Corros. Mater. Degrad., Volume 3, Issue 3 (September 2022) – 13 articles

Many heritage objects consist of glass in contact with metals. By ion exchange with absorbed water, alkaline aqueous films are formed on the glass surface. They contain sodium and/or potassium, hydroxide, and carbonate (uptake of carbon dioxide) ions. These electrolytes induce corrosion while in contact with metal. Surprisingly, this phenomenon has only been realised by research in Stuttgart in the last two decades. About 350 affected objects were detected in the meantime in a number of heritage collections. Because of the special electrolytes, unusual corrosion products are often formed. The unknown structure and formula of three of them could be determined by modern X-ray powder diffraction data evaluation. One example is the basic potassium lead carbonate, KOH‧2PbCO₃, detected on a pewter lid of a glass jug. The sodium analogon of already known structure was found in hollow glass balls mirrored on the inside with molten lead. Chalconatronite, Na₂[Cu(CO₃)₂]‧3H₂O, is known as a corrosion product of copper alloys in contact with soda solutions (here: from glass degradation). Exposed to acetic acid emissions (e.g., from wood), it transforms to a sodium copper acetate carbonate of hitherto undetermined structure. The ubiquitous pollutant formaldehyde reacts directly to formate in the alkaline medium provided by glass degradation. On copper alloys in contact with glass, formates are, therefore, frequent: Na₄Cu₄O(HCOO)₈(OH)₂‧4H₂O in 50% of all cases and in 33% Cu₂(HCOO)(OH)₃. Zinc (from brass) forms Zn(HCOO)₂‧2H₂O and Zn₄Cu₃(Zn_1−xCu_x)₆(HCOO)₈ (OH)₁₈·6H₂O. There are a number of other corrosion products, e.g., containing zinc and carboxylates awaiting further characterisation. Preventive conservation needs to slow down corrosion by dry storage (not lower than 35% rH). Pollutants need to be avoided by careful selection of materials for storage, display, and conservation. Full article

To investigate the corrosion protection behavior of naturally derived cocoyl sarcosine in combination with N-b-hydroxyethyl oleyl imidazole for steel CR4 in 0.1 M NaCl, different evaluation systems (weight loss, electrochemical measurements, and spray corrosion tests) were used. Both compounds were tested in different concentrations (25–100 mmol/L) and with variable dip coating times (1–30 min), first individually and then in combination, to check any synergistic effects for surface protection. Both showed only an insignificant corrosion inhibiting effect with less than 50% efficiency at all concentrations and dip coating times if used alone. In contrast, compound combinations revealed an improved corrosion inhibition correlated with higher concentrations. Across all methods, the compound combination concentration of 100 mmol/L resulted in improved efficiency of up to 83% for gravimetric tests, up to 84% for the impedance measure and more than 91% for potentiodynamic polarization. Dip coating variations proved 10 min to be the best option for all compounds with a maximum efficiency of up to 86% for the compound combination. Full article

A critical review is presented on modeling of the radiolysis of the coolant water in nuclear power reactors with emphasis on ITER. The review is presented in two parts: In Part I, we assess previous work in terms of compliance with important chemical principles and conclude that no model proposed to date is completely satisfactory, in this regard. Thus, some reactions that have been proposed in various radiolysis models are not elementary in nature and can be decomposed into two or more elementary reactions, some of which are already included in the models. These reactions must be removed in formulating a viable model. Furthermore, elementary reactions between species of like charge are also commonly included, but they can be discounted upon the basis of Coulombic repulsion under the prevailing conditions (T < 350 °C) and must also be removed. Likewise, it is concluded that the current state of knowledge with respect to radiolytic yields (i.e., G-values) is also unsatisfactory. More work is required to ensure that the yields used in radiolysis models are truly “primary” yields corresponding to a time scale of nanoseconds or less. This is necessary to ensure that the impact of the reactions that occur outside of the spurs (ionizing particle tracks in the medium) are not counted twice. In Part II, the authors review the use of the radiolysis models coupled with electrochemical models to predict the water chemistry, corrosion potential, crack growth rate in Type 304 SS, and accumulated damage in the coolant circuits of boiling water reactors, pressurized water reactors, and the test fusion reactor, ITER. Based on experience with fission reactors, the emphasis should be placed on the control of the electrochemical corrosion potential because it is the parameter that best describes the state of corrosion in coolant circuits. Full article

Carbon steel rebar (ASTM A615) has been widely used in reinforced concrete (RC), but its susceptibility to chloride ions remains a critical issue. Low alloy chromium steel has been used to increase corrosion resistance and extend service life, such as in 9% Cr rebar (ASTM A1035-CS). In this work, we characterized two electrochemical systems over time: ASTM A615 and A1035-CS corrugated rebar immersed in SCPS in the presence of NaCl for 12 months. The interfacial processes evolution for the ASTM A1035-CS rebar for both general and local corrosion showed different active-passive responses from those of carbon steel. Because the 3.5% wt. NaCl exceeded the chloride threshold for passive breakdown of both materials, the ASTM A1035-CS showed a five-fold higher impedance and lower general corrosion rate. In localized conditions, the low alloy chrome content rebar showed less density localized attack than the ASTM A615 rebar. These results were attributed to the overall damage evolution involving the formation and stability of corrosion products over time. The local attack appeared to be a random spatial process due to changes in the local environment. Full article

