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In the geological repository of radioactive nuclear waste, anaerobic corrosion can generate hydrogen, and may conservatively lead to the production of hydrogen-air layer. The accumulated hydrogen may cause a hazardous flame propagation resulting from any potential ignition sources. This study numerically investigates the processes of ignition and flame propagation in the layered mixture. Simple geometry was chosen to represent the geological repository, and reactive flow simulations were performed with different ignition power, energy, and locations. The simulation results revealed the effects of power and energy of ignition source, which were also analyzed theoretically. The mechanism of layered flame propagation was suggested, which includes three stages: propagation into the hydrogen area, downward propagation due to the product gas, and horizontal propagation along the top wall. To investigate the effect of the ignition source location, simulations with eight different positions were performed, and the boundary of hazardous ignition area was identified. The simulation results were also explained through scaling analysis. This study evaluates the potential risk of the accumulated hydrogen in geological repository, and illustrates the layered flame propagation in related ignition scenarios.

Increasing groundwater temperatures caused by global warming, subsurface infrastructure, or heat storage projects may interfere with groundwater remediation techniques using zero-valent iron (ZVI) technology by accelerating anaerobic corrosion. The corrosion behavior of three ZVIs widely used in permeable reactive barriers (PRBs), Peerless cast iron (PL), Gotthart-Maier cast iron (GM), and an ISPAT iron sponge (IS), was investigated at temperatures between 25 and 70 °C in half-open batch reactors by measuring the volume of hydrogen gas generated. Initially, the corrosion rates of all tested ZVIs increased with temperature; at temperatures ≤40 °C, a material-specific steady state is reached, and at temperatures >40 °C, passivation causes a decrease in long-term corrosion rates. The observed corrosion behavior was therefore assumed to be superimposed by accelerating and inhibiting effects, caused by surface precipitates where the fitting of measured corrosion rates by a modeling approach, using the corroded amount of Fe0 to account for passivating minerals, yields intrinsic activation energies (Ea, ZVI) of 81, 90, and 107 kJ mol-1 for IS, GM, and PL, respectively. An increase in H2 production might not be directly transferable to an increase in general ZVI reactivity; however, the results suggest that an increase in chlorinated hydrocarbon degradation rates can be expected for ZVI-PRBs in the immediate vicinity of low-temperature underground thermal energy storages (UTESs) or in the impact areas of high-temperature UTES with temperatures of ≤40 °C.

In the Belgian supercontainer concept, a carbon steel overpack will surround high-level waste and spent fuel containers and be encased in a cementitious buffer material. A programme of research has...

Financiado para publicación en acceso aberto: Universidade da Coruña/CISUG [Abstract] Developing innovative bioprocess strategies for carbon capture and utilization has been a major focus of research over the past decade as a way of creating a more resilient world. In this study, zero-valent iron (ZVI) was utilized to generate hydrogen, which was then utilized as an electron donor for CO2 reduction by either Clostridium aceticum or Clostridium carboxidivorans. For this bioprocess, an early acidic condition in the reactors facilitated more hydrogen production and thereby more acetic acid accumulation, in contrast to later acidification, elucidating the role of pH in ZVI-CO2 bioconversion. Acetic acid was produced as single end product of the process in both batch bottle studies with no pH control as well as in reactor studies with pH regulation. This is, to the best of our knowledge, the first report on selective pure CO2 bioconversion to acetic acid by clostridia, with ZVI. In order to minimize costs, scrap iron rather than pure ZVI can be used for scaling-up. By lowering the pH to 6.6 for C. aceticum, in reactor studies with 75 g/L ZVI, some ethanol production (125 mg/L) was also observed, besides acetic acid. In reactor studies, a maximum acetic acid concentration of about 2 g/L was obtained at ZVI concentrations of 50 and 75 g/L. Thus, ZVI dosage and medium pH have a major effect on the metabolites generated during CO2 utilization. This research was partly financed by the Spanish Ministry of Science and Innovation Through Project PID2020-117805RB-I00 and European FEDER funds. BB thanks Xunta de Galicia for funding her predoctoral fellowship (ED481A-2020/226) to undertake research at the BIOENGIN group. The BIOENGIN group also thanks Xunta de Galicia for financial support to Competitive Reference Research Groups (ED431C 2021/55). Funding for open access charge provided by Universidade da Coruña/CISUG Xunta de Galicia; ED481A-2020/226 Xunta de Galicia; ED431C 2021/55

The materials corrosion test (MaCoTe) is a long‐term, multinational in situ corrosion experiment setup at the Grimsel Test Site, Switzerland. The experiment has been operating since 2014 with a focus on the corrosion behaviour of container materials for the disposal of high‐level waste and spent nuclear fuel under conditions representing a granitic deep geological repository. The experiment consists of eight modules containing metal coupons and bentonite. Two of the modules, each with a different bentonite density, have been retrieved after 394 days of exposure and have been analysed using a range of techniques aimed at studying the corrosion behaviour of the metals and the mineralogical evolution of the bentonite. Weight loss measurements show that carbon steel had a relatively low average corrosion rate (~2 µm year−1). Much lower average corrosion rates were measured for the various types of copper (0.13–0.32 µm year−1). No detectable corrosion was measured on stainless steel coupons. To date, no significant differences were observed in the corrosion behaviour and rate of the test metals in bentonite with different dry densities.

Some three hundred mainly steel shipwrecks from both World Wars lie buried at shallow depths along the Belgian North Sea coast. They were examined recently to estimate corrosion rates over periods ...

