Abstract
This study aims to investigate the diffusion stabilization process of nano-Co2O3 during the non-precursor transformation of 3Y-TZP. 3Y-TZP was set as the control group, and the experimental groups were 0.1–0.3 mol% nano-Co2O3-doped 3Y-TZP. The samples were prepared by the ball milling process, isostatic cool pressing, and sintering. All samples were hydrothermally treated at 134°C and 2 bar for different time periods. The resistance to low-temperature degradation of nano-Co2O3-doped 3Y-TZP was analyzed by X-ray diffraction. The microstructure of zirconia ceramic samples was determined by scanning electron microscopy, transmission electron microscopy, atomic force microscopy, and electron paramagnetic resonance studies. The addition of nano-Co2O3 into 3Y-TZP resulted in higher hydrothermal aging resistance than 3Y-TZP. The addition of 0.2 mol% nano-Co2O3 dopants resulted in the highest hydrothermal aging resistance among nano-Co2O3-doped 3Y-TZP ceramics. The grain sizes of 3Y-0.2Co are smaller than those in the control group. With the increase of cobaltous oxide doping contents, the segregation of Co3+ ions at the crystal boundary increased. The content of oxygen vacancies on the surface of the sample increased with the increase of the Co2O3 doping content. The oxygen vacancy concentrations of 3Y-0.2Co increased obviously after aging. 3Y-0.1Co, 3Y-0.3Co, and the control showed decreased oxygen vacancy concentrations after aging. Trivalent element doping of 3Y-TZP effectively improved the aging resistance of 3Y-TZP. The addition of 0.2 mol% nano-Co2O3 resulted in the highest hydrothermal aging resistance. Improved aging resistance is attributed to the nano-Co2O3 doping resulting in the 3Y-TZP grain size inhibition, grain boundary segregation of cobalt ions, and oxygen vacancy maintenance. This work is expected to provide an effective reference for the development and application of budget dental materials by regulating grain boundary engineering.
1 Introduction
3Y-TZP (3% yttria-stabilized tetragonal polycrystalline) has a high fracture toughness and strength and is widely used for hip prostheses ball-heads, dental implants, and dental prostheses [1–3]. However, when subjected to a humid and complex internal environment for an extended period, their surface will spontaneously transform into the martensitic phase [4,5]. The transformation of the tetragonal phase (t) to the monoclinic phase (m) will lead to surface microcracking and water molecules passing through these cracks and then penetrating the material, which leads to an obvious decrease in the mechanical properties of 3Y-TZP. This phenomenon is known as low-temperature degradation (LTD). The clinical survival rate of 3Y-TZP can thus be inevitably impacted in aqueous environments. For instance, hundreds of 3Y-TZP total hip prostheses ball-heads were reported to have failed between 1999 and 2000, which directly resulted in their withdrawal from the market [6,7]. Hydrothermal aging is a progressive process induced by water molecule invasion, starting from the surface and propagating into the ceramic component, leading to microcracking and surface roughening [8,9].
Studies showed that doping of lower-valence oxides, such as Al2O3 and Co2O3, in 3Y-TZP is an effective method to improve its LTD performance since the doping of lower-valence oxides can stabilize zirconia in the cubic or tetragonal crystal structure [10,11]. Studies showed that doping of 3Y-TZP with a small amount of trivalent ions, e.g., Al3+, Fe3+, Pr3+, Bi3+, and La3+, provides an adequate balance between aging resistance, mechanical properties, as well as aesthetics, i.e., color and translucency [12–14].
Trivalent cations that segregate at the zirconia grain boundary can effectively retard the aging rate of 3Y-TZP ceramics without sacrificing the excellent mechanical properties [13]. The law of cation segregation at the boundary and its influence on the LTD effect of 3Y-TZP doped with trivalent cations of large radii, i.e., Sc3+, Nd3+, and La3+ have been primarily explored [15]. However, there is no data available for the hydrothermal aging behavior and the underlying mechanism for Co3+-doped 3Y-TZP. The large radii mismatch between the dopants and host cations is acknowledged as an essential driving force for the segregation at the grain boundary [13]. Since the mismatch between Co3+ (54.5 pm) and Zr4+ (84.0 pm) is large, Co3+ is expected to segregate obviously at the grain boundary which decrease the LTD susceptibility of 3Y-TZP ceramics. At the same time, Co2O3 is widely used as a colorant for clinically used dental 3-YTZP ceramics.
