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  • Chromate replacement: what does the future hold?
    npj Mater. Degrad. Pub Date : 2018-04-12
    Oumaïma Gharbi, Sebastian Thomas, Craig Smith, Nick Birbilis

    The ubiquitous use of chromium and its derivatives as corrosion preventative compounds accelerated rapidly after the second industrial revolution, with such compounds now integral to modern society. However, the detrimental impact of chromium compounds on the environment and human health has prompted the need to revisit the majority of current industrial corrosion protection measures. This review retraces the origins of chromium replacement motivations, introducing the various legislative actions aimed at diminishing the use of chromium compounds, and critically reviews alternative corrosion preventative technologies developed in the recent decades to now. The review, herein, is intended for a broad audience in order to provide a concise update to an increasingly timely issue.

  • Carbon dioxide sequestration through silicate degradation and carbon mineralisation: promises and uncertainties
    npj Mater. Degrad. Pub Date : 2018-04-04
    Damien Daval

    Turning carbon dioxide (CO2) into rocks: controlling this process, which naturally operates at the Earth’s surface over geological timescales, is likely to represent a major technological challenge of this century. One of the recurring criticisms with the carbonation reactions is their sluggishness, as it is commonly admitted that converting silicates into carbonates within geologic reservoirs may take up to several thousands of years, i.e., a duration which is hardly compatible with the goal of achieving net zero emissions by mid-century. Last year, a study that generated substantial interest suggested that after 2 years, more than 95% of the CO2 injected over the course of a pilot project of CO2 injection in lava flows in Iceland might have been mineralised into carbonates. While such results could have been considered as a green light for industrial applications, a new high-profile study based on the same pilot experiment tempered this idea, as it revealed unexpected modifications of deep ecosystems in response to CO2 injection, evidencing a bloom of chemolithoautotrophic bacteria, which have the ability to promote autotrophic C-fixation. Stated in other words, part of the CO2 that was initially thought to be mineralised under the form of stable carbonates might instead have been converted into (much more labile) biomass. Assessing the respective contributions of carbonates and biomass to the C-sequestration should therefore represent a prerequisite prior to large-scale carbon capture and storage through mineral carbonation, to make sure that the cure is not worse than the disease.

  • Tracking the evolution of intergranular corrosion through twin-related domains in grain boundary networks
    npj Mater. Degrad. Pub Date : 2018-04-03
    Christopher M. Barr, Sebastian Thomas, James L. Hart, Wayne Harlow, Elaf Anber, Mitra L. Taheri

    Tailoring the grain boundary network is desired to improve grain boundary-dependent phenomena such as intergranular corrosion. An important grain boundary network descriptor in heavily twinned microstructures is the twin-related domain, a cluster of twin-related grains. We indicate the advantages of using twin-related domains and subsequent statistics to provide new insight into how a grain boundary networks respond to intergranular corrosion in a heavily twinned grain boundary engineered 316L stainless steel. The results highlight that intergranular corrosion is typically arrested inside twin-related domains at coherent twins or low-angle grain boundaries. Isolated scenarios exist, however, where intergranular corrosion propagation persists in the grain boundary network through higher-order twin-related boundaries.

  • Passivation behaviour of aluminium current collector in ionic liquid alkyl carbonate (hybrid) electrolytes
    npj Mater. Degrad. Pub Date : 2018-03-29
    Sowmiya Theivaprakasam, Gaetan Girard, Patrick Howlett, Maria Forsyth, Sagar Mitra, Douglas MacFarlane

