Moderate Thermal Conductivity Research Articles

Performance of advanced ceramic round tools when turning Inconel 718

Nickel-based superalloys, like Inconel 718, are very attractive metals for aerospace applications due to their excellent mechanical properties and thermal stability. However, these materials pose a significant challenge to the metal machining industry due to their very low machinability, especially in terms of reduced tool life because of the high heat generated during cutting. Nevertheless, it can be improved using high-performing tools that retain their hardness when exposed to high temperatures, such as ceramic tools. In this context, the study aims to compare the performance of two advanced ceramic tools, namely an alumina ceramic tool reinforced with SiC whiskers and a Bidemics™ one, when turning Inconel 718 at different cutting speeds, using as a baseline a conventional coated cemented carbide tool. First, the three inserts were characterized in terms of topography, thermal conductivity, and hot hardness to fully understand their operational behavior. Then, turning trials were conducted showing that both the ceramic tools outperform the coated carbide one in terms of tool life, with Bidemics™ demonstrating the best performance among all. This can be ascribed to its very high hardness maintained even at high temperatures, as well as its moderate thermal conductivity.

Extending the Transient Plane Source Scanning method for determining the specific heat capacity of low thermal conductivity materials through a numerical study

In contrast to the conventional Transient Plane Source (TPS) method, the Transient Plane Source Scanning (TPSS) technique allows for the direct determination of the specific heat capacity and requires the use of a specially designed sample holder for accurate measurements. While this method correctly determines the specific heat capacity of samples with moderate and high thermal conductivity, it tends to underestimate the values for those with low thermal conductivity. This paper demonstrates that the underestimated specific heat capacity results from heat loss during the measurement process. To precisely quantify the heat loss, a numerical model based on the finite element method was developed, with key material properties tuned based on measurement data. This model can closely describe the curve of measured thermal response, thereby enabling the precise determination of the specific heat capacity. Consequently, this study introduces a novel approach that incorporates numerical simulation to enhance TPSS measurements of poorly conducting samples, providing a reliable alternative for determining specific heat capacity.

Synergistic performance enhancement of lead-acid battery packs at low- and high-temperature conditions using flexible phase change material sheets

Thermal management of lead-acid batteries includes heat dissipation at high-temperature conditions (similar to other batteries) and thermal insulation at low-temperature conditions due to significant performance deterioration. To address this trader-off, this work proposes a thermal management solution based on flexible phase change materials (PCMs) with moderate thermal conductivity and other favourable properties including high specific heat capacity and high latent heat. A novel type of flexible PCM sheets is prepared with paraffin, olefin block copolymers (OBC) and expanded graphite using the co-melting method. The flexible PCM sheets are attached to a common type of lead-acid battery packs (12 Ah, dimensions of 151 × 98 × 97 mm) and thermal management performance is experimentally investigated at –10 °C and 40 °C as low- and high-temperature conditions, respectively, along with 25 °C as a baseline case for comparison purposes. Thermal properties of the battery packs such as temperature regulation and electric properties including charge/discharge capacities and rates are studied synchronously based on a standard high-performance battery detection facility. The results indicate that at –10 °C condition, the PCM sheet enhances thermal insulation of the battery pack and significantly promotes the service temperature during the charging processes. Compared with a benchmark pack attached with an encapsulated sheet, the charge and discharge capacities of the PCM-attached pack are improved by 3.7% and 5.9%, respectively. At 40 °C condition, phase transition of the PCM sheet restrains the temperature rise of the battery pack, with a maximum temperature decrease of 4.2 °C during the charging processes relative to the benchmark pack, and the temperature of the PCM-attached pack is maintained below 45 °C across 60% of the overall charge period. The overcharge and overdischarge have also been alleviated by 3.2% and 2.8%, respectively, and thus the running stability and service lifespan can be improved. The proposed PCM sheets with preferable thermal properties demonstrate potential to promote performance of lead-acid battery packs and such components are also expected to improve heat dissipation and thermal insulation in similar applications including building energy saving, thermal management of electronic chips and thermal regulation of electronic devices.