Moreover, from the perspective of the hydrothermal aging mechanism, the behavior of oxygen vacancies in 3Y-TZP ceramics should be evaluated to explain the varied hydrothermal aging kinetics. Although the mechanism of hydrothermal aging has not been completely recovered, studies showed that rapid annihilation of surface oxygen vacancies largely contributes to the hydrothermal aging of zirconia ceramics [16,17]. Reportedly, the oxygen vacancies adjacent to the Zr4+ ions might be a stabilizer for ZrO2 of the tetragonal phase [18]. Additionally, it was shown that the activation energy of the aging kinetics (73–106 kJ·mol−1) was comparable to that of ionic conductivity of 3Y-TZP ceramics below 500°C (88–89 kJ·mol−1) [19]. Thus, it is commonly believed that the diffusion of water-derived species into the lattice of 3Y-TZP ceramics and the filling of oxygen vacancies (Vo) contributes to the aging process of 3Y-TZP ceramics [20].
Therefore, this study investigated the effect of the trivalent dopant’s ionic radius on the LTD behavior in 3Y-TZP ceramics to understand the diffusion stabilization process of Co2O3 during the non-precursor transformation of 3Y-TZP. The hydrothermal aging kinetics of 3Y-TZP ceramics with a nano-Co2O3 dopant concentration of 0.1–0.3 mol% were studied since the concentration of dopant also has a crucial influence on the aging kinetics of 3Y-TZP.
2 Materials and methods
2.1 Preparation of samples
The 3 mol% yttria-stabilized zirconia nanosized powder (3Y-TZP, TZ-3Y, purity > 99.9%, Tosoh, Japan) with approximately 0.1 wt% of additives, including SiO2, Fe2O3, NaO2 and Al2O3 was used. The specific surface area of 3Y-TZP ceramics is 16 ± 3 m2·g−1 and the mean particle diameter is 0.6 μm. The 3Y-TZP ceramic powders were mixed with nano-Co2O3 powders (purity > 99.999%, Aladdin) at concentrations of 0.1, 0.2, and 0.3 mol%, respectively. The mixed powders were added with ethanol as the mixing medium and were then milled in a Teflon jar for 24 h with 5 and 1 mm zirconia milling balls. Milled powders were dried in an oven to obtain 3Y-xCo powders at 80°C for 8 h and then cold isostatically pressed at 250 MPa for 2 min and pressure-less sintered in air at 1,450°C for 2 h. The constant heating and cooling rates were set as 3 and 10°C·min−1, respectively. The sample blocks (40 × 40 × 3 mm) were then cut into 36 × 4 × 3 mm rods and then ground orderly with SiC papers of 120, 240, 600, 800, 1,200, 2,000, 3,000, 4,000, and 5,000 grades, and polished with 1 and 0.05 μm diamond pastes to obtain an optically reflective surface subsequently.
2.2 Assessment of aging kinetics
Polished samples (n = 3) of each group were tested for LTD in deionized water for 10, 15, 20, and 30 h at 134°C and under a pressure of 2 bar in an autoclave. The amount of transformation in all specimens was measured by X-ray diffraction (XRD, Japan Smartlab) using Cu-Kα radiation at 40 kV and 40 mA, a scan range of 20°–80° (2θ), with a step size of 0.02 s−1. Fractions of m-ZrO2 and t-ZrO2 were measured by the diffraction patterns in accordance with the method used by Garvie [21] and modified by Toraya [22]:
where X m is the relative amount of the monoclinic phase, and I m and I t are the intensities of the monoclinic and tetragonal peaks, respectively.
2.3 Microstructure of samples
The density of the eventual samples was tested in deionized water according to Archimedes’ principle. The grain size distributions were obtained on polished surfaces after thermal etching at 1,350°C for 20 min. At least 1,000 grains were counted with NANO MEASURER 1.2.5 software, and the results were reported as average results (±standard deviation). The distribution of dopant cations (Co3+ and Y3+) near the grain boundaries was analyzed by scanning transmission electron microscopy (STEM, FEI Talos F200X, America), energy-dispersive X-ray spectroscopy (EDS), and high-angle annular dark-field detector in thin foils. ESR (ES-FA200, JEOL, Japan) was used to quantitatively detect the oxygen vacancies. Surface topography and roughness were determined using atomic force microscopy (AFM, MFP-3D-S, Asylum Research, USA). Electron paramagnetic resonance (EPR) measurements were recorded with an X-band CW-EPR Bruker EMX with a 100 kHz modulation frequency and a microwave power of 1 mW.