    The compatibility of current collectors with the electrolyte plays a major role in the overall performance of lithium batteries, critical to obtain high storage capacity as well as excellent capacity retention. In lithium-ion batteries, in particular with cathodes that operate at high voltage such as lithium nickel cobalt manganese oxide, the cathodic current collector is aluminium and it is subjected to high oxidation potentials (>4 V vs. Li/Li+). As a result, the composition of the electrolyte needs to be carefully designed in order to stabilise the battery performance as well as to protect the current collectors against corrosion. This study examines the role of a hybrid electrolyte composed of an ionic liquid (N-methyl-N-propyl pyrrolidinium bis(trifluoromethanesulfonyl)imide or N-methyl-N-propyl pyrrolidinium bis(fluorosulfonyl)imide) and a conventional electrolyte mixture (LiPF6 salt and alkyl carbonate solvents) with correlation to their electrochemical behaviour and corrosion inhibition efficiency. The hybrid electrolyte was tested against battery grade aluminium current collectors electrochemically in a three-electrode cell configuration and the treated aluminium surface was characterised by SEM/EDXS, optical profilometry, FTIR, and XPS analysis. Based on the experimental results, the hybrid electrolytes allow an effective and improved passivation of aluminium and lower the extent of aluminium dissolution in comparison with the conventional lithium battery electrolytes and the neat ionic liquids at high anodic potentials (4.7 V vs. Li/Li+). The mechanism of passivation behaviour is also further investigated. These observations provide a potential direction for developing improved hybrid electrolytes, based on ionic liquids, for higher energy density devices.

  • In situ electrochemical dissolution of platinum and gold in organic-based solvent
    npj Mater. Degrad. Pub Date : 2018-03-21
    Primož Jovanovič, Vid Simon Šelih, Martin Šala, Nejc Hodnik

    In situ highly sensitive potential- and time-resolved monitoring of polycrystalline gold and platinum electrochemical dissolution in pure organic media is reported. This was achieved by successfully upgrading electrochemical flow cell coupled to inductively coupled plasma mass spectrometry. Similar to the aqueous media, aggressive transient dissolution takes place during oxide formation and reduction. In contrary to the aqueous electrolyte, both gold and platinum exhibit enhanced anodic compared to the cathodic oxide-assisted dissolution in organic media. This study intends to highlight the capabilities of the new methodology, which will expand the studies of metals dissolution to the fields like organic electrocatalysis, corrosion, battery research, and sensors among others.

  • Understanding the reactivity of CoCrMo-implant wear particles
    npj Mater. Degrad. Pub Date : 2018-03-12
    Mohamed A. Koronfel, Angela E. Goode, Johanna Nelson Weker, Stephen E. R. Tay, Camilla A. Stitt, Thiago A. Simoes, J. Frederick. W. Mosselmans, Paul Quinn, Rik Brydson, Alister Hart, Michael F. Toney, Alexandra E. Porter, Mary P. Ryan

    CoCrMo-based metal-on-metal hip implants experienced unexpectedly high failure rates despite the high wear and corrosion resistance of the bulk material. Although they exhibit a lower volumetric wear compared to other implant materials, CoCrMo-based implants produced a significantly larger 'number' of smaller wear particles. CoCrMo is nominally an extremely stable material with high Cr content providing passivity. However, despite the Co:Cr ratio in the original alloy being 2:1; chemical analyses of wear particles from periprosthetic tissue have found the particles to be composed predominately of Cr species, with only trace amounts of Co remaining. Here a correlative spectroscopy and microscopy approach has shown that these particles dissolve via a non-stoichiometric, and geometrically inhomogeneous, mechanism similar to de-alloying. This mechanism is previously unreported for this material and was not apparent in any of the regulatory required tests, suggesting that such tests are insufficiently discriminating.

  • Time-dependent in situ measurement of atmospheric corrosion rates of duplex stainless steel wires
    npj Mater. Degrad. Pub Date : 2018-03-07
    Cem Örnek, Fabien Léonard, Samuel A. McDonald, Anuj Prajapati, Philip J. Withers, Dirk L. Engelberg

    Corrosion rates of strained grade UNS S32202 (2202) and UNS S32205 (2205) duplex stainless steel wires have been measured, in situ, using time-lapse X-ray computed tomography. Exposures to chloride-containing (MgCl2) atmospheric environments at 50 °C (12–15 M Cl− and pH ~5) with different mechanical elastic and elastic/plastic loads were carried out over a period of 21 months. The corrosion rates for grade 2202 increased over time, showing selective dissolution with shallow corrosion sites, coalescing along the surface of the wire. Corrosion rates of grade 2205 decreased over time, showing both selective and pitting corrosion with more localised attack, growing preferentially in depth. The nucleation of stress corrosion cracking was observed in both wires.

