CALCINATION EFFECT on the RECYCLED 3Y-TZP: OPTICAL and MECHANICAL CHARACTERIZATION

Objectives: This study endeavors to assess the impact of the calcination process on the recycling of 3Y-TZP powder establishing a protocol for producing ceramics with superior optical and mechanical properties.
Methods: Zirconia powder was obtained from the milling waste of 3Y-TZP pucks. Recycled 3Y-TZP powder, sieved within the granulometric range of ≤5 μm, was obtained, and half of powder was subjected to calcination at 900°C for 1 hour. Sixty-two discs of recycled 3Y-TZP, with a diameter of 12 mm and a thickness of 1 mm, were fabricated by uniaxial pressing and then sintered at 1550°C for 2 hours (n=31/group). The influence of calcination process on recycled 3Y-TZP was assessed on its optical properties (translucency parameter and contrast ratio) (n=10). Mechanical properties were evaluated through Vickers hardness, fracture toughness tests (n=5), and biaxial flexural strength tests to obtain the probability of survival (n=16), according to the ISO 6872:2016. Optical parameters, hardness and fracture toughness values were analyzed by one-way ANOVA and Tukey test (P<0.05). The Weibull statistics were performed to assess probability of survival. Furthermore, SEM fractographic images were obtained to evaluate the origin of the fractures.
Results: The non-calcined specimens (0.80) exhibited lower contrast ratio compared to calcined group (0.91) (P<0.05), and higher translucency parameter (6.18) regarding calcined 3Y-TZP (3.58) (P<0.05). There were no significance differences evaluating the non-calcined and calcined 3Y-TZP on hardness (11.95 and 12.33 GPa, respectively) and fracture toughness (2.66 and 2.80 MPa.m^½, respectively) (P>0.05). However, the calcined [57 (74-35)] group exhibited higher probability of survival regarding non-calcined [0 (1-0)] powder for missions above than 800 MPa. Fractographic analysis suggested that fracture origins were related to defects on the tensile side, which propagated to the compression side of the specimens.
Conclusions: Calcination process improved the optical and mechanical properties of the recycled 3Y-TZP.