Effect of Bottom Bubbling Conditions on Surface Reaction Rate in Oxygen-Water System

In secondary steelmaking, the enhancement of the reaction rate in the low carbon period during the decarburization of steel is considered the most effective method to produce ultralow carbon steel. In a previous study, it was revealed that the surface reaction is dominant during the final stage of the actual refining process. In order to improve the surface reaction rate, it is necessary to enlarge the reaction region, which is usually achieved by increasing the plume eye area. In this study, water model experiments were carried out to estimate the influence of bottom stirring conditions on the gas-liquid reaction rate; for this purpose, the deoxidation rate during the bottom bubbling process was measured. Five types of nozzle configurations were used to study the effect of the plume eye area on the reaction rate at various gas flow rates. The results reveal that the surface reaction rate is influenced by the gas flow rate and the plume eye area. An empirical correlation was developed for the reaction rate and the plume eye area. This correlation was applied to estimate the gas-liquid reaction rate mat the bath surface.

Compatibility of RuO2 electrodes with PZT ceramics

Because of its high electrical conductivity and good diffusion barrier properties ruthenium dioxide (RuO2) is a good electrode material for use with ferroelectric lead zirconate-titanate (PZT) solid solutions. Under certain conditions, RuO2 can react with PZT to form lead ruthenate (Pb2Ru2O6.5) during processing at elevated temperatures resulting in lead depletion from PZT. The standard Gibbs energies of formation of RuO2 and Pb2Ru2O6.5 and activities of components of the PZT solid solution have been determined recently. Using this data along with older thermodynamic information on PbZrO3 and PbTiO3, the stability domain of Pb2Ru2O6.5 is computed as a function of PZT composition, temperature and oxygen partial pressure in the gas phase. The results show PbZrO3-rich compositions are more prone to react with RuO2 at all temperatures. Increasing temperature and decreasing oxygen partial pressure suppress the reaction. Graphically displayed are the reaction zones as a function of oxygen partial pressure and PZT composition at temperatures 973, 1173 and 1373 K.

Diffusion of flexible, charged, nanoscopic molecules in solution: Size and pH dependence for PAMAM dendrimer

In order to understand self-diffusion (D) of a charged, flexible, and porous nanoscopic molecule in water, we carry out very long, fully atomistic molecular dynamics simulation of PAMAM dendrimer up to eight generations in explicit salt water under varying pH. We find that while the radius of gyration (R-g) varies as N-1/3, the self-diffusion constant (D) scales, surprisingly, as N-alpha, with alpha=0.39 at high pH and 0.5 at neutral pH, indicating a dramatic breakdown of Stokes-Einstein relation for diffusion of charged nanoscopic molecules. The variation in D as a function of radius of gyration demonstrates the importance of treating water and ions explicitly in the diffusion process of a flexible nanoscopic molecule. In agreement with recent experiments, the self-diffusion constant increases with pH, revealing the importance of dielectric friction in the diffusion process. The shape of a dendrimer is found to fluctuate on a nanosecond time scale. We argue that this flexibility (and also the porosity) of the dendrimer may play an important role in determining the mean square displacement of the dendrimer and the breakdown of the Stokes-Einstein relation between diffusion constant and the radius.

Effect of diffusion-layer porosity on the performance of polymer electrolyte fuel cells

The gas-diffusion layer (GDL) influences the performance of electrodes employed with polymer electrolyte fuel cells (PEFCs). A simple and effective method for incorporating a porous structure in the electrode GDL using sucrose as the pore former is reported. Optimal (50 w/o) incorporation of a pore former in the electrode GDL facilitates the access of the gaseous reactants to the catalyst sites and improves the fuel cell performance. Data obtained from permeability and porosity measurements, single-cell performance, and impedance spectroscopy suggest that an optimal porosity helps mitigating mass-polarization losses in the fuel cell resulting in a substantially enhanced performance.

Grain boundary sliding during diffusion and dislocation creep in a Mg-0.7 pct Al alloy

Early studies on grain boundary sliding (GBS) in Mg alloys have suggested frequently that the contribution of GBS to creep is high even under conditions corresponding to dislocation creep. The role of creep strain and grain size in influencing the experimental measurements has not been clearly identified. Grain boundary sliding measurements were conducted in detail over experimental conditions corresponding to diffusion creep as well as dislocation creep in a single-phase Mg-0.7 wt pet Al alloy. The results indicated clearly that the GBS contribution to creep was Very high during,, diffusion creep at low stresses (similar to 75 pct) and substantially reduced during dislocation creep at high stresses (similar to 15 pct). These measurements were consistent with the observation of significant intragranular slip band activity observed in most grains at high stresses and very little slip band activity at low stresses. The experimental measurements and analysis indicated also that the GBS contribution to creep was high during the initial stages of creep and decreased to a steady-state value at large strains.

