Treatment of Metal Surface by Atmospheric Microwave Plasma Jet

Atmospheric microwave plasma jets generated in Ar gas or Ar/O₂ and Ar/H₂ gas mixtures were applied to a surface modification of metal. The nozzle-type microwave plasma jet is excited in a rectangular waveguide, operated at a frequency of 2.45 GHz, and is stabilized by the flowing channel of a working gas through the nozzle. The charged particles, with a high kinetic energy produced from the plasma jet, caused a surface in a rough morphology to be smooth, showing a change in the water contact angle. A scanning electron microscopy and a water contact-angle analyzer characterized the samples treated in different gas mixtures. The water contact angles of the samples were plotted as a function of the recovery time, showing that the sample treated by Ar/H₂ plasma jet has the smallest contact angle (~3deg) and the slowest recovery of the angle. In the estimation of the aluminum-surface free energy, after the H₂/Ar plasma treatment, the total surface free energy of the Al sample increased from 18.71 to 82.81 mJ/m² drastically