The microstructure of non-ohmic zinc oxide ceramics

The microstructure and the nature of some crystal phases in non-ohmic ZnO ceramics containing 0·5 Bi₂O₃, 0·5 CoO, 0·5 MnO and 0·5 TiO₂ mol% were investigated by using various analytical techniques. The ceramics consist primarily of ZnO grains, and in addition, two titanium containing phases were found, a needle-like Zn₂TiO₄ spinel phase doped with bismuth and cobalt, and a cubic-Zn₂Ti₃O₈ phase with some cobalt and manganese. The Bi₂O₃ phase among the grains was found to be TiO₂ stabilized γ* Bi₂O₃.     

Interfacial reactions and silicate formation in highly dispersed Lu2O3– SiO2 system

Solid state interface reactions in highly dispersed Lu₂O₃– SiO₂ binary oxide system were studied at 600–1100 °C with X‐ray powder diffraction (XRD), high‐resolution transmission electron microscopy (HRTEM) and Fourier Transform Infrared spectroscopy (FTIR). The results show that at 600–900 °C an amorphous, nanometer thick Lu‐O‐Si layer covering SiO₂ particles exists in the system. At higher temperatures the breakage of the layer into amorphous islands occurs and crystalline silicates with various structures are formed. In particular, Lu₄[Si₃O₁₀][SiO₄] silicate, analogue of B‐type Dy – Tm disilicates, forms at 1000 °C.     

Surface micromorphology of dental composites [CE‐TZP]‐[Al2O3] with Ca+2 modifier

The objective of this study was to characterize the three‐dimensional (3D) surface micromorphology of the ceramics produced from nanoparticles of alumina and tetragonal zirconia (t‐ZrO₂) with addition of Ca⁺² for sintering improvement. The 3D surface roughness of samples was studied by atomic force microscopy (AFM), fractal analysis of the 3D AFM‐images, and statistical analysis of surface roughness parameters. Cube counting method, based on the linear interpolation type, applied for AFM data was used for fractal analysis. The morphology of non‐modified ceramic sample was characterized by the rather big (1–2 μm) grains of α‐Al₂O₃ phase with a habit close to hexagonal drowned in solid solution of t‐ZrO₂ with smooth surface. The pattern surfaces of modified composite content a little amount of elongated prismatic grains with composition close to the phase of СаСеAl₃О₇ as well as hexahedral α‐Al₂O₃‐grains. Fractal dimension, D, as well as height values distribution have been determined for the surfaces of the samples with and without modifying. It can be concluded that the smoothest surface is of the modified samples with Ca⁺² modifier but the most regular one is of the non‐modified samples. A connection was observed between the surface morphology and the physical properties as assessed in previous works. Microsc. Res. Tech. 78:840–846, 2015. © 2015 Wiley Periodicals, Inc.     

Investigation of Annealing Temperature on Structural and Morphological Properties of Cr<Subscript>2</Subscript>O<Subscript>3</Subscript> Nanoparticles for Humidity Sensor Application

Cr₂O₃ nanoparticles have been prepared for precipitation technique at reaction temperature 50 °C. The prepared samples were annealed different temperatures at 500,700 and 1000 °C. Synthesized powders were characterized as X-ray diffraction, optical, transmission electron microscope, SEM with EDAX, humidity sensor, FTIR. The annealing temperature has been found to be playing a crucial role in the controlling particle size. XRD study shows the rhombohedral crystal structure of highly preferential orientation along (1 0 4) direction. FTIR reveals that the presence Cr–O bonds in the structure. The TEM images show that the size of NPs of Cr₂O₃ varied from 26 to 60 nm with average crystalline size 43 nm. UV–visible spectrum shows the absorption band of Cr₂O₃ nanoparticles at 400 nm. The humidity sensor of the Cr₂O₃ nanoparticles was studied by two temperature method. 1000 °C annealed Cr₂O₃ nanoparticles show better sensing properties and exhibits good linearity in response than 500 °C. SEM images show the clusters and agglomeration of nanoparticles. EDAX spectrum confirms the presence of Cr₂O₃ nanoparticles. Each samples have been characterized as sensing materials to determine relative humidity in the range of 20–90%. The humidity sensing property increased with increasing of annealing temperature and the resistance was decreased.     

