High-performance SiO2 matrix glass ceramics

Silica-based glass ceramics are widely used in biomedical applications due to their exceptional biocompatibility and tailorable properties. However, their application is often limited by low mechanical strength, which can be improved by optimizing the crystalline phase that determines their final properties. Silicon nitride (Si3N4) and Zirconia (ZrO2) are particularly appealing ceramics due to their favorable combination of mechanical strength and biological compatibility. In this thesis, the development of two types of glass ceramics, Si3N4-SiO2 and ZrO2-SiO2 glass ceramics is explored to address these challenges by controlling their microstructure and engineering the nanointerfaces between ceramic/ceramic grains and ceramic grain/glass matrix. In Si3N4-SiO2 glass ceramics, raw powders containing three different Si3N4 contents were prepared. The results showed that the β-Si3N4 crystalline phase is well distributed within the SiO2 matrix. The mechanical properties of the glass ceramics improved with increasing Si3N4 content and increasing sintering temperature, reaching a maximum flexural strength of 452±33 MPa and fracture toughness of 6.4±0.5 MPa∙m1/2 at 70 wt% Si3N4 composition. The highest antibacterial rate against S. epidermidis was observed in the 50SiN samples, at 79%. In the ZrO2-SiO2 glass ceramics, the raw powders with varying types (K+, Mg2+, Al3+, Ce4+, and Ta5+) and amounts of dopants were prepared by a modified sol-gel method. TEM results showed the ZrO2 crystals were embedded within the amorphous SiO2 matrix, with Mg2+, Al3+, and Ce4+ ions primarily segregating at the grain boundaries of ZrO2 crystals while K+ and Ta5+ ions mainly dissolved within the grains. The Mg-doped samples showed the highest toughness at 12.39±1.34 MPa∙m1/2, attributed to the enhanced interfacial strength between the dopants and ZrO2 crystals. FEM simulation shows that enhanced interfacial bonding lead to more diffused cracking and dissipating energy compared to the conventional interfacial weakening theory. The antibacterial performance of the ZrO2-SiO2 was improved by nitrogen ion implantation of the surface. The antibacterial rate against S.aureus reached 49 ± 24% for samples implanted at fluences of 1×1017 ions/cm². In conclusion, different SiO2 matrix glass ceramics were developed with enhancing mechanical strength and antibacterial properties. The results indicate that these materials hold significant potential for biomedical applications.