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Probing polycrystals' stress The way that a polycrystalline material deforms is in part determined by internal stresses between and within crystal grains. Hayashi et al. developed an x-ray method for mapping the intragranular stresses in a polycrystalline material. They found surprisingly large stresses, which are important for the fundamental understanding of how these materials will fail. This method will work for other materials and provides important information for multiscale deformation modeling. Science , this issue p. 1492

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.

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 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 and corners in the inverse pole figure.

A scanning three-dimensional X-ray diffraction (3DXRD) microscope apparatus with a high-energy microbeam was installed at the BL33XU Toyota beamline at SPring-8. The size of the 50keV beam focused using Kirkpatrick-Baez mirrors was 1.3 μm wide and 1.6 μm high in full width at half maximum. The scanning 3DXRD method was tested for a cold-rolled carbon steel sheet sample. A three-dimensional orientation map with 37 3 voxels was obtained.

We have investigated hexagonal silicon carbide with low dislocation density to reveal inherent dislocation types and structures using the bulk-sensitive synchrotron X-ray topography. This topographic study reveals that: (1) Basal-plane dislocations with the Burgers vector of 1 3 〈1 1 2 ¯ 0〉 preferred to be screw dislocations along 〈1 1 2 ¯ 0〉 in straight shape. (2) Threading dislocations containing the Burgers vector component of 〈0 0 0 1〉 are mostly mixed dislocations containing that of 1 3 〈1 1 2 ¯ 0〉. (3) Threading edge dislocations with the Burgers vector of 1 3 〈1 1 2 ¯ 0〉 are of short lengths, about 30–100 μm. (4) All these dislocations are connected to convert, combine and dissociate to each other. We discuss the dislocation types and structures in terms of both the Peierls energy and elastic interaction. Moreover, we propose that the source of dislocations with the Burgers vector of 1 3 〈1 1 2 ¯ 0〉 is due to the propagation from a seed crystal rather than due to the Frank–Read mechanism.

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 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.

The UV-vis absorption, MCD and fluorescence spectra of phthalocyaninatosilicon ( SiPc ) covalently linked to one or two TEMPO radicals have been studied in comparison with those of (dihydroxy) SiPc . The electronic absorption and MCD spectra show little change on substitution of TEMPO radicals, indicating that the electronic interaction between excited singlet SiPc (1 SiPc *) and doublet TEMPO (2 TEMPO ) is very weak or non-existent. In contrast, fluorescence quantum yields decrease markedly with increasing number of TEMPO radicals. This result is interpreted reasonably by assuming that the decay from 1 SiPc * to excited triplet SiPc (3 SiPc *) partially becomes a spin-allowed transition owing to the interaction between 3 SiPc * and 2 TEMPO .

Phthalocyaninatosilicon(IV) covalently linked to a 2,2,6,6-tetramethyl-1-piperidinyloxy (TEMPO) radical, SiPc-TEMPO, has been studied by time-resolved electron paramagnetic resonance (TREPR). A TREPR spectrum at 20 K is assigned to the doublet ground (D0) state and the excited quartet (Q1) state consisting of the excited triplet SiPc and the doublet TEMPO radical. The excited quartet spectrum is simulated using zero field splitting parameters D = 4.3 × 10-3 and E = 3.3 × 10-4 cm-1. The D value observed is almost identical with that calculated under a point charge approximation (= 4.7 × 10-3 cm-1). The electron spin polarization of the Q1 state is reproduced by selective intersystem crossing (ISC) from the excited doublet states to the |±1/2> sublevels in the Q1 state. This selective ISC is explained by spin−orbit coupling between the Px and Py orbitals on oxygen atoms of axial-ligands. In the TREPR spectrum at 293 K, SiPc-TEMPO molecules in the Q1 and D0 states exhibit A and E polarizations, respectively,...

The damage layer of a Si(100) surface induced by low-energy (300–600 eV) rare-gas (Ne, Ar, or Xe) ion bombardment was in situ analyzed by x-ray photoelectron spectroscopy (XPS). The XPS analysis showed that, irrespective of the ionic species, an amorphous Si (a-Si) layer with a thickness of 10–30 A was formed and saturated by the dose of 1015 cm−2. It also showed that the thickness increased linearly with the ion energy and Ne ions formed the thickest a-Si layer. The saturated thickness measured with the XPS analysis has been confirmed by cross-sectional transmission electron microscopy. Formation process of the a-Si layer under small dose of ions can be explained in terms of the Poisson process. As a result, the size of an a-Si region formed by single ion bombardment was estimated. The region, which is supposed to have a cylindrical shape, has a radius of 2–4 A and a height of 10–30 A for each ionic species and energy. In situ XPS analysis for the Si surface bombarded with ion beams revealed the growth p...

