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Integral Analysis of the Process of Electro-Remediation of Andisols Polluted by Heavy Metals
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by M. V. Vázquez, F. Hernández-Luis, M. Lemus, C. D. Arbelo
387-398
DOI:
An integral analysis was carried out on the results obtained in laboratory experiments on electro-remediation of soils using two heavy metal-contaminated volcanic soils from the region of Antioquia, Colombia. Measurements of pH, conductivity, and pollutant concentration were made on each soil. The results were related to the structural characteristics of the soils employed in the experiments. Under the present experimental conditions it was shown that the soil with the lower concentration of organic matter had a lower pH regulatory capacity, that treatment without using wash solutions was more efficient for the mobilization of the metals, and that the particular characteristics of each soil conditioned the efficiency of the treatment.
Study of the Electrical Resistance of Andisols Subjected to Electro-Remediation Treatment
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by M. V. Vázquez, F. Hernández-Luis, D. Grandoso, C. D. Arbelo
399-410
DOI:
Studies of soil resistance suggest that this type of measurement when carried out simultaneously with decontamination treatment, serves as a rapid method for analyzing the behavior of different soils under study, especially when an electric field is not applied.The variation observed in the first step of electro-remediation is related to the ionic content of the segments adjacent to the electrodes. The use of a wash flow facilitates the formation of "ionic batches" near the electrodes. The soil with the higher content of organic material shows lower resistance in the first stage of the treatment. Measuring the electrolysis current without the use of wash flow, together with the other experimental parameters, allows the evaluation of the soil characteristics in experiments of relatively short duration.
Electropolymerisation of Phenylacetylene on Pt Electrodes with Propylene Carbonate and Acetonitryle as Solvents
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by J. G. Cañadas, A. Lafuente, G. Rodríguez, M. L. Marcos, J. G. Velasco
411-431
DOI:
The electropolymerization of phenylacetylene on a Pt electrode has been carried out in two different solvents, acetonitryle and propylene carbonate. The kinetic study carried out leads to values in the kinetic parameters which are significantly different in both solvents. The values deduced for na, Z (reaction order with respect to the phenylacetylene concentration) and activation enthalpy and entropy, were 0.75, 1, 25.3 kJ mol-1 and -87.0 J mol-1 K-1, respectively, in acetonitrile, and 0.25, 0.5, 33.6 kJ mol-1 and -105 J mol-1 K-1, when working in propylene carbonate. The discrepancy in the values can be explained as a consequence of the change in the initiation step of the polymerisation induced by the adsorption of the acetonitryle molecules. The product obtained was isolated, purified and characterised to be formed by a polyenic chain with a linear trans structure. The average molar mass of the product was 3095, corresponding to a polymer formed from around 30 units of monomer.
by V. M. M. Lobo
433-434
DOI:
by V. M. M. Lobo
435-437
DOI:
by M. H. Florêncio, J. C. R. Reis
177-178
DOI:
Temperature Effects on Conductivities and Association Constants of Lithium and Tetra-Ethylammonium Salts in Six Aprotic Solvents of Medium to High Permittivities from - 30 ºC to + 10 ºC
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by C. A. N. Viana, M. Dilo, M. A. P. Segurado
179-192
DOI:
A few non-aqueous dipolar aprotic solvents of medium to high permittivities, low viscosities and large temperature intervals between freezing and boiling points have been used to prepare electrolyte solutions applicable to primary and rechargeable high energy batteries. Lithium perchlorate is a salt often chosen to obtain those systems. In this work low temperature effects on conductivities and association constants of LiClO4 and Et4NBr in six different solvents have been analyzed, using the tetraethylammonium bromide salt for comparative reasons. The temperature interval was -30 ºC to 10 ºC. A few thermodynamic functions resulting from KA, T variations were determined being the results discussed on this basis. The accuracy and precision of results are high; whenever possible they are compared with others previously published.
