Papers by Author: B. Campillo

Abstract: The Nafion perfluorinated membranes are one of the best electrolytes used in the Proton Exchange Membrane Fuel Cell (PEMFC). Some methods have been used to study the electrical properties of Nafion; nevertheless, there are some aspects of the conduction process that are not well understood, such as the contribution of the bulk and the interfacial phenomena to the total proton conduction process. In this work the Electrochemical Impedance Spectroscopy (EIS) was employed in a four electrode system to study the protonic charge transport under conditions that simulate the operation of the PEMFC. Two Nafion membranes were evaluated to determine the relation of the activation procedure with the resistance to the protonic charge transference. The results are not only consistent with other measurements but also allow to separate the protonic charge transference process in two stages. Each stage was studied and their electrical parameters were calculated using Electrical Equivalent Circuits.

Abstract: The microstructure of directional solidified Al-Zn-Mg alloys is characterized and predicted by means of thermal analysis data, multicomponent equations for dendrite growth and data from ternary AlZnMg phase diagram. The resulting microstructure consists of α-Al dendrites with τ precipitates and eutectic in interdendritic regions. Predictions show that at growth velocities up to 9 x 10-4 m/s, the α-Al and τ intermetallic grew simultaneously. Predictions for solute concentration according to the model for dendrite solidification of multicomponent alloys with unequal liquid diffusion coefficients show a good agreement with experimental results.

Abstract: The purpose of this work is to explore the effect of the presence of two different primary phases on the microstructure and solidification kinetics of Pb-Sn alloys. The experimental results have been compared with predictions obtained from the Newton Thermal Analysis of cooling curves generated by a conventional heat transfer-solidification kinetics model. Three Pb-Sn alloys have been considered in this work in order to explore the solidification characteristics of the eutectic in hypoeutectic, hypereutectic and eutectic compositions. Experimental results indicate that the Pb-Sn eutectic morphology and the solidification rate depend on the nature of the pre-existent primary phase during eutectic solidification. From the observed discrepancies between experimental and simulated results it is concluded that further improvements are needed to simulate the solidification kinetics of eutectic microconstituents in the presence of pre-existing primary phases.

Abstract: This work explores the feasibility of using the Newton Thermal Analysis method (NTA) as an alternative technique for quantitative determination of the relative volume fractions of the microconstituents formed during solidification of three hypereutectic Pb-Sn alloys. The results suggest that NTA has a good potential as a quantitative microstructure analysis tool. However, it is required to further improve the method in order to match the microstructure predictions with the experimental measurements obtained by quantitative metallography.

Abstract: The microstructural and mechanical properties of an ultra-clean low carbon steel sheet with 0.035% Cr have been evaluated. The isothermal recrystallization kinetics at 800 oC is analyzed by using the Kolomogorov-Johnson-Mehl-Avrami (KJMA) equation. The obtained results indicate that Cr retards the recrystallization kinetics owing to the presence of fine particles of chromium carbides. The annealing process produces a fully recrystallized microstructure. The main texture components in the specimens are: {111}<112>, {112}<110> and {111}<110>. These are related with the Lankford value and the elongation. The obtained results suggest that the formability of this steel is excellent.