Advanced Materials Research Vols. 26-28

Abstract: Carbon blacks were used as catalysts for hydrogen production through hydrocarbon decomposition. The aim of this work is to find suitable conditions for decomposition reaction to cut down the net cost of hydrogen production. Carbon blacks after hydrocarbon decomposition under different operation conditions were mixed with NBR rubber. The surface area of carbon black increased with low weight gain in methane decomposition caused by carbon deposits on the surface of carbon black aggregates, and the decrease of surface area with further weight gain might be due to the carbon deposits adhering to each other and forming bigger aggregates. The same results were gotten from decomposition of mixture gas of methane and propane. The surface area of carbon black always decreased with the development of propane decomposition reaction. With the same carbon black loading, the composites filled by carbon blacks with low weight gain in methane and methane-propane mixture gas decompositions showed higher tensile strength than those mixed with raw carbon blacks, but there were no significant differences in 300% modulus. With the increase of carbon blacks loading in all composites, 300% modulus and tensile strength always increased. The surface resistivity of composites showed that it was much easier for carbon blacks with low weight gain in methane and methane-propane mixture gas decompositions to dissipate well in the in rubber system.

Abstract: Electromagnetic interference (EMI) shielding refers to the reflection and/or adsorption of electromagnetic radiation by materials, which acts as a shield against the penetration of the radiation through the shield. In this study, two directional carbon fibers reinforced composites with carbon nanotubes as fillers were studied for the high frequency electromagnetic properties and mechanical properties. Carbon nanotubes were prepared by a catalytic chemical vapor deposition method with ferrocene/xylene mixture. The electromagnetic insulating properties were measured by micro strip line method in this study. Electromagnetic interference shielding properties of composites were investigated in the frequency region of 0.3-6 GHz. The experimental results indicated that the EMI shielding effectiveness of carbon composite is sensitive to the existence of CNT.

Abstract: Shape memory alloy (SMA) has been used to improve the tensile strength of composite materials. Because it produces compressive residual stress in the matrix by using its shape memory effect. In order to fabricate a shape memory alloy composite, TiNi alloy and Al2024, Al6061 were used as reinforcing material and matrix, respectively. In this study, TiNi/Al2024 and TiNi/Al6061 shape memory alloy composites were made by the hot press method. The fatigue limit of a shape memory alloy composite determined the volume ratio and reduction ratio. The probabilistic stresslife curve (P-S-N curve) about the shape memory alloy composite makes up using statistical method.

Abstract: The superconductive MgB2/Al composite material with low and high volume fractions of particles were fabricated by our special 3-dimensional penetration casting (3DPC) method. The composite material showed homogeneous distribution of MgB2 particles in the Al-matrix with neither any aggregation of particles nor defects such as cracks or cavities. The critical temperature of superconducting transition (TC) was obtained via electrical resistivity and magnetization to be about 37 ~ 39K. The Meissner effect was also verified in the liquid He, in which a piece of the composite floated above a permanent magnet. Extruded rod and wire were successfully fabricated and they also showed onset TC of 39 K on their electrical resistivities as the same as the billet sample.

Abstract: Based on three dimensional cubic unit cell models containing several particulates with certain particulate arrangements, the monotonic tensile and uniaxial ratcheting behaviors of particulate reinforced metal matrix composites (i.e., T6-treated SiCP/6061Al composites) were numerically simulated by using elastic-plastic finite element code ABAQUS with help of newly developed user material subroutine (UMAT). In the simulations, the effects of different particulate arrangements inside the unit cell models on the monotonic tensile and ratcheting behaviors of the composites were discussed. It is shown that the effect of particulate arrangement on the ratcheting of the composite depends on the arranged modes and the number of particulates contained in the model, and the interaction between particulates can be represented reasonably by the cubic unit cell model with a suitable distribution of multi-particulates.

