Applied Mechanics and Materials Vols. 719-720

Abstract: Experiments of vertical unsteady-state directional solidification were carried out in order to permit the influence of copper alloying to Al-Si alloys on the scale of secondary dendritic arm (λ₂) to be investigated. The microstructures of Al-nSi-3wt%Cu alloys, with “n” equal to 5.5wt%Si and 9.0wt%Si, were characterized and correlated with solidification thermal parameters: the growth rate (V_L), the tip cooling rate (Ṫ) and the local solidification time (t_SL). A comparative analysis between the present results and those from the literature related to the secondary dendrite growth during directional solidification of Al-nSi alloys is also conducted. It is shown that the addition of Cu to both Al-nSi alloys decreases λ_2, and experimental growth laws relating λ₂ to V_L and Ṫ_L are proposed for the ternary alloys examined. The experimental scatter of λ₂ is also compared with the only theoretical dendritic growth model from the literature for multicomponent alloys, and it is shown that the theoretical predictions overestimate the present experimental results.

Abstract: The Ni-Cr-Co based superalloy, Inconel 740, was corroded between 700 and 900°C for 20 h in 75% Na₂SO₄-25% NaCl salt. The scale consisted primarily of Cr₂O₃, (Ni,Co)Cr₂O₄, NiO, and Ni₃S₂. During corrosion, oxidation dominated rather than sulfidation. The scale was neither dense nor compact owing to the formation of the (oxides, sulfides)-mixed scale where Na₂SO₄ and NaCl were incoporated.

Abstract: A hyperbranched poly (butylene adipate) (HPBA) polymer was compared with a commercial dendritic polyol (Boltorn H311) as toughening agent for a commercial one-part epoxy resin, Cycom 890 RTM. Both modifiers were added in a weight percentage 1, 3, 5 and 10 %. Blends obtained were characterized through DMA and impact resistance (K_IC). SEM morphology were also evaluated. The toughness improvement was achieved without substantial impairment on thermomechanical properties. Fractography analysis has evidenced the fracture standard changing from brittle to ductile by modifiers addition.

Abstract: A conducting solid biodegradable polymer electrolytes based carboxymethyl cellulose (CMC) doped ammonium thiocyanate (NH₄SCN) system with concentration in the range 0 – 25 wt.% of NH₄SCN have been prepared via solution casting method. The impedance study of CMC-NH₄SCN system was measured via Electrical Impedance Spectroscopy (EIS) in the temperature range 303 K – 353 K. The highest ionic conductivity at room temperature (303 K) is 6.48 x 10^-5 Scm^-1 for sample containing 25 wt.% NH₄SCN. The temperature dependence of CMC-NH₄SCN system was found to obey the Arrhenius behaviour where the ionic conductivity increases with increase of temperature. Dielectric data were analyzed using complex permittivity, Ɛ_i for sample with the highest ionic conductivity at various temperatures and found was non Debye behavior. The conduction mechanism of the charge carrier of CMC-NH₄SCN system can be presented by quantum mechanical tunneling (QMT) model.

Abstract: Porous graphene has been easily synthesized by hydrothermal treating reduced graphene oxide in alkaline solution, and the porous structure was confirmed by transmission electron microscope. When used as supercapacitor electrode, porous graphene holds a specific capacitance of 88 F g^-1 at an ultra-high current density of 50 A g^-1, an increase of about 83% compared with that for the pristine graphene sheets. The results demonstrate that porous graphene opens a new and short way for ion transportation. Furthermore our findings provide a novel strategy to fabricate porous graphene and the process is simple, low-cost and environmentally friendly.

Abstract: Porous graphene is a collection of graphene-related materials which exhibits properties distinct from those of graphene, and it has widespread potential applications in various fields. Several approaches have been developed to produce porous graphene. However, the large-scale production of porous graphene nanosheets still remains a great challenge. Moreover, the costs of some methods are prohibitive for its commercial production and the processes are too complicated and time-consuming. In this work, we propose a simple and green method by which graphene nanosheets can be etched by sodium hydroxide under autogenous pressure at 180 °C. The morphologies and surface elements of the porous graphene nanosheets and sizes of pores were characterized. It is demonstrated that the one-step etching of graphene nanosheets is an effective method to obtain large-scale porous graphene nanosheets with high and uniform porosity. The pores in the porous graphene nanosheets were 6 nm depth (the same as the thickness of the graphene nanosheets) and 30-50 nm width.

Abstract: TiAlCrSiN thin films consisting of alternating TiCrN and AlSiN nanolayers were deposited by cathodic arc plasma deposition, and oxidized at 1000°C in air. When oxidized for 10 h, about 1 μm-thick oxide sale formed, and its surface was covered with numerous tiny oxide crystallites. When oxidized for 30 h, about 2.5 μm-thick oxide scale formed, and began to spall from the surface. When oxidized for 80 h, the oxide sale was about 12.2 μm-thick. The film had a reasonable oxidation resistance due mainly to Al, Cr, and Si, which formed protective oxides.

Abstract: This study presents comparisons between the morphologies and photoluminescence properties of tin oxide (SnO₂) nanoparticles prepared by two methods, namely the sol gel and the co-precipitation methods. The characteristics of the particles were analyzed using X-ray diffraction (XRD), fourier transform infrared spectroscopy (FTIR), and scanning electron microscopy (SEM). The particles prepared using the sol-gel method have a finer particle size and more spherical shape. However, no significant difference was observed in terms of morphology and homogeneity in the samples produced by either the co-precipitation or sol-gel methods. In contrast, the photoluminescence study shows that the emission peak for powder prepared using the sol-gel method was higher than that of the co-precipitation method.

Abstract: BCN nanoparticles sandwiched between carbon nanosheets were synthesized with the P123 and borate ammonium under nitrogen atmosphere. The samples were characterized by SEM, TEM, and EELS. The SEM and TEM images show BCN nanoparticles are attached on the carbon nanosheets. Cyclic voltammetry (CV) and galvanostatic charge-discharge measurements are used to evaluate electrochemical properties of the composites. The samples show the specific capacitance of 102 F/g at current density of 200mA/g and good durability.

Abstract: This study proposed a method to improve the mechanical properties and thermal conductivity of epoxy composites by incorporating multi-walled carbon nanotubes (MWCNTs) and multi-graphene platelets (MGPs) hybrid materials. The MWCNT can bridge adjacent MGPs and inhibit their aggregation effectively, leading to an increased contact surface area between MGP/MWCNT hybrid materials and epoxy matrix. From observing the fractured surface of composite by scanning electron microscope, MWCNT/MGP hybrid materials exhibited better compatibility than individual MWCNT and MGP did.The tensile strength of GD400-MWCNT/MGP/epoxy composites was 35.4% higher than that of epoxy, compared to only a 0.9% increase in tensile strength for MGP/epoxy composites. Thermal conductivity enhanced by 146.9% through incorporating MWCNT/MGP hybrid materials and 23.9% for MGP fillers, compared to non-derivatised epoxy.