Pure Crystalline Material Research Articles

High-throughput analysis for preparation, processing and analysis of TiO2 coatings on steel by chemical solution deposition

A high-throughput preparation, processing and analysis of titania coatings prepared by chemical solution deposition from water-based precursors at low temperature (≈250°C) on two different types of steel substrates (Aluzinc® and bright annealed) is presented. The use of the high-throughput equipment allows fast preparation of multiple samples saving time, energy and material; and helps to test the scalability of the process. The process itself includes the use of IR curing for aqueous ceramic precursors and possibilities of using UV irradiation before the final sintering step. The IR curing method permits a much faster curing step compared to normal high temperature treatments in traditional convection devices (i.e., tube furnaces).The formulations, also prepared by high-throughput equipment, are found to be stable in the operational pH range of the substrates (6.5–8.5). Titanium alkoxides itself lack stability in pure water-based environments, but the presence of the different organic complexing agents prevents it from hydrolysis and precipitation reactions. The wetting interaction between the substrates and the various formulations is studied by the determination of the surface free energy of the substrates and the polar and dispersive components of the surface tension of the solutions. The mild temperature program used for preparation of the coatings however does not lead to the formation of pure crystalline material, necessary for the desired photocatalytic and super-hydrophilic behavior of these coatings. Nevertheless, some activity can be reported for these amorphous coatings by monitoring the discoloration of methylene blue in water under UV irradiation.

Effect of Electron Irradiation on the Thermodynamical and Optical Properties of Cholesteryl Pelargonate

Thermodynamical and optical properties of pure and electron beam irradiated (20, 80 and 100 kGy doses) liquid crystalline material cholesteryl pelargonate (nonanoate) have been investigated by differential scanning calorimeter, polarized light microscopy and ultraviolet-visible spectroscopy. Transition temperatures, enthalpies and entropies are found to be lowered due to the irradiation. A donor-acceptor type charge transfer complex peak is observed besides the pure sample peak in the ultraviolet-visible spectra due to irradiation. The concentrations of impurities have been estimated by the area of the pure and charge transfer complex peaks besides using the Van't Hoff equation. The concentration of impurity is found to increase linearly with the irradiation dose.

Mechanochemically enhanced synthesis of isomorphously substituted kaolinites

A mechanochemical method for the rapid, bulk synthesis of kaolinite has been developed. Metal hydroxides and silicic acid are mechanically ground and hydrothermally treated for as little as a day at 250 °C to produce X-ray pure crystalline materials. This approach has been expanded to allow the synthesis of kaolinites with a portion of the aluminum sites isomorphously substituted with other trivalent metals. The synthetic parameters, such as length of mechanical and hydrothermal treatment, were studied. Products were analyzed by powder X-ray diffraction, attenuated total reflectance infrared spectrometry, scanning electron microscopy, and transmission electron microscopy. The samples exhibited strong order along the c axis and less order along the a and b axes. Trivalent transition and rare earth metals were used to replace aluminum in the structure. These metals included Cr, La, Ce, Pr, Nd, Eu, Gd, Ho, and Er. Cerium (III) substituted kaolinite was successfully synthesized utilizing air-free conditions. This approach allows bulk quantities of substituted kaolinites to be prepared in a relatively short amount of time and offers a new route to synthesize pure and substituted kaolinites that may have novel catalytic properties.

Synthesis and characterization of monoclinic rare earth titanates, RE2Ti2O7 (RE = La, Pr, Nd), by a modified SHS method using inorganic activator

The nano particles of phase pure rare earth titanates, synthesized by the SHS technique, get well sintered at lower temperatures compared to the compounds formed by the solid-state method. These dielectrics are highly stable and can be used in the microwave frequency range. We report here a modified SHS method to synthesize phase pure monoclinic RE2Ti2O7 at 350°C through the oxide/nitrate precursors using an inorganic compound, ammonium acetate, in place of the general type of organic activators such as urea, alanine etc. The nanopowders of La2Ti2O7, Pr2Ti2O7 and Nd2Ti2O7 on heating exhibit an exothermic behaviour with a broad maxima in the range 267–284°C and become endothermic with maxima in the range 1043–1220°C; interestingly, the phase pure crystalline material is formed at the temperature of exothermic maxima, as confirmed by XRD.

