Effect of calcination temperature and atmosphere on crystal structure of BaTiO<Subscript>3</Subscript> nanofibers

Barium titanate (BaTiO₃, BT) nanofibers with a diameter range of 160 nm to 300 nm were prepared by drying electrospun BT/polyvinylpyrrolidone (BT/PVP) composite fibers for 1 h at 80 °C in vacuum with a subsequent calcination in air for 1 h at a temperature range of 650 °C to 750 °C. The morphology and crystal structure of calcined BT nanofibers were characterized with the aid of XRD, FT-IR, SEM, and TEM. The XRD and FR-IR measurements confirm that BT nanofibers with a diameter of about 160 nm and a tetragonal perovskite structure were present in the electrospun fibers after calcination for 1 h at 750 °C. The FR-IR analysis of the BT fibers reveals that the intensity level of the O-H stretching vibration bands (at 3430 cm⁻¹ and 1425 cm⁻¹) become weaker as the calcination temperature is increased and that a broad band at 570 cm⁻¹, which represents the Ti-O vibration, appears sharper and narrower after calcination at 750 °C due to the formation of metal oxide bonds. In contrast, BT fibers prepared by a refluxing process in a nitrogen atmosphere show a dramatic change in crystal structure: the tetragonal structure changes to a cubic perovskite structure, probably due to the suppression of carbonate contamination. Thus, the calcination temperature and atmosphere appear to have a significant influence on the crystal structure of BT.     

Synthesis of ferromagnetic nickel ferrite nanofibers via electrospinning with iron acetate as an iron precursor

We report the synthesis of nickel ferrite nanofibers via an elecrospinning technique particularly using iron (II) acetate as an iron precursor. Nanofibers of a single-phase nickel ferrite with a uniform diameter of ??90 nm were successfully synthesized by adopting a properly prepared solution and calcination condition. Individual nickel ferrite nanofibers synthesized by electrospinning were made up of nanograins of ??20 nm in diameter. In addition, the hysteresis observed in a magnetization measurement confirmed their ferromagnetism, supporting their potential use in magnetic devices. These results demonstrate that the use of iron (II) acetate as an iron precursor is another way to synthesize ferromagnetic nickel ferrite nanofibers.     

Preparation and magnetic properties of Fe<Subscript>2</Subscript>O<Subscript>3</Subscript> microtubules prepared by sol-gel template method

Fe(OH)₃ precursor sol was prepared by a sol-gel method. The precursor sol was dipped onto the absorbent cotton, and gel was formed on the absorbent cotton template after the volatilization of moisture. Fe₂O₃ microtubules were synthesized after the process of self-propagation or calcination. The phase, morphology, and particle diameter of the samples were examined by X-ray diffraction (XRD) and scanning electron microscopy (SEM), and the magnetic properties of the samples were measured using a vibrating sample magnetometer (VSM). The external diameters of Fe₂O₃ microtubules ranged between 8 and 13 μm, and the wall thicknesses ranged between 0.5 and 2 μm. The type of the calcination method plays a significant role in developing the Fe₂O₃ phase and the variation in the magnetic properties in the sol-gel template complexing method. γ-Fe₂O₃ was synthesized by a self-propagation method. However, α-Fe₂O₃ was synthesized after calcination at 400°C for 2 h. The coercivity of the samples synthesized by calcination at 400°C for 2 h after self-propagation was found to increase significantly, thereby presenting hard magnetic properties.     

~ ~ 3＋ Sol-gel synthesis and photoluminescence characterization of La2Ti2O7.EU3＋nanocrystals

Eu³⁺ doped La₂Ti₂O₇ nanocrystals with pure monoclinic phase and size of about 100 nm were prepared by a citric acid (CA) assisted sol-gel method. Techniques of thermo-gravimetric (TG) and differential scanning calorimetry (DSC), X-ray diffraction (XRD), as well as transmission electron microscopy (TEM) were employed to characterize the as-synthesized nanoparticles. Furthermore, photoluminescence (PL) performances of the Eu³⁺ doped La₂Ti₂O₇ nanocrystals were evaluated with focus on the effects of calcination temperature and Eu³⁺ doping concentration on the photoluminescence properties.     

