Hollow Alumina Microsphere Chain Networks

Hollow Al₂O₃ microsphere chain networks have been synthesized via a simple two-staged pyrolysis of a precursor using active carbon powders as the template. The obtained networks are characterized using scanning electron microscopy, X-ray diffraction, and transmission electron microscopy. The chain networks are formed by subsequent aggregation of the prior formed hollow Al₂O₃ microspheres. The obtained chain networks are promising for the applications in catalyst support, filtration, and other applications due to their lightweight and highly porous nature.     

Magnesium Aluminate (MgAl2O4) Spinel Powders from Water-Based Sols

Magnesium aluminate (MgAl₂O₄) spinel powders of irregular and spherical morphologies were obtained from the bi-component water-based sols following the sol–gel and sol–emulsion–gel methods, respectively. For the synthesis of the oxide microspheres, the surfactant concentration and viscosity of the sols were found to affect the characteristics of the derived microspheres. The gel and calcined powders were investigated by using thermogravimetry analysis, differential thermal analysis, X-ray diffraction (XRD), optical and scanning electron microscopy (SEM), Fourier transformed infrared spectroscopy, and particle size analysis. XRD results indicated crystallization of the only phase MgAl₂O₄ spinel from 200° to 1000°C. Formation of hollow microspheres with a single cavity was identified by SEM.     

Hollow Al2O3 Microspheres Derived from Al/AlOOH·nH2O Core-Shell Particles

Hollow Al₂O₃ spheres with ∼2 μm in diameter and ∼200 nm in wall thickness were prepared successfully via the calcination of the Al/AlOOH· n H₂O core-shell particles, prepared by wet-chemical method using commercial microscale aluminum powders as raw materials, at 900°–1100°C in air. X-ray powder diffraction, differential scanning calorimetric analysis, scanning electron microscopy, and transmission electron microscopy were used to characterize the obtained samples, and the possible formation mechanism was discussed. These hollow Al₂O₃ microspheres may have promising applications in insulators, lightweight fillers, and catalyst carriers because of their unique hollow structure.     

Barium Holmium Zirconate, A New Perovskite Oxide: II, Synthesis as Nanoparticles through a Modified Combustion Process

Nanoparticles of barium holmium zirconate, a new complex perovskite ceramic oxide, has been synthesized using a modified self-propagating combustion process. The solid combustion products obtained were characterized by X-ray diffraction (XRD), electron diffraction, differential thermal analysis, thermogravimetric analysis, infrared spectroscopy, particle size analysis, surface area determination, and high-resolution transmission electron microscopy. The XRD and electron diffraction studies have shown that the as-prepared powder is phase pure Ba₂HoZrO_5.5 and has a complex cubic perovskite (A₂BB'O₆) structure with a lattice constant a = 8.428 Å. The transmission electron microscopic investigation has shown that the particle size of the as-prepared powder was in the range 4–16 nm with a mean grain size of 8.2 nm. The nanoparticles of Ba₂HoZrO_5.5 obtained by the present method could be sintered to 98% theoretical density at 1500°C.     

Synthesis of Yttrium–Aluminum–Garnet Hollow Microspheres by Reverse-Emulsion Technique

Yttrium–aluminum–garnet (YAG, Y₃Al₅O₁₂) hollow microspheres were synthesized by reverse-emulsion (w/o) technique starting with aqua-based precursors of oxides. The non-ionic surfactant was used as the emulsifying agent. The gel powders were calcined at 700°–1200°C. The synthesized powders were characterized by differential thermal analysis (DTA), thermogravimetry, Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), and scanning electron microscopy (SEM). The appearance of an exothermic peak at 932°C in the DTA curve revealed the crystallization of YAG, which was further confirmed by XRD and FTIR studies. SEM confirmed the formation of hollow microspheres.     

