High Temperature Thermal Properties Research Articles

Heat transfer mechanism and performance optimization scheme of refractory oxide solid heat storage materials

Clean energy advances can drive solid heat storage technology. Because of their high-temperature, corrosion, and excellent thermal shock resistance properties, refractory oxides are widely used as solid heat storage materials. However, their applications are limited owing to their poor heat-transfer performance resulting from their multicomponent, multiphase, and complex nature and thus understanding their heat-transfer mechanism will be crucial for their performance optimization. In this study, the thermal properties and mechanisms of corundum, high-alumina, and magnesia bricks were characterized using heat-transfer theories and models. Macroscopic analysis of the bricks revealed that they are all “internal porosity” materials. By comparing the weighting parameter j, the multiphase high-alumina brick shows poor heat-transfer path patency and the measured thermal conductivity is the lowest at 3.55 W m−1 K−1. Microscopic analysis found that in contrast to the thermal conductivity of other materials, the thermal conductivity of high-alumina bricks was significantly affected by phonon intrinsic scattering. Moreover, corundum and magnesia bricks exhibited a wider range of ultimate heat-transfer performance than the high-alumina brick. Hence, the heat-transfer performance of refractory oxide can be enhanced by increasing their particle contact, reducing the negative effects of microcracks, phases, and impurities, and by reducing the number of defects on phonon heat transfer, thereby providing an optimization scheme for improving the heat-transfer performance of the materials.

High temperature oxidation and thermal properties of laminated Ti3Al(Si)C2-TiC/Nb based composites obtained by spark plasma sintering

This paper describes high-temperature oxidation behavior and thermal properties of metal-ceramic laminated composites fabricated by spark plasma sintering of Ti3Al(Si)C2-filled preceramic papers (TAC) and Nb foils. The high-temperature oxidation tests were carried out in air at 800–1300 °C. The phase composition and microstructure of the oxide layers were analyzed by X-ray diffraction and scanning electron microscopy, respectively. The thermal properties were measured by the laser flash method in the temperature range of 30–800 °C. The evolution of the microstructure of the reaction layer (RL) formed at TAC/Nb interfaces was studied. The passive oxidation of the surface TAC layers results in the formation of outer TiO2 and inner continuous Al2O3 phase at temperatures up to 1100 °C, while local accelerated oxidation occurs above 1100 °C. As a result of breakaway oxidation, a multilayer oxide structure consisting of TiO2, Al2TiO5, Al2O3 and SiO2 phases were formed. The oxidation of inner Nb layers from the side surface can lead to high volume expansion and generation of stresses in the ceramic and metal layers due to the formation of Nb2O5 oxide phase. The stress relaxation occurred by complex mechanisms, including plastic deformation of the Nb layers, delamination at the interfaces, and formation of cracks in the reaction and TAC layers. The high temperature exposure results in slight increase in columnar grains in the reaction layers at 1200 °C, while the thickness of RL remains unchanged. The TAC/Nb composites exhibit higher thermal conductivity and diffusivity compared to monolithic TAC ceramic composites.

Effect of Ti and Zr on high temperature mechanical and thermal properties of MoCu composites

Based on the design concept of diversified alloys, the reinforcement of TZM alloys was combined in the fabrication of MoCu composites. The MoCu composites were prepared by vacuum hot press sintering under the effect of Ti, Zr elements added separately or simultaneously, and the microstructure adjustment was realized by mechanical ball milling on the pretreatment of the original alloy powder. The results show that Ti and Zr elements form metal-based solid solutions and intermetallic compounds by diffusion with Mo and Cu matrix during the sintering process. It can not only reduce the sintering activation energy of MoCu composites to improve the densification, but also improve the mechanical properties of the composites through certain solid solution strengthening and second phase strengthening. When Ti, Zr elements are added at the same time, Zr elements can enhance the β-stabilizing effect of Mo on Ti elements and improve the solid solution effect between Ti and Mo, Cu matrix, which further improves the interfacial bonding. Therefore, the 60Mo35Cu2.5Ti2.5Zr composites have the best overall performance, and their thermal properties and mechanical properties at room and high temperatures are greatly improved compared with the original 60Mo40Cu composites.

