O presente estudo investigou a participação do H2S04, como agente corrosivo no carste do Grupo Una, na bacia de Irecê e na bacia do rio Salitre, tendo como base o monitoramento hidroquímico e a determinação de fácies hidroquímicas. A fácies escoamento superficial alogênico é caracterizada por baixos valores de pH (\'X BARRA\'=4,79 ; CV=3,15%) e dos principais cátions e ânions, com destaque para S\'O IND. 4 POT. 2-\' (x=0,57 mg/L ; CV10,32%); A fácies fluxo freático profundo carbonático representa a maior concentração de HC\'O IND. 3 POT. -\' de todo conjunto amostrado, com média igual a 359,08 mg/L. Na média as águas desta fácies encontram-se saturadas para calcita (S\'l IND. c\' = 0,02) e insaturadas para gipsita (S\'l IND. g\' = -1,51). A concentração de S\'O IND. 4 POT. 2-\' também é alta (\'X BARRA\'=204,50 mg/L ; CV 135,00%), destacando-se um ponto de amostragem que exibe elevado valor médio para \'SO IND. 4 POT. 2-\' (\'X BARRA\'= 746,07 ; CV = 13,79%); Na fácies percolação vadosa a concentração de S\'O IND. 4 POT. 2-\' é expressiva, com média igual a 305,09mg/L; Nos reservatórios subterrâneos destaca-se a alta concentração de HC\'O IND. 3\'(média - 305,10 mg/L), Índice de Saturação para calcita muito próximo do equilíbrio (S\'l IND. c\'=-0,02) e concentração média para S\'O IND. 4 POT. 2-\' (\'X BARRA\'=17,79 mg/L; CV = 52,03%); Nas nascentes cársticas observou-se alto teor de HC\'O IND. 3 POT. -\' (\'X BARRA\'=246,96 mg/L ; CV = 11,0%), S\'l IND. c\'=0,00 (0,28 a -0,37), em equilíbrio de saturação para o mineral calcita e concentração de S\'O IND. 4 POT. 2-\' (\'X BARRA\'= 19,30mg/L ; CV = 31,47%). As águas meteóricas são caracterizadas por baixas concentrações dos principais cátions e ânions, com médias inferiores a 0,5mg/L. Cálculos estequiométricos foram aplicados aos dados hidroquímicos e conclui-se que no balanço molar as águas não seguem as razões clássicas para dissolução exclusiva por ácido carbônico, mas sim, adequam-se ao sistema \'H IND. 2\'S\'O IND. 4\' - CaMgC\'O IND. 3\'. Minerais secundários de cavernas foram analisados e detectou-se ocorrências expressivas de gipsita, sob a forma de crostas, estalactites e filamentos, que, vinculadas ao ambiente de formação, indicam a participação de soluções ricas em sulfato em seus processos. O evento principal de deposição de gipsita foi associado ao rebaixamento do NA após fase de ampliação paragenética dos condutos. Análises isotópicas de \'\'delta\' POT. 13\'CHC\'O IND. 3 POT. -\' em amostras de águas subterrâneas indicam valores enriquecidos (-10,4%o PDB-V) em relação ao esperado para a reação de dissolução da rocha carbonática por ácido carbônico (-17,1%o), condição relacionada à influência de \'ANTPOT. 13 C\' oriundo da rocha por ação do ácido sulfúrico. O \'delta\' POT. 34\'S de sulfato em água subterrânea (\'X BARRA\'=17,7%o CDT) é levemente empobrecido em relação à pirita (\'X BARRA\'=21,3%o), com valores na faixa de amplitude prevista para o processo de oxidação, condição que atesta a participação de ácido sulfúrico na dissolução da rocha carbonática. Análises microbiológicas na água subterrânea do aqüífero cárstico indicaram a presença de bactérias do gênero Acidithiobacillus e bactérias redutoras de sulfato (BRS), ambas presentes no ciclo do enxofre e responsáveis pela produção de ácido sulfúrico. Neste sentido, as variáveis estudadas possibilitam a confirmação da participação do ácido sulfúrico na dinâmica do sistema cárstico do Grupo Una no