Transmission Electron Microscopy-energy Dispersive Spectroscopy Research Articles

Influence of organic fertilization on clay mineral transformation and soil phosphorous retention: Evidence from an 8-year fertilization experiment

Organic fertilizer can improve phosphorus (P) bioavailability, while the mechanism of microbial-driven clay mineral transformation on P retention and utilization with organic fertilization is still unclear. An 8-year organic fertilization experiment was carried out in saline alkaline paddy soil with five treatments: (1) CK, no fertilization; (2) NK, mineral N and K fertilization; (3) NPK, NK with mineral P fertilization; (4) NPKC1, NPK with 450 kg C ha−1 year−1; (5) NPKC2, NPK with 900 kg C ha−1 year−1. The results showed that, compared with NPK treatment, the percentage of illite with more P adsorption sites was increased by 26.8% and 20.7% in NPKC1 and NPKC2 treatments, respectively. Meanwhile, transmission electron microscopy-energy dispersive X-ray spectroscopy analysis further confirmed that there was more P adsorption on silicate clay minerals. Compared with NK treatment, the content of total P and available P was significantly increased with organic fertilization. Besides, the diversity of bacterial community was also increased by organic fertilizer addition, redundancy analysis showed that soil organic carbon was the main factor in the diversity of bacterial community. The relative abundance of Firmicutes and Gemmatimonadetes was promoted, which drove the transformation of clay minerals and improved P availability, respectively. Compared with NPK treatment, P use efficiency in NPKC1 and NPKC2 treatments was increased by 47.2% and 58.2%, respectively, while no significant difference was found between the two treatments. Therefore, appropriate organic fertilization was a better fertilization practice to improve P retention and utilization through bacteria-driven clay mineral transformation in saline-alkaline paddy soil.

Degradation-induced energy level mismatch in cohost-dopant blue phosphorescent OLEDs after device operation

Phosphorescent organic light-emitting diodes (PhOLEDs) have been considered potential candidates for high-efficiency blue emission. However, their short lifetime has been an issue, and much effort has been put into resolving this. Among such efforts, understanding energy level alignments (ELA) is one of the essential factors in understanding the degradation. However, ELA inside the actual PhOLED is rarely studied due to technical limitations. Here, we comprehensively investigate the degradation mechanism of blue PhOLEDs consisting of a cohost-dopant type emissive layer (EML). The blue PhOLEDs are aged with typical operating conditions until the luminance performance degrades. Ultraviolet and X-ray photoelectron spectroscopy (UPS and XPS) combined with a damage-free gas cluster ion beam (GCIB) etching and transmission electron microscopy-energy dispersive X-ray spectroscopy (TEM-EDX) unveil the buried interfaces inside the PhOLEDs. XPS and TEM-EDX measurements show that the dopant is unlikely to be the primary origin of the device degradation. Instead, UPS measurements show that the ELAs at the interfaces facing the EML are significantly altered unfavorably after device aging. This implies that the changes in the ELA are the leading cause of PhOLED degradation. Our results highlight the importance of retaining the ELAs during device operation to achieve long-lifetime blue PhOLEDs.

Enhanced Energetic Performance of Aluminum Nanoparticles by Plasma Deposition of Perfluorinated Nanofilms.

The performance of Al as nanoenergetic material in solid fuel propulsion or additive in liquid fuels is limited by the presence of the native oxide layer at the surface, which represents a significant weight fraction, does not contribute to heat release during oxidation, and acts as a diffusion barrier to Al oxidation. We develop an efficient technique in which the oxide layer is effectively turned into an energetic component via a reaction with fluorine that is coated in the form of a fluorocarbon nanofilm on the Al surface by plasma-enhanced chemical vapor deposition. Perfluorodecalin vapors are introduced in a low-pressure plasma reactor to produce nanofilms on the surface of Al nanoparticles, whose thickness is controlled with nanolevel precision as demonstrated by high-resolution transmission electron microscopy images. Coated particles show superior heat release, with a maximum enhancement of 50% at a thickness of 10 nm. This significant improvement is attributed to the chemical interaction between Al2O3 and F to form AlF3, which removes the oxide barrier via an exothermic reaction and contributes to the amount of heat released during thermal oxidation. The chemistry and mechanism of the enhancement effect of the plasma nanofilms are explained with the help of X-ray photoelectron spectroscopy, X-ray diffraction, high-angle annular dark-field scanning transmission electron microscopy-energy dispersive spectroscopy, thermogravimetric analysis, and differential scanning calorimetry.

