Effects of enthalpy-enhancing gas on ionic conductivity of atmospheric plasma-sprayed 3.9YSZ electrolyte for 45-75 μm particles

Enthalpy-enhancing gas is used to optimize the ionic conductivity of atmospheric plasma-sprayed 3.9 mol% yttria-stabilized zirconia (3.9YSZ) electrolyte. In the experiment, three hydrogen gas-flow rates were used to control the plasma energy. The size of the 3.9YSZ feedstock powder was sieved to be set in the range of 45-75 μm. When the hydrogen gas-flow rate was increased, the electrolyte became harder, and the sprayed surfaces became smoother. However, the lowest apparent porosity and the highest bulk density of the electrolyte were obtained at a hydrogen gas-flow rate of 7 L/min. A 3.9YSZ electrolyte with an ionic conductivity of 2860 μ(S/cm) and the lowest dissociation energy was obtained at 800 C with a hydrogen gas-flow rate of 12 L/min. It was controlled by the intragrain conductivities. A higher hydrogen gas-flow rate enhanced the growth of columnar grains and suppressed the appearance of the monoclinic phase, which led to the greater intragrain conductivities. The increase in grain-boundary conductivities is closely related to the decrease in grain size.