Synthesis of uniformly sized Cu2O crystals with star-like and flower-like morphologies

Uniformly sized single-crystalline Cu₂O crystals with star-like and flower-like morphologies have been successfully prepared via the reaction of d-glucose, copper (II) chloride and sodium hydroxide in aqueous solution. The products were characterized by X-ray powder diffraction (XRD), transmission electron microscopy (TEM) and electron diffraction (ED).     

Co-precipitation synthesis and characterization of NiO-Ce0.8Sm0.2O1.9 nanocomposite powders: effect of precipitation agents

NiO-Ce0.8Sm0.2O1.9 (NiO-SDC) nanocomposite powders applied as promising anode material for low-temperature solid oxide fuel cells (SOFCs) were synthesized by hydroxide co-precipitation method using NH3 x H2O, NaOH and NH3 x H2O + NaOH as precipitation agents. The crystal phases, morphologies and sintering behavior of the synthesized NiO-SDC nanocomposite powders were investigated by means of X-ray diffraction (XRD), transmission electron microscopy (TEM) and sintering experiments. The effect of precipitation agents on the synthesis of the NiO-SDC nanocomposite powders was discussed. Results show that different precipitation agents influence greatly the synthesis and characteristics of the NiO-SDC nanocomposite powders. The NiO-SDC nanocomposite powders synthesized with NH3 x H2O deviate from the original composition due to the loss of Ni. The loss of Ni is avoided and nano-sized NiO-SDC composite powders are synthesized, when NaOH and NH3 x H2O + NaOH are used as precipitation agents. The NiO-SDC nanocomposite powders can be synthesized at relatively low temperature using NH3 x H2O + NaOH as precipitation agent, and the synthesized NiO-SDC nanocomposite powders show good sintering characteristics.     

Effect of content of Mg(NO3)2 x 6H2O on fabrication of alpha-alumina nanopowders by thermal decomposition of ammonium aluminum carbonate (AACH)

An alpha-Al2O3 and MgAl2O3 spinel phase doped alpha-Al2O3 nanopowders were fabricated by the thermal decomposition and synthetic of ammonium aluminum carbonate hydroxide (AACH). Crystallite size of 5 to 8 nm were fabricated when reaction temperature of AACH was low, 8 degrees C, and the highest [NH4+][AlO(OH)2-][HCO3] ionic concentration of pH 10 from the ammonium hydrogen carbonate (AHC) aqueous solution. The phase transformation of amorphous-s, theta-, alpha-Al2O3, MgAl2O3 spinel phases was examined at each temperature according to the amount of Mg(NO3)2 x 6H2O and AACH. A time-temperature-transformation (TTT) diagram for thermal decomposition in air was determined. Homogeneous, spherical alpha-Al2O3 nanopowders with a particle size of 60 nm were obtained by firing the crystallites, which had been synthesized from AACH at pH 10 and 8 degrees C, at 1050 degrees C for 6 h in air.     

纳米碳酸铝铵前驱体制备的研究

以硫酸铝铵(NH4Al(SO4)2)和碳酸氢铵(NH4HCO3)为主要原料,采用沉淀法制备纳米碳酸铝铵(AACH)前驱体,并利用X射线衍射(XRD),透射电镜(TEM)对前驱体的物相和形貌进行表征.研究表明,滴定速度和陈化时间对前驱体的形貌略有影响,而滴定方式和pH值对其影响较大.将硫酸铝铵溶液滴入碳酸氢铵溶液中,调节体系的pH值9-10,并将其陈化12小时,可以得到较好的前驱体.     

Visible cathodoluminescence of Er ions in β-Ga(2)O(3) nanowires and microwires

Erbium doped β-Ga(2)O(3) nanowires and microwires have been obtained by a vapour-solid process from an initial mixture of Ga(2)O(3) and Er(2)O(3) powders. X-ray diffraction (XRD) analysis reveals the presence of erbium gallium garnet as well as β-Ga(2)O(3) phases in the microwires. Scanning electron microscopy (SEM) images show that the larger microwires have a nearly rectangular cross-section. Transmission electron microscopy (TEM) and high-resolution TEM (HRTEM) analysis show good crystal quality of the β-Ga(2)O(3) nanowires. The nanostructures have been studied by means of the cathodoluminescence technique in the scanning electron microscope. Er intraionic blue, green and red emission lines are observed in luminescence spectra even at room temperature, which confirms the optical activity of the rare earth ions in?the grown structures. Mapping of the main 555?nm emission intensity shows a non-homogeneous distribution of Er ions in the microstructures.     

