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In the present study, changes in thermal properties, microstructure and microhardness were investigated when 0.5, 1, 1.5 wt % Sb were added to Sn–1 wt % Ag–0.5 wt % Cu (SAC105) solder alloy system. The addition of Sb caused a significant improvement in microhardness while decreasing the melting temperature range, thermal conductivity and electrical conductivity. Addition of 0.5, 1, 1.5 wt % Sb to SAC105 alloy system decreased the thermal conductivity by 48% and electrical conductivity by 27%. The addition of Sb at the same rate increased the microhardness by 27%. [ABSTRACT FROM AUTHOR]

The performance of microwave devices is significantly influenced by the substrates employed. In this study, we introduce a novel microwave composite substrate material exhibiting high dielectric constant and exceptional thermal conductivity, comprising dopamine-modified boron nitride nanosheets (BNNS@PDA) and SrTiO 3 /polyolefin. With an 8 wt% BNNS@PDA filler content, the composite material achieves a high dielectric constant of 17.7 (@10 GHz) and remarkable thermal conductivity of 1.604 W/(m·K), representing enhancements of 34% and 104% compared to SrTiO 3 /polyolefin, respectively. Additionally, a low dielectric loss of 2.95 × 10−3 and minimal water absorption of 0.15% are attained. The incorporation of BNNS@PDA augments the compatibility between the ceramic particles and resin matrix, contributing to increased dielectric constant, superior density and improved mechanical properties of composite materials. As an interval within the thermal conductive pathway, the PDA coating diminishes the system's thermal conductivity. And its interplay with polymer matrix influences the resin's curing process, subtly reducing the composite's thermal stability. In summary, BNNS@PDA/SrTiO 3 /polyolefin represents a promising microwave dielectric substrate material, offering high dielectric constant and excellent thermal conductivity. [ABSTRACT FROM AUTHOR]

In the paper, generalized boundary conditions were used for the homogenization of coefficients of the Laplace partial differential equation in the context of Darcy flow and heat diffusion phenomena. The mesoscopic boundary value problem was defined and analyzed from the variational perspective and the finite element formulation of the homogenization problem was provided. The matrix equation for the apparent macroscopic properties, resulting from FEM discretization, was derived and utilized in two illustrative examples: homogenization of the filtration coefficient of clay amended with expanded shale and thermal conductivity of the soil with multiple fractions. It is shown, that generalized boundary conditions can provide very good homogenization results without the assumption of the periodicity of the material. For best results, the microscopic length parameter has to be properly estimated. [ABSTRACT FROM AUTHOR]

This paper reports an experimental investigation of the thermal properties of frozen tap, demineralized, and sea water. The presented research assists in a better understanding of the thermal properties of ice and the processes within it and contributes regarding the generation of novel experimental data. The thermal conductivity was measured in a range from −14 °C to −33 °C using the Transient Plane Source (TPS) method. Ice blocks were placed in an expanded polystyrene box in the freezer, which is where the measurements took place. The thermal conductivity of the tap water ice was observed to vary in a range from 1.915 ± 0.005 Wm−1K−1 at −14 °C to 2.060 ± 0.004 Wm−1K−1 at −33 °C. The values obtained for the ice made of demineralized water differed by less than 10%. The thermal conductivity of the sea ice was shown to be more temperature dependent, with the values ranging from 1.262 ± 0.005 Wm−1K−1 at −14 °C to 1.970 Wm−1K−1 ± 0.004 at −33 °C. A noticeable fall in the thermal conductivity of the sea ice was observed in the temperature range from −26 °C to −19 °C. A possible reason for this could be the increased precipitation of salt in that temperature range. Measurements of thermal diffusivity displayed similar trends as those of thermal conductivity. Specific volumetric heat capacity was indirectly calculated. [ABSTRACT FROM AUTHOR]

Polyimide-based composite films with high thermal conductivity, good mechanical property and electrical insulating performance are urgently needed in the electronics and microelectronics fields. As one of the key technical challenges to be solved, interfacial compatibility between filler and matrix plays an important role for composite film. Herein, boron nitride was modified by grafting polyimide brushes via a two-step method, and a series of thermally conductive polyimide/boron nitride composite films were prepared. Both characterization and performance results proved that the interfacial interaction and compatibility was greatly enhanced, resulting in a significant reduction in defects and interfacial thermal resistance. The interphase width of transition zone between two phases was also efficiently enlarged due to polyimide brushes grafted on filler surface. As a result, composite films based on polyimide-grafted boron nitride exhibited significantly improved properties compared with those based on pristine filler. Tensile strength can reach up to 80 MPa even if the filler content is as high as 50 wt%. The out-of-plane and in-plane thermal conductivity of composite film increased to 0.841 and 0.850 W·m−1·K−1, respectively. In addition, thermal and dielectric properties of composite films were also enhanced to some extent. The above results indicate that surface modification by chemically grafting polymer brushes is an effective method to improve two-phase interfacial compatibility so as to prepare composite film with enhanced properties. [ABSTRACT FROM AUTHOR]

For the removal of elevated thermal flux in high‐temperature applications, there is an urgent need for robust and lightweight thermally conductive thermoplastic materials with suitable mechanical integrity. In current work, multiscale hexagonal boron nitride (hBN) and titanium dioxide (TiO2) fillers are integrated into polyetheretherketone (PEEK) polymer to create a synergistic effect regarding thermal conductivity. An optimized twin‐screw extrusion is utilized to disperse the fillers uniformly in the host polymer by changing the screw design in terms of kneading, mixing, and reverse elements, feeding zones of the fillers/polymer, and the feeding cycles. Various specimens were developed by systematically varying the relative filler amount of the thermally anisotropic hBN and the thermally isotropic TiO2, while the total filler content was fixed to 60 wt%. As a result, 50B‐10T composite exhibited an ultrahigh thermal conductivity of 8.195 W/(m.K), with a 3139% enhancement compared to unfilled PEEK. Moreover, as the PEEK‐mediated regions are occupied with nano‐sized TiO2, efficient channels for phonon transport are formed between hybrid fillers, and the through‐plane thermal conductivity reached 1.704 W/(m.K) in 50B‐10T sample. The potential application of prepared composites as a heat spreader is demonstrated by monitoring surface temperature distribution and numerical simulation. Meanwhile, we achieved a synchronous improvement in mechanical stiffness within hybrid composites; and failure mechanisms including crack bridging at TiO2‐PEEK interface, and debonding at hBN‐PEEK interface are observed in hybrid composites. Lastly, the high thermal stability makes the PEEK/hBN/TiO2 specimens suitable for heat dissipation in demanding applications in the energy and aerospace sectors. Highlights: Bespoke screw design developed for scalable manufacturing of Polyetheretherketone (PEEK) matrix composites reinforced with Hexagonal Boron Nitride (hBN) and Titanium Dioxide (TiO2) via twin‐screw melt compounding.Interconnected 3D filler networks were achieved due to the filler dimension effect, allowing us to reach an ultrahigh in‐plane thermal conductivity value of 8.2 W/(m.K) and through‐plane thermal conductivity value of 1.7 W/(m.K) for 50B‐10T specimen.Manufactured hybrid PEEK/hBN/TiO2 composite specimens possess excellent mechanical stiffness. [ABSTRACT FROM AUTHOR]

