The constant penetration of road deicers into the soil threatens the durability and reliability of buried pipes, most of which are made of ferrous alloys. In this work, the corrosion behavior of C1008 carbon steel, 65-45-12 ductile iron and CL35 gray cast iron in the simulated soil solution in the presence and absence of beet juice, as a common bio-additive to road deicers, was studied. To simulate the near-road pipeline scenario, two types of road deicers including 23% NaCl and 30% MgCl₂ with different dilution ratios (1:90 and 1:30) were added to the test solution. Beet juice was analyzed by Fourier transform infrared spectroscopy (FT-IR) and liquid chromatography-mass spectrometry (LC-MS). The corrosion behavior of the test coupons was studied using linear polarization resistance (LPR) and electrochemical impedance spectroscopy (EIS). The corrosion product layer was also evaluated by energy dispersive X-ray spectroscopy (EDS) and scanning electron microscopy (SEM). Laboratory data showed new insights into the mechanism of pipe protection by beet juice and the effect of road deicer composition, dilution ratio and alloy type on external corrosion of buried pipes.

Most of the metals exposed at atmospheric condition can be easily corroded. Especially the presence of humidity, salinity and high temperature accelerates this type of corrosion. Such type of environment is common in most part of the Saudi Arabia. The open exposed metal and their structures such as pipelines, storage tanks, pillars of solar energy, and infrastructures corroded shortly in Kingdom. Different organic coatings usually used to protect this metal and metal structures. The protection worked properly at early stage. The coating failed before the expected duration. It has been found that the UV-degradation of coating hugely affect this failure. In this study polyurethane (PU) formulations with dual function as corrosion and UV-degradation protection-based coating developed. Oil fly ash, a local industry biproduct, also used in formulation to improve the corrosion and UV-degradation resistance.

Since the planet requires environmentally sustainable and recycled materials, scientists all over the world are trying to create new materials that will benefit the environment. Natural fiber composites have been one of the most researched research subjects in recent years as a result of the need for new environmentally friendly materials. Many studies show that natural fiber hybrid composites can be a viable structural or semi-structural component alternative to synthetic fiber-reinforced composites, particularly in lightweight applications.

In industrial field, manufacturing time is one of the most important factors affecting the production costs. Structural adhesives require long curing times (i.e. 3-4 weeks) before the joined components can be safely employed. The aim of the present work is to test the effect of several thermal treatments on a commercial epoxy structural adhesive, on the final resistance of single lap joints, trying to attain the possibility of a curing time reduction. Aluminum alloy 5083, typically employed in marine applications, is used as substrate. Both the adhesive and the joints will be treated at different temperatures/times, then tensile tests will be carried out to obtain the mechanical resistance and study the failure modes. A statistical analysis will allow the evaluation of the effects of the thermal cycles on the mechanical performances of the joints and the comparison with the ones cured with the standard procedure.

Aluminum alloy (AA) 2024-T3 is commonly used in the aerospace industry due to its lightweight, high mechanical strength, and low cost. However, this alloy is highly susceptible to corrosion in chloride-containing solutions due to alloying elements such as Cu, Fe, Mn, etc. In the past, chromium (VI) compounds have been used for alloy protection against corrosion. These compounds have been strictly regulated in various countries due to their harmful effects on humans and the environment. Among possible environmentally acceptable surface treatments, the sol-gel coating is considered as an alternative. The sol-gel chemistry is based on the hydrolysis and condensation reactions of initial organically modified silica and silane reagents and also the copolymerization reactions between functional groups such as acrylates present in the reaction solution.

In this study, the corrosion performance was studied for uncoated and coated AA2024-T3. The synthesis of hybrid sol-gel was performed using 3-(trimethoxysilyl)propyl methacrylate (MAPTMS), methyl methacrylate (MMA), tetraethyl orthosilicate (TEOS) [1,2], and the addition of various fluorinated (meth)acrylates with different chain length.

