Developing scaling relations for the yield strength of nanoporous gold

In this work, the applicability of Gibson and Ashby’s porous scaling relations to nanoporous metals is discussed, and an updated equation is proposed for relating the yield strength of nanoporous gold to the yield strength of individual gold ligaments that form the porous structure. This new relation is derived from experimental measurements obtained by small-scale tensile testing and by nanoindentation, and incorporates the average ligament diameter. Nanoindentation data, obtained experimentally by the authors as well as reported by others in the literature, are reconciled with tensile test measurements previously reported by the present authors. The values of ligament yield strength calculated with the new scaling relation are found to agree with data reported from mechanical testing of nanowires, and the scaling relation thus represents a bridge between nanowire and nanoporous metal behaviour. In addition, calculations of yield strength for nanoporous gold samples with various ligament size and relative density are consistent with the experimentally determined values.     

Cure kinetics of epoxy resin-natural zeolite composites

The cure kinetics of epoxy resin and epoxy resin containing 10 mass% of natural zeolite were investigated using differential scanning calorimetry (DSC). The conformity of the cure kinetic data of epoxy and epoxy-zeolite system was checked with the auto-catalytic cure rate model. The results indicated that the hydroxyl group on the zeolite surface played a significant role in the autocatalytic reaction mechanism. This group was able to form a new transition state between anhydride hardener and epoxide group. The natural zeolite particles acted as catalyst for the epoxy system by promoting its curing rate.     

Diffusion of Butylated Hydroxy Toluol (BHT) in PVC Films

Abstract

The diffusion coefficient of butylated hydroxy toluol (BHT) in solvent casted PVC films from tetrahydrofurane (THF) was studied by UV spectroscopy. Diffusion coefficient of BHT in PVC at 140, 160 and 180°C were determined as 1.0 × 10^?12 3.0 × 10^?12 and 6.0 × 10^?12 m²/s. The activation energy of diffusion (E_a) was 66 kj/mol.

IR spectroscopic work showed that the complete removal of THF was possible by heating films 15 minutes at 140 °C, but that caused formation of C=0 groups in PVC. No dehydrochlorination of films was observed even for heating them at 180 °C for 60 minutes.

Antioxidant BHT is volatile at high temperatures, so it is not advisable to use it for high temperature applications.     

Pipe-diffusion ripening of Si precipitates in Al-0.5%Cu-1%Si thin films

Al-0.5%Cu-1%Si thin films deposited onto oxidized Si substrates were subjected to both wafer curvature and in situ transmission electron microscopy thermal cycling experiments between room temperature and 450°C. The evolution of precipitates was monitored during cycling. Chemical analysis revealed that the precipitates are pure Si. Their average size increased from 80?nm in the as-deposited state to 300?nm after thermal cycling. The Si precipitates serve as anchoring points for dislocations and grain boundaries. Direct evidence for pipe-diffusion ripening was found in the vicinity of a dissolving precipitate. Real-time measurement of the radius of the precipitate allowed us to estimate the coefficient of pipe diffusion of Si in Al at this temperature. As expected, this coefficient is several orders of magnitude larger than the volume diffusion coefficient. The impact of precipitate ripening on the mechanical behavior of these alloyed Al films will also be discussed.     

Electrical properties of thin PECVD silicon oxynitride films

Thin silicon oxynitride films with excellent uniformity were prepared by plasma enhanced CVD. Oxygen incorporation leads to improved breakdown behavior and to reduction of the film conductivity compared to PECVD silicon nitride layers. Thin PECVD silicon oxynitride films deposited on single crystal and poly-Si exhibit good insulation properties in both cases.     

Ferroelectric domain structures in (Pb,La)(Zr,Ti)O<Subscript>3</Subscript> ceramics observed by scanning force microscopy in acoustic mode

Ferroelectric domain structures of transparent (Pb,La)(Zr,Ti)O₃ (PLZT) ceramics were investigated by scanning force microscopy (SFM) in the acoustic mode. The antiparallel domain configuration with a periodic distribution and local inhomogeneity in PLZT ceramics were clearly revealed with this new domain-imaging technique. The imaging mechanism of ferroelectric domains in SFM acoustic mode is discussed in terms of a local piezoelectric vibrator model. PACS 77.84.Dy; 77.80.Dj; 77.65.-j; 77.22.Ej; 07.79.-v     

Doping behavior of sulfur during growth of GaAs from the vapor phase

A study has been made of sulfur doping from H₂S in the vapor growth of GaAs using the Ga-AsCl₃-H₂ system. In order to separate the effects of the gaseous components the AsH₃-HC1-Ga-H₂ system was also investigated. A linear relationship was found to exist between the measured electron concentrations and PH₂S over a wide range. The $\text{P}{}^{\mathrm{<mtext>-1</mtext><mtext>2</mtext>}}{}_{\mathrm{<mtext>AS</mtext>}}{}_4$ and P^-2_GaCl (or: P^-2_HCl or P^-1_GaCl or P^-1_HCl) dependence of the rate of sulfur uptake combined with the pronounced increase in this uptake upon approaching the exact <100 > orientation suggests that the process is kinetically limited. Some model considerations are presented, based on the hypothesis that the sulphur is competing for adsorption on As sites with the reactive components in the system.