Search Results (25)

Fully dense monoclinic zirconia ceramics were successfully fabricated by pressureless sintering and/or HIP. Although monoclinic zirconia exhibits unique physicochemical properties, fabrication of fully dense polycrystalline bodies has remained challenging due to catastrophic volume expansion during the tetragonal-to-monoclinic transformation. By introducing a synergistic ternary (Ga₂O₃-ZnO-TiO₂) sintering aid, a relative density exceeding 99.6% with an average grain size of 0.5–2 µm was achieved by sintering under an oxygen atmosphere at 1070 °C for 3–100 h, well below the phase-transition temperature. X-ray diffractometry confirmed a single-phase monoclinic structure. Subsequent hot isostatic pressing at 1080 °C and 180 MPa for 2 h eliminated residual porosity, yielding a 4-point bending strength of 328 MPa, a fracture toughness of 2.7 MPa·m^0.5, and a Vickers hardness HV₁ of 805. This monoclinic zirconia ceramic exhibited ~30% total transmittance, while in-line transmittance remained below 0.1% due to intrinsic birefringence of the monoclinic lattice. These results established a low-temperature route for densifying phase-sensitive ceramics while achieving long-term stability. Full article

To simulate the erosion damage behavior of thermal barrier coatings (TBCs) under actual service conditions in an aircraft engine environment, this study developed a multi-factor coupled test setup capable of simulating combined loading under high-temperature (1150 °C), high-speed (0.4 Mach), and solid-particle erosion conditions. Yttria-stabilized zirconia (YSZ) TBCs were prepared using electron beam physical vapor deposition (EB-PVD). For different erosion durations (2 h, 5 h, 8 h, 12 h), the evolution of macroscopic and microscopic morphologies as well as the development of residual stresses in the thermally grown oxide (TGO) layer were systematically investigated. The results indicate that the erosion process of the YSZ coating can be divided into three stages. During the initial high-erosion-rate stage (8.17 g/kg), erosion damage was confined to the grain tips of the columnar crystals, primarily caused by brittle fracture at the grain tips, and the TGO stress was relatively low (−0.6 GPa). During the intermediate stage, the erosion rate was lower (2.74 g/kg). Impact stresses induced microcracks within the columnar grains, which gradually connected to form intergranular fractures. This led to the expansion of localized spalling pits. The interface began to wrinkle, and the stress rose to −2.2 GPa. In the final accelerated failure stage (5.88 g/kg), horizontal cracks fully propagated, leading to large-scale peeling of the coating. The stress was released to −0.9 GPa. The coating failure mechanism evolves from surface damage to interfacial peeling, which is closely related to the coating structure, stress evolution, and interfacial state. Full article

Aim: This study aimed to compare two-piece zirconia and two-piece titanium implants inserted into the anterior mandible for removable overdentures in a 3-year randomized split-mouth clinical trial. Methods: Twenty fully edentulous mandibular patients received two zirconia and two titanium implants allocated by computer-generated randomization. The primary endpoint was bleeding-on-probing (BOP) at 12 months. Secondary outcomes included implant survival and success (Albrektsson criteria), marginal bone level changes, peri-implant cytokines (IL-1β, IL-6, and TNFα), prosthetic complications, and patient-reported outcomes (PROMs). Results: After 3 years, overall survival was 98.61% and overall success was 84.72%. Titanium implants showed higher success compared with zirconia implants (91.70% vs. 77.78%), while survival was 100% and 97.22%, respectively. Marginal bone loss was significantly greater around zirconia implants at 36 months (p < 0.01). No significant differences were observed in IL-1β, IL-6, or TNFα levels up to 12 months. PROMs revealed a trade-off, with zirconia favored for esthetics and cleaning perception, while titanium was rated superior for stability. Conclusions: Within the limitations of this split-mouth RCT, zirconia implants demonstrated reduced success and inferior marginal bone stability compared with titanium implants in overdenture therapy. Careful case selection and close follow-up appear essential when zirconia implants are used in this indication. Full article

