Photocatalytic activities of hollow and hierarchical Bi<Subscript>3.15</Subscript>Nd<Subscript>0.85</Subscript>Ti<Subscript>3</Subscript>O<Subscript>12</Subscript> microspheres synthesized through a hydrothermal process

Hollow and hierarchical Bi_3.15Nd_0.85Ti₃O₁₂ (BNdT) microspheres of 0.5–1.2 μm in diameter were synthesized through a hydrothermal process. Each hollow microsphere is constructed across by many single-crystalline BNdT nanoplates with in-plane dimension of ~400 nm. The BNdT nanoplates are of layered perovskites. The UV–visible absorption characteristics demonstrated that the band gap of the BNdT microspheres is 3.33 eV. The hierarchical microspheres exhibit significant photocatalytic activity. Up to 75% methyl orange was decolorized after UV irradiation for 210 min, whereas lower than 10% methyl orange decolorized using BNdT powders prepared from single crystals as catalyst. The photocatalytic decolorization of methyl orange solution is a pseudo-first-order reaction and its kinetics can be expressed as ln(C/C ₀) = kt.     

熔盐镁热还原法合成ZrB2超细粉体

为了降低ZrB_2粉体的合成温度,并在此基础上合成粒径细小、纯度高的ZrB_2粉体,以ZrO2及B4C为原料,以Mg粉为还原剂,以NaCl-KCl为熔盐介质,研究熔盐镁热还原法低温合成ZrB_2超细粉体的工艺。探讨了反应温度、B/Zr物质的量比及Mg粉用量对合成ZrB_2超细粉体的影响,并对粉体的物相组成及显微结构进行了表征。结果表明合成ZrB_2的起始温度为1 173K,最佳合成温度为1 473K。合成纯相的ZrB_2粉体最佳工艺条件为:B/Zr物质的量比为2.2,Mg过量50%(质量分数),1 473K反应3h。所合成ZrB_2粉体的晶粒尺寸为30~300nm。     

Effect of Y(NO3)3 additive on morphologies and size of metallic W particles produced by hydrogen reduction

Tungsten, one of the refractory metals, has lots of excellent properties, making tungsten powders become a choice of raw material for many applications. This work reported a simple method (the salt-assisted hydrogen reduction of WO₃ powders) for preparing tungsten powders with desired morphologies and size. By adjusting the amount of additive (Y(NO₃)₃) and reduction temperature, metallic tungsten particles with different morphologies and size were obtained. It was found that both temperature and additive had apparent effects on the morphology and size of metallic W particles, and the large parallelepiped-shaped powders disappeared and large irregular blocky-shaped powders were degraded under the influence of additive. With the increase of temperature and amount of salt, particles became more dispersed and the size increased at higher temperatures, and the shape of particles was changed from spherical to polyhedral as well. On the contrary, the size of sub-particles became smaller as increasing amount of Y(NO₃)₃ at lower temperatures. Based on the results, the reaction and refining mechanisms for preparing tungsten were proposed as well.     

Direct synthesis of highly crystalline single-phase hexagonal tungsten oxide nanorods by spray pyrolysis

The metastable state hexagonal-tungsten oxide (h-WO₃) has been attracting attention over the past decade because of its high reactivity that arises from the hexagonal channels in its crystal structure. Simplification of the process used to synthesize h-WO₃ is an important step to facilitate the industrial applications of this material. In this study, we addressed this challenge by developing a spray pyrolysis process to synthesize highly crystalline h-WO₃. The ratio of the monoclinic to the hexagonal phase was controlled by adjusting the segregation time. Single-phase h-WO₃ nanorods were synthesized using a carrier gas flow rate of 1?L/min, which was equivalent to a segregation time of 18.4?s. The ability of the h-WO₃ nanorods to adsorb nitrogen and carbon dioxide was evaluated to confirm the presence of hexagonal channels in the crystal structure.     

