Applied Mechanics and Materials Vols. 789-790

Abstract: The composition YSr₂Fe_3-xCo_xO₈ (for x = 0.5, 3.0) has been investigated as an alternative cathode material for Solid Oxide Fuel Cells (SOFCs). X-ray diffraction (XRD) pattern shows that the composition YSr₂Fe_2.5Co_0.5O₈ crystallizes with cubic symmetry in the space group Pm-3m and YSr₂Co₃O₈ crystallizes with tetragonal symmetry in the space group P4/mmm. Rietveld refinement of XRD data shows the cell parameter of the cubic YSr₂Fe_2.5Co_0.5O₈ is a = b = c = 4.1964(2) (Å) and tetragonal YSr₂Co₃O₈ is a = b = 9.8998(9) (Å) and c = 8.9617(6) (Å). Scanning electron microscropy (SEM) images show porous structure for both the samples, which is favourable as a cathode for Solid Oxide Fuel Cells.

Abstract: In this study, the parameters of the photo-electrochemical properties, such as the ground state geometries, excitation energy, electronic structures, optical properties and electronics transition of lawsone were investigated by using density functional theory ( DFT ) and time dependent - DFT with B3LYP/6-31G( d) method. The solvent effect was considered in the DFT calculations and compared with the value of vacuum. From the analyses of electronic and optical properties, it is found that the lawsone satisfy the condition for good conversion efficiency as DSSCs device.

Abstract: Environment and the health concerns due to the hazardous effects of lead resulted in significant activities to find a replacement for lead-contained solders for electronics industrial. Majority of the semiconductor industrial are now replacing lead solders with Tin-Silver-Copper (SAC 387) solder balls. However, dropped balls in SAC 387 for Ball Grid Array (BGA) products due to poor solder joint strength caused by high thermal stress are a major concern in the semiconductor industries. Polymer core inside the solder ball (polymer core/Cu/Sn) is thus integrated to improve the solder ball joint strength. The function of polymer core inside the solder ball is to absorb and released the stress better as compared to the SAC 387 solder ball. Since the diffusion rate of Cu is faster than the diffusion rate of Sn, hence, this could caused the Kirkendall voids tends to form in between the Cu and Sn IMC layer. This would affect the solder ball joint strength and causing drop balls issue. By implement with an extra of Ni layer to the polymer core solder ball (core/Cu/Ni/Sn), could reduce the diffusion from Cu to Sn, thus to overcome the Kirkendall voids and to further improve the solder ball joint strength. This research work studies the performance of the solder ball shear strength of the two types of solder balls applied to MAPBGA device. In this research, both SAC 387 and polymer solder balls were went through under AC (Autoclave) and TC (Temperature Cycle) reliability test up to 144 hours and 1000 cycles, respectively. Solder ball shear strength test was conducted via Dage 4000 series bond tester. From the research work results of the two types of solder balls, the ball shear strength were decreased with an increased of aging and cycles. Overall, it can be concluded that the polymer core solder ball with an additional of Ni layer showed better performance than the polymer core without Ni layer and SAC 387 solder balls, after subjected to the AC and TC reliability test.

Abstract: Application of microwave absorber (MWA) does affect the yield of microwave pyrolysis process. In this study, activated carbon and graphite have been used as microwave absorbers and the results were then compared with the microwave pyrolysis process without microwave absorber. The yield of solid and liquid increased while the yield of gas decreased with the application of MWA. Chemical functional group inside MWA also affected by the microwave pyrolysis process and energy content of MWA slightly increased from 24.54 MJ/kg to 29.57 MJ/kg and 32.17 MJ/kg to 32.24 MJ/kg for activated carbon and graphite, respectively.

Abstract: High modulus Poly (p-phenyleneterephalamide)(PPTA) fibers was prepared by heat drawing process, in which the fibers rearranged their structures for further improvements in their crystalline perfection, crystal line orientation. The modulus of PPTA fibers could be improved when fibers treated in an appropriate condition. The influences of heat treating time on the structures of the fibers and their properties were investigated by using two-dimensional wide-angle scattering (WAXS).

