No presente trabalho foi estudada a utilização do ozônio como auxiliar no pós-tratamento de reatores anaeróbios por reatores de lodos ativados. Foi estudada a influência da ozonização no aumento da biodegradabilidade da matéria orgânica recalcitrante de efluente anaeróbio antes de ser submetido ao tratamento aeróbio. A pesquisa foi dividida em três etapas. Na primeira e segunda etapas foram utilizados quatro amostras, uma bruta e três ozonizadas com dosagens de 5, 10 e 15 mg O3/L. As amostras da primeira e segunda etapa tiveram tempos de ozonização de 30 e 50 minutos, respectivamente. Os reatores de lodos ativados tiveram tempo de retenção celular de 10 dias e tempo de detenção hidráulica de 24 horas. Na terceira etapa foram utilizadas três amostras, uma bruta e duas ozonizadas cuja dosagem de ozônio foi de 15 mg/L, valor que obteve melhores resultados nas etapas anteriores. Os tempos de ozonização de cada amostra foram de 30 e 50 minutos. Nesta fase, o reator de lodos ativados teve tempo de retenção celular de 10 dias e tempo de detenção hidráulica de 12 horas. Entretanto, amostras ozonizadas submetidas a pós-tratamento em reator de lodos ativados, apresentaram aumento da biodegradabilidade quando expostas a maiores tempos de ozonização. A alimentação do reator de lodos ativados com amostras ozonizadas trouxe benefícios ao seu desempenho. / On this research was studied the utilization of ozone as auxiliary on the post-treatment of anaerobics reactors by activated sludges reactors. It was studied the influence of ozonization of anaerobic effluent before being submitted to an aerobic treatment on the increase of the biodegradability of recalcitrant organic matter. The research was divided in three stages. In the first and second stage was used four samples, one brute and three ozonizades with doses of 5, 10 and 15 mg O3/L. The samples used on first and second stages had being ozonization times of 30 and 50 minutes, respectively. The activated sludges reactors had time of cellular retention of 10 days and hydraulic time of detention of 24 hours. On the third stage were used three samples, one brute and two ozonizades whose doses of ozone was of 15 mg/L, this value achieved the best results in the previous stages. The ozonizations times of each sample were of 30 and 50 minutes. On this stage the activated sludges reactors had time of cellular retention of 10 days and hydraulic time of detention of 12 hours. It was observed that ozonizades samples submitted to post-treatment in activated sludges reactors presented increase of the biodegradability when exposed at largest times of ozonization. The feeding of activated sludges reactors with ozonizades samples benefit its perfomance.

O presente trabalho apresenta um estudo sistemático sobre a adsorção e a eletrooxidação do CO sobre eletrodos monocristalinos de platina. A partir da análise das intensidades das bandas integradas e das freqüências do Pt(111)-CO, apresenta-se uma interpretação dos efeitos de acoplamento dipolo-dipolo e de interconversão do COads.. Assim, sobre a Pt(111) os espectros de FTIR in situ mostram que o aumento na razão da intensidade das bandas integradas ACOB/ACOL e nas freqüências do νCOB quando θCO,total diminue é devido à redução do acoplamento dipolo-dipolo entre as moléculas do CO em diferentes sítios e, adicionalmente, à interconversão das formas inclinadas dos COL e COB para a forma do COB. No sentido de explicar esta interconversão, propomos um mechanism baseado nas interações dos orbitais de fronteiras do CO e do metal, associado com a retrodoação de elétrons. Nesse modelo, os deslocamentos das formas inclinadas do COL e do COB em direção à forma do COB são favoráveis provavelmente porque a retrodoação de elétrons, Ptd → CO2π* (LUMO), aumenta quando θCO,total diminui. Experimentos potenciostáticos sugerem que a cinética de nucleação e crescimento é o melhor modelo para descrever a eletrooxidação do CO. Propomos que no potencial de oxidação, ECO oxi. pode existir uma via muito rápida de formação do precursores oxigenados e que este pode lateralmente colidir com as ilhas de CO, impedindo que ocorra a dissipação das ilhas do COads. no potencial de oxidação, ECO oxi.. Apresentamos a evolução do crescimento e da oxidação de sub-monocamada de CO sobre monocristais de platina facetados. Em baixo grau de recobrimento do CO foi observado que a adsorção dessa molécula ocorre sem ocupação preferencial de sítios quinas ou terraças. Assim, sugerimos que a adsorção é um processo randômico e que depois que as moléculas do CO são adsorvidas estas não apresentam apreciáveis deslocamentos a partir de CO-(111) em direção aos sítios CO-(110). Isto significa que depois da adsorção, as moléculas do CO têm um