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In this study, Boron Nitride Quantum Dots (BNQDs) are successfully synthesized via the hydrothermal method. Additionally, the hydrothermal method is employed to synthesize BNQDs decorated TiO2 nanograss (BNQDs/TiO2 NG) from BNQDs decorated TiO2 (BNQDs/TiO2). To validate the synthesis of different BNQDs samples, fluorescence spectroscopy (FL) is performed, revealing a strong quantum confinement effect resulting from variations in the precursor ratio. The bandgap energies of TiO2, BNQDs/TiO2, and BNQDs/TiO2 NG are determined using UV–Vis diffuse reflectance spectroscopy (UV-DRS), demonstrating a reduction in the band gap. A smaller band gap corresponds to a higher thermal conductivity, as there is a negative correlation between thermal conductivity and band gap energy. The study suggests that BNQDs/TiO2 NG exhibit higher thermal conductivity compared to TiO2 and BNQDs/TiO2. X-ray photoelectron spectroscopy (XPS) reveals the elemental composition of both BNQDs and TiO2, including Ti–O, B–N and B–O bonds. High Resolution Transmission Electron Microscopy (HR-TEM) is utilized to examine the morphological attributes of BNQDs/TiO2 NG. The crystalline structure of the synthesized composites is ascertained using X-ray diffraction (XRD). The photocatalytic degradation of methylene blue (MB) by TiO2, BNQDs/TiO2, and BNQDs/TiO2 NG under visible light is also compared. Based on the results, BNQDs/TiO2 NG is determined to be an effective material for treating wastewater containing organic dyes. [ABSTRACT FROM AUTHOR]

(Ba0.5Sr0.5)(Co0.8Fe0.2)O3−δ (BSCF) with mixed ionic and electronic conductivity is promising as oxygen separation membrane. However, its exceptional oxygen permeability is linked to the cubic perovskite phase, which destabilizes below 825 °C. This work is concerned with the stabilizing effect of partial B-site substitution in BSCF by Ti (10%) and Nb (5% and 10%). In addition, the effect of B-site substoichiometry on the formation of CoO precipitates as nucleation sites for other secondary phases is studied. The focus of this work is laid on the analysis of the phase constitution in bulk material between 600 and 800 °C. Scanning electron microscopy and (scanning) transmission electron microscopy with high spatial resolution in combination with energy-dispersive X-ray spectroscopy are applied which allow to detect even small volume fractions of secondary phases. It is confirmed by quantitative analysis that Ti and Nb substitution reduces the formation of secondary phases up to ~ 95%. There is a solubility limit of Nb in BSCF, which leads to the precipitation of Nb-rich precipitates already at 5% Nb substitution in contrast to Ti which is fully soluble even at 10% substitution. Despite of that, BSCF doped with 5% Nb in combination with 5% substoichiometric B-site occupation is the most promising material, because it shows the lowest overall volume fraction of secondary phases (~ 0.8 vol% at 700 °C) and an almost negligible degradation rate in additionally recorded long-term resistivity measurements. [ABSTRACT FROM AUTHOR]

(Ba0.5Sr0.5)(Co0.8Fe0.2)O3−δ (BSCF) with mixed ionic and electronic conductivity is promising as oxygen separation membrane. However, its exceptional oxygen permeability is linked to the cubic perovskite phase, which destabilizes below 825 °C. This work is concerned with the stabilizing effect of partial B-site substitution in BSCF by Ti (10%) and Nb (5% and 10%). In addition, the effect of B-site substoichiometry on the formation of CoO precipitates as nucleation sites for other secondary phases is studied. The focus of this work is laid on the analysis of the phase constitution in bulk material between 600 and 800 °C. Scanning electron microscopy and (scanning) transmission electron microscopy with high spatial resolution in combination with energy-dispersive X-ray spectroscopy are applied which allow to detect even small volume fractions of secondary phases. It is confirmed by quantitative analysis that Ti and Nb substitution reduces the formation of secondary phases up to ~ 95%. There is a solubility limit of Nb in BSCF, which leads to the precipitation of Nb-rich precipitates already at 5% Nb substitution in contrast to Ti which is fully soluble even at 10% substitution. Despite of that, BSCF doped with 5% Nb in combination with 5% substoichiometric B-site occupation is the most promising material, because it shows the lowest overall volume fraction of secondary phases (~ 0.8 vol% at 700 °C) and an almost negligible degradation rate in additionally recorded long-term resistivity measurements. [ABSTRACT FROM AUTHOR]

