Papers by Author: D. Jaramillo-Vigueras

Abstract: Synthesis of intermetallic PbSe induced by high-energy ball milling has been studied. Systematic analysis of transformation in the resulting phases of milling from 0 to 10 h has been traced by characterizing the microstructures in terms of morphology, crystallite size, and percentages of phases formed as a function of milling time. Results reveal the formation of two phases. Where the system of PbO-Se transforms gradually to PbSe. Complete transformation is achieved after 10 h of milling time. Study of particle structure by the Rietveld Method further corroborates the value of the nano-order crystallite diameters as evaluated from the microscopic studies.

Abstract: In this work, we present a modification of the sol-gel based, Stöber, Fink and Bohn’s (SBF) procedure for the preparation of nanometric spheres of silica with a monomodal distribution of size and controlled diameter. In the SBF method, tetraethyl orthosilicate (TEOS) is used as a precursor molecule and hydrolysis and condensation reactions to form chains and branches of Si-O bonds are carried out. The novelty of this work consists in the use of an aqueous ammonium hydroxide solution as ammonia source. Graphics of particle size as a function of reagent contents are presented (reaction yield control) and differences to the results from the original SBF method are discussed. This procedure is the very first step for the development of a sol-gel synthetic opals preparation process. As a result, the best route to prepare monodisperse spheres in the whole range of 250 to 850 nm is that of keeping constant the TEOS and NH3 contents at 0.28:1M varying water contents in the range of 8 – 12.5 M.

Abstract: Nanocrystalline intermetallic Mg2Ni is successfully produced on a batch production scale from elemental powder blends by mechanical alloying using a high-energy rotor ball mill (Simoloyer). Different ball-to-powder mass ratios are used in order to provide results for scaling to industrial production. Transformation of elemental Mg-Ni powders into the Mg2Ni intermetallic is observed by x-ray diffraction. Particle morphology during milling is observed by scanning electron microscopy. A relatively low Fe contamination is estimated by energy dispersive spectrometry.