Field Emission Gun Transmission Electron Microscope Research Articles

An Aggregation‐Induced Change in the Fluorescence of Carbon Dots: Naked Eye Water Detection in a Selective Organic Solvent

AbstractIn this study, newly synthesized crystalline carbon dots shows the concentration and solvent‐dependent multicolor emission. The carbon dots have been characterized by several techniques like Fourier transformed infrared spectroscopy (FT‐IR), X‐ray photoelectron spectroscopy (XPS), UV‐visible and fluorescence spectroscopy, and field emission gun transmission electron microscopy (FEG‐TEM). The high polarity of the solvents and the high concentration of the carbon dots help it to aggregate which opens up a new red‐shifted emission band. It has been revealed that the Förster resonance energy transfer (FRET) between the dispersed and aggregated state of the carbon dots becomes the actual cause behind this change. These carbon dots selectively shows the white light emission in the dioxane. The particular polarity of the dioxane selectively helps for the coexistence of the blue and greenish‐yellow emission bands with the same intensity which eventually turns the emission very much near to white light. It has been found that the very minute amount of water present in dioxane (0.1 % V/V) can change the emission nature of the carbon dots. This observation has finally helped these carbon dots for highly selective and perceptible water detection in dioxane.

2D and 3D TEM Characterisation of Benzene and Ethylene Soot

Flame-generated soot particles from two different fuels, benzene (B) and ethylene (E), at different ageing conditions, were analysed to assess their morphological and structural features. Samples were collected at 6, 10 and 14 mm from the nozzle location. Traditional 2D transmission electron microscopy (TEM) and a novel 3D TEM were used to investigate morphology variations. High-resolution TEM (HRTEM) was used to capture structural characteristics. Samples were then placed on lacey carbon microgrids. A field emission gun TEM was used to capture images of the agglomerates. Tilt series of ±60 degrees were acquired at 1-degree steps to perform the 3D reconstruction. IMOD software and backwards projection were used to reconstruct the tomogram from the tilt series. The 2D analysis revealed that soot particles’ agglomerations for both fuels change from a bundle to a chain-like structure as they “age”, i.e., extracted at a higher “flame height”. In B, the primary particle diameter increases as they get “older,” whereas in E, the opposite happens, and overall, E particles are bigger than B ones. The nanostructure presents ordered regions with parallel-stacked layers of carbon lamellae. This is more evident in the aged soot samples, with the difference that in E a thick amorphous layer is present at the edge of the particles, which is not observable for B. A nanostructure analysis suggests a trend of increasing fringes length as the soot ages, going from 1.04 nm of B6 to 1.22 nm of B10 to 1.05 nm of B14 and from 1.139 nm of E6 to 1.20 nm of E14 (±0.02 nm). The tortuosity does not vary greatly across all the samples, ranging between 1.132 and 1.149 (±0.004). Separation is also quite similar everywhere, with 0.404 nm of B6, 0.392 nm of B10, 0.399 nm of B14, 0.397 nm of E6 and 0.396 nm of E14 (±0.002 nm). Ring structures and particle overlaps, two examples of geometrical characteristics concealed in 2D, can be seen in the 3D reconstructions. Furthermore, the comparison between 3D and 2D volume and surface area raises questions about the reliability of those parameters as derived from 2D measurements. This study advances knowledge of how soot structure can be affected by the fuel type and emphasises the significance of how soot is investigated.

Impact of La on Structural, Morphological and Magnetic Properties of NiCoFe2O4 Nano Ferrites

Abstract: Ni0.2Co0.8Fe2-xLaxO4 (x = 0.02, 0.06, 0.10) nano ferrites have been synthesized by Sol-gel auto combustion method using urea as a fuel. The sample calcinations have been performed at 800 oC for 4 hours. The synthesized samples were subjected to study X-ray diffraction spectroscopy (XRD) for structural investigations. All the samples were found to constitute Face Centered Cubic (FCC) spinel structure belonging to the Fd3m space group. The XRD results show the single cubical phase formation in the heated samples. Energy-dispersive X-ray spectra confirmed the presence of Ni, Co, La Fe and O elements with no existence of any impurity. The average crystallite size was decreased by varying the concentration of La from 10 to 8 nm. The Field Emission Gun Scanning Electron microscopy (FEG-SEM) and Field Emission Gun transmission electron microscopy (FEG-TEM) have given the morphological study of the samples. It is also found that the value of the lattice constant decreases with increases in La concentration. The magnetic properties of the samples were investigated by using a vibrating sample magnetometer (VSM). The results obtained from VSM show that the value of both magnetization (Ms) and coercivity (Hc) decreases with an increase in diamagnetic La concentration. Keywords: Spinel ferrites, Sol-gel, SEM, TEM, VSM.

