Synthesis of lanthanum hydroxide and lanthanum oxide nanoparticles by sonochemical method

In this work lanthanum hydroxide nanoparticles were synthesized by sonochemical method. La₂O₃ nanoparticles were obtained after calcination of the La(OH)₃ nanoparticles precursor in air at 600 °C for 2 h. The effect of some parameters such as concentration of precursors, pulse time of sonication, time of sonication, and addition of PEG as surfactant on the morphology and the particle size were studied. The as-prepared products were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray photoelectron spectrum (XPS) and Fourier transform infrared (FT-IR) spectra.     

Lanthanum ferrite ferromagnetic nanocrystallites by a polymeric precursor route

Reactive lanthanum orthoferrite nanoparticles were obtained by a polymeric precursor route. Nanoparticle growth and crystallization from amorphous precursor, as well as the formation of a grain boundary network in polycrystalline aggregates at different calcination temperatures were studied by conventional and high-resolution electron microscopy; electron and X-ray diffraction analysis; Raman; IR; and UV-vis spectroscopy. Microstructure measurements were compared to X-ray diffraction and chemical analysis results. Electron diffraction, combined with electron microscopy results were used to determine the content of amorphous phase. The coherent crystalline domain size and the particle size have been monitored by XRD and electron microscopy in order to determine the evolution of both crystal size and the onset temperature for crystallites formation. The results demonstrate that at 550 °C we obtain pure single-phase nanocrystalline LaFeO₃, sized ∼40 nm, without the presence of amorphous phase. The magnetization curves in the 5-350 K range indicate weak ferromagnetism of the LaFeO₃ powders.     

Ultrasonic-assisted in situ synthesis and characterization of superparamagnetic Fe3O4 nanoparticles

Superparamagnetic Fe₃O₄ nanoparticles were synthesized via a modified coprecipitation method, and were characterized with X-ray diffraction (XRD), vibrating sample magnetometer (VSM), Zeta potential and FT-IR, respectively. The influences of different kinds of surfactants (sodium dodecyl benzene sulfonate, polyethyleneglycol, oleic acid and dextran), temperatures and pH values on the grain size and properties were also investigated. In this method, Fe³⁺ was used as the only Fe source and partially reduced to Fe²⁺ by the reducing agent with precise content. The following reaction between Fe³⁺, Fe²⁺ and hydroxide radical brought pure Fe₃O₄ nanoparticles. The tiny fresh nanoparticles were coated in situ with surfactant under the action of sonication. Comparing with uncoated sample, the mean grain size and saturation magnetization of coated Fe₃O₄ nanoparticles decrease from 18.4 nm to 5.9-9.0 nm, and from 63.89 emu g⁻¹ to 52-58 emu g⁻¹ respectively. When oleic was used as the surfactant, the mean grain size of Fe₃O₄ nanoparticles firstly decreases with the increase of reaction temperature, but when the temperature is exceed to 80 °C, the continuous increase of temperature resulted in larger nanoparticles. the grain size decreases gradually with the increasing of pH values, and it remains unchanged when the PH value is up to 11. The saturation magnetization of as-prepared Fe₃O₄ nanoparticles always decreases with the fall of grain size.     

Synthesis and phosphorescence properties of Mn, La and Ho in MgAl2Si2O8

Mn⁴⁺, La³⁺ and Ho³⁺ doped MgAl₂Si₂O₈-based phosphors were first synthesized by solid state reaction. They were characterized by thermogravimetry (TG), differential thermal analysis (DTA), X-ray powder diffraction (XRD), photoluminescence (PL) and scanning electron microscopy (SEM). The phosphors were obtained at about 1300 °C. They showed broad red and fuchsia-pink emission bands in the range of 610-715 nm and had a different maximum intensity when activated by UV illumination. Such a fuchsia-pink emission can be attributed to the intrinsic d-d transitions of Mn⁴⁺.     

Sol-gel synthesis of Bi3.25La0.75Ti3O12 nanotubes

Ferroelectric Bi_3.25La_0.75Ti₃O₁₂ (BLT) nanotubes were synthesized by sol-gel technique using nanochannel porous anodic aluminum oxide (AAO) templates, and were characterized by X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM) and high resolution transmission electron microscopy (HRTEM). BLT nanotubes with diameter of around 240 nm and the wall thickness of about 25 nm exhibited a single orthorhombic perovskite structure and highly preferential crystal growth along the [1 1 7] orientation, which have smooth wall morphologies and well-defined diameters corresponding to the diameter of the applied template. The formation mechanism of BLT nanotubes was discussed.     

