Role of lattice defects and crystallite morphology in the UV and visible-light-induced photo-catalytic properties of combustion-prepared TiO2

The physico-chemical, photo-physical and micro-structural properties responsible for the strikingly different photocatalytic behavior of combustion-prepared TiO2 (c.TiO2) and Degussa P25 (d.TiO2) samples are elucidated in this study. Electron microscopy and selected area electron diffraction micrographs revealed that the two samples exhibited different morphologies. The grains of c.TiO2 were spherical and comprised of 5-6 nm size primary particle. On the other hand, d.TiO2 consisted of large (0.5-3.0 mu m) size and irregular shape aggregates having primary particles of 15-40 nm cross-sectional diameter. The ESR study revealed that the presence of certain defect states in c.TiO2 helped in stabilization of O-. and Ti3+-OH type species during room-temperature UV-irradiation. No such paramagnetic species were however formed over d.TiO2 under similar conditions. C1s and Ti 2p XPS spectra provide evidence for the presence of some lattice vacancies in c.TiO2 and also for the bulk Ti4+ -> Ti3+ conversion during its UV-irradiation. Compared to d.TiO2, c.TiO2 displayed considerably higher activity for discoloration of methyl orange but very poor activity for splitting of water, both under UV and visible light radiations. This is attributed to enhanced surface adsorption of dye molecules over c.TiO2, because of its textural features and also the presence of photo-active ion-radicals. On the other hand, the poor activity of c.TiO2 for water splitting is related to certain defect-induced inter-band charge trapping states in the close vicinity of valence and conduction bands of c.TiO2, as revealed by thermoluminescence spectroscopy. Further, the dispersion of nanosize gold particles gave rise to augmented activity of both the catalysts, particularly for water splitting. This is explained by the promotional role of Au-0 or Au-0/TiO2 interfacial sites in the adsorption and charge-adsorbate interaction processes. (C) 2011 Elsevier B.V. All rights reserved.

Multifractal analysis, a method to investigate the morphology of materials

Using the multifractal formalism, we discuss the results obtained to characterized the morphology of polymer alloys and granular discontinuous metallic thin films. In the first case we have found a correlation between the multifractality and the mechanical properties of the alloys. In the second case, we have found that it is possible to measure the differences between the morphology of thin films induced by a growth process on a subtrate and that of percolation clusters of the classical theory of percolation.

Effect of SDS on human hair: Study on the molecular structure and morphology

This paper presents a model study to understand the effect of surfactants on the physicochemical properties of human hair. FT-IR ATR spectroscopy has been employed to understand the chemical changes induced by sodium dodecyl sulfate (SDS) on human scalp hair. In particular, the SDS induced changes in the secondary structure of protein present in the outer protective layer of hair, i.e. cuticle, have been investigated. Conformational changes in the secondary structure of protein were studied by curve fitting of the amide I band after every phase of SDS treatment. It has been found that SDS brings rearrangements in the protein backbone conformations by transforming beta-sheet structure to random coil and beta-turn. Additionally, AFM and SEM studies were carried out to understand the morphological changes induced on the hair surface. SEM and AFM images demonstrated the rupture and partial erosion of cuticle sublayers.

Influence of growth below and above T-c on the morphology and domain structure in flux-grown KTP crystals

KTP crystals have been grown below and above the ferroelectric transition temperature by flux method employing both spontaneous and top-seeded solution growth techniques. A slight morphological difference has been observed in these crystals when grown below and above the T-c. Ferroelectric domains are studied in these crystals by selective domain etching. It is seen that the ferroelectric domains in crystals grown spontaneously below T, show a complicated structure. A systematic investigation of the factors influencing domain structure has been carried out. Stress to some extent has been shown to affect the domain structure. Finally, a convenient way of converting the multidomain crystals into monodomain ones is described.

The effect of SiC particles on the size and morphology of eutectic silicon in cast A356/SiCp composites

Properties of cast aluminium matrix composites are greatly influenced by the nature of distribution of reinforcing phase in the matrix and matrix microstructural length scales, such as grain size, dendrite arm spacing, size and morphology of secondary matrix phases, etc. Earlier workers have shown that SIC reinforcements can act as heterogeneous nucleation sites for Si during solidification of Al-Si-SiC composites. The present study aims at a quantitative understanding of the effect of SiC reinforcements on secondary matrix phases, namely eutectic Si, during solidification of A356 Al-SiC composites. Effect of volume fraction of SiC particulate on size and shape of eutectic Si has been studied at different cooling rates. Results indicate that an increase in SiC volume fraction leads to a reduction in the size of eutectic Si and also changes its morphology from needle-like to equiaxed. This is attributed to the heterogeneous nucleation of eutectic Si on SiC particles. However, SiC particles are found to have negligible influence on DAS. Under all the solidification conditions studied in the present investigation, SiC particles are found to be rejected by the growing dendrites. (C) 1999 Elsevier Science Ltd. All rights reserved.

