Search Results (251)

Addressing the challenges of bulky, low-efficiency sound-insulation materials at low frequencies, this work proposes an acoustic metamaterial based on curve fractal channels. Each unit cell comprises a concentric circular-ring channel recursively iterated: as the fractal order increases, the channel path length grows exponentially, enabling outstanding sound-insulation performance within a deep-subwavelength thickness. Finite-element and transfer-matrix analyses show that increasing the fractal order from one to three raises the number of bandgaps from three to five and expands total stop-band coverage from 17% to over 40% within a deep-subwavelength thickness. Four-microphone impedance-tube measurements on the third-order sample validate a peak transmission loss of 75 dB at 495 Hz, in excellent agreement with simulations. Compared to conventional zigzag and Hilbert-maze designs, this curve fractal architecture delivers enhanced low-frequency broadband insulation, structural lightweighting, and ease of fabrication, making it a promising solution for noise control in machine rooms, ducting systems, and traffic environments. The method proposed in this paper can be applied to noise reduction of transmission parts for ceramic automation production. Full article

Phonolite is a fine-grained, shallow extrusive rock rich in alkali minerals and containing iron/titanium-bearing minerals. This rock is widely used as a construction material for building exteriors due to its excellent abrasion resistance and insulation properties. However, during the cutting process, approximately 70% of the rock is discarded as tailing. So, this study aims to repurpose tailings from a phonolite cutting and sizing plant into a high-alkali ceramic raw mineral concentrate. To enable the use of phonolite tailings in ceramic manufacturing, it is necessary to remove coloring iron/titanium-bearing minerals, which negatively affect the final product. To achieve this removal, dry/wet magnetic separation processes, along with flotation, were employed both individually and in combination. The results demonstrated that using dry high-intensity magnetic separation (DHIMS) resulted in a concentrate with an Fe₂O₃ + TiO₂ grade of 0.95% and a removal efficiency of 85%. The wet high-intensity magnetic separation (WHIMS) process reduced the Fe₂O₃ + TiO₂ grade of the concentrate to 1.2%, with 70% removal efficiency. During flotation tests, both pH levels and collector concentration impacted the efficiency and Fe₂O₃ + TiO₂ grade (%) of the concentrate. The lowest Fe₂O₃ + TiO₂ grade of 1.65% was achieved at a pH level of 10 with a collector concentration of 2000 g/t. Flotation concentrates processed with DHIMS achieved a minimum Fe₂O₃ + TiO₂ grade of 0.90%, while those processed with WHIMS exhibited higher Fe₂O₃ + TiO₂ grades (>1.1%) and higher recovery rates (80%). Additionally, studies on flotation applied to WHIMS concentrates showed that collector concentration, pulp density, and conditioning time significantly influenced the Fe₂O₃ + TiO₂ grade of the final concentrate. Full article

This research presents the development and management principles of mobile resonant electrical systems designed for high-voltage generation, intended for non-destructive diagnostics of insulation in high-power electrical equipment. The core of the system is a series inductive–capacitive (LC) circuit characterized by a high quality (Q) factor and operating at high frequencies, typically in the range of 40–50 kHz or higher. Practical implementations of the LC circuit with Q-factors exceeding 200 have been achieved using advanced materials and configurations. Specifically, ceramic capacitors with a capacitance of approximately 3.5 nF and Q-factors over 1000, in conjunction with custom-made coils possessing Q-factors above 280, have been employed. These coils are constructed using multi-core, insulated, and twisted copper wires of the Litzendraht type to minimize losses at high frequencies. Voltage amplification within the system is effectively controlled by adjusting the current frequency, thereby maximizing voltage across the load without increasing the system’s size or complexity. This frequency-tuning mechanism enables significant reductions in the weight and dimensional characteristics of the electrical system, facilitating the development of compact, mobile installations. These systems are particularly suitable for on-site testing and diagnostics of high-voltage insulation in power cables, large rotating machines such as turbogenerators, and other critical infrastructure components. Beyond insulation diagnostics, the proposed system architecture offers potential for broader applications, including the charging of capacitive energy storage units used in high-voltage pulse systems. Such applications extend to the synthesis of micro- and nanopowders with tailored properties and the electrohydropulse processing of materials and fluids. Overall, this research demonstrates a versatile, efficient, and portable solution for advanced electrical diagnostics and energy applications in the high-voltage domain. Full article

