Thermal analysis of trapped hydrogen in pure iron

Abstract

The relative amount of trapped hydrogen and the activation energy for its evolution from various lattice defects in iron were calculated by monitoring the pressure change caused by release of hydrogen from charged specimens heated at uniform heating rates. Hydrogen release peaks were observed at 385 K, 488 K, and 578 K, respectively, when the hydrogen charged specimen were heated at 2.6 K per minute. Analysis suggests that the peak at 385 K corresponds to hydrogen release from grain boundaries, and the peak at 488 K corresponds to release from dislocations, while the peak at 578 K results from release from micro voids. The activation energies for evolution of trapped hydrogen were determined experimentally from measured peak temperatures at different heating rates and were found to be 17.2 KJ/mol, 26.8 KJ/mol, and 35.2 KJ/mol, respectively, in grain boundaries, dislocations, and microvoids. It was also observed that most of hydrogen is trapped on dislocations if the density of specimen is greater than 98.95 pct, and in microvoids if less than 98.95 pct.