On the stabilizing behavior of zirconia: A combined experimental and theoretical study

Reactive zirconia powder was synthesized by the complexation of zirconium metal from zirconium hydroxide using a solution of 8-hydroxiquinoline. The kinetics of zirconia crystallization was followed by X-ray diffraction, scanning electron microscopy and surface area measured by the nitrogen adsorption/desorption technique. The results indicated that zirconia with a surface area as high as 100 m(2)/g can be obtained by this method after calcination at 500degreesC. Zirconia presents three polymorphic phases (monoclinic, tetragonal and cubic), which are reversibly interconversible. The cluster model Zr4O8 and Z(r)4O(7)(+2) was used for a theoretical study of the stabilization process. The ab initio RHF method was employed with the Gaussian94 program and the total energies and the energy gap of the different phases were calculated and compared with the experimental energy gap. The theoretical results show good reproducibility of the energy gap for zirconia. (C) 2004 Kluwer Academic Publishers.

Crystallization and preliminary X-ray diffraction analysis of suramin, a highly charged polysulfonated napthylurea, complexed with a myotoxic PLA(2) from Bothrops asper venom

Suramin is a highly charged polysulfonated napthylurea that interferes in a number of physiologically relevant processes such as myotoxicity, blood coagulation and several kinds of cancers. This synthetic compound was complexed with a myotoxic Lys49 PLA(2) from Bothrops asper venom and crystallized by the hanging-drop vapor diffusion method at 18 degreesC. The crystals belong to the orthorhombic space group P2(1)2(1)2(1), with unit cell parameters a=49.05, b=63.84 and c=85.67 Angstrom, Diffraction data was collected to 1.78 Angstrom. (C) 2004 Elsevier B.V. All rights reserved.

Luminescence effect in amorphous PLT

Amorphous and crystalline powder of PLT phase was synthesized by using the Pechini method. Infrared (FTIR) analysis of the polymeric resin shows intense bands of organic materials from 250 to 1620 cm(-1). X-ray diffraction (XRD) and Raman spectra of calcined powder at different temperatures show amorphous phase at 450 degrees C/3 h, semi-crystalline phase at 550 degrees C/3 h and a crystalline phase at 800 degrees C/3 h. Luminescence effect was observed in amorphous powder calcined from 300 to 350 degrees/3 h with broad absorption peaks in 579 nm at 300 degrees C/3 h and 603 rum at 350 degrees C/3 h, respectively. The photoluminescence effect is attributed to emissions of Ti -> 0 directly from the oxygen 2p orbital (valence band) to the titanate 3d orbital (conduction bands). (c) 2004 Elsevier Ltd. All rights reserved.

Composition and electronic structure of Zn7-xMxSb2O12 (M = Ni and Co) spinel compounds

The relation between the composition and electronic structure of the perfectly inverse spinel compound Zn7-xMxSb2O12 (M = Ni and Co) has been studied by powder X-ray diffraction and X-ray photoelectron spectroscopy. Changes in the site occupancy are associated with shifts in the core levels as observed in the core level spectral analyses. The configuration of the density of states in the valence band due to the Co and Ni states can be observed in the valence band spectra. (C) 2004 Elsevier B.V. All rights reserved.

Effect of maltodextrin and arabic gum in water vapor sorption thermodynamic properties of vacuum dried pineapple pulp powder

Moisture equilibrium data of pineapple pulp (PP) powders with and without additives - 18% maltodextrin (MD) or 18% gum Arabic (GA) - were determined at 20, 30, 40 and 50 degrees C by using the static gravimetric method in a water activity range of 0.06-0.90. The obtained isotherms were sigmoid, typical type 111, and the Guggenhein-Anderson-de Boer (GAB) model was fitted to the experimental data of equilibrium moisture content versus water activity. Addition of additives was shown to affect the isotherms in such a way that, at the same water activity, samples PP + GA and PP + MD presented lower equilibrium moisture content and were not so affected by varying temperature. The net isosteric heats of sorption of pulp powders with additives were higher (less negative) than those of pineapple pulp powders, suggesting that there are more active polar sites in the product without addition of GA or MD. An empirical exponential relationship could describe the heat of sorption dependence on the material moisture content. (C) 2007 Elsevier Ltd. All rights reserved.

