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Seafloor hydrothermal chimneys from back-arc basins are important hosts for metals such as Cu, Zn, Pb, Ag, and Au. Although the general growth history of chimneys has been well documented, recent studies have revealed that the fine-scale mineralogy can be highly complex and reflects variable physicochemical conditions of formation. This study utilized a novel combination of scanning electron microscopy (SEM)-based electron backscattered diffraction (EBSD) and synchrotron X-ray fluorescence microscopy (SXFM) to uncover the detailed growth processes of multiple chalcopyrite-lined conduits within a modern chalcopyrite-sphalerite chimney from Manus Basin and to assess the controls on native gold precipitation. On the basis of previous studies, the chimney conduit was thought to develop from an initial sulfate-dominated wall, which was subsequently dissolved and replaced by sphalerite and chalcopyrite during gradual mixing of hydrothermal fluids and seawater. During this process, sphalerite was epitaxially overgrown by chalcopyrite. Accretionary growth of chalcopyrite onto this early formed substrate thickened the chimney walls by bi-directional growth inward and outward from the original tube wall, also enclosing the outgrown pyrite cluster. A group of similar conduits with slightly different mineral assemblages continued to form in the vicinity of the main conduit during the further fluid mixing process. Four types of distinct native gold-sulfide/sulfosalt associations were developed during the varying mixing of hydrothermal fluids and seawater. Previously unobserved chains of gold nanoparticles occur at the boundary of early sphalerite and chalcopyrite, distinct from gold observed in massive sphalerite as identified in other studies. These observations provide baseline data in a well-preserved modern system for studies of enrichment mechanisms of native gold in hydrothermal chimneys. Furthermore, native gold is relatively rarely observed in chalcopyrite-lined conduit walls. Our observations imply that: (1) native gold is closely associated with various sulfides/sulfosalts in chalcopyrite-lined conduit walls rather than limited to the association with tennantite, Bi-rich minerals, and bornite as reported previously; and (2) the broad spectrum of gold occurrence in chalcopyrite-line conduits is likely to be determined by the various mixing process between hot hydrothermal fluids with surrounding fluids or seawater. Quantitative modeling of fluid mixing processes is recommended in the future to probe the precise gold deposition stages to efficiently locate gold in modern hydrothermal chimneys.

This study investigates the stress corrosion cracking (SCC) behavior of type 316L stainless steel (SS316L) produced with sinter-based material extrusion additive manufacturing (AM). This technology has been shown to produce SS316L with microstructures and mechanical properties comparable to its wrought counterpart in the annealed condition. However, despite plenty of research on SCC of SS316L, little is known about SCC in sinter-based AM SS316L. This study focuses on the influence of sintered microstructures on susceptibility to SCC initiation and crack-branching. Custom-made C-rings were exposed to different stress levels in acidic chloride solutions at various temperatures. To better understand the SCC behavior of SS316L, solution-annealed (SA) and cold-drawn (CD) wrought SS316L were tested for comparison. Results showed that sinter-based AM SS316L was more susceptible to SCC initiation than SA wrought SS316L but more resistant than CD wrought SS316L. Moreover, sinter-based AM SS316L showed noticeably better resistance to crack-branching than both wrought SS316L counterparts. The investigation was supported by comprehensive pre- and post-test microanalysis using light optical microscopy (LOM), scanning electron microscopy (SEM), electron backscatter diffraction (EBSD), and micro-computed tomography (micro-CT)

There is a fast-growing interest in the use of selective laser melting (SLM) for metal/alloy additive manufacturing. Our current knowledge of SLM printed 316 stainless steel (SS316) is limited and sometimes appears sporadic, presumably due to the complex interdependent effects of a large number of process variables of the SLM processing. This is reflected from the discrepant findings in the crystallographic textures and microstructures in this investigation with those reported in the literatures, which also vary itself. The as-printed material is macroscopically asymmetric in both the structures and crystallographic textures. The and crystallographic directions align parallel with the SLM scanning direction (SD) and build direction (BD), respectively. Like-wise, some characteristic low angle boundary features are reported crystallographic, while this investigation unequivocally proves them non-crystallographic since they always maintain an identical alignment with the SLM laser scanning direction irrespective of the matrix material’s crystal orientation. There is also 500±200 nm columnar or cellular features, depending on the cross-section, generally found all over the sample. These columnar or cellular features are formed with walls made of dense packing of dislocations entangled with Mn, Si and O enriched amorphous inclusions. They remain stable after the ASM solution treatments at 1050 °C temperatures, and therefore, are capable of hindering boundary migration events of recrystallization and grain growth. Thus, the nanoscale structures can be retained at high temperatures. Large 2-4 µm inclusions form during the solution treatment, within which the chemical and phase distribution are heterogeneous.

Selective laser melting (SLM) or powder bed fusion is a type of additive manufacturing technology with applications in, e.g., the orthopedics, energy, and aerospace industries. Several studies investigated the localized corrosion behavior of SLM-fabricated Type 316L (UNS S31603) stainless steel. However, little is known about the effects of tribocorrosive conditions on the response of stainless steels fabricated by SLM. In this study, the effects of third-body abrasive particles on the tribo-electrochemical behavior of SLM 316L stainless steel produced by SLM were investigated and compared with wrought counterparts (including UNS S31703, 317W) in 0.6 M NaCl. It was found that the presence of Mo played a more decisive role in the tribocorrosion behavior than the manufacturing method, i.e., 317W revealed the best tribocorrosion behavior vis-a-vis wrought 316L and the SLM-fabricated specimens. The improved tribocorrosion behavior contrasted with the much higher breakdown potential of the SLM-fabricated samples. Nano-scale secondary ion mass spectroscopy was used to investigate the effects of Mo on passivity. The implications of passivity and tribocorrosion behavior are discussed.

