Transmission Electron Microscope-energy Dispersive Spectrometer Research Articles

Experimental Study of the Thermally Grown Oxide and Interface of Thermal Barrier Coatings Using TEM In-Situ Heating.

Thermal barrier coating (TBC) materials play important roles in gas turbine engines to protect the Ni-based superalloys from high-temperature airflow damage. In this work, the nano-mechanism of TBC failure is analyzed. A scanning transmission electron microscopy-energy dispersive spectrometer (STEM-EDS)-based analysis method was used to study the influence of element migration on the deformation behavior of the bond-coat (BC) layer during heating. The content of elements in the same region varied greatly at different temperatures, which could prove the contribution of element migration to the deformation of the BC layer. TEM in-situ heating experiments were designed and carried out to study the deformation behavior near the ceramic topcoat (TC)/thermally grown oxide (TGO) and the TGO/BC interface. The TC/TGO interface was deformed violently during heating, and obvious deformation occurred at 100 °C, while the TGO/BC interface was relatively stable. A subset geometric phase analysis method was used for full field-strain measurement. The strain value near the TGO/BC interface was relatively small and did not change significantly at lower temperatures. The TC/TGO interface is more unstable and easier to deform than the TGO/BC interface. The stress and strain evolution in the internal region of TGO at high temperatures was quantitatively analyzed. The TGO layer has a tensile stress of GPa magnitude along the interface direction at the peak position, and the shear stress is small.

Mechanistic insights into rapid sulfite activation with cobalt sulfide towards iohexol abatement: Contribution of sulfur conversion

Recently, activation of sulfite for production of sulfate radical (SO4•−) has emerged for abatement of organic contaminants. Herein, with regard to the excellent activation efficacy of Co(II) and the enhanced electron donating capacity by sulfur species, cobalt sulfide (CoS) was proposed for efficient sulfite activation towards iohexol abatement via SO4•−–based advanced oxidation processes. CoS exhibited better activation performance than typical CoO and Co3O4 with a sharp decline of iohexol within 0.5 min, for which superior electron transfer efficiency of CoS was confirmed by Electrochemical impedance spectroscopy (EIS). The contribution of SO4•− and HO• to iohexol abatement was demonstrated by radical quenching experiment and Electron paramagnetic resonance (EPR). The influences of various parameters (solution pH, CoS and sulfite dosage, iohexol concentration), co-existing anions (HCO3−, HPO42−, Cl− and NO3−) and humic acid on iohexol abatement were investigated, as well as, the effect of different water matrixes on iohexol abatement was also evaluated. A possible mechanism was proposed based on ionic strength experiment, Transmission electron microscope-Energy dispersive spectrometer (TEM-EDS), X-ray photoelectron spectroscopy (XPS) and Raman. The superior activation performance of CoS could be attributed to the inner-sphere complexation between CoS and sulfite and enhanced > Co(III)/>Co(II) recycling induced by reductive sulfur species via rapid electron transfer. In addition, the iohexol degradation pathways were analyzed. This study highlights the contribution of sulfur conversion in the sulfite activation process and is expected to provide a facile CoS enhanced sulfite activation method for efficient abatement of organic contaminants.

Nonselective uptake of silver and gold nanoparticles by wheat

Metallic nanoparticles (NPs) show unique reactivity to crop plants, but the uptake mechanisms remain unclear. We quantitatively evaluated the phytoavailability of particles to wheat (Triticum aestivum L.) in hydroponics upon exposure to AgNPs (15 nm) or AuNPs (13 and 33 nm). Particles were physically separated from the released Ag ions by a dialysis membrane, under which particle-specific uptake of AgNPs could be discerned. Plants did not differentiate AgNPs and AuNPs during particle uptake, with uptake rate constants of 1.1 ± 0.1, 1.2 ± 0.3, and 1.2 ± 0.1 L kg−1 h−1 for AgNPs, AuNPs (13 nm), and AuNPs (33 nm), respectively. We found little effect of particle size (13 or 33 nm AuNPs) or core composition (Ag or Au) on particle bioavailability. Plants stimulated the subsequent uptake of Evans blue stain and showed cell damage in root tips. These results imply similar physiological processes involved in particle-specific uptake of AgNPs and AuNPs. The internalization of particles was further confirmed by single particle inductively coupled plasma mass spectrometry (spICP-MS) and transmission electron microscope-energy dispersive spectrometer (TEM-EDS) analysis. The work here builds the knowledge base for the nature of particle-specific uptake of different NP types by crop plants.

Enhancing stress corrosion cracking resistance of low Cu-containing Al-Zn-Mg-Cu alloys by slow quench rate

The corrosion behavior of Al-Zn-Mg-Cu alloy on different Cu content and quench rate has been investigated by inter-granular corrosion (IGC), exfoliation corrosion (EXCO), and stress corrosion cracking (SCC) test, and combined with scanning electron microscopy (SEM) and transmission electron microscopy-energy dispersive spectrometer (TEM-EDS) microstructural observation. The results showed that slow quench rate can effectively improve the SCC resistance of low Cu-containing alloys, especially decreasing crack propagation rate (the SCC propagation velocity (VII) is about an order of magnitude lower for slowly-quenched low Cu-containing alloys than fast quenched one), while it has less effect on high Cu-containing alloys. The IGC, EXCO, and SCC resistance with different Cu content and quench rate are analyzed by distribution, size and Cu content of grain boundary precipitates and width of precipitate-free zone. The corrosion mechanism has been studied in detail.

