24,698 research outputs found
The influence of compact and ordered carbon coating on solid-state behaviors of silicon during electrochemical processes
To address the issues of large volume change and low conductivity of silicon (Si) materials, carbon coatings have been widely employed as surface protection agent and conductive medium to encapsulate the Si materials, which can improve the electrochemical performance of Si-based electrodes. There has been a strong demand to gain a deeper understanding of the impact of efficient carbon coating over the lithiation and delithiation process of Si materials. Here, we report the first observation of the extended two-phase transformation of carbon-coated Si nanoparticles (Si/C) during electrochemical processes. The Si/C nanoparticles were prepared by sintering Si nanoparticles with polyvinylidene chloride precursor. The Si/C electrode underwent a two-phase transition during the first 20 cycles at 0.2 C, but started to engage in solid solution reaction when the ordered compact carbon coating began to crack. Under higher current density conditions, the electrode was also found to be involved in solid solution reaction, which, however, was due to the overwhelming demand of kinetic property rather than the breaking of the carbon coating. In comparison, the Si/C composites prepared with sucrose possessed more disordered and porous carbon structures, and presented solid solution reaction throughout the entire cycling process
Evolution of pore structure, submaceral composition and produced gases of two Chinese coals during thermal treatment
This research was funded by the Research Program for Excellent Doctoral Dissertation Supervisor of Beijing (grant no. YB20101141501), the Fundamental Research Funds for Central Universities (grant no. 35832015136) and Key Project of Coal-based Science and Technology in Shanxi Province-CBM accumulation model and reservoir evaluation in Shanxi province (grant no. MQ2014-01).Peer reviewedPostprin
Phase Field Characterization of Rock Fractures in Brazilian Splitting Test Specimens Containing Voids and Inclusions
The Brazilian splitting test is a widely used testing procedure for
characterizing the tensile strength of natural rock or rock-like material due
to the fact. However, the results of Brazilian tests on specimens with
naturally existing voids and inclusions are strongly influenced by size effects
and boundary conditions, while numerical modeling can assist in explaining and
understanding the mechanisms. On the other hand, the potential of utilizing
Brazilian test to characterize inhomogeneous deformation of rock samples with
voids and inclusions of dissimilar materials still awaits to be explored. In
the present study, fracture mechanisms in Brazilian discs with circular voids
and filled inclusions are investigated by using the phase field model (PFM).
The PFM is implemented within the framework of finite element method to study
the influence of diameter, eccentricity, and quantity of the voids and
inclusions on the fracture patterns and stress-strain curves. The phase field
simulations can reproduce previous experimental phenomena and furthermore it
deepens the understanding of the influence of inclusion and voids on the
fracture pattern, overall strength and deformation behavior of inhomogeneous
rock. The findings in the study highlight the potential of characterizing
inhomogeneous rock through combining Brazilian tests and numerical modeling
Aspect ratio dependence of heat transport by turbulent Rayleigh-B\'{e}nard convection in rectangular cells
We report high-precision measurements of the Nusselt number as a
function of the Rayleigh number in water-filled rectangular
Rayleigh-B\'{e}nard convection cells. The horizontal length and width
of the cells are 50.0 cm and 15.0 cm, respectively, and the heights ,
25.0, 12.5, 6.9, 3.5, and 2.4 cm, corresponding to the aspect ratios
, , ,
, , and . The measurements were carried out
over the Rayleigh number range and the
Prandtl number range . Our results show that for
rectangular geometry turbulent heat transport is independent of the cells'
aspect ratios and hence is insensitive to the nature and structures of the
large-scale mean flows of the system. This is slightly different from the
observations in cylindrical cells where is found to be in general a
decreasing function of , at least for and larger. Such a
difference is probably a manifestation of the finite plate conductivity effect.
Corrections for the influence of the finite conductivity of the top and bottom
plates are made to obtain the estimates of for plates with
perfect conductivity. The local scaling exponents of are calculated and found to increase from 0.243 at
to 0.327 at .Comment: 15 pages, 7 figures, Accepted by Journal of Fluid Mechanic
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