Papers by Keyword: Coprecipitation

Abstract: The purpose of this study is to determine the effect of the addition of 2 % SrO on physical, magnetic properties and crystal structure of BaO6Fe₂O₃. In this study, the coprecipitation method was used with raw materials BaCl₂, FeCl₃ and SrCl₃ and Ba-ferrite composition is used based on the ratio of mole BaO: Fe₂O₃ = 1: 6, while SrO is used 2% of the weight of Ba-ferrite. The raw materials are dissolved in distilled water, then added a solution (50%) of ammonia to form a perfect precipitate. The precipitate after filtering was dried in an oven at 100°C until dry, then crushed with mortar and partially taken for analysis with DTA / TG. The fine powder was calcined at 800 ° C and held for one hour using an electric furnace. The calcined samples were crushed with mortar and fine powder was added 1% wt.of PVA adhesive and formed with a pressure of 40 MPa to obtaine a pellet sample. The pellet samples were then sintered at 1150°C and hold for 1 hour. Furthermore, the sintered samples were characterized such as measurement of bulk density, magnetic properties with gauss meters and VSM and measurements with XRD. The results of characterization show that the addition of additives 2% of SrO can provide an increase in physical properties and magnetic properties (remanence). But for the crystal structure of XRD analysis there is no change, a single phase is formed, namely BaFe₁₂O₁₉.

Abstract: The functionalization of superparamagnetic iron oxide (SPIO) nanoparticles with bioactive molecules enables new applications of these nanomaterials due to their magnetic properties, which is affected by the surface coating of the nanoparticles. In this work, Fe₃O₄ nanoparticles type / core layer were synthesized by co-precipitation wet method and coated with a polymer mixture of polyethylene glycol (PEG). It was performed a study about duration in encapsulation of nanoparticles in their final size in order to get different thickness of coated layer and varied coating properties. With this study was expected to obtain different thicknesses and thus the coating properties. Five samples were synthesized according to the same procedure and amount of reactants used synthetic sequence for all samples, only varying the time spent by each sample coating process with polyethylene glycol. The different times for the coating samples were 10 minutes, 20 minutes, 30 minutes, 50 minutes and finally 60 minutes. The nanoparticles were characterized by Nanosight, TGA and DSC techniques. The results showed that the particle size suffers an increase during the first 30 minutes of duration of the coating step and then stabilizes.

Abstract: Natural sand-based magnetite nanoparticles have been succesfully synthesized by coprecipitation method at room temperature. Magnetite nanoparticles were investigated by X-ray Diffractometer (XRD) and Vibrating Sample Magnetometer (VSM). The morphology of magnetite nanoparticles has been evaluated by Transmission Electron Microscopy (TEM). Qualitative analysis of XRD data reveals that the structure of magnetite nanoparticles have the same phase of ICSD No. 82237. On the other hand, quantitative analysis shows that the crystallite size of magnetite nanoparticles have ranges between 8.89 nm to 12.49 nm. The average diameter of magnetite nanoparticles increase with the increase the stirring rate of reaction when the stirring rate is lower than 1000 rpm, while the crystallite size of magnetite particles decrease with the increase the stirring rate when the stirring rate is higher than 1000 rpm. The stirring rate of reaction influence the the magnetic properties of magnetite nanoparticles. The results of the best magnetic respon are revealed for the stirring rate of 1000 rpm with the larger the crystallite size of magnetite nanoparticles due to its stronger saturation magnetization.

Abstract: Yttria-stabilized tetragonal zirconia polycrystals (Y-TZP) is used for dental prosthodontics, however, it can present accelerated tetragonal to monoclinic phase transformation in oral environment. The aim of this study was to compare the behavior of a Y-TZP synthesized in laboratory by the coprecipitation method to a commercial Y-TZP, after hydrothermal aging in pressurized reactor (150°C/ 35 hours). The discs were sintered at 1520°C for two hours. The kinetics curve of phase transformation was determined through the data collect by XRD diffractograms treated by the Rietveld method. The experimental and commercial control groups did not present monoclinic phase. After 35 hours of aging, the experimental group presented 69% of monoclinic phase compared to 67% for the commercial group. Scanning electron microscopy and atomic force microscopy images suggested that the commercial group presented heterogeneity of grain size and that the experimental group was more homogeneous. All groups presented superficial degradation process.

