Energy Dispersive Electron Research Articles

Correlated microstructure and magnetic properties of Ce-substituted sintered Nd-Fe-B magnets: Role of various phases at triple junctions and grain boundaries

We report the investigation of the microstructure and magnetic properties of a sintered (Nd,Pr)30.3-xCexFebalM1.4B0.92 (in wt.%, xCe = 0) magnet with varying Ce substitutions (xCe = 2, 4, 6, 8). Structure analysis revealed a lattice contraction with Ce addition of up to xCe < 6, and the further increase in the Ce content to 6 wt.% led to a suppression in lattice contraction. The magnetic properties showed a notable deviation from the linear trend in coercivity and remanent magnetization for the magnets with Ce content of xCe > 4. The detailed microstructure analysis revealed that the magnets with xCe > 4 exhibit the REFe2 phase at the expense of a reduced mass fraction of a REOx phase, suggesting that the generation of the REFe2 phase suppressed the formation of the REOx phase. The site occupancy and valence state of Ce, analyzed using atomic-resolution energy dispersive spectroscopy and electron energy loss spectrometry, established that the suppressed lattice contraction is accompanied by a preferential site occupation of Ce from a random case to a 4f-centric site, along with a valence change from a mixed state to a trivalent state, inferring that Ce3+ ions are rejected from the 4g site of the RE2Fe14B phase to occupy the 4f site with a subsequently reduced number of Ce4+ ions due to the magneto-volume and chemical bonding effects. These findings display a new phase formation pathway of the REFe2 phase from a valence state perspective, i.e., the part of Ce4+ ions is considered to be rejected from the RE2Fe14B phase to nucleate the REFe2 phase, which is later found to separate chemically into RE-rich and Fe-rich regions. Further, a bi-layer interfacial structure, composed of Fe-rich and RE-rich layers, is formed in between the RE2Fe14B and the REFe2 phases due to the weak wettability of the REFe2 phase and a slightly positive mixing enthalpy between Ce and Fe. The deviation in magnetic properties is discussed based on the structural and microstructural results. These findings provide structural insight for developing low-cost and high-performance Ce-substituted Nd-Fe-B magnets.

Oxidation behavior and microstructural evolution of FeCoNiTiCu five-element high-entropy alloy nanoparticles

High-entropy alloys (HEAs) have attracted extensive attention ascribed to their unique physical and chemical properties induced by the cocktail effect. However, their oxidation behaviors, in particular at nanoscale, are still lack because of multi-element complexity, which could also be completely different from the bulk counterparts. In this work, we synthesized FeCoNiTiCu five-element HEA nanoparticles(NPs) with uniform elemental distribution by arc-discharging approach, and further investigated their oxidation behaviors at 250 °C, and 350 °C. The morphology, structure and element distribution of NPs were analyzed by transmission electron microscopy (TEM), energy dispersive spectroscopy (EDS) and electron energy loss spectroscopy (EELS). The surface oxidation in FeCoNiTiCu NPs during the high-temperature process can induce nanoscale pores at core/shell interfaces by Kirkendall effect, and even the eventual coalescence into a single cavity. Additionally, the oxidation states of NPs with diameters (d) varying from 60 to 350 nm were analyzed in detail, revealing two typical configurations: hollow (d < 150 nm) and yolk-shell structures (d > 150 nm). The experimental results were complemented by first-principles calculations to investigate the diffusion behaviors of five elements, evidencing that the surface oxidation strongly alters the surface segregation preferences: (1) in the initial stage, Cu and Ni appear to prefer segregating on the surface, while Co, Ti and Fe tend to stay in the bulk; (2) in the oxidation process, Cu prefers to stay in the center, while Ti segregates to the surface ascribed to the reduced potential energies. The study gives new insights into oxidation of nanoscale HEA, and also provides a way for fabrication of high-entropy oxides with controllable architectures.

