Yoshiharu Hirose

Thermal expansion of hot-pressed cordierite glass ceramics

Mesure du coefficient de dilatation thermique de plusieurs echantillons de vitroceramique de cordierite pressee a chaud. Le large spectre de valeurs est relie aux microfissures qui apparaissent au cours du refroidissement et a la transformation de phase hexagonale→orthorhombique

Deformation of ionic polymer gel films in electric fields

Deformation of ionic polymer gel films in electrolyte solutions was studied under the influence of electric fields. The ionic polymer gel films used were poly(vinyl alcohol)-poly(sodium acrylate) composite gel films with a thickness of the order of submillimetres. The vibration of gel films in a.c. electric fields, has been observed for the first time. It was suggested that the vibration behaviour was based on a differential swelling. The vibration of the ionic gel films was roughly analysed as a mechanical bending of a uniform cantilever beam by sinusoidally varying forces.

Electroviscoelastic effect of polymeric composites consisting of polyelectrolyte particles and polymer gel

The dynamic viscoelasticity of polymeric composites consisting of silicone gel and polymethacrylic acid cobalt(II) salt (PMACo) particles was studied in d.c. electric fields. It was measured by applying sinusoidally varying shear strain or compressive strain to the composites. It was found that the electric fields enhanced the storage and loss moduli of the composites, and changed the loss tangent (electroviscoelastic effect). The amount of the electroviscoelastic effect was influenced by the content of absorbed water in the PMACo particle, the fraction of PMACo particles, and the intensity of the electric field. It also depended on the amplitude and frequency of the applied strain. The increments of the compressive moduli due to the electroviscoelastic effect were much larger than those of the shear moduli.

Synthesis, crystal structure and non-linear optical properties of 2-amino-5-nitropyridine-L-(+)-tartrate, a new second-harmonic generation crystal

A new second-harmonic-generation (SHG) crystal 2-amino-5-nitropyridine-L-(+)-tartrate (ANPT) has been synthesized and its crystal structure determined by X-ray structure analysis. ANPT showed broad transparency, a high degree of hardness and a high melting point, which are preferred for non-linear optical (NLO) devices. The optical axes and refractive indices of ANPT were determined by analyses of reflective polarized light intensity changes depending on both the direction of incident polarized light and the configuration of crystal reflective surface. The crystalline NLO coefficient of ANPT was determined by the Maker fringe method as d33= 41 pm V–1 at 1.06 µm.

Electrically Driven Polymer Gel Finger Working in the Air

Using ionic polymer gel that demonstrated an electric field-associated bending mo tion in aqueous solutions, an electrically driven polymer gel finger has been constructed. The material used for the finger was a hybrid gel of a cylindrical poly(vinyl alcohol)-poly(sodium acrylate) composite gel (PVA-PAA gel) rod and PVA gel film containing sodium carbonate as a skin. The working gel finger has been designed by equipping the PVA gel film of the hybrid gel with two platinum wires as electrodes. When a dc voltage was applied, the finger bent smoothly toward the positive electrode at a relatively high speed in the air. The bending of the finger occurred through a differential swelling of the PVA-PAA gel in the hybrid gel. A prototype of a microrobot hand with two gel fingers has also been designed. The hand grasped or released a piece of paper in response to electric signals.

Deformation Behaviors of Polymer Gels in Electric Field

A polymer gel is a crosslinked polymer network swollen in a liquid medium. Polymer gels, solid-liquid coexistent materials, are candidate biomimetic materials. Recently, their mechanical strength has become very close to that of living muscle. In a soft structure of gels, as shown in Fig. 1, the motion of polymer networks and the diffusion of ions take place easily by an external stimulus. The large volume or shape change, induced by supplying thermal, chemical or electrical energy, is an inherent nature of swollen gels.1‒4 Therefore, polymer gels have various possibilities as advanced functional polymers.