2.4 Characterization of mechanical properties
According to ISO 6872 [23], blocks were cut into 36 × 4 × 3 mm3 test bars (n = 5) and the three-point bending strength was tested:
where F represents the maximum load, L represents the space of fixtures, b is the sample’s width, and d is the sample’s thickness.
The fracture toughness and Vickers hardness [24,25] were tested by micro-indentation. The indentations were fabricated on the surfaces of samples of different compositions at 98.1 N, and the expected cracks originated at the corners of the indentation after loading. Indentations were imaged by scanning electron microscopy (SEM). The fracture toughness of apparent indentation was analyzed using the equation proposed by Niihara et al. [26].
2.5 Cell culture and cytotoxicity tests
Human oral epithelial cells (HOECs) were chosen to conduct the cytotoxicity experiments of doped 3Y-TZP. HOECs were cultured in Dulbecco’s modified Eagle’s medium containing 10% (v/v) heat-inactivated fetal bovine serum and antibiotics (100 μg·mL−1 streptomycin and 100 IU·mL−1 penicillin) for 24 h at 37°C in a humidified atmosphere with 5% CO2. Cells were seeded on each test substrate at 1 × 105 cells·mL−1 in the same media for all assays. Untreated HOECs were set as control. The CCK-8 assay kit (Sangon Biotech, China) was used for the evaluation of cytotoxicity according to the manufacturer’s instructions. About 10 μL of CCK-8 solution was added to each well. The plate was then incubated for 1 h at 37°C, and the optical density at 450 nm was measured with a plate spectrophotometer (NanoDrop ND-1000, Thermo Scientific, Waltham, MA, USA). Measurements were made in triplicate for each sample and the mean values were recorded.
2.6 Statistical analysis
One-way analysis of variance with Tukey’s post hoc test and Tukey’s multiple comparisons test were employed in the statistical analysis. GraphPad Prism 8 software was employed in the analysis, where α was set to 0.05. Mean values plus standard deviations are presented in the results, and different letters in the figures show statistical significance.
3 Results and discussion
3.1 Phase analysis
Figure 1a shows that before aging all samples consisted of ZrO2 of tetragonal phase regardless of doping of Co2O3. Figure 1a shows the characteristics tetragonal peak (I m (111)) at 2θ values of 30.2° regardless of the amount of Co2O3 dopants (see XRD analysis in Figure 1a). This revealed that doping of Co2O3 in 3Y-TZP ceramics did not bring impurity and a second phase. After hydrothermal degradation for 20 h (Figure 1b and c), the control showed the highest monolithic peak (I m (111)) and 3Y-0.2Co showed the lowest monolithic peak (I m (111)) at 2θ values of 28.2°. Moreover, the 3Y-0.2Co samples showed the lowest monoclinic phase content than 3Y-0.1Co, 3Y-0.3Co, and the control group from 0 to 20 h in steam.
XRD diffraction patterns and the monoclinic phase content of Co2O3-doped 3Y-TZP before and after hydrothermal degradation. (a) XRD diffraction patterns of 3Y-xCo (x = 0, 0.1, 0.2, 0.3 mol%) before aging. (b) XRD patterns of 3Y-xCo (x = 0, 0.1, 0.2, 0.3 mol%) after aging. (c) Monoclinic phase content of 3Y-xCo (x = 0, 0.1, 0.2, 0.3 mol%) after aging.
3.2 Microstructure observation
A density of ≥6.00 g·cm−3 is required for the application of 3Y-TZP ceramics as a load-bearing biomaterial [27]. The densification of doped 3Y-TZP ceramics is a challenge as proved by studies that the addition of dopants such as La2O3 and Al2O3 significantly decreased the densification of 3Y-TZP ceramics [13]. However, the grain size of 3Y-xCo (x = 0.1, 0.2, 0.3 mol%) is smaller than the control group (P < 0.05), indicating that doping of Co2O3 suppresses the grain growth. Densified surfaces with clear grain boundaries were also observed by SEM for sintered 3Y-TZP ceramics doped with Co2O3 that can be parallel to the 3Y-TZP ceramics (Figure 2). 3Y-xCo (x = 0.1, 0.2, 0.3 mol%) showed no statistically significant difference among the results of each group (P > 0.05). This verified that the dopants have a pinning effect at the grain boundary, thereby retarding the grain boundary mobility that can enhance the densification of 3Y-TZP and reduce the accumulation of water grain boundary [28]. Thus, Co2O3-doped 3Y-TZP ceramics are expected to exhibit higher mechanical strength for their densified surface structure and decreased grain size.
