Papers by Keyword: Cubic Zirconia

Abstract: Solid electrolytes based on stabilized zirconia have been studied a long time ago in its cubic phase because of its electrical properties, which make them excellent candidates to be used in applications such as oxygen sensors and solid oxide fuel cells [1], [2]. Lambda sensor or oxygen sensor, as it is also known, is a device that measures the oxygen concentration of the gases that flow through the exhaust pipe. Physically, the lambda sensor has two electrodes. The outer which is exposed to the exhaust gases and the inner to the air (reference) [3]; these electrodes are made, generally, of porous platinum. The ceramic material, i.e., zirconium oxide, is placed in between the electrodes, so the oxygen ions can move from one electrode to another. As one of the electrodes is exposed to the reference gas, the voltage generated is a measure of the concentration of oxygen in the exhaust gases [4].

Abstract: Analysis of structural and mechanical properties of cubic zirconia was conducted using a simulation code (GULP) that is based on the concept of energy minimization. Some mechanical properties of zirconia were computed such as elastic constant tensors, shear modulus, bulk modulus, Youngs modulus and others along the lattice planes. The stiffness constants obtained (C₁₁, C₂₂ and C₃₃) were equal, implying that zirconia is flexible in all directions of the lattice plane. The predicted bulk modulus was 285 GPa with the shear modulus ranging between 78 and 105 GPa. The Youngs modulus of 577 GPa indicates higher ductile behavior as confirmed by the compressibility of 0.0035. The Poissons ratio with values ranging from 0.16 to 0.31 may indicate high anisotropy. Other acoustic features related to mechanical properties of zirconia such as velocity wave ratio, stress matrix dielectric constants and others were also analyzed. All estimations obtained show good agreement to recent measured properties of zirconia.

Abstract: Molecular modelling methods were used to investigate the structural and interatomic potential of bulk cubic zirconia. To widen the scope of the expected outcome, GULP and CASTEP software were used based on the concept of minimizing the energy of the crystal structure with respect to atomic coordinates. The crystal structure of cubic zirconia was modelled and optimized; the lattice parameter of 5.10 Å obtained is similar to available calculated and experimental values. The developed interatomic potential is based on Born model for ionic solids without defects. The calculated interatomic potential of 109.67eV per atom is also within acceptable range, but variation was observed depending on the relative position of individual atoms. The modelling gave a better understanding of the bulk crystal structure of cubic zirconia due to detailed parameters that were obtained. Also, the determined parameters were used to estimate the Young’s Modulus of bulk zirconia as 397GPa.

Abstract: In a high-purity 8Y-CSZ, the doping of 0.15 - 5 mass% pure silica introduces a glass phase dispersing uniformly along grain-boundary facets and at multiple junctions. For materials with grain sizes of 0.75 - 2.4 m, the dispersion of the glass phase decreases the elastic modulus, the Vickers hardness and the elastic modulus-to-hardness ratio, whereas it affects little in the fracture toughness measured by a Vickers-indentation method and a single-crack-precracked-beam method. Inspection of crack propagation paths shows that the glass phase with sizes smaller than those of the matrix grains is not a site for easy crack-propagation, but provides a site for a crack-deflection mechanism.

Abstract: Yttria-stabilized cubic zirconia is well known the material that possesses high oxygen ionic conductivity and chemical stability over wide ranges of temperature and oxygen partial pressure and thus it is widely used as an oxygen sensor, thermal barrier and solid oxide fuel cell (SOFC) electrolyte. In the present study, 8 mol% yttria-stabilized cubic zirconia with SiO2 addition up to 10 wt% was studied with respect to the microstructure, fracture toughness and hardness. XRD results showed that SiO2 had very limited solubility of 0.3 wt% in cubic zirconia. This suggests that only small part of SiO2 dissolved in cubic zirconia and the rest of SiO2 segregated at grain boundaries and multiple junctions. This glassy phase also wetted the zirconia grains and prevented the grain growth and the formation of facetted grains. Both hardness and fracture toughness were measured using a Vickers indenter. It is observed that the introduction of SiO2 decreased the hardness and increased the fracture toughness of cubic zirconia. The hardness and fracture toughness also showed the same trend with increasing SiO2 content.