Growth, spectroscopic, thermal and laser frequency doubling properties of CTGAS crystal

A novel nonlinear optical crystal Ca3Ta(Ga0.7Al0.3)3Si2O14 (CTGAS) was successfully grown by the Czochralski method. The structural, spectroscopic and thermal properties have been systematically investigated, and the laser frequency doubling process has also been explored. Excellent thermal properties have been presented, such as moderate thermal conductivity, high specific heat, and low thermal expansion anisotropy. The electronic structure and optical properties have been investigated using the XPS technique and simultaneous assisted first-principles calculations. The optimal phase matching in type I (40.45°, 30.0°) and type II (64.73°, 0°) orientations were determined, frequency-doubling output was achieved in type I and type II, with laser energies of up to 10.04 mJ and 10.14 mJ obtained @ 532 nm, and optical-to-optical conversion efficiencies of 14.04 % and 17.21 %, respectively. The experimental findings demonstrate the great potential of CTGAS crystal as a frequency-doubling material.

INVESTIGATION OF THE REFRACTORY PROPERTIES OF KANKARA CLAY FOR ENGINEERING AND INDUSTRIAL APPLICATIONS

The refractory properties of Kankara clay have been investigated with a view to understanding its suitability for various engineering and industrial applications. The experimental procedures include thermal shock resistance, thermal conductivity, shrinkage, apparent porosity, refractoriness under load with rising temperature mode, and refractoriness under loadmaintained temperature mode. The results obtained from the research work showed the clay has good refractory properties that can be used for both Engineering and industrial applications. The value obtained through the thermal conductivity test 0.48W/m℃ , as compared with 0.35- 0.45 W/moC for insulating fire brick and 1.05- 1.45W/m℃ for dense fire brick. 2kg/cm2 of the sample was further subjected to refractoriness test where the sample was heated to 1405oC as compared to 1750oC for the production of fire bricks. Further investigation indicated that a glassy surface structure was formed when the samples was heated above 1400℃ . The value obtained as regard the porosity level was 25% which fell between 20-30% as the acceptable standard. The sample was also subjected to apparent porosity and a value of 38% was obtained. Kankara clay formed a glassy and surfaces when heated above 1400oC. In this research, these bricks porous with an apparent porosity of 38.07%. Attempts to produce these bricks with acceptable porosity level of 20-30% were not successful. Kankara clay exhibits moderate thermal shock resistance, moderate thermal conductivity, moderate shrinkage, high apparent porosity, and high refractoriness under load in both rising temperature mode and maintained temperature mode. "Based on these results, Kankara clay appears to be well-suited for use in applications where moderate levels of thermal shock resistance, thermal conductivity, and shrinkage are acceptable, such as in the manufacture of low-temperature bricks, but less suited for high-temperature applications, such as furnace linings, due to its high apparent porosity and susceptibility to deformation under load. Further research could be conducted to explore strategies for reducing the porosity and improving the refractoriness of this clay for broader applications.

Study on the mechanical and thermal properties of aramid fibre reinforced with sawdust particulates in an epoxy matrix composite: a novel material for structural applications

AbstractThis study investigates the development and characterization of a novel composite material for structural applications, aiming to address the growing demand for lightweight, durable and versatile materials. The composite integrates aramid fibre reinforced with sawdust particulates within an epoxy matrix. Methodologically, the composite was fabricated using a hand layup process, ensuring even distribution and strong adhesion between components. Mechanical testing revealed significant enhancements in tensile strength (up to 135.29 MPa) and flexural strength (up to 136.92 MPa) with the inclusion of sawdust particulates, optimizing stress distribution and impact resistance. Hardness was also improved, peaking at a Rockwell hardness number of 94. Thermal analysis demonstrated moderate thermal conductivity (1.92 W mK−1) and a high heat deflection temperature (109 °C), indicating excellent thermal stability. SEM provided insights into the composite's microstructure, confirming uniform sawdust distribution and robust fibre–matrix adhesion. These findings underscore the potential of this composite for lightweight, durable and thermally stable structural applications. © 2024 Society of Chemical Industry.