Caracterização Cronoamperométrica da Redução do Filme de Estanho Electrogerado em Bicarbonato de Sódio
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by S. H. Bonilla, B. F. Giannetti, T. Rabóczkay
193-203
DOI:
Os estudos cronoamperométricos foram motivados pela observação de histerese de corrente nos perfis de redução dos voltamogramas realizados no sistema Sn/bicarnonato, já que é sabido na literatura que a presença de histerese é considerada indicativo de ocorrência de processos de nucleação. A ocorrência de nucleação foi verificada mediante técnica cronoamperométrica quando filmes eletrogerados na região de passivação são reduzidos. Empregando rotinas de análise de mínimos quadrados não lineares, foi obtido o ajuste entre os resultados experimentais e os calculados usando modelos teóricos que descrevem a nucleação eletroquímica. Assim, a eletrorredução do filme formado no extremo inferior da região estudada, pode ser explicada em termos de difusão e nucleação progressiva e crescimento 3-D controlado por transferência de carga. Por outro lado, a redução do filme electrogerado no extremo superior segue o modelo de nucleação progressiva e crescimento 3-D controlado por transferência de carga, com a presença de tempo de indução. A análise da variação dos parâmetros modelísticos com o tamanho do degrau de potencial permitiu estabelecer a influência dos valores das constantes de velocidade paralela e perpendicular à superfície para cada caso experimental.
The Effect of Sour Gases and Some Anions on the Corrosion Behavior of Carbon Steel
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by S. A. Salih, A.A. Mazhar, M. H. Mahanny
205-225
DOI:
The effect of the presence of CO2 and H2S in the well water used in the petroleum plant on corrosion of carbon steel has been tested using impedance measurements. Carbon dioxide leads to decrease in the resistivity of the film developed on the metallic surface, while the effect of hydrogen sulfide is less pronounced. Scanning electron micrographs have shown that corrosion products cover only small part of metallic surface in water containing CO2. Studies under polarization conditions will allow concluding that the dissolved gases in the well water reduce the ability of the film to protect the metal against corrosion. The influence of the oxoanions and halide ions on the corrosion rate of steel has also been analyzed.
Effect of Iodide Ions on Corrosion Inhibition of Mild Steel in 0.5 M H2SO4 by Poly(4-Vinylpyridine)
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by L. Larabi, Y. Harek
227-247
DOI:
The effect of iodide ions on the corrosion inhibition of mild steel in 0.5 M sulfuric acid in the presence of poly(4-vinylpyridine) (p4vp) was studied by weight loss and different electrochemical techniques such as electrochemical impedance spectroscopy, potentiodynamic polarization and polarization resistance measurements. The obtained results showed that poly(4-vinylpyridine) effectively reduces the corrosion rate of mild steel. The addition of potassium iodide (KI) enhanced the inhibition efficiency (P%). The synergism parameter (Sp) calculated from inhibition efficiency was found to be greater than unity, suggesting that the phenomenon of synergism exists between P4VP and iodide ions. The adsorption of p4vp alone and in combination with KI followed Frumkin adsorption isotherm. The effect of temperature indicated that the inhibition efficiency of p4vp decreases with increasing temperature. Study of temperature effect showed also that inhibition efficiency of (P4VP + KI) does not depend on temperature. The apparent activation energies in the absence and in the presence of P4Vp and ( P4VP + KI ) were determined.
Automatic Determination of Uric Acid in Urine in a FIA System with a Tubular Amperometric Detecto
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by M. B. Q. Garcia, J. L. F. C. Lima, M. L. Silva, J. P. Sousa
249-262
DOI:
This paper describes the use of a FIA system for the automatic determination of uric acid in urine, using a tubular amperometric detector. In this system, glassy carbon electrodes of tubular configuration were activated by successive cyclical scans from - 0.30 to 2.00 V versus Ag/AgCl reference electrode in 0.50 mol.L-1 sulphuric acid solution. Samples were diluted in supporting electrolyte before analysis and no other pre-treatment was employed. Such dilution enabled the matrix effects to be reduced and therefore improving the sensitivity provided by the activation step that allows the uric acid (UA) to be detected at lower concentration levels after dilution. Uric acid determination was performed in a single channel FIA manifold, which provided reproducibility of sample transport to the detector and enabled a sampling rate of 120 samples per hour to be achieved. The tubular configuration of the cell offered robustness to the system since it was rigidly fixed to the manifold, allowing the manifold to be generalised for routine analysis application. The results obtained with the FIA system for UA determination in urine were compared with those from the enzymatic method used in clinical analysis laboratories. No statistical difference between methods was found at the 95% confidence level. Relative deviations between both methods were within ± 4% and the proposed system showed good repeatability (about 3%, n = 10).
Influence of the Chemical Composition of Stainless Steels on the Electronic Structure of Passive Films Formed in Artificial Sea Water
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by M. J. J. Ferreira, M. C. Belo
263-278
DOI:
The electronic structure of the passive films formed on stainless steels of different chemical composition in artificial sea water is examined by capacitance measurements (Mott-Schottky approach) and photo-electrochemistry. Analytical characterization is carried out by Auger Electron Spectroscopy. The influence of the main alloying elements (Cr, Ni) on the development of space charge regions, which can be described as a depletion or accumulation layers are discussed.
