The processes of the coupling graft of -Si(OCH3)3 groups between 7-aminopropyl trimethoxysilane molecules and iron microparticles and the preparation of Fe/SiO2 core-shell composite particles in the alcohol-alkali-wat...
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The processes of the coupling graft of -Si(OCH3)3 groups between 7-aminopropyl trimethoxysilane molecules and iron microparticles and the preparation of Fe/SiO2 core-shell composite particles in the alcohol-alkali-water solution were investigated in the paper. The as-prepared and heat-treated composite particles were characterized with XRD, SEM, and pickling tests. The results showed that the formation of free SiO2 could be effectively prevented by decreasing the rate of adding ammonia, and that Fe/SiO2 core-shell composite particles almost without free SiO2 were successfully fabricated with a controlling rate about 5 drops of ammonia per minute. The optimal temperature range for the densification of SiO2 nanoshell is about 600 [similar to] 700 °C. The SiO2 nanoshells were badly melt and dropped off when the composite particles were heat-treated at 900 °C. The acid resistance of the composite particles increases as the temperature rose from 200 °C to 700 °C.
The microstructure and microwave dielectric properties of the CuO-doping CaTiO3-Ca(Zn1/3Nb2/3)O3 ceramics prepared by the conventional solid-method were investigated. XRD results indicate the ceramics with orthorhombi...
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Mullite-based nanocomposite powders with embedded iron nanoparticles were synthesized by reduction of sol-gel prepared Al5.4Fe 0.6Si2O13 solid solution in hydrogen. Structural characterization studied by TEM revealed ...
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ISBN:
(纸本)0470080337
Mullite-based nanocomposite powders with embedded iron nanoparticles were synthesized by reduction of sol-gel prepared Al5.4Fe 0.6Si2O13 solid solution in hydrogen. Structural characterization studied by TEM revealed that the intra-granular iron nanoparticles along with inter-type iron grains were obtained in mullite matrix. The magnetic properties of nanocomposite powders after reduction at 1200°C were measured by SQUID. It suggests that the intergranular and intragranular α-iron nanoparticles had the ferromagnetic and superparamagnetic behavior at room temperature, respectively. Dense Mullite-based iron composites were prepared from the nanocomposite powders reduced at different temperatures by hot pressing. The mechanical and magnetic properties were strongly affected by the reduction temperature. Flexural strength of mullite based iron nanocomposite reduced at 1200°C and successively hot pressed at 1650°C is one times higher than monothetic mullite. Furthermore, dense composites also behave ferromagnetic property at room temperature.
Aluminum nitride-boron nitride (AlN/BN) composite ceramics were prepared by spark plasma sintering (SPS). The sintering behaviors of AlN/BN composites with 5-15% volume fraction of BN were studied. The influences of B...
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Aluminum nitride-boron nitride (AlN/BN) composite ceramics were prepared by spark plasma sintering (SPS). The sintering behaviors of AlN/BN composites with 5-15% volume fraction of BN were studied. The influences of BN content, as well as the sintering temperature on the density, microstructure, mechanical strength, thermal conductivity and machinability of the composites were also investigated. The results showed that the full densification of AlN/BN composite ceramics could be realized by SPS technique at the temperature no higher than 1800°C for 3 minutes. The thermal conductivity of AlN/BN composites is in the range of 66-79W/mK, and AlN/BN composites can be cut or drilled by carbides or even steel tools when BN content is 15% volume fraction. The mechanical strength of AlN/BN composites is about 330MPa and is not remarkably affected by the addition of BN. The improvement of mechanical properties of AlN/BN composite ceramics is due to the fine and homogenous microstructure developed in the SPS process.
In this paper, the effect of imperfect inner interface on the stress fields in the coated inclusion composite is investigated, the spring-layer of vanishing thickness model is introduced to simulate the imperfect inte...
