Thermal Conductivity Values Research Articles

Exploring superconductivity, supercapacitance and thermoelectric properties of NbCr[formula omitted] and its alloys with Li and Mg: A first-principles Investigation

In the present study, the superconductivity, supercapacitance, and thermoelectric properties of the NbCr2 and its alloys with Li and Mg (with alloy composition of x=0.5 in replacement with Cr atoms) have been surveyed using density functional theory. The mechanical, thermodynamic, and dynamic stability of the pure and alloy compositions have been checked by the results of the cohesive energy, enthalpy of formation energy, and phonon density of states. Moreover, the largest value of the critical temperature (Tc) which has been achieved belongs to the pure NbCr2 with a value of 13.76 K. In addition, the largest values of Tc for Li and Mg alloys are 11.83 and 3.42 K, respectively. Furthermore, the largest peak of the quantum capacitance at room temperature and as a function of the applied voltage is also related to the pure NbCr2 with a value of 676.77 μF/cm2 at the voltage of −1.86 V. In addition, the largest value of the surface charge storage occurred at the negative bias of −1.88 V with a value of −1261.27 μC/cm2. For thermoelectric properties, the largest peak of the thermoelectric power factor per relaxation time as a function of chemical potential and at room temperature belongs to Li alloy with a value 20.03 × 1016μW/(m K2 s) at the negative chemical potentials of −0.73 eV. The largest value of electronic thermal conductivity per relaxation time belongs the Li alloy at 500 K with a value of 48.71 × 1014 W/(m K s) and the largest value of lattice thermal conductivity is also related to Li alloy with the value of 22.8 W/(m K) at 100 K. All of these results represent the materials which not only have the superconductivity property but also supercapacitance and thermoelectric properties that could be useful as electrode materials in the energy storage industries.

Physical, mechanical, and thermal properties of heat-treated poplar and beech wood

Air-dried density, weight loss (WL), impact bending strength (IBS), Shore-D hardness, and thermal conductivity values were determined for heat-treated poplar (Populus nigra L.) and beech (Fagus orientalis Lipsky) wood and compared with those for untreated samples. The test samples were heat-treated at 140, 160, 180, and 200 °C for 2 h. The results showed that density decreased and WL increased with increasing temperature for all temperatures. Additionally, during the heat treatment, the IBS increased in beech wood samples at 140 °C, but at higher temperatures, these values gradually decreased in both wood species. The highest decline in IBS values, found at a temperature of 200 °C, was 66.5% for beech and 55.7% for poplar. The Shore-D hardness of both wood species increased after heat treatment and regarding beech wood, the hardness increasing rate at temperature at 140 °C, 160 °C, 180 °C and 200 °C, 8.94%, 14.19%, 8.27% and 11.7%, respectively according to control samples. Regarding poplar wood, hardness increasing rates were 6.20% at 140 °C, 4.41% at 160°C, 5.88% at 180°C and 5.31% at 200°C according to control samples. The thermal conductivity of poplar and beech wood samples decreased after heat treatment, except for samples heat treated at 160 °C.

Liquefaction optimization of grape pulp using response surface methodology for biopolyol production and bio-based polyurethane foam synthesis.

Both environmental and economic disadvantages of using petroleum-based products have been forcing researchers to work on environmentally friendly, sustainable, and economical alternatives. The purpose of this study is to optimize the solvothermal liquefaction process of grape pomace using response surface methodology coupled with a central composite design. After investigating the physicochemical properties of the liquified products (biopolyol) in detail, a bio-based rigid polyurethane foam (RPUF) was synthesized and characterized. The hydroxyl and acid numbers and viscosity values of all the biopolyols were analyzed. According to variance analysis results (%95 confidence range), both the reaction temperature and catalyst loading were determined as significant parameters on the liquefaction yield (LY). The model was validated experimentally in the following reaction conditions: 4.25% catalyst loading, 50 min reaction time, and 165 °C reaction temperature, which yields an LY of 81.3%. The biopolyols produced by the validation experiment display similar characteristics (hydroxyl number: 470.5 mg KOH/g; acid number: 2.31 mg KOH/g; viscosity: 1785 cP at 25 °C) to those of commercial polyols widely preferred in the production of polyurethane foam. The physicochemical properties of bio-based foam obtained from the biopolyol were determined and the thermal conductivity, closed-cell content, apparent density, and compressive strength values of bio-based RPUF were 31.3 mW/m·K, 71.1%, 33.4 kg/m3, and 105.3 kPa, respectively.