Perchloroethene (PCE) is a hazardous and persistent groundwater pollutant. Both treatment with nanoscaled zero-valent iron (nZVI) and biological degradation by bacteria have downsides. Distribution of nZVI underground is difficult and a high percentage of injected nZVI is consumed by anaerobic corrosion, forming H2 rather than being available for PCE dechlorination. On the other hand, microbial PCE degradation can suffer from the absence of H2. This can cause the accumulation of the hazardous metabolites cis-1,2-dichloroethene (DCE) or vinylchloride (VC). The combination of chemical and biological PCE degradation is a promising approach to overcome the disadvantages of each method alone. In this lysimeter study, artificial aquifers were created to test the influence of nZVI on anaerobic microbial PCE dechlorination by a commercially available culture containing Dehalococcoides spp. under field-like conditions. The effect of the combined treatment was investigated with molasses as an additional electron source and after cessation of molasses addition. The combination of nZVI and the Dehalococcoides spp. containing culture led to a PCE discharge in the lysimeter outflow that was 4.7 times smaller than that with nZVI and 1.6 times smaller than with bacterial treatment. Moreover, fully dechlorinated end-products showed an 11-fold increase compared to nZVI and a 4.2-fold increase compared to the microbial culture. The addition of nZVI to the microbial culture also decreased the accumulation of hazardous metabolites by 1.7 (cis-DCE) and 1.2 fold (VC). The stimulatory effect of nZVI on microbial degradation was most obvious after the addition of molasses was stopped.

When using cathodic protection of steel in sea water, hydrogen can be accumulated on the cathode surface and penetrate deep into the metal. This rather dangerous phenomenon of hydrogen corrosion can lead to hydrogen embrittlement, i.e., to destruction of the metal. We present the results of studying the impact of the temperature and external tensile stresses on the hydrogenation of cathodically protected steel in calm and mobile Baltic sea water. Dependence of the inhibitory hydrogenation on the temperature and applied load under the action of benzenesulfapyridine chloride as an inhibitor was analyzed. An MIP-102 machine (wire samples) and special equipment (half-ring and plate lamellar samples) were used to provide smooth control of the applied load set by the deflection and controlled by dynamometers (lamellar samples were tested under constant deformation). When studying the effect of temperature on steel hydrogenation, the working cell was thermostatically controlled. The wire and plate samples were polarized for 96 h, and half-ring samples for 1 h. The potential was measured with respect to the silver chloride reference electrode. The layered distribution of absorbed hydrogen in the metal was determined using anodic dissolution. It is shown that external tensile stresses increase the hydrogen content in the surface layers of steel. Hydrogen absorbed by a metal changes the potential of the steel surface (the more absorbed hydrogen, the stronger change). It is also shown that hydrogen is absorbed by the metal more actively in moving seawater than in calm water, and an increase in the load contributes to an increase in hydrogen content in the metal both in calm and mobile seawater. However, the load did not affect the hydrogen absorption with the inhibitor present, thus providing reduction of the hydrogen content in the metal under loading.

Anaerobic corrosion at the metal/bentonite interface determines the performance of bentonite-based high-level radioactive waste (HLRW) barriers. Both magnetite and Fe-silicate formation were previo...

The structure, the static tensile properties, the impact toughness, and the fracture mechanisms of the 12GSB pipe steel specimens cut from the defect regions in a pipeline 530 mm in diameter are studied. Hydrogen corrosion is found to affect the anomalous character of the temperature dependences of the impact toughness and the fraction of ductile component in a fracture surface. Sulfur is shown to substantially influence the ductile crack propagation energy in the transverse direction and to weakly influence this energy along the rolling direction. The development of hydrogen corrosion in the pipeline is found to be accompanied by a significant increase in the reduced fraction of intergranular fracture (15.8–35%) in brittle fracture surfaces, and this fraction in the separation plane reaches 50.5%. The relation between the impact toughness of the transverse specimens and the fraction of ductile component in a fracture surface has an anomalous character: this relation has two linear segments, the fracture energies in which differ by an order of magnitude. The segment with a low fracture energy (4.4–16.1 J/cm2) characterizes the action of the sear component of separation in the rolling plane, and the segment with a high fracture energy (38–246 J/cm2), the action of a ductile mode I fracture mechanism. The impact toughness anisotropy coefficient is found to be high, Ka = 2.31.

The Belgian reactor 1 fuel cladding is made of aluminium. If disposed of in a geological disposal repository, aluminium could come into contact with ordinary Portland cement and is going to corrode to form hydrogen gas and aluminium hydroxide. In this study, the long‐term corrosion was evaluated by electrochemical impedance spectroscopy on metal embedded in cement paste immersed in saturated calcium hydroxide solution under anaerobic conditions. Mass transfer effects were investigated by embedding aluminium in cement paste with two different porosities. LiNO3 was also added to the systems to study its corrosion inhibiting effect. After high initial values, the corrosion rate rapidly declined to reach a steady state after a few days. After ~100 days, the corrosion rate was the lowest when cement paste possessing a low porosity with the addition of LiNO3 was used and the highest when cement paste with high porosity without LiNO3 was used. Finally, scanning electron microscopy–energy X‐ray dispersive spectroscopy revealed that the corrosion product layer was thicker than expected by electrochemical impedance spectroscopy measurements, while it is only composed of aluminium and oxygen. Aluminium was found to diffuse into the cement paste close to this corrosion product layer.

