Ethanol electrooxidation on Pt-Sn and Pt-Sn-W bulk alloys

Ethanol oxidation has been studied on Pt-Sn and Pt-Sn-W electrodes prepared in an arc-melting furnace. Different electrochemical techniques like cyclic voltammetry and chronoamperometry were used to evaluate the catalytic activity of these materials. The electro-oxidation process was also investigated by in situ infrared reflectance spectroscopy in order to determine adsorbed intermediates and reaction products. Experimental results indicated that Pt-Sn and Pt-Sn-W alloys are able to oxidize ethanol mainly to acetaldehyde and acetic acid. Adsorbed CO was also detected, demonstrating the viability of splitting the C-C bond in the ethanol molecule during the oxidation process. The adsorbed CO was further oxidized to CO2.This reaction product was clearly detected by SNIFTIRS. Pt-Sn-W catalyst showed a better electrochemical performance than Pt-Sn that, in it turn, is better than Pt-alone.

Determination and fractionation of barium in Brazil nuts

Several sample preparation strategies were employed for determination and fractionation of barium in Brazil nuts using measurements by graphite furnace atomic absorption spectrometry (GF AAS) and inductively coupled plasma optical emission spectrometry with axial view (ICP OES). This food is widely consumed because of its nutritional value and good taste. The chemical analysis of Brazil nuts is not trivial due to their complex matrix. The fractionation of barium in Brazil nuts was studied owing to the toxicity of this element and the strong correlation between chemical form and absorption. Total concentrations of barium varied from 860 to 2084 mg kg-1. Sequential extractions were performed based on solubility in different media and also according to lipids, proteins and low molecular weight fractions (LMW). The greatest contents of barium were determined in the LMW and in the water insoluble fractions with concentrations in the range 778 to 1606 and 551 to 1520 mg kg-1, respectively. Based on these results it can be inferred that Ba is not absorbed when Brazil nuts are ingested. Considering both the contents of barium and sulfur in different fractions and stoichiometric calculations it was also possible to assume that barium occurs mainly in the BaSO4 form. The presence of this chemical form was also confirmed by thermogravimetric measurements.

Association of dental enamel lead levels with risk factors for environmental exposure

OBJECTIVE: To analyze household risk factors associated with high lead levels in surface dental enamel. METHODS: A cross-sectional study was conducted with 160 Brazilian adolescents aged 14-18 years living in poor neighborhoods in the city of Bauru, southeastern Brazil, from August to December 2008. Body lead concentrations were assessed in surface dental enamel acid-etch microbiopsies. Dental enamel lead levels were measured by graphite furnace atomic absorption spectrometry and phosphorus levels were measured by inductively coupled plasma optical emission spectrometry. The parents answered a questionnaire about their children's potential early (05 years old) exposure to well-known lead sources. Logistic regression was used to identify associations between dental enamel lead levels and each environmental risk factor studied. Social and familial covariables were included in the models. RESULTS: The results suggest that the adolescents studied were exposed to lead sources during their first years of life. Risk factors associated with high dental enamel lead levels were living in or close to a contaminated area (OR = 4.49; 95% CI: 1.69;11.97); and member of the household worked in the manufacturing of paints, paint pigments, ceramics or batteries (OR = 3.43; 95% CI: 1.31;9.00). Home-based use of lead-glazed ceramics, low-quality pirated toys, anticorrosive paint on gates and/or sale of used car batteries (OR = 1.31; 95% CI: 0.56;3.03) and smoking (OR = 1.66; 95% CI: 0.52;5.28) were not found to be associated with high dental enamel lead levels. CONCLUSIONS: Surface dental enamel can be used as a marker of past environmental exposure to lead and lead concentrations detected are associated to well-known sources of lead contamination.

Determinação de As, Cd e Pb em amêndoas e mesocarpo de babaçu, sapucaia, xixá e castanha-do-pará por espectrometria de absorção atômica

This work describes methods for the simultaneous determination of Cd and Pb by graphite furnace atomic absorption spectrometry and As by hydride generation atomic absorption spectrometry in Brazilian nuts. The samples (~ 0.300 g) were digested to clear solutions in a closed vessel microwave oven. The pyrolysis and atomization temperatures for simultaneous determinations of Cd and Pb were 1100 and 2100 °C, respectively, using 0.5% (w v-1) NH4H2PO4 + 0.03% (w v-1) Mg(NO3)2 as chemical modifier. The limits of detection (3Δ) were 3.8 μg kg-1 for As, 0.86 μg kg-1 for Cd and 13 μg kg-1 for Pb. The reliability of the entire procedures was confirmed by peach leaves (No. 1547 - NIST) certified reference material analysis and addition and recovery tests. The found concentrations presented no statistical differences at the 95% confidence level.

