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| 2. |
- Fu, Le, et al.
(författare)
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Doping of tantalum, niobium, and hafnium in a translucent ZrO2-SiO2 nanocrystalline glass-ceramic
- 2022
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Ingår i: Journal of the European Ceramic Society. - : Elsevier. - 0955-2219 .- 1873-619X. ; 42:4, s. 1731-1742
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Tidskriftsartikel (refereegranskat)abstract
- The addition of dopant(s) is an effective strategy to regulate the microstructure and properties of ZrO2-based ceramics. In this study, we investigated the effects of ternary element alloying, namely tantalum (Ta), niobium (Nb), and hafnium (Hf) elements, on the microstructure and transformability of ZrO2 nanocrystallites in a ZrO2SiO2 nanocrystalline glass-ceramic (NCGC) during sintering and thermal treatments. The ternary dopants enhanced the transformability of tetragonal ZrO2 (t-ZrO2) nanocrystallites during sintering, i.e., the dopants acted as t-ZrO2 destabilizer. The Ta, Nb and Hf elements dissolved in ZrO2 nanocrystallites, forming ZrO2 solid solution. Meanwhile, lamella nanotwins were formed within many ZrO2 nanocrystallites. No obvious segregation of dopants was detected at ZrO2 grain boundaries. t-ZrO2 and monoclinic (m) ZrO2 nanocrystallites were metastable in thermal treatments process, with "t" to "m" and the reverse "m" to "t" polymorphic transformation occurred simultaneously. Meanwhile, t-ZrO2 and m-ZrO2 nanocrystallites had a great tendency to grow larger during thermal treatments.
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| 3. |
- Fu, Le, et al.
(författare)
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Liquid-phase sintering of ZrO2-based nanocrystalline glass-ceramics achieved by multielement co-doping
- 2023
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Ingår i: Journal of The American Ceramic Society. - : John Wiley & Sons. - 0002-7820 .- 1551-2916. ; 106:4, s. 2702-2715
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Tidskriftsartikel (refereegranskat)abstract
- Liquid-phase sintering (LPS) is an effective pathway to assist the densification of ceramics. However, it has seldom been used to densify glass-ceramics. In the present study, a multielement co-doping strategy has been utilized to achieve LPS of a ZrO2-SiO2 nanocrystalline glass-ceramic. Compared with undoped samples densified by solid-state sintering, doping of equimolar Al, Y, and Ca promoted the densification of the glass-ceramic at lower temperatures with a faster densification rate. Ternary doping enhanced coarsening of ZrO2 nanocrystallites during sintering and annealing. The distribution of dopants was carefully observed with X-ray energy-dispersive spectrometry technique in scanning electron transmission microscopy mode. Results showed that the three dopants showed different distribution behaviors. After sintering, Y dopants were predominately distributed in ZrO2 nanocrystallites, whereas parts of Al and Ca dopants were distributed in ZrO2 nanocrystallites and part of them co-segregated at the ZrO2/SiO2 heterointerfaces. Meanwhile, the segregation of Ca dopant at some intergranular films among ZrO2 nanocrystallites was observed. Redistribution of dopants did not occur during annealing.
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| 4. |
- Fu, Le, et al.
(författare)
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Size-driven phase transformation and microstructure evolution of ZrO2 nanocrystallites associated with thermal treatments
- 2021
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Ingår i: Journal of the European Ceramic Society. - : Elsevier. - 0955-2219 .- 1873-619X. ; 41:11, s. 5624-5633
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Tidskriftsartikel (refereegranskat)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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| 5. |
- Fu, Le, et al.
(författare)
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Structural integrity and damage of glass-ceramics after He ion irradiation : Insights from ZrO2-SiO2 nanocrystalline glass-ceramics
- 2023
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Ingår i: Journal of the European Ceramic Society. - : Elsevier. - 0955-2219 .- 1873-619X. ; 43:6, s. 2624-2633
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Tidskriftsartikel (refereegranskat)abstract
- Developing new radiation-resistant materials and understanding the structural damages caused by radiation are persistent goals of material scientists. Here, we report on the structural integrity and damage to ZrO2-SiO2 nanocrystalline glass-ceramics after radiation with 1.4 MeV He ions at three different fluences: 1.0 x 1016 ions/ cm2 (low), 5.0 x 1016 ions/cm2 (moderate), and 1.0 x 1017 ions/cm2 (high) at 500 degrees C. Grazing incident X-ray diffraction shows the tetragonal-ZrO2 to monoclinic-ZrO2 phase transformation induced by microstrain from the irradiation. The addition of yttrium indicated tetragonal-ZrO2 stabilization effect during irradiation. The irra-diated glass-ceramics show a Raman signal-enhancement effect probably related to the electronic structure changes of the amorphous SiO2 component in the glass-ceramics. The formation of microcracks and lattice de-fects within ZrO2 nanocrystallites is the main structural damage caused by irradiation. There was no observable amorphization of ZrO2 nanocrystallites due to irradiation. No obvious He bubbles were detected, either. The formation of microcracks results in a decrease of in the nanohardness of the glass-ceramics. The results provide fundamental experimental data to understand the structural integrity and damage caused by radiation, which could be useful to design radiation-resistant nanocrystalline glass-ceramics for extremely radioactive environments.
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| 6. |
- Fu, Le, et al.