A phenomenological model of size-dependent hardening in crystal plasticity

A phenomenological model of plastic deformation is proposed, which captures the size-dependence of plastic flow strength and work-hardening in pure FCC crystalline materials. Guided by discrete dislocation dynamics analyses, the treatment is based on two structural variables determining the mechanical state of the material. A complete description of plastic behaviour is achieved, giving two inherently different statements for the evolution of structure, supplemented by a new kinetic equation, which specifies the hardening law in differential form at fixed structure. Evolution of the first state variable is set by phenomenology; it accounts for the cardinal bulk phenomena of athermal hardening and dynamic recovery, in addition to geometric storage. The second state variable is kinematically determined so that an evolution equation need not be formulated explicitly in rate form. The model formulation leaves the classical treatment of dynamic recovery unaltered. However, since there is virtually no experimental data on the temperature and strain-rate dependence of plastic flow at the micron scale, emphasis is laid on athermal behaviour. In this limit, the model equations are integrated, following specified strain paths to give the flow strength at the current structure. Model predictions are assessed through comparison with results from discrete dislocation analyses of geometrically similar crystals subject to compression.

Carbon K-edge XANES spectromicroscopy of natural graphite

Carbon K-edge soft X-ray spectromicroscopy was used to obtain information on the orientation, purity and chemical composition of graphite within natural samples. Highly crystalline natural graphite had spectra indistinguishable from highly ordered pyrolytic graphite, but contained a wide variety of internal structures in the 100–500 nm size range. These structures were both physical (domains with differing sheet orientations) and chemical in nature. Graphite sheet orientations could vary from normal to the X-ray beam to nearly perpendicular within a few hundred nanometers. Chemical compositions ranged from pure crystalline material to nearly amorphous carbon. Little evidence for significant addition of O- or N-bearing groups was observed in these samples, although this may have been a result of the extraction techniques used. The range of carbon types found in the environment may provide clues to the types of thermal alteration and source mechanisms behind graphitic kerogen fractions.

The Catalyst-Assisted Synthesis of High Quality CdS Single-Crystal Nanowires Through an Epitaxy Mechanism

High quality wurtzite CdS nanowires have been synthesized by thermal evaporation of CdS powder onto Si substrate in the presence of Au catalyst at 650 degrees C by using pure H2 as a carrier gas. The nanowires were 10 nm in diameter and a few tens of micrometers in length. XRD patterns demonstrated that as prepared CdS is a pure crystalline material. High-resolution transmission electron microscopy of the materials showed that all CdS nanowires grew along (0001). According to analysis of selective area electron diffraction patterns taken from the interface, we proposed that there is a kind of epitaxy relationship in the interface region between Au catalyst and CdS grown, i.e., (0001)CdS // (111)Au, and [1210]CdS // [011]Au.

Thin crystalline 3C-SiC layer growth through carbonization of differently oriented Si substrates

The growth of thin cubic silicon carbide (3C-SiC) buffer layers in an horizontal hot-wall chemical vapor deposition reactor, through the carbonization of differently oriented Si surfaces, is presented. A qualitative and quantitative study has been performed on statistical parameters related to voids due to the buffer layer growth on the different substrate orientations emphasizing shape, size, and density as a function of the substrate orientation. Variation in the void parameters can be attributed to the atomic packing density related to the substrate orientations, which were (100) Si, (111) Si, and (110) Si in this study. Scanning electron microscopy and transmission electron microscopy were performed to analyze the surface and the crystalline quality of the 3C-SiC films grown and, eventually, an empirical model for the carbonization of Si surfaces formulated. Large platens characterize the 3C-SiC films with shapes related to the orientations of the substrate. These platens derive from the two-dimensional growth of different SiC islands which enlarge during the process due to the continuous reaction between Si and C atoms. The interior part of platens was characterized by the presence of a pure crystalline material with the presence of small tilts affecting some grains in the 3C-SiC layer in order to relief the stress generated with the substrate.

Hierarchically Porous Rutile Titania: Harnessing Spontaneous Compositional Change in Mixed-Metal Oxides

In numerous applications involving fluid flow through a porous structure, performance improvements, such as better flow characteristics and increased fluid−solid contact, are obtained when multiple length scales of porosity are present in the porous medium. To this end, we have developed a route to hierarchically porous rutile titania that obviates the need for preformed or preassembled structure-directing agents. The preparation involves the successive leaching of phases and components from a dense composite of wurtzite ZnO and inverse spinel Zn2TiO4. The resulting monoliths are composed of grains of highly crystalline rutile titania and possess a hierarchy of interconnected pores with length scales of 5 μm and 100 nm. Ex situ solid-state 67Zn and 47,49Ti NMR has helped probe local environments around these elements in both the mixed and pure crystalline materials that are formed during the leaching processes.

