Structure refinement and thermal stability of creedite

The crystal structure of the mineral creedite (hydrous calcium aluminum sulfate fluoride, Ca₃Al₂(F,OH)₁₀(SO₄) · 2H₂O) has been determined by Rietveld powder diffraction analysis. X-ray diffraction data obtained in the temperature range from 25 to 470°C indicate that the crystal structure of creedite is stable up to 390°C. We have measured the unit-cell parameters of creedite as functions of temperature and determined its thermal expansion coefficients. Above 390°C, the mineral decomposes.     

Electron microdiffraction studies of zirconia particles

A batch of zirconia was prepared at a pH of 2.95 using a sol-gel technique. The crystal structures formed during 500 °C calcination was followed by X-ray diffraction. The tetragonal phase was the major component after the initial calcination period of 15.5 h; however, it gradually transformed to the monoclinic crystal form during 200 h of calcination at 500 °C. Electron microdiffraction was employed in the present investigation to determine the crystal structure of individual particles, and to identify whether these particles contained twin variants. A technique has been developed to get a dispersion of agglomerated particles by condensing and spreading the beam on the agglomerates at 200 kV. The data revealed that some of the individual zirconia particles are featureless and some of them appear to contain single or multiple twin variants.     

Photoelectrochemically active surfactant free single step hydrothermal mediated titanium dioxide nanorods

Titanium dioxide (TiO₂) nanorods have been successfully synthesized by a simple and cost-effective hydrothermal deposition method onto the conducting glass substrates. Effect of reaction temperature on the growth of TiO₂ nanorods have been investigated by varying the reaction temperature from 140 to 200 °C. The optical, structural, compositional, morphological properties of the synthesized films are studied. X-ray diffraction patterns reveal the formation of polycrystalline TiO₂ with the tetragonal crystal structure possessing rutile phase. The chemical composition and valence states of the constituent elements were analysed by X-ray photoelectron spectroscopy. Field emission scanning electron microscopy images shows the formation of nanorod-like structure with variation in diameter. The optical band gap energy was found to increase from 3.07 to 3.15 eV with the increase in reaction temperature exhibiting a blue shift. The films were photo electrochemically active with the maximum current density of 216 µA/cm² for the sample prepared at 180 °C.     

Structural analysis of electrodeposited copper microstructures fabricated through template synthesis

The electrochemical template synthesis of high aspect ratio copper microcylinders in the track-etch membranes of polycarbonate having nominal pore size of 800, 600 and 200 nm is considered. The morphological and structural analyses have been carried out through scanning electron microscopy and X-ray diffraction, respectively. The X-ray diffraction studies reveal that the material has FCC lattice structure with a high texture coefficient for (200) planes. Regardless of the nominal pore-size of the template membrane, the texturing has been found to decrease significantly when the electrolyte temperature during fabrication is increased from 30 to 60 °C.     

Investigation of ethanol gas sensing properties of Dy-doped SnO<Subscript>2</Subscript> nanostructures

In this paper we report doping induced enhanced sensor response of SnO₂ based sensor towards ethanol at a working temperature of 200 °C. Undoped and dysprosium-doped (Dy-doped) SnO₂ nanoparticles were characterized by X-ray diffraction (XRD), Raman spectroscopy, transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS). XRD and Raman results verified tetragonal rutile structure of the prepared samples. It has been observed that crystallite size reduced with increase in dopant concentration. In addition, the particle size has been calculated from Raman spectroscopy using phonon confinement model and the values match very well with results obtained from TEM and X-ray diffraction investigations. Dy-doped SnO₂ sensors exhibited significantly enhanced response towards ethanol as compared to undoped sensor. The optimum operating temperature of doped sensor reduced to 200 °C as compared to 320 °C for that of undoped sensor. Moreover, sensor fabricated from Dy-doped SnO₂ nanostructures was highly selective toward ethanol which signifies its potential use for commercial applications. The gas sensing mechanism of SnO₂ and possible origin of enhanced sensor response has been discussed.     

Dielectric,ferroelectric and optical behaviour of terbium hydrogen tartrate trihydrate crystals

Gel diffusion technique, using agar–agar as gel medium, has been employed to obtain single crystals of terbium hydrogen tartrate trihydrate. The grown crystals are characterised by X-ray diffraction, scanning electron microscopy, CHN technique, thermogravimetric methods and UV–Vis spectroscopy. Dielectric, ferroelectric and optical studies on this metal–organic compound have been carried out. The dielectric constant has been measured as a function of temperature and frequency in the ranges of 20–250 °C and 20 Hz–3 MHz, respectively. The study of dielectric behaviour as a function of temperature reveals two dielectric anomalies at 95 and 198 °C. The dielectric anomaly at 95 °C is suggested to be due to ferroelectric phase transition brought about in the material. The study of polarisation versus electric field shows a hysteresis loop which thereby confirms the ferroelectric nature of terbium hydrogen tartrate trihydrate crystals. The dielectric anomaly at 198 °C is suggested to be due to loss of water molecules in the compound. The results of thermal study show that the material is thermally stable up to temperature of about 200 °C. Optical studies show that the terbium hydrogen tartrate trihydrate crystal has good transparency in the entire visible and infra red range of the spectrum.     

