Search Results (2,049)

This article presents the results of a numerical study of the construction and technical characteristics of multilayer concrete wall blocks. The study focuses on the development of wall building elements that integrate structural strength, thermal insulation, and protective–decorative functions by creating a stable multilayer concrete structure consisting of concretes with different compositions, variatropic architecture, and discretely graded density. The development of durable multilayer concrete technologies is hindered by several major challenges, including the absence of a scientifically validated methodology for designing multilayer concrete structures, which complicates the determination of the optimal geometric parameters of the elements, as well as the difficulty of forming individual layers with the required thickness. The objective of the study was to analyze the thermal and strength properties of numerical models of a multilayer wall block consisting of two to five concrete layers of variable densities. ELCUT-7 (thermal properties) and SolidWorks Simulation 2022 SP4.0 (strength properties) software packages were used to create and study the numerical models. The initial data for creating the numerical models were the results of experimental studies of concrete of various compositions and structures with a density of 500–2200 kg/m³. Several variants of block models with two to five layers were studied. The variants differed in the thickness and composition of the concrete layers, as well as the position of the layers in the block structure. A comparative analysis of the calculated values of thermal transfer resistance for blocks with a different number of layers and variable concrete density was performed. The appropriateness of concrete blocks containing three or more layers was proven. Increasing the number of layers in blocks creates a variatropic structure for multilayer concrete, eliminating sharp variations in the density of adjacent layers while maintaining the thermal efficiency of the wall enclosure. Increasing the number of layers in concrete blocks expands the possibilities for combining layer compositions and thicknesses. In multilayer concrete blocks, it is possible to reduce the thickness of the highly porous layer by thickening the less porous adjacent layers without compromising thermal performance. Blocks with four and five layers of concrete of variable densities are comparable in strength and structural efficiency to blocks with fewer layers. For the same thermal resistance, the thickness of the five-layer block is 38–48% less than that of a conventional single-layer concrete element. Furthermore, the structural efficiency coefficient of the four- and five-layer blocks is 1.08–1.12 times higher than that of a three-layer block with equivalent load-bearing capacity. The results of these numerical studies serve as the basis for designing manufacturing processes for wall blocks with variatropic structures. Full article

Yttria-stabilized zirconia (YSZ) thermal barrier coatings suffer from t′ phase destabilization and insufficient thermal insulation above 1200 ℃. In this work, YbO_1.5-stabilized ZrO₂ powders (xYbSZ, x = 4–12 mol% YbO_1.5 on a cation basis, equivalent to 2–6 mol% Yb₂O₃) were synthesized by chemical co-precipitation, consolidated by spark plasma sintering, and evaluated at 1300 ℃ in terms of phase stability, sintering behavior, thermal conductivity, and fracture toughness. A common compositional boundary near 8 mol% YbO_1.5 was identified across all four responses. 8YbSZ retained the metastable t′ phase with a monoclinic content below 10 mol% after 300 h at 1300 ℃, whereas grain coarsening accelerated markedly and the thermal conductivity reduction efficiency per unit doping at 1000 ℃ was approximately halved beyond this composition, with κ decreasing from 2.41 to 1.96 W·m⁻¹·K⁻¹ across the series. The toughness gain produced by thermal treatment fell from 34% (4YbSZ) to about 10% (10–12YbSZ) as the dominant toughening mechanism shifted from transformation and microcrack toughening (4–6 mol%) to ferroelastic domain switching (8 mol%), with both being lost in the compositions in which the cubic phase predominated. These results identify 8 mol% YbO_1.5 as the optimal composition balancing phase stability, sintering resistance, thermal insulation, and mechanical integrity for TBC applications at 1300 ℃. Full article

Unmanned aerial vehicles (UAVs) are experiencing rapid growth across diverse sectors, creating an increasing demand for lightweight, high-performance and environmentally sustainable materials. Conventional drone materials offer excellent mechanical properties but pose environmental concerns due to their high carbon footprint, energy-intensive production and limited biodegradability. Kenaf fibre, a renewable natural fibre, presents a promising alternative owing to its low density, high specific strength, cost-effectiveness and eco-friendly characteristics. This review and research proposal explores the current and potential applications of kenaf-based materials in drone manufacturing, including kenaf fibre-reinforced biocomposites, pressed paper, composite pellets and 3D printing filaments for structural, functional and electrical housing components. Kenaf-based materials have demonstrated mechanical strengths approaching 300 MPa, dielectric constants of approximately 2.5 and electrical breakdown strengths exceeding 150 kV/mm, highlighting their potential for lightweight UAV structures and electronic insulation applications. The proposed research focuses on optimising kenaf fibre treatment, fibre–matrix compatibility, hybrid reinforcement strategies and additive manufacturing parameters to develop lightweight, durable and multifunctional kenaf-based UAV components. The framework aims to establish a systematic pathway for the development and validation of kenaf-based materials for next-generation sustainable UAVs. Full article