In this study, a facile, cheap, scalable, and environmentally friendly method has been developed to prepare nanostructured TiO2 coatings with a high catalytic activity. In addition, a protocol to characterize the prepared films in order to obtain consistent results between their texture, their structure, their microstructure, and their catalytic behavior has been established. For that, two types of TiO2 coatings have been fabricated by applying once TiO2 aqueous suspensions, prepared from commercial nanopowders, by immersion followed by an adequate thermal treatment. The first type of films is constituted by coatings with anatase as single phase, and the second one by films with a rutile molar fraction of XR = 0.07 ± 0.02, determined from grazing incidence X-ray diffraction (GI-XRD) data. High spatial resolution chemical imaging, obtained by confocal Raman microscopy (CRM), of the surface and of the cross section for the films showed a good distribution of rutile without any segregation of this phase. Furthermore, high resolution electron microscopy (HREM) confirmed the presence of anatase/rutile biphasic domains in those areas in which both phases were previously found together by CRM. In addition, the catalytic data fit to a first-order kinetic model with high catalytic reaction constants (k′), especially when rutile is present. Furthermore, consistent results have been found in this study between the textural, structural, and microstructural studied features with the catalytic properties for the prepared TiO2 films. [ABSTRACT FROM AUTHOR]

Freestanding wurtzite GaN nanoprotruded microbelts with GaO core, with typical thickness 1-10 μm, and length of few millimeters are synthesized by thermal annealing of Ga metal and subsequent reaction with ammonia at a low flow rate. They are of distinctive rectangular shape with a typical width of 10-100 μm. Thickness of the belt is about 1/10th of the width and length up to a few millimeters. The GaN, GaO layers and the GaN-GaO interface are characterized by high-resolution transmission electron microscopy after focused ion beam sectioning of the belt. Initially, GaO nucleates after reaction with the O available in the environment, and subsequent reaction with NH results in the formation of core-shell structure in the catalyst-free vapor-solid growth process. Having a low-symmetry phase, GaO can grow only in certain preferred directions thus controlling the final morphology of the belt. Nanoscale protrusions ~50-100 nm found on the surface of the belts could be an ideal system for building functional devices. [ABSTRACT FROM AUTHOR]

The microstructural evolution of Al-2.24 Cu-1.42 Mg-0.9 Fe-0.9 Ni (AA2618) alloy after 195 °C/18 h aging, as well as after 180 and 240 °C/100 h creep, has been studied by transmission electron microscopy and high resolution electron microscopy (HREM). The Guinier-Preston-Bagaryatsky (GPB) zones/co-clusters, S″, S, and AlFeNi phases co-exist in the alloys after the 195 °C/18 h aging. After creep, precipitates become coarser and the transformation of GPB zones/co-clusters and S″ to S phase take place. A large number of GPB zones/co-clusters as those in aging state exist after 180 °C/100 h creep which possibly dynamically precipitates during the creep process. After the 240 °C/100 h creep, most of the precipitates are S variants with a few GPB zones and S″ phase. More dislocations appear upon which precipitate colonies form after creep. HREM images show that most of the early precipitates less than about 5 nm cannot exhibit perfect lattice image for the existence of stress. However, certain GPB/co-clusters possessing coherent relationship with the matrix can also be observed. HREM demonstrates that certain S particles viewed along [100] and [013] have classic orientation relationship with the matrix, and that those upon the dislocations depart from the standard orientation. [ABSTRACT FROM AUTHOR]

In this article the authors discuss aspects of a study showing the first experimental evidence of single-layered niobium nitride (NbN) Guinier and Preston (GP) zones in steel. The team used high-resolution electron microscopy (HREM) and atom probe tomography (APT) to analyze low-alloyed steel samples that were prepared via a combination of homogenization, water quenching, and annealing processes. Imaging results are discussed.

