Resolution Scanning Electron Microscopy Images Research Articles

Spectral induced polarization signatures of smoldering remediation enhanced with colloidal activated carbon: An experimental study

Monitoring the remediation of soil and groundwater contaminated by organic compounds remains highly challenging. Thermal treatments, such as smoldering combustion, have become established remediation techniques for destroying contaminants. Smoldering combustion can now be supported by colloidal activated carbon (CAC), with CAC being able to both adsorb contaminants and supplement the fuel source for destroying them. Despite this potential, effective performance monitoring of smoldering remediation remains limited. The objective of this study is to investigate the potential of the spectral induced polarization (SIP) geoelectrical technique to assess the performance of smoldering remediation of soils supplemented with CAC. SIP column experiments were first conducted to assess the response of SIP (i.e., real and imaginary components of the complex electrical conductivity) to varying concentrations of CAC in imitated field soils that contain, or do not contain, organic matter (OM). Results demonstrate that increasing OM and CAC contents increase both the real and imaginary conductivities, with the imaginary conductivity also showing frequency dependence. Smoldering and SIP column experiments were then conducted to assess the effectiveness of SIP for detecting changes in soils of varying OM and CAC contents that have been remediated by smoldering. Examination of the soils before and after smoldering indicates that SIP can track the evolving real conductivity and imaginary conductivity (in particular) between different soil compositions and different stages of the remedial process. High resolution scanning electron microscopy imaging was performed on all samples to validate the SIP and smoldering experiments, confirming significant reductions in carbon after smoldering. Overall, this study suggests that SIP has potential to track changes associated with the addition of remedial fluids like CAC in the subsurface, and the destruction of contaminants adsorbed to CAC by smoldering combustion.

Degradation of tetracycline drug in aquatic environment by visible light active CuS/CdS photocatalyst

Photocatalysis is the best approach to degrade tetracycline antibiotic (TC) under sunlight. Hydrothermal approach was used to synthesize a potential CuS/CdS photocatalyst. The prepared catalysts were used to treat the TC in aquatic environment under visible light illumination. X-ray diffraction pattern confirmed that the CuS and CdS are in hexagonal structure, the corresponding planes are presented in the prepared CuS/CdS nanocomposite. High resolution scanning electron microscope images disclosed that the mixed morphologies of nanoplates and nanorods obtained in CuS/CdS nanocomposite. The synthesized CuS/CdS photocatalyst has absorption in visible region. The bandgap of CuS/CdS as calculated to be 2.30 eV. The CuS/CdS nanocomposite which exhibits high photocatalytic performance with degradation efficiency of 90% in 50 min, which was 2.3 and 1.4 times higher than that of CuS and CdS respectively. A series of radicals trapping experiment revealed that h+ and •O2- are the dominant active species during the degradation process. Additionally, a possible photocatalytic mechanism of the prepared CuS/CdS was also provided. The prepared CuS/CdS photocatalyst exhibits excellent photocatalytic stability even after four cycles, it reveals that the material has good chemical property. This result indicates that the synthesized CuS/CdS photocatalyst was favourable for the degradation of TC antibiotics in aquatic environments.

Argon broad ion beam sectioning and high resolution scanning electron microscopy imaging of hydrated alite

Scanning electron microscopy (SEM) imaging is able to visualize micro- to nano-structures of cement and concrete. A prerequisite is that the sample preparation preserves the native structure of the specimen. In this study, argon broad ion beam (BIB) sectioning is compared to state-of-the-art sample preparation (resin embedding, polishing) for hydrated alite. Additionally, it is investigated if during BIB, sample cooling is beneficial to avoid deterioration of cement hydrates. The aim is to quantitatively measure pore size distributions in hardened alite pastes.Therefore, not only optimized sample preparation but also optimized imaging conditions are investigated. Finally, it is demonstrated that by image analysis pores down to a diameter of 5 nm in hydrated alite pastes can be quantitatively analysed.

