High-resolution Transmission Electron Microscopy Techniques Research Articles

The Chemical and Alignment Structural Properties of Coal: Insights from Raman, Solid-State 13C NMR, XRD, and HRTEM Techniques.

The chemical and alignment structures of coal impacts coalbed methane behavior: adsorption, desorption, and diffusion. Recently, the research on accurate characterization techniques for coal structure has received widespread attention. In particular, spatial alignment is critical for the molecular modeling of coal. However, due to the great challenges of quantification, spatial alignment has often been ignored in previous studies. In this study, high-resolution transmission electron microscopy (HRTEM) was employed to quantitatively characterize the fringe length, orientation, and stacking distributions of these five coal samples with different ranks. Raman spectroscopy was utilized to investigate the overall structural disorder of the coal molecules. 13C nuclear magnetic resonance (13C NMR) was conducted to characterize the chemical structures of coals, and XRD experiments recorded the transition of the microcrystallite structure. The results show that in the range of %Ro = 0.39–2.07%, the distributions of the aromatic structural units were similar: mainly composed of fringes of size equivalent to naphthalene and 2 × 2 and 3 × 3 rings. When %Ro > 2.07%, the distribution shifted to longer fringes. Moreover, all the samples showed a regional orientation, and when %Ro > 2.07%, there was significantly higher alignment. The degree of stacking of fringes were limited, most of which appeared in the form of a single layer. When %Ro < 2.07%, the stacking appeared in the form of two or three layers. However, five-layer stacking merely appeared in the sample with %Ro = 2.47%. In addition, based on the Raman data, the evolution of carbon disorder was divided into three stages: %Ro = 0.39–1.23%, 1.23–2.07%, and 2.07–2.47%, and aromatization caused the overall disorder to decrease. The 13C NMR data indicated that the chemical structure also transitioned in stages, with aliphatic carbon and oxygen-containing groups gradually decreasing and aromatic carbon increasing. Meanwhile, the XRD data supported increased organization (lower d002 values) with maturities. Thus, this study provides quantitative information about the spatial alignment and the size of aromatic rings, which helps to improve a comprehensive understanding of the chemical structure of coal and coalbed methane behaviors.

Superficial Synthesis of CdS Quantum Dots for an Efficient Perovskite-Sensitized Solar Cell

In this paper, a thorough investigation of cadmium sulfide nanoparticle characteristics has been studied as a result of the wide attention and enormous application in a solar cell. Perovskite-sensitized solar cells (PSSCs) are a favorably effectual and sanitary hybrid, organic–inorganic solar cell device. The simple way uses synthesized cost-effective CdS quantum dots (QDs) via the sol–gel approach and also investigates their structural, electronic, and vibrational properties of CdS nanoparticles with the density functional theory method in B3LYP. Moreover, we use high-resolution transmission electron microscopy (HRTEM) techniques to confirm our calculations and acquire good agreement to the structural analysis of CdS QD formation. The maximum grain diameter is obtained from a HRTEM image, at ∼4 nm. The particle size analyzer that obtained ∼4 nm of CdS QD nanoparticles was determine via a dynamic light scattering study. The results demonstrated that the fabricated CdS QD-based dye-sensitized solar cell and PSSC represented a maximum power conversion efficiency (η) of 0.5 and 1.8% at 1 sun condition. This efficiency was improved by approximately 72%, associated with that of the reference cell.

Chemical and phase inhomogeneity in LaNiO3 electrodes prepared by chemical solution deposition

The structure of lanthanum nickelate (LNO) thin film electrodes prepared by chemical solution deposition has been investigated. Features of LNO microstructure have been studied using high-resolution transmission electron microscopy techniques, electron diffraction, and elemental mapping by energy dispersive X-ray analysis. Structure evolution of LNO after crystallization in the temperature range of 550 ÷ 800 °C has been visualized. Chemical and phase delamination within each sublayer was revealed in the LNO structure over the entire temperature range. Nanograins of Ni3O4 (С2/m), La2O3 (С2/m), LaNiO3 (), and La2Ni2O5 (С2/m) phases were identified in the annealed LNO layer.

