The Experts below are selected from a list of 63927 Experts worldwide ranked by ideXlab platform
Junmin Xue - One of the best experts on this subject based on the ideXlab platform.
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Layer Structured Calcium Bismuth Titanate by Mechanical Activation
Journal of Metastable and Nanocrystalline Materials, 2005Co-Authors: M.h. Sim, Junmin Xue, John WangAbstract:Nanocrystalline calcium bismuth titanate (CaBi4Ti4O15), which exhibits a layer structure, has been successfully synthesized by Mechanical Activation of constituent oxides of CaO, Bi2O3 and TiO2 in a nitrogen atmosphere at room temperature. The phase-forming calcination at elevated temperatures that is always required is skipped. CaBi4Ti4O15 derived from Mechanical Activation consists of nanocrystallites, which occur as aggregates of ~50 nm in sizes. It demonstrates an improved sinterability and was sintered to a density of 93.4% theoretical density at 1175oC for 2 hours. Ferroelectric properties of sintered CaBi4Ti4O15 derived from Mechanical Activation have been studied. A peak dielectric constant of 1049 at the Curie temperature of 774oC was measured at 1MHz for CaBi4Ti4O15 sintered at 1175oC.
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Nanocrystalline Maghemite (γ‐Fe2O3) in Silica by Mechanical Activation of Precursors
Journal of the American Ceramic Society, 2004Co-Authors: Junmin Xue, Zhaohui Zhou, John WangAbstract:γ-Fe2O3 nanocrystallites dispersed in an amorphous silica matrix have been successfully prepared for the first time by Mechanical Activation of a chemistry-derived precursor at room temperature. The initial 10 h of Mechanical Activation triggered the formation of nanocrystallites of Fe3O4 in a highly activated matrix. Increasing the Mechanical-Activation time led to a phase transformation from Fe3O4 to γ-Fe2O3. The γ-Fe2O3 phase was well established after Mechanical Activation of the precursor for 30 h. Further increasing the Mechanical-Activation time to 40 h induced the formation of α-Fe2O3. The Mechanical-Activation-grown γ-Fe2O3 nanocrystallites were ∼10–12 nm in size and well dispersed in the silica matrix, as observed using TEM. They demonstrated superparamagnetic behavior at room temperature when measured using a Mossbauer spectrometer and a vibrating sample magnetometer (VSM). In addition, the γ-Fe2O3 derived from 30 h of Mechanical Activation exhibited a value of saturation magnetization as high as 62.6 emu/g.
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Mechanical Activation‐Assisted Synthesis of Pb(Fe2/3W1/3)O3
Journal of the American Ceramic Society, 2004Co-Authors: Seok Khim Ang, Dongmei Wan, John Wang, Junmin XueAbstract:Perovskite Pb(Fe 2/3 W 1/3 )O 3 (PFW) was prepared via a Mechanical Activation-assisted synthesis route from mixed oxides of PbO, Fe 2 O 3 , and WO 3 . The Mechanically activated oxide mixture, which exhibited a specific area of >10 m 2 /g, underwent phase conversion from nanocrystalline lead tungstate (PbWO 4 ) and pyrochlore (Pb 2 FeWO 6.5 ) phases on sintering to yield perovskite PFW, although the formation of perovskite phase was not triggered by Mechanical Activation. When heated to 700°C, >98% perovskite phase was formed in the Mechanically activated oxide mixture. The perovskite phase was sintered to a density of ∼99% of theoretical density at 870°C for 2 h. The sintered PFW exhibited a dielectric constant of 9800 at 10 kHz, which was ∼30% higher than that of the PFW derived from the oxide mixture that was not subjected to Mechanical Activation.
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NiFe2O4 nanoparticles formed in situ in silica matrix by Mechanical Activation
Journal of Applied Physics, 2002Co-Authors: Z. H. Zhou, Junmin Xue, Jun Wang, H. S. O. Chan, Zexiang ShenAbstract:Nanocrystalline nickel ferrite (NiFe2O4) particles were successfully synthesized in situ in an amorphous silica matrix by Mechanical Activation at room temperature. Phase development in the amorphous precursors, derived via a modified sol–gel synthesis route, with increasing Mechanical Activation time was studied in detail by employing transmission electron microscopy, x-ray diffraction, and Raman spectroscopy. NiFe2O4 nanoparticles of 8.05 nm in mean particle size with a standard deviation of 1.24 nm, which were well dispersed in the silica matrix, were realized by 30 h of Mechanical Activation. The phase formation of nanocrystalline NiFe2O4 particles involves the nucleation of Fe3O4 in amorphous silica at the initial stage of Mechanical Activation, followed by the growth of nickel ferrite by incorporation of Ni2+ caions into Fe3O4. Their magnetic anisotropy, surface spin disorder, and cation distribution are investigated by considering both the strain imposed by silica matrix and the buffer effect durin...
