Low Thermal Conductivity Values Research Articles

Influence on energy demand of thickness, thermal conductivity, and volumetric heat capacity of ladle working lining in secondary steel-making process

The secondary steel-making process involves several steps during which steel is kept in a ladle, that is, a vessel made of an outer steel layer (carpentry), an intermediate refractory layer, and an internal refractory layer. Unlike the intermediate layer, the internal layer undergoes a progressive reduction in thickness and a periodic restoration. Traditionally, it is made of alumina or magnesite. During the process, the ladle undergoes unsteady heating and cooling; therefore, heat transfer depends on thermal conductivity and heat capacity. This study aims to identify the ladle internal layer characteristics that affect the energy demand. This analysis investigates the effect of the internal layer thickness S, volumetric heat capacity C, and thermal conductivity λ. Through the Design Of the Experiments (DOE), different scenarios have been selected and analyzed by means of numerical simulations performed on a numerical model defined in COMSOL Multiphysics. The energy demand as a function of the internal layer properties has been estimated, and it has emerged that low thermal conductivity and heat capacity values require a lower amount of energy.

Experimental Thermal Conductivity Measurement of Hollow-Structured Polypropylene Material by DTC-25 and Hot Box Test

In this study, experimental measurements of porous polypropylene (PP) using the DTC-25 TA laboratory equipment and a hot box test are compared. The thermal conductivity of building materials indicates their insulation capability. Excellent building materials will have a lower thermal conductivity value as well as other building insulator performance metrics. While results show that increasing the volume fraction of fluid in porous PP has an inverse association with the thermal conductivity of the material, as predicted by porous media theories, there is a marked difference in the measured values of thermal conductivity using the two methods. The thermal conductivity values of porous PP from the DTC-25 and the hot box test were 0.21 and 0.0033 W/mK, respectively. The difference in the thermal conductivity values was due to the misapplication of the Fourier’s guarded heat flow model in the DTC-25 device to a convective fluid porous medium.

Influence of Anatomy, Microstructure, and Composition of Natural Fibers on the Performance of Thermal Insulation Panels.

The growing interest in environmentally friendly materials is leading to a re-evaluation of natural fibers for industrial applications in order to meet sustainability and low-cost objectives, especially for thermal insulation of buildings. This paper deals with the chemical and physical characterization of fibers extracted from seagrass (Posidonia oceanica) and alfa grass (Stipa tenacissima) for a possible substitution of synthetic materials for thermal insulation. Hemp (Cannabis sativa), a fiber broadly used, was also studied for comparison. The parameters characterized include porosity, thermal degradation, elemental composition, skeletal and particle density of the fibers as well as investigation of the thermal conductivity of fiber-based panels. Several technologies were involved in investigating these parameters, including mercury intrusion, thermogravimetric analysis, fluorescence spectroscopy, and fluid pycnometry. The fibers showed a degradation temperature between 316 and 340 °C for Posidonia, between 292 and 326 °C for alfa, and between 300 and 336 °C for hemp fibers. A high porosity allied with a reduced pore size was revealed for Posidonia (77%, 0.54 μm) compared to hemp (75%, 0.61 μm) and alfa (57%, 2.1 μm) raw fibers, leading to lower thermal conductivity values for the nonwoven panels based on Posidonia (0.0356-0.0392 W/m.K) compared to alfa (0.0365-0.0397 W/m.K) and hemp (0.0387-0.0427 W/m.K). Bulk density, operating temperature, and humidity conditions have been shown to be determining factors for the thermal performance of the panels.

Computational study of lattice and thermoelectric properties of Rb2LiTlF6 double perovskite

We applied the density functional theory formalism to compute the lattice thermal conductivity, transport and thermoelectric properties of Rb2LiTlF6 double perovskite in the cubic phase. To gain some insights on lattice related dynamic behaviour of this material, we determined its phonon lifetimes and Grüneisen parameters within the considered frequency range. This quaternary compound has a very low value of lattice thermal conductivity, with the predicted value of 0.687 W/mK at 300 K. The highest value of dimensionless figure of merit was determined to be 5.73 × 10−3 at 800 K when hole concentration is 1020 cm−3, this low ZT value could be attributed to the wide band gap nature of this compound. Our results will serve as a benchmark for future experimental and theoretical research on lattice and thermoelectric properties of this material.

