分类： 物理学 >> 凝聚态:结构、力学和热性能 提交时间： 2017-03-26
摘要： Dislocations would be induced after plastic deformation, which might change the mechanical properties of solids. FeCrNi austenitic model alloy and its Mo-diluted alloy were cold rolled with different degree of thickness reduction. Positrons are sensitive to point defects, which are easily trapped and annihilated around the trapping sites. The mean positron lifetimes have been used to estimate the average dislocation concentration in solids. Meanwhile, the trapping efficiency μ was calculated from the lifetime results. The trapping efficiency value is estimated about 3.31×10-7 cm3s-1 for FeCrNi alloy and 3.31×10-7 cm3s-1 for Mo-diluted alloy, respectively. The increment of the hardness value during plastic deformation is related to the increase of the dislocation density and dislocation pile up in solids.
分类： 物理学 >> 凝聚态:结构、力学和热性能 提交时间： 2017-03-26
Jing Zhang
Abu Zayed Mohammad Saliqur Rahman
Yuxiao Li
Jing Yang
Bozhen Zhao
Eryang Lu
Peng Zhang
Xingzhong Cao
Runsheng Yu
Baoyi Wang
摘要： A series of Sm-doped LDPE-Na2SO4 composites were successfully achieved by melt mixing and hot pressing methods. Their morphology, structure and luminescent properties were characterized by scanning electron microscope (SEM), Energy Dispersive X-ray spectroscopy (EDX), X-ray diffraction (XRD) and photoexcitation (PE), photoluminescence (PL) spectra, respectively. The sizes and concentrations of free volume cavities in composites were studied by positron annihilation lifetime spectroscopy (PALS). SEM micrographs showed that Na2SO4:Sm3+ particles were well-distributed in the polymer matrix. XRD analyses revealed that the addition of Na2SO4:Sm3+ had no effect on the original crystal structure of LDPE. The dominant photoexcitation peak was observed at about 402 nm. The photoluminescence spectra consisted of four main peaks at 563, 598, 644 and 706 nm which could be associated to the transitions 4G5/2→6HJ (J=5/2, 7/2, 9/2 and 11/2, respectively) within the 4f5 electronic configuration of Sm3+. The effect of different doping concentration of Na2SO4:Sm3+ on the luminescent properties of the composites was investigated. The luminescent intensity of the composites increased with phosphor concentration.
分类： 物理学 >> 凝聚态:结构、力学和热性能 提交时间： 2017-03-23
Jing Zhang
Abu Zayed Mohammad Saliqur Rahman
Yuxiao Li
Jing Yang
Yaru Wu
Daqing Yuan
Xingzhong Cao
Runsheng Yu
Baoyi Wang
摘要： A comparative study on the morphology, structure and luminescence modifications of LDPE–Na2SO4:Sm3+ composite induced by gamma irradiation was reported for the first time. The composites were irradiated with irradiation doses of 10, 30, and 50 kGy in air at room temperature. Modifications on structural and luminescence properties of LDPE–Na2SO4:Sm3+ composites were investigated by using several analytical methods. The X-ray diffraction (XRD) patterns revealed that the cross-linking improved the crystallinity of the composites. Scanning electron microscope (SEM) images illustrated the surface modifications of composites induced by irradiation. Results of positron annihilation lifetime spectroscopy (PALS) suggested that gamma irradiation affected the free volumes concentrations in the samples. The photoluminescence (PL) spectra of non-irradiated and irradiated composites consisted of four main peaks at 563, 598, 644 and 706 nm which could be assigned to the 4G5/2 6HJ (J =5/2, 7/2, 9/2 and 11/2, respectively) transitions within the electronic configuration of Sm3+. Meanwhile, we observed an additional peak at about 686 nm in the irradiated composites, owing to the conversion of Sm3+ Sm2+. Concentrations of the Sm2+ centers linearly increased with gamma irradiation doses, which partly accounted for the degradation of PL intensity of Sm3+ peaks.
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