Magnetic nanocomposites of mixed oxides of iron and barium synthesized under different oxidative environments

Synthesis of nanocomposites of mixed oxides of iron and barium in a copolymer matrix of aniline and formaldehyde using a chemical route at room temperature is reported. X-ray diffraction, infrared, ⁵⁷Fe Mossbauer studies, and scanning electron microscopy on as-synthesized samples, as well as samples obtained on heating at different temperatures, are described. X-ray diffraction, ⁵⁷Fe Mossbauer, and scanning electron microscopy show the formation of nanoparticles of barium ferrites in the polymer matrix. These studies further show the formation of solid solution of iron and barium oxide on heating the samples at temperatures from 400 to 700°C. From the Mossbauer and x-ray diffraction studies, it has been found that γ-Fe₂O₃, which normally transforms into α-Fe₂O₃ on heating at 500°C, persists up to 700°C in the present samples containing barium ions. Infrared studies indicate that the polymeric backbone is strongly influenced by different reaction conditions and lead to variable magnetic character in the heated samples. The text was submitted by the authors in English.     

MgO nanostructures synthesized by thermal evaporation

MgO nanostructures with various morphologies were fabricated by thermal evaporation through controlling the growth temperature and gas flow, including MgO polyhedral shells, nanotubes, cubes and nanowires. MgO polyhedral shells and nanotubes were fabricated when H₂ was introduced to the system in the beginning of the thermal process, MgO cubes and nanowires were fabricated when Ar/O₂ was introduced. MgO polyhedral shells and MgO cubes were collected in the lower temperature zone, while MgO nanotubes and nanowires were collected in the relative higher temperature zone. The growth mechanism was proposed based on the crystal structure and analysis of growth conditions.     

Chemically synthesized FePt nanoparticle material for ultrahigh-density recording

We have examined the magnetic anisotropy of the "heat-treated FePt nanoparticles" annealed in a magnetic field. The magnetic easy axis of the "heat-treated FePt nanoparticles" is found to be three-dimensional (3-D) random and a partial ordering fct structure is observed before annealing in the presence of a magnetic field. The value of M/sub r//M/sub s/ obtained is 0.5. After annealing in the presence of a magnetic field, the M-H loop indicates that the easy axis is oriented preferably in the perpendicular direction than along the in-plane direction. The value of H/sub c/(//)/H/sub c/(/spl perp/) at 10 K is 0.62 (1410 Oe/2250 Oe). The value of M/sub r//M/sub s/(/spl perp/) is 0.58 at 10 K larger than the value of M/sub r//M/sub s/(//). Therefore, a weak magnetic easy axis orientation is fundamentally possible on the chemically synthesized FePt nanoparticles. We have studied the recording characteristics of a 3-D random nanoparticle medium using a GUZIK spinstand and observed the recorded patterns for the medium by imaging with a magnetic force microscopy.     

Hydrothermal synthesis of spindle-like ZnS hollow nanostructures

Spindle-like hollow nanostructures of zinc sulfide (ZnS) have been successfully synthesized by hydrothermal process using a simple surfactant emulsion template. The morphologies of ZnS nanostructures were characterized by transmission electron microscopy (TEM), high-resolution transmission electron microscopy (HRTEM) and field-emission scanning electron microscopy (FE-SEM). It is found that most of the products including twin ellipsoids with connected hollow cores are reminiscent of spindle-like structures. The lengths, widths and the thickness of the shell are in the range of 1-2 μm, 300-450 nm and 20-40 nm, respectively. Selected area electron diffraction (SAED) and X-ray powder diffraction (XRD) patterns show that the shell is composed of sphalerite ZnS polycrystals.     

CuS纳米空心管结构的水热合成

以氯化铜和硫代乙酰胺为原料,在碱性条件下,利用低温简单水热法合成了硫化铜纳米空心管结构。通过XRD、TEM、FT-IR等检测方法对产品进行了结构和形貌分析。结果表明,所得硫化铜产品为六方相铜蓝矿结构,纳米空心管结构,纳米管的直径为150～200nm,长度为1.5～2.5μm;在1110cm-1处出现Cu-S键的红外特征吸收峰;同时对可能的生长机理做了阐述。     

Magnetic properties of nanocomposites of mixed oxides of iron and chromium synthesized under different oxidative environments

Synthesis of nanocomposites of mixed oxides of Fe and Cr in a copolymer matrix of aniline and formaldehyde at room temperature along with IR, XRD and⁵⁷Fe Mössbauer studies on as synthesized as well as the samples on heating at different temperatures is described. The XRD and⁵⁷Fe Mössbauer studies show the formation of nanosized iron oxide particles. These studies further show the formation of nanosized particles of metal oxides and formation of solid solution of iron and chromium oxide on heating the samples at 700°C. Further, the IR studies show that the polymeric backbone is strongly influenced by different reaction conditions and lead to variable magnetic character in the heated samples as shown by their Mössbauer studies.     