Interface microstructure and mechanical response of similar and dissimilar joints of (γ + α2) titanium aluminide and α-titanium alloy produced by diffusion bonding

Titanium aluminides are one of the potential materials for aerospace applications because of their high specific strength and good resistance to creep and oxidation at elevated temperatures. However, it is quite challenging to obtain similar and dissimilar joints with these materials by fusion welding due to their high crack sensitivity, limited ductility, and low thermal conductivity. In this study, joints of (γ + α2)-titanium aluminide (TiAl) to itself and with α-Ti alloy were produced by solid-state diffusion bonding performed under vacuum in the temperature range of 750–950 °C and pressure of 10–20 MPa for 10–30 min. The resultant interface microchemistry and microstructures were examined in-detail by scanning electron microscope in conjunction with energy dispersive spectroscopy and electron backscattered diffraction. Instrumented indentation and shear testing were employed to examine hardness variation across the interface and to evaluate the bond strength of the joints, respectively. The TiAl/TiAl joint possessed a single thin interface layer of α2 (Ti3Al), whereas two interphase layers comprised, viz. α + α2 (layer 1) and α2 (layer 2) were formed at interface of the α-Ti/TiAl joint. The minimum bonding temperatures of 900 °C and 800 °C were identified for producing metallurgically sound joints of TiAl/TiAl and α-Ti/TiAl, respectively, under an applied pressure of 10 MPa for 30 min. The bond strength of ∼400 MPa, which is ∼90% shear strength of TiAl base alloy, was achieved for TiAl/TiAl joints produced at 900 °C and above. The α-Ti/TiAl joint produced at 950 °C showed a maximum bond strength of ∼504 MPa. The intimate contact of surfaces through the complete collapse of their asperities and formation of phases, similar to that present in TiAl base alloy, at the interface led to enhanced joint strengths. The fracture surface of the shear tested specimens displayed a transition in failure mode from brittle to transgranular failure of the interface along with TiAl base alloy with an increase in bonding temperature.

Hofstadter-like spectrum and magnetization of artificial graphene constructed with cylindrical and elliptical quantum dots

A comparative study of the electronic and magnetic properties of quasi-two-dimensional electrons in an artificial graphene-like superlattice composed of circular and elliptical quantum dots is presented. A complete orthonormal set of basis functions has been implemented for calculation of the energy dispersions, Hofstadter spectra, density of states and orbital magnetization of the considered systems. Our calculations indicate a topological change in the miniband structure due to the ellipticity of the quantum dots, and non-trivial modifications of the electron energy dispersion surfaces with the change of the magnetic flux per unite cell. The ellipticity of the quantum dots leads to an opening of a gap and considerable modifications of the Hofstadter spectrum. The orbital magnetization is shown to reveal significant oscillations with the change of the magnetic flux. The ellipticity of quantum dots has a qualitative impact on the dependencies of the magnetization on both the magnetic flux and the temperature.

Assessment of corrosion inhibition performance of olive leaf extract mediated chitosan–Ag nanocomposites and influence of KI addition for X60 steel in acid solution

Chitosan–silver (CHT–Ag) nanocomposite (NCP) containing various dosages of chitosan (0.5, 1.0 and 2.0 g) was synthesized in-situ using olive leaf extract (OLE) as reducing and capping agent. The OLE mediated CHT–Ag NCP was characterized using UV–vis spectrometer, attenuated total reflectance-infrared spectroscopy (ATR-IR), X-ray diffraction (XRD), energy dispersive X-ray spectroscopy (EDS) and transmission electron microscopy (TEM) techniques. The prepared NCP was assessed as corrosion inhibitor for X60 steel in 5% HCl solution using weight loss (WL) and electrochemical (electrochemical impedance spectroscopy (EIS), linear polarization resistance (LPR) and potentiodynamic polarization (PDP)) methods complemented by surface analysis of the corroded carbon steel (CS) without and with the NCPs utilizing scanning electron microscopy (SEM)/EDS, 3D optical profilometer and atomic force microscopy (AFM). The influence of adding KI on the corrosion inhibition performance of NCPs was investigated as well. TEM results indicate that CHT–Ag nanocomposites are polydisperse and spherical in shape with sizes in the range of 3.7–18.1 nm. The crystalline nature of Ag nanoparticles in the nanocomposites was confirmed by XRD and TEM examination. The prepared NCPs function as effective inhibitors for X60 CS corrosion in the acidic environment. Corrosion inhibition effect was observed to increase with rise in the NCPs concentration with the optimum inhibition efficiency (IE) obtained at the maximum dosage of 0.5% studied. The order of corrosion inhibition performance followed the trend CHT2.0 – Ag > CHT1.0 – Ag > CHT0.5 – Ag NCP. Also, IE was found to decrease with rise in temperature. The PDP data indicates that the NCPs alone and in combination with KI, reduced X60 CS corrosion via the mechanism of active site blocking effect. The addition of KI to the NCPs improves IE but not due to synergism. The surface assessment data confirms the establishment of a protective layer due to NCPs adsorption on the X60 CS surface.