  • Chemical durability of peraluminous glasses for nuclear waste conditioning
    npj Mater. Degrad. Pub Date : 2018-03-02
    Victor Piovesan, Isabelle Bardez-Giboire, Maxime Fournier, Pierre Frugier, Patrick Jollivet, Valérie Montouillout, Nadia Pellerin, Stéphane Gin

    For the handling of high level nuclear waste (HLW), new glass formulations with a high waste capacity and an enhanced thermal stability, chemical durability, and processability are under consideration. This study focuses on the durability of peraluminous glasses in the SiO2–Al2O3–B2O3–Na2O–CaO–La2O3 system, defined by an excess of Al3+ ions compared with the network-modifying cations Na+ and Ca2+. To qualify the behavior of such a peraluminous glass in a geological storage situation, its chemical durability was studied in various environments (pure water, groundwater, and alkaline solutions related to a cement environment) and glass alteration regimes (initial rate, residual rate, and resumption of alteration). The alteration solution was characterized by inductively coupled plasma, and the altered glass by scanning electron microscopy, X-ray diffraction and secondary ion mass spectrometry. A comparative study of the chemical durability of these and reference glasses (ISG and SON68) over all timescales highlights the remarkable properties of the former. While their initial dissolution rate is of the same order as the reference glasses, the gel formed under silica saturation conditions is more passivating, making its dissolution rate at least one order of magnitude lower, while its low alkalinity makes it less susceptible to clayey groundwater and highly alkaline solutions.

  • Integrated computational materials engineering of corrosion resistant alloys
    npj Mater. Degrad. Pub Date : 2018-02-20
    Christopher D. Taylor, Pin Lu, James Saal, G. S. Frankel, J. R. Scully

    Structure, composition and surface properties dictate corrosion resistance in any given environment. The degrees of freedom in alloy design are too numerous in emerging materials such as high entropy alloys and bulk metallic glasses for the use of high-throughput methods or trial and error. We review three domains of knowledge that can be applied towards the goal of corrosion resistant alloy (CRA) design: (a) the aggregation of knowledge gained through experience in developing CRAs empirically, (b) data-driven approaches that use descriptive metrics for alloy composition optimization, and (c) first-principles models of elementary processes that regulate corrosion informed by theory and inspired by phenomenological models in the literature. A path forward for integrated computational materials engineering (ICME) of CRAs that unites these three knowledge domains is introduced.

  • The role of titanium in the initiation of localized corrosion of stainless steel 444
    npj Mater. Degrad. Pub Date : 2018-02-14
    Samantha Michelle Gateman, Lisa Irene Stephens, Samuel Charles Perry, Robert Lacasse, Robert Schulz, Janine Mauzeroll

    Titanium has been added to ferritic stainless steels to combat the detrimental effects of intergranular corrosion. While this has proven to be a successful strategy, we have found that the resulting Ti-rich inclusions present on the surface play a significant role in the initiation of other forms of localized corrosion. Herein, we report the effect of these inclusions on the localized corrosion of a stainless steel using macro and micro electrochemical techniques. Through the use of scanning electrochemical microscopy, we observe the microgalvanic couple formed between the conductive inclusions and passivated metal matrix. The difference in local reactivity across the material’s surface was quantified using a 3D finite element model specifically built to respect the geometry of the corrosion-initiating features. Combined with electron microscopy and micro elemental analysis, localization of other alloying elements has been reported to provide new insight on their significance in localized corrosion resistance.