Ultrathin ZnO nanostructures synthesized by thermal oxidation of hexagonal Zn micro/nanostructures

Ultrathin (<5 nm) ZnO nanobelts, as well as porous nanotubes/nanosheets were successfully synthesized via a very simple process: thermal oxidation of hexagonal Zn micro/nanostructures in a tube furnace in 50 sccm N2 flow. The ZnO nanobelt clusters were largely grown from the (0001) end surface of the Zn nanoprisms at 300 degrees C. The porous nanotubes and nanosheets were formed on the downstream substrate by 370-400 degrees C thermal oxidation of Zn films in low pressure. These structures are related to the anisotropic oxidation of Zn and differences of melting point between Zn and ZnO. We propose that the ultrathin nanobelts were formed in a vapor-liquid-solid process while the ultrathin nanotubes and nanosheets were formed via a vapor-solid-resublimation process. The structure of the nanostructures was characterized by transmission electron microscopy. The ultrathin mesoporous nanotubes and nanosheets have been found to possess rich surface defects. These structures may have potential applications in gas sensors, catalysts and hydrogen storage due to their large specific surface area.     

Thermochromic VO2 nanorods and other vanadium oxides nanostructures

Thermochromic VO₂ nanorods were prepared via thermal conversion of the metastable VO₂–B phase synthesized by hydrothermal methods. We observe an increased thermochromic transition temperature to ∼75–80 °C by variable-temperature infrared spectroscopy. Nano- and sub-micron structures of other vanadium oxides (V₃O₇, (NH₄)_0.5V₂O₅, and V₂O₅) were obtained simply by varying the starting materials in the hydrothermal synthesis. We also obtained nanostructures of the high temperature tetragonal rutile phase of VO₂ by thermolysis of single-source vanadium (IV) precursors.     

Self-rising approach to synthesize porous hollow metal oxides

Porous hollow metal oxides are prepared using a novel self-rising approach. The method is 'hard-template' free and relatively easy to perform, utilizes inexpensive precursors and processing conditions, and is versatile, thus offering tremendous opportunities with a wide variety of conditions to explore to synthesize materials with hollow structures. Co3O4 and amorphous Sm(0.5)Sr(0.5)CoO3 as a model has been successfully synthesized, showing hollow structure with porous shell and possessing high BET surface areas. A tentative scheme is given to illustrate its synthetic mechanism.     

Submicrometer-sized hollow nickel spheres synthesized by autocatalytic reduction

A facile method to fabricate submicrometer-sized hollow nickel spheres by autocatalyzing the redox reaction around a sacrificial colloidal particle surface is presented in this paper. The size distribution of these spheres can be controlled by regulating the concentration of the alkali solution. The hollow nickel particles were characterized by field emission scanning electron microscopy, transmission electron microscopy and X-ray powder diffraction. The hollow spheres produced by this process may have potential applications in many fields, including chemistry, biotechnology and materials science.     

Synthesis of hollow silver nanostructures by a simple strategy

Various silver nanostructures with hollow interiors, including nanoscaled cubic or quasi-cubic boxes, tubes, triangular rings, trapeziform rings and hybrid structures composed of tubes and cubic boxes, were synthesized via an extremely simple route. The method involved the modification of the solid silver nanocrystals by dithiol, and subsequent dissolving of the interior metal and assembly of the outer surface. In the whole process, only one simple step of pretreatment was needed before the transformation from Ag solid nanostructures to their corresponding hollow nanostructures. According to the morphological, spectral and structural changes in the evolution from silver solid nanostructures to their corresponding hollow nanostructures, a layer-by-layer assembly mechanism was proposed. The method is believed to open up a simple and versatile route to the fabrication of metallic hollow nanostructures with various morphologies according to the starting templates.     

Field-emission stability of hydrothermally synthesized aluminum-doped zinc oxide nanostructures

The Al-doped ZnO (AZO) nanostructures field-emission arrays (FEAs) were hydrothermally synthesized on AZO/glass substrate. The samples with Al-dosage of 3 at.% show the morphology as nanowires vertically grown on the substrates and a structure of c-axis elongated single-crystalline wurtzite. The good field-emission (i.e., the large anode current and low fluctuation of 15.9%) can be found by AZO nanostructure FEAs with well-designed Al-dosage (i.e., 3 at.%) because of the vertical nanowires with the less structural defects and superior crystallinity. Moreover, the Full width at half maximum (FWHM) of near band-edge emission (NBE) decreased as the increase of annealing temperature, representing the compensated structural defects during oxygen ambient annealing. After the oxygen annealing at 500 degrees C, the hydrothermal AZO nanostructure FEAs revealed the excellent electrical characteristics (i.e., the larger anode current and uniform distribution of induced fluorescence) and enhanced field-emission stability (i.e., the lowest current fluctuation of 5.97%).     