Copper bioreduction and nanoparticle synthesis by an enrichment culture from a former copper mine.

Microorganisms can facilitate the reduction of Cu2+ , altering its speciation and mobility in environmental systems and producing Cu-based nanoparticles with useful catalytic properties. However, only a few model organisms have been studied in relation to Cu2+ bioreduction and little work has been carried out on microbes from Cu-contaminated environments. This study aimed to enrich for Cu-resistant microbes from a Cu-contaminated soil and explore their potential to facilitate Cu2+ reduction and biomineralisation from solution. We show that an enrichment grown in a Cu-amended medium, dominated by species closely related to Geothrix fermentans, Azospira restricta and Cellulomonas oligotrophica, can reduce Cu2+ with subsequent precipitation of Cu nanoparticles. Characterisation of the nanoparticles with (scanning) transmission electron microscopy, energy-dispersive x-ray spectroscopy and electron energy loss spectroscopy supports the presence of both metallic Cu(0) and S-rich Cu(I) nanoparticles. This study provides new insights into the diversity of microorganisms capable of facilitating copper reduction and highlights the potential for the formation of distinct nanoparticle phases resulting from bioreduction or biomineralisation reactions. The implications of these findings for the biogeochemical cycling of copper and the potential biotechnological synthesis of commercially useful copper nanoparticles are discussed.

WNMS: A New Basaltic Simulant of Mars Regolith

The use of planetary regolith can be explored via the utilization of simulants. The existing Martian simulants have differences due to varying source materials and design parameters. Additional simulants are needed because the few available simulants do not replicate the compositional diversity of Martian regolith. This study discusses the development of a low-cost construction simulant of Mars. The area of Winder Nai in Pakistan was selected for field sampling of basalt because of local availability and easy access. The dust was produced from rock samples through mechanical crushing and grinding. The physical properties, composition, mineralogy, and surface morphology were evaluated via geotechnical tests, Energy Dispersive X-ray (EDX) spectroscopy, X-ray Diffraction (XRD), and Scanning Electron Microscopy (SEM), respectively. The designed simulant has a well-graded particle size distribution with a particle density and bulk density of 2.58 g/cm3 and 1.16 g/cm3, respectively. The elemental composition of Winder Nai Mars Simulant (WNMS) is within ±5 wt% of the Rocknest and the average Martian regolith composition except for SO3. For SiO2, Al2O3, and Fe2O3, WNMS has a good match with the Martian regolith. The content of CaO and TiO2 in WNMS is higher than, and content of MgO is lower than, the average Martian values. The rock can be classified as basalt based on the Total Alkali Silica (TAS) diagram. XRD spectrum indicates the occurrence of plagioclase and pyroxene as the main signature minerals of basalt. The particle morphology of WNMS is angular to subangular, and the simulant indicates the presence of 3.8 wt% highly paramagnetic particles. The volatile loss is 0.25 wt% at 100 °C, 1.73 wt% at 500 °C, and 3.05 wt% at 950 °C. The composition of WNMS, basaltic mineralogy, morphology, magnetic properties, and volatile content are comparable with MMS-2 and a few other simulants.

Microstructure and deformation workability of Ni-based superalloy Udimet720Li fabricated by composite shear flow casting

In this study, the effect of composite shear flow casting (CSFC) on microstructure and hot deformation process of Ni-based superalloy Udimet720Li has been investigated. Udimet720Li superalloy was produced by using CSFC and conventional casting methods, followed with the same isothermal forging process. The microstructures of both CSFC and conventionally solidified (CS) samples were characterized using optical microscope, scanning electron microscope, energy dispersive X-ray spectroscopy and electron backscatter diffraction. Results show that the CSFC sample owns excellent microstructural uniformity with a reduced area fraction of segregation regions, leading to a wider processing window for subsequent deformation, compared to the CS sample. Besides, the deformation resistance and the thermal workability of CSFC sample are significantly improved because of the homogeneous microstructure, resulting in the uniform deformation during subsequent isothermal forging.

Nanocomposites from spent coffee grounds and iron/zinc oxide: green synthesis, characterization, and application in textile wastewater treatment.

