Corrosion Resistance of Metallic Materials in High Temperature Gases Composed of Iodine, Hydrogen Iodide and Water (Environment of the 3rd and 4th Stage Reactions)

Abstract

In order to select candidate materials for the equipment of the 3rd and 4th reaction of Mg-I thermochemical hydrogen production cycle, screening test of metallic materials was conducted. The corrosive constituents concerned in the 3rd reaction are hydrogen iodide, iodine, and water, and in the 4th reaction, hydrogen iodide, iodine, water, and hydrogen. Therefore, for the 1st screening test, the testing environment was made up of hydrogen iodide, iodine, and water under the condition of linearly increasing temperature from 250C to 700C. The several materials which passed the 1st screening test were examined isothermally for 200hrs in the iodide and iodine atmosphere with and without hydrogen. The results are as follows: (1) Common engineering materials, such as the austenitic and ferritic stainless steels, nickel-base alloys, and cobalt-base alloys are unsuitable because of their inability to resist the high corrosive atmosphere. (2) Corrosion rates of niobium, zirconium, and tantalum are very low in the atmosphere at 200C, but they absorb hydrogen to some degree and then may be sensitive to hydrogen brittleness. (3) Corrosion rates of titanium and its alloys are negligible at 350C, but also may be sensitive to hydrogen brittleness. (4) Molybdenum is the best choice below 450C at present, because its corrosion rate is very low, and it does not absorb hydrogen. The oxide scale on the molybdenum shows the tendency of evaporation at 450C, but the rate is extremely low. (5) Chromium, tungusten, aluminum, gold, and platinum can withstand the corrosive atmosphere at higher temperature also. It is, however, impossible to use them because of expensiveness (Au, Pt), low tensile strength in high temperature (Al), or brittleness (Cr, W). (b) Several surface treatments such as plasmaspray coating of oxides, electroplating of chromium, and diffusion coating of aluminum and chromium are yet incredible at present. struction Materials for the Magnesium-Iodine Cycle of Thermochemical Hydrogen Production Process (Part 4))

Corrosion Resistance of Nickel-Based Alloy to Gaseous Hydrogen Iodide Decomposition Environment in Thermochemical Water-Splitting Iodine-Sulfur Process

“…Bunsen reaction (1) produces sulfuric acid (H 2 SO 4 ) and hydrogen iodide (HI) from iodine (I 2 ), sulfur dioxide gas (SO 2 ) and raw material of water (H 2 O). H 2 SO 4 is decomposed into SO 2 , H 2 O, and product oxygen (O 2 ) by the reaction (2). Also, HI is decomposed into I 2 and product hydrogen (H 2 ) by the reaction (3).…”

“…In the HI decomposition reaction (3) environment, structural materials are attacked by gaseous halogen compounds such as HI and I 2 around 500°C. Candidate structural materials were e screened by corrosion resistant tests [2]- [6] in the HI decomposition reaction (3) environment. The studies found that ceramic materials such as alumina, mullite, SiC etc.…”