Yttrium aluminum garnet (Y_3A_(l5)O_(12)) nanopowders synthesized by the chemical method

The homogeneously dispersed, less agglomerated YAG nanopowders are synthesized by the citrate-gel method followed by low-temperature self-propagating combustion reaction, using Y2O3, Al(NO3)3?9H2O and citric acid as starting materials. This method effectively solves the problems caused by solid-state reaction at high temperature and the hard ag-glomerates brought by the chemical precipitation method. The powders are characterized by TG-DTA, XRD, FT-IR and TEM respectively. The experiments show that the forming temperature of YAG crystal phase is 850°C and the pseudo-YAG crystalline appears during the calcination and transforms to pure YAG at 1050°C. The powders with sizes less than 50 nm are observed by TEM micrography, which is consistent with the result calculated by Scherrer's formula. The powders consist of single grains.

Synthesis and Characterization of Rare Earth-Doped CuO Nanopowder and Its Infrared Characteristic

The nano composite powder of rare earth-doped CuO were prepared by the stearic gel method and characterized by means of X-ray (XRD) and transmission electron microscopy (TEM) and scanning electron microscope (SEM) and IR. Microscopic investigation of the nanopowder was measured by AFM. The result shows that the grain sizes are in the order of nanometers, approximately 10, 12, 22, 32 and 40 nm for the nanopowder deposited at 600, 650, 700, 750 and 800 ℃. The grains grow up with the increase of sintering temperature. There are some agglomeration and selfassemble phenomenon in the particles. IR result indicates that the vibration kurtosis was changed with the different sintering temperature.

Raman Spectroscopic Study of Silicon Nanopowders

Vibrational properties of silicon nanopowders are discussed with reference to Raman spectroscopic measurements. The powders were produced in a low pressure rf plasma from the cluster induced agglomeration of positive ions formed during the dissociation of silane. Influence of thermal treatment and the crystallization phenomena of the powder were studied. Raman spectroscopic measurements reveal size quantization effects for the particles as well as the existence of partially ordered regions in the apparently amorphous primary particles. The crystalline and amorphous volume fraction in the material were calculated from the relative spectraI intensities. The results obtained in these experiments are consistent with the observations from recent high resolution transmission electron microscopy studies of these powders

Development of Nanopowder Synthesis Using Induction Plasma

The application of induction plasma technology developed for the synthesis of nano- metric powders is summarized. A brief description of the scientific basis for the induction plasma processes is given, followed by the presentation of an induction plasma system developed by Tekna, together with various examples of the nanopowders synthesized using its facilities. The advantages of the induction plasma process over alternative techniques and its adaptability into industrial- scale operation is particularly illustrated. Some specific issues related to the nanopowder synthesis process are also discussed.

Effect of Surface Modification on Behaviors of Cerium Oxide Nanopowders

Study was made on the effect of surface modification on the behaviors of cerium oxide nanopowders.A surfactant-sodium dodecyl sulfate（C12H25SO4Na）was used to modify the surface of CeO2 powder particles.The unmodified and modified CeO2 powders were characterized by using a powder comprehensive characteristic tester,laser particle size analyzer,specific surface area tester,X-ray diffraction tester,and a scanning electron microscope.The testing and analysis results showed that C12H25SO4Na surface modification might increase the flowability and dispersity,and decrease the specific surface area and agglomeration of CeO2 powders.The mechanism of the surface modification of CeO2 powder particles was also discussed.

