No description available.

D. Tech. Chemical, Metallurgical and Materials Engineering / Corrosion is the chemical or electrochemical interaction between a material, especially metals, and their environment resulting in mild to severe deterioration of the material and its properties. The economic impact and problems resulting from corrosion has drawn strong attention from scientists and engineers worldwide. Stainless steel is the most important engineering metal worldwide, and industrially stainless steel is used extensively due to its resistance to corrosion e.g. in acid pickling, industrial acid cleaning, acid descaling, oil well acidizing and the petroleum industry. The corrosion resistance of stainless steels is due to the formation of a protective film which covers the steel surface instantaneously when exposed to mild operational conditions in the presence of oxygen; however, the oxide is most often porous and insufficient to protect the steel from further oxidation and corrosion attack in harsh environments. It is hypothesized that: In-depth understanding of the electrochemical behaviour of ferrous alloys in interaction with selected organic compounds in acidic environments will enhance inhibitor application for corrosion control; Failure and poor performance of most inhibitor admixtures can be eliminated with comprehensive knowledge of electrochemical interaction at the metal-inhibitor interface, passive film formation, duration and breakdown, adsorption characteristics, bond formation and molecular structure effect; Optimization of the current electroanalytical method will enhance effective pitting corrosion detection, analysis and control with the use of organic inhibiting compounds. The primary aim of this research is to develop the science required for the effective assessment, development and confident use of organic compounds (heterocyclic compound, organosulphur compound, simple alcohol, aromatic amine compound, aromatic amine derivative and aminoalcohol) and tested alloys (austenitic stainless steel type 304 and mild steel) for applications in astringent environments through conventional and optimized corrosion monitoring techniques.

No description available.

Extruded Al-Mn alloy are used in heat exchanger applications due to their light weight and good thermal conductivity. Depending on the application, the units may be subjected to external corrosion, which can lead to perforation of the tube. The industrial test most commonly used to assess heat exchanger alloys is the seawater acetic acid test (SWAAT). This is a cyclic fog at 40°C and pH 2.9. In the present study, it was found that pits developing in extruded Al-Mn tubes during the SWAAT test are purely crystallographic. Furthermore, a mechanistic understanding for crystallographic pitting has been developed. The SWAAT test can be of relatively long duration and, typically, does not yield information on the underlying corrosion initiation and propagation mechanisms. In the present study, alternate methods to assess pitting corrosion were elaborated. A drop testing procedure has been successfully implemented to study the mechanism of pit initiation. It was revealed that pits initiated within the aluminium matrix in the vicinity of grain boundaries. A close link between large second-phase particles and pit initiation was established. No preferred grain orientation for pit initiation was evident. Scanning electron microscopy and associated tomography were undertaken for the first time to clarify the mechanism of pit propagation. The pit walls were oriented {100}, while the fast-dissolving planes were {110} and {111}. The findings were in accordance with previous literature. Corrosion penetrated deeper into the alloy when the corrosion front was close to a grain boundary. Pit walls were cathodic to the aluminium matrix, possibly due to enrichment of alloying elements at pit walls. The effect of alloy additions on the corrosion behaviour of extruded aluminium alloys was investigated. Alloys with varying copper, iron and manganese contents were compared. Shot noise analysis and post-mortem analyses were undertaken. The increased amount of manganese in solid solution delayed the transition from micropits to stable pitting. This delay is attributable to second-phase particles that are less cathodic to the aluminium matrix in alloys with increased manganese content. Increasing copper decreased the size of the dissolved polyhedra during stable pitting. Furthermore, pits propagated faster in alloys rich in copper. This could be attributed to an increased level of copper enrichment at the pit walls. Finally, more second-phase particles were present in alloys with increased iron levels. Additionally, pits located in those alloys propagated deeper than pits located in alloys with low levels of iron. A competition between two different types of cathodes, enrichment layer and second-phase particles, is suggested. In conclusion, the effect of microstructure and alloy additions on the corrosion mechanism for crystallographic pitting developed during the project was clarified.

In applications where resistance to localised corrosion is required, stainless steel alloys containing molybdenum are generally used thanks to their superior resistance to localised attack in aggressive environments. For ferritic stainless steels, vanadium additions have been found to also have a beneficial effect on the resistance to localised corrosion. In this study vanadium and molybdenum were compared directly as alloying elements in 18% chromium ferritic stainless steel as far as their effect on increasing the resistance to localised corrosion is concerned. Pitting potentials in a neutral chloride solution were used as the criterion for qualifying resistance to localised corrosion and it was shown that vanadium gave similar or slightly higher pitting potentials at addition levels of up to 4% (weight percent). It was subsequently found that the mechanism by which the molybdenum and the vanadium increase the resistance to localised corrosion, are not the same. The experimental data for the molybdenum containing alloys corresponded well with other work done in this field. The positive effect of molybdenum additions on the pitting resistance of these alloys could be explained through its effect in lowering the dissolution rate in the active dissolution region by enriching on the dissolving surface. The vanadium additions to these alloys were shown not to have an effect on the active dissolution kinetics. The effect of these two alloying elements on the initiation of metastable pits were examined, but no meaningful advantage for the vanadium containing alloys over the rest could be found. It is suggested that vanadium play a role in changing the dissolution kinetics of the salt film, which forms during the growth of a metastable pit. A delayed dissolution of salt film remnants would lead to a loss of the enriched pit solution, which would cause the metastable pit to repassivate. / Dissertation (M Eng (Metallurgical Engineering))--University of Pretoria, 2007. / Materials Science and Metallurgical Engineering / unrestricted

Thesis (Ph. D.)--Ohio State University, 2008. / Title from first page of PDF file. Includes bibliographical references (p. 160-164).

A dissertation submitted to the faculty of engineering, University of the Witwatersrand, Johannesburg in fulfillment of the requirements for the degree of master of science / Steel 3CR12 is a 12 chromium, titanium stabilized, corrosion resisting steel which was developed in South Africa in the recent past (Abbreviation abstract) / AC2017

Thesis (Ph.D.) -- McMaster University, 1999. / Includes bibliographical references (leaves 220-228). Also available via World Wide Web.

Thesis (M.S.)--University of North Texas, Dec., 2009. / Title from title page display. Includes bibliographical references.

University of Macau / Faculty of Science and Technology / Department of Electromechanical Engineering