Development of Dysprosium Titanate Based Ceramics

Abstract

Dysprosium titanate (Dy2TiO5) based ceramic is one of the control rod materials for thermal reactors. This ceramic has been prepared by conventional mixing and calcination technique. The formation of Dy2TiO5 phase from the Dy2O3–TiO2 starting mixture has been found to be a two‐step process. In the first step, the formation of dysprosium dititanate (Dy2Ti2O7) phase takes place at 700°C. This Dy2Ti2O7 reacts at around 1100°C with remaining Dy2O3 present in the mixture to form Dy2TiO5. The Dy2TiO5 phase has three polymorphs (orthorhombic, hexagonal, and fluorite). The fluorite phase is reported to have lowest in‐service irradiation swelling characteristics when used as control rod elements in thermal reactors. In the present investigation, the fluorite polymorph of Dy2TiO5 has been stabilized by doping with molybdenum trioxide.

Relationship Between the Orthorhombic and Hexagonal Phases in Dy2TiO5

“…[3][4][5] Several materials have been studied in an effort to find a suitable replacement. 1,2 Radiation damage caused by (n, a)-reactions with 10 B isotopes results in helium formation, causing swelling to occur and cracks to nucleate and grow, ensuring decreased operational lifespans.…”

Thermal Expansion of the Orthorhombic Phase in the Ln2TiO5 System

“…Several materials have been studied in an effort to find a suitable replacement. Among those, Dy 2 TiO 5 and Gd 2 TiO 5 are promising candidates due to the large neutron absorption cross sections of their rare‐earth cations, good mechanical properties, resistance to chemical attack, simple fabrication, and low degree of swelling under neutron radiation …”

“…Central to those who intend to use these material in an industrial setting is information regarding their behaviour in an operational situation, most notably their thermal expansion behavior. Little work has been done to characterize this property in situ or in atmospheres reflecting the materials' operational conditions, which tend to significantly impact the thermal expansion …”

“…Among those, Dy 2 TiO 5 and Gd 2 TiO 5 are promising candidates due to the large neutron absorption cross sections of their rare-earth cations, good mechanical properties, resistance to chemical attack, simple fabrication, and low degree of swelling under neutron radiation. 6 Using conventional solid-state processing techniques, members of the Ln 2 TiO 5 system with relatively large rare-earth cations (Ln = La-Dy, Y) are stabilized in the orthorhombic phase (Pnma) at room temperature, while smaller rare-earth cations (Ln = Ho-Lu) form in the cubic phase (Fm 3m or Fd 3m). At higher temperatures, some members (Ln = Gd-Y) undergo a phase transformation from orthorhombic to hexagonal structure (P6 3 /mmc) before melting.…”

The effect of synthesis conditions on the structure of compounds formed in the Dy2O3–TiO2 system

“…It is noteworthy that the multiphase composition and the features of variation of the phase composition of samples synthesized by "co-precipitation" (the initial formation of single TiO 2 and Dy 2 O 3 oxides, reaction between the oxides to give Dy 2 Ti 2 O 7 , and subsequent formation of Dy 2 TiO 5 only above 1000°C) (Figs. 2, 3) are typical of the solid-state synthesis of dysprosium monotitanate [1,8,26].…”