Shape controlable polyhedron-type cavity; Image crystal

Serizawa, Hiroyuki  ; Oishi, Yuji*; Haga, Yoshinori   ; Yamanaka, Shinsuke*; Tsuru, Tomohito   ; Kaji, Yoshiyuki  ; Matsunaga, Junji*; Kashibe, Shinji*

We found that porous UO grain was formed by the precipitation of helium injected by HIP. SEM analysis showed that polyhedral negative crystals were formed in the sample. The shape of the negative crystal changes dramatically with the conditions of helium precipitation. The change in the precipitation condition means the variation in the activity of helium in matrix. So, our study implies that the shape of the negative crystal should changes depending on the helium inner pressure enclosed in the negative crystal. It is difficult to arbitrarily control the shapes of these polyhedral negative crystals embedded in a solid medium. However, the shape of the negative crystal can easily be controlled by helium injection method. In this article, we call shape controlled negative crystal as image crystal. Here, we report a relationship between the surface energy and the shape and discuss the transformation mechanism of image crystal.