Corros. Mater. Degrad., Volume 2, Issue 2 (June 2021) – 10 articles

A multi-analytical non-destructive testing (NDT) methodology was applied to copper-based artifacts originated from various archaeological sites of Greece. X-ray fluorescence (XRF), fiber optics diffuse reflectance spectroscopy (FORS) and scanning electron microscopy coupled with an energy dispersive X-ray detector (ESEM-EDX) were used for the characterization of the alloys and the corrosion products. The key elements of the artifacts belonging to the Early Bronze Age (2700–2300 BC) were copper and arsenic, while tin bronze was used for the fabrication of the Late Bronze Age (1600–1100 BC) artifacts. The effectiveness of XRF for the determination of the bulk composition was confirmed by comparative study with the previously applied atomic absorption spectroscopy (AAS) and inductively coupled plasma–atomic emission spectrometry (ICP-AES) destructive techniques. Significant differences between the artifacts were revealed through the spectral measurement of their surface corrosion products color by FORS. ESEM-EDX provided information on the microstructure, the elemental composition of the corrosion layers and bulk, as well as the distribution of the corrosion products on the surface. Conclusively, the combined NDT methodology could be regarded as a valuable and appropriate tool for the elemental composition of the bulk alloy, thus leading to the classification of their historical period and the corrosion products, contributing significantly to their conservation–restoration. Full article

Downhole heavy oil production and oil sand processing are associated with severe damage and failures of production equipment components, e.g., production tubing and pumping systems, due to erosion-corrosion resulting in processing losses, production downtime, high maintenance and replacement cost. Protective coatings (layers) on the production components mostly fabricated from low-alloy steels can be applied to minimize these problems. In the present work, the performance of hard boronized coating on carbon steel obtained through the thermal diffusion process and consisted of two iron boride layers (FeB and Fe₂B) was studied in synergistic erosion-abrasion-corrosion conditions simulating oil production environment in comparison with bare steel. Special wear testing equipment was designed and fabricated. In this testing, the inner surface of tubular sections was subjected to high velocity erosive flows of water-oil slurries containing silica sand and salts combined with rotating and oscillating motions of steel pony rods. Structural examination of the studied materials’ surfaces and their profilometry after wear testing were conducted. The iron boride coating demonstrated significantly higher performance in abrasion and erosion-abrasion-corrosion conditions compared to bare carbon steel due to its high hardness, high chemical inertness, dual-layer architecture and diffusion-induced bonding with the substrate. The boronized steel tubing and casing with inner surface protection can be effectively employed in the most critical operation conditions. Full article

The instability of iron artefacts is rooted in salt contamination during burial and damages associated with exposure to alternative oxygen levels and high relative humidity once excavated. While a combination of chemical and mechanical treatments is utilised to remove the harmful ions (chlorides, sulphur species) and excess bulky corrosion products, these methods can be hazardous for conservation staff’s health, have limited success, or require extensive treatment times. Bio-based treatments provide a potentially greener alternative for removing damaging corrosion and creating biogenic mineral passivation layers, thus remediating concerns over costs, duration, and health and safety. Pseudomonas putida mt-2 (KT2440) is capable of utilising iron under certain conditions and for phosphating mild steel; however, applications have not been made in the cultural heritage sector. To address the potential of using bacteria for conservation purposes, Pseudomonas was assessed for both the bioremediation of salt contaminates and the production of a passivation layer suitable for iron artefacts, with specific conservation concerns in mind. Key factors for optimisation include the role of agitation, chloride content, and oxygen content on bacterial growth and biomineralisation. The initial results indicate a growth preference, not reliance, for NaCl and agitation with partial success of bioconversion of a mineral source. Full article

This paper describes the methods and results of analytical TEM examinations and autoclave testing of two highly-irradiated flux thimble tube materials harvested from a commercial pressurized water reactor. The materials are cold-worked 316L, and accumulated 65 dpa and 100 dpa of radiation dose. To set the baseline for a broader study, the materials were examined in the as-irradiated condition and tested as O-ring specimens at relatively high constant loads in simulated PWR water conditions. Tests were also conducted with elevated hydrogen. For a given load, more rapid cracking was associated with higher radiation dose, and with the elevated hydrogen. Full article

The local patterns at the interfaces of corrosion stratification, developed on two archaeometallurgical bronzes (a Cu-Sn-Pb and a Cu-Zn-Sn-Pb alloy), in the as-cast condition, were assessed by OM and SEM-EDS systematic elemental chemical analyses. Previously, the alloys—whose metallurgical features and electrochemical behaviour were already well studied—have been subjected to laboratory corrosion experiments. The corrosion procedures involved electrochemical anodic polarization experiments in various chloride media: 0.1 mol/L NaCl, 0.6 mol/L NaCl and two other synthetic chloride-containing solutions, representing electrolytes present in marine urban atmosphere and in the soil of coastal sites. The characterization of the Cu-Sn-Pb alloy electrochemical patinas after anodic sweep (OCP+ 0.6 V) revealed that the metal in all electrolytes undergoes extensive chloride attack and selective dissolution of copper which initiates from the dendritic areas acting as anodic sites. The most abundant corrosion products identified by FTIR in all electrochemical patinas were Cu₂(OH)₃Cl), Cu₂(OH)₂CO₃ and amorphous Cu and Sn oxides. The characterization of the Cu-Sn-Pb alloy electrochemical patina after slow anodic sweep (OCP+ 1.5 V) in 0.1 mol/L NaCl reveals selective oxidation of dendrites and higher decuprification rate in these areas. Corrosion products of Sn-rich interdendritic areas are dominated by oxygen species (oxides, hydroxides, hydroxyoxides) and Cu-rich dendrites by chlorides. In the case of Cu-Zn-Sn-Pb, Zn in dendritic areas is preferentially attacked. The alloy undergoes simultaneous dezincification and decuprification, with the former progressing faster, especially in dendritic areas. The two processes at the alloy/patina interface leave behind a metal surface where α-dendrites are enriched in Sn compared to the alloy matrix. The results of this study highlight the dynamic profile of corrosion layer build-up in bronze and brass. Moreover, the perception of the dealloying mechanisms progression on casting features, at mid-term corrosion stages, is extended. Full article