Estado da Bahia. / The main goal of this study is to determine the effectiveness of sulfuric acid as a corrosive agent in the karst system of the Una Group (lrecê geological basin and Salitre river basin), based on hydrochemical monitoring and the respective hydrochemical facies. The allogenic surface runoff is characterized by low ion concentrations and pH (ph=4,79 ; CV=3,15%). Sulfate is also low for this facies (\'X BARRA\'=0,57 mg/L ; CV 10,32%). With respect to the HC\'O IND. 3 POT. -\' content, the deep phreatic flux in the carbonate aquifer has the highest concentration compared to the other facies, with a mean of 359,08 mg/L. This deep phreatic flux is saturated with respect to calcite and undersaturated with respect to gypsum, showing average concentrations of 204,5 mg/L (CV 135,00%) for S\'O IND. 4 POT. 2-\', including one sampling site with average concentration of 746,07 mg/L (CV = 13,79%). Expressive sulfate concentration was also detected in the vadose seepage, with a mean of 305,09 mg/L. Underground reservoirs have high HC\'O IND. 3 POT. -\' content (\'X BARRA\'=305,10 mg/L) together with calcite saturation index close to equilibrium (S\'l IND. c\'=-0,02) and lower sulfate concentration (mean of 17,79 mg/L; CV = 52.03%). The karst springs revealed similar chemistry to the underground reservoirs, with high HC\'O IND. 3 POT. -\' content (\'X BARRA\'=246,96 mg/L ; CV = 11,0%), saturated with respect to calcite (mean of S\'l IND. c\' = 0,00; varying between 0,28 and -0,37) and mean sulfate concentration of 19,30mg/L (CV = 31.47%). The meteoric recharge has a very low solute load, with means of all ions lower than 0.5 mg/L. Stoichiometric balance calculations applied to the hydrochemical results showed that the molar balances of the various water facies do not follow the classical ratios of carbonate dissolution only due to carbonic acid, but on the contrary, they follow better the chemical system of \'H IND. 2\'S\'O IND. 4\' - CaMgC\'O IND. 3\'. The study of the expressive secondary gypsum deposits in caves, represented by crusts, stalactites and filaments, showed that their origin is related to the deep phreatic water and that the major deposition event of these deposits occurred during the water table lowering after the high water table period related to the paragenetic conduit enlargement. Isotopic composition of dissolved inorganic carbon in groundwater samples showed values of \'\'delta\' POT. 13\'CHC\'O IND. 3 POT. -\' around -10,4%o PDB-V, which are relatively enriched with respect to the predicted \'\'delta\' POT. 13\'CHC\'O IND. 3 POT. -\' of -17,1%o, if the system would be affected only by carbonic acid. This enrichment is attributed to the \'ANTPOT. 13 C\' originated by the reaction between carbonate rock and sulfuric acid. The \'delta\' POT. 34\'S of sulfate in water (\'X BARRA\'=17,7%o CDT) is slightly depleted than that of pyrite disseminated in carbonate rock (\'X BARRA\'=21,3%o), but still in the range predicted for the fractionation due to pyrite oxidation, indicating that carbonate rock is dissolved by sulfuric acid. Microbiological analysis of groundwater in the karstic aquifer revealed the presence of bacteria of the genera Acidithiobacillus and sulfate reducing bacteria (SRB). Both are typical of the sulfur cycle and produce sulfuric acid. Finally, it can be stated, based on the above described results, that sulfuric acid is an important agent in the dynamics of the studied karst.

