Search Results (167)

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

The failure of a porcelain insulator on a transmission line is a crucial cause of power supply interruptions, leading to poor reliability and revenue loss. The insulator’s performance is adversely affected by environmental contaminants, and wettability intensifies this adverse effect by developing a conductive path along the insulator’s surface, leading to premature flashover and insulator failure. This work aims to analyze the response of the electric field distribution and current density using the finite element method (FEM) under different wettability conditions. Discrete water droplets were placed along the surface, and the contact angle was varied to represent different levels of surface hydrophobicity. Abrupt rises and spikes were observed on the plots for the electric field and current density distribution, indicating distortion; however, the distortion kept on decreasing with the increase in the contact angle. Overall, the average stress followed a declining pattern, where the values of the electric field were reduced from 2.588 to 2.412 kV/cm, and current the density was reduced from 0.187 to 0.068 nA/cm² for an increase in the contact angle from 60° to 140°. Simulation results advocate for hydrophobic insulator surfaces. Therefore, a proper coating is necessary to enrich hydrophobicity and mitigate the adversity of wettability. Polyurethane, due to its excellent hydrophobic and insulating properties, offers a potential coating. Flashover voltage tests have been performed for the coated insulator under dry and wet conditions, where the flashover voltage improved from 79.14 kV to 82.04 kV and 48.4 kV to 53.8 kV, respectively, which supports the simulations’ outcomes. Full article

Composite insulators are deployed globally for outdoor insulation owing to their light weight, excellent pollution resistance, good mechanical strength, ease of installation, and low maintenance costs. The core rod in composite long-rod insulators plays a critical role in both mechanical load-bearing and internal insulation for overhead transmission lines, and its performance directly affects the overall operational condition of the insulator. However, it remains susceptible to failures induced by complex actions of mechanical, electrical, thermal, and environmental stresses. This paper systematically reviews the major failure modes of core rods, including mechanical failures (normal fracture, brittle fracture, and decay-like fracture) and electrical failures (flashunder and abnormal heating of the core rod). Through analysis of extensive field data and research findings, key failure mechanisms are identified. Preventive strategies encompassing material modification (such as superhydrophobic coatings, self-diagnostic materials, and self-healing epoxy resin), structural optimization (like the optimization of grading rings), and advanced inspection methods (such as IRT detection, Terahertz (THz) detection, X-ray computed tomography (XCT)) are proposed. Furthermore, the limitations of current technologies are discussed, emphasizing the need for in-depth studies on deterioration mechanisms, materials innovation, and defect detection technologies to enhance the long-term reliability of composite insulators in transmission networks. Full article

Polyimides (PIs) are materials that are resistant to high temperatures and crucial for the manufacturing of films, fibers, coatings, and 3D-printed items. PIs are widely used as electrically insulating materials in electronics and electrical engineering. This study investigated how the chemical structure (i.e., choice of initial monomers), the synthesis conditions of the prepolymer (i.e., choice of amide solvent), and the conditions for forming polyimide films (i.e., final curing temperature) affect the thermophysical properties and short-term electrical strength of obtained polyimide films of different chemical structures. In this work, we varied the compositions of the dianhydrides used for synthesizing polyamic acids—pyromellitic acid (PMDA), tetracarboxylic acid diphenyl oxide (ODPA) and 1,3-bis(3′,4-dicarboxyphenoxy)benzene acid (R)—with a constant diamine: 4,4′-oxydianiline (ODA). Additionally, we varied the amide solvents employed: N,N-dimethylacetamide (DMAc), N,N-dimethylformamide (DMF), and N-methyl-2-pyrrolidone (NMP). This study represents the first investigation into how the choice of solvent in the synthesis of thermoplastic polyimide prepolymers affects their short-term electrical strength. The molecular weights of the polyamic acids were determined using gel permeation chromatography (GPC). The deformation and strength characteristics of the investigated films were also assessed. The thermophysical properties of the polyimides were evaluated via dynamic mechanical analysis (DMA), differential scanning calorimetry (DSC), and thermogravimetric analysis (TGA). X-ray diffraction analysis and infrared spectroscopy (IR) were conducted on the examined film samples. The short-term electrical strength was also evaluated. Full article

