Treatment techniques to prevent cracking of amorphous microspheres made by the internal gelation process

The internal gelation process has been used to make plutonium gel spheres and zirconium gel spheres with stabilized yttrium. However, attempts to convert these amorphous gel spheres into kernels have failed due to cracking during the subsequent heat treatments. The porosity of the amorphous microspheres is typically not sufficient to permit the gases that are formed during subsequent heat treatments to escape. The microspheres will crack when the internal pressure becomes too great. In this study, several treatment techniques were applied to zirconium microspheres stabilized with yttrium in an effort to reduce or eliminate cracking. A combination of water washes, a pressurized water treatment at 473 K for 3 h, and a Dowanol PM treatment was shown to eliminate the cracking problem with the zirconium microspheres, which were heated to 1438 K.