Antiviral application of colloidal and immobilized silver nanoparticles

This study explored the application of colloidal and immobilized silver nanoparticles (AgNPs) for inactivation of bacteriophages. Coliphages that are commonly used as indicators for enteric viruses, were used in this study. Colloidal AgNPs were synthesized via a chemical reduction approach using sodium borohydride as reducing agent and trisodium citrate as stabilizing agent. AgNP-immobilized glass substrate was prepared by immobilizing AgNPs on amine-functionalized glass substrate by post-immobilization method. The AgNP-immobilized glass substrate was also tested so as to minimize the release of AgNPs in the treated water. The characterization of AgNPs and the AgNP-immobilized glass surface was done using field emission gun-transmission electron microscopy and scanning electron microscopy. Studies conducted with varying concentrations of colloidal AgNPs displayed good antiviral activity for MS2 and T4 bacteriophage. Colloidal AgNPs at a dose of 60 μg ml−1 could completely inactivate MS2 and T4 bacteriophage within 30 and 50 min with an initial concentration of 103 PFU ml−1. Contaminated water (100 ml) in an unstirred batch reactor with an initial bacteriophage concentration of 103 PFU ml−1 could be inactivated by the AgNP-immobilized glass substrate (1 cm × 1 cm, containing 3.7 μg cm−2 silver) suspended centrally in the batch reactor. Complete 3-Log bacteriophage inactivation was achieved within 70 and 80 min for MS2 and T4 bacteriophage, respectively, while the aqueous silver concentration was less than 25 μg l−1. This is significantly lower than the recommended standard for silver in drinking water (i.e. 100 μg l−1, US EPA). Thus, AgNP-immobilized glass may have good potential for generating virus-free drinking water.

Enhanced antibacterial activity of decahedral silver nanoparticles

The size and shape of silver nanoparticles (AgNPs) can potentially influence their antibacterial activity. In this study, a photochemical approach was adopted for the synthesis of decahedral AgNPs and their antibacterial activity was tested and compared against that of spherical AgNPs of similar size synthesized using the chemical reduction approach. The UV–vis spectra indicated the synthesis of decahedral AgNPs with a localized surface plasmon resonance (LSPR) peak at 502 nm. The spherical AgNPs exhibited the LSPR peak at 416 nm. Analysis of field emission gun-transmission electron microscopy (FEG-TEM) micrographs demonstrated the average diameter of decahedral silver nanoparticles as 52.1 ± 5.7 nm with side length as 33.2 ± 3.1 nm. In contrast, the average size of spherical AgNPs was 44.2 ± 6.3 nm. The decahedral AgNPs demonstrated ten times higher bactericidal activity as compared to the spherical AgNPs across all the bacterial strains tested. The minimum inhibitory concentration (MIC) for decahedral AgNPs was in the range of 4–8 μg/ml for all the four bacterial strains tested, whereas, for spherical nanoparticles of comparable size, the MIC was in the range of 40–80 μg/ml. The minimum bactericidal concentration (MBC) for decahedral AgNPs was in the range of 6–10 μg/ml. At the same time, spherical AgNPs of comparable size exhibited MBC in the range of 60–100 μg/ml for the four bacterial strains. In terms of bactericidal effect, Escherichia coli MTCC 443 was found as the most sensitive strain, while in terms of growth inhibition, Bacillus subtilis was the most sensitive strain. Staphylococcus aureus NCIM 5021 was the most resistant among the tested bacterial strains.

Stimuli responsive multicolour fluorescence emission in carbon nanodots and application in metal free hydrogen evolution from water.