FTIR Spectra of the M(EDTA) n− Complexes in the Process of Sol-Gel Technique

Sol-gel is one of the effective techniques for preparing YBa₂Cu₃O_{7 ? δ} (YBCO) coatings at relatively low cost. Its process from gel to oxide coatings, however, was not yet fully understood. This is one of the obstacles for achieving YBCO coatings with good superconducting properties. In this paper, we chose EDTA as the complexant to prepare gels with different kinds of M(EDTA)^n? complexes, where M is any combination of Y, Ba, and Cu cations, in order to investigate the decomposition process of the gels with the help of Fourier transform infrared (FTIR) spectra. Comparing the FTIR spectra of the gel powders with those of the calcined powders, we found that the decomposed temperatures were different for different M(EDTA)^n? complexes. We considered this was the cause of the Ba segregation (as BaCO₃) in the coatings at low heating temperature, which in turn blocked the formation of high quality YBa₂Cu₃O_7?δ.     

Preparation of nanoplates assembled 4CaO·5B2O3·7H2O oval-like microspheres via a hydrothermal method

4CaO·5B₂O₃·7H₂O uniform oval-like microspheres morphology has been prepared at 120 °C by a simple hydrothermal method with the help of the surfactant polyethylene glycol(PEG-300). The result indicates that 4CaO·5B₂O₃·7H₂O oval-like microspheres are constructed by ladder-like layers, and each layer is made up of numerous densely packed nanoplates with the thickness of 50–100 nm and the diameter of several microns. The nanoplates in each layer are interconnected with the nanoplates in next layer, which leads to form the multilayered structural oval-like microspheres. The PEG-300 plays an important role in the formation of this oval-like microspheres morphology.     

Controllable synthesis of beta-Mn2V2O7 microtubes and hollow microspheres

β-Mn₂V₂O₇ microtubes with the range of 15-25 μm in length, 2.5-3.5 μm in external diameter, and ca 0.4 μm of the wall in thickness, as well as β-Mn₂V₂O₇ hollow microspheres with an average outer diameter of 2 μm were successfully synthesized in a suitable molar ratio of NH₄VO₃ and MnCO₃ powders via a hydrothermal process. XRD and FESEM were used to characterize the products, and the magnetic susceptibility curve was also measured. In the whole process, the concentration of Mn²⁺ cations derived from MnCO₃ dissolution plays a crucial role in the formation of β-Mn₂V₂O₇ microtubes and hollow microspheres.     

Influence of atomized powder size on microstructures and mechanical properties of rapidly solidified Al–Cr–Y–Zr aluminum alloys

Rapidly solidified powders of Al–5.0Cr–4.0Y–1.5Zr (wt%) were prepared by using a multi-stage atomization-rapid solidification powder-making device. The atomized powders were sieved into four shares with various nominal diameter level and were fabricated into hot-extruded bars after cold-isostatically pressing and vaccum degassing process. Influence of atomized powder size on microstructures and mechanical properties of the hot-extruded bars was investigated by optical microscopy, X-ray diffraction, transmission electronic microscopy with EPSX and scanning electron microscopy. The results show that the fine atomized powders of rapidly solidified Al–5.0Cr–4.0Y–1.5Zr aluminum alloy attains supersaturated solid solution state under the exist condition of multi-stage rapid solidification. With the powder size increasing, there are Al₂₀Cr₂Y (cubic, a = 1.437 nm) and Ll₂ Al₃Zr (FCC, a = 0.407 nm) phase forming in the powders, and even lumpish particles of Al₂₀Cr₂Y appearing in the coarse atomized powders, as can be found in the as-cast master alloy. Typical microstructures of the extruded bars of rapidly solidified Al–5.0Cr–4.0Y–1.5Zr aluminum alloy can be characterized by fine grain FCC α-Al matrix with ultra-fine spherical particles of Al₂₀Cr₂Y and Al₃Zr. But a small quantity of Al₂₀Cr₂Y coarse lumpish particles with micro-twin structures can be found, originating from lumpish particles of the coarse powders. The extruded bars of rapidly solidified Al–5.0Cr–4.0Y–1.5Zr aluminum alloy by using the fine powders eliminated out too coarse powders have good tensile properties of σ_0.2 = 403 MPa, σ_b = 442 MPa and δ = 9.4% at room temperature, and σ_0.2 = 153 MPa, σ_b = 164 MPa and δ = 8.1% at high temperature of 350 °C.     