Preparation of CuIn1−xGaxS2 (x = 0.5) flowers consisting of nanoflakes via a solvothermal method

CuIn_1−xGa_xS₂ (x = 0.5) flowers consisting of nanoflakes were successfully prepared by a biomolecule-assisted solvothermal route at 220 °C for 10 h, employing copper chloride, gallium chloride, indium chloride and l-cysteine as precursors. The biomolecule l-cysteine acting as sulfur source was found to play a very important role in the formation of the final product. The diameter of the CuIn_0.5Ga_0.5S₂ flowers was 1-2 μm, and the thickness of the flakes was about 15 nm. The obtained products were characterized by X-ray diffraction (XRD), energy dispersion spectroscopy (EDS), X-ray photoelectron spectroscopy (XPS), field-emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), high-resolution transmission electron microscopy (HRTEM), selected area electron diffraction spectroscopy (SAED), and UV-vis absorption spectroscopy. The influences of the reaction temperature, reaction time, sulfur source and the molar ratio of Cu-to-l-cysteine (reactants) on the formation of the target compound were investigated. The formation mechanism of the CuIn_0.5Ga_0.5S₂ flowers consisting of flakes was discussed.     

Characterisation of HVOF sprayed Cr3C2-50(Ni20Cr) coating and the influence of binder properties on solid particle erosion behaviour

The coating Cr₃C₂ with 50 wt.% Ni20Cr deposited by high velocity oxy-fuel (HVOF) spray process was characterized in detail to investigate the effect of annealing on the solid particle erosion behaviour and understand the influence of the binder properties. Systematic characterization of the coating was carried out using electron microscopy (scanning electron microscopy (SEM), transmission electron microscopy (TEM) and electron probe microanalysis (EPMA)), X-ray diffraction (XRD), microindentation and nanoindentation techniques. The solid particle erosion tests were done on the as-sprayed coating and coatings annealed at 400 °C, 600 °C and 800 °C using silica erodent particles. The coefficient of restitution of the coated samples was also measured by WC ball impact tests to simulate dynamic impacts. The as-sprayed coating consisted of primary carbides and binder that was a mixture of amorphous and nanocrystalline phases. Annealing leads to recrystallisation of binder phase and precipitation of secondary carbides. The coating hardness and binder ductility change with annealing temperature. The erosion resistance improves with annealing up to 600 °C. In the as-sprayed coating, the amorphous phase, inter-splat boundaries and the elastic rebound characteristics affect the erosion response. While in the case of the coating annealed at 600 °C, the presence of ductile crystalline binder, fine carbide precipitates and embedment of erodent particles together improve solid particle erosion resistance.     

Combustion synthesis of CaSc2O4:Ce nano-phosphors in a closed system

The CaSc₂O₄:Ce³⁺ nano-phosphors were successfully prepared by a single-step combustion method at an ignition temperature as low as 200 °C in a closed autoclave using glycine as a fuel and PEG4000 as a dispersant. The samples were characterized by X-ray diffraction (XRD), photoluminescence (PL) spectroscopy, scanning electron microscopy (SEM) and transmission electron microscope (TEM). The results revealed that CaSc₂O₄:Ce³⁺ nano-phosphors can be conveniently prepared at an ignition temperature as low as 200 °C, which was much lower than that in the ordinary combustion methods. The optimized ignition temperature was 220 °C. The CaSc₂O₄:Ce³⁺ nano-phosphors give a uniform particle size in the range of 15-20 nm. The low ignition temperature and the addition of PEG4000 dispersant play important roles in the formation of small sized nanoparticles. The as-prepared nano-phosphors were incompact aggregates, but highly dispersed nano-phosphors can be obtained after further ultrasonic treatment. The CaSc₂O₄:Ce³⁺ nano-phosphors give satisfactory luminescence characteristic benefiting from the closed circumstance, in which cerium atoms can be isolated from the oxidizing atmosphere and non-fluorescent Ce⁴⁺ ions can be ruled out. The present highly dispersed CaSc₂O₄:Ce³⁺ nano-phosphors with efficient fluorescence are promising in the field of biological labeling, and the present low temperature combustion method is facile and convenient and can be applied as a universal process for preparing non-aggregate oxide nano-phosphors, especially those being sensitive to air at high temperature.     