Carbon Nanotubes Doped Poly (arylene) Ether Copolymerised Multiblock Based Proton Exchange Composite Membranes for Fuel Cell Application

The article reports the synthesis of nanophase-separated multiblock poly(arylene ether ketone sulfone) copolymers. A series of hydrophobic oligomers end-capped with decafluorobiphenyl (DFBP) group was reacted with disulphonated poly(arylene ether ketone) copolymer containing 4, 4′-bis (4-hydroxyphenyl) valeric acid moieties to synthesize multiblock copolymer. The copolymers were characterized using 1H-NMR, 13C-NMR, 19F-NMR spectroscopy and Gel Permeation Chromatography. The membranes with high dimensional and thermal stability were obtained through solution casting method. The multiblock copolymers were crosslinked with 6F-bisphenol-A (6F-BPA) based novolac epoxy resin. The functionalized multi-walled carbon nanotubes (f-MWCNTs), in 0.5, 0.7, and 0.9 wt.%, were also incorporated into the polymer matrix in order to prepare nanocomposite membranes. Polymer nanocomposite membranes showed high oxidative stability, and proton conductivity. The surface morphology and composition of polymer nanocomposite membranes were studied using field emission-scanning electron microscopic (FE-SEM), and high-resolution transmission electron microscopic (HR-TEM) techniques. The fuel cell related parameters such as water uptake, proton conductivity, ion exchange capacity, oxidative stability, and methanol permeability were also evaluated. The thermal performance and mechanical behavior of the synthesized polymer nanocomposite membranes were also studied. The nanocomposite membranes showed better fuel cell performance as compared to the pristine membranes.

Evidence of improved tolerance to electronic excitation in nanostructured Nd2Zr2O7

Grain size driven effects on electronic excitation-induced structural modifications have been investigated in nanocrystalline (NC) Nd2Zr2O7 on irradiation with 100 MeV iodine ions. Characterizations have been performed with in situ x-ray diffraction, Raman spectroscopy, and plane-view high-resolution transmission electron microscopy techniques. NC-powders of Nd2Zr2O7 were synthesized by auto gel-combustion and sintered at different temperatures to obtain different grain-sized samples. XRD analysis of the smallest grain-sized sample reveals the highest order–disorder transition (from pyrochlore to a more radiation-resistant phase; anion-deficient fluorite) rate at initial ion fluences followed by least amorphization at higher ion fluences. A strong correlation of the transformation build-up with the double ion impact model confirms the two step amorphization process in NC-Nd2Zr2O7 with the disordered anion-deficient fluorite structure as an intermediate phase. TEM result supports the formation of circular ion track consisting of randomly distributed regions (anion-deficient fluorite structure and amorphous regions), surrounded by a microstrain induced defect-rich pyrochlore superstructure. Lesser ordering at cationic sites and a relatively larger number of grain boundaries are responsible for the highest radiation tolerance exhibited by the smallest grain-sized sample. The present study reports a relatively higher radiation stability of NC-ternary pyrochlore oxide, Nd2Zr2O7, with a grain size of a few tens of nm, which establishes its application as a potential inert matrix for nuclear applications.

Facile In-Situ Synthesis of Biopolymer Capped Nano Sized Silver Particles: Smartphone Aided Paper-Based Selective Detection of CYS and TC Drugs in Biological and Drug Samples