Influence of the Addition of Palm (Borassus Aethiopum Mart.) Fibers on the Durability of Compressed Earth Blocks

This study aims to determine the influence of the content and length of the palm (borassus aethiopum mart.) fibers on the physical, mechanical and thermal properties of Compressed Earth Blocks (CEB). Three fiber contents (0.2%, 0.4% and 0.8%) of different lengths (10 mm, 20 mm, or 40 mm) were used to make CEB. CEB with 0% fiber content were manufactured to serve as control samples. CEB specimens stabilized with palm fibers or not were subjected to various tests according to standard XP P 13-901 for the determination of the following properties: dry density, water absorption, dry compressive strength, abrasion resistance and thermal conductivity. The results show that the dry density of CEB decreases from 4% to 7% when the content and length of the fibers increase respectively from 0.2% and 10 mm in length to 0.8% and 40 mm in length. The water absorption of fiber-containing CEBs ranges from 14% to 22% with increasing fiber content and length. The results also indicate that the mechanical and thermal properties are improved for well-chosen fiber contents. Thus, the dry compressive strength of the fibers increases by more than 13% for a fiber content of 0.2% and a length of 10 mm compared to CEB with 0% fibers. On the other hand, the optimal abrasion resistance values are obtained for a fiber content of 0.4% and a length of 40 mm. For all CEBs, the thermal conductivity values vary from 0.51 W/mK to 0.38 W/mK when the fiber content varies from 0.2% to 0.8%. Overall, palm fiber content has a greater influence on the measured physical, mechanical and thermal characteristics than fiber length.

Enhancing the thermoelectric performance of Sr0.6La0.4Nb2O6-δ-based ceramics through composite effects

Donor-doped SrNb2O6-based materials are regarded as highly promising candidates for high-temperature thermoelectric applications. The Sr0.6La0.4Nb2O6-δ/x wt% Ti (x = 1, 5, 10, 15) composite ceramics thermoelectric materials were prepared and the mechanism for enhancing their thermoelectric properties was investigated. The experimental results demonstrate that during sintering, nano-additive titanium powder undergoes oxidation to form TiO2. The inclusion of a secondary phase ultimately leads to successful reduction in electrical resistivity within the composite oxides. Due to crystal defects, complex structure and phonon scattering at grain boundaries, the samples consistently exhibit low thermal conductivity values below 3.0 W m−1K−1. Among them, the sample doped with 10 wt% Ti shows the highest PF value (470.0 μW/mK2 at 1073 K), demonstrating a significant increase in power factor of 280 % compared to Sr0.6La0.4Nb2O6 without the Ti composite. Consequently, the Sr0.6La0.4Nb2O6-δ/10 wt% Ti composite material achieved a maximum ZT value of 0.20, representing a fifty-three percent enhancement compared to the undoped sample.

Acoustic and thermal performance of wood strands-rock wool-cement composite boards as eco-friendly construction materials