Localization of nanospheres in pheochromocytoma-like cells following exposure to high-frequency electromagnetic fields at 18 GHz.

Exposure to high-frequency (HF) electromagnetic fields (EMFs) at 18 GHz was previously found to induce reversible cell permeabilization in eukaryotic cells; however, the fate of internalized foreign objects inside the cell remains unclear. Here, silica core–shell gold nanospheres (Au NS) of 20 ± 5 nm diameter were used to study the localization of Au NS in pheochromocytoma (PC 12) cells after exposure to HF EMFs at 18 GHz. Internalization of Au NS was confirmed using fluorescence microscopy and transmission electron microscopy. Analysis based on corresponding scanning transmission electron microscopy energy-dispersive spectroscopy revealed the presence of the Au NS free within the PC 12 cell membrane, cytoplasm, enclosed within intracellular vesicles and sequestered in vacuoles. The results obtained in this work highlight that exposure to HF EMFs could be used as an efficient technique with potential for effective delivery of drugs, genetic material, and nanomaterials into cells for the purpose of cellular manipulation or therapy.

Carbonate accelerated transformation of ferrihydrite in the presence of phosphate

In soils and rhizospheres, iron (oxyhydr)oxides and oxyanions like carbonate and phosphate occur ubiquitously and their interaction have important implications for nutrients and metals cycling. An elevated activity of carbonate in soils and sediments (e.g., pCO2, ∼2%) above current atmospheric CO2 (∼0.04%) is observed. The level of agronomic soil test phosphorus (P) in intensively managed agricultural soils can be up to several hundred mg kg−1. Although it is known that the transformation of iron (oxyhydr)oxides is suppressed by phosphate adsorption, it is unclear how increasing carbonate activities exert the reaction process. Here, the effects of carbonate on the transformation of ferrihydrite were evaluated at pH 7.5 in the presence of phosphate using experimental geochemistry, Fe K-edge X-ray absorption spectroscopy, transmission electron microscopy-energy dispersive X-ray spectroscopy, and Fourier transform infrared spectroscopy. Our results, for the first time, showed that the inhibitory effect of phosphate on ferrihydrite transformation was retarded by carbonate, and it transformed into hematite. Under pCO2 = 408 ppm (0.213 mM carbonate), an increase in [phosphate]o from 0 to 0.5 mM decreased the transformation rate of ferrihydrite from 0.009 to 0.003 d−1. However, the suppression was drastically perturbed when carbonate was added to the phosphate-ferrihydrite system. When 11.42 mM carbonate (pCO2 = 20000 ppmv) was present, the rate increased from 0.009 to 0.033 d−1 without phosphate and from 0.003 to 0.018 d−1 with 0.5 mM of phosphate. Moreover, carbonate promoted the formation of more crystalline rhombic hematite particles, while phosphate modified the morphology of hematite from rhombic to ellipsoidal-like with rough surfaces. The distinctive difference of the influence of carbonate and phosphate on the transformation kinetics, products distribution, and morphologies come from the interaction between carbonate/phosphate and ferrihydrite. Although phosphate formed strong inner-sphere complexes on the ferrihydrite surface, which inhibited the direct contact and dissolution of ferrihydrite, co-adsorbed carbonate still promoted the olation reaction, facilitating the formation of hematite. These results suggest that as an important geochemical process, the increasing activity of carbonate or pCO2 can override the retarding impact of phosphate on the transformation of ferrihydrite and control the occurrence/crystallization of hematite in the subsurface soils under the scenario of climate change.