Properties of a Mixed-Valence (FeII)2(FeIII)2 Square Cell for Utilization in the Quantum Cellular Automata Paradigm for Molecular Electronics

The di-mixed-valence complex [{(eta(5)-C5H5)Fe(eta(5)-C5H4)}4(eta(4)-C4)Co(eta(5)-C5H5)]2+, 1(2+), has been evaluated as a molecular four-dot cell for the quantum cellular automata paradigm for electronic devices. The cations 1(1+) and 1(2+) are prepared in good yield by selective chemical oxidation of 1(0) and are isolated as pure crystalline materials. The solid-state structures of 1(0) and 1(1+) and the midrange- and near-IR spectra of 1(0), 1(1+), 1(2+), and 1(3+) have been determined. Further, the variable-temperature EPR spectra of 1(1+) and 1(2+), magnetic susceptibility of 1(1+) and 1(2+), Mössbauer spectra of 1(0), 1(1+), and 1(2+), NMR spectra of 1(0), and paramagnetic NMR spectra of 1(1+) and 1(2+) have been measured. The X-ray structure determination reveals four ferrocene "dots" arranged in a square by C-C bonds to the corners of a cyclobutadiene linker. The four ferrocene units project from alternating sides of the cyclobutadiene ring and are twisted to minimize steric interactions both with the Co(eta(5)-C5H5) fragment and with each other. In the solid state 1(2+) is a valence-trapped Robin and Day class II compound on the 10(-12) s infrared time scale, the fastest technique used herein, and unambiguous evidence for two Fe(II) and two Fe(III) sites is observed in both the infrared and Mössbauer spectra. Both EPR and magnetic susceptibility measurements show no measurable spin-spin interaction in the solid state. In solution, the NMR spectra show that free rotation around the C-C bonds connecting the ferrocene units to the cyclobutadiene ring becomes increasingly hindered with decreasing temperature, leading to spectra at the lowest temperature that are consistent with the solid-state structure. Localization of the charges in the cations, which is observed in the paramagnetic NMR spectra as a function of temperature, correlates with the fluxional behavior. Hence, the alignment between the pi systems of the central linker and the ferrocene moieties most likely controls the rate of electron exchange between the dots.

Charge Transport in Liquid Crystalline Semiconductor and Crosslinked Polymer Composite

We have fabricated a novel charge carrier transport material composed of a liquid crystalline molecule and a cross-linked polymer. This composite system exhibited high hole mobility comparable with that of the pure liquid crystalline material. The charge carrier transport properties were influenced by the polymerization temperature, i.e., by the mesophase during polymerization. The hole mobility did not depend on temperature and electric field in the case of polymerized samples in the mesophase. We discussed the carrier transport properties in the polymer composites in comparison with those of the pure liquid crystalline material and the conventional polymer composite of the molecularly doped polymers, in addition to the resulting domain structures in the polymer composites with reference to the carrier transport properties in smectic mesophase as well as in the isotropic phase.

Partial order in the non-Fermi-liquid phase of MnSi.

Only a few metallic phases have been identified in pure crystalline materials. These include normal, ferromagnetic and antiferromagnetic metals, systems with spin and charge density wave order, and superconductors. Fermi-liquid theory provides a basis for the description of all of these phases. It has been suggested that non-Fermi-liquid phases of metals may exist in some heavy-fermion compounds and oxide materials, but the discovery of a characteristic microscopic signature of such phases presents a major challenge. The transition-metal compound MnSi above a certain pressure (p(c) = 14.6 kbar) provides what may be the cleanest example of an extended non-Fermi-liquid phase in a three-dimensional metal. The bulk properties of MnSi suggest that long-range magnetic order is suppressed at p(c) (refs 7-12). Here we report neutron diffraction measurements of MnSi, revealing that sizeable quasi-static magnetic moments survive far into the non-Fermi-liquid phase. These moments are organized in an unusual pattern with partial long-range order. Our observation supports the existence of novel metallic phases with partial ordering of the conduction electrons (reminiscent of liquid crystals), as proposed for the high-temperature superconductors and heavy-fermion compounds.

