The Experts below are selected from a list of 360 Experts worldwide ranked by ideXlab platform
Bernd Friedrich - One of the best experts on this subject based on the ideXlab platform.
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synthesis of nano crystalline spherical cobalt iron co fe alloy particles by ultrasonic spray pyrolysis and Hydrogen Reduction
Journal of Alloys and Compounds, 2009Co-Authors: Sebahattin Gurmen, Burcak Ebin, S Stopic, Aybars Guven, Bernd FriedrichAbstract:Abstract Spherical nano-crystalline Co–Fe particles were produced by ultrasonic spray pyrolysis (USP) of aqueous solutions of cobalt–iron chloride followed by thermal decomposition of generated aerosols in Hydrogen atmosphere. The effect of the precursor solution in the range of 0.05 M, 0.1 M, 0.2 M and 0.4 M on the morphology and crystallite size of the Co–Fe alloy particles are investigated under the conditions of 1.5 h running time, 800 °C Reduction temperature, and 1.0 l/min H 2 volumetric flow rate. X-ray diffraction (XRD) studies and Scherer crystallite size calculations show that the crystallite size varies between 25 nm and 27 nm. Scanning electron microscopy (SEM) observations reveal that the the precursor solution strongly influences the particle size of the synthesized Co–Fe alloy particles. Energy dispersive spectroscopy (EDS) results indicate that particles consist of iron and cobalt. Spherical nano-crystalline Co–Fe alloy particles in the range of 100–920 nm were obtained at 800 °C.
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nanocrystalline spherical iron nickel fe ni alloy particles prepared by ultrasonic spray pyrolysis and Hydrogen Reduction usp hr
Journal of Alloys and Compounds, 2009Co-Authors: Sebahattin Gurmen, Burcak Ebin, S Stopic, Bernd FriedrichAbstract:FeCl2 and NiCl2 were used for synthesis of nanocrystalline spherical Fe–Ni alloy particles by ultrasonic spray pyrolysis and Hydrogen Reduction (USP-HR). Spherical ultrafine Fe–Ni particles were obtained by USP of aqueous solutions of iron–nickel chloride followed by thermal decomposition of generated aerosols in Hydrogen atmosphere. Particle sizes of the produced Fe–Ni particles can be controlled by the change of the concentration of an initial solution. The effect of the precursor solution in the range of 0.05, 0.1, 0.2 and 0.4 M on the morphology and crystallite size of the Fe–Ni alloy particles are investigated under the conditions of 1.5 h running time, 900 ◦ C Reduction temperature, and 1.0 L/min H2 volumetric flow rate. X-ray diffraction (XRD) studies and Scherrer crystallite size calculations show that the crystalline size was nearly 28 nm. Energy dispersive spectroscopy (EDS) was performed to determine the chemical composition of the particles. Transmission electron microscope (TEM) was used to confirm the crystalline size, that was determined using XRD results. Scanning electron microscopy (SEM) observations reveal that the precursor solution strongly influences the particle size of the synthesized Fe–Ni alloy particles. Spherical nanocrystalline Fe–Ni alloy particles in the range of 80 and 878 nm were obtained at 900 ◦C.
Sebahattin Gurmen - One of the best experts on this subject based on the ideXlab platform.
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synthesis of nano crystalline spherical cobalt iron co fe alloy particles by ultrasonic spray pyrolysis and Hydrogen Reduction
Journal of Alloys and Compounds, 2009Co-Authors: Sebahattin Gurmen, Burcak Ebin, S Stopic, Aybars Guven, Bernd FriedrichAbstract:Abstract Spherical nano-crystalline Co–Fe particles were produced by ultrasonic spray pyrolysis (USP) of aqueous solutions of cobalt–iron chloride followed by thermal decomposition of generated aerosols in Hydrogen atmosphere. The effect of the precursor solution in the range of 0.05 M, 0.1 M, 0.2 M and 0.4 M on the morphology and crystallite size of the Co–Fe alloy particles are investigated under the conditions of 1.5 h running time, 800 °C Reduction temperature, and 1.0 l/min H 2 volumetric flow rate. X-ray diffraction (XRD) studies and Scherer crystallite size calculations show that the crystallite size varies between 25 nm and 27 nm. Scanning electron microscopy (SEM) observations reveal that the the precursor solution strongly influences the particle size of the synthesized Co–Fe alloy particles. Energy dispersive spectroscopy (EDS) results indicate that particles consist of iron and cobalt. Spherical nano-crystalline Co–Fe alloy particles in the range of 100–920 nm were obtained at 800 °C.