Annealing effects on structural and optical properties of ZnMgO films grown by RF magnetron sputtering

Two sets of ZnMgO thin films have been fabricated on Si (111) substrates by RF magnetron sputtering, and were annealed at air atmosphere afterwards. The effects of annealing temperature and time on structural and optical properties were also characterized by X-ray diffraction, scanning electron microscopy and photoluminescence (PL) spectra. For samples fabricated at a lower temperature (200 °C, defined as samples I), the experimental results revealed that only hexagonal phase was observed for the films annealed at the temperature range from 180 to 420 °C, and the best crystal quality for the films was found at 240 °C. For samples synthesized at 220 °C (defined as samples II), the crystal structures exhibited anneal-time dependent. The experimental results revealed coexistence of hexagonal and cubic phase when they were annealed at a set temperature of 220 °C with the different annealing time, and the best one can be observed when the anneal time was 30 min. PL spectra showed blue shift for UV peak with the increase of annealing temperature for samples I, and the UV emission occurred red shift and then blue shift when the anneal time increased from 20 to 30 min for samples II.     

A new route for the synthesis of submicron-sized LaB6

Submicron crystalline LaB₆ has been successfully synthesized by a solid-state reaction of La₂O₃ with NaBH₄ at 1200 °C. The effects of reaction temperature on the crystal structure, grain size and morphology were investigated by X-ray diffraction, scanning electron microscope and transmission electron microscope. It is found that when the reaction temperature is in the range of 1000–1100 °C, there are ultrafine nanoparticles and nanocrystals that coexist. When the reaction temperature elevated to 1200 °C, the grain morphology transformed from ultrafine nanoparticle to submicron crystals completely. High resolution transmission electron microscope images fully confirm the formation of LaB₆ cubic structure.     

Effect of extrusion temperature on mechanical properties of as-extruded Zn–22Al alloys

ABSTRACT

The effect of extrusion temperature on the microstructures and mechanical properties of as-extruded Zn–22Al alloys was investigated in this study. With decrease of extrusion temperature from 350 to 200°C, the elongation of as-extruded Zn–22Al alloys increases remarkably at low strain rate and has no change at high strain rate, which implies that the Zn–22Al alloys extruded at lower temperature exhibit high-ductility behaviour. X-ray diffraction and electron back-scattered diffraction analysis demonstrated that the maximum elongation of Zn–22Al alloys extruded at the extrusion temperature of 200°C can be attributed to the elimination of the lamellar structure and the refinement in grain size of the Zn-rich phase.     

Annealing Effect on Structural and Magnetic Properties of Cu2MnAl Heusler Alloy Films

Cu₂MnAl Heusler alloy films were grown on MgO (001) substrates by using the ion beam sputtering technique. The films were post-annealed at varying temperatures in order to investigate the influence of annealing on crystal structure and magnetic properties. The structural properties of Cu₂MnAl films have been investigated by using x-ray diffraction (XRD) and magnetic properties have been investigated by both vibrating sample magnetometer (VSM) and ferromagnetic resonance (FMR) techniques. The experimental data indicates that the crystal structure of the films strongly depends on the annealing temperature. When the films were annealed at 200?°C, the saturation magnetization (M _s =250?emu/cm³) achieved its maximum and the coercive field (H _c ??7?Oe) reached its minimum with B2 ordered structure. In addition, FMR results have revealed that the Cu₂MnAl film annealed 200?°C has the highest effective magnetization. The combination of structural and magnetic characterization indicates that the optimum growth temperature is 200?°C for the Cu₂MnAl Heusler alloy films on MgO substrates.     

