Advanced sintering techniques for development silicon nitride based ceramics
Silicon nitride (Si3N4) ceramics have been thoroughly researched as potential biomaterials due to their superior mechanical properties, biocompatibility and antibacterial properties. When compared with other commonly used spinal implant materials, it has been found that Si3N4 outperforms them in most aspects. Dense, bulk silicon nitride ceramic objects can be created through liquid phase sintering. The strong covalent bonding between silicon and nitrogen atoms, makes sintering additives necessary for consolidating Si3N4 ceramics. During sintering, at a temperature between 1500oC and 1800oC a phase transformation from the α-phase to the β-phase of silicon nitride, with the sintering additives forming an intergranular glass phase per Eq.1:
α-Si3N4 + SiO2 + MxOy → β-Si3N4 + M-Si-O-N phase (Eq. 1)
The general objective of my project is to find ways to improve the biological behavior of silicon nitride materials without their mechanical degradation. This objective will be achieved through three main pathways. Firstly, thermochemical surface modifications will be applied to Si3N4 samples in order to increase their bioactivity that would lead to faster and stronger bonding with bone. Secondly, an effort will be made to substitute currently used sintering aids with oxides known to elicit a positive biological response by the host. Finally, an investigation will be made into the potential of creating silicon nitride composites (mainly with zirconia), in an effort to transfer its unique antibacterial properties to other materials.