High-Temperature Reliability of Nano-Ag Sintered Joints on Ag-Plated Cu Substrates

As an emerging lead-free packaging interconnect material, Nano-Ag paste exhibits superior high-temperature mechanical, electrical, and thermal properties. It can meet the stringent high-temperature and high-density packaging requirements of future high-power semiconductor devices and is garnering widespread attention. However, research on the high-temperature reliability of sintered joints remains rather limited. In this study, we fabricated high-strength hot-press sintered nano-Ag joints using a hot-press sintering process. These joints underwent aging at high temperatures of 200°C and 300°C, yielding insights into the variations in mechanical properties at different temperatures. The reasons behind joint failure were analyzed by investigating the evolution of joint microstructures and fracture surfaces. The results indicate that even after extended aging at 200°C, the joint strength can still be maintained at 176 MPa. However, after aging for over 100 hours at 300°C, the joint fails. The growth of Cu oxides was observed within the joint microstructure, which constitutes the primary cause of joint failure at 300°C.

High-temperature and high-pressure thermal property measurements of SiO2 crystals.

The investigation of materials' behavior under high-temperature and high-pressure conditions, such as the correlation with structural characteristics and thermal properties, holds significant importance. However, the challenges associated with the experimental implementation have, to a certain extent, constrained such research endeavors. We utilized the ultrafast laser based non-contact thermal measurement method combined with an externally heated moissanite-anvil-cell to characterize the thermal conductivity of [10-10] oriented SiO2 crystals under high temperature (300-830K) and high pressure (0-15GPa) conditions. We investigated the impact of extreme conditions on the microstructure from both Raman spectroscopy and thermal perspectives. The presence of kinetic hindrances associated with the transformation of α-quartz to coesite and stishovite was identified and confirmed. It expands the comprehension and application of the SiO2 pressure-temperature phase diagram in this range and provides insights into the intricate relationship between extreme environments and material structure formation through the analysis of thermal characteristics.

Effect of temperature on thermal properties and residual strength of coal gangue concrete

Key factors for assessing the high-temperature resistance of coal gangue concrete are high-temperature residual strength and thermal properties. The high-temperature residual strength, high-temperature thermal conductivity, high-temperature specific heat capacity, and high-temperature density of concrete with various coal gangue coarse aggregate replacement ratios were tested using experimental methods in this paper to study the high-temperature resistance of coal gangue concrete. Thermal density and high-temperature residual strength tests took into account influencing factors like the water-cement ratio (0.50, 0.45, 0.40), aggregate replacement ratio (0, 25 %, 50 %, 75 %, 100 %), and temperature variation (room temperature, 200 °C，300 °C，400 °C，500 °C，600 °C，700 °C，800 °C), while thermal properties tests considered the effects of various coarse aggregate replacement ratios and temperatures. The study showed that when the temperature rises, coal gangue concrete's thermal density falls, mass loss rises, residual strength declines, thermal conductivity rises, and its specific heat capacity fluctuates. At temperatures between 20 °C and 400 °C, concrete's residual strength decreases with an increase in the coal gangue coarse aggregate replacement ratio, while thermal conductivity and specific heat capacity increase. At temperatures between 500 °C and 800 °C, however, concrete's residual strength slightly improves with an increased coal gangue coarse aggregate replacement ratio, while mass loss changes more. The research finally provides the formulae for calculating the high-temperature residual strength and thermal properties of coal gangue concrete based on the test results.