Magnesium and its alloys are considered one of the most promising materials for reversible hydrogen storage. However, their high thermodynamic stability is unfavorable for dehydrogenation processes. In order to improve their properties, understanding of the bonding nature of Mg and H is essential. In this study, we reveal the precise experimental charge density distribution in MgH 2 . X-ray powder diffraction data were obtained using the synchrotron radiation. The charge density distribution was calculated by the MEM (maximum entropy method)/Rietveld analysis. At room temperature, the charge density distribution around Mg is spherical, whereas the lower charge density distribution around H is non-spherical and slightly spread in the direction of the nearest neighbor Mg and H atoms. The number of electrons within the sphere around the Mg and the H atoms were estimated from the obtained distribution. As the result, Mg is almost fully ionized as Mg 2+ , whereas hydrogen is very weakly ionized. The ionic charge of hydrogen is lower than the theoretical value.

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.

The heterogeneous structure of poly (vinyl alcohol)-poly(sodium acrylate) composite hydrogels (PVA-PAA gels), prepared by repeatedly freezing and thawing mixed aqueous solutions of PVA and PAA, has been studied using pulsed NMR. The free induction decay (FID) signals of the transverse magnetization for the PVA-PAA gels were measured by both Carr-Purcell-Meiboom-Gill and solid-echo pulse sequences. The FID signal was decomposed into two or three decaying signals with various spin-spin relaxation times, based upon differences in the molecular mobility that reflected structural heterogeneity. The structural heterogeneity of the PVA-PAA gel is quite different from that of PVA gel free of PAA

MgH2 is one of the promising base materials for hydrogen storage, which is a key technology of clean energy source. In this study, the bonding nature of hydrogen in MgH2 was fully uncovered by examining the charge density distribution of this substance obtained by the maximum entropy method from the synchrotron radiation powder data. MgH2 can be expressed as Mg1.91+ H0.26−, which is much weaker ionicity than the theoretical expectations. It also shows weak covalence between Mg and H. Though the bonding nature of hydrogen in MgH2 is rather complex, i.e., the mixture of ionic and covalent bonding, it is certain that hydrogen is weakly bonded to Mg, which must be a big advantage of hydrogenation–dehydrogenation of this substance.

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.

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.

Deformation of poly(vinyl alcohol)–poly(sodium acrylate) composite hydrogel (PVA–PAA gel) under sinusoidally varying electric fields was studied in electrolyte solutions. The PVA–PAA gel was prepared by repeatedly freezing and thawing a mixed solution of PVA and polyacrylic acid. A cyclic bending–straightening motion of the PVA–PAA gel rods of about 1 mm in diameter have been observed in Na2CO3 aqueous solutions under the fields. The PVA–PAA gel had a response time of less than several hundreds milliseconds. The bending has also been observed in organic solvents containing an electrolyte when the organic solvent is electrolyzed. It was found that the motion of the gel under electric fields of less than 1 Hz occurred mainly through swelling due to the change of the osmotic pressure based upon the difference of the ion concentration. However, it has not been determined whether the motion at higher frequencies is caused by the osmotic effect. © 1993 John Wiley & Sons, Inc.

ポリ (3-ブチルチオフェン) ゲル (P3BTゲル) の有機溶媒中での外部電場による変形挙動を検討した. P3BTゲルは3-ブチルチオフェンと1, 8-ジ (3-チエニル) オクタンを定電流電解重合し, その生成物をTHFに浸漬することにより得た. P3BTゲルは支持電解質を含むテトラヒドロフラン (THF) 中で1.5V以上の直流電圧の作用で収縮し, また同時にオレンジ色から青色に変化することが明らかになった. これらの変化は電場に対して可逆的であった. 可視スペクトル変化, 化学ドーピングとの比較考察から, 電場による体積と色の変化はP3BTゲル中のポリチオフェン鎖の電気的なドーピングと脱ドーピングによるものと考えられた.

