Papers by Keyword: Palladium

Abstract: In this work, Pd metal layer was deposited on in-house prepared macro-porous disc alumina support by electroless plating. The in-house prepared support were repeatedly seeded for 4 cycles to obtain Pd nuclei before repeatedly electroless plated for 4 cycles. The 4-cycle Pd plating was to obtain the full layer of Pd metal observing from changing support surface from black to light grey. The plated membrane samples were annealed at 550 and 600oC for using in high-temperature H₂ separation. The annealed samples were observed morphology by SEM and confirm the occurrence of Pd layer with EDS. The SEM images revealed incomplete Pd layer. The over 4 cycles of plating were needed to form complete Pd layer since the numerous Pd ions diffused into macro-pores alumina support instead of depositing on the surface of macro-porous support. The higher annealing temperature of 600oC led to denser layer of Pd with the presence of small cracks due to the contraction of Pd particles.

Abstract: Pure ZnO and Palladium (Pd)-loaded ZnO nanoparticles containing 0.25, 0.50, 0.75 and 1.0 mol% of Pd were successfully synthesized by flame spray pyrolysis (FSP) and characterized for hydrogen and ethanol sensing applications. The crystalline phase, morphology and size of these nanoparticles were characterized by X-ray diffraction (XRD) and transmission electron microscopy (TEM) in order to correlate physical properties with gas sensing performance. The sensing films were fabricated by coating nanoparticles with organic paste composed of terpineol and ethyl cellulose as a vehicle binder on Al₂O₃ substrate interdigitated with gold electrodes. The film thicknesses were varied by controlling the numbers of coating. Film morphologies of gas sensors were characterized by atomic force microscopy (AFM) and scanning electron microscopy (SEM). Moreover, response time and sensitivity of these sensors towards hydrogen and ethanol were evaluated under operating temperatures ranging from 200 ̶ 350°C in dry air. Finally, The optimum amount of loading Pd and film thickness were investigated.

Abstract: The oil industry increasingly exploits ‘heavy oils’ which are highly viscous and difficult to extract in a ‘clean’ way. Heat and ‘cracking’ catalysts facilitate extraction e.g. by applying the ‘Toe-to-Heel Air Injection’ (THAI) and ‘Catalytic Process In-Situ’ (CAPRI) techniques. Cracking catalysts include palladium. Use of Pd-catalyst is uneconomic but by using palladium deposited on bacterial cells (in combination with other PMs) a waste can be turned into a valuable product. Road dusts contain precious metals (PMs) which arise from automotive catalytic converters. Once washed from roads the PMs are dispersed to the environment. Model r oad dust solutions were produced to simulate acid leaching of road dust to solubilise the PMs. Bacteria cannot directly recover PMs from acidic leachate but by lightly depositing Pd(0) ‘seeds’ enzymatically the resulting ‘bio-Pd’-catalyst accumulates PMs from waste model leachate. The bio-catalyst was assessed in the reduction of heavy oil viscosity compared to a commercial catalyst, achieving this reduction with significantly less coke formation, which was not attributable to the biomass component alone.

Abstract: In this work we report the results of a set of experiments carried out to assess the ability of recombination lifetime measurements for the detection of palladium contamination in silicon. Palladium is found to be a very effective recombination center, so recombination lifetime measurements are a very sensitive method to detect palladium in silicon. The surface segregation of palladium was monitored by the reduction of its recombination activity in the silicon volume. The palladium segregation at the wafer surface was checked by selective etching, and by Transmission Electron Microscopy (TEM) and Energy Dispersive X-ray (EDX) analysis.After validating recombination lifetime measurements for palladium detection, we use these measurements to define suitable approaches to the prevention of palladium contamination of silicon devices. The efficiency of a diffusion barrier layer (silicon nitride) and of decontamination by wet cleaning are tested.

