Structure of yttria stabilized zirconia beads produced by gel supported precipitation

Yttria stabilized zirconia (YSZ) is one of the inert matrix candidates selected for investigation as host matrix for minor actinide (MA) transmutation. The structural properties of (Zr0.84, Y0.16)O1.92 beads prepared by a sol–gel method for MA infiltration, are characterized as calcined (850 C) and sintered (1,600 C) beads. The calcined YSZ beads are finegrained and homogenous over the entire sphere and are surrounded by a uniform outer layer of approximately 30 lm thickness. After sintering at 1,600 C, the beads are compacted to 51% of their initial volume and exhibit a granular structure. The thermal expansion is nearly linear for the calcined material, but shows a parabolic behavior for the sintered (1,400 C) beads. In addition, the thermal expansion of calcined material is 20–25% less than after sintering. During heating up to 1,400 C, two processes can be distinguished. The first occurs between 900 and 1,000 C and is related to an increase in unit cell order. The second process involves grain-growth of the less crystalline calcined material between 1,100 and 1,300 C. These results have implications for preparation of YSZ and its use as an inert MA transmutation matix.