With a growing emphasis on eco-friendly building materials, wood strands-rock wool-cement boards (WRCB) offer a promising solution due to their composition of renewable wood fibers and cementitious binder. This study delves into the intricate balance between sound absorption, thermal insulation, and cost-effectiveness of WRCB, all of which are crucial factors shaping indoor comfort, energy efficiency, and the economic viability of constructions. WRCB incorporating wood strands, Portland cement, rock wool, and calcium chloride were manufactured at various thicknesses (20–60 mm) and densities (400, 500, and 600 kg/m³). The WRCB exhibited sound absorption average (SAA) and effective thermal conductivity (Keff) values ranging from 0.28 to 0.56 and 0.285–0.381 W/(mK), respectively. These results underscore the remarkable SAA and Keff of the panels, showcasing their potential as sustainable construction materials. Notably, WRCB with thicknesses ranging from 30 mm to 50 mm and densities of 400–500 kg/m³ exhibited nearly ideal absorption levels between 1000 and 2000 Hz, indicating their practical suitability for speech-related scenarios in architectural environments. The utilization of the Response Surface Methodology allowed the optimal conditions for maximizing SAA while simultaneously minimizing Keff and cost to be identified through the optimization process. A density of 452.8 kg/m³ and a thickness of 37.8 mm were determined as the optimal parameters. Under these conditions, the resultant SAA reached 0.554, with a corresponding cost of 1724 IRR and Keff of 0.317 W/(mK). The results also demonstrated the significant impact of thickness and density on the acoustic and thermal performance of the WRCB. The acoustic performance of WRCB was further analyzed through predictive modeling using the Johnson-Champoux-Allard (JCA) and Delany-Bazley (DB) models. The results revealed that the JCA model exhibited superior predictive accuracy compared to the DB model.

Anomalous lattice thermal conductivity increase with temperature in cubic GeTe correlated with strengthening of second-nearest neighbor bonds

Understanding thermal transport mechanisms in phase change materials is critical to elucidating the microscopic picture of phase transitions and advancing thermal energy conversion and storage. Experiments consistently show that cubic phase germanium telluride (GeTe) has an unexpected increase in lattice thermal conductivity with rising temperature. Despite its ubiquity, resolving its origin has remained elusive. In this work, we carry out temperature-dependent lattice thermal conductivity calculations for cubic GeTe through efficient, high-order machine-learned models and additional corrections for coherence effects. We corroborate the calculated phonon properties with our inelastic X-ray scattering measurements. Our calculated lattice thermal conductivity values agree well with experiments and show a similar increasing trend. Through additional bonding strength calculations, we propose that a major contributor to the increasing lattice thermal conductivity is the strengthening of second-nearest neighbor interactions. The findings herein serve to deepen our understanding of thermal transport in phase-change materials.

AsTe3: A novel crystalline semiconductor with ultralow thermal conductivity obtained by congruent crystallization from parent glass

The synthesis of novel narrow-band-gap semiconductors with ultralow thermal conductivity opens a pathway to the design of functional materials with high thermoelectric performance or with interesting optical sensitivity in the infrared range. Here, we report on the discovery of the novel crystalline binary AsTe3 (c-AsTe3) prepared by spark plasma sintering (SPS) from full and congruent crystallization of amorphous AsTe3 (a-AsTe3) previously prepared by twin roller quenching. X-ray diffraction suggests that the structure of c-AsTe3 can be described as a superstructure of elementary Te with a specific distribution of As and Te atoms. More specifically, it appears as an intergrowth of a Te subunit (3 atoms) and As2Te5 subunit (6 As + 15 Te atoms) separated with interlayer spaces. The optical transmittance measured on both crystalline and amorphous AsTe3 indicates a maximum transmittance of 22 % over the infrared range 10–25 µm. Transport properties measurements, performed between 5 and 375 K, reveal that AsTe3 behaves as a lightly doped, p-type semiconductor. The complex crystal structure combined with a small-grain-size microstructure of the sample yields extremely low lattice thermal conductivity values of 0.35 W m−1 K−1 near 300 K. This poor ability to conduct heat is the main property that gives rise to an estimated dimensionless thermoelectric figure of merit ZT of ∼0.3 at 375 K. These findings show that the recrystallization of amorphous phases by SPS provides an effective approach for stabilizing novel phases with interesting functional properties.

The diamond-silicon carbide composite Skeleton® as a promising material for substrates of intense X-ray beam optics.

