Plasma spray processes are widely used for ceramics coatings. Lots of efforts the quality of the coatings can be improved via increasing the in-flight particles temperature and their melting conditions. By increasing the enthalpy of the plasma gases and also improvement of the plasma jet, heat transfer through replacement of the conventional gases such as argon and helium with molecular gases such as (CO 2 , CH 4 ), the temperature and melting conditions of the in-flight particles can be improved. Yttrium oxide (Yttria) has properties in the form of coating with high chemical and heat stability and no phase changes up to 2200 0 C. One of important applica tion of yttria is its use in semiconductor manufacturing industry as a protective coating against plasma erosion atmosphere. In this research, Yttria powders were sprayed by two plasma guns (argon and CO 2 +CH 4 plasma) on aluminum substrates. Some of their physical and structural properties were investigated. Microscopic images of yttria coating deposited by CO 2 +CH 4 plasma have shown better cohesion, less porosities and non-melting particles due to the higher temperature of the in-flight particles. The results obtained from the phase analysis tests indicated the formation of a small amount of monoclinic phase. This phase could be converted to the cubic phase after heat treatment of the coatings. To study the erossion resistance of the yttria coating, two systems of plasma; plasma focus dry etching and reactive ion were employed. The results confirmed better resistance of yttria coatings deposited by CO 2 +CH 4 gases in plasma focus etching atmosphere. The effective factor is the smaller amount of structural defects, wider splats and lower density of splat boundaries on the surface of the coating. Keywords : Yttria, CACT and SG-100 Plasma Torch, Microstructue, Phase analysis, Reaction ion etching (RIE), Plasma focus (PF)