3D electron diffraction study of terrestrial iron oxide alteration in the Mineo pallasite

AbstractThe Mineo pallasite is a relatively poorly known meteorite, which shows interesting features that are not fully understood, such as the occurrence of iron oxide regions bordering both the olivine grain boundaries and the (Fe,Ni) metal. In this study, the Fe oxides have been characterised by Raman spectroscopy, electron microprobe analysis, field emission scanning electron microscopy, transmission electron microscopy (TEM), energy dispersive spectroscopy (EDS) and 3D electron diffraction (3D ED). The combination of TEM–EDS and 3D ED yields a reliable identification of the chemical and crystallographic features of the cryptocrystalline portion of the sample investigated, enabling the Fe-oxide regions to be positively identified as goethite, FeO(OH).The occurrence of goethite was unambiguously associated with terrestrial alteration, also confirmed by the presence of calcite, detected by TEM-EDS and 3D ED. Goethite contains minor elements such as Na, Si and Ca, probably coming from alumino-silicates in the terrestrial environment, and Ni associated with the (Fe,Ni) metal. The observation of goethite along olivine grain boundaries, as an alteration product of the (Fe,Ni) metal diagenesis, is also very intriguing as it might be related to the (Fe,Ni) metal intruded into the sub-micrometric olivine fragments during pallasite formation. Further work is needed to extensively analyse the texture and composition of olivine/metal boundaries.

Sequential microwave-ultrasound-assisted silver nanoparticles synthesis: A swift approach, their antioxidant, antimicrobial, and in-silico studies

The present research work unravels the novel optimization of microwave-ultrasound-assisted rapid synthesis of Olea europaea capped silver nanoparticles (O-AgNps) as a capping and stabilizing agent that is not previously studied. The synthesized O-AgNps were characterized using UV–Visible spectroscopy, Fourier transform infrared spectroscopy (ATR-FTIR), proton nuclear magnetic resonance (1H NMR), dynamic light scattering-zeta potential (DLS-Zeta potential), high-resolution transmission electron microscopy-energy dispersive X-ray spectroscopy (HR-TEM-EDAX), and atomic force microscopy (AFM) techniques. The HR-TEM-EDAX revealed that O-AgNps were ∼ 10 nm in diameter with a polydispersity index of 0.191 and were spherical to elliptical. The nanoparticles were analysed for the in-vitro 2,2-diphenyl-1-picrylhydrazyl (DPPH) antioxidant, agar-well diffusion antibacterial assay, minimum inhibitory concentration (MIC), minimum bactericidal concentration (MBC) assays. The results were promising with a half-maximal inhibitory concentration (IC50) of 155.08 µg/mL for the antioxidant assay. The antimicrobial agar-well diffusion assay showed maximum zones of 24.9 ± 0.14 mm diameters at 8 mg/mL for Staphylococcus aureus (S. aureus) and 24.5 ± 0.7 mm at 8 mg/mL for Escherichia coli (E. coli). The MICs and MBCs were 156.25 µg/mL and 625 µg/mL for the antimicrobial assays againstS. aureusandE. coli. Additionally, the research throws limelight on the in-silico molecular docking analysis using AutoDock Vina software and arrives at a possible elucidation to support the experimental work.

Rare earth elements (REEs) recovery from coal waste of the Western Kentucky No. 13 and Fire Clay Seams. Part I: Mineralogical characterization using SEM-EDS and TEM-EDS

The mineralogy of rare earth elements (REEs, including 15 lanthanides plus Sc and Y) in the Western Kentucky No. 13 and Fire Clay coal waste was studied based on elemental composition analyses using scanning electron microscopy- and transmission electron microscopy-energy dispersive X-ray spectroscopy (SEM-EDS and TEM-EDS). A total of 49 and 50 REE-bearing particles were found from the SEM-EDS specimens of the two materials, respectively. For both materials, light REEs were found in apatite, monazite, and crandallite-group minerals, while heavy REEs primarily existed in zircon and xenotime. Based on the number and REE contents of the REE-bearing particles, it was concluded that monazite, xenotime, and crandallite-group minerals were major contributors to the total REE contents in both materials. The number of crandallite-group mineral particles found from the Western Kentucky No. 13 material was more than that of monazite and xenotime particles. However, for the Fire Clay material, the number and size of crandallite-group mineral particles were close to those of monazite and xenotime particles. Since the monazite and xenotime particles contained more REEs relative to the crandallite-group mineral particles, it was inferred that the majority of the REEs, especially the light REEs, existing in the Fire Clay coal waste occurred as monazite and xenotime. In addition, comparing with the Western Kentucky No. 13 material, a larger portion of the heavy REEs in the Fire Clay material were comprised in zircon. SEM images of the REE-bearing particles indicated that both liberated particles and particles locked within dominant minerals (e.g., clays) existed in the two materials. A few of the particles found in the Western Kentucky No. 13 material were completely encapsulated within the dominant minerals. Findings from the current study will promote REE recovery from coal-related materials, particularly coal waste.

