Sintering and characterization of PLZT (9/65/35)

PLZT(9/65/35) obtained by association between the Pechini method (ZT) and partial oxalate (PLZT) was prepared. The stoichiometric phase and monophasic (cubic) PLZT obtained by calcination did not occur after sintering. The sintering process, by using two stages, caused a liquid phase formation due to a PbO excess (5 and 10 wt%). Samples with high density (similar to 8 g/cm(3)) and optical transparency(similar to 12%) were obtained. However, an equilibrium between the excess of PbO of sample/atmosphere PbO leads to a segregated PbO phase on the boundaries of the microstructure. A diffusion of Zr, Ti and La ions from PLZT to PbO phase promoted a stoichiometric deviation of the matrix and modified the optical and dielectric characteristics. (C) 2000 Elsevier B.V. Ltd and Techna S.r.l. All rights reserved.

Renewable drops electrochemical sensor for sulfide ions detection

The design and characteristics of a novel electrochemical system, which uses a drop as a renewable electroanalytical sensor, are described. This article describes the performance of the electrochemical system, the coupling of the experimental arrangement with flow injection technique and a demonstration of its applicability for the measurement of sulfide. The method is based on renewable drops of ferricyanide ions, buffered by borate. The ferrocyanide ions, product of the reaction between ferricyanide and sulfide ions, are oxidized on a platinum microelectrode and the current measured is related to sulfide concentration. The measurements can be done in continuous or static flow mode. In continuous mode, the detection limit is 5.0 x 10(-5) mol L-1.

Structural and magnetic transformation of monodispersed iron oxide particles in a reducing atmosphere

Uniform metal iron ellipsoidal particles of around 200 nm in length were obtained by reduction and passivation of alumina-coated alpha-Fe2O3 (hematite) particles under different conditions of temperature and hydrogen flow rate. The monodispersed hematite particles were prepared by the controlled hydrolysis of ferric sulfate and further coated with a homogeneous thin layer of Al2O3 by careful selection of the experimental conditions, mainly pH and aluminum salt concentration. The reduction mechanism of alpha-Fe2O3 into alpha-Fe was followed by x-ray and electron diffraction, and also by the measurements of the irreversible magnetic susceptibility. The transformation was found to be topotactic with the [001] direction of hematite particles, which lies along the long axis of the particles, becoming the [111] direction of magnetite and finally the [111] direction of metal iron. Temperature and hydrogen flow rate during the reduction have been found to be important parameters, which determine not only the degree of reduction but also the crystallite size of the final particles. Magnetic characterization of the samples shows that the only parameters affected by the crystallite size are the saturation magnetization and magnetic time-dependence effect, i.e., activation volume. (C) 2002 American Institute of Physics.

Precipitation chemistry and wet deposition in Kruger National Park, South Africa

The chemical composition, as well as the sources contributing to rainwater chemistry have been determined at Skukuza, in the Kruger National Park, South Africa. Major inorganic and organic ions were determined in 93 rainwater samples collected using an automated wet-only sampler from July 1999 to June 2002. The results indicate that the rain is acidic and the averaged precipitation pH was 4.72. This acidity results from a mixture of mineral acids (82%, of which 50% is H2SO4) and organic acids (18%). Most of the H2SO4 component can be attributed to the emissions of sulphur dioxide from the industrial region on the Highveld. The wet deposition of S and N is 5.9 kgS.ha(-1).yr(-1) and 2.8 kgN.ha(-1).yr(-1), respectively. The N deposition was mainly in the form of NH4+. Terrigenous, sea salt component, nitrogenous and anthropogenic pollutants have been identified as potential sources of chemical components in rainwater. The results are compared to observations from other African regions.

