Synthesis of Ce:YAG Phosphor via Homogeneous Precipitation under Microwave Irradiation

Ultra-fine Ce:YAG phosphors were prepared by homogeneous precipitation under microwave irradiation method . The formation of Ce: YAG was investigated by means of XRD and DTA/TG. The purified YAG crystallized phase was obtained at a lower temperature (1100℃). Basically spherical Ce:YAG powders were indicated from TEM images, and the size of the particles is about 80 nm. Two peaks of 436 and 473 nm can be seen from the excitation spectrum in the range of 402 -510 nm. A broad emission band located at 480 ~ 630 nm shows the phosphors prepared by this method have good emission properties.

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.

Preparation and growth mechanism of plate-like basic magnesium carbonate by template-mediated/homogeneous precipitation method

In order to expand the application of the basic magnesium carbonate in the field of flame retardant,the plate-like basic magnesium carbonate(Mg5(CO3)4(OH)2.4H2O)was prepared successfully by template-mediated/homogeneous precipitation method,using magnesium chloride hexahydrate(MgCl2.6H2O)and urea(CO(NH2)2)as reaction materials.Phase and morphology of the product were characterized by X-ray diffraction(XRD),scanning electron microscope(SEM)and atomic force microscope(AFM),respectively.The results showed that well-crystallized plate-like Mg5(CO3)4(OH)2.4H2O can be prepared at the water bath temperature of 100°C,water bath time of 24 h,the aging time of 5 h after adding organic template agent.The investigation on organic template mediated mechanism shows that the template affects the crystal morphology by changing surface energy of different crystal plane.Through a preliminary study on the growth mechanism of the product,it is found that the generation of the plate-like Mg5(CO3)4(OH)2.4H2O could be explained by two-dimensional nucleation/step growth mechanism.

TiO2 preparation by improved homogeneous precipitation and application in SCR catalyst

Ultrasonic treatment and hydrothermal method were applied in the traditional homogeneous precipitation for nano-TiO_2 preparation, which was used as carrier material for the production of honeycomb selective catalytic reduction(SCR) catalyst. The influence rules of the two improved methods on characterization of TiO_2 samples, denitration activity and mechanical strength of honeycomb SCR catalyst samples were mainly focused on. The results indicate that the specific surface area, particle size and uniformity of TiO_2 samples are significantly improved by both of the ultrasonic and hydrothermal treatments compared with the traditional homogeneous precipitation. Also, the denitration activities of catalyst samples are enhanced by the two improved methods(the NO_x reduction ratio increases from 88.89% to 95.45% by ultrasonic homogeneous precipitation process, and to 94.12% by hydrothermal homogeneous precipitation process). On the other hand, because of good spherical shape and high particle distribution of TiO_2 sample from hydrothermal homogeneous precipitation process, the corresponding honeycomb catalyst samples get the best mechanical strength, which is even higher than that of the reference sample from commercial nano-TiO_2. So, it is concluded that the hydrothermal homogeneous precipitation can be a feasible and effective preparation method of TiO_2 carrier for the honeycomb SCR catalyst production.

Synthesis and luminescence properties of nanocrystalline Gd_3Ga_5O_(12):Eu^(3+) by a homogeneous precipitation method

Nanocrystalline Gd3Ga5O12:Eu3+ with cubic phase was prepared by a urea homogeneous precipitation method. X-ray diffraction (XRD), field emission scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FT-IR), thermo-gravimetric and differential thermal analysis (TG-DTA) and photoluminescence spectra were used to characterize the samples. The effects of the initial solution pH value and urea content on the structure of the sample were studied. The XRD results show that pure phase Gd3Ga5O12 can be obtained at pH =6 and pH =8 of the initial solution. The average crystallite size can be calculated as in the range of 24~33 nm. The average crystallite size decreases with increasing molar ratio of urea to metal ion. The results of excitation spectra and emission spectra show that the emission peaks are ascribed to 5D0→7FJ transitions of Eu3+, and the magnetic dipole transition originated from 5D0 →7F1 of Eu3+ is the strongest; the broad excitation bands belong to change transfer band of Eu?O and the host absorption of Gd3Ga5O12. An efficient energy transfer occurs from Gd3+ to Eu3+.

Octacalcium Phosphate Fiber Synthesized by Homogeneous Precipitation Method

Calcium phosphate fiber was synthesized by homogeneous precipitation method using urea as precipitation agent. Effects of the reactant concentration and hydrothermal temperature on the calcium phosphate morphology and composition were studied using SEM, FTIR and XRD. It is found that fine octacalcium phosphate（OCP）fiber can be synthesized when the reactant concentrations are 0.167 mol/L for Ca（NO3）2, 0.1 mol/L for （NH4）2HPO4, and 0.6-0.7 mol/L for （NH2）2CO, respectively, with the initial reactant solution pH value around 2.2, hydrothermal temperature 90 ℃ and termination reaction at pH value around 5.0. At very low urea concentration, the product size distribution is highly inhomogeneous, however, at an excessively high concentration the product becomes larger and shorter and a mixture of OCP and hydroxyapatite （HA）. Increasing the hydrothermal temperature is favorable to the fast precipitation of OCP, higher productivity and finer product.

