Auto ignition processing and hot isostatic pressing of nanocrystalline zirconia.

摘要

Two zirconia systems, CeO2-ZrO2 and CaO-ZrO2, are investigated in the current dissertation.; In the current study, Auto Ignition Process was successfully utilized in synthesizing nanocrystalline ZrO2 containing 2, 4, 6, 8, and 10mol% CaO and ZrO2 containing 4, 8, 12, 16, and 20mol% CeO 2. XRD, TEM, and Raman spectroscopy are used to characterize the as-synthesized powders. For both systems, the as-produced powders are tetragonal and the crystal sizes are less than 50nm. The crystalline size obtained decrease with increasing of CaO/CeO2 content. For CaO-ZrO2 system, the dominant defect in the produced ZrO2 is Cazr ″ and Vo··. The oxygen vacancy sits in the nearest-neighbor sites to Ca2+. The coordination number of Ca2+ is 7. For CeO2-ZrO2 system, neither Ce2O3, nor significant oxygen vacancy existed in the powders produced. The coordination number of Ce4+ in ZrO2 is 8. Vegard's law is obeyed in the current investigation of CeO2-ZrO2 system.; In the current study, as-synthesized ZrO2-6, 8, and 10mol% CaO and ZrO2-12, 16, and 20mol% CeO2 powders are successfully densified with retained nanocrystalline size and tetragonal structure using Hot Isostatic Pressing (HIPing). The mechanical properties testing found that hardness increases and fracture toughness decreases with CaO/CeO2 content in the above compositions. The hardness and fracture toughness of nanocrystalline zirconia are lower than those values of coarse grain zirconia. For ZrO2-6mol% CaO, the hardness obtained is 3.8GPa and the fracture toughness obtained is 4.10MPa.m1/2. For ZrO2-12mol% CeO2, the hardness obtained is 2.9GPa and the fracture toughness obtained is 5.18MPa.m1/2. These properties obtained can be explained by grain boundary sliding and absence of transformation toughening. A HIPing model developed in the current study indicates that diffusions is favored over power-law creep in the initial stage of HIPing and grain boundary diffusion is favored over lattice diffusion in the final stage of HIPing of nanocrystalline zirconia.