Thermal Conductivity Research Articles

Impact of carbon dioxide loading on the thermal conductivity of metal organic frameworks.

Owing to their unrivaled porosities and high surface areas, metal organic frameworks (MOFs) hold great promise for mitigating the global warming crisis through capturing and storing CO2 gas. However, the exothermic process of CO2 uptake can lead to temperature rises that can severely compromise the efficiency of these materials for such purposes. In this work, we employ reactive molecular dynamics simulations and anharmonic lattice dynamics calculations to investigate the influence of varying levels of CO2 uptake in dictating the heat transfer mechanisms in MOF-5. Compared to the empty framework, we find that the thermal conductivity of the gas loaded framework is highly dependent on the gas diffusivities and temperatures. At low temperatures, where the gases have low diffusivities and are predominantly adsorbed to the pore walls, vibrational scattering from the solid-gas interactions leads to drastically reduced thermal conductivities. At higher temperatures (above ∼200K), however, we find that the CO2 molecules with increased diffusivities can lead to additional channels of heat conduction for high gas densities. Our spectral analyses show that the addition of gas adsorbates has a negligible influence on the heat carrying acoustic modes of the framework at such relatively higher temperatures. Contrastingly, at lower temperatures, gas infiltration leads to considerable scattering and reduced lifetimes of the acoustic vibrational modes of the framework. These findings provide critical insights into the mechanistic processes dictating heat conduction in guest-infiltrated MOFs and offer a pathway to tailor their thermal properties for advanced applications in gas storage, separation, catalysis, and thermoelectrics.

Bi‐Directional Assembly of Boron Nitride µ‐Platelets by Micro‐Molding for Advanced Thermal Interface Materials

AbstractWith dramatically growing demand for highly complicated, high power‐consumed 3D stacked integrated circuit electronics, the advancement of effective thermal management has become a key technology to secure both performance and stability. To ensure better heat management of integrated microelectronics, especially pursuing unconventional devices assembled on a sheet of paper or plastics, more feasible and effective heat management is inevitable. In this study, the mechanically robust and bi‐directionally thermal conductive material are presented by micro‐molding with boron‐nitride (BN) microscale platelets (µ‐platelets) dispersed in the polymeric matrix. Micro‐pattern‐induced bifurcation of assembly orientation of the BN µ‐platelets and bi‐directionality of heat conduction characteristics are observed. The bifurcated orientations of the BN µ‐platelets are optimized by the geometry of the micro‐pattern and unit size of the platelets with the assistance of particle‐fluid simulation. Indeed, exceptionally enhanced thermal conductivities through both directions: 6.9 W m−1 K−1 in the through‐plane and 7.4 W m−1 K−1 in the in‐plane, respectively are achieved. It also exhibits flexibility with a minimum radius of curvature ≈1 mm and the capability of conformal contact to diverse morphologies to stably secure heat flow even in mechanically deformed device structures. The developed TIM can be applied to high‐power, high‐temperature, and mechanically deformable application environments of 3D‐integrated electronics.

Engineering a Novel Ceramic Composite for High‐Temperature Thermal Insulation

Thermal insulations play a pivotal role in energy conservation and carbon footprint reduction by mitigating energy losses at elevated temperatures. The thermal insulation of large energy systems faces challenges of in situ application and rise in thermal conductivity of the insulation with the increasing application surface temperature. This work develops, characterizes, and investigates a high‐temperature ceramic composite (HTCC) insulation to address these challenges for high‐temperature (≥300 °C) applications. Ceramic wool fiber, hollow ceramic microspheres, and silica form a multiscale porous structure in the HTCC that minimizes heat loss at high temperatures due to the infinite hot plate effect and phonon scattering phenomena. The rise in thermal conductivity for HTCC is 38%, whereas for conventional insulation, ceramic fiber (CF) it is 56%, when the application temperature increases from 300 to 500 °C. Moreover, the thermal diffusivity of the developed composite is 58% lower than CF. The efficacy of the HTCC is investigated experimentally using a model of thermal energy storage. The HTCC insulation, at 55% less thickness, reduces the heat loss by 37%, saving around 4780 kWh m−2 yearly compared to conventional insulation. Significant energy savings are expected when HTCC is applied to large‐scale industrial energy systems.