Microstructure observation of Co2O3-doped 3Y-TZP. (a–d) SEM patterns of 3Y-xCo (x = 0, 0.1, 0.2, 0.3 mol%). (e and f) Grain size distribution of 3Y-xCo (x = 0, 0.1, 0.2, 0.3 mol%). AFM (e) and HR-TEM (f) images of the surface and internal microscopic changes in crystals after hydrothermal degradation of 3Y-TZP-xCo (x = 0, 0.1, 0.2, 0.3 mol%).
AFM images after hydrothermal degradation of 3Y-TZP-0.2Co (Figure 3a) showed that the phase transition from the tetragonal phase to the monoclinic phase of the first single grain on the surface triggered the phase transition of the adjacent grain, which eventually resulted in grain agglomerates and surface roughening. The surface of 3Y-TZP-0.2Co became rough with the vertical heights ranging from 7.6 to 23.2 nm 5 h after aging. Transmission electron microscopy (TEM) images of internal microscopic changes of crystals after hydrothermal degradation of 3Y-0.2Co (Figure 3b) revealed the presence of microcracks and intergranular fractures. The intergranular cracking accompanying the hydrothermal aging [12,27] clearly indicated the weakness of the grain boundary. Reportedly, after hydrothermal aging, the reduction of the ionic conductivity in the grain boundary region was more severe than the reduction in the bulk area [29], revealing that grain boundary regions are active sites for hydrothermal aging.
Grain boundary structure of Co2O3-doped 3Y-TZP before hydrothermal degradation. (a) TEM observation of the grain boundary and EDS mapping of chemical ion distribution across the grain boundaries of 3Y-0.1Co. (b) TEM observation of the grain boundary and EDS mapping of chemical ion distribution across the grain boundaries of 3Y-0.2Co. (c) TEM observation of the grain boundary and EDS mapping of chemical ion distribution across the grain boundaries of 3Y-0.3Co.
3.3 Grain boundary segregation analysis
TEM and EDS energy spectrum mapping of 3Y-TZP-doped Co2O3 (Figures 3 and 4) showed Co3+ ions segregated at the grain boundaries, while Y3+ ions are evenly distributed at the grain boundaries both before and after aging degradation. Zr4+ and O2+ ions showed no segregation at the grain boundaries before aging. With the increase of doping of the Co2O3 content, the segregation of Co3+ ions increased. The concentration of segregated Co3+ ions was 1.2% for 3Y-0.1Co, 1.6% for 3Y-0.2Co, and 2.0% for 3Y-0.3Co after aging degradation (Figure 4). The mismatch in the cation size between Co3+ (54.5 pm) and Zr4+ ions (84.0 pm) is larger than that between Y3+ (90.0 pm) and Zr4+ ions, thus resulting in stronger grain boundary segregation behavior of Co2O3-doped 3Y-TZP ceramics than 3Y-TZP [30]. Increased tetravalent element grain boundary segregation can strengthen the grain boundaries and inhibit the diffusion of water molecules, therefore leading to excellent aging resistance of Co2O3-doped 3Y-TZP ceramics. The ideal amount of dopant concentrations should be the maximum amount that can be dissolved at the zirconia grain boundaries after cooling without introducing a secondary phase. However, in this study, 3Y-0.2Co showed superior anti-aging behavior than 3Y-0.3Co. This can be explained as follows: the lattice parameters and constituent phases of the remaining ZrO2 of the tetragonal phase also have a critical influence on the aging resistance of the 3Y-TZP ceramics added with dopants [17].
Grain boundary structure of Co2O3-doped 3Y-TZP after hydrothermal degradation. (a) EDS mapping and Y3+ distribution across the grain boundaries of 3Y-xCo (x = 0, 0.1, 0.2, 0.3 mol%). (b) EDS mapping and corresponding chemical compositions of Co3+ across the grain boundaries of 3Y-xCo (x = 0, 0.1, 0.2, 0.3 mol%). (c) Percentage of deviated atoms of Co3+ ions before and after hydrothermal degradation of 3Y-xCo (x = 0, 0.1, 0.2, 0.3 mol%).
