Stainless steels are widely deployed in marine, chemical-processing, and energy infrastructures, yet their long-term integrity is threatened by chloride-induced pitting corrosion—a highly localized process that initiates stochastically and accelerates unpredictably. Conventional electrochemical methods (e.g., polarization scans, impedance) offer bulk averages and often miss the earliest, transient signatures of pit nucleation. Acoustic emission (AE) monitoring can, in principle, capture those fast microevents, but the physical origin of AE during corrosion remains debated (e.g., hydrogen bubble rupture vs. passive-film breakdown vs. pit growth), limiting interpretability and trust in early-warning use. To investigate this gap, AE was integrated with electrochemical noise (EN) in a passive, time-aligned framework to directly correlate acoustic bursts with electrochemical transients and strengthen source attribution. Using AISI 304 stainless steel exposed to 3.5 wt% NaCl at pH 2 under open-circuit conditions, we observe clear temporal coincidence between burst-type AE events and EN spikes. As corrosion evolves, AE amplitudes and durations increase, indicating a transition from pit nucleation to stable growth; microscopy confirms localized pits (~20–80 μm) with surface deposits. Sensor resonance (~150–170 kHz) shapes observed peak frequencies, highlighting the need for multi-parameter interpretation. The proposed AE+EN approach is promising in earlier, more reliable detection and mechanism discrimination for pitting, and could be extended to other alloy–environment systems. ... Read more

Corrosion and fouling are considered major factors affecting the performance of water-steam cycles (WSC). Flow-accelerated corrosion (FAC), present in feed and condensate systems, is a well known corrosion mechanism, eroding and dissolving the protective magnetite layers. Fouling of the boiler, by suspended magnetite particles, is partly controlled by forces arising due to surface charging. Film forming amines (FFA) are gaining acceptance as means to control FAC. However, its performance in low pH regions is unknown. In addition, despite FFA being a surfactant, its effect on the colloidal magnetite surface charge and point of zero charge (pzc) are unknown. This research set out to determine the effect
of FFAs on the formation of a protective magnetite layer and its resistance against acidic FAC, and to determine the effect of FFAs on the surface charge of colloidal magnetite. This study focused on two FFAs, Octadecylamine (ODA) and Oleyl Propylenediamine (OLDA). In 48h 230-250 ºC immersion corrosion tests magnetite layers were formed on C1010 coupons, inside a high pressure high temperature autoclave under different treatments: untreated (blank), 2ppm ODA and 2ppm Ammonia, 2ppm OLDA and 2ppm Ammonia, and only 2ppm Ammonia. 48h 150 ºC re-immersion corrosion tests were performed to test the magnetite layer performance under acidic (acetate 0.08ppm) FAC. After the corrosion tests, the layers were verified using XRD, EDS + SEM and Weigh-loss measurements. Potentiometric titrations were employed to measure the proton induced surface charge of magnetite particles (10g/L) at an ionic strength of 0.01, and 0.1 mol/kg (KNO3) in the presence or absence of ODA, or OLDA (2ppm) over a wide pH range, at 25, and 150 ºC. This gave the magnetite surface charge density curves. The pzc was determined using the inflection point of titrations (pHinfl) and common intersection point (pHcip). XRD confirmed the presence of magnetite layers on all coupons after the immersion and re-immersion tests. The SEM measured magnetite layer decrease after the re-immersion tests was: 19.1%, 14.5%, 8.6%, and 23.3% for blank, ODA, OLDA, and ammonia treatment respectively. Weight loss determined corrosion rates taken over both immersion and re-immersion tests were: 0.070, 0.057, 0.060, and 0.073 mm/y for blank, ODA, OLDA, and ammonia treatment respectively. All magnetite surface charge density curves were unaffected by the presence of ODA, and OLDA, except for ODA at 0.1 mol/kg KNO3 and 25 ºC, which resulted in a raised/neutralized surface charge density curve in the alkaline pH region. Magnetite layers formed under ODA, and OLDA additions were smoother, thinner, and more uniform compared to layers formed under an ammonia only chemistry, and blank chemistry. Layers formed under the ODA, and OLDA chemistries were better resistant against acidic FAC and offered better protection, in terms of corrosion rate. At the applied concentration ratio, and ionic strength of 0.01M, ODA, and OLDA did not affect the magnetite colloid surface charge over pH. However, both caused magnetite particles to agglomerate. At higher ionic strengths of 0.1M, ODA neutralized the magnetite surface charge in the alkaline region. ... Read more