Analysis of heat transfer characteristics of sandwich cylindrical shell with an aerogel-metal-rubber composite core

Metal-rubber sandwich cylindrical shell displays a broad range of potential applications in the field of thermal insulation due to its advantages of lightweight, high-temperature stability, and superior high-temperature thermal insulation properties. To optimize the thermal insulation performance of a sandwich cylindrical shell with a metal-rubber core, this study proposes the idea of filling the pores of the metal-rubber with aerogel, thereby forming a composite structure of aerogel and metal-rubber (AMR). Through finite element analysis, the law of internal temperature changes in the AMR composite structure and the distribution laws of the velocity field, viscosity field, and pressure field of the sandwich cylindrical shell under varying wind speeds are investigated. These findings are further verified through heat transfer and forced convection tests. The results reveal that the thermal conductivity of the AMR composite structure at the same density is lower than that of the metal-rubber, and the thermal insulation performance of the AMR composite structure is directly proportional to its density. Meanwhile, through the analysis of forced convection heat transfer in the cylindrical shell, it is found that wind speed has a direct relationship with the pressure field, velocity field, and viscosity field. In addition, there is a relatively high viscosity and a low flow rate near the wall of the cylindrical shell, with a higher flow rate at the axis of the cylindrical shell. At the same wind speed, the temperature rise of the sandwich cylindrical shell shows a positive correlation with an increase in density, and the maximum stable temperature also increases correspondingly. Moreover, at the same density, the thermal conductivity demonstrates a negative correlation with increasing temperature.

Effect of Gd doping on phase evolution, mechanical and thermal characteristics of 1La-xGd-2Yb-3.5YSZ solid solutions

Thermal barrier coatings (TBCs) are critical for the reliability and lifespan of aircraft engine turbine blades. In this study, a novel quaternary rare-earth oxide (La2O3, Gd2O3, Yb2O3, and Y2O3) co-doped ZrO2 solid solution, referred to as 1La-xGd-2Yb-3.5YSZ, was synthesized by varying the doping amount of Gd2O3 from 0 to 6 mol. %. The impact of co-doping-induced lattice distortion on the phase composition, high-temperature phase stability, sintering resistance, and mechanical and thermal properties of the solid solution has been explored. It is found that the addition of Gd2O3 stabilizer effectively increased the lattice distortion of the solid solution, which led to improved phase stability and sintering resistance, enhanced mechanical properties, and low thermal conductivity. Our findings highlight the promising properties of the 1La-xGd-2Yb-3.5YSZ solid solution, making it an attractive candidate for TBC materials.

Fabrication of mullite micro/nano fiber-based porous ceramic with excellent mechanical and thermal insulation properties

Mullite fiber-based porous ceramics is one of the most commonly used high-temperature insulation materials. However, how to further reduce the thermal conductivity and improve the strength of such materials has been a challenge in the field of high-temperature insulation. In this paper, mullite micro/nano fiber-based porous ceramic was prepared by introducing mullite nanofibers into mullite microfiber-based porous ceramics and the effect of microfiber/nanofiber weight ratio on the samples properties were characterized and analyzed. Results showed that the compressive strength and high-temperature thermal insulation properties of the porous ceramics increased significantly with an increase in the nanofiber content. For the porous ceramics with similar density (about 0.50 g/cm3), the compressive strength of the sample with a microfibers/nanofibers weight ratio of 1:2 was 1.43 MPa, which was much higher than that of the porous ceramics prepared with only microfibers (0.26 MPa). Meanwhile, the backside thermal equilibrium temperature of the sample with a microfiber/nanofiber weight ratio of 1:2 at 900 °C environment was 355.8 °C, which was much lower than that of the porous ceramic prepared with only microfibers (476.5 °C). In addition, in order to investigate the temperature resistance of mullite micro/nano fiber-based porous ceramics, the sintering temperatures was increased from 1400 °C to 1500 °C. Results shows that the high-temperature thermal insulation performance of mullite micro/nano fiber-based porous ceramics with high mullite nanofiber content decays more seriously. The back-temperature test showed that the thermal equilibrium temperature of the samples with a mullite micron/nanofiber weight ratio of 1:1 in 900 °C environment increased rapidly from 386.3 °C to 454.2 °C when the sintering temperature was increased from 1400 °C to 1500 °C. The preparation of mullite micro/nanofiber-based porous ceramics provides a new strategy to improve the performance of fiber-based porous ceramics.