The paper considers the possibility of using the diamond-silicon carbide composite Skeleton® with a technological coating of polycrystalline silicon as a substrate for X-ray mirrors used with powerful synchrotron radiation sources (third+ and fourth generation). Samples were studied after polishing to provide the following surface parameters: root-mean-square flatness ≃ 50 nm, micro-roughness on the frame 2 µm × 2 µm σ ≃ 0.15 nm. The heat capacity, thermal conductivity and coefficient of linear thermal expansion were investigated. For comparison, a monocrystalline silicon sample was studied under the same conditions using the same methods. The value of the coefficient of linear thermal expansion turned out to be higher than that of monocrystalline silicon and amounted to 4.3 × 10-6 K-1, and the values of thermal conductivity (5.0 W cm-1 K-1) and heat capacity (1.2 J K-1 g-1) also exceeded the values for Si. Thermally induced deformations of both Skeleton® and monocrystalline silicon samples under irradiation with a CO2 laser beam have also been experimentally studied. Taking into account the obtained thermophysical constants, the calculation of thermally induced deformation under irradiation with hard (20 keV) X-rays showed almost three times less deformation of the Skeleton® sample than of the monocrystalline silicon sample.

Numerical analysis of transient MHD natural convection in a channel with four heat-generating cylindrical solids filled with in a non-Newtonian Fe3O4 ferrofluid

This article presents a numerical investigation and analysis of the cooling effectiveness of thermomagnetic transient natural convection in a long channel, equipped with four cylindrical heat-generating blocks. A non-Newtonian power-law ferrofluid was employed for the present investigation to achieve optimum cooling. The governing equations are the continuity equation, the momentum equation and the energy equation. The finite volume method was used to solve the resulting algebraic system. From an energy-saving point of view, this configuration can provide a good approximation for selecting effective physical and geometrical parameters to design a reliable thermal system. For this purpose, the study was carried out for various geometric and thermophysical parameters. Different values of thermal conductivity, power law index, Rayleigh number, Hartmann number and ferrofluid volume fraction, were considered. The results are illustrated in the form of streamlines, isotherms, average Nusselt and a spatio-temporal characterization of the mean ferrofluid velocity. From the results presented, we can conclude that the choice of non-Newtonian, pseudoplastic ferrofluid with a low thermal conductivity ratio subjected to a uniform magnetic field proves to be a crucial solution for efficient and stable cooling of heat-generating cylindrical blocks, which will have to be close to the cold walls of the channel.

Outstanding Room‐Temperature Thermoelectric Performance of n‐type Mg3Bi2‐Based Compounds Through Synergistically Combined Band Engineering Approaches

AbstractThermoelectric cooling materials based on Bi2Te3 have a long history of unsurpassed performance near room temperature. Recently, research into price‐competitive Mg3(Bi, Sb)2‐based materials are focused on replacing traditional cooling materials. Here, the thermoelectric properties of Mg3.2Bi1.998−xSbxTe0.002Cu0.005 (x = 0.0, 0.1, 0.2, 0.3, 0.4, and 0.5) polycrystalline compounds are investigated. In all temperature regions, electrical resistivity and Seebeck coefficient are increased with Sb concentration. The electronic transport properties of Sb‐alloyed compounds are maximized by synergistically combined band engineering approaches such as band structure change caused by lattice strain, increased electronic density of states, and chemical potential shift, leading to exceptionally high‐power factor values of over 3.0 mW m−1 K−2 at room temperature. Furthermore, with increasing Sb content, thermal conductivity values are systematically reduced due to the promotion of alloy scattering of phonons and suppression of the bipolar contribution. Consequently, these multiple approaches significantly enhance thermoelectric performance, resulting in an enhancement of thermoelectric figure‐of‐merit zT above 1.1 at 348–423 K. Additionally, a zTavg of 1.1 is recorded at 300–450 K, making it an unrivaled value among the reported n‐type Mg3Bi2‐based thermoelectric materials. Overall, this work demonstrates that Mg3Bi2‐based materials are more promising for thermoelectric cooling applications compared to Bi2Te3‐based materials.

Influence of Carbonyl Iron Particles (CIP) and Glass Microspheres on Thermal Properties of Poly(lactic acid) (PLA).

