Browsing by Author "Samarin, S"

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    Characterisation 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, SJ
    The 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
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    Positron annihilation in off-stoichiometric and ta-doped Zn2TiO4
    (John Wiley and Sons, 2013-08-08) Guagliardo, PR; Vance, ER; Lumpkin, GR; Blackford, MG; Sudarshan, K; Davis, J; Samarin, S; Williams, JF
    While Zn vacancies are regarded as the charge compensators in Ti-rich Zn2TiO4, no evidence of cation vacancies in essentially single-phase samples containing up to 13 wt% excess TiO2 was evident from positron annihilation lifetime spectroscopy (PALS). Nor was there strong evidence of cation vacancies in Ta-doped samples targeted to contain either tetrahedral or octahedral vacancies, although there was a small increase in the lifetime as the doping level increased and the structure changed from cubic to tetragonal. © 2013, The American Ceramic Society.
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    Study of porosity of synthetic polymer nanoparticles using PALS
    (Institute of Physics, 2010-08-01) Pham, B; Guagliardo, P; Williams, J; Samarin, S; Smith, SV
    Positron annihilation lifetime spectroscopy (PALS) has been used to study the free volume in dry synthetic polymer nanoparticles of various sizes. A series of poly(styrene/divinyl benzene) particles with diameters in the range of 100 to 500 nm were synthesized and then carefully chemically treated using the sulfonation process, to increase their porosity. The particles were characterised by Scanning Electron Microscopy (SEM), light scattering and PALS. Light scattering gave larger size for the treated particles, reflecting the hydration effect and therefore the increase in porosity. PALS spectra of untreated and treated particles gave four and three life-time components, respectively. Analysis by PAScual version 1.3.0 program indicated there was a reduction in the intensity and the type of the micropores in the treated particles. The data suggest PALS is a sensitive tool for detecting changes in microporosity in particles. The conflicting results obtained for light scattering compared to PALS for chemically treated particles is difficult to resolve and suggests sample preparation of polymeric materials for PALS is the critical factor.