V. Garibay-Febles

Mechanical properties of nanocrystalline Ti-Al-X alloys

Abstract Nanocrystalline alloys have been produced by means of mechanical milling and spark plasma sintering. Two types of materials have been obtained, TiAl–X and Al 3 Ti–X alloys, X represents Cr, Mn or Fe. Sintered TiAl–X alloys have a two-phase microstructure consisting of the γ-TiAl phase and the α 2 phase, this last one with a globular morphology. Their average grain size varies between 100 and 150 nm. The Al 3 Ti–X alloys are constituted by a single phase with an L1 2 structure and an average grain size of about 30 nm. Compression tests are used to evaluate the mechanical properties of these materials at temperatures ranging from 298 to 773 K. Very high flow stresses are found for the TiAl–X alloys, with maximum values of approximately 3 GPa. Surface traces develop during deformation at room temperature of these materials. Microscopic observation reveals dislocation activity in the larger grains. The nanocrystalline Al 3 Ti–X alloys show no ductility at room temperature and a rather high fracture strength of about 2.5 GPa. Deformation of heat-treated Al 3 Ti–X alloys (larger grain sizes) produces plastic deformation with dislocation activity and lower flow stresses (∼1 GPa).

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.

A Comparative Study of Physical and Chemical Processes for Removal of Biomass in Biofilters

After 6 months of operation a long-term biofilter was stopped for two weeks and then it was started up again for a second experimental period of almost 1.3 years, with high toluene loads and submitted to several physical and chemical treatments in order to remove excess biomass that could affect the reactor’s performance due to clogging, whose main effect is a high pressure drop. Elimination capacity and removal efficiency were determined after each treatment. The methods applied were: filling with water and draining, backwashing, and air sparging. Different flows and temperatures (20, 30, 45 and 60 °C) were applied, either with distilled water or with different chemicals in aqueous solutions. Treatments with chemicals caused a decrease of the biofilter performance, requiring periods of 1 to 2 weeks to recover previous values. The results indicate that air sparging with pure distilled water as well as with solutions of NaOH (0.01% w/v) and NaOCl (0.01% w/v) were the treatments that removed more biomass, working either at 20, 30 or 45 °C and at relatively low flow rates (below 320 L h−1), but with a high biodegradation inhibition after the treatments. Dry biomass (g VS) content was determined at three different heights of the biofilter in order to carry out each experiment under the same conditions. The same amount of dry biomass when applying a treatment was established so it could be considered that the biofilm conditions were identical. Wet biomass was used as a control of the biofilter’s water content during treatments. Several batch assays were performed to support and quantify the observed inhibitory effects of the different chemicals and temperatures applied.

Fullerene-Metal Composites: Phase Transformations During Milling and Sintering

Composites of Fe-C60 and Al C60 produced by mechanical milling and sinterized by Spark Plasma Sintering are investigated with special attention to the mechanical properties of the products. The processing involves phase transformations of the fullerenes that are interesting to follow and characterize. This involves formation of tetragonal/rhombohedral diamond and carbides during sintering and milling. Transmission Electron Microscopy (TEM) and Raman Spectroscopy techniques are also used to confirm preliminary results of X Ray Diffraction (XRD) related to the formation of nanostructures i.e., grain size of the crystals during mechanical milling and after sintering, spatial distribution of phases and the different phases that are developed during processing.

Carbon Nanotubes Functionalized by Nanoparticles of Platinum

Carbon nanotubes (CNT) based gas sensors have attracted interest due to their excellent properties. Several studies have reported changes in the CNT’s electrical properties when functionalized with platinum (Pt) nanoparticles. In this investigation, the vapor phase impregnation decomposition (VPID) method was employed to incorporate Pt nanoparticles on CNT. Both, Pt nanoparticles and CNT were characterized by high resolution transmission electron microscopy (HR-TEM). The sensitivity of sensors based on CNT doped with Pt, was evaluated with ozone molecules. TEM images showed low and heterogeneous distribution on the surface of carbon nanotubes. The gas evaluation of CNT-Pt sensor presents good and quick response to ozone molecules at different concentrations and temperatures. The best response was found to be at 120 °C.