Fractionation of natural algal organic matter and its preservation on the surfaces of clay minerals

The sequestration of algal organic matter (AOM) in clays constitute important carbon sinks in lake sediments. The composition of AOM was proven recently to critically influence its preservation in sediments. Yet it remains unclear which AOM components and types of clay minerals contribute to AOM burial in lake sediments. Here we investigated the AOM fractionation in kaolinite and illite via their adsorption, to ascertain the distribution of AOM components on these clay surfaces. The results showed that the AOM adsorbed quantity was 2-fold higher for illite than kaolinite. The adsorption isotherm data of illite and kaolinite were well fitted by a Freundlich model. The three-dimensional excitation emission matrix fluorescence spectroscopy (3D EEM) with parallel factor analysis (PARAFAC) modeling identified the AOM component under fractionation. The AOM solution mainly consisted of humic acid-like, tyrosine-like, and tryptophan-like components. Notably, large amounts of the hydrophilic tyrosine-like components were adsorbed onto the surface of both kaolinite and illite, whereas the hydrophobic tryptophan-like components were seldom adsorbed onto neither of the clay materials, while humic acid-like components were only adsorbed onto illite. Therefore, illite is more suitable for the preservation of AOM. Both transmission electron microscopy-energy dispersive X-ray spectroscopy (TEM-EDS) and the X-ray photoelectron spectroscopy (XPS) analysis further confirmed the high adsorption of AOM on the surface of illite; i.e., the molar content of carbon in AOM adsorbed to illite was 22.04%, almost a double of that adsorbed to kaolinite (11.59%). Overall, our results demonstrate the selective preservation of AOM on clay surfaces and highlight the role of clay minerals as sequesters of organic matter in eutrophic lakes.

Corrosion and high temperature compressive strength behaviour of 17Cr ferritic ODS steel with addition of aluminium through vacuum hot pressing

ABSTRACT The structural materials are essential for the present important advancements in economics, for reliability, safety, sustainability, etc., over presently operating reactor technologies of Generation IV reactors, advanced fast reactor core and fusion reactors. In order to avoid the release of radioactive fission products in the environment, the consistency of the cladding tube is necessary. Thus, increasing the operating temperature of these steels by oxide dispersion strengthening (ODS) makes them promising candidate materials. For the present study, the samples were prepared from the 430 L pre-alloyed powder using mechanical alloying through vacuum hot pressing. The hot-pressed alloys A, B, and C structural changes were examined through transmission electron microscope-energy dispersive spectroscopy (TEM-EDS) analysis and the mechanical properties, such as sintered density(g/cc), Vickers hardness (HV), compressive strength (650°C), and elongation (%) were measured. The corrosion resistance was measured through an electrochemical corrosion test of the alloys A, B, and C. From the TEM-EDS analysis, it was observed that the nano oxide particles and complex oxides particles were uniformly distributed. Alloy A has a higher compressive strength of 1307 MPa when compared to alloy Band alloy C. Moreover, alloy Chas higher corrosion resistance was observed than alloys A& B.

Effect of the addition mechanism of ZnO sintering aid on densification, microstructure and electrical properties of Ba(Zr,Y)O3-δ proton-conducting perovskite

We explore three different potential mechanisms to introduce 4 mol% ZnO sintering additive to the promising yttrium-doped barium zirconate (Ba(Zr,Y)O3-δ, BZY) proton conductor. The mechanisms involve Zn substitution for Y, Zr, or B-site cation excess. The addition of ZnO promotes high densification levels (up to 98% of the theoretical value) at 1300 °C, irrespective of the mechanism. However, scanning electron microscopy shows that the B-site cation excess mechanism leads to an impaired grain growth compared to the other mechanisms. Rietveld refinement of the lattice-parameters and scanning transmission electron microscopy-energy dispersive X-ray spectroscopy indicates that Zn resides in both grains and grain boundaries in all cases. Determination of partial conductivities demonstrates that the Zr substitution mechanism provides slightly higher values of bulk protonic conductivity, as well as a higher hydration enthalpy. In contrast, the B-site excess mechanism provides the highest specific grain-boundary conductivity, as a result of greater Zn segregation to the grain boundary.