The aim of the present research was to synthesize protective composite layers from biodegradable cellulose and biocompatible, sol–gel-derived silica cryogel. An important task in the present work was to achieve good applicability on distinct (smooth and rough) surfaces of various materials (from metallic to ceramic). The aim was to utilize the composite layers as thermal and electric insulation coating. The investigation put some effort into the enhancement of mechanical strength and the elasticity of the thin layer as well as a reduction in its water solubility. The removal of the alkali content leads successfully to a significant reduction in water solubility (97 wt% → 1–3 wt%). Adhesion properties were measured using a specialized measurement technique developed in our laboratory. Treatments of the substrate surface, such as alkaline or acidic etching (i.e., Na₂CO₃, HF, water glass), mechanical roughening, or the application of a thin alkali-containing primer layer, strongly increase adhesion. SEM analyses revealed the interactions between the matrix and the reinforcement phase and their morphology. Full article

Microstructural, mechanical and qualitative phase identification of durable mullite-based ceramics obtained by utilization of waste clay–diatomite has been studied. Mullite-based ceramics were fabricated using waste clay–diatomite from the Baroševac open-cast coal mine, Kolubara (Serbia). The raw material consists mainly of SiO₂ (70.5 wt%) and a moderately high content of Al₂O₃ (13.8 wt%). In order to achieve the stoichiometric mullite composition (3Al₂O₃-2SiO₂), the raw material was mixed with an appropriate amount of Al(NO₃)₃·9H₂O. After preparing the precursor powder, the green compacts were sintered at 1300, 1400 and 1500 °C for 2 h. During the process, rod-shaped mullite grains were formed, measuring approximately 5 µm in length and a diameter of 500 nm (aspect ratio 10:1). The microstructure of the sample sintered at 1500 °C resulted in a well-developed, porous, nest-like morphology. According to the X-ray diffraction analysis, the sample at 1400 °C consisted of mullite, cristobalite and corundum phases, while the sample sintered at 1500 °C contained mullite (63.24 wt%) and an amorphous phase that reached 36.7 wt%. Both samples exhibited exceptional compressive strength—up to 188 MPa at 1400 °C. However, the decrease in compressive strength to 136 MPa at 1500 °C is attributed to changes in the phase composition, the disappearance of the corundum phase and alterations in the microstructure. This occurred despite an increase in bulk density to 2.36 g/cm³ (approximately 82% of theoretical density) and a complete reduction in open porosity. The residual glassy phase (36.7 wt% at 1500 °C) is probably the key factor influencing the mechanical properties at room temperature in these ceramics produced from waste clay–diatomite. However, the excellent mechanical stability of the samples sintered at 1400 and 1500 °C, achieved without binders or additives and using mined diatomaceous earth, supports further research into mullite-based insulating materials. Mullite-based materials obtained from mining waste might be successfully used in the field of energy-efficient refractory materials and thermal insulators. for high-temperature applications Full article

Concerning building acoustics, the impact of sound propagation in the building structure can be considered one of the most relevant problems. Floating floors are an efficient solution, composed of a rigid walking surface above a resilient material. Functioning as a spring, the resilient layer must have adequate damping properties and compressive strength against permanent and imposed loads to guarantee its performance over time. In this context, this study aims to completely evaluate the impact sound reduction of composite lightweight floating floors formed by ceramic tiles and recycled rubber mats when subjected to prolonged loads, from material characterization to their application in a hypothetical scenario. This study was based on the dynamic stiffness (ISO 9052-1) and compressive creep (ISO 16534) of the resilient layer and the physical characterization of the ceramic tiles, predicting the present and future (15 years) impact sound reductions and their application in a hypothetical room, considering direct and indirect transmissions paths (ISO 12354-2). The results showed that the lightweight floating floor compositions lost their damping capability to a degree that can reduce their weighted reduction in the impact sound pressure level by up to 2 dB over prolonged periods (15 years). Howsoever, the compositions had considerable initial impact sound insulation capability and adequate performance maintenance over time. Full article

