Materials Science Forum Vols. 654-656

Abstract: Precious metallic nanoparticles have attracted considerable attention because of their unique properties (optical, electronic, and chemical properties) and potential applications in many areas such as optical probes, biochemical sensors, and surface enhanced Raman Spectrum. Despite many successes in synthesis of anisotropic nanoparticles (rods, plates), some limitations still exist in generating monodispersed silver nanoparticles. This study intends to elucidate the influence of crystalline seeds on the shape, size, and size distribution of nanoparticles through a seed-mediated method. The crystalline seeds can be modified by using different ways, such as heating treatment and oxidative etching. The shape and size of the generated particles will be characterized by TEM, and the particle formation and growth is tracked by UV-vis spectrometry. The findings would be useful for the shape-controlled synthesis of metal nanoparticles for desired functional properties.

Abstract: Mesoporous TiO2 with highly crystalline pore wall has an enormous potential for applications in photocatalysis, catalyst support, drug delivery, etc. However, with the sintering temperature increasing, the crystallinity of the pore wall increases while the mesopore structure tends to collapse. In this work, we presented a novel strategy for creating highly crystalline mesoporous TiO2 (MT800) by using carbon to protect the pore structure at elevated temperature. The structural characterization indicates that MT800 has highly crystalline anatase phase and processes high surface area. The photocatalysis performance was evaluated by organic degradation and the results show that MT800 has superior photocatalysis activity to the TiO2 (T800) calcined at 800°C without carbon, because of the synergies of crystallinity and mesostructure.

Abstract: The green density and roughness of green ceramic layers determine their mechanical and micro structural properties after final sintering. These properties can be measured precisely by laser profilometry. The green density of thin layers (20-50 µm) could quickly be determined as accurately as 0.5% theoretical density. The influence of paste parameters (powder conditioning, solid content, binder, and dispersing agent) on the green density was studied systematically for electrolyte pastes (8 mol.-% yttria stabilised zirconia = 8YSZ) typically used in solid oxide fuel cell applications. It could be shown that a minimal binder content is required to achieve acceptable green densities. Pre-calcination of the powder yielded also significantly higher film densities. Dispersant agents contributed to a smoother surface in any case, however a significant effect on the packing density was only observed for the fine, non-calcined powder.

Abstract: Chemiluminescence (CL) is a straightforward method for studying the free radical degradation of organic and biological materials. A simple modification to a commercial thermal CL instrument and an effective experimental protocol allows the study of photoinduced chemiluminescence (PICL) emission. PICL originates from the reactions of macroperoxy radical intermediates formed during the autoxidation chain reaction. We have applied the PICL technique to study the photooxidation of polymer films and coatings, fibrous webs such as textile fabrics or paper, and powdered samples. Oxygen permeability appears to be a key factor affecting the intensity of PICL emission from polymer films.

Abstract: The polarization curves and electrochemical impedance spectroscopy of coated steel after scratching cross-lines or cathodic polarization using COLT system connected to electrochemical workstation IM6ex in seawater are investigated and from the measured polarization data, potential distribution on hull surface under waterline are predicted using Beasy CP software. It is shown that an more pricise method for gaining polarization data of the coated steel in seawater is the electrochemical measurement carried out by COLT system and the method of scratching cross-lines or cathodic polarization for coating damage is simple and convenient for estimating the polarization data of a new coated hull that is closely related to the coating properties.

Abstract: The surface preparation and hydrogen embrittlement in particular are research challenges facing the practical application of vanadium alloy membranes. These two issues are addressed by surface characterization and fracture analysis in order to find the reasons why delamination and crack failures occur during hydrogen permeation. Post-failure analysis of the hydrogen-induced cracking membrane specimen suggests a new failure mechanism for hydrogen embrittlement.

Abstract: In this paper, a new high-throughput evaluation method for crystallization temperature (Tx) of thin film amorphous alloy is introduced. For measurement of Tx on integrated thin film samples, thermography is used. The order of one hundred Pd-Cu-Si thin film amorphous samples with different composition are integrated on one chip and measured their Tx at once. The validity of measured Tx are examined by comparing with results of differential scanning calorimeter that is a conventional method for Tx measurement, and equilibrium phase diagram of Pd-Si. As results, the difference of two methods is within 10 K and the trend of Tx map has strong correlation with the phase diagram, respectively.

Abstract: Nickel-iron nanocrystalline alloy films were prepared on copper substrates by electrochemical deposition at various current densities of 6, 9.7, 11.5 and 15.2 A dm-2. X-ray diffraction measurements confirmed that all nickel-iron alloy films formed have face-centered cubic structure. The structural parameters such as the lattice constant, crystallite size, microstrain and dislocation density were determined for the nickel-iron alloy films. The crystallite size of the films reduced from 17 to 12.9 nm when the current densities were decreased. The reduction in crystallite size increased the dislocation density. Magnetic property measurements using alternating gradient magnetometer indicated that these alloys were ferromagnetic. The saturation magnetization Ms of nickel-iron alloy films increased with decreasing deposition current density, which was attributed to the increase of iron content. Nickel-iron alloy film prepared at deposition current density of 6 A dm-2 showed the maximum value of Ms. The coercivity of nickel-iron alloy films increased with decreasing current density, which was likely caused by reduction in crystallite size.

Abstract: This paper discusses experiments investigating the effect of lubrication on surface damage in riveted lap joints which experience fatigue loading in aircraft structure. As part of a larger investigation into the effect of lubricants (specifically Corrosion Inhibiting Compounds, CICs) on fatigue performance, the fracture surfaces were examined to determine the crack initiation sites, and the failure modes involved. Scanning Electron Microscopy was also utilized to assess the nature of the fracture surfaces. The results showed that under the loading used, all the specimens which had not been treated with the CICs, and some treated specimens, failed by tensile failure of the sheet. Some treated specimens failed by rivet shearing. The results suggested that the presence of lubrication at the contacting surface might have reduced frictional load transfer, contributing to the change in failure mode. For specimens that failed in the sheet material, fatigue cracking and micro-void coalescence were the fracture modes, with the potential influence of fretting as a fatigue source.

Abstract: The trend in the aluminium smelting industry today is to operate cells with graphitized carbon cathode linings, increased current density and acidic bath chemistry. The resulting problem is an accelerated wear of graphitized cathode blocks, thought to be caused by formation and subsequent dissolution of Al4C3 at the cathode lining surface. The cycle of formation and subsequent dissolution Al4C3 is recognized as one of the most important mechanism causing pothole and surface wear, which results in limiting of the cell lifetime and loss efficiency. A special laboratory test method was developed to elucidate the mechanism of Al4C3 formation in electrolytic cell. The Al4C3 formation in the region between the carbon surface and aluminium as well as between the carbon surface and electrolytic bath has also been studied using X-ray diffraction, as well as optical and scanning electron microscopy. Solid Al4C3 layer was observed at the carbon surface. A possible mechanism which explains the presence of Al4C3 at the metal-bath interface is the transfer of dissolved carbide in the bath from metal-carbon interface.