Synthesis of Polycrystalline Yb:Gd_3Ga_5O_(12) Nanopowders by Homogeneous Precipitation Method

The Ytterbium doped gadolinium gallium garnet [Yb3＋：Gd3Ga5O12, Yb：GGG] precursor powders were synthesized via homogeneous precipitation method using Yb2O3, Ga2O3, Gd2O3 and ammonium bicarbonate [NH4HCO3] as precipitator, and ammonium sulfate [（NH4）2SO4] as additive. The evolution of phase composition and micro-structure of the powders were characterized by TG- DTA, XRD, IR, and TEM. The results indicate that all precursor powders completely transform to Yb：GGG phase by calcining at 900 ℃ for 8 h, the resultant powders are well dispersed and have smaller particle size approximately 80 nm owing to the electrostatic effect.

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.

Controlled Synthesis of Dental Enamel-like Hydroxyapatite Whiskers via Hydrothermal Homogeneous Precipitation

Dental enamel-like hydroxyapatite whiskers with high crystallinity and homogeneous morphology were synthesized by a hydrothermal homogeneous precipitation method.The composition,crystallinity and morphology of prepared hydroxyapatite whiskers were characterized by Ⅹ-ray diffraction and scanning electron microscopy.The effects of urea and sorbitol on their morphology and composition were investigated.Homogeneous and well crystallized enamel-like hydroxyapatite whiskers with 1.17±0.08 μm in length and 84± 14 nm in width were obtained at 0.80 mol · L-1 urea and 0.26 mol · L-1 sorbitol.These hydroxyapatite whiskers may be close to nature hydroxyapatite dental enamel in terms of the morphology and composition,suggesting that they could have potential application as dental restorative materials in the field of stomatology.

studies on the Mechanism of Producing Tungstic Acid by Complex-Homogeneous Precipitation Method

A new method of producing tungstic acid with a yield over 98% at room temperature and low acidity is advanced and referred to as Complcx -Homogeneous Precipitation Method. If combined with the treatment of activated charcoal in recovering the remnant tungsten left in the filter liquor, a perfect closed technological process can be obtained. The key to this method is to prevent the formation of pseudo-metatungstatc during scdium rungstate being acidified directly with the aid of the complexing-protecting agent H2O2, The perexo-mtermediate, which was prepated and identified as dipcroxytetratnngstate by IR and Raman analysis by comparison with diperorytetramolybdate, can be decomposed by SO2 tapidly and quantitatively. The tungstic acid precipitate can be filtered and washed easily. The related mechanisin is studied.

PREPARATION OF La_2O_3 ULTRAFINE PARTICLE BY HOMOGENEOUS PRECIPITATION

Y_2O_3 ultrafine particles have been prepared by means of precipitation in Japan and U.S.A., and ultrafine particles of rare earth oxide have been prepared with dicarboxyl precipitate by Wang Zenglin et al. It has not been reported, however, to prepare La_2O_3 ultrafine particles with urea as the hydrolytic agent. This method is easy to operate, and the materials are cheap and easily available, besides, it is easy to obtain homogeneous spherical precursors of ultrafine particles. The present, paper describes the preparation of La_2O_3 ultrafine particles with urea as hydrolytic agent, and observes some of its characteristics.

Effect of Sulfate Ions on YAG Powders Synthesized by Microwave Homogeneous Precipitation

Using A1(NO3)3·9H2O, NH4Al(SO4)2·12H2O, Y(NO3)3as mother salts, and urea as precipitant, YAG nano-powders were synthesized by microwave homogeneous precipitation. The composition, morphology, and phase transformation of precursor were analyzed by IR, XRD and TEM. The size distribution of YAG powders was characterized using laser diffraction method. The results show that sulfate ions influence the dispersion, composition and morphology of the YAG precursors. The addition of moderate sulfate ions can produce YAG powders with nano size and excellent dispersion at 1100℃.

Synthesis of SmOHCO_3 micro/nano particles from the coupling route of homogeneous precipitation with microemulsion

SmOHCO3micro/nano particles were prepared in water/oil （W/O） reverse microemulsion composed of cetyltrimethyl ammonium bromide （CTAB）, n-octane, n-butanol, Sm（NO3）3·6H2O and urea aqueous solution by the coupling route of homogeneous precipitation with microemulsion. The nanoparticles were characterized and analyzed by X-ray powder diffraction （XRD）, thermal gravimetric and differential thermal gravimetric analysis （TG-DTG）, Fourier transform infrared absorption spectra （FT-IR） and scan-ning electron microscope （SEM）. The results showed that the phase SmOHCO3 micro/nano particles was in agreement with pure or-thorhombic phase. The different morphologies of SmOHCO3 micro/nano particles with good monodispersity and size were obtained by regulating the reaction temperature and reaction time. Possible formation mechanisms of the morphological structure of SmO-HCO3 were proposed and discussed.