The growing demand for CO₂ emission reduction and efficient waste management has created a need for the development of sustainable construction materials. This study presents a comparative investigation of geopolymer and cement-based composites modified with bio-based additives originating from two abundant and underutilized waste streams: apple-processing waste and biomass collected during lake restoration activities. Geopolymer and cement composites containing 5 and 10 wt.% apple-processing waste or 5 and 10 vol.% lake fibers were prepared, and their compressive strength, flexural strength, density, and thermal conductivity were experimentally evaluated. The results revealed substantial differences between the investigated binder systems. Apple-processing waste significantly deteriorated the mechanical performance of both materials, particularly in cement-based composites, where disturbances in cement hydration and loss of structural integrity were observed. Although geopolymer composites also exhibited reduced compressive strength after the incorporation of apple residues, their structural cohesion was maintained. In contrast, biomass fibers obtained from lake restoration demonstrated considerably better compatibility with the geopolymer matrix, limiting compressive strength reductions to approximately 13–16% while contributing to improved crack resistance and post-failure integrity. The incorporation of bio-based additives reduced composite density and decreased thermal conductivity, resulting in enhanced thermal insulation performance. The lowest thermal conductivity was obtained for the geopolymer containing 10 wt.% wet apple waste, reaching 0.4216 W/(m·K), compared with 0.7067 W/(m·K) for the reference geopolymer. The findings indicate that lake-restoration biomass represents a promising reinforcement for geopolymer-based construction materials, whereas fruit-processing residues require further pretreatment before practical application. Overall, the study highlights the superior compatibility of geopolymers with organic waste streams and demonstrates their potential as sustainable, non-structural construction materials supporting circular economy strategies, waste valorization, and environmental remediation efforts. Full article

Mullite porous ceramics show exceptional promise for high-temperature insulation applications. However, the mechanical strength and thermal insulation performance of porous ceramics typically cannot be optimized simultaneously. Herein, we proposed a novel method to overcome this limitation by synthesizing hierarchically porous mullite ceramics assembled from ultrathin two-dimensional nanosheets. A chemical blowing method first synthesized ultrathin mullite nanosheets approximately 2–3 nm thick, which were subsequently assembled into a rigid hierarchical network by gel casting and freeze-drying. The influence of solid content and sintering temperature on the phase composition, microstructure, mechanical properties, and high-temperature thermal stability of porous ceramics was systematically investigated. The results indicate that the 20 wt.% sample sintered at 1200 °C exhibited the best performance. This optimal sample achieved a porosity of 90.75%, a compressive strength of 0.38 MPa, and excellent thermal insulation properties, including a low apparent thermal conductivity of 0.0756 W/(m·K) at room temperature and a back surface temperature of 253.2 °C after exposure to a 1200 °C flame. Crucially, this porous ceramic maintained structural stability up to 1500 °C. This nanosheet assembly strategy successfully reinforced the structural skeleton while inhibiting heat transfer. This strategy has great promise for the fabrication of lightweight porous ceramics designed for extreme environments. Full article

