Preparation and Characterization of Nanocrystalline CeO_2 by Precipitation Method

CeO 2 nanocrystalline particulates with different sizes were prepared by precipitation method using ethanol as dispersive and protective reagent. XRD spectra show that the synthesized CeO 2 has cubic crystalline structure of space group O 5 H-F M3M, when calcination temperature is in the range of 250～800 ℃. TEM images reveal that CeO 2 particles are spherical in shape. The average size of the particles increases with the increase of calcination temperature. Thermogravimetric analysis indicates that the weight loss of precursor mainly depends on the calcination temperature, and little depends on the calcination time. Measurements of CeO 2 relative density show that the relative density of CeO 2 nanocrystalline powders increases with increasing CeO 2 particle size.

Preparation of Rare Earth Hydroxide and Oxide Nanoparticles by Precipitation Method

A series of rare earth hydroxide and oxide nanoparticles have been prepared by precipitation method with alcohol as the dispersive and protective reagent. Transmission electron microscope （TEM） images indicate that the particles are spherical in shape and smaller than 100 nm in size. The crystallite sizes of cubic Ln2O3 have lanthanide shrinking effect, while average crystal lattice distortion rates possess lanthanide swelling effect. The diffraction peak intensity of heavy rare earth oxide nanometer powders is remarkably stronger than that of light rare earth oxide nanometer powders. The variation of diffraction intensity with atomic number presents an inverted W type, forming a double peak structure. Fourier transform infrared （FTIR） spectrums reveal that Ln2O3 nanopowders have higher surface activity than that of ordinary Ln2O3 powders. The UV-vis spectra show that Ln-O bond of these particles is slightly blue-shifted, and its absorption intensity decreases.

Upconversion luminescence of Y_2O_3:Er^(3+), Yb^(3+) nanoparticles prepared by a homogeneous precipitation method

Y2O3： Er^3＋, Yb^3＋ nanoparticles were synthesized by a homogeneous precipitation method without and with different concentrations of EDTA 2Na. Upconversion luminescence spectra of the samples were studied under 980 nm laser excitation. The results of XRD showed that the obtained Y2O3：Er^3＋,Yb^3＋ nanoparticles were of a cubic structure. The average crystallite sizes calculated were in the range of 28-40 nm. Green and red upconversion emission were observed, and attributed to ^2H11/2,^4S3/2→^4I15/2 and ^4F9/2→^4I15/2 transitions of the ion, respectively. The ratio of the intensity of green emission to that of red emission drastically changed with a change in the EDTA 2Na concentration. In the sample synthesized without EDTA, the relative intensity of the green emission was weaker than that of the red emission. The relative intensities of green emission increased with the increased amount of EDTA 2Na used. The possible upconversion luminescence mechanisms were discussed.

Synthesis and Characterization of Y-Doped Mesoporous CeO_2 Using A Chemical Precipitation Method

Using cetyltrimethylammonium bromide （CTAB） as the template agent, cerium nitrate as the cerium resource, yttrium nitrate as the yttrium resource, and ammonium carbonate as the precipitating agent, mesoporous CeO2 powders doped with different yttrium contents were successfully synthesized using a chemical precipitation method, under an alkalescent condition. Properties of the obtained samples were characterized and analyzed with X-ray diffraction （XRD）, energy dispersive analysis of X-rays （EDAX）, transmission electron microscopy （TEM）, infrared （IR） absorbance, and the BET method. For the prepared samples with 20% （molar ratio） Y-doped content, a BET specific surface area of 106. 6 m^2 · g^- 1, with an average pore size of3~27 nm were obtained. XRD patterns showed that the doped samples were with a cubic fluorite structure. TEM micrographs revealed that the doped samples showed a spherical morphology with a diameter ranging from 20 to 30 nm and a round pore shape. IR results indicated that the Ce-O-Ce vibration intensity decreased as the Y-doped content increased. N2 adsorption-desorption isotherms showed that the samples possessed typical mesopore characteristics. The average pore size of the samples decreased alter mesoporous CeO2 was doped with yttrium, and the average pore size decreased largely as the Y-doped content increased.

Synthesis and Characterization of Large Surface Area Yttrium Oxide by Precipitation Method

The method for preparing yttrium oxide with large specific surface area was introduced. By means of BET, SEM, TG and DTA analysis, the effects of precipitant, stirring velocity, non-RE impurity in solution, calcination temperature, on the surface area were studied respectively. The Y_2O_3 sample with specific surface area of more than 60 m^2·g^(-1) and L.O.I less than 1% was prepared in the suitable precipitation condition and calcinations temperature when the ammonia used as precipitant. The SEM shows that the Y_2O_3 prepared with large surface area is the aggregation of about 50 nm particles.

