Synthesis and characterization of lead zirconate titanate powders obtained by the oxidant peroxo method

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

Development of metal oxide nanoparticles by soft chemical method

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

Nanocompósito de alumina com inclusão nonométricas de zircônia para infraestruturas de próteses odontológicas livres de metal: avaliação de prosperidades mecânicas e análise microestrutural. -

Pós-graduação em Reabilitação Oral - FOAR

Parameters optimization of heat treatment for obtaining luminescent PZT powders

Low crystalline PZT powder samples were successfully synthesized using polymeric precursor method and slow decomposition steps. The polymeric resin precursor was thermal treated in a muffle type oven varying the temperature from 250 °C to 700 °C and the time from 3 to 24 hours in order to investigate the order/disorder mechanism toward the amorphous powders. Powder samples with low crystalline phases were obtained at lower temperatures and long time of thermal treatment, demonstrating a kinetic dependence for organic removal and a thermodynamic barrier for crystallization processes. Through XRD and FTIR spectroscopy characterizations the long time thermal treated samples showed to be composed of the solid solution of metal oxides in absent of organic matter, originating broad XRD peaks profiles and no carbonaceous bands in FTIR spectra. A Photoluminescence characterization showed that the peak emission is higher for disordered and homogeneous phases, which only can be reached through the long time of thermal treatment.

Rapid synthesis of Mn3O4 powder from pyro-synthesis of ethylene glycol-metal nitrate precursor assisted by nitric acid

The rapid synthesis of Mn3O4 powders by a two-step process of pyro-synthesis of ethylene glycol-metal nitrate precursor assisted by nitric acid is reported. A new strategy that accelerates the synthesis and allows obtaining highly pure crystalline Mn3O4 is discussed. The structural and morphological characteristics of the Mn3O4 powders are presented and discussed. The mechanism of formation of the Mn3O4 is also discussed. In comparison with other synthesis methods, the present method shows that the proposed route of synthesis has the main advantage of high production of the powder material in a very short time.

Structural characterization of Li-MN doped powders prepared by Pechini's method

Pechini's method has been successfully used to prepare Li-doped MgNb2O6(MN) at short time and low temperature. It consists in the preparation of metal citrate solution, which is polymerized at 250°C to form a high viscous resin. This resin was burned in a box type furnace at 400°C/2h and ground in a mortar. Successive steps of calcination up to 900°C were used to form a crystalline precursor. SEM, DTA and XRD were used to characterize the powders. MN precursor powders containing from 0.1 to 5.0 mol% of LiNbO3 additive was prepared aiming better dielectric properties and microstructural characteristics of the PMN prepared from columbite route. SEM analysis showed that particles increased by sintering, forming large agglomerates. The surface area is also substantially reduced with the increase in additive amount above 1.0 mol%. In XRD pattern of the precursor material with 5.0 mol% of additive was observed the LiNbO3 phase of trigonal structure. XRD data were used for Rietveld refinement and a decrease in microstrain and pronounced increase in crystallite size with the increase of LiNbO3 were observed. It is in agreement with the particle morphologies observed by SEM analysis.

Development of a new analytical approach based on cellulose membrane and chelator for differentiation of labile and inert metal species in aquatic systems

A new procedure was developed in this study, based on a system equipped with a cellulose membrane and a tetraethylenepentamine hexaacetate chelator (MD-TEPHA) for in situ characterization of the lability of metal species in aquatic systems. To this end, the DM-TEPHA system was prepared by adding TEPHA chelator to cellulose bags pre-purified with 1.0 mol L-1 of HCl and NaOH solutions. After the MD-TEPHA system was sealed, it was examined in the laboratory to evaluate the influence of complexation time (0-24 h), pH (3.0, 4.0, 5.0, 6.0 and 7.0), metal ions (Cu, Cd, Fe, Mn and Ni) and concentration of organic matter (15, 30 and 60 mg L-1) on the relative lability of metal species by TEPHA chelator. The results showed that Fe and Cu metals were complexed more slowly by TEPHA chelator in the MD-TEPHA system than were Cd, Ni and Mn in all pH used. It was also found that the pH strongly influences the process of metal complexation by the MD-TEPHA system. At all the pH levels, Cd, Mn and Ni showed greater complexation with TEPHA chelator (recovery of about 95-75%) than did Cu and Fe metals. Time also affects the lability of metal species complexed by aquatic humic substances (AHS); while Cd, Ni and Mn showed a faster kinetics, reaching equilibrium after about 100 min, and Cu and Fe approached equilibrium after 400 min. Increasing the AHS concentration decreases the lability of metal species by shifting the equilibrium to AHS-metal complexes. Our results indicate that the system under study offers an interesting alternative that can be applied to in situ experiments for differentiation of labile and inert metal species in aquatic systems. (c) 2006 Elsevier B.V. All rights reserved.

In situ differentiation of labile/inert metal species in Brazilian tropical rivers by means of a time-controlled batch-procedure based on TEPHA resin

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

Transition metal rates in latosol twice treated with sewage sludge

A reciclagem agrícola do lodo de esgoto tem provocado o acúmulo de metais pesados no solo e na água, podendo atingir níveis tóxicos e causar danos às plantas cultivadas, aos animais e ao homem, por meio da cadeia trófica. Neste intuito foi desenvolvido o presente experimento, em condições de campo, entre 2000 e 2002, onde foram avaliados os efeitos da aplicação de lodo de esgoto por dois anos, sobre a extração de metais de transição (essenciais e não) pelo extrator DTPA em um Latossolo Vermelho distrófico (LVd) de textura média. As concentrações dos elementos metálicos: Mn, Fe, Cd, Ni, Co, Pb e Cr não foram detectados pelo método da absorção atômica na solução obtida com o extrator DTPA. A aplicação de lodo de esgoto causou inicialmente pequena elevação no pH do solo, posteriormente a diminuição do mesmo, e manteve-se próximo ao original. Foi possível concluir que, com a aplicação consecutiva do lodo, os teores extraíveis de Fe e Mn nas amostras de solos aumentaram gradativamente nos dois anos agrícolas, com as doses do lodo de esgoto aplicado, época de amostragens, e foram superiores ao tratamento testemunha. O extrator apresentou capacidade restrita para avaliação da fitodisponibilidade dos metais pesados decorrentes das baixas concentrações nas amostras de solo.