A Low-Cost, Non-hazardous Protocol for Surface Texturing of Glass Particles

We present a cheap, efficient, and non-hazardous protocol for altering the roughness of hard particles at the nanometer-scale using a stone tumbler, a tool which is normally used for polishing stones. Six different textures were achieved by lining the tumbler with sandpaper of mean grit diameters d_{mathrm{g}}=201, 58.5, 18.3, 12.6, and 8.4,upmu hbox {m}. Two textures were created by tumbling a batch of glass spheres for 4 h and for 12 h with the 12.6,upmu hbox {m} sandpaper; all other textures were established by tumbling for 12 h. Surface roughness was characterized by the integral length scale, xi, evaluated from 7 nm/pix resolution scanning electron microscope images. Roughness size increased from xi = 24 to 31 nm as the grit size decreased from d_{mathrm{g}} = 201 to 18.3,upmu hbox {m}, and then decreased to xi = 6.4,hbox {nm} at the smallest d_{mathrm{g}}. The largest xi ,(= 34,hbox {nm}) was achieved using a 12.6,upmu hbox {m} sandpaper and the shorter tumbling time of 4 h. The permeability of a packed column of the particles broadly decreased with increasing xi, indicating that permeability decreases with increasing roughness size.

Investigation of Rare Earth Garnet and its Physical Properties Synthesized by Facile Sol-Gel Method

To meet the demand of electronic devices pure polycrystalline yttrium iron garnet with cubic structure is investigated by sol gel method. The crystalline information and identification of garnet phases is confirmed using X-ray Diffraction. The X-ray diffraction pattern is analyzed by utilizing Rietveld Refinement method using Fullprof Software suite. Well defined domain morphology is observed in the High Resolution Scanning Electron Microscope image (HR-SEM). Pure YIG is inspected by Impedance Spectroscopy (IS) using Cole-Cole plot and Bode plot. It is interpreted using electrical circuit which is the combination of resistors and capacitors. The effect of g value of the sample is measured using Electron Spin Resonance (ESR).

Computational models evaluating the impact of sieve plates and radial water exchange on phloem pressure gradients.

The sugar conducting phloem in angiosperms is a high resistance pathway made up of sieve elements bounded by sieve plates. The high resistance generated by sieve plates may be a trade-off for promoting quick sealing in the event of injury. However, previous modeling efforts have demonstrated a wide variation in the contribution of sieve plates towards total sieve tube resistance. In the current study, we generated high resolution scanning electron microscope images of sieve plates from balsam poplar and integrated them into a mathematical model using Comsol Multiphysics software. We found that sieve plates contribute upwards of 85% towards total sieve tube resistance. Utilizing the Navier-Stokes equations, we found that oblong pores may create over 50% more resistance in comparison with round pores of the same area. Although radial water flows in phloem sieve tubes have been previously considered, their impact on alleviating pressure gradients has not been fully studied. Our novel simulations find that radial water flow can reduce pressure requirements by half in comparison with modeled sieve tubes with no radial permeability. We discuss the implication that sieve tubes may alleviate pressure requirements to overcome high resistances by regulating their membrane permeability along the entire transport pathway.

Synthesis and characterization of NiZnO nanoparticles

ABSTRACTThis article deals with the synthesis and characterization of undoped and zinc doped nickel oxide nanoparticles. Prepared nanopowders have been characterized by x-ray diffraction method, high resolution scanning electron microscope, ultraviolet visible spectrometer, photoluminescence spectrometer, Fourier transform infrared spectrometer, impedance meter and thermal gravimetric analyzer. X – ray diffraction study confirmed the average crystallite sizes of the nanopowders are less than 20 nm. Ultraviolet-visible spectrometer recorded the absorption peaks between 336 – 346 nm, corresponds the energy gap of 3.70 – 3.58 eV. Photoluminescence spectrum confirms the near band edge emission. Fourier transform infrared spectroscopy analysis established the formation of the nickel oxide and the doping of zinc. The high resolution scanning electron microscope image depicts that the particles are uniform in size and they are in severe agglomeration. The dielectric studies recognized the decrease in dielectric losses with increasing the temperature as well as frequency. Thermo gravimetric study shows that the prepared samples have good stability.

