Reticulated vitreous carbon/polypyrrole composites as electrodes for lithium batteries: Preparation,electrochemical characterization and charge–discharge performance

Polypyrrole (PPy) composites were prepared via electrochemical deposition onto reticulated vitreous carbon (RVC) – a tridimensional material – and tested as cathodes in lithium batteries. Different RVC/polypyrrole electrodes were prepared and characterized: PPy doped with ClO₄^? (RVC/PPy) as an anion-exchanger film; PPy doped with a large anion – poly(styrenesulphonate) – (RVC/PPyPSS) as a cation-exchanger film; and a bi-layer polymeric film formed by an inner layer of the former and an outer layer of the latter (RVC/PPy/PPyPSS). Photomicrographies, voltammetric profiles and electrochemical impedance spectroscopy data have shown different morphological and electrochemical characteristics for polypyrrole doped with small or large anions, and a peculiar behavior for the bi-layer electrodes. Charge/discharge results indicated that the RVC/PPy electrode can attain specific capacities as high as 95 mAh g^?1. PSS-doped polypyrrole electrodes also presented high specific-capacity values when the bi-layer configuration (RVC/PPy/PPyPSS) and lower charge–discharge currents were used. Impedance data indicated that the counter-ion diffusion within the bi-layer is hindered, which explains the slower activation of this composite when compared to that of RVC/PPy.     

Residual stresses in cold-wire gas metal arc welding

This work compares the welding residual stresses of the cold-wire gas metal arc welding and conventional gas metal arc welding processes. Two techniques were used to measure the residual stresses: X-ray diffraction and acoustic birefringence. The base metal used was carbon manganese steel plates of 9.5-?mm thickness. The results showed that the introduction of the cold-wire tends to decrease the residual stresses, suggesting that the introduction of the cold wire decreases the amount of heat given to the base metal, and consequently lowers residual stresses.     

Effects of Niobium Ammonium Oxalate and Benzotriazole on the Corrosion Resistance of Zinc Phosphate Layer

In this study, the viability of nickel replacement in zinc phosphate baths by niobium ammonium oxalate (Ox) and benzotriazole (BTAH) was studied. Samples of carbon steel (SAE 1010) were phosphated in two zinc phosphate baths, one containing nickel (PZn+Ni) and another containing Ox and BTAH (PZn+Ox+BTAH). The corrosion resistance of the phosphated samples was analyzed in a NaCl 0.5 mol/L solution using open circuit potential measurements, anodic and cathodic polarization curves, and electrochemical impedance spectroscopy. Surface analysis was carried out by scanning electron microscopy and energy dispersive spectroscopy. The results showed that the PZn+Ni layer presented a needle-like morphology and that the crystals of PZn+Ox+BTAH showed granular morphology. The electrochemical results showed that the highest corrosion resistance was associated to the PZn+Ox+BTAH layer.     

The development of conventional welding processes in naval construction

In recent years, analysis of the development of joining processes has resulted in the identification of two trends: the refinement and specialization of traditional processes on the one hand, and the development of novel technologies on the other hand. This dual line of trends has sometimes led to points of contact, with the development of the so-called hybrid technologies, involving the use of joining processes based on different physical principles for the creation of a single joint. The scope of this article is to provide a framework view of the state of development of conventional joining technologies with regard to shipbuilding applications.     

The effect of thermal cycling on oxide scale structure and morphology on a hot-pressed silicon nitride

Dense Si₃N₄ hot-pressed with the aid of 9 wt% Y₂O₃ was oxidised in ‘dry’ synthetic air at both 1000 and 1200°C for up to 500 h under thermal cycling conditions. The experiments revealed that thermal cycling has little effect on oxidation kinetics although the morphology of surface oxidation products is affected by the cycling frequency. Cracks formed in the oxide layers on cooling healed immediately on re-exposure to high temperature, and there was no apparent change in the oxidation rate controlling mechanism over the time period investigated. The exposure of the material at 1000°C did not result in catastrophic oxidation as observed for some other Y₂O₃-doped hot-pressed Si₃N₄ compositions. Additionally, it was observed that crystallisation of the oxide layer with time (assisted in part by the outward diffusion of intergranular phase cations from the bulk ceramic to the surface scale) leads to non-parabolic kinetics owing to reduced rates of diffusion through crystalline phases in the surface scale. ©     

Simulation of Fe-Cr-X Alloy Exposed to an Oxyfuel Combustion Atmosphere at 600 °C

In coal-fired power plants using oxyfuel combustion process with carbon capture and sequestration, instead of air, a mixture of oxygen and recirculated flue gas is injected in the boiler. A series of steels were exposed to CO₂-SO₂-Ar-H₂O gas mixtures at 600 °C for 1000 h to compare their high temperature corrosion behavior. During the corrosion process, carburization, decarburization and recrystallization were observed underneath the oxide scale depending on the gas mixture and alloy composition. The conditions that lead to carburization are not yet completely understood, but decarburization can be simulated using thermodynamic and kinetic models. In this work, the results of these simulations are compared with measured values for one of the alloys that displayed a decarburized region. Since the mobility of carbon in the scale is not known, two strategies were adopted: simulation of alloy-atmosphere contact; and estimation of the carbon flux to produce the observed decarburization. The second approach might give an insight on how permeable to carbon the scale is.     