Low alloy steels combine relatively low cost with exceptional mechanical properties, making them commonplace in oil and gas equipment. However, their strength and hardness are restricted for sour environments to prevent different forms of hydrogen embrittlement. Materials used in sour services are regulated by the ISO 15156-2 standard, which imposes a maximum hardness of 250 HV (22 HRC) and allows up to 1.0 wt% Ni additions due to hydrogen embrittlement concerns. Low alloy steels that exceed the ISO 15156-2 limit have to be qualified for service, lowering their commercial appeal. As a result, high-performing, usually high-nickel, low alloy steels used successfully in other industries are rarely considered for sour service. In this work, the hydrogen stress cracking resistance of the high-nickel (3.41 wt%), quenched and tempered, nuclear-grade ASTM A508 Gr.4N low alloy steel was investigated using slow strain rate testing as a function of applied cathodic potential. Results showed that the yield strength and ultimate tensile strength were unaffected by hydrogen, even at a high negative potential of −2.00 VAg/AgCl. Hydrogen embrittlement effects were observed once the material started necking, manifested by a loss in ductility with increasing applied cathodic potentials. Indeed, A508 Gr.4N was less affected by hydrogen at high cathodic potentials than a low-strength (yield strength = 340 MPa) ferritic-pearlitic low alloy steel of similar nickel content. Additionally, hydrogen diffusivity was measured using the hydrogen permeation test. The calculated hydrogen diffusion coefficient of the ASTM A508 Gr.4N was two orders of magnitude smaller when compared to that of ferritic-pearlitic steels. Hydrogen embrittlement and diffusion results were linked to the microstructure features. The microstructure consisted of a bainitic/martensitic matrix with the presence of Cr23C6 carbides as well as Mo- and V-rich precipitates, which might have played a role in retarding hydrogen diffusion, kept responsible for the improved HE resistance.

To evaluate the mechanisms driving nanoscale trace element mobility in radiation-damaged zircon, we analyzed two well-characterized Archean zircons from the Kaapvaal Craton (southern Africa): one zircon remained untreated and the other was experimentally heated in the laboratory at 1450 °C for 24 h. Atom probe tomography (APT) of the untreated zircon reveals homogeneously distributed trace elements. In contrast, APT of the experimentally heated zircon shows that Y, Mg, Al, and Pb+Yb segregate to a set of two morphologically and crystallographically distinct cluster populations that range from 5 nm tori to 25 nm toroidal polyhedra, which are confirmed to be dislocation loops by transmission electron microscopy (TEM). The dislocation loops lie in {100} and {001} planes; the edges are aligned with , , and . The largest loops (up to 25 nm diameter) are located in {100} and characterized by high concentrations of Mg and Al, which are aligned with . The 207Pb/206Pb measured from Pb atoms located within all of the loops (0.264 ± 0.025; 1σ) is consistent with present-day segregation and confirms that the dislocation loops formed during our experimental treatment. These experimentally induced loops are similar to clusters observed in zircon affected by natural geologic processes. We interpret that differences in cluster distribution, density, and composition between experimentally heated and geologically affected zircon are a function of the radiation dose, the pressure-temperature-time history, and the original composition of the zircon. These findings provide a framework for interpreting the significance of clustered trace elements and their isotopic characteristics in zircon. Our findings also suggest that the processes driving cluster formation in zircon can be replicated under laboratory conditions over human timescales, which may have practical implications for the mineralogical entrapment of significant nuclear elements.

The isotopic composition of water in Earth’s oceans is challenging to recreate using a plausible mixture of known extraterrestrial sources such as asteroids—an additional isotopically light reservoir is required. The Sun’s solar wind could provide an answer to balance Earth’s water budget. We used atom probe tomography to directly observe an average ~1 mol% enrichment in water and hydroxyls in the solar-wind-irradiated rim of an olivine grain from the S-type asteroid Itokawa. We also experimentally confirm that H+ irradiation of silicate mineral surfaces produces water molecules. These results suggest that the Itokawa regolith could contain ~20 l m−3 of solar-wind-derived water and that such water reservoirs are probably ubiquitous on airless worlds throughout our Galaxy. The production of this isotopically light water reservoir by solar wind implantation into fine-grained silicates may have been a particularly important process in the early Solar System, potentially providing a means to recreate Earth’s current water isotope ratios. Water and hydroxyl enrichment in the solar-wind-irradiated rim of an olivine grain from asteroid Itokawa suggests that its regolith could contain ~20 l m−3 of water from solar wind—a potential water source for airless planetary bodies.

