SIMS study of deuterium distribution in chemically charged aluminum containing oxide layer defects and trapping sites

Hydrogen (deuterium) distribution that occurred during electrochemical and chemical charging in a high purity single aluminum crystal (grown in [1 1 0] direction) was studied, using Secondary Ion Mass Spectrometry (SIMS). Deuterium distribution was measured for specimens that were electrochemically charged in H2SO4 solutions or chemically charged in NaOH solutions, for various charging times at room and higher temperatures. The effect of “aging” related defect formation in aluminum was determined. In the hydrogenation of aluminum under high fugacity conditions (such as electrochemical and chemical charging), non-steady state diffusion produces concentration–distance profiles that may not be calculated by assuming simple diffusion behavior. Moreover, the hydrogen–vacancy interactions and microstructural changes (defect formations) must be taken into account in the process of the characterizing the state of hydrogen in aluminum. Interstitially hydrogen enters the aluminum lattice poorly. Hydrogen penetrates the aluminum matrix accompanied by vacancies formed at the surface during conditions of high fugacity. Aluminum hydroxide and hydrogen interactions form hydrogen–vacancy complex at the surface, which diffuses into the volume and then clusters to form H2 interior bubbles in the aluminum. The SIMS technique was used to characterize hydrogen (deuterium) distributions in chemically charged aluminum in the order to obtain concentrations–depth profiles. The advantages of this method are that the actual concentrations–depth profiles are obtained and they include microstructural changes, such as defects (vacancies, voids, bubbles, micro-cracks, dislocations and surface oxides) formed during the electrochemical and chemical reactions in aluminum with aqueous solutions.