Influence of heat treatment on the optical properties of SnO2 : Sb thin films deposited by dip coating using aqueous solution

Antimony doped tin oxide thin films were deposited on glass by a chemical route derived from Pechini method. Particular emphasis was given to the microstructure of crystallized films. Crystalline phase formation was studied by grazing incident X-ray diffraction and by thermal analyses. Scanning electron microscopy was carried out for microstructure characterization, surface roughness was observed using scanning tunneling microscope and the optical transmittance measurements were performed in the wavelength range of 200-800 nm. (C) 2002 Kluwer Academic Publishers.

Electrochemical impedance spectroscopy characterization of passive film formed on implant Ti-6Al-7Nb alloy in Hank's solution

The influence of potential on electrochemical behavior of Ti-6Al-7Nb alloy under simulate physiological conditions was investigated by electrochemical impedance spectroscopy (EIS). The experimental results were compared with those obtained by potentiodynamic polarization curves. All measurements were carried out in Hank's aerated solution at 25degreesC, at pH 7.8 and at different potentials (corrosion potential, 0 mV(SCE), 1000 mV(SCE), and 2000 mV(SCE)). The EIS spectra exhibited a two-step or a two-time constant system, suggesting the formation of a two-layer oxide film on the metal surface. The high corrosion resistance, displayed by this alloy in electrochemical polarization tests, is due to the dense inner layer, while its osseointegration ability can be ascribed to the presence of the outer porous layer. (C) 2004 Kluwer Academic Publishers.

Ferroelectric characteristics of BiFeO3 thin films prepared via a simple chemical solution deposition

BiFeO3 (BFO) thin films were fabricated on Pt(111)/Ti/SiO2/Si substrates by using a polymeric precursor solution under appropriate crystallization conditions. The capacitance dependence on voltage is strongly nonlinear, confirming the ferroelectric properties of the films resulting from the domain switching. The leakage current density increases with annealing temperature. The polarization electric field curves could be obtained in BFO films annealed at 500 degrees C, free of secondary phases. X-ray photoelectron spectroscopy spectra of films annealed at 500 degrees C indicated that the oxidation state of Fe was purely 3+, demonstrating that our films possess stable chemical configurations. (c) 2007 American Institute of Physics.

Aqueous solution behavior of thermosensitive (N-isopropylacrylamide-acrylic acid-ethyl methacrylate) terpolymers

A series of N-isopropylacrylamide (NIPAM)-acrylic acid-ethyl methacrylate terpolymers with varied monomer compositions was prepared by radical polymerization. The solution behavior of these polymers was studied in dilute aqueous solution using spectrophotometry, fluorescence spectroscopy and high-sensitivity differential scanning calorimetry. The results obtained revealed that the lower critical solution temperatures depend strongly on the copolymer composition, solution pH and ionic strength. At a high pH, the ionization of acrylic acid (AA) units leads to an increase in solution cloud points (T-c). Solutions of polymers containing 10% or less of AA display a constant T-c for pH above 5.5, with 15% there is a continuous increase in T-c with pH and, for higher AA contents, no clouding was observed within the studied temperature range. Fluorescence probe studies were conducted by following the I (1)/I (3) ratio of pyrene vibronic bands and the emission of anilinonaphtalene sulfonic acid, sodium salt (ANS), both approaches revealing the existence of hydrophobic domains for polymers with higher ethyl methacrylate content at temperatures lower than T-c, suggesting some extent of aggregation and/or a coil-to-globule transition. Scanning calorimetry measurements showed an endothermic transition at temperatures agreeing with the previously detected cloud points. Moreover, the transition curves became broader and with a smaller transition enthalpy, as both the AA content and the solution pH were increased. These broader transitions were interpreted to be the result of a wider molecular distribution upon polymer ionization, hence, displaying varied solution properties. The decrease in transition enthalpy was rationalized as a consequence of reminiscent hydration of NIPAM units, even after phase separation, owing to the presence of electric charges along the polymer chain.

ITERATIVE NUMERICAL-SOLUTION OF SCATTERING PROBLEMS

An iterative Neumann series method, employing a real auxiliary scattering integral equation, is used to calculate scattering lengths and phase shifts for the atomic Yukawa and exponential potentials. For these potentials the original Neumann series diverges. The present iterative method yields results that are far better, in convergence, stability and precision, than other momentum space methods. Accurate result is obtained in both cases with an estimated error of about 1 in 10(10) after some 8-10 iterations.

Ionic medium effects on equilibrium constants .1. Proton, copper(II), cadmium(II), lead(II) and acetate activity coefficients in aqueous solution

The molar single ion activity coefficients associated with hydrogen, copper(II), cadmium(II) and lead(II) ions were determined at 25 degrees C and ionic strengths between 0.100 and 3.00 M (NaClO4), whereas for acetate the ionic strengths were fixed between 0.300 and 2.00 M, held with the same inert electrolyte. The investigation was carried out potentiometrically by using proton-sensitive glass, copper, cadmium and lead ion-selective electrodes and a second-class Hg\Hg-2(CH3COO)(2) electrode. It was found that the activity coefficients of these ions (y(i)) can be assessed through the following empirical equations:log y(H) = -0.542I(0.5) + 0.451I; log y(Cu) = -1.249I(0.5) + 0.912I; log y(Cd) = -0.829I(0.5) + 0.448I(1.5);log y(Pb) = -0.404I(0.5) + 0.117I(2); and log y(Ac) = 0.0370I .

