Thermal spray torches commonly use argon for plasma generation. Low thermal properties of argon, however, limit the thermal efficiency of the torches. Use of molecular gases, which must dissociate before ionization, requires larger energy input resulting in enthalpy increase of the plasma. In this paper, the effect of various gas compositions (Ar, Ar+H2, and CO2+CH4) on the torch voltage-current characteristics, power and thermal efficiency were studied. At the same time, in-flight YSZ particle conditions were compared. The higher thermal conductivity and efficiency of CH4+CO2 gas mixture produce more favorable sprayed particle conditions, in particular temperature. At a 50mm spray distance, YSZ particle temperatures were 2470°C and 2896°C for Ar+H2 and CH4+CO2, respectively. Typical arc voltage for the torch operating in CO2+CH4 was 130-180V compared to 45-60 V for Ar+H2. Thermal efficiency was also 20-40% higher.

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