Narrow Results

Eco-friendly, nontoxic and high-energy storage materials are very important for flexible electrode materials. Bi₄Ti₃${\text{O}}_{12}$ lead-free, perovskite phase may prove suitable as filler in composites for electrode materials because of its large spontaneous polarization. We have synthesized Bi₄Ti₃${\text{O}}_{12}$/polystyrene (BTO/PS) composites and carried out their structural, morphological and bonding studies with the help of X-ray diffraction (XRD), scanning electron microscopy (SEM) and Fourier transform infrared spectroscopy (FTIR), in that order. Dielectric measurements in the broad frequency range of synthesized composites determined by Impedance analyzer. We observed that the dielectric constant of composites increased with filler concentration and decreased with applied field frequency. Bi₄Ti₃${\text{O}}_{12}$/PS composites can be good electrode materials.

We analyze a random resistor–inductor–capacitor (RLC) lattice model of two-dimensional metal–insulator composites. The results are compared with Bruggeman's and Landauer's Effective Medium Approximations where a discrepancy was observed for some frequency zones. Such a discrepancy is mainly caused by the strong conductivity fluctuations. Indeed, a two-branches distribution is observed for low frequencies. We show also by increasing the system size that at p_c the so-called Drude peak vanishes; it increases for vanishing losses.

Classical percolation theory is concerned with the onset of geometrical connectivity and the accompanied onset of electrical connectivity in disordered systems. It was found, however, that in many systems, such as various composites, the geometrical and electrical onsets of the connectivity are not simultaneous and the correlation between them depends on physical processes such as tunneling. The difference between the above two types of systems and the consequences for the electrical transport properties of the latter composites have been largely ignored in the past. The application of scanning local probe microscopies and some recent theoretical developments have enabled a better understanding of the latter systems and their sometimes "strange" behavior as bona fide percolation systems. In this review we consider the above issues and their manifestation in three types of systems: Carbon Black–Polymer composites, metal–insulator cermets and hydrogenated microcrystalline silicon.

The TiAl3/Al2O3 metal-ceramic composite was synthesized using high energy ball milling, powder compaction and thermal treatment. Micron sized powders of titanium oxide (TiO2) and aluminum were subjected to high energy ball milling under an argon protected atmosphere. Milling of this powder mixture although reduced crystallites sizes to a nano scale, did not result in a reaction between the reactants. Further compaction of the milled powder and annealing, paved the way to a reduction reaction and led to the formation of an ultrafine grained composite structure. The reaction appeared to proceed through two-steps. Titanium oxide was first reduced to TiO and later on, TiO was reduced to Ti. The resulting Ti was alloyed with extra Al to produce TiAl3 intermetallic in which alumina particles were dispersed. Also, mechanical activation was found to reduce the reaction temperature between Al and TiO2. The morphology and phase composition of the milling products were evaluated by scanning electron microscopy (SEM) and X-ray diffraction (XRD) analysis.

Mg-Cu-Zn ultrafine eutectic composites with different length scale heterogeneity, consisting of micrometer size dendrites and/or ultrafine scale bimodal eutectics, exhibit high yield strength as well as good plasticity at room temperature compression. Among these alloys, micron-scale α-Mg dendrites reinforced ultrafine eutectic composites exhibit high yield strength of 310 ~ 420 MPa and large plasticity of 7 ~ 12%. Meanwhile, a Mg₇₂Cu₅Zn₂₃ alloy comprising a bimodal eutectic structure without the micron-scale α-Mg dendrites shows the optimized mechanical properties the highest yield strength of 455 MPa combined with a considerable plastic strain of ~5%.

