Effect of Co-doping NiO and Nb2O5 on Phase Stability and Mechanical Properties of Yttria-Stabilized Zirconia (YSZ)/Alumina Composite
Date Issued
2015
Date
2015
Author(s)
Chen, Pei-Chia
Abstract
The 20% alumina added 3mol% yttria-stabilized zirconia exhibits outstanding mechanical properties. The doping of aliovalent ions into zirconia alters its concentration of oxygen vacancy owing to the compensation effect. The addition also changes the phase stability of zirconia at room temperature. Although many studies had been conducted on 3YSZ, few of them focus on the effect of co-doping. In the present study, both NiO and Nb2O5 were incorporated into alumina-strengthened yttria-stabilized zirconia. These dopants alter the concentration of oxygen vacancies. The phase evolution during sintering is consequently affected. The defects may also interact with each other. The YSZ/Al2O3/NiO/Nb2O5 composites were prepared using the pressureless sintering at 1600°C to achieve full densification. Apart from phase analysis and mechanical properties, thermal conductivity and electrical impedance were measured to evaluate the effects of these dopants. The results demonstrated that the tetragonal phase is less stable with the higher dopant content. The fracture toughness is therefore increased owing to the transformation toughening. The fracture toughness of the co-doped system is almost two times than that of un-doped alumina-strengthened yttria-stabilized zirconia after the addition of 1 mol% NiO and 0.5 mol% Nb2O5. The impedance analysis demonstrates that the co-doping of NiO and Nb2O5 increases the gain boundary resistance and the grain resistance. The concentration of oxygen vacancy is likely increased with the increase of dopant content. Therefore, the change of the resistance may be resulted from the formation of defect associations.
Subjects
Yttria-stabilized zirconia
alumina-toughened zirconia
co-doping
phase analysis
transformation toughening
mechanical properties
thermal conductivity
impedance spectroscopy
Type
thesis
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