Thermal Transport in 3D Nanostructures Zhan, Haifei; Nie, Yihan; Chen, Yongnan ...
Advanced functional materials,
02/2020, Letnik:
30, Številka:
8
Journal Article
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This work summarizes the recent progress on the thermal transport properties of 3D nanostructures, with an emphasis on experimental results. Depending on the applications, different 3D nanostructures ...can be prepared or designed to either achieve a low thermal conductivity for thermal insulation or thermoelectric devices or a high thermal conductivity for thermal interface materials used in the continuing miniaturization of electronics. A broad range of 3D nanostructures are discussed, ranging from colloidal crystals/assemblies, array structures, holey structures, hierarchical structures, to 3D nanostructured fillers for metal matrix composites and polymer composites. Different factors that impact the thermal conductivity of these 3D structures are compared and analyzed. This work provides an overall understanding of the thermal transport properties of various 3D nanostructures, which will shed light on the thermal management at nanoscale.
Diverse 3D nanostructures are fabricated to meet specific thermal management purposes, including nanoarchitectures (such as colloidal assemblies and carbon nanotube arrays) and nanocomposites from polymer matrix or metal matrix. It is shown that the use of nanostructuring of materials is an effective strategy to modify the thermal conductivity of materials.
The excellent mechanical properties of carbon nanofibers bring promise for energy-related applications. Through in silico studies and continuum elasticity theory, here we show that the ultra-thin ...carbon nanothreads-based bundles exhibit a high mechanical energy storage density. Specifically, the gravimetric energy density is found to decrease with the number of filaments, with torsion and tension as the two dominant contributors. Due to the coupled stresses, the nanothread bundle experiences fracture before reaching the elastic limit of any individual deformation mode. Our results show that nanothread bundles have similar mechanical energy storage capacity compared to (10,10) carbon nanotube bundles, but possess their own advantages. For instance, the structure of the nanothread allows us to realize the full mechanical energy storage potential of its bundle structure through pure tension, with a gravimetric energy density of up to 1.76 MJ kg
, which makes them appealing alternative building blocks for energy storage devices.
Carbon fibres have attracted interest from both the scientific and engineering communities due to their outstanding physical properties. Here we report that recently synthesized ultrathin diamond ...nanothread not only possesses excellent torsional deformation capability, but also excellent interfacial load-transfer efficiency. Compared with (10,10) carbon nanotube bundles, the flattening of nanotubes is not observed in diamond nanothread bundles, which leads to a high-torsional elastic limit that is almost three times higher. Pull-out tests reveal that the diamond nanothread bundle has an interface transfer load of more than twice that of the carbon nanotube bundle, corresponding to an order of magnitude higher in terms of the interfacial shear strength. Such high load-transfer efficiency is attributed to the strong mechanical interlocking effect at the interface. These intriguing features suggest that diamond nanothread could be an excellent candidate for constructing next-generation carbon fibres.
The extremely high thermal conductivity of graphene has received great attention both in experiments and calculations. Obviously, new features in thermal properties are of primary importance for ...application of graphene-based materials in thermal management in nanoscale. Here, we studied the thermal conductivity of graphene helicoid, a newly reported graphene-related nanostructure, using molecular dynamics simulation. Interestingly, in contrast to the converged cross-plane thermal conductivity in multilayer graphene, axial thermal conductivity of graphene helicoid keeps increasing with thickness with a power law scaling relationship, which is a consequence of the divergent in-plane thermal conductivity of two-dimensional graphene. Moreover, the large overlap between adjacent layers in graphene helicoid also promotes higher thermal conductivity than multilayer graphene. Furthermore, in the small strain regime (<10%), compressive strain can effectively increase the thermal conductivity of graphene helicoid, while in the ultra large strain regime (∼100% to 500%), tensile strain does not decrease the heat current, unlike that in generic solid-state materials. Our results reveal that the divergence in thermal conductivity, associated with the anomalous strain dependence and the unique structural flexibility, makes graphene helicoid a new platform for studying fascinating phenomena of key relevance to the scientific understanding and technological applications of graphene-related materials.
Based on the non-equilibrium molecular dynamics simulations, we have studied the thermal conductivities of a novel ultra-thin one-dimensional carbon nanomaterial – diamond nanothread (DNT). Unlike ...single-wall carbon nanotube (CNT), the existence of the Stone-Wales (SW) transformations in DNT endows it with richer thermal transport characteristics. There is a transition from wave-dominated to particle-dominated transport region, which depends on the length of poly-benzene rings. However, independent of the transport region, strong length dependence in thermal conductivity is observed in DNTs with different lengths of poly-benzene ring. The distinctive SW characteristic in DNT provides more to tune the thermal conductivity not found in the homogeneous structure of CNT. Therefore, DNT is an ideal platform to investigate various thermal transport mechanisms at the nanoscale. Its high tunability raises the potential to design DNTs for different applications, such as thermal connection and temperature management.
