ICMCTF2010 Session TSP: TSP Poster Session

Carbon-free LiFePO₄ thin films have been mixed with Ag by sputtering from a pure LiFePO₄ target with silver sheets attached, or by depositing on Ag/stainless steel (SS) substrates. The deposited films were annealed at 700^oC for 1 hr in H₂/Ar (5 %) atmosphere. The morphologies of the LiFePO₄ thin films fabricated using different methods were similar. Both showed a grain size of 200-50 nm. Energy dispersion spectra (EDX) and x-ray photoelectron spectra (XPS) revealed that Ag was mixed in the LiFePO₄ films. The film conductivity (5 x 10^-3 Scm^-1) is therefore elevated by an order of six, compared with pure LiFePO₄ (10^-9 Scm^-1). The electrochemical measurements of the LiFePO₄-Ag films showed a flat plateau at 3.4 V (v.s. Li/Li⁺) and a reversible capacity of 80 mAh/g. Optimization of Ag contents may further improve the discharge capacity.

The performances of direct methanol fuel cells (DMFC) are affected by the methanol cross-over, due to the concentration gradient and electrosmosis between the anodes and cathodes. In this study, Polyterafluorethylene (PTFE) has been sputter deposited on conventional proton conducting membranes, Nafion117. It was found that the problem of the methanol cross-over was eased by the PTFE coating. The properties of coated and uncoated Nafion117 were investigated by scanning electron microscopy, electron spectroscopy for chemical analysis, gas chromatography and AC impedance spectroscopy. The coated film can form a barrier layer between the methanol solution and the polymer membrane. The PTFE barrier layer can effectively retard the methanol molecules, whereas the proton conductivities were not significantly influenced. The conductivity/permeability ratio of ~10⁴ at 80^oC, which is one order higher than conventional Nafion117 membranes, has been achieved under an optimized coating time. This technique developed shows great potential for the applications in DMFCs.

Carbon based nanocomposites and/or nanolaminate coatings display low friction coefficients of less than 0.06 and low wear rates when subjected in nano-triboscope tests. In this work we investigate the possibility of using such coatings not only as wear resistant films in biomedical implants, but also as a bioactive coating that promotes bone ingrowth for areas in medical implants that are in direct contact with bone. To confirm the tissue compatibility of the films carbon-based nanocomposites and nanolaminates were deposited on polished and anodic nanoporous template on CrMo and Ti6Al4V substrate coupons. Human osteoblasts and fibroblasts were then cultured on the treated surfaces in order to study cellular adhesion, proliferation and viability. To further assess the bone-bonding capabilities of the coatings, “in vitro” mineralisation studies were performed where human osteoblasts were grown on the treated samples, leading to the formation of mineralised structures. Samples were subjected to morphological analysis using standard and electron microscopy techniques. To assess their biochemical compatibility cultured surfaces were investigated using x-ray microanalysis.

In general, vegetable oils exhibit superior lubrication properties to, but lack the thermal stability of petroleum base stocks. However, vegetable oils could make an ideal candidate as a base stock for lubrication applications involving high humidity levels, such as marine and offshore applications. This study focuses on the friction and wear rate of unmodified soybean and sunflower oils in comparison to an unformulated mineral oil at various levels of relative humidity, ranging from 10-98% RH. It was observed that the vegetable oils retain their friction and wear reducing capabilities much better than the mineral oil at high humidity levels. This was attributed to their inherent ability to react with the metallic contacting surfaces and form multilayers of soap films. Furthermore, the soybean oil provided a superior level of wear resistance when compared to the sunflower oil at extremely high levels of relative humidity due to its lower viscosity and differences in chemical compositions.

Experimentally, thin c-BN films can be deposited by rf magnetron sputtering of a hexagonal boron nitride (h-BN) target in Ar/N₂ atmosphere. Variations of the ion rates and impact energies result in different sputter yields and are important for the formation of the c-BN films. All variables such as vacancy energy, migration and surface binding energy were analysed by the method of molecular dynamics simulations, using the ITAP Molecular Dynamics (IMD) software package. A Tersoff potential was used to simulate B-N-interactions within the bulk and on the surface while the interaction with Argon was described by the Ziegler-Biersack-Littmark (ZBL) potential. At first, the vacancy energy of h-BN and c-BN was analysed by comparing two equivalent specimens with and without vacancy inside. Secondly, the migration energy was defined as the energy barrier between two neighboring lattice sites, one occupied, other vacant. The knowledge of these energy values is important for the understanding of the penetration depths of argon ions and the forward sputtering of B and N atoms. For the process of their back sputtering, the surface binding energy with and without the recombination of the crystal surface was analyzed.

Using these energy values, the sputter yield of BN was determined as a function of ion impact energy, within the range of 20-1000 eV, the impact site on the surface and the crystal orientation. These simulation results have been compared with experimental values as determined by plasma diagnostics and by Ar ion etching of a thick BN film in a microwave plasma.

An analysis of the retrieved data such as back sputter yield with the distinction to atom type and cluster size was performed. Additionally, penetration depths of argon ions as well as the forward sputter yield were analysed.