Investigation on thermal and microstructural characterization of the TeO2-WO3 system

Thermal and microstructural characterization of the TeO₂-WO₃ binary system was accomplished by applying differential thermal analysis (DTA), X-ray diffraction (XRD) and scanning electron microscopy (SEM) techniques. Different compositions of the (1 − x)TeO₂-xWO₃ system, where x varies between 0.02 and 0.80 in molar ratio were studied. The samples were prepared by melting high purity powder mixtures of TeO₂ and WO₃ in a platinum crucible with a closed lid at 750 °C for 30 min and quenching in water bath. The glass forming range of the binary system was detected as 0.04 ≤ x ≤ 0.35 in molar ratio. As-cast samples were heat-treated above the crystallization peak temperatures at 550 °C for 24 h to obtain thermal stability and the phase stability of the binary system was investigated by performing systematical thermal, phase and microstructural characterizations with the heat-treated samples. The eutectic reaction of the binary system was detected at 617 ± 3 °C, the endothermic reaction indicating the phase transformation reaction of WO₃ from orthorhombic to tetragonal was determined at 743 ± 1 °C. α-TeO₂ and orthorhombic WO₃ crystalline phases were found to be present in the final structure when the total crystallization was achieved. Microstructural characterization of the TeO₂-WO₃ system was realized for a wide compositional range for the first time in the literature.     

Synthesis of Ti3SiC2 by infiltration of molten Si

High-purity Ti₃SiC₂ compounds have been fabricated by infiltration of molten Si into a precursor, a partially sintered TiC_x (x = 0.67) preform. The Si source and the TiC_x preform were placed side by side on carbon cloth, and the system was heated to 1550 °C. Molten Si infiltrated the preform through the carbon cloth, and a direct reaction between TiC_x and molten Si immediately occurred at the reaction temperature to yield pure Ti₃SiC₂. We could observe phase formation and the microstructure of the bulk products with time, which were investigated by X-ray diffraction (XRD) and scanning electron microscopy (SEM) equipped with energy-dispersive spectroscopy (EDS). Pure Ti₃SiC₂ compounds were formed on the exterior of the TiC_x preform at 1550 °C when the sintered TiC_x:Si ingot molar ratio was 3:1.4. At 1550 °C, no other minor phases were detected for any of the sintering time ranges.     

Hydrothermal synthesis of YBO3:Tb microflowers and their luminescence properties

Three-dimensional flowerlike YBO₃:Tb³⁺ phosphors have been successfully prepared by an efficient surfactant-free hydrothermal process directly without further sintering treatment. X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), energy-dispersive X-ray (EDS) spectrometry, selected area electron diffraction (SAED), photoluminescence (PL) spectra were used to characterize the samples. The as-obtained samples present flowerlike agglomerates composed of nanoflakes with thickness of 20 nm and high crystallinity in spite of the moderate reaction temperature of 180 °C. The reaction mechanism has been considered as a dissolution/precipitation mechanism; the self-assembly evolution process has been proposed on homocentric layer-by-layer growth style. The different luminescent intensity with different molar ratio of Y-Tb [Y:Tb = 8:2; 7:3; 6:4; 5:5; 4:6], YBO₃:Tb³⁺ phosphors exhibit different light (white, red, green) under ultraviolet excitation, which might find potential applications in the fields such as light display systems and optoelectronic devices.     

Low temperature synthesis of Fe3O4 micro-spheres and its application in lithium ion battery

Fe₃O₄ micro-spheres with nanoparticles close-packed architectures were synthesized via a simple chemical method using (NH₄)₂Fe(SO₄)₂·6H₂O, hexamethylenetetramine, and NaF as reaction materials. This chemical synthesis took place in a vitreous jar under low temperature (90 °C) and atmospheric pressure. The morphology and structure of the as-synthesized products were characterized by field emission scanning electron microscopy (FE-SEM), X-ray diffraction (XRD), and Raman spectrum. Electrochemical properties of the as-synthesized Fe₃O₄ micro-spheres as anode electrode of lithium ion batteries were studied by conventional charge/discharge tests, which exhibit steady charge/discharge platforms at different current densities. The as-prepared Fe₃O₄ electrode shows high initial discharge capacity of 1166 and 1082 mAh g⁻¹ at current density of 0.05 and 0.1 mA cm⁻², respectively.     

