Papers by Keyword: Zirconia

Abstract: Composite mold samples used in squeeze casting was fabricated by plasma spraying with 5CrMnMo and 3YSZ, which was shown high bonding strength and good thermal shock resistance. The best parameters with transition coat were explored by mechanical analyses. As results, the transition layer structure made of 75 percent NiCoCrAlY powders showed bonding strength was higher to 34.35MPa and that thermal cycles were up to 46.8 times. The effect of the transition layer was analyzed by microstructures and the failure mechanism of the coating material with a transition layer was discussed. The conclusion was that the physical mismatch and thermodynamic mismatch between the matrix and ceramic layers were the main cause of the failure.

Abstract: Hydroxyapatite (HA)-Zirconia (ZrO2) composite with varying zirconia composition ranging from 1 to 10 wt% was investigated for biomedical applications in order to produce high compressive strength. Precipitation method was used to prepare both hydroxyapatite and zirconia powders. To find the ideal composition, mixture-containing 1, 3, 5 and 10 wt% ZrO2 powder was added. Each mixture was sintered for 4 hours at 750^oC, 1050^oC and 1250^oC. Hardness and compressive strength test were used for evaluation. It was found that with 1 wt% of ZrO2 sintered at 1250^oC showed the greatest structural strength as its volume fraction porosity is the lowest. The hardness and compressive strength of this sample were found to be 2.75 GPa and 72.0 MPa respectively. This can be useful for biomedical applications especially in promoting osteo-integration.

Abstract: Temperature-programmed reduction (TPR) was used to observe the chemical reduction behaviour of molybdenum trioxide (MoO₃) and zirconia (Zr)-doped MoO₃ catalyst by using carbon monoxide (CO) as the reductant. The characterisation of catalysts was performed by X-ray diffraction (XRD), Brunauer-Emmett-Teller (BET) and transmission electron microscopy (TEM) analyses. The reduction performance were examined up to 700°C and reduction was continued for 60 min at 700°C in a stream of 20 vol. % CO in nitrogen. The TPR profile showed that the doped MoO­₃ catalyst was slightly moved to a higher temperature (580°C) as compared to the undoped MoO₃ catalyst, which began at around 550°C. The interaction between zirconia and molybdenum ions in doped MoO₃ catalyst led to an increase in the reduction temperature. According to characterisation of the reduction products by using XRD, it revealed that the reduction behaviour of pure MoO₃ to MoO₂ by CO reductant involved two reduction stages with the formation of Mo₄O₁₁ as the intermediate product. Meanwhile, MoO₃ catalyst doped with zirconia caused a delay in the reduction process and was proven by the presence of Mo₄O₁₁ species at the end of reactions. Physical analysis by using BET showed a slight increase in surface area of 3% Zr-MoO₃ from 6.85 m²/g to 7.24 m²/g. As for TEM analysis, black tiny spots located around MoO₃ particles revealed that the zirconia was successfully intercalated into MoO₃ particles. This confirmed that formation of intermetallic between Zr-MoO₃ catalyst will give new chemical and physical properties which has a remarkable chemical effect by disturbing the reduction progression of MoO₃ catalyst.

Abstract: The plasma spraying is commonly used in medical application. The Atmospheric Plasma Spray (APS) method was applied for production of yttria-stabilized zirconia (YSZ) on AISI 316L stainless steel surface and also on Ti6Al4V titanium alloy surface. In present article two examples of coatings production were presented. In first experimental the YSZ was plasma sprayed (APS) on 316L stainless steel surface. The coating was deposited using A60 (Thermico) plasma torch. The initial parameters were selected and it was concluded that minimal power current was 500A. The thickness of obtained coating was in range 100-150 micrometers. The X-ray phase analysis showed the presence of tetragonal t-phase of ZrO₂. The lamellar structure of coatings with large porosity was observed. In second experimental the newly developed Plasma Spray Physical Vapor Deposition method (PS-PVD) was used. The YSZ coating was deposited on titanium Grade 5 surface. The conducted research showed the formation of two types of coatings structure. When the power current was lower (2000 A) the dense lamellar-like coatings was obtained. If the power current was increased (up to 2200A) the columnar ceramic coating was observed.

Abstract: The phase composition and microstructure of ZrO₂ metering nozzle matrix doped with different content stabilizer were researched by XRD, SEM and EDS. Result showed that the content of cubic phase increased accompanied with monoclinic phase decreased after sintering, different content of stabilizer made phase transition not the same; After sintering in the solid solution formed by MgO and ZrO₂, with closer location to the MgO particles, substitution degree was more obvious, but the diffusion and solid solution state of the stabilizer were far from uniform.

