Hard and tough carbon nanotube-reinforced zirconia-toughened alumina composites prepared by spark plasma sintering
Echeberria, J; Rodríguez, N; Vleugels, J; Vanmeensel, K; Reyes Rojas, A ; García Reyes, A ; Domínguez Ríos, C; Aguilar Elguezabal, A; Bocanegra Bernal, MH.
Carbon. F. I. 4.896. 50, 706-717 (2012)
It is demonstrated that 0.1 wt% of multi-walled carbon nanotubes (MWCNTs) or single-walled carbon nanotubes (SWCNTs) added to zirconia toughened alumina (ZTA) composites is enough to obtain high hardness and fracture toughness at indentation loads of 1, 5, and 10 kg. ZTA composites with 0.01 and 0.1 wt% of MWCNTs or SWCNTs were densified by spark plasma sintering (SPS) at 1520 degrees C resulting in a higher hardness and comparable fracture toughness to the ZTA matrix material. The observed toughening mechanisms include crack deflection, pullout of CNTs as well as bridged cracks leading to improved fracture toughness without evidence of transformation toughening of the ZrO(2) phase. Scanning electron microscopy showed that MWCNTs rupture by a sword-in-sheath mechanism in the tensile direction contributing to an additional increase in fracture toughness.
Synthesis of sulfonated graphene/polyaniline composites with improved electro activity
Elcin Coskun, Erasto A. Zaragoza Contreras, Horacio J. Salavagione.
Carbon. F. I. 4.896. 50, 2235–2243 (2012)
The sulfonation of graphene by coupling with the diazonium salts of sulfanilic (SA) acid and amino-4-hydroxy-2-naphthalenesulfonic (NSA) acid is studied. Coupling with the diazonium salt of NSA gives the highest degree of sulfonation. Composites of polyaniline (PANI) and sulfonated graphene (SG) are prepared by the polymerization of aniline in the presence of the SG. The materials have been characterized by Raman, Fourier transformed infrared spectroscopy, thermogravimetric analysis and cyclic voltammetry. These materials are electrochemically active at pHs close to physiological pH due to the doping of PANI with the sulfonic groups in SG trapped in the polymer. Furthermore, good conductivity values are obtained.
Evaluation of bimetallic catalyst PtAg/C as a glucose-tolerant oxygen reduction cathode
Guerra Balcázar, M; Cuevas Muñiz, FM; Álvarez Contreras, L; Arriaga, LG; Ledesma García, J.
J Power Sources. F. I. 4.29. 197, 121-124 (2012)
PtAg/C nanoparticles were synthesized by chemical reduction and evaluated for the oxygen reduction reaction (ORR) in the absence and presence of glucose. PtAg/C catalyst formed onion-like layered structures, which are uniformly distributed on the support. PtAg/C showed activity comparable to that of Pt/C ETEK for ORR. Further, the catalyst exhibited high selectivity for ORR in the presence of glucose. PtAg/C was evaluated as cathode in a microfluidic fuel cell operated with high concentration of glucose (100 mM) as fuel. The results demonstrated that the use of PtAg/C as cathode electrode achieved higher selectivity and better performance compared with Pt/C catalyst.
Influence of magnetoelectric coupling on electric field induced magnetization reversal in a composite unstrained multiferroic chain
Paul P. Horley, Alexander Sukhov, Chenglong Jia, Eduardo Martínez, and Jamal Berakdar
Phys Rev B. F. I. 3.774. 85, 54401 (2012)
We study theoretically the multiferroic dynamics in a composite one-dimensional system consisting of BaTiO3 multiferroically coupled to an iron chain. The method treats magnetization and polarization as thermodynamic quantities describable via a combination of the Landau-Lifshits-Gilbert and the Ginzburg-Landau dynamics coupled via an additional term in the total free energy density. This term stems from the multiferroic interaction at the interface. For a wide range of strengths of this coupling, we predict the possibility of obtaining a well-developed hysteresis in the ferromagnetic part of the system induced by an external electric field. The dependence of the reversal modes on the electric field frequency is also investigated and we predict a considerable stability of the magnetization reversal for frequencies in the range of 0.5-12 GHz.
Nanoindentation characterization of the micro-lamellar arrangement of black coral skeleton
B.A. Juárez de la Rosa, J. Muñoz Saldaña, D. Torres Torres, P.L. Ardisson, J.J. Alvarado Gil,
J. Struct. Biol.. F. I. 3.5. 177, 349–357 (2012)
Black corals (antipatharians) are colonial cnidarians whose branched tree-like skeleton is mostly constituted of chitin fibrils inside a lipoproteic matrix. The skeleton exhibits growth rings formed by chitin layers (micro-lamellae). In order to know the effect of the arrangement microlamellae of chitin of black corals and to improve the understanding of the role of chitin structure in the antipatharian skeleton, the mechanical properties of the skeleton of two black corals, Antipathes caribbeana and Antipathes pennacea, were examined using nanoindentation tests. Measurements of reduced elastic modulus, nanohardness and the viscoelastic behavior were measured with a spheroconical indenter. The results indicate variations in the values of the mechanical properties clearly associated with different structures present in the skeletons, the core being the one that invariably shows the maximum values. The solid multilamellar arrangement of black coral chitin, its viscoelastic behavior, and the anisotropic mechanical response, are relevant factors contributing to the successful adaptation of black coral colonies to shallow as well as to very deep waters.