(författare)
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Understanding microstructure-mechanical properties relationship in ZrO2-SiO2 nanocrystalline glass-ceramics : The effect of ZrO2 content
- 2022
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Ingår i: Materials Science & Engineering. - : Elsevier. - 0921-5093 .- 1873-4936. ; 840
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Tidskriftsartikel (refereegranskat)abstract
- The content of crystalline phase plays a significant role in manipulating the microstructure and mechanical properties of glass-ceramics. This study aims at exploring the optimum content of crystalline phase in ZrO2-SiO2 nanocrystalline glass-ceramics (NCGCs) in terms of obtaining the highest mechanical properties. To this end, the mechanical properties of ZrO2-SiO2 NCGCs with 70 mol%, 75 mol%, 80 mol% ZrO2 were tested and compared with those of the previously prepared NCGCs with ZrO2 content ranging from 35 mol% to 65 mol%. Results showed that 65 mol% was the optimum content of ZrO2 in terms of obtaining the highest flexural strength. The flexural strength of NCGCs with ZrO2 content over 65 mol% was lower than that of the NCGCs with 65 mol% ZrO2. This was because the NCGC with 65 mol% ZrO2 had a homogenous microstructure, with ZrO2 nano crystallites homogeneously distributed in an amorphous SiO2 matrix. Whereas, when ZrO2 content was increased to 75 mol%, ZrO2 nanocrystallites were not homogeneously distributed in the SiO2 matrix anymore. The formation of SiO2 "holes/canyon " due to ZrO2 grain coalescence resulted in the decrease of flexural strength. The fracture mechanism and wear properties of the NCGCs were also investigated.
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| 7. |
- Li, Bo, et al.
(författare)
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Fabrication and characterization of bioactive zirconia-based nanocrystalline glass-ceramics for dental abutment
- 2021
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Ingår i: Ceramics International. - : Elsevier. - 0272-8842 .- 1873-3956. ; 47:19, s. 26877-26890
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Tidskriftsartikel (refereegranskat)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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| 8. |
- Wang, Bohan, et al.
(författare)
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Effects of dopants with various valences on densification behavior and phase composition of a ZrO2-SiO2 nanocrystalline glass-ceramic
- 2022
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Ingår i: Ceramics International. - : Elsevier. - 0272-8842 .- 1873-3956. ; 48:7, s. 9495-9505
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Tidskriftsartikel (refereegranskat)abstract
- Effects of dopants with different valences on the densification behavior and phase composition of a ZrO2-SiO2 nanocrystalline glass-ceramic (NCGC) during pressureless sintering were investigated in this study. The raw powder of Ca2+, La3+, Ce4+ and Ta5+ ions doped ZrO2-SiO2 (referred to as Ca-ZS, La-ZS, Ce-ZS, Ta-ZS, respectively) and pure ZrO2-SiO2 (PZS) sample were synthesized by sol-gel method, followed by pressureless sintering. Compared with the PZS sample, doping of Ca2+ and La3+ ions significantly promoted the densification of the NCGCs. The "densification promotion " effect was attributed to the formation of oxygen vacancies and the decrease of SiO2 viscosity due to doping of aliovalent cations. The dopants with various valences showed significant effects on the phase compositions of the NCGCs during sintering. Doping of Ca2+ ion accelerated the reaction kinetics between ZrO2 nanocrystallites and amorphous SiO2 to yield ZrSiO4. The La3+ ion acted as destabilizer of t-ZrO2, which resulted in a rapid tetragonal (t) to monoclinic (m) ZrO2 phase transformation during sintering, while in the Ta5+ and Ce4+ ions doped sample, the phase transformation occurred gradually. All the doping ions increased the lattice parameters and the volume of t-ZrO2 unit cell, while the effects of the doping ions on the lattice parameters of m-ZrO2 unit cell were more complex.
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| 9. |
- Wang, Bohan, et al.
(författare)
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Low-temperature and flexible strategy to in-situ fabricate ZrSiO4-based ceramic composites via doping and tuning solid-state reaction
- 2023
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Ingår i: JOURNAL OF ADVANCED CERAMICS. - : Tsinghua University Press. - 2226-4108 .- 2227-8508. ; 12:6, s. 1238-1257
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Tidskriftsartikel (refereegranskat)abstract
- Synthetic zircon (ZrSiO4) ceramics are typically fabricated at elevated temperatures (over 1500 degrees C), which would lead to high manufacturing cost. Meanwhile, reports about preparing ZrSiO4-based ceramic composites via controlling the solid-state reaction between zirconia (ZrO2) and silica (SiO2) are limited. In this work, we proposed a low-temperature strategy to flexibly design and fabricate ZrSiO4-based ceramic composites via doping and tuning the solid-state reaction. Two ceramic composites and ZrSiO4 ceramics were in-situ prepared by reactive fast hot pressing (FHP) at approximately 1250 degrees C based on the proposed strategy, i.e., a ZrSiO4-SiO2 dual-phase composite with bicontinuous interpenetrating and hierarchical microstructures, a ZrSiO4-ZrO2 dual-phase composite with a microstructure of ZrO2 submicron- and nano-particles embedded in a micron ZrSiO4 matrix, and ZrSiO4 ceramics with a small amount of residual ZrO2 nanoparticles. The results showed that the phase compositions, microstructure configurations, mechanical properties, and wear resistance of the materials can be flexibly regulated by the proposed strategy. Hence, ZrSiO4-based ceramic composites with different properties can be easily fabricated based on different application scenarios. These findings would offer useful guidance for researchers to flexibly fabricate ZrSiO4-based ceramic composites at low temperatures and tailor their microstructures and properties through doping and tuning the solid-state reaction.
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