Akihiko Koiwai

The effect of oxygen deficiency on the structural phase transition and electronic and magnetic properties of the spinel

The effect of oxygen deficiency on a phase transition from cubic to tetragonal phase has been investigated for the spinels with by measurements of differential scanning calorimetry (DSC), magnetic susceptibility nuclear magnetic resonance ( NMR) and electronic resistivity . According to the DSC measurements, the transition temperature for a stoichiometric compound is determined to be K. As increases from zero to 0.066, the magnitude of is found to decrease by about 4 K; then, the magnitude of increases by about 41 K with further increase of up to 0.10; thus, the curve exhibits a broad minimum at around . This relationship between and is also observed by the measurements of NMR and . The dependence of on is considered to be a result of a competition between a decrease in the average valence of Mn ions and a dilution of the nearest-neighbour interaction between Mn ions. Both effects are caused by the oxygen deficiency; the former raises , whereas the latter reduces it.

Nonresonant third‐order nonlinear optical susceptibility of CdS clusters encapsulated in zeolite A and X

Nonresonant third‐order harmonic generation from CdS clusters encapsulated in zeolite A and X was observed at a fundamental wavelength of 1900 nm. To avoid scattering from the surfaces of the small zeolite crystals, the powder samples were dispersed in a liquid with nearly the same refractive index as that of the samples. The third‐order optical susceptibilities of CdS‐encapsulated zeolite A and X estimated from the intensity of their Maker fringe patterns were 4.1×10−12 and 1.1×10−11 esu, respectively. These values were slightly smaller than those reported for the 1.5 nm surface‐capped CdS cluster. The hyperpolarizabilities of CdS clusters encapsulated in zeolite A and X were estimated by assuming the Lorentz local field to be in the range of 380–480×10−36 and 270–390×10−36 esu, respectively.

Synthesis of polymers with densely-grafted oligo(ethylene glycol)s by Pd-initiated polymerization of oxyethylene-containing diazoacetates

Synthesis and characterization of polymers with densely-grafted oligo(ethylene glycol)s (OEGs) are described. Polymerization of OEG-containing diazoacetates with (η3-C3H5)PdCl-based initiating systems afforded C–C main chain polymers bearing OEGs on each main chain carbon atom. The polymers with a short OEG side chain showed a lower critical solution temperature-type phase separation in an aqueous medium; the transition temperatures were higher than those of the corresponding vinyl polymers with the same oxyethylene chain length. In addition, the Li-ion conductivity was examined to reveal that the polymers with densely-grafted OEGs showed higher values than the corresponding vinyl polymers, despite the fact that no significant difference in the glass transition temperature was observed between the two types of polymers.

A 7Li nuclear magnetic resonance study on spinel LiMn2O4 − δ

Abstract A 7 Li nuclear magnetic resonance ( 7 Li-NMR) study was carried out to investigate the magnetic properties of powder samples of LiMn 2 O 4 and LiMn 2 O 3.9 in the temperature range between 160 and 400 K. Lowering the temperature from 400 K to ∼300 K, the width of the 7 Li-NMR line was found to increase monotonically, then increased rapidly at temperatures below 260 K for LiMn 2 O 4 and 290 K for LiMn 2 O 3.9 . Combining these results with those of differential scanning calorimetry (DSC) analyses, the transition temperature ( T C ) was determined to be ∼250 K for LiMn 2 O 4 and ∼290K for LiMn 2 O 3.9 . This indicated that the magnitude of T C of LiMn 2 O 4 − δ depends on the oxygen deficiency ( δ ). In addition, at temperatures below T C , the NMR line seemed to decompose into two Gaussian peaks; it was a symmetrical singlet at temperatures above T C . Thus, it is deduced that there are two possible sites for the lithium ions in the sample at temperatures below T C , and one equivalent site above T C .

Characteristics of Flow Curves for Blends of Immiscible Polymers with Intersecting Flow Curves

and Kunihiro OSAKI*2 *1 Toyota Central Research and Development Laboratories, Inc., Nagakute-cho, Aichi-gun, Aichi-ken 480-11, Japan *2 Institute for Chemical Research, Kyoto University, Uji 611, Japan Characteristics of flow curves for the blends of immiscible polymers , whose flow curves intersect each other, were investigated by computer simulation based on the concentric multi-layer model proposed previously. Flow curves of component polymers were approximated by the power-law. Calculations were performed for a few combinations of power-law indexes and for various blending ratios. Following results were obtained.(1)Flow curves for the blends with various ratios intersect at the same point as those of parent polymers do.(2)Flow curves lie in the order of blending ratio . (3)Flow curves are similar to that of a lower viscosity component at either side of the cross point on flow curves of parent polymers.(4)The region on flow curves, where the conventional blending rules on viscosity are applicable , depends on the ratio of power-law indexes of parent polymers and the value of shear rate and viscosity at the cross point. A good agreement between predicted and experimental results were attained for the blends of polystyrene and high density polyethylene .

Study on reaction and heat transfer of reactive polyurethane system for reaction injection molding (abstract)

A rheometer with a wide-gap Couette geometry was developed to study reactive kinetics and rheological properties of the reactive polyurethane systems for a reaction injection molding (RIM) . Viscosity and temperature changes during the adiabatic reactions were measured for three different polyurethane systems which had gelation times of a few seconds. The viscosity and temperature changes during the RIM process were predicted by a simple rheo-kinetic theory using the material parameters determined from the adiabatic measurements. A one-dimensional heat transfer analysis program of the RIM system was developed and the temperature profile in the urethan plate was calculated by the pre-determined material parameters. A good agreement was obtained between the measured temperature and the calculated one.

COMPUTER SIMULATION IN INJECTION MOLDING OF THERMOPLASTICS

In injection molding of thermoplastics, computer simulation is recognized to be a useful tool for parts and molds design. Mold cooling, polymer filling-packing-cooling, fiber orientation, material properties and stress analysis programs have been developed and applied to practical usage as computer aided engineering. This paper presents an outline of each analysis and its applications.