Abstract: The in vitro biostability of ethyl vinyl acetate (EVA) nanocomposite incorporating the organically modified montmorillonite (organo-MMT) was investgated as a new material for biomedical applications. The effects of compounding process and filler loadings on the ambient and in vitro (exposed in oxidizing condition, 37°C) mechanical properties were studied. We have observed that, the melt compounded EVA copolymer by internal mixer (Brabender plasticoder) achieved the highest ambient and in vitro mechanical properties at low nanofiller content (1wt% organo-MMT). In contrast, the melt compounded EVA copolymer by twin screw extruder achieved the highest ambient and in vitro mechanical properties at high nanofiller content (5wt% organo-MMT). We suggest that this was due to the capability of the twin screw extruder to provide greater shear force for the exfoliation and dispersion of the high content organo-MMT as compared to internal mixer (Brabender plasticoder). However, compounding by twin screw extruder caused more severe reduction in tensile toughness of the EVA containing 5 wt% organo-MMT, after this material was exposed to oxidative agent, 37°C. These studies show that the melt compounding method may bring significant effect to both the ambient and in vitro mechanical performance of the EVA nanocomposites, and hence further investigation towards optimization should be pursued.

Abstract: Synthetic based mud has been widely used in the drilling operation because of its good properties. However, prolonged exposure of the mud in high temperature causes degradation of the good mud properties because of chemical instability. Because of that concern, this study intends to improve the performance of SBM with nanosilica at different concentration in high temperature high pressure (HTHP) applications. nanosilica with size of 10-20 nm has been selected for this study. The involving parameters in this study include the manipulation of nanoparticles concentration by total mud weight between 0 to 1.78 wt. %, and performance at temperature up to 350°F. The enhanced formulation has given significant benefits by reducing the filtration up to 41.67% and act as the rheology modifier in HTHP condition. Moreover, the optimum amount of nanosilica is 0.71% of total mud weight to avoid further rheological and filtration degradation.

Abstract: Moving to a more sustainable and healthy future, the world has decided to invest on researches to make good use of waste vegetable oil rather than letting them clog the drains and hence, polluting the environment. One of the useful projects which uses these waste cooking oil is to synthesize polyols. Solidifying the polyols using cross linker produces a Sustainable Polymer (SP). These SP are compounded with the High-Density Polyethylene (HDPE) by melt-mixing using injection molding machine. Injection molding is capable of producing many useful products. Therefore, aiming to analyse the processing conditions of injection molding, the corresponding mechanical properties of the compounds produced were examined. The results indicated that increasing the SP content will increase the toughness of the compound if compared to neat HDPE. It was concluded that the processing temperature and composition of SP will both influence the quality and mechanical behavior of the injected polymer compounds.

Abstract: Presents a study of optical properties from transmittance measurements as a function of wavelength to CZTSe thin films (Cu₂ZnSnSe₄) using Bhattacharyya model and basic elements from the Swanepoel theory. The optical constants such as the absorption coefficient (α), the refractive index (n), the extinction coefficient (k) and physical properties such as gap (Eg), the real and imaginary part of the dielectric function (ε₁ and ε₂) and the film thickness (d), were determined. Gap values between 1.2 and 1.7 eV were obtained for compound when the mass (M_X) of ZnSe was varied during the deposition stage. Inhomogeneity and high surface roughness were observed by SEM measurements for all samples. Size grain varying between 458.16 and 630.28 nm were obtained while the ZnSe binary mass varied from 0.171 to 0.153 g. Refractive index and extinction coefficient of Cu₂ZnSnSe₄ films were obtained for λ = 800 nm. A decrease of ε₁ and ε₂ was observed as the wavelength increases; it is associated with the presence of binary phases in the XRD patterns.

Abstract: Grain growth of Aluminium alloys at high temperature reduces their strength significantly. Therefore it is essential to control the grain growth by suitable techniques. The effect of Cr on refining the grain structure of Al alloys is investigated in the present work. Cr is added into Al-Si-Mg alloy by stir casting techniques. Subsequently the alloys were subjected to annealing at 500oC for 1 hour to study the grain growth behavior of these alloys. An optical microscope is used to analyze the grain size and microstructure. The mechanical properties of these alloys were studied using a universal testing machine. The Cr additions were varied between 0.5 to 4 weight percent. The Cr addition had shown a significant effect in refining the grain size of Al-Si-Mg alloys. The average grain diameter after annealing was found to be about 151 μm in unalloyed samples while, the 2 wt % Cr added samples showed about 92 μm. The second phase particles, Al₇Cr found precipitated along the grain boundaries apart from Al₂Si and Mg₂Si. However Cr additions more than 2% does not show significant role in refining the grain size. Cr also improved the mechanical properties such as yield strength, ultimate tensile strength and fracture toughness moderately.