Synthesis and Characterization of Sm_xGd_yCe_(1-x-y)O_(2-δ) Nanopowders

SmxGdyCe1-x-yO2-δ (x+y=0.2 and x=0, 0.04, 0.08, 0.12, 0.16, 0.2) nanopowders were prepared by a copre-cipitation method. The zeta potential and sedimentation volume of Ce(OH)4 aqueous dispersions at different pH values were measured. The isoelectric point (IEP) of Ce(OH)4 suspensions is 7.0. The maximum potential value of -18.5 mV and maximum sedimentation volume of 19 ml are reached at pH=10. The evolution behaviors of the xSm(OH)3·yGd(OH)3·(1-x-y)Ce(OH)4 dried powders in the heating process was characterized by DTA/TG and XRO. The powders decompose to ceria based solid solution at a temperature below 300℃ and forms cubic fluorite structure ceria at about 650℃. The properties of SmxGdyCe1-x-yO2-δ solid solutions were characterized by XRD, TEM and BET. The lattice parameter of doped Ce02 increases linearly with increasing Sm3+ substitution (or decreasing Gd3+ substitution). The particle size of the doped ceria powders is from 5 nm to 10 nm.     

Effect of mechanical activation of coprecipitated precursor on synthesis of La2Zr2O7

A lanthanum zirconate (La₂Zr₂O₇, LZ) precursor has been prepared by coprecipitation of the relevant hydroxides from nitrate solution. The effect of the mechanical activation of the precursor on its thermal decomposition and LZ formation in the temperature range of 700–1100 °C has been investigated. After mechanical activation, the precursor releases volatile components (H₂O and CO₂) at lower temperatures. Mechanical activation accelerates the LZ crystallisation and results in the formation of phase-pure LZ without admixtures of unreacted zirconia and lanthana. The LZ powder prepared from the mechanically activated precursor is characterised by a larger BET surface area, in comparison to that synthesised from the as-prepared precursor under the same calcination conditions.     

Photocatalytic performance of β-Ga2O3 microcubes towards efficient degradation of malachite green

In this work, the photocatalytic degradation of malachite green (MG) solutions by β-Ga₂O₃ was investigated. The latter was synthetized by reacting gallium nitrate with concentrated formic acid, which produced gallium formate. The thermal decomposition of this compound at 850 °C produced single-phase β-Ga₂O₃. The resulting morphology corresponds to non-agglomerated microcubes, with a size in the range of 0.8 and 2.3 μm. The surface chemical composition and bandgap energy of this oxide were determined by X-ray photoelectron spectroscopy (XPS) and the Tauc method, respectively. The photodegradation of MG was carried out under violet light (λ = 405 nm), at room temperature, using the as-prepared powder. The results revealed a fast degradation of the dye during the first 20 min, which attenuates over time. The rate of photodegradation depends on the amount of β-Ga₂O₃ used and can be fitted by an exponential equation. The role of free hydroxyl radicals and reactive oxygen species in photocatalysis was addressed by using analytic techniques (FTIR and XPS).     

New synthesis route for lead zirconate titanate powder

Phase pure lead zirconate titanate (PZT) powder was produced via a new aqueous coprecipitation method. A suite of characterization techniques, including FTIR, Raman, X-ray diffraction, SEM as well as nitrogen sorption were employed to investigate the structural evolution of the synthesized and calcined powder. The dried precipitate formed in aqueous phase yielded approximately 80 wt% final product after calcination. The PZT perovskite structure was obtained after calcination at 550 °C for 3 h. Milling of the calcined powder reduced the mean particle size from approximately 10 µm to 2 µm. With increasing calcination temperature from 550 °C to 700 °C, both surface area and pore volume decreased while pore size increased from 3.4 nm to 9.8 nm. The bulk density of pelletized samples increased from 4.83 to 7.57 g/cm³ with increasing sintering temperature from 800 °C to 1200 °C. Powder processing using this aqueous route is simple and reproducible leading to a method that is readily scalable for industrial applications.     

Sn 和Cu掺杂对Zn0.98Fe0.02O块材样品磁性的影响

采用共沉淀法在600oC制备了Sn 和Cu掺杂的Zn0.98Fe0.02O多晶块材样品。X射线衍射分析结果显示：所有的样品均为单相,具有ZnO纤锌矿结构。M-T曲线显示Sn掺杂严重削弱了系统铁磁性,而Cu掺杂则增强了系统铁磁性。这个结果与磁极化子模型一致,额外的Sn掺杂降低了系统中的空穴浓度,冻结了样品中的铁磁耦合作用。     

Preparation of ZrO2/Gd2O3 composite ceramic materials by coprecipitation method

High burnup is a goal for further development of advanced nuclear power in the future. However, along with the increase of burnup, it becomes more diffidult to control reactor reactivity, which affects the operation safety of the nuclear reactor. Al₂O₃/B₄C burnable poison materials widely used in pressurized water reactor currently will not meet the requirements of burnable poison materials in high burnup nuclear power. Because of the better performance of ZrO₂/Gd₂O₃ burnable poison materials than that of Al₂O₃/B₄C, this paper studies the preparation of ZrO₂/Gd₂O₃ composite ceramic materials by the coprecipitation method. The experimental results show that at the sintering temperature of 1500–1650 °C, ZrO₂/Gd₂O₃ composite ceramic grains are small, compact and uniform with the generation of homogeneous solid solution. At 1600 °C, ZrO₂–10%Gd₂O₃ has the highest density and mechanical strength.     

