Synthesis of Al–Cr decagonal quasicrystal nanoparticles and their temperature of phase transformation to stable crystal phase

The synthesis of Al–Cr single quasicrystal (QC) nanoparticles of the decagonal phase was achieved by introducing an advanced gas flow evaporation method. By obtaining successive electron diffraction patterns for single-QC nanoparticles, the phase transformation temperature of a single-QC nanoparticle was determined to be 700 °C. It was also determined that part of the QC nanoparticle decomposed into hex-Al₈Cr₅ and Al during the phase transformation. Since the grain growth did not occur during the phase transformation in the present experiment, the inherent phase transformation temperature could be measured.     

Structure of Al deposits on nanometer-size islands of aluminum-oxide

Because of the immense structural mismatch between a crystal and a quasicrystal, the aluminum-oxide domains that grow on the pentagonal surface of icosahedral Al–Pd–Mn at high temperatures are in the order of a few nm large. Here, we exploit the small lateral extension of the oxide domains to grow crystalline Al particles in the same size-region by vapor deposition on them. Low-energy-electron diffraction and secondary-electron imaging investigations show that the nanocrystals expose their (1 1 1) faces parallel to the pentagonal surface of the quasicrystal, while the in-plane orientation of the crystallites is random. Spot-profile analysis of the diffracted beams indicate that the Al nanocrystals grow in 3 nm large domains up to a deposition thickness of 51 monolayers.     

The electronic behaviors of TiO2/MnO2/carbon clusters composite materials obtained by the calcination of a TiO(acac)2/Mn(acac)3/epoxy resin complex

The calcination of a TiO(acac)₂/Mn(acac)₃/epoxy resin complex under an oxygen atmosphere successfully produced nano-sized TiO₂/MnO₂/carbon clusters composite material. The surface characterizations of the resulting composites indicate that they are composed of nano-sized particles of TiO₂, MnO₂ and carbon clusters. ESR spectral examination suggests the possibility of an electron transfer in the process of MnO₂ → carbon clusters → TiO₂. The visible light-responsive oxidation–reduction function of the composite materials has also been confirmed.     

Luminescence from ZnO/MgO nanoparticle structures prepared by solution techniques

The optical and structural properties of mixed ZnO/MgO particles prepared by solution techniques are investigated by the cathodoluminescence and electron microscopy techniques. The samples annealed at 400–1000 °C show well crystalline wurtzite structure of the ZnO (MgZnO) particles with the size in range of 10–100 nm. Annealing at high temperatures (>700 °C) leads to Mg diffusion in ZnO and Mg_xZn_1−xO alloy formation. The blue shifts of the near-band-edge emission as a result of the alloy band gap widening and quantum confinement effect for the small size particles are demonstrated.     

Enhanced ferromagnetism in Mn-doped TiO2 films during the structural phase transition

The crystal structures and magnetic properties of Ti_0.9747Mn_0.0253O₂ films prepared by sol–gel dip coating have been investigated. Room temperature ferromagnetism was observed both in the films of pure anatase phase and of mixed anatase and rutile phases. For the first time, enhancement of the ferromagnetism was revealed as the phase transition from anatase to rutile occurs: from 0.7±0.01μ_B/Mn to 1.1±0.05μ_B/Mn. The possible mechanism for the observed magnetism enhancement is discussed.     

Studies on the preparation and ethanol gas sensing properties of spinel Zn0.6Mn0.4Fe2O4 nanomaterials

Zn_1−xMn_xFe₂O₄ (x = 0, 0.2 and 0.4) nanomaterials were synthesized by sol–gel citrate method and studied structural and gas sensing properties. The structural characteristics of synthesized nanomaterials were studied by X-ray diffraction measurement (XRD) and transmission electron microscope (TEM). The results revealed that the particle size is in the range of 30–35 nm for Mn–Zn ferrite with good crystallinity. The gas sensing properties were studied towards reducing gases like LPG, CH_4, CO and ethanol and it is observed that Mn–Zn ferrite shows high response to ethanol at relatively lower operating temperature. The Zn_0.6Mn_0.4Fe₂O₄ nanomaterial shows better sensitivity towards ethanol at an operating temperature 300 °C. Incorporation of 1.5 wt.% Pd improved the sensitivity, selectivity, response time and reduced the operating temperature from 300 °C to 230 °C for ethanol sensor. The response time of 200 ppm ethanol in air is about 10s.     

