Search Results (478)

Hexagonal boron nitride nanosheets (BNNSs) have emerged as one of the most promising materials for next-generation thermal management, driven by the intensifying heat dissipation demands of highly integrated electronics. While conventional polymer-based packaging materials are lightweight and electrically insulating, their intrinsically low thermal conductivity severely limits effectiveness in high-power devices. The remarkable thermal transport, wide bandgap, chemical robustness, and mechanical strength of BNNSs offer a compelling solution. This review provides a comprehensive overview of the structural and physical foundations that underpin the anisotropic yet exceptional thermal properties of bulk h-BN and BNNSs. We examine major synthesis routes including tape exfoliation, ball milling, liquid-phase exfoliation, chemical vapor deposition, and metal–organic chemical vapor deposition, highlighting how process mechanisms govern nanosheet thickness, defect density, crystallinity, and scalability. Particular emphasis is placed on the advantages of BNNSs in thermal management systems, from their use as high-efficiency thermally conductive fillers and advanced thermal interface materials. We conclude by examining key challenges including large-area growth, filler alignment, and interfacial engineering, and by presenting future research directions that could enable the practical deployment of BNNSs-based thermal management technologies. Full article

This paper presents an experimental investigation of the shear connection between outer layers of lightweight precast concrete sandwich panels (PCSP) made of high-performance concrete (HPC). The shear-transfer mechanism is based on reinforcing ribs composed of rigid polymer-based thermal insulation combined with carbon-fibre-reinforced polymer (CFRP) shear reinforcement. A total of seven full-scale sandwich panels were tested in four-point bending. This study compares three types of rigid thermal insulation used in the shear ribs—Purenit, Compacfoam CF400, and Foamglass F—and investigates the influence of the amount of CFRP shear reinforcement on the structural behavior of the panels. Additional specimens were used to evaluate the effect of reinforcing ribs and of polymer-based thermal insulation placed between the ribs. The experimental results show that panels with shear ribs made of Purenit and Compacfoam CF400 achieved significantly higher load-bearing capacities compared to Foamglass F, which proved unsuitable due to its brittle behavior. Increasing the amount of CFRP shear reinforcement increased the load-bearing capacity but had a limited effect on panel stiffness. The experimentally determined composite interaction coefficient ranged around α ≈ 0.03, indicating partial shear interaction between the outer concrete layers. A simplified strut-and-tie model was applied to predict the load-bearing capacity and showed conservative agreement with experimental results. The findings demonstrate that polymer-based materials, particularly CFRP reinforcement combined with rigid polymer insulation, enable efficient shear transfer without thermal bridging, making them suitable for lightweight and thermally efficient precast concrete sandwich panels. Full article

An alkali-activated slag binder based on biochar was developed in this research. The biochar was produced from waste wood and is referred to as biochar waste (BW). In the alkali-activated slag system, a small amount of biochar (up to 0.5%) was used as an additive, and a larger amount (from 1% to 25%) was used as a filler. The influence of the biochar powder on compressive strength was determined. The hydrated samples were investigated using X-ray diffraction (XRD) analysis and scanning electron microscopy (SEM), and the thermal, acoustical properties, and hydration temperature were also determined. The compressive strength of the alkali-activated slag composite, especially after 7 days, was found to increase slightly due to the introduction of a small amount (0.05–0.5%) of BW powder. The powder in the alkali-activated slag matrix was distributed homogenously, resulting in a reduction in the crack propagation. A larger amount of BW led to a non-homogeneous distribution, and this resulted in a gradual reduction in compressive strength with increasing BW. The highest values of compressive strength at 28 days of hydration (44.4 MPa) were recorded for samples with 0.25% of BW. According to mathematical analysis methods, the compressive strength is mainly influenced by the specific surface area of the initial mix ingredients and the amount of BW additive. In the alkali-activated slag matrix, BW acted as an inert micro-filler, with the dilution effect possibly being the reason for the decrease in the hydration temperature. SEM analysis demonstrated that the BW had a good adhesion with the alkali-activated slag matrix. The thermal and acoustic insulation performance of samples with BW improved. These investigations suggest that BW can be successfully incorporated in alkali-activated material, resulting in low thermal conductivity and adequate acoustic insulation performance. Full article