Microstructural and optical characterization of CaWO4 and SrWO4 thin films prepared by a chemical solution method

Stoichiometric CaWO4 and SrWO4 thin films were synthesized using a chemical solution processing, the so-called polymeric precursor method. In this soft chemical method, soluble precursors such as strontium carbonate, calcium carbonate and tungstic acid, as starting materials, were mixed in an aqueous solution. The thin films were deposited on glass substrates by means of the spinning technique. The surface morphology and crystal structure of the thin films were investigated using X-ray diffraction (XRD), scanning electron microscopy (SEM), and atomic force microscopy (AFM). Nucleation stages and surface morphology evolution of the thin films on glass substrates were studied by atomic force microscopy. The films nucleate at 300 degreesC, after the coalescence of small nuclei into larger grains yielding a homogeneous dense surface. XRD characterization of these films showed that the CaWO4 and SrWO4 phases crystallize at 400 degreesC from an inorganic amorphous phase. No intermediate crystalline phase was identified. The optical properties were also studied. It was found that CaWO4 and SrWO4 thin films have an optical band gap, E-gap=5.27 and 5.78 eV, respectively, of a direct transition nature. The excellent microstructural quality and chemical homogeneity confirmed that this soft solution processing provides an inexpensive and environmentally friendly route for the preparation of CaWO4 and SrWO4 thin films. (C) 2003 Elsevier B.V. All rights reserved.

Crystallization, preliminary X-ray analysis and molecular-replacement solution of the carboxy form of haemoglobin I from the fish Brycon cephalus

Haemoglobin, the 'honorary enzyme' [Brunori (1999), Trends Biochem. Sci. 24, 158-161], constitutes a prime prototype for allosteric models. Here, the crystallization and preliminary X-ray analysis of haemoglobin I from the South American fish Brycon cephalus are reported. X-ray diffraction data have been collected to 2.5 Angstrom resolution using synchrotron radiation (LNLS). Crystals were determined to belong to the space group P6(1)22 and preliminary structural analysis revealed the presence of one dimer (alpha beta) in the asymmetric unit. The structure was determined using standard molecular-replacement techniques.

Influence of membrane-solution interface on the selectivity of SnO2 ultrafiltration membranes

SnO2 supported membranes, presenting 3.0 nm average pore size, have been produced by sol casting on alumina tubular substrate using aqueous colloidal suspensions prepared by sol-gel route. The selectivity and flux throughout SnO2 membrane were analyzed by permeation experiments, using a laboratory tangential filtration pilot equipped with a monotubular membrane. To evaluate the effect of the surface charge at the membrane-solution interface, aqueous salt solutions (NaCl, Na2SO4, CaCl, and CaSO4) of different ionic strength have been filtered and the results correlated with the values of zeta potential measured at several pH. The results show that the retention coefficient is dependent on the electrolyte present in aqueous solution decreasing as: (dication, monoanion) > (monocation, monoanion) approximate to (monocation, dianion) > (dication, dianion). The surface charge and the cation adsorption capacity play a determinant role in these selectivity sequences. (C) 2001 Elsevier B.V. B.V. All rights reserved.

Spatial distribution of solutes and water in sucrose solution dehydrated apples

Half-fresh apples were immersed in sucrose solution (50% w/w, 27 degrees C) during different times of exposition (2, 4, and 8 h). Then each fruit was sliced from the transversal exposed surface. Density, water, and sugar content were determined for each slice. A mathematical model was fitted to experimental data of water and sucrose content considering the global flux and the tissue shrinkage. By numerical analysis, the binary effective diffusion coefficients as a function of concentration were calculated, using material coordinates and integrating simultaneously two differential equations (for water and sucrose). The coefficients obtained are one or even two orders of magnitude lower than the ones for pure solutions and present an unusual concentration dependence. This comparison shows the influence of the tissue resistance to the diffusion.

Synthesis, ferroelectric and optical properties of (Pb,Ca)TiO3 thin films by soft solution processing

Calcium modified lead titanate sol was synthesized using a soft solution processing, the so-called polymeric precursor method. In soft chemistry method, soluble precursors such as lead acetate trihydrate, calcium carbonate and titanium isopropoxide, as starting materials, were mixed in aqueous solution. Pb0.7Ca0.3TiO3 thin films were deposited on platinum-coated silicon and quartz substrates by means of the spinning technique. The surface morphology and crystal structure, dielectric and optical properties of the thin films were investigated. The electrical measurements were conducted on metal-ferroelectric-metal (MFM) capacitors. The typical measured small signal dielectric constant and dissipation factor at a frequency of 100 kHz were 299 and 0.065, respectively, for a thin film with 230 nm thickness annealed at 600degreesC for 2 h. The remanent polarization (2P(r)) and coercive field (E-c) were 32 muC/cm(2) and 100 kV/cm, respectively. Transmission spectra were recorded and from them, refractive index, extinction coefficient, and band gap energy were calculated. Thin films exhibited good optical transmissivity, and had optical direct transitions. The present study confirms the validity of the DiDomenico model for the interband transition, with a single electronic oscillator at 6.858 eV. The optical dispersion behavior of PCT thin film was found to fit well the Sellmeir dispersion equation. The band gap energy of the thin film, annealed at 600degreesC, was 3.56 eV. The results confirmed that soft solution processing provides an inexpensive and environmentally friendly route for the preparation of PCT thin films.

Solution approaches for the soft drink integrated production lot sizing and scheduling problem

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

SAE 1045 steel/WC-Co/Ni-Cu-Ni/SAE 1045 steel joints prepared by dynamic diffusion bonding: Microelectrochemical studies in 0.6 M NaCl solution

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)