Polydimethylsiloxane (PDMS) has been extensively employed in electrical insulation applications owing to its excellent thermal stability, hydrophobicity, and dielectric properties. However, its inherent mechanical limitations require structural reinforcement to enhance its performance under more demanding operational conditions. In this study, the mechanical, thermal, and surface properties of PDMS-SiO₂ nanocomposites synthesized via in situ sol–gel process was systematically investigated. The influence of different SiO₂ nanoparticle concentrations (5, 10, and 15 wt%), sol–gel catalyst type (acidic and alkaline), and tetraethyl orthosilicate (TEOS) crosslinking agent ratios (15:1, 10:1, 5:1) was evaluated. Tensile mechanical testing, dynamic mechanical analysis (DMA), and thermogravimetric analysis (TGA) revealed that the incorporation of SiO₂ notably improved both the mechanical strength and thermal stability of the composites. The 5-15b and 10-15a composites exhibited the highest tensile stress and viscoelastic modulus among all samples. Furthermore, the composites retained key functional properties, including hydrophobicity, high volumetric electrical resistivity (~10¹¹ Ω·cm), and strong adhesion. These findings confirm the potential of in situ PDMS-SiO₂ nanocomposites for use as high-performance insulating coatings in advanced electrical applications. Full article

As an indispensable component of power transmission systems, the performance of porcelain insulators directly impacts the reliability and operational stability of electrical networks. To enhance the anti-fouling flashover capability of transmission lines, porcelain insulators are commonly coated with RTV (Room Temperature Vulcanizing) silicone rubber coatings. However, the unique environmental conditions prevalent in high-altitude regions, such as those in Qinghai, impose distinctive stresses on the performance and longevity of RTV coatings. This study provides an in-depth analysis of the operational and aging characteristics of RTV-coated porcelain insulators under such extreme conditions, with a focus on evaluating performance degradation mechanisms. By conducting comprehensive field investigations of climatic and environmental parameters in Qinghai, this research elucidates the effects of high-altitude environments on RTV coatings and proposes a systematic methodology for detecting and analyzing aging-related phenomena. This study discerns the aging patterns of insulator surface coatings in high-altitude regions and examines the pollution accumulation mechanisms of insulators under adverse climatic conditions. These findings offer critical insights for optimizing the selection, maintenance, and replacement strategies of insulators in high-altitude transmission networks, thereby enhancing the safety, reliability, and operational efficiency of power systems in such challenging environments. Full article

This paper deals with one of the methods for protecting against an electrostatic charge by using a conductive coating. We focus on methyl-silicone resin with the addition of a conductive polymer. The individual electrical parameters of these coatings are studied because these parameters determine the ability of charge leakage. The purpose of this study was to find out if the coating would change its electrical parameters after some time and if the antistatic protection purpose of the coating would deteriorate. We used the dielectric spectroscopy method for the measurements. This method was chosen because conductive polymers are basically semiconductors, and the insulation parameters were measured by this method. After aging, another set of measurements was made, and the results were compared. We found that the electrical parameters of the antistatic coating were considerably changed by the aging process. The reliability of antistatic paints was proven in these experiments. The paints presented had high values of conductivity in general, and after our experiments, the most reliable conductive paintings appeared to be the ones with the PANI polymer. For reliable electrostatic charge elimination on non-conductive surfaces, the BISIL paint proved to be the best choice. Our experiments also proved the influence of the underlying surface material on the electrical parameters of the paintings. Furthermore, we proved that the aging process influenced the loss factor of the paintings. Full article

A critical challenge in wearable electrothermal textiles is achieving effective insulation while maintaining sheath flexibility, which is essential for enhancing the mechanical properties and durability of conductive materials under everyday conditions, such as washing, stretching, and twisting. In this work, we employ a coaxial tubular braiding technique to coat a high-conductivity carbon nanotube (CNT) yarn with a high-strength insulation layer made of ultra-high-molecular-weight polyethylene (UHMWPE) multifilaments, resulting in a core–sheath-structure CNT yarn with excellent electrothermal performance. By adjusting the number of UHMWPE multifilaments and the sheath braiding angle, we achieve high flexibility, high tensile strength, and abrasion and wash resistance, as well as improved electrical stability for the CNT yarns. Additionally, the CNT yarns with an insulation layer effectively prevent short-circuiting during use and achieve superior thermal management, with a significant increase in steady-state temperature under operational conditions, exhibiting significant potential for applications in wearable electronic devices. Full article

