Exceptional Thermal Conductivity Research Articles

Compressive properties and underlying mechanisms of nickel coated carbon nanotubes modified concrete

Nickel coated multi-walled carbon nanotubes (Ni-MWCNTs) having exceptional mechanical properties, thermal conductivity and dispersibility can effectively overlap in cementitious matrix, thus forming an enhanced and thermal conductive network. They are therefore a promising nanofiller for modifying cement and concrete materials. This paper studies the compressive properties of reactive powder concrete (RPC) filled with different aspect ratios of Ni-MWCNTs, including strength, toughness, Young's modulus and Poisson’s ratio. It is concluded that the incorporation of 0.06 vol.% Ni-MWCNTs with an aspect ratio of 1500 maximally increases the compressive strength and toughness of RPC by 20.24%/20.39 MPa and 43.89%/56.35 (N·m), respectively. However, Young's modulus and Poisson's ratio of Ni-MWCNTs modified composites do not significantly be improved. Besides, a constitutive model of Ni-MWCNTs reinforced RPC under uniaxial compression is established based on the continuum damage mechanics theory, reasonably predicting the relationship between compressive strength and deformation of composites. The modification mechanism of Ni-MWCNTs is also investigated through the temperature distribution monitoring inside composites, Scanning Electron Microscope (SEM) observation and energy dispersive x-ray spectrometry (EDS) analysis of Ni-MWCNTs reinforced RPC. The thermal conductive network formed by Ni-MWCNTs in matrix reduces the temperature difference and improves the temperature uniformity inside composites, thereby decreasing thermal stresses, primary cracks and defects of composites. Furthermore, the incorporation of Ni-MWCNTs makes the RPC microstructures dense, decreases the average CaO to SiO2 ratio, and inhibits the development of cracks inside RPC, thus achieving effective enhancement to RPC.

UN and U3Si2 composites densified by spark plasma sintering for accident-tolerant fuels

Both UN and U3Si2 are potential candidates for accident tolerant fuels due to their high fissile element density and exceptional thermal conductivity. However, they display a high susceptibility to oxidation and corrosion in steam environments. UN and U3Si2 composites were synthesized by conventional vacuum sintering but suffered significant micro-cracks in the silicide phase due to a mismatch in their thermal expansion. In this work, we report promising results of synthesizing UN-U3Si2 composites by spark plasma sintering and the micro-cracks can be significantly mitigated by controlling the cooling. Composite fuel pellets with a density of over 95% theoretical density and a uniform distribution of nitride and silicide phases can be achieved without micro-crack formation. The composite with 50 wt% UN and 50 wt% U3Si2 displays simultaneously-enhanced strength and fracture toughness, and possesses excellent thermal conductivity. The onset temperatures of all composites tested through dynamic oxidation testing are close to 540 °C, suggesting significantly improved oxidation resistance than the monolithic UN. These results demonstrate the potential of synergizing UN and U3Si2 in composites with enhanced fuel properties.

Significantly enhanced thermal conductivity of polymer composites via establishing double-percolated expanded graphite/multi-layer graphene hybrid filler network

Utilization of hybrid fillers with high thermal conductivity enhancement (TCE) efficiency is an effective method for the large-scale fabrication of polymeric thermal interface materials (TIMs) with exceptional thermal conductivity. Herein, we report the thermally conductive properties of thermoplastic urethane (TPU) composites incorporated with expanded graphite (EG) and multi-layer graphene (MLG). The effect of percolation behavior of EG/MLG hybrid fillers on the thermal conductivity is systematically revealed. It is found that the high-loading TPU composite with 20 wt% EG and 10 wt% MLG reveals an exceptional thermal conductivity of 8.52 Wm−1K−1, which corresponds to a TCE of 3450% compared to that (0.24 Wm−1K−1) of pure TPU matrix. Notably, the TCE per 1 wt% filler reaches a substantial value of 115%. The thermally conductive mechanism is proposed based on morphology and thermal contact resistance analyses. Moreover, the application of such TPU composites in thermal management of light-emitting diode lamps is exhibited, and the effectiveness is further verified through finite element simulation. Our results shed light on the significant thermal synergy between EG and MLG and demonstrate their application potential in high-performance TIMs.