Synthesis, Characterization and Electromagnetic Studies on Nanocrystalline Nickel Zinc Ferrite by Polyacrylamide Gel

Nanocrystalline nickel zinc ferrite powders （Ni=Zn1-xFe2O4, A for x=0, B for x=0.2, C for x=0.5, D for x= 0.8 and E for x= 1） were synthesized by polyacrylamide gel method. X-ray diffraction （XRD）, transmission electron microscopy （TEM） and wave-guide were used to characterize the composition. The XRD results show that the dried gel powders are amorphous, and the characteristic peaks of the spinel Ni0.5Zn0.5Fe2O4 appear after the gel is calcined at 400℃ for 1 h. When the calcining temperatures are 600 and 800℃, the average grain sizes are identified by TEM to be 10 and 30 nm, respectively. The NixZn1-xFe2O4 powders have both dielectric loss and magnetic loss in the frequency range of 8.2-11.0GHz. With the increase of Ni^2＋ ions content, the dielectric parameters （ε′） and permeability （u′） of the NixZn1-xFe2O4 powders decrease while the dielectric loss （ε″）, magnetic loss （u″） and the reflection loss increase.     

乙酸异戊酯共沸干燥法制备低团聚掺锑氧化锡纳米微粉

以SnCl4·5H2O和SbCl3乙醇溶液为原料,用阴离子树脂交换除氯水解法制备得到无氯离子的前驱体掺锑氢氧化锡胶体沉淀。首次对以含氧官能团为主的系列憎水有机溶剂进行了共沸干燥脱水研究,并对所得粉体团聚程度进行比较。实验发现掺锑氧化锡共沸脱水干燥效果与有机溶剂分子结构之间有密切关系,提出了选择共沸有机溶剂的3个原则,在一系列有机溶剂中选择了最符合的乙酸异戊酯进行干燥实验,与常用的正丁醇共沸溶剂进行了消除粉体团聚效果的比较。运用IR、BET、TEM、XRD等方法对掺锑氢氧化锡粉体的结构、比表面积、形貌、物相进行表征。结果表明,乙酸异戊酯溶剂是理想的共沸干燥有机溶剂,其干燥所得掺锑氢氧化锡蓬松粉体的比表面积为284.44m2/g,比用正丁醇处理的增大了22%。将乙酸异戊酯干燥所得的掺锑氢氧化锡微粉经热处理后得到了低团聚的掺锑氧化锡纳米微粉。     

From cobalt nitrate carbonate hydroxide hydrate nanowires to porous Co(3)O(4) nanorods for high performance lithium-ion battery electrodes

We have developed a simple approach for the large-scale synthesis of cobalt nitrate carbonate hydroxide hydrate (Co(CO(3))(0.35)(NO(3))(0.2)(OH)(1.1)·1.74H(2)O) nanowires via the hydrothermal process using sodium hydroxide and formaldehyde as mineralizers at 120?°C. The porous Co(3)O(4) nanorods 10-30?nm in diameter and hundreds of nanometres in length have been fabricated from the above-mentioned multicomponent nanowires by calcination at 400?°C. The morphology and structure of cobalt nitrate carbonate hydroxide hydrate nanowires and Co(3)O(4) nanorods have been characterized by transmission electron microscopy (TEM), field emission scanning electron microscopy (FESEM), high resolution transmission electron microscopy (HRTEM) and x-ray powder diffraction (XRD). Moreover, the porous Co(3)O(4) nanorods have been applied in the negative electrode materials for lithium ion batteries, which exhibit high electrochemical performance.     

Mesoscale organization of CuO nanoslices: Formation of sphere

The nanocrystalline CuO powders were prepared by precipitation method using Cu(NO₃)₂ as copper raw material, water and ethanol as dispersants, and NaOH and ammonia solution as precipitates. The structure, particle size and morphology of resulting CuO powders were characterized by X-ray diffraction (XRD), field-emission scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The mechanism of CuO formation was discussed.     

Synthesis and characterization of indium hydroxide truncated polyhedral microcrystals

Indium Hydroxide Truncated Polyhedral Microcrystals (IHTPM) have been synthesized by hydrothermally treating commercial indium oxide powders in the sodium hydroxide solution without the aid of any surfactants. The formation mechanism of the IHTPM has been proposed by adjusting the reaction time, which indicates the excessive NaOH in the system plays an important role in the formation process of the IHTPM. X-ray powder diffraction (XRD), field scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM) and photoluminescence (PL) spectra have been used to characterize the products. The emission spectrum shows that the IHTPM display an emission wave band from about 415 to 550 nm and exhibit two emission peaks locating at 419.2 nm and 496.6 nm, respectively.     

