The crystallization behaviour of the laser synthesized nanometric amorphous Si3N4 powders with the particle size of 15 nm in diameter has been studied between 1200° and 1700℃ by XRD,TEM and FTIR techniques. A sm...The crystallization behaviour of the laser synthesized nanometric amorphous Si3N4 powders with the particle size of 15 nm in diameter has been studied between 1200° and 1700℃ by XRD,TEM and FTIR techniques. A small amount of β-Si3N4 formed at 1250℃ and increased slowly until the α- β transformation happened at 1700℃, whereas α-Si3N4 appeared at 1300℃ andincreased rapidly between 1500-1600℃. The formation of β phase at the lower temperature was caused by the nitridation of free Si due to the preexisted β-nuclei in the Si3N4 particles, whereasthe α phase was formed by solid crystallization from the amorphous matrix. There were α and β SiC formed at 1700℃ due to the presence of Sio and Co gases in the system. FTIR analysis shows that two new IR absorption at 1356 and 1420 cm-1, and an overall strong absorption in wide wavenumber range resulted from the powders annealed at 1600 and 1700℃ respectively展开更多
The objectives of this paper are to understand the crystallization behavior of polypropylene （PP） composites with surface modified tetra-needle-shaped zinc oxide whisker （T-ZnOw）. T-ZnOw was surface modified with ...The objectives of this paper are to understand the crystallization behavior of polypropylene （PP） composites with surface modified tetra-needle-shaped zinc oxide whisker （T-ZnOw）. T-ZnOw was surface modified with different coupling agents, such as silane coupling agents （KH-550, KH-560） and titanate coupling agent （NDZ-105）, in order to improve the compatibility between PP and T-ZnOw. DSC and POM were used to characterize the melt and crystallization behavior and the crystalline structures of the composites, respectively. The results show that the surface modified T-ZnOw acts as a nucleating agent of PP crystallization, depending on the coupling agent used for modification. KH-550 and KH-560 have more apparent role in improving the interfacial interaction than NDZ-105 and induce PP crystallization at higher temperature and with smaller spherulites size. The results also suggest that the crystallization behavior depends on not only the content of coupling agent, but also the content of the surface modified T-ZnOw used in the composites.展开更多
The crystalline behavior of urethane substitute polydiacetylene was studied by using pohrized light and electron microscopy. The lamellar morphological structure was observed in the crystallized films. The thickness o...The crystalline behavior of urethane substitute polydiacetylene was studied by using pohrized light and electron microscopy. The lamellar morphological structure was observed in the crystallized films. The thickness of lamellae is about 300A, being independent of the crystalline temperature. But the size and density of lamellae were dependent on the crystallization temperature. If the molten film was sheared during the crystallzation process the oriented lamellae grew with their long axes perpendicular to the direction of shear and the chain direction was normal to the lamellar surface.展开更多
The effect of different initial microstructures deftned by γ' precipitate morphology has been investigated at the creep/fatigue conditions of 900℃ and 500 MPa. The wave form of stress as a function of time for c...The effect of different initial microstructures deftned by γ' precipitate morphology has been investigated at the creep/fatigue conditions of 900℃ and 500 MPa. The wave form of stress as a function of time for cyclic load was of trapezoidal shape with a hold time of 10s at the upper stress level. The TEM was employed to examine the deformation process in strengthened γ' matrix in dependence of γ' precipitate morphology. The fracture lifetime and cycle number up to fracture were the criteria to evaluate the additional cyclic component efFect on the course of deformation展开更多
A cross-linkable comonomer containing a diacetylene group,named dimethyl 4,4＇-（buta-l,3-diyne-l,4-diyl）dibenzoate（DA） was synthesized and copolymerized with dimethyl succinate and 1,4-butanediol to prepare a seri...A cross-linkable comonomer containing a diacetylene group,named dimethyl 4,4＇-（buta-l,3-diyne-l,4-diyl）dibenzoate（DA） was synthesized and copolymerized with dimethyl succinate and 1,4-butanediol to prepare a series of slightly cross-linked PBS copolyesters（PBDASx）.The chemical structure,crystallization and Theological behaviours of PBDASx were well investigated.Compared to neat PBS,PBDASx showed the greatly increased crystallization rate because of the promoting nucleation of the cross-linking domains,and the XRD results indicated that it had no influence on crystallization structure of PBS.The rheological behaviours indicate that PBDASx possessed higher viscosity than neat PBS even at high shear rate and temperature.PBDAS0.3 exhibited better comprehensive properties than neat PBS,which will widen applications of PBS.展开更多