Degradation of a Textile Dye C. I. Direct Red 80 by Electrochemical Processes
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by A. Lopes, S. Martins, A. Morão, M. Magrinho, I. Gonçalves
279-294
DOI:
The electrochemical removal of the textile dye C. I. Direct Red 80 (DR80) was carried out using three different materials as anodes: iron, polypyrrole (PPy) and boron doped diamond (BDD). Iron electrodes are consumed during the electrolysis, and promote flocculation/coagulation of the dye. Polypyrrole, a conducting polymer, was prepared by chemical/electrochemical precipitation over a cotton cloth; it enables the precipitation of the dissolved dye through a conversion reaction in a less soluble compound. Boron doped diamond electrode was used to achieve the complete mineralization of the dye. Bulk electrolysis were studied using Na2SO4 as electrolyte. In the case of the PPy electrode, NH4NO3 was also used as electrolyte. The variation of the dye concentration was followed by UV-visible absorbance measurements and chemical oxygen demand (COD) tests were also performed, to compare the rates of colour and COD removal in each case. From the COD measurements over the time of electrolysis, using the BDD anode, a mass transfer coefficient for the DR80 molecule was determined. The obtained results show an almost complete colour removal for all the electrodes tested and a COD removal between 50 and 90 %, being the best results obtained with the BDD electrode.
Semiconductor Electrochemistry and Localised Corrosion
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by C. M. Rangel, M. C. Belo
295-304
DOI:
In the present work, the electronic structure of the passive film formed on austenitic stainless steel of the 304 type and its implications on the initiation of localised corrosion are investigated taking into account concepts developed in semiconductor physics and semiconductor electrochemistry. Capacitance measurements (Mott-Schottky approach), show that the susceptibility of AISI 304 stainless steel to stress corrosion cracking (SCC) in boiling chloride containing aqueous solutions is closely linked to the formation of a chromium rich passive oxide film with p-type semiconductivity. A small polarisation is required to drastically change the electric field at the film-electrolyte interface, as a consequence of the high doping level of the passive film. Initiation of the SCC phenomenon is described as the consequence of localised changes in the semiconductive properties of the passive film.
Electrocatalysis and Determination of Ascorbic Acid Through Graphite Paste Electrode Modified With Iron Nitroprusside
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by D. R. Carmo, R. M. Silva, N. R. Stradiotto
71-79
DOI:
Iron nitroprusside, Fe(II)NP was incorporated into a carbon paste electrode and the electrochemical studies were performed by cyclic voltammetry. The cyclic voltammogram of the modified electrode, Fe(II)NP showed two redox couples ( E½ox)1 = 0.24 and (E½ox)2 = 0.85 V vs. SCE attributed to Fe(II)/Fe(III) and Fe(II)(CN)5NO / Fe(III)(CN)5NO, respectively. The redox couple at (E½ox)1 = 0.24 V presents an electrocatalytic response for ascorbic acid. The modified paste electrode exhibits a decrease of 180 mV in the ascorbic acid oxidation. The modified graphite paste electrode gives a linear range from 1.0 × 10-3 to 2.6 × 10-2 mol L-1 of ascorbic acid with a detection limit of 1.4 × 10-3 (±1.2%) mol L-1 (n =3). The electrocatalytic oxidation of ascorbic acid compounds by the mediator has been used for the determination of ascorbic acid in a commercially pharmaceutical available product.
Cuprous Oxide Layers Grown on Copper: Effect of CO Adsorption
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by L. M. Gassa, A. M. Castro-Luna, R. M. Torres-Sánchez, J. O. Zerbino
81-91
DOI:
The semiconducting properties of anodic passive films formed on polycrystalline copper in aqueous borax solutions, pH 9.2, are studied using electrochemical impedance spectroscopy (EIS) and voltammetry. The semiconducting nature of the cuprous passive layer is analysed in the potential region near de rest potential as a function of the electrode potential and the presence of CO dissolved in the electrolyte. The oxide formation is explained as a sequence of Cu2O growth, cation adsorption, Cu(II), and dissolution steps similarly to previous reported investigationsfor the metal in CO free solutions. The different growth conditions change the defect or excess of cations accumulated in the outer side of the cuprous layer/electrolyte interface leading to different semiconducting properties.
