Preparation And Characterization Of High-performance Li₂Si₂O₅ Whisker-reinforced Glass-ceramics

Objective:lithium disilicate（Li₂Si₂O₅）glass-ceramics have excellent mechanical and aesthetic properties,which are considered promising candidates for restorative dentistry applications.However,the inherent brittleness and low defect tolerance of Li₂Si₂O₅glass-ceramics limit their scope of clinical large-scale applications.Furthermore,most failures of Li₂Si₂O₅glass-ceramics in clinical applications were related to their low fracture toughness and high brittleness.To expand the large-scale application of Li₂Si₂O₅glass-ceramics in the field of oral prosthetics and prolong the life of restorations,it is necessary to improve the mechanical properties of Li₂Si₂O₅glass ceramics,especially the fracture toughness.In this study,Li₂Si₂O₅whiskers were creatively synthesized via a mild-condition hydrothermal reaction.Self-reinforced Li₂Si₂O₅ glass-ceramics were sintered by introducing the Li₂Si₂O₅ whiskers,and their effects on phase,microstructure,and mechanical properties were systematically studied.The crystal-growth and toughening mechanisms were also discussed.Methods:In this study,Li₂Si₂O₅whiskers were synthesized via a mild-condition hydrothermal reaction.Li₂Si₂O₅whiskers（0,1,3,and 5 wt%）were then added to the glass powders to obtain Li₂Si₂O₅glass-ceramics after reaction sintering.The phase,microstructure,and mechanical properties were analyzed by X-ray powder diffractometer,scanning electron microscope,and universal mechanical testing machine,and the effect of the content of Li₂Si₂O₅ whiskers on the properties of glass-ceramics was studied.Results:1.With an increase in the amount of Li₂Si₂O₅ whiskers,the main precipitated crystalline phase of all samples was Li₂Si₂O₅.The diffraction peak intensity of the Li₂Si₂O₅increased from LDW0 to LDW5,with a slightly shifted in diffraction peak intensity and a significantly increased crystallinity from 75.98±5.72 to 86.86±7.18%.2.The crystal sizes of the LDW0 samples were uniform,and no large crystals were found.In the LDW1,LDW3,and LDW5 samples,a bimodal crystal size distribution in which both large,elongated Li₂Si₂O₅ crystals and fine crystals existed was observed.The average length and width of the Li₂Si₂O₅ crystals increased from 1.85±0.53 to3.23±1.14μm and 0.39±0.07 to 0.66±0.2μm,respectively,moving from LDW0 to LDW5.Further,the porosity increased after first decreasing.3.With increasing Li₂Si₂O₅whisker amount,the flexural strength increased and then decreased after its peak value,increasing from 356.8±8.4 MPa for LDW1 to389.5±11.77 MPa for LDW3,then slightly decreasing for LDW5.The fracture toughness of the glass-ceramics strongly improved with the addition of the Li₂Si₂O₅whiskers,reaching a maximum(3.46±0.1 MPa·m^1/2)for the LDW5 specimens.Conclusion:In this study,we reported a simple hydrothermal approach for the synthesis of Li₂Si₂O₅ whiskers.Self-reinforced Li₂Si₂O₅ glass-ceramics were sintered by introducing the Li₂Si₂O₅ whiskers.The Li₂Si₂O₅ whiskers played an important role in inducing crystallization and improving the microstructure and properties of the glass ceramics.With increasing amounts of Li₂Si₂O₅ whiskers,the crystallinities increased slightly,and the average crystal size also increased.The microstructure was composed of crystals of bimodal size distributions,in which some large,rod-like Li₂Si₂O₅ crystals epitaxially grew along with the whiskers,and small crystals directly crystallized from the parent glass-ceramic powders.The Li₂Si₂O₅glass-ceramics exhibited high flexural strength and fracture toughness.The improved properties were attributed mainly to crack deflection and bridge-toughening mechanisms.These findings indicate that the obtained Li₂Si₂O₅glass-ceramics offer a new route for the preparation of toughened glass-ceramics.