Cement production requires thermo-mechanical processing of limestone for the activation of clinker phases and this energy intensive manufacturing process contributes to global CO2 emissions. Supplementary cementitious materials (SCMs) are generally derived from industrial waste streams, and these can reduce clinker usage to enhance sustainability when appropriately activated. In this study, copper heap leach residue (CHLR) obtained from secondary copper refineries was calcined at 300, 600, 900˚C and used as a SCM to compare their pozzolanic activity with class-F fly ash (FA) and silica fume (SF). Raw CHLR fines possess 88.3% SiO2 + Al2O3 + Fe2O3, 31.31% amorphousness, and specific surface area of 725 m2/kg, making it a suitable candidate as a SCM. At 28 days, the CHLR600˚C consumed 864 mg Ca(OH)2/g of SCM, demonstrating significant pozzolanic reactivity and reduced 91% of initial electrical conductivity in a fixed lime test. In addition, CHLR600˚C mortar achieved 85% strength activity index (SAI) at 28 days and 185 J/g SCM hydration heat in R3 test at 7 days for 20% cement and 25% lime replaced systems, respectively. In contrast, FA and SF yielded SAIs of 77% and 91%, respectively. The pozzolanic activity and hydration product development of these SCMs were supported by XRD and TEM-EDS microscopies.

Australia is one of the main reserves of rare earth elements phosphate (P-REE) minerals. Phosphate-solubilising bacteria (PSB) are capable of dissolving the phosphate content of such minerals. It has been demonstrated that P-REE leaching efficiency is greater when microorganisms are in direct contact with the ore surface. This study investigated biofilm formation by the PSB Klebsiella aerogenes on the surface of monazite. Initial attachment occurred during the early hours of exposure and was affected by extracellular DNA (eDNA) production, particle size, physico-chemical properties of the surface, total available area for attachment, and inoculation size. K. aerogenes produced eDNA, which provides high attachment-affinity towards the surface of P-REE, hence, playing an important role during initial attachment. Attachment occurred preferentially on larger-sized particles. Analysis of the dynamics of planktonic and sessile equilibrium during initial attachment revealed greater biofilm formation in the presence of monazite compared to a glass surface, in which lowering the initial cell concentration shifted the equilibrium towards a greater sessile population promoting biofilm formation, as did increasing the total available area. Given enough time PSBs colonise the surface of these minerals and form mature biofilms, which cover almost the whole surface. Microscopy analysis of biofilm cross-sections showed a thin-layer structure. Biofilm selectively formed on and around physical imperfections but showed no selectivity towards particular mineralogy.

In this study, lithium slag was utilised as a supplementary cementitious material (SCM) to develop pozzolanic activity and reduce CO2 emissions related to cement production, with a focus on comprehensive chemical tests and microstructural assessments. Lithium slag was primarily characterised through laser particle size analyser, X-ray fluorescence, X-ray diffraction, scanning transmission electron microscopy coupled with energy dispersive X-ray spectroscopy, and thermogravimetry. These tests indicate that lithium slag holds 31.6% amorphous phase with rich aluminosilicate minerals, making it an excellent candidate as pozzolan. The unsaturated lime and electrical conductivity pozzolanic activity precursor tests evaluated the potentiality of using lithium slag as a low carbon pozzolan. The optimum percentage of lithium slag as a supplementary cementitious material was determined from Frattini, strength activity index, and R3 tests by replacing 0–60% cement. Results show that 40% lithium slag mortar could achieve 93% strength activity index in 28 days. The microstructure development of lithium slag was assessed and ettringite, monocarboaluminate, and intermixed calcium aluminosilicate hydrates were formed at 56 days.