Hierarchically Structured Composite Decorated with Core-Sheath CoC@Carbon Fiber Felt: Exceptional Electromagnetic Interference Shielding and Applications in Thermal Management and Electro/Photo-Thermal Conversion.

In the microelectronics era, electromagnetic radiation and heat accumulation in electronic devices are urgent challenges requiring solutions, particularly through the use of structure-function integrated and lightweight materials for electromagnetic interference (EMI) shielding and thermal management. Hierarchically structured polyether-ether-ketone-based composites are prepared in this study by in situ deposition and dip coating using a simple and scalable method. Magnetic cobalt nanoparticles derived from magnetic metal-organic frameworks are deposited on carbon fiber felt featuring a macroscopic continuous conductive network. Next, a hybrid slurry is applied to connect the isolated fibers, which bridge the fiber gaps to create new electron and phonon transport channels, increasing the thermal conductivity (23.43 Wm-1K-1 in plane, 4.84 Wm-1K-1 through plane) for efficient heat dissipation. Owing to the stable 3D crosslinked network with high electrical conductivity (13608 Sm-1), the composite offers ultra-high EMI shielding in the X-band (101.64dB with stability in extreme environments), excellent Joule heating performance (220°C at 4V), and excellent photothermal conversion (94°C at 500 mWcm-2). This multifunctional composite material has great application prospects in precision electronic equipment.

Palm Oil as a Transformer Insulating Fluid: A Review

Traditionally, mineral oil has dominated the industry due to its reliable dielectric properties and effective thermal conductivity. However, the increasing environmental concerns surrounding the use of non-renewable and ecologically hazardous mineral oil have initiated research into alternative, sustainable insulating fluids. Palm oil has emerged as a potential candidate due to its biodegradable nature and renewable source. This paper provides a comprehensive review of palm oil’s suitability as a transformer insulating fluid, comparing its dielectric properties, thermal stability, and environmental benefits to those of mineral oil. Besides, palm oil exhibits promising characteristics, including a breakdown voltage of up to 60 kV, superior moisture tolerance, and a higher relative permittivity, making it suitable for high-voltage applications. However, challenges remain, particularly regarding oxidation stability and viscosity, which require further refinement for broader adoption. The study emphasizes the potential of palm oil to align with global sustainability goals while addressing the technical requirements of transformers.

Antiferroelectric Behavior in Mixed‐Anion Bi2TiO4F2 Induced by Rotation of TiO3F3 Octahedra

AbstractAntiferroelectric materials, known for their structural transitions from paraelectric to ferroelectric phases under an electric field, have attracted significant interest due to their high energy storage capacity and rapid thermal conductivity switching capabilities. Traditionally, research on antiferroelectric properties has focused on modifying metal cations or crystal structures, with cation displacement playing a central role in the mechanism. However, antiferroelectric states have not been reported in mixed‐anion systems, where some oxide ions (O2–) are replaced by other anions such as nitride or fluoride (F–). This study demonstrates that Bi2TiO4F2, a layered Aurivillius‐type oxyfluoride film, exhibits antiferroelectric behavior, undergoing structural transitions from non‐polar to polar phases under an electric field. Theoretical calculations reveal that this behavior is driven by the rotation of TiO3F3 octahedra within the perovskite layers, leading to displacements of O2– and F– ions along the c‐axis due to their valence differences. Unlike conventional metal oxides, where antiferroelectricity is governed by cation displacements, oxyfluorides present a novel mechanism based on anion valence disparities. This finding paves the way for designing advanced antiferroelectric materials with mechanisms distinct from those of traditional oxides.

