Papers by Francisco Quintero
The goal of this research was to describe the effects of the main anodization variables on the mo... more The goal of this research was to describe the effects of the main anodization variables on the morphology of the resulting titania nanotube arrays. Four variables were considered in this study: applied voltage, fluoride and water concentrations, and time. The first three variables were studied simultaneously in a central composite design of experiments using SEM measurements of tube length as the response variable. The effect of time was modeled using transferred charge as the response variable. A field assisted oxidation-dissolution growth model was validated over a broad range of experimental conditions under which tube growth can be accurately predicted directly from the current transients using Faraday's laws. The effects of anodization variables were described based on this model and a simple, empirical kinetic expression was obtained and successfully tested against data from other authors with fairly small errors over a broad range of conditions.
Effect of fluoride and water content on the growth of TiO2 nanotubes synthesized via ethylene glycol with voltage changes during anodizing process
Journal of Physics: Conference Series, 2015
ABSTRACT
The construction and performance of a second generation of super dielectric material based electr... more The construction and performance of a second generation of super dielectric material based electrostatic capacitors (EC), with energy density greater than 200 J·cm−3, which rival the best reported energy density of electric double layer capacitors (EDLC), also known as supercapacitors, are reported. The first generation super dielectric materials (SDM) are multi-material mixtures with dielectric constants greater than 1.0 × 105, composed of a porous, electrically insulating powder filled with a polarizable, ion-containing liquid. Second-generation SDMs (TSDM), introduced here, are anodic titania nanotube arrays filled with concentrated aqueous salt solutions. Capacitors using TiO2 based TSDM were found to have dielectric constants at ~0 Hz greater than 107 in all cases, a maximum operating voltage of greater than 2 volts and remarkable energy density that surpasses the highest previously reported for EC capacitors by approximately one order of magnitude. A simple model based on the classic ponderable media model was shown to be largely consistent with data from nine EC type capacitors employing TSDM.
Novel Materials with Effective Super Dielectric Constants for Energy Storage
Journal of Electronic Materials, 2015
Qualitative determination of acetaldehyde produced by oxidation of ethanol in a photoelectrochemi... more Qualitative determination of acetaldehyde produced by oxidation of ethanol in a photoelectrochemical cell is reported as an indicator of the effectiveness of a nanotubular titanium dioxide thin film for hydrogen production by photolysis in separate chambers. The titanium dioxide thin film was grown using a novel anodizing procedure on a 2cm2 titanium foil, varying the anodizing voltage between 80V and 20V during one and five minutes, respectively, for two hours in a 0.10%wt. NH 4 F solution in ethylene glycol and using a 4cm2 titanium foil as cathode. The photoelectrochemical cell was formed by two borosilicate glasschambers separated by a salt bridge of agar-agar and LiCl, UVA lamps, a Ti cathode and the anodized foil as anode, submerged in ethanol 93vol.% and connected by a copper wire in series with a voltmeter. For acetaldehyde determination, two qualitative methods were used: first, the reaction of the ethanol-water solution, after 4 hours of photolysis, with NaOH and heating; the second test was the reaction of a different solution with 2,4-dinitrodiphenyl hydrazine dissolved in methanol. Both assays were positive for aldehyde.
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Papers by Francisco Quintero