Residual solutions containing Cr(VI) ions can be harmful to the environment as well as to human health. Hence, practical and efficient methods for the treatment of such solutions are welcome. In this note, the treatment with commercial steel wool pads of a Cr(VI) residual solution from electrochemical coloration processes of stainless steel is described in detail. Successful treatment was achieved when an amount of steel wool equivalent to 20% in excess in relation to the theoretical stoichiometric amount was used, followed by chemical precipitation with sodium hydroxide up to pH 10-11 and separation by filtration under reduced pressure. The treatment yielded a final solution with concentrations of Cr(III) and Cr(VI) ions of only 0.29 ± 0.02 mg L-1 and < 0.01 mg L-1, respectively. These concentration values are significantly lower than the maximum limits established by CONAMA for industrial wastewaters, attesting the efficiency of the treatment.

The Direct Black 22 dye was electrooxidized at 30 mA cm-2 in a flow cell using a BDD or β-PbO2 anode, varying pH (3, 7, 11), temperature (10, 25, 45 °C), and [NaCl] (0 or 1.5 g L-1). In the presence of NaCl, decolorization rates were similar for all conditions investigated, but much higher than predicted through a theoretical model assuming mass-transport control; similar behavior was observed for COD removal (at pH 7, 25 °C), independently of the anode. With no NaCl, COD removals were also higher than predicted with a theoretical model, which suggests the existence of distinct dye degradation pathways.

A combined chemical-electrochemical oxidation method to obtain porous bioactive TiO2 films on titanium is reported. In this case, a titanium chemical pre-etching followed by the micro-arc oxidation (MAO) treatment is proposed and optimized, to obtain a high-roughness and porous surface which benefits the titanium/bone integration. The MAO treatment at various rates (different current densities) allowed to define the influence of the oxide growth rate on the surface morphology and to design the best features for each case. Titanium samples were pre-etched using a 2% HF solution as a function of the etching time, and then anodized by the MAO treatment in a 0.5 M H3PO4 solution at current densities in the 10 to 90 mA.cm-2 range. High porosity (0.5 to 1 µm-diameter pores) and higher phosphorous content for TiO2 films were achieved by first etching the Ti sample for 180 seconds in the HF solution, and then applying current densities in the 80 to 90 mA.cm-2 range for the micro-arc oxidation process.

A remoção de íons Pb2+ a partir de soluções diluídas foi estudada, em condições galvanostáticas, usando uma célula de fluxo sem membrana com eletrodos de esponja de aço inoxidável (SSW). A metodologia de superfície de resposta (variáveis independentes: corrente elétrica e vazão) foi usada para obter as condições ótimas para a remoção de Pb2+ a partir de 2 L de uma solução de Pb(NO3)2 50 mg L-1 em NaNO3 0,10 mol L-1 + H3BO3 0,10 mol L-1 (pH 4,8). A partir das superfícies de respostas, concluiu-se que a vazão (59-341 L h-1) não influencia significativamente no processo de remoção de Pb2+. Por outro lado, o aumento da corrente elétrica leva a uma maior remoção de Pb2+, com valores significantemente melhores de consumo de energia específica e eficiência de corrente quando comparados àqueles relatados na literatura. Para um experimento realizado na região de condições ótimas (70 mA e 200 L h-1), uma conversão de Pb2+ de 99,6% foi atingida depois de 90 min de eletrólise. A utilização da célula de fluxo sem membrana com eletrodos de SSW, além de ser energeticamente mais eficiente, levou à remoção de Pb2+ em ambos os eletrodos, mais predominantemente no anodo, sobre o qual 95% dos íons Pb2+ foram convertidos a PbO2.

The removal of Pb2+ ions from dilute solutions was investigated under galvanostatic conditions using a membrane-less flow-through cell with stainless steel wool (SSW) electrodes. The response surface methodology (independent variables: electric current and volumetric flow rate) was used to find the optimal conditions for Pb2+ removal from 2 L of an aqueous solution of 50 mg L-1 Pb(NO3)2 in 0.10 mol L-1 NaNO3 + 0.10 mol L-1 H3BO3 (pH 4.8). The obtained response surfaces revealed that the volumetric flow rate (59-341 L h-1) does not substantially affect the Pb2+ removal process. On the other hand, the electric current increase led to higher Pb2+ removal, with significantly improved values of specific energy consumption and current efficiency when compared with those reported in the literature. For an experiment carried out in the optimum-condition region (70 mA and 200 L h-1), a Pb2+ conversion of 99.6% was attained after 90 min of electrolysis. The use of the membrane-less flow-through cell with SSW electrodes, besides being significantly more energy efficient, led to Pb2+ removal on both electrodes, but predominantly in the SSW anode, on which more than 95% of the Pb2+ ions were converted to PbO2.

