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Artigo IPEN-doc 29901 Optical coherence tomography (OCT) for the analysis of zirconia crystalline phase transformation2023 - ARATA FOUND, ANELYSE; PRETTO, L.R. de; USSUI, V.; LIMA, N.B. de; SOUZA, G.M. de; MACHADO, J.P.B.; TANGO, R.N.; FREITAS, A.Z.; LAZAR, D.R.R.This study aimed to validate the Optical coherence tomography (OCT) for the analysis of the transformed zone of two dental zirconia-based materials after hydrothermal ageing and correlate the values with biaxial flexural strength. Kinetics of tetragonal to monoclinic phase transformation (t→m) was calculated. X-ray diffraction (XRD) results showed a sigmoidal transformation rate over time due to the limited X-ray maximum penetration depth. Scanning electron microscope (SEM) and OCT showed a linear relationship between the thickness of the transformed layer and the ageing time. The apparent activation energy was 104.5 kJ/mol and 106.7 kJ/mol (SEM) and 106 kJ/mol and 99.4 kJ/mol (OCT) for the infrastructure and monolithic dental zirconia, respectively. Mechanical strength decreased after 150 h. of ageing at 150 ◦C for both materials showing a correlation with the depth of the transformed zone observed by OCT. Therefore, both monoclinic phase percentage and the depth of the transformed layer are critical concerning zirconia mechanical properties upon hydrothermal ageing. OCT is a non-destructive, fast, innovative, and accurate method for the analysis of zirconia’s t→m phase transformation depth kinetics after hydrothermal ageing.Resumo IPEN-doc 24482 New method for depth analysis of Y-TZP t-m phase transformation2017 - ARATA, A.; PRETTO, L.R. de; USSUI, V.; LIMA, N.B.; FREITAS, A.Z.; MACHADO, J.P.B.; TANGO, R.N.; SOUZA, G.M. de; LAZAR, D.R.R.Purpose/aim: The aim of this studywas to validate the optical coherence tomography (OCT) as a nondestructive method of analysis to evaluate the depth of tetragonal to monoclinic (t-m) transformed zone and to calculate the kinetics of phase transformation of a monolithic Y-TZP after hydrothermal aging. Specifically, to compare the activation energy of t-m transformation calculated by the depth of the transformed zone using scanning electron microscopy (SEM) and OCT. Materials and methods: Fully sintered (1450 ◦C/2 h) discs of dentalY-TZP (LAVAPLUS, 3M-ESPE)were aged in hydrothermal pressurized reactor to follow the phase transformation kinetics at 120 to 150 ◦C. Four samples per aging time were analyzed by OCT (OCP930SR, Thorlabs Inc.), = 930 nm, spectral bandwidth (FWHM) of 100 nm, nominal resolution of 6 m (lateral and axial) in air, declared digital resolution 3.09 m (axial). Three areas of 3mm (lateral) were observed to calculate the phase transformation depth (Image J). X-ray diffraction analysis (XRD) were performed, Cu-K , 20◦ to 80◦, 2 . The data were refined using the Rietveld method (GSAS). The transversal section of one specimen of each group was submitted to backscattered SEM analysis to calculate the phase transformation depth (Image J). The speed of the transformation zone front was determined plotting the phase transformation depth versus aging time. Results: XRD results indicated that Y-TZP that 66% is the maximum value of monoclinic phase concentration for all aged Y-TZP. The activation energy for the monolithic Y-TZP was 107.53 kJ/mol. One year and 5 years of hydrothermal aging at 37 ◦C will present approximately 4.21% and 15% of monoclinic phase, respectively. The comparison of the depth of the transformed zone using SEM and OCT were similar, showing a linear behavior and providing information that the opaque layer observed by OCT is related to the depth of the transformed zone (Fig. 1), any difference among the results could be a result of the refraction index correction. The energy of activation calculated by SEM and OCT were 114 kJ/mol and 100 kJ/mol, respectively. The speed calculated for the phase transformation into the bulk of the transformed zone estimated for 37 ◦C was 0.04 m/year (SEM) and 0.16 m/year (OCT). Conclusions: The results indicate that activation energy values determined by SEM and OCT observations were similar allowing the use of the OCT as a tool for monolithic Y-TZP t-m phase transformation kinetic evaluation. Moreover, OCT method has the advantage of a shorter analysis time, without the need of sample preparation steps.Resumo IPEN-doc 23549 Y-TZP low temperature degradation: a sigmoidal or a linear behavior?2016 - ARATA, A.; PRETTO, L.R. de; USSUI, V.; LIMA, N.B.; FREITAS, A.Z.; MACHADO, J.P.B.; TANGO, R.N.; SOUZA, G.M.D. de; LAZAR, D.R.R.