longo tempo de residência ou que apresentam um coeficiente de difusão muito baixo. Mas, para alto grau de recobrimento por CO, os resultados mostram que é possível que laterais interações desempanham importantes papéis na distribuição de ocupação dos sítios e observamos que durante a eletrooxidação, são liberados simultaneamente sítios quinas e sítios terraços. Quanto à pré-oxidação, foi observado que quatro condições experimentais precisam ser satisfeitas para que ela ocorra sobre os monocristais de platina: (i) alto grau de recobrimento por CO; (ii) que a superfície onde oncorre a oxidação do CO tenha defeitos, como sítios quinas (110); (iii) que a camada do CO seja formada sob potenciais mais negativos do que o potencial de carga total zero do metal; (iv) e que exista pequena quantidade de CO dissolvido. As condições (i) e (ii) precisam ser satisfeitas simultaneamente para promover a pré-oxidação do CO; as condições (iii) e (iv) essencialmente contribuem correspondendo à condição (i). Observamos que a magnitude do pre-pico aumenta com o aumento do grau de recobrimento por CO. Então, isto pode ser indicativo que a pré-oxidação não tem relação com a difusão do CO em superfície porque o aumento do grau de recobrimento reduz a probabilidade de difusão em superfície. O modelo de ilhas comprimidas parece ser mais apropriado para descrever a pré-oxidação do CO. / This work presents a systematic study on the CO adsorption and its oxidation at platinum single crystal electrodes. From analysis of integrated band intensity and band frequency position of the Pt(111)-CO interface in acid, it is presented an interpretation of the dipole-dipole coupling effect and surface site inter-conversions of COads.. Thus, on Pt(111), in situ FTIR data show that the increase in both ratio integrated band intensity ACOB/ACOL and frequency of νCOB when θCO,total reduces it is indicative of reduce in dipole-dipole coupling interactions between CO molecules in different surface active sites and a mechanism where the tilted COL and COB in CO pressed adlayer displace or inter-convert in favor of increase of COB concentration. In order to explain that CO interconversion, we propose a mechanism based in frontier molecular orbitals of CO and the orbitals of the metal associated with the electron back bond donation. Thus, the displacement of tilted COL and COB on the surface towards COB is more stable because probably the back bond electron donation, Ptd → CO2π* (LUMO), increase when θCO,total diminishes. Potentiostatic experiments suggest that the nucleation and growth is the better model to describe the CO oxidation. It is proposed here that close to ECO oxi. might there is a fast pathway toward formation of oxygenated species and it might reach the CO islands by side and this hinder the dissipation of COads. islands at ECO oxi.. We report also time evolution studies of low CO adsorption coverage and oxidative stripping on stepped platinum surfaces. In low CO coverage, it was observed that there is no preferential site occupancy for CO adsorption on step or terrace. It is proposed that CO adsorption onto these surfaces is a random process, and after CO adsorption there is no appreciable shift from CO-(111) to CO-(110) sites. This implies that after adsorption, CO molecules either have a very long residence time, or that the diffusion coefficient is much lower than previously thought. But, in high CO coverage, the results show that it is possible that the lateral interaction might play important role in CO site occupancy and it was observed that during the CO electrooxidation the sites released included both terrace (111) and step (110) orientations. Among the CO oxidation a clear CO preoxidation process also occurs. It was observed four experimental conditions which were verified to be fulfilled to promote CO pre-oxidation on platinum single crystal: (i) the CO coverage is should be higher than minimum threshold; (ii) the surface where CO oxidation take place should have defects, such as (110) steps; (ii) the CO monolayer should be formed at potentials below the potential of zero total charge; (iv) and in a small amount of dissolved CO should be present in the electrolyte solution. In both conditions (i) and (ii) are necessary to take place simultaneously to promote CO pre-oxidation, (iii) and (iv) essentially contribute in fulfilling condition (i). It was verified that the magnitude of pre-peak increases with the amount of CO coverage. Thus, this might indicate that the CO pre-oxidation is not having relationship with the CO diffusion on the surface, because the increase of CO coverage diminishes surface diffusion. A picture model of compressed CO islands seems the most to describe CO pre-oxidation.