Gels exposed to stationary electric fields on the order of 0.1 to 1.0 V/cm were found to develop pH gradients. The development of these pH gradients appears to be a relevant phenomenon in explaining the phase transitions and volume changes of ionic gels induced by an electric field. It was also found that the occurrence of pH gradients is strongly affected by the type and concentration of the ions present in the gel. The ions in a gel could be classified into different categories, depending on whether they were counter-ions of the charged groups on the polymer network or free ions, and whether they would participate in electrochemical reactions or not. Using a simple theoretical consideration, which takes into account diffusion, ionic drift, dissociation equilibria and electroneutrality, the pH profiles of gels under stationary electric fields have been evaluated and compared with experimental results.

The influence of de electric fields on sodium acrylate—acrylamide copolymer gel near a phase transition point in acetone—water mixtures containing NaOH was studied. In the mixtures free of NaOH, the shrunken-state gel near a phase transition point was not influenced by dc electric fields, while the swollen-state gel near it shrank from its part facing to the positive electrode in dc electric fields. In the presence of NaOH, unprecedented swelling of the shrunken-state gel has been observed. The swollen-state gel showed swelling or shrinking in the field. The type of deformation was determined by the concentration of NaOH. The drift of mobile ions played a role in the deformation. The shrinking occurred through the conformational change of polymer network caused by the drift. The swelling was observed by the change of the osmotic pressure based upon the ion concentration difference between the inside and the outside of a gel.

When an electric field is applied to an ionic gel in a buffer solution, the anode side of the gel shrinks if the gel is contacting with the electrode, while it swells if the gel is placed with sufficient separation from the electrode. The changes of ion concentration profiles under an electric field are calculated, taking account of ion transports and electrochemical reactions. Combining these results with Flory's theory for the swelling of ionic gels, the above phenomena are explained. It is predicted that the swelling behavior is governed by the concentration of the dominant ions and that the swelling speed is proportional to the square of the electric current

Bending of poly(vinyl alcohol) hydrogel mixed with poly(sodium acrylate) chains, PVA–PAA gel, under the influence of dc electric fields was studied. The PVA–PAA gel was prepared by repeatedly freezing and thawing a mixture of PVA and polyacrylic acid aqueous solutions. The PVA–PAA gel was a hydrogel with the PAA chains, which were entangled with the PVA polymer network and were fixed in the gel. The PVA–PAA gel bent toward the negative electrode in electrolyte solutions under dc electric fields as did the polyelectrolyte gel with negatively charged polyions. The PVA gel, free of PAA, was insensitive to dc electric fields. The deflection of the bending and the bending speed were influenced by the filed intensity, the concentration of the polyion in the gel, and the thickness of the gel. The bending of the PVA–PAA gel was qualitatively explained by a bending theory of polyelectrolyte gel, based upon the change of the osmotic pressure due to the ion concentration difference between the inside and the outside of the gel.

微量の水分を吸着した架橋ポリメタクリル酸のナトリウム塩及びコバルト塩をハロゲン化パラフィンに分散してなる電気粘性流体のER効果について粒子鎖モデルによる解析ならびに実験結果との比較を行った. 粒子鎖モデルでは分散粒子は電場により瞬時に分極して質点双極子を形成し, かつ隣接する二つの粒子間のみに双極子間相互作用が働いて電極間で直鎖を形成すると仮定した. ER効果を反映する降伏応力に対する粒子の分散濃度, 粒径及び誘電率, 電場強度の影響を検討したところ, 導電性の低いコバルト塩粒子系流体は定性的かつ定量的にも粒子鎖モデルに従ってほぼ挙動することが明らかにされた. しかし, 導電性の高いナトリウム塩粒子系流体の挙動は粒子鎖モデルでは十分に説明できないことが分かった.

微粒子を分散した高分子ゲルの電場下における粘弾性挙動を検討した. 微粒子には少量の水分を含むポリメタクリル酸コバルト塩の粒子を, 高分子ゲルには二液反応型のシリコーンゲルをそれぞれ用いた. 試料はシリコーンゲルの反応に微粒子を所定量均一に分散させた後, 加熱することにより得た. 微粒子分散高分子ゲルは電場の作用でその粘弾性を可逆的に変化させることが明らかになった. この電気粘弾性効果は分散粒子濃度が高く, 電場印加前に微粒子が互いに接触している状態のときに観測された. 粘弾性変化の大きさは印加電場の強度, せん断ひずみの大きさと周波数などに依存した. 電場下では電流が観測された. 微粒子分散高分子ゲルの示す電気粘弾性効果はマトリックスが絶縁油である懸濁液の示すそれよりも大きいことが明らかにされた.

