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The morphology of $$ \{ 10\overline{1} 2\} \left\langle {\overline{1} 011} \right\rangle $$ deformation twins formed in commercial purity titanium during an initial pass of equal-channel angular pressing was studied by transmission electron microscopy (TEM). The corresponding diffraction patterns show a symmetry line splitting of $$ (10\overline{1} 2) $$ twin boundaries (TB) which is related to the presence of interfacial defects. A simple modeling for the interaction between non-screw a-slip lattice dislocations (Burgers vector b = $$ \frac{1}{3}[\overline{1} \overline{1} 20] $$ ) and the $$ (10\overline{1} 2) $$ twin plane is used according to crystallographic geometry and vector conservation. The results show that dislocation dissociation into different Frank partial dislocations on the interfacial plane is more favorable than its transmission to the other side of the interface. The formation of the Frank partials at the TB can produce a small change in the TB misorientation angle and this is consistent with the symmetry line splitting of the $$ (10\overline{1} 2) $$ twin boundaries observed by TEM. [ABSTRACT FROM AUTHOR]

The article offers information on the voltage-dependent investigation regarding the detachment process of free-standing crystalline TiO2 nanotube (TNT) membranes. It states that TNT arrays were fabricated after annealing and were subjected to anodization. It also examines the effect of voltage on the detachment process. Findings show that resulting membranes have high-quality surfaces for several application systems including photoelectric devices, drug release systems, and photocatalysis.

brief introduction of the historical background of grain boundary engineering for structural and functional polycrystalline materials is presented herewith. It has been emphasized that the accumulation of fundamental knowledge about the structure and properties of grain boundaries and interfaces has been extensively done by many researchers during the past one century. A new approach in terms of the concept of grain boundary and interface engineering is discussed for the design and development of high performance materials with desirable bulk properties. Recent advancements based on these concepts clearly demonstrate the high potential and general applicability of grain boundary engineering for various kinds of structural and functional materials. Future prospects of the grain boundary and interface engineering have been outlined, hoping that a new dimension will emerge pertaining to the discovery of new materials and the generation of a new property originating from the presence of grain boundaries and interfaces in advanced polycrystalline materials. [ABSTRACT FROM AUTHOR]

TiO2 nanotube arrays were synthesized by anodization of Ti metal sheets followed by thermal annealing at elevated temperatures from 400 to 600 °C. Scanning electron microscopic measurements showed that dense arrays of nanotubes were produced with the inner diameter about 100 nm, wall thickness 35 nm, and length about 10 μm. X-ray diffraction measurements showed that the as-prepared nanotubes were largely amorphous, whereas thermal annealing led to the formation of well-defined anatase crystalline phase. More interestingly, at 470 °C, the brookite crystalline phase also started to emerge, which became better defined at 500 °C and disappeared eventually at higher temperatures, a phenomenon that has not been observed previously in TiO2 nanotube arrays prepared by anodization. The impacts of the TiO2 nanocrystalline structure on the photocatalytic activity were then examined by using the reduction of methylene blue in water as an illustrating example. Upon exposure to UV lights, the visible absorption profiles of methylene blue exhibited apparent diminishment. Based on these spectrophotometric measurements, the corresponding pseudo-first-order rate constant was estimated, and the sample thermally annealed at 500 °C was found to exhibit the highest activity. The strong correlation between the TiO2 crystalline characteristics and photocatalytic performance suggests that the synergistic coupling of the anatase and brookite crystalline domains led to effective charge separation upon photoirradiation and hence improved photocatalytic activity, most probably as a consequence of the vectorial displacement at the nanoscale junctions between these crystalline grains that impeded the dynamics of electron–hole recombination. These results demonstrate the significance of nanoscale engineering in the manipulation of oxide photocatalytic performance. [ABSTRACT FROM AUTHOR]