Morphology and thermal characteristics of nano-sized Pb-Sn inclusions in Al

Nanoembedded aluminum alloys with bimetallic dispersoids of Sn and Pb of compositions Sn-82-Pb-18,Pb- Sn-64-Pb-36, and Sn-54-Pb-46 were synthesized by rapid solidification. The two phases, face-centered-cubic Pb and tetragonal Sn solid-solution, coexist in all the particles. The crystallographic relation between the two phases and the matrix depends upon the solidification pathways adopted by the particles. For Al-(Sn-82-Pb-18), we report a new orientation relation given by [011]Al//[010]Sn and (011)Al//(101)Sn. Pb exhibits a cube-on-cube orientation with Al in few particles, while in others no orientation relationship could be observed. In contrast, Pb in Sn-64-Pb-36 and Sn-54-Pb-46 particles always exhibits cube-on-cube orientation with the matrix. Sn does not show any orientation relationship with Al or Pb in these cases. Differential scanning calorimetry studies revealed melting at eutectic temperature for all compositions, although solidification pathways are different. Attempts were made to correlate these with the melting and heterogeneous nucleation. characteristics.

Synthesis of acicular hydrogoethite (alpha-FeOOH center dot xH(2)O; 0.1 < x < 0.22) particles using morphology controlling cationic additives and magnetic properties of maghemite derived from hydrogoethite

A method for the preparation of acicular hydrogoethite (alpha -FeOOH.xH(2)O, 0.1 < x < 0.22) particles of 0.3-1 mm length has been optimized by air oxidation of Fe( II) hydroxide gel precipitated from aqueous (NH4)(2)Fe(SO4)(2) solutions containing 0.005-0.02 atom% of cationic Pt, Pd or Rh additives as morphology controlling agents. Hydrogoethite particles are evolved from the amorphous ferrous hydroxide gel by heterogeneous nucleation and growth. Preferential adsorption of additives on certain crystallographic planes thereby retarding the growth in the perpendicular direction, allows the particles to acquire acicular shapes with high aspect ratios of 8-15. Synthetic hydrogoethite showed a mass loss of about 14% at similar to 280 degreesC, revealing the presence of strongly coordinated water of hydration in the interior of the goethite crystallites. As evident from IR spectra, excess H2O molecules (0.1- 0.22 per formula unit) are located in the strands of channels formed in between the double ribbons of FeO6 octahedra running parallel to the c- axis. Hydrogoethite particles constituted of multicrystallites are formed with Pt as additive, whereas single crystallite particles are obtained with Pd (or Rh). For both dehydroxylation as well as H-2 reduction, a lower reaction temperature (similar to 220 degreesC) was observed for the former (Pt treated) compared to the latter (Pd or Rh) (similar to 260 degreesC). Acicular magnetite (Fe3O4) was prepared either by reducing hydrogoethite (magnetite route) or dehydroxylating hydrogoethite to hematite and then reducing it to magnetite (hematite- magnetite route). According to TEM studies, preferential dehydroxylation of hydrogoethite along < 010 > leads to microporous hematite. Maghemite (gamma -Fe2O3 (-) (delta), 0 < < 0.25) was obtained by reoxidation of magnetite. The micropores are retained during the topotactic transformation to magnetite and finally to maghemite, whereas cylindrical mesopores are formed due to rearrangement of the oxygen sublattice from hexagonal to cubic close packing during the conversion of hydrogoethite to magnetite and then to maghemite. Accordingly, three different types of maghemite particles are realized: strongly oriented multicrystalline particles, single crystalline acicular particles with micropores or crystallites having mesopores. Higher values of saturation magnetization ((s) = 74 emu g(-1)) and coercivity (H-c = 320 Oe) are obtained for single crystalline mesoporous particles. In the other cases, the smaller size of particles and larger distribution of micropores decreases sigma (s) considerably ( < 60 emu g(-1)) due to relaxation effects of spins on the surface atoms as revealed by Mossbauer spectroscopy.

