Applied Mechanics and Materials Vols. 548-549

Abstract: A novel and well-organized study for the synthesis and enhanced catalytic activity of Au/TiO₂ catalysts has been developed. A momentous improvement in the catalytic activity of Au/TiO₂ in CO oxidation and preferential oxidation reaction by thermal treatment has been studied. Au/TiO₂ catalyst (Au (1 wt.%) supported on TiO₂) was prepared by conventional deposition-precipitation method with NaOH followed by washing, drying and calcination in air at 400 °C for 4 h. Thermal treatment of Au/TiO₂ was performed at 450 °C under 0.05 mTorr. The activity of the catalysts has been examined in the reaction of CO oxidation and preferential oxidation (PROX) at 25-250 °C. The catalytic performance was found to be strongly affected by thermal treatment of the prepared catalyst prior to the reaction. Heat treatment after Au deposition has a positive effect on the CO oxidation performance. This is attributed to the introduction of a stronger interaction between the oxide and Au which improves the catalytic activity.

Abstract: Particularly in karat gold alloys in jewelry applications, many alloy formulations include a small amount of silicon for filigree castings and brightening effect [1]. On the other hand, some alloy manufacturers stayed away from silicon or set a maximum amount of silicon to avoid embrittlement [1-3]. However recent development of gold-based bulk metallic glass involved a large addition of silicon (16.3 at% Si) in the alloy formulation [4-6]. No silicon segregation had been observed in large ingots that were cooled at 100 K/s and above. In the current study of Au55Cu25Si20 alloy, extra silicon has been added to investigate the segregation effect using three different techniques for cross references: equilibrium solidification path, Scheil-Gulliver solidification with ThermoCalc® and microstructural study with varying cooling rates. The amounts of solidified primary and eutectic silicon were measured in three differently cooled ingots. Image analysis using ImageJ® was used to obtain size distributions, area fractions, and volume fractions of silicon in both primary silicon and eutectic silicon.

Abstract: Dye-sensitized solar cells based on Y-doped TiO₂ thin film prepared by the hydrothermal method show a photovoltaic efficiency of 5.11%, which is higher than that of the undoped TiO₂ thin film (4.72%). The Y-doped films exhibit an elevated electron Fermi level,which may enhance band bending to lower the density of empty trap states.Because of this Y-doping, the Dsscs can alleviate the decay of light to electric energy conversion efficiency due to light intensity reduction.

Abstract: The objective of this research work is to investigate the effect of Aluminum addition in cast nickel base superalloy grade GTD-111 by vacuum arc melting process on microstructural modification and oxidation behavior at elevated temperatures of 900°C and 1000°C. The Al element, basically, could be added in cast nickel base superalloys in proper amount to form precipitated intermetallic phase with nickel atoms as gamma prime phase (γ’, Ni₃Al) to increase mechanical properties at elevated temperatures. Furthermore, Al can assist nickel base superalloy to form protective oxide film, Al₂O₃ for better oxidation resistance at very high temperatures. In this research, all casted samples of GTD-111 with various Al additions for 1, 2 and 3 percent by weight were solutioning treated at 1125°C for 6 hours and following with precipitatation aging at 845°C for 24 hours. The oxidation tests were carried out at temperatures of 900°C and 1000°C up to 110 hours. From all obtained results, it was found that the sample that has the most microstructural stability after long-term heating as simulated working conditions is GTD-111 sample with 2%wt. Al addition. Furthermore, more Al addition had resulted in higher oxidation resistances for both testing temperatures.

Abstract: The nickel base alloy, grade Hastelloy X was modified by Aluminum and Titanium additions by means of vacuum arc melting process in order to improve microstructural characteristics and oxidation resistance. The arc melted Hastelloy X was added Aluminum and Titanium each for 2%, 4% and 6% by weight. Then all specimens were performed with heat treatment, which consists of solutioning treatment at 1125°C for 24 hours and precipitation aging at temperatures of 760°C, 800°C and 845°C for 24 hours. Both aluminum and titanium additions resulted in network intermetalic phase formation, namely, σ-phase, throughout the matrix. Furthermore, the addition of both elements provided the better oxidation resistance for the alloys.