In this investigation, composite poly(lactic acid) (PLA) systems of hollow glass microspheres (MS) and carbonyl iron particles (CIP) were processed and characterized to investigate the effects of using conductive and insulating particles as additives in a polymer system. PLA-MS and PLA-CIP were set at the two levels of 3.94 and 7.77 vol.% for each particle type to study the effects of the particle material type and loading on neat PLA's thermal properties. It was observed during the twin-screw extrusion that the addition of CIP greatly decreased the viscosity of the PLA melt during processing. Correlations determined using thermogravimetric analysis, differential scanning calorimetry, thermal conductivity, and shear rheology provided insights into how thermal stability was affected. The incorporation of MS and CIP altered thermal properties such as the glass transition temperature (Tg), melting temperature (Tm), and cold crystallization temperature (Tcc). The metal CIP-filled systems had large increases in their thermal conductivity values and viscoelastic transitions compared to those with PLA that were correlated with the observed overheating during extrusion.

Nanostructured inclusions enhancing the thermoelectric performance of Higher Manganese Silicide by modulating the transport properties

Higher Manganese Silicides (HMS) are the best p-type materials beneficial for intermediate-temperature range thermoelectric device applications due to their high thermal stability and inexpensive constituent elements. Although the cost-effective HMS materials possess high thermal stability, they are concerned with high thermal conductivity values. The nanocomposite approach was promised to lower the thermal transport properties without affecting the electrical transport properties, which is experimented in the present work. The higher manganese silicide with varying weight percentages of nano-structured Si0.8Ge0.2B0.02 inclusions was experimented to decrease the thermal conductivity and to enhance the electrical properties. The lowest thermal conductivity value of ≃ 2.24 W/mK was reported with 2 wt% Si0.8Ge0.2B0.02 addition in HMS material. Also, the HMS-2 wt. % Si0.8Ge0.2B0.02 improved the transport properties, electrical conductivity and Seebeck coefficient values of ≃ 4 × 104 S/m and ≃ 220 μV/K respectively. Furthermore, various mathematical models were proposed here to simulate the composite approach results, which were then correlated with experimental results.

A thermal conductivity model for alpine meadow soils on the Tibetan Plateau and validation analysis

Under the background of global warming, natural disasters such as landslides and mudslides are becoming more frequent on the Tibetan Plateau. It is important to study the thermal behavior of alpine meadow soils, which are widely distributed on the Tibetan Plateau due to the high altitude and extreme climate. In this paper, a quantitative mathematical model of thermal conductivity for alpine meadow soils is presented, which successfully describes the influence of plant roots and organic matter on the thermal behavior of alpine meadow soils. A series of thermal conductivity experiments are carried out on thirty alpine meadow soils collected from Nangqian district, located east of Tibetan Plateau, China. The results of the proposed model are compared with the experimental measured data to validate the model efficiency and satisfactory agreement is achieved. Furthermore, Root mean square error (RMSE) and bias are also used to evaluate the performance of the proposed model and other available models. The results of the validation analysis show that the proposed model, with an RMSE of 0.041 W m−1 K−1 and a bias of 0.005 W m−1 K−1, provides reliable and accurate estimated values of thermal conductivity for alpine meadow soils. This study is beneficial for understanding the thermal behaviors of soil-root system on the Tibetan Plateau.

Pengaruh Perbandingan Nilai Termal Terhadap Deformasi Fondasi Tiang Energi Menggunakan Metode Numerik

A thermal energy foundation is an innovative combination of a foundation structure with thermal pipes that can absorb geothermal heat. This allows it to serve as an alternative source of electricity for the building above it. The goal of this technology is to help achieve sustainable infrastructure targets by minimizing the use of fossil fuels from a geotechnical perspective. This study aims to analyze the thermal effect on foundation deformation using the Finite Element Method approach. The modelling is done using PLAXIS software with element meshes to provide comprehensive deformation results. Additionally, the model is used to vary the thermal parameters of the soil and the quality of the foundation concrete. The analysis results indicate that variations in thermal conductivity values lead to a 34.112% decrease in deformation due to reduced thermal conductivity, while variations in the quality of concrete used in the foundation show a relatively small or insignificant effect on the deformation.

