Hidehiro Kamiya

The mechanism of defluidization of iron particles in a fluidized bed

To develop a qualitative model for the fluidization characteristics of cohesive iron particles, a systematic investigation was performed focusing attention on the mechanism of defluidization and the particle-to-particle neck growth. The neck growth rate determined by a scanning electron microscope (SEM) agreed fairly well with the prediction by the surface diffusion model. Below 1200 K, cohesion force was successfully explained by the neck growth model with the surface diffusion mechanism. The tensile strength of a neck measured by the diametral compression test was 20 MPa. This value agreed with the one obtained from the bed breaking velocity measurement. Defluidization criterion was discussed based on the balance between bubble buoyancy force and neck force. The prediction was validated experimentally.

Surface modification and characterization for dispersion stability of inorganic nanometer-scaled particles in liquid media

Abstract Inorganic nanoparticles are indispensable for science and technology as materials, pigments and cosmetics products. Improving the dispersion stability of nanoparticles in various liquids is essential for those applications. In this review, we discuss why it is difficult to control the stability of nanoparticles in liquids. We also overview the role of surface interaction between nanoparticles in their dispersion and characterization, e.g. by colloid probe atomic force microscopy (CP-AFM). Two types of surface modification concepts, post-synthesis and in situ modification, were investigated in many previous studies. Here, we focus on post-synthesis modification using adsorption of various kinds of polymer dispersants and surfactants on the particle surface, as well as surface chemical reactions of silane coupling agents. We discuss CP-AFM as a technique to analyze the surface interaction between nanoparticles and the effect of surface modification on the nanoparticle dispersion in liquids.

Anionic Surfactant with Hydrophobic and Hydrophilic Chains for Nanoparticle Dispersion and Shape Memory Polymer Nanocomposites

An anionic surfactant comprising a hydrophilic poly(ethylene glycol) (PEG) chain, hydrophobic alkyl chain, and polymerizable vinyl group was synthesized as a capping agent of nanoparticles. TiO(2) nanoparticles modified by this surfactant were completely dispersible in various organic solvents with a wide range of polarities, such as nitriles, alcohols, ketones, and acetates. Furthermore, these particles were found to be dispersible in various polymers with different properties, such as thermosetting epoxy resins and radical polymerized poly(methylmethacrylate) (PMMA). A polymer composite of surface-modified TiO(2) nanoparticles in epoxy resins prepared by using the developed surfactant also possessed temperature-induced shape memory properties.

Tuning the stability of TiO2 nanoparticles in various solvents by mixed silane alkoxides.

The surface of TiO(2) nanoparticles which were well dispersed into acidic aqueous solution was successfully modified by silane alkoxides without strong aggregate formations. By adding decyltrimethoxysilane (DTMS) as silane alkoxides into the TiO(2) aqueous solution which were carefully diluted with methanol, DTMS slowly attached onto the TiO(2) surface without rapid hydrolysis and condensation reaction among DTMS. Because of the hydrophobicity of DTMS, the dispersed TiO(2) nanoparticles slowly formed flocks as DTMS reacted on TiO(2). These flocks were able to be completely redispersed into nonpolar solvents even after they were collected by centrifugation and drying under vacuum as dry powder. Furthermore the surface of TiO(2) nanoparticles have been successfully tuned by combining silane alkoxides which contains hydrophobic and hydrophilic groups such as DTMS and 3-aminopropyltrimethoxysilane (APTMS), respectively, toward their complete redispersion into various solvents. While TiO(2) nanoparticles modified by DTMS were redispersible into toluene, those modified by mixed alkoxides of 50 mol % DTMS and 50 mol % APTMS were redispersible into a mixed solution of toluene and methanol. Further when they were modified by mixed alkoxides of 25 mol % DTMS and 75 mol % APTMS, they were redispersible into polar solvents such as methanol with a little addition of acids.

Modelling of sintering of iron particles in high-temperature gas fluidisation

A recently published theory of de-fluidisation of gas fluidised beds has been extended to the case of sintering produced by surface and volume diffusion. The theory was tested against a recently published investigation of the sintering and de-fluidisation behaviour of iron particles at temperatures above 700 K. The theory successfully predicted the dependence on temperature of the gas velocity required to prevent de-fluidisation as a function of the activation energy for surface diffusion. The assumptions made in the theory and the effects of scale are discussed.

