SPS sintered β-Si3N4-SiO2 glass-ceramics for biomedical applications
ZHOU H. 1,2, PERSSON C. 2, ENGQVIST H. 1, XIA W. 1
1 Division of Applied Materials Science, Department of Materials Science and Engineering, Uppsala University, Uppsala, Sweden; 2 Division of Biomedical Engineering, Department of Materials Science and Engineering, Uppsala University, Uppsala, Sweden
Introduction
Since glass-ceramics were discovered accidentally in 1953, this material has attracted great attention [1]. Glass-ceramics are prepared by controlling the crystallization of the glass phase through thermal treatments, enabling them to be tailored for specific applications. Recently, we developed a ZrO2-SiO2 glass-ceramic, in which the ZrO2 crystalline phase is embedded in the glassy SiO2 phase [1]. This glass-ceramic has a high strength of up to 1000 MPa while retaining a high translucency, showing great potential for certain biomedical applications. Silicon nitride (Si3N4), on the other hand, is another attractive candidate for biomedical applications due to its high mechanical properties, superior wear resistance, and particularly, biological properties (such as antibacterial properties and biocompatibility) [2]. Thus, with the aim of combining the advantages of glass ceramics and silicon nitride, in this study, a new Si3N4-SiO2 glass-ceramic was prepared through spark plasma sintering. Different compositions containing different percentages of the Si3N4 crystalline phase were prepared, and the effect of Si3N4 content on the microstructure, mechanical and antibacterial properties were investigated.
Experimental methods
The raw SiO2 powers were prepared by a sol-gel method using tetraethyl orthosilicate (Sigma-Aldrich, St Louis, MO, USA) as starting precursor. Then, the SiO2 powders and β-Si3N4 powders (US Research Nanomaterials, Inc, USA) were mixed by planetary ball milling for 1.5 h using ethanol as solvent. Three compositions in x % Si3N4 – (100-x) %SiO2 (x=30wt%, 50wt% and 70wt%) were prepared, denoted as 30SiN, 50SiN and 70SiN, respectively. After that, the raw powders were sintered using the spark plasma sintering technique (SPS 825, Fuji Electronic Industrial Co., Ltd, Japan). Finally, the samples were polished and characterized by XRD, SEM, nanoindenter and piston-on-three-ball test.
Results and discussion
The XRD results showed that the powder was mainly composed of β-Si3N4 as the crystalline phase (ICDD: 96-210-2551). A small diffraction peak attributed to SiO2 (ICDD: 96-412-4029) was found at around 30.5?. The degree of peak broadening increased with increasing SiO2 content, which is due to the increasing amount of amorphous phase. Sample 70SiN exhibited the highest flexural strength, while the 30SiN samples showed the lowest, as expected. The fracture surface was analysed by SEM, and the results showed a higher number of pores in the 70SiN than the 30SiN samples, indicating that the higher amount of glassy phase could promote densification. The 70 SiN samples also exhibited the highest hardness and elastic modulus compared to the other two groups. The mechanical properties are comparable to other commercial glass-ceramics [1].
Conclusion
Si3N4-SiO2 glass-ceramics with different Si3N4 crystalline content were successfully prepared and sintered by SPS. The mechanical strength is promising compared to the commercial glass ceramics, and could be further improved in the next step. Considering the unique properties of silicon nitride, the Si3N4-SiO2 glass ceramic could give benefits in biomedical applications.
References
[1] Fu, L., et al. (2020). Materials, 13(5), p.1049.
[2] Bal, B.S., et al. (2012). Acta biomaterialia, 8(8), pp.2889-2898.
Acknowledgements
This research received support from the European Union’s Horizon 2020 (No 812765), Swedish Research Council (VR, 2020-04341) and Myfab Uppsala.