No full-text available
To read the full-text of this research,
you can request a copy directly from the authors.
Physical methods in corrosion technology
Abstract
After a review of some of the corrosion transport mechanisms the importance of physical techniques and theories in the understanding and measurement of corrosion is outlined
... (ii) The aqueous corrosion science has unequivocally shown that at pH > 5 the iron surface is always covered by an oxide film. In this regard Holmes and Meadowcroft [20] described an interesting thumbnail sketch in which without the protective action of a fence (oxide-film) the rabbit (Fe 0 surface) is a defenceless prey for a rapacious dog (corroding environment). The oxide film generated by corroding Fe 0 is primary porous. ...
... It is interesting to notice that the observed effect of shaking speed on the Fe 0 reactivity is qualitatively the same as the often-enunciated effect of mixing intensity on reaction rate constant to demonstrate the possibility of mass transfer limitations for reactions with elemental metals in batch systems [39]. Thereafter, the overall rate of contaminant reduction [20,44,[63][64][65][66][67], the results of the present study suggest that the rate of contaminant reduction by Fe 0 materials is always mass-transfer limited. Moreover, the reported reaction mechanism difference at slow and high mixing speeds is likely to be the result of the interference of iron precipitation on the removal process. ...
Despite two decades of intensive laboratory investigations, several aspects of contaminant removal from aqueous solutions by elemental iron materials (e.g., in Fe0/H2O systems) are not really understood. One of the main reasons for this is the lack of a unified procedure for conducting batch removal experiments. This study gives a qualitative and semi-quantitative characterization of the effect of the mixing intensity on the oxidative dissolution of iron from two Fe0-materials (material A and B) in a diluted aqueous ethylenediaminetetraacetic solution (2 mM EDTA). Material A (fillings) was a scrap iron and material B (spherical) a commercial material. The Fe0/H2O/EDTA systems were shaken on a rotational shaker at shaking intensities between 0 and 250 min-1 and the time dependence evolution of the iron concentration was recorded. The systems were characterized by the initial iron dissolution rate (kEDTA). The results showed an increased rate of iron dissolution with increasing shaking intensity for both materials. The increased corrosion through shaking was also evidenced through the characterization of the effects of pre-shaking time on kEDTA from material A. Altogether, the results disprove the popular assumption that mixing batch experiments is a tool to limit or eliminate diffusion as dominant transport process of contaminant to the Fe0 surface.
... (ii) The aqueous corrosion science has unequivocally shown that at pH > 5 the iron surface is always covered by an oxide film. In this regard Holmes and Meadowcroft [20] described an interesting thumbnail sketch in which without the protective action of a fence (oxide-film) the rabbit (Fe 0 surface) is a defenceless prey for a rapacious dog (corroding environment). The oxide film generated by corroding Fe 0 is primary porous. ...
... As an example, Warren et al. [62] worked with Fe 0 and Zn 0 and came to the conclusion that the overall rate of reaction may have been mass-transfer limited in the experiments involving Fe 0 , and reaction-limited in the Zn 0 experiments. Concordantly to the results of Warren and co-workers [34,62] and evidences from the open corrosion literature [20,44,6364656667, the results of the present study suggest that the rate of contaminant reduction by Fe 0 materials is always mass-transfer limited. Moreover, the reported reaction mechanism difference at slow and high mixing speeds is likely to be the result of the interference of iron precipitation on the removal process. ...
Despite two decades of intensive laboratory investigations, several aspects of contaminant removal from aqueous solutions by elemental iron materials (e.g., in Fe(0)/H2O systems) are not really understood. One of the main reasons for this is the lack of a unified procedure for conducting batch removal experiments. This study gives a qualitative and semi-quantitative characterization of the effect of the mixing intensity on the oxidative dissolution of iron from two Fe(0)-materials (materials A and B) in a diluted aqueous ethylenediaminetetraacetic solution (2 mM EDTA). Material A (fillings) was a scrap iron and material B (spherical) a commercial material. The Fe(0)/H2O/EDTA systems were shaken on a rotational shaker at shaking intensities between 0 and 250 min(-1) and the time dependence evolution of the iron concentration was recorded. The systems were characterized by the initial iron dissolution rate (k(EDTA)). The results showed an increased rate of iron dissolution with increasing shaking intensity for both materials. The increased corrosion through shaking was also evidenced through the characterization of the effects of pre-shaking time on k(EDTA) from material A. Altogether, the results disprove the popular assumption that mixing batch experiments is a tool to limit or eliminate diffusion as dominant transport process of contaminant to the Fe(0) surface.