Y2O3:Eu microstructures: Hydrothermal synthesis and photoluminescence properties

Hexagonal microprisms of yttrium hydroxide (Y(OH)₃) with tuned diameter and height have been successfully prepared for the first time via a facile hydrothermal process using sodium citrate as the shape modifying agent. Y(OH)₃ microspheres with diameter of ca. 2.5 μm and microtubes with an average length about 13 μm, outer diameter about 3 μm and tube thickness about 800 nm were also obtained in current reaction systems. The possible formation mechanism for the Y(OH)₃ microstructures was briefly proposed. Y₂O₃:Eu³⁺ (5%) microstructures with similar morphologies was obtained after thermal treatment of the as-prepared Y(OH)₃:Eu³⁺ microstructures at 700 °C for 4 h. Results show that the relative emission intensity of the Y₂O₃:Eu³⁺ microprisms is about 8 times as those of the Y₂O₃:Eu³⁺ microtubes and microspheres under excitation of 259 nm ultraviolet light. The products were characterized by XRD, SEM, and EDS.     

Influence of yttrium dopant on the synthesis of ultrafine AlN powders by CRN route from a sol–gel low temperature combustion precursor

Y-doped ultrafine AlN powders were synthesized by a carbothermal reduction nitridation (CRN) route from precursors of Al₂O₃, C and Y₂O₃ prepared by a sol–gel low temperature combustion technology. The Y dopant reacted with alumina and thus forming yttrium aluminate of AlYO₃, Al₃Y₅O₁₂ and Al₂Y₄O₉, which formed a liquid at about 1400 °C and promoted the transformation of Al₂O₃ to AlN and the growth of AlN particles. Compared with the conventional solid CRN process, Y dopant reduced the synthesis temperature by 150 °C, and Al₂O₃ transformed to AlN completely at 1450 °C. The content of Y dopant had little effect on the synthesis temperature of AlN whereas it influenced the phase of Y compounds in the products. As the Y/Al molar ratio was in the range of 0.007648–0.022944, the particle sizes of Y-doped AlN powders synthesized at 1450 °C were 150–300 nm.     

Vacuum activation assisted hydrogenation-dehydrogenation for preparing high-quality zirconium powder

The vacuum activation assisted hydrogenation-dehydrogenation (HDH) method was applied to fabricate the high-purity and ultrafine nuclear grade zirconium powders. An additional vacuum activation process was specially used prior to the hydrogenation to suppress the oxygen content and increase the hydrogen content. It was found that this extra process was not only efficient in shortening the length of the whole process, but also critical in improving the quality of Zr powders. The detailed investigations on the mechanism indicated that the merits could be both attributed to the removal of the oxygen sources on the sponge zirconium surface and the formation of micro-cracks on the ZrO₂ film. By adjusting the parameters of the vacuum activation assisted HDH process, the oxygen content of the intermediate material ZrH₂ was decreased down to 0.16 wt.%, while the hydrogen content was increased up to 2.14 wt.%, nearly approaching to the theoretical value. Based on this high-quality ZrH₂ bulks, the Zr powders with oxygen content of 0.21 wt.% and D₅₀ of ~2.9 μm could be fabricated after the ball-milling and dehydrogenation process. An efficient approach to produce high-quality Zr powders was systematically investigated in this paper to satisfy with the demand of the nuclear industry.     

Preparation of hexagonal WO3 from hexagonal ammonium tungsten bronze for sensing NH3

Hexagonal tungsten oxide (h-WO₃) was prepared by annealing hexagonal ammonium tungsten bronze, (NH₄)_0.07(NH₃)_0.04(H₂O)_0.09WO_2.95. The structure, composition and morphology of h-WO₃ were studied by XRD, XPS, Raman, ¹H MAS (magic angle spinning) NMR, scanning electron microscopy (SEM), and BET-N₂ specific surface area measurement, while its thermal stability was investigated by in situ XRD. The h-WO₃ sample was built up by 50-100 nm particles, had an average specific surface area of 8.3 m²/g and was thermally stable up to 450 °C. Gas sensing tests showed that h-WO₃ was sensitive to various levels (10-50 ppm) of NH₃, with the shortest response and recovery times (1.3 and 3.8 min, respectively) to 50 ppm NH₃. To this NH₃ concentration, the sensor had significantly higher sensitivity than h-WO₃ samples prepared by wet chemical methods.     