Carbon steel is a potential canister material for the disposal of high-level radioactive waste in deep geological repositories in clays and clay rocks. Bentonite is considered as a potential backfill material for those multi-barrier systems. To predict the long-term performance and for safety assessment the knowledge of canister corrosion behavior is important. The corrosion products formed and mineralogically altered bentonite at the canister/bentonite interface can potentially provide an additional barrier against radionuclide migration. In-situ corrosion experiments were performed at the Mont Terri underground research laboratory. Coupons of carbon steel were embedded in Volclay MX-80 bentonite with controlled densities, installed in a borehole under simulated repository and anaerobic conditions and exposed to natural Opalinus clay porewater for a period up to 5.5 years (Smart et al., 2017). In the present study, the bentonite layer at the canister/bentonite interface was characterized by complementary microscopic and spectroscopic techniques (XPS, SEM-EDX, µXANES) under anoxic conditions. The interface revealed reddish-brown staining up to 2 mm depth into the bentonite in the zone adjacent to the steel in all three obtained samples. The XPS analysis revealed formation of sulfides at the interface consisting of iron and other trace metals present in the steel. The SEM-EDX analyses of the interface (embedded cross-cut with steel removed) showed different degrees of calcium enrichment in the bentonite adjacent to the metal for various samples. The µXRF analysis performed on the bentonite at the interface showed a scarce or distinct calcium-enriched rim up to 100 µm into the bentonite and iron-enriched rim depending on the sample (one sample in Fig. 1), while µXANES analysis revealed formation of iron silicate compounds in the reacted reddish-brown zone. The iron appears to displace calcium from the interlayer sites in montmorillonite. The calcium then precipitates at the interface as calcite. The extent of this process seems to be strongly related to the bentonite density. The steel coupon was removed prior to embedding, with the location marked as resin in Fig. 1. A line scan from the edge towards the bulk bentonite did not indicate any systematic gradient in the Fe2+/3+ ratio. The formation of mixed Fe2+/3+ silicate compounds appears to be heterogeneous. This work contributes to an increasing understanding of steel corrosion mechanisms in clay, which can improve the robustness of canister lifetime predictions.

Since 2012, a long-term in situ corrosion experiment (IC-A) has been conducted in the Mont Terri Underground Research Laboratory in Switzerland. The aims of the project with international partners are to confirm the long-term anaerobic corrosion rate of carbon steel and copper in compacted bentonite under repository-relevant environmental conditions, to gather in situ corrosion data supporting canister lifetime predictions, to provide confirmation of the effect of the bentonite buffer on microbial activity and microbially influenced corrosion, and to study the effects of welding (steel) and deposition technique (copper) on the corrosion properties of these candidate materials for disposal canisters. To date, carbon steel and cold sprayed and electrodeposited copper coatings have been retrieved after different exposure periods up to 3 years and characterised to establish the composition of the corrosion product, the morphology of the corroded surface, and to measure the rate of corrosion. For carbon steel specimens, a complex corrosion product was identified, consisting predominantly of magnetite. Low average anaerobic corrosion rates were measured for carbon steel and a very modest amount of alteration was identified on copper. The density and the initial form of the bentonite had a small influence on the rate of corrosion, across all materials.

There have been many studies on TCE degradation by synthesized nanoscale zero-valent iron (nZVIB) and commercial nanoscale zero-valent iron (nZVIH), but the effect of anaerobic corrosion on the dechlorination pathways and speciation distribution of chlorine is still unclear. Compared with nZVIH, nZVIB has a faster degradation rate of TCE and formation rate of Cl−(aq) (kSA, TCE = 3.67 ± 0.85 × 10−4 & 2.17 ± 0.13 × 10−4 L·h−1·m−2 and kobs, Cl− = 0.344 ± 0.027 & 0.166 ± 0.010 μM·h−1 for nZVIB & nZVIH, respectively). Based on the characterization of XRD, XPS and TEM during the anaerobic corrosion, the corrosion of nZVIB was dramatic under the dissolution-reprecipitation mechanism; but that of nZVIH was moderate and inward by maintaining the core-shell structure and shaping slightly rough and lumpy surface. Due to the different corrosion products (FeOOH for nZVIB and Fe3O4/γ-Fe2O3 for nZVIH) and the catalysis of boron on the nZVIB surface, the preferential dechlorination pathway of TCE was not identical by hydrogenolysis (nZVIB) vs. reductive β-elimination (nZVIH). Meanwhile, the dechlorination pathway of nZVIH was similar to that of ZVI and the reductive pathway to acetylene bypassed the formation of more toxic VC. This study shows that the high reactivity of nZVIB results in rapid corrosion with the side effect of enhanced adsorption of VC while nZVIH has a stable core-shell structure and less sorbed chlorine, which provides a new sight to access the ecological risk of nZVI due to the overlooked effect of non-identical corrosion.

Gas production from low- and intermediate-level nuclear waste (LLW/ILW) is important to the safety of near surface and deep geological nuclear waste repositories through the release of gaseous radionuclides and pressurization that can ultimately affect the transport of radionuclides in groundwater. The main gases generated from LLW/ILW are H2 from anaerobic corrosion of steel and CH4 from organic (cellulose) wastes. Microbes mediate CH4 generation and also can consume H2 as an energy source such as for the reduction of sulfate. A 20-year Gas Generation Experiment at Olkiluoto, Finland has furthered the understanding that microbes play in mediating gas production from LLW. The processes involved in gas generation from the experiment have been elucidated by, interpretation of gas and chemical data, DNA pyrosequencing and biogeochemical modeling. Methanogenesis develops initially mainly by utilizing hydrogen formed by anaerobic corrosion. In contrast, generation of CH4 from cellulose develops more slowly as a consequence of the complexity of the preceding cellulose degradation, fermentation processes, competition with sulfate reduction processes, and inhibition effects related to high pH and aqueous sulfide. The maximum rate of CH4 production develops after 8 years, when concrete buffered high pH regions of the experiment are neutralized by cellulose degradation and fermentation.

Since 2012, a long‐term in situ corrosion experiment (IC‐A) is being conducted in the Mont Terri Underground Research Laboratory in Switzerland to investigate the corrosion behaviour of candidate canister materials in conditions representative of the Swiss concept for the disposal of high‐level waste and spent nuclear fuel. To date, carbon steel and various types of copper coatings have been retrieved after different exposure periods of up to 3 years, and characterised to establish the composition of the corrosion product, the morphology of the corroded surface, the nature of the interaction between the metal and the surrounding bentonite, and the microbial populations in the bentonite and surrounding porewater. For carbon steel specimens, a complex corrosion product was identified, consisting predominantly of magnetite. Much less alteration on either the metal or the bentonite was observed in the case of copper samples. Low average anaerobic corrosion rates were measured for carbon steel and a very modest amount of alteration was identified on copper. The density and the initial form of the bentonite had a small influence on the rate of corrosion, across all materials. This paper summarises the results of the experimental programme obtained to date and discusses the relationship observed between exposure time and the evolution of the metal–bentonite interface for both carbon steel and copper.

