Browsing by Author "Leonhard, Paul G."

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    Sulfur chemistry in a borosilicate melt Part 1. Redox equilibria and solubility
    (Offenbach : Verlag der Deutschen Glastechnischen Gesellschaft, 1987) Schreiber, Henry D.; Kozak, Samuel J.; Leonhard, Paul G.; McManus, Kimberly K.
    The solubility and redox state of sulfur have been determined in an alkali borosilicate melt representative of those glass compositions under consideration for nuclear waste immobilization. The solubility of sulfur has been ascertained as a function of the melt temperature, imposed oxygen fugacity, and imposed sulfur fugacity. Sulfur dissolves predominantly as the sulfate (SO4 2-) ion under oxidizing conditions, and as the sulfide (S2-) ion under reducing conditions. There is only a very narrow range of oxygen fugacities at which both sulfate and sulfide ions coexist in the melt. The presence of sulfide ions in the melt becomes significant at an oxygen fugacity of about 10^-9 bar at 1150 °C, thus establishing a lower limit in terms of redox state for melter operation in nuclear waste immobilization.
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    Sulfur chemistry in a borosilicate melt Part 2. Kinetic properties
    (Offenbach : Verlag der Deutschen Glastechnischen Gesellschaft, 1988) Schreiber, Henry D.; Kozak, Samuel J.; Leonhard, Paul G.; McManus, Kimberly K.; Schreiber, Charlotte W.
    The diffusion of gaseous sulfur compounds under both oxidizing and reducing conditions has been determined in an alkali borosilicate melt representative of compositions under consideration for nuclear waste immobilization. The diffusion coefficients D of these sulfur gases as a function of melt temperature Τ (in K) can be expressed as: log D = -3.08 - (3300/T) regardless of whether the sulfur is being incorporated as the sulfate ion in oxidized melts or as the sulfide ion in reduced melts. The rate-determining step for the diffusion is probably the diffusion of SO2 gas into the melt. Even though sulfate and sulfide ions are the two equilibrium redox states of sulfur in this melt, transient sulfur species of intermediate redox state can be produced in the melts by placing an initially oxidized melt in a reduced sulfur atmosphere. Metastable polysulfide ions of the general formula Sx 2- and Sy - are formed which slowly decay to the more stable sulfide ions under these conditions.