Abstract: Reactive infiltration is a manufacturing process of metal matrix composites with low cost and low environmental impacts. In this study, reactive infiltration of a NiO/Ti blended powder preform with molten Al was examined. Titanium powder as an infiltration aid was mixed with NiO powder by various blending ratios. The preform and the Al ingot were then heated together up to 1273K ~1673K and held at these processing temperatures for 60 minutes by an induction furnace in N2 gas atmosphere. After the heating process, the vertical cross section was observed to see whether the infiltration and the in situ reaction occurred successfully. Spontaneous infiltration of molten aluminum into the powder preform did not occur when either processing temperature or blending ratio of titanium was not sufficiently high enough. Spontaneous infiltration occurred when processing temperature and volume fraction of titanium were 1273K, 1373K and 15%, 20%. But when volume fraction of titanium was 25%, the preform exploded by an extremely high. It was confirmed that Al3Ti, Al3Ni2 and Al2O3 were formed after the infiltration.

Abstract: It is favorable to disperse fine strengthening particles under 1μm to expect the effective dispersion strengthening mechanism of metal matrix composites. In this research, TiB2 particle was synthesized in Al matrix by a combustion reaction and the influence of the powder blending ratio was examined in detail. The mole mixture ratio of Ti and B powder was fixed to B/Ti=2, and the blending ratio of Al powder was varied from 40 to 70vol%. The compacted blended powder was heated under an Ar atmosphere in an induction furnace, and heating was stopped immediately after the combustion reaction took place. The synthesized TiB2 particle became finer by increasing the blending ratio of Al, and the dispersion of particles about 0.3μm was achieved. However, large quantity of Al-Ti intermetallic compounds remained when 70vol% Al was blended, indicating that the combustion reaction was not completed in this specimen.

Abstract: The concrete-filled steel tubes have been widely used in buildings and civil structures. However the corrosion of the steel tubes results in the loss of load carrying capacities of the members and, therefore, there is a need for regular maintenance. To mitigate such maintenance issues and prevent the loss of load carrying capacity, FRP composite were suggested as the candidate material. A number of research works has shown that the use of FRP tubes produced by filament winding technique was very effective on the improvement of compressive strength of the concrete-filled FRP tubes (CFFT). However the filament wound FRP tubes did mot contribute to the increase of the flexural strength of a CFFT. In this paper, a new type of FRP tube which consists of several pultruded open sections assembled by filament winding technique is proposed to improve compressive strength as well as flexural strength of a CFFT. The load carrying capacity of proposed CFFT is discussed through the analytical investigation.

Abstract: Carbonaceous material has been used as an anode in lithium-ion secondary batteries due to their good stability during charging and discharging. But this material has the problems like irreversible capacity and low specific capacity that is about 372mAh/g. Because of the problems as stated above, silicon-based materials have been reported as possible anode materials to replace carbon. But they have high electrical resistivity and large volume changes associated with alloying and dealloying of lithium during electrochemical cycling. This study is performed to obtain higher capacity of anode material with a good cycle performance and to reduce electrical resistivity. It is expected that phosphor doping silicon and graphite mixture exhibit higher capacity than that of raw graphite and the doping of phosphorous will be able to decrease electrical resistivity of anode materials.

Abstract: The strengths of PFRP thin-walled columns are determined according to the modes of buckling which consist of local mode for short columns, global mode for long columns, and interaction mode between local and global modes for intermediate columns. Unlike the local and global buckling, the buckling strength of interaction mode is not theoretically predictable. Refined theoretical approaches which can account for different elastic properties of each plate component consisting of a PFRP thin-walled member are used. Based on both the analytical buckling loads and the experimentally measured buckling loads from literatures, the accuracies of Ylinen’s equation and modified AISC/LRFD column design equation for isotropic steel columns were compared. From the comparison, it was found that the modified AISC/LRFD column design equation is more suitable for the prediction of the buckling loads of PFRP thin-walled members than Ylinen’s equations.