The present study convincingly demonstrates visible light induced continuous tuning of the fluorescence of carbon nanodots from yellow to cyan within two hours. These carbon dots are well characterized using field emission gun transmission electron microscopy (FEG-TEM), X-ray photoelectron spectroscopy (XPS), Fourier-transform infrared spectroscopy (FT-IR), fluorescence spectroscopy and UV-visible spectroscopy. Moreover, solid state fluorescence of different wavelengths has also been obtained from these colour tunable carbon dots by circumventing the common problem of aggregation induced quenching of fluorescence in the solid state. These carbon dots have also shown a very low band gap and the yellow emissive C-dots have been successfully utilized as a photocathode in metal free photo-electrochemical hydrogen evolution from water.

Effective killing of bacteria under blue-light irradiation promoted by green synthesized silver nanoparticles loaded on reduced graphene oxide sheets.

Graphene oxide (GO) materials loaded with silver nanoparticles (AgNPs) have drawn considerable attention due to their capacity to efficiently inactivate bacteria though a multifaceted mechanism of action, as well as for presenting a synergetic effect against bacteria when compared to the activity of AgNPs and GO alone. In this investigation, we present an inexpensive and environmentally-friendly method for synthesizing reduced GO sheets coated with silver nanoparticles (AgNPs/r-GO) using a coffee extract solution as a green reducing agent. The physical and chemical properties of the produced materials were extensively characterized by scanning electron microscopy (SEM), field-emission gun transmission electron microscopy (FEG-TEM), ultraviolet and visible absorption (UV-Vis), Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), inductively coupled plasma-optical emission spectroscopy (ICP-OES) and ion release determination. The results demonstrated that AgNPs/r-GO composites were successfully produced, revealing the formation of micrometer-sized r-GO sheets decorated by AgNPs of approximately 70nm diameter. Finally, bactericidal and photobactericidal effects of the AgNPs/r-GO composites were tested against Staphylococcus aureus, in which the results showed that the composites presented antimicrobial and photoantimicrobial activities. Moreover, our results demonstrated for the first time, to our knowledge, that an efficient process of bacterial inactivation can be achieved by using AgNPs/r-GO composites under blue light irradiation as a result of three different bacterial killing processes: (i) chemical effect promoted by Ag+ ion release from AgNPs; (ii) photocatalytic activity induced by AgNPs/r-GO composites, enhancing the bacterial photoinactivation due to the excited-Plasmons of the AgNPs when anchored on r-GO; and (iii) photodynamic effect produced by bacterial endogenous photosensitizers under blue-light irradiation. In summary, the present findings demonstrated that AgNPs/r-GO can be obtained by a non-toxic procedure with great potential for biomedical-related applications.

InN Nanowires Based Near-Infrared Broadband Optical Detector

We have reported a new method of synthesis of InN nanowires (NWs) on p-Si (100) substrate by the vapour transport cum glancing angle deposition (GLAD) technique. The field emission gun transmission electron microscopy (FEG-TEM) reveals that the InN NWs are crystalline in nature. Photoluminescence (PL) analysis shows that the optical bandgap of the NW is ~1.07 eV at 300 K. Metal-Semiconductor-Metal (M-S-M) photodetecor has been fabricated using InN NWs. The device produced trivial dark current ~7.31 μA cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-2</sup> at 3 V applied voltage. The broad band near-infrared (NIR) photo-response from 900-1400 nm was recorded for the device.

Newly emerging mesoporous strontium hydroxyapatite nanorods: microwave synthesis and relevance as doxorubicin nanocarrier

A new synthesis method is developed for preparation of mesoporous strontium hydroxyapatite (SrHAp) nanorods using CEM Discover microwave synthesizer. Nanorods preparation with surfactants SrHAp(+) and without surfactants SrHAp(−) were successfully achieved at 160 °C temperature and 15 min of hold time. Particle sizes with standard deviation were found to be 67 ± 18 and 69 ± 24 nm respectively. Mesoporous nanorods were thoroughly characterized using different methods, such as Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), field-emission gun transmission electron microscopy (FEG-TEM), scanning electron microscopy (SEM), Brunauer–Emmett–Teller (BET) surface area and porosity measurement. It was observed that use of trisodium citrate and CTAB resulted in quite agglomerated particles, whereas nanorods synthesized without citrate and CTAB were well dispersed. Cell toxicity of both these materials synthesized was tested in MCF-7 and Zr-75 cell lines using MTT assay. SrHAp nanorods concentration up to 0.25 mg/ml was non-toxic at 48 hours (h) time point in both the cell lines. As SrHAp(−) were found to serve better in terms of cytotoxicity, they were chosen for doxorubicin (Dox) loading, pH depended release and cell uptake study. The successful loading of Dox was ascertained by UV-Visible and FTIR spectroscopy. Entrapment efficiency of Dox in SrHAp nanoparticles was found to be 83.71%, and loading capacity was 0.017 μg Dox per μg SrHAp nanoparticles. Rapid release was observed in the initial hours followed by slow release. Even until 31 days, only 27 and 32% drug was released at pH 7.4 and pH 4.5 respectively, which shows controlled release behavior. Further, cellular uptake of Dox-loaded nanoparticles at different time points was studied in the two breast cancer cell lines by fluorescence imaging. These nanoparticles were found to internalize within both these cells after 3 h of incubation and continued further until 24 h. Overall, high Dox loading efficacy, sustained release behavior, and cell uptake potential render SrHAp nanoparticles to give promising results when applied in vivo and emerge as a robust drug carrier towards solving purpose of slow and prolonged drug release.