Influence of polymer solution on the morphology and local structure of NH_(4)ZnPO_(4)powders synthesized by a simple precipitation method at room temperature

NH_(4)Zn PO_(4)powders were synthesized using a simple precipitation method at room temperature.The effects of polyvinyl pyrrolidone(PVP),polyvinyl alcohol(PVA),glucose,and hexadecyltrimethylammonium bromide(CTAB)solutions on the morphology and structure of the prepared samples were investigated.The phase composition and morphology of the prepared samples were characterized using X-ray diffraction and scanning electron microscopy,respectively.Depending on the polymer sources,the hexagonal structure prepared using non-surfactant of water completely changed to monoclinic structure when CTAB was added.X-ray absorption near-edge structure(XANES)and X-ray photoelectron spectroscopy(XPS)were performed to study the local structure and surface electronic structure of the prepared samples,confirming that the oxidation states of P and Zn ions are^(5+)and^(2+),respectively.On the basis of the results of inductively coupled plasma atomic emission spectroscopy(ICP-OES),the NH_(4)Zn PO_(4)powders can be classified as a slow-release fertilizer where less than 15%of the ions were released in 24 h.A simple precipitation method using water,PVP,PVA,sucrose,and CTAB as a template can be used to synthesize NH4 Zn PO4 powders.In addition,this method may be extended for the preparation of other oxide materials.

Preparation of Nanocrystalline ZrO_2 by Reverse Precipitation Method

Nanncrystalline ZrO2 particulates with different sizes were prepared by precipitation method using ethanol as dispersive and protective reagent. XRD patterns show that the synthesized ZrO2 is monnclinic in structure with space group P21/a when calcination temperature is in the range of 400- 1000 ℃ . It is found that the smaller the particle, the bigger the crystal lattice distortion, the worse the costal growth, and the lower the diffrnction intensity. TEM images reveal that ZrO2 particles are spherical in shape, and the particle size distribution is in narrow range. The mean sizes of the particles increase with the increase of calcination temperatures . It is first to observe tbe streaks of different crystallographic planes. Thermogravimetric analysis indicates that the crystallization temperature of ZrO2 is 461.32 ℃ . Measurement of ZrO2 relative density shows that the relative density of nanocrystalline ZrO2 powders increases witb the increasing of ZrO2 particle sizes.

Grain Growth Kinetics of SnO_2 Nanocrystals Synthesized by Precipitation Method

Monodispersed spheroidal SnO2 nanocrystals with the grain size of 8-30 nm were synthesized by the precipitation method using SnCl4·5H2O （stannic chloride hydrate） as raw materials.Differential scanning calorimetry/thermogravimetry （DSC/TG）,X-ray diffraction （XRD） and transmission electron microscope （TEM） were used to characterize the structure of SnO2 nanocrystals.The influences of the calcination temperature and time on the lattice constant,the lattice distortion and the grain size of SnO2 nanocrystals were discussed based on the XRD results.The grain growth kinetics of SnO2 nanocrystals during calcination process was simulated with a conventional grain growth model which only took into account of diffusion and with a new isothermal model proposed by our group,which took into account of both diffusion and surface reactions.Using conventional model,the grain growth rate constant of SnO2 crystals is 1.55×104nm5/min with a pre-exponential factor of 5 and an activation energy of 108.62 kJ/mol.Compared with the convention model,the new isothermal model is more realistic in reflecting the grain growth behavior of SnO2 nanocrystals during the calcination process.This indicates that the grain growth of SnO2 nanocrystals is controlled by both diffusion and reaction factors,and the effect of surface reactivity on the grain growth of SnO2 nanocrystals could not be ignored.A combined activation energy estimated with the new isothermal model is 53.46 kJ/mol.

Preparation and Characteristics of Hydroxyapatite Whiskers by Homogeneous Precipitation Method

Hydroxyapatite whilkers were prepared by the homogeneousprecipitation method. Soluble calci- um ion and phosphate ion wereused as initial materials, they were refluxed respectively at 85 deg.C, 90 deg. C and 95 deg. C for various lengths of time. A properprecipitation agent was selected to control the releasing speed ofions in the system; it induced the hydroxyapatite crystal to grow indesired way. The pH each solutions were mea- sured continuouslyduring the reaction.

Photocatalysis of Cd-doped ZnO synthesized with precipitation method

ZnO particles doped with 0 mol%-5 mol% Cd dopant were successfully synthesized by a precipitation method.The as-synthesized products were characterized by thermogravimetric analysis(TGA),differential scanning calorimetry(DSC),X-ray diffraction(XRD),photoluminescence(PL) spectroscopy,Raman spectroscopy,scanning electron microscopy(SEM) coupled with an energydispersive X-ray(EDX) spectroscopy and transmission electron microscopy(TEM).The precursors showed weight loss at 35-700℃ caused by phase transformation and evaporation processes.The as-synthesized products were specified as hexagonal wurtzite ZnO.The crystallite size of ZnO samples doped with 0 mol%-5 mol% Cd gradually increased with the increase in Cd content.The photocatalytic activities of 0 mol%-5 mol% Cd-doped ZnO samples were evaluated through photodecolorization of methylene blue(MB) under ultraviolet(UV) radiation.In this research,ZnO doped with 3 mol% Cd shows the best photocatalytic activity in degrading of MB molecules as much as 89% within 240 min.