Robust Biomimetic Nacreous Aramid Nanofiber Composite Films with Ultrahigh Thermal Conductivity by Introducing Graphene Oxide and Edge-Hydroxylated Boron Nitride Nanosheet.

Dielectric materials with excellent thermally conductive and mechanical properties can enable disruptive performance enhancement in the areas of advanced electronics and high-power devices. However, simultaneously achieving high thermal conductivity and mechanical strength for a single material remains a challenge. Herein, we report a new strategy for preparing mechanically strong and thermally conductive composite films by combining aramid nanofibers (ANFs) with graphene oxide (GO) and edge-hydroxylated boron nitride nanosheet (BNNS-OH) via a vacuum-assisted filtration and hot-pressing technique. The obtained ANF/GO/BNNS film exhibits an ultrahigh in-plane thermal conductivity of 33.4 Wm−1 K−1 at the loading of 10 wt.% GO and 50 wt.% BNNS-OH, which is 2080% higher than that of pure ANF film. The exceptional thermal conductivity results from the biomimetic nacreous “brick-and-mortar” layered structure of the composite film, in which favorable contacting and overlapping between the BNNS-OH and GO is generated, resulting in tightly packed thermal conduction networks. In addition, an outstanding tensile strength of 93.3 MPa is achieved for the composite film, owing to the special biomimetic nacreous structure as well as the strong π−π interactions and extensive hydrogen bonding between the GO and ANFs framework. Meanwhile, the obtained composite film displays excellent thermostability (Td = 555 °C, Tg > 400 °C) and electrical insulation (4.2 × 1014 Ω·cm). We believe that these findings shed some light on the design and fabrication of multifunctional materials for thermal management applications.

Numerical Approximation of Microorganisms Hybrid Nanofluid Flow Induced by a Wavy Fluctuating Spinning Disc

The analysis explored a numerical simulation of microorganisms, carbon nanotubes (CNTs) and ferric oxide water-based hybrid nanofluid flow induced by a wavy fluctuating spinning disc with energy propagation. In the presence of CNTs and magnetic nanoparticulates, the nanofluid is synthesized. The exceptional tensile strength, flexibility, and electrical and thermal conductivity of carbon nanotubes and iron nanoparticles have been extensively reported. The motive of the proposed analysis is to optimize thermal energy conveyance efficiency for a spectrum of industrial and biomedical applications. The phenomena have been expressed as a system of partial differential equations (PDEs) which contain the momentum, energy, concentration, and motile microorganism equations. The modeled equations have been diminished to the dimensionless system of nonlinear ODEs through a similarity framework. The Matlab built-in package boundary value solver has been utilized to solve the obtained system of ODEs. The findings are compared to the PCM technique for validity purposes. The results are illustrated graphically and discussed. The layout of a rotating disc has a positive effect on energy transition and velocity profile. The irregular rotating surface increases energy progression up to 15% relative to a smooth surface. The accumulation of nanocomposites (CNTs and magnetic nanoparticles) significantly enhanced the thermal capabilities of the liquid medium. When operating with a low distribution, it is more impactful.

Carbon Nanotube Mask Filters and Their Hydrophobic Barrier and Hyperthermic Antiviral Effects on SARS-CoV-2.

Carbon nanotube face mask filters have strong and uniform hydrophobicity, high durability, and high thermal conductivity and exhibit excellent barrier and antiviral effects against SARS-CoV-2. The nanocarbon filter functions as a superior barrier compared to those in conventional masks owing to the stronger, more uniform, and more durable hydrophobic nature of the carbon nanotubes. A tightly knit carbon nanotube network has a pore size smaller than that of the average coronavirus; nevertheless, the breathability is equal to that of the conventional polypropylene filter. The exceptional thermal conductivity of carbon nanotubes transpires hyperthermic antiviral effects, which offers stronger protection against the virus, as well as reusability. The facile processability, low cost, and light weight of the aerosol-synthesized carbon nanotube filter warrants its viability, reinforcing the fight against the COVID-19 pandemic.