Carbon steel is a potential canister material for the disposal of high-level radioactive waste in deep geological repositories in clays and clay rocks. Bentonite is considered as a potential backfill material for those multi-barrier systems. To predict the long-term performance and for safety assessment the knowledge of canister corrosion behavior is important. The formed corrosion products and mineralogically altered bentonite at the canister/bentonite interface can potentially provide an additional barrier against radionuclide migration. In-situ corrosion experiments were performed at the Mt. Terri underground research laboratory. Coupons of carbon steel were embedded in Volclay MX-80 bentonite with controlled densities, installed in a borehole under simulated repository and anaerobic conditions and exposed to natural Opalinus Clay porewater for a period up to 5.5 years. The bentonite layer at the canister/bentonite interface was characterized by complementary microscopic and spectroscopic techniques (XPS, SEM-EDX, XRD) under anoxic conditions. The interface revealed reddish-brown staining up to 2 mm depth into the bentonite in the zone adjacent to the steel. The SEM-EDX analyses of the interface (embedded crosscut with steel removed) showed calcium and iron enrichment in the bentonite adjacent to the metal. µXRF analysis performed on the bentonite at the interface showed calcium enriched rim up to 100 µm into the bentonite, while µXANES analysis revealed formation of iron silicate compounds in the reacted reddish-brown zone. The steel coupon was removed prior embedding. A line scan from the edge towards bulk bentonite did not indicate any systematic gradient in the Fe2+ / Fe3+ ratio. The formation of mixed Fe2+/3+ silicate compounds appears to be heterogeneous. This work contributes to an increased understanding of steel corrosion mechanisms in clay, which can improve the robustness of canister lifetime predictions. We acknowledge the German Federal Ministry of Education and Research (BMBF) and the Helmholtz association for the financial support. We thank the Mont Terri IC-A Partners and Swisstopo for providing the samples. We acknowledge the provision of the beamtime at the KIT Light Source, KARA, Germany.

One of the causes of pipeline corrosion and a way to solve it are considered

The effect of low temperatures on abiotic and biotic nitrate (NO3−) reduction by zero-valent iron (ZVI) were examined at temperatures below 25 °C. The extent and rate of nitrate removal in batch ZVI reactors were determined in the presence and absence of microorganisms at 3.5, 10, 17, and 25 °C. Under anoxic conditions, NO3− reduction rates in both ZVI-only and ZVI-cell reactors declined as temperature decreased. In ZVI-only reactor, 62% and 17% of initial nitrate concentration were reduced in 6 days at 25 and 3.5 °C, respectively. The reduced nitrate was completely recovered as ammonium ions (NH4+) at both temperatures. The temperature-dependent abiotic reduction rates enabled us to calculate the activation energy (Ea) using the Arrhenius relationship, which was 50 kJ/mol. Nitrate in ZVI-cell reactors was completely removed within 1–2 days at 25 and 10 °C, and 67% of reduction was achieved at 3.5 °C. Only 18–25% of the reduced nitrate was recovered as NH4+ in the ZVI-cell reactors. Soluble iron concentrations (Fe2+ and Fe3+) in the ZVI reactors were also measured as the indicators of anaerobic corrosion. In the ZVI-cell reactors, soluble iron concentrations were 1.7 times higher than that in ZVI-only reactors at 25 °C, suggesting that the enhanced nitrate reduction in the ZVI-cell reactors may be partly due to increased redox activity (i.e., corrosion) on iron surfaces. Anaerobic corrosion of ZVI was also temperature-dependent as substantially lower concentrations of corrosion product were detected at lower incubation temperatures; however, microbially induced corrosion (MIC) of ZVI was much less impacted at lower temperatures than abiotic ZVI corrosion. This study demonstrated that ZVI-supported microbial denitrification is not only more sustainable at lower temperatures, but it becomes more dominant reaction for nitrate removal in microbial-ZVI systems at low temperatures.

This paper reports the results of research on the effect of hydrogen permeation and the absence of passive layers on the variations in the corrosive properties of aluminum alloys. The study demonstrated that such variations contribute to the deterioration of corrosive properties, which in turn contributes to shortening the reliability time associated with the operation of aluminum alloy structures. The analysis involved structural aluminum alloys: EN AW-1050A, EN AW-5754, and EN AW-6060. It was demonstrated that the absorption of hydrogen by the analyzed alloys led to the shift of the electrode potential to the negative side. The built hydrogen corrosion cells demonstrate in each case the formation of electromotive force (EMF) cells. The initial EMF value of the cell and its duration depends on the duration of hydrogenation. As a result of removing the passive layers, the electrode potential also changes to the negative side. Following the removal of the passive layer from one of the electrodes, the cells also generated a galvanic (metal) cell. The duration of such a cell is equivalent to the time of restoration of the passive layer. The formation of such hydrogen and metal galvanic cells changes the electrochemical properties of aluminum alloys, therefore deteriorates the corrosive properties of aluminum alloys.

Modified supermartensitic stainless steel surfaces were investigated as protective means against deterioration in Cl−- and H+-rich media. Nitrogen plasma immersion ion implantation at the 300–400 °C range produced top nitride-rich layers (with mainly γ′-Fe4N and e-Fe2-3N, but also with α′N, according to the treatment temperature) followed by underneath expanded martensite cases. The 400 °C nitrided sample presented the best performance in potentiodynamic polarization tests with NaCl electrolyte, featured by 4.3 times increase in the corrosion potential and the absence of pits, attributed to the thickest and continuous e-phase containing nitride-rich layer. The hydrogen embrittlement was assessed through cathodic hydrogenation tests. Both reference and 400 °C nitrided surfaces disclosed the phenomenon of intensified plastic flow under normal and tangential loadings. A decrease in hardness, elastic modulus and scratch resistance featured a ductile-to-brittle transition on the nitrided surface, possibly due to improved hydrogen trapping by nitride species with subsequent effects in plasticity. In summary, while the nitride layer played an advantageous role in protecting SMSS from chlorine attack, it was susceptible against the hydrogen corrosion.

