Inclusion of carbon nanotubes in a TiO2 sol-gel matrix

We report here the successful inclusion of carbon nanotubes (CNs) into a TiO₂ matrix prepared by a sol-gel method. The presence of CNs in the sol-gel matrix and the structure of the film were analyzed principally by transmission electron microscopy. Complementary information about the behavior of embedded carbon nanotubes versus heat treatment and ion irradiation were obtained by X-ray photoelectron spectroscopy. The elaboration of an inorganic matrix containing embedded carbon nanotubes leads to a new nanocomposite. The possible applications of this nanocomposite are discussed.     

THE USE OF THERMOELASTICITY TO EVALUATE STRESS REDISTRIBUTION AND NOTCH SENSITIVITY IN CERAMIC MATRIX COMPOSITES

Thermoelastic stress analysis was used to document the effect of composite damage on the stress distribution in three ceramic matrix composites. Composite damage was found to significantly alter the thermoelastic response of each material, with the greatest effect noted in SiC/CAS. Thermoelastic imaging of these materials affords a more complete picture of how the various damage mechanisms affect the stress distribution. In particular, a stress concentration factor computed from thermoelastic images, serves as an indicator of stress redistribution. The stress concentration factors were computed by comparing notch root to far field temperatures, and monitored after the introduction of various amounts of damage. In each material, the stress concentration factor diminished as the damaging load approached the ultimate stress. Reduction in the stress concentration is associated with local changes in modulus, mechanistically arising from combinations of fiber, matrix and interface fracture. Stress redistribution occurs as a consequence of modulus changes, leading to lower notch sensitivity in each of the tested composites.     

The crystal structure of 4,4′-dipyridinium tetracyanooxothiocyanatorhenate(V)

Summary The light purple crystals of (4,4-dipyridinium) [ReO(NCS)(CN)₄] crystallize in the monoclinic space group P2₁/m witha=6.615(1),b=16.043(1),c=8.405(1) Å,=93.20(1)°,z=2. The anisotropic refinement of the 1770 observed reflections converged to R=0.041.The [ReO(NCS)(CN)₄]^2– ion has a distorted octahedral geometry. The rhenium atom is displaced by 0.30 Å out of the plane formed by the four carbon atoms towards the terminal oxo ligand. Bond distances: Re=0 =1.67(1), Re–N=2.12(1) and Re–C_av=2.11(1)Å. The thiocyanate ion is nitrogen bonded to the rhenium atom.     

The crystal structure of tetraethylammonium aquatetracyanooxorhenate(V)

Summary The crystal structure of the tetraethylammonium salt of [ReO(H₂O)(CN)₄]^– has been determined from threedimensional x-ray diffraction data. The light blue crystals are monoclinic, space group P2₁/m witha=8.760(1),b=9.518(5),c=11.718(1) Å, =102.63(1)^o with two molecules per unit cell. The final R value using 2009 observed reflections and anisotropic thermal parameters for all the non-hydrogen atoms was 0.038. The [ReO(H₂O)(CN)₄]^– ion has a distorted octahedral geometry with the rhenium atom displaced by 0.30 Å out of the plane formed by the four carbon atoms of the cyano ligands towards the oxo ligand. Bond distances: Re=O=1.667(8), Re–OH₂=2.142(7) and Re–C (average)=2.11(1) Å.