Browsing by Autor "Jairo Arturo Escobar"

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2D Model for Ball Mills
(Trans Tech Publications, 2006) Felipe Campo; Jairo Arturo Escobar
This work develops a mathematical model that explains the ball mills operational speed. The scope of the model is defined by the powder as the number of particles per cm3 and the Relevance defined as the ratio between different forces. In this study, the Relevance is defined as the ratio between superficial tension and inertial forces. The conditions for a free flowing powder and a single particle are differenced and non-dimensional numbers are found. The model proposed use the friction force between mill walls and the powder mass is related by a friction coefficient that can be calculated from angle repose. An experimental approach proves that the suppositions made in order to develop the model were adequate in this way the existence of the non-dimensional numbers is confirmed. It is also discussed the use of non-dimensional numbers to increase processing speeds with by increasing gravity clarifying that a given Relevancy, it is not dependent of the non-dimensional numbers. Thus, the model can help in the design process of ball mills with a deeper understanding of the phenomena.
Characterization of SOFCS: A Crystallographic Analysis and First Steps towards an Impedance Spectroscopy Approach
(Trans Tech Publications, 2012) Albert Avila; Juan Carlos Poveda; Darwing Villalta Gómez; Dachamir Hotza; Jairo Arturo Escobar
Solid oxide fuel cells (SOFCs) have emerged as an efficient way to transform chemical energy into electrical energy. However, a major disadvantage of this technology is related to the high temperatures required for SOFC operation. In this way, new materials are necessary to maintain the electrical properties of the cell at intermediate temperatures. Based on these ideas, it is necessary to study both the structural variation of the cells components at different temperatures and their electrochemical behavior. In this work, a crystallographic characterization is presented, which was performed in a commercial SOFC cell using X-ray diffraction (XRD). An equivalent linear electrical model to predict SOFC losses is developed as well. Keywords: Solid oxide fuel cells (SOFCs); AC impedance; Electrochemical impedance spectroscopy (EIS); Equivalent circuit models.
Continuum Isotropic Elastic Model for Sintering of Ceramic Materials <sup></sup>
(Trans Tech Publications, 2012) Vergel C. Serrano; Jairo Arturo Escobar; G.O. Porras
In this work a sintering model that assumes infinitesimal displacements rates has been structured using the continuum theory of sintering develop by Olevsky and Skorokhod [1, 2] and the sintering model develop by Sasan Kiani et al. [3, 4]. The model was used to estimate dimensional change and the density distribution using linear displacement rates (LRDs) as the only input. Furthermore, if the sintering potential and dense material shear viscosity are known, the stress distribution can be approximated. The magnitude of two stress norms (i.e. Von Misses stress and the stress tensor first invariant) determined using experimental and calculated LDRs are compared using three different geometries. From FEM simulation results it was inferred that densification can occur in presence of tension stresses if their magnitude is lower than the calculated sintering potential.
Manufacture and Characterization of Alumina Ceramic Foams for Porous Burners
(Trans Tech Publications, 2012) Ana María Herrera; Verônica Moreno; Amir Antônio Martins Oliveira; Dachamir Hotza; Óscar Álvarez; Jairo Arturo Escobar
Hazardous byproducts emissions such as nitrogen oxides (NOx) and carbon monoxide (CO) might be controlled by the use of radiant porous burners. Those heaters require a solid porous matrix where combustion reaction takes place, reason why the heat transfer is much more efficient. This project was based on a rheology study of an alumina slurry, where parameters like viscosity and tixotropy were the guide to select the appropriate formulation to be used in the fabrication of ceramic foams by the replica method. Low strength samples were produced after the first thermal treatment, explained by the absence of a plasticizer when using PVA as a binder. Incomplete sintered foams were obtained due to an insufficient soak time.
Manufacture of YSZ-LSM Semi-Cell by Colloidal Processing
(Trans Tech Publications, 2012) Laura Piedad Chia Gómez; Jairo Arturo Escobar; M.T. Colomer; Rodrigo Moreno
Yttria stabilized zirconia (YSZ) is the most common electrolyte in solid oxide fuel cells (SOFC). The planar configuration is widely used for designing single cells, in which a thick cathode layer can be used as the supporting electrolyte film. The manufacture of the semi-cell formed by anode and electrolyte has been widely studied and there are many works dealing with its colloidal processing. However, the semi-cell formed by cathode and electrolyte has received much lower attention. This work deals with the manufacture of a semi-cell consisting of YSZ as electrolyte and strontium-doped lanthanum manganite (LSM) as a cathode through a colloidal processing route. The colloidal behavior of diluted suspensions of YSZ and the rheology of their concentrated suspensions were studied as a function of deflocculant content, mixing time by using ultrasounds probe and ageing time. The colloidal stability of aqueous suspensions of LSM was studied by measuring the zeta potential as a function of pH and deflocculant content. These concentrated suspensions were used to obtain thick self-sustained substrates by casting methods. The YSZ electrolyte and LSM cathode were prepared by tape casting in water medium.