3.4 Oxygen vacancy analysis
EPR results (Figure 5) showed that the oxygen vacancy concentrations of 3Y-0.2Co increased obviously after aging. 3Y-0.1Co, 3Y-0.3Co, and the control showed decreased oxygen vacancy concentrations after aging. Previous studies have shown that rapid annihilation of surface oxygen vacancies is the main mechanism of hydrothermal aging degradation of zirconia ceramics [16,17]. Further study (Figure 5) showed that the content of oxygen vacancies on the surface of the sample varies with the increase of the Co2O3 doping content and further verified that changes in oxygen vacancy of 3Y-TZP samples resulted from doping of Co2O3. This result is in accordance with previous studies that the doping of oxide of low valence states (divalent and trivalent cations) can maintain oxygen vacancies of 3Y-TZP ceramics [31] since the segregated cations can bind to the oxygen vacancies at the grain boundary and obviously interrupt the annihilation of oxygen vacancies [13]. The filling of oxygen vacancies by “water-derived species” at the grain boundary is found to induce the hydrothermal aging of 3Y-TZP ceramics [20]. Thus, the oxygen vacancy concentration has a direct influence on the aging kinetics of 3Y-TZP ceramics for the ionic resistivity and is given by[32]
Oxygen vacancy characterization of Co2O3-doped 3Y-TZP before and after hydrothermal degradation (EPR measurements were recorded with an X-band CW-EPR Bruker EMX with a 100 kHz modulation frequency and a microwave power of 1 mW). (a) Change in the oxygen vacancy content for 3Y-xCo (x = 0, 0.1, 0.2, 0.3 mol%) before and after hydrothermal degradation. (b) Characterization of oxygen vacancy of 3Y-xCo (x = 0, 0.1, 0.2, 0.3 mol%) after hydrothermal degradation.
Here, μ is the mobility of the oxygen vacancy, [Vo¨] is the oxygen vacancy concentration and F is the Faraday constant. A higher concentration of oxygen vacancies at the grain boundary leads to a higher aging resistance of 3Y-TZP ceramics. Moreover, smaller undersized dopant cations (such as Al3+ and Co3+) retard the aging process well due to their stronger bonding of the oxygen vacancy [13,33]. Thus, maintaining the oxygen vacancy induced by doping of Co2O3 improved the aging resistance of 3Y-TZP ceramics. The highest aging resistance of 3Y-0.2Co among all tested samples is mainly attributed to their maintained oxygen vacancy concentrations.
Based on the above results, improved aging resistance is attributed to tCo2O3 doping resulting in 3Y-TZP grain size inhibition, grain boundary segregation of Co3+ irons, and oxygen vacancy maintenance. Not only the type of dopant but also the amount of dopant was crucial for designing aging-resistant 3Y-TZP ceramics. The hydrothermal aging behavior suggested that 3Y-0.2Co displayed greater aging resistance than 3Y-0.1Co, 3Y-0.3Co, and the control group, which corresponded to 0–60 years in the human body [34].
3.5 Mechanical properties
Currently, maintaining the mechanical strength of 3Y-TZP ceramics after adding cation dopants is a challenge. For instance, a previous study confirmed the addition of 3Y-TZP ceramics with a small amount of La3+ dopants to statistically decrease the mechanical strength of 3Y-TZP ceramics [35], although it improved the aesthetic appearance for dental applications. However, the three-point bending strength, the fracture toughness and Vickers hardness (Figure 6a–c) were not significantly different for 3Y-0.2Co and the control (P < 0.05) both before and after aging, indicating that the addition of Co cation dopants into 3Y-TZP did not decrease the mechanical strength of 3Y-TZP both before and after aging.
Mechanical properties and biocompatibility of 3Y-0.2Co before and after hydrothermal degradation. (a) Three-point bending strength of 3Y-0.2Co; (b) the Vickers hardness of 3Y-0.2Co; (c) fracture toughness of 3Y-0.2Co; and (d) Proliferation of oral epithelial cells on 3Y-0.2Co.
3.6 Biocompatibility
CCK-8 results (Figure 6d) showed that hydrothermal aging had no impact on the cytotoxicity of 3Y-0.2Co and the control (P > 0.05). The cytotoxicity of 3Y-0.2Co and the control were not statistically different both before and after aging (P > 0.05). This revealed that the addition of trivalent cation dopants into 3Y-TZP did not decrease the biocompatibility of 3Y-TZP both before and after aging. Reportedly, Co was safe towards the normal cells [36]. Adequate Co ion release could facilitate angiogenesis [37]. Furthermore, as shown in Figures 3–5, 3Y-0.2Co composites have good phase stability, which will not accelerate the release of Co ions and cause biotoxicity.
