Understanding Of Corrosion Processes Research Articles

Atmospheric corrosion modeling

AbstractA better understanding of corrosion processes during the last years is leading to an increased demand for numerical corrosion models. Corrosion models become increasingly relevant toward simulations, lifetime predictions, and the optimization of corrosion prevention. Also, the improvements in computational power and capacity give rise to an increased number of research projects in this field. Totally different modeling approaches are applied to a wide range of different corrosion processes. This leads to a dispersion of information in the literature. The aim of this paper is to give an overview of the present approaches in atmospheric corrosion modeling. In the past, atmospheric corrosion has been modeled based on empirical, historical data. These models provide fitted functions of the corrosion rate or damage as a function of time for different environmental parameters. These methods give no or little information about the underlying physicochemical phenomena that determine the corrosion processes. During the last decade, more and more work has been done on causal approaches. Therefore, the focus will be on these recent advances in atmospheric corrosion modeling. The links will be made to the microscopic models of isolated corrosion phenomena. The examples are crevice corrosion, corrosion under porous layers, and the modeling of local electrochemical methods. Also, some more general, macroscopic approaches will be discussed. These macroscopic approaches will be compared to each other and positioned into the scope of multiscale modeling. The first goal of atmospheric corrosion modeling is to provide tools in the understanding and quantification of the processes under the influence of external atmospheric conditions. These models could reduce the current corrosion assessment methods that essentially rely on empirical models. On a longer term, modeling would aid in optimizing the material selection, structural design, and maintenance management.

Localized Impedance Measurements for Electrochemical Surface Science

An approach for in-depth characterization of complex electrode/electrolyte interfaces based on localized impedance measurements is described in detail. The local ac probing of the interface is performed at different frequencies by means of scanning electrochemical microscopy (SECM) using ultramicroelectrodes (SECM tips) which enables visualization of dependences of the localized impedance spectra as a function of spatial coordinates. Subsequent fitting of these spectra to physical models visualize the local distribution of parameters describing the electrochemical interface, such as the electric double layer capacitance and the charge transfer resistance. Three model examples are analyzed dealing with typical situations, when the measurements are either affected or not by specific adsorption of anions at the SECM-tips. It is demonstrated that the approach holds promise for electrochemical surface science, particularly for better understanding of corrosion processes taking place at metal surfaces in aggres...

Microbial Aspects in Corrosion Studies of Stainless Steels

Microbially influenced corrosion (MIC) has been focusing increasing attention from different research areas in the last years, as an answer to the demand of wide variety of industries and degradation cases. The difficulty in reaching an adequate understanding of corrosion processes induced by microorganisms has result in cross-fertilization of ideas between researchers from different disciplines like microbiology, electrochemistry, metallurgy and materials engineering. Different MIC mechanisms can be simultaneously or alternately occuring on various materials, where a complex boundary layer of corrosion products, bacterial cells and other environmental factors are present on the surface. The paper discusses new aspects of MIC mechanisms induced by sulphate reducing bacteria species, taking into consideration modern techniques and new approaches in the study. Practical cases concerning microbial risks, failures illustrate the complexity of this phenomena: from local corrosion problems through stress corrosion cracking and hydrogen damage. The role of microstructure and chemical composition of materials is also highlited as a key factor in microbial damaging. In addition to this, the principal morphologies of attack and cracking are described.

Use of electrochemical techniques for the conservation of metal artefacts: a review

Electrochemical techniques like mechanical and chemical ones should be among the panoply of techniques conservators normally use when they conserve metal artefacts. Often though, they are discarded because they are considered as too complicated and dangerous. As a consequence, not much development in the use of these techniques in conservation was observed before the 1990s when their application to marine artefacts once again drew the attention of conservation professionals. More recently, the latter have recognised the importance of these techniques in the understanding of corrosion processes as well as their monitoring and in the solving of specific conservation issues. Furthermore, instruments that were previously only used by corrosion scientists are today entering the conservation field. Portable tools have even been designed so that treatments can be carried out in situ. The current trend is to cluster electrochemical and analytical techniques in parallel in order to fully understand the behaviour of metal artefacts when conserved.

Analysis of the effects of outdoor and accelerated ageing on the optical properties of reflector materials for solar energy applications

Lifetime tests of solar reflector materials are eligible prior to application, to prove the stability of the optical properties. In this work, six reflector materials were aged outdoors and in a climatic test chamber. The surfaces of the samples were inspected using profilometry and optical microscopy. The total and specular reflectance spectra were measured using spectrophotometry and the weighted solar reflectance values were calculated before and after ageing. Reflectors of silvered glass, anodised aluminium, thin film-coated anodised aluminium, and lacquered rolled aluminium withstood accelerated testing well, while a laminated evaporated aluminium reflector, which was specular initially, became diffuse. Laminated and lacquered reflectors withstood outdoor ageing better than expected from accelerated ageing and better than unprotected thin film-coated and anodised aluminium, which degraded significantly outdoors. Thus, optical degradation depends on climatic conditions and on the protective layer, if applicable. The discrepancy between results from outdoor and accelerated ageing shows that a thorough understanding of corrosion processes is necessary for drawing conclusions about long-term performance from accelerated ageing tests.

Theories of Corrosion as Applied to Preservation of Archaeological Ceramics

ABSTRACTAn understanding of corrosion processes is beneficial in the preservation of ancient ceramic artifacts. A wealth of information is available on this topic in the materials science and engineering literature. Significant contributions to the corrosion literature have been made over the last 15 years due to the extensive research performed on nuclear wasteform systems. This paper will review the current state of understanding of aqueous corrosion of glasses. We will discuss how this information can be applied to some of the current issues in preservation of archaeological ceramics.

A Systematic Scheme for Examining CORRODED METAL SPECIMENS

Many corrosion problems have to be investigated by post mortem examination, and it is often through the medium of such investigations that valuable progress has been made in the understanding of corrosion processes. To quote but one example—one form of corrosion of copper tube, which very occasionally occurs in domestic water and which, more often than not, used to be ascribed rather vaguely to ‘deposit attack,’ was eventually explained, after three or four years of intensive laboratory work, to the conjoint existence of a discontinuous cathodic film on the metal and the lack of natural inhibitor in the water. The first tangible clues to the solution of this problem, in fact, first became evident from a painstaking examination of failed specimens. To obtain sufficient evidence to explain a corrosion failure often involves the use of such diverse techniques as micro‐chemical analysis, x‐ray examination and metallography, and the principal object of this article is to describe in detail the way in which such techniques are employed.