Search Results (69)

This work presents a comprehensive study on the synthesis and application of Al₂O₃ fibers derived from an ammonium aluminum carbonate hydroxide (AACH) precursor. Through a hydrothermal route, the influence of critical synthesis parameters, including aluminum nitrate and urea concentrations, reaction temperature and time, and stirring conditions, on fiber morphology and aspect ratio was systematically investigated. The as-synthesized AACH fibers were subsequently converted into thermodynamically stable α-alumina fibers via controlled annealing. These high-aspect ratio alumina fibers were incorporated into polydimethylsiloxane (PDMS) to produce electrically insulating, thermally conductive composites. The thermal performance of fiber-filled composites was benchmarked against that of particle-filled counterparts, with the former exhibiting significantly enhanced thermal conductivity. Furthermore, the dielectrophoretic alignment of alumina fibers led to an additional increase in thermal conductivity, underlining the importance of high-aspect ratio fillers. This study uniquely combines the controlled synthesis of alumina fibers with their incorporation and alignment in a polymer matrix, presenting a novel and effective approach for engineering anisotropic, thermally conductive, and electrically insulating composite materials. Dielectrophoretic alignment of α-Al₂O₃ fibers synthesized through optimized hydrothermal conditions and incorporated into PDMS composites deliver over 95 % higher thermal conductivity than spherical fillers. Full article

Polytetrafluoroethylene (PTFE) is one of the alternative materials suitable for seawater-lubricated bearings, favored for its excellent corrosion resistance and good self-lubricating properties. As marine equipment develops towards higher load, higher reliability, and longer service life, more stringent requirements are imposed on the wear resistance of bearing materials. However, traditional PTFE materials struggle to meet the performance requirements for long-term stable operation in modern marine environments. To improve the wear resistance of PTFE, this study used alumina (Al₂O₃) particles with three different particle sizes (50 nm, 3 μm, and 80 μm) as fillers and prepared Al₂O₃/PTFE composites via the cold pressing and sintering process. Tribological performance tests were conducted using a ball-on-disk reciprocating friction and wear tester, with Cr12 steel balls as counterparts, under an artificial seawater lubrication environment, applying a normal load of 10 N for 40 min. The microstructure and wear scar morphology were characterized by scanning electron microscopy (SEM), and mechanical properties were measured using a Shore hardness tester. A systematic study was carried out on the microstructure, mechanical properties, friction coefficient, wear rate, and limiting PV value of the composites. The results show that the particle size of Al₂O₃ particles significantly affects the mechanical properties, friction coefficient, wear rate, and limiting PV value of the composites. The 50 nm Al₂O₃/PTFE formed a uniformly spread friction film and transfer film during the friction process, which has better friction and wear reduction performance and load bearing capacity. The 80 μm Al₂O₃ group exhibited poor friction properties despite higher hardness. The nanoscale Al₂O₃ filler was superior in improving the wear resistance, stabilizing the coefficient of friction, and prolonging the service life of the material, and demonstrated good seawater lubrication bearing suitability. This study provides theoretical support and an experimental basis for the design optimization and engineering application of PTFE-based composites in harsh marine environments. Full article

The insulating rod of aramid fiber-reinforced epoxy resin composites (AFRP) is an important component of gas-insulated switchgear (GIS). Under complex working conditions, the high temperature caused by voltage, current, and external climate change becomes one of the important factors that aggravate the interface degradation between aramid fiber (AF) and epoxy resin (EP). In this paper, molecular dynamics (MD) simulation software is used to study the effect of temperature on the interfacial properties of AF/EP. At the same time, the mechanism of improving the interfacial properties of three nanoparticles with different properties (insulator Al₂O₃, semiconductor ZnO, and conductor carbon nanotube (CNT)) is explored. The results show that the increase in temperature will greatly reduce the interfacial van der Waals force, thereby reducing the interfacial binding energy between AF and EP, making the interfacial wettability worse. Furthermore, the addition of the three fillers can improve the interfacial adhesion of the composite material. Among them, Al₂O₃ and CNT maintain a large dipole moment at high temperature, making the van der Waals force more stable and the adhesion performance attenuation less. The Mulliken charge and energy gap of Al₂O₃ and ZnO decrease slightly with temperature but are still higher than AF, which is conducive to maintaining good interfacial insulation performance. Full article