4 Conclusion
The present investigation has shown that nano trivalent oxide (Co2O3) dopants at concentrations from 0.1 to 0.3 mol% improved the aging resistance of 3Y-TZP ceramics. The addition of 0.2 mol% of Co2O3 resulted in the highest hydrothermal aging resistance. Improved aging resistance is attributed to the Co2O3 doping resulting in 3Y-TZP grain size inhibition, grain boundary segregation of cobalt ions, and oxygen vacancy maintenance. This study provides theoretical guidance for reasonable dopant alterations and possible methods to decrease LTD susceptibility of 3Y-TZP in clinics.
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Funding information: This work was supported by the Guangdong Medical Science and Technology Research Fund Project (A2022358) and Natural Science Foundation of Guangdong Province (2019A1515010263).
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Author contributions: All authors have accepted responsibility for the entire content of this manuscript and approved its submission.
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Conflict of interest: The authors state no conflict of interest.
References
[1] Tovar-Vargas, D., B. Ferrari, A. J. Sanchez-Herencia, M. Anglada, and E. Jimenez-Pique. Low temperature degradation and mechanical properties of alumina reinforced ceria-zirconia by colloidal processing. Journal of the European Ceramic Society, Vol. 41, No. 2, 2021, pp. 1459–1470.10.1016/j.jeurceramsoc.2020.09.031Search in Google Scholar
[2] Sun, T., X. Liu, X. Zhan, L. Ou, and R. Lai. Hepatic distribution and toxicity of zirconia nanoparticles in vivo and in vitro. Process Safety and Environmental Protection, Vol. 147, 2021, pp. 134–145.10.1016/j.psep.2020.09.021Search in Google Scholar
[3] Sun, T., Y. Kang, J. Liu, Y. Zhang, L. Ou, X. Liu, et al. Nanomaterials and hepatic disease: toxicokinetics, disease types, intrinsic mechanisms, liver susceptibility, and influencing factors. Journal of nanobiotechnology, Vol. 19, No. 1, 2021, id. 108.10.1186/s12951-021-00843-2Search in Google Scholar PubMed PubMed Central
[4] Nishihara, H., M. H. Adanez, and W. Att. Current status of zirconia implants in dentistry: Preclinical tests. Journal of Prosthodontic Research, Vol. 63, No. 1, 2019, pp. 1–14.10.1016/j.jpor.2018.07.006Search in Google Scholar PubMed
[5] Sun, T., R. Liu, X. Liu, X. Feng, Y. Zhang, and R. Lai. The biocompatibility of dental graded nano-glass-zirconia material after aging. Nanoscale Research Letters, Vol. 13, No. 1, 2018, id. 61.10.1186/s11671-018-2479-4Search in Google Scholar PubMed PubMed Central
[6] Chevalier, J. What future for zirconia as a biomaterial? Biomaterials, Vol. 27, No. 4, 2006, pp. 535–543.10.1016/j.biomaterials.2005.07.034Search in Google Scholar PubMed
[7] Masonis, J. L., R. B. Bourne, M. D. Ries, R. W. McCalden, A. Salehi, and D. C. Kelman. Zirconia femoral head fractures: A clinical and retrieval analysis. The Journal of arthroplasty, Vol. 19, No. 7, 2004, pp. 898–905.10.1016/j.arth.2004.02.045Search in Google Scholar PubMed
[8] Ban, S. Chemical durability of high translucent dental zirconia. Dental materials journal, Vol. 39, No. 1, 2020, pp. 12–23.10.4012/dmj.2019-109Search in Google Scholar PubMed
[9] Badarneh, A., J. J. Eun Choi, K. Lyons, G. Porter, N. Waddell, and K. Chun Li. The effect of aging on the wear performance of monolithic zirconia. Dental Materials: Official Publication of the Academy of Dental Materials, Vol. 38, No. 5, 2022, pp. e136–e146.10.1016/j.dental.2022.04.018Search in Google Scholar PubMed
[10] Takigawa, Y., T. Shibano, Y. Kanzawa, and K. Higashi. Effect of small amount of insoluble dopant on tetragonal to monoclinic phase transformation in tetragonal zirconia polycrystal. Materials Transactions, Vol. 50, No. 5, 2009, pp. 1091–1095.10.2320/matertrans.MC200832Search in Google Scholar