Texture in a ternary Nd16.2Fe78.2B5.6 powder using a modified hydrogenation–disproportionation–desorption–recombination process

A modified hydrogenation–disproportionation desorption-recombination (HDDR) process consisting of (i) solid disproportionation and (ii) slow recombination under partial hydrogen pressure has been applied to a Nd_16.2Fe_78.2B_5.6 alloy. Scanning electron microscopy shows that an initially fine rod-like structure of NdH_2±x and Fe observed after 15 min of hydrogenation at 900°C is transformed into a granular morphology with prolonged annealing. Simultaneously, finely dispersed tetragonal Fe₃B particles of 10–50 nm diameter exist. XRD studies show that this metastable Fe₃B phase is transformed to Fe₂B and Fe on further annealing. Short solid-disproportionation times result in a higher degree of anisotropy after recombination, whereas long annealing times and conventional processing lead to isotropic material. It is concluded that the formation of the intermediate tetragonal Fe₃B phase after solid disproportionation is pivotal for the inducement of texture in HDDR processed ternary NdFeB-type alloys.     

Preignition characteristics of nano- and micrometer-scale aluminum particles in Al–CO2 oxidation systems

The objective of this study was to gain understanding of the preignition oxidation of Al powders in CO₂. The thermal behavior and reaction energy was studied using simultaneous thermogravimetric analysis and differential scanning calorimetry (TG–DSC). The particle morphology was examined at different stages of the process using field emission gun scanning electron microscopy (FEG-SEM) and transmission electron microscopy (TEM). The corresponding chemical changes were analyzed by X-ray diffraction spectrometry (XRD) and energy dispersion X-ray spectrometry (EDS). Dimensional properties of Al particles have a significant influence on the oxidation processes. Distinctly different properties were shown between nm-Al and μm-Al, where the reactions are found to occur at different temperature ranges. The powder behavior is controlled by the oxide layer that coats each particle and prevents exposure of the metal core to the reactive CO₂ gas. The properties of the oxide layer are related to the particle size. Carbon has been shown to play an important role in the reacting Al–CO₂ system. A new mechanism of nano-Al particle oxidation in CO₂ under gradually increasing temperature was proposed.     

Magnetic properties of FexCo1−x/CoyFe1−yFe2O4 composite under hydrothermal condition

The metal–ferrite composites Fe_xCo_1−x/Co_yFe_1−yFe₂O₄ are synthesized by using disproportion of Fe (II) and reduction of Co (II) by Fe⁰ under hydrothermal condition. The size of the particles of the composites decreases as the [KOH] decreasing. The composites are measured by TEM and it can be deduced that when [KOH] = 0.1, the size of the alloy body-centered cubic (BCC) in composites is 20 ± 7 nm, the size of the Cobalt ferrite (spinel) is 170 ± 50 nm. The maximal value of the saturation magnetization (Ms) of the composite is about 100.14 emu/g, which is synthesized under Co (II)/Fe (II) = 0.05, [KOH] = 1 N, T = 150 °C and t = 3 h. The value of Hc of the composite synthesized under Co (II)/Fe (II) = 0.5, t = 3 h, T = 150 °C and [KOH] = 10.2 mol/L is about 2878.19 Oe. The Fe–Co alloy is synthesized through a reduction reaction of the composites in a flowing gaseous mixture. There is a maximal value (302.9 emu/g) of the Ms for the alloys generated at 1000 °C, which is the Co_0.412Fe_0.588 alloy.     