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nanocrystalline spherical iron nickel fe ni alloy particles prepared by ultrasonic spray pyrolysis and Hydrogen Reduction usp hr
Journal of Alloys and Compounds, 2009Co-Authors: Sebahattin Gurmen, Burcak Ebin, S Stopic, Bernd FriedrichAbstract:FeCl2 and NiCl2 were used for synthesis of nanocrystalline spherical Fe–Ni alloy particles by ultrasonic spray pyrolysis and Hydrogen Reduction (USP-HR). Spherical ultrafine Fe–Ni particles were obtained by USP of aqueous solutions of iron–nickel chloride followed by thermal decomposition of generated aerosols in Hydrogen atmosphere. Particle sizes of the produced Fe–Ni particles can be controlled by the change of the concentration of an initial solution. The effect of the precursor solution in the range of 0.05, 0.1, 0.2 and 0.4 M on the morphology and crystallite size of the Fe–Ni alloy particles are investigated under the conditions of 1.5 h running time, 900 ◦ C Reduction temperature, and 1.0 L/min H2 volumetric flow rate. X-ray diffraction (XRD) studies and Scherrer crystallite size calculations show that the crystalline size was nearly 28 nm. Energy dispersive spectroscopy (EDS) was performed to determine the chemical composition of the particles. Transmission electron microscope (TEM) was used to confirm the crystalline size, that was determined using XRD results. Scanning electron microscopy (SEM) observations reveal that the precursor solution strongly influences the particle size of the synthesized Fe–Ni alloy particles. Spherical nanocrystalline Fe–Ni alloy particles in the range of 80 and 878 nm were obtained at 900 ◦C.
Guo-hua Zhang - One of the best experts on this subject based on the ideXlab platform.
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preparation of ultrafine w powder via carbothermic preReduction of tungsten oxide followed by deep Reduction with Hydrogen
JOM, 2020Co-Authors: Chengmin Song, Guo-hua Zhang, Kuo-chih Chou, Baijun YanAbstract:A two-step Reduction method to synthesize tungsten powder with controllable size is proposed. Firstly, precursors composed of W and WO2 were synthesized via carbothermic preReduction of tungsten trioxide with different C/WO3 ratios at 1323 K, then the precursors were completely reduced by Hydrogen to remove residual oxygen at 1023 K and 1223 K, respectively. It was observed that increasing the C/WO3 molar ratio in the preReduction stage was beneficial to decrease the particle size of the W powder. In the subsequent Hydrogen Reduction stage, the presence of the gaseous intermediate phase W-O-H had a great influence on the morphology of the final product. Tungsten powders with particle size ranging from micron to nanometer range could be prepared by controlling the C/WO3 ratio and Hydrogen Reduction temperature.
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preparation of ultrafine mo powders via carbothermic pre Reduction of molybdenum oxide and deep Reduction by Hydrogen
International Journal of Refractory Metals & Hard Materials, 2018Co-Authors: Dahang Wang, Guodong Sun, Guo-hua ZhangAbstract:Abstract A novel route to synthesize molybdenum (Mo) powders via carbothermic pre-Reduction of molybdenum oxide followed by deep Reduction by Hydrogen was proposed. The pre-reduced Mo powders containing a small amount of molybdenum dioxide (MoO2) were produced first by reacting molybdenum trioxide (MoO3) with insufficient carbon. Then the pre-reduced Mo powders were further reduced by Hydrogen at 1173 K to remove the residual oxygen. Mo particle with a much smaller size could be obtained by the carbothermic Reduction owing to the absence of Mo-O-H gaseous intermediate phase which leads to the increase of particle size during the Hydrogen Reduction process. In the carbothermic pre-Reduction process, the existence of a few MoO2 can avoid the residue of carbon in the prepared pre-reduced Mo powders which is hard to remove during the following Hydrogen Reduction process. It was observed that increasing the C/MoO3 molar ratio was beneficial for the decrease of the particle size of Mo powders. Mo powders with submicron-size could be obtained after further Hydrogen Reduction. This new method provides a simple and low cost route to prepare ultrafine Mo powders.
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Study on Hydrogen Reduction of Ultrafine MoO2 To Produce Ultrafine Mo
Journal of Physical Chemistry C, 2016Co-Authors: Lu Wang, Jingsong Wang, Guo-hua Zhang, Kuo-chih ChouAbstract:In the present study, the Hydrogen Reduction of ultrafine MoO2 to produce ultrafine Mo powders has been carried out. It is found that ultrafine spherical Mo powders can be obtained when the reaction temperature is above 923 K, and the Reduction reaction obeys the chemical vapor transport (CVT) mechanism. Whereas when the Reduction temperature is below 883 K, the final products of Mo powders appear to have the same morphology as the initial materials MoO2. In this case, the Reduction reaction obeys the pseudomorphic transport mechanism. It was found that when the temperatures are in the range of 923–1023 K, the rate-controlling step for the Reduction reaction is interfacial chemical reaction. While in the range of 863–883 K, the rate-controlling step changes with the Reduction extent: when the Reduction extent is in the range of 0–0.8, it obeys the nucleation and growth model; when the Reduction extent is in the range of 0.8–1, the diffusion model is obeyed.