This study investigates the influence of Luffa Fiber (LF) inclusions on the mechanical and thermal characteristics of unsaturated polyester resin composites. LFs, manually extracted from luffa plants, are integrated at volumetric fractions of 10%, 15%, 20%, and 25% into the resin using a hand lay-up technique at ambient conditions. Subsequent machining prepares the samples for mechanical analysis. It is observed that mechanical properties enhance progressively with increased LF incorporation. The optimal impact resistance reaches 2.34KJ/m², with maximum hardness and compressive strength values of 81.5N/mm2 and 43.9MPa, respectively. Concurrently, a notable reduction in thermal conductivity is evident, particularly at the 25% LF volume, where it measures approximately 0.105W/m.℃. These findings indicate that the LF-reinforced polyester composites exhibit potential for varied engineering applications. Particularly, their augmented mechanical robustness suits components such as sofa parts and door handles, while their improved thermal insulation properties render them suitable for building insulation. This investigation underscores the viability of LF as a reinforcing agent in polymeric composites, offering a balance of enhanced mechanical strength and thermal efficiency, thereby broadening the scope of their application in engineering domains. [ABSTRACT FROM AUTHOR]

Snow significantly impacts the seasonal growth of Arctic sea ice due to its thermally insulating properties. Various measurements and parameterizations of thermal properties exist, but an assessment of the entire seasonal evolution of thermal conductivity and snow resistance is hitherto lacking. Using the comprehensive snow dataset from the Multidisciplinary Drifting Observatory for the Study of Arctic Climate (MOSAiC) expedition, we have evaluated for the first time the seasonal evolution of the snow's and denser snow-ice interface layers' thermal conductivity above different ice ages (refrozen leads, first-year ice, and second-year ice) and topographic features (ridges). Our dataset has a density range of snow and ice between 50 and 900 kgm-3 , and corresponding anisotropy measurements, meaning we can test the current parameterizations of thermal conductivity for this density range. Combining different measurement parameterizations and assessing the robustness against spatial heterogeneity, we found the average thermal conductivity of snow (<550 kgm-3) on sea ice remains approximately constant (0.26 ± 0.05 WK-1m-1) over time irrespective of underlying ice type, with substantial spatial and vertical variability. Due to this consistency, we can state that the thermal resistance is mainly influenced by snow height, resulting in a 2.7 times higher average thermal resistance on ridges (1.42 m2KW-1) compared to first-year level ice (0.51 m2KW-1). Our findings explain how the scatter of thermal conductivity values directly results from structural properties. Now, the only step is to find a quick method to measure snow anisotropy in the field. Suggestions to do this are listed in the discussion. [ABSTRACT FROM AUTHOR]

With the rapid development of the electronics, communication, and energy industries, there is an increasing demand for flexible materials with high thermal conductivity and electrical insulation properties. Silicone rubber (SR) is widely used in various fields due to its excellent mechanical properties. However, its intrinsic low thermal conductivity requires the addition of thermally conductive fillers to enhance its thermal conductivity. Insulating thermally conductive composites are prepared by adding thermally conductive fillers such as boron nitride (BN) and graphite into a silicone rubber matrix. When BN is added as a single filler up to 20 wt%, the thermal conductivity of BN/SR reaches 0.526 W m−1 K−1, which is a 126% improvement compared to the SR matrix. When the total filler content is 20 wt%, and the ratio of BN to graphite is 1:1, the thermal conductivity of BN/graphite/SR composite is 0.685 W m−1 K−1. This represents a 194% and 30% increase in thermal conductivity compared to the SR matrix and BN/SR composite with the same filler content, respectively. On the cured silicone rubber substrate, the incremental cured BN/SR acts as an insulation coating. This allows for a significant reduction in the electrical conductivity of the composite without the use of adhesives, while preserving the thermal conductivity. Moreover, the interface formed through incremental curing retains high tensile and compressive strength. [ABSTRACT FROM AUTHOR]

With the gradual miniaturization of electronic devices, the thermal conductivity of electronic components is increasingly required. Epoxy (EP) resins are easy to process, exhibit excellent electrical insulation properties, and are light in weight and low in cost, making them the preferred material for thermal management applications. In order to endow EPs with better dielectric and thermal conductivity properties, bromo-oxygen-bismuth (BiOBr) prepared using the hydrothermal method was used as a filler to obtain BiOBr/EP composites, and the effect of BiOBr addition on the properties of the BiOBr/EP composites was also studied. The results showed that the addition of a small amount of BiOBr could greatly optimize the dielectric properties and thermal conductivity of EP resin, and when the content of BiOBr was 0.75 wt% and 1.00 wt%, the dielectric properties and thermal conductivity of the composite could reach the optimum, respectively. The high dielectric constant and excellent thermal conductivity of BiOBr/EP composites are mainly due to the good layered structure of BiOBr, which can provide good interfacial polarization and thermal conductivity. [ABSTRACT FROM AUTHOR]

Silicone foam (SF) is a porous silicone rubber with a lower density, higher elasticity, and good thermal stability. In this work, we selected aluminum spheres and carbon fiber (CF) as thermally conductive fillers to prepare hybrid SF. After optimization, we found that Al and CF hybrid SF (Al-CF-SF) has a higher thermal conductivity (1.37 W·m-1·K-1) than the single-filler filled SF (CF-SF, 1.2 W·m-1·K-1 or Al-SF, 0.52 W·m-1·K-1) under the same filling amount of 60 wt%. The finite element simulation was used further to explore the thermal conductive mechanism of the hybrid SF. Meanwhile, the compressive and tensile modulus of the material (CF-SF) was increased to 10.8 and 3.3 MPa compared with pure SF, respectively, and the mechanical properties were improved. In addition, infrared thermography further demonstrated that Al-CF-SF has a faster heat transfer rate under relaxation and applied pressure. [ABSTRACT FROM AUTHOR]

The mesoscopic finite element model of ceramic matrix composites is developed by reconstructing computed tomography images. The relationship between microstructure and macroscopic properties and their dispersion are explored. Firstly, a three-dimensional reconstructed computed tomography model was carried out to calculate the orientation of the components. Secondly, the orientation and gray value of images were used to identify the basic structure of composites including fiber tows, matrix, and porosities. Finally, the two-dimensional finite element model was developed to analyze the macroscopic thermal and mechanical properties. The numerical results showed that: (1) the geometries and distributions of pores had a significant effect on the through-thickness modulus and thermal conductivity; (2) the stress and heat flow concentration area on the material surface usually occurred in narrow gaps between closely spaced longitudinal tows; (3) the elastic modulus and thermal conductivity were dispersive, and their distribution followed by two-parameter Weibull distribution. [ABSTRACT FROM AUTHOR]

Fused Filament Fabrication (FFF) is a 3D‐printing technique that enables the production of complex geometries with a high level of customization at low cost. The poor mechanical properties of FFF‐printed parts often undermine the application of this technology for structural purposes. To overcome this limitation, a two‐step metallization method is performed to deposit a copper layer on the exterior of an Acrylonitrile–Butadiene–Styrene (ABS) substrate, using a non‐toxic and cost‐effective plating solution. Electroplating over the exposed grid infill, at various densities, is exploited to improve the load transfer between copper and ABS. The resulting samples are characterized mechanically and thermally, and finite element modeling simulations are used to better understand the characterization results. It is found that an infill of 50–60% provides the best compromise between mechanical performance and thermal conductivity because the infill density is low enough to allow copper penetration into the material to create a strong mechanical interlocking with ABS, yet high enough to create multiple conductive bridges through the thickness of the sample. This study demonstrates the effectiveness of electroplating as a post‐processing technique to simultaneously enhance the mechanical and thermal properties of FFF‐printed parts and provides insights into the optimal design parameters for achieving this goal. [ABSTRACT FROM AUTHOR]