文摘The crystallization behaviour of the laser synthesized nanometric amorphous Si3N4 powders with the particle size of 15 nm in diameter has been studied between 1200° and 1700℃ by XRD,TEM and FTIR techniques. A small amount of β-Si3N4 formed at 1250℃ and increased slowly until the α- β transformation happened at 1700℃, whereas α-Si3N4 appeared at 1300℃ andincreased rapidly between 1500-1600℃. The formation of β phase at the lower temperature was caused by the nitridation of free Si due to the preexisted β-nuclei in the Si3N4 particles, whereasthe α phase was formed by solid crystallization from the amorphous matrix. There were α and β SiC formed at 1700℃ due to the presence of Sio and Co gases in the system. FTIR analysis shows that two new IR absorption at 1356 and 1420 cm-1, and an overall strong absorption in wide wavenumber range resulted from the powders annealed at 1600 and 1700℃ respectively
基金This work was supported by the National Natural Science Foundation of China(Youth Foundation:50403019)partly supported by the Opening Project of State Key Laboratory of Polymer Materials Engineering(Sichuan University).
文摘The objectives of this paper are to understand the crystallization behavior of polypropylene （PP） composites with surface modified tetra-needle-shaped zinc oxide whisker （T-ZnOw）. T-ZnOw was surface modified with different coupling agents, such as silane coupling agents （KH-550, KH-560） and titanate coupling agent （NDZ-105）, in order to improve the compatibility between PP and T-ZnOw. DSC and POM were used to characterize the melt and crystallization behavior and the crystalline structures of the composites, respectively. The results show that the surface modified T-ZnOw acts as a nucleating agent of PP crystallization, depending on the coupling agent used for modification. KH-550 and KH-560 have more apparent role in improving the interfacial interaction than NDZ-105 and induce PP crystallization at higher temperature and with smaller spherulites size. The results also suggest that the crystallization behavior depends on not only the content of coupling agent, but also the content of the surface modified T-ZnOw used in the composites.
文摘The crystalline behavior of urethane substitute polydiacetylene was studied by using pohrized light and electron microscopy. The lamellar morphological structure was observed in the crystallized films. The thickness of lamellae is about 300A, being independent of the crystalline temperature. But the size and density of lamellae were dependent on the crystallization temperature. If the molten film was sheared during the crystallzation process the oriented lamellae grew with their long axes perpendicular to the direction of shear and the chain direction was normal to the lamellar surface.
文摘The effect of different initial microstructures deftned by γ' precipitate morphology has been investigated at the creep/fatigue conditions of 900℃ and 500 MPa. The wave form of stress as a function of time for cyclic load was of trapezoidal shape with a hold time of 10s at the upper stress level. The TEM was employed to examine the deformation process in strengthened γ' matrix in dependence of γ' precipitate morphology. The fracture lifetime and cycle number up to fracture were the criteria to evaluate the additional cyclic component efFect on the course of deformation
基金supported financially by the National Natural Science Foundation of China (Nos. 21634006 and 51121001)the Program for Changjiang Scholars and Innovative Research Teams in University of China (No. IRT1026)
文摘A cross-linkable comonomer containing a diacetylene group,named dimethyl 4,4＇-（buta-l,3-diyne-l,4-diyl）dibenzoate（DA） was synthesized and copolymerized with dimethyl succinate and 1,4-butanediol to prepare a series of slightly cross-linked PBS copolyesters（PBDASx）.The chemical structure,crystallization and Theological behaviours of PBDASx were well investigated.Compared to neat PBS,PBDASx showed the greatly increased crystallization rate because of the promoting nucleation of the cross-linking domains,and the XRD results indicated that it had no influence on crystallization structure of PBS.The rheological behaviours indicate that PBDASx possessed higher viscosity than neat PBS even at high shear rate and temperature.PBDAS0.3 exhibited better comprehensive properties than neat PBS,which will widen applications of PBS.