Effect of Ni Precipitation Method on CO Methanation over Ni/TiO2 Catalysts

A Ni/TiO2（TBT） catalyst was prepared through in situ precipitation, using tetrabutyl titanate（TBT） as the TiO2 precursor, and was studied in CO methanation. A Ni catalyst supported on conunercial TiO2 was also prepared through post precipitation and studied to compare the influence of Ni precipitation conditions on the catalyst＇s performance. To gain insight on their structure and physicochemical properties, the catalysts were characterized with N2-adsorption, X-ray diffraction, transimission electron microscopy, H2 temperature programmed reduction and temperatttre programmed desorption. The results showed that the in situ precipitation method was beneficial to the dispersion of Ni and the formation of more active sites on the Ni/TiO2 catalyst. In addition, the density of the metal- support boundary and its interaction with the active component were also increased. These characteristics of Ni/TiO2（TBT） led to a lower light-off temperature and a suppression of Ni sintering during CO methanation. As a consequence, the Ni/TiO2（TBT） exhibited better catalytic behavior, with a CO conversion of 99.4% and CH4 selectivity of 90.4% tinder the following conditions： p=1 MPa, t=320℃, n（H2）/n（CO）=3, gas hour space velocity （GHSV）=2×10^4 mL·g^-1·h^-1. The life test results of the two catalysts showed that Ni/TiO2（TBT） was more stable and the catalytic activity remained at its initial level after being used for 30 h.

Studies of Process and Mechanism for Preparing Nano-Sized CeO_2 Powders via Homogeneous Precipitation in Alcohol-Water Solvent

Nano-sized CeO_2 powders were synthesized by homogeneous precipitation method in alcohol-water solution with HMT as precipitator and the nano-particles were characterized by TEM and BET. The process parameters which influenced the sizes and agglomeration of nanometer CeO_2 powders were studied and the influence mechanism was discussed. The results show that the average size of the particles prepared by the above method with the best process parameters is about 8 nm, and the particles are of smaller size and better dispersion than those obtained from the ordinary powders synthesized by homogeneous precipitation in water solution.

Application of the Attenuation Correction Technology in C-band Radar Precipitation Estimation

[ Objective] The research aimed to study application of the attenuation correction technology in C-band radar precipitation estimation. [ Method~ Based on CINRAD-CB radar data in Shaanxi, we conducted the attenuation correction experiment by using iteration method and Kufa method respectively. Moreover, we conducted application expedment of the Kufa attenuation correction method in the quantitative precipitation esti- mation. [ Result~ Attenuation correction technology could compensate for attenuation problem of the echo at the distant range. Calculation result of the iteration method finally tended to that of the Kufa method. Moreover, iteration method spent more time. Therefore, Kufa attenuation correction technology was more suitable for business operation. When strong echo was near radar, generated attenuation was more obvious, and application value of the attenuation correction was bigger. Attenuation correction technology was used for quantitative precipitation estimation, which was favor- able for improving accuracy of the precipitation estimation. But we should conduct detailed planning on calculation scheme of the precipitation esti- mation because that different calculation schemes had great influences on accuracy of the quantitative precipitation estimation. [ Cendusien] This research provided a basis for improving accuracy of the quantitative precipitation estimation in Shaanxi. Key words Attenuation correction

Comparison of methods for vibration analysis of electrostatic precipitators

The paper presents two methods for the formulation of free vibration analysis of collecting electrodes of precipitators.The first,called the hybrid finite element method, combines the finit element method used for calculations of spring deformations with the rigid finite element method used to reflect mass and geometrical features,which is called the hybrid finite element method.As a result,a model with a diagonal mass matrix is obtained.Due to a specific geometry of the electrodes,which are long plates of complicated shapes,the second method proposed is the strip method which is a semi-analytical method.The strip method allows us to formulate the equations of motion with a considerably smaller number of generalized coordinates.Results of numerical calculations obtained by both methods are compared with those obtained using commercial software like ANSYS and ABAQUS.Good compatibility of results is achieved.

