カテゴリー: Hydrogen embrittlement 水素脆化
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https://ja.wikipedia.org/wiki/%E6%B0%B4%E7%B4%A0%E8%84%86%E5%8C%96
overview
This is a phenomenon in which metal strength deteriorates in all metal materials due to hydrogen intrusion [1]. Also called hydrogen embrittlement or hydrogen fragility [1]. This phenomenon is unique to hydrogen because the hydrogen ion is a very small cation with a diameter of 1 fm, which is only 1/100,000 times the size of a normal atom or ion, which has a diameter of 0.1 nm. This is because they easily invade and diffuse into metal bonds containing free electrons. As a result, hydrogen has become a substance that is difficult to handle with metallic materials.
Hydrogen embrittlement is thought to be caused by hydrogen absorption during corrosion, welding, pickling, electroplating, etc. This destruction due to hydrogen absorption is also called “delayed destruction.” Hydrogen embrittlement fracture is likely to occur at grain boundaries, locations where tensile stress is applied, and areas where stress is concentrated. This problem is known to have plagued the development of the Haber-Bosch method. For example, steel in an acidic solution may suddenly crack, but this is due to hydrogen ions in the solution penetrating into the steel and making it brittle. These are problems that have been recognized for a long time.
Research on hydrogen embrittlement has been conducted for a long time and is still being conducted extensively. However, there are many influencing factors that cause embrittlement, which are intricately intertwined with materials, stress, and the environment, and their true nature is still unclear [2].
Hydrogen embrittlement is a phenomenon related to the localization of diffusible hydrogen, so in addition to the amount of hydrogen, parameters related to diffusion such as time and temperature, stress state (stress triaxiality), strain, and the original material are also important. It also depends on the strength. In addition, it is difficult to understand the behavior of diffusible hydrogen in materials, and these factors hinder fundamental elucidation.
There are many examples where hydrogen embrittlement has become a problem, such as in the development of rocket engines that use hydrogen as fuel and the development of engines for hydrogen fuel cell vehicles. Some metals have the property of absorbing hydrogen, so once exposed to hydrogen, the problem of hydrogen embrittlement arises. In particular, the strength and ductility of stainless steel deteriorates significantly due to hydrogen, so by limiting its use to low-strength materials, that is, materials with low hydrogen sensitivity, or by applying dehydrogenation (baking) treatment, A temporary solution has been obtained. At this time, hydrogen atoms that have penetrated into the metal crystal lattice become metal hydrides.
Currently, there is a strong demand for lighter weight and higher strength, including from the perspective of environmental issues, and high stress designs for structural parts are becoming necessary. If we try to maximize the performance of metal materials closer to their limits, we can no longer limit ourselves to using only low-strength materials, as was the case with the stainless steel solution mentioned above, and hydrogen embrittlement becomes a problem. . For this reason, there is an increasing need to elucidate the mechanism and find a fundamental solution.
countermeasure
In 2010, a research group from Kyushu University and the National Institute of Advanced Industrial Science and Technology [3] found that, contrary to common wisdom, when a large amount of hydrogen enters stainless steel, the strength of the metal decreases. On the contrary, they found that the fatigue strength properties were significantly improved [5].
In 2013, research groups including the International Institute for Carbon-Neutral Energy Research (I2CNER) at Kyushu University and Sandia National Laboratories in the United States discovered that metal fatigue could be suppressed by adding oxygen to hydrogen. In addition to discovering this, he also succeeded in formulating it. This is because oxygen is preferentially adsorbed on the crack surface within the metal and prevents hydrogen atoms from entering [6].
To eliminate hydrogen embrittlement, there are methods such as reducing hydrogen by heating and putting an aluminum coating inside the hydrogen tank [7].
use
On the other hand, there are also examples of utilizing hydrogen uptake in metals. Some hydrogen-absorbing alloys show the phenomenon of pulverization during the absorption/release cycle. In addition, a method of pulverizing raw materials by utilizing this phenomenon is also used in the manufacturing process of rare earth magnets. The possibility that deuterium atoms occluded in palladium may be involved in cold fusion is also being discussed.
Hitachi-GE Nuclear Energy is considering using hydrogen embrittlement to crush molten core debris when removing it from reactors that have experienced core meltdown.[8 ].
footnote
[How to use footnotes]
^ a b “Hydrogen brittleness”. Britannica International Encyclopedia Small Encyclopedia Accessed December 11, 2017.
^ Kenichi Takai "Importance and new developments in analytical technology to overcome hydrogen embrittlement of metal materials" (PDF) "SCAC NEWS" 2009-II, pp. 3-6. Original archive as of March 20, 2014. Accessed March 20, 2014.
^ Takayoshi Murakami, professor emeritus of Kyushu University, is the leader.
^ Impregnated with over 70 ppm of hydrogen under high pressure.
^ AIST: Hydrogen improves the strength of metal materials
^ Succeeded in discovering and formulating a method to suppress metal fatigue in hydrogen
^ "Hydrogen reverses metal deterioration" June 15, 2014 Nihon Keizai Shimbun page 17
^ How to dispose of damaged or melted nuclear fuel (archive version)