Influence of Mg doping on the morphology and optical properties of ZnO films for enhanced H2 sensing

Highly oriented ZnO and Mg doped ZnO thin films were fabricated on Al₂O₃ substrate by sputtering at room temperature. The effect of Mg doping on the structural, optical, and morphological properties of ZnO film was investigated. The intensity of (002) peak in X‐ray diffraction measurements revealed the influence of Mg doping on the crystallinity and orientation of ZnO film. Photoluminescence (PL) results show that the Ultraviolet (UV) emission peak was shifted to lower wavelength side for Mg:ZnO film indicating the possibility for quantum confinement. UV–vis–NIR optical absorption revealed an improvement in optical transmittance from 70 to 85%, and corresponding optical band gap from 3.25 to 3.54 eV. Atomic force microscope (AFM) images revealed the nano‐size particulate microstructure of the films. The surface topography of Mg doped ZnO film confirmed decreased grain size with large surface roughness and increased surface area, favorable for sensing. Pure ZnO and Mg doped ZnO film were used as active layer and tested for its sensing performance to hydrogen. Compared to undoped ZnO, 22 at.% Mg doped ZnO film showed much higher sensor response to H₂ at a concentration as low as 200 ppm and at a lower operating temperature of 180°C. A linear sensor response was observed for H₂ concentration in the range of 100–500 ppm. Microsc. Res. Tech. 76:1118–1124, 2013. © 2013 Wiley Periodicals, Inc.     

Real‐space observation of strong metal‐support interaction: state‐of‐the‐art and what's the next

The real‐space resolving of the encapsulated overlayer in the well‐known model and industry catalysts, ascribed to the advent of dedicated transmission electron microscopy, enables us to probe novel nano/micro architecture chemistry for better application, revisiting our understanding of this key issue in heterogeneous catalysis. In this review, we summarize the latest progress of real‐space observation of SMSI in several well‐known systems mainly covered from the metal catalysts (mostly Pt) supported by the TiO₂, CeO₂ and Fe₃O₄. As a comparison with the model catalyst Pt/Fe₃O₄, the industrial catalyst Cu/ZnO is also listed, followed with the suggested ongoing directions in the field.     

Mapping the chemistry of resinite,funginite and associated vitrinite in coal with micro‐FTIR

Micro‐FTIR mapping is a powerful tool for nondestructive, in situ chemical characterization of coal macerals at high resolution. In this study, the chemistry of resinite, funginite and associated vitrinite is characterized via reflectance micro‐FTIR for Cenozoic high volatile C bituminous coals from Colombia. In comparison with the micro‐FTIR spectra of vitrinite and inertinite, the corresponding spectra of liptinite macerals in the same coals are characterized by stronger aliphatic CH_x absorbance at 3000–2800 and 1460–1450 cm^?1, but less intense aromatic C=C ring stretching vibration and aromatic CH_x out‐of‐plane deformation at 700–900 cm^?1. The aliphatic components in resinite have the longest carbon chains and are least branched, bestowing the highest hydrocarbon generation potential on resinite among the three macerals studied. In contrast, funginite exhibits the strongest aromatic character, the highest aromaticity, the lowest ‘A’ factor values and the lowest C=O/C=C ratios among the three maceral groups. Vitrinite generally displays intermediate chemical characteristics. Reflectance micro‐FTIR mapping of coal samples further confirms the aliphatic character of resinite and the aromatic nature of funginite. In addition, chemical mapping of resinite and adjacent vitrinite shows that vitrinite immediately adjacent to resinite displays higher aliphatic CH_x stretching intensity than more distant vitrinite, suggesting that chemical components from resinite can diffuse over short distances into adjacent vitrinite, specifically causing hydrogen enrichment. It needs to be pointed out, however, that the region of influence is localized and limited to a narrow zone, whose extent likely depends on resinite's properties, such as its size and aliphatic material content. This way, the chemical map of resinite and associated vitrinite provides direct evidence of the intermaceral effects occurring during the peat forming stage or during later coalification. No influence of funginite (primarily fungal spores and sclerotia) on the chemistry of adjacent vitrinite has been demonstrated, which is likely due to the highly aromatic structure of this type of funginite.     

