Magnesium-Iodine cycle is based on the four main reactions containing corrosive iodine and iodide at temperatures of 150° to 700°C, therefore the selection of construction materials for this cycle is very hard and the study of that is prime importance. The study was shared for every basic reaction and allotted to four laboratories. This part 1 report summarized the experimental results of exposure of metallic and nonmetallic materials to some. testing environments corresponding to the first stage reaction. Among the four basic reactions only the environment of the first stage reaction is an aqueous solution. And then the corrosion behavior in this environment appeared somewhat specific unlike that in the environments of the other three stages. The metallic materials selected from the viewpoint of corrosion resistance were tantalum, niobium and zirconium; and the corrosion resistance of the first two metals was almost perfect. But these three metals are very expensive and then not practical as construction material except special parts such as a nozzle. Therefore it is prefered to develop the non-porous coating method of these metals on some inexpensive metal. On the otherhand, almost all nonmetallic materials (oxide ceramics, ceramics coating, carbon products, plastics et al.) absorbed the solution of iodine and iodide without regard to their corrosion resistance. Then the practical evaluation of nonmetallic materials for the first stage reaction seemed difficult and was reserved for some time.

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Corrosion tests of 26 metallic materials and 8 non-metallic materials were conducted in an atmosphere containing iodine vapor, oxygen gas and steam in a temperature range from 100°C to 700°C. The purpose of the test was to find corrosion-resisting materials under the secondary reaction of the thermochemical hydrogen production process based on the Mg-I₂ cycle. The test results obtained are as follows:
(1) Metallic materials containing chromium such as SUS 304, SUS 310S, SUS 316, SUS 316L, SUS 317, SUS 317L, SUS 347, SUS 316JIL, Hastelloy C and Hastelloy C 276 are resistant to corrosion and appear promising. On the other hand, copper alloys, Carpenter 20, Hastelloy B, nickel, tantalum and zirconium exhibited severe corrosion and are not usable.
(2) No corrosion damage was observed on fire bricks and castables whose major elements are alumina and silica. They are, therefore, usable as the construction materials of internal combustion furnaces. However, steps are required to protect the furnace against damage due to spalling, softening-shrinkage, etc.

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The corrosion resistances of Fe-Cr-Ni alloys in high temperature gases composed of iodine and oxygen have been investigated in order to develop the construction materials for the second stage reaction of the magnesium-iodine thermochemical cycle. The results obtained are summarised as follows; (1) The corrosion of Fe-Cr-Ni alloys is appreciably accerelated by coexistence of I₂ and O₂ gases. (2) Cr is the most predominant alloying element that improves the corrosion resistance of Fe-Cr-Ni alloys, and this beneficial effect of Cr is considered to be related to the formation of the protective layer of chromium oxide. (3) The corrosion resistance of 25Cr-20Ni steel, which has been selected as the most practical material, can be improved by the alloying of small amounts of Si+Al, Y or Ca. For example, the tendency toward uneven attack of 25Cr-20Ni steel was appreciably reduced. The effect of such alloying elements may be attributed to the characteristics of protective layer improved. (4) The addition of H₂O vapor (up to 10vol. %) to the gas mixture of I₂ and O₂ and the deposit of Mg(IO₃)₂ on the metal surface have little influence on the depression of the corrosion resistances of 25Cr-20Ni steels.

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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 250°C to 700°C. 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 200°C, 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 350°C, but also may be sensitive to hydrogen brittleness. (4) Molybdenum is the best choice below 450°C 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 450°C, 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.

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In order to find out the construction materials for the process of reactions (3) and (4) of the magnesium-iodine thermochemical cycle the corrosion tests of ceramics (alumina, mullite, periclase, graphite, glass linings, etc.) and some jointing mortars were carried out for test durations up to 1000 hours and at temperatures up to 700°C in the atmosphere of a HI-I₂-H₂O mixed gas. The atmosphere was prepared without hydrogen, since hydrogen has little effect on the corrosion of ceramics. The corrosion resistance has been evaluated by observing the change in appearance, weight, and strength after the test. The test results were as follows: (1) The oxide materials (alumina, mullite, etc.) and graphites showed a good corrosion resistance at 500°C and 700°C. (2) Aluminum phosphate type jointing mortar was favorable. On the other hand, sodium silicate type mortar showed remarkable weight gain and decrease of bending strength accompanied by deposition of sodium iodide, and could not be assessable as candidate materials. (3) The pyroceram type glass lining specimens did not show any changes in its appearance and in weight at temperature range between 200°C and 500°C, while standard type were damaged.

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This article reviews the application of surface analytical techniques by which convenient information has been obtained on the surface layer of container materials. Included are the application for tinplate, TFS (Tin free steel) and Aluminum. By use of these techniques, the thickness and the composition of the surface layer, which significantly affect the corrosion resistance and lacquer adhesion, can be determined and provide us with some aspects to improve the performance.
The corrosion resistance of tinplate depends on the surface nature of steel substrate. The surface enriched constituents, which could not be completely removed in the preparation section of electrolytic tinning line, act to turnish the apearence and also result in high ISV (Iron solution) and ATC (Alloy-tin couple) value. Concerning the passivation film on tinplate, the thickness and composition of surface oxide film have a correlation to the lacquer adhesion. The nature of hydrated chromic oxide on TFS, which correlates to the deterioration of lacquer adhesion in a hot citric acid solution, has also been proposed from a new aspect. Analysis of the stained layer on aluminum reveals that the layer is contaminated by iron and other elements originated from city water and that iron plays an important role in staining.

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