Ligas de níquel têm atualmente uma vasta gama de aplicações, sendo a agressividade do meio e as elevadas temperaturas que estas ligas suportam, um diferencial excepcional. A liga UNS N07090, objeto deste trabalho, encontra aplicações muito diversas, entre elas turbocompressores, sistemas de exaustão e de pós-tratamento de motores a diesel. Nestas aplicações a liga está exposta a gases, que ao condensarem formam ácido sulfúrico (H2SO4). Torna-se, assim, importante, o conhecimento da resistência à corrosão da liga nesse meio. O presente trabalho tem como objetivo caracterizar o comportamento eletroquímico da liga através de curvas de polarização potenciodinâmica em diferentes concentrações de ácido sulfúrico. Observou-se que quanto maior a concentração de ácido, maior é a corrosão da liga. Este fato pode ser discutido pela adsorção do íon sulfato (SO42-), que prejudica tanto a formação quanto a cinética de crescimento da película passiva do níquel. Em contrapartida, a presença de Cr na liga UNS N07090 apresentou um benefício sobre a resistência à corrosão desta muito acima do esperado, influenciando de forma direta as curvas de polarização da liga e mantendo-a em condição de elevada resistência à corrosão em detrimento do pior desempenho observado em outros elementos pertecentes à liga, como Co, Al e Ti. Tempos de imersão de 24h em ácido sulfúrico elevam discretamente os parâmetros de corrosão da liga, mantendo-os, no entanto em patamares bastante baixos, permitindo finalmente concluir que a liga UNS N07090, quando exposta a concentrações que variam de 1M a 4M H2SO4, a 25°C, apresenta boa resistência à corrosão e que esta não se altera com o tempo de exposição. A análise dos resultados mostrou que o processo corrosivo é controlado por reações catódicas de sulfato e hidrogênio, as quais podem ter diferentes contribuições dependendo da concentração do ácido e do tempo de imersão da liga UNS N07090 no meio corrosivo. / Nickel alloys have a wide range of application nowadays due to their excellent resistance to aggressive media and high temperatures. UNS N07090, the nickel alloy studied herein, is used for turbochargers, exhaust and after treatment systems of diesel engines. These applications expose the alloy to hot gases, which condensate forming sulfuric acid (H2SO4). It is thus important to know the corrosion resistance of the alloy in this media. The goal of this work is the characterization of the electrochemical behaviour of UNS N07090 alloy through potentiodynamic polarization curves in different sulfuric acid concentrations. On the one hand, higher acid concentrations were noticed to lead to higher corrosion of the alloy. This phenomenon can be discussed by sulfate (SO42-) adsorption, which negatively influences not only the formation but also the growth of the passive film on nickel. On the other hand, the presence of Cr in UNS N07090 composition, improves the corrosion resistance of the alloy far more than expected, directly affecting the shape of the polarization curves of the alloy, placing it in a condition of high corrosion resistance despite the worst performance shown by the other elements present in the chemical composition of the alloy, such as Co, Al and Ti. 24h immersion periods in sulfuric acid slightly raise corrosion parameters of UNS N07090 alloy, but still ranking the alloy in very good corrosion resistance. Finally, it can be concluded that UNS N07090 alloy exposed to 1M to 4M H2SO4 at 25°C presents good corrosion resistance and that this is not affected by longer immersion periods. The results showed that the corrosion process of alloy UNS N07090 is controlled by sulfate and hidrogen cathodic reactions, which have stronger or weaker contribution depending on acid concentration and immersion time on the corrosive media.