Limitations and Advances in Optical Thermal Transport Measurements: Extremes in Properties, Length Scales, and Temperature

Conductive and radiative thermal transport play a critical role in the design, development, and performance of a wide array of technologies and applications. In this review, we focus on the challenges associated with nano- and microscale thermal measurements and the strategies developed thus far to overcome them. For measurements below ∼1,000°C, numerous thermoreflectance techniques are already in wide use; however, uncertainty and measurement error may limit the measurement of samples in certain regimes. These regimes include materials of high thermal conductivity (≳2,000 W/m·K), thin films (≲100 nm), or interfaces located well below the sample surface. A rigorous treatment of uncertainty and error is thus required for measuring these samples and for the development of future metrology tools. At higher temperatures, pyrometry techniques are being developed; however, several physical and experimental limitations exist. Some methods rely on a known emissivity for the measurement of temperature, and significant radiative transport can introduce error in modeling. Both of these mean that knowledge of spectrally dependent and temperature-dependent emissivity properties may be required.

A systematic review of knowledge graph and computational schemes related to soil thermal conductivity

A systematic review of knowledge graph and computational schemes related to soil thermal conductivity

Research on the Thermal Conductivity and Microstructure of Calcium Lignosulfonate-Magnesium Oxide Solidified Loess

Loess, characterized by high porosity, a loose structure, and weak cementation, is highly prone to deformation and cracking under thermal stress, which significantly affects the bearing capacity of foundations and the stability of underground engineering structures. This study introduces an innovative approach that utilizes the eco-friendly modifier calcium lignosulfonate (CL) in combination with magnesium oxide (MgO) for the carbonation solidification treatment of loess. The research systematically investigated the thermal conductivity and underlying micro-mechanisms of the treated soil. A series of tests, including analyses of basic physical properties, measurements of thermal conductivity, X-ray diffraction (XRD), and scanning electron microscopy (SEM), were conducted to evaluate the effects of CL dosage, freeze–thaw cycles, moisture content, and dry density on the thermal conductivity of carbonation-solidified loess. The results indicate that carbonated solidified loess absorbed approximately 6% of CO2, while effectively reducing its collapsibility grade to a slightly collapsible classification. Additionally, its thermal conductivity decreased by 16.7%, thereby mitigating the influence of various environmental factors. Based on the experimental results, a microscopic mechanism model was developed. This study presents a sustainable and innovative technical solution for stabilizing loess foundations in cold regions.

Uncooled Microbolometers Based on Nitrogen-Doped Hydrogenated Amorphous Silicon-Germanium (a-SiGe:H,N)

An uncooled microbolometer is a thermal sensor consisting of a membrane suspended from the substrate to provide thermal insulation. Typically, the membrane is composed of a stack of three films integrated by a supporting film, an IR sensing film, and an IR absorbing film. However, the above increases the thickness of the device and affects its mechanical stability and thermal mass, thereby reducing its performance. One solution is to use a single film as a membrane with both IR sensing and IR absorbing properties. In this regard, this work presents the fabrication and evaluation of uncooled microbolometers using nitrogen-doped hydrogenated amorphous silicon-germanium (a-SiGe:H,N) as a single IR-absorber/IR sensing membrane. The films were deposited via low frequency Plasma Enhanced Chemical Vapor Deposition (PECVD) at 200 °C. Three microbolometer configurations were fabricated using a-SiGe:H,N films deposited from a SiH4, GeH4, N2, and H2 gas mixture with different SiH4 and GeH4 flow rates and, consequently, with different properties, such as temperature coefficient of resistance (TCR) and conductivity at room temperature. The microbolometer that exhibited the best performance achieved a voltage responsivity of 7.26 × 105 V/W and a NETD of 22.35 mK at 140 Hz, which is comparable to state-of-the-art uncooled infrared (IR) sensors. These results confirm that the optimization of the deposition parameters of the a-SiGe:H,N films significantly affects the microbolometers final performance, enabling an optimal balance between thermal sensitivity (TCR) and conductivity.

