An energy-saving sorbent is proposed to capture CO 2 from ambient air simply by controlling the amount of water (moisture) in contact with it. The system binds CO 2 from the air when the surrounding is dry, whereas it desorbs CO 2 when it is wet. Various microporous and ion-exchange materials can be employed in subsequent studies. The study sheds light on ways to optimize an efficient direct air capture system and therefore contributes to the development of ''negative emission technologies.''
A new hybrid monitoring technique for chloride stress corrosion cracking (SCC) is proposed. It uses both the acoustic emission (AE) and corrosion potential fluctuation (CPF) techniques. This paper discusses the results of SCC tests on butt-welded Type 304 stainless steel pipes. The weld pipe suffered transgranular (TG)-SCC in a concentrated magnesium chloride solution (40 mass%), but suffered intergranular (IG) attack and falling-off of grains in a heat-affected zone (HAZ) in a dilute chloride solution (35 mass%). SCC initiations in both concentrated and dilute corrodants were successfully monitored using a CPF technique. However, the CPF technique could not monitor the propagation of the SCC. This propagation could be detected using an AE technique. Secondary AE was produced by hydrogen gas evolution and by the cracking of corrosion products, and the primary AE was produced by the falling-off of grains due to the mutual actions of anodic dissolution and the mechanical fracture along a chromium-depleted zone in the grain boundary. The volume of metal loss by the dissolution was predicted from the local anodic current due to the fluctuation of the corrosion potential, and was found to correspond to the volume of the grain boundary attack. The fact that the primary AE was detected just after rapid drop (RD)-type CPF suggested that the grain boundary corrosion caused the falling-off of the grain that produced the primary AE.
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