Experimental research on residual carbon of Y211 inclusions in a melt-textured Y123/Y211 composite

The inherent doping of residual carbon during the preparation of Y₂BaCuO₅ (Y211) inclusions would degrade the physical and mechanical performance of the Y₁Ba₂Cu₃O_7-x (Y123) superconducting matrix. Y211 precursor powders were prepared by the oxalate coprecipitation process in this study. Residual carbon contents of Y211 powders under different heat treatment processes were studied by the high-frequency combustion infrared absorption method. The residual carbon content of Y211 reached the current best level ～0.012% when calcined in O₂ flow at 950°C for 20?h. Y211 powders with the lowest carbon content were used to prepare a small batch of melt-textured Y123/Y211 composites. All samples were single-domain crystals without macro defects, which were usually caused by the emission of CO₂. Among them, one sample (Ø27?mm?×?14?mm) has a maximum levitation force of 71?N (77?K, 0.5?T), with critical current density J_c of 3.2?×?10⁸ A/m² (77?K, 0?T).     

Synthesis, microstructure and dielectric properties of zirconium doped barium strontium titanate obtained by solvothermal method

(Ba_0.8Sr_0.2Zr_yTi_1?yO₃) (y = 0.05, 0.1, 0.15 and 0.2) nanosized powders is synthesized by solvothermal method. The formation of (Ba_0.8Sr_0.2Zr_yTi_1?yO₃) was confirmed by XRD, FT-IR and XPS analysis. The purity of the (Ba_0.8Sr_0.2Zr_yTi_1?yO₃) was examined using FT-IR spectroscopy. The X-ray analysis proves that all as-synthesized Ba_0.8Sr_0.2Zr_yTi_1?yO₃ powders have a cubic perovskite structure. The surface characterization indicates the powder contains Zr and Sr elements. SEM investigation shows that the average particle size is reduced with increasing the Zr content and the average particle size is in the range 37–50 nm, the well dispersed nano powders have narrow particle size distribution. The study of dielectric properties shows that the Curie peaks of dielectric constant become broader and shift towards lower temperature on the basis of Ba_0.8Sr_0.2TiO₃ and the dielectric loss decreases with increasing Zr content.     

Hierarchical BiOI and hollow Bi2WO6 microspheres: Topochemical conversion and photocatalytic activities

We present here a facile one-pot surfactant-free solvothermal route to synthesize hierarchical BiOI microspheres assembled from nanosheets at 120 °C for 16 h. The as-synthesized BiOI microspheres could be topochemically converted into hollow hierarchical Bi₂WO₆ ones built by nanoplates for the first time under hydrothermal condition because of the analogies of crystal structures. The transformation process of hierarchical BiOI microspheres to hollow Bi₂WO₆ ones was surveyed through XRD analyses and FE-SEM observations of the intermediates at different reaction stages. Rhodamine B (RhB) was selected as pollutant model and visible-light-driven photocatalytic activities of hierarchical BiOI and Bi₂WO₆ microspheres under the same measurement conditions were comparatively studied. As a result, the photocatalytic activities of BiOI obviously outshone Bi₂WO₆. The present study not only develops a new method for fabricating hierarchical architectures but also provides some useful information on relative visible-light-responding photocatalytic activity of hierarchical BiOI and Bi₂WO₆ microspheres.     

Solvothermal synthesis of hierarchical Co3O4 flower-like microspheres for superior ethanol gas sensing properties

In this paper, hierarchical Co₃O₄ flower-like microspheres have been successfully synthesized on the basis of morphology-conserved transformation method. The key step of this method is to construct flower-like microstructures of the cobalt-containing precursors via manipulating the synthetic parameters in a facile ethylene glycol mediated solvothermal reaction. The as-prepared flower-like microspheres are formed from the assembly of many two-dimensional nanosheets, accompanied by an outside-in dissolution and recrystallization process. Finally, hierarchical Co₃O₄ microspheres with conserved flower-like morphology are obtained through the moderate calcination. When evaluated as a gas sensor, the obtained Co₃O₄ flower-like microspheres exhibit a good response and sensitivity towards ethanol gas, suggesting their promising potential for gas sensors application.     