Ultrafine eutectic alloys have been developed in Ti-Ni, Ti-Fe and Ti-(Ni, Fe)-Sn alloys. The Ti₇₆Ni₂₄ and (Ti₇₄Ni₂₆)₉₇Sn₃ ultrafine eutectic alloys consist of a mixture of α-Ti and Ti₂Ni phases, and β-Ti(Sn) and Ti₂Ni phases, respectively, whereas the Ti_70.5Fe_29.5 and (Ti_70.5Fe_29.5)₉₇Sn₃ alloys are composed by a mixture of β-Ti(Sn) and FeTi phases with relatively spherical colony. The compression tests of Ti₇₆Ni₂₄, (Ti₇₄Ni₂₆)₉₇Sn₃ and Ti_70.5Fe_29.5 ultrafine eutectic alloys reveal a strength of 1400 ~ 1800 MPa with very limited plastic strain of 0.1 ~ 1%. On the contrary, a (Ti_70.5Fe_29.5)₉₇Sn₃ alloy exhibits high strength of 2270 MPa with enhanced plastic strain of 3.1%. Based on these results, it is feasible to suggest that the eutectic morphology and interfacial coherency between the Ti solid solution and intermetallic phases influence to control the macroscopic plasticity of the Ti-Ni and Ti-Fe ultrafine eutectic alloys.

A new kind of composite with a bi-continuous structure was produced by pressure infiltrating melt Zr_41.2Ti_13.8Cu_12.5Ni₁₀Be_22.5 into porous SiC which was made by powder metallurgy. Microstructure investigations of the composite show that the melt alloy was fully infiltrated into the voids of porous SiC and quenched into amorphous state. Both the amorphous alloy and the porous SiC exhibit a three-dimensional interconnected net structure. The study of thermal properties reveals that the addition of porous SiC reduces the width of supercooled liquid region of the composite. The bi-continuous composite presents 2% plastic strain and ultimate strength of 1250MPa.

Porous Si₃N₄-SiO₂-BN composites were prepared by adding starch as both pore former and consolidator. Bruggeman effective-medium model, Maxwell-Garnett model and logarithmic model were used to describe and predict the dielectric constant of porous Si₃N₄-SiO₂-BN ceramics. Relative dielectric constant of porous Si₃N₄-SiO₂-BN composites decreases with the increase of apparent porosity within limits, and these models can forecast the change of the dielectric constant of the porous ceramics quite well. The minimum relative dielectric constant is 2.5 at the apparent porosity of 0.555 at room-temperature. The relationship between dielectric constant and temperature were investigated. It was found dielectric constant varied a lot with the increase of temperature, and Debye relaxation theory was employed to explain the variation of the dielectric constant with temperature increment. But the Debye relaxation theory can not explain the reason of variation of dielectric constant at the temperature range from 300°C to 900°C. To ascertain the cause of changes of dielectric constant at this temperature region, differential scanning calorimentry (DSC) measurement was performed. In this temperature region, phase transition behavior occurs at nearly 300°C in the porous composites. The new phase probably has a tidy large dielectric constant, and the dielectric constant increases sharply.

The superconductors Bi₂Sr₂CaCu₂O_x (Bi2212 ) and Ag/Bi2212 composites samples were prepared by the powder metallurgy method. The frictional behaviors of Bi2212 pins in contact with stainless steel plate were examined from -196 to 20°C on friction and wear tester. When the temperature was lower than the superconducting transition temperature, the friction coefficient of Bi2212 dropped sharply, and it kept 0.11 with increase of the test time. The microstructure and morphology of Ag/Bi2212 composites were investigated by means of X-ray diffraction (XRD), transmission electronic microscope (TEM) and high resolution transmission electronic microscope (HRTEM). The elemental compositions of the worn surfaces of Ag/Bi2212 composites were determined by using energy dispersive X-ray analysis (EDXA). The results showed that the superconducting structure of Bi2212 was not changed and Ag was distributed in the Bi2212 matrix. Ag doping improved the toughness of oxide ceramics Bi2212. The friction test results of Ag/Bi2212 composites showed the tribological properties were improved at room temperature. The friction coefficient of 10%Ag/Bi2212 against stainless steel showed a lower value (0.2) and the wear rate of 15%Ag/Bi2212 was minimum (9.5×10^-5 mm³·(N·m)^-1 ). The lubrication of soft metallic film and load of hard matrix were the mechanism of decreased friction and anti-wear of Ag/Bi2212 composites.