One of the most common types of metal destruction in the oil and gas industry is hydrogen embrittlement. Hydrogen corrosion is a complex of negative effects of hydrogen on steel, leading to the destruction of metal structures. Hydrogen passes through a defect-free metal, without lingering in it. In the presence of defects, hydrogen is retained in the metal forming a brittle solid solution, metal stratification along the segregation streamer, blistering. Studies of the metal of a gas pipeline made of steel 09G2S are presented in the article. The sample was selected from the local zone of destruction in the condensate collector, the metal of the pipe had typical for hydrogen corrosion stratifications. The scope of the study was identification of the most dangerous part of hydrogen corrosion on the sample taken from the local zone of destruction. Studies on the chemical composition and mechanical properties of 09G2S steel were also carried out. Stress-related characteristics of the metal microstructure of the failed gas pipeline were obtained and the character of the destruction progress was revealed. The presence of sulfides cluster in the metal of studied pipe was determined applying metallographic method for determining nonmetallic inclusions.

Recent studies suggest that the supplementation of powdered Fe° generates a positive effect on anaerobic fermentation processes but the exact relationship between metals with biological systems has not been fully elucidated. Experimental tests on dark fermentation (DF) were carried out at different Fe° concentrations. The anaerobic corrosion (AC) of Fe° and the production of H2 through DF of Organic Waste Market (OWM) were tested separately, and subsequently DF tests with Fe° at 1 g/L and 2 g/L were carried out. A macroscopic dynamic study was conducted, using Roels approach based on relaxation times (τR) to establish whether interactions between AC and DF phenomena exist. Experimental bioH2 production and Fe° AC were fit by Gompertz and saturative models, respectively to estimate τR. The results of the macro-analysis suggest that both phenomena are concurrent, with τR of the same order of magnitude, generating a positive symbiotic effect. The experimental tests of hydrogen production via DF in presence of 2 g/L of Fe° showed an increase of 46% compared with the control tests, of amount of gas and a greater H2/CO2 ratio. The results suggest an enhancement of key enzymes activity due to the action of iron increasing bioH2 production.

To determine the contributions of elastic strain energy to chemical driving force of uranium hydride growth, an elastic fields model was set up by a spherical hydride particle growing at sub-surface of parent metal, which was used to interpret strain energy influence on the evolution of microstructure and kinetics characteristics of the hydride precipitates. The results showed that strain energy during hydride expansile growth in the matrix is considerably different for the three U materials. When hydride grows, the order of the strain energy value is U-5.7%Nb > U > U-2.5%Nb(mass fraction), which indicated that the U-2.5%Nb alloy is the most susceptible to hydrogen corrosion, followed by U, while U-5.7%Nb is the most resistant to hydrogen corrosion basing on reaction activation theory. Agreement of calculated strain energy with experimental results of hydride growth kinetics showed that the model in this work is correct, in which the large strain energy from volume change during hydride growth plays an important role in determination of growth kinetics. In addition to strain energy calculation, the stress distribution associated with hydride precipitate was used to interpret the interaction between hydride pattern and stress. The study provides quantificational evidences to understand the association of strain energy and stress with hydride of metals, which will lead to novel process opportunities.

Speciation of carbon during the anoxic corrosion of steel is poorly known, whereas its knowledge would be of great importance in connection with assessments of the safe disposal of 14C-con...

In this work we have experimentally studied the impact of bentonite clay on the process of radiation-induced copper corrosion in anoxic water. The motivation for this is to further develop our unde ...

The characteristics of hydride formation on metallic U at the early stages were investigated for three differently treated samples. The first sample reacted in its as-received state, the second was thermally annealed and the third sample underwent cold work-hardening prior to reaction with deuterium. From the analysis, the vacuum heat-treated sample was found to be more resilient to hydriding at the nucleation and growth stage, exhibiting a reduced number of nucleation points when compared to the as-cast uranium. The work-hardened sample was observed to be more susceptible to H2 corrosion, displaying very dissimilar hydriding behaviour when compared to the other.

The hydrogenation and corrosion behaviour of La2Ni9 · CoSn0.2 alloy was analysed in respect of its use in Ni–MH batteries. It has been proved that the presence of tin in the alloy causes a decrease in hydrogen equilibrium pressure. In the electrochemical studies several techniques, such as chronopotentiometry, multi-potential steps, linear sweep voltammetry and the potentiokinetic polarization were applied to characterize the electrochemical properties of a La2Ni9CoSn0.2 powder composite electrode. During long cycling, powder particles undergo micro-cracking or other forms of surface development causing a progressive increase in the exchange current density of the H2O/H2 system, but, on the other hand, this increase favours corrosion processes such as the electrode material's oxidation. This is also reflected in the capacity loss values.

This paper presents an efficiency and mechanism analysis of impressed current cathodic protection (ICCP) for corroded steel reinforcements in concrete by means of electrochemical noise (EN), which is an advanced technique that allows real-time monitoring without any disturbance. The considered variables include protection method (non-protection, ICCP) and current density of ICCP (30 mA/m2, 90 mA/m2). In the cases of ICCP, carbon fiber sheet is adopted as the anode thanks to its good electrochemical properties and durability. Electrochemical potential noise (EPN) and electrochemical current noise (ECN) of steel reinforcement in concrete are measured every 30 d during the 120-d exposure period and analyzed from the perspectives of time and frequency domains. The results show that ICCP treatment with a current density of 30 mA/m2 leads to slighter fluctuations in ECN signals, an improvement in noise resistance Rn, and decreases in the low frequency plateau WL in power density diagram (PSD) of ECN signals. It indicates that the corrosion of steel is alleviated. However, the results of the specimen protected with a current density of 90 mA/m2 are the opposite, which is overprotected and hydrogen corrosion may happen. Compared to the specimen with no protection, the specimen treated with 30 mA/m2 ICCP shows an evident increase in energy proportion of d1-d3 wavelet crystals. Additionally, with increasing the treatment duration, the energy proportion of d1-d3 wavelet crystals increases. This illustrates that ICCP is more effective in inhibiting general corrosion than pitting corrosion. Extra caution should be paid to EPN signals of specimens subjected to ICCP, namely polarization, because EPN signals may anomalously exhibit severer fluctuations as a result of insufficient depolarization. It is suggested to use ECN signals instead of EPN signals to analyze the corrosion behavior of specimens subjected to ICCP.

