Interest of Raman spectroscopy for the study of dental material: The zirconia material example
Résumé
The mechanical properties, the biocompatibility and the aesthetic aspect make of zirconia a material of interest for orthopaedics and dental prosthetics. This ceramic presents a transformation of phase ability, which is responsible for its high mechanical resistance and fracture toughness. In biomedical applications, tetragonal metastable zirconia is used. Under mechanical stresses, zirconia grains experience a transformation towards a monoclinic structure. This phenomenon exists also under hydrothermal stresses and is known as low temperature degradation, it is well described for yttria partially stabilised zirconia, 3Y-TZP. Kinetics of transformation is usually studied using X-ray diffraction or AFM. The aim of this article is to present Raman spectroscopy as an alternative and non-destructive method to study the transformation of zirconia. After a presentation of Raman scattering, examples of tetragonal, cubic and monoclinic zirconia Raman spectra are presented. The calibration procedure to assess the penetration of the laser probe in the material is detailed and found to reach 70 [mu]m. The quantitative measurement of monoclinic zirconia volume is explained. An example illustrates the decrease of the transformation from 12 at the material subsurface to 2% in a 70 [mu]m depth.