The electrochemical performance of electrodeposited Ti/β-PbO2 and Ti-Pt/β-PbO2 anodes was galvanostatically evaluated (batch mode, 50 mA cm-2) to degrade the Direct Yellow 86 dye (100 or 200 mg L-1 in 0.1 mol L-1 Na2SO4 + 1.5 g L-1 NaCl), investigating the effect of pH and temperature. Similar results were obtained for both electrodes and the best conditions for removal of color and chemical oxygen demand are pH 7 and 40 °C, when 90% decolorization is attained by passing a charge of only ~0.13 A h L-1 and total mineralization is achieved with expenditure of ~5 kW h m-3.

Neste trabalho foi avaliada a resistência à corrosão por pites de filmes de óxidos coloridos crescidos sobre aço inoxidável AISI 304 em H2SO4 e H2SO4 + CrO3. A morfologia e topografia dos filmes foram examinadas por MEV (microscopia eletrônica de varredura) e AFM (microscopia de força atômica), respectivamente. As caracterizações eletroquímicas foram conduzidas por curvas de polarização e medidas de impedância em tampão borato pH 9,2. A corrosão por pites foi avaliada por curvas de polarização realizadas na mesma solução contendo NaCl. Todos os filmes coloridos apresentaram valores semelhantes de Epite, mas maiores que dos filmes não coloridos. Os valores de (Epite - Ecor) resultaram no intervalo de 0,45-0,57 V; 0,78-0,92 V e 0,98-1,12 V para filmes nativos e crescidos na presença e ausência de ácido crômico, respectivamente. Portanto, os filmes crescidos sobre o aço na ausência de ácido crômico apresentaram o maior intervalo de potencial livre de corrosão por pites.

In this work, pitting corrosion resistance of coloured oxides films grown on AISI-304 stainless-steel in H2SO4 and H2SO4 + CrO3 was evaluated. Surface morphology and topography of the films were examined by SEM (scanning electron microscopy) and AFM (atomic force microscopy), respectively. Electrochemical characterizations were conducted by polarization curves and impedance measurements in borate buffer pH 9.2. The pitting corrosion was evaluated by polarization curves carried out in the same solution containing NaCl. All coloured films presented similar values of Epit, but they were higher than those for non-coloured ones. The values of (Epit - Ecor) were in the range of 0.45-0.57 V, 0.78-0.92 V and 0.98-1.12 V for native films and films grown in the presence and absence of chromic acid, respectively. Therefore, the films grown on stainless steel in the absence of chromic acid presented the highest potential range free of pitting corrosion.

A degradação eletroquímica do corante Vermelho Reativo 141 foi investigada por meio da aplicação da metodologia de superfície de respostas, utilizando reator filtro-prensa com anodo de β-PbO2. A carga requerida para 90% de descoloração (Q90) e a remoção da demanda química de oxigênio após 30 min de eletrólise (COD30) foram utilizadas para modelar o sistema. As variáveis investigadas foram a densidade de corrente, pH, concentração de NaCl e temperatura. Baixos valores de Q90 (0,2-0,3 A h L-1) foram obtidos em condições ácidas (pH 1-3) e em altas concentrações de NaCl (1,0-2,0 g L-1), quando as espécies oxidantes Cl2 e HOCl estão presentes. Os melhores valores para COD30 foram obtidos com altas densidades de corrente e em condições de pH ácido a neutro; entretanto, o consumo energético resultante torna o processo economicamente não viável. Para soluções extremamente ácidas foram obtidos valores reduzidos de consumo de energia, relacionado ao Q90, em torno de 0,79 kW h m-3.