The reactions taking place during preparation were characterized using real-time Fourier transform infrared spectroscopy. The solution characteristics were evaluated by measurements of thermal stability determined by thermogravimetric analysis. The optimal temperature for the condensation reaction was determined with the help of high-pressure differential scanning calorimetry. Once deposited on 2024-T3 substrates, the coatings were evaluated using a field emission scanning electron microscope coupled to an energy dispersive spectrometer to determine surface morphology, topography, composition, and coating thickness. The corrosion characterization was performed in 0.1 M NaCl using electrochemical impedance spectra (EIS) and salt spray test according to the ASTM B117-07A standard.

The results revealed the importance of the copolymerization process of added fluorinated (meth)acrylates and hydrolysis and condensation reactions to obtain a coating with low-porosity with an absence of cracks. Prepared coatings present durable barrier corrosion protection of the AA2024-T3 (EIS remain unchanged for more than one year).

References:

[1] Rodič, P.; Korošec, R.C.; Kapun, B.; Mertelj, A.; Milošev, I. Acrylate-Based Hybrid Sol-Gel Coating for Corrosion Protection of AA7075-T6 in Aircraft Applications: The Effect of Copolymerization Time. Polymers 2020, 12, 948. https://doi.org/10.3390/polym12040948

[2] Rodič, P.; Lekka, M.; Andreatta, F.; Fedrizzi L.; Milošev, I. The effect of copolymerisation on the performance of acrylate-based hybrid sol-gel coating for corrosion protection of AA2024-T3, Progress in organic coatings, 2020, 147. https://10.1016/j.porgcoat.2020.105701

This study deals with cathodic protection of carbon steel in the tidal zone. Actually, the metal can be polarized even when it is not immersed in seawater because a liquid film remains on the surface during the emersion period. The efficiency of cathodic protection then depends on the properties of this thin liquid film. The aim of the present work was to study the mineral layer formed on carbon steel coupons under cathodic protection in the tidal zone. A specific experimental system was designed, with 10X10 cm steel coupons simulating a continuous vertical structure of 5.1 m height, i.e. extending all along the tidal zone, from the low water zone to the splash zone. An Al-Zn-In galvanic anode permanently immersed in seawater ensured the protection of the coupons. After 32 months of experiment, the mineral layer covering the coupons was scraped, rapidly carried to the laboratory for analysis by XRD and µ-Raman spectroscopy. The evolution of the mineral layer from the low water zone to the splash zone was due to (i) the decreasing efficiency of the cathodic protection and (ii) the changes of corrosion processes (from those typical of a permanent immersion to those typical of atmospheric corrosion).

The inhibiting effect of 5-(4-Pyridyl)-1,3,4-oxadiazole-2-thiol on the corrosion of carbon steel in 1M HCl solution was investigated by electrochemical methods (potentiodynamic polarization and electrochemical impedance spectroscopy) and surface analysis (Raman spectroscopy and SEM-EDX). The polarization curves revealed that 5-(4-Pyridyl)-1,3,4-oxadiazole-2-thiol is able to retard the corrosion process, acting as a mixed-type inhibitor. The inhibition efficiency increases with the inhibitor concentration, reaching a maximum value of 93% at 5mM. EIS measurements showed that the anticorrosive effectiveness of 5-(4-Pyridyl)-1,3,4-oxadiazole-2-thiol is time-dependent. SEM analysis revealed that the metallic surface damage is significantly reduced due to the inhibitor adsorption on carbon steel surface. The presence of the adsorbed organic molecules on the metal was confirmed by the nitrogen and sulfur atoms detected in EDX and Raman spectra. The adsorption of the organic inhibitor on carbon steel surface obeys Langmuir isotherm.

