We study the electronic, phonon vibration, thermal, and optical properties of an orthorhombic BC2N structure with two different space groups, PMM2 and P2221. The two phases are identified as BC2N-1 ...and BC2N-2, respectively. The calculations of the phonon band structure and the molecular dynamic simulations confirm that both phases of BC2N are dynamically and thermally stable. BC2N-2 has a higher symmetry than BC2N-1 causing more degenerate energy levels around the Fermi energy leading a larger band gap of BC2N-2. The BC2N-2 has also more phonon bands as it has more atoms per unit-cell leading to a higher phonon density of states and heat capacity. However, the group velocity of both phases is similar, but the lattice thermal conductivity of BC2N-2 is higher due to its high heat capacity. Furthermore, both phases of BC2N have optical response in the visible light region with different refractive indices and reflectivities. Finally, most of the physical properties of the orthorhombic BC2N are compared to other phases of the structure such as the hexagonal monolayer, the nanoribbon, the nanotube, and the porous tetragonal shape.
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•High lattice thermal conductivity is found for orthorhombic BC2N.•Two different phase groups of BC2N give different electronic and optical behaviors.•Orthorhombic BC2N is dynamically and thermally stable.•Group velocity of orthorhombic BC2N does not sensitive for space groups.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
Thermal conductive polymer composites attract lots of research due to the continuous miniaturization and multi-function of electronic equipment. As a common ceramic, Al2O3 owns relatively high ...thermal conductivity, high electrical resistivity and satisfactory cost performance, which is considered as the high-quality filler to prepare thermal conductive and electrical insulated composites. This paper reviews current progress in the development of Al2O3 reinforced polymer composites. We firstly summarize the preparation methods of spherical Al2O3, then heat conduction mechanisms and main factors affecting thermal conductivity are introduced. Next, we focus on the common research of Al2O3 in improving the thermal conductivity of polymers, including surface modification, filler hybridization and construction of Al2O3 network by various processing methods, and some emerging applications of thermal conductive polymer composites are introduced subsequently. After a critique of recent studies, we identify several outstanding issues must be addressed if higher thermal conductivity is fully realized.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
This article presents a numerical investigation on heat transfer performance and pressure drop of nanofluids flows through a straight circular pipe in a laminar flow regime and constant heat flux ...boundary condition. Al
2O
3, CuO, carbon nanotube (CNT) and titanate nanotube (TNT) nanoparticles dispersed in water and ethylene glycol/water with particle concentrations ranging between 0 and 6
vol.% were used as working fluids for simulating the heat transfer and flow behaviours of nanofluids. The proposed model has been validated with the available experimental data and correlations. The effects of particle concentrations, particle diameter, particles Brownian motions, Reynolds number, type of the nanoparticles and base fluid on the heat transfer coefficient and pressure drop of nanofluids were determined and discussed in details. The results indicated that the particle volume concentration, Brownian motion and aspect ratio of nanoparticles similar to flow Reynolds number increase the heat transfer coefficient, while the nanoparticle diameter has an opposite effect on the heat transfer coefficient. Finally, the present study provides some considerations for the appropriate choice of the nanofluids for practical applications.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
We derive, implement, and apply equilibrium solvation site analysis for biomolecules. Our method utilizes 3D-RISM calculations to quickly obtain equilibrium solvent distributions without either ...necessity of simulation or limits of solvent sampling. Our analysis of these distributions extracts highest likelihood poses of solvent as well as localized entropies, enthalpies, and solvation free energies. We demonstrate our method on a structure of HIV-1 protease where excellent structural and thermodynamic data are available for comparison. Our results, obtained within minutes, show systematic agreement with available experimental data. Further, our results are in good agreement with established simulation-based solvent analysis methods. This method can be used not only for visual analysis of active site solvation but also for virtual screening methods and experimental refinement.
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IJS, KILJ, NUK, PNG, UL, UM
•Aromatic bismaleimides and aliphatic bismaleimides were prepared.•Aliphatic bismaleimides have lower activation energy.•Aromatic bismaleimides possess superior thermal stability and lower dielectric ...loss.•Aliphatic bismaleimides exhibit lower dielectric constant and low water absorption.