Turning waste and hazard into thermal conduction material: A promising destination of waste pyrrhotite and polystyrene

The demand for efficient heat dissipation in electronic and electrical equipment enclosures is rising due to the pursuit of higher performance. However, the predominant challenge lies in the use of plastic as the primary material, which lacks favorable thermal conductivity (TC) despite its good machinability. Compared with common fillers, pyrrhotite (Pyr) exhibits moderate TC, insulation properties, and abundant active polysulfide sites on its surface. To turn waste into treasure, we prepared an economic thermal conductive material by powder mixing of Pyr tailings and waste polystyrene (WPS). Hexagonal and monoclinic crystalline Pyr were also prepared respectively, and the results showed that the hexagonal crystalline Pyr exhibited better application potential of TC filler. Furthermore, the strengthening mechanism of polysulfide bonds on the TC was analyzed and demonstrated. The results of the performance evaluation showed that the TC of the composite with optimal conditions improved by 1162.5 % compared to the WPS matrix. Based on the concept of green chemistry and the universality of raw materials, the research provides a method with excellent cost advantages in the future. This method also opens up a new vision for boundary applications such as heat exchange coatings. It is believed that this work provided a green and economic perspective for the disposal of sulfide minerals tailings and waste plastics.

Evidence of Higher Order Phonon Anharmonicity in Gray Arsenic Crystal.

Phonons play a key role in the heat transport process of quantum materials. The understanding of thermal behaviors of phonons will be beneficial for designing modern electronic devices. In this study, we utilize specific heat, Raman spectroscopy, and first-principles calculations combined with the phonon Boltzmann transport equation to explore the thermal transport of gray arsenic. Our specific heat data indicate the presence of the phonon anharmonicity at high temperature. This is further supported by temperature-dependent Raman data showing evident phonon softening and line width broadening. More interestingly, from the analysis of temperature-dependent Raman modes, we found that the four-phonon scattering process is indispensable for interpreting the line width broadening at high temperatures. Moreover, we evaluate the importance of the four-phonon scattering process in the heat transport of gray arsenic using the moment tensor potential method. Our work sheds light on the importance of a higher order phonon scattering process in heat transport of the materials with moderate thermal conductivity.

Microstructure, Thermal and Mechanical Properties of AlN-MgO Composites Prepared by Spark Plasma Sintering

AlN-MgO composites with different compositions were prepared by spark plasma sintering, and the effects of their composition on their microstructure, thermal properties, and mechanical properties were systemically investigated. MgO compositions in the AlN-MgO composites were controlled from 20 to 80 wt%. The results indicated that a phase transition did not occur during the sintering process, and different solid solutions were formed within the MgO and AlN lattices. The AlN-MgO composites exhibited finer-grain microstructures than those of the sintered pure AlN and MgO samples. Transmission electron microscopy analysis showed that both oxygen-rich, low-density grain boundaries and clean boundaries with spinel phases were present in the composites. The sintered pure AlN sample exhibited the highest thermal conductivity (53.2 W/mK) and lowest coefficient of thermal expansion (4.47 × 10<sup>-6</sup> /K) at 100 °C. And, the sintered pure MgO sample exhibited moderate thermal conductivity (39.7 W/mK) and a high coefficient of thermal expansion (13.05 × 10<sup>-6</sup> /K). With increasing MgO contents in the AlN-MgO composites, however, the thermal conductivity of the AlN-MgO composites decreased, from 33.3 to 14.9 W/mK, while their coefficient of thermal expansion generally increased, from 6.49×10<sup>-6</sup> to 10.73×10<sup>-6</sup> /K with increasing MgO content. The composite with an MgO content of 60 wt% exhibited the best mechanical properties overall. Thus, the composition and microstructure of AlN-MgO composites have a determining effect on their thermal and mechanical properties.

