A novel way was used to prepare dense B4C ceramics at a lower temperature by reactive sintering from carbon and boron elemental powders. Spark Plasma Sintering (SPS) technique, a rapid and non-conventional powder cons...
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ISBN:
(纸本)9780470927151
A novel way was used to prepare dense B4C ceramics at a lower temperature by reactive sintering from carbon and boron elemental powders. Spark Plasma Sintering (SPS) technique, a rapid and non-conventional powder consolidation method, was employed. The densification, microstructure and mechanical property of the as-prepared B4C ceramics were investigated. The reactive sintering process could be divided into two stages, corresponding to synthesis (1300∼1700°C) and densification (1700∼1900°C), respectively. At those stages, boron first reacted with carbon to form B4C, and then the in-situ densification of the as-synthesized B4C occurred and was enhanced by increasing sintering temperature. B4C ceramics with grain size of several hundred nanometers and high densification (98%) were obtained at 1800°C, a lower sintering temperature as compared with general hot press. Due to the high densification and purity as well as fine texture, the SPS-sintered B4C ceramics had high Vickers hardness (48.8GPa), Young's modulus (264.5GPa), fracture toughness (3.9MPa·m1/2) and flexure strength (450MPa).
In the present work, tetragonal BaTiO3 particles down to 20 nm have been synthesized by low temperature aqueous co-precipitation method through composition control. Field emission scanning electron microscopy (FE-SEM)...
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In the present work, tetragonal BaTiO3 particles down to 20 nm have been synthesized by low temperature aqueous co-precipitation method through composition control. Field emission scanning electron microscopy (FE-SEM) images indicated that the precipitates contained fine (about 20-30 nm) faceted particles. The Raman spectra revealed that tetragonal phase appeared with the increase in Ba/Ti ratio in the precursor solution. The appearance of tetragonal phase in BaTiO3 nanoparticle was related with the lattice defect revealed by lattice parameter and lattice strain calculated by XRD results. The lattice defect can be modified through composition control.
The Fe2O3 nanoparticles activated V2O5 nanotubes were achieved via a hydrolysis method. The TEM and SEM images of the nanotubes indicated that the Fe2O3 nanoparticles with the particle size of about 15 nm were dispers...
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ZnO-B2O3-SiO2 additive with 0.55: 0.35: 0.10 molar ratio was added to Ba0.3Sr0.7TiO3 ceramics in order to lower the sintering temperature. The densification behavior, crystalline structure, microstructure, dielectric ...
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ZnO-B2O3-SiO2 additive with 0.55: 0.35: 0.10 molar ratio was added to Ba0.3Sr0.7TiO3 ceramics in order to lower the sintering temperature. The densification behavior, crystalline structure, microstructure, dielectric properties and breakdown strength of ceramics were studied. When 9 wt.% additive was mixed with pure Ba0.3Sr0.7TiO3 powder, the densification temperature of samples decreased from 1350°C to 1100°C compared with no additive system, and the sintered ceramics revealed dielectric properties at room temperature as follows: dielectric constant Εr = 413, dielectric loss tanδ = 0.00231 under 1 kHz and the breakdown strength Eb = 9.2 kV/mm.
Lead free textured K_(0.5)Na_(0.5)NbO_(3) piezoelectric ceramics have been prepared by reactive-templated grain growth method by using NaNbO_(3) with different morphologies as templates. The NaNbO_(3) template particl...
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ISBN:
(纸本)9781457711626
Lead free textured K_(0.5)Na_(0.5)NbO_(3) piezoelectric ceramics have been prepared by reactive-templated grain growth method by using NaNbO_(3) with different morphologies as templates. The NaNbO_(3) template particles with different edge length (10-20 (mu)m) and thickness (0.5-2.5 (mu)m) was synthesized through controlling Bi_(1.5)Na_(x-1.5)Nb_(x)O_(3x+3) precursor's layer numbers x from 2 to 6 by two-step molten salt methods. The crystalline phases and microstructure of textured K_(0.5)Na_(0.5)NbO_(3) were characterized by X-ray diffraction and scanning electron microscopy, respectively. It shows that all the K_(0.5)Na_(0.5)NbO_(3) ceramics are orthorhombic perovskite structure with {001} orientation. By using the template particles with a ratio of edge length to thickness (l/h)(velence)approx10, the textured ceramics with optimized piezoelectric properties was prepared. The results indicate that the enhanced properties of textured ceramics are concerned with the template morphology.
Based on a facile glucose-guided hydrolyzing-heat-treating approach, urchin-like α-Fe2O3 nanomaterials with controllable morphology and crystallinity were prepared via adjusting the heat-treating temperature, and the...
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Based on a facile glucose-guided hydrolyzing-heat-treating approach, urchin-like α-Fe2O3 nanomaterials with controllable morphology and crystallinity were prepared via adjusting the heat-treating temperature, and their electrochemical performances were investigated. The results showed that changing the heat-treating temperature can effectively control the structure and electrochemical property of the as-made products. The urchin-like α-Fe2O3 nanomaterials obtained by heat-treating at 300°C, composed of a mass of the shuttle fibrous brunches, had higher initial discharge capacity(1475 mAhg-1) than those consisting of nanorods formed at 700°C. The above difference is ascribed to the urchin-like samples obtained at the relatively low heat-treating temperature, which, with low crystallinity, large SBET, and well-regulated porous, is helpful to the adsorption of electrolyte and the transport of lithium ion, resulting in the high activity and discharge-charge capacity.
Morphotropic phase boundary (MPB) of (0.8-x)PMT-xPbTiO3(PT)-0. 2PbZrO3(PZ) ternary system (x = 0.4) was studied by X-ray diffraction (XRD). It shows that by comparing with 0.4PMT-0.2PZ-0.4PT sample, after doping with ...
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Morphotropic phase boundary (MPB) of (0.8-x)PMT-xPbTiO3(PT)-0. 2PbZrO3(PZ) ternary system (x = 0.4) was studied by X-ray diffraction (XRD). It shows that by comparing with 0.4PMT-0.2PZ-0.4PT sample, after doping with Ni, c/a remains almost same (about1.009), while both c and a decrease indicating that lattice shrinks. Content of the tetragonal phase TP% of Ni-doped samples increase up to 81.1% when the doping limit of the nickel is reached (y = 0.05), and the dielectric constant Ε was found to increase up to 4570 when y = 0.05 and the Curie temperatures of doping samples were found to decrease from 175°C to 157°C.
The relation among electronic structure, chemical bond and thermoelectric property of Ca3Co2O6 and Cu-doped is studied by first-principle theory. The results indicate that the highest valence band(HVB) and the lowest ...
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