HYDRIDE DISSOCIATION AND HYDROGEN EVOLUTION BEHAVIOR OF ELECTROCHEMICALLY CHARGED PURE TITANIUM

A commercially pure alpha-titanium was electrochemically charged with hydrogen in a 5% H2SO4 solution at a current density of 5 kA m(-2) for 14.4 ks (4 h), and the dissociation process of the electrochemically formed hydride and the evolution behavior of hydrogen from the samples were investigated by means of high temperature X-ray diffractometry, thermal desorption spectroscopy (TDS) and differential thermal analysi s (DTA). The electrochemical charging produced delta-titanium hydride; this dissociated completely at temperatures around 600 K; (alpha+beta ) titanium then appeared, indicating that the hydride formed eutectoid aily. The DTA detected the dissociation of the hydride (or (alpha + de lta)-(alpha + beta) boundary in the titanium-hydrogen system) as an en dothermic peak. The TDS analysis, however, revealed that the accelerat ed hydrogen evolution could not be found at the dissociation temperatu re of the hydride but could be at higher temperatures. It was suggeste d that the hydride dissociation, (alpha+delta), into (alpha+beta) two- phase region was not accompanied by hydrogen evolution from the sample s, but the free hydrogen owing to the hydride dissociation was diffuse d into the samples. The peak temperatures of both DTA and TDS analyses shifted to lower temperatures with decreasing heating rate. The Kissi nger plots fitted these results fairly well and indicated that the app arent activation energies for b-hydride dissociation and hydrogen evol ution were estimated to be about 106 kJ mol(-1) and about 49 kT mol(-1 ) respectively.