TY - JOUR
T1 - Enthalpies of formation and phase stability relations of USi, U3Si5 and U3Si2
AU - Chung, Cheng Kai
AU - Guo, Xiaofeng
AU - Wang, Gaoxue
AU - Wilson, Tashiema L.
AU - White, Joshua T.
AU - Nelson, Andrew T.
AU - Shelyug, Anna
AU - Boukhalfa, Hakim
AU - Yang, Ping
AU - Batista, Enrique R.
AU - Migdisov, Artaches A.
AU - Roback, Robert C.
AU - Navrotsky, Alexandra
AU - Xu, Hongwu
N1 - Publisher Copyright:
© 2019 Elsevier B.V.
PY - 2019/9
Y1 - 2019/9
N2 - U–Si intermetallic compounds have drawn great attention due to their potential application as nuclear fuels. However, the thermodynamic properties and phase equilibria of this binary system from ambient to high temperature conditions are not fully understood. Via high temperature oxidative drop calorimetry and detailed characterization of the initial and final phases, we have experimentally determined the standard enthalpies of formation of USi and U3Si5.07 at 298 K to be −43.2 ± 6.2 and −43.8 ± 9.0 kJ/mol·atom, respectively. The energetics of the tetragonal USi (t-USi, space group I4/mmm) phase has also been calculated with Density Functional Theory (DFT) for the first time. Combining the obtained formation enthalpies with the heat capacities measured previously, we assessed the thermodynamic stability of t-USi relative to a phase assemblage of two other U–Si phases, U3Si5.07 and U3Si2, from ambient temperature to 1200 K. The tetragonal USi is thermodynamically more stable than U3Si5.07 + U3Si2, which supports previously published phase diagram (H. Okamoto and T. Massalski, 1990 [1]): specifically, at least one stable USi phase exists when the U content is 50 at.%. Further thermodynamic and phase equilibrium studies are needed for a more comprehensive understanding of the U–Si system across broader compositional and temperature ranges.
AB - U–Si intermetallic compounds have drawn great attention due to their potential application as nuclear fuels. However, the thermodynamic properties and phase equilibria of this binary system from ambient to high temperature conditions are not fully understood. Via high temperature oxidative drop calorimetry and detailed characterization of the initial and final phases, we have experimentally determined the standard enthalpies of formation of USi and U3Si5.07 at 298 K to be −43.2 ± 6.2 and −43.8 ± 9.0 kJ/mol·atom, respectively. The energetics of the tetragonal USi (t-USi, space group I4/mmm) phase has also been calculated with Density Functional Theory (DFT) for the first time. Combining the obtained formation enthalpies with the heat capacities measured previously, we assessed the thermodynamic stability of t-USi relative to a phase assemblage of two other U–Si phases, U3Si5.07 and U3Si2, from ambient temperature to 1200 K. The tetragonal USi is thermodynamically more stable than U3Si5.07 + U3Si2, which supports previously published phase diagram (H. Okamoto and T. Massalski, 1990 [1]): specifically, at least one stable USi phase exists when the U content is 50 at.%. Further thermodynamic and phase equilibrium studies are needed for a more comprehensive understanding of the U–Si system across broader compositional and temperature ranges.
KW - Calorimetry
KW - Density functional theory
KW - Intermetallics
KW - Nuclear reactor fuel
KW - Phase stability
KW - Thermodynamic properties
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U2 - 10.1016/j.jnucmat.2019.05.052
DO - 10.1016/j.jnucmat.2019.05.052
M3 - Article
AN - SCOPUS:85066801747
SN - 0022-3115
VL - 523
SP - 101
EP - 110
JO - Journal of Nuclear Materials
JF - Journal of Nuclear Materials
ER -