Preparation and thermal behavior of mixture of basic carbonate and 4-dimethylaminocinnamylidenepyruvate with lanthanides (III) and yttrium (III) in the solid state

Solid Ln-OKCO3-DMCP compounds, where Ln represents lanthanides (III) and yttrium (III) ions and DMCP is the anion 4-dimethyiaminocinnamylidenepyruvate, have been prepared. Thermogravimetry, derivative thermogravimetry (TG, DTG), differential scanning calorimetry (DSC), X-ray diffraction powder patterns and elemental analysis have been used to characterize the compounds. The thermal stability as well as the thermal decomposition of these compounds were studied using an alumina crucible in an air atmosphere.

Photoluminescence in amorphous PLZ

Amorphous and crystalline powder of PLZ was prepared by using the polymeric precursor method. TGA-DSC (Thermal analysis and Differential Scanning Calorimetry) shows the decomposition of polymeric resin, an amorphous phase and the crystallization of powder. Raman scattering of powder shows an amorphous and semicrystalline phase at 450 and 550 degreesC, respectively. XRD (X-ray diffraction pattern) of powder shows high crystallinity at 700 degreesC/3 h. PL (Photoluminescence) analysis of powder at 300 degreesC/3 h shows a broad asymmetric peak at 585 nm and increases of calcining time led to intense peaks of PL at 300 degreesC/6 h. This emission could be attributed to Zr --> O from the oxygen-2p orbitals to the zirconate-3d orbitals. (C) 2003 Elsevier Ltd and Techna S.r.l. All rights reserved.

Sol-gel entrapped cobalt complex

This work describes optimized conditions for preparation of a cobalt complex entrapped in alumina amorphous materials in the form of powder. The hybrid materials, CoNHG, were obtained by a nonhydrolytic sol-gel route through condensation of aluminum chloride with diisopropylether in the presence of cobalt chloride. The materials were calcined at various temperatures. The presence of cobalt entrapped in the alumina matrix is confirmed by ultraviolet visible spectroscopy. The materials have been characterized by X-ray diffraction (XRD), surface area analysis, thermogravimetric analysis (TGA), differential thermal analyses (DTA) and transmission electron microscopy (TEM). The prepared alumina matrix materials are amorphous, even after heat treatment up to 750 degreesC. The XRD, TGA/DTA and TEM data support the increase of sample crystallization with increasing temperature. The specific surface area, pore size and pore diameter changed as a function of the heat treatment temperature employed. Different heat treatment temperatures result in materials with different compositions and structures, and influence their catalytic activity. The entrapped cobalt materials calcined at 750 degreesC efficiently catalyzed the epoxidation of (Z)-cyclooctene using iodozylbenzene as the oxygen donor. (C) 2003 Elsevier B.V. All rights reserved.

Effects of processing on the structure of zein/oleic acid films investigated by X-ray diffraction

Zein films plasticized with oleic acid were formed by solution casting, by the stretching of moldable resins, and by blown film extrusion. The effects of the forming process on film structure were investigated by X-ray diffraction. Wide-angle X-ray scattering (WAXS) patterns showed d-spacings at 4.5 and 10 angstrom, which were attributed to the zein alpha-helix backbone and inter-helix packing, respectively. The 4.5.angstrom d-spacing remained stable under processing while the 10 angstrom d-spacing varied with processing treatment. Small-angle X-ray scattering (SAXS) detected a long-range periodicity for the formed films but not for unprocessed zein, which suggests that the forming process-promoted film structure development is possibly aided by oleic acid. The SAXS d-spacing varied among the samples (130-238 angstrom) according to zein origin and film-forming method. X-ray scattering data suggest that the zein molecular structure resists processing but the zein supramolecular arrangements in the formed films are dependent on processing methods.

The effectiveness of alumina powder on carious dentin removal

This study determined the size of aluminum oxide particles used in an air abrasion system that is able to remove carious dentin tissue with maximum preservation of sound structure. Thirty extracted and carious-free third molars were used in this study. The dentin sample was obtained by sectioning the middle of the crown longitudinal to the long axis of the tooth in a mesio-distal direction. One half of the crown corresponded to the sound dentin group (SD), while the other half was used to develop artificial caries, constituting the, carious dentin group (CD). The specimens were air abraded for 15 seconds. The SD and CD groups were each randomly divided into three subgroups (N=10) according to the particle diameter employed (27, 50 and 125 pm). The prepared cavity was perpendicularly cut in half, and the profiles of all hemi-fragments were observed using SEM microscopy. The cavity measurements were made using a modified cephalometric analysis. The 27, 50 and 125 pun aluminum oxide particles did not present selectivity in the removal of carious dentin. However, when using the air abrasive technique for carious dentin treatment, the use of 27 and 50 pun aluminum oxide particles is recommended, due to their capacity to remove less sound tissue than the 125 pun particles.

