A thermal shock experiment is designed to explore the thermal shock properties of ceramic/metal gradient thermal barrier coating. The specimens are heated up by oxygen-acetylene flame and cooled by water spray. The ex...
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A thermal shock experiment is designed to explore the thermal shock properties of ceramic/metal gradient thermal barrier coating. The specimens are heated up by oxygen-acetylene flame and cooled by water spray. The experiment procedure includes two stages, heating the specimen from the initial temperature 30°C for 40s, and then cooling for 20s. The heat transfer and the associated thermal stresses produced during the thermal shock procedure are simulated by finite element method. Experimental results indicated that the specimen of gradient coating behaves better in thermal shock experiments, which agree with the results of simulation.
The Yb-filled Yb x Co 4 Sb 12 (times=0.2-0.5) bulk materials with special nanostructure were prepared by combining melt spinning method with spark plasma sintering (SPS). The microstructure and thermal transport prop...
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The Yb-filled Yb x Co 4 Sb 12 (times=0.2-0.5) bulk materials with special nanostructure were prepared by combining melt spinning method with spark plasma sintering (SPS). The microstructure and thermal transport property of Yb x Co 4 Sb 12 were investigated. The microstructure observations were performed by using high-resolution transmission electron microscopy and field emitted scanning electron microscopy (HRTEM and FESEM). The results show that ribbon-shaped samples after melt spinning are composed of nanocrystals and amorphous-like phases, and possess preferable crystal granularity and evengranular distribution with roller linear speed of 30 m/s and nozzle pressure of 0.02 MPa; the bulk materials after SPS are composed of minicrystals with 200 nm average diameter which is formed by nanocrystals with 5-20 nm diameter. This special microstructure increases grain boundary scattering notably, and has great effect on phonon behavior. As a result, the thermal conductivity of the material is decreased remarkably. Compared with the sample prepared by melting-quench-diffusion annealing method with the same filling fraction (times=0.5), thermal conductivity of the sample prepared by melt spinning method decreased 50% from 4.0 Wm -1 K -1 to 2.0 Wm -1 K -1 at 600 K, and the sample still possesses relatively high power factor.
P-type Bi 0.5 Sb 1.5 Te 3 bulk material with fine nanostructure has been prepared by combining melt spinning technique with spark plasma sintering (SPS), and the effects of microstructure on the thermoelectric transp...
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P-type Bi 0.5 Sb 1.5 Te 3 bulk material with fine nanostructure has been prepared by combining melt spinning technique with spark plasma sintering (SPS), and the effects of microstructure on the thermoelectric transport properties are investigated. Bi 0.5 Sb 1.5 Te 3 ribbons with fine nanostructure are obtained during the melt spinning process and the grain sizes of Bi 0.5 Sb 1.5 Te 3 are about 5-15 nm observed by High-resolution transmission electron microscopy. Such structure has great influence on thermoelectric transport properties of Bi 0.5 Sb 1.5 Te 3 compound. Compared with zone melting and directing SPS samples, the lattice thermal conductivity of the sample processed by melt spinning decreases significantly due to the intensive phonon scattering induced by the fine nanostructure. The greatest thermoelectric figure of merit (ZT) of 1.20 is obtained at 300K for the sample which is prepared by melt spinning with roller linear speed of 10 m/s.
P-type Ba 8 Ga 16 Cd x Ge 30-x (x=0.95, 1.00, 1.05, 1.10) type-I clathrates with different Cd contents were synthesized by combining melt method with spark plasma sintering (SPS). The effects of Cd content on electri...
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P-type Ba 8 Ga 16 Cd x Ge 30-x (x=0.95, 1.00, 1.05, 1.10) type-I clathrates with different Cd contents were synthesized by combining melt method with spark plasma sintering (SPS). The effects of Cd content on electrical transport properties have been investigated. The results show that all samples exhibit p-type conduction. The Seebeck coefficient alpha and room temperature carrier mobility mu H decrease with the increasing Cd content. The electrical conductivity sigma and the room temperature carrier concentration N p increase with the increase of Cd content. In the low temperature range (T<150 K), the carrier scattering mechanism is mainly ionized impurity mechanism, and gradually changes to an acoustical mechanism with the rising temperature. The maximum power factor value of 0.35times10 -3 Wm -1 K -2 is obtained at 550 K for Ba 8 Ga 16 Cd 1.00 Ge 29.00 .
Sr-filled skutterudite compounds SryCo4Sb 12 (y=0-0.20) were synthesized by melting method. XRD and EPMA results revealed that the obtained samples are single skutterudite phase with homogeneous chemical composition. ...