Synthesis of flower-like,pinon-like and faceted nanoplates (BiO)2CO3 micro/nanostructures with morphology-dependent photocatalytic activity

The flower-like, pinon-like and faceted nanoplates (BiO)₂CO₃ micro/nanostructures were fabricated by a one-pot template-free method based on hydrothermal treatment of the aqueous mixture of bismuth citrate and sodium carbonate. The morphology of (BiO)₂CO₃ can be simply controlled by the reaction temperature. X-ray diffraction, scanning electron microscopy, UV–vis diffuse reflection spectra, and photoluminescence spectra were applied to analyze the microstructures and properties of the samples. The flower-like and pinon-like (BiO)₂CO₃ superstructures were hierarchically self-assembled by nanoplates and showed increased light absorption owing to the multiple light reflection between the nanoplates. The thickness of nanoplates was increased with the increasing reaction temperatures due to the preferred growth along the (110) plane. The (BiO)₂CO₃ with various micro/nanostructures showed morphology-dependent photocatalytic activity toward removal of aqueous RhB. The as-prepared flower-like (BiO)₂CO₃ microspheres exhibited highest photocatalytic activity due to the large surface area, increased light absorption, enhanced charge carriers separation, and special architectures of hierarchical nanoplates microspheres, exceeding that of the P25.     

Preparation and crystallization of ultrafine Li2O-Al2O3-SiO2 powders

Ultrafine powders of Li₂O-Al₂O₃-SiO₂ (LAS) glass-ceramic were prepared by the sol-gel process using tetraethoxysilane, titanium butoxide, lithium, magnesium, aluminium (and zinc) inorganic salts as starting materials. The effect of pH on the sol-gel transition and particle sizes of the Li₂O-Al₂O₃-SiO₂ system was studied. The nucleation and crystallization process of LAS powders were also investigated by differential thermal analysis and X-ray diffraction. The results show that a surface nucleation process occurs for ultrafine LAS powders. The LAS glass-ceramics fabricated from ultrafine LAS powders have a low thermal expansion coefficient, <10×10^–7 °C.     

Phase evolution and gas-phase particle size distributions during spray pyrolysis of (Bi,Pb)SrCaCuO and Ag(Bi,Pb)SrCaCuO powders

Phase evolution, gas-phase particle size distributions and lead loss were studied during formation of (Bi,Pb)SrCaCuO powders and their composites with silver by spray pyrolysis starting from nitrate solutions. The 10 wt% Ag/90 wt% Bi_1.8Pb_0.44Sr₂Ca_2.2Cu₃O_x composite powders made at 700°C consisted of 20–60 nm grains of silver and mixed-oxide phases with a fine dispersion of Ag grains within the particles. At 700°C, the primary phases present in (Bi,Pb)SrCaCuO powders were (Bi,Pb)₂Sr₂CuO_x (2201), Ca₂PbO₄ (plumbate), (Bi,Pb)₂Sr₂CaCu₂O_x(2212), and (Bi,Pb)₃Sr₂Ca₂Cu₁O_x(3221). For T≥800°C, the powders were considerably depleted in lead, and the plumbate and 3221 phases were absent. For T = 900°C, a large number of ultrafine particles (<30 nm) were formed, probably from the PbO vapor released from the reactor walls. Using spray pyrolysis, it is easy to control stoichiometry and limit the phase segregation at the nanometer-scale so that homogeneous and phase-pure materials can be obtained rapidly during subsequent processing.     

Photocatalytic activities of Mo-doped Bi2WO6 three-dimensional hierarchical microspheres

The Mo-doped Bi₂WO₆ three-dimensional (3D) hierarchical microspheres from nanoplates have been synthesized by a hydrothermal route. The products were characterized in detail by multiform techniques: X-ray diffraction (XRD), energy-dispersive X-ray analysis (EDS), scanning electron microscopy (SEM), and UV-vis absorption spectrum. The results of the photocatalytic degradation of Rhodamine-B (RhB) in aqueous solution showed that molybdenum ions doping greatly improved the photocatalytic efficiency of Bi₂WO₆ 3D hierarchical microspheres. The Mo-doped Bi₂WO₆ microspheres with atomic ratio of Mo-W of 0.05 had the best activity in photodegradation of RhB in aqueous solution under 500 W Xe lamp light irradiation.