Improvement In Thermal Conductivity Research Articles

Preparation and thermal performance study of a novel hydrated salt composite PCM for space heating

In order to effectively address the mismatch between thermal energy supply and demand in buildings, latent heat storage (LHS) based on phase change material (PCM) stands out as a key technology. While hydrated salt has emerged as a promising PCM, it encounters common issues such as substantial supercooling, phase separation, and low thermal conductivity, hindering its development. To mitigate these limitations, this study focused on modifying Ba(OH)2·8H2O by incorporating various nucleating agents and thickening agents to reduce supercooling, enhancing the composite PCM's thermal properties by introducing expanded graphite (EG) to elevate thermal conductivity. Subsequently, the thermal stability of the PCM was evaluated through accelerated thermal cycling tests, encompassing the assessment of critical thermal parameters, including supercooling degree, enthalpy, and thermal conductivity of the composite PCM. Experimental findings unveiled the effectiveness of incorporating 2 wt% BaCl2·2H2O and 1 wt% CMC to Ba(OH)2·8H2O, effectively diminishing the supercooling degree from 14 °C to 1.42 °C. Further integration of 3.5 wt% EG led to a substantial decrease in the supercooling degree to 0.24 °C. Simultaneously, the addition of EG resulted in an improvement in thermal conductivity, elevating it from 0.62 W/(m·K) to 1.03 W/(m·K), while the enthalpy decreased from 283.68 J/g to 252.81 J/g. Notably, the composite PCM exhibited notable thermal reliability with a latent heat drop of 15.9 % following 1000 accelerated cycles of testing. Moreover, the composite PCM demonstrated superior thermal storage density, measuring at 2.36 times that of traditional paraffin wax, yet with a thermal storage cost merely a quarter of paraffin wax, rendering it more favorable for extensive deployment in building energy systems.

Enhancing high-speed CNC milling performance of Ti6Al4V alloy through the application of ZnO-Ag hybrid nanofluids

Abstract This research investigates the performance of high-speed CNC milling operations on Ti6Al4V alloy by employing a novel ZnO-Ag hybrid nanofluid. The study involves the preparation and characterization of nanofluids with varying concentrations of nanoparticles, focusing on thermal conductivity and stability. The machining experiments encompass four critical input parameters: Minimum Quantity Lubrication (MQL) flow rate, cutting speed, nanofluid concentration, and feed rate. Performance evaluation is based on average surface roughness (Ra) and cutting temperature. Key findings include a remarkable 21.05% improvement in thermal conductivity for the ZnO-Ag-based sunflower oil at 0.2% volume concentration compared to 0.05% concentration. The prepared nanofluids exhibit good stability. Moreover, cutting speed and MQL flow rate emerge as significant contributors to Ra, accounting for 35.62% and 34.82%, respectively. Interestingly, MQL flow rate is identified as the most influential factor, surpassing even cutting speed. SEM images for tool wear reveals that the ZnO-Ag based sunflower oil reduced tool wear significantly. In conclusion, the proposed ZnO-Ag-based sunflower oil at 0.2% concentration emerges as the good option for sustainable high-speed machining of Ti6Al4V alloy, showcasing

Sintering and toughening of self-reinforced AlN with integrated AlN whiskers via spark plasma sintering