This study reports on a novel composite of bimetallic FeO/ZnO nanoparticles supported by spent coffee grounds (SCGs). The leaves of eucalyptus (Eucalyptus globulus Labill) and trumpet (Cuphea aequipetala Cav), with their high antioxidant content, serve as bio-reductant agents for the green synthesis of nanoparticles. It was characterized using Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS), X-ray diffraction (XRD), and transmission electron microscopy (TEM). Stable nanoparticles were produced with different diameters of 5-30 nm, and they were applied as catalysts in Fenton-like processes. Box-Behnken experimental design (BBD) was used to determine the optimal removal efficiency with three factors and was used in the degradation of textile dyes from wastewater. The nanocomposite displayed a high decolorization ratio (88%) of indigo carmine in the presence of H2O2 combined. This resulted in a reduction in chemical oxygen demand (COD) of 56% at 120 min of contact time at an initial pH of 3.0 and a 0.5 g/L of catalyst dose, a H2O2 concentration of 8.8 mM/L, an initial dye concentration of 100 mg/L, and a temperature of 25 °C.

Improved oxidation resistance of Cr/FeCrAl coating on Zr alloy in high-temperature steam environment

A new bi-layer Cr/FeCrAl coating was successfully fabricated on the Zr-4 plates through multi-arc ion plating in order to take advantage of the two materials of FeCrAl and Cr. The high-temperature steam oxidation behavior of the Cr/FeCrAl-coated Zr-4 at 1000–1200 °C was investigated and compared with that of bare and single-layer FeCrAl-coated Zr-4. Various analytical techniques including scanning electron microscopy with energy dispersive spectroscopy (SEM/EDS), X-ray diffraction (XRD) and transmission electron microscopy (TEM) were used for the microstructural and compositional analysis of the as-deposited and oxidized samples. Results indicated that the FeCrAl-coated Zr-4 could only withstand up to 1000 °C because of the severe FeZr interdiffusion. Whereas the introduction of the Cr interlayer effectively prevented fast FeZr interdiffusion and consequently improves the overall oxidation resistance of the Zr substrate below 1200 °C steam environment. After 1100 °C steam oxidation, the weight gain of the Cr/FeCrAl-coated Zr-4 was about 8 times and 2 times lower than that of the uncoated and FeCrAl-coated Zr-4 alloys, respectively. These facts make possible the use of FeCrAl coating on Zr cladding which has excellent high-temperature mechanical properties and oxidation resistance.

Purity and properties of spherical shaped Co3O4 nanocrystals prepared by a polyol route using a domestic microwave oven

Obtaining spherical shaped Co3O4 nanocrystals/nanoparticles (considered to be a very promising functional material) at low-cost with chemical purity, reduced crystallite size and useful physicochemical properties has been considered to be challenging. The present work (an attempt in this direction) involves the preparation of spherical shaped Co3O4 nanocrystals from cobalt acetate (dissolved in ethylene glycol) by a polyol synthesis route using a domestic microwave oven along with calcination at a suitable temperature (100/200/300/400 °C used to understand the phase evolution). X-ray diffraction (XRD, including Rietveld), infrared spectral, Raman spectral, energy dispersive X-ray absorption spectral and electron microscopic (SEM/TEM, including SAED) analyses have shown good crystallinity, chemical phase purity, spherical shape, reduced crystallite/particle size and narrow size distribution for the Co3O4 nanocrystal sample calcined at 400 °C. UV-Vis-NIR spectral analysis has shown the existence of multiple bandgap energies (1.51–1.98, 2.44–2.61 and 2.81–3.43 eV). Magnetic measurements have confirmed the antiferromagnetic nature possessing considerable magnetization below and above Neel temperature (TN), which indicates the presence of weak ferromagnetic ordering. The crystallite/particle sizes obtained for the sample calcined at 400 °C through XRD analysis, TEM analysis and using TN value (37.3 K) are 32.0, 33.6 and 31.3 nm, respectively. The method of preparation used is highly yielding, low-cost and more advantageous than many other methods used in the past.