Comparison of Electrophoretic Protein Profiles from Sheep and Goat Parotid Saliva

Saliva provides a medium for short-term adaptation to changes in diet composition, namely, the presence of plant secondary metabolites. Salivary proteins have biological functions that have particular influence on oral homeostasis, taste, and digestive function. Some salivary proteins, such as proline-rich proteins, are present in browsers but absent in grazers. Despite the significance of salivary proteins, their expression patterns in many herbivores are unknown. We investigated the sodium dodecyl sulfate-polyacrylamide gel electrophoresis profile of parotid salivary proteins from two domesticated species, one a grazer, the sheep, Ovis aries, and the other a mixed feeder, the goat, Capra hircus, both fed on the same conventional diet. With 12.5% polyacrylamide linear gels, we observed uniform patterns of salivary proteins within the two species. In the goat profile, 21 major bands were observed, and 19 in the sheep profile. Each band was subjected to peptide mass fingerprinting for purposes of identification, allowing for 16 successful protein identifications. Marked differences were observed between the species in the region of 25–35 kDa molecular weights: one band was present in significantly different intensities; three bands were present only in goats; and one band was present only in sheep. This is the first report of a comparison of the protein salivary composition of sheep and goats and suggests that future research should be conducted to reveal a physiological function for salivary proteins related to the differences in feeding behavior of these species.     

Methane reforming of syngas produced by co-gasification of coal and wastes. Effect of catalysts and of experimental conditions

Syngas obtained by co-gasification of coal and wastes was hot cleaned in two catalytic reactors, which allowed destroying tar and gaseous hydrocarbons with more than one carbon atom. H₂S and NH₃ contents were also significantly reduced, but CH₄ concentrations varying between 2% and 10% and small amounts of H₂S (below 100 ppmv) were still found in syngas, depending on coal type and waste composition. This paper studies the effect of experimental conditions on CH₄ destruction by reforming reactions in absence and in presence of catalysts. The effect of experimental conditions (temperature, steam flow rate and syngas composition) on CH₄ destruction and on CO conversion into CO₂ in the absence of catalyst was studied first, using the Equilibrium Reactor model from CHEMKIN modelling software. The selected experimental conditions were then tested in a fixed bed reactor with and without catalyst and the results obtained were consistent with CHEMKIN Equilibrium Reactor model predictions. Commercial Ni-based catalysts were tested (G-90 B5 and G 56B from C&CS). These catalysts were capable of significantly reducing CH₄ content, by promoting reforming reactions. At the experimental conditions used and in absence of steam, G 56B seems to be more effective in CH₄ conversion, as lower CH₄ contents were obtained. In presence of steam both catalysts were capable of completely destroying CH₄. Both catalysts also promoted WGS (water gas shift) reaction to some extent, though they are not specific catalysts for this reaction. Thus, a high increase in H₂ content was observed, due to its formation by both reforming and WGS reactions. For a complete conversion of CO into CO₂ and H₂ a specific catalyst for WGS reaction is still needed.     

Evaluation of urea-formaldehyde adhesives performance by recently developed mechanical tests

In the open literature, two main strategies can be found for synthesizing urea-formaldehyde (UF) resins. One is the alkaline-acid process, which takes place in three steps, usually an alkaline methylolation followed by an acid condensation and then the addition of a final amount of urea. The other process consists of four steps, the main difference being an initial condensation in strongly acid environment.In this work, we evaluate the curing behaviour of four resins produced using the aforementioned processes by the Integrated Pressing and Testing System (IPATES) and the Automated Bonding Evaluation System (ABES).The characterisation of the bond strength development during hot pressing by ABES and IPATES shows that the four resins will have different performances in the bonding process of wood-based composites. For each resin, the effect of pressing parameters such as temperature, adhesive and hardener ratios on shear strength (ABES) and internal bond (IPATES) during hot pressing is put into evidence.     

On the quantification of the controlling regimes in automotive catalytic converters

The conversion of pollutants in automotive catalytic converters is influenced by a number of physical and chemical processes that take place in the gaseous and solid phases as the exhaust gases flow through the converter. A detailed understanding of the complex processes involving flow dynamics, heat and mass transport and heterogeneous surface reactions is of crucial importance to improve the converter design. The main objective of the present study is to quantify the magnitudes of the external and internal mass transfer as well as chemical reaction limiting processes as a function of the converter operating temperature. To this end, experimental data, obtained for a three way catalyst (TWC) under real world operating conditions, are analyzed and compared against analytical expressions that allow for the quantification of the different limiting processes involved. The results demonstrate that (i) the external mass transfer resistance overlaps the reaction resistance only at moderate operating temperatures and not immediately above the ignition temperature as generally considered in the literature, (ii) the transport phenomena (external and internal mass transfer) represents 90% of the total resistance for temperatures higher than 792 K, (iii) the internal mass transfer in the porous washcoat presents a larger resistance than the external mass transfer from the bulk fluid to the washcoat wall even at high operating temperatures, and (iv) based on the quantification of the individual resistances as a function of the TWC operating temperature, it was demonstrated both the influence of the substrate cell density and of the effective diffusivity on the TWC conversions. © 2010 American Institute of Chemical Engineers AIChE J, 2011