Nanosized Se and Te, respectively, doped titania was prepared by homogeneous hydrolysis of titanium oxo-sulfate with urea in aqueous solutions in the presence of amorphous selenium and tellurium. The prepared samples were annealing at temperature 200 and 400 °C. The structure of prepared samples was characterized by X-ray powder diffraction (XRD), selected area electron diffraction (SAED), surface area (BET), and porosity determination (BJH). The morphology and microstructure characteristics were obtained by scanning electron microscopy (SEM) and high-resolution electron microscopy (HRTEM). The method of UV/Vis diffuse reflectance spectroscopy was employed to estimate band-gap energies of the Se and Te-doped titania. The photocatalytic activity of the prepared samples was assessed by the photocatalytic decomposition of Orange II dye in an aqueous slurry during irradiation at 365 and 400 nm wavelength. The best photocatalytic activity in UV and visible area exhibit the Se and Te-doped titania samples labeled TiSe3 (~11.5 wt% Se) and TiTe3 (~8.0% Te), respectively. [ABSTRACT FROM AUTHOR]

This article reports the use of Gallium phosphide (GaP) and Ag/GaP nanoparticles, which can harness visible light to decompose organic dye in aqueous solution. The Ag(1.139 wt%)/GaP and Ag(5.225 wt%)/GaP nanoparticles were prepared by the liquid phase reduction of silver nitrate with hydrazine hydrate. The application of X-ray fluorescence and high-resolution transmission electron micrograph morphology has provided direct evidence of the presence of silver on the GaP nanoparticles. Under visible light, the experiments on the photocatalytic degradation of crystal violet in solution over the GaP and Ag/GaP nanoparticles were carried out. The results reveal that small size and number density of Ag domains deposited on GaP nanoparticles have enhanced photocatalytic efficiencies, as compared to large size and number density of Ag domains. This study suggests the potential of both GaP and Ag/GaP nanoparticles as photofunctional materials for waste-water cleaning. [ABSTRACT FROM AUTHOR]

Carbon nanotubes (CNTs) are nanomaterials of high interest due to their unique structural, electrical, and mechanical properties. Carbon materials have been widely employed to support metallic nanoparticles for catalysis and electrochemical applications. In this work, we investigated the synthesis of platinum nanoparticles generated from the complex Pt(dba) (tris(dibenzylideneacetone) diplatinum) and stabilized with a long alkyl chain amine, hexadecylamine (HDA) and supported on functionalized single-walled carbon nanotubes (SWCNTs). High resolution transmission electron microscopy (HRTEM) studies revealed isolated Pt nanoparticles (2-3 nm) on SWCNTs. Powder X-ray diffraction (XRD) was used to assess the structure of Pt nanoparticles dispersed on SWCNTs assigned to Pt face-centered cubic (fcc). Additionally, infrared Fourier transform spectroscopy confirmed the presence of the stabilizer at the surface of the Pt nanoparticles even after the purification step and functional groups at the surface of pre-treated SWCNTs. This synthetic method may be an alternative route to prepare small size Pt nanoparticles supported on functionalized SWCNTs. [ABSTRACT FROM AUTHOR]

