Acoustic Emission Measurements on Palladium Hydrogenation Process by Using New Gas Pressure Cell

Abstract

A hydrogenation process of palladium has been studied by acoustic emission (AE) methods with a new gas pressure cell. By using noble Ar gas, the AE events were observed intermittently for the stepwise pressurization. On the repetition of the re-pressurization, the AE events showed the Kaiser effect, i.e., a dislocation motion induced effect. The typical power spectrum of AE signal by noble gas demonstrated the fundamental signal modes of 250 and 550 kHz. By the hydrogen gas re-pressurization, the characteristic AE behavior was recognized as following: (1) The continuous AE events were observed by the stepwise pressurization, (2) in the early stage of primary H solid solution of Pd, the fundamental AE modes were measured as 250 and 550 kHz, (3) in the hydride formation stage, the continuous AE events were also observed, and the typical AE mode was changed to 250 kHz mainly. The hydride formation mechanism was discussed on the basis of the dislocation theory.