Characterisation of silver release from nanoparticle-treated baby products

ABSTRACTWe tested six kinds of commercially available baby products containing nano-silver and divided them into two categories: baby food containers and baby oral care products, according to usage. We measured the total mass of silver, particle size, particle number concentration and the mobility under different simulated conditions. The total mass of silver in baby products and migration solutions was quantified by ICP-MS analysis, and the size of the migrated particles was investigated by single particle ICP-MS and transmission electron microscopy-energy dispersive spectrometer. Nano-silver has different migration behaviour in different materials, and the total mass of silver released in 3% acetic acid was generally highest for plastic material, while highest in 10% ethanol for silicone material. For baby food containers and baby oral care products, the total amount of silver in the migration solutions varied from 2.98 to 126.46 ng/dm2 and from 2.01 to 2.83 ng/g, respectively. The research shows that the use of baby products containing silver may expose babies to silver nanoparticles.

Improved corrosion resistance of CoCrMo alloy with self-passivation ability facilitated by carbon ion implantation

Herein, carbon ion implantation was employed as a method for improving the corrosion resistance of CoCrMo alloy. The structural changes emerging as a result of carbon ion implantation were investigated by using grazing incidence X-ray diffraction (GIXRD) and high-resolution transmission electron microscopy (HRTEM). The corrosion behavior was characterized by electrochemical impedance spectroscopy (EIS) and polarization tests. Following the corrosion test, HRTEM and scanning transmission electron microscopy-energy dispersive spectrometer (STEM-EDS) were employed for the analysis of corrosion related structural and compositional change at the nanometer scale. The results showed that carbon ion implantation promotes surface amorphization in the CoCrMo alloy. In fact, the corrosion resistance of CoCrMo alloy improves significantly, as evidenced by the order of magnitude reduction in corrosion current density (icorr). The surface amorphization improves the corrosion resistance of CoCrMo alloy through three mechanisms: the amorphous layer formed (i) acts as barrier layer, (ii) suppresses localized corrosion, and (iii) facilitates spontaneous formation of a passive layer (self-passivation).

Synthesis of bulk nanocrystalline samarium hexaboride

This study reports on the preparation and consolidation of nano-sized SmB6 powders via mechanochemical synthesis (MCS) performed at room-temperature using Sm2O3–B2O3–Mg powder blends followed by cold pressing/pressureless sintering. Milling duration was used as an MCS parameter to reveal the optimum production conditions of nanoscale SmB6 powders, which were subsequently subjected to HCl leaching to remove the intermediate products. Microstructural, physical and magnetic properties of the SmB6 powders were evaluated using X-ray diffractometer (XRD), differential scanning calorimeter (DSC), particle size analyzer (PSA), stereomicroscope (SM), scanning electron microscope (SEM), transmission electron microscope/energy dispersive spectrometer (TEM/EDS), atomic absorption spectrometer (AAS), surface area analyzer (SAA) and vibrating sample magnetometer (VSM). The bulk properties of the SmB6 sintered from nanocrystalline SmB6 powders with an average particle size of ∼80nm and a minimum purity of 99.99% were described in terms of their microstructure, density, electrical resistivity, surface roughness, friction coefficient, hardness and wear rate.

Preparation of Fe3O4/MnOOH core–shell nanoparticles by a high-frequency impinging stream reactor

Well-defined Fe3O4/MnOOH nanoparticles with 61.1emu·g−1 in magnetization intensity and 90.53m2·g−1 in surface area have been synthesized by a new-style of high-frequency impinging stream (HFIS) reactor. In this reactor, two streams first collided together to form nano Fe3O4 suspension, which subsequently flew through an S-shaped main channel to generate high-frequency reversing high-gravity fields. At the same time, 24 thin liquid sheets impinged into the main channel at the frequencies higher than 100Hz to create nano Fe3O4/MnOOH colloids. The obtained powders were characterized by transmission electron microscopy/energy dispersive spectrometer (TEM/EDS), X-ray diffraction (XRD), Brunner–Emmet–Teller (BET) and vibrating sample magnetometer (VSM). Experimental results indicated that low coating ratio prolonged the induction period of heterogeneous nucleation. The high-frequency impingements of 24 thin liquid sheets greatly accelerated the macro-mixing and the initial dispersion. The high-frequency reversing high-gravity fields promoted the meso- and micro-mixing. As a result, nano Fe3O4 cores were fleetly and uniformly covered by MnOOH precursor. As a continuously operated and static high-gravity reactor, the high-frequency impinging stream (HFIS) reactor is being developed to the large-scaled and low-cost production of various nanocomposites.

