Apparatus for forming compactible material into a body

In the growth of gadolinium gallium garnet monocrystals, a crucible is charged with a preformed body (65) of oxide powders to form a melt. In preparation therefor, the oxide powders are formulated into a typical particulate material (16) which is compacted into a body (65) having a desired size and shape. For holding material (16), there is provided a pouch (38) of a first size having elastic walls expandable to a second size, larger than body (65). The pouch (38) is disposed within a chamber (36) having inside walls conforming to the desired shape of the body (65) but of the second size. An open neck (42) of the pouch (38) extends through and is sealed to an opening (60) in chamber (36). Then a vacuum is drawn between the pouch (38) and chamber (36) to expand pouch (38) to said shape and second size formed by the chamber walls. As the particulate material (16) is introduced into the expanded pouch (38), such material conforms to the shape and second size of such expanded pouch. The vacuum is broken, permitting pouch (38) to compress the loaded material (16) and maintain the shape for subsequent compacting. The loaded pouch (38) is removed from the chamber (36) and is thereafter isostatically compacted with sufficient pressure to form the body (65) therewithin having the desired size and shape.