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Nanosized Barium Titanate Powder by Mechanical Activation
Journal of the American Ceramic Society, 2000Co-Authors: Junmin Xue, John Wang, Dongmei WanAbstract:Mechanical Activation, without any additional heat treatment, is used to trigger the formation of a perovskite BaTiO3 phase in an oxide matrix that consists of BaO and TiO2 in a nitrogen atmosphere. The resulting BaTiO3 powder exhibits a well-established nanocrystalline structure, as indicated by phase analysis using X-ray diffractometry. A crystallite size of ∼14 nm is calculated, based on the half-width of the BaTiO3 (110) peak, using the Scherrer equation, and an average particle size of 20–30 nm is observed using transmission electron microscopy for the Activation-derived BaTiO3 powder.
N Z Lyakhov - One of the best experts on this subject based on the ideXlab platform.
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Obtaining composites Cu/TiO2 by combining Mechanical Activation and self-propagating high temperature synthesis
Russian Journal of Applied Chemistry, 2011Co-Authors: T. F. Grigor’eva, A P Barinova, A. I. Letsko, T. L. Talako, S. V. Tsybulya, I. A. Vorsina, A. F. Il’yushchenko, N Z LyakhovAbstract:The possibility of obtaining nanostructured composites Cu/TiO2 by combining Mechanical Activation and self-propagating high temperature synthesis was investigated by X-ray diffraction and electron microscopy.
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solid state combustion in Mechanically activated shs systems ii effect of Mechanical Activation conditions on process parameters and combustion product composition
Combustion Explosion and Shock Waves, 2003Co-Authors: M A Korchagin, T F Grigoreva, Boris B Bokhonov, M R Sharafutdinov, A P Barinova, N Z LyakhovAbstract:The effect of Mechanical Activation conditions in a planetary ball mill on the main parameters of SHS‐processes and combustion product composition was studied for Ni + 13 wt. % Al and Ni + 45 wt. % Ti compositions. From results of experiments at elevated initial temperatures, it is concluded that because of reverse quenching, the defects produced by Mechanical Activation are not annealed in the heating zone and are retained in the sample until the beginning of chemical interaction in the leading zone of the SHS wave. The process of annealing of the activated samples was studied in situ on a transmission electron microscope and a synchrotron radiation diffractometer. The energy stored in the samples as a result of Mechanical Activation is estimated by calorimetric studies.
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Solid‐State Combustion in Mechanically Activated SHS Systems. II. Effect of Mechanical Activation Conditions on Process Parameters and Combustion Product Composition
Combustion Explosion and Shock Waves, 2003Co-Authors: M A Korchagin, Boris B Bokhonov, M R Sharafutdinov, A P Barinova, T. F. Grigor’eva, N Z LyakhovAbstract:The effect of Mechanical Activation conditions in a planetary ball mill on the main parameters of SHS‐processes and combustion product composition was studied for Ni + 13 wt. % Al and Ni + 45 wt. % Ti compositions. From results of experiments at elevated initial temperatures, it is concluded that because of reverse quenching, the defects produced by Mechanical Activation are not annealed in the heating zone and are retained in the sample until the beginning of chemical interaction in the leading zone of the SHS wave. The process of annealing of the activated samples was studied in situ on a transmission electron microscope and a synchrotron radiation diffractometer. The energy stored in the samples as a result of Mechanical Activation is estimated by calorimetric studies.
Z A Munir - One of the best experts on this subject based on the ideXlab platform.
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role of Mechanical Activation in shs synthesis of tic
Journal of Materials Science, 2004Co-Authors: Filippo Maglia, Francesco Delogu, Umberto Anselmitamburini, Claudio Deidda, G Cocco, Z A MunirAbstract:The effect of the Mechanical Activation of the reactants on the self-propagating high-temperature synthesis (SHS) of titanium carbide was investigated. The SHS experiments were performed on two compositions, Ti50C50 and Ti70C30, which define the homogeneity range of the TiC equilibrium carbide. Milling times were progressively increased up to the time at which a combustion-like process ignites spontaneously under milling. The combustion peak temperature, wave velocity, and ignition temperature were markedly influenced by the degree of Mechanical Activation of the reactants. In particular the ignition temperature was observed to decrease from a temperature corresponding to the melting point of Ti to 500°C. The apparent Activation energy for propagation of the combustion wave was also determined (∼100 kJ·mol−1) and was found to be independent of both the degree of Mechanical Activation and the composition of the starting mixture.
John Wang - One of the best experts on this subject based on the ideXlab platform.