  • Structure of International Simple Glass and properties of passivating layer formed in circumneutral pH conditions
    npj Mater. Degrad. Pub Date : 2018-02-05
    Marie Collin, Maxime Fournier, Pierre Frugier, Thibault Charpentier, Mélanie Moskura, Lu Deng, Mengguo Ren, Jincheng Du, Stéphane Gin

    Knowing the structure of a material is necessary to understand its evolution under various influences; here, the alteration by water of a reference glass of nuclear interest, called International Simple Glass (ISG), is studied. The ISG atomic structure has not yet been thoroughly characterized. Short- and medium-range order in this six-oxide glass was investigated by molecular dynamics (MD) methods. Combining the simulated data with experimental observations acquired from both pristine and altered ISG provided new insight into the formation of surface layers and passivation of the underlying glass. In the tested conditions of 90 °C, silica-saturated solution, and pH90°C 7, the passivating layer partly inherits the structure of the pristine glass network despite the release of mobile elements (Na, B, and some Ca), with a reorganization of the silicate network following B release. The layer appears to minimize its internal energy by relaxing strain accumulated during glass quenching. The resulting passivated glass shows a strong resistance to hydrolysis. The nanopores of this hydrated material, displaying a mean pore size of ∼1 nm, are filled with various water species. Water speciation determination inside the nanopores is therefore an achievement for future water dynamic study in the passivated glass.

  • Hydrogen blistering under extreme radiation conditions
    npj Mater. Degrad. Pub Date : 2018-01-23
    Maciej Sznajder, Ulrich Geppert, Mirosław R. Dudek

    Metallic surfaces, exposed to a proton flux, start to degradate by molecular hydrogen blisters. These are created by recombination of protons with metal electrons. Continued irradiation progresses blistering, which is undesired for many technical applications. In this work, the effect of the proton flux magnitude onto the degradation of native metal oxide layers and its consequences for blister formation has been examined. To study this phenomenon, we performed proton irradiation experiments of aluminium surfaces. The proton kinetic energy was chosen so that all recombined hydrogen is trapped within the metal structure. As a result, we discovered that intense proton irradiation increases the permeability of aluminium oxide layers for hydrogen atoms, thereby counteracting blister formation. These findings may improve the understanding of the hydrogen blistering process, are valid for all metals kept under terrestrial ambient conditions, and important for the design of proton irradiation tests.

  • High resolution NanoSIMS imaging of deuterium distributions in 316 stainless steel specimens after fatigue testing in high pressure deuterium environment
    npj Mater. Degrad. Pub Date : 2018-01-16
    Greg McMahon, Bryan D. Miller, M. Grace Burke

    It is irrefutable that the presence of hydrogen reduces the mechanical performance of many metals and alloys used for structural components. Several mechanisms of hydrogen-assisted cracking (HAC) of steels have been postulated. The direct evidence of the mechanisms by which hydrogen embrittles these materials has remained elusive. This is by virtue of our difficulty to directly observe the hydrogen distribution at spatial resolutions less than 100 nm and analysis volumes greater than 1 × 109 atoms at microstructural features such as grain boundaries, dislocations, twins, stacking faults and sub-micron inclusions that are all potential hydrogen trapping sites postulated to be responsible for the degradation of mechanical performance. Here, we report on an experimental methodology combining an elaborate fatigue testing protocol in an enriched gaseous deuterium environment with NanoSIMS (secondary ion mass spectrometry) imaging for detection of deuterium at spatial resolutions as low as 100 nm and accompanying TEM analysis. Type 316 stainless steel compact tension specimens were precharged in deuterium followed by fatigue testing at high stress ratio (0.7), low delta K (~11 MPa √m), and a frequency of 1 cycle per minute using a sawtooth waveform with a rise time of 30 s in high pressure (68.9 MPa) gaseous deuterium (99.999% purity) environment at room temperature. High resolution NanoSIMS imaging was then used to measure the deuterium distribution at the tip of and in the wake of secondary and tertiary fatigue cracks as well as at MnS inclusions. The use of deuterium eliminates the difficulties of interpreting hydrogen measurements by SIMS relating to the ubiquitous presence of hydrogen in all high vacuum systems and guarantees that deuterium measured by the NanoSIMS must be attributed to the fatigue testing protocol. This methodology has allowed us to directly observe the distribution of hydrogen in dislocation tangles ahead and in the wake of fatigue crack tips and at the interface of MnS inclusions. The protocol provides an avenue by which the path and speed with which hydrogen proceeds along its embrittling course of action may be directly followed through modifications of the fatigue testing parameters and/or alloy type and allows a means to validate at least qualitatively recently published models of enhanced hydrogen transport by dislocations.