Abstract: Chromobacterium violaceum is able to produce and detoxify small amounts of cyanide that has been used to recover gold from Electronic scrap materials (ESM). The particle size ≤75 μm fraction was used, containing 0.22% Au and 33.0% Cu. The bioleaching was carried out in 500 ml Erlenmeyer flask with 200 ml LB medium at 0.5% pulp density in pH 9 and shaking in an incubator shaker (200 rpm) at 30°C. The experiment featured two variables, copper removal with nitric acid and 2 leaching times, 1-step and 2-step bioleaching for enhanced cyanide production and gold dissolution. The maximum cyanide production was observed after 1 day before ESM adding. The results showed high efficiency of gold bioleaching from treated EMS containing 0.21% Au and 3.67% Cu. Dissolution of gold increased from 1.63% (0.13 mg/L) to 13.62% (1.43 mg/L) after 7 days in 2-step bioleaching. This study increased the efficiency of gold recovery by bioleaching significantly and can be recycled in an environmental friendly manner.

Abstract: Chemically and mechanically protective coatings are formed on surface of Magnesium alloys by micro-arc oxidation (MAO) methods. From manufacturing perspectives, modification of the obtained MAO surfaces was made in two aspects. Firstly, the protection is enhanced by forming super-hydrophobic surfaces, with water contact angle higher than 120^o, attributed to hierarchical nanomicro structures. The overall process involves alkaline etching to form nanoscale structures on top of micro-porous surface achieved during micro-arc oxidation processes. Secondly, the electrical property of the MAO surfaces is modified. A film with electrical conductivity of 2.4Ω/sq is achieved by Ni deposition and characterized by four point probe measurement. The morphology, phase, and chemical composition of all surfaces are investigated by SEM and XRD analysis.

Abstract: The objective of this study was to develop clad layer by producing a Silicon Carbide (SiC) particle reinforced Metal Matrix Composite (MMC) using the iron based alloys (P25) as the matrix material. Direct laser cladding was carried out by melting the clad materials and depositing them onto a mild steel substrate. A two gravity feed system was used in this study which contained of SiC particles and iron based powder as separate powders. The intention was to melt the iron based powder and incorporate the SiC particles. Decomposition of SiC particles was observed and only a few SiC particles were found in the clad matrix. Microhardness results showed that laser clad layer had higher hardness which more than 1000 HV and hence potentially better wear resistance that base material. However, most of the SiC had evaporated which created porosity in the melt pool due to the decomposition of SiC and the resultant gas which was trapped in clad layer did not have enough time to escape from the melt pool due to the rapid solidification. Therefore, a blown powder technique is recommended for overcome this problem.

Abstract: Selective Laser Sintering (SLS) is a combined technology of computer and laser to produce complex 3D prototypes directly from CAD modeling. One of the main advantages of employing this technology is that the non-sintered powder can be recycled and reused for another fabrication. However, the fabricated part could be affected by rough and unacceptable surface texture. As a result, the parts may have to be scrapped and the build has to be repeated with a higher ratio of new material. This paper presents an experimental study of the thermal properties of new and recycled of PA12 powder in the Laser Sintering process. The influence of melting temperature, glass transition temperature and crystallization temperature on these properties is investigated. The experimental results have shown that PA12 powder with high melt flow rate, low melting temperature, low glass transition temperature and low degree of crystallization temperature could improve the sintering process.

Abstract: Studies on electromagnetic impact welding between similar or dissimilar flat sheet metals using the flat one turn coil have been recently achieved. In this study, three dimensional electromagnetic-mechanical coupled numerical simulations are performed for the electromagnetic impact welding of aluminum alloy sheets with flat rectangular one turn coil. The deformation behavior during impact welding was examined. The effect of process parameters such as charge voltage, standoff distance and gap distance were investigated.