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In this paper, the effect of imperfect inner interface on the stress fields in the coated inclusion composite is investigated, the spring-layer of vanishing thickness model is introduced to simulate the imperfect interface, assuming that across the interface between the inclusion and the coating the interfacial traction is continuous while displacement discontinuities are permitted through interfacial traction-displacement jump relations. Numerical examples corresponding to the composites containing single coated spherical and fibrous inclusion, respectively, under shear loading at infinity, are calculated, which indicate that the imperfect inner interfaces have significant effect on stress fields of the composites.
SiCp/Al composites containing high volume fraction of SiC particles were fabricated by spark plasma sintering (SPS), and their thermophysical properties, such as thermal conductivity (TC) and coefficient of thermal ex...
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ISBN:
(纸本)0470081562
SiCp/Al composites containing high volume fraction of SiC particles were fabricated by spark plasma sintering (SPS), and their thermophysical properties, such as thermal conductivity (TC) and coefficient of thermal expansion (CTE), were characterized. The principle of the fabrication was analyzed. Spark can be generated by electric field if the cavity in the green body is large enough. The melted Al by spark densify the compact which is similar to the pressure infiltration but with simple method. High relative density (R-D) of composites was successfully achieved through the optimization of sintering parameters. The measured TCs of SiCp/Al composites fabricated by SPS are higher than 195W/m·k.
C/BN laminated composites were obtained by hot-pressing, and the micro-structure and property of the sintered bodies were investigated. The results indicated that the relative density of the samples was 99%. SEM indic...
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C/BN laminated composites were obtained by hot-pressing, and the micro-structure and property of the sintered bodies were investigated. The results indicated that the relative density of the samples was 99%. SEM indicated that the combined interface between graphite and BN was good, and the transition of graphite and BN was gradual. The sintered bodies between the graphite and BN were destroyed at 1200°C after thermal shocks for 30 times. The tensile strength of materials reached 8.9 MPa.
C/BN laminated composites were obtained by spark plasma sintering. The relationship between sintering conditions, microstructure and properties were studied. The analysis of micro structure indicated that with increas...
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C/BN laminated composites were obtained by spark plasma sintering. The relationship between sintering conditions, microstructure and properties were studied. The analysis of micro structure indicated that with increasing the temperature and time of heat preservation the coalescent between graphite and BN was increased gradually. The bonding strength transformed from molecular gravitation to the union of molecular gravitation and mechanical strength. The circulation times of materials reached 40 times at sintering temperature of 1750°C for 5 min. The test of mechanical properties of the materials indicated that the largest tensile strength reached 18.2 MPa.
A single flat-plate Solid Oxide Fuel Cell (SOFC) with Ni-YSZ|YSZ|LSM configuration was developed, the test system and the fuel control system was established. The electrical properties were examined with H2 as the fue...
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A single flat-plate Solid Oxide Fuel Cell (SOFC) with Ni-YSZ|YSZ|LSM configuration was developed, the test system and the fuel control system was established. The electrical properties were examined with H2 as the fuel and the air as the oxidant in a temperature range of 800 to 1000°C. Results showed that the open-circuit voltage (OCV) was over 1.01 V, the maximum power density at 1000°C reached to 7.73 mW/cm2. It was found that the large ohmic losses of the electrolyte were the main factor responsible for the relative low output power density. The relations of OCV vs. operating temperature and OCV vs. fuel flow rates were also investigated.
Spark or not in insulator materials sintered by pulse electric current or spark plasma sintering is still in dispute. In this paper, the electric field in the graphite die was calculated by Maxwell theory. The calcula...
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ISBN:
(纸本)0470081562
Spark or not in insulator materials sintered by pulse electric current or spark plasma sintering is still in dispute. In this paper, the electric field in the graphite die was calculated by Maxwell theory. The calculated results indicate that the distribution of electric field is in heterogeneous. The intensity of electric field is enhanced at the centre area contacting with punch surface, weakened in circumference contacting with the die. It is deduced from the calculated results that the most possible area to generate spark lies on the punch surface if any spark could be generated in the sintered sample. Some experimental results are accordance with the calculated distribution of electric field and the spark of punch surface.
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