Electrochemical synthesis of a biomedically important Co–Cr alloy

Co–30 wt.% Cr alloy was prepared by electro-deoxidation in molten calcium chloride at 1123 K. A preliminary study was conducted into the preparation of the mixture of the Co₃O₄ and Cr₂O₃ and the formation of the non-stoichiometric, spinel structured, mixed oxide nominally labeled Co_xCr_yO₄. Constant voltage chronoamperometry was used both to prepare the alloy and to investigate its mechanism of formation. Electro-deoxidation proceeds by the simultaneous rapid reduction of CoO to Co and the slower reduction/substitution of Co_xCr_yO₄ to CaCr₂O₄ and Co metal. The final step of the electro-deoxidation is the reduction of CaCr₂O₄ to Cr metal, which alloys with the Co metal, and release of Ca²⁺ back into the electrolyte.     

Water absorption in epoxy resins: The effects of the crosslinking agent and curing temperature

Epoxy systems were prepared with the same epoxide (diglycidyl ether of bisphenol A) with five different hardeners: 4,4′‐diaminodiphenylmethane (H1), diethylenetriamine (H2), a cycloaliphatic amine based on isophorone diamine (H3), a polyaminoimidazoline‐based hardener (H4), and a polyamidoamine‐based adduct hardener (H5). Samples were subjected to four different postcure treatment temperatures (23, 55, 75, and 150°C). Water absorption kinetics were obtained for each material and for each postcure treatment. The water absorption behaviors for the materials with H1, H2, and H3 were similar, whereas those for H4 and H5 were quite different. This is discussed in terms of the molecular structures of the hardeners. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 98: 2544–2549, 2005     

Use and recycling of Ca-alginate biocatalyst for removal of phenol from wastewater

The objective of the current work is the exhaustive study of the phenol degradation potential in both free cell and immobilized bacterium (Pseudomonas aeruginosa) in calcium alginate beads (biocatalyst) was investigated for its ability to grow and degrade phenol as its sole source of carbon and energy.The biodegradation assays were performed in liquid medium with phenol being the only substrate. It was found that P. aeruginosa is able to degrade phenol up to 500 mg L^?1 in 50 h as free cell and 900 mg L^?1 in 80 h when immobilized in the calcium alginate beads. However, for 1200 mg L^?1 concentration, the immobilized cells took much more time (290 h) for a complete degradation.The reuse of these beads in different concentrations of phenol (100–900 mg L^?1) showed that the cells keep their phenol degradation ability up to 900 mg L^?1in 78.5 h with 99% removal efficiency.Similarly, the reuse of the biocatalyst in the same initial phenol concentration (500 mg L^?1), allows us to get 9 cycles.     

Forced transverse vibration of composite sandwich beam with magnetorheological elastomer core

We studied, experimentally and numerically, the vibrational response of a magnetorheological elastomer sandwich beam, clampedfree, delimited by two skins aluminum 7075T6, first subjected to a variable magnetic field perpendicular to the skin of the beam, and second to a harmonic excitation by magnetic force applied at the free end. Our main objective was to predict the effect of the intensity of the current flowing through a coil on several dynamic factors. The maximum amplitude of resonance and the variation of the loss factor as a function of structural stiffness are adjusted simultaneously by the application of different magnetic fields. The results of both methods are compared.     

Influence of Submicron TiO2 Particles on the Mechanical Properties and Fracture Characteristics of Cured Epoxy Resin

Submicron titanium dioxide (TiO₂) was used in different weight fractions as a toughening agent for amine-cured epoxy resin. After the use of X-ray photoelectron spectroscopy (XPS), which confirmed that the TiO₂ particles were evenly distributed in the cross-linked epoxy resin matrix, the composites were characterized by tensile and impact testing, followed by scanning electron microscopy of the fracture surfaces. The results indicated that the submicron TiO₂ toughening particles markedly improved the mechanical properties of the cured epoxy resin compared to the untoughened epoxy resin. The optimal properties were achieved at a TiO₂ concentration of 4 wt. %, at which point the toughness and the impact resistance values increased by 65% and 60%, respectively. The results also indicated that an increase in the amount of TiO₂ causes a decrease in toughness. Stress whitening, out-of-plane flaking, and thumbnail markings were the major visible features of the toughening mechanisms.

It is suggested that, at 4 wt. % of the submicron TiO₂ particles, microvoids are developed in the epoxy matrix. These microvoids are able to absorb some of the deformation work applied to the material, and thus enhance the toughness of the material. On increasing the TiO₂ content in the matrix (> 4 wt. %), the submicron particles got closer to each other and the microvoids were converted to macrovoids, which may act as stress concentrating flaws, leading to the deterioration of the mechanical properties of the epoxy resin.     

Etude de diverses roches au laboratoire par ondes ultrasonores

The wave propagation velocity in the rocks is a well known tool with many applications in their structure and conditions studies (porosity, microcracks, saturation) or for the relationship with their mechanical properties (R_c, dynamic modulus, ...). In this paper, the interest of the signal shape study is pointed out for a better characterization of the porous medium. An examination of the transmitted frequencies looks particularly promising for materials quality determination.     

Thermal buckling analysis of functionally graded sandwich plates

Thermal buckling of functionally graded sandwich plates are presented in this article. Two common types of FGM sandwich plates, namely, homogeneous face layers with FGM core and FGM face layers with homogeneous core are considered. Material properties and thermal expansion coe?cient of FGM layers are assumed to vary continuously through-the-thickness according to a simple power-law distribution in terms of the volume fractions of the constituents. Equilibrium and stability equations of FGM sandwich plate with simply supported boundary conditions are derived using the higher-order shear deformation plate theory. The influence of the plate aspect ratio, the relative thickness, the gradient index, and the thermal loading conditions on the critical buckling temperature of FGM sandwich plates are investigated. The thermal loads are assumed to be uniform, linear, and nonlinear distribution through-the-thickness. A new simple solution for thermal buckling of FGM sandwich plates under nonlinear temperature rise is presented.     

Thermodynamic effect on the bending response of elastic foundation FG plate by using a novel four variable refined plate theory

This article deals with the study of the thermodynamic behavior of functionally graded material plates resting on two-parameter elastic foundation. An analytical solution based on a new shear refined deformation theory is presented. The displacement field used in the present refined theory contains undetermined integral forms and involves only four unknowns to derive. The plate is assumed simply supported and subjected to two different temperatures fields across its thickness. The mechanical characteristics of the plate are assumed to be varied across the thickness according to a simple exponential law distribution. The governing equations and boundary conditions are derived using the principle of virtual displacements and Navier solution technique is adopted to derive analytical solutions. A detailed numerical study of the present new refined theory is carried out to examine the influence of the time’s parameter, foundation’s parameters and deflection on the bending response of the FG plate.