Polycrystal orientation mapping using scanning three‐dimensional X‐ray diffraction microscopy

A modified three-dimensional X-ray diffraction (3DXRD) technique is proposed as a solution to the main problem with 3DXRD-type experiments, namely, polycrystalline diffraction spot overlap. The modified method, termed scanning 3DXRD, enables three-dimensional crystallographic orientation mapping in polycrystals using a narrow incident X-ray beam with a beam size sufficiently smaller than the average grain size. This method can potentially allow one to apply a 3DXRD-type technique to specimens with a larger number of grains. Moreover, because of the use of a far-field area detector, scanning 3DXRD provides spacious specimen surroundings for equipment such as stress rigs, which are not feasible in 3DXRD methods using a near-field detector. As a first demonstration, a three-dimensional orientation map was obtained by an experiment using a 20 × 20 µm beam and a well annealed iron specimen with an average grain size of 60 µm. Scanning 3DXRD compared reasonably well with orientation image microscopy by electron backscatter diffraction (EBSD), considering the influence of the beam size in the case of scanning 3DXRD. The spatial resolution was estimated to be about twice the incident beam size from a scanning 3DXRD reconstruction simulation using an orientation map modeled on the EBSD orientation image of the specimen.

Direct determination of Burgers vector sense and magnitude of elementary dislocations by synchrotron white x-ray topography

The x-ray topography by using highly coherent beam obtained at third-generation synchrotron facilities can provide higher spatial resolution and higher lattice-distortion sensitivity than those by former-generation facilities. Here, we report the direct determination of the Burgers vector senses and magnitudes of elementary dislocations in a high-quality silicon carbide single crystal using white x-ray section topography with a long sample-to-film distance. Our data strongly indicate that there are very weak but extraordinarily long-range elastic interactions between elementary screw dislocations. Those interactions govern dislocation-propagation behavior and the distribution of dislocations. Moreover, we found that white x-ray projection topography with a long sample-to-film distance can also be a powerful tool to effectively examine the detailed structure of elementary dislocations in single crystals.The x-ray topography by using highly coherent beam obtained at third-generation synchrotron facilities can provide higher spatial resolution and higher lattice-distortion sensitivity than those by former-generation facilities. Here, we report the direct determination of the Burgers vector senses and magnitudes of elementary dislocations in a high-quality silicon carbide single crystal using white x-ray section topography with a long sample-to-film distance. Our data strongly indicate that there are very weak but extraordinarily long-range elastic interactions between elementary screw dislocations. Those interactions govern dislocation-propagation behavior and the distribution of dislocations. Moreover, we found that white x-ray projection topography with a long sample-to-film distance can also be a powerful tool to effectively examine the detailed structure of elementary dislocations in single crystals.

In Situ Three-Dimensional Orientation Mapping in Plastically-Deformed Polycrystalline Iron by Three-Dimensional X-Ray Diffraction

In situ three-dimensional crystallographic orientation mapping in plastically-deformed polycrystalline iron is demonstrated using a modified three-dimensional x-ray diffraction method. This voxel-by-voxel measurement method enables the observation of intragranular orientation distribution. The experiment is performed using coarse-grained ferrite with a mean grain size of ~ 60 μm and an incident x-ray beam with a beam size of 20 μm × 20 μm. Grains averagely rotate approximately toward the <110> preferred orientation of body-centered cubic uniaxial tensile texture. Intragranular orientation distributions are spread as the tensile strain increases to 10.7 %. Furthermore, intragranular multidirectional rotations are observed in grains near the <100> and <111> corners in the inverse pole figure.

Synchrotron X-ray Topographic Analysis of Dislocation Structures in Bulk SiC Single Crystal

The detailed properties of the dislocations of SiC crystals were analyzed using ultrahigh-quality substrates manufactured by RAF (repeated a-face) growth method by means of bulk X-ray topography. From this analysis, we could reveal the detailed features of one type of basal plane dislocations and two types of threading dislocations. The basal plane dislocations were screw type with Burgers vector were parallel to <11-20> direction. One of the threading dislocations was mixed type close to screw dislocation parallel to the growth direction with Burgers vector of 1c+na (n=0, 1, 2, …). Another was the edge type parallel to the c-axis, which was lying between two basal plane dislocations. Moreover, these dislocations were found to be connecting with each other, constituting large network structures.