Method for the prediction of nuclear waste solution decontamination by coprecipitation of strontium ions with barium sulphate using the experimental data obtained in non-radioactive environment

The theoretical and experimental prediction of the decontamination factor during the treatment of nuclear waste solutions is generally a cumbersome problem due to their complex composition and extremely dangerous environment. Here, a methodology is proposed and experimentally validated allowing the prediction of the decontamination factor by carrying out experiments in small pilot installations in non-radioactive environment. These experiments provide the population density and the crystal growth data of the coprecipitating agent which serve for calculations according to the general relation presented in this paper.     

Coprecipitation of Cefuroxime Axetil-PVP composite microparticles by batch supercritical antisolvent process

Batch supercritical antisolvent precipitation (SAS) process was used to coprecipitate Cefuroxime Axetil amorphous (CFA, antibiotic) and Polyvinylpyrrolidone (PVP-K30) for preparing drug-polymer composite particles. Solutions of CFA and PVP-K30 in methanol with overall concentrations of 50-150 mg/ml and polymer/drug ratios of 1/1-4/1 were sprayed into the CO₂ at 70-200 bar and 35-50 °C with drug + polymer solution injection rates of 0.85 and 2.5 ml/min. Spherical particles having mean diameters of 1.88-3.97 μm, distribution ranges of 0.82-9.7 μm (the narrowest distribution) and 0.91-46.64 μm (the broadest distribution) were obtained. Mean particle size was not affected significantly with the change of process parameters. It was only affected by pressure change. On the other hand particle size distribution was affected by pressure, temperature, drug + polymer solution injection rate and concentration. It was observed that temperature and polymer/drug ratio affected the particle morphology most. The drug release rate of SAS-coprecipitated CFA-PVP (1/1) particles was almost 10 times slower than the drug alone. As the ratio of the polymer increased drug release rate also increased due to the wetting effect of PVP.     

Study on removing Mo from tungstate solution using coprecipitation adsorption method based on novel Mo sulphidation process

Abstract

A coprecipitation–adsorption method based on a novel Mo sulphidation process is proposed for deep removal of molybdenum from tungstate solutions. First, a new sulphur source, P₂S₅, is used to provide HS^? for the Mo sulphidation process. The MoO₄^2? can be thoroughly converted into MoS₄^2? while tungsten still exists as WO₄^2?. Next, in the sodium tungstate solution, 99·4% of MoS₄^2? is removed with precipitated ‘nascent’ CuS under 6 h reaction at 30°C when the molar ratio Cu/Mo is 3. Similarly, in a commercial (NH₄)₂WO₄ solution, by controlling the molar ratio Cu/Mo at 6, 98·4% of MoS₄^2? is removed after 1 h at 30°C. Subsequently, phosphorus introduced during Mo sulphidation is removed using the magnesium ammonium phosphate method allowing the ammonium paratungstate to reach the GB 10116-88 APT-0 standard.

On propose une méthode de co-précipitation et adsorption basée sur un nouveau procédé de sulfuration du Mo pour l’enlèvement en profondeur du molybdène de solutions de tungstate. Premièrement, on utilise une nouvelle source de soufre, P₂S₅, pour obtenir le HS^? pour le procédé de sulfuration du Mo. Le MoO₄^2? est entièrement converti en MoS₄^2? alors que le tungstène existe encore sous la forme de WO₄^2?. Ensuite, 99·4% du MoS₄^2? est enlevé de la solution de tungstate de sodium avec le CuS ‘naissant’ précipité, en moins de 6 heures de réaction à 30°C lorsque le rapport molaire de Cu/Mo est de 3. De façon similaire, 98·4% du MoS₄^2? est enlevé d’une solution commerciale de (NH₄)₂WO₄, après une heure à 30°C, en contrôlant à une valeur de 6 le rapport molaire de Cu/Mo. Subséquemment, le phosphore introduit lors de la sulfuration du Mo est enlevé en utilisant la méthode du phosphate ammoniaco-magnésien, permettant ainsi au paratungstate d’ammonium d’atteindre la norme GB de 10116-88 APT-0.