Low-Temperature Processing of ZrB2-ZrC Composites by Reactive Hot Pressing

Dense ZrB2-ZrC and ZrB2-ZrC x∼0.67 composites have been produced by reactive hot pressing (RHP) of stoichiometric and nonstoichiometric mixtures of Zr and B4C powders at 40 MPa and temperatures up to 1600 °C for 30 minutes. The role of Ni addition on reaction kinetics and densification of the composites has been studied. Composites of ∼97 pct relative density (RD) have been produced with the stoichiometric mixture at 1600 °C, while the composite with ∼99 pct RD has been obtained with excess Zr at 1200 °C, suggesting the formation of carbon deficient ZrC x that significantly aids densification by plastic flow and vacancy diffusion mechanism. Stoichiometric and nonstoichiometric composites have a hardness of ∼20 GPa. The grain sizes of ZrB2 and ZrC x∼0.67 are ∼0.6 and 0.4 μm, respectively, which are finer than those reported in the literature.

Phase Diagram for the System RuO2-TiO2 in Air

There are conflicting reports in the literature regarding solid solubility in the system RuO2-TiO2. To resolve this issue a few experiments were conducted in air at 1673, 1723, and 1773 K. The results show limited terminal solid solubility. There is an extended solid-state miscibility gap that intersects the decomposition curve for the RuO2-rich solid solution generating a peritectoid reaction at 1698 K. The measured equilibrium compositions of the solid solutions are used to develop a thermodynamic description of the oxide solid solution with rutile structure. Using the subregular solution model, the enthalpy of mixing can be represented by the expression, Delta H-M/J center dot mol(-1) = XTiO2XRuO2 ( 34,100X(TiO2) + 30,750X(RuO2)). The binodal and spinodal curves and T-X phase diagram in air are computed using this datum and Gibbs energy of formation of RuO2 available in the literature. The computed results suggest that equilibrium was not attained during solubility measurements at lower temperatures reported in the literature.

Diffusion of Pure CH4 and Its Binary Mixture with CO2 in Faujasite NaY: A Combination of Neutron Scattering Experiments and Molecular Dynamics Simulations

The self-diffusion properties of pure CH4 and its binary mixture with CO2 within MY zeolite have been investigated by combining an experimental quasi-elastic neutron scattering (QENS) technique and classical Molecular dynamics simulations. The QENS measurements carried out at 200 K led to an unexpected self-diffusivity profile for Pure CH4 with the presence of a maximum for a loading of 32 CH4/unit cell, which was never observed before for the diffusion of apolar species in azeolite system With large windows. Molecular dynamics simulations were performed using two distinct microscopic models for representing the CH4/NaY interactions. Depending on the model, we are able to fairly reproduce either the magnitude or the profile of the self-diffusivity.Further analysis allowed LIS to provide some molecular insight into the diffusion mechanism in play. The QENS measurements report only a slight decrease of the self-diffusivity of CH4 in the presence of CO2 when the CO2 loading increases. Molecular dynamics simulations successfully capture this experimental trend and suggest a plausible microscopic diffusion mechanism in the case of this binary mixture.

Unfolding of Plasmodium falciparum Triosephosphate Isomerase in Urea and Guanidinium Chloride: Evidence for a Novel Disulfide Exchange Reaction in a Covalently Cross-Linked Mutant†

The conformational stability of Plasmodium falciparum triosephosphate isomerase (TIMWT) enzyme has been investigated in urea and guanidinium chloride (GdmCl) solutions using circular dichroism, fluorescence, and size-exclusion chromatography. The dimeric enzyme is remarkably stable in urea solutions. It retains considerable secondary, tertiary, and quaternary structure even in 8 M urea. In contrast, the unfolding transition is complete by 2.4 M GdmCl. Although the secondary as well as the tertiary interactions melt before the perturbation of the quaternary structure, these studies imply that the dissociation of the dimer into monomers ultimately leads to the collapse of the structure, suggesting that the interfacial interactions play a major role in determining multimeric protein stability. The C-m(urea)/C-m(GdmCl) ratio (where C-m is the concentration of the denaturant required at the transition midpoint) is unusually high for triosephosphate isomerase as compared to other monomeric and dimeric proteins. A disulfide crosslinked mutant protein (Y74C) engineered to form two disulfide cross-links across the interface (13-74') and (13'-74) is dramatically destablized in urea. The unfolding transition is complete by 6 M urea and involves a novel mechanism of dimer dissociation through intramolecular thiol-disulfide exchange.