[11] Kumar, C. S., R. Bauri, and G. S. Reddy. Phase stability and conductivity of rare earth co-doped nanocrystalline zirconia electrolytes for solid oxide fuel cells. Journal of Alloys and Compounds, Vol. 833, 2020, id. 155100.10.1016/j.jallcom.2020.155100Search in Google Scholar
[12] Samodurova, A., A. Kocjan, M. V. Swain, and T. Kosmač. The combined effect of alumina and silica co-doping on the ageing resistance of 3Y-TZP bioceramics. Acta Biomaterialia, Vol. 11, 2015, pp. 477–487.10.1016/j.actbio.2014.09.009Search in Google Scholar PubMed
[13] Zhang, F., K. Vanmeensel, M. Batuk, J. Hadermann, M. Inokoshi, B. Van Meerbeek, et al. Highly-translucent, strong and aging-resistant 3Y-TZP ceramics for dental restoration by grain boundary segregation. Acta Biomaterialia, Vol. 16, 2015, pp. 215–222.10.1016/j.actbio.2015.01.037Search in Google Scholar PubMed
[14] Ramesh, S., K. S. Lee, and C. Tan. A review on the hydrothermal ageing behaviour of Y-TZP ceramics. Ceramics International, Vol. 44, No. 17, 2018, pp. 20620–20634.10.1016/j.ceramint.2018.08.216Search in Google Scholar
[15] Khan, M., S. Ramesh, L. Bang, Y. Wong, S. Ubenthiran, C. Tan, et al. Effect of copper oxide and manganese oxide on properties and low temperature degradation of sintered Y-TZP ceramic. Journal of Materials Engineering and Performance, Vol. 23, No. 12, 2014, pp. 4328–4335.10.1007/s11665-014-1231-1Search in Google Scholar
[16] Pandoleon, P., E. Kontonasaki, N. Kantiranis, N. Pliatsikas, P. Patsalas, L. Papadopoulou, et al. Aging of 3Y-TZP dental zirconia and yttrium depletion. Dental Materials: Official Publication of the Academy of Dental Materials, Vol. 33, No. 11, 2017, pp. e385–e392.10.1016/j.dental.2017.07.011Search in Google Scholar PubMed
[17] Zhang, F., M. Batuk, J. Hadermann, G. Manfredi, A. Mariën, K. Vanmeensel, et al. Effect of cation dopant radius on the hydrothermal stability of tetragonal zirconia: Grain boundary segregation and oxygen vacancy annihilation. Acta Materialia, Vol. 106, 2016, pp. 48–58.10.1016/j.actamat.2015.12.051Search in Google Scholar
[18] Fabris, S., A. T. Paxton, and M. W. Finnis. A stabilization mechanism of zirconia based on oxygen vacancies only. Acta Materialia, Vol. 50, No. 20, 2002, pp. 5171–5178.10.1016/S1359-6454(02)00385-3Search in Google Scholar
[19] Fabbri, P., C. Piconi, E. Burresi, G. Magnani, F. Mazzanti, and C. Mingazzini. Lifetime estimation of a zirconia-alumina composite for biomedical applications. Dental Materials: Official Publication of the Academy of Dental Materials, Vol. 30, No. 2, 2014, pp. 138–142.10.1016/j.dental.2013.10.006Search in Google Scholar PubMed
[20] Pezzotti, G., M. C. Munisso, A. A. Porporati, and K. Lessnau. On the role of oxygen vacancies and lattice strain in the tetragonal to monoclinic transformation in alumina/zirconia composites and improved environmental stability. Biomaterials, Vol. 31, No. 27, 2010, pp. 6901–6908.10.1016/j.biomaterials.2010.05.035Search in Google Scholar PubMed
[21] de Paula Miranda, R. B., T. P. Leite, A. C. F. Pedroni, M. M. Marques, N. B. de Lima, J. Marchi, et al. Effect of titania addition and sintering temperature on the microstructure, optical, mechanical and biological properties of the Y-TZP/TiO(2) composite. Dental Materials: Official Publication of the Academy of Dental Materials, Vol. 36, No. 11, 2020, pp. 1418–1429.10.1016/j.dental.2020.08.014Search in Google Scholar PubMed
[22] Chen, T., S. Tekeli, R. P. Dillon, and M. L. Mecartney. Phase stability, microstructural evolution and room temperature mechanical properties of TiO2 doped 8 mol% Y2O3 stabilized ZrO2 (8Y-CSZ). Ceramics International, Vol. 34, No. 2, 2008, pp. 365–370.10.1016/j.ceramint.2006.10.015Search in Google Scholar
[23] Standardization IOf. ISO 6872: 2008. Dentistry: Ceramic materials. ISO Geneva; 2008.Search in Google Scholar
