The effects of the initial framework SiO2/Al2O3 ratio and temperature on the structural changes of NaY zeolites during hydrothermal treatments are studied. Two samples with different framework SiO2/Al2O3 ratios are ...The effects of the initial framework SiO2/Al2O3 ratio and temperature on the structural changes of NaY zeolites during hydrothermal treatments are studied. Two samples with different framework SiO2/Al2O3 ratios are subjected to hydrothermal treatment at four different temperatures. For zeolite with a lower initial SiO2/Al2O3 ratio of 4.2, mesopores are easily formed because more framework aluminum is detached. Moreover, two kinds of mesopores are produced at a higher temperature due to the interconnection of vacancies and smaller mesopores. For zeolite with a higher initial SiO2/Al2O3 ratio of 6.0, there are less mesopores formed as compared with the lower initial SiO2/Al2O3 ratio sample, but there are some macropores formed. This may be attributed to the isolation of vacancies and the different distributions of aluminum in the crystal lattice of the zeolite. The experiment data show that NaY with the SiO2/Al2O3 ratio of 6.0 retains a high relative crystallinity during the hydrothermal treatment. This proves that a high framework SiO2/Al2O3 ratio benefits the stability of zeolite.展开更多
Three-dimensional （3D） five-directional braided （SiO2）/SiO2 composites were prepared by silicasol-infiltration-sintering （SIS） method. The flexural properties and microstructures were studied. The flexural stren...Three-dimensional （3D） five-directional braided （SiO2）/SiO2 composites were prepared by silicasol-infiltration-sintering （SIS） method. The flexural properties and microstructures were studied. The flexural strength and flexural elastic modulus were found to be 73 MPa and 12 GPa, respectively. The results of stress vs deflection curve and SEM examinations revealed that the fracture mechanism of 3D, five-directional braided （SiO2）/SiO2 composite was a mixture mode of ductile and brittle. The ductile mode was attributed to the weak bonding strength of fiber/matrix at low temperature. The brittle fracture might be caused by the propagation of micro defect or crack, which existed in the as-prepared composites for the ten-cycle process.展开更多
文摘The effects of the initial framework SiO2/Al2O3 ratio and temperature on the structural changes of NaY zeolites during hydrothermal treatments are studied. Two samples with different framework SiO2/Al2O3 ratios are subjected to hydrothermal treatment at four different temperatures. For zeolite with a lower initial SiO2/Al2O3 ratio of 4.2, mesopores are easily formed because more framework aluminum is detached. Moreover, two kinds of mesopores are produced at a higher temperature due to the interconnection of vacancies and smaller mesopores. For zeolite with a higher initial SiO2/Al2O3 ratio of 6.0, there are less mesopores formed as compared with the lower initial SiO2/Al2O3 ratio sample, but there are some macropores formed. This may be attributed to the isolation of vacancies and the different distributions of aluminum in the crystal lattice of the zeolite. The experiment data show that NaY with the SiO2/Al2O3 ratio of 6.0 retains a high relative crystallinity during the hydrothermal treatment. This proves that a high framework SiO2/Al2O3 ratio benefits the stability of zeolite.
基金Funded by the Basic Research Project of Science and Technology of Jiangsu Province(No.BK2009002)the National Natural ScienceFoundation of China(No.61176062)the Fundamental Research Funds for the Central Universities(No.NS2013061)
文摘Three-dimensional （3D） five-directional braided （SiO2）/SiO2 composites were prepared by silicasol-infiltration-sintering （SIS） method. The flexural properties and microstructures were studied. The flexural strength and flexural elastic modulus were found to be 73 MPa and 12 GPa, respectively. The results of stress vs deflection curve and SEM examinations revealed that the fracture mechanism of 3D, five-directional braided （SiO2）/SiO2 composite was a mixture mode of ductile and brittle. The ductile mode was attributed to the weak bonding strength of fiber/matrix at low temperature. The brittle fracture might be caused by the propagation of micro defect or crack, which existed in the as-prepared composites for the ten-cycle process.