Tungsten Oxide-Modified SSZ-13 Zeolite as an Efficient Catalyst for Ethylene-To-Propylene Reaction

Among the zeolitic catalysts for the ethylene-to-propylene (ETP) reaction, the SSZ-13 zeolite shows the highest catalytic activity based on both its suitable pore architecture and tunable acidity. In this study, in order to improve the propylene selectivity further, the surface of the SSZ-13 zeolite was modified with various amounts of tungsten oxide ranging from 1 wt% to 15 wt% via a simple incipient wetness impregnation method. The prepared catalysts were characterized with several analysis techniques, specifically, powder X-ray diffraction (PXRD), Raman spectroscopy, temperature-programmed reduction of hydrogen (H2-TPR), temperature-programmed desorption of ammonia (NH3-TPD), inductively coupled plasma-atomic emission spectroscopy (ICP-AES), and N2 sorption, and their catalytic activities were investigated in a fixed-bed reactor system. The tungsten oxide-modified SSZ-13 catalysts demonstrated significantly improved propylene selectivity and yield compared to the parent H-SSZ-13 catalyst. For the tungsten oxide loading, 10 wt% loading showed the highest propylene yield of 64.9 wt%, which was 6.5 wt% higher than the pristine H-SSZ-13 catalyst. This can be related to not only the milder and decreased strong acid sites but also the diffusion restriction of bulky byproducts, as supported by scanning transmission electron microscopy-energy dispersive X-ray spectroscopy (STEM-EDS) observation.

Deformation twinning in Ti48.9Zr32.0Nb12.6Ta6.5 medium entropy alloy

Abstract The {112} β deformation twinning has never been confirmed in refractory high or medium entropy alloys (HEAs or MEAs) at room temperature. Here a Ti48.9Zr32.0Nb12.6Ta6.5 MEA shows {112} β twins was designed based on the d-electron alloy design method learned from β Ti alloys. The solution-treated (ST) samples show equiaxed grains, single β phase, homogenous chemical composition and good tensile properties. Transmission electron microscopy (TEM) investigation shows that the ST samples is free of athermal ω phase. Following TEM results revealed abundant dislocations and their structures such as jogs, loops, cross-slips and slip bands in the deformed samples. The {112} β twins were observed in the fractured samples, with interfacial ω phase on the twin boundary. Elemental segregation has not been detected in the twinned region by scanning transmission electron microscopy-energy dispersive spectroscopy (STEM-EDS) mapping. The interaction between dislocations and twins was revealed by low-angle annular dark field (LAADF), thus twins in addition to the dislocation jogs, loops, cross-slips and slip bands, contribute to the work hardening in the present MEA. Deformation twinning in HEAs and MEAs has been discussed and twins can be expected in these alloys when the effects of their constituent elements were carefully considered. In particular, the present strategy of starting from β Ti alloys can be applied to design refractory HEAs and MEAs with desirable deformation microstructures.

Bioremediation potential of hexavalent chromium by a novel bacterium Stenotrophomonas acidaminiphila 4-1

Abstract A gram-negative bacterial strain capable of resisting hexavalent chromium was isolated and evaluated for its characteristics. The strain was designated as Stenotrophomonas acidaminiphila 4-1 according to the 16S rDNA sequence and phylogenic analysis. It was founded that sufficient nutrients were more suitable for intracellular enrichment of chromium, such as LB medium. Extracellular polymeric substances were observed as binding sites for chromium entering bacterial cells by transmission electron microscopy (TEM) and scanning transmission electron microscope-energy dispersive spectroscopy (STEM-EDS) analysis. Two sharp peaks at 577.18 eV and 578.24 eV were assigned to Cr 2p3/2 in X-ray photoelectron spectroscopy (XPS) spectra, illustrating only Cr(III) and Cr(VI) forms existed in stain 4-1. Possible removal mechanisms of chromium were also described. The removal rate of Cr(VI) was 75.69% with initial substrate concentration of 15 mg L −1 after 7d incubation. The microbial biomasses which cultured below Cr(VI) of 100 mg L −1 were varied slightly. And strain 4-1 could tolerate high concentration of Cr(VI) up to 1000 mg L −1. Removal rate of Cr(VI) was not obviously affected with diesel. The results showed that Stenotrophomonas acidaminiphila 4-1 is an excellent bacterial candidate for the bioremediation of chromium or combined with diesel contaminated sites.