Electrochemical modified electrodes based on metal-salen complexes

A general view of the electroanalytical applications of metal-salen complexes is discussed in this review. The family of Schiff bases derived from ethylenediamine and ortho-phenolic aldehydes (N,N'-ethylenebis(salicylideneiminato) - salen) and their complexes of various transition metals, such as Al, Ce, Co, Cu, Cr, Fe, Ga, Hg, Mn, Mo, Ni, and V have been used in many fields of chemical research for a wide range of applications such as catalysts for the oxygenation of organic molecules, epoxidation of alkenes, oxidation of hydrocarbons and many other catalyzed reactions; as electrocatalyst for novel sensors development; and mimicking the catalytic functions of enzymes. A brief history of the synthesis and reactivity of metal-salen complexes will be presented. The potentialities and possibilities of metal-Salen complexes modified electrodes in the development of electrochemical sensors as well as other types of sensors, their construction and methods of fabrication, and the potential application of these modified electrodes will be illustrated and discussed.

Electrical properties of polymer/metal interface in polymer light-emitting devices: electron injection barrier suppression

The electrical characterization of a high efficient multilayer polymer light emitting diode using poly[(2-methoxy-5-hexyloxy)-p-phenylenevinylene] as the emissive layer and an anionic fluorinated surfactant as the electron transport layer was performed. For the sake of comparison, a conventional single layer device was fabricated. The density current vs. voltage measurements revealed that the conventional device has a higher threshold voltage and lower current compared to the surfactant modified device. The effective barrier height for electron injection was suppressed. The influence of the interfaces and bulk contributions to the dc and high frequencies conductivities of the devices was also discussed. (c) 2006 Springer Science + Business Media, Inc.

Separating interface state response from parasitic effects in conductance measurements on organic metal-insulator-semiconductor capacitors

A simple model is developed for the admittance of a metal-insulator-semiconductor (MIS) capacitor which includes the effect of a guard ring surrounding the Ohmic contact to the semiconductor. The model predicts most of the features observed in a MIS capacitor fabricated using regioregular poly(3-hexylthiophene) as the active semiconductor and polysilsesquioxane as the gate insulator. In particular, it shows that when the capacitor is driven into accumulation, the parasitic transistor formed by the guard ring and Ohmic contact can give rise to an additional feature in the admittance-voltage plot that could be mistaken for interface states. When this artifact and underlying losses in the bulk semiconductor are accounted for, the remaining experimental feature, a peak in the loss-voltage plot when the capacitor is in depletion, is identified as an interface (or near interface) state of density of similar to 4 x 10(10) cm(-2) eV(-1). Application of the model shows that exposure of a vacuum-annealed device to laboratory air produces a rapid change in the doping density in the channel region of the parasitic transistor but only slow changes in the bulk semiconductor covered by the gold Ohmic contact. (C) 2008 American Institute of Physics.

Determining the interfacial density of states in metal-insulator-semiconductor devices based on poly(3-hexylthiophene)

Low frequency admittance measurements are used to determine the density of interface states in metal-insulator-semiconductor diodes based on the unintentionally doped, p-type semiconductor poly(3-hexylthiophene). After vacuum annealing at 90 degrees C, interface hole trapping states are shown to be distributed in energy with their density decreasing approximately linearly from similar to 20x10(10) to 5x10(10) cm(-2) eV(-1) over an energy range extending from 0.05 to 0.25 eV above the bulk Fermi level. (c) 2008 American Institute of Physics.

Morphological and Structural changes of CaxSr1-xTiO3 Powders Obtained by the Microwave-Assisted Hydrothermal Method

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

Ultrathin films of lignins as a potential transducer in sensing applications involving heavy metal ions

Lignins extracted from sugar cane bagasse using different alcohols in the organosolv-CO(2) supercritical pulping process have been applied in the fabrication of ultrathin films through the Langmuir-Blodgett technique. Langmuir films were characterized by surface pressure versus mean molecular area (Pi-A) isotherms to exploit the sensitivity of nanostructured lignin films to metallic ions (Cu(2+), Cd(2+) and Pb(2+)). The Pi-A isotherms were shifted to larger molecular areas when heavy metal ions are present into the subphase, which might be related to electrostatic repulsions between metallic ions entrapped within the lignin molecular structure. Taking the advantage of metal incorporation, Langmuir monolayers were transferred onto solid substrates forming Langmuir-Blodgett (LB) films to be used as a transducer in an "electronic tongue" system to detect Cu(2+) in aqueous solution below threshold standard established by the Brazilian regulation. Both techniques impedance spectroscopy and electrochemistry have been used in these experiments. Complementary, Fourier transform infrared (FTIR) spectroscopy recorded for LB films before and after soaking into Cu(2+) aqueous solution revealed an interaction between the lignin phenyl groups and the metallic ion. (C) 2007 Elsevier B.V.. All rights reserved.