Thomas W. Chapman
Centro de Investigación y Desarrollo Tecnológico en Electroquímica
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Publication
Featured researches published by Thomas W. Chapman.
Journal of The Electrochemical Society | 2000
Suh-Cem Pang; Marc A. Anderson; Thomas W. Chapman
Thin films of manganese dioxide were formed on nickel foils by electrodeposition and by both dip‐coating and drop‐coating with manganese dioxide suspensions (sols) and their subsequent gelation and calcination. The performance of these films as ultracapacitors was studied by cyclic voltammetry in the range 0.0–0.9 V (SCE) and by chronopotentiometry in unbuffered solution. The cyclic voltammograms of ultrathin, dip‐coated sol‐gel‐derived films indicated better capacitive behavior and gave differential specific capacitance values as high as 698 F/g compared to values half to two‐thirds as great for the electrodeposited films. Multilayer drop‐coated sol‐gel films were prepared to attain film thicknesses comparable to the electrodeposited films, and these were found to provide charge‐storage capacity as high as , more than three times greater than that of the electrodeposited films. All films, except electrodeposited films that were not thermally cured, exhibited good cycling stability, losing not much more than 10% of capacity after 1500 cycles.
Talanta | 2007
Erika Bustos; Ma. Guadalupe García Jiménez; Blanca Rosa Díaz-Sánchez; Eusebio Juaristi; Thomas W. Chapman; Luis A. Godínez
Composites of hydroxyl-terminated PAMAM dendrimers, generation 4.0 (64 peripheral OH groups) containing either Ir, Pt or Rh nanoparticles were synthesized and characterized in solution. Each one of these composites was then immobilized on a glassy carbon electrode (GC) and incorporated as an amperometric detector for dopamine in a high-performance liquid chromatograph (HPLC). Comparison of the analytical performance of the novel electrochemical detectors with a typical UV-vis optical detector for dopamine revealed that the sensitivity of the GC electrode modified with dendrimer-Rh composite is comparable to that of the spectroscopic detector, with a detection limit of 0.15muM, and is linear up to at least 1.0mM (R(2)=0.998). Furthermore, it was found that the electroanalytical approach suffers minimal matrix effects that arise in the analysis of dopamine in samples of urine.
Journal of The Electrochemical Society | 1990
Mark Mathias; Thomas W. Chapman
Measurements of radial variations of composition and thickness of electrodeposited zinc-nickel alloys on a rotating disk electrode were made for deposits obtained at steady state from chloride electrolytes at different bath compositions, electrode rotation rates, and applied voltages. A two-dimensional transport model, which accounts for migration and complexation of the zinc by chloride, was used to calculate the radially dependent interfacial concentration and potential profiles for each set of experimental conditions
Journal of Applied Electrochemistry | 2013
José Luis Ortiz-Aparicio; Yunny Meas; G. Trejo; R. Ortega; Thomas W. Chapman; Eric Chainet
This work reports the effects of four organic compounds (referred to as levelers) on the electrodeposition of Zn on steel from alkaline free-cyanide electrolytes. The additives tested included polyvinylalcohol (PVA) and the condensation products of epichlorhydrin with amines, called polyamines (PAs), that were synthesized using an aliphatic amine (PA-I, from diethylamine and PA-II from diethylamine-triethylamine), and a heterocyclic quaternary imidazolium molecule (PA-Imid, from imidazole). These compounds were evaluated in the absence and in addition to a quaternary ammonium brightener, N-benzyl-3-carboxylpyridinium chloride (3NCP). The imidazole derivative-based polyamine (PA-Imid) causes greater inhibition of the zinc reduction process than the aliphatic polyamine, and more cathodic overpotential is necessary to promote massive metal deposition. The morphology of the deposits is modified when polyamines are added to the bath; more compact and smaller crystals are obtained with PVA as well as with polyamine PA-I. The addition of PA-II as well as PA-Imid yields crystals growing perpendicular to the substrate. The addition of 3NCP with PVA, PA, or PA-Imid increased the deposition overpotential and modified the morphology by diminishing the grain size. In the absence of additives, crystallographic orientation favored the basal Zn(002) with high atomic packing. The addition of the levelers favored the high-angle pyramidal Zn(101) with low atomic packing. The combination of the levelers with (3NCP) favored the prismatic Zn(100) crystallographic orientation. Additives decrease the size of zinc crystals and tend to increase the energy of lattice favoring the growth of pyramidal and prismatic planes.
Journal of The Electrochemical Society | 1987
William J. Wruck; Reinaldo M. Machado; Thomas W. Chapman
This paper describes an electronic circuit for periodic interruption of current to a cell with simultaneous observation of closed‐circuit and open‐circuit electrode potentials. The open‐circuit potential may be observed at interruption times ranging from 2.0 μs to 2.0s or longer. The duty cycle of the cell may be adjusted between 40 and 99.93%. Application of the circuit to observe relaxation of polarization is demonstrated with simple electrical test circuits, with commercial dry cells, and with a mass‐transfer controlled rotating disk electrode. The latter example shows that interruption can provide not only resistance measurements but also estimates of mass‐transfer parameters.
Materials Science and Engineering | 1966
Thomas W. Chapman
Abstract The heat capacity of a liquid metal is made up of several contributions: a kinetic term, an electronic term, a dilation term, and a configurational term due to interactomic forces. The theory of the radial distribution function is used to establish a corresponding states correlation of the configurational heat capacities of six low-melting metals. It is suggested that this correlation may be used to estimate the configurational contribution to the specific heats of other liquid metals. For instance, it might be used to decompose the abnormally high heat capacity of a molten transition metal in order to investigate its electronic energies. The theory is also used to explain the observed temperature dependence of liquid metal heat capacities.
