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  • Open access
  • 104 Reads
Influence of organic matter/bacteria on the formation and transformation of sulfate green rust

Corrosion processes of carbon steel permanently immersed in natural seawater are in any case influenced by microorganisms due to the important biological activity. The influence of sulfide-producing bacteria is well known but various microorganisms, the biofilm itself, and the numerous organic species associated with biological activity may also play a role. Because the sulfate green rust GRSO4 is one of the main corrosion products of carbon steel in seawater, the role of organic matter/bacteria on its formation and transformation was addressed. GRSO4 was precipitated from Fe(II) and Fe(III) salts in the presence of various marine bacterial species. Abiotic experiments were performed for comparison, a first one without any organic species, a second one with sodium acetate added. The obtained aqueous suspensions were aged at room temperature for 1 week. The number of bacteria (UFC/mL) was followed over time and the solid phases were characterized by XRD. Whatever the fate of the bacteria (no activity, or activity and growth), the formation of GRSO4 was favored and its transformation to magnetite completely inhibited. This effect is attributed to the adsorption of organic molecules on the surface of the GRSO4 crystals. A similar effect, though less important, was observed with acetate.

  • Open access
  • 268 Reads
Modelling of time-dependent behaviour of corroded reinforced concrete elements

Nowadays, the durability of reinforced concrete (RC) elements affected by corrosion has become a worldwide research topic, especially after some catastrophic failures that have involved corroded structures and infrastructures. One of the main purposes related to durability reduction is the evaluation of the maintenance of adequate safety and residual capacity throughout the life of the structure. Generally, the corrosion deterioration induces cross-sectional area reduction and degradation of mechanical properties of steel and concrete. Furthermore, referring to long-term prediction, creep and shrinkage play a fundamental role on the overall response of RC structures. For this reason, a nonlinear finite element approach, called PARC_CL 2.1 crack model, has been used to investigate the behaviour of reinforced concrete elements characterized by corrosion of reinforcements. The PARC_CL 2.1 model is a fixed crack model based on multi-layer shell elements, developed at the University of Parma and implemented in a user subroutine UMAT.for for ABAQUS. The paper focuses on the modelling description and the comparison between the results of the analysis with the experimental data available in literature.

  • Open access
  • 106 Reads
Comparison of progressive sealing methods of anodized aluminium as potential substitute for the chromate sealing

Comparison of progressive sealing methods of anodized aluminium as potential substitute for chromate sealing was analysed. Among them sealing in rare earth metal salt solution (Ce3+), so called cold impregnation and sealing in zirconium solution were compared to the standard sealing in boiling water. The sealed specimens were exposed to a corrosive environment (1 wt.% NaCl solution). The decisive qualitative parameters of the sealing layers were the sealing coefficient Kp applying the standard ISO 3210 and the resistance inside the pores applying EIS measurements (filling resistance). Based on the proposed equivalent circuit, the filling resistance can be considered as the indicator of the sealing quality for anodized aluminium. The results of EIS analysis are supported by EDX and IR measurements. It can be concluded that the sealing in zirconium solution provides the most satisfactory results and it can be used as an adequate substitute for chromate sealing.

  • Open access
  • 181 Reads
Corrosion properties of biodegradable AZ31 and ZK60 magnesium alloys: in situ study

Biodegradable magnesium alloys is promising materials for medicine application. The corrosion rate and type of corrosion are ones of most important properties for this kind of materials. Fine-grained biodegradable alloys AZ31 (hot-rolled) and ZK60 (extruded) were studied in present work with using in-situ methods such as hydrogen evolve corrosion rate evaluating and incessant surface observation and ex-situ methods such as weight loss and confocal laser scanning microscopy investigation. Experiment methodic include immersion test in SBF (0.9% NaCl aqueous solution) in 120 hours with 37 oC with recirculating corrosion media. Hydrogen evolve was measuring with burette with frequency 1 hour, surface observation made by high-definition camera, pH was measuring twice a day. Corrosion rate curves, 3D corrosion surface morphology and videos shown staging of corrosion damage were received. As a result, ZK60 is less corrosion resistant and addicted to pitting corrosion, whereas AZ31 shown filiform corrosion.

  • Open access
  • 75 Reads
Corrosion inhibition of 3003 aluminum alloy in molar hydrochloric acid solution by olive oil mill liquid by-product

According to the literature, the works on the inhibition of aluminum alloy corrosion using naturally occurring compounds are limited. For this, the inhibiting effect of oil mill liquid by-product (OMW) on the corrosion of 3003 aluminum alloy (AA3003) in molar hydrochloric acid solution was evaluated using electrochemical techniques. In parallel, a computational approach based on DFT/B3LYP and Monte Carlo methods was used to understand the inhibition process under electronic and atomic scales, respectively. The experimental results reveal that OMW has a good inhibiting effect on the corrosion of AA3003 alloy in the tested solution and acts as a cathodic inhibitor. The inhibitory efficiency increases by increasing OMW concentration to attain 89% at 6.0 ppm. The effect of temperature shows that the inhibition efficiency of OMW decreases with temperature rising. Nevertheless, a good prevention capacity of 83% is obtained at 338 K. Such interesting achieved protection property was attributed to the adsorption of OMW constituents onto the alloy surface via a mixed physichemisorption process. This process is found to obey the Langmuir adsorption isotherm. Furthermore, the activation thermodynamic parameters of the corrosion process of AA3003 alloy were also determined and discussed. The computational outcomes outlined the ability of the OMW components to interact favorably with the metal surface, hence the formation of a protective layer, which justified the observed inhibition behaviors. Conferring to the present study, OMW can be used as a good green corrosion inhibitor for AA3003 alloy in the acidic medium.