Conventional asphalt has been used along the time with relatively satisfactory performance. However better performance in terms of development, environment, and economic benefits needs to be addressed. Asphalt binder modification has been one of the most common methods to improve the performance of bitumen over time. The objective of this study is to provide insight into the modification of asphalt binders to reduce thermal cycling by introducing Aerogel. Several tests were conducted including Softening Point (SP), Rotational Viscosity (RV), Dynamic Shear Modulus (G*), Multiple Stress Creep Recovery (MSCR), Flexural Creep Stiffness (BBR), Binder Bond Strength (BBS), and Thermal Conductivity (TC) tests. The response of five aerogel products was assessed based on performance. The outcomes of this study were encouraging and promising. Thermal resistance properties and cost per kilogram of each product were used to determine the more suitable aerogel product for further utilisation. The addition of aerogel reduced the susceptibility to damaging thermal effects of bitumen, reducing the permanent deformation and thermal cracking potential. However, the implementation of aerogel in binder must be enhanced to overcome the workability and safety concerns, which restrict the feasibility of its usage. [ABSTRACT FROM AUTHOR]

Algeria is currently undergoing an evolution in civil engineering, which has resulted in a higher use of aggregates, especially sand. This study contributes to the development of locally produced materials. Its goal is to explore how the type of sand and waste marble powder (WMP), which can be used as a partial replacement of cement and aluminum powder (Al) with different percentages as an expansive agent, can affect physico-mechanical properties such as the bulk density and mechanical strength at 28 and 90 days, as well as the thermal conductivity of lightweight cellular concrete. Non-autoclaved cellular concretes (CC) were investigated based on three types of sand, i.e., sea sand (SS), river sand (RS), and waste marble sand (WMS); a hydraulic binder (a mix of cement and waste marble powder), and aluminum powder. The experimental results indicate that the nature and particle size distribution of the sand used had an impact on the properties of the CCs. Furthermore, it can be seen that the increased aluminum contents decrease the density, mechanical strength, and thermal characteristics of the CCs. Using 10-15% WMP as a cement substitute improves the mechanical strength, offers better thermal conductivity values, and contributes to sustainable development by developing a new class of environmentally friendly cellular concrete. [ABSTRACT FROM AUTHOR]

This work investigates the physical–thermal properties of nanofluids made from graphene powder, propylene glycol, and water. Propylene glycol and water were mixed in the following ratios to make nanofluids: 100:0, 75:25, and 50:50. Graphene was added at 0.25 and 0.5% of the mixture's volume to the three base fluids. Nanofluids' viscosity, density, thermal conductivity, and specific heat are studied. After mixing with graphene nanopowder, critical fluids increased in density and thermal conductivity. Essential fluids showed these advantages. When the temperature was elevated, viscosity and specific heat decreased. Despite constant temperatures, this was the case. Increasing graphene concentration increases thermal conductivity by 10–16%. The viscosity of nanofluids with graphene nanopowder is less affected by temperature. As temperature rises, nanofluid density falls. Temperature and density are inversely related; thus, this makes sense. Adding graphene to propylene glycol at different concentrations increased its specific heat by 8–14%, depending on the concentration. [ABSTRACT FROM AUTHOR]

To understand the transient heat transfer characteristics of nanoporous aerogel insulating composites, solving the inverse heat transfer problem would be crucial for identifying the temperature-dependent thermal properties of composites. In this study, with constructed a forward model to numerically investigate the heat transfer in composites, a deep neural network (DNN) model and a particle swarm optimized deep neural network (PSO-DNN) model are conducted to rapidly estimate the effective temperature-dependent thermal conductivity of the desiccated and moist composites from the temperature response measurements. With the DNN model, the retrieved thermal conductivities for desiccated composites possess low deviation to experimental measurements (<3.2%) and constantly low errors (<5.2%) from 280 K to 1080 K. The precision of the DNN solver could be enhanced by adjusting the hyperparameters of the neural networks using PSO. The retrieved thermal conductivities possess low deviation from experiments (<2.5%) and low relative errors within 1.5%. Furthermore, the robustness of the PSO-DNN solver is discussed when commercial thermocouple measurement errors are considered, within retrieving the thermal properties of desiccated and moist aerogel composites. [ABSTRACT FROM AUTHOR]

In this work, composite phase change materials (CPCM) containing myristic acid (MA), bentonite, and graphene were prepared by melt blending method, where MA is phase change material (PCM), bentonite is supporting material, and graphene is thermal conductivity enhancer. The CPCM containing 50 wt% MA can still maintain the stable morphology during phase change process. The chemical structure, crystal structure and microstructures of CPCM were examined by Fourier transformation infrared spectroscope (FT-IR), X-ray diffractometer (XRD) and scanning electron microscope (SEM), respectively. Differential scanning calorimeter (DSC) analysis indicate that the melting enthalpy is 94 to 97 J·g−1. Thermogravimetric analysis (TGA) demonstrates good thermal stability of the CPCM. Thermal conductivity of the CPCM with 3 wt% graphene can reach 1.09 W⋅(m⋅K)−1, that is 2.37 times that of MA/bentonite. Experimental results indicate that the CPCM have significant improvement with regard to stability and thermal conductivity as compared to the pristine PCM. Moreover, the CPCM still remain good thermal properties after undergoing 100 thermal cycles. [ABSTRACT FROM AUTHOR]

In this study, pine sapwood was first impregnated with micronized copper (Cu) solution at concentrations of 5 and 10%, the samples then dried and impregnated with ethyl palmitate as a bio-based phase change material (BPCM). The leakage test showed slightly less leakage in this scenario compare to controls without copper. The mould test showed using copper solution, significattly improves the resistance of the composites to mould growth. Thermal tests showed using BPCM improves thermal conductivity and thermal mass of the composites, enabling them to store and release energy within the temperature range of 20-25°C. It is observed that the copper did not improve thermal conductivity, and 5% copper showed the best performance in thermal mass improvement. [ABSTRACT FROM AUTHOR]

The trend of using natural materials for consumer goods has been increasingly pronounced recently. Construction industry is no exception here, with wooden house construction developing within it rapidly, and board structures utilized on a large scale. Given this, the task of searching for new technical solutions in manufacturing natural material board structures seems a crucial one. The paper describes the patented structure of corrugated veneer panel developed by the authors. Its heat insulating properties are evaluated by finding the thermal conductivity coefficient. Another advantage of the corrugated veneer panel under consideration is its capacity to help expand the scope of use of birch wood, which is currently highly limited. [ABSTRACT FROM AUTHOR]