M3B2 and M5B3 Formation in Diffusion-Affected Zone During Transient Liquid Phase Bonding Single-Crystal Superalloys

Precipitates in the diffusion-affected zone (DAZ) during transient liquid phase bonding (TLP) single-crystal superalloys were observed and investigated. Small size and dendritic-shaped precipitates were identified to be M3B2 borides and intergrowth of M3B2/M5B3 borides. The orientation relationships among M3B2, M5B3, and matrix were determined using transmission electron microscope (TEM). Composition characteristics of these borides were also analyzed by TEM energy-dispersive spectrometer. Because this precipitating phenomenon deviates from the traditional parabolic transient liquid phase bonding model which assumed a precipitates free DAZ during TLP bonding, some correlations between the deviation of the isothermal solidification kinetics and these newly observed precipitating behaviors were discussed and rationalized when bonding the interlayer containing the high diffusivity melting point depressant elements and substrates of low solubility.

Radio-frequency thermal plasma preparation of nano-sized Ni catalysts supported on MgO nano-rods for partial oxidation of methane

Nano-sized Ni catalysts supported on MgO nano-rods were prepared by RF thermal plasma treatment of Ni metal (~5μm) and MgO powders (~100nm). For this purpose, each powder was ball-milled at pre-set molar ratio of 5:5, and then, injected into RF thermal plasma generated at the power level of ~25.5kW. From FE-SEM (field emission scanning electron microscopy) and TEM-EDS (transmission electron microscopy-energy dispersive spectrometer) analyses, it is found that as-prepared catalysts mainly consist of very small Ni particles (<100nm) attached to MgO nano-rods with diameter of 10–20nm. In order to investigate their catalytic performance, methane partial oxidation experiment was also conducted at atmospheric pressure, 400°C<T<800°C and reaction mixture of CH4:O2=2:1mol% with Ar diluents. Test results revealed that as-prepared MgO nano-rods supported Ni catalysts showed thermodynamic equilibrium values of methane conversion rate (>99%) and high selectivity more than 90% and 80% for CO and H2 at T=750°C, respectively. In spite of relatively high Ni content of 50mol%, little carbon deposition is found in the TEM images and the derivative curves of TGA (thermogravimetry analysis) data for as-prepared catalysts after 24h test at 750°C, which are attributed to the structural features of Nano-sized Ni catalysts supported on MgO nano-rods prepared by RF thermal plasma.

Preparation and optical properties of Ta 2O 5− x thin films

Thin films of tantalum pentoxide (Ta 2O 5− x ) were deposited on glass substrates by RF magnetron sputtering under different Ar/O 2 flow ratios. Characterization of the coatings was investigated by UV–vis spectroscopy, ellipsometry (at a wavelength of 632.8 nm), Fourier transform infrared (FTIR) spectroscopy, atomic force microscope (AFM), and transmission electron microscope energy dispersive spectrometer (TEMEDS). It was obtained that the Ta 2O 5− x films produced with different Ar/O 2 ratios ranging from 10/6 to 8/10 exhibit good visible optical transmissions, 80–90%. The optical band gap of the films from 10/6 to 8/10 decreased from 4.25 to 3.70 eV from the transmission spectra. The film thickness decreased from 108.1 to 99.4 nm and refractive index increased from 2.02 to 2.15 for the films produced with different Ar/O 2 ratios ranging from 10/6 to 8/10. In addition, the results indicate that the films prepared at high Ar/O 2 flow ratios (8/10) have featureless peak of suboxide for FTIR spectra and exhibit atomic ratio Ta:O = 1:2.41 for TEMEDS analysis.

Synthesis and catalytic properties of perovskite-related phases in the La–Sr–Co–Cu–Ru–O system

A series of oxides of the composition La0.8Sr0.2Co1–2yCuyRuyO3 with the perovskite structure were synthesized and characterized by their X-ray diffraction (XRD) patterns and by element analysis in a transmission electron microscope (TEM) equipped with an energy-dispersive spectrometer (EDS). The XRD and TEM–EDS studies confirmed that almost monophasic samples with the perovskite structure having rhombohedral (hexagonal) symmetry were obtained for 0 ⩽y⩽ 0.20, although the simultaneous formation of a by product with the K2NiF4-type structure was observed for high y values. The lattice parameters and rhombohedral distortion increased monotonically with increasing y value due to the fact that the average ionic radius of the substituting Cu/Ru pair is larger than that of the host Co ion. Temperature-programmed desorption (TPD) studies showed that the substitution of the Cu/Ru pair for Co caused a decrease in the amount of oxygen desorbed from the bulk of the oxide, and the catalytic activity for CO oxidation and CO–NO reactions decreased. The Cu/Ru substitution did, however, selectivity increase the N2 formation and decreased that of N2O in the CO–NO reactions. Synthesis of K2NiF4-type oxides with the overall compositions (La0.8Sr0.2)2Co0.50Cu0.50–zRuzO4 with z= 0.05 and 0.10 was also attempted. In both cases, tetragonal K2NiF4-type oxides having a composition close to (La0.8Sr0.2)2(Co,Cu)0.97Ru0.03O4 were obtained, implying that the solubility of Ru into the given K2NiF4-type framework is very low.