Herein we are reporting, the in-situ synthesis of polydopamine capped silver nanoparticles (PDA-AgNPs) and its cysteamine (CYS) and tetracycline (TC) drugs sensor applications. The synthesized PDA-AgNPs was characterized by UV–Visible, Fourier Transformed–Infrared, X-Ray Diffraction, Zeta Potential, and High Resolution-Transmission Electron Microscope techniques. We have utilized PDA-AgNPs as probes for the detection of CYS and TC by spectrophotometry method. The addition of CYS has led to a decrease in the absorption of PDA-AgNPs. The yellow color solution becomes colorless and observed the aggregated particles in the TEM image. In contrast, the addition of TC, into the same solution, absorption of PDA-AgNPs was increased. The color of the solution became dark yellow and the particles are obtained de-aggregation. Based on the Surface Plasmon Resonance (SPR) band absorption changes, the detection limit of CYS and TC was calculated to be 180 nM and 17 nM, respectively. Interestingly, 600-fold of common interferences did not interfere with the detection of CYS and TC. PDA-AgNPs was successfully utilized to detect CYS and TC in serum, urine, and drug samples. Finally, we have prepared a paper-based colorimetric kit for on-site monitoring of CYS and TC.

Incorporation of incompatible trace elements into molybdenite: Layered PbS precipitates within molybdenite

Abstract Trace elements in molybdenite can provide important information regarding the composition of ore-forming fluid and the evolution and genesis of ore deposits. However, the occurrence states and behavior of relatively incompatible trace elements (e.g., Pb and Os) in natural molybdenite remain ambiguous. Here, we report an abnormally high enrichment of Pb and layered PbS precipitate within molybdenite grains from the Huanglongpu carbonatite-hosted Mo-Pb deposit in the Qinling orogenic belt of Northern China. High-resolution transmission electron microscopy (HRTEM) and related nanobeam techniques were applied to characterize the occurrence states of Pb within molybdenite at the atomic scale. The results show that up to several weight percent of Pb can be incorporated into the molybdenite structure during initial crystallization, which can lead to the formation of screw dislocations and 3R/disordered stacking of S-Mo-S sandwich layers. Observations using a scanning transmission electron microscope also reveal that Pb diffuses from the host molybdenite into the layered PbS precipitates under prolonged electron beam irradiation. Pb-bearing molybdenite tends to transform into a Pb-poor ordered 2H1 polytype upon Pb exsolution during cooling. Pb preferentially exsolves along the (001) plane of molybdenite and is stored in structural defects (e.g., dislocation loops) and grain boundaries, resulting in nano-scale Pb heterogeneities in molybdenite. Further coarsening of the exsolved Pb results in the formation of layered PbS precipitates along the (001) plane of molybdenite. This study provides an example of the consequences of the incorporation and exsolution of incompatible trace elements in molybdenite and demonstrates that careful mineralogical examination is required to interpret geochemical data obtained by in situ analysis techniques.

Formation of β-Be3N2 nanocrystallites in Be-implanted GaN

A small Be ion dose of 5 × 1014 cm−2 was implanted in a 2 μm thick GaN epilayer at an energy of 50 keV. The sample was characterized by high-resolution transmission electron microscopy (HRTEM) and Raman spectroscopy techniques after a post-implantation rapid thermal annealing (RTA) treatment. The HRTEM images show the crystallographic (1 1 0) and (0 0 2) planes of β-Be3N2. Two characteristic parallelograms drawn in Fast Fourier transform (FFT) image support the formation of β-Be3N2 nanocrystallites in RTA treated sample. Two Raman peaks at 168 and 199 cm−1 are observed in the Raman spectrum of the sample that are assigned to β-Be3N2 on the basis of group theory and HRTEM data. The Raman peak at 168 cm−1 is found close to the K point in the first Brillouin zone of β-Be3N2 while the peak at 199 cm−1 is assigned as a combination mode of the fundamental Raman modes of β-Be3N2.

Single-Crystalline Ultrathin 2D Porous Nanosheets of Chiral Metal-Organic Frameworks.