Carbon steel structures employed to convey hydrocarbons and other dangerous fluids, such as oil or flammable liquids, are equipped with degradation prevention systems, which typically consist of a cathodic protection (CP) system combined with an external insulating coating, both designed to reduce the corrosion rate below 10 µm/year. The presence of electrical interference, both AC and DC, can cause significant corrosion damage to metallic structures, even when CP is applied. DC interference is determined by the presence of a third-party CP system or public transportation system. AC interference may occur through conduction or induction mechanisms, caused by high-voltage powerlines or high-speed trains, powered by AC. Both interferences may lead to localized corrosion at coating defects, despite compliance with the −0.850 V saturated Cu/CuSO₄ reference electrode (CSE) protection criterion. Considering AC-induced corrosion, both field failures and laboratory investigations have demonstrated that corrosion can occur at industrial frequencies, and when CP is applied following the standards. Even though AC-induced degradation is generally not as severe as DC interference, uncertainties remain regarding the protection potential range necessary to achieve acceptable corrosion prevention under AC interference. To formulate a CP criterion under AC interference, weight loss measurements were conducted on carbon steel samples under cathodic protection in solutions that simulate real soil conditions. Carbon steel coupons protected by CP were interfered with AC densities ranging from 1 A/m² to 800 A/m² for four months. During this time interval, polarization potential, protection current density and AC density were monitored. Based on the experimental data gathered during this study, a proposal for a risk map is also suggested. The results indicate that overprotection (potentials < −1.2 V CSE) represents the most dangerous scenario when AC interference is involved. Full article

Today, the machining of heat-resistant alloys based on triple, quad, or penta equilibria high-entropy alloy systems of elements (ternary, quaternary, quinary iron-, titanium-, or nickel-rich alloys), including dual-phase by Gibb’s phase rule, steels of the austenite class, and nickel- and titanium-based alloys, are highly relevant for the airspace and aviation industry, especially for the production of gas turbine engines. Cutting tools in contact with those alloys should withstand intensive mechanical and thermal loads (tense state of 1.38·10⁸–1.54·10⁸ N/m², temperature up to 900–1200 °C). The most spread material for those tools is cutting ceramics based on oxides, nitrides of the transition and post-transition metals, and metalloids. This work considers the wear resistance of the cutting insert of silicon nitride with two unique development coatings — titanium–zirconium nitride coating (Ti,Zr)N and complex quad nitride coating with TiN content up to 70% (Ti,Al,Cr,Si)N with a thickness of 3.8–4.0 µm on which microtextures were produced by the assisted electric discharge machining with the electrode-tool of ø0.25 mm. The microtextures were three parallel microgrooves of R0.13^+0.02 mm at a depth of 0.025₋₀.₀₅. The operational life was increased by ~1.33 when the failure criterion in turning nickel alloy was 0.4 mm. Full article

To improve the adhesion strength of polymer functional films, corona treatment is required. Corona rollers are key components for corona treatment, which are used in high-voltage electric fields for a long time. In this work, in order to improve electrical insulation, arc resistance, wear resistance, and chemical stability, a coating is usually sprayed on the surface of the corona roller. Al₂O₃/h-BN composite coatings are prepared on the surface substrate of a corona roller (20 steel) by atmospheric plasma spraying (APS) technology. Scanning Electron Microscope (SEM) and X-ray diffraction (XRD) analysis showed that the Al₂O₃/h-BN composite coating had a layered structure and compactness. Two kinds of Al₂O₃/h-BN composite coatings are prepared under different APS process parameters; the porosities of A coating and B coating are 6.04% and 4.75%, the microhardnesses are 781 ± 0.5 Hv and 840.5 ± 0.5 Hv, and the adhesion strengths are 22.0 MPa and 22.3 MPa, respectively. The A and B volume resistivity of the coatings are 9.29 × 10¹⁰ Ω·cm and 3.55 × 10¹⁰ Ω·cm, respectively. The volume resistivity and porosity of the coatings are negatively correlated, and they decrease with the increase in spraying current. But for both coatings, volume resistivity is greater than 1 × 10¹⁰ Ω cm. These results indicate that the Al₂O₃/h-BN composite coatings, as a new type of electrode roller coating, satisfy the use requirement. Al₂O₃/h-BN composite coatings can become the potential for ceramic coatings that have good mechanics and insulation performance. Full article

The considerable heat generated in electronic devices, resulting from their high-power consumption and dense component integration, underscores the importance of developing effective thermal interface materials. While composite materials are ideal for this application, the random distribution of filling materials leads to numerous interfaces, limiting improvements in thermal transfer capabilities. An effective method to improve the thermal conductivity of composites is the alignment of anisotropic fillers, such as hexagonal boron nitride (BN). In this study, the repeat blade coating method was employed to horizontally align BN within a polydimethylsiloxane (PDMS) matrix, followed by flipping and cutting to prepare BN/PDMS composites with vertically aligned BN (V-BP). The V-BP composite with 30 wt.% BN exhibited an enhanced out-of-plane thermal conductivity of up to 1.24 W/mK. Compared to the PDMS, the V-BP composite exhibited outstanding heat dissipation capacities. In addition, its low density and exceptional electrical insulation properties showcase its potential for being used in electronic devices. The impact of coating velocity on the performance of the composites was further studied through computational fluid dynamics simulation. The results showed that increasing the coating velocity enhanced the out-of-plane thermal conductivity of the V-BP composite by approximately 40% compared to those prepared at slower coating velocities. This study provides a promising approach for producing thermal interface materials on a large scale to effectively dissipate the accumulated heat in densely integrated electronic devices. Full article