This study focuses on the low-temperature mineralogical response of xenotime, a phosphate mineral routinely used as a geochronometer, to fluid-assisted alteration. The studied xenotime grain (z6413) comes from a similar to 1000 Ma pegmatite from the Grenville Province, Canada, and is commonly used as reference material for U-Pb analyses. At the microscale, the grain has a mottled texture, sub-micrometer porosity, and small domains dark in backscattered electron (BSE) images that are characterised by curviplanar, sharp boundaries. The small dark BSE domains are associated with Th-U-rich inclusions and larger porosity (2-3 mu m) and are interpreted to result from localised fluid-assisted coupled dissolution-reprecipitation. Sensitive high-resolution ion microprobe (SHRIMP) U-Pb analyses of unaltered and fluid-affected domains yield concordant crystallisation dates, irrespective of the textural domains. The apparently unaltered xenotime domain was characterised at the nanoscale to determine if the grain was affected by fluids beyond the altered domains defined by BSE imaging. Transmission electron microscopy (TEM) imaging results indicate the presence of randomly distributed Ca + Pb nanoscale precipitates. Atom probe tomography (APT) reveals the presence of spherical clusters (4 to 18 nm in size) enriched in radiogenic Pb, Ca, and Si atoms, which, combined with TEM observations, are interpreted as nanoscale inclusions of apatite. In addition to the inclusions, a dislocation enriched in Ca and fluid mobile elements such as Cl, Li, Na, and Mn was imaged from APT data indicating percolating of fluids further than the reaction front. APT 206Pb/238U nanogeochronology indicates that the nanoscale inclusions of apatite formed at 863 +/- 28 Ma, 100-150 Ma after crystallisation of the host xenotime, with its formation attributed to fluid metasomatism. This study shows that fluid-xenotime reaction caused Pb* to be redistributed at the nanoscale, recording the timing of metasomatism. However, at the scale of SHRIMP analytical spot (10 mu m), xenotime is concordant, indicating that Pb was not mobile at the microscale and fluid-altered xenotime can preserve its crystallisation age. Although the studied grain shows a limited amount of altered domains in BSE imaging, nanoscale analyses reveal a more pervasive re-equilibration of the minerals through the percolation of fluids along dislocations.

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.

Impurity doping is one of the common approaches to enhance the photoactivity of semiconductor nanomaterials by increasing photon-capture efficiency in the visible light range. However, many studies on the doping effects have produced inconclusive and conflicting results. There are some misleading assumptions and errors that are frequently made in the data interpretation, which can lead to inconsistent results about the doping effects on photocatalysis. One of them is the determination of the location of dopants. Even using advanced analytical techniques, it is still challenging to distinguish between bulk modification and surface modification. The paper provides a case study of transition-metal-doped ZnO nanoparticles, whereby demonstrating common pitfalls in the interpretation of the results of widely-used analytical methods in detail, and discussing the importance of using a combination of many characterization techniques to correctly determine the location of added impurities, for elucidating the influence of metal doping on the photocatalytic activities of semiconductor nanoparticles.

Highly sensitive room temperature gas sensors consisting of ultraporous ZnO nanoparticle networks decorated with Ag nanoparticles (NPs) were fabricated by nanoparticle aerosol self-assembly and sequential sputtering. Optimization of the AgNPs loading and the thickness of ultraporous ZnO networks lead to a sensor response, defined as the ratio of resistance change, of 1.8 and 7.4 at 0.1 and 1 ppm ethanol concentrations, respectively, at room temperature under light irradiation. This is similar to 10 times higher than that of pure ultraporous ZnO film under the same experimental conditions. Furthermore, the optimal AgNPs-decorated ultraporous ZnO films can detect as low as 5 ppb of ethanol gas at room temperature under light illumination. The high sensitivity of AgNPs-decorated ZnO film can be ascribed to the synergistic effects of the ultraporous nanoparticle network morphology, AgNPs sensitization and light-assisted photo-excited gas-sensing process. These provide directions for the design of high sensitive metal-oxide semiconductor-based gas sensors capable to operate at room temperature.