Polycrystalline silicon obtained by the crystallization of thin amorphous silicon films has been an important material for microelectronics technology during the last decades. Many properties are improved in crystallized amorphous silicon compared to the as-deposited polysilicon such as larger grain size, smoother surface, and higher-carrier mobility. In this work, the crystallization of amorphous silicon is investigated by combining transmission electron microscopy (TEM) observations and molecular dynamics calculations. TEM observations on a series of specimens have shown that the majority of the silicon grains are oriented with a $$ {\left\langle {110} \right\rangle} $$ zone axis normal to the surface. In order to understand the crystallization mechanism molecular dynamic simulations were performed. It is found that the $$ {\left\langle {110} \right\rangle} $$ c/amorphous interface exhibits the lowest reduced interfacial energy density while the $$ {\left\langle {111} \right\rangle} $$ c/amorphous has the lowest reduced energy differences per unit interfacial area. The most energetically unfavorable interface is $$ {\left\langle {001} \right\rangle} $$ c/amorphous. [ABSTRACT FROM AUTHOR]

Mechanical properties of Ti/Al–7Si assemblies produced by insert moulding were studied with a classical push-out test and a variant that is the circular-bending test. Special care has been taken for controlling both the reactivity at the Ti/Al–7Si interface and the metallurgical health of the Al–7Si matrix. Mechanical tests until complete debonding have been completed with interrupted tests, metallographic characterizations and FEM analysis of elastic stress state. A mean shear strength of the interface of about 120 MPa was obtained. When the Ti insert is solely fretted in the matrix, without chemical interaction between Ti and the Al–7Si alloy, the mean shear strength is significantly lower (48 MPa). This result clearly shows that chemical interaction at the interface (formation of a thin TiSi layer at the Ti side and a thick Al3Ti(Si) layer at the Al–7Si alloy side) improves the mechanical properties of the assembly. It is also shown that the failure sequence is characterized both by crack propagation from bottom to top and matrix yielding from top to bottom. Actually, interface damaging begins by crack initiation at the specimen bottom face (not at the top face and under the indenter) in a nearly pure mode I solicitation at a radial tensile stress of about 100 MPa. [ABSTRACT FROM AUTHOR]

The thermal behaviour of the animal by-product meat and bone meal (MBM) has been investigated in order to assess how it is affected structurally and chemically by incineration. Initially composed of intergrown collagen and hydroxyapatite (HAP), combustion of the organic component is complete by 650 °C, with most mass loss (50–55%) occurring by 500 °C. No original proteins were detected in samples heated at 400 °C or above. Combustion of collagen is accompanied by an increase in HAP mean crystallite size at temperatures greater than 400 °C, from 10 nm to a constant value of 120 nm at 800 °C or more. Newly formed crystalline phases appear beyond 400 °C, and include β-tricalcium phosphate, NaCaPO4, halite (NaCl) and sylvite (KCl). Crystallite thickness as judged by small angle X-ray scattering (SAXS) increases from 2 nm (25–400 °C) to 8–9 nm very rapidly at 550 °C, and then gradually increases to approximately 10 nm. The original texture of HAP within a collagen matrix is progressively lost, producing a porous HAP dominated solid at 700 °C, and a very low porosity sintered HAP product at 900 °C. [ABSTRACT FROM AUTHOR]

Novel bulk glassy samples of the pseudoternary chalcohalide Ge–S–AgI system have been prepared. Glasses have been obtained by monotemperature synthesis in evacuated ampoules and standard melt-quenching technique. The glass-forming region in the system determined by X-ray diffraction is situated in the S-rich region on the Ge–S side (S/Ge = 1.2, 1.5, 2 and 3) with AgI content up to 20 mol.%. Some physicochemical properties of the amorphous materials and their compositional dependence have been investigated. In addition, the theoretical average coordination number (Z), the total constraints per atom (Nco), the radial (Na) and axial (Nb) strength of the bonds have been calculated and related to the experimental results. [ABSTRACT FROM AUTHOR]