The electrochemical degradation of the Reactive Red 141 dye using a filter-press reactor with a β-PbO2 anode was investigated through the application of the response surface methodology. The charge required for 90% decolorization (Q90) and the chemical oxygen demand removal percentage after 30 min electrolysis (COD30) were used to model the system. The investigated independent variables were the current density, pH, NaCl concentration, and temperature. Low values of Q90 (0.2-0.3 A h L-1) were obtained at acidic conditions (pH 1-3) and high concentrations of NaCl (1.0-2.0 g L-1), when Cl2 and HOCl are the predominant oxidant species. The best values of COD30 were obtained at high current densities and acidic to neutral conditions (pH 5-7); however, the consequent energy consumption makes the process not economically feasible under these conditions. For strongly acidic solutions, specific energy consumptions associated to Q90 as low as 0.79 kW h m-3 were attained.

The physical and electrochemical properties of Ti-SnO2/Sb electrodes obtained by the thermal decomposition of solutions of the precursor salts SnCl2×2H2O/SbCl3 and SnSO4/Sb2(SO4)3 were investigated. The reversibility of the cyclic voltammetric response of the Fe(CN)6(4-)/Fe(CN)6(3-) redox couple was assessed using the obtained electrodes. Their catalytic activity for the oxygen-evolving reaction and maximum capacity for electronic transfer were also evaluated by potential and current linear scans in 0.5 mol L-1 H2SO4. Additionally, scanning electron microscopy analyses allowed the visualization of the morphology of the oxide films obtained. The best results were presented by the electrodes obtained from the chloride salt precursors.

Filmes de óxidos coloridos foram crescidos sobre amostras de aço inoxidável AISI 304 por métodos químico e eletroquímicos usando diferentes tempos de coloração. Os métodos eletroquímicos utilizados foram pulsos alternados de potencial e varreduras triangulares de corrente. Os filmes coloridos foram caracterizados na região do visível por espectrofotometria no modo de refletância. A resistência à corrosão por pites das diferentes amostras coloridas foi avaliada a 25 ºC em NaCl 0,62 mol L-1, usando curvas de polarização potenciodinâmicas, e em HCl 0,40 mol L-1, por espectroscopia de impedância eletroquímica. Independentemente do método de coloração usado, os filmes de óxido colorido apresentam um efeito protetor contra a corrosão por pites somente nas primeiras horas de exposição. Para tempos de exposição mais longos (8-10 h), as amostras de aço coloridas ou não coloridas apresentaram comportamentos semelhantes.

Colored oxide films were grown on AISI-304 stainless-steel samples by chemical and electrochemical methods using different coloring times. The electrochemical methods involved the use of alternating potential pulses and triangular current scans. The colored films were characterized in the visible region by reflectance spectrophotometry. Pitting corrosion resistance of the different colored steel samples was evaluated at 25 ºC in 0.62 mol L-1 NaCl, using potentiodynamic polarization curves, and in 0.4 mol L-1 HCl, by electrochemical impedance spectroscopy. Independently of the coloring method used, the colored oxide films showed a protective effect against pitting corrosion only in the first hours of exposition. For longer exposition times (8-10 h) the colored and non-colored steel samples presented similar behaviors.

As propriedades eletroquímicas de compósitos do tipo Pani(DMcT-íon Cu)/fibra de carbono, obtidos eletroquimicamente, são analisadas em função tanto do procedimento de preparação como do sal de cobre (CuCl2.2H2O ou CuSO4) utilizado para a incorporação de íons Cu2+ no compósito. Dois procedimentos foram utilizados: adicionando-se o sal de cobre diretamente ao eletrólito durante a eletropolimerização da polianilina (procedimento A), ou adsorvendo-se os íons cobre juntamente com o DMcT sobre a fibra de carbono antes da eletropolimerização (procedimento B). A estabilidade eletroquímica, as propriedades elétricas e a morfologia desses compósitos foram analisadas, por voltametria cíclica, espectroscopia de impedância eletroquímica e microscopia eletrônica de varredura, respectivamente.

