Browsing by Author "Sullivan, J"
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- ItemCharacterisation of metakaolin-based geopolymers using beam-based and conventional PALS(Institute of Physics, 2010-08-01) Guagliardo, P; Roberts, J; Vance, ER; Weed, R; Sergeant, AD; Howie, A; Wilkie, P; Went, M; Sullivan, J; Williams, J; Samarin, S; Buckman, SJThe nano-porosity of metakaolin-based geopolymers and the effect of heat-treatment on porosity have been studied with conventional and beam-based positron annihilation lifetime spectroscopy (PALS). Conventional PALS found significant nano-porosity in the geopolymers, as indicated by the presence in the PALS spectrum of two long lifetime components, τ3 = 1.58 ns and τ4 = 47 ns, associated with pore diameters of approximately 0.5 and 3 nm respectively. The lifetime of the shorter component was found to decrease monotonically with successive heat treatments of 300°C and 600°C. Beam-based PALS, conducted at 5 keV, also indicated two long lifetime components, τ3 = 4.84 ns and τ4 = 54.6 ns. These are significantly longer than those observed by conventional PALS and the monotonic decrease of τ3 with successive heat treatments was not observed. As the beam-based PALS probed only the near-surface region, with an average implantation depth of about 350 nm, these results suggest that the near-surface structure may vary significantly from that of the bulk. This could be an inherent property of the samples or an artefact caused by surface effects or sample outgassing. © Copyright 2020 IOP Publishing
- ItemLeaching behaviour of and Cs disposition in a UMo powellite glass–ceramic(Elsevier, 2014-05) Vance, ER; Davis, J; Olufson, KP; Gregg, DJ; Blackford, MG; Griffiths, GJ; Farnan, J; Sullivan, J; Sprouster, D; Campbell, C; Hughes, JA UMo powellite glass–ceramic designed by French workers to immobilise Mo-rich intermediate-level waste was found to be quite leach resistant in water at 90 °C with the dissolution of Cs, Mo, Na, B and Ca not exceeding 2 g/L in normalised PCT tests. 133Cs solid state nuclear magnetic resonance and scanning electron microscopy (SEM) showed the Cs to inhabit the glass phase. The microstructures were not greatly affected by cooling rates between 1 and 5 °C/min or by introducing 10 times as much Cs and Sr. Protracted leach tests at 90 °C showed surface alteration as evidenced by SEM and particularly transmission electron microscopy; the main alteration phase was a Zn aluminosilicate but several other alteration phases were evident. Voidage in the alteration layers was indicated from enhanced lifetimes in po sitron annihilation lifetime spectroscopy. © 2014, Elsevier B.V.