Preparation of Hydroxyapatite Fibers by the Homogeneous Precipitation Method

This paper discussed the preparing process of hydroxyapatite fibers which were widely used as reinforcement for biomedical materials by homogeneous precipitation method.The needle like hydroxyapatite crystals were synthesized in an aqueous system.They were transferred from precursors dicalcium phosphate anhydrate and octacalcium phosphate crystals.The reaction conditions were well controlled in order to obtain crystals in given morphology.The products were characterized by X ray powder diffractometry(XRD),scanning electron microscopy (SEM) and infrared spectroscopy(IR).They were verified to be hydroxyapatite crystals with needle like in shape.

Homogeneous precipitation of α-phase Co-Ni hydroxides hexagonal platelets

This paper describes the synthesis of （x-phase Co-Ni hydroxides hexagonal platelets through homo- geneous precipitation, using hexamethylenetetramine （HMT） or urea as a hydrolytic agent. In the CoC12-NiC12-HMT system, pure β-phase can be synthesized at the concentrations of both metal ions higher than 20 raM, while in the CoCl2-NiCl2-urea system, the formation of pure α-phase is independent of the concentrations of the metal ions. When using HMT, monodisperse hexagonal platelets of α-phase Co-Ni hydroxides can be produced in the presence of polyvinylpyrrolidone （PVP）. Cyclic voltammogram curve of the hexagonal platelets prepared with HMT demonstrates electrochemical performance superior to that of urea.

Efficient Removal of Phosphate from Aqueous Solutions Using Corundum-hollow-spheres Supported Caclined Hydrotalcite Porous Thin Films

Phosphate was removed from aqueous environment by corundum-hollow-spheres supported caclined hydrotalcite (cHT) thin films. Mg-Al-CO3 hydrotalcite (HT) thin films were deposited on corundumhollow-sphere substrates by hydrothermal homogeneous precipitation at 120℃for 30-240 min and cHT thin films were obtained by annealing of the HT thin films at 500℃for 180 min. Their crystal phase, morphology and microstructure were characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM).The results show that homogeneous, well-crystallized and hierarchical flower-like thin films were deposited firmly on the surface of the corundum. The mechanism of nucleation and growth of the HT thin films was fitted well with the anion coordination polyhedron growth unit model. To determine the absorption of phosphate by this adsorbent, different bed depth (10-30 cm) and flow rate (1.0-3.0 m L/min) were examined by column experiments. The highest removal efficiency of phosphate amounted to 98.5%under optimum condition (pH=7.2). The adsorption capacity increased as the bed depth increased and decreased as the flow rate increased.

Effects of Temperature on the Preparation of Magnesium Carbonate Hydrates by Reaction of MgCI2 with Na2CO3

Homogeneous(unseeded)precipitation of magnesium carbonate hydrates by the reaction of MgCl2 with Na2CO3 in supersaturated solutions between 273 and 363K was investigated.The compositions,morphologies and filtration characteristics of the precipitates were studied in detail.The magnesium carbonate hydrates obtained at 313K and in the range of 343-363K showed good morphologies and filtration characteristics.Magnesium oxides(MgO)with high purity(97.6%-99.4%)were obtained by calcining magnesium carbonate hydrates at 1073K.

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.

Morphology Controlling of the Ultrafine Cerium Dioxide (CeO_2) Precursor

The synthesis of ultrafine cerium dioxide precursor via homogeneous precipitation was studied. Mixed aqueous solution of anhydrous cerium nitrate and urea was first heated to 85℃ for 2 h, and the prepared suspension was then aged at room temperature for various periods of time. White precipitate was finally collected by centrifuging and washed with distilled water and anhydrous ethanol. The obtained cerium dioxide (CeO2) precursor was observed with SEM. It was found that the morphology and size of the precursor were strongly affected by aging time and stirring conditions (with or without stirring). The precipitated fine spherical particles of the precursor changed their shape from ellipse to slice or directly to slice. Fine spherical monodispersed (300 nm) precursor powders could be obtained by controlling the aging time. Stirring the solution also could change the reaction process and thus the morphology and size of the precursor were changed.

Effect of anions on preparation of ultrafine α-Al_2O_3 powder

Ultrafine alumina power was obtained by calcining the precursor at 1 200 ℃ for 2 h, which was prepared by homogeneous precipitation method using aluminium salts and urea as raw materials. The effects of anions on the morphology, particle size, surface area and configuration of the precursors were studied. The results show that the reactions of urea with aluminium nitrate and aluminium chloride result in agglomerates gels with bad filtering performance, the morphology is fibrillar. Aluminium sulphate-urea reactions result in the direct formation of amorphous powders with good filtering performance, of which morphology are regular spherical particles with larger granularity and smaller surface area. The reaction of mutual compound of aluminium sulphate and aluminium nitrate with molar ratio of 40:60 with urea can produce precursor with good filtering performance, spherical morphology, and uniform granularity distribution in the particle size range of 2-3 μm.