## 3 Key Component Update  
### Selection of Corrosion-Resistant Materials  
The issue of material corrosion is particularly critical due to the involvement of media such as H\({}_{2}\)SO\({}_{4}\) and HI. Earlier studies investigated the corrosion resistance of metallic materials, but these were limited to conventional single-metal materials, which exhibited severe corrosion in practical applications. In this study, we selected nine alloy materials (HC276, HC2000, HB-3, TA2, TC4, Monel400, Inconel617, Inconel601, Inconel690) from those that are commonly used and perform well on the market as research subjects for corrosion resistance testing. During previous pilot-scale tests, we observed significant metal corrosion during the phase transition of H\({}_{2}\)SO\({}_{4}\). Therefore, in addition to traditional gaseous HI and H\({}_{2}\)SO\({}_{4}\) corrosion tests, we specifically examined H\({}_{2}\)SO\({}_{4}\) corrosion during phase transition. Furthermore, three ceramic materials (SiC, Al\({}_{2}\)O\({}_{3}\), WC) were included in the corrosion experiments to provide guidance for subsequent reactor development. In the corrosion testing, the samples were placed in quartz tubes and heated in a tubular furnace to specified temperatures: 500 \({}^{\circ}\)C for gaseous HI corrosion, 850 \({}^{\circ}\)C for gaseous H\({}_{2}\)SO\({}_{4}\) corrosion, and 400 \({}^{\circ}\)C for H\({}_{2}\)SO\({}_{4}\) phase transition corrosion. Upon reaching the target temperature, the corrosive solution was injected into the evaporator via a peristaltic pump at a constant rate (1 mL/min). The gasified materials were then tested under a stable nitrogen carrier gas flow of 200 mL/min. The corrosion rates of different materials are shown in Table 3. HC276, TC4, and TA2 exhibited negative corrosion rates under gaseous HI decomposition conditions, attributed to the formation of dense oxide protective films on their surfaces, which effectively resisted acidic gas corrosion. HC2000 and HB-3 demonstrated excellent corrosion resistance, with corrosion rates of 0.0171 mm/a and 0.0053 mm/a, respectively. Monel and Inconel alloys showed poor corrosion resistance in gaseous HI environments, leading to the selection of the TC4 alloy for the HI decomposer design. In gaseous H\({}_{2}\)SO\({}_{4}\) decomposition conditions, TA2 and Monel400 displayed negative corrosion rates. However, post-experiment analysis revealed spalling of brittle surface layers on TC4, TA2, and Monel400, with TC4 showing the most severe detachment. This indicates that although passivation films formed on these metals, the films were unstable and prone to mechanical failure. Hastelloy and Inconel alloys exhibited superior corrosion resistance in gaseous sulfuric acid, particularly Inconel690 with a corrosion rate of only 0.076 mm/a, demonstrating high stability. Considering material processability and cost, HC276 was selected for sulfuric acid module reactor development. \begin{table}
\begin{tabular}{c c c c} \hline \hline
**Sample** & **Corrosion Rate (Gaseous HI)** & **Corrosion Rate (Gaseous H\({}_{2}\)SO\({}_{4}\))** & **Corrosion Rate (Phase** \\  & **/mm/a** & **/mm/a** & **Transition H\({}_{2}\)SO\({}_{4}\))/mm/a** \\ \hline HC276 & \(-\)0.0167 & 0.1449 & 5.6627 \\ HC2000 & 0.0171 & 0.1595 & 5.8633 \\ HB-3 & 0.0053 & 0.2311 & 5.4791 \\ TC4 & \(-\)0.0322 & 5.7240 & 11.5554 \\ TA2 & \(-\)0.0107 & \(-\)0.7410 & 11.0722 \\ Monel400 & 0.2727 & \(-\)2.2756 & 5.0259 \\ Inconel601 & 0.0597 & 0.1553 & 6.5753 \\ Inconel690 & 0.9276 & 0.0760 & 6.0625 \\ Inconel617 & 0.3998 & 0.1217 & 8.1631 \\ SiC & / & / & 0.0287 \\ Al\({}_{2}\)O\({}_{3}\) & / & / & 0.1349 \\ WC & / & / & 0.0239 \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Corrosion resistance of materials. Hastelloy, titanium alloys, and Inconel alloys showed unsatisfactory corrosion resistance during H\({}_{2}\)SO\({}_{4}\) phase transition, with titanium alloys being the most severely affected. In contrast, ceramic materials maintained excellent stability during sulfuric acid boiling and phase transition.