In the fabrication of soft magnetic composites, the lattice mismatch between the inorganic insulation layer and the iron matrix often leads to the formation of cracks during the molding process, which significantly impairs the operational performance of the materials. Consequently, it is imperative to develop novel strategies for inorganic insulation coatings that offer high electrical resistivity and thermal stability and are less susceptible to cracking during formation. This paper presents a new structure for soft magnetic composites that incorporates FePO₄ as an intermediate transition layer between the iron-based soft magnetic particles and the inorganic ceramic insulation layer. This configuration is designed to provide insulation coatings with superior voltage and thermal resistance, as well as high electrical resistivity. The research details the processes forming the FePO₄ intermediate transition layer and the SiO₂ insulation layer on the iron powder surface, along with their interaction mechanisms. An analysis comparing the scenarios with and without the FePO₄ intermediate transition layer shows its beneficial impact on the magnetic properties and mechanical strength of the soft magnetic composites. Further investigations reveal that at a phosphoric acid concentration of 1 wt.%, the FePO₄ layer significantly enhances the interface compatibility between the Fe powder matrix and the SiO₂ insulation layer. Under these conditions, the Fe@ FePO₄/SiO₂ soft magnetic composites demonstrate outstanding overall performance: the saturation magnetization stands at 215.60 emu/g, effective permeability at 83.2, resistivity at 57.42 Ω·m, power loss at 375.0 kW/m³ under 30 mT/100 kHz, and radial compressive strength at 15.95 Kgf. These findings offer novel insights and practical approaches for advancing inorganic insulation coating strategies and provide vital scientific support for further enhancing the magnetic and mechanical properties of soft magnetic composites. Full article

Saudi Arabia faces significant challenges in managing the rising energy consumption in buildings driven largely by its hot climatic conditions. As a result, retrofitting building facades to enhance energy efficiency has become a critical strategy. This study assesses the effectiveness of various façade retrofit strategies in reducing cooling electricity consumption using a real-time case study in Dhahran, Saudi Arabia. The strategies explored include external wall upgrades, window replacements, and installation of shading devices. Each strategy was evaluated individually, considering the reduction in heat gains, cooling load, and payback period as key performance indicators. To further maximize energy efficiency, these strategies were also analyzed in combination using the genetic algorithm optimization method, yielding 224 possible facade configurations. The optimal solution included the use of an External Thermal Insulation Composite System (ETCIS) in walls, louvers in windows, and low-emissivity coating with Argon gas-filled glazing, achieving a cooling energy reduction of approximately 16% and a payback period of 14.8 years. This study provides several recommendations for improving the efficiency of retrofitting building façades in hot climatic conditions. Full article

The acrylic polymer composites in this study are made up of various weight ratios of cement or silica nanoparticles (1, 3, 5, and 10 wt%) using the casting method. The effects of doping ratio/type on mechanical, dielectric, thermal, and hydrophobic properties were investigated. Acrylic polymer composites containing 5 wt% cement or silica nanoparticles had the lowest abrasion wear rates and the highest shore-D hardness and impact strength. The increase in the inclusion of cement or silica nanoparticles enhanced surface roughness, water contact angle (WCA), and thermal insulation. Acrylic/cement composites demonstrated higher mechanical, electrical, and thermal insulation properties than acrylic/silica composites because of their lower particle size and their low thermal/electrical conductivity. Furthermore, to improve the surface hydrophobic characteristics of acrylic composites, the surface was treated with a dielectric barrier discharge (DBD) plasma jet. The DBD plasma jet treatment significantly enhanced the hydrophobicity of acrylic polymer composites. For example, the WCA of acrylic composites containing 5 wt% silica or cement nanoparticles increased from 35.3° to 55° and 44.7° to 73°, respectively, by plasma treatment performed at an Ar flow rate of 5 L/min and for an exposure interval of 25 s. The DBD plasma jet treatment is an excellent and inexpensive technique for improving the hydrophobic properties of acrylic polymer composites. These findings offer important perspectives on the development of materials coating for technical applications. Full article