Interfaces are often believed to play a role in the mechanical behavior of mineralized biological and biomimetic materials. This motivates the micromechanical description of the elasticity and brittle failure of interfaces between crystals in a (dense) polycrystal, which serves as the skeleton of a porous material defined one observation scale above. Equilibrium and compatibility conditions, together with a suitable matrix-inclusion problem with a compliant interface, yield the homogenized elastic properties of the polycrystal, and of the porous material with polycrystalline solid phase. Incompressibility of single crystals guarantees finite shear stiffness of the polycrystal, even for vanishing interface stiffness, while increasing the latter generally leads to an increase of polycrystal shear stiffness. Corresponding elastic energy expressions give access to effective stresses representing the stress heterogeneities in the microstructures, which induce brittle failure. Thereby, Coulomb-type brittle failure of the crystalline interfaces implies Drucker–Prager-type (brittle, elastic limit-type) failure properties at the scale of the polycrystal. At the even higher scale of the porous material, high interfacial rigidities or low interfacial friction angles may result in closed elastic domains, indicating material failure even under hydrostatic pressure. This micromechanics model can satisfactorily reproduce the experimental strength data of different (brittle) hydroxyapatite biomaterials, across largely variable porosities. Thereby, the brittle failure criteria can be well approximated by micromechanically derived criteria referring to ductile solid matrices, both criteria being even identical if the solid matrix is incompressible. [ABSTRACT FROM AUTHOR]

The synthesis of single crystalline and polycrystalline material is reported in the system ZnO1 – x S x . Substitution of oxygen by sulphur yields hexagonal wurtzite-type mixed crystals in the range 0 ≤ x ≤ 0.05. The cubic zincblende structure is observed for oxygen incorporation into ZnS for 0.96 ≤ x ≤ 1. At intermediate compositions, the system is two-phase. For both types of anion substitution, the band gap energies, as determined from optical transmission and remission experiments, are found to decrease from the pure end members. Quantum chemical calculations at density functional level identify local structural changes as the main factor responsible for the reduction of band gap energies. [ABSTRACT FROM AUTHOR]

The effect of defect ion concentration on conductivity in the CaNd2S4 system has been investigated by varying the CaS:Nd2S3 ratio. Samples with the formula xCaS:Nd2S3 x = 0.7–1.0 have been prepared using solid state methods by high temperature synthesis in evacuated quartz tubes followed by annealing in hydrogen sulfide. The structures of the materials were determined using the Rietveld refinement of powder neutron diffraction data. The phases crystallise with a defect version of the cubic Th3P4 structure in the space group I-43d with cell parameter a ≈ 8.53 Å. Temperature programmed oxidation (TPO) in a 5 Vol.% O2/Ar atmosphere show that the materials resist oxidation up to a temperature of approximately 680 °C. TPO also indicates that there is only one type of sulfide ion present in the system, based on the presence of only one peak in the TPO trace. In-situ impedance spectroscopy was carried out in an Ar and H2S/Ar atmosphere between 300 °C and 500 °C. Bulk conductivities, activation energies and time constants for ion hopping processes were determined. The sample, 0.9CaS:Nd2S3, was found to exhibit three impedance arcs in the Nyquist plot suggesting ionic conduction. The independence of the material’s bulk conductivity when exposed to an H2S/Ar atmosphere supports this statement. The xCaS:Nd2S3 sample with x ≤ 0.8 show strong electronic contributions to the overall conductivity. The total ionic conductivity for 0.9CaS:Nd2S3 of 1.09 × 10−6 S cm−1 measured at 500 °C, matches conductivity values reported using galvanic cells. [ABSTRACT FROM AUTHOR]

The interfaces between liquid or solid Pb islands and single- or poly-crystalline Cu substrates are investigated. EBSD (Electron backscattered diffraction) analyses show that when Pb is solidified from droplets, a cube-on-cube orientation relationship prevails between the Pb crystals and each Cu grain surface, whatever its surface orientation, even though the lattice parameter of Pb is 1.37 times larger than that of Cu. Scanning electron microscope (SEM) and atomic force microscope (AFM) analyses show that during annealing of Pb droplets, ridges develop at the droplet-substrate triple lines, indicating that the interfaces evolve towards equilibrium by diffusional processes. These features are discussed in comparison with experiments and calculations performed on Pb nanocrystals embedded in Al, another fcc solid with a lattice parameter smaller than that of Pb. It is proposed that the cube-on-cube orientation relationship results from the solidification of Pb along the {111} planes of the solid Cu/liquid Pb interface which have developed by diffusion during the process of equilibration of the interface shape. [ABSTRACT FROM AUTHOR]