A technique for the preparation of cross-sectional TEM samples of ZnSe/GaAs heterostructures which eliminates process-induced defects

Cross-sectional transmission electron microscopy (TEM) sample preparation of ZnSe/GaAs epitaxial films is investigated. Conventional argon ion milling is shown to produce a high density (～ 5–8 × 10¹¹/cm²) of small (diameter ～ 60–80 Å) extended defects (stacking faults, microtwins, double positioning twins, etc.). In addition, transmission electron diffraction results indicate a thin ZnO layer can also occasionally form upon ion milling or electron-beam irradiation although the exact conditions for ZnO formation are not well understood. Conventional TEM (amplitude contrast) and high-resolution TEM (phase contrast) imaging in combination with transmission electron diffraction studies were performed to determine the optimum method of removing the ion milling related damage and ZnO layers during sample preparation. HF/HCl, NaOH/H₂O, H₂SO₄/H₂O₂/H₂O and Br₂/CH₃OH etching mixtures as well as low voltage argon or iodine ion milling were studied. A low energy (2 ke V) iodine or argon ion milling step was shown to remove the ZnO layer and reduced the density of the extended defects associated with Ar⁺ ion milling, but was unsuccessful in removing all of the defects. Auger electron spectroscopy results indicate residual iodine was either left on the surface or implanted beneath the surface during iodine ion milling. Etching the XTEM samples in HF/HCl was shown to be effective in removing the ZnO layer but had little or no effect on the ion milling induced defects. Etching the samples in a 0.5% Br₂/CH₃OH solution resulted in complete elimination of the ion milling induced extended defects including the residual defects associated with iodine ion milling. In addition the Br₂/CH₃OH etch produced the best surface morphology. Thus a brief (1–2 seconds) Br₂/CH₃OH etch after conventional preparation (argon ion milling) of cross-sectional ZnSe/GaAs TEM samples appears to be an inexpensive and superior alternative to iodine ion milling.     

Hot deformation behaviour of bimodal sized Al2O3/Al nanocomposites fabricated by spark plasma sintering

The deformation behaviour of bimodal sized Al₂O₃/Al nanocomposites were investigated by hot compression tests conducted in the temperature range 350–500°C and strain rates of 0.001, 0.01 and 0.1 s^–1. The dynamic recrystallisation behaviour of the nanocomposites strongly depended on the forming parameters. The bimodal sized Al₂O₃ particles played a crucial role in the recrystallised microstructure. The addition of bimodal sized Al₂O₃ particles led to a significant increase of activation energy of plastic deformation, corroborating the enhanced resistance of the nanocomposite to hot deformation. This was also reflected by the increased compressive yield strength in the nanocomposite due to both dislocation strengthening caused by n‐Al₂O₃ and preventing the grain growth due to the presence of μ‐Al₂O₃ at grain boundaries. It was found that with the decrease of Z values, local strain induced by deformation was released and the grain size of aluminium matrix gradually increased, indicating that the main softening mechanism of the bimodal sized Al₂O₃/Al nanocomposites was dynamic recrystallisation (DRX). The lower the Z value was, the easier the DRX occurred. The highly beneficial role of the bimodal sized Al₂O₃ reinforcement in improving the high‐temperature performance of aluminium matrix nanocomposite was discussed.     