Poly (vinyl alcohol) supported thermally reduced graphene oxide (TRGO) nanosheets exhibit enhanced electrical and mechanical behavior

In the present work thermally reduced graphene oxide was reinforced into polyvinyl alcohol (PVA) film by the solution cast method. The structural and morphological characterization of prepared nanocomposite materials was done using Fourier transform infrared (FTIR), X-ray diffraction (XRD), and Raman spectroscopy, scanning electron microscopy(SEM), field emission gun-transmission electron microscopy (FEG-TEM) and atomic force microscopy (AFM) techniques. The microscopic observations revealed by the SEM and TEM suggested for complete dispersion of thermally reduced graphene oxide (TRGO) into the PVA film. The XRD studies of nanocomposite revealed an enhanced crystallinity in comparison to the native PVA film. The thermal reduction process enabled homogenous dispersion of reduced graphene oxide sheets and improved the electrical conductivity of nanocomposites due to their low damage level of conjugate-structures. As a result, the percolation threshold of PVA-TRGO nanocomposites was ∼0.189 wt% which is lower than the presently reported one (2 to 10 wt%). At the TRGO content of 2 wt%, the electrical conductivity of PVA-TRGO nanocomposite reached from 0.2491 to 0.2631Scm−1. The enhancement mechanism of the composite was explained by the existence of multi-hydrogen bonds between the hydroxyl (-OH) groups of PVA and oxygen-containing functional groups of graphene oxide (GO). The AC electrical conductivity and mechanical studies results indicated that the performance of nanocomposites was significantly improved as compared to the native PVA and offered the possibilities to use the prepared nanocompsoite films to be used in electronic devices.

Structure and topography of thermally reduced graphene oxide reinforced poly(vinyl alcohol‐g‐acrylonitrile) films and study of their mechanical and electrical behavior

Thermally reduced graphene oxide (TRGO) reinforced poly(vinyl alcohol‐g‐acrylonitrile) (PVA‐g‐PAN) films were prepared by carrying out graft co‐polymerization of acrylonitrile onto poly(vinyl alcohol) in a thermally and mechanically stabilized and reduced suspension of GO using potassium persulfate as initiator and N,N′methylene bis acrylamide as a crosslinking agent. The structural and morphological characterization of the TRGO reinforced (PVA‐g‐PAN) films were performed using fourier transform infrared (FTIR) spectroscopy, X‐ray diffraction (XRD), Raman spectroscopy, scanning electron microscopy (SEM), field emission gun‐transmission electron microscopy (FEG‐TEM), zeta potential analysis, dynamic light scattering (DLS) measurements, and atomic force microscopy techniques. The FTIR analysis confirmed the presence of TRGO, PVA, and PAN in the prepared nanocomposite film, whereas zeta potential and DLS analysis provided information regarding the charge carried and particle size distribution of the TRGO nanosheets. The effect of variation in TRGO content on electrical conductivity, and mechanical properties of the TRGO reinforced (PVA‐g‐PAN) films were also investigated. The optimum tensile strength and Young's modulus of the 10%TRGO‐reinforced nanocomposite were found to be 85.06 and 33.33 MPa, respectively which were significantly higher than those for the native PVA‐g‐PAN film. The microhardness of the same nanocomposite was found to be 9.86 kg/mm2 which is nearly double than that of the native graft copolymer film. POLYM. COMPOS., 40:E409–E421, 2019. © 2018 Society of Plastics Engineers

