G.F. de la Fuente

Production of high-density single-walled nanotube material by a simple laser-ablation method

Abstract A continuous-wave 250 W CO2-laser operating at 10.6 μm has been employed to evaporate graphite/bi-metal targets in a vertical evaporation chamber. Without the help of an additional furnace, web-like soot material has been easily produced. This contains high densities of bundles of single-walled nanotubes (SWNTs). Electron microscopy, Raman spectroscopy and neutron diffraction show the high quality of the SWNT material. The use of this simple laser-ablation system offers additional possibilities to study experimental parameters important for the formation of SWNTs leading to a better understanding of its growth mechanism.

ZrO2–Al2O3 eutectic plates produced by laser zone melting

Abstract This paper describes a procedure for preparing large surfaces of eutectic composites directionally solidified from the melt, with very fine and uniform microstructures. Large surface plates of the Al 2 O 3 –ZrO 2 eutectic, with thickness up to 250 μm, have been grown by solidification using a modified laser zone melting method suitable for the preparation of large area samples. The surface of a ceramic precursor is scanned with a rectangular CO 2 laser beam of 20×0.5 mm 2 size which induces surface melting. The resulting microstructure is colony free and it consists of fine and alternating interpenetrating Al 2 O 3 and ZrO 2 single crystal lamellae. This microstructure is the basis for improvement of mechanical behaviour in the processed material. The interspacing, crystal structure and orientation relationship between the phases has been determined. Solidification fronts were studied as a function of the processing conditions. A mapping of the residual stresses has also been performed along the transverse plate sections using micro-luminescence techniques.

Raman characterization of singlewalled carbon nanotubes and PMMA-nanotubes composites

The Raman spectroscopy have allowed us to perform studies on singlewalled nanotubes (SWNTs) produced by following methods: electric arc, laser ablation and solar energy. As this characterization method provides a great deal of informations, we will present a comparison between the nanotubes produced by all these processes and the influence of some synthesis parameters. By using spin casting, we have produced thin films of PMMA-SWNTs for different concentrations. Then, we have characterized these new materials by Raman spectroscopy. The aim of these investigations is to get information on the possible interactions between these two materials. In particular, we have studied the evolution of the composites films spectra as a function of the nanotubes concentration in the polymer.

Isolation of microorganisms with lignin transformation potential from soil of Tenerife island

Abstract A total of 44 fungi, 15 actinomycetes and 23 bacteria, isolated from ferrallitic and fersiallitic types of soil of Tenerife (Canary Islands) were capable of abundant growth on solid media supplemented with the polymeric fraction of industrial lignin as a single C source. Of 44 fungal strains grown on the media with lignin, 22 showed a positive Sundmans test and decolorization of polymeric dye Poly R-478. However, from the above 22 fungal strains, only Penicillium chrysogenum, Fusarium oxysporum, Pestalotia oxyanthi, Fusarium solani and a strain of basidiomycete fungus gave positive results for peroxidase, Bavendamm, Nobles, and laccase plate tests. Each of these 5 fungi metabolized hydroxylated and non-hydroxylated lignin-related phenylpropanoid acids, either as a single C source or in the presence of carbohydrate. These fungi were also capable of catabolizing lignin-model dehydrogenative polymerizate of coniferyl alcohol (DHP), 14 CO 2 evolving both from 14 C-labelled ring- and 14 C-β-side-chain labelled-DHP. The maximum rate of 14 CO 2 release by fungi imperfecti appeared to be during the initial stages of the metabolism of these fungi.

Laccase activities of Penicillium chrysogenum in relation to lignin degradation

Abstract An extracellular laccase capable of oxidizing ABTS (the diammonium salt of 2,2′-azinobis-3-ethylbenzothiazoline-6-sulfonic acid) was detected in ligninolytic cultures of Penicillium chrysogenum. By contrast, no lignin peroxidase, manganese-dependent peroxidase or aryl-alcohol oxidase was detected at any time during culturing. Both ABTS laccase activity and mineralization of dehydrogenative polymerizate of coniferyl alcohol were regulated by the C/N ratio in the medium and partially inhibited in the presence of thioglycolic acid, suggesting that both events are associated. In the presence of several known laccase inducers neither ABTS laccase activity nor mineralization rates were enhanced. However, a new laccase was detected in P. chrysogenum, able to oxidize 2,6-dimethoxyphenol but not involved in lignin mineralization. Studies with the known ligninolytic basidiomycete Trametes villosa suggest that lignin degradation by this fungus also involves the action of laccase.