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.

Layer-by-layer surface modification of functional nanoparticles for dispersion in organic solvents.

In order to prepare SiO(2) nanoparticles that are dispersible in various organic solvents, an anionic surfactant 1, which branches into a hydrophobic chain and a hydrophilic chain, was adsorbed on to SiO(2) nanoparticles through a layer-by-layer surface modification route using polyethyleneimine (PEI). First, the relationship among the additive content of PEI, adsorbed content of PEI, and the redispersion stability of the SiO(2) nanoparticles in water was investigated. While almost the entire PEI was adsorbed when the additive PEI content was lower than 67 mg/g of SiO(2), the adsorbed content of PEI became saturated when the additive content was increased above 90 mg/g of SiO(2). SiO(2) nanoparticles that were saturated with PEI could be redispersed into water at sizes close to their primary particle size without the large-scale formation of aggregates. Next, the anionic surfactant 1 was adsorbed on the SiO(2) nanoparticles by using a SiO(2) aqueous suspension saturated with adsorbed PEI. It was found that the adsorbed content of 1 increased almost linearly as the additive content was increased when the additive condition was below 1400 mg/g of SiO(2). Furthermore, SiO(2) nanoparticles adsorbed with 80 mg/g of SiO(2) of PEI and 810 mg/g of SiO(2) of 1 could be dispersed into various organic solvents with different polarities. This layer-by-layer modification technique can also be applied to Ag nanoparticles in order to prepare Ag nanoparticles that can be dispersed in various organic solvents.

Microscopic analysis on the consolidation process of granule beds

The effect of deformation properties of individual granules on the consolidation process of granule beds was investigated. Four kinds of alumina granules were used as sample materials for the tests. The consolidation process of granule beds was examined using a uniaxial compression tester, and the deformation behavior of a single granule under the compressive force was investigated with a diametral microcompression testing machine. The deformation curve of a single granule was characterized by the yield value and the breakage force, which were correlated with the consolidation starting stress of the granule bed. As a result, it was found that the yield value of a single granule was proportional to the compressive force between granules, which was calculated by applying Rumpfs equation for the granule bed at the consolidation starting stress.

Development of a split-type tensile-strength tester and analysis of mechanism of increase of adhesion behavior of inorganic fine powder bed at high-temperature conditions

To analyze the phenomenon of the increase in cohesive force between fine particles under elevated temperature conditions, a new split-type tensile-strength tester of powder beds for high temperature was developed. Fused silica glass with low thermal expansion coefficient was used as the material for the suspended cell of a commercial split-type tensile-strength measuring device at room temperature. The powder samples used were pure fine silica and two kinds of fly ash powders collected in a pulverized coal (PC) combustion and a pressurized fluidized coal combustion systems. Under conditions of relatively low temperatures below 1000 K, the adhesive force of all powders increased gradually in proportion to the temperature. Rapid increases of tensile strength of both fly ash powder beds were observed in the high-temperature range (above 1100 K). Based on the results of thermo-mechanical analysis (TMA), it was estimated that a viscous flow sintering mechanism controlled this rapid increase phenomenon of adhesive behavior of ash powders at high-temperature conditions above 1100 K. On the other hand, using FT-IR analysis, it was demonstrated that the increase of the van der Waals force with the change of surface molecular structure controlled the stickiness of pure silica and both ash powders at relatively low-temperature conditions below 1000 K.

Spontaneous gelcasting of translucent alumina ceramics

Translucent alumina ceramics was fabricated by a novel and simple gelling system using a water-soluble co-polymer of isobutylene and maleic anhydride (Isobam), acting as dispersant and gelling agent. Alumina slurry was prepared by mixing alumina powder, deionized water and 0.5wt% Isobam. Both rheological properties and gelling behaviors of the slurry were evaluated. Without an initiator or any other additives, gelation of the slurry occurred at room temperature in air atmosphere. After dried and presintered, the green body was sintered at 1850°C for 5h in vacuum furnace. In-line transmittance of the resultant alumina ceramics (1mm thick) was 29.5% at 600nm.