With the continuous increase in energy density of lithium-ion batteries, thermal safety has become a critical constraint on their further development. To address the limitations of mechanical brittleness and high-temperature infrared transparency in SiO₂ aerogels for thermal safety applications in lithium-ion batteries, this study developed a novel nanofiber aerogel composite by incorporating chitosan and MXene into a SiO₂ aerogel matrix. This material retains the characteristics of being ultra-lightweight and highly elastic while significantly enhancing mechanical strength and high-temperature insulation performance. It exhibits a thermal conductivity of 0.034 W/m K at room temperature and 0.053 W/m K at 400 °C, alongside a compressive strength of 1.172 MPa. In battery thermal runaway propagation tests, the aerogel successfully prevented propagation in serially connected and electrically isolated systems, and delayed thermal runaway propagation by 35 s in a parallel system, demonstrating excellent thermal runaway suppression capability. This work provides an effective material solution for the practical application of high-performance thermal insulation aerogels in battery safety protection and offers inspiration for developing new insulating ceramic aerogels. Full article

Foamed concrete is a lightweight, environmentally friendly civil engineering material with excellent absorption capacity. It has been widely applied in engineering fields such as building thermal insulation and pore filling of underground buried pipelines. But the mechanical properties of existing foamed concrete cannot meet the engineering requirements for support, pressure relief and filling of weak surrounding rock. The mechanical properties of foamed concrete were improved with CNTs to prepare CNT foamed concrete (CNTFC) pressure-relieving filling materials. The effects of five factors (the fly ash (FA) incorporation rate, aggregate–cement ratio, water–binder ratio, CNT incorporation rate and foam volume fraction) on the density and 2:1 cylinder strength (the ratio of uniaxial compressive strength to apparent density), splitting tensile (the ratio of splitting tensile strength to apparent density) and specific strength of the CNTFC were analyzed. By combining stress–strain and scanning electron microscopy analyses, the mechanism of improvement of the mechanical strength of CNTFC due to CNTs was clarified. The results show that the foam volume fraction, water–binder ratio and aggregate–cement ratio are the top three factors affecting its strength, followed by the CNT incorporation rate and FA incorporation rate. Among the five influencing factors, only the incorporation of CNTs increases the 2:1 cylinder strength, splitting tensile strength and specific strength. When the doping rate is 0.05%, this ratio specifically refers to the mass of CNTs accounting for 0.05% of the mass of the total cementitious materials of cement and fly ash. At this doping dosage, compared with the condition without CNTs (0% doping dosage), the uniaxial compressive strength increased from 6.23 MPa to 7.18 MPa (with an increase rate of 15.3%). The splitting tensile strength increased from 0.958 MPa to 1.02 MPa (with an increase rate of 6.5%). The density only slightly increased from 0.98 g/cm³ to 1.0 g/cm³ (with an increase rate of 2.0%), achieving the balance of “high strength-low density”. CNTs and cement hydrates are interwoven into a network structure, and the mechanical properties of the CNTFC are effectively improved by the excellent nanoscopic tensile properties. Excessive doping of CNTs takes 0.05% as the threshold. Exceeding this doping dosage (such as 0.10% and 0.15%) leads to a decrease in its strength and ductility due to CNT agglomeration and deterioration of pore structure. And 0.05% is the ratio of the mass of CNTs to the total cementitious materials of cement and fly ash. At this doping dosage, CNTs are uniformly dispersed and can balance the strength and density of CNTFC. The optimum proportion of CNTs is 0.05%. Full article

Phenolic aerogels offer low thermal conductivity, excellent thermal stability, and high char yield, but they suffer from intrinsic brittleness, low compressive modulus, and limited compressive strain. To overcome these limitations, phenolic aerogels modified with graphene oxide were synthesized and their structural, mechanical, and thermal insulation properties were evaluated. The GO fillers were uniformly dispersed in the phenolic matrix without disrupting its porous structure. Mechanical testing revealed that the modified aerogel achieved a compressive modulus of 265.52 MPa, representing a 67% increase over the pure phenolic aerogel’s value of 158.49 MPa, and a compressive strength of 40.19 MPa, compared to 6.18 MPa, for the pure sample. At the same time, the composite maintained good thermal insulation performance, with a thermal conductivity of 0.063 W·m⁻¹·K⁻¹. This work demonstrates a feasible approach to tailoring the structure–property relationship of phenolic aerogels via GO modification, supporting their potential use in high-temperature insulation and lightweight structural applications. Full article