Synthesis and characterization of cubic BC2N grown by reactive laser ablation

Cubic boron-carbon-nitrogen c-BC₂N films were synthesized in a laser ablation system using a target of B₄C with 99.99% of purity and silicon substrates (111). The discharge atmosphere for the films growth was a CH₄ + N₂ mixture. The substrate temperature increased from room temperature to 650 °C. The chemical composition and bonding configuration were studied by X-ray photoelectron spectroscopy (XPS) and Auger electron spectroscopy (AES), finding B-N, B-C and C-C bonds. Moreover, the crystallographic microstructure was analyzed by means of X ray diffraction (XRD) and transmission electron microscopy (TEM), showing the presence of (111), (200) and (220) planes belonging to a diamond like cubic structure. Finally, an increase in the coating hardness as a function of the substrate temperature was observed, especially for temperatures higher than 530 °C.     

Modification of TiO2 nanorods by Bi2MoO6 nanoparticles for high performance visible-light photocatalysis

In this work, TiO₂ nanorods were prepared by a hydrothermal process and then Bi₂MoO₆ nanoparticles were deposited onto the TiO₂ nanorods by a solvothermal process. The nanostructured Bi₂MoO₆/TiO₂ composites were extensively characterized by X-ray diffraction, scanning and transmission electron microscopy, X-ray photoelectron spectroscopy and UV-vis diffuse reflectance spectroscopy. The photocatalytic activity of the Bi₂MoO₆/TiO₂ composites was evaluated by degradation of methylene blue. The Bi₂MoO₆/TiO₂ composites exhibit higher catalytic activity than pure Bi₂MoO₆ and TiO₂ for degradation of methylene blue under visible light irradiation (λ > 420 nm). Further investigation revealed that the ratio of Bi₂MoO₆ to TiO₂ in the composites greatly influenced their photocatalytic activity. The experimental results indicated that the composite with Bi₂MoO₆:TiO₂ = 1:3 exhibited the highest photocatalytic activity. The enhancement mechanism of the composite catalysts was also discussed.     

Process–structure–property relations of micron thick Gd2O3 films deposited by reactive electron-beam physical vapor deposition (EB-PVD)

Thick polycrystalline gadolinium oxide (Gd₂O₃) films up to 11 μm in thickness were deposited via reactive electron beam-physical vapor deposition (EB-PVD) on silicon (111) substrates for use in neutron radiation detection. The effects of coating thickness, substrate temperature, and oxygen flow on film structural, electrical and optical properties were investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM), atomic force microscopy (AFM), transmission electron microscopy (TEM), capacitance–voltage (C–V) measurements, and ultraviolet–visible (UV–Vis) spectroscopy. Films were characterized as either monoclinic or mixed monoclinic and cubic phase depending on deposition parameters. Increasing the deposition temperature resulted in increased film crystallinity and cubic phase volume while decreasing the O₂ flow rate resulted in increased volume of the monoclinic phase. Evidence of a thickness dependent crystallography is also presented. Electrical property measurements showed thin film dielectric constant could be tailored between 12 and 20 at 1 MHz frequency by decreasing the oxygen flow rate at deposition temperatures of 250 °C which is attributed to an increased presence of the monoclinic phase and increased film density. Band gap values were calculated from transmission measurements and ranged between 5.44 and 5.96 eV.     

A new temperature stable microwave dielectric ceramics: ZnTiNb2O8 sintered at low temperatures

The phases, microstructure and microwave dielectric properties of ZnTiNb₂O₈-xTiO₂ composite ceramics with different weight percentages of BaCu(B₂O₅) additive prepared by solid-state reaction method have been investigated using the X-ray diffraction (XRD), scanning electron microscopy (SEM) and energy-dispersive spectroscopy (EDS). The results showed that the microwave dielectric properties were strongly dependent on densification, grain sizes and crystalline phases. The sintering temperature of ZnTiNb₂O₈ ceramics was reduced from 1250 °C to 950 °C by doping BaCu(B₂O₅) additive and the temperature coefficient of resonant frequency (τ_f) was adjusted from negative value of −52 ppm/°C to 0 ppm/°C by incorporating TiO₂. Addition of 2 wt% BaCu(B₂O₅) in ZnTiNb₂O₈-xTiO₂ (x = 0.8) ceramics sintered at 950 °C showed excellent dielectric properties of ?_r = 38.89, Q × f = 14,500 GHz (f = 4.715 GHz) and τ_f = 0 ppm/°C, which represented very promising candidates as LTCC dielectrics for LTCC applications.     