Purpose When concrete is manufactured, it can be instantaneously contaminated by chloride (Cl−) ions or later by their intrusion from the environment. This work aims to study the electrochemical behavior of the passive layer formed on the reinforcing steel surface in the presence of the same Cl− ion concentration, with and without passivation time. This will, undoubtedly, affect the corrosion threshold values thereafter. Design/methodology/approach Electrochemical polarizations were carried out in two concrete pore solutions. The surfaces of samples immersed for 255 days in saturated Ca(OH)2 solution were examined with optical and scanning electron microscopy and Raman microspectroscopy. Findings Cl− ion origins in reinforced concrete lead to different values of corrosion thresholds. The passive layer behaves like a physicochemical barrier, and corrosion occurs at higher NaCl concentration thresholds. The formed passive film on the steel surface shows differences in the chemical composition and the morphology. The results show a rich presence of hematite. Maghemite, lepidocrocite, akaganeite and goethite are also present in much lower concentrations. The Cl− ion presence in fresh concrete at the beginning of the manufacture harms the good formation and the good stability of these oxides, leading to corrosion initiation. Originality/value This study contributes to a better understanding of the passive layer role, not only in reducing the corrosion rate value but also in reconsidering new Cl− ion corrosion threshold values.

This paper summarizes experimental results obtained from a series of laboratory scale electrowinning tests conducted over 5 months to quantify the effects of halides (chloride, fluoride and bromide) on the performance and corrosion of lead-silver anodes under conditions similar to those used during the electrowinning of zinc. The parameters investigated include operating anode potential, corrosion rate and anode scale/cell mud generation rates. Information was also obtained on the consumption of halides and manganese ions and the composition of the anode scale and cell mud. The results have confirmed plant observations of excessive anode corrosion and chlorine emissions at a chloride concentration of 400 mg/L but not at a concentration of 200 mg/L. It has also confirmed the importance of maintaining a suitable manganese(II) concentration in the electrolyte. Bromide and fluoride ions, albeit at lower concentrations, do not have measurable effects on anode corrosion. Although a definitive explanation for enhanced local corrosion at high chloride concentrations has not been advanced, the nature of the accelerated corrosion suggests that a crevice-like corrosion process is responsible for localized massive corrosion. This has been attributed to the presence of high acidity and permanganate ions between the manganese oxide layer and the alloy surface.

This study introduces a novel approach intertwining analytics of spatial microbial distribution with chemical, mineralogical and (micro)structural related aspects in corroded concrete sewer environments. Samples containing up to 4 cm thick corrosion layers were collected from concrete manholes and analysed using hydro-geochemical, microbiological, biochemical and mineralogical methods. Opposed to the current opinion DNA and RNA indicating microbial activity were found throughout the entire deterioration layer down to the corrosion front. Elemental distributions of corresponding areas revealed a dynamic pH- and diffusion-controlled system in which a distinct succession of elemental accumulations was unequivocally correlated with responding pH levels, associated dissolution and precipitation of solids, as well as with the spatially resolved presence of microbes. Microbial activity further coincided with massive iron deposition zones, within the inner anoxic to anaerobic corrosion layers. As a possible microbial catalyst for iron oxidation and in-situ acid production in this zone, we propose Acidithiobacillus ferrooxidans which were isolated from the deteriorated concrete. Based on the data we propose a new model in which biogenic induced in-situ acid production is a decisive factor, steering high concrete corrosion rates of > 1 cm yr − 1 .

Bio-concrete is known for its self-healing capacity although the corrosion resistance was not investigated previously. This study presents an innovative bio-concrete by mixing anaerobic granular sludge into concrete to mitigate sewer corrosion. The control concrete and bio-concrete (with granular sludge at 1% and 2% of the cement weight) were partially submerged in a corrosion chamber for 6 months, simulating the tidal-region corrosion in sewers. The corrosion rates of 1% and 2% bio-concrete were about 17.2% and 42.8% less than that of the control concrete, together with 14.6% and 35.0% less sulfide uptake rates, 15.3% and 55.6% less sulfate concentrations, and higher surface pH (up to 1.8 units). Gypsum and ettringite were major corrosion products but in smaller sizes on bio-concrete than that of control concrete. The total relative abundance of corrosion-causing microorganisms, i.e. sulfide-oxidizing bacteria, was significantly reduced on bio-concrete, while more sulfate-reducing bacteria (SRB) was detected. The corrosion-resistance of bio-concrete was mainly attributed to activities of SRB derived from the granular sludge, which supported the sulfur cycle between the aerobic and anaerobic corrosion sub-layers. This significantly reduced the net production of biogenic sulfuric acid and thus corrosion. The results suggested that the novel granular sludge-based bio-concrete provides a highly potential solution to reduce sewer corrosion.

Experimental evidence related to the interactions between steel corrosion and bentonite in deep geological repositories is reconsidered. The released Fe2+ interacts with the smectite and precipitates as Fe3+ when oxidised by residual immobile oxygen. This leads to the development of coloured fronts in the bentonite. The evolution of these fronts can be reproduced by a reactive transport model that takes account of the competition between diffusion and precipitation. Furthermore, two-phase flow modelling indicates that the consumption of water by the corrosion outpaces the diffusion of water through the bentonite, leading to shrinkage microfractures in bentonite that act as preferential pathways for corrosion products.