... Iron corrosion produces iron oxides and hydroxides that are larger in size than iron atoms (Fe 0 ) in the lattice system (V oxide > V iron ) (Pilling and Bedworth 1923, Holmes and Meadowcroft 1977, Lazzari 2008. This evidence means that the volumetric expansive nature of iron corrosion should be considered wherever Fe 0 oxidative dissolution is likely to produce iron oxides/hydroxides. ...
The use of metallic iron (Fe0) for environmental remediation is applied industrially with a great degree of empiricism. Rules of thumb seem to be the only guide followed by the greater part of the Fe0 remediation community. The present communication demonstrates the validity of such a harsh statement and hopes that the research community will now follow the 10-year-old path concealing Fe0 remediation and mainstream science. A promising application is safe drinking water provision on a decentralized manner.
... The complexity of the process of aqueous iron corrosion which has traditionally been controversially discussed among chemists, electrochemmists and physicists [55,56]. This controversy could be regarded as a plausible explanation for the mistakes discussed above. ...
The starting argument of using metallic iron (Fe0) as an environmental remediation agent considered Fe0 oxidative dissolution as the anodic half-reaction of contaminant reduction. However, it has been repeatedly observed that both reactions are not simultaneous. The present article challenges the adequacy of the peer-review system when the starting position is biased. First, it argues that the presumption of contaminant reductive transformation (e.g. the status quo) is preferred by most Fe0 experts, including journal editors. Second, it recalls that the status quo strongly distorts the facts. Third, most Fe0 researchers have backed the status quo without question. Fourth, the legitimacy that experts and researchers lend to the status quo limits innovation opportunities. Abandoning the comfortable status quo is suggested as the way to restore room for constructive innovation in Fe0 research.
... As can be seen from Eq. (19) in order to estimate t cr a value of k p needs to be determined. This can be done using experimental results, e.g., data showing the growth of W rust with time (e.g., [44,45]). However, Liu and Weyers [4] did not determine k p correctly. ...
Water pollution is calling for a sustainable remediation method such as the use of metallic iron (Fe ⁰ ) to reduce and filter some pollutants, yet the reactivity and hydraulic conductivity of iron filters decline over time under field conditions. Here we review iron filters with focus on metallic corrosion in porous media, flaws in designing iron filters, next-generation filters and perspectives such as safe drinking water supply, iron for anaemia control and coping with a reactive material. We argue that assumptions sustaining the design of current Fe ⁰ filters are not valid because proposed solutions address the issues of declining iron reactivity and hydraulic conductivity separately. Alternatively, a recent approach suggest that each individual Fe ⁰ atom corroding within a filter contributes to both reactivity and permeability loss. This approach applies well to alternative iron materials such as bimetallics, composites, hybrid aggregates, e.g. Fe ⁰ /sand, and nano-Fe ⁰ . Characterizing the intrinsic reactivity of individual Fe ⁰ materials is a prerequisite to designing sustainable filters. Indeed, Fe ⁰ ratio, Fe ⁰ type, Fe ⁰ shape, initial porosity, e.g. pore size and pore size distribution, and nature and size of admixing aggregates, e.g. pumice, pyrite and sand, are interrelated parameters which all influence the generation and accumulation of iron corrosion products. Fe ⁰ should be characterized in long-term experiments, e.g. 12 months or longer, for Fe dissolution, H 2 generation and removal of contaminants in three media, i.e., tap water, spring water and saline water, to allow reactivity comparison and designing field-scale filters.