Gas-phase Crystallization of Titanium Dioxide Nanoparticles

We have investigated the development of crystal morphology and phase in ultrafine titanium dioxide particles. The particles were produced by a droplet-to-particle method starting from propanolic titanium tetraisopropoxide solution, and calcined in a vertical aerosol reactor in air. Mobility size classified 40-nm diameter particles were conveyed to the aerosol reactor to investigate particle size changes at 20–1200°C with 5–1-s residence time. In addition, polydisperse particles were used to study morphology and phase formation by electron microscopy. According to differential mobility analysis, the particle diameter was reduced to 21–23-nm at 600°C and above. Precursor decomposition occurred between 20°C and 500°C. The increased mobility particle size at 700°C and above was observed to coincide with irregular particles at 700°C and 800°C and faceted particles between 900°C and 1200°C, according to transmission electron microscopy. The faceted anatase particles were observed to approach a minimized surface energy by forming {101} and {001} crystallographic surfaces. Anatase phase was observed at 500–1200°C and above 600°C the particles were single crystals. Indications of minor rutile formation were observed at 1200°C. The relatively stable anatase phase vs. temperature is attributed to the defect free structure of the observed particles and a lack of crystal–crystal attachment points.     

Effect of surface roughness of TiO2 films on short-circuit current density of photoelectrochemical cell of ITO/TiO2/PVC-LiClO4/graphite

This paper reports the effect of surface topography of titanium dioxide films on short-circuit current density of photoelectrochemical solar cell of ITO/TiO₂/PVC-LiCLO₄/graphite. The films were deposited onto ITO-covered glass substrate by screen-printing technique. The films were tempered at 300 °C, 350 °C, 400 °C, 450 °C and 500 °C for 30 min to burn out the organic parts and to achieve the films with porous structure. The surface roughness of the films were studied using scanning electron microscope (SEM). Current–voltage relationship of the devices were characterized in dark at room temperature and under illumination of 100 mW cm⁻² light from tungsten halogen lamp at 50 °C. The device utilising the TiO₂ film annealed at 400 °C produces the highest short-circuit current density and open-circuit voltage as it posses the smoothest surface topography with the electrolyte. The short-circuit current density and open-circuit voltage of the devices increase with the decreasing grain size of the TiO₂ films. The short-circuit current density and open-circuit voltage are 0.6 μA/cm² and 109 mV respectively.     

Novel nanostructures of β-Ga2O3 synthesized by thermal evaporation

In this study, we report the novel β-Ga₂O₃ nanostructures synthesized by the thermal evaporation of Ga droplet in the presence of Au catalysts at 900 °C. The morphology and structure of the products were analyzed by scanning electron microscopy (SEM), transmission electron microscopy (TEM), and X-ray diffraction (XRD). The single-crystalline β-Ga₂O₃ nanosheets have lateral dimensions up to several tens of microns. Large arrays of column-like layered crystal β-Ga₂O₃ structures that consisted of many nanosheets were formed on the Au-coated silicon substrate under the suitable vapor concentration. These novel β-Ga₂O₃ nanostructures are expected to have potential application in functional nanodevices.     

Effect of the synthesis route on the structural properties and shape of the indium oxide (In2O3) nano-particles

Nano-crystalline indium oxide (In₂O₃) particles have been synthesized by sol–gel and hydro-thermal techniques. A simple hydro-alcoholic solution consisting indium nitrate hydrate and citric acid (in sol–gel method) and 1, 4-butandiol (in hydro-thermal method) have been utilized. The structural properties of indium oxide nano-powders annealed at 450 °C (for both methods) have been characterized by the X-ray diffraction (XRD), transmission electron microscopy (TEM), scanning electron microscopy (SEM), and specific surface area (SSA) analysis. Structural analysis of the samples shows cubic phase in sol–gel and cubic-hexagonal phase mixture in hydro-thermally prepared particles. The nano-particles prepared by sol–gel method have nearly spherical shape, whereas hydro-thermally-made ones display wire- and needle-like shape in addition to the spherical shape. The obtained In₂O₃ nano-particles surface areas were 23.2 and 55.3 in sol–gel and hydro-thermal methods, respectively. The optical direct band gap of In₂O₃ nano-particles were determined to be 4.32 and 4.24 eV for sol–gel and hydro-thermal methods, respectively. These values exhibit 0.5 eV blue shift from that the bulk In₂O₃ (3.75 eV), which is related to the particle size reduction and approaching the quantum confinement limit of nano-particles.     