Aluminum nitride (AlN), prized for its high thermal conductivity and electronic insulating properties, finds widespread use in electronic applications, particularly as a substrate material. However, its relatively low fracture toughness limits its application. In this study, to enhance both the thermal and mechanical properties of AlN ceramics, we thoroughly investigate the microstructure, thermal, and mechanical properties of self-reinforced AlN ceramics fabricated by spark plasma sintering, with self-reinforcement achieved through the integration of AlN whiskers within the AlN matrix. Unlike previous studies utilizing conventional pressureless sintering with limited sintering conditions, this work employs spark plasma sintering with a wide range of temperatures (1600–1900°C) and holding times (10–30 min), providing a comprehensive understanding of the sintering behavior. Microstructural features, observed through optical and scanning electron microscopy, reveal distinct toughening mechanisms via crack deflection and branching, with a maximum 20% enhancement. The self-reinforced AlN ceramics exhibit remarkable improvements in thermal conductivity, reaching up to 150Wm−1K−1, surpassing reported values for spark plasma-sintered AlN ceramics. Adding AlN whiskers enhances the thermal and mechanical properties of AlN simultaneously, particularly at 1800°C for 10 min with controlled grain size and nicely integrated AlN whiskers. This work not only contributes valuable insights into the complex relationship between processing parameters, microstructure, and resulting thermal and mechanical properties but also highlights the enhanced thermal and mechanical properties of self-reinforced AlN ceramics.

Techniques for Enhancing Thermal Conductivity and Heat Transfer in Phase Change Materials in Hybrid Phase Change Material–Water Storage Tanks

In recent years, extensive research has been dedicated to enhancing energy efficiency and promoting environmental sustainability in heating and cooling systems. Among the promising solutions, phase change materials (PCM) technology stands out as a key area of exploration. This study focuses on improving the thermal performance of PCM–water hybrid tanks by investigating methods to enhance thermal conductivity and heat transfer. Through experimental testing using techniques such as copper matrices, steel twisted matrices, and copper spirals, this study demonstrates significant improvements in thermal conductivity, particularly with the use of copper matrices. The integration of a copper matrix placed in the PCM reservoir increased the heat transfer coefficient and thermal conductivity of the PCM, and thus, the total phase transformation time for solidification was reduced by 79.19% and for melting by 54.7%. Our experimental results demonstrate that the integration of a copper matrix can increase latent heat transfer from 55,677.6 J up to 125,274.6 J, marking a 125% enhancement over the experiment with pure PCM. Additionally, comparisons of the energy storage potentials for different PCMs underscore the benefits of integrating PCMs into hybrid storage tanks. These findings highlight the immense potential of PCM technology to increase energy storage efficiency in heating and cooling applications.

Temperature dependency of electric field treatment for improvement of effective thermal conductivity of functional carbon/silicone rubber composite sheets

Temperature dependency of electric field treatment for improvement of effective thermal conductivity of functional carbon/silicone rubber composite sheets

Why Carbon Nanotubes Improve Aqueous Nanofluid Thermal Conductivity: A Qualitative Model Critical Review

Media thermal conductivity is important in various heat-transfer processes. Many conventional fluid conductors suffered low conductivity and environmental issues. Therefore, research was active in finding out alternative systems, mostly relying on aqueous liquids that are low-cost and ecofriendly. After the emergence of carbon nanotubes (CNTs), with their many special structural, electrical and thermal properties, they have been examined for many applications, including heat-transfer processes. Adding CNTs to water yields CNT aqueous nanofluids that have been widely investigated as heat-transfer media. The literature shows that CNT addition improves water thermal conductivity and other water properties, such as viscosity, surface tension, freezing point and boiling point. The literature also shows that nanofluid thermal conductivity improvement is affected by CNT type and concentration, in addition to other factors such as surfactant addition. All these subjects were widely described in literature, focusing on experimental, modelling and theoretical accounts. Despite the wide literature, there exist inconsistencies and discrepancies between reports that need to be justified. In addition to technical papers, many reviews were published on various aspects of the subject including experimental results and mathematical modeling. However, the very basic question here is as follows: Why does adding CNT to water affect its thermal conductivity? In spite of the wide published literature, this issue was not targeted in a simple qualitative approach. This review provides a clear understanding of how CNTs improve thermal conductivity of aqueous nanofluids. A qualitative model is presented to explain mechanisms behind improvement as presented in the literature. CNT type effects are discussed with other factors such as aspect ratio, Reynold number, dispersion quality, composition, temperature and additives. CNT functionalization is described. Relations to estimate nanofluid thermal conductivity are discussed. The model will help specialists to tailor CNT aqueous nanofluid characteristics as desired by varying types and concentrations of CNT and surfactant, and other factors.