Influence of additive nano calcium carbonate (CaCO3) on SAE 10W-30 engine oil: A study on thermophysical, rheological and performance

Researchers have used nanomaterials as additives in base oil to improve its specifications, especially to minimize wear and friction during its applications. In this study, calcium carbonate (CaCO3) nanoparticles were selected as an additive to serve as a protective layer between components and anti-wear properties. In this study, calcium carbonate (CaCO3) nanoparticles were selected as an additive to serve as a protective layer between components and anti-wear properties. Nano lubricant samples were prepared using mass variations of CaCO3 and SAE 10W-30 base oil with concentrations of 0.05, 0.1, 0.15, and 0.2%, then homogenized. The nanolubricant samples obtained were analyzed for thermophysical, rheological properties and lubricant performance with the addition of nano CaCO3 in improving the wear resistance of FC25 cast iron. The results of thermophysical and rheological properties analysis suggest that the nanolubricant has better tribological properties compared to base lubricants. The highest values of thermal conductivity, density, and viscosity (40 oC) are 0.139 W/m.K, 812.203 kg/m3, and 106 mPa.s (40 oC). Meanwhile, the highest CoF, disc mass loss, and surface roughness of nanolubricant are 0.0706, 0.0037 grams, and 0.50 µm, respectively. These results indicate that the greatest wear-reducing agent is from the nanolubricant with the addition of CaCO3 nanopowder additives at 0.1 wt% concentration. These results are expected to give significant insights into the advancement of nano technology-based lubricants in the future.

Enhanced intrinsic thermal conductivity of liquid crystalline polyester dispersed films through hydrogen bond interaction

Polymer-dispersed liquid crystal (MHxFy) films comprising liquid crystal polymer (LCPH and LCPF) were successfully obtained by the method of solution casting & thermal compressing. At a LCPH mass fraction of 67 %, thermal conductivity (λ) value in through-plane (λ⊥) and in-plane (λ∥) direction of MH2F1 films reach up to 0.305 W/(m·K) and 2.879 W/(m·K), respectively. In comparison to pure LCPF, the thermal conductivity of MH2F1 exhibited an increase of 4.42 times, which is 14.4 times than that of conventional thermoplastics. Meanwhile, the crystallinity of MHxFy films around 50 % which is indicate the crystal phase become more integrated and regular. The FTIR spectra reveals a significant blue shift (3432 cm−1 to 3421 cm−1) in the absorption peak of the –OH group in MH2F1, suggesting a robust interaction between LCPF and LCPH. The primary cause of elevated thermal conduction in these films was determined to be the consistent presence of “thermal bridges” and a high degree of crystallinity. Furthermore, the T5%, Tmax and residual carbon at 800 °C of MH2F1 were 347.8 °C, 409.4 °C and 8 %, respectively. This is attributed to the ordered distribution of LCPH in LCPF matrix through hydrogen bonding interaction, forming an interpenetrating network of LCPF-LCPH. The result show that MHxFy films demonstrating superior intrinsic thermal conductivities, thermal stabilities, and mechanical properties.

Investigation on the influence of waste-based fillers on the mechanical and thermal characteristics of rigid polyurethane foams

An investigation was conducted to analyze the impact of incorporating coal powder particles at different weight ratios (5, 10, 15, 25, and 35) on the mechanical properties and thermal conductivity coefficient of the polyurethane polymer. The thermal conductivity coefficient of the samples was calculated using Holmarc's Lee's Disc apparatus device. The mechanical properties like compressive, tensile, and bending strengths were measured using a universal machine. The results indicated that increasing the coal powder ratio leads to an improvement in the thermal insulation ability due to a decrease in the value of thermal conductivity. Also, the addition of these percentages led to a rise in the values of the mechanical qualities represented by the compressive strength, especially at the ratio of 25 wt. %, with a value equal to 2.79 MPa (MPa). The flexural resistance and tensile strength increase at a ratio of 35 wt. %, with values equal to 20.4 MPa and 2.86 MPa respectively. The results indicate that the addition of coal powder enhances the ability of thermal conductivity at the ratios (5 %, 10) wt. %, with values equal to 0.119 W/m ºC and 0.114 W/m ºC, respectively, by increasing the thermal conductivities of the samples. The aim of this study is, investigate the effect of filler used coal powder waste on the mechanical and thermal properties of PU. The filler materials show the advantages of recycling waste. Filler influences the morphology and strengthens the brittleness. Additionally, the technology of polyurethane materials conforms to the use of coal powder. The overall amount of energy used to produce PU composites is decreased when waste of filler is used to partially replace petrochemical components