Two-dimensional (2D) materials with highly ordered in-plane nanopores are crucial for numerous applications, but their rational synthesis and local structural characterization remain two grand challenges. We illustrate here that single-crystalline ultrathin 2D MOF nanosheets (MONs) with intrinsic porosity can be prepared by exfoliating layered metal-organic frameworks (MOFs), whose layers are stabilized by sterically bulky groups. As a result, three three-dimensional (3D) isostructural lanthanide MOFs possessing porous layer structures are constructed by coordinating metal ions with an angular dicarboxylate linker derived from chiral 1,1'-biphenyl phosphoric acid with pendant mesityl groups. The Eu-MOF is readily ultrasonic exfoliated into single-crystalline nanosheets with a thickness of ca. 6.0 nm (2 layers) and a lateral size of 1.5 × 3.0 μm2. The detailed structural information, i.e., the pore channels and individual organic and inorganic building units in the framework, is clearly visualized by a low-dose high-resolution transmission electron microscopy (HRTEM) technique. Benefiting from their ultrathin feature, the nanosheets are well embedded into the polymer matrix to form free-standing mixed-matrix membranes. In both the solution and membrane phase, the fluorescence of the MONs can be effectively quenched by a total of 17 chiral terpenes and terpenoids through supramolecular interactions with uncoordinated chiral phosphoric acids, leading to a chiral optical sensor for detecting vapor enantiomers, which is among the most challenging molecular recognition tasks.

Perylenetetracarboxylic acid–incorporated silver nanocluster for cost-effective visible-light-driven photocatalysis and catalytic reduction

Herein, we demonstrated photocatalytic applications of organic semiconductor (perylenetetracarboxylic acid (PTCA))–incorporated silver nanocluster in the degradation of a model dye (malachite green) using a low-cost and energy-efficient visible LED light source. The utility of this material in the catalytic reduction of MG dye in the presence of a reducing agent (i.e. NaBH4) is also evaluated. This nanocluster was prepared using a facile one-pot methodology utilising biocompatible captopril and PTCA as protecting ligands. In this synthetic protocol, tetraoctylammonium bromide facilitates the cation induced aggregation process. It was characterised by UV-Vis, high-resolution transmission electron microscopy (HRTEM) and energy-dispersive X-ray spectroscopy (EDX) techniques. HRTEM and EDX spectroscopy confirms the average diameter of the nanocluster to be 2.9 ±1 nm and the presence of N, C, S, O and Ag as the main elements respectively. As revealed in photocatalysis, the model dye malachite green (MG) was degraded by ~80% in 52 min. The kinetics of catalytic reduction reaction of MG in the presence of a reducing agent sodium borohydride reveals an acceleration of the reduction of MG in the presence of as-prepared PTCA/AgNC compared to having no catalyst. Superior water solubility and stable colloidal dispersion of the as-prepared nanocluster allowed highly efficient catalysis in homogenous conditions. Furthermore, it can find a wide range of potential applications in catalysis, sensors and organic field-effect transistor.

Poirierite, a dense metastable polymorph of magnesium iron silicate in shocked meteorites

A dense magnesium iron silicate polymorph with a structure intermediate between olivine, ringwoodite, and wadsleyite was theoretically predicted about four decades ago. As this group of minerals constitute the major component of shocked meteorites, constraining their transitional forms and behaviour is of potential importance for understanding impact events on their parent bodies. Here we use high-resolution transmission electron microscopy techniques and single-crystal X-ray diffraction analyses to identify naturally occurring examples of this mineral – recently named poirierite – in shocked chondritic meteorites. We observe nanoscale lamellar poirierite topotactically intergrown within wadsleyite, and additionally within ringwoodite as recently reported. Our results confirm the intermediate structure of poirierite and suggest it might be a relay point in the shear transformations between its polymorphs. We propose that poirierite formed during rapid decompression at relatively low temperature in retrograde shock metamorphism of the meteorites.

