Papers by Keyword: Y-TZP

Abstract: The purpose of this study was to evaluate the effects of different polishing techniques on the topographical features and phase transformation of monolithic zirconia. Four brands of zirconia were ground and polished using one of four systems. All zirconia specimens were ground with a fine-grit diamond bur (GB) prior to polishing procedures. The surface roughness and phase transition (XRD) were evaluated, and surface characterizations (SEM and XPS) were performed. The highest roughness was obtained with the Tob system. The strongest diffraction peak in the obtained XRD patterns was at 2θ=30.246°. No monoclinic phase change was found in any group. The XPS analysis showed that the atomic percentages of yttrium in the specimens of Cercon before and after polishing were the highest of any sample. All the polishing systems tested may not adversely affect the phase transformation of monolithic zirconia. The Tob system resulted in the highest roughness. The XPS analysis showed that grinding and polishing had some effects on the properties of zirconia from a microscopic point of view.

Abstract: In order to gain acceleration of the osseointegration process after implant placement, micro retention using inorganic elements such as Hydroxyapatite (HA) were commonly used as a coating material in dental implant. Meanwhile, another inorganic material such as Carbonate Apatite (CO₃Ap) has been known as bone substitute for decades. The purpose of this study is to investigate the flexural strength of Yttria-Stabilized Zirconia (Y-TZP) as dental implant material after being coated with CO₃Ap. Ten specimens of Y-TZP were divided into two groups. The first group was coated with CO₃Ap while other groups without coatings were used as the control. Biaxial flexural strength was determined using piston on three balls-technique and data were evaluated by statistical analysis. The specimens surface were analyzed through images taken by Scanning Electron Microscope (SEM). As the result, this study showed that there was no statistically significant found between the group with coating and the control group (p>0.05). The biaxial flexural strength’s mean of the group with coating and control were 212.80 MPa and 209.35 MPa; while micro Vickers hardness’ means were 229.56 HV and 245.40 HV. It can be concluded that there was no difference in the mean flexural strength between Y-TZP before and after coating.

Abstract: Alumina-Y-TZP composites between 0 to 25 vol% Y-TZP content produced via conventional two-stage sintering with T₁ ranging between 1400°C and 1550°C, heating rate of 20°C/min, followed by T₂ of 1350°C and 12 hours dwelling time. The microstructure, density, Vickers hardness (H_V), Young’s modulus (E) and fracture toughness (K_IC) of the sintered samples were then evaluated. It is observed that all samples up to 10 vol% Y-TZP achieved > 98% T.D. as the T₁ increases. Samples with Y-TZP content above 10 vol% resulted in a significant decrease in density and hardness. Samples with ≤ 10 vol% Y-TZP sintered at T₁ of 1450°C was able to achieve density > 98% T.D., Vickers hardness > 18 GPa and Young’s modulus > 380 GPa and fracture toughness > 6 MPam^1/2 when compared to pure Al₂O₃ ceramics.

Abstract: Addition of CeO₂ into ZTA and its effects on microstructure and mechanical properties were investigated. CeO₂ was detected with significant amounts only above 10 wt%. Viscosity was measured for slurry preparartions and characterization of mechanical properties of ZTA. Additions of CeO₂ of more than 10 wt% surpassed the solubility limit and formed Ce₂Zr₃O_10. Ce₂Zr₃O₁₀ increased the tetragonality factor, prevented excessive grain growth through a pinning effect, which is attributed to the segregation of Ce₂Zr₃O₁₀ to the grain boundaries and showed a peak in fracture toughness with a value of 9.3 MPam^1/2 with 10 wt% additions of CeO₂. Further additions of CeO₂ reduced ZTA’s mechanical strength. Maximum value of H_v was 17700 MPa with 10 wt% CeO₂. Porosities have been attributed as the underlying reason as to why theoretical density were always higher than measured densities.

Abstract: In this study, the effect of second step sintering holding time on LTD of 3 mol% yttria tetragonal zirconia polycrystals (3Y-TZP) ceramic was studied. The Zirconia powder was die pressed followed by cold isostatically pressed (CIP) at 200 MPa, and the samples were initially heated to a first step temperature of 1400°C with constant heating rate 10°C/min and the samples were stand still for 1 minute. Then cooled down to the second step temperature of 1200°C and maintained at that temperature for 2 and 10 hours before cooled down to the room temperature. The other sample was sintered by using Single Step Sintering (SSS) at 1400°C for two hours. The phase content in the zirconia samples was measured by using X-ray diffractometer. Average grain size was calculated by using Field Emission Scanning Electron Microscope (FESEM). The low temperature degradation study was conducted in an autoclave containing superheated steam at 180°C and 10 bar pressures for periods up to 60 hours. Results revealed that the two-step sintering (TSS) effectively controlled the grain growth than SSS and subsequently ageing. Increase in second step sintering holding time from two to ten hours also increased the densification and hydrothermal ageing resistance of Y-TZP ceramics.