The effects of impurities on the generation of voids in composites fabricated by vacuum-assisted resin transfer molding was investigated to help reduce mechanical weakening in large structures. Impurities were intentionally inserted into laminates, which were then observed optically. Internal voids were generated in specimens with impurities of 2 – 3mm thickness. The voids grew as the impurities' thicknesses increased to 4 – 5 mm. The voids' diameters were proportional to the thickness of the impurity. Void generation was shown to depend on the thickness of impurities. Environmental control during vacuum-assisted resin transfer molding was shown to be important for ensuring the quality of the resulting composites.

The purpose of this study is to determine the correct estimation of the concept design for high strength composites applied to the intermediate shaft of a ship. Recently, the application of composites has increased in the ship industry area for weight reduction and marine environmental protection. Carbon fiber reinforced plastic (CFRP) has characteristics of high strength, high elasticity and high corrosion resistance. Therefore, it is a suitable material for reducing the weight of the ship. So, weight reduction and high fuel efficiency can be expected. However, little research has been carried out on the technology development of a composites shaft for ships. In this study, analysis is carried out on the application of a high-strength CFRP shaft.

The purpose of this study is to determine the correct estimation of laminate patterns for high-strength composites applied to a ship. Recently, the need for developing a ship component has been increasing to improve the capability of maritime operations. Composites with excellent specific strength and specific stiffness are emerging as next-generation materials. In the composite material, the mechanical properties vary depending on the laminated pattern of the reinforcing material. Therefore, in this study, the properties of the composite materials were calculated using the computer simulation program. The ply calibration performance results show that the initial values of the mechanical properties of the carbon/epoxy composites in the E11 direction are higher than the calculated values, and the remaining values are the same. The laminate mechanics results show that the tensile strength in the S11T direction was 1515 MPa, which is almost the same as the initial value of 1500 MPa.

In order to overcome the weak bonding force between the interface of the composite materials, research for improving the interfacial bonding force by adding nanoparticles has been actively conducted. However, despite the improvement of characteristics through the addition of nanoparticles, it is not widely used because the particles are relatively expensive and it is difficult to control the aggregation between the particles. In this study, we compared the mechanical properties of relatively low-cost halloysite nanotube (HNT) nanoparticles with micro-sized milled carbon. Based on the similar mechanical properties of the composites with two particles added, we found that milled carbon could replace HNT particles. In addition, if the cohesion of HNT is reduced based on the strengthening effect of milled carbon having a relatively low cohesive strength, it is expected that the strengthening effect can be obtained more than that found in the existing studies.

Copper matrix composites reinforced with graphene nanoplatelets (GNPs) were prepared by vacuum hot pressing of ball milled mixtures of powders. Two grades of GNPs were used; one with average thickness of 2 nm and average lateral size of 6 $\mu$m and another with much larger lateral size of 80 $\mu$m. Microstructure and properties of as-prepared composites containing 10 vol.% GNPs were studied. The GNPs sheets are uniformly distributed and well aligned in the Cu matrix. The microstructure observation shows that the GNPs-2–6 exhibits a better dispersion in the Cu matrix than GNPs-2–80. The addition of fine GNPs-2–6 lead to $\sim$31% higher tensile strength and approximately same electrical conductivity of the Cu matrix, while the GNPs-2–80/Cu composite only shows a $\sim$15% increase of tensile strength and a lower electrical conductivity than the Cu matrix.

The purpose of this study is to develop a lightweight design model for an 18ft leisure boat. The existing leisure boat is manufactured using glass fiber-reinforced plastics (GFRP) material and the hand lay-up process. Carbon fiber-reinforced plastics (CFRP) was applied to the new design to reduce the boat’s weight, while an automated tape laying machine was applied to the lightweight boat’s manufacturing process to increase boat manufacturing productivity. The newly designed CFRP model is 25% lighter than the existing GFRP model. It was confirmed that the newly designed lightweight hull has sufficient structural integrity compared to the existing hull through the structural integrity evaluation by the FEA.

