Papers by Keyword: Stabilized Zirconia

Abstract: Achieving an appropriate dispersion of Carbon Nanotubes (CNTs) within a ceramic matrix should be referred to as the main challenge for the synthesis of CNTs reinforced ceramics with enhanced toughening properties. In the present paper, dispersion of 1 wt% MWCNTs within 3YTZP based ceramics has been investigated through the comparison of three conventional approaches based on using surfactants, functionalization, and planetary milling. Addition of 2 wt% Sodium Dodecyl Sulfate (SDS) as the surfactant material followed by 2 hours ultrasonication was found successful to disperse carbon nanotubes in a water media, while chemical functionalization of the CNTs surface using a mixture of H₂SO₄/HNO₃ (3:1) could result in identical well dispersed powder mixtures. Formation of functional groups on the surface of CNTs was confirmed by FTIR spectroscopy and efficiency of the above methods to result in well dispersed powders was detected using UV-Vis spectroscopy. The surfactant method was, accordingly, found to result in the highest dispersion of nanotubes within the ceramic microstructure. In the planetary milling method, well dispersed CNTs within 3YTZP particles could be attained through the optimization of processing conditions such as 24 h milling time, 250 RPM, and 2 BPR. The accuracy of the above results could be verified by SEM as well as Raman spectroscopy. On the other hand, although the dispersed powders provided through functionalization and planetary milling methods revealed CNTs bundles in few scopes of the SEM results and minor damages were also observed in the Raman spectroscopy report, they were both at acceptable levels.

Abstract: Thermodynamic analysis on destabilizing effect of zirconia products caused by aluminum is carried on by using material Gibbs free energy function, and then the experimental verification was tested by scanning electron microscope (SEM). The results show that: 1) aluminum reacts with calcium oxide, the stabilizer of zirconia, forming some sheet-like calcium hexaluminate. It results in the stabilizer loss and the volume destabilization of zirconia. 2) Aluminum reacts with magnesium oxide, the stabilizer of zirconia, forming some octahedral magnesia-alumina spinel. It results in the stabilizer loss and the volume destabilization of zirconia. 3) The destabilizing effect of zirconia caused by aluminum can be defined three layers, which are original layer, transition layer and reaction layer.

Abstract: Oxygen diffusion in MgO stabilized zirconia has been studied by molecular dynamics simulation method with MOLDY software. The results illustrate that oxygen diffusion in MgO stabilized zirconia can be decided by temperature and amount of MgO. Both increase of amount of MgO and temperature in the system may promote the oxygen diffusion. Further increase in temperature is helpful to the oxide ions diffusion. There is always a maximum value of oxygen diffusion coefficient, which is represented by the slope of MSD curves, corresponding to a certain amount of MgO. In MgO stabilized zirconia, the most suitable doped amount of MgO exists in a range , which is decided by the working temperature of MgO stabilized zirconia.

Abstract: Stabilized zirconia shows rather high microwave absorbency at room temperature, and the absorbency become higher with increasing temperature. In this study, stabilized zirconia powder, partially stabilized zirconia powder and zirconia fiber were subjected for microwave absorption measurements at elevated temperature. Microwave absorption measurements were done by using a system consists of a microwave vector network analyzer, a circular wave-guide fixture and a vacuum furnace. Microwave absorbency was evaluated by the reflection power change from the sample in the circular wave-guide fixture under vacuum heating. Microwave absorbency of stabilized zirconia powder, partially stabilized zirconia powder and zirconia fiber gradually increased with the increase of temperature. We supposed that the increase of microwave absorbency is related to the ionic (oxygen) conduction behavior of stabilized zirconia. Stoichiometric composition ZrO2 powder was also subjected for a measurement to consider the relation between microwave absorbency and ion conduction of zirconia. As the result, stoichiometric composition ZrO2 powder was not absorbed microwave power even when the powder was heated up to 900oC because it isn’t an oxygen ion conductor.

Abstract: Applications of stabilized zirconia include uses related to its low thermal conductivity, strength and electrical properties. Rare earth oxides (REO) were used as additives to stabilize appropriate crystalline phases at zirconia compacts. In this work zirconia based solid electrolytes were sintered with 10, 15 and 20 wt % of REO as sintering aids. Samples were prepared by uniaxial cold press and sintered at 1400 °C, followed by electric properties determination via impedance spectroscopy. Complimentary characterization was made by X-Ray diffractometry and quantitative phase analysis by Rietveld refinement. The ionic conductivity is affected by the amount of REO additive and this effect is correlated to the existing tetragonal and cubic phases for each composition