چكيده به لاتين
Glass-ceramics are materials which synthesized through controlled nucleation and crystallization of glass. This process involves melting, forming, and heat-treating the glasses to produce crystalline ceramics. Efficient nucleation is fundamental to controlled internal crystallization, facilitating the formation of small, randomly oriented crystals that are typically devoid of voids, microcracks, or porosities. Glass-ceramics are particularly valued in dental applications due to their distinctive properties, including high mechanical strength, excellent hardness and fracture toughness, superior chemical resistance, and aesthetic appearance.
Spinel glass-ceramics are among the glass-ceramics currently being explored for dental applications. Magnesium aluminate spinel (MgAl2O4), a material with a cubic crystal structure and unique properties, such as high strength at high temperatures, high chemical resistance in the oral environment, low coefficient of thermal expansion, high thermal shock resistance, impact resistance, machinability and suitable optical properties. In this study, the synthesis of spinel-based glass-ceramics was conducted using the melting and casting method. The research examined the effects of modifying the glass composition and incorporating TiO2 as a nucleating agent on the crystallization behavior and microstructure of the MgO-Al2O3-SiO2 (MAS) glass system. Differential thermal analysis (DTA), X-ray diffraction (XRD), and field emission scanning electron microscopy (FE-SEM) were utilized to investigate these effects.
Four glass compositions with varying percentages of nucleating agents were melted at 1500˚C in an electric furnace and subsequently heat-treated at the optimal temperatures determined by differential thermal analysis (DTA). X-ray diffraction analysis revealed that mullite and cordierite phases crystallized in GTi and G2Ti glass-ceramics, with no spinel phase observed in these samples. By adjusting the composition from the mullite region to the spinel phase region (while maintaining a constant nucleating agent), the crystallized phases changed from mullite and cordierite to spinel. further experiment demonstrated that within the spinel composition region, the amount of spinel phase increased with higher TiO2 content.
This study also investigated the microstructure, mechanical properties, chemical properties, and optical properties of GTi2 glass-ceramics heat-treated at 940℃ and 1000℃, and G2Ti2 heat-treated at 940℃. The optimal values for hardness (9.850 ± 0.05 GPa), flexural strength (203.84 MPa), fracture toughness (2.57 MPa·m1/2), and chemical solubility (332 µg/cm²) were measured for the G2Ti2(940℃) sample. Additionally, the best machinability (brittleness index of 3.11 µm1/2) was recorded for the GTi2(1000℃) sample , while the highest transparency was achieved for the GTi2(940℃) sample.