High-performance thermoplastics are gaining increasing attention for space applications. However, the extreme lunar environment requires multifunctional materials that combine electrical conductivity for electrostatic charge dissipation with low thermal conductivity for thermal insulation. One promising strategy to achieve this balance is through conductive polymer nanocomposites with controlled morphology. In this study, the localization, migration, and network formation of carbon nanotubes (CNTs) in two-phase blends of polyetheretherketone/polyetherimide (PEEK/PEI) were systematically investigated to establish the relationships between processing, morphology, and the resulting electrical and thermal properties. Despite the strong thermodynamic preference of CNTs for the PEI phase, both PEEK/CNT and PEEK/PEI/CNT nanocomposites exhibit similar electrical percolation thresholds (0.25–0.5 wt.%), attributed to spatial confinement arising from PEEK crystallinity in PEEK/CNT and from phase-selective localization in the blend system, which limits the effective volume available for CNT dispersion. Morphological characterization confirmed co-continuous blend structures and complete CNT migration into the PEI phase in the PEEK/PEI/CNT system, while rheological studies revealed percolated networks forming below the electrical percolation threshold. Processing conditions strongly impacted conductivity: short mixing times preserved interconnected CNT agglomerates and enhanced conductivity, whereas prolonged mixing promoted dispersion but destroyed conductive pathways. Furthermore, thermal annealing induced agglomeration and weakened networks in PEEK/CNT systems but had a negligible effect on PEEK/PEI/CNT composites due to improved CNT–PEI compatibility. Finally, thermal conductivity remained low across all systems, maintaining the material’s insulating performance for the harsh thermal environment of the Moon. Full article

The rapid development of implantable medical electronics requires robust biocompatible coatings capable of ensuring long-term stability in aggressive physiological environments. Although Grade 1 titanium is widely used for its excellent mechanical properties and corrosion resistance, active implants require defect-free insulating coatings to prevent electrical leakage and metal ion release. This study presents a systematic evaluation of Parylene C (P-C) thin films deposited by the Gorham chemical vapor deposition (CVD) process onto implant-grade titanium substrates. Four coating thicknesses (1, 5, 10, and 20 µm) were deposited and characterized using complementary chemical, morphological, optical, and mechanical techniques. Contact-angle measurements confirmed uniform hydrophobicity (90.56 ± 1.86°), while FTIR and EDX verified the characteristic chemical composition of P-C. Reflectometry, ellipsometry, and interferometry demonstrated excellent thickness control and deposition reproducibility. Pull-off testing showed high initial mechanical integrity, with detachment forces ranging from 52 to 73 N. However, accelerated PBS ageing (21 days at 90 °C) induced significant degradation, particularly for thicker coatings, reducing pull-off forces to 19–42 N. Likewise, thermal-shock cycling (−80 °C to +220 °C) caused severe interfacial damage, decreasing the required detachment force to approximately 5.5 N for 20 µm coatings because of extensive cracking and delamination. These results demonstrate that Parylene C provides excellent conformal coverage and chemical stability on titanium but that its durability is significantly affected by prolonged hydrothermal ageing and extreme thermal loading. This study provides practical guidelines for the design of reliable encapsulation systems for active implantable medical devices and highlights the need for improved interfacial engineering through optimized adhesion-promoting layers or hybrid protective architectures. Full article

Sustainable building materials development is essential for improving energy efficiency, addressing environmental concerns and optimizing resources use. This study investigates the development and characterization of sorghum stalk fiber-reinforced cement mortar bio-composite for thermal insulation application. Sorghum stalk fiber was added to cement mortar at varying fiber contents (0%, 15%, 30% and 45%), fiber lengths (0.5 cm and 1.5 cm) and varying water–cement ratios (0.4 and 0.6). The composites were characterized for thermal conductivity, thermal diffusivity, density, and compressive and flexural strengths, as well as water absorption and drying kinetics. The result showed that the addition of fiber led to significantly improved thermal insulation performance, accompanied by decreased mechanical strength. The thermal conductivity decreased from 1.57 W/m·K for the control mortar to 0.18 W/m·K (about 88.5% reduction) for 0.5 cm fiber and 0.16 W/m·K (about 89.8% reduction) for 1.5 cm at 45% of fiber. The composite with 15% fiber provided the best balance between thermal and mechanical performance suitable for low load-bearing application, particularly thermal conductivity of 0.90 W/m·K (43% lower) and compressive strength of 10.56 MPa that exceeds the minimum standard to be used in low load-bearing applications; the 30% and 45% fiber composites are suitable for non-structural and thermal insulation applications only. The results obtained demonstrate that the sorghum stalk fiber-reinforced cement mortar is a lightweight, ecological and insulative bio-composite with strong applicability in energy-efficient buildings. Full article