Abstract: In the present work, positron annihilation spectroscopy was employed for investigation of hydrogen-induced defects in Pd. Well annealed Pd samples were electrochemically charged with hydrogen and development of defects during hydrogen loading was investigated. At low concentrations (α-phase, x_H < 0.017 H/Pd) hydrogen loading introduced vacancies. When the hydrogen concentration exceeds 0.017 H/Pd, particles of hydrogen rich α’-phase are formed. This generates dislocations in the sample in order to accommodate the volume mismatch between the α and the α’-phase. Moreover, additional vacancies are introduced into the sample by crossing dislocations. Vickers hardness testing revealed that absorbed hydrogen causes hardening of the sample. In the α-phase region the hardness increases due to solid solution hardening caused by dissolved hydrogen. At higher hydrogen concentrations when dislocations were created hardness increases due to strain hardening caused by dislocations.

Abstract: A Pd-H system is a model system suitable for studying interactions of hydrogen with metals. In the present work, we studied hydrogen-induced buckling of thin Pd films deposited on various substrates with different bonding strengths (sapphire, glimmer) and also the effect of deposition temperature. Lattice expansion and phase transitions were investigated by X-ray diffraction of synchrotron radiation. The influence of the substrate and microstructure of the film on the buckling process and phase transformation to palladium hydride are discussed.

Abstract: Hydrogen interaction with vacancies and dislocations in Pd were investigated in the present work. Well annealed and plastically deformed Pd samples were electrochemically doped with hydrogen up to various hydrogen concentrations. Subsequently the samples were subjected to linear annealing (10 K/min) and hydrogen desorption was studied by differential scanning calorimetry (DSC). An endothermic peak caused by hydrogen desorption was observed in the DSC curve of well annealed sample at ∼ 178 °C. In plastically deformed samples this peak is shifted to higher temperatures since hydrogen is trapped at dislocations and its diffusivity is suppressed. Moreover, it was found that if the atmosphere surrounding the heated sample contains oxygen the endothermic hydrogen desorption peak is followed by a strong exothermal peak caused by fusion of desorbed hydrogen with oxygen into water vapour molecules. To avoid this undesired effect DSC measurements have to be done in a protective atmosphere which does not contain oxygen.

Abstract: This paper presents the development and fabrication of fiber Bragg grating hydrogen sensor by using magnetron sputtering method to overcome the problem of hydrogen embrittlement.With compact, smooth and high quality thin films deposited by magnetron sputtering, two layers have been sputtered around the fiber cladding: titanium (Ti) layer (20nm) and palladium (Pd) layer (500nm). Between the two layers, Ti is acted as adhesive coatings to ensure connection between fiber and Pd film. Finally, the performance of the developed FBG hydrogen sensor was tested in the laboratory under low hydrogen concentration. The results prove that the fabricated hydrogen sensor has a high sensitivity of 22.67pm/%H₂.

Abstract: Spatial distributions of a potential established inside a crystal by an externally applied potential are investigated theoretically in Pd and PdH. The calculations were performed in the framework of the linear-response approach with full inclusion of the electron band structure obtained within a self-consistent pseudopotential scheme. Analysis shows that in clean palladium the potential amplitude is maximal at the octahedral sites of the fcc lattice where the hydrogen ions predominantly reside. On the other hand the corresponding amplitude is significantly lower at the palladium ion positions. We observe drastic modifications in the screening properties in Pd upon hydrogen absorption. Nevertheless, the potential amplitude in PdH is also small at the Pd sites, whereas that at the H sites is significantly larger. However, in PdH the H ions are located at places where a local shallow minimum in the induced potential amplitude is observed. These results only slightly depend on the magnitude of the momentum transfer.

Abstract: To promote the alcohol catalytic oxidation of Pd/C catalysts, it was implemented that the lanthanide Yb was introduced to the catalyst via the precipitation thermal decomposition and chemical reduction methods. The structure analysis and surface morphology of Pd-Yb/C catalysts were investigated by XRD and SEM. The ethanol electrocatalytic oxidation activity of in alkaline media was studied by cyclic voltammetry. The results show that the performance of ethanol catalytic oxidation on Pd-Yb/C electrode is better than that on the Pd/C electrode. The introduction of Yb can promote Pd/C catalytic oxidation alcohol and its poisoning tolerance ability.