This present study investigates the recovery of wood biomass ash (WBA) as chemical stabilize in compacted earth bricks. The specimens were tested for compressive and thermal properties in dry state. The tests were performed at 7 and 28 days of age in order to evaluate the effect of the partial substitution of soil with WBA on the mechanical and thermal properties of the compressed earth bricks. The results indicate that bricks manufactured with 20% of partial substitution showed better performance than those containing only soil. Nevertheless, the use of WBA as source of lime improved the compressive strength and the thermal conductivity of the bricks stabilized with different proportions (5, 10, 15 and 20% wt) when compared with bricks fabricated with 100% soil. This improvement is owing to the pozzolanic reaction produced between the soil components and the WBA as well as the soil microstructure. It was also concluded that the combination of the soil components and lime containing in WBA in the stabilization of compressed earth bricks seems to be a promising alternative when considering issues of energy consumption and pollution. [ABSTRACT FROM AUTHOR]

In our investigation of poly(vinylidene fluoride) (PVDF) films embedded with Au-BaTiO3 (AuBT) nanoparticles, we noted a synergistic improvement in both thermal stability and dielectric properties. PVDF films with varying concentrations of AuBT were expertly fabricated. Remarkably, the films retained their flexibility even at a high volume fraction of filler (fAuBT = 0.5). The predominant phases of PVDF (α, β, and γ) were observed. An increase in fAuBT resulted in a modest decrease in the melting temperature, while simultaneously causing a significant 40% increase in thermal conductivity compared to pure PVDF. The dielectric permittivity reached ∼160 at 1 kHz, while maintaining a loss tangent of ∼0.05. These improvements were attributed to discrete Au growth on BT particles, hindering conduction in PVDF. The rise in dielectric response resulted from interfacial polarization and inherent high dielectric permittivity of BT. [ABSTRACT FROM AUTHOR]

Metal-reinforced polymer composites are suitable materials for applications requiring special thermal, electrical or magnetic properties. Three-dimensional printing technologies enable these materials to be quickly shaped in any design directly and without the need for expensive moulds. However, processing data correlating specific information on how the metal particles influence the rheological behaviour of such composites is lacking, which has a direct effect on the processability of these composites through melt processing additive manufacturing. This study reports the compounding and characterisation of ABS composites filled with aluminium and copper particulates. Experimental results demonstrated that the tensile modulus increased with the incorporation of metal particles; however, there was also an intense embrittling effect. Mechanical testing and rheological analysis indicated poor affinity between the fillers and matrix, and the volume fraction proved to be a crucial factor for complex viscosity, storage modulus and thermal conductivity. However, a promising set of properties was achieved, paving the way for polymer–metal composites with optimised processability, microstructure and properties in melt processing additive manufacturing. [ABSTRACT FROM AUTHOR]

In the context of the energy transition, new construction materials are emerging, notably bio-based materials such as wood concrete. This paper investigates the hygrothermal performance of walls constructed with wood–cement concrete. First, the thermal properties of wooden concrete, namely thermal conductivity, effusivity, and diffusivity, are experimentally characterized in both dry and wet conditions. Second, in situ measurements are carried out on a house in Lyon, a city in France, constructed with mono-layered wood–cement walls. This involves monitoring the temperature and relative humidity levels both inside and outside the building, as well as at three distinct positions within the wood walls over a 6-month period (from 20 April 2023 to 20 October 2023). The hygrothermal analysis at the center of the wall reveals that the wood wall effectively moderates fluctuations in the external temperature and relative humidity. Following this, a numerical study is performed to check the reliability of the adopted Reduced Heat, Air, and Mass (HAM) model to reproduce the hygrothermal performance of the wood–cement wall. The results show a strong agreement between the simulated and measured data, confirming the applicability of the 'Reduced HAM' model for the prediction of the hygrothermal behavior of wood–cement walls. [ABSTRACT FROM AUTHOR]

As an advanced amorphous material, sp3 amorphous carbon exhibits exceptional mechanical, thermal and optical properties, but it cannot be synthesized by using traditional processes such as fast cooling liquid carbon and an efficient strategy to tune its structure and properties is thus lacking. Here we show that the structures and physical properties of sp3 amorphous carbon can be modified by changing the concentration of carbon pentagons and hexagons in the fullerene precursor from the topological transition point of view. A highly transparent, nearly pure sp3−hybridized bulk amorphous carbon, which inherits more hexagonal-diamond structural feature, was synthesized from C70 at high pressure and high temperature. This amorphous carbon shows more hexagonal-diamond-like clusters, stronger short/medium-range structural order, and significantly enhanced thermal conductivity (36.3 ± 2.2 W m−1 K−1) and higher hardness (109.8 ± 5.6 GPa) compared to that synthesized from C60. Our work thus provides a valid strategy to modify the microstructure of amorphous solids for desirable properties. sp3 amorphous carbon exhibits exceptional mechanical, thermal, and optical properties, but cannot be synthesized using traditional processes. Here authors report a nearly pure sp3−hybridized amorphous carbon synthesized from C70 which shows more short/medium-range order and enhanced thermal conductivity compared to C60. [ABSTRACT FROM AUTHOR]

Highlights: A core-sheath structured coaxial composite fiber with highly aligned and densely stacked boron nitride nanosheets arrangements in the sheath was successfully fabricated. The coaxial fibers have an ultrahigh axial Herman orientation parameter of 0.81, thermal conductivity of 17.2 W m−1 K−1, and tensile strength of 192.5 MPa. The coaxial fibers exhibit intensively potential applications in the wearable thermal management textile. Hexagonal boron nitride nanosheets (BNNSs) exhibit remarkable thermal and dielectric properties. However, their self-assembly and alignment in macroscopic forms remain challenging due to the chemical inertness of boron nitride, thereby limiting their performance in applications such as thermal management. In this study, we present a coaxial wet spinning approach for the fabrication of BNNSs/polymer composite fibers with high nanosheet orientation. The composite fibers were prepared using a superacid-based solvent system and showed a layered structure comprising an aramid core and an aramid/BNNSs sheath. Notably, the coaxial fibers exhibited significantly higher BNNSs alignment compared to uniaxial aramid/BNNSs fibers, primarily due to the additional compressive forces exerted at the core-sheath interface during the hot drawing process. With a BNNSs loading of 60 wt%, the resulting coaxial fibers showed exceptional properties, including an ultrahigh Herman orientation parameter of 0.81, thermal conductivity of 17.2 W m−1 K−1, and tensile strength of 192.5 MPa. These results surpassed those of uniaxial fibers and previously reported BNNSs composite fibers, making them highly suitable for applications such as wearable thermal management textiles. Our findings present a promising strategy for fabricating high-performance composite fibers based on BNNSs. [ABSTRACT FROM AUTHOR]

Phase change materials (PCMs) are increasingly gaining prominence in thermal energy storage due to their impressive energy storage capacity per unit volume, especially in applications with low and medium temperatures. Nevertheless, PCMs have significant limitations regarding their ability to conduct and store heat, primarily due to their inadequate thermal conductivity. One potential solution for improving the thermal conductivity of PCMs involves the inclusion of nanoparticles into them. However, a recurring issue arises after several thermal cycles, as most nanoparticles have a tendency to clump together and settle at the container's base due to their low interfacial strength and poor compatibility. To address this challenge, including surfactants such as sodium dodecylbenzene sulfonate (SDBS) has emerged as a prevalent and economically viable approach, demonstrating a substantial impact on the dispersion of carbon nanoparticles within PCMs. The foremost objective is to investigate the improvement of thermal energy storage by utilizing graphene nanoplatelets (GNP), which are dispersed in A70 PCM at various weight percentages (0.1, 0.3, 0.5, 0.7, and 1.0), both with and without the use of surfactants. The findings indicate a remarkable enhancement in thermal conductivity when GNP with surfactants is added to the PCM, showing an impressive increase of 122.26% with a loading of 1.0 wt.% compared to conventional PCM. However, when 1.0 wt.% pure GNP was added, the thermal conductivity only increased by 48.83%. Additionally, the optical transmittance of the composite containing ASG-1.0 was significantly reduced by 84.95% compared to conventional PCM. Furthermore, this newly developed nanocomposite exhibits excellent stability, enduring 1000 thermal cycles and demonstrating superior thermal and chemical stability up to 257.51 °C. Due to its high thermal stability, the composite NePCM is an ideal candidate for preheating in industrial and photovoltaic thermal (PVT) applications, where it can effectively store thermal energy. [ABSTRACT FROM AUTHOR]