Sequencing wasp venom peptides by endopeptidase digestion and nested collision-induced dissociation/post-source decay methods

A method incorporating nested collision-induced dissociation/post-source decay (CID/PSD) combined with endopeptidase digestion is described as an approach to determine the sequence of N-terminally modified peptides. The information from immonium and related ions observed in the CID/PSD spectrum was used for the selection of a suitable endopeptidase for the digestion of peptides. Rapid and reliable assignment of peptide sequence was performed by the comparison of CID/PSD spectra of both intact and endopeptidese-digested peptide fragments, since the assignments of the observed fragment ions to either N- or C-terminal ions can thus be carried out unambiguously. This nested CID/PSD method was applied to the sequence determination of two peptides from the solitary wasps Anoplius samariensis and Batozonellus maculifrons (pompilid wasps), which could not be sequenced by the Edman method due to N-terminal modification. Copyright (C) 2002 John Wiley Sons, Ltd.

Tolerance to copper and zinc of Acidithiobacillus thiooxidans isolated from sewage sludge

The effect of copper and zinc ions on sulphur oxidation by Acidithiobacillus thiooxidans, strain SFR01, isolated from anaerobic sewage sludge was assessed, resulting in tolerance levels up to 20 and 200 mmol l(-1) for copper and zinc, respectively. The tolerance levels obtained were higher than the concentration of copper and zinc usually found in the collected sewage sludge. The tolerance levels obtained indicate no constraints for sludge bioleaching of those metals due to their toxicities to the indigenous A. thiooxidans.

Role of the surface state and structural feature in the thermoreversible sol-gel transition of a zirconyl aqueous precursor modified by sulfuric acid

The sols produced by admixture of ZrOCl2 acidified solutions to hot H2SO4 aqueous solutions were studied to clarify the effects of Cl- and SO42- ions on the kinetic stability of nanoparticles and to obtain some new evidence concerning the mechanism of a thermoreversible sol-gel transition observed in this system. The study of suspensions prepared with different molar ratios R-S = [Zr]/[SO42-] and R-Cl = [Zr]/[Cl-] revealed domains of composition of formation of thermoreversible gels, thermostable sols, and powder precipitation. The effects of R-S and R-Cl on the structural features of nanoparticles and on the particle solution interface were systematically analyzed for samples of thermoreversible and thermostable sol domains. Small-angle X-ray scattering measurements revealed the presence of small fractal aggregates in all samples of thermoreversible domains, while compact packing aggregates of primary particles are present in the thermostable sol. Extended X-ray absorption fine structure and elemental chemical analysis revealed that irrespective of the nominal value of R-S and R-Cl all studied samples of the thermoreversible domain are constituted by a well-defined compound possessing an inner core made of hydroxyl and oxo groups bridging together zirconium atoms surrounded on the surface by complexing sulfate ligands. zeta potentials of powders extracted by freeze-drying from the thermoreversible gel revealed a point of surface charge inversion attributed to the specific adsorption of SO42- ion. Thermoreversible gel formation is rationalized by considering the effect of the specific adsorption on the electrical double-layer repulsion together with the temperature dependency of the physical chemical properties of ions in solution.

Upconversion luminescence and thermal effects in terbium-ytterbium codoped fluorogermanate glass-ceramic

Cooperative energy transfer upconversion luminescence is investigated in Tb(3+)/Yb(3+)-codoped PbGeO(3)-PbF(2)-CdF(2) glass-ceramic and its precursor glass under resonant and off resonance infrared excitation. Bright UV-visible emission signals around 384, 415, 438 nm, and 473-490, 545, 587, and 623 nm are identified as due to the (5)D(3)((5)G(6))->(7)F(1) (J=6,5,4) and (5)D(4)->(7)F(1) (J=6,5,4,3) transitions, respectively, and readily observed. The results indicate that cooperative energy transfer between ytterbium and terbium. ions followed by excited state absorption are the dominant upconversion excitation mechanisms involved. Comparison of the upconversion process in a glass-ceramic sample and its glassy precursor revealed that the former present much higher upconversion efficiency. The dependence of the upconversion emission upon pump power, temperature, and doping content is also examined.

An image processing method for morphology characterization and pitting corrosion evaluation

A digital image processing and analysis method has been developed to classify shape and evaluate size and morphology parameters of corrosion pits. This method seems to be effective to analyze surfaces with low or high degree of pitting formation. Theoretical geometry data have been compared against experimental data obtained for titanium and aluminum alloys subjected to different corrosion tests. (C) 2002 Elsevier B.V. B.V. All rights reserved.