Cathodic protection efficiency of complex carbon steel structures in confined seawater environment was studied using a specific experimental device. Schematically, this device consisted of a Plexiglas matrix, crossed by a channel 50 cm long, 5 mm deep, 1.5 to 5 cm wide, which moreover included four bends at 90°. Seawater flowed continuously inside the channel over 12 steel coupons embedded in the Plexiglas matrix. Cathodic protection was applied at a constant potential of −1060 mV vs. Ag/AgCl-seawater with respect to a reference electrode located outside the channel, at the seawater flow entry. The potential of four selected coupons was monitored over time via a microelectrode set close to each coupon. It varied significantly with the distance separating the coupons from the channel entry. At the end of the 3.5-month experiment, a polarization curve was acquired. The residual corrosion rate under cathodic protection was estimated via the extrapolation of the anodic Tafel line. It varied from <1 µm yr⁻¹ to 16 µm yr⁻¹, depending on the potential reached by the coupon (between −900 and −1040 mV vs. Ag/AgCl-seawater) at the end of the experiment and on the properties of the calcareous deposit formed on the steel surface. Full article

The corrosion behavior of two stainless steels (316L and 304L) was evaluated using a CO₂-loaded aqueous solution of 30 wt.% monoethanolamine (MEA) with a view to simulating corrosion related mechanisms in amine treatment procedures. Corrosion behavior was experimentally evaluated as a function of CO₂ loading and solution temperature, using electrochemical techniques (polarization curves, cyclic polarization, and EIS measurement). The results reveal that the aqueous MEA solution containing CO₂ creates a favorable environment for the corrosion of both stainless steels. The rate of corrosion is accelerated when the temperature of the loaded MEA solution rises, which was attributed to the thermal degradation of the loaded MEA, thus causing higher kinetics of the cathodic reactions at higher temperatures. More specifically, for the SS 304L the corrosion rate is almost doubled when the solution temperature is increased from 25 °C to 40 °C and is quadrupled when the solution temperature rises to 80 °C. For the SS 316L, the corrosion rate becomes almost threefold and sixfold upon increasing temperature of the load amine solution to 40 °C and 80 °C, respectively. The overall corrosion rate of SS 316L is lower with respect to the SS 304L for the same temperature and loading conditions. The essential dependency of corrosion rate on solution type (unloaded and loaded MEA solution) demonstrates that the corrosion process and reactions are controlled by a diffusion mechanism. Full article

Post-tensioning structures with metallic ducts risk corrosion, rupture or collapses due to chloride ingress. The use of tight corrugated polymer ducts combined with electrically isolated anchorages (EIT) changed the situation. Laboratory and many field applications proved the tightness of the duct, showing resistance values higher or much higher than 50 kΩm, the acceptance criteria for a tight duct. The most important fact is that EIT tendons allow quality control and long-term monitoring of the duct tightness. EIT ducts (also with resistance values below the threshold criteria) can be monitored over the whole service life: only a progressive decrease of the measured resistance indicates a corrosion risk for this specific tendon. The most important structural elements can be easily monitored for the first time and damage initiation can be detected early. After a successful use in Europe EIT technology is now expanding progressively in the US. Full article

Improved corrosion barrier coatings (CBCs) to protect metals will allow future metal structures to operate for extended periods, ensuring improved safety by reducing environmental pollution and maintenance costs. Many production methods and design of corrosion barrier coatings (CBCs) have been developed. This review focuses only on CBCs made with chemistry techniques. These CBCs can be passive and active with remarkable performance. Today, most of the work focuses on the discovery and application of “smart nanomaterials,” which, if incorporated into “passive CBCs,” will turn them into “active CBCs,” giving them the phenomenon of “self-healing” that extends their service life. Today, many efforts are focused on developing sensors to diagnose corrosion at an early stage and CBCs that self-diagnose the environment and respond on demand. In addition, recent technological developments are reviewed, and a comprehensive strategy is proposed for the faster development of new CBC materials. Full article