High-temperature particulate matter (PM) filtration remains a fundamental challenge, because most fiber filters not only face the challenge of high temperatures but also suffer from an inherent trade-off between capture efficiency, pressure drop, and service life. This paper reports a hierarchical layered zirconia (ZrO₂) ceramic fiber aerogel featuring a continuous multiscale gradient. The aerogel was prepared by gradient air-blown spinning, and the resulting structure has directional order, with the fiber diameter gradually decreasing from upstream to downstream, thus forming a pore size gradient and achieving hierarchical particle interception across multiple scales. This rational design simultaneously suppresses surface clogging and reduces flow resistance, resolving the longstanding trade-off between efficiency and permeability. Consequently, this aerogel achieves an ultra-high filtration efficiency of 99.96%, a low pressure drop of 156 Pa, and a high dust-holding capacity of 101 g m⁻². The material also exhibits outstanding mechanical toughness (80% compressive strain elasticity and 25.75% tensile fracture strain) and thermal stability up to 1000 °C. Moreover, it maintains over 99.95% filtration efficiency at high temperatures and can be fully regenerated through 800 °C heat treatment. This work establishes a structure-based design paradigm for high-temperature filtration media and provides a scalable pathway for next-generation industrial flue gas purification. Full article

Aim: This in vitro study aimed to evaluate the marginal and internal fit of three monolithic CAD/CAM zirconia ceramics with different Y-TZP contents, prepared with chamfer and rounded shoulder finish lines. Methods. Sixty monolithic zirconia crowns were fabricated and divided into three groups (n = 20) based on their yttria content: (1) multilayer zirconia consisting of a dentin layer of 3 mol% yttria-stabilized tetragonal zirconia polycrystal (3Y-TZP) and an incisal layer of 5 mol% partially stabilized zirconia (5Y-PSZ), (2) shade-gradient zirconia fully composed of 3Y-TZP, and (3) shade-gradient zirconia containing 4 mol% partially stabilized zirconia (4Y-PSZ). Each group was further divided into two finish line configurations (chamfer and rounded shoulder). Marginal and internal gaps were measured using the silicone replica technique under a stereomicroscope by a single operator. Data were analyzed using three-way ANOVA followed by Tukey’s post hoc test (α = 0.05). Marginal and internal gaps were assessed using the silicone replica technique under a stereomicroscope by a single operator. Statistical analysis was performed with three-way ANOVA and Tukey’s post hoc test (p < 0.05). Results: The occlusal region exhibited the largest gap values, while the axial region showed the smallest across all groups. Mean marginal and internal gaps were 33.79 µm for chamfer and 43.37 µm for rounded shoulder finish lines. Zirconia with higher Y-TZP content demonstrated significantly greater gap values than those with lower percentages (p < 0.05). Significant interactions were found among finish line design, material type, and measurement region (p < 0.05), with rounded shoulder margins showing larger gaps (p = 0.001). Conclusions: Y-TZP content significantly affects marginal and internal adaptation, with higher percentages associated with increased gap values. Both finish line types produced clinically acceptable fits, although chamfer margins provided superior adaptation. Full article

MnO₂-doped 9 mol% CaO-stabilized zirconia (CSZ) was investigated in terms of phase stability, microstructure, and mechanical properties before and after thermal cycling. As the MnO₂ content increased from 2 to 4 mol%, the monoclinic phase fraction decreased significantly (from 32.6% to 2.5%), while the tetragonal phase fraction increased (from 58.2% to 90.3%), indicating an enhanced phase stability comparable to fully stabilized ZrO₂. The cubic phase fraction decreased from 9.2% to 3.4% with 2–3 mol% MnO₂, but increased to 7.2% at 4 mol%. The 9 mol% CSZ showed a mixture of grains around 2 μm and 10 μm, while the MnO₂-doped CSZ exhibited only grains larger than 30 μm, suggesting that MnO₂ acted as a sintering aid. After thermal cycling, increasing the MnO₂ content from 2 to 4 mol% led to an increase in the monoclinic phase fraction (from 7.8% to 17.2%) and a decrease in the tetragonal phase fraction (from 53.6% to 21.8%). The Vickers hardness and wear resistance of MnO₂-doped CSZ were superior to those of undoped 9-CSZ, and improved as the MnO₂ doping level increased. These mechanical properties were maximized in the CSZ doped with 3 mol% MnO₂, and this trend persisted after thermal cycling. These results demonstrate that MnO₂ doping effectively enhances the phase stability and mechanical performance of CaO-partially stabilized zirconia under thermal stress cycling conditions. Full article