The electrochemical properties of Pani(DMcT-Cu ion)/carbon fiber composites, obtained by electrochemical means, are analysed as a function of the preparation procedure and the different copper salts (CuCl2.2H2O or CuSO4) used as source of Cu2+ ions to be incorporated into the Pani(DMcT)/carbon fiber composite. The composites were prepared according to two procedures: by adding the copper salt directly to the electrolyte during the polyaniline electrosynthesis (procedure A), or by allowing the copper ion to be physically adsorbed onto the carbon fiber prior to the polymer electroformation (procedure B). The electrochemical stability, electrical properties and morphology of the composites were analysed by cyclic voltammetry, electrochemical impedance spectroscopy and scanning electron microscopy, respectively.

Estudos sobre a estabilidade de óxidos anódicos crescidos sobre zircônio e suas ligas biocompatíveis Ti-50Zr %at. e Zr-2,5Nb %m., em solução fisiológica de Ringer aerada, a 25 e 37 ºC, foram feitos por meio da comparação entre as cargas de sua formação e de sua reconstrução após dissolução a circuito aberto na solução fisiológica. A estabilidade de óxidos crescidos na solução de Ringer e em solução de Na2SO4 0,15 mol L-1 foi comparada. Os resultados obtidos mostram que a estabilidade desses óxidos é aumentada por envelhecimento sob condições potenciostáticas e que ela pode ser decrescida pela presença de íons cloreto no eletrólito durante o processo de anodização.

Studies on the stability of anodic oxides grown on zirconium and its biocompatible alloys Ti-50Zr at.% and Zr-2.5Nb wt.%, in aerated Ringer physiological solution, at 25 and 37 °C, were carried out by comparing their formation charge and their reconstruction charge after dissolution at open circuit in the physiological solution. The stability of oxides grown in the Ringer solution and in a 0.15 mol L-1 Na2SO4 solution was compared. The obtained results show that the stability of these oxides is increased by aging under potentiostatic conditions and can be decreased by the presence of chloride ions in the electrolyte during the anodization process.

Visando obter eletrodos com alto sobrepotencial para a reação de desprendimento de oxigênio (RDO), úteis para a oxidação de poluentes orgânicos, prepararam-se eletrodos de Ti/PbO2 por um método térmico-eletroquímico e compararam-se seus desempenhos com o de eletrodepositados. O potencial de circuito aberto em solução de H2SO4 0,5 mol L-1 para esses eletrodos apresentou valores bastante estáveis, próximos entre si, na faixa de potenciais para a região de estabilidade de PbO2 em diagramas de Pourbaix. Análises por difração de raios X mostraram que o óxido térmico-eletroquímico é uma mistura de ort-PbO, tetr-PbO e ort-PbO2. Já os eletrodos produzidos por eletrodeposição se apresentaram mais provavelmente na forma tetr-PbO2. Micrografias obtidas por microscopia eletrônica de varredura mostraram que a morfologia básica do PbO2 térmico-eletroquímico é determinada na etapa térmica, sendo bem distinta da dos eletrodos eletrodepositados. Curvas de polarização, em H2SO4 0,5 mol L-1, mostraram que no caso dos eletrodos de Ti/PbO2 térmico-eletroquímicos a RDO foi deslocada para potenciais mais positivos. Entretanto, os valores dos coeficientes de Tafel, bastante altos, indicam que possivelmente houve formação de filmes passivantes sobre os substratos de Ti, o que pode eventualmente explicar os valores de corrente algo baixos para a RDO.

Looking for electrodes with a high overpotential for the oxygen evolution reaction (OER), useful for the oxidation of organic pollutants, Ti/PbO2 electrodes were prepared by a thermal-electrochemical method and their performance was compared with that of electrodeposited electrodes. The open-circuit potential for these electrodes in 0.5 mol L-1 H2SO4 presented quite stable similar values. X-ray diffraction analyses showed the thermal-electrochemical oxide to be a mixture of ort-PbO, tetr-PbO and ort-PbO2. On the other hand, the electrodes obtained by electrodeposition were in the tetr-PbO2 form. Analyses by scanning electron microscopy showed that the basic morphology of the thermal-electrochemical PbO2 is determined in the thermal step, being quite distinct from that of the electrodeposited electrodes. Polarization curves in 0.5 mol L-1 H2SO4 showed that in the case of the thermal-electrochemical PbO2 electrodes the OER was shifted to more positive potentials. However, the values of the Tafel slopes, quite high, indicate that passivating films were possibly formed on the Ti substrates, which could eventually explain the somewhat low current values for OER.