Resorbable, porous glass scaffolds for tissue engineering were prepared by sintering borate glass with salt (sodium chloride). Subsequently, the sodium chloride was dissolved in water resulting in a highly porous material. By modifying the process parameters including salt particle size, salt volume percentage, sintering temperature and sintering time, sintered matrix structures were optimized. Analysis of the structure data indicates that the 50 vol% glass—50 vol% salt with particle sizes from 250–315 μm sintered at a temperature of 520°C for 10 min resulted in an optimum structure with 76.5% porosity and 29.3 N/cm2 compressive strength. The process of HAP formation on the scaffolds in 0.25 M K2HPO4 solutions with pH 9.0 at 37°C was evaluated. The structural changes were analyzed by X-ray diffraction and scanning electron microscopy. An amorphous phosphate was formed on the surface of the scaffolds within 1d and crystalline hydroxyapatite (HA) within 10d. [ABSTRACT FROM AUTHOR]

Thin PVA/magnesium acetate composite fibres were prepared by using sol-gel processing and electrospinning technique. After calcinations of the above precursor fibres, MgO nanofibres with a diameter of 50–150 nm could be successfully obtained. The fibres were characterized by SEM, FT-IR, XRD, respectively. The results showed that the crystalline phase and morphology of MgO fibres were largely influenced by the calcination temperature. [ABSTRACT FROM AUTHOR]

Extensive theoretical analysis and experimental observations show surface roughening transitions of crystals. The surface roughening is characterized by step free energy, which gradually decreases to 0 at the roughening transition temperature. For a crystal of finite size, the surface roughening transition is manifested by gradual increase of the curved edge and corner areas. In alloys, the interfaces between the solid and the liquid phases can be either singular, partially rough, or completely rough at different temperatures. Their thermally induced roughening transitions are similar to those of the solid-vapor interfaces. The interface roughening and the reverse transition to singular structures can also be induced by additives. The grain boundaries of any misorientation angles in oxides and metals also show roughening transitions. The singular grain boundaries have either flat, hill-and-valley, or kinked shapes, and with temperature increase or composition changes, they become defaceted to curved shapes. These defaceted grain boundaries are rough. It is thus possible to produce either singular or rough grain boundaries by heat-treatment or additives to vary their properties. [ABSTRACT FROM AUTHOR]

A microstructural characterisation of the family of N-methyl-N-alkylpyrrolidinium tetrafluoroborate organic salts was carried out by observation of powder surface morphologies with the aim of extending the microstructure-property correlation. Inherent difficulties limiting extensive studies of organic solids by SEM, including volatility under vacuum, charging due to electron beam irradiation, and air-sensitivity were overcome with the use of a Field Emission SEM and cryostage attachment. This technique, providing considerable improvements in image quality at low accelerating voltages, enabled direct observation of complex microstructural features in samples exhibiting high temperature plastic crystalline phases (N,N-dimethylpyrrolidinium tetrafluoroborate [P11BF4]; N-methyl-N-ethylpyrrolidinium tetrafluoroborate [P12BF4]; N-methyl-N-propylpyrrolidinium tetrafluoroborate [P13BF4]). Extensive lattice imperfections including grain boundaries, slip planes and dislocation pits were observed within particles of approximately 200 μm diameter. The N-methyl-N-butylpyrrolidinium tetrafluoroborate (P14BF4) sample in this series revealed columnar single crystals with high aspect ratios. The origin of plastic flow properties is discussed using single crystal and polycrystalline slip observations and a relationship proposed between defect characteristics and transport properties. [ABSTRACT FROM AUTHOR]

TiO2 colloidal particles with a fixed crystalline phase of anatase or rutile were heat-treated under different conditions (air-heating and hydrothermal-heating) to modify their surface characters which essentially affected the adsorption behavior of a Ru-complex dye on the surfaces. Changes in the number of surface OH group (N(OH)), apparent crystallite size, pore structure were evaluated as a function of heat-treatment conditions for various TiO2 nanoparticles. The amount of a Ru-complex dye adsorbed (N(dye)) was correlated to those surface properties of TiO2 samples. N(dye) values tended to increase with increasing crystallinity for only the anatase-type TiO2 particles. However, there was no simple, common relationship between N(dye) and N(OH) for all the TiO2 nanoparticles examined. Considerable difference in N(dye) values obtained in different nanoparticles might be explained on the basis of the surface pore structures of those particles. [ABSTRACT FROM AUTHOR]