Comparative study of Hiemenz flow in hybrid Carreau nanofluid (Fe3O4-Cu/kerosene-engine oil): nonlinear effects, Newtonian heating and viscous dissipation

ABSTRACT This study is important because it helps us understand how different factors affect the flow of a special liquid with nanoparticles, giving us useful insights for real-world applications in engineering and technology. This research endeavours to explore and contrast the distinctive characteristics of steady, 2-D magnetohydrodynamic (MHD) and stagnation point (Hiemenz) flow in Carreau hybrid nanofluid {Fe3O4-Cu/kerosene-engine Oil} over a nonlinear stretching-shrinking surface with its counterpart, Carreau nanofluid. Employing the laws of conservation encompassing mass, momentum, energy, and concentration, our methodology probes into the multifaceted effects induced by factors like the suction-injection, viscous dissipation, Newtonian heating, Hiemenz flow, thermophoresis, and Brownian motion. This exploration involves the transformation of governing partial differential equations (PDEs) into a system of ordinary differential equations (ODEs) through similarity transformations. Subsequently, the intricate non-linear ODEs are meticulously solved using the bvp4c technique, an adept MATLAB built-in function, facilitating a comprehensive understanding of the intricate dynamics within the system. In addition, the study considers the Newtonian heating effect and a numerical comparison is performed to verify the results. Using two different types of nanoparticles dispersed in kerosene-engine oil, it was demonstrated that increasing Weissenberg parameter values resulted in significant improvements in thermal conductivity and thermal velocity. A comparison of Carreau nanofluid thermal and concentration velocities with Carreau hybrid nanofluid showed that Carreau nanofluid values are lower (Weissenberg parameter). Higher Biot numbers are associated with reduced temperature velocity and elevated concentration velocity.

Keller box numerical analysis of power-law rotating disk for nanofluid flow with chemical reaction

The present study concentrates on the numerical treatment of the flow of the 3D boundary layer on a nanofluid above a rotating disk. The chemical reaction and generation or absorption of heat has been incorporated. According to published literature nanofluids play a key role in the improvement of thermal conductivity. More significantly, nanofluids are utilized in medical field, engineering and in industry. In addition, this attempt will be helpful for the researcher to analyze energy and mass transport rates for nanofluids. Further, in this study, Brownian motion and thermophoretic impacts are taken into account. The governing flow equations are converted to ODEs (ordinary differential equations) via suitable similarity transformations. The numerical outcomes are recovered with the utilization of well know technique KBM (Keller box method). The velocity and energy transport rates are discussed graphically for power law index, thermophorsis, and Brownian motion. Graphs present the temperature and concentration distribution increase for the upturn of thermophoretic impacts. While, temperature and concentration distribution show decreasing behavior for Brownian movement factor. In addition, increment in power index factor diminishes the temperature distribution and concentration of the liquid.

Novel Approach to Augment Thermal Conductivity of Dihybrid Nanofluids

In this experimental study, the copper oxide (CuO) nano–particle (NP) was mixed with a water/ethylene glycol hybrid base fluid to form a hybrid nano–fluid (HNF). Further, this HNF was mixed with a MgO nano–particle and also separately with a TiO2 nano–particle to form two different dihybrid nano–fluids (DHNFs). For the preparation of nano–fluids, two-step procedure was used. In all three cases, the volume fraction of the NP was 0.25, 0.5, 0.75, 1.0, and 1.25%. The thermal conductivity (TC) of HNF was measured with KD2 pro and compared with the DHNFs' at temperatures 26, 28, 30, and 32°C. It was inferred that the CuO/TiO2 nano–particle addition in the water/ethylene glycol hybrid base fluid resulted in an average of 0.8% rise in thermal conductivity at chosen temperatures and volume fraction. Also, the agglomeration due to the presence of CuO/MgO was a critical issue at higher volume fractions such as 0.75, 1, and 1.25%. The MgO nano–particle addition in the CuO nano–particle also resulted in a 0.6% increase in thermal conductivity at 0.25 and 0.5% volume fraction. The result was that in the CuO/MgO - water-ethylene glycol nano–fluid combination the TC was enhanced by 29.57% compared with CuO/water/ethylene glycol at a volume fraction increase of 0.5%. Also, it was noted that the nano–particles volume fraction has little effect on thermal conductivity improvement at higher proportion.

