Synthesis of an ATZ nanocomposite (80%ZrO220%Al2O3) and microstructural, optical and survival characterization before and after aging

Author(s)

Mariana Miranda de Toledo Piza

• Document type: Master's Dissertation
• Press: Bauru.
• Institution: Universidade de São Paulo (USP). Faculdade de Odontologia de Bauru (FOB/SDB)
• Defense date: 2022-08-03

Examining board members

Estevam Augusto Bonfante; Tiago Moreira Bastos Campos; Paulo Francisco Cesar; Pedro Cesar Garcia de Oliveira

• Advisor: Estevam Augusto Bonfante; Edmara Tatiely Pedroso Bergamo

Abstract

This study aimed to perform the processing of an ATZ nanocomposite (alumina-toughened zirconia - 80%ZrO2-20%Al2O3) from a nanometric ceramic powder and characterize its crystalline content, microstructure, residual stress, mechanical and optical properties before and after being submitted to artificial aging by two methodologies: autoclave and hydrothermal reactor. One hundred and sixty-five (n=165) disk-shaped ATZnano specimens (12 x 1.2 mm) were processed from ATZ-20/80-BA nanoceramic powder (Nanoe, France). Previous pilot tests led to the following pressing and sintering protocol: uniaxial pressing at 3000 kgf/cm2 for 30 seconds and pre-sintering at 1000ºC for one hour followed by sintering at 1500ºC for 2 hours. Sintered, the specimens were polished with diamond discs and suspensions up to 1 m and divided into three groups according to the aging methodology (n=55/group): ATZ-I (immediate), ATZ-A (aged in an autoclave for 20h, at 134ºC and 2.2 bar) and ATZ-R (aged in a hydrothermal reactor for 20h, at 134ºC and 2.2 bar). X-ray diffraction (XRD) was used to characterize the crystalline content and scanning electron microscopy (SEM) to observe the microstructure and measure the grain size. Raman spectroscopy was used to analyze residual stress. Optical properties were measured by the calculation of contrast ratio (CR) and translucency parameter (00). The mechanical properties were evaluated by Vickers microhardness and fracture toughness (KIC), in addition to biaxial flexural strength test (RFB) to determine characteristic stress (MPa), Weibull modulus (m) and probability of survival for estimated missions of 300, 500 and 800 MPa (ISO 6872:2015). The results demonstrated the success of the proposed processing method, with typical peaks of alumina and tetragonal zirconia in the XRD spectra. Quantitative analysis revealed a statistically significant increase in the amount of monoclinic content in the ATZ-R group (30.6%) when compared to the ATZ-A (20.3%). SEM micrographs showed a dense microstructure, with an average grain size of 0.43 m for ATZ-I. Raman spectroscopy demonstrated the formation of compressive residual stress in the aged groups, being higher for ATZ-R (-215.1 MPa). Optical properties described the material as opaque, with high masking ability (RC: 0.99; 00: 0.26), with no statistical difference after aging protocols. The analysis of mechanical properties revealed hardness values around 1247 HV and fracture toughness of 1.9 MPa.m1/2. As for the characteristic strength results, the three groups were statistically different from each other, being ATZ-R the one with the highest value (879 MPa). The Weibull modulus was high for all groups (m>16) pointing the success of the pilot tests in optimizing the processing method. Thus, ATZnano proved to be a reliable material for use in missions of 300 and 500 MPa, corresponding to indications for monolithic prostheses or frameworks up to 3 elements involving molars. For use as 4-element prostheses (800 MPa), further developments and innovations are necessary. (AU)

• FAPESP's process: 20/16500-6 - Synthesis of an ATZ nanocomposite (80%ZrO2-20%Al2O3) and microstructural, optical and survival characterization before and after aging
• Grantee: Mariana Miranda de Toledo Piza
• Support Opportunities: Scholarships in Brazil - Master