In recent times, fiber reinforced polymer composite materials have become more popular due to their remarkable features such as high specific strength, high stiffness and durability. Particularly, Carbon Fiber Reinforced Polymer (CFRP) composites are one of the most prominent materials used in the field of transportation and building engineering, replacing conventional materials due to their attractive properties as mentioned. In this work, a CFRP laminate is fabricated with carbon fiber mats and epoxy by a hand layup technique. Alumina (Al₂O₃) micro particles are used as a filler material, mixed with epoxy at different weight fractions of 0% to 4% during the fabrication of CFRP laminates. The important objective of the study is to investigate the influence of alumina micro particles on the mechanical performance of the laminates through characterization for various physical and mechanical properties. It is revealed from the results of study that the mass density of the laminates steadily increased with the quantity of alumina micro particles added and subsequently, the porosity of the laminates is reduced significantly. The SEM micrograph confirmed the constituents of the laminate and uniform distribution of Al₂O₃ micro particles with no significant agglomeration. The hardness of the CFRP laminates increased significantly for about 60% with an increase in weight % of Al₂O₃ from 0% to 4%, whereas the water gain % gradually drops from 0 to 2%, after which a substantial rise is observed for 3 to 4%. The improved interlocking due to the addition of filler material reduced the voids in the interfaces and thereby resist the absorption of water and in turn reduced the plasticity of the resin too. Tensile, flexural and inter-laminar shear strengths of the CFRP laminate were improved appreciably with the addition of alumina particles through extended grain boundary and enhanced interfacial bonding between the fibers, epoxy and alumina particles, except at 1 and 3 wt.% of Al₂O₃, which may be due to the pooling of alumina particles within the matrix. Inclusion of hard alumina particles resulted in a significant drop in impact strength due to appreciable reduction in softness of the core region of the laminates. Full article

Biomimetic restorative protocols aim to preserve natural tooth structure while enhancing restoration longevity. This in vitro study aimed to evaluate the shear bond strength (SBS) in the repair of additively and subtractively manufactured CAD/CAM materials using bulk-fill resin composites and to assess the effect of thermocycling. Forty rectangular specimens (14.5 × 7 × 3 mm) were prepared from Grandio Blocs (GB, VOCO) and VarseoSmile Crown^Plus (VS, BEGO), and thermocycled (5000 cycles, 5–55 °C, 20 s dwell time). All surfaces were roughened with 50 μm Al₂O₃. Samples were repaired using VisCalor (VCB, VOCO) and Charisma Bulk Flow One (CBO, Kulzer) composites (n = 10 per group) with their respective adhesives. Each group was further divided into immediate and post-thermocycling subgroups. All specimens were tested under shear force until failure, and failure types were examined under a stereomicroscope. Representative samples were examined by SEM to evaluate filler morphology. Statistical analysis was performed with SPSS v23 (p < 0.05). No statistically significant differences in SBS were found between groups (p > 0.05). Mean SBS values were highest in VS-CBO and lowest in GB-CBO. Cohesive failures were more frequent in immediate groups, while adhesive failures predominated after thermocycling. Bulk-fill composites did not influence the repair bond strength of indirect materials. Thermocycling affected the failure type, though not the SBS values. Full article

As one of the most widely used packaging materials, epoxy composite (EP) offers excellent insulation properties; however, its intrinsic low thermal conductivity (TC) limits its application in high-frequency and high-power devices. To enhance the TC of EP, six highly thermally conductive inorganic fillers, namely, Al₂O₃, MgO, ZnO, Si₃N₄, h-BN, and AlN, were incorporated into the EP matrix at varying contents (60–90 wt.%). The resulting epoxy molding compounds (EMCs) demonstrated significant improvement in thermal conductivity coefficient (λ) at high filler contents (90 wt.%), ranging from 0.67 W m⁻¹ K⁻¹ to 1.19 W m⁻¹ K⁻¹, compared to the pristine epoxy composite preform (ECP, 0.36 W m⁻¹ K⁻¹). However, it was found that the interfacial thermal resistance (ITR) between EP and filler materials is a major hindrance restricting TC improvement. In order to address this challenge, graphene nanosheets (GNSs) and carbon nanotubes (CNTs) were introduced as additives to reduce the ITR. The experimental results indicated that CNTs were effective in enhancing the TC, with the optimized EMC achieving a λ value of 1.14 W m⁻¹ K⁻¹ using 60 wt.% Si₃N₄ + 2 wt.% CNTs. Through the introduction of a small amount of CNT (2 wt.%), the inorganic filler content was significantly reduced from 90 wt.% to 60 wt.% while still maintaining high thermal conductivity (1.14 W m⁻¹ K⁻¹). We propose that the addition of CNTs helps in the construction of a partial heat conduction network within the EP matrix, thereby facilitating interfacial heat transfer. Full article