Abstract: The effect of flyash (FA) additions of 0.05 wt% to 1 wt% on yttria-stabilized tetragonal zirconia polycrystals (Y-TZP), sintered in air at temperatures ranging from 1250°C to 1500°C, was examined. The bulk density, Young’s modulus, Vickers hardness and fracture toughness for each addition were determined while ageing behaviour were observed by subjecting them to superheated steam at 180°C/10 bar in an autoclave for 24 hours. Additions of FA, particularly of 0.05 wt% and 0.1 wt%, were found to be beneficial in aiding densification and increasing Young’s modulus beyond 200 GPa for sintering temperatures up to 1350°C. A common trend was observed for the Vickers hardness of all additions including undoped; hardness continues to rise from 1250°C and peaked at 1350°C before gradually decreasing as the sintering temperature increases further. No pronounced effect of flyash was seen on the fracture toughness of all samples. The ageing resistance of Y-TZP improved with addition of FA resulting in relatively lower amount of ageing-induced tetragonal to monoclinic phase transformation exhibited by doped samples compared to the undoped.

Abstract: The effects of adding Al₂O₃ and CeO₂ on the microstructure, mechanical and physical properties of 3 mol% yttria-stabilized zirconia (3Y-TZP) ceramics is presented over a wide sintering regime by pressureless sintering. It has been revealed that small additions of dopant to Y-TZP were beneficial in enhancing the mechanical properties of Y-TZP. Sintered samples were used to evaluate the bulk density, Vickers’s hardness, Young’s modulus, and shrinkage of the material. Al₂O₃ and CeO₂ doped Y-TZPs sintered at 1450^∘ C retained high bulk density (>97% of theoretical density) and Young’s modulus (>200 GPa) without sacrificing tetragonal phase stability. The optimum level of dopant was found to be at 0.3 Al₂O₃ / 0.5 CeO₂ at sintering temperature between 1250^∘ C and 1450^∘C using the standard 12 min holding time cycle, with sintered body exhibiting excellent combination of properties when compared to the undoped ceramics.

Abstract: The effect of manganese oxide (MnO₂) and aluminum oxide (Al₂O₃) addition of up to 1 wt% in yttria-stabilized tetragonal zirconia polycrystals (Y-TZP), sintered in air at 1450oC, was examined. The low temperature degradation resistance was observed by immersing the sample in Ringer solution at 37oC over a period of 8 weeks, whereby the weight loss and the SEM image of sample was analyzed to generate the degradation pattern of the sample. Additions of 0.6wt% Al₂O₃/ 0.4wt% MnO₂ were found to be beneficial in retarding the ageing of the ceramics sample. Therefore the sample was deemed beneficial in the use of orthopedic applications.

Abstract: A small amount of iron oxide (Fe₂O₃) was added to the commercially available 3 mol% Y-TZP as a sintering aid over a temperature range of 1250°C to 1500°C. Sintered samples were then evaluated to determine the bulk density, Vickers hardness, and fracture toughness. In addition, hydrothermal ageing experiments to determine the tetragonal phase stability were performed on selected sintered samples in superheated steam at 180°C / 10 bar for up to 24 hours. Based on the work carried out, it was revealed that additions of Fe₂O₃ particularly 0.3 wt% was indeed beneficial in aiding densification, improving the matrix stiffness and hardness when compared to undoped Y-TZP sintered at temperatures below 1350°C. Addition of Fe₂O₃ was found to have negligible effects on the fracture toughness of all samples with the exception of the 0.5 and 1 wt% doped Y-YZP sintered above 1400°C. Hydrothermal ageing resistance of Y-TZP was found to be enhanced with the addition of Fe₂O₃ in the Y-TZP matrix.

Abstract: Yttria-stabilized tetragonal zirconia polycrystals (Y-TZP) is used for dental prosthodontics, however, it can present accelerated tetragonal to monoclinic phase transformation in oral environment. The aim of this study was to compare the behavior of a Y-TZP synthesized in laboratory by the coprecipitation method to a commercial Y-TZP, after hydrothermal aging in pressurized reactor (150°C/ 35 hours). The discs were sintered at 1520°C for two hours. The kinetics curve of phase transformation was determined through the data collect by XRD diffractograms treated by the Rietveld method. The experimental and commercial control groups did not present monoclinic phase. After 35 hours of aging, the experimental group presented 69% of monoclinic phase compared to 67% for the commercial group. Scanning electron microscopy and atomic force microscopy images suggested that the commercial group presented heterogeneity of grain size and that the experimental group was more homogeneous. All groups presented superficial degradation process.