  • Utilization of chemical stability diagrams for improved understanding of electrochemical systems: evolution of solution chemistry towards equilibrium
    npj Mater. Degrad. Pub Date : 
    R. J. Santucci Jr., M. E. McMahon, J. R. Scully

    Predicting the stability of chemical compounds as a function of solution chemistry is crucial towards understanding the electrochemical characteristics of materials in real-world applications. There are several commonly considered factors that affect the stability of a chemical compound, such as metal ion concentration, mixtures of ion concentrations, pH, buffering agents, complexation agents, and temperature. Chemical stability diagrams graphically describe the relative stabilities of chemical compounds, ions, and complexes of a single element as a function of bulk solution chemistry (pH and metal ion concentration) and also describe how solution chemistry changes upon the thermodynamically driven dissolution of a species into solution as the system progresses towards equilibrium. Herein, we set forth a framework for constructing chemical stability diagrams, as well as their application to Mg-based and Mg–Zn-based protective coatings and lightweight Mg–Li alloys. These systems are analyzed to demonstrate the effects of solution chemistry, alloy composition, and environmental conditions on the stability of chemical compounds pertinent to chemical protection. New expressions and procedures are developed for predicting the final thermodynamic equilibrium between dissolved metal ions, protons, hydroxyl ions and their oxides/hydroxides for metal-based aqueous systems, including those involving more than one element. The effect of initial solution chemistry, buffering agents, complexation agents, and binary alloy composition on the final equilibrium state of a dissolving system are described by mathematical expressions developed here. This work establishes a foundation for developing and using chemical stability diagrams for experimental design, data interpretation, and material development in corroding systems.

  • Development of a microfluidic setup to study the corrosion product deposition in accelerated flow regions
    npj Mater. Degrad. Pub Date : 2017-12-14
    John McGrady, Jonathan Duff, Nicholas Stevens, Andrea Cioncolini, Michele Curioni, Andrew Banks, Fabio Scenini

    CRUD (Chalk River Unidentified Deposit) forms in the water circuits of nuclear reactors due to corrosion of structural materials and the consequent release of species into the coolant. The deposition of CRUD is known to occur preferentially in regions of the primary circuit of pressurised water reactors (PWRs) where the water flow accelerates. In order to investigate this phenomenon, a micro-fluidic system, recreating plant conditions while using a simplified experimental set-up, was realised. A flow cell, comprising a stainless steel disc with a central micro-orifice, was used to create accelerated flow under representative operating conditions. By monitoring the pressure drop across the cell, the build-up rate (BUR) of CRUD within the micro-orifice was monitored in real time. By this setup, the conditions inducing deposition of CRUD under PWR conditions were emulated and CRUD deposition was induced in the accelerated flow region. Further effects associated with the presence of lithium hydroxide were investigated in real-time.

  • Multi-scale investigation of uranium attenuation by arsenic at an abandoned uranium mine, South Terras
    npj Mater. Degrad. Pub Date : 2017-12-14
    Claire L. Corkhill, Daniel E. Crean, Daniel J. Bailey, Carmen Makepeace, Martin C. Stennett, Ryan Tappero, Daniel Grolimund, Neil C. Hyatt

    Detailed mineralogical analysis of soils from the UK’s historical uranium mine, South Terras, was performed to elucidate the mechanisms of uranium degradation and migration in the 86 years since abandonment. Soils were sampled from the surface (0–2 cm) and near-surface (25 cm) in two distinct areas of ore processing activities. Bulk soil analysis revealed the presence of high concentrations of uranium (<1690 p.p.m.), arsenic (1830 p.p.m.) and beryllium (~250 p.p.m.), suggesting pedogenic weathering of the country rock and ore extraction processes to be the mechanisms of uranium ore degradation. Micro-focus XRF analysis indicated the association of uranium with arsenic, phosphate and copper; µ-XRD data confirmed the presence of the uranyl-arsenate minerals metazeunerite (Cu(UO2)2(AsO4)2·8H2O) and metatorbernite (Cu(UO2)2(PO4)2·8H2O) to be ubiquitous. Our data are consistent with the solid solution of these two uranyl-mica minerals, not previously observed at uranium-contaminated sites. Crystallites of uranyl-mica minerals were observed to coat particles of jarosite and muscovite, suggesting that the mobility of uranium from degraded ores is attenuated by co-precipitation with arsenic and phosphate, which was not previously considered at this site.