Grain size dependent bandgap shift of SnO2 nanofibers

SnO₂ nanofibers with various grain sizes ranging from 18.5 to 31.6 nm in diameter were fabricated by electrospinning a polymeric solution and subsequent controlled calcination of the as-spun fibers. The calcined fibers were polycrystalline and composed of densely packed nano-sized SnO₂ grains. The effect of the nanograin size on the optical bandgap of SnO₂ nanofibers was examined by ultraviolet-visible spectroscopy. The bandgap showed a strong dependence on the nanograin size. The bandgap decreased with increasing nanograin size. Some calculations were performed to understand the relationship between the experimentally obtained bandgaps of the SnO₂ nanofibers and the theoretical ones. Quantum confinement and lattice strain of the SnO₂ nanofibers are likely responsible for the bandgap shift. This suggests that optimization of the nanograin size is essential not only for achieving the required optical properties of oxide nanofibers, but also to secure superior working properties of electronic devices that are fabricated with electrospinning-synthesized oxide nanofibers.     

Calcination/acid-activation treatment of an anodic oxidation TiO<Subscript>2</Subscript>/Ti film catalyst

The aim of this work was to investigate the effects of calcination/acid-activation on the composition, structure, and photocatalytic (PC) reduction property of an anodic oxidation TiO₂/Ti film catalyst. The surface morphology and phase composition were examined by scanning electron microscopy and X-ray diffraction. The catalytic property of the film catalysts was evaluated through the removal rate of potassium chromate during the PC reduction process. The results showed that the film catalysts were composed of anatase and rutile TiO₂ with a micro-porous surface structure. The calcination treatment increased the content of TiO₂ in the film, changed the relative ratio of anatase and rutile TiO₂, and decreased the size of the micro pores of the film catalysts. The removal rate of potassium chromate was related to the technique parameters of calcination/acid-activation treatment. When the anodic oxidation TiO₂/Ti film catalyst was calcined at 873 K for 30 min and then acid-activated in the concentrated H₂SO₄ for 60 min, it presented the highest catalytic property, with the removal rate of potassium chromate of 96.3% during the PC reduction process under the experimental conditions.     

Effects of processing parameters on the synthesis of TiO2 nanofibers by electrospinning

TiO² nanofibers were synthesized by an electrospinning technique using polyvinyl pyrrolidone and titanium tetraisopropoxide as precursors. The effects of processing parameters including the precursor ratio, calcination time, temperature and atmosphere were investigated. The calcination temperature determines the TiO₂ phases as either anatase or rutile. The diameter of the synthesized TiO₂ nanofibers is not sensitive to the calcination atmosphere or the time. However, the surface microstructure of the synthesized nanofibers depends highly on calcination atmosphere. Calcination in an N₂ atmosphere produces smooth surfaces. In contrast, surfaces that are more granular evolve when they are calcined in an O₂ atmosphere. In addition, less Ti precursor in the electrospinning solution results in slim nanofibers.     

Microstructure Characterization of the FeAl<Subscript>2</Subscript>O<Subscript>4</Subscript>-Based Nanostructured Composite Coating Synthesized by Plasma Spraying Fe<Subscript>2</Subscript>O<Subscript>3</Subscript>/Al Powders

The microstructure of the coating prepared by reactive plasma spraying Fe₂O₃/Al composite powders was characterized by x-ray diffraction, scanning electron microscopy, and transmission electron microscopy. The results indicated that the coating exhibited nanostructured microstructure which consisted of FeAl₂O₄, Fe or Fe solid solution, Al₂O₃ and a little FeAl. In the composite coating, spherical Fe particles (tens of nanometers to hundreds of nanometers) were distributed uniformly within the equiaxed and columnar nanograins FeAl₂O₄ matrix. There were two kinds of Al₂O₃ phases present in the composite coating. One kind was nano-sized Al₂O₃ particles uniformly dispersed within the matrix, forming eutectic structure of (FeAl₂O₄ + γ-Al₂O₃); the other was 1-1.5 μm Al₂O₃ particles embedded individually within the matrix. The composite coating had higher toughness than the conventional microstructured Al₂O₃ coating.     