Orientador: Gustava Paim Valença / Dissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Engenharia Química / Made available in DSpace on 2018-08-24T00:06:11Z (GMT). No. of bitstreams: 1 Campos_Kurts_M.pdf: 1571455 bytes, checksum: be3e0b10fcf0076c5a292b9ff9f8e965 (MD5) Previous issue date: 2013 / Resumo: Em parques industriais produtores de ácido fosfórico, um grande problema é a quantidade de rejeito gerado, o fosfogesso (gesso com impurezas de ácido fosfórico e sulfúrico). A estocagem deste material no meio ambiente resulta em problemas graves para a fauna e flora nos locais onde é depositado. Neste trabalho, a viabilidade técnica de uma alternativa para o problema de descarte deste subproduto é discutida a partir da recuperação do dióxido de enxofre (SO2) de fosfogesso para utilização em plantas de ácido sulfúrico. Algumas simulações de processo das plantas de ácido sulfúrico serão apresentadas, apontando alternativas industriais para utilização de SO2 recuperado / Abstract: In industrial parks that produce phosphoric acid, the major problem is the amount of waste generated: the phosphogypsum (gypsum with impurities such as phosphoric and sulfuric acid). The storage of this material in the environment results in serious problems for wildlife and flora in places where it is deposited. An alternative to the problem of disposal of this waste as well as its technical feasibility is discussed, recovering sulfur dioxide SO2 from phosphogypsum for use in sulfuric acid plants. In this work, some simulations of sulfuric acid operation were made and the proposal is presented, pointing out the best alternative for SO2 reuse from phosphogypsum / Mestrado / Engenharia de Processos / Mestre em Engenharia Química

[pt] A degradação do concreto pode ocorrer a partir de processos bioquímicos, especialmente no caso de elementos que fazem parte das redes do sistema de esgoto devido a produção de ácido sulfúrico (H2SO4) de maneira biogênica por certos tipos de bactérias. O presente estudo tem como objetivo investigar esse processo corrosivo e as propriedades mecânicas residuais de amostras de concreto expostas a soluções de H2SO4 de diferentes concentrações (0,5 por cento, 1 por cento e 3 por cento) e ao esgoto doméstico. Foram produzidos dois concretos: um com fator a/c igual a 0,83 e um de alto desempenho, com a/c de 0,28. As amostras foram curadas por períodos de 28, 63 e 91 dias e avaliadas após períodos de imersão nas soluções por 28 e 84 dias, com monitoramento do pH das soluções e da perda de massa das amostras. Após o fim da imersão, os concretos tiveram suas propriedades mecânicas residuais avaliadas por meio de ensaios de resistência à compressão direta e à tração indireta. Os resultados da pesquisa mostram uma maior perda de massa, assim como uma maior redução da resistência mecânica nas amostras com maior volume de cimento. As amostras de concreto convencionais imersos em ácido apresentaram perda de até 42 por cento na resistência à compressão, enquanto que as amostras de alto desempenho apresentaram redução de até 87 por cento em comparação com amostras não atacadas. Em relação aos corpos de prova imersos em esgoto doméstico, nenhum concreto sofreu perda significativa de massa e resistência, provavelmente devido ao tempo de exposição limitado. / [en] The degradation of concrete may occur from biochemical processes, especially where concrete elements of the sewage system networks due to the production of biogenic sulfuric acid (H2SO4) by certain types of bacteria. This study aims to study this corrosion process and residual mechanical properties of concrete samples exposed to H2SO4 solutions on different concentrations (0.5 percent, 1 percent and 3 percent) and domestic sewage. Two concretes were produced: one with 0.83 w/c ratio with high performance, with w/c ratio of 0.28. The samples were cured for periods of 28, 63 and 91 days and were evaluated in periods of 28 and 84 days of immersion, with the pH of the solutions and the weight loss of the samples being monitored. After the immersion periods, the concretes had their residual mechanical properties evaluated by compressive strength and Brazilian split tests. Research results have shown a greater weight loss and higher reduction of mechanical strength on specimens with higher percentage of cement. The conventional concrete specimens immersed in acid showed 42 percent loss in compressive strength, whereas the high-performance samples showed a reduction up to 87 percent when compared to non-attacked samples. Regarding the specimens immersed in domestic sewage, neither concrete suffered significant loss of mass and strength, probably due to limited exposure time.

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No description available.