Magnesium oxide nanoparticle-loaded polycaprolactone composite electrospun fiber scaffolds for bone–soft tissue engineering applications: in-vitro and in-vivo evaluation

The objective of the present investigation was to assess the potential of magnesium oxide nanoparticle (MgO NP)-loaded electrospun polycaprolactone (PCL) polymer composites as a bone–soft tissue engineering scaffold. MgO NPs were synthesized using a hydroxide precipitation sol-gel method and characterized using field emission gun–scanning electron microscopy/energy-dispersive x-ray spectroscopy (FEG-SEM/EDS), field emission gun–transmission electron microscopy (FEG-TEM), and x-ray diffraction (XRD) analysis. PCL and MgO–PCL nanocomposite fibers were fabricated using electrospinning with trifluoroethanol as solvent at 19 kV applied voltage and 1.9 ml h−1 flow rate as optimized process parameters, and were characterized by FEG-TEM, FEG-SEM/EDS, XRD, and differential scanning calorimetry analyses. Characterization studies of as-synthesized nanoparticles revealed diffraction peaks indexed to various crystalline planes peculiar to MgO particles with hexagonal and cubical shape, and 40–60 nm size range. Significant improvement in mechanical properties (tensile strength and elastic modulus) of nanocomposites was observed as compared to neat polymer specimens (fourfold and threefold, respectively), due to uniform dispersion of nanofillers along the polymer fiber length. There was a remarkable bioactivity shown by nanocomposite scaffolds in immersion test, as indicated by formation of surface hydroxyapatite layer by the third day of incubation. MgO-loaded electrospun PCL mats showed enhanced in-vitro biological performance with osteoblast-like MG-63 cells in terms of adhesion, proliferation, and marked differentiation marker activity owing to greater surface roughness, nanotopography, and hydrophilicity facilitating higher protein adsorption. In-vivo subcutaneous implantation study in Sprague Dawley rats revealed initial moderate inflammatory tissue response near implant site at the second week timepoint that subsided later (eighth week) with no adverse effect on vital organ functionalities as seen in histopathological analysis supported by serum biochemical and hematological parameters which did not deviate significantly from normal physiological range, indicating good biocompatibility in-vivo. Thus, MgO–PCL nanocomposite electrospun fibers have potential as an efficient scaffold material for bone–soft tissue engineering applications.

Green synthesis of seaweed surfactant based CdO-ZnO nanoparticles for better thermal and photocatalytic activity

Green synthesis of seaweed-macro algae based cadmium oxide-zinc oxide (SCZ) nanoparticles was prepared by the simple chemical precipitation method. The functional group characteristics and crystalline properties of the nanoparticles were analyzed by Fourier transform infra-red spectroscopy and X-ray diffraction analysis. The optical band gap energy of SCZ nanoparticles showed in lower value (3.11 eV), these can be due to the incorporation of seaweed (SW) and cadmium oxide (CdO). Small fiber like seaweed constituent was entangled over the CdO-ZnO nanoparticles, these were confirmed with High resolution scanning electron microscope and Field emission gun-transmission electron microscope analysis. The particle size of SCZ nanoparticles was obtained in the range of 20–50 nm. Thermal characteristics of SCZ nanoparticles have higher stability than SW and SW-ZnO. The photo catalytic degradation performance of SCZ nanoparticles was significantly improved and their efficiency was achieved to 99.57, 95.2 and 94.3%, under sunlight, visible light and UV light irradiation using RB198 dye molecules, respectively. The higher percentage of RB198 dyes degraded within 15 min interval under sunlight irradiation. In addition, their photo degradation characteristics of nanoparticles were further tested to pollutants of phenol solution. These results indicate that the surfactant based CdO-ZnO nanoparticles could be employed as an efficient photo catalyst for the degradation of industrial effluents.

Evolution of thiol-capped gold nanoclusters into larger gold nanoparticles under electron beam irradiation

We report in situ transformation of glutathione-capped red-fluorescent gold nanoclusters (AuNCs) into larger gold nanoparticles (AuNPs) embedded on a copper grid under high energy electron beam of Field Emission Gun Transmission Electron Microscope (FEG-TEM). Electron beam irradiation causes coalescing of individual finer AuNCs into bigger discrete AuNPs as a function of electron dose rate and time. The coalescence was closely studied over time and the mechanism is discussed. The study will help to understand the structural and morphological changes that occur in AuNCs inside FEG-TEM due to prolonged electron beam exposure.