Microstructure and properties of SiO2 matrix reinforced by BN nanotubes and nanoparticles

In order to overcome intrinsic brittleness and poor mechanical properties of SiO₂, two kinds of hexagonal boron nitride (h-BN) (boron nitride nanotubes (BNNTs) and boron nitride nanoparticles (BNNPs)) were employed to reinforce SiO₂ matrix. The mechanical properties, relative density and dielectric constant of the composites were investigated detailedly. Compared to the monolithic SiO₂, 5 wt% BNNTs/SiO₂ and 5 wt% BNNPs/SiO₂ composites exhibited excellent mechanical properties and low dielectric constant. Furthermore, phase composition and microstructure of the composites were analyzed thoroughly by X-ray diffraction, transmission electron microscopy, and field emission scanning electron microscopy.     

Microwave ECR plasma CVD of cubic Y2O3 coatings and their characterization

Yttrium oxide (Y₂O₃) thin films are deposited by microwave electron cyclotron resonance (ECR) plasma assisted metal organic chemical vapour deposition (MOCVD) process at a substrate temperature of 350 °C using indigenously developed metal organic precursors (2,2,6,6-tetra methyl-3,5-heptane dionate) yttrium, commonly known as Y(thd)₃ synthesized by ultrasound method. The deposited coatings are characterized by X-ray photoelectron spectroscopy, glancing angle X-ray diffraction, scanning electron microscopy, EDS and infrared spectroscopy. The characterization results indicate that it is possible to deposit non-porous coatings with excellent uniformity of a single phase cubic Y₂O₃ on various substrates by this process at reasonably low substrate temperature that is desirable in various manufacturing processes.     

In situ template polymerization of aniline on the surface of negatively charged TiO2 nanoparticles

The in situ oxidative template polymerization of aniline was performed successfully on the surface of negatively charged titania (TiO₂) nanoparticles with a mean diameter of 40 nm using ammonium persulfate and a Chem-Solv solution at pH 1 and 25 °C. SEM showed that the resulting polyaniline (PANI)/TiO₂ composites were well dispersed in solution due to the electrostatic repulsion force. Ultraviolet/visible spectroscopy, thermogravimetric analysis, Fourier-transform infrared spectroscopy, and cyclic voltammetry showed that the optical, thermal, and electrical properties of PANI/TiO₂ composites were quite different from those of pure PANI or TiO₂, which was attributed to the strong interaction between the two components. The conductivity of the PANI/TiO₂ composite was estimated to be 0.91 × 10⁻¹ S/cm at 25 °C in the range of semiconductor.     

Direct synthesis and characterization of mesoporous Fe3O4 through pyrolysis of ferric nitrate-ethylene glycol gel

Mesoporous magnetite (Fe₃O₄) was successfully synthesized on a large scale by direct pyrolysis of ferric nitrate-EG (EG = ethylene glycol) gel in a one-end closed horizontal tube furnace in the air without using any template, additions, and carrier gas. The as-synthesized mesoporous Fe₃O₄ were characterized by powder X-ray diffraction (XRD), infrared spectra (IR), transmission electron microscopy (TEM), high-resolution transmission electron microscopy (HRTEM), selected area electron diffraction (SAED), Brunauer-Emmett-Teller (BET), Barrett-Joyner-Halenda (BJH), and thermal gravimetric analysis (TGA). Results from TEM showed that the as-obtained Fe₃O₄ has mesoporous structure formed by the loose agglomeration of nanoparticles with diameter of about 6 nm, which was also confirmed by small-angle XRD and nitrogen adsorption analysis. Furthermore, vibrating sample magnetometer (VSM) measurements indicated that the saturated magnetization of the as-obtained mesoporous Fe₃O₄ was ferromagnetic with the saturation magnetization (Ms) and coercivity (Hc) of 46 emu/g and 136 Oe, respectively. In addition, a possible growth mechanism of mesoporous Fe₃O₄ was also discussed.