Corrosion resistance of structural materials in hightemperature aqueous sulfuric acids in thermochemical watersplitting iodine-sulfur process

摘要

Very harsh environments exist in the iodine-sulfur process for hydrogen production. Structural materials for sulfuric acid vaporizers and concentrators are exposed to high-temperature corrosive environments. Immersion tests were carried out to evaluate the corrosion resistance of ceramics and to evaluate corrosion-resistant metals exposed to environments of aqueous sulfuric acids at temperatures of 320, 380, and 460 ℃, and pressure of 2 MPa. The aqueous sulfuric acid concentrations for the temperatures were 75, 85, and 95 wt%, respectively. Ceramic specimens of silicon carbides (SiC), silicon-impregnated silicon carbides (Si-SiC), and silicon nitrides (Si_3N_4) showed excellent corro-sion resistance from weight loss measurements after exposure to 75, 85, and 95 wt% sul-furic acid. High-silicon irons with silicon content of 20 wt% showed a fair measure of corrosion resistance. However, evidence of crack formation was detected via microscopy. Silicon enriched steels severely suffered from uniform corrosion with a corrosion rate in 95 wt% sulfuric acid of approximately 1 g m~2 h~(-1). Among the tested materials, the ce-ramics SiC, Si-SiC, and Si_3N_4 were found to be suitable candidates for structural materials in direct contact with the considered environments.