Influence of martensite content and morphology on the toughness and fatigue behavior of high-martensite dual-phase steels

A series of high-martensite dual-phase (HMDP) steels exhibiting a 0.3 to 0.8 volume fraction of martensite (V m ), produced by intermediate quenching (IQ) of a vanadium and boron-containing microalloyed steel, have been studied for toughness and fatigue behavior to supplement the contents of a recent report by the present authors on the unusual tensile behavior of these steels. The studies included assessment of the quasi-static and dynamic fracture toughness and fatigue-crack growth (FCG) behavior of the developed steels. The experimental results show that the quasi-static fracturetoughness (K ICV ) increases with increasing V m in the range between V m =0.3 and 0.6 and then decreases, whereas the dynamic fracture-toughness parameters (K ID , K D , and J ID ) exhibit a significant increase in their magnitudes for steels containing 0.45 to 0.60 V m before achieving a saturation plateau. Both the quasi-static and dynamic fracture-toughness values exhibit the best range of toughnesses for specimens containing approximately equal amounts of precipitate-free ferrite and martensite in a refined microstructural state. The magnitudes of the fatigue threshold in HMDP steels, for V m between 0.55 and 0.60, appear to be superior to those of structural steels of a similar strength level. The Paris-law exponents (m) for the developed HMDP steels increase with increasing V m , with an attendant decrease in the pre-exponential factor (C).

Morphology and thermal characteristics of nano-sized Pb–Sn inclusions in Al

Nanoembedded aluminum alloys with bimetallic dispersoids of Sn and Pb of compositions Sn82–Pb18, Sn64–Pb36, and Sn54–Pb46 were synthesized by rapid solidification. The two phases, face-centered-cubic Pb and tetragonal Sn solid-solution, coexist in all the particles. The crystallographic relation between the two phases and the matrix depends upon the solidification pathways adopted by the particles. For Al–(Sn82–Pb18), we report a new orientation relation given by [011]Al//[010]Sn and (o11)A1//(101)Sn. Pb exhibits a cube-on-cube orientation with Al in few particles, while in others no orientation relationship could be observed. In contrast, Pb in Sn64–Pb36 and Sn54–Pb46 particles always exhibits cube-on-cube orientation with the matrix. Sn does not show any orientation relationship with Al or Pb in these cases. Differential scanning calorimetry studies revealed melting at eutectic temperature for all compositions, although solidification pathways are different. Attempts were made to correlate these with the melting and heterogeneous nucleation characteristics.

Tailoring of Structural Morphology of Silver Nanowires in Electrochemical Growth

Noble metal such as Ag normally exists in an fcc crystal structure. However as the size of the material is decreased to nanometer lengthscales, a structural transformation from that of its bulk state can be expected with new atomic arrangements due to competition between internal packing and minimization of surface energy. In many previous studies, it has been shown that silver nanowires (AGNWs) grown inside anodic alumina (AAO) templates by ac or dc electrochemical deposition from silver salts or complexes, adopt fcc structure and below some critical diameter ∼ 20 nm they may acquire hcp structure at low temperature. This is, however, critically dependant on the nature of confinement, as AgNWs grown inside nanotube confinement with subnanometer diameter have been reported to have fcc structure. Hence the question of the crystal structure of metal nanowires under combined influence of confinement, temperature and deposition condition remains open. In this abstract we show that the alternative crystal structures of AGNWs at room temperature can be achieved with electrochemical growth processes under specific conditions determined by the deposition parameters and nature of confinement. We fabricated AgNWs of 4H hexagonal structure with diameters 30 – 80 nm inside polycarbonate (PC) templates with a modified dc electrodeposition technique, where the nanowires were grown at deposition potentials as low as 10 mV in 2 M silver nitrate solution[1]. We call this low-potential electrodeposition (LPED) since the electrodeposition process occurs at potential much less than the standard Nernst potential (770 mV) of silver. Two types of electrodes were used – stainless steel and sputtered thin Pt film, neither of which had any influence on the crystal structure of the nanowires. EDS elemental analysis showed the nanowires to consist only of silver. Although the precise atomic dynamics during the LPED process is unclear at present, we investigated this with HRTEM (high-resolution transmission electron microscopy) characterization of nanowires grown over various deposition times, as well as electrical conductivity measurements. These experiments indicate that nanowire growth does not occur through a three-dimensional diffusion controlled process, as proposed for conventional over-potential deposition, but follow a novel instantaneous linear growth mechanism. Further experiments showed that, (a) conventional electrochemical growth at a small over-potential in a 2 mM AgNO3 solution yields nanowires with expected fcc structure inside the same PC templates, and (2) no nanowire was observed under the LPED conditions inside hard AAO templates, indicating that LPED-growth process, and hcp structure of the corresponding nanowires depend on deposition parameters, as well as nature of confinement.

Influence of growth parameters on the surface morphology and crystallinity of InSb epilayers grown by liquid phase epitaxy

Unintentionally doped homoepitaxial InSb films have been grown by liquid phase epitaxy employing ramp cooling and step cooling growth modes. The effect of growth temperature, degree of supercooling and growth duration on the surface morphology and crystallinity were investigated. The major surface features of the grown film like terracing, inclusions, meniscus lines, etc are presented step-by-step and a variety of methods devised to overcome such undesirable features are described in sufficient detail. The optimization of growth parameters have led to the growth of smooth and continuous films. From the detailed morphological, X-ray diffraction, scanning electron microscopic and Raman studies, a correlation between the surface morphology and crystallinity has been established.

