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    Application of Model-free Methods for Analysis of Combustion Kinetics of Coals with Different Ranks
    (Taylor & Francis Inc, 2009) Sis, H.
    Model-free kinetic approaches were employed to investigate the combustion kinetics of coals with different ranks, namely, lignite, bituminous coal, and anthracite. The experimental data were provided under non-isothermal conditions at different heating rates in the range of 2-25C min-1. The activation energy values were estimated by two model-free methods, that is, Ozawa-Flynn-Wall and Kissinger-Akahira-Sunose methods. Slightly higher activation energy values were obtained by Ozawa-Flynn-Wall method at a wide range of conversion extent. Variation of activation energy was found to be comparably more significant for lower rank lignite (between 44.82 and 287.56 kJ mol-1) while less significant for higher rank bituminous coal (between 101.97 and 155.64 kJ mol-1) and anthracite (between 106.04 and 160.31 kJ mol-1).
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    Effect of nonionic and ionic surfactants on zeta potential and dispersion properties of carbon black powders
    (Elsevier, 2009) Sis, H.; Birinci, M.
    Dispersion of carbon black powders in aqueous medium was investigated by using anionic surfactant sodium oleate and a series of nonionic surfactants which were selected systematically to represent varying degrees of ethoxylation. Single and binary mixtures of the nonionic and ionic surfactants were employed in zeta potential and particle size measurements and a high affinity of surfactants on carbon black powders was beheld as they significantly changed the zeta potential and size distribution of the powders. But, noticeable differences between the surfactants were also observed, for example, as the nonionic surfactants reduced the absolute magnitude of zeta potential of powders in a wide pH range of 3.0-11.0, Na oleate made the zeta potential of the powders more negative under similar experimental conditions. The carbon black suspensions were agitated in a vessel having a standard geometry and the particle size measurements wet e carried out at desired time intervals without disturbance of the suspensions and interruption of agitation. Effect of surfactants on stability and dispersion of the powders were recognized with the reduction in mean particle sizes, as, in the absence of surfactant, the inean particle size could not be reduced below 24.0 mu m even after 210 min of stirring, it could be reduced to 5.35 mu m after 120 min of stirring in the presence of only 30 g/L of nonionic surfactant. Generally, it Was found that nonionic surfactants could wet and stabilize carbon black powders in aqueous medium better than anionic surfactant. The reason was explained by molecular structure and bulk properties of surfactants. (C) 2009 Elsevier B.V. All rights reserved.