Browsing by Author "Schreiber, Henry D."

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    Redox chemistry of iron-manganese and iron-chromium interactions in soda lime Silicate glass melts
    (Offenbach : Verlag der Deutschen Glastechnischen Gesellschaft, 1996) Schreiber, Henry D.; Peters, Lyle J.; Beckmann, Joseph W.; Schreiber, Charlotte W.
    Redox interacdons between the Fe²⁺-Fe³⁺ and Mn²⁺-Mn³⁺ redox couples and the Fe²⁺-Fe³⁺ and Cr⁶⁺-Cr³⁺ redox couples were spectrophotometrically determined in soda lime Silicate compositions quenched from different melting temperatures (1100 to 1400°C) at air. Both Mn³⁺ and Cr⁶⁺ stoichiometrically oxidized Fe²⁺. Thus, for example in the iron-manganese System, the color of the glass was determined by Fe³⁺ and Mn²⁺ along with either Fe²⁺ o r Μn²⁺, whichever one being in excess at that temperature. The electron exchange between the redox couples occurred during equilibration at melt temperature and not as an artifact of the quench. No evidence was obtained for a rapid internal re-equilibrium of redox states with decreasing temperature during the normal cooling of a melt to a glass. The degree of redox interaction of manganese or chromium with iron is independent of the manganese or chromium Compound added, as long as the oxygen fugacity over the glass-forming melt is held constant externally.
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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.
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    Sulfur chemistry in a borosilicate melt Part 3. Iron-sulfur interactions and the amber chromophore
    (Offenbach : Verlag der Deutschen Glastechnischen Gesellschaft, 1990) Schreiber, Henry D.; Kozak, Samuel J.; Schreiber, Charlotte W.; Wetmore, Douglas G.; Riethmiller, Margaret W.
    The mutual interactions of iron and sulfur in a borosilicate melt were defined as a function of the iron content, sulfur concentration, melt temperature, and oxygen fugacity. Over the range of conditions for which ions of SO4 2- - Fe3+ - Fe2+ or S2- - Fe2+ - Fe0 existed in the melt, sulfur and iron behaved as two independent redox systems. Mutual interaction occurred only for the conditions when S2- ions were in equilibrium with Fe3+ ions in the melt (for example, an oxygen fugacity of 10^-9 to 10^-11 bar at 1150 °C). The Fe3+ ion oxidized the S2- ion to the supersulfide ion, S2 -, which was identified as the amber chromophore. When the iron content of the melt was 1 wt% or less, the supersulfide ion was produced only in low concentrations; and consequently, the redox reaction producing it did not measurably affect sulfur solubility in the melt. In melts containing 10 wt% total iron, the mutual interaction of Fe3+ and S2- ions was sufficient to enhance the sulfur solubility through the formation of polysulfide species in the melt.