The layered fibers of carbon-fiber-reinforced polymer (CFRP) composites exhibit low thermal conductivity (TC) throughout their thickness due to the poor TC of the polymeric resin. Improved heat transmission inside the hydrogen storage tank during the filling process can reduce further compression work, and improved heat insulation can minimize energy loss. Therefore, it is crucial to understand the thermal properties of composites. This paper reports the thermal behavior of plain-woven CFRP composite using simulation at the micro-, meso-, and macro-scales. The TC was predicted numerically and compared to experimental findings and analytical models. Good results were found. Using the approach of multi-scale modeling, a parametric study was carried out to analyze in depth the influence of certain variables on thermal properties. The study revealed that both fiber volume fraction and temperature significantly influenced the TC of the composite, with the interphase fiber/matrix thickness following closely in terms of impact. The matrix porosity was found to have a relatively slighter impact, particularly within the porosity range of 5 to 15%. [ABSTRACT FROM AUTHOR]

The research presented in this article was conducted to evaluate the suitability of recycled foam concrete (RFC) as an ingredient in newly created cement mortars. The basis for an analysis was the assumption that the waste is collected selectively after separation from other waste generated during demolition. The motivation for the research and its main problem is a comparison of the performance of RFC used in various forms. RFC was used in two forms: (1) recycled foam concrete dust (RFCD) as a 25 and 50% replacement of cement, and (2) recycled foam concrete fine aggregate (RFCA) as a 10, 20, and 30% replacement of sand. The basic properties of fresh and hardened mortars were determined: consistency, density, initial setting time, absorbability, compressive strength, thermal conductivity coefficient, and heat capacity. Research is complemented with SEM observations. The properties of fresh mortars and mechanical parameters were decreased with the usage of any dosage of RFC in any form, but the thermal properties were improved. The required superplasticizer amount for proper consistency was raised four times for replacing cement with 50% of RFCD than for 25% of such replacement. The mix density dropped by about 8% and 9% for mortars with the replacement of 50% cement by RFCD and 30% sand by RFCA in comparison to reference mortar. A 30% decrease in initial setting time was observed for cement replacement. In the case of sand replacement, it was the opposite—an increase of 100%. The dry density decreased by about 14% and 11% for mortars with the replacement of 50% cement by RFCD and 30% sand by RFCA in comparison to reference mortar. Absorbability was raised by about two times after replacement with both RFCD and RFCA. Compressive strength after 28 days dropped significantly by 75% and 60%, and the thermal conductivity coefficient decreased by 20% and 50% with 50% RFCD added instead of cement and 30% RFCA replacing sand. It indicates greater efficiency in thermomechanical means from RFCA in comparison to RFCD. This material can be used especially in the production of plaster and masonry mortar. Linear correlations of dry density and thermal conductivity coefficient and the latter and compressive strength were proven as reliable for RFCD replacement of cement and RFCA replacement of sand in mortars with greater w/c ratio. [ABSTRACT FROM AUTHOR]

Using thermal storage materials with excellent thermal properties in the energy utilization system enables efficient use of renewable energy sources. Organic phase change materials (PCMs) have the advantages of high heat storage density, no corrosion, and low cost, but low thermal conductivity and insufficient heat transfer capacity have always been the bottlenecks in their application. In this paper, melamine foam@ reduction graphene oxide (MF@rGO) and carbon foam@ reduction graphene oxide (CF@rGO) composite foams with double carbon networks were prepared by self-assembly method and further employed in 1-octadecinal (OD) PCMs. The microstructure, chemical composition, phase change behavior, thermal conductivity, and photothermal conversion performance of MF@rGO/OD and CF@rGO/OD were studied in detail using SEM, FTIR, Raman DSC, and LFA. The melting and solidification enthalpies of CF@rGO/OD composite PCMs were 208.3 J/g and 191.4 J/g, respectively, its thermal conductivity increased to 1.54 W/m·K, which is 6.42 times that of pure OD. The porous structure and high thermal conductivity of the double carbon network substantially enhance the efficiency of energy storage and release in composite PCMs. CF@rGO/OD composite PCMs have excellent heat storage performance and heat transfer capacity, and a wide range of application prospects in the fields of low-temperature solar heat storage, precision instrument temperature control, and intelligent buildings. [ABSTRACT FROM AUTHOR]

Due to the installation of energy piles, the surrounding soil will be inevitably disturbed, leading to a smaller void ratio and larger thermal conductivity. This study proposes a new closed‐form solution to calculate the heat exchange of energy pile foundations considering smear effects on the different soil thermal properties in the smear zone and undisturbed zone. The analytical model adopts the separation of variables to solve the governing equations. The eigenvalues are obtained according to a series of recurrence formulas and a transcendental equation. The solution is verified against existing analytical solutions in literature and numerical simulation, and an excellent agreement is obtained. The parametric study shows that a larger thermal conductivity of the soil in the smear zone results in a lower temperature at any given time. If the smear effects are not considered, the temperature will be overpredicted, especially for the pile and the soil in the smear zone. The proposed solution precisely predicts the soil temperature in the smear zone and undisturbed zone, which can contribute to the thermo‐mechanical behaviour of energy pile foundations in further work. [ABSTRACT FROM AUTHOR]

ZIF-L, a metal-organic framework (MOF) material, has a two-dimensional (2D) foliation, a large specific surface area, excellent thermal stability and CO 2 adsorption performance, respectively. In this work, in order to further improve the thermal insulation performance of SiO 2 aerogel composite fabrics, ZIF-L powder was first prepared as a reinforcing particle, and then added to silica aerogel. Finally, SiO 2 /AF/ZIF-L composites were obtained by solution impregnation method. The influence of different ZIF-L concentrations on the insulation performance of composites and their influencing factors were studied. Furthermore, these composites were fully characterized using BET measurement, Instron 5967, precision transient thermal performance tester, infrared thermal imager, insulation performance test, thermogravimetric analyzer, and dynamic thermomechanical analyzer. The results showed that 0.12% SiO 2 /AF/ZIF-L composites had excellent thermal insulation performance, with a thermal conductivity as low as 0.029 W/(m·K). In addition, SiO 2 /AF/ZIF-L composites fabricated by atmospheric drying method had the best thermal insulation performance under the conditions of gel time of 24 h, hydrolysis time of 5 h, and polycondensation pH value of 5–6. [ABSTRACT FROM AUTHOR]