Hrtem Observation of Morphological and Structural Evolution of Aromatic Fringes During the Transition from Coal to Graphite

The maximum reflectance of vitrinite or graphite microcrystals in Yongan Coalfield, Fujian Province, China, ranges from 5.33% to 10.21%, comprising meta-anthracite, semi-graphite, and graphite. The morphological characteristics of aromatic fringes during different evolution stages were quantitatively analyzed using high-resolution transmission electron microscopy and image processing techniques. The results show that a nonlinear evolution of aromatic fringe morphology in the process of coal graphitization is manifested in four aspects, involves the rapid connection and growth, enhancement of ordering alignment, increase of stacking and development of straightening. The stage evolution of aromatic fringe morphology and remained almost constant of mainly organic elements, implying the evolution of aromatic fringes in meta-anthracite originated from ring condensation dominated by late coalification, graphitization starts at semi-graphite stage and enhanced during graphite stage. The making up, originating from linkup and pileup, considered as a special mechanism for the graphitization of aromatic fringes.

Structural and luminescence study of Ce3+ and Eu3+ doped ZnAl12O19 nano-structured novel phosphors

Cerium and Europium ions activated ZnAl12O19 nano-phosphors were first time prepared by solution combustion synthesis. The prepared powder samples were characterized by X-Ray Diffraction (XRD), High-resolution transmission electron microscopy (HR-TEM), Ultraviolet visible spectroscopy (UV–vis), Fourier transform infrared spectroscopy (FT-IR) and Photoluminescence technique (PL). The crystal structure of the prepared ZnAl12O19 host, and Ce3+ and Eu3+ doped ZnAl12O19 phosphors were calculated by XRD technique. The nano-structured nature of the prepared samples was confirmed by the HR-TEM technique. The band gap energies of prepared undoped, and Ce3+ / Eu3+ doped ZnAl12O19 nano-phosphor were calculated using the UV spectroscopy technique. The bonding nature in the prepared samples was studied by the FT-IR technique. Under 320 nm excitation wavelength, the PL emission spectrum of Ce3+ activated ZnAl12O19 nano-phosphor shows broad emission centered at 420 nm, which is ascribed due to the transitions of the 5d excited state to its ground-state configurations of the 2F7/2 of the Ce3+ ions. Furthermore, under 390 nm excitation the PL emission spectra of Eu3+ activated ZnAl12O19 nano-phosphor shows sharp emission peak at 590 nm corresponding to the 5D0→7F1 transition of Eu3+ ions. The CIE chromaticity coordinates for the optimum nano-phosphor were found to be (0.1573, 0.0693) and (0.5717, 0.4276) for Ce3+ / Eu3+ doped ZnAl12O19 phosphors, respectively. Therefore these synthesized phosphors may be applicable in display devices and solid state lighting applications.

Nanomolar detection of L-cysteine and Cu2+ ions based on Trehalose capped silver nanoparticles

This work describes the solvent-free solid-state synthesis of Trehalose capped silver nanoparticles (Th-AgNPs) and its L-Cysteine and Cu2+ ions sensor application. We have prepared Th-AgNPs by the solid-state method within 5 min by simple grinding. During the synthesis of AgNPs, trehalose in alkaline medium acts as reducing as well as capping agent. The Th-AgNPs were well characterized by Ultraviolet–visible (UV–vis) spectroscopy, Fourier Transform Infrared (FT-IR) Spectroscopy, X-Ray Diffraction (XRD) and High-Resolution Transmission Electron Microscopy (HR-TEM) techniques. FT-IR spectral studies confirmed that Trehalose –OH, groups were adsorbed on the surface of AgNPs. XRD pattern of Th-AgNPs revealed that synthesized Th-AgNPs presented good crystalline nature and face-centred cubic structure. The particles size was calculated to be 9.312 ± 0.23 nm by HR-TEM image. Interestingly, after the addition of L-Cysteine into Th-AgNPs, the particles are aggregated, followed by the decreases in SPR band absorbance at 400 nm was observed and a new peak appears at 550 nm. In contrast, the addition of Cu2+ ions led to an increase of the SPR band at 400 nm and 550 nm and the color of the solution changed to yellowish red. The reverted SPR peak shift and color changes are expected due to the deaggregation of nanoparticles, which was further confirmed by HR-TEM. Based on the changes in SPR band, the concentration of L-Cysteine and Cu2+ ions were sensed, and the limit of detection (LOD) was found to be 1.48 and 1.92 nM (LOD = 3S/m), respectively. 750-fold (2.94 × 10−4 M) of common amino acids and 300-fold (4.89 × 10−4 M) of common metal ions did not interfere with the specific detection of 0.33 μM of L-Cysteine and 1.63 μM of Cu2+ ions. We have successfully applied this system for the detection of L-Cysteine and Cu2+ ions in different environmental, biological and drug samples. Importantly, we have prepared a paper-based kit for on-site monitoring of L-Cysteine and Cu2+ ions. This new synthesis protocol and the developed paper-based kit will provide an insight in the field of material science, nanotechnology and biosensor applications.

