Eduardo Terrés-Rojas

Shrinkage and Deformation of Agave atrovirens Karw Tissue during Convective Drying: Influence of Structural Arrangements

The influence of structural arrangements of Agave discs cut transversally (ADCT) and longitudinally (ADCL) on moisture loss, shrinkage, and shape was evaluated during convective drying by physical and image parameters. ADCT showed lower drying and shrinkage rates than ADCL. The fractal exponent (d) relating volume and thickness of samples rose from 1.552 ± 0.126 to 2.394 ± 0.128 and from 1.662 ± 0.111 to 1.848 ± 0.070 for ADCT and ADCL, respectively, which indicates that shrinkage was nonisotropic for both cases. Parameters considered for evaluating the changes of size and shape of Agave discs at macro- and microscopic levels during drying were projected area (PA), major length (ML), shape factor (SF), and fractal dimension of contour (FDC). The values obtained for these parameters demonstrated that changes in shrinkage and shape of both samples were dependent on structural arrangements of the samples. During the drying of ADCT samples, which have short and rigid structures, pronounced creasing was observed compared to ADCL materials, which are mainly formed by long and rigid structures. Also, it was observed that orientation of fibers influenced shrinkage and deformation.

Microstructure of alumina-matrix composites reinforced with nanometric titanium and titanium carbide dispersions

-titanium powders which were thoroughly mixed under high energy ball-milling and through the second step it was induced the formation of titanium carbide during different times at 500 °C by the cementation packing process. SEM and EDS analysis of the microstructures obtained in both sintered and cemented bodies were performed in order to know the effect of the activated carbon used as cementing agent on the titanium for each studied composite. It was observed that a titanium carbide layer growth from the surface into the bulk and reaches different depth as the titanium content in the composites increases. On the other hand, the use of ductile titanium notably enhanced density level and fracture toughness of the composites.

Effect of Nickel Addition on Microstructure and Mechanical Properties of Aluminum-Based Alloys

In this work a comparative study between microstructure and mechanical properties of aluminum-nickel alloys with different contents of nickel was carried out. Alloys were produced by powders metallurgy. Characterization results indicates that the microstructure of the aluminum-nickel alloys present a thin and homogeneous distribution of an intermetallic compound in the aluminum’s matrix, identified as Al3Ni. Furthermore, it was find out that the amount of intermetallic Al3Ni increase as the nickel content in the alloy rises. Regarding the mechanical properties evaluated; it was establishes that the hardness, compression and flexion resistances also were improved due to the presence of the intermetallic compound.

Studies on the Catalytic Activity of Sulfated Zirconia Promoted with Cerium Oxide

Pure zirconia, sulfated zirconia and sulfated zirconia modified with 2, 3, 5 and 10 wt. % of cerium oxide were synthesized by sol-gel method. Pt phase was impregnated on the supports using the incipient wet technique. Sulfated zirconium oxide showed tetragonal phase only. Addition of cerium to sulfated zirconia did not modify the tetragonal phase but produced a marked effect on the surface area. Low cerium content may greatly increase the surface area; however, too high cerium content (10 wt.%) may decrease the surface area. Pore size had influence on the catalytic activity and ZrO2 acidity was favored by the sulfate ion incorporation. All catalysts having Brönsted and Lewis acid sites were active in the n-hexane isomerization. The highest n-hexane conversion (40%) and selectivity towards DMB (26%), 2-methyl pentane (61%) and 3-methyl pentane (13%) were reached over the catalyst with 10 wt. % cerium oxide. In addition, sulfated zirconium oxide presented high selectivity of light products (< C6), which indicated that the addition of this doping agent (CeO2) made the catalysts more selective toward the desired reaction products.

Titanium Effect on Microstructure and Fracture toughness of Al2O3-BASED Composites

The effect of different titanium additions (0.5, 1, 2, 3 and 10 vol. %), milling intensity (4 and 8 h) and sintered temperature (1500 and 1600 °C) on microstructure and fracture toughness of Al2O3-based composites was analyzed in this study. After high energy milling of a titanium and Al2O3 mixtures, powder mixture presents fine distribution and good homogenization between ceramic and metal. After milling powders during 8 h they were obtained very fine particles with 200 nm average sizes. Microstructures of the sintered bodies were analyzed with a scanning electron microscopy, where it was observed that the microstructure presents the formation of a small and fine metallic net inside the ceramic matrix. From fracture toughness measurements realized by the fracture indentation method, it had that when titanium content in the composite increases, fracture toughness is enhanced until 83% with respect to the fracture toughness of pure Al2O3. This behavior is due to the formation of metallic bridges by titanium in the Al2O3 matrix.