Microbiologically Influenced Corrosion (MIC) is a process influenced by microbial presence and their metabolic activities. This study examined the microbial effects on metal corrosion under different environmental conditions with nutrient supplements. Experiments were conducted by inserting stainless steel 304 and mild steel coupons (2.5 x 2.5 cm²) into loam soil and a simulated seawater/sediment system with various nutrient conditions (sterilized, without supplement, 5 mM NaNO₃ or NH₄NO₃). Two mild and stainless steel coupons were removed monthly and the corrosion rate was evaluated based on the weight loss. Bacterial populations were enumerated using the most probable number (MPN) technique. The presence and adhesion of microbes on mild steel coupons were examined using Scanning Electron Microscopy (SEM). The extent of the corrosion process on the surface of the metal coupons were visualized by using the Stereo Microscope. The elemental composition of the corrosion products formed on the coupon surface were determined by Energy Dispersive X-Ray analyses. Isolation and identification of aerobic microorganisms were conducted and examined for its potential in either accelerating or inhibiting corrosion. The bacterial populations present on the mild steel surface were analyzed by fluorescent in situ hybridization. Denaturing gradient gel electrophoresis (DGGE) analyses of PCR-amplified 16S rDNA fragments were conducted to determine the microbial community complexity of the biofilm. Greater weight losses of mild steel in loam soil and the seawater/sediment system with NaNO₃ (48.86 mg/g and 19.96 mg/g of weight loss, respectively after 20 weeks) were observed with total heterotrophic bacterial population presented (106.695 MPN/ml and 0.11187 MPN/ml respectively) compared to the autoclaved control (7.17845 mg/g and 0.12082 mg/g of weight loss respectively). Supplementation of 5 mM NH₄NO₃ increased the total heterotrophic bacterial population and resulted in a decrease in weight loss measurements on the stainless steel coupons (211.4 MPN/ml with a 0.01 mg/g weight loss) after 20 weeks compared to the non-autoclaved loam soil and loam soil supplemented with NaNO₃ (139.2 MPN/ml and 134.9 MPN/ml respectively with no weight loss). SEM images of the mild steel coupons confirmed the presence and adherence of bacteria on the metal surface. Stereo microscopic images displayed reddish-brown deposits and pitting on the coupon surface. Isolation, identification and sequence analysis revealed that most microorganisms were the Bacillus species. This group of microorganisms are iron-oxidizing bacteria that could also promote the corrosion process. After 20 weeks of incubation, the total SRB cell counts were lower in samples supplemented with NaNO₃ in both loam soil and the seawater/sediment system. This study also indicated that the isolated aerobic microorganisms do play a role in the corrosion process in both stainless and mild steel. DGGE analysis revealed microbial diversity in the corrosion products especially those affiliated to the bacterial phyla Firmicutes and Gamma-Proteobacteria. Fluorescent in situ hybridization analysis allowed for an overall estimation of Eubacteria and sulphate-reducing bacteria present in the biofilm formed on the surface of mild steel. The current study indicates that the addition of nitrates did not significantly reduce the rates of corrosion of both mild and stainless steel. However, it does seem that environmental conditions did pose as an important factor in the corrosion process. Therefore, further studies need to be implemented to analyze the environmental type, microbial composition and optimization of the concentration of nitrates for possible mitigation of metal corrosion. To optimize MIC prevention and control, collaboration between engineers and microbiologists proves advantageous to develop an environmentally sound and potentially cost-effective approach to control corrosion. / Thesis (Ph.D.)-University of KwaZulu-Natal, Westville, 2012.

Note: / as hip and knee prosthesis, orthopaedic fixations and coronary stents. The definition of a material's biocompatibility necessitates meeting a number of criteria, including high corrosion resistance and desirable interactions of the material's surface with biological species, such as cells, platelets, and serum proteins. SSs offer acceptable resistance to uniform (general) corrosion when used as materials of construction in sorne industrial applications, which is due to the formation of a thin passive oxide film on their surface. [...] / Les aciers inoxydables (AI) 316-L sont fréquemment utilisés dans le domaine biomédical. Par exemple, nous les retrouvons dans les prothèses de hanche et de genou, dans les fixatures orthopédiques et dans les prothèse vasculaires. Pour qu'un matériel soit biocompatible, il doit avoir une résistence élevée à la corrosion. De plus, la surface du matériel doit avoir des intéractions favorables avec les différentes espèces biologiques c'est-à-dire les cellules.[...]

Thesis (M.S.)--Brigham Young University. Dept. of Mechanical Engineering, 2005. / Includes bibliographical references (leaves 65-67).

