State of art of microbiologically induced corrsion of carbon steel and stainless steel in aqueous environments
Başlık çevirisi mevcut değil.
- Tez No: 796381
- Danışmanlar: PROF. MARCO ORMELLESE
- Tez Türü: Yüksek Lisans
- Konular: Kimya Mühendisliği, Metalurji Mühendisliği, Chemical Engineering, Metallurgical Engineering
- Anahtar Kelimeler: Belirtilmemiş.
- Yıl: 2019
- Dil: İngilizce
- Üniversite: Politecnico di Milano
- Enstitü: Yurtdışı Enstitü
- Ana Bilim Dalı: Belirtilmemiş.
- Bilim Dalı: Belirtilmemiş.
- Sayfa Sayısı: 58
Özet
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Özet (Çeviri)
Microbiologically induced corrosion (MIC) is a complex phenomenon and interdisciplinary approach is needed including biology, electrochemistry and material science. Rather than being an individual mechanism, MIC is generally act together with other abiotic corrosion mechanisms. Individual microorganisms are extensively studied to understand each bacterium type specific mechanisms. SRB is the most studied one among them. In general, there are two types of MIC; type I is direct contribution of microorganisms by either direct electron uptake from metallic material or involvement to cathodic or anodic reactions. Type II MIC is the secretion of corrosive metabolites. SRB exhibit both types of MIC, as the biocatalytic cathodic sulfate reduction theory suggests they can catalyze sulfate reduction reaction and so iron oxidation. It is showed that they can provide electrons directly from the metallic iron. SRB can produce corrosive metabolites especially when they present together with sulfur oxidizing bacteria (SOB), sulfuric acid production by establishing a sulfur cycle. Iron bacteria including iron oxidizing (IOB) and iron reducing bacteria (IRB) can participate in iron redox cycle directly. IOB can oxidize Fe(II) ion and resulting the formation of iron hydroxide products. They can provide anoxic niches which are very suitable environments for SRB growth. Acid producing bacteria (APB) is a general term define organisms secreting organic acid as their metabolites. They reduce organic acid which can be coupled to iron oxidation or they can modify the pH to very acidic values. When they present together with other organisms like SRB, the damage increases by their synergistic effect. Other corrosion related microorganisms are nitrate reducing bacteria (NRB), manganese oxidizing bacteria (MOB) and methane producing bacteria, methanogens. Real field applications, however, includes more than one bacteria specie presenting together in a biofilm. Biofilm is dynamic structure and can cause formation of differential aeration cells, pH modifications, chemical and surface modifications. Initial stages of biofilm formation can cause very severe localized corrosion attacks due to non-uniformity of the film. Carbon steel in aqueous environments suffers from corrosion and biotic contribution is always a concern especially in marine, freshwater environments or water distribution systems. IOB is the first 3 surface colonizer of steel materials. Because of their action iron hydroxide corrosion products form. After depletion of oxygen and formation of anoxic niches, anaerobic type of microbes, like SRB, become to develop inside biofilm. At this stage an increase in corrosion rate is observed generally. At very long time exposures a dangerous type of corrosion, so called accelerated low water corrosion (ALWC) may occur. Sulfur cycle mechanism initiated by SRB and SOB lead to secretion of corrosive compounds like sulfuric acid. Because SOB is an aerobe while SRB is an anaerobe, special conditions are needed for this type. Stainless steels also show similar colonization patterns when they immersed in aqueous environments. However, their corrosion mechanism is different than carbon steel due to protective passive layer. Ennoblement is a positive shift of corrosion potential of stainless steel and increases pitting risk in the presence of chloride ions. Some mechanisms are proposed to understand ennoblement including pH decrease, peroxide formation, heavy metal influence, siderophores formation and the role of manganese dioxide and direct contribution of electroactive bacteria. Another MIC mechanism of stainless steels is formation CrO3 with the biologic activities consequently leads to breakdown of passive film and possible localized corrosion attacks. There are some models, mathematical or not, to predict MIC susceptibility of systems. They can be divided into two categories; bacteria specific and process specific. Bacteria specific ones pay attention on single species so their application on real field application can be problematic. Process specific models picture more general situation including abiotic corrosion mechanisms may act together with MIC. Almost all models make assessment on the risk of MIC rather than predicting corrosion rate.
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