Análise direta de sólidos por espectrometria de absorção atômica com atomização em forno de grafite: uma revisão

This is a review of direct analysis using solid sampling graphite furnace atomic absorption spectrometry. Greater emphasis is dedicated to sample preparation, sample homogeneity, calibration and its application to microanalysis and micro-homogeneity studies. The main advantages and some difficulties related to the applicability of this technique are discussed. A literature search on the application of solid sampling graphite furnace atomic absorption spectrometry in trace element determination in many kinds of samples, including biological, clinical, technological and environmental ones, is also presented.

Effect of experimental heat treatment on mechanical properties of resin composites

The aim of this study was to verify the influence of an experimental heat treatment (170ºC/10 min) using a casting furnace on the mechanical properties (hardness and flexural strength) of 2 commercial direct resin composites (TPH Spectrum and Filtek P60) compared to a commercial indirect resin system (BelleGlass). Heat treatment temperature was determined after thermal characterization by thermogravimetry (TG) and differential scanning calorimetry (DSC). Data was analyzed by ANOVA and Tukey's test at 5% significance level. There was statistical significance for the main factor heat treatment (p=0.03) and composite (p=0.02), for flexural strength. For Knoop hardness, only the main factor composite was statistically significant (p=0.00). P60 presented higher hardness than TPH. No statistically significant correlation between mechanical properties tested was detected. Based on these results, it was possible to conclude that heat treatment influenced flexural strength of direct composites, while it was not observed for hardness. The association of direct composites with a simple post-cure heat treatment may be an alternative for current indirect composite systems, although more studies are needed to verify other properties of the composites for this application.

Surface dental enamel lead levels and antisocial behavior in Brazilian adolescents

Lead poisoning has been reportedly linked to a high risk of learning disabilities, aggression and criminal offenses. To study the association between lead exposure and antisocial/delinquent behavior, a cross-sectional study was conducted with 173 Brazilian youths aged 14\201318 and their parents (n = 93), living in impoverished neighborhoods of Bauru-SP, with high criminality indices. Self-Reported Delinquency (SRD) and Child Behavior Checklist (CBCL) questionnaires were used to evaluate delinquent/antisocial behavior. Body lead burdens were evaluated in surface dental enamel acid microbiopsies. The dental enamel lead levels (DELL) were quantified by graphite furnace atomic absorption spectrometry (GFAAS) and phosphorus content was measured using inductively coupled plasma optical emission spectrometry (ICP-OES). Logistic regression was used to identify associations between DELL and each scale defined by CBCL and SRD scores. Odd ratios adjusted for familial and social covariates, considering a group of youths exposed to high lead levels (\2265 75 percentile), indicated that high DELL is associated with increased risk of exceeding the clinical score for somatic complaints, social problems, rule-breaking behavior and externalizing problems (CI 95 per cent). High DELL was not found to be associated with elevated SRD scores. In conclusion, our data support the hypothesis that high-level lead exposure can trigger antisocial behavior, which calls for public policies to prevent lead poisoning

In vivo bioavailability of selenium in enriched Pleurotus ostreatus mushrooms

The in vivo bioavailability of Se was investigated in enriched Pleurotus ostreatus mushrooms. A bioavailability study was performed using 64 Wistar male rats separated in 8 groups and fed with different diets: without Se, with mushrooms without Se, with enriched mushrooms containing 0.15, 0.30 or 0.45 mg kg(-1) Se and a normal diet containing 0.15 mg kg(-1) of Se using sodium selenate. The experiment was performed in two periods: depletion (14 days) and repletion (21 days), according to the Association of Official Analytical Chemists. After five weeks, the rats were sacrificed under carbon dioxide, and blood was drawn by heart puncture. Blood plasma was separated by centrifugation. The total Se concentration in the plasma of rats fed with enriched mushrooms was higher than in rats fed with a normal diet containing sodium selenate. The plasma protein profiles were obtained using size exclusion chromatography (SEC) and UV detectors. Aliquots of effluents (0.5 mL per minute) were collected throughout in the end of the chomatographic column. However, Se was determined by graphite furnace atomic absorption spectrometry (GF AAS) only in the aliquots where proteins were detected by SEC-UV. The plasma protein pro. le of rats fed with different diets was similar. The highest Se concentration was observed in a peptide presenting 8 kDa. Furthermore, the higher Se concentration in this peptide was obtained for rats fed with a diet using enriched mushrooms (7 mu g L(-1) Se) compared to other diets (2-5 mu g L(-1) Se). These results showed that Se-enriched mushrooms can be considered as an alternative Se food source for humans, due to their high bioavailability.