Biomining technologies have been developed to use acidophilic microorganisms and the reactions that they catalyze to extract metals from ores in the mining industry. This biological processing through hydrometallurgy is responsible for the production of a significant portion of the world’s copper and gold supplies. Acidithiobacillus ferrooxidans is one of the better-studied and important chemolithotrophic bacterial species that is a part of the natural consortia found in mines across the world. This acidophile is unique in the array of redox reactions it participates in as it is capable of oxidizing both iron and reduced inorganic sulfur species, enabling dissolution of metal from minerals. As the transition to renewable energy continues and the demand for electronic devices grows, more copper and other valuable metals will need to be extracted from increasingly low-grade ores, such as chalcopyrite. Additionally, there has been a growing interest in further developing this biotechnology for the leaching and the recovery of valuable metals from scrap alloys and electronic waste as these feedstock streams can contain rare metals at concentrations above those found in the earth. However, the challenge in deploying biomining to these applications involves understanding the interactions that can potentially inhibit the extraction of these metals. In this dissertation, we expanded the genetic toolbox for A. ferrooxidans by using a transposition technique for the chromosomal integration of exogenous genes. The ability to permanently modify the genome enables engineering of strains that can be used in industry without the need of maintaining selective pressure for plasmid-based expression. Next, we investigated the potential role of A. ferrooxidans in microbially influenced corrosion. We focused on finding conditions that would enable the corrosion of stainless steel, which is resistant to the medium typically used for the growth of the bacterium. Additionally, the further optimization of the corrosive environment and the introduction of genetically engineered cells led to additional corrosion of a higher-grade stainless steel. Then, we explored how altering the bioavailability of sulfur in different formulations could shift the population phenotypes in A. ferrooxidans. We found that a unified description with a few parameters could describe the wide range of behaviors observed in the presence of iron and sulfur. Thus, using this improved understanding of A. ferrooxidans, we are able to engineer phenotypes of interest to generate robust strains that can modulate leaching conditions.

Note:

No description available.

The influence of impurities in magnesium chloride upon the rate of attack of stress corrosion cracking in AISI 304 stainless steel has been investigated. Previous investigations in this laboratory indicated that different batches of technical grade magnesium chloride produced poor reproducibility of results. These inconsistencies were attributed to the presence of varying amounts of impurities which are commonly found in technical grade magnesium chloride. In this investigation, certified grade magnesium chloride was used with impurities intentionally added in order to determine how each affected the constants M and C in the following equation, which relates the maximum crack depth D, to the time of exposure to the corrosive medium, t: log t • D/M + log C The constant C represents the time of exposure to the corrosive media to nucleate cracking, and M is a function of the rate at which cracks propagate. It was determined that the impurity ions most commonly found in magnesium chloride were nitrate, sulfate, and calcium. A significant difference in the constants V and M was found to exist with the presence of each impurity. It was not determined, however, if a change in pH resulted from the addition of the impurity compounds. Hence, a further study is required in order to determine the pH of the corrosive media and the effects of its changes. / Master of Science

Orientador: Rodnei Bertazzoli / Tese (doutorado) - Universidade Estadual de Campinas, Faculdade de Engenharia Mecânica / Made available in DSpace on 2018-08-20T09:33:23Z (GMT). No. of bitstreams: 1 Costa_RytneySantos_D.pdf: 3018655 bytes, checksum: 4c710836a20f71e366fa51b7e28fddfe (MD5) Previous issue date: 2012 / Resumo: O Brasil, em busca de combustíveis alternativos, menos poluentes e com sustentabilidade econômica eficiente, apresentou uma solução para suas necessidades, acrescentando na sua matriz energética o etanol combustível e com isto, submeteu materiais metálicos dos sistemas veiculares e tanques de armazenamento de combustível a processos corrosivos. Aços inoxidáveis têm se mostrado uma alternativa viável, no entanto é necessário estudos para obter dados que permitam averiguar a suscetibilidade desse material a processos corrosivos neste novo meio. O enfoque deste trabalho é analisar os efeitos da corrosão do álcool etílico hidratado combustível (AEHC) sobre o aço inox AISI 304 nas condições de sobtensão e sem tensão, fundamentando-se na possível influência da corrosão nas propriedades mecânicas da liga. Foram realizados ensaios de imersão em longo prazo para avaliação de perda de massa e observação por microscopia eletrônica de varredura (MEV). Paralelamente, amostras na forma de corpos de prova para ensaios de tração e fadiga, foram imersos no meio (AEHC) para avaliação dessas propriedades. Os resultados acusaram, a partir de 3456 horas de imersão, ganho de massa nas condições tensionadas e não tensionadas, sugerindo a ocorrência de passivação do metal. Imagens obtidas por MEV mostraram a formação de pites, cujo tamanho evoluiu em função do tempo de imersão. O ensaio eletroquímico com utilização arranjos de microeletrodos de diâmetros de 10, 20, 30, 100, 200 e 500 ?m acusou baixa corrente de corrosão. As propriedades mecânicas de resistência à tração, limite de escoamento e deformação específica não se mostraram influenciáveis aos efeitos corrosivos do meio sobre a liga. O ensaio de fadiga, usando os parâmetros da distribuição de probabilidade de Weibull e a durabilidade característica (?), mostrou redução da resistência à fadiga da liga quando imersa em AEHC, evidenciando que o meio corrosivo, contendo cloreto, inicializou a nucleação de pites e potencializou a formação de trincas durante os ensaios de fadiga, favorecendo a redução do limite de resistência à fadiga do aço inox AISI 304 / Abstract: The Brazil, in search of alternative fuels, cleaner and with economic efficiency, presented a solution to their needs, adding its energy in the fuel ethanol and with that submitted materials of metal vehicle systems and storage tanks of fuel processes corrosive. Stainless steels have proven a viable alternative; however it is necessary studies to obtain data to determine the susceptibility of this material to corrosive processes in this new medium. The focus of this paper is to analyze the effects of corrosion of hydrous ethanol (AEHC) on AISI 304 stainless steel under conditions of tension and without tension, the ground of the possible influence of corrosion on the mechanical properties of the alloy. Immersion tests were conducted to evaluate long-term weight loss and observation by scanning electron microscopy (SEM). In parallel, samples as specimens for tensile and fatigue, were immersed in the medium (AEHC) for evaluation of these properties. The results showed, as of 3456 hours of immersion, the weight gain of not tensioned and stressed conditions, suggesting the occurrence of passivation of the metal. Images obtained by SEM showed the formation of pits whose size has evolved as a function of immersion time. The electrochemical assay using microelectrode arrays of diameters 10, 20, 30, 100, 200 and 500 ?m charged low-current corrosion. The mechanical properties of tensile strength, yield strength and strain specific were not influenced to the corrosive effects of the medium on the league. The fatigue test, using the parameters of the Weibull probability distribution and durability characteristic (?), showed a reduction in fatigue resistance of the alloy when immersed in AEHC, indicating that the corrosive medium, containing chloride, initiated the nucleation of pits and potentiated the formation of cracks during the fatigue tests, favoring the reduction of the fatigue endurance limit of stainless steel AISI 304 / Doutorado / Materiais e Processos de Fabricação / Doutor em Engenharia Mecânica

