•Metal and carbon based materials are used to enhance the heat transfer rate in PCM.•Melting point of the PCMs becomes slightly lower for PCM/foam composites.•Higher porosity foams are suitable for ...convection heat transfer.•Latent heat and specific heats are reduced for PCM/foam composites.•Charging and discharging period of composite PCMs become lower.
Phase change material (PCM) is promising media for thermal energy storage owing to its extensive value of latent heat (140–970 KJ/Kg). However, thermal conductivity of PCMs is too low which obstructs energy storage and retrieval rate. In recent days, thermally enhanced PCMs are considered promising materials for efficient heat transfer in many applications. This article designates the review on improved thermal properties and heat transfer of PCMs by using porous materials. Enhanced heat transfer of PCMs can be achieved using extended surfaces (triangular, conical, square, and rectangular fins), heat pipes, and addition of highly conductive nanoparticles (e.g. Cu, Al2O3, Au, SiC, SiO2 and TiO2). Major focus of this article is to study the enhanced heat transfer of PCMs through metallic (copper, nickel, and aluminum) and carbon based (carbon, graphite and expanded graphite) porous materials/foams. Effects of porosity and pore density on heat transfer, thermal conductivity, specific heat, latent heat and charging/discharging time are critically reviewed. Porous materials/foams are reported to be efficient for heat transfer/thermal conductivity enhancement by 3–500 times. Furthermore, correlations to find the effective thermal conductivity of PCM/foam are reported. Important applications of PCM/foam reported by different researchers are also discussed in this paper. Finally, conclusions and recommendations are presented to highlight the research gap in this area.
Owing to the growing heat removal issue of modern electronic devices, polymer composites with high thermal conductivity have drawn much attention in the past few years. However, a traditional method ...to enhance the thermal conductivity of the polymers by addition of inorganic fillers usually creates composite with not only limited thermal conductivity but also other detrimental effects due to large amount of fillers required. Here, novel polymer composites are reported by first constructing 3D boron nitride nanosheets (3D‐BNNS) network using ice‐templated approach and then infiltrating them with epoxy matrix. The obtained polymer composites exhibit a high thermal conductivity (2.85 W m−1 K−1), a low thermal expansion coefficient (24–32 ppm K−1), and an increased glass transition temperature (Tg) at relatively low BNNSs loading (9.29 vol%). These results demonstrate that this approach opens a new avenue for design and preparation of polymer composites with high thermal conductivity. The polymer composites are potentially useful in advanced electronic packaging techniques, namely, thermal interface materials, underfill materials, molding compounds, and organic substrates.
Polymer composites are fabricated by constructing 3D boron nitride nanosheet (3D‐BNNS) networks using an ice‐templated approach. The polymer composites exhibit a high thermal conductivity, low coefficient of thermal expansion, and an increased glass transition temperature at relatively low BNNS loading (9.29 vol%). This approach finds uses in the preparation of the polymer composites with high thermal conductivity.
Ceramic Conductors Mielewczyk-Gryń, Aleksandra; Gazda, Maria
01/2019
eBook
Open access
This Special Issue of Crystals contains papers focusing on various properties of conducting ceramics. Multiple aspects of both the research and application of this group of materials have been ...addressed. Conducting ceramics are the wide group of mostly oxide materials which play crucial roles in various technical applications, especially in the context of the harvesting and storage of energy. Without ion-conducting oxides, such as yttria-stabilized zirconia, doped ceria devices such as solid oxide fuel cells would not exist, not to mention the wide group of other ion conductors which can be applied in batteries or even electrolyzers, besides fuel cells. The works published in this Special Issue tackle experimental results as well as general theoretical trends in the field of ceramic conductors, or electroceramics, as it is often referred to.
The d-wave superconductor CeCoIn5 has been proposed as a strong candidate for supporting the Fulde-Ferrell-Larkin-Ovchinnikov (FFLO) state near the low-temperature boundary of its upper critical ...field. Neutron diffraction, however, finds spin-density-wave (SDW) order in this part of the phase diagram for field in the a−b plane, and evidence for the SDW disappears as the applied field is rotated toward the tetragonal c axis. It is important to understand the interplay between the SDW and a possible FFLO state in CeCoIn5, as the mere existence of an SDW does not necessarily exclude an FFLO state. Here, based on a model constructed on the basis of available experiments, we show that an FFLO state competes with an SDW phase. The SDW state in CeCoIn5 is stabilized when the field is directed close to the a−b plane. When the field is rotated toward the c axis, the FFLO state emerges, and the SDW phase disappears. In the FFLO state, the nodal planes with extra quasiparticles (where the superconducting order parameter is zero) are perpendicular to the field, and in the SDW phase, the quasiparticle density of states is reduced. We test this model prediction by measuring heat transported by normal quasiparticles in the superconducting state. As a function of field, we observe a reduction of thermal conductivity for field close to the a−b plane and an enhancement of thermal conductivity when field is close to the c axis, consistent with theoretical expectations. Our modeling and experiments, therefore, indicate the existence of the FFLO state when field is parallel to the c axis.
