scholarly journals A continuum model for yttria-stabilized zirconia incorporating triple phase boundary, lattice structure and immobile oxide ions

2019 ◽  
Vol 23 (10) ◽  
pp. 2907-2926 ◽  
Author(s):  
Petr Vágner ◽  
Clemens Guhlke ◽  
Vojtěch Miloš ◽  
Rüdiger Müller ◽  
Jürgen Fuhrmann
Keyword(s):  
Phase Boundary ◽  
Continuum Model ◽  
Lattice Structure ◽  
Surface Reactions ◽  
Yttria Stabilized Zirconia ◽  
Cyclic Voltammograms ◽  
Stabilized Zirconia ◽  
Triple Phase Boundary ◽  
The Impact ◽  
Oxide Ions

Abstract A continuum model for yttria-stabilized zirconia (YSZ) in the framework of non-equilibrium thermodynamics is developed. Particular attention is given to (i) modeling of the YSZ-metal-gas triple phase boundary, (ii) incorporation of the lattice structure and immobile oxide ions within the free energy model and (iii) surface reactions. A finite volume discretization method based on modified Scharfetter-Gummel fluxes is derived in order to perform numerical simulations. The model is used to study the impact of yttria and immobile oxide ions on the structure of the charged boundary layer and the double layer capacitance. Cyclic voltammograms of an air-half cell are simulated to study the effect of parameter variations on surface reactions, adsorption and anion diffusion.

scholarly journals Revisiting the Birth of 7YSZ Thermal Barrier Coatings: Stephan Stecura †

Coatings ◽  
2018 ◽  
Vol 8 (7) ◽  
pp. 255 ◽  
Author(s):  
James Smialek ◽  
Robert Miller
Keyword(s):  
Thermal Barrier Coatings ◽  
Yttria Stabilized Zirconia ◽  
Turbine Engines ◽  
Thermal Barrier ◽  
Stabilized Zirconia ◽  
Barrier Coatings ◽  
Turbine Engine ◽  
Power Turbine ◽  
Plasma Sprayed ◽  
The Impact

Thermal barrier coatings are widely used in all turbine engines, typically using a 7 wt.% Y2O3–ZrO2 formulation. Extensive research and development over many decades have refined the processing and structure of these coatings for increased durability and reliability. New compositions demonstrate some unique advantages and are gaining in application. However, the “7YSZ” (7 wt.% yttria stabilized zirconia) formulation predominates and is still in widespread use. This special composition has been universally found to produce nanoscale precipitates of metastable t’ tetragonal phase, giving rise to a unique toughening mechanism via ferro-elastic switching under stress. This note recalls the original study that identified superior properties of 6–8 wt.% yttria stabilized zirconia (YSZ) plasma sprayed thermal barrier coatings, published in 1978. The impact of this discovery, arguably, continues in some form to this day. At one point, 7YSZ thermal barrier coatings were used in every new aircraft and ground power turbine engine produced worldwide. 7YSZ is a tribute to its inventor, Dr. Stephan Stecura, NASA retiree.

Electrical Polarization Depresses Low Temperature Degradation and Promotes Bioactivity of Chemically Treated Yttria-Stabilized Zirconia

2011 ◽  
Vol 493-494 ◽  
pp. 11-15
Author(s):  
Miho Nakamura ◽  
Naohiro Horiuchi ◽  
Akiko Nagai ◽  
Kimihiro Yamashita
Keyword(s):  
Oxygen Vacancies ◽  
Water Adsorption ◽  
Alkaline Treatment ◽  
Yttria Stabilized Zirconia ◽  
Charged Surface ◽  
Stabilized Zirconia ◽  
Electrical Polarization ◽  
Oxide Ions ◽  
Positively Charged