Sb2S3 Nanorods Based Electrochemical Catalyst for Triiodide Reduction in Dye-Sensitized Solar Cells

In this study, we report on the synthesis of Sb2S3 nanorods by using a hot-injection process in short processing time (1 h). Synthesized Sb2S3 nanorods are used as an electrochemical catalyst (counter electrode) for triiodide reduction in dye-sensitized solar cells (DSSCs). X-ray diffraction and field emission gun-transmission electron microscopy (FEG-TEM) analysis confirm the crystallinity of synthesized nanorods. The size and shape of synthesized materials are measured with the help of FEG-TEM analysis. Electrocatalytic activity study of Sb2S3 nanorods demonstrates the suitability of this material as an alternative electrochemical catalyst for DSSCs. The photoconversion efficiency of DSSCs fabricated using Sb2S3 as counter electrodes is found to be 4.1%.

Size specific emission in peptide capped gold quantum clusters with tunable photoswitching behavior.

Three different types of fluorescent gold clusters (namely blue, green and red emitting) have been prepared from a gold precursor (chloroauric acid) under moderate conditions in aqueous medium. A cysteine containing dipeptide has been used for the formation of these quantum clusters as this peptide molecule contains a thiol group in the side chain to cap these nascently formed clusters and the free amino and carboxylic moieties assist in water solubility. Thus, the clusters are also environmentally friendly as the capped peptide is made up of only naturally occurring protein amino acids. These clusters have been well characterized by using UV-visible, fluorescence, X-ray photoelectron spectroscopy (XPS)spectroscopy, matrix-assisted laser desorption ionization time-of-flight mass spectrometry (MALDI-TOF MS) and ultrahigh resolution field emission gun-transmission electron microscopy (UHR-FEG-TEM). Arrangements of gold atoms and their interaction with the corresponding ligands in three different fluorescent clusters have been predicted computationally. The excited state behavior of three different clusters has also been studied using time dependent density functional theory (TD-DFT). Time correlated single photon counting (TCSPC) and computational studies suggest intersystem crossing (S1 → T1) in the case of red-emitting Au23 clusters. Interestingly, these gold clusters exhibit semiconducting and photoswitching properties (Ion/Ioff), which are shown to be controlled by varying the size of these clusters. This holds future promise of using these gold cluster based nanomaterials for optoelectronic applications.

Influence of Li Additions on the Microstructure and Corrosion Response of 2XXX Series Aluminium Alloys

This paper discusses two Al-Cu alloys for aerospace applications, one of which has an addition of between 1.6 and 2.0 wt.% of Li. The alloys are AA2024-T3 (Al-Cu) and AA2099-T8E77 (Al-Cu-Li). Microstructural analysis via Field Emission Gun Transmission Electron Microscope (FEGTEM) and Field Emission Gun Scanning Electron Microscope (FEGSEM) utilising Energy Dispersive Spectroscopy (EDS) and Electron Backscatter Detector (EBSD) techniques have been used to characterise the two microstructures and phases contained within them. Anodic polarisation and immersion testing in a 3.5 wt.% NaCl solution have been carried out and a comparison of the corrosion mechanisms has been made. AA2024-T3 had a fine, equiaxed grain structure, whereas AA2099-T8E77 had a substantial amount of recrystallized grains. Finer grains were also observed on AA2099-T8E77, however, the vast majority were larger than the maximum detection limit of the EBSD technique. Intergranular and pitting corrosion were observed on both alloys following immersion testing, however, the intergranular corrosion (IGC) was more prominent on AA2099-T8E77. Anodic polarisation indicated that AA2024-T3 was more noble, highlighting that the Li-containing AA2099-T8E77 alloy was more susceptible to corrosion. The T1 (Al2CuLi) phase within AA2099-T8E77 was seen to be highly active following immersion and anodic polarisation tests. The corrosion pits on AA2099-T8E77 were seen to propagate to a depth of ~ 80 to 100 μm, with a maximum of 126 μm recorded. For AA2024-T3 the maximum depth recorded was 77 μm and the average depth was between 60 and 70 μm.

