Microstructural characterization and mechanical properties of glass-ceramics crystallized by microwave energy

Author(s)

Ana Beatriz Gomes de Carvalho

• Document type: Master's Dissertation
• Press: São José dos Campos. 2020-03-26.
• Institution: Universidade Estadual Paulista (Unesp). Instituto de Ciência e Tecnologia. São José dos Campos
• Defense date: 2020-01-31
• Advisor: Guilherme de Siqueira Ferreira Anzaloni Saavedra

Abstract

The aim of this study was to verify the viability of an alternative process of crystallization using microwave energy and to establish a crystallization protocol for three commercial glass-ceramics; besides evaluating the effect of this process on the microstructure and mechanical properties of them. The null hypothesis was that the crystallization by microwave energy did not affect the microstructural characteristics and consequently the mechanical properties of these ceramic materials. 180 discs were made from blocks of three different glass-ceramics: lithium disilicate (IPS e.max CAD, Ivoclar Vivadent) and lithium silicates reinforced by zirconia (I - Suprinity, Vita Zahnfabrik; II - Celtra, Dentsply); according to ISO 6872 (dimensions: 12 x 1.2 mm). Three crystallization temperatures were tested in a microwave oven (700ºC, 770ºC and 850ºC), and the biaxial flexure, SEM and XRD tests were performed to define the temperature in which the ceramics presented their best behavior. Density, translucency, surface roughness, Vickers hardness and three and two-body wear tests were performed with the crystallized samples only at the selected temperatures for each ceramic. For DL-mo group, the crystallization temperature was 850ºC and material’s resistance increased (422.4 ± 63.53). For SLZ1-mo and SLZ2-mo groups, the crystallization temperature was 770ºC, with resistances approximately similar to the conventional group (302.8 ± 37.86 and 268.7 ± 44.85 respectively). Translucency and density tests showed that the higher the density, the higher the translucency. The roughness test showed no statistical difference for Ra and Rsm parameters, only for Rz. For the three-body wear test, the microwave crystallized group suffered lower wear rate (0.22 ± 0.71) than the conventional group (0.62 ± 0.4); while for the two-body wear test the crystallization approach was not a statistically significant variable. SLZ1 presented higher wear rates, regardless of the crystallization approach (1.30 ± 1.79). It was concluded that the crystallization process is viable for glass ceramics, and that different crystallization temperatures result in different microstructures and mechanical properties. The crystallization temperature for DL using microwave energy is 850ºC and for SLZ1 and SLZ2 is 770ºC. Microwave oven crystallized ceramics have a lower wear rate, higher flexural resistance, higher Weibull modulus, and consequently higher longevity. (AU)

• FAPESP's process: 18/09577-2 - Microstructural characterization and mechanical behavior of glass-ceramics crystallized by microwave energy
• Grantee: Ana Beatriz Gomes de Carvalho
• Support Opportunities: Scholarships in Brazil - Master