Fabrication of Superhydrophobic Ceramic Coatings via Solution Precursor Plasma Spray Under Atmospheric and Low-Pressure Conditions

Abstract

The plasma jet in the vacuum plasma spray process presents characteristics such as supersonic flow, expanded jet dimensions, and a smaller decay rate for jet velocity and temperature that are distinctly different from those of atmospheric plasma spray. In this work, a solution precursor vacuum plasma spray (SPVPS) process is described, which combines vacuum plasma spray with solution precursor as the feedstock. The deposition of superhydrophobic ceramic coatings via the SPVPS process is explored. Yb2O3 coatings are deposited by a radial injection of Yb(NO3)3 solution in the anode of an F4-VB torch operating under a pressure of 150-250 mbar. Coatings with different wetting behaviors were deposited by manipulating the process parameters of the SPVPS process. Solution precursor atmospheric plasma spray (SPAPS) is also applied to deposit superhydrophobic Yb2O3 coatings for comparison with the SPVPS process. The wetting behaviors of the coatings are characterized by water contact angle measurement, water roll-off test, and dynamic water impact test. The formation of different coating microstructures was explained via the different plasma jet characteristics, interactions of solution droplets and plasma, and droplets motions upon the impact on surface. The different wetting behaviors of coatings were correlated with the coating surface structures and topographies.