Effect of the Dispersion State in Y5O4F7 Suspension on YOF Coating Deposited by Suspension Plasma Spray

The stable Y5O4F7 suspension for dense yttrium oxyfluoride (YOF) coating by suspension plasma spraying (SPS) was developed. Electrostatically and electrosterically stabilized aqueous Y5O4F7 suspensions were prepared and compared with a commercially available Y5O4F7 suspension without dispersant. The wettability and dispersibility of the Y5O4F7 suspensions were evaluated in terms of the zeta potential, average particle size, and size distribution with electrophoretic light scattering (ELS) and dynamic light scattering (DLS). The viscosity was measured and the sedimentation was tested to examine the fluidity and stability of the Y5O4F7 suspensions. When electrostatic (BYK-154) and electrosteric (BYK-199) dispersants were added to the Y5O4F7 suspension, the isoelectric point (IEP) of Y5O4F7 particles in the suspension shifted to lower pH. The zeta potential of both of electrostatically and electrosterically stabilized Y5O4F7 suspensions were higher than ±40 mV at pH of 8.6, respectively, which were much higher than of the Y5O4F7 suspension without dispersant. Meanwhile, the average particle size of the electrosterically stabilized Y5O4F7 suspension was much smaller than that of the electrostatically stabilized one. The electrosteric stabilization had a great effect on improving the wettability and dispersibility of the Y5O4F7 suspension. The coating rate of the electrosterically stabilized Y5O4F7 suspension was the highest among the three tested suspensions. In addition, the YOF coating deposited with the electrosterically stabilized Y5O4F7 suspension had the highest hardness and the lowest porosity.