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Layer Structured Calcium Bismuth Titanate by Mechanical Activation
Journal of Metastable and Nanocrystalline Materials, 2005Co-Authors: M.h. Sim, Junmin Xue, John WangAbstract:Nanocrystalline calcium bismuth titanate (CaBi4Ti4O15), which exhibits a layer structure, has been successfully synthesized by Mechanical Activation of constituent oxides of CaO, Bi2O3 and TiO2 in a nitrogen atmosphere at room temperature. The phase-forming calcination at elevated temperatures that is always required is skipped. CaBi4Ti4O15 derived from Mechanical Activation consists of nanocrystallites, which occur as aggregates of ~50 nm in sizes. It demonstrates an improved sinterability and was sintered to a density of 93.4% theoretical density at 1175oC for 2 hours. Ferroelectric properties of sintered CaBi4Ti4O15 derived from Mechanical Activation have been studied. A peak dielectric constant of 1049 at the Curie temperature of 774oC was measured at 1MHz for CaBi4Ti4O15 sintered at 1175oC.
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Nanocrystalline Maghemite (γ‐Fe2O3) in Silica by Mechanical Activation of Precursors
Journal of the American Ceramic Society, 2004Co-Authors: Junmin Xue, Zhaohui Zhou, John WangAbstract:γ-Fe2O3 nanocrystallites dispersed in an amorphous silica matrix have been successfully prepared for the first time by Mechanical Activation of a chemistry-derived precursor at room temperature. The initial 10 h of Mechanical Activation triggered the formation of nanocrystallites of Fe3O4 in a highly activated matrix. Increasing the Mechanical-Activation time led to a phase transformation from Fe3O4 to γ-Fe2O3. The γ-Fe2O3 phase was well established after Mechanical Activation of the precursor for 30 h. Further increasing the Mechanical-Activation time to 40 h induced the formation of α-Fe2O3. The Mechanical-Activation-grown γ-Fe2O3 nanocrystallites were ∼10–12 nm in size and well dispersed in the silica matrix, as observed using TEM. They demonstrated superparamagnetic behavior at room temperature when measured using a Mossbauer spectrometer and a vibrating sample magnetometer (VSM). In addition, the γ-Fe2O3 derived from 30 h of Mechanical Activation exhibited a value of saturation magnetization as high as 62.6 emu/g.
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Mechanical Activation‐Assisted Synthesis of Pb(Fe2/3W1/3)O3
Journal of the American Ceramic Society, 2004Co-Authors: Seok Khim Ang, Dongmei Wan, John Wang, Junmin XueAbstract:Perovskite Pb(Fe 2/3 W 1/3 )O 3 (PFW) was prepared via a Mechanical Activation-assisted synthesis route from mixed oxides of PbO, Fe 2 O 3 , and WO 3 . The Mechanically activated oxide mixture, which exhibited a specific area of >10 m 2 /g, underwent phase conversion from nanocrystalline lead tungstate (PbWO 4 ) and pyrochlore (Pb 2 FeWO 6.5 ) phases on sintering to yield perovskite PFW, although the formation of perovskite phase was not triggered by Mechanical Activation. When heated to 700°C, >98% perovskite phase was formed in the Mechanically activated oxide mixture. The perovskite phase was sintered to a density of ∼99% of theoretical density at 870°C for 2 h. The sintered PFW exhibited a dielectric constant of 9800 at 10 kHz, which was ∼30% higher than that of the PFW derived from the oxide mixture that was not subjected to Mechanical Activation.
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Nanosized Barium Titanate Powder by Mechanical Activation
Journal of the American Ceramic Society, 2000Co-Authors: Junmin Xue, John Wang, Dongmei WanAbstract:Mechanical Activation, without any additional heat treatment, is used to trigger the formation of a perovskite BaTiO3 phase in an oxide matrix that consists of BaO and TiO2 in a nitrogen atmosphere. The resulting BaTiO3 powder exhibits a well-established nanocrystalline structure, as indicated by phase analysis using X-ray diffractometry. A crystallite size of ∼14 nm is calculated, based on the half-width of the BaTiO3 (110) peak, using the Scherrer equation, and an average particle size of 20–30 nm is observed using transmission electron microscopy for the Activation-derived BaTiO3 powder.
Umberto Anselmitamburini - One of the best experts on this subject based on the ideXlab platform.
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role of Mechanical Activation in shs synthesis of tic
Journal of Materials Science, 2004Co-Authors: Filippo Maglia, Francesco Delogu, Umberto Anselmitamburini, Claudio Deidda, G Cocco, Z A MunirAbstract:The effect of the Mechanical Activation of the reactants on the self-propagating high-temperature synthesis (SHS) of titanium carbide was investigated. The SHS experiments were performed on two compositions, Ti50C50 and Ti70C30, which define the homogeneity range of the TiC equilibrium carbide. Milling times were progressively increased up to the time at which a combustion-like process ignites spontaneously under milling. The combustion peak temperature, wave velocity, and ignition temperature were markedly influenced by the degree of Mechanical Activation of the reactants. In particular the ignition temperature was observed to decrease from a temperature corresponding to the melting point of Ti to 500°C. The apparent Activation energy for propagation of the combustion wave was also determined (∼100 kJ·mol−1) and was found to be independent of both the degree of Mechanical Activation and the composition of the starting mixture.