Fabrication and magnetic properties of NiFe<Subscript>2</Subscript>O<Subscript>4</Subscript> nanorods

NiFe₂O₄ nanorods have been successfully synthesized via thermal treatment of the rod-like precursor fabricated by Ni-doped α-FeOOH, which was enwrapped by the complex of citric acid and Ni²⁺. The morphology evolution during the calcination of the precursor nanorods was investigated with transmission electron microscopy (TEM), and the phase and the magnetic properties of samples were analyzed through X-ray diffraction (XRD) and vibrating sample magnetometer (VSM). The results indicated that the diameter of the NiFe₂O₄ nanorods obtained ranged between 30 and 50 nm, and the length ranged between 2 and 3 μm. As the calcination temperature was up to 600°C, the coercivity, saturation magnetization, and remanent magnetization of the samples were 36.1 kA·m⁻¹, 27.2 A·m²·kg⁻¹, and 5.3 A·m²·kg⁻¹, respectively. The NiFe₂O₄ nanorods prepared have higher shape anisotropy and superior magnetic properties than those with irregular shapes.     

Synthesis and characterization of cobalt-free Ba0.5Sr0.5Fe0.8Cu0.2O3−δ perovskite oxide cathode nanofibers

The cobalt-free perovskite-oxide, Ba_0.5Sr_0.5Fe_0.8Cu_0.2O_3−δ (BSFC) is a very important cathode material for intermediate-temperature proton-conducting solid oxide fuel cells. Ba_0.5Sr_0.5Fe_0.8Cu_0.2O_3−δ nanofibers were synthesized for the first time by a sol-gel electrospinning. Process wherein a combination of polyvinylpyrrolidone and acetic acid was used as the spinning aid and barium, strontium, iron and copper nitrates were used as precursors for the synthesis of BSFC nanofibers. X-ray diffraction studies on products prepared at different calcination temperatures revealed a cubic perovskite structure at 900 °C. The temperature of calcination has a direct effect on the crystallization and surface morphology of the nanofibers. High porosity, and surface area, in addition to an electrical conductivity of 69.54 S cm⁻¹ at 600 °C demonstrate the capability of BSFC nanofibers to serve as effective cathode materials for intermediate-temperature solid oxide fuel cells.     

Processing and Performance of MOF (Metal Organic Framework)-Loaded PAN Nanofibrous Membrane for CO<Subscript>2</Subscript> Adsorption

The objective of this experimental study is to produce a nanofibrous membrane functionalized with adsorbent particles called metal organic framework (MOF) in order to adsorb CO₂ from a gas source. Therefore, Polyacrylonitrile (PAN) was chosen as the precursor for nanofibers and HKUST-1, a Cu-based MOF, was chosen as adsorbent. The experimental process consists of electrospinning PAN solution blended with HKUST-1 to produce a nanofibrous mat as working substrates. The fibers were collected in a cylindrical canister model. SEM image of this mat showed nanofibers with the presence of small adsorbent particles, impregnated into the as-spun fibers discretely. To increase the amount of MOF particles for effectual gas adsorption, a secondary solvothermal process of producing MOF particles on the fibers was required. This process consists of multiple growth cycles of HKUST-1 particles by using a sol-gel precursor. SEM images showed uniform distribution of porous MOF particles of 2-4 µm in size on the fiber surface. Energy dispersive spectroscopy report of the fiber confirmed the presence of MOF particles through the identification of characteristic Copper elemental peaks of HKUST-1. To determine the thermal stability of the fibrous membrane, Thermogravimetric analysis of HKUST-1 consisting of PAN fiber was performed where a total weight loss of 40% between 210 and 360 °C was observed, hence proving the high-temperature durability of the synthesized membrane. BET surface area of the fiber membrane was measured as 540.73 m²/g. The fiber membrane was then placed into an experimental test bench containing a mixed gas inflow of CO₂ and N₂. Using non-dispersive infrared CO₂ sensors connected to the inlet and outlet port of the bench, significant reduction of CO₂ in concentration was measured. Comparative IR spectroscopic analysis between the gas-treated and gas untreated fiber samples showed the presence of characteristic peak in the vicinity of 2300 and 2400 cm^?1 which verifies the adsorption of CO₂.     