Single layer diamond—diamane, has been reported with excellent mechanical properties. In this work, molecular dynamics (MD) simulation and Kirchhoff plate model are utilized to investigate the ...vibrational characteristics of diamane sheets. The mechanical parameters of diamane sheets, including bending stiffness, Young’s modulus, Poisson’s ratio and coefficient of thermal expansion, are calibrated by using MD simulations. The natural frequencies and corresponding modal shapes of the diamane sheets predicted by the Kirchhoff plate model agree well with that obtained from the MD simulations. It is found that the edges exert marginal effect on the modal shapes when free boundary conditions are applied. Additionally, the Kirchhoff plate model considering the thermal expansion provides reasonable prediction for the natural frequencies of the diamane sheets with all boundary clamped under varying temperatures. This study offers valuable insights into the vibrational properties of diamane sheets, from both a simulation and theoretical standpoint. The findings would be beneficial for the design of nanoscale mechanical resonators utilizing these novel carbon materials.
•Analytical solution to tooth strength of spiral bevel gear with friction is proposed.•Shear strength check of gears is necessary to be implemented with poor lubrication.•Exact determination of gear ...strength is beneficial in load capacity and performance.•The solution can be extended to investigate load capacity of other mechanism.
Friction is not considered in the calculation of load capacity for spiral bevel gears according to either ISO or AGMA gear standard, and friction effects on the bending, contact and shear of the gears have rarely been discussed. In this regard, the present work establishes analytical solutions to calculate bending and contact strength for spiral bevel gears incorporating friction on the tooth surface, which are verified by ISO gear standard and finite element method (FEM). The bending strength is calculated based on Lewis cantilever beam approximation, utilizing the modified normal force and the friction component. The modified normal force is derived at the highest point of single tooth contact (HPSTC) in the normal equivalent gear. Follow Hertz contact theory, the contact strength is calculated when the modified normal force and the friction component are exerted at the lowest point of single tooth contact (LPSTC) in the normal equivalent gear. The calculated bending and contact stresses agree well with those obtained from the FEM analysis while considering the influence of friction. Both theoretical predictions and FEM analysis have shown that friction has a crucial effect on load capacity of a spiral bevel gear drive, and that it exerts stronger influence on the bending strength (compared with the contact strength). When friction coefficients become larger (with the same input torque), the bending stress considering only the modified normal force decreases at HPSTC, whereas it increases if both the modified normal force and the friction component are included. In comparison, the contact stress will increase at LPSTC under both scenarios. Furthermore, it is illustrated that shear strength check of the tooth is necessary as large friction occurs in the contact zone. This developed analytical solution can be well applied to the determination of load capacity of spiral bevel gears, especially under harsh working conditions or in the demand for higher performance.
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•A toughened ZrO2/MgO nanocomposite coating is in-situ synthesized during the plasma electrolytic oxidation process (PEO).•The ZrO2/MgO toughening behavior occurs with dislocation ...slipping and pinning caused by semicoherent interface lattice distortion.•The toughness (KIC) of the ZrO2/MgO nanocomposite coating is 2.7 times that of the traditional PEO coating.
Ceramic coatings are in general a kind of brittle material because they are predominantly made up of ionic crystals that avoid dislocation motion caused by lattice distortion. In this regard, a remarkable toughened ZrO2/MgO nanocomposite coating is obtained by the plasma electrolytic oxidation (PEO) process and in-situ synthesized ZrO2 with quantitative control approach. It is revealed that the toughening behavior of the ZrO2/MgO coating is related to the coordination and diversion of lattice distortion at the metallic oxide interface, which induces distinct dislocation motion at the interface. The semicoherent interface between m-ZrO2 and MgO is verified to act as a buffer to realize toughening of the nanocomposite coating through dislocation slipping induced by lattice coordinated distortion. Simultaneously, significant interfacial lattice distortion transfer and dislocation pinning are discovered at the semicoherent interface between t-ZrO2 and MgO, which are beneficial to toughness enhancement of the nanocomposite coating. The results indicate that the toughening effect occurs along with dislocation slipping and pinning caused by lattice distortion of the ZrO2/MgO semicoherent interface, which enables the toughness of novel nanocomposite coating to reach 2.7 times of the traditional PEO coating.
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•The negative linear correlation between phase transition temperature and grain size of t-ZrO2 was established.•t-ZrO2 achieves phase stability, which cannot occur martensitic ...transformation when grain size below the critical size.•The dislocation tangle and interfacial cohesion enhance the stability of t-ZrO2.
In this work, the trade-off between transformation toughening of ZrO2/TiO2 ceramic coatings and low temperature (293.15 K∼203.15 K) was achieved by adjusting the grain size of t-ZrO2 (dt-ZrO2). A negative correlation between dt-ZrO2 and phase transition temperature (Ms) was also established based on strain energy and chemical free energy in ZrO2/TiO2 ceramic coatings. Interestingly, t-ZrO2 grains lost toughening effects when the dt-ZrO2 reaches the critical size (20 nm) even under cooling and stress. This is attributed to the number of dislocations per unit volume increases 1.5 times with the dt-ZrO2 decreases from 40 nm to 20 nm, which aggravates the lattice distortion and dislocation tangle and leads to the fracture toughness increases by 32.5% at 203.15 K. Therefore, the interfacial cohesion of the semi-coherent interface between (011) t-ZrO2 and (110) TiO2 was enhanced and t-ZrO2 was completely stabilized when dt-ZrO2 reaches critical size. This work elucidates the effect of size effect on Ms and provides a reference for transformation toughening of ceramic coatings at cryogenic temperature.
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