Graphene for Thermal Storage Applications: Characterization, Simulation and Modelling

In recent years, interest in the thermal properties of graphene constituents has seen rapid growth in the fields of science and engineering. The removal of heat in the continuous processes in the electronics industry has had major issues in thermal transmission in lower-dimensional assemblies. It has also shown fascinating topographies as the carbon allotropes and their derivative compounds expel heat. Numerous research articles reported within the past 15 years have demonstrated enhanced electron flexibility, exceptional thermal conductivity and mechanical behaviour, as well as excellent optical properties of graphene as a single atomic layer. This review article tries to provide a detailed summary of the heat exchange properties of graphene structures and graphene-based materials such as nanoribbons with few-layered graphene. Thermal and energy storage management systems have played a major role in the increase in marketable products in recent times. The purpose of this review is to summarize the current research on thermal properties with regard to the management and energy storage of graphene materials, focusing on characteristic properties, industrialization, modelling and simulation, and their applications in specific thermal storage systems.

The adverse effects of injected functionalized multi-walled carbon nanotube (f-MWCNT) on in vivo neurosecretory brain cells of Jamaican field cricket, Gryllus assimilis.

Carbon nanotubes (CNTs) have been increasingly more prevalent due to their use in product technology owing to their exceptional electrical and thermal conductivity and tensile strength because of their nanostructure and strength of the bonds among carbon atoms. The potential increase of CNTs in the environment is a concern, and studies to assess the toxic effects of these nanomaterials (NMs) are needed. However, so far, most of the studies are focused on aquatic species and much less is understood about the effects of NM in terrestrial organisms. This investigation used a functionalized multi-walled carbon nanotube (f-MWCNT) and the Jamaican cricket Gryllus assimilis to assess the effects of this NM. Cricket nymphs were injected with f-MWCNT suspension-at three different concentrations. The insecticide Fipronil was used as a positive control. Survival was monitored, and histological analysis was made in the brains. Pyknotic cells were quantified in two brain regions, a neurosecretory called Pars intercerebralis (PI), and an associative region called mushroom body (MB). No mortality was observed in any f-MWCNT concentration tested. A significant increase in pyknotic cells was observed as sub-lethal effect for the intermediate concentration of f-MWCNT, at PI, while any significant change was observed at the Kenyon cells of the MB. These results are discussed in the context of agglomeration and dispersion of the f-MWCNT at different concentrations, and availability of the f-MWCNT on the circulatory system, as well as the natural decay of pyknotic cells with time and different patterns of adult cricket neurogenesis. Our results showed that f-MWCNT had negative effects in the neurosecretory region of the brain.

Preparation and mechanism research of bio-inspired dopamine decorated expanded graphite/silicone rubber composite with high thermal conductivity and excellent insulation

This study looked at the process of designing and synthesized expanded graphite (EG) and modifying it with bio-inspired dopamine (DOPA). This is a process used to improve the thermal conductivity and dielectric properties of methyl vinyl silicone rubber (VMQ). The results demonstrated that the EG-DOPA-VMQ composites acquired an exceptional thermal conductivity of 1.015 W mK−1 at the loading of 10 wt%, approximately 480% higher than that of pure silicone rubber (0.175 W mK−1). This enhancement is mainly attributed to the improved dispersion capability of EG-DOPA and the robust interfacial interaction between EG-DOPA-VMQ interfaces; specifically, this is the result when compared with pristine EG. Moreover, throughout this process, the composites maintained an excellent insulating property with a resistance of ≈1012 Ω · cm; this particular result was due to the DOPA deposited on EG surfaces because they acted as an insulating layer, inhibiting the electron transfer in composites. Overall, this work demonstrated that it could present a promising strategy for synchronized manufacturing of polymer composites with high thermal conductivity and insulating capability.

A high-performance, thermal and electrical conductive elastomer composite based on Ti3C2 MXene

In this study, a single-layered Ti3C2 hybrid SiO2 filler (Ti3C2-h-SiO2) was proposed to fabricate high-performance styrene-butadiene rubber (SBR) elastomer composites. It was found that incorporating SiO2 not only facilitated the uniform dispersion of Ti3C2-h-SiO2 in the SBR matrix but also endowed the surface of Ti3C2-h-SiO2 with nano protuberances for immobilizing more rubber chains, resulting in the improvement of the interfacial interaction between Ti3C2-h-SiO2 and SBR matrix. Thus, the tensile strength of the SBR/Ti3C2-h-SiO2 elastomer composite was reinforced by 174% compared with the unfilled SBR. Moreover, the wet skid resistance and rolling resistance of the SBR/Ti3C2-h-SiO2 elastomer composite were also remarkably improved. Noteworthily, the exceptional thermal conductivity (0.401 W m−1 k−1) and electrical conductivity (4.87 × 10−4 S m−1) of the SBR/Ti3C2-h-SiO2 elastomer composite were comparable to the SBR/reduced graphene oxide (rGO) elastomer composite, implying that the conductivity of Ti3C2-h-SiO2 may be competitive with the rGO.