Abstract: Zirconia has a number of remarkable properties, including a very low thermal conductivity. In this research, the phonon thermal conductivity of two phases (cubic and monoclinic) of zirconia (ZrO₂) are calculated. For this purpose, an equilibrium molecular dynamics simulation employing the Green-Kubo formalism is used. The results are presented in detail over a wide temperature range, from 100 K to 2400 K and 100 K to 1400 K for the above-mentioned structures, respectively, with a 100K temperature step. The temperature dependence of the equilibrium atomic volume demonstrated a reasonable agreement with the experimental data. Moreover, the lattice thermal conductivity was calculated by analysing the heat current autocorrelation function. The results showed that zirconia has a low thermal conductivity that is dependent on the temperature. It was also shown that the lattice thermal conductivity of the two phases of zirconia can be decomposed into three contributions due to the acoustic shortrange and long-range phonon and optical phonon modes. Finally, the results from this research are compared with the available experimental data.

Abstract: This paper reports a tunable luminescence of europium (Eu ³⁺) doped zirconia (ZrO₂) nanoparticles as a function of hydrothermal temperature, europium concentrations, time and pH value. The nano-sized Eu doped ZrO₂ (Eu:ZrO₂) particle was synthesized by hydrothermal method at the temperature of 200 °C and time up to 48 h. The nano-sized Eu:ZrO₂ particles have a diameter of about 10 nm. The luminescent properties of nano-sized Eu:ZrO₂ particle was enhanced in the sample when high temperature, high Eu ³⁺ concentration and prolonging hydrothermal time were used at pH 7. These results suggest the use of Eu:ZrO₂ nanoparticles followed by thermal annealing in tuning the luminescence of Eu:ZrO₂ nanoparticles which have potential applications as phosphors in solid state lighting.

Abstract: Abstract. Various bioactive calcium phosphates such as hydroxyapatite (HA) and carbonate apatite (CO₃Ap) have been widely studied due to their biocompatibility and osteoconductivity when implanted into bone defects. CO₃Ap has the ability to adapt bone structure and induce bone regeneration; so that it can be categorized as resorbable bioactive materials. CO₃Ap induced much stronger response such as cell adhesion and actin ring formation to osteoclast-like cells rather than HA. The aim of this study is to evaluate the bioactivity on zirconia (Y-TZP) coated with CO₃Ap using simulated body fluid (SBF). Twenty Y-TZP ZrO₂ disks with a 12-mm diameter and 1-mm thickness were employed as the samples. The disks were divided into two groups which the control group without CO₃Ap coating and tested group with CO₃Ap coating. Disks samples are dipped into CO₃Ap suspension for one minute and stored in 37°C incubator for 24 hours. The disks were soaked in SBF for 1, 4, and 7 day(s) at 36.5°C. The obtained apatite crystals were characterized by scanning electron microscopy (SEM). It was found that the apatite formation on the tested group was greater than the control group. The EDS pattern showed the presence of Ca and P on the control and tested group after SBF soaking, which indicate the apatite deposition on the disks’ surface. However, the Ca and P on the tested group was higher compared to the control group. The formation of apatite layer on the disks’ surface is bioactivity indicator of CO₃Ap.

Abstract: In this study, we aimed to introduce bioactivity to bioinert zirconia by performing sandblasting process and subsequently depositing apatite nuclei (AN), which are fine particles of calcium phosphate precipitated by raising pH of SBF, on the surface of the zirconia samples. By soaking the AN treated zirconia samples in SBF, hydroxyapatite formation was observed in 1 day and high hydroxyapatite-forming ability was attained.

Abstract: Sintering of zirconia usually takes a long time. In recent years, new products with extremely short sintering time have been released. Therefore, it is useful to study in detail the effect of sintering temperature and time on translucency of zirconia. The prepared discs were sintered under four conditions; 30 minutes, 40 minutes, 50 minutes and 60 minutes as firing temperature rising time up to 1500°C. Samples were measured with a spectrophotometer and translucency parameter (TP), opalescence parameter (OP) and contrast ratio (CR) were calculated. In this study, there were no statistically significant differences between TP, OP and CR due to the differences in heating rates. There is a possibility that a heating time up to the sintering temperature does not affect translucency of zirconia.