# Theoretical Description of Carbon Felt Electrical Properties Affected by Compression
## 2 Methodology of Experimental Research
### Conductivity Measurements  
The results of resistance measurements are presented here both for dry felt electrodes and for those immersed in several dielectric (nonconductive) liquids. Dielectric liquids were used in order to eliminate the influences of the ionic conductivity of the liquid itself on the resistance of the felt. A major assumption for the conductivity description was that the resistance of the felt is determined mainly by the density of filament interconnections within the felt along with the density of filament contacts with the electrode surfaces.  
Three dissimilar dielectric liquids were chosen: glycerol, ethanol, and cyclohexane, with significantly different values of relative electric permittivity's (dielectric constant) \(\varepsilon_{\text{r}}\). Below is Table 2, which represents the most important physical parameters of each. It should be noted that resistance properties of carbon material used for CF producing are represented in Table 2 by specific electrical conductivity measured in (\(\Omega\)-cm)\({}^{-1}\).  
Resistance values of dry CF are shown in Table 3 measured in AC and DC currents. For ensuring the exactness of tests, the conductivity of each liquid (without a CF presence in the cell) was measured preliminary. Only if the conductivity had a zero value (in accordance with the exactness of applied devices), the following experiments with CF were produced.  
As a measure of felt conductivity the average square conductivity (ASC) (1/(\(\Omega\)-cm\({}^{2}\)) parameter was chosen equal to the reciprocal of the total resistance of the felt in the experimental cell multiplied by its area. The indicator of conductivity was taken its average value obtained for alternating and direct currents.  
Where: h-current CF width, mm; R\({}_{\text{dc}}\) - resistance is measured by direct current (DC), \(\Omega\); R\({}_{\text{ac}}\) - resistance is measured by alternate current (AC), \(\Omega\).  
The measurements of CF resistivity, whose results are shown in Table 3, confirm the decrease of CF resistivity during compression applied perpendicular to the surface. Initially, CF resistivity falls precipitously; subsequently, the resistance decrease slows. The measurements results for CF immersed in glycerol, alcohol, and cyclohexane are placed in Appendix A. The typical change of relative resistivity for CF in ethanol is presented in Figure 4. Further analysis is given in the following section.  
\begin{table}
\begin{tabular}{c c c c} \hline \hline \multirow{2}{*}{**Parameter**} & \multicolumn{3}{c}{**Liquid**} \\ \cline{2-4}  & **Glycerol** & **Ethanol** & **Cyclohexane** \\ \hline Density, [g/cm\({}^{3}\)] (25 \({}^{\circ}\)C) & 1.26 & 0.789 & 0.8 \\ Relative permittivity, \(\varepsilon_{\text{r}}\), (0.57 MHz, 25 \({}^{\circ}\)C) & \(\sim\)42.5 & \(\sim\)21.6 & \(\sim\)2.02 \\ Specific electrical conductivity, [(\(\Omega\)-cm)\({}^{-1}\)], 25 \({}^{\circ}\)C & 5\(\cdot\)10\({}^{-8}\) & \(\sim\)1\(\cdot\)10\({}^{-6}\) & \(<\)5 \(\times\) 10\({}^{-9}\) \\ Viscosity, [Pa-s], 20 \({}^{\circ}\)C (30 \({}^{\circ}\)C) & 141 (61.2) & \(\sim\)0.11 & 0.61 \\ \hline \hline \end{tabular}
\end{table}
Table 2: Physical parameters of glycerol, alcohol, and cyclohexane.