Because of its excellent mechanical properties, yttria-stabilized zirconia is currently used as an orthopedic and dental material. In this study, we have improved the bioactivity of yttria-stabilized zirconia by a combination of electrical polarization and chemical treatment. The phase transformation from tetragonal to monoclinic ZrO2 after alkaline treatment was inhibited on positively-charged yttria-stabilized zirconia surfaces compared with negatively charged and conventional surfaces. During polarization, some oxide ions move from the positively-charged surface to the negatively charged surface, leading to an increase in oxygen vacancies on the positive surface and hence greater formation of Zr-OH when this surface was exposed to alkaline solution. This then reduced the water adsorption at this surface and consequently reduced the rate of cleavage of Zr-O-Zr bonds. The bioactivity was assessed by immersing the samples in simulated body fluid and evaluating the growth of apatite on the surfaces. The combination of polarization and alkaline treatment increased the bioactivity in vitro.

Microstructural examination of modified yttria stabilized zirconia by EM analytical techniques

1986 ◽  
Vol 44 ◽  
pp. 842-843
Author(s):  
W. W. Davison ◽  
R. C. Buchanan
Keyword(s):  
Mechanical Properties ◽  
Analytical Techniques ◽  
Yttria Stabilized Zirconia ◽  
Stabilized Zirconia ◽  
Transmission Microscopy ◽  
Sintering Aid ◽  
Densification Temperature ◽  
Chemical Inertness ◽  
Scanning Transmission ◽  
Microstructural Examination

Yttria stabilized zirconia (YSZ) has become a significant technological material due to its high ionic conductivity, chemical inertness, and good mechanical properties. Temperatures on the order of 1700°C are required, however, to densify YSZ to the degree necessary for good electrical and mechanical properties. A technique for lowering the densification temperature is the addition of small amounts of material which facilitate the formation of a liquid phase at comparatively low temperatures. In this study, sintered microstructures obtained from the use of Al2O3 as a sintering aid were examined with scanning, transmission, and scanning transmission microscopy (SEM, TEM, and STEM).

Characterizations of Synthetic 8mol% YSZ with Comparison to 3mol %YSZ for HT-SOFC

2020 ◽  
Vol 38 (4A) ◽  
pp. 491-500
Author(s):  
Abeer F. Al-Attar ◽  
Saad B. H. Farid ◽  
Fadhil A. Hashim
Keyword(s):  
Ionic Conductivity ◽  
Electrochemical Impedance ◽  
Structural Information ◽  
Impedance Analysis ◽  
High Energy ◽  
Yttria Stabilized Zirconia ◽  
X Ray Diffraction ◽  
Stabilized Zirconia ◽  
Powder Morphology ◽  
X Ray

In this work, Yttria (Y2O3) was successfully doped into tetragonal 3mol% yttria stabilized Zirconia (3YSZ) by high energy-mechanical milling to synthesize 8mol% yttria stabilized Zirconia (8YSZ) used as an electrolyte for high temperature solid oxide fuel cells (HT-SOFC). This work aims to evaluate the densification and ionic conductivity of the sintered electrolytes at 1650°C. The bulk density was measured according to ASTM C373-17. The powder morphology and the microstructure of the sintered electrolytes were analyzed via Field Emission Scanning Electron Microscopy (FESEM). The chemical analysis was obtained with Energy-dispersive X-ray spectroscopy (EDS). Also, X-ray diffraction (XRD) was used to obtain structural information of the starting materials and the sintered electrolytes. The ionic conductivity was obtained through electrochemical impedance spectroscopy (EIS) in the air as a function of temperatures at a frequency range of 100(mHz)-100(kHz). It is found that the 3YSZ has a higher density than the 8YSZ. The impedance analysis showed that the ionic conductivity of the prepared 8YSZ at 800°C is0.906 (S.cm) and it was 0.214(S.cm) of the 3YSZ. Besides, 8YSZ has a lower activation energy 0.774(eV) than that of the 3YSZ 0.901(eV). Thus, the prepared 8YSZ can be nominated as an electrolyte for the HT-SOFC.

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