Thermal conductivity reduction of multilayer graphene with fine grain sizes

JMST Advances ◽  
2019 ◽  
Vol 1 (1-2) ◽  
pp. 191-195 ◽  
Author(s):  
Woomin Lee ◽  
Kenneth David Kihm ◽  
Seung Hwan Ko
Hydrology ◽  
2021 ◽  
Vol 8 (3) ◽  
pp. 98
Author(s):  
Leigh A. Provost ◽  
Robert Weaver ◽  
Nezamoddin N. Kachouie

The changing climate affects the agricultural lands, and, in turn, the changes in agricultural lands alter the watershed. A major concern regarding waterbodies is the increased sedimentation rates due to climate change. To improve the water quality, it is crucial to remove fine sediments. Using current environmental dredging methods is challenging because of the sediment volumes that must be dredged, the absence of nearby disposal sites, and the shoreline infrastructure at the dredging locations. To address these issues, we used a surgical dredging method with a variable area suction head that can easily maneuver around the docks, pilings, and other infrastructures. It can also isolate the fine grain material to better manage the dredged volumes in the seabed where nutrients are typically adhered. To this end, a statistical analysis of the dredged samples is essential to improve the design efficiency. In this work, we collected several samples using a variable area suction head with different design settings. The collected samples using each design setting were then used to model the distributions of the different grain sizes in the dredged sediments. The proposed statistical model can be effectively used for the prediction of sediment sampling outcomes to improve the gradation of the fine sediments.


Author(s):  
Jazael Gómez ◽  
Arturo Estrada ◽  
Argelia Balbuena Ortega ◽  
Oscar Arredondo ◽  
Rocío Nava ◽  
...  

2013 ◽  
Vol 347-350 ◽  
pp. 1171-1175 ◽  
Author(s):  
Bin Wang ◽  
Hong Mei Hu ◽  
Cui Zhou

The transverse properties were inferior to the longitudinal properties for the existence of banded structure in 20G steel. In order to eliminate the banded structure and improve the transverse performance of 20G steel, different heat treatment processes were adopted. The results showed that conventional normalizing could reduce the banded structure and refine the grain sizes. When 20G was heated with 10°C/min heating rated and then held at 920°C for 2h, the banded structure in the steel was almost eliminated and the microstructure was homogeneous with fine grain size, the strength increased by 14%. The non-metallic inclusion and carbide in the microstructure leaded to stress concentration and separation with the base metal. To some extent, heat treatment can improve the distribution and form of non-metallic inclusions.


Materials ◽  
2021 ◽  
Vol 14 (23) ◽  
pp. 7199
Author(s):  
Hyunbin Nam ◽  
Jeongwon Kim ◽  
Namkyu Kim ◽  
Sangwoo Song ◽  
Youngsang Na ◽  
...  

In this study, the carburization characteristics of cast and cold-rolled CoCrFeMnNi high-entropy alloys (HEAs) with various grain sizes were investigated. All specimens were prepared by vacuum carburization at 940 °C for 8 h. The carburized/diffused layer was mainly composed of face-centered cubic structures and Cr7C3 carbide precipitates. The carburized/diffused layer of the cold-rolled specimen with a fine grain size (~1 μm) was thicker (~400 μm) than that of the carburized cast specimen (~200 μm) with a coarse grain size (~1.1 mm). In all specimens, the carbides were formed primarily through grain boundaries, and their distribution varied with the grain sizes of the specimens. However, the carbide precipitates of the cast specimen were formed primarily at the grain boundaries and were unequally distributed in the specific grains. Owing to the non-uniform formation of carbides in the carburized cast specimen, the areas in the diffused layer exhibited various carbide densities and hardness distributions. Therefore, to improve the carburization efficiency of equiatomic CoCrFeMnNi HEAs, it is necessary to refine the grain sizes.


2005 ◽  
Author(s):  
Zhanrong Zhong ◽  
Xinwei Wang

In this work, thermal transport in nanocrystalline materials is studied using large-scale equilibrium molecular dynamics (MD) simulation. Nanocrystalline materials with different grain sizes are studied to explore how and to what extent the size of nanograins affects the thermal conductivity and specific heat. Substantial thermal conductivity reduction is observed and the reduction is stronger for nanocrystalline materials with smaller grains. On the other hand, the specific heat of nanocrystalline materials shows little change with the grain size. The simulation results are compared with the thermal transport in individual nanograins based on MD simulation. Further discussions are provided to explain the fundamental physics behind the observed thermal phenomena in this work.


1994 ◽  
Vol 362 ◽  
Author(s):  
M. A. Otooni

AbstractCrystallization in amorphous materials produces polycrystalline materials with fine grains which can be on the order of 1–2 microns, depending on the extent of annealing. Ductility in these materials with this range of grain sizes is generally low. This paper deals primarily with the lack of ductility in these classes of materials and will present a quasi-mathematical approach to this phenomenon. It will be shown that the influence of the plastic zone, the dislocation-free zone, and the grain size can be expressed by a unique formalism from which the propagation of cracks, and the lack of ductility, can be readily predicted. These deductions will become evident from the results of recent simulation experiments which will provide evidence to support the most essential elements of the approach presented in this paper.


2010 ◽  
Vol 42 (1) ◽  
pp. 69-79 ◽  
Author(s):  
Vesna Paunovic ◽  
Lj. Zivkovic ◽  
V. Mitic

A series of La/Mn, Sm/Mn and Dy/Mn codoped BaTiO3 samples were prepared by the conventional solid state procedure with dopant concentrations ranging from 0.1 up to 2.0 at%. The specimens were sintered at 1320?C and 1350?C in an air atmosphere for two hours. The low doped samples demonstrated a mainly uniform and homogeneous microstructure with average grain sizes ranging from 0.3 ?m to 5.0 ?m. The appearance of secondary abnormal grains in the fine grain matrix and core-shell structure were observed in highly doped La/BaTiO3 and Dy/BaTiO3 sintered at 1350?C. The low doped samples, sintered at 1350?C, display a high value of dielectric permittivity at room temperature, 6800 for Sm/BaTiO3, 5900 for Dy/BaTiO3 and 3100 for La/BaTiO3. A nearly flat permittivity-response was obtained in specimens with 2.0 at% additive content. Using a modified Curie-Weiss law the Curie-like constant C? and a critical exponent ? were calculated. The obtained values of ? pointed out the diffuse phase transformation in heavily doped BaTiO3 samples.


2010 ◽  
Vol 45 (11) ◽  
pp. 1209-1216 ◽  
Author(s):  
A.M. Zihlif ◽  
Ziad Elimat ◽  
G. Ragosta

The thermal, viscoelastic, mechanical behavior of polymers filled with dispersed zeolite and oil shale is studied as a function of temperature, grain size, and filler concentration. It was found that the thermal conductivity of epoxy—zeolite composite increases with different zeolite grain sizes and takes a higher value in case of the 63 μm grain size composite. The observed enhancement in the thermal conductivity of zeolite composites correlates well with that of the electrical conductivity. The thermodynamic results exhibit a slight increase in the glass transition temperature of the polystyrene/oil shale composites, and shift in the observed relaxation peaks with increasing the oil shale content. The plastic deformation of PS/oil shale composites shows that the elastic modulus increases and the compressive yield stress decreases with oil shale content. The Eyring theory of yielding could predict the dependence of the yield stress on the applied strain rate. The predicted activation volume and activation energy showed dependence on the oil shale grains sizes and content.


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