Asymmetrical LaO9 polyhedron inducing anisotropic positive thermal expansion and moderate lattice thermal conductivity in LaBO3 with isolated planar [BO3] group

Thermal physical properties of inorganic borates are important in application of optical device working under high temperature. Herein, we investigate the temperature-dependent thermoelasticity, thermal expansion(α), and lattice thermal conductivity(κ) of simple orthohomibic LaBO3 with a two dimension like crystal structure though first principles for the first time. The calculated rate of temperature-dependent second elastic constant C11 is significantly larger than that of C22 and C33, and the theoretical slopes of corresponding bulk, shear, and Young's moduli in the range of 300–900 K are −0.0289 GPa•K−1, −0.0156 GPa•K−1, and −0.0398 GPa•K−1, respectively. The predicted α is positive and increases with the rise of temperature. The anisotropic ratio αc/αa or αc/αb is approximately 2 at 300 K, which might be attributed to the difference of elastic compliance S12 and S13. Besides, the anisotropic lattice thermal conductivity κa, κb and κc of LaBO3 is predicted to be 1.43, 1.40 and 0.80 W/m-K at 300 K via Debye-Callaway model. Most importantly, the atomic projected Grüneisen parameters γ reveal that asymmetrical LaO9 polyhedra in the crystal lattice dominate the thermal expansion and lattice thermal conductivity. Our results indicate that LaBO3 has good thermal physical properties working under high temperature.

Electronic, Thermal and Mechanical Properties of Carbon and Boron Nitride Holey Graphyne Monolayers.

In a recent experimental accomplishment, a two-dimensional holey graphyne semiconducting nanosheet with unusual annulative π-extension has been fabricated. Motivated by the aforementioned advance, herein we theoretically explore the electronic, dynamical stability, thermal and mechanical properties of carbon (C) and boron nitride (BN) holey graphyne (HGY) monolayers. Density functional theory (DFT) results reveal that while the C-HGY monolayer shows an appealing direct gap of 1.00 (0.50) eV according to the HSE06(PBE) functional, the BNHGY monolayer is an indirect insulator with large band gaps of 5.58 (4.20) eV. Furthermore, the elastic modulus (ultimate tensile strength) values of the single-layer C- and BN-HGY are predicted to be 127(41) and 105(29) GPa, respectively. The phononic and thermal properties are further investigated using machine learning interatomic potentials (MLIPs). The predicted phonon spectra confirm the dynamical stability of these novel nanoporous lattices. The room temperature lattice thermal conductivity of the considered monolayers is estimated to be very close, around 14.0 ± 1.5 W/mK. At room temperature, the C-HGY and BN-HGY monolayers are predicted to yield an ultrahigh negative thermal expansion coefficient, by more than one order of magnitude larger than that of the graphene. The presented results reveal decent stability, anomalously low elastic modulus to tensile strength ratio, ultrahigh negative thermal expansion coefficients and moderate lattice thermal conductivity of the semiconducting C-HGY and insulating BN-HGY monolayers.

Manufacturing Scalable Carbon Nanotube-Silicone/Kevlar Fabrics.

Carbon nanotube (CNT) hybrid composites were formed by combining a CNT and silicone elastomer solution with Kevlar yarn, Kevlar fabric, and Kevlar veil materials. The integration of a CNT-silicone matrix with Kevlar yarn and fabric materials produced a composite with moderate electrical and thermal conductivity due to CNT fabric combined with the strength of Kevlar fabric or yarn. In the material synthesis, a notable difficulty was that the CNT-silicone did not bond strongly to the Kevlar. The composites passed the Vertical Flame Test ASTM D6413 and the Forced Air Oven Test NFPA 1971. These hybrid composites can have multiple applications in areas requiring favorable conductivity, strength, and flame and heat resistance. The application areas include firefighter apparel, military equipment, conductive/smart structures, and flexible electronics. The synthesis process used to manufacture CNT-silicone/Kevlar composites yielded composite sheets with an area of 2250 cm2. The process is scalable and customizable for the synthesis of CNT composites with tailored properties. Improvements in the bonding of CNT-silicone to Kevlar are being investigated.