Nature's Swiss Army Knives: Ovipositor Structure Mirrors Ecology in a Multitrophic Fig Wasp Community

Background: Resource partitioning is facilitated by adaptations along niche dimensions that range from morphology to behaviour. The exploitation of hidden resources may require specially adapted morphological or sensory tools for resource location and utilisation. Differences in tool diversity and complexity can determine not only how many species can utilize these hidden resources but also how they do so. Methodology and Principal Findings: The sclerotisation, gross morphology and ultrastructure of the ovipositors of a seven-member community of parasitic wasps comprising of gallers and parasitoids developing within the globular syconia (closed inflorescences) of Ficus racemosa (Moraceae) was investigated. These wasps also differ in their parasitism mode (external versus internal oviposition) and their timing of oviposition into the expanding syconium during its development. The number and diversity of sensilla, as well as ovipositor teeth, increased from internally ovipositing to externally ovipositing species and from gallers to parasitoids. The extent of sclerotisation of the ovipositor tip matched the force required to penetrate the syconium at the time of oviposition of each species. The internally ovipositing pollinator had only one type of sensillum and a single notch on the ovipositor tip. Externally ovipositing species had multiple sensilla types and teeth on their ovipositors. Chemosensilla were most concentrated at ovipositor tips while mechanoreceptors were more widely distributed, facilitating the precise location of hidden hosts in these wasps which lack larval host-seeking behaviour. Ovipositor traits of one parasitoid differed from those of its syntopic galler congeners and clustered with those of parasitoids within a different wasp subfamily. Thus ovipositor tools can show lability based on adaptive necessity, and are not constrained by phylogeny. Conclusions/Significance: Ovipositor structure mirrored the increasingly complex trophic ecology and requirements for host accessibility in this parasite community. Ovipositor structure could be a useful surrogate for predicting the biology of parasites in other communities.

Thermally induced phase separation in P alpha MSAN/PMMA blends in presence of functionalized multiwall carbon nanotubes: Rheology, morphology and electrical conductivity

The focus of this work is the evaluation and analysis of the state of dispersion of functionalized multiwall carbon nanotubes (CNTs), within different morphologies formed, in a model LCST blend (poly[(alpha-methylstyrene)-co-(acrylonitrile)]/poly(methyl-methacryla te), P alpha MSAN/PMMA). Blend compositions that are expected to yield droplet-matrix (85/15 P alpha MSAN/PMMA and 15/85 P alpha MSAN/PMMA, wt/wt) and co-continuous morphologies (60/40 P alpha MSAN/PMMA, wt/wt) upon phase separation have been combined with two types of CNTs; carboxylic acid functionalized (CNTCOOH) and polyethylene modified (CNTPE) up to 2 wt%. Thermally induced phase separation in the blends has been studied in-situ by rheology and dielectric (conductivity) spectroscopy in terms of morphological evolution and CNT percolation. The state of dispersion of CNTs has been evaluated by transmission electron microscopy. The experimental results indicate that the final blend morphology and the surface functionalization of CNT are the main factors that govern percolation. In presence of either of the CNTs, 60/40 P alpha MSAN/PMMA blends yield a droplet-matrix morphology rather than co-continuous and do not show any percolation. On the other hand, both 85/15 P alpha MSAN/PMMA and 15/85 P alpha MSAN/PMMA blends containing CNTPEs show percolation in the rheological and electrical properties. Interestingly, the conductivity spectroscopy measurements demonstrate that the 15/85 P alpha MSAN/PMMA blends with CNTPEs that show insulating properties at room temperature for the miscible blends reveal highly conducting properties in the phase separated blends (melt state) as a result of phase separation. By quenching this morphology, the conductivity can be retained in the blends even in the solid state. (C) 2011 Elsevier Ltd. All rights reserved.

Morphology Dependence of Ag-Ni Solid Solubility

Electrodeposition produced features with a dendritic morphology and features with a branched wire like morphology made up of about 20 nm sized particles. Both the features contained Ag and Ni atoms in a solid solution arrangement. However, the feature made up of nanoparticles contained a greater concentration of Ni as compared to the Ni content in the dendritic feature. The greater Ni content in the Ag-Ni solid solution for the features with nanoparticles when compared to the dendritic morphology features strongly indicated the effect of curvature in increasing the extent of miscibility between bulk immiscible atoms. (C) 2011 The Electrochemical Society. [DOI: 10.1149/2.003202esl] All rights reserved.