Pt/NiO纳米纤维的制备及电导率性能

采用电纺丝法制备了金属铂(Pt)与氧化镍(NiO)复合纳米纤维,并利用XRD、SEM、TEM、半导体分析仪表征了其晶体结构、微观形貌和电导率等性能。结果表明,Pt/NiO纳米纤维具有很高的长径比,表面比较粗糙。加入的氧化镍抑制了串珠的形成,并维持了一维材料连续的结构。Pt/NiO纳米纤维电导率约为5.95×10~2 S/cm,这说明铂纳米颗粒在复合材料中构成了穿插的连续网络。     

Synthesis of nano-sized Co<Subscript>3</Subscript>O<Subscript>4</Subscript> powder by spray conversion method for anode material of lithium battery

A nano-sized Co₃O₄ powder was prepared using a spray conversion method that could be applied for mass production. The spray-conversion process consisted of spray drying of a metallic liquid solution, a calcination treatment, and a ball milling process. The calcined Co₃O₄ powder consisted of agglomerated spherical clusters with nano-sized particles. After milling for 24 h, agglomerated powders were fragmented into fine powders sized below 60 nm. The lithium/cobalt oxide cell was charge-discharged at a constant current density of 0.2 mAcm⁻² and showed a first discharge capacity of 1100 mAhg⁻¹. The discharge capacity of the Li/Co₃O₄ cell drastically decreased with cycle number. By increasing the carbon content of the anode, the cycle life was improved. For a Co₃O₄ electrode containing 40 wt.% carbon, the discharge capacity was over 400 mAhg⁻¹ after 50 cycles. The spray conversion method might be a useful method to prepare nano-sized Co₃O₄ powder for the anode material of lithium batteries.     

Fabrication and electromagnetic properties of fe nanofibers composites

In order to develop electromagnetic (EM) wave absorbing materials in the giga-hertz (GHz) frequency range, Fe nanofibers have been prepared by multi-nozzle electrospinning process (ESP) and heat treatments. The effects of applied voltage and feed rate on the morphology of electrospun PVP/Fe salt nanofibers have been studied in the electrospinning process. The average diameter and the standard deviation of electrospun nanofibers tend to decrease with the increase of the applied voltage and the decrease of the feed rate, respectively. Through the heat treatments of calcination and H₂ reduction, as-spun PVP/Fe salt has been stepwise transformed into Fe₂O₃, Fe₃O₄, and Fe phases. To evaluate the EM characteristic of the prepared Fe nanofibers, epoxy matrix composites containing Fe nanofibers of 10 and 30 wt% have been fabricated. The Fe nanofibers have improved the EM characteristics of composites as compared to those of nano-sized metallic particles.     

Solvothermal synthesis and thermoelectric properties of skutterudite compound Fe（0.25）Ni（0.25）Co（0.5）Sb3

Nanostructured skutterudite-related compound Fe_0.25Ni_0.25Co_0.5Sb₃ was synthesized by a solvothermal method using FeCl₃, NiCl₂, CoCl₂, and SbCl₃ as the precursors and NaBH₄ as the reductant. The solvothermally synthesized powders consisted of fine granules with an average particle size of tens of nanometers. The bulk material was prepared by hot pressing the powders. Transport property measurements indicated a heavily doped semiconductor behavior with n-type conduction. The thermal conductivity is about 1.83 W·m⁻¹·K⁻¹ at room temperature and decreases to 1.57 W·m⁻¹·K⁻¹ at 673 K. The low thermal conductivity is attributed to small grain size and high porosity. A maximum dimensionless figure of merit of 0.15 is obtained at 673 K.     