Aerogels are recognized as exceptional thermal insulation materials, but poor mechanical strength and flammability problems hinder their application in high-temperature environments. Thermal management materials that combine high mechanical strength with superior flame retardancy are, therefore, critically important for thermal insulation. Herein, ultra-lightweight aerogels were facilely fabricated using chitosan (CS) and acidified attapulgite (SATP) as the primary components. The optimal composite, CS-SATP30%, exhibited a compressive strength of 633.15 kPa at 80% strain, demonstrating significant improvement in mechanical properties. Structural analysis revealed that the hydroxyl groups and amino groups of CS molecules formed hydrogen bonds with SATP, ensuring excellent interfacial affinity among the constituents. Compared to pure CS aerogel, the total heat release (THR) and peak heat release rate (PHRR) of CS-SATP30% were substantially reduced to 3.83 MJ/m² and 37.00 kW/m², respectively. Furthermore, the limiting oxygen index (LOI) of CS-SATP30% increased to 34% and passed the vertical burning test (UL-94). This study provides a feasible way to construct advanced chitosan-based thermal insulation aerogels. Full article

This work contributes to reinforcing cork-based mortar, with the potential of developing a new eco-friendly lightweight mortar for specific structural applications. Thirteen lightweight mortars were produced by adding cork aggregates (CAs) at fractions of 0.30%, 0.60%, and 0.90% of mortar weight. For each level of CA content, three volume fractions of polyethylene fibers (PFs) were added: 0.25%, 0.50%, and 0.75%. The results indicate that lightening mortar with CA considerably reduces its workability, density, mechanical strengths, and thermal conductivity, as well as increasing its porosity. However, adding PFs to the matrix significantly improves the mortar’s flexural strength by up to 26% and reduces its cracking and brittleness. The 28-day compressive strengths of all mortars remain higher than 15 MPa and can be used in the production of structural elements, according to the RILEM recommendations. The thermal conductivity and dry density decreased, respectively, from 1.73 W/m·K and 2050 kg/m³ for the control mixture to 0.73 W/m·K and 1583 kg/m³ for mortar with 0.90% CA and 0.75% PF. The combination of up to 0.90% CA with 0.75% PF demonstrates satisfactory mechanical and thermal properties and is strongly recommended for use in construction across numerous types of mortar, such as screed mortar for repair and flooring. Full article

Biosourced materials made of a combination of raw earth and fibers are attracting increasing interest for low-carbon construction due to their reduced environmental impact and good thermal and hygric performance. This study investigates several soil–fiber composites selected and formulated at different densities to assess their thermal conductivity, enabling the selection of two complementary materials: a structural earthen mix and a lightweight insulating mix. Experimental measurements were taken under controlled conditions and used to characterize heat and moisture fluxes, and numerical calculations were carried out to evaluate the performance of single and double-layer wall configurations. The results showed that an increase in thermal gradients accelerates vapor migration and alters the internal distribution of moisture. The evaluation of wall configurations demonstrated that placing the earthen insulating layer externally optimizes thermal fluxes and eliminates condensation risks at the interface between materials, while internal insulation can be sensitive to hygrothermal gradients and prone to moisture accumulation. The combined experimental–numerical approach provides new insights into high-performance designs of bio-based earthen envelopes, establishing guidelines for minimizing moisture-related risks in low-carbon building systems. Full article