Understanding creep—a review

A simple model based on the Orowan equation and the dynamic evolution of the dislocation structure by generation and merging of slipped areas is used to see which experimental results on creep of pure and solute-hardened crystalline materials can or cannot be explained with regard to creep with refinement or coarsening of the dislocation structure and steady-state creep. Quantitative deficiencies of the model for pure materials are discussed; most of them are related to neglection of subgrain formation.

Ion irradiation effects in nonmetals: formation of nanocrystals and novel microstructures

Ion implantation is a versatile and powerful technique for producing nanocrystal precipitates embedded in the near-surface region of materials. Radiation effects that occur during the implantation process can lead to complex microstructures and particle size distributions, and in the present work, we focus on the application of these effects to produce novel microstructural properties for insulating or semiconducting nanocrystals formed in optical host materials. Nanocrystal precipitates can be produced in two ways: by irradiation of pure (i.e., non-implanted) crystalline or amorphous materials, or by ion implantation followed by either thermal annealing or subsequent additional irradiation. Different methods for the formation of novel structural relationships between embedded nanocrystals and their hosts have been developed, and the results presented here demonstrate the general flexibility of ion implantation and irradiation techniques for producing unique near-surface nanocomposite microstructures in irradiated host materials.

Fermentative production of acetic acid from various pure and natural cellulosic materials by Clostridium lentocellum SG6

Clostridium lentocellum SG6 fermented various pure crystalline cellulosic materials efficiently with maximum acetic acid yield (gram acetic acid/gram substrate) of 0.67, at low substrate (8 g l−1) concentration. The strain grew poorly on crude biopolymers but fermented them easily after alkali treatment, when grown with 8 g substrate l−1 concentration of alkali-extracted cotton straw (AECS), paddy straw (AEPS) and sorghum stover (AESS) etc. The acetic acid to substrate (A/S) ratios were similar to those obtained with pure cellulosic materials. An increase in substrate concentration led to a decreased A/S ratio and a decreased percentage of substrate degraded. At high substrate concentration of 75 g filter paper l−1, the strain SG6 converted 63.2 g filter paper into 31.28 g acetic acid l−1. At 100 g l−1 concentrations, AECS and AEPS served as the best substrates for acetic acid production when compared with other biopolymers. A maximum amount of 30.98 and 30.86 g acetic acid was produced from 70.6 g AEPS and 70.1 g AESS l−1 of medium by strain SG6, respectively. Acetic acid production of 0.67 g g−1 pure cellulose (Whatman No. 1 filter paper), 0.63 g g−1 of alkali-treated cotton straw (AECS) are the highest among the cellulolytic bacteria reported so far in mono culture fermentations with pure and native cellulosic materials.

Experimental investigations of a new TGBC mesophase

We report on optical and structural X-ray studies on a smectic C twist grain boundary phase (TGBC) of a pure liquid crystalline material. It is shown that this TGBC phase, which exists over a large range of temperature, is definitely different from previously reported and predicted TGBC phases. The two main experimental features are: (i) the observation in planar geometry of an optical texture exhibiting a square grid pattern, and (ii) the detection of a broad Bragg ring in reciprocal space instead of one (TGBA) or two (TGBC) sharp rings. We suggest a few possible tracks that can be explored to understand the complex structure of this new phase.

Production of ethanol from various pure and natural cellulosic biomass by Clostridium thermocellum strains SS21 and SS22

Clostridium thermocellum strains SS21 and SS22, fermented a variety of pure crystalline cellulose materials efficiently with a maximum ethanol yield (gram ethanol/gram substrate (g/g) of 0.37 and 0.35, respectively at low substrate (8 g/litre) concentration. With 80 g/litre filter paper, the strain SS21 converted 71 g filter paper into 18.46 g ethanol and strain SS22 fermented 75.4 g filter paper into 20.36 g ethanol per litre of the medium. Both the strains grew poorly on crude biopolymers but fermented them easily after alkali treatment. When grown with 8 g/litre alkali extracted paddy straw (AEPS), alkali extracted sorghum stover (AESS) or alkali extracted deshelled corn cobs (AECC) the ethanol yields were similar to those obtained with pure cellulosic materials. At high substrate (100 g/litre) concentrations, AEPS served as the best substrate for ethanol production when compared with filter paper and other biopolymers. A maximum amount of 21.47 g and 23.57 g ethanol was produced from 82.6 g and 87.3 g AEPS per litre of medium by strains SS21 and SS22, respectively. This is the highest ethanol production among the strains of C. thermocellum so far reported.