To investigate the mechanism of the influence of the sintering additive ratio on the microstructure evolution of silicon nitride (Si 3 N 4) ceramics, Si 3 N 4 ceramics were prepared by gas pressure sintering using different ratios of Y 2 O 3 /MgSiN 2 as additives. Varying the ratio of Y 2 O 3 /MgSiN 2 changed the composition of the liquid phase, thereby affecting the densification process and phase transformation rate of Si 3 N 4 ceramics, and ultimately changing their microstructure. The reduction in the Y 2 O 3 /MgSiN 2 ratio raised the N/O and Si/O ratios in the system, which increased the liquid phase viscosity. The Si 3 N 4 grain distribution varied from "normal to bimodal". In the case of increasing the proportion of MgSiN 2 and prolonging the sintering time, more of the glass phase evaporated, which reduced the content of the low thermal conductivity phase and increased the continuity of Si 3 N 4 /Si 3 N 4. Therefore, Si 3 N 4 ceramics with 1 wt% Y 2 O 3 and 5 wt% MgSiN 2 exhibited excellent properties after sintering at 1900 °C for 12 h, with thermal conductivity, bending strength, and fracture toughness of 106.7 Wm−1K−1, 776 MPa, and 11.66 MPa m1/2, respectively. [ABSTRACT FROM AUTHOR]

In recent years, the MgO-Nd 2 Zr 2 O 7 composite ceramics inert matrix (IM) was proposed as a candidate for the transmutation of Pu and minor actinides (MA) in light water reactors (LWR) or accelerator driven sub-critical system (ADS). To take full advantage of the pyrochlore structure of Nd 2 Zr 2 O 7 to accommodate different types of MA and Pu, in this work, Y and Ce co-doped ω MgO-(1- ω)(Nd 1- x Y x) 2 (Zr 1- x Ce x) 2 O 7 (M-NYZC) composite ceramics used as a candidate IM for inert matrix fuel were prepared by solid-state one-step sintering method at 1500 °C for 3 h. The phase structure and microstructure of M-NYZC composite ceramics were characterized by XRD and SEM-EDS. Also, the thermal physical properties of M-NYZC composite ceramics including the thermal expansion coefficient and thermal conductivity were investigated systematically. Results from XRD and SEM-EDS showed that the magnesium oxide and NYZC pyrochlore solid solution are intermixed well with each other, and the M-NYZC samples present uniform element distribution with a grain size of about 1 μm. Also, the as-prepared samples possessed well densified microstructure, and the average relative density of all samples could exceed 95 %. Moreover, the thermal expansion coefficient and thermal conductivity of 0.5M-0.5NYZC (x = 0, 0.15, 0.2, 0.5, 0.9) samples were located in the range of 13.4 × 10-6–14.4 × 10-6 K-1 and 16.34–3.70 W·m-1·K-1 respectively. By comparison, the thermal physical properties of 0.5M-0.5NYZC samples are superior to that of traditional UO 2 and MOX fuels. It is suggested that the M-NYZC composite ceramics prepared in this study can meet the thermal physical performances of inert matrix fuel. [ABSTRACT FROM AUTHOR]

Magnesium aluminate (MA) spinel has shown potential as a refractory material under harsh environments, such as high temperatures and frequent temperature variations. However, understanding the mechanical and thermal properties of MA spinel is a key step towards further improvement of MA spinel refractory materials in high-temperature fields. The formation of solid solution represents a prominent strategy to improve mechanical and thermal properties. The present study develops novel (1- x)MgAl 2 O 4 - x Mg 2 TiO 4 (0≤ x ≤ 0.1) solid solutions by single-step reaction sintering method using light-burned magnesia, reactive alumina, and as-prepared Mg 2 TiO 4 (M 2 T) powders. The effects of M 2 T content on the crystal structure, mechanical properties, and thermal properties of the MgAl 2 O 4 -Mg 2 TiO 4 solid solutions (MATss) were studied. Based on XRD, TEM, and HRTEM results, MATss were highly crystallized with a cubic spinel structure. Besides, the M 2 T addition facilitated the flexural strength, hardness, and elastic modulus in the MA spinel. Among these solid solutions, the x = 0.08 sample exhibited the highest flexural strength, hardness, and elastic modulus of 219.47 MPa, 19.99 GPa, and 270.2 GPa, respectively. M 2 T additive played a solid-solution strengthening role, which enhanced the inherent resistance to microstructural damage. Additionally, the x = 0.08 sample had the highest thermal conductivity and thermal diffusivity of 12.45 W/(m·K) and 7.98 mm2/s, respectively. In comparison with pure MA spinel, the x = 0.08 sample showed a lower thermal expansion coefficient (8.63 × 10-6 K-1 at 1550 °C). These excellent mechanical properties and exceptional thermal behavior enabled its widespread application in refractory materials. [ABSTRACT FROM AUTHOR]

In this study, a type of red mud/slag-based cenospheres/geopolymer foam was directly fabricated using the direct foaming method at room temperature. The effects of high-temperature exposure (700–1100 °C) on the phase evolution, pore structure, and properties of the foams were investigated. The results showed that the untreated foam was amorphous structure. The porosity of the foams increased from 36.4 ± 0.6% (1 wt%) to 71.9 ± 0.1% (5 wt%) with the addition of H 2 O 2. The compressive strength of the foams was 1.20–18.15 MPa, which was attributed to the good bond between the cenospheres and red mud/slag-based geopolymer matrix, the fractured spheres, and the crack deflection. After this high-temperature exposure, the foam crystallized mainly into the leucite and mullite phases. The density and compressive strength of the foams decreased as the exposure temperature increased. The thermal conductivity of the foams reached the lowest value of 0.169 W/(m⋅K) and 0.108 W/(m⋅K) with 5 wt% H 2 O 2 before and after the exposure, respectively. These foams have demonstrated good potential for application in the building insulation field. [ABSTRACT FROM AUTHOR]

5at.% Yb:Lu2O3 transparent ceramics were fabricated successfully by vacuum sintering along with hot isostatic pressing posttreatment from the nanopowders. The influences of calcination temperature on morphology and microstructures of powders and ceramics were studied systematically. The optimal ceramic sample from the nanopowder calcined at 1050°C shows uniform and dense microstructure with the in‐line transmittance of 81.5% at 1100 nm. The results of the thermal measurements, that is, thermal conductivity and specific heat, were related to the changes occurring in the microstructure of the ceramics studied. It was shown on this basis that appropriate control of the technological process of sintering ceramics makes it possible to obtain laser ceramics with very good thermal properties as well as maintaining their high optical quality. Concerning the laser performance, the highest‐optical quality 5at.% Yb:Lu2O3 sample was pumped in quasi‐continuous wave conditions measuring a maximum output power of 2.59 W with a corresponding slope efficiency of 32.4%. [ABSTRACT FROM AUTHOR]

The purpose of this study was to analyze the effects of sludge biochar (BC) application (2, 5, 10, 15% w/w) on the physico-chemical and thermal properties (thermal capacity, thermal conductivity and thermal diffusivity) of loess and the mechanism of action. The results showed that the application of BC changed the soil particle size distribution, reduced the soil bulk density, increased the soil total porosity (1.19–11.51%), organic matter content (10.94–85.02%), saturated water content (1.85–7.15%) and field water capacity (0.09–13.00%), and decreased the soil thermal capacity, thermal conductivity and thermal diffusivity, with an average decreasing amplitude of 2.13, 5.45 and 7.54%, respectively. Soil bulk density and water content (<30%) were positively correlated with soil thermal capacity, thermal diffusivity and thermal conductivity. The mechanisms are mainly that the negative impact of changing soil solid composition and increasing total porosity by biochar with low density and thermal parameter values; and the positive effect of raising water content by improving soil water holding capacity. Sludge biochar shows great potential in soil improvement and can realize sludge sustainable management. [ABSTRACT FROM AUTHOR]