In this paper, cross-plane thermal conductivities of the nanoporous glass alumina film (NGAF) and its composites (Ag/NGAF, with Ag nanowires embedded in) were measured. And a model was setup to predict the thermal conductivity of the nanoporous material. Results show that the thermal conductivity of the NGAF is about 50 times smaller than that of the ceramic alumina. It is about 0.5 W ⋅ m^-1⋅ K^-1 and depends on both the pore radius and the porosity. The thermal conductivity of the Ag/NGAF is not larger than that of the NGAF. The contact resistance and the unfilled space between Ag nanowires and the matrix are responsible for that.

With the improvements in quality of life and better awareness about the requirement for a secure environment, fire-resistant materials have gradually attracted the world’s attention and recognition. This paper investigates a proprietary process to manufacture glass fiber (GF) reinforced brominated-epoxy (BEP) flame retardant composites through pultrusion. BEP resin is manufactured with fillers as matrices, GF as reinforcements for pultrusion. The dynamic mechanical properties (DMA) and flame retardant properties of the GF reinforced BEP composites manufactured through pultrusion have been investigated. The DMA test showed higher dynamic storage modulus $(E^{\prime })$ and lower curve of tan $\delta$ of pultruded composites when the filler content, postcure temperature and postcure time increased. At the same time, the glass transition temperature $(T_g)$ of the pultruded composites were shifted to a higher temperature when the filler content, postcure temperature and postcure time increased. From the flame retardant test for UL-94 and limited oxygen index (LOI), all of the pultruded GF reinforced BEP composites as well as the BEP resin showed excellent flame retardant properties.

A strategy for continuous fabrication of a microscale 3D-patterned hybrid composite film composed of alumina and acrylate resin was developed using roll-to-roll production. Conventional thermal curing was replaced with a UV curing procedure to facilitate rapid and economical processing. A seamless engraved soft urethane mold was first produced using a patterned metal roll. Subsequently, alumina and acrylate resin were cured on the engraved mold via UV irradiation to produce patterned hybrid films. The dispersion of alumina particles in acylate resin was enhanced by utilizing amine acrylate. Photopolymerization was measured using Fourier-transform infrared spectroscopy. The morphology of the soft engraved mold and the patterned hybrid film was investigated using scanning electron microscopy.

In this study, a three-point bending test was carried out to determine the mechanical properties of hexagonal-shaped honeycomb core sandwich panels made of jute yarn with two distinct fiber orientations. A custom-made handloom was used to weave the unidirectional jute mat, and hand-layup with the cold press process was applied to fabricate the hexagonal honeycomb sandwich panel. To explore the effectiveness of different natural fibers for producing honeycomb core sandwich panels, a Finite Element Method (FEM) analysis was performed on different natural fibers with different fiber orientations. The resistance to environmental deterioration of bending properties was also investigated. Overall, this work offers perceptive information about the mechanical characteristics of sandwich panels made of jute honeycomb core and their behavior under various climatic circumstances, which may be relevant in a variety of engineering applications. Finally, it is noteworthy that the mechanical properties of jute fibers are anisotropic, which implies that their strength varies with the direction of loading. Sandwich panels with horizontal fiber orientation of hexagonal honeycomb core withstand a 36% higher bending strength than those with vertical fiber orientation.

In this work, we propose a new model for the dielectric constant and thermal conductivity, and apply it to the design of composites with low dielectric constant and high thermal conductivity based on fractal theory and effective medium theory. In particular, we use this model to prepare porous AlN/BN/SiOC composites with low dielectric constant and high thermal conductivity in different component fractions. We successfully synthesize ceramic samples with low dielectric constants $(<3)$ and high thermal conductivity ($\ge 2\mathrm{\text{W}}\cdot {\mathrm{\text{m}}}^{-1}\cdot {\mathrm{\text{K}}}^{-1}$). These results indicate that the proposed fractal design is valid.