Evaluation of laser induced breakdown spectroscopy for cadmium determination in soils

Cadmium is known to be a toxic agent that accumulates in the living organisms and present high toxicity potential over lifetime. Efforts towards the development of methods for microanalysis of environmental samples, including the determination of this element by graphite furnace atomic absorption spectrometry (GFAAS). inductively coupled plasma optical emission spectrometry (ICP OES), and inductively coupled plasma-mass spectrometry (ICP-MS) techniques, have been increasing. Laser induced breakdown spectroscopy (UBS) is an emerging technique dedicated to microanalysis and there is a lack of information dealing with the determination of cadmium. The aim of this work is to demonstrate the feasibility of LIBS for cadmium detection in soils. The experimental setup was designed using a laser Q-switched (Nd:YAG, 10 Hz, lambda = 1064 nm) and the emission signals were collimated by lenses into an optical fiber Coupled to a high-resolution intensified charge-coupled device (ICCD)-echelle spectrometer. Samples were cryogenically ground and thereafter pelletized before LIBS analysis. Best results were achieved by exploring a test portion (i.e. sampling spots) with larger surface area, which contributes to diminish the uncertainty due to element specific microheterogeneity. Calibration curves for cadmium determination were achieved using certified reference materials. The metrological figures of merit indicate that LIBS can be recommended for screening of cadmium contamination in soils. (C) 2009 Elsevier B.V. All rights reserved.

Nickel sorption capacity of ground xylem of Quercus ilex trees and effects of selected ligands present in the xylem sap

In this work the influence of four different ligands present in the xylem sap of Quercus ilex (histidine, citric, oxalic and aspartic acids) on Ni(II) adsorption by xylem was investigated. Grinded xylem was trapped in acrylic columns and solutions of Ni(II), in the absence and presence of the four ligands prepared in KNO(3) 0-1 mol L(-1) at pH 5.5, were percolated through the column. Aliquots of solutions were recovered in the column end for Ni determination by graphite furnace atomic absorption spectrometry (GFAAS). The experimental. data to describe Ni sorption by xylem in both the presence and absence of ligands was better explained by the Freundlich isotherm model. The decreasing affinity order of ligands for Ni was: oxalic acid > citric acid > histidine > aspartic acid. On the other hand, the Ni(II) adsorption by xylem increased following the inverse sequence of ligands. Potentiometric titrations of acidic groups were carried out to elucidate the sorption site groups available in Q. ilex xylem. The potentiometric titration has shown three sorption sites: pK(a) 2.6 (57.7% of the sorption sites), related to monobasic aliphatic carboxylic acids or nitrogen aromatic bases, pK(a) 8.1 (9.6%) and pK(a) 9.9 (32.7%), related to phenolic groups. (C) 2008 Elsevier GmbH. All rights reserved.

Surface characterization of Ti-7.5Mo alloy modified by biomimetic method

Titanium and its alloys have been used in dentistry due to their excellent corrosion resistance and biocompatibility. It was shown that even a pure titanium metal and its alloys spontaneously form a bone-like apatite layer on their surfaces within a living body. The purpose of this work was to evaluate the growth of calcium phosphates at the surface of the experimental alloy Ti-7.5Mo. We produced ingots from pure titanium and molybdenum using an arc-melting furnace We then submitted these Ingots to heat treatment at 1100 degrees C for one hour, cooled the samples in water, and cold-worked the cooled material by swaging and machining. We measured the media roughness (Ra) with a roughness meter (1.3 and 2.6 mu m) and cut discs (13 mm in diameter and 4 mm in thickness) from each sample group. The samples were treated by biomimetic methods for 7 or 14 days to form an apatite coating on the surface. We then characterized the surfaces with an optical profilometer, a scanning electron microscope and contact angle measurements. The results of this study indicate that apatite can form on the surface of a Ti-7.5Mo alloy, and that a more complete apatite layer formed on the Ra = 2 6 mu m material. This Increased apatite formation resulted in a lower contact angle (C) 2010 Elsevier B.V. All rights reserved

Behaviour of biofuel addition on metallurgical properties of sinter

Blast furnace gas yield is essentially controlled by a gas-solid reaction phenomenon, which strongly influences hot metal manufacturing costs. As a result of rising prices for reducing agents on the international market, Companhia Siderurgica Nacional decided to inject natural gas into its blast furnaces. With more gas inside the furnace, the burden permeability became even more critical. To improve blast furnace gas yield, a new technological approach was adopted; raising the metallic burden reaction surface. To that end, a special sinter was developed with permeability being controlled by adding micropore nucleus forming agents, cellulignin coal, without, however, degrading its mechanical properties. This paper shows the main process parameters and the results from physicochemical characterisation of a sinter with controlled permeability, on a pilot scale, compared to those of conventional sinter. Gas flow laboratory simulations have conclusively corroborated the positive effects of micropore nucleus forming agents on enhancing sinter permeability.