The splash and spray and tidal zones are generally assumed to be the most severe marine exposure environments with respect to steel reinforcement corrosion in concrete structures. However, it has been observed in several aged marine structures along the Southern African coastlines, that there is usually relatively insignificant reinforcement corrosion damage in the tidal zone, despite very high (above-threshold) chloride contents. To develop a full understanding of the severity of marine exposure conditions with regard to the actual deterioration, it is imperative that other factors that directly affect corrosion, such as oxygen availability at the steel surface (which is influenced by concrete quality, cover thickness and moisture condition), are carefully considered. The laboratory experimental work in the study presented in this paper comprised of different cover depths (10, 20 and 30 mm) and w/b ratios (0.5 and 0.8) and simulated marine tidal, splash and submerged environments. The results show that for any give exposure environment, the relative influence of each of the various factors considered should be considered in conjunction with the other factors; this finding can be generalized to include all relevant factors that can affect corrosion in a given exposure environment including ambient temperature. For example, a cover depth of 30 mm in the tidal zone with a simulated intertidal duration of 6 h effectively resulted in similar corrosion behavior to that in the submerged zone. The paper concludes that engineers should consider these factors when applying standard exposure classes in the design for durability of marine structures. Full article

Surface chloride concentration (Cs) is a key parameter used to feed models adopted to simulate chloride penetration into concrete and evaluate the initial period of corrosion. Although there are several models that have been proposed for the representation of Cs behaviour in the marine atmosphere zone, such models are still scarce. In this context, we analysed the behaviour of surface chloride concentration in concrete specimens exposed over 12.5 years in a marine atmosphere zone in the northeast of Brazil. The experimental work was carried out in two steps: environmental characterization, which was undertaken for temperature, relative humidity, rainfall, wind characteristics and sea-salt data; and chloride concentration measurements for the concrete surface considering three different concrete mixtures with w/b ratios of 0.65, 0.57 and 0.50. The results showed that the Cs increase over time followed three stages: a first short stage characterised by an initial dispersion, followed by an increase period and then a final period of stabilisation, which was not fully reached in the present study. This behaviour can be represented by a power function or a sigmoidal function, with a better fit with the latter. Chloride concentration in the atmosphere plays an important role in Cs behaviour. Higher availability of chlorides means higher Cs values. The relationship between Cs and the rate of chloride deposition on a wet candle was analysed and the function $Cs=C_0+k_{cs}·{(Dac)}^n$ was the one that best fit the experimental data. Full article

The worldwide current practice of the structural design of sewers is based on procedures which usually include the effects caused by chemical and biological deterioration. However, in the last few decades, many sewer pipes have been designed using reinforced concrete which have succinctly considered such deterioration promoters. Indeed, knowledge related to reinforced concrete deterioration processes has become an important issue when forecasting the expected or remaining lifespan of sewers. Within these processes, thickness and strength losses and porosity augments have been found to be the result of the vital activity of sulfur-oxidizing bacteria and some types of fungus. This paper presents a rational methodology that uses biodeterioration measurements to describe how biodeterioration effects can affect the probability of failure during the lifetime of sewers. The probability of failure was obtained using Monte Carlo simulations based on numerical sampling from lognormal and uniform distributions. The concrete and reinforcement strength, geometric properties, H₂S concentration in the headspace, and load values were considered as the main sources of uncertainty. The results indicate that the expected service lifespan can vary between 55 and 37 years for low and high H₂S concentrations, respectively. Full article

The design processes for reinforced concrete are changing. More often, durability targets are being achieved by using modelling. This paper compares some of the models available and the precision undertaken to obtain the data that underpins the calculations, and it reflects on the change in the environment that is known to be occurring. In addition, a review of the sustainability implications of durability is considered. It is concluded that there may be more sustainable methods to achieve a long life than simply increasing cement contents and covers. Full article

Organic-inorganic coatings based on polymethyl methacrylate (PMMA)–silica–lithium are an efficient alternative to protect metals against corrosion. Although the preparation methodology is established and the thin coatings (~10 µm) are highly protective, the use of an environmentally friendly solvent has not yet been addressed. In this work, PMMA–silica coatings were synthesized using 2-propanol as a solvent and deposited on aluminum alloy AA7075, widely used in the aeronautical industry. Different concentrations of lithium carbonate (0–4000 ppm) were incorporated into the hybrid matrix to study the structural and inhibitive effects of Li⁺ in terms of barrier efficiency of the coatings in contact with saline solution (3.5% NaCl). Structural and morphological characterization by low-angle X-ray scattering, X-ray photoelectron spectroscopy, atomic force microscopy, thermogravimetric analysis, thickness, and adhesion measurements, showed for intermediate lithium content (500–2000 ppm) the formation of a highly polymerized PMMA phase covalently cross-linked by silica nodes, which provide strong adhesion to the aluminum substrate (15 MPa). Electrochemical impedance spectroscopy (EIS) results revealed an excellent barrier property in the GΩ cm² range and durability of more than two years in a 3.5% NaCl solution. This performance can be attributed to the formation of a highly reticulated phase in the presence of Li, which hinders the permeation of water and ions. Additionally, the self-healing ability of scratched samples was evidenced by EIS assays showing a fast Li-induced formation of insoluble products in damaged areas; thus, constituting an excellent eco-friendly solution for corrosion protection of aerospace components. Full article