Translucent multi-layered zirconia: Sandblasting effect on optical and mechanical properties

The aim of this study was to evaluate the influence of the sandblasting treatment on the microstructure, optical and mechanical properties of multi-layered translucent zirconia.

Samples of yttria-stabilized zirconia were prepared by stratifying four layers (L1, L2, L3 and L4) of ML-type KATANA multi-layered monolithic discs, whose surfaces were then sandblasted with alumina particles (110 µm and 0.2 MPa) in order to evaluate its effect on the presence of different crystalline phases as well as on the optical and mechanical properties of each of the four layers. The optical characterization was carried out by measuring the reflectance spectrum and colorimetric parameters by UV-Vis spectrophotometric analysis and the transmittance curves were indirectly obtained using the Kubelka-Munk model (KM). Microstructural, structural, mechanical and roughness characterizations were also performed using SEM, XRD, biaxial flexural strength B3B, and light interferometry, respectively RESULTS: According to the KM model there are different degrees of translucency between the upper and lower layers of the monolithic discs, but there was no influence of the Al₂O₃-sandblasting treatment on this optical property. The disk pigmentation causes greater absorption of light below 600 nm, decreasing the transmittance rate to values below 25% in this region of the spectrum. The yellowing index presented higher values for inner disk layers L3 and L4, in agreement with the highest values of the light absorption coefficient K observed for these layers. The roughness of the samples did not change significantly with the surface treatment performed and the sandblasting did not result in new crystalline phases. SEM analysis showed the presence of different grain sizes in all layers analyzed, being related to the co-occurring presence of cubic (c-ZrO₂) and tetragonal (t-ZrO₂) phases in similar contents (∼ 50 wt%). The Weibull statistical analysis, in turn, showed an increase in the Weibull characteristic stress value (σ₀) for most layers subjected to sandblasting, except for the second layer (central region of the disk). It was also verified an increase in the value of the structural reliability of the material (m), referring to the samples of the central region of the disc (L2 and L3 layers) after sandblasting.

The pigmentation in the disk causes a decrease of the transmittance rate to values well below 25% in the region of the spectrum 400-600 nm and the inner layers (L3 and L4) have even lower transmittance than the outer layers in this spectrum range. Although the CR index indicates variation related to the Al₂O₃-sandblasting treatment, the transmittance spectra of KM model show that the sandblasting did not cause a significant change in the transmittance rate of the four analyzed layers. Also, there is no significant difference in the light scattering of the different layers of the disc, either before or after Al₂O₃-sandblasting treatment.