Phosphonic acid functionalization of nanostructured Ni–W coatings on steel

The functionalization of nanocrystalline Ni–W coatings, formed by galvanostatic pulsed electrodeposition on steel, by thermal treatment of octadecylphosphonic acid self-assembled on the oxidized alloy surface is studied by Raman spectroscopy, contact angle measurements, X-ray photoelectron spectroscopy, AFM and electrochemical techniques. Results show that this procedure preserves the surface topography and the optimum mechanical properties of the alloy. More importantly, it turns the alloy surface highly hydrophobic and markedly improves its corrosion resistance, in particular to pitting corrosion in aggressive solutions containing chloride anions. The ability of the phosphonate layer to improve surface properties arises from the barrier properties introduced by the hydrocarbon chains and the strong bonds between the phosphonate head and the underlying surface oxides.Fil: Orrillo, Patricio Andrés. Universidad Nacional de Tucumán. Facultad de Bioquímica, Química y Farmacia. Instituto de Química Física; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Ribotta, Susana Beatriz. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Universidad Nacional de Tucumán. Facultad de Bioquímica, Química y Farmacia. Instituto de Química Física; ArgentinaFil: Gassa, Liliana Mabel. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Instituto de Investigaciones Fisicoquímicas Teóricas y Aplicadas. Universidad Nacional de La Plata. Facultad de Ciencias Exactas. Instituto de Investigaciones Fisicoquímicas Teóricas y Aplicadas; ArgentinaFil: Benitez, Guillermo Alfredo. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Instituto de Investigaciones Fisicoquímicas Teóricas y Aplicadas. Universidad Nacional de La Plata. Facultad de Ciencias Exactas. Instituto de Investigaciones Fisicoquímicas Teóricas y Aplicadas; ArgentinaFil: Salvarezza, Roberto Carlos. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Instituto de Investigaciones Fisicoquímicas Teóricas y Aplicadas. Universidad Nacional de La Plata. Facultad de Ciencias Exactas. Instituto de Investigaciones Fisicoquímicas Teóricas y Aplicadas; ArgentinaFil: Vela, Maria Elena. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Instituto de Investigaciones Fisicoquímicas Teóricas y Aplicadas. Universidad Nacional de La Plata. Facultad de Ciencias Exactas. Instituto de Investigaciones Fisicoquímicas Teóricas y Aplicadas; Argentin

Growth of columnar gold electrodes by electroreducing hydrous gold oxide layers : Kinetics and mechanistic interpretation

Rough columnar structured gold electrodeposits were prepared in aqueous 0.5 M M H2SO4 by electroreducing a hydrous gold oxide layer built up on a gold substrate by means of a fast periodic potential routine. The analysis of potentiodynamic and potentiostatic hydrous oxide layer electroreduction data indicated the initial nucleation of gold clusters at the metals|oxide interface. The growth of gold nuclei proceeded under a constant capture area condition for depositing gold ions contained in the hydrous oxide layer. Columnar gold electrodeposition was assisted by the gel-like characteristics of the hydrous gold oxide layer. Gold columnar growth ended as soon as the column tips reached the oxide s| solution interfacc. The proposed kinetic model accounts for the high surface area development and surface fractal properties of this type of metal electrode.Instituto de Investigaciones Fisicoquímicas Teóricas y Aplicada

Electroformation of quasi-two-dimensional silver patterns in the absence of supporting electrolyte

Quasi-two-dimensional (2D) growth patterns of silver electrodeposits obtained from aqueous silver sulfate solution in the absence of supporting electrolyte using a quasi-2D cylindrical cell involve domains with morphologies covering from dense to needle-like branching. The prevailing morphology depends on the electrolyte concentration, applied electric potential and electrolysis time. From the time dependence of the maximum radius circumscribing each electrodeposit, its dimension was obtained. The growth of the solid phase was also analysed in terms of dimensionless numbers to estimate the ionic mass-transfer contributions to the electrochemical process. For a single-growing branch the axial-to-radial growth velocity is close to 10. Phenomena promoting silver electrodeposits with irregular edges and an open structure compete with others operating in the opposite direction. These phenomena are influenced by changes in the concentration and electric potential field around the growing electrodeposit.Instituto de Investigaciones Fisicoquímicas Teóricas y Aplicada

