Efeito dos óxidos de nitrogênio e de enxofre na corrosão de cobre e zinco: Um experimento para o ensino da corrosão

This paper proposes a didactic experience on the simulation of the atmospheric corrosion of copper and zinc due to the presence of sulfur and nitrogen oxides. Quantitative parameters of corrosion such as gain and loss of mass were determined to assess the variation of the layer thickness of the metal and of the corrosion products. This proposal aims a better understanding of some basic aspects of acid rain formation using fundamental concepts of chemistry such as the reactivity of gases.

Rerrefino de óleo lubrificante usado

The lubricant oil used in engines of internal combustion must be, periodically, changed. Its mainly function in the engines is to reduce the friction between the pieces, but its presence also promotes the cleanness and the refrigeration of the equipment. These attributions, at the end of some cycles of operation, make the oil to be dirty, that is, full of contaminating substances such as water, gasoline, diesel, additives, oxidized hydro-carbons and rests of metals, not being recommended, therefore, its discarding in the environment. Thus, all the used lubricant oil that leaves the automobiles engine has been thrust, waiting for a solution. The pollution generated by the discarding of a ton of used oil per day in the soil or in the rivers is equivalent to a domestic sewer of 40 thousand of people. The indiscriminate burning of the used lubricant oil generates significant emissions of metallic oxides, besides other toxic gases, like the dioxin and sulphur oxides. In this context, the mean objective of this essay was to effectuate the rerrefine of the used lubricant oil, aiming the increase of its life cycle and consequently contributing for the reduction of the environmental pollution. According to the used process, it was possible to get a rerrefine oil, of good quality, which physicistchemistries properties are in compliance with the norms of NBR and ASTM

Effect of steeping conditions (sulfur dioxide, lactic acid, and temperature) on starch yield, starch quality, and germ quality from the Intermittent Milling and Dynamic Steeping process (IMDS) for a Brazilian corn hybrid

Effect of lactic acid, SO2, temperature, and their interactions were assessed on the dynamic steeping of a Brazilian dent corn (hybrid XL 606) to determine the ideal relationship among these variables to improve the wet-milling process for starch and corn by-products production. A 2x2x3 factorial experimental design was used with SO2 levels of 0.05 and 0.1% (w/v), lactic acid levels of 0 and 0.5% (v/v), and temperatures of 52, 60, and 68degreesC. Starch yield was used as deciding factor to choose the best treatment. Lactic acid added in the steep solution improved the starch yield by an average of 5.6 percentage points. SO2 was more available to break down the structural protein network at 0.1% than at the 0.05% level. Starch-gluten separation was difficult at 68degreesC. The lactic acid and SO2 concentrations and steeping temperatures for better starch recovery were 0.5, 0.1, and 52degreesC, respectively. The Intermittent Milling and Dynamic Steeping (IMDS) process produced, on average, 1.4% more starch than the conventional 36- hr steeping process. Protein in starch, oil content in germ, and germ damage were used as quality factors. Total steep time can be reduced from 36 hr for conventional wet-milling to 8 hr for the IMDS process.

Nickel adsorption by soils in relation to pH, organic matter, and iron oxides

There is little information on nickel adsorption by Brazilian soils. The objective of this experiment was to determine the effect of pH, organic matter, and iron oxides on nickel adsorption by three soils: a clayey Anionic Rhodic Acrudox, a sandy clay loam Anionic Xanthic Acrudox, and a clayey Rhodic Hapludalf. Soil samples were collected from the 0-0.2 in layer and treated to eliminate organic matter and iron oxides. The nickel adsorption was evaluated in the original samples and in those treated to remove organic matter and to remove both, organic matter and iron oxides, using 2 g soil + 20 mL of 0.01 mol L-1 CaCl2 solution containing 5 mg L-1 Ni, pH varying from 3.5 to 7.5. The nickel adsorption decreased with the elimination of organic matter. For the samples without organic matter and iron oxides, adsorption decreased only in the Anionic Rhodic Acrudox. The pH was the main factor involved in nickel adsorption variation, and for soil samples without organic matter and iron oxides, the maximum adsorption occurred at higher pH values.

