Materials Science Forum Vol. 840

Abstract: TiO₂/ZnO nanostructured thin films were grown using sol-gel route. The nanostructured thin films were deposited by dip coating method on glass substrates and calcined at different temperatures (400°C, 500°C, and 600°C). The thin films were characterized using X-Ray Diffraction method (XRD), Atomic Force Microscope (AFM), and Ultraviolet Visible Spectroscopy (UV-Vis). The XRD pattern showed that the crystallinity of the calcined thin films had improved when the calcination temperature was increased. According to AFM observation and analysis, surface roughness of the thin films controllable via growth condition. While the transmittance percentage of ultraviolet by Titanium Dioxide (TiO₂) thin films through UV-Vis could be improved by combination with Zinc Oxide (ZnO). The percentage of transmittance by TiO₂/ZnO nanostructured thin films continue to improve as the calcination temperature were increased.

Abstract: Colloidal gold nanoparticles have been successfully synthesized using electro-dissolution-reduction process that consists of a simple two-electrode cells connected to a DC power supply. Throughout the process, bulk gold at the anode was oxidized into gold cations which then reacted with the chloride ions to form aurochloride complex. The complex ions were then reduced by the citrate ion to form colloidal gold nanoparticles. The size and shape of the nanoparticles were modulated by varying the citrate concentration. The colloidal gold nanoparticles obtained were characterized by field-emission scanning electron microscope (FESEM), transmission electron microscope (TEM) and ultraviolet-visible spectrophotometer (UV-Vis). From FESEM analysis, it was found that by increasing the citrate concentration, the size of colloidal gold nanoparticles produced marginally increased. The mean sizes of gold nanoparticles were roughly about 18.7 nm, 19.3 nm, 20.5 nm and 21.3 nm for citrate concentrations of 0.05 M, 0.10 M, 0.15 M and 0.20 M, respectively. However, sample prepared without the addition of citrate, remained colorless indicating that aurochloride complex ions were not reduced to colloidal gold nanoparticles. TEM micrographs showed that the shape of gold nanoparticles obtained is almost spherical. The characteristic peaks of UV-Vis spectra revealed that the suspension was indeed colloidal gold nanoparticles.Keywords: Gold, Nanoparticles, Electro-dissolution-reduction

Abstract: Thermoelectric (TE) nanogenerators are solid state devices that can directly convert thermal energy into electrical power. The family of bismuth telluride (BiTe)-based semiconductor materials is a good candidate for room-temperature thermoelectric applications. This work aims to synthesize the binary and ternary TE nanowire arrays from BiTe and BiSbTe using template-assisted electrochemical deposition. The compositions and lengths of the nanowires fabricated were precisely tuned by controlling the deposition conditions, while their diameters were confined by the pore sizes of the anodized alumina oxide (AAO) templates used. Chemical compositions of the nanowires were evaluated using Energy Dispersive X-ray (EDX) Spectroscopy and their microstructures were characterized by X-ray diffractometry (XRD), scanning electron microscopy (SEM), conventional transmission electron microscopy (CTEM) and high resolution transmission electron microscopy (HRTEM). TE nanogenerator modules comprising of BiTe and BiSbTe nanowires/AAO composite arrays were fabricated for TE performance evaluation on the basis of their power outputs.

Abstract: The phase evolution of yttrium iron garnet (YIG) during reaction 3Y₂O₃-5Fe₂O₃ was investigated by modifying Fe₂O₃ particle sizes (FPS). Five different sizes of Fe₂O₃, (d₅₀) are used to prepare YIG powder. Solid state reaction (SSR) was applied at 1200 °C in order to gain insight on the effect of FPS towards the YIG formation. Rietveld refinement method was used to quantify the amount of YIG yielded (%). Larger FPS (> 50 μm) initiates only 5Fe₂O₃ + 3Y₂O₃ à 3YFeO₃ + Fe₂O₃ + Y₃Fe₅O_12.. However, when the fine FPS (5 μm) is used, the reaction pathway was changed into 5Fe₂O₃ + 3Y₂O₃ à 6YFeO₃ + 2Fe₂O₃ à 2Y₃Fe₅O_12. These behaviors is explained that the smaller FPS consumed quickly to form YIG due to the smaller particle distance between Fe₂O₃ and Y₂O₃. This shall be leading to higher reaction rates (mass-transfer kinetics).

Abstract: 4H-SiC Schottky barrier diodes (SBDs) were irradiated to neutron fluence of 3.55 x10¹⁶ cm^-2 and 6.6 x 10¹⁵ cm^-2 (15,000 kGy) electrons respectively. In general, characterization of the irradiated samples show that the current characteristics of the diodes decreased. The performance of Schottky gate contact is less for electron irradiated sample compared to neutron irradiated sample. The d-spacing, crystallite sizes and lattice strains were calculated from X-ray diffraction (XRD) measurements. SiC Schottky interface damage and radiation defects, as observed in atomic force microscopy (AFM) topography and scanning electron microscope (SEM) morphology images is possibly the main reason for this reduction in performance.