Crystallization behaviour of meso-Λ(δλ)-[Co{trans-(R,S)(meen)2}(C2O4)][Pb2Cl5]·2H2O, Λ(λλ)-[{[Co{trans-(R,R)(meen)2}(C2O4)]Br}2]·3H2O and meso-Δ(δλ)-[Co{cis-(R,S)(meen)2}(C2O4)]I (meen =N-methylethylenediamine)

Proton NMR spectroscopy of a D2O solution of the solid obtained by evaporating to dryness a reaction solution containing HCl, [Co(O2CMe)2]·4H2O, PbO2, H2C2O4 and meen (meen =N-methylethylene-diamine in water revealed the presence of two different isomers of the cation [Co(meen)2(C2O4)]+. Three isomers [Co(meen)2(C2O4)][Pb2Cl5]·2H2O 1, [{[Co(meen)2(C2O4)]Br}2]2 and [Co(meen)2-(C2O4)]l 3 were isolated eventually by the selective use of appropriate counter anions and their crystal structures determined. The 1H NMR spectra of D2O solutions of pure crystalline material from the same batch as that from which the structural crystals were derived showed the presence of single species of each of the three isolated compounds. Given their structures it is evident that the isomer with both methyls in the equatorial plane (trans to the oxalato oxygens) was either not formed or it rearranged soon after being formed. Complexes 1 and 2 are conformational isomers differing only in the relative position of one of the two axial methyl groups; 1 is stable in solution for at least 1 week at 21 °C, as demonstrated by its 1H NMR spectrum and rearrangement of cation 2 to 1 and 3 takes several days. Compound 3 contains the expected axial–equatorial isomer.

Capsaicin: identification, nomenclature, and pharmacotherapy.

To provide a brief overview of the chemical history, analysis, nomenclature, biology, pharmacology, and pharmacotherapy of capsaicin. Chemical Abstracts, Biological Abstracts, and a MEDLINE search were used to identify pertinent literature; selected literature was used in this review. Original articles, reviews, and abstracts of articles were used to select material pertinent to the objectives of the review. The volume of material available prohibits comprehensive data extraction. A history of the use of Capsicum spp. and the predominant active ingredient, capsaicin, the parent compound of a group of vanillyl fatty acid amides, is presented. Distinct structural differences are noted between this compound and the capsaicinoids, especially the synthetic analog nonivamide, which has appeared as an adulterant in capsaicin-labeled products. Analysis shows that although some of these synthetic analogs eventually may prove to be true natural products, conclusive evidence based on isolation and structure elucidation is still absent after decades of attempted isolation from several potential natural sources. Although the crude, dark oleoresin extract of capsicum contains over 100 distinct volatile compounds and therefore may function in many ways dissimilar to capsaicin, the oleoresin continues to be marketed in products with a high degree of variability in efficacy. Capsaicin as a pure white crystalline material, however, acts specifically by depleting stores of substance P from sensory neurons, and has been successful in the treatment of several painful conditions (e.g., rheumatoid arthritis, osteoarthritis, peripheral neuropathies.

Radiation-induced conductivity: High-speed detection of X rays and neutrons

Radiation-induced conductivity (RIC) is a generalized term for photoconductivity expanded to include nonelectromagnetic radiation. RIC offers several distinct advantages for the detection of high-energy radiation: (i) the speed of response of a detector is determined by a bulk property of the material, the carrier lifetime; (ii) the detector can be directly illuminated by the signal radiation-no dead layer; and (iii) the selection of the detector material and its geometry is very flexible. This paper will discuss the principles of RIC for X rays and neutrons, the fabrication of detectors, and applications. RIC detectors have been fabricated from Si, InP, GaAs, and diamond. Bulk and thin film materials have been used. The carrier lifetime was varied by the introduction of trapping sites in the material. This can be done in the material production process in the case of doping (e.g., Fe in InP) and thin films or produced from radiation damage of a pure crystalline material. Lifetimes as short as a few picoseconds have been observed. A variety of detectors have been tested using pulsed optical, X ray, and neutron sources. Absolute sensitivities and temporal response has been measured and compared to theoretical models of the detector's performance for both X rays and neutrons. Finally, applications of these detectors to inertial confinement fusion measurement will be shown.