Mayumi Tsukada

Gas motion and bubble formation at the distributor of a fluidized bed

Abstract The hydrodynamic structure of the grid zone, i.e. , the region between the bed bottom and the jet top, was investigated by using semicylindrical fluidized beds having a transparent front wall. It was found that in the grid zone there were two different regions: the lower region named the ‘jet stem’ region where jets exist stably and the upper region named the ‘bubble-forming’ region. The effects of particle diameter and superficial gas velocity on the heights of these regions were experimentally investigated. It was found that the fraction of the bubble-forming region in the whole jet height was strongly dependent on particle diameter.

Direct measurement of interactions between stimulation-responsive drug delivery vehicles and artificial mucin layers by colloid probe atomic force microscopy.

A novel thermo- and pH-sensitive nanogel particle, which is a core-shell structured particle with a poly(N-isopropylacrylamide) (p(NIPAAm)) hydrogel core and a poly(ethylene glycol) monomethacrylate grafted poly(methacrylic acid) (p(MMA-g-EG)) shell, is of interest as a vehicle for the controlled release of peptide drugs. The interactions between such nanogel particles and artificial mucin layers during both approach and separation were successfully measured by using colloid probe atomic force microscopy (AFM) under various compression forces, scan velocities, and pH values. While the magnitudes of the compression forces and scan velocities did not affect the interactions during the approach process, the adhesive force during the separation process increased with these parameters. The pH values significantly influenced the interactions between the nanogel particles and a mucin layer. A large steric repulsive force and a long-range adhesive force were measured at neutral pH due to the swollen p(MMA-g-EG) shell. On the other hand, at low pH values, the steric repulsive force disappeared and a short-range adhesive force was detected, which resulted from the collapse of the shell layer. The nanogel particles possessed a pH response that was sufficient to protect the incorporated peptide drug under the harsh acidic conditions in the stomach and to effectively adhere to the mucin layer of the small intestine, where the pH is neutral. The relationships among the nanogel particle-mucin layer interactions, pH conditions, scan velocities, and compression forces were systemically investigated and discussed.

THE EFFECT OF PRESSURE ON THE PHASE TRANSITION FROM BUBBLING TO TURBULENT FLUIDIZATION

Abstract Bubbling, turbulent and fast fluidized beds are the major phases of gas-solid dense suspensions. In this paper the effect of pressure on the phase transition from bubbling to turbulent fluidization was investigated over the pressure range 0.1–0.7 MPa with a small-scale circulating fluidized bed placed in a pressure vessel. It has been found that the gas velocity at which the transition takes place decreases with increasing pressure but the solid mass flux at the transition remains almost constant. Detailed measurements on the meso-scale flow structures were made to explain the transition characteristics.

Analysis of biomass combustion ash behavior at elevated temperatures

Abstract Change in tensile strength of a biomass ash powder bed measured by a split-cell type tester at a variety of temperatures up to 900°C was discussed corresponding to the microscopic behavior of ash particles observed by a field emission scanning electron microscope (FE-SEM) with a computer-controlled stage, a heat treatment chamber and an energy dispersive X-ray spectrometer. Tensile strength of a biomass powder bed increased with temperature by two different steps. In temperatures ranging from400 to 700°C, the powder bed had liquid-phase bridging between particles, which caused the relatively large fracture distance in fracture curves. FE-SEM observation showing rounded ash particles after heat treatment at 500°C supported this phenomena. On the other hand, at temperatures higher than 700°C, powder beds showed brittle fracture, which means the absence of any liquid bridge due to evaporation. FE-SEM observation revealed successive evaporation from ash samples in this temperature region.

Instrumentation and Measurements

The calibration of capacitors at the National Physical Laboratory in Britain is discussed in a paper by Rayner and Ford.1 Their primary standard of reactance is a standard inductor which is used to calibrate capacitors with a Carey-Foster Bridge. Then a precision Schering Bridge is used for comparing capacitors with an error of ± 1 in 10,000 and ± .00002 in power factor. L. H. ford2 has measured the effect of humidity on the capacitance end power factor of precision air capacitors and notes that changes in capacitance of 3 in 10,000 are noted at relative humidity of 65%. This is more than the amount predicted by the change in the dielectric constant of air by the water vapor. The power factor also increases at relative humidity above 40% reaching 0.00008 at 65% R.H. The measurements were made so as to eliminate the effect of insulators. New standards of very small capacitance from 0.001 to 100 F were developed by Moon and Sparks3 in which they placed the measuring electrode at the bottom of a well with the guard electrode surrounding it and much closer to the opposite electrode.

Metal powder granulation in a plasma-spouted/fluidized bed

Abstract D.c. plasma-spouted/fluidized bed was applied to the granulation of spherical alloy grains from metal powder mixtures. From a mixture of iron powder (dp = 149−210 μm) and aluminum powder (dp = 74−88 μm and 125−149 μm) alloy grains of 1–5 mm in diameter were obtained. The grains exhibited a dense homogeneous core and a porous nonhomogeneous shell structure. The grains were quite spherical; the average aspect ratio of the grains was larger than 0.85. The mass fraction of iron in the core section of product grains depended on the Al Fe ratio of initial powder mixtures but was insensitive to the size of product grains and to the size of initial aluminum particles. The growth mechanism was discussed based on the growth rate measurement. Selective growth of seed grains was observed when sufficient seed grains were added to the starting powder mixture.

Microstructure of iron particles reduced from silica-coated hematite in hydrogen

Poly- and nearly monocrystalline hematite particles having diameters of around 2 and 0.1 μm, respectively, were prepared by the gel-sol method and coated with a uniform silica layer by the sol-gel method. The core in the silica shell was reduced to iron without agglomerate formation between the particles by using a hydrogen stream. The microstructure and morphology of these cores and the silica layers were examined by high-resolution transmission electron microscopy, and electron and X-ray diffraction analysis. In hematite particles, around 2 μm in diameter, the reduced products were mostly α-Fe, but partially magnetite. In hematite particles, around 0.1 μm in diameter, only α-Fe was observed. Most of the raw hematite and iron particles produced were monocrystalline, and part of core grew hexagonal prism-shaped monocrystalline particles. In the case of the growth of a crystal to a hexagonal prism, a nanometer-scaled space at the interface between the iron crystal core and the silica layer was discovered.

Analysis of Anionic Polymer Dispersant Behavior in Dense Silicon Nitride and Carbide Suspensions Using an AFM

The paper focuses on the interaction mechanism caused by anionic polymer dispersants in dense silicon nitride and silicon carbide suspensions. An atomic force microscope (AFM) was used to determine the relationship between the macroscopic suspension viscosity and the microscopic structure adsorbing of a polymer dispersant at the solid/liquid interface. The surface interactions within the suspensions were analyzed under various dispersant pH values and additive conditions. The addition of an anionic polymer dispersant decreased the viscosity of silicon nitride and silicon carbide suspension and increased the electrosteric repulsive force on the non-oxide surface in solution at pH > 6, which was the isoelectric point of the materials. Based on the above results, we estimated the adsorption mechanism of anionic polymer dispersants on each solid surface in solution under relatively high pH conditions.