Cristobalite is a low-pressure, high-temperature SiO2 polymorph that occurs as a metastable phase in many geologic settings, including as crystals deposited from vapor within the pores of volcanic rocks. Such vapor-phase cristobalite (VPC) has been inferred to result from silica redistribution by acidic volcanic gases but a precise mechanism for its formation has not been established. We address this by investigating the composition and structure of VPC deposited on plagioclase substrates within a rhyolite lava flow, at the micrometer to nanometer scale. The VPC contains impurities of the form [AlO4/Na+]0—coupled substitution of Al3+ charge-balanced by interstitial Na+—which are typical of cristobalite. However, new electron probe microanalysis (EPMA) element maps show individual crystals to have impurity concentrations that systematically decline from crystal cores-to-rims, and atom probe tomography reveals localized segregation of impurities to dislocations. Impurity concentrations are inversely correlated with degrees of crystallinity [observed by electron backscatter diffraction (EBSD), hyperspectral cathodoluminescence, laser Raman, and transmission electron microscopy (TEM)], such that crystal cores are poorly crystalline and rims are highly ordered tetragonal α-cristobalite. The VPC-plagioclase interfaces show evidence that dissolution-reprecipitation reactions between acidic gases and plagioclase crystals yield precursory amorphous SiO2 coatings that are suitable substrates for initial deposition of impure cristobalite. Successive layers of cubic β-cristobalite are deposited with impurity concentrations that decline as Al-bearing gases rapidly become unstable in the vapor cooling within pores. Final cooling to ambient temperature causes a displacive transformation from β→α cristobalite, but with locally expanded unit cells where impurities are abundant. We interpret this mechanism of VPC deposition to be a natural proxy for dopant-modulated Chemical Vapor Deposition, where halogen-rich acidic gases uptake silica, react with plagioclase surfaces to form suitable substrates and then deposit SiO2 as impure cristobalite. Our results have implications for volcanic hazards, as it has been established that the toxicity of crystalline silica is positively correlated with its purity. Furthermore, we note that VPC commonly goes unreported, but has been observed in silicic lavas of virtually all compositions and eruptive settings. We therefore suggest that despite being metastable at Earth's surface, cristobalite may be the most widely occurring SiO2 polymorph in extrusive volcanic rocks and a useful indicator of gas-solid reaction having occurred in cooling magma bodies.

Glassy melt inclusions are unique geological repositories that preserve evidence of the formation and evolution of mantle and crustal-derived magmas. However, the mechanisms responsible for their preservation in slowly cooled crustal rocks remain contentious, in some part due to their small size (commonly

The Hall–Petch relation has long been used to relate the yield strength of a metal to its grain sizes in which the effectiveness of grain size strengthening in the metal is dictated by the Hall–Petch coefficient (slope). Therefore, understanding the microstructural dependence of the Hall–Petch slope would be very useful in designing new high-strength ultrafine grained (UFG) metallic materials. In this study, we investigated the microstructural factors affecting the Hall–Petch slope in UFG Al-Mg alloys with an average grain size range from 374 to 639 nm and different Mg contents of 0, 2.5, 5, and 7.5 at. pct. The rods prepared by extrusion of mechanically alloyed powder compacts were annealed for 5 hours at 380 °C, 420 °C, and 500 °C respectively followed by water quenching to produce the alloy samples in this study. The measured Hall–Petch slopes of the samples were found to increase with increasing Mg content and had higher values than those previously reported for Al(Mg) solid solutions with Mg concentrations comparable to the Mg contents in this study. Analysis of X-ray diffraction, transmission electron microscopy, and atom probe tomography experimental data as well as strengthening mechanisms demonstrates that the formation of nanoscale MgO dispersions plays a major role in the improved Hall–Petch slope observed in Al-Mg alloys.

A recent subsea failure of two subsea connectors made of UNS S32760, a 25 wt% Cr super duplex stainless steel, led to an extensive root cause failure analysis. The components showed a single longit...

The plastic anisotropies of two hot-rolled Lean Duplex Stainless Steels (commercially known as LDX 2101 and LDX 2404) were investigated by applying compressive strains, at 10−3 s−1 rate, along the rolling- and transverse-directions (RD and TD). The microstructural changes were elucidated by Electron Backscatter Diffraction (EBSD) as a function of strain level and loading direction. In both alloy grades, the austenite phase shows a weaker texture development than the ferrite phase; the later develops {001} and {110} textures in LDX 2101 and LDX 2404 alloys, respectively. Also, in both alloys, the yield stress along the TD is larger by 10% than along the RD. Anisotropies are also detected in the rate of property changes with deformations; after 30% true strain, the flow stress along the RD in LDX 2101 alloy starts exceeding the stress along the TD. Microstructural studies indicate that the load partitioning, grains shape, phase boundaries and austenite to martensite phase transformations are the origins of the anisotropic phenomena in LDX 2101 alloy, whereas the crystallographic texture of ferrite phase, phase boundaries and load partitioning are the plausible origins of plastic anisotropies in LDX 2404 alloy.

In a hypervelocity impact event, the temperatures and pressures generated by the shock waves far exceed the values produced by endogenic processes. The shock-induced processes can modify the distribution of trace elements in zircon grains located in target rocks, potentially affecting the geochemical reliability of zircon, but also providing an opportunity to better understand the mechanisms of shock deformation. The formation of reidite lamellae by the shock-induced phase change of zircon has previously been proposed to be a diffusionless, martensitic transformation, with no associated atomic mobility over nanometre length scales. However, nanoscale characterization of the zircon–reidite interface and a low-angle boundary within the reidite by atom probe tomography, transmission electron microscopy and correlative analytical techniques, shows localised enrichment of particular trace elements (Y, Al, Ca, Be, Mg, Mn, and Ti). These observations indicate the presence of additional short-range diffusional components to explain the local compositional variations observed at the nanoscale for the high-pressure transformation of zircon to reidite lamellae. A new model for this transformation is proposed that consists of two stages: 1) the early stage of the impact event where the shock waves induce defects in the zircon grain and trigger a phase transformation, resulting in trace element segregation by interface migration; and 2) the recovery stage where the trace elements and shock induced defects migrate to areas of lower energy.