Synthesis of Y_2O_3 Nano-Powder from Yttrium Oxalate under Ambient Temperature

High purity Y_2O_3 nano-powders was synthesized directly from solution ofindustrial YCl_3 by method of oxalate precipitation through super-micro-reactors made by complexnon-ionic surfactant. The purity and diameter of Y_2O_3 particles were controlled by such processingparameters as concentration of YCl_3 and oxalic acid and complex non-ionic surfactant etc. TEMphotomicrographs show that Y_2O_3 particles are spherical in shape, with an average diameter of lessthan 30 nm. Test results certify that the purity and particle diameter as well as the dispersion ofY_2O_3 nano-powder depend on the concentrations of YCl_3, oxalic acid and complex non-ionicsurfactant. The optimum ranges of the concentrations for YCl_3 and complex non-ionic surfactant whenthe diameter of Y_2O_3 particles is smaller than 100 nm are 0.43 ～1.4 mol ? L^(-1) and0.031～0.112 mol·L^(-1) respectively, while the mass fraction range of oxalic acid is 10% ～18% .The purity of Y_2O_3 nano-powder tested by ICP-AES analysis is 99.99% .

Effect of Yb^(3+) concentration on the structures and upconversion luminescence properties of Y_2O_3:Er^(3+) ultrafine phosphors

Y2O3：Er^3＋ ultrafine phosphors with a varying Yb^3＋ ion concentration were prepared by a urea homogeneous precipitation method. The results of XRD show that all the samples are of a pure cubic structure and the average crystallite sizes can be calculated as 45, 34, and 28 nm for Y2O3：Er^3＋ ultrafine phosphors with Yb^3＋ ion concentrations of 0, 10%, and 20%, respectively. The lattice constant and cell volume of the ultrafine phosphors decrease with enhancing Yb^3＋ ion concentration. The upconversion luminescence spectra of all the samples were studied under 980 nm laser excitation. The strong green and red upconversion emission were observed, and attributed to the ^2H11/2→^4I15/2, ^4S3/2 → ^4I15/2 and ^4F9/2 →^4I15/2 transitions of Er^3＋, respectively. The intensity of red emission increases with increasing Yb^3＋ ion concentration. The effect of Yb^3＋ ion concentration on the structures and upconversion luminescence mechanism were discussed.

Preparation and Characterization of CeO_2 Superfine Powder

The CeO_2 superfine powder was prepared by the co-precipitation method, using the industrial grade Ce_2(CO_3)_3 and NH_4HCO_3 as starting material and precipitating reagent, respectively. The precipitated precursons and the calcinated products were characterized by the thermogravimetric analysis/thermoanalysis (TGA/DTA), X-ray diffraction analysis (XRD) and transmission electron microscopy (TEM). The results show that using NH_4HCO_3 as a precipitating reagent, the precipitate decomposed full as it was heated to 360 ℃. The CeO_2 superfine powder formed by calcinating the precipitate belongs to a cubic CaF_2-type structure and has the first mean particle diameter 140 nm and second mean particle diameter 630 nm. The CeO_2 powder particles aggregate and grow with raising the calcination temperature.

Preparation and Characterization of Three-dimensional Chrysanthemun Flower-like Calcium Carbonate

Calcium carbonate with three-dimensional chrysanthemun flower-like structure was successfully prepared from calcium chloride and sodium carbonate ethanol/water mixed solution by a simple precipitation method,using trisodium citrate as crystal modifier.The experimental results show that the three-dimensional structure of chrysanthemun flower-like calcium carbonate is built up with several symmetrical micrometer multi-layer petals arranged around the multi-layer pancake-liked center,and the micrometer center and petals are assemblied by a large number of nanometer spherical particles with size 10-20 nm.It is found that the amount of trisodium citrate,the ethanol volume content has an important influence on the formation of this morphology.A possible mechanism is proposed to explain the formation of three-dimensional chrysanthemun flower-like calcium carbonate according the results.Scanning electron microscopy（SEM）,X-ray powder diffraction（XRD）,flourier transform infrared spectroscopy（FT-IR）,thermogravimety analysis（TG）,transmission electron microscopy（TEM） equipped with energy-dispersive X-ray（EDX）,and selected area electron diffraction（SAED） were used to characterize the crystals.

The Influence of Morphology on Photo-catalytic Activity and Optical Properties of Nanocrystalline ZnO Powder

ZnO nano-particles were synthesized via an ammonical ammonium carbonate solution by precipitation method in presence of some additives such as urea, oleic and stearic acid. The morphology and crystallinity of the obtained zinc oxide particles depend critically on the type of additive which was used. Additives also affected the crystal orientation of precipitate nano-particles. SEM, XRD, BET and UV-visible were used to characterize morphology, microstructure, specific surface area and optical properties of the products.Photo-catalysis properties of the as-prepared ZnO powders were evaluated by degradation of methyl red(acid red) in aqueous solution exposed to UV-light. Results suggested a close relationship among the morphology,size and surface area on photo-catalysis and optical properties of the particles. The widest Egvalue(3.56 e V),highest degradation and decolorization efficiency(99%) were obtained from a sample with the smallest grain size(largest surface area) which were used urea as an additive.