Materials Literature
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In the hexagonal columnar phase of chiral polymers a bias towards cholesteric twist competes with braiding along an average direction. When the chirality is strong, screw dislocations proliferate, leading to either a tilt grain boundary phase or a new ``moir\'e state'' with twisted bond order. In the latter case, poly…
We report on a generalized Wulff construction that allows for the calculation of the shape of two-dimensional materials with orientational order but no positional order. We demonstrate that for sufficiently large domain radii, the shape necessarily develops mathematical singularities, similar to those recently observe…
Light emitting porous silicon thin films with thicknesses from ∼0.1 to ∼100 μm were produced by electrochemical etching and subsequently lifted off the silicon wafer by an electropolishing step. The structural integrity of the thinner layers was maintained by deposition on sapphire windows where they remain attached b…
The influence of sample preparation on the resistivity and magnetoresistance (MR) behavior of doped manganese oxides has been studied. Two systems, Nd0.7Sr0.3MnO3−δ and La0.67Ba0.33MnO3−δ thin films, have been chosen for this study. The former has the largest reported MR ratio at 60 K and the latter has a large MR rat…
In situ thin films of (1−x)Pb(Mg1/3Nb2/3)O3–xPbTiO3, (PMN-PT), with composition x=0.1, 0.3, 0.35, and 0.4, were deposited on MgO(100) substrates by pulsed laser deposition. The optimum conditions to form (100) oriented PMN-PT perovskite phase were at substrate temperatures in the range of 535 to 575 °C with an oxygen…
Two-dimensional solids of particles with short-range attraction exhibit a solid-solid critical point. We report computer simulations that show that, near this point, the crystal becomes unstable to dislocation unbinding. Since the concentration of free dislocations is very small the resulting phase should be a stable…
Erbium implanted sodalime silicate glass was covered with a range of transparent liquids. The spontaneous emission rate of ${\mathrm{Er}}^{3+}$ around 1.54 $\ensuremath{\mu}$m shows clear changes depending on the liquid refractive index and Er depth. A rigorous quantum mechanical calculation shows that the effect of t…
We study the antiferrodistortive instability and its interaction with ferroelectricity in cubic perovskite compounds. Our first-principles calculations show that coexistence of both instabilities is very common. We develop a first-principles scheme to study the thermodynamics of these compounds when both instabilities…
Abstract Localized corrosion of carbon steel wire rope stored in a humid environment on wooden spools was caused by organic acid and carbon dioxide production by fungi growing directly on the wood. Fungal growth was observed on the interiors of wooden spools and corrosion was most severe on the wrap of wire in direct…
Abstract Evidence of intergranular attack in the absence of stress, together with dissolution kinetics, indicate that the intergranular stress corrosion cracking of ferritic steels in various environments is by a dissolution mechanism. Film rupture can play an important role in the rate of growth of cracks, but film r…
Abstract Erosion corrosion is an important consideration in the design of systems in which materials are exposed to nonuniform fluid flow. There have been inconsistent experiences with the relationship of seawater flow rates and wastage of copper alloys. This study specifically addresses corrosion of NiAl-bronze (Allo…
Abstract Environmental concerns are increasingly likely to influence the choice of oilfield production and drilling chemicals. The Paris Commission (PARCOM) is currently developing legislation for the North Sea. The regulations which emerge may well restrict the use of many current products. Uncertainty over the event…
Abstract A computational procedure for predicting CO2 corrosion rates of carbon steels given the field conditions (e.g. CO2 partial pressure, temperature, velocity, solution composition, gas/liquid ratio) is desirable for use by the oil and gas industry. A model based on the current understanding of the mechanism and…
Abstract Corrosion tests using a flow loop and rotating cylinder electrode are used to select corrosion inhibitors for downhole and flowline application. The results show tests incorporating high flow rates and high shear stress levels will differentiate the performance of different inhibitor formulations. The effect…
Abstract A finite difference hydrogen induced crack (HIC) growth model has been developed, enabling for the first time an accurate simulation of the growth of HIC cracks in the wall of pipelines and/or pressure vessels. In the model, parameters such as defect size, location, fracture toughness and hydrogen concentrati…
Abstract Corrosion accounts for more than one third of the integrity problems on pipelines operating in Alberta. Gas pipelines in particular suffer the threat of external corrosion where protective coatings have fail and created shielding disbondments. This paper will review the sampling and analysis of corrosion prod…
Abstract CO2 corrosion rates of carbon steel obtained from a large number of experiments in a high pressure test loop with various strictly controlled environments and flow conditions were fitted to a semi-empirical model equation. This model combines a contribution of the flow-independent kinetics of the corrosion re…
Simulations of the structure and dynamics of fluid films confined to a thickness of a few molecular diameters are described. Confining walls introduce layering and in-plane order in the adjacent fluid. The latter is essential to transfer of shear stress. As the film thickness is decreased, by increasing pressure or de…
Mutual arrangement of large volume atomic cells (defined as the Voronoi polyhedra) is investigated in molecular dynamics models of Lennard-Jones liquid, crystal and amorphous solid by the percolation theory methods on the Delaunay network. In addition to ordinary percolation some extended formulations of the percolati…
We report on a new, more precise structural characterization of n-octadecane thiol monolayer self-assembled on the UHV-prepared Au(001) surface using a combination of helium atom diffraction, grazing incidence x-ray diffraction, and x-ray reflectivity measurements. Our results show that the equilibrated alkane chains…