Preparation and optical properties of Y<Subscript>2</Subscript>O<Subscript>3</Subscript>/SiO<Subscript>2</Subscript> powder

Y(NO3)3 and NH3·H2O were used as a raw materials,and nano-Y2O3 powder was successfully synthesized by a precipitation method.Employing TEOS as a raw material,SiO2 powder was successfully prepared by a alkoxide-hydrolysis method,and a Y2O3/SiO2 composite powder was obtained by coating.The Y2O3,SiO2,and Y2O3/SiO2 powders were characterized using X-ray diffraction(XRD),scanning electron microscopy(SEM),and Fourier transform infrared spectrophotometer(FT-IR);the Y2O3 and Y2O3/SiO2 powders were further examined ...     

Microemulsion synthesis and magnetic properies of BaAl<Subscript>4</Subscript>Fe<Subscript>8</Subscript>O<Subscript>19</Subscript> powders

Al-substituted M-type hexaferrite is a highly anisotropic ferromagnetic material. In the present study, we report the synthesis and the characterization of BaAl₄Fe₈O₁₉ powder from two microemulsion systems of po1yoxyethylene octylphenol ether/1, 2-propylene glycol, or ethanol/cyclohexane/water and cetrimonium bromide/1, 2-propylene glycol/cyclohexane/water. Two microemulsion systems were found to give wide stable regions. The synthesized powders were characterized with x-ray diffraction, scanning electron microscopy, and vibrating sample magnetometer. The experiment results indicated that the surfactant, co-surfactant, and oil/water ratio remarkably affected the particle size, size distribution, anisotropy and magnetic property of the powders. The powder prepared with microemulsion of po1yoxyethylene octylphenol ether/1, 2-propylene glycol/cyclohexane/water exhibited best particle character, that is, uniform thin particle morphology, large shape anisotropy, small particle size, large coercivity of 8.73 kOe, and saturation magnetization of 20.821 emu·g⁻¹.     

Grain refinement and mechanism of CAl_（0.5）W_（0.5） compound in Mg-Al alloys

The effect of CAl0.5W0.5(CAW) compound on the grain refinement of Mg-Al based alloys was investigated.The results show that CAW compound is an effective and active grain refiner.The grain size of binary Mg-Al alloys is more than 500 μm,and it is changed to about 110 μm with a 1 wt.% CAW addition.The hardness increased with the decease of grain size monotonously.The mechanical properties are improved by the addition.The fine grain size is mainly ascribed to the dispersed Al2CO particles,which are very potent nucleating substrates for Mg-Al alloys.The nucleation cores formed by chemical reaction directly are well-distributed in the matrix.     

Structure and electrical resistance of dispersion-strengthened vacuum-deposited Cu–Al<Subscript>2</Subscript>O<Subscript>3</Subscript> nanocomposites

Methods of X-ray diffraction and transmission electron microscopy were used to study the microstructure of dispersion-strengthened Cu-Al₂O₃ nanocomposites obtained by the method of simultaneous deposition of Cu and Al₂O₃ from the vapor phase. The effect of the size of particles of the oxide (Al₂O₃) and of their content on the electrical resistance of the composite has been considered. The results obtained make it possible to suppose that the main structural factor that determines the electrical resistance of the composite are nanodispersed particles of Al₂O₃ with a size of less than 20 nm.     

Hetero-Orientation Epitaxial Growth of TiO<Subscript>2</Subscript> Splats on Polycrystalline TiO<Subscript>2</Subscript> Substrate

In the present study, the effect of titania (TiO₂) substrate grain size and orientation on the epitaxial growth of TiO₂ splat was investigated. Interestingly, the splat presented comparable grain size with that of substrate, indicating the hereditary feature of grain size. In addition, hetero- and homo-orientation epitaxial growth was observed at deposition temperatures below 400 °C and above 500 °C, respectively. The preferential growth of high-energy (001) face was also observed at low deposition temperatures (≤?400 °C), which was found to result from dynamic nonequilibrium effect during the thermal spray deposition. Moreover, thermal spray deposition paves the way for a new approach to prepare high-energy (001) facets of TiO₂ crystals.