Surface erosion of the coaxial thermocouple probe initiates continuous bridging of thermoelectric materials on the insulation layer surface, forming new temperature measurement junctions. This inherent ability to measure continuous self-erosion ensures the operational reliability of the coaxial thermocouples in high-temperature ablative environments. However, the fabrication of a high-temperature electrical insulation layer and a high-adhesion insulating layer in the coaxial thermocouples remains a challenge. Inspired by calcium carbonate/oxalate crystals in jujube leaves that strengthen the leaves, a bioinspired structural ceramic (BSC) mimicking these needle-like crystals is designed. This BSC demonstrates excellent high-temperature insulation (with insulation impedance of 2.55 kΩ at 1210 °C) and adhesion strength (35.3 Newtons). The BSC is successfully used as the insulating layer in a K-type coaxial thermocouple. The generation rules for surface junctions are systematically studied, revealing that stable and reliable measurement junctions can be created when the sandpaper grit does not exceed 600#. Static test results show that the K-type coaxial thermocouple ranges from 200 °C to 1200 °C with an accuracy of 1.1%, a drift rate better than 0.0137%/h, and hysteresis better than 0.81%. Dynamic test results show that the response time is 1.08 ms. The K-type coaxial thermocouple can withstand a high-temperature flame impact for 300 s at 1200 °C, as well as over forty cycles of high-power laser thermal shock, while maintaining good response characteristics. Therefore, the K-type coaxial thermocouple designed in this study provides an ideal solution for long-term temperature monitoring of the thermal components of aerospace engines under extremely high-temperature, high-speed, and strong thermal shock conditions. Full article

Battery thermal runaway (TR) is usually accompanied by a large amount of heat release, as well as a jet of flame. This not only causes harm to the surrounding environment but even exacerbates thermal runaway propagation (TRP). At this stage, many types of materials are used to suppress TRP, and people tend to focus on improving one characteristic of the material while ignoring other properties of the material. This may leave potential pitfalls for TRP suppression, suggesting the need to study multiple properties of multiple materials. In order to better weigh the advantages and disadvantages of different types of materials when suppressing TRP, we compared three typical materials for suppressing TRP behavior in lithium-ion batteries (LIBs). These materials are phase change materials (PCM), ceramic fibers, and glass fibers. They are all available in two different thicknesses, 2 mm and 3 mm. The experiments started with a comparative analysis of the TR experimental phenomena in the presence of the different materials. Then, the temperature and mass loss of the battery module during TR were analyzed separately and comparatively. The 3 mm glass fiber showed the best inhibition effect, which extended the TR interval between cells 1 and 2 to 894 s and successfully inhibited the TR of cell 3. Compared with the blank group, the total mass loss decreased from 194.3 g to 182.2 g, which is a 6.2% reduction. Subsequently, we comprehensively analyzed the performance of the three materials in suppressing TRP by combining their suppressing mechanisms. The experimental results show that glass fiber has the best effect in suppressing TRP due to its excellent thermal insulation and mechanical properties. This study may provide new insights into how to trade-off material properties for TRP suppression in the future. Full article

Over 2 million tonnes of ceramic waste are generated annually in South Africa, with the majority disposed of in landfills, contributing to environmental degradation. Meanwhile, researchers are actively seeking sustainable alternatives to Portland cement (PC), which is associated with significant environmental challenges. Ceramic waste powder (CWP) refers to finely milled ceramic waste and powder derived from the polishing and finishing stages of ceramic production. This review examines the potential of CWP as a partial replacement for PC in concrete, focusing on its effects on workability, mechanical durability, and microstructural properties. The findings indicate that moderate replacement levels (up to 20%) enhance the compressive and flexural strengths of concrete. However, these benefits are not consistently reported across all studies. Additionally, CWP improves the microstructural properties of the concrete. This is probably due to the pozzolanic reactions of CWP, which result in a denser concrete matrix and enhanced long-term durability. Notable durability benefits include reduced water absorption, increased resistance to chemical attacks, and improved thermal insulation. However, the performance of concrete with higher CWP replacement levels (above 30%) remains unclear. Some studies have reported strength reductions and increased susceptibility to durability loss at this level. Further studies should focus on clarifying its pozzolanic reactivity, durability in aggressive environments, and optimum replacement percentage. Full article