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kinetics and mechanism of Hydrogen Reduction of moo3 to moo2
International Journal of Refractory Metals & Hard Materials, 2013Co-Authors: Jie Dang, Guo-hua Zhang, Kuo-chih Chou, Ramana G Reddy, Yuanjun SunAbstract:Abstract Kinetics and mechanism of the Hydrogen Reduction of MoO3 to MoO2 were studied in this work. The experimental findings confirmed that the Reduction of MoO3 to MoO2 was a consecutive reaction with the intermediate product Mo4O11. The dual reactions (MoO3 → Mo4O11, Mo4O11 → MoO2) occurred simultaneously, and the rate of the first reaction was higher than that of the second one. The Reduction kinetics of MoO3 was analyzed according to a two-interface model, the predicted curves of which agreed well with the experimental results. Using this model, the rate controlling steps and the corresponding activation energies were obtained.
Frank A Nuesch - One of the best experts on this subject based on the ideXlab platform.
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Hydrogen Reduction of molybdenum oxide at room temperature
Scientific Reports, 2017Co-Authors: Andreas Borgschulte, Olga Sambalova, Renaud Delmelle, Sandra Jenatsch, Roland Hany, Frank A NueschAbstract:The color changes in chemo- and photochromic MoO3 used in sensors and in organic photovoltaic (OPV) cells can be traced back to intercalated Hydrogen atoms stemming either from gaseous Hydrogen dissociated at catalytic surfaces or from photocatalytically split water. In applications, the reversibility of the process is of utmost importance, and deterioration of the layer functionality due to side reactions is a critical challenge. Using the membrane approach for high-pressure XPS, we are able to follow the Hydrogen Reduction of MoO3 thin films using atomic Hydrogen in a water free environment. Hydrogen intercalates into MoO3 forming HxMoO3, which slowly decomposes into MoO2 +1/2 H2O as evidenced by the fast Reduction of Mo6+ into Mo5+ states and slow but simultaneous formation of Mo4+ states. We measure the decrease in oxygen/metal ratio in the thin film explaining the limited reversibility of Hydrogen sensors based on transition metal oxides. The results also enlighten the recent debate on the mechanism of the high temperature Hydrogen Reduction of bulk molybdenum oxide. The specific mechanism is a result of the balance between the Reduction by Hydrogen and water formation, desorption of water as well as nucleation and growth of new phases.
Sung-tag Oh - One of the best experts on this subject based on the ideXlab platform.
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The behavior of tungsten oxides in the presence of copper during Hydrogen Reduction
Journal of Alloys and Compounds, 2006Co-Authors: Sung-tag OhAbstract:Abstract The behavior of tungsten oxides during Hydrogen Reduction in the presence of copper was investigated by measuring the changes in humidity and electrical resistance during the Reduction process. A non-isothermal analysis of the humidity changes could manifest an effect of copper on the Reduction of tungsten dioxide during the Hydrogen Reduction process of ball-milled WO 3 –CuO powder mixtures. To investigate the detailed effect of copper on tungsten oxide Reduction, raw tungsten oxide powder was reduced under a coiled copper wire, while changes in the electrical resistance change were simultaneously measured by the dc four-point probe method. The results of this analysis showed a deviation from a tungsten oxide-free reference over the Reduction temperature of tungsten dioxide. These results were confirmed by observing the microstructure of the copper surface. Deposited tungsten was observed on the copper surface after the Hydrogen Reduction of tungsten oxide beneath the copper wire.
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the initial stage of sintering for the w cu nanocomposite powder prepared from w cuo mixture
Materials Letters, 2004Co-Authors: Sung-tag OhAbstract:Abstract W–15 wt.% Cu nanocomposite powder was fabricated using W and CuO powder with the ball-milling and Hydrogen-Reduction process. The ball-milled W–CuO mixture was very fine and homogeneously distributed in the aggregates. During the Hydrogen-Reduction process of the ball-milled W–CuO mixture, the fine and homogeneous microstructure was maintained without microstructural change. In the sintering process of the W–Cu nanocomposite powder, the solid state sintering was certainly observed around 850 °C. It is considered that the solid state sintering at low temperature range should occur as a result of the sintering of Cu phase.
