Alumina-(0-20 vol. pct) iron composites were fabricated by hot-pressing of well-mixed alumina and iron powders at 1400℃ and 30 MPa for 30 mm. Hot-pressed bodies with nearly theoretical density were obtained for addit...Alumina-(0-20 vol. pct) iron composites were fabricated by hot-pressing of well-mixed alumina and iron powders at 1400℃ and 30 MPa for 30 mm. Hot-pressed bodies with nearly theoretical density were obtained for addition up to 10 vol. pct Fe, but relative density decreased gradually with further increase in Fe addition. The materials exhibit a homogeneous dispersion of Fe. Fracture strength of the composites exhibits a maximum value of 604 MPa at 15 vol. pct Fe, which is 1.5 times that of alumina alone. Fracture toughness increases with the increase in Fe content, reaching 7.5 MPa.m1/2 at 20 vol. pct Fe. The theoretical values of fracture toughness was calculated and compared with the experimental one. Toughening mechanisms of the composites are also discussed.展开更多
The Fe3O4@SiO2 composite nanoparticles were obtained from as-synthesized magnetite (Fe3O4) nanoparticles through the modified St?ber method. Then, the Fe3O4 nanoparticles and Fe3O4@SiO2 composite nanoparticles were ch...The Fe3O4@SiO2 composite nanoparticles were obtained from as-synthesized magnetite (Fe3O4) nanoparticles through the modified St?ber method. Then, the Fe3O4 nanoparticles and Fe3O4@SiO2 composite nanoparticles were characterized by means of X-ray diffraction (XRD), Raman spectra, scanning electron microscope (SEM) and vibrating sample magnetometer (VSM). Recently, the studies focus on how to improve the dispersion of composite particle and achieve good magnetic performance. Hence effects of the volume ratio of tetraethyl orthosilicate (TEOS) and magnetite colloid on the structural, morphological and magnetic properties of the composite nanoparticles were systematically investi-gated. The results revealed that the Fe3O4@SiO2 had better thermal stability and dispersion than the magnetite nanoparticles. Furthermore, the particle size and magnetic property of the Fe3O4@SiO2 composite nanoparticles can be adjusted by changing the volume ratio of TEOS and magnetite colloid.展开更多
Magnetic α-Fe2O3,γ-Fe2O3 and Fe3O4 were prepared by facile calcination under different temperature from K4[Fe(CN)6]as raw materials,in which the calcined products areα-Fe2O3,Fe3O4 and γ-Fe2O3 at 400 or 700,500,and...Magnetic α-Fe2O3,γ-Fe2O3 and Fe3O4 were prepared by facile calcination under different temperature from K4[Fe(CN)6]as raw materials,in which the calcined products areα-Fe2O3,Fe3O4 and γ-Fe2O3 at 400 or 700,500,and 600 ℃,respectively.The as-prepared compounds were characterized by X-ray powder diffraction and scanning electron microscopy,and their magnetic behavior at room temperature was also studied.This method provided a simple approach to prepare different polymorphic forms of magnetic iron oxides,which may have potential applications in magnetic science,magnetic composite materials,magnetic core,magnetic separation and medical diagnostics.展开更多
The equilibrium phases and adiabatic temperature for combustion synthesis and reaction hot pressing of Al 2O 3/B 4C employing ① Al, B 2O 3 and C ② C, B, Al 2O 3 as starting reactants were analyzed by the CALPHAD tec...The equilibrium phases and adiabatic temperature for combustion synthesis and reaction hot pressing of Al 2O 3/B 4C employing ① Al, B 2O 3 and C ② C, B, Al 2O 3 as starting reactants were analyzed by the CALPHAD technique. It is shown that the equilibrium phases at the adiabatic temperature in the combusion system (1) are not the intended composite Al 2O 3/B 4C but other phases. Good agreement with the experimental data was achieved for the calculated adiabatic temperature. The results were discussed with respect to the elimination of the by product in the combustion synthesis. It also revealed that the reactant mixture (2) is a weak exothermic or endothermic reaction system, which can be employed in the reaction hot pressing.展开更多
文摘Alumina-(0-20 vol. pct) iron composites were fabricated by hot-pressing of well-mixed alumina and iron powders at 1400℃ and 30 MPa for 30 mm. Hot-pressed bodies with nearly theoretical density were obtained for addition up to 10 vol. pct Fe, but relative density decreased gradually with further increase in Fe addition. The materials exhibit a homogeneous dispersion of Fe. Fracture strength of the composites exhibits a maximum value of 604 MPa at 15 vol. pct Fe, which is 1.5 times that of alumina alone. Fracture toughness increases with the increase in Fe content, reaching 7.5 MPa.m1/2 at 20 vol. pct Fe. The theoretical values of fracture toughness was calculated and compared with the experimental one. Toughening mechanisms of the composites are also discussed.
文摘The Fe3O4@SiO2 composite nanoparticles were obtained from as-synthesized magnetite (Fe3O4) nanoparticles through the modified St?ber method. Then, the Fe3O4 nanoparticles and Fe3O4@SiO2 composite nanoparticles were characterized by means of X-ray diffraction (XRD), Raman spectra, scanning electron microscope (SEM) and vibrating sample magnetometer (VSM). Recently, the studies focus on how to improve the dispersion of composite particle and achieve good magnetic performance. Hence effects of the volume ratio of tetraethyl orthosilicate (TEOS) and magnetite colloid on the structural, morphological and magnetic properties of the composite nanoparticles were systematically investi-gated. The results revealed that the Fe3O4@SiO2 had better thermal stability and dispersion than the magnetite nanoparticles. Furthermore, the particle size and magnetic property of the Fe3O4@SiO2 composite nanoparticles can be adjusted by changing the volume ratio of TEOS and magnetite colloid.
基金supported by the Funds of Fujian province department of education(No.JA14199)
文摘Magnetic α-Fe2O3,γ-Fe2O3 and Fe3O4 were prepared by facile calcination under different temperature from K4[Fe(CN)6]as raw materials,in which the calcined products areα-Fe2O3,Fe3O4 and γ-Fe2O3 at 400 or 700,500,and 600 ℃,respectively.The as-prepared compounds were characterized by X-ray powder diffraction and scanning electron microscopy,and their magnetic behavior at room temperature was also studied.This method provided a simple approach to prepare different polymorphic forms of magnetic iron oxides,which may have potential applications in magnetic science,magnetic composite materials,magnetic core,magnetic separation and medical diagnostics.
基金supported by the Fund for Young Scientists of Sichuan University, China (2011SCU11081)Research Fund for the Doctoral Program of Higher Education, Ministry of Education of China (20120181120103)~~
文摘The equilibrium phases and adiabatic temperature for combustion synthesis and reaction hot pressing of Al 2O 3/B 4C employing ① Al, B 2O 3 and C ② C, B, Al 2O 3 as starting reactants were analyzed by the CALPHAD technique. It is shown that the equilibrium phases at the adiabatic temperature in the combusion system (1) are not the intended composite Al 2O 3/B 4C but other phases. Good agreement with the experimental data was achieved for the calculated adiabatic temperature. The results were discussed with respect to the elimination of the by product in the combustion synthesis. It also revealed that the reactant mixture (2) is a weak exothermic or endothermic reaction system, which can be employed in the reaction hot pressing.