Growth of three-dimensional silver fractal electrodeposits under damped free convection

Quasispherical three-dimensional Ag electrodeposits grown at constant potential and damped free convection exhibit a quasi-isotropic radial growth up to a critical radius rc≃0.3 cm and a mass fractal dimension DM=2.5. For r≫rc, DM→3. The product vrη’ is nearly constant, vr being the radial growth velocity, and η’ the apparent medium viscosity. It appears that vr is determined by the Laplacian field operating between cathode and anode.Instituto de Investigaciones Fisicoquímicas Teóricas y Aplicada

Mass-transport-induced kinetic transitions during the electrochemical formation of three-dimensional dendritic silver deposits under ohmic control

The influence of mass transport processes on the growth of three-dimensional dendritic Ag deposits on a Pt quasi-spherical substrate at a relatively large cathodic overpotential has been investigated. After a certain induction time a first stage of dendritic growth of Ag can be observed. The deposit formed at this stage exhibits a fractal surface and non-fractal mass—volume properties. For charge densities greater than a certain critical value, a second stage of growth can be distinguished. At this second stage the contribution of free convection changes the shape of the deposit. The fastest growth of the Ag electrodeposit is determined by the rate of migration of sulphate ions in the electric field. A model accounting for the parametric relationships derived from the experiments is presented.Instituto de Investigaciones Fisicoquímicas Teóricas y Aplicada

Aleaciones Ni-W nanoestructuradas obtenidas por electrodeposición sobre acero

Las aleaciones de Ni-W presentan óptima dureza y buena resistencia a la corrosión. Si los depósitos poseen tamaño de grano en el orden de las escalas nanométricas se obtienen características excepcionales en cuanto a ductilidad y resistencia térmica, que resultan particularmente útiles para proteger superficies metálicas (cobre y acero) de la corrosión. Para lograr estos objetivos es de crucial importancia controlar las variables del proceso de electrodeposición tales como densidad de corriente (constante o pulsante), composición de las soluciones, pH, temperatura del baño, y condiciones hidrodinámicas. En este trabajo se muestran los estudios realizados con superficies de aleaciones de Ni-W electrodepositadas sobre acero empleando diferentes programas de corriente pulsante, para lograr una nanoestructura que presente una óptima resistencia a la corrosión.Instituto de Investigaciones Fisicoquímicas Teóricas y Aplicada

The same cellular signaling pathways mediate survival in sensory neurons that switch their trophic requirements during development

A distinct subpopulation of rat dorsal root sensory (DRG) neurons, termed P-neurons, switch their trophic requirements for survival during development from nerve growth factor (NGF) at embryonic stages to basic fibroblast growth factor (bFGF) just after birth. We investigated in cultured P-neurons the intracellular signaling pathways mediating survival before and after this switch. The NGF-induced survival was completely blocked by either wortmannin (100 nM) or PD98059 (25-50 nM), which selectively inhibit the phosphatidylinositol 3-kinase-AKT (PI3 kinase-AKT) and mitogen-activated kinase kinase extracellular regulated kinase (MEK-ERKs) pathways, respectively. NGF activated AKT and ERKs in single embryonic P-neurons, as assayed by immunofluorescence of phorphorylated proteins. In concordance with the survival assays, wortmannin and PD98059 blocked AKT and ERKs activation, respectively. Following the trophic switch, bFGF used the same signaling pathways to promote survival of postnatal P-neurons, as either wortmannin or PD98059 blocked its effect. Also, bFGF activated AKT and ERKs in single P-neurons, and this activation was blocked by the same inhibitors. These results strongly suggest that both pathways concurrently mediate the action of NGF and bFGF during embryonic and post-natal periods, respectively. Thus, we report the novel result that the switch in trophic requirements occurs with conservation of the signaling pathways mediating survival.Fil: Salvarezza, Susana B.. Universidad Nacional de Córdoba. Facultad de Ciencias Exactas, Físicas y Naturales. Cátedra de Biología Celular; ArgentinaFil: Lopez, Hector Salvador. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Investigación Médica Mercedes y Martín Ferreyra. Universidad Nacional de Córdoba. Instituto de Investigación Médica Mercedes y Martín Ferreyra; ArgentinaFil: Masco, Daniel Hugo. Universidad Nacional de Córdoba. Facultad de Ciencias Exactas, Físicas y Naturales. Cátedra de Biología Celular; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba; Argentin

Adsorción de cromo hexavalente en la cáscara de arroz modificada químicamente.