Conselho Nacional de Desenvolvimento Científico e Tecnológico / Nesta dissertação é modelado computacionalmente o processo de corrosão por pites em aço inoxidável. Foi implementado um programa computacional que modela a distribuição da concentração local de espécies agressivas, o grau de dano do filme passivo, a suscetibilidade a pites e a distribuição dos pites, com base no modelo de PUNCKT et al. [2004]. Como uma contribuição desta dissertação foi considerada uma dependência entre a concentração local de espécies agressivas e a corrente anódica simulada. Também foi considerada, como outra contribuição do presente trabalho, a existência de pites estáveis e o efeito determinístico decorrente das regiões de inclusões de MnS em aços inoxidáveis. A geração de pites sobre uma superfície metálica é modelada usando um processo randômico de nucleação de pites, e a solução do modelo matemático permite a visualização da superfície corroída. / In the present work a computational model of the pitting corrosion process in stainless steal is developed. A computational program was implemented for the determination of the distribution of the local concentration of aggressive species, the degree of the passive film damage, the susceptibility of pitting and the pitting distribution, based on the PUNCKT et al. [2004] model. As a contribution of the present work dependence between the local concentration of aggressive species and the simulated anodic current is considered. It was also considered, as another contribution, the existence of stable pits and the deterministic effect of regions of MnS inclusions in stainless steel. The generation of pits over a metallic surface is modeled using a random process of pits nucleation, and the mathematical model solution gives the corroded surface visualization.

Conselho Nacional de Desenvolvimento Científico e Tecnológico / Nesta dissertação é modelado computacionalmente o processo de corrosão por pites em aço inoxidável. Foi implementado um programa computacional que modela a distribuição da concentração local de espécies agressivas, o grau de dano do filme passivo, a suscetibilidade a pites e a distribuição dos pites, com base no modelo de PUNCKT et al. [2004]. Como uma contribuição desta dissertação foi considerada uma dependência entre a concentração local de espécies agressivas e a corrente anódica simulada. Também foi considerada, como outra contribuição do presente trabalho, a existência de pites estáveis e o efeito determinístico decorrente das regiões de inclusões de MnS em aços inoxidáveis. A geração de pites sobre uma superfície metálica é modelada usando um processo randômico de nucleação de pites, e a solução do modelo matemático permite a visualização da superfície corroída. / In the present work a computational model of the pitting corrosion process in stainless steal is developed. A computational program was implemented for the determination of the distribution of the local concentration of aggressive species, the degree of the passive film damage, the susceptibility of pitting and the pitting distribution, based on the PUNCKT et al. [2004] model. As a contribution of the present work dependence between the local concentration of aggressive species and the simulated anodic current is considered. It was also considered, as another contribution, the existence of stable pits and the deterministic effect of regions of MnS inclusions in stainless steel. The generation of pits over a metallic surface is modeled using a random process of pits nucleation, and the mathematical model solution gives the corroded surface visualization.