This study attempts to use fly ash as the brazing filler additive to increase the sustainable use of coal-fired power plant by-product materials. The experimental results show that adding 5 wt% fly ash into the Ag paste filler contributes to the interfacial reactions in heterogeneous reactive air brazing (RAB) of the ZrO₂ and Crofer alloy. The Ag-rich phase dominates the brazed zone. The interfacial reaction layers contain oxidation of the Cu-Ti coating layer, Crofer alloy, and the Si/Al-rich oxides from the fly ash particles. The 5% fly ash RAB joint maintained airtightness for 280 h under 2 psig helium at room temperature. When the test temperature was raised to 600 °C for 24 h, the pressure of the joint assembly still did not drop. When the fly ash addition was increased to 10 wt%, the joint assembly was no longer leak-free at room temperature. Many visible voids and cracks exist in the brazed zone and at the ZrO₂/braze and braze/Crofer interfaces. A high volume fraction of the fly ash particles results in many brittle Si/Al-rich oxides in the joint after RAB, and the fracture of these oxides significantly deteriorates the airtightness of the joint. This study shows the feasibility and potential of introducing 5 wt% fly ash particles to the Ag-rich paste filler during the RAB of ZrO₂ and Crofer for airtight applications. Full article

As the communication band gradually approaches the terahertz (THz) range, there is an urgent need to explore materials with ideal dielectric properties for THz communication devices. Nevertheless, most polymers present a low dielectric constant (Dk), and the regulation of their dielectric properties in the THz range has rarely been reported. In this work, the isotactic polypropylene (iPP)/α-Al₂O₃ whisker composites were synthesized and their THz dielectric parameters were optimized. The Dk values increased from 2.23 to 3.13 with filler (α-Al₂O₃ whisker) concentration, ranging from 0 to 20 vol%, but were almost independent of the test frequency. The loss tangent (Df) values presented an increasing tendency along with both filler concentrations and test frequency. All composites exhibited Df values of less than 4.0 × 10⁻³. Particularly, the dielectric properties of composites can be further regulated by adjusting the orientation direction of the whisker fillers. The orientation of the whisker fillers was adjusted via the injection molding method. Along the direction of the whisker orientation distribution, the composites exhibit higher Dk values and lower Df values. This work presented a schematic to design polymer composites with higher Dk but controlled Df in the THz range and is significant for the development of advanced materials-based THz devices. Full article

Combining large-sized flaky alumina and spherical alumina as thermally conductive fillers in thermal management materials can effectively establish heat-conducting pathways and significantly increase the system’s heat conduction value. Conventional preparation processes typically produce flaky alumina with a small size and a low diameter-to-thickness ratio, often failing to meet the requirements for applications as thermally conductive fillers. By combining the conventional molten salt method with gas-phase fluoride ions, this study produced large-sized, flaky α-Al₂O₃ with a diameter ranging from 10 to 50 μm, a thickness of 200–500 nm, and a diameter-to-thickness ratio between 80 and 150. This study revealed that as the size of the flaky alumina increases, so does the thermal conductivity value, but the viscosity also rises, and the limit filling rate decreases. When 3% of the large-sized flaky alumina was added to the compounded thermal conductive filler system, the thermal conductivity of the gel increased by 25%. Full article