Polymer-Based Graphene Derivatives and Microwave-Assisted Silver Nanoparticles Decoration as a Potential Antibacterial Agent.

Nanocomposites obtained by the decoration of graphene-based materials with silver nanoparticles (AgNPs) have received increasing attention owing to their antimicrobial activity. However, the complex synthetic methods for their preparation have limited practical applications. This study aims to synthesize novel NanoHybrid Systems based on graphene, polymer, and AgNPs (namely, NanoHy-GPS) through an easy microwave irradiation approach free of reductants and surfactants. The polymer plays a crucial role, as it assures the coating layer/substrate compatibility making the platform easily adaptable for a specific substrate. AgNPs’ loading (from 5% to 87%) can be tuned by the amount of Silver salt used during the microwave-assisted reaction, obtaining spherical AgNPs with average sizes of 5–12 nm homogeneously distributed on a polymer-graphene nanosystem. Interestingly, microwave irradiation partially restored the graphene sp2 network without damage of ester bonds. The structure, morphology, and chemical composition of NanoHy-GPS and its subunits were characterized by means of UV-vis spectroscopy, thermal analysis, differential light scattering (DLS), Field Emission Scanning Electron Microscopy (FE-SEM), Energy Dispersive X-ray analysis (EDX), Atomic Force Microscopy (AFM), and High-Resolution Transmission Electron Microscopy (HRTEM) techniques. A preliminary qualitative empirical assay against the typical bacterial load on common hand-contacted surfaces has been performed to assess the antibacterial properties of NanoHy-GPS, evidencing a significative reduction of bacterial colonies spreading.

Effect of Mg and Cu doping on structural, optical, electronic, and thermal properties of ZnS quantum dots

Undoped and 10% Mg or Cu-doped ZnS quantum dots (Zn0.9Mg0.1S and Zn0.9Cu0.1S) were prepared by a simple chemical method at low temperature (300 °C). The effect of doping on structural characteristics was investigated using Rietveld profile method and the high-resolution transmission electron microscope techniques. Differential scanning calorimetry (DSC) scans were recorded in the temperature range 23–600 °C with different heating rates (5 to 30 °C/min). The model-free isoconversional method was applied to explore the effect of doping on the reaction and the growth mechanism of nano-ZnS. Diffuse UV reflectance revealed an increase of the optical energy gap upon doping with Mg, while it decreased as ZnS was doped with Cu. The change in energy gap upon doping was explained using density function theory calculation. The photoluminescence (PL) spectra revealed violet, blue, green colors depended on the composition and excitation wavelength used in the study. The intensity of PL has been increased for doped samples compared with pristine ZnS. Tuning the energy gap of ZnS through doping enable applications for light-harvesting and photocatalytic degradation in the visible region.

Superplastic deformation of Mg\u20139Li\u20132Al\u20130.5Sc alloy after grain refinement by KoBo extrusion and cyclic forging