Background: Digital technologies enable the accurate replication of occlusion, which is pivotal for stability in maximum intercuspation and dynamic occlusion. CAD softwares generates standardized occlusal morphologies requiring significant adjustments. The consideration of individual mandibular movements during restoration leads to better functional integration. This pilot study evaluates the efficacy of a novel, fully digital protocol for occlusal analysis recording in prosthodontics. Methods: Patients needing single or multiple metal-free restorations were included. Teeth underwent horizontal finish line preparation, while restorations on implants were either directly screwed or used multi-unit abutments. A digital impression (Trios 3 Intraoral Scanner) captured the mouth’s elements. Dynamic occlusion was recorded via Patient Specific Motion (PSM). After the placement and functionalization of temporary restorations, subsequent scans included various elements, and CAD software (Dental system) was used for the restoration design. Restorations were milled in monolithic zirconia, pressed from CAD/CAM-milled wax, and sintered. Results: An evaluation of 52 restorations in 37 patients indicated high accuracy in restorations manufactured via the fully digital workflow. Monolithic zirconia was predominantly used. Subtractive (17.3%) and additive (7.7%) occlusal adjustments were mainly chairside. Conclusion: This study underscores the efficacy of meticulous verification measures and a centric contact system in reducing the need for clinical occlusal refinements in prosthetic restorations. Full article

This study aimed to investigate a bidirectional switching functionality absorber, which exhibited an ultra-wideband characteristic in one direction, while in the other direction it demonstrated the absorption of three different resonant wavelengths (frequencies). The fully layered planar structure of the absorber consisted of Al₂O₃, Zr, yttria-stabilized zirconia (YSZ), Zr, YSZ, Al, YSZ, and Al. The simulations were conducted using the COMSOL Multiphysics^® simulation software (version 6.1) for analyses, and this study introduced three pivotal innovations. Firstly, there had been scarce exploration of YSZ and Zr as the materials for designing absorbers. The uses of YSZ and Zr in this context were a relatively uncharted territory, and our research endeavored to showcase their distinctive performance as absorber materials. Secondly, the development of a planar absorber with multifunctional characteristics was a rarity in the existing literature. This encompassed the integrations of an ultra-wideband optical absorber and the creation of a multi-wavelength resonant absorber featuring three resonant wavelengths. The design of such a multi-wavelength resonant absorber holds promise for diverse applications in optical detection and communication systems, presenting novel possibilities in related fields. Lastly, a notable discovery was demonstrated: a discernible redshift phenomenon in the wavelengths of the three resonant peaks when the thickness of YSZ, serving as the material of resonant absorber layer, was increased. Full article

Thin, supported inorganic mesoporous membranes are used for the removal of salts, small molecules (PFAS, dyes, and polyanions) and particulate species (oil droplets) from aqueous sources with high flux and selectivity. Nanofiltration membranes can reject simple salts with 80–100% selectivity through a space charge mechanism. Rejection by size selectivity can be near 100% since the membranes can have a very narrow size distribution. Mesoporous membranes have received particular interest due to their (potential) stability under operational conditions and during defouling operations. More recently, membranes with extreme stability became interesting with the advent of in situ fouling mitigation by means of ultrasound emitted from within the membrane structure. For this reason, we explored the stability of available and new membranes with accelerated lifetime tests in aqueous solutions at various temperatures and pH values. Of the available ceria, titania, and magnetite membranes, none were actually stable under all test conditions. In earlier work, it was established that mesoporous alumina membranes have very poor stability. A new nanofiltration membrane was made of cubic zirconia membranes that exhibited near-perfect stability. A new ultrafiltration membrane was made of amorphous silica that was fully stable in ultrapure water at 80 °C. This work provides details of membrane synthesis, stability characterization and data and their interpretation. Full article

