Si-clathrate compounds, n-type Ba8 Ga16 Znx Si30-x (x = 0, 1, 2, 3, 4), are synthesized by using the solid-state reaction method and the melting method. The effects of the replacement of Si with Zn on the structure an...
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Si-clathrate compounds, n-type Ba8 Ga16 Znx Si30-x (x = 0, 1, 2, 3, 4), are synthesized by using the solid-state reaction method and the melting method. The effects of the replacement of Si with Zn on the structure and the electrical transmission characteristics are investigated for n-type Ba8Ga16Znx Si30-x. The results indicate that the sample with the value of x = 1 has the maximal bond angle distortion Δθ, Δθ = 4.4°. The electrical conductivity of samples with x = 0, 2, 4 is higher than that of samples with x = 1, 3. Among the samples, the electrical conductivity of Ba8 Ga16 Zn1 Si29 is the lowest. The samples with x = 0, 2, 4 exhibit a higher Seebeck coefficient than that of samples with x = 1, 3, and the value of the Seebeck coefficient decreases with the increase of the Zn composition. The power factor of Ba8Ga16Zn2Si28 compound is as large as 1.03 × 10-3 W/(m· K2) at 1000K.
High-energy ball mill method was used to fabricate the stainless steel nanocomposite powder from stainless steel powder, carbon powder and titanium powder as raw materials. The X-ray diffraction, SEM and the BET metho...
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High-energy ball mill method was used to fabricate the stainless steel nanocomposite powder from stainless steel powder, carbon powder and titanium powder as raw materials. The X-ray diffraction, SEM and the BET method were used to evaluate the microstructure of treated samples. The results showed that in vacuum condition, with ball mill time increase, stainless steel powder become more and finer, the grain size can reach nanometer level. At the same time, the nano TiC can be formed during ball milling, the stainless steel-TiC nano composite powder can be obtained.
Using the microwave sintering technology, the samples of WC-10Co cemented carbide were put separately at the pure electric field, the pure magnetic field and the mixture E field and H field in a single-mode TE103 cavi...
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Using the microwave sintering technology, the samples of WC-10Co cemented carbide were put separately at the pure electric field, the pure magnetic field and the mixture E field and H field in a single-mode TE103 cavity. The sintering behaviors of WC-10Co cemented carbide were researched and the effects of these positions on their properties also were analyzed.
Extensive dislocation structure was observed by transmission electron microscopy (TEM) in polycrystalline alumina ceramic sintered under a short-time high temperature 1800°C and pressure 100 MPa. There existed lo...
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Extensive dislocation structure was observed by transmission electron microscopy (TEM) in polycrystalline alumina ceramic sintered under a short-time high temperature 1800°C and pressure 100 MPa. There existed lots of dislocation structures: dislocation coalescence, dislocation arrays and dislocation network. The burgers vector of the dislocation array was determined by diffraction contrast as 1/3 less than or equal 11 over-bar 00>. The dislocation network formation was discussed, and it belonged to basal slip system l/3 less than or equal 112 over-bar 0>. Plastic deformation occured mainly by basal plane slip and prime plane slip.
In the present study, Si2N4 whisker was prepared by thermal decomposition of Si(NH)2, the experimental principles and process were described in detail. Influence factors such as temperature, residual carbon(C), a smal...
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In the present study, Si2N4 whisker was prepared by thermal decomposition of Si(NH)2, the experimental principles and process were described in detail. Influence factors such as temperature, residual carbon(C), a small quantity of oxygen and crucible material that could influence the growth of whisker was analyzed and discussed. The influence degree of each factor and mechanism were explained as well. High quality and modified Si3N4 whisker could be prepared by controlling the influence factors during the experimental process. As a result, it was significant to fabricate batch production of high performance Si3N4 whisker by utilizing this method.
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.
In this study, spark plasma sintering (SPS) was applied to prepare α-Si3N4 ceramics of different densities with magnesia, silicon dioxide, alumina as the sintering aids. The sintering behavior and liquid phase sinter...
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In this study, spark plasma sintering (SPS) was applied to prepare α-Si3N4 ceramics of different densities with magnesia, silicon dioxide, alumina as the sintering aids. The sintering behavior and liquid phase sintering (LPS) mechanism were discussed and the factors influencing the density of the prepared samples were analyzed. Microstructures of sintered samples were observed and the phase compositions were analyzed. The results showed that α-Si3N4 ceramics can be sintered by SPS based on the reaction among α-Si3N4 and sintering additives which lead to the liquid phase and the density can be well controlled from 2.48 to 3.09 g/cm3 while the content of the sintering aids changes from 10% to 28.5% and sintering temperature from 1400°C to 1500°C.
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.
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.
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.
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