Encapsulated Pseudomonas putida for phenol biodegradation: Use of a structural membrane for construction of a well-organized confined particle

Phenols are toxic byproducts from a wide range of industry sectors. If not treated, they form effluents that are very hazardous to the environment. This study presents the use of a Pseudomonas putida F1 culture encapsulated within a confined environment particle as an efficient technique for phenol biodegradation. The innovative encapsulation technique method, named the “Small Bioreactor Platform” (SBP) technology, enables the use of a microfiltration membrane constructed as a physical barrier for creating a confined environment for the encapsulated culture. The phenol biodegradation rate of the encapsulated culture was compared to its suspended state in order to evaluate the effectiveness of the encapsulation technique for phenol biodegradation. A maximal phenol biodegradation rate (q) of 2.12/d was exhibited by encapsulated P. putida at an initial phenol concentration of 100 mg/L. The biodegradation rate decreased significantly at lower and higher initial phenol concentrations of 50 and up to 3000 mg/L, reaching a rate of 0.1018/d. The results also indicate similar and up to double the degradation rate between the two bacterial states (encapsulated vs. suspended). High resolution scanning electron microscopy images of the SBP capsule's membrane morphology demonstrated a highly porous microfiltration membrane. These results, together with the long-term activity of the SBP capsules and verification that the culture remains pure after 60 days using 16S rRNA gene phylogenetic affiliation tests, provide evidence for a successful application of this new encapsulation technique for bioaugmentation of selected microbial cultures in water treatment processes.

Structural, Optical and Magnetic Properties of Ni-Zn Ferrite Nanoparticles Prepared by a Microwave Assisted Combustion Method.

Ni-doped ZnFe₂O₄(Ni(x)Zn₁₋xFe₂O₄; x = 0.0 to 0.5) nanoparticles were synthesized by a simple microwave combustion method. The X-ray diffraction confirms the presence of cubic spinel ZnFe₂O₄for all compositions. The lattice parameter decreases with an increase in Ni content resulting in the reduction of lattice strain. High resolution scanning electron microscope images revealed that the as-prepared samples are crystalline with particle size distribution in 40-50 nm range. Optical properties were determined by UV-Visible diffuse reflectance and photoluminescence spectroscopy respectively. The saturation magnetization (Ms) shows the super paramagnetic nature of the sample for x = 0.0-0.2, whereas for x = 0.3-0.5, it shows ferromagnetic nature. The Ms value is 1.638 emu/g for pure ZnFe₂O₄ sample and it increases with increase in Ni content.

Structural, optical and antibacterial activity studies of neodymium doped ZnO nanoparticles

Trivalent neodymium doped ZnO (Zn1−xNdxO, x = 0.0, 0.03, 0.06 and 0.09) nanoparticles (NPs) synthesized by co-precipitation method with improved optical and antibacterial performance is reported. X-ray diffraction pattern indicates most of Nd3+ ions are incorporated in Zn2+ ions of ZnO lattice and hence there is no secondary peak of NdO3 in synthesized ZnO NPs. Fourier transform infrared spectroscopy analysis of synthesized NPs exhibits similar patterns in Zn/Nd–O bands observed at 480 cm−1. High resolution scanning electron microscopy images revealed the formation of spindle like morphology and the incorporation of Nd ions is confirmed by energy dispersive spectra analysis. UV–visible absorption spectra of pure and Nd doped ZnO NPs showed the variation of the band gap in the range of 3.06–2.65 eV. Raman analysis confirmed the formation of wurtzite structure of NPs was distorted due to Nd substitution in ZnO matrix. X-ray photoelectron spectroscopy confirmed the Nd incorporation in the ZnO lattice as Nd3+. The prepared Nd doped ZnO NPs showed potential application in antibacterial activities.