Multilayered mullite ceramics with anisotropic properties

Anisotropic layered porous ceramics are crucial to satisfy the demand for devices with directional functions. However, challenges, such as complicated preparation processes and difficulties in regulating the oriented structure, severely limit their application. Here, multilayered mullite ceramics (MLMCs) with specific porosities and strongly anisotropy properties, were prepared by designing porous thin-layered units and an interlayer layout, in combination with a simple gel-casting. Benefiting from the suitable slurry properties, the samples did not show obvious defects, and a perfect bonding was observed between the layers. The optimized MLMCs exhibited a porosity of 65.12%, the differences in compressive and flexural strengths of 14 (±0.7) and 5 (±0.2) MPa in different pressure directions respectively, and the anisotropy factor of thermal conductivity up to 0.98, as well as exhibited good high temperature thermal insulation properties. Ultimately, the MLMCs formed transverse heat conductor and longitudinal heat insulation heat-transfer patterns, with promising applications in thermal insulation.

High thermal insulation and high strength SiBCN@SiC double network ceramic composite aerogel

Silicon carbide (SiC) fiber materials prepared by precursor conversion method have attracted extensive attention in recent years due to their excellent high temperature resistance and thermal insulation properties. Herein, a novel SiBCN/SiC dual network ceramic composite aerogel with the three-dimensional (3D) porous SiC fiber network obtained by direct electrospinning as the first network and SiBCN aerogel as the second network was prepared by combining electrospinning with sol-gel technology and supercritical drying technology. The microstructure, phase composition, pore size distribution, compressive resistance, thermal insulation and related mechanisms of the 3D SiC fiber network and composite aerogel at different heat treatment temperatures were investigated in detail. The results show that the constructed double-network structure can make up for the heat transfer problem of a single SiC fiber network and further reduce its thermal conductivity, so that the prepared composite aerogel exhibits a lower thermal conductivity (∼0.0316 W m−1 K−1). In addition, the unique double network structure endows the composite aerogel with excellent compressive properties (2.56–2.89 MPa).

Ultralight Ceramic Fiber Aerogel for High-Temperature Thermal Superinsulation.

Emerging fiber aerogels with excellent mechanical properties are considered as promising thermal insulation materials. However, their applications in extreme environments are hindered by unsatisfactory high-temperature thermal insulation properties resulting from severely increased radiative heat transfer. Here, numerical simulations are innovatively employed for structural design of fiber aerogels, demonstrating that adding SiC opacifiers to directionally arranged ZrO2 fiber aerogels (SZFAs) can substantially reduce high-temperature thermal conductivity. As expected, SZFAs obtained by directional freeze-drying technique demonstrate far superior high-temperature thermal insulation performance over existing ZrO2-based fiber aerogels, with a thermal conductivity of only 0.0663 W·m-1·K-1 at 1000 °C. Furthermore, SZFAs also exhibit excellent comprehensive properties, including ultralow density (6.24-37.25 mg·cm-3), superior elasticity (500 compression cycles at 60% strain) and outstanding heat resistance (up to 1200 °C). The birth of SZFAs provides theoretical guidance and simple construction methods for the fabrication of fiber aerogels with excellent high-temperature thermal insulation properties used for extreme conditions.

Fiber-reinforced alumina-carbon core-shell aerogel composite with heat-induced gradient structure for thermal protection up to 1800 °C