Lightweight eco-materials are in high demand in many sectors, such as aerospace, industry, and building due to their several characteristics. The present paper is an experimental investigation of the thermal characteristics of novel sandwich panels made with local and ecological materials namely agglomerated cork for the core and bio-composite materials for the skin. Three configurations (symmetric, asymmetric, and two layers) were studied with different cork core thicknesses. Density values have been measured and compared. Thermal characterization consists of determining thermal conductivity and specific heat using a HFM apparatus; whilst thermal diffusivity and thermal effusivity have been calculated using the experimental findings. The panels are lightweight and thermally insulating. The values of thermal conductivity are in the range 0.071 and 0.102 W.m−1.K−1. The comparison between experimental results of thermal conductivity to theoretical values highlights the accuracy of method for multi-layer thermal characterization and the good adhesion between layers. Finally, a life cycle assessment of the new sandwich panels has been carried out and compared with common insulation materials. The sandwich panels are efficient in terms of embodied energy and CO2 emissions compared to commercialized insulators and some insulators based on recycled or natural materials, the embodied energy for symmetric configuration with 4 cm cork core are 79.73, 94.75, and 89.35 MJ/FU corresponding to an embodied carbon 5.33, 6.32, and 6.01 CO2/FU respectively. They can be classified in the middle between synthetic and natural insulators. Based on the findings, it was concluded that utilizing these sandwich panels as construction materials for interior paneling or partition walls could offer benefits in terms of being environmentally sustainable and cost-efficient. [ABSTRACT FROM AUTHOR]

Natural fiber reinforced polymer composites (NFRPCs) have emerged as promising eco‐friendly alternatives over conventional synthetic fiber composites due to their inherent biodegradability, renewability, low environmental impact, and lightweight properties. It has been seen a significant growth in both invention and innovation in the field of NFRPCs. Natural fibers (NFs) reduce the cost of the material by 5%, the weight of the composite by 10%, and the energy required for production by 80%. In terms of thermal, and acoustic properties, NFs can successfully compete with synthetic fibers. As a result, the development of NFRPCs for industrial use has increased significantly in the past decade to meet the growing demands of industrial sectors. To improve the thermal and acoustic properties of NFRPCs, researchers have done a lot of investigation. The aim of the current review is to provide a comprehensive analysis of the existing literature on the thermal and acoustic properties of natural fiber reinforced polymer composites. Thermal properties such as thermal conductivity, TGA, DSC, DMA, and acoustic properties of natural fiber reinforced composites with several parameters, such as different fiber types, different matrix types, fiber weight ratio, fiber to matrix ratio, chemical treatment of fiber have been summarized and analyzed very concisely. This review also emphasizes a summary of different natural fibers, their chemical compositions, composite preparation, characterizations, and future research directions. This article enables the readers, researchers, and manufacturers to realize several opportunities about the latest developments in NFRPCs for the application of thermal and acoustic purposes. Highlights: Natural fibers can successfully compete with synthetic fibers, in terms of thermal and acoustic properties.Thermal properties of natural fiber reinforced composites including thermal conductivity, TGA, DSC, and DMA are summarized.Acoustic properties of natural fiber reinforced polymer composites are discussed.Composite materials made of treated fibers result better thermal stability than untreated fiber composites.Sound absorption coefficient generally increases as fiber content increases. [ABSTRACT FROM AUTHOR]

Novel phenolic resin/silicone aerogels (PR-Si) were prepared through a facile sol-gel polymerization and ambient pressure drying process without solvent exchange. Without the addition of an additional catalyst, the hydroxyl condensation reaction between the siloxane oligomer and the phenolic resin resulted in the silicon being incorporated into the PR. The obtained aerogels exhibited high compressive strength (0.84–21.11 MPa) and low thermal conductivities [0.046–0.077 W/(m·K)]. The introduction of a Si–O network structure in the PR effectively improved the mechanical properties and thermal stability of aerogels. It is clear from the TGA plot that the mass loss temperature of the PR-Si aerogel was increased by 73 and 79 °C for the weight loss temperatures of 5 and 10% compared to cured pure PR. [ABSTRACT FROM AUTHOR]

Rolled‐up nanostructures provide new opportunities to control and modify thermal properties. The topology and geometry of nanoscale architectures have a strong influence on phonon spectrum and thermal conductivity. In the theoretical description, rolled‐up nanotubes are often approximated with nanotubes constructed from concentric multiwalled nanotubes. Herein, the phonon spectrum is shown not to differ for these two nanotubes if the radius of the nanotube is much larger than the lattice constant. If the contact between layers of the rolled‐up or concentric nanotubes is weak, the thermal conductivity is not influenced by the contact, and it can be approximated by the conductivity of the one‐layered flat membrane. In the limit of weak contact, the diffusive heat transfer is shown to demonstrate an appreciable difference between rolled‐up and concentric nanotubes with large radii. The experimental measurements can be significantly distorted by the effects of the weak interlayer contact. [ABSTRACT FROM AUTHOR]

Balancing the contradictory relationship between thermoelectric parameters, such as effective mass and carrier mobility, is a challenge to optimize thermoelectric performance. Herein, the exceptional thermoelectric performance is realized in GeTe through collaboratively optimizing the carrier and phonon transport via stepwise alloying Pb and CuSbSe2. The formation energy of Ge vacancy is efficiently bolstered by alloying Pb, which reduces carrier density and carrier scattering to maintain superior carrier mobility in GeTe. Additionally, CuSbSe2, acting as an n‐type dopant, further modulates carrier density and validly equilibrates carrier mobility and effective mass. Accordingly, the promising power factor of 45 µW cm−1 K−2 is achieved at 723 K. Meanwhile, point defects are found to significantly suppress phonons transport to descend lattice thermal conductivity by Pb and CuSbSe2 alloying, which barely impacts the carrier mobility. A combination with superior carrier mobility and lower lattice thermal conductivity, a maximum ZT of 2.2 is attained in Ge0.925Pb0.075Cu0.005Sb0.005TeSe0.01, which corresponds to a 100% promotion compared with that of intrinsic GeTe. This study provides a new indicator for optimizing carrier and phonon transport properties by balancing interrelated thermoelectric parameters. [ABSTRACT FROM AUTHOR]

A solid-phase metallurgy combined with spark plasma sintering technology was used to prepare U3Si2 pellets. The thermal conductivity and oxidation behavior of the pellets were studied. The pellets were highly dense (> 98% theoretical density) and had an ultra-high phase purity. The thermal conductivity of the U3Si2 pellets increased linearly with temperature from 300 to 973 K. By further annealing the pellets at 300 °C in air for two hours, the oxidation onset temperature was increased from 490 to 520 °C. A mechanism of pore passivation was proposed to account for the enhanced oxidation resistance. [ABSTRACT FROM AUTHOR]