Surface modification of spherical silica micro‐powder using silane coupling agents and their application in epoxy resin‐based composite materials

AbstractIn recent years, the packaging industry has utilized electronic packaging materials with epoxy resin (EP) and high‐performance fillers, exhibiting superior mechanical properties and thermal conductivity. Spherical silica micro‐powder (SSP) is a critical thermal conductive filler but faces challenges due to its inorganic nature. Surface modification is essential to improve SSP's compatibility and dispersion in organic matrices for effective use in EP‐based composites. In this paper, the effects of the following four modification methods on SSP/EP composites were studied: (1) the processes include co‐modification with dimethyldimethoxysilane (DMDMS) and trimethylethoxysilane (MTES), (2) modification with NaOH, (3) co‐modification with DMDMS and MTES in an alkaline environment after NaOH modification, and (4) co‐modification with methyltrimethoxysilane (MTMS) and propyltrimethoxysilane (PTMOS). Through comprehensive characterization and evaluation, it is evident that modification schemes 1, 3, and 4 significantly enhance SSP's hydrophobicity, dispersibility, and compatibility with EP. This led to the improvement of thermal conductivity and stability of the composite, and modification scheme 4 showed the highest enhancement, with a 42.6% increase in thermal conductivity. Moreover, the mechanical properties of modified composite materials, such as bending strength, impact resistance, and tensile strength, surpass those of unmodified SSP/EP composite materials. The study provides valuable insights for reducing manufacturing costs and enhancing productivity in the electronic packaging sector.

Investigation into the underlying mechanisms of the improvement of thermal conductivity of the hybrid nanofluids

More and more applications of hybrid nanofluids are emerging in various fields such as energy engineering, chemical engineering, and automotive engineering. However, the existing literature only employs the term "synergistic effect" to explain the improvement of thermal conductivity of hybrid nanofluids. In order to elucidate the underlying reasons behind the improvement in thermal conductivity of hybrid nanofluids compared to that of conventional ones (mono nanofluids), molecular dynamics simulations were conducted to examine three types of hybrid nanofluids, including Ag-Cu nanocomposites, Au-Cu Janus nanoparticles, and Ag-Cu binary nanoparticles. The results suggest that hybrid nanofluids including Ag-Cu nanocomposites, Au-Cu Janus nanoparticles, and Ag-Cu binary nanoparticles improve the thermal conductivity of 2 vol% nanofluid by 34.3 %, 12.1 %, and 10.4 %, respectively, compared to Cu monofluid. The improvement in thermal conductivity for hybrid nanofluids containing nanocomposites in single-particle systems can be attributed primarily to the stronger Brownian motion, while the improvement in thermal conductivity for hybrid nanofluids containing Au-Cu Janus nanoparticles and Ag-Cu binary nanoparticles is due to the looser aggregation morphology in multi-particle systems. This observation allows us to appreciate the significance of aggregation morphology as a crucial mechanism when considering interactions between nanoparticles. It provides a theoretical basis for the preparation of high-performance nanofluids as heat transfer media.