Hydrothermal Synthesis of CdMoO4 Nano-Particles

CdMoO₄ nano-particles were successfully synthesized by a hydrothermal process at a low temperature of 90°C, and the powders were characterized in detail by X-ray diffraction, transmission electron microscopy, scanning electron microscopy, and photoluminescent spectra techniques (PL), respectively. CdMoO₄ particles could be obtained under the hydrothermal condition from micrometer to nanometer sizes by varying their precursors. The PL spectra results showed that the optical properties of CdMoO₄ crystallites obviously relied on their particle sizes.     

A Rapidly Responding Sensor for Methanol Based on Electrospun In2O3–SnO2 Nanofibers

In this paper, we presented a simple and effective electrospinning technique for the preparation of In₂O₃–SnO₂ composite nanofibers. The morphology and chemical structure of the as-prepared samples were analyzed by scanning electron microscopy, transmission electron microscopy, and X-ray diffraction. The results showed that large quantities of In₂O₃–SnO₂ composite nanofibers with diameters from 60 to 100 nm were obtained. The In₂O₃–SnO₂ composite nanofibers exhibited excellent gas sensing properties to methanol, such as fast response/recovery properties, high sensitivity, and good selectivity.     

Low-Temperature Synthesis of 0.65 PbMg1/3Nb2/3O3–0.35PbTiO3 Ceramics

Nanocrystalline 0.65 PbMg_1/3Nb_2/3O₃–0.35PbTiO₃ powders were synthesized by citrate gel method. The gel was prepared using citrate (titanium and niobium) and nitrate (lead and magnesium) salts. The hard gel obtained after completion of the reaction was treated to get the desired phase. Thermal analysis of the gel was done to optimize the calcination temperature. The calcined powders were characterized by X-ray diffraction, scanning electron microscopy, and transmission electron microscopy. The crystallite size and the effective strain were found to be 50 nm and 0.03584 N, respectively.     

Synthesis and Photoluminescence of Eu2+-Doped α-Silicon Nitride Nanowires Coated with Thin BN Film

A feasible doping strategy is introduced to synthesize Eu²⁺-doped α-Si₃N₄ nanowires coated with a thin BN film. The nanowires were characterized by X-ray diffraction, scanning electron microscopy, high-resolution transmission electron microscopy, and a fluorescence spectrophotometer. The Eu²⁺-doped α-Si₃N₄ nanowires emitted strong yellow light, which is related to the 4 f ⁶5 d –4 f ⁷ transition of Eu²⁺, upon a broad excitation wavelength range between 250 and 450 nm. The obtained nanowires provided a potential candidate for application in optical nanodevices, as well as in white LEDs.     

Nature of Intergranular Phase in Nonohmic ZnO Ceramics Containing 0.5 Mol% Bi2O3

The intergranular phase obtained by sintering a binary mixture of ZnO + 0.5 mol% Bi₂O₃ was isolated by using a dilute solution of HCIO₄, which etches ZnO preferentially. The combined results of selected-area electron diffraction and microscopy, microprobe analysis, and X-ray diffraction strongly indicate that the intergranular material is a polycrystalline phase of tetragonal β-Bi₂O₃ ( P 42₁ c ), rather than the amorphous ZnO-Bi₂O₃ phase reported earlier. It appears that the nonohmic behavior in this prototype metal-oxide varistor must be an interfacial property associated with the semiconducting ZnO grains separated by thin layers of high-resistivity Bi₂O₃.     

Molten-Salt Synthesis and Characterization of Nickel-Doped Forsterite Nanocrystals

Nickel-doped forsterite (Ni²⁺:Mg₂SiO₄) nanocrystals have been synthesized by a facile molten-salt approach in the presence of NaCl and a surfactant (NP-7.5). The products were characterized by X-ray diffraction, transmission electron microscopy (TEM), high-resolution TEM, selected area electron diffraction (SAED), and luminescence spectra measurements. The crystal size could be controlled by tailoring the synthesis parameters. TEM, high-resolution TEM, and SAED results revealed the single crystalline character of Mg₂SiO₄ nanoparticles. A possible model for the growth of Ni²⁺:Mg₂SiO₄ nanocrystals was postulated. The obtained Ni²⁺:Mg₂SiO₄ nanocrystals show strong, super broad, near-infrared luminescence at room temperature. These doped Mg₂SiO₄ nanocrystals are promising gain mediums for super broadband optical amplification.     