In this paper, three aromatic bismaleimides (BMI-70, BMI-DE and BMI-80) and two aliphatic bismaleimides (BMI-DDA and BMI-C36) were synthesized. The structures were characterized using nuclear magnetic resonance (NMR) spectra and Fourier transform infrared (FT-IR) spectra. Their polymerization behaviors were discussed by non-isothermal differential scanning calorimetry (DSC). The thermal and dielectric properties of the poly(bismaleimide) were investigated using thermogravimetric analysis (TGA), dynamic thermo-mechanical analysis (DMA), and an impedance analyzer. The results indicate that the aliphatic bismaleimides exhibit lower apparent activation energies and dielectric properties, with BMI-DDA displaying an average activation energy of 105.5 kJ mol−1 and the dielectric constant of P(BMI-C36) is 2.558 @ 10 MHz. The aromatic polybismaleimides possessed better thermal stability, among which, the 5 % thermal decomposition temperature (Td,5) of P(BMI-70) was 513.5 °C, and the residual carbon rate at 800 °C was 44.6 %. In additional, water absorption was studied and their saturated water absorption was less than 4 %.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
Using density functional theory (DFT) calculations, we have systematically investigated the thermodynamic properties and structural stabilities of thorium dioxide (ThO2). Based on the calculated ...phonon dispersion curves, we have calculated the thermal expansion coefficient, bulk modulus, and heat capacities at different temperatures for ThO2 under the quasi-harmonic approximation. All the results are in good agreement with corresponding experiments proving the validity of our methods. Our theoretical studies can aid a clearer understanding of the thermodynamic behaviors of ThO2 at different temperatures. In addition, we have also studied possible defect formations and diffusion behaviors of helium in ThO2, to discuss its structural stability. It is found that in intrinsic ThO2 without any Fermi energy shifts, the interstitial defect rather than oxygen or thorium vacancies, interstitial oxygen, or any kinds of Frenkel pairs, is the most probable to form with an energy release of 1.74 eV. However, after upshifting the Fermi energy, the formation of the other defects also becomes possible. Regarding helium diffusion, we find that only through the thorium vacancy can it occur with the small energy barrier of 0.52 eV. Otherwise, helium atoms can hardly incorporate or diffuse in ThO2. Our results indicate that upward shifting of the Fermi energy of ThO2 should be prevented to avoid the formation of thorium vacancies so as to avert helium caused damage.
Metal-doped iron silicides (β-FeSi2) are promising thermoelectric materials for high-temperature applications. However, the addition of metal dopants usually causes the formation of secondary ...metallic phases, resulting in the degradation of thermopower. Here we report the stability of semiconducting β-phase (higher than 95 %) of Mn-doped β-FeSi2 obtained at Mn concentration from 1 % to 5 %, where the samples were prepared through direct arc melting and heat treatment process. The carrier density remarkably increases with Mn content, but the mobility decreases. The electrical resistivity significantly decreases with Mn content. The Seebeck coefficient of Mn-doped samples is improved and stable at high-temperature regions because of the reduction of the bipolar effect and β-phase stability. The thermal conductivity slightly increases with Mn. As a result, the maximum thermoelectric power factor PF = 970 μWm−1K−2 and dimensionless figure of merit ZT = 0.12 at 800 K are obtained in a 3 % Mn-doped sample. The stability of β-phase and the improved carrier density are the origins of enhanced thermoelectric properties, where the Seebeck coefficient is improved, and the electrical resistivity is reduced. Our study provides insight into the importance of phase stability for enhancing thermoelectric transport in Mn-doped β-FeSi2.
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•We investigate phase stability and thermoelectric properties of β-Fe1−xMnxSi2.•95 % of semiconducting phase β-FeSi2 is stabilized for Mn content up to 5 %.•The addition of Mn significantly increases the carrier density.•β-FeSi2 stability and increased carrier density improve thermoelectric properties.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
We use density-functional theory and the nonequilibrium Green’s function method as well as phonon dispersion calculations to study the thermal conductance of graphene nanoribbons with armchair and ...zigzag edges, with and without hydrogen passivation. We find that low-frequency phonon bands of the zigzag ribbons are more dispersive than those of the armchair ribbons and that this difference accounts for the anisotropy in the thermal conductance of graphene nanoribbons. Comparing our results with data on large-area graphene, edge effects are shown to contribute to thermal conductance, enhance the anisotropy in thermal conductance of graphene nanoribbons, and increase thermal conductance per unit width. The edges with and without hydrogen passivation modify the atomic structure and ultimately influence the phonon thermal transport differently for the two ribbon types.
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This work is focused on the numerical modeling of steady laminar mixed convection flow in single and double-lid square cavities filled with a water–Al2O3 nanofluid. Two viscosity models are used to ...approximate nanofluid viscosity, namely, the Brinkman model and the Pak and Cho correlation. The developed equations are given in terms of the stream function–vorticity formulation and are non-dimensionalized and then solved numerically by a second-order accurate finite-volume method. Comparisons with previously published work are performed and found to be in good agreement. A parametric study is conducted and a selective set of graphical results is presented and discussed to illustrate the effects of the presence of nanoparticles and the Richardson number on the flow and heat transfer characteristics in both cavity configurations and to compare the predictions obtained by the two different nanofluid models. It is found that significant heat transfer enhancement can be obtained due to the presence of nanoparticles and that this is accentuated by increasing the nanoparticle volume fractions at moderate and large Richardson numbers using both nanofluid models for both single- and double-lid cavity configurations. However, for small Richardson number, the Pak and Cho model predicts that the presence of nanoparticle causes reductions in the average Nusselt number in the single-lid cavity configuration.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
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