In the present work, Fe-montmorillonite (Fe-MMT) was synthesized by hydrothermal method, and then was modified by cetyltrimethyl ammonium bromide (CTAB). The polyamide6 (PA6)/organic-modified Fe-montmorillonite (Fe-OMT) composite nanofibers were prepared by facile compounding and electrospinning. Fe-OMT was first dispersed in N, N-dimethyl formamide and then compounded with PA6 which was dissolved in formic acid. The composite solutions were electrospun to form PA6/Fe-OMT composite nanofibers. The structure, morphology, thermal stability, and crystalline properties of the composite nanofibers were characterized by Fourier transfer infrared (FTIR) spectra, Energy dispersive X-ray spectroscopy (EDX), X-ray diffraction (XRD), High-resolution electron microscopy (HREM), Scanning electron microscopy (SEM), and Thermogravimetric analyses (TGA), respectively. It was found that the silicate clay layers were well exfoliated within the composite nanofibers and were oriented along the fiber axis. The SEM images indicated that the loading of Fe-OMT decreased the diameters of composite nanofibers. TGA analyses revealed that the thermal stability was notably improved in the presence of silicate clay. It was also observed from wide-angle XRD analyses that the presence of nanoclays improved the γ-form crystals and induced the formations of α-form crystals of the PA6, attributed to effective nucleating effects of silicate clay platelets. [ABSTRACT FROM AUTHOR]

The effects of copper addition on the machinability and corrosion resistance of martensitic stainless steel 4Cr16Mo are presented in the article. The results showed that the machinability of stainless steel 4Cr16Mo was obviously improved by adding Cu. When the content of copper in the stainless steel was 1.4%, the machinability of stainless steel was optimal. With the increase in the content of copper, the corrosion resistance of stainless steel 4Cr16Mo was improved. From the observation of the electron backscattered diffraction (EBSD) and high resolution electron microscopy (HREM), it can be seen that Cu-rich phases were dispersed in the stainless steel, and determined to be about 10 nm. [ABSTRACT FROM AUTHOR]

Composition of the intergranular film (IGF) found between alumina crystals has been shown to affect growth. Here, we employ molecular dynamics (MD) computer simulations to study the effect of the composition of calcium alumino-silicate IGFs on preferential adsorption and grain growth in α-Al2O3 at an atomistic level. The IGF is formed while in contact with two differently oriented crystals, with results showing preferential adsorption and growth along the [ $$11\overline 2 0$$ ] direction of the ( $$11\overline 2 0$$ ) surface in comparison to that along the surface normal on the (0001) surface for certain calcium alumino-silicate compositions. Such preferential growth is consistent with experimentally observed anisotropic grain growth in alumina, where platelets form because of faster outward growth of the prism orientations than the basal orientation. The simulations show the mechanism by which Ca ions in the IGF inhibit growth on the basal surface and the important role that the Ca/Al ratio in the IGF plays in the change from isotropic to anisotropic grain growth. At compositions with high or low Ca/Al ratios, growth along each surface normal is equivalent, indicating isotropic grain growth. The simulations provide an atomistic view of attachment onto crystal surfaces, affecting grain growth in alumina, and the importance of local chemistry of the IGF on local adsorption and growth behavior. [ABSTRACT FROM AUTHOR]

The atomic structure of AlN/Al2O3 interface fabricated by pulsed laser deposition is characterized by high-resolution transmission electron microscopy (HRTEM) combined with systematic multi-slice HRTEM image simulations. It is found that the AlN film deposited on a (0001) Al2O3 substrate grows epitaxially with the orientation relationship of (0001)AlN//(0001) Al2O3 and [ $$\bar 1100$$ ]AlN//[ $$11\bar 20$$ ]Al2O3, with an atomically sharp interface. The observed interface showed best correspondence with the rigid structural model that AlN is terminated by Al at the interface, while the Al2O3 substrate is terminated by O. Detailed structural analysis indicates that Al sites at the interface are coordinated by both oxygen and nitrogen in this model, with similar coordination environment in AlN. This favored coordination state at the interface may stabilize the AlN/Al2O3 interface. [ABSTRACT FROM AUTHOR]

Solid solutions of the composition Li xAl12 − 3 xSi2 xN12 (1 ≤ x ≤ 3) have been prepared via a precursor route. According to XRD studies all phases obtained have wurtzite-type substructures with an orthorhombic superstructure related to LiSi2N3. However, observed powder patterns cannot be adequately described in orthorhombic symmetry, and the significant diffusiveness of the superstructure reflections indicates the presence of disorder. High resolution electron microscopy emphasizes the highly defective nature of the microstructure and the presence of nanoscale domains of apparently varying symmetry. Local ordering of metal ions and slight spatial variations of the composition are assumed to be possible reasons for the long-range inconsistencies of the structures. The Li+ ion conductivity, as measured on selected solid solutions, is lower, than that of LiSi2N3. [ABSTRACT FROM AUTHOR]