A new technique for the measurement of the product CO/CO2 ratio at the surface of char particles burning in a fluidized bed

A new experimental technique is proposed to measure the product CO/CO₂ ratio at the surface of spherical char particles during fluidized bed combustion. It is based on the measurement of the burning rate of a single char particle under low oxygen concentration conditions and on the use of an accurate prediction of the particle Sherwood number. This technique was applied to spherical char particles obtained from a bituminous coal which is characterized by a low attrition and fragmentation propensity. The product CO/CO₂ ratio was measured at a bed temperature of 850 °C and at a fluidization velocity of 0.3 m/s in a lab-scale apparatus operated with a bed of 0.5–0.6 mm sand. The char particle size was varied between 2 and 7 mm and the inlet oxygen concentration between 0.1% and 2.0%. Results showed that under the experimental conditions investigated carbon was mostly oxidized to CO₂ within the particle boundary layer, with a maximum fraction of carbon escaping as CO of 10–20% at the lowest oxygen concentrations and largest particle sizes.     

溅射法制备Ag/Ag2O超微粒子的分析

用Ｘ射线衍射、Ｘ射线光电子能谱、透射电子显微镜和差示扫描量热法对溅射法制备的Ａｇ超微粒子的晶体学结构、表面组成、微粒形态和热力学性质进行了分析。结果表明，所制备的微粒为内部为Ａｇ、表面为Ａｇ₂Ｏ的两相微粒，以及单一的Ａｇ₂Ｏ微粒，粒径在１０ｎｍ以上的微粒没有确定的外形，粒径在１０ｎｍ以下的微粒为球形。微粒有不同于块体金属Ａｇ的异常热效应。到４０天时，沉积在碳膜上的Ａｇ，Ａｇ₂Ｏ两相微粒有一部份还原形成了单一的金属Ａｇ超微粒子。 关键词：     

Molecular dynamics simulation comparison of atomic scale intermixing at the amorphous Al2O3/semiconductor interface for a-Al2O3/Ge, a-Al2O3/InGaAs, and a-Al2O3/InAlAs/InGaAs

The structural properties of a-Al₂O₃/Ge, a-Al₂O₃/In_0.5Ga_0.5As and a-Al₂O₃/In_0.5Al_0.5As/InGaAs interfaces were investigated by density-functional theory (DFT) molecular dynamics (MD) simulations. Realistic a-Al₂O₃ samples were generated using a hybrid classical-DFT MD “melt and quench” approach. The interfaces were formed by annealing at 700 K/800 K and 1100 K with subsequent cooling and relaxation. The a-Al₂O₃/Ge interface demonstrates pronounced interface intermixing and interface bonding exclusively through Al–O–Ge bonds generating high interface polarity. In contrast, the a-Al₂O₃/InGaAs interface has no intermixing, Al–As and O–In/Ga bonding, low interface polarity due to nearly compensating interface dipoles, and low substrate deformation. The a-Al₂O₃/InAlAs interface demonstrated mild intermixing with some substrate Al atoms being adsorbed into the oxide, mixed Al–As/O and O–Al/In bonding, medium interface polarity, and medium substrate deformation. The simulated results demonstrate strong correlation to experimental measurements and illustrate the role of weak bonding in generating an unpinned interface for metal oxide/semiconductor interfaces.     