  • Open access
  • 198 Reads
The halo effect and its electrochemical repair in reinforced concrete

Repaired reinforced concrete structures often suffer from a reinforcement corrosion problem known as the incipient anode (or halo) effect. The diagnosis of this problem is widely reported to be macrocell activity caused by small changes in reinforcement potential in the parent and repair concrete. Cathodic protection is a technique that is used to prevent or arrest such corrosion by inducing small potential changes on the reinforcement. This study looks at the effects potential in both causing and arresting corrosion in concrete. Potential measurements on repaired structures suggest that potential changes on passive steel cannot cause corrosion. Further, the protective effects of a negative steel potential shift induced by the relatively small practical current densities applied in cathodic protection are negligible when oxygen has easy access to the reinforcement. Other factors are suggested to affect both of these processes.

  • Open access
  • 182 Reads
Adverse effect of 2,5Pyridinedicarboxylate corrosion inhibitor on PEO coated Mg

Incorporation of corrosion inhibitors into coatings on metallic substrates is an effective approach to achieve active corrosion protection and improve the overall corrosion resistance of the coated metallic substrate. PEO (Plasma Electrolytic Oxidation), apart from its good corrosion and wear properties, features a highly porous microstructure that can be leveraged as a suitable host for the corrosion inhibitors. The positive corrosion inhibition effect of a chemical on a bare metallic substrate is usually considered as the primary criterion for the selection of inhibitors to be incorporated into a PEO coating system. However, in this study, we demonstrate that 2,5Pyridinedicarboxylate (2,5PDC), as an effective universal inhibitor for bare Mg alloys, does not improve the corrosion protection performance of a PEO-coated Mg substrate and causes the PEO layer to fail faster. To uncover this adverse effect of 2,5PDC, the degradation process of the PEO-coated magnesium during immersion in 3.5 wt% NaCl solution in the presence and absence of 2,5PDC was investigated by Electrochemical Impedance Spectroscopy (EIS). In addition, local concentrations of H2 and O2 in the solution were measured to gain insight into the cathodic reaction rates on the magnesium substrate. The deteriorative behavior of 2,5PDC towards the PEO-coated magnesium is discussed based on the obtained results as well as the STEM and SEM observations of the PEO coating cross-section after the immersion. Complementary ToF-SIMS depth profile analysis of the corrosion product layer on a bare magnesium surface provided further insight into the mechanism of early failure of PEO-coated magnesium in the presence of 2,5PDC. The findings of this study provide a criterion for choosing an effective inhibitor for PEO-coated Mg alloys based on the interaction of the inhibitor with the PEO layer and the bare magnesium.

  • Open access
  • 162 Reads
Development of deficient grout and corrosion due to water and solute transport

Abstract: Prestressed concrete has been used all over the world for bridge construction, but severe corrosion of steel strand in post-tensioned tendons has been documented. Recently, the corrosion was associated with physically and chemically deficient segregated grout with elevated moisture and concentrations of aggressive chemical species that allowed for early aggressive corrosion to develop. The transport of moisture and ionic species was thought to be related to capillary transport through the braided steel wires, but other transport mechanisms within the tendon duct may be possible as well. The grout mass pressure within the grout column increases the hydrostatic pressure in the system. Vertical elevation of the grout with the hydrostatic pressure of grout mass may elevate the moisture content at higher elevations. The paper reviews the results of lab and field testing characterizing deficient grouts and the various transport mechanisms that can be formed in post-tensioned tendons, including modeling efforts of unsaturated flow and solute transport using HYDRUS-1D.

  • Open access
  • 201 Reads
Advances in smart coatings: classification, improvements and applications

The concept of intelligence has many applications, such as coating and cyber security. Smart coatings have the ability to sense, response to several cycles and interact with their environment. Properties that are affected by either momentary or continuous external stimuli in smart coatings can be related to corrosion, fouling, fungal, self-healing, piezoelectric, microbiological, etc. These coating properties can be obtained via combinations of either organic or inorganic polymer phases, additives and pigments. In this study, a review on smart coatings with corrosion protective properties is reported from two aspects of intrinsic and extrinsic self-healing ability. The concept of extrinsic self-healing smart anticorrosive coatings is based on the use of capsules or multichannel vascular systems loaded with amount of healing agent/inhibitor. On the other hand, the idea of intrinsic self-healing ability relies on the chemical and physical structure of polymer matrix that under the stimulation of heat, light, and other external stimuli, the reactions among polymer chains are easily triggered. The outcome is that smart coatings exhibit improved properties compare to traditional coatings. It is mentioned that smart anticorrosive coating not only has enhanced passive barrier function, but also realizes active defense. As a result, there is a significant improvement of the service life and overall performance of the coating.

  • Open access
  • 94 Reads
Field corrosion monitoring in marine atmosphere by electrochemical noise: Theoretical and Mathematical Models towards Quantitative Analysis

Electrochemical noise (EN) can be used in situ to investigate corrosion processes and to detect and monitor the corrosion of metallic materials in marine atmosphere. We developed several sensors and probes that can be used in field corrosion detection. EN data are largely influenced by the measurement mode, the surface area of the working electrodes, the electrolyte resistance, and the symmetry of the electrode system. Herein, the advantages and limitations of electrochemical kinetics, equivalent circuit, and shot noise methods for quantifying corrosion rates with EN are discussed.