Advanced Materials Research Vol. 501

Abstract: The development of lead-free solders has been an essential task in the electronics industry because of the restriction of lead use by legislation. Among the candidates, Sn-Ag-Cu group of solder alloys have great advantages to replace the conventional Sn-Pb solder. In this study, the wetting and intermetallic study between Sn-3.5Ag-1.0Cu-xZn lead-free solder reacting on copper substrate were investigated under different soldering conditions. The addition of 0.7wt% of Zn improved the wettability on Cu substrate since it has the highest spreading area at 310°C. The Cu6Sn5 and Cu3Sn phases are the main interface intermetallic formed and these intermetallics increased in thickness with time and temperature. At 270°C, the addition of 0.7wt% Zn retarded the growth of Cu3Sn intermetallic until 10 min of the soldering time. Generally the addition of Zn was beneficial in retarding the total intermetallic thickness.

Abstract: Al-Si-Mg/AlN composites were prepared by stir casting technique. The amount of AlN added to Al-Si-Mg alloy was from 2 to 10 wt%. As-cast composites were solutionised at 540 °C for 4 h, quenched in warm water, 60 °C then artificially aged at 180 °C for 4 h. The microstructure of Al-Si-Mg matrix alloy contained dendritic α-Al, needle-like Si and very little inter-metallic compounds. As-cast Al-Si-Mg/AlN composites have rounded α-Al phase and needle-like Si where AlN particles dispersed surrounding α-Al. Needle-like Si transformed to spheroid after artificial aging. The size of α-Al phases of heat-treated composites containing 2 and 5 wt% AlN was bigger than that of as-cast composites whereas the heat-treated Al-Si-Mg/10% AlN composite has thin and elongated dendritic α-Al phases, and larger AlN particles.

Abstract: The toxicity in the Sn-Pb solder has promoted the development of Pb-free solder in the electronics industries. Among the Pb-solders, the Sn-3.5Ag-1.0Cu solder is considered a potential replacement and being studied by many researchers. In the present study, the characteristics of Sn-3.5Ag-1.0Cu lead-free solder were studied. The raw materials were tin, silver and copper powders in micron size. The solder was prepared using powder metallurgy route which includes blending, compacting and sintering. Four blending times and two compacting pressures were used to investigate for optimum condition. The melting temperature of the samples were studied using differential scanning calorimeter (DSC) and the presence of Sn Ag, Cu were confirmed using x-ray diffraction analysis (XRD). Finally the effect of variables on the hardness of the solders is reported.

Abstract: A plate of Fe-30Cr (wt%) were subjected to isothermal furnace at 600 °C in flowing CO2 gas at total pressure of approximately 1 atm. The reacted samples morphology and microstructure were characterized by using visual inspection, optical microscope, SEM and EDAX. The weight change measurement showed a fluctuating result during the exposure. The significant weight loss was observed after five hours exposure due to oxide scale exfoliation. Formation of different oxide and element presents on the interface of the specimen such as Cr2O3, C and Fe3C were revealed by X-ray diffraction and with supported by EDAX analysis. This behavior of the high temperature corrosion on Fe-30Cr was discussed based on morphology and microstructure observation.

Abstract: Electrophoretically deposition of Biphasic calcium phosphate on 25 × 10 × 1.2 mm (length, width, and thickness) 316L stainless steel plates using ethanol as dispersing medium; It was achieved on the cathode with constant voltages 20, 30, 50, and 100 V during 20, 30, 60, 90 and 120 seconds, respectively. After deposition, the samples were dried at room temperature for 24 hours and deposition weight and thickness of the coatings were measured. The coated samples were sintered in a tube furnace at 800 °C for 1 h in an argon atmosphere. After the sintering, the surface morphology and structure and phase composition of the samples were studied by a scanning electron microscope (SEM), energy dispersive spectrometry (EDX) and phase purity of the coating material by X-ray diffraction.

Abstract: The influence of annealing on the optical properties of as-grown ZnO nanostructures prepared in pellets has been investigated by photoluminescence (PL) and Raman spectroscopy. The annealing temperatures of ZnO nanostructure at 600°C, 650°C and 700 °C were conducted in oxygen (O2) and nitrogen (N2) ambient. The near band edge emission (NBE) of samples recorded in the PL spectra demonstrates significant changes on optical signal whereby the NBE is redshifted after O2 annealed and became slightly higher in N2 annealed. Apart from that, weak green luminescence (GL) namely deep band emission (DBE) is observed centre at 532.95 nm (2.23 eV) and 511.00 nm (2.42 eV) for annealed in O2 and N2 respectively, whereas lower DBE observed in as-grown ZnO. On the other hand, Raman shift reveal the phonon mode of the ZnO nanostructures and the E2 (high) mode were downshifted as annealed in O2 ambient, and upshifted in N2 ambient. The downshift and upshift of the E2 (high) mode are correlated to tensile and compressive stress. Moreover the crystallite sizes were calculated from FWHM of XRD and TEM microscopy reveals the nanoplates structure of ZnO nanostructures.