Uma avaliação sistemática de um eletrodo tubular de Fe2O3 em grafite epóxi foi realizada através de medições de pH em um sistema de injeção em fluxo de linha única. O eletrodo tubular foi obtido pela deposição de uma mistura de óxido de ferro(III), pó de grafite e resina epóxi no interior de um orifício feito previamente no canal de injeção (de resina poliuretana). O efeito da composição do eletrodo e dos parâmetros do sistema de injeção em fluxo (vazão e volume amostra) sobre a resposta do eletrodo foram avaliados em quintuplicata (limite de confiança de 95%). A melhor resposta potenciométrica (E/mV = 178,2 - 26,5 pH; r = 0,9995) foi obtida no intervalo de pH de 2 a 12 com um eletrodo de composição em massa 30% de Fe2O3, 20% de grafite e 50% de resina epóxi, volume de injeção de amostra de 300 mL e vazão de 3,2 mL min-1. A frequência analítica foi 90 h-1 e um tempo de vida útil de pelo menos 6 meses (mais de 2000 determinações) foi obtido.

A systematic evaluation of a Fe2O3 graphite-epoxy tubular electrode was investigated through pH measurements in a single-channel flow injection system. The tubular electrode was obtained by deposition of a mixture of iron(III) oxide, graphite powder and epoxy resin into a hole previously made in the injection channel (of a polyuretane resin block). The effect of electrode composition and flow injection parameters (flow rate and injection sample volume) on the Fe2O3-tubular-electrode response was initially evaluated in quintuplicate (confidence level of 95%). The best potentiometric response (E/mV = 178.2 - 26.5 pH; r = 0.9995) was reached in the pH range 2 to 12 with an electrode composition in mass of 30% Fe2O3, 20% graphite and 50% epoxy resin, injection sample volume of 300 mL and a flow rate of 3.2 mL min-1. The frequency rate was 90 h-1 and a useful lifetime of at least six months (more than 2000 determinations) was obtained.

The <FONT FACE="Symbol">e</font> phase of electrolytic manganese dioxide (EMD) is the structural form most easily converted in the LiMn2O4 spinel used as cathode in lithium batteries. Thus, employing titanium as anode, a study of electrolysis parameters was carried out in order to determine the best conditions to produce an <FONT FACE="Symbol">e</font>-EMD suitable for that spinel preparation. The influence of solution temperature (65oC and 90oC) and current density (between 1 mA/cm2 and 17.5 mA/cm2) on the anode potential and the EMD properties was investigated using an aqueous 2.0 mol/L MnSO4 + 0.30 mol/L H2SO4 solution. In any of the electrolysis conditions tested only the e-EMD structure was obtained, but its specific surface area varied with the applied current density and temperature. Drying the <FONT FACE="Symbol">e</font>-EMD at temperatures between 60oC and 120oC did not cause any phase changes. To produce a suitable EMD at the highest current density possible without passivation of the titanium anode, the best electrolysis parameters were determined to be 90oC and 15 mA/cm2. The <FONT FACE="Symbol">e</font>-EMD thus obtained had a specific surface area (BET) of ca. 65 m2/g.

An analysis of the different activities carried out during the first twenty annual meetings (1978-1997) of the Brazilian Chemical Society (SBQ) is presented. The number of papers in the abstract book increased from around 300 in the biennium 78/79 to around 1230 in 96/97. The papers contained in the different sections of the abstract book in the 1st (1978), 10th (1987) and 19th (1996) annual meetings were grouped according to the regions of Brazil the authors' institutions were from, or abroad, and also considering whether the paper came from one institution or was a collaboration between two or more institutions. The relative contribution of the southeastern and northern regions decreased from 77% and 3.0% of the total in 1978 to 63% and 1.2% in 1996, respectively, while those of the northeastern, southern and midwestern regions increased from 12%, 4.8% and 0.6% to 15%, 13%, and 2.6%, respectively; the relative contribution of institutions from abroad also increased from 2.4% to 4.0%. Chemistry of Natural Products and Organic Chemistry decreased their relative contribution from around 55% in 1978 to around 28% in 1996, an evolution towards a more balanced development of the different areas of chemistry in Brazil.