Carbon deposition on transition metal- and uranium-oxides

Advanced gas cooled nuclear reactors (AGRs) contain a range of alloys, selected for their physical and chemical performance in the conditions present. Carbon deposition on boiler and fuel pin heat transfer surfaces affects a reactor's efficiency and may necessitate downrating to maintain safety margins. This is believed to arise from decomposition of some of the coolant gas constituents. Deposition minimisation, while maintaining the structural integrity of the reactor, is technologically and economically important. This study has looked at deposition on a range of transition metal spinels, manganese oxides, uranium oxides and single crystal magnetite samples with a view to furthering knowledge of catalytic reactions that may occur within an AGR. In particular, the effect of mixed valency on deposition rates was studied. The spinels were successfully prepared by solid state reactions between the relevant oxides, oxalates and I or carbonates. A range of elemental and chemical analytical techniques were used to characterise the samples both before and after exposure under controlled gas and radiological conditions. Deposition was induced, to varying extents, on all the samples exposed. No filamentary deposits were observed. The spinels gave quantities of deposition in the order: Manganese spinels gave increasing deposition with increasing manganese content at 650°C, but decreasing deposition at 550°C. Iron-cobalt spinels showed no consistent increase or decrease in carbon deposition with changing composition. Nickel rich spinels were unstable in the reaction gas mixture and generated metallic nickel during exposure. At both temperatures, this gave levels of carbon deposition which increased with increasing nickel content of the original oxide. NiF~04 exposed at 550°C fragmented as it catalysed carbon formation. Manganese oxides converted to MnO during exposure, MnO proving also to be a most effective catalyst. Mn304' an Mn2+ I Mn3+ compound where the manganese ions do not form an electron exchanging octahedrally coordinated pair, did not yield large quantities of deposit. The uranium oxides examined converted to the interacting mixed valence U409' which gave copious carbon deposition. The U4+ I U6+ non interacting mixed valence Ot-U30 S gave the least deposition. Magnetite slices gave laminar carbon deposits, but no filamentary growth. Structured deposit was seen in two cases, including on one face oriented approximately parallel to the [111] plane, the plane previously expected to catalyse deposition most effectively

Catalytic Reductive Degradation of Methyl Orange Using Air Resilient Copper Nanostructures

The study describes the application of oxidation resistant copper nanostructures as an efficient heterogeneous catalyst for the treatment of organic dye containing waste waters. Copper nanostructures were synthesized in an aqueous environment using modified surfactant assisted chemical reduction route. The synthesized nanostructures have been characterized by UV-Vis, Fourier transform infrared spectroscopy FTIR spectroscopy, Atomic force microscopy (AFM), Scanning Electron Microscopy (SEM), and X-ray diffractometry (XRD). These surfactant capped Cu nanostructures have been used as a heterogeneous catalyst for the comparative reductive degradation of methyl orange (MO) in the presence of sodium borohydride (NaBH4) used as a potential reductant. Copper nanoparticles (Cu NPs) were found to be more efficient compared to copper nanorods (Cu NRds) with the degradation reaction obeying pseudofirst order reaction kinetics. Shape dependent catalytic efficiency was further evaluated from activation energy (EA) of reductive degradation reaction. The more efficient Cu NPs were further employed for reductive degradation of real waste water samples containing dyes collected from the drain of different local textile industries situated in Hyderabad region, Pakistan

Chitin and carbon nanotube composites as biocompatible scaffolds for neuron growth

Preparation of biocompatible and electrically-conducting chitin nanotube composite scaffold for potential use in implantable electrode for stimulation and repair of neurons.</p

Reprocessing with GANEX:Methodology for Ligand Radiation Tolerance Testing

Results demonstrating the methodology for testing the radiation tolerance of organic ligands are presented. A high activity sealed source was used to irradiate samples which were sequentially removed and analysed using a sensitive mass spectrometer. The degradation of a candidate ligand for a new reprocessing process “GANEX” was found to be around 50% after 567 kGy exposure to gamma from Cs-137.<br/