Thèse doctorat : Génie des Matériaux : Villeurbanne, INSA : 2005. / Titre provenant de l'écran-titre. Bibliogr. p. 189-197. Communications de l'auteur, 1 p.

Thèse doctorat : Génie des matériaux : Ecully, Ecole centrale de Lyon : 2008. / 80 références.

Thèse doctorat : Génie des matériaux : Ecully, Ecole centrale de Lyon : 2008. / Titre provenant de l'écran-titre. 80 références.

Thesis (Ph. D.)--University of Florida, 2000. / Title from first page of PDF file. Document formatted into pages; contains xxii, 263 p.; also contains graphics. Abbreviated abstract copied from student-submitted information. Vita. Includes bibliographical references (p. 252-262).

The forensic analysis of fourteen post-tensioned beam specimens after six years of aggressive exposure testing is the focus of this thesis. Funding for this research came from TxDOT and FHWA. Current post-tensioning materials and construction practices have been deemed inadequate due to fairly recent corrosion failures. Recently developed post-tensioning components and systems were assessed to determine their suitability to prevent durability concerns that had been found in older structures. Testing was conducted on the following variables: Strand Type, Duct Type, Duct Coupler Type, Anchorage Type, Electrically Isolated Tendons. Non-destructive and destructive testing methods were used to study the specimens and were evaluated on their effectiveness in predicting corrosion. Service life analysis was done on a structure using the strands and ducts study in the project. Galvanized duct showed substantial pitting and area loss. The majority of the plastic ducts had no observed damage. However, tendon grout chloride concentrations in most cases were extremely elevated with both galvanized and plastic ducts. This indicated that moisture had entered the duct, through either the couplers and/or grout vents. Except for strands from one specimen, the strands had minor corrosion with occasional mild pitting. The exception had heavy mild pitting confined to a small portion of the strand due to a hole in the duct. Backfill quality was good but it did not bond well with the base concrete. Therefore, moisture and chlorides entered the anchorage region. The electrically isolated tendon did not perform as well as expected. The grout chloride concentrations and level of corrosion damage were comparable to the concentrations and corrosion damage from the more conventionally protected specimens. / text

The development of biofilms on mild and stainless steel surfaces in pure and mixed batch cultures of the bacterial species Pseudomonas fluorescens and Desulfovibrio desulfuricans and the role of these biofilms in corrosion of steel has been investigated. Early events leading to the formation of biofilms have been elucidated by studying the attachment of bacterial cells to steel using epifluorescence microscopy. To identify the nature of the bacterial surface components involved in the initial adhesion to mild steel, lectins, their sugar inhibitors and saccharolytic and proteolytic enzymes have been employed. Polyclonal antibodies have been raised against bacteriallipopolysaccharides (LPS) and their influence on bacterial adhesion assessed. LPS have been analysed chemically by gas-chromatography (GC-FID) and gas chromatography-mass spectrometry (GC-MS) to determine their ~arbohydrate composition and fatty acid content. On the basis of the results obtained the ~nvolv~~~nt of glucose and N-acetylglucosamine, present in O-antigenic fractions of LPS, 10 the lOlnal attachment of the two bacterial species to mild steel is suggested. Both types of carbohydrates are likely to be involved in early attachment of Pseudomonas to mild steel, whereas only a polymeric fonn of N-acetylglucosamine seems to participate in adhesion of Desulfovibrio. The subsequent biofilm development on steel surfaces and their accompanying corrosion h~s been monitored by scanning electron microscopy (SEM). SEM studies reveal very different patterns of bacterial biofilms on mild and stainless steel and show varied degrees of corrosion occurring on these surfaces. Thin and patchy Pseudomonas biofilms are accompanied by little corrosion whilst thick. more continuous, Desul/ovibrio biofilms are associated with higher levels of corrosion. Energy dispersive X-ray analysis (BOAX) of corrosion products present on steel surfaces indicates ferrous sulphides as the major components in Desul/ovibrio biofilms. The corrosion of steel in bacterial cultures has also been investigated by kinetic polarisation measurements. The results obtained from cathodic and anodic polarisation curves, combined with SEM and EDAX analyses confmn the SEM observation. Stainless steel is not subjected to any great degree of fouling or corrosion under the chosen experimental conditions. The EPS associated with biofilms and released into the liquid phase of the culture media (free EPS) has been characterised. Proteins and carbohydrates in these polymers are detected colorimenically and by SDS-gel electrophoresis. Uronic acids, found in biofilmbound BPS. are not detected in free EPS. The GC-MS and GC-FIO analyses have aided in establishing types and quantities of neutral carbohydrates present in bacterial exopolymers and show that the neutral sugar composition of free and surface-associated BPS is not identical for a given bacterial culture. The biofilm-bound BPS are believed not to play a major role in corrosion of mild steel but to provide additional mechanisms in its facilitation. No correlation between levels of free BPS and corrosion of steel is found.