Magnetism and Thermal Transport of Exchange-Spring-Coupled La2/3Sr1/3MnO3/La2MnCoO6 Superlattices with Perpendicular Magnetic Anisotropy.

Superlattices (SLs) comprising layers of a soft ferromagnetic metal La2/3Sr1/3MnO3 (LSMO) with in-plane (IP) magnetic easy axis and a hard ferromagnetic insulator La2MnCoO6 (LMCO, out-of-plane anisotropy) were grown on SrTiO3 (100)(STO) substrates by a metalorganic aerosol deposition technique. Exchange spring magnetic (ESM) behavior between LSMO and LMCO, manifested by a spin reorientation transition of the LSMO layers towards perpendicular magnetic anisotropy below TSR = 260 K, was observed. Further, 3ω measurements of the [(LMCO)9/(LSMO)9]11/STO(100) superlattices revealed extremely low values of the cross-plane thermal conductivity κ(300 K) = 0.32 Wm-1K-1. Additionally, the thermal conductivity shows a peculiar dependence on the applied IP magnetic field, either decreasing or increasing in accordance with the magnetic disorder induced by ESM. Furthermore, both positive and negative magnetoresistance were observed in the SL in the respective temperature regions due to the formation of 90°-Néel domain walls within the ESM, when applying IP magnetic fields. The results are discussed in the framework of electronic contribution to thermal conductivity originating from the LSMO layers.

Drought Tolerant Plants’ Fiber and Recycled PET Co-Fibrous Composite as Acoustic Absorbers and Thermal Insulators

ABSTRACT In this paper, the series of co-fibrous composite materials combining natural fiber derived from drought-tolerant plants (pineapple, hemp, sisal, and agave) and recycled-polyethylene terephthalate (r-PET) were successfully prepared using a mixing-hot-pressing method. The area density and thickness of prepared co-fibrous materials were controlled and porosity was calculated. The co-fibrous materials with higher porosity showed better performance in sound absorption and thermal insulation. Furthermore, all prepared co-fibrous materials have a noise reduction coefficient (NRC) higher than the high-efficiency sound absorber standard at 0.56, making them comparable to commercially available products. Regarding sound absorption performance at a high frequency of 2–5 kHz, the prepared co-fibrous materials exhibited exceptional sound absorbing performance with a sound absorption coefficient (SAC, αH) ranging from 0.94 to 0.97. In terms of thermal insulation performance, both pineapple and hemp co-fibrous materials demonstrated a low thermal conductivity value of 0.029 W/mK, placing them in the range of commercial polyurethane (PU) insulating materials. In conclusion, the pineapple and hemp co-fibrous composite demonstrate potential as alternative eco-friendly commercial sound absorbers and insulators that can subsidizing petroleum-based products.

Study of the physical aspects of Pt3T (T = Mn, Ni) intermetallic compounds using first principles method

Platinum based transitional intermetallic compounds creates significant interest in the research area because of having their promising physical, optical, and electronic properties with the large scale of thermodynamic applications. The main purpose of this study is to examine the several physical properties of intermetallic compounds Pt3T (T = Mn, Ni) explored through density functional theory (DFT). The reliability of this work was made by comparing the investigated mechanical features with previously studied compounds of similar types. The calculated structural parameters have a similarity with experimental values. For the first time, we have calculated as well as presented the elastic constants, Cauchy pressure, bulk, shear, and Young's moduli. The mechanical stability of these compounds is proven by the calculation of elastic constants which meets necessary stability requirements. Metallic and ductile nature of Pt3Mn and Pt3Ni is represented by the Cauchy pressure and Pugh's ratio respectively. High machinability index of Pt3Ni ensured its low friction and huge application in industry. Band structure and DOS calculations also represented the metallic behavior of these compounds. High reflectivity in UV region refers the high conductance characteristics of Pt3T (T = Mn, Ni) in low energy regions. Very high absorption in the UV region is observed here. In the infrared region high refractive index is noticed. The dielectric constant's ε1(ω) large negative value in the real part demonstrates the Drude-like behaviors which are the metallic system's common characteristics. Very high melting temperature of Pt3T (T = Mn, Ni) ensured their probable applications in the high temperature technology. TBC nature of these phases has been ensured from their very low thermal conductivity values.