The presence of harmful pollutants and toxic pathogens in water is a risk to both living beings and the environment. Water treatment plays a crucial role in the removal of these contaminants through different stages of filtration. Among the existing pollutants, a family of per-and polyfluoroalkyl substances (PFAS) escapes from all treatment methods and ends up in our food, water and, finally, in our blood. Current treatment methods are not effective due to their inability to break the strong C-F bonds in PFAS. Perfluorooctanoic acid (PFOA) and perfluorooctanesulfonate (PFOS) are the most widely studied PFAS due to their widespread contamination of various environmental and biological matrices. Due to the global ban of PFOA, a short-chain fluorinated compound named GenX (the ammonium salt of hexafluoropropylene oxide dimer acid) is currently used as an alternative. However, recent studies have shown that GenX has higher toxicity compared to PFOA and is more easily soluble in water, thus making it more difficult for removal. Hence, this research surveys the potential of using boron-doped diamond (BDD) anodes, which are known to have the largest potential window and high stability over time, for GenX degradation. During the electrochemical advanced oxidation process (EAOP), the highly reactive hydroxyl radicals (OH•) produced at the BDD surface break the C-F bonds to form fluoride (Fˉ) and CO2 products. Till date, very limited research is reported on the GenX degradation and they present a contradiction on the effect of sulfate radicals (SO4•ˉ), considered for their high redox potential, in the GenX degradation. In the present study, we investigate the degradation and defluorination efficiency of GenX using boron-doped diamond anodes in EAOP. This study aims to elucidate the first step in the degradation mechanism of GenX and to clarify the contradictions previously reported on the role of sulfate radicals. Experiments are performed separately with sodium sulfate and sodium perchlorate to assess the effect of SO4•ˉ. The results demonstrate that sulfate radicals are ineffective in GenX degradation due to the steric hindrance by the -CF3 branch which blocks the trajectory of SO4•ˉ for electron transfer reaction. The effects of electrolyte concentration, current density, and chloride radicals on the degradation and defluorination are investigated for the first time to provide in-depth understanding of the degradation mechanism. A possible degradation pathway is proposed by determination of the intermediate products using mass spectrometry. From the proposed pathway, it is inferred that GenX completely mineralizes to CO2 and Fˉ via formation of three intermediates. By comparing the electrochemical degradation of GenX with that of PFOA, it is observed that the presence of the -CF3 branch increases the complexity of electron transfer in the GenX degradation even though the mineralization rate is faster for GenX than for PFOA due to lesser number of intermediates. Hence, the direct electron transfer from GenX to the BDD anode is observed to be the rate-determining step in the GenX degradation. Additionally, by comparing different BDD anodes based on their material properties and surface morphology, it is observed that the presence of sp2 regions which act as active sites for effective electron transfer is necessary to initiate the GenX degradation mechanism. Electrochemical degradation of GenX using the BDD anodes has resulted in the complete mineralization to CO2 and Fˉ which supports EAOP using BDD anodes as a promising approach towards effective PFAS degradation.
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In recent years, Tata Steel Europe has increased their focus on Physical Vapor Deposition (PVD) for the zinc coating application of their steel substrates, as an alternative to Hot Dip Galvanizing (HDG). PVD offers some benefits over HDG like multilayer structures and lower heat impact on the steel.
To achieve sufficient coating adhesion strength of the zinc coating, before deposition the steel substrate is normally cleaned and activated by a plasma sputter unit. As this sputtering takes place in the vacuum chamber, like the deposition, it is prone to precipitation of sputtered material in the vacuum chamber. If the PVD process is scaled up to an industrial coating line, the volumes of sputtered material and precipitated material will become problematic for the service reliability. Therefore it has been investigated whether an acid etching surface pre-treatment step before the vacuum chamber could reduce the needed plasma intensity, and thereby decrease the sputtered volume in the vacuum chamber.
A range of acid etching times and plasma sputtering times were tested, to obtain the range in which the coating adhesion was sufficient. To test the coating adhesion, two (automotive) tests were used. It was found that by pickling, the plasma sputter intensity could not be reduced. So the coating adhesion strength seemed not directly related to the pickling time, for the particular steel used in this project.
After the limits of good adhesion were determined, the characterization started to identify what in the elemental composition or the surface morphology could determine whether there was good adhesion or not. It was found that (even very short) pickling completely removes the surface enrichment of the first 50 nm, while plasma sputtering only lowers the surface enrichments. It was found that plasma sputtering does not influence the morphology, while pickling smoothens the surface out, with increasing pickling. As the oxygen concentration profile did not change significantly as function of pickling time, but its enrichment thickness was about equal to the minimum plasma sputter depth, it is thought that the oxygen concentration is the major influence on good and bad adhesion.
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