M. Tech. Engineering Metallurgy. / Aims to improve the mechanical and chemical properties of mild steel, by developing highly corrosion resistant surface coatings of zinc-aluminum using the electro-deposition techniques. Properties that are targeted are specifically hardness, wear and corrosion resistances.

The use of XPS and AFS technique has been explored in the stLrly of the surface chemistry of a whole electrode surface (XPS) and the surface chemistry of natural pits (AFS). EDXA and to a snall extend SIMS were also used in the investigation of the individual pits. A high resolution Auger electron microscope which has an analytical resolution as snall as 0.1 .un enables a nevly formed pit of less than 2 .un in diameter to be investigated. By using a Cl/Mg ratio an attempt had been made to correlate the surface chemistry of whole electrodes exposed at different potentials in 1M MgCl2 solution to the surface chemistry of individual pits naturally produced qy means of a simulated metal to metal crevice made of cammercial stainless steels (SS316 and SS304) immersed in 1M MgCl2 solution. '!he correlation was fomd to be good and within the expected limit of the data produced by XPS and AFS. The estimated val ue of potentials of the surface of pit and its immediate vicinity was based on a theoretical model of variation of potential aromd a pit by Melville and also on the potential-current curve of the steel sample in the test sol ution. The Q/Mg ratio was shown to be useful in determining the activity of pits. In repassivated pits in the crevice mouth zone magnesiun was a dominant species relative to chlorine, this is in contrast to the pits in the central part of the crevice which were (ii) engulfed in general corrosion. Active pits in the area between the two regions have higher value of Cl./Mg ratio in their surface than that in the surface in their immediate vicinity. The role of chraniun in pitting corrosion is suggested to counter the pitting attack by the fonnation of chramiun oxide and oxy-chloride on the surface of pit. Molybdenun when present, also concentrates on the surface of pit. The type of corrosion attacks on sulphide inclusions in stainless steel depend on the copper content of the inclusions. Pitting will be likely to take place on pure MnS incl usions but not on copper enriched-MnS inclusions. The fonnation of copper sulphide is suggested to be important in reducing the amount of active species of sulphur on the corroded inclusions.

No description available.

In the present study, the corrosion behaviour of several magnesia-chrome (MC) and magnesia-alumina spinel (MA) bricks against fayalite type slags was investigated and the role of the spinel phases was highlighted . The experimental results revealed that the corrosion resistance of the MC bricks was superior to the MA bricks against KIVCET slags in static and dynamic conditions . As a result of the interaction between MgO from MC bricks and the slag, a modified forsterite phase (Mg, Fe, Zn, Ca)₂SiO₄ was formed, which destroyed the precipitated complex spinel bonds at the grain boundaries of periclase and magnesia-chromia spinel . Furthermore, both MgO and MgO-MgAl₂O₄ spinel in the MA brick dissolved into the slag, which resulted in modified forsterite phases of (Mg, Fe, Zn, Ca)₂SiO₄ and (Mg, Fe, Zn)(Fe, Al)₂O₄ complex spinels, respectively. In addition, the accretion formation in the KIVCET furnace was investigated through solubility experiments of Cr₂0₃ in the KIVCET slag with various amounts of lead, which revealed that the net contribution of Cr₂0₃ to the spinel formation is the highest in the barren (no Pb) slag, followed by high-lead (11% Pb) and it is the lowest for the low-lead (6% Pb) slag. The amount of spinel solid solution increased consistently with increasing Cr₂0₃ dissolved and the PbO existent in the slag. From examinations of several used bricks from the tuyere area of a Peirce Smith nickel converter, it was found that the corrosion is due to the interaction of the partially oxidized matte penetrating deep into the brick and the magnesia grains forming (Mg, Fe, Ni, Co) xOy spinels . Analyses of brick samples used in the KIVCET Electric Furnace roof identified deep reaching sulphation, which weakened the bonding phase between coarse magnesia grains. In the Bottom Blown Oxygen Converter, a highly aggressive lead and bismuth oxide rich slag penetrated deep into the brick, which destroyed the grain boundaries, causing the refractory to be easily eroded at the refractory-slag interface. Our studies concluded that the spinel phases, either as magnesium chromate, magnesium aluminate or complex spinel [(Mg, Fe)(Cr, Al, Fe)₂O₄], enhanced the corrosion resistance of a basic refractory to fayalite type slags from the non-ferrous smelting and converting furnaces.