Abstract: Improvements of the catalytic efficiency of nickel–aluminum oxides in reforming reactions for hydrogen production have been achieved by the development of synthesis processes that provide powders with high surface area. The reduction of the crystallization temperature is one of the procedures in this direction. In this work, the effect of solvothermal treatment on coprecipitated gels with 15 wt% nickel content in alumina matrix was evaluated. Powders were obtained by coprecipitation with and without treatment of gels under n-butanol vapor pressure at 150oC. Products were characterized by TG/DTA, X-ray diffraction, specific surface area measurements, scanning electron microscopy and laser beam scattering for granulometric distribution determination. The results showed that calcined powders have high specific surface area (ranging from 170 to 260 m².g^-1) and are composed by gamma alumina and nickel aluminate phases. Aging treatment did not promote hydroxides decomposition under solvothermal conditions, indicating the need of calcination step.

Abstract: ZnNb₂O₆ powder was successfully synthesized via coprecipitation method with Nb₂O₅、Zn(NO₃)₂·6H₂O as raw materials and ammonia as precipitant agent. This precursor on heating at750°C, produced ZN powders. Phase composition, morphology and chemical composition were studied via a combination of XRD, TEM and EDS technique. The effects of synthesis temperature on phase composition and particle morphology were investigated in this paper. The results showed that with the increase of the synthesis temperature, the particle size decreases. We could get the ZnNb₂O₆ powder with high purity, fine crystalline when the synthesis temperature is at 50°C.

Abstract: The copper catalyst was prepared by coprecipitation method and used for treating the Acid Red B wastewater with catalytic wet air oxidation method. Results showed that when (NH₄)₂CO₃ was used as precipitating agent, and the concentration was 0.6mol / L, reaction temperature was 40 °C, calcination temperature was 700 °C, the copper catalysts prepared by direct addition method showed better stability in treating the wastewater.

Abstract: A series of copper catalysts were prepared by coprecipitation method and used for treating the Acid Red B wastewater with catalytic wet air oxidation method. Various parameters which influence the activity the catalyst in the process were optimized. Results showed that when (NH₄)₂CO₃ was used as precipitating agent, and the concentration was 0.8mol / L, precipitation temperature was 40 °C, calcination temperature was 600 °C, the copper catalysts prepared by direct addition method showed better activity in treating the wastewater.

Abstract: The effect of a microwave-assisted hydrothermal (MWH) treatment on the structural, thermal, and electrical properties of NiO/ZrO₂:8 mol%Y₂O₃(YSZ)/CeO₂ (60/20/20 wt.%) composite was investigated. Powders were synthesized by a hydroxide coprecipitation-impregnation technique, in which Ni and Ce oxides were coprecipitaed in a suspension containing YSZ. Simultaneous thermogravimetry and differential thermal analysis revealed that MWH treatment promotes the crystallization of coprecipitated phases. X-ray diffraction analysis was used for phase identification and the calculated lattice parameters indicated the formation of YSZ:CeO₂ solid solution during sintering. Impedance spectroscopy measurements showed that the electrical properties of the composite samples were not significantly affected by the MHW.

Abstract: A series of Eu³⁺, Dy³⁺ actived Ca_1-xBa_xSnO₃ phosphors were synthesized by coprecipitation method. The structure, morphology and fluorescence property of phosphors were investigated by using X-ray diffraction (XRD), scanning electron microscopy (SEM) and fluorescence spectroscopy. SEM results showed that the as-prepared phosphors are smooth and uniform with the cubic morphology. The incorporation of a small amount of Ba to CaBaSnO₃ improved the emission characteristics. Fluorescence spectrum showed the emission intensity is the best with the incorporation of Ba²⁺ (x = 0.3), when calcination temperature is 900°C.