TY - JOUR
T1 - Thermochemistry and crystallization of glass-forming Y-substituted Sr-analogues of fresnoite (Sr2TiSi2O8)
AU - Park, Tae Jin
AU - Navrotsky, Alexandra
N1 - Copyright:
Copyright 2010 Elsevier B.V., All rights reserved.
PY - 2010/7
Y1 - 2010/7
N2 - Strontium titanosilicate (Sr2TiSi2O8) is the Sr-analogue of fresnoite (Ba2TiSi2O8). It may provide useful properties due to the unusual five-coordinate titanium in its structure. Sr2TiSi2O8 is also a possible oxide form for the immobilization of short-lived fission products in radioactive waste. Through β decay, strontium decays to yttrium and then to zirconium. Therefore, not only the stability of Sr-loaded waste forms but also that of a potential decay product series with charge-balance in a naturally occurring mineral or ceramic is of fundamental importance. To incorporate the reaction 3Sr2+=2Y3++vacancy in the fresnoite composition, Y-substituted Sr-analogues of fresnoite, (Sr2-xY23x) TiSi2O8 (x=0, 0.5, 0.75, 1, 1.25, and 1.5) were prepared by a high-temperature synthesis and were found to form glass upon cooling. The Y-end-member (Y1.33TiSi2O8, x=2) crystallized to a mixture of Y2TiSiO7, TiO2, and SiO 2 upon quenching in air. The enthalpies of formation of Y-substituted Sr-fresnoite glasses were obtained from drop solution calorimetry in a molten lead borate (2PbO·B2O3) solvent at 702°C. The enthalpies of formation from constituent oxides were exothermic but become less so with increasing Y content. The enthalpy of vitrification of Sr 2TiSi2O8 composition was measured to be 68.5 ± 6.2 kJmol. The thermodynamic stability of the Y-substituted Sr-analogue of crystalline fresnoite may become marginal with increasing yttrium content. Their ready glass formation, even in the absence of radiation, suggests that amorphous phases may dominate as the Sr- and Cs-containing waste forms decay.
AB - Strontium titanosilicate (Sr2TiSi2O8) is the Sr-analogue of fresnoite (Ba2TiSi2O8). It may provide useful properties due to the unusual five-coordinate titanium in its structure. Sr2TiSi2O8 is also a possible oxide form for the immobilization of short-lived fission products in radioactive waste. Through β decay, strontium decays to yttrium and then to zirconium. Therefore, not only the stability of Sr-loaded waste forms but also that of a potential decay product series with charge-balance in a naturally occurring mineral or ceramic is of fundamental importance. To incorporate the reaction 3Sr2+=2Y3++vacancy in the fresnoite composition, Y-substituted Sr-analogues of fresnoite, (Sr2-xY23x) TiSi2O8 (x=0, 0.5, 0.75, 1, 1.25, and 1.5) were prepared by a high-temperature synthesis and were found to form glass upon cooling. The Y-end-member (Y1.33TiSi2O8, x=2) crystallized to a mixture of Y2TiSiO7, TiO2, and SiO 2 upon quenching in air. The enthalpies of formation of Y-substituted Sr-fresnoite glasses were obtained from drop solution calorimetry in a molten lead borate (2PbO·B2O3) solvent at 702°C. The enthalpies of formation from constituent oxides were exothermic but become less so with increasing Y content. The enthalpy of vitrification of Sr 2TiSi2O8 composition was measured to be 68.5 ± 6.2 kJmol. The thermodynamic stability of the Y-substituted Sr-analogue of crystalline fresnoite may become marginal with increasing yttrium content. Their ready glass formation, even in the absence of radiation, suggests that amorphous phases may dominate as the Sr- and Cs-containing waste forms decay.
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U2 - 10.1111/j.1551-2916.2010.03698.x
DO - 10.1111/j.1551-2916.2010.03698.x
M3 - Article
AN - SCOPUS:77953749035
SN - 0002-7820
VL - 93
SP - 2055
EP - 2061
JO - Journal of the American Ceramic Society
JF - Journal of the American Ceramic Society
IS - 7
ER -