| 1. |
- Fu, Le, et al.
(author)
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Size-driven phase transformation and microstructure evolution of ZrO2 nanocrystallites associated with thermal treatments
- 2021
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In: Journal of the European Ceramic Society. - : Elsevier. - 0955-2219 .- 1873-619X. ; 41:11, s. 5624-5633
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Journal article (peer-reviewed)abstract
- Thermal stability of nanocrystallites plays an important role in the manufacturing and application of nanocrystalline ceramics/glass-ceramics. This study explores the effects of thermal treatments on the microstructures of two ZrO2-SiO2 nanocrystalline glass-ceramics (NCGCs), an undoped one and a yttria-doped one. The two assintered NCGCs were composed of tetragonal (t) and monoclinic (m) ZrO2 nanocrystallites, and SiO2 component was amorphous. t-ZrO2 and m-ZrO2 nanocrystallites were metastable during thermal treatment. The content of m-ZrO2 in the undoped ZrO2-SiO2 NCGC first increased after thermal treating at 850 degrees C for 5 h, then decreased after thermal treating at and above 950 degrees C. After thermal treating at 1250 degrees C for 5 h, t-ZrO2 nanocrystallites experienced a rapid phase transformation during cooling, resulting the formation of 88.6 vol% m-ZrO2. Sizedriven phase transformation was utilized to explain the metastability of t-ZrO2 and m-ZrO2 nanocrystallites. In contrast, the content of m-ZrO2 in the yttria-doped ZrO2-SiO2 NCGC continuously decreased with the increase of thermal treatment temperature. The addition of yttria improved the phase stability of t-ZrO2 up to at least 1250 degrees C. Crystallite size of both t-ZrO2 and m-ZrO2 nanocrystallites increased with the increase of thermal treatment temperature in the two NCGCs. The presence of residual thermal stress in the as-sintered NCGCs changed the lattice spacing of t-ZrO2 and m-ZrO2 nanocrystallites, and the stress can be released after thermal treatment. Thermal treatment exerts significant influences on the microstructure of ZrO2-SiO2 NCGCs.
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| 2. |
- Li, Bo, et al.
(author)
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Fabrication and characterization of bioactive zirconia-based nanocrystalline glass-ceramics for dental abutment
- 2021
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In: Ceramics International. - : Elsevier. - 0272-8842 .- 1873-3956. ; 47:19, s. 26877-26890
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Journal article (peer-reviewed)abstract
- Zirconia-based ceramics are becoming a popular biomaterial in dental implantology due to their natural silver-white color, excellent mechanical properties, and good biocompatibility. However, zirconia-based ceramics are biologically inert, which limits their ability to integrate with the surrounding human tissues. To solve this problem, the bioactive elements of calcium (Ca) and phosphorus (P) were doped in high-strength ZrO2-SiO2 nanocrystalline glass-ceramics (NCGCs) to overcome the biological inertness of ZrO2-based ceramics. XRD results showed that tetragonal zirconia (t-ZrO2) and monoclinic zirconia (m-ZrO2) were the only two crystalline phases after spark plasma sintering. Ca and P dopants acted as destabilizer of t-ZrO2, enhancing its transformability to m-ZrO2 during sintering. The amount of t-ZrO2 exerted significant effects on the average flexural strength of the NCGCs. The NCGC with 45 mol% ZrO2 were composed of 64.5 vol% t-ZrO2 and 35.5 vol% m-ZrO2 after sintering at 1230 degrees C. And, the average flexural strength and Vickers hardness of the NCGC was 615 MPa and 1049 HV, respectively. In comparison, the NCGC with 65 mol% ZrO2 were composed of 12.6 vol% t-ZrO2 and 87.4 vol% m-ZrO2 after sintering at 1150 degrees C. The average flexural strength and Vickers hardness of the NCGC was 293 MPa and 839 HV, respectively. Interestingly, the NCGCs exhibited a plastic deformation behavior during flexural strength test, which was different from traditional brittle ceramics. The ion release results demonstrated that Ca2+ and Si4+ ions kept on releasing from the surface of the material. The formation of hydroxyapatite in the in-vitro apatite formation test indicated that the NCGCs had good biological activity. The doped ZrO2-based NCGCs combined moderate strength and good bioactivity. Hence, the NCGCs show promising potential to be used in sub-gingival regions, such as dental abutments.
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