Facile green synthesis approach for the production of chromium oxide nanoparticles and their different in vitro biological activities

Green synthesis of nanoparticles using plants has become a promising substitute for the conventional chemical synthesis methods. In the present study, our aim was to synthesize chromium oxide nanoparticles (Cr₂O₃NPs) through a facile, low‐cost, eco‐friendly route using leaf extract of Rhamnus virgata (RV). The formation of Cr₂O₃NPs was confirmed and characterized by spectroscopic profile of UV–Vis, EDX, FTIR, and XRD analyses. The UV‐visible spectroscopy has confirmed the formation of Cr₂O₃NPs by the change of color owing to surface plasmon resonance. The bioactive functional groups present in the leaf extract of RV involved in reduction and stabilization of Cr₂O₃NPs were determined by FTIR analysis. Based on XRD analysis, crystalline nature of Cr₂O₃NPs was determined. The morphological shape and elemental composition of Cr₂O₃NPs were investigated using SEM and EDX analyses, respectively. With growing applications of Cr₂O₃NPs in biological perspectives, Cr₂O₃NPs were evaluated for diverse biopotentials. Cr₂O₃NPs were further investigated for its cytotoxicity potentials against HepG2 and HUH‐7 cancer cell lines (IC₅₀: 39.66 and 45.87 μg/ml), respectively. Cytotoxicity potential of Cr₂O₃NPs was confirmed against promastigotes (IC₅₀: 33.24 μg/ml) and amastigotes (IC₅₀: 44.31 μg/ml) using Leishmania tropica (KMH₂₃). The Cr₂O₃NPs were further evaluated for antioxidants, biostatic, alpha‐amylase, and protein kinase inhibition properties. Biocompatibility assay was investigated against human macrophages which confirmed the nontoxic nature of Cr₂O₃NPs. Overall, the synthesized Cr₂O₃NPs are biocompatible and nontoxic and proved to possess significant biopotentials. In future, different in vivo studies are needed to fully investigate the cytotoxicity and mechanism of action associated with these Cr₂O₃NPs.     

Particle size distribution and morphological changes in activated carbon‐metal oxide hybrid catalysts prepared under different heating conditions

In catalysis processes, activated carbon (AC) and metal oxides (MOs) are widely used either as catalysts or as catalyst supports because of their unique properties. A combination of AC and a MO in a single hybrid material entails changes not only in the composition, microstructure and texture but also in the morphology, which may largely influence the catalytic behaviour of the resulting product. This work is aimed at investigating the modifications in the morphology and particle size distribution (PSD) for AC‐MO hybrid catalysts as a result of their preparation under markedly different heating conditions. From a commercial AC and six MO (Al₂O₃, Fe₂O₃, ZnO, SnO₂, TiO₂ and WO₃) precursors, two series of such catalysts are prepared by wet impregnation, oven‐drying at 120ºC, and subsequent heat treatment at 200ºC or 850ºC in inert atmosphere. The resulting samples are characterized in terms of their morphology and PSD by scanning electron microscopy and ImageJ processing program. Obtained results indicate that the morphology, PSD and degree of dispersion of the supported catalysts are strongly dependent both on the MO precursor and the heat treatment temperature. With the temperature rise, trends are towards the improvement of crystallinity, the broadening of the PSD and the increase in the average particle size, thus suggesting the involvement of sintering mechanisms. Such effects are more pronounced for the Fe, Sn and W catalysts due to the reduction of the corresponding MOs by AC during the heat treatment at 850ºC.     

Multiferroic behavior of the functionalized surface of a flexible substrate by deposition of Bi2O3 and Fe2O3

Thin films of bismuth and iron oxides were obtained by atomic layer deposition (ALD) on the surface of a flexible substrate poly(4,4′-oxydiphenylene-pyromellitimide) (Kapton) at a temperature of 250°C. The layer thickness was 50 nm. The samples were examined by secondary-ion mass spectrometry, and uniform distribution of elements in the film layer was observed. Surface morphology, electrical polarization, and mechanical properties were investigated by atomic force microscope, piezoelectric force microscopy, and force modulation microscopy. The values of current in the near-surface layer varied in the range of ±80 pA when a potential of 5 V was applied. Chemical analysis was performed by X-ray photoelectron spectroscopy, where the formation of Bi₂O₃ and Fe₂O₃ phases, as well as intermediate phases in the Bi–Fe–O system, was observed. Magnetic measurements were carried out by a vibrating sample magnetometer that showed a ferromagnetic response. The low-temperature method of functionalization of the Kapton surface with bismuth and iron oxides will make it possible to adapt the Bi–Fe–O system to flexible electronics.     