High-Throughput screening of inorganic lead-free halide perovskites CsCu2X3 (X = Cl, Br, I) for optoelectronics applications

This study effectively explores in detail the structural, optical, electronic, elastic, mechanical, lattice vibrational and thermodynamic features of orthorhombic CsCu2X3(X = Cl, Br, I) perovskites using first-principles calculations. Formation energy, Born stability criterion, and phonon dispersion validated our compounds thermodynamic, mechanical, and dynamical stability. All the studied compounds possess significant elastic anisotropy and are fairly machinable with CsCu2I3 are relatively hard than the other two. UV light can be efficiently absorbed by CsCu2X3(X = Cl, Br, I) compounds. Due to their strong UV reflectivity, all the compounds have the potential to be utilized as shielding to reduce solar heating by up to ∼ 20 eV with CsCu2Cl3 being more efficient. The compounds under study have low Debye temperatures, low melting points, and low minimum phonon thermal conductivities. Relatively low values of Debye temperature and minimum thermal conductivity for CsCu2X3 making them potential as thermal barrier coatings (TBC) materials.

Mixed Convective Flow of Tri-Hybrid Nanofluid TiO2–Al2O3–SiO2/H2O Past a Variably Thicked Stretching Sheet with Newtonian Heating

Tri-hybrid nanofluids are formed by involving three different types of nanoparticles in the base fluid. In recent years, studies have been done to properly understand the factors that affect the heat transfer properties of these tri-hybrid nanofluids under various circumstances. The purpose of this study is to execute a study on an advanced tri-hybrid nanofluid model for heat transfer. No previous analysis has been executed for the flow of tri-hybrid nanofluid TiO2–Al2O3–SiO2/H2O past a variably thickened stretching sheet with the inclusion of Newtonian heating, magnetic field, mixed convection, thermal radiation, and viscous dissipation. This investigation confronts the heat transfer characteristics of boundary layer mixed convective flow of TiO2–Al2O3–SiO2/H2O tri-hybrid nanofluid on a variably thickened stretching sheet along with the inclusion of thermal radiation, viscous dissipation, and Newtonian heating. The ruling boundary layer equations are manipulated into an arrangement of ODEs using appropriate similarity transformations which are worked out with the bvp4c program in MATLAB for solutions. The plots obtained reveal that the variation in the non-dimensional discrete parameters induced in the investigation significantly affects the flow inside the boundary layer. The variation in Cfx and Nux are presented via 3D graphs. The reason for picking the tri-hybrid nanoparticles TiO2, Al2O3, and SiO2 is the raise in thermal conductivity with the addition of Al2O3 in comparison with low thermal conductivity values of SiO2 and TiO2 combination. This study reports that the Newtonian heating at the surface of the sheet assists the flow of tri-hybrid nanofluid TiO2–Al2O3–SiO2/H2O and conducts heat at a better rate. Also, the temperature profile of the tri-hybrid nanofluid TiO2–Al2O3–SiO2/H2O is more prominent than the plots of hybrid nanofluid TiO2–Al2O3/H2O, nanofluid TiO2/H2O, and fluid H2O.

Enhanced Thermoelectric Performance of p-Type Mg3-xZnxSb2/Sb Composites: The Role of ZnSb/Sb Composites.