Global coal consumption is continuously increasing. It is still the primary fuel used in power plants. Despite policies in the European Union aimed at reducing coal consumption, there are countries in the world where coal use continues to rise (China and India are the largest consumers of coal). Coal combustion produces waste, 70% of which is fly ash. It consists mainly of SiO₂ and Al₂O₃. Fly ash also includes Fe₂O₃, TiO₂, MgO, K₂O, and CaO. This article describes various methods of using fly ash. Fly ash can be used in the cement industry, as a filler in materials, in zeolite synthesis, in cenosphere separation, in agriculture, in water purification, in road construction as an asphalt filler, and in mine backfilling. An interesting method of using fly ash as a filler in the production of rigid polyurethane foam was also described. The article concerns potential uses in accordance with the principles of a Circular Economy. The environmental, energy, and material aspects are discussed. Full article

The grain growth in the fusion zone (FZ) and heat-affected zone (HAZ) of metal inert gas (MIG) welding processes negatively affect the mechanical properties of aluminum alloy MIG welds used in automotive components. Although the addition of Sc- and Zr-based filler wires can refine weld microstructures and enhance the mechanical properties, conditions resembling actual automotive component joints have not been sufficiently investigated. In this study, 5083-O aluminum alloy base material was welded into butt and lap joints using conventional 5000-series aluminum alloy filler wires (Al-5.0Mg) and wires containing Sc and Zr (Al-4.8Mg-0.7Sc-0.3Zr) under various heat input conditions. The mechanical properties of the welds were evaluated via tensile tests, and the microstructures in the FZ and HAZ were analyzed. In butt joints, Al-4.8Mg-0.7Sc-0.3Zr exhibited a finer and more uniform grain structure with increased tensile strength compared with those welded using Al-5.0Mg. The microstructure became coarser with the increased heat input, and the tensile strength tended to decrease. In lap joints, the tensile-shear strength of Al-4.8Mg-0.7Sc-0.3Zr was higher than that of Al-5.0Mg; it further increased with the increase in the amount of deposited metal. The coarsening of the microstructure with the increased heat input was disadvantageous for the tensile-shear strength, and the increased weld size offset the adverse effects of the coarse microstructure. These results indicate that the heat input and the amount of deposited metal must be optimized to ensure stiffness in various joints of automotive components. Full article

Civil briquette furnace slag (FS), as a type of industrial solid waste, is not currently being recycled as a resource by the building materials industry. This study focuses on the potential of FS in the formulation of alkali-activated materials (AAMs) compared with calcium carbide slag (CS). This study encompasses three distinct AAM systems: alkali-activated fly ash alone (AAFA), fly ash–slag powder blends (AAFB), and slag powder alone (AABS). Electrical conductivity, fluidity, drying shrinkage, and flexural and compressive strengths were also assessed. Advanced characterization techniques, including SEM-EDS, XRD, FTIR, and TG-DSC, were utilized to examine the morphology, mineralogy, and reaction products. Despite the chemical similarity between FS and CS, FS exhibits limited active chemical components (SiO₂, Al₂O₃, CaO, and MgO) and primarily functions as a physical filler, and thus lacks the chemical binding properties of CS. FS has a positive effect on the long-term compressive strength of the AABS system but not on the AAFA and AAFB systems. The NaOH-activated SP mortar sample with 20% FS reaches a compressive strength of 29.8 MPa at 360 days. The binding strength in AAMs incorporating FS is predominantly attributed to the gel formation within the alkali-activated matrix. This research offers valuable insights into the strategic use and substitution of CS, FS, and other silico–aluminon additives within the context of AAMs development. Full article

This study presents data on the use of shungite ore (the Bakyrchik deposit, Kazakhstan) and its concentrate as fillers in elastomer composites based on nitrile butadiene rubber. In addition to carbon, these shungite materials contain oxides of Si, Fe, K, Ca, Ti, Mn, and Al. The shungite concentrate was obtained through a flotation process involving five stages. The chemical composition analysis of these natural fillers revealed that during flotation, the carbon content increased 3.5 times (from 11.0 wt% to 39.0 wt%), while the silicon oxide content decreased threefold (from 49.4 wt% to 13.6 wt%). The contents of oxides of K, Ca, Ti, Mn, and Al decreased by less than 1%, and iron oxide content increased by 40% (from 6.7 wt% to 9.4 wt%). The study explored the impact of partial or full replacement of carbon black (CB) of P 324 grade with the shungite ore (ShO) and the shungite concentrate (ShC) on the vulcanization process and the physical–mechanical properties of the rubber. It was found that replacing CB with ShO and ShC reduces Mooney viscosity ML (1 + 4) 100 °C of the rubber compounds by up to 29% compared to the standard CB-filled sample. The use of the shungite fillers also increased scorch time (t_s) by up to 36% and cure time (t₉₀) by up to 35%. The carbon content in the shungite fillers had little influence on these parameters. Furthermore, it was demonstrated that replacing 5–10 wt% of CB with ShO or ShC improves the tensile strength of the rubber. The results of the flotation enrichment process enable the assessment of how these shungite fillers affect the properties of the composites for producing rubbers with specific characteristics. It was also found that substituting CB with ShO or ShC does not significantly affect the rubber’s resistance to standard oil-based media. The findings indicate that Kazakhstan’s shungite materials can be used as fillers in rubber to partially replace CB. Full article