Development of alpha-SiAlON-SiC ceramic composites by liquid phase sintering

In this work, in situ alpha-SiAlON-SiC ceramic composites were obtained,by, liquid phase sintering, using SiC as reinforcement. Different beta-SiC powder contents (0-20 wt.%), were added to Si3N4-AlN-RE2O3. powder mixtures, and compacted by cold isostatic pressing. The samples were sintered at 1950 degrees C for 1 h, in N-2 atmosphere. Sintered: samples were characterized by relative density, weight loss, X-ray diffraction and scanning electron microscopy. Furthermore, mechanical properties such as hardness and fracture toughness were determined by Vickers indentation method. Lattice parameters of the alpha' phase did not considerably change with increase of SiC content. However, morphology, average grain size and aspect ratio of the alpha' phase were considerably changed with increase of the SiC content. These behavior influences significantly the mechanical properties of this hard ceramic composite. (C) 2006 Elsevier Ltd. All rights reserved.

Photoluminescent property of mechanically milled BaWO4 powder

Crystalline BaWO4 (BWO) powder obtained by the polymeric precursor method was structurally disordered by means of high-energy mechanical milling. For the first time a strong and broad photoluminescence (PL) has been measured at room temperature for mechanically milled BWO powder and interpreted by ground-state quantum mechanical calculations in the density functional theory framework. Two periodic models have been studied; one representing the crystalline form and the other one representing the disordered BWO powder. These models allowed the calculation of electronic properties, which are consistent with the experimental results, showing that structural disorder in the lattice is an important condition to generate an intense and broad PL band. (c) 2006 Elsevier B.V. All rights reserved.

Synthesis of nanocrystalline tetragonal zirconia by a polymeric organometallic method

A polymeric precursor method based on the Pechini process was successfully used to synthesize zirconia-12 mol% ceria ceramic powders, the influence of the main process variables (citric acid-ethylene glycol ratio, citric acid-total oxides ratio and calcination temperature) on phase formation and powder morphology (surface area and crystallite size) were investigated. The thermal decomposition behavior of the precursor is presented. X-ray diffraction (XRD) patterns of powders revealed a crystalline tetragonal zirconia single-phase, with crystallite diameter ranging from 6 to 15 nm. The BET surface areas were relatively high, reaching 95 m(2) g(-1) Nitrogen adsorption/desorption on the powders suggested that nonaggregated powders could be attained, depending on the synthesis conditions. Copyright (C) 1999 John Wiley & Sons, Ltd.

Crytallization and high-resolution X-ray diffraction data collection of an Asp49 PLA(2) from Bothrops jararacussu venom both in the presence and absence of Ca2+ ions

Snake venom PLA(2)s have been extensively studied due to their role in mediating and disrupting physiological processes such as coagulation, platelet aggregation and myotoxicity. The Ca2+ ion bound to the putative calcium-binding loop is essential for hydrolytic activity. We report the crystallization in the presence and absence of Ca2+ and X-ray diffraction data collection at 1.60 Angstrom (with Ca2+) and 1.36 Angstrom (without Ca2+) of an Asp49 PLA(2) from Bothrops jararacussu venom. The crystals belong to orthorhombic space group C222(1). Initial refinement and electron density analysis indicate significant conformational. changes upon Ca2+ binding. (C) 2004 Elsevier B.V. All fights reserved.

CRYSTALLIZATION AND PRELIMINARY DIFFRACTION DATA OF BOTHROPSTOXIN-I ISOLATED FROM THE VENOM OF BOTHROPS-JARARACUSSU

The myotoxic Lys-49 phospholipase bothropstoxin I was crystallized, and X-ray diffraction data were collected to 3.5 Angstrom resolution. Preliminary analysis reveals the presence of four molecules in the asymmetric unit.