Papers by Author: Alberto C. Ferro

Abstract: This paper reports preliminary studies regarding a new fabrication process for aluminium alloy matrix particulate reinforced composites, which uses ceramic preforms with alumina and tailored amounts of reactive copper oxide, CuO. An Al2O3-CuO mixture with 75 mol% CuO was selected, aiming at a 10-40vol% reinforcement phase fraction in the final composite, after aluminium infiltration. Molten aluminium infiltration progress was studied as a function of ceramic’s composition, doping, and infiltration time. The resulting microstructures were investigated by OM, SEM, FESEM and EDS in order to establish the liquid aluminium infiltration profile at the metal/ceramic interface. Infiltration experiments showed that the 3CuO (s) + 2Al (l) → 3Cu (l) + Al2O3 (s) redox reaction is triggered at the experimental conditions used, but the infiltration process is slow and does not go to completion. The use of NaOH as a doping agent promotes effective infiltration of molten aluminium upon the ceramic green mixture.

Abstract: A new algorithm to determine Voronoi partitions of space using periodic boundary conditions has been implemented in GAMGI free software package. This algorithm was used to study the topological and geometric properties of Voronoi polyhedra obtained for Poisson and Laguerre seeding distributions. The Random Sequential Adsorption (RSA) method was used to generate a Laguerre seeding distribution with a volume fraction of spheres φ ≈ 0.36. The resulting normalised cell volume distributions were compared with the gamma and lognormal density functions using χ2 goodness of fit testing, and in both cases the gamma function provides a better description. The Lewis and Aboav empirical relations approximately apply to both partitions, with least square correlation factors R2 equal to 0.98 for the Lewis law and 0.95 for the Aboav law.

Abstract: Obtaining ceramic bodies with enhanced mechanical properties via colloidal processing requires efficient dispersion of the ceramic powders. In this work, the dispersive effect of three low molecular weight quaternary ammonium hydroxides with different alkyl groups upon stabilisation of CuO aqueous suspensions is studied and compared with that of Tiron, a compound based on the benzene molecule. The purpose is to illustrate the effect of molecular structure, size and charge location upon dispersing effectiveness. To access these parameters, rheological and electrophoretic measurements using both bare and surface charge modified CuO were made. Tiron® revealed to be the most efficient dispersant for CuO in water, rendering viscosity values below 1 Pa⋅s and the highest variation in zeta potential amplitude.

Abstract: The development of solid electrolytic tantalum capacitors with MnO2 as counter electrode has been carried out in order to decrease the equivalent series resistance (ESR). Capacitor samples produced under different pyrolysis conditions have been characterized in terms of equivalent circuit parameters. The Ta/Ta2O5/MnO2 system has also been characterized by X-ray diffraction (XRD) and transmission electron microscopy (TEM). X-ray powder diffraction patterns obtained were inconclusive due to the MnO2 complex structure and to the presence of highly intense tantalum peaks that shadow interesting MnO2 diffraction peaks. Electron diffraction TEM results enabled the characterization of the microstructure and furthermore revealed the complex crystalline structure that affects the electrical properties of the semiconductor layer. A relation between the calculated circuit parameters and microstructure of MnO2 is discussed.