PARTICLE SIZE AND MICROSTRUCTURE OF Ni NANOPOWDERS PREPARED BY ANODIC ARC PLASMA

Pure Ni nanopowders were successfully prepared by the method of anodic arc disch arged plasma with homemade experimental apparatus. The particle size, mircostruc ture and morphology of the particles by this process were characterized via X-ra y powder diffraction (XRD), transmission electron microscopy (TEM) and the corre sponding selected area electron diffraction (SAED); The specific surface area an d pore parameters were investigated by multi-point full analysis of nitrogen ads orption-desorption isotherms at 77K by Brunauer- Emmett-Teller (BET) surface are a analyzer; The chemical composition were determined by X-ray energy dispersive spectrometry (XEDS) equipped in SEM and element analyze instrument. The experime nt results indicate that the samples by this method with high purity,the crystal structure of the particles is as same as the bulk material, is fcc structure, w ith average particle sizes about 47nm, ranging from 20 to 70nm, and distributed uniformly in spherical chain shapes, the specific surface areavis 14.23m2/g, po re volume of pore is 0.09cm3/g and average pore diameter is 23nm.

Intense up-conversion emissions of yb3＋/Dy3＋ co-doped A12O3 nanopowders prepared by non-aqueous sol-gel method＊

yb3＋/Dy3＋ co-doped A1203 nanopowders have been prepared by the non-aqueous sol-gel method and their up- conversion photoluminescence spectra are measured under excitation by a 980-nm semiconductor laser. The results show that there are comparatively abundant spectra of up-conversion emissions centered at 378, 408, 527 and 543, and 663 nm, corresponding to 4C9/2→ 6H13/2, 4C9/2→ 6Hll/2, 4115/2 → 6H13/2, and 4F9/2 →6Hll/2 transitions of Dy3＋, respectively. Two-photon and three-photon processes are involved in ultraviolet, violet, green, and red up-conversion emissions. The energy transition between Yb3＋ and Dy3＋ is discussed.

Surface treatment of titanium dioxide nanopowder using rotary electrode dielectric barrier discharge reactor

Titanium dioxide(Ti O_(2))nanopowder(P-25;Degussa AG)was treated using dielectric barrier discharge(DBD)in a rotary electrode DBD(RE-DBD)reactor.Its electrical and optical characteristics were investigated during RE-DBD generation.The treated TiO_(2)nanopowder properties and structures were analyzed using x-ray diffraction(XRD)and Fourier-transform infrared spectroscopy(FTIR).After RE-DBD treatment,XRD measurements indicated that the anatase peak theta positions shifted from 25.3°to 25.1°,which can be attributed to the substitution of new functional groups in the TiO_(2)lattice.The FTIR results show that hydroxyl groups(OH)at 3400 cm-1 increased considerably.The mechanism used to modify the TiO_(2)nanopowder surface by air DBD treatment was confirmed from optical emission spectrum measurements.Reactive species,such as OH radical,ozone and atomic oxygen can play key roles in hydroxyl formation on the TiO_(2)nanopowder surface.

MICROSTRUCTURE AND PREPARATION OF Ni,Al AND Fe NANOPOWDERS

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Novel Salt-Assisted Combustion Synthesis of High Surface Area Ceria Nanopowders by An Ethylene Glycol-Nitrate Combustion Process

A novel salt-assisted combustion process with ethylene glycol as a fuel and nitrate as an oxidant to synthesize high surface area celia nanopowders was reported. The effects of various tunable conditions, such as fuel-to-oxidant ratio, type of salts, and amount of added salts, on the characteristics of the as-prepared powders were investigated by X-ray diffraction, transmission electron microscopy and BET surface area measurement. A mechanism scheme was proposed to illustrate the possible formation processes of well-dispersed ceria nanoparticles in the salt-assisted combustion synthesis. It was verified that the simple introduction of leachable inert inorganic salts as an excellent agglomeration inhibitor into the redox mixture precursor leads to the formation of well-dispersed ceria particles with particle size in the range of 4 ～6 nm and a drastic increase in the surface area. The presence of KCl results in an over ten-fold increment in specific surface area from 14.10 m^2·g^-1 for the produced ceria powders via the conventional combustion synthesis process to 156.74 m^2·g^-1 for the product by the salt-assisted combustion synthesis process at the same molar ratio of ethylene glycol-nitrate.