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Controlling the flow of thermal energy is crucial to numerous applications ranging from microelectronic devices to energy storage and energy conversion devices. Here, we report ultralow lattice ...thermal conductivities of solution-synthesized, single-crystalline all-inorganic halide perovskite nanowires composed of CsPbI₃ (0.45 ± 0.05 W·m−1·K−1), CsPbBr₃ (0.42 ± 0.04 W·m−1·K−1), and CsSnI₃ (0.38 ± 0.04 W·m−1·K−1). We attribute this ultralow thermal conductivity to the cluster rattling mechanism, wherein strong optical–acoustic phonon scatterings are driven by a mixture of 0D/1D/2D collective motions. Remarkably, CsSnI₃ possesses a rare combination of ultralow thermal conductivity, high electrical conductivity (282 S·cm−1), and high hole mobility (394 cm²·V−1·s−1). The unique thermal transport properties in all-inorganic halide perovskites hold promise for diverse applications such as phononic and thermoelectric devices. Furthermore, the insights obtained from this work suggest an opportunity to discover low thermal conductivity materials among unexplored inorganic crystals beyond caged and layered structures.
Semiconductors with very low lattice thermal conductivities are highly desired for applications relevant to thermal energy conversion and management, such as thermoelectrics and thermal barrier ...coatings. Although the crystal structure and chemical bonding are known to play vital roles in shaping heat transfer behavior, material design approaches of lowering lattice thermal conductivity using chemical bonding principles are uncommon. In this work, an effective strategy of weakening interatomic interactions and therefore suppressing lattice thermal conductivity based on chemical bonding principles is presented and a high‐efficiency approach of discovering low κL materials by screening the local coordination environments of crystalline compounds is developed. The resulting first‐principles calculations uncover 30 hitherto unexplored compounds with (ultra)low lattice thermal conductivities from 13 prototype crystal structures contained in the Inorganic Crystal Structure Database. Furthermore, an approach of rationally designing high‐performance thermoelectrics is demonstrated by additionally incorporating cations with stereochemically active lone‐pair electrons. These results not only provide atomic‐level insights into the physical origin of the low lattice thermal conductivity in a large family of copper/silver‐based compounds but also offer an efficient approach to discover and design materials with targeted thermal transport properties.
A strategy for suppressing lattice thermal conductivity based on chemical bonding principles is developed. The filling of the p‐d antibonding states formed between Cu/Ag‐d and anion‐p and edge/face‐sharing polyhedra jointly weaken chemical bonds and lead to low lattice thermal conductivity. A fast screening based on local coordination environments and first‐principles calculations uncovers 30 new compounds with ultralow lattice thermal conductivities.
Owing to their ultralow thermal conductivity and open pore structure
, silica aerogels are widely used in thermal insulation
, catalysis
, physics
, environmental remediation
, optical devices
and ...hypervelocity particle capture
. Thermal insulation is by far the largest market for silica aerogels, which are ideal materials when space is limited. One drawback of silica aerogels is their brittleness. Fibre reinforcement and binders can be used to overcome this for large-volume applications in building and industrial insulation
, but their poor machinability, combined with the difficulty of precisely casting small objects, limits the miniaturization potential of silica aerogels. Additive manufacturing provides an alternative route to miniaturization, but was "considered not feasible for silica aerogel"
. Here we present a direct ink writing protocol to create miniaturized silica aerogel objects from a slurry of silica aerogel powder in a dilute silica nanoparticle suspension (sol). The inks exhibit shear-thinning behaviour, owing to the high volume fraction of gel particles. As a result, they flow easily through the nozzle during printing, but their viscosity increases rapidly after printing, ensuring that the printed objects retain their shape. After printing, the silica sol is gelled in an ammonia atmosphere to enable subsequent processing into aerogels. The printed aerogel objects are pure silica and retain the high specific surface area (751 square metres per gram) and ultralow thermal conductivity (15.9 milliwatts per metre per kelvin) typical of silica aerogels. Furthermore, we demonstrate the ease with which functional nanoparticles can be incorporated. The printed silica aerogel objects can be used for thermal management, as miniaturized gas pumps and to degrade volatile organic compounds, illustrating the potential of our protocol.
Crystal defects affect the thermal and heat-transport properties of materials by scattering phonons and modifying phonon spectra
. To appreciate how imperfections in solids influence thermal ...conductivity and diffusivity, it is thus essential to understand phonon-defect interactions. Sophisticated theories are available to explore such interactions, but experimental validation is limited because most phonon-detecting spectroscopic methods do not reach the high spatial resolution needed to resolve local vibrational spectra near individual defects. Here we demonstrate that space- and angle-resolved vibrational spectroscopy in a transmission electron microscope makes it possible to map the vibrational spectra of individual crystal defects. We detect a red shift of several millielectronvolts in the energy of acoustic vibration modes near a single stacking fault in cubic silicon carbide, together with substantial changes in their intensity, and find that these changes are confined to within a few nanometres of the stacking fault. These observations illustrate that the capabilities of a state-of-the-art transmission electron microscope open the door to the direct mapping of phonon propagation around defects, which is expected to provide useful guidance for engineering the thermal properties of materials.
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