High-performance ceramics with low thermal conductivity, high mechanical properties, and idea thermal expansion coefficients have important applications in fields such as turbine blades and automotive engines. Currently, the thermal conductivity of ceramics has been significantly reduced by local doping/substitution or further high-entropy reconfiguration of the composition, but the mechanical properties, especially the fracture toughness, are insufficient and still need to be improved. In this work, based on the high-entropy titanate pyrochlore, TiO 2 was introduced for composite toughening and the high-entropy (Ho 0.2 Y 0.2 Dy 0.2 Gd 0.2 Eu 0.2) 2 Ti 2 O 7 -xTiO 2 (x = 0, 0.2, 0.4, 1.0 and 2.0) composites with high hardness (16.17 GPa), Young's modulus (289.3 GPa) and fracture toughness (3.612 MPa·m0.5), low thermal conductivity (1.22 W·m−1·K−1), and thermal expansion coefficients close to the substrate material (9.5 ×10−6/K) were successfully prepared by the solidification method. The fracture toughness of the composite toughened sample is 2.25 times higher than that before toughening, which exceeds most of the current low-thermal conductivity ceramics. • Preparation of high-entropy pyrochlore/TiO 2 composites by rapid melt solidification. • The composite toughened samples have ultrahigh fracture toughness (3.612 MPa·m0.5). • The solidified composites exhibit excellent mechanical and thermal properties. [ABSTRACT FROM AUTHOR]

Single phase (Lu 0.2 Yb 0.2 Er 0.2 Y 0.2 Gd 0.2)PO 4 was synthesized, and its thermal properties and CMAS resistance were investigated to explore its potential as an environmental barrier coating (EBC) candidate. The high entropy phosphate (Lu 0.2 Yb 0.2 Er 0.2 Y 0.2 Gd 0.2)PO 4 displays a lower thermal conductivity (2.86 W m−1 K−1 at 1250 K) than all the single component xenotime phase rare-earth phosphates. Interaction of (Lu 0.2 Yb 0.2 Er 0.2 Y 0.2 Gd 0.2)PO 4 pellets with CMAS at 1300 °C led to the formation of a dense and uniformed Ca 8 MgRE(PO 4) 7 reaction layer, which halted the CMAS penetration into the bulk pellet. At 1400 and 1500 °C the (Lu 0.2 Yb 0.2 Er 0.2 Y 0.2 Gd 0.2)PO 4 -CMAS corrosion showed CMAS penetrating beyond the reaction layer into the bulk pellet via the grain boundaries, and SiO 2 precipitates remaining at the pellet surface. The effects of duration, temperature, and compositions on the resistance against CMAS corrosion are discussed within the context of optimizing materials design and performance of high entropy rare-earth phosphates as candidates for advanced EBC applications. [ABSTRACT FROM AUTHOR]

Low elastic properties, high hardness, and low thermal conductivity are desirable for a rare-earth zirconate thermal barrier coating material. Realizing nonstoichiometry is a significant way to improve the elastic properties, hardness and thermal conductivity of rare-earth zirconate to further meet the requirements of thermal barrier coating materials, nonstoichiometric Gd 2-x Zr 2+x O 7+0.5x (x = 0, ±0.125, and ±0.25) was studied by first-principles calculations first and then verified by the solid-state reaction methods. Calculations revealed that excess Gd3+ and Zr4+ decrease the elastic modulus, sound velocity, and Debye temperature of Gd 2 Zr 2 O 7 , and increase its ductility. The elastic properties of the material exhibit significant anisotropy, which further increases with increasing Gd3+ and Zr4+ contents, resulting from lattice distortion caused by excess Gd3+ and Zr4+ entering the lattice. The hardness of Gd 2 Zr 2 O 7 increases with a moderate excess of Zr4+, while it decreases with an excess of Zr4+ and Gd3+. In addition, with the disordered occupation of lattice atoms, the anharmonicity of lattice waves is increased, and phonon scattering is enhanced as the concentrations of Gd3+ and Zr4+ increase, resulting in the reduction of the phonon thermal conductivity. Moreover, Zr4+ is more conducive to the decrease in the thermal conductivity. The experimental consequences match well with the calculation consequences. This work is expected to provide support for improving mechanical properties and thermal conductivity of rare-earth zirconate materials. [ABSTRACT FROM AUTHOR]

Carbon-metal carbide composites are a novel family of materials with potential application in heat dissipation due to the lightness and thermal-mechanical properties. Within these composites, those of graphite-chromium carbide have been still few studied. Therefore, this research focuses on both the influence of the powder preparation method (mechanical mixing (MM) and colloidal synthesis (CS)) and the spark plasma sintering (SPS) temperature (1600, 1700, 1800, 1900 and 2000 °C) in the properties of the composite graphite-7 vol. Cr. Results indicate that the composites sintered from powders processed by CS exhibit better properties, which can be explained by the better dispersion of the chromium carbide, formed during the sintering process, in the matrix of composite. Apart from the powder preparation method, sintering temperature has influence on the properties of the composite: 1900 °C is the best in the case of the route CS + SPS, while 2000 °C is the best option in the route MM + SPS. The thermal conductivity in-plane is 1.75 times greater in the CS than in the MM route, which suggests a better performance in the composite processed by colloidal route in heat dissipation applications. [ABSTRACT FROM AUTHOR]

The porous SiC-Mullite porous ceramics with different pore size were prepared by SiC particles, kaolin, Al(OH) 3 , and flake graphite, V 2 O 5 and AlF 3 were used as mineralizers, the pore size was controllable by adjusting the size of flake graphite. Then the improved empirical formula and grey theory were used to study the effect of the change in pore size on the material properties. The results showed that with the increase of mean pore size from 1.1 μm to 8.5 μm, the cold modulus of rupture and cold crushing strength decreased by 20.8 MPa and 13.7 MPa, respectively. And the thermal conductivity increased from 1.213 W⋅m−1⋅K−1 to 1.721 W⋅m−1⋅K−1 at 800 °C. The <5 μm pores were helped enhance the strength and decreased the thermal conductivity. [ABSTRACT FROM AUTHOR]

This article investigates the impact of gamma irradiation on the thermal properties of porous silicon with varying levels of porosity. Porous silicon is a crucial nanomaterial in modern materials science, widely utilized in electronics, optoelectronics, and various applications. Understanding how its thermal transport properties change under gamma irradiation is of importance for various industries, including military, space, and nuclear technologies, where materials may be exposed to ionizing radiation. For this purpose, we employed the non-destructive photoacoustic method with gas-microphone registration. We assessed thermal conductivity as a function of porosity and irradiation time by simulating the experimental amplitude-frequency dependencies using an appropriate model. Our findings reveal that prolonged gamma irradiation of samples using Iridium-192 with an activity of 50 Curie for up to 20 minutes leads to a decrease in thermal conductivity in porous silicon. This is due to the emergence of defects in the crystalline structure of porous silicon and even its possible amorphization. These defects and alterations in the material's structure restrict the movement of heat carriers, thereby reducing its thermal conductivity. It is worth noting that the most significant change observed in this study is a two-fold reduction in thermal conductivity, particularly evident in samples with the highest level of porosity (60 %). Samples with higher porosity exhibit a stronger response to gamma irradiation because they contain less material within their volume that can conduct heat. The constraints within the crystalline structure of samples with greater porosity create additional barriers to heat transfer, leading to increased vulnerability of the material to radiation and a decrease in its thermal conductivity [ABSTRACT FROM AUTHOR]