Investigations of Wear Response of Pure Mg and Mg-0.4 Ce-Y2O3/ZnO Nanocomposites Using a Single and Repeated Scratch Tests

ABSTRACT

This work examines the micrometer-scale wear behavior of pure Mg and its composites at various loads (100–500 mN) under single and multiple scratch conditions. The Mg-0.4Ce alloy reinforced with nanoparticles of zinc oxide (ZnO) and yttrium oxide (Y₂O₃) is investigated. The effect of reinforcement addition on wear characteristics and the coefficient of friction (COF) was evaluated. Moreover, the influence of number of scratches on wear quantification and wear mechanism was deduced at different loads. The results suggest that both the mechanical and tribological performance of ZnO-reinforced composite is significantly better than that of the Y₂O₃-reinforced composite, which can be attributed to a low COF and higher strengthening due to ZnO addition.     

单价银离子在 CaO-P2O5 系统玻璃中的发光特性

在弱还原气氛下制备了单价银离子(Ag⁺)掺杂的CaO-P₂O₅系统玻璃,测试了其在室温下的吸收光谱、激发光谱和发射光谱。Ag⁺-CaO-P₂O₅玻璃的吸收光谱表明两个吸收峰。高能峰位于220nm波长,由4d¹⁰→4d⁹5P¹跃迁引起,低能峰中心位于240nm波长,归因于4d¹⁰→4d⁹5s¹跃迁,该吸收与其发射特性有关。紫外波段的宽带吸收产生了可见波段强烈的荧光发射,发光峰位于440nm波长,半宽度为130nm.研究了掺质浓度与发光特性的关系,随着掺质浓度的增加(0.05～0.25mol%),发光峰向较长波段移动。在Ag₂O含量为0.5mol%时,出现了浓度猝灭现象。为了比较起见,同时还研制了Cu⁺-CaO-P₂O₅及Cu⁺-Ag⁺-CaO-P₂O₅玻璃。     

Wear properties of two-phase Al2O3/ZrO2 (Y2O3) ceramics at temperatures from 296 to 1073 K

Reciprocating sliding friction experiments were conducted with various two-phase, directionally solidified Al₂O₃/ZrO₂ (Y₂O₃) pins sliding on B₄C flats in air at temperatures of 296, 873, and 1073 K under dry sliding conditions. Results indicate that all the Al₂O₃/ZrO₂ (Y₂O₃) ceramics, from highly Al₂O₃-rich to ZrO₂-rich, exceed the main wear criterion requirement of 10⁻⁶ mm³ N⁻¹ m⁻¹ or lower for effective wear-resistant applications. Particularly, the eutectics and Al₂O₃-rich ceramics showed superior wear properties. The composition and microstructure of Al₂O₃/ZrO₂ (Y₂O₃) ceramics played a dominant role in controlling the wear and friction properties. The controlling mechanism of the ceramic wear, friction, and hardness was an intrinsic effect involving the resistance to shear fracture of heterophase bonding and cohesive bonding and the interlocking microstructures at different scales in the ceramics.     

Tribofilm formation and mild wear by tribo-sintering of nanometer-sized oxide particles on rubbing steel surfaces

The present study is the first to show that the supply of nanometer-sized particles of Fe₂O₃, SnO₂, CuO, or Bi₂O₃ oxide on rubbing steel surfaces induces transition to mild wear with sliding distance, and that the wear transition behavior depends on the type of supplied oxide. The mild wear is due to formation of the wear-protective tribofilm on the rubbing surfaces, and observations confirm that the tribofilms are produced by tribo-sintering of the supplied oxide particles. The mild wear transition behavior is explained by the sintering rate of the supplied oxide particles, which is related to the oxygen diffusion coefficient in the oxide and the particle diameter. When the supplied oxide is of high diffusivity, the tribofilm formation rate is high, owing to the high sintering rate of the oxide particles, and the mild wear transition occurs at a short sliding distance. In the case of Fe₂O₃ oxide, the sliding distance of the transition from severe to mild wear is decreased when finer particles are supplied, suggesting that fine particles are easily sintered on the wear surface.     