Solubilization profiles of metal ions from bioleaching of sewage sludge as a function of pH

Two patterns of solubilization of metal ions resulting from bioleaching of sewage sludge by sulphur-oxidizing Thiobacillus spp. were established as a function of pH. Chromium and copper ions required a pH of 2-3 to initiate their solubilization, whereas nickel and zinc ions had their solubilization initiated at pH 6-6.5. The patterns obtained were independent of the sludge solids concentrations investigated (10, 17, 25, 32.5 and 40 g l(-1)).

Upconversion luminescence in Ho3+/Yb3+- and Tb3+/Yb3+-codoped fluorogermanate glass and glass ceramic

Energy-transfer excited upconversion luminescence in Ho3+/Yb3+- and Tb3+/Yb3+ -codoped PbGeO3-PbF2-CdF2 glass and glass-ceramic under infrared excitation is investigated. In Ho3+/Yb3+-codoped samples, green (545 nm), red (652 nm), and near-infrared (754 nm) upconversion emission corresponding to the S-5(2) (F-5(4)) -> I-5(8), F-5(5) -> I-5(8), and S-5(2)(F-5(4)) -> I-5(7) transitions, respectively, was observed. Blue (490 nm) emission assigned to the F-5(2,3) -> I-5(8) transition was also detected. In the Tb3+/Yb3+-codoped system, bright UV-visible emission around 384, 415, 438, 473-490, 545, 587, and 623 nm, identified as due to the D-5(3)((5)G(6)) -> F-7(J)(J = 6, 5, 4) and D-5(4) -> F-7(J)(J = 6, 5, 4, 3) transitions, was measured. The comparison of the upconversion process in glass ceramic and its glassy precursor revealed that the former samples present much higher upconversion efficiencies. The dependence of the upconversion emission upon pump power, and doping contents was also examined. The results indicated that successive energy-transfer between ytterbium and holmium ions and cooperative energy-transfer between ytterbium and terbium ions followed by excited-state absorption are the dominant upconversion excitation mechanisms herein involved. The viability of using the samples for three-dimensional solid-state color displays is also discussed. (c) 2007 Elsevier B.V. All rights reserved.

Use of levoglucosan, potassium, and water-soluble organic carbon to characterize the origins of biomass-burning aerosols

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

Synthesis, thermal properties and spectroscopic study of solid mandelate of light trivalent lanthanides

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

Simultaneous solidification of two catalyst wastes and their effect on the early stages of cement hydration

Two catalyst wastes (RNi and RAI) from polyol production were considered as hazardous, due to their respective high concentration of nickel and aluminum contents. This article presents the study, done to avoid environmental impacts, of the simultaneous solidification/stabilization of both catalyst wastes with type II Portland cement (CP) by non-conventional differential thermal analysis (NCDTA). This technique allows one to monitor the initial stages of cement hydration to evaluate the accelerating and/or retarding effects on the process due to the presence of the wastes and to identify the steps where the changes occur. Pastes with water/cement ratio equal to 0.5 were prepared, into which different amounts of each waste were added. NCDTA has the same basic principle of Differential Thermal Analysis (DTA), but differs in the fact that there is no external heating or cooling system as in the case of DTA. The thermal effects of the cement paste hydration with and without waste presence were evaluated from the energy released during the process in real time by acquiring the temperature data of the sample and reference using thermistors with 0.03 A degrees C resolution, coupled to an analog-digital interface. In the early stages of cement hydration retarding and accelerating effects occur, respectively due to RNi and RAl presence, with significant thermal effects. During the simultaneous use of the two waste catalysts for their stabilization process by solidification in cement, there is a synergic resulting effect, which allows better hydration operating conditions than when each waste is solidified separately. Thermogravimetric (TG) and derivative thermogravimetric analysis (DTG) of 4 and 24 h pastes allow a quantitative information about the main cement hydrated phases and confirm the same accelerating or retarding effects due to the presence of wastes indicated from respective NCDTA curves.

Characterization of nanosized ZnAl2O4 spinel synthesized by the sol-gel method

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