Foi estudado o comportamento eletroquímico de interfases Cu/H2SO4 0,5 mol L-1 na ausência e presença de compostos triazólicos - benzotriazol (BTAH) e tolitriazol (TTAH) e de surfactantes: dodecilsulfato de sódio (SDS aniônico) e cloreto de dodecilamônio (DAC catiônico) a 25ºC, empregando eletrodo parado e de disco rotativo (EDR). Foram empregadas como técnicas medidas de potencial de circuito aberto, polarização potenciostática e potenciodinâmica, cronoamperometria, espectroscopia de impedância eletroquímica e microscopia óptica. As características inibidoras do filme formado dependem da natureza dos aditivos e das condições hidrodinâmicas. As interfases contendo BTAH, TTAH, BTAH + TTAH, BTAH + SDS e TTAH + SDS apresentaram uma faixa ampla de potencial em que o cobre se mostrou passivado, chegando a 200 mV para a mistura BTAH + SDS empregando EDR. Densidades de corrente de passivação tão baixas quanto 2µA cm-2 foram observadas com EDR na presença de BTAH + TTAH. As misturas composto triazólico - surfactante mostraram filmes menos resistentes. Os surfactantes isolados não produzem faixa passiva e antecipam o potencial de oxidação do cobre com eletrodo parado. As misturas triazol - DAC só produzem faixa passiva com EDR. Todos os aditivos se mostraram inibidores para a reação H+/H2, destacando-se, com eletrodo parado, BTAH, TTAH e BTAH + TTAH. / The electrochemical behavior of 0.5 mol.L-1 Cu/H2SO4 interphases has been studied in the presence and in the absence of triazolic compounds-benzotriazole (BTAH) and tolitriazole (TTAH) and of surfactants - sodium dodecylsulphate (anionic, SDS) and dodecylammonium chloride (cationic, DAC) at 25ºC, using non-stirred electrode and rotating disc electrode (RDE). Open circuit potential, potentiostatic and potenctiodinamic polarization, chronoamperometry, electrochemical impedance spectroscopy, and optical microscopy were used as techniques. The inhibitive features of the formed film depend on both the nature of the additives and on the hydrodynamic conditions. The interphases containing BTAH, TTAH, BTAH + TTAH, BTAH + SDS e TTAH + SDS presented a wide potential range where the copper is passivated, reaching to 200 mV for BTAH + SDS mixture using RDE. Low passivating current densities (2µA cm-2) were observed with RDE in the presence of BTAH + TTAH. Triazolic compound?surfactant mixtures have originated less resistant films. Isolated surfactants do not originate passive ranges and anticipate the oxidation potential of copper under non stationary conditions. The mixtures triazole-DAC only produce passive range at stationary conditions. All the additives have shown to be inhibitors for the H+/H2 reaction, specially BTAH, TTAH e BTAH + TTAH using non stirred conditions.

Bio-deterioration of concrete, which is very common in sewer system and waste water treatment plant, results in significant structure degradation. Normally, the process can be described by the two following parts: 1) Biochemistry reactions producing biogenic aggressive species in biofilms which are spread on the surface of concrete. As one of the most significant biogenic acid in sewer pipes, sulfuric acid (H2SO4) is produced by sulfur oxidizing bacteria (SOB). 2) Chemical reactions between biogenic aggressive species and cement hydration products which is responsible for concrete deterioration. A reactive transport model is proposed to simulate the bio-chemical and chemical deterioration processes of cementitious materials in contact with SOB and H2S or sulfuric acid solution. This model aims at solving simultaneously transport and biochemistry/chemistry in biofilms and cementitious materials by a global coupled approach. To provide an appropriate environment for SOB to grow, the surface neutralization of concrete (i.e., the absorption of H2S and aqueous H2S corrosion) is considered. To obtain the amount of biogenic H2SO4, the bio-oxidation of H2S by the activation of bacteria is simulated via a simplified model. To provide a suitable environment for SOB to grow, the abiotic pH reduction of concrete process is introduced. The production rate of H2SO4 is governed by the pH in the biofilms and the content of H2S in gas.It is assumed that all chemical processes are in thermodynamical equilibrium. The dissolution of portlandite (CH) and calcium silicate hydrates (C-S-H) and the precipitation of gypsum (C¯S H2) and calcium sulfide are described by mass action law and threshold of ion activity