Fast one-step synthesis of ZnO sub-microspheres in PEG200

ZnO sub-microspheres were synthesized via a new, simple, and one-step method by using zinc acetate dihydrate as a precursor and PEG200 as a solvent and modifier. The effect of temperature (160–210 °C) on the crystallization, surface morphology, and luminescence properties of ZnO spheres was investigated using different characterization techniques, including X-ray diffraction, scanning electron microscopy, transmission electron microscopy, Fourier transform infrared spectroscopy, UV–Vis spectroscopy, and room temperature photoluminescence. The results show that the ZnO crystal has a hexagonal wurtzite structure. The products have monodispersed spherical morphology with diameters in the range of 200–600 nm. They have intensive UV emission peaks at ~380 nm and relatively weak and broad green peaks at ~550 nm. The PEG200 molecules adsorb on the surface of ZnO spheres. On the basis of the experimental results, a mechanism was proposed to elucidate the formation of ZnO sub-micron spheres.     

Enhanced optoelectronic,thermal, mechanical and third order nonlinear optical properties of dichlorobis(thiourea)zinc(II) crystal: an effect of Phenol red dye

For the first time the growth of dichlorobis (thiourea) zinc(II) (ZTC) monocrystal in presence of Phenol red dye of considerably good size (~13 mm?×?5 mm) has been achieved from aqueous solution using slow evaporation solution technique at room temperature. The solubility was calculated at different temperatures. The crystal structure was confirmed through X-ray diffraction analysis. The crystallinity of the dyed crystals has been enhanced revealed by Powder X-ray diffraction study. The presence of dye was inveterate by FT-IR and FT-Raman spectroscopic studies. The scanning electron microscopy analyses show that the grown crystals with dye are better than pure. Diffused reflectance was measured and optical band gap was calculated found to be enhanced from 4.5 to 4.65 eV for dyed crystals. The enhancement in the PL intensity has been observed in the dyed crystals. DSC study shows that the thermal stability has been remarkably enhanced from 163?°C (pure) to 203?°C (dyed) and various other thermal parameters are calculated. The surface study shows that the grown crystals with dye possess less dislocation than pure. Mechanical strength of the dyed crystal is found to be remarkably enhanced. Third-order nonlinear optical susceptibility (χ3) of PRZTC was found to be 2 times higher than pure. All results suggest that the properties of ZTC crystals grown in presence of dye are enhanced and can be considered as better contender in various nonlinear devices.     

Effect of pyrolytic temperature on the properties of nano-structured Cuo optimized for ethanol sensing applications

In the present work, copper oxide thin films have been deposited at different substrate temperatures from 250 to 400 °C by spray pyrolysis technique. The desired properties of phase pure CuO with good crystal quality and conductivity have been optimized with respect to pyrolytic temperature. X-ray diffraction studies and Hall effect measurements indicated that these two properties are achieved at an optimum temperature of 350 °C. The band gap of CuO films was found to decrease from 1.8 to 1.2 eV with increase in substrate temperature, based on the UV-absorption spectrum of the film. The microstructures revealed that the film optimized at 350 °C, showed uniform surface with trapezium shaped particles, which are well compacted. The dynamic sensing behavior of the optimized p-type CuO sensor, prepared at a substrate temperature of 350 °C, was used to sense ethanol for concentrations: 100 and 200 ppm. The response time and the recovery time were within the range of 15–20 s and 15–18 s, respectively. The results revealed good response even at room temperature, with characteristics dependent on the size of the grains and the concentration of ethanol.     

Synthesis, characterization and thermal history dependence of the polymorphic structure of nylon6/montmorillonite nanocomposites

Nylon6/clay nanocomposites with 5-wt% montmorillonite (NCN5) were prepared by a twin-screw extruder. The effects of thermal histories including annealing temperature (195 °C, solid-state annealing; 245 °C, melt-state annealing), annealing time and cooling rate on the polymorphic behavior and thermal property of NCN5 have been studied using Modulated Differential Scanning Calorimetry (MDSC) and wide angle X-ray diffraction. It was found that longer annealing time and faster cooling rate favored the formation of the γ crystal when NCN5 samples were annealed at 195 °C. As the annealing temperature was elevated to 245 °C, the α crystal became the absolutely dominating crystalline phase independent on the annealing durations and cooling rate. Moreover, a small endothermic peak was observed around 195 °C in NCN5 samples and this new transition peak was also found to be dependent on the thermal history.     

Structure of metastable precipitate in some Al–Cu–Mg–Ag alloys

Abstract

The high strength of some Al–Cu–Mg–Ag alloys has been attributed to very thin (~2·5 nm), but broad, hexagonal-shaped precipitates. Previous work has shown that the precipitates have a hexagonal unit cell, but different lattice parameters have been reported. In the present paper, the intensities of X-ray diffraction reflections from the precipitates have been measured on Buerger precession photographs, and it is shown that the crystal structure is monoclinic (space group P2/m) with the parameters a = b = 0·496 nm, c = 0·848 nm, γ = 120°. The special values of these parameters confer a hexagonal symmetry on the lattice. This unusual structure is a slightly distorted form of θ-CuAl₂, to which it appears to change after long aging times at 200°C.     