Dissimilar autogenous TIG joint of Alloy 617 and AISI 304H steel for AUSC application

To reduce costs and improve high-temperature performance in Advanced Ultra Super Critical (AUSC) boilers, it is necessary to weld austenitic steel to Inconel alloy. In this study, the autogenous tungsten inert gas (TIG) welding process was used to join Alloy 617 and an austenitic AISI 304H steel plate of thickness 5 mm. Microstructural analysis showed that the microstructure formation was uneven along the weldments, with columnar and cellular dendrites near the interface while the central area of the weld exhibited a combination of columnar, cellular, and equiaxed dendrites. The use of energy dispersive spectroscopy and electron probe micro-analysis unveiled the presence of an unmixed layer at the interface between the weld and AISI 304H steel. Furthermore, a notable variation in the concentration of alloying elements such as Fe, Cr, Ni, Co, and Mo was observed. Within the weld metal, inter-dendritic areas showed the presence of precipitates rich in Cr, Ti, and Mo. Meanwhile, the heat-affected zone (HAZ) of Alloy 617 exhibited the presence of phases like Cr and Mo-rich M23C6 as well as Mo-rich M6C. Hardness tests showed non-uniform hardness along the weldments, with a hardness of 199 ± 6 HV in the weld metal and 225 ± 4 HV in Alloy 617 HAZ, and 207 ± 7 HV in AISI 304H HAZ. The Mo and Cr segregation in the inter-dendritic spaces led to a decline in the tensile properties of the welded parts and resulted in failure from the region of the weld metal.

Combinatorial Alloy Design and Microstructure Evolution in Laser-cladded Al–Co–Cr–Fe–Ni–Ti Compositionally Complex Alloys

In this work, we propose a strategy for high-throughput design and development of compositionally complex alloys combining theoretical and experimental alloy screening. This methodology was applied for the exploration of the (Co2CrFeNi2)1-x-yTixAly subsystem of so-called high entropy superalloys in the Al–Co–Cr–Fe–Ni–Ti alloy system. Alloy design was guided by thermodynamic calculations based on the CALPHAD approach. The evolution of the microstructure with increasing Al and Ti content was analyzed in the as-built, homogenized and age-hardened conditions by means of scanning electron microscopy, energy-dispersive X-ray spectroscopy and electron backscattered diffraction. Additionally, the evolution of the sample hardness with increasing Al and Ti contents was determined for all conditions. Based on the experimental results, the reliability of the CALPHAD calculations was assessed. Generally, a good agreement between calculations and experiments is achieved in the homogenized state. In the aged conditions, the CALPHAD predictions of the precipitation processes are partly inaccurate and need improvement. Optimal Al and Ti concentrations are derived for age hardening through L12 and combined L12 + B2 precipitations.

Rapid hydration and weakening of anhydrite under stress: implications for natural hydration in the Earth's crust and mantle

Abstract. Mineral hydration is an important geological process that influences the rheology and geochemistry of rocks and the fluid budget of the Earth's crust and mantle. Constant-stress differential compaction (CSDC) tests, dry and “wet” tests under confining pressure, and axial-stress tests were conducted for the first time to investigate the influence of triaxial stress on hydration in anhydrite–gypsum aggregates. Characterization of the samples before and after triaxial experiments was performed with optical and scanning electron microscopy, including energy-dispersive spectroscopy and electron backscatter diffraction mapping. Stress–strain data reveal that samples that underwent constant-stress differential compaction in the presence of fluids are ∼ 14 % to ∼ 41 % weaker than samples deformed under wet conditions. The microstructural analysis shows that there is a strong temporal and spatial connection between the geometry, distribution, and evolution of fractures and hydration products. The increasing reaction surface area in combination with pre-existing gypsum in a gypsum-bearing anhydrite rock led to rapid gypsification. The crystallographic orientations of newly formed vein gypsum have a systematic preferred orientation for long distances along veins, beyond the grain boundaries of wall-rock anhydrite. Gypsum crystallographic orientations in {100} and {010} are systematically and preferentially aligned parallel to the direction of maximum shear stress (45∘ to σ1). Gypsum is also not always topotactically linked to the wall-rock anhydrite in the immediate vicinity. This study proposes that the selective inheritance of crystal orientations from favourably oriented wall-rock anhydrite grains for the minimization of free energy for nucleation under stress leads to the systematic preferred orientation of large, new gypsum grains. A sequence is suggested for hydration under stress that requires the development of fractures accompanied by localized hydration. Hydration along fractures with a range of apertures up to 120 µm occurred in under 6 h. Once formed, gypsum-filled veins represent weak surfaces and are the locations of further shear fracturing, brecciation, and eventual brittle failure. These findings imply that non-hydrostatic stress has a significant influence on hydration rates and subsequent mechanical strength of rocks. This phenomenon is applicable across a wide range of geological environments in the Earth's crust and upper mantle.