Thermal-mechanical enhancement investigation of shape memory polymer nanocomposite for anti-/deicing

The oriented arrangement of graphene oxide (GO) and magnetic graphene oxide (MGO) in shape memory epoxy resin (EP) by employing the coupling effect of electric and magnetic fields were investigated. The heat transfer experiments showed that the thermal conductivity of the aligned shape memory MGO/GO/EP composites was 90.29% higher than that of the random doped composites. Through the two-dimensional aligned of MGO, the tensile strength of the shape memory MGO/GO/EP composite was significantly improved. The tensile strength reaches 24.52 and 22.67 MPa along the X and Y direction respectively, which increased of 53.92% and 42.31%. The shape recovery experiments showed that the shape recovery and shape fixity of the two-dimensional aligned composites were 95.55% and 91.49%, which increased by 4.44% and 7.82%. The results demonstrated that the two-dimensional directional arrangements of MGO layers significantly enhance the heat transfer and mechanical properties of shape memory polymer. The improvement of thermal conductivity and mechanical properties directly affected the anti-deicing performance of the composites. Hence, the deicing time of the shape memory MGO/GO/EP composite was 324 s, which represented an 18.2% improvement of the deicing efficiency.

A study of some relevant properties of concrete incorporating waste ceramic powder as a cement replacement agent

Cement, the key ingredient in concrete, is responsible for 8% of the world's CO2 emissions. Thus, reducing the amount of cement used in concrete is highly desirable to lower the total embodied carbon in concrete manufacturing. Furthermore, an increasing amount of ceramic waste powder (CWP) is generated during the ceramics manufacturing process, which can result in severe environmental problems such as soil, air, and groundwater pollution. This paper reports the use of CWP as a cement replacement agent in concrete to reduce environmental pollution in both concrete production and CWP waste management fields. For this purpose, comprehensive laboratory work was carried out to replace different levels of cement with CWP. It was found that changes in compressive strength and water absorption value are within the acceptable tolerance when 20% CWP replaces cement. In addition, there was an improvement in thermal conductivity, and no significant damage to the mechanical properties of concrete after 30 min of fire exposure when CWP replaced 20% of cement was observed. Therefore, using up to 20% of CWP to replace cement in concrete manufacturing is feasible without compromising the essential properties of the finished products. The microstructural studies of the test specimens further proved that the added CWP was evenly scattered in the concrete matrix.

Preparation and thermal properties of nano-microcapsule and simulation heat storage application

The prevention of material leakage and improvement of thermal conductivity are very important for thermal energy storage application. In this work, nano-TiO2@n-docosane microcapsules were synthesized by the fine emulsion interface polymerization method using tetra-n-butyl titanate (TBT). This approach enhances the encapsulation rate and efficiency of phase change microcapsules. The microcapsules formation process was observed using a biological microscope. The diameter of the microcapsules decreased significantly with the increase of stirring rate. The phase transition temperature of the optimal microcapsules is 42.4 °C. The encapsulation rate and efficiency reach up to 90.7% and 91.0%, respectively. The average thermal conductivity of nano-TiO2@n-docosane microcapsules is 215% higher than that of n-docosane. SEM and infrared spectroscopy testing results confirm the successful coating of n-docosane by TiO2. Thermogravimetric analysis presents that TiO2 forms a shell, which reduces the leakage of n-docosane. The melting and solidification processes of n-docosane and nano-TiO2@n-docosane microcapsules were simulated numerically. In comparison to n-docosane, nano-TiO2@n-docosane microcapsules exhibit a 14.89% increase in peak storage power and a 12.47% increase in heat transfer coefficient during charging. Additionally, during discharging, these values rise by 3.23% and 6.46%, respectively. Nano-TiO2@n-docosane microcapsules enhance heat transfer and the charging/discharging process of phase change materials.

Development of PCM-based shell-and-tube thermal energy storages for efficient EV thermal management

Electric vehicles face significant challenges in cold climates. Battery efficiency decreases, and cabin heating demands additional electricity, which diminishes the energy available for vehicle propulsion. In this context, a thermal energy storage system based on a phase change material (PCM) with diverse designs of shell-and-tube heat exchangers is investigated to meet cabin thermal load demands independently. A simulation model for a two-phase PCM heat exchanger is developed and validated using experimental data. The comparison revealed average temperature differences of 1.59 K and 1.61 K for the melting and solidification processes, respectively. Compared to the single tube design, the heat transfer performance of finned multitube design improved the melting process and reduced the melting time by 92.9% and reduced the solidification time by 87.6%. The average heat transfer rate of the finned multitube during the solidification process is 2.9 times higher than that of the single tube. Additionally, the use of PCM incorporating different types of nanomaterials is explored to enhance the melting and solidification performance through increased thermal conductivity. The graphene nanoplatelet PCM exhibited the most substantial improvements in thermal conductivity, resulting in melting and solidification time reductions by 54.2% and 48.9%, respectively.