The microstructure transitions during leaching of a rapidly solidified Ni-Al alloy have been investigated by means of X-ray diffraction, transmission electron microscopic (TEM) and high resolution electron microscopic (HREM) techniques. Ni2Al3 was the main phase in the starting Ni-Al alloy. The microstructure of the Raney nickel catalyst consists of nano-scale nickel crystallites, residue of source phases surrounded by nano-scale boundary regions. The transformation during leaching of Ni2Al3 phase was an advancing interface type process. Clusters of AuCu-structure type face-centrered tetragonal Ni3Al2 as an intermediate phase seems to appear in the reaction front. Based on an analysis of the atomic configurations of phases Ni2Al3, Ni3Al2 and nickel, a reasonable explanation for the transition mechanism during leaching of Ni2Al3 phase and the arc characteristic of diffraction spots was proposed. The nickel crystallites generated during leaching obey an orientation relationship with the source Ni2Al3 phase, which is consistent with the Delannay's orientation relationship proposed for nickel and NiAl phases. The nano-scale structural characteristic of the Raney nickel catalyst, especially its porous structure at the boundary regions, provides an excellent hydrogenation catalytic activity and selectivity of the catalyst. [ABSTRACT FROM AUTHOR]

A technique that uses high resolution infrared (IR) imaging was developed to track and analyze damage evolution of thermal barrier coatings (TBCs) during controlled mechanical testing of a TBC specimen. Coating debonding and spallation were examined during a monotonic load-to-TBC-failure test. The infrared imaging, in concert with a controlled thermal gradient in the specimen, was particularly effective in identifying and tracking localized damage evolution because the damage in the TBC was always associated with a measurable surface-temperature change. It is demonstrated that the combined use of high-resolution infrared imaging and controlled mechanical testing of TBCs is an effective method to characterize the evolution of their failure. [ABSTRACT FROM AUTHOR]

The precipitation of three new types of metastable phases, i.e., TYPE-A, TYPE-B and TYPE-C, with different crystal structures from the β′ phase is proposed from our research on the change in crystal structures and formation sequence of metastable phases during the aging of the Al-1.0mass% Mg2Si-0.4mass% Si alloy by a combination of analytical high resolution electron microscopy and energy dispersive X-ray spectroscopy. The sequence of their formation is explained as follows. First, precipitation of the β′ phase and TYPE-B precipitate, then β′ dissolution into the matrix and degradation of the TYPE-B precipitate. Finally, predominant precipitation of the metastable TYPE-A precipitate. The TYPE-C precipitate appeared heterogeneously in the over-aged condition. [ABSTRACT FROM AUTHOR]

The high resolution electron microscopy was used to investigate the microstructure of AlN whiskers. The growth mechanisms of AlN whiskers were VLS and VS mechanism. The phenomenon of stacking fault was analyzed. Moreover, the growth mechanism of dendritic crystal was proposed. [ABSTRACT FROM AUTHOR]

We have studied the structure and properties of palygorskite clays. A structure analysis was performed using two different models to reproduce the monoclinic and orthorhombic lattices, using the atomic positions and cell parameters of palygorskite structure suggested by several authors, we simulated structures using Molecular Dynamics and Quantum Mechanics. Modifications on the structure and elemental atom changes were made to obtain more stable configurations. X-ray diffraction patterns and high resolution electron microscopy images from simulated structures were compared with experimental results. It could be observed that orthorhombic model shows a better fitting than monoclinic models. These results might help to understand many of the properties of archaeological pigments, such as, Maya Blue, in which palygorskite clay was the main component. [ABSTRACT FROM AUTHOR]