A dendritic porous supported microstructure simultaneously creates small pore size and broad gas diffusion pathways in a solid oxide fuel cell anode membrane. This micro-structure also achieves pore sizes that reduce with increasing depth within the membrane without increasing the structure tortuosity. Such a microstructure supplies high triple phase boundary density, fast gas diffusion and low polarization resistance. Here we characterise the performance of a porous anode with such a dendritic microstructure. The solid oxide fuel cell with this high performance anode achieved 0.92 W cm(-2 )power density at 600 degrees C. Crown Copyright (C) 2018 Published by Elsevier Ltd on behalf of Hydrogen Energy Publications LLC. All rights reserved.

Engineering of highly performing nanomaterials, capable of rapid detection of trace concentrations of gas molecules at room temperature, is key to the development of the next generation of miniaturized chemical sensors. Here, a highly performing nanoheterojunctions layout is presented for the rapid room‐temperature chemical sensing of volatile organic compounds down to ten particles per billion concentrations. The layout consists of a 3D network of nickel oxide–zinc oxide (NiO–ZnO) p–n semiconductors with grain size of ≈20 nm nanometers and a porosity of ≈98%. Notably, it is observed that the formation of the p–n heterojunctions by decoration of a ZnO nanoparticle networks with NiO increases the sensor response by more than four times while improving the lower limit of detection. Under solar light irradiation, the optimal NiO–ZnO nanoheterojunction networks demonstrate a strong and selective room‐temperature response to two important volatile organic compounds utilized for breath analysis, namely acetone and ethanol. Furthermore, these NiO–ZnO nanoheterojunctions show an inverse response to acetone from that observed for all others reducing gas molecules (i.e., ethanol, propane, and ethylbenzene). It is believed that these novel insights of the optoelectrochemical properties of ultraporous nanoheterojunction networks provide guidelines for the future design of low‐power solid‐state chemical sensors.

Magnetite from hydrothermal ore deposits can contain up to tens of thousands of parts per million (ppm) of elements such as Ti, Si, V, Al, Ca, Mg, Na, which tend to either structurally incorporate into growth and sector zones or form mineral micro- to nano-sized particles. Here, we report micro- to nano-structural and chemical data of hydrothermal magnetite from the Los Colorados iron oxide–apatite deposit in Chile, where magnetite displays both types of trace element incorporation. Three generations of magnetites (X–Z) were identified with concentrations of minor and trace elements that vary significantly: SiO2, from below detection limit (bdl) to 3.1 wt%; Al2O3, 0.3–2.3 wt%; CaO, bdl–0.9 wt%; MgO, 0.02–2.5 wt%; TiO2, 0.1–0.4 wt%; MnO, 0.04–0.2 wt%; Na2O, bdl–0.4 wt%; and K2O, bdl–0.4 wt%. An exception is V2O3, which is remarkably constant, ranging from 0.3 to 0.4 wt%. Six types of crystalline nanoparticles (NPs) were identified by means of transmission electron microscopy in the trace element-rich zones, which are each a few micrometres wide: (1) diopside, (2) clinoenstatite; (3) amphibole, (4) mica, (5) ulvöspinel, and (6) Ti-rich magnetite. In addition, Al-rich nanodomains, which contain 2–3 wt% of Al, occur within a single crystal of magnetite. The accumulation of NPs in the trace element-rich zones suggest that they form owing to supersaturation from a hydrothermal fluid, followed by entrapment during continuous growth of the magnetite surface. It is also concluded that mineral NPs promote exsolution of new phases from the mineral host, otherwise preserved as structurally bound trace elements. The presence of abundant mineral NPs in magnetite points to a complex incorporation of trace elements during growth, and provides a cautionary note on the interpretation of micron-scale chemical data of magnetite.

To increase the analytical precision in identifying structural forms of heavy metals, it is necessary to refine the methodology for analysis of mineral crystals. The aim of this study was to characterize clay crystals in soils, and relate their mineralogy to the structural occurrence of Pb using scanning transmission electron microscopy (STEM) together with energy dispersive X-ray (EDX) spectrometry. We sampled soils from two areas naturally rich in heavy metals, with known occurrences of mineral deposits (PbS) in carbonate and phyllite/mica schist rocks. There was an association of P with Pb, and the main mineral phase containing Pb in the soil clay fractions was plumbogummite. No associations between Pb and Fe oxides were observed. Secondary phyllosilicate minerals, such as kaolinite and smectite, did not contain structural Pb. There was isomorphous substitution of Ti by Pb in an anatase crystal, despite the differences in ionic radii. The chemical analysis of individual crystals by STEM-EDX was hampered by the high occurrence of microaggregates of clay minerals.

