Effects of pressure and atmosphere on the crystallization and grain refinement of zirconia fibers

The effects of pressure and atmosphere on the crystallization and grain refinement of zirconia fibers have been investigated. The polyaceticzirconium (PEZ) fibers, used as precursor fibers, were pretreated under high pressure vapor (HPV) atmosphere in an autoclave and atmospheric pressure steam (APS), and then sintered at high temperature in air. Under an HPV environment, the crystallization temperature decreases significantly owing to the reduction of the critical free energy used for the formation of the stable nuclei. The fibers crystallized at 250 degrees C after the HPV pretreatment as indicated by the appearance of expected diffraction peaks. However, the crystallization begins at 400 degrees C for the fibers pretreated by the APS process. Furthermore, the fibers sintered at 1200 degrees C subjected to HPV pretreatment exhibit more homogeneous microstructures and smaller grain sizes. Hence, the existence of pressure is beneficial for crystallization and grain refinement. (C) 2016 Elsevier Ltd and Techna Group S.r.l. All rights reserved.