Modeling and simulation of a single direct carbon fuel cell

A mathematical model was developed to simulate the performance of a direct carbon fuel cell. The model takes account of the electrochemical reaction dynamics, mass-transfer and the electrode processes. An improved packed bed anode was adopted. Polarization losses for the cell components were examined supposing graphite as the fuel and molten carbonate as the electrolyte. The results indicated that the anode activation polarization was the major potential loss in 923–1023 K. The effects of temperature, anode dimension, and carbon particle size on the cell performance were investigated. The model predicted that the power density can be as high as 200–500 W m⁻², with carbon particle size in the range 1.0 × 10⁻⁷ to 1.0 × 10⁻⁴ m and in 923–1023 K and that the overall efficiency of the cell is higher than 55% for low current density and is 45–50% for high current density.     

Effect of activated gas plasma treatment time on adhesive bondability of polymers

The bondability of the following polymers as a function of length of exposure to excited helium or oxygen was investigated: low-density polyethylene, high-density polyethylene (two types), poly(4-methyl-1-pentene), poly(vinyl fluoride), poly(vinylidene fluoride), FEP Teflon, poly(oxymethylene) copolymer, nylon 6, nylon 66, poly(ethylene terephthalate), and polystyrene. Generally, the bond strength increase rapidly initially and then remains nearly constant, perhaps decreasing in some cases at long exposure times. A method is presented for calculating bond strength-versus-exposure time curves. The calculated curves generally fit the data reasonably well. Polypropylene showed a rapid increase in bondability with exposure to excited oxygen. Helium was ineffective toward this polymer under normal conditions, but could produce good bond strength at higher temperatures.     

Aqueous polyurethane dispersions: A comparative study of polymerization processes

Restrictions on volatile organic compounds have forced the producers of solvent‐based polymers to develop safer products. Water dispersions of polyurethanes are successfully replacing solvent‐borne products in the coating industry, but relatively little systematic work has been reported that compares polyurethanes obtained by different processes. In this study, polyurethanes were produced with three polymerization processes: in a solution, in a dispersion with the acetone process, and in a dispersion with the prepolymer mixing process. The same prepolymer was synthesized in all cases, and the reaction was concluded under the conditions required by the three different methods. In the first phase, nonextended polyurethanes were prepared with different functional group ratios (NCO/OH), and an evaluation of the quality of the dispersions and solutions and of the morphology of the dry polymers was made by a comparison of the products from the three preparation routes. Second, the growth of the molecular weight in water was studied for the prepolymer mixing process. NCO‐terminated prepolymers were dispersed in water and then extended by aliphatic diamines. The extender was added in different percentages that referred to the NCO equivalents of the prepolymer. This led to an evaluation of the effect of the dispersing medium on chain extension. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 88: 716–723, 2003     

Processing and Performance of an All-Oxide Ceramic Composite

Continuous fiber ceramic composites (CFCCs) based on oxides are of interest for high-temperature applications owing to their inherent oxidative stability. An enabling element is a matrix with an optimum combination of toughness and strength, which may be achieved by incorporating a controlled amount of fine, well-distributed porosity. Implementation of this concept by vacuum infiltration of aqueous mullite-alumina slurries into two-dimensional woven preforms of alumina fibers has been investigated. Evaluation of these materials shows stress-strain characteristics similar to other CFCCs, especially carbon-matrix composites. Moreover, promising notch and creep properties have been found. Microstructural and processing issues relevant to the attainment of these behaviors are discussed.     

Catalyst effect on the crosslinking kinetics of a fluorine containing polyurethane network

A bicomponent fluorinated polyurethane coating was obtained by crosslinking a bifunctional, OH terminated perfluoropolyether oligomer with a fluorinated polyisocyanate based on the isophorone diisocyanate (IPDI) cyclic trimer. Three different tin containing catalysts (dibutyltin dilaurate (DBTDL), dibutyltin dimercaptide (DBTDM), tin octoate (TO)) were evaluated during the crosslinking reaction through gel time measurements and IR spectroscopy at various temperatures from +15 to +45°C. Both the methods showed a substantial higher activity of the first two catalysts, tin octoate being almost ineffective (latent) at ambient temperature. The spectroscopic measurements allowed the determination of apparent second‐order kinetic constants (k) of the crosslinking reaction. The activation energies E_a in the temperature range considered were obtained from the corresponding Arrhenius plot, showing a temperature dependence higher for DBTDM than DBTDL (8.5 vs. 7.0 kcal/mol). Finally, the conversion of the crosslinking reaction on the dry polymer film was estimated to be around 60–80% after 8 h at ambient temperature for DBTDM and DBTDL, but only 20–25% for TO catalyzed reactions. The formation of a hard urethane phase having a glass transition temperature T_g higher than the crosslinking temperature was considered as the main limiting factor of the overall reaction rate.     

Structural Differences Between Biogenic Amorphous Calcium Carbonate Phases Using X‐ray Absorption Spectroscopy

We compare the organization of the first coordination shells around the calcium ion in biogenic ACC phases from three different sources. The results show that although the three biogenic samples have the same chemical composition, which is referred to collectively under the name “amorphous calcium carbonate”, they are structurally different from one another. These differences may be attributed to the diverse modes of formation of such biogenic materials and may account for their known variations in stability.     

Hybrid intermetallic Ru/Pt-modified bond coatings for thermal barrier systems

NiAl-based bond coatings for thermal barrier coating (TBC) systems containing varying amounts of Ru and Pt have been investigated. The addition of Ru to bulk NiAl has shown substantial increases in the creep strength of these aluminide materials, while Pt-modifications are known to improve the oxidation resistance of NiAl. The oxidation and interdiffusion behavior of these hybrid Ru/Pt bond coat systems are compared to conventional Pt-modified aluminide bond coats. The Ru/Pt-modified aluminide bond coats demonstrate cyclic oxidation lives comparable to those of Pt-modified aluminide bond coatings. These hybrid Ru/Pt-modified bond coats exhibit better creep properties than traditional Pt-modified coatings and suppress the rumpling mechanism typically responsible for the spallation of TBC from Ni(Pt)Al bond coatings. The evolution of coating microstructures at various stages of cyclic life was studied, and phase equilibria issues relevant to the fabrication and oxidation behavior of these multilayer systems are discussed.     

Neural plasticity in adults with amblyopia

Amblyopia is a neuronal abnormality of vision that is often considered irreversible in adults. We found strong and significant improvement of Vernier acuity in human adults with naturally occurring amblyopia following practice. Learning was strongest at the trained orientation and did not transfer to an untrained task (detection), but it did transfer partially to the untrained eye (primarily at the trained orientation). We conclude that this perceptual learning reflects alterations in early neural processes that are localized beyond the site of convergence of the two eyes. Our results suggest a significant degree of plasticity in the visual system of adults with amblyopia.