This paper presents an analysis of energy savings and sustainability measures to improve the environmental performance of glass wool fiberizing, the latter being the most energy intensive production step in manufacturing glass wool thermal insulation, involving conversion of hot molten glass into fibers. The first part evaluates two refractory designs—business as usual (BAU) and modified (MOD), over four trials. BAU refractory has higher density whereas MOD is an innovative lightweight design, with lower density and improved thermal conductivity. The key operational parameters analyzed include energy demand and CO₂ emissions in the fiberizing stage, along with burner pressure, temperature and fiber diameter. The results show that MOD has better thermal performance, leading to an average energy demand reduction potential of up to 10%. The second part focuses on promoting a circular economy for the end-of-life refractory, underpinned by the potential for recovery and reuse of spent refractory materials. Based on a total refractory mass of 1.2 tons for the six burners, the end-of-life refractory material recovery is estimated as 0.78 ton (65% of the aggregate). Balancing the recovery costs with the acquired value of the recovered aggregates, results demonstrate significant material and environmental cost avoidance on a 3-year refractory relining cycle. Full article

This study investigates the deterioration of the thermal and mechanical properties of geopolymer foam concrete (GFC) subjected to accelerated weathering through carbonation, salt fog, and UV radiation. GFC blocks were synthesized using metakaolin as the aluminosilicate precursor, activated with an alkaline solution consisting of 8 M NaOH and sodium silicate (Na₂SiO₃) at a NaOH/Na₂SiO₃ ratio of 0.51 wt.%. A 30% (v/v) H₂O₂ solution served as the foaming agent, and olive oil was used as the surfactant. Accelerated carbonation tests were conducted at 25 ± 3 °C and 40 ± 3 °C, under 60 ± 5% relative humidity and 5% CO₂, with carbonation depth, carbonation percentage, density, porosity, and thermal conductivity evaluated over a 7-day period. In parallel, specimens were exposed to salt fog and UV radiation for 12 weeks in accordance with ASTM B117-19 and ASTM G154-23, respectively. Compressive strength was monitored every week throughout the exposure period. Results show that carbonation temperature governs the type and kinetics of carbonate formation. The carbonation process, at 40 °C for 7 days, increased the density and reduced the porosity of GFC, resulting in a ~48% increase in thermal conductivity. Salt fog exposure led to severe mechanical degradation, with NaCl penetration reducing compressive strength by 69%. In contrast, UV radiation caused only minor deterioration, decreasing compressive strength by up to 7%, likely due to surface-level carbonation. Full article

The utilization and transformation of heat have played pivotal roles in numerous significant stages of human societal evolution and advancement. Recently, more rigorous and precise requirements have been imposed on thermal functional materials for applications including microelectronic device cooling, personal thermal regulation in extreme environments, green building initiatives, flexible wearable electronics, and solar thermal collection. Thermal functional fibers offer advantages such as lightweight construction, versatile functional design, and integrated manufacturing capabilities. By modifying the composition, structure, and fabrication techniques of fibers, control over heat transfer, storage, and conversion processes can be optimized. This review underscores the latest developments in thermal functional fibers, emphasizing high thermal conductivity fibers, thermal insulation fibers, thermal radiation regulation fibers, phase-change thermal storage fibers, thermoelectric fibers, Joule heating fibers, photothermal conversion fibers, thermally actuated fibers, and multifunctional composite fibers. It elucidates how these various fibers enhance thermal performance through innovative material selection, fabrication methods, and structural design. Finally, the review discusses prevailing developmental trends, current challenges, and future directions in the design and fabrication of thermal functional fibers. Full article

Overhead transmission lines have long relied on cross-linked polyethylene (XLPE) insulation. The production of XLPE insulation requires silane cross-linking, which generates by-products, consumes high energy, and results in poor recyclability-retired XLPE insulation can only be disposed of through incineration or landfilling. Additionally, its high density leads to increased cable weight and sag, reducing the service life of the cables. Therefore, there is an urgent need to develop recyclable and lightweight insulation materials. In this study, recyclable polypropylene (PP) was used as a substitute for XLPE. Hollow glass microspheres (HGM) were incorporated to reduce weight, and hydrogenated styrene-ethylene-butylene-styrene block copolymer (SEBS) was added for toughening, thereby constructing a PP/HGM/SEBS ternary composite system. The results show that the introduction of HGM into the PP matrix effectively reduces the material density, decreasing from 0.890 g/cm³ (pure PP) to 0.757 g/cm³—a reduction of 15%. With the addition of SEBS, the mechanical properties of the composite are significantly improved: the tensile strength increases from 14.94 MPa (PP/HGM) to 32.40 MPa, and the elongation at break jumps sharply from 72.02% to 671.22%, achieving the synergistic optimization of “weight reduction” and “strengthening-toughening”. Electrical performance tests indicate that the PP/HGM/SEBS composite exhibits a volume resistivity of 1.66 × 10¹² Ω·m, a characteristic breakdown strength of 108.6 kV/mm, a low dielectric loss tangent of 2.76 × 10⁻⁴, and a dielectric constant of 2.24. It achieves density reduction while maintaining low dielectric loss and high insulation strength, verifying its feasibility for application in lightweight insulation scenarios of overhead transmission lines. Full article