In order to extend the service life of metallic structures special protection systems are developed. The usefulness of multifunctional molecular layers that can control not only the chemical/electrochemical corrosion but the microbiologically influenced material deterioration too, will be discussed focusing on the surface characteristics of nanocoatings. Several examples will enlighten the impact of the nanofilms on the microbial life (metabolisms, multiplication, microbial adhesion, biofilm formation). From the point of view of the microbiologically influenced corrosion (MIC) the inhibition of biofilm formation (that starts with the microbial adhesion) is a crucial factor. The other group of coatings (that is much thicker than nanofilms) can prevent the material degradation with different mechanisms. In one case the chemicals with antimicrobial activity are enclosed into small particles surrounded by shell walls, and the spheres are dispersed in paints. When the active antimicrobial material (together with other additives) will get free on mechanical or chemical impacts, the damaged paint will be recovered and the coating keeps its original inhibitive characteristics. The other class of the special paints is the so-called slow-release coatings when the active antimicrobial material is released continuously. Advantages and disadvantages of these surface modifications will be compared.

The role of lithium in the mechanisms of aqueous stability of Mg-Li alloys was explored by combining in situ and ex situ surface and solution characterization. In situ surface evolution of a corrosion resistant Mg-Li(-Al-Y-Zr)-alloy in aqueous NaCl solution was studied by confocal Raman Microscopy and Kinetic Raman Mapping [1], real time solution analysis was made with Atomic Emission SpectroElectroChemistry [2]. Additional ex situ surface characterizations by Photoluminiscence Spectroscopy, Auger Electron Spectroscopy and Glow Discharge Optical Emission Spectroscopy were made immediately after the aqueous exposure and after exposure to ambient air.

In situ analyses demonstrated that both Li and Mg dissolved in aqueous solutions from visually intact anodic areas, leaving a Li-depleted metallic layer under an approximately 100 nm thick Li-doped MgO. Interestingly, in these areas the growth of magnesium hydroxide (Mg(OH)₂) was very slow than in pure Mg, suggesting that the kinetics of the transformation MgO→Mg(OH)₂ was strongly inhibited. On the cathodic areas, local accumulation of Li₂[Al₂(OH)₆]₂·CO₃·nH₂O (Li-Al layered double hydroxide), LiAlO₂, Y₂O₃ and Mg(OH)₂ was observed. Li₂CO₃, previously considered as a component of a protective film responsible for corrosion resistance of Mg-Li alloys [3], was not present in situ on the surface evolving in aqueous solution and was detected only ex situ after the exposure to ambient air.

The proposed corrosion mechanism attributes the improvement of aqueous corrosion resistance of Mg-Li alloys to the increase of the chemical stability of MgO doped by Li⁺ [4]. The latter could be formed thanks to selectively leached in the solution Li⁺. Additionally, cathodic activation of Mg can be reduced on Li-doped MgO and Li-Al layered double hydroxide, detected in situ on cathodic areas. Pilling Bedworth ratios (PBR), calculated for lithium doped MgO film on Mg-Li alloys with different Li content, demonstrated that the condition of a protective film on Mg-Li alloy (PBR>1) requires a minimal Li concentration in the alloy close to 15-18 at. %.

[1] A. Maltseva, V. Shkirskiy, G. Lefèvre, P. Volovitch, Corrosion Science, 153 (2019) 272-282.

[2] Y. Yan, P. Zhou, O. Gharbi, Z. Zeng, X. Chen, P. Volovitch, K. Ogle, N. Birbilis, Electrochemistry Communications, 99 (2019) 46-50

[3] L. Hou, M. Raveggi, X.-B. Chen, W. Xu, K.J. Laws, Y. Wei, M. Ferry, N. Birbilis, Journal of The Electrochemical Society, 163 (2016) C324-C329

[4] Y.M. Yan, A. Maltseva, P. Zhou, X.J. Li, Z.R. Zeng, O. Gharbi, K. Ogle, M. La Haye, M. Vaudescal, M. Esmaily, N. Birbilis, P. Volovitch, Corrosion Science, 2020, 164, 108342

There are presented case studies of MIC in various industrial systems, mainly from carbon and stainless steels, which failed - water pipeline, sprinkler systems, sewage pipeline, cooling pipeline, water tanks, etc.. The identification of MIC was done according to morphology of corroded surface, chemical analysis of deposits, water analysis, etc. Bacterial tests for BSR and IRB were done, too.