Hydrogen gas is formed when Mg corrodes in water; however, the manner and extent to which the hydrogen may also enter the Mg metal is poorly understood. Such knowledge is critical as stress corrosion cracking (SCC)/embrittlement phenomena limit many otherwise promising structural and functional uses of Mg. Here, we report via D2O/D isotopic tracer and H2O exposures with characterization by secondary ion mass spectrometry, inelastic neutron scattering vibrational spectrometry, electron microscopy, and atom probe tomography techniques direct evidence that hydrogen rapidly penetrated tens of micrometers into Mg metal after only 4 h of exposure to water at room temperature. Further, technologically important microalloying additions of

The corrosion behavior of X65 steel in water-saturated supercritical CO 2 system containing NO 2 with or without O 2 , H 2 S and SO 2 impurities was investigated using weight loss measurement and surface analysis techniques. The interactions between NO 2 and O 2 , SO 2 or H 2 S promoted the formation of extra corrosive species and subsequently changed the corrosion film characteristics. In water-saturated supercritical CO 2 -NO 2 -O 2 -SO 2 -H 2 S system, FeSO 4 and S preferentially formed in the early corrosion stage due to the impurity interactions. As the corrosion time prolonged, (NH 4 )Fe 3 (SO 4 ) 2 (OH) 6 and FeOOH formed due to the subsequent reactions of the impurity interaction products, and S disappeared in the corrosion scale via participating in the subsequent corrosion reactions during long-term corrosion. Localized corrosion was initiated by the inhomogeneous precipitation of acid-rich water in the presence of NO 2 . However, the propagation rate of the corrosion pit in depth direction greatly reduced with time, and the corrosion morphology of X65 steel shifted from localized corrosion towards general corrosion during long-term corrosion.

The influence of superficial defects (induced by surface sputtering) on uranium oxidation and hydriding behaviors has been studied. Depleted uranium surface was etched by Ar + sputtering, the etched surface morphology was investigated by scanning electron microscope. The initial oxidation kinetics of sputtered uranium surface and mechanical polished uranium surface in ambient atmosphere were characterized using spectroscopic ellipsometry. As-polished and sputtered samples, as well as sequence sputtered samples ambient oxidized for different time, were compared in hydriding kinetics to investigate the co-influence of surface oxidation and superficial defects induced by Ar + ion bombardment. The morphologic characteristics of hydride sites in a few grains were also revealed and enhanced by sputtering, showing a network of fractures for fast hydride transportation.

Six bioreactors with different additives of nanoscale zero valent iron (nZVI), zeolite, nZVI and zeolite mixture (IMZ), and nZVI coated zeolite (ICZ) particles were tested to evaluate the overall anaerobic digestion performance of domestic sludge under 37 °C. For 14 days’ long, the daily biogas production, methane content, pH, soluble chemical oxygen demand (soluble COD), total alkalinity and total ammonia nitrogen variations were measured, and the overall performance of anaerobic digestion was assessed. The results showed that ICZ addition caused a lag period before starting to generate a significant biogas volume then the cumulative production increased more than the other bioreactors, and the higher the iron particles coated zeolite were added the more the biogas generated. Compared to the control bioreactor, the two highest methane contents were depicted with the addition of the only nZVI and the IMZ mixture and the methane content was stimulated up to 88 and 74%, respectively. However, the maximum cumulative methane volume was obtained with supplementing of ICZ particles with a loading of 1000 mg/L of iron nanoparticles. These results might be attributed to the high reactivity of nanoparticles, which can be assigned to the anaerobic corrosion of nZVI and electrons generation that could be utilized effectively the methanogens utilization and methane production. Considering its high efficiency and good performance, the iron zeolite system can be extended to practical engineering application for biomethane production.

In vitro degradation is an important approach to screening appropriate biomedical magnesium (Mg) alloys at low cost. However, corrosion products deposited on Mg alloys exert a critical impact on corrosion resistance. There are no acceptable criteria on the evaluation on degradation rate of Mg alloys. Understanding the degradation behavior of Mg alloys in presence of Tris buffer is necessary. An investigation was made to compare the influence of Tris-HCl and Tris on the corrosion behavior of Mg alloy AZ31 in the presence of various anions of simulated body fluids via hydrogen evolution, pH value and electrochemical tests. The results demonstrated that the Tris-HCl buffer resulted in general corrosion due to the inhibition of the formation of corrosion products and thus increased the corrosion rate of the AZ31 alloy. Whereas Tris gave rise to pitting corrosion or general corrosion due to the fact that the hydrolysis of the amino-group of Tris led to an increase in solution pH value, and promoted the formation of corrosion products and thus a significant reduction in corrosion rate. In addition, the corrosion mechanisms in the presence of Tris-HCl and Tris were proposed. Tris-HCl as a buffer prevented the formation of precipitates of HCO3−, SO42−, HPO42− and H2PO4− ions during the corrosion of the AZ31 alloy due to its lower buffering pH value (x.x). Thus, both the hydrogen evolution rate and corrosion current density of the alloy were approximately one order of magnitude higher in presence of Tris-HCl than Tris and Tris-free saline solutions.

The electrochemical impedance spectroscopy and Electrochemical Noise were employed to investigate the electrochemical behavior of Fe3Al in H2S-CO2-Cl− environment under normal pressures and temperatures. The results indicate that Fe3Al has excellent self-passivating repair ability in H2S-CO2-Cl− environment. Meanwhile, by extending corrosion time, the type of corrosion changes from pitting corrosion to intergranular corrosion and finally to denudation. The flocculent and porous corrosion products are formed on the surface of Fe3Al. After the corrosion product falling off, fracturing morphology is observed and the corrosion products mainly include FeS, FeCO3, Al(OH)3, Al2O3, Cr2O3, etc.