Background: Zirconia is a widely used material in the dental industry due to its excellent mechanical and aesthetic properties. Recently, a new 3D printing process called suspension-enclosing projection stereolithography (SEPS) was introduced to fabricate zirconia dental restorations. However, the effect of the sintering time and temperature on the properties of zirconia produced via SEPS has not been fully investigated. Methods: Zirconia slurries were prepared with varying percentages of zirconia powders and 3D printing resins, and 5Y-TZP (5 mol% yttria-stabilized zirconia) (n = 40) and 3Y-TZP (3 mol% yttria-stabilized zirconia) (n = 40) bar specimens were fabricated via SEPS manufacturing. The specimens were sintered at different temperatures and dwell times, and their flexural strength, density, and phase composition were measured. The viscosity of the slurries was also measured. Statistical analysis was performed using Welch’s ANOVA and Kruskal–Wallis tests to evaluate the impact of the sintering conditions. Results: Significant differences in flexural strength (p < 0.01) were observed between the 5Y-TZP samples, with those sintered at 1530 °C for 120 min showing an average strength of 268.34 ± 44.66 MPa, compared to 174.16 ± 42.29 MPa for those sintered at 1450 °C for 120 min. In terms of density, significant differences (p < 0.01) were noted for the 3Y-TZP specimens, with an average density of 6.66 ± 0.49 g/cm³ for samples sintered at 1530 °C for 120 min, versus 5.75 ± 0.55 g/cm³ for those sintered at 1530 °C for 10 min. X-ray diffraction confirmed the presence of a predominantly tetragonal phase in both materials. Conclusions: Zirconia printed via SEPS manufacturing can be sintered at a higher temperature with shorter dwell times, thereby producing high density samples. Different sintering conditions can be used to fully sinter 3D-printed zirconia for potential dental applications. Full article

Electrochemical NOx sensors based on yttria-stabilized zirconia (YSZ) provide a reliable onboard way to control NOx emissions from glass-melting furnaces. The main limitation is the poisoning of this sensor by sulfur oxides (SOx) contained in the stream. To overcome this drawback, an “SO₂ trap” with high SOx storage capacity and low affinity to NOx is required. Two CuO/BaO/SBA-15 traps with the same CuO loading (6.5 wt.%) and different BaO loadings (5 and 24.5 wt.%, respectively) were synthetized, thoroughly characterized and evaluated as SO₂ traps. The results show that the 6.5%CuO/5%BaO/SBA-15 trap displays the highest SO₂ adsorption capacity and can fully adsorb SO₂ for a specific period of time, while additionally displaying a very low NO adsorption capacity. A suitable quantity of this material located upstream of the sensor could provide total protection of the NOx sensor against sulfur poisoning in glass-furnace exhausts. Full article

As dental 5 mol% yttria-stabilized (5Y-) zirconia demand high esthetics, it is necessary to clarify how the optical properties are affected by high-speed sintering, which is not yet fully understood. Our study aimed to investigate the effect of high-speed sintering on the translucency and opalescence parameters (TP and OP, respectively), as well as their related microstructure and phase distribution, using two types of multilayered 5Y-zirconia. Multilayered 5Y-zirconia (Cercon xt ML, Lava Esthetic) were cut layer-by-layer, followed by conventional and high-speed sintering. The TP and OP values were subsequently obtained using a spectrophotometer, and field emission scanning electron microscopy images were used to analyze the average grain size. The phase fractions were analyzed using X-ray diffraction. Regardless of the zirconia type, the TP was slightly lowered by high-speed sintering in all the layers except the dentin layer (DL) for Lava Esthetic (p < 0.05). The OP decreased by high-speed sintering in the DL for Cercon xt ML and in all the layers for Lava Esthetic (p < 0.05). The decrease in translucency after high-speed sintering was attributed to a decrease in the yttria-rich t’-phase with low tetragonality, along with an increase in the yttria-lean t-phase with high tetragonality. Full article

