Low Shrinkage Nanoscaled Transition-Alumina Crystal Aggregates of Gibbsite.

The low volume shrinkage phenomena occurring during thermal treatments of gibbsite (Al(OH)3) crystal were examined using TEM techniques. Normally, gibbsite shows a pseudomorphic transformation. The outward gibbsite crystal form can be preserved despite the fact that phase transformation proceeds from gibbsite to χ-, to κ-, then to α-phase alumina. Examinations revealed that a sequential nanocrystal habit evolution developed, from χ-flak to κ-pillar or pole, then to α-pea pods, as phase transformation proceeded. Calculations relating the increases in sequential density with the corresponding new packing patterns exhibited as transition phases occur demonstrate that pseudomorphic transformation can be performed perfectly. It is this mechanism that eventually leads to the low volume shrinkage of gibbsite aggregates. [ABSTRACT FROM AUTHOR]