Characterization of YSZ Ceramic Nanopowders Synthesized at Different Temperatures via Polyacrylamide Gel Method

Tetragonal zirconia (T-ZrO2) ceramic nanopowders stabilized with 3 mol% Y2O3 were synthesized via polyacrylamide gel method, using ZrOCl2?8H2O and Y(NO3)3?6H2O as raw materials. The effect of temperature on phase composition and morphology of YSZ nanopowders and sintering behavior of YSZ ceramics was investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM) and Vickers hardness tester. The aging-resistance of YSZ ceramics was measured by means of aging experiments. The results demonstrated that the phase composition of YSZ ceramic nanopowders had no obvious change and it was composed of T-ZrO2. Particle size of well-dispersed YSZ ceramic nanopowders increased from 17 to 35 nm with increasing calcining temperature from 600 to 800 ℃. There was noticeable negative correlation between calcining temperature and the relative density of YSZ ceramic at the same sintering temperature. The aging experiments showed that water vapor facilitated tetragonal to monoclinic phase transformation, and the sample that had smaller grain size exhibited better aging-resistance. It can be concluded that when the calcining temperature is 600 ℃ and sintering temperature is 1550 ℃, the relative density and hardness of YSZ ceramic arrive at the peak of 96.64% and 11.135 GPa respectively, and it has less microcracks and excellent aging-resistance.

Annealing effect on structure and green emission of ZnO nanopowder by decomposing precursors

ZnO nanopowder is successfully synthesized by annealing the precursors in oxygen gas using the chemical precipitation method. Structural and optical properties of thus synthesized ZnO nanopowder are characterized by scanning electron microscopy （SEM） and photoluminescence （PL）. The morphology of ZnO nanopowders evolves from nanorod to cobble as annealing temperature increases from 500 to 1000℃, while spiral structures are observed in the samples annealed at 900 and 1000℃. The PL spectra of ZnO nanopowder consist of largely green and yellow emission bands. The green emission from ZnO nanopowder depends strongly on the annealing temperature with a peak intensity at a temperature lower than 800℃ while the yellow emission is associated with interstitial oxygen Oi.

Synthesis of Vanadium Carbide Nanopowders via Mechanical Alloying and Microwave Heating Methods

A simple and fast method of preparation of vanadium carbide(V_8 C_7) nanopowders using mechanical alloying assisted microwave heating method was demonstrated. The micron-sized V_2O_5 and nano-sized carbon black were used as starting materials. The as-prepared powders were characterized by X-ray diffraction(XRD), scanning electron microscopy(SEM), thermogravimetric and differential scanning calorimetry(TG-DSC), transmission electron microscopy(TEM), and X-ray photoelectron spectroscopy(XPS) techniques. The experimental results show that the V_8C_7 powders can be obtained by microwave heating at 1 100 ℃ for 1 h(34 wt% C). The synthesized powders show good dispersion and are mainly composed of spherical or near-spherical particles with a mean diameter of about 30 nm. The XPS spectra show that the surface of the specimen mainly consists of V, C, and O three species elements.

The graphene nanopowder for electro-catalytic oxidation of dopamine and uric acid in the presence of ascorbic acid

The graphene nanopowder for electro-catalytic oxidation of dopamine and uric acid in the presence of ascorbic acid has been investigated by cyclic voltammetry,linear polarization and chronoamperometry.The graphene nanopowder modified electrode was prepared using the drop coating method,which displayed excellent electrocatalytic activity towards the oxidation of dopamine and uric acid compared with the bare glassy carbon electrode in phosphate buffer solution at pH=7.0.Linear responses for dopamine and uric acid were obtained in the ranges of3.3μmol/L to 249.1μmol/L and 6.7μmol/L to 386.3μmol/L with detection limits of 1.5μmol/L and 2.7μmol/L(S/N=3),respectively.The response time was less than 2 s in case of dopamine and 3 s in case of uric acid,respectively.The results demonstrated that the graphene nanopowder had potential for detecting dopamine and uric acid.