Thermal regulation of surface soil is critical for vegetation establishment in degraded mining environments, yet the systematic design of insulation layers tailored to mine restoration remains underdeveloped. Fifteen candidate thermal insulation materials from six categories were evaluated under simulated solar radiation, and a two-stage optimization framework was established. The first stage employed response surface methodology (RSM) for preliminary screening; the second used Gaussian process regression with Bayesian optimization (GPR-BO) for mixture refinement. RSM identified hollow glass microspheres as the strongest positive contributor and wood chips as the most detrimental component. The GPR-BO framework yielded an optimal formulation achieving T₉₀ = 12.80 °C, heating rate v = 0.0311 °C/min, and heat resistance efficiency η = 65.85%, with R² exceeding 0.95 for all response variables. The observed thermal regulation arose from the synergy of three mechanisms: surface radiative heat suppression, internal conductive path interruption, and transient thermal buffering. These findings offer a practical design route for high-performance insulation layers in cold-region mine ecological restoration. Full article

The valorization of waste cooking oil (WCO) offers a sustainable pathway for improving building’s energy efficiency while supporting circular economy principles. This study developed a novel shape-stabilized bio-based phase change material (Bb-PCM) derived from WCO fatty acids for passive thermal regulation of building envelopes. Purified fatty acids were obtained through filtration, saponification, acidification, and solvent purification. The resulting Bb-PCM was then incorporated into a natural clay–cellulose supporting matrix containing four activated-carbon loading levels using a direct impregnation method. The composites were characterized using spectroscopic, thermal, and microstructural techniques. Differential scanning calorimetry under nitrogen at 2 °C min⁻¹ showed melting temperatures of 34–35 °C and melting latent heats of 35.2–45.9 J g⁻¹. Thermogravimetric analysis confirmed thermal stability below 100 °C, while microstructural characterization demonstrated differences in matrix densification and structural ordering among the composite formulations investigated. The composite containing 25 wt.% activated carbon exhibited the highest melting latent heat (45.9 J g⁻¹) and favorable thermal conductivity (0.29 W m⁻¹ K⁻¹), representing the optimum composite formulation that balances thermal storage capacity, heat transfer, and structural stability. Outdoor evaluation demonstrated stable thermal performance, reducing indoor temperatures by approximately 2 °C, indicating strong potential for sustainable passive cooling applications in buildings. Full article

This review evaluates how clay mineralogy, waste composition, and processing conditions govern the thermal, physical, and mechanical performance of fired clay ceramics containing organic and inorganic residues. Following PRISMA 2020, 125 original studies published between 2000 and 2025 were selected from Scopus and Web of Science. Keyword co-occurrence analysis and relative-change matrices were used to examine research trends and variations in apparent porosity, water absorption, bulk density, compressive strength, and thermal conductivity. Organic residues generally promoted pore formation, reduced density, and lowered thermal conductivity, but these changes were often accompanied by proportionally greater losses in compressive strength. Inorganic residues showed more heterogeneous responses because they may act as pore-forming, fluxing, filler, or phase-forming components, depending on their chemical composition, interaction with the clay matrix, and firing conditions. The results confirm that total porosity or residue content alone cannot predict thermal performance, since pore geometry, connectivity, phase development, and solid-matrix continuity also govern heat transfer and mechanical behavior. Relative-change matrices summarized net property trajectories within each experimental configuration, and intermediate incorporation levels were considered when they altered the apparent thermal–mechanical balance. Technically suitable formulations must balance thermal insulation, mechanical integrity, moisture stability, processing reproducibility, durability, and environmental safety. Full article

The growing demand for low-carbon building materials and the challenges of handling agroforestry waste and discarded EPS particles have spurred research toward developing novel building composites that utilize solid waste. Therefore, this study aims to develop a lightweight geopolymer composite incorporating these recycled materials to balance thermal insulation, mechanical strength, and waterproofing properties. In this work, geopolymer served as the binder, with various types of raw biomass (sawdust, rice husk, rice straw, and coconut fiber) as the primary aggregates and EPS particles as an additive to create a closed-pore structure. The microstructure of the raw biomass was characterized by SEM, while its specific surface area and average pore diameter were determined by BET analysis. Furthermore, the prepared composites were comprehensively evaluated in terms of their microstructure, pore structure (MIP), density, thermal conductivity, compressive strength, total water absorption, capillary water absorption, surface wettability, and UV aging behavior. The results showed that the prepared composites exhibited a porosity of 59.9–65.7%, a density of 492.9–586.3 kg/m³, a compressive strength of 7.3–10.9 MPa, a thermal conductivity of 0.115–0.142 W/(m·K), a total water absorption of 35.2–42.2%, capillary water uptake coefficients of 4.9–11 kg/m², and a water contact angle exceeding 140° (after modification). In addition, the developed composites offered significant environmental and economic benefits, with a low carbon footprint and an estimated cost of 100.6–150.3 USD/m³, making them more competitive compared to traditional insulation materials. Meanwhile, this study provides a scientific basis for developing high-strength building insulation materials from agroforestry waste, thus outlining a promising direction for future research and industry development. Full article