Tribo-mechanical characterization of Cu-Cr-Zr ternary alloy aimed at fin-tube resistance welding electrode material

PurposeLow performance life and increased machine downtime due to wear of resistance welding copper electrode is of major concern in fin–tube resistance welding in waste heat recovery boilers. The purpose of this study is to investigate an alternative material with good wear resistance to replace the currently utilized C11000 electrolytic tough pitch (ETP) copper electrode.Design/methodology/approachIn this study, a Cu-Cr-Zr ternary alloy was developed for fin-to-tube welding electrode by melting commercial grade electrolytic copper (99.9% purity) plates, chips of chromium, powder of zirconium at 1100°–1300°C, followed by hot forging and precipitation hardening at 450°–550°C to attain appropriate grain flow. Microstructures of Cu-Cr-Zr alloys were analysed using scanning electron microscopy coupled with energy-dispersive backscatter electron spectrometry.FindingsWear performance of Cu-Cr-Zr and C11000 ETP Cu was evaluated using pin-on-disc set-up with Taguchi’s L8 orthogonal array. Ranking of the parameters was done, and it was observed that the material and temperature play a very significant role in controlling the wear of an electrode.Practical implicationsRate of fin–tube resistance welding was increased by 26% with Cu-Cr-Zr alloy. Further investigation on effect of plasma on the metallurgical characteristics of Cu-Cr-Zr is recommended.Originality/valueTribo-mechanical performance of newly developed Cu-Cr-Zr ternary alloy was compared with C11000 ETP copper.Peer reviewThe peer review history for this article is available at: https://publons.com/publon/10.1108/ILT-04-2023-0092/

Intratubular crystal formation in the exposed dentin from nano-sized calcium silicate for dentin hypersensitivity treatment

The aim of this study is to evaluate intratubular crystal formation from the experimental material consisting of dicalcium silicate (C2S) and tricalcium silicate (C3S) with nano-scaled particle size. A total of twenty-four specimens were made by isolating 8 mm of the cervical part centered at the cementoenamel junction of extracted premolars. Twelve specimens were not treated and considered as control. The experimental material was applied to the other twelve specimens by brushing for 10,000 strokes. Each group was randomly divided into four subgroups according to the period of immersion in phosphate buffer saline (PBS) for 1, 30, 60, and 90 days each. The specimens were sectioned longitudinally and examined with scanning electron microscopy and energy dispersion X-ray spectroscopy. The intratubular crystal were formed in PBS and densely filled the dentinal tubules over time. The crystal formation occurred at a depth of more than 50 μm from the dentin surface. The Ca/P ratio of formed intratubular crystals was 1.68 after 3 months. The experimental material consisting of C2S and C3S with a nanoscale particle size can form hydroxyapatite-like crystals in dentinal tubules in PBS, and there is a possibility of reducing dentin hypersensitivity by blocking the dentinal fluid flow.

Influence of Cu content on mechanical and tribological properties of Al–7Si–Cu alloy

In this study, Al–7Si–Cu alloys with different contents of Cu were prepared by ultrasonic agitation casting method. The microstructures were characterized by scanning electron microscopy (SEM) and energy dispersion spectroscopy (EDS). Dry sliding friction and wear properties with different Cu contents and loads were investigated. The results indicated that the alloy with 3.0 wt% Cu content revealed the optimal microstructure, comprehensive mechanical properties, and tribological properties. The hardness, tensile strength, and yield strength were enhanced by 83%, 57%, and 59%, respectively. The friction coefficient and wear rate reduced by 33% and 24% at 40 N load, respectively. The wear mechanism of Al–7Si–Cu alloy was mainly abrasive wear and delamination wear accompanied by oxidation wear. The improvement of the tribological properties of the alloy was attributed to the combined improvement of the microstructure and mechanical properties.

