The lanthana-doped mullite fibers were prepared via a sol-gel method from the aluminum isopropoxide-aluminum nitrate-tetraethyl orthosilicate system. The structure evolution and thermal stability of the mullite fibers...The lanthana-doped mullite fibers were prepared via a sol-gel method from the aluminum isopropoxide-aluminum nitrate-tetraethyl orthosilicate system. The structure evolution and thermal stability of the mullite fibers were investigated by means of X-ray diffraction (XRD), Fourier transform infrared (FT-IR) spectroscopy, differential scanning calorimetry (DSC), scanning electron microscopy (SEM) and trans-mission electron microscopy (TEM). The results showed that the fibers obtained after calcination at 1000℃ was in the form of Al2O3-rich mullite, which tended to transform to stoichiometric mullite with the lanthana content increasing. The lattice parameter a exhibited a decline trend with the lanthana content increasing, while b showed an upward tendency. Correspondingly, the redshift of Si-O-Si bond from 1255 to 1245 cm-1 was observed. The grain growth was inhibited for the doped fibers, among which the 5% La2O3-doped sample presented a mini-mum crystallite size (17.2 nm) after calcination at 1000 ℃ for 1 h.展开更多
To prepare the three-dimensional braided carbon fiber reinforced mullite (3D C/mullite) composites, an Al2O3-SiO2 solwith a solid content of 20% (mass fraction) and an Al2O3/SiO2 mass ratio of 2:1 was selected as...To prepare the three-dimensional braided carbon fiber reinforced mullite (3D C/mullite) composites, an Al2O3-SiO2 solwith a solid content of 20% (mass fraction) and an Al2O3/SiO2 mass ratio of 2:1 was selected as the raw material. Characteristics andmullitization of the sol were analyzed throughly. It is found that the formation of mullite is basically completed at 1300℃ and thegel powders exhibit favorable sintering shrinkage. The 3D C/mullite composites without interfacial coating were fabricated throughthe route of vacuum impregnation-drying-heat treatment. Satisfied mechanical properties with a flexural strength of 241.2 MPa anda fracture toughness of 10.9 MPa·m1/2are obtained although the total porosity reaches 26.0%. Oxidation resistances of the compositesat 1200, 1400 and 1600 ℃ were investigated. Due to the further densification of matrix, the 3D C/mullite composites show tiny massloss and their mechanical properties are well retained after oxidation at 1600 ℃ for 30 min.展开更多
The perovskite-type La_(0.8)Sr_(0.2)CoO_(3) supported on the mullite fiber porous ceramics was prepared by means of the impregnating method,and was then characterized by scanning electron microscopy(SEM)and X-ray diff...The perovskite-type La_(0.8)Sr_(0.2)CoO_(3) supported on the mullite fiber porous ceramics was prepared by means of the impregnating method,and was then characterized by scanning electron microscopy(SEM)and X-ray diffraction(XRD);thus we can come to the conclusion that the perovskite-type composite oxidant can disperse on the surface of mullite fiber ceramics.The catalytic activity of the La_(0.8)Sr_(0.2)CoO_(3) for NO and CO was evaluated.The effect of the doped 0.1 wt-%PdCl_(2) on the catalytic activity of the perovskite-type La_(0.8)Sr_(0.2)CoO_(3) was also discussed.The results show that the conversion rates of NO and CO respectively reaches 74.5% and 99% at 601℃ without doped Pd,and both reach 100%at 350℃ with a little doped Pd.展开更多
基金Project supported by the Ministry of Science and Technology of China (2009AA064801)
文摘The lanthana-doped mullite fibers were prepared via a sol-gel method from the aluminum isopropoxide-aluminum nitrate-tetraethyl orthosilicate system. The structure evolution and thermal stability of the mullite fibers were investigated by means of X-ray diffraction (XRD), Fourier transform infrared (FT-IR) spectroscopy, differential scanning calorimetry (DSC), scanning electron microscopy (SEM) and trans-mission electron microscopy (TEM). The results showed that the fibers obtained after calcination at 1000℃ was in the form of Al2O3-rich mullite, which tended to transform to stoichiometric mullite with the lanthana content increasing. The lattice parameter a exhibited a decline trend with the lanthana content increasing, while b showed an upward tendency. Correspondingly, the redshift of Si-O-Si bond from 1255 to 1245 cm-1 was observed. The grain growth was inhibited for the doped fibers, among which the 5% La2O3-doped sample presented a mini-mum crystallite size (17.2 nm) after calcination at 1000 ℃ for 1 h.
基金Project(SAST2015043)supported by the Science Innovation Foundation of Shanghai Academy of Spaceflight Technology,ChinaProject(614291102010117)supported by the Open Foundation of Science and Technology on Thermostructural Composite Materials Laboratory,ChinaProject(11572277)supported by the National Natural Science Foundation of China
文摘To prepare the three-dimensional braided carbon fiber reinforced mullite (3D C/mullite) composites, an Al2O3-SiO2 solwith a solid content of 20% (mass fraction) and an Al2O3/SiO2 mass ratio of 2:1 was selected as the raw material. Characteristics andmullitization of the sol were analyzed throughly. It is found that the formation of mullite is basically completed at 1300℃ and thegel powders exhibit favorable sintering shrinkage. The 3D C/mullite composites without interfacial coating were fabricated throughthe route of vacuum impregnation-drying-heat treatment. Satisfied mechanical properties with a flexural strength of 241.2 MPa anda fracture toughness of 10.9 MPa·m1/2are obtained although the total porosity reaches 26.0%. Oxidation resistances of the compositesat 1200, 1400 and 1600 ℃ were investigated. Due to the further densification of matrix, the 3D C/mullite composites show tiny massloss and their mechanical properties are well retained after oxidation at 1600 ℃ for 30 min.
基金The work was supported by the National Natural Science Foundation of China(Grant No.50276017)the Natural Science Foundation of Guangdong Province,China(Grant No.2005B10301026).
文摘The perovskite-type La_(0.8)Sr_(0.2)CoO_(3) supported on the mullite fiber porous ceramics was prepared by means of the impregnating method,and was then characterized by scanning electron microscopy(SEM)and X-ray diffraction(XRD);thus we can come to the conclusion that the perovskite-type composite oxidant can disperse on the surface of mullite fiber ceramics.The catalytic activity of the La_(0.8)Sr_(0.2)CoO_(3) for NO and CO was evaluated.The effect of the doped 0.1 wt-%PdCl_(2) on the catalytic activity of the perovskite-type La_(0.8)Sr_(0.2)CoO_(3) was also discussed.The results show that the conversion rates of NO and CO respectively reaches 74.5% and 99% at 601℃ without doped Pd,and both reach 100%at 350℃ with a little doped Pd.