Structural,morphological, and optical properties of W-doped VO2 thin films prepared by sol-gel spin coating method

Thermochromic VO₂ thin films were deposited on soda-lime glass via sol-gel method. Doping was done through adding tungstic acid solution to the vanadium solution precursor. Grazing incidence x-ray diffractometer (GIXRD) results showed that VO₂ and V₆O₁₃ phases were formed together in the heat-treated sample. According to the GIXRD result of the W-doped sample, only VO₂ remained. Field-emission scanning electron microscopy (FESEM) micrographs showed that the VO₂ grain size decreased from about 70 to about 25 nm for undoped film and 2 wt% W-doped films, respectively. Atomic force microscopy (AFM) results showed that the root mean square roughness for the film with 180 nm thickness was about 18 nm, and 2 wt% W-doped film had a smoother surface. Diffuse reflectance spectroscopy (DRS) results showed that the band gap energy for undoped, 1 wt% W- doped, and 2 wt% W-doped VO₂ thin films was 1.7, 1.3, and 0 eV, respectively. Four-point probe resistivity measurements showed a significant decrement, from approximately 1 MΩ at 15°C to <100 Ω at 80°C. Regarding Vis-NIR spectroscopy results, maximum optical transmission for undoped and W-doped films was approximately 75% and 35%, respectively.     

Synthesis of Y(Al,Cr)O3 red pigments by co-precipitation method and their interactions with glazes

New red pigment based on the system YAl_1−yCr_yO₃ (y = 0.01–0.1) was synthesized by co-precipitation method. The precipitant was attained by mixing solutions of yttrium, aluminum and chromium nitrates, respectively, and addition of ammonia as the precipitator. The effects of chromium as dopant and glaze composition on the color shade of resulting pigments were studied. EDX analysis of the prepared pigment particles, which was embedded in glaze, showed the occurrence of reactions between some glaze constituents and pigment particles. Accordingly, a glaze which was enriched in Al₂O₃ and poor in ZnO was more suitable in point of achieving a reddish shade. The resulting pigments were characterized by using X-ray diffraction (XRD), SEM and UV–vis spectrophotometer.     

Crystallization Behavior,Mechanical Properties,and Chemical Resistance of Leucite–Fluoroapatite Glass-Ceramic Glazes

The roles of Li₂O and B₂O₃ and heat-treatment condition on crystallization behavior and flowability of leucite–fluoroapatite-based glass-ceramic glazes were investigated. The thermal expansion coefficient, mechanical, and chemical properties of the optimum specimen were determined. Glaze firing was performed in the 650–1100°C interval, in one and two step processes. Based on the results, B₂O₃ was more effective than Li₂O in point of flowability view. Also, the microstructures varied with the adopted firing process, so that the two-step heat-treated sample showed superior mechanical properties than the one-step heat-treated specimens.     

Production of lactic acid from beet molasses by calcium alginate immobilized Lactobacillus delbrueckii IFO 3202

Lactic acid was produced from pretreated beet molasses by the homofermentative organism Lactobacillus delbrueckii subsp delbrueckii IFO 3202 entrapped in calcium alginate gel using batch, repeated batch and continuous fermentation systems. In batch fermentation studies successful results were obtained with 2.0–2.4 mm diameter beads prepared from 2% sodium alginate solution. The highest effective yield (82.0%) and conversion yield (90.0%) were obtained from substrate concentrations of 52.1 and 78.2 g dm⁻³ respectively. The gel beads produced lactic acid for 14 consecutive batch fermentations without marked activity loss and deformation. In the continuous fermentation, the highest lactic acid (4.22%) was obtained at a dilution rate of 0.1 h⁻¹ while the highest productivity (13.92 g dm⁻³ h⁻¹) was obtained at a dilution rate of 0.4 h⁻¹. © 1999 Society of Chemical Industry     

Non-isothermal crystallization kinetics and microstructure of a silver doped calcium aluminophosphate glass