Investigation of the growth and local stoichiometric point group symmetry of titania nanotubes during potentiostatic anodization of titanium in phosphate electrolytes

Potentiostatic anodization of commercially pure, 50µm-thick titanium (Ti) foil was performed in aqueous, phosphate electrolytes at increasing experimental timeframes at a fixed applied potential for the synthesis of titania nanotube arrays (TNAs). High resolution scanning electron microscopy images, combined with energy dispersive spectroscopy and x-ray diffraction spectra reveal that anodization of the Ti foil in a 1M NaF+0.5M H3PO4 electrolyte for 4h yields a titanate surface with pore diameters ranging between 100 and 500nm. The presence of rods on the Ti foil surface with lengths exceeding 20µm and containing high concentrations of phosphor on the exterior was also detected at these conditions, along with micro-sized coral reef-like titanate balls. We propose that the formation of these structures play a major role during the anodization process and impedes nanotube growth during the anodization process. High spatially resolved scanning transmission electron microscopy-electron energy loss spectroscopy (STEM-EELS) performed along the length of a single anodized TiO2 nanotube reveals a gradual evolution of the nanotube crystallinity, from a rutile-rich bottom to a predominantly anatase TiO2 structure along its length.

High Performance Na0.5[Ni0.23Fe0.13Mn0.63]O2 Cathode for Sodium‐Ion Batteries

The synthesis of a new layered cathode material, Na0.5[Ni0.23Fe0.13Mn0.63]O2, and its characterization in terms of crystalline structure and electrochemical performance in a sodium cell is reported. X‐ray diffraction studies and high resolution scanning electron microscopy images reveal a well‐defined P2‐type layered structure, while the electrochemical tests demonstrate excellent characteristics in terms of high capacity and cycle life. This performance, the low cost, and the environmental compatibility of its component poses Na0.5[Ni0.23Fe0.13Mn0.63]O2 to be among the most promising materials for the next generation of sodium‐ion batteries.

Influence of stress triaxiality and strain rate on the failure behavior of a dual-phase DP780 steel

To better understand the in-service mechanical behavior of advanced high-strength steels, the influence of stress triaxiality and strain rate on the failure behavior of a dual-phase (DP) 780 steel sheet was investigated. Three flat, notched mini-tensile geometries with varying notch severities and initial stress triaxialities of 0.36, 0.45, and 0.74 were considered in the experiments. Miniature specimens were adopted to facilitate high strain rate testing in addition to quasi-static experiments. Tensile tests were conducted at strain rates of 0.001, 0.01, 0.1, 1, 10, and 100s−1 for all three notched geometries and compared to mini-tensile uniaxial samples. Additional tests at a strain rate of 1500s−1 were performed using a tensile split Hopkinson bar apparatus. The results showed that the stress–strain response of the DP780 steel exhibited mainly positive strain rate sensitivity for all geometries, with mild negative strain rate sensitivity up to 0.1s−1 for the uniaxial specimens. The strain at failure was observed to decrease with strain rate at low strain rates of 0.001–0.1s−1; however, it increased by 26% for an increase in strain rate from 0.1 to 1500s−1 for the uniaxial condition. Initial triaxiality was found to have a significant negative impact on true failure strain with a decrease of 32% at the highest triaxiality compared to the uniaxial condition at a strain rate of 0.001s−1. High resolution scanning electron microscopy images of the failure surfaces revealed a dimpled surface while optical micrographs revealed shearing through the thickness indicating failure occurred via ductile-shear. Finite element simulations of the tests were used to predict the effective plastic strain versus triaxiality history within the deforming specimens. These predictions were combined with the measured conditions at the onset of failure in order to construct limit strain versus triaxiality failure criteria.

Control of the Ge nanocrystal synthesis by co-implantation of Si+

The synthesis of Ge nanocrystals (Ge-nc) prepared by 74Ge+ implantation into fused silica followed by co-implantation of Si+ has been investigated for annealing temperatures varying between 850 and 1150 °C. By limiting the thermal diffusion of Ge, co-implanting Si reduces the Ge desorption and affects the growth of Ge-nc, through a Ge trapping mechanism involving the formation of Ge-Si chemical bonds. This is supported by Raman analysis, providing information regarding the material composition for a large variety of fabrication parameters, as well as high resolution scanning electron microscopy imaging, indicating that the average dimension of the synthesized Ge-nc decreases for increasing doses of co-implanted Si. From the spectral analysis of Raman measurements, a systematic evolution of the Ge-Ge, Ge-Si, and Si-Si bond concentrations is characterized as a function of the co-implantation fluences. Two different regimes are clearly identified for each annealing temperature. The first is associated with a linear increase of the residual Ge content with respect to the co-implanted Si, having a slope of ∼1, independent of the annealing temperature. Here, the nucleation of pure Ge-nc and Ge-nc containing Si impurities occurs at similar rates, for co-implanted Si fluences generally lower than the dose of implanted Ge. The second regime occurs for greater co-implantation fluence thresholds that depend on the annealing temperature. It is related to the saturation of the Ge trapping efficiency. In this regime, the formation of Si-Ge bonds dominates, sufficiently reducing the diffusion of Ge to prevent the formation of pure Ge-nc. In addition to limiting the unwanted and critical Ge desorption effects, Si co-implantation is a promising technique for precisely controlling the Ge-nc density, diameter, and uniformity at nanoscale dimensions, parameters which cannot be solely set from the local Ge concentration and/or the annealing parameters due to the high thermal diffusivity of Ge.