Optical properties of polydisperse submicrometer aggregates of sulfur-containing zinc oxide consisting of spherical nanocrystallites

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

Oxygen diffusion in superconducting oxides

Since the discovery of high-temperature superconductivity of cuprate oxides, it has been clear that it is strongly affected by the oxygen content, which is also a crucial factor to determine other physical properties of high T-c superconductors. Non-stoichiometric (interstitial) oxygen strongly influences the physical properties of various superconducting oxides, in particular by creating conducting holes. It is now ascertained that the amount of holes injected depends not only on the content of interstitial oxygen, but also on its ordering. Rearrangement of the oxygen ordering may occur even below room temperature due to the unusual high mobility of these atoms. This way, mechanical spectroscopy is one of the most adequate techniques for the study of the mobility (diffusion) of oxygen atoms. This technique allows the determination of the jump frequency of an atomic species precisely, regardless of the model or the different possible types of jumps. In order to evaluate the mobility and the effect of oxygen content on these oxides, ceramic samples we prepared and submitted to several oxygen removal cycles alternately with mechanical relaxation measurements. As for SBCO, it was assumed that the peak was due to O(1)-O(5) jumps of oxygen atoms at the chain terminals or in chain fragments in the orthorhombic phase. In the case of BSCCO, the results showed complex anelastic relaxation structures, which were attributed to interstitial oxygen atom jumps between two adjacent CuO planes.

ZnO-TiO2 composite formed by mixed oxides via polyol

Among the researches on preparation and test of nanostructured materials, titanium dioxide and zinc oxide have been the most frequent studied oxides. In order to extend their properties, composites have been prepared using three different methods: Polyol Method, Sol-gel Process and a combination of the two processes (hybrid process). Recent research showed best properties in composite materials than in pure oxides. In this work is presented the preparation and the structural characterization of ZnO-TiO2 composite nanostructures to be tested for their performance in electrocatalysis and in further trial on photovoltaic cells.

Electrochemical Behavior of a Glassy Carbon Electrode Chemically Modified with Nickel Pentacyanonitrosylferrate in Presence of Sulfur Compounds

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

Alloys and oxides on carbon-supported Pt-Sn electrocatalysts for ethanol oxidation

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

Platinum-coated nanostructured oxides for active catalytic electrodes

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)

Determination of sulfur compounds in gasoline using mercury film electrode by square wave voltammetry

A sensitive method based on square wave voltammetry is described for the quantitative determination of elemental sulfur, disulfide and mercaptan in gasoline using a mercury film electrode. These sulfur compounds can be quantified by direct dissolution of gasoline in a supporting electrolyte followed by subsequent voltammetric measurement. The supporting electrolyte is 1.4 mol L-1 sodium acetate and No acetic acid in methanol. Chemical and optimum operational conditions for the formation of the mercury film were analyzed in this study. The values obtained were a 4.3 mu m thickness for the mercury film, a 1000 rpm rotation frequency, -0.9 V applied potential and 600 s depositing time. Voltammetric measurements were obtained using square wave voltammetry with detection limits of the 3.0 x 10(-9), 1.6 x 10(-7) and 4.9 x 10(-7) mol L-1 for elemental sulfur, disulfide and mercaptan, respectively. (C) 2007 Elsevier Ltd. All rights reserved.

Evaluation of rare earth oxides doping SnO2.(Co1/4,Mn3/4)O-based varistor system

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

Magnetic oxides of spinel structure: Study of CoxCuyMnzO4 and MgxNiyMnzO4 manganites (x+y+z=3)

Systematic studies in manganites of spinel structure have been undertaken. We report on the magnetic properties of two particular cases, in which one of the transition metals, Mg2+ is non-magnetic (NiMgxMn2-xO4) or presents a stable oxidation state, Cu2+ (CoxCuyMnzO4, x + y + z = 3). The magnetic behaviour is described with respect to varying contents of cobalt, copper or manganese. A ferrimagnetic transition is observed at 110-120 K, which depends on the cobalt content. Presence of copper increases the coercive field by a factor of ten with respect to the parent compound NiMn2O4. (c) 2006 Elsevier B.V. All rights reserved.