Preparation and stability analysis of glycine water-based phase change materials modified with potassium sorbate for cold chain logistics

Organic water-based phase change material (PCM) shows great potential for cold chain logistics below 0 °C. However, its poor stability limits its application. The purpose of this study is to develop an organic water-based PCM with high latent heat and melting temperature of −4 °C to −6 °C based on solving the problem of poor stability. Glycine and mannitol aqueous solution were selected as the base PCM, and the static stability was improved effectively with 0.1 wt% potassium sorbate modification. The prepared 6-PCM5 composed of 6 wt% glycine, 1.5 wt% mannitol, and 0.1 wt% potassium sorbate, demonstrated moderate thermal conductivity of 0.6017 W/(m·K) and a suitable melting temperature of −5.78 °C as well as an enthalpy of fusion of 292.64 J/g. After 100 thermal cycles, the melting temperature, enthalpy of fusion, and thermal conductivity were −5.91 °C, 290.66 J/g, and 0.5886 W/(m·K), which decreased only by 2.24%, 0.68%, and 2.18%, respectively. Furthermore, the cold storage performances of 6-PCM5 and ice were compared and evaluated by loading strawberries. Compared with ice storage, the pre-cooling time and average temperature of strawberries in the cold storage box with 6-PCM5 was reduced by 68.4% and 2.55 °C, and the effective cold storage time was lasted for 22.83 h at a temperature range of 0.45 °C to 3 °C, which effectively improved the cold storage quality of strawberries. Overall, the developed 6-PCM5 cold storage material possesses good static and cyclic stability, providing an effective solution for pre-cooling and short-distance cold chain transportation of perishable food.

Influence of landscape elements in the park on thermal environment – using a metropolitan park in Taichung city as an example

Population growth and rapid urban development have led to urbanization, caused environmental problems such as: heat islands and air pollution. The installation of park green space system is widely regarded as effective in alleviating the thermal environment and improving the surrounding air quality. Therefore, this study focuses on parks in highly developed cities, The measurements of terrain and topography were conducted using unmanned aerial vehicles (UAVs) to establish a terrain model. This model was combined with environmental factors such as wind speed, direction, solar radiation, temperature, and soil infiltration were measured to assess the correlation between different landscape elements and the environment in various parks. In addition, an air particulate monitor (Arduino Uno) was developed to measure the contribution of green space systems to urban air pollution. Furthermore, by integrating measurements of multiple factors and employing the Pearson's correlation method and three-dimensional scatter plots, this study explored the relationships between many variables of park. Test results show that 1. The materials of the landscape elements should have moderate thermal conductivity; 2. The moisture content of the soil of grassland should be monitored; 3. To improve the air quality, the correlation between wind speed and wind direction should be considered in the placement of landscape elements.

A progressive review of hybrid nanofluid utilization in solar parabolic trough collector

The most reliable, cleanest, and accessible alternative energy source today is solar energy. Alternative forms of solar energy cause the least environmental damage. The period demands the use of renewable resources due to the depletion of fossil fuels and the rising cost of electricity. Additionally, unlike these renewable sources, fossil fuels emit CO2. Therefore, the usage of alternate sources assists to diminish greenhouse gases and prevent climate warming. Through the process of using solar energy, which is then transformed into electrical energy and then thermal energy with the aid of a steam turbine, the typical heat transfer fluids have a moderate thermal conductivity; in this case, solid nanomaterials are used to boost this conductivity, and nanofluids play a crucial role. The most widely used solar concentrating technique worldwide is the parabolic trough collector (PTC). In order to present various models and media used to assess the consequences of nanofluids on thermal characteristics for PTC delivering an optimal result, this study compares work conducted earlier in the field. The study also demonstrates that the thermal and optical properties can be improved by utilizing hybrid nanofluids as the heat transfer fluid (HTF) inside the absorber tube of the PTC. Numerous experimental experiments have shown that employing hybrid nanofluids improves thermal characteristics more significantly than using monofluids.