Spectrally resolved thermoluminescence measurements in fluorescence spectrometer

Registration of thermoluminescence (TL) spectra technique for irradiated samples in Perkin Elmer LS 55 spectrometer using developed high-temperature accessory during single heating cycle is shown. Functionality of serial instrument for RT–773 K temperature range is significantly widen. Spectrally resolved TL dependencies for h-BN micropowders and bulk AlN single crystals following UV irradiation are studied. TL spectral features of h-BN powders, synthesized by carbamide and plasma-chemical techniques, are determined and quantified. It is shown that the difference between TL curves obtained by the described and the standard modes does not exceed 10%.     

Scanning electron microscopy of bio‐fabricated Fe2O3 nanoparticles and their application to control brown rot of citrus

Citrus is the leading fruit crop of Pakistan and exported to different parts of the world. Due to suitable weather condition, this crop is affected by different biotic factors which seriously deteriorate its quality and quantity. During the months of November 2018 to January 2019, citrus brown rot symptoms were recurrently observed on sweet oranges in National Agricultural Research Centre (NARC), Islamabad. Causal agent of citrus brown rot was isolated, characterized, and identified as Fusarium oxysporum. For environment‐friendly control of this disease, leaf extract of Azadirachta indica was used for the green synthesis of iron oxide (Fe₂O₃) nanoparticles. These nanoparticles were characterized before their application for disease control. Fourier transform infrared spectroscopy (FTIR) of these synthesized nanoparticles described the presence of stabilizing and reducing compounds like alcohol, phenol, carboxylic acid, and alkaline and aromatic compounds. X‐Ray diffraction (XRD) analysis revealed the crystalline nature and size (24 nm) of these nanoparticles. Energy dispersive X‐Ray (EDX) analysis elaborated the presence of major elements in the samples. Scanning electron microscopy (SEM) confirmed the spinal shaped morphology of prepared nanoparticles. Successfully synthesized nanoparticles were evaluated for their antifungal potential. Different concentrations of Fe₂O₃ nanoparticles were used and maximum mycelial inhibition was observed at 1.0 mg/ml concentration. On the basis of these findings, it could be concluded that Fe₂O₃ nanoparticles, synthesized in the leaf extract of A. indica, can be successfully used for the control of brown rot of sweet oranges.     

Independent trafficking of flavocytochrome b558 and myeloperoxidase to phagosomes during phagocytosis visualised by energy‐filtering and energy‐dispersive spectroscopy‐scanning transmission electron microscopy

When polymorphonuclear leukocytes (PMNs) phagocytose opsonised zymosan particles (OPZ), free radicals and reactive oxygen species (ROS) are formed in the phagosomes. ROS production is mediated by NADPH oxidase (Nox), which transfers electrons in converting oxygen to superoxide (O₂^?). Nox‐generated O₂^? is rapidly converted to other ROS. Free radical‐forming secretory vesicles containing the Nox redox center flavocytochrome b558, a membrane protein, and azurophil granules with packaged myeloperoxidase (MPO) have been described. Presuming the probable fusion of these vesicular and granular organelles with phagosomes, the translation process of the enzymes was investigated using energy‐filtering and energy‐dispersive spectroscopy‐scanning transmission electron microscopy. In this work, the primary method for imaging cerium (Ce) ions demonstrated the localisation of H₂O₂ generated by phagocytosing PMNs. The MPO activity of the same PMNs was continuously monitored using 0.1% 3,3′‐diaminobenzidine‐tetrahydrochloride (DAB) and 0.01% H₂O₂. A detailed view of these vesicular and granular structures was created by overlaying each electron micrograph with pseudocolors: blue for Ce and green for nitrogen (N).