products. To take into account the continuous decrease of the Ca/Si ratio during the dissolution of C-S-H a generalization of the mass action law is applied. By simplifying the precipitation process of gypsum, a damage model is introduced to characterize the deterioration of concrete due to the swelling of gypsum. Thus, the porosity evolution and deterioration depth during deterioration process are taken into account. Only diffusion of aqueous species are considered. Different diffusion coefficients are employed for various ions and Nernst-Planck equation was implemented. The effect of the microstructure change during deterioration on transport properties is considered as well. For both biofilms and cementitious materials, the balance equations of total mass of each atom (Ca, Si, S, K, Cl) are used to couple transport equations and (bio-)chemical reactions. The model is implemented within a finite-volume code, Bil. Following the introduction of principle of the finite volume method, the coupling of the bio-chemistry process in biofilms and chemistry process in cementitious materials is illustrated. By this model, some experiments reported in literature, including chemical immersion tests (statical solution condition and flow solution condition) and microbiological simulation tests, are simulated. The numerical results and the experimental observations are compared and discussed. The influence of properties of cementitious materials (initial porosity, carbonated layer, etc.) and environmental factors (concentration of H2SO4, content of H2S, etc.) are investigated by this model as well. Furthermore, a long term predictionis conducted

Im Oktober 1875 erschien Clemens Winklers Schlüsselpublikation zum Schwefelsäure-Kontaktverfahren. Der Freiberger Chemiker lieferte nicht nur die wesentlichen Grundlagen des Prozesses, sondern initiierte eine Entwicklung, die der chemischen Industrie ein modernes Produktionsverfahren für eine wichtige Grundchemikalie in die Hand gab und damit ihre Entwicklung entscheidend beförderte. Neben Winklers Leistungen werden auch die bisher wenig gewürdigten Anstrengungen der Freiberger Hüttenwerke herausgestellt, denen es nach einigen Umwegen 1879 gelungen war, die erste wirklich funktionsfähige Kontaktanlage in Betrieb zu nehmen.

Aluminum alloys are widely used materials in the aircraft industry due to their high specific strength and durability. The natural corrosion resistance of aluminum can be improved through an electrochemical anodizing process. Due to recent restrictions in the use of chromic acid with toxic hexavalent chromium as electrolyte, the industry has shifted towards the use of the functional comparable tartaric sulfuric acid (TSA). TSA anodizing provides a porous alumina layer with good corrosion resistance, yet there is a desire to tune the process to fit other purposes. For instance, ice accretion to aircraft surfaces implies a safety risk and reduced energy efficiency. Due to insufficient active anti-icing systems, aircraft manufacturers are in the search for passive anti-acing materials. The ice adhesion properties of a material are thought to be affected by wettability. In turn, the wettability is affected by the morphology of the alumina influenced by the anodizing conditions. Herein, the effects of the anodizing voltage, electrolyte temperature and anodizing time on the morphology and wettability of TSA-anodized aluminum alloy 2024-T3 were studied by scanning electron microscopy (SEM) and contact angle (CA) measurements. The morphology in relation to wettability and ice adhesion strength as well as the use of posttreatments such as hydrothermal sealing and silanization was investigated. SEM images show a clear influence by the anodizing conditions on the porosity, interpore distance and pore diameter of the porous alumina. The morphology has influence on the wettability although the relationship needs further investigation. A superhydrophobic surface obtained by silanization of a surface anodized at high voltage characterized by a rod-like morphology has potential as a passive anti-icing surface. Future work may include additional polishing pretreatments, testing of additional parameters, investigating the CA hysteresis and roll-off angle as well as measuring the adhesion strength of high-impact ice. By tuning the morphology of sustainable anodic coatings, the research area is one step closer to implementing passive anti-icing materials in aircrafts.