Encapsulation of stearic-palmitic acid in alkali-activated coconut shell and corn cob biochar to optimize energy storage

Biochar has gained attention as a green and low-cost energy utilization resource. However, the application of biochar as a carrier for form-stable phase change materials (FSPCMs) has been limited by leakage and low encapsulation ratio. This study investigated the potential of alkali-activated biochar as a carrier for FSPCMs. Commercial coconut shell and corn cob biochar were activated with different ratios of NaOH, and the resulting materials were impregnated with a stearic-palmitic acid binary eutectic mixture to obtain FSPCMs. The activation process enriched the pore structure of the biochar without generating negatively impacting chemical compatibility. The maximum melting latent heats of NaOH-activated coconut shell and corn cob biochar were 80.15 J/g and 127.69 J/g, respectively, and the encapsulation efficiencies were 15.96 % and 23.77 % higher than that of the original biochar, respectively. Synthetic FSPCMs also showed improved thermal stability, leak resistance, moderate thermal conductivity, and excellent temperature regulation. The study demonstrates that the activation of biochar with an appropriate ratio of NaOH can be a promising approach for converting waste into an effective carrier of PCMs for various temperature regulation systems, contributing to energy conservation and environmental protection.

Enhanced thermoelectricity in Bi-sprayed bismuth sulphide particles

Bismuth sulphide (Bi2S3), an n-type semiconductor that critically demonstrates the Seebeck effect with Seebeck coefficients of about 300 μVK−1. However, its poor electrical conductivity makes it unsuitable for thermoelectric applications. In this study, we present a facile preparation method for fabricating Bi-sprayed Bi2S3 particles that alters their thermoelectric properties. Samples were created with differing Bi concentrations into the Bi2S3 compound to test for enhanced thermoelectric properties of the resulting Bi/Bi2S3 composites. The incorporation of excess Bi into Bi2S3 significantly improves the compound's electrical conductivity and optimises overall thermoelectric performance. The electrical conductivity of the Bi/Bi2S3 composites improved from 6.5 Scm−1 (for pristine Bi2S3) to 154 Scm−1 (for highest Bi added Bi2S3). Although the Seebeck coefficient of samples decreased with Bi incorporation, a high power factor (∼390 μWm−1K−2) has been achieved for an optimised composition of the composite. Incorporation of metallic Bi has led to an increase in the thermal conductivity of the samples, but the increase is not significant for the optimised composition of the composites where a high thermoelectric performance has been observed. Therefore, enhanced power factor and moderate thermal conductivity have resulted in a peak ZT value of 0.11 at room temperature. The strategy proposed here improves the thermoelectricity in Bi2S3 and shows excellent potential for developing better-performing thermoelectric compounds with excess elemental contents.

High heat producing granites and prolonged extraction of tungsten and tin from melts

