Sintering and Properties of Sialons without Externally Added Liquid Phase

β'-Sialon has the general formula Si_6-ZAl_ZO_ZN₈-Z The synthesis of pure β'-sialon with three different Z values of 0.5, 1.0, and 2.0 in the system Si₃N₄-AlN-Al₂O₃-SiO₂ has been reported without the addition of a foreign sintering aid. A small shift in the composition toward the SiO₂ corner has been made in each case. The Z=1.0 and 2.0 sialon can be sintered almost to full density while that with Z=0.5 sialon is difficult even with a higher amount of excess oxide addition. A packing bed of Si₃N₄ and SiO₂ in a weight ratio of 7:3 was found to be most useful. The coefficient of linear thermal expansion of Z=1.0 sialon is 2.2°10^-6/°C (25° to 1000°C). The room-temperature modulus of rupture value can be retained up to 90% of the value at 1400°C. A similar trend has also been observed in the K_lC value with temperature. The steady-state flexural creep rate varies from 0.5°10^-6 to 2.5°10^-6 h^-1 in the temperature and load ranges of 1200° to 1300°C and 100 to 250 MPa.     

Thermal plasma spraying for SOFCs: Applications, potential advantages, and challenges

In this article, the applications, potential advantages, and challenges of thermal plasma spray (PS) processing for nanopowder production and cell fabrication of solid oxide fuel cells (SOFCs) are reviewed. PS processing creates sufficiently high temperatures to melt all materials fed into the plasma. The heated material can either be quenched into oxide powders or deposited as coatings. This technique has been applied to directly deposit functional layers as well as nanopowder for SOFCs application. In particularly, low melting point and highly active electrodes can be directly fabricated on zirconia-based electrolytes. This is a simple processing technique that does not require the use of organic solvents, offering the opportunity for flexible adjustment of process parameters, and significant time saving in production of the cell and cost reduction compared with tape casting, screen printing and sintering processing steps. Most importantly, PS processing shows strong potential to enable the deposition of metal-supported SOFCs through the integrated fabrication of membrane-electrode assemblies (MEA) on porous metallic substrates with consecutive deposition steps. On the other hand, the application of PS processing to produce SOFCs faces some challenges, such as insufficient porosity of the electrodes, the difficulty of obtaining a thin (<10 μm) and dense electrolyte layer. Fed with H₂ as the fuel gas and oxygen as the oxidant gas, the plasma sprayed cell reached high power densities of 770 mW cm⁻² at 900 °C and 430 mW cm⁻² at 800 °C at a cell voltage of 0.7 V.     

Process modelling for the production of hydrogen-rich gas from gasification of coal using oxygen,CO2 and steam reactants

This process modelling studied the effect of different reactants on syngas composition and gasifier heat duty (heat energy required to carry out the operation) and the downstream treatment of CO rich syngas to maximise hydrogen yield. The process modelling was validated against experimental data obtained from a large bench-scale entrained flow gasifier. Results show that considering the H₂/CO ratio, the steam-O₂ reactant favours the most compared to those of the pure oxygen and oxygen-CO₂ reactants. Under comparable operating conditions, the highest H₂/CO ratio of 0.74 was determined using steam-O₂ reactant compared to that of 0.31 and 0.33 using steam-CO₂ and pure oxygen reactant. The catalytic water-gas shift reaction (WGSR) favours the yield of H₂ with complete CO conversion at a temperature of 400 °C using the steam/coal ratio of 1.2. Supplying steam in the gasifier requires more heat energy to be supplied to drive endothermic gasification reaction and maintain the gasifier temperature. Under complete carbon conversion, steam-CO₂ and steam-oxygen reactants require 5–65 kW more energy than pure oxygen.     

Influence of ionic pretreatment on the performance of solid electrolyte dye-sensitized solar cells

Dye-sensitized solar cells (DSSCs) were manufactured with liquid iodine/iodide electrolyte solution in acetonitrile and a solid electrolyte based on plasticized poly(ethylene oxide) (PEO). Two types of titania electrodes manufactured from two-ingredient precursors were used to assess the efficacy of the solid electrolyte and the improvement produced by two chemical treatments. Solid electrolyte devices with a liquid electrolyte pretreatment applied to the electrolyte-oxide interface demonstrated improved photovoltaic performance compared to untreated solid electrolyte devices and solid electrolyte devices given an electrode-bulking sol treatment. Devices using electrodes made from hydrothermally synthesized titanate nanotubes resulted in lower performance than those made from the typically-used titania nanopowder, with significant performance loss resulting from the substitution of solid for liquid electrolyte, indicating the critical dependence of performance on electrolyte infiltration into the oxide layer.     