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Sr-filled skutterudite compounds SryCo4Sb 12 (y=0-0.20) were synthesized by melting method. XRD and EPMA results revealed that the obtained samples are single skutterudite phase with homogeneous chemical composition. The lattice parameters increase linearly with increasing Sr content in the range of y=0-0.20. The thermal conductivity, electrical conductivity and Seebeck coefficient were measured in the temperature range of 300-850K. The measurement of Hall effect was performed by Van de Pauw method at room temperature. The obtained Sr-filled skutterudite exhibits n-type conduction. The absolute value of the Seebeck coefficient of Sr yCo4Sb12 decreases with the increase of Sr content. The electrical conductivity increases with the increase of Sr content. The lattice thermal conductivity of SryCo4Sb12 is significantly depressed as compared with unfilled CoSb3. The maximum dimensionless thermoelectric figure of merit is 0.7 for Sr 0.20Co4Sb12 at 850K. Further optimization of chemical composition would improve the thermoelectric performance.
After combining the PVDF and BST powders with different particle sizes, the anti-voltage strengths of composites was tested. Although the concentrates of ceramic were all the same, their anti-voltage strengths were di...
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After combining the PVDF and BST powders with different particle sizes, the anti-voltage strengths of composites was tested. Although the concentrates of ceramic were all the same, their anti-voltage strengths were distinguished. The results showed that the bigger particles or less thickness of material could benefit to the anti-voltage strength and ultimately enhanced the energy storage density of composites. Moreover, the distribution of particle dimension also influenced the strengths of materials. Composite with homogeneous particles performed higher strength than that of composites with inhomogeneous particles.
Cubic Boron Nitride powder was heat treated in N2 or in vacuum at different temperatures and dwell time. Its phase composition and morphology were investigated by means of X-ray diffraction (XRD) and scanning electron...
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Cubic Boron Nitride powder was heat treated in N2 or in vacuum at different temperatures and dwell time. Its phase composition and morphology were investigated by means of X-ray diffraction (XRD) and scanning electron microscopy (SEM) analysis. Results showed that the cubic Boron Nitride was transformed into hexagonal phase after heat treatment in N2 at 1350°C for 10 h, or in vacuum (pressure = 1-5 Pa) at 1550°C for 5 h, while no changes occurred in particle size and morphology.
Al2O3/ZrO2 ceramic composites with asymmetric double-layer structure have been investigated. The factors that influence the toughness and the strength of the layered ceramic composites were discussed. Based on the res...
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Al2O3/ZrO2 ceramic composites with asymmetric double-layer structure have been investigated. The factors that influence the toughness and the strength of the layered ceramic composites were discussed. Based on the research, a new approach is tried to present for design and preparation of laminated ceramic composites with high toughness and high strength.
Permittivity and anti-voltage ability commonly determined the energy storage density of material. Although composite could be molded easier than ceramic, its lower energy storage density prevented the material from ap...
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Permittivity and anti-voltage ability commonly determined the energy storage density of material. Although composite could be molded easier than ceramic, its lower energy storage density prevented the material from application since the polymer usually took on poor dielectric constant. In order to enhance the energy storage performance of composite, PAn was introduced to PVDF by emulsion polymerization. SEM of the co-polymers showed that they could construct continuous media till the concentrate of aniline reached 25% while polymerizing. The permittivity of polymer rose along with the concentrate increasing of aniline and pH falling value of retreating solution. The permittivity and anti-voltage strength of composite also charged correspondingly. As a consequence, the energy storage density innovated much higher than ever. The maximum energy storage density could approach 0.9185Johr/cc.
Diamond films were deposited by using CH4/A1-/H2 gas system and silicon (111) wafers as substrate in microwave plasma CVD (MPCVD) at low temperature about 350°C . The effects of the gas system and proportion, dif...
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Diamond films were deposited by using CH4/A1-/H2 gas system and silicon (111) wafers as substrate in microwave plasma CVD (MPCVD) at low temperature about 350°C . The effects of the gas system and proportion, different microwave power, and different pretreatment methods of substrate on the microstructure of diamond films were respectively discussed. The diamond film samples were investigated by X-ray-diffraction (XRD) and scanning electron microscopy (SEM). The results showed that diamond (111) peak of XRD patterns was very low because of non-diamond phase and defects. The SEM images showed that diamond films were stacked with regular ranged and about 200 nm ball-like diamond secondary nucleation particles. The diamond films are consisted of no well-faceted particles.
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