Preparation of MgAl2O4 Spinel Powders via Freeze-Drying of Alkoxide Precursors

High-sinterability MgAl₂O₄ powder has been produced from alkoxide precursors via a freeze-drying method. Clear alumina sol and magnesium methoxide were used as starting materials in the process. The spinel powders were characterized by various techniques, such as thermal analysis, X-ray diffraction, scanning electron microscopy, and transmission electron microscopy. The tap density and sinterability of the spinel power are affected by the ball-milling techniques. Highly dense, transparent, polycrystalline MgAl₂O₄ has been obtained from these powders by sintering and hot isostatic pressing. Bimodal grain-size microstructure is observed in a HIPed sample.     

Synthesis and Characterization of Several α-Silicon Nitride Nanostructures

Silicon nitride (Si₃N₄) nanowires and nanobelts have been successfully prepared via direct crystallization of amorphous Si₃N₄ nanoparticles under high temperature in a N₂ flow. The products were characterized by X-ray powder diffraction, scanning electron microscopy, transmission electron microscopy, high-resolution electron microscopy, and electron diffraction. They are pure α-phase hexagonal single-crystal structures. The nanowires are long and smooth; nanobelts are long and twisted. In our samples, there exist some special nanostructures, such as wire-inserted hexagonal nanosheet and hollow-chain-shaped structure. The different growth modes were understood upon the observations and characterization of those microstructures. The solid–liquid–solid growth mechanism is also discussed.     

Synthesis of Diamond from Carbon Disulfide in Hydrogen

The synthesis of diamond has been accomplished from carbon disulfide (CS₂) in hydrogen (H₂) using tungsten hot filament chemical vapor deposition. A continuous layer was deposited on silicon and characterized using Raman spectroscopy, X-ray diffraction (XRD), and scanning electron microscopy. The polycrystalline film exhibited a sharp Raman peak at 1331.4 cm⁻¹ and a broad low–intensity peak at approximately 1500 cm⁻¹. X–ray diffraction analysis showed peaks corresponding to the {111}, {220}, and {311} reflections of diamond with evidence of (110) texture. Diamond growth from CS₂ in H₂ was observed to be highly faceted by scanning electron microscopy.     

Reactive Hot Pressing of SiC/MoSi2 Nanocomposites

Dense SiC/MoSi₂ nanocomposites were fabricated by reactive hot pressing the mixed powders of Mo, Si, and nano-SiC particles coated homogeneously on the surface of Si powder by polymer processing. Phase composition and microstructure were determined by methods of X-ray diffraction, scanning electron microscopy, transmission electron microscopy, and energy-dispersive spectrometry. The nanocomposites obtained consisted of MoSi₂, β-SiC, less Mo₅Si₃, and SiO₂. A uniform dispersion of nano-SiC particles was obtained in the MoSi₂ matrix. The relative densities of the monolithic material and nanocomposite were above 98%. The room-temperature flexural strength of 15 vol% SiC/MoSi₂ nanocomposite was 610 MPa, which increased 141% compared with that of the monolithic MoSi₂. The fracture toughness of the nanocomposite exceeded that of pure MoSi₂, and the 1200°C yield strength measured for the nanocomposite reached 720 MPa.     