A microscale zero-valent iron (mZVI)-based in situ reactive zone is a promising technology for contaminated groundwater remediation. Estimation of mZVI aging behavior after its injection into the subsurface is essential for efficiency and longevity assessments. In this study, batch tests were conducted to investigate the effect of initial pH on mZVI aging dynamics, as well as the formation and evolution of aging products over 112 days. Results indicated that mZVI aging accelerated with decreasing initial pH. Corrosion rates of mZVI particles under pH 6.0 and 7.5 were approximately two orders of magnitude higher than those observed at pH 9.0. The morphological, structural, and compositional evolution of mZVI particles in three systems (pH = 6.0, 7.5, and 9.0) were investigated using scanning electron microscopy, X-ray diffraction, and X-ray photoelectron spectroscopy. In acidic and neutral solutions, a thick passivation layer with loosely and unevenly distributed aging precipitates was observed, and Fe3O4 was the final aging precipitate. Nevertheless, in alkaline solutions, minute aging precipitates were detected on the mZVI surface at 112 day. Characterization results suggested that mZVI was oxidized via the Fe0–Fe(OH)2–Fe3O4 route. These findings shed new light on mZVI aging mechanisms, particularly its physicochemical characteristics and the structural evolution of mZVI in field-scale groundwater remediation applications.

The effect of ions of d-metals on the processes of corrosion in a movable and immovable neutral aqueous environment has been investigated. It was shown that a number of ions, such as zinc, chromium, lead, under conditions of high aeration and temperature of 20 oС at concentrations of 2−5 mg/dm3, are effective inhibitors of steel corrosion. This is due to the formation of a passivation oxygen film on the surface of metal. The degree of corrosion protection is maintained at the level of 80−90 %. In the case of elevating the temperature to 50 oС, a significant (up to 40 %) decrease in the inhibitory properties of ions of d-metals is observed. This is due both to the destabilization of the oxygen passivation film and the growth of oxidation rate of steel with increasing temperature. It was demonstrated that phosphonic acids, such as oxyethyldidiphosphone acid, nitrilotrimethylphosphonium acid, due to the interaction of complexons with the surface of metals, stabilize the passivation oxygen film, providing a degree of protection against corrosion at 95−98 % at acid dose of 10 mg/dm3. However, when the temperature rises to 50 °C, a protective effect is reduced. It was established that the use of compositions based on OEDPhA/NTMPhA and Zn/Pb/Cr ions in the range of temperatures 20−50 oC provides a degree of protection of steel from corrosion at the level of 90 %. This is explained by the formation of three-dimensional complexes of phosphonic acids with metal ions and corroded iron

Corrosion in oil-fired boilers is accelerated in the presence of V, Cl and S which derive from low-grade fuels or the environment. 10CrMo9-10 steel is commonly used in such boilers. In order to evaluate the salts corrosion behavior of such low Cr steels, samples were immersed in several vanadate salt combinations of Cl, S, Na and Ca in air at 600 °C. Even during short-term exposure, different dominant corrosion mechanisms could be identified such as active oxidation, sulfidation and acidic or basic fluxing, depending on the exact salt composition. The aggressiveness of the different salt mixtures was ranked with regard to the metal loss. It is also demonstrated that corrosion can be reduced by the addition of a calcium-containing inhibitor.

The corrosion behavior of 316 SS and three Ni-based alloys 625, 600 and 800 was evaluated by exposing in SCW at 400 °C and 24 MPa with 6000 ppm NH 4 Cl for 70 h. Various of analytical techniques were used for corrosion analysis. 316 SS underwent severe corrosion attack for general corrosion, pitting corrosion and intergranular attack. Inconel 625 showed the best corrosion resistance in the test environment. Fe oxides and spinel were identified by XRD on all of the SCW-exposed samples. Trace amounts of NiO was also identified on the surface of samples, however, Ni was selectively dissolved and depleted in oxide films, and nickel ammine may form at the relatively low temperature during the heating and cooling process.

Localized corrosion of carbon steel pipelines in oilfield environments is a serious concern. In environments containing both CO2 and H2S gases, pitting corrosion of carbon steel is considered to be a common occurrence which is particularly complex and still not fully understood. This paper presents a parametric study investigating the pitting corrosion behavior of carbon steel in CO2-H2S-containing environments. The work presented is divided into two parts. Part one focuses on understanding the impact of changes in three key process parameters (namely: temperature, absence/presence of 10% H2S, and absence/presence of CO2 in the gas phase) on FeS film formation process and overall the corrosion behavior of carbon steel with emphasis on general corrosion of carbon steel in a 3.5 wt% NaCl brine at 30°C and 80°C. Part two focuses on understanding the early and later stages of the pitting corrosion process, with consideration afforded to general corrosion and iron sulfide (FeS) film formation mechanisms, kinet...

The corrosion behavior of newly developed API X120 C-steel that is commenced to be used for oil pipelines was studied in a H2S saturated 3.5 wt.% NaCl solution between 20 and 60 °C using potentiodynamic polarization and electrochemical impedance spectroscopy techniques. The corrosion products formed on the surface of the alloy were characterized using x-ray diffraction and scanning electron microscopy. It has been noticed that the formation of corrosion product layer takes place at both lower and higher temperatures which is mainly comprised of iron oxides and sulfides. The electrochemical results confirmed that the corrosion rate decreases with increasing temperature up to 60 °C. This decrease in corrosion rate with increasing temperature can be attributed to the formation of a protective layer of mackinawite layer. However, cracking in the formed mackinawite layer may not be responsible for the increase in the corrosion rate. More specifically, developed pourbaix diagrams at different temperatures showed that the formed protective layer belongs to mackinawite (FeS), a group of classified polymorphous iron sulfide, which is in good agreement with the experimental results. It is also noticed that the thickness of corrosion products layer increases significantly with decrease in the corrosion rate of API X120 steel exposed to H2S environment. These findings indicate that API X120 C-steel is susceptible to sour corrosion under the above stated experimental conditions.