Complex resistivity signatures of ethanol biodegradation in porous media

Numerous adverse effects are associated with the accidental release of ethanol (EtOH) and its persistence in the subsurface. Geophysical techniques may permit non-invasive, real time monitoring of microbial degradation of hydrocarbon. We performed complex resistivity (CR) measurements in conjunction with geochemical data analysis on three microbial-stimulated and two control columns to investigate changes in electrical properties during EtOH biodegradation processes in porous media. A Debye Decomposition approach was applied to determine the chargeability (m), normalized chargeability (m(n)) and time constant (τ) of the polarization magnitude and relaxation length scale as a function of time. The CR responses showed a clear distinction between the bioaugmented and control columns in terms of real (σ') and imaginary (σ″) conductivity, phase (ϕ) and apparent formation factor (F(app)). Unlike the control columns, a substantial decrease in σ' and increase in F(app) occurred at an early time (within 4 days) of the experiment for all three bioaugmented columns. The observed decrease in σ' is opposite to previous studies on hydrocarbon biodegradation. These columns also exhibited increases in ϕ (up to ~9 mrad) and σ″ (up to two order of magnitude higher) 5 weeks after microbial inoculation. Variations in m and m(n) were consistent with temporal changes in ϕ and σ″ responses, respectively. Temporal geochemical changes and high resolution scanning electron microscopy imaging corroborated the CR findings, thus indicating the sensitivity of CR measurements to EtOH biodegradation processes. Our results offer insight into the potential application of CR measurements for long-term monitoring of biogeochemical and mineralogical changes during intrinsic and induced EtOH biodegradation in the subsurface.

Assessment of stress relaxation experiments on diamond coatings analyzed by digital image correlation and micro-Raman spectroscopy

The analysis and control of residual stresses are important for understanding the fracture and delamination behavior of coatings and thin films. In this work, the stress relaxation in microcrystalline diamond coatings after focused ion beam (FIB) milling was assessed by micro-Raman spectroscopy and digital image correlation. Using the FIB, the so called H-Bar geometry was milled in the diamond coating. The cutting introduced a strain relief in the coating perpendicular to the longer sides of the bar. The relaxation strains were recorded from high resolution scanning electron microscopy images of the H-Bar before and after FIB cutting. Using finite element modeling of the milled geometry, the residual stress level in the coating is evaluated from the relaxation strains. Furthermore, μ-Raman spectroscopy was used to assess the biaxial residual stress level in the coating before and after FIB cutting. The μ-Raman signal inside the bar showed strong incidence for stress relaxation and confirmed to some extent the applicability of the FIB–DIC method.

Modulating molecular and nanoparticle transport in flexible polydimethylsiloxane membranes

The ability to fabricate flexible filtration membranes that can selectively separate particles of different sizes is of considerable interest. In this article, we describe a facile, reproducible and simple one-step method to produce pores in polydimethylsiloxane (PDMS) membranes. We embedded micron-sized NaHCO3 particles in 50μm thick PDMS films. After curing, the membranes were immersed in concentrated HCl acid. Pores were generated in the membrane by the evolution of CO2 gas from the reaction of NaHCO3 and HCl. High resolution scanning electron microscope images clearly reveal the presence of openings on the surface and the cross-section of the membranes. Fluorescence and back-scattered electron imaging of porous PDMS membrane with embedded gold nanoparticles and comparison with non-porous PDMS membranes provided unambiguous evidence of pores in the membrane. Transport studies of molecular fluoresceinate ions, ions (sodium and chloride) and 240nm polystyrene nanoparticles through these membranes demonstrate passable pores and existence of channels within the body of the membrane. Mechanically stretching the porous PDMS membrane and comparing the flow rates of fluoresceinate ions and the polystyrene beads through the stretched and unstretched membranes allowed a direct proof of the modulation of transport rate in the membranes. We show that stretching the membranes by 10% increases the flow rate of fluorescein molecules by 2.8 times and by a factor of approximately ∼40% for the polystyrene nanoparticles.