Thanks to the performance improvement introduced by micro sized functional fillers, application of epoxy composites for electrical insulation purposes has become popular. This paper investigates the dielectric properties of epoxy micro-composites filled with alumina (Al₂O₃). In particular, measurements of relative permittivity, dissipation factor, and electrical breakdown are performed, and a comprehensive statistical analysis on dielectric properties was conducted. AC breakdown strength (AC-BDS) was analyzed for normal distribution using four methods (Anderson–Darling, Shapiro–Wilk, Ryan–Joiner, and Kolmogorov–Smirnov). In addition, the AC-BDS was analyzed at risk probabilities of 1%, 5%, 10%, and 50% using Weibull distribution functions. Both normal and Weibull distributions were evaluated using the Anderson–Darling (A-D) statistic and p-value. Additionally, the log-normal, gamma, and exponential distributions of AC-BDS were examined by A-D goodness-of-fit test. The hypothesis test results of AC-BDS were fit by normal and Weibull distributions, and the compliance was evaluated by p-value and each method statistics. In addition, the experimental results of AC-BDS were fit by log-normal and gamma distributions, and the goodness-of-fit was evaluated by p-value and A-D testing. On the other hand, exponential distribution was not suitable for p-value and A-D testing. The results showed that the distributions of AC-BDS were the best using log-normal distribution. Meanwhile, statistical analysis results verified the apparent effect of temperature on dielectric properties using a paired t-test. The analysis results of this paper not only contribute to better characterization of epoxy/Al₂O₃ micro-composites but also introduce a comprehensive approach for performing statistical analysis for electrical insulation materials. Full article

The adsorption efficiency of Cr(VI) and anionic textile dyes onto MgAl-layered double hydroxides (LDHs) and MgAl-LDH coated on bio-silica (b-SiO₂) nanoparticles (MgAl-LDH@SiO₂) derived from waste rice husks was studied in this work. The material was characterized using field-emission scanning electron microscopy (FE-SEM/EDS), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), and X-ray photoelectron spectroscopic (XPS) techniques. The adsorption capacities of MgAl-LDH@SiO₂ were increased by 12.2%, 11.7%, 10.6%, and 10.0% in the processes of Cr(VI), Acid Blue 225 (AB-225), Acid Violet 109 (AV-109), and Acid Green 40 (AG-40) dye removal versus MgAl-LDH. The obtained results indicated the contribution of b-SiO₂ to the development of active surface functionalities of MgAl-LDH. A kinetic study indicated lower intraparticle diffusional transport resistance. Physisorption is the dominant mechanism for dye removal, while surface complexation dominates in the processes of Cr(VI) removal. The disposal of effluent water after five adsorption/desorption cycles was attained using enzymatic decolorization, photocatalytic degradation of the dyes, and chromate reduction, satisfying the prescribed national legislation. Under optimal conditions and using immobilized horseradish peroxidase (HRP), efficient decolorization of effluent solutions containing AB-225 and AV-109 dyes was achieved. Exhausted MgAl-LDH@SiO₂ was processed by dissolution/precipitation of Mg and Al hydroxides, while residual silica was used as a reinforcing filler in polyester composites. The fire-proofing properties of composites with Mg and Al hydroxides were also improved, which provides a closed loop with zero waste generation. The development of wastewater treatment technologies and the production of potentially marketable composites led to the successful achievement of both low environmental impacts and circular economy implementation. Full article