Preparation and electromagnetic property of Al-doped SnO2 powders by coprecipitation method in the GHz range

Al-doped SnO₂ powders have been prepared by coprecipitation method at 550 °C, using tin chloride (SnCl₄·5H₂O) as the raw material, ammonium hydroxide (NH₃·H₂O) as the precipitator, and aluminum nitrate (Al(NO₃)₃·9H₂O) as the doping source, respectively. The microstructure of the prepared powders has been characterized by X-ray diffraction and scanning electron microscope, respectively. Results show that the prepared powders were Sn_(1?x)Al_xO₂ (x = 0, 0.03, 0.06, and 0.09) solid solution powders and the lattice constant decreased with increasing Al doping content. The electromagnetic property in the frequency range of 8.2–12.4 GHz of prepared powders has been determined. The real part (ε′) and imaginary part (ε″) of permittivity of prepared powders increased with increasing Al doping content. There was little change of real part (μ′) and imaginary part (μ″) of permeability of prepared powders. The electromagnetic loss mechanism has been discussed.     

Anticorrosion properties of CeO2-modified aluminosilicate nanotubes

Ceria nanoparticles 4–15 nm in size have been obtained on halloysite nanotubes (HNTs) in solution by reacting cerium nitrate and sodium hydroxide. The HNT/CeO₂ composites were characterized by transmission electron microscopy, scanning electron microscopy, X-ray diffraction, and infrared spectroscopy. Modified HNTs containing about 5 wt % ceria showed high anticorrosion performance on 2024-T3 air-craft-grade aluminum alloy.     

Preparation of nanostructured NiFe2O4 catalysts by combustion reaction

Nanosize nickel ferrite powders (NiFe₂O₄) have been prepared by combustion reaction using nitrates and urea as fuel. The resulting powders were characterized by X-ray diffraction (XRD), nitrogen physical adsorption (BET), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and catalytic activity. The results showed nanosize nickel ferrite powders with high specific surface area (55.21 m²/g). The powders showed extensive XRD line broadening and the crystallite size calculated from the XRD line broadening was 18.0 nm. The nickel ferrite powder presented significant activity as catalyst for the water gas shift reaction, over the temperature range of 250–450 °C.     

Dopants adsorbed as single atoms prevent degradation of catalysts

The design of catalysts with desired chemical and thermal properties is viewed as a grand challenge for scientists and engineers. For operation at high temperatures, stability against structural transformations is a key requirement. Although doping has been found to impede degradation, the lack of atomistic understanding of the pertinent mechanism has hindered optimization. For example, porous gamma-Al(2)O(3), a widely used catalyst and catalytic support, transforms to non-porous alpha-Al(2)O(3) at approximately 1,100 degrees C (refs 7-10). Doping with La raises the transformation temperature to approximately 1,250 degrees C, but it has not been possible to establish if La atoms enter the bulk, adsorb on surfaces as single atoms or clusters, or form surface compounds. Here, we use direct imaging by aberration-corrected Z-contrast scanning transmission electron microscopy coupled with extended X-ray absorption fine structure and first-principles calculations to demonstrate that, contrary to expectations, stabilization is achieved by isolated La atoms adsorbed on the surface. Strong binding and mutual repulsion of La atoms effectively pin the surface and inhibit both sintering and the transformation to alpha-Al(2)O(3). The results provide the first guidelines for the choice of dopants to prevent thermal degradation of catalysts and other porous materials.     

超细镁铝复合阻燃剂的制备与表征

采用化学共沉淀的方法,在相同的工艺条件下,固定Mg2+的浓度,通过改变Al3+的量,分别制备Mg与Al的物质的量比为5∶1、4∶1、3∶1、2∶1、1∶1的复合粉体和单一的氢氧化镁与氢氧化铝,通过X射线衍射、透射电镜、热重-差热分析、氮气吸附测定比表面积、堆密度等手段对合成样品进行表征。结果表明,合成样品为类水滑石结构Mg6Al2(OH)18.4.5H2O为主的混合物,呈现卷曲片状的形貌;Mg与Al的物质的量比为4∶1时制备的粉体为Mg(OH)2和Mg6Al2(OH)18.4.5H2O的混合物,分散性好,分解温度高,是一种优良的阻燃剂。     

Processing of Ceramic Based Nanocomposite Using α-Al2O3 Powder and FeCl2 Solution as Starting Materials

