Polymer coatings on steel substrates: An infrared spectroscopic study of temperature effects

Polymer coatings on steel substrates were analyzed by reflectance/absorbance infrared spectroscopy. Initial studies were performed ex-situ on samples which had been cured at a variety of temperatures on two different substrates. Further studies were done in-situ under both air and nitrogen atmospheres. The two substrates studied were untreated cold-rolled steel and cold-rolled steel with a conversion coating of zinc phosphate. Changes in the spectra of the phosphate conversion layer correlated well with anti-corrosion properties. Mechanisms of degradation and cure could be determined from the in-situ studies (1).     

Observation of columnar microstructure in step-graded Si1-xGex/Si films using high-resolution X-ray microdiffraction

Columnar microstructure in step-graded Si(1-x)Ge(x)/Si(001) structures with low threading dislocation densities has been determined using high angular resolution (approximately 0.005 degrees ) x-ray microdiffraction. X-ray rocking curves of a 3-microm-thick strain-relaxed Si(0.83)Ge(0.17) film show many sharp peaks and can be simulated with a model having a set of Gaussians having narrow angular widths (0.013 degrees -0.02 degrees ) and local ranges of tilt angles varying from 0.05 degrees to 0.2 degrees. These peaks correspond to individual tilted rectangular columnar micrograins having similar (001) lattice spacings and average areas of 0.8 to 2.0 microm(2).     

Diffusion and solubility of methane in polyisobutylene

Diffusion coefficients and solubilities of methane in polyisobutylene have been measured at four temperatures between 102 and 188°C. in the pressure range 23–341 atm. Diffusion coefficients extrapolated to atmospheric pressure range from 1.72 × 10^?6 cm.²/sec. at 102°C. to 1.5 × 10^?5 cm.²/sec. at 188°C. corresponding to an activation energy for diffusion of 8.7 ± 0.4 kcal./mole. Solubilities are small, about one molecule of methane for every forty carbon atoms in the polyisobutylene at 300 atm. partial pressure of methane. Solubilities vary little with temperature, but show an apparent minimum between 127 and 188°C. With improved methods of data analysis, diffusion coefficients and solubilities have been recalculated from previously reported studies on nitrogen in branched polyethylene and methane in branched polyethylene, linear polyethylene, and polystyrene. Recalculated diffusion coefficients are essentially the same as those reported previously, but the recalculated solubilities are decreased from 2 to 30%. The solubilities of all five systems show strong deviations from Henry's law, i.e., increases in partial pressure of methane and nitrogen with respect to solubility exceed linearity. The partial pressure (or fugacity)—solubility data may be interpreted in terms of a sorption model in which sorbed molecules are accommodated in widely dispersed, unoccupied volumes or sites in the polymer. An almost equivalent, solution model in which the first sorbed molecules to enter the polymer are accommodated to a large extent in existing volumes in the polymer, with successively sorbed molecules swelling the polymer to a greater extent (i.e., partial molal volume of sorbed molecules, V ₁, increasing with concentration) can also account for these data.     

Hysteresis of charge tunneling in assemblies of carboxylic acid-modified gold nanoparticles

We report on charge transport measurements through laterally contacted assemblies of Au nanoparticles capped with 11-mercaptoundecanoic acid ligands. Both alternating- and direct-current data indicate that although the nanoparticles behave as electrically isolated metallic islands, there is a significant influence from the nanoparticle environment, indicating the existence of a slow reorganization process linked to charge transport. On the basis of the observation of temperature-dependent hysteresis of charge tunneling, we propose that this process is due to proton transfer between the carboxylic acid tails of the ligands.     

Characterising the metric and topological evolution of OpenStreetMap network representations

OpenStreetMap (OSM) is a collaborative project to create a free editable map database of the world. This paper presents an analysis of the evolution of OSM street network representations. Three urban areas in Ireland were analysed where each evolves from containing little street network detail to a highly detailed street network. In order to characterise this evolution a number of metric and topological characteristics were computed. Some characteristics exhibited broadly similar behaviour in each region. This may be a attributed to similarities in the degree of contributor activity and intrinsic universal mapping procedures exhibited by contributors.