[24] Quinn, G. D. and R. C. Bradt. On the Vickers indentation fracture toughness test. Journal of the American Ceramic Society, Vol. 90, No. 3, 2007, pp. 673–680.10.1111/j.1551-2916.2006.01482.xSearch in Google Scholar
[25] Furtado de Mendonca, A., M. Shahmoradi, C. V. D. Gouvêa, G. M. De Souza, and A. Ellakwa. Microstructural and mechanical characterization of CAD/CAM materials for monolithic dental restorations. Journal of prosthodontics: Official Journal of the American College of Prosthodontists, Vol. 28, No. 2, 2019, pp. e587–e594.10.1111/jopr.12964Search in Google Scholar PubMed
[26] Niihara, K., R. Morena, and D. Hasselman. Evaluation of K Ic of brittle solids by the indentation method with low crack-to-indent ratios. Journal of Materials Science Letters, Vol. 1, 1982, pp. 13–16.10.1007/BF00724706Search in Google Scholar
[27] Xu, S., X. Tan, F. Liu, L. Zhang, Y. Huang, B. A. Goodman, et al. Growth and optical properties of thulia-doped cubic yttria stabilized zirconia single crystals. Ceramics International, Vol. 45, No. 13, 2019, pp. 15974–15979.10.1016/j.ceramint.2019.05.106Search in Google Scholar
[28] Hallmann, L., A. Mehl, P. Ulmer, E. Reusser, J. Stadler, R. Zenobi, et al. The influence of grain size on low-temperature degradation of dental zirconia. Journal of Biomedical Materials Research Part B, Applied Biomaterials, Vol. 100, No. 2, 2012, pp. 447–456.10.1002/jbm.b.31969Search in Google Scholar PubMed
[29] Bowen, C., S. Ramesh, C. Gill, and S. Lawson. Impedance spectroscopy of CuO-doped Y-TZP ceramics. Journal of Materials Science, Vol. 33, 1998, pp. 5103–5110.10.1023/A:1004455130927Search in Google Scholar
[30] Chen, I.-W. Mobility control of ceramic grain boundaries and interfaces. Materials Science and Engineering: A, Vol. 166, No. 1–2, 1993, pp. 51–58.10.1016/0921-5093(93)90309-3Search in Google Scholar
[31] Stepanov, S., O. Khasanov, E. Dvilis, V. Paygin, D. Valiev, and M. Ferrari. Luminescence performance of yttrium-stabilized zirconia ceramics doped with Eu3+ ions fabricated by Spark Plasma Sintering technique. Ceramics International, Vol. 47, No. 5, 2021, pp. 6608–6613.10.1016/j.ceramint.2020.10.250Search in Google Scholar
[32] Guo, X. Hydrothermal degradation mechanism of tetragonal zirconia. Journal of Materials Science, Vol. 36, 2001, pp. 3737–3744.10.1023/A:1017925800904Search in Google Scholar
[33] Nogiwa-Valdez, A. A., W. M. Rainforth, P. Zeng, and I. M. Ross. Deceleration of hydrothermal degradation of 3Y-TZP by alumina and lanthana co-doping. Acta Biomaterialia, Vol. 9, No. 4, 2013, pp. 6226–6235.10.1016/j.actbio.2012.11.027Search in Google Scholar PubMed
[34] Gremillard, L., J. Chevalier, T. Epicier, and G. Fantozzi. Improving the durability of a biomedical‐grade zirconia ceramic by the addition of silica. Journal of the American Ceramic Society, Vol. 85, No. 2, 2002, pp. 401–407.10.1111/j.1151-2916.2002.tb00103.xSearch in Google Scholar
[35] Chevalier, J., L. Gremillard, A. V. Virkar, and D. R. Clarke. The tetragonal‐monoclinic transformation in zirconia: lessons learned and future trends. Journal of the American Ceramic Society, Vol. 92, No. 9, 2009, pp. 1901–1920.10.1111/j.1551-2916.2009.03278.xSearch in Google Scholar
[36] Ansari, S., R. Bhor, K. Pai, D. Sen, S. Mazumder, K. Ghosh, et al. Cobalt nanoparticles for biomedical applications: Facile synthesis, physiochemical characterization, cytotoxicity behavior and biocompatibility. Applied Surface Science, Vol. 414, 2017, pp. 171–187.10.1016/j.apsusc.2017.03.002Search in Google Scholar
[37] Baino, F., M. Montazerian, and E. Verné. Cobalt-doped bioactive glasses for biomedical applications: A review. Materials, Vol. 16, No. 14, 2023, p. 4994.10.3390/ma16144994Search in Google Scholar PubMed PubMed Central
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