Electrochemical and Solid State Letters | 2009
E. J. Ruiz; R. Ortega-Borges; J. L. Jurado; Thomas W. Chapman; Y. Meas
Sodium percarbonate (SPC) can be produced electrochemically from aqueous Na 2 CO 3 solution in both its 2Na 2 CO 3 ·3H 2 O 2 and Na 2 C 2 O 6 forms simultaneously. This was achieved in a two-compartment cell separated by a cation-exchange membrane. Na 2 C 2 O 6 was produced on the anodic side by water oxidation on a boron-doped diamond electrode, with anodic current efficiencies of 20-40%. On the cathodic side, SPC was synthesized from carbonate through generation of H 2 O 2 by oxygen reduction on high-surface-area carbon felt. Cathodic current efficiency was 60% and nearly constant. The effect of Na 2 SiO 3 as a percarbonate stabilizer was studied during electrolysis and during storage, with 4 g/L giving the best performance.
Journal of The Electrochemical Society | 1977
Ralph E. White; James Arthur Trainham; John Newman; Thomas W. Chapman
The hydrometallurgy of copper may involve leaching of the metal from its ore with an aqueous solution containing cupric and ferric chloride. The subsequent deposition of copper from such a process stream is modeled here in an idealized electrochemical cell with a rotating-disk electrode. The potential distribution and concentration profiles within the diffusion layer are predicted for given potential differences between the electrode and the solution. The cuprous ion, which is formed by the reduction of the complexed cupric ion at the electrode, is stabilized in the chloride solution and can react either at the electrode or with ferric species within the diffusion layer. The assumption is that this fast and irreversible homogeneous reaction generates a reaction plane, whose position is shown in the concentration and potential profiles. In addition, the position of the reaction plane is plotted as a function of the potential difference between the electrode and the adjacent solution. Predicted currentpotential and current efficiency-poten tial curves are also reported. Finally, the iron contamination of the deposited copper is estimated to be less than 10-~ atom percent for some cases. Also, because some of the partial current densities are below their limiting values, the analysis is strictly valid only at the center of the disk.
Journal of The Electrochemical Society | 2008
José Luis Ortiz-Aparicio; Yunny Meas; G. Trejo; R. Ortega; Thomas W. Chapman; Eric Chainet; Patrick Ozil
The effect of quaternary ammonium compounds on the electrodeposition of ZnCo alloys from an alkaline chloride-gluconate electrolyte was studied. A thermodynamic analysis was performed which indicated that Zn(OH) 2- 4 should be the predominant zinc species, whereas for cobalt the mixed hydroxy-gluconate complexes CoL 3 (OH) 2 and CoL(OH) 2 are expected to be prevalent. The electrodeposition of the alloy from this alkaline medium was found to be anomalous, but increasing the cobalt content in the bath caused the cobalt content in the deposit to increase. The effects of three quaternary ammonium compounds, N-benzyl-3-carboxylpyridinium chloride (3NCP), N-benzyl-triethylammonium chloride, and tetraethylammonium hydroxide, on the electrochemical behavior of ZnCo deposition were studied. The incorporation of these additives in the electrolytes modified the composition, morphology, and crystallographic structure of the ZnCo-alloy deposits. Cyclic voltammetry indicated the formation of several alloy phases as cobalt was added to these zinc baths. 3NCP had the greatest impact on the process, limiting the Co content and changing the structure of the deposit.
Journal of The Electrochemical Society | 2009
José Luis Ortiz-Aparicio; Yunny Meas; G. Trejo; R. Ortega; Thomas W. Chapman; Eric Chainet; Patrick Ozil
This paper reports a study of the electrodeposition of Zn–Co alloys from alkaline chloride-gluconate electrolytes containing quaternary amines as additives. The effects on the electrochemical behavior of ZnCo deposition of two quaternary ammonium compounds, N -benzyl-3-carboxylpyridinium chloride (3NCP) and a polyamine (PA) were investigated, and the influence of the cobalt content in the plating bath was studied. The mechanism of electrodeposition of the ZnCo alloys in these alkaline media was anomalous. The two additives caused different inhibition degrees of the cathodic process, the effect of PA being stronger. Also, the results first showed that the cobalt complexes shift the cathodic peak of ZnCo electrodeposition due to de-adsorption of cobalt-gluconate complexes. According to the results, the adsorption of PA partially inhibited the zinc–alloy deposition, and the deposition of ZnCo occurred in two voltammetric steps. The incorporation of the organic additives in the bath modified the composition, morphology, and crystallographic structure of the ZnCo deposits, with PA forming compact grains oriented preferentially to high index pyramidal and prismatic textures and 3NCP producing more highly oriented, compact, and fine-grained deposits. The combination of the two additives induced a synergistic effect, producing deposits whose morphology was refined, with crystals formed on the nanometric scale with a prismatic orientation.
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Centro de Investigación y Desarrollo Tecnológico en Electroquímica
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View shared research outputsCentro de Investigación y Desarrollo Tecnológico en Electroquímica
View shared research outputsCentro de Investigación y Desarrollo Tecnológico en Electroquímica
View shared research outputsCentro de Investigación y Desarrollo Tecnológico en Electroquímica
View shared research outputsCentro de Investigación y Desarrollo Tecnológico en Electroquímica
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