Lightweight, high-temperature thermal insulation materials play a critical role in aerospace applications, where extreme temperature conditions necessitate lightweight, high-performance solutions. This paper explores advancements in lightweight, high-temperature insulation materials specifically designed for aerospace environments, focusing on innovative flexible ceramic fiber felts, thermal insulation tiles, nano-insulation materials (aerogels), and multilayer insulations (MLIs). These materials exhibit superior thermal resistance, low density, and durability under dynamic and harsh conditions. Key developments include the integration of nanostructures to enhance thermal conductivity control and improve mechanical stability. This paper also highlights applications in spacecraft thermal protection systems, providing insights into the challenges of future material design strategies. These advancements underscore the growing potential of thermal insulations to improve energy efficiency, safety, and performance in aerospace missions. Full article

Ensuring the fire resistance and thermal stability of power cables is crucial for their reliable performance in fire environments, essential for sustainable power distribution, and allowing for more time to extinguish fires and for evacuation. This study utilises numerical simulation to analyse the thermal behaviour of fire-resistant medium-voltage cable, focusing on the impact of conductor radius and material properties under external heat flux. A heat transfer model of cables with conductor radii of 3 mm, 5 mm, and 7 mm under a localised external heat flux of 750 °C was developed. The results show that smaller conductors stabilise faster (reaching the steady state at 45 min for 3 mm vs. 79 min for 7 mm) but experience higher thermal stress, with conductor temperatures peaking at 692.5 °C. Larger conductors enhance axial heat conduction, reduce steady-state temperature by up to 25%, and improve heat dissipation by over 360%. The 5 mm conductor radius provided balanced performance, lowering the temperature by 65 °C compared to 3 mm, although it remained 20.1% hotter than the 7 mm. The ceramic layer played a crucial role in reducing heat flux in the heat source section. Optimised polyethylene insulation and ceramic material improved heat retention and surface temperature control in non-heat source sections. Also, thermal resistance analysis decreased from 1.00 K/W (3 mm) to 0.65 K/W (7 mm). Among material properties, increasing ceramic thermal conductivity had a more significant impact on reducing core temperature than improving insulation. These findings provide practical recommendations for optimising conductor geometry and material properties for more fire-resistant cables. Full article

Traditional nanoparticle aerogels suffer from inherent brittleness and thermal instability at elevated temperatures. In recent years, ceramic nanofiber aerogels, utilizing flexible nanofibers as structural units, have emerged as mechanically resilient alternatives with ultrahigh porosity (>90%). However, their thermal insulation capabilities are compromised by micron-scale pores (10–100 μm) and overdependence on ultralow density, which exacerbates mechanical fragility. This study pioneers a gas-phase self-assembly strategy to fabricate Si₃N₄ nanoparticle reinforced Si₃N₄ nanofiber aerogels (SNP-R-SNFA) with gradient pore architectures. By leveraging methyltrimethoxysilane/vinyltriethoxysilane composite aerogel (MVa) as a reactive template, we achieved spontaneous growth of Si₃N₄ nanofiber films (SNP-R-SNF) featuring nanoparticle-fiber interpenetration and porosity gradients. The microstructure formation mechanism of SNP-R-SNF was analyzed using field-emission scanning electron microscopy. Layer assembly and hot-pressing composite technology were employed to prepare the SNP-R-SNFA, which showed low density (0.033 g/cm³), exceptional compression resilience, insensitive frequency dependence of dielectric properties (ε′ = 2.31–2.39, tan δ < 0.08 across 8–18 GHz). Infrared imaging displayed backside 893 °C cooler than front, demonstrating superior insulation performance. This study not only provides material solutions for integrated electromagnetic wave-transparent/thermal insulation applications but more importantly establishes an innovative paradigm for enhancing the mechanical robustness of nanofiber-based aerogels. Full article