Failure analysis of a gas pipeline at the kinked dent location with crack indications

Pipeline failure causes can be divided in two groups: corrosion damage and mechanical damage. Mechanical damage usually includes dents, wrinkles, gouges, and combinations thereof. Dents can be considered the most common mechanical damage. In our study, a dent was located atthelower pipe region (5–7o’clock) as a consequence of indentation of the rocks on which the pipe was placed. The damaged pipe section was analyzed using visual, non-destructive testing (NDT), optical microscopy, scanning electron microscopy (SEM) with energy dispersive spectroscopy (EDS), hardness testing and transmission electron microscopy (TEM) analyses were performed to determine the origin, form, and mechanism of the crack indications at the dent location. Finite element method (FEM) was used for the creation and propagation cracks. The presence of micro-cracks in the dent region was confirmed, the formation of which on both pipe surfaces was related to the corrosion process. A deformation hardening was identified in the refined structure region in the kinked dent location. TEM analysis confirmed ahigher concentration of dislocations in the deformed area compared to recrystallized area (undeformed area). The hardness and TEM analyses of the crack indications date them from tomanufacturing process of the gas pipe. The FEM models of the pipe dent process supported this contention and confirm random presence of the crack indications in the dent location. Theindications detected by NDT and the associated change in microstructure and mechanical properties occurred during the production process of the pipe. The dent, which included thementioned indications, occurred during the operation of the pipeline.

The Structure-Performance Relation for Alkaline OER Electrocatalyst Investigated Using Analytical Electron Microscopy

Water electrolysis technology plays a key role in reducing carbon emission by converting renewable energy to clean hydrogen. Among various types of electrolyzers, anion exchange membrane water electrolyzer (AEMWE) receives growing effort of research due to its potential of comparable power density as its counterpart, proton exchange membrane water electrolyzer (PEMWE), while offering less corrosive environment on the oxygen evolution electrode which permits the use of non-noble metal catalysts [1].Nickel-iron oxides/hydroxides are among the most active electrocatalysts for oxygen evolution reaction (OER) in alkaline environment [2]. Recently, aerogel-like Ni-Fe oxides developed at Los Alamos National Laboratory have shown promising performance in AEMWE. The modified sol-gel approach followed by drying under supercritical condition produces high-surface-area oxides which likely contributes to high OER activity with enhanced number of active sites compared to other synthesis methods [3].In this work, we aim to elucidate the structure-performance relation for aerogel-like Ni-Fe oxides. Analytical electron microscopy methods, namely, energy-dispersive X-ray spectroscopy (EDS) and electron energy-loss spectroscopy (EELS) are used to investigate the distribution of Fe in the oxides and the oxidation states of Ni and Fe. The effect of annealing temperature in air on the oxide structure and OER activity has been investigated. Moreover, the structural changes before and after catalyst activation and long-term operation at OER potentials have been studied. Finally, results from analytical electron microscopy have been correlated with X-ray absorption spectroscopy and 57Fe Mossbauer spectroscopy to obtain a comprehensive picture of the oxide composition, especially the chemical environment of Fe.

Fractal-like kinetic modelling for sorption of diclofenac onto graphene oxide/polypyrrole composite: Mechanism analysis and response surface methodology for optimization

Graphene oxide/polypyrrole (GO/PPy) composite material was prepared to explore its utility in the removal of diclofenac from aqueous system. The characterization was achieved using Fourier transform infrared spectroscopy, X-ray powder diffraction analysis, thermogravimetry-differential thermal analyses, scanning electron microscopy coupled with energy dispersive X-ray analysis and transmission electron microscopy analysis. Response surface methodology was exploited to optimize the process variables for the sorption of diclofenac onto GO/PPy. Three variables such as contact time, adsorbent dose and initial concentration of diclofenac were selected for optimization to achieve maximum removal of diclofenac. All experiments were conducted at pH 5. The contact time, adsorbent dose and initial concentration of diclofenac were examined in the ranges of 03–37 min, 13–147 mg/25 mL and 10–110 mg/L, respectively. The optimum values obtained were: contact time: 20 min; GO/PPy dose: 80 mg/25 mL and initial diclofenac concentration: 60 mg/L. The maximum sorption capacity and percent removal of diclofenac were found to be 29.50 mg/g and 98.50 %, respectively. The measured data (at equilibrium) were investigated using different isotherm models and best described by Freundlich model (R2 = 0.9943–0.9952, χ2 = 0.0062–0.0077, APE = 1.45–1.61). The experimental kinetic data were analyzed with the help of fractal-like kinetic models. The kinetic data are best fitted by fractal-like mixed 1,2 order (R2 = 0.9830–0.9886, χ2 = 0.0014–0.0036, APE = 0.6780–1.1059). Adsorption mechanism has been discussed based on kinetic, FTIR and molecular docking studies which indicated the participation of π-π interactions and hydrogen bonding on energetically heterogeneous surface. The adsorption/desorption test demonstrated that GO/PPy had excellent reusability performance up to 15 cycles.