## 3 Results  
An amount of 300 mL of Bluesil 550 HT sample was tested at nominal temperatures of 425, 450 and 475 \({}^{\circ}\)C, with the results from the latter temperature acting as a reference for the mostly aged material. The GC experimental results obtained allow for the quantitative measuring of the permanent gasses produced during the reaction period, as shown in Table 2. The gaseous, non condensable stream contains quite a significant amount of hydrogen together with methane. Additionally, ethane, ethylene and carbon dioxide were detected at all reaction temperatures, in good accordance with the behavior reported for the thermal decomposition of MM and MDM siloxanes [26; 28], but in very small quantities, close to the instrument detection limit.  
From the comparison of the hydrogen and methane production rates, reported in Figure 2, it is clearly visible that the dependence on temperature is much greater for hydrogen formation. The slope of the line in Figure 3 provides the activation energy of the degradation process (202.4 kJ/mol). A 10% experimental error, according to GC accuracy, was considered.  
The hydrogen production rate at 425 \({}^{\circ}\)C is very similar to the one reported at the same temperature after 3000 s for the thermal decomposition of a PDMS [21].  
Confronted with the chemical stability of other oils, hydrogen production by thermal degradation was previously investigated for Therminol 66 [29] and Therminol SP [30] with the same experimental equipment and by testing the same amount (300 mL) of oil, with activation energies of, respectively, 166.5 kJ/mol and 280.6 kJ/mol. In Table 3, the literature data are compared with the ones of Bluesil 550 HT. Although no methane was produced with the aromatic oils, it clearly resulted in greater stability for the silicone fluid, for which a gas partial pressure of 8 bar was reached at 475 \({}^{\circ}\)C, while 12 bar of gas was produced at 405 \({}^{\circ}\)C with Therminol SP. Also, the amount of produced condensable materials is far more relevant for the Therminol oils.  
\begin{table}
\begin{tabular}{c c c c} \hline \hline \(\mathbf{T_{set}}\) (\({}^{\circ}\mathbf{C}\)) & \(\mathbf{T_{oil}}\) (\({}^{\circ}\mathbf{C}\)) & \(\mathbf{H_{2}}\) (\(\mathbf{\mu mol/g}\)) & \(\mathbf{CH_{4}}\) (\(\mathbf{\mu mol/g}\)) \\ \hline
425 & 403 & 27 & 26 \\
450 & 428 & 85 & 37 \\
475 & 453 & 529 & 79 \\ \hline \hline \end{tabular}
\end{table}
Table 2: Measured Hydrogen and Methane (\(\mathbf{\mu mol/grams}\) of oil) as a function of temperature.  
Figure 2: Hydrogen and methane production rate as a function of temperature. The bars across the symbols stand for the experimental errors calculated according to instrumental accuracy.  
Figure 4 shows the GC-MS analysis performed on the condensable fraction produced by Bluesil 550 HT at the highest decomposition temperature (475 \({}^{\circ}\)C); the main compounds were identified by the NIST [32] and are reported. Bluesil behavior is similar to PDMS, with cyclic and linear siloxanes acting as main elements [22; 23].  
Figure 4: GC-MS analysis of the degradation products at 475 \({}^{\circ}\)C condensable at room temperature, with main compounds identified (NIST library).  
Figure 3: Plot to obtain the activation energy (Ea, curve slope) and pre-exponential factor (A, from the curve intercept on the ordinate) regarding the kinetics for hydrogen production. The bars across the symbols stand for the experimental errors calculated according to instrumental accuracy.  
\begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Tested Oil** & **Temperature** & **Overheating** & **Partial** & **Amount of** \\  & **Range Tested** & **Temperature** & **Pressure** & **Condensable** \\ \hline  & \({}^{\circ}\)C & \({}^{\circ}\)C & bar & mL \\ Therminol66 [29] & 350–415 & 430 & 9 & 35 \\ Therminol SP [30] & 350–390 & 405 & 12 & 25 \\ Bluesil & 400–475 & 475 & 8 & 8 \\ \hline \hline \end{tabular}
\end{table}
Table 3: Summary results of the thermal stability tests results, comparison with Therminol 66 [29] and Therminol SP [30].