Tribo-electrochemical behavior of a high chromium white cast iron (high-Cr WCI) used in, e.g., slurry pumps in mining and mineral processing applications, was investigated using a combination of electrochemical techniques, including zero resistance amperometry as well as potentiostatic and potentiodynamic polarisation. The effects of third body particles angularity on the localised tribocorrosion response of the cast alloy was studied during and post abrasion-corrosion by round ceramic beads and semi-angular silica sand particles. Advanced characterization methods such as electron backscatter diffraction and focused-ion beam cross-sectioning of affected areas were also employed to understand the wear and corrosion interactive actions. It was found that in chloride-free solutions, the behavior of high-Cr WCI resembled that of the austenitic 316 SS studied before. In contrast, in chloride-containing electrolytes, the semi-angular silica sand particles increased interfacial (carbide/matrix) localised corrosion susceptibility during and post-abrasion as indicated by the stark increase in anodic current and the morphology of the attack. Semi-angular silica sand abrasives had a greater adverse impact on post-abrasion interfacial corrosion vulnerability, compared to round ceramic beads. The complex behavior observed indicates that any material developed for tribocorrosive conditions must account for the particles angularity and their subsequent effects on localised corrosion.

Acid mine drainage (AMD) is a serious environmental issue associated with mining due to its acidic pH and potentially toxic elements (PTE) content. This study investigated the performance of the Fe-Al bimetallic particles for the treatment of combined AMD-gold processing effluents. Batch experiments were conducted in order to eliminate potentially toxic elements (including Hg, As, Cu, Pb, Ni, Zn, and Mn) from a simulated waste solution at various bimetal dosages (5, 10, and 20 g/L) and time intervals (0 to 90 min). The findings show that metal ions with greater electrode potentials than Fe and Al have higher affinities for electrons released from the bimetal. Therefore, a high removal (&gt, 95%) was obtained for Hg, As, Cu, and Pb using 20 g/L bimetal in 90 min. Higher uptakes of Hg, As, Cu, and Pb than Ni, Zn, and Mn also suggest that electrochemical reduction and adsorption by Fe-Al (oxy) hydroxides as the primary and secondary removal mechanisms, respectively. The total Al3+ dissolution in the experiments with a higher bimetal content (10 and 20 g/L) were insignificant, while a high release of Fe ions was recorded for various bimetal dosages. Although the secondary Fe pollution can be considered as a drawback of using the Fe-Al bimetal, this issue can be tackled by a simple neutralization and Fe precipitation process. A rapid increase in the solution pH (initial pH 2 to &gt, 5 in 90 min) was also observed, which means that bimetallic particles can act as a neutralizing agent in AMD treatment system and promote the precipitation of the dissolved metals. The presence of chloride ions in the system may cause akaganeite formation, which has shown a high removal capacity for PTE. Moreover, nitrate ions may affect the process by competing for the released electrons from the bimetal owing to their higher electrode potential than the metals. Finally, the Fe-Al bimetallic material showed promising results for AMD remediation by electrochemical reduction of PTE content, as well as acid-neutralization/metal precipitation.

Nanoscale analyses of zircon have demonstrated that trace elements, including Pb, can be mobilized to discrete sites in radiation damaged zircon. Although several mechanisms for trace element mobility and segregation in zircon have been proposed, most of this work has been conducted on zircon grains with complex geologic histories, making it difficult to directly determine the mechanisms driving trace element mobility and segregation in zircon. To test among the existing hypotheses for mechanisms driving trace element mobility and segregation, we analyzed both untreated and experimentally heated (1450°C for 24h) Archean zircon using atom probe tomography and transmission electron microscopy (TEM). The sample has a simple, well-characterized thermal history, with no significant thermal events since original crystallization. Despite a high calculated radiation dose (>4 x 1018 a/g), the untreated zircon does not contain anomalous nanoscale features. In contrast, the experimentally heated zircon contains abundant clusters of Y, Mg, Al, Pb + Yb that range from 5 nm to 25 nm in diameter with toroidal polyhedral morphologies. The 207Pb/206Pb measured from Pb atoms located within these features is consistent with present-day segregation, thus confirming that these nanoscale features were produced by experimental heating in the laboratory. TEM analysis determined that the clusters are dislocation loops, and that cluster morphology is therefore crystallographically controlled. The largest loops are located in {100} and contain high concentrations of Mg and Al.These experimentally induced, trace-element-enriched clusters are similar in size, morphology, composition, and crystallographic orientation to clusters observed in zircon affected by natural geologic processes (cf. Valley et al., 2015; Peterman et al., 2016). Although the calculated radiation doses for all analyzed grains are high, comparison of the nanoscale features indicates no apparent correlation between the radiation dose and the density or distribution of clusters. We also observe that trace-element-enriched clusters are conspicuously absent from zircon grains that lack younger igneous or metamorphic rims. These findings suggest that the pressure-temperature-time (P-T-t) history and the dT/dt significantly impact both the nanoscale redistribution of trace elements and the density of these features within zircon. Systematic evaluation of the composition and distribution of these features provides a framework for understanding the nanoscale record of metamorphism. References:Peterman, E.M., Reddy, S.M, Saxey, D.W., Snoeyenbos, D.R., Rickard, W.D.A., Fougerouse, D., and Kylander-Clark, A.R.C. (2016) Nanogeochronology of discordant zircon measured by atom probe microscopy of Pb-enriched dislocation loops. Science Advances, 2, e:1601218.Valley, J.W., Reinhard, D.A., Cavosie, A.J., Ushikubo, T., Lawrence, D.F., Larson, D.J., Kelly, T.F., Snoeyenbos, DR., and Strickland, A. (2015) Nano-and micro-geochronology in Hadean and Archean zircons by atom-probe tomography and SIMS: New tools for old minerals. American Mineralogist, 100, 1355-1377.