In this study, a battery case was developed using a 3D (three dimensional)-printed composite of hexagonal boron nitride (hBN) and polylactic acid (PLA) to enhance the thermal performance of lithium-ion battery (LiB) modules. A 10 wt.% amount of hBN was incorporated into the PLA matrix to improve the composite’s thermal conductivity while maintaining electrical insulation. A 3S2P (3 series and 2 parallel) battery configuration was initially evaluated based on the results of a baseline study for comparison and subsequently subjected to a newly developed test procedure to assess the thermal behavior of the designed case under identical environmental conditions. Initially, X-ray diffraction (XRD) and scanning electron microscopy (SEM) analyses were utilized for material characterization, and their results verified the successful integration of hBN by confirming its presence in the hBN-PLA composite. In thermal tests, experimental results revealed that the fabricated hBN-PLA composite battery case significantly enhanced heat conduction and reduced surface temperature gradients compared to the previous baseline study with no case. Specifically, the maximum cell temperature (T_max) decreased from 48.54 °C to 45.84 °C, and the temperature difference (ΔT) between the hottest and coldest cells was reduced from 4.65 °C to 3.75 °C, corresponding to an improvement of approximately 20%. A 3S2P LiB module was also tested under identical environmental conditions using a multi-cycle charge–discharge procedure designed to replicate real electric vehicle (EV) operation. Each cycle consisted of sequential low and high discharge zones with gradually increased current values from 2 A to 14 A followed by controlled charging and rest intervals. During the experimental procedure, the average ΔT between the cells was recorded as 2.38 °C, with a maximum value of 3.50 °C. These results collectively demonstrate that the 3D-printed hBN-PLA composite provides an effective and lightweight passive cooling solution for improving the thermal stability and safety of LiB modules in EV applications. Full article

In cold regions, flexible pavements are vulnerable to frost-induced damage, necessitating effective insulation strategies. Foam glass aggregate (FGA) insulation layers, made from recycled glass, offer promising thermal insulation properties but are mechanically fragile and susceptible to permanent deformation under repeated loading. Manufacturers provide technical recommendations, particularly regarding load limits for installation and the dimensions of the thermal protection layer. These are considered insufficient to assist pavement designers in their work. The definition of critical criteria for permissible loads was deemed necessary to design mechanically durable structures using this alternative technology. This study investigates the critical stress conditions that FGA layers can tolerate within flexible pavement systems to ensure long-term structural integrity. Laboratory cyclic triaxial tests and full-scale accelerated pavement testing using a heavy vehicle simulator were conducted to evaluate the resilient modulus and permanent deformation behavior of FGA. The results show that FGA exhibits stress-dependent elastoplastic behavior, with resilient modulus values ranging from 70 to 200 MPa. Most samples exhibited plastic creep or incremental collapse behavior, underscoring the importance of careful stress management. A strain-hardening model was calibrated using both laboratory and full-scale data, incorporating a reliability level of 95%. This study identifies critical deviatoric stress thresholds (15–25 kPa) to maintain stable deformation behavior (Range A) under realistic confining pressures. FGA performs well as a lightweight, insulating, and draining layer, but design criteria remain to be defined for the design of multi-layer road structures adapted to local materials and traffic conditions. Establishing allowable critical stress levels would help designers mechanically validate the geometry, particularly the adequacy of the overlying layers. These findings support the development of mechanistic design criteria for FGA insulation layers, ensuring their durability and optimal performance in cold climate pavements. Full article