Flux pinning improvement in Bi-2212 silver sheathed tapes with submicron SrZrO3 inclusions

Abstract Silver sheathed tapes of Bi-2212 undoped and doped with SrZrO 3 have been prepared, using co-precipitated oxalates as precursors. Thermal treatment conditions have been optimised, varying the maximum processing temperature T max . A comparative study on thermal treatment conditions, microstructure, and flux pinning properties for doped and undoped samples has been performed in order to evaluate the effect of SrZrO 3 addition. The doped samples contain SrZrO 3 submicron particles, appearing as aggregates included between Bi-2212 lamellae with a Cu-free phase and the rest of the liquid, and also distributed inside Bi-2212 grains. The presence of SrZrO 3 surplus leads to higher critical current densities in samples prepared in a wide T max range; in addition, the lowest T max , at which high J c can be obtained, becomes 5 deg lower (875°C). At T = 5 K critical currents for all the samples are of the order of 10 5 A/cm 2 and are independent of doping, while at 60 K doped samples exhibit roughly two times higher J c in zero field and more than an order of magnitude higher J c at H = 40 mT. A magnetisation decay study reveals that samples with SrZrO 3 surplus have a larger fraction of pinning centres with high energy. The enhanced pinning properties can be related to the finely dispersed zirconate inclusions found in the superconductor matrix.

Activated oxygen species and two extracellular enzymes : laccase and aryl-alcohol oxidase, novel for the lignin-degrading fungus Fusarium proliferatum

Abstract Laccase, aryl-alcohol oxidase and superoxide radicals were detected in ligninolytic cultures of Fusarium proliferatum. Enzyme activities were present during the secondary metabolism and seen as single protein bands after non-denaturing electrophoresis. In contrast, superoxide radicals were detected during primary growth, correlating with maximal lignin mineralization. Moreover, ligninolysis decreased when scavengers of both superoxide and hydroxyl radicals were added to cultures, indicating that activated oxygen species are involved in lignin degradation.

Gas and pressure effects on the production of single-walled carbon nanotubes by laser ablation

Abstract We report the production of single-walled carbon nanotubes (SWNTs) under argon, nitrogen and helium atmospheres in the pressure range of 50 to 500 Torr using a continuous wave 10.6-μm CO 2 -laser. Both argon and nitrogen can be equally used as buffer gas to synthesize SWNTs in high yield between 200 and 400 Torr. Below 200 Torr the amount of SWNTs in the soot is drastically decreased and the material is dominated by amorphous carbon. Negligible amounts of SWNTs were formed using helium. These gas and pressure effects are assigned to changes on the local temperature environment.

Polymer solution processing of (Bi, Pb)SrCaCuO

Abstract A simple polymer processing route to the 110 K phase (Bi, Pb) 2 Sr 2 Ca 2 Cu 3 O 10+δ superconductor has been developed. The influence of the polymer to metal starting ratio, as well as the sintering temperature and time on the quality of the resulting superconducting powders has been studied by XRD, a.c. susceptibility and resistivity measurements. Microstructure of ceramic compacts has been studied by SEM, and qualitatively analysed by EDS for compositional homogeneity. The results indicate that the polymer synthesis route described here may offer a good alternative to the conventional solid state preparation methods towards attaining homogeneous 110 K superconductor powder within a reasonable processing time.

Growth rate effects on thin Bi2Sr2CaCu2O8+δ textured rods

Abstract Cylindrical polycrystalline textured Bi-2212 samples of lengths up to 10 cm and 1 mm of diameter have been grown using a Laser Float Zone (LFZ) melting technique. In order to improve their transport critical current density ( J c ) at 77 K, the influence of growth rate on their microstructure has been analysed. The final transport properties of the textured materials are determined by the balance between better grain alignment and larger grain size, that takes place at the lowest growth rates, and the simultaneous appearance of cracks. The potential of LFZ grown BSCCO rods for the development of current leads at low fields is suggested. Optimum transport properties correspond to thin rods obtained using intermediate growth rates of 15 to 30 mm/h, with J c (77 K) values up to 5500 A/cm 2 in the self field. These also exhibit minimum resistivity values above T c and irreversibility lines shifted towards higher temperatures and fields.