# Electron Impact Cross Sections and Transport Studies of C\({}_{3}\)F\({}_{6}\)[PERSON]
## 3 Results and Discussion
### Buffer Gas Mixtures  
As mentioned earlier, pure C3F6O must be mixed with buffer gases to reduce the liquefaction temperature so that the new gas is suitable for electrical applications. In Figure 6, we plot the critical field values of the C3F6O and N2/CO2/O2 gas mixtures. The dotted lines shown in the graph are values obtained according to the proportion and critical field strength of the two pure gases in the mixture. The curve obtained using Equation (11) was not linear and, hence, the critical field strength was not a function of the gas proportions. This suggests a synergistic effect in the gas mixtures, which represents the  
Figure 4: Density normalized diffusion coefficient (ND) comparison of SF6 and PMVE. interaction of pure gases in the mixture. This was also useful to decide an optimal ratio of the gases in the mixture. If we maintained the PMVE proportion above 55 % for the C\({}_{3}\)F\({}_{6}\)O/N\({}_{2}\), 60 % for the C\({}_{3}\)F\({}_{6}\)O/O\({}_{2}\), and 65 % for the C\({}_{3}\)F\({}_{6}\)O/CO\({}_{2}\) mixture, the critical field strength was greater than that of SF\({}_{6}\). We further plot the synergistic effect coefficient \(h\), as suggested by [7], in Figure 7. The values obtained for the three mixtures were always greater than 0, which points to the presence of synergism among the gases in the respective mixtures. This again supports the observation of synergism through the critical field plot. The \(h\) value was 0 \(<h<\) 1 indicating that there were positive synergistic phenomena happening. A positive synergistic effect occurs when the breakdown voltage or the dielectric strength of the mixture is greater than that of the weighted sum of the individual gases. Figure 6: Critical field comparison for PMVE and N\({}_{2}\)/CO\({}_{2}\)/O\({}_{2}\) gas mixtures. Figure 7: Synergistic coefficient h for PMVE and N\({}_{2}\)/CO\({}_{2}\)/O\({}_{2}\) gas mixtures. Having established the presence of synergism in the selected gas mixtures, we studied the breakdown properties of the mixtures. Here, we present the Paschen curve to decide the best-suited buffer gas and optimal gas ratio for the mixture for a better breakdown characteristic. As described in the theory section, the ionization coefficients were first fitted to Equation (12), and A and B were determined. The fitted curve for C3F6O and SF6 is shown in Figure 8. We performed a similar fitting for all the mixture proportions considered in this work. The obtained constants were then utilized to obtain the Paschen curve for different buffer gases, which are further discussed here. The Paschen curve is plotted for a limited pressure range as the main objective was to study the effect of adding buffer gas to the mixture. In Figure 9, we plot the Paschen curve for C3F6O and CO2 mixture. With the increase in the proportion of CO2 in the mixture, the breakdown voltage increased. However, it still lagged behind the values for SF6 in the higher _pd_ range. For applications requiring _pd_ values less than 0.3 Pa m, the 5% C3F6O and 95% CO2 mixture should replace SF6. However, above this range, the buffer gas CO2 does not serve the purpose of increasing the breakdown voltage. We then studied the effect of adding O2 as a buffer gas, as shown in Figure 10. The observation is similar to that of CO2. The C3F6O and O2 gas mixture at different gas ratios always had a lower breakdown voltage than SF6. Thus, O2 was not effective as a buffer gas in the present case. Figure 8: Fitting of the ionization coefficient for C3F6O and SF6: (a) C3F6O; (b) SF6. Figure 9: Paschen curve for C3F6O and CO2 mixture. In Figure 11, the Paschen curve for the C\({}_{3}\)F\({}_{6}\)O and N\({}_{2}\) gas mixture is plotted. In contrast to the previous two cases, the mixture of 1% C\({}_{3}\)F\({}_{6}\)O and 99% N\({}_{2}\) produced similar or better breakdown results in the entire investigation range. Any proportion below 10% for C\({}_{3}\)F\({}_{6}\)O performed better than SF\({}_{6}\) in the higher operational range.