High coercivity of iron-filled carbon nanotubes synthesized on austenitic stainless steel

Multiwalled carbon nanotubes synthesized directly on austenitic stainless steel result in being filled with pure iron nanoparticles. X-ray diffraction shows that the nanoparticles are either in the γ- or α-phase, although iron in the original alloy is in γ-phase because of the presence of nickel. This phase transformation is due to the selective extraction of iron, performed by carbon nanotubes during their growth. A high coercivity of iron-filled carbon nanotubes is measured although the starting steel is paramagnetic. The presence of the α-phase, the magnetic anisotropy and the single domain character of the Fe nanoparticles explain their magnetic behavior.     

Design optimization of a self-cleaning moving-bed bioreactor for seawater denitrification

The hydrodynamic behavior and denitrification capacity of a down flow self-cleaning moving bed bioreactor (MBBR) using floating packed-bed carriers were investigated. Water mixing in the MBBR was determined by tracer studies, which showed a completely stirred tank reactor. Eleven different types of patented plastic packed-bed carriers were selected based on their density, shape and specific surface area. Video studies of the carriers were used to determine operating conditions and select the Cascade 1A and Tri-Pack 1 carriers for denitrification experiments. Both carriers showed a similar performance level in terms of the denitrification capacity of the resulting MBBR. The improvement in liquid circulation is thought to explain the high denitrification rates that reached 27 gNm(-2)d(-1) and the maintenance of a thin biofilm. Increasing the overall liquid velocity profile led to an increase of up to 30% in the denitrification rate in conditions with a 1-month-old biofilm. This MBBR design seemed to control biofilm development and could easily be scaled up to denitrify seawater or freshwater systems.     

Long-term storage conditions for carriers with denitrifying biomass of the fluidized, methanol-fed denitrification reactor of the Montreal Biodome, and the impact on denitrifying activity and bacterial population

The Montreal Biodome has a denitrification system to stabilize the nitrate concentration in its 3 million liter seawater aquarium. However, this microbial process has failed periodically due to various technical problems. The system can take several weeks to recover its full denitrification capacity. In order to provide the denitrification system with a backup of active biomass, different freezing conditions for the denitrifying biomass were tested. The biomass was conserved for 1 week-17 months at -20 degrees C with and without glycerol or at -80 degrees C with and without glycerol, and the denitrifying activity was tested in batch culture for 140 h periods at various intervals. Our results showed that glycerol was required for fast recovery of the microbial community's denitrifying activity. The -20 degrees C and -80 degrees C conservation temperatures with glycerol gave similar results although there was a short period of nitrite accumulation in the -20 degrees C sample. There were no substantial changes in the microbial community of any of the frozen samples after 17 months of conservation as monitored by denaturing gradient gel electrophoresis. This is the first report on the long-term conservation of a complex denitrifying population by freezing.     

Seawater denitrification in a closed mesocosm by a submerged moving bed biofilm reactor

The performance of a submerged moving bed biofilm reactor (MBBR) for the denitrification of seawater in a 3.25 million closed circuit mesocosm was investigated at pilot scale, using methanol as a carbon source at various C/N ratios. Nitrate accumulation in closed systems where water changes are expensive and problematic may cause toxicity problems to marine life. Seawater was pretreated in a recirculated fixed bed to remove oxygen prior to the denitrification step. The 110l MBBR was partly filled (25%) with spherical positively buoyant polyethylene carriers with an effective surface area of approximately 100 m2 m(-3), which represents 35% of the total surface area. Carriers were maintained submerged by a conical grid and circulated by the downflow jet of an eductor. The MBBR mixing system was designed to prevent dead mixing zones and carrier fouling to avoid sulfate reduction while treating seawater containing as high as 2150 mg SO4-Sl(-1). NO3-N reduction from 53 to as low as 1.7+/-0.7 mg l(-1) and a maximum denitrification rate of 17.7+/-1.4 g Nm(-2) d(-1) were achieved at 4.2-4.3 applied COD/N (w/w) ratio. Methanol consumption corresponded to denitrification stoichiometric values, indicating the absence of sulfate reduction. Denitrification rates and effluent residual dissolved organic carbon were proportional to the C/N ratio. Such reactors could be scaled up in closed systems where water changes must be minimized.     

Microstructure and properties of Nb<Subscript>3</Subscript>Sn superconductors for the magnet system of the international thermonuclear experimental reactor

Results of a study of promising Nb₃Sn superconductors fabricated with the use of a “bronze” method and a method of “internal source of tin” for toroidal coils of the magnet system of the international thermonuclear experimental reactor (ITER) are presented. The main structural parameters and factors of the process of manufacturing technical superconductors based on Nb₃Sn, which determine the superconducting properties, are analyzed. The current-carrying capacity and the losses to hysteresis are determined for conductors with various diameters. The structure of the layer of superconducting Nb₃Sn compound is studied, and the relation between the structural parameters and the superconducting properties of the developed conductors is described. Examples of Nb₃Sn superconductors with a reinforcing element from a nanocomposite alloy Cu - 18% Nb are presented. Strength characteristics of the reinforced conductors are studied. Prospects of further enhancement of superconducting properties of Nb₃Sn superconductors obtained by both methods are estimated.     

Effect of spin finish on fiber/binder adhesion in chemically bonded nonwovens

The purpose of this study is to better understand the mechanisms governing the phenomena of fiber/matrix adhesion by controlling the fiber surface properties. This adhesion is evaluated by studying the micromechanical and thermodynamical behavior of the fiber/matrix interface. The complexity of the interactions at the interface requires a global approach that takes into account the chemistry, morphology, and mechanics. The thermodynamical affinity between the binder and fibers is evaluated by the wetting behavior, whereas the mechanical resistance of the fiber/matrix interface is characterized with the pull‐out test. Three distinct approaches are used to classify the different systems according to the nature of the binder and the fiber surface. It is found that there is better adhesion when the spin finish is removed from the fibers, revealing the surface roughness on which the latex can mechanically anchor. © 2006 Wiley Periodicals Inc. J Appl Polym Sci 102: 4092–4100, 2006