Abstract
The entirely accidental observation of increased sintering performance of nickel-infiltrated yttria-stabilized zirconia (8YSZ) in a molybdenum and oxygen rich atmosphere was explored. Molybdenum and nickel were found to be synergistic sintering aids for 8YSZ. However, sintering had to take place in an atmosphere of flowing oxygen. Samples sintered in air consistently burst. The sintering performance, microstructure, and crystal structure of 8YSZ with additions of both Mo and Ni together are compared to the sintering performance, microstructure, and crystal structure of pure 8YSZ, 8YSZ with only Ni added as a sintering aid, and 8YSZ with only Mo added as a sintering aid. Enhanced densification and grain growth is observed in the Mo–Ni 8YSZ samples when compared to all other sintering samples. Order of magnitude sintering rate increases are observed in the Mo–Ni 8YSZ over that of pure 8YSZ. With a maximum sintering temperature of 1200 °C and a one-hour dwell, sintered densities of 85% theoretical density (5.02 g⁄cm3) are achieved with the Mo–Ni samples: a 57% increase in density over pure 8YSZ sintered with the same sintering profile. EIS results suggest conductivity may not be negatively impacted by the use of these two sintering aids at temperatures above 750 °C. Finally, the spontaneous generation of nickel-molybdenum nano-rods was observed on the 5, and 10 mol.% Mo–Ni infiltrated 8YSZ samples after being left under vacuum in a scanning electron microscope chamber, suggesting evaporation of a possible nickel–molybdenum compound from the sample fracture surfaces.
Highlights
The structural stabilization of the cubic and tetragonal polymorphs of zirconium oxide with the addition of yttrium has yielded an incredibly versatile ceramic with numerous functional and structural applications
Mo–Ni samples: a 57% increase in density over pure 8YSZ sintered with the same sintering profile
The time-density curves determined from the dilatometry measurements of the sintering performance of 8YSZ (Sample Set 1), 8YSZ infiltrated with Ni(NO3 )2 (Sample Set 2), 8YSZ with
Summary
The structural stabilization of the cubic and tetragonal polymorphs of zirconium oxide with the addition of yttrium has yielded an incredibly versatile ceramic with numerous functional and structural applications. This material is currently used to produce kitchen knives, mechanical bearings, artificial gemstones, and medical and dental implants. The tetragonal phase of zirconia is mechanically tough and is the phase of the polymorphic material used to make bearings, knives, and dental implants [4]. The low electronic conductivity and the relatively high oxygen ion conductivity make polycrystalline cubic zirconia an excellent candidate for the SOFC electrolyte [5,6]
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