Thermal spray torches commonly use argon for plasmageneration. Low thermal properties of argon, however, limit thethermal efficiency of the torches. Use of molecular gases,which must dissociate before ionization, requires larger energyinput resulting in enthalpy increase of the plasma. In this paper,the effect of various gas compositions (Ar, Ar+HH2, andCO, CO2+CH +CH4) on the torch voltage-current characteristics, powerand thermal efficiency were studied. At the same time, in-flightYSZ particle conditions were compared. The higher thermalconductivity and efficiency of CH) CH4+CO +CO2 gas mixture producemore favorable sprayed particle conditions, in particulartemperature. At a 50mm spray distance, YSZ particletemperatures were 2470°C and 2896°C for Ar+HH2 andCHCH4+CO +CO2, respectively. Typical arc voltage for the torchoperating in CO, CO2+CH +CH4 was 130-180V compared to 45-60 V forAr+HH2. Thermal efficiency was also 20-40% higher.
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