The role of metallic silver in crystallization behavior of CaO–Al₂O₃–TiO₂–P₂O₅ system glasses was investigated utilizing differential thermal analysis, X-ray diffractometry, atomic force microscope and scanning electron microscopy. Initial glasses were heat treated in hydrogen atmosphere to convert silver ions to the metallic state, prior to crystallization. The presence of metallic silver led to noticeable decreasing of crystallization temperatures as well as effective crystallization of calcium titanium phosphate (CaTi₄(PO₄)₆), calcium metaphosphate (Ca(PO₃)₂) and calcium pyrophosphate (Ca₂P₂O₇) phases. Kinetic of crystallization was also evaluated before and after hydrogen heat treatment under non-isothermal conditions. It was found that activation energy for crystallization was not significantly influenced by the metallic silver. However, the calculated Avrami exponents confirmed the dominant role of metallic silver as an effective nucleating agent in bulk crystallization of the reduced glasses. By leaching of the silver free and silver containing glass–ceramics, calcium pyrophosphate (Ca₂P₂O₇) phase was selectively dissolved out and left porous microstructures with various pore morphologies and dimensions.     

Synergistic effect of micro- and nano-TiO2 on hydrophobic,mechanical, and electrical properties of hybrid polyurethane composites

Journal of Materials Science: Materials in Electronics - One of the ways to improve the performance of ceramic insulators in polluted climates is to use polymer coatings reinforced with ceramic...     

Purification,structural characterization,and technological properties of an aspartyl proteinase from submerged cultures of Mucor mucedo DSM 809

An extracellular aspartyl proteinase from Mucor mucedo DSM 809 submerged cultures was purified by a two-steps chromatographic procedure. The enzyme had a molecular weight (MW) of 32.7 kDa, and an isoelectric point (pI) value of 4.29; no evidence of N-linked glycosylation was found. As judged by mass spectrometry, the primary structure of the M. mucedo enzyme presented homology with Rhizopus spp. proteinases. The secondary structure showed 4% α-helix, 48% β-sheet and 48% random coil structure in 20 mM phosphate buffer (pH 5.8), as evidenced by circular dichroism spectroscopy. When acting on milk to provoke curd formation, the proteinase showed maximum potency at pH 5.0 and at 40 °C. The enzyme was heat-sensitive and became completely inactivated after incubation at 55 °C for 10 min. These results indicate that the milk-clotting enzyme from M. mucedo can be considered as a potential substitute for bovine chymosin in cheese manufacturing.     

Rheology and gelation behavior of gel-cast cordierite-based glass suspensions

A cordierite-based glass suspension was shaped by gel-casting method. Effects of various parameters like pH, volume fraction of glass particles, gelling agents and dispersant on the rheology of the prepared slurries were investigated. The results demonstrated that using sodium tripolyphosphate (STPP) dispersant brings about a suspension of minimum viscosity. The bending strength of the dried gels was increased with the gelling agents. In addition, the utilization of cross linkers at a fixed concentration of monomer led to the gradual enhancement of the bending strength of the dried bodies. A bending strength of ∼11 MPa was obtained for the most promising dried gel cast bodies.     

Optimization of pullulan production using Ca‐alginate‐immobilized Aureobasidium pullulans by response surface methodology

BACKGROUND: The production of pullulan from synthetic medium by Aureobasidium pullulans P56 immobilized in Ca‐alginate beads was investigated using batch and repeated batch fermentation systems. RESULTS: The highest pullulan concentration (19.52 ± 0.37 g dm^?3) was obtained with 2.0‐2.4 mm beads prepared from 2% sodium alginate solution. Pullulan production was mainly accomplished by immobilized fungal cells since leaked cells in the fermentation medium comprised 17.4% of the total fungal population at the end of fermentation. The pullulan proportion was 84.5% of the total polysaccharide in the fermentation medium. Response surface methodology was used to investigate the effects of three fermentation parameters (initial pH, agitation speed and incubation time) on the concentration of pullulan. Results of the statistical analysis showed that the fit of the model was good in all cases. The maximum pullulan concentration of 21.07 ± 0.48 g dm^?3 was obtained at the optimum concentrations of process variables (pH 7.31, agitation speed 191.5 rpm, incubation time 101.2 h). The gel beads produced pullulan under the optimized conditions for six consecutive batch fermentations without marked activity loss and deformation. CONCLUSION: The results of this study suggest that the immobilization of A. pullulans cells in Ca‐alginate gel beads is suitable for batch and repeated batch production of pullulan. Copyright © 2007 Society of Chemical Industry