  • The controlling role of sodium and carbonate on the atmospheric corrosion rate of aluminum
    npj Mater. Degrad. Pub Date : 2017-11-14
    Rebecca F. Schaller, Carlos F. Jove-Colon, Jason M. Taylor, Eric J. Schindelholz

    Aluminum and aluminum alloys are widely used in many outdoor applications due to their inherent corrosion resistance attributed to the formation of a protective oxide layer. While corrosion rates are generally considered low for aluminum in many atmospheric environments, understanding of the corrosion performance over time is necessary to predict the cost, safety, and esthetics of these materials. The vast majority of the knowledgebase of atmospheric aluminum corrosion is built on environment–response relationships; often based on statistical correlation of corrosion rate data with atmospheric environmental conditions. However, there is still a limited mechanistic understanding of corrosion processes associated with this linkage. This lack in knowledge prevents interpretation and limits the extrapolation of these statistical datasets for prediction purposes. Here, the mechanistic dependence of aluminum corrosion rate on salt loading is explored through complimentary experimental and theoretical analysis relating corrosion rate to electrolyte chemistry, volume and corrosion products. From these results a reaction pathway is proposed for the atmospheric corrosion of aluminum that accounts for the governing effects of CO2 and salt loading on corrosion rate. This reaction pathway provides a new perspective that highlights the importance of the formation and growth of dawsonite (NaAlCO3(OH)2), and the subsequent gettering of sodium from the electrolyte leading to the stifling of corrosion kinetics. This study highlights the importance of accounting for the dynamic physical and chemical state of the electrolyte during corrosion in process models and measurement techniques to better understand and predict atmospheric corrosion behavior.

  • Interphase engineering of reactive metal surfaces using ionic liquids and deep eutectic solvents—from corrosion control to next-generation batteries
    npj Mater. Degrad. Pub Date : 2017-11-13
    Maria Forsyth, Patrick C. Howlett, Anthony E. Somers, Douglas R. MacFarlane, Andrew Basile

    Ionic liquids are unique solvents composed entirely of ions and have recently been considered for applications ranging from synthesis, separations, electrochemical devices, tribology and corrosion. In this perspective, we summarise the literature, and look at the future prospects, surrounding the use of ionic liquids in the engineering of interphases to control charge transport thereby leading to improved performance of high-energy density batteries, including Mg, Li and Na metal as well as corrosion protection of reactive engineering alloys, such as aluminium, magnesium and steel alloys. The ability to create task-specific ionic liquids by controlling the chemistry of either the anion or the cation means that interphases can be engineered for specific substrates and applications. Thus far, fluorine containing anions, such as bis(trifluoromethane) sulfonamide and its analogues, have been favoured for controlling the conductive solid–electrolyte interphase layer on Li and Na, while ionic liquids containing organophosphate anions have been used to form nanometre thick protective interphases on Mg alloys. Recently, ionic liquids based on carboxylate anions have also been shown to provide excellent corrosion inhibition for steel. In the search for cost-effective solutions, a relatively new class of ionic liquids, termed deep eutectic solvents, have also been explored as potential media for controlling surface films on reactive metals. The deep eutectic solvents class of ionic liquid materials offers many possible combinations of chemistry that can be targeted to produce desired properties in this context.