Synthesis, phase and microstructure characteristics of Pb(Zr0.52Ti0.48)O3–(Bi3.25La0.75)Ti3O12 ceramics

Ceramics with formula (1 − x)Pb(Zr_0.52Ti_0.48)O₃–x(Bi_3.25La_0.75)Ti₃O₁₂ (when x = 0, 0.1, 0.3, 0.5, 0.7, 0.9 and 1.0) were prepared by a solid-state mixed-oxide method and sintered at temperatures between 950 °C and 1250 °C. It was found that the optimum sintering temperature was 1150 °C at which all the samples had densities at least 95% of theoretical values. Phase analysis using X-ray diffraction indicated the existence of BLT- as well as PZT-based solid solutions with corresponding lattice distortion. Scanning electron micrographs of ceramic surfaces showed a plate-like structure in BLT-rich phase while the typical grain structure was observed for PZT-rich phase. The grain sizes of both pure BLT and PZT ceramics were found to decrease as the relative amount of the other phase increased. This study suggested that tailoring of properties of this PZT–BLT system was possible especially on the BLT-rich side due to its large solubility limit.     

Nano-designing of Mg doped phosphate tungsten bronzes and SiO2 composite obtained by ultrasonic spray pyrolysis method

In this study, the structure and substructure of SiO₂–Mg phosphate tungsten bronzes, MgPTB, (MgHPW₁₂O₄₀ · 29H₂O) obtained by ultrasonic spray pyrolysis method from a silica sol, and a MgPTB solution, obtained by the ion exchange method, as precursors were investigated.The mechanism of the formation of aerosol droplets is discussed. Phase composition, structure and substructure of SiO₂–MgPTB particles were investigated by X-ray powder diffraction (XRPD) analysis, transmission electron microscopy (TEM), and scanning electron microscopy (SEM).Good agreement between the theoretically predicted values for the mean diameters of particles and subparticles (1.27 μm and 75.4 nm, respectively) and the experimentally obtained ones (1.17 μm and 65–90 nm) was found.This agreement confirms the applicability of the model to get a satisfactory prediction of the most important data related to the nano-structural design of SiO₂–MgPTB powders.     

Preparation and properties of composite ceramic coating containing Al2O3–ZrO2–Y2O3 on AZ91D magnesium alloy by plasma electrolytic oxidation

A composite ceramic coating containing Al₂O₃–ZrO₂–Y₂O₃ was successfully prepared on AZ91D magnesium alloy by plasma electrolytic oxidation (PEO) technique in an alkaline aluminate electrolyte. The morphology, elemental and phase composition, corrosion behavior and thermal stability of the uncoated and coated samples were studied by environmental scanning electron microscopy (ESEM), energy dispersive X-ray spectrometer (EDS), X-ray diffractometer (XRD), electrochemical corrosion test, high temperature oxidation test and thermal shock test. The results showed that the composite ceramic coating was composed of Al₂O₃, c-ZrO₂, t-ZrO₂, Y₂O₃ and some magnesium compounds, such as MgO, MgF₂ and MgAl₂O₄. After PEO treatment, the corrosion potential of AZ91D alloy was increased and the corrosion current density was significantly reduced. Besides, the coated magnesium alloys also showed excellent high temperature oxidation resistance and thermal shock resistance at 500 °C environment.     

Preparation of α-Fe2O3 nanoparticles by high-energy ball milling

α-Fe₂O₃ nanoparticles were prepared by high-energy ball milling using α-FeOOH as raw materials. The prepared samples were characterized by transmission electron microscopy (TEM), Mössbauer spectroscopy, X-ray diffraction (XRD) and differential thermal analysis–thermogravimetric analysis (DTA–TGA). The results showed that after 90 h milling α-Fe₂O₃ nanoparticles were obtained, and the particle size is about 20 nm. The mechanism of reaction during milling is supposed that the initial α-FeOOH powder turned smaller and smaller by the high-speed collision during ball milling, later these particles turned to be superparamagnetic, at last these superparamagnetic α-FeOOH particles were dehydrated and transformed into α-Fe₂O₃.