Role of ALD Al2O3 Surface Passivation on the Performance of p-Type Cu2O Thin Film Transistors.

High-performance p-type oxide thin film transistors (TFTs) have great potential for many semiconductor applications. However, these devices typically suffer from low hole mobility and high off-state currents. We fabricated p-type TFTs with a phase-pure polycrystalline Cu2O semiconductor channel grown by atomic layer deposition (ALD). The TFT switching characteristics were improved by applying a thin ALD Al2O3 passivation layer on the Cu2O channel, followed by vacuum annealing at 300 °C. Detailed characterization by transmission electron microscopy-energy dispersive X-ray analysis and X-ray photoelectron spectroscopy shows that the surface of Cu2O is reduced following Al2O3 deposition and indicates the formation of a 1-2 nm thick CuAlO2 interfacial layer. This, together with field-effect passivation caused by the high negative fixed charge of the ALD Al2O3, leads to an improvement in the TFT performance by reducing the density of deep trap states as well as by reducing the accumulation of electrons in the semiconducting layer in the device off-state.

Anthracene-Bisimidazole Tetraacid Linker-Based Metal–Organic Nanosheets for Turn-On Fluorescence Sensing of Nerve Agent Mimics

A fluorescent 4-connecting bisimidazole-tetraacid linker endowed with anthracene as the bulged core, that is, H4ANTBI, was rationally designed to access a metal–organic layered material, that is, Cd-ANTBI, with ca. 36% solvent-accesssible volume. Fluorescence is significantly suppressed in its crystalline state due to self quenching (ϕfl ca. 5%). However, 2D metal–organic framework nanosheets (MONs) generated by solvent-assisted exfoliation of the layered material in methanol were found to exhibit enhanced fluorescence (ϕfl ca. 20%). The formation of 2D MONs was unequivocally established by microscopic techniques such as atomic force microscopy, high-resolution transmission electron microscopy, and transmission electron microscopy–energy-dispersive spectroscopy analyses. Indeed, the extent of exfoliation in different solvents such as methanol, ethanol, and dimethyl sulfoxide was found to correlate with solvent properties (Gutmann’s donor numbers), attesting to the fact that solvents that can form hydrogen bonds with the imidazolium ions bring about exfoliation effectively. It is further shown for the first time that the suspension of 2D MONs serves as an efficient “turn-on” fluorescent material for sensing of the toxic nerve agent mimics; the observed detection limit for diethyl chlorophosphate is ca. 0.52 ppm.

Silver Nanoparticle Interactions with Surfactant-Based Household Surface Cleaners.

Silver nanoparticles (AgNPs) are the most widely used engineered nanomaterials in consumer products, primarily due to their antimicrobial properties. This widespread usage has resulted in concerns regarding potential adverse environmental impacts and increased probability of human exposure. As the number of AgNP consumer products grows, the likelihood of interactions with other household materials increases. AgNP products have the potential to interact with household cleaning products in laundry, dishwashers, or during general use of all-purpose surface cleaners. This study has investigated the interaction between surfactant-based surface cleaning products and AgNPs of different sizes and with different capping agents. One AgNP consumer product, two laboratory-synthesized AgNPs, and ionic silver were selected for interaction with one cationic, one anionic, and one nonionic surfactant product to simulate AgNP transformations during consumer product usage before disposal and subsequent environmental release. Changes in size, morphology, and chemical composition were detected during a 60 min exposure to surfactant-based surface cleaning products using ultraviolet-visible (UV/Vis) spectroscopy, transmission electron microscopy-energy dispersive X-ray spectroscopy (TEM-EDX), and dynamic light scattering (DLS). Generally, once AgNP suspensions were exposed to surfactant-based surface cleaning products, all the particles showed an initial aggregation, likely due to disruption of their capping agents. Over the 60 min exposure, cleaning agent-1 (cationic) showed more significant particle aggregates than cleaning agent-2 (anionic) and cleaning agent-3 (nonionic). In addition, UV/Vis, TEM-EDX, and DLS confirmed formation of incidental AgNPs from interaction of ionic silver with all surfactant types.