Investigation of thermo-optical properties and photothermal conversion performance of MWCNT, Fe3O4, and ATO nanofluid for volumetric absorption solar collector

For the use of volumetric absorption solar thermal collector (VASTC), the thermo-optical properties, photothermal conversion characteristics and economics of MWCNT (Multi-walled carbon nanotube) (0.0005–0.004 wt%), Fe3O4 (0.025–0.1 wt%), and antimony-doped tin oxide (ATO) (0.05–0.25 wt%) nanofluids (NFs) were comprehensively investigated. As a result, The improvement of thermal conductivity, specific heat, and viscosity of MWCNT, Fe3O4, and ATO NFs was insignificant in the concentration range where optical absorbance can improve. The photothermal conversion efficiency (ηPTC) and receiving efficiency (ηrec) were significantly improved according to the increase in the concentration. Among NFs, the 0.002 wt% MWCNT, 0.075 wt% Fe3O4, and 0.1 wt% ATO NFs had maximum ηPTC (93.3%, 90%, and 89.2%) and ηrec (83.7%, 81.4%, and 77.7%). Regarding dispersion stability, the optical transmittance of MWCNT, Fe3O4, and ATO NFs slightly increased, and long-term dispersion stability is required for the use of VASTC. Economically, the cost required per unit photothermal conversion energy (CUPTE) of 0.002 wt% MWCNT NF is 0.102–0.538 $/g, which is cheaper than 0.075 wt% Fe3O4 and 0.1 wt% ATO NFs. Overall, MWCNTs can be used as working fluid for VASTC due to their excellent optical absorption and low price once long-term dispersion stability is achieved.

Experimental measurement of thermal conductivity and viscosity of Al2O3-GO (80:20) hybrid and mono nanofluids: A new correlation

This study examines the thermophysical properties of Aluminum oxide (Al2O3) and graphene oxide (GO) based mono and hybrid nanofluid mixture at different volume concentrations for heat transfer application. Firstly, Al2O3 and GO nanoparticles were mixed with base fluid (deionized water) separately at 1.0 % of volume concentration for mono nanofluid preparation. Then, Al2O3-GO hybrid nanofluid (80:20) was prepared for volume concentrations of 0.25 %, 0.5 %, 0.75 % and 1.0 %. The stability of both nanofluids was evaluated based on Zeta potential and pH measurements. Meanwhile, the viscosity and thermal conductivity were investigated for temperatures starting from 30 °C to 50 °C. The experimental thermal conductivity and viscosity measurements were correlated using the analytical regression method to predict the thermal conductivity and dynamic viscosity of Al2O3-GO hybrid nanofluid. The maximum thermal conductivity improvement of hybrid Al2O3-GO nanofluid (1 %) was about 4.30 % and 4.34 % higher than Al2O3 and GO mono nanofluid, respectively. In contrast, the viscosity of 1 % Al2O3-GO hybrid nanofluid showed the least reduction of 4.6 %, which is 4.1 % and 6.6 % less than both Al2O3 and GO mono nanofluids. Compared to experimental values, the new model resulted in a high level of predictive accuracy for both thermal conductivity and viscosity, with a maximum error of 6 % and 4 %.