Oxidation Process and Addition of Zn and Te Lead to the Enhancement of Thermoelectric Figure of Merit in p-Type Bi2Te3.

To date, Bi2Te3-based systems are the most promising thermoelectric materials near room temperature for Peltier cooling and energy harvesting. Further improvement of the thermoelectric figure of merit zT is required to broaden the application of Bi2Te3-based thermoelectrics. In this study, we investigated the critical role of oxidation in the thermoelectric performance of p-type Bi0.45Sb1.55Te3 and proposed a way to improve the performance. Impurity oxides inevitably formed during the fabrication processes of constituent elements, leading to lowered mobility. To solve this problem, an oxygen getter element, Zn, was added to capture the oxygen from the Bi0.45Sb1.55Te3 matrix to increase the mobility. Moreover, the formed byproduct ZnO effectively scattered heat-carrying phonons simultaneously. The control of the oxidation process and the addition of Zn and Te led to a 30% enhancement in the zT of Bi0.45Sb1.55Te3 with the decoupling of improved electronic properties and reduced lattice thermal conductivity.

High-Performance Oxide Thin-Film Transistors with Atomic Layer Deposition-Grown HfO2/BeO Hetero-Dielectric.

Atomic layer deposition-grown beryllium oxide (BeO) is gaining attention as a dielectric material that can minimize device power consumption because of its high dielectric constant, high thermal conductivity, and low leakage current enabled by its wide bandgap energy. In this study, the impact of BeO dielectrics on InSnZnO (ITZO) thin-film transistors (TFTs) was investigated, revealing that adding a hafnium dioxide (HfO2) layer can enhance electrical performance and bias stress reliability. Time-of-flight secondary-ion mass spectrometry and X-ray photoelectron spectroscopy confirmed that the single-BeO dielectric-based ITZO TFTs exhibited a low mobility of 27.6 cm2/V·s due to Be migration and demonstrated abnormal threshold voltage (VTH) shifts under bias stress. Conversely, the HfO2 20 nm/BeO hetero-dielectric ITZO TFTs exhibited a high mobility of 76.6 cm2/V·s and enhanced abnormal VTH shift characteristics. Therefore, these results demonstrate that our high-performance HfO2/BeO hetero-dielectric-based ITZO TFTs could be utilized in back-end-of-line devices for monolithic three-dimensional memory technologies.

Enhancing Precision in Arc Welding Simulations: A Comprehensive Study of the Ellipsoidal Heat Source Model

Arc welding is a complex multiphysics mitigation process, and the related finite element simulation requires significant computational resources for multiphysics modeling to determine the temperature distributions in engineering problems accurately. Engineers and researchers aim to achieve reliable results from finite element analysis while minimizing computational costs. This research extensively studies the application of conventional ellipsoidal heat source formulation to obtain improved temperature distribution during arc welding for practical applications. The ellipsoidal heat source model, which artificially modifies the coefficient of thermal conductivity in the welding pool area to simulate stirring effects, is proven to be scientifically valid by comparing its results with those of COMSOL’s multiphysics arc welding analyses. The findings from finite element analyses demonstrate that the temperature fields generated using the modified ellipsoidal approach exhibit strong agreement with those obtained from multiphysics simulations, especially within the core regions of the weld pool. The method can easily be implemented in all different welding methods in which a stirring effect is formed by either electromagnetic or buoyancy-driven flows in the weld pool area. Furthermore, the method offers computational efficiency without sacrificing accuracy, making it suitable for industrial applications where multiphysics modeling is not feasible but reliable thermal and structural predictions are essential.