Ultralight graphene/graphite hybrid fibers via entirely water-based processes and their application to density-controlled, high performance composites

Fabrication of lightweight graphene/graphite fibers (GFs) with high thermal and electrical conductivity, and good mechanical properties via facile processing method is yet a challenge for industries. The common fabrication of reduced graphene oxide fibers originated from graphite, requires several cost-intensive steps of oxidation and reduction and still, exceptional thermal and electrical conductivity and stiffness of the graphene sheet as a single layer, has not been translated in such fibers. We report the fabrication of ultralight graphene/graphite fibers with the density of 0.25 g/cm3, and an exceptional thermal and electrical conductivity of 2✕103 W/K-m and 2✕105 S/m, respectively as well as impressive mechanical properties of ∼0.5 GPa strength and 40 GPa Young’s modulus via entirely water based process, from achieving exfoliation of graphite through assembling into fibers. Furthermore, the resulting ultralight high performance GFs have been incorporated into epoxy resin, producing self-floating, lightweight composites with enhanced electrical and mechanical properties.

High-speed video analyzes microcracking during additive manufacturing of tungsten

Most of our day-to-day encounters with tungsten metal are limited to seeing its glowing coils in outdated incandescent light bulbs. However, the exceptional thermal conductivity and excellent radiation shielding properties of this very dense metal suggest that it is ideally suited to use as a plasma facing material in containment systems in emerging fusion reactors. In order for that to happen, however, researchers must overcome a critical roadblock. When tungsten cools down—from either high-temperature processing or after use in extreme environments—it stops being ductile and becomes brittle. In turn, the material develops microcracks and loses its strength. This is particularly problematic for the additive manufacturing of tungsten components, which uses laser heating to melt this metal and conform it to custom curvatures and shapes. Moreover, while researchers have examined failed tungsten articles and analyzed the networks of fractures that had formed, postmortem analyses have not provided much insight into the mechanisms that drive microcrack formation.

Fabrication of branching poly (butylene succinate)/cellulose nanocrystal foams with exceptional thermal insulation

Branching poly (butylene succinate) (BPBS) nanocomposite foams incorporated with cellulose nanocrystals (CNCs) were prepared by supercritical CO2. Surface modification of CNCs by acetylation was achieved through replacing hydrophilic hydroxyl groups with hydrophobic acetyl groups, which improved the dispersibility of CNCs significantly. The crystallite sizes of CNCs and acetylated CNCs were calculated by Scherrer's formula as 25 and 19 nm, respectively. The initial crystallization temperature of diverse poly (butylene succinate) (PBS) specimens, a crucial factor for regulating cell nucleation type, increased remarkably by 11.8 °C as well as their storage modulus increased by 2 orders of magnitudes, due to branching reaction and bio-filler addition. BPBS/CNCs foam possessed a high volume expansion ratio as 37.1 times and displayed an exceptional thermal conductivity as 0.021 W(m K)−1. This study provided a promising potential strategy to develop exceptional thermal-insulation polymer foams for composite structures, energy conservation and environment protection.

Highly Flexible Graphene Derivative Hybrid Film: An Outstanding Nonflammable Thermally Conductive yet Electrically Insulating Material for Efficient Thermal Management.

