Effect of Twin/Tilt on the Growth of Graphite

1984 ◽  
Vol 34 ◽  
Author(s):  
Zhu Peiyue ◽  
Sha Rozeng ◽  
Li Yanxiang
Keyword(s):  
Solidification Process ◽  
Twin Plane ◽  
Liquid Interface ◽  
Tilt Boundary ◽  
Twin Defects ◽  
Solid Liquid Interface ◽  
Graphite Growth ◽  
Solid Liquid

ABSTRACTThe effect of twin/tilt initiated in the process of graphite growth making the graphite curling and change from flake to vermicular and spheroidal is discussed. With the developing of the solidification process,the modifying elements enrich in the front of solid-liquid interface, the amount of twin defects in the graphite increases,its tilt fashion changes and the graphite formed varies from flake to vermicular and spheroidal. The modifying elements promote the formation of twin/tilt. When the modifying elements are insufficient for spheroidizing,the tilt orientation of twins is changeable,and the graphite formed is twisted. When the modifying elements are sufficient enough, the tilt orientation of twins becomes singular, and the graphite formed tends to be round. According to the energy and kinetics consideration of the formation of twin/tilt boundary, it is predicted that the twin plane would firstly adopt (10Tm), especially the (10T2) plane. This result coincides well with the experimental observations. It is proposed that the formation of SG can be divided into two steps: growth of graphite nucleus into spherulite by twin/tilt mechanism and brancing on it in a spiral mode.

Numerical Simulation of the Effect of the Size of Nanoparticles on the Solidification Process of Nanoparticle-Enhanced Phase Change Materials

2012 ◽  
Author(s):  
Yousef M. F. El Hasadi ◽  
J. M. Khodadadi
Keyword(s):  
Particle Size ◽  
Phase Change ◽  
Phase Change Materials ◽  
Concentration Field ◽  
Solidification Process ◽  
Liquid Interface ◽  
Constitutional Supercooling ◽  
Fluid Mixture ◽  
Solid Liquid Interface ◽  
Solid Liquid

Nanoparticle-enhanced phase change materials (NEPCM) were proposed recently as alternatives to conventional phase change materials due to their enhanced thermophysical properties. In this study, the effect of the size of the nanoparticles on the morphology of the solid-liquid interface and evolving concentration field, during solidification had been reported. The numerical method that was used is based on the one-fluid-mixture model. The model takes into account the thermal as well as the solutal convection effects. A square cavity model was used in the simulation. The NEPCM that was composed of a suspension of copper nanoparticles in water was solidified from the bottom. The nanoparticles size used were 5 nm and 2 nm. The temperature difference between the hot and cold sides was 5 degrees centigrade and the loading of the nanoparticles that have been used in the simulation was 10% by mass. The results obtained from the model were compared with those existing in the literature, and the comparison was satisfactory. The solid-liquid interface for the case of NEPCM with 5 nm particle size was almost planar throughout the solidification process. However, for the case of the NEPCM with particle size of 2 nm, the solid-liquid interface evolved from a planar stable shape to an unstable dendritic shape, as the solidification process proceeded with time. This was attributed to the constitutional supercooling effect. It has been observed that the constitutional supercooling effect is more pronounced as the particle size decreases. Furthermore, the freezing time increases as the particle size decreases.

Numerical Simulation on the Heat Transfer Performance of Multicrystalline Silicon in Directional Solidification Process

2013 ◽  
Vol 444-445 ◽  
pp. 1412-1416 ◽  
Author(s):  
Xi Yang ◽  
Ming Li ◽  
Wen Hui Ma ◽  
Guo Qiang Lv ◽  
Tao Luo ◽  
...  
Keyword(s):  
Temperature Field ◽  
Temperature Distribution ◽  
Directional Solidification ◽  
Solidification Process ◽  
Liquid Interface ◽  
Multicrystalline Silicon ◽  
Interface Shape ◽  
Directional Solidification Process ◽  
Solid Liquid Interface ◽  
Solid Liquid

The temperature distribution has important influence on the position and shape of solid-liquid interface during directional solidification process. So the calculation of temperature field is fairly significant for both structural analysis and temperature control. In this paper, the finite element method is applied to establish the 2D axisymmetric model for modeling the temperature distribution and the solid-liquid interface shape of multicrystalline silicon in semi-industrial directional solidification furnace. The numerical results show that the temperature field and solid-liquid interface shape can be controlled by adjusting the pulling rate in directional solidification process, and an optimized pulling rate of this system was obtained for large diameter silicon crystals with low defect density and uniform dopant distribution.

Numerical Simulation of the Effect of the Size of Suspensions on the Solidification Process of Nanoparticle-Enhanced Phase Change Materials

2013 ◽  
Vol 135 (5) ◽  
Author(s):  
Yousef M. F. El Hasadi ◽  
J. M. Khodadadi
Keyword(s):  
Thermal Conductivity ◽  
Particle Size ◽  
Phase Change ◽  
Phase Change Materials ◽  
Solidification Process ◽  
Liquid Interface ◽  
Local Concentration ◽  
Solutal Convection ◽  
Solid Liquid Interface ◽  
Solid Liquid

Nanostructure-enhanced phase change materials (NePCM) have been widely studied in recent years due to their enhanced thermal conductivity and improved charge/discharge in thermal energy storage applications. In this study, the effect of the size of the nanoparticles on the morphology of the solid–liquid interface and the evolving concentration field during solidification is reported. Combining a one-fluid-mixture approach with the single-domain enthalpy-porosity model for phase change and assuming a linear dependence of the liquidus and solidus temperatures of the mushy zone on the local concentration of the nanoparticles subject to a constant value of the segregation coefficient, thermal-solutal convection as well as the Brownian and thermophoretic effects are taken into account. A square cavity containing a suspension of copper nanoparticles (diameter of 5 and 2 nm) in water was the model NePCM considered. Subject to a 5 °C temperature difference between the hot (top) and cold (bottom) sides and with an initial loading of the nanoparticles equal to 10 wt. % (1.22 vol. %), the colloid was solidified from the bottom. The solid–liquid interface for the case of NePCM with 5 nm particle size was almost planar throughout the solidification process. However, for the case of the NePCM with particle size of 2 nm, the solid–liquid interface evolved from a stable planar shape to an unstable dendritic structure. This transition was attributed to the constitutional supercooling effect, whereby the rejected particles that are pushed away from the interface into the liquid zone form regions of high concentration thus leading to a lower solidus temperature. Moreover, for the smaller particle size of 2 nm, the ensuing solutal convection at the liquid–solid interface due to the concentration gradient is affected by the increased Brownian diffusivity. Due to size-dependent rejection of nanoparticles, the frozen layer that resulted from a dendritic growth contains regions of depleted concentration. Despite the higher thermal conductivity of the colloids, the amount of frozen phase during a fixed time period diminished as the particle size decreased.

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