Bilayer zirconia restoration is one of the most commonly used restorations in dental practice, but the high frequency of the cohesive/adhesive fracture of veneered porcelain is still a problem. This paper focuses on the development of nanostructured glass-zirconia to improve the interface stability of dental zirconia substrate and veneered porcelain. A novel SiO₂-Li₂O-Al₂O₃ (SLA) glass was prepared and infiltrated into the surface of fully sintered dental zirconia to obtain nanostructured glass-zirconia structure. The prepared glass-zirconia was analyzed with scanning electron microscopes (SEM), energy dispersive spectroscopy (EDS) and X-ray diffraction spectroscopy (XRD). The wettability, roughness and 3D morphology of zirconia were altered, and shear bonding strength (SBS) test demonstrated almost double increase in SBS values of the nanostructured glass-zirconia structure. The failure modes and microstructure characteristics also verified the improved interfacial stability. This investigation provides a promising method for enhancing the structural stability of bilayer zirconia restorations. Full article

We herein report manufacturing of dental crowns made of 5-mol% yttria partially stabilized zirconia (5Y-PSZ) with desired mechanical properties, optical translucency and dimensional accuracy using digital light processing (DLP). To this end, all processing parameters were carefully controlled and optimized. First, 5Y-PSZ particles with a bimodal distribution were prepared via calcination of as-received granules and subsequent ball-milling and then used to formulate 5Y-PSZ suspensions with a high solid loading of 50 vol% required for high densification after sintering. Dispersant content was also optimized. To provide high dimensional accuracy, initial dimensions of dental crowns for 3D printing were precisely determined by considering increase and decrease in dimensions during photopolymerization and sintering, respectively. Photopolymerization time was also optimized for a given layer thickness of 50 μm to ensure good bonding between layers. A multi-step debinding schedule with a slow heating rate was employed to avoid formation of any defects. After sintering at 1500 °C for 2 h, 5Y-PSZ could be almost fully densified without noticeable defects within layers and at interfaces between layers. They had high relative densities (99.03 ± 0.39%) with a high cubic phase content (59.1%). These characteristics allowed for achievement of reasonably high mechanical properties (flexural strength = 625.4 ± 75.5 MPa and Weibull modulus = 7.9) and % transmittance (31.4 ± 0.7%). In addition, 5Y-PSZ dental crowns showed excellent dimensional accuracy (root mean square (RMS) for marginal discrepancy = 44.4 ± 10.8 μm and RMS for internal gap = 22.8 ± 1.6 μm) evaluated by the 3D scanning technique. Full article

The differences in the optical properties of multi-layered zirconia with and without yttria-gradient are not fully understood. This study aimed to evaluate and compare the optical properties, related microstructures, and phase fractions of multi-layered zirconia with and without yttria-gradient. For this, multi-layered zirconia of 5 mol% yttria (5Y) stabilized (Katana STML) and 4Y/5Y stabilized (e.max MT Multi) were cut layerwise, sintered, and analyzed using the opalescence parameter (OP), average transmittance (AT%), translucency parameter (TP), and contrast ratio (CR). The average grain size and phase fractions were obtained from field-emission scanning electron micrographs and X-ray diffraction patterns, respectively. Although the TP values of Katana STML and e.max MT Multi did not show a significant difference (except for transition layer 1), the results of AT and CR showed that the translucency of e.max MT Multi was slightly higher than that of Katana STML (p < 0.05). The opalescence gradient was higher in Katana STML than in the e.max MT Multi. In both zirconia types, translucency increased from the dentin to enamel layer based on the AT, TP, and CR results, while OP decreased (p < 0.05). The higher translucency from the dentin to enamel layer in Katana STML was caused by the pigmentation gradient, while in e.max MT Multi, it was caused by the difference in phase fraction and the pigmentation gradient. Full article