Controlling Dielectric and Magnetic Properties of PVdF/Magnetite Nanocomposite Fibre Webs

The ability of filtration and separation media containing fibres to remove impurities from oil, water, and blood can be enhanced using magnetic fields. The ability to regulate the dielectric and magnetic behaviour of fibrous webs in terms of superparamagnetic or ferromagnetic properties by adjusting material composition is fundamental to meeting end-use requirements. Electrospun fibres were produced from PVdF (polyvinylidene fluoride) and nanomagnetite (Fe3O4nanoparticles) from solutions of PVdF in dimethylacetamide containing Fe3O4nanoparticle contents ranging from 3 to 10 wt%. Fibre dimensions, morphology, and nanoparticle agglomeration were characterised by environmental scanning electron microscopy (ESEM) and field emission gun transmission electron microscopy (FEGTEM). Dielectric behaviour of the fibre webs was influenced by web porosity and the Fe3O4nanoparticle content. Impedance analysis of the webs indicated an increase in dielectric constant of∼80% by the addition of 10 wt% Fe3O4nanoparticles compared to 100 wt% PVdF. The dielectric constants of the webs were compared with those obtained from the theoretical mixing models of Maxwell and Lichtenecker. Vibrating sample magnetometer (VSM) magnetisation measurements indicated a blocking temperature above 300 K suggesting ferrimagnetic rather than superparamagnetic behaviour as a result of Fe3O4nanoparticle agglomeration within fibres.

Effect of Annealing Temperature on the Photocatalytic Activity of TiO2 Thin Films

TiO2 thin films were spin coated on soda-lime-silica glass substrates under identical conditions and then annealed for 2h in air in the range of 300°-500°C in increments of 50°C. The mineralogical, morphological, optical, and photocatalytic properties then were assessed for the films. The techniques used were glancing-angle X-ray diffraction (GAXRD), field emission gun transmission electron microscopy (FEGTEM), field emission scanning electron microscopy (FESEM), atomic force microscopy (AFM), UV-VIS spectrophotometry (UV-VIS), and methylene blue (MB) degradation. The films had a consistent thickness of ∼255nm. Anatase peaks recrystallised at the annealing temperature of 400°C, with the crystallinity increasing with increasing annealing temperatures. Although recrystallisation caused a significant increase in grain size, the crystalline films showed only a slight increase in the grain size with increasing annealing temperatures. In contrast, the surface roughness of all of the films increased significantly with increasing annealing temperatures. This was associated with increased grain faceting, which was supported by the X-ray diffraction data.All of the films showed high transparency in the visible region, with the optical indirect band gap of the crystalline films decreasing slightly from 3.49eV to 3.43eV with increasing annealing temperatures. Four regimes of photocatalytic performance could be identified, which depended principally on the degree of crystallinity and the level of contamination. In short, a blank was used to negate heating effects, the amorphous films were inert, the onset of crystallisation established photoactivity, and the photoactivity of the films annealed at 400°-500°C decreased in a trend consistent with the trends in increasing grain size, increasing surface roughness, increasing crystallinity, decreasing band gap, and increasing contamination. Since this consistency was the case, these variables could not be decoupled.For the samples that were fabricated using the specified materials and methods, characterised, and tested, the optimal temperature for annealing was found to be 400°C.

Nanometric Scale Investigation of Phase Transformations in Advanced Steels for Automotive Application

The current trend toward producing lighter vehicles in the automotive industry is driven by the need to conform to the new exhaust emission control regulations. This objective presents a challenge to steel manufacturers. The difficulty lies in designing new alloys with an optimum strength/formability/cost balance for the various components. Here, the key to success lies in controlling the steel microstructure and especially the phase transformations at the smallest possible scale. Among the different alloying elements, light elements such as carbon and boron are of prime importance due to their major effects on the kinetics of phase transformations. Characterization tools combining high spatial and analytical resolution such as secondary ion mass spectrometry (SIMS) and field emission gun-transmission electron microscopy (TEM) were used. In this article, the examples presented are as follows. (1) Boron segregation and precipitation effects to control hardenability in martensitic steels. (2) Local carbon distribution in advanced high-strength steels, with a specific emphasis on martensite tempering. Links have been established between the boron and carbon distribution and the formability.