The influence of peak compressive stress on the dyamic tensile fracture (spall) in a multi-phase steel, austenite, ferrite and martensite phases, was investigated in as-received and pre-strained conditions. Plate impact experiments were done at ⁓3.0 GPa and ⁓6.0 GPa compressive peak stresses. Results showed that peak stress increase results in about 20% increase in the spall strength for samples tested in the as-received condition, and about 15% increase for the pre-strained samples. These increases could be related to the effects of peak stress on the tensile stress that causes spallation. However, introducing plastic deformations in the pre-strained samples had negligible effects on the spall strength. Microstructural examinations revealed that incipient spall damage was parallel to the phase boundaries and mainly accommodated by ferrite grains as quasi-cleavage transgranular fracture. Samples shocked in the as-received condition with full spallation experienced a quasi-cleavage fracture within the ferrite compared with a cleavage fracture within the ferrite for samples shocked in the pre-strained condition. Deformation within the austenite phase due to plate-impact testing was dependent on the initial sample condition, the pre-strained samples showed more deformation than the as-received samples.

A better understanding of structural coarsening mechanisms is of significance to effectively tackle structural instabilities in nanostructured materials. In this work, the microstructural evolution of nanostructured metallic powder particles during thermomechanical consolidation has been investigated to gain new insights into the evolution of reinforcing particles and matrix grains of a mechanically alloyed nanostructured Cu-5 vol.% Al2O3 composite powder extruded at either 300 or 900 °C, respectively. Unusual coarsening of Al2O3 particles and rapid growth of Cu grains occurred during extrusion at a low temperature of 300 °C; meanwhile the formation of elongated micron Cu grains was observed at a high extrusion temperature of 900 °C. Both the applied shear stress/strain and the sizes and distribution of second-phase nanoparticles were found to determine the grain structure of the Cu matrix after extrusion. Specifically, the shear stress-induced dynamic and particle-stimulated recrystallization and the movement of the Al2O3 particles are respectively responsible for the low-temperature rapid growth of the Cu grains and the coarsening of the Al2O3 particles. The development of the elongated micron Cu grains during extrusion at 900 °C is associated with anisotropic grain boundary migration and particle re-distribution.

Precipitation of a LiBH4 solution into an antisolvent led to formation of nanoparticles in the size range of 2 to 18 nm. By direct deposition of these nanoparticles onto a nickel(II) phthalocyanine substrate, LiBH4 was destabilized and the hydrogen release temperature was dramatically reduced to 350 °C through a single step decomposition. Remarkably, upon hydrogen release and uptakes, the morphology of the material evolved to single crystal “plates”-like particles and a reversible hydrogen storage capacity of 3.2 mass% at 350 °C under 6 MPa H2 pressure was observed. As evident by X-ray photoelectron spectroscopy analysis, such an enhancement is believed to result from the effective electron transfer interplay between LiBH4, LiH, B, and the nickel(II) phthalocyanine, enabling a destabilization of LiBH4 and the facile rehydrogenation of LiH and B into LiBH4. This study thus reveals a novel approach to destabilize LiBH4 by the use of an “electron active” substrate.

This work was financially supported by the Australian Research Council under the Discovery Project Scheme (project numbers: DP180100731 and DP180100568), and by the Guangdong Provincial Department of Science and Technology Agency (GDST) under the GDST-NOW Science-Industry Cooperation Program (No. 2017A050501053). The establishment of intimate electrode/electrolyte interface is very important in solid oxide fuel cells (SOFCs), because it plays a critical role in the overall cell performance and durability. In this study, Mn segregation and interface formation between directly assembled La0.8Sr0.2MnO3 (LSM) electrode and yttrium-stabilized zirconia (YSZ) or gadolinium-doped ceria (GDC) electrolytes are studied using combined focused ion beam and scanning transmission electron microscopy (FIB-STEM). In the case of LSM/YSZ and LSM/GDC electrodes, a significant reduction in the electrode ohmic resistance is observed after cathodic polarization at 900 °C and 500 mA cm−2, indicating the formation of an intimate interface. However, LSM particles start to disintegrate at the electrode/electrolyte interface with the increase of polarization time in the case of LSM/YSZ electrode. On the other hand, the LSM/GDC interface is very stable with negligible microstructure change at the interface. Mn segregation from the LSM perovskite structure is identified under the influence of polarization in both LSM/YSZ and LSM/GDC electrodes. The results demonstrate that nature of the electrolyte plays a critical role in the electrochemical activity, microstructure, morphology and stability of LSM/electrolyte interface under SOFC operation conditions. Postprint