The quaternary Mg–9Li–2Al–0.5Sc alloy (in wt%) was prepared from pure components. After homogenization, the alloy was subjected to severe plastic deformation by KoBo extrusion and cyclic forging leading to grain refinement in the range of 0.5–2 µm of hexagonal close-packed (HCP) α phase. Deformed alloys showed high ultimate tensile strength near 200 MPa and good elongation in the range 30–40% at room temperature (RT). Large elongations close to 200% were obtained during the tensile test at a temperature of 200 °C. Deformed samples showed the presence of multiple voids confirming grain boundary sliding mechanism of deformation. Twins on {10overline{1}2} planes were identified using electron backscatter diffraction analysis, being in a good agreement with the earlier observation of Mg–Li and Mg–Sc alloys. Intermetallic phases such as cubic MgSc were identified in deformed alloys mostly within HCP α phase, whereas HCP MgSc2 particles were observed within body-centered cubic (BCC) β phase. Intermetallic phases were responsible for RT strengthening of alloys and slightly lower tensile elongation during superplastic deformation. Formation of the HCP α phase was observed within the BCC β phase in tensile deformed alloys. Atomic-level nucleation of HCP phase within the β phase was identified by the use of high-resolution transmission electron microscopy technique.

Strong spin-orbit interactions in a correlated two-dimensional electron system formed in SrTiO3(001) films grown epitaxially on p−Si(001)

We observe strong spin-orbit interactions in a two-dimensional electron system formed on $\mathrm{SrTi}{\mathrm{O}}_{3}(001)$ films grown epitaxially on p-Si(001). High-resolution transmission electron microscopy and related analytical techniques reveal a sharp interface between Si and $\mathrm{SrTi}{\mathrm{O}}_{3}$. Strain mapping analysis shows in-plane strain in $\mathrm{SrTi}{\mathrm{O}}_{3}$ very close to the interface. Analysis of the low temperature magnetoconductance measurements reveals that both quantum interference and electron-electron interactions are important. The contributions of these two quantum phenomena to the temperature and magnetic field dependence of the conductance and Hall effect are separated. The electron system has carrier concentrations larger than ${10}^{14}\mathrm{c}{\mathrm{m}}^{\ensuremath{-}2}$, appears to be confined within \ensuremath{\sim}4 nm, and has an estimated spin-splitting energy \ensuremath{\sim}12 meV.

Structural Evolution in the Quenched Al–Zn–Mg–Fe–Ni Alloy during Severe Plastic Deformation and Annealing

The evolution of the structure and phase composition of the Al–Zn–Mg–Fe–Ni alloy (nikalin) during severe plastic deformation by high pressure torsion and annealing has been investigated using high-resolution TEM techniques. The deformation of the quenched alloy has been found to result in a submicron composite comprising an Al matrix and various fine aluminides. The severe structural refinement takes place along with phase transformations, which dissolve the metastable Al3Zr-phase particles and cause the nanosized strengthening phases Т (Al2Mg3Zn3) and η' (MgZn2) to precipitate from the Al solid solution which has been supersaturated in result of quenching and deformation. Nikalin has been determined to retain its submicrocrystalline state during low-temperature annealing (200°C, 4 h) due to the barrier effect of fine hardening phase particles, fixing grain boundaries. High-temperature heating to 400°C for four hours transfers nikalin to the overaged state, in which it is characterized to consist of a recrystallized matrix with grains 2–3 µm in size, eutectic micron-sized aluminides, and stable Al2Mg3Zn3 and MgZn2-phase particles with sizes of no more or equal to 500 nm.

Anisotropic morphology, formation mechanisms, and fluorescence properties of zirconia nanocrystals

ZrO2 nanocrystals with spheres and elongated platelets were systemically prepared through a simple hydrothermal method by the use of ZrOCl2·8H2O and CH3COOK as raw materials. The anisotropic morphology and formation mechanism of the monoclinic and/or tetragonal ZrO2 were investigated by X-ray diffraction, Fourier transform infrared spectroscopy, Raman spectroscopy, scanning electron microscope, and high-resolution transmission electron microscope techniques. The uniform elongated platelets and star-like structures were composed of short nanorods with a diameter of approximately 5 nm and a length of approximately 10 nm. The different morphologies were formed due to the different contents of CH3COO− and Cl− and their synergy. The fluorescence band position and the band shape remained about the same for excitation wavelengths below 290 nm and the different morphologies of the nanocrystals.