The aim of this study was to evaluate kinetic factors that affect the adsorption of chromium (VI) in solution using as bioadsorbent the chemically modified rice husk with either potassium hydroxide 1% m/m or 1M phosphoric acid. It was studied the adsorption of chromium (VI) by considering the following parameters pH, incubation time, bioadsorbent mass and poison initial concentration. The determination of hexavalent and total chromium was performed by the method of diphenylcarbazide and atomic absorption spectrophotometry, respectively. Chemical treatment with potassium hydroxide or phosphoric acid rice husk showed an increase in the adsorption of the poison. Kinetic analysis of the adsorption of chromium (VI) suggests that the process is favorable when working at acidic pH (less than 2), increases with the mass of bioadsorbent and contact time.El objetivo del presente estudio fue analizar los factores cinéticos que afectan la adsorción de cromo (VI) en solución empleando como bioadsorbente la cáscara de arroz modificada químicamente, con hidróxido de potasio 1% m/m o con ácido fosfórico 1M. Se estudió la adsorción de cromo (VI) considerando los siguientes parámetros pH, tiempo de incubación, masa del bioadsorbente y concentración inicial del tóxico. La determinación de cromo hexavalente y total se realizó por el método de la difenilcarbazida y por espectrofotometría de absorción atómica, respectivamente. El tratamiento químico con hidróxido de potasio o con ácido fosfórico de la cáscara de arroz produjo un aumento en la adsorción del tóxico. El análisis cinético de la adsorción de cromo (VI) sugiere que el proceso es favorable cuando se trabaja a pH ácido (inferior a 2), se incrementa con la masa de bioadsorbente y con el tiempo de contacto

The electrochemistry of nanostructured Ni–W alloys

This work reports on the features that Ni–W nanostructured alloys, electrodeposited on carbon steel by different current pulse programs, may present depending on their surface morphology and surface composition. The Ni–W nanostructured coating, with a cauliflower structure, lack of fragility, and high WO3/W surface composition ratio, is a stable electrode to catalyze hydrogen evolution reaction, exceeding bulk and electrodeposited Ni catalytic activity. Also, the nanostructured alloys must have a low WO3/W surface composition ratio for Ni and its oxides to provide protection and improve corrosion resistance in sulfate media.Fil: Quiroga Argañaraz, María Pía. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Tucumán. Instituto de Quimica del Noroeste; Argentina. Universidad Nacional de Tucumán; ArgentinaFil: Ribotta, Susana Beatriz. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Tucumán. Instituto de Quimica del Noroeste; Argentina. Universidad Nacional de Tucumán; ArgentinaFil: Folquer, Maria Eugenia. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Tucumán. Instituto de Quimica del Noroeste; Argentina. Universidad Nacional de Tucumán; ArgentinaFil: Benitez, Guillermo Alfredo. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico la Plata. Instituto de Investigaciones Fisicoquímicas Teóricas y Aplicadas; Argentina. Universidad Nacional de La Plata; ArgentinaFil: Rubert, Aldo Alberto. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico la Plata. Instituto de Investigaciones Fisicoquímicas Teóricas y Aplicadas; Argentina. Universidad Nacional de La Plata; ArgentinaFil: Gassa, Liliana Mabel. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico la Plata. Instituto de Investigaciones Fisicoquímicas Teóricas y Aplicadas; Argentina. Universidad Nacional de La Plata; ArgentinaFil: Vela, Maria Elena. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico la Plata. Instituto de Investigaciones Fisicoquímicas Teóricas y Aplicadas; Argentina. Universidad Nacional de La Plata; ArgentinaFil: Salvarezza, Roberto Carlos. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico la Plata. Instituto de Investigaciones Fisicoquímicas Teóricas y Aplicadas; Argentina. Universidad Nacional de La Plata; Argentin