Alumina-iron nanocomposite powders were prepared by a two-step process. In the first step, α-Al2O3-FeCl2 powder mixture was formed by mixing α-Al2O3 powders with FeCl2 solution followed by drying. In the second step, the FeCl2 in the dry power mixture was selectively reduced to iron particles. A reduction temperature of 750℃ for 15 min in dry H2 was chosen based on the thermodynamic calculations. The concentration of iron in FeCl2 solution was calculated to be 20 vol. pct in the final composite. Two techniques were used to produce composite bulk materials. The Al2O3 nanocomposite powders were divided to two batches. The first batch of the produced mixture was hot pressed at 1400℃ and 27 MPa for 30 min in a graphite die. To study the effect of oxygen on the Al2O3/Fe interface bonding and mechanical properties of the composite, the second batch was heat treated in air at 700℃ for 20 min to partially oxidize the iron particles before hot pressing. Characterization of the composites was undertaken by conventional density measurements, X-ray diffractometry （XRD）, scanning electron microscopy （SEM）, transmission electron microscopy （TEM） and electron probe micro analysis （EPMA）. The suggested processing route （mixing, reduction and hot pressing） produces ceramic-metal nanocomposite much tougher than the pure Al2O3. The fracture strength of the produced Al2O3/Fe nanocomposite is nearly twice that of the pure Al2O3. The presence of spinel phase, FeAl204, as thick layer around the Fe particles in the Al2O3 matrix has a detrimental effect on interfacial bonding between Fe and AI203 and the fracture properties of the composite.     

Processing of Ceramic Based Nanocomposite Using α-Al2O3 Powder and FeCl2 Solution as Starting Materials

Alumina-iron nanocomposite powders were prepared by a two-step process. In the first step, α-Al2O3-FeCl2 powder mixture was formed by mixing α-Al2O3 powders with FeCl2 solution followed by drying. In the second step, the FeCl2 in the dry power mixture was selectively reduced to iron particles. A reduction temperature of 750℃ for 15 min in dry H2 was chosen based on the thermodynamic calculations. The concentration of iron in FeCl2 solution was calculated to be 20 vol. pct in the final composite. Two techniques were used to produce composite bulk materials. The Al2O3 nanocomposite powders were divided to two batches. The first batch of the produced mixture was hot pressed at 1400℃ and 27 MPa for 30 min in a graphite die. To study the effect of oxygen on the Al2O3/Fe interface bonding and mechanical properties of the composite,the second batch was heat treated in air at 700℃ for 20 min to partially oxidize the iron particles before hot pressing. Characterization of the composites was undertaken by conventional density measurements, X-ray diffractometry (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and electron probe micro analysis (EPMA). The suggested processing route (mixing, reduction and hot pressing)produces ceramic-metal nanocomposite much tougher than the pure Al2O3. The fracture strength of the produced Al2O3/Fe nanocomposite is nearly twice that of the pure Al2O3. The presence of spinel phase,FeAl2O4, as thick layer around the Fe particles in the Al2O3 matrix has a detrimental effect on interfacial bonding between Fe and Al2O3 and the fracture properties of the composite.     

A low temperature route to prepare LaFeO3 and LaCoO3

A combination of digestion and further low temperature calcination to crystallize the product was employed to prepare LaFeO₃ (LF) and LaCoO₃ (LC) powders. Freshly co-precipitated lanthanum and ferric (or cobalt) hydroxide gels by sodium hydroxide were allowed to react at 100 °C under refluxing and stirring conditions for 4-6 h. These oven dried powders were heated at 450 °C to form crystalline LF (or LC) powders. The phase contents and lattice parameters were investigated by X-ray diffraction (XRD). Transmission electron microscope (TEM) investigations were carried out to examine the morphology and average particle size of these powders.     

Self-assembly growth of BiFeO3 powders prepared by microwave-hydrothermal method

With FeCl₃·6H₂O and Bi(NO₃)₃·5H₂O powder as raw materials and KOH as a mineralizer, the pure phase BiFeO₃ (BFO) powder was synthesized by microwave-hydrothermal (MH) method at 200 °C, with the reaction time as little as 30 min. The range of preparing the BFO powders had been summarized. The field emission scanning electron microscopy (FE-SEM) images revealed that the little BFO plate grew together forming rock sugar-like BFO powders, and then they grew further to form the mussel-like BFO powders. The transmission electron microscope (TEM) images also improved the self-assembly growth of BFO powders. The X-ray diffraction (XRD), the high resolution transmission electron microscopy (HRTEM) and the selected area electron diffraction (SAED) results indicated that the BFO powders grew along the [110] and [104] crystal orientation. The B-H loops of BFO indicated that the weak magnetism existed in the pure phase BFO powders.     

One-pot synthesis of porous hematite hollow microspheres and their application in water treatment

Alpha-Fe2O3 hollow micospheres have been successfully synthesized by solvothermal method at 200 degrees C. The synthesized products are characterized by X-ray diffraction (XRD), field-emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), and the nitrogen adsorption-desorption isotherm technique. The alpha-Fe2O3 hollow microspheres have an average diameter of 2-3 microm, the shell consists of numerous aligned nanorods with length of about 200-400 nm. The effects of solvent and reaction time have been studied. The Ostwald ripening mechanism is proposed to account for the formation of alpha-Fe2O3 hollow microspheres. Because of the porous hollow microstructure and large specific surface area, the microspheres were found to be effective sorbents for the removal of Cr(VI) ions from wastewater.