High performance thermal insulation materials are urgently demanded for hypersonic spacecraft. Aerogels are considered as promising candidates owing to their low density and low thermal conductivity. However, some deficiencies, such as the unsatisfactory high-temperature thermal insulation properties and the non-exfoliation-resistant particle porous structure of ceramic aerogels, the ease of oxidation and large carbonization shrinkage of carbon aerogels, remain great challenges for their further applications in high-temperature aerobic ablation environments. Here, we report a multiscale fiber-reinforced Al2O3-carbon core–shell aerogel composites with low density (0.23–0.31 g·cm−3), excellent mechanical properties (4.89 MPa at 10% strain) and ultra-low carbonization shrinkage (as low as 1.33%). Benefiting from the synergistic effect of in situ nano-doped light-shading carbon layers, porous Al2O3 ceramic rod skeleton and oriented fibers, the composites demonstrate an extremely low high-temperature thermal conductivity (0.055 W·m−1·K−1 at 1200 °C) that is far superior to those of existing high-temperature insulating aerogel composites. In addition, the unique heat-induced gradient structure also confers outstanding thermal protection properties to the composite at 1800 °C with a liner ablation rate of 6.44 μm·s-1and a mass loss rate of 0.167 mg·s−1. This work not only opens a new path for the preparation of thermal superinsulating materials used for spacecraft, but also provides a simple solution to the difficulty of compatibility between low-density insulating porous skeleton and ablation-resistant tough structures, thereby enabling thermal insulation materials to possess desired ablation-resistant properties.

First-Principles Investigation on the High-Temperature Mechanical Properties and Thermal Properties of Pt-40Rh

First-Principles Investigation on the High-Temperature Mechanical Properties and Thermal Properties of Pt-40Rh

Structure and Thermophysical Properties of Molten Calcium-Containing Multi-Component Chlorides by Using Specific BMH Potential Parameters

Chloride molten salts have become a potential heat storage material for the design of a new generation of concentrating solar power (CSP) (>700 °C) due to its abundant reserves and low cost. The difficulty of measuring the high-temperature thermal properties of chlorides can be effectively solved by using molecular dynamics simulation. However, it is challenging to get the thermophysical properties of multi-component molten salts containing CaCl2 due to the lack of Born–Mayer–Huggins (BMH) potential parameters of CaCl2. Through comparative analysis of the structure and thermal properties of CaCl2, including density and thermal conductivity, a set of Born–Mayer–Huggins (BMH) potential parameters of CaCl2 named SP2 is determined in this study. The density, specific heat capacity, and thermal conductivity of nine eutectic molten salts are simulated, including NaCl-CaCl2, KCl-CaCl2, NaCl-CaCl2-MgCl2, and NaCl-CaCl2-KCl, and the simulation results are found to be in good agreement with the experimental results. It is also found that the SP2 parameters are able to predict the thermal properties and structure of molten multicomponent chlorides including calcium.

Thermal Analysis of Ni-Cu Alloy Nanocomposites Processed by Sand Mold Casting

Ni-Cu based alloy metal matrix nanocomposites are in great demand for advanced technological applications due to their high temperature, strength, and better thermal properties. The aim is to investigate the thermal conductivity and coefficient of thermal expansion of the nickel based alloy nanocomposites reinforced with titanium dioxide (TiO2) which varies from 3 to 12 weight % nanoparticulates (45 to 60 nm). The thermal conductivity was measured using a comparative cut bar method (ASTM E1225), and thermal expansion was analyzed using a push-rod dilatometer method (ASTM E228). From experimentation, it was observed that thermal conductivity of the nanocomposites activity increases with inclusion of the nanoparticles up to 9 weight % after descent due to the temperature effects in nanocomposites, and thermal expansion of the nanocomposites decreases with addition of the nanoparticles up to 9 weight % and further rises marginally due to ductility of composites. Due to the incorporation of hard ceramic particles into the matrix, the composites’ thermal conductivity increases to 57.42 W/m℃, and their thermal expansion decreases to 12 × 10−6. Nickel alloys are widely used in marine, automotive, valve, pump, and aircraft applications.

In-situ synthesis of phosphorus-doped graphene paper with adenosine triphosphate and its application for intelligent fire warning

Design of intelligent sensors for detecting early fire warning before combustion is a challenging for the fire safety. Herein, a nacre-biomimetic paper based on graphene oxide (GO) and adenosine triphosphate (ATP) was fabricated via a low-temperature evaporation assembly approach. Then the fire-alarm sensor was designed according to the high temperature thermal reduction properties of GO. The GO-ATP paper exhibited a well-organized ‘‘brick and mortar” structure due to the presence of hydrogen bonds and electrostatic attraction interaction between GO and ATP molecules. The paper containing 50 wt% of ATP presented a rapid flame detection response (1.36 s) and a long continuous alarm time (1300 s) due to in-situ phosphorus doping and the honeycomb-like char forming during fire exposure. Moreover, the GO-ATP-50 also exhibited flexibility, flame retardant performance, heat insulation ability and char-forming properties. This work provides a bright application prospect for fire safety and prevention of combustible materials.