Application of Voronoi Tessellation to the Additive Manufacturing of Thermal Barriers of Irregular Porous Materials—Experimental Determination of Thermal Properties

The issue of energy transfer is extremely important. In order to achieve the lowest possible energy consumption and the required thermal efficiency in energy-efficient buildings, it is necessary, among other things, to minimize the heat-transfer coefficient, which depends on the properties of the insulating material. Analyses of the relationship between the structure of a material and its thermal conductivity coefficient have shown that lower values of this coefficient can be achieved with a more complex structure that mimics natural forms. This paper presents a design method based on the Voronoi diagram to obtain a three-dimensional structure of a porous composite material. The method was found to be effective in producing structures with predefined and functionally graded porosity. The porous specimens were fabricated from a biodegradable soybean oil-based resin using mSLA additive technology. Analyses were performed to determine the thermal parameters of the anisotropic composites. Experimental results showed that both porosity and irregularity affect the thermal properties. The lowest thermal conductivity coefficients were obtained for a 100 mm-thick prototype composite with the following parameters: wall thickness D = 0.2 mm, cell size S = 4 mm, number of structural layers n = 2, and degree of irregularity R = 4. The lowest possible thermal conductivity of the insulation was 0.026 W/(m·K), and the highest possible thermal resistance was 3.92 (m2·K)/W. The method presented in this study provides an effective solution for nature-inspired design and topological optimization of porous structures.

Heterogeneous and Monolithic 3D Integrated Full‐Color Micro‐Light‐Emitting Diodes via CMOS‐Compatible Oxide Bonding for µLEDoS

AbstractMicro‐light emitting diode (µLED) based LED on silicon (LEDoS) is a promising candidate for next‐generation AR and VR displays due to superior pixel performance and potential for high resolution. Traditional RGB pixels are placed on a single plane, which limits the resolution. To overcome this, vertically stacked RGB pixels using heterogeneous and monolithic 3D integration (M3D) have been explored. However, previously reported vertical µLED pixels have not considered the heat dissipation capability of the pixels, which is indeed important in future micro displays, and utilized materials incompatible with standard CMOS processes, further limiting their practicality for LEDoS. The critical regions for constraint, the bonding medium, are typically organic polymer materials. Therefore, to handle issue, vertically stacked full‐color µLEDs are demonstrated using silicon oxide (SiO2) and yttrium oxide (Y2O3), as bonding mediums. These materials are CMOS‐compatible and offer thermal conductivity at least 10 times higher than conventional polymers. The InGaN/GaN blue µLEDs bonded with oxides show improved thermal management, leading to higher external quantum efficiency (EQE) and better color characteristics, including narrower full width at half maximum (FWHM) and higher color purity. Precise control over bonding layer thickness is achieved, minimizing pixel thickness and enhancing manufacturability for high‐resolution displays.

Equivalent doping of Te leads to optimized electrical and thermal transport properties in thermoelectric Cu2MnSnSe4 alloys

Quaternary chalcogenides have garnered considerable interest within the field of thermoelectric due to their intrinsic low thermal conductivity, wide bandgap and high element enrichment advantages. In this work, the thermoelectric performance of Cu2MnSnSe4 was enhanced by co-optimizing the carrier concentration and lattice thermal conductivity through self-doping with Cu and doping with Te. A series of Cu2MnSnSe4 and Cu2.1Mn0.9SnSe4-x Tex (x = 0, 0.01, 0.05, 0.10) samples were prepared by ball-milling and hot-pressing methods. The carrier concentration of the samples was significantly increased after Cu self-doping, leading to optimized electrical transport performance. The notable reduction in lattice thermal conductivity was attributed to the scattering effect caused by Te substitution-induced point defects. At 673 K, the lattice thermal conductivity of the Cu2.1Mn0.9SnSe3.9Te0.1 sample obtained the lowest value of 0.62 W m-1K-1. Finally, it achieved a maximum zT ~ 0.5 at 673 K in the Cu2.1Mn0.9SnSe3.9Te0.1 sample, roughly twice that of the Cu2MnSnSe4 sample.

