Fundamental properties of CO2 mixed with CF3I were investigated in terms of (i) electrical and thermal conductivities at temperatures up to 30 000 K, (ii) a decay process of an arc conductance around a current zero under a free transient-recovery-voltage condition and (iii) an arc extinguishing capability in a thermal re-ignition region. The electrical conductivity at temperatures below 10 000 K proved to increase gradually with the admixture amount of CF3I. The thermal conductivity, in particular around 7000 K, was found to have marked dependence on the CF3I concentration. The result for the decay process of the residual-arc conductance under the free transient-recovery-voltage situation showed that the arc conductance attenuated more rapidly for CO2 mixed with CF3I at concentrations above 0.9 than for pure CO2. The mixture gas having the same concentrations was also revealed to cause the arc to be extinguished under a higher transient-recovery voltage than pure CO2.

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