Effect of Recycled Concrete Aggregate Utilization Ratio on Thermal Properties of Self-Cleaning Lightweight Concrete Facades

In today’s environment, where energy is desired to be used more efficiently, it has been understood that the interest in the use of lightweight concrete with superior performance in terms of thermal insulation properties has increased. On the other hand, it has been stated that construction waste increases rapidly, especially after severe earthquakes. In this context, encouraging the use of recycled concrete waste and efficient disposal of construction and demolition waste is of great importance for the European Green Deal. It is also known that pollutants such as COx and NOx stick to facades over time, causing environmental pollution and visual deterioration. It has been reported that materials with photocatalytic properties are used in lightweight concrete facade elements to prevent such problems. This study examines the effect of using recycled concrete aggregates on the thermal properties of self-cleaning lightweight concrete mixtures (SCLWC). For this purpose, an SCLWC containing 1% TiO2 and 100% pumice aggregate was prepared. By replacing pumice aggregate with recycled concrete aggregate at the rates of 15%, 25%, 35%, 45% and 50%, four different SCLWCs with self-cleaning properties were produced. High-temperature resistance, thermal conductivity performance, microstructure analysis and photocatalytic properties of the produced mixtures were examined. It has been understood that the unit volume weight loss of SCLWC mixtures exposed to high temperatures generally decreases due to the increase in the recycled concrete-aggregate substitution rate. However, it was determined that the loss of compressive strength increased with the increase in the amount of recycled concrete-aggregate replacement. Additionally, it was determined that the thermal-conductivity coefficient values of the mixtures decreased with the use of pumice. After SCLWC mixtures were exposed to 900 °C, small round-shaped crystals formed instead of C–S–H crystals.

Microwave solvothermal synthesis and HTHP sintering of CoSb3/rGO composites: In-situ synthesis and enhanced thermoelectric properties

The utilization of CoSb3-based thermoelectric materials is currently confined to aviation applications, primarily attributed to their elevated thermal conductivity (κ) values. The incorporation of a nanostructuring approach, coupled with the introduction of a secondary phase, has demonstrated efficacy in diminishing the thermal conductivity (κ) values of CoSb3 materials. Here, the CoSb3/reduced graphene oxide (CoSb3/rGO) composites are obtained by sintering the as-synthesized powders, which ultra-fast synthesized in situ via microwave solvothermal method, under the High-temperature and High-Pressure (HTHP) conditions. The influence of reduced graphene oxide (rGO) on the structural and thermoelectric characteristics of CoSb3 composites has been systematically explored. In this study, CoSb3 nanoparticles with an average size of ∼33 nm exhibit uniform distribution, being effectively anchored onto the 2D sheets of rGO. In this work, the lattice thermal conductivity of CoSb3/rGO composites decreased with the addition of rGO. Based on the Debye-Callaway model, we attribute this to the effective scattering of phonons by the interface formed between the CoSb3 nanocrystals and the lamellar rGO. As a result, the CoSb3/rGO composite, containing 2 wt% graphene, exhibits a significantly enhanced maximum thermoelectric figure of merit (ZT) value, reaching ∼0.325 at 700 K. This represents an impressive improvement of approximately 300 % compared to the ZT value of the graphene-free CoSb3 bulk counterpart, which is ∼0.106. This study demonstrates the microwave solvothermal synthesis and HTHP sintering are in favor for an efficient, economical, and controllable synthesis of CoSb3/rGO composites, which provides a novel strategy for securing better thermoelectric performance.