Mg3Sb2-based Zintl compounds have garnered recent attention as promising materials for thermoelectric applications due to their low thermal conductivity and high zT values as n-type materials. However, the zT values of p-type materials are lower compared to their n-type counterparts. Through a straightforward process involving cold pressing and evacuating-and-encapsulating sintering, we have successfully synthesized a variety of p-type Mg3-xZnxSb2/Sb composites by adding the ZnSb-4%Sb composite into the Mg3Sb2 host material. Structural analyses have provided insights into the role of the ZnSb-4%Sb composite, demonstrating its significance in Zn doping on the Mg sites and Sb acting as an additive in the composite. The introduction of Zn on the Mg tetrahedral sites enhances the concentration of carriers, while the presence of highly conductive Sb grains facilitates the movement of charge carriers between adjacent Mg3-xZnxSb2 grains, thereby promoting mobility. Consequently, the electrical resistivity of the Mg3-xZnxSb2/Sb composites decreases as the Zn content increases. At 710 K, the Mg1.91Zn1.09Sb2/Sb composite exhibits the lowest resistivity, measuring 5.1 mΩ-cm, which is 46 times lower than that of the Mg3Sb2 host. Furthermore, the zT value of the Mg3-xZnxSb2/Sb composites increases with higher Zn content (x), benefiting from a combination of an improved power factor and reduced thermal conductivity. Significantly, our straightforward fabrication process enables us to achieve a maximum zT value of 0.58 at 710 K for the Mg1.91Zn1.09Sb2/Sb composite. This achievement can primarily be attributed to the 8-fold enhancement in power factor compared to the Mg3Sb2 host.

Improved thermoelectric properties of AB stacking bilayer graphene by Sr-intercalation according to chemical potential

This study investigated the use of graphene intercalation compounds as thermoelectric (TE) materials. The electronic and TE properties of AB stacking bilayer graphene (BG) with Sr-intercalation were investigated using Density Functional Theory (DFT) ab initio calculations and the self-consistent full potential linearized augmented plane wave (FP-LAPW) approach. The theoretical TE properties were calculated using the Boltztrap2 package’s semi-classical Boltzmann transport equations (BTE) approximation asset. By breaking the BG’s symmetry, The findings demonstrated that atom intercalation could impact electronic and TE properties and contribute to the lifting degeneracy between the charge neutrality point and the Fermi level. Moreover, the calculated TE properties show that the intercalation of Sr in AB stacking BG proved the high values of the Seebeck coefficient for the n-type and p-type behavior and lower values of thermal conductivity leading to an increase of figure of merit values reaching 3.3 at room temperature. These findings imply that Sr-intercalated material in BG has TE device-relevant properties. Furthermore, at very low temperatures (100 K), the Sr-intercalated material exhibits outstanding thermoelectric characteristics, making it perfect for generating electricity from waste heat or cooling microelectronics.

Microstructure and thermal barrier coating properties of plasma sprayed SrCeO3

The trend to improve the efficiency of gas turbine engines leads to an increase in requirements for thermal barrier coating (TBC) materials. Strontium cerate (SrCeO3) is a promising perovskite-like type oxide with a low thermal conductivity and moderate thermal expansion coefficient (TEC) value. In this work, TBC was applied by atmospheric plasma spraying to a nickel superalloy ZhS 32 VI, and the change in its microstructure and phase composition after thermal cycles was investigated. It was found that during spraying, SrCeO3 crystals orientated along the most densely packed directions, which led to the structuring of the coating. In the process of thermal cycling, Sr diffuses to the top coat – bond coat boundary with the formation of strontium chromate. SrCrO4 together with NiO form a layer of thermally grown oxide (TGO). TBC failed after 44 ± 3 thermal cycles of rapid heating up to 1200 °C followed by air cooling with 5 min of holding time at each stage. The absence of direct reactions of the top coat and bond coat, the TGO formation from components of both layers as well as low TEC mismatch allows to resist onset of exfoliation for about 30 cycles. The thermal conductivity value of nickel superalloy covered by SrCeO3 is only 1.65 ± 0.05 W·m−1·K−1 in the temperature range of 25–100 °C and mainly determines by top coat properties. The new experimental data being obtained highlights the prospects of the considered TBC based on SrCeO3.