Polyisocyanurate (PIR) insulation boards are widely used in buildings because of their low thermal conductivity, however their long-term performance is affected by aging. This study investigates the effect of accelerated thermal aging at +70 °C on the thermal conductivity and gas composition of pentane-blown PIR boards. Thermal conductivity was monitored over time, while changes in blowing-agent composition were analyzed using gas chromatography/mass spectrometry (GC/MS). Thermal conductivity increased from 0.0201–0.0211 W/(m·K) to 0.0243–0.0247 W/(m·K), corresponding to an increase of approximately 18–22%, with the most pronounced changes occurring during the first 40–50 days before stabilizing. GC/MS identified isopentane, cyclopentane, and pentane as the main gases in the foam cells, with isopentane as the dominant component. Accelerated aging caused a progressive decrease in blowing-agent concentration, explaining the deterioration in thermal insulation performance. Thermal outgassing proved more reliable than solvent extraction, providing higher sensitivity and reproducibility. Sample location, sample size, and outgassing temperature significantly affected the measured gas quantities, while higher outgassing temperatures improved analytical sensitivity without changing gas composition trends. The results confirm that the aging-induced increase in thermal conductivity is primarily caused by the loss of low-conductivity blowing agents, improving understanding of the long-term performance of PIR insulation materials. Full article

Bridge-arm reactors subjected to long-term AC–DC composite currents with multiple harmonics may develop non-uniform winding temperature rise and thermal-expansion mismatch, leading to localized thermal stress concentrations and potential insulation cracking. Unlike previous studies focused mainly on purely AC conditions, this study investigates a ±800 kV dry-type air-core bridge-arm reactor and develops a thermo-mechanical model incorporating AC–DC composite currents and harmonic losses. To mitigate thermal stress concentration, an axially segmented configuration is proposed to relieve the restraint associated with cumulative axial thermal expansion. The results show that a 65% axial segmentation ratio provides the best stress-regulation performance among the investigated cases. Under AC–DC composite conditions containing second- and fifth-order harmonics, the maximum Von Mises stress and maximum first-principal stress decrease by 33.42% and 38.11%, respectively, while the stress distribution becomes more uniform. The analysis is based on a two-dimensional axisymmetric model with one-way thermo-mechanical coupling and excludes long-term cyclic thermal aging and interfacial slip between winding and insulation layers. These findings provide theoretical support for the stress-oriented structural design and reliability assessment of high-capacity bridge-arm reactors. Full article

This study evaluates high-silica fiber/silica aerogel composites (HSFACs) for the passive fire protection of bridge cables. The primary objective is to reveal the high-temperature degradation mechanism of HSFAC and quantitatively determine a reliable thickness scheme for long-term hydrocarbon-fire protection of bridge cables. HSFAC specimens were heat-treated and characterized by thermal conductivity, tensile testing, SEM/TEM, FTIR, and TG analysis. A self-built furnace was used to assess an HSFAC-based cable protection system under hydrocarbon-fire exposure. Increasing heat-treatment temperature enlarged the pore and particle sizes of HSFAC and reduced its thermal-insulation performance. During 120 min of fire exposure, the cable protected by a single 5 mm HSFAC layer reached 300 °C within 45 min, whereas the cable protected by a double-layer 5 + 5 mm HSFAC system remained below 300 °C throughout the test. Finite element simulations validated against the experimental results confirmed that increasing HSFAC thickness improved thermal protection. After 90 min, the predicted cable-surface temperatures were 556 °C and 314 °C for HSFAC thicknesses of 5 mm and 10 mm, respectively. By integrating high-temperature material characterization, HC-fire testing, and thickness-dependent numerical analysis, this study links material degradation to system-level fire performance and provides a quantitative basis for HSFAC thickness design. Full article