Experimental study on the characteristics of DBD plasma coal liquefaction by using coal nanopowder

A new method for liquefying coal using dielectric barrier discharge plasma has been studied.By utilizing waste oil as the solvent and processing coal nano powder in the plasma for 10 min,we have attained a liquid yield of more than 80%.The experiment shows that not only the coal nanopowder promoted the liquefaction process,but hydrogen radicals improved the liquid yield effectively.In the plasma processing,the phenomenon of the changing color of the nanopowder solution and not producing a solid residue has been obviously observed.The rational parameters that affected the liquefaction of coal nanopowder have been achieved through the experiment,and the liquefied products have been analyzed.

Synthesis of ZnO：Dy Nanopowder and Photoluminescence of Dy^3＋ in ZnO

A type of dysprosium-doped ZnO （ZnO：Dy） nanopowder was synthesized by high temperature calcinations. XRD was used to analyze the structure. Photoluminescence spectra were used to study the optical characteristic. PL of ZnO：Dy shows two different spectra which are broad band resulted from the defect of Dy in ZnO and sharp lines from the 4f→4f transition of isolated Dy^3 ＋ luminescence center. The emission and excitation spectra depend on the excitation wavelength and the concentration of Dy^3＋ . The broad bands with peaks at 600 and 760 nm are attributed to the recombination from an electron of the defect Dy in ZnO to a hole in VB.

Synthesis and Spectral Properties of Nd^(3+)∶Gd_3Ga_5O_(12) Nanopowder for Transparent Laser Ceramics

Nd^3＋： Gd3Ga5O12（Nd ： GGG） nanopowder for transparent laser ceramics was synthesized using sol-gel method. XRD, SEM, and fluorescence spectrum were used to study the properties of Nd^3＋ ：Gd3Ga5O12 nanopowder. XRD patterns of samples show that it has a cubic structure. Meanwhile, pure Nd：GGG crystals were obtained at 1000 ℃ for 12 h. SEM photographs show that dispersed, uniform, ball-like Nd：GGG nanopowder is obtained. Both XRD and SEM results show that the crystallization degree and the grain size increase with the increase in calcining temperature. Analysis of fluorescence spectrum shows that fluorescence emission occurs at 1062.7 nm, which is the result of Nd^3＋ （^4F3/2→^4I11/2） transition. Homogenous Nd ： GGG nanopewder with a small grain size synthesized using the sol-gel method is favorable for sintering the transparent ceramic, which proves that the nanopewder obtained is suitable as a precursor for preparing GGG transparent ceramics.

Exploring the Microstructure of YBCO Nanopowders

High temperature superconductor YBa2Cu3O7–x (YBCO) nanopowders were successfully prepared by a citrate pyrolysis technique. The phase formation and microstructure of the nanopowders were studied. The microstructure analysis shows that the obtained YBCO powders have very fine grains with a size around several tens of nanometers. The superfine morphology reveals that the thermal agglomeration of the particles decreases with decreasing the annealing temperature and shortening the annealing time. In addition, the complete phase formation of YBCO depends upon the annealing temperature and the annealing time as well. So far, these nanopowders have been used to fabricate the melt-textured YBCO bulk materials.

Preparation of Y_2O_3 Nanopowders by Sol-Gel Method

Using the inexpensive inorganic salts as the starting materials,pure yttria nanopowders were prepared by sol-gel method. The primary particles are spherical and about 60 nm in diameter with a narrow size distribution. Moderate sulfate ions used as additive were the key to the formation of precursor and the preparation of spherical Y_2O_3 nanopowders. Transformation of the precursor was investigated during the calcining. The influence of calcination temperature on size and purity of production was analyzed. The results show that higher temperature is beneficial to the preparation of pure and complete crystallization of yttria powders under the condition of not making particles excessively grow.