High-temperature microtexture, microstructure evolution, and thermal insulation properties of porous Si3N4/silica aerogel composites produced by impregnation

High-temperature microtexture, microstructure evolution, and thermal insulation properties of porous Si3N4/silica aerogel composites produced by impregnation

A high-temperature thermal stability and optical property study of inorganic coatings on ceramic particles for potential thermal energy storage applications

Ceramic-based packed bed solutions are becoming more common in the energy fields as both thermal energy storage and heat exchanger. Such solutions are usually designed for the working temperature ranges above 600 °C, thus thermal radiation becomes significant and even acts as the dominant heat transfer mechanism. Therefore, applying high-temperature coatings with different thermal properties could be an efficient way in enhancing the performance of these applications. In this work, the high-temperature long residency and cyclic thermal stability of six inorganic coatings applied on a ceramic substrate are investigated. Both qualitative and quantitative assessments are performed. The results show that HIE-Coat 840MX and Pyropaint 634 ZO exhibit excellent thermal stability performance both at high-temperature testing (1000 °C) and under thermal cycle testing (400 °C–800 °C). TiO 2 based coatings could be a viable solution if the powder is pre-treated to avoid polymorph transition during the operation. Stainless steel 304 powder-based coating could also be a possible solution, since the adhesive curbs the oxidation and hinders the coating from deterioration. Contrarily, Pyromark 2500 and MgO based coating show different degradation problems that limit their exploitation in high-temperature applications undergoing thermal cycles. The investigated coatings show a wide range of thermal emissivity (between 0.6 and 0.9), with stable or decreasing trends with temperature. This enables a potential 20% change of the effective thermal conductivity for the packing structure. This work is a stepping-stone towards further detailed experimental studies on the influence of coatings on various packed bed thermal storage systems, and thus offer a new option in improving the performances of the energy equipment with packed bed systems. • Thermal stability of six inorganic coatings on ceramic particles tested at 1000 °C. • Pyro-Paint 634-ZO and HIE-Coat 840MX show excellent thermal stability. • MgO coating on ceramic particles shows cracks after 30 thermal cycles (400–800 °C). • Optical properties of selected coatings are studied in the λ range 250–26000 nm. • Effective thermal conductivity increases of 27% at 1000 °C can be attained.

Mechanically flexible polyimide foams with different chain structures for high temperature thermal insulation purposes

Mechanically flexible polyimide foams (PIFs) with exceptional high temperature thermal insulation properties were fabricated by microwave-assisted foaming and post thermal imidization process, using polyester ammonium salt (PEAS) precursor powders which consisted of different molecular chain structures as the derivatives. A comparison of foaming behavior, pore morphology, mechanical and thermal insulation properties between PIFs prepared with mono-dianhydride and copolymerized dianhydride structures was systematically studied. Results showed that the optimum foaming temperatures of PEASs was in the range of 85–150 °C, which correlated with the volatilization of solvents such as H2O, tetrahydrofuran and methanol. The introduction of copolymerized dianhydride structure altered the chain rigidity and melt viscosity of PEAS, which improved the cellular structure and mechanical flexibility of PIFs. Moreover, the micron-scale cellular structure of PIFs was determined by melt viscosity, chain rigidity, volatile content and foaming temperatures. The PIFs exhibited low apparent densities (25–30 kg/m3), high open cell rate (95–97%) and mechanical flexibility (compression/release recover rate: 96–99%). All PIFs possessed exceptional thermal stability and thermal insulation properties which can be targeted for thermal insulation applications in the fields of aerospace, transportation, and microelectronics among others.