Aluminium hydride (AlH3) is a promising hydrogen storage material due to its competitive hydrogen storage density and moderate decomposition temperature. However, there is no convenient way to prepare/regenerate AlH3 from (spent) Al by direct hydrogenation. Herein, we report on a novel approach to generate AlH3 from the decomposition of triethylaluminium (Et3Al) under mild hydrogen pressures (10 MPa) with the use of surfactants. With tetraoctylammonium bromide (TOAB), the synthesis led to the formation of nanosized AlH3 with the known α phase, and these nanoparticles released hydrogen from 40 °C instead of the 125 °C observed with bulk α-AlH3. However, when tetrabutylammonium bromide (TBAB) was used instead of TOAB, larger nanoparticles believed to be related to the formation of β-AlH3 were obtained, and these decomposed through a single exothermic process. Despite the possibility to form α-AlH3 under low conditions of temperature (180 °C) and pressure (10 MPa), TOAB stabilised AlH3 was found to be irreversible when subjected to hydrogen cycling at 150 °C and 7 MPa hydrogen pressure.

With the impetus for less reliance on fossil fuels and an increasing demand for environmentally friendly energy materials, lithium is emerging as an important material of the future. The ability to extract lithium from ores economically is essential. However, a comprehensive understanding of the deportment of lithium and associated minerals in some ore bodies is limited. A combination of analytical microscopy and mass spectrometry techniques has been used to allow detection and characterisation of different lithium minerals in three micaceous Li-bearing ores. To quantify the different Li-bearing ore minerals, the chemistry and structural characteristics of a suite of lithium mineral specimens were first examined. The micas can be classified and grouped based on their compositions (Al/Si ratio; F, Na content) and used to distinguish different micas with different lithium grades. Micas exist as different polymorphs that are generally related to composition and also geological environment. The mineralogy, mineral associations and liberation characteristics of both ore-bearing and gangue minerals were characterised using automated mineralogy techniques and the Li content and elemental distribution within minerals defined using instrumentation with secondary mass spectrometry capabilities. The majority of lithium in the ore samples (1.2–1.5% Li) examined is associated with lepidolite or zinnwaldite particle compositions which are made up of Li muscovite, trilithionite and polylithionite grains. The morphology of the Li-bearing micas varies in different deposits. The gangue materials are predominately quartz and albite and make up ≤20 w% of the sample. Only minor amounts (∼1%) of other Li-bearing minerals (e.g. spodumene, elbaite, beryl) were observed in these samples. The Ta grade associated with minerals rynersonite and columbite-tantalite in some samples may be economic. The majority of the Li mica particles were liberated from the major gangue minerals under the conditions used to treat and screen samples to pass a 4 mm sieve. Further grinding will be required to breakup and expose fine grains of Li muscovite, polylithionite, and trilithionite, for further treatment to extract Li. The processes used to breakdown the micas to extract Li will also require stabilising and removal of F, Fe, Al, Mn and monovalent ions K and Na from process streams. The high concentration of Rb (0.9–3.6 wt%) and Cs (0.1–0.8 wt%) make mica a favourable resource for these elements and they can ultimately be recovered along with Li.

A member of the family of compounds with the formula Na3V2O2x(PO4)2F3−2x is synthesized by carbothermal reduction and 2 consecutive hydrothermal processes. The initial structural and spectroscopic characterization indicates that there are two phases in the as-synthesized material, a mixed valent phase with an intermediate V oxidation state adopting a P42/mnm space group at about 66%, and another phase with a V oxidation state close to V3+ adopting an Amam space group at about 33%. The role of each species in the electrode function is interrogated using in situ synchrotron X-ray diffraction and these data indicate that soon after charge begins, the Amam phase transforms into the P42/mnm phase. Further structural evolution of the material shows a prevailing two-phase reaction at lower potentials and a significant solid solution region during the high potential feature in the electrochemical curve with a final two-phase region at the end of charge. The conversion of the Amam component into P42/mnm showed no reversibility upon discharge. This phase-mixed electrode appears to illustrate that the mixed valent P42/mnm phase dominates electrochemical behavior during cycling and this may prove vital when preparing members in the sodium vanadium fluorophosphate family, especially if there is an energetically preferred phase for cycling.

Ultrafine-grained Cu–5 vol%Al2O3 nanocomposite rods were fabricated by a combination of high-energy mechanical milling of Cu and Al2O3 powders and powder compact extrusion at 300, 500, 700 and 900 °C. The extruded rods were investigated to evaluate microstructures, mechanical properties, fracture behavior and electrical resistivity. It was found that the extrusion temperature has a pronounced effect on Cu grain growth, Al2O3 particle coarsening and particle distribution. High-temperature extrusion leads to directional coarsening of certain grains. As such, a heterogeneous matrix structure of large elongated and equiaxed grains is created, and this unique matrix structure brings beneficial effects in tensile ductility and electrical resistivity. While Al2O3 dispersions in the matrix improve the overall performance of the nanocomposite, an incorrect selection of the extrusion temperature may have detrimental effects on yield strength and resistivity. Tensile fractography investigation shows that the presence of Al2O3 results in failures along grain boundaries. This study also provides a framework for modeling the mechanical and electrical properties of such complex matrix structures. Modeling tools/formulae can be used to predict mechanical/electrical properties via microscopic characteristics and hence can also be used to understand the effect of processing variables.