Nanotechnology in fibrous materials-a new perspective

This issue reviews various areas where nanotechnology has come up predominately in fibrous materials, namely in electrospun polymeric nanofibers and polymer layered silicate nanocomposites. It includes synthesis, characterization, various methods of collecting nanofibers, factors affecting electrospinning, methods of increasing the productivity of the electrospinning process, and different electrospinning designs. It also covers synthesis and characterization of polymer nanocomposites. Various properties of nanocomposites are discussed. The rheological behavior and morphology of nanocomposites are covered. Different modeling and simulation methods applicable to electrospun nanofibers and polymer layered silicate nanocomposites are discussed. Some of the potential application areas of electrospun nanofibers, polymer layered silicate nanocomposites, and various products available in the market based on nanotechnology are also discussed. Some of the lacking areas and future prospects in nanofibrous structures (nanofibers and nanocomposites) are emphasized in this issue.     

Thermodynamic modeling of the Pd-X (X=Ag, Co, Fe, Ni) systems

A set of self-consistent thermodynamic model parameters is presented to describe the phase equilibria of the Ag-Pd, Co-Pd, Fe-Pd, and Ni-Pd systems. In most cases, the calculated values using the optimized model parameters agree very well with the experimental data. The FePd and FePd₃ phases with large homogeneity ranges are described by the compound energy formalism. At present, insufficient thermodynamic data are available for these two phases. Therefore, experimental data on the heat of formation and/or the first-principle calculation of cohesive energies will be very useful for further refinement of thermodynamic parameters of FePd and FePd₃ phases.     

Inhibition of replication of rinderpest virus by 5-fluorouracil

Groups of male Wistar rats lived in cages capable of monitoring feeding and drinking continuously at 0.1-s intervals, 24 h per day. Intact animals were subjected to 20 min of restraint stress or to brief handling (Brief Pick-Up), daily or every third day, 6 h after the beginning of the 12-h light period. In both studies, food-intake increased in the first hour after restraint, peaking between 15 and 45 min. Smaller increases were seen following Brief Pick-Up. More interestingly, the amount of food eaten increased across test sessions, indicating sensitization of the response to stress. Drinking also increased following stress, occurring before feeding and diminishing after the first 15 min. In adrenalectomized animals implanted with slow-release pellets to replace basal diurnal levels of corticosterone (ADX animals), sensitization of the feeding response to restraint stress developed across test sessions, although in these animals, the acute increase in food-intake following restraint stress was attenuated. ADX animals subjected only to Brief Pick-Up showed no increases in food-intake. Daily injections of 3.0 mg/kg corticosterone given to such ADX animals were unable to mimic the effects of restraint on either food-intake or drinking, nor did they augment the effects of restraint in ADX animals. We conclude that sensitization to the effects of brief restraint stress on food-intake can occur independently of a stress-induced rise in plasma corticosterone.     

GMR in Ni/Cu multilayers: an electronic structure study

Ab initio self-consistent semi-relativistic spin-polarized TB-LMTO energy band calculations have been carried out on Ni/Cu(100) multilayers, to study the in-plane as well as perpendicular to plane giant magnetoresistance (GMR) effects. The magnetic interaction energies, evaluated as a function of layer thickness, indicate that the antiferromagnetic ordering is a possible ground state for manifestation of GMR. Using the density of states at Fermi level and the Fermi velocity, GMR has been estimated as a function of the Cu spacer thickness.     

Design and Biopharmaceutical Evaluation of Nitrofurantoin-Loaded Eudragit RS100 Micropellets

Nitrofurantoin, a synthetic bactericidal drug, was encapsulated with Eudragit RS 100 polymer by a coacervation phase separation technique using variable proportions of polyisobutylene (0% to 3%) as a protective colloid. The micropellets were evaluated by scanning electron microscopy (SEM), particle size distribution, wall thickness, and loss of wall polymer were determined. The in vitro release experiments were carried out over the entire pH range of the gastrointestinal tract, the data obtained from the dissolution profiles were compared in the light of different kinetic models, and the regression coefficients were compared. The in vivo studies were performed on female human volunteers. A linear correlation was obtained from in vitro-in vivo studies.