The granites associated with world–class W and Sn deposits generally have high concentrations of U, Th, and K and can be classified as high heat producing (HHP) granites (>5 μW m−3) because of high radiogenic heat production, but how long radiogenic heat can prolong the suprasolidus lifetime of magmas and whether radiogenic heat exerts an impact on W and Sn mineralization is poorly understood. To answer these questions, finite element numerical modeling was established to link magma cooling by heat conduction with diffusion of W, Sn, and H2O from silicate melts to coexisting aqueous fluids before the solidus is reached. The magma in the models is emplaced to a depth of 5 km and its size (vertical thickness of 4–5 km and horizontal length of 20 km) is constrained by the granites associated with world–class W and Sn deposits. Fluid convection was not considered in the models. The sensitivity analysis and comparison results suggest that the suprasolidus lifetimes of HHP magmas are positively correlated with the heat production and magma thickness and negatively correlated with the solidus temperatures and the thermal conductivity of host rocks. Average radiogenic heat of 5–10 μW m−3, together with decreased solidus temperatures due to magmatic differentiation and a moderate thermal conductivity of host rocks, can prolong the suprasolidus lifetime of HHP magmas by 49–427 ka (1 Ma = 1000 ka), corresponding to 11–85% of the suprasolidus lifetime of equally sized magmas with normal radiogenic heat (2 μW m−3). From the available gravity modeling data, over half of the granites associated with world–class W and Sn deposits are at least 1 km thicker than the values calculated from the empirical power–law equation, and the modeling results indicate that an increase of 500–1000 m in magma thickness prolongs the suprasolidus lifetimes of HHP magmas (5 μW m−3) by 50–74%. During magma cooling before solidus is reached, the diffusion of W and Sn is at least several orders of magnitude slower than that of H2O in hydrous melts; thus, the equilibrium partitioning of these two metals between silicate melts and coexisting aqueous fluids is not reached, and the metal diffusion from melts is a rate-limiting step. The prolongation of the suprasolidus lifetimes by radiogenic heat and decreased solidus temperatures can allow extraction of 17–95% more W and Sn from silicate melts before the solidus is reached and increase the possibility of producing W and Sn mineralization at later stages. Therefore, the coexistence of HHP granites and world–class W and Sn deposits is not accidental.

X2Pd3Se4 (X = K, Rb, Cs): Unexplored 2D semiconductors with high n-type transport performance

Two-dimensional (2D) materials have attracted much interest because of their special morphology and novel physical properties. In this work, we proposed three unexplored 2D materials, X2Pd3Se4 (X = K, Rb, Cs), and further investigated their stability, electronic and thermoelectric transport properties. We revealed that these materials are indirect semiconductors with band-gaps of 1.74 ∼ 1.95 eV, and show “multi-valleys” convergence near conduction band minimums. Besides, the monolayers also possess high electron mobility of 103 ∼ 104 cm2·V−1·s−1, leading to high conductivity (106 ∼ 107 Ω-1m−1), as well as high thermoelectric power factor (∼102 mW·K−2·m−1). Also, because of the high group velocity and low phonon scattering rate, they also show moderate lattice thermal conductivity of 19.21 ∼ 75.78 W/mK at 300 K. Nevertheless, they still deliver high thermoelectric figure of merit of 0.20 ∼ 1.04 at 300 K, and increase further to 0.67 ∼ 1.94 at 700 K, suggesting that they have potential applications in the field of low-medium temperature thermoelectric devices.

Phase diagram prediction and experimental verification of a binary hydrated salt mixture as phase change thermal storage materials

As an important inorganic phase change materials (PCMs), hydrated salts have many advantages such as high latent heat, moderate thermal conductivity, low cost and excellent fire safety compared with organic PCMs. The phase change process of hydrated salts has a significant effect on thermal storage performance. It is meaningful to predict the phase change process by the thermodynamic models. The modified BET model is an effective method to predict the phase diagram of water–salt system. In this work, an applicability of modified BET model used for Na2SO4·10H2O and KAl(SO4)2·12H2O binary hydrated salt mixture was confirmed. According to the BET parameters and solubility constants, the solubility phase diagram of this binary hydrated salt mixture was predicted with modified BET model, and Na2SO4·7H2O was found when Na2SO4·10H2O was lower than 44 wt%. Besides, the phase diagram and the existence of Na2SO4·7H2O were validated in the DSC and XRD measurements. The function of Na2SO4·7H2O to eliminate phase separation was interpreted as that it acts as a thickener to prevent water molecules from escaping from the liquid and avoids the formation of anhydrous Na2SO4. This work could guide the design of binary hydrated salt mixtures as thermal storage materials, and provide new insights for phase separation elimination of hydrated salt mixtures.