  • Atomistic computer simulations of water interactions and dissolution of inorganic glasses
    npj Mater. Degrad. Pub Date : 2017-11-13
    Jincheng Du, Jessica M. Rimsza

    Computer simulations at the atomistic scale play an increasing important role in understanding the structure features, and the structure–property relationships of glass and amorphous materials. In this paper, we reviewed atomistic simulation methods ranging from first principles calculations and ab initio molecular dynamics (AIMD) simulations, to classical molecular dynamics (MD), and meso-scale kinetic Monte Carlo (KMC) simulations and their applications to study the reactions and interactions of inorganic glasses with water and the dissolution behaviors of inorganic glasses. Particularly, the use of these simulation methods in understanding the reaction mechanisms of water with oxide glasses, water–glass interfaces, hydrated porous silica gels formation, the structure and properties of multicomponent glasses, and microstructure evolution are reviewed. The advantages and disadvantageous of these simulation methods are discussed and the current challenges and future direction of atomistic simulations in glass dissolution presented.

  • Contribution of zeolite-seeded experiments to the understanding of resumption of glass alteration
    npj Mater. Degrad. Pub Date : 2017-11-13
    Maxime Fournier, Stéphane Gin, Pierre Frugier, Sara Mercado-Depierre

    Understanding the origin and the consequences of glass alteration regimes is necessary for the prediction of nuclear glass durability. The so-called “stage 3” or “resumption of alteration regime” of glasses used to sequester nuclear waste by vitrification, is characterized by a sudden acceleration of glass alteration rate arising from the precipitation of secondary minerals, mainly zeolites. To study this process, a promising approach is developed, based on seeding by synthesized zeolite seeds. This study quantitatively links the alteration of a six-oxide reference borosilicate glass (ISG) and the precipitation of zeolites that affects concentrations of key species—in particular aluminum—and thus the glass dissolution rate. The characterization of stage 3—easier at alkaline pH—can now be extended to pH conditions more representative of those found in a geological repository thanks to seeding that reduces, or even eliminates, the latency period preceding a resumption of glass alteration. The resumption occurrence and glass dissolution rate are related with temperature and pH. This study shows that the detrimental effect of zeolite precipitation decreases with decreasing pH and temperature, until it is no longer detectable at a pH around 9 imposed by the dissolution of the ISG glass. Even for both high temperature and high pH, the resumption rate is lower than the initial alteration rate, which remains the fastest kinetic regime.

  • Siderite micro-modification for enhanced corrosion protection
    npj Mater. Degrad. Pub Date : 2017-10-16
    Wassim Taleb, Frederick Pessu, Chun Wang, Thibaut Charpentier, Richard Barker, Anne Neville

    Production of oil and gas results in the creation of carbon dioxide (CO2) which when wet is extremely corrosive owing to the speciation of carbonic acid. Severe production losses and safety incidents occur when carbon steel (CS) is used as a pipeline material if corrosion is not properly managed. Currently corrosion inhibitor (CI) chemicals are used to ensure that the material degradation rates are properly controlled; this imposes operational constraints, costs of deployment and environmental issues. In specific conditions, a naturally growing corrosion product known as siderite or iron carbonate (FeCO3) precipitates onto the internal pipe wall providing protection from electrochemical degradation. Many parameters influence the thermodynamics of FeCO3 precipitation which is generally favoured at high values of temperatures, pressure and pH. In this paper, a new approach for corrosion management is presented; micro-modifying the corrosion product. This novel mitigation approach relies on enhancing the crystallisation of FeCO3 and improving its density, protectiveness and mechanical properties. The addition of a silicon-rich nanofiller is shown to augment the growth of FeCO3 at lower pH and temperature without affecting the bulk pH. The hybrid FeCO3 exhibits superior general and localised corrosion properties. The findings herein indicate that it is possible to locally alter the environment in the vicinity of the corroding steel in order to grow a dense and therefore protective FeCO3 film via the incorporation of hybrid organic-inorganic silsesquioxane moieties. The durability and mechanical integrity of the film is also significantly improved.