Transition metal silicides have attracted great interest for their potential use in optoelectronic devices, photovoltaic cells, and thermoelectric conversion elements because of their high melting point, high oxidation resistance, and satisfactory thermoelectric properties. This study focuses on the effect of the deposition time and the heating temperature on the morphology and structure of the chromium silicides synthesized by the pack cementation method. A series of experiments were carried out at various temperatures (1000–1150 °C) with different deposition times (15–120 min). The morphology and the chemical composition of the samples were determined using SEM with an EDS analyzer. The structure determination and phase identification were performed by XRD analysis. The examination of the as-formed materials was completed by performing thermal stability tests. The most suitable conditions for producing CrSi₂ sample with satisfactory properties and simultaneously minimizing the cost and production time are listed. It was found that the sample synthesized at 1000 °C for 15 min during the chromizing step, in combination with the siliconizing step at 1000 °C for 60 min, presents the best thermal stability and these selected temperatures offer appropriate, economical, and repeatable results. Full article

The corrosion behaviour of a new titanium-based alloy, with nickel, molybdenum and zirconium as the main alloying elements, was studied in a simulated geothermal environment at various phase conditions of a corrosive fluid. Corrosion testing of carbon steel was also conducted for comparison. Both materials were tested at an elevated temperature between 180 and 350 °C and at a 10 bar gauge pressure in H₂O containing HCl, H₂S, and CO₂ gases with an acidic condensate of pH = 3. The study found that the titanium alloy demonstrated good corrosion resistance in a single- and multiphase geothermal environment. In the testing volume, where the boiling of testing fluid occurred, the carbon steel was prone to localized damage of oxide, sulphide and chloride corrosion products. In the superheated testing volume, a homogeneous oxide corrosion layer was observed on the carbon steel. In the testing volume where condensation of the testing fluid occurred, a sulphide layer with an oxide sublayer was formed on the carbon steel. Full article

Electrodeposited zinc and zinc-alloy coatings have been extensively used in a wide variety of applications such as transport, automotive, marine, and aerospace owing to their good corrosion resistance and the potential to be economically competitive. As a consequence, these coatings have become the industry choice for many applications to protect carbon and low alloy steels against degradation upon their exposure in different corrosive environments such as industrial, marine, coastal, etc. Significant works on the electrodeposition of Zn, Zn-alloys and their composites from conventional chloride, sulfate, aqueous and non-aqueous electrolyte media have been progressed over the past decade. This paper provides a review covering the corrosion performance of the electrodeposited Zn, Zn-alloy and composite with different coating properties that have been developed over the past decade employing low-toxic aqueous and halide-free non-aqueous electrolyte media. The influence of additives, nano-particle addition to the electrolyte media on the morphology, texture in relation to the corrosion performance of coatings with additional functionalities are reviewed in detail. In addition, the review covers the recent developments along with cost considerations and the future scope of Zn and Zn-alloy coatings. Full article

The corrosion performance of Aluminium (Al) and zinc (Zn) is of interest in repositories for radioactive waste as the production of hydrogen gas during their anoxic corrosion may create open pathways for the transport of radioactive ions. Al and Zn rods were embedded in concrete cylinders and immersed in artificial groundwater at anaerobic conditions for 2 weeks and up to 2 years in laboratory conditions. Corrosion rates were determined to enable predictions and estimations of risks for gas evolution and the assessment of the potential impact of corrosion on the structural integrity of concrete in the final repository of low and intermediate level metal-containing waste from dismantled nuclear power plants. Samples were collected after 2, 4, 12, 26, 52 and 104 weeks. The observed corrosion rates were higher for Al compared with Zn, as expected, but both materials revealed comparatively high initial corrosion rates that decreased with time, reaching steady state after 26–52 weeks. Some of the Al containing concrete cylinders were cracked as a result of the corrosion processes after 2 years of exposure, thereby providing free passage between the embedded metal and the surrounding environment. No such effects were observed for Zn. Comparative studies were performed on non-concrete-embedded Al and Zn immersed in artificial groundwater. Observed long-term corrosion rates (1–2 years) were similar to corresponding corrosion rates in concrete. The results indicate that immersion studies in artificial groundwater can be used to estimate the long-term corrosion performance of Zn and Al in concrete. Full article

Microbially influenced corrosion (MIC) is responsible for significant damage to major marine infrastructure worldwide. While the microbes responsible for MIC typically exist in the environment in a synergistic combination of different species, the vast majority of laboratory-based MIC experiments are performed with single microbial pure cultures. In this work, marine grade steel was exposed to a single sulfate reducing bacterium (SRB, Desulfovibrio desulfuricans) and various combinations of bacteria (both pure cultures and mixed communities), and the steel corrosion studied. Differences in the microbial biofilm composition and succession, steel weight loss and pitting attack were observed for the various test configurations studied. The sulfate reduction phenotype was successfully shown in half-strength marine broth for both single and mixed communities. The highest corrosion according to steel weight loss and pitting, was recorded in the tests with D. desulfuricans alone when incubated in a nominally aerobic environment. The multispecies microbial consortia yielded lower general corrosion rates compared to D. desulfuricans or for the uninoculated control. Full article