New Electrocatalysts for Electro-Oxidation of Methanol Prepared by Bönnemann´s Method
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by A. O. Neto, E. G. Franco, E. Aricó, M. Linardi
93-101
DOI:
Pt-Ru/C, Pt-Dy and Pt-Ru-Mo/C electrocatalysts prepared by Bönnemann´s method have been studied as porous thin films on high surface area carbon electrodes, in order to evaluate their electroactivity on CO desorption in PEM fuel cells. For comparison electrode precursor powders with and without thermal treatment were considered. Cyclic voltammetry showed that addition of Mo in the well-established Pt/Ru system is very promising for methanol oxidation. In order to compare the electroactivity of different catalysts a normalization procedure based on the amount of Pt was used.
Effect of Non-aqueous Solvents on the Rate of Production of Copper Powder from Copper Sulphate Solution by Cementation on Stationary Zinc Sheet and Rotating Zinc Cylinder
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by A. A. Taha
103-125
DOI:
The rate of copper II/zinc cementation from copper sulphate solutions in the absence and in the presence of methanol (CH3OH) and dimethyl sulphoxide (DMSO) has been studied and the reaction was found to follow first-order kinetics. The influence of several parameters on the course of the reaction, such as cylinder rotation speed, initial concentration of Cu2+ ions, temperature and concentration of organic solvent, was investigated. In the case of CH3OH, rotating zinc cylinder was used, while in the presence of DMSO stationary zinc sheet and rotating zinc cylinder were used. It was found that (1) the percentage inhibition caused by methanol ranged from 10.70 to 58.38 depending on the concentration of the alcohol used; (2) the rate of cementation in the presence of DMSO using rotating zinc cylinder > the rate of cementation in the presence of DMSO using stationary zinc sheet; (3) the rate of cementation on zinc cylinder in the presence of DMSO < the rate of cementation in the presence of CH3OH. Different reaction conditions, and the physical properties of solutions are studied to obtain dimensionless correlation among all these parameters. Thermodynamic parameters ΔS*, ΔH* and ΔG* were studied.
Substituted Dithiobiurets, their Molybdenum and Tungsten Complexes as Corrosion Inhibitors for Mild Steel in Sulphuric Acid
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by R. B. Rastogi, M. Yadav, K. Singh, M. M. Singh
127-147
DOI:
The inhibition of mild steel corrosion in 1N sulphuric acid was studied in the presence of various concentrations (10-150 ppm) of substituted dithiobiurets and their molybdenum and tungsten complexes at 25 °C. All the compounds behaved as ambiodic corrosion inhibitors for mild steel and were considered to inhibit the corrosion by getting adsorbed on the surface. The inhibition efficiencies (IEs) of the complexes, in general, were found to be appreciably higher than those of corresponding ligands. However, the IE values of the complexes of molybdenum and tungsten of the same ligand did not differ much in their magnitude indicating thereby that the nature of central metal ions hardly influenced the inhibition efficiency. The slight difference in the IEs of the complexes at a given concentration seems to be caused by the slight difference in their size. The variation in IEs of different derivatives of ligands has been attributed to change in their size, number of active sites for adsorption and the electron density on these active sites. Scanning Electron Microscopy was used to study the surface of corroded and inhibited specimens.
Characterization of Plasticized PEO Based Solid Polymer Electrolyte by XRD and AC Impedance Methods
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by K. Ragavendran, P. Kalyani, A. Veluchamy, S. Banumathi, R. Thirunakaran, T. J. Benedict
149-159
DOI:
The ionic conductivity of lithium based solid polymer films prepared from poly (ethylene oxide) (PEO) and lithium hexafluoarsenate (LiAsF6) with varying compositions of plasticizers likedibutyl sebacate (DBS) and ethylene carbonate (EC) was measured by AC impedance method. Polymer film composition viz. (PEO)8-LiAsF6-(DBS)0.4-(EC)0.1 has been evaluated as an optimum composition as evidenced from its high conductivity and freestanding ability. The high conductivity observed for the polymer electrolyte with this composition has been attributed to an enhanced amorphous character and a reduced energy barrier to the segmental motion of lithium ions in the matrix. The temperature dependence of conductivity on the polymer films, with and without plasticizers, appears to obey the Arrhenius law. However, the activation energy of the plasticized polymer film is 0.81 KJ/mol, a value considerably lower than 10 KJ/mol obtained for the unplasticized electrolyte, making the polymer to be a prospective candidate as lithium-ion conducting electrolyte for rechargeable lithium batteries.