Nanocrystalline Y-TZP tape casts were used as interlayers to join conventional Y-TZP ceramic pellets. The joining experiments were performed by hot pressing at 1000°C to 1300°C under constant pressure of 55 MPa. Two types of joints were obtained with and without a nanocrystalline interlayer. At 1100°C, the successful joints were enabled only with the interlayer; four point bending test results revealed an average joint strength of 206 ± 10 MPa. The joint strength increased with the joining temperature. The specimens joined at 1300°C with an interlayer exhibited a joint strength of 613 ± 40 MPa, which is ∼96% of the strength of the ceramic pellets. The interlayer at the joint exhibited homogeneous and crack free microstructure and preserved its nanocrystalline nature at all temperatures. The advantage of the nanocrystalline interlayer for joining is pronounced at lower joining temperatures and most probably for pellets with large grain size. [ABSTRACT FROM AUTHOR]

The two glass-ceramics studied here derive from the complex system (MgO,ZnO,Li2O)-Al2O3-SiO2 and are obtained by controlled devitrification of the same parent glass. Although they have the same chemical composition, one is a “β-quartz” (or “β-eucryptite”) type while the other one is a “β-spodumene” glass-ceramic. A detailed microstructural analysis of these materials has been performed at different scales by several complementary characterization methods (SEM, TEM, DTA, XRD and FTIR). This extensive study has shown the great microstructure difference (grain distribution, grain size, nature of vitreous and crystalline phases) between these two glass-ceramics obtained from the same parent glass. [ABSTRACT FROM AUTHOR]

Single crystalline Al crystals were bonded via surface activated bonding at room temperature with the crystallographic orientation of (111)∥(111) and [110]∥[110]. The interfacial microstructure was investigated by high-resolution transmission electron microscopy (TEM) to investigate the process of the interface formation of the system. The interface was found to form first between the tops of the protrusions which existed on the Al surfaces as roughness before bonding. At those formed bonded regions, no intermediate and damage layer was observed in the lattice images. It means that the fast atom beam irradiation used for surface activation of the metal surfaces does not alter the surface crystallinity as far as TEM observation allows. The bonded regions, however, exhibited a different contour from what could be conjectured without taking atomic rearrangement into consideration. This change in the geometrical configuration indicates that the protrusions had deformed during the bonding procedure. Microscopically, however, no disordering of the lattice was seen near the interface. Therefore, it is concluded that the heads of the protrusions have deformed plastically and then rearrangement of the atoms took place. Moreover, the defects found at the interface exhibit a delocalized core structure, indicating that the interface should have a relaxed structure. [ABSTRACT FROM AUTHOR]

Microhardness measurements of homogeneous and layered polymorphous PbSe films as well of the KCl and BaF2 substrates on which the films were deposited were undertaken. The interpretation of the experimental results lead to a formula describing more adequately the indentation size effect. It is also shown that an extremum in the microhardness depth profile appears whenever the indentor crosses an interface. [ABSTRACT FROM AUTHOR]

A number of glass samples were prepared from a mixture of Na2B4O7 and CuO. The prepared glasses were irradiated with a low-level fast neutron beam (flux density 108 n cm-2). The alternating current (a.c.)-electrical conductivity and the dielectric constant at a frequency of 1 kHz of these glasses have been studied as a function of temperature in the range 300–600 K. The measurements showed that an amorphous–crystalline phase transition characterized these samples. This phase transition was affected by neutron irradiation. Also a decrease in the activation energy for the irradiated undoped sample and an increase in the activation energy for the irradiated doped samples were found. After irradiation, the maximum peak, which characterized the dielectric constant of the samples before irradiation, disappeared. © 1998 Chapman & Hall [ABSTRACT FROM AUTHOR]