The low field nuclear magnetic resonance (NMR), as a nondestructive and noninvasive technique, was employed to investigate the water distribution and content in cement paste with different water-to-cement ratio (w/c r...The low field nuclear magnetic resonance (NMR), as a nondestructive and noninvasive technique, was employed to investigate the water distribution and content in cement paste with different water-to-cement ratio (w/c ratio) during early and later hydration stages. From the water distribution spectrum deduced from relaxation time distribution in paste, it is suggested that the water fills in the capillary pores at initial period, and then diffuses to the mesopores and gel pores in hydration products with the hydration proceeding. The decrease of peak area in water distribution spectrum reflects the transformation from physically bound water to chemically bound water. In addition, based on the connection between relaxation time and pore size, the relative content changes of water in various states and constrained in different types of pores were also measured. The results demonstrate that it is influenced by the formation of pore system and the original water-to-cement ratio in the paste. Consequently, the relative content of capillary water is dropped to less than 2% in the paste with low w/c ratio of 0.3 when being hydrated for 1 d, while the contents are still 16% and 36% in the pastes with w/c ratios of 0.4 and 0.5, respectively.展开更多
The effect of precipitation on the internal friction(IF)of AZ91 magnesium alloy was investigated by using X-ray diffraction(XRD)analysis,scanning electron microscope(SEM)observation,and dynamic mechanical analysis(DMA...The effect of precipitation on the internal friction(IF)of AZ91 magnesium alloy was investigated by using X-ray diffraction(XRD)analysis,scanning electron microscope(SEM)observation,and dynamic mechanical analysis(DMA).Six different states of alloy were prepared by applying different heat treatment processes:as-cast,in-complete solid solution,complete solid solution,micro-precipitation,continuous precipitation and continuous-discontinuous precipitation.It was found that the internal friction of in-completely solid-solutionized,completely solid-solutionized and micro-precipitated specimens showed a similar characteristic,and the grain boundary relaxation is completed depressed due to the Al atoms supersaturated in theα-Mg solution.However,a thermal relaxation internal friction peak was observed for continuously precipitated and continuously-discontinuously precipitated specimens at around 438 K and frequency of about 1 Hz,which was attributed to the grain boundaries relaxation.Furthermore,it was found that the relaxation of theβ-Mg17Al12/α-Mg phase interfaces should give its contribution to the background internal friction in the as-cast,continuously precipitated and continuously-discontinuously precipitated specimens.展开更多
A 3D mixed-valence Co（Ⅲ）-Co（Ⅱ） compound [Co9（bta）10（Hbta）2（H2O）10]n·[22（H2O）]n （1） （H2bta=N,N-bis（1H-tetrazole-5- yl）-amine） was hydrothermally synthesized by reaction of Co（NO3）2·6H2O ...A 3D mixed-valence Co（Ⅲ）-Co（Ⅱ） compound [Co9（bta）10（Hbta）2（H2O）10]n·[22（H2O）]n （1） （H2bta=N,N-bis（1H-tetrazole-5- yl）-amine） was hydrothermally synthesized by reaction of Co（NO3）2·6H2O with H2bta·H2O. Compound 1 consists of three kinds of distorted-octahedral [CoⅡ（N4O2）] paramagnetic nodes which are separated by [CoⅢ（bta）2（Hbta）]2-/[CoⅢ（bta）3]3- dia- magnetic linkers to generate a 3D porous metal-organic framework （MOF） with alternative …Co（Ⅲ）…Co（II）… array and channels incorporating water molecules. Under an applied magnetic field of 4000 Oe, compound 1 exhibits slow relaxation of magnetization at low temperatures, giving AE/kB=30.O0 K and ι0=2.0×10^-8 s.展开更多
基金Project(2009CB623105) supported by the National Basic Research Program of ChinaProject(51108341) supported by the National Natural Science Foundation of ChinaProjects(20110490703, 2012T50437) supported by China Postdoctoral Science Foundation
文摘The low field nuclear magnetic resonance (NMR), as a nondestructive and noninvasive technique, was employed to investigate the water distribution and content in cement paste with different water-to-cement ratio (w/c ratio) during early and later hydration stages. From the water distribution spectrum deduced from relaxation time distribution in paste, it is suggested that the water fills in the capillary pores at initial period, and then diffuses to the mesopores and gel pores in hydration products with the hydration proceeding. The decrease of peak area in water distribution spectrum reflects the transformation from physically bound water to chemically bound water. In addition, based on the connection between relaxation time and pore size, the relative content changes of water in various states and constrained in different types of pores were also measured. The results demonstrate that it is influenced by the formation of pore system and the original water-to-cement ratio in the paste. Consequently, the relative content of capillary water is dropped to less than 2% in the paste with low w/c ratio of 0.3 when being hydrated for 1 d, while the contents are still 16% and 36% in the pastes with w/c ratios of 0.4 and 0.5, respectively.
文摘The effect of precipitation on the internal friction(IF)of AZ91 magnesium alloy was investigated by using X-ray diffraction(XRD)analysis,scanning electron microscope(SEM)observation,and dynamic mechanical analysis(DMA).Six different states of alloy were prepared by applying different heat treatment processes:as-cast,in-complete solid solution,complete solid solution,micro-precipitation,continuous precipitation and continuous-discontinuous precipitation.It was found that the internal friction of in-completely solid-solutionized,completely solid-solutionized and micro-precipitated specimens showed a similar characteristic,and the grain boundary relaxation is completed depressed due to the Al atoms supersaturated in theα-Mg solution.However,a thermal relaxation internal friction peak was observed for continuously precipitated and continuously-discontinuously precipitated specimens at around 438 K and frequency of about 1 Hz,which was attributed to the grain boundaries relaxation.Furthermore,it was found that the relaxation of theβ-Mg17Al12/α-Mg phase interfaces should give its contribution to the background internal friction in the as-cast,continuously precipitated and continuously-discontinuously precipitated specimens.
基金supported by the National Natural Science Foundation of China(21373162,21127004,21173168,21203149,21463020)the Natural Science Foundation of Shaanxi Province(11JS110,FF10091,SJ08B09)
文摘A 3D mixed-valence Co（Ⅲ）-Co（Ⅱ） compound [Co9（bta）10（Hbta）2（H2O）10]n·[22（H2O）]n （1） （H2bta=N,N-bis（1H-tetrazole-5- yl）-amine） was hydrothermally synthesized by reaction of Co（NO3）2·6H2O with H2bta·H2O. Compound 1 consists of three kinds of distorted-octahedral [CoⅡ（N4O2）] paramagnetic nodes which are separated by [CoⅢ（bta）2（Hbta）]2-/[CoⅢ（bta）3]3- dia- magnetic linkers to generate a 3D porous metal-organic framework （MOF） with alternative …Co（Ⅲ）…Co（II）… array and channels incorporating water molecules. Under an applied magnetic field of 4000 Oe, compound 1 exhibits slow relaxation of magnetization at low temperatures, giving AE/kB=30.O0 K and ι0=2.0×10^-8 s.