Lithium aluminium hydride (LiAlH 4 ) is a promising hydrogen storage material with a storage capacity of 10.6 mass % H 2 . However, its practical use is hampered by the lack of direct rehydrogenation routes. In this study, we report on the confinement of LiAlH 4 into the nanoporosity of a high surface area graphite resulting in a remarkable improvement of its hydrogen storage properties. Nanoconfined LiAlH 4 started hydrogen desorption near 135 °C and after full dehydrogenation at 300 °C limited rehydrogenation was observed at the same temperature and 7 MPa of hydrogen pressure. Rehydrogenation took place through the formation of Li 3 AlH 6 with some limited rehydrogenation back to LiAlH 4 indicating the existence of different (de)hydrogenation paths upon nanoconfinement as compared to the known dehydrogenation path of bulk LiAlH 4 .

Body-centred cubic magnesium-lithium-aluminium-base alloys are the lightest of all the structural alloys, with recently developed alloy compositions showing a unique multi-dimensional property profile. By hitherto unrecognised mechanisms, such alloys also exhibit exceptional immediate strengthening after solution treatment and water quenching, but strength eventually decreases during prolonged low temperature ageing. We show that such phenomena are due to the precipitation of semi-coherent D03-Mg3Al nanoparticles during rapid cooling followed by gradual coarsening and subsequent loss of coherency. Physical explanation of these phenomena allowed the creation of an exceptionally low-density alloy that is also structurally stable by controlling the lattice mismatch and volume fraction of the Mg3Al nanoparticles. The outcome is one of highest specific-strength engineering alloys ever developed., Solution treatment and quenching can strengthen magnesium-lithium-aluminium alloys, but this strength decreases with ageing. Here, the authors show this is due to semi-coherent nanoparticle precipitation followed by coarsening, and control the lattice mismatch to stabilise the microstructure.

The blast response of a High Strength Steel (HSS), classified as a High Hardness Armour (HHA), subjected to a 60 g charge mass at a Stand-Off Distance (SOD) of 25 mm has been investigated. Electron Backscatter Diffraction (EBSD) and microhardness measurements were used to determine the microstructural evolution in the through thickness and the associated mechanical properties changes. Results show that the blast wave travelling through the material increased the deformation and reduced the grain size. These observations correlated with the hardness increasing along the direction of travel of the blast wave.

The formation of interconnected grain boundary (GB) phases in precipitation hardening (PH) nickel Alloy 725 (UNS N07725) compromises its mechanical properties and has been linked to hydrogen embrittlement failures. However, normative industry standards such as API 6ACRA are inadequate for differentiating between Alloy 725 batches with a critical extent of GB precipitation, creating the need for a complementary qualification method. In Alloy 725, intergranular phases produce a Cr and Mo depletion adjacent to GBs (i.e., sensitization). In Part I of this work, this impoverishment in Cr and Mo was used as the basis to develop a double-loop electrochemical potentiokinetic reactivation (DL-EPR) test, optimized to quantify the extent of GB precipitation in Alloy 725. Part II explores the reproducibility and sensitivity of the new approach using three new independent commercial batches containing different extents of precipitation. Results were highly reproducible and confirmed the method’s sensitivity to detect small amounts of GB phases. Additionally, the DL-EPR procedure revealed clear microstructural inhomogeneities across the bars’ thickness, which increased with increasing bar diameter. This investigation strongly supports the validity of the new DL-EPR technique as a reliable and straightforward industry-friendly qualification method to quantify the extent of intergranular phases in Alloy 725.

Precipitation hardened nickel-based Alloy 725 (UNS N07725) has been proven susceptible to hydrogen embrittlement in oil and gas production. Moreover, current standards cannot differentiate unequivocally between acceptable and affected microstructures, making the development of an appropriate quality control test a priority for the oil and gas industry. Recently, Alloy 725 failures were associated with the precipitation of nanoscale Cr- and Mo-rich phases at grain boundaries (GBs). Since these intergranular precipitates could lead to Cr- and Mo-depletion along the decorated GBs (i.e., sensitization), the double-loop electrochemical potentiokinetic reactivation (DL-EPR) test was explored as an alternative approach to detect affected microstructures. Herein, the DL-EPR technique was optimized for Alloy 725 by testing three types of samples with different degrees of sensitization, including a full GB-decorated microstructure that was shown prone to hydrogen embrittlement in oil and gas service. The optimized DL-EPR test conditions were 2 M HCl + 1 M H2SO4 + 10−4 M KSCN aqueous solution at 30 °C with a 1.667 mV s−1 scan rate and a vertex potential of Ecorr + 700 mV. Results were reproducible and consistent with the degree of GB decoration determined using metallographic methods. The test procedure developed herein could lead to the standardization of the DL-EPR method for Alloy 725.

Microstructural changes and ferrite phase transformation under shock loading, between 8.5 GPa and 17.5 GPa, in a hot-rolled Lean Duplex Stainless Steel (commercially known as LDX 2101) were investigated in as-received and pre-deformed conditions. The latter condition was considered to distinguish classical deformation twins at high strain rates from those associated to the reversible ferrite phase transformation. Plate impact experiments were used to introduce compressive shock loading at peak stresses below and above the stress threshold of the ferrite phase transformation, 13 GPa. Effects of shock loading were also examined by compressing shocked samples quasi-statically and comparing their response with those tested in the as-received condition. The microstructural examinations revealed that the ferrite in LDX 2101 experienced a reversible phase transformation at a peak stress of ~17 GPa. The fingerprints for this transformation were {112} primary twins and {332} primary and secondary twins. In addition, the yield stress of the sample pre-shocked at ~17 GPa showed a considerable increase (⁓150 MPa) compared to the flow stress in as-received conditions.