Kinetics and the Mechanism of Interaction of the Endoplasmic Reticulum Chaperone, Calreticulin, with Monoglucosylated (Glc1Man9GlcNAc2) Substrate

Calreticulin is a lectin-like molecular chaperone of the endoplasmic reticulum in eukaryotes. Its interaction with N-glycosylated polypeptides is mediated by the glycan, Glc(1)Man(9)GlcNAc(2), present on the target glycoproteins. In this work, binding of monoglucosyl IgG (chicken) substrate to calreticulin has been studied using real time association kinetics of the interaction with the biosensor based on surface plasmon resonance (SPR). By SPR, accurate association and dissociation rate constants were determined, and these yielded a micromolar association constant. The nature of reaction was unaffected by immobilization of either of the reactants. The Scatchard analysis values for K-a agreed web crith the one obtained by the ratio k(1)/k(-1). The interaction was completely inhibited by free oligosaccharide, Glc(1)Man(9)GlcNAc(2), whereas Man(9)GlcNAc(2) did not bind to the calreticulin-substrate complex, attesting to the exquisite specificity of this interaction. The binding of calreticulin to IgG was used for the development of immunoassay and the relative affinity of the lectin-substrate association was indirectly measured. The values are in agreement with those obtained with SPR. Although the reactions are several orders of magnitude slower than the diffusion controlled processes, the data are qualitatively and quantitatively consistent with single-step bimolecular association and dissociation reaction. Analyses of the activation parameters indicate that reaction is enthalpically driven and does not involve a highly ordered transition state. Based on these data, the mechanism of its chaperone activity is briefly discussed.

Stress concentration and load diffusion in rectangular panels with constant stress flanges

The stress concentration that occurs when load is diffused from a constant stress member into thin sheet is an important problem in the design of light weight structures. By using solutions in biharmonic polar-trigonometric series, the stress concentration can be effectively isolated so that highly accurate information necessary for design can be obtained. A method of analysis yielding high accuracy with limited effort is presented for rectangular panels with transverse edges free or supported by inextensional end ribs. Numerical data are given for panels with length twice the width.

A Mechanistic Model for the Water-Gas Shift Reaction over Noble Metal Substituted Ceria

The water-gas shift (WGS) reaction was carried out in the presence of Pd and Pt substituted nanocrystalline ceria catalysts synthesized by solution combustion technique. The catalysts were characterized by powder XRD and XPS. The noble metals were found to be present in ionic form substituted for the cerium atoms. The catalysts showed highactivity for the WGS reaction with high conversions below 250 degrees C. The products of reaction were only carbon dioxide and hydrogen, and no hydrocarbons were observed even in trace quantities. The reactions were carried out with different amounts of noble metal ion substitution and 2% Pt substituted ceria was found to be the best catalyst. The various possible mechanisms for the reaction were proposed and tested for their consistency with experimental data. The dual site mechanism best described the kinetics of the reaction and the corresponding rate parameters were obtained.

Studies on the Diels-Alder reaction of maleic anhydride and β-trans-ocimene

The structure of the by-product, obtained in the Diels-Alder condensation of maleic anhydride with β-trans-ocimene followed by distillation of the adduct formed, has been established as 2-isopropylidene-4-methyl-7-carboxy- ,3,3a,6,7,7a-hexahydroindanone (IVa) and the mechanism of its formation from the adduct (II) discussed. Some hitherto unreported reactions of the maleic anhydride adduct (II) and its derivatives are described. These throw light on the stereochemistry of the adduct and derived products.

The specificity of the colour reaction between ammonia and 3-phenyl-2-thiohydantoin

The colour reaction between 3-phenyl-2-thiohydantoin and ammonia is studied quantitatively. Determinations of 0.1–0.6 μmoles of 3-phenyl-2-thiohydantoin are possible with a precision close to 2%. In analyses of amino acid mixtures for glycine after conversion to 3-phenyl-2-thiohydantoin, only derivatives of serine and threonine interfere to a slight extent. The specificity of the primary colour reaction with ammonia, and the structural requirements for it are discussed; a structure for the pigment species is proposed.