Synergetic improvement of dielectric properties and thermal conductivity in Zn@ZnO/carbon fiber reinforced silicone rubber dielectric elastomers

Dielectric elastomers (DEs) with large dielectric permittivity (ε') but low loss, high thermal conductivity (TC), are highly pursued in artificial muscles. To elevate the ε' and TC of raw zinc (Zn)/silicone rubber (SR), raw Zn particles were oxidized to Zn@ZnO (zinc oxide), and then incorporated into SR. Compared to raw Zn/SR, the Zn@ZnO/SR showcases the enhanced ε' and TC because the ZnO interlayer induces intraparticle polarization and promotes interfacial phonon transport. Further, synergetic improvement of ε' and TC is found when modicums carbon fibers (CF) was added into Zn@ZnO/SR. The ε' and TC of Zn@ZnO/CF/SR are 23.83 and 1.53 W/(m·K), corresponding to 3.41 and 0.48 W/(m·K) for raw Zn/SR at 60 phr fillers. However, dielectric loss and electric conductivity of Zn@ZnO/CF/SR are remained at low levels. This work provides a strategy for design and preparation of robust SR DEs with high ε' and TC but low loss for prospective applications.

Exploiting synergies for high thermoelectric performance in higher manganese silicide-based semiconductors through element Co-doping, energy filtering, and phonon scattering

Higher manganese silicide (HMS) is a promising thermoelectric (TE) semiconductor that operates effectively at medium temperatures. It is characterized by its abundance, environmental friendliness, and desirable impact resistance properties. To enhance the TE properties of HMS, this study employs isoelectronic anion and cation codoping, combined with embedded quantum dot (QD) techniques. The introduction of element doping and nanoinclusions, such as Mn0.96Re0.04(Si0.96Ge0.04)1.79+1.5%Ag2Pt QDs sample, leads to an approximately 85% increase in electrical conductivity. This boost is attributed to the adjustment of the band structure through Re, Ge, and Ag element doping and the charge transfer facilitated by MnSi, Si, and Pt precipitates. Furthermore, the enhanced PF of 1.85 × 10−3 W m−1 K−2 at 773 K is approximately 29% higher than that of pure HMS. Simultaneously, the increase in point defects hampers the improvement of lattice thermal conductivity (κl) by intensively scattering short-wave phonons. This effect is complemented by the precipitation of Si, MnSi, Ag, and Pt nanoparticles, which increases the density of grain boundaries, enhances medium-wave phonon scattering, and substantially reduces κl to 1.45 W m–l K−1 (at 773 K), ∼30% lower than that of pure HMS. The figure of merit of the sample containing 1.5%Ag2Pt QDs at 823 K attains a value of 0.69, which is ∼52% and ∼19% higher than that of pure HMS and Re-Ge-double-doped samples, respectively. The incorporation of isoelectronic codoping, along with the integration of metastable QDs, is demonstrated as an effective strategy for enhancing TE properties.

Multifunctional boron nitride nanosheets/fluorinated‐polyimide composites with ultra‐low dielectric constant and high thermal conductivity

AbstractThermally conductive polymeric composites with low dielectric constant are highly promising for the packaging materials in the field of modern communication. Therefore, the synergistic improvement of low dielectric constant and high thermal conductivity has become a current research hotspot. In this work, we propose a one‐step alkylation of boron nitride nanosheet (BNNS) with ultrasonic stratification using 1‐hexanol, and then hot press the films to make Alkyl‐BNNSs orient in the fluorinated polyimide (f‐PI). The resulting Alkyl‐BNNS/f‐PI composite successfully realizes the synergistic improvement of thermal property and dielectric properties, exhibiting a high heat conductivity coefficient of 2.36 Wm−1 K−1 with a filler content of 4.99 wt.%. Moreover, the permittivity and dielectric loss of the film are as low as 1.76 and 0.0065 at 1 MHz, respectively. This work provides a facile strategy for breaking the bottleneck of making polyimide composites simultaneously with high thermal conduction and low dielectric performance.Highlights The composite exhibits a high heat‐conducting coefficient of 2.36 Wm−1 K−1. Ultra‐low dielectric constant of 1.76 was achieved by the modification of film. Excellent breakdown resistance and flexibility were endowed with the composites.