Abstract: Zinc oxide (ZnO) pellets were prepared by agglomeration of ZnO nanopowder with distilled water in this study. Annealing at 800oC in different ambient was done on the surface of the pellets in order to change the photoluminescence and structural properties of the sample. The ZnO pellets that were annealed in air, oxygen and nitrogen ambient reduce the intensity of near-band-edge emission in photoluminescence spectra. The observed change in green luminescence after the annealing process suggests that the oxygen vacancies are the recombination centers for green luminescence in the samples. Red luminescence was also observed and it is attributed to oxygen vacancies in different energy level. Different annealing ambient had significantly modified the green and red luminescence. Structural investigation carried out by X-ray diffraction (XRD) revealed the polycrystalline nature for ZnO pellets with hexagonal phase and annealing process increased the cystallinity of the ZnO pellets.

Abstract: The interdependence parameters in the growth of silicon self-assembled nanodots are investigated. Accordingly, the critical radius, critical energy change and surface energy can be interpreted in terms of cubic function, where it produced a critical surface energy NS* and the corresponding r* and G*, called a CRESE point at a fixed growth temperature T when solved mathematically. It is defined as a limiting point at which equilibrium of the critical parameters take place at a constant temperature. Experiments were performed on the samples of amorphous silicon nanodots fabricated onto different non-crystalline substrates. A further analysis on the NS*-T plots revealed inverse linear relationships which converged at a CID point (o*,T*) when projected near the solidification temperature of silicon. The results suggested strong influence of atomic bonding at the nucleus-surface interface combined with higher surface roughness. In conclusion, there exists an equilibrium condition among the growth parameters which stabilizes the growth of amorphous silicon nanodots, as well as the existence of CRESE’s ideal destination (CID).

Abstract: This paper discusses the processing of a hybrid of TPNR-MWNTs-OMMT nanocomposites with different percentages of filler to determine the optimum mechanical properties of the hybrid nanocomposites. Three types of hybrid nanocomposites with various MWNTs-OMMT compositions (1%wt MWNTs+3%wt OMMT), (2%wt MWNTs+2%wt OMMT) and (3%wt MWNTs+1%wt OMMT) were prepared. The OMMT layers were found to be separated further with higher nanotubes content as exhibited by X-ray diffraction. The result of tensile test showed that tensile strength and Young's modulus increase in the presence of nanotubes and maximum value were obtained for the nanocomposites with highest nanotubes (3%wt) which increased about 33% and 36%, respectively compared with pure TPNR matrix. On other hand, the elongation at break considerably decreased with increasing the percentage of MWNTs. TEM micrographs revealed aspect ratio and fillers orientation in the TPNR matrix also promoted strongly to interfacial adhesion between fillers and the matrix which contributed significantly to the improvement of the mechanical properties

Abstract: Inverted type bulk heterojunction organic solar cell based on ZnO nanorod arrays have been used to overcome the degradation problem of conjugated polymer and low work function electrode. ZnO nanorods and Eosin-Y are widely used to increase the charge mobility and light absorbance, respectively. The effects of Eosin-Y coating temperature (30 – 50 oC) on the performance of organic solar cells based on a blend of poly[2-methoxy-5-(2-ethylhexyloxy)-1,4-phenylenevinylene] (MEHPPV) as donor and (6,6)-phenyl-C61 butyric acid methyl ester (PC61BM) as acceptor with a structure of fluorine-doped tin oxide (FTO)/Eosin-Y coated ZnO nanorod arrays/MEHPPV:PCBM/Ag were investigated. By using FTO as a substrate, sol-gel and spin coating method was used to deposit ZnO seed layer on FTO surface. The ZnO nanorods were then grown on the ZnO seed layer by chemical bath deposition method and coated with dye by immersing the substrates into Eosin-Y solution at different temperatures. The result shows that absorption of Eosin-Y coated ZnO nanorods increased with dye coating temperature. The optimum power conversion efficiency of η = 1.24 × 10-2 % was achieved at dye coating temperature 50 oC under 100 mW/cm2 simulated AM 1.5 G sunlight.