Effect of Potassium Oxide Addition on Viscosity of Calcium Aluminosilicate Melts at 1673–1873 K

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    • Higo Tomoyuki
    • Department of Materials Science and Engineering, Kyushu University
    • Sukenaga Sohei
    • Institute of Multidisciplinary Research for Advanced Materials, Tohoku University
    • Kanehashi Koji
    • Materials Characterization Research Laboratory, Advanced Technology Research Laboratories, Nippon Steel and Sumitomo Metal Corporation
    • Shibata Hiroyuki
    • Institute of Multidisciplinary Research for Advanced Materials, Tohoku University
    • Osugi Takeshi
    • Department of Materials Science and Engineering, Kyushu University|Department of Decommissioning and Waste Management, Nuclear Science Research Institute, Tokai Research and Development Center, Japan Atomic Energy Agency
    • Saito Noritaka
    • Department of Materials Science and Engineering, Kyushu University


We investigated the changes induced in the viscosities of CaO–SiO<sub>2</sub>–Al<sub>2</sub>O<sub>3</sub>–K<sub>2</sub>O melts (CaO/SiO<sub>2</sub> molar ratio = 0.68 ± 0.04, Al<sub>2</sub>O<sub>3</sub> content = 13.4 ± 0.6 mol%) with the addition of K<sub>2</sub>O in amounts of 0–17.4 mol% for temperatures of 1673–1873 K using the rotating crucible method. The viscosity increased with an increase in the K<sub>2</sub>O content when K<sub>2</sub>O/Al<sub>2</sub>O<sub>3</sub> molar ratio < 0.7. On the other hand, the viscosity decreased with the addition of K<sub>2</sub>O for K<sub>2</sub>O/Al<sub>2</sub>O<sub>3</sub> molar ratio > 0.9. The maximum values of the viscosities were noticed in the range of 0.7 < K<sub>2</sub>O/Al<sub>2</sub>O<sub>3</sub> molar ratio < 0.9. This behavior could not be explained on the basis of the polymerization degree of the aluminosilicate network structure. The <sup>17</sup>O magic angle spinning nuclear magnetic resonance (MAS NMR) spectrum of the 31.6CaO-44.2SiO<sub>2</sub>-13.4Al<sub>2</sub>O<sub>3</sub>-10.8K<sub>2</sub>O (mol%) glass suggested that K<sup>+</sup> ions preferentially compensate the negative charge of AlO<sub>4</sub>, while the Ca<sup>2+</sup> ions primarily create non-bridging oxygens (NBOs). The viscosity data and the <sup>17</sup>O MAS NMR spectrum also suggested that the increase in viscosity for K<sub>2</sub>O/Al<sub>2</sub>O<sub>3</sub> molar ratio < 0.7 was because of the increase in the average bond strength of the aluminosilicate framework, which was attributable to the substitution of Ca<sup>2+</sup> ions by K<sup>+</sup> ions at the charge compensator sites. The activation energies for viscous flow indicated that the NBOs bonded with K<sup>+</sup> ions, forming NBO-K species, for K<sub>2</sub>O contents greater than those corresponding to the viscosity maxima. Thus, the viscosities of aluminosilicate melts are indicative of the average bond strengths of the melts.


  • ISIJ International

    ISIJ International 54(9), 2039-2044, 2014

    The Iron and Steel Institute of Japan


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