Zinc vacancy mediated structural phase transition and photoluminescence in nanocrystalline ZnS thin films

Nanocrystalline thin films of zinc sulphide were prepared on glass substrate at various deposition temperatures by thermal evaporation technique. The variation of the structural and optical properties of films deposited at various substrate temperatures was investigated in detailed. X-ray diffraction spectra showed that films deposited at 300 and 400 °C are polycrystalline in nature having cubic and both cubic and wurtzite structure, respectively. However, film deposited at temperature of 200 °C was found to be amorphous in nature. The ultra-violet and visible absorption studies showed that the band gap of films increases with increase in deposition temperatures. Photoluminescence spectra displayed emission near 396 and 444 nm, which arises due to zinc vacancies and sulphur vacancies, respectively and has been correlated to phase transition of the films.     

Composition and structure of chemically deposited CulnSe2 thin films

The composition, morphology and crystallographic structure of CuInSe₂ films grown at 50°C and 90°C by the chemical method are discussed. Characterization includes EDS, X-ray and transmission electron diffraction and optical absorption spectroscopy. Nearly stoichiometric CuInSe₂ thin films are obtained with chalcopyrite structure and with thickness in the range 1–3 μm and the grain size in the range 0.2–1.5 μm, band gap near 0.9 eV and absorption coefficient α ≅ 10⁵ cm⁻¹.The effect of deposition mixture temperature on film orientation has been studied by X-ray and electron diffraction. Preferred orientation along [112] direction occurs at a deposition-mixture temperature of 90°C.     

热处理对铜锌阻垢合金性能的影响

为研究热处理温度对合金微观形貌、晶体结构和电化学性能的影响,对阻垢铜锌合金进行热处理,结合水质参数及水垢晶体结构的变化,优化阻垢合金的热处理条件,并利用X-射线衍射、金相显微镜、接触角测量、扫描电镜和电化学分析等多种测试手段表征材料结构及表面性能变化.结果表明,600℃热处理2h后,合金的表面自由能和极性分量分别比铸态时提高了33.4%和74.3%,600℃热处理能够有效地改善合金的阻垢效能.     

Dehydration and Hydration Ktnetics,Phase Change,Solubility and Dissolution Behavior of Fenoprofen Calcium

Abstract

The role of water of hydration on the crystal structure, the solubility and the rate of dissolution of fenoprofen calcium dihydrate was examined. The rate of dehydration of fenoprofen calcium dihydrate at 0% relative humidity (R.H.) increased from 0.0400 to 0.7488 fraction dehydratedhour over a temperature range of 50°C to 80 °C and appeared to occur by a combination of diffusion and nucleation processes. The enthalpy of dehydration was 21.897 kcal/mole. Hydration of dehydrated fenoprofen calcium occurred rapidly at 100% R.H. X-ray powder diffraction analysis showed that the upon dehydration fenoprofen calcium dihydrate underwent a change in its crystal structure to form anhydrous fenoprofen calcium. The rate of dissolution of fenoprofen calcium dihydrate tablets at 37°C was not significantly different than that of tablets containing anhydrous fenoprofen. The enthalpies of solution (δH_sol) of fenoprofen calcium dihydrate and anhydrous fenoprofen calcium were 2.0504 and 3.5583 kcaYmole respectively. The transition temperature at which the dihydrate and anhydrous fenoprofen had equal solubilities was approximately 59.91 °C.     

Dehydration transformation in Ca-montmorillonite

The present work deals with the dehydration transformation of Ca-montmorillonite in the temperature range 30°–500°C. Thermal, infrared (IR), and X-ray diffraction (XRD) analyses were used to describe the thermal transformation. The microstructural and layer disorder parameters like crystallite size, r.m.s. strain (〈e²〉^1/2), variation of interlayer spacing (g), and proportion of planes which were affected by the defect (γ), have all been calculated from the (001) basal reflection using the method of variance and Fourier line shape analysis. These investigations revealed that sample underwent transformation from hydrated phase to dehydrated phase at 200°C, and as a consequence, its basal spacing collapsed from 1602 Å (30°C) to around 10 Å (200°C). This transformation occurred through a wide range of temperature, i.e. within the range 120°–200°C. The crystallite size was maximum at room temperature (30°C), however, the size decreased with increasing temperature in the hydrated phase, whereas the size increased with increasing temperature for the dehydrated phase. Theg, γ and 〈e²〉^1/2 of the hydrated and the dehydrated phase increased and decreased, respectively with increase of heating temperature.