A mechanically activated solid-state displacement reaction has been investigated as a means of manufacturing apatite nanoparticles. Mechanical milling and subsequent heat treatment of a CaCl2, Na3PO4 and NaCl reactant mixture resulted in the formation of chlorapatite nanoparticles embedded within a solid salt matrix. The size and morphology of the chlorapatite nanoparticles was found to depend on the temperature of the post-milling heat treatment. A low temperature of 400°C yielded largely equiaxed nanoparticles with an average diameter less than 100nm. In contrast, heat treatment at 775°C resulted in the formation of chlorapatite nanorods with an average diameter below 200nm and a [001] growth direction. In both cases, removal of the salt matrix by washing with water gave powders with low levels of agglomeration.

In high temperature solid oxide fuel cells (SOFCs), electrode/electrolyte interfaces play an ultimate role in the electrocatalytic activity and durability of the cells. In this study, thermally and electrochemically induced electrode/electrolyte interfaces were investigated on pre-sintered and in situ assembled La0.8Sr0.2MnO3 (LSM) electrode on Y2O3-ZrO2 (YSZ) electrolyte, using focus ion beam and high resolution scanning transmission electron microscopy (FIB-STEM). The results indicate that thermally induced interface is characterized by convex contact rings with depth of 100-400 nm and diameter in agreement with the particle size of pre-sintered LSM electrodes, while the cathodic polarization induced interfaces on in situ assembled electrodes are characterized by particle-shaped contact marks (20-50 nm in diameter). The results show that the electrochemical activity of the cathodic polarization induced electrode/electrolyte interface is comparable to the thermally induced one for the O2 reduction reaction under SOFC operation conditions. The FIB-STEM analysis clearly shows that along the rim of the contact rings of pre-sintered LSM electrode, there is formation of a thin layer of La and Sr on the YSZ electrolyte surface, while Mn diffuses into YSZ and the distribution of Mn inside YSZ electrolyte follows closely the profile of the contact rings. The preliminary results provide direct evidences that Mn cation inter-diffusion plays a critical role in the formation of LSM/YSZ interface of SOFCs.

Polarization can induce an LSM/YSZ interface which is electrochemically compatible with the one formed under high temperature sintering.

This paper reports a facile synthesis of N,S-doped carbon–silica nanospheres with smooth and rough surfaces by using an extended Stöber method.

The effect of the presence of an Fe-Cr alloy metallic interconnect on the performance and stability of La(0.8)Sr(0.2)MnO3 (LSM) oxygen electrodes is studied for the first time under solid oxide electrolysis cell (SOEC) operating conditions at 800 °C. The presence of the Fe-Cr interconnect accelerates the degradation and delamination processes of the LSM oxygen electrodes. The disintegration of LSM particles and the formation of nanoparticles at the electrode/electrolyte interface are much faster as compared to that in the absence of the interconnect. Cr deposition occurs in the bulk of the LSM oxygen electrode with a high intensity on the YSZ electrolyte surface and on the LSM electrode inner surface close to the electrode/electrolyte interface. SIMS, GI-XRD, EDS and XPS analyses clearly identify the deposition and formation of chromium oxides and strontium chromate on both the electrolyte surface and electrode inner surface. The anodic polarization promotes the surface segregation of SrO and depresses the generation of manganese species such as Mn(2+). This is evidently supported by the observation of the deposition of SrCrO4, rather than (Cr,Mn)3O4 spinels as in the case under the operating conditions of solid oxide fuel cells. The present results demonstrate that the Cr deposition is essentially a chemical process, initiated by the nucleation and grain growth reaction between the gaseous Cr species and segregated SrO on LSM oxygen electrodes under SOEC operating conditions.