Monoclinic zirconium oxide nanostructures synthesized by a hydrothermal route

Zirconium oxide (ZrO(2)) nanostructures were synthesized by a hydrothermal route. Surface morphology analysis depicts the formation of rice-grain-like and fiber-like ZrO(2) nanostructures at different synthesis conditions. The structural analysis confirms that the as-synthesized ZrO(2) product is of pure monoclinic phase (m-ZrO(2)). The clear and equally spaced lattice fringes in high-resolution transmission electron microscopy (HRTEM) images and discrete spot pattern of selected area electron diffraction (SAED) confirm the high quality of the synthesized product. The product consists of monodispersed nanoparticles of uniform composition, high purity, and crystallinity. The Raman spectra are quantitatively analyzed and the observed peaks are attributed to various vibration modes of m-ZrO(2).     

Photocatalytic activities of hydrothermal synthesized copper zinc tin sulfide nanostructures

Journal of Materials Science: Materials in Electronics - We report the hydrothermal synthesis of visible light absorbing and direct energy bandgap kesterite-structured Cu2ZnSnS4 (CZTS)...     

Shrinkage in compacts of iron oxides and ores

Compacts have been pressed from (i) four, finely ground, iron ores and (ii) mixtures of subsieve ferric oxide with up to 40 wt % of either lime, alumina, silica, or water, and have been sintered in oxygen at temperatures in the range 1000 to 1400 C. Shrinkage, macro- and micro-appearance were recorded at each sintering stage.The iron ores were classified into two groups: one was characterised by the red ferric oxide appearance and by significant shrinkage at 1000 C; the other was predominantly black and required a temperature of 1200 C to initiate shrinkage in 1 h. The shrinkages of the ores are discussed in terms of the presence of black ferric oxide, particle size, lime content, and dilution of the iron-bearing grains with inert oxides.The mixtures were used to study the effect of inert oxides on the sintering of ferric oxide. The reduction in shrinkage in the case of alumina and silica is shown to be largely a consequence of dilution; the abnormally high shrinkage at 1000 C induced by 5 wt % of lime is probably due to the presence of low-melting-point ferrites.     

The behavior of iron oxides in reducing atmospheres

Comparison of unpromoted α-Fe₂O₃, K, and Tl promoted α-Fe₂O₃ in atmospheres of H₂, CO, 1:1 $\text{H}{}_2\text{CO}$, and CO following an H₂ prereduction showed that K or Tl promoters do not significantly modify the reduction behavior of α-Fe₂O₃, but can either increase (K) or decrease (Tl) the rate of growth of surface carbon in CO-containing atmospheres.     

Ferrite grade iron oxides from ore rejects

Iron oxyhydroxides and hydroxides were synthesized from chemically beneficiated high SiO₂/Al₂O₃ low-grade iron ore (57.49% Fe₂O₃) rejects and heated to get iron oxides of 96–99.73% purity. The infrared band positions, isothermal weight loss and thermogravimetric and chemical analysis established the chemical formulas of iron-oxyhydroxides as γ-FeOOH.0.3H₂O; α-FeOOH.0.2H₂O and amorphous FeOOH. The thermal products of all these were α-Fe₂O₃ excepting that of γ-FeOOH.0.3H₂O which gave mainly γ-Fe₂O₃ and some admixture of α-Fe₂O₃. The hydrazinated iron hydroxides and oxyhydroxides, on the other hand, decomposed autocatalytically to mainly γ-Fe₂O₃. Hydrazine method modifies the thermal decomposition path of the hydroxides. The saturation magnetization,J _s, values were found to be in the range 60–71 emu g⁻¹ which are close to the reported values for γ-Fe₂O₃. Mechanism of the γ-Fe₂O₃ formation by hydrazine method is discussed.     

Controlled synthesis and electrochemical properties of vanadium oxides with different nanostructures

Vanadium oxides (V₃O₇·H₂O and VO₂) with different morphologies have been selectively synthesized by a facile hydrothermal approach using glucose as the reducing and structure-directing reagent. The as-obtained V₃O₇·H₂O nanobelts have a length up to several tens of micrometers, width of about 60?C150?nm and thickness of about 5?C10?nm, while the as-prepared VO ₂ (B) nanobelts have a length of about 1·0?C2·7???m, width, 80?C140?nm and thickness, 2?C8?nm. It was found that the quantity of glucose, the reaction temperature and the reaction time had significant influence on the compositions and morphologies of final products. Vanadium oxides with different morphologies were easily synthesized by controlling the concentration of glucose. The formation mechanism was also briefly discussed, indicating that glucose played different roles in synthesizing various vanadium oxides. The phase transition from VO₂(B) to VO₂(M) were investigated and the phase transition temperature of the VO₂(M) appeared at around 68 °C. Furthermore, the electrochemical properties of V₃O₇·H₂O nanobelts, VO₂(B) nanobelts and VO₂(B) nanosheets were investigated and they exhibited a high initial discharge capacity of 296, 247 and 227 mAh/g, respectively.