Electronic band structure, magnetic and thermoelectric properties of sodium and lanthanum cobaltites: ab initio PAW approach

ABSTRACT The electronic band structure and thermoelectric properties of the NaCoO2 and LaCoO3 cobaltites have been studied by the PAW method. The thermoelectric characteristics were calculated on the basis of Boltzmann–Onsager theory taking into account electron scattering by optical phonons, and the thermal conductivity coefficient was calculated using the Slack approximation. For LaCoO3 with electronic conductivity, in accordance with experimental data, the change of sign of Seebeck coefficient is noted at high temperatures. It is shown for NaCoO2 with hole conductivity that the sign of Seebeck coefficient can also be expected to change at high temperature. By varying starting magnetic moments, five solutions compatible with the LaCoO3 semiconductor conductivity were achieved. The magnetic states of cobalt atoms at semiconductor conductivity may have spin value S = 0 or 3/2.

Study of heat transfer model and buried thermocouple test of bell-type annealing furnace based on thermal equilibrium

The bell-type annealing furnace is a key equipment in the cold rolling process, and the heat transfer process inside the furnace has a significant impact on the annealing process and product quality. At present, there are shortcomings in the calculation accuracy of model research based on heat transfer theory and practical experience. In addition, existing research has not fully considered the influence of gas flow distribution and corresponding heat transfer coefficient in each channel of multi tube steel coils on the temperature field. The aim of this study is to develop a more accurate heat transfer model for bell type annealing furnaces and verify its reliability. In this work, a heat transfer model for a bell jar furnace was established based on the thermal equilibrium method, and its accuracy was verified through industrial buried thermocouple tests. The results indicate that the heat transfer model has high accuracy due to considering the distribution of protective gas flow rate, convective heat transfer coefficient, and radial thermal conductivity of the steel coil. The average relative error of the cold spot temperature calculated by the model is less than 0.5%, and the hot spot temperature does not exceed 5%, which proves the accuracy and reliability of the model, especially for cold spot temperature. When the relative error of the cold spot temperature is within 2.5%, the accuracy of the coil is above 95%. This study provides an accurate heat transfer model for fitting the heat transfer process of bell type annealing furnaces.

Correction: Comprehensive experimental investigation on using single size glass granular as partial replacement of sand on the fresh and mechanical, durability, thermal conductivity properties of mortar

Correction: Comprehensive experimental investigation on using single size glass granular as partial replacement of sand on the fresh and mechanical, durability, thermal conductivity properties of mortar

Weak Chemical Bonds and High Electrical Conductivities Lead to High Thermoelectric Performance in Zintl Compounds Sr2CdX2 (X = As, Sb, and Bi).

Zintl semiconductors are known to exhibit exceptional thermoelectric properties, due to their high electron transport and low lattice thermal conductivity (κL). In this work, thermoelectric properties of Zintl compounds Sr2CdX2 (X = As, Sb, Bi) were studied by using first-principles calculations in conjunction with Boltzmann transport theory. Both Sr2CdSb2 and Sr2CdBi2 adopt the same structure as Sr2CdAs2 (Cmc21) and are synthesizable. All of these compounds demonstrate low lattice thermal conductivities, ranging from 2.3 to 0.5 Wm1- K-1 at 300 K, attributed to their low sound velocity and significant three-phonon scattering, which originate from the weak chemical bonds and strong interaction between acoustic phonons and low-lying optical phonons. The low polar-optical phonon scattering is a result of the relatively small contributions of ions to dielectric constants. Notably, the electrical conductivities (σ) and κL of these compounds exhibit significant anisotropy, with the highest and lowest values being along the x- and z-axis, respectively. Consequently, the highest ZT values of Sr2CdAs2 (1.39), Sr2CdSb2 (1.97), and Sr2CdBi2 (1.74) are achieved along the x-direction at 800 K under n-type doping, respectively, which is comparable or even superior to the well-studied thermoelectric material Mg3Sb2, positioning them as promising candidates for thermoelectric applications.