Abstract: Nowadays, the 316L stainless steel metal foams (SS316L) have acknowledged important attention in various fields and are required to be used as engineering materials including heat exchange, sound absorption, filtration and others. So, in this study the production of SS316L foams using different composition through compaction method by using a starch powder as space holder was studied. The range of selected composition of SS316L that obtained is between 50 wt% to 60 wt% while the remaining percentages are space holder and binder. The SS316L compact is prepared by mixing SS316L alloy powder, starch powder, and Polyethylene Glycol (PEG). Then, the mixture is compact into a mould under 8 tonnes of controlled pressure using hydraulic press machine. This is later sintered in a vacuum furnace. The sintered SS316L foams were characterised using a Scanning Electron Microscopy (SEM) analysis. Then, the physical properties of SS316L foam was also analysed by Archimedes method that includes porosity and bulk density test. As a result, the sample with 60 wt% were produced a good and finer pores and struts. Meanwhile, for that sample the percentage of porosity and bulk density are 0.19% and 7.44 g/cm³, respectively.

Abstract: Taguchi approach was applied to evaluate the processing parameter to determine the most influential control factors which will yield better tensile strength of friction stir welded joint of 6061-T6 aluminium alloy. The processing parameters involved are tool shoulder diameter, in mm (18 ,20, 22), tool rotational speed, in rpm (410, 865, 1140), and feed rate, in mm/min (22, 32, 45). Taguchi parametric design and optimization approach was used. Through the Taguchi parametric design approach, the optimum levels of process parameters were determined. The results indicate that the shoulder size, rotational speed, and feed rate are the significant parameters influencing the tensile strength and hardness of the joint. The predicted optimal values of tensile strength 6061-T6 aluminium alloy is 321.16 MPa. The results was confirmed by further experiments, where the experimented values for tensile strength is 301.28 MPa.

Abstract: The reduction behavior of molybdenum trioxide (MoO₃) by carbon monoxide (CO) has been studied using temperature programmed reduction (TPR) and was characterized using X-ray diffraction spectroscopy (XRD). The TPR result shows that the first reduction peak of MoO₃ under 20 vol. % CO in nitrogen started at 530 °C and second reduction peaks observed was at 700 °C. The XRD technique was employed to identify the changes in the sample. It was found that after non-isothermal reduction up to 700 °C, the intermediate phases Mo₄O₁₁ were observed. Completed reduction to MoO₂ achieved after continued reduction with isothermal mode at 700 °C for 60 minutes. Based on the XRD analysis, it is confirmed that the reduction of MoO₃ to MoO₂ in CO atmosphere consists of two reduction stages, i) Mo⁶⁺ → Mo⁵⁺ and ii) Mo⁵⁺ → Mo⁴⁺. While, CO excess have resulted the formation of molybdenum carbide (Mo₂C) rather than formation of metallic molybdenum (Mo).

Abstract: The reduction behaviour of tungsten oxide has been studied by using temperature programmed reduction (TPR) and X-ray diffraction (XRD). The reduction behavior were examine by nonisothermal reduction up to 900 oC then continued with isothermal reduction at 900 oC for 45 min time under (40% v/v) carbon monoxide in nitrogen (CO in N₂) atmosphere. The TPR signal clearly shows one peak attributed to formation of suboxide W₁₈O₄₉ (more) and WO₂ (less) observed at 80 min. The reduction product was investigated by varying the holding reaction time. Based on the characterization of the reduction products by using XRD, it was found that, nonisothermal reduction of WO₃ at temperature 900 oC partially converted to some W₁₈O₄₉ and WO₂ phases. However, after increased the reaction holding time for 45 min, WO₃ phases disappeared and converted to WO₂ and W metal phases. It is obviously shows that by hold the reduction time could improve the reducibility of the sample oxide. Furthermore, it is suggested that reduction by using CO as reducing agent follows the consecutives steps WO₃ → WO_2.92 → W₁₈O₄₉ → WO₂ → W.

Abstract: Corrosion of metals in soil be able to change from comparatively fast material loss to insignificant effects, depending on soil environment. Corrosion is a process of deterioration of metal surfaces degraded into another compound. Soil is one of the medium known to have constituted to corrosion of metals. The soil creates an environment for the corrosion to react. The buried pipelines are exposed to the soil that may experience corrosion attack. The study of the soil as corrosion environment is important to mitigate the problem due to the environment and economy. There are factors that contribute to the corrosion process. This study concentrates on corrosion properties that expose to soil environment particularly underground pipelines. The mild steel coupons taken from actual pipelines, stimulating and analyzing the physic-chemical characteristics of the soil environment. The soil is sandy clay in natural. A total summed index of 2 numerical scale, thus, indicates that the soil tested was mildly to non-corrosive. The corrosion rate increase with increasing of moisture content and pH value. The observations on the coupon surface also did in order to study the morphology.