Microstructure and texture evolution of commercially pure Ni processed by accumulative roll-bonding (ARB) up to eight cycles were studied using electron back scattered diffraction (EBSD). During ARB processing, the original coarse equiaxed grains were gradually transformed into refined lamellar grains along the rolling direction (RD). Shear bands started forming after three cycles. The fraction of low angle grain boundaries (LAGBs) increased after the first and second cycle because of orientation spreading within the original grains. However, their fraction decreased with the evolution of high angle grain boundaries (HAGBs) during subsequent deformations, until saturation was reached after six cycles. Overall, the typical deformation texture components (S, Copper and Brass) were enhanced up to six ARB cycles and then only Copper was further strengthened. At higher cycles a higher Copper concentration was found near sample surface than the interiors due to a high frictional shear of ARB processing.

In this study the effects of heating rate on the sharpness and size of Goss oriented ({110}) grains during secondary recrystallization annealing at 900 °C was observed. The results show that, at the same annealing temperature, rapid heating of the samples to this temperature generates a higher drag force compared to a slower heating rate (5°C/min). The two groups of samples show different growth kinetics for Goss grains, in which at the longest annealing time, the rapid heating sample exhibits larger maximum Goss grain size compared to the slower heated samples.

LiH has great potential as a high capacity hydrogen storage material (12 wt.%), however its thermodynamic stability has so far precluded practical application. Temperatures near 700 °C are required for hydrogen release and uptake. Herein, we report on a novel method to realise hydrogen uptake and release under milder temperature conditions without using any catalyst or alloying. Through nanoconfinement within the pores (2–20 nm) of high surface area graphite (HSAG) LiH displayed remarkable hydrogen storage properties and was able to release 1.9 wt.% of hydrogen from 200 °C. Reversibility was also achieved under the moderate conditions of 300 °C and 6 MPa hydrogen pressure. This demonstrates that the properties of LiH are particle size dependent and thus leads to new possibilities to realise the potential of LiH as a practical high capacity hydrogen storage material.

Unravelling complex microbial activity in modern hydrothermal vents can provide crucial insights into the evolution of ancient life on Earth. It is well established that microorganisms in hydrothermal vents have a significant impact on the cycling of metals and mineral formation. However, the detailed roles played by microorganisms in driving sulfide deposition and cycling of toxic metals, like arsenic (As) and lead (Pb), in high-temperature deep-sea hydrothermal vents remain unknown. The understanding of these mechanisms in extreme environments is of particular importance as As has been postulated as a driver of microbial activities on the early Earth. Here, we present the first geologic evidence of Pb As rich microbial filamentous clusters observed in a modern high-temperature black smoker from the Manus back-arc basin, Papua New Guinea. The clusters occur as net-like structures on the surface of barite and sulfides and are composed of multiple filaments and fine-grained Pb As sulfosalt. Each of the filaments includes an As-Pb-rich sulfosalt core and organic-rich shell structure with elevated carbon, nitrogen and phosphorus. Further synchrotron X-ray absorption near edge structure analysis shows that the clusters contain a mixture of As (II) and As (III). Additionally, those filaments show a close association with realgar (As4S4), by penetrating and dissolving this As-sulfide mineral. We interpret the filaments to be a result of As-related microbial activity in As- and Pb-enriched hydrothermal environments. The findings show possible processes through which extremophiles live in Pb and As-rich environments during chimney growth. In addition, as hydrothermal vents are regarded as modern analogs of ancient volcanogenic massive sulfide deposits, the observed biominerals present the potential to be used as proxies to trace the signatures of early life in ancient geological systems.

A member of the family of compounds with the formula Na

Fracture of silicon wafers is responsible for lower than desirable manufacturing yields in the photovoltaic industry. This study investigates the fracture response of polycrystalline silicon wafers under sliding contacts at different length scales, by means of macro and microscratch tests which simulate cutting processes. The dominant fracture modes were found to be partial cone cracking (macro) and radial cracking (micro). Statistical analysis of the critical loads for crack initiation showed that polycrystalline wafers are weaker than their single-crystal counterparts, that is, they crack at lower applied loads under comparable conditions. Moreover, the Weibull modulus of polycrystalline silicon was found to be the average of the relevant single-crystal directions. Subsequent microscopic observations and flexure tests reveal that the lower resistance of polycrystalline silicon to scratch fracture is due mainly to the presence of relatively large polishing defects, and not to the weakness of its grain boundaries. Alternatives are proposed to minimize damage during ingot cutting, with a view to minimizing wafer breakages during wafer handling and machining.

Copious recrystallization occurs during the very early stages of annealing in some deformed grains in 85% cold rolled IF steel. This event happens to certain regions in γ oriented grains while the α oriented grains remain unrecrystallized. The orientations of the newly forming grains are near either {111} or {554} , and as a result the intensity at these orientations are high in the recrystallization texture. An investigation by scanning electron microscope (SEM) and electron backscatter diffraction (EBSD) shows that such copious recrystallization event originates from the frequent presence of high crystallographic gradients, at the locations where two set shear bands intersect.