Phase stability and thermoelectricity in topological Dirac semimetal Na3Bi

A vibrant research field in condensed matter is the study of topological materials, which range from topological insulators to Dirac semimetals and Weyl semimetals. Na3Bi is predicted to be Dirac semimetal with a Dirac node near the Fermi level. Hence, to validate the presence of Dirac cone and to check the stability of Na3Bi in cubic and hexagonal phases for its practical applications an ab-initio calculation has been performed. A structural phase transition has been observed from hexagonal to cubic phase at 0.89 GPa pressure for Na3Bi. The computed elastic constants satisfy Born-Huang stability criteria for both phases indicating the mechanical stability of the present compound. But it has been found that the P63/mmc phase of Na3Bi is dynamically unstable at ambient conditions therefore, the thermoelectric properties of c-Na3Bi have been investigated by employing Boltzmann transport theory. The low lattice thermal conductivity (1.89 W/mK) and high value of the figure of merit (0.32) at 1200K suggest a good thermoelectric response of the material at high temperatures. Hence, Na3Bi is a potential material that can be used in quantum electronic and thermoelectric devices.

Thermo‐mechanical property enhancement of rigid polyurethane foam using silica and alumina as hybrid fillers over single filler

AbstractSilica and alumina particles were loaded in the rigid polyurethane foam composite as hybrid fillers. After the successful addition of silica and alumina as fillers, various properties of the foam composite were enhanced up to a particular weight percentage (7.5 wt% of silica and alumina each) with respect to alumina loaded foams. Hard urea domains are well distributed in the urethane matrix which indicates the absence of the peak representing H‐bonded urea in the Fourier‐transform infrared spectroscopy results. The addition of hybrid fillers into the rigid polyurethane foam matrix improved the compressive strength of the foam composite by 14% in comparison to alumina loaded foams due to the synergistic effect of the hybrid fillers. The foam composite at 7.5 wt% loading of hybrid fillers was successful in decreasing the thermal conductivity by 9% with respect to the thermal conductivity of the unloaded foam. There was a reduction in the gross calorific value up to 7% in the hybrid filler loaded foam composite when compared with that of the alumina loaded composite. Hence, hybrid fillers should be added to enhance the composite's properties by a greater extent.Highlights From the compressive test results, an increase in the compressive strength up to 14% was observed in the samples loaded with hybrid fillers with respect to the samples loaded with alumina due to the synergistic effects of the two fillers. For the foam composite loaded with alumina, the gross calorific value decreased up to 6% when compared to the unloaded foam. The gross calorific value decreased by a further 7% when hybrid fillers were added to the polyurethane foam composite with respect to the alumina loaded foam composite. The foam composite loaded with 7.5 weight % of hybrid fillers had lower values of thermal conductivity when compared with that of the unloaded polyurethane foam. We propose the addition of both alumina and silica as hybrid filler particles as they enhanced the various properties of the polyurethane foam composite to a greater extent than the addition of alumina particles as a single filler and have potential to replace unloaded polyurethane foams in different applications.

Thermophysical characterization of mustard husk (MSH) and MSH char synthesized by the microwave pyrolysis of MSH

Abstract Thermophysical properties are calculated to determine performance parameters comprising specific heat capacity, thermal conductivity, thermal diffusivity and they are directly related to the dynamics of the material at atomic level and for thermal treatment of mustard husk (MSH) and MSH char, they play a vital role. Temperature dependence of thermophysical properties of MSH and MSH char have been investigated within the temperature range between 30 and 110 °C. MSH char is synthesized by the microwave pyrolysis of MSH. Thermogravimetric analysis of MSH and MSH char confirmed that MSH is more thermally stable as compared to MSH char. Moreover, it gave information about the degradation behaviour of MSH and MSH char. Thermophysical properties are measured by thermal analyser, based on the transient hot wire technique which is suitable to measure the thermal conductivity at elevated temperatures. At room temperature, thermal conductivity and thermal diffusivity of MSH are 0.187 W m−1 K−1 and 0.132 mm2 s−1, respectively. Specific heat capacity of MSH and MSH char are found to be almost same (1.349 kJ kg−1 K−1 for MSH and 1.310 kJ kg−1 K−1 for MSH char). Thermal conductivity and thermal diffusivity values are decreasing on increasing the temperature while specific heat capacity is increasing linearly on increasing the temperature. Low thermal conductivity and thermal diffusivity values of MSH imply that the conventional conductive heating is less effective and inefficient for the thermal treatment of MSH.