Electrocatalysts for Methanol Oxidation Based on Platinum/Carbon Nanofibers Nanocomposite

New carbon nanomaterials, i.e., carbon nanotubes and nanofibers, with special physico-chemical properties, are recently studied as support for methanol oxidation reaction electrocatalysts replacing the most widely used carbon black. Particularly, carbon fibrous structures with high surface area and available open edges are thought to be promising. Platelet type carbon nanofibers, which have the graphene layers oriented perpendicularly to the fiber axis, exhibit a high ratio of edge to basal atoms. Different types of carbon nanofibers (tubular and platelet) were grown by plasma enhanced chemical vapour deposition on carbon paper substrates. The process was controlled and optimised in term of growth pressure and temperature. Carbon nanofibers were characterised by high resolution scanning electron microscopy and X-ray photoelectron spectroscopy to assess the morphological properties. Then carbon nanofibers of both morphologies were used as substrates for Pt electrodeposition. High resolution scanning electron microscopy images showed that the Pt nanoparticles distribution was well controlled and the particles size went down to few nanometers. Pt/carbon nanofibers nanocomposites were tested as electrocatalysts for methanol oxidation reaction. Cyclic voltammetry in H2SO4 revealed a catalyst with a high surface area. Cyclic voltammetry in presence of methanol indicated a high electrochemical activity for methanol oxidation reaction and a good long time stability compared to a carbon black supported Pt catalyst.

Surface Cation Segregation and its Effect on the Oxygen Reduction Reaction on Mixed Conducting Electrodes Investigated by ToF-SIMS and ICP-OES

La0.6Sr0.4CoO3-δ (LSC) thin film electrodes on yttria stabilized zirconia (YSZ) were investigated by impedance spectroscopy, inductively coupled plasma optical emission spectrometry (ICP-OES) and time of flight secondary ion mass spectrometry (ToF-SIMS). Effects caused by different film deposition temperatures, thermal annealing and chemical etching were studied. Correlations between changes in electrode polarization resistance of oxygen reduction and surface composition were found. The surface cation composition was analyzed by ToF-SIMS and ICP-OES measurements of in situ etched LSC films allowing depth resolved compositional analysis with nominally sub nm resolution. High resolution scanning electron microscopy images illustrate changes in surface morphology.

Relationship between Cation Segregation and the Electrochemical Oxygen Reduction Kinetics of La0.6Sr0.4CoO3−δ Thin Film Electrodes

Pulsed laser deposited La0.6Sr0.4CoO3−δ (LSC) thin film electrodes on yttria stabilized zirconia (YSZ) single crystals were investigated by impedance spectroscopy, time of flight secondary ion mass spectrometry (ToF-SIMS) and inductively coupled plasma optical emission spectrometry (ICP-OES). Effects caused by different film deposition temperatures, thermal annealing and chemical etching were studied. Correlations between changes in electrode polarization resistance of oxygen reduction and surface composition were found. At high deposition temperatures and after thermal annealing an inhomogeneous cation distribution was detected in the surface-near region, most manifest in a significant Sr enrichment at the surface. An activating effect of chemical etching of LSC is described, which can lower the polarization resistance by orders of magnitude. Chemistry behind this activation and thermal degradation was analyzed by ToF-SIMS and ICP-OES measurements of in-situ etched LSC films. The latter allow quantitative depth resolved compositional analysis with nominally sub nm resolution. High resolution scanning electron microscopy images illustrate the accompanying changes in surface morphology. All measurements suggest that stoichiometric LSC surfaces intrinsically exhibit very high activity towards oxygen reduction.