Selection of new glass-forming compositions in Al-La system using a combination of topological instability and thermodynamic criteria

A combination of an extension of the topological instability ""lambda criterion"" and a thermodynamic criterion were applied to the Al-La system, indicating the best range of compositions for glass formation. Alloy compositions in this range were prepared by melt-spinning and casting in an arc-melting furnace with a wedge-section copper mold. The GFA of these samples was evaluated by X-ray diffraction, differential scanning calorimetry and scanning electron microscopy. The results indicated that the gamma* parameter of compositions with high GFA is higher, corresponding to a range in which the lambda parameter is greater than 0.1, which are compositions far from Al solid solution. A new alloy was identified with the best GFA reported so far for this system, showing a maximum thickness of 286 mu m in a wedge-section copper mold. Crown Copyright (C) 2009 Published by Elsevier B.V. All rights reserved.

Emissions of NO(x) and SO(2) from Coals of Various Ranks, Bagasse, and Coal-Bagasse Blends Burning in O(2)/N(2) and O(2)/CO(2) Environments

Oxy-coal combustion is a viable technology, for new and existing coal-fired power plants, as it facilitates carbon capture and, thereby, can mitigate climate change. Pulverized coals of various ranks, biomass, and their blends were burned to assess the evolution of combustion effluent gases, such as NO(x), SO(2), and CO, under a variety of background gas compositions. The fuels were burned in an electrically heated laboratory drop-tube furnace in O(2)/N(2) and O(2)/CO(2) environments with oxygen mole fractions of 20%, 40%, 60%, 80%, and 100%, at a furnace temperature of 1400 K. The fuel mass flow rate was kept constant in most cases, and combustion was fuel-lean. Results showed that in the case of four coals studied, NO(x) emissions in O(2)/CO(2) environments were lower than those in O(2)/N(2) environments by amounts that ranged from 19 to 43% at the same oxygen concentration. In the case of bagasse and coal/bagasse blends, the corresponding NO(x) reductions ranged from 22 to 39%. NO(x) emissions were found to increase with increasing oxygen mole fraction until similar to 50% O(2) was reached; thereafter, they monotonically decreased with increasing oxygen concentration. NO(x) emissions from the various fuels burned did not clearly reflect their nitrogen content (0.2-1.4%), except when large content differences were present. SO(2) emissions from all fuels remained largely unaffected by the replacement of the N(2) diluent gas with CO(2), whereas they typically increased with increasing sulfur content of the fuels (0.07-1.4%) and decreased with increasing calcium content of the fuels (0.28-2.7%). Under the conditions of this work, 20-50% of the fuel-nitrogen was converted to NO(x). The amount of fuel-sulfur converted to SO(2) varied widely, depending on the fuel and, in the case of the bituminous coal, also depending on the O(2) mole fraction. Blending the sub-bituminous coal with bagasse reduced its SO(2) yields, whereas blending the bituminous coal with bagasse reduced both its SO(2) and NO(x) yields. CO emissions were generally very low in all cases. The emission trends were interpreted on the basis of separate combustion observations.

Quantitative analysis of aluminum dross by the Rietveld method

Aluminum white dross is a valuable material principally due to its high metallic aluminum content. The aim of this work is to develop a method for quantitative analysis of aluminum white dross with high accuracy. Initially, the material was separated into four granulometric fractions by means of screening. Two samples of each fraction were obtained, which were analyzed by means of X-ray fluorescence and energy dispersive spectroscopy in order to determine the elements present in the samples. The crystalline phases aluminum, corundum, spinel, defect spinel, diaoyudaoite, aluminum nitride, silicon and quartz low were identified by X-ray diffraction. The quantitative phase analysis was performed by fitting the X-ray diffraction profile with the Rietveld method using the GSAS software. The following quantitative results were found: 77.8% aluminum, 7.3% corundum, 2.6% spinel, 7.6% defect spinel, 1.8% diaoyudaoite, 2.9% aluminum nitride, and values not significant of quartz and silicon.