Ba3GeTeS4: A new quaternary heteroanionic chalcogenide semiconductor

We report the synthesis and characterization of a new quaternary heteroanionic chalcogenide phase, Ba3GeTeS4. A single-crystal X-ray diffraction study of a yellow-colored crystal of Ba3GeTeS4 shows that the compound is stoichiometric and crystallizes in the orthorhombic Cmcm space group having cell parameters of a ​= ​6.8583(12) Å, b ​= ​16.207(3) Å, c ​= ​9.6239(19) Å, with four formula units (Z ​= ​4) per unit cell. The unit cell of the structure consists of two Ba, one Ge, one Te, and two S sites. All the crystallographically independent atoms occupy special positions. The Ba3GeTeS4 structure is made up of zero-dimensional [GeS4]4– anionic units along with Ba2+ cations, each of that is surrounded by the Te and S atoms. An optical UV–Vis absorption study on a polycrystalline sample of Ba3GeTeS4 establishes its semiconducting nature with a direct bandgap of 2.5(2) eV consistent with the yellow color of the sample. The polycrystalline Ba3GeTeS4 shows an extremely low value of thermal conductivity (∼0.46 W/mK) at 723 ​K. The ab-initio DFT calculations predict a high value of the thermoelectric figure of merit (zT ​> ​1) for the hole doped-Ba3GeTeS4 sample. The crystal orbital Hamilton population (COHP) analysis shows that the Ge–S bonds are strongest in the structure, while the strengths of the Ba–S and Ba–Te interactions are similar.

Thermoelectric Properties of Porous SiC/SiO2/C Composite from Carbonized Cryptomeria japonica Wood

Electric power generation by thermoelectric material utilizing radiated heat of from roof’s house, engine and others is potential clean energy in tropical areas such as Indonesia. In this study, thermoelectric materials such as silicon carbide (SiC/SiO2/C) composites were developed from carbonized Cryptomeria japonica wood infiltrated ethyl silicate-40 by sintering at 1400, 1600 and 1800 ºC for 30 min under N2 atmosphere. This study aimed to examine the morphology, microstructure and thermoelectric properties of porous SiC/SiO2/C composites. SiC/SiO2/C composites sintered at 1600 ºC with low value of thermal conductivity was potential for the development of thermoelectric material. The oxidation of SiC/SiO2/C composite sintered at 1600 °C which removed parts of residual silica and carbon, transformed the composite exhibiting p-type semiconductor with low values of Seebeck coefficient of to that exhibiting n-type semiconductor with high values Seebeck coefficient. A maximum of figure of merit of 6.25 x 10--5 K-1 was obtained at 140 ºC in the oxidized SiC/SiO2/C composite sintered at 1600 °C. The comparatively high figure of merit indicates the potentiality the material for thermoelectric purpose.

Experimental Study of Thermal Resistance Values of Natural Fiber Insulating Materials under Different Mean Temperatures