  • Chemical and electrochemical conditions within stress corrosion and corrosion fatigue cracks
    npj Mater. Degrad. Pub Date : 2017-10-16
    Leslie G. Bland, Jenifer S. (Warner) Locke

    In the area of environment assisted cracking, literature aimed at understanding the chemical and electrochemical conditions at/near the crack tip establishes that the crack tip is occluded and not well represented by bulk conditions. A review of the relevant literature, both modeling and experimental, is presented here and shows that crack tip conditions are determined by the balance between high metal ion concentrations resulting from crack tip anodic reactions and subsequent hydrolysis, mass transport (including ion migration, diffusion, and advection), and electrochemical polarization of the bold surface, which determines the extent of anodic and cathodic reactions occurring in the crack environment. Under both freely corroding conditions and anodic polarizations, the crack tip pH decreases with increasing polarization above the freely corroding condition, most often leading to a very acidic crack environment. Under sufficient cathodic polarization, the crack tip pH increases. Because of high-anion and -cation concentrations in the crack environment, an IR drop down the crack exists, leaving the crack tip relatively unpolarizable. Ion migration enhances the occluded nature of the crack tip by supplying anions from the bulk solution to maintain electroneutrality at the crack tip. Diffusion to counteract this concentration gradient is minimal and only plays a role in crack tip conditions at very small crack lengths. When cyclic loading conditions are encountered, the occluded nature of the crack tip can be counteracted by advection; although, the role decreases with decreasing f and increasing R, essentially as corrosion fatigue conditions approach those of stress corrosion cracking.

  • Crevice corrosion of nickel-based alloys considered as engineering barriers of geological repositories
    npj Mater. Degrad. Pub Date : 2017-10-16
    Ricardo M. Carranza, Martín A. Rodríguez

    Nickel-based alloys are considered among other candidate materials as engineering barriers of geological repositories due to their excellent corrosion resistance. These alloys possess unique advantages: they may be used in saturated and unsaturated repositories, hosted by practically any rock type, while also compatible with any (or no) backfill, and have minimal impact in other barriers. Alloy-22 (UNS N06022) has been the most studied of this class of alloys for its potential application in the proposed repositories (namely Yucca Mountain, USA). Crevice corrosion is however an important and often unintended degradation process that may limit the waste container lifetime if a nickel-based alloy is selected. Alloy susceptibility to crevice corrosion is influenced by environmental and metallurgical variables. This review gives an account of the current knowledge regarding crevice corrosion of nickel-based alloys as candidate materials for the corrosion-resistant layer of high-level nuclear waste containers. Although there is a significant amount of research supporting the use of nickel-based alloys for this application, the effect of the different variables on crevice corrosion resistance is described. Special focus is given to the current criterion for crevice corrosion occurrence in repository environments, recent works and criticisms. The presently established criterion appears robust for ruling out crevice corrosion in saturated repositories; however, the development of a less conservative criterion for crevice corrosion occurrence is necessary to use these alloys in unsaturated repositories.

  • The contribution of hydrogen evolution processes during corrosion of aluminium and aluminium alloys investigated by potentiodynamic polarisation coupled with real-time hydrogen measurement
    npj Mater. Degrad. Pub Date : 2017-09-18
    Christophe Laurent, Fabio Scenini, Tullio Monetta, Francesco Bellucci, Michele Curioni

    Water reduction, which leads to the evolution of hydrogen, is a key cathodic process for corrosion of many metals of technological interest such as magnesium, aluminium, and zinc; and its understanding is critical for design of new alloys or protective treatments. In this work, real-time hydrogen evolution measurement was coupled with potentiodynamic measurements on high-purity aluminium and AA2024-T3 aluminium alloy. The results show that both materials exhibit superfluous hydrogen evolution during anodic polarisation and that the presence of cathodically active alloying elements enhances hydrogen evolution. Furthermore, it was observed for the first time that superfluous hydrogen evolution also occurs during cathodic polarisation. Both the anodic and cathodic behaviours can be rationalised by a model assuming that superfluous hydrogen evolution occurs locally where the naturally formed oxide is disrupted. Specifically, during anodic polarisation, oxide disruption is due to the combined presence of chloride ions and acidification, whereas during cathodic polarisation, such disruption is due to alkalinisation. Furthermore, the presence of cathodically active alloying elements enhances superfluous hydrogen evolution in response to either anodic or cathodic polarisation, and results in ‘cathodic activation’ of the dissolved regions.

Some contents have been Reproduced with permission of the American Chemical Society.
Some contents have been Reproduced by permission of The Royal Society of Chemistry.
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