This paper presents the development of two solutions for sandwich panels composed of a thin-layer alkali-activated composite (AAc) layer and a thicker insulation layer, formed by extruded polystyrene foam or expanded cork agglomerate (panels named AP_XPS or AP_ICB, respectively). The AAc combined ceramic waste from clay bricks and roof tiles (75%) with ladle furnace slag (25%), activated with sodium silicate. The AAc layer was further reinforced with polyacrylonitrile (PAN) fibers (1% content). The mechanical behavior was assessed by measuring the uniaxial compressive strength of cubic AAc specimens, shear bond strength, pull-off strength between the AAc layer and the insulation material, and the flexural behavior of the sandwich panels. The thermal performance was characterized by heat flux, inner surface temperatures, the thermal transmission coefficient, thermal resistance, and thermal conductivity. Mechanical test results indicated clear differences between the two proposed solutions. Although AP_XPS panels exhibited higher tensile bond strength values, the AP_ICB panels demonstrated superior interlayer bond performance. Similar findings were observed for the shear bond strength, where the irregular surface of the ICB positively influenced the adhesion to the AAc layer. In terms of flexural behavior, after the initial peak load, the AP_XPS exhibited a deflection-hardening response, achieving greater load-bearing capacity and energy absorption capacity compared to the AP_ICB. Finally, thermal resistance values of 1.02 m² °C/W and 1.14 m² °C/W for AP_ICB and AP_XPS were estimated, respectively, showing promising results in comparison to currently available building materials. Full article

The stability of thermal barrier coating (TBC) materials during service is a prerequisite for the normal operation of aircraft engines. The high-temperature corrosion of CaO–MgO–Al₂O₃–SiO₂ (CMAS) is an important factor that affects the stability of TBCs on turbine blades and causes premature engine failure. For traditional 6-8 YSZ, at temperatures of more than 1200 °C, the thermal insulation performance is significantly reduced, which makes it necessary to find new, alternative materials. La₂Zr₂O₇ has good thermal physical properties; the addition of Ce⁴⁺ improves its mechanical properties, while adding Gd₂O₃ affects its corrosion resistance. Herein, high-temperature corrosion studies of (La_1−xGd_x)₂(Zr_0.7Ce_0.3)₂O₇ (L-GZC) (x = 0, 0.3, 0.5, 0.7) ceramic TBC were conducted using CMAS glass at 1250 °C. The results indicate that CMAS rapidly dissolves L-GZC and separates the (La, Gd)₈Ca₂(SiO₄)₆O₂ apatite phase, ZrO₂, and other crystalline phases. These products form a crystalline layer at the contact boundary, which can inhibit further CMAS reactions. Among the coatings examined, the L-GZC ceramic (x = 0.7) exhibits better corrosion resistance, and the penetration depth is <200 μm after high-temperature corrosion at 1250 °C for 5, 10, and 20 h. The failure mechanism and potential risk of CMAS were also analyzed and discussed. The L-GZC ceramic material has good thermal corrosion resistance and is expected to replace the traditional YSZ to better meet the high-temperature working requirements of gas turbines and aircraft engines. Full article

The current deformation scheme used in the 4D printing of ceramics has several disadvantages, such as a poor deformation capacity, high process complexity, and the poor mechanical properties of the product. In order to solve these problems, the deformation scheme introduced in this study utilizes the pyrolytic expansion of polyurethane and the resulting pores to hinder the contraction of the specimen during the ceramization stage. Then, the specimen is composited with a polyurethane-free portion that has a high rate of shrinkage, and deformation is initiated through the interlayer stress mismatch generated by the difference in the shrinkage of the different layers, thus enabling the preparation of complex structural ceramics. This solution is simple and efficient; heat treatment is performed in a single pass, and the precursor specimen is highly deformable. The incorporation capacity of the aluminum oxide ceramic powder was increased by replacing part of the Dow Corning SE 1700 polydimethylsiloxane silicone rubber in the raw material with Dow Corning DC 184 polydimethylsiloxane silicone rubber, which, in turn, improved the mechanical properties of the obtained ceramics by enhancing the solid-phase content of the ceramic powder. Due to the introduction of polyurethane, the ceramic has a secondary pore structure, which has the potential for application in the field of engineering materials and heat insulation materials. Full article