The purpose of this paper is to experimentally study the thermal resistance (RSI value) of building insulation materials made mainly from natural fiber. Natural fibrous materials or renewable resources and their reinforcement composites are currently being used in building and construction as a potential solution to significantly reduce thermal load and energy consumption. The RSI value is used in describing the thermal efficiency of insulating material and in an analysis of heat transfer through the structural components of a building (such as walls, roofs, and windows) under steady-state conditions. In this study, the thermal resistance values of several samples made from coir fiber, rice straw fiber, energy reed fiber, and coconut wood were calculated from the thermal conductivity which was measured at mean temperature of 20°C, using the heat flow apparatus. The lowest RSI value was recorded in the phenol-formaldehyde polymer composites reinforced by rice straw fiber (0.115 m2·K·W-1) and coir fiber (0.128 m2·K·W-1) due to the relative thinness of the tested samples (8 and 12 mm). However, these samples can be used as an additional layer in multi-layered assemblies because of their low thermal conductivity value. The highest RSI value was reported on the binderless coir fiber panel (0.909 m2·K·W-1) at the thickness of 50 mm. Another investigation examined the relationship between RSI value and mean temperature to observe the influence of variations of ambient temperature on the heat resistivity of building insulation materials. Practical data showed the decreased linear proportion between thermal resistance and specific mean temperatures increased from 0 to 40°C. It is apparent that an increase in the interior and exterior temperature of a building significantly influences the thermal resistance of its insulation materials. Based on the experimental study, once the thermal conductivity coefficient of each sample was determined, the calculated RSI value was a valuable parameter to evaluate the thermal resistant effectiveness of a multi-layered installation, which allows us to investigate practically the effect of the thickness of additional layers from different insulating materials used in building envelopes.

Synergistic effect of fibres on the physical, mechanical, and microstructural properties of aerogel-based thermal insulating renders

There is an increasing demand for highly efficient thermal insulating materials in buildings. This study presents a novel solution incorporating nanomaterials, such as silica aerogel, which can achieve low thermal conductivity values (below 0.030 W m−1 K−1) in renders. A key challenge of using aerogels is their low mechanical strength and high capillary water absorption. Here we describe a novel approach employing fibres which mitigates against some key properties which are decreased as a consequence of using aerogel. The incorporation of aramid (0.50%), sisal (0.10%), and biomass (0.10%) fibres (by total volume) was evaluated experimentally in terms of physical, mechanical, and microstructural properties. A synergistic effect between the fibres and aerogel increased mechanical resistance and a reduction in the capillary water absorption, when compared to the reference render (without fibres), whilst maintaining the low thermal conductivity. However, these properties depended significantly on whether the fibres were synthetic or organic. This study is important as it demonstrates that aerogel-based fibre-enhanced thermal renders can contribute to higher energy efficiency in both new construction and retrofitting. The use of these materials will have a direct positive impact on addressing the climate crisis.

Hygrothermal and microstructural characterization of self-consolidating earth concrete (SCEC)

The incorporation of earth-based materials offers the construction industry superior hygrothermal performance, hence ensuring significant ecological and environmental benefits. The hygrothermal and microstructural characteristics of self-consolidating earth concrete (SCEC) are investigated in this study. These traits include the sorption isotherm, permeability, heat capacity, thermal parameters (conductivity, diffusivity, and effusivity), moisture buffer value (MBV), total porosity, pores distribution, and microstructural characteristics. The sorption isotherm tests revealed that the investigated SCEC mixtures gained lower water content (around half) compared with the reference self-consolidating concrete (SCC) mixture (1.5% vs. 3.3% at 90% relative humidity). These results are comparable to those reported for clay bricks in the literature. The SCEC mixtures also showed higher permeability due to their higher porosity and connected pores. Thermal conductivity, diffusivity, and effusivity of the investigated SCEC mixtures showed lower values than those of the reference mixture. At 10 °C, the investigated SCEC mixtures exhibited lower thermal conductivity values of 0.400–0.500 W m−1 K−1 compared with those of the reference mixture (0.765 W m−1 K−1). Since the diffusivity and effusivity of the earthen materials are higher than those of wood, SCEC mixtures can offer both low diffusivity and high effusivity among different construction materials. Furthermore, the investigated SCEC mixtures exhibited lower mass losses attributed to calcium silicate hydrate (CSH), dehydroxylation of portlandite, and decarbonation than the reference mixture. The water vapor and gas permeability of SCEC were in good agreement with cumulative pore volume in the ranges of 100–200 nm and 100–300 nm, respectively. On the other hand, the drying shrinkage and compressive strength values were dependent on the cumulative pore volume of pore sizes less than 1 μm.