Assembly and Deagglomeration of Lanthanum Orthoborate Nanobundles

LaBO₃ bundle-like nanorods are self-assembled through a novel oxide-hydrothermal method. In this route, the stoichiometric amounts of La₂O₃ and boric oxide B₂O₃ are mixed in proper amounts of water in a surfactant/ligand-free sealed hydrothermal system. The nanobundles are de-agglomerated to nanorods by tiny Sm³⁺ replacing La³⁺. The characterization of these materials has been carried out by X-ray powder diffraction, FTIR, thermo-gravimetric and differential scanning calorimetry, scanning electron microscopy, transmission electron microscopy, and selected area electron diffraction. As-prepared aragonite-type LaBO₃ nanorods are fairly controlled to have a high purity, homogeneous, and bundled morphology composed of numerous nanorods with diameter ca. 90 nm. The formation processes and mechanics of LaBO₃ nanobundles and nanorods are investigated. The room-temperature fluorescence properties of various Sm³⁺-doped LaBO₃ are investigated.     

Synthesis and Properties of Porous Single-Phase β'-SiAlON Ceramics

Single-phase β'-SiAlON (Si_{6− z} Al _z O _z N_{8− z} , z = 0–4.2) ceramics with porous structure have been prepared by pressureless sintering of powder mixtures of á-Si₃N₄, AlN, and Al₂O₃ of the SiAlON compositions. A solution of AlN and Al₂O₃ into Si₃N₄ resulted in the β'-SiAlON, and full densification was prohibited because no other sintering additives were used. Relative densities ranging from 50%–90% were adjusted with the z -value and sintering temperature. The results of X-ray diffraction, scanning electron microscopy, and transmission electron microscopy analyses indicated that single-phase β'-SiAlON free from a grain boundary glassy phase could be obtained. Both grain and pore sizes increased with increasing z -value. Low z -value resulted in a relatively high flexural strength.     

Crystalline Intermediate Phases in the Sol–Gel-Based Synthesis of La2NiO4+δ

X-ray diffraction and transmission electron microscopy were applied to investigate a sol–gel synthetic process for the mixed oxygen ion and electron conductor La₂NiO_4+δ with a K₂NiF₄ structure type. The development of the La₂NiO_4+δ is elucidated considering the influence of calcination temperatures and dwell times. Following the thermal decomposition of nitrate and organic precursors in an intermediate step, the lanthanum nickel oxide is obtained after a short dwell time above 750°C. This occurs by the transformation of an ultrafinely dispersed powder consisting of lanthanum oxycarbonate, lanthanum oxide, and nickel oxide. The pure La₂NiO_4+δ phase was obtained by similar solid-state reactions between nanocrystalline powder particles at just 950°C.     

Preparation of Monodispersed Y-Ba-Cu-O Superconductor Particles via Sol—Gel Methods

The high-T _c superconducting material YBa₂Cu₃O_{7- x} was synthesized using a modified amorphous citrate or oxalate process. Phase-pure superconducting powders were obtained by firing the citrate precursor to 900°C and the oxalate precursor to 950°C inflowing O₂. The preparation is highly reproducible and leads to powders with excellent homogeneity and sinterability. The resulting material was examined by transmission electron microscopy, thermogravimetry, and X-ray diffraction. Particle sizes for the superconductors obtained varied from 75 to 3300 Å (7.5 to 330 nm).     

Morphology Transformation of Nanoscale Magnesium Hydroxide: from Nanosheets to Nanodisks

Nanoscale Mg(OH)₂ with different morphologies, from nanosheets, nanosquares, and nanodisks, have been successfully synthesized via a simple hydrothermal reaction of Mg(CH₃COO)₂ and sodium hydroxide in the presence of citrate. Direct observation of transformation from nanosheets to nanodisks indicates clearly the growth of a Mg(OH)₂ nanocrystal. The structure and morphology of the resultant Mg(OH)₂ nanostructures were characterized by X-ray powder diffraction (XRD), transmission electron microscopy (TEM), high-resolution transmission electron microscopy (HRTEM), and selected area electron diffraction patterns (SAED). A possible formation mechanism of the Mg(OH)₂ nanostructures is proposed based on the oriented aggregation mechanism.