In modern society, advanced technology has facilitated the emergence of multifunctional appliances, particularly, portable electronic devices, which have been growing rapidly. Therefore, flexible thermally conductive materials with the combination of properties like outstanding thermal conductivity, excellent electrical insulation, mechanical flexibility, and strong flame retardancy, which could be used to efficiently dissipate heat generated from electronic components, are the demand of the day. In this study, graphite fluoride, a derivative of graphene, was exfoliated into graphene fluoride sheets (GFS) via the ball-milling process. Then, a suspension of graphene oxide (GO) and GFSs was vacuum-filtrated to obtain a mixed mass, and subsequently, the mixed mass was subjected to reduction under the action hydrogen iodide at low temperature to transform the GO to reduced graphene oxide (rGO). Finally, a highly flexible and thermally conductive 30-μm thick GFS@rGO hybrid film was prepared, which showed an exceptional in-plane thermal conductivity (212 W·m-1·K-1) and an excellent electrical insulating property (a volume resistivity of 1.1 × 1011 Ω·cm). The extraordinary in-plane thermal conductivity of the GFS@rGO hybrid films was attributed to the high intrinsic thermal conductivity of the filler components and the highly ordered filler alignment. Additionally, the GFS@rGO films showed a tolerance to bending cycles and high-temperature flame. The tensile strength and Young's modulus of the GFS@rGO films increased with increasing the rGO content and reached a tensile strength of 69.3 MPa and a Young's modulus of 10.2 GPa at 20 wt % rGO. An experiment of exposing the films to high-temperature flame demonstrated that the GFS@rGO films could efficiently prevent fire spreading. The microcombustion calorimetry results indicated that the GFS@rGO had significantly lower heat release rate (HRR) compared to the GO film. The peak HRR of GFS@rGO10 was only 21 W·g-1 at 323 °C, while that of GO was 198 W·g-1 at 159 °C.

Influence of the grain size of CVD diamond on the thermal conductivity, material removal depth and surface roughness in nanosecond laser machining

Due to the exceptional thermal conductivity and material hardness, CVD diamonds have been ideal materials for cutting tools; however, the specific properties of CVD diamonds vary with the grain size. An experimental study was carried out on chemical vapor deposition (CVD) diamonds with varying grain sizes in laser processing. This study aims to analyze the behavior of polycrystalline CVD diamonds under different thermal processing based on its thermal conductivity model. The pit formed under a single laser pulse on the material with a small grain size is shallow and tiny, because of its small thermal conductivity, a value calculated using the established model. The results show that for laser-machined surface, the material with a small grain size can obtain a better machined surface but a small material-removal depth; conversely, material with a large grain size provided opposite experimental results. Additionally, reasonable laser parameters achieved the desired material-removal depth of up to or even exceeding 180 μm and surface roughness Sa as low as 0.2 μm. Overall, both the grain sizes of polycrystalline CVD diamonds and laser parameters affect the machining result. However, there are considerable obstacles in simultaneously achieving a good surface and massive material removal. Hence, a tradeoff between the two aspects is essential in an actual machining process, and this study provides some useful guidance to practitioners and academicians.

Evaluating the characteristics of magnetic dipole for shear-thinning Williamson nanofluid with thermal radiation

AbstractObjective A recent evolution in fluid dynamics has been the consideration of nanoliquids which retains exceptional thermal conductivity characteristics and upsurge heat transportation in fluids. Inspired by this, the current attempt develops a nonlinear mathematical model (Williamson fluid) towards moving surface heated convectively. Formulated problem further encompasses thermophoresis, magnetic dipole, heat source, Brownian diffusion, thermal radiation and thermo-solutal convective conditions. Upshots are simulated and unveiled graphically. Drag force along with heat/mass transportation rates is addressed numerically.Method The dimensionless expressions are highly non-linear and exact/analytic computations for such expressions are not possible. Thus we employed numeric (bvp4c) scheme for solution development.Conclusions Temperature of Williamson nanofluid intesifies through larger Nb (Brownian movement) factor and Nt (thermophoretic variable). Moreover, Buongiorno relation has reverse behavior for concentration ϕ(η) of Williamson nanofluid regarding Nt and Nt. Transportation rate of heat dwindles against both Nt and Nb.

Highly compact nanochannel thin films with exceptional thermal conductivity and water pumping for efficient solar steam generation

Highly compact nano-channelled thin films, assembled from cellulose nanofibers and reduced graphene oxide via van der Waals' interactions, exhibit exceptional thermal conductivity and water pumping, allowing for efficient solar-steam generation.