Grain boundary structure and chemical bonding state were characterized in high-purity Al2O3, 0.1 wt% MgO, 0.1 wt% Y2O3 or 0.1 wt% ZrO2-doped Al2O3. High resolution electron microscopy (HREM) and energy dispersive X-ray spectroscopy (EDS) revealed that all samples examined have single phase structure, and that doped cations segregate along grain boundaries. Electron energy loss spectroscopy (EELS) spectra taken from grain boundaries in doped Al2O3 shows slight chemical shift in comparison with those from grain interior. This result suggests that the chemical bonding state in grain boundaries changes by the segregated ions. The change in chemical bonding state seems to affect the grain boundary fracture energy of Al2O3. [ABSTRACT FROM AUTHOR]

The structure, structure evolution and microhardness of nanocrystalline Ni-Mo-B alloys were studied by X-ray diffraction, differential scanning calorimetry, transmission and high resolution electron microscopy and microhardness measurements. The nanocrystalline structure was produced by controlled crystallization of amorphous alloys. The annealed samples consist of the FCC nanocrystals with the amorphous regions between them. The grain size of the nanocrystals is about 20 nm and depends on the chemical composition of the alloy. The chemical composition of the amorphous phase between the nanocrystals changes at the annealing. A slight grain growth was observed when the annealing time increases. The diffusion of Mo and B from FCC to the amorphous phase occurs at the annealing. It results in the lattice parameter change. The microhardness of the alloys increases during the annealing. The microhardness values are the same in all alloys before the nanocrystalline structure decomposition. The microhardness is inconsistent with the Petch-Hall equation. The microhardness of the alloys is determined by the microhardness of the amorphous phase bands located between the nanocrystalline grains. [ABSTRACT FROM AUTHOR]

The effect of systematic modifications in the chemistry of the phase-boundary film on the macroscopic mechanical properties of Si3N4-matrix composites was investigated. Model composite materials, containing SiC or WC platelets, were prepared and only the bulk anion composition of the glassy-SiO2 intergranular phase was varied by adding increasing amounts of fluorine to the material. Detailed material characterizations by high-resolution electron microscopy (HREM) and Raman spectroscopy on both undoped and F-doped composites allowed to derive a structural model of the phase-boundary film as well as to evaluate the average microscopic stresses acting on it. In addition, high-temperature internal friction measurements provided an estimate of the grain-boundary relaxation temperature as a function of the F content. Noticeable variations of both elastic modulus and fracture energy of the composite were detected upon F addition, which were related to a spontaneous process of phase-boundary microcracking upon cooling. A threshold of the F-content was found for microcrack formation and its existence is theoretically explained according to a percolation process of non-bridged SiO4-tetrahedra, which arises from the incorporation of F into the intergranular film network. [ABSTRACT FROM AUTHOR]

The microstructure of TiB2-particle-reinforced Ni–Al–Fe matrix composite has been investigated by means of transmission electron microscopy, energy-dispersive X-ray analysis and high-resolution electron microscopy. The dendritic phase is found to be Fe(Ni, Al, Ti), which has a body-centred cubic crystal with lattice parameter a=1.068 nm. High-resolution images indicate that the Fe(Ni, Al, Ti) phase bonds the matrix very well. © 1998 Chapman & Hall [ABSTRACT FROM AUTHOR]

The structures of martensites in a Cu–11.2 wt% Al–3 wt% Ni specimen, which was quenched from 1173 K, have been studied by high resolution electron microscopy (HREM) and diffraction techniques. Two kinds of martensites, i.e. β′1 and γ′1, coexisting adjacent to each other in the specimen were observed. The γ′1 matensite consists of microtwins with monoclinic structure. Three variants of the twin structure, i.e. {1 2 1}, {2 1 0} and {1 0 1} twins, are arranged within a single plate. The β′1 martensite possesses basically ordered N9R structure, but mixed with thin 2H domains. Some diffraction spots of this martensite shift along the [0 0 1] direction. In addition, extra weak reflections appear in the diffraction pattern due to heterogeneous atomic displacements. The microstructural features of the martensites are examined and discussed. [ABSTRACT FROM AUTHOR]