The excited state characteristics of phenylene (Ph)-bridged periodic mesoporous organosilica (PMO) powders with crystal-like and amorphous wall structures are investigated. Crystal-like Ph-PMO has a molecular ordering of the bridging organic moieties with intervals of 0.76 and 0.44 nm parallel and perpendicular to the mesochannel direction, respectively, whereas amorphous Ph-PMO has no molecular-level periodicity in the wall. Fluorescence from the exciton and excimer of the Ph moieties and the defect center in the silicate network were detected at room temperature, but fluorescence from the excimer and the defect center were not detected at 77 K for crystal-like Ph-PMO dispersed in a methanol/ethanol mixed solvent. The decay curve of the exciton fluorescence of crystal-like Ph-PMO at room temperature was analyzed successfully using a one-dimensional diffusion model quenched by the defect center and the excimer site. The results were discussed in comparison with those for the crystal-like biphenylene-bridged PMO reported in the preceding paper (Yamanaka et al., Phys. Chem. Chem. Phys., 2010, 12, 11688-11696). The existence of excited states with various conformations including ground state dimers or aggregates of the Ph moieties was suggested for amorphous Ph-PMO. It was clearly apparent that the differences in the excited state dynamics reflected the differences in the molecular-level structure in the wall.

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 electrorheological (ER) effects of suspensions of poly‐p‐phenylene (PPP) particles dispersed in a silicone oil were studied experimentally. The experimental results were analyzed qualitatively using a model in which the particles act as points dipoles in electric fields and then formed many chains due to dipole–dipole interactions at a short range. Large ER effect has been observed in the suspension by using the PPP particles with small amount of adsorbed CuCl2. The magnitude of the ER effect could be controlled by the content of CuCl2. The suspension showed the high temperature working limit of at least 100 °C. The effects of particle concentration, field intensity, and particle dielectric constant on the ER effect were not qualitatively similar to the model. It was found that the increase of the real part of the complex dielectric constant of the PPP particles at lower frequencies played an important role in producing the ER effect.

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.

Reentrant volume–phase transitions are observed in N‐isopropyoacrylamide gels in the methanol–water mixtures. When the solvent composition is varied systematically, the gel undergoes two transitions: a discontinuous collapsing followed by a discontinuous swelling. The reentrant transition defines a closed‐loop instability phase boundary having both upper and lower critical points. The closed‐loop phase boundary depends on temperature and diminishes to a point at approximately 0 °C. A simple mean field theory is presented to describe the phenomenon, which reveals an alteration of free energy of alcohol–water interaction by presence of polymer network. In the case of ethanol–water mixtures, there appear two closed‐loop phase boundaries, whose physico‐chemical basis are not yet clear.

Polymer gels, consisting of a cross-linked polymer network immersed in liquid, undergo a volume phase transition: when external conditions such as temperature or solvent composition change, a gel reversibly swells or shrinks, but does so discontinuously1–5. The volume change at the transition can be as large as a factor of one thousand2, and the phenomenon occurs in all gels6,7. The equilibrium aspects of the phase transition have been extensively studied, but its kinetics have not yet been fully explored. In particular, the appearance of patterns on the originally smooth surface of a gel during the transition makes the kinetic process difficult to understand. Here we elucidate the physical basis underlying the formation and evolution of the pattern.

Transition de phase de spheres de gels ionises de N-isopropylacrylamide avec des diametres compris entre 0,2 et 1 μm

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

A multidetector whole-body single photon emission computed tomography (SPECT) scanner has been developed for high-resolution dynamic SPECT imaging. The scanner consists of three detector rings with 128 NaI crystals (14 x 26 x 30 mm) in each ring, providing three tomographic images at 30 mm intervals. This system uses a rotation of collimator around the patient combined with the detector rotation for fine data sampling. The in-plane spatial resolution is 14.2 mm (full width of half maximum) with high-resolution (HR) collimator, 22.0 mm with high-sensitivity (HS) collimator, and 10.6 mm with high-resolution brain (HRB) collimator. The axial resolution is 24.0, 34.0, and 23.5 mm with HR, HS, and HRB collimator, respectively. The sensitivity measured with a 20% energy window for /sup 99m/Tc in a 20 cm diameter phantom is 5.7, 17.0 and 6.6 kcps/muCi/ml with HR, HS, and HRB collimator, respectively. This scanner allows dynamic SPECT imaging both for brain and body organs with good spatial resolution.

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.

Etude de la possibilite d'utilisation de la methode IR pour la determination de la teneur en phase vitreuse residuelle dans des echantillons de cordierite frittee