| Abstract Scope |
Zirconia ceramics mostly 3Y-TZP has been used in the Bioceramics mostly dental application because of several merits: (1) high strengths, (2) high toughness, (3) opacisity and (4) XRD sensitive, etc. They have been caused by transformation toughning of these ceramics,which is based on metastable nature of these ceramics (t’) have been made by cooling from high temperature tetragonal stable phase (t). Since toughened zirconia has been based upon metastable (t’) phase, it has been transformed to more stable but still metastable monoclinic (m’) phase by kinetically via the accumulation of local stress(es): which would be caused by (a) mechanically, (b) chemically, and (c) both of them. Therefore the transformation would be depended upon,(i) grain size and shape,(ii) grain boundary thus (iii) thermal history and processing, etc. For example, larger grains might have high possibility of stress accumulation. Moreover moisture(H2O) might accelerate to form chemical stresses by the substitution of O2- by OH- then break Zr-O-Zr bond(s),Which have been called as Low-Temperature Degradation(LTD) at 100-200 C. |