A knowledge system (KS) is a knowledge that is unique to a given group of persons. This form of knowledge may have a local or natural origin and is linked to the community that has produced it. On the contrary, the core of mainstream science (MS) is the desire to profoundly understand processes, through sequential studies such as hypothesis formulation, experiment and prediction. Thus, KS is communitarian and MS is universal. KS can be understood and rendered universal through MS. In general, a process discovery (know-how) may be intuitive, accidental, conjectural or inspirational but outcomes should be predictable and repeatable as soon as the know-why is achieved by MS. This paper argues that the technology of using metallic iron for water treatment has all the characteristics of a KS and that promoters of this technology have deliberately rejected scientific arguments leading to the know-why of the fortuitous discovery. Consequently, the technology has developed into an impasse where controversial discoveries are reported on all relevant aspects. It is concluded that the integrity of science in endangered by this communitarian behaviour.
Despite two decades of intensive laboratory investigations, the removal mechanism of several contaminants from aqueous solutions by elemental iron (e.g. in Fe0/H2O systems) are not really elucidated. Two of the major reasons for this are: (i) the failure to consider Fe0/H2O systems as consisted of the elemental iron material (Fe0) covered by a layer of corrosion products (oxide-film), and (ii) the failure to treat properly the combined problem of mass transport and chemical reaction in these complex systems. Well-mixed batch experiments that have been undertaken in order to circumvent the mass-transport problem associated with bulk solutions have not always adequately addressed these key issues. Mixing intensity may not only affect the hydrodynamic but also the chemical dynamics, in particular the formation of the oxide-film. The present work presents a critical review on the process of oxide-film formation and its impact on the process of mass-transport to the Fe0 surface. It is shown that well-mixed batch systems are not necessarily an effective tool for investigating the mechanism of contaminant removal by Fe0 since mixing may increase corrosion rate, avoid/delay the formation of oxide-films and/or provoke their abrasion. This discussion suggests that quantitative abiotic contaminant reduction in Fe0/H2O systems may mostly occur within the oxide-film as result of: (i) electron transfer from Fe0 surface, (ii) catalytic activity of secondary reductants (FeII, H2/H). Non-shaken batch experiments are proposed as a simple tool to investigate mass-transport limitation through oxide-films at laboratory scale. Working with stationary Fe0 samples and controlled stirring speeds may allow the investigation of oxide-film effect under more realistic conditions.
The article considers analytical modelling of crack initiation in the concrete cover caused by corrosion of reinforcing steel. Initially, existing analytical models describing this phenomenon are critically reviewed. A new analytical model proposed by the authors is then presented and calibrated against available experimental data. The model is based on a thick-walled cylinder approach. To account for partial cracking of the concrete cover the cylinder is divided into two parts – a cracked inner cylinder and an uncracked outer one. The model ensures a consistent stress–strain formulation within both the inner and outer cylinders and enables to achieve complete continuity of stresses and strains on the boundary between the cylinders that distinguish it from the previously published analytical models. The model is then used to estimate the amount of corrosion products, which have diffused into concrete pores and cracks before full cracking of the concrete cover. It is shown that this amount may be larger than has been previously assumed. It is also shown that the assumption that corrosion products diffuse into concrete only until they fully fill the so-called ‘porous’ zone around a reinforcing bar leads to results, which are difficult to explain from a physical point of view. An alternative approach to account for the diffusion of corrosion products into concrete is proposed. Finally, a possible decrease in the corrosion rate with time and its influence on the prediction of the time to crack initiation are considered.
An investigation was conducted concerning the possibility to use lasers in nuclear reactors to measure oxide thickness on components, in temperatures up to 200 C, and in radiation fields in the order of hundreds of rads per hour. Experiments in the laboratory are discussed and the design of the monitor is considered. Attention is also given to a number of difficulties found in reactor trials of the instrument and the approaches used to overcome these difficulties.
The growth of magnetite (Fe3O4) on a polycrystalline iron substrate has been continuously followed in situ in the S.E.M. at 500°C in 13.3 N m−2 CO2. Medium resolution (250 Å) micrographs of the same area have been taken at time intervals over periods of oxidation in excess of 200 hr. Successive layers of oxide crystallites grow according to the same logarithmic rate law, but the overall thickening rate of the oxide film conforms to the parabolic rate law. A theoretical analysis of this situation suggests that the dominant factor determining the overall growth kinetics is the frequency of oxide nucleation steps. It can be shown that the basic logarithmic growth of individual oxide crystallites could lead to a variety of overall growth processes, depending upon the conditions required for nucleation.
- Cabrera N
- Evans U R
- Wagner C