Page 9 - PR 2014 2016 10 Materials and Nanotechnology

Materials and Nanotechnology | Progress Report 285

ciation of hydrothermal aging and fatigue with Y-TZP ceramics even overestimating the life
biaxial flexural strength was also evaluated. of a human being in a hundred years.

The results indicate that the sigmoidal behav- Y-TZP composites are also promising dental
ior of phase transformation during hydrother- materials that have been studied in our labora-
mal aging, described in the literature, was a tory. Alumina, for example, can form a physical
consequence of the limitation of X-ray depth barrier against low temperature degradation,
penetration during X-ray diffraction analy- with hardness increasing, despite the reduction
sis (Figure 7). It has been proven by scanning in fracture toughness (Figure 9). On the other
electron microscopy (Figure 8) and optical hand, titania addition can enhance ceramic
coherence tomography (OCT) that Y-TZP sub- bioactivity as the presence of TiOH groups
mitted to hydrothermal aging present a linear on ceramic surface induce apatite nucleation
front of phase transformation as a function of when in contact with blood fluids (Figure 10).
aging time with decrease of the biaxial flexural In both cases, coprecipitation route has been
strength after 140 h of aging at 150°C, 3,01 bar. employed for powder synthesis, allowing the
Additionally, it was determined by kinetics study of additive composition effect. The ce-
studies that the phase transformation speed ramic processing includes powder forming
rate at the body temperature (37°C) is very by uniaxial pressing followed by sintering
low and will not cause deleterious effect on using different techniques such as conven-

Figure 8: SEM and FEG-SEM images comparing the transformed zone microstructure and the untransformed zone of Y-TZP hydrothermally
aged for 140h at 150°C.