Structural and electronic properties of spinel type Mg1+yCo2-x-yMnxO4 for cathode applications in magnesium rechargeable batteries

Mg1+yCo2-x-yMnxO4 (x = 0, 0.4, 0.5, 0.6; y = 0, 0.04, 0.05, 0.4) was synthesized by the reverse co-precipitation method. Powder X-ray diffraction measurements of the obtained product indicated a spinel structure with the space group Fd3¯m. The compositional homogeneity of the synthesized material was confirmed by scanning transmission electron microscopy-energy dispersive X-ray spectroscopy mapping. Charge and discharge cycle tests showed a discharge capacity higher than 220 mAh g−1 at 90 °C with a cut-off voltage ranging from 0.345 to −1.055 V vs. Ag/Ag+ (2.945–1.545 V vs. Mg/Mg2+). The electronic structure was analyzed by the maximum-entropy method (MEM) based on Rietveld analysis results, which showed that Mg insertion was easier in Mg1+yCo2-x-yMnxO4 than in MgCo2O4, and that the strong covalency of M(16d)-O in Mg1+yCo2-x-yMnxO4 enabled Mg ion conduction at the 8a sites. The strain in MO6 octahedra decreased with increasing Mn substitution. The valence of the transition metals was examined by X-ray absorption fine structure (XAFS) measurements, and the Co and Mn K-edge spectra revealed that Co and Mn are present as trivalent to bivalent and tetravalent to trivalent species, respectively. Both Co and Mn redox processes are considered to contribute to the specific capacity during the first charge-discharge process. Rietveld analysis after charge/discharge confirmed a partly reversible phase transition from the spinel phase to the rock salt type phase.

Failure Analysis and Defects Characterization of Polymer Electrolyte Membrane Fuel Cells after Relative Humidity Cycling

Commercial catalyst coated membrane (CCM) was tested under a relative humidity (RH) cycling accelerated stress test (AST). The morphology around the failed regions, identified by the bubble jig test, were examined by scanning electron microscopy (SEM), scanning transmission electron microscopy-energy dispersive spectroscopy (STEM-EDS), and X-ray computed tomography (XCT) and compared with beginning of life (BOL) sample. The SEM images showed the defects in forms of catalyst layer (CL) and membrane cracks, delamination, and bulging along with CL thickness alterations. The XCT scans confirmed the presence of circular and volcano-shape defects protruded throughout the CCM, as well as MPL irregularities. Defects were correlated to the morphology of the microporous layer (MPL), suggesting that MPL structure may affect the degradation of CCMs. The STEM-EDS microstructural evaluations and analysis revealed changes in the CL porosity with respect to the BOL, confirming the thickness changes and defect formation observed in SEM and XCT.

Dynamic Strain Aging and Embrittlement Behavior of IN718 During High-Temperature Deformation

The high-temperature deformation behavior of nickel-base superalloy IN718 was investigated in the solution-treated (ST) condition. High-temperature tensile tests were performed between 600 °C and 850 °C at strain rates of 1 × 10−3, 1 × 10−2, and 1 × 10−1 s−1. The deformation behavior of this material was analyzed using optical microscopy, scanning electron microscopy, and transmission electron microscopy. In the investigated temperature–strain rate regime, material undergoes partial precipitation, serrated yielding, and embrittlement. Serrated yielding was observed at 600 °C, 650 °C, and 700 °C and is attributed to dynamic strain aging. The appearance of serrated flow at high temperatures up to 700 °C in the ST condition can be attributed to the availability of excess Nb in the matrix. Beyond 700 °C, Nb concentration significantly decreases in the matrix due to the formation of Ni3Nb precipitate. Nb is responsible for the appearance and disappearance of serrations at high temperature. The alloy exhibits embrittlement phenomenon in the range of 750 °C to 850 °C when thermally exposed in air. The alloy shows a ductile mode of fracture when tested at 600 °C and 700 °C, whereas completely brittle fracture was observed at the 800 °C test temperature. Formation of brittle oxides at grain boundaries in the presence of atmospheric oxygen resulted in the embrittlement of the alloy at 750 °C to 850 °C. An oxidation-assisted intergranular cracking mechanism is responsible for embrittlement of this alloy, which was proved by scanning transmission electron microscopy-energy dispersive spectroscopy.