Impact of different surfactants and ultrasonication time on the stability and thermophysical properties of hybrid nanofluids

Graphene based nanofluids are getting more attention among researchers due to their exceptional thermal conductivity. In the present study, stable hybrid nanofluids were produced by dispersing graphene nanoplatelets (GnPs) and titanium dioxide (TiO2) in a mixture of distilled water and ethylene glycol (DW/EG) using a two-step method. For comparison purpose, GnPs were dispersed into the same base fluid and labelled as mono nanofluid. The impact of different surfactants and sonication time on nanofluids' stability was determined by sedimentation method, zeta potential analysis, and absorbency test. It was observed that the addition of hexadecyltrimethylammonium bromide (CTAB) showed the highest degree of stability in all analyses, with minimal sedimentation up to 40 days. Thermophysical properties of nanofluids with CTAB were measured from 30 °C to 70 °C at 0.1, 0.075, 0.05, and 0.025 wt% concentrations of nanoparticles. The maximum thermal conductivity enhancement of base fluid was found to be 23.74% when 0.1 wt% of COOH-GnP was added at 60 °C. Hybrid nanofluid showed higher thermal conductivity than mono nanofluid at all concentration and temperature ranged from 30 to 50 °C. Both mono and hybrid nanofluids showed Newtonian behaviour in which shear stress increased linearly with increasing shear rate. Mono nanofluid with 0.1 wt% concentration showed the highest viscosity at 40 °C, which was 32.54% and 4.85% higher than base fluid and 0.1 wt% hybrid nanofluid, respectively. The enhanced properties of this hybrid nanofluid could be used as an alternate heat transfer medium in an automobile cooling system.

Temperature distribution of cubic boron nitride–coated cutting tools by finite element analysis

Heat generation in cutting process has a great influence on performance and lifetime of cutting tools. Cubic boron nitride (cBN), combination of exceptional thermal conductivity and hardness, is a promising super-hard material as protective coatings on the cutting tools. However, the temperature distributions of micron-thickness coatings on cutting tools are very difficult to be examined by experiment methods. In this paper, finite element method (FEM) simulation was introduced to determine the temperature distribution of cBN/diamond coatings on silicon nitride (Si3N4) cutting tools with various parameters compared with titanium aluminum nitride (TiAlN) coatings. The finite element (FE) model of cBN/diamond–coated Si3N4 tools was built and validated by machining experiments. The effects of cutting speed and tool rake angle on temperature distribution of cBN/diamond–coated tools were investigated compared to TiAlN coatings based on developed model. The results show that the temperature is increased with the increase of cutting speed while decreased with the increase of tool rake angle. The temperature of cBN-coated tools is decreased by approximately 20.4–28.6% than TiAlN-coated tools under identical conditions. Additionally, the preferred cutting speed and rake angle were obtained among employed cutting parameters. The results demonstrated that using advanced cBN coatings can substantially improve the cutting performance of the tools. This work may offer a guideline to explore the temperature distribution of cBN-coated cutting tools in mechanical machining application for machining difficult-to-cut ferrous materials.

Ultrathin thermally conductive yet electrically insulating exfoliated graphene fluoride film for high performance heat dissipation

Abstract With the development of portable and flexible electronic devices, demends for high-performance thermal management materials with high thermal conductivity and electrical insulation are growing. Recently, graphene fluoride has received numerous attention from science community due to its high thermal conductivity and electrical insulation. Here, we report an advanced exfoliated graphene fluoride (EGF) film as a high performance heat spreader and thermal interface material for flexible electronic devices, which simultaneously exhibits ultrahigh thermal conductivity, excellent electrical insulation, and satisfactory flexibility. Commercially available graphite fluoride was directly exfoliated into graphene fluoride solution using ball milling method, followed by preparing ultrathin graphene fluoride films to take full advantage of graphene fluoride properties for heat dissipating applications. The resultant films show a tunable thermal conductivity by altering the thickness of films and show a superior in-plane thermal conductivity of 242 W m−1 K−1 and exceptional through-plane thermal conductivity of 21.8 W